U.S. patent application number 09/741877 was filed with the patent office on 2001-06-28 for brake system having brake assist feature.
Invention is credited to Kamiya, Masahiko.
Application Number | 20010005100 09/741877 |
Document ID | / |
Family ID | 26581760 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005100 |
Kind Code |
A1 |
Kamiya, Masahiko |
June 28, 2001 |
Brake system having brake assist feature
Abstract
A brake system includes first brake assist means arranged in a
first brake circuit to increase a first wheel cylinder pressure to
a level higher than a master cylinder pressure. The brake system
further includes second brake assist means arranged in a second
brake circuit to increase a second wheel cylinder pressure to a
level higher than the master cylinder pressure. The second brake
assist means includes a brake regulator mechanism that uses the
increased first wheel cylinder pressure as a pilot pressure and
adjusts the increased second wheel cylinder pressure to a pressure
falling within a predetermined range from the increased first wheel
cylinder pressure when the first brake assist means is
activated.
Inventors: |
Kamiya, Masahiko;
(Anjo-city, JP) |
Correspondence
Address: |
Pillsbury, Madison & Sutro, LLP
East Tower, Ninth Floor
1100 New York Avenue, N.W.
Washington
DC
20005-3918
US
|
Family ID: |
26581760 |
Appl. No.: |
09/741877 |
Filed: |
December 22, 2000 |
Current U.S.
Class: |
303/5 ;
303/10 |
Current CPC
Class: |
B60T 8/341 20130101;
B60T 8/58 20130101; B60T 8/4872 20130101; B60T 8/442 20130101; B60T
8/3275 20130101; B60T 8/348 20130101; B60T 13/686 20130101; B60T
7/12 20130101 |
Class at
Publication: |
303/5 ;
303/10 |
International
Class: |
B60T 013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
JP |
11 - 366259 |
Sep 1, 2000 |
JP |
2000 - 265583 |
Claims
What is claimed is:
1. A brake system for a vehicle comprising: a master cylinder
having first and second chambers in each of which a master cylinder
pressure is generated in response to brake operation by a vehicle
driver; first and second wheel cylinders for exerting a first
braking force on first and second vehicle wheels, respectively, by
a first wheel cylinder pressure generated based on said master
cylinder pressure in said first chamber of said master cylinder; a
first brake circuit for connecting said master cylinder to said
first and second wheel cylinders; third and fourth wheel cylinders
for exerting a second braking force on third and fourth vehicle
wheels, respectively, by a second wheel cylinder pressure generated
based on said master cylinder pressure in said second chamber of
said master cylinder; a second brake circuit for connecting said
master cylinder to said third and fourth wheel cylinders; first
brake assist means arranged in said first brake circuit to increase
said first wheel cylinder pressure to a level higher than said
master cylinder pressure in said first chamber and to conduct said
increased first wheel cylinder pressure to at least one of said
first and second wheel cylinders in response to at least one of a
state of said brake operation by said vehicle driver and a braking
state of said vehicle; and second brake assist means arranged in
said second brake circuit to increase said second wheel cylinder
pressure to a level higher than said master cylinder pressure in
said second chamber and to conduct said increased second wheel
cylinder pressure to at least one of said third and fourth wheel
cylinders in response to at least one of said state of said brake
operation by said vehicle driver and said braking state of said
vehicle, wherein said second brake assist means includes a brake
regulator mechanism that uses said increased first wheel cylinder
pressure as a pilot pressure and adjusts said increased second
wheel cylinder pressure in said third and fourth wheel cylinders to
a pressure falling within a predetermined range from said increased
first wheel cylinder pressure in said first and second wheel
cylinders when said first brake assist means is activated.
2. A brake system according to claim 1, wherein: said regulator
mechanism includes a first chamber, which is supplied with said
increased first wheel cylinder pressure of said first brake circuit
as a back pressure, and a second chamber, which is supplied with
said master cylinder pressure in said second chamber of said master
cylinder and is communicated to said third and fourth wheel
cylinders in said second brake circuit; and said first chamber and
said second chamber of said regulator mechanism are fluid-tightly
separated from each other by a piston having a regulator valve
element that communicates or blocks between said master cylinder
and said third and fourth wheel cylinders in said second brake
circuit in response to a differential pressure between said back
pressure and said increased second wheel cylinder pressure of said
second brake circuit.
3. A brake system according to claim 2, wherein said piston has a
first pressure receiving surface disposed to said first chamber of
said regulator mechanism and a second pressure receiving surface
disposed to said second chamber of said regulator mechanism,
wherein there is provided a difference in surface area between said
first pressure receiving surface and said second pressure receiving
surface.
4. A brake system according to claim 3, wherein: one of said first
and second brake circuits is arranged to apply said first braking
force to vehicle rear wheels, and the other of said first and
second brake circuits is arranged to apply said second braking
force to vehicle front wheels; and one of said first and second
pressure receiving surfaces of said piston, which is in fluid
communication with said one of said first and second brake circuits
arranged to apply said first braking force to said vehicle rear
wheels, is larger than the other of said first and second pressure
receiving surfaces of said piston, which is in fluid communication
with said other of said first and second brake circuits arranged to
apply said second braking force to said vehicle front wheels.
5. A brake system according to claim 2, wherein said piston has
seal means extending along an outer peripheral surface of said
piston for fluid-tightly sealing between said first chamber and
said second chamber of said regulator mechanism.
6. A brake system according to claim 5, wherein said piston is in
an initial position while said vehicle driver is not conducting
said brake operation, wherein said piston is urged to return to
said initial position by a restoring force of said seal means after
said seal means is deformed due to movement of said piston away
from said initial position.
7. A brake system according to claim 5, wherein said piston is in
an initial position while said vehicle driver is not conducting
said brake operation, wherein said regulator mechanism has spring
means for urging said piston to said initial position.
8. A brake system according to claim 5, wherein said seal means
includes first and second seal elements extending along said outer
peripheral surface of said piston, wherein said first and second
seal elements are arranged in series between said first chamber and
said second chamber of said regulator mechanism.
9. A brake system according to claim 8, wherein a space between
said first seal element and said second seal element is in fluid
communication with a communication passage to atmosphere for
allowing part of said brake fluid leaked into said space between
said first seal element and said second seal element to egress
through said communication passage.
10. A brake system according to claim 2, wherein said first and
second brake circuits and said regulator mechanism are arranged in
a housing, wherein said piston slides along an inner side-wall
surface of a recess defined in said housing.
