JPS62265064A - Booster brake master cylinder - Google Patents

Abstract

PURPOSE:To reduce operating strokes of a brake, by interconnecting a power pressure chamber of a booster to a constant-volume chamber of a master cylinder, and installing an on-off valve in the interconnecting passage. CONSTITUTION:When a brake is slightly operated and a control valve 84 has a power chamber 34 interconnected to an external hydraulic pressure source, a brake fluid flows into a constant-volume chamber 21 of a master cylinder by way of an interconnecting passage 130 and an on-off valve 132 in a state of being opened. Thus, when a brake clearance is brought to nothing and hydraulic pressure in a pressure chamber 19 goes up, the hydraulic pressure in the interconnecting passage 130 also goes up, and if the hydraulic pressure exceeds the specified value, the on-off valve 132 is closed. Therefore, the constant-volume chamber 21 of the master cylinder and the pressure chamber 19 are all interrupted from the power chamber 34 of a booster.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a brake master cylinder that generates brake fluid pressure for operating a hydraulic brake, and in particular to a brake master cylinder that generates brake fluid pressure for operating a hydraulic brake. This invention relates to a booster-equipped brake master cylinder equipped with a hydraulic pressure booster operated by.

Prior art booster brake master cylinders are already known, one of which is described in US Pat. No. 4,523,791. In this brake master cylinder with a booster, the pressurizing piston having a recess (an annular groove in the embodiment) on the outer peripheral surface of the intermediate portion in the axial direction is slidably fitted into the cylinder housing. Accordingly, a pressurizing chamber is formed in front of the pressurizing piston, and a constant volume chamber is formed within the recess. The pressurizing piston is provided with a cup seal as a one-way seal means that allows the brake fluid to flow from the constant volume chamber to the pressurizing chamber, but blocks the flow from the pressurizing chamber to the constant volume chamber, In addition, when the pressurizing piston is at the retreating end position, the pressurizing chamber is communicated with the reservoir to eliminate residual pressure in the pressurizing chamber. A valve is provided that allows the

In addition, in the brake booster, the power piston is slidably fitted in the booster housing in a fluid-tight manner, so that a power pressure chamber is formed behind the power piston.
The hydraulic pressure in the power pressure chamber is controlled by a control valve. The control valve operates based on the relative movement between the power piston and an input member operated by a brake operating mechanism such as a brake pedal, and has two states: communicating the power pressure chamber with an external hydraulic pressure source and communicating with the reservoir. ,
The power piston is actuated by the hydraulic pressure in the power pressure chamber controlled by the control valve to advance the pressurizing piston of the brake master cylinder.

In addition, the brake master cylinder is a tandem type with two pressurizing pistons in series, and the hydraulic pressure generated in two independent pressurizing chambers is supplied to the left front wheel cylinder and the right front wheel cylinder, respectively. On the other hand, the hydraulic pressure in the power pressure chamber of the brake booster is directly transmitted to the left and right rear wheel cylinders. The hydraulic pressure in the power pressure chamber is controlled by the control valve to a level that corresponds to the operating force of the brake operating mechanism, so if this hydraulic pressure is directly supplied to the rear wheel cylinder, the pressure of the brake operating mechanism will be applied to the rear wheel brake. It is possible to generate a braking force commensurate with the operating force.

Moreover, since brake fluid is supplied to the power pressure chamber from an external hydraulic pressure source such as a pump or an accumulator, almost no operating stroke of the brake operating mechanism is required to operate the rear wheel brakes; The required operating stroke of the mechanism can be reduced.

Problems to be Solved by the Invention However, in a hydraulic brake system equipped with this mask cylinder with a booster, if the external hydraulic pressure source fails, the assisting force of the brake booster cannot be obtained and is generated in the brake master cylinder. In addition to the drop in hydraulic pressure, the rear wheel brakes, which are operated by hydraulic pressure transmitted from an external hydraulic pressure source through the power pressure chamber, no longer operate, resulting in a significant reduction in the braking ability of the vehicle as a whole. there were.

In view of this point, the present invention can reduce the operating stroke of the brake operating mechanism while the external hydraulic pressure source is normal, and furthermore, prevents the reduction in the braking ability of the entire vehicle when the external hydraulic pressure source fails. This was done in order to provide a brake master cylinder with a booster that can minimize damage.

