U.S. patent application number 11/900406 was filed with the patent office on 2008-04-03 for brake system.
This patent application is currently assigned to Honda Motor Co., Ltd.. Invention is credited to Kunimichi Hatano, Takaaki Ohnishi.
Application Number | 20080079309 11/900406 |
Document ID | / |
Family ID | 39260420 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080079309 |
Kind Code |
A1 |
Hatano; Kunimichi ; et
al. |
April 3, 2008 |
Brake system
Abstract
When an electrical fluid pressure generator fails and a wheel
cylinder is operated by brake fluid pressure generated by a master
cylinder, if a first fluid pressure system leading to a rear fluid
chamber of the electrical fluid pressure generator fails and is
opened to the atmosphere, braking is performed by brake fluid
pressure of a second fluid pressure system transmitted from the
master cylinder through a front fluid chamber of the electrical
fluid pressure generator to a wheel cylinder. At this time, a front
supply port, which communicates through a front second cup seal
facing rearward with the rear fluid chamber opened to the
atmosphere due to the failure, does not communicate with the master
cylinder but with a reservoir. Therefore, it is possible to prevent
leakage of the brake fluid pressure generated by the master
cylinder through the front supply port, the front second cup seal
and the rear fluid chamber, thereby ensuring braking by the second
fluid pressure system leading to the front fluid chamber of the
electrical fluid pressure generator.
Inventors: |
Hatano; Kunimichi; (Saitama,
JP) ; Ohnishi; Takaaki; (Saitama, JP) |
Correspondence
Address: |
CARRIER BLACKMAN AND ASSOCIATES
24101 NOVI ROAD, SUITE 100
NOVI
MI
48375
US
|
Assignee: |
Honda Motor Co., Ltd.
Tokyo
JP
|
Family ID: |
39260420 |
Appl. No.: |
11/900406 |
Filed: |
September 11, 2007 |
Current U.S.
Class: |
303/113.5 |
Current CPC
Class: |
B60T 8/4081
20130101 |
Class at
Publication: |
303/113.5 |
International
Class: |
B60T 15/14 20060101
B60T015/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2006 |
JP |
2006-270556 |
Claims
1. A brake system comprising: a master cylinder for generating
brake fluid pressure based on braking operation of a driver; an
electrical fluid pressure generator communicating with the master
cylinder, and having a rear fluid chamber and a front fluid chamber
generating brake fluid pressure by an electrically controllable
actuator; and a plurality of wheel cylinders communicating with the
rear fluid chamber and the front fluid chamber, respectively, and
generating a braking force for braking wheels so that when the
electrical fluid pressure generator fails, the wheel cylinders are
operated by the brake fluid pressure generated by the master
cylinder; the electrical fluid pressure generator including: a rear
piston and a front piston which are advanced by the actuator to
generate brake fluid pressure in the rear fluid chamber and the
front fluid chamber, respectively; a rear inlet port and a rear
outlet port which are formed in the rear fluid chamber and
connected to the master cylinder and the wheel cylinder,
respectively; a front inlet port and a front outlet port which are
formed in the front fluid chamber and connected to the master
cylinder and the wheel cylinder, respectively; a rear first cup
seal arranged at a front end of the rear piston so as to face
forward; a rear second cup seal arranged at a rear end of the rear
piston so as to face forward; a front first cup seal arranged at a
front end of the front piston so as to face forward; a front second
cup seal arranged at a rear end of the front piston so as to face
rearward; and a rear supply port formed adjacent to and in the rear
of the rear inlet port, and a front supply port formed adjacent to
and in the rear of the front inlet port, the rear and front supply
ports being connected to a reservoir.
2. The brake system according to claim 1, further comprising an
anti-lock braking system ("ABS") provided between the electrical
fluid pressure generator and the wheel cylinder, the ABS
decreasing, maintaining and increasing brake fluid pressure
transmitted to the wheel cylinder in order to suppress locking of a
wheel upon braking.
3. The brake system according to claim 2, further comprising a
shutoff valve provided between the master cylinder and the
electrical fluid pressure generator, the shutoff valve being closed
at least during operation of the ABS.