11. A brake system according to claim 10, wherein: said regulator
mechanism has a seat valve unit having a valve seat provided for
engaging with said regulator valve element and also has a guide for
securing said seat valve unit to said housing; Said inner side-wall
surface of said recess of said housing is provided with a first
port passage in fluid communication with said master cylinder and a
second port passage in fluid communication with said third and
fourth wheel cylinders, wherein said first port passage is arranged
closer to an entry opening of said recess of said housing than said
second port passage; and an outer peripheral portion and a distal
end portion of said guide are caulked to said housing, wherein said
caulking between said outer peripheral portion of said guide and
said housing secures said guide to said housing and also seals
between said first port passage and an exterior of said housing,
and said caulking between said distal end portion of said guide and
said housing seals between said first port passage and said second
port passage around said guide.
12. A brake system according to claim 11, wherein said seat valve
unit has a check valve that allows flow of said brake fluid only in
a direction from said first port passage to said second port
passage.
13. A brake system according to claim 12, wherein: said seat valve
unit has a check valve seat of said check valve and a check valve
element of said check valve; said inner side-wall surface of said
recess of said housing is provided with a filter covering said
second port passage; and said filter is positioned adjacent to said
seat valve unit, wherein said filter acts as a mechanical stopper
for said check valve element and also acts as a shaft support
holder for said regulator valve element.
14. A brake system according to claim 1, further comprising a
differential pressure measurement mechanism for measuring a
differential pressure between said increased first wheel cylinder
pressure in said first brake circuit and said increased second
wheel cylinder pressure of said second brake circuit, wherein if
said differential pressure measured with said differential pressure
measurement mechanism is equal to or greater than a predetermined
amount, at least one of a plurality of countermeasures is taken,
wherein said plurality of countermeasures include giving a warning
or notification to said vehicle driver; interrupting or prohibiting
operation of said first and second brake assist means; and reducing
said increased first wheel cylinder pressure in said first brake
circuit.
15. A brake system according to claim 1, further comprising a first
hydraulic pressure sensor for measuring said increased first wheel
cylinder pressure in said first brake circuit and a second
hydraulic pressure sensor for measuring said increased second wheel
cylinder pressure of said second brake circuit, wherein if a
differential pressure that is equal to or greater than a
predetermined amount is developed between a measured pressure value
of said first hydraulic pressure sensor and a measured pressure
value of said second hydraulic pressure sensor, at least one of a
plurality of countermeasures is taken, wherein said plurality of
countermeasures include giving a warning or notification to said
vehicle driver; interrupting or prohibiting operation of said first
and second brake assist means; and reducing said increased first
wheel cylinder pressure in said first brake circuit.
16. A brake system according to claim 1, further comprising a
differential pressure measurement pipeline and a differential
pressure switch that is inserted in said differential pressure
measurement pipeline and is activated by a predetermined amount of
differential pressure developed in said differential pressure
measurement pipeline, wherein: said differential pressure
measurement pipeline is extended out from anywhere where said
increased first wheel cylinder pressure is supplied in said first
brake circuit to anywhere where said increased second wheel
cylinder pressure is supplied in said second brake circuit; and if
said predetermined differential pressure is developed in said
differential pressure measurement pipeline, and thereby said
differential pressure switch is activated, at least one of a
plurality of countermeasures is taken, wherein said plurality of
countermeasures include giving a warning or notification to said
vehicle driver; interrupting or prohibiting operation of said first
and second brake assist means; and reducing said increased first
wheel cylinder pressure in said first brake circuit.
17. A brake system according to claim 1, further comprising a check
valve disposed in said second brake circuit in parallel with said
regulator mechanism for allowing flow of said brake fluid only in a
direction from said master cylinder to said third and fourth wheel
cylinders.
18. A brake system according to claim 1, wherein said regulator
mechanism includes a check valve mechanism that allows flow of said
brake fluid only in a direction from said master cylinder to said
third and fourth wheel cylinders.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 11-366259 filed on Dec.
24, 1999 and Japanese Patent Application No. 2000-265583 filed on
Sep. 1, 2000.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a brake system that has a
brake assist feature implemented in brake circuits and activated
during sudden or panic braking.
[0003] For example, Japanese Unexamined Patent Publication No.
11-108230 discloses such a brake system. This brake system has a
couple of brake circuits, one for a pair of vehicle wheels and one
for another pair of vehicle wheels. The brake assist feature is
implemented in the brake circuits by a couple of pumps (one for
each brake circuit) and a couple of differential pressure retaining
valves (one for each brake circuit).
[0004] In the above-described brake system, if a discharge capacity
differs between the pumps, or if differential pressure retaining
ability differs between the differential pressure retaining valves,
a second brake fluid pressure, which is generated in each brake
circuit and is higher than the master cylinder pressure, may differ
between the brake circuits. For instance, the difference in the
second brake fluid pressure can be created when a difference in
resistance of electric lines provided for supplying electric power
to each pump or differential pressure retaining valve exists
between the brake circuits for some reasons. Furthermore, the
difference in the second brake fluid pressure can also be created
when a difference in pressure-sealing performance of the pump
exists between the brake circuits due to, for example, aging.
[0005] The creation of the differential pressure between the brake
circuits causes some problems. For instance, in a diagonally split
brake system having one brake circuit for the right front wheel and
the left rear wheel and one brake circuit for the left front wheel
and the right rear wheel, it causes a difference in braking force
between a left side and a right side of the vehicle. Furthermore,
in a vertically split brake system having one brake circuit for the
right front wheel and the left front wheel and one brake circuit
for the right rear wheel and the left rear wheel, it causes a
difference in braking force between a front side and a rear side of
the vehicle.
[0006] The difference (unbalance) in the braking force can be
particularly large in the vehicles having the brake assist feature.
That is, during panic braking, during malfunction of a brake
booster or during the operation beyond a dead point of the brake
booster, when the wheel cylinder pressure greater than the master
cylinder pressure is generated in the brake lines and is supplied
to each wheel, the wheel cylinder pressure supplied to each wheel
may have no relationship or a relatively smaller degree of
relationship with the master cylinder pressure. Thus, a difference
in brake fluid pressure between the wheels or between the brake
circuits cannot be substantially compensated. Furthermore, since
the high brake fluid pressure supplied to each wheel is greater
than the master cylinder pressure, the difference in the brake
fluid pressure that causes the above-described difference in the
braking force may be increased.
SUMMARY OF THE INVENTION
[0007] The present invention addresses the above-described
disadvantages. Therefore, it is an objective of the present
invention to provide a brake system having a brake assist feature
implemented in brake circuits and being capable of compensating a
difference in brake fluid pressure between the brake circuits and
thereby keeping the difference in the brake fluid pressure between
the brake circuits to be less than or equal to a predetermined
amount to assure a sufficient stability of vehicle motion during
braking aided by the brake assist. In a case of vertically split
brake system, the difference in the brake fluid pressure between a
front wheel brake circuit and a rear wheel brake circuit should
remain less than a predetermined amount to maintain a predetermined
brake force allocation between the front wheels and the rear
wheels.