Means for Solving the Problems Therefore, the present invention provides a brake master cylinder with a booster comprising a brake master cylinder having the pressurizing chamber and the constant volume chamber, and a brake booster having the control valve and the power pressure chamber. A communication passage is provided to communicate the power pressure chamber and the constant volume chamber, and the communication passage opens when the hydraulic pressure in the communication passage is equal to or higher than a certain value,
This LJ is equipped with an on-off valve that closes when a certain value is exceeded.

This opening/closing valve includes a check valve that blocks the flow of brake fluid from the power pressure chamber to the constant volume chamber, and a check valve that is normally held at the forward end position by an urging means to force the check valve to open. However, it is preferable that the check valve includes a valve opening piston that is caused to retreat against the biasing means by the hydraulic pressure when the hydraulic pressure in the communication passage exceeds a certain value, thereby allowing the check valve to close. .

Further, a communication passage connecting the power pressure chamber and the constant volume chamber is connected to a passage on the power pressure chamber side that connects the control valve and the power pressure chamber, and a passage on the constant volume chamber side that connects the control valve and the constant volume chamber. It is desirable that the power pressure chamber side passage be provided with a restriction that makes it difficult for liquid to flow compared to the constant volume chamber side passage.

Operation In the brake master cylinder with booster according to the present invention, when the brake operating mechanism is slightly operated and the control valve communicates the power pressure chamber with the external hydraulic pressure source, the hydraulic pressure flows from the external hydraulic pressure source into the power pressure chamber. The brake fluid flows into the fixed volume chamber of the brake master cylinder via the communication path and the open/close valve that is in the open state. This brake fluid further flows into the pressurizing chamber through the one-way sealing means, and is supplied from there to the wheel cylinder to eliminate the brake clearance. That is, at the beginning of operation, the brake fluid supplied from the external hydraulic pressure source to the brake booster is supplied to the brake wheel cylinder to perform a so-called first fill, and the operation stroke of the brake operation mechanism required for this purpose is determined by the control valve. It only needs to be large enough to switch between the two.

If the brake clearance disappears and the hydraulic pressure in the pressurizing chamber increases, the hydraulic pressure in the communication passage will also rise, and if the hydraulic pressure exceeds a certain value, the on-off valve will close and cut off the communication passage. The constant volume chamber and pressurizing chamber of the brake master cylinder are isolated from the power pressure chamber of the brake booster, and thereafter operate in the same manner as a normal mask cylinder with a booster. At this time, the backflow of brake fluid from the pressurizing chamber to the constant volume chamber is prevented by the one-way sealing means, so that sufficient hydraulic pressure is generated in the pressurizing chamber.

When the pressurizing piston retreats to the rearward end position when the brake is released, the pressurizing chamber is communicated with the reservoir by the residual pressure release means, and the brake fluid supplied to the pressurizing chamber and the wheel cylinder at the initial stage of operation is transferred to the reservoir. It is allowed to return and no hydraulic pressure remains in the pressurization chamber and wheel cylinder.

Furthermore, in a desirable embodiment in which the on-off valve provided in the communication passage is equipped with a check valve and a valve-opening piston as described above, the on-off valve opens and closes in response to the hydraulic pressure itself in the communication passage. Therefore, the purpose can be definitely achieved with a simple structure.

Furthermore, in a desirable embodiment in which the power pressure chamber side passage is provided with a restriction, the flow of brake fluid from the external hydraulic pressure source to the power pressure chamber is suppressed to some extent by the restriction, whereas the flow of brake fluid from the external hydraulic pressure source to the power pressure chamber is suppressed to some extent by the restriction; Since the flow of supplied brake fluid is not restricted, the brake fluid supplied from the external hydraulic pressure source is preferentially supplied to the brake master cylinder at the beginning of operation, and even if a sudden brake operation is performed, the brake fluid is supplied first. This means that the filling will be sufficient.

Effects of the Invention As is clear from the above description, according to the present invention, brake fluid is supplied from an external hydraulic pressure source to a wheel cylinder via a brake booster and a first fill is performed by a slight operation of a brake operating mechanism. Therefore,
Brake operation stroke can be reduced.

