GB2103319A - Hydraulic anti-skid brake systems - Google Patents

Abstract

A hydraulic anti-skid brake system is proposed for multi-circuit brakes, in which a multi-circuit brake booster (2) has a master cylinder (3, 4) for each brake circuit (I, II), a brake control valve (32) which controls communication between a pressure supply source (21/22) and a booster cylinder (5) connected to the primary side (8, 9) of each of the master cylinders and between the booster cylinder (5) and a relief point (23), and short- circuit lines (17, 18) connected between the booster cylinder (5) and the secondary side (15, 16) of each master cylinder (3, 4) and each incorporating a changeover valve arrangement (19/20) which normally isolates the short-circuit connection but establishes the connection during operation of the anti-skid system, the connection being established only when the anti-skid system introduces the first pressure drop in a wheel brake circuit and pressure can then be supplied directly to the secondary side (15, 16) of the master cylinder (3, 4) by the booster (2) during operation of the anti-skid system. <IMAGE>

Description

SPECIFICATION Improvements in or relating to hydraulic anti-skid brake systems The present invention relates to anti-skid brake systems.

In one known system (German Offenlegungsschrift 2,750,491) having a pressure supply device including a pump and an accumulator, a multi-circuit brake booster equipped with a master cylinder for each brake circuit and with a control valve which controls communication between the pressure supply device and a booster cylinder connected to the primary side of each of the master cylinders and communication between the booster cylinder and a relief point, antiskid control valves are provided in a closed brake circuit and also in a booster circuit.

However, there are also systems which have open brake circuits and anti-skid control valves disposed in these open circuits, as is described in, for example, German Offenlegungsschrift 29 33 536. The last-mentioned systems have the disadvantage that a defective brake circuit and also a pressure supply fails in the event of a leak. Such a disadvantage is avoided in the first-mentioned systems, since, in these systems, the piston of the master cylinder of the defective circuit moves to the end of its stroke, and the intact circuit is maintained, since the pressure supply does not fail.However, a system of this kind has the disadvantage that the cost of the valves for the anti-skid system is too high for many purposes; Furthermore, this system has the disadvantage that, owing to the fact that the anti-skid control valves are disposed in the closed brake circuit and in the booster circuit, pressure regulation in the closed brake circuit is only determined by cooperation of the two valves.

In this manner, only a coupled regulation is possible which limits the degree of freedom for the operation of the anti-skid system, that is to say, the independent reduction of pressure in one brake circuit with a simultaneous build-up of pressure in the second brake circuit, that is to say, in the booster circuit.

According to the present invention a hydraulic anti-skid brake system comprises a pressure supply device including a pump and an accumulator, a multi-circuit brake booster which is equipped with a master cylinder for each brake circuit and with a control valve which controls communication between the pressure supply device and a booster cylinder connected to the primary side of each of the master cylinders and communication between the booster cylinder and a relief point, shortcircuit lines connected between the booster cylinder and the secondary side of a respective master cylinder and each incorporating a change-over valve arrangement which normally isolates the short-circuit connection but by which the short-circuit connection can be established during operation of the anti-skid system.

An anti-skid brake system embodying the present invention can have the advantage that each regulating channel operates independently by way of its corresponding anti-skid control valves.

Although the pressure supply would fail in the event of a leak and a simultaneous buildup of pressure during anti-skid operation, the probability is very slight, since the period of the operation of the anti-skid system compared with the total operating time of the brakes is very short, since relatively small use is made of the anti-skid system.

Furthermore, it is advantageous that a return pump is not required, that the brake is virtually inexhaustible, and that a rapid pressure rise is possible for the pressure build-up phase at any given time. Finally, it is also advantageous that relatively inexpensive multiposition valves can be used.

The present invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic part sectional illustration of a first embodiment of the invention having a separate change-over valve arrangement, Figure 2 is a diagrammatic illustration of a second embodiment in which change-over valve arrangement is integrated in multi-position valves, and Figure 3 is a diagrammatic illustration of a further development of the embodiment of Fig. 2.

