GB2051272A

GB2051272A - Vehicle brake valve

Info

Publication number: GB2051272A
Application number: GB8011333A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1979-04-06
Filing date: 1980-04-03
Publication date: 1981-01-14
Also published as: FR2453059A1; SE8001482L; DE2913847A1; AT385957B; IT1128401B; ATA89780A; DE2913847C2; GB2051272B; IT8067543A0; FR2453059B1; SE445725B

Abstract

A vehicle brake valve is described for a brake system having a service brake and a retarder both operated by the same pressure medium. A foot plate 2, which operates the brake valve, is coupled to a main plunger 3 which, in turn, is connected directly. when a clearance 7 is taken up, to a service brake valve mechanism 5 and, via an actuating plate 8, to a plunger 10 in a retarder brake valve mechanism 9. As the foot plate 2 is depressed, the actuating plate 8 first tilts to actuate the retarder brake valve mechanism and increasingly operate the retarder in a continuous manner up to a predetermined level when the plate 8 engages a stop 11, whereupon the tilting movement of the plate ceases and the main plunger 3 thereafter actuates the service brake valve mechanism 5 to operate the service brake. <IMAGE>

Description

SPECIFICATION Vehicle brake valve The invention relates to a vehicle brake valve for pressure medium-actuated brake systems. In particular, the invention relates to a brake valve which provides control of both a main and an auxiliary brake.

A brake-actuating combination in which both a service brake and an auxiliary brake are actuated by depressing the brake pedal has been proposed, in which the auxiliary brake switches itself in automatically in fixed stages by closing electrical contacts. In order to allow the driver to feel when a switching stage of the auxiliary brake comes into operation, mechanical pressure points are provided in this arrangement, being located either in the brake pedal or on a pedal-operated plunger.

In the case of another device of a similar type, it is proposed that the pressure points should be produced by rneans of springs, and the driver should be able to feel when the tension of the springs is overcome as he depresses the pedal.

The above-mentioned methods for switching in an auxiliary brake suffer from the disadvantage that the braking action only occurs in the fixed stages and that an electrical control system is required for the auxiliary brake in addition to the pressure medium braking system.

The problem with which the present invention is concerned is that of providing vehicle brake valve which enables an auxiliary brake to be controlled in a continuous manner (i.e. without stages) using the same actuating means pneumatic or hydraulic -- as those of the service brake system.

The present invention provides a vehicle brake valve including first and second brake valve mechanisms, and a brake valve operating member comprising a first plunger coupled to the first valve mechanism for actuating the latter, the second valve mechanism being actuable by a second plunger coupled to the first plunger by an actuating plate which transmits actuating movement of the first plunger to the second plunger.

The invention will now be described in greater detail with reference to an illustrative embodiment which is shown in the accompanying drawings, in which: Figure 1 shows a pneumatic motor vehicle brake valve constructed in accordance with the invention, and Figure 2 is a diagram showing pressure curves for the service and auxiliary brakes controlled by the brake valve of Fig. 1, and illustrating the action of the brake valve.

Portions of the vehicle brake valve 1 shown in Figure 1 are of known construction so that a detailed description of Figure 1 will be given only insofar as this is necessary in order to understand the invention.

The brake valve shown in Figure 1 has an actuating device consisting of a foot-operated plate 2 and a plunger 3, with the lower end 4 of the plunger 3 coupled to a control piston 5 of the brake valve 1. A screw 6 serves as a stop for the plate 2 and, by adjusting the screw 6, the idle travel 7 of the plunger 3, before it engages with the piston 5, can be adjusted.

An actuating plate 8, firmly connected to the plunger 3 which passes through it, produces a mechanical connection with a pressure control valve 9 which is flanged onto the main body of the motor vehicle brake valve 1. The actuating plate 8 is so constructed and arranged that the downward movement of the plunger 3 when the footoperated plate 2 is actuated is transmitted to a plunger 10 of the pressure control valve 9 by a tilting movement of the actuating plate 8. An eccentric screw 11 is engageable with one side of the actuating plate 8 to limit the tilting movement in one direction and, by adjusting this screw, it is possible to set the beginning of pressure modulation by control valve 9 so that it coincides with the start of actuation of the foot-operated plate 2.A second eccentric screw 12 adjacent the control valve 9 provides a stop 14 engageable with the other side of the actuating plate 8 to limit the tilting movement in the other direction and so serves to limit the travel 13 of the plunger 10 of the pressure control valve 9. By adjusting the screw 12, the travel 13 of the plunger 10 is also adjusted.

The tilting movement 1 3 of the actuating plate 8, limited by the eccentric screws 11 and 12, is made possible by the free play of an appropriatelyshaped bushing 1 5 arranged between the plunger 3 and the hole in the actuating plate 8. The actuating plate 8 rests on a disc 1 6 which follows the tilting movement of the plate, this being made possible by a rolier 17 arranged in the plunger 3 below the disc 16. The bushing 1 5 is pressed against the actuating plate 8 and the two parts 1 5 and 8 are pressed against the disc 1 6 by a pretensioned spring 1 8 in the direction of movement of the foot-operated plate 2.

Further details of the brake valve are explained in the following description of the method of operation.

