U.S. patent application number 09/820676 was filed with the patent office on 2001-10-04 for hydraulic brake apparatus for a vehicle.
Invention is credited to Nishii, Michiharu, Oishi, Masaki.
Application Number | 20010025750 09/820676 |
Document ID | / |
Family ID | 18607979 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010025750 |
Kind Code |
A1 |
Oishi, Masaki ; et
al. |
October 4, 2001 |
Hydraulic brake apparatus for a vehicle
Abstract
The present invention is directed to a hydraulic brake
apparatus, which includes wheel brake cylinders, and a master
cylinder for advancing a master piston in response to operation of
a brake pedal. A power chamber is formed behind the master piston.
A reaction piston is disposed, with the front end thereof exposed
in the power chamber, so as to transmit a reaction force produced
by the pressure in the power chamber to the brake pedal. A power
source is provided for pressurizing brake fluid stored in a
reservoir to supply power pressure to the power chamber. A solenoid
valve is provided for opening and closing a return passage which
connects the power chamber to the reservoir, thereby to return the
brake fluid thereto. A detection device is provided for detecting
the amount of operation of the brake pedal. The solenoid valve is
controlled in response to the amount of operation detected by the
detection device to reduce the amount of the brake fluid in the
power chamber. As a result, even if the brake pedal is operated
during the automatic pressurization, with the power pressure
supplied by the power source, the brake fluid in the power chamber
is reduced by controlling the solenoid valve to be opened and
closed, to obtain a sufficient stroke of the brake pedal, so that
an adequate brake feeling can be obtained.
Inventors: |
Oishi, Masaki; (Toyota city,
JP) ; Nishii, Michiharu; (Toyota city, JP) |
Correspondence
Address: |
Platon N. Mandros
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
18607979 |
Appl. No.: |
09/820676 |
Filed: |
March 30, 2001 |
Current U.S.
Class: |
188/151R ;
303/113.1 |
Current CPC
Class: |
B60T 8/3655 20130101;
B60T 7/042 20130101; B60T 8/4845 20130101; B60T 8/4054 20130101;
B60T 13/686 20130101; B60T 8/441 20130101 |
Class at
Publication: |
188/151.00R ;
303/113.1 |
International
Class: |
B60T 008/34; B60T
011/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2000 |
JP |
2000-92658 |
Claims
What is claimed is:
1. A hydraulic brake apparatus for a vehicle comprising: wheel
brake cylinders operatively mounted on wheels of said vehicle,
respectively; a master cylinder for advancing a master piston in
response to operation of a brake pedal to supply hydraulic braking
pressure to said wheel brake cylinders; a power chamber formed
behind said master piston; a reaction piston with the front end
thereof exposed in said power chamber for transmitting a reaction
force produced by the pressure in said power chamber to said brake
pedal; a reservoir for storing brake fluid; a power source for
pressurizing the brake fluid stored in said reservoir to supply
power pressure to said power chamber; a return passage for
connecting said power chamber to said reservoir to return the brake
fluid thereto; valve means for opening and closing said return
passage; detection means for detecting the amount of operation of
said brake pedal; and control means for controlling said valve
means to be opened and closed in response to the amount of
operation of said brake pedal detected by said detection means to
reduce the amount of the brake fluid in said power chamber.
2. A hydraulic brake apparatus as set forth in claim 1, wherein
said control means controls said valve means to increase the amount
of brake fluid returned from said power chamber to said reservoir
through said return passage, in response to increase of the amount
of operation of said brake pedal detected by said detection
means.
3. A hydraulic brake apparatus as set forth in claim 2, wherein
said control means controls said valve means to control the amount
of brake fluid returned from said power chamber to said reservoir
through said return passage to be smaller than the amount of brake
fluid discharged from said master cylinder in response to operation
of said brake pedal.
4. A hydraulic brake apparatus as set forth in claim 2, wherein
said valve means includes a linear solenoid valve for opening and
closing said return passage, and wherein said control means
controls said linear solenoid valve to be opened or closed in
response to the amount of operation of said brake pedal detected by
said detection means.
