Brake system

A brake system has wheel cylinders for producing a braking force in wheels using pressurized brake fluid transmitted through a main conduit from a master cylinder, a reservoir for storing brake fluid, a sideslip preventing device for when a sideslip state of the vehicle is detected supplying brake fluid to the wheel cylinder corresponding to a sideslip controlled wheel and producing a braking force in the sideslip controlled wheel, a first conduit used for supplying brake fluid from the reservoir to the wheel cylinders by the pump and a first valve for switching this first conduit between an open state and a closed state. The sideslip preventing device, when the sideslip state is detected during non-braking of the vehicle, makes the first valve open-state and thereby conducts supply of brake fluid through the first conduit from the reservoir to the wheel cylinder by a pump. When the sideslip state is detected during braking of the vehicle, the sideslip preventing device makes the first valve device closed-state and thereby prohibits supply of brake fluid from the reservoir to the wheel cylinder.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a vehicle brake system having a sideslip 
prevention system. 
2. Description of Related Art 
Conventionally, brake systems having a sideslip prevention system are known 
in the art. As an example of one such brake system, see the brake system 
shown in Japanese Patent Application Laid-Open No. 7-117654. A few 
fundamental components of a brake system include a master cylinder which 
produces a brake fluid pressure corresponding to a force created when a 
driver steps on the brake pedal and a low-pressure reservoir having an 
essentially atmospheric pressure which provides brake fluid to a 
self-supplying pump. Also, most brake systems have a plurality of main 
conduits for transmitting a master cylinder pressure produced in the 
master cylinder to wheel cylinders. Pressure increase control valves are 
provided in each main conduit for controlling the increase of pressure 
applied to the wheel cylinders. Also provided in each main conduit are 
pressure decrease control valves that control the reduction of pressure in 
the wheel cylinders. The common brake system has a conduit which connects 
the self-supplying pump to a brake fluid delivery section between the 
pressure increase control valve and the pressure decrease control valve to 
supply brake fluid from the self-supplying pump, and a control valve for 
cutting off the master cylinder from the brake fluid delivery section when 
the pump draws and delivers brake fluid. 
Brake systems have been modified to prevent or control sideslip. In 
sideslip prevention control, or trace characteristic increase control, 
when not braking, the self-supplying pump draws brake fluid directly from 
the low-pressure reservoir and delivers the brake fluid toward the wheel 
cylinders, thereby increasing the wheel cylinder pressure. When the driver 
begins to brake while in the process of sideslip prevention control, first 
a master cylinder pressure resulting from the pedal operation is applied 
to the wheel cylinders. After that, the master cylinder and the brake 
fluid delivery section are cut off by the control valve. As a result, the 
master cylinder pressure is sealed into the conduits on the wheel cylinder 
side. In this state, brake fluid is pumped to a wheel cylinder of a 
control object wheel. 
However, in the above-described brake system, the brake fluid pressure 
formed in the conduits on the wheel cylinder side may become larger than 
the pressure formed by the brake fluid supplied from the port of the 
master cylinder in response to the brake pedal operation. For example, 
when sideslip control is carried out from the application of the brake 
pedal, a pressure resulting from a brake fluid amount supplied from the 
reservoir is added to the master cylinder pressure produced as a result of 
applying the brake pedal. Because of the additional pressure from the 
reservoir, the wheel cylinder pressure is higher than the master cylinder 
pressure. 
In this case, after control termination counterflow of brake fluid 
accompanying brake fluid from the reservoir is carried out simultaneously, 
a large brake fluid pressure is applied to the port or seal parts of the 
master cylinder. Consequently, the performance characteristics of the 
master cylinder part or seal deteriorates. 
Also, when rising brake fluid pressure inside the master cylinder due to 
brake fluid counterflowing occurs simultaneously with when the driver 
steps on the brake, the brake pedal may become difficult to depress. 
Some vehicle brake systems have two piping systems in order to have both a 
sideslip prevention system and an anti-lock brake system as shown in 
Japanese Patent Application Laid-Open No. 6-87426. In this type of brake 
system, two pumps are provided to carry out sideslip prevention control 
and for supplying brake fluid from a reservoir to a first piping system 
and a second piping system. Braking forces are produced in the controlled 
wheels by driving these two pumps. 
However, using separate pumps for a first piping system and a second piping 
system increases the complexity of the piping arrangement. Therefore, 
there is a demand for the ability to carry out sideslip prevention control 
with a single pump. In this case, applying braking forces to both the 
wheels in the first piping system and the wheels in the second piping 
system by means of a pump supplying brake fluid in a master reservoir to 
the first piping system is conceivable. That is, when in sideslip 
prevention control, the system increases the brake fluid pressure of the 
first piping system by delivering brake fluid supplied from the master 
reservoir to the first piping system, whereby a braking force is produced 
in the controlled wheel. If the controlled wheel is on the second piping 
system during sideslip prevention control, brake fluid supplied from the 
master reservoir is delivered to the first piping system. Delivering brake 
fluid to the first piping system increases the brake fluid pressure of a 
primary chamber of a master cylinder. The brake fluid pressure of a 
secondary chamber of the master cylinder is also increased due to the 
pressure increase within the primary chamber, whereby the brake fluid 
pressure of the second piping system is increased to produce a braking 
force in the controlled wheel. 
However, because the primary chamber and the master reservoir are connected 
through an orifice, even when the primary chamber is increased in pressure 
there is a limit to that pressure increase. Consequently, even if the 
secondary chamber is increased in pressure along with pressure increase of 
the primary chamber, it is necessary to increase the brake fluid pressure 
in the second piping system by means of a pump for ABS control or the like 
thereafter. This deficiency increases the complexity of such a braking 
system. 
SUMMARY OF THE INVENTION 
The present invention was made in view of the deficiencies in the related 
art mentioned above. It is a first object of the invention to provide a 
brake system wherein during sideslip prevention control, the 
responsiveness to sideslip prevent control is good and the problems caused 
by excess brake fluid supplied from the reservoir are eliminated. 
A second object of the present invention is to make it possible to carry 
out sideslip prevention control using only one pump of one piping system 
and to simplify the piping construction. 
To achieve the above-mentioned first object, a brake system of the present 
invention comprises a wheel braking force producing device for producing a 
braking force in wheels using pressurized brake fluid transmitted through 
a main conduit from a brake fluid pressure producing source, a 
low-pressure reservoir for storing brake fluid, and a sideslip preventing 
device. When a sideslip state of the vehicle is detected, the sideslip 
preventing device supplies brake fluid from the brake fluid pressure 
producing source to the wheel braking force producing device corresponding 
to a controlled wheel. This supply of brake fluid produces a braking force 
in the controlled wheel. The brake system of the present invention further 
comprises a first conduit that supplies brake fluid from the low-pressure 
reservoir to the wheel braking force producing device and a first valve 
device that switches this first conduit between an open state and a closed 
stated. 
When the sideslip state is detected during non-braking of the vehicle, the 
sideslip preventing device opens the first valve device to thereby supply 
brake fluid through the first conduit from the reservoir to the wheel 
braking force producing device corresponding to the controlled wheel. When 
the sideslip state is detected during braking, the sideslip preventing 
device closes the first valve device to prevent the reservoir from 
supplying brake fluid to the wheel braking force producing device 
corresponding to the controlled wheel. 
Using this approach, the responsiveness of the sideslip prevention control 
is good because brake fluid is drawn from the reservoir. Further, during 
braking, when a brake fluid pressure is produced in the brake fluid 
pressure producing source, it is possible to prevent brake fluid from 
being drawn from the reservoir, thereby avoiding drawing excess brake 
fluid from the reservoir. The arrangement according to the present 
invention prevents excess brake fluid from counterflowing to the brake 
fluid pressure producing source, which protects the brake fluid pressure 
producing source and makes it easier for the driver to depress the brake 
pedal. 
The present invention may have a pressure detecting device for detecting a 
brake fluid pressure in the brake fluid pressure producing source. The 
sideslip preventing device, when the pressure detected by the pressure 
detecting device is smaller than a predetermined pressure, and even if the 
sideslip state has been detected during braking, may open the first valve 
device and supply brake fluid through the first conduit. In this manner, 
when the pressure in the brake fluid pressure producing source is smaller 
than a predetermined pressure, it is not possible to supply enough brake 
fluid using only the brake fluid pressure producing source. Therefore, 
even during braking, when the pressure in the brake fluid pressure 
producing source is smaller than the predetermined pressure, supplying 
brake fluid from the reservoir side improves the responsiveness of 
sideslip prevention control. 
The present invention may have a second conduit which supplies brake fluid 
from the brake fluid pressure producing source to the wheel braking force 
producing device and a pump for delivering brake fluid supplied through 
the first conduit and the second conduit toward the wheel braking force 
producing device. By providing the pump which can deliver brake fluid 
supplied through both the first conduit and the second conduit toward the 
wheel braking force producing device, it is possible to use the same pump 
required for drawing brake fluid from each of these. This arrangement 
decreases the complexity of the system and reduces production costs. 
The present invention may have an accelerating slip preventing device for 
producing a braking force in the driving wheels when an accelerating slip 
state of the vehicle is detected while not braking. This accelerating slip 
preventing device opens the first valve device and the second valve device 
and supplies brake fluid, which is supplied from the reservoir through the 
first conduit, from the pump by way of the second valve device to the 
brake fluid pressure producing source. It is to be noted that the second 
valve device is disposed between the brake fluid pressure producing source 
and the wheel braking force producing device. That is, when the brake 
fluid pressure in the brake fluid pressure producing source is small, it 
is not easy for the pump to draw brake fluid from this brake fluid 
pressure producing source. Therefore, by supplying brake fluid from inside 
the reservoir to the brake fluid pressure producing source by means of the 
pump, it is possible to increase the brake fluid pressure in the brake 
fluid pressure producing source. As a result, this facilitates drawing 
brake fluid from the brake fluid pressure producing source. 
In the present invention, brake fluid that the pump delivers may be 
supplied to a first chamber of the brake fluid pressure producing source. 
A first brake fluid pressure in the first chamber can be regulated on the 
basis of this supplied brake fluid. By supplying brake fluid that the pump 
delivers to the first chamber of the brake fluid pressure producing source 
in this way, it is possible to regulate the first brake fluid pressure of 
the first chamber. As a result, a second brake fluid pressure may be 
produced which is equal to the first brake fluid pressure in a second 
chamber of the brake fluid pressure producing source. On the basis of this 
second brake fluid pressure, a brake fluid pressure in a second wheel 
cylinder through another piping system may be provided. 
With this arrangement, because a brake fluid pressure in the second wheel 
cylinder is produced even when the brake pedal is not depressed, it is 
possible to execute automatic braking during non-braking. 
Also, a first orifice connected to the first chamber of the brake fluid 
pressure producing source may be provided in the present invention. If the 
first brake fluid pressure in the first chamber is low when compared to 
the force with which the driver steps on the brake pedal, the first 
orifice closes. to the pedal stepping force the first brake fluid pressure 
is high. The first orifice opens when the first brake fluid pressure is 
high. As a result, it is possible to regulate the first brake fluid 
pressure to a pressure corresponding to the pedal stepping force. 
In this case, when the driver applies a small amount of pressure to the 
brake pedal, it is possible to produce a brake fluid pressure in the first 
and second wheel cylinders by means of the first brake fluid pressure 
generated in the first chamber. Therefore, the pedal stroke amount may be 
shortened. 
When a master cylinder is used as the brake fluid pressure producing 
source, opening and closing of the first orifice is carried out by a 
master piston provided in the master cylinder. 
The present invention may have a pressure detecting device for detecting a 
brake fluid pressure in the brake fluid pressure producing source. On the 
basis of a detection result of the pressure detecting device an amount of 
brake fluid supplied to the first chamber may be duty-controlled. If the 
brake fluid amount supplied to the first chamber is duty-controlled on the 
basis of the detection result of the pressure detecting device in this 
way, it is possible to carry out good brake operation on the basis of the 
state of the vehicle and the like. 
