U.S. patent application number 09/803017 was filed with the patent office on 2001-10-18 for braking control apparatus for vehicles.
Invention is credited to Hamada, Toshiaki, Nitta, Hirofumi, Tanaka, Wataru.
Application Number | 20010030463 09/803017 |
Document ID | / |
Family ID | 18597886 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030463 |
Kind Code |
A1 |
Tanaka, Wataru ; et
al. |
October 18, 2001 |
Braking control apparatus for vehicles
Abstract
A braking control apparatus for vehicles which is capable of
generating a braking force in response to a pedal depression force
to non-controlled wheels while continuing vehicle stability
control. The apparatus generates a brake fluid pressure including a
pedal input pressure in response to the pedal depression force and
a servo pressure in response to a fluid pressure introduced from a
pressure apply unit. A fluid pressure control apparatus supplies
brake fluid pressure, an electric control unit controls the braking
force of each wheel by driving, and a pedal input pressure estimate
portion estimates the pedal input pressure. The electric control
unit controls the braking force of the non-controlled wheels during
vehicle stability control based on the pedal input pressure
estimated by the pedal input pressure estimate portion of the
electric control unit.
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: |
18597886 |
Appl. No.: |
09/803017 |
Filed: |
March 12, 2001 |
Current U.S.
Class: |
303/113.1 |
Current CPC
Class: |
B60T 8/3655 20130101;
B60T 13/662 20130101; B60T 8/4845 20130101; B60T 8/4054
20130101 |
Class at
Publication: |
303/113.1 |
International
Class: |
B60T 008/34 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2000 |
JP |
2000-080850 |
Claims
What is claimed is:
1. A braking control apparatus for vehicles comprising: fluid
pressure generating means for generating a brake fluid pressure
including a pedal input pressure in response to a pedal depression
force and a servo pressure in response to fluid pressure introduced
by a pressure apply means; fluid supplying means supplying the
brake fluid to a wheel cylinder associated with each wheel from a
master cylinder; control means controlling the fluid pressure
introduced by the pressure apply means in response to a vehicle
condition and controlling a braking force of each wheel by driving
the fluid supplying means in response to the pedal depression force
or the vehicle condition; pedal input pressure estimating means for
estimating the pedal input pressure; and the control means
controlling a braking force of a non-controlled wheel during
vehicle stability control based on the pedal input pressure
estimated by the pedal input pressure estimating means.
2. The braking control apparatus for vehicles as defined in claim
1, further comprising a fluid pressure sensor detecting a master
cylinder pressure of the brake fluid pressure generated in the
master cylinder; and the pedal input pressure estimating means
calculating the servo pressure based on a value of a control signal
outputted from the control means to the pressure apply means, and
estimating the pedal input pressure by subtracting the calculated
value of the servo pressure from that of the master cylinder
pressure.
3. The braking control apparatus for vehicles as defined in claim
1, wherein the pedal input pressure estimating means holds an
estimated value of the pedal input pressure calculated previously
when a pressure increase signal increasing brake fluid pressure of
the wheel cylinder of any wheel is outputted during the vehicle
stability control, and the control means controls the braking force
of the non-controlled wheel based on the estimated value of the
pedal input pressure held previously.
4. The braking control apparatus for vehicles as defined in claim
3, wherein the pedal input pressure estimating means holds the
estimated value of the pedal input pressure when the master
cylinder pressure detected by the fluid pressure sensor turns to
increasing while a predetermined period has passed from an end of
the output of the pressure increase signal, and estimates the value
decreased by a predetermined value from the estimated value of the
pedal input pressure held previously when the master cylinder
pressure continues to decrease.
5. The braking control apparatus for vehicles as defined in claim
3, wherein the pedal input pressure estimating means increases a
pressure change correcting amount added to the estimated value of
the pedal input pressure calculated previously when the pressure
increase signal is outputted, and decreases the pressure change
correcting amount after the end of the outputting of the pressure
increase signal.
6. A method of controlling brake fluid to wheel cylinders
associated with respective wheels of a vehicle, comprising:
generating brake fluid pressure in a master cylinder that includes
a pedal input pressure in response to a brake pedal depression
force and a servo pressure in response to fluid pressure introduced
by a pump; supplying the brake fluid pressure to the wheel
cylinders from the master cylinder; controlling the fluid pressure
introduced by the pump in response to a vehicle condition and
controlling a braking force applied to the wheel cylinders of the
wheels in response to the brake pedal depression force or the
vehicle condition; estimating a pedal input pressure; and
controlling a braking force applied to a non-controlled wheel
during vehicle stability control based on the estimated pedal input
pressure.
7. The method as defined in claim 6, including detecting a master
cylinder pressure of the brake fluid pressure generated in the
master cylinder, calculating the servo pressure based on a value of
a control signal outputted by a controller to the pump, and
estimating the pedal input pressure by subtracting the calculated
value of the servo pressure from that of the master cylinder
pressure.
8. The method as defined in claim 6, including holding an estimated
value of the pedal input pressure calculated previously when a
pressure increase signal of the wheel cylinder of any wheel is
outputted during vehicle stability control, and controlling the
braking force of the non-controlled wheel based on the estimated
value of the pedal input pressure held previously.
9. The method as defined in claim 8, wherein the estimated value of
the pedal input pressure is held when the detected master cylinder
pressure turns to increasing while a predetermined period has
passed from an end of an output of the pressure increase signal,
and estimating the value decreased by a predetermined value from
the estimated value of the pedal input pressure held previously
when the master cylinder pressure continues to decrease.