5. A hydraulic brake apparatus as set forth in claim 1, further
comprising: a regulator for regulating the power pressure
discharged from said power source to produce a regulated pressure;
a regulated pressure chamber formed behind said reaction piston,
and connected to said regulator for receiving the regulated
pressure discharged therefrom; and a normally closed solenoid valve
disposed between said power chamber and said power source, wherein
said valve means includes a normally open solenoid valve disposed
between said power chamber and said resevoir, and wherein said
control means controls said normally closed solenoid valve to be
opened when said brake pedal is operated, and said control means
controls said normally open solenoid valve to be opened and closed
in response to the amount of operation of said brake pedal detected
by said detection means to reduce the amount of the brake fluid in
said power chamber.
6. A hydraulic brake apparatus as set forth in claim 5, wherein
said control means controls said normally open solenoid valve to be
opened and closed, to increase the amount of brake fluid returned
from said power chamber to said reservoir through said return
passage, in response to increase of the amount of operation of said
brake pedal detected by said detection means.
7. A hydraulic brake apparatus as set forth in claim 1, wherein
said power source includes a hydraulic pressure pump for
pressurizing the brake fluid stored in said reservoir to discharge
the power pressure, and an electric motor for actuating said
pump.
8. A hydraulic brake apparatus as set forth in claim 1, wherein
said detection means includes a sensor for detecting the hydraulic
braking pressure output from said master cylinder, and a sensor for
detecting a stroke of said brake pedal, and wherein said detection
means detects the amount of operation of said brake pedal in
response to at least one of the outputs from said sensors.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a hydraulic brake apparatus
for a vehicle, which is adapted to actuate a master piston by
hydraulic braking pressure discharged from a hydraulic pressure
source, in response to operation of a brake pedal, or irrespective
of operation of the brake pedal.
[0003] 2. Description of the Related Arts
[0004] In German Patent No.DE19542656A1, a hydraulic brake
apparatus having a hydraulic pressure source in addition to a
master cylinder is disclosed. In the patent, there is disclosed a
technology for performing an automatic pressurization by applying
hydraulic pressure of a pressure source to a back of a power piston
which is integrally connected to a brake pedal. The pressure source
includes a hydraulic pressure pump, accumulator or the like. The
automatic pressurization is a control for generating the hydraulic
braking pressure from the master cylinder so as to perform a
traction control, vehicle stability control or the like, when the
brake pedal is not operated.
[0005] According to the apparatus as disclosed in the
above-described German Patent No.DE19542656A1, when the automatic
pressurization is performed, the brake pedal is advanced, without
being operated, by a stroke (Sto) of the brake pedal corresponding
to the automatically pressurized amount, as indicated by a
two-dotted chain line in FIG. 6. Therefore, when the brake pedal is
operated in that state, i.e., when the brake pedal is depressed
further, while the automatic pressurization is being performed, the
brake pedal will be in such a state as to receive a reaction force
of load (Of) which corresponds to the hydraulic braking pressure
produced by the automatic pressurization with the position of the
stroke (Sto) advanced. Thereafter, the pedal load (reaction force)
is increased in response to increase of the stroke according to a
stroke--pedal load characteristic for a normal operation of the
brake pedal. As a result, when the brake pedal is operated further,
while the automatic pressurization is being performed, the starting
position of the stroke is not placed at the position of the stroke
(0), but placed at the position of the stroke (Sto), whereby a
stroke stiffness is made so high that it will be difficult to
advance the brake pedal.
SUMMARY OF THE INVENTION
[0006] Accordingly, it is an object of the present invention to
provide a hydraulic brake apparatus having a power chamber formed
behind a master piston, and supplied with power pressure by a power
source to perform automatic pressurization, wherein a proper brake
feeling can be obtained, even if the brake pedal is operated while
the automatic pressurization is being performed.
[0007] In accomplishing the above and other objects, the hydraulic
brake apparatus for a vehicle includes wheel brake cylinders
operatively mounted on wheels of the vehicle, respectively, and a
master cylinder for advancing a master piston in response to
operation of a brake pedal to apply a hydraulic braking pressure to
the wheel brake cylinders. A power chamber is formed behind the
master piston. A reaction piston is disposed, with the front end
thereof exposed in the power chamber, to transmit a reaction force
produced by the pressure in the power chamber to the brake pedal.
