U.S. patent application number 09/886008 was filed with the patent office on 2001-10-25 for electrically operated braking system having a device for operating electric motor of brake to obtain relationship between motor power and braking torque.
Invention is credited to Shirai, Kenji, Yoshino, Yasunori.
Application Number | 20010033106 09/886008 |
Document ID | / |
Family ID | 26513927 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033106 |
Kind Code |
A1 |
Shirai, Kenji ; et
al. |
October 25, 2001 |
Electrically operated braking system having a device for operating
electric motor of brake to obtain relationship between motor power
and braking torque
Abstract
An electrically operated braking system of a motor vehicle,
including a brake having a friction member movable to be forced
onto a rotor rotating with a vehicle wheel, and an electric motor
operated by an electric power supplied from an electric power
source to generate a drive force for forcing the friction member
onto the rotor and thereby braking the wheel, a controller which
determines an amount of the electric power to be supplied to the
motor, depending upon an operating amount of the brake operating
member, and a relationship estimating and utilizing device for
obtaining an actual value of the electric power supplied to the
motor during an operation of the brake while the vehicle is
running, and an actual value of a braking torque applied from the
brake to the wheel during the brake operation, for estimating a
relationship between the electric power to be supplied to the motor
and the braking torque to be applied to the wheel, on the basis of
the actual values obtained, and for utilizing the estimated
relationship.
Inventors: |
Shirai, Kenji; (Mishima-shi,
JP) ; Yoshino, Yasunori; (Toyota-shi, JP) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
26513927 |
Appl. No.: |
09/886008 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09886008 |
Jun 22, 2001 |
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09097269 |
Jun 15, 1998 |
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6270172 |
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Current U.S.
Class: |
303/177 |
Current CPC
Class: |
F16D 66/00 20130101;
F16D 2125/40 20130101; F16D 65/18 20130101; F16D 2121/24 20130101;
B60T 13/74 20130101; F16D 2066/005 20130101; B60T 8/3255 20130101;
F16D 2127/10 20130101; F16D 2125/66 20130101; B60T 8/00 20130101;
F16D 65/0972 20130101; B60T 8/4809 20130101; B60T 7/042 20130101;
F16D 51/48 20130101 |
Class at
Publication: |
303/177 |
International
Class: |
B60T 008/74 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 29, 1997 |
JP |
9-203454 |
Dec 11, 1997 |
JP |
9-341290 |
Claims
What is claimed is:
1. An electrically operated braking system of a motor vehicle
having a wheel, comprising: a rotor rotating with said wheel; a
brake operating member which is operated by an operator of the
motor vehicle; an electric power source; a brake including a
friction member movable to be forced onto said rotor, and an
electric motor which is operated by an electric power supplied from
the electric power source, to generate a drive force for forcing
said friction member onto said rotor and thereby braking said
wheel; a controller which determines an amount of the electric
power to be supplied from said electric power source to said
electric motor, depending upon an operating amount of said brake
operating member, for thereby controlling an operation of said
brake; a relationship estimating and utilizing device provided for
obtaining an actual value of the electric power supplied from said
electric power source to said electric motor during an operation of
said brake while the motor vehicle is running, and an actual value
of a braking torque applied from said brake to said wheel during
said operation of said brake, for estimating a relationship between
said electric power to be supplied to said electric motor and said
braking torque to be applied to said wheel, on the basis of said
actual values obtained, and for utilizing said relationship, said
relationship being formulated such that said braking torque to be
applied to said wheel being changed with a change in said electric
power to be supplied to said electric motor.
2. An electrically operated braking system according to claim 1,
wherein said controller includes said relationship estimating and
utilizing device, and said relationship estimating and utilizing
device includes relationship utilizing means for determining an
desired value of said braking torque on the basis of the operating
amount of said brake operating member, and determining the value of
said electric power to be supplied to said electric motor, on the
basis of the determined desired value of said braking torque and
according to said relationship estimated.
3. An electrically operated braking system according to claim 1,
wherein said relationship estimating and utilizing device includes
means for supplying a predetermined amount of the electric power
from said electric power source to said electric motor for a
predetermined length of time to thereby activate said brake while
the motor vehicle is running without an operation of said brake
operating member, and obtaining said actual values of said electric
power and said braking torque during activation of said brake.
4. An electrically operated braking system according to claims 1,
wherein said relationship estimating and utilizing device includes
a vehicle deceleration detecting means for detecting a deceleration
value of said motor vehicle, and obtains said actual value of the
braking torque on the basis of said deceleration value detected by
said vehicle deceleration detecting means.
5. An electrically operated braking system according to claim 1,
wherein said relationship estimating and utilizing device includes
a wheel speed sensor for detecting a rotating speed of said wheel,
obtains a deceleration value of said wheel on the basis of a rate
of change of the rotating speed of the wheel detected by said wheel
speed sensor, and obtains said actual value of the braking torque
on the basis of said deceleration value of the wheel obtained.
6. An electrically operated braking system according to claim 3,
further comprising first inhibiting means for inhibiting said
relationship estimating and utilizing device from operating said
brake to obtain said relationship while the motor vehicle is
running under a condition in which the operation of said brake is
likely to be felt unusual by the operator of the motor vehicle.
7. An electrically operated braking system according to claim 6,
wherein said first inhibiting means includes means for inhibiting
said relationship estimating and utilizing device from operating
said brake when the motor vehicle is running at a speed lower than
a predetermined threshold.
8. An electrically operated braking system according to claim 1,
further comprising second inhibiting means for inhibiting said
relationship estimating and utilizing device from at least
utilizing said relationship while the motor vehicle is running
under a condition in which said relationship estimating and
utilizing device is not likely to accurately estimate said
relationship.
9. An electrically operated braking system according to claim 8,
wherein said second inhibiting means includes means for inhibiting
said relationship estimating and utilizing device from at least
utilizing said relationship while a drive force for driving the
motor vehicle is being changed.
10. An electrically operated braking system according to claim 8,
wherein said second inhibiting means includes means for inhibiting
said relationship estimating and utilizing device from at least
utilizing said relationship while the motor vehicle is turning.
11. An electrically operated braking system according to claim 1,
wherein said brake includes a support member for supporting said
friction member in frictional contact with said rotor so as to
prevent said friction member from being rotated with said rotor,
and said relationship estimating and utilizing device includes a
force switch which is interposed between said friction member and
said support member, so as to receive a force from said friction
member in frictional contact with said rotor, said force switch
being selectively placed in one of two states, depending upon
whether said force received from said friction member is larger
than a predetermined threshold which is not zero, said relationship
estimating and utilizing device utilizing an output of said force
switch to obtain said actual value of said braking torque.
12. An electrically operated braking system according to claim 11,
wherein said rotor is a disc having a friction surface, and said
friction member is a brake pad which is movable into frictional
contact with said friction surface, said force switch being
disposed in a position at which a spacing between said brake pad
and said support member decreases with an increase in an amount of
rotation of said brake pad with said disc.
13. An electrically operated braking system according to claim 11,
wherein said relationship estimating and utilizing device further
includes a pressing-force-related quantity sensor whose output
varies continuously with a quantity relating to a pressing force
generated by said electric motor to force said friction member onto
said rotor, said relationship estimating and utilizing device using
said output of said pressing-force-related quantity sensor as a
quantity relating to said actual value of said electric power
supplied to said electric motor.
14. An electrically operated braking system according to claim 13,
wherein said relationship estimating and utilizing device further
includes a braking force estimating device for estimating said
braking torque to be applied to said wheel, on the basis of said
output of said pressing-force-related quantity sensor and according
to a predetermined relationship between said output and said
braking torque, said braking force estimating device compensating
said predetermined relationship on the basis of said output when
said force switch is switched from one of said two states to the
other.
15. An electrically operated braking system according to claim 14,
wherein said said braking force estimating device includes
relationship compensating means for compensating said predetermined
relationship, on the basis of a difference between an actual value
of said output and a nominal value of said output when said force
sensor is switched from one of said two states to the other.
16. An electrically operated braking system of a motor vehicle
having a wheel, comprising: a rotor rotating with said wheel; a
brake operating member which is operated by an operator of the
motor vehicle; an electric power source; a brake including a
friction member movable to be forced onto said rotor, and an
electric motor which is operated by an electric power supplied from
the electric power source, to generate a drive force for forcing
said friction member onto said rotor and thereby braking said
wheel; a controller which determines an amount of the electric
power to be supplied from said electric power source to said
electric motor, depending upon an operating amount of said brake
operating member, for thereby controlling an operation of said
brake; a relationship estimating and utilizing device provided for
obtaining an actual value of a physical quantity relating to the
electric power supplied from said electric power source to said
electric motor during an operation of said brake while the motor
vehicle is running, and an actual value of a physical quantity
relating to a braking torque applied from said brake to said wheel
during said operation of said brake, for estimating a relationship
between said electric power to be supplied to said electric motor
and said braking torque to be applied to said wheel, on the basis
of said actual values obtained, and for utilizing said
relationship, said relationship being formulated such that said
braking torque to be applied to said wheel being changed with a
change in said electric power to be supplied to said electric
motor.
17. A braking system for a motor vehicle having a wheel,
comprising: a rotor rotating with said wheel; a friction member
movable to be forced onto said rotor, for braking said wheel; a
support member for supporting said friction member in frictional
contact with said rotor so as to prevent said friction member from
being rotated with said rotor; a pressing device for forcing said
friction member into frictional contact with said rotor; and a
force switch which is interposed between said friction member and
said support member, so as to receive a force from said friction
member in frictional contact with said rotor, said force switch
being selectively placed in one of two states, depending upon
whether said force received from said friction member is larger
than a predetermined threshold which is not zero.
18. A braking system according to claim 17, wherein said rotor is a
disc having a friction surface, and said friction member is a brake
pad which is movable into frictional contact with said friction
surface, said force switch being disposed in a position at which a
spacing between said brake pad and said support member decreases
with an increase in an amount of rotation of said brake pad with
said disc.
19. A braking system according to claim 17, further comprising: a
pressing-force-related quantity sensor whose output varies
continuously with a quantity relating to a pressing force by which
said friction member is forced onto said rotor by said pressing
device; and a friction coefficient estimating device for estimating
a friction coefficient of said friction member, on the basis of a
relationship between said output of said pressing-force-related
quantity sensor and said predetermined threshold.
20. A braking system according to claim 17, further comprising: a
force-related quantity sensor whose output varies continuously with
a quantity relating to one of a braking force generated by the
braking system and applied to said wheel and a pressing force
generated by said pressing device to force said friction member
onto said rotor; a wheel braking force estimating device for
estimating said braking force to be applied to said wheel, on the
basis of said output of said force-related quantity sensor and
according to a predetermined relationship between said output and
said braking force, said wheel braking force estimating device
compensating said predetermined relationship on the basis of said
output when said force switch is switched from one of said two
states to the other.
21. A braking system according to claim 20, wherein said wheel
braking force estimating device includes relationship compensating
means for compensating said predetermined relationship, on the
basis of a difference between an actual value of said output and a
nominal value of said output when said force sensor is switched
from one of said two states to the other.
Description
[0001] This application is based on Japanese Patent Applications
Nos. 9-203454 and 9-341290 filed Jul. 29 and Dec. 11, 1997,
respectively, the contents of which are incorporated hereinto by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an electrically operated
braking system of a motor vehicle, which includes a brake employing
an electric motor as a drive source.
[0004] 2. Discussion of the Related Art
[0005] An electrically operated braking system of a motor vehicle
generally includes (a) a brake operating member such as a brake
pedal, which is operated by an operator of a motor vehicle, (b) an
electric power source such as a battery, (c) a brake including an
electric motor which is operated by an electric power supplied from
the electric power source, to generate a drive force for forcing a
friction member onto a rotor rotating with a wheel of the vehicle,
for thereby braking the wheel, and (d) a controller which
determines an amount of the electric power to be supplied from the
electric power source to the electric motor, depending upon an
operating amount of the brake operating member, for thereby
controlling an operation of the brake.
[0006] A friction coefficient of friction members such as brake
pads or brake linings used in a brake generally varies due to
gradual deterioration or wearing of the friction members, or due to
temperature or humidity of the friction members. Further, the
friction members have different friction coefficient values due to
variations associated with the manufacture. In an electrically
operated braking system as described above, a change in the
friction coefficient of the friction members will cause a change in
the relationship between the amount of electric power actually
supplied from the electric power source to the electric motor of
the brake and the braking torque actually applied from the brake to
the corresponding wheel. In other words, the relationship between
the amount of electric power supplied to the motor and the braking
torque generated by the brake is not necessarily held constant.
[0007] However, the conventional electrically operated braking
system does not obtain and utilize the actual relationship between
the supplied amount of electric power and the braking torque
generated by the brake. That is, the conventional system uses a
predetermined nominal relationship between the electric power
amount and the braking torque, to determine the amount of electric
power to be supplied to the electric motor, depending upon the
operating amount of the brake operating member, on the assumption
that the relationship is held constant. Therefore, the conventional
electrically operated braking system is not capable of accurately
controlling the braking torque of the brake in relation to the
operating amount of the brake operating member.
SUMMARY OF THE INVENTION
[0008] It is an object of this invention to provide an electrically
operated braking system which obtains an actual relationship
between the amount of electric power supplied to an electric motor
and the braking torque generated by the brake, and utilizes the
obtained relationship.
[0009] The above object may be achieved according to any one of the
following modes or embodiments of the present invention, which are
numbered to indicate possible combinations of various features of
the invention:
[0010] (1) An electrically operated braking system of a motor
vehicle having a wheel, comprising: (a) a rotor rotating with the
wheel; (b) a brake operating member which is operated by an
operator of the motor vehicle; (c) an electric power source; (d) a
brake including a friction member movable to be forced onto the
rotor, and an electric motor which is operated by an electric power
supplied from the electric power source, to generate a drive force
for forcing the friction member onto the rotor and thereby braking
the wheel; and (e) a controller which determines an amount of the
electric power to be supplied from the electric power source to the
electric motor, depending upon an operating amount of the brake
operating member, for thereby controlling an operation of the
brake, the braking system being characterized by further comprising
(e) a relationship estimating and utilizing device for obtaining an
actual value of the electric power supplied from the electric power
source to the electric motor during an operation of the brake while
the motor vehicle is running, and an actual value of a braking
torque applied from the brake to the wheel during the operation of
the brake. The relationship estimating and utilizing device is
adapted to estimate a relationship between the electric power to be
supplied to the electric motor and the braking torque to be applied
to the wheel, on the basis of the actual values obtained, and
utilize the relationship. The relationship is formulated such that
the braking torque to be applied to the wheel being changed with a
change in the electric power to be supplied to the electric
motor.
[0011] In the braking system constructed according to the above
mode (1) of the present invention, the relationship estimating and
utilizing device is capable of obtaining the relationship between
the electric power to be supplied to the electric motor of the
brake and the braking torque to be applied from the brake to the
wheel. The relationship estimating and utilizing device is further
adapted to utilize the obtained relationship for various purposes,
for instance, for controlling the brake and providing the vehicle
operator with information helpful to operate the vehicle.
[0012] The electric power to be applied to the electric motor may
be expressed by a voltage or current. The electric motor of the
brake may be a ultrasonic motor or DC motor. The operating amount
of the brake operating member may be expressed as an operating
force acting on the brake operating member, or an operating stroke
or distance of the brake operating member. The operation of the
brake while the vehicle is running may be a normal operation
initiated by an operation of the brake operating member by the
vehicle operator, or a special operation which is performed without
an operation of the brake operating member, for the sole purpose of
estimating the above-indicated relationship.
[0013] (2) An electrically operated braking system according to the
above mode (1), wherein said relationship is a pattern of change of
said braking torque with a change of said electric power, and said
relationship estimating and utilizing device comprises relationship
estimating means for selecting one of a plurality of candidate
patterns which corresponds to a combination of the actual values
obtained during the operation of the brake while the motor vehicle
is running.
[0014] (3) An electrically operated braking system according to the
above mode (2), wherein said relationship estimating means includes
pattern memory means for storing the above-indicated plurality of
candidate patterns, and pattern selecting means for selecting the
above-indicated one of the plurality of candidate patterns stored
in the pattern memory means.
[0015] (4) An electrically operated braking system according to any
one of the above modes (1)-(3), wherein the relationship estimating
and utilizing device obtains the above-indicated relationship from
a plurality of different relationships between the electric power
to be supplied to the electric motor and the braking torque to be
applied to the wheel.
[0016] In the braking system according to the above mode (4), the
control load of the relationship estimating and utilizing device is
made smaller than in the braking system in which the relationship
is estimated in a continuous fashion.
[0017] (5) An electrically operated braking system according to any
one of the above modes (1)-(4), wherein the controller includes the
relationship estimating and utilizing device, and the relationship
estimating and utilizing device includes relationship utilizing
means for determining an desired value of the braking torque on the
basis of the operating amount of the brake operating member, and
determining the value of the electric power to be supplied to the
electric motor, on the basis of the determined desired value of the
braking torque and according to the estimated relationship.
[0018] In this braking system, the electric motor to be supplied to
the electric motor during an operation of the brake is determined
according to the actual relationship between the electric motor and
the braking torque, as well as depending upon the operating amount
of the brake operating member, so that the brake can be accurately
controlled so as to provide the braking torque corresponding to the
operating amount of the brake operating member, irrespective of a
variation in the friction coefficient of the friction members used
in the brake.
[0019] (6) An electrically operated braking system according to any
one of claims 1-5, wherein the relationship estimating and
utilizing device includes means for supplying a predetermined
amount of the electric power from the electric power source to the
electric motor for a predetermined length of time to thereby
activate the brake while the motor vehicle is running without an
operation of the brake operating member, and obtaining the actual
values of the electric power and the braking torque during
activation of the brake.
[0020] In the braking system according to the above mode (6), the
brake is activated for the sole purpose of estimating the
relationship, while the brake operating member is not in operation,
that is, while the vehicle is running under a condition that does
not require a normal operation of the brake. Since the relationship
is estimated in this condition without an operation of the brake
operating member, the accuracy of estimation of the relationship is
made relatively high.
[0021] In a usual run of the motor vehicle, the relationship
estimating and utilizing device is operated to activate the brake
for estimating the relationship, prior to a normal operation of the
brake by an operation of the brake operating member by the vehicle
operator. Accordingly, the estimated actual relationship between
the electric power to be supplied to the electric motor of the
brake and the braking torque to be generated by the brake can be
utilized to control the brake upon initial activation of the brake
during the vehicle run.
[0022] While the actual value of the braking torque generated by
the brake with the predetermined amount of the electric power
supplied to the electric motor is obtained while the brake
operating member is not in operation, the estimation of the
relationship on the basis of the above-indicated predetermined
amount of the electric power and the obtained braking torque may be
effected either immediately after the actual braking torque value
is obtained during running of the vehicle without an operation of
the brake operating member, or during the next normal operation of
the brake initiated by an operation of the brake operating
member.
[0023] (7) An electrically operated braking system according to the
above mode (6), wherein the means for supplying the predetermined
amount of the electric power to the electric motor for the
predetermined length of time while the vehicle is running without
an operation of the brake operating member comprises a brake
operation detecting sensor for detecting an operation of the brake
operating member, and a vehicle run detecting sensor for detecting
a running of the vehicle, and activates the brake by suppling the
predetermined amount of the electric power to the electric motor
when the above sensors detect that the vehicle is running without
an operation of the brake operating member.
[0024] (8) An electrically operated braking system according to the
above mode (6) or (7), wherein the motor vehicle has a front left
wheel and a front right wheel, and the braking system comprises the
brake for each of the front left and right wheels, and wherein the
means for supplying the predetermined amount of the electric power
to the electric motor while the vehicle is running without an
operation of the brake operating member is adapted to concurrently
activate the brakes for the two front wheels.
[0025] In this braking system wherein the brakes for the front left
and right wheels are concurrently activated while the vehicle is
running without an operation of the brake operating member, the
same amounts of the electric power are preferably applied to the
electric motors for the two front brakes to generate the same
braking torque, so as to avoid generation of a yaw moment acting on
the vehicle body during activation of the front brakes by the
relationship estimating and utilizing device. This arrangement is
effective to prevent yawing of the vehicle during activation of the
front brakes by the relationship estimating and utilizing device,
which may be felt unusual or abnormal by the vehicle operator.
[0026] (9) An electrically operated braking system according to any
one of the above modes (6)-(8), wherein the motor vehicle has a
front wheel and a rear wheel, and the braking system comprises the
brake for each of the front and rear wheels, and wherein the means
for supplying the predetermined amount of the electric power to the
electric motor while the motor vehicle is running without an
operation of the brake operating member is adapted to activate the
brakes for the front and rear wheels at different times.
[0027] In the braking system according to the above mode (9)
wherein the deceleration value of the vehicle body during
activation of the brake for each of the front and rear wheels is
made lower than in the braking system wherein the brakes for the
front and rear wheels are activated concurrently. This arrangement
makes it possible to estimate the relationship without the vehicle
operator feeling unusual or uncomfortable with excessive
deceleration of the vehicle while the vehicle is running without an
operation of the brake operating member. Further, the predetermined
amount of the electric power to be supplied to the electric motor
of the brake for each of the front and rear wheels can be increased
to improve the accuracy of estimation of the relationship, because
the two brakes for the front and rear wheels are activated at
different times, with the relatively low deceleration value of the
vehicle body during activation of each brake.
[0028] (10) An electrically operated braking system according to
any one of the above modes (6)-(9), wherein said means for
supplying the predetermined amount of the electric power to the
electric motor while the vehicle is running without an operation of
the brake operating member is operated to activate the brake only
once during a run of the motor vehicle, to, obtain the actual value
of the braking torque to be applied to the wheel.
[0029] (11) An electrically operated braking system according to
the above mode (10), further comprising a vehicle start member
which is operated by the vehicle operator when the run of the
vehicle is initiated, and wherein the means for suppling the
predetermined amount of the electric power to the electric motor
determines, upon operation of the vehicle start member, that the
run of the vehicle has been initiated.
[0030] (12) An electrically operated braking system according to
any one of the above modes (1)-(11), wherein the relationship
estimating and utilizing device comprises standard relationship
utilizing means for provisionally utilizing a predetermined
standard relationship stored in a memory, before said relationship
is estimated for the first time during a run of the motor vehicle
on the basis of the actual values of the electric power and braking
torque which are obtained during activation of the brake without an
operation of the brake operating member.
[0031] (13) An electrically operated braking system according to
any one of the above modes (1)-(11), wherein the relationship
estimating and utilizing device stores in a memory the relationship
which is estimated during each run of the motor vehicle, and before
the relationship is estimated during a present run of the vehicle,
provisionally utilizes the relationship which was obtained during
the preceding run of the motor vehicle and which is stored in the
memory.
