U.S. patent application number 09/802967 was filed with the patent office on 2001-12-27 for braking control apparatus for vehicles.
Invention is credited to Hamada, Toshiaki, Nitta, Hirofumi, Tanaka, Wataru.
Application Number | 20010054842 09/802967 |
Document ID | / |
Family ID | 18597887 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010054842 |
Kind Code |
A1 |
Tanaka, Wataru ; et
al. |
December 27, 2001 |
Braking control apparatus for vehicles
Abstract
A vehicle braking control apparatus carries out a pressure apply
check to determine if the automatic pressure apply is calculated
normally when the vehicle is started. The apparatus includes a
fluid pressure generator that generates a master cylinder pressure
in response to a pedal depression force, a fluid supplying device
that supplies a braking fluid pressure to the wheel cylinders from
the master cylinder, and a pressure apply device that introduces
the fluid pressure to the pressure chamber of the fluid pressure
generator. A controller controls the braking force of each wheel by
driving the fluid pressure supplying device and controls
pressurization of the master cylinder pressure by automatically
controlling the pressure apply device. A pressure apply check
device starts a pressure apply check to determine that the
automatic pressure apply is calculated normally when the master
cylinder pressure is increased up to a fixed value within a fixed
time after the pressure apply check is started.
Inventors: |
Tanaka, Wataru; (Anjo-shi,
JP) ; Hamada, Toshiaki; (Okazaki-shi, JP) ;
Nitta, Hirofumi; (Obu-shi, JP) |
Correspondence
Address: |
Platon N. Mandros, Esquire
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
18597887 |
Appl. No.: |
09/802967 |
Filed: |
March 12, 2001 |
Current U.S.
Class: |
303/113.1 |
Current CPC
Class: |
B60T 8/90 20130101; B60T
8/4845 20130101; B60T 17/221 20130101; B60T 13/686 20130101 |
Class at
Publication: |
303/113.1 |
International
Class: |
B60T 008/34 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2000 |
JP |
2000-080851 |
Claims
What is claimed is:
1. A braking control apparatus for a vehicle that includes an
engine, a brake pedal and wheels, comprising; fluid pressure
generating means for generating a brake fluid pressure in response
to a brake pedal depression force; fluid supplying means for
supplying the brake fluid pressure from the fluid pressure
generating means to wheel cylinders associated with the wheels to
apply a braking force; pressure apply means for introducing fluid
pressure to a pressure chamber of the fluid pressure generating
means; and control means for automatically increasing the brake
fluid pressure by controlling the pressure apply means and for
controlling the braking force of each wheel by controlling a
driving operation of the fluid supplying means; the control means
including pressure apply check means for starting a pressure apply
check when the vehicle is started to determine whether the
automatic pressure increase of the brake fluid pressure is properly
performed; the pressure apply check means determining the automatic
pressure increase is properly made when the master cylinder
pressure is increased to a predetermined value within a
predetermined time after the pressure apply check is started.
2. The braking control apparatus for a vehicle as defined in claim
1, further comprising: a brake pedal depression force detecting
means outputting a first signal when the brake pedal is depressed
and outputting a second signal when the brake pedal is released;
the pressure apply check means starts the pressure apply check when
the second signal is outputted after an initial first signal has
been outputted following starting of the engine; and the pressure
apply check means holds the brake fluid pressure of the wheel
cylinders of each wheel by maintaining the fluid supply means at a
holding condition and starting automatic pressure increase
operation by controlling the pressure apply means at the start of
the pressure apply check.
3. The braking control apparatus for a vehicle as defined in claim
2, wherein: the pressure apply means includes a pump supplying the
brake fluid pressure to the pressure chamber, a motor driving the
pump, and a linear valve generating a servo pressure in response to
a control current outputted by the control means; and the pressure
apply check means starts the driving of the pump by the motor after
the initial first signal is outputted and before an initial second
signal is outputted after the engine is started.
4. The braking control apparatus for a vehicle as defined in claim
2, wherein the pressure apply check means ends the pressure apply
check when the first signal is outputted during the pressure apply
check.
5. The braking control apparatus for a vehicle as defined in claim
3, wherein the pressure apply check means ends the pressure apply
check when a changing speed of the master cylinder pressure becomes
zero during the pressure apply check, and including executing a
learning process correction of a pre-stored pressure modulating
characteristic of the pressure apply means based on the control
current value to the linear valve and the master cylinder
pressure.
6. The braking control apparatus for a vehicle as defined in claim
3, wherein the pressure apply check means controls the pressure
apply means to gradually decrease the control current outputted to
the linear valve when the pressure apply check is ended.
7. A braking control apparatus for a vehicle that includes an
engine, a brake pedal and wheels, comprising; a master cylinder
generating a brake fluid pressure in response to a brake pedal
depression force, the master cylinder including a pressure chamber
connected to at least one wheel cylinder associated with one of the
wheels; a fluid pressure sensor detecting a master cylinder
pressure in the pressure chamber; a pressure apply unit performing
pressure apply by introducing fluid pressure to the pressure
chamber of the master cylinder; a controller automatically
increasing the brake fluid pressure by controlling the pressure
apply unit; and pressure apply check means for starting a pressure
apply check when the vehicle is started to determine whether the
pressure apply is abnormal, the pressure apply check means
determining the pressure apply is abnormal when the master cylinder
pressure determined by the fluid pressure sensor fails to reach a
predetermined value within a predetermined time.
