GB2159222A

GB2159222A - Anti wheel-locking brake control system

Info

Publication number: GB2159222A
Application number: GB08510658A
Authority: GB
Inventors: Heinz Leiber
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1984-05-26
Filing date: 1985-04-26
Publication date: 1985-11-27
Also published as: GB2159222B; FR2564794B1; GB8510658D0; FR2564794A1; DE3419717C2; DE3419717A1

Abstract

The anti wheel-locking brake control system described controls the braking pressure separately on all the wheels (only two are shown) and cuts out the skid control in the event of failure of the controller 4. On failure, the control-valve 3 for one of the rear wheels 1 moves into a switching position 1 in which no brake pressure can be supplied to the wheel brake of this rear wheel in the interests of vehicle stability, the control-valve 4 remaining in its switching position 1 to allow braking of the other rear wheel 2 from the twin-circuit master cylinder 5. <IMAGE>

Description

SPECIFICATION Anti-locking control system The invention relates to an anti-locking control system having the features of the precharacterising clause of Claim 1.

Such an anti-locking control system is known, for example from German Offenlegungsschrift 3,126,102.

Anti-locking control systems known at the present time cut out the ALS function in the event of a fault. The normal brake is then pre-effective. Because of the driving stability which is necessary in the event of a fault, as mentioned above, many vehicles, especially vehicles with a front-wheel drive, use a brake-pressure reducer for the rear axle. Since the front axle becomes unstable before the rear axle when the ALS is cut out, the driver usually does not increase the brake pressure any further when the front axle locks, so that the rear axle which is free of locking then ensures driving stability. An appropriate design of the brakes is prescribed by law in many countries.

The use according to the invention of a non-brake rear wheel, for example by means of an ALS valve shut off without current in a rear-axle circuit, preferably with a diagonal brake-circuit distribution, prevents the rear wheel from receiving brake pressure in the event of a fault of the anti-locking controller. It is consequently impossible for the wheel to lock. In a diagonal brakecircuit distribution which is suitable in a particularly advantageous way for putting into practice the idea of the invention, a rear wheel is therefore not braked in the event of a fault, thus resulting in a slight reduction in the braking effect for the benefit of driving stability. This restriction is permissible because of the high reliability of ALS systems.

There are also vehicles which have been in production for a fairly long time and which have a brake-circuit distribution where a brake circuit acts on two front wheels and one rear wheel and the same braking result is obtained in the event of a fault.

According to the proposed solution of the invention, the solenoid-valve arrangement is switched-in via the evaluation circuit, that is to say is energised during the entire journey or even only during the braking operation and thus gives the vehicle the full braking effect. This valve switching makes it possible to dispense with the pressure reducer for the rear axle; especially on vehicles with a diagonal brake-circuit distribution and two pressure reducers, these represent-a considerable outlay.

The invention is explained in more detail with reference to an exemplary embodiment in the drawing in which: Figure 1 shows an embodiment, Figure 2 shows a modified valve arrangement.

Fig. 1 shows two wheels of a rear axle, to the brake of which two brake circuits I and II are connected. Valve arrangements 3 and 4 designed as three-way valves are switched-in the brake lines to the wheels 1 and 2.

A conventional valve arrangement which transmits in a currentless state is switched-in the brake circuit II. In contrast to this, the valve arrangement 3 in the brake circuit I is closed in the currentless state. The wheel-brake cylinder connection is connected to a pressureless return R.

The second switching position of the valve device 3 serves to maintain a constant pressure in the wheel brake. In the third switching position, a free passage from the main brake cylinder 5 to the wheel-brake cylinder is provided, with the return closed. This valve arrangement 3 is cut in by an evaluation circuit 4 and is energised during normal driving. To save current consumption, the valve can also be switched into the third switching position, without an ALS function, via the brake-light switch BS. During ALS operation, the switching positions 1 to 3 change for the purpose of pressure reduction, pressure build-up and stabilisation. When the ALS function is cut out, the valve arrangements 3 and 4 move into the switching position 1, in which the wheel 2, but not the wheel 1, can be braked.

Fig. 2 shows, instead of the three-way valve 3, a valve configuration consisting of two twoway valves 6 and 7 which likewise correspond to the state of the art. In this valve configuration, the valve 7 is cut in by the evaluation circuit 4 under normal circumstances (position 2). In the event of a fault, the connection between the main brake cylinder 5 and the wheel-brake cylinder of the wheel 1 is shut off (position 1). The wheel cylinder is then connected to the return R. The ALS function is achieved by means of a combined control of the two valves 6 and 7: Valve number Valve position Pressure build-up 6 1 7 2 Stabilisation 6 2 7 2 Pressure reduction 1 1 or 2 7 1 The front wheels unnecessary for explaining the invention, their sensors and the brakepressure control devices are not shown in the drawing for the sake of simplicity.

Claims

1. Anti-locking control system for a motor vehicle, contaning sensors for detecting the wheel-movement behaviour, or evaluation circuit for evaluating the sensor signals and for generating brake-pressure control signals, valve arrangements which are assigned to the individual wheels and to which these brake-pressure control signals are fed to vary the brake pressure, and a monitoring device which cuts out the anti-locking control system in the event of a fault, characterised in that the valve arrangement assigned to one of the rear wheels and/or the evaluation circuit are designed in such a way that, when the anti-locking control system is cut out, this rear wheel cannot be subjected to brake pressure.

2. Anti-locking control system according to Claim 1, characterised in that in the currentless state the valve arrangement shuts off the connection between the brake-pressure generator and the brake of the one rear wheel.

3. Anti-locking control system according to Claim 2, characterised in that in the currentless state the valve arrangement connects the brake to a pressureless return.

4. Anti-locking control system according to Claim 2 or 3, characterised in that under normal circumstances the evaluation circuit controls the valve arrangement into a position in which the brake-pressure source is connected to the wheel brake.

5. Anti-locking control system according to one of Claims 1 to 4, characterised in that the valve arrangement can be controlled in three positions (pressure build-up, holding, pressure reduction).

6. Anti-locking control system according to one of Claims 1 to 5, characterised by its use in a diagonal brake-circuit distribution.