[0032] In the braking system according to the above mode (13), the
stored relationship obtained during the preceding run of the
vehicle is provisionally utilized until the relationship is
obtained during the present run of the vehicle. The relationship
which was actually obtained during the preceding run of the vehicle
is more reliable than the standard relationship which is not
actually obtained.
[0033] (14) An electrically operated braking system according to
any one of the above modes (1)-(5), wherein the relationship
estimating and utilizing device comprises means for obtaining the
actual values of the electric power supplied to the electric motor
and the braking torque generated by the brake activated while the
vehicle is running with an operation of the brake operating member,
and estimates the relationship on the basis of the above-indicated
actual values.
[0034] The braking system according to the above mode (14) may
include the feature according to any one of the above modes (11),
(12) and (13).
[0035] (15) An electrically operated braking system according to
any one of the above modes (11)-(14), further comprising a driver
connected between the electric power source and the electric motor
so that the electric power is supplied from the electric power
source to the electric motor through the driver according to an
external control command applied to the driver, and the
relationship estimating and utilizing device electric power
estimating means for estimating the actual value of the electric
power supplied from the electric power source to the electric
motor, on the basis of the external control command, and for
estimating the relationship on the basis of the estimated actual
value of the electric power.
[0036] The braking system according to the above mode (15) does not
require an electric power sensor for detecting the electric power
actually supplied to the electric motor, since the actual value of
the electric power supplied to the electric motor is estimated from
the control command applied to the driver. Where the relationship
estimating and utilizing device comprises the means for suppling
the predetermined amount of the electric power to the electric
motor while the vehicle is running without an operation of the
brake operating member, as described above with respect to the mode
(5) of this invention, this means applies the control command to
the driver. Where the relationship estimating and utilizing device
comprises means for obtaining the actual values of the electric
power supplied to the electric motor and the braking torque
generated by the brake activated while the vehicle is running with
an operation of the brake operating member, as described above with
respect to the mode (14) of this invention, the controller for the
brake applies the control command to the driver.
[0037] (16) An electrically operated braking system according to
any one of the above modes (1)-(14), wherein the relationship
estimating and utilizing device comprises an electric power sensor
for detecting the electric power actually supplied to the electric
motor, and estimates the relationship on the basis of the actual
value of the supplied electrical power detected by the electric
power sensor.
[0038] The value of the electric power represented by the control
command applied to the driver is not necessarily equal to the value
of the electric power actually supplied to the electric motor.
Further, the value of the electric power actually supplied to the
electric motor may vary with a change in the load of the electric
motor, even when the same control command is applied to the driver.
Therefore, the actual value of the electric power supplied to the
electric motor may not be estimated with high accuracy in the
braking system according to the above mode (15). In this respect,
the braking system according to the above mode (16) in which the
actually supplied electric power is detected by the sensor permits
improved accuracy of estimation of the actual relationship between
the electric motor to be supplied to the electric motor and the
braking torque to be generated by the brake.
[0039] (17) An electrically operated braking system according to
any one of the above modes (1)-(16), wherein the relationship
estimating and utilizing device comprises a braking torque sensor
for detecting the actual value of the braking torque applied from
the brake to the wheel, and estimates the relationship on the basis
of the actual value of the braking torque detected by the braking
torque sensor.
[0040] (18) An electrically operated braking system according to
any one of the above modes (1)-(16), wherein the relationship
estimating and utilizing device includes vehicle deceleration
detecting means for detecting a deceleration value of the motor
vehicle, and obtains the actual value of the braking torque on the
basis of the deceleration value detected by the vehicle
deceleration detecting means.
[0041] In the braking system according to the above mode (18), the
actual value of the braking torque is obtained on the basis of the
detected deceleration value of the vehicle, based on a fact that
the vehicle deceleration value increases with an increase in the
actual braking torque. In this respect, it is also noted that the
vehicle deceleration value can be detected more easily than the
actual braking torque. That is, the actual value of the braking
torque can be obtained relatively easily on the basis of the
detected vehicle deceleration value.
[0042] The vehicle deceleration detecting means may be adapted to
directly detect the deceleration value of the vehicle body, or may
be a combination of a vehicle speed sensor for detecting the
running speed of the vehicle, and means for calculating the
deceleration value of the vehicle based on the detected vehicle
running speed. Alternatively, the vehicle deceleration detecting
means may comprise wheel speed sensors for detecting rotating
speeds of a plurality of wheels of the motor vehicle, vehicle speed
estimating means for determining as an estimated vehicle running
speed a highest one of the wheel speeds detected by the respective
wheel speed sensors (on the basis of a fact that the highest wheel
speed is closest to the actual running speed of the vehicle), and
vehicle deceleration calculating means for calculating the
deceleration value of the vehicle on the basis of the estimated
vehicle running speed.
[0043] (19) An electrically operated braking system according to
any one of the above modes (1)-(16), wherein the relationship
estimating and utilizing device comprises vehicle deceleration
detecting means for detecting a deceleration value of the motor
vehicle while a gradient of a road surface on which the motor
vehicle is running is substantially zero, and obtains the actual
value of the braking torque on the basis of the deceleration value
detected by the vehicle deceleration detecting means.
[0044] While the vehicle deceleration value increases with an
increase in the actual braking torque, as described above, the
vehicle deceleration value may vary with the gradient of the road
surface, even when the actual braking torque is kept constant.
Based on this fact, the vehicle deceleration detecting means used
in the braking system according to the above mode (19) is adapted
to detect the vehicle deceleration value while the road surface
gradient is substantially zero, and the relationship estimating and
utilizing means is adapted to obtain the actual braking torque
based on the vehicle deceleration value detected while the road
surface gradient is substantially zero. Thus, the actual braking
torque can be obtained with high accuracy based on the detected
vehicle deceleration value.
[0045] (20) An electrically operated braking system according to
any one of the above modes (1)-(16), wherein the relationship
estimating and utilizing device includes a wheel speed sensor for
detecting a rotating speed of the wheel, obtains a deceleration
value of the wheel on the basis of a rate of change of the rotating
speed of the wheel detected by the wheel speed sensor, and obtains
the actual value of the braking torque on the basis of the
deceleration value of the wheel obtained.
[0046] In the braking system according to the above mode (20), the
actual value of the braking torque is obtained on the basis of the
detected deceleration value of the vehicle wheel, based on a fact
that the wheel deceleration value increases with an increase in the
actual braking torque. In this respect, it is also noted that the
wheel deceleration value can be detected more easily than the
actual braking torque. That is, the actual value of the braking
torque can be obtained relatively easily on the basis of the
detected wheel deceleration value.
[0047] Where the braking system comprises a plurality of brakes for
respective wheels, the deceleration value of the vehicle is
influenced by the braking effects provided by all or some of the
brakes which are activated. Therefore, it is difficult to
accurately obtain the actual braking effect of the brake for each
wheel based on the deceleration value of the vehicle. In the
braking system according to the above mode (20), however, the
actual braking torque generated by the brake for each wheel can be
accurately obtained on the basis of the rate of change of the
rotating speed of the wheel. According to this arrangement, the
relationship between the electric power to be supplied to the
electric motor and the braking torque to be generated by the brake
can be estimated for each of the plurality of wheels, so that the
estimated relationship can be utilized for controlling the brake
for each wheel, depending upon the specific condition of each
brake.
[0048] (21) An electrically operated braking system according to
the above mode (6) or (7), wherein the brake is provided for each
of a plurality of wheels provided for the motor vehicle, and the
means for supplying the predetermined amount of the electric power
to the electric motor while the motor vehicle is running without an
operation of the brake operating member is adapted to activate the
brakes for the respective wheels at different times, detect the
deceleration values of the motor vehicle during the activation of
the respective brakes, and obtain the actual value of the braking
torque of each brake on the basis of the vehicle deceleration value
detected during the activation of that brake.
[0049] In the braking system according to the above mode (21)
wherein the brakes for the respective wheels are activated at
different times during running of the motor vehicle without an
operation of the brake operating member, the vehicle deceleration
values are detected during the activation of the respective brakes.
In this arrangement, the vehicle deceleration value detected during
activation of a given one of the brakes reflects only the actual
braking torque generated by that brake. Thus, the actual braking
torque of each brake can be accurately obtained based on the
vehicle deceleration value detected during operation of that brake,
and the relationship can be obtained for each of the brakes.
[0050] (22) An electrically operated braking system according to
the above mode (6) or (7), wherein the brake is provided for each
of a front wheel and a rear wheel provided for the motor vehicle,
and the means for supplying the predetermined amount of the
electric power to the electric motor while the motor vehicle is
running without an operation of the brake operating member is
adapted to concurrently activate the brakes for the respective
wheels, detect the deceleration value of the motor vehicle during
the concurrent activation of the brakes, obtain the actual values
of the braking torque values of the brakes for the front and rear
wheels on the basis of the detected vehicle deceleration value, and
estimate the relationship on the basis of the obtained actual
braking torque value of each brake.
[0051] In the braking system according to the above mode (22)
wherein the brakes for the front and rear wheels are concurrently
activated, the required time of activation of the brakes can be
reduced as compared with the required time where the brakes are
activated at different times.
[0052] Since the brakes for the front and rear wheels are
concurrently activated, the vehicle deceleration value detected is
influenced by both of the actual braking torque values of the front
and rear brakes. However, the actual braking torque values of the
front and rear brakes can be estimated by calculation based on the
detected vehicle deceleration value, and the relationship for each
of the front and rear wheels is estimated on the basis of the
actual braking torque value obtained for each wheel, although the
vehicle deceleration value detected during the concurrent
activation of the front and rear brakes is influenced by the actual
braking torque values of the respective brakes.
[0053] (23) An electrically operated braking system according to
the above mode (6) or (7), further comprising first inhibiting
means for inhibiting the relationship estimating and utilizing
device from operating the brake to obtain the relationship while
the motor vehicle is running under a condition in which the
operation of the brake is likely to be felt unusual or
uncomfortable by the operator of the motor vehicle.
[0054] In the braking system according to the above mode (23) of
this invention, the actual braking torque of the brake during
activation of the brake without an operation of the brake operating
member can be obtained without the vehicle operator feeling unusual
with the activation of the brake.
[0055] (24) An electrically operated braking system according to
the above mode (23), wherein the first inhibiting means includes
means for inhibiting the relationship estimating and utilizing
device from operating the brake when the motor vehicle is running
at a speed lower than a predetermined threshold.
[0056] In the braking system according to the above mode (24), the
operation of the relationship estimating and utilizing device
without an operation of the brake operating member is inhibited
when the vehicle running speed is lower than the predetermined
lower limit. This arrangement is based on a finding that the
vehicle operator is more likely to feel unusual or uncomfortable
with the activation of the brake during running of the vehicle at a
relatively low speed, than at a relatively high speed.
[0057] (25) An electrically operated braking system according to
the above mode (24), wherein said means for inhibiting the
relationship estimating and utilizing device from operating the
brake when the vehicle is running at a speed lower than a
predetermined threshold includes vehicle speed detecting means for
detecting the running speed of the vehicle, and inhibits the
operation of the relationship estimating and utilizing means from
operating to activate the brake when the detected vehicle running
speed is lower than the predetermined threshold.
[0058] In the braking system according to the above mode (25), the
vehicle speed detecting means may be adapted to directly detect the
running speed of the vehicle. Alternatively, the vehicle speed
detecting means comprises wheel speed sensors for detecting
rotating speeds of respective wheels of the vehicle, and vehicle
speed estimating means for determining as an estimated vehicle
running speed a highest one of the wheel speeds detected by the
respective wheel speed sensors on the basis of a fact that the
highest wheel speed is closest to the actual running speed of the
vehicle.
[0059] (26) An electrically operated braking system according to
any one of the above modes (23)-(25), wherein said first inhibiting
means comprises means for inhibiting the relationship estimating
and utilizing means from operating the brake when the vehicle is
turning.
[0060] In the braking system according to the above mode (26), the
operation of the relationship estimating and utilizing means is
inhibited during turning of the vehicle, based on a finding that
the operation of the brake during turning of the vehicle is likely
to cause the vehicle to have a behavior which is felt unusual or
comfortable by the vehicle operator.
[0061] (27) An electrically operated braking system according to
the above mode (26), wherein the means for inhibiting the
relationship estimating and utilizing means from operating the
brake when the vehicle is turning includes a vehicle turning sensor
for detecting turning of the vehicle, and inhibits the operation of
the relationship estimating and utilizing device to activate the
brake when the turning of the vehicle is detected by the vehicle
turning sensor.
[0062] (28) An electrically operated braking system according to
any one of the above modes (1)-(27), further comprising second
inhibiting means for inhibiting the relationship estimating and
utilizing device from at least utilizing the relationship while the
motor vehicle is running under a condition in which the
relationship estimating and utilizing device is not likely to
accurately estimate the relationship.
[0063] In the braking system according to the above mode (28), the
relationship estimating and utilizing device is inhibited from at
least utilizing the relationship while the motor vehicle is running
under a condition in which the relationship estimating and
utilizing device is not likely to accurately estimate the
relationship. This arrangement is based on a finding that the
relationship cannot always be estimated with high accuracy. Thus,
the present arrangement assures increased reliability of the
relationship estimating and utilizing device. Where the estimated
relationship is utilized to control the brake, the relationship
estimated in the above-indicated running condition of the vehicle
is not utilized for controlling the vehicle, whereby the accuracy
of control of the brake is improved.
[0064] (29) An electrically operated braking system according to
the above mode (28), wherein the second inhibiting means includes
means for inhibiting the relationship estimating and utilizing
device from at least utilizing the relationship while a drive force
for driving the motor vehicle is being changed.
[0065] In the braking system according to the above mode (28), the
relationship estimating and utilizing device is inhibited from at
least utilizing the relationship while the motor vehicle is running
with a drive force being changed. This arrangement is based on a
finding that the relationship is not likely to be estimated
accurately while the drive force for driving the vehicle is being
changed. The vehicle drive force may be changed due to a change in
the output of a drive power source of the vehicle, or in the speed
ratio of a power transmission of the vehicle as described
below.
[0066] (30) An electrically operated braking system according to
the above mode (28), wherein the motor vehicle includes a drive
power source for driving the motor vehicle, and an accelerator
operating member which is operated by the operator of the motor
vehicle to increase an output of the drive power source for
accelerating the motor vehicle, and wherein said means for
inhibiting the relationship estimating and utilizing device from at
least utilizing the relationship comprises means for inhibiting the
relationship estimating and utilizing device from at least
utilizing the relationship while said accelerator operating member
is in operation.
[0067] In the braking system according to the above mode (30), the
relationship estimating and utilizing device is inhibited from at
least utilizing the relationship during operation of the
accelerator operating member. This arrangement is based on a
finding that the relationship is not likely to be estimated
accurately while the accelerator operating member is in operation.
The drive power source may be an engine such as an internal
combustion engine, or an electric motor, or a combination of an
engine and an electric motor.
[0068] The accelerator operating member may be considered to be "in
operation", when the accelerator operating member is placed in one
of the following states: a first transient state in which the
accelerator operating member is operated to increase the output of
the drive power source to accelerate the motor vehicle; a steady
state in which the accelerator operating member is held at the same
position to maintain the output of the drive power source at the
same value; and a second transient state in which the accelerator
operating member is operated to reduce the output of the drive
power source to decelerate the motor vehicle. However, the
accelerator operating member may be considered to be "in operation"
only when the accelerator operating member is placed in the first
transient state, or in the first or second transient state. In
other words, the relationship estimating and utilizing device may
be inhibited from at least utilizing the relationship when the
accelerator operating member is in one of the first and second
transient states and the steady state, or in one of the first and
second transient states, or in the first transient state.
[0069] The operating state of the accelerator operating member may
be detected by either a switch for detecting whether the
accelerator operating member is placed in a non-operated position
or an operated position, or a position sensor capable of
continuously detecting an amount of operation of the accelerator
operating member from the non-operated position. The switch is
usually used for detecting a moment at which the accelerator
operating member is operated from the non-operated position to an
operated position, or returned from the operated position to the
non-operated position. However, this switch cannot detect a change
in the operating position of the accelerator operating member, or
the operating amount of the accelerator operating member. That is,
while the switch is capable of detecting whether the accelerator
operating member is in operation or not, but is not capable of
detecting whether the accelerator operating member is placed in the
first transient state (vehicle accelerating state) or the second
transient (vehicle decelerating state), or held in the steady state
(same operating position). On the other hand, the position sensor
is capable of detecting whether the accelerator operating member is
placed in the first transient or accelerating state or in the
second transient or decelerating state. The above-indicated switch
may be a switch for detecting an operation of an accelerator pedal
as the accelerator operating member. The above-indicated sensor may
be a sensor for detecting an amount of operation of the accelerator
pedal, or a sensor for detecting an angle of opening of a throttle
valve provided in an intake valve of an engine (internal combustion
engine) which is provided as the drive power source. The throttle
valve may be operated according to only an operation of the
accelerator operating member, or according to selectively an
operation of the accelerator operating member or a control command
applied to an electrically operated throttle actuator provided for
automatically operating the throttle valve. To accurately detect a
change in the output of the engine, the throttle valve sensor for
detecting the opening angle of the throttle valve is preferably
used.
[0070] (31) An electrically operated braking system according to
the above mode (29), wherein the motor vehicle includes an engine
for driving the vehicle, and a fuel supply device for supplying a
fuel to a combustion chamber of the engine, and wherein the means
for inhibiting the relationship estimating and utilizing device
from at least utilizing the relationship while the drive force for
driving the engine is being changed comprises means for inhibiting
the relationship estimating and utilizing device from at least
utilizing the relationship when the fuel supply device is switched
between an operated state thereof in which the fuel is supplied to
the combustion chamber and a non-operated state thereof in which
the fuel is not supplied to the combustion chamber.
[0071] In the braking system according to the above mode (31), the
relationship estimating and utilizing device is inhibited from at
least utilizing the relationship when the fuel supply device is
switched between the operated and non-operated state. This
arrangement is based on a finding that the relationship is not
likely to be estimated accurately when the fuel supply device is
switched between the operated and non-operated states.
[0072] In a certain type of motor vehicles, the fuel supply device
may be switched between the operated and non-operated states, even
while the accelerator operating member is not in operation. In this
type of motor vehicle wherein the relationship is not likely to be
estimated accurately due to a change in the output of the engine
even while the accelerator operating member is not in operation,
the arrangement according to the above mode (31) is effective to
prevent utilization of the relationship estimated while the engine
output is changing.
[0073] (32) An electrically operated braking system according to
any one of the above modes (29)-(31), wherein the motor vehicle
includes a drive power source, and a power transmission for
transmitting the drive force of the drive power source to the wheel
at a selected one of a plurality of speed ratios, and wherein the
means for inhibiting the relationship estimating and utilizing
device from at least utilizing the relationship comprises means for
inhibiting the relationship estimating and utilizing device from at
least utilizing the relationship while the power transmission is in
the process of a shifting action to change the speed ratio.
[0074] In the braking system according to the above mode (32), the
relationship estimating and utilizing device is inhibited from at
least utilizing the relationship while the power transmission is in
the process of a shifting action. This arrangement is based on a
finding that the relationship is not likely to be estimated
accurately in the process of a shifting action of the power
transmission.
[0075] (33) An electrically operated braking system according to
the above mode (32), wherein the means for inhibiting the
relationship estimating and utilizing device from at least
utilizing the relationship while the power transmission is in the
process of a shifting action comprises a shift sensor for detecting
the shifting action of the power transmission.
[0076] (34) An electrically operated braking system according to
any one of the above modes (28)-(33), wherein the second inhibiting
means includes means for inhibiting the relationship estimating and
utilizing device from at least utilizing the relationship while the
motor vehicle is turning.
[0077] In the braking system according to the above mode (34), the
relationship estimating and utilizing device is inhibited from at
least utilizing the relationship during turning of the vehicle.
This arrangement is based on a finding that the relationship is not
likely to be estimated accurately while the vehicle is turning.
[0078] (35) An electrically operated braking system according to
the above mode (34), wherein the means for inhibiting the
relationship estimating and utilizing device from at least
utilizing the relationship while the motor vehicle is turning
includes a vehicle turning sensor for detecting a turning of the
motor vehicle.
[0079] (36) An electrically operated braking system according to
any one of the above modes (28)-(35), wherein the second inhibiting
means comprises means for inhibiting the relationship estimating
and utilizing device from at least utilizing the relationship while
the motor vehicle is running on a bad road surface.
[0080] In the braking system according to the above mode (36), the
relationship estimating and utilizing device is inhibited from at
least utilizing the relationship during running of the vehicle on a
bad road surface This arrangement is based on a finding that the
relationship is not likely to be estimated accurately while the
vehicle is running of a bad road surface.
[0081] The bad road surface may be a graveled road surface, a
Belgian brick- or stone-paved road surface, a non-paved road
surface, or any other bumpy road surface.
[0082] (37) An electrically operated braking system according to
the above mode (36), wherein the means for inhibiting the
relationship estimating and utilizing device from at least
utilizing the relationship while the motor vehicle is running on a
bad road surface includes means for detecting the bad road
surface.
[0083] (38) An electrically operated braking system according to
any one of the above modes (28)-(37), wherein the second inhibiting
means comprises means for inhibiting the relationship estimating
and utilizing device from at least utilizing the relationship while
a slip ratio of the wheel is higher than a predetermined
threshold.
[0084] (39) An electrically operated braking system according to
the above mode (38), wherein the means for inhibiting the
relationship estimating and utilizing device from at least
utilizing the relationship while the slip ratio of the wheel is
higher than a predetermined threshold includes means for detecting
that the slip ratio is higher than the predetermined threshold.
[0085] (40) An electrically operated braking system according to
any one of the above modes (1)-(39), wherein said relationship
estimating and utilizing device comprises means braking torque
obtaining means for obtaining the actual value of the braking
torque for obtaining the actual value of the braking torque on the
basis of a rate of change of the deceleration value of the motor
vehicle or a rate of change of the deceleration value of the
wheel.
[0086] Where the actual value of the braking torque of the brake is
obtained on the basis of the deceleration value of the motor
vehicle or the drive wheel, the obtained actual value of the
braking torque is likely to be influenced by the overall drive
force of the vehicle or the drive force of the drive wheel. Where
the actual value of the braking torque is obtained on the basis of
the rate of change of the vehicle or wheel deceleration value, the
obtained actual value of the braking torque is relatively less
likely to be influenced by the drive force. In the braking system
according to the above mode (40), therefore, the actual value of
the braking torque can be obtained with a reduced influence by the
drive force of the vehicle or drive wheel.
[0087] (41) An electrically operated braking system according to
any one of the above modes (1)-(40), wherein the brake includes a
self-servo mechanism operated such that a friction force between
the friction member and the rotor is increased by the friction
force.