The apparatus further includes a reservoir for storing brake fluid,
a power source for pressurizing the brake fluid stored in the
reservoir to supply power pressure to the power chamber, a return
passage for connecting the power chamber to the reservoir to return
the brake fluid thereto, and a valve device for opening and closing
the return passage. A detection device is provided for detecting
the amount of operation of the brake pedal. And, a controller is
provided for controlling the valve device to be opened and closed
in response to the amount of operation of the brake pedal detected
by the detection device to reduce the amount of the brake fluid in
the power chamber. According to the apparatus as described above,
therefore, even if the brake pedal is operated during the automatic
pressurization, with the power pressure supplied by the power
source, the brake fluid in the power chamber is reduced by
controlling the valve device to be opened and closed, to obtain a
sufficient stroke of the brake pedal, so that an adequate brake
feeling can be obtained.
[0008] In the apparatus as described above, the controller is
preferably adapted to control the valve device to increase the
amount of brake fluid returned from the power chamber to the
reservoir through the return passage, in response to increase of
the amount of operation of the brake pedal detected by the
detection device.
[0009] The controller may be adapted to control the valve device to
control the amount of brake fluid returned from the power chamber
to the reservoir through the return passage to be smaller than the
amount of brake fluid discharged from the master cylinder in
response to operation of the brake pedal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The above stated object and following description will
become readily apparent with reference to the accompanying
drawings, wherein like reference numerals denote like elements, and
in which:
[0011] FIG. 1 is a schematic block diagram illustrating a hydraulic
brake apparatus according to an embodiment of the present
invention;
[0012] FIG. 2 is a sectional view of a hydraulic brake apparatus
according to another embodiment of the present invention;
[0013] FIG. 3 is an enlarged sectional view of a part of a
hydraulic brake apparatus including a master cylinder and a
hydraulic booster according to another embodiment of the present
invention;
[0014] FIG. 4 is a flowchart showing a routine for reducing the
amount of brake fluid in a power chamber according to another
embodiment of the present invention;
[0015] FIG. 5 is a diagram showing a characteristic of pedal
stroke--master cylinder pressure according to the present
invention; and
[0016] FIG. 6 is a diagram showing characteristics of pedal
stroke--pedal load according to an embodiment of the present
invention and a prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] Referring to FIG. 1, there is schematically illustrated a
hydraulic brake apparatus for a vehicle according to an embodiment
of the present invention. As shown in FIG. 1, the hydraulic brake
apparatus according to the present embodiment includes a
conventional master cylinder MC and a hydraulic booster HB, and is
so constituted that when a master piston MP is advanced in response
to operation of a brake pedal BP, the brake fluid supplied from a
low pressure reservoir LRS is compressed to generate hydraulic
braking pressure from pressure chambers R1 and R2, respectively.
This hydraulic braking pressure, i.e., master cylinder pressure, is
supplied to wheel brake cylinders (not shown in FIG. 1) operatively
mounted on wheels of the vehicle.
[0018] The hydraulic booster HB according to the present embodiment
is provided for assisting the master piston MP to be moved in
response to operation of the brake pedal BP. In the hydraulic
booster HB, a power chamber R3 is formed behind the master piston
MP. A reaction piston PP is disposed, with its front end exposed in
the power chamber R3, to transmit a reaction force produced by the
pressure in the power chamber R3 to the brake pedal BP. The
reaction piston PP is disposed so as to be engaged with the master
piston MP at the rear end thereof, and connected to the brake pedal
BP as shown in FIG. 1. These are so arranged that the master piston
MP is movable through the reaction piston PP directly in response
to operation of the brake pedal BP, and also the master piston MP
can be advanced independently, and that the brake pedal BP can be
moved rearward in response to a rearward movement of the reaction
piston PP.
[0019] A power source PS includes a hydraulic pressure pump HP
which has an outlet port connected to the power chamber R3, and
which is actuated by an electric motor M. An inlet port of the
hydraulic pressure pump HP is connected to the reservoir RS, and
its outlet port is connected to the power chamber R3 of the
hydraulic booster HB. When the hydraulic braking pressure
discharged from the hydraulic pressure pump HP (i.e., power
pressure) is supplied into the power chamber R3, the master piston
MP is forced to be advanced. The reservoir RS includes a case
having a predetermined capacity, and a piston and a spring which
are accommodated in the case. An opening portion of the case is
connected to the inlet port of the hydraulic pressure pump HP. The
reservoir RS is provided separately from the low pressure reservoir
LRS in FIG. 1, while they may be formed in a body.