When the driver of the vehicle actuates the foot-operated plate 2, the plunger 3 of the brake valve 1 at first moves without causing the control piston 5 to move downwards. Tilting movement of the actuating plate 8 attached to the plunger 3, on the other hand, is initiated simultaneously (by appropriate adjustment of the eccentric screw 11 as described above) and moves the plunger 10 of the pressure control valve 9 downwards. This movement of the plunger 10 closes an outlet valve 19 of the control valve 9 and opens an inlet valve 20 to allow pressure medium to flow through to a retarder (auxiliary brake) by way of an inlet connection 21 and an outlet connection 22.

Throughout the travel 1 3 of the actuating plate 8 (set by means of the eccentric screw 12) stageless (i.e. continuous) sensitive braking of the vehicle by the retarder occurs until the actuating plate 8 meets the stop 14.

When the stop 14 is reached, the idle travel 7 of the plunger 3 is simultaneously at an end: in other words, the adjusting screw 6 is set so that the idle travel 7 of the plunger 3 corresponds to the travel 13 of the actuating plate 8. The control piston 5 is now carried along by the plunger 3, and closes an outlet valve 5, 23 while opening an inlet valve 5, 24 in the main body of the brake valve.

Compressed air now flows by way of an inlet connection 25 and by way of an outlet connection 26 to the wheel brake cylinders. In the case of a two-circuit motor vehicle brake valve 1 (such as that shown here), compressed air also flows simultaneously (with the closing of a second outlet valve 27 and opening of a second valve 29) by way of a second inlet connection 28 and a second outlet connection 30 into the wheel brake cylinders of the second brake circuit.

The overcoming of the force of the pretensioned spring 18 arranged round the plunger 3 causes the vehicle driver to feel the point of pressure on the foot-operated plate 2 at which the plunger 3 engages the piston 5 and the actuation of the service brake circuits begins. From this point onwards, the pressure level in the auxiliary brake, i.e. the braking action of the retarder, remains constant.

The action of the brake valve is illustrated in Figure 2 which shows, as a dotted line, the force on the foot plate 2, at a distance of 160 mm from the fuicrum, as a function of the travel of the foot plate. The Figure also shows, in solid lines, the pressure curves (as a function of travel of the foot plate 2) for the auxiliary brake and first circuit of the service brake and, in the broken line, for the second circuit of the service brake.

Figure 2 illustrates that, as the foot plate 2 is depressed, operation of the control valve 9 commences immediately to pressurize the auxiliary brake increasingly in a continuous manner until the point is reached at which the actuating plate 8 moves into engagement with the stop 14, and the plunger 3 overcomes the spring 1 8 and moves into engagement with the piston 5.

At this point as shown by the dotted-line curve, there is a change in the force on the foot plate 2 which is felt by the driver and serves as an indication that this point has been reached. As the foot pedal is depressed further, the pressure level in the auxiliary brake remains constant while the first and second circuits of the service brake are brought into operation.

The constructional features of the brake valve shown in Figure 1 may also be used in vehicle brakes in which the plate 2 is not directly connected to the plunger 3 but, rather, actuation of the pedal is transmitted to the brake valve by way of a connecting mechanism.

Due to the fact that, in Figure 1 the pressure control valve 9 used for the control of the retarder has a mechanical connection with the plunger 3 of the brake valve, sensitive and stageless braking of the vehicle by the retarder is possible, with the pressure being exerted by means of the same pressure media as that of the service brake system.

Claims

1. A vehicle brake valve including first and second brake valve mechanisms, and a brake valve operating member comprising a first plunger coupled to the first valve mechanism for actuating the latter, the second valve mechanism being actuable by a second plunger coupled to the first plunger by an actuating plate which transmits actuating movement of the first plunger to the second plunger.

2. A vehicle brake valve according to Claim 1, in which actuating movement of the first plunger is transmitted to the second plunger by tilting movement of the plate.

3. A vehicle brake valve according to Claim 1 or Claim 2, in which there is a fixed connection between the actuating plate and the first plunger which is guided through a hole in the actuating plate.

4. A vehicle brake valve according to Claim 3, in which the fixed connection between the first plunger and the actuating plate consists of: a disc fitted round the first plunger and forming a support for the actuating plate; a roller which supports the disc and is mounted in the first plunger; a bushing arranged between the hole in the actuating plate and the first plunger, and resilient means which tensions the bushing against the actuating plate, and the bushing and the actuating plate together against the disc.

5. A vehicle brake valve according to Claim 4, in which the bushing is convex on the surface which rests against the first plunger, to allow a tilting movement of the actuating plate.

6. A vehicle brake valve according to Claim 2, in which the actuating plate rests with one end against the second plunger.

7. A vehicle brake valve according to Claim 6, in which an eccentric screw engageable with the actuating plate is provided to determine the point of contact between the actuating plate and the second plunger.

8. A vehicle brake valve according to Claim 6, in which a second eccentric screw engageable with the actuating plate is provided as an adjustable stop to determine the stroke of the second plunger.

9. A vehicle brake valve as claimed in any one of the preceding Claims, in which the second valve mechanism is progressively actuable in a continuous manner by the second plunger over a predetermined range.

10. A vehicle brake valve as claimed in Claim 9, in which the first plunger is arranged to commence actuation of the first valve mechanism at the end of the said predetermined range.

11. A pressure medium-operated brake system including pressure medium-operated main and auxiliary brakes, and a brake valve as claimed in any one of the preceding claims, in which the first and second valve mechanisms are connected to the control pressure medium for operating the main and auxiliary brakes respectively.

12. A vehicle brake valve substantially as described herein with reference to, and as illustrated by the accompanying drawings.