[0088] Referring to the graph of FIG. 8, there are indicated a
plurality of I-T relationships between an electric current I
(electric power) to be supplied to the electric motor and the
braking torque T in the brake including a self-servo mechanism,
which relationship correspond to respective different values .mu.
of a friction coefficient of the friction member. It will be
understood from the graph that the rate of increase of the braking
torque T with an increase in the electric current I is higher when
the friction coefficient .mu. of the friction member is relatively
high than when it is relatively low. Where the brake includes the
self-servo mechanism, therefore, the need of estimating the actual
relationship between the electric power and the braking torque and
utilizing the estimated relationship for controlling the brake is
relatively high. This need is satisfied in the braking system
according to the above mode (41), wherein the braking torque
generated by the brake can be accurately controlled in relation to
the operating amount of the brake operating member, even where the
brake is provided with the self-servo mechanism.
[0089] (42) An electrically operated braking system according to
the above mode (41), wherein the brake including the self-servo
mechanism includes a drum brake which has brake linings as the
friction member and a drum as the rotor.
[0090] (43) An electrically operated braking system according to
the above mode (41) or (42), wherein the brake including the
self-servo mechanism includes a disc brake which has brake pads as
the friction member and a disc as the rotor.
[0091] (44) An electrically operated braking system according to
any one of the above modes (1)-(39), wherein the relationship
estimating and utilizing device obtains the actual value of the
braking torque on the basis of a change in a running condition of
the motor vehicle due to the operation of the brake.
[0092] The "change in a running condition of the motor vehicle"
indicated above may include a change in the deceleration value of
the motor vehicle.
[0093] (45) An electrically operated braking system according to
any one of the above modes (1)-(39), wherein the relationship
estimating and utilizing device comprises means for obtaining the
actual value of the braking torque on the basis of a change in a
rotating state of the wheel due to the operation of the brake.
[0094] The "change in a rotating state of the wheel" indicated
above may include a change the deceleration value of the wheel, and
a rate of change of the deceleration value of the wheel.
[0095] (46) An electrically operated braking system according to
any one of the above modes (1)-(45), wherein the brake includes a
support member for supporting the friction member in frictional
contact with the rotor so as to prevent the friction member from
being rotated with the rotor, and the relationship estimating and
utilizing device includes a force switch which is interposed
between the friction member and the support member, so as to
receive a force from the friction member in frictional contact with
the rotor, the force switch being selectively placed in one of two
states, depending upon whether the force received from the friction
member is larger than a predetermined threshold which is not zero,
the relationship estimating and utilizing device utilizing an
output of the force switch to obtain the actual value of the
braking torque.
[0096] (47) An electrically operated braking system according to
the above mode (46), wherein the rotor is a disc having a friction
surface, and the friction member is a brake pad which is movable
into frictional contact with the friction surface, the force switch
being disposed in a position at which a spacing between the brake
pad and the support member decreases with an increase in an amount
of rotation of the brake pad with the disc.
[0097] (48) An electrically operated braking system according to
the above mode (46) or (47), wherein the relationship estimating
and utilizing device further includes a pressing-force-related
quantity sensor whose output varies continuously with a quantity
relating to a pressing force generated by the electric motor to
force the friction member onto the rotor, the relationship
estimating and utilizing device using the output of the
pressing-force-related quantity sensor as a quantity relating to
the actual value of the electric power supplied to the electric
motor.
[0098] (49) An electrically operated braking system according to
the above mode (48), wherein the the relationship estimating and
utilizing device further includes a braking force estimating device
for estimating the braking torque to be applied to the wheel, on
the basis of the output of the pressing-force-related quantity
sensor and according to a predetermined relationship between the
output and the braking torque, the braking force estimating device
compensating the predetermined relationship on the basis of the
output when the force switch is switched from one of the two states
to the other states.
[0099] (50) An electrically operated braking system according to
the above mode (49), wherein the braking force estimating device
includes relationship compensating means for compensating the
predetermined relationship, on the basis of a difference between an
actual value of the output and a nominal value of the output when
the force sensor is switched from one of the two states to the
other.
[0100] (51) An electrically operated braking system of a motor
vehicle having a wheel, comprising: (a) a rotor rotating with the
wheel; (b) a brake operating member which is operated by an
operator of the motor vehicle; (c) an electric power source; (d) a
brake including a friction member movable to be forced onto the
rotor, and an electric motor which is operated by an electric power
supplied from the electric power source, to generate a drive force
for forcing the friction member onto the rotor and thereby braking
the wheel; and (e) a controller which determines an amount of the
electric power to be supplied from the electric power source to the
electric motor, depending upon an operating amount of the brake
operating member, for thereby controlling an operation of the
brake, the braking system characterized by further comprising (f) a
relationship estimating and utilizing device for obtaining an
actual value of a physical quantity relating to the electric power
supplied from the electric power source to the electric motor
during an operation of the brake while the motor vehicle is
running, and an actual value of a physical quantity relating to a
braking torque applied from the brake to the wheel during the
operation of the brake, for estimating a relationship between the
electric power to be supplied to the electric motor and the braking
torque to be applied to the wheel, on the basis of the actual
values obtained, and for utilizing the relationship, the
relationship being formulated such that the braking torque to be
applied to the wheel being changed with a change in the electric
power to be supplied to the electric motor.
[0101] According to the present invention, there is also
provided:
[0102] (52) An electrically operated brake for a motor vehicle
having a wheel, comprising a rotor rotating with the wheel, a
friction member movable to be forced onto the rotor, an electric
motor operated to generate a drive force for forcing the friction
member onto the rotor, and a self-servo mechanism which is operated
such that a friction force between the friction member and the
rotor is increased by the friction force, the electrically operated
brake being characterized by further comprising a biasing mechanism
interposed between the friction member and a stationary member
which supports the friction member, the biasing mechanism biasing
the friction member in a direction for moving the friction member
away from the rotor.
[0103] In an electrically operated brake provided with a self-servo
mechanism, there is a general tendency that the friction member
cannot be moved away from the rotor with a high response to a
command generated to return the electric motor to its initial
position, once the self-servo mechanism is activated to provide a
self-servo effect. Therefore, the braking torque cannot be rapidly
reduced to zero. In the brake according to the above mode (52) in
which the biasing mechanism is provided, the biasing mechanism is
effective to rapidly move the friction member away from the rotor,
thereby permitting rapid reduction of the braking torque.
[0104] The biasing mechanism may be adapted to hold the friction
member in the biased state, or bias the friction member only when
it is required to rapidly reduce the braking torque.
[0105] (53) A braking system for a motor vehicle having a wheel,
comprising: (a) a rotor rotating with the wheel; (b) a friction
member movable to be forced onto the rotor, for braking the wheel;
(c) a support member for supporting the friction member in
frictional contact with the rotor so as to prevent the friction
member from being rotated with the rotor; (d) a pressing device for
forcing the friction member into frictional contact with the rotor;
and (e) a force switch which is interposed between the friction
member and the support member, so as to receive a force from the
friction member in frictional contact with the rotor, the force
switch being selectively placed in one of two states, depending
upon whether the force received from the friction member is larger
than a predetermined threshold which is not zero.
[0106] The braking system constructed according to the above mode
(53) of this invention provides an improvement over a conventional
braking system which uses a braking-force-related quantity sensor
for continuously detecting a physical quantity relating to braking
force generated by a brake. This sensor may be a strain gage using
an electrically resistive wire, or a piezoelectric sensor. The
quantity which is detected by the sensor and which relates to the
braking force changes over a relatively wide range. Accordingly, it
is generally difficult for the sensor to detect the quantity with
high accuracy over the entire range. Further, the operating
environment of the sensor is considerably severe. Namely, the
sensor may be subject to a considerable amount of change in the
operating temperature and a considerably intense vibration, and is
likely to be exposed to foreign matters such as mud, water and dust
or grit. Thus, the braking-force-related quantity sensor used in
the conventional braking system is not capable of detecting a
quantity relating to the braking force, with a high degree of
reliability, and does not have a satisfactory degree of
durability.
[0107] The force switch used according to the above mode of the
present invention is different from a sensor in that like a
commonly used switch, the force switch is not capable of
continuously detecting a physical quantity. However, the force
sensor is less likely to be influenced by the operating
environment, as compared with a sensor, since the force switch is
simpler in construction and operating principle. For instance, a
relationship between the actual value of the physical quantity and
the output of the force sensor is less likely to be influenced by
the operating environment, that a relationship between the actual
value of the quantity and the output of a sensor. Accordingly, the
force switch is capable of detecting, with high reliability and
durability, whether the force which the support member receives
from the friction member as a physical quantity relating to the
braking force has exceeded the predetermined value or has been
reduced to the predetermined value.
[0108] (54) A braking system according to the above mode (53),
wherein the rotor is a disc having a friction surface, and the
friction member is a brake pad which is movable into frictional
contact with the friction surface, the force switch being disposed
in a position at which a spacing between the brake pad and the
support member decreases with an increase in an amount of rotation
of the brake pad with the disc.
[0109] (55) A braking system according to the above mode (1) or
(2), wherein the force sensor is provided at each of a plurality of
positions between the friction member and the support member, and
the force sensors at the different positions have respective
different predetermined threshold values of the force received from
the friction member.
[0110] In the braking system according to the above mode (55), the
quantity relating to the braking force can be detected in two or
more steps by the respective force sensors.
[0111] (56) A braking system according to any one of the above
modes (53)-(55), wherein the force sensor includes a pair of
contacts which are movable relative to each other between two
positions corresponding to the above-indicated two states, and one
of the contacts is fixed to the friction member while the other
contact is fixed to the support member.
[0112] The force sensor in the braking system according to the
above mode (56) is relatively simple in construction and operating
principle, and accordingly assures increased operating reliability
and durability.
[0113] (57) A braking system according to the above mode (56),
wherein the contact fixed to the friction member is a movable
contact, while the contact fixed to the support member is a
stationary contact.
[0114] (58) A braking system according to any one of the above
modes (53)-(57), wherein the pressing device includes an electric
motor as a drive source, and does not use a pressurized hydraulic
fluid.
[0115] (59) A braking system according to any one of the above
modes (53)-(57), wherein the pressing device uses a pressurized
hydraulic fluid.
[0116] (60) A braking system according to any one of the above
modes (53)-(59), wherein the friction member, support member,
pressing device and force switch cooperate to constitute a major
portion of a brake, the braking system further comprising a brake
information obtaining device for obtaining brake information
relating to an operation of the brake.
[0117] In the braking system according to the above mode (60), the
brake information may include a friction coefficient of the
friction member, information as to whether the friction coefficient
of the friction member is unacceptably low or not, information as
to whether the brake is abnormal, and a friction coefficient
between the wheel and the road surface.
[0118] (61) A braking system according to any one of the above
modes (53)-(59), further comprising: a pressing-force-related
quantity sensor whose output varies continuously with a quantity
relating to a pressing force by which the friction member is forced
onto the rotor by the pressing device; and a friction coefficient
estimating device for estimating a friction coefficient of the
friction member, on the basis of a relationship between the output
of the pressing-force-related quantity sensor and the predetermined
threshold.
[0119] In the braking system according to the above mode (61), the
friction coefficient of the friction member can be estimated by the
friction coefficient estimating device, so that the braking system
can be controlled with high accuracy, by utilizing the estimated
friction coefficient.
[0120] (62) A braking system according to the above mode (61),
wherein the pressing device includes a presser member which is
disposed on one of opposite sides of the friction member remote
from the rotor, so as to force the friction member onto the rotor,
and the pressing-force-related quantity sensor includes a
pressing-force sensor provided on the presser member to
continuously detect a force which acts on the presser member in a
direction of movement of the presser member toward the friction
member.
[0121] (63) A braking system according to the above mode (61),
wherein the pressing device includes an electric motor for forcing
the friction member onto the rotor, and the pressing-force-related
quantity sensor includes an electric power sensor for continuously
detecting an amount of electric power supplied to the electric
motor.
[0122] (64) A braking system according to the above mode (63),
wherein the electric power sensor is a motor current sensor for
continuously detecting an amount of electric current supplied to
the electric motor.
[0123] (65) A braking system according to any one of the above
modes (61)-(64), wherein the above-indicated two states of the
force sensor consists of an on state and an off state, the state of
the force sensor being changed from one of the on and off states to
the other when the force received from the friction member has
increased and exceeded the above-indicated predetermined threshold,
and is changed from the above-indicated other state to the
above-indicated one state, and wherein the friction coefficient
estimating device estimates the friction coefficient of the
friction member when at least one of a change from the
above-indicated one state to the other state and a change from the
above-indicated other state to the above-indicated one state takes
place.
[0124] (66) A braking system according to the above mode (65),
wherein the friction coefficient estimating device estimates the
friction coefficient of the friction member when each of the
changes between the on and off states takes place.
[0125] In the braking system according to the above mode (66), the
friction coefficient is estimated at the two opportunities, namely,
when the force switch is turned on and when the force switch is
turned off. Accordingly, the accuracy of estimation of the friction
coefficient can be improved, as compared with the accuracy of
estimation where the friction coefficient is estimated only once,
that is, when the force switch is turned on or turned off.
[0126] (67) A braking system according to any one of the above
modes (61)-(66), wherein said friction coefficient estimating
device estimates the friction coefficient of the friction member,
by dividing the above-indicated predetermined threshold by the
quantity as detected by the pressing-force-related quantity sensor
when the state of the force switch is changed from one of the
above-indicated two states to the other.
[0127] (68) A braking system according to any one of the above
modes (61)-(67), further comprising a brake pad fade detecting
device for detecting that the friction coefficient estimated by the
friction coefficient estimating device is lower than a
predetermined lower limit.
[0128] (69) A braking system according to any one of the above
modes (53)-(59), wherein the friction member, support member,
pressing device and force switch cooperate to constitute a major
portion of a brake, the braking system further comprising: a
physical quantity sensor for detecting a physical quantity which
relates to an operation of the brake and which excludes a the force
acting on the force switch, the physical quantity changing in
relation to the force acting on the force switch, depending upon
whether the brake is abnormal or not; and a brake failure detecting
device for detecting whether the brake is abnormal or not, on the
basis of a relationship between an output of the physical quantity
sensor and an output of the force sensor.
[0129] (70) A braking system according to any one of the above
modes (53)-(59), wherein the friction member, support member,
pressing device and force switch cooperate to constitute a major
portion of a brake, the braking system further comprising a road
surface friction coefficient estimating device for estimating a
friction coefficient between the wheel and a road surface on which
the motor vehicle is running, on the basis of an output of the
force switch.
[0130] (71) A braking system according to any one of the above
modes (53)-(70), wherein said pressing device includes an electric
motor for forcing the friction member onto the rotor, and
cooperates with the rotor, friction member, support member and
force sensor to constitute an electrically operated brake, the
braking system further comprising a mechanically operated brake
which is operated mechanically to brake the wheel by a force
generated by a manually operated brake operating member, and a
manual brake control device disposed between the mechanically
operated brake and the brake operating member, for permitting an
operation of the mechanically operated brake when the electrically
operated brake is abnormal, and inhibiting the operation of the
mechanically operated brake when the electrically operated brake is
normal.
[0131] In the braking system according to the above mode (71), the
electrically operated brake is used as a normal brake, and the
mechanically operated brake is used as an emergency brake which is
activated by the force generated by the brake operating member.
Thus, the present braking system is provided with an electrically
operated sub-system including the brake operating member and the
electrically operated brake, and a mechanically operated sub-system
including the brake operating member, the manual brake control
device and the mechanically operated brake. Therefore, the present
braking system is capable of braking the wheel with the braking
force corresponding to the operating force acting on the brake
operating member, even when the electrically operated brake is
abnormal or defective. Accordingly, the present braking system has
increased operating reliability and improved safety of the
vehicle.
[0132] In the present braking system, the mechanically operated
brake and the manual brake control device may or may not use a
pressurized hydraulic fluid.
[0133] The electrically operated brake may be adapted to be
operated according to an intention of the vehicle operator, which
is represented by an operation of the brake operating member. For
instance, the electrically operated brake may be operated according
to the operating force acting on the brake operating member, or the
operating amount or stroke of the brake operating member.
[0134] In the present braking system, the friction member and the
rotor may be commonly used for the electrically and mechanically
operated brakes. Alternatively, the electrically and mechanically
operated brakes may use respective sets of the friction member and
rotor.
[0135] (72) A braking system according to the above mode (71),
further comprising a brake information obtaining device for
obtaining information relating to the electrically operated brake,
on the basis of an output of the force switch, and wherein the
brake information obtaining device is inhibited from operating when
the manual brake control device is operated.
[0136] In the braking system according to the above mode (72), the
information relating to the electrically operated brake includes
information which has been described above with respect to the
above mode (60).
[0137] (73) A braking system according to any one of the above
modes (53)-(59), wherein the friction member, support member,
pressing device and force switch constitute a major portion of a
brake, the braking system further comprising: a force-related
quantity sensor whose output varies continuously with a quantity
relating to one of a braking force generated by the brake and
applied to the wheel and a pressing force generated by the pressing
device to force the friction member onto the rotor; a wheel braking
force estimating device for estimating the braking torque to be
applied to the wheel, on the basis of the output of the
force-related quantity sensor and according to a predetermined
relationship between the output and the braking torque, the wheel
braking force estimating device compensating the predetermined
relationship on the basis of the output when the force switch is
switched from one of the two states to the other state.
[0138] It will be understood from the foregoing description that
the force switch is advantageous for its comparatively high
operating reliability but is disadvantageous for its incapability
of continuous detection of the force, while on the other hand the
force-related quantity sensor is advantageous for its capability of
continuous detection of the force-related quantity but is
disadvantageous for its comparatively low operating reliability.
Thus, the force switch and the force-related quantity sensor
mutually supplement their disadvantages, cooperating with each
other to permit continuous detection of the force-related quantity
with high reliability. The braking system according to the above
mode (73) is based on this finding.
[0139] Where the force-related quantity sensor in the braking
system according to the above mode (73) is a pressing-force-related
quantity sensor adapted to continuously detect a quantity relating
to the pressing force generated by the pressing device, the
quantity detected by this pressing-force-related quantity sensor is
not influenced by a variation in the friction coefficient of the
friction member, but the output of the force switch is influenced
by the variation. In this case, the wheel braking force estimating
compensates the above-indicated relationship by taking account of
both the variation in the operating characteristic of the
pressing-force-related sensor and the variation in the friction
coefficient of the friction member. Where the force-related
quantity sensor is a braking-force-related quantity sensor adapted
to continuously detect a quantity relating to the braking force
applied to the wheel, the force detected by the force switch and
the quantity detected by the braking-force-related quantity sensor
are substantially the same physical quantities which are not
influenced by the variation in the friction coefficient of the
friction member. In this case, the wheel braking force estimating
device compensates the above-indicated relationship by adjusting
the calibration of the braking-force-related quantity sensor.
[0140] The above-indicated relationship may be either directly
compensated, or indirectly or eventually compensated. In the latter
case, the output of the force-related quantity sensor may be
compensated, or alternatively the wheel braking force provisionally
estimated may be compensated on the basis of the output of the
sensor and the predetermined relationship.
[0141] (74) A braking system according to the above mode (73),
wherein the force-related quantity sensor includes a pressing force
sensor whose output continuously varies with the pressing force
acting thereon.
[0142] The operating environment of the pressing force sensor is
not so severe as compared with that of the a braking force sensor
which will be described. In the braking system according to the
above mode (74), therefore, the operating reliability and
durability of the pressing force sensor can be relatively easily
improved.
[0143] (75) A braking system according to the above mode (73),
wherein the force-related quantity sensor includes a braking force
sensor whose output continuously varies with the force which the
support member receives from the friction member as the braking
force applied to the wheel.
[0144] (76) A braking system according to any one of the above
modes (73)-(75), wherein the wheel braking force estimating device
includes relationship compensating means for compensating the
predetermined relationship, on the basis of a difference between an
actual value of the output and a nominal value of the output when
the force sensor is switched from one of the two states to the
other.
[0145] (77) A braking system according to the above mode (76),
wherein the relationship compensating means compensates the
predetermined relationship such that the pressing force obtained on
the basis of the actual value of the output of the braking force
sensor coincides with the actual value of the pressing force, even
in the presence of the above-indicated difference.
[0146] (78) A braking system according to any one of the above
modes (73)-(77), further comprising a brake information estimating
device for obtaining brake information relating to an operation of
the brake, on the basis of the output of the force switch.
[0147] The brake information estimating device and "brake
information relating to an operation of the brake" in the above
mode (78) are similar to those which have been discussed above with
respect to the above mode (60) of this invention.
[0148] (79) A braking system according to the above mode (78),
wherein the brake information estimating device includes a friction
coefficient estimating device for estimating a friction coefficient
of the friction member, on the basis of a relationship between the
output of the brake-related quantity sensor and the above-indicated
predetermined threshold of the force switch when the force switch
is switched from one of the two states to the other.
[0149] The friction coefficient estimating device according to the
above mode (79) is similar to that which has been discussed above
with respect to the above mode (61).
BRIEF DESCRIPTION OF THE DRAWINGS
[0150] The above and optional objects, features, advantages and
technical and industrial significance of this invention will become
more apparent by reading the following detailed description of
presently preferred embodiments or modes of the invention, when
considered in connection with the accompanying drawings, in
which:
[0151] FIG. 1 is a schematic view showing an arrangement of an
electrically operated braking system constructed according to one
embodiment of this invention;
[0152] FIG. 2 is an enlarged plan view partly in cross section of
an electrically operated disc brake used in the braking system of
FIG. 1;
[0153] FIG. 3 is an enlarged front elevational view partly in cross
section of an electrically operated drum brake used in the braking
system of FIG. 1;
[0154] FIG. 4 is an enlarged, fragmentary side elevational view
partly in cross section of a shoe expanding actuator used in the
drum brake of FIG. 3;
[0155] FIG. 5 is a flow chart illustrating a brake control routine
executed according to a program stored in a ROM of a computer of
the braking system of FIG. 1;
[0156] FIG. 6 is a flow chart illustrating a friction coefficient
estimating routine executed according to a program stored in the
ROM, to estimate the friction coefficient of friction members used
in the braking system;
[0157] FIG. 7 is a graph indicating a pattern of relationship
between an operating force F acting on a brake pedal and a braking
torque T generated by the brake in the first embodiment;
[0158] FIG. 8 is a graph indicating patterns of relationship
between an current I applied to a motor of the brake and the
braking torque T;
[0159] FIG. 9 is a diagram showing a concept of a braking operation
of the braking system of the first embodiment;
[0160] FIG. 10 is a view showing a change in vehicle speed V when
the braking system of the first embodiment is operated without an
operation of brake pedal;
[0161] FIG. 11 is a flow chart illustrating a friction coefficient
estimating routine executed according to a program stored in a ROM
of a computer of an electrically operated braking system according
to a second embodiment of this invention;
[0162] FIG. 12 is a flow chart illustrating a friction coefficient
estimating routine executed according to a program stored in a ROM
of a computer of an electrically operated braking system according
to a third embodiment of this invention;
[0163] FIG. 13 is a schematic view showing an arrangement of an
electrically operated braking system constructed according to a
fourth embodiment of this invention;
[0164] FIG. 14 is a flow chart illustrating a friction coefficient
estimating routine executed according to a program stored in a ROM
of a computer of the braking system of the fourth embodiment of
FIG. 13;
[0165] FIG. 15 is a schematic view showing an arrangement of an
electrically operated braking system constructed according to a
fifth embodiment of this invention;
[0166] FIG. 16 is a flow chart illustrating a friction coefficient
estimating routine executed according to a program stored in a ROM
of a computer of the braking system of the fifth embodiment of FIG.
