GB2127919A

GB2127919A - Pressure-retaining valve for a vehicular brake system

Info

Publication number: GB2127919A
Application number: GB08319183A
Authority: GB
Inventors: Hans-Dieter Reinartz; Waldemar Vatter
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1982-09-14
Filing date: 1983-07-15
Publication date: 1984-04-18
Also published as: GB2127919B; FR2532900B1; DE3233961A1; GB8319183D0; DE3233961C2; IT8322730A0; JPS5970253A; ES274268U; ES274268Y; IT1167373B; FR2532900A1

Abstract

The pressure-retaining valve (1) with a housing (4) forming a chamber has on one side an opening towards a master brake cylinder and has on the other side an opening towards the wheel cylinders, a double valve (2) being arranged in the chamber subdividing the chamber into two compartments, this double valve (2) comprising a first spring-loaded valve body (24) opening in the direction of the wheel cylinders and a second spring- loaded valve body (25) opening in the direction of the master cylinder. To provide a pressure-retaining valve applicable to an automotive vehicle adapted for vacuum bleeding, wherein the double valve (2) remains inactive during the vacuum bleeding and is not penetrated by fluid, a third valve (3) is arranged in parallel to the double valve (2) which, in operation, affords limited valve travel and the lowest possible amount of friction. <IMAGE>

Description

SPECIFICATION Pressure-retaining valve for a vehicular brake system The present invention relates to a pressure retaining valve for a vehicular brake system of- the kind including a housing which forms a chamber and which has on its one side an opening towards a master brake cylinder and on its other side an opening towards the wheel cylinders, with a double valve being disposed in the chamber subdividing the latter into two compartments, the double valve comprising a first spring-loaded valve body opening in the direction of the wheel cylinders and a second spring-loaded valve body opening in the direction of the master cylinder.

A pressure-retaining valve of this kind is known from German utility model 1 896 381.

The housing of this pressure-retaining valve accommodates a rigid partition wall subdividing the housing into two compartments. The partition wall contains an aperture which is closable by a first valve body. The first valve body contains another aperture which is closable by a second valve body.

In the manufacture of automotive vehicles, brake systems equipped with a pressure-retaining valve have to be filled and simultaineously bled in a rapid and simple manner. At present, this filling and bleeding process is regularly effected by pressure fluid being urged through the master brake cylinder into the brake circuits up to the individual wheel cylinders. Filling and bleeding, respectively, of a brake system is enabled by the fact that the direction of movement that opens the pressure-retaining valve is identical with the direction of flow of the brake fluid.

However since this process occupies much time at the assembly line, it is desired to fill and to bleed respectively, brake systems by means of a sub-atmospheric pressure. To this end, first a specific pressure below atmospheric has to be produced in the brake system by the master brake cylinder which subsequently during filling will cause the brake fluid to be sucked into the individual brake circuits. If this method were used in the drum brake line of a brake system comprising a pressure-retaining valve as disclosed in German utility model 1 896 381, a comparatively high amount of sub-atmospheric pressure would have to be generated at the master cylinder, until the pressure-retaining valve would lift and release the brake circuit. In practical applications, however, such subatmospheric pressures can be obtained only with great effort.If it were desired to avoid this in the known pressure-retaining valve, the residual pressure would be affected, i.e. the residual pressure to be retained would have to be reduced, which is however not possible in many cases.

A pressure-retaining valve for a vehicular brake system has already been proposed by the German patent application P 31 07 419.7, wherein a piston is arranged in the housing in a sealed and axially slidable manner which piston is on its one side acted upon by the pressure of the chamber connected to the master cylinder, while it is on its other side acted upon by atmospheric pressure and acts in an opening sense on a valve body.

This pressure-retaining valve enables one to bleed and fill a brake system with a pressureretaining valve already in the event of a relatively low sub-atmospheric pressure prevailing on the master cylinder side. To this end, it is however required in this pressureretaining valve to move likewise the double valve in the vacuum bleeding operation, since the air has to flow through the double valve.

To this end, relatively long travels are required and there are produced high friction forces.

It is therefore an object of the present invention to provide a pressure-retaining valve of the kind referred to which is appropriate for vacuum bleeding and wherein the double valve remains inactive during the vacuum bleeding and is not penetrated by fluid, as a result whereof large valve travels and high friction forces will be avoided.

According to the invention in its broadest aspect, a pressure-retaining valve for a vehicular braking system of the kind referred to is characterised in that a third spring-loaded valve which opens in the direction of the master cylinder is arranged in parallel to the double valve. By this, there will be accomplished a pressure-retaining valve for a vehicular brake system filled with sub-atmospheric pressure wherein the function of the double valve that is essential for the braking action will not be impaired by the vacuum bleeding, since the air will not flow through the double valve during bleeding but in parallel to the latter, the double valve remaining in its inactive condition as a result. Therefore, the pressure-retaining valve requires but the smallest of valve travels, while very low friction occurs.

