GB2186647A

GB2186647A - Brake system with wheel slip control

Info

Publication number: GB2186647A
Application number: GB08701826A
Authority: GB
Inventors: Norbert Ocvirk; Horst Peter Becker; Guenter Trach
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1986-02-14
Filing date: 1987-01-28
Publication date: 1987-08-19
Also published as: FR2594395B1; GB2186647B; FR2594395A1; DE3604697A1; GB8701826D0; JPS62258847A

Abstract

A brake system with wheel slip control, comprises a pedal-actuated vacuum booster (3) with a master cylinder (2) to which the wheel brakes (31, 32, 33, 34) are connected via pressure fluid conduits, an hydraulic auxiliary-pressure supply system with a hydraulic pump (26), a pressure-compensating and pressure-fluid supply reservoir (20), and wheel sensors (S1, S2, S3, S4) and electronic circuitries (44) for the determination of wheel rotational behaviour and for the generation of electrical braking-pressure control signals serving to govern electromagnetically actuatable pressure-fluid inlet valves and outlet valves (29, 30, 35, 36) inserted into pressure fluid conduits for wheel slip control, one single valve (23) is provided for the control of the pressure of the auxiliary-pressure supply system and for monitoring possible pressure differences in the brake circuits (I and II), the said valve being formed of three pressure chambers (22, 51, 54) with three pistons (24, 52, 55) arranged coaxially relative to one another, as well as a differential- pressure switch (43). <IMAGE>

Description

SPECIFICATION Brake system with wheel slip control This invention relates to a brake system with wheel slip control comprising a pedal-actuated booster with a master cylinder to which wheel brakes are connected via pressure-fluid lines, an hydraulic auxiliary-pressure supply system with a hydraulic pump and with a pressurecompensating and pressure-fluid supply reservoir, and comprising wheel sensors and electronic circuits for determining wheel rotational behaviour and for generating electrical brakingpressure control signals which serve to control electromagnetically controllable pressure-fluid inlet valves and outlet valves inserted into the pressure fluid lines for the purpose of wheel slip control.

In a dual-circuit brake system of the aforementioned type according to West German Patent application P 35 02 451.8, there is provided a control valve which controls the pressure in a pressure fluid conduit leading from the pump to the two brake lines in dependence on the pressure in a working chamber of the master cylinder, with non-return valves being inserted into said pressure fluid conduit between the brake lines and the pump. Besides, this brake system still includes a differential-pressure switch which is interposed into the electronic circuit and which permits to recognise and to evaluate the presence of a differential pressure. This differential-pressure switch is via special pressure lines communicating both with the pressure fluid conduit which leads from the pump to the brake lines and with a working chamber of the master cylinder.

It is an object of the present invention to simplify the brake system and to devise one single unit of comparatively simple design and special efficiency instead of several switches, valves and lines, for the purpose of monitoring and modulating the pump pressure.

According to the present invention there is provided a brake system with wheel slip control comprising a pedal-actuated booster with a tandem master cylinder to which wheel brakes are connected via pressure-fluid lines, an hydraulic auxiliary-pressure supply system with a hydraulic pump and with a pressurecompensating and pressure-fluid supply reservoir, and comprising wheel sensors and electronic circuits for determining wheel rotational behaviour and for generating electrical brakingpressure control signals which serve to control electromagnetically controllable pressure-fluid inlet valves and outlet valves inserted into the pressure fluid lines for the purpose of wheel slip control, characterised by a control and pressure-monitoring valve comprising first, second and third control chambers and first, second and third pistons co-operating with these control chambers, the first control chamber being connected via a pressure fluid conduit to one working chamber of the tandem master cylinder and the second control chamber being connected via another pressure fluid conduit to the other working chamber of the tandem master cylinder, and the third control chamber comprising as a valve chamber communicating with the pressure-fluid supply reservoir, on the one hand, and with a pressure line of the pump, on the other hand, the first piston extending into both the first control chamber and the second control chamber and co-operating with the second piston extending into both the second and the third control chamber, the second piston, via a valve member, moving into abutment on a valve seat of the third piston, which third piston is accommodated in the third control chamber and slidable therein between two stops and contains a longitudinal bore which interconnects the valve seat and a part of the third control chamber that communicates with the pressure line of the pump.

Preferably, the third piston is provided with a butt ramp which coacts with a probe of a differential-pressure switch that is connected to the electronic circuit, the said probe being held and guided in a housing of the valve.

