GB2057611A

GB2057611A - Vehicle brake system

Info

Publication number: GB2057611A
Application number: GB8024692A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-08-03
Filing date: 1980-07-29
Publication date: 1981-04-01
Also published as: GB2057611B; JPS5625042A; DE2931491C2; FR2463031B1; DE2931491C3; JPS6366704B2; DE2931491A1; FR2463031A1

Abstract

A brake system for a motor vehicle comprises service brakes, a retarder and an anti-skid system, the control device of the anti-skid system which monitors the rotational behaviour of the wheels to cause regulation of the service brakes also regulating the operation of the retarder independently of actuation of the service brakes.

Description

SPECIFICATION Vehicle brake system The invention relates to a vehicle brake system incorporating a permanent brake or retarder which can be switched on so as to remain applied independently of other actions of the driver.

A retarder is described in German Patent specification (Auslegeschrift) No. 23 22 446. In this known retarder, there is arranged downstream of a service brake valve a pressure switch by means of which an anti-skid control can be switched on. The anti-skid control is in turn connected to the retarder. However, the retarder is thereby only monitored with respect to the antiskid function when the service brake is operative.

Consequently, the rotational behaviour of the wheel is dependent upon the sum of the brake forces of the service brake and the retarder and, with many states of the roadway, this total brake force can lie far in excess of the available static friction at the road surface.

In practice, it has been found that vehicle wheels also enter the critical range of static friction, or a wheel can even fully lock when only the retarder is actuated. Such sole actuation of the retarder is actuated. Such sole actuation of the retarder is quite usual in many vehicles, namely by means of a so-called "brake force controller" of a special on-off switch for the retarder. In some cases, the operating instructions call the driver's attention to the fact that he must not on any account actuate the retarder on slippery roads.

However, it is very difficult for the driver to assess the prevailing road conditions on the one hand, and, on the other hand, to take measures (countersteering or the like) effectively to counter a skid initiated by the sole action of the retarder. In this connection, it may be mentioned that a retarder generally has a relatively long release time, so that the danger can scarcely be reduced even by rapid return of the brake force controller to its starting position.

The present invention resides in a brake system for a motor vehicle, comprising a service brake having a brake valve and wheel brake cylinders, a retarder and an anti-skid system, a control device which monitors the rotational behaviour of the wheels to regulate the service brake and also regulates the operation of the retarder independently of the actuation of the service brake.

This has the advantage that the risk of wheelrock occurring whilst the retarder is effective is detected at a very early instant by the rotational behaviour of the wheels and is reduced, namely independently of the actuation of the service brake.

In this manner, anti-skid control is provided even during sole action of the retarder.

The invention is further described, by way of example, with reference to the drawings, in which: Figure 1 is a block diagram of a first embodiment of brake system incorporating a retarder, Figure 2 is a detail to show a modification of the embodiment of Figure 1, and Figure 3 is a detail to show a further modification.

A brake system for a commercial vehicle incorporates a retarder 1, 2, 4, 5 which is in the form of an eddy-current brake and has a brake force controller 1 connected to a housing 4 by way of a control device 2. The housing 4 of the eddy-current brake is connected by way of a shaft 5 to a differential 7 located in the rear axle 6 of a vehicle. Two rear wheels are designated 8 and 9.

A sensor 10 acting as a rotational speed sensor is arranged on the differential 7. Alternatively, it is also possible to provide each wheel 8, 9 with a respective sensor. The sensor 10 is connected by way of a lead to an electronic control device 11 which is in turn connected to an anti-skid control valve 14 by way of two electrical leads 12 and 13 (one for holding pressure and the other for reducing pressure). The parts 10, 11, 12, 13 and 14 form an anti-skid system 10 to 14. The retarder control device 2 is connected to the antiskid system 10 to 14 by way of the branch leads 19, 20 or, alternatively, only by way of a separate lead 26 (shown by a broken line).A service brake 15, 16, 17 and 18 has a brake valve 15 which is actuated during braking and allows compressed air to flow from a reservoir 16 by way of the control valve 14 to a brake cylinder 1 7 or 1 8 associated with the wheels 8 and 9 respectively.

The service brake 15 to 18 and the anti-skid system 10 to 14 operate in a conventional manner which needs no further explanation.