[0008] To achieve the objective of the present invention, there is
provided a brake system for a vehicle having a master cylinder,
first and second wheel cylinders, a first brake circuit, third and
fourth wheel cylinders, a second brake circuit, first brake assist
means and second brake assist means. The master cylinder has first
and second chambers in each of which a master cylinder pressure is
generated in response to brake operation by a vehicle driver. The
first and second wheel cylinders are provided for exerting a first
braking force on first and second vehicle wheels, respectively, by
a first wheel cylinder pressure generated based on the master
cylinder pressure in the first chamber of the master cylinder. The
first brake circuit connects the master cylinder to the first and
second wheel cylinders. The third and fourth wheel cylinders are
provided for exerting a second braking force on third and fourth
vehicle wheels, respectively, by a second wheel cylinder pressure
generated based on the master cylinder pressure in the second
chamber of the master cylinder. The second brake circuit is
provided for connecting the master cylinder to the third and fourth
wheel cylinders. The first brake assist means is arranged in the
first brake circuit to increase the first wheel cylinder pressure
to a level higher than the master cylinder pressure in the first
chamber and to conduct the increased first wheel cylinder pressure
to at least one of the first and second wheel cylinders in response
to at least one of a state of the brake operation by the vehicle
driver and a braking state of the vehicle. The second brake assist
means is arranged in the second brake circuit to increase the
second wheel cylinder pressure to a level higher than the master
cylinder pressure in the second chamber and to conduct the
increased second wheel cylinder pressure to at least one of the
third and fourth wheel cylinders in response to at least one of the
state of the brake operation by the vehicle driver and the braking
state of the vehicle. The second brake assist means includes a
brake regulator mechanism that uses the increased first wheel
cylinder pressure as a pilot pressure and adjusts the increased
second wheel cylinder pressure in the third and fourth wheel
cylinders to a pressure falling within a predetermined range from
the increased first wheel cylinder pressure in the first and second
wheel cylinders when the first brake assist means is activated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention, together with additional objects, features
and advantages thereof, will be best understood from the following
description, the appended claims and the accompanying drawings in
which:
[0010] FIG. 1 is a schematic view of a brake system according to a
first embodiment of the present invention;
[0011] FIG. 2 is a partial longitudinal cross-sectional view of an
exemplary regulator valve of the brake system shown in FIG. 1;
[0012] FIG. 3 is a schematic partial view showing a linear
differential pressure valve of a brake system according to a second
embodiment of the present invention;
[0013] FIG. 4 is a schematic partial view showing a regulator valve
of a brake system according to a third embodiment of the present
invention;
[0014] FIG. 5 is a schematic partial view showing a regulator valve
of a brake system according to a fourth embodiment of the present
invention;
[0015] FIG. 6 is a schematic view of a brake system having a
regulator valve according to a fifth embodiment of the present
invention;
[0016] FIG. 7 is a schematic view of a brake system having a
regulator valve according to a sixth embodiment of the present
invention;
[0017] FIG. 8 is a schematic view of a brake system having a
regulator valve according to a seventh embodiment of the present
invention;
[0018] FIG. 9 is a schematic view of a brake system having a
regulator valve according to an eighth embodiment of the present
invention;
[0019] FIG. 10 is a schematic view of a brake system having a
regulator valve according to a ninth embodiment of the present
invention;
[0020] FIG. 11 is a schematic view of a brake system according to
other embodiment of the present invention;
[0021] FIG. 12 is a schematic view of a brake system according to
still other embodiment of the present invention;
[0022] FIG. 13 is a schematic view of a brake system according to
still other embodiment of the present invention;
[0023] FIG. 14 is a schematic view of a brake system according to
still other embodiment of the present invention; and
[0024] FIG. 15 is a schematic view of a brake system according to
still other embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] A brake system according to a first embodiment of the
present invention will now be described with reference to FIG. 1. A
booster 2 is connected to a brake pedal 1 via a rod. When the brake
pedal 1 is depressed by a vehicle driver, the booster 2 multiplies
a force applied on the brake pedal 1 with the aid of a negative
pressure developed in an intake manifold of an engine and transmits
the multiplied force to a master cylinder 3 until the negative
pressure in the intake manifold reaches a dead point negative
pressure. Primary and secondary chambers 6, 5 are arranged in the
master cylinder 3 and are fluid-tightly separated from each other
by pistons. The primary and secondary chambers 6, 5 are connected
to a master cylinder reservoir 4 through a center valve (not
shown).
[0026] Furthermore, the primary and secondary chambers 6, 5 are
connected to corresponding vehicle wheels (a right front wheel FR;
a left front wheel FL, a right rear wheel RR and a left rear wheel
RL) through a brake line system 100.
[0027] The brake line system 100 includes first and second brake
circuits 11, 21. The first brake circuit 11 connects the secondary
chamber 5 to a wheel cylinder 7 of the right front wheel FR and a
wheel cylinder 8 of the left rear wheel RL. The second brake
circuit 21 connects the primary chamber 6 to a wheel cylinder 9 of
the left front wheel FL and a wheel cylinder 10 of the right rear
wheel RR.
[0028] In the first brake circuit 11, pressurization control valves
31, 32 are provided for the wheel cylinder 7 and the wheel cylinder
8, respectively, to increase and maintain the pressure within the
corresponding wheel cylinders 7, 8 during anti-skid control. A
depressurization pipeline 12 branches off between each of the
pressurization control valves 31, 32 and a corresponding one of the
wheel cylinders 7, 8. In the depressurization pipeline 12,
depressurization control valves 33, 34 are provided to decrease and
maintain the pressure within the corresponding wheel cylinders 7, 8
during the anti-skid control. The depressurization pipeline 12 is
further connected to a reservoir 35. Brake fluid reserved in the
reservoir 35 is suctioned by a pump 36 and is discharged into the
first brake circuit 11 between the pressurization control valves
31, 32 and a linear differential pressure valve 101 (which will be
described in great detail below) through a damper 37 and an orifice
38. The pump 36 is driven by a motor 30. The motor 30 also drives a
pump 46 arranged in the second brake circuit 21. Check valves 40,
39 are inserted at a suction port and a discharge port of the pump
36, respectively.
[0029] The linear differential pressure valve 101 is inserted in
the first brake circuit 11 between the secondary chamber 5 and the
pressurization control valves 31, 32. The linear differential
pressure valve 101 can adjust a differential pressure between the
master cylinder side and the wheel cylinder side by varying the
amount of restriction of the pipeline to vary the amount of the
flow in consistent with the amount of electric power supplied to
the linear differential pressure valve 101. A one way valve 103 is
arranged in parallel with the linear differential pressure valve
101. The one way valve 103 allows flow of brake fluid only in the
direction from the master cylinder side to the wheel cylinder side
when a pressure within the secondary chamber 5 reaches a
predetermined level.
