GB2113786A

GB2113786A - Combined braking and steering brake system for vehicles

Info

Publication number: GB2113786A
Application number: GB08301722A
Authority: GB
Inventors: Lucas Heinz Haar
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1982-01-27
Filing date: 1983-01-21
Publication date: 1983-08-10
Also published as: FR2520318B1; IT8319291A0; GB8301722D0; DE3202572A1; FR2520318A1; IT1178454B; DE3202572C2; GB2113786B

Abstract

In this brake system, there are provided for the purpose of braking a driven vehicle wheel for each of two oppositely lying vehicle sides a brake pedal (3, 4), a tandem master cylinder (1, 2) actuated by the latter, as well as a first brake (19, 20) connected to the push-rod circuit of the tandem master cylinder. The push-rod circuits of both tandem master cylinders (1, 2) are interconnected via a connecting line (21). Branching off from the connecting line (21) is a line which leads to second brakes (23, 24) meant for braking a non-driven vehicle axle. This arrangement enables without any additional valves to independently actuate a first brake (for steering) by depression of the assigned brake pedal and to simultaneously actuate the first and second brakes with full pressure compensation by the simultaneous depression of both brake pedals. The brake system can be used for braking and assisting steering of an agricultural tractor or combine harvester. <IMAGE>

Description

SPECIFICATION Combined braking and steering brake system for vehicles The present invention relates to a combined braking and steering brake system for vehicles, wherein there is provided for each one of two opposite vehicle sides a first brake, and actuating device for the actuation of this brake and a master cylinder for the actuation of a second brake, said master cylinder being adapted to be acted upon by the actuating force of the actuating device or its opposing force.

Combined braking and steering brake systems are mainly used in tractors, combined harvesters and other agricultural vehicles. In these vehicles, they serve to carry out normal braking actions during which the brakes are applied simultaneously at several vehicle axles and to carry out steering brake actions during which only the curve-inward driving wheel is braked to boost the steering action.

To fulfil these requirement, a known brake system of the type initially referred to (German Patent Specification 1 6 55 258) is provided with a change-over valve which is actuable by the pressure in the two master cylinders, which valve, in the event of pressure prevailing in both master cylinders, opens a pressure-medium connection between the respective master cylinder and the second vehicle brake that is connected to the master cylinder and has no part in the steering brake action, and closes said connection in the event of pressure prevailing in one master cylinder only. This change-over valve is comparatively complicated in its design, since it compares the pressures in both master cylinders without admitting a hydraulic connection between the pressure chambers of the two master cylinders.

Furthermore, it is a disadvantage of the changeover valve that it has to interrupt the connection between the second brake which does not participate in the steering brake action and the master cylinder upon actuation of the steering brake. When the steering brake is actuated quickly, this can have as a result that the second brake is applied by pressure prior to the closing of the change-over valve and the steering brake action is impaired thereby. It is another disadvantage in the known brake system that, in the event of simultaneous actuation of both actuating devices, different application travels of the brakes on the one and the other vehicle side can only be balanced by a displacement of the pistons of the change-over valve. Therefore, the change-over valve necessitates large valve chambers.

It is an object of the present invention to arrange for a combined brake and steering brake system of the type initially referred to which is of a particularly straightforward design and which does not require pressure-controlled valves to disconnect the second brake from the master brake cylinders in the case of a steering brake action.

According to the present invention there is provided combined braking and steering brake system for vehicles, wherein there is provided for each one of two opposite vehicle sides a first brake, an actuating device for the actuation of a second brake, said master cylinder being adapted to be acted upon by the actuating force of the actuating device or its opposing force, wherein pressure chambers of both master cylinders are in permanent communication with one another, the actuating travel that is available at each actuating device is greater by the actuating travel necessary to actuate the first brake than the actuating travel of a first piston of the respective master cylinder, which latter travel is limited by a stop.

It will be attained thereby that pressure is allowed to develop in the pressure chambers of both master cylinders only if both master cylinders are actuated simultaneously, since solely in this case will the valves connecting the pressure chambers with the feed reservoir be closed in both master cylinders and pressure be able to develop in the pressure chambers. When during a steering brake action, only one actuating device is started, the master-cylinder piston connected with this actuating device will be moved up to its stop, while the pressure fluid displaced by the piston flows via the open equalizing valve of the nonactuated master cylinder into the feed reservoir.

The development of pressure for the actuation of the second brake is therefore not possible. When the master-cylinder piston, abuts on the stop, the latter stop will either transmit the actuating force onto the device for the actuating of the first brake, or it forms a countersupport for the actuating device which countersupport is now able to support the opposing force resulting from the actuating force.