Moreover, the brake fluid from the external hydraulic pressure source is supplied to the wheel cylinders through the one-way sealing means of the mask cylinder and the pressurizing chamber, so if the external hydraulic pressure source fails, the assisting force of the brake booster is However, the brake fluid is normally supplied to the wheel cylinder from the mask cylinder, so compared to the brake master cylinder with booster of the above-mentioned U.S. patent specification, the external hydraulic pressure source is It is possible to minimize the reduction in the braking ability of the entire vehicle in the event of a failure.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

In the accompanying drawings, reference numeral 2 indicates a brake master cylinder (hereinafter simply referred to as a mask cylinder), and reference numeral 4 indicates a brake booster (hereinafter simply referred to as a booster). The mask cylinder 2 is attached to a bottomed cylindrical cylinder housing 6.
This is a tandem type in which two pressurizing pistons 8 and 10 are slidably fitted in series. Each pressure piston 8.1
0 are each biased in the backward direction by return springs 12.13, the limit of which is set by a pin 14.15 fixed to the cylinder housing 6. Pressure piston 8. Each IO is provided with an annular groove 16, 17 in its axially intermediate portion, and its pressurizing piston 8
, 10 are fitted into the cylinder housing 6, so that a pressurizing chamber 18, 19 is formed in front of each pressurizing piston 8.
Furthermore, constant volume chambers 20.21 are formed within the annular grooves 16.17, respectively. Pressurizing chamber 1 of pressurizing piston 8.10
A communication hole 22.23 is provided at the portion separating the constant volume chamber 20.21 from the constant volume chamber 20.21, and a cup seal 24.25 is attached thereto. cup seal 2
4.25 are the communication holes 2 from the constant volume chambers 20 and 21, respectively.
2.23 into the pressurizing chambers 18, 19, but has a function of blocking the flow in the opposite direction, and constitutes a one-way sealing means.

In addition, each pressurizing piston 8, 1o has a constant volume chamber 20.21.
Another communication hole 26.2 that communicates between the pressurized chamber 18.19 and the pressurized chamber 18.19
7, and opening/closing valves 28.29 are provided at the openings of the communication holes 26.27 on the pressurizing chamber 18.19 side. These on-off valves 28.29 are connected to the pressurizing piston 8.1.
0 are at their respective rearward end positions, the bins 14
．． The pressurized chamber 1 is kept open by 15.
8.19 to the constant volume chamber 20.21, and pressurized chamber 18
．． 19 to the constant volume chamber 20.21, but after the pressure piston 8.10 has moved forward a short distance, it closes to prevent the brake fluid from flowing out from the pressure chamber 18.19. prevent. Communication hole 26.27 and on-off valve 28
．． 29 constitutes a residual pressure eliminating means.

A booster housing 30 is fixed to the rear end of the cylinder housing 6. This booster housing 3
A power piston 32 is fluid-tightly and slidably fitted within the booster housing 30, thereby dividing the space within the booster housing 30 into a power pressure chamber 34 and a low pressure chamber 36. A small diameter portion 50 projects from the center of the rear surface of the power screw 1-32, and this small diameter portion 50 penetrates the end wall of the booster housing 30 in a fluid-tight and slidable manner and is exposed to the atmosphere. . A bottomed hole 52 is formed in the small diameter portion 50 from its rear end surface, into which a reaction piston 54 is fitted in a fluid-tight and slidable manner. As a result, a space is formed between the reaction piston 54 and the bottom of the bottomed hole 52, but this space is constantly communicated with the power pressure chamber 34 through the communication passage 56, and the reaction piston 54 The hydraulic pressure of the power pressure chamber 34 acts on this. The power piston 32 is urged toward the rearward end position by a return spring 58.

The low pressure chamber 36 is constantly connected to the reservoir 8 at the port 80.
2, but the power pressure chamber 34 is connected to the control valve 8.
4, it can be switched between a state in which it communicates with the accumulator 86 of the external hydraulic pressure source, a state in which it communicates with the reservoir 82, and a state in which it communicates with neither.

The accumulator 86 has a pump 88 from the reservoir 82.
The brake fluid pumped up by the pump is stored at a certain range of fluid pressure.