10. The method as defined in claim 8, including increasing a
pressure change correcting amount added to the estimated value of
the pedal input pressure calculated previously when the pressure
increase signal is outputted, and decreasing the pressure change
correcting amount after an end of the outputting of the pressure
increase signal.
Description
[0001] This application is based on and claims priority under 35
U.S.C. .sctn.119 with respect to Japanese Application No.
2000-080850 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 a vehicle braking
control apparatus. More specifically, the present invention
pertains to a braking control apparatus for vehicles which is able
to generate a master cylinder pressure including a first fluid
pressure in response to a pedal depression force and a second fluid
pressure corresponding to a fluid pressure introduced by a pressure
apply device and to control a braking force of each wheel in
response to the pedal depression force or a vehicle condition.
BACKGROUND OF THE INVENTION
[0003] A known vehicle braking control apparatus is disclosed in
German Offenlegungsschrift No. DE 197 03 776 A1. In this apparatus,
pressure responsive to the pedal depression force is detected by a
pressure sensor and the pedal depression force is amplified by a
hydraulic booster and transmitted to the piston of a master
cylinder by moving a booster piston by the boosted fluid pressure.
When used in vehicle stability control, the boosted fluid pressure
is amplified in the hydraulic booster and transmitted to the piston
of the master cylinder by introducing the boosted fluid pressure
necessary for generating the desired brake fluid pressure to the
booster chamber. Accordingly, during the turning of the vehicle,
the vehicle stability control is operated by introducing the
boosted fluid pressure in response to a vehicle condition. Vehicle
stability control refers to the control of the braking force of
each wheel in order to decrease the difference between a target
running line for the vehicle and an actual running line of the
vehicle based on the detected results of the vehicle condition (the
amount of the vehicle condition) during steering while the vehicle
is turning for instance.
[0004] In the known apparatus, brake fluid pressure in response to
the pedal depression force is continuously supplied to the wheel
brake cylinder of each wheel from the master cylinder. This is
because a signal from the pressure sensor takes precedence over the
vehicle stability control sensor. Accordingly the vehicle stability
control is stopped even when vehicle stability control may still be
necessary. That is, the control is stopped in spite of a vehicle
condition in which vehicle stability control is still needed. The
problem is that the stability of the vehicle is not assured during
turning because the vehicle stability control for reducing
understeer or oversteer is stopped by the depression of the brake
pedal in the case of strong understeering or oversteering during
the turning. In other words, the braking force which satisfies a
deceleration demand to the non-controlled wheels cannot be
generated while continuing the vehicle stability control when a
driver needs to decrease the vehicle speed and thus depresses the
brake pedal during vehicle stability control.
[0005] In light of the foregoing, a need exists for a braking
control apparatus for vehicles that is capable of generating a
braking force in response to a pedal depression force to the
non-controlled wheels while still continuing the vehicle stability
control.
SUMMARY OF THE INVENTION
[0006] In accordance with one aspect of the invention, a vehicle
braking control apparatus includes a fluid pressure generator that
generates a brake fluid pressure including a pedal input pressure
component in response to a pedal depression force and a servo
pressure component in response to fluid pressure introduced by a
pressure apply device, a fluid supplying mechanism supplying the
brake fluid to wheel cylinders of each wheel from a master
cylinder, and a controller controlling the fluid pressure
introduced by the pressure apply mechanism in response to a vehicle
condition and controlling the braking force of each wheel by
driving the fluid supplying mechanism in response to the pedal
depression force or the vehicle condition. A pedal input pressure
estimating device estimates the pedal input pressure, and the
controller controls the braking force of the non-controlled wheels
during vehicle stability control based on the pedal input pressure
estimated by the pedal input pressure estimate device.
[0007] With the present invention, when the brake pedal is
depressed during vehicle stability control, the pedal input
pressure in response to the pedal depression force is estimated
correctly and the braking force of the non-controlled wheels during
vehicle stability control is controlled. As a result, the vehicle
can be decelerated with a deceleration in response to the pedal
depression force. That is, the deceleration does not give any
undesirable feeling to the driver even during vehicle stability
control.
[0008] The vehicle braking control apparatus also includes a fluid
pressure sensor detecting the master cylinder pressure of the brake
fluid pressure generated in the master cylinder. The pedal input
pressure estimating device calculates the servo pressure based on a
value of a control signal outputted from the controller to the
pressure apply device, and estimates the pedal input pressure by
subtracting the calculated value of the servo pressure from that of
the master cylinder pressure. The pedal input pressure in response
to the amplified pedal depression force is thus estimated correctly
based on the value of the control signal outputted to the pressure
apply device and the master cylinder pressure detected by the fluid
sensor.
[0009] The pedal input pressure estimating device holds the
estimated value of the pedal input pressure calculated previously
when a pressure increase signal increasing the brake fluid pressure
of any of the wheel cylinders of the wheels is outputted during
vehicle stability control, and the controller controls the braking
force of the non-controlled wheels based on the estimated value of
the pedal input pressure held previously. Thus, when the pressure
increase signal amplifying the brake fluid of any wheel cylinder
during vehicle stability is outputted, the estimated value of the
pedal input pressure calculated previously is assured. As a result,
when the master cylinder pressure starts to decrease by the opening
of a holding valve receiving the pressure increase signal and by a
fluid amount consumption of the wheel cylinders while the pedal
depression force is constant or increasing, a fault judgment in
which the pedal input pressure is also decreased can be
prevented.
