GB1592937A

GB1592937A - Brake pressure control valve arrangement

Info

Publication number: GB1592937A
Application number: GB13528/78A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-04-14
Filing date: 1978-04-06
Publication date: 1981-07-15
Also published as: JPS53129328A; DE2716495C2; ATA114378A; FR2387472A1; AT379992B; FR2387472B1; SE7803512L; IT7867834A0; SE421600B; DE2716495B1; IT1203176B

Description

(54) BRAKE PRESSURE CONTROL VALVE ARRANGEMENT (71) We, WABCO FAHRZEUGBREMSEN GMBH (formerly WABCO WESTINGHOUSE GM3H), a company organised according to the laws of the Federal Republic of Germany, of Am Lindener Hafen 21 3000 Hannover 91, 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 brake pressure control valve arrangement, in particular for a brake system in a motor vehicle and especially for such a system employing compressed air.

As a result of the ever increasing need for compressed air in brake systems and for so-called secondary consumers, the pressure level of the compressed air supply must be raised since the alternative solution, namely the use of large reservoirs, is becoming increasingly more difficult owing to lack of space. However, the working pressure in the brake system must be limited compared with the high pressure in the brake system in the compressed air generating unit, and pressure control valves have already been proposed with this in view.

One brake pressure control valve arrangement is described in the Specification of British Patent Application No. 38522/75 (Serial No. 1516736).

In this valve arrangement the pressure control is provided by connecting a resilient arrangement between the foot (brake) pedal of the vehicle and a piston that graduates the brake force, with the aid of which arrangement any desired adjustment can be made within a pressure range. For reasons of safety, this resilient arrangement consists of three steel springs of equal strength so that in the event of one of the three springs breaking, 2/3 of the pressure control is still maintained. However, it has been found that the maintained level of 2/3 of the pressure control may not be sufficient under extreme conditions of use or braking con ditions -- above all when braking with a trailer - so that insufficient braking of the trailer train can result in critical moments of danger.Also, as a result of this additional arrangement of three springs between the brake pedal and the graduating piston, the dimensions of the installation are not exactly ideal, particularly in respect of the length of the installation.

The present invention provides a brake pressure control valve arrangement having a pressure control valve operable by a pressure control piston which is pretensioned by a resilient arrangement comprising at least two springs connected in series, between which springs there is arranged a spring support member having a Irange of movement limited at each end by stops, the support member engaging one or other of the stops if one or other of the springs fails.

The invention will now be described in more detail with the aid of the attached drawings in which, by way of example, embodiments of the invention are shown. In the drawings: Figure 1 shows a dual-circuit motor ve hicle brake valve having a pressure control valve arrangement con structed according to the invention, and Figure 2 also shows a motor vehicle brake valve but having another pressure control valve arrangement construct ed according to the invention.

The brake valve shown in Figure 1 has a housing 1, 2 which, as seen in the drawing, consists of an upper portion 1 and a lower portion 2, each of which portions contains pressure control valve elements for controlling the passage therethrough of pressure medium to a respective brake circuit. Inlet connections 3 and 4 from a source of the pressure medium open into the housing.

Outlet connections 5 and 6 are connected to the brake cylinders, not shown, of the two brake circuits.

The upper portion 1 of the housing is subdivided into an inlet chamber 7 and a brake pressure chamber 8 which are separated from one another by a fixed valve seat 9 formed in the housing, which valve seat, when the brakes are not being operated, is closed by a combined inlet and outlet valve member 10. This valve member 10 is accommodated by an upper flange 11 of a valve sleeve 11' which is displaceably arranged in an annular seal 12. On the lip of this sealing ring 12 there is supported the lower end of a spring 13 the upper end of which is supported at the upper flange 11 of the valve sleeve 11', and which spring pretensions the valve member 10 in the direction of closurc.

The compressed air control valve may be operated by means of a foot pedal, for example. By operating the foot pedal (not shown) a force is exerted on a spring plate 14 at the upper end of the assembly, which force is transmitted by means of a resilient member 15 to an actuating piston 16.

The actuating piston 16 is displaceably arranged in the brake pressure chamber 8 and, when the brakes are not being operated is held in the upper position by a spring 17 which is located between, and supported at, the base of the chamber 8 and an intermediate shoulder on the piston 16.