15;
[0167] FIG. 17 is a view showing a change in vehicle speed Vw when
the braking system of the fifth embodiment is operated without an
operation of brake pedal;
[0168] FIG. 18 is a flow chart illustrating a friction coefficient
estimating routine executed according to a program stored in a ROM
of a computer of an electrically operated braking system according
to a sixth embodiment of the invention;
[0169] FIG. 19 is a schematic view showing an arrangement of an
electrically operated braking system constructed according to a
seventh embodiment of this invention;
[0170] FIG. 20 is an enlarged plan view partly in cross section of
an electrically operated disc brake used in the braking system of
FIG. 19;
[0171] FIG. 21 is an enlarged front elevational view partly in
cross section of an electrically operated drum brake used in the
braking system of FIG. 19;
[0172] FIG. 22 is a flow chart illustrating a brake control routine
executed according to a program stored in a ROM of a computer of
the braking system of FIG. 19;
[0173] FIG. 23 is a schematic view showing an arrangement of an
electrically operated braking system constructed according to an
eighth embodiment of the present invention;
[0174] FIG. 24 is a plan view partly in cross section of an
electrically operated disc brake used in the braking system of FIG.
23;
[0175] FIG. 25 is a cross sectional view of the disc brake of FIG.
24 taken along in a surface of inner brake pad 606b;
[0176] FIG. 26 is a front elevational view partly in cross section
of an electrically operated drum brake used for each of rear left
and right wheels in the braking system of FIG. 23;
[0177] FIG. 27 is an enlarged side elevational view of a manual
brake control device in the braking system of FIG. 23;
[0178] FIG. 28 is a graph for explaining a relationship between
brake pedal pedal operating force f and vehicle deceleration value
G during initial period of movement of second piston provided in
the manual brake control device of FIG. 27;
[0179] FIG. 29 is a flow chart illustrating a brake control routine
executed according to a program stored in a ROM of a computer of an
electronic control unit used in the braking system of FIG. 23;
[0180] FIG. 30 is a flow chart illustrating a basic brake control
sub-routine executed in step S2 of the routine of FIG. 29;
[0181] FIG. 31 is a flow chart illustrating a friction coefficient
calculating routine executed according to a program stored in the
ROM of the braking system of FIG. 23;
[0182] FIG. 32 is a schematic view showing an arrangement of an
electrically operated braking system according to a ninth
embodiment of this invention;
[0183] FIG. 33 is a flow chart illustrating a friction coefficient
calculating routine executed according to a pogrom stored in a ROM
of a computer of an electronic control unit used in the braking
system of FIG. 32;
[0184] FIG. 34 is a flow chart illustrating a brake pad fade
detecting routine executed according a program stored in a ROM of a
computer used in a braking system of a tenth embodiment of this
invention;
[0185] FIG. 35 is a flow chart illustrating a brake failure
detecting routine executed according to a program stored in a ROM
of a computer used in a braking system of an eleventh embodiment of
the invention;
[0186] FIG. 36 is a plan view partly in cross section of an
electrically operated disc brake used for each of front left and
right wheels in a braking system according to a twelfth embodiment
of the present invention;
[0187] FIG. 37 is a flow chart illustrating a front brake control
routine executed according to a program stored in a ROM of a
computer used in the braking system of FIG. 36;
[0188] FIG. 38 is a flow chart illustrating a conversion function
compensating routine executed according to a program stored in the
ROM of the braking system of FIG. 36;
[0189] FIG. 39 is a graph for explaining the conversion function
compensating routine of FIG. 38;
[0190] FIG. 40 is also a graph for explaining the routine of FIG.
38;
[0191] FIG. 41 is a plan view partly in cross section of an
electrically operated disc brake used for each of front left and
right wheels in a braking system according to a thirteenth
embodiment of this invention;
[0192] FIG. 42 is a flow chart illustrating a front brake control
routine executed according to a program stored in a ROM of a
computer used in the braking system of FIG. 41; and
[0193] FIG. 43 is a flow chart illustrating a conversion function
compensating routine executed according to a program stored in the
ROM of the braking system of FIG. 41.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0194] Referring first to FIG. 1, there is shown an arrangement of
an electrically operated braking system constructed according to a
first embodiment of this invention. This electrically operated
braking system is adapted for use on a four-wheel motor vehicle
having a front left wheel FL, a front right wheel FR, a rear left
wheel RL and a rear right wheel RR. The motor vehicle has a drive
power source in the form of an internal combustion engine 10, and a
power transmission in the form of an automatic transmission 12. The
motor vehicle is run with a drive force generated by the engine 10
and transmitted through the automatic transmission 12 to the front
wheels FL, FR and/or the rear wheels RL, RR.
[0195] The front left and right wheels FL, FR have respective
electrically operated disc brakes 22, 22 each including an electric
motor 20 as a drive source, while the rear left and right wheels
RL, RR have respective electrically operated drum brakes 32, 32
each including an electric motor 30 as a drive source. In the
present first embodiment of the invention, each of these electric
motors 20, 30 is a DC motor. However, all of the motors 20, 30 may
be ultrasonic motors. Alternatively, the motors 20 for the front
wheels FL, FR and the motors 30 for the rear wheels RL, RR may be
ultrasonic motors and DC motors, respectively, or vice versa.
[0196] The motor vehicle is provided with various
operator-controlled members including: a brake pedal 40 as a
primary brake operating member (one of brake operating members); a
parking brake pedal 42 as a parking brake operating member; an
accelerator pedal 44 as an accelerator operating member; and a
steering wheel 46. When the brake pedal 40 is operated, the
electrically operated disc and drum brakes 22, 32 for the four
wheels FL, FR, RL, RR are activated to apply a brake to the
vehicle. When the parking brake pedal 42 is operated, the
electrically operated drum brakes 32 for the rear left and right
wheels RL, RR are activated to apply a parking brake to the
vehicle. When the accelerator pedal 44 is operated, the drive force
or power generated by the engine 10 is increased to accelerate the
vehicle. When the steering wheel 46 is rotated, a steering device
as well known in the art is activated to change the steering angles
of the front wheels FL, FR (or front and rear wheels).
[0197] In the present electrically operated braking system, an
operation of the brake pedal 40 as the primary brake operating
member causes a controller 50 to energize the electric motors 20,
30 for activating the disc and drum brakes 22, 32 to generate
braking forces for braking the four wheels. Thus, the force
produced by the brake pedal 40 upon operation thereof by the
vehicle operator is not used to brake the vehicle. However, the
operating amount of the brake pedal 40 should change depending upon
the operating force acting on the brake pedal 40, so that the
vehicle operator is given an operating feel of the brake pedal 40
similar to that in the conventional hydraulically operated braking
system. To this end, the brake pedal 40 is connected to a stroke
simulator 52, so that the operating amount of the brake pedal 40
will change depending upon the operating force applied to the brake
pedal 40. The stroke simulator 52 includes (a) a linking member 54
linked with the brake pedal 40, (b) a guide member 56 for guiding
the linking member 54, and (c) an elastic member in the form of a
spring 58 whose elastic force changes due to contraction and
expansion thereof as the linking member 54 is moved by the brake
pedal 40. The operating amount (stroke) of the brake pedal 40
changes with a change in the elastic force of the spring 58
depending upon the operating force of the brake pedal 40.
[0198] Referring to FIG. 2, the construction of the electrically
operated disc brake 22 for the front right wheel FR is shown in
detail, by way of example. The disc brake 22 for the front left
wheel FL has the same construction.
[0199] The electrically operated disc brake 22 includes a mounting
bracket 100 which is a stationary member fixed to the body of the
motor vehicle, and a disc rotor 104 which has opposite friction
surfaces 102 and which is rotated with the front right wheel FR.
The mounting bracket 100 includes (a) a support portion for
supporting a pair of friction members in the form of brake pads
106a, 106b on the opposite sides of the disc rotor 104 such that
the brake pads 106a, 106b are movable in the axial direction of the
disc rotor 104, and (b) a torque receiving portion for receiving
friction forces generated between the friction surfaces 102 of the
disc rotor 104 and the brake pads 106a, 106b during frictional
contact therebetween. Character "X" in FIG. 2 represents a rotating
direction of the disc rotor 104 for forward running of the motor
vehicle.
[0200] The outer brake pad 106a located on the outer side (right
side as seen in FIG. 2) of the disc rotor 104 is supported by the
mounting bracket 100 such that the outer brake pad 106a is
substantially prevented from rotating with the disc rotor 104
during its friction contact with the outer friction surface 102,
namely, substantially prevented from being "dragged" by the disc
rotor 104. On the other hand, the inner brake pad 106b on the inner
side (left side as seen in FIG. 2) of the disc rotor 104 is
supported by the mounting bracket 100 such that the inner brake pad
106b is allowed to be "dragged" by the disc rotor 104 due to
friction contact of the pad 106b with the inner friction surface
102. Character "Y" in FIG. 2 represents a direction of "dragging"
movement of the inner brake pad 106b due to its frictional contact
with the disc rotor 104.
[0201] The dragging movement of the inner brake pad 106b is
prevented when the friction force generated between the disc rotor
104 and the brake pad 106b is smaller than a predetermined
threshold value, and is allowed after the friction force has
exceeded the threshold value. To this end, the inner brake pad 106b
has a rear portion 110 which engages the mounting bracket 100
through an elastic member in the form of a spring 112. When the
friction force between the inner brake pad 106b and the disc rotor
104 is smaller than the threshold, the spring 112 does not undergo
elastic deformation and prevents the dragging movement of the inner
brake pad 106b with the disc rotor 104. When the friction force of
the inner brake pad 106b has exceeded the threshold, the spring 112
starts elastic deformation and allows the inner brake pad 106b to
be dragged with the disc rotor 104. In the present embodiment, the
rear portion 110 of the inner brake pad 106b is associated with a
stop 114 which is adapted to abut on the mounting bracket 100, for
thereby limiting the distance of the dragging movement of the brake
pad 106b after the friction force of the inner brake pad 106b has
exceeded the threshold. Thus, the stop 114 prevents an excessive
degree of a self-servo effect which will be described.
[0202] The disc brake 22 further includes a caliper 120 which is
movable in the axial direction of the disc rotor 104 but is not
rotatable about the axis of rotation of the disc rotor 104. The
caliper 120 is slidably supported by a plurality of pins (not
shown) which are fixed to the vehicle body so as to extend in the
axial direction of the rotor 104. The caliper 120 includes (a) a
reaction portion 126 located on the outer side of the disc rotor
104, for abutting contact with the outer surface of the outer brake
pad 106a, (b) a presser portion 128 located on the inner side of
the disc rotor 104, for abutting contact with the inner surface of
the inner brake pad 106b, and (c) a connecting portion 130
connecting the reaction and presser portions 126, 128 together.
[0203] The presser portion 128 accommodates the electric motor 20,
and carries a presser member 134 which is linked with the motor 20
through a motion converting mechanism in the form of a ballscrew
mechanism 132 such that the presser member 134 and the motor 20 are
coaxial with each other. The presser member 134 is supported by the
presser portion 128 such that the presser member 134 is not
rotatable about the axis of rotation of the motor 20, but is
movable in the axial direction of the motor 20. A rotary motion of
the motor 20 is converted by the ballscrew mechanism 132 into a
linear motion of the presser member 134 in the axial direction of
the motor 20, so that a drive force generated by the motor 20 is
applied to the inner brake pad 106b, and also to the outer brake
pad 106a through the caliper 120, whereby the outer and inner brake
pads 106a, 106b are forced onto the opposite friction surfaces 102
of the disc rotor 104.
[0204] The outer brake pad 106a has a backing plate 140 whose
thickness is constant in the rotating direction X. On the other
hand, the inner brake pad 106b has a backing plate 140 whose
thickness continuously decreases in the direction Y of the dragging
movement, that is, in the forward running direction of the vehicle.
Described in detail, the backing plate 140 of the inner brake pad
106b has a slant back surface 142 which is remote from the inner
friction surface 102 of the disc rotor 104 and which is inclined
with respect to the inner friction surface 102. Thus, the presser
member 134 is adapted to contact at its front end with the slant
back surface 142 of the inner brake pad 106b. Further, the presser
member 134 is provided at its front end face with means for
facilitating movement of the inner brake pad 106b relative to the
presser member 134 while the front end face of the presser member
134 is in contact with the slant back surface 142 of the backing
plate 140. This arrangement makes it possible to provide a wedge
effect between the inner brake pad 106b and the presser member 134
during the dragging movement of the inner brake pad 106b, so that
the dragging movement of the inner brake pad 106b provides a
self-servo effect in the disc brake 22. In this embodiment, the
axis of the motor 20 (presser member 134) is perpendicular to the
slant back surface 142 of the inner brake pad 106b.
[0205] The above-indicated means for facilitating the relative
movement between the inner brake pad 106b and the presser member
134 includes a plurality of balls 144 which are arranged on the
front end face of the presser member 134 along a circle coaxial
with the motor 20, at a substantially equal angular interval. The
balls 144 are held on the front end face such that the balls 144
may roll in contact with the slant back surface 142. Thus, the
balls 144 serve as a thrust bearing 146 through which the presser
member 134 comes into contact with the inner brake pad 106b, so
that the thrust bearing 146 reduces the friction between the front
end face of the presser member 134 and the slant back surface 142
of the inner brake pad 106b. The balls 144 may be replaced by
rollers.
[0206] There will be described an operation of the electrically
operated disc brake 22 of FIG. 22.
[0207] When the brake pedal 40 is depressed by the vehicle
operator, the motor 20 is operated to advance the presser member
134 from its non-operated position, for forcing the outer and inner
brake pads 106a, 106b against the respective friction surfaces 102
of the disc rotor 104, so that the front wheel FR is braked with
the friction forces generated between the disc rotor 104 and the
brake pads 106a, 106b.
[0208] When the friction force between the inner brake pad 106b and
the disc rotor 104 is smaller than a predetermined elastic or
biasing force of the spring 112, the dragging movement of the inner
brake pad 106b is prevented by the spring 112, so as to prevent the
self-servo effect. In an initial period of operation of the disc
brake 22 with a relatively small operating force acting on the
brake pedal 40, the friction force between the inner brake pad 106b
and the disc rotor 104 is smaller than the elastic force of the
spring 112, the front right wheel is braked by only the drive force
generated by the motor 20.
[0209] When the friction force of the inner brake pad 106b becomes
larger than the elastic force of the spring 112, the spring 112
allows the inner brake pad 106b to be dragged with the disc rotor
104. With the movement of the slant back surface 142 relative to
the presser member 134, the distances between the slant back
surface 142 and the friction surface 102 at the points of contacts
between the balls 144 and the slant back surface 142 increase, with
a result of an increase in the force by which the brake pads 106a,
106b are forced onto the disc rotor 104. Therefore, when the brake
pedal 40 is depressed with a relatively large force (e.g., a force
enough to achieve vehicle deceleration of about 0.3-0.6 G), there
arises a wedge effect between the inner brake pad 106b and the
presser member 134 which contact each other at the slang back
surface 142, so that the front right wheel FR is braked by both the
drive force of the motor 20 and the self-servo effect owing to the
dragging movement of the inner brake pad 106b.
[0210] When the stop 114 has come into abutting contact with the
mounting bracket 100 with a further increase in the friction force
between the inner brake pad 106b and the disc rotor 104, a further
dragging movement of the brake pad 106b is prevented or inhibited
by the stop 114, whereby an excessive degree of the self-servo
effect is prevented.
[0211] Referring next to FIG. 3, the construction of the
electrically operated drum brake 32 for the rear left wheel RL is
shown in detail, by way of example. The drum brake 32 for the rear
right wheel RR has the same construction.
[0212] The electrically operated drum brake 32 includes a
stationary member in the form of a substantially circular backing
plate 200 fixed to the vehicle body, and a drum 204 which has an
inner circumferential friction surface 202 and which rotates with
the rear right wheel RR. The backing plate 200 has an anchor member
in the form of an anchor pin 206 fixed to a relatively radially
outer portion thereof at a given circumferential position thereof.
At another circumferential position of the backing plate 200 which
is diametrically opposite to the circumferential position at which
the anchor pin 206 is fixed, there is disposed a connecting link in
the form of an adjuster 208 of a floating type not directly fixed
to the backing plate 200. A pair of friction members in the form of
a pair of brake shoes 210a, 210b are disposed between and so as to
connect the anchor pin 206 and the adjuster 208, such that the
brake shoes 210a, 210b face the inner friction surface 202 of the
drum 204. Each of the brake shoes 210a, 210b has an arcuate shape.
The brake shoes 210a, 210b are fixed by respective hold-down
devices 212a, 212b to the backing plate 200 such that the brake
shoes 210a, 210b are movable in a plane parallel to the backing
plate 200. The backing plate 200 has a central opening through
which a rear axle shaft extends so as to be rotatable.
[0213] Each of the brake shoes 210a, 210b is operated connected at
one end thereof to the corresponding end portion of the adjuster
208, and is held at the other end in abutting engagement with the
anchor pin 206, so that the shoe 210a, 210b is pivotable about the
anchor pin 206. An adjuster spring 214 is connected to the end
portions of the brake shoes 210a, 210b operatively connected to the
adjuster 208, so that the end portions are biased by the adjuster
spring 214 toward each other. A return spring 215a, 215b is
connected to the other end portions of the brake shoes 210a, 210b,
so that these end portions are biased by the return spring 215a,
215b toward the anchor pin 206. The arcuate brake shoes 210a, 210b
have respective arcuate brake linings 216a, 216b held at their
outer surfaces such that the brake linings 216a, 216b face the
circumferential friction surface 202 of the drum 204. With friction
contact of these brake linings 216a, 216b with the friction surface
202, there arise friction forces between the brake linings 216a,
216b and the drum 204. The adjuster 208 is provided for the purpose
of changing the radial distance between the friction surface 202
and the inner arcuate surfaces of the brake shoes 210a, 210b, so as
to maintain a desired radial clearance between the friction surface
202 and the surfaces of the brake linings 216a, 216b, irrespective
of gradual wearing of the brake linings.
[0214] Each brake shoe 210a, 210b consists of a rim 220 and a web
222. A lever 230 is pivotably connected at one end thereof to a
lever support member in the form of a pin 232 fixed to the web 222
of the brake shoe 210a. The lever 230 and the web 222 of the other
brake shoe 210b have respective cutouts which engages respective
opposite ends of a strut 236 serving as a power transmitting
member. The lever 230 and the strut 236 enable both of the brake
shoes 210a, 210b of the present drum brake 32 to provide a
self-servo effect during both forward and backward runs of the
vehicle. Namely, the present drum brake 32 is a duo-servo type drum
brake. In the present embodiment, the lever 230 is connected to the
brake shoe 210a which functions as a secondary brake shoe during
the forward running of the vehicle. However, the lever 230 may be
connected to the brake shoe 210b which functions as a primary brake
shoe during the forward running of the vehicle.
[0215] The present electrically operated drum brake 32 is activated
by pivotal movement of the lever 230 about the pin 232 at its one
end when the parking brake pedal 42 is operated, as well as when
the brake pedal (primary brake pedal) 40 is operated. To this end,
not only a primary brake cable 240 but also a parking brake cable
242 are connected to the other end of the lever 230. Each of these
brake cables 240, 242 consists of a strand of a plurality of wires,
and is accordingly flexible. A compression coil spring 244 is
connected at its one end to the above-indicated other end of the
lever 230 and at the other end to the backing plate 200, as in the
conventional hydraulically operated braking system. The spring 244
extends coaxially with the parking brake cable 242.
[0216] The primary brake capable 240 is connected to a shoe
expanding actuator 250 attached to the backing plate 200. As shown
in enlargement in FIG. 4, the shoe expanding actuator 250 includes
the electric motor 30 indicated above, a speed reducer 252 whose
input shaft is connected to the output shaft of the motor 30, and a
ballscrew mechanism 254 whose input member is connected to an
output shaft of the speed reducer 252. The end of the primary brake
cable 240 remote from the lever 230 is connected to an output
member of the ballscrew mechanism 254. A rotary motion of the motor
30 is converted by the ballscrew mechanism 254 into a linear
movement of the primary brake cable 240. In FIG. 4, reference
numerals 256 and 258 denote brackets, while reference numerals 260
and 262 denote mounting screws for mounting the brackets 256, 258
to the backing plate 200.
[0217] The ballscrew mechanism 254 includes an externally threaded
member 264 as the input member, a nut 266 as the output member, and
a plurality of balls through which the externally threaded member
264 and the nut 266 engage each other. The nut 266 engages a
stationary housing 267 such that the nut 266 is not rotatable and
is axially movable relative to the housing 267. A rotary motion of
the externally threaded member 264 is converted into a linear or
axial motion of the nut 266. The nut 266 has an output shaft 268
fixed to its one end remote from the externally threaded member
264, such that the output shaft 268 is coaxial with the nut 266.
The externally threaded member 264, nut 266 and output shaft 268
are protected against exposure of their engaging portions to dust
or other foreign matters, by the housing 267 and an elastic dust
boot 270.
[0218] The primary brake cable 240 is connected to the output shaft
268 through an externally threaded member 272 and a nut 274. The
externally threaded member 272 is formed so as to extend from the
end of the output shaft 268 remote from the ballscrew mechanism
254, while the nut 274 engages the externally threaded member 272
and is connected to the primary brake cable 240. A lock nut 276 is
screwed on the externally threaded member 272 so as to lock the nut
274.
[0219] The shoe expanding actuator 250 constructed as described
above is operated in one direction to pull the primary brake cable
240 upon operation of the brake pedal 40, so that the lever 230 is
pivoted about the pin 232 such that the end portion of the lever
230 to which the primary brake cable 240 is connected is moved
toward the brake shoe 210b. As a result, the two brake shoes 210a,
210b are moved away from each other.