[0010] The pedal input pressure estimating device holds the
estimated value of the pedal input pressure when the master
cylinder pressure detected by the fluid pressure sensor is turned
to be increased while a predetermined period is passed from the
ending of the outputting of the pressure increase signal, and
estimates the value decreased by a predetermined value from the
estimated value of the pedal input pressure held previously when
the master cylinder pressure continues to decrease. Accordingly,
when the master cylinder pressure begins to increase from a
decreasing state within a predetermined time from the ending of the
pressure increase outputting, the estimated value of the pedal
input pressure calculated previously is assured. On the other hand,
when the master cylinder pressure continues to decrease within the
predetermined time, the pedal input pressure is decreased from the
estimated value calculated previously because the pedal depression
force is judged to be decreased. As a result, whether or not the
brake pedal is still depressed is judged correctly after the
pressure increase outputting, and the braking force of the
non-controlled wheels can be generated correctly.
[0011] The pedal input pressure estimating device increases a
pressure change correcting amount added to the estimated value of
the pedal input pressure calculated previously when the pressure
increase signal is outputted, and decreases the pressure change
correcting amount after the ending of outputting of the pressure
increase signal. Because the pressure change correcting amount
increased or decreased in response to the pressure changing of the
master cylinder pressure is added to the pedal input pressure
calculated from the master cylinder pressure, the pedal depression
force after the correcting can be estimated to the correct value
which is not influenced by the pressure changing of the master
cylinder pressure.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0012] 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:
[0013] FIG. 1 is a block diagram of the braking control apparatus
according to a first embodiment of the present invention;
[0014] FIG. 2 is a schematic illustration of the overall braking
system embodying the braking control apparatus according to the
first embodiment of the present invention;
[0015] FIG. 3 is a flow chart of the main operation of the braking
control apparatus according to the first embodiment of the present
invention;
[0016] FIG. 4 is a flow chart of the operation of the control for
the non-controlled wheels according to the first embodiment of the
present invention;
[0017] FIG. 5 is a timing chart explaining the operation of the
braking control apparatus according to the first embodiment of the
present invention;
[0018] FIG. 6 is a flow chart similar to FIG. 4, but showing the
operation of the control for the non-controlled wheels according to
the second embodiment of the present invention;
[0019] FIG. 7 is a timing chart explaining the operation of the
braking control apparatus according to the second embodiment of the
present invention; and
[0020] FIG. 8 is a flow chart showing the operation of the control
for the noncontrolled wheels according to the second embodiment of
the present invention;
DETAILED DESCRIPTION OF THE INVENTION
[0021] Referring initially to FIG. 2, the vehicle braking control
apparatus of the present invention, which has an automatic pressure
apply function, is provided with a fluid pressure generating
apparatus 11 that generates brake fluid pressure and a pressure
apply unit 12 functioning as a pressure apply device that
introduces fluid pressure for automatic pressure application to the
apparatus. In addition, the braking control apparatus is provided
with a fluid pressure control apparatus 17 supplying the brake
fluid pressure to the wheel cylinders 13-16 installed at a front
right wheel, a front left wheel, a rear right wheel, and a rear
left wheel respectively of a vehicle. Also, the braking control
apparatus includes an electric control unit 18 (shown in FIG. 1)
functioning as a control device that controls the braking force
applied to each wheel.
[0022] The fluid pressure generating apparatus 11 is provided with
a vacuum booster 19 and a master cylinder 20. For purposes of
simplifying the overall illustration and facilitating an
understanding of the invention, certain structural characteristics
of the master cylinder 20 that are known to persons skilled in the
art are omitted from FIG. 2, such as the seal members. In the fluid
pressure generating apparatus 11, a pedal depression force of a
brake pedal 21 amplified by the lever ratio of a link mechanism is
transmitted to an operating rod 22 and the operating rod 22 is
pushed by the pedal depression force. The pushing force of the rod
22 is amplified by the vacuum booster 19 and pushes a first piston
23 of the master cylinder 20. When the first piston 23 is pushed
against the 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.
[0023] The master cylinder also includes a second piston 26. When
the second piston 26 is pushed by the fluid pressure against the
force of a spring from the position shown in FIG. 2, communication
between a second pressure chamber 27 and the reservoir 25 is cut
off and the fluid pressure is generated in the second pressure
chamber 27.
[0024] 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 corresponding to the pedal input
pressure (Pmcin) in response to the pedal depression force in the
first pressure chamber 24 is generated. 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. Pressure increase by vacuum booster
includes pressure increase by the lever ratio of the link
mechanism.
[0025] The master cylinder 20 is also provided with a third
pressure chamber 28 which applies the fluid pressure to the end
surface of the first piston 23 on 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 A between the
pressure receiving areas of the first piston 23 of the booster side
and the anti-booster side.
[0026] In this way, the master cylinder pressure (Pmc) generated in
the master cylinder 20 includes the pedal input pressure (Pmcin)
component in response to the pedal depression force amplified by
the vacuum booster 19 and the third chamber servo pressure (Pmc3)
component in response to the fluid pressure introduced by the
pressure apply unit 12.
[0027] The pressure apply unit 12 is composed of a pump 29 which
compresses the brake fluid stored in the reservoir 25 and applies
it to the third pressure chamber 28, a motor 30 driving the pump
29, and a linear valve 31 that opens in response to the current
value of an input signal (control signal) and introduces the brake
fluid discharged from the pump 29 to the reservoir 25. In
accordance with the control signal (current value) outputted from
the electric control unit (ECU) 18 to the linear valve 31, the
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. The introduced fluid
pressure is the differential pressure between the pressure of the
brake fluid discharged by the pump 29 and the decreased percentage
or amount of the pressure in response to the degree of opening of
the linear valve 31.