4. A brake system comprising: a master cylinder for generating
brake fluid pressure based on braking operation of a driver; an
electrical fluid pressure generator communicating with the master
cylinder, and having a rear fluid chamber and a front fluid chamber
generating brake fluid pressure by an electrically controllable
actuator; and a plurality of wheel cylinders communicating with the
rear fluid chamber and the front fluid chamber, respectively, and
generating a braking force for braking wheels so that when the
electrical fluid pressure generator fails, the wheel cylinders are
operated by the brake fluid pressure generated by the master
cylinder; the electrical fluid pressure generator including: a rear
piston and a front piston which are advanced by the actuator to
generate brake fluid pressure in the rear fluid chamber and the
front fluid chamber, respectively; a rear inlet port and a rear
outlet port which are formed in the rear fluid chamber and
connected to the master cylinder and the wheel cylinder,
respectively; a rear supply port formed adjacent to and in the rear
of the rear inlet port and connected to the master cylinder; a
front inlet port and a front outlet port which are formed in the
front fluid chamber and connected to the master cylinder and the
wheel cylinder, respectively; a front supply port formed adjacent
to and in the rear of the front inlet port and connected to the
master cylinder; a rear first cup seal arranged at a front end of
the rear piston so as to face forward; a rear second cup seal
arranged at a rear end of the rear piston so as to face forward; a
front first cup seal arranged at a front end of the front piston so
as to face forward; a front second cup seal arranged at a rear end
of the front piston so as to face rearward; and a front third cup
seal arranged adjacent to and in front of the front second cup seal
of the front piston so as to face forward.
5. The brake system according to claim 4, further comprising an
anti-lock braking system ("ABS") provided between the electrical
fluid pressure generator and the wheel cylinder, the ABS
decreasing, maintaining and increasing brake fluid pressure
transmitted to the wheel cylinder in order to suppress locking of a
wheel upon braking.
6. The brake system according to claim 5, further comprising a
shutoff valve provided between the master cylinder and the
electrical fluid pressure generator, the shutoff valve being closed
at least during operation of the ABS.
7. A brake system comprising: a master cylinder for generating
brake fluid pressure based on braking operation of a driver; an
electrical fluid pressure generator communicating with the master
cylinder, and having a rear fluid chamber and a front fluid chamber
generating brake fluid pressure by an electrically controllable
actuator; and a plurality of wheel cylinders communicating with the
rear fluid chamber and the front fluid chamber, respectively, and
generating a braking force for braking wheels so that when the
electrical fluid pressure generator fails, the wheel cylinders are
operated by the brake fluid pressure generated by the master
cylinder; the electrical fluid pressure generator including: a rear
piston and a front piston which are advanced by the actuator to
generate brake fluid pressure in the rear fluid chamber and the
front fluid chamber, respectively; a rear inlet port and a rear
outlet port which are formed in the rear fluid chamber and
connected to the master cylinder and the wheel cylinder,
respectively; a front inlet port and a front outlet port which are
formed in the front fluid chamber and connected to the master
cylinder and the wheel cylinder, respectively; a rear first cup
seal arranged at a front end of the rear piston so as to face
forward; a rear second cup seal arranged at a rear end of the rear
piston so as to face forward; a front first cup seal arranged at a
front end of the front piston so as to face forward; a front second
cup seal arranged at a rear end of the front piston so as to face
rearward; and a means for preventing leakage of the brake fluid of
the front fluid chamber through the rear fluid chamber.
8. The brake system according to claim 7, wherein the means for
preventing leakage of the brake fluid of the front fluid chamber
through the rear fluid chamber comprises a rear supply port formed
adjacent to and in the rear of the rear inlet port, and a front
supply port formed adjacent to and in the rear of the front inlet
port, the rear and front supply ports being connected to a
reservoir.
9. The brake system according to claim 7, wherein the means for
preventing leakage of the brake fluid of the front fluid chamber
through the rear fluid chamber comprises a front third cup seal
arranged adjacent to and in front of the front second cup seal of
the front piston so as to face forward.
10. The brake system according to claim 7, further comprising an
anti-lock braking system ("ABS") provided between the electrical
fluid pressure generator and the wheel cylinder, the ABS
decreasing, maintaining and increasing brake fluid pressure
transmitted to the wheel cylinder in order to suppress locking of a
wheel upon braking.
11. The brake system according to claim 10, further comprising a
shutoff valve provided between the master cylinder and the
electrical fluid pressure generator, the shutoff valve being closed
at least during operation of the ABS.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims priority under 35 USC .sctn.
119 based on Japanese patent application No. 2006-270556, filed on
Oct. 2, 2006. The subject matter of this priority document is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a brake system having a
master cylinder for generating brake fluid pressure based on a
brake operation of a driver, and an electrically controlled fluid
pressure generator (herein after "electrical fluid pressure
generator") for generating brake fluid pressure by an electrically
controllable actuator.
[0004] 2. Description of the Related Art
[0005] Japanese Patent Application Laid-open No. 2003-137084
discloses a brake system of the type referred to as a brake by wire
(BBW) brake system, which converts a brake operation of a driver
into an electrical signal used to operate an electrical fluid
pressure generator, and operates a wheel cylinder by brake fluid
pressure generated by the electrical fluid pressure generator.
