GB2061434A

GB2061434A - Improvements in and Relating to Anti-lock Brake Systems

Info

Publication number: GB2061434A
Application number: GB8024329A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1979-07-25
Filing date: 1980-07-24
Publication date: 1981-05-13
Also published as: GB2061434B; DE2930054A1; FR2462316A1; FR2462316B1

Abstract

In an anti-lock braking system for avoiding vehicle wheel-lock and in which the vehicle wheels are controlled in pairs lying along respective diagonals of the vehicle, control being effected by means of an electrical control system which is arranged to receive reference signals, derived from the wheels, for use in the control operation, a safety circuit is included in the braking system for monitoring control signals from the electrical control system, and the safety circuit is arranged to switch off control of each pair of wheels independently of any other pair when a defect is detected in the control system. <IMAGE>

Description

SPECIFICATION Improvements in and Relating to Anti-lock Brake Systems The invention relates to an anti-lock system for wheel-lock on a vehicle during braking.

In the field of anti-lock systems the most effective but also the most expensive system is the so-called individual control system. In an individual control system the anti-lock system is so constructed that each wheel of the vehicle has its own velocity sensor for scanning the rotational behaviour of the wheel, its own solenoid valve for actuating the brake cylinder and its own control channel. In a lock-prevented braking action, where each wheel is controlled, the object is to produce an optimum slip condition leading to the vehicle having a minimum braking distance while its steering capability is maintained.

It is now customary to provide anti-lock systems with a safety circuit. The safety circuit detects the signals that, for example, are supplied from the sensors or are used for actuating the solenoid valves, and monitors them for inadmissible gradients. An inadmissible gradient can mean, for example, that a signal has lasted for too long. When an inadmissible signal gradient is detected, the safety circuit switches off the control system and as a result ensures normal braking action without control.

If, during a braking action in which the anti-lock system is operating, this anti-lock system is suddenly switched off by the safety circuit because a defect has been detected, then the solenoid valves of the anti-lock system remain in the open position. Consequently all the braking pressure admitted by the driver is passed to the brake cylinders. This generally means that all the wheels of the vehicle suddenly lock, and as a result, the wheels lose their side stability. It is no longer possible to steer the vehicle and the vehicle has a tendency to skid.

With known anti-lock systems it is also conceivable that during operation a defect will occur in the safety circuit. In this event a defect occurring simultaneously in the control circuit will not be noticed or indicated.

It is also known to form a vehicle reference velocity from the velocities of at least two wheels, the actual wheel velocity being compared with this reference velocity (DE-OS 25 24 427). Here, a non-driven (front) wheel is used to form a minimum reference velocity, as in this way it is possible to control stably the rear wheels, which are very sluggish because of their connection to the gears and motor, in conditions of very low road friction.

However, where a common vehicle reference velocity is used for controlling all the wheels and a defect occurs, there is the problem that if the reference velocity is too high, that is to say, incorrect, the braking action is lost simultaneously at several wheels.

An object of the present invention is to provide an anti-lock system that has stable control behaviour even in very low friction conditions and which nevertheless ensures high braking reliability and driving safety when a defect occurs.

That is to say, when any kind of defect in the safety circuit, the highest possible braking action, or at least the braking action corresponding to brake pedal pressure at that time, and adequate driving stability, are retained.

According to the present invention, an antilock braking system for avoiding vehicle wheel lock during braking and arranged to control all the wheels of the vehicle, includes an electrical control system, circuit components arranged to form vehicle reference velocities, and a safey circuit arranged to render the electrical control system ineffective on the occurrence of inadmissible output signals from the electrical control system, wherein (i) the electrical control system is arranged to control the vehicle wheels in pairs lying along respective diagonals of the vehicle, (ii) the vehicle reference velocity for any pair of wheels lying on a diagonal of the vehicle is derived from one or both of that pair of wheels, and (iii) control of each pair of wheels can be switched off separately by a safety circuit.

Advantageously, the anti-lock brake system is so arranged that the electrical control system is divided into two blocks and each block contains a control circuit for one pair of wheels and a safety circuit for the other block.

Alternatively, the anti-lock brake system is so arranged that the electrical control system is divided into two blocks and each block contains two control circuits for one pair of wheels, each control circuit including a safety circuit belonging to the other control circuit of that block.

The anti-lock system operates in such a manner that a vehicle reference velocity is formed for the wheels on each diagonal of the vehicle and is used for controlling the wheels of that same diagonal.

If, in the anti-lock system, the associated safety circuit switches off the electrical system of one diagonal of the vehicle, this leads only to the locking of the wheels of this diagonal of the vehicle, while the wheels of the other diagonal continue to be controlled. As a result, it is still largely possible to steer the vehicle and the vehicle is stable to drive.

Further, when any type of defect occurs in the control system, the deceleration values required by a two circuit brake system are fully achieved.

The invention will now be described in more detail with reference to the drawings which show diagrammatically the construction of anti-lock systems according to the invention in which: Figure 1 shows a system having mutual monitoring of the two electronics blocks, Figure 2 shows a system having completely separate electronics blocks.