[0028] The brake fluid pressure generated in the master cylinder 20
is supplied to each wheel cylinder by way of a front wheel side
hydraulic circuit and a rear wheel side hydraulic circuit. That is,
the fluid pressure control apparatus 17 which connects between the
master cylinder 20 and the wheel cylinders 13-16 of each wheel is
longitudinally piped.
[0029] 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 to the wheel cylinders 13, 14 through
the front wheel side circuit portion of the fluid pressure control
apparatus 17. The main passage 32 is connected to the wheel
cylinders 13, 14 through holding valves 33a, 34a provided in
respective passages that branch from the main passage on the way to
the wheel cylinders. The passage connecting the wheel cylinder 13
and the holding valve 33a is connected to a reservoir 38 by way of
a pressure reducing valve 33b, and the passage connecting the wheel
cylinder 14 and the holding valve 34a is connected to the reservoir
38 through a pressure reducing valve 34b.
[0030] In a similar manner as that described above, 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 to the wheel cylinders 15, 16 by way of the
rear wheel side circuit of the fluid pressure control apparatus 17.
That is, the main passage 37 is connected with the wheel cylinders
15, 16 by way of respective holding valves 35a, 36a provided in
respective passages that branch from the main passage 37 on the way
to the wheel cylinders. A passage connecting the wheel cylinder 15
and the holding valve 35a is connected with a reservoir 39 through
a pressure reducing valve 35b, and a passage connecting the wheel
cylinder 16 and the holding valve 36a is connected with the
reservoir 39 through a pressure reducing valve 36b.
[0031] The holding valves 33a, 34a, 35a, 36a are normally open
solenoid valves and the pressure reducing valves 33b, 34b, 35b, 36b
are normally closed solenoid valves. These solenoid valves are
excited or energized by the fluid pressure control signal (control
current) outputted from the ECU 18.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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. Hereafter, the output of a pressure increase signal by the ECU
refers to the output of the fluid pressure control signal which
unenergizes or unexcites the holding valve (which has been
energized or excited) of any wheel cylinder under the holding
condition.
[0036] In the front wheel side circuit 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 the damper being provided in a pump passage
42.
[0037] In the same way, in the rear wheel side circuit 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.
[0038] In the front side wheel circuit, 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.
[0039] Likewise, in the rear wheel side circuit, 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.
[0040] 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.
[0041] 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 in response to the vehicle
condition is controlled by driving or operating the fluid pressure
control apparatus 17 under the control of the ECU 18.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] The vehicle condition (the amount of the vehicle condition)
during steering operation under vehicle turning is detected by the
wheel speed sensors 63-66, and the sensors 81-83. In the vehicle
stability control portion 75 operated by the calculation or
operation of the CPU 70 based on the detected result, the vehicle
stability control controlling the braking force of each wheel
respectively in order to decrease the difference between the
vehicle target running line (target vehicle path) and the actual
vehicle running line (actual vehicle path) during steering such as
vehicle turning. The vehicle stability control portion 75 controls
the value of the control signal (current value I ) outputted to the
motor 30 of the pressure apply unit 12 and the linear valve 31 in
response to the detected amount of the vehicle condition.
Additionally, the vehicle stability control portion 75 controls
various devices such as the holding valves 33a -36a, the pressure
decrease valves 33b -36b, and the motor 40.
[0046] A pedal input pressure estimate portion 76 estimating the
pedal input pressure (Pmcin) in response to the pedal depression
force amplified in the vacuum booster 19 is provided in the ECU 18.
The pedal input pressure estimate portion 76 is operated by the
calculation or operation of the CPU 70.
[0047] Moreover, the ECU 18 is provided with an anti skid control
portion controlling the fluid pressure device 17 for controlling
the braking force applied to each wheel to prevent the locking of
the wheels during the vehicle braking operation and a traction
control portion controlling the pressure apply unit 12 and the
fluid pressure device 17 for applying the braking force to the
driving wheels to prevent the slipping of the driving wheels during
vehicle driving.
[0048] Referring to FIG. 3, the process or program carried out by
the ECU and the operation of the vehicle braking control apparatus
in accordance with the present invention is as follows. The routine
shown in the flowchart of FIG. 3 starts when the ignition switch of
the vehicle is turned on. At this time, any necessary initial set
up is performed. In step S100, an input process is carried out in
which the detected signals outputted by the fluid pressure sensor
62, the stop lamp switch 67, the wheel speed sensor 63-66, the
steering angle sensor 81, the vehicle acceleration sensor 82, and
the yaw rate sensor 83 are read.
[0049] Next, in step S102, the wheel speed of each wheel, the wheel
acceleration, the estimated vehicle speeds at the gravitational
center position of the vehicle and at each wheel position, and the
actual slip ratio of each wheel are computed. In step S104, the
various control modes such as the anti-skid control and the vehicle
stability control are set up and a target slip ratio for the
various control modes is set up.
[0050] Then, in step S106, the pressure apply unit 12 and the fluid
pressure control apparatus 17 are properly controlled in response
to the various control modes and the braking force applied to each
wheel is appropriately controlled. After step S106, a
non-controlled wheel control, which is discussed in more detail
below, is performed in step S200 and then the program returns to
step S100. The above-described process is repeated at a
predetermined period or interval in the ECU 18.
[0051] The non-controlled wheel control of step S200 in FIG. 3 is
performed in the following manner with reference to FIG. 4 and FIG.
5. In step S202, the system determines whether or not the vehicle
stability control is under operation based on the amount of the
vehicle condition calculated from the detected value of each of the
sensors 63-66 and each of the sensors 81-83 from the inputting
process. If it is determined that the vehicle stability control is
under operation, the program proceeds to step S204. If the system
judges that the vehicle stability control is not under operation,
the program returns to step S100 shown in FIG. 3.