When the retarder is switched on by way of the brake force controller, and when the roadway is slippery and does not offer sufficient adhesion for the wheels, the anti-skid system 10 to 14 responds, since the rotational behaviour of the wheels 8 and 9 is monitored by the anti-skid system. However, the control valve 14, which thereby receives control signals from the control device 11, cannot avert the risk of wheel lock, since this valve can only control the risk of wheel lock initiated by the action of the service brake.

It is only possible to monitor and regulate the retarder by combining the anti-skid control signals, fed by way of the leads 12, 13, with the control device 2. It is thereby conceivable to convert these control signals in the control device 2 by way of a transistorized or relay circuit such that the brake-pressure-reducing signal is reduced by the action of the retarder, and the brakepressure-holding signal also prevents the action of the retarder from increasing.

Alternatively, however, it is also possible to allow a regulating memory (not illustrated) of the anti-skid control device 11 to become effective by way of the lead 26, instead of the anti-skid control signals. The function of the regulating memory in the control device 11 is to allow specific logic criteria to become effective. It is set only upon the first arrival of control signals and then switches the retarder control device 2 by way of the lead 26.

Figure 2 shows a simple circuit arrangement for converting the anti-skid control signals fed by way of the leads 12 and 13 or, alternatively, the regulating memory signal fed by way of the lead 26 for the purpose of regulating the action of the retarder. The lead 3 connecting the brake force controller 1 to the control device 2 incorporates a relay 21 which completes the connection via the lead 3 in the absence of anti-skid control signals or a regulating memory signal.

The anti-skid control signals from the control device 11 are tapped from the leads 12 and 13 by way of the branch leads 19 and 20 and are fed to an AND gate 23 by way of an OR gate 22. When the control signal (tapped from the lead 3) from the brake force controller 1 is simultaneously present at the AND gate 23, the anti-skid control signals from the control device 11 pull in the relay 21, so that the lead 3 is interrupted.

By virtue of the fact that the relay 21 in the illustrated arrangement is wired so as to be selfholding, the lead 3 remains interrupted, and thus the action of the retarder remains inoperative, until the driver returns the brake force controller 1 to its starting position and braking is again effected by the retarder by renewed actuation of the brake force controller 1.

The advantage of this self-holding circuit of the relay 21 resides in the fact that there is no need to adapt the anti-skid control signals or the regulating memory signal to the time characteristic of the retarder, since the action of the retarder is cancelled immediately upon the first response of one of these signals. Furthermore, the necessity for renewed actuation of the brake force controller 1 informs the driver that the retarder is over-braked and that he must switch his brake force controller to a lower stage.

Automatic adaptation of the action of the retarder by the control device 11 is possible by omitting the self-holding circuit, in the same manner as illustrated in Figure 2. However, the response and release times of the various retarders, some of which vary to a considerable extent, have to be taken into account. In a retarder in the form of a control brake, control has to be effected by way of an additional solenoid valve owing to the hydraulics which are used.

Alternatively, a switching transistor can be used instead of the relay 21.

Figure 3 shows an arrangement by which the anti-skid control signals, some of which are present only for a short time, are adapted by timing circuits 24 and 25 in the branch leads 1 9 and 20 to response and release times which byre of long duration, particularly when the retarder is in the form of a hydrodynamic retarder.

Claims

1. A brake system for a motor vehicle, comprising a service brake having a brake valve and wheel brake cylinders, a retarder and an antiskid system, a control device which monitors the rotational behaviour of the wheels to regulate the service brake and also regulates the operation of the retarder independently of the actuation of the service brake.

2. A brake system as claimed in claim 1, in which the control signals of the control device of the anti-skid system are adapted to the time characteristic of the retarder.

3. A brake system as claimed in claim 1 or 2, in which the retarder has a brake force controller by means of which the retarder can be switched on and in which the anti-skid system is arranged to switch off the retarder after the first appearance of anti-skid control signals, renewed actuation of the brake force controller being needed to switch the retarder on again.

4. A brake system as claimed in claim 3, in which the connection between the brake-force controller regulating the operation of the retarder and the retarder includes a relay and/or switching transistors or a solenoid valve, operated by the anti-skid system.

5. A brake system as claimed in claim 1 ar 2, in which the anti-skid control signals of the anti-skid system are applied to the retarder.

6. A brake system as claimed in any of claims 1 to 5, in which a regulating memory signal of the anti-skid system is jointly used for monitoring the permanent brake.

7. A brake system for a motor vehicle, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.