According to another aspect of the invention there is provided a master cylinder for a combined braking and steering brake system for vehicles wherein there is provided for each one of two opposite vehicle sides a first brake, an actuating device for the actuation of this brake and the master cylinder for the actuation of a second brake, said master cylinder being adapted to be acted upon by the actuating force of the actuating device or its opposing force, and having a pressure chamber and a connection port for enabling the pressure chambers of both master cylinders to be in permanent communication with one another, the master cylinder having a push-rod piston and an actuating travel available at the actuating device that is greater than the actuating travel of the push-rod piston by the actuating travel necessary to actuate the first brake, the actuating travel of the push-rod piston being limited by a stop.

The present invention enables thus to merely apply one brake on one vehicle side by actuation of the actuating device assigned to this brake with a view to obtaining a steering brake action, and to jointly apply all brakes by actuation of both actuating devices with a view to obtaining a normal braking action, without there being the need for pressure-controlled valves to this end. In this arrangement, the actuating travel in a steering brake action is larger than in a normal braking action, since the respective master-cylinder piston has to be shifted to its stop first in a steering brake action before the actuating force can be built up.

This is, however, no disadvantage. On the contrary, the type of braking action taking place becomes obvious to the one operating the brake system so that he makes an early detection of an error actuation by the indication of the actuating travel and is enabled to cancel it.

It is another advantage that brake circuits independent of one another are provided for the first brakes and the second brake, thereby increasing the reliability of the brake system against failure. As the second brake is connected to both master cylinders, it can be compensated by the master cylinders if the first brakes have different distances to travel for application. To this effect, the compensating travels of the mastercylinder pistons may be comparatively small.

A preferred embodiment of this invention which is characterized by great simplicity consists in that the first brakes are actuable hydraulically and in that each actuating device comprises a tandem master cylinder whose one brake circuit is connected to the first brake and whose other brake circuit communicates with the second brake and with the corresponding brake circuit of the tandem master cylinder of the respective other actuating device. In this arrangement, the floatingpiston circuits of both tandem master cylinders are favourably connected to the first brakes, since as a result thereof the lost travel remains small upon failure of a brake circuit.

To retain the ratio between actuating force exerted and the pressure generated in the respective brake circuits at an approximately constant amount during a steering brake action and a normal braking action, according to another proposal of the present invention, the hydraulic effective surfaces of the floating pistions of both tandem master cylinders are both by the same amount larger than, preferably twice as large as, the hydraulic effective surfaces of the push-rod pistons. No matter, whether he actuates both tandem master cylinders or only one thereof, the operator will thus actuate in each case approximately the same effective surface and therefore needs not modify the dosing rate of the braking force when changing from a steering brake action to a normal braking action and vice versa.In particular when a steering brake action is carried out, the danger of overbraking will be avoided thereby.

If the increase of the actuating travel is desired to be maintained at a lowest possible amount during a steering brake action, and if in a steering brake action an actuating force/pressure ratio can be put up with that is different from that in a normal braking action, this aim can be advantageously achieved in that the hydraulic effective surfaces of the floating pistons of both tandem master cylinders are by the same amount both smaller than the hydraulic effective surfaces of the push-rod pistons, with the push-rod circuits of both tandem master cylinders communicating with the first brakes and the floating piston circuits communicating with one another and with the second brake.Owing to this arrangement, the approximation of floating piston and push-rod piston during actuating of both tandem master cylinders can be reduced so that the distance between the push-rod pistons and their stop on the floating pistons can be dimensioned small in the brake-release position of the pistons.

In another advantageous embodiment of the present invention the pressure chambers of the two tandem master cylinders connected to the first brakes communicate with one another through a channel which latter is closed by a pressure-controlled spring-loaded valve which will be opened in opposition to the spring force by pressure prevailing in the pressure chambers that are connected to the second brake. Due to this actuation of both tandem master cylinders will arrange in a very simple fashion for direct interconnection of the pressure chambers of the tandem master cylinders, said pressure chambers communicating with the first brakes, so that different application travels of the first brakes do not have to be compensated for by different travels of the floating pistons.The distance between the floating pistons and the push-rod pistons may therefore be dimensioned correspondingly smaller what leads to a reduction of the actuating travel in a steering brake action.

Furthermore, this embodiment offers the advantage that, in the event of failure of a pushrod circuit or a first brake, respectiveiy, actuation of the otherfirst brake and thus braking on only one side is prevented. Braking will then be carried out exclusively by means of the second brake which has brakes symmetrically arranged on both vehicle sides.

