GB2196708A

GB2196708A - Brake pressure generator

Info

Publication number: GB2196708A
Application number: GB08722734A
Authority: GB
Inventors: Juan Belart; Wolfram Seibert; Norbert Ocvirk
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1986-10-06
Filing date: 1987-09-28
Publication date: 1988-05-05
Anticipated expiration: 2007-09-28
Also published as: IT8721385A0; GB2196708B; GB8722734D0; IT1223286B; FR2604673A1; DE3633969A1

Abstract

A brake pressure generator for a hydraulic brake system of an automotive vehicle comprises a booster piston (22) operating in a master brake cyclinder (1), with an auxiliary pressure in a booster chamber (26) being applicable to the booster piston (22). To keep the reaction force low during actuation of the brake pressure generator, a pressure-reducing valve (46) is coupled ahead of the valve mechanism (28,29) of the brake pressure generator through which the booster chamber (25) can be connected to a high-pressure source (49) containing a pressure accumulator (61). The pressure in the booster chamber (25) is applicable, via line (45), to the control piston (55) of the pressure-reducing valve (46) to effect a decrease in the pressure reduction. <IMAGE>

Description

SPECIFICATION Brake pressure generator The present invention is concerned with a brake pressure generator for a hydraulic brake system of an automotive vehicle, of the kind comprising a booster piston for actuating a master brake cylinder to which booster piston a hydraulic auxiliary pressure prevailing in a booster chamber can be applied, further comprising an actuating means cooperating with the booster piston, and a valve mechanism for controlling the auxiliary pressure, which valve mechanism is actuable by a relative movement between the booster piston and the actuating means and includes a double-seated valve, through which valve mechanism the booster chamber can be connected to a non-pressurised container or to a high-pressure source containing a pressure accumulator.

Brake pressure generators of the kind referred to exhibit a high performance, involving low structural efforts, and are characterised by a satisfactory controllability. In particular, they are suitabie for brake systems of automotive vehicles comprising a brake skid control means and, thanks to the provision of a pressure accumulator, are especially safe against failure.

In practice, a successful brake pressure generator energised by a high-pressure source (as shown in DE-OS 3108908) includes for controlling the auxiliary pressure, a slide valve actuable via a shear lever, through relative movement between the booster piston and the actuating mechanism. Although this construction permits low reaction forces for initiating a brake operation, the manufacture thereof involves high mechanical and financial efforts as the requirements-placed upon the manufacturing precision of the valve slide and the lever force transmission are high.

To reduce the structural efforts, in a brake pressure generator of the kind referred to according to DE-OS No. 3440991, the valve means comprises two mechanically series-connected seat valves housed in the booster piston and jointly actuable by a control piston, However, this involves the disadvantage that, through the hydraulic working surface of the high-pressure seat valve to which the pressure from the accumulator is applied, a higher force of response arises affecting the comfort of operation and the controllability of low brake forces.

It is, therefore, an object of the present invention to provide a brake pressure generator of the kind referred to which, in maintaining its structural advantage relative to a valve means provided with seated valves, exhibits a low force of response.

According to the invention there is provided a brake pressure generator for a hydraulic brake system of an automotive vehicle, of the kind comprising a booster piston for actuating a master brake cylinder to which booster piston a hydraulic auxiliary pressure prevailing in a booster chamber can be applied, further comprising an actuating means cooperating with the booster piston, and a valve mechanism for controlling the auxiliary pressure, which valve mechanism is actuable by a relative movement between the booster piston and the actuating means and includes a double-seated valve, through which valve mechanism the booster chamber can be connected to a non-pressurised container or to a highpressure source containing a pressure accumulator, characterised in that provided in the connecting conduit between the high-pressure source and the valve mechanism is a pressure-reducing valve to the control piston of which the pressure prevailing in the booster chamber can be applied to effect a decrease in the pressure reduction. Thanks to this arrangement of the pressure reducing valve, the pressure at the inlet of the brake pressure generator, in the brake releasing position wherein the booster chamber is in communication with the non-pressurised container, is reduced to such a degree that a favourably low force of reaction arises.Once the brake pressure generator is actuated, the auxiliary pressure rising in the booster chamber decreases the pressure reduction to such an extent that, virtually, the full accumulator pressure prevailing on the inlet of the brake pressure generator is available for the auxiliary pressure generation. The configuration of the brake pressure generator as provided by the invention, moreover, involves the advantage that it is very simple as the pressure reducing valve is not connected with any substantial building requirements and is easily integrated into the brake pressure generator. Moreover, it is of advantage that the pressure-reducing valve, in the brake-releasing position, retains the high loading pressure of the pressure accumulator such that the sealants, on the highpressure side in the brake pressure generator, are exposed only to a comparatively low pressure load.This will increase the life of the sealants; and the losses due to leakage, in the brake-releasing position, likely to result in emptying the pressure accumulator, are substantially reduced.