[0052] In step S204, the third chamber pressure P3, namely the
fluid pressure of the third pressure chamber 28 of the master
cylinder 20 introduced by the pressure apply unit 12, is estimated
by calculation through use of the below formula (1) based on the
current value I of the control signal which the ECU 18 outputs to
the linear valve 31.
P3=i F(I) (1)
[0053] The term F(I) refers to the function of the fluid pressure
with respect to the current valve, corresponding to the
characteristic of the linear valve 31 between the fluid pressure
(P3) and the current value.
[0054] After estimating the third chamber pressure P3, the program
proceeds to step S206 at which the third chamber servo pressure
Pmc3 generated in the first pressure chamber 24 by the first piston
23 pushed by the third chamber pressure P3 is calculated using the
formula (2) below based on the third chamber pressure P3 calculated
in step S204 and the pressure receiving area ratio A of the first
piston 23 mentioned above.
Pmc3=P3/A (2)
[0055] Afterward, in step S208, the pedal input pressure Pmcin
generated in the first pressure chamber 24 in response to the pedal
depression force amplified in the vacuum booster 19 when the brake
pedal 21 is depressed during the vehicle stability control is
estimated by calculation through use of the formula (3) below.
Pmcin=Pmc-Pmc3 (3)
[0056] In this formula, Pmc refers to the master cylinder pressure
detected by the fluid pressure sensor 62.
[0057] The program then moves to step S210 at which it is
determined whether or not the fluid pressure control signal (the
pressure increase signal) increasing the brake fluid pressure of
any wheel cylinder of the control wheels for controlling the
vehicle stability control is outputted to the respective holding
valve of the wheel cylinder. For instance, if the fluid pressure
control signal is outputted from the ECU 18 to the holding valve
35a directing the valve 35a to be off so that the holding valve 35a
is open (the pressure increase is outputted) at the time t1 in FIG.
5(a) in order to increase the brake fluid supplied to the wheel
cylinder 15 of the wheel RR amongst the three control wheels FL,
RR, RF, the routine moves to step S214. If such fluid pressure
control signal is not outputted, the program proceeds to step
S212.
[0058] In step S214, the estimated value of the pedal input
pressure Pmcin previously calculated in the step S208 is maintained
to be constant. For instance, when the timing is t1 shown in FIG.
5(a), the estimated value of the pedal input pressure Pmcin
previously calculated is assured (part C of FIG. 5 (c)).
Accordingly, even if the master cylinder pressure Pmc starts to
decrease from the time t1 when the holding valve 35a is opened as
shown in FIG. 5(b) when the pedal depression force is constant or
increased, the fault estimation of the decreasing of the pedal
input pressure Pmcin can be prevented.
[0059] Next, in step S215, the depression of the brake pedal 21 is
judged by judging if the estimated value of the pedal input
pressure Pmcin assured in step S214 exceeds a brake judgment
threshold value STP. When the pedal input pressure Pmcin is the
same or less than the brake judgment threshold value STP, the brake
pedal 21 is judged not to be depressed and the program returns to
step S100. When the pedal input pressure Pmcin is more than the
brake judgment threshold value STP, the brake pedal 21 is judged to
be depressed and the program proceeds to step S216.
[0060] In step S216, the brake fluid pressure supplied to the wheel
cylinder of a non-controlled wheel, the wheel cylinder 13 of the FR
for instance, is controlled and the controlling force of the
non-controlled wheel is controlled (an outputting process to a W/C)
based on the estimated value of the pedal input pressure assured in
the step S214. More specifically, the holding valve 33a previously
energized and closed, for instance, is Unenergizes to be opened and
the brake fluid pressure in response to the pedal input pressure
Pmcin is supplied to the wheel cylinder 13 of the FR. A duty
supplied to the holding valve in this time is calculated by formula
(4) below.
duty=.DELTA.Pmcin/(Pmc-Pmcin).multidot.Kgain (4)
[0061] In this formula (4), .DELTA.Pmcin represents the changing
ratio of the pedal depression force Pmcin (the difference between
the previously estimated value Pmcin' and the presently estimated
value Pmcin) and Kgain represents a conversion constant of the
pressure and the duty. After executing step S216, the program
returns to step S100.
[0062] When the pressure increase output for opening any of the
holding valves of the control wheels (the holding valve 33a for
instance) is ended, that is when the fluid pressure control signal
outputted to the holding valve 35a is turned on from off (time T1
in FIG. 5 (a)), the program moves to step S212 from step S210. At
step S212, the system determines whether or not the time after
pressure increase outputting is within a predetermined time test
(test=50 msec for instance). For instance, in FIG. 5 (a), it is
determined whether or not the predetermined time test has elapsed
since the ending time T1 of the pressure increase outputting. When
it is judged that the time since the ending time T1 of the pressure
increase outputting is within the predetermined time, the program
moves to step S218. When it is judged that the time since the
ending of the pressure increase outputting is not within the
predetermined time, the program proceeds to step S215 and then
moves back to step S100 after operating the outputting process to
the W/C.
[0063] In step S218, it is determined whether or not the changing
ratio of the master cylinder pressure Pmc is negative, that is
whether the master cylinder pressure Pmc turns to an increase from
a decrease. When the master cylinder pressure Pmc begins to
increase from a decreasing state and the changing ratio turns to
positive (part B in FIG. 5 (b)), the program moves to step S214
because the pressure Pmc starts to increase by the brake fluid
discharged from the pump 29 while the pedal depression force is
constant. Then the estimated value of the pedal input pressure
Pmcin calculated previously is assured.
