GB2038966A

GB2038966A - Load-dependent control of brake force regulators

Info

Publication number: GB2038966A
Application number: GB7937937A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1978-11-17
Filing date: 1979-11-01
Publication date: 1980-07-30
Also published as: JPH0156011B2; FR2441522A1; DE2849879A1; IT1119385B; IT7968979A0; FR2441522B1; JPS5568448A; DE2849879C2; GB2038966B

Abstract

A load-dependent brake force regulating device for a vehicle has an adjusting element 1 supported on a cam member which is carried by a resiliently-biased piston 6 controlled by the hydraulic axle compensation system of the vehicle or by the load- dependent brake pressure of the spring bellows of the pneumatic suspension system of the vehicle, as the case may be. The cam member has a control cam surface 5 on which the adjusting element is supported during normal operation and an emergency braking cam surface 18 which, under the resilient bias on the piston, is moved into co-operation with the adjusting element in the event of a failure of the control pressure acting on the piston to give braking equivalent to that of a half laden vehicle. To enable an adequate emergency braking action to be achieved, the resilient-basing of the piston is provided by a control spring 13 in series with an auxiliary spring 16 with a substantially lower spring constant. <IMAGE>

Description

SPECIFICATION Load-dependent control of brake force regulators The invention relates to a load-dependent brake force regulating device for a pressure-medium actuated brake system of a vehicle, and in particular for a vehicle equipped with a pneumatic suspension system or with an hydraulic axle compensation system.

Brake force regulating devices of this kind are already known and are used to adapt the brake pressure in the brake cylinders of a vehicle ta the particular loaded state of the vehicle. This matching process occurs automatically and involves the use of a control pressure which is dependent on the load on the axle to adjust, via the brake force regulating device, the level of the brake pressure admitted by the brake valve.

It is a requirement of these brake force regulating devices that, in the event of the service brake pressure failing, it must be possible to bring a vehicle,to a halt under thetcondi.tions which are admissible for the prescribed auxiliary brake action. A corresponding requirement is also laid down by the legislative authorities in the Federal Republic of Germany.

In one known form of regulating device however, if the control pressure should fail, the brake force-regulating device is influenced such that the braking action (even with a fully laden vehicle) corresponds only to the level of an unladen vehicle, that is to say, the prescribed braking action cannot be achieved.

In another known form of regulating device, the adjustment of the device in dependence on vehicle loading is effected via a tapered piece (or cam member) by a control piston loaded from the pneumatic spring bellows of the vehicle suspension system. This device is designed such that, when the pneumatic spring bellows control pressure fails, a control spring moves the control piston, and with it the tapered piece, in such a direction as to initiate the introduction of brake pressure at a level that is required for a fully laden vehicle with a fully intact braking system.The braking system is, in general, designed in accordance with the intended use of the vehicle and, depending on this intended use and especially in a commercial capacity, it may be that the control spring, which has been designed for normal operation, is not able to switch the control piston to the position of the tapered piece which ensures a safe deceleration of a fully laden vehicle.

The present invention provides a loaddependent brake force-regulating device for a pressure-medium actuated brake system for a vehicle equipped with a pneumatic suspension system or with an hydraulic axle compensation system, the device including an adjusting element supported on a cam member, which is movable by the load-dependent brake pressure of the pneumatic system, against the resilient bias of an arrangement comprising a control spring and an auxiliary spring in series therewith, the cam member comprising a control cam surface and, as an extension thereof, on emergency braking cam surface. Advantageously, the auxiliary spring is arranged inside the control spring.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing.

The drawing shows a longitudinal section through a brake force-regulating device, the loaddependent controlling action of which is effected via the pressure in the pneumatic spring bellows or in the hydraulic axle compensation system of the vehicle in question.

In the arrangement shown in the drawing, a thrust rod 1 produces, in the brake force regulator, a load-controlling connection between a control part (indicated generally at 2) and an air brake part (indicated generally at 3). The thrust rod 1 slides with its lower end 4 on a control cam 5 mounted on a hollow control piston 6 in the control part 2 of the regulator, one end 7 of the piston being mounted in a tightly sealed manner in a cylinder 8.

The cylinder 8 is loaded via control connections 9 and 10 with the pressure from two control circuits (not shown) of the pneumatic suspension system or the hydraulic axle compensation system (as the case may be) of the vehicle, and this pressure acts via pressure chambers 11 and 12 on the control piston 6 in one direction.

A control spring 13 is arranged in the hollow space 14 of the control piston 6 in such a manner that is acts on the piston in the opposite direction to the control pressure in chambers 11 and 12.

