GB2064036A

GB2064036A - An hydraulic power-assisted brake system

Info

Publication number: GB2064036A
Application number: GB8038207A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-11-29
Filing date: 1980-11-28
Publication date: 1981-06-10
Also published as: SE8008367L; DE2948085A1; JPS5690758A; SE446170B; JPH0116704B2; GB2064036B

Abstract

A brake system comprises: a booster (1) controlled by a valve which actuates, by boost pressure a master cylinder (2) which supplies pressure medium to wheel brake cylinders (26, 27) via a primary brake line (11); and a boost pressure source (4, 5) which supplies pressure to the booster and to a second brake line (13) connectible to the brake cylinders (4, 5). When an anti-skid system (e.g. having solenoids 15, 16, 17) is operated a control valve within valve (12) may disconnect primary brake line (11) from the wheel cylinders and connect it to bias a proportioning or pressure limiting valve through which boost pressure from line (13) may then accordingly flow to the brake cylinders (4, 5). <IMAGE>

Description

SPECIFICATION An hydraulic auxiliary force brake system The present invention relates to an hydraulic auxiliary force brake system.

An auxiliary force brake system described in German Patent Specification No. 1,655,448 has a brake booster which is equipped with a control valve and which actuates by auxiliary force a master brake cylinder which is connected downstream and which is intended for supplying pressure medium to wheel brake cylinders by way of a primary brake line.

In this known auxiliary force brake system, the servo force is introduced by the control valve, and the final pressure introduced is as high as the maximum pressure in the energy supply device.

Dangerous over-braking of vehicle is rendered possible by the absence of a feedback signal of the pressure introduced.

According to the present invention there is provided an hydraulic auxiliary force brake system for motor vehicles, having a brake booster which is equipped with a control valve and which actuates by auxiliary force a master brake cylinder which is connected downstream and which is intended for supplying pressure medium to wheel brake cylinders by way of a primary brake line, an energy supply device associated with the auxiliary force supplying pressure medium to the brake booster and also to a secondary brake line likewise leading to the wheel brake cylinders.

In contrast to this prior art, the hydraulic auxiliary force brake system has the advantage that the brake pressure is limited by a feedback, such that unintentional over-braking is avoided in all cases.

Advantageously, in accordance with the invention the externally introduced servo pressure is limited during anti-skid regulation to the pressure introduced.

The present invention will now be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a hydraulic auxiliary force brake having an anti-skid pressure-control valve; Figures 2 and 3 show details of the pressurecontrol valve, wherein Figure 2 shows a relay valve and Figure 3 shows a pressure limiter; Figure 4 shows an hydraulic auxiliary force brake in which a pressure-control valve has a pressure limiter and three solenoid valves; Figure 5 shows an hydraulic auxiliary force brake whose pressure-control valve has a relay and safety valve and three solenoid valves, and Figures 6 and 7 show two embodiments each having a pressure limiter safety valve and a plurality of solenoid valves.

An hydraulic brake booster 1 is equipped with a pedal-operated control valve and is assembled with an hydraulic tandem master cylinder 2 to form a built-in unit. A multi-chamber topping-up reservoir 3 is mounted on the built-in unit.

An energy supply device is connected to the brake booster 1 and comprises a pump 4 and an accumulator 5. The energy supply device 4/5 is connected to the auxiliary force brake by way of a non-return valve 6 incorporated in a pressure line 7, an overflow valve 8 between the pressure line 7 and a relief line 9.

Two brake lines 10 and 11 are connected to the tandem master cylinder 2 and are associated with two brake circuits I and II. An anti-skid system is provided in the two brake circuits, although, for the sake of simplicity, only brake circuit I is illustrated in detail. An anti-skid pressure-control valve 12 is provided in brake circuit I. A pressure line 1 3 leads from the energy supply device 4/5 to the pressure-control valve 12, and a return line 14 is connected to the valve 12 and leads back to the relief line 9.

Three solenoid valves 1 5, 16 and 1 7 of the anti-skid system and a relay valve 1 8 or a pressure limiter 1 9 are disposed in the pressure-control valve 12.

The relay valve 1 8 is illustrated in Figure 2 and the pressure limiter 19 is illustrated in Figure 3.

The relay valve 1 8 and the pressure limiter 19 each have a respective valve spool 20, 21 which is movable on the one hand by hydraulic pressure and, on the other hand, by the force of a respective spring 22, 23. The corresponding line connections have the same reference numerals as those of Figure 1.