8. The braking control apparatus for a vehicle as defined in claim
7, including a brake pedal depression detector for outputting a
first signal when the brake pedal is depressed and outputting a
second signal when the brake pedal is released, the pressure apply
check means starting the pressure apply check when the second
signal is outputted after an initial first signal has been
outputted following starting of the engine,
9. The braking control apparatus for a vehicle as defined in claim
8, wherein the pressure apply means includes a pump supplying the
brake fluid pressure to the pressure chamber, a motor driving the
pump, and a linear valve generating a servo pressure in response to
a control current outputted by the control means, the pressure
apply check means starting the driving of the pump by the motor
after the initial first signal is outputted and before an initial
second signal is outputted after the engine is started.
10. The braking control apparatus for a vehicle as defined in claim
8, wherein the pressure apply check means ends the pressure apply
check when the first signal is outputted during the pressure apply
check.
11. The braking control apparatus for a vehicle as defined in claim
7, wherein the pressure apply check means ends the pressure apply
check when the changing speed of the master cylinder pressure
becomes zero during the pressure apply check.
12. The braking control apparatus for a vehicle as defined in claim
11, wherein the pressure apply check means controls the pressure
apply means to gradually decrease the control current outputted to
the linear valve when the pressure apply check is ended.
13. The braking control apparatus for a vehicle as defined in claim
7, including executing a learning process correction of a
pre-stored pressure modulating characteristic of the pressure apply
means based on the control current value to the linear valve and
the master cylinder pressure.
14. A method for determining proper automatic pressure increase in
a braking control apparatus for a vehicle that includes an engine,
a brake pedal, wheels, a master cylinder that generates a master
cylinder pressure in response to depression of the brake pedal, and
a pressure apply unit for introducing fluid pressure into a
pressure chamber of the master cylinder to effect automatic
pressure increase, the method comprising: initiating pressure apply
check upon starting the vehicle to determine that the automatic
pressure increase is proper; measuring the master cylinder pressure
after initiation of the pressure apply check; and determining that
the automatic pressure increase is proper when the master cylinder
pressure has reached a predetermined value within a predetermined
time after initiation of the pressure apply check.
15. The method as defined in claim 14, wherein the pressure apply
check is initiated when the brake pedal is released after the brake
pedal is first depressed following starting of the vehicle.
16. The method as defined in claim 14, wherein the pressure apply
unit includes a pump supplying the brake fluid pressure to the
pressure chamber, a motor driving the pump, and a linear valve
generating a servo pressure, and including initiating driving
operation of the pump after the brake pedal is first depressed
after starting the vehicle and before the brake pedal is
released.
17. The method as defined in claim 14, wherein the pressure apply
check is stopped when the brake pedal is depressed during the
pressure apply check.
18. The method as defined in claim 14, including ending the
pressure apply check when a changing speed of the master cylinder
pressure becomes zero during the pressure apply check
Description
[0001] This application is based on and claims priority under 35
U.S.C. .sctn. 119 with respect to Japanese Application No.
2000-080851 filed on Mar. 22, 2000, the entire content of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention generally relates to vehicle braking systems.
More particularly, the present invention pertains to a braking
control apparatus for vehicles which is adapted to generate a
master cylinder pressure in response to a pedal depression force
and to automatically increase the master cylinder pressure through
operation of a booster.
BACKGROUND OF THE INVENTION
[0003] One known braking control apparatus is disclosed in German
Patent Offenlegungsschrift No. 197 03 776 A1. This braking control
apparatus includes a fluid pressure generating device for
generating a master cylinder pressure in response to a pedal
depression force and a pressurizing device for introducing fluid
pressure to a pressure chamber of the fluid pressure generating
device in order to obtain a boosted force for the pedal depression
force by automatically increasing the master cylinder pressure by
the pressurizing device.
[0004] With this known braking control apparatus, it is necessary
to check the automatic pressure increasing function to assess
whether it is correctly calculated before starting the vehicle so
that the increased pressure is always assured without giving any
undesired feeling to the driver of the vehicle.
[0005] A need thus exists for a vehicle braking control apparatus
that is able to readily and reliably check the automatic pressure
increase function and assess whether it is calculated correctly
when the vehicle starts.
SUMMARY OF THE INVENTION
[0006] A braking control apparatus for a vehicle includes a fluid
pressure generator that generates a master cylinder pressure in a
master cylinder in response to a pedal depression force, a fluid
supplying device that supplies braking fluid pressure to wheel
cylinders of each wheel of the vehicle from the master cylinder, a
pressure apply device that introduces fluid pressure to the
pressure chamber of the fluid pressure generator, and a controller
that automatically increases the master cylinder pressure by
controlling the pressure apply device and for controlling the
braking force of each wheel by driving the fluid supplying device.
The controller includes a pressure apply check device for starting
pressure apply check when the vehicle is started to determine
whether the automatic pressure increase function is properly
performed. The pressure apply check device judges that the proper
automatic pressure increase is made when the master cylinder
pressure is increased to a predetermined valve within a
predetermined time after the pressure apply check starts.
[0007] According to the present invention, the pressure apply check
is performed when the vehicle is started because the pressure apply
check is started in synchronization with the starting of the
vehicle. Additionally, in the pressure apply check device, the
automatic pressure apply is judged normal when the master cylinder
pressure is increased up to the fixed value. The pressure apply
check device is able to detect an abnormality of the automatic
pressure apply caused by a failure in the pressure apply device
when the master cylinder pressure is not increased up to the fixed
value.
