GB2186042A - Brake system with wheel slip control - Google Patents

Abstract

In a brake system with a braking pressure generator (1) to which wheel brakes (31 to 34) are connected via pressure-fluid conduits (I, II), an auxiliary-pressure hydraulic supply system with a hydraulic pump (26), a pressure-compensating and pressure-fluid supply reservoir (20), and an auxiliary-pressure control valve (23) as well as of wheel sensors (S1 to S4) and electronic circuitries (28), a closure valve (29, 30) having little throttling effect is inserted in each pressure-fluid conduit (I, II) leading from a master cylinder pressure chamber (8, 9) to the connected wheel brakes (31, 32, 33, 34). A respective supply line (45, 46) terminates in the pressure-fluid conduit between the closure valve (29, 30) and the wheel brake (31, 32, 33, 34), which supply lines each contain an intake valve (43, 44) having a comparatively greater throttling effect and being in turn in communication with the auxiliary-pressure source (23, 26) via a feed line (40), while a fluid return line (37) to the reservoir (20) communicates with the wheel brakes (31, 32, 33, 34) via respective outlet valve (35, 36) for each circuit so that, for the purpose of pressure development in the wheel brakes on actuation of the master cylinder (2), only the closure valve (29, 30) is penetrated by fluid, while during control action only the intake valve (43, 44) is penetrated by fluid. <IMAGE>

Description

SPECIFICATION Brake system with slip control This invention relates to a brake system with slip control, which brake system comprises a pedal-actuated, preferably auxiliary-force-assisted braking pressure generator, to which wheel brakes are connected via pressure-fluid conduits, an auxiliary-pressure hydraulic supply system with an hydraulic pump, a pressurecompensating and pressure-fluid supply reservoir, an auxliary-pressure control valve, and wheel sensors and electronic circuits for determining the wheel rotational behaviour and for generating electric braking-pressure control signals serving to control electromagnetically actuatable pressure-fluid inlet valves and outlet valves inserted into the pressure-fluid conduits for the purpose of slip control.

In known brake systems of this type (West German published patent applications 30 40 561, 30 40 562), a master cylinder with a hydraulic brake power booster connected upstream thereof is used as a braking pressure generator. The auxiliary-pressure supply system comprises a hydraulic pump and a hydraulic accumulator, out of which auxiliary pressure proportional to pedal force is delivered on brake application with the aid of a control valve. On the one hand, this dynamic pressure is transmitted via the master cylinder into the static brake circuits connected to the master cylinder. On the other hand, the wheel brakes of one axle, preferably those of the rear axle, are in direct communication with a pressure (booster) chamber into which the pressure proportional to pedal force is introduced through the control valve (dynamic brake circuit).For the purpose of slip control, moreover, inlet valves are inserted both into the static circuits and into the dynamic circuit, which valves normally assume their opened position and which, in the event of an imminent locked condition of a wheel, serve to shut off the pressure-fluid flow to the wheel brake concerned. Besides, there are provided outlet valves which allow the discharge of pressure fluid from the wheel brake to the pressure-compensating reservoir in case of need. On commencement of slip control, the booster chamber in which the controlled pressure introduced out of the auxiliary-pressure supply system is prevailing will be connected via a so-termed main valve with the static brake circuits of the master cylinder in order to be able to replenish the quantity of pressure fluid, removed through the outlet valves, in the static circuits again.In addition, for safety reasons, the piston (or pistons) in the (tandem) master cylinder will be reset or fixed by means of a positioning device. The structural efforts needed for generating, storing and controlling the hydraulic auxiliary pressure, for dynamic fluid delivery into the static circuits and for safeguarding the brake functions on failure of individual circuits are considerable.

In brake systems of this type, the control signals for the inlet valves and outlet valves are generated by means of electronic circuits, the inputs of which are connected with wheel sensors, e.g. inductive pickups for measuring data, and which thereby are able to react on a variation of the wheel rotational behaviour indicative of an imminent locked condition by maintaining the pressure at the wheel concerned constant, by reducing it and by reincreasing it anew.

It is an object of the present invention to design the brake system such that fewest valves possible are penetrated by fluid on brake application and also in the event of brake pressure control. It is in particular desired to reduce the noise of the system during control action and to improve the pedal feeling.