Two brake lines 24 and 25 lead from the pressure-control valve 12 to two wheel brake cylinders 26 and 27 which are associated with wheels equipped with sensors. The sensors and the electrical connections of the solenoid valves 1 5, 16 and 1 7 are connected (in a manner not illustrated) to an electronic control device (also not illustrated) which processes the electrical control commands. A secondary brake line (not visible) is disposed in the pressure-control valve 12.

The brake line connections are open during normal braking, and the brake pressure from the master cylinder 3 can build up as far as the brake cylinders 26 and 27 in an unobstructed manner.

When there is a tendency for the wheels to lock, this connection (not illustrated in Figure 1) is interrupted by one of the solenoid valves 1 5, 1 6 or 17, such as the solenoid valve 1 5. When a relay valve 1 8 is used in the pressure-control valve 12, the pressure in the brake line 11 urges the valve spool 20 to the right and, dependent upon the prevailing position of the solenoid valve 15, either the return line 14 of the pressure line 13 is connected to the brake line 24, 25 by the valve spool 20. The replay valve 18 enables a proportional build-up of pressure in the brake line 24, 25. The admission of the pressure, introduced at any given time, to the rear face of the valve spool 20 results in a retroactive effect upon the master cylinder 2 by way of the brake line 11.This results in a feedback which enables the driver to sense the brake force which is effective at any given time.

When a pressure limiter 1 9 is used instead of the relay valve 18, the pressure introduced into the brake line 24, 25 is limited relative to the pressure prevailing in the pressure line 13. The driver can also sense this limited pressure by way of the line 11. Thus, the maximum pressure introduced into the brake line 24, 25 is limited to the pressure in the master cylinder.

If the energy supply device 4/5 should fail, a further valve (not illustrated) provided in the pressure-control valve 12 shuts off the pressure line 13.

The auxiliary force brake of Figure 4 has a pressure-control valve 28 (bordered by dash-dot lines in the drawing) which is of different construction from that of Figure 1. The parts corresponding to the embodiment of Figure 1 are provided with the same reference numerals. A secondary brake line 29, connected to the pressure limiter 19, and the primary brake line 11 leads to a three-port, two-position solenoid valve 30. A brake line 31 is connected to the solenoid valve 30 and leads to the wheel brake cylinders 26 and 27 which have associated therewith a respective three-port, three-position solenoid valve 32 and 33. The two three-port, threeposition solenoid valves 32 and 33 also control communication with a return line 14.

The anti-skid control of the pressure-control valve 28 is performed by the three solenoid valves 30, 32, 33. The three-port, two-position solenoid valve 30, when non-energized, connects the master cylinder 2 to the wheel cylinders 26 and 27. When the solenoid valve 30 is energized, it isolates the master cylinder 2 from the brake cylinders 26 and 27, and connects the brakes to the energy supply device 4/5. The three-port, twoposition solenoid valve 30 then monitors the build-up of pressure, while, according to their switching positions, the other two solenoid valves 32 and 33 effect a pressure-holding operation, a build-up of pressure, or by way of the return line 14 a pressure-drop.

In addition to the advantages already stated in the description of the embodiment of Figure 1, this embodiment has the advantage that only a simple three-port, two-position solenoid valve and two three-port, three-position solenoid valves need to be used for the pressure-control valve 28.

Together with the pressure limiter 19 ensuring the pressure, they result in the function necessary for anti-skid regulation.

Figure 5 shows a type of construction in which a pressure-control valve 35 is equipped with different solenoid valves and a relay valve 36 has also been modified relative to the embodiment of Figure 2. The solenoid valves are a three-port, two-position solenoid valves 37 and two two-port, two-position solenoid valves 38 and 39 connected downstream thereof for each circuit. In addition to the connections, already described with reference to Figure 4, for the pressure line 13, the return line 14 and the secondary brake line 29, the relay valve 36 has a further connection for a parallel brake line 40.

During normal function, a pressure proportional to the pressure in the line 11 is introduced into the brake line 29 in a substantially travel-less manner by the pressure, originating from the master cylinder 2, in the relay valve 36 by way of the connection comprising the lines 13 and 29. All three solenoid valves 37, 38 and 39 are open when in their non-energized states. The pedal travel required on the brake booster 1 for actuation which can be sensed can be simulated by means of a travel-giving spring 41 provided at the inlet of the booster.