A pressure control piston 18 is arranged coaxially in the actuating piston 16 so that it may be displaced, and is pretensioned with regard to downward movement by a resilient arrangement 20 which consists of two series-connected springs 22 and 24, arranged concentrically with respect to one another and supported at their adjacent ends by a spring support member 26. The spring support member 26 is in the shape of an annular hat section, the spring 24 being supported at one end by an inner annular flange 28 of the support member and at the other end by a stop disc 30 the position of which is adjustable, and the spring 22 being supported at one end by an annular outer flange 32 of the support member and at the other end by the upper side of the pressure control piston 18.The control piston 18 is provided with a lower annular portion 34 which is constructed as a valve seat and forms together with the valve member 10, the inlet valve mentioned at the beginning.

By means of this inlet valve, a connection may be made between the inlet chamber 7 and the brake pressure chamber 8 so that pressure medium can flow by way of the outlet connection 5 to the brake cylinders of the first brake circuit.

The spring support member 26 separating the two springs 22 and 24 is, so to speak, float-mounted by its annular inner flange 28 between two stops 36 and 38. The stop 36 is constructed on a central axially extending guide 40, whereas the stop 38 is provided on the upper side of the control piston 18.

The surface itself of the control piston 18 can, alternatively serve as a stop, of course.

In the lower portion 2 of the valve housing a relay chamber 42 is separated from a second brake pressure chamber 46 by a relay piston 44. When the brakes are not being operated the relay piston 44 is held in the upper position by a spring 48 and may be moved downwards when pressure medium is supplied from the chamber 8 through a bore 50 into the chamber 42. The lower end of the piston 44 is constructed as an outlet valve seat 52; an inlet valve seat 54 is provided at the lower housing portion.

A valve member 56 co-operates with the two valve seats, which valve member is formed at the upper end of a valve sleeve 58. When the relay piston 44 moves downwards, the inlet valve 56, 54 is opened in order to connect the inlet connection 4 to the outlet connection 6. As soon as a pressure has built up in the brake pressure chamber 46 it acts on the lower face of the piston 44 moving it upwards until both the outlet valve 56, 52 and the inlet valve 56, 54 are closed so that a closed position of the brakes of the second circuit is achieved.

The operation of the brake valve is as follows: By operating the brake pedal (not shown) the actuating piston 16 is moved downwards by means of the rubber spring member 15, the outlet valve 10, 34 is closed and the inlet valve 9, 10 is opened. As a result, pressure medium is supplied to the brake cylinders of the first circuit from connection 3 by way of connection 5, in dependence on the force used to operate the brakes.

When the inlet valve 9, 10 opens, pressure builds up in the chamber 8 under both the pistons 16 and 18, and, simultaneously, through the bore 50 in the chamber 42 above the relay piston 44. The piston 44 moves downwards against the force of the spring 48, closing the outlet valve 52, 56 and opening the inlet valve 54, 56. Pressure medium then flows from connection 4 by way of the connection 6 into the brake cylinders of the second circuit, the pressure medium being supplied to these cylinders in accordance with the controlling pressure in the chamber 42.

The pressure building up in the chamber 8 acts on the lower end of the control piston 18 and moves this piston upwards against the force of the resilient member 20 until the forces on either side of the piston are equalised. In this position, the inlet valve 9, 10 and the outlet valve 10, 34 are closed, i.e. the closed position of the brakes, of the first circuit is achieved.

In a corresponding manner, under the action of the increasing pressure in chamber 46, which together with the spring 48 acts from below on the piston 44, this piston 44 moves upwards until the inlet valve 56, 54 and the outlet valve 56, 52 are closed (closed position of the brakes of the second circuit).

Releasing the brakes, i.e. removing air from the two brake circuits, takes place similarly in the reverse order and can also be carried out in stages.

If the second circuit fails, the first circuit (upper circuit) continues to operate in the manner described. If the first circuit fails, activation of the relay piston 44 by com pressed air does not take place but the second circuit is then set in operation mechanically as follows. When the brakes are operated the pistons 16 and 18 are pres sed downwards until a mechanical connec tion is made by means of stops 60 and 62, and the relay piston 44 is moved downwards.

Further operation is as described above. The no-load stroke between the two stops 60 and 62 may be adjusted.

The level of the pressure control provided by the piston 18 is adjustable by means of the pretension of the resilient arrangement 20 and this pretension itself may be adjusted by varying the height of the stop disc 30.