[0006] In this type of BBW brake system, if/when the electrical
fluid pressure generator fails, brake fluid pressure generated by a
master cylinder is directly transmitted to a wheel cylinder in
order to brake the wheel, thereby exerting a failsafe function.
Also, the master cylinder is of a tandem type in which the brake
fluid pressure is supplied separately to two fluid pressure
systems, so that even if a leakage occurs in one of the fluid
pressure systems, the other fluid pressure system can brake any of
wheels.
[0007] FIG. 7 shows a relevant portion of the structure of a
conventional electrical fluid pressure generator (motor cylinder
123), excluding the motor and actuator. A rear piston 138A and a
front piston 138B are slidably arranged within a cylinder main body
136, and urged by a pair of return springs 137A and 137B in a
retreating direction. A rear fluid chamber 139A is defined in front
of the rear piston 138A. A front fluid chamber 139B is defined in
front of the front piston 138B.
[0008] Formed around an outer periphery of the rear piston 138A is
a rear reservoir chamber 138a for preventing intrusion of air into
the rear fluid chamber 139A. Formed around an outer periphery of
the front piston 138B is a front reservoir chamber 138b for
preventing intrusion of air into the front fluid chamber 139B. A
rear inlet port 140A of the rear fluid chamber 139A and a rear
supply port 149A of the rear reservoir chamber 138a communicate
with the master cylinder. A rear outlet port 141A of the rear fluid
chamber 139A communicates with a wheel cylinder. A front inlet port
140B of the front fluid chamber 139B and a front supply port 149B
of the front reservoir chamber 138b communicate with the master
cylinder. A front outlet port 141B of the front fluid chamber 139B
communicates with the wheel cylinder.
[0009] A rear first cup seal C1' is provided at a front end of the
rear piston 138A so as to face forward (so that the seal function
is exerted in moving forward). A rear second cup seal C2' is
provided at a rear end of the rear piston 138A so as to face
forward. A front first cup seal C3' is provided at a front end of
the front piston 138B so as to face forward. A front second cup
seal C4' is provided at a rear end of the front piston 138B so as
to face rearward (so that the seal function is exerted in moving
rearward).
[0010] In the structure of this conventional motor cylinder 123,
because the front supply port 149B is connected to the master
cylinder, when the motor cylinder 123 fails and the wheel cylinder
is operated by brake fluid pressure generated by the master
cylinder, if the first fluid pressure system fails and the rear
fluid chamber 139A of the motor cylinder 123 is opened to the
atmosphere, the brake fluid pressure generated by the master
cylinder leaks into a route through the front supply port 149B, the
front reservoir chamber 138b, the front second cup seal C4', and
the rear fluid chamber 139A. Therefore, there is a possibility that
the second fluid pressure system leading to the front fluid chamber
139B might fail at the same time.
SUMMARY OF THE INVENTION
[0011] The present invention has been made in view of the above
situation, and an object of the present invention is to provide a
BBW brake system having two fluid pressure systems in which, when
one of the fluid pressure systems fails, function of the other
fluid pressure system is secured.
[0012] To achieve the above object, according to a first aspect of
the present invention, there is provided a brake system comprising:
a master cylinder for generating brake fluid pressure based on
braking operation of a driver; an electrical fluid pressure
generator communicating with the master cylinder which has a rear
fluid chamber and a front fluid chamber generating brake fluid
pressure by an electrically controllable actuator; and a plurality
of wheel cylinders communicating with the rear fluid chamber and
the front fluid chamber, respectively, and generating a braking
force for braking wheels so that when the electrical fluid pressure
generator fails, the wheel cylinders are operated by the brake
fluid pressure generated by the master cylinder. The electrical
fluid pressure generator includes: a rear piston and a front piston
which are advanced by the actuator to generate brake fluid pressure
in the rear fluid chamber and the front fluid chamber,
respectively; a rear inlet port and a rear outlet port which are
formed in the rear fluid chamber and connected to the master
cylinder and the wheel cylinder, respectively; a front inlet port
and a front outlet port which are formed in the front fluid chamber
and connected to the master cylinder and the wheel cylinder,
respectively; a rear first cup seal arranged at a front end of the
rear piston so as to face forward; a rear second cup seal arranged
at a rear end of the rear piston so as to face forward; a front
first cup seal arranged at a front end of the front piston so as to
face forward; a front second cup seal arranged at a rear end of the
front piston so as to face rearward; and a rear supply port formed
adjacent to and in the rear of the rear inlet port, and a front
supply port formed adjacent to and in the rear of the front inlet
port, the rear and front supply ports being connected to a
reservoir.