In the present invention, particularly during automatic braking when the 
driver has not initiated a braking operation, brake fluid can be supplied 
to the first chamber and/or the second chamber by a brake fluid supplying 
device such as a pump. A brake fluid pressure is simultaneously applied to 
the wheel cylinder side to produce a wheel braking force. Because at this 
time a pressure-regulating action is carried out so that the first chamber 
and the second chamber have the same brake-fluid pressure, it is possible 
to apply a substantially equal brake fluid pressure to the first and 
second wheel cylinders. The first chamber and the second chamber are for 
example a primary chamber and a secondary chamber in a master cylinder. 
The primary chamber and secondary chamber of a master cylinder may be 
provided for first and second brake piping systems. Along with vehicle 
braking corresponding to a pedal operation of a driver, brake fluid is 
drawn by a pump and force-fed to the first brake piping system including 
the primary chamber. As a result, the brake fluid pressure of the primary 
chamber increases and the primary chamber enlarges so that the pedal 
stepping force of the driver and the pressure of the primary chamber 
become balanced. Along with this enlarging of the primary chamber an 
operation of whether or not brake fluid is allowed to escape through a 
passage leading to a master reservoir arises. At this time the primary 
chamber and the secondary chamber become substantially the same pressure 
and also a brake fluid pressure equal to the first brake piping system is 
applied to the second brake piping system. Along with enlargement of the 
primary chamber, the pedal stepping stroke for the driver shortens. 
To achieve the above-mentioned second object, the present invention 
comprises a pump for drawing brake fluid from a reservoir and delivering 
the brake fluid to a first conduit connecting a primary chamber of a brake 
fluid pressure producing source and a first wheel braking force generating 
device and a connection control valve for controlling the open/closed 
state of a connecting passage connecting the primary chamber and the 
reservoir. When a braking force of a controlled wheel is produced 
according to a sideslip state by means of a first wheel braking force 
producing device, second pressure increasing control valve disposed in a 
second conduit connecting a secondary chamber of the brake fluid pressure 
producing source and a second wheel braking force producing device is 
closed. As a result, brake fluid is supplied to first wheel braking force 
producing device without brake fluid supplied to the second wheel braking 
force producing device. When a braking force in the controlled wheel is 
produced by means of the second wheel braking force producing device, the 
connection control valve and the first pressure increase control valve are 
closed. As a result, brake fluid is supplied only to the second wheel 
braking force producing device. 
By providing a connection control valve in a passage connecting the 
reservoir and the primary chamber of the brake fluid pressure producing 
device, even when producing a braking force of the controlled wheel by 
means of the second wheel braking force producing device, it is possible 
to produce a braking force in the controlled wheel by driving the pump and 
thereby carry out sideslip prevention control. That is, when brake fluid 
is delivered by the pump to the first conduit, because it is possible to 
increase the brake fluid pressure in the primary chamber by means of this 
delivered brake fluid, along with the pressure increase of this primary 
chamber, the brake fluid pressure of the secondary chamber increases. 
Consequently, it is possible to supply brake fluid to the second wheel 
braking force producing device according to the increase of this brake 
fluid pressure. Therefore, the second wheel braking force producing device 
can produce a braking force in the controlled wheel. By this means, it is 
possible to carry out sideslip prevention control only by driving a single 
pump and it is possible to achieve simplification of the piping 
construction. 
The present invention may comprise a pressure detecting device for 
detecting a brake fluid pressure in at least one of the first conduit and 
the second conduit. When the brake fluid pressure detected by the pressure 
detecting device is higher than a brake fluid pressure used for sideslip 
prevention control, the system determines that the driver applied the 
brake. Therefore, a braking force is produced in the controlled wheel (51) 
on the basis of a brake fluid pressure in the brake fluid pressure 
producing device which is increased according to a braking operation of 
the driver. 
Because the first conduit and the second conduit connect the first and 
second wheel braking force producing devices, if it is determined whether 
or not the braking operation is being made according to the brake fluid 
pressure detected in these conduits, it is possible to carry out sideslip 
prevention control corresponding to the brake fluid pressure of the first 
and second wheel braking force producing devices. That is, because the 
brake fluid pressure of the first and second wheel braking force producing 
devices is related to the road surface .mu. in sideslip prevention 
control, it is possible to carry out sideslip prevention control 
corresponding to the road surface .mu.. If a braking force can be produced 
in the controlled wheel with the brake fluid pressure in the brake fluid 
pressure producing device, when the braking operation is detected it is 
possible to produce a braking force in each wheel corresponding to the 
braking operation of the driver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to embodiments 
shown in the drawings. 
[First Embodiment] 
FIG. 1 is a diagram of a hydraulic circuit in a brake system according to 
the first embodiment. This brake system has a side slip prevention system, 
an anti-lock braking system ("ABS"), and a traction control system 
("TRC"). 
The basic construction of the brake system shown in this embodiment will 
now be described with reference to FIG. 1. In this embodiment, a brake 
system is applied to a rear wheel drive four wheeled vehicle having two 
piping systems (front and rear piping). A front wheel piping system 
controls brakes of the left and right front wheels and a rear wheel piping 
system controls brakes of the left and right rear wheels. 
As shown in FIG. 1, a driver applies a brake pedal 1 to apply a braking 
force to the vehicle. The brake pedal 1 is connected to a master cylinder 
2 constituting a brake fluid pressure producing source. When the driver 
steps on the brake pedal 1 the brake pedal 1 pushes on master pistons 2a, 
2b disposed in the master cylinder 2. These master pistons 2a, 2b and the 
inner wall of the master cylinder 2 are contacted through seal members not 
shown in the diagram. A primary chamber 2A and a secondary chamber 2B of 
the master cylinder 2 are thereby liquid tightly separated. The master 
pistons 2a, 2b are connected by a spring constituting an elastic member 
and generate the same master cylinder pressure ("M/C pressure") in both 
the primary chamber 2A and the secondary chamber 2B of the master cylinder 
2. A spring constituting an elastic member is also disposed between the 
master piston 2b farther from the brake pedal 1 and the inner end of the 
master cylinder 2, and acts to swiftly restore the pedal position along 
with return operation of the brake pedal 1. 
A master reservoir 3 having passages connected to the master cylinder 2 is 
provided. Specifically, two passages connecting the master cylinder 2 and 
the master reservoir 3 are provided so as to respectively connect each of 
both the primary chamber 2A and the secondary chamber 2B of the master 
cylinder 2 to the master reservoir 3. The master reservoir 3 supplies 
brake fluid to the inside of the master cylinder 2 and holds surplus brake 
fluid from inside the master cylinder 2. Because the passages each have a 
diameter much smaller than the conduit diameters of main conduits 
extending from the primary chamber 2A and the secondary chamber 2B, they 
exhibit an orifice effect when brake fluid flows into the master reservoir 
3 from the primary chamber 2A and the secondary chamber 2B of the master 
cylinder 2. 
The M/C pressure is transmitted to the front wheel piping system and the 
rear wheel piping system. Here, since the front wheel piping system and 
the rear wheel piping system are of the same construction, the front wheel 
piping system will be described. With respect to the rear wheel piping 
system, only construction differing from the front wheel piping system 
will be described. 
The front wheel piping system has a conduit A constituting a main conduit 
transmitting the above-mentioned MIC pressure to each of wheel braking 
force producing devices, namely a first wheel cylinder 4 for the right 
front wheel and a second wheel cylinder 5 for the left front wheel. By 
means of the conduit A, a wheel cylinder pressure ("W/C pressure") is 
produced in each of the wheel cylinders 4, 5. 
A front wheel differential pressure control valve 6 is provided in conduit 
A. The control valve 6 comprises a second valve device which can be 
controlled between two positions of open and a differential pressure 
producing states. In a normal braking state the valve position is open. 
When electrical power is supplied to a solenoid coil (not shown in the 
diagram of this differential pressure control valve 6), the valve position 
becomes the differential pressure producing state. With the differential 
pressure producing state valve position in the differential pressure 
control valve 6, when the brake pressure of the wheel cylinder side 
becomes higher by a predetermined pressure than the M/C pressure, only 
flow of brake fluid from the wheel cylinder side to the M/C side is 
allowed. The respective conduits are protected by the pressure of the 
wheel cylinders 4, 5 side being prevented from rising higher by a 
predetermined pressure than the pressure of the master cylinder 2 side at 
all times. 
The conduit A on the downstream or wheel cylinder side of this differential 
pressure control valve 6 branches into two conduits A1 and A2. Also, one 
conduit contains a first pressure increase control valve 7 for controlling 
increase of the brake fluid pressure to the first wheel cylinder 4 and the 
other conduit contains a second pressure increase control valve 8 for 
controlling increase of the brake fluid pressure to the second wheel 
cylinder 5. These first and second pressure increase control valves 7, 8 
are constructed as two-position valves which can be controlled between 
open and closed states. When these first and second pressure increase 
control valves 7, 8 are opened, the M/C pressure or a brake fluid pressure 
created by the delivery of brake fluid of a front wheel pump 9 can be 
applied to the first and second wheel cylinders 4, 5. 
During normal braking by the driver, the differential pressure control 
valve 6 and the first and second pressure increase control valves 7, 8 are 
always controlled to be open. Safety valves 6a, 7a, 8a are disposed in 
parallel with the differential pressure control valve 6 and the first and 
second pressure increase control valves 7, 8, respectively. The safety 
valve 6a disposed in parallel with the differential pressure control valve 
6 allows the M/C pressure to flow to the wheel cylinders of the left and 
right front wheels when the driver applies the brake pedal 1 when the 
valve position of the differential pressure control valve 6 is that of the 
differential pressure producing state. The safety valves 7a, 8a disposed 
in parallel with the pressure increase control valves 7, 8 are provided to 
allow the wheel cylinder pressures of the left and right front wheels to 
decrease corresponding to a brake pedal return operation when, 
particularly during anti-skid control, the first and second pressure 
increase control valves 7, 8 closed and the brake pedal 1 has been 
returned by the driver. 
In conduits B connecting the conduits A between the first and second 
pressure increase control valves 7, 8 and the wheel cylinders 4, 5 to the 
reservoir hole 10a of a reservoir 10 for ABS control use, a first pressure 
decrease control valve 11 and a second pressure decrease control valve 12 
are respectively provided as two-position valves which can be controlled 
by an ECU between open and closed states. These first and second pressure 
decrease control valves 11, 12 are always closed during normal braking. 
A conduit C connects the ABS control use reservoir 10 and conduit A, which 
is the main conduit. In conduit C a self-supplying front wheel pump 9 
receives and delivers brake fluid from the ABS control use reservoir 10 to 
the master cylinder side or toward the wheel cylinders 4, 5. The front 
wheel pump 9 has safety valves 9a, 9b so that one-way intake and delivery 
is made possible. To moderate pulsations of brake fluid delivered by the 
front wheel pump 9 a fixed capacity damper 13 is disposed in the conduit C 
on the delivery side of the front wheel pump 9. The ABS control use 
reservoir 10 is provided to hold surplus brake fluid from the wheel 
cylinders, irrespective of whether during ABS control or not. 
A conduit D is connected to the conduit C between the ABS control use 
reservoir 10 and the front wheel pump 9. Conduit D branches into two 
conduits, and a first conduit D1 is connected to the primary chamber 2A of 
the master cylinder 2 and a second conduit D2 is connected to the master 
reservoir 3. A first control valve 14 and a second control valve (first 
valve devices) 15 which can be controlled between an open state and a 
closed state are provided in the conduits D1, D2 respectively. A nonreturn 
valve 15a for preventing brake fluid from moving toward the master 
reservoir 3 is provided in conduit D2. Therefore, the front wheel pump 9 
can take in brake fluid through the conduit D from the master cylinder 2 
and the master reservoir 3 and deliver it to the conduit A. That is, by 
means of this one pump 9, it is possible to take in brake fluid from the 
master cylinder 2 and the master reservoir 3 during TRC control, during 
ABS control and during sideslip prevention control. 
The rear wheel piping system is substantially the same as the construction 
in the front wheel piping system. That is, the differential pressure 
control valve 6 corresponds to a rear wheel differential pressure control 
valve 36. The first and second pressure increase control valves 7, 8 
respectively correspond to third and fourth pressure increase control 
valves 37, 38. The first and second pressure decrease control valves 11, 
12 respectively correspond to third and fourth pressure decrease control 
valves 41, 42. The front wheel first control valve 14 corresponds to a 
rear wheel first control valve 44. The front wheel pump 9 corresponds to a 
rear wheel pump 39. The conduit A, conduit B, conduit C and conduit D 
respectively correspond to conduit E, conduit F, conduit G and conduit H. 