Prefereably, the inlet chamber of the pressure-reducing valve in communication with the high-pressure source contains a normallyseated valve closure member, thereby providing by simple structural means, a valve which, in the brake-releasing position, permanently and tightly seals the connection between the pressure accumulator and the brake pressure generator thereby precluding a. gradual rise in the reducing pressure on the inlet of the brake pressure generator.

The pressure-reducing valve, according to one embodiment of the invention, is confi gured such that the valve closure member closes in the direction of flow and that the control piston, in the valve-closing direction, is exposed to the initial pressure and, in the valve-opening direction, is exposed to the force of a compression spring and to the pressure prevailing in the booster chamber. To insure that the pressure reducing valve, upon applying the brake, opens reliably in whatever circumstances, in the practice of the invention, it can, moreover, be provided that the spring force of the compression spring exceeds the pressure force acting on the valve closure member in the closing direction.

According to another embodiment of the invention, the construction can be simplified in that the control piston counteracts the initial pressure and the pressure in the booster chamber by identical hydraulic working faces.

Moreover, it has been found that a favourable actuating pattern and an advantageously low force of reaction is attainable by the brake pressure generator of the invention of the pressure-reducing factor of the pressure-reducing valve is 10 or more than 10 if the booster chamber is non-pressurised.

An embodiment of the invention will now be described by way of example with reference to the single Figure of the drawing which shows a hydraulic brake system for an automotive vehicle comprising a brake pressure generator as provided by the invention, and a pressure-reducing valve illustrated in longitudinal section.

The brake pressure generator shown comprises a master cylinder 1 actuable by a hydraulic force booster 2. The master cylinder 1 contains a working chamber 3 and a connecting bore 4 to which is connected a first brake circuit 5, through which two wheel brakes 6,7 of an automotive vehicle are actuable.

The master cylinder 1 is of a conventional configuration and comprises a master cylinder piston 8 guided, in axially-displaceable manner, in a cylinder bore 9, and carrying a sleeve sealant 10 and, through a compression spring 11, being biased in the brake-releasing direction. The compression spring 11 is supported on a spring cup 12 in which is disposed a valve tappet 13 the one end of which (in the drawing, the right-hand one) carries a closure member 14 cooperating with a bore 15 in the master cylinder piston 8 to form a central valve through which, in the brake-releasing position, the working chamber 3 is in communication with a chamber 16 which is in turn in communication, through a housing connection 17 and a pressure conduit 18, with a nonpressurised container 19.Moreover, the master cylinder piston 8 is provided with axial bores 20 leading from chamber 16 to the back of the sleeve sealant 10 and permitting an overflow of pressure fluid from the chamber 16 beyond the rim of the sleeve sealant 10 into the working chamber 3.

The hydraulic force booster substantially comprises a booster piston 22 guided in a housing bore 21, with the area of the cylindrical surface of the booster piston being stepped by a piston step 23. By its largerdiameter section, the booster piston 22 confines a circumferential ring chamber 24 and, by the piston step 23, it forms, in cooperation with the housing bore 21, a booster chamber 25. Disposed in the interior of the booster piston 22 is a closure piston 27 provided with an axial bore 26, the central section of which comprises a shoulder forming a valve closure member 28 which, in the brake-releasing position shown, is held in abutment by a compression spring 30, with a valve seat 29. The closure piston 27 is surrounded by an annular chamber 31 which, through radial bores 32,33, is hydraulically connected to the circumferential annular chamber 24.The master cylinder piston 8 is supported on a booster piston 22 through a push rod 34.

