GB2118652A

GB2118652A - Control valve in a hydraulic brake booster

Info

Publication number: GB2118652A
Application number: GB08306713A
Authority: GB
Inventors: Reinhard Rauschenbach
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1982-04-15
Filing date: 1983-03-11
Publication date: 1983-11-02
Also published as: DE3230791A1; GB8306713D0; FR2525168A1; GB2118652B; FR2525168B1

Abstract

The control valve is based on a hydraulic brake booster, with a slidable piston (1) accommodated in a housing (39) and having rigidly arranged in it a booster piston (3) which confines a booster chamber (5), the latter communicating with a low pressure reservoir (22) in the release position. In the booster piston (3), there is axially slidably arranged a valve spool (24), which is actuatable by an actuating piston (31) connected to a brake pedal (32) to first close the connection to the supply reservoir (22) and then open, a seat valve (16, 41) actuatable by the valve spool (24) which is normally seated in a line which connects a pressure fluid source (14) to the booster chamber (5). To accomplish a control valve which is simple in respect of design and operation, solely the seat valve (16, 41) is inserted into the line (13, 12, 11, 15, 26, 28, 29, 30) leading from the pressure fluid source (14) to the booster chamber (5) for the purpose of actuation of the booster. <IMAGE>

Description

SPECIFICATION Control valve for a hydraulic brake booster The present invention relates to a control valve for a hydraulic brake booster, with a transmitting piston which is accommodated in a housing and which has rigidly arranged therein a booster piston that defines a booster chamber which latter, in the brake release position, communicates with a supply reservoir, with a valve spool axially slidably arranged in the booster piston, the said valve spool being actuatable by an actuating piston connected to a brake pedal with a view to closing the connection to the supply reservoir, and with a seat valve actuatable by the valve spool and seated in a line connecting a pressure fluid source to the booster chamber.

A like control valve is known from German patent specification 23 43 882. The said control valve includes a control casing acting as the booster piston and the transmitting piston and having located in it the valve spool which is rigidly connected to the brake pedal. In the inactive position of the valve spool, a pressure chamber (booster chamber) close to the brake pedal is in connection with the supply reservoir for this control valve. Upon forward movement of the valve spool caused by depression of the brake pedal, the pressure chamber is acted upon by pressure fluid. To this end, the valve spool contains a ramp by which the seat valve is movable to assume its open position. Upon depression of the brake pedal, first an accumulator-charging valve is caused to adopt its open position. As a result, the pressure fluid from the pressure accumulator prevails at the control casing.Upon further displacement of the valve spool, the connection between the pressure chamber and the supply reservoir will be interrupted. Subsequently, a control groove of the valve spool moves in overlapping engagement with a fluid-supplying control groove of the control casing, as a result whereof the pressure chamber is acted upon by pressure fluid. Admittedly, owing to the insertion of the seat valve into the line leading from the fluid source to the pressure chamber, it is ensured in this control valve that the pressure reservoir maintains the pressure in the inactive position. However, the control valve is relatively complicated and expensive due to the insertion of the seat valve and the actuating device pertaining thereto.

It is therefore an object of the present invention to improve upon the known control valve to the effect that it is rendered simpler in design and operation and thus cheaper in manufacture.

According to the present invention there is provided a control valve for a hydraulic brake booster, with a transmitting piston which is accommodated in a housing and which has rigidly arranged therein a booster piston that defines a booster chamber which latter, in the brake release position, communicates with a supply reservoir, with a valve spool axially slidably arranged in the booster piston, the said valve spool being actuatable by an actuating piston connected to a brake pedal with a view to closing the connection to the supply reservoir, and with a seat valve actuatable by the valve spool and seated in a line connecting a pressure fluid source to the booster chamber, characterised in that only the seat valve is inserted into the line leading from the pressure fluid source to the booster chamber for the purpose of actuating the pressure fluid.

Thus inserted into the line leading from the pressure fluid source to the booster chamber is merely the seat valve for the actuation of the pressure fluid. Thereby a control valve will be obtained which is extremely simple in design and in operation. This will be accomplished in that the seat valve which is available already in the known control valve takes care of the actuation of the pressure fluid so that solely the line to the supply reservoir will be closed by the valve spool. By making use of the seat valve for the actuation of the pressure fluid, the better sealing properties of such valves can be utilised in an advantageous manner, in contrast to slide valves where the accumulator's charge is exhausted already after about three to four hours unless the pressure accumulator is topped up inbetween.