The pre-stress of this spring 1 3 is adjustable by means of a screw 15. A change in pressure in the chambers 11 and 12 causes a movement of the piston 6 and through the cam 5 and thrust rod 1 effects in the portion 3 of the regulator and loaddependent control in brake pressure passing to the brake cylinders.

An additional second spring 1 6 is arranged inside the spring 13 and is connected in series with the spring 13 via a cup-shaped intermediate piece 1 7. At the same time, the control cam 5 which is generally cone-shaped in form is designed with an extension which, as described below, constitutes a cone-shaped emergency braking cam 1 8.

A description of the components of the brake pressure part 3 of the regulator is not required for an understanding of the present invention and, accordingly, the following description of the operation of the regulator deals with the operation in the brake pressure portion 3 only in so far as is necessary for understanding the operation of the control part 2.

The brake force regulator is secured to the vehicle framework and the cylinder 8 of the control part is in communication via connections 9 and 10 with the pneumatic spring bellows mounted on the vehicle axles or with the hydraulic compensation system of the vehicle. When the vehicle is empty (unladen), the pressure in the pneumatic spring bellows or in the hydraulic axle compensation system is at its lowest value, and the control piston 6 is in the position corresponding to the iowermost position of the thrust rod lfon the.control cam 5.

If the vehicle is loaded, then the pressure in the pneumatic spring bellows or in the hydraulic axle compensation system rises, and the compressed air flowing into the chambers 11 and 12 through the connections 9 and 10 of the cylinder 8 transfers this increase in pressure to the piston 6 so that this moves towards the fully laden position (that is, to the left as shown in the drawing). The lower end 4 of the thrust rod t rides up on the cam 5 and the resultant changing position of the thrust rod 1 effects a load-dependent control of the brake pressure entering the regulator via a connection 20 and continuing via a connection 21 into the brake cylinder.

When the brake pressure is released, the air in the brake cylinders escapes via a bore 22 in the thrust rod 1 into the atmosphere.

Throughout normal operation of the regulator, a return movement of the piston 6 (that is, to the right as shown in the drawing) in response to a pressure reduction in the pneumatic spring bellows or hydraulic axle compensation system is effected by the control spring 13. During such normal operation, the auxiliary spring 16 advantageously remains in the rest position.

If the control pressure in the cylinder 8 fails owing to leaks, then the control spring 13 is again effective to move the piston 6 to such an extent that the lower end 4 of the thrust rod 1 rides up on the emergency braking cam 18, and it has proved to be advantageous that the end 4 should ride up on the cam 18 to a height corresponding to the vehicle being half-laden because the braking action for a fully-laden vehicle could, in the case of an unladen vehicle, lead to overbraking (locking. If it is possible, in any particular case, for the control spring 13 alone to move the piston 6 into the desired emergency braking position then the auxiliary spring 16 will again remain in the rest position. In general, however, it is found that operating conditions are not favourable to this and thatforthe reasons mentioned in the introduction, the high spring constant of the control spring 13 is unable to move the control piston 6 safely into the emergency-braking position. In this case, the additional spring 16, which has a relatively low spring constant and is connected in series with the control spring 13 via the intermediate piece 17, becomes operative to move the control piston 6 into the required position on the emergency braking cam 18.

The arrangement of the auxiliary spring 16 within the control spring 13, as shown in the drawing, is a space-saving and, therefore, advantageous arrangement.

Claims

1. A load-dependent brake force-regulating device for a pressure-medium actuated brake system for a vehicle equipped with a pneumatic suspension system or with a hydraulic axle compensation system, the device including an adjusting element supported on a cam member which is movable by the load-dependent brake pressure of the pneumatic spring bellows, or by the hydraulic axle compensation system, against the resilient bias of an arrangement comprising a control spring and an auxiliary spring in series therewith, the cam member comprising a control cam surface and, as an extension thereof, an emergency braking cam surface.

2. A device according to claim 1, in which the spring constant of the auxiliary spring is less than the spring constant of the control spring.

3. A device according to claim 1 or claim 2, in which the cam member is movable by a piston controllable by the load-dependent brake pressure of the pneumatic spring bellows or by the hydraulic axle compensation system.

4. A device according to claim 3, in which the control spring is arranged in a hollow space within lile control piston.

5. A device according to any one of the preceding claims in which the auxiliary spring is arranged inside the control spring.

6. A device according to any one of the preceding claims, in which the connection of the control spring to the auxiliary spring is formed by a cup-shaped intermediate piece which simultaneously serves to accommodate the auxiliary spring.

7. A device according to any one of the preceding claims, in which the pre-stress of the control spring is adjustable by means of a screw.

8. A device according to any one of the preceding claims, in which each cam surface is an oblique surface and the cam surfaces together form a depression.

9. A load-dependent brake force regulating device substantially as described herein with reference to, and as shown in, the accompanying drawing.