GB2045398A

GB2045398A - Pressure limiting valve

Info

Publication number: GB2045398A
Application number: GB7943994A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1978-12-22
Filing date: 1979-12-20
Publication date: 1980-10-29
Also published as: DE2855554A1; FR2444824A1; IT1207948B; FR2444824B1; IT7969467A0; GB2045398B; NL7907824A

Abstract

The valve for supplying pressure medium to a steering stabilizing unit for a trailing axle of a vehicle in dependence on the loading of a plurality of reference points of the vehicle is provided with two pistons 25, 26 the one of which is subjected to the higher fluid pressure acting to supplement the loading by spring 15 on the self-lapping valve 11, 12, 23 to regulate the pressure at outlet 19. A minimum outlet pressure is determined by the pre-compression of spring 15 by the adjusting device 33. <IMAGE>

Description

SPECIFICATION Pressure limiting valve The invention relates to a pressure limiting valve and, more especially to a valve suitable for use with a pressure medium-operated dynamic unit, especially a steering stabilising unit for a trailing axle of a vehicle.

A pressure limiting valve for a steering stabilizing unit is required, in order to operate the unit, to deliver increased pressure as the load of the unit increases and reduced pressure as the load decreases. One suitable form of valve is described, for example, in DE-AS 25 56 532, and can be actuated load-dependently by way of a mechanical linkage in dependence on the distance between an axle and the vehicle body.

Disadvantages of this are that the control elements require a substantial amount of space and are complicated with regard to their manufacture and assembly, and that the loaddependent actuation of the valve is unsatisfactory in the case of a varying load on the two sides of a vehicle, for example when the vehicle is cornering.

The problem with which the present invention is concerned is the provision of a pressure limiting valve which is suitable for a steering stabilizing unit of a vehicle capable of delivering to the unit a pressure which, at any time, is dependent upon the loading of the most highly-loaded reference point of the vehicle, whilst being comparatively simple and compact in construction.

The present invention provides a pressure limiting valve assembly having an outlet which can be connected to an inlet by way of a valve; a piston operable to control the valve, in dependence on the loading of the piston, against the action of the pressure at the outlet; a vent connectable to the outlet by way of the valve control piston when the action of the pressure at the outlet predominates as compared with the loading on the piston; a control device having a plurality of control inlets and actuable by-the pressure at those inlets to load the piston under the action of the highest of those pressures, and an adjustable device operable to load the piston to a predetermined constant extent in the same direction as the control device.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which shows a longitudinal section through a pressure limiting valve suitable for a pressure medium-operable stabilising device of a trailing axle of a vehicle.

The pressure limiting valve shown has a housing consisting of a housing portion 1, having arranged therein a blind bore 2 which is double stepped towards the outside, and a housing portion 3, having a blind bore 4 arranged therein.

The stepped blind bore 2 and the blind bore 4 are arranged coaxially and with their open ends towards each other.

The smallest-diameter section of the blind bore 2 (formed at the base of the bore) has an annular housing recess 5 which is connected to an inlet 6 arranged in the housing portion 1. The smallestdiameter section of the bore 2 houses a cylindrical member 7 which projects into the mediumdiameter section of the bore and is displaceablyguided and mounted in a sealed manner relative to the annular housing recess 5. The cylindrical member 7, on the one hand, defines an adjusting space 8 which is formed at the base of the blind bore 2 and is connected to the atmosphere and, on the other hand, has a blind bore 9 arranged coaxially with and opening towards the open end of the bore 2.

The starting position of the cylindrical member 7 can be altered by means of an adjusting screw 32 which is arranged in the housing portion 1 so as to be operable from the outside to be screwed axially into or out of the adjusting space 8. The front end of the screw co-operates with the cylindrical member 7, and the screw can be secured in the chosen position in the usual manner by means of a nut 34 which can be tightened against the housing portion 1.

Irrespective of the position of the cylindrical member 7 (within the range of adjustment of the screw) the. blind bore 9 of the cylindrical member is connected to the inlet 6 by way of a radial bore 10 and the annular housing recess 5.

In the blind bore 9 there is arranged a valve 11, 12 comprising an annular valve seat 1 formed on a member located in the open end of the blind bore 9, and a closure member 12 resiliently biased by a spring 13 supported at the base of the bore 9.

If, under the action of spring 13, the closure member 1 2 moves onto the valve seat 11 then the blind bore 9, which is connected to the inlet 6, will be blocked-off from the medium-diameter section of the double-stepped blind bore 2.

In the medium-diameter section of the bore 2, a piston 14 is slidably arranged in sealed manner.

The piston 14 is resiliently-biased, by a spring 1 5 which is supported on the other housing portion 3, towards a position in which a stop 1 6 on the piston rests against a stop 1 7 formed at the front of the cylindrical member 7. In this position, a sleeve-shaped extension 1 8 of the piston which projects through the annular valve seat 11 with clearance, holds the closure member 12 in a position raised from the annular valve seat 11 against the action of the spring 13.