In an expedient embodiment of the present invention, the third valve comprises a valve body which is axially slidably arranged in the chamber, whereby a compact construction unit will be attained.

To attain guiding of the valve body of the third valve in a simple way, the valve body advantageously includes a guide piston which is located in a bore disposed coaxially relative to the chamber. This guide piston contains an annular groove in which an annular seal is arranged.

According to another favourable embodiment of the invention, the valve body of the third valve has a conical sealing shoulder, and the associated valve seat is formed by a step provided in the housing or by a sealing edge of the chamber.

In an improvement of the inventive idea, an annular groove is arranged between the sealing shoulder and the guide piston terminating into which is a radial bore which leads to the wheel cylinders.

In another embodiment of this invention, the valve body of the third valve forms a cavity in which the double valve is arranged, with a through-bore which is located in the direction of the wheel cylinders in front of the double valve leading from the cavity into the chamber.

In this arrangement, the cavity in the third valve body is suitably formed by an axial stepped bore, the second valve body being arranged in a first bore section provided on the master cylinder side, while the first valve body is arranged in a second bore section provided on the wheel cylinder side.

The second bore section may comprise a cone on the wheel cylinder side which leads to a third bore section into which terminates a radial bore connected to the annular groove.

To load the third valve body, a cup spring can be provided in a space-saving manner which, on the one hand, is supported on the annular end portion of the third valve body while, on the other hand, it is supported on an annular plate located in the housing. This function can likewise be taken care of by an annular seal with "roll-back effect" that is provided at the third valve body for loading the latter.

To load the second valve body, a helical spring can be provided in the first bore section for loading the second valve body, the spring bearing with its one end against a ring inserted in the valve body.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure I is an embodiment of a pressureretaining valve, wherein a double valve and a third valve are combined to form a construction unit and integrated in a master brake cylinder, and Figure 2 is another embodiment of a pressure-retaining valve similar to the pressureretaining valve of Fig. 1, provided however with a thread for screwing into a master brake cylinder.

In the pressure-retaining valve 1 shown in Fig. 1, a double valve 2 and a third valve 3 acting as a vacuum valve are combined to form a construction unit. The pressure-retaining valve 1 comprises a housing 4 provided with a bore 5 stepped several times. A first bore section 6, which is open relative to the master cylinder side, accommodates axially slidably a valve body 7 of the third valve 3. A guide piston 9 which is integrally designed with the third valve body 7 is arranged in a second bore section 8 which is adjacent to the first bore section 6. The guide piston 9 contains an annular groove 10 receiving an annular seal 11.

The third valve body 7 is substantially composed of a hollowcylindrical portion 12, of a conical sealing shoulder 1 3 adjacent thereto which cooperates with a valve seat 14 designed as a sealing edge in the housing 4, and of a cylindrical portion 1 5 of reduced diameter, adjacent to which latter is the guide piston 9. The cylindrical portion 1 5 of reduced diameter forms an annular groove 16 terminating into which is a cross bore 1 7 which, in turn, leads to an axial longitudinal bore 18.

Inside, the third valve body 7 is designed with a stepped bore. A first bore section 1 9 close to the master cylinder contains a radial bore 20 which leads into an annular chamber 21 which is placed between the outer wall of the third valve body 7 and the wall of the first bore section 6. Adjacent to the first bore section 1 9 is a second bore section 22 of reduced diameter which is followed via a cone 23 by a third bore section, i.e. the axial longitudinal bore 1 8.

The double valve 2 is arranged in the interior of the hollow-cylindrical portion 12 of the third valve body 7 in the area of the first and the second bore sections 19 and 22. It contains a first valve body 24 whose valve seat is formed by a second valve body 25, the valve seat of the second valve body 25 being formed by a step 26 that is provided between the first bore section 1 9 and the second bore section 22.

The first valve body 24 comprises a valve stem 27 which extends through a central bore 28 of the second valve body 25 in the direction of the master cylinder. The valve stem 27 is surrounded by a helical spring 29 which, on the one hand, bears against the second valve body 25 and, on the other hand, against a stop 30 which is provided at the end of the valve stem 27. A second helical spring 31 arranged in the interior of the hollow-cylindrical portion 12 abuts with its one end on the second valve body 25 and bears with its other end against a ring 32 inserted in the hollow-cylindrical portion 1 2.

Arranged between the annular end portion 33 of the third valve body 7 and a springsupported annular plate 34 is a cup spring 35 which normally urges the third valve body 7 against its valve seat 14.