[0030] A suction pipeline 13 branches off between the secondary
chamber 5 and the linear differential pressure valve 101 and
extends to the suction port of the pump 36. A suction valve 102,
which is normally closed, is inserted in the suction pipeline 13. A
check valve 105 is inserted between the suction port of the pump 36
and the reservoir 35 to prevent flow of the brake fluid from the
master cylinder side to the reservoir 35 through the suction
pipeline 13 during the brake assist operation. The prevention of
the flow of the brake fluid to the reservoir 35 by the check valve
105 allows depressurization control of the wheel cylinder pressure
during the anti-skid control that is conducted during the brake
assist operation.
[0031] A hydraulic pressure sensor 300 is arranged between the
secondary chamber 5 and the linear differential pressure valve 101
in the first brake circuit 11. The hydraulic pressure sensor 300
substantially measures a master cylinder pressure. That is, when
the brake pedal is depressed, the same pressure is generated in
each of the primary and secondary chambers 6, 5. The hydraulic
pressure sensor 300 measures this pressure.
[0032] The above-described pressurization control valve 31, 32, the
depressurization control valve 33, 34 and the suction valve 102 are
two-position valves and are fixed in the position shown in FIG. 1
during a non-braking period and a normal braking period (i.e., a
period during which the anti-skid control, the brake assist control
or the like is not conducted) as well as during a de-energization
period of these valves. The linear differential pressure valve 101
is also normally in a communicated state while it is not
energized.
[0033] The second brake circuit 21 has a similar construction as
that of the first brake circuit 11. Pressurization control valves
41, 42, depressurization control valves 43, 44, a depressurization
pipeline 22, a reservoir 45, a pump 46, check valves 49, 50, 209, a
suction pipeline 23, a suction valve 207, a damper 47 and an
orifice 48 of the second brake circuit 21 correspond with and act
like the pressurization control valves 31, 32, the depressurization
control vales 33, 34, the depressurization pipeline 12, the
reservoir 35, the pump 36, the check valves 39, 40, 105, the
suction pipeline 13, the suction valve 102, the damper 37 and the
orifice 38 of the first brake circuit 11, respectively.
[0034] A regulator valve 201 acting as a mechanical regulator
mechanism is arranged in the second brake circuit 21 between the
primary chamber 6 and a branch point where the second brake circuit
21 branches to the wheel cylinder 9 of the left front wheel FL and
the wheel cylinder 10 of the right rear wheel RR. A one way valve
208 is arranged in parallel with the regulator valve 201. Similar
to the one way valve 103 of the first brake circuit 11, the one way
valve 208 can apply the master cylinder pressure to the wheel
cylinders 9, 10 by bypassing the regulator valve 201, for example,
when the vehicle driver depresses the brake pedal during the
traction control.
[0035] The regulator valve 201 includes first to third port
passages A, B, C communicated with an interior of a regulator
chamber 202. The first port passage A receives the master cylinder
pressure from the primary chamber 6. A valve seat 203 and a valve
element 204 are arranged at the first port passage A side of the
regulator chamber 202. A piston 205, to which the valve element 204
is secured by caulking, welding or the like, is urged toward the
third port passage C by a spring 206.
[0036] The second port passage B is communicated to the first port
passage A through the regulator chamber 202 while the valve element
204 is lifted from the valve seat 203. The second port passage B is
communicated to the wheel cylinders 9, 10.
[0037] The third port passage C is communicated to a regulator
pipeline 25. The regulator pipeline 25 is connected to the first
brake circuit 11 at a connection point a between the linear
differential pressure valve 101 and the pressurization control
valves 31, 32 in the first brake circuit 11.
[0038] The piston 205 has a seal 205a for fluid-tightly separating
a second side 202b (communicated with the first and second port
passages A, B) of the regulator chamber 202 and a first side 202a
(communicated with the third port passage C) of the regulator
chamber 202.
[0039] An exemplary structure of the regulator valve 201 is shown
in FIG. 2. The above-described brake line system 100 is
manufactured by forming pipelines in a housing 150 made, for
example, of aluminum and then fitting various valves, reservoirs
and the like to the housing 150. The regulator valve 201 is also
fitted to the housing 150.
[0040] The regulator chamber 202 is formed by a recess 150a defined
in the housing 150. The piston 205 and the seal 205a are arranged
to slide along the inner side-wall surface of the regulator chamber
202 in the housing 150. The first and second port passages A, B are
formed in the inner side-wall surface of the recess 150a, and the
third port passage C is formed in a bottom-wall surface of the
recess 150a.
[0041] The seat valve unit 210 including the valve seat 203 is
arranged closer to the entry opening (left side of FIG. 2) of the
recess 150a than the piston 205 and is secured to the housing 150
via a guide 211 having a hollow part. The seat valve unit 210 is
press fitted into the hollow part of the guide 211 that is in turn
secured to the housing 150 by caulking. With this arrangement, the
seat valve unit 210 is secured to the housing 150 along with the
guide 211. The guide 211 is caulked to the housing 150 at two
points, i.e., at an outer peripheral part and a distal end step
211b of the guide 211. The caulking at the outer peripheral part of
the guide 211 is achieved by caulking portion of the housing 150 to
a channel 211a formed along the outer peripheral surface of the
guide 211. The caulking at the outer peripheral part of the guide
211 secures the guide 211 to the housing 150 and seals the first
port passage A from the exterior of the housing 150. Caulking of
the distal end step 211b of the guide 211 to the housing 150 seals
between the first port passage A and the second port passage B at
the outer peripheral surface of the guide 211.
[0042] A communication passage 212 extends through the outer
peripheral wall of the guide 211 to communicate the hollow part of
the guide 211 to the exterior of the guide 211. The brake fluid
pressure of the master cylinder 3 is conducted to the piston 205
via the communication passage 212. A filter 213 is arranged to
cover the communication passage 212 around the outer peripheral
surface of the guide 211 to prevent foreign debris from entering
the regulator valve 201. The above-described one way valve 208 is
constituted by a valve seat 208a arranged in the seat valve unit
210 and a ball valve 208b provided adjacent to the valve seat
208a.
[0043] A filter 214 is arranged between the seat valve unit 210 and
the piston 205 to cover the second port passage B. The filter 214
prevents foreign debris from entering the regulator valve 201 and
also acts as a mechanical stopper for the ball valve 208b of the
one way valve 208.
[0044] The above-described regulator valve 201 can be applied to
the brake system in accordance with the present embodiment.
[0045] Operations of the brake system having the above-described
construction will now be described.