[0008] The braking control apparatus also includes a brake pedal
depression force device that outputs a first signal when the brake
pedal is depressed and outputs a second signal when the brake pedal
is released. The pressure apply check device starts the pressure
apply check when the second signal is outputted after an initial
first signal has been outputted after the engine is started. The
pressure apply check device holds the brake fluid pressure of the
wheel cylinders of each wheel by maintaining the fluid supply
device in a holding condition and starts automatic pressure
increase operation by controlling the pressure apply device at the
start of the pressure apply check.
[0009] Thus, the increasing of the master cylinder pressure by the
automatic pressure apply is not transmitted to the wheel cylinders
and the pressure apply check can be practiced without disturbing
the vehicle start because the brake fluid of the wheel cylinders of
all the wheels is assured when the pressure apply check is
started.
[0010] The pressure apply check device ends the pressure apply
check when the first signal is outputted during the pressure apply
check. Thus, when the applied check is practiced after the vehicle
actually starts, if the brake pedal is depressed by the
deceleration demand of the driver, the pressure apply check is
ended and the deceleration demand is performed.
[0011] The pressure apply check means ends the pressure apply check
when the changing speed of the master cylinder pressure becomes
zero during the pressure apply check, A learning process correction
of a pre-set pressure modulating characteristic of the pressure
apply device is then performed based on the control current value
to the linear valve and the master cylinder pressure. Because the
correction of the pressure control or modulating characteristic is
performed based on the stable master cylinder pressure when the
master cylinder pressure is increased and the pressure changing
speed becomes zero and based on the control current value to the
linear valve, the subsequent automatic pressure apply control
carried out more correctly.
[0012] According to another aspect of the invention, a braking
control apparatus for a vehicle includes a master cylinder
generating a brake fluid pressure in response to a brake pedal
depression force, with the master cylinder including a pressure
chamber connected to at least one wheel cylinder associated with
one of the wheels, a fluid pressure sensor detecting the master
cylinder pressure in the pressure chamber, a pressure apply unit
performing pressure apply by introducing fluid pressure to the
pressure chamber of the master cylinder, a controller automatically
increasing the brake fluid pressure by controlling the pressure
apply unit, and a pressure apply check device for starting a
pressure apply check when the vehicle is started to determine
whether the pressure apply is abnormal. The he pressure apply check
device determines that the pressure apply is abnormal when the
master cylinder pressure determined by the fluid pressure sensor
fails to reach a predetermined value within a predetermined
time.
[0013] Another aspect of the invention involves a method for
determining proper automatic pressure increase in a braking control
apparatus for a vehicle that includes an engine, a brake pedal,
wheels, a master cylinder that generates a master cylinder pressure
in response to depression of the brake pedal, and a pressure apply
unit for introducing fluid pressure into a pressure chamber of the
master cylinder to effect automatic pressure increase. The method
includes initiating a pressure apply check upon starting the
vehicle to determine that the automatic pressure increase is
proper, measuring the master cylinder pressure after initiation of
the pressure apply check, and determining that the automatic
pressure increase is proper when the master cylinder pressure has
reached a predetermined value within a predetermined time after
initiation of the pressure apply check.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0014] The foregoing and additional features and characteristics of
the present invention will become more apparent from the following
detailed description considered with reference to the accompanying
drawing figures in which like reference numerals designate like
elements and wherein:
[0015] FIG. 1 is a block diagram of the electronic control unit
used in the vehicle brake control apparatus of the present
invention;
[0016] FIG. 2 is a schematic illustration of the overall braking
control apparatus of the present invention;
[0017] FIG. 3 is a flow chart illustrating the main routine
associated with the operation of the braking control apparatus of
the present invention; and
[0018] FIG. 4 is a flow chart illustrating a subroutine associated
with the pressure apply check carried out in the main routine shown
in FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Referring initially to FIG. 2, the vehicle braking control
apparatus which performs an automatic pressure applying function in
accordance with the present invention includes a fluid pressure
generating apparatus 11 that generates brake fluid pressure and a
pressure apply unit 12 functioning as a pressure applying means for
introducing fluid pressure for automatic pressure application to
the apparatus. In addition, the braking control apparatus is
provided with a fluid pressure control apparatus 17 for supplying
the brake fluid pressure to the wheel cylinders 13, 14, 15, 16 and
an electric control unit 18 (shown in FIG. 1) for controlling the
braking force applied at each wheel. The wheel cylinders 13, 14,
15, 16 are respectively installed at the front right wheel, the
front left wheel, the rear right wheel, and the rear left wheel of
the vehicle.
[0020] The fluid pressure generating apparatus 11 is provided with
a vacuum booster 19 and a master cylinder 20. A first piston 23 and
a second piston 26 are disposed within the master cylinder 20. To
simplify the overall structure and the illustrated features of the
master cylinder 20, various known features associated with the
master cylinder 20 such as the seal members are omitted.
[0021] In the fluid pressure generating apparatus 11, a pedal
depression force of a brake pedal 21, amplified by the lever ratio
of the associated link mechanism, is transmitted to an operating
rod 22 so that the operating rod 22 is pushed by the pedal
depression force. The pushing force received by the rod 22 is
amplified by the vacuum booster 19 and pushes the first piston 23
of the master cylinder 20. When the first piston 23 moves in
opposition to the urging force of a spring from the position shown
in FIG. 2, communication between a first pressure chamber 24 of the
master cylinder 20 and a reservoir 25 is cut off, and fluid
pressure is generated in the first pressure chamber 24. When the
second piston 26 is pushed against the urging force of a spring
from the position shown in FIG. 2 by the fluid pressure,
communication between a second pressure chamber 27 and the
reservoir 25 is cut off and fluid pressure is generated in the
second pressure chamber 27.