This function can be performed in a very simple and expedient manner also by the annular seal 11 which, in this case, has to provide for a "roll-back effect", i.e. when the third valve 3 is opened causing the valve body 7 to be displaced to the right (as seen in the drawing), the annular seal 11 will be deformed and will then exert a restoring force on the valve body 7. The cup spring 35 may be dispensed with in this design.

A line by-passing the double valve 2 is established by the radial bore 20, the annular chamber 21 and the annular groove 16, this line communicating with a bore 36 which leads to a wheel cylinder port 37.

There will now be described the method of operation of the pressure-retaining valve 1 illustrated in Fig. 1: to evacuate the wheel cylinders, a sub-atmospheric pressure is produced by the master brake cylinder side which, with the double valve 2 closed, lifts the valve body 7 from its valve seat 1 4 in opposition to the force of the cup spring 35.

When filling by pressure, the valve body 7 will be urged against the valve seat 1 4 again by the cup spring 35. The double valve 2 opens in the direction of the wheel cylinders thereby enabling these to be filled. After the filling operation, the double valve 2 closes and retains the residual pressure desired. The double valve 2 will open upon every braking action and retain the residual pressure, while the valve body 7 of the third valve 3 remains always in its inactive position after filling by means of a vacuum filling unit.

The pressure-retaining valve 38 illustrated in Fig. 2 differs from the pressure-retaining valve 1 only in that it can be screwed into the tandem master brake cylinder (not shown) and has a threaded portion 39 for this purpose.

Claims

1. A pressure retaining valve for a vehicular brake system of the kind including a housing which forms a chamber and which has on its one side an opening towards a master brake cylinder and on its other side an opening towards the wheel cylinders, with a double valve being disposed in the chamber sub-dividing said into two compartments, the double valve comprising a first spring-loaded valve body opening in the direction of the wheel cylinders and a second spring-loaded valve body opening in the direction of the master cylinder, characterised in that a third spring-loaded valve (3) which opens in the direction of the master cylinder is arranged in parallel to the double valve.

2. A pressure-retaining valve as claimed in claim 1, characterised in that the third valve (3) comprises a valve body (7) which is axially slidably arranged in the chamber (6).

3. A pressure-retaining valve as claimed in claim 2, characterised in that the valve body (7) of the third valve (3) comprises a guide piston (9) which is located in a bore (8) disposed coaxially relative to the chamber (6).

4. A pressure-retaining valve as claimed in claim 3, characterised in that the guide piston (9) contains an annular groove (10) in which an annular seal (11) is arranged.

5. A pressure-retaining valve as claimed in any one of claims 1 to 4, characterised in that the valve body (7) of the third valve (3) has a conical sealing shoulder (13) and in that the associated valve seat (14) is formed by a step provided in the housing (4) or by a sealing edge of the chamber (6).

6. A pressure-retaining valve as claimed in claim 5, characterised in that an annular groove (16) is arranged between the sealing shoulder (1 3) and the guide piston (9) terminating into which is a radial bore (1 7) which leads to the wheel cylinders.

7. A pressure-retaining valve as claimed in any one of the preceding claims, characterised in that the valve body (7) of the third valve (3) forms a cavity (19, 22) in which the double valve (2) is arranged, with a through-bore (21) which is located in the direction of the wheel cylinders in front of the double valve (2) leading from the cavity (19, 22) into the chamber (6).

8. A pressure-retaining valve as claimed in claim 7, characterised in that the cavity (19, 22) in the third valve body (7) is formed by an axial stepped bore, the second valve body (25) being arranged in a first bore section (19) provided on the master cylinder side, while the first valve body (24) is arranged in a second bore section (22) provided on the wheel cylinder side.

9. A pressure-retaining valve as claimed in claim 8, characterised in that the second bore section (22) comprises a cone (23) on the wheel cylinder side which leads to a third bore section (18) into which terminates a radial bore (17) connected to the annular groove (16).

1 0. A pressure-retaining valve as claimed in any one of the preceding claims, characterised in that a cup spring (35) is provided for loading the third valve body (7).

11. A pressure-retaining valve as claimed in claim 10, characterised in that the cup spring (35) on the one hand, is supported on the annular end portion (33) of the third valve body (7) while, on the other hand, it is supported on an annular plate (34) located in the housing.

1 2. A pressure-retaining valve as claimed in any one of claims 7 to 11, characterised in that a helical spring (31) is provided in the first bore section (19) for loading the second valve body (25) the spring bearing with its one end against a ring (32) inserted in the valve body (7).

1 3. A pressure-retaining valve as claimed in any one of claims 1 to 9 or 12, characterised in that an annular seal (25) with "rollback effect" is provided at the third valve body (7) for loading the latter.

14. A pressure-retaining valve for a vehicular brake system substantially as described with reference to the accompanying drawings.