The timing of the upward movement of the control piston 18 (i.e. whether it occurs at a lesser or greater introduced pressure) into the closed position of the brakes, in which both the inlet valve 9, 10 and the outlet valve 10, 34 are closed, depends on the pre tension of the resilient arrangement 20.

The resilient arrangement 20 is so con structed that even if one of the springs breaks, the level of the pressure control, once set, is practically unaltered. If, for example, the outer spring 22 fails, the spring plate 26 is brought downwards, in the drawing, by the inner spring 24 to rest against the upper end of the control piston 18 and the spring tension is maintained by the spring 24. The reduction in the level of pressure control caused by the small no-load stroke of the spring plate is practically negli gible. The resilient arrangement 20 be haves in an analogous manner when the inner spring 24 fails. In this case the outer spring 22 presses the spring plate by its inner annular flange against the stop 36 con structed on the guide portion 40 and the pretension is produced by the spring 22 with practically no loss.

Figure 2 shows a brake valve with an other form of resilient arrangement which, in this case, has two springs 70 and 72, arranged in tandem, between which springs a supporting annular plate 74 is float mounted. The upper spring 70 is supported at one end on the surface of this ring and at the other end by a stop disc 76, the posi tion of which disc may be adjusted in order to set the pre-tension of the resilient arrangement.

The lower spring 72 is supported at one end by the lower side of the plate 74 and at the other end on the upper end of a pressure control piston 78 which has an annular or cylindrical upper projection. An axial, fixed guide portion 82 has a stop 84. The support plate 74 is float-mounted between the end of the projection 80 and the stop 84 in such a manner that, if one of the springs fails, it comes to rest (after a very short travel of the spring remaining in operation) either against the stop 84 or on the projection 80, depending on which spring has broken. This ensures that the reduction in the level of the set pressure control when one spring fails is practically negligible. The embodiment according to Figure 2 has, however, the disadvantage as compared with the embodiment according to Figure 1 that it is larger as a result of the tandem arrangement of the two springs.

Although in each of the brake valves described above and shown in the drawings, the resilient arrangement 20 acting on the pressure control piston 18 or 78 comprises two springs only and a single spring support member, additional springs and support members could be provided.

The designs of the pressure control valve arrangements in the brake valve described above ensure that if, for example, one spring of the resilient arrangement 20 breaks, the spring support member 26 or 74 is stopped after a short distance and enable the no-load stroke of the spring support member (which conditions the decrease in the pressure control) to be made as small as desired, so that, in fact, the danger of insufficient braking can be avoided with certainty when, as described, at least two springs in series connection are provided because the remaining spring(s) maintain the pretension and hence the set level of pressure control practically unchanged.

Moreover, the resilient arrangements described make it possible to use springs with relatively flat characteristic curves.

WHAT WE CLAIM IS: 1. A brake pressure control valve arrangement having a pressure control valve operable by a pressure control piston which is pretensioned by a resilient arrangement comprising at least two springs connected in series, between which springs there is arranged a spring support member having a range of movement limited at each end by stops, the support member engaging one or other of the stops if one or other of the springs fails.

2. A brake pressure control valve according to claim 1, in which the resilient arrangement has two springs only.

3. A brake pressure control valve according to claim 2, in which the two springs are arranged concentrically with respect to one another.

4. A brake pressure control valve according to claim 2 or claim 3, in which the

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Claims

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circuit).

Releasing the brakes, i.e. removing air from the two brake circuits, takes place similarly in the reverse order and can also be carried out in stages.

If the second circuit fails, the first circuit (upper circuit) continues to operate in the manner described. If the first circuit fails, activation of the relay piston 44 by com pressed air does not take place but the second circuit is then set in operation mechanically as follows. When the brakes are operated the pistons 16 and 18 are pres sed downwards until a mechanical connec tion is made by means of stops 60 and 62, and the relay piston 44 is moved downwards.

Further operation is as described above. The no-load stroke between the two stops 60 and 62 may be adjusted.

The level of the pressure control provided by the piston 18 is adjustable by means of the pretension of the resilient arrangement

20 and this pretension itself may be adjusted by varying the height of the stop disc 30.

The timing of the upward movement of the control piston 18 (i.e. whether it occurs at a lesser or greater introduced pressure) into the closed position of the brakes, in which both the inlet valve 9, 10 and the outlet valve 10, 34 are closed, depends on the pre tension of the resilient arrangement 20.