[0022] Accordingly, when the first piston 23 is pushed by the pedal
depression force amplified by the link mechanism and the vacuum
booster 19, a brake pressure is generated corresponding to the
pedal input pressure Pmcin and responsive to the pedal depression
force in the first pressure chamber 24. In addition, when the
second piston 26 is pushed by the brake fluid pressure in the first
pressure chamber 24, a brake fluid pressure is generated in the
second pressure chamber 27. It is to be recognized that pressure
increase by vacuum booster includes pressure increase by the lever
ratio of the link mechanism.
[0023] The master cylinder 20 is also provided with a third
pressure chamber 28 which applies fluid pressure to the end surface
of the first piston 23 at the booster side of the first piston 23.
The fluid pressure generated in the pressure apply unit 12 is
introduced into the third pressure chamber 28. The brake fluid
pressure of the third chamber servo pressure Pmc3 is generated in
the first pressure chamber 24 since the first piston 23 is pushed
by the fluid pressure (the third chamber pressure P3). In this case
the third chamber servo pressure Pmc3 is given by the third chamber
pressure P3 corresponding to the ratio between the pressure
receiving areas of the first piston 23 of the booster side and of
the anti-booster side.
[0024] In this way, the master cylinder pressure Pmc generated by
the master cylinder includes the pedal input pressure Pmcin
component associated with the pedal depression force amplified by
the vacuum booster 19 and the third chamber servo pressure Pmc3
component associated with the fluid pressure introduced by the
pressure apply unit 12.
[0025] The pressure apply unit 12 includes a pump 29 that
compresses or pressurizes brake fluid stored in the reservoir 25
and supplies the pressurized brake fluid to the third pressure
chamber 28, a motor 30 that drives the pump 29, and a linear valve
31 that opens in response to the current value of an input signal
(control signal) for introducing brake fluid discharged from the
pump 29 into the reservoir 25. In accordance with the control
signal (current value) outputted from the electric control unit
(ECU) 18 to the linear valve 31, fluid pressure corresponding to
the value of the control signal (the current value) is introduced
into the third pressure chamber 28 based on the characteristic of
the linear valve 31 between the fluid pressure (P3) and the current
value.
[0026] The brake fluid pressure generated in the master cylinder 20
is supplied to each wheel cylinder, with the wheel cylinders being
divided into a front wheel side that includes the two wheel
cylinders 13, 14 associated with the front wheels FL, FR and a rear
wheel side that includes the two wheel cylinders 15, 16 associated
with the rear wheels RL, RR. Thus, the fluid pressure control
apparatus 17 which connects the master cylinder 20 and the wheel
cylinders 13-16 directs fluid pressure to the wheel cylinders 13,
14 on the front side of the vehicle and directs fluid pressure to
the wheel cylinders 15, 16 on the rear side of the vehicle.
[0027] More specifically, the brake fluid pressure generated in the
first pressure chamber 24 is introduced into a main passage 32. The
main passage 32 is connected with the wheel cylinders 13, 14
through the front side system circuit portion of the fluid pressure
control apparatus 17. The main passage 32 is connected with the
wheel cylinder 13 through a holding valve 33a, while the main
passage 32 is connected with the wheel cylinder 14 through a
holding valve 34a. A passage extending between the wheel cylinder
13 and the holding valve 33a is connected with a reservoir 38
through a pressure reducing valve 33b and a passage extending
between the wheel cylinder 14 and the holding valve 34a is
connected with the reservoir 38 through a pressure reducing valve
34b.
[0028] On the other hand, the brake fluid pressure generated in the
second pressure chamber 27 of the master cylinder 20 is introduced
into the main passage 37. The main passage 37 is connected with the
wheel cylinders 15, 16 through the rear side system circuit portion
of the fluid pressure control apparatus 17. The main passage 37 is
connected with the wheel cylinder 15 through a holding valve 35a,
while the main passage 37 is connected with the wheel cylinder 16
through a holding valve 36a. A passage extending between the wheel
cylinder 15 and the holding valve 35a is connected with a reservoir
39 through a pressure reducing valve 35b and a passage extending
between the wheel cylinder 16 and the holding valve 36a is
connected to the reservoir 39 through a pressure reducing valve
36b.
[0029] The holding valves 33a, 34a, 35a, 36a are normally open type
solenoid valves, while the pressure reducing valves 33b, 34b, 35b,
36b are normally closed type solenoid valves. These solenoid valves
are excited or energized by the fluid pressure control signal
(control current) outputted from the ECU 18.
[0030] The function and operation of the holding valve 33a and the
pressure reducing valve 33b associated with the front right side
wheel is described below. It is to be understood that the function
and operation of the other holding valves 34a, 35a, 36a and the
other reducing valves 34b, 35b, 36b associated with the other three
wheels are similar. When the holding valve 33a is not energized
(i.e., the off condition) and the pressure reducing valve 33b is
not energized (i.e., the off condition), a pressure increasing
condition exists because the wheel cylinder 13 is in communication
with the master cylinder 20 and is prevented from communicating
with the reservoir 38. In this pressure increasing condition, the
brake fluid pressure in the wheel cylinder 13 is increased.
[0031] When the holding valve 33a and the pressure reducing valve
33b are both energized (i.e., they are both in the on condition), a
pressure decreasing condition exists because the wheel cylinder 13
is in communication with the reservoir 38 and is prevented from
communicating with the master cylinder 20. In the pressure
decreasing condition, the brake fluid pressure in the wheel
cylinder 13 is decreased.