[0046] While the brake pedal 1 is not depressed, the valve element
of each described valve is at the position shown in FIG. 1, and the
valve element 204 of the regulator valve 201 is being lifted from
the valve seat 203.
[0047] When the brake pedal 1 is depressed by the vehicle driver,
the same master cylinder pressure is developed in each of the
primary and secondary chambers 6, 5 of the master cylinder 3. The
master cylinder pressure is conducted to the wheel cylinders 7, 8
as well as to the wheel cylinders 9, 10. The master cylinder
pressure is conducted to the wheel cylinders 9, 10 through the
second brake circuit 21 via the first port passage A of the
regulator valve 201. The conduction of the master cylinder pressure
via the first port passage A is allowed since the piston 205 is
urged toward the third port passage C by the spring 206.
[0048] When the anti-skid control is carried out, the respective
wheel cylinders 7-10 are independently pressure-controlled by the
corresponding pressurization control valves 31, 32, 41, 42 and the
corresponding depressurization control valves 33, 34, 43, 44. Also,
the motor 30 is driven to drive the pumps 36, 46 to recirculate the
brake fluid reserved in the reservoirs 35, 45 back to the master
cylinder 3. The linear differential pressure valve 101 and the
suction valves 102, 207 are in the position shown in FIG. 1 while
these valves are not energized. Furthermore, in the regulator valve
201, the piston 205 is still urged toward the third port passage C
located on the right side of the FIG. 1 by the spring force since
the hydraulic pressure in the connection point .alpha. is the same
as the hydraulic pressure in the second port passage B.
[0049] When the brake assist control is carried out, the motor 30
is driven, and the suction valves 102, 207 are energized and are
thereby opened. Furthermore, the linear differential pressure valve
101 is also energized. Thus, the pump 36 suctions the brake fluid
from the secondary chamber 5 and discharges it between the linear
differential pressure valve 101 and the pressurization control
valves 31, 32. In the brake assist control, the panic brake pedal
depression by the vehicle driver is detected when at least one of a
master cylinder pressure gradient, a wheel acceleration, a vehicle
body deceleration and a master cylinder pressure exceeds its
predetermined value. The hydraulic pressure measured with the
hydraulic pressure sensor 300 is regarded as the vehicle driver's
will to depress the brake pedal 1, and the amount of the electric
power supplied to the linear differential pressure valve 101 is
controlled based on a hydraulic pressure measured with the
hydraulic pressure sensor 300. For example, as the hydraulic
pressure measured with the hydraulic pressure sensor 300 rises, the
amount of the electric power is correspondingly increased, and vice
versa. In this way, if the brake pedal is depressed deeply by the
vehicle driver, a large differential pressure is generated by the
linear differential pressure valve 101. Consistent with the brake
pedal depression, the pressure in the wheel cylinders 7, 8 is kept
higher than the pressure in the master cylinder 3.
[0050] This pressure is also conducted from the connection point
.alpha. to the first side 202a of the regulator chamber 202 through
the regulator pipeline 25 and the third port passage C.
[0051] Similarly, in the second brake circuit 21, the pump 46
suctions the brake fluid from the primary chamber 6 and discharges
it. At this stage, the brake fluid is recirculated to the primary
chamber 6 of the master cylinder 3 through the second port passage
B and the first port passage A of the regulator valve 201, and
thereby the pressure in the wheel cylinders 9, 10 will never get a
pressure higher than the master cylinder pressure.
[0052] However, the pressure conducted from the connection point
.alpha. to the regulator chamber 202 through the third port passage
C is higher than the wheel cylinder pressure of the second brake
circuit 21, so that the piston 205 is moved toward the valve seat
203 of the first port passage A by overcoming the spring force of
the spring 206 and the wheel cylinder pressure of the second brake
circuit 21. When the valve element 204 is seated against the valve
seat 203, the flow of the brake fluid from the wheel cylinders 9,
10 to the primary chamber 6 is prevented, so that the pressure in
the wheel cylinders 9, 10 is increased. At this stage, the pressure
in the wheel cylinders 7, 8 is equal to a sum of the pressure in
the wheel cylinders 9, 10 and the spring force of the spring 206.
However, the spring force of the spring 206 can be very small since
the spring force of the spring 206 is only that required to
overcome the frictional resistance between the seal member of the
piston 205 and the opposing inner wall surface of the housing 150
to urge the piston 205 toward the right side of FIG. 2. As a
result, the valve element 204 will be kept seated against the valve
seat 203 until the brake fluid pressure in the wheel cylinders 7, 8
becomes substantially equal to the brake fluid pressure in the
wheel cylinders 9, 10.
[0053] The operation of the brake system in accordance with the
present embodiment will be further discussed in connection with a
situation where a differential pressure between the pressure in the
wheel cylinders 9, 10 and the pressure in the wheel cylinders 7, 8
is developed due to, for example, a difference in discharge
capacity between the pump 46 and the pump 36.
[0054] First, it is assumed that the discharge capacity of the pump
46 becomes higher than that of the pump 36, and thereby the
pressure in the wheel cylinders 9, 10 in the second brake circuit
21 becomes higher than the pressure in the wheel cylinders 7, 8 in
the first brake circuit 11. In such a case, the higher pressure is
supplied to the regulator chamber 202 through the second port
passage B, and thereby the pressure in the second port passage B
becomes higher than the pressure supplied from the regulator
pipeline 25. Thus, the piston 205 is urged toward the right side of
FIG. 2 to lift the valve element 204 from the valve seat 203. Then,
when the pressure in the wheel cylinders 9, 10 is supplied to the
primary chamber 6 and becomes equal to the pressure in the wheel
cylinders 7, 8, the valve element 204 is seated against the valve
seat 203 to dicommunicate the primary chamber 6 from the wheel
cylinders 9, 10.
[0055] Then, it is assumed that the discharge capacity of the pump
36 becomes higher than that of the pump 46, and thereby the
pressure in the wheel cylinders 7, 8 in the first brake circuit 11
becomes higher than the pressure in the wheel cylinders 9, 10 in
the second brake circuit 21. In such a case, the higher pressure is
supplied from the connection point .alpha. to the regulator chamber
202 through the third port passage C. Thus, the piston 205 is moved
toward the left side of FIG. 2, so that the valve element 204 is
seated against the valve seat 203 to dicommunicate the primary
chamber 6 from the wheel cylinders 9, 10. As a result, the pressure
in the second side 202b of the regulator chamber 202 is increased
by the pump 46 until it becomes substantially equal to the pressure
in the first side 202a of the regulator chamber 202. As described
above, the difference in the discharge capacity between these pumps
36, 46 is due to, for example, the difference in the amount of the
supplied electric power (for example, due to a difference in
resistance of the conductive lines) between these pumps 36, 46
and/or a difference in the sealing performance between these pumps
36, 46. Thus, there is a difference in the ability to raise the
pressure between these pumps 36, 46, but there is no significant
difference in the maximum discharge pressure (or the maximum
pressure (bar) in each pipeline developed by each pump 36, 46)
between these pumps 36, 46. Furthermore, each pump 36, 46 generally
has a maximum discharge pressure of 250 bar. With this maximum
discharge pressure, it is possible to substantially eliminate a
difference between the first brake circuit 11 and the second brake
circuit 21.