However, the rear wheel piping system does not provide a conduit 
(equivalent to the second conduit D2 in the front wheel piping system) 
connecting the conduit G between an ABS control use reservoir 40 and the 
rear wheel pump 39 to the master reservoir 3. This is to reduce the cost 
of this conduit part and to increase the failsafe ability of the system. 
With respect to resistance of the system to failure, for example, in the 
front wheel piping system, because the conduit D2 is connected to the 
master reservoir 3, there is a possibility of the front wheel second 
control valve 15 and the nonreturn valve 15a failing to open. However, if 
a conduit equivalent to the conduit D2 is not provided in one of the two 
piping systems of the front wheel side and rear wheel side, there is no 
possibility of the piping system failing to open and the failsafe 
characteristic of the system improves. 
A pressure sensor or pressure detecting device 50 for essentially detecting 
the M/C pressure is disposed in the conduit H in the vicinity of the 
master cylinder 2. 
The control valves disposed in the front and rear piping systems are 
controlled by a brake system electronic control unit (the "ECU") 60 in 
FIG. 2 on the basis of signals sent from various sensors 50, 61 through 
65. 
Next, TRC control, sideslip prevention control, and ABS control shown in 
FIG. 3, carried out by the ECU 60 will be described using flow charts. 
First, as shown in FIG. 3, the system carries out a determination of 
whether control starting conditions of TRC control, sideslip prevention 
control or ABS control are established or if any control is in progress. 
That is, step 101 represents determining whether or not TRC control 
starting conditions are established. If TRL control starting conditions 
are established, processing proceeds to step 103 for TRC control and then 
proceeds to step 104. When the TRC control starting conditions are 
satisfied, a flag is set or the like to establish a record that TRC 
control is in progress by a flag being set or the like. 
As an example of the TRC control starting conditions, one condition may be 
an accelerating slip ratio of 25% or over and the like. This accelerating 
slip ratio is computed from a vehicle acceleration and wheel speeds 
detected by an acceleration sensor 61 for detecting the vehicle 
acceleration and wheel speed sensors 62 mounted in correspondence with the 
wheels. 
When in step 101 the TRC control starting conditions are not established, 
processing proceeds to step 102. Step 102 represents determining whether 
or not TRC control is in progress, and if TRC control is in progress, 
proceeding to step 103 and continuing TRC control. If in step 102 TRC 
control is not in progress then processing proceeds to step 104. 
Step 104 represents determining whether sideslip prevention control 
starting conditions are established. If they are established, the process 
proceeds to step 105 to carry out sideslip prevention control and then 
proceeds to step 106. This sideslip prevention control includes, for 
example, increasing the trace characteristic while turning the vehicle. 
These sideslip prevention control starting conditions include, for example, 
the error between an actual vehicle turning angle and a target tuning 
angle exceeding a predetermined value and the like. The actual vehicle 
turning angle is obtained from a yaw rate detected by a yaw rate detector 
63. The target turning angle is set from a steering angle detected by a 
steering sensor 64 and a vehicle speed detected by the wheel speed sensors 
62. As the control starting conditions, the error between an actual 
lateral acceleration and an estimated lateral acceleration of the vehicle 
and the like can be adopted. Which wheel will be used for sideslip 
prevention control to be executed is determined on the basis of the actual 
vehicle turning angle and a target vehicle 25 turning angle. 
In step 106 it is determined whether or not ABS control starting conditions 
are established. If they are established, the process proceeds to step 108 
and carries out ABS control. As these ABS control starting conditions, a 
braking slip ratio being 20% or more and the like can be adopted. This 
braking slip ratio is obtained in the same way as the accelerating slip 
ratio mentioned above. 
If in step 106 the ABS control starting conditions are not established, 
processing proceeds to step 107. In step 107 it is determined whether or 
not ABS control is in progress. If ABS control is in progress, processing 
proceeds to step 108 and continues ABS control. If in step 107 ABS control 
is not in progress, processing proceeds to step 109. 
In step 109, it is determined whether or not TRC control, sideslip 
prevention control or ABS control is in progress. If any of them is in 
progress processing proceeds to step 110 and drives the pumps 9, 39. If 
none of them are in progress processing proceeds to step 111 and stops the 
pumps 9, 39. 
The processings in the above-mentioned step 103, step 105 and step 108 
correspond with the flow charts in FIG. 4, FIG. 6 and FIG. 9, 
respectively. The brake system ECU 60 drives solenoids disposed in the 
control valves to move the valve positions of the control valves on the 
basis of these processes. 
Solenoid drive patterns are shown in FIG. 5, FIG. 8 and FIG. 10B. Regarding 
the ON and the OFF states shown in these figures, when there is no 
movement from the valve position in normal braking (showing the state of 
FIG. 1) it is shown with OFF and conversely when the valve position is 
moved it is shown with ON. 
TRC control, sideslip prevention control and ABS control will each be 
described below. 
(Processing in TRC Control) 
The TRC control of step 103 is shown in detail in FIG. 4. This processing 
is carried out for each driving wheel, for example when a determination is 
ended for the left rear wheel, a determination is carried out for the 
right rear wheel and the process ends after all the driving wheels are 
finished. 
First, step 201, represents determining whether or not the slip ratio is 
larger than a first predetermined value, for example 20%. If it is larger, 
processing proceeds to step 202 and sets a pulse increasing output. When 
the pulse increasing output is set, the valve positions of the control 
valves are brought to the positions according to the solenoid drive 
pattern (A) shown in FIG. 5. That is, the front wheel differential 
pressure control valve 6 is brought to its on-state (open state), the 
front wheel first control valve 14 to its off-state (closed state), the 
front wheel second control valve 15 to its on-state (open state) , the 
rear wheel differential pressure control valve 36 to its on-state 
(differential pressure producing state), the rear wheel control valve 44 
to is on-state (open state), and the first and second pressure increase 
control valves 7, 8 to their closed states. Further, because when TRC 
control is in progress because as a result of the processing of step 110 
the front wheel pump 9 and the rear wheel pump 39 become in the 
driven-state, when the rear wheel control valve 44 opens the master 
cylinder 2 and the rear wheel pump 39 become in the connected-state and 
brake fluid is drawn in from the master cylinder 2 through the conduit H. 
According to the accelerating slip ratio of that time, duty control is 
carried out for the third and fourth pressure increase control valves 37, 
38. By the valve positions of these being suitably changed, brake fluid of 
a required portion of the brake fluid taken in by the pump 39 is supplied 
to the third and fourth wheel cylinders 34, 35. In this way braking can be 
applied to both of the rear wheels, which are the driving wheels. 
Because the front wheel second control valve 15 is open, when the front 
wheel pump 9 is driven brake fluid is drawn from the master reservoir 3 
through the conduit D. Then, because the first and second pressure 
increase control valves 7, 8 are closed, the brake fluid drawn by the 
front wheel pump 9 is supplied through the open front wheel differential 
pressure control valve 6 to the primary chamber 2A (the cylinder chamber 
on the pedal side of the master cylinder 2 shown in FIG. 1) of the master 
cylinder 2. Due to the orifice effect of the passages between the master 
reservoir 3 and the primary chamber 2A as well as the secondary chamber 2B 
an M/C pressure is produced in the primary chamber 2A (for example 2 to 5 
atmospheres). 
When brake fluid from the master reservoir 3 is drawn into the front wheel 
pump 9, because the master reservoir 3 is essentially opened to 
atmospheric pressure, the drawing resistance due to negative pressure is 
small. That is, when the rear wheel pump 39 in the rear wheel piping 
system draws brake fluid from the secondary chamber 2B of the master 
cylinder 2, if it is assumed that there is no pushing force from the 
primary chamber 2A side to the secondary chamber 2B side, a negative 
pressure arises in the secondary chamber 2B and the drawing resistance 
becomes large. As a result, the pressure increase gradient of the wheel 
cylinder pressure may fall because the rear wheel pump 39 cannot deliver 
the sufficient amount of brake fluid. However, because as a result of the 
delivery of the front wheel pump 9 whose drawing resistance is low and 
whose responsiveness is good, an M/C pressure is produced in the primary 
chamber and an equal pressure is produced in the secondary chamber also. 
Therefore, it is possible to enhance the responsiveness of drawing and 
delivery of the rear wheel pump by means of this pressure. 
For the rear wheel pump 39, a self-supplying pump may be used, but since as 
mentioned above a pressure produced in the master cylinder 2 acts at the 
inlet of the rear wheel pump 39 by way of the control valve 44, it is also 
possible to employ a non-self-supplying pump for the rear wheel pump 39. 
Also, since the amount of brake fluid drawn from he master reservoir 3 is 
essentially the amount of brake fluid required for applying a back 
pressure to the rear heel pump 39, a poor condition does not arise in the 
master cylinder 2 due to the brake fluid drawn by the front wheel pump 9. 
The reason is that an amount of brake fluid and a brake fluid pressure 
surplus to requirements in the primary chamber of the master cylinder 2 
are returned to the master reservoir 3 through the passages having an 
orifice effect. 
Further, because the rear wheel piping system is only receiving a pump back 
pressure created by brake fluid introduced into the primary chamber 2A of 
the master cylinder 2, and brake fluid originally existing in the 
secondary chamber 2B is drawn and delivered to the wheel cylinder side by 
the rear wheel pump 39, when brake fluid having produced the W/C pressure 
is returned to the master cylinder 2 only an amount of brake fluid drawn 
from the secondary chamber 2B is returned to the secondary chamber 2B. 
Consequently, an excessive load does not act on the seals and so on of the 
master cylinder 2. 
If in step 201, the accelerating slip ratio is smaller than the first 
predetermined value, processing proceeds to step 203. In step 203 it is 
determined whether or not the accelerating slip ratio is smaller than a 
second predetermined value, for example 10%, and if it is larger 
processing proceeds to step 204 and a holding output is set. 
When a holding output is set, the valve positions of the control valves are 
made according to a solenoid drive pattern (B) shown in FIG. 5. That is, 
the third and fourth pressure increase control valves 37, 38 are closed 
and the W/C pressure increased as described above is held. 
When in step 203 the accelerating slip rate is smaller than the second 
predetermined value, a pulse decreasing output is set. When a pulse 
decreasing output is set, the valve positions of the control valves are 
made the positioned according to a solenoid drive pattern (C) shown in 
FIG. 5. That is, the third and fourth pressure decrease control valves 41, 
42 are duty-controlled and brake fluid is allowed to escape to the ABS 
control use reservoir 40 and the W/C pressure held as described above is 
thereby reduced. 
When after this pulse decreasing output is set a predetermined time elapses 
without the setting being changed to a holding output or an increasing 
output, the flag indicating that TRC control is in progress is reset. 
(Processing for Sideslip Prevention Control) 
The sideslip prevention control processing of step 105 is shown in FIG. 6. 
This processing is carried out in parallel for all the wheels, and 
processing is ended when it has finished for all four wheels. 
In this sideslip prevention control, when oversteering while turning the 
vehicle occurs, by applying a braking force to one of the left and right 
front wheels according to the turning direction, the oversteering can be 
cancelled. For example, as shown in FIG. 7, when the vehicle is turning to 
the left and oversteering state has occurred, as shown by the hatched part 
of FIG. 7, a braking force is applied to the right front wheel 51. Also, 
if understeering occurs in the vehicle (not shown in drawings), a braking 
force may be applied to the inner front wheel of a turning line. The 
understeering state can also be reduced by applying a braking force to 
both of the rear wheels 53, 54. 
In the following description, sideslip prevention control for applying a 
braking force to the right front wheel 51 is carried out for oversteering 
as shown in FIG. 7. Also, the description will be divided into a time of 
non-braking of the vehicle and a time of braking. 
(a) Processing while not braking 
The processing shown in FIG. 6 is carried out simultaneously for a 
controlled wheel for which sideslip prevention control is carried out and 
non-controlled wheels for which sideslip prevention control is not carried 
out. Whether or not a wheel is a sideslip prevention controlled wheel is 
determined according to whether or not in step 104 the actual vehicle 
turning angle has deviated in either direction 32 from the target turning 
angle. 