[0013] According to the first aspect of the invention, when the
electrical fluid pressure generator fails and the wheel cylinder is
operated by the brake fluid pressure generated by the master
cylinder, if a first fluid pressure system leading to the rear
fluid chamber of the electrical fluid pressure generator fails and
is opened to the atmosphere, braking is performed by brake fluid
pressure of the second fluid pressure system transmitted from the
master cylinder through the front fluid chamber of the electrical
fluid pressure generator to the wheel cylinder. At this time, the
front supply port, which communicates through the front second cup
seal facing rearward with the rear fluid chamber opened to the
atmosphere due to the failure, does not communicate with the master
cylinder but with the reservoir. Therefore, it is possible to
prevent leakage of the brake fluid pressure generated by the master
cylinder through the front supply port, the front second cup seal
and the rear fluid chamber, thereby ensuring braking by the second
fluid pressure system leading to the front fluid chamber of the
electrical fluid pressure generator.
[0014] According to a second aspect of the present invention, there
is provided a brake system comprising: a master cylinder for
generating brake fluid pressure based on braking operation of a
driver; an electrical fluid pressure generator communicating with
the master cylinder which has a rear fluid chamber and a front
fluid chamber generating brake fluid pressure by an electrically
controllable actuator; and a plurality of wheel cylinders
communicating with the rear fluid chamber and the front fluid
chamber, respectively, and generating a braking force for braking
wheels so that when the electrical fluid pressure generator fails,
the wheel cylinders are operated by the brake fluid pressure
generated by the master cylinder. The electrical fluid pressure
generator including: a rear piston and a front piston which are
advanced by the actuator to generate brake fluid pressure in the
rear fluid chamber and the front fluid chamber, respectively; a
rear inlet port and a rear outlet port which are formed in the rear
fluid chamber and connected to the master cylinder and the wheel
cylinder, respectively; a rear supply port formed adjacent to and
in the rear of the rear inlet port and connected to the master
cylinder; a front inlet port and a front outlet port which are
formed in the front fluid chamber and connected to the master
cylinder and the wheel cylinder, respectively; a front supply port
formed adjacent to and in the rear of the front inlet port and
connected to the master cylinder; a rear first cup seal arranged at
a front end of the rear piston so as to face forward; a rear second
cup seal arranged at a rear end of the rear piston so as to face
forward; a front first cup seal arranged at a front end of the
front piston so as to face forward; a front second cup seal
arranged at a rear end of the front piston so as to face rearward;
and a front third cup seal arranged adjacent to and in front of the
front second cup seal of the front piston so as to face
forward.
[0015] According to the second aspect of this invention, when the
electrical fluid pressure generator fails and the wheel cylinder is
operated by the brake fluid pressure generated by the master
cylinder, if the first fluid pressure system leading to the rear
fluid chamber of the electrical fluid pressure generator fails and
is opened to the atmosphere, braking is performed by the brake
fluid pressure of the second fluid pressure system transmitted from
the master cylinder through the front fluid chamber of the
electrical fluid pressure generator to the wheel cylinder. At this
time, the front third cup seal facing forward is arranged between
the front supply port communicating with the master cylinder and
the rear fluid chamber opened to the atmosphere due to the failure.
Therefore, the front third cup seal prevents leakage of the brake
fluid pressure generated by the master cylinder from the front
supply port through the rear fluid chamber, thereby ensuring
braking by the second fluid pressure system leading to the front
fluid chamber of the electrical fluid pressure generator.
[0016] According to a third aspect of the present invention, in
addition to the first or second aspect, the brake system further
comprises an anti-lock braking system ("ABS") provided between the
electrical fluid pressure generator and the wheel cylinder, the ABS
decreasing, maintaining and increasing brake fluid pressure
transmitted to the wheel cylinder in order to suppress locking of a
wheel upon braking.
[0017] According to the third aspect of the present invention,
because the ABS for decreasing, maintaining and increasing the
brake fluid pressure transmitted to the wheel cylinder is arranged
between the electrical fluid pressure generator and the wheel
cylinder, locking of a wheel upon braking can be suppressed and a
braking distance can be reduced.
[0018] According to a fourth aspect of the present invention, in
addition to the third aspect, the brake system further comprises a
shutoff valve provided between the master cylinder and the
electrical fluid pressure generator, the shutoff valve being closed
at least during operation of the ABS.
[0019] According to the fourth aspect of this invention, because
the shutoff valve closing at least during operation of the ABS is
arranged between the master cylinder and the electrical fluid
pressure generator, it thereby prevents hydraulic pressure change
due to the operation of the ABS from being transmitted as a
kickback to the master cylinder.