[0220] After the shoe expanding actuator 250 is operated in the
reverse direction and returned to its initial non-operated
position, the brake shoes 210a, 210b are moved toward each other by
a shoe contracting mechanism in the form of a primary brake return
spring 280, against a self-servo effect. The primary brake return
spring 280 is a compression coil spring 280 which is connected at
its one end to the lever 230 and at the other end to a stationary
portion of the actuator 250. The compression coil spring 280 is
disposed coaxially with the primary brake cable 240. Upon releasing
of the brake pedal 40, the actuator 250 is returned to the initial
position, and the lever 230 is pivoted to be returned to its
initial non-operated position under the biasing force of the
primary brake return spring 280. However, the spring 280 serving as
the shoe contracting mechanism is not essential, and may be
eliminated, particularly where the adjuster spring 214 and the shoe
return springs 215a, 215b have relatively large elastic forces.
[0221] As shown in FIG. 1, the parking brake cable 242 is
connected, at its end remote from the lever 230, to a parking
control 284, which is mechanically operated by the parking brake
pedal 42 so as to pull the parking brake cable 242 for pivoting the
lever 230 in the shoe expanding direction for moving the two brake
shoes 210a, 210b away from each other.
[0222] When the brake pedal 40 is operated, the shoe expanding
actuator 250 is operated to pull the primary brake cable 240 for
pivoting the lever 230 in the above-indicated shoe expanding
direction. In this case, the parking brake cable 242 becomes slack.
When the parking brake pedal 42 is operated, the parking control
284 is operated to pull the parking brake cable 242 for pivoting
the lever 230 also in the shoe expanding direction. In this case,
the primary brake cable 240 becomes slack. Since the two brake
cables 240, 242 which are both connected to the lever 230 and
pulled at different times are flexible, the operation of one these
brake cables is not influenced or disturbed by the other brake
cable.
[0223] While the structural arrangement of the present electrically
operated braking system has been described, there will next be
described a control arrangement of the braking system.
[0224] Referring back to FIG. 1, the braking system employs a
controller 50 which is principally constituted by a computer 300
incorporating a central processing unit (CPU), a read-only memory
(ROM and a random-access memory (RAM). The controller 50 is adapted
to receive various inputs, namely, output signals of various
sensors and switches including an operating force sensor 302, a
brake pedal operation detecting switch 304, an accelerator pedal
operation detecting switch 306, a steering angle sensor 308, a
vehicle deceleration sensor 310, a vehicle speed sensor, four wheel
speed sensors 314 and a motor current sensor 316.
[0225] The operation force sensor 302 generates an output signal
indicative of an operation force F which acts on the brake pedal
40. The brake pedal operation detecting switch 304 generates an
output signal indicating whether the brake pedal 40 is in operation
or not. The accelerator pedal operation detecting switch 306
generates an output signal indicating whether the accelerator pedal
44 is in operation or not. The steering angle sensor 308 generates
an output signal indicative of a rotation angle .theta. of the
steering wheel 46. This sensor 308 serves as a sensor for detecting
whether the vehicle is turning or not. The vehicle deceleration
sensor 310 generates an output signal indicative of a deceleration
value G of the motor vehicle in the running or forward direction.
The vehicle speed sensor 312 generates an output signal indicative
of a running speed V of the motor vehicle. The four wheel speed
sensors 314 generate respective output signals indicative of
rotating speed Vw of the respective wheels FL, FR, RL, RR. The
motor current sensor 316 is connected to coils of the motors 20, 30
of the disc and drum rakes 22, 32, and generates output signals
indicative of electric currents I which are actually applied to the
respective coils of the motors 20, 30 from a battery 320 through a
driver 322. The output signals of the motor current sensor 316 are
voltage signals representative of the electric current values
I.
[0226] The controller 50 provides output signals including current
control signals to be applied to the above-indicated driver 322.
Upon operation of the brake pedal 40, the controller 50 applies the
current control signals to the driver 322 so that the electric
current values I to be applied from the battery 320 through the
driver 322 to the respective motors 20, 30 of the brakes 22, 32 are
controlled based on the current control signals. The output signals
provided by the controller 50 also include signals to be applied to
an engine output control device and a transmission control device.
The engine output control device includes a throttle valve control
device, a fuel supply control device and an ignition timing control
device, while the transmission control device includes various
solenoid-operated valves. The engine output control device and the
transmission control device are controlled according to the signals
from the controller 50, so as to control the wheel drive forces to
be applied to the drive wheels, for preventing excessive amounts of
spinning of the drive wheels during starting or acceleration of the
vehicle, that is, for effecting a so-called "traction control" of
the vehicle.
[0227] The ROM of the computer 300 stores various programs such as
those for executing a brake control routine illustrated in the flow
chart of FIG. 5 and a friction coefficient estimating routine
illustrated in the flow chart of FIG. 6. The ROM is also used for
storing data tables or functional equations which represent F-T
relationship patterns and I-T relationship patterns.
[0228] Each of the F-T relationships is a relationship between the
operating force F acting on the brake pedal 40 and a braking torque
T applied to each wheel by operation of the corresponding brake 22,
32. An example of the F-T relationship patterns is indicated in the
graph of FIG. 7. Each of the I-T relationships is a relationship
between the electric current I to be applied to each motor 20, 30
and the braking torque T applied to each wheel by operation of the
corresponding brake 22, 32. The I-T relationships are obtained by
experiments or by calculation. Examples of the I-T relationship
patterns are indicated in the graph of FIG. 8. The F-T relationship
patterns and I-T relationship patterns generally differ for the
front wheels FL, FR and the rear wheels RL, RR, and are therefore
stored in the ROM in relation to the front wheels and the rear
wheels.
[0229] Each I-T relationship pattern indicates a change of the
braking torque value T wit a change in the electric current value
I. This I-T relationship pattern is stored for each of different
friction coefficient values .mu. of the friction members used in
the brakes 22, 32. That is, the ROM stores a plurality of I-T
relationship patterns corresponding to the respective different
friction coefficient values .mu.. The friction members consist of
the brake pads 106a, 106b of the disc brakes 22 for the front
wheels FL, FR, and the brake linings 216a, 216b of the drum brakes
32 for the rear wheels RL, RR.
[0230] Before explaining in detail the brake control routine of
FIG. 5 and the friction coefficient estimating routine of FIG. 6,
the brake control and the friction coefficient estimation will
first be briefly described.
[0231] Referring to FIG. 9, there is schematically illustrated a
relationship between the controller 50, motor 20, 30, friction
member 330 and wheel 332. The controller 50 receives the operating
force F acting on the brake pedal 40 operated by the vehicle
operator. Depending upon the operating force F, the controller 50
determines the electric current I to be applied to the motor 20,
30. In response to the electric current I supplied, the motor 20,
30 generates a drive force D for forcing the friction member 330
onto the disc rotor 104 or drum 204. The friction member 330 having
a specific friction coefficient .mu. cooperates with the disc rotor
104 or drum 204 to apply a braking torque T to the wheel 332, based
on the drive force D generated by the motor 20, 30. As a result,
the vehicle is given a deceleration value G, while the wheel 332 is
given a deceleration value Gw.
[0232] In the brake control, the electric current I to be applied
to the motor 20, 30 is determined on the basis of the operating
force F applied to the brake pedal 40. Described more specifically,
a desired braking torque T* for each wheel 332 is determined on the
basis of the operating force F and according to the appropriate F-T
relationship pattern. On the basis of the thus determined desired
braking torque T*, the electric current I to be applied to the
wheel is determined according to the I-T relationship pattern.
[0233] The friction coefficient .mu. of the friction member 330 is
estimated by activating the motor 20, 30 of the brake 22, 32 under
predetermined conditions, namely: when the brake pedal 40 is not in
operation; when the accelerator pedal 42 is not in operation; when
the vehicle is running straight, that is, is not turning; when the
vehicle is not running on a bad road surface; when the vehicle is
not running at a speed lower than a predetermined threshold; and
when the automatic transmission 12 is not in the process of a
shifting action. When the vehicle running speed V is zero (when the
vehicle is stopped), the controller 50 determines that the vehicle
is running at a speed lower than the predetermined threshold, the
brake 22 is not operated to estimate the friction coefficient .mu.
of the friction member 330, even then the brake pedal 40 is not in
operation. That is, the estimation of the friction coefficient .mu.
is effected while the vehicle is coasting straight at a relatively
high speed on a good road surface.
[0234] During operation of the brake 22, 32 to estimate the
friction coefficient .mu., the electric current I supplied to the
motor 20, 30 and the vehicle deceleration value G are obtained, and
the actual braking torque value T of each wheel is obtained based
on the obtained vehicle deceleration value G. Further, one of the
I-T relationship patterns which has a point located on or closest
to a point indicative of a combination of the obtained actual
braking torque value T and the obtained electric current I is
selected as the presently effective I-T relationship pattern. The
friction coefficient .mu. corresponding to the selected or
presently effective I-T relationship pattern is determined as the
estimated friction coefficient .mu. of the friction member 330,
which is stored in the RAM.
[0235] Although the friction coefficient .mu. of the friction
member 330 is preferably estimated for each of the four wheels, the
estimation in the present embodiment is effected for each of the
front and rear wheel pairs F, R, since the disc brakes 22 for the
two front wheels FL, FR use the same friction members in the form
of the brake pads 106a, 106b, while the drum brakes 32 for the two
rear wheels RL, RR use the same friction members in the form of the
brake linings 216a, 216b.
[0236] While the friction coefficient .mu. estimated in the present
run of the vehicle is stored in the RAM, the I-T relationship
pattern corresponding to this last estimated friction coefficient
.mu. is selected to determine the electric current I on the basis
of the determined desired braking torque T*. While the friction
coefficient .mu. estimated in the present vehicle run is not stored
in the RAM, the I-T relationship pattern corresponding to the
friction coefficient .mu. which was estimated in the previous run
of the vehicle and which is stored in the RAM is provisionally used
to determine the electric current I, until the friction coefficient
is estimated in the present vehicle run (until the estimation is
updated). If the friction coefficient .mu. was not estimated in the
previous vehicle run and is not stored in the RAM, the I-T
relationship pattern corresponding to the predetermined standard
value (stored in the ROM) of the friction coefficient .mu. is
provisionally used to determine the electric current I, until the
friction coefficient is estimated in the present vehicle run.
[0237] Then, the brake control routine of FIG. 5 and the friction
coefficient estimating routine of FIG. 6 will be described in
detail.
[0238] The brake control routine of FIG. 5 is executed while an
ignition switch of the vehicle is on. The brake control routine is
initiated with step S1 in which the operating force F acting on the
brake pedal 40 is detected by the operation force sensor 402. Step
S1 is followed by step S2 to determine whether the friction
coefficient value .mu. estimated in the present run of the vehicle
is stored in the RAM of the controller 50. If an affirmative
decision (YES) is obtained in step S2, the control flow goes to
step S3 in which the friction coefficient value .mu. estimated in
the present vehicle run and stored in the RAM is selected as the
effective friction coefficient value. If a negative decision (NO)
is obtained in step S2, the control flow goes to step S4 to
determine whether the friction coefficient value .mu. estimated in
the previous vehicle run is stored in the RAM. If an affirmative
decision (YES) is obtained in step S4, the control flow goes to
step S5 in which the previously estimated friction coefficient
value .mu. is selected as the effective value. If a negative
decision (NO) is obtained in step S4, the control flow goes to step
S6 in which the predetermined standard value of the friction
coefficient .mu. is selected as the effective value.
[0239] Step S3, S5 and S6 are followed by step S7 in which one of
the stored I-T relationship patterns which corresponds to the
currently selected effective friction coefficient value .mu. is
selected as the effective I-T relationship pattern. Then, step S8
is implemented to determine the desired braking torque value T* for
each wheel, on the basis of the detected operating force F and
according to the F-T relationship pattern. Step S8 is followed by
step S9 in which a desired value I* of the electric current I for
each wheel is determined on the basis of the desired braking torque
value T* and according to the currently selected effective I-T
relationship pattern. The control flow then goes to step S10 in
which the electric current of the determined desired value I* is
applied to the electric motor 20, 30 of each brake 22, 32. Thus,
one cycle of execution of the brake control routine of FIG. 5 is
terminated, and the control flow returns to step S1.
[0240] The friction coefficient estimating routine of FIG. 6 is
also executed with a predetermined cycle time while the ignition
switch is on. The routine is initiated with step S11 to effect
initialization in which an ESTIMATION flag is reset to "0". When
this flag is set at "0", it means that the friction coefficient
.mu. has not been estimated during the present run of the vehicle.
When the flag is set at "1", it means that the friction coefficient
.mu. has been estimated once during the present run of the
vehicle.
[0241] Step S11 is followed by steps S12-S18 to determine whether
the predetermined conditions that should be satisfied to estimate
the friction coefficient .mu. have been satisfied. Described in
detail, step S12 is implemented to determine whether the ESTIMATION
flag is set at "0". If an affirmative decision (YES) is obtained in
step S12, the control flow goes to step S13 to determine whether
the brake pedal operation detecting switch 304 is off, that is, to
determine whether the brake pedal 40 is placed at its non-operated
position. If an affirmative decision (YES) is obtained in step S13,
the control flow goes to step S14 to determine whether the
accelerator pedal operation detecting switch 306 is off, that is,
to determine whether the accelerator pedal 42 is placed at its
non-operated position. If an affirmative decision (YES) is obtained
in step S14, the control flow goes to step S15 to determine whether
the vehicle is turning, that is, to determine whether the rotation
angle .theta. of the steering wheel 46 detected by the steering
angle sensor 308 is larger than a threshold value which is close to
zero. If a negative decision (NO) is obtained in step S15, the
control flow goes to step S16 to determine whether the vehicle is
running on a bad road surface. The determination in step S16 is
effected by determining whether the frequency of change of the sign
of the wheel deceleration value Gw is higher than a predetermined
threshold value. The wheel deceleration value Gw is obtained by
obtaining a time derivative of the wheel speed Vw detected by the
wheel speed sensor 314. If a negative decision (NO) is obtained in
step S16, the control flow goes to step S17 to determine whether
the vehicle running speed V detected by the vehicle speed sensor
312 is lower than a predetermined threshold Vo. If a negative
decision (NO) is obtained in step S17, the control flow goes to
step S19 to determine whether the automatic transmission 12 is in
the process of a shifting action. This determination in step S19 is
effected based on a signal received from the automatic transmission
12. If the affirmative decision (YES) is obtained in steps S12-S14
while the negative decision (NO) is obtained in steps S15-S18, the
control flow goes to step S19. In the other cases, the control flow
goes back to step S12.
[0242] In step S19, a predetermined amount of electric current Io
is applied to the electric motors 20 of the disc brakes 22 for the
front left and right wheels FL, FR, for a predetermined time
.DELTA.t. Step S19 is followed by step S20 in which the electric
current I actually applied to the motors 20 is detected by the
motor current sensor 316. Step S20 is followed by step S21 in which
the deceleration value G of the vehicle during activation of the
disc brakes 22 is detected by the vehicle deceleration sensor 310.
Then, step S22 is implemented to estimate the friction coefficient
.mu. of the brake pads 106a, 106b of the disc brakes 22, on the
basis of the detected electric current I and vehicle deceleration
value G. Described in detail, the actual braking torque value T of
the front disc brakes 22 is calculated on the basis of the detected
vehicle deceleration value G. One of the I-T relationship patterns
which has a point located on or closest to a point indicative of a
combination of the detected electric current I and the calculated
actual braking torque value T is selected as the effective I-T
relationship pattern. The friction coefficient value .mu.
corresponding to the selected effective I-T relationship pattern is
determined as the estimated value of the friction coefficient of
the brake pads 106a, 106b. Then, steps S23 through S26 similar to
the above-indicated steps S19-S22 are implemented for the rear drum
brakes 32, to estimate the friction coefficient value .mu. of the
brake linings 216a, 216b of the drum brakes 32. Step S26 is
followed by step S27 in which the ESTIMATION flag is set to "1".
Then, the control flow goes to step S12. However, since the
ESTIMATION flag has been set to "1", the negative decision (NO) is
subsequently obtained in step S12, and the estimation of the
friction coefficient .mu. of the friction members 106a, 106b, 210a,
210b is not implemented, until the present vehicle run is
terminated.
[0243] As described above, the present embodiment is adapted to
effect the estimation of the friction coefficient .mu. of the
friction members only once during each run of the vehicle. Once the
estimation has been effected during the present vehicle run, the
friction coefficient is not updated during the present vehicle run.
However, the friction coefficient may be updated during the same
vehicle run.
[0244] The graph of FIG. 10 shows a gradual drop of the vehicle
speed V as a result of the activation of the disc and drum brakes
22, 32 during the estimation of the friction coefficient .mu. of
the friction members while the vehicle is coasting without the
brake pedal 40 being depressed.
[0245] When the conditions for initiating the estimation of the
friction coefficient .mu. have been satisfied at point of time t1,
the predetermined amount Io of electric current I is applied to the
electric motors 20 of the front disc brakes 22, so that the vehicle
speed V is reduced. The rate of reduction of the vehicle speed V,
that is, the deceleration value G of the vehicle depends upon the
friction coefficient .mu. of the brake pads 106a, 106b of the disc
brakes 22. Where the friction coefficient .mu. of the brake pads
106a, 106b is relatively high, the vehicle is decelerated with a
relatively high deceleration value G1. Where the friction
coefficient .mu. is relatively low, the vehicle is decelerated with
a relatively low deceleration value G2. When the predetermined time
.DELTA.t has passed from the point of time t1, that is, at a point
of time t2, the supply of the electric current to the electric
motors 20 is terminated, and the motors 20 are restored to the
non-operated state.
[0246] At a point of time t3 short time after the point of time t2,
the predetermined amount Io of current is applied to the electric
motors 30 of the rear drum brakes 32. As a result, the vehicle
speed V is further reduced. The rate of reduction of the vehicle
speed V or the deceleration value G of the vehicle at this time
depends upon the friction coefficient m of the brake linings 216a,
216b. Where the friction coefficient is relatively high, the
vehicle is decelerated with a relatively high deceleration value
G3. Where the friction coefficient is relatively low, the vehicle
is decelerated with a relatively low deceleration value G4. When
the predetermined time .DELTA.t has passed after the point of time
t3, that is, at a point of time t4, the supply of the electric
current to the electric motors 30 is terminated, and the motors 30
are restored to the non-operated state.
[0247] It will be understood from the above description of the
present embodiment of this invention that portions of the
controller 50 assigned to execute the brake control routine of FIG.
5 and the friction coefficient estimating routine of FIG. 6
constitute a relationship estimating and utilizing device for
estimating a relationship between the electric current I to be
supplied to the electric motors 20, 30 and the braking torque or
force to be applied from the disc and drum brakes 22, 32 to the
wheels, on the basis of the actual value of the electric current I
supplied from the battery 320 to the electric motors 20, 30 and the
actual values of the braking torque T of the disc and drum brakes
22, 32, which actual values are detected during operations of the
brakes 22, 32 while the vehicle is running. The values of the
braking torque to be applied to the wheels is changed with a change
in the electric current to be applied to the electric motors. The
relationship estimating and utilizing device is further adapted to
utilize the estimated relationship for controlling the brakes 22,
32. It will also be understood that the portion of the controller
50 assigned to execute the brake control routine of FIG. 5
constitutes relationship utilizing means for utilizing the obtained
relationship, while the portion of the controller 50 assigned to
implement steps S13 and S19-S26 of the friction coefficient
estimating routine of FIG. 16 constitutes means for estimating the
relationship while the vehicle is running without an operation of
the brake pedal 40. It will further be understood that the vehicle
deceleration sensor 310 serves as means for detecting the vehicle
deceleration G. It will also be understood that the portion of the
controller 50 assigned to implement steps S15 and S17 of the
routine of FIG. 6 constitutes first inhibiting means for inhibiting
the relationship estimating and utilizing device from operating the
disc and drum brakes 22, 32 to obtain the relationship, while the
vehicle is running under a condition in which the operations of the
drum and disc brakes 22, 32 by the relationship estimating and
utilizing device are likely to be felt unusual or uncomfortable by
the vehicle operator. It will further be understood that the
portion of the controller 50 assigned to implement step S17 of the
routine of FIG. 6 constitutes means for inhibiting the relationship
estimating and utilizing device from operating the disc and drum
brakes 22, 32 while the vehicle is running at a speed lower than a
predetermined threshold value. It will also be understood that the
portion of the controller 50 assigned to implement steps S14-S16
and S18 of the routine of FIG. 6 constitutes second inhibiting
means for inhibiting the relationship estimating and utilizing
device from estimating and/or utilizing the relationship while the
vehicle is running under a condition in which the relationship is
not likely to be accurately estimated. It will also be understood
that the portion of the controller 50 assigned to implement steps
S14 and S18 of the routine of FIG. 6 constitutes means for
inhibiting the relationship estimating and utilizing device from at
least utilizing the estimated relationship while a drive force for
driving the vehicle is changing. It will further be understood that
the portion of the controller 50 assigned to implement step S15 of
the routine of FIG. 6 constitutes means for inhibiting the
relationship estimating and utilizing device from at least
utilizing the estimated relationship while the vehicle is
turning.
[0248] Referring to FIGS. 11-22, there will be described other
embodiments of the present invention. The same reference numerals
as used in the first embodiment will be used to identify the same
elements in these other embodiments, and only differences of these
embodiments from the first embodiment will be described, to avoid
redundant explanation.
[0249] A second embodiment of this invention is adapted to
concurrently activate the disc and drum brakes 22, 32 for the four
wheels while the vehicle is coasting without an operation of the
brake pedal 40, and the vehicle deceleration value G is obtained
during the activation of the brakes 22, 32 so that the actual
braking torque values T of the brakes 22, 32 are obtained on the
basis of the obtained deceleration value G. In this respect, the
second embodiment is different from the first embodiment which is
adapted to activate the front disc brakes 22 and the rear drum
brakes 32 at different times in steps S19 and S23,
respectively.
[0250] A friction coefficient estimating routine according to the
second embodiment is illustrated in the flow chart of FIG. 11. In
the following description of this routine, steps similar to those
in the routine of FIG. 6 will be described only briefly.
[0251] The friction coefficient estimating routine of FIG. 11 is
initiated with step S51 to effect initialization in which the
ESTIMATION flag is reset to "0". Step S11 is followed by step S52
to determine whether the ESTIMATION flag is set at "0". If an
affirmative decision (YES) is obtained in step S52, the control
flow goes to step S53 to determine whether the brake pedal
operation detecting switch 304 is off, that is, to determine
whether the brake pedal 40 is placed at its non-operated position.