Referring first to the embodiment of Fig. 1 a hydraulic anti-skid system 1 has a dualcircuit brake booster 2 which is combined with two master cylinders 3 and 4. The booster 2 has a booster cylinder 5 to which two primary sides 8 and 9 of the master cylinders 3 and 4 are connected by way of conduits 6 and 7. The primary sides are in part defined by pistons 10 and 11 which, on the one hand, can be actuated by a brake pedal 14 by way of rods 1 2 and 1 3 and, on the other hand, respond to pressure introduced from the booster cylinder 5 through the conduits 6 and 7. The pistons 10 and 11 produce on their secondary sides 1 5 and 1 6 a brake pressure in brake circuits I and il.

Furthermore, the booster 2 has an associated control valve 32 which controls communication between the booster cylinder 5 and a pressure supply device 21/22 on the one hand, and between the booster cylinder 5 and a topping-up reservoir 23 on the other hand.

A spool 33 of the control valve 32 can be actuated by the pedal 14 by way of a reaction spring 34.

The primary side 8, 9 of each master cylinder 3, 4 respectively is connected to the secondary side 15, 1 6 respectively by way of a short-circuit lines 17, 1 8 respectively. Each of the short-circuit lines 17, 1 8 incorporates a two-port, two-position solenoid valve 19, 20 respectively, the solenoid valves 1 9 and 20 together forming a change-over valve arrange ment 19/20, that is to say, an individual solenoid valve 1 9 or 20 is located in each brake circuit I and II.

Communication between the primary and secondary sides is interrupted when the change-over valve arrangement 19/20 is in its illustrated normal position, although the short-circuit connection between the primary and secondary sides is established after the valve arrangement has been changed over.

The pressure supply device 21/22, com prising a pump 21 and an accumulator 22, and a topping-up reservoir 23 are associated with the brake booster 2. Furthermore, a shutoff piston 24 and a piston 25 responsive to accumulator pressure and actuating switch 26 are fitted in the brake booster 2 and the pistons 24 and 25 respond to a pressure drop in the accumulator.

Furthermore, four anti-skid control valves 27, 28, 29 and 30 are provided, one for each wheel of a four-wheel vehicle. The control valves 27, 28, 29 and 30 are multi-position valves. They are solenoid-operated and are connected to an electronic control device 31 by way of electrical leads (not shown). The control device 31 is also connected to the two two-port, two-position solenoid valves 1 9 and 20 of the change-over valve arrangement 19/20.

The system illustrated in Fig. 1 operates as follows: Upon actuation of the pedal 14, with a small amount of pedal travel the control valve 32 is first changed over, and the primary sides 8, 9 of the two master cylinders 3, 4 are connected to the pressure supply device 21/22. The two pistons 10, 11 move to the left and on their secondary sides 15, 1 6 produce the brake pressure for the brake circuits I and II. In the event of a lack of accumulator pressure, the shut-off piston 24 blocks a larger movement of the control valve 32 and the piston 25 responsive to accumulator pressure 25 is released, so that as the pedal 14 continues to be moved at least a non-boosted brake pressure can be produced in the master cylinders 3, 4 by the force exerted on the pedal. The fault is indicated by way of the switch 26.If the wheels are braked to so great an extent that the anti-skid system comes into operation, the control valves 27, 28, 29, 30 are selectively actuated. They thus enable individual brake pressure to be reduced or held constant or builtup.

At the same time, that is to say, with the first reduction in brake pressure, the solenoid valves 1 9 and 20 of the change-over valve arrangement 19/20 are also energized, so that they assume their other positions. The primary sides 8, 9 are then short-circuited to the secondary sides 15, 1 6 by way of the short-circuit lines 17, 1 8 respectively. The change-over valve arrangement 19/20 remains in its changed-over position for the entire period of time during which the antiskid system is in operation. As a result of this switching state, pressure medium from the pressure supply device 21/22 is supplied directly to the secondary sides 15, 1 6 of the master cylinders 3, 4 by the booster cylinder 5.This has the advantage that a rapid pressure rise is possible in each pressure build-up phase. Furthermore, it is advantageous that a separate return pump is not required, since when the pedal is released, the pressure medium flowing back from the brake cylinder is immediately fed to the secondary sides 15, 1 6 of the brake booster 2 again. Thus, the brake system is inexhaustible under these conditions.