[0056] As discussed above, even if a differential pressure is
generated between the wheel cylinders 7, 8 of the first brake
circuit 11 and the wheel cylinders 9, 10 of the second brake
circuit 21, it is possible to substantially eliminate the
differential pressure by use of the regulator valve 201 and the
regulator pipeline 25.
[0057] In the described embodiment, the regulator valve 201 is
provided for the primary chamber 6, and the linear differential
pressure valve 101 is provided for the secondary chamber 5.
Alternatively, the regulator valve 201 can be provided for the
secondary chamber 5, and the linear differential pressure valve 101
can be provided for the primary chamber 6.
[0058] The use of the mechanical regulator valve 201 as in the
first embodiment provides higher reliability than an electrical
regulator valve that electrically compensates the differential
pressure between the first and second brake circuits. Furthermore,
the seal provided by the piston 205 substantially separates between
the first brake circuit 11 and the second brake circuit 21. Thus,
even if the brake fluid leaks out from the pipeline in the first
brake circuit 11 due to a mechanical damage to the pipeline, and
thereby the wheel cylinder pressure cannot be provided through the
first brake circuit 11, the wheel cylinder pressure can be provided
from the master cylinder through the second brake circuit 21 to
ensure the sufficient wheel braking force. Furthermore, in the
event of a failure (damage) of the first or second brake circuit
11, 21, it is important to provide means for applying a large
enough hydraulic pressure to the remaining one of the first and
second brake circuits 11, 21 by a volume of the brake fluid in the
primary chamber 6 or the secondary chamber 5 of the master cylinder
3 even if the piston 205 is urged to the left or right end position
in FIG. 2. In other words, each of a maximum volume of the
hydraulic fluid in the first side 202a of the regulator chamber 202
and a maximum volume of the hydraulic fluid in the second side 202b
of the regulator chamber 202 should be sufficiently smaller than
either a volume of the hydraulic fluid in the primary chamber 6 or
a volume of the hydraulic fluid in the secondary chamber 5,
whichever is smaller. However, the volume of the primary chamber 6
and the volume of the secondary chamber 5 are normally the
same.
Second Embodiment
[0059] In this embodiment, the linear differential pressure valve
101 of the first embodiment is replaced with other type of
arrangement. Since other components in this embodiment are the same
as those shown in FIG. 1, these components are not further
discussed herein. FIG. 3 shows the arrangement that is used in
place of the linear differential pressure valve 101 of FIG. 1. As
shown in FIG. 3, the linear differential pressure valve 101 and the
check valve 103 arranged in the first brake circuit 11 in the first
embodiment are replaced with a two position valve 110, which is
shiftable between a communicating position and a blocking position,
a check valve 113 and a differential pressure check valve 114.
[0060] In this arrangement, while the two position valve 110 is
energized, a differential pressure that is mechanically set by the
differential pressure check valve 114 is developed between the
master cylinder pressure and the pressure in the wheel cylinders 7,
8 to make the pressure in the wheel cylinders 7, 8 higher than the
master cylinder pressure by the amount of the differential
pressure.
Third Embodiment
[0061] In this embodiment, the regulator valve 201 of the first
embodiment is replaced with other type of arrangement. Since other
components in this embodiment are the same as those shown in FIG.
1, these components are not further discussed herein. FIG. 4 shows
the arrangement that is used in place of the regulator valve 201
shown in FIG. 1. As shown in FIG. 4, the mechanical regulator valve
201 in the first embodiment is replaced with a valve 301 capable of
electrically maintaining the pressure in the wheel cylinders 9, 10
to be higher than the pressure in the primary chamber 6. That is,
the hydraulic pressure in the connection point a is measured, for
example, with a pressure sensor, and a signal indicative of the
measured hydraulic pressure is inputted from the pressure sensor to
the valve 301. Based on the signal inputted to the valve 301, the
differential pressure between the pressure in the wheel cylinders
9, 10 and the pressure in the primary chamber 6 in the second brake
circuit 21 is generated. With this arrangement, it is possible to
compensate the differential pressure between the first and second
brake circuits 11, 21 induced, for example, by the difference in
the capacity between the pump 36 and the pump 46.
Fourth Embodiment
[0062] FIG. 5 shows a longitudinal cross-sectional view of a
regulator valve 401 according to the present embodiment used in
place of the regulator valve 201 of the first embodiment. Since
other components in this embodiment are the same as those shown in
FIG. 1, these components are not further discussed herein.
Although, only one seal means (seal 205a) is provided in the
regulator valve 201 in the first embodiment, two seal means (first
and second seals 205a, 205b) that are arranged in series are
provided in the regulator valve 401 in this embodiment. That is,
the seal that fluid-tightly separates between the third port
passage C and the first and second port passages A, B is
constituted by the first and second seals 205a, 205b. With this
construction, even if one of the two seals 205a, 205b has failed
when the pipeline in one of the two brake circuits is damaged, the
remaining normal brake circuit can be used for braking action,
implementing further enhanced fail-safe backup to improve the
reliability of the brake system.
Fifth Embodiment
[0063] FIG. 6 shows an entire structure of a brake system according
to a fifth embodiment of the present invention. In the present
embodiment, a regulator valve 501 is arranged in a vertically split
brake system. Since the basic construction of the present
embodiment is the same as that of FIG. 1, similar parts are
designated by similar numerals and are not further discussed
herein.
[0064] The first brake circuit 11 is connected to the right rear
wheel RR and the left rear wheel RL. The second brake circuit 21 is
connected to the right front wheel FR and the left front wheel
FL.
[0065] Similar to the regulator valve 201 shown in FIG. 1, the
regulator valve 501 has the first to third port passages A, B, C
arranged in the regulator chamber 202 as well as the valve seat 203
and the valve element 204 that are fitted in a manner similar to
that discussed with reference to FIG. 1. However, a piston 505 of
the regulator valve 501 differs from the piston 205 shown in FIG. 1
and is made as a stepped piston. One piston surface S2 of the
stepped piston 505, which is disposed adjacent to the third port
passage C communicated with the connection point .alpha., is larger
than other piston surface S1, which is disposed in the regulator
chamber 202 adjacent to the first and second port passages A, B.
