Brake fluid pressure control device

A brake fluid pressure control device has a wheel brake fluid pressure control valve including a discharge valve provided in a main fluid passage extending from a master cylinder to wheel brakes. A discharged fluid reservoir is provided to temporarily store the brake fluid discharged from the discharge valve. A pump is provided to pump the brake fluid out of the discharged fluid reservoir to return it to the main passage. A fluid supply passage branches from the main passage at a point upstream of a flow return point from the pump and extends to the discharged fluid reservoir. A traction control changeover valve is provided to check a fluid flow from the flow return point toward the master cylinder during traction control. A shutoff valve is provided to check a fluid flow from the master cylinder to the discharged fluid reservoir through the fluid supply passage while the master cylinder is pressurized. Further, the control device has an intermediate fluid reservoir provided upstream of the shutoff valve so as to be brought into communication with the supply passage during the traction control.

BACKGROUND OF THE INVENTION 
The present invention relates to a brake fluid pressure control device of a 
simple structure and having both the function of antilock and traction 
control. 
The simplest antilock device known is the so-called recirculating type 
which comprises a wheel brake fluid pressure control valve including a 
discharge valve provided in the main fluid passage extending from the 
master cylinder to each wheel brake, a discharged fluid reservoir for 
temporarily storing the brake fluid discharged from the discharge valve, 
and a pump for pumping the brake fluid out of the discharged fluid 
reservoir and returning it to the main passage. If it is desired to add 
the traction control function to this device, the structure of the entire 
device can be simplified most effectively by using the circulation pump 
for the antilock device as a pressure source for the traction control. 
In order to employ such a structure, brake fluid has to be supplied to the 
inlet port of the pump. This can be done in several known ways. 
These known ways are classified into two types. In one type, a supply 
passage is provided so as to extend directly from the reservoir for the 
master cylinder to the pump inlet port. In the other type, the supply 
passage is provided so as to branch from the main passage connecting the 
master cylinder outlet port to each wheel brake. Of these two types, the 
latter is advantageous in view of the easy mounting on a vehicle and the 
non-necessity of returning any redundant brake fluid to the reservoir for 
the master cylinder through its inlet port. 
The latter method, in which the supply passage branches from the main 
passage, has a problem in that the amount of brake fluid that can be 
supplied into the pump is limited due to the resistance at the master 
cylinder inlet port, the resistance of the piping from the master cylinder 
to the brake fluid pressure control device and the flow resistance in a 
shutoff valve for shutting the supply passage during normal braking. Thus, 
there is a possibility that the brake fluid pressure may not increase 
sufficiently quickly when the traction control starts. 
SUMMARY OF THE INVENTION 
An object of the present invention is to improve the brake fluid supply 
capacity of a brake fluid pressure control device of the type described 
above, that is, the type in which a supply passage connecting to a 
discharged fluid reservoir branches from the main passage at a point 
upstream of the fluid-flow-return point from the pump. 
The characterizing feature of the present invention consists in the 
provision of an intermediate fluid reservoir communicating with a fluid 
supply passage in order to eliminate the fluid intake resistance at the 
inlet port of the master cylinder and the resistance of the piping 
extending from the master cylinder to the brake fluid pressure control 
device. 
The intermediate fluid reservoir has to be in communication with both the 
master cylinder and the discharged fluid reservoir during the traction 
control. In contrast, while the brake pressure is being applied in the 
normal braking mode, it has to be kept out of communication with the 
discharge fluid reservoir. According to the present invention, the 
intermediate fluid reservoir is provided at such a point that the two 
positions or phases can be reliably changed over. 
Namely, a conventional device of the same type, as well as the device of 
the present invention, requires a traction control changeover valve for 
checking fluid flow from the flow return point from the pump toward the 
master cylinder during traction control and a shutoff valve for checking 
fluid flow from the fluid supply passage toward the discharged fluid 
reservoir during the normal braking mode (while the pressure in the master 
cylinder is being applied). 
According to the present invention, the intermediate fluid reservoir is 
provided upstream of the shutoff valve. With this arrangement, the shutoff 
valve can be used to change over the communication of the intermediate 
fluid reservoir. 
The shutoff valve may be provided as an extra valve independent of the 
traction control changeover valve (first form) or may be in the form of a 
three-port two-position traction control changeover valve provided at a 
branch point between the main passage and the fluid supply passage (second 
form). This latter changeover valve can selectively bring the master 
cylinder into communication with the flow return point from the pump or 
with the fluid supply passage. Thus, the use of the above extra valve can 
be eliminated. The present invention is applicable to either form. 
In the first form, the intermediate fluid reservoir may be provided either 
in the main passage or in the fluid supply passage, as far as it is 
provided upstream of the shutoff valve. But in the second form, it has to 
be provided in the main passage, upstream of the traction control 
changeover valve, because this valve also serves as a shutoff valve. 