[0020] As shown in FIG. 1, the outlet port and inlet port are
connected to the hydraulic pressure pump HP through a return
passage B, in which a normally closed linear solenoid valve V1,
which serves as the valve device according to the present
invention. The linear solenoid valve V1 is a proportional control
valve for controlling a pressure difference between the pressure at
its inlet and the pressure at its outlet to be varied in proportion
to electric current fed to the solenoid valve for actuating the
same. The linear solenoid valve V1 is controlled by an electronic
controller ECU as described later, so as to control the amount of
brake fluid supplied through the return passage B at least in
response to operation of the brake pedal BP. When the linear
solenoid valve V1 is placed in its open position, the brake fluid
in the power chamber R3 is returned to the reservoir RS through the
valve V1, so that the amount of brake fluid in the power chamber R3
is reduced. At the same time, the brake fluid discharged from the
hydraulic pressure pump HP is returned to the reservoir RS and
stored therein, so that the hydraulic braking pressure applied to
the power chamber R3 is reduced. In addition to the linear solenoid
valve V1, as shown by a two-dotted chain line in FIG. 1, a return
passage may be provided for connecting the power chamber R3 to the
reservoir RS, and in this return passage may be disposed a linear
solenoid valve V2, which may serve as the valve device according to
the present invention.
[0021] In the present embodiment, there are disposed a pressure
sensor S1 for detecting the hydraulic braking pressure discharged
from the master cylinder MC (i.e., master cylinder pressure), and a
stroke sensor S2 for detecting a stroke of the brake pedal BP,
which serve together as the detection device for detecting the
amount of operation of the brake pedal BP according to the present
invention. When both of the outputs of the sensors S1 and S2 exceed
respective predetermined values, it is determined that the brake
pedal BP was depressed during the automatic pressurization. The
electronic controller ECU of the present embodiment is provided
with a microcomputer, which includes a central processing unit or
CPU (not shown), ROM (not shown), RAM (not shown), input and output
ports (not shown) and the like. The output signals of the sensors
as described above are fed to the input port, and then to the CPU
via respective amplification circuits (not shown).
[0022] According to the hydraulic brake apparatus as constituted
above, when the electronic controller ECU determines that a
traction control mode is to be initiated, for example, the
automatic pressurization control starts, so that the electric motor
M is driven to actuate the hydraulic pressure pump HP, by which the
power pressure is supplied to the power chamber R3 of the hydraulic
booster HB, thereby to actuate the master cylinder MC. Then, the
hydraulic pressure control for the traction control mode is
performed by a pressure control apparatus (not shown in FIG. 1).
Instead, by determining a vehicle state on the basis of the outputs
of various sensors (not shown), and then controlling the linear
solenoid valve V1 to control the amount of brake fluid supplied
through the return passage B according to the determined vehicle
state, the automatic pressurization for the traction control,
steering control by braking, and the like can be performed.
[0023] During the automatic pressurization control as described
above, when it is determined on the basis of the outputs detected
by the pressure sensor S1 and stroke sensor S2 that the brake pedal
BP was operated, the linear solenoid valve V1 (or, the linear
solenoid valve V2) is placed in its open position at first, so that
the brake fluid in the power chamber R3 starts to be discharged to
the reservoir RS. In this case, the linear solenoid valve V1 (or,
the linear solenoid valve V2) is controlled to be opened or closed,
so that the amount of brake fluid supplied through the return
passage B is controlled, so as to gradually reduce the amount of
brake fluid in the power chamber R3.
[0024] Referring to FIG. 6, for example, when the brake pedal BP is
depressed during the automatic pressurization (at the position (0)
in FIG. 6), a pedal load is already "Fo", while the stroke of the
brake pedal BP is zero, as shown by a solid line in FIG. 6.
According to the present embodiment, however, the linear solenoid
valve V1 (or, the linear solenoid valve V2) is controlled to
gradually reduce the amount of brake fluid in the power chamber R3.
Therefore, the pedal load (i.e., reaction force) is gradually
increased in response to increase of the stroke of the brake pedal
BP, until when the load will be increased by "Fa" in response to
the amount of operation of the brake pedal BP applied from the
position (0) in FIG. 6 (i.e., additionally depressed amount). In
other words, the amount of brake fluid in the power chamber R3 is
gradually decreased such that the master cylinder pressure is
gradually increased, in response to increase of the stroke of the
brake pedal BP.