Advantageously, the first piston of the control valve and pressure-monitoring valve is applied by a spring which, in the brake's release position, presses the first piston against the second piston and the second piston, in turn, via the valve member, for example a valve ball, onto the valve seat at the third piston and thereby causes the valve comprised by the valve member and the valve seat to assume its closed position.

Expediently, the first and the second piston of the control and pressure-monitoring valve comprise plunger pistons, while the third piston containing the longitudinal bore and the valve seat is sealingly held and guided in a cylindrical portion of the third control chamber.

One stop in the third control chamber forming the valve chamber confines the travel of the third piston in the event of a pressure drop in the other two control chambers and hence permits the valve member to lift from the valve seat, thereby allowing the presssure fluid delivered by the pump to flow back into the pressure-fluid supply reservoir through the longitudinal bore, the valve chamber and a return line.

An embodiment of the invention will now be described with reference to the accompanying drawing which, in a simplified view, partially in cross-section and partially purely schematically, shows the most important component parts of a wheel slip-controlled brake system of an embodiment of this invention and of a control valve with pressure monitoring function.

In the embodiment illustrated, the brake system comprises as a braking pressure genera tor 1 a hydraulic unit which is substantially composed of a tandem master cylinder 2 and a vacuum booster 3 connected in front thereof. In a known manner, the pedal force F applied on a brake pedal 5 is transmitted via a push rod 4 onto the vacuum booster 3 and from it, boosted by auxiliary force, onto working pistons 6 and 7 of the tandem master cylinder 2.

In the brake's release position shown, the pressure (working) chambers 8, 9 of the master cylinder are in communication with a pressure-compensating and pressure-fluid supply reservoir 20 via open central valves 10, 11, via connecting channels 12, 13 in the interior of the pistons 6, 7 as well as finally via annular chambers 14, 15, via connecting bores 16, 17 and via hydraulic lines 18, 19.

Connected to one of the two pressure chambers, herein the pressure chamber 8, is a control input 21 and via it a first control chamber 22 of a control valve 23 with a pressure monitoring function. Via plunger pistons 24, 52 in the interior of the control valve 23, the control pressure is transmitted onto a spherical seat valve 25 which, on the one hand, is connected hydraulically to the pressure side of a hydraulic pump 26 and, on the other hand, is connected to the pressure-compensating reservoir 20. The suction side of the pump 26 is likewise in connection with the reservoir 20. Said pump is an electromotively (motor M) driven hydraulic pump. The electrical connections 'm' and ground are likewise illustrated symbolically.It should also be mentioned that the piston 24 is sealed in relation to its guide bore in the housing of the control valve 23 by means of two ring seals which, however, are not shown in detail in the drawing for the sake of clarity.

The two brake circuits I, II of the master cylinder 2 are each connected with two wheel brakes 31, 32; and 33, 34, respectively, via hydraulically actuatable valves 27, 28 which are open when unpressurised, and via electromagnetically actuatable valves, namely socalled inlet valves 29, 30 which are likewise opened in their initial position. The wheel brakes 31, 32 and 33, 34, respectively, connected in parallel may e.g., as herein, be allocated to the wheels of one axle (rear wheels HR, HL, front wheels VR, VL) or to the diagonals.

The wheel brakes are connected to electromagnetically actuatable outlet valves 35, 36, closed in their inactive position, which are in communication with the pressure-compensating reservoir 20 via a hydraulic return line 37.

The brake circuits I, II are each via a respective non-return valve 38, 39 and via a connecting line 40 connected to the auxiliarypressure supply system, that is to the hydraulic pump 26 and the control valve 23. The non-return valves 38, 39 open as soon as the auxiliary pressure exceeds by a defined mini mum-value that pressure which is then prevailing in the brake circuits I, II between the inlet valves 29, 30 and the valves 27, 28. Besides, the auxiliary pressure causes the valves 27, 28 to switch over to a second switch position in which only a pressure reduction in the direction of the braking pressure generator 1 is still possible. To this end, corresponding nonreturn valves 41, 42 are connected in parallel to the valves 27, 28 or are structurally united with these valves.Said valves are designed as hydraulically actuatable or as electromagnetically actuatable valves.