Preferably, both tandem master cylinders have one joint feed reservoir with a first reservoir chamber to which the floating-piston circuits are connected, and with a second reservoir chamber to which the push-rod circuits are connected. It will be ensured thereby that the pressure chambers of a tandem master cylinder may not be exhausted in the case of frequent steering brake actuation on one vehicle side.

This invention permits a great number of embodiments. Thus, the application of the first brakes can be effected mechanically through a rope, a linkage or through levers. To provide for a mechanical coupling to the first brake, either tension-type cylinders can be employed which transmit the actuating force onto a linkage, or pressure master cylinders can be used whose pistons form countersupports for brake pedals or levers. Upon hydraulic actuation of the first brake, all conventional and proved types of construction of tandem master cylinders can be employed. It is likewise possible to boost the actuating force of each actuating device by a brake booster of orthodox design.

The present invention will be explained in more detail in the following by way of one embodiment illustrated in the accompanying drawing.

The one and only Figure of the drawing shows a combined braking and steering brake system for a vehicle. The braking system comprises two tandem master cylinders 1, 2 which are actuated by one respective brake pedal 3, 4. The tandem master cylinder 1 disposes of a push-rod piston 5 connected to the brake pedal 3 as weil as a floating piston 6 which are both urged by return springs 7, 8 against a stop defining the brake's release position. Interposed between the push-rod piston 5 and the floating piston 6 is a pressure chamber 9, while a pressure chamber 10 is located between the floating piston 6 and the bottom of the tandem master cylinder 1. Both pressure chambers 9, 10 communicates via equalizing valves 11, 1 2 with connecting bores 13, 14 leading to a supply reservoir.The end surfaces of the push-rod piston 5 and of the floating piston 6, said surfaces being close to the pressure chamber, are isolated by ring sleeves from feed chambers 15, 16 which latter are through bores likewise in communication with the connecting bores 13, 14.

The tandem master cylinder 2 is designed alike the tandem master cylinder 1. It is located in the drawing mirror-symmetrically to said. Each tandem master cylinder is assigned to one side of the vehicle, e.g. the tandem master cylinder 1 to the left vehicle side and the tandem master cylinder 2 to the right one.

Connecting sockets 17, 1 8 containing a pressure-retaining valve serve to connect the pressure chamber 10 of the tandem master cylinder 1 to a brake 1 9 on the left vehicle side and the corresponding pressure chamber of the master cylinder 2 to a brake 20 on the right vehicle side. The brakes 1 9, 20 are meant to brake the driven wheels of the vehicle. The pressure chamber 9 of the tandem master cylinder 1 is via a lisee 21 in communication with the corresponding pressure chamber of the tandem master cylinder 2. Said line 21 contains a fitting 22 providing connection between the line 21 and the brakes 23, 24 of the non-driven vehicle axle via a pressure-retained valve.

The mode of effect of the braking system is as follows: During a normal braking action, for instance, when driving on the road, both brake pedals 3, 4 will be actuated at the same time. For this, the brake pedals can be interconnected mechanically by a latch. As both tandem master cylinders are actuated evenly, pressure develops in the pressure chambers 9, 10 and in the corresponding pressure chambers of the tandem master cylinder 2 so that all brakes 19, 20, 23 and 24 will be applied.

Different application travels of the brakes 19 and 20 are compensated by different travels of the floating pistons. The even distribution of pressure will, however, not be affected hereby, since a constant pressure equalization takes place via the line 21.

If, for instance, when driving off-road, the vehicle is desired to be steered to the left and this steering action is to be boosted by application of the brake, solely the brake pedal 3 will be depressed. To this effect, the push-rod piston 5 will be pressed into the pressure chamber 9 until it abuts on the floating piston 6. The pressure fluid displaced by this out of the pressure chamber 9 flows via the line 21 into the corresponding pressure chamber of the tandem master cylinder 2 and from there through the open equalizing valve that corresponds to the equalizing valve 11 into the feed reservoir. Therefore, no pressure build-up is allowed to take place in the pressure chamber 9 so that the brakes 23, 24 of the non-driven vehicle axle remain unactuated.As soon as the push-rod piston 5 abuts on the floating piston 6, the floating piston 6 can be mechanically displaced by the brake pedal 3, and pressure to actuate the brake 19 can be built up in the pressure chamber 10.

When merely the brake pedal 4 is depressed, exclusively the brake 20 will be actuated in a corresponding fashion.