The control valve 84 includes a valve spool 90 as a valve element held movably in a direction parallel to the moving direction of the power piston 32 by a valve bousing 89 formed integrally with the booster housing 30. This valve spool 90 is connected to the power piston 32 and the reaction piston 5 which is an input member by a motion conversion mechanism 92.
4. The motion conversion mechanism 92 includes a first link 96 and a second link 98 whose intermediate portions are rotatably connected to each other by a pin 94. One end of the first link 96 is connected to a support member 100 fixed to the housing 3o.
The other end is rotatably engaged with the reaction piston 54. Further, one end of the second link 98 is rotatably engaged with an annular groove 102 formed on the outer peripheral surface of the small diameter portion 50 of the power piston 32, and 41hm is brought into contact with the rear end surface of the valve spool 90. ing. As a result, if the reaction piston 54 is moved forward while the power piston 32 is stationary, the valve spool 90 will also be moved forward, but the position of the pin 94 will be different from that between the first link 96 and the second link 98. Since the position is closer to the reaction piston 54 than the center position in the longitudinal direction, the movement of the reaction piston 54 is expanded and the valve spool 90
This will be communicated to

An annular groove 108 is formed on the outer peripheral surface of the valve spool 90, and this annular groove 108 is formed by a restriction 109 formed in the radial direction within the valve spool 90 and a communication passage 110 formed through the valve spool 90 in the axial direction. It is communicated with a power pressure chamber 34. The valve spool 90 is biased in the backward direction by a spring 112, and the annular groove 108 normally communicates with the port 114, thereby communicating the power pressure chamber 34 with the reservoir 82. If the valve spool 90 is advanced a certain distance from this state, the ring 11
08 Cahoot 114 Nemo;t! - The power pressure chamber 34 is not in communication with the reservoir 82 or the accumulator 86, and if the valve spool 9o is further advanced, the annular groove 108 is in communication with the port 116. The power pressure chamber 34 is brought into communication with the accumulator 86.

The power piston 32 is connected to the pressure piston I of the mask cylinder 2 via a bushing rod 120 as an output member.
On the other hand, the reaction piston 54 is engaged with a brake pedal 124, which is a brake operation mechanism, via a bushing rod 122.

The power pressure chamber 34 of the booster 4 and the constant volume chamber 21 of the master cylinder 2 are communicated with each other through a communication passage 130. The communication passage 130 includes a power chamber side passage formed in the valve spool 90 and consisting of a communication passage 110 and a throttle 109 that communicate the power pressure chamber 34 and the annular groove 108, and a valve housing 89 and a cylinder housing 6. It consists of a constant volume chamber side passage that connects the annular ring 11j1108 and the constant volume chamber 21.

An on-off valve 132 is provided in the middle of this constant volume chamber side passage. This on-off valve 132 includes a check valve 134 and a valve opening piston 136. The check valve 134 allows the brake fluid to flow from the constant volume chamber 21 toward the annular groove 108, but prevents the brake fluid from flowing in the opposite direction, and is normally forcibly opened by the valve opening piston 136. ing. The valve opening piston 136 receives the hydraulic pressure in the communication passage 130 on the pressure receiving surface on the side of the check valve 134, and the other pressure receiving surface faces the atmospheric pressure chamber 138, but is always held at the forward end position by the spring 140. This keeps the check valve 134 open.

Further, the constant volume chamber 20 is constantly communicated with the reservoir 82 at the port 1-141.

The pressurizing chamber 18 of the brake master cylinder with booster configured as described above is connected to the front wheel cylinder 142, which is a wheel cylinder for the brakes of the left and right front wheels, through a fluid passage 144. A rear wheel cylinder 146 is connected by a fluid passage 148.

Next, the operation will be explained.

In a normal state in which the brake pedal 124 is not depressed, the power piston 32 is at the rearward end position,
The valve spool 90 is also at the rearward end position. In this state, the power pressure chamber 34 is isolated from the accumulator 86 and communicated with the reservoir 82. That is, the high hydraulic pressure within the accumulator 86 is shut off by the control valve 84 at the inlet of the booster 4, and no hydraulic pressure acts within the booster 4, thereby preventing deterioration of the sealing member.

If the brake pedal 124 is slightly depressed from this state, the reaction piston 54 is moved forward.
The power piston 32 does not move forward because it is prevented from moving forward by the return spring 58, and the reaction piston 54 moves forward relative to the power piston 32. The signal is magnified and transmitted to the valve spool 90 of the control valve 84. Then, the annular groove 108 of the valve spool 90 is separated from the bow LI 14,
It communicates with boat 116.