According to the present invention there is provided a brake system with slip control, which brake system comprises a pedal-actuated, braking pressure generator, to which wheel brakes are connected via pressure-fluid conduits, an auxiliary-pressure hydraulic supply system with a hydraulic pump, with a pressure-compensating and pressure-fluid supply reservoir and with an auxiliary-pressure control valve, and wheel sensors and electronic circuits for determining the wheel rotational behaviour and for generating electric braking-pressure control signals serving to control electromagnetically actuatable pressure-fluid inlet valves and outlet valves inserted into the pressure-fluid conduits for the purpose of slip control, characterised by a respective separating valve having little throttling effect inserted into each pressure-fluid conduit (I, II)- from the pressure chamber to the wheel brakes, by there being provision of a respective supply line terminating into each pressure-fluid conduit from the respective separating valve to the respective wheel brake, which supply lines each contain one intake valve of comparatively greater throttling effect which, in turn, is in communication via a feed line with the auxiliary-pressure source, with a return line being connected to the wheel brakes, into which return line a respective outlet valve is interposed so that, for the purpose of pressure build-up in the wheel brakes on actuation of the master cylinder, only the separating valve and in the event of control action only the intake valve will be penetrated by fluid.

Preferably, each non-return valve is interposed into the feed line connecting the auxiliary-pressure supply system with the intake valve, the said non-return valve precluding the return flow of pressure fluid from the wheel brake or the brake line to the auxiliary-pressure supply system.

Expediently, there is connected in parallel to each separating valve a respective non-return valve so that, with the separating valve shut off, by-pass of this shut-off valve takes place from the wheel brake to the pressure chamber of the master cylinder, if the pressure in the wheel brake is higher than the pressure in the pressure chamber.

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, displays the most important component parts of a slip-controlled brake system according to an embodiment of this invention.

In the embodiment illustrated, the brake system includes as braking pressure genrator 1, a hydraulic unit which is substantially composed of a tandem master cylinder 2, with a vacuum booster 3 connected upstream thereof. Via a push rod 4, a pedal force F applied on a brake pedal 5 is transmitted in a known fashion onto the vacuum booster 3 and from said, boosted by auxiliary force, onto working pistons 6 and 7 of the tandem master cylinder 2.

In the shown release position of the brake, the pressure (working) chambers 8, 9 of the master cylinder 2 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 to pressure chamber 8, is a control input 21 and via it the control chamber 22 of an auxiliary-pressure control valve 23. Via a piston 24 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, to the pressurecompensating reservoir 20. The suction side of the pump 26 is likewise in communication with the reservoir 20. Said pump is a hydraulic pump driven electromotively (motor M).

The electrical connections 'm' and ground are likewise illustrated symbolically.

The two brake circuits I, II of the master cylinder 2 are each connected with two wheel brakes 31, 32; 33, 34 via electromagnetically actuatable valves opened in the initial position, namely so-called separating or inlet valves 29, 30. The wheel brakes 31, 32 and 33, 34, respectively, connected in parallel may e.g., like 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 communicating with the pressure-compensating reservoir 20 via a hydraulic return line 37.

Besides, the brake circuits I, II are each via an intake valve 43, 44 and a respective nonreturn valve 38, 39 and via a connecting line 40 communication with the auxiliary-pressure supply system, that is with the hydraulic pump 26 and with the auxiliary-pressure control valve 23. The non-return valves 38, 39 will open as soon as the auxiliary pressure exceeds by a defined minimum value that pressure which is instantaneously prevailing in the brake circuits I, II and as soon as the intake valves 43, 44 assume their opened position.

The vehicle wheels are equipped with inductive sensors S, to S4 which co-operate with a toothed disc co-rotating synchronously to the wheel rotation and generate electric signals indicative of the wheel rotational behaviour, that means the wheel speed and variations thereof.

These signals are fed via the inputs S1 to S4 to an electronic signal-processing and combining circuitry 28 which generates braking-pressure control signals serving to temporarily switch over the intake, separating and outlet valves 29, 30, 35, 36, 43, 44 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, the actuating magnets of the inlet and outlet valves are driven via the outputs A, to A4. The electrical connecting lines between the ports A, to A4 and the coils of the valves 29, 30, 35