[0064] The routine then advances to step S215 and the above
mentioned control judgment is operated. When the brake depression
Pmcin is the same or less than the control threshold value STP, the
brake pedal 21 is judged not to be depressed and the routine
returns to step S100. When the brake depression Pmcin is more than
the control threshold value STP, the brake pedal 21 is judged to be
depressed and the program advances to step S216. Then, after
operating the outputting process to the W/C, the program returns to
step S100.
[0065] In step S218, when the master cylinder pressure Pmc
continues to be decreased and the changing ratio of the pressure is
still negative (part D in FIG. 5 (d)), the program moves to step
S220 because the driver has released the brake pedal 21 and it is
determined that the pedal depression force is starting to decrease.
In step S220, the pedal input pressure Pmcin is decreased from the
estimated value calculated previously (part E part in FIG. 5 (e)).
After that, the program advances to step S215 where the depression
of the brake pedal is judged as described previously. Here, the
brake fluid pressure supplied to the wheel cylinders of the
non-controlled wheels, the wheel cylinder 13 of the FR for
instance, is controlled based on the estimated value of the pedal
input pressure Pmcin decreased in step S220 and the braking force
of the non-controlled wheels is controlled. The program then
proceeds back to step S100. The routine described above is carried
out every predetermined time period or interval.
[0066] According to the present invention, when the brake pedal 21
is depressed during vehicle stability control, the pedal input
pressure Pmcin in response to the pedal depression force amplified
in the vacuum booster 19 is estimated correctly based on the
current value I of the control signal outputted to the linear valve
31 and the master cylinder pressure Pmc detected by the fluid
pressure sensor 62.
[0067] Concurrently, the controlling force of the non-controlled
wheels during the vehicle stability control is controlled based on
the estimated value. Accordingly, even during the vehicle stability
control, the vehicle is able to be decelerated in response to the
pedal depression force, thus providing deceleration without any
undesirable feeling for the driver. Consequently, when the driver
depresses the brake pedal 21 to effect deceleration during vehicle
stability control, the controlling force which satisfies the
deceleration demand to the non-controlled wheels is able to be
generated.
[0068] When pressure increase signal amplifying the brake fluid
pressure of any of the wheel cylinders 13-16 of each wheel is
outputted during vehicle stability control and under braking, the
estimated value of the pedal input pressure Pmcin previously
calculated (at step S208) is maintained to be constant.
Accordingly, even if the master cylinder pressure Pmc starts to
decrease by virtue of fluid consumption in the wheel cylinders by
the opening of the holding valves receiving a pressure increase
signal while the pedal depression force is constant or being
increased, the fault judgment in which the pedal input pressure
Pmcin is judged to be decreased can be prevented. Consequently,
when the pressure increase signal is outputted during the vehicle
stability control, the pedal input pressure Pmcin is estimated
correctly. Then the braking force which satisfies the deceleration
demand to the non-controlled wheels can be generated.
[0069] When the master cylinder pressure Pmc turns to increase from
decreasing (i.e., begins to increase after decreasing) within the
predetermined period from the ending of the pressure increase
outputting, the estimated value of the pedal input pressure Pmcin
calculated previously is assured because the pressure Pmc is judged
to start increasing by the brake fluid discharged from the pump 29
while the pedal depression force is constant. In contrast, when the
master cylinder pressure Pmc keeps decreasing within the
predetermined period, the pedal input pressure Pmcin is decreased
from the estimated value calculated previously because the driver
releases the brake pedal 21 and the pedal depression force is
judged to be decreasing. As a result, whether or not the brake
pedal is still being depressed is judged after the ending of the
pressure increase output and the braking force of the
non-controlled wheels is generated more accurately.
[0070] After the end of the pressure increase output, it is
accurately determined whether the master cylinder pressure Pmc
restored by the discharge from the pump 41, 44 begins to increase
or the pedal depression force itself goes down and the pressure Pmc
keeps decreasing because the predetermined period after the ending
of the pressure increase output is made to be variable in response
to the period of pressure increase output (the period from t1 to T1
in FIG. 5 (a)).
[0071] A vehicle braking control apparatus according to a second
preferred embodiment of the present invention is illustrated in
FIGS. 6 and 7. The second embodiment is similar to the first
embodiment, except that the non-controlled wheels control is
different from that of the first embodiment. In this second
embodiment, in the pedal input pressure estimate portion 76, when
the pressure increase signal is outputted during the vehicle
stability control and under braking, a pressure change correction
amount Pmch is increased (as described below at step S308), and the
value which is produced by adding the pressure change correction
amount Pmch to the estimated value Pmcin of the pedal input
pressure (calculated at step S304) which is decreased in response
to the decreasing of the master cylinder pressure Pmc during the
outputting period of the pressure increase signal is applied as the
corrected estimated value Pmcin of the pedal input pressure
(calculated at step S312). The other structure and features
associated with this second embodiment are the same as those
described above in connection with the first embodiment.
[0072] The performed by the ECU 18 in the second preferred
embodiment is illustrated in FIGS. 6 and 7. In the routine shown in
the flowchart of FIG. 6, steps S300, S302 and S104 are the same as
steps S200, S202 and S208 shown in FIG. 4 and described above and
so the explanation is not repeated again here. In step S306, it is
determined whether or not the pressure increase signal is outputted
to the holding valve of any wheel cylinder of the control wheels.
This is performed similar to step S210 in FIG. 4. When the pressure
increase is outputted after outputting the pressure increase signal
(t1 shown in FIG. 7(a) for instance), the program proceeds to step
S308. When the pressure increase output ends (t2 shown in FIG. 7(a)
for instance), the routine advances to step S310.