As a result, the accumulator 86 comes into communication with the power pressure chamber 34, but at this point, the power pressure chamber 34
The on-off valve 132 of the communication passage 130 that communicates with the constant volume chamber 21 is open, and the inflow of brake fluid into the power pressure chamber 34 is suppressed to some extent by the throttle 109, so the brake The liquid flows preferentially to the constant volume chamber 21,
Pressure chamber 1 passes through communication hole 23 and cup seal 25
9 and from there is supplied to the rear wheel cylinder 146 via a liquid passage 148. At the same time, pressurization chamber 19
As the hydraulic pressure of
Brake fluid is supplied to 2, and the brake clearance of the front wheel brake is also eliminated. That is, when the brake pedal 124 is depressed only by a short distance sufficient to switch the control valve 84, the brake clearance between the front and rear wheels is eliminated.

In this way, the power piston 32 and the pressure piston 8.
Wheel cylinder 142.146 prior to forward movement of io
In order to unconditionally guarantee that brake fluid is supplied to the power piston 32 and the pressure piston 1
It is necessary that the cross-sectional area of 0 satisfies the following equation, but depending on how the biasing force of the return spring 13.58 is set, it may not be necessary to satisfy the following equation.

Sl-32- (Sl-34) However, Sl: Cross-sectional area of the pressurizing piston 10 S2: Cross-sectional area of the power piston 32 S3-34: Cross-sectional area of the exposed portion of the small diameter portion 50 When the brake clearance disappears as described above For example, the hydraulic pressure in the wheel cylinders 142 and 146 and the pressurizing chambers 18 and 19 increases, and the hydraulic pressure in the communication passage 130 also increases, causing the valve opening piston 13 to increase.
Move 6 back.

The biasing force of the spring 140 is set in this manner. The check valve 13 is opened by the retreat of the valve opening piston 136.
4 closes and isolates the constant volume chamber 21 from the power pressure chamber 34. From now on, all the hydraulic fluid supplied from the external hydraulic pressure source flows into the power pressure chamber 34, and the hydraulic pressure in the power pressure chamber 34 increases. do. Therefore, the power piston 32 moves forward and pressurizes the pressure piston 1 of the booster 2 via the bushing rod 120.
Advance 0. As a result, the hydraulic pressure in the pressurizing chamber 19 is increased and transmitted to the rear wheel cylinder 146, and the hydraulic pressure in the pressurizing chamber 18 and the front wheel cylinder 142 is also increased via the pressurizing piston 8.

If the brake pedal 124 is kept depressed, the control valve 84 will soon become in a state where the power pressure chamber 34 is not communicated with the reservoir 82 or the accumulator 86, the operation of the booster 4 is stopped, and the wheel cylinders 142, 1 are stopped.
46 fluid pressure is kept constant.

Then, when the brake pedal 124 is released, the reaction piston 54 retreats, and the control valve 84 switches to a state in which the power pressure chamber 34 is communicated with the reservoir 82. As a result, the power piston 32 and the pressure piston 8.10 move back, the hydraulic pressure in the wheel cylinder 142, 146 is reduced, and the brake is released. When lO has retreated to the vicinity of the retreat end, the on-off valves 28.29 are opened by the bottle 14.15, and the pressurized chambers 18.19 are communicated with the reservoirs 82 via the constant volume chambers 20.21, and the brake fluid is removed. Free flow is allowed to prevent residual hydraulic pressure in the wheel cylinders 142,146.

The above is the operation of the brake master cylinder with booster when the external hydraulic pressure source consisting of the accumulator 86 and the pump 88 is normal, but this mask cylinder operates without any problem even if the external hydraulic pressure source is out of order. If the brake pedal 12 is depressed, it is a reaction piston! - The pressurized piston 120 contacts the power piston 32 and moves it mechanically forward through the pressurized piston 120.
O is also moved forward, and the mask cylinder 2 operates normally except that the assisting force of the booster 4 is not available.

Further, if the brake pedal 124 is suddenly released and the pressurizing piston 8.10 is suddenly retreated, the pressurizing chamber 18
After passing through the port 1-141 and the constant volume chamber 20,
The pressurizing chamber 19 is replenished with brake fluid through the liquid passage 130 and the constant volume chamber 21, thereby preventing the inside of the pressurizing chambers 18 and 19 from becoming negative pressure.