[0032] When the holding valve 33a is energized (i.e., the on
condition) and the pressure reducing valve 33b is not energized
(i.e., in the off condition), the pressure in the wheel cylinder is
held because the wheel cylinder 13 is prevented from communicating
with both the master cylinder 20 and the reservoir 38. In the
pressure holding condition, the brake fluid pressure of the wheel
cylinder 13 is maintained without being increased or decreased.
[0033] Through operation of the valves in the above-described
manner, the braking force applied to each wheel is individually
controlled by controlling the brake fluid pressure supplied to each
wheel cylinder 13, 14, 15, 16 as a result of changing the fluid
pressure control signal (i.e., on or off) outputted to the holding
valves and the pressure reducing valves of each wheel from the ECU
18.
[0034] In the front side system circuit portion of the fluid
pressure control apparatus 17, the brake fluid stored in the
reservoir 38 is pumped by the motor driven pump 41 and discharged
to the up stream passage of the holding valves 33a, 34a by way of
two check valves located on opposite sides of the pump 41 and a
damper 43, with the check valves and damper being provided in a
pump passage 42.
[0035] In the same way, in the rear system circuit portion of the
fluid pressure control apparatus 17, the brake fluid stored in the
reservoir 39 is pumped by the motor driven pump 44 and discharged
to the up stream passage of the holding valves 35a, 36a by way of
two check valves located on opposite sides of the pump 44 and a
damper 46, with the check valves and damper being provided in a
pump passage 45.
[0036] In the front system circuit portion, return passages 47, 48
are provided for permitting the return of brake fluid from each
wheel cylinder 13, 14 into the master cylinder 20 while bypassing
the holding valves 33a, 34a. Respective inverse stop valves 49, 50
preventing the back flow of the brake fluid into the wheel
cylinders are provided in each return passage 47, 48.
[0037] Likewise, in the rear system circuit portion, return
passages 51, 52 are provided for permitting the return of brake
fluid from each wheel cylinder 15, 16 into the master cylinder 20
while bypassing the holding valves 35a, 36a. Respective inverse
stop valves 53, 54 preventing the back flow of the brake fluid into
the wheel cylinders are provided in each return passage 51, 52.
[0038] A fluid pressure sensor 62 detecting the master cylinder
pressure (Pmc) as a brake fluid pressure generated in the master
cylinder 20 is provided in the main passage 32. Wheel speed sensors
63, 64, 65, 66 are operatively associated with each respective
wheel FR, FL, RR, RL to detect the wheel speed of each wheel. A
stop lamp switch (SLS) 67 operatively associated with the brake
pedal 21 operates as a detecting sensor for detecting the
depression of the brake pedal 21. The stop lamp switch (SLS) 67
outputs a first signal (e.g., an on signal) if the pedal 21 is
depressed and outputs a second signal (e.g., an off signal) if the
brake pedal is released is provided in the brake pedal 21.
[0039] The structure of the ECU shown in FIG. 1 is as follows. The
current supplied to the linear valve 31 of the pressure apply unit
12 is controlled by the ECU 18 in response to the pedal depression
force or the condition of the vehicle. The master cylinder pressure
is pressurized automatically by changing the fluid pressure (the
third chamber pressure P3) introduced into the third pressure
chamber 28 of the master cylinder 20 by the pressure apply unit 12
and the braking force of each wheel is controlled by driving the
fluid pressure control apparatus 17 under the control of the ECU
18.
[0040] The ECU 18 is an electric control unit mainly comprised of
micro computers. More specifically, the ECU 18 is comprised of a
CPU (central processing unit) 70, a RAM (random access memory) 71,
a ROM (read only memory) 72, an input circuit portion 73 and an
output circuit portion 74.
[0041] The fluid pressure sensor 62, the stop lamp switch 67, and
the wheel speed sensors 63, 64, 65, 66 are connected to the input
circuit portion 73. A steering angle sensor 81 detecting the
steering angle, a vehicle acceleration sensor 82 detecting the
acceleration in the longitudinal or the lateral direction of the
vehicle, and a yaw rate sensor 83 detecting the yaw rate generated
in the vehicle are also connected with the input circuit portion
73.
[0042] The motor 30 and the linear valve 31 of the pressure apply
unit 12, and the holding valves 33a, 34a, 35a, 36a, the pressure
reducing valves 33b, 34b, 35b, 36b and the motor 40 of the fluid
pressure control apparatus 17 are connected to the output circuit
portion 74.
[0043] The ECU is also provided with a vehicle stability control
portion 75, an automatic pressure apply control portion 76, a
pressure apply check portion 77 serving as a pressure apply check,
a pressure apply characteristic learning portion 78, an anti-skid
control portion 79, and a traction control portion 80. These
portions are operated under the control of the CPU 70.
[0044] The vehicle stability control that controls the braking
force of each wheel is operated or carried out by the vehicle
stability control portion 75 based on the vehicle condition
detected by the wheel speed sensors 63, 64, 65, 66, and the sensors
81, 82, 83 to reduce the difference between a target line or
desired path of travel of the vehicle and the actual target line or
path of travel of the vehicle (i.e., a detected vehicle condition)
during steering or turning for instance. Accordingly, the operation
of the motor 30 of the pressure apply unit 12 and the value
(current value I) of the control signal outputted to the linear
valve 31 are controlled by the vehicle stability control portion 75
in response to the vehicle condition detected. Additionally, the
holding valves 33a, 34a, 35a, 36a, the pressure reducing valves
33b, 34b, 35b, 36b and the motor 40 of the fluid pressure control
apparatus 17 are controlled by the vehicle stability control
portion 75.