During traction control, the intermediate fluid reservoir communicates with 
the pump, so that the brake fluid is supplied through the pump from the 
intermediate fluid reservoir. This serves to reduce the fluid intake 
resistance at the inlet port of the master cylinder and the resistance of 
the piping extending from the master cylinder to the brake fluid pressure 
control device, thereby reducing the fluid intake resistance and 
increasing the fluid supply capacity. 
Also, by supplying fluid from the intermediate fluid reservoir, the amount 
of brake fluid drawn in through the master cylinder from its reservoir 
during traction control decreases. This serves to reduce the difference 
between the pedal stroke when the brake pedal is depressed during or 
immediately after traction control and the pedal stroke when the pedal is 
depressed during normal braking, thereby improving the pedal feeling. The 
smaller the amount of decrease in the pressure in the intermediate fluid 
reservoir below the atmospheric pressure, the greater these effects. Thus, 
it is extremely effective to provide the intermediate fluid reservoir with 
a volume control means to be described in the description of the 
embodiments. 
As described above, according to the present invention, the intermediate 
fluid reservoir is provided in the main passage or the supply passage and 
it is adapted to be brought into communication, during traction control, 
with the supply passage branching from the main passage. Thus, the fluid 
supply capacity to the pump is kept high because it is not affected by the 
fluid intake resistance at the inlet port of the master cylinder or the 
resistance of the passage extending from the master cylinder to the brake 
fluid pressure control device. This allows simplification of the structure 
of the control device without delaying the rise of the brake fluid 
pressure at the initial stage of the traction control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an example in which a main passage and a supply passage are 
normally in communication with each other, and a traction control 
changeover valve is a two-port two-position valve provided between the 
point at which the supply passage branches from the main passage and the 
flow return point from the pump. 
A master cylinder 1 (a booster of any type may be attached thereto) has two 
outlet ports. We shall describe hereinafter only one line of the two 
lines, because the same explanation or discussion is applicable to both 
lines. 
Wheel brake fluid pressure control valves 5-1 and 5-2 are provided in 
respective main passages connecting an outlet port 2 to wheel brakes 4-1 
and 4-2. The wheel brake fluid pressure control valves may be a 
three-position type valve (as shown in FIG. 1) having pressure-increase, 
pressure-hold and pressure-decrease positions, or a two-position typle 
valve having no pressure-hold position. In many cases, a check valve (not 
shown) is attached to each of the control valves in parallel therewith to 
allow the brake fluid pressure to drop quickly when the pressure on the 
brake pedal is relaxed during antilock control. 
When the brake fluid pressure control valves 5-1 and 5-2 are in their 
discharge positions, the wheel brakes 4-1 and 4-2 are in communication 
with a discharged fluid reservoir 6. 
A pump 7 pumps the brake fluid out of the discharged fluid reservoir 6 and 
returns it to a flow return point 8 of one of the main passages. In order 
to prevent a pulsating flow of the fluid discharged from the pump 7, a 
buffer fluid reservoir 9(ER) and a throttle 10 are used in combination. 
Described above is the basic structure of a recirculating type of antilock 
brake fluid pressure control device. In order to add a traction control 
function to this device, the following elements are added. 
A supply passage 11 is provided that branches from the main passage at a 
branch point upstream of the flow return point 8 and extends to the 
discharged fluid reservoir 6. An intermediate reservoir 12 IR is provided 
which always communicates with the supply passage 11. 
The discharged fluid reservoir 6 is provided with a stroke-responsive type 
of check valve 13 which serves as a shutoff valve to prevent the flow of 
fluid from the supply passage 11 to the discharged fluid reservoir 6 when 
the amount of brake fluid in the reservoir 6 exceeds a predetermined level 
and to allow the passage of fluid only while the amount of brake fluid in 
the reservoir is below the predetermined level. 
The shutoff valve may also be a solenoid valve or a pressure-responsive 
valve. But, the stroke-responsive type of check valve as shown is 
advantageous over these valves in that its structure is simple and its 
cost is low. If the stroke-reponsive type check valve is used, the amount 
of fluid necessary for moving the piston in the discharged fluid reservoir 
6 from its stroke end to the position in which the check valve is closed 
increases the initial dead stroke of the brake pedal. Thus, the piston 
stroke from the stroke end to the valve closing position is required to be 
as short as possible. 
A traction control changeover valve 14 is provided between the circulation 
point 8 and the branch point to prevent the pressurized fluid from flowing 
back into the master cylinder during the traction control. Also, in order 
to allow backward fluid flow toward the intermediate reservoir when the 
pump discharge pressure has increased excessively, a high-pressure 
(corresponding to the upper limit of the fluid pressure necessary for the 
traction control, e.g. 100 bar) relief valve 15 is provided in parallel 
with the changeover valve 14. 
