GB1575209A

GB1575209A - Braking force boosters for example in motor vehicles

Info

Publication number: GB1575209A
Application number: GB1489477A
Authority: GB
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1976-04-13
Filing date: 1977-04-07
Publication date: 1980-09-17
Also published as: DE2616240A1; DE2616240C2; FR2348086B1; FR2348086A1

Description

(54) BRAKING FORCE BOOSTER, FOR EXAMPLE IN MOTOR VEHICLES (71) We, DAIMLER-BENZ AKTIEN GESELLSCHAFT, of Stuttgart-Untertürkheim, Germany, a Company organised under the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The invention relates to a braking force booster, for example in a motor vehicle, the booster having a control piston operated preferably by the brake pedal, which cooperates with a pressure control valve connected to a pressure fluid medium source and by which a fluid medium for the actuation of said valve is displaceable from its cylinder chamber, and having a working piston, which is acted upon by the pressure controlled by the pressure control valve.

A braking force booster with a control piston, upon the actuation of which a control pressure is built-up which actuates a connecting valve controlling the working pressure is already known. In this known construction of a braking force booster, which operates with a pressure medium, although a mechanical drive connection exists between the control piston and the working piston, in the case of the amplifier failing, nevertheless this braking force amplifier does not exhibit a direct feed-back of the working pressure to the input piston and hence to the driver's foot. In other known booster constructions the control piston is arranged so that the pressure controlled by the pressure medium source through the connecting valves does not act directly upon the actuating piston. A lack of a direct pressure reaction has disadvantageous effects upon the feel communicated to the driver.

Another disadvantage of this booster which has become known is the lack of a mechanical drive connection control piston and drive piston, due to which the brake installation fails completely if a leakage occurs between the control piston and the control cylinder.

It is the underlying aim of the invention to produce a braking force booster which is free from the disadvantages mentioned and in which, when the device is intact, a transmission ratio greater than unity exists between the travel of the control piston and the travel of the working piston.

The invention also seeks to provide a direct feed-back of the prevailing work pressure to the control piston and to the brake operating member.

According to the invention, there is provided a braking force booster comprising a housing containing a control piston actuatable in a cylinder chamber by a brake operation member and a working piston disposed in a working pressure chamber, the control piston cooperating with a pressure control valve connected to a source of pressure fluid medium, said valve being displaceable to supply said fluid medium in response to the actuation of the control piston, the working piston being acted upon by the pressure fluid medium supplied by the valve, the control piston having a working end face and an integral annular piston of larger diameter than said end face and being supported by a sealing means disposed in the region of the entry of said control piston into the housing and by sealing means disposed in the region of said working end face, the working face of the control piston being in contact with the working piston in its working pressure chamber and the pressure control valve being actuated by fluid medium displaced by the annular piston from a chamber defined by the annular piston and the sealing means in the region of the working end face of the control piston.

In an embodiment of the invention the booster is so constructed that a valve spring is disposed between a valve seat pin actuating the pressure control valve and a pressure control piston acting on the valve seat pin, the pressure developed by the control piston acting on the side of the pressure control piston opposite said valve spring, said valve spring, determining the actuating force for the control valve as a function of the stroke of the pressure control piston.

It is desirable that upon the reduction of the pedal pressure the fluid medium no longer required can be discharged rapidly.

For this purpose, when the control pressure decreases and after the control valve has reopened, a return valve is disposed between the pressure control valve and the valve seatpin, said return valve enabling the return flow of pressure fluid medium through a bore extending through the valve seat pin to the source of pressure fluid medium when control pressure is decreasing and the pressure-control valve has closed. The return flow is ensured by the return valve, and in order~that it will always open when required, the valve spring is attached to a captive sleeve associated with the valve seat pin and the pressure control piston, enabling the provision of a return spring acting on the Valve seat pin to ensure opening of the return valve in response to a fall in the pressure produced by the pressure control piston.

An embodiment of the invention will now be explained more fully by way of example and with reference to the accompanying drawing, which shows a longitudinal section through a braking force booster in a motor vehicle in which the housing of the pressure control valve is included in the booster housing proper; a single component therefore serves as housing for the master cylinder, the control piston and for the pressure control valve.

The booster housing 1 accommodates the working pistons 2 and 3 which co-operate with connections 4 and 5, to which pipes for the individual brake circuits can be connected.

The working pistons 2 and 3 are braced against return springs 6 and 7. An end face 9 of an actuating member 8 acting as a control piston is arranged to contact the adjacent end face 11 of the working piston 3. A brake pedal actuable by a driver, not shown, is connected to the control piston 8.