[0045] The automatic pressure apply control portion 76 controls the
current of the linear valve 31 of the pressure apply unit 12 so
that the master cylinder pressure is pressurized automatically to
change the fluid pressure (the third chamber pressure P3)
introduced into the third pressure chamber 28 by the pressure apply
unit 12. Accordingly, in the automatic pressure apply control
portion 76, for instance, the fluid pressure (the third chamber
pressure P3) is changed and the master cylinder pressure Pmc is
pressurized automatically by the third servo pressure Pmc3 in
response to the fluid pressure by the master cylinder pressure Pmc
when the amplified pressure limit of the pedal depression force by
the vacuum booster 19 is exceeded.
[0046] The pressure apply check for checking or determining if the
automatic pressure apply is normally calculated when the vehicle
starts is carried out by the pressure apply check portion 77 based
on the output signal of the stop lamp switch 67 and the master
cylinder pressure Pmc detected by the fluid pressure sensor 62.
[0047] The pressure apply characteristic learning portion 78
performs a learning process which corrects the pressure control
characteristic of the pressure apply unit 12 memorized in advance
from the control current value I to the linear valve 31 and the
master cylinder pressure Pmc obtained during the pressure apply
check by the pressure apply check portion 77 or the end of the
checking. The fluid pressure control apparatus 17 is controlled by
the anti-skid control portion 79 for controlling the braking force
applied to each wheel in order to prevent the locking of the wheels
during braking, and the pressure apply unit 12 and the fluid
pressure control apparatus 17 are controlled by the traction
control portion 80 for applying a braking force to the driving
wheels to prevent slip of the driving wheels during driving.
[0048] The operating procedure performed by the ECU and the
operation of the vehicle braking control apparatus according to the
present invention is explained hereinafter with reference to FIG.
3. The routine shown in the flowchart of FIG. 3 starts when the
engine operation is initiated upon turning on the ignition switch
of the vehicle. At this time, any necessary initial set up is
carried out. In step S100, an input process is performed involving
reading the detected signals outputted by the fluid pressure sensor
62, the stop lamp switch 67, the wheel speed sensor 63, 64, 65, 66,
the steering angle sensor 81, the vehicle acceleration sensor 82,
and the yaw rate sensor 83. In addition, the master cylinder
pressure changing speed (rate) dPmc is calculated based on the
following formula (1)
dPmc=Pmc'-Pmc (1)
[0049] wherein, Pmc' represents the present calculated value for
the master cylinder pressure and Pmc represents the previous
calculated value for the master cylinder pressure. The cycle time
of the program calculation (cycle time of the FIG. 3 routine) is
very short and can thus be considered as a constant, and so the
master cylinder pressure changing speed can be determined by the
change in pressure Pmc. The master cylinder pressure changing speed
can thus also be referred to as a master cylinder pressure changing
rate.
[0050] Next, in step S101, the wheel speed of each wheel, the wheel
acceleration, the estimated vehicle speed at the gravitational
center position of the vehicle and at each wheel position, and the
actual slip ratio of each wheel are computed.
[0051] The routine then proceeds to step S200 at which the pressure
apply check process, described below in more detail, is performed.
Then, in step S102, various control modes such as the anti-skid
control are set up and a target slip ratios for the various control
modes are set up.
[0052] Then, in a step S103, the pressure apply unit 12 and the
fluid pressure control apparatus 17 are properly controlled in
response to the control modes, and the braking force applied to
each wheel is controlled. After carrying out step S103, the routine
returns to step S100.
[0053] The routine for the pressure apply check process of step
S200 is carried out in accordance with the subroutine shown in FIG.
4. In step S202, it is determined whether or not the pressure apply
check process is being performed. In the event the pressure apply
check is being performed, the program proceeds to step S204. If the
pressure apply check is not being performed, step S206 is carried
out. If the ignition switch has just been turned on (i.e., the
engine has just been started), the program proceeds to step S206
because the pressure apply check is not being processed.
[0054] In step S206, the system determines whether the stop lamp
switch 67 is turned on during the previously calculated time and is
turned off during the presently calculated time. If the
determination in step S206 is YES, the program proceeds to step
S216. On the other hand, if the determination in step S206 is NO,
the program proceeds to step S208. If the brake pedal is maintained
in a depressed state after the ignition switch is turned on, the
program proceeds to step S208 from step S206 because the stop lamp
switch 67 is on.
[0055] In step S208, a determination is made regarding whether the
master cylinder pressure Pmc is less than a first fixed value KP1.
If the master cylinder pressure Pmc is less than the first fixed
value KP1, the routine advances to step S210, and if the master
cylinder pressure Pmc is equal to or greater than the first fixed
value KP1 the program advances to S224. Under the condition that
the brake pedal 21 is depressed immediately after the ignition
switch is turned on, the program proceeds to step S224 because the
master cylinder pressure is more than the fixed value KP1, and
while under the condition immediately before the brake pedal 21 is
released, the program proceeds to step S210 because the master
cylinder pressure is less than the fixed value KP1. The master
cylinder pressure is less than the fixed value KP1 immediately
before the brake pedal 21 is released because the brake pedal
depressing force becomes small enough for the master cylinder
pressure to be less than the fixed value KP1 immediately before the
brake pedal 21 is released.
[0056] In step S210, the system determines whether the master
cylinder pressure changing speed dPmc calculated in step S100 is
less than a negative fixed value KT. If the master cylinder
pressure changing speed dPmc is less than the negative fixed value
KT, the routine proceeds to step S212. On the other hand, if the
master cylinder pressure changing speed dPmc calculated in the step
S100 is equal to or greater than the negative fixed value KT, the
program advances to step S224. Immediately before the brake pedal
is released, the master cylinder pressure changing speed dPmc is
less than the negative fixed value KT and so the program advances
to step S212.