The three-port, two-position solenoid valve 37 undertakes the modulation of the control pressure at the relay valve 36 and thus at the same time undertakes the modulation in the secondary brake line 29. When the three-port, two-position solenoid valve 37 is changed over during anti-skid switching, communication with the master cylinder 3 is shut off, and the valve spool 21 in the relay valve 36 is relieved. The two two-port, twoposition solenoid valves 38 and 39 are pressureholding valves; they then take over the holding phase during anti-skid control.

In the event of failure of the auxiliary force, a pressure opposing the brake pressure is not built up at the valve spool 21 in the relay valve 36, so that the brake pressure displaces the valve spool 21 to the left against the force of the spring 23.

The pressureless pressure line 13 is closed by the valve spool 21, and the valve spool 21 connects the primary brake line 11 to the parallel brake line 40. In this manner, in the event of failure of the auxiliary force, the brake pressure is introduced through the lines 11 and 40 in conformity with the foot force applied to the pedal.

In the event of failure of the brake lines disposed downstream of the relay valve 36, the spring 23 displaces the valves spool 21 to the right against a stop 42. The pressure line 13 is closed when the valve spool is in this position. The energy supply device 4/5 thereby remains operative for the other brake circuit 11. In this manner, the relay valve 36 also assumes the function of a safety valve, since a two-circuit accumulator protective device is then not required.

Two non-return valves 43 and 44 are also shown in Figure 5. However, these non-return valves are not required when the stop 42 in the relay valve 36 is arranged such that the secondary brake line 29 can also be relieved by way of the return line 14. This embodiment is advantageous - in that an advantageous "unit composed arrangement" can be provided by equipping a brake system with a mass-produced master cylinder and an inexpensive pressure-control valve 35.

The required pressure-control valve function can be fulfilled by the exclusive use of simple twoposition solenoid valves 37, 38, 39, (one threeport, two-position valve and two two-port, twoposition valves) and a relay valve 35 having safety features.

This solution is also advantageous in that the pedal travel can be simulated in the case of the brake booster 1 (in the same manner as in the case of the brake valves for external force). Since the master cylinder 2 only has to apply the control volume for the relay valve 36 when the system is intact, the adjustment of the master cylinder 2 can be designed in accordance with the criteria of the auxiliary force braking action in the event of failure of the servo energy. It is thereby possible to obtain more favourable brake pedal forces or higher pressures in the event of energy failure.

Figure 6 shows an auxiliary force brake system in which a pressure-control valve 45 is equipped with four solenoid valves 46, 47, 48 and 49, that is to say, it is provided with one three-port, twoposition solenoid valve 46 and three two-port two-position solenoid valves 47, 48 and 49. A pressure limiter is of the same construction as that shown in Figure 4 and is therefore provided with the same reference numeral 1 9.

All the solenoid valves 46, 47, 48 and 49 are non-energized when in the travelling position and a through connection exists between the master cylinder 2 and the brake cylinders 26, 27. The pressure limiter 1 9 has closed the pressure line 1 3 by the force of the spring. During partial braking, the driver determines the braking action by the pressure introduced into the brake line 13. During full braking (tendency of the wheels to lock), the anti-skid regulation comes into operation by activation of the solenoid valves. During anti-skid regulation, the solenoid valve 47 is closed and the master cylinder circuit is isolated.The three-port, two-position valve 46 assumes the pressure modulation function by reducing the pressure in the brake circuit or by connection to the energy supply device 4/5 by way of the pressure limiter 19. The solenoid holding valves 48 and 49 hold the pressure in the brake cylinders 26 and 27 when they are in their shut-off positions, or permit the pressure modulation introduced by the solenoid valve 46.

The pressure phases required, that is to say, the pressure-holding phase, the pressure-drop phase and the pressure build-up phase, are thus individually possible at each wheel.

The feedback or return signalling of the brake pressure introduced is effected by way of the pressure limiter 1 9 in the manner already described. When the spring force and the pressure force from the brake line 13, acting upon the valve spool 21, correspond to the pressure force from the brake line 11, the pressure line 13 is closed and a further pressure rise in the brake circuit is prevented. In the event of energy failure (servo failure), the valve spool 21 of the pressure limiter is adjusted by brake pressure introduced by muscle power until the valve spool 21 closes the line 29.

A counter-pressure cannot build up at the pressure limiter valve spool, since the auxiliary force pressure = 0.