If a negative decision (NO) is obtained in step S53, the control
flow returns to step S52. If an affirmative decision (YES) is
obtained in step S53, the control flow goes to step S54 to
determine whether the vehicle running speed V detected by the
vehicle speed sensor 312 is lower than a predetermined threshold
Vo. If an affirmative decision decision (YES) is obtained in step
S54, the control flow returns to step S52. If a negative decision
(YES) is obtained in step S54, the control flow goes to step S55 to
determine whether the vehicle is running under any conditions in
which the friction coefficient values .mu. of the friction members
are not likely to be accurately estimated. These conditions
include: an operation of the accelerator pedal 42 to accelerate the
vehicle; a turning of the vehicle; a running of the vehicle on a
bad road surface; and a shifting action of the automatic
transmission 12, as discussed above with respect to steps S14, S14,
S16 and S18 of the routine of FIG. 6 of the first embodiment. If an
affirmative decision (YES) is obtained in step S55, the control
flow returns to step S52. If a negative decision (NO) is obtained
in step S55, the control flow goes to step S56.
[0252] In step S56, the front disc brakes 22 for the front wheels
and the rear drum brakes 32 for the rear wheels are substantially
concurrently or simultaneously activated. Step S56 is followed by
step S57 in which the electric current I actually applied to each
of the motors 20, 30 is detected by the motor current sensor 316.
Step S57 is followed by step S58 in which the deceleration value G
of the vehicle during activation of the four brakes 22, 32 is
detected by the vehicle deceleration sensor 310.
[0253] Then, step S59 is implemented to estimate the friction
coefficient value .mu. of the brake pads 106a, 106b of the disc
brakes 22 and the friction coefficient value .mu. of the brake
linings 216a, 216b of the drum brakes 32, on the basis of the
detected electric current values I and vehicle deceleration value
G. Described in detail, the actual braking torque values T of the
front disc brakes 22 and the actual braking torque values T of the
rear drum brakes 32 are estimated on the basis of the detected
vehicle deceleration value G, and depending upon a difference
between the braking capacities of the disc and drum brakes 22, 32
and a difference between the load acting on the front wheels and
the load acting on the rear wheels. A sum of the estimated braking
torque values T of the front disc brakes 22 and a sum of the
estimated braking torque values T of the rear drum brakes 32 are
then calculated. A half of the former sum is determined as the
actual braking torque T of each front disc brake 22, while a half
of the latter sum is determined as the actual braking torque T of
each rear drum brake 32. One of the I-T relationship patterns which
has a point located on or closest to a point indicative of a
combination of the detected electric current I and the calculated
actual braking torque T of each front disc brake 22 is selected as
the effective I-T relationship pattern. The friction coefficient
value .mu. corresponding to the selected effective I-T relationship
pattern is obtained as the estimated value of the friction
coefficient of the brake pads 106a, 106b of each front disc brake
22. Similarly, the estimated friction coefficient value of the
brake linings 216a, 216b of each rear drum brake 32 is
obtained.
[0254] As described above, the second embodiment is adapted such
that the actual braking torque value T of the front disc brakes 22
and the actual braking torque value T of the rear drum brakes 32
are obtained on the basis of the same vehicle deceleration value G
which is obtained during concurrent operations of the four brakes
22, 32, and the friction coefficient value .mu. of the brake pads
106a, 106b of the front disc brakes 22 and the friction coefficient
value .mu. of the brake linings 216a, 216b of the rear drum brakes
32 are estimated independently of each other on the basis of the
obtained actual front and rear braking torque values T.
[0255] Step S59 is followed by step S60 to set the ESTIMATION flag
to "1". Then, the control flow goes back to step S52.
[0256] A third embodiment of the invention is adapted to activate
the four brakes 22, 32 one after another at different times, and
detect the deceleration values G for the respective brakes 22, 32
and obtain the actual braking torque values T for the respective
brakes independently of each other.
[0257] A friction coefficient estimating routine according to the
third embodiment is illustrated in the flow chart of FIG. 12. In
the following description of this routine, steps similar to those
in the routine of FIG. 6 will be described only briefly.
[0258] The friction coefficient estimating routine of FIG. 12 is
initiated with step S71 to effect initialization in which the
ESTIMATION flag is reset to "0". Step S71 is followed by step S72
to determine whether the ESTIMATION flag is set at "0". If an
affirmative decision (YES) is obtained in step S72, the control
flow goes to step S73 to determine whether the brake pedal
operation detecting switch 304 is off. If a negative decision (NO)
is obtained in step S73, the control flow returns to step S72. If
an affirmative decision (YES) is obtained in step S73, the control
flow goes to step S74 to determine whether the vehicle running
speed V is lower than a predetermined threshold Vo. If an
affirmative decision (YES) is obtained in step S74, the control
flow goes back to step S72. If a negative decision (NO) is obtained
in step S54, the control flow goes to step S75 to determine whether
the vehicle is running under any conditions in which the friction
coefficient values .mu. of the friction members are not likely to
be accurately estimated. These conditions include: an operation of
the accelerator pedal 42 to accelerate the vehicle; a turning of
the vehicle; a running of the vehicle on a bad road surface; and a
shifting action of the automatic transmission 12, as discussed
above with respect to steps S14, S14, S16 and S18 of the routine of
FIG. 6 of the first embodiment. If an affirmative decision (YES) is
obtained in step S75, the control flow returns to step S72. If a
negative decision (NO) is obtained in step S75, the control flow
goes to step S76.
[0259] In step S76, the two front disc brakes 22 and the two rear
drum brakes 32 are sequentially activated one after another, for
instance, in the order of the disc brake 22 for the front left
wheel FL, the disc brake 22 for the front right wheel FR, the drum
brake 32 for the rear left wheel RL, and the drum brake 32 for the
rear right wheel RR. Step S76 is followed by step S77 in which the
values of the electric current I actually supplied to the motors
20, 30 are detected during sequential activations of the four
brakes 22, 32. Step S77 is followed by step S78 in which the
deceleration values G are detected during the sequential
activations of the four brakes 22, 32. It is noted that while steps
S76-S78 are sequentially and repeatedly implemented for each of the
four brakes 22, 32, although the flow chart of FIG. 12 does not
explicitly show this arrangement. The thus detected vehicle
acceleration values G accurately reflect the actual braking torque
values T of the respective brakes 22, 32.
[0260] Then, step S79 is implemented to estimate the friction
coefficient values .mu. of the brake pads 106a, 106b of the disc
brakes 22 and the friction coefficient values .mu. of the brake
linings 216a, 216b of the drum brakes 32, on the basis of the
detected electric current values I and vehicle deceleration values
G. Described in detail, the actual braking torque value T of each
brake 22, 32 is estimated on the basis of the corresponding vehicle
deceleration value G. Then, One of the I-T relationship patterns
which has a point located on or closest to a point indicative of a
combination of the detected electric current I and the calculated
actual braking torque T of each brake 22, 32 is selected as the
effective I-T relationship pattern. The friction coefficient value
.mu. corresponding to the selected effective I-T relationship
pattern is obtained as the estimated value of the friction
coefficient of the brake pad or lining of each brake 22, 32. Step
S79 is followed by step S80 to set the ESTIMATION flag to "1".
Then, the control flow returns to step S72.
[0261] A fourth embodiment of this invention is adapted to inhibit
the detection of the vehicle deceleration G to obtain the actual
braking torque T where the gradient of the road surface on which
the vehicle is running is higher than a predetermined threshold. In
the first embodiment, the vehicle deceleration G is detected
irrespective of the gradient of the road surface.
[0262] Referring to FIG. 13, there is shown an arrangement of an
electrically operated braking system according to the fourth
embodiment, which includes a road gradient sensor 340 for detecting
the gradient of the road surface.
[0263] A friction coefficient estimating routine executed according
to a program stored in a ROM of a computer 344 of a controller 342
of the braking system of the present fourth embodiment is
illustrated in the flow chart of FIG. 14. In the following
description of the routine of FIG. 14, steps similar to those in
the first embodiment will be described only briefly.
[0264] The friction coefficient estimating routine of FIG. 14 is
initiated with step S81 to effect initialization in which the
ESTIMATION flag is reset to "0". Step S81 is followed by step S82
to determine whether the ESTIMATION flag is set at "0". If an
affirmative decision (YES) is obtained in step S82, the control
flow goes to step S83 to determine whether the brake pedal
operation detecting switch 304 is off. If a negative decision (NO)
is obtained in step S83, the control flow returns to step S72. If
an affirmative decision (YES) is obtained in step S83, the control
flow goes to step S84 to determine whether the vehicle running
speed V is lower than a predetermined threshold Vo. If an
affirmative decision (YES) is obtained in step S84, the control
flow goes back to step S82. If a negative decision (NO) is obtained
in step S84, the control flow goes to step S85 to determine whether
the vehicle is running under any conditions in which the friction
coefficient values .mu. of the friction members are not likely to
be accurately estimated. These conditions include: an operation of
the accelerator pedal 42 to accelerate the vehicle; a turning of
the vehicle; a running of the vehicle on a bad road surface; and a
shifting action of the automatic transmission 12, as discussed
above with respect to steps S14, S14, S16 and S18 of the routine of
FIG. 6 of the first embodiment. In the present fourth embodiment,
the conditions that inhibit the estimation of the friction
coefficient .mu. also include a condition that the gradient of the
road surface on which the vehicle is running is higher than the
predetermined threshold value. If an affirmative decision (YES) is
obtained in step S85, the control flow returns to step S82. If a
negative decision (NO) is obtained in step S85, the control flow
goes to step S86.
[0265] In step S86, the disc and drum brakes 22, 32 are activated
in one of the following modes: (a) The four brakes 22, 32 are
substantially concurrently activated, as in the second embodiment
of FIG. 11; (b) the front disc brakes 22 are concurrently
activated, and the rear drum brakes 32 are concurrently activated,
but after or before the activation of the disc brakes 22, as in the
first embodiment of FIG. 6; and (c) the four brakes 22, 32 are
sequentially activated, as in the third embodiment of FIG. 12. Step
S86 is followed by step S87 in which the electric current I
supplied to each brake 22, 32 is detected. Step S87 is followed by
step S88 in which the deceleration value or values G is/are
detected during the activation of the four brakes 22, 32. Then,
step S89 is implemented to estimate the friction coefficient values
.mu. of the friction members of the brakes 22, 32, on the basis of
the detected electric current values I and vehicle deceleration
value or values G, in one of the manners described with steps S26,
S59 and S79. Step S89 is followed by step S90 to set the ESTIMATION
flag to "1". Then, the control flow returns to step S82.
[0266] A fifth embodiment of this invention is adapted to obtain
the actual braking torque values T on the basis of deceleration
values Gw of the wheels. In the preceding embodiments, the actual
braking torque T is obtained on the basis of the detected vehicle
deceleration G.
[0267] Referring to FIG. 15, there is shown an arrangement of an
electrically operated braking system according to the fourth
embodiment, which does not include the vehicle deceleration sensor
310, since the vehicle deceleration G is not used to obtain the
actual braking torque T in the present fifth embodiment.
[0268] A friction coefficient estimating routine executed according
to a program stored in a ROM of a computer 362 of a controller 360
of the braking system of the present fifth embodiment is
illustrated in the flow chart of FIG. 16. In the following
description of the routine of FIG. 16, steps similar to those in
the first embodiment will be described only briefly.
[0269] The friction coefficient estimating routine of FIG. 16 is
initiated with step S101 to effect initialization in which the
ESTIMATION flag is reset to "0". Step S101 is followed by step S102
to determine whether the ESTIMATION flag is set at "0". If an
affirmative decision (YES) is obtained in step S102, the control
flow goes to step S103 to determine whether the brake pedal
operation detecting switch 304 is off. If a negative decision (NO)
is obtained in step S103, the control flow returns to step S102. If
an affirmative decision (YES) is obtained in step S103, the control
flow goes to step S104 to determine whether the vehicle running
speed V is lower than a predetermined threshold Vo. If an
affirmative decision (YES) is obtained in step S104, the control
flow goes back to step S102. If a negative decision (NO) is
obtained in step S104, the control flow goes to step S105 to
determine whether the vehicle is running under any conditions in
which the friction coefficient values .mu. of the friction members
are not likely to be accurately estimated. These conditions
include: an operation of the accelerator pedal 42 to accelerate the
vehicle; a turning of the vehicle; a running of the vehicle on a
bad road surface; and a shifting action of the automatic
transmission 12, as discussed above with respect to steps S14, S14,
S16 and S18 of the routine of FIG. 6 of the first embodiment. If an
affirmative decision (YES) is obtained in step S105, the control
flow returns to step S102. If a negative decision (NO) is obtained
in step S105, the control flow goes to step S106.
[0270] In step S106, the front disc brakes 22 for the front wheels
and the rear drum brakes 32 for the rear wheels are substantially
concurrently or simultaneously activated. Step S106 is followed by
step S107 in which the electric current I actually applied to each
of the motors 20, 30 is detected by the motor current sensor 316.
Step S107 is followed by step S108 in which the deceleration value
Gw of each of the four wheels FL, FR, RL, RR is calculated. The
deceleration value Gw of each wheel is calculated by obtaining a
time derivative of the rotating speed Vw of that wheel detected by
the wheel speed sensor 314.
[0271] The graph of FIG. 17 shows a change in the wheel speed Vw
during activation of the brakes 22, 32. When the friction
coefficient .mu. of the friction members of the brake 22, 32 is
relatively high, the rate of reduction of the wheel speed Vw, that
is, the deceleration value Gw of the wheel is relatively high. When
the friction coefficient is relatively low, the wheel deceleration
value Gw is relatively low.
[0272] Then, step S109 is implemented to estimate the friction
coefficient values .mu. of the friction members of the four brakes
22, 32, on the basis of the detected electric current values I and
calculated wheel deceleration values Gw. Described in detail, the
actual braking torque values T of the brakes 22, are estimated on
the basis of the calculated wheel deceleration values Gw. One of
the I-T relationship patterns which has a point located on or
closest to a point indicative of a combination of the detected
electric current I and the calculated actual braking torque T of
each brake 22, 32 is selected as the effective I-T relationship
pattern. The friction coefficient value .mu. corresponding to the
selected effective I-T relationship pattern is obtained as the
estimated value of the friction coefficient of each brake 22, 32.
Then, step S110 is implemented to set the ESTIMATION flag to "1".
The control flow then goes back to step S102.
[0273] A sixth embodiment of the invention is different from the
fifth embodiment, only in the friction coefficient estimating
routine illustrated in the flow chart of FIG. 18.
[0274] In the friction coefficient estimating routine of FIG. 18
according to the sixth embodiment, the friction coefficient .mu. of
the friction members of the brakes 22, 32 is effected while the
brake pedal 40 is operated. The routine is initiated with step S201
to effect initialization in which the ESTIMATION flag is reset to
"0". Step S201 is followed by step S202 to determine whether the
ESTIMATION flag is set at "0". If an affirmative decision (YES) is
obtained in step S202, the control flow goes to step S203 to
determine whether the brake pedal operation detecting switch 304 is
on, that is whether the brake pedal 40 is in operation. If a
negative decision (NO) is obtained in step S203, the control flow
returns to step S202. If an affirmative decision (YES) is obtained
in step S203, the control flow goes to step S204 to determine
whether the whether the vehicle is running under any conditions in
which the friction coefficient values .mu. of the friction members
are not likely to be accurately estimated. These conditions
include: an operation of the accelerator pedal 42 to accelerate the
vehicle; a turning of the vehicle; a running of the vehicle on a
bad road surface; and a shifting action of the automatic
transmission 12, as in the fifth embodiment. In this sixth
embodiment, the conditions that inhibits the estimation of the
friction coefficient .mu. include an operation of the braking
system in an anti-lock fashion, and stopping of the vehicle. The
anti-lock control of the disc and drum brakes 22, 32 is effected
with the electric motors 20, 30 being controlled by the controller
50 on the basis of the output signals of the wheel speed sensors
314. The stopping of the vehicle is detected if the vehicle running
speed V detected by the vehicle speed sensor 312 is lower than a
predetermined lower limit. If an affirmative decision (YES) is
obtained in step S204, the control flow returns to step S202. If a
negative decision (NO) is obtained in step S205, the control flow
goes to steps S205-S209, which are similar to steps S106-S110 of
the routine of FIG. 16 in the fifth embodiment.
[0275] A seventh embodiment of the present invention is different
from the first embodiment, in that the actual braking torque values
T of the brakes 22, 32 are detected by sensors exclusively provided
for this purpose.
[0276] The arrangement of an electrically operated braking system
according to the seventh embodiment is schematically shown in FIG.
19. This braking system includes (a) a first force sensor 380
provided in each front disc brake 22, to detect the actual braking
torque T, and (b) a second force sensor 382 provided in each rear
drum brake 32, to detect the actual braking torque T. Unlike the
braking system of the first embodiment, the present braking system
does not include the vehicle deceleration sensor 310.
[0277] Referring to FIG. 20, there is shown the electrically
operated disc brake 22 for each front wheel, wherein the first
force sensor 380 is interposed between the spring 112 and the
mounting bracket 100. Referring next to FIG. 21, there is shown the
electrically operated drum brake 32 for each rear wheel, wherein
the second force sensor 382 is disposed on one of the brake shoes
210a, 210b, that is, the secondary shoe 210a which will receive a
larger load than the primary shoe 210b. The second force sensor 382
may be disposed on the anchor pin 206.
[0278] A friction coefficient estimating routine executed according
to a program stored in a ROM of a computer 386 of a controller 384
of the present braking system is illustrated in the flow chart of
FIG. 22. In the description of the routine of FIG. 22, steps
similar to those in the first embodiment will be described only
briefly.
[0279] The routine of FIG. 22 is initiated with step S301 to effect
initialization in which an ESTIMATION flag is reset to "0". Step
S301 is followed by step S302 to determine whether the whether the
ESTIMATION flag is set at "0". If an affirmative decision (YES) is
obtained in step S202, the control flow goes to step S303 to
determine whether the brake pedal operation detecting switch 304 is
off. If a negative decision (NO) is obtained in step S303, the
control flow goes back to step S302. If an affirmative decision
(YES) is obtained in step S303, the control flow goes to step S304
to determine whether the vehicle speed V is lower than a
predetermined threshold Vo. If an affirmative decision (YES) is
obtained in step S304, the control flow goes back to step S302. If
a negative decision (NO) is obtained in step S304, the control flow
goes to step S305 to determine whether the vehicle is running under
any conditions in which the friction coefficient .mu. is not likely
to be accurately estimated. These running conditions include: an
operation of the accelerator pedal 42; a turning of the vehicle; a
running of the vehicle on a bad road surface; and a shifting action
of the automatic transmission 12, as described above with respect
to the first embodiment. If an affirmative decision (YES) is
obtained in step S305, the control flow goes back to step S302. If
a negative decision (NO) is obtained in step S305, the control flow
goes to step S306.
[0280] In step S306, the disc and drum brakes 22, 32 are activated
in one of the following modes: (a) The four brakes 22, 32 are
substantially concurrently activated, as in the second embodiment
of FIG. 11; (b) the front disc brakes 22 are concurrently
activated, and the rear drum brakes 32 are concurrently activated,
but after or before the activation of the disc brakes 22, as in the
first embodiment of FIG. 6; and (c) the four brakes 22, 32 are
sequentially activated, as in the third embodiment of FIG. 12. Step
S306 is followed by step S307 in which the electric current I
supplied to each brake 22, 32 is detected. Step S307 is followed by
step S308 in which the actual braking torque values T of the disc
and drum brakes 22, 32 are detected by the first and second force
sensors 380, 382, respectively, during the activation of the brakes
22, 32. Then, step S309 is implemented to estimate the friction
coefficient values .mu. of the friction members of the brakes 22,
32, on the basis of the detected electric current values I and
actual braking torque values T. One of the I-T relationship
patterns which has a point located on or closest to a point
indicative of a combination of the electric current I and the
braking torque value T of each brake 22, 32 is selected as the
effective I-T relationship pattern. The friction coefficient .mu.
corresponding to the selected I-T relationship pattern is obtained
as the estimated friction coefficient value for each brake. The
control flow then goes to step S309 to the ESTIMATION flag to "1".
Then, the control flow returns to step S310.
[0281] The embodiments which have been described are adapted to
detect various physical parameters such as the electric current I
supplied to each electric motor 20, 30, vehicle deceleration G,
wheel deceleration Gw and actual braking torque T of the brakes 22,
32. Each of these physical parameters is detected for a
predetermined time period. The peak value or an average of a
plurality of values obtained in the detection period may be used as
the detected value. Alternatively, an integral value of the values
obtained in the detection period may be used as the detected
value.
[0282] Referring to FIGS. 23-43, further embodiments of this
invention will be described.
[0283] FIG. 23 shows an electrically operated braking system
constructed according to an eighth embodiment of the invention,
which includes electrically operated front disc brakes 522 each
having the electric motor 20 described above, and electrically
operated rear drum brakes 532 each having the electric motor 30
also described above. These disc and drum brakes 530, 532 do not
use a hydraulic working fluid. Like the braking system of the first
embodiment of FIG. 1, the braking system of FIG. 23 includes the
engine 10, automatic transmission 12, parking brake pedal 43,
accelerator pedal 44 and steering wheel 46.
[0284] Unlike the braking system of FIG. 1, the braking system of
FIG. 23 further includes mechanically operated rear drum brakes 536
which are operated as emergency brakes, by a force produced as a
result of an operation of a brake operating member in the form of a
brake pedal 534. This drum brake 536 does not use a hydraulic
working fluid, either. Thus, each of the rear left and right wheels
RL, RR is provided with both the electrically operated drum brake
532 and the mechanically operated drum brake 536. These drum brakes
532, 536 commonly use the same drum 204 and the same brake shoes
210a, 210b (brake linings 216a, 216b).
[0285] Upon operation of the brake pedal 534, the vehicle is braked
by at least one of the three pairs of brakes 522, 532, 536. That
is, there are the following four cases:
[0286] (a) Where the electrically operated disc brakes 522 and drum
brakes 532 are both normal, the vehicle is braked by these brakes
522, 532;
[0287] (b),Where the electrically operated disc brakes 522 are not
normal while the electrically operated drum brakes 532 are normal,
the vehicle is braked by only the drum brakes 532;
[0288] (c) Where the electrically operated disc brakes 522 are
normal while the electrically operated drum brakes 532 are not
normal, the vehicle is braked by both the disc brakes 522 and the
mechanically operated drum brakes 536;
[0289] (d) Where the electrically operated disc and drum brakes
522, 532 are both abnormal due to abnormality of an electric power
source (primary battery 874) or an electronic control unit (ECU)
550, the vehicle is braked by only the mechanically operated drum
brakes 536.