When the switch 26 is actuation response to lack of accumulator pressure, the power supply for the change-over valve arrangement 19/20 is switched off, so that, under these circumstances the change-over operation which has been described does not take place.

Fig. 2 shows substantially the same antiskid system as is illustrated in Fig. 1. For this reason, corresponding parts are provided with the same reference numerals. In this anti-skid system 41, in contrast to the embodiment illustrated in Fig. 1, the two valves 42 and 43 of a change-over valve arrangement 42/43 are integrated in two of four anti-skid control valves 44, 45, 46 and 47 in the form of fourposition valves.

Free communication between the master cylinders and the wheel brake cylinders is established when the control valves 44, 45, 46 and 47 are each in a first position. When the control valves are each in a second position, the valves 42 and 43 of the change-over valve arrangement 42/43 are changed over, such that pressure medium from the pressure supply device flows from the secondary sides 15, 1 6 to the wheel brake cylinders by way of the control valve 32. A third position of a control valve is "pressure-holding" position, and, when a control valve is in a fourth position, pressure medium is discharged from the respective wheel brake cylinders and flows back into the reservoir 23 and not to a secondary side 15, 16.

Fig. 3 illustrates an anti-skid system 51 which is a further development of the anti-skid system illustrated in Fig. 2. In the present instance, only one four-position control valve 52, 53 respectively is used for each brake circuit I and II. By virtue of corresponding connections and line systems in these control valves 52, 53, communication between the booster circuit and the brake circuit at the same time acts upon a three-port, three-position solenoid valve 54, 55 when the valves 52, 53 are in their second positions in which the valves 42, 43 of the change-over valve arrangement 42/43 are operated.

It may also be mentioned that the changeover valve arrangement 19/20 or 42/43 can each be combined with a non-return valve which opens towards the topping-up reservoir 23, so that it is possible to reduce the pressure above a predetermined pressure limit.

Finally, limit switches 56, 57 respectively can be provided on the master cylinders 3 and 4 (see Fig. 1) to signal failure of a brake circuit and over-travel of the master cylinder.

Claims (9)

1. A hydraulic anti-skid brake system, comprising a pressure supply device including a pump and an accumulator, a multi-circuit brake booster which is equipped with a master cylinder for each brake circuit and with a control valve which controls communication between the pressure supply device and a booster cylinder connected to the primary side of each of the master cylinders and communication between the booster cylinder and a relief point, and short-circuit lines connected between the booster cylinder and the secondary side of a respective master cylinder and each incorporating a change-over valve arrangement which normally isolates the shortcircuit connection but by which the shortcircuit connection can be established during operation of the anti-skid system.

2. An anti-skid brake system as claimed in claim 1, in which each change-over valve arrangement comprises a respective two-port, two-position solenoid valve disposed in each short-circuit line, which solenoid valves can be switched on by means of an electronic control device to establish the short-circuit connection after a first wheel brake pressure reduction initiated by the said control device.

3. An anti-skid brake system as claimed in claim 2, in which two multi-position valves are provided in each of two brake circuits for controlling anti-skid operation and are switchable by the electronic control device and are connected in parallel and disposed downstream of the change-over valve arrangement.

4. An anti-skid brake system as claimed in claim 2 or 3, in which the short-circuit connection can be interrupted by a switching signal applied to the electronic control device by way of a switch responsive to lack of pressure in the accumulator of the pressure supply device.

5. An anti-skid brake system as claimed in claim 1, in which the change-over valve arrangement is integrated in multi-position valves of the anti-skid system.

6. An anti-skid brake system as claimed in claim 5, in which each multi-position valve integrated with a change-over valve arrangement is in the form of a four-port, fourposition valve.

7. An anti-skid brake system as claimed in any of claims 1 to 6, in which the changeover valve arrangement is combined with a non-return valve opening towards the relief point.

8. An anti-skid brake system as claimed in any of claims 1 to 7, in which a limit switch is provided on the master cylinder and is actuatable by a piston rod of the master cylinder in the event of over-travel of the master cylinder upon failure of the corresponding brake circuit.

9. An anti-skid brake system, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 or Fig. 2 or Fig. 3 of the accompanying drawings.