[0020] A motor cylinder 23 in non-limiting, exemplary embodiments
of the invention discussed below corresponds to the electrical
fluid pressure generator in the present invention.
[0021] The above-mentioned object, other objects, characteristics,
and advantages of the present invention will become apparent from
preferred embodiments, which will be described in detail below by
reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a fluid pressure circuit diagram of a vehicle
brake system according to a first embodiment of the present
invention, showing a configuration for normal operating
conditions.
[0023] FIG. 2 is the fluid pressure circuit diagram of FIG. 1,
showing a configuration for abnormal operating conditions.
[0024] FIG. 3 is an enlarged view of an essential part of the
electrical fluid pressure generator of FIG. 1.
[0025] FIG. 4 is a fluid pressure circuit diagram of a vehicle
brake system according to a second embodiment of the present
invention, showing a configuration for normal operating
conditions.
[0026] FIG. 5 is the fluid pressure circuit diagram of FIG. 4,
showing a configuration for abnormal operating conditions.
[0027] FIG. 6 is an enlarged view of an essential part of the
electrical fluid pressure generator of FIG. 4.
[0028] FIG. 7 is a structure of a conventional electrical fluid
pressure generator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Selected illustrative embodiments of the invention will now
be described in some detail, with reference to the drawings. It
should be understood that only structures considered necessary for
clarifying the present invention are described herein. Other
conventional structures, and those of ancillary and auxiliary
components of the system, are assumed to be known and understood by
those skilled in the art.
[0030] A first embodiment of the present invention will be
described with reference to FIGS. 1 to 3.
[0031] As shown in FIG. 1, a tandem master cylinder 11 has two
first fluid pressure chambers 13A and 13B which output brake fluid
pressure according to a force applied to a brake pedal 12 by a
driver treading on the brake pedal 12. One of the first fluid
pressure chambers 13A is connected to wheel cylinders 16 and 17 of
disc brake devices 14 and 15 for braking, for example, a left front
wheel and a right rear wheel through fluid passages Pa, Pb, Pc, Pd,
and Pe. The other first fluid pressure chamber 13B is connected to
wheel cylinders 20 and 21 of disc brake devices 18 and 19 for
braking, for example, a right front wheel and a left rear wheel
through fluid passages Qa, Qb, Qc, Qd, and Qe.
[0032] A shutoff valve 22A, which is a normally open solenoid
valve, is provided between the fluid passages Pa and Pb. A shutoff
valve 22B, which is a normally open solenoid valve, is provided
between the fluid passages Qa and Qb. A motor cylinder 23 is
provided between the fluid passages Pb, Qb and the fluid passages
Pc, Qc. An ABS 24 is provided between the fluid passages Pc, Qc and
the fluid passages Pd, Pe; Qd, Qe.
[0033] A reaction force permission valve 25, which is a normally
closed solenoid valve, is connected between a fluid passage Ra
branching from the fluid passage Qa and a fluid passage Rb. A
stroke simulator 26 is connected to the fluid passage Rb. The
stroke simulator 26 has a cylinder 27 and a piston 29 slidably
fitted in the cylinder 27 while being urged by a spring 28. A fluid
chamber 30, formed on the side of the piston 29 opposite from the
spring 28, communicates with the fluid passage Rb.
[0034] An actuator 31 of the motor cylinder 23 has a drive bevel
gear 33 provided on the output shaft of an electric motor 32, a
follower bevel gear 34 meshing with the drive bevel gear 33, and a
ball screw mechanism 35 operated by the follower bevel gear 34. A
pair of pistons 38A and 38B urged in a retreat direction by a pair
of return springs 37A and 37B are slidably disposed in a cylinder
body 36 of the motor cylinder 23. A rear fluid chamber 39A is
defined on a front face of the rear piston 38A. A front fluid
chamber 39B is defined on a front face of the front piston 38B.
[0035] As obvious from FIGS. 1 and 3, the rear fluid chamber 39A
communicates with the fluid passages Pb and Pc, respectively,
through the rear inlet port 40A and the rear outlet port 41A, and
with the reservoir 50 through the rear supply port 49A and the
fluid passages Rc, Re. The front fluid chamber 39B communicates
with the fluid passages Qb and, Qc through the front inlet port 40B
and the front outlet port 41B, and with the reservoir 50 through
the front supply port 49B and the fluid passages Rd, Re.