It is provided in embodiments of the idea of the invention that the seat valve comprises a valve body supported in the booster piston, the said valve body being axially slidably located in a central bore of the booster piston. This results in a particularly compact arrangement.

It will be particularly expedient, if the line that connects the pressure fluid source to the booster chamber disposes of a valve seat in the booster piston which is adapted to be closed axially by the valve body, with the line that leads from the supply reservoir to the booster chamber containing preferably a radial bore in the booster piston, the said bore terminating into an axial valve spool bore in the booster piston.

In further favourable embodiments of the present invention, the valve spool has a central extension which extends slidably through the valve body of the seat valve, and an actuating stop for the valve body is provided at the valve spool, which actuating stop is suitably formed by a projection arranged at said valve spool.

To achieve further simplification with respect to construction and manufacturing technique, the axial pressure fluid bore and the valve spool bore form expediently one single longitudinal throughbore, and the central extension of the valve spool forms together with the pressure-fluid bore encompassing it an annular chamber which terminates into the valve spool bore, while the valve spool contains an axial bore extending from which are two radial bores, the one thereof terminating in the booster chamber while the other one thereof terminates into the valve spool bore.

An embodiment of the present invention will now be described in more detail with reference to the accompanying drawing.

The Figure shows in a longitudinal section an only partially illustrated transmitting piston 1 of a hydraulic brake booster, which piston is arranged axially slidably in a housing 39 and contains a bore 2 extending in a longitudinal direction and having rigidly arranged in it a booster piston 3. A valve spool 24 extends through a booster chamber 5, and at its end close to the brake pedal is secured in an actuating piston 31, a face 4 of which piston 31 abuts one end wall of the housing bore in booster chamber 5. With its end surface 42 close to the brake pedal, the transmitting piston 1 abuts the one end wall of the housing 39. In the opposite end surface 6 of the booster piston 3, there is provided a cylindrical recess 7 into which a cylindrical extension 8 of a plug 9 is projecting.

In a hemispherical recess 10 of said plug 9, a nonillustrated push rod of a master.brake cylinder can be supported.

The booster piston 3 contains a first cross bore 11 which is aligned with a cross bore in the transmitting piston that terminates in a groove 12 in the transmitting piston 1 and which is in communication with a hydraulic reservoir 14, shown only schematically, via a line 13 that extends through the housing 39.The first cross bore 11 which will be referred to as pressure fluid bore 11 in the following terminates into a central longitudinal bore 1 5 in the booster piston 3 in which latter longitudinal bore a valve body 1 6 is axially slidably located with a view to closing the seat 41 of an annular insert 1 7 and thereby indirectly also the pressure fluid bore 11, with the alternative to re-open same, the said insert being arranged in a corresponding recess 1 8 of the booster piston 3.

Spaced from the pressure-fluid bore 11, a second cross bore 1 9 is arranged in the booster piston 3 on the side close to the brake pedal. This second cross bore 1 9 extends via a corresponding cross-bore in the transmitting piston 1, a groove 20 and a line 21 to a supply reservoir 22 which is likewise illustrated schematically only. Within the booster piston 3, the second cross bore 1 9 terminates in a central longitudinal bore 23 in which latter the valve spool 24 is axially slidably accommodated.

The valve spool 24 has a stepped central extension 25 which extends through the booster piston 3, the valve insert 1 7 and the valve body 1 6. The central longitudinal bore 23 is, via a connecting bore 26 in the insert and piston 3, coupled to a central longitudinal bore 40. The latter, in turn, is in communication with the cylindrical recess 7 so that a through-bore which is stepped severai times is formed for the central extension 25 of the valve spool 24 enabling the said extension to directly move into engagement with the cylindrical extension 8 of the plug 9.

In the area of the annular insert 17 and the connecting bore 26, the central extension 25 is of reduced diameter in relation to the insert 1 7 and the connecting bore 26, an annular chamber 27 being constituted thereby which establishes a connection between the central longitudinal bores 23 and 40. In this area, the extension 25 has a step 37 which - upon actuation of the valve spool 24 - will entrain the valve body 1 6 in order to open the seat valve.

In the area of the central longitudinal bore 23, the central extension 25 accommodates a cross bore 28 which, on the one hand, terminates into the longitudinal bore 23 and, on the other hand, into an axial bore 29 in the valve spool 24.

Terminating into this axial bore 29 contained in the portion of the valve spool 24 that projects from the booster piston 3 is another cross bore 30 which is in communication with the booster chamber 5.