[0290] In the present braking system, parking brake is applied to
the front left and right wheels FL, FR by the disc brakes 522 upon
operation of the parking brake pedal 42. The parking brake is
applied by holding the electric motors 20 (ultrasonic motors) of
the disc brakes 522 stationary with a holding torque while the
parking brake pedal 42 is kept operated.
[0291] The disc brake 522 for the front right wheel FR is shown in
detail in FIG. 24. The disc brake 533 for the front left wheel FL
has the same construction as shown in FIG. 24. The disc brake 522
of FIG. 24 is identical with the disc brake 22 of FIG. 2 of the
first embodiment, except for the configuration of brake pads 606
(more specifically, inner brake pad 606b) and the provision of a
force switch 650 provided in a stationary member in the form of the
mounting bracket 100. Unlike the inner brake pad 110b of the disc
brake 22 of FIG. 2, the inner brake pad 606b of the disc brake 522
has a backing plate 640 which has a constant thickness. When the
outer and inner pads 606a, 606b are forced onto the friction
surfaces 102 of the disc rotor 102, the pads 606a, 606b are
"dragged" or rotated with the disc rotor 102 in the direction X.
However, the amounts of rotation of the pads 606a, 606b are limited
by respective torque receiving portions 610a, 610b of the mounting
bracket 100. Namely, the amount of rotation of the outer pad 606a
is limited by abutting contact of its end face with the outer
torque receiving portion 610a, while the amount of rotation of the
inner pad 606b is limited by abutting contact of the force switch
650 with the inner torque receiving portion 610b, as described
below by reference to FIG. 25. The torque receiving portions 610a,
610b function as support members for supporting the friction
members so as to prevent rotation of the friction members in the
form of the brake pads 606a, 606b with the rotor 104 when the
friction members are held in frictional contact with the rotor
104.
[0292] The presser portion 134 moved by the electric motor 20
through the ballscrew mechanism 136 is not provided at its front
end with such a thrust bearing as provided in the disc brake 22 of
FIG. 22. The presser portion 134 cooperates with the ballscrew
mechanism 132 to constitute a pressing device for forcing the brake
pads 606a, 606b onto the rotor 104.
[0293] The force switch 650 is provided in the inner torque
receiving portion 610b which is adapted to receive a torque from
the inner brake pad 606b. As shown in enlargement in FIG. 25, the
force switch 650 consists of a movable member 652 and an elastic
member in the form of a coned disc spring 654. The movable member
652 is a stepped cylindrical member including a large-diameter
portion 656 and a small-diameter portion 658 which both have a
circular cross sectional shape and are coaxial with each other. The
large-diameter portion 656 is received axially movably within the
inner torque receiving portion 610b, while the small-diameter
portion 658 extends through a center opening of the coned disc
spring 654. The coned disc spring 654 biases the movable member 652
toward the inner brake pad 606b. Normally, the movable member 652
is held in abutting contact with a stop portion 659 formed with the
mounting bracket 100. In other words, the stop portion 659
determines the fully retracted position of the movable member 652.
When the inner brake pad 606b is rotated with the disc rotor 104 in
the direction Y as indicated in FIG. 25, the movable member 652 is
moved away from the fully retracted position against the biasing
force of the spring 654.
[0294] The small-diameter portion 658 has a movable contact 660
fixed to its end face. The inner torque receiving portion 610b has
a stationary contact 662 which is an elastic member. The movable
contact 660 comes into contact with the stationary contact 662 when
the movable member 652 is moved to its fully advanced position by
the inner brake pad 606b against the biasing action of the coned
disc spring 654. The fully advanced position of the movable member
652 is determined by abutting contact of the end face of the
small-diameter portion 658 with the surface of the inner torque
receiving portion 610b. In this arrangement, a force generated by
friction contact of the inner brake pad 610b with the rotor 104 is
transmitted to the inner torque receiving portion 610b through the
movable member 652.
[0295] The stationary contact 662 is electrically connected through
a wire 664 to the electronic control unit 550. The wire 664 extends
through the mounting bracket 100. The stationary contact 662 and
the wire 664 are electrically insulated from the mounting bracket
100 by an insulator 665. On the other hand, the movable contact 660
is grounded through the electrically conductive movable member 652
and mounting bracket 100 and through a wire 666 connected to the
mounting bracket 100.
[0296] The movable contact 660 is normally held away from the
stationary contact 662 with the movable member 652 held in its
fully retracted position under the biasing force of the coned disc
spring 654. Thus, the force switch 650 is normally held in its off
state. When the force which the movable member 652 receives from
the inner brake pad 606b exceeds a predetermined value (a pre-load
given to the coned disc spring 654), the movable member 652 starts
moving with the inner brake pad 606b against the biasing force of
the spring 654, from the fully retracted position toward the fully
advanced position in which the movable contact 660 contacts the
stationary contact 662, whereby the force switch 650 is turned
on.
[0297] It will be understood that the force switch 650 may be
provided in the outer torque receiving portion 610a of the mounting
bracket 100.
[0298] Referring to FIG. 26, there is shown the electrically
operated drum brake 532 for the rear right wheel RR. The drum brake
532 for the rear left wheel RL has the same construction as shown
in FIG. 26.
[0299] The drum brake 532 is identical with the drum brake 32 of
FIG. 3 of the first embodiment, except for a strut 736 provided in
place of the strut 236. This strut 736 incorporates a length
adjusting mechanism including a screw device, which is manipulated
to adjust a clearance or gap between the brake shoes 210a, 10b and
the drum 204.
[0300] The mechanically operated drum brake 536 for each rear wheel
will be described.
[0301] All the elements of the electrically operated drum brake 532
except the primary brake cable 240, shoe expanding actuator 250 and
return spring 280 are also used for the mechanically drum brake
536. This drum brake 536 uses an emergency brake cable 782 and a
return spring 784, which are similar to the parking brake cable 242
and the return spring 244 provided in the drum brake 32 of FIG. 3.
The emergency brake cable 782 is connected at one end thereof to
the end of the lever 230 to which the primary brake cable 240 of
the electrically operated drum brake 532 is connected. When the
mechanically operated drum brake 536 is activated, the lever 230 is
pivoted to force the brake linings 216a, 216b onto the drum 204,
for thereby braking the rear right wheel RR. The emergency brake
cable 782 is guided through an outer tubing 786, as indicated in
FIG. 23.
[0302] The emergency brake cable 782 connected at its one end to
the mechanically operated drum brake 536 for each rear wheel is
operatively connected at the other end to the brake pedal 534
through a manual brake control device 800, as shown in FIG. 23.
[0303] The manual brake control device 800 is shown in enlargement
in FIG. 27, together with a brake pedal device 802. The brake pedal
device 802 includes a pedal bracket 804 fixed to the vehicle body.
The brake pedal 534 is supported at a proximal end thereof by the
pedal bracket 804 such that the brake pedal 534 is pivotable at its
proximal end about an axis which extends in the lateral or
transverse direction of the vehicle. Normally, the brake pedal 534
is held in its non-operated position, which is determined by
abutting contact of the brake pedal 534 with a stop 806 under a
biasing action of a return spring 808. The brake pedal 834 is
pivotally connected to the rear end of a push rod 312 through a
clevis 810, which serves as a pivotal link mechanism. In this
arrangement, the push rod 312 is movable in the longitudinal or
running direction of the vehicle. A pivotal motion of the brake
pedal 534 is converted into a linear motion of the push rod
312.
[0304] The manual brake control device 800 includes a housing 814
fixed to the vehicle body. Within a bore formed in the housing 814,
there are slidably received a first piston 816 and a second piston
818 which are disposed coaxially with each other such that the
pistons 816, 818 are movable relative to each other in the
longitudinal direction of the vehicle. The push rod 812 engages at
its front end with the rear end of the first piston 816. An
operating force f acting on the brake pedal 534 is transmitted in
the forward direction to the first piston 816 through the push rod
812. Thus, the brake pedal 534 is mechanically connected to the
first piston 816. Between the first piston 816 and the housing 814,
there is disposed an elastic member in the form of a spring 820,
which biases the first piston 816 toward the push rod 812, so as to
hold the brake pedal 534 in its non-operated position. Upon
operation of the brake pedal 534 when the electrically operated
drum brake 532 is normal, the brake pedal 534 is moved by a
distance corresponding to the operating force f acting on the brake
pedal 534. Thus, the manual brake control device 800 gives the
vehicle operator an operating feel of the brake pedal 534 as
obtained with a brake pedal in a hydraulically operated braking
system. In the present eighth embodiment, the first piston 816 and
the spring 320 cooperate to constitute a pedal stroke simulator
generally indicated at 812 in FIG. 27.
[0305] The first piston 816 has an engaging portion in the form of
a projection 822 which extends toward the second piston 818 such
that the projection 822 is coaxial with the pistons 816, 818. The
second piston 818 has a fully retracted position determined by a
stop 824. The retracted position of the second piston 818 or the
position of the stop 824, which determines an initial distance
between the two pistons 816, 818, is determined so that the
projection 822 is spaced apart from the second piston 818 when the
brake pedal 534 is placed in its non-operated position of FIG. 27,
but is brought into abutting contact with the second piston 818
when the operating force f acting on the brake pedal 534 has
reached a reference value f.sub.0. This reference value f.sub.0 is
determined such that the operating force f equal to the reference
value f.sub.0 produces a relatively high deceleration value G
(e.g., 1.2 G) of the vehicle which is not usually obtained when the
electrically operated disc and drum brakes 522, 532 are both
normal. If and after the operating force f exceeds the thus
determined reference value f.sub.0 when the disc and drum brakes
522, 532 are both normal, the second piston 818 is moved forward
from the fully retracted position, and the mechanically operated
drum brake 536 is also activated simultaneously, the rate of
increase of the vehicle deceleration value G with an increase in
the operating force f is raised, as indicated in the graph of FIG.
28.
[0306] The second piston 818 is connected through a lever device
826 to the rear end of the emergency brake cable 782 of the
mechanically operated drum brake 536 for each rear wheel, as shown
in FIG. 27.
[0307] The lever device 826 includes a lever 828 and a lever
bracket 830 fixed to the vehicle body. The lever 828 is supported
at a proximal end thereof by the lever bracket 830 such that the
lever 828 is pivotable about the proximal end in a plane which
includes the axis of the second piston 818. The lever 828 is
connected at an intermediate portion thereof to the front end of
the second piston 818 through a clevis 832, and is held in its
fully retracted position under a biasing action of a return spring
834 such that the clevis 832 is held in abutting contact with the
front end of the second piston 818. The lever 828 is connected at a
free end thereof to the end of the emergency brake cable 782 of
each drum brake 536 through a clevis 836. In this arrangement, a
forward movement of the second piston 818 (in the left direction as
seen in FIG. 27) will cause the lever 828 to be pivoted in the
clockwise direction (as seen in FIG. 27), pulling the emergency
brake cable 782 in the left direction as seen in FIG. 27, out of
the outer tubing 786, whereby the movement of the second piston 818
is boosted into the movement of the emergency brake cable 782.
Reference numeral 838 in FIG. 27 denotes a bracket fixed to the
vehicle body for fixing the outer tubing 786 for the emergency
brake cable 782.
[0308] When the brake pedal 534 is operated while the electrically
operated drum brakes 532 are normal, the electric motors 30 of the
actuators 250 are operated to pull the primary brake cables 240 to
force the brake shoes 210a, 210b onto the drum 204. At this time,
the flexible emergency brake cables 782 are contracted, so that the
actions of the brake shoes 210a, 210b by operation of the
electrically operated drum brakes 532 are not disturbed by the
manual brake control device 800.
[0309] When the brake pedal 534 is operated while the electrically
operated drum brakes 4=532 are not normal, the emergency brake
cables 782 are pulled by the brake pedal 534, and the lever 230 is
pivoted to force the brake shoes 210a, 210b onto the drum 204. At
this time, the flexible primary brake cables 240 are contracted, so
that the actions of the brake shoes 210a, 210b by operation of the
mechanically operated drum brakes 536 are not disturbed by the
electrically operated drum brakes 532.
[0310] Thus, the primary brake cables 240 and the emergency brake
cables 782 which are both flexible and connected to the same lever
230 are not disturbed by the emergency brake cables 782 and the
primary brake cables 240, respectively, when the electrically and
mechanically operated drum brakes 532, 536 are operated at
different times.
[0311] Referring back to FIG. 23, there will be described a control
system of the braking system according to the eighth embodiment of
the invention. The control system includes the electronic control
unit (ECU) 350, which is principally constituted by a computer 836
incorporating a read-only memory (ROM) 842 and a random-access
memory (RAM) 844. To the ECU 850, there are connected various
sensors and switches including: the above-indicated force switches
650 of the disc brakes 522 for the front left and right wheels FL,
FR; a brake pedal switch 850; an operation force sensor 848; a
parking pedal switch 851; an accelerator pedal switch 852; an
accelerator operation amount sensor 853; a steering angle sensor
854; a yaw rate sensor 855; a longitudinal acceleration sensor 856;
a lateral acceleration sensor 857; a front wheel load sensor 858; a
rear wheel load sensor 859; four wheel speed sensors 860; four
motor position sensors 862 and four motor current sensors 864.
[0312] The operation force sensor 848 generates an output signal
indicative of the operating force f acting on the brake pedal 534.
The brake pedal switch 850, which is a primary brake operation
sensor, generates an output signal indicative of whether the brake
pedal 34 is in operation. That is, the brake pedal switch 850 is
placed in an off state when the brake pedal 534 is not in
operation, and in an on state when the brake pedal 534 is in
operation. The parking pedal switch 851, which is a parking brake
operation sensor, generates an output signal indicative of whether
the parking brake pedal 42 is in operation. That is, the parking
brake pedal switch 851 is placed in an off state when the parking
brake pedal 42 is not in operation, and in an on state when the
parking brake pedal 42 is in operation. The accelerator pedal
switch 852, which is an accelerator operation sensor, generates an
output signal indicative of whether the accelerator pedal 44 is in
operation. That is, the accelerator pedal switch 852 is placed in
an off state when the accelerator pedal 44 is not in operation, and
in an on state when the accelerator pedal 44 is in operation. The
accelerator pedal operation amount sensor 853 generates an output
signal indicative of an operating amount of the accelerator pedal
44. The steering angle sensor 354, which is a sensor for detecting
an angle of turn of the vehicle, generates an output signal
indicative of the angle of rotation of the steering wheel 46. The
yaw rate sensor 855 generates an output signal indicative of a yaw
rate .gamma. of the vehicle. The longitudinal acceleration sensor
856 generates an output signal indicative of a deceleration value
G.sub.FR of the vehicle in the longitudinal direction of the
vehicle. The lateral acceleration sensor 857 generates an output
signal indicative of a lateral acceleration value G.sub.LR of the
vehicle in the lateral direction of the vehicle. The front wheel
load sensor 858 generates an output signal indicative of a load
W.sub.F acting on the front axle in the vertical direction, while
the rear wheel load sensor 859 generates an output signal
indicative of a load W.sub.R acting on the rear axle in the
vertical direction. Each of the four wheel speed sensors 860
generates an output signal indicative of the rotating speed Vw of
the corresponding wheel. Each of the motor position sensors 860
generates an output signal indicative of the angular position of
the corresponding electric motor 20, 30. Each of the motor current
sensors 864 generates an output signal indicative of an electric
current supplied to the coil of the corresponding motor 20, 30.
[0313] The ECU 550 is also connected to a first driver 866 and a
second driver 868. The first driver 866 is connected between an
electric power source in the form of a first battery 870 and the
electric motor 20 of each electrically operated disc brake 522. On
the other hand, the second driver 868 is connected between an
electric power source in the form of a second battery 872 and the
electric motor 30 of each electrically operated drum brake 532.
Upon operation of the brake pedal 534, the ECU 550 applies control
commands to the first and second drivers 866, 868, so that the
amounts of the electric current to be supplied from the first and
second batteries 870, 872 to the respective electric motors 20, 30
are controlled according to the control commands, which are
determined by the operating force f acting on the brake pedal
534.
[0314] The braking system also includes a primary battery 874
independent of the first and second batteries 870, 872. This
primary battery 874 is used for operating all electrical components
of the vehicle, except the electric motors 20, 30 of the brakes
522, 532. The ECU 550 is powered by the primary battery 874, rather
than the first and second batteries 870, 872.
[0315] The ECU 550 is further connected to an engine output control
device (throttle control unit, a fuel supply control unit, ignition
timing control unit, etc.) for controlling the engine 10, and a
shift control device (solenoid-operated valves, etc.) for
controlling the automatic transmission 12. The ECU 550 applies
control commands to these engine output control device and shift
control device to effect a traction control of the vehicle, namely,
to control the running vehicle so as to avoid excessive spinning or
slipping of the drive wheels.
[0316] The ECU 550 is also connected to a brake failure indicator
light 876 which is turned on in the event of an electrical or other
failure or defect of the electrically operated disc and drum brakes
522, 532.
[0317] The ROM 842 of the computer 846 stores various control
programs including programs for executing various routines such as
a brake control routine and a friction coefficient calculating
routine.
[0318] The brake control routine is formulated to control the
brakes 522, 532 in various modes such as a basic control mode, an
anti-lock control mode, a traction control mode and vehicle
stability control (VSC) mode. In the basic control mode, the
electric motors 20, 30 of the disc and drum brakes 522, 532 are
controlled so as to achieve the vehicle deceleration corresponding
to the operating force f acting on the brake pedal 534, on the
basis of the output signals of the operation force sensor 848,
brake pedal switch 850, front and rear wheel load sensors 858, 859,
motor position sensors 862 and motor current sensors 864, while
monitoring the detected angular positions of the motors 20, 30 and
the detected amounts of electric current supplied to the motors 20,
30, such that the braking force is suitably distributed to the
front wheels FL, FR and the rear wheels RL, RR. In the anti-lock
control mode, the electric motors 20, 30 are controlled to control
the braking torque values of the wheels, so as to avoid an
excessive locking tendency of each wheel, on the basis of the
output signals of the brake pedal switch 850, wheel speed sensors
860, motor position sensors 862 and motor current sensors 864. In
the traction control mode, the electric motors 20, 30 are
controlled to control the driving torque values of the drive
wheels, so as to avoid an excessive spinning or slipping tendency
of each drive wheel, on the basis of the output signals of the
accelerator pedal switch 852, accelerator operation amount sensor
853, wheel speed sensors 860, motor position sensors 862 and motor
current sensors 864. In the VSC mode, the electric motors 20, 30
are controlled to control a yaw movement of the vehicle, by
controlling a difference between the braking forces of the left and
right wheels, so as to avoid an excessive drift-out or spinning
tendency of the vehicle, on the basis of the steering angle sensor
854, yaw rate sensor 855, lateral acceleration sensor 858, wheel
speed sensors 860, motor position sensors 862 and motor current
sensors 864.
[0319] The brake control routine is illustrated in the flow chart
of FIG. 29. This routine is repeatedly executed while the ignition
switch of the vehicle is held on. The routine is initiated with
step S501 to determine whether the brake pedal 534 is in operation,
that is, whether the brake pedal switch 530 is in the on state. If
an affirmative decision (YES) is obtained, the control flow goes to
step S2 in which the braking system is controlled in the basic
control mode according to a basic control mode sub-routine
illustrated in the flow chart of FIG. 30, which will be
described.
[0320] The sub-routine of FIG. 30 is initiated with step S521 in
which the operating force f acting on the brake pedal 534 is
detected on the basis of the output signal of the operation force
sensor 848. Then, step S522 is implemented to read the longitudinal
acceleration value G.sub.FR, lateral acceleration value G.sub.LR,
front wheel load W.sub.F, rear wheel load W.sub.R and yaw rate
.gamma., which are represented by the output signals of the
appropriate sensors. The control flow then goes to step S523 in
which a desired braking torque or force F* for each wheel is
determined on the basis of the detected values G.sub.FR, F.sub.LR,
W.sub.F, W.sub.R, .gamma., so as to achieve an optimum or ideal
front-rear distribution of the braking force depending upon the
vehicle weight and deceleration values G, and so as to avoid yawing
and/or lateral slipping tendency of the vehicle due to a large
difference between the braking force of the left wheels and the
braking force of the right wheels.
[0321] Step S523 is followed by step S524 to read the friction
coefficient .mu. of the inner brake pad 606b of each front disc
brake 522, which is stored in the RAM 844. Upon power application
to the computer 846, the standard value of the friction coefficient
.mu. is stored in the RAM 844, and is provisionally used before the
friction coefficient .mu. is calculated according to a friction
coefficient calculating routine (which will be described) and
stored in the RAM 844. Each time the friction coefficient
calculating routine is executed, the friction coefficient value
.mu. stored in the RAM 844 is updated.
[0322] Then, the control flow goes to step S525 to determine a
desired value I* of the electric current I to be supplied to the
motor 20, 30 of each brake 522, 532. The desired electric current
value I* for the motor 30 of each rear drum brake 532 is determined
on the basis of the determined desired braking force F* and
according to a predetermined relationship between the desired
braking force F* and the desired electric current I*. This
relationship is stored in the ROM 842. The desired electric current
value I* for the motor 30 of each front disc brake 522 is
determined according to the following equation, based on a fact
that the desired electric current I* corresponds to a force N by
which the brake pads 606a, 606b are forced onto the disc rotor
104.
I*=F*/(.mu..multidot.K)
[0323] In the above equation, K represents a constant.
[0324] Then, the control flow goes to step S526 in which each motor
20, 30 is activated with the determined desired electric current I*
supplied thereto. Thus, one cycle of execution of the basic control
mode sub-routine of FIG. 30 is terminated in step S502 of the brake
control routine of FIG. 29.
[0325] Step S502 of the routine of FIG. 29 is followed by step S503
to determine whether it is necessary to control the brakes 522, 532
in the anti-lock control mode, that is, whether the vehicle wheels
have an excessive locking tendency. If a negative decision (NO) is
obtained in step S503, one cycle of execution of the routine of
FIG. 29 is terminated. If an affirmative decision (YES) is obtained
in step S503, the control flow goes to step S504 in which the
braking system is controlled in the anti-lock control mode. Step
S504 is followed by step S505 to determine whether the anti-lock
brake control becomes unnecessary. If a negative decision (NO) is
obtained, the control flow goes back to step S504, and step S504 is
repeatedly implemented until an affirmative decision (YES) is
obtained in step S505, that is, until the excessive locking
tendency of the wheels has been removed. If the affirmative
decision (YES) is obtained in step S505, one cycle of execution of
the routine is terminated.