[0036] A rear first cup seal C1 is provided at a front end of the
rear piston 38A so as to face forward (so that the seal function is
exerted in moving forward). A rear second cup seal C2 is provided
at a rear end of the rear piston 38A so as to face forward. A front
first cup seal C3 is provided at a front end of the front piston
38B so as to face forward. A front second cup seal C4 is provided
at a rear end of the front piston 38B so as to face rearward (so
that the seal function is exerted in rearward moving).
[0037] A rear reservoir chamber 38a is formed at an intermediate
portion of the rear piston 38A so as to be held between the rear
first and second cup seals C1 and C2. A rear supply port 49A
communicates with the rear reservoir chamber 38a. A front reservoir
chamber 38b is formed at an intermediate portion of the front
piston 38B so as to be held between the front first and second cup
seals C3 and C4. A front supply port 49B communicates with the
front reservoir chamber 38b.
[0038] The rear fluid chamber 39A is held between the
forward-facing rear first cup seal C1 and the rearward-facing front
second cup seal C4 so as to ensure fluid tightness. The
forward-facing rear second cup seal C2 prevents rearward leakage
from the rear reservoir chamber 38a of the rear piston 38A.
[0039] When the motor cylinder 23 is not in operation, the rear
first cup seal C l of the rear piston 38A is located immediately in
the rear of the rear inlet port 40A. When the rear piston 38A
slightly advances, the rear first cup seal C1 passes over the rear
inlet port 40A, and brake fluid pressure is generated in the rear
fluid chamber 39A. When the motor cylinder 23 is not in operation,
the front first cup seal C3 of the front piston 38B is located
immediately in the rear of the front inlet port 40B. When the front
piston 38B slightly advances, the front first cup seal C3 passes
over the front inlet port 40B, and the brake fluid pressure is
generated at the front fluid chamber 39B.
[0040] When the electric motor 32 is driven in one direction, the
rear and the front pistons 38A and 38B are advanced by the drive
bevel gear 33, the follower bevel gear 34, and the ball screw
mechanism 35. At a moment when the rear and the front inlet ports
40A and 40B communicating with the fluid passages Pb and Qb are
closed, the brake fluid pressure is generated in the rear and the
front fluid chambers 39A and 39B, so that the brake fluid pressure
can be outputted to the fluid passages Pc and Qc through the rear
and the front output ports 41A and 41B.
[0041] As shown in FIG. 1, the structure of the ABS 24 is of a
well-known type. The ABS 24 has two streams structurally identical
to each other: one stream including the disc brake devices 14 and
15 for braking the left front wheel and the right rear wheel; and
the other stream for the disc brake devices 18 and 19 for braking
the right front wheel and the left rear wheel. Of these streams,
the stream for the disc brake devices 14 and 15 will be described
as a representative. A pair of in-valves 42 comprising normally
open solenoid valves are provided between the fluid passage Pc and
the fluid passages Pd, Pe. A pair of out-valves 44 comprising
normally closed solenoid valves are provided between the fluid
passages Pd, Pe on the downstream side of the in-valves 42 and a
reservoir 43. A fluid pressure pump 47 interposed between a pair of
check valves 45 and 46 is provided between the reservoir 43 and the
fluid passage Pc. The fluid pressure pump 47 is driven by an
electric motor 48.
[0042] Connected to an electronic control unit (not shown) for
controlling the operation of the shutoff valves 22A and 22B, the
reaction force permission valve 25, the motor cylinder 23 and the
ABS 24, are a fluid pressure sensor Sa for detecting the brake
fluid pressure generated by the master cylinder 11, a fluid
pressure sensor Sb for detecting the brake fluid pressure
transmitted to the disc brake devices 18 and 19, and a vehicle
wheel speed sensors Sc for detecting the vehicle wheel speeds of
the vehicle wheels.
[0043] The operation of the embodiments of the present invention
having the above-described arrangement will now be described.
[0044] In a normal situation where the system operates normally,
the shutoff valves 22A and 22B, comprising normally open solenoid
valves, are demagnetized so as to be in an open state, and the
reaction force permission valve 25, comprising a normally closed
solenoid valve, is magnetized so as to be in an open state. In this
state, when the fluid pressure sensor Sa provided in the fluid
passage Qa detects a depression on the brake pedal 12 by the
driver, the actuator 31 of the motor cylinder 23 operates to
advance the rear and front pistons 38A and 38B, thereby generating
brake fluid pressure in the rear and front fluid chambers 39A and
39B. This brake fluid pressure is transmitted to the wheel
cylinders 16, 17, 20, and 21 of the disc brake devices 14, 15, 18,
and 19 through the opened in-valves 42 of the ABS 24, thereby
braking the vehicle wheels.