The vehicle wheels are equipped with inductive sensors S1 to S4 which co-operate with a toothed disc (not shown) co-rotating synchronously to the wheel rotation and which generate electric signals indicative of the wheel rotational behaviour, that means the wheel speed and variations thereof. These signals are fed via the inputs S'1 to S'4 to an electronic signal-processing and combining circuitry 44 which generates braking-pressure control signals serving to temporarily switch over the inlet and outlet valves 29, 30, 35, 36 on detection of an imminent locked condition and to thereby keep the braking pressure constant, to decrease it and to re-increase it at the appropriate time. To this end, actuating magnets of the inlet and outlet valves are driven via the outputs A1 to A4.The electrical connecting lines between the ports A, to A4 and the coils of the valves 29, 30, 34, 35 are not illustrated for the sake of simplicity.

The circuitry 44 can be realised in a known fashion by hard-wired circuits or by programmed electornic units, such as microcomputers or microcontrollers.

When generating the braking-pressure control signals, additionally, the switching condition of a differential-pressure switch 43, which is part of the control valve 23, and, if present, still further signals are evaluated. The signal input d is provided for this purpose.

The switch-on signal for the start-up of the drive motor of the hydraulic pump 26 which runs only during a wheel slip control action is applied to the motor M via the connection m.

The brake system operates as follows: On brake application, the pedal force F, boosted by the vacuum in the booster 3, is transmitted onto the master-cylinder pistons 6, 7. The central valves 10, 11 close so that now braking pressure is allowed to develop in the pressure chambers 8, 9 and thus in the brake circuits I, II which propagates via the valves 27, 29 and 28, 30, respectively, to the wheel brakes 31, 32 and 33, 34, respectively.

The pressure in the chamber 8 is supplied further to the control input 21 and to the control chamber 22 of the control valve 23 and increases the closing force of the seat valve 25 which is produced by a controller spring 49. Likewise, there is communication via the pressure line 50 between the brake circuit II and the pressure chamber 9, respectively, and a second control chamber 51, into which the two pistons 24, 52 extend. However, this remains without any effect because the hydraulic pump 26 is not yet in operation.

On detection of an imminent locked condition at one or more of the wheels by means of the sensors S1 to S4 and the circuitry 44, wheel slip control will commence. The drive motor M of the pump 26 is switched on so that now an auxiliary presure proportional to the pressure in the control chambers 22, 51 and in the pressure chambers 8, 9, respectively, and thus to the pedal force F may develop in the auxiliary-pressure supply system and in the supply line 40.

The auxiliary pressure leads to change-over of the hydraulically drivable valves 41, 42 and thus to closure of the brake circuits I, II (instead of actuating the valves 41, 42 hydraulically, alternatively they may be actuated electromagnetically). Further displacement of the master cylinder pistons 6, 7 in the direction of the pedal force F, as well as emptying of the pressure chambers 8, 9 is precluded. As soon as a sufficient pressure is attained, the auxiliary-pressure supply system takes over the performing of the function of the braking pressure generator 1 via the supply line 40 and the non-return valves 38, 39 which are now open. Pressure fluid flows dynamically into the brake circuits I, II via the non-return valves 38, 39.The actual braking pressure variation in the wheel brakes 31 to 34 is determined by the inlet and outlet valves 29, 30, 35, 36 which are supplied with wheel slip-controlling braking pressure control signals via the lines A1 to A4 Defects of various type can be detected reliably when comparing the pressure in the pressure chambers 8 and 9 of the master cylinder 2 and, respectively, in the lines 48, 50 leading to the auxiliary-pressure control valve 23, with the instantaneous auxiliary pressure caused by the pump 26 and the control valve 23 while taking into consideration the condition of operation, that means is it a normal braking action or a response of the wheel slip control.

In the case of a braking action without wheel slip control, pressure must build up in the pressure chambers 8, 9, but not in the auxiliary-pressure supply system. Failure of the brake circuit II, e.g. due to leakage, can be detected by means of the differential pressure switch 43. With the system intact, the pressure difference becomes little or zero when wheel slip control commences. In the event of failure or disturbance of the pump 26, of the control valve 23, upon the occurrence of a defect in the switch-on conduit of the motor M or the like, a pressure will be maintained in the pressure chamber 9 that is in excess of that in the auxiliary-pressure supply line 40 even after the commencement of wheel slip control. Hence it follows that defects can be detected and signalled by logically combining this condition and others by means of the circuitry 44.Depending on the type of error, the circuitry 44 will then automatically disconnect the wheel slip control completely or partially, that means limited to some wheel brakes, in order to still render possible effective braking through the intact brake circuit.