[0073] In step S308, the pressure change correction amount Pmch is
increased from t1 as shown in FIG. 7(c). After that, the program
moves to step S312 and a correcting process is performed adding the
pedal input pressure Pmcin estimated in step S304 to the pressure
change correction amount estimated in step S308. In response to the
correction, the pedal input pressure Pmcin is estimated to the
value which is not influenced by the decreasing of the decreasing
master cylinder pressure Pmc shown in FIG. 7(b). That is, the pedal
input pressure Pmc is not estimated to the decreasing value shown
as the dashed lines in FIGS. 7(d) and 7(e) in response to the
decreasing of the master cylinder pressure Pmc, but is estimated to
the value which is not influenced by the decreasing of the
decreasing master cylinder pressure Pmc shown as the solid line in
FIG. 7(d) when the pedal depression force is increasing, and shown
as a solid line in FIG. 7(e) when the pedal depression force is
constant.
[0074] The routine then advances to step S313 and it is judged
whether or not the brake pedal 21 is depressed by the judging
whether or not the pedal input pressure Pmcin exceeds the brake
judgment threshold value KSTP. When the pedal input pressure Pmcin
is the same as or less than the brake judgment threshold value
KSTP, the routine goes back to step S100 because the brake pedal 21
is judged to not be depressed. When the pedal input pressure Pmcin
is more than the brake judgment threshold value KSTP, the program
advances to step S314 because the brake pedal 21 is judged to be
depressed.
[0075] At step S314, the outputting process to the W/C is operated
based on the estimated value of the pedal input depression after
the correction in a manner similar to step S216 in FIG. 4. After
executing step S314, the routine returns to step S100.
[0076] When the output of the pressure increase signal is ended (t2
of FIG. 7(a)), the program advances to step S310 from step S306.
Here it is determined whether or not the pressure change correction
amount is zero. Because the pressure change correction amount is
not zero immediately after the output of the pressure increase
signal, the program advances to step S316 and the pressure change
correction amount is decreased. That is, the pressure change
correction amount is being decreased gradually from t2 as shown in
FIG. 7(c). Then, in step S312, the decreased pressure change
correction amount is added to the pedal input pressure Pmcin
estimated in step S304 and the value is estimated as the pedal
input pressure Pmcin after correcting. The pressure change
correction amount added to the pedal input pressure Pmcin is
capable of being decreased in response to the switching of the
master cylinder pressure Pmc to an increasing amount from t2 by the
correcting process and the pedal input pressure Pmcin is capable of
being estimated to the value which is not influenced by the
decreasing of the master cylinder pressure Pmc. The program then
advances to step S313 and returns to step S100 when the pedal input
pressure Pmcin is the same as or less than the brake judgment
threshold value KSTP. When the pedal input pressure Pmcin is
determined to be more than the brake judgment threshold value KSTP
in step S313, the outputting process is operated based on the
estimated value of the pedal input pressure Pmcin after the
correction, and the program returns to step S100.
[0077] After the pressure increase output is ended, the decreasing
process of step S316 is carried out until the pressure change
correction amount becomes zero (up to t3 shown in FIG. 7(c)). When
the pressure change correction amount becomes zero, the program
moves to step S312 from step S310. Accordingly, the processes of
the step S308 and the step S316 are not operated until the next
pressure increase signal is outputted. In step S312, the pressure
change correction amount that is used in the correction is zero.
The routine described above is carried out at a predetermined
period or time interval.
[0078] The increasing ratio of the pressure change correction
amount could vary in response to the detected value of the master
cylinder pressure at that time and one of the detected value or the
estimated value of the wheel cylinder pressure of the wheel
cylinder to which the pressure increase output is outputted at that
time. The decreasing ratio of the pressure change correction amount
can be set in response to the capacity of the pressure increasing
rate of the pump 29.
[0079] According to the second embodiment of the present invention,
the pedal input pressure after the correction is estimated to a
correct value which is not influenced by the pressure changing
master cylinder pressure because the pressure change correction
amount increased or decreased in response to the pressure change of
the master cylinder pressure Pmc is added to the pedal input
pressure Pmcin calculated from the master cylinder pressure Pmc. As
a result, even if the pressure increase outputting is outputted
during vehicle stability control, the pedal input pressure Pmcin is
estimated correctly. Then the braking which satisfies the
decreasing demand to the non-controlled wheels can be
generated.
[0080] The vehicle braking control apparatus according to a third
embodiment of the present invention is illustrated in FIG. 8. In
the third embodiment, when the brake pedal 21 is depressed during
vehicle stability control, the pedal depression force is detected
and the pedal input pressure Pmcin in response to the pedal
depression force amplified in the vacuum booster 19 is estimated
based on the detected value. A depression sensor 85 detecting the
pedal depression force is operatively associated with the operating
rod 22 for instance. The depression sensor 85 is provided with a
distortion sensor detecting the load applied to the operating rod
22 for instance and is connected to the input circuit portion 73 of
the ECU 18. Other features and aspects of this embodiment are the
same as those described above in connection with the first
embodiment.
[0081] Referring to FIG. 8, the process or routine carried out by
the ECU 18 in this third preferred embodiment is as follows. The
routine shown in the flow chart of FIG. 8 includes steps S300 and
S302 that are the same as similar steps described above and so a
detailed discussion is not repeated here.
[0082] In step S302, when it is determined that the vehicle is not
under vehicle stability controlling, the program returns to step
S300. When it is determined that the vehicle is operating under
vehicle stability controlling, the routine advances to step S320.