The control piston 8 is of constant diameter with an integral stepped annular piston 12. It is sealed with respect to the exterior by a seal 13 in the region of its entry into the booster housing 1 and is guided by a shoulder 14.

A seal 1 3a seals one end of an annular chamber 15 also defined by the annular piston 12 to form a supplementary suction chamber 15a. On the other side, that is in the region - of and adjacent to the end face 9, the control piston 8 is supported in and sealed by seals 16 which separate the annular chamber 15 from a working pressure chamber 17, from which the fluid medium acts upon the end face 11 of the working piston 3. This working piston 3 moves in a cylindrical chamber 18 which is sealed with reference to the working pressure chamber 17 by the seals 19. The annular chamber 15 is connected by a bore 21 to a pressure control chamber 22. Fluid medium urged into this chamber by the control piston 8 acts upon a pressure control valve actuating piston 23.

A valve spring 26 is attached to the piston 23 by a fixing screw 24 and a hat-shaped captive sleeve 25. Due to the retention of the valve spring 26, a return spring 27-for the valve seat pin 28 need not be so powerful.

The relative movement of the valve seat pin 28 towards the prcssure control valve actuating piston 23 which is caused by the return spring 27 is limited by a stop pin 40. When pressure increases in the pressure control chamber 22, the valve seat pin is displaceable towards a valve tappet 29 with a ball 30, to actuate a pressure control valve 32.

Pressure medium is fed to the pressure control valve from a pressure medium tank or accumulator (not shown).

The annular chamber 15 communicates through a compensating bore 33 and a further bore 34 with a supply tank (not shown).

When the control piston 8 is actuated, the seal element 13a travels over the compensating bore 33, which is thereby closed. Pressure medium is then displaced out of the annular chamber 15 through the bore 21 into the pressure control chamber 22. Due to the pressure generated in the latter, the pressure control valve actuating piston 23 is shifted in its cylindrical bore 35. The valve seat pin 28 is displaced towards the valve tappet 29 with compression of the captive valve spring 26. When the ball 30 is touched by the valve seat pin a valve seat bore 36 is closed and the valve tappet 29 can slide towards the valve hall 31, with compression of a spring 37 and the pressure control valve 32 is thereby opened. This causes pressure medium to be fed from the pressure medium tank (not shown) to the bore 38, which is introduced through the valve 32, the connecting bore 39, a groove 41 and bores 42, 43 and 44 into the working pressure chamber 17. This causes the working piston 3 to be shifted in the working piston chamber 18 and as a consequence of this the working piston 2 is likewise displaced, and both pistons act upon their resnective brake circuits (not shown).

The brakes are brought into operation in known manner by sliding of the work pistons 2 and 3 while simultaneously, the control piston 8 communicates a direct reactive pressure to the brake pedal.

When the pressure upon the end face of the valve seat pin 28, which is closed by the valve ball 30, exceeds a sDecific value determined by the strength of the spring 26, the valve seat pin is displaced counter to the force of the valve spring 26 until equilibrium is established between the spring force and the reactive force acting upon the valve seat pin 28. The pressure control valve 32 is then closed and the connection of pressure medium to the working cylinder is thereby interrupted.

When the control piston 8 is retracted, due to the consequent enlargement of volume of the annular chamber 15, the pressure in the control pressure chamber 22 decreases and a limited spring relaxation thereby becomes possible through the return of the pressure control valve actuating piston 23. The return valve constituted by the ball 30 and the valve seat pin 28 then opens freeing the bore 36 in the seat pin 28 through which part of the working pressure medium can flow back through the valve seat pin 28, the cylindrical bore chamber 35 and a bore 45 to the supply tank (not shown). The reduction of the working pressure fluid medium continues until an equilibrium of forces is obtained between the spring force of the valve spring 26 and a pressure acting upon the end face of the valve seat of the valve seat pin. 28.

Simultaneously with the reduction in working pressure, the working piston 3 moves back in the working piston chamber 18 and the braking force is thereby reduced in known manner.

The pressure control valve 32 and the associated actuating elements can be dimensioned so that a transmission ratio greater than unity is obtained between the working piston stroke and the control piston stroke during the actuation of the braking force booster when the device is intact.

In the case where the device has failed, i.e. no pressure medium is fed to the pressure control valve 32 through the bore 38, the brake can also be operated without boost. As illustrated in the drawing, the control piston 8 is directly in contact with the working piston 3. Therefore when the brake is actuated, the working piston 3 can be actuated mechanically directly by the movement of the control piston 8. The ratio of travel between the working piston 3 and the control piston 8 is then equal to unity.

In this case the fluid medium which is present in the annular chamber 15 will continue to be displaced out of the latter through the bore 21 and directed into the pressure control chamber 22. The valve actuating piston 23 will thereby be displaced counter to the thrust of the valve spring 26.