Actuation of the valve spool 24 is effected by the actuating piston 31 which is on the one side connected to a brake pedal 32 and which contains on the other side a recess 33 in which latter the valve spool 24 is axially supported. The actuation of the actuating piston 31 will take place in opposition to the force of a compression spring 34 which urges piston 31 into abutment with the housing 39 in the brake released position. Since the valve spool is rigidly connected to the actuating piston 31 , the compression spring 34 effectively urges the valve spool 24 to the right when viewing the drawing effectively. The spring 34 is supported between the booster piston 3 and a pressure plate 35 acting on which is the actuating piston 31.

The operation of the control valve is as described hereinbelow: upon actuation of the actuating piston 31 in opposition to the compression spring 34, the valve.spool 24 will be displaced to the left when viewing the drawing and closes with its control surface 36 the second cross bore 1 9 that leads to the supply reservoir 22. Upon further depression of the brake pedal, the valve spool 24 will entrain with its step 37 the valve body 1 6 in opposition to the force of a compression spring 38 interposed between the valve body 16 and the plug 9 and thereby opens the seat 41 , thus establishing a connection between the pressure fluid bore 11 and the booster chamber 5.The magnitude of the actuation is dependent upon the amount the brake pedal 32 is depressed and therefore upon the displacement of the actuating piston 31 and thus upon the cross-section of the opening between the valve body 16 and the annular insert 17.

Through this opening, pressure fluid can be supplied from the hydraulic reservoir 14 via the line 13, the recess 12, the pressure-fluid bore 11, the longitudinal bore 15, the annular chamber 27, the connecting bore 26 and through the bores 28, 29 and 30 into the pressure chamber 5. By the action of the pressure introduced, the booster piston 3 and the transmitting piston 1 will be displaced to the left, as a result whereof the pressure fluid bore leading to the hydraulic reservoir 14 will be closed again at the seat 41 caused by the compression spring 38. Only upon further displacement of the booster piston,3 to the left or upon relief of the actuating piston 31 will the cross bore 1 9 that leads to the supply reservoir 22 be re-opened.

Claims

1. A control valve for a hydraulic brake booster, with a transmitting piston which is accommodated in a housing and which has rigidly arranged therein a booster piston that defines a booster chamber which latter, in the brake release position, communicates with a supply reservoir, with a valve spool axially slidably arranged in the booster piston, the said valve spool being actuatable by an actuating piston connected to a brake pedal with a view to closing the connection to the supply reservoir, and with a seat valve actuatable by the valve spool and seated in a line connecting a pressure fluid source to the booster chamber, characterised in that only the seat valve (16,41)isinsertedintotheline(13,12,11,15, 26, 28, 29, 30) leading from the pressure fluid source (14) to the booster chamber (5) for the purpose of actuating the pressure fluid.

2. A control valve as claimed in claim 1, characterised in that the seat valve (16,41) comprises a valve body (16) which is supported in the booster piston (3).

3. A control valve as claimed in claim 2, characterised in that the valve body (16) is axially slidably located in a central longitudinal bore (15) of the booster piston (3).

4. A control valve as claimed in claim 2 or 3, characterised in that the line (13, 12, 11, 15,26, 28, 29, 30) which interconnects the pressure fluid source (14) and the booster chamber (5) contains a valve seat (41) in the booster piston (3), the said valve seat being adapted to be closed axially by means of the valve body (16).

5. A control valve as claimed in claim 4, characterised in that the line (21, 20, 19, 23, 28, 29, 30) leading from the supply reservoir (22) to the booster chamber (5) contains a radial bore (19) in the booster piston (3) which terminates into an axial valve spool bore (23) in the booster piston (3).

6. A control valve as claimed in claim 5, characterised in that the valve spool (24) has a central extension (25) which extends slidably through the valve body (16) of the seat valve, and in that an actuating stop (37) is provided for the valve body (16) on the valve spool (24).

7. A control valve as claimed in claim 6, characterised in that the actuating stop (37) for the valve body (16) is a step (37) formed at the extension (25) of the valve spool (24).

8. A control valve as claimed in claim 6 or claim 7, characterised in that the axial bore (15) and the valve spool bore (23) form a stepped longitudinal through-bore, in that the central extension (25) of the valve spool (24) forms together with the bore encompassing it an annular chamber (27) which latter terminates into the valve spool bore (23), and in that the valve spool (24) contains an axial bore (29) extending from which are two cross bores (28, 30), the one (30) thereof terminating into the booster chamber (5) while the other (28) thereof terminates into the valve spool bore (23).

9. A control valve for a hydraulic brake booster substantially as herein described with reference to and as illustrated in the accompanying drawing.