With this arrangement, the pressure in the third port passage C and
the pressure in the first port passage A are balanced only when a
wheel cylinder pressure ratio between the first and second brake
circuits reaches S2/S1 (in this instance, the spring force of the
spring 206 is assumed to be very small in comparison to the
hydraulic pressure force, so that the spring force of the spring
206 is ignored).
[0066] When the brake assist control is carried out in the
vertically split brake system, and thereby the pressure in the
wheel cylinders 7-10 becomes higher than the master cylinder
pressure, the regulator valve 501 can be used to appropriately
allocate the front wheel braking force and the rear wheel braking
force. A seal 505a, 505b is arranged at each step of the piston
505.
Sixth Embodiment
[0067] FIG. 7 shows an entire structure of a brake system according
to a sixth embodiment of the present invention. In the present
embodiment, there is provided a regulator valve 601 containing a
check valve mechanism therein. Since the basic construction of the
present embodiment is the same as that of FIG. 1, similar parts are
designated by similar numerals and are not further discussed
herein.
[0068] Within the piston 605, there is provided a check valve
spring 610 for urging a rod 611 provided with the valve element 204
toward the left side of FIG. 7. The hydraulic pressure supplied
from the second port passage B is conducted to a chamber within the
piston 605 where the check valve spring 610 is disposed. With this
construction, during a normal state, i.e., a non-braking state, a
normal braking state, an anti-skid braking state or a brake-assist
state, the piston 605 and the rod 611 are moved together.
[0069] During the brake assist control, when a pressure that is
equal to or greater than the hydraulic pressure in the connection
point .alpha. is developed in the master cylinder 3, that is, the
vehicle driver depresses the brake pedal 1 further, the rod 611
compresses the check valve spring 610 and moves toward the right
side of FIG. 7 to lift the valve element 204 from the valve seat
203, allowing conduction of, the master cylinder pressure to the
wheel cylinders 9, 10.
Seventh Embodiment
[0070] FIG. 8 shows an entire structure of a brake system according
to a seventh embodiment of the present invention. The brake system
according to the present embodiment is substantially the same as
that of the first embodiment except that the spring 206 of the
regulator valve 201 is eliminated.
[0071] In the present embodiment, the force comparable with the
spring force of the spring 206 of the first embedment is
implemented by a restoring force of the seal 205a made of elastic
material, such as rubber, generated after deformation of the seal
205a.
[0072] That is, the seal 205a can slide along the inner side-wall
surface of the regulator chamber 202 as the piston 205 moves.
However, before the seal 205a initiates this sliding motion, the
seal 205a is deformed and thereby provides the restoring force. As
a result, when the piston 205 moves toward the left side of FIG. 8,
the restoring force is generated by the seal 205a, so that the
piston 205 can be pulled back toward the right side of FIG. 8 by
the restoring force of the seal 205a. The amount of the valve lift
of the valve element 204 is very small, so that the regulator valve
201 can be effectively opened or closed by the deformation of the
seal 205a without actually sliding the seal 205a along the inner
side-wall surface of the regulator chamber 202. The seal 205a and a
channel formed along the outer peripheral of the piston 205 for
accommodating the seal 205a are closely engaged with each other
without forming a gap between them in a sliding direction of the
piston 205. This arrangement advantageously allows the piston 205
to return to its initial position. This is due to the fact that if
the gap is provided between the seal 205a and the channel in a
sliding direction of the piston 205, the seal 205a moves through
the gap when the piston 205 slides, so that the piston is no longer
able to return to its initial position by the restoring force of
the seal 205a alone.
[0073] Since the spring 206 shown in FIG. 1 is eliminated in this
embodiment, the piston can be moved with a much smaller
differential pressure than the differential pressure required in
the case of the spring 206. As a result, advantageously, the
pressure in the first brake circuit 11 and the pressure in the
second brake circuit 21 can be substantially equalized, and the
number of components can be reduced.
Eighth Embodiment
[0074] FIG. 9 shows an entire structure of a brake system according
to an eighth embodiment of the present invention. The brake system
according to the present embodiment is substantially the same as
that of the fourth embodiment except that a space between the first
seal 205a and the second seal 205b is communicated to atmosphere
through a communication passage 701.
[0075] As described in connection with the fourth embodiment, the
two seals 205a, 205b are provided to ensure the sealing between the
second side 202b of the regulator chamber 202 and the first side
202a of the regulator chamber 202. However, there is a chance that
both the seals 205a, 205b fail due to, for example, a damage. In
such a case, it is advantageous to allow detection of the failure
of one seal before other seal is failed, so that an effective
countermeasure can be taken before the other seal is failed.
[0076] The communication passage 701 extends outwardly from a space
between the first seal 205a and the second seal 205b to allow
egress of the brake fluid through the communication passage 701
upon the failure of the one seal, allowing the detection of the
failure of the one seal.
[0077] In this case, although the egress of the brake fluid can be
directly detected by observing the brake fluid dropped on the
ground, the egress of the brake fluid can be also indirectly
detected based on a fluid level signal outputted from a fluid level
switch arranged in the master cylinder reservoir 4 when a brake
fluid level within the master cylinder reservoir 4 drops below a
predetermined level and thereby activates the fluid level switch.
Furthermore, the egress of the brake fluid can be also indirectly
detected based on an increase in the amount of the stroke of the
brake pedal 1 induced by the decrease in the amount of the brake
fluid.
[0078] Preferably, the brake fluid is egressed to a place where the
egress of the brake fluid has a minimum effect. The brake fluid can
be egressed, for example, into a spring chamber located at a rear
surface of an ABS reservoir, or into an intermediate air chamber
located between the pump and the motor.
Ninth Embodiment
[0079] FIG. 10 shows an entire structure of a brake system
according to a ninth embodiment of the present invention. The brake
system according to the present embodiment is substantially the
same as that of the fifth embodiment except that a space between
the first seal 505a and the second seal 505b is communicated to
atmosphere through a communication passage 701.
[0080] Even in such a case where the size difference is made
between the opposing piston surfaces S1, S2 of the piston 505, the
provision of the communication passage 701 to atmosphere can
provide advantages similar to those of the eighth embodiment.
Other Embodiments
[0081] 1. Although the present invention is discussed in connection
with the diagonally split brake system in the first embodiment and
several other embodiments, the diagonally split brake system can be
changed to a vertically split brake system. That is, the first
brake circuit 11 can be arranged for the right front wheel FR and
the left front wheel FL, and the second brake circuit 21 can be
arranged for the right rear wheel RR and the left rear wheel RL.