[0057] In step S212, a pressure apply check pre-process is
performed. During this operation, the holding valves 33a, 34a, 35a,
36a of all four wheels are off, the control current of the linear
valve 31 is off and only the pump 29 is driven by the motor 30. In
this way, if the master cylinder pressure Pmc is less than the
first fixed value KP1 and the master cylinder changing speed dPmc
is less than the fixed value KT before the stop lamp switch changes
to off from on, the pressurization of the master cylinder pressure
is started in advance by driving the pump 29. The reason is to
shorten the time needed to increase the master cylinder pressure up
to the second fixed value KP2 as a criterion of the normal judgment
of the pressure apply check.
[0058] Afterward, the program proceeds back to step S200 and then
moves to step S202. At this time, because the pressure apply check
has not been started, the program moves to step S206. If the driver
releases his/her foot from the brake pedal so that the stop lamp
switch 67 is off, the process moves to step S216 from step S206 and
the pressure apply check process is started.
[0059] In the pressure apply check process, the holding valves 33a,
34a, 35a, 36a of all of four wheels are on. Accordingly, the brake
fluid pressure of the wheel cylinders 13, 14, 15, 16 of all four
wheels is maintained to be constant. Simultaneously, the control
current starts to be outputted to the linear valve 31 (the linear
valve 31 is on). The pump 29 which is already being driven by the
motor 30 (step S212) is further maintained to be driven.
Additionally, the incrementing of the time counter (ctcheck) during
pressure apply check is started.
[0060] The program then returns to step S202 by way of step S200.
Because the pressure apply check process has been already started,
the program proceeds to step S204 from step S202. In step S204, the
system judges whether or not the stop lamp switch 67 is presently
off. If the stop lamp switch is off, the program moves to step
S214. If the stop lamp switch is on, the program moves to step S224
and the pressure apply check process is ended.
[0061] Immediately after the beginning of the pressure apply check,
the program advances to step S215 from step S204 because the stop
lamp switch 67 is off. In step S215, it is determined whether or
not the pressure apply check time counter (ctcheck) exceeds a fixed
time KT1. If the automatic pressure apply is judged abnormal
because of a failure of the pressure apply unit 12 (i.e., the
pressure apply check time counter (ctcheck) exceeds the fixed time
KT1), the routine moves to step S221 and a pressure apply abnormal
judging operation is carried out. In the pressure apply abnormal
judging process, a warning light (not shown) informing the driver
of the abnormal pressure apply is turned on and the setting up of
the various control modes in the step S102 is prohibited.
[0062] If the master cylinder pressure Pmc is less than the second
fixed value KP2 in step S214, the program moves to step S216. On
the other hand, if the master cylinder pressure Pmc is greater than
the second fixed value KP2, the routine advances to step S218.
Immediately after the beginning of the pressure apply check, the
program advances to step S216 because the master cylinder pressure
Pmc is less than the second fixed value KP2 and the pressure apply
check process is to be continued.
[0063] If the master cylinder pressure Pmc is more than the second
fixed value KP2 during the pressure apply check process, the
program advances to step S218 from step S214 where it is judged
whether or not the master cylinder pressure changing speed dPmc is
zero. When the master cylinder pressure changing speed dPmc is
increasing (i.e., the changing speed dPmc is not zero), the routine
advances to step S216 and the pressure apply check is continued.
When the master cylinder pressure changing speed dPmc becomes zero
during the pressure apply check process, the routine moves to step
S220 where it is judged that the automatic pressure apply of the
master cylinder pressure Pmc of the pressure apply unit 12 is
operating normally.
[0064] The program then advances to step S222 and the learning
process correcting the pre-stored pressure control characteristic
of the pressure apply unit 12 performed by the control current
value I and the master cylinder pressure Pmc when the master
cylinder pressure changing speed dPmc becomes zero. Namely, the
pressure control characteristic coefficient (ktokusei) of the
pressure apply unit 12 is calculated using the following formula
(2) by the control current value I and the master cylinder pressure
Pmc when the master cylinder pressure changing speed dPmc becomes
zero.
ktokusei=Pmc/1 (2)
[0065] The program then proceeds to step S224, the pressure apply
check process is ended and the non-pressure apply check process is
performed. In this non-pressure apply check process, the holding
valves 33a, 34a, 35a, 36a of all four wheels are off, the control
current of the linear valve 31 is off and the driving of the pump
29 by the motor 30 is stopped. The control current of the linear
valve 31 is reduced continuously to avoid fluid shooting noise.
This phrase refers to the noise caused by the collision of parts of
the fluid in the linear valve 31, which occurs when the control
current of the linear valve 31 is immediately shut off to reduce
the third chamber pressure P3 quickly. After this, the program
returns to the main routine.
[0066] According to the present invention, because the pressure
apply check is initiated when the vehicle is started, that is when
the stop lamp switch is turned to off from on, the pressure apply
check is practiced every time when the vehicle is started. In the
pressure apply check portion 77, the automatic pressure apply is
judged normal when the master cylinder pressure is increased up to
the fixed value KP2, that is when the determination in step S214 is
YES.
[0067] From the foregoing, it can be seen that the pressure apply
check for assessing whether or not the automatic pressure apply is
normal is performed every time the vehicle starts. As a result, a
driver can check at all times if the automatic pressure apply is
assured by the pressure apply unit 12 during driving. Additionally,
a manufacturer can check the automatic pressure apply of the
manufactured brake apparatus before performing an inspection such
as brake failure inspection.