The resilient arrangement 20 is so con structed that even if one of the springs breaks, the level of the pressure control, once set, is practically unaltered. If, for example, the outer spring 22 fails, the spring plate 26 is brought downwards, in the drawing, by the inner spring 24 to rest against the upper end of the control piston

18 and the spring tension is maintained by the spring 24. The reduction in the level of pressure control caused by the small no-load stroke of the spring plate is practically negli gible. The resilient arrangement 20 be haves in an analogous manner when the inner spring 24 fails. In this case the outer spring 22 presses the spring plate by its inner annular flange against the stop 36 con structed on the guide portion 40 and the pretension is produced by the spring 22 with practically no loss.

Figure 2 shows a brake valve with an other form of resilient arrangement which, in this case, has two springs 70 and 72, arranged in tandem, between which springs a supporting annular plate 74 is float mounted. The upper spring 70 is supported at one end on the surface of this ring and at the other end by a stop disc 76, the posi tion of which disc may be adjusted in order to set the pre-tension of the resilient arrangement.

The lower spring 72 is supported at one end by the lower side of the plate 74 and at the other end on the upper end of a pressure control piston 78 which has an annular or cylindrical upper projection. An axial, fixed guide portion 82 has a stop 84. The support plate 74 is float-mounted between the end of the projection 80 and the stop 84 in such a manner that, if one of the springs fails, it comes to rest (after a very short travel of the spring remaining in operation) either against the stop 84 or on the projection 80, depending on which spring has broken. This ensures that the reduction in the level of the set pressure control when one spring fails is practically negligible. The embodiment according to Figure 2 has, however, the disadvantage as compared with the embodiment according to Figure 1 that it is larger as a result of the tandem arrangement of the two springs.

Although in each of the brake valves described above and shown in the drawings, the resilient arrangement 20 acting on the pressure control piston 18 or 78 comprises two springs only and a single spring support member, additional springs and support members could be provided.

The designs of the pressure control valve arrangements in the brake valve described above ensure that if, for example, one spring of the resilient arrangement 20 breaks, the spring support member 26 or 74 is stopped after a short distance and enable the no-load stroke of the spring support member (which conditions the decrease in the pressure control) to be made as small as desired, so that, in fact, the danger of insufficient braking can be avoided with certainty when, as described, at least two springs in series connection are provided because the remaining spring(s) maintain the pretension and hence the set level of pressure control practically unchanged.

Moreover, the resilient arrangements described make it possible to use springs with relatively flat characteristic curves.

WHAT WE CLAIM IS: 1. A brake pressure control valve arrangement having a pressure control valve operable by a pressure control piston which is pretensioned by a resilient arrangement comprising at least two springs connected in series, between which springs there is arranged a spring support member having a range of movement limited at each end by stops, the support member engaging one or other of the stops if one or other of the springs fails.
2. A brake pressure control valve according to claim 1, in which the resilient arrangement has two springs only.
3. A brake pressure control valve according to claim 2, in which the two springs are arranged concentrically with respect to one another.
4. A brake pressure control valve according to claim 2 or claim 3, in which the

spring support member is a hat-shaped spring plate, a first one of the springs being supported at one end in the spring plate and the second spring being supported at one end on an annular outer flange of the spring plate.
5. A brake pressure control valve according to claim 4, in which the spring plate is an annular hat-shaped section having an annular inner flange on which the first spring is supported.
6. A brake pressure control valve according to claim 4 or claim 5, in which the first spring is supported at its other end on a rigid, adjustable stop.
7. A brake pressure control valve according to any one of claims 4 to 6, in which the second spring is supported at its other end on the pressure control piston.
8. A brake pressure control valve according to claim 2, in which the two springs are arranged in tandem.
9. A brake pressure control valve according to claim 2 or claim 8, in which the spring support member is an annular plate on the opposing annular faces of which there is supported in each case, one of the springs by one end, the springs being supported, at the other end, by a rigid, adjustable stop and on the pressure control piston, repectively.
10. A brake pressure control valve according to any one of the preceding claims, in which the range of movement of the spring support member is limited, at one end, by a stop on a central guide that extends in the axial direction of the valve arrangement and, at the other end, by a stop on the pressure control piston.
11. A pressure control valve according to any one of the preceding claims, in which the spring support member and the pressure control piston are annular and are arranged concentrically inside an annular actuating piston to which the control piston is coupled by the resilient arrangement.
12. A pressure control valve substantially as described herein with reference to, and as illustrated by, Fig. 1 or Fig. 2 of the accompanying drawings.