Further, a throttle 16 may be added, if necessary, as long as it would not 
hinder the normal braking performance. It serves, in cooperation with the 
intermediate fluid reservoir 12, to strengthen the buffering effect by the 
combination of the buffer fluid reservoir 9 and the throttle 10. 
When there are one driven wheel brake and one non-driven wheel brake in one 
output line of the master cylinder, the wheel brake 4-2 at the non-driven 
wheel side and the brake fluid pressure control valve 5-2 may be connected 
to the line branching from the point downstream of the traction control 
changeover valve 14 in the same manner as the wheel brake 4-1 and its 
brake fluid pressure control valve 5-1 at the driven wheel side. But 
preferably, they should be connected to a line branching from a point 
upstream of the valve 14. This is because, with this arrangement, it is 
not necessary to keep the control valve 5-2 activated during the traction 
control, and the pressure on the non-driven side wheel brakes can be 
increased instantly upon depression of the brake pedal. 
The intermediate fluid reservoir 12 may be a simple fluid chamber as with 
the buffer fluid reservoir 9. But, for higher fluid supply capacity to the 
pump, it should preferably be provided with a volume control means for 
reducing the volume of the intermediate fluid reservoir when the internal 
fluid pressure drops below the atmospheric pressure, thereby keeping the 
internal pressure not much lower than the atmospheric pressure. 
This volume control means should be capable of keeping the drop of the 
internal fluid pressure from the atmospheric pressure at a minimum. At the 
end of traction control, it should also have the function of pushing back 
the intermediate fluid reservoir to its initial volume prior to the brake 
fluid flowing back to the master cylinder reservoir via the master 
cylinder inlet port. 
Without the latter function, the intermediate fluid reservoir might be 
pushed back at the next braking pressure application after the traction 
control has ended. This leads to a loss in the pedal stroke. The throttle 
16 helps to preferentially push back the intermediate fluid reservoir. 
The most effective way to increase the intake capacity of the pump is to 
keep the internal pressure of the intermediate fluid reservoir above the 
atmospheric pressure. But, for this purpose, the structure of the shutoff 
valve and the like will have to be complicated. 
In order to attain both of the above functions efficiently, the volume 
control means should be designed so that its resistance to deformation 
becomes minimum. 
An ordinary cylinder and piston assembly can therefore be used as the 
volume control means, provided the seal friction can be kept sufficiently 
small. 
FIGS. 2A and 2B show examples which can reduce the resistance to 
deformation still further. 
In FIG. 2A, the intermediate fluid reservoir 12 has a diaphragm 121 made of 
a resilient material such as rubber. A metallic outer wall 122 is provided 
with vent holes 123. A slightly arched, springy thin plate 124 is disposed 
between the outer wall 122 and the diaphragm 121 to prevent the diaphragm 
121 from getting into the vent holes 123. A plurality of small holes 125 
are formed in the thin plate 124 so as not to be overlapped with the vent 
holes 123. If a negative pressure is produced in the space defined by the 
diaphragm 121, the diaphragm will be deformed due to the atmospheric 
pressure that acts on the outside of the diaphragm through the vent holes 
123, the space formed by the arched shape of the thin plate 124 and the 
holes 125. Thus, the internal volume in the fluid reservoir decreases 
until the internal pressure balances with the external pressure, at which 
time the deformation of the diaphragm stops. In this way, the internal 
pressure is kept at a value near the atmospheric pressure. 
In this arrangement, the degree of arching of the thin plate 124 
contributes to the initial dead stroke of the brake pedal. Thus, care must 
be taken that the thin plate would not be arched excessively. 
The structure shown in FIG. 2B is characterized in that the diaphragm 121 
can be deformed easily and is more durable against the internal pressure. 
This structure is similar to one generally used as a high-pressure gas 
sealed accumulator. The only difference from the accumulator is that the 
portions used as the high-pressure gas chamber and the hydraulic fluid 
chamber in an ordinary accumulator are used, in this example, as a fluid 
storage chamber and an atmospheric chamber, respectively. In this example, 
in place of the thin plate 124, a metal piece 126 molded integrally with 
the diaphragm 121 prevents the diaphragm from getting into the vent holes 
123. 
The stroke-responsive type check valve 13 of this example has a critical 
pressure that is determined by the balance between the effective sectional 
area of the valve body and the force of the return spring in the 
discharged fluid reservoir 6. Thus, in the structure shown in FIG. 1, if 
the brake fluid in the discharged fluid reservoir 6 is completely pumped 
out by the pump 7 during the antilock control and if the master cylinder 
pressure is lower than the critical pressure, the supply passage 11 and 
the discharged fluid reservoir 6, which have been shut off from each 
other, would communicate again. Thus, the pump will keep discharging 
fluid, instead of running idle, with a discharge pressure which is equal 
to the master cylinder pressure at that moment. If the critical pressure 
is sufficiently low, this will be of no problem in practice. But in a 
situation where this is not desirable, the stroke-responsive type check 
valve may be replaced with a pressure-responsive valve or a solenoid 
valve. 