[0025] According to the prior apparatus as disclosed in the
aforementioned German patent No.DE19542656A1, when the brake pedal
BP is additionally depressed during the automatic pressurization,
the stroke which is obtained, starting from the state where the
reaction force of the load (Of) was applied at the position of the
stroke (Sto), until the state where the pedal load is increased by
"Fa" in response to increase of the stroke, is as short as the
stroke of "Stp1". And, when the control for reducing the brake
fluid in the power chamber R3 is not performed (as shown by a thick
one-dotted chain line in FIG. 6), the stroke which is obtained
until the state where the pedal load is increased by "Fa" of the
additional depression, is as short as the stroke of "Stp2". In
contrast to this prior art, according to the present embodiment,
the stroke of the brake pedal BP is gradually increased, starting
from the state where the reaction force of the load (Of) was
applied at the position of the stroke (0), until the state where
the pedal load is increased by "Fa" corresponding to the
additionally depressed amount, to provide a sufficient stroke of
"Sti".
[0026] FIGS. 2 and 3 illustrate another embodiment of the hydraulic
brake apparatus, wherein a regulator 2 is provided for assisting a
master cylinder 3 by regulated pressure output from the regulator
2. A pressure source 10 having a hydraulic pressure pump (not
shown) is connected to the regulator 2 and a power chamber R3
formed behind the master cylinder 3 as shown in FIG. 3. The
pressure source 10 as shown in FIG. 2 includes the hydraulic
pressure pump HP and the electric motor M as shown in FIG. 1, and
an accumulator (not shown), if necessary. In this embodiment, a
pressure sensor S1 for detecting the master cylinder pressure and a
stroke sensor S2 for detecting the stroke of a brake pedal 5 are
provided for serving as the detection device for detecting the
amount of operation of the brake pedal 5. Furthermore, a brake
switch which is turned on when the brake pedal 5 is depressed, and
wheel speed sensors, lateral acceleration sensor or the like (these
are indicated by "S" in FIG. 2) are connected to the electronic
controller ECU. As shown in FIG. 2, in the front portion of a
cylinder body 1a of the hydraulic brake apparatus 1 (at the left
side in FIG. 2), the regulator 2 is provided, and the master
cylinder 3 is provided behind the regulator 2, and further a
hydraulic booster 4 is provided behind the master cylinder 3 and
connected to the brake pedal 5. In the cylinder body 1a, cylinder
bores 1b and 1c are formed, and a plug 6 is fitted into the opening
end of the cylinder bore 1c.
[0027] FIG. 3 is an enlarged figure of a portion directly related
to the present invention in FIG. 2. In the cylinder bore 1b, a
control piston 21 of the regulator 2 is received fluid-tightly and
slidably. At a stepped portion mating with the cylinder bore 1b
within the cylinder bore 1c, a ring-like sealing member 32 is
fitted, and the plug 6 is disposed to abut on the member 32, in
which the master piston 31 of the master cylinder 3 is received
fluid-tightly and slidably. In the plug 6, there is formed a
stepped bore having a small diameter cylinder bore 6a and a large
diameter cylinder bore 6b. In the stepped bore, a power piston 41,
which also acts as a reaction piston according to the present
invention, is received fluid-tightly and slidably. A spring 7 is
disposed between the master piston 31 and the control piston 21 to
expand the distance between them, with the maximum distance limited
by a rod 8 engaged with a retainer 31c. According to the present
embodiment, therefore, a pressure chamber R2 is formed between the
master piston 31 and the control piston 21. The master piston 31 is
formed at its front portion with a communication hole 31f, which
faces a port 1f when it is placed at its initial position, so that
the pressure chamber R2 is communicated with a low pressure
reservoir 9 through the port 1f. Between a land portion 41d of the
power piston 41 and the sealing member 32, the power chamber R3 is
defined. Behind the master piston 31, an axial portion 31a is
formed to extend rearward. In front of the power piston 41, there
is formed a recess 41a, in which the axial portion 31a of the
master piston 31 is slidably received. Thus, the master piston 31
and the power piston 41 are arranged to be movable back and forth
relative to each other. The axial portion 31a of the master piston
31 has a slit 31b formed longitudinally. And, a pin 41c is disposed
through the slit 31b and fixed to the power piston 41, so that when
the pin 41c abuts on the rear side wall of the slit 31b, the
forward movement of the master piston 31 relative to the power
piston 41 is prevented, thereby to act as a stopper.