[0326] If a negative decision (NO) is obtained in step S501, the
control flow goes to step S506 to determine whether it is necessary
to control the brakes 522, 532 in the traction control mode, that
is, whether the drive wheels have an excessive spinning or slipping
tendency. If an affirmative decision (YES) is obtained in step
S506, the control flow goes to step S507 in which the braking
system is controlled in the traction control mode. Step S507 is
followed by step S508 to determine whether the traction control
becomes unnecessary. If a negative decision (NO) is obtained in
step S507, the control flow goes to step S507, and step S507 is
repeatedly implemented until an affirmative decision (YES) is
obtained in step S508, that is, until the excessive slipping
tendency of the drive wheels has been removed. If the affirmative
decision (YES) is obtained in step S508, one cycle of execution of
the routine is terminated.
[0327] If the brake pedal switch 850 is off and if the traction
control is not necessary, that is, if a negative decision (NO) is
obtained in steps S501 and S506, the control flow goes to step S509
to determine whether the VSC control (vehicle stability control) is
necessary, that is, whether the vehicle has an excessive drift-out
or spinning tendency. If an affirmative decision (YES) is obtained
in step S509, the control flow goes to step S510 in which the
braking system is controlled in the VSC control mode. Step S510 is
followed by step S511 to determine whether the VSC control becomes
unnecessary. If a negative decision (NO) is obtained in step S511,
the control flow goes back to step S510, and step S510 is
repeatedly implemented until an affirmative decision (YES) is
obtained in step S510, that is, until the VSC control becomes
unnecessary. If the affirmative decision (YES) is obtained in step
S511, one cycle of execution of the routine is terminated.
[0328] The friction coefficient calculating routine indicated above
is illustrated in the flow chart of FIG. 31.
[0329] The friction coefficient calculating routine is routine is
also repeatedly executed while the ignition switch of the vehicle
is held on. The routine is executed alternately for the disc brakes
522 for the front left and right wheels FL, FR. The routine is
initiated with step S531 to determine whether the disc brake 522 in
question is controlled in any of the anti-lock, traction and VSC
control modes. If an affirmative decision (YES) is obtained in step
S531, one cycle of execution of the routine is terminated. If a
negative decision (NO) Is obtained in step S531, that is, if none
of the anti-lock, traction and VSC controls is currently effected,
the control flow goes to step S532.
[0330] Step S532 is provided to determine whether the force switch
650 is turned on or off, that is, whether the state of the force
switch 650 is changed from the off state to the on state or vice
versa. If the force switch 650 is turned on, it means that the
force transmitted from the inner brake pad 606b to the force switch
650 has increased to the predetermined value. If the force switch
650 is turned off, it means that the force transmitted from the
inner brake pad 606b has decreased to the predetermined value. If a
negative decision (NO) is obtained in step S532, one cycle of
execution of the routine is terminated. If an affirmative decision
(YES) is obtained in step S532, the control flow goes to step
S533.
[0331] In step S533, the actual value of the electric current
I.sub.A supplied to the electric motor 20 is detected on the basis
of the output signal of the appropriate motor current sensor 864.
Then, step S534 is implemented to calculate the friction
coefficient .mu. of the brake pads 606 of the disc brake 522 in
question, on the basis of the calculated motor current I.sub.A and
an optimum braking force F.sub.0 which should act on the inner
brake pad 606b when the force switch 650 is turned from the off
state to the on state or vice versa. Namely, the friction
coefficient .mu. is calculated according to the following
equation:
.mu.=F.sub.0/(K.multidot.I.sub.A)
[0332] Then, the control flow goes to step S535 in which the
calculated friction coefficient .mu. of the brake pads 606 is
stored in the RAM 844. Thus, one cycle of execution of the routine
of FIG. 31 is terminated.
[0333] It will be understood from the above description of the
eighth embodiment of the invention that the motor current sensors
864 serve as a force-related quantity sensor for detecting a
quantity relating to the braking force generated by the disc brake
522, and a pressing-force-related quantity sensor for detecting a
physical quantity relating to the pressing force by which the
friction member 606b is forced onto the rotor 104 by the pressing
device. It will also be understood that a portion of the ECU 550
assigned to implement steps S531-S534 constitutes a friction
coefficient estimating device for estimating the friction
coefficient of the friction members 606 of the disc brakes 522.
This friction coefficient estimating device may be considered to be
a relationship estimating means for estimating the relationship
between the electric current I to be applied to the electric motor
20 and the braking force or torque F to be generated by the brake
and applied to the wheel. It will also be understood that a portion
of the ECU 550 assigned to execute the routine of FIG. 30
constitutes relationship utilizing means for utilizing the
estimated relationship, for controlling the disc brake 522.
[0334] There will next be described a ninth embodiment of this
invention, in which the same reference numerals as used in the
eighth embodiment will be used to identify the same elements.
[0335] In the eighth embodiment, the manual brake control device
600 and the mechanically operated drum brakes 536 serving as the
emergency brakes are provided for the rear left and right wheels
RL, RR. In the present ninth embodiment, the manual brake control
device 600 and the mechanically operated drum brakes 536 are
provided for the front left and right wheels FL, FR. As shown in
FIG. 32, the brake pedal 534 is operatively connected to the brake
pads 606b, 606b of the electrically operated disc brakes 522 for
the front left and right wheels FL, FR, through a manual brake
control device 900, emergency brake cables 902 and mechanically
operated brakes 906. The mechanically operated brakes 906 may be in
operation when a friction coefficient calculating routine is
executed for the disc brakes 522. The operation of the mechanically
operated brakes 906 during execution of the friction coefficient
calculating routine may lower the accuracy of calculation of the
friction coefficient .mu.. In view of this, the execution of the
friction coefficient calculating routine is inhibited while the
mechanically operated brakes 906 are in operation. In the present
ninth embodiment, a switch 910 is provided to detect an operation
of the mechanically operated brakes 906. The switch 910 is turned
on when a second piston (similar to the second piston 818 of the
manual brake control device 900 of the eighth embodiment) is moved
from the fully retracted position. The switch 910 is held off when
the second piston is placed in the fully retracted position.
[0336] In the present ninth embodiment, the ROM 842 stores a
program for executing the friction coefficient calculating routine
illustrated in the flow chart of FIG. 33.
[0337] The routine of FIG. 33 is initiated with step S601 to
determine whether the switch 910 is off, namely, whether the second
piston of the manual brake control device 910 is held in its fully
retracted position. If a negative decision (NO) Is obtained in step
S601, one cycle of execution of the routine is terminated. If an
affirmative decision (YES) is obtained in step S601, the control
flow goes to step S602-606 identical with steps S531-S535 of the
routine of FIG. 31.
[0338] A tenth embodiment of the invention will be described. This
embodiment is a modification of the eighth embodiment.
[0339] The tenth embodiment is adapted to execute a brake pad fade
detecting routine as well as the brake control routine of FIG. 29
and the friction coefficient calculating routine of FIG. 31. The
brake pad fade detecting routine is illustrated in the flow chart
of FIG. 34.
[0340] The brake pad fade detecting routine is executed alternately
for the front left and right wheels FL, FR. The routine is
initiated with step S801 to determine whether the force switch 650
is turned on or off. If a negative decision (NO) is obtained in
step S801, one cycle of execution of the routine is terminated. If
an affirmative decision (YES) is obtained in step S801, the control
flow goes to step S802 to detect the motor current I.sub.A based on
the output signal of the motor current sensor 864. Then, step S803
is implemented to calculate the friction coefficient .mu. of the
brake pad 606, in the same manner as described above with respect
to step S534 of the eighth embodiment. Step S803 is followed by
step S804 to determine whether the calculated friction coefficient
.mu. is equal to or smaller than a predetermined threshold
.mu..sub.0. If an affirmative decision (YES) is obtained in step
S804, the control flow goes to step S805 to determine that the
friction coefficient .mu. of the brake pad 606 is unacceptably low
due to fading of the brake pad. In this case, the brake failure
indicator light 876 is turned on to inform the vehicle operator of
some failure or defect of the disc brake 522 in question. If a
negative decision (NO) is obtained in step S806, the control flow
goes to step S806 to determine that the friction coefficient .mu.
is acceptably high. One cycle of execution of the routine of FIG.
34 is terminated with step S805 or S806.
[0341] An eleventh embodiment of the invention will be described.
This embodiment is another modification of the eighth
embodiment.
[0342] The eleventh embodiment is adapted to execute a brake
failure detecting routine as well as the brake control routine of
FIG. 29 and the friction coefficient calculating routine of FIG.
31. The brake failure detecting routine is illustrated in the flow
chart of FIG. 34.
[0343] The brake failure detecting routine is also executed
alternately for the front left and right wheels FL, FR. The routine
is initiated with step S901 to detect the operating force f based
on the operating force sensor 848. Then, step S902 is implemented
to determine whether the detected operating force f is larger than
the predetermined reference value f.sub.0. If an affirmative
decision (YES) is obtained in step S902, the control flow goes to
step S903 to determine whether the force switch 650 is in the on
state. The reference value f.sub.0 is determined such that the
force switch 650 is in the on state when the operating force f is
larger than the reference value f.sub.0, as long as the disc brake
522 is normal. In other words, if the force switch 650 is in the
off state when the operating force f is larger than the reference
value f.sub.0, it means that the disc brake 522 is abnormal.
Therefore, if a negative decision (NO) is obtained in step S903,
the control flow goes to step S906 to determine that the disc brake
522 is abnormal. In this case, the brake failure indicator light
876 is turned on. Thus, one cycle of execution of the routine is
terminated.
[0344] If an affirmative decision (YES) is obtained in step S903,
the control flow goes to step S904 to determine whether the
operating force f is smaller than a predetermined reference value
f.sub.1. If an affirmative decision (YES) is obtained in step S904,
the control flow goes to step S905 to determine whether the force
switch 650 is placed in the off state. The reference value f.sub.1
is determined such that the force switch 650 is in the off state
when the operating force f is smaller than the reference value
f.sub.1, as long as the disc brake 522 is normal. In other words,
if the force switch 650 is in the on state when the operating force
f is smaller than the reference value f.sub.1, it means that the
disc brake 522 is abnormal. Therefore, if a negative decision (NO)
is obtained in step S905, the control flow goes to step S906 to
determine that the disc brake 522 is abnormal. In this case, too,
the brake failure indicator light 876 is turned on. Thus, one cycle
of execution of the routine is terminated.
[0345] If a negative decision (NO) is obtained in step S902, the
control flow goes to step S904. If a negative decision (NO) is
obtained in step S904, one cycle of execution of the routine of
FIG. 35 is terminated.
[0346] It is noted that the reference value f.sub.0 is larger than
the reference value f.sub.1, so that the affirmative decision (YES)
is not obtained in step S904 when the affirmative decision (YES) is
obtained in step S902.
[0347] There will be described a twelfth embodiment of this
invention, in which the same reference numerals as used in the
eighth embodiment will be used to identify the same elements.
[0348] The braking system according to this twelfth embodiment
includes a pressing force sensor 930 provided on the presser member
134 of each front disc brake 522. This pressing force sensor 930 is
adapted to continuously detect a force by which the presser member
134 forces the inner brake pad 606b the onto the friction surface
102 of the disc rotor 104. The pressing force sensor 930 functions
as a force-related quantity sensor for detecting a quantity
relating to a quantity relating to the braking force generated by
the disc brake 522 or the pressing force by which the friction
member 606b is forced onto the rotor 104.
[0349] In the present twelfth embodiment, the ROM 842 stores a
program for executing a front brake control routine illustrated in
the flow chart of FIG. 37.
[0350] The front brake control routine of FIG. 37 is executed
alternately for the front left and right wheels FL, FR. The routine
is initiated with step S951 to determine whether the brake pedal
switch 850 is on. If a negative decision (NO) is obtained in step
S951, one cycle of execution of the routine is terminated. If an
affirmative decision (YES) is obtained in step S951, the control
flow goes to step S952 to detect the operating force f on the basis
of the operating force sensor 848. Then, step S953 is implemented
to determine the desired braking force F* on the basis of the
detected operating force f. Step S953 is similar to step S523 of
the eighth embodiment of FIG. 30. Then, the control flow goes to
step S954 to read an output S.sub.A of the pressing force sensor
930. Step S954 is followed by step S955 to read a conversion
function g(S) stored in the RAM 844. The conversion function g(S)
is used to convert the output S.sub.A into an actual braking force
F.sub.A. Upon power application to the computer 846, a standard
conversion function g(S)* is stored in the RAM 844, and is
provisionally used before the conversion function g(S) is obtained
according to a conversion function compensating routine (which will
be described) and stored in the RAM 844. Each time the conversion
function compensating routine is executed, the conversion function
g(S) stored in the RAM 844 is updated.
[0351] Then, the control flow goes to step S956 to calculate the
actual braking force F.sub.A according to the conversion function
g(S). Then, step S957 is implemented to determine a control amount
.DELTA.I of the electric current I to be supplied to the electric
motor 20. This determination is effected on the basis of the
calculated actual braking force F.sub.A and the determined desired
braking force F*, more precisely, on the basis of a difference
between the actual and desired braking force values F.sub.A and F*.
The control amount .DELTA.I permits the actual braking force
F.sub.A to coincide with the desired value F*. Step S957 is
followed by step S958 in which the electric motor 20 is activated
according to the control amount .DELTA.I.
[0352] The conversion function compensating routine indicated above
is illustrated in the flow chart of FIG. 38.
[0353] This routine of FIG. 38 is also executed alternately for the
front left and right wheels FL, FR. The routine is initiated with
step S1001 to determine whether the force switch 650 is turned on
or off. If a negative decision (NO) is obtained in step S951, one
cycle of execution of the routine is terminated. If an affirmative
decision (YES) is obtained in step S1001, the control flow goes to
step S1002 to read the output S.sub.A of the pressing force sensor
930. Step S1003 is then implemented to calculate an error .DELTA.S
between the output S.sub.A and a nominal value S.sub.T of the
output S.sub.A. The error .DELTA.S=S.sub.A-S.sub.T corresponds to a
difference of an actual characteristic of the pressing force sensor
930 from a nominal or designed characteristic, as indicated in the
graph of FIG. 39. The characteristic is represented by a
relationship between the pressing force f and the output S of the
pressing force sensor 930. The nominal characteristic is
represented by the standard conversion function g(S)* while the
actual characteristic is represented by the conversion function
g(S-.DELTA.S), as indicated in the graph of FIG. 40.
[0354] Then, the control flow goes to step S1004 to determine
whether the absolute value .vertline..DELTA.S.vertline. of the
error .DELTA.S is larger than a predetermined threshold
.DELTA.S.sub.0. If an affirmative decision (YES) is obtained in
step S1004, the control flow goes to step S1005 to compensate the
conversion function g(S)* or g(S) stored in the RAM 844. Namely,
the conversion function g(S-.DELTA.S) is set as the conversion
function g(S), so that the actual braking force F.sub.A is
calculated according to the conversion function g(S-.DELTA.S) in
step S956 upon next execution of the front brake control routine of
FIG. 37. In other words, the f-S relationship which is used in the
routine of FIG. 37 is shifted to the right by an amount equal to
the error .DELTA.S, as indicated in the graph of FIG. 40. Then, the
control flow goes to step S1006 to store the compensated conversion
function g(S) in the RAM 844, that is, store the conversion
function g(S-.DELTA.S) as the compensated or updated conversion
function g(S). If a negative decision (NO) is obtained in step
S1004, one cycle of execution of the conversion function
compensating routine of FIG. 38 is terminated.
[0355] It will be understood from the above description of the
twelfth embodiment that the conversion function g(S) represents a
relationship between the output S.sub.A of the pressing force
sensor 930 and the actual braking force F.sub.A when the force
sensor 650 is turned on. Since the output S.sub.A reflects the
amount of electric current I supplied to the electric motor 20, the
conversion function g(S) is considered to represent a relationship
between the electric current I to be supplied to the electric motor
20 and the braking force F to be applied to the front wheel.
Therefore, a portion of the ECU assigned to execute the conversion
function compensating routine of FIG. 38 is considered to
constitute a relationship estimating device for estimating the
relationship between the electric current I to be applied to the
electric motor 20 and the braking force F to be applied to the
front wheel. It will be understood that a portion of the ECU 550
assigned to execute the front brake control routine of FIG. 37
constitutes relationship utilizing means for utilizing the
estimated relationship for controlling the front disc brake 522. It
will also be understood that a portion of the ECU 550 assigned to
implement steps S954-S956 and S1001-S1005 constitutes a wheel
braking force estimating device for estimating the braking force F
to be applied to the front wheel. It will further be understood
that a portion of the ECU 550 assigned to implement steps S1003 and
S1005 constitutes relationship compensating means for compensating
the above-indicated relationship.
[0356] There will be described a thirteenth embodiment of this
invention, which is a modification of the twelfth embodiment. The
same reference numerals as used in the twelfth embodiment will be
used in the thirteenth embodiment, to identify the same
elements.
[0357] In the braking system according to the thirteenth
embodiment, a braking force sensor 950 is used in place of the
pressing force sensor 930, as shown in FIG. 41. The braking force
sensor 950 is capable of continuously detecting a force received
from the inner brake pad 606b during activation of the front disc
brake 522. The braking force sensor 950 is interposed between the
force switch 650 and the inner torque receiving portion 610b of the
mounting bracket 100, such that the coned disc spring of the force
switch 650 is held in contact with the braking force sensor 950.
The braking force sensor 950 may be a strain gage or a
piezoelectric element, or consists principally of a rubber material
whose electrical conductivity changes with a pressure applied
thereto. The braking force sensor 950 functions as a force-related
quantity sensor or a braking-force-related quantity sensor for
detecting a quantity relating to the braking force generated by the
pressing device 20, 134, 136.
[0358] The ROM 842 of the present braking system stores a program
for executing a front brake control routine illustrated in the flow
chart of FIG. 42.
[0359] The front brake control routine of FIG. 42 is executed
alternately for the front left and right wheels FL, FR. The routine
is initiated with step S1051 to determine whether the brake pedal
switch 850 is on. If a negative decision (NO) is obtained in step
S951, one cycle of execution of the routine is terminated. If an
affirmative decision (YES) is obtained in step S1051, the control
flow goes to step S1052 to detect the operating force f on the
basis of the operating force sensor 848. Then, step S1053 is
implemented to determine the desired braking force F* on the basis
of the detected operating force f. Step S1053 is similar to step
S523 of the eighth embodiment of FIG. 30. Then, the control flow
goes to step S1054 to read an output S.sub.A of the braking force
sensor 950. Step S1054 is followed by step S1055 to read a
conversion function h(S) stored in the RAM 844. The conversion
function h(S) is used to convert the output S.sub.A into an actual
braking force F.sub.A. Upon power application to the computer 846,
a standard conversion function h(S)* is stored in the RAM 844, and
is provisionally used before the conversion function h(S) is
obtained according to a conversion function compensating routine
(which will be described) and stored in the RAM 844. Each time the
conversion function compensating routine is executed, the
conversion function h(S) stored in the RAM 844 is updated.
[0360] Then, the control flow goes to step S1056 to calculate the
actual braking force F.sub.A according to the conversion function
h(S). Then, step S1057 is implemented to determine a control amount
.DELTA.I of the electric current I to be supplied to the electric
motor 20. This determination is effected on the basis of the
calculated actual braking force F.sub.A and the determined desired
braking force F*, more precisely, on the basis of a difference
between the actual and desired braking force values F.sub.A and F*.
The control amount .DELTA.I permits the actual braking force
F.sub.A to coincide with the desired value F*. Step S1057 is
followed by step S1058 in which the electric motor 20 is activated
according to the control amount .DELTA.I.
[0361] The conversion function compensating routine indicated above
is illustrated in the flow chart of FIG. 43.
[0362] This routine of FIG. 43 is also executed alternately for the
front left and right wheels FL, FR. The routine is initiated with
step S1101 to determine whether the force switch 650 is turned on
or off. If a negative decision (NO) is obtained in step S1101, one
cycle of execution of the routine is terminated. If an affirmative
decision (YES) is obtained in step S1101, the control flow goes to
step S1102 to read the output S.sub.A of the braking force sensor
950. Step S1103 is then implemented to calculate an error .DELTA.S
between the output S.sub.A and a nominal value S.sub.T of the
output S.sub.A. The significance of this error
.DELTA.S=S.sub.A-S.sub.T has been described with respect to the
routine of FIG. 38.
[0363] Then, the control flow goes to step S1104 to determine
whether the absolute value .vertline..DELTA.S.vertline. of the
error .DELTA.S is larger than the predetermined threshold
.DELTA.S.sub.0. If an affirmative decision (YES) is obtained in
step S1104, the control flow goes to step S1105 to compensate the
conversion function h(S)* or h(S) stored in the RAM 844. Namely,
the conversion function h(S-.DELTA.S) is set as the conversion
function h(S), so that the actual braking force F.sub.A is
calculated according to the conversion function g(S-.DELTA.S) in
step S1056 upon next execution of the front brake control routine
of FIG. 42. Step S1105 is similar to step S1005 of the routine of
FIG. 38. Then, the control flow goes to step S1106 to store the
compensated conversion function h(S) in the RAM 844, that is, store
the conversion function h(S-.DELTA.S) as the compensated or updated
conversion function h(S). If a negative decision (NO) is obtained
in step S1104, one cycle of execution of the conversion function
compensating routine of FIG. 43 is terminated.
[0364] It will be understood from the above description of the
thirteen embodiment that the conversion function h(S) represents a
relationship between the output S.sub.A of the braking force sensor
950 and the actual braking force F.sub.A when the force sensor 650
is turned on. Since the output S.sub.A reflects the amount of
electric current I supplied to the electric motor 20, the
conversion function h(S) is considered to represent a relationship
between the electric current I to be supplied to the electric motor
20 and the braking force F to be applied to the front wheel.
Therefore, a portion of the ECU assigned to execute the conversion
function compensating routine of FIG. 43 is considered to
constitute a relationship estimating device for estimating the
relationship between the electric current I to be applied to the
electric motor 20 and the braking force F to be applied to the
front wheel. It will be understood that a portion of the ECU 550
assigned to execute the front brake control routine of FIG. 42
constitutes relationship utilizing means for utilizing the
estimated relationship for controlling the front disc brake 522. It
will also be understood that a portion of the ECU 550 assigned to
implement steps S1054-S1056 and S1101-S1105 constitutes a wheel
braking force estimating device for estimating the braking force F
to be applied to the front wheel. It will further be understood
that a portion of the ECU 550 assigned to implement steps S1103 and
S1105 constitutes relationship compensating means for compensating
the above-indicated relationship.
[0365] While the presently preferred embodiments of the present
invention have been described above in detail by reference to the
accompanying drawings, it is to be understood that the present
invention may be embodied with various changes, modifications and
improvements, which may occur to those skilled in the art, without
departing from the spirit and scope of the invention defined in the
following claims:
* * * * *