Although during this movement the valve 32 will also open, nevertheless this has no effect because pressure medium is not fed through the bore 38.

WHAT WE CLAIM IS: - 1. A braking force booster comprising a housing containing a control piston actuatable in a cylinder chamber by a brake operating member and a working piston disposed in a working pressure chamber, the control piston cooperating with a pressure control valve connected to a source of pressure fluid medium, said valve being displaceable to supply said fluid medium in response to the actuation of the control piston, the working piston being acted on by the pressure fluid medium supplied by the valve; the control piston having a working end face and an integral annular piston of larger diameter than said end face and being supported by a sealing means disposed in the region of the entry of said control piston into the housing and by sealing means disposed in the region of said working end face, the working end face of the control piston being in contact with the working piston in its working pressure chamber and the pressure control valve being actuated by fluid medium displaced by the annular piston from a chamber defined by the annular piston and the sealing means in the region of the working end face of the control piston.

2. A booster according to Claim 1, wherein a valve spring is disposed between a valve seat pin actuating the pressure control valve and a pressure control piston acting on the valve seat pin, the pressure developed by the control piston acting on the side of the pressure control piston opposite said valve spring, said valve spring determining the actuating force for the control valves as a function of the stroke of the pressure control piston.

3. A booster according to Claim 1 or Claim 2, wherein a return valve is disposed between the pressure control valve and the valve seat pin, said return valve enabling the return flow of pressure fluid medium through a bore extending through the valve seat pin to the source of pressure fluid medium when control pressure is decreasing and the pressure control also has closed.

4. A booster according to Claim 3 when dependent on Claim 2, wherein the valve spring is attached to a captive sleeve associated with the valve seat pin and the pressure control piston, enabling the provision of a return spring acting on the valve seat pin to ensure opening of the return valve in response to a fall in the pressure produced by the pressure control piston.

5. A braking force booster substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the force of the valve spring 26 until equilibrium is established between the spring force and the reactive force acting upon the valve seat pin 28. The pressure control valve 32 is then closed and the connection of pressure medium to the working cylinder is thereby interrupted. When the control piston 8 is retracted, due to the consequent enlargement of volume of the annular chamber 15, the pressure in the control pressure chamber 22 decreases and a limited spring relaxation thereby becomes possible through the return of the pressure control valve actuating piston 23. The return valve constituted by the ball 30 and the valve seat pin 28 then opens freeing the bore 36 in the seat pin 28 through which part of the working pressure medium can flow back through the valve seat pin 28, the cylindrical bore chamber 35 and a bore 45 to the supply tank (not shown). The reduction of the working pressure fluid medium continues until an equilibrium of forces is obtained between the spring force of the valve spring 26 and a pressure acting upon the end face of the valve seat of the valve seat pin. 28. Simultaneously with the reduction in working pressure, the working piston 3 moves back in the working piston chamber 18 and the braking force is thereby reduced in known manner. The pressure control valve 32 and the associated actuating elements can be dimensioned so that a transmission ratio greater than unity is obtained between the working piston stroke and the control piston stroke during the actuation of the braking force booster when the device is intact. In the case where the device has failed, i.e. no pressure medium is fed to the pressure control valve 32 through the bore 38, the brake can also be operated without boost. As illustrated in the drawing, the control piston 8 is directly in contact with the working piston 3. Therefore when the brake is actuated, the working piston 3 can be actuated mechanically directly by the movement of the control piston 8. The ratio of travel between the working piston 3 and the control piston 8 is then equal to unity. In this case the fluid medium which is present in the annular chamber 15 will continue to be displaced out of the latter through the bore 21 and directed into the pressure control chamber 22. The valve actuating piston 23 will thereby be displaced counter to the thrust of the valve spring 26. Although during this movement the valve 32 will also open, nevertheless this has no effect because pressure medium is not fed through the bore 38. WHAT WE CLAIM IS: -

1. A braking force booster comprising a housing containing a control piston actuatable in a cylinder chamber by a brake operating member and a working piston disposed in a working pressure chamber, the control piston cooperating with a pressure control valve connected to a source of pressure fluid medium, said valve being displaceable to supply said fluid medium in response to the actuation of the control piston, the working piston being acted on by the pressure fluid medium supplied by the valve; the control piston having a working end face and an integral annular piston of larger diameter than said end face and being supported by a sealing means disposed in the region of the entry of said control piston into the housing and by sealing means disposed in the region of said working end face, the working end face of the control piston being in contact with the working piston in its working pressure chamber and the pressure control valve being actuated by fluid medium displaced by the annular piston from a chamber defined by the annular piston and the sealing means in the region of the working end face of the control piston.