During oversteering in FIG. 7, because the wheel being sideslip prevention 
controlled is the right front wheel 51, step 301 is executed with respect 
to the right front wheel 51. In step 301, a target wheel speed set as a 
wheel speed corresponding to the current state of the slip angle is 
compared to the actual wheel speed at the right front wheel 51. That is, 
it is determined whether or not the speed of the right front wheel 51 
being controlled has exceeded the target wheel speed. If the actual wheel 
speed has exceeded the target wheel speed, processing proceeds to step 303 
and sets a pulse increasing output to reduce the actual wheel speed. 
When the pulse increasing output is set, the brake system ECU 60 drives the 
solenoids of the control valves and moves their valve positions according 
to a solenoid drive pattern (A) shown in FIG. 8. That is, when the pulse 
increasing output is set, the front and rear wheel differential pressure 
control valves 6, 36 are brought to their on-state (differential pressure 
producing state), the front wheel first control valve 14, the rear wheel 
control valve 44 and the front wheel second control valve 15 to their 
on-state (open state), and the first pressure decrease control valve 11 to 
its off-state (closed state) . For the first pressure increase control 
valve 7 pertaining to the right front wheel 51 (controlled wheel), duty 
control is carried out. 
When sideslip control is in progress, the front wheel pump 9 and the rear 
wheel pump 39 are in a driven-state as a result of the processing of step 
110. Consequently, when, as a result of the processing described above, 
the front wheel second control valve 15 opens, brake fluid in the master 
reservoir 3 is drawn through the opened conduit D and that drawn brake 
fluid is delivered to the conduit A. Because the front wheel first control 
valve 14 is also opened, brake fluid in the master cylinder 2 is also 
drawn by the front wheel pump 9. Then, brake fluid delivered into the 
conduit A is supplied to the first wheel cylinder 4 through the first 
pressure increase control valve 7, which is being duty controlled to 
increase the W/C pressure thereof. 
Thus, during non-braking or when an M/C pressure has not been produced, 
because brake fluid is drawn not just from the master cylinder 2 but also 
directly from the master reservoir 3, the flow resistance can be made 
small. In particular, even at low temperatures when the flow resistance of 
brake fluid increases, the responsiveness in sideslip prevention control 
can remain good. 
In step 301, if the actual wheel speed is lower than the target wheel 
speed, processing proceeds to step 303 and sets a pulse decreasing output 
to increase the actual wheel speed. When a pulse decreasing output is set, 
the solenoids in the control valve are driven to move to the valve 
positions according to the solenoid drive pattern (B) shown in FIG. 8. 
That is, the first pressure increase control valve 7 pertaining to the 
right front wheel 51 is brought to its on-state (closed state) and duty 
control is carried out for the first pressure decrease control valve 11. 
Brake fluid is then allowed to escape to the ABS control use reservoir 10 
through the conduit B and the W/C pressure is thereby reduced. 
With respect to the non-controlled wheels, processing proceeding to step 
304 is executed. In step 304, after M/C pressure introduction 
determination (the details thereof will be discussed later) is carried 
out, processing proceeds to step 305 and selection of a solenoid drive 
pattern is carried out according to a result of the M/C pressure 
introduction determination. 
The detailed processing for selecting the solenoid drive pattern is shown 
in FIGS. 10A and 10B. First, in step 501, it is determined whether or not 
either of the front wheels is in sideslip prevention control. In this 
description, because it is being assumed that sideslip prevention control 
is being carried out for the right front wheel 51, that determination is 
YES and processing proceeds to step 502. In step 502, it is determined 
whether or not the driver is currently applying the brake. This 
determination is accomplished by detecting whether or not the brake pedal 
1 is in a moving state based on the signal of a stroke sensor 65. Because 
in this example, the driver is currently not braking, the solenoid drive 
pattern (A) shown in FIG. 10B is selected. That is, the pressure increase 
valve of the non-controlled wheel is brought to the on-state (closed 
state), and the pressure decrease valve to the off-state (closed state) . 
The valve positions of the other control valves are the same as the valve 
positions selected in the processing for the controlled wheel. 
Therefore, for the non-controlled wheel, because the pressure increase 
control valves are closed, a braking force is not applied to the 
non-controlled wheels. 
(b) Processing while Braking 
Next, processing while braking, i.e., when the driver has stepped on the 
brake pedal 1 and a braking force is applied to the vehicle, will be 
described. This processing during braking includes both cases where 
application of the brake pedal after oversteering occurred during 
non-braking and when oversteering occurred after the brake pedal was 
stepped on. 
At the time of braking, for the right front wheel 51 that is the controlled 
wheel, by the processing of steps 301 through 304, control is carried out 
to make the wheel speed of the right front wheel 51 approach the target 
wheel speed. With respect to the non-controlled wheels, the W/C pressure 
of each wheel is increased, held, or decreased to apply a suitable W/C 
pressure. In the M/C pressure introduction determination of step 304, it 
is determined which command should be output: increase, holding, or 
decrease of the W/C pressure with respect to each of the non-controlled 
wheels. The detailed processing of step 304 is shown in FIG. 9. First, in 
step 401, it is determined whether or not the difference between this 
time's M/C pressure detected by the pressure sensor 50 and the M/C 
pressure detected by the pressure sensor 50 at the time of the previous 
determination (this time's M/C pressure--the previous time's M/C pressure) 
is greater than a positive predetermined reference value (for example 5 
atmospheres). That is, in the M/C pressure introduction determination of 
the previous time, the M/C pressure of that time was stored and that 
stored M/C pressure and the M/C pressure at the time of the present 
processing are compared. In the M/C pressure introduction determination of 
the initial time, the M/C pressure base has been set to zero and a 
comparison of this value (zero) and the M/C pressure of the initial time 
is carried out. If the difference between the previous time and this time 
is equal to or greater than a predetermined value, processing proceeds to 
step 402 and outputs a pressure increase command because it is determined 
that the driver is still stepping on the brake pedal 1. 
When the determination in step 401 is NO, processing proceeds to step 403 
and determines whether or not the difference between this time's M/C 
pressure and the previous time's M/C pressure is smaller than a negative 
predetermined reference value (for example -5 atmospheres). When the 
difference between the previous time and this time is equal to or greater 
than the negative predetermined value, a holding command is outputted in 
step 404. If the difference between the previous time and this time is 
lower than the negative predetermined value, a pressure decreasing command 
is outputted in step 405 because it is determined that the driver returned 
the brake pedal 1. That is, in a case where during braking the driver has 
stepped on the brake pedal 1 further than the previous time ("during brake 
stepping"), a pressure increasing command is issued as a result of the 
processing described above. When there is almost no change in the position 
of the brake pedal 1 ("during brake holding") a holding command is issued 
as a result of the processing described above. When the stepping force on 
the brake pedal 1 has been reduced ("during brake releasing") a pressure 
decreasing command is issued as a result of the processing described 
above. 
Operations described below will be divided into different states: during 
brake stepping, during brake holding and during brake releasing. 
(1) During Brake Stepping 
During brake stepping, while processing the M/C pressure introduction 
determination, a W/C pressure increasing command is issued. Therefore, 
when selecting the solenoid drive pattern shown in step 305, the process 
has reached step 502, because it is during braking the determination 
thereof is YES and processing proceeds to step 503. In step 503, because a 
W/C pressure increasing command has been issued, the solenoid drive 
pattern (B) shown in FIG. 10B is selected. When processing during braking, 
a solenoid drive pattern selected for non-controlled wheels is given 
priority over the solenoid drive pattern selected for the controlled wheel 
(in the cases of holding and pressure decreasing discussed later, priority 
is also given to the solenoid drive pattern selected for the 
non-controlled wheels). 
That is, even when after this selection for the non-controlled wheels has 
been made, a solenoid drive pattern is selected for the controlled wheel 
as shown in FIG. 6. According to the solenoid drive pattern selected for 
the non-controlled wheels, the valve positions of the front and rear wheel 
differential pressure control valves 6, 36, the front wheel first and 
second control valves 14, 15 and the rear wheel control valve 44 are set. 
Therefore, on the basis of the selected solenoid drive pattern the front 
and rear wheel differential pressure control valves 6, 36 are brought to 
the on-state (differential pressure producing state), the front wheel 
second control valve 15 to a duty-controlled state (open and closed 
states), and the front wheel first control valve 14 and the rear wheel 
control valve 44 to the on-state (open state). Also, of the non-controlled 
wheels, duty control is carried out for the pressure increase control 
valve pertaining to a wheel for which a WIC pressure increasing command 
has been issued at the present processing. 
For example, if the left front wheel 52 is the wheel for which the W/C 
pressure increasing command has been issued, duty control is carried out 
for the second pressure increase control valve 8 pertaining to the left 
front wheel 52. In this case, brake fluid is delivered by the front wheel 
pump 9 from conduit D1 to conduit A which increases the W/C pressure in 
the left front wheel 52. 
As a result of this pressure increasing command, in wheel cylinders of 
wheels other than the right front wheel 51 that are the non-controlled 
wheels, brake fluid is increased to substantially the same pressure as the 
M/C pressure (if pressure decreasing control has not been executed) and a 
pressure adjusted by sideslip prevention control is applied to the right 
front wheel (the wheel to be controlled). 
Also, at this time, because the conduit D2 is in the duty-controlled state 
of the second control valve 15, a small amount of brake fluid is drawn 
from the master reservoir 3 and assists the brake fluid pressure of the 
non-controlled wheel to rapidly increase. It is to be noted that the 
second control valve may be in the closed state instead of the 
duty-controlled state. In this case, there is no counterflowing of surplus 
brake fluid all at once to the master cylinder 2 when the brake pedal 1 is 
released. Consequently, it is possible to achieve protection of the master 
cylinder 2 and to avoid a state wherein the driver cannot apply the brake 
pedal 1. 
(2) During Brake Holding 
During brake holding, when the process reaches step 504 and the 
determination therein is YES, the solenoid drive pattern (C) shown in FIG. 
10B is selected. Therefore, on the basis of the selected solenoid drive 
pattern, the front and rear wheel differential pressure control valves 6, 
36 are controlled to be in the on-state (differential pressure producing 
state), the front wheel second control valve 15 to the off-state (closed 
state), and the front wheel first control valve 14 and the rear wheel 
control valve 44 to the on-state (open state) . Also, of the 
non-controlled wheels, the pressure increase control valve pertaining to a 
wheel for which a W/C pressure holding command has been issued at the 
present processing is controlled to be in the on-state (closed state) and 
the pressure decrease control valve is made off-state (closed state). 
Thus, because the pressure increase control valve of a wheel for which a 
W/C pressure holding command has been issued is made closed-state, that 
W/C pressure is held. 
(3) During Brake Release 
During brake release, the determination in step 504 is NO, and the solenoid 
drive pattern (D), is selected. Therefore, on the basis of the selected 
solenoid drive pattern (D), the front and rear wheel differential pressure 
control valves 6, 36 are brought to the on-state (differential pressure 
producing state), the front wheel second control valve 15 to the off-state 
(closed state), and the front wheel first control valve 14 and the rear 
wheel control valve 44 to the on-state (open state). Also, of the 
non-controlled wheels, the pressure increase control valve pertaining to a 
wheel for which a W/C pressure decreasing command has been issued at the 
present processing is made on-state (closed state) and for the pressure 
decrease control valve pertaining thereto, duty control is carried out. 
On the basis of this solenoid drive pattern (D), of the non-controlled 
wheels, if it is supposed that the wheel for which a W/C pressure 
decreasing command has been issued at present processing is for example 
the left front wheel 52, duty control is carried out for the second 
pressure decrease control valve 12 pertaining to that left front wheel 52. 
As a result, the brake fluid in the conduit A between the closed second 
pressure increase control valve 8 and the wheel cylinder 5 is suitably 
allowed to escape to the ABS control use reservoir 10 and the W/C pressure 
in the left front wheel 52 is thereby decreased. 