[0068] Also, because the brake fluid of the wheel cylinders 13, 14,
15, 16 of all the wheels is held in the holding condition, (the
step S216) when the pressure apply check is started, the increase
in the master cylinder pressure by the automatic pressure apply is
not applied to the wheel cylinders and the pressure apply check can
be practiced without disturbing the vehicle upon start.
[0069] According to the present invention, the driving of the pump
29 is started before the pressure apply check is started and so the
time required to increase the master cylinder pressure up to the
second fixed value KP2 is shortened. As a result, the time during
which the driver experiences an undesirable feeling in the holding
condition of all wheels is shortened.
[0070] If the stop lamp switch 67 is on (the determination in step
S204 is NO) indicating depression of the brake pedal 21 during the
pressure apply check, the program advances to step S224 and the
pressure apply check is ended. As a result, if the brake pedal 21
is depressed by the driver for effecting deceleration when the
pressure apply check is being performed, the pressure apply check
is ended and the deceleration demand is performed.
[0071] By virtue of the learning process correcting of the pressure
control characteristic coefficient (ktokusei) of the pressure apply
unit 12 when the pressure apply check is ended, the automatic
pressure apply control afterward is performed correctly using the
pressure control characteristic after the correction.
[0072] Additionally, because the correction of the pressure control
characteristic coefficient is based on a stable master cylinder
pressure once the master cylinder pressure has been increased to a
predetermined value and the master cylinder pressure changing speed
becomes zero, and based on the control current value to the linear
valve (i.e., step S222), the subsequent automatic pressure apply
control afterward is carried out more correctly.
[0073] Since the control current outputted into the linear valve 31
is reduced continuously in step S224 when the pressure apply check
is ended, the generation of fluid shooting noise can be prevented
when the pressure apply check is ended.
[0074] Although the present invention has been described as
including the features noted above, it is to be understood that
variations can be incorporated into the invention. For example, the
applicable pressure apply unit of this invention applies not only
to the pressure apply unit 12 described above, but also to any
other pressure apply units.
[0075] Also, although the learning process of step S222 is
practiced when the pressure apply check is ended, the learning
process can also be practiced during the pressure apply check. For
instance, the learning process can be practiced when the master
cylinder pressure is increased up to the fixed value or after the
fixed time has passed since the starting of the pressure apply
check.
[0076] As described above, the present invention involves a
learning process correcting of the pressure control characteristic
coefficient (ktokusei) of the pressure apply unit 12. However, an
alternative would involve renewing an I-P map pre-stored in a ROM
72 showing the relationship between the control current I outputted
to the linear valve 31 and the master cylinder pressure Pmc.
[0077] In addition, although the stop lamp switch 67 is used as a
detecting means for detecting the brake pedal depression, other
structures could be accepted as the detecting means. For instance,
a pedal depression force sensor in the form of a depression sensor
outputting an ON signal when the brake pedal 21 is moved could be
employed as well as a distortion sensor outputting an ON signal
when the pedal depression force equal to or greater than a fixed
value is applied to the operating rod 22.
[0078] While the fluid pressure control apparatus 17 providing
connection between the master cylinder 20 and the wheel cylinders
13, 14, 15, 16 of each wheel is arranged in the manner shown in
FIG. 2, the fluid pressure control apparatus 17 could include an
X-piping arrangement.
[0079] In place of the vacuum booster 19, the pedal depression
force could be amplified by a fluid pressure servo mechanism such
as discussed in the background portion above. In such a case, the
apparatus could be structured so that the fluid pressure generated
in the pressure apply unit 12 in response to the amount of the
condition of the vehicle is introduced and the booster piston is
pushed by the fluid pressure in the booster chamber of the fluid
pressure servo mechanism.
[0080] It is also possible to utilize a master cylinder having one
piston in place of the master cylinder 20 having the tandem
arrangement.
[0081] The present invention is advantageous in that the pressure
apply check for assessing whether or not the automatic pressure
apply is normal is carried out every time the vehicle starts. Also,
the increasing of the master cylinder pressure by the automatic
pressure apply during the pressure apply check is not applied to
the wheel cylinders and so the pressure apply check can be
performed without disturbing the vehicle start. Additionally,
because it is possible to shorten the time required for the master
cylinder pressure to reach the fixed value, the time period during
which the undesirable driver feeling associated with the holding
the condition of all of the wheels is shortened.
[0082] With the present invention, if the brake pedal is depressed
by the deceleration demand of the driver, the pressure apply check
is ended and the deceleration demand is carried out. Also, the
correction of the pressure control characteristic is performed from
the stable master cylinder pressure when the master cylinder
pressure is increased and the changing speed becomes zero and the
control current value to the linear valve, the automatic pressure
apply control performed afterward is more correct. Further, it is
possible with the present invention to reduce or prevent the
generation of fluid shooting noise when the pressure apply check is
ended.
[0083] The principles, preferred embodiments and modes of operation
of the present invention have been described in the foregoing
specification. However, the invention which is intended to be
protected is not to be construed as limited to the particular
embodiments disclosed. Further, the embodiments described herein
are to be regarded as illustrative rather than restrictive.
Variations and changes may be made by others, and equivalents
employed, without departing from the spirit of the present
invention. Accordingly, it is expressly intended that all such
variations, changes and equivalents which fall within the spirit
and scope of the present invention as defined in the claims, be
embraced thereby.
* * * * *