To avoid that upon depression of only one brake pedal a predetermined actuating force generates a considerably higher pressure than in the case of depression of both brake pedals, the hydraulic effective surfaces F2 of the floating pistons of both tandem master cylinders 1, 2 are dimensioned about twice as large as the hydraulic effective surfaces F1 of the push-rod pistons. The effective surface actuated will then be approximately equal in both cases. In the event of depression of both brake pedals 3, 4, both pushrod pistons with their total effective surface F, + F1 will be decisive for the pressure generation. In this case, the floating pistons will merely form displaceable partition walls between the two pressure chambers of each tandem master cylinder.When only one brake pedal is depressed, the brake pedal acts directly on the floating piston with the effective surface F2 = F1 + F1. The actuated surface is thus equal in both cases so that in both cases the same amount of pressure can be obtained by the aid of a predetermined actuating force. The actuation of the brake system requires therefore no change in the usual dosing of force when switching from a normal braking action to a steering brake action and vice-versa.

If the brake circuit connected to the brakes 23, 24 fails due to a defect, the brakes 19, 20 remain actuable, while both tandem master cylinders 1, 2 will act like a steering action even when actuated simultaneously, i.e. the push-rod pistons abut directly on the floating piston. However, there is no hydraulic equalization of the actuating pressures of both tandem master cylinders in this case.

If, for example, the brake circuit connected to the brake 19 fails due to a defect, the brakes 20, 23, 24 can be actuated furthermore. When both brake pedals 3, 4 are depressed simultaneously, first the push-rod pistons of both tandem master cylinders 1, 2 serve to displace the fluid necessary to shift the floating piston 6 until it abuts on the bottom of the tandem master cylinder 1.

Subsequently, the pressure required to actuate the brakes 20, 23 24 can be built up in the pressure chamber 9 and the two pressure chambers of the tandem master cylinder 2. As both tandem master cylinders 1, 2 remain in communication with one another via the line 21, the actuating pressures will equalize in this working order.

Claims

1. Combined braking and steering braking system for vehicles, wherein there is provided for each one of two opposite vehicle sides a first brake, an actuating device for the actuation of a second brake, said master cylinder being adapted to be acted upon by the actuating force of the actuating device or its opposing force, wherein pressure chambers of both master cylinders are in permanent communication with one another, the actuating travel that is available at each actuating device is greater by the actuating travel necessary to actuate the first brake than the actuating travel of a first pistion of the respective master cylinder, which latter travel is limited by a stop.

2. Brake system as claimed in claim 1 , wherein the first brakes are hydraulically actuable, and each actuating device comprises a tandem master cylinder having its one brake circuit connected with the first brake and its other brake circuit connected with the second brake and with the corresponding brake circuit of the tandem master cylinder of the respective other actuating device.

3. Brake system as claimed in claim 2, wherein the floating-piston circuits of both tandem master cylinders are connected to the first brakes.

4. Brake system as claimed in claim 3, wherein the hydraulic effective surfaces of the floating pistons of both tandem master cylinders are by the same amount both larger than, preferably twice as large as, the hydraulic effective surfaces of the first pistons.

5. Brake system as claimed in claim 2, wherein the hydraulic effective surfaces of the floating pistons of both tandem master cylinders are set by the same amount both smaller than the hydraulic effective surfaces of the first pistons, with the push-rod circuits of both tandem master cylinders being connected with the first brakes, while the floating-piston circuits communicate with one another and with the second brakes.

6. Brake system as claimed in any one of the claims 2 through 5, wherein the pressure chambers of the two tandem master cylinders communicating with the first brakes are interconnected by a channel with latter is closed by a pressure-controlled valve that is springloaded in the closing direction and that will be opened in opposition to the spring force only by a pressure prevailing in the pressure chambers which are connected to the second brake.

7. Brake system as claimed in any one of the preceding claims, wherein both tandem master cylinders have one joint feed reservoir with a first reservoir chamber to which the floating-piston circuits are connected and with a second reservoir chamber to which the first piston circuits are connected.

8. Brake system substantially as hereinbefore described with reference to the accompanying drawing.

9. A master cylinder for a combined braking and steering brake system for vehicles, where there is provided for each one of two opposite vehicle sides a first brake, an actuating device for the actuation of this brake and the master cylinder for the actuation of a second brake, said master cylinder being adapted to be acted upon by the actuating force of the actuating device or its opposing force, and having a pressure chamber and a connection port for enabling the pressure chambers of both master cylinders to be in permanent communication with one another, the master cylinder having a push-rod piston and an actuating travel available at the actuating device that is greater than the actuating travel of the push-rod piston by the actuating travel necessary to actuate the first brake, the actuating travel of the push-rod piston being limited by a stop.

10. A master cylinder substantially as hereinbefore described with reference to numeral 1 of the accompanying drawing.