[0045] When the rear and front pistons 38A and 38B of the motor
cylinder 23 slightly advance, the rear and front inlet ports 40A
and 40B are closed to shut off the communication between the fluid
passages Pb, Qb and the rear and front fluid chambers 39A and 39B.
Therefore, the brake fluid pressure generated by the master
cylinder 11 is not transmitted to the disc brake devices 14, 15,
18, and 19. At this time, the brake fluid pressure generated in the
other first fluid pressure chamber 13B of the master cylinder 11 is
transmitted to the fluid chamber 30 of the stroke simulator 26
through the opened reaction force permission valve 25 to move the
piston 29 against the spring 28, thereby generating a pseudo pedal
reaction force while permitting the stroke of the brake pedal 12 to
eliminate an uncomfortable feeling to the driver.
[0046] The operation of the actuator 31 for the motor cylinder 23
is controlled so that the brake fluid pressure generated by the
motor cylinder 23 and detected by the fluid pressure sensor Sb
provided in the fluid passage Qc has a value corresponding to the
brake fluid pressure generated by the master cylinder 11 and
detected by the fluid pressure sensor Sa provided in the fluid
passage Qa, thereby generating the braking force in the disc brake
devices 14, 15, 18, and 19 according to the depressing force input
to the brake pedal 12 by the driver.
[0047] If slip ratio of any vehicle wheel is increased and a
tendency of locking is detected based on the output from the wheel
speed sensor Sc corresponding to the vehicle wheel during the
above-described braking, the shutoff valves 22A and 22B, comprising
normally open solenoid valves, are energized so as to close, the
motor cylinder 23 is maintained in the operating state, and in this
state the ABS 24 is operated to prevent locking of the vehicle
wheel.
[0048] That is, when any vehicle wheel has a tendency of locking, a
pressure reducing operation is performed to release the brake fluid
pressure in the wheel cylinder by opening the out-valve 44 in a
state where the transmission of the brake fluid pressure from the
motor cylinder 23 is shut off by closing the in-valve 42
communicating with the wheel cylinder; and a pressure maintaining
operation is subsequently performed to maintain the brake fluid
pressure in the wheel cylinder by closing the out-valve 44, thereby
reducing the braking force to avoid locking of the vehicle
wheel.
[0049] When the vehicle wheel speed is recovered to reduce the slip
ratio, a pressure increasing operation is performed to increase the
brake fluid pressure in the wheel cylinder by opening the in-valve
42, thereby increasing the braking force for braking the vehicle
wheel. When the vehicle wheel again has a tendency of locking due
to this pressure increasing operation, the above-described pressure
reducing, maintaining and increasing operation is performed again.
The operation is repeatedly performed to generate the maximum
braking force while preventing locking of the vehicle wheels. The
brake fluid flowing into the reservoir 43 during this process is
returned by the fluid pressure pump 47 to the fluid passages Pc and
Qc on the upstream side.
[0050] During the above-described ABS control, the shutoff valves
22A and 22B are maintained in the valve closed state, thereby
preventing a fluid pressure fluctuation associated with the
operation of the ABS 24 from being transmitted as a kickback from
the master cylinder 11 to the brake pedal 12.
[0051] When the motor cylinder 23 becomes inoperable, due to power
failure for example, braking by the brake fluid pressure generated
by the master cylinder 11 is performed in place of the brake fluid
pressure generated by the motor cylinder 23.
[0052] In the event of power failure, as shown in FIG. 2, the
shutoff valves 22A and 22B, comprising normally open solenoid
valves, remain open; the reaction force permission valve 25
comprising a normally closed solenoid valve is automatically
closed; the in-valves 42, comprising normally open solenoid valves,
are automatically opened; and the out-valves 44, comprising
normally closed solenoid valves, are automatically closed. In this
state, the brake fluid pressure generated in the fluid chambers 13A
and 13B of the master cylinder 11 passes through the shutoff valves
22A and 22B, the fluid chambers 39A and 39B of the motor cylinder
23 and the in-valves 42, without being absorbed by the stroke
simulator 26; and operates the wheel cylinders 16, 17, 20, and 21
of the disc brake devices 14, 15, 18, and 19 for respectively
braking the vehicle wheels, thus generating the braking force
without any problem.