In response to the W/C pressure increasing command, the WIC pressure 
decreasing command and the W/C pressure holding command, the front wheel 
first control valve 14 and the front wheel second control valve 15 can 
also be suitably made on-state or off-state or duty-controlled. For 
example, when the M/C pressure has become less than 5 atmospheres, the 
front wheel second control valve 15 may be made on-state. When the front 
wheel second control valve 15 is made on-state, the front wheel pump 9 can 
draw brake fluid from the master reservoir 3 and this brake fluid is 
delivered to the master cylinder 2 side, whereby an M/C pressure is 
produced. As a result, the rear wheel pump 39 can easily draw brake fluid 
inside the master cylinder 2. 
Also, when a W/C pressure increasing command issues, at times such as 
immediately before sideslip prevention control is started, ABS control may 
be concurrently carried out. At this time, carrying out duty control for 
the front wheel first control valve 14 and making the amount of brake 
fluid in the conduit C slightly low makes it easier for brake fluid stored 
in the ABS control use reservoir 10 to be drawn by the front wheel pump 9. 
Also, a timing chart in sideslip prevention control is shown in FIGS. 11A 
to 11K. This timing chart represents a simulation result in a case wherein 
a driver has rotated the steering wheel to the left. 
That is, as shown in FIGS. 11A and 11B, when the driver turns the steering 
wheel and the sideslip prevention control starting conditions are 
established, sideslip prevention control begins (t1 in FIGS. 11A to 11K). 
A pulse increasing output is set and as shown in FIGS. 11F through 11K, 
and signals for moving the valve positions ("C", "g") of the respective 
valves are transmitted and a motor (not shown) drives the pumps 9, 39. As 
a result, as shown in FIG. 11D, brake fluid pressure is produced in the 
wheel cylinder of the sideslip prevention controlled wheel. 
Next, when the driver applies the brake 43 pedal 1, as shown in FIG. 11C, 
the M/C pressure increases. Then, in the M/C pressure introduction 
determination, processing accompanying generation of the M/C pressure is 
carried out. In other words, along with M/C pressure increasing, a W/C 
pressure increasing command (see FIG. 11E) is set and the W/C pressures of 
the non-controlled wheels are suitably increased (time t2 in FIG. 11E). 
Then, when pressure increasing has ended, a W/C pressure holding command 
(see FIG. 11E) is set and the W/C pressures of the non-controlled wheels 
are maintained. 
Then, when the driver stops applying the brake pedal 1, i.e., the driver 
returns the brake pedal 1, the M/C pressure decreases. Along with this 
decrease of the M/C pressure, a W/C pressure decreasing command (see FIG. 
11E) is set and the W/C pressures of the non-controlled wheels are 
suitably reduced (time t3 in FIG. 11E). 
When sideslip prevention control is carried out in this way the following 
kinds of effect are obtained. 
First, when during non-braking an M/C pressure has not been produced, 
because the front wheel pump 9 draws brake fluid from the master reservoir 
3 not only through the front wheel first control valve 14 but also through 
the front wheel second control valve 15, the drawing resistance is low and 
the increase gradient of the W/C pressure can be made large so that the 
responsiveness can be improved. 
In sideslip prevention control during braking, because an M/C pressure 
exists because the brake pedal is applied, there is not a large drawing 
resistance even if the brake fluid is drawn from the master cylinder 2. 
Further, during the increase of W/C pressures of the non-controlled 
wheels, the front wheel second control valve 15 is duty-controlled. 
Thereby, excess brake fluid is not added to the wheel cylinders 4, 5 from 
the master cylinder 2. As a result, during return of brake fluid of the 
wheel cylinders 4, 5 side to the master cylinder 2, an amount of brake 
fluid much greater than the amount of brake fluid having originally flowed 
out to the wheel cylinders 4, 5 from the master cylinder 2 is not returned 
at once to the master cylinder 2. Therefore, this protects the seal parts 
of the master cylinder 2 and prevents a large brake fluid shock to the 
master cylinder 2 accompanying brake fluid return. 
In sideslip prevention control, in the above description, a brake fluid 
pressure was applied to the wheel cylinders 4, 5 of the left and right 
front wheel side only during non-braking to control the sideslip of the 
vehicle. However, in an alternate embodiment, a brake fluid pressure may 
be applied to the third and fourth wheel cylinders 34, 35 of the rear 
wheel side during non-braking, as described earlier. In this case, or as 
described above with traction control, the front wheel differential 
pressure control valve 6 may be made open-state and a brake fluid pressure 
transmitted to the rear wheel side through the master cylinder 2 in the 
order of the primary chamber 2A, the secondary chamber 2B of the master 
cylinder 2. 
(Processing in ABS Control) 
On the basis of FIG. 12, the processing in ABS control of step 108 will be 
described. ABS control according to this process is carried out for each 
wheel. 
First, in step 601, it is determined whether or not the wheel for which ABS 
control processing is currently being carried out is a sideslip prevention 
controlled wheel. When the wheel for which ABS control processing is 
currently being carried out is the right front wheel 51, in step 601 it is 
determined that it is a sideslip prevention controlled wheel and 
processing is ended directly. In other words, with respect to a sideslip 
prevention controlled wheel, sideslip prevention control processing is 
given preference over ABS control processing. For example, if ABS control 
processing is currently being carried out in the left front wheel, which 
is other than the sideslip prevention controlled wheel, step 601 
determines that it is not a sideslip prevention controlled wheel and 
processing proceeds to step 602. 
Step 602 determines whether or not a decelerating slip ratio in the left 
front wheel 52 for which ABS control processing is currently being carried 
out is greater than 10% (as an example). If the slip ratio is smaller than 
10%, processing proceeds to step 603 and sets a pulse increasing output 
and ends processing. After this pulse increasing output is set, when a 
predetermined time elapses without the setting being changed to a holding 
output or a pulse decreasing output, a flag indicating that ABS control is 
in progress is reset. 
This pulse increasing output is set when the wheel has only a decelerating 
slip ratio of a level such that ABS control is not necessary. When the 
pulse increasing output is set, the valve positions of the respective 
valves are set according to solenoid drive pattern (A) shown in FIG. 13. 
That is, the front wheel first and second control valves 14, 15, the front 
wheel differential pressure control valve 6, the rear wheel differential 
pressure control valve 36 and the rear wheel control valve 44 are all made 
off-state and for the second pressure increase control valve 8 pertaining 
to the left front wheel 52 constituting the object of ABS control at 
present duty control is carried out, whereby the W/C pressure in the left 
front wheel 52 is suitably increased. 
If in step 602 the decelerating slip ratio in the left front wheel 52 is 
greater than the predetermined value, processing proceeds to step 604. In 
step 604, it is determined whether or not the wheel speed in the left 
front wheel 52 is in the process of increasing. If the wheel speed in the 
left front wheel 52 is increasing, processing proceeds to step 605 and 
sets a holding output and then ends. Whether or not this wheel speed is in 
the process of increasing can be determined by whether the wheel 
acceleration is positive or negative. 
When a holding output is set, the valve positions of the respective valves 
are made the positions according to the solenoid drive pattern (B) shown 
in FIG. 13. That is, the front wheel first and second control valves 14, 
15, the front wheel differential pressure control valve 6, the rear wheel 
differential pressure control valve 36 and the rear wheel control valve 44 
are all made off-state and the second pressure increase control valve 8 is 
closed, whereby the W/C pressure acting on the left front wheel 52 is 
held. 
If in step 604 the wheel speed in the left front wheel 52 is not 
increasing, a decreasing output is set. When the decreasing output is set, 
the valve positions of the respective valves are set according to the 
solenoid drive pattern (C) shown in FIG. 13. That is, the second pressure 
increase control valve 8 is closed and the second pressure decrease 
control valve 12 is opened. Therefore, by brake fluid being discharged 
into the ABS control use reservoir 10 through the conduit B the W/C 
pressure is reduced and increase of the wheel speed in the left front 
wheel 52 is promoted. Then, brake fluid having collected in the ABS 
control use reservoir 10 is drawn by the front wheel pump 9 and that brake 
fluid is made to counterflow into the conduit A. 
When the ABS control processing of this time controlled wheel ends, ABS 
control processing of another wheel is then carried out. 
As described above, in the respective processings of TRC control, sideslip 
prevention control and ABS control, only one pump for drawing brake fluid 
inside the hydraulic pressure circuit can be provided for each of the 
front and rear wheel piping systems. By this means it is possible to 
reduce the cost of the brake system. 
In this embodiment, a brake system in a front-rear piping arrangement was 
shown, but it is not limited to this and may also be applied to an X 
(diagonal) piping arrangement. 
Also, although in this embodiment the invention was applied to a rear wheel 
drive vehicle, it is not limited to this and may alternatively be applied 
to a front wheel drive vehicle or a four wheel drive vehicle. 
When applying the present invention to a brake system of an X piping 
arrangement or to a front wheel drive vehicle or a four wheel drive 
vehicle, it is only necessary to change the control method of the 
respective valves described above. 
For example, in a case where the brake system of FIG. 1 is applied to a 
front wheel drive vehicle, it is naturally necessary for the TRC control 
to apply a braking force to the front wheels, which are the driving 
wheels. Therefore, the front wheel differential pressure control valve 6 
is made on-state (differential pressure producing state), the front wheel 
first and second control valves 14, 15 are made on-state (open state), and 
the first and second pressure increase control valves 7, 8 are made 
off-state (open state). Brake fluid is drawn by the pump 9 through the 
conduit D from the master cylinder 2 and the master reservoir 3. The drawn 
brake fluid is delivered into the conduit A to produce a braking force on 
the two front wheels. Besides this, it is also possible to execute 
sideslip prevention control and ABS control by changing the control method 
of the respective valves. 
According to the brake system in this embodiment, by feeding brake fluid to 
the primary chamber 2A of the master cylinder 2 with the delivery of the 
front wheel pump 9, the master cylinder 2 is used as regulating device (a 
regulator). That is, the master cylinder 2 plays the role of making the 
brake fluid pressure in the front wheel piping system and the brake fluid 
pressure in the rear wheel piping system roughly the same. Consequently, 
it is also possible to carry out the following kind of braking operations. 
Firstly, an example wherein the master cylinder 2 is used as a regulating 
device during non-braking will be given. For example, in sideslip 
prevention control described above, the master cylinder 2 can produce 
approximately the same brake fluid pressure not only in the front wheel 
side but also in the rear wheel side during non-braking when the brake 
fluid pressure of the front wheel side is transmitted to the rear wheel 
side through the master cylinder 2. That is, the same pressure arises in 
the primary chamber and the secondary chamber as the result that brake 
fluid is fed to the primary chamber 2A of the master cylinder 2. 
This function of the master cylinder 2 is also useful in automatic brakes 
used for keeping a substantially constant inter-vehicle distance during 
non-braking and automatic brakes used in constant speed travel devices for 
realizing constant speed travel on hills and the like. 
As an example, suppose that only the front wheel pump is driven and the 
rear wheel pump is not driven when applying an automatic brake in this 
brake system. At this time, the front wheel first control valve 14 is 
closed and the front wheel second control valve 15 is opened, and the 
other valves are brought to the valve positions in the normal braking 
state (the valve positions of FIG. 1). If this is done, brake fluid that 
the front wheel pump 9 has drawn from the master reservoir 3 is delivered 
to the primary chamber 2A and the wheel cylinders of the left and right 
front wheels 51, 52, and a predetermined brake fluid pressure P1 is 
produced in the primary chamber 2A by the orifice effect of the passage 
connecting the primary chamber 2A and the master reservoir 3. This 
predetermined brake fluid pressure P1 is also transmitted to the secondary 
chamber 2B of the master cylinder 2 and the pressure of the secondary 
chamber 2B also becomes the predetermined brake fluid pressure P1. Thus, 
it is possible to apply substantially the same brake pressure to wheel 
cylinders of all the wheels by only driving the front wheel pump 9. At 
this time, because excess brake fluid escapes through the passages serving 
as the orifice to the master reservoir 3, it is possible to keep each 
wheel cylinder pressure (the pressure produced in the master cylinder) 
down to a pressure of about 10 kgf/mm.sup.2 or less which is not 
considered large. 
Considering the front-rear braking force distribution, in a vehicle wherein 
the wheel cylinder cross-sectional area on the rear wheel side is set 
smaller than the wheel cylinder cross-sectional area on the front wheel 
side or a vehicle in which is disposed a proportioning valve for 
pressure-attenuating the M/C pressure while transmitting it to the rear 
wheel side, it is possible to satisfy a front wheel leading lock even when 
an equal brake fluid pressure is applied to the front and rear wheel 
cylinders. 