FIG. 3 shows another embodiment. 
In FIG. 3, a three-port two-position changeover valve 17 is provided at the 
branch point between the main passage and the supply passage. It has both 
the traction control changeover function and the shutoff function. There 
is no valve exclusively for shutoff as used in FIG. 1. Except for this 
fact, and except for the fact that the intermediate fluid reservoir 12 is 
provided in a main passage 3 at a point upstream of the changeover valve 
17, this structure is the same as that of FIG. 1. 
The structure shown in FIG. 3 is apparently very simple. But if the 
changeover valve 17 were not returned to its deactivated position as soon 
as the brake pedal is depressed during the traction control, the brake 
fluid in the master cylinder would flow into the discharged fluid 
reservoir 6 without resistance, thereby making it impossible to get a 
sufficient brake force even if the brake pedal is trod further. In this 
state, the subsequent antilock control function would be lost, too. This 
potential danger can be avoided by adding a pressure-responsive valve. But 
this will complicate the otherwise simple structure. Thus, in this 
example, for reliable functioning of the changeover valve 17, it is 
necessary to increase the reliability of the electric system including the 
brake switch. 
In the structures shown in FIGS. 1 and 3, when the brakes are applied 
during traction control, and as a result the master cylinder is pushed in, 
the wheel brake control valves have to be changed over to the pressure 
re-increase position immediately. Otherwise, the wheel brake fluid 
pressure would not rise quickly enough. In this respect, too, it is 
necessary to increase the reliability of the electric system sufficiently. 
FIG. 4 shows a structure which can solve this problem. In FIG. 4, in order 
to increase the reliability of the system, the three-port two-position 
changeover valve 17 shown in FIG. 3 is used for traction control 
changeover and the stroke-responsive type check valve 13 is used as a 
shutoff valve. 
By providing the stroke-responsive type check valve 13 downstream of the 
traction control changeover valve 17, the check valve 13 communicates with 
the main passage 3 only during the traction control. This prevents the 
dead stroke of the brake pedal which occurs when the check valve is 
arranged in the manner as shown in FIG. 1. Also, the idling of the pump is 
assured even in the case as discussed with reference to FIG. 1. 
Also, by providing a circuit extending from the supply passage 11 to the 
wheel brake 4-1 and providing a check valve 18 in this circuit, the wheel 
brake fluid pressure can be increased quickly even if the master cylinder 
is pushed in during traction control without the need of switching the 
changeover valve 17 to the pressure reincrease position. 
FIG. 4 shows the driven wheel brake control valve 5-1 and the non-driven 
wheel brake control valve 5-2 as each being separated, respectively, into 
three parts, 51-1, 52-1 and 53-1, and 51-2, 52-2 and 53-2, of which 53-1 
and 53-2 are check valves that are not shown in FIGS. 1 and 3. 
With the structures shown in FIGS. 1 and 3, the intermediate fluid 
reservoir 12 also serves to suppress the pump pulsation during antilock 
control, because it is kept in communication with the main passage 3 
during antilock control. 
In the structure of FIG. 4, by providing the intermediate fluid reservoir 
12 in the main passage 3 as shown by solid line, it also serves to 
restrain the pump pulsation during antilock control. 
On the other hand, by providing it in the supply passage as shown by chain 
line, it will serve to prolong the life of the diaphragm in the 
intermediate fluid reservoir. This arrangement also serves to prevent any 
bad influence on the pedal stroke during normal braking even if the 
intermediate fluid reservoir has a slightly poor rigidity or has a 
tendency to consume a small amount of ineffective fluid at the initial 
stage of pressure increase of the master cylinder. Another advantage is 
that the flow resistance in the changeover valve 17 when the valve 
position is switched to the traction control position may not reduce the 
brake fluid supply capacity to the pump. 
But in the latter arrangement (the arrangement shown by chain line), it is 
necessary for the intermediate fluid reservoir to recover its initial 
volume upon completion of the traction control while the main passage and 
the supply passage are in communication through the traction control 
changeover valve 17. 
The provision of a check valve 18 makes this arrangement possible because 
even if the timing of the changeover valve 17 to return to its original 
position is set to delay slightly in order to allow the intermediate fluid 
reservoir to recover its initial volume reliably, the brake pressure can 
be increased reliably during this delay. 
Also, in the structure of FIG. 4, the relief valve 15 may be provided 
between the circulation point and the supply passage instead of between 
the circulation point and the main passage, in the same manner as the 
intermediate fluid reservoir 12, which may be provided not in the main 
passage, but in the supply passage.