Note that in this embodiment, the communication path 130 is connected to the annular groove 108.
Although the spring 11 of the control valve 84
It is also possible to make the power pressure chamber 34 and the fixed volume chamber 21 communicate with each other by communicating with a space in which the power pressure chamber 34 and the constant volume chamber 21 are arranged, or it is also possible to make the power pressure chamber 34 communicate with the constant volume chamber 21 directly.

In addition, the on-off valve 132 also includes a check valve 134 and a valve opening piston 13.
6, and the communication path 1
Any device that opens when the hydraulic pressure inside 30 is below a certain value and closes when it exceeds a certain value can be adopted.

Furthermore, the one-way sealing means provided on the pressurizing piston of the mask cylinder is not limited to a cup seal, but can also be a combination of an O-ring and a check valve, and can also be used to eliminate residual pressure. As a means, it is also possible to employ a compensating boat that communicates each pressurizing chamber with the reservoir when the pressurizing piston is retracted to the retracted end position.

In addition, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art, such as changing the structures of the mask cylinder, booster, control valve, etc.

[Brief explanation of drawings]

The attached drawing is a front sectional view of a brake master cylinder with a booster, which is an embodiment of the present invention, and is also a system diagram of a hydraulic brake device including the same. 2 Brake master cylinder (mask cylinder) 4 Brake booster (booster) 6: Cylinder housing 8.1.0: Pressure piston 14.15: Pin 16, 17: Annular groove 18.19:
Pressurizing chamber 20.21: Constant volume chamber 24.25: Cup seal 2B, 29: Opening/closing valve 30: Booster housing 32: Power piston 34: Power pressure chamber 54: Reaction piston 82: Reservoir 84: Control valve
86: Accumulator 90: Valve spool 9
2: Motion conversion mechanism 108: Annular groove 120, 122: Brake pedal 124

Claims (3)

[Claims] (1) Consisting of a brake master cylinder and a brake booster, the brake master cylinder is pressurized by a pressurizing piston having a recessed portion on the outer circumferential surface of the intermediate portion in the axial direction, which is slidably fitted into the cylinder housing. A pressurizing chamber is formed in front of the piston, and a constant volume chamber is formed in the recess, and the pressurizing piston is configured to allow brake fluid to flow from the constant volume chamber to the pressurizing chamber, but not to pressurize the piston. A one-way seal means is provided to prevent the flow from the pressure chamber to the constant volume chamber, and when the pressure piston is at the retracted end position, the pressurization chamber is communicated with the reservoir to drain the remainder in the pressure chamber. The brake booster is equipped with a residual pressure eliminating means for eliminating residual pressure, and a power pressure chamber is formed behind the power piston by fitting the power piston into the booster housing in a fluid-tight and slidable manner. and, based on the relative movement between the input member operated by the brake operation mechanism and the power piston, the power pressure chamber is communicated with an external hydraulic pressure source and the power pressure chamber is communicated with the reservoir. In the brake master cylinder with a booster, the brake master cylinder with a booster is provided with a control valve that switches between a state in which the power pressure chamber is not in communication with the power pressure chamber, and the pressure piston is moved forward by the operating force of the power piston based on the hydraulic pressure in the power pressure chamber. In addition to providing a communication passage that communicates between the and the fixed volume chamber, the communication passage is provided with an on-off valve that opens when the fluid pressure in the communication passage is below a certain value and closes when it exceeds a certain value. Brake master cylinder with booster features. (2) A communication passage that communicates the power pressure chamber and the constant volume chamber includes a power pressure chamber side passage that connects the control valve and the power pressure chamber, and a constant volume chamber that connects the control valve and the constant volume chamber. The booster-equipped brake according to claim 1, wherein the power pressure chamber side passage is provided with a restriction that makes liquid flow more difficult than in the constant volume chamber side passage. master cylinder. (3) The opening/closing valve includes a check valve that blocks the flow of brake fluid from the power pressure chamber to the constant volume chamber, and is normally kept at the forward end position by a biasing means to force the check valve. an open valve that is generally open, but when the hydraulic pressure in the communication passage exceeds the certain value, the hydraulic pressure causes the check valve to retreat against the biasing means and close the check valve; Claim 1 or 2 includes a piston.
Brake master cylinder with booster as described in section.