Moroever, a control piston 36 actuable by a brake pedal 35 is disposed in the booster piston 22, the control piston 36 being displaceable relative to the booster piston 22 and, with a front face in this instance carrying a closure member 37 of spherical configuration, protruding into the booster chamber 25. In the brakereleasing direction, the control piston 36 is exposed to the action of a compression spring 38 supported on the valve seat 29 fixed in the booster piston 22. The closure member 37 cooperates with a valve seat 39 formed by the end of the closure piston 27 protruding through the valve seat 29. Through abutment with the valve seat 39, the closure member 37 blocks the aperture of the axial bore 26 in the closure piston 27 thereby separating the booster chamber 25 from the chamber 16 communicating with the axial bore 26 through bores 40.

A connecting bore 41 branches off the booster chamber 25 of the force booster 2, connected to which is a second brake circuit 42 through which are actuable two further wheel brakes 43,44 of the automotive vehicle.

The booster chamber 25 is, moreover, through a connecting conduit 45, in communication with a pressure-reducing valve 46 inserted into a connecting conduit 47 leading from a connecting bore 48 terminating in the circumferential ring chamber 24 to a high-pressure source 49 through which the force booster 2 is provided with pressure fluid.

The pressure-reducing valve 46 comprises a seat valve 50 provided with a closure member 5 1 of spherical configuration that closes in the direction of flow and cooperates with a valve seat 52 rigidly secured to the housing.

Through the seat valve 50, a valve inlet chamber 53 in communication with the high-pressure source 49 is separable from a valve outlet chamber 54 in communication with the connecting bore 48 of the force booster 2.

The valve outlet chamber 54 is confined by a control piston 55 which, with a journal 56, is in abutment with the closure member 51. The control piston 55 separates the valve outlet chamber 54 from a control chamber 57 in communication with the connecting conduit 45 and containing a biased compression spring 58 applying a spring force to the control piston 55 in a direction toward the valve outlet chamber 54. The magnitude of the spring force is sufficient to overcome the maximum hydraulic closing force capable of acting upon the closure member 51.

The high-pressure source 49 comprises a motor-driven pump 59 charging, from the container 19, through a check valve 60, a pressure accumulator 61, the pump drive being switched in response to the accumulator loading pressure.

The way of operation of the brake system as desribed is as follows: In the brake-releasing position as shown, the brake circuit 5, through the open central valve 14,15, is in communication with the chamber 16 connected, through the pressure conduit 18, to the non-pressurised container 19. The control piston 36 is in its retracted end position wherein the closure member 37 is lifted off the valve seat 39 so that the brake circuit 42, through the open axial bore 26 and the bore 40, is equally in communication with the chamber 16. The valve closure member 28, in the closing position, is in abutment with the valve seat 29 thereby keeping the annular chamber 31 closed.The pressure in the annular chamber 31 and in the circumferential annular chamber 24 coupled ahead theroef, as well as in the valve outlet chamber 54, through the pressure-reducing valve 46, is held at the lowest reducing level as the control chamber 57 is non-pressurised, as is the booster chamber 25. The full accumulator pressure of the high-pressure source 49 only prevails in the valve inlet chamber 53, which is retained therein by the closed seated valve 50.

Once the brake pedal 35 is actuated for initiating a braking process, first the control piston 36 is displaced thereby forcing the closure member 37 against the valve seat 39 and separating the booster chamber 25 from chamber 16. To enable a pressure now to be built up in the booster chamber 25 for applying the brake, the valve closure member 28 is lifted off its valve seat 29. For that purpose, in addition to the relatively low force of the comrpession spring 30, the hydraulic closing force arising from applying'pressure to the differential face between the cros-sections D2 and D, will have to be overcome. As the pressure in the ring chamber 31 is substan tiaily reduced by the pressure-reducing valve 46, the hydraulic closing force is not excessively high so that the valve closure member 28 can be opened by applying a relatively low force.Once the valve closure member 28 is opened and the annular chamber 31 is connected to the booster chamber 25, the pressure in the booster chamber 25 rises to push the booster piston 22 along with the master cylinder piston 8 in the actuating direction.