[0053] The first and second fluid pressure lines are completely
separate and independent from each other. That is, the first fluid
pressure line extends from one first fluid pressure chamber 13A in
the master cylinder 11 to the wheel cylinders 16 and 17 of the disc
brake devices 14 and 15 for the left front wheel and the right rear
wheel, through the fluid passage Pa, the shutoff valve 22A, the
fluid passage Pb, one fluid chamber 39A of the motor cylinder 23
and the fluid passages Pc, Pd, and Pe; and the second fluid
pressure line extends from the other first fluid pressure chamber
13B in the master cylinder 11 to the wheel cylinders 20 and 21 of
the disc brake devices 18 and 19 for the right front wheel and the
left rear wheel, through the fluid passage Qa, the shutoff valve
22B, the fluid passage Qb, the other fluid chamber 39B of the motor
cylinder 23 and the fluid passages Qc, Qd, and Qe. Therefore, even
when trouble such as leakage or clogging of the brake fluid
pressure occurs in one of the first and second fluid pressure
lines, braking force can be generated in at least two of the four
wheels to achieve fail-safe operation of the system.
[0054] In conventional system, as shown by way of example in FIG.
7, because the front supply port 49B is connected not to the
reservoir 50 but to the master cylinder 11, when the first fluid
pressure system fails and the rear fluid chamber 39A of the motor
cylinder 23 is opened to the atmosphere, the brake fluid pressure
generated in the fluid chamber 13B of the master cylinder 11 leaks
via the route through the front supply port 49B, the front
reservoir chamber 38b, the front second cup seal C4, and the rear
fluid chamber 39A. Therefore, there is a possibility that the
second fluid chamber system leading to the front fluid chamber 39B
might fail at the same time.
[0055] However, according to the first embodiment shown in FIG. 3,
because the front supply port 49B is connected to the reservoir 50,
even if the first fluid chamber system fails and the rear fluid
chamber 39A of the motor cylinder 23 is opened to the atmosphere,
the brake fluid pressure generated in the fluid chamber 13B of the
master cylinder 11 is not transmitted to the front supply port 49B,
and thus, the brake fluid pressure does not leak to the route
through the front reservoir chamber 38b, the front second cup seal
C4, and the rear fluid chamber 39A. Therefore, it is possible to
prevent the second fluid pressure system leading to the front fluid
chamber 39B from failing at the same time.
[0056] Next, a second embodiment of the present invention will be
described based on FIGS. 4 to 6.
[0057] In the first embodiment as described above, the rear and
front supply ports 49A and 49B of the motor cylinder 23 are
connected to the reservoir 50, but in the second embodiment, the
rear and front supply ports 49A and 49B are connected to the pair
of fluid chambers 13A and 13B of the master cylinder 11 as in the
case of the conventional example shown in FIG. 7. Additionally,
however, according to the second embodiment, a forward-facing front
third cup seal C5 is arranged immediately in front of the front
second cup seal C4 of the front piston 38B, so as to be opposed to
the rear end of the front reservoir chamber 38b.
[0058] Therefore, when an abnormality occurs, the first fluid
pressure system, which extends from the fluid chamber 13A of the
master cylinder 11 through the fluid passage Pa, the shutoff valve
22A, the fluid passage Pb, the rear fluid chamber 39A of the motor
cylinder 23, the fluid passage Pc and the fluid passages Pd, Pe to
the wheel cylinders 16 and 17 of the disc brake devices 14 and 15
of the left front wheel and the right rear wheel, does not leak
brake fluid. Even if the brake fluid pressure is transmitted from
the other fluid chamber 13B of the master cylinder through the
fluid passage Qa, the shutoff valve 22B and the fluid passage Qb to
the front fluid chamber 39B of the motor cylinder 23 and a front
reservoir chamber 38b, because the front reservoir chamber 38b is
no longer in communication with the rear fluid chamber 39A, which
is opened to the atmosphere, due to the front third cup seal C5,
leakage of the brake fluid pressure of the front fluid chamber 39B
through the rear fluid chamber 39A is prevented. Thus, the first
and second fluid pressure systems do not fail at the same time.
[0059] As will be understood, each of the above two embodiments
includes a means for preventing leakage of the brake fluid pressure
of the front fluid chamber 39B through the rear fluid chamber 39A.
In the first embodiment, the means for preventing leakage of the
brake fluid pressure of the front fluid chamber 39B through the
rear fluid chamber 39A comprises a rear supply port formed adjacent
to and in the rear of the rear inlet port, and a front supply port
formed adjacent to and in the rear of the front inlet port, the
rear and front supply ports being connected to a reservoir. In the
second embodiment, the means for preventing leakage of the brake
fluid pressure of the front fluid chamber 39B through the rear
fluid chamber 39A comprises a front third cup seal arranged
adjacent to and in front of the front second cup seal of the front
piston so as to face forward.
[0060] The embodiments of the present invention have been described
above, but various changes in design may be made without departing
from the subject matter of the present invention as indicated by
the appended claims.
[0061] For example, the brake systems of the embodiments comprise
the ABS 24, but the present invention is also applicable to a brake
system not having the ABS 24.
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