The control valve 23 with the pressure monitoring function which, as a whole, is referred to by 23 comprises four chambers 22, 51, 53, 54 located coaxially to one another and isolated from one another by three pistons 24, 52, 55. While the two pistons 24, 52 acted upon by the pressures in the brake circuits I and II are of like design, the valve piston 55 is furnished with a longitudinal bore 56 closable by a valve ball 57 which is arranged between the valve seat 45 and the piston 52. The outer peripheral surface of the valve piston 55 has a butt ramp 46 which coacts with a probe 47 incorporated in a cross bore of the valve housing and slidable in opposition to the force of a contact spring 58 of the differential-pressure switch 43. If the hydraulic pressure generated by the pump 26 is higher than the pressure prevailing in the control chambers 22 and/or 51, then the valve piston 55 will be displaced to the right until it bears against the shoulder 59. Subsequently, the valve ball 57 can lift from the valve seat 45 so that part of the pressure fluid delivered by the pump 26 can return via the return line 60 into the reservoir 20 for pressure relief. If, as has been described hereinabove, the valve piston 55 displaces in the direction of the first control chamber 22, simultaneously, the probe 47 will be displaced in opposition to the force of the contact spring 58 so that the differential pressure switch 43 closes and a corresponding signal is issued to the circuitry 44.

Claims

1. A brake system with wheel slip control comprising a pedal-actuated booster with a tandem master cylinder to which wheel brakes are connected via pressure-fluid lines, an hydraulic auxiliary-pressure supply system with a hydraulic pump and with a pressure-compensating and pressure-fluid supply reservoir, and comprising wheel sensors and electronic circuits for determining wheel rotational behaviour and for generating electrical braking-pressure control signals which serve to control electromagnetically controllable pressure-fluid inlet valves and outlet valves inserted into the pressure fluid lines for the purpose of wheel slip; control, characterised by a control and pressure-monitoring valve (23) comprising first, second and third control chambers (22, 51, 54) and first, second and third pistons (24, 52, 55) co-operating with these control chambers, the first control chamber (22) being connected via a pressure fluid conduit (48) to one working chamber (8) of the tandem master cylinder and the second control chamber (51) being connected via another pressure fluid conduit (50) to the other working chamber (9) of the tandem master cylinder (2), and the third control chamber (54) comprising as a valve chamber communicating with the pressure-fluid supply reservoir, on the one hand, and with a pressure line (40) of the pump (26), on the other hand, the first piston (24) extending into both the first control chamber (22) and the second control chamber (51) and co-operating with the second piston (52) extending into both the second and the third control chamber (51 and 54, respectively), the second piston (52), via a valve member (57), moving into abutment on a valve seat (45) of the third piston (55), which third piston (55) is accommodated in the third control chamber (54) and slidable therein between two stops (59, 61) and contains a longitudinal bore (56) which interconnects the valve seat (45) and a part of the third control chamber (54) that communicates with the pressure line (40) of the pump (26).

2. A brake system as claimed in claim 1, characterised in that the valve member is a valve ball (57).

3. A brake system as claimed in claim 1, characterised in that the third piston (55) is provided with a butt ramp (46) which coacts with a probe (47) of a differential-pressure switch (43), the said probe being held and guided in a housing of the valve.

4. A brake system as claimed in any one of the preceding claims, characterised in that the first piston (24) of the control and pressuremonitoring valve (23) is applied by a spring (49) which, in the brake's release position, presses the first piston (24) against the second piston (52) and the second piston, in turn, via the valve member (57), onto the valve seat (45) at the third piston (55) and thereby causes the valve (25) comprised by the valve member (57) and the valve seat (45) to assume its closed position.

5. A brake system as claimed in any one of the claims 1 to 4, characterised in that the first and the second pistons (24 and 52) of the control and pressure-monitoring valve (23) comprise plunger pistons, and in that the third piston (55) containing the longitudinal bore (56) and the valve seat (45) is sealingly held and guided in a cylindrical portion of the third control chamber (54).

6. A brake system as claimed in any one of the preceding claims, characterised in that one stop (59) in the third control chamber (54) forming the valve chamber confines the travel of the third piston (55) in the event of a pressure drop in the other two control chambers (22, 51) and hence permits the valve member (57) to lift from the valve seat (45), thereby allowing pressure fluid delivered by the pump (26) to flow back into the pressure-fluid supply reservoir (20) through the longitudinal bore (56), the valve chamber (54) and a return line (60).

7. A brake system as claimed in claim 3, characterised in that the differential-pressure switch (43) which is actuated by the butt ramp (46) of the third piston (55) is part of the electronic circuit.

8. A brake system with wheel slip control substantially as herein described with reference to and as illustrated in the accompanying drawing.