The pressure limiter 1 9 isolates the brake circuit from the pressureless servo circuit and thus acts as a safety valve.

In the event of brake circuit failure, the spring 23 acting upon the valve spool of the pressure limiter closes the pressure line 1 3 and thus prevents a drop in the servo pressure. The second circuit thus continues to be subjected to the full boosting action.

The advantages of this solution resides in the unchanged construction of the hydraulic brake system (master cylinder and brake booster). The control and shut-off functions required are obtained by simple two-position solenoid valves.

Finally, Figure 7 shows a single four-port, threeposition solenoid valve 50 instead of the two solenoid valves 46 and 47 of Figure 6.

When in its first position (illustrated), the fourport, three-position solenoid valve 50 permits pressure control of the brake pressure from the master cylinder 2 to the brake cylinders 26 and 27. When the solenoid valve 50 is in its second position, the master cylinder 2 is isolated and the brake circuit connected downstream is relieved by way of the return line 14. When the solenoid valve 50 is in its third position, the master cylinder 2 is isolated and the brake circuit connected downstream is charged by way of the pressure limiter 19, and the brake line 29 is charged by the energy supply device 4/5, to a pressure which corresponds to the maximum pressure of the master brake cylinder. The two two-port, twoposition solenoid valves 48 and 49 connected downstream operate as holding valves in the manner described.

Here also, the pressure limiter operates as a safety valve by virtue of the fact that the valve spool 21 can shut off the pressure line 13 in the event of failure of the energy supply.

Claims

1. A hydraulic auxiliary force brake system for motor vehicles, having a brake booster which is equipped with a control valve and which actuates by auxiliary force a master brake cylinder which is connected downstream and which is intended for supplying pressure medium to wheel brake cylinders by way of a primary brake line, an energy supply device associated with the auxiliary force supplying pressure medium the the brake booster and also to a secondary brake line likewise leading to the wheel brake cylinders.

2. An hydraulic auxiliary force brake system as claimed in claim 1, in which a relay valve or a pressure limiter is fitted in the secondary brake line, which relay valve or pressure limiter is equipped with at least one valve member which is subjected at one end to the pressure in the primary brake line and at the other end to the force of a return spring.

3. A hydraulic auxiliary force brake system as claimed in claim 2, in which the valve member is a valve spool which controls a connection of the secondary brake line.

4. An hydraulic auxiliary force brake system as claimed in claim 2 or 3, in which the relay valve has a connection for pressure relief.

5. An hydraulic auxiliary force brake system as claimed in any of claims 2 to 4, having an anti-skid system incorporating at least one solenoid valve connected upstream of the relay valve and two solenoid valves associated with the wheels of one axle, in which the relay valve or the pressure limiter is combined with a solenoid valve, connected upstream, of the anti-skid system to form a series-connected working unit.

6. An hydraulic auxiliary force brake system as claimed in claim 5, in which the relay valve has a further connection for a parallel brake line by which the primary brake line is connectable to the secondary brake line during a normal rise in the brake pressure.

7. An hydraulic auxiliary brake system as claimed in claim 5 or 6, in which the solenoid valve connected upstream of the relay valve is a three-port, two-position solenoid valve and is disposed in the primary brake line.

8. An hydraulic auxiliary force brake system as claimed in claim 5, in which the solenoid valve connected upstream of the relay valve is a threeport, two-position solenoid valve, and the two solenoid valves associated with the wheels are three-port, three-position solenoid valves.

9. An hydraulic auxiliary force brake system as claimed in claim 5, in which the solenoid valve connected upstream of the relay valve is a fourport, three-position solenoid valve which, when in a first position, establishes a through connection between the primary brake line and the wheel cylinders, the portion of the brake line at the brake cylinder end thereof being connectible to a return line when the said solenoid valve is in a second position, and the secondary brake line being connectible to the brake cylinders when the said solenoid valve is in a third position.

10. An hydraulic auxiliary force brake system as claimed in claim 5, in which two solenoid valves are connected upstream, of the relay valve, one being a two-port, two-position solenoid valve which can open and close the primary brake line, and the other being a three-port, two-position solenoid valve which connects the wheel brake cylinders to either the secondary brake line supplied by the energy supply device or to a relief point.

11. An hydraulic auxiliary force brake system as claimed in claim 5 or 6, in which the relay valve or the pressure limiter is combined with the anti-skid solenoid valves in a single valve unit.

12. An hydraulic auxiliary force brake system constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.