[0028] The power piston 41 has an axial portion 41b extending
rearward therefrom, which is supported fluid-tightly and slidably
in the cylinder bore 6a of the plug 6, and which extends from the
cylinder body la rearward, to be connected with the brake pedal 5
(shown in FIG. 2). In the initial state as shown in FIGS. 2 and 3,
the front end of the power piston 41 and the rear end of main body
of the master piston 31 are in contact with each other. When the
rear end of main body of the master piston 31 abuts on the stepped
portion between the cylinder bores 6a and 6b, the power piston 41
is prevented from being moved rearward. Thus, the brake pedal 5 and
master piston 31 are connected together to be movable relative to
each other through the power piston 41, so that when the brake
pedal 5 is depressed, the master piston 31 is actuated to be
advanced.
[0029] Behind the power piston 41, a regulated pressure chamber R4
is formed to act as a power chamber of a conventional hydraulic
booster, according to the present embodiment. The regulated
pressure chamber R4 is communicated with the regulator 2 through
the communication hole 6b of the plug 6 and a pressure passage 1h.
Furthermore, a regulated pressure chamber R5 is formed in the
regulator 2, and communicated with the wheel brake cylinders Wrr
and Wrl as shown in FIG. 2 through an output port 1j and a pressure
control apparatus HC. The pressure chamber R2 is communicated with
the wheel brake cylinders Wfr and Wfl through an output port 1k and
the pressure control apparatus HC. The regulator 2 is not directly
related with the present invention, so that the detailed
explanation of its structure will be omitted, but its operation
will be explained hereinafter. When the control piston 21 is moved,
the spool 22 is moved, and also the valve member 23 (FIG. 2) is
activated, so that the output pressure (power pressure) of the
pressure source 10 is supplied to the regulated pressure chambers
R5 and R4 to increase the pressure therein, or the regulated
pressure chambers R5 and R4 are communicated with the low pressure
reservoir 9 through a port 1g to decrease the pressure in the
chambers R5 and R4, thereby to provide a predetermined regulated
pressure.
[0030] The power chamber R3 is connected to the power source 10
through a normally closed linear solenoid valve Va. When the linear
solenoid valve Va is placed in its open position, the power chamber
R3 is communicated with the power source 10 to be supplied with the
power pressure. Also, the power chamber R3 is connected to a port
1g through a normally open linear solenoid valve Vb. Normally, the
linear solenoid valve Vb is placed in its open position, so that
the power chamber R3 is communicated with the low pressure
reservoir 9 through the port 1g. When the linear solenoid valve Vb
is placed in its closed position, and the linear solenoid valve Va
is placed in its open position, the power pressure will be supplied
from the power source 10 to the power chamber R3, so that the
master piston 31 will be advanced irrespective of operation of the
brake pedal 5 to apply the reaction force to the power piston
41.
[0031] According to the hydraulic brake apparatus as constituted
above, the linear solenoid valve Va is placed in its closed
position, and the linear solenoid valve Vb is placed in its open
position, in the initial state as shown in FIGS. 2 and 3, so that
the power chamber R3 is communicated with the low pressure
reservoir 9. When the brake pedal 5 is depressed in this state, the
power piston 41 connected thereto abuts on the master piston 31, so
that these are advanced together. Consequently, the pressure
chamber R2 is closed and pressurized to advance the control piston
21, whereby the regulated pressure is discharged from the regulator
2. The regulated pressure is supplied to the regulated pressure
chambers R4, R5, and supplied to the wheel brake cylinders Wrr and
Wrl through the output port 1j, to advance the power piston 41 and
assist the master piston 31 to be advanced, whereby the master
cylinder pressure is supplied to the wheel brake cylinders Wrr and
Wrl through the output port 1k.
[0032] Next, when the traction control, for example, is performed,
with the brake pedal 5 held in its inoperative state, the linear
solenoid valve Vb is placed in its closed position, and the linear
solenoid valve Va is placed in its open position, so that the power
pressure is supplied from the power source 10 to the power chamber
R3. Consequently, the master piston 31 is advanced to discharge the
master cylinder pressure from the output port 1k, and the control
piston 21 is advanced to discharge the regulated pressure from the
regulator 2. In this state for performing the automatic
pressurization, if the brake pedal 5 is depressed, and the
operation of the brake pedal 5 is detected on the basis of the
outputs of the pressure sensor S1 and stroke sensor S2, the linear
solenoid valve Va is placed in its closed position, and the linear
solenoid valve Vb is controlled to be opened or closed.