Fig. 1 shows a vehicle having the four wheels 3 to 6. The wheels are provided with sensors 13 to 16 and with solenoid valves 17 to 20. The output signals of the sensors 13 and 1 5 of one diagonal of the vehicle are supplied to a first electrical block 1. This electrical block in its turn actuates the solenoid valves 17 and 19 of the same diagonal. The braking pressure portion of the brake system and the brake cylinders, which are actuated by the solenoid valves, are not shown for the sake of simplicity.

The second electrical block 2 actuates the two wheels 4, 6 of the other diagonal of the vehicle in analogous mannner.

In addition to the electrical systems E3, E5 and Ee,E4, respectively, the electrical blocks 1 and 2 also contain the safety circuits SIS,, SIS4 and SIS3, SITS, respectively. The safety circuits SIS,, SIS4 that are responsble for the electrical block 2 are housed wholly or partially in block 1 and correspondingly the safety circuits SITS3, SIS5, that are responsible for the block 1 are housed wholly or partially in block 2. For safety reasons, it is possible to arrange the electrical blocks on separate boards or chips.

The current supply for the two blocks 1 and 2 is provided by a vehicle battery 11 by way of two fuses 9, 10. The safety circuits SISe, SIS4 in block 1 receive, via lines 22, the signals to be monitored from the electrical systems E6, E4 of block 2 and in the event of a defect switch off the control of block 2 by a signal to the relays R6, R4. The safety circuits SIS3, SIS5 monitor the electrical systems E3,E6 in a corresponding manner. When a defect occurs a warning lamp (not shown) is actuated.

Instead of the relays R3to R6 it is also possible to use electronic switches that are known per se, such as, for example, transistors or thyristors.

The arrangement shown in Fig. 2 is identical in principle to that of Fig. 1, but differs in that here the control circuits of the two electrical blocks 1, 2 are completely independent of one another. For this reason there are no connection lines 22. The safety circuits SIS3 and SIS5 that are responsible for one block, (for example, block 1), are arranged in this same block. Here, the safety circuit SIS, is arranged on the integrated switching circuit 13 belonging to the electrical system E3 and correspondingly the safety circuit SIS3 is arranged on the integrated switching circuit 15 belonging to the electrical system E5.

With the arrangement shown in Fig. 2, the electrical blocks 1 and 2 are completely independent with respect to the electrical systems E3 to Es, the safety circuits SIS3 to SITS6, the fuse protection 9, 10 of the power supply, the electrical connections and with respect to the sensors and the control valves, for each of the diagonals of the vehicle, and therefore, the occurrence of a defect in the control system does not lead to unacceptable effect on the braking action even when the safety circuit itself becomes defective before a defect occurs in any electrical system. A defect at any point in the system can affect the braking action of only one diagonal.

Dividing the whole electronics system into two blocks, each of which is responsible for one diagonal of the vehicle, substantially increases the entire reliability of the system while entailing relatively little expense.

Claims

1. An anti-lock braking system for avoiding vehicle wheel-lock during braking and arrangement to control all the wheels of the vehicle, the anti-lock braking system including an electrical control system, circuit components arranged to form vehicle reference velocities, and a safety circuit arranged to render the electrical control system ineffective on the occurrence of inadmissible output signals from the electrical control system, wherein: (i) the electrical control system is arranged to control the vehicle wheels in pairs lying along respective diagonals of the vehicle, (ii) the vehicle reference velocity for any pair of wheels lying on a diagonal of the vehicle is derived from one or both of that pair of wheels, and (iii) control of each pair of wheels can be switched off separately by a safety circuit.

2. An anti-lock brake system as claimed in claim 1, wherein the electrical control system is divided into two blocks and each block contains a control circuit for one pair of wheels and a safety circuit for the other block.

3. An anti-lock brake system as claimed in claim 1, wherein the electrical control system is divided into two blocks and each block contains two control circuits for one pair of wheels, each control circuit including a safety circuit belonging to the other control circuit of that block.

4. An anti-lock brake system as claimed in claim 3, wherein control of each wheel can be switched off separately.

5. An anti-lock brake system as claimed in any one of claims 1 to 4, wherein the electrical control system is arranged to be disconnected from the remainder of the brake system when control is switched off by the safety circuit.

6. An anti-lock brake system as claimed in claim 5, wherein the electrical system connected to the remainder of the brake system by a plurality of switch means controllable by the safety circuit.

7. An anti-lock brake system as claimed in any one of claims 2 to 6, wherein the blocks are connected to separate power supply circuits.

8. An anti-lock brake system as claimed in claim 7, wherein the power supply circuits include fuses.

9. An anti-lock brake system as claimed in any one of claims 2 to 8, wherein the blocks are - formed by circuits on separate boards.

10. An anti-lock brake system substantially as herein described with reference to and as illustrated by Fig. 1 or Fig. 2 of the accompanying drawings.