The booster piston 22 starts to move already at a low pressure rises as due to the reduced pressure in the circumferential chamber 24, the frictional resistances on the booster piston sealants 62,63,64 are low.

Once the central valve 14,15 is closed, the pressure in the booster chamber 25 and in the working chamber 3 of the master cylinder 1 rises to cause an actuation of the wheel brakes 6,7,43,44.

The pressure rise in the booster chamber 25, moreover, causes a decrease in the pressure reduction through the pressure-reducing valve 46 as the pressure, in the control chamber 57, supports the compression spring 58 so that seated valve 50 can again take a closing position only with a corresponding rise in the pressure in the valve outlet chamber 54.

As the control piston 55, on both sides has identical working faces, closure of the pressure-reducing valve will be possible only if the pressure in the valve outlet chamber 54 is higher than the pressure in the control chamber 57 by the amount arising from the sum of the spring force of the compression spring 58 and the cross-sectional face of the control piston 55. The pressure-reducing valve 46, therefore, always tends to provide the force booster 2, on the inlet side, with a pressure higher by the aforementioned amount than the pressure developed in the booster chamber 25, thereby safeguarding, in each actuating phase, an adequate reactivity of the brake pressure generator.Once the pressure difference between the pressure on the inlet of the force booster and the pressure developed in the booster chamber drops below the aforementioned amount, the pressure-reducing valve remains permanently opened. This may occur at higher actuating pressures and in that case will no longer be disadvantageous to the actuating process.

During releasing of the brake, the pistons and valve of the brake pressure generator are restored to the initial position as shown in the drawing, with the pressures over the chamber 16 leading to the container 19 being decreased. As the control chamber 57 also is thereby again rendered depressurised, the reduced pressure predetermined by the spring force of the compression spring 58, is readjusted in the valve outlet chamber 54 of the pressure reducing valve 46, thereby advantageously reducing again the reaction forces upon re-actuation of the brake pressure generator.

Claims

1. A. brake pressure generator for a hydrau lic brake system of an automotive vehicle, of the kind comprising a booster piston for actuating a master brake cylinder to which booster piston a hydraulic auxiliary pressure prevailing in a booster chamber can be applied, further comprising an actuating means cooperating with the booster piston, and a valve mechanism for controlling the auxiliary pressure, which valve mechanism is actuable by a relative movement between the booster piston and the actuating means and includes a double-seated valve, through which valve mechanism the booster chamber can be connected to a non-pressurised container or to a highpressure source containing a pressure accumulator, characterised in that provided in the connecting conduit (47) between the highpressure source (49) and the valve mechanism (28,29) is a pressure-reducing valve (26) to the control piston (55) of which the pressure prevailing in the booster chamber (25) can be applied to effect a decrease in the pressure reduction.

2. A brake pressure generator according to claim 1, characterised in that the inlet chamber (53) of the pressure-reducing valve (26) in communication with the high-pressure source (49) contains a normally-seated valve closure member (51).

3. A brake pressure generator according to claim 2, characterised in that the valve closure member (51) closes in the direction of flow, and that the control piston (55), in the valveclosing direction, is exposed to the initial pressure and, in the valve-opening direction, is exposed to the force of a compression spring (58) and to the pressure prevailing in the booster chamber (25).

4. A brake pressure generator according to claim 3, characterised in that the spring force of the compression spring (58) exceeds the pressure force acting upon the valve closure member (51) in the closing direction.

5. A brake pressure generator according to any one of the preceding claims, characterised in that the control piston (55) counteracts the initial pressure and the pressure in the booster chamber (25) by identical hydraulic working faces.

6. A brake pressure generator according to any one of the preceding claims, characterised in that the pressure-reducing factor of the pressure-reducing valve is 10 or more than 10 if the booster chamber (25) is non-pressurised.

7. A brake pressure generator for a hydraulic brake system substantially as described with reference to the accompanying drawing.