Furthermore, although the spring-load of the spring 206 is very
small in the first embodiment and several other embodiments, the
spring-load can be set to provide a differential pressure, which is
equal to the spring-load, between the wheel cylinder pressure of
the first brake circuit 11 and the wheel cylinder pressure of the
second brake circuit 21. That is, the spring 206 also provides a
function of a general proportional valve. If the spring load of the
spring 206 is adjusted in the above-described manner, a
predetermined difference in the braking force between the front
wheels and the rear wheels can be provided during the brake assist
operation to stabilize the vehicle body motion. During the brake
assist operation, the forward directional weight shift of the
vehicle body is greater than the normal braking operation, so that
this arrangement will provide a substantial advantage.
[0082] 2. In the fifth embodiment, although the invention is
discussed in connection with the vertically split brake system, the
discussion in the fifth embodiment can be equally applicable to the
diagonally split brake system. In such a case, although the spring
load of the spring 206 is very small so the effect of the spring
load is ignorable, the spring load of the spring 206 can be
modified as follows to more precisely control the balance of the
braking forces between the left wheel brake circuit and the right
wheel brake circuit.
[0083] That is, the wheel cylinder pressure of the first brake
circuit 11 (i.e., the pressure in the connection point .alpha.) is
set to be equal to a sum of the spring force of the spring 206 and
the wheel cylinder pressure of the second brake circuit 21 (i.e.,
the pressure conducted through the second port passage B). In this
way, the wheel cylinder pressure of the first brake circuit 11
becomes greater than the wheel cylinder pressure of the second
brake circuit 21 by the amount corresponding to the spring force of
the spring 206. However, if the sizes of the piston surfaces S1, S2
of the stepped piston 505 of FIG. 5 are appropriately selected to
eliminate the spring force of the spring 206, the wheel cylinder
pressure of the first brake circuit 11 and the wheel cylinder
pressure of the second brake circuit 21 can be equalized.
[0084] 3. Each of the above-described embodiments can be modified
as follows. As shown in FIG. 11, a hydraulic pressure sensor 801 is
inserted in the first brake circuit 11 between the pressurization
control valves 31, 32 and the linear differential pressure valve
101. Furthermore, another hydraulic pressure sensor 802 is inserted
in the second brake circuit 21 between the pressurization control
valves 41, 42 and the second port passage B of the regulator valve
201. If a differential pressure is detected based on the hydraulic
pressure values measured with the hydraulic pressure sensors 801,
802, a warning (or notification) can be given to the vehicle
driver. That is, if the regulator valve 201 (or 301, 401, 501, 601)
is failed, for example, due to presence of debris between the valve
seat 203 and the valve element 204, a differential pressure may be
generated between the wheel cylinder pressure of the first brake
circuit 11 and the wheel cylinder pressure of the second brake
circuit 21. If this has occurred, the warning may be given to the
vehicle driver. Instead of giving the warning, the brake assist
control may be interrupted or prohibited.
[0085] 4. The position of the hydraulic pressure sensor is not
limited to between the pressurization control valves 31, 32 and the
linear differential pressure valve 101 but can be between any one
of the wheel cylinders 7-10 and the corresponding one of the
pressurization control valves 31, 32, 41, 42, as shown in FIG. 12.
For example, the hydraulic pressure sensor 801 can be arranged
between the pressurization control valve 31 and the wheel cylinder
7 in the first brake circuit 11, and the hydraulic pressure sensor
802 can be arranged between the pressurization control valve 41 and
the wheel cylinder 9 in the second brake circuit 21. If a
differential pressure between the wheel cylinder pressure of the
first brake circuit 11 and the wheel cylinder pressure of the
second brake circuit 21 is measured with the hydraulic pressure
sensors 801, 802, a warning (or notification) may be given to the
vehicle driver, or alternatively the brake assist control may be
interrupted or prohibited.
[0086] 5. In each of the above-described embodiment, as shown in
FIG. 13, a differential pressure measurement pipeline 803 may be
extended out from anywhere between the pressurization control
valves 31, 32 and the linear differential pressure valve 101 in the
first brake circuit 11 to anywhere between the pressurization
control valves 41, 42 and the second port passage B of the
regulator valve 201 in the second brake circuit 21. A differential
pressure switch 804 may be inserted in the differential pressure
measurement pipeline 803. If a differential pressure between the
wheel cylinder pressure of the first brake circuit 11 and the wheel
cylinder pressure of the second brake circuit 21 is measured with
the differential pressure switch, a warning (or notification) may
be given to the vehicle driver, or alternatively the brake assist
control may be interrupted or prohibited.
[0087] 6. In the described case, as shown in FIG. 14,
alternatively, a differential pressure measurement pipeline 805 may
be extended out from anywhere between the pressurization control
valves 31, 32 and the wheel cylinders 7, 8 in the first brake
circuit 11 to anywhere between the pressurization control valves
41, 42 and the wheel cylinders 9, 10 in the second brake circuit
21. A differential pressure switch 806 may be inserted in the
differential pressure measurement pipeline 805.
[0088] 7. In each of the above-described embodiment, as shown in
FIG. 15, well known switching reservoirs 901, 902 may be used in
the place of the reservoirs 35, 45 and the suction valves 102, 207.
Each switching reservoir 901, 902 allows the brake fluid in the
master cylinder 3 to flow toward the suction port of the
corresponding pump 36, 46, thereby reducing the master cylinder
pressure. When the amount of the brake fluid in the switching
reservoir 901, 902 is above a predetermined level, the brake fluid
in the switching reservoir 901, 902 is suctioned by the pump 36,
46. When the amount of the brake fluid in the switching reservoir
901, 902 is below or equal to the predetermined level, the brake
fluid in the master cylinder 3 is suctioned by the pump 36, 46.
[0089] By use of the switching reservoir 901, 902, the brake fluid
pressure supplied to the suction port of the pump 36, 46 can be
maintained at a predetermined pressure value. As a result, when a
gear pump, such as a trochoid pump, is used as the pump 36, 46,
hydraulic pressure pulsation can be eliminated by the switching
reservoir 901, 902, so that the pressure regulating action of the
regulator valve 201 can be advantageously stabilized.
[0090] In this instance, as shown in FIG. 15, a pipe line 807 is
extended out from the master cylinder reservoir 4 to a point
between the suction port of the pump 36 and the switching reservoir
901 in the first brake circuit 11 and also to a point between the
suction port of the pump 46 and the switching reservoir 902 in the
second brake circuit 21 to allow suctioning of the brake fluid from
the master cylinder reservoir 4 by the pumps 36, 46. To prevent
back flow of the brake fluid from these points to the master
cylinder 4, check valves 903-906 are inserted in the pipe line
807.
[0091] Additional advantages and modifications will readily occur
to those skilled in the art. The invention in its broader terms is
therefore, not limited to the specific details, representative
apparatus, and illustrative examples shown and described.
* * * * *