As the regulating action of the master cylinder 2 during non-braking the 
following things are also conceivable. For example, in the piping 
construction shown in FIG. 1, although in FIG. 1 the second conduit D2 was 
provided on the front wheel side only, a conduit and a valve equivalent to 
this second conduit D2 and the front wheel second control valve 15 can be 
provided on the rear wheel side also. Furthermore, both the front wheel 
pump 9 and the rear wheel pump 39 can be made self-supplying pumps. When 
this kind of piping construction is used, for example, it will be supposed 
that in automatic braking during non-braking, both of the front wheel and 
rear wheel pumps 9, 39 are driven and also the front wheel second control 
valve 15 and the rear wheel second control valve equivalent to this are 
opened. As a result, a brake fluid pressure is applied to the wheel 
cylinders of all the wheels. At this time, it will be supposed that the 
front wheel differential pressure control valve 6 and the rear wheel 
differential pressure control valve 36 are made differential pressure 
producing state, and therefore the master cylinder 2 and the wheel 
cylinders on the front wheel side and the wheel cylinders on the rear 
wheel side are essentially cut off. When this is done, as a result of a 
difference in the drawing and delivering performance of the front wheel 
pump 9 and the rear wheel pump 39 due to an assembly error or some other 
reason, there is not always a possibility of the wheel cylinder pressure 
of the front wheel side and the wheel cylinder pressure of the rear wheel 
side becoming substantially the same. Consequently, if the delivery 
performance of the pump on the rear wheel side is large, a possibility of 
rear wheel leading lock occurring also exists. 
However, as in the above described embodiment, in automatic braking during 
non-braking, when both of the front wheel and rear wheel pumps 9, 39 are 
driven and the front wheel second control valve 15 and the rear wheel 
second control valve equivalent to this are opened and a brake fluid 
pressure is applied to the wheel cylinders of all the wheels, if both the 
front wheel differential pressure control valve 6 and the rear wheel 
differential pressure control valve 36 are open and the primary chamber 2A 
and the secondary chamber 2B of the master cylinder 2 and the main conduit 
D1 to the front wheel side wheel cylinders and the main conduit to the 
rear wheel side wheel cylinders are opened respectively, the master 
cylinder 2 fulfills the role of the regulating device. That is, it is 
possible to apply substantially the same brake fluid pressure to the wheel 
cylinders of the front wheel side and the rear wheel side. That is, in the 
primary chamber 2A and the secondary chamber 2B of the master cylinder 2, 
it is possible to make the brake fluid pressures of the front wheel side 
and the rear wheel side piping systems the same. Further, not only when it 
is necessary to apply substantially the same brake fluid pressure to the 
wheel cylinders of all the wheels, if the master cylinder 2 is used as the 
regulating device it is possible to make at least one of the wheel 
cylinders of the front wheel side and at least one of the wheel cylinders 
of the rear wheel side substantially the same pressure. 
If the W/C pressure during automatic braking and non-braking is detected by 
the pressure sensor 50 and the front wheel pump 9 and the front wheel 
second control valve 15 are on-off duty controlled on the basis of this 
detection result, it is also possible to carry out regulation of the W/C 
pressure during automatic braking. 
Secondly, an example wherein the master cylinder 2 is used as the 
regulating device during braking will be given. By regulating the master 
cylinder 2 during braking, shown in FIG. 1, an M/C pressure produced in 
the primary chamber 2A due to brake fluid amount drawn from the master 
reservoir 3 by the front wheel pump 9 can be regulated in response to the 
driver applying the brake pedal 1. This regulation of the M/C pressure 
produced by the front wheel pump 9 in response to the brake stepping force 
will be described on the basis of the master cylinder 2 operation diagram 
shown in FIGS. 14A to 14D. The x signs in the diagrams show pedal 
operation amount (pedal stepping stroke) of the driver. 
First, when the brake pedal 1 is not applied by the driver, as shown in 
FIG. 14A, the pressures in the primary chamber 2A and the secondary 
chamber 2B are substantially equal. Because the master reservoir 3 is open 
to the atmospheric pressure, the pressures in the primary and secondary 
chambers 2A, 2B are roughly one atmosphere. 
Next, if the front wheel pump 9 is operates according to the application of 
the brake pedal 1 by the driver, brake fluid delivered from the front 
wheel pump 9 flows into the primary chamber 2A. A pressure arises as a 
result of this brake fluid amount having flowed in. As shown in FIGS. 14B, 
14C the master pistons 2a, 2b forming the primary chamber 2A mutually move 
to depart from each other. The amount of brake fluid which the front wheel 
pump 9 draws from the master reservoir 3 and delivers to the primary 
chamber 2A will be assumed to be substantially constant with respect to 
time. 
When the stepping force of the brake pedal is large with respect to the 
brake fluid amount delivered from the front wheel pump 9 to the primary 
chamber 2A, the passage connecting the master cylinder 2 and the master 
reservoir 3 is blocked by the pedal side master piston 2a which is pushed 
in by the pedal stepping force. As a result, an M/C pressure corresponding 
with the brake pedal stepping force (brake pedal stroke) is produced with 
the use of the brake fluid amount sent by the front wheel pump 9. The 
brake fluid pressure of the primary chamber 2A and the brake fluid 
pressure of the secondary chamber 2B become equal pressures. 
When, on the other hand, the pressure of the primary chamber 2A due to the 
brake fluid delivery of the front wheel pump 9 is relatively large 
compared with the pedal stepping force, in other words when the amount of 
brake fluid sent from the front wheel pump 9 is relatively large, the 
master piston 2a moves to the brake pedal 1 side so that the brake pedal 1 
is returned by a high M/C pressure. As a result, the passage connecting 
the master cylinder 2 and the master reservoir 3 becomes open and excess 
brake fluid is allowed to escape. Because of this, the brake fluid 
pressure of the primary chamber 2A is regulated to a pressure 
corresponding to the pedal stepping force. Consequently, at the same time, 
the secondary chamber 2B is also regulated to a pressure corresponding to 
the pedal stepping force. 
By the brake fluid amount sent from the front wheel pump 9 to the primary 
chamber 2A, which is adjusted by the passage connecting the master 
cylinder 2 and the master reservoir 3 and the master piston 2a as 
described above, it is possible to produce M/C pressure corresponding to 
the pedal stepping force with a relatively small brake pedal stroke. 
FIG. 14D illustrates a view of the operation of a master cylinder in a 
conventional brake system. This view shows a state in which the master 
pistons have moved as a result of applying the brake pedal. When the pedal 
stroke amount of this conventional brake system shown in FIG. 14D is 
compared to the brake system in the embodiment shown in FIGS. 14B and 14C, 
it can be seen that the pedal stroke amount is larger with the 
conventional brake system. This is because the volume of the primary 
chamber 2A increases in the present embodiment due to the brake fluid sent 
from the front wheel pump 9 to the primary chamber 2A. As a result, the 
master pistons 2a, 2b move apart from each other and the master piston 2a 
of the brake pedal 1 side approaches the brake pedal 1. If brake fluid is 
sent to the primary chamber 2A as described above and the pressure in the 
primary chamber 2A is regulated corresponding to the pedal stepping force 
with the use of the brake fluid sent from the front wheel pump 9, even 
when the pedal stroke amount is small an M/C pressure corresponding to the 
pedal stepping force can be produced. Therefore, it is possible to make 
the pedal stroke amount small. At this time it is possible to made the 
brake fluid pressure with respect to the front wheel side piping system 
and the brake fluid pressure with respect to the rear wheel side piping 
system substantially equal. 
That is, to produce a required M/C pressure, the driver applies the brake 
pedal 1. However, in a conventional brake system because the M/C pressure 
is simply produced corresponding to the pedal stroke amount, a long pedal 
stroke is necessary to produce a high M/C pressure. Consequently, with a 
conventional brake system it has not been possible to satisfy the 
requirement of producing a high M/C pressure even if the pedal stroke is 
short. In contrast to the conventional brake system, the brake system of 
this embodiment satisfies the need for a high M/C pressure with a short 
pedal stroke. 
Further, the discharge port of the front wheel pump 9 and the primary 
chamber 2A are directly connected and brake fluid discharged from the 
front wheel pump 9 is directly sent to the primary chamber 2A. Even if 
excess brake fluid is sent to the primary chamber 2A, this brake fluid 
counterflows to the master reservoir 3 through the orifice of the passage 
connecting the master cylinder 2 and the master reservoir 3. Because of 
this, when brake fluid that the pump has drawn in sideslip prevention 
control or the like counterflows to the master reservoir 3, moderately 
increase and decrease of the M/C pressure can be carried out. 
FIG. 15 illustrates an example of the steps in regulation control when the 
master cylinder 2 is used as a regulating device. As described above, this 
regulation control has the object of shortening the stroke of the brake 
pedal even when a high M/C pressure is to be produced. Therefore, 
independently from ABS control, sideslip prevention control or TRC 
control, the following processing of regulation control may be carried 
out. 
As shown in FIG. 15, in a step 701, using a brake switch (not shown), it is 
determined whether or not the brake pedal 1 has been applied by the driver 
and the vehicle is essentially in a braking state. When the brake pedal 1 
is being applied, the front wheel pump 9 is driven in step 702. Also, in 
step 703, the front wheel second control valve 15 is opened. When, in step 
701, it is determined that the brake is not being applied, the pump drive 
and the front wheel second control valve 15 drive are stopped in step 704. 
By this means, during braking by the brake pedal by the driver 1, the 
brake fluid amount is drawn from the master reservoir 3 and delivered to 
the primary chamber 2 by the front wheel pump 9. As a result, brake fluid 
pressure is regulated in the primary chamber 2A to be consistent with the 
pedal stepping force while the master piston 2b make a stroke by 
essentially only the volume of the secondary chamber 2B. That is, when the 
pedal stepping force is increased, a suitable pressure is produced in the 
primary chamber 2A by the brake fluid amount delivered from the front 
wheel pump 9. 
In this regulating action of the primary chamber 2A of the master cylinder 
2 during braking, and as shown in the piping construction of FIG. 1, the 
second conduit D2 is provided only on the front wheel side. However, a 
conduit and a valve equivalent to this second conduit D2 and the front 
wheel second control valve 15 may also be provided for the rear wheels and 
both the front wheel pump 9 and the rear wheel pump 39 made self-supplying 
pumps. In this case, in response to the brake switch of step 701 being ON 
(the brake is applied) , both the front wheel pump 9 and the rear wheel 
pump 39 are driven and also the front wheel second control valve 15 and 
the valve for the rear wheels equivalent to the front wheel second control 
valve 15 are opened. If this is done, it is possible to regulate brake 
fluid pressure in both the primary chamber 2A and the secondary chamber 2B 
to be inconsistent with the pedal stepping force while using the brake 
fluid amounts delivered by both of the pumps 9, 39. Consequently, it is 
possible to further shorten the pedal stroke compared to when a second 
conduit D2 is provided only in the front wheel side piping system and 
regulation is carried out in only the primary chamber 2A as shown in FIG. 
1. In this case, since the master cylinder 2 goes through as a regulating 
device it is possible to make the front wheel side piping system and the 
rear wheel side piping system substantially the same pressure. 
This embodiment describes an example wherein the invention is applied to a 
brake system having a master cylinder 2 made up of two chambers that are 
the primary chamber 2A and the secondary chamber 2B. However, the 
invention may also be applied to a brake system comprising a regulator and 
one chamber like a hydraulic booster. In this case, if the throttling of a 
passage connecting the regulator with the reservoir is utilized to give a 
hydraulic pressure to a regulator system, it is possible to obtain the 
same effects as the embodiment described above. 
Irrespective of the brake piping system of the front and rear piping 
arrangements, the present invention may also be applied to a brake piping 
system having an X piping arrangement. 
During non-braking, when the driver does not apply the brake pedal, when a 
brake fluid pressure is applied to the wheel cylinders by automatic 
braking, the flow chart in FIG. 15 can be modified as follows. Instead of 
determining whether or not the brake switch is ON in step 701, it is 
determined whether or not automatic braking in sideslip prevention 
control, constant speed travel control during non-braking or the like has 
been executed. When an affirmative determination is made processing 
proceeds to step 702 and when a negative determination is made processing 
proceeds to step 704. Naturally, it may also be applied to control during 
braking in the sideslip prevention control described above. 