On the valve side of the piston 14 there is formed, within the medium diameter section of the bore 2, a chamber 20 which is connected to an outlet 19. When the valve 11, 12 is open, the chamber 20 is connected by way of the valve to the blind bore 9 of the cylindrical member 7, and hence to the inlet 6.

On the other side of the piston 14 and in the largest diameter section of the double stepped blind bore 2, a space 21 is formed, which accommodates the spring 1 5 and is connected to the atmosphere.

The space 21 communicates with a venting bore 22 which is arranged axially through the piston 14 and its sleeve-shaped extension 18. If the piston 14 is moved against the action of the spring 1 5 so that an annular valve seat 25 formed at the end of the extension is moved away from the closure member 12, allowing the latter to seat on the other annular valve seat 11, then the space 21 at one end of the piston is placed in communication, through the bore 22 with the chamber 20 at the other end of the piston.

In the second housing portion 3 there is arranged a control device 24 which can be actuated by several pressure medium sources and loads the piston 14 in the direction of the valve 11, 12 in dependence on the highest pressure of one of these pressure medium sources, as will be described below.

The control device 24 has first and second pistons 25, 26 which are each displaceably arranged in sealed manner in the blind bore 4.

The first piston 25 defines a control chamber 28 formed at the base of the blind bore 44 and connected to a control inlet 27.

The second piston 26 defines a further control chamber 30, formed between it and the first piston 25, and connected to a control inlet 29.

The second piston 26 is furthermore arranged so as to co-operate with the piston 14 by means of an extension 31 which projects into the space 21 through the spring 1 5, with the front of the extension 31 resting against the piston 14. The connection of the venting bore 22 to the space 21 is ensured by transverse grooves, not shown, at the front of the extension 31. The spring 1 5 and adjusting screw 32 in combination constitute a device 33 which constantly raises the piston 14 in the same direction as the control device 24 (in dependence on the action of the predeterminably pretensioned spring 15) or, when the control device 24 fails to operate, constantly loads this piston.The manner in which this is achieved is described below, it being of importance to note from the preceding description that the spring 1 5 loads the piston 14 in the direction of closure of the valve 23, 12 and in the direction of opening of the other valve 11, 12 and the adjusting screw 32 determines the position of the cylindrical member 7 and also, by means of the stop 17 of the cylindrical member which limits the path of the piston 14 on the valve side, the pre-tension of the spring 1 5.

The operation of the pressure limiting valve shown in the drawing is as follows: The pressure limiting valve is shown in its starting position in the case of an unpressurised inlet 6 and outlet 19. In this position, the piston 14 (either under the action of the device 33 or, when the control device 24 is actuated, under the action of the highest pressure in the control chambers 28 and 30) rests with the stop 1 6 against the stop 1 7 of the cylindrical member 7, and the sleeve-shaped extension 18 holds the valve 23, 12 in the closed position and the valve 11, 1 2 in the open position. As a result, the chamber 20 and hence the outlet 19 are connected to the inlet 6 whilst the venting bore 22 is blocked.

Actuation of the control device 24 is effected by connecting the control inlets 27'and 29 to two static pressure medium sources which are independent of each other and provided by the hydraulic equalisation of the axle load at the two sides of a multiple axle unit of a vehicle.

As soon as the inlet 6 is connected to a pressure medium source, for example a compressed air reservoir, a pressure is delivered at the outlet 19 by way of the open valve 11, 12 and the chamber 20. The piston 14 is loaded by the pressure delivered, against the action of the spring 1 5 of the device 33 and against the action of the control device 24, and finally can be moved under the predominant action of the pressure delivered against the combined action of the spring 1 5 and the actuating device 24. As a result, the closure member 12 (which follows under the action of the spring 13) adopts its closed position on the annular valve seat 11, in which position the outlet 19 is blocked from the inlet 6 and the chamber 20 is blocked from the venting bore 22.This prevents the further increase of pressure in the chamber 20 and thus an end position is reached.

It is assumed hereinafter that the loaddependent loading of the piston 14 which is determined by the control device 24 takes place on the basis of a higher pressure in the control chamber 28 than in the control chamber 30. In this case, the second piston 26 rests against the piston 14, whilst the first piston 25 rests against the second piston 26. As soon as the other loaddependent pressure medium source is able to introduce a higher pressure into the other control chamber 30 (for example, owing to a displacement of the axle load) there will occur an actuation of the piston 14 according to this higher pressure whilst the first and second pistons 25 and 26 will be loaded in opposite directions. In this case, the first piston 25 will rest against the base of the blind bore 4, whilst the second piston 26 will continue to rest against the piston 14 by way of the extension 31.

If the load-dependent actuation pressure on the control device 24 is increased, the piston 14 moves under the increased action against the pressure in chamber 20, as a result of which the closure member 12 is lifted from its annular valve seat 11 by the sleeve-shaped extension 18, and a higher pressure corresponding to the increased actuating action can be delivered by way of the open valve 11,12.