Consequently, with the stroke of the brake pedal 5 increased, the
brake fluid in the power chamber R3 is reduced gradually, to
increase the master cylinder pressure and the regulated pressure,
gradually.
[0033] Referring to the flowchart in FIG. 4, the control for
reducing the brake fluid in the power chamber R3 will described
hereinafter. At the outset, it is determined at Step 101 whether
the automatic pressurization is being performed or not. If it is
determined that the automatic pressurization is being performed,
the program proceeds to Step 102, where it is determined whether
the brake pedal 5 is depressed to turn on the brake switch (not
shown). If it is determined that the brake switch is turned on, the
program further proceeds to Steps 103 and 104, where it is
determined whether the stroke of the brake pedal 5 has been
increased or not, on the basis of the output of the stroke sensor
S2, and determined whether the master cylinder pressure has been
increased or not, on the basis of the output of the pressure sensor
S1. When it is determined that both of the stroke and the pressure
have been increased, the program proceeds to Step 105. If the
result is negative at any one of the Steps 101-104, the program
returns to a main routine (not shown), without performing the
control for reducing the brake fluid.
[0034] At Step 105, a control target zone is set, as defined by a
pair of thin one-dotted chain lines in FIG. 5. According to a
conventional apparatus, when the brake pedal 5 is depressed during
the automatic pressurization, the master cylinder pressure has been
increased to a certain pressure (Po), at the position where the
stroke is zero (0), as shown in FIG. 5. Therefore, the stroke of
the brake pedal 5 for increasing the master cylinder pressure from
the pressure (Po) up to the pressure added thereto by an
additionally depressed stroke is relatively small, to provide a
property of the master cylinder pressure increased rapidly in
response to increase of the stroke as indicated by a thick
one-dotted chain line, normally. In other words, the stiffness of
the brake pedal 5 is so high that the brake pedal 5 is hardly
depressed.
[0035] In contrast to the conventional property, according to the
present embodiment, the area enclosed by the thin one-dotted chain
lines is set for the control target zone, in order that the master
cylinder pressure is controlled to trace a solid line from the
state applied with the reaction force of the load corresponding to
the master cylinder pressure (Po) at the position of the stroke
(0). That is, the control target zone is set such that the master
cylinder pressure after the brake pedal was operated is controlled
to exceed always the pressure (Po), and controlled to be gradually
increased, with the stroke of the brake pedal 5 increased. The area
enclosed by a pair of thin broken lines is a zone having a
predetermined range provided for the property of the master
cylinder pressure to the stroke of the brake pedal in a normal
braking operation (hereinafter, referred to as a normal braking
property zone).
[0036] Accordingly, a pressure increasing solenoid valve, i.e., the
linear solenoid valve Va is placed in its closed position at Step
106, and a pressure decreasing solenoid valve, i.e., the linear
solenoid valve Vb is controlled to be opened and closed at Step
107. That is, the linear solenoid valve Vb is controlled to be
opened and closed, in order that the brake pedal stroke and the
master cylinder pressure are fallen within the control target zone
as shown in FIG. 5. The Steps 101-107 are repeated, until it is
determined at Step 108 that they are fallen within the normal
braking property zone. When it is determined at Step 108 that they
are fallen within the normal braking property zone, the program
further proceeds to Step 109, where the linear solenoid valve Vb
which acts as the pressure decreasing solenoid valve is turned off
to be placed in its open position, so that the control for
decreasing the brake fluid is terminated. As indicated by the solid
line in FIG. 6, therefore, according to the present embodiment, the
stroke of the brake pedal 5 is gradually increased, starting from
the state where the reaction force of the load (Of) was applied at
the position of the stroke (0), until the state where the load is
increased by "Fa" corresponding to the additionally depressed
amount, to provide a sufficient stroke of "Sti" for the stroke of
the brake pedal 5.
[0037] It should be apparent to one skilled in the art that the
above-described embodiment is merely illustrative of but one of the
many possible specific embodiments of the present invention.
Numerous and various other arrangements can be readily devised by
those skilled in the art without departing from the spirit and
scope of the invention as defined in the following claims.
* * * * *