In the embodiment described above, a brake system may be constructed so 
that a pedal stepping force of the driver is mechanically transmitted to 
the master piston 2a via a servo device (booster) through a rod connected 
to the brake pedal. Further, the present invention can also be applied to 
a so-called brake-by-wire system wherein a pedal stepping force or stroke 
from the driver is converted into an electrical signal and an actuator 
(specifically a pump or a hydraulic booster or the like) receiving this 
electrical signal produces a pressure in the master cylinder equal to the 
amount of the pedal stepping force or stroke from the driver. 
[Second Embodiment] 
Next, the second embodiment of the present invention will be described. 
FIG. 16 is a brake piping diagram in a brake system, and this brake system 
has a sideslip prevention system and an ABS. 
The brake system shown in FIG. 16 is a brake system applied to a rear wheel 
drive four wheeled vehicle having two piping systems (x piping system) 
consisting of a first piping system for controlling brakes of the left 
front wheel and the right rear wheel and a second piping system for 
controlling brakes of the right front wheel and the left rear wheel. 
As shown in FIG. 16, a brake pedal 1 stepped on by a driver to apply a 
braking force to the vehicle is connected to a master cylinder 2 
constituting a brake fluid pressure producing source. When the driver 
steps on the brake pedal 1, master pistons 2a, 2b disposed in the master 
cylinder 2 are pushed thereby producing a master cylinder pressure ("the 
M/C pressure"). 
This master cylinder 2 is divided into two rooms that are a primary chamber 
2A and a secondary chamber 2B. A primary chamber 2A side produces a brake 
fluid pressure to be transmitted to the first piping system and a 
secondary chamber 2B side produces a brake fluid pressure to be 
transmitted to the second piping system. To the master cylinder 2 is 
provided a master reservoir 3 having connecting passages 20, 21 
respectively connecting with the two rooms of the master cylinder 2. The 
master reservoir 3 supplies brake fluid to the master cylinder 2 and 
receives excess brake fluid inside the master cylinder 2 through the 
connecting passages 20, 21. 
A first control valve (connection control valve) 25 for controlling 
connection and disconnection of the primary chamber 2A of the master 
cylinder 2 and the master reservoir 3 is provided in the connecting 
passage 20 connecting the primary chamber 2A and the master reservoir 3. 
By means of the first control valve 25, high-pressurization of the primary 
chamber 2a is made possible. 
An M/C pressure produced by the application of the brake pedal by the 
driver is transmitted to the first piping system and the second piping 
system. Because the first piping system and the second piping system are 
of substantially the same construction, the first piping system only will 
be described. With respect to the second piping system, only construction 
differing from the first piping system will be described. 
The first piping system comprises conduit A constituting a main conduit for 
transmitting the above-mentioned M/C pressure to wheel braking force 
producing devices, namely a wheel cylinder 5 for the left front wheel and 
a wheel cylinder 34 for the right rear wheel. As a result, wheel cylinder 
pressures ("W/C pressures") are produced in the wheel cylinders 5, 34. 
Specifically, the conduit A branches into two conduits A1, A2, and the 
conduit A1 transmits brake fluid to the wheel cylinder 5, and the conduit 
A2 transmits brake fluid to the wheel cylinder 34. In the conduit A1 a 
first pressure increase control valve 7 for controlling pressure increase 
to the wheel cylinder 5 is provided. In the conduit A2 a second pressure 
increase control valve 8 for controlling pressure increase to the wheel 
cylinder 34 is provided. These first and second pressure increase control 
valves 7, 8 are two-position valves which can be controlled between open 
and closed states. When these first and second pressure increase control 
valves 7, 8 are controlled to their open states, an M/C pressure or a 
brake fluid pressure produced by delivery of brake fluid of a first pump 9 
which will be further discussed later can be applied to the wheel 
cylinders 5, 34. 
At a time of normal braking ("during normal braking") arising from the 
driver applying a brake pedal, the first and second pressure increase 
control valves 7, 8 are always controlled to be opened. Safety valves 7a, 
8a are disposed in parallel with the first and second pressure increase 
control valves 7, 8 respectively so that when brake pedal stepping is 
stopped and ABS control has finished brake fluid can be promptly removed 
from the wheel cylinders 5, 34. In a conduit B connecting the conduits A1, 
A2 between the first and second pressure increase control valves 7, 8 and 
the wheel cylinders 5, 34 to an ABS control use reservoir 10, a first 
pressure decrease control valve 11 and a second pressure decrease control 
valve 12 are respectively disposed. These first and second pressure 
decrease control valves 11, 12 are constructed as two-position valves 
which can be controlled between open and closed states. During normal 
braking these first and second pressure decrease control valves 11, 12 are 
always closed. 
In a conduit C connecting the conduit A between the master cylinder 2 and 
the first and second pressure increase control valves 7, 8 to the ABS 
control use reservoir 10, a first pump 9 is disposed with safety valves 
9a, 9b on either side. By means of this first pump 9, drawing and delivery 
of brake fluid is carried out. Also, to moderate pulsation of brake fluid 
that the first pump 9 delivers, in the conduit C on the delivery side of 
the first pump 9, a first damper 13 of a fixed capacity is disposed. 
A conduit D is connected to the conduit C between the ABS control use 
reservoir 10 and the first pump 9. This conduit D is connected to the 
master reservoir 3. A second control valve 15 is provided in this conduit 
D. This second control valve 15 is constructed as a two-position valve 
which can be controlled between open and closed states, and during normal 
braking is always closed. Through this conduit D the above-mentioned first 
pump 9 can draw brake fluid from inside the master reservoir 3 and deliver 
it toward the conduit A. That is, during sideslip prevention control and 
the like, the first pump 9 draws brake fluid from the master reservoir 3 
and can carry out supply of brake fluid. A nonreturn valve 16 is disposed 
between the ABS control reservoir 10 and the point of connection between 
the conduit D and the conduit C so that brake fluid does not escape into 
the ABS control use reservoir 10 through the conduit D. 
The second piping system is of almost the same construction as the first 
piping system. That is, the first and second pressure increase control 
valves 7, 8 respectively correspond to third and fourth pressure increase 
control valves 37, 38 and the first and second pressure decrease control 
valves 11, 12 correspond to third and fourth pressure decrease control 
valves 41, 42. The wheel cylinders 5, 34 respectively correspond to wheel 
cylinders 4, 35, the ABS control use reservoir 10 corresponds to an ABS 
control use reservoir 40, the first pump 9 corresponds to a second pump 39 
and the first damper 13 corresponds to a second damper 33. Also, the 
conduit A, the conduit B and the conduit C correspond to a conduit E, a 
conduit F and a conduit G. 
However, in the second piping system, a conduit corresponding to the 
conduit D is not provided. Also, in the conduit E in the vicinity of the 
master cylinder 2, a pressure sensor (pressure detecting device) 50 which 
can detect a brake fluid pressure is disposed. 
Next, in FIG. 17, the construction of a brake system electronic control 
unit ("the ECU") 100 is shown. As shown in the figure, various detection 
signals are sent from the pressure sensor 50 to the brake system ECU: an 
acceleration sensor 61, wheel speed sensors 62, a yaw rate sensor 63, a 
steering sensor 64 and a stroke sensor 65. On the basis of these detection 
signals, the ECU 100 controls opening and closing of the various control 
valves disposed in the first and second piping systems. 
Next, sideslip prevention control will be described on the basis of the 
flow charts shown in FIG. 18 through FIG. 20. FIG. 18 is a flow chart 
showing the overall sideslip prevention control, FIG. 19 is a flow chart 
showing control of a non-controlled wheel in sideslip prevention control, 
and FIG. 20 is a flow chart showing control of an controlled wheel in 
sideslip prevention control. 
First, the overall processing of sideslip prevention control shown in FIG. 
3 will be described. This processing is carried out wheel by wheel. For 
example, when processing ends for the left front wheel, processing is then 
carried out for the right rear wheel. When processing finishes for all the 
wheels, processing for the left front wheel is carried out again. 
In this sideslip prevention control, when the vehicle is in an oversteering 
state during turning, the oversteering state is cancelled by applying a 
braking force to either of the left and right front wheels according to 
the direction of the turn. 
For example, as shown in FIG. 7, when the vehicle is turning to the left 
and oversteering by the driver causes the actual turning pattern of the 
vehicle to vary from the target path, as shown by the hatched part in the 
figure, a braking force may be applied to the right front wheel 51. 
With respect to an oversteering state in a case of turning to the right, 
the oversteering state may be cancelled by applying a braking force to the 
left front wheel 52. When the vehicle has entered an understeering state, 
the degree of the understeering state is reduced by applying braking 
forces to both of the rear wheels 53, 54 The following description 
discusses a case wherein the kind of oversteering state shown in FIG. 6 
has occurred and sideslip prevention control for applying a braking force 
to the right front wheel 51 is carried out. 
In step 801, the starting conditions of sideslip prevention control are 
determined. That is, it is determined whether or not a sideslip angle of 
the vehicle is greater than a predetermined angle. This sideslip angle is 
obtained as a difference between an actual vehicle turn angle obtained 
from a yaw rate detected by the yaw rate sensor 63 and a target turn angle 
set from a steering angle detected by the steering sensor 64 and a vehicle 
speed detected by wheel speed sensors 62. 
If in step 801 the determination is YES, processing proceeds to step 803. 
If in step 801, it is NO, processing proceeds to step 809 which determines 
whether or not the driver is not applying the brake pedal 1. If the 
determination in step 809 is YES, processing proceeds to step 811 and 
resets a braking determination flag which will be further discussed later. 
In step 803, determination of whether or not the wheel currently being 
processed is the outer wheel of the turning line is carried out. At the 
time of the oversteering state shown in FIG. 7, because the sideslip 
prevention controlled wheel is the right front wheel 51 which is the outer 
wheel of the turning line, processing proceeds to step 805. For the other 
wheels, processing proceeds to step 807. Concerning the right front wheel 
51, after processing for a controlled wheel is carried out in step 805, 
processing proceeds to step 809. Concerning the wheels other than the 
right front wheel 51, after processing for a non-controlled wheel is 
carried out in step 807, processing proceeds to step 809. 
In step 809, whether or not braking is in progress is determined. Whether 
or not braking is in progress is determined on the basis of the M/C 
pressure detected by the pressure sensor 50. That is, when a pressure 
increasing output command (discussed below) has not been issued with 
respect to the controlled wheel, unless the driver steps on the brake 
pedal 1, the M/C pressure does not increase. Therefore, when a pressure 
increasing output command has not been issued and when the M/C pressure 
increases, a braking determination flag is set and it is deemed that 
braking is in progress. 
Since the brake system in this embodiment is of the construction shown in 
FIG. 16 and normally the master cylinder 2 and the wheel cylinders 4, 5, 
34, 35 are always connected, the M/C pressure and the wheel cylinder 
pressure are substantially the same. Consequently, if the above-mentioned 
braking determination is carried out on the basis of the M/C pressure, it 
is possible to carry out control corresponding to the W/C pressure. That 
is, because it is possible to estimate the road surface friction 
coefficient (road surface .mu.) on the basis of the W/C pressure, control 
corresponding to the road surface .mu. is possible by carrying out control 
on the basis of the M/C pressure substantially equal to the W/C pressure. 
In step 809, if braking is not in progress, the braking determination flag 
is reset in step 811 and processing of the wheel for which processing is 
currently being carried out is ended and processing shifts to another 
wheel. If in step 809 braking is in progress, processing of the wheel for 
which processing is currently being carried out is ended directly and 
processing shifts to another wheel. 
Next, control of a controlled wheel and control of a non-controlled wheel 
will be described on the basis of FIG. 19 and FIG. 20. Here, the 
description will be divided according to whether the vehicle is in the 
process of braking or not in the process of braking. 
(Processing During Non-braking) 
(1) Processing in Non-controlled Wheel 
In step 901, whether or not braking is in progress is determined. This 
determination is made by whether or not the above-mentioned braking 
determination flag has been set. Because this example is now during 
non-braking, the determination of step 901 is NO and processing proceeds 
to step 905 which sets a pressure-holding output and ends processing. 