In step S320, the pedal depression force detected by the depression
sensor 85 is read. Next, in step S222, the pedal input pressure
Pmcin is calculated and estimated based on the amplification ratio
between the pedal depression force detected by the depression
sensor 85 and the known value of the pedal depression force
associated with the vacuum booster 19 operation, namely the booster
ratio.
[0083] The program then proceeds to step S324. Here, if it
determined that the pedal input pressure Pmcin is the same as or
less than the brake judgment threshold value KSTP, the routine
returns to step S300. When the pedal input pressure Pmcin is more
than the brake judgment threshold value KSTP, the program advances
to step S314. Then the brake fluid supplied to the wheel cylinders
of the non-controlled wheels during vehicle stability control is
controlled and the braking of the non-controlled wheels is
controlled (the outputting process to the W/C) based on the
estimated value of the pedal input pressure Pmcin detected in step
S322. After that, the program returns to step S300. This routine is
operated or carried out at a predetermined period or time
interval.
[0084] There are several advantages associated with this third
embodiment. For example, the pedal input pressure Pmcin is
estimated correctly based on the amplification ratio between the
pedal depression force detected in the depression sensor 85 and the
known value of the pedal depression force by the vacuum booster 19,
namely the booster ratio. Accordingly, as in the other embodiments,
when the brake pedal 21 is depressed by the deceleration demand of
the driver during vehicle stability control without considering the
pressure change of the master cylinder pressure Pmc by the output
of the pressure increase signal, the braking force satisfying the
deceleration demand to the non-controlled wheels is generated while
continuing the control.
[0085] In addition, it is possible to correctly judge or determine
whether or not the pedal is depressed. Also, the detecting signal
of the depression sensor 85 can be used as a signal which stops the
traction control (TRC control). That is, the detecting signal of
the depression sensor is available for use in judging whether or
not the brake pedal 21 is depressed.
[0086] In the embodiments described above, a fluid pressure sensor
detecting the fluid pressure of the third pressure chamber 28 (the
third chamber pressure P3) of the master cylinder 20 can be
provided and the third chamber servo pressure Pmc3 is estimated by
the calculation using the previously shown formula (2) from the
third chamber pressure P3 detected by the sensor and the area ratio
A. Moreover, the pedal input pressure Pmcin can be estimated by the
calculation using the formula (3) based on the third chamber servo
pressure Pmc3 and the master cylinder pressure Pmc.
[0087] As for the brake judgment threshold value KSTP in the
various embodiments (step S215 in FIG. 4, step S313 in FIG. 6, step
S324 in FIG. 8), the value KSTP can vary in response to the master
cylinder pressure at each time. The value KSTP also can be variable
in response to a vehicle speed at each time. The value KSTP also
can be varied in response to a linear valve outputting current I at
each time. Further, the value KSTP also can be varied in response
to a driving condition of each solenoid valve (the holding valves
and the pressure reducing valves) for the wheel cylinder
control.
[0088] In each embodiment, the fluid pressure control apparatus 17
connecting the master cylinder 20 with the wheel cylinders 13-16 of
each wheel is a front and rear piping system, but a diagonal piping
system can be also used. Also, in each embodiment, the pedal
depression force can be amplified by the known hydraulic booster in
place of the vacuum booster 19. In this case, the fluid pressure
generated in the pressure unit 12 in response to the amount of the
vehicle condition is introduced into the booster chamber of the
hydraulic booster and the booster piston is pushed by the fluid
pressure. Accordingly, the brake fluid pressure (the master
cylinder pressure Pmc) including the pedal input pressure Pmcin in
response to the pedal depression force amplified by the booster and
the third chamber servo pressure Pmc3 increased automatically by
the fluid pressure in response to the vehicle condition can be
generated by the master cylinder.
[0089] It is also possible in each embodiment to employ a master
cylinder having one piston in place of the tandem master cylinder
20 described.
[0090] In the third embodiment, the depression of brake pedal 21 is
judged by judging whether or not the estimated pedal input pressure
Pmcin exceeds the brake judgment threshold value KSTP. In addition,
when the stop lamp switch 67 is turned on, the brake pedal 21 can
be judged to be depressed.
[0091] In each of the described embodiments, each wheel cylinder is
provided with a holding valve and a pressure reducing valve. In
place of this construction, each wheel cylinder can be provided
with a solenoid valve which is switchable between three positions;
a pressure increase condition, a holding condition, and a pressure
decrease condition.
[0092] As explained above, according to the present invention, when
the driver depresses the brake pedal to effect deceleration during
vehicle stability control, the braking force which satisfies the
deceleration demand to the non-controlled wheels is advantageously
capable of being generated. Also, the pedal input pressure is
estimated correctly based on the value of the control signal
outputted to the pressure apply means and the master cylinder
pressure detected in the fluid pressure sensor. Even if the
pressure increase output is outputted during vehicle stability
control, the pedal input pressure Pmcin is estimated correctly.
Then the braking force which satisfies the decreasing demand to the
non-controlled wheels is capable of being generated.
[0093] Also in accordance with the present invention, it is
determined whether or not the brake pedal is still depressed after
the pressure increase output. As a result, the braking force of the
non-controlled wheels can be generated more correctly.
Additionally, the pedal input pressure after the correcting is
estimated correctly and is not influenced by the pressure changing
master cylinder pressure because the pressure change correcting
amount increased or decreased in response to the master cylinder
pressure is added to the pedal input pressure estimated from the
master cylinder pressure. Accordingly, even if the pressure
increase signal is outputted during vehicle stability control, the
pedal input pressure Pmcin is estimated correctly. Then the braking
force which satisfies the decreasing demand to the non-controlled
wheels is generated.
[0094] 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.
* * * * *