If, on the other hand, the load-dependent actuation pressure on the control device 24 is reduced, the piston 14 moves under the predominant action of the pressure in chamber 20 against the action of the control device 24 and the spring 1 5 of the device 33, as a result of which, with the closure member 1 2 remaining on the annular valve seat 11, the other annular valve seat 23 formed on the sleeve-shaped extension 18 is moved away from the closure member 12 and a reduction in the pressure at outlet 19, corresponding to the reduced actuating action, is obtained by way of the open valve 23, 12, the venting bore 22 and the space 21 which is connected to the atmosPhere.

In this manner, the pressure limiting valve shown is able, owing to the control device 24, to deliver via the outlet 1 9 a pressure for a pressure medium operable dynamic unit, for example, a steering stabilising device of a trailing axle of a vehicle, which pressure is dependent on the maximum (load-dependent) actuation pressure of one of several static pressure medium sources.

The load-dependent control action, and hence also the load-dependent pressure delivered by the valve at outlet 19, is constantly increased by the device 33 which operates in the same direction as the control device 24 according to the action of the spring 15.

This constant increase of the load-dependent pressure delivered by the valve can be adapted to suit the requirements of the pressure medium operable dynamic unit connected to valve outlet 19, the adaptation being effected by the device 33, that is to say, by the pre-tension of the spring 1 5 which can be adjusted by means of the adjusting screw 32.

If the load-dependent actuation of the control device 24 fails to operate, it is possible to deliver a constant pressure which can be predetermined by the device 33, for example for the minimum supply of the dynamic unit (the steering stabilising device) connected to outlet 1 9 of the valve.

As soon as the inlet 6 and the outlet 19 are unpressurised, the pressure limiting valve adopts its starting position described above, either under the combined actions of the control device 24 and the device 33 or - when the control device 24 fails to operate -- solely under the action of the device 33.

It may also be mentioned that the pressure limiting valve may be actuated by only one static pressure medium source or by any other control pressure (rather than two static pressures as described above) it being possible then to simplify the control device 24 by omitting the control inlet 27 of the piston 25.

The advantages that can be gained by the pressure limiting valve described above are that the valve, which can overall be assembled comparatively easily and compactly, can be actuated directly by several load-dependent pressure medium sources, for example by the hydraulic equalisation of the axle load on the one and the other side of a multiple axle vehicle unit and is capable of delivering a load-dependent pressure corresponding to the highest pressure of one of these pressure medium sources.The device 33, operating in the same direction as the control device 24, produces a constant, adaptable, increase of the load-dependently delivered pressure and, when the static pressure medium sources fail to operate, ensures a constant minimum delivery of pressure, for supplying a pressure medium operable dynamic unit, for example the steering stabilizing device of the trailing axle of the multiple axle unit mentioned above. Finally, the control device 24 which is based on two pistons 25, 26 of equal diameter, and the device 33 operating in the same direction as the control device, can be constructed in an uncomplicated manner using series elements which are simple to manufacture. In the device 33, the pre-tensioned spring 1 5 which can be adjusted by the adjusting screw 32, and the displaceably-mounted valve housing 7 can easily be arranged to co-operate directly with the piston 14 of the pressure limiting valve and be adapted subsequently to suit the circumstances of use.

Claims

1. A pressure limiting valve assembly having an outlet which can be connected to an inlet by way of a valve; a piston operable to control the valve in dependence on the loading of the piston, against the action of the pressure at the outlet; a vent connectable to the outlet by way of the valve control piston when the action of the pressure at the outlet predominates as compared with the loading on the piston; a control device having a plurality of control inlets and actuable by the pressures at those inlets to load the piston under the action of the highest of those pressures, and an adjustable device operable to load the piston to predetermined constant extent in the same direction as the control device.

2. A valve assembly according to claim 1, in which the control device includes two control pistons, a first one of which is exposed to the pressure at a first control inlet to be moved thereby, together with second control piston, to load the valve control piston; the first and second control pistons both being exposed to the pressure at a second control inlet to be moved thereby in opposite directions, whereby the second control piston only loads the valve control piston.

3. A valve assembly as claimed in claim 2, in which the first control inlet is located on one side of the first control piston and the second control piston on the other, and in which the second control inlet is located between the first and second and control pistons.

4. A valve assembly as claimed in claim 2 or claim 3, in which the control pistons are slidably arranged in a blind bore in a control device housing, the first control piston being movable, by pressure at the second control inlet, to rest against the end of the blind bore.

5. A valve assembly according to any one of the preceding claims, in which the adjustable device includes resilient means located on one side of the valve control piston to load the piston in the same direction as the control device, the pre-tension of which resilient means is adjustable by means located on the other side of the valve control piston.

6. A valve assembly according to claim 5, in which the adjusting means is arranged to cooperate with a displaceable cylindrical member which houses the said valve and includes a stop arranged to limit the movement of the valve control piston.

7. A valve assembly according to claim 5 or claim 6, in which the adjusting means comprises an adjusting screw and a nut with which a preselected adjusting position of the screw can be secured.

8. A pressure limiting valve assembly substantially as described herein with reference to, and as shown in the accompanying drawing.