When this holding output is set, the brake system ECU drives solenoids of 
the control valves corresponding to the non-controlled wheels (for example 
if it is the left front wheel 52 the first pressure increase control valve 
7 and the pressure decrease control valve 11 corresponding to the wheel 
cylinder 5 in the left front wheel 52), and moves their valve positions to 
the solenoid drive pattern (C) shown in FIG. 21. That is, when a holding 
output is set, the pressure increase control valve is brought to its 
on-state (closed state), the pressure decrease control valve to its 
off-state (closed state), the first control valve 25 to its on-state 
(closed state), and the second control valve 15 to its off-state (closed 
state). However, during non-braking, if the valve states of the first 
control valve 25 and the second control valve 15 according to the solenoid 
drive pattern (C) for the non-controlled wheel is different from those 
according to the solenoid drive pattern for the controlled wheel, the 
valve states of the first control valve 25 and the second control valve 15 
is determined based on the solenoid drive pattern for the controlled 
wheel. In other words, the solenoid drive pattern set for the controlled 
wheel has priority over the solenoid drive pattern set for the 
non-controlled wheel with respect to the valve states of the first and 
second control valves 25, 15 during non-braking. 
(2) Processing in Controlled Wheel 
In step 1001, whether or not braking is in progress is determined. This 
determination is the same as that for the non-controlled. If the 
determination is NO, then processing proceeds to step 1003 for non-braking 
processing. 
In step 1003, it is determined whether or not the actual wheel speed of the 
controlled wheel (here, the right front wheel 51) is larger than a target 
wheel speed. This target wheel speed is set as a wheel speed corresponding 
to the current slip angle state. At this moment, it is determined whether 
or not the actual wheel speed of the right front wheel 51 is greater than 
this target wheel speed. 
Then, when in step 1003 the determination is YES, pressure increasing 
output processing is carried out to make the actual wheel speed approach 
the target wheel speed and processing is ended. When this pressure 
increasing output command is issued, the ECU drives solenoids of the 
control valves corresponding to the controlled wheel and moves the valve 
members of the control valves to the valve positions of the solenoid drive 
pattern (A) shown in FIG. 21. That is, when the pressure increasing output 
command is set, the third pressure increase control valve 37 corresponding 
to the right front wheel 51 is brought to its off-state (open state), the 
third pressure decrease control valve 41 to its off-state (closed-state), 
the first control valve 25 to its on-state (closed state) and the second 
control valve 15 to its on-state (open state). 
When this pressure increasing output command is issued the first pump 9 is 
driven. When the first pump 9 is driven brake fluid from inside the master 
reservoir 3 is drawn through the conduit D and this drawn brake fluid is 
delivered to the conduit A. 
Because as mentioned above the pressure increase control valves 7, 8, 38 of 
the non-controlled wheel are in their on-states (closed states), the brake 
fluid delivered to the conduit A is supplied to the primary chamber 2a of 
the master cylinder 2 and increases the brake fluid pressure in the 
primary chamber 2a. At this time, because the master reservoir 3 and the 
primary chamber 2a are cut off from each other by the first control valve 
25 between the master reservoir 3 and the primary chamber 2a, the brake 
fluid supplied into the primary chamber 2a cannot escape to the master 
reservoir 3. Therefore, the brake fluid pressure of the primary chamber 2a 
increases greatly. 
Also, due to the increase in pressure of the primary chamber 2A, the master 
pistons 2a, 2b inside the master cylinder 2 move. The brake fluid pressure 
inside the secondary chamber 2b increases due to the movement of the 
master pistons 2a, 2b. This increased brake fluid pressure is given to the 
wheel cylinder 4 corresponding to the controlled wheel (the right front 
wheel 51) through the conduit E to increase the W/C pressure thereof. As a 
result, it is possible to increase the W/C pressure of the wheel cylinder 
corresponding to the controlled wheel in the second piping system without 
driving the second pump 39. 
When the determination in step 1003 is NO, processing proceeds to step 1005 
and determines whether or not the actual wheel speed in the controlled 
wheel (the right front wheel 51) is smaller than the target wheel speed. 
When in step 1005 the determination is YES, a pressure decreasing output 
command is issued and processing ends. When this pressure decreasing 
output command issues, the ECU drives solenoids of the control valves 
corresponding to the controlled wheel and moves the valve members of the 
control valves to the valve positions of the solenoid drive pattern (B) 
shown in FIG. 21. That is, when the pressure decreasing output command is 
set, the third pressure increase control valve 37 corresponding to the 
right front wheel 51 is brought to its on-state (closed state) and the 
third pressure decrease control valve 41 to its on-state (open state), and 
the first control valve 25 is brought to its off-state (open state) and 
the second control valve 15 to its off-state (closed state). 
As a result, brake fluid creating the W/C pressure is allowed to escape to 
the ABS control use reservoir 40 through the conduit F which is opened by 
the third pressure decrease control valve 41. As a result, the W/C 
pressure in the right front wheel 51 is decreased and the actual wheel 
speed of the right front wheel 51 is made to approach the target wheel 
speed. It is to be noted that the second pump 39 takes in brake fluid 
discharged in the ABS control use reservoir 40 and returns the brake fluid 
into the conduit E. 
When the determination in step 1005 is NO, a holding output command issues 
and processing ends. When this holding output command issues, the ECU 100 
drives solenoids of control valves corresponding to the controlled wheel 
and moves the valve members of the control valves to the valve positions 
of the solenoid drive pattern (C) shown in FIG. 21. That is, when the 
holding output command is set, the third pressure increase control valve 
37 is brought to its on-state (closed state) and the third pressure 
decrease control valve 41 to its off-state (closed state), and the first 
control valve 25 is brought to its on-state (closed state) and the second 
control valve 15 to its off-state (closed state) so they are all brought 
to their closed states. 
By this means, the W/C pressure in the right front wheel 51 is kept 
unchanged in its present state. That is, because the actual wheel speed of 
the right front wheel 51 is the same as the target wheel speed, control to 
maintain this wheel speed is carried out. 
(Processing During Braking) 
(1) Processing in Non-controlled Wheel 
In step 901, because braking is in progress, the determination is YES and 
processing proceeds to step 203 and a braking pressure increasing output 
command is set and processing ends. 
When this braking pressure increasing output command is set, the ECU 100 
drives the solenoids of the control valves corresponding to the 
non-controlled wheels and moves the valve members of the control valves to 
the valve positions of the solenoid drive pattern (D) shown in FIG. 21. 
That is, when the braking pressure increasing output command is set, the 
pressure increase control valves are brought to the off-state (open 
state), the pressure decrease control valves to the off-state (closed 
state), the first control valve 25 to the off-state (open state) and the 
second control valve 15 to the off-state (closed state). 
Because of this, when the M/C pressure increases as a result of operation 
of the brake pedal 1 by the driver, the W/C pressures of the 
non-controlled wheels are increased through the pressure increase control 
valves. 
(2) Processing in Controlled Wheel 
In step 1001, because braking is in progress, the determination is YES and 
processing proceeds to step 1013. In step 1013, it is determined whether 
or not the actual wheel speed of the controlled wheel (the right front 
wheel 51) is larger than a target wheel speed. When in step 1013 the 
determination is YES, a braking pressure increasing output command issues 
to make the actual wheel speed approach the target wheel speed and 
processing ends. When this braking pressure increasing output command is 
set, the ECU 100 drives solenoids of the control valves corresponding to 
the controlled wheel and moves the valve members of the control valves to 
the valve positions of the solenoid drive pattern (D) shown in FIG. 21. 
That is, when the braking pressure increasing output command is issued, 
the third pressure increase control valve 37 corresponding to the right 
front wheel 51 is brought to its off-state (open state), the-third 
pressure decrease control valve 41 to its off-state (closed state), the 
first control valve 25 to its off-state (open state), and the second 
control valve 15 to its off-state (closed state). 
That is, when the braking pressure increasing output command issues, 
increasing of the W/C pressure in the right front wheel 51 is carried out 
using the M/C pressure increased by the operation of the brake pedal 1 by 
the driver. In other words, rather than increasing the W/C pressure of the 
controlled wheel by driving the first pump 9 the W/C pressure is increased 
by the operation of the brake pedal 1 by the driver. 
When in step 1013 the determination is NO, processing proceeds to step 1015 
and determines whether or not the actual wheel speed in the right front 
wheel 51 is smaller than the target wheel speed. When in step 1015 the 
determination is YES, a braking pressure decreasing output command issues 
at step 1019 and processing ends. When this braking pressure decreasing 
output command is outputted, the ECU 100 drives solenoids of the control 
valves corresponding to the controlled wheel and moves the valve members 
of the control valves to the valve positions of the solenoid drive pattern 
(E) shown in FIG. 21. That is, when the braking pressure decreasing output 
command is set, the third pressure increase control valve 37 is brought to 
its on-state (closed state) and the third pressure decrease control valve 
41 to its on-state (open state), the first control valve 25 is brought to 
its off-state (open state) and the second control valve 15 to its 
off-state (closed state). 
This processing is the same as when a pressure decreasing output is set 
during non-braking, and decreases the W/C pressure corresponding to the 
controlled wheel and makes the actual wheel speed of the controlled wheel 
approach he target wheel speed. 
When in step 1015 the determination is NO, a braking holding output command 
issues at step 1021 and processing ends. When this braking holding output 
command is set, the ECU 100 drives solenoids of the control valves 
corresponding to the controlled wheel and moves the valve members of the 
control valves to the valve positions of the solenoid drive pattern (F) 
shown in FIG. 21. That is, when the braking holding output command is set, 
the third pressure increase control valve 37 corresponding to the right 
front wheel 51 is brought to the on-state (closed state) and the third 
pressure decrease control valve 41 to its off-state (closed state), and 
the first control valve 25 is brought to its off-state (open state) and 
the second control valve 15 to its off-state (closed state). That is, the 
W/C pressure corresponding to the controlled wheel is kept unchanged at 
its present state and supply of brake fluid from the master reservoir 3 to 
the non-controlled wheels is possible. 
By providing in the connecting passage 20 connecting the master reservoir 3 
and the primary chamber 2A of the master cylinder 2 a first control valve 
25 for controlling opening and closing of this connecting passage 20 in 
this way it is possible to make the brake fluid pressure inside the 
primary chamber 2A increase greatly just with driving of the first pump 9 
in the first piping system. Consequently, during sideslip prevention 
control, without using the second pump 39 disposed in the second piping 
system, it is possible to make possible increase of the W/C pressure in 
the second piping system. 
By this means, in sideslip prevention control, because it is possible to 
eliminate a construction (equivalent to the conduit D and the second 
control valve 15 in the first piping system) necessary for using a second 
pump 39 disposed in the second piping system, it is possible to achieve 
simplification of the piping construction. 
Also, because the second pump 39 in the second piping system need only be 
used for decreasing the W/C pressure, it is not necessary to use a 
self-supplying pump like the first pump 9 in the first piping system and 
it is possible to achieve cost reductions. 
Also, because braking determination is carried out on the basis of an M/C 
pressure substantially the same as the W/C pressure, it is possible to 
carry out sideslip prevention control corresponding to the road surface 
.mu.. 
With respect to ABS control, by making the pressure decrease control valves 
11, 12, 41, 42 provided corresponding to the wheels open-state and 
allowing brake fluid to escape to the ABS control use reservoir 10, 40, it 
is possible to carry it out by the same method as conventionally of 
carrying out pressure reduction of the W/C pressure of the wheel cylinders 
of the wheels. 
The brake system in this embodiment can also carry out traction control. 
Specifically, when the vehicle is accelerating, if an accelerating slip 
ratio detected by the wheel speed sensors 62 and the acceleration sensor 
61 is above a predetermined value, it is deemed that the vehicle is in a 
state of accelerating slip. Brake fluid of the master reservoir 3 is drawn 
by the first pump 9 and the W/C pressure corresponding to the rear wheels, 
which are the driving wheels, is increased. As a result, a braking force 
is thereby applied to the driving wheels and it is possible to carry out 
traction control. 
The above description should not be construed as limiting the invention but 
merely to provide illustrations of some of the present preferred 
embodiments. Thus the scope of the invention should be determined by the 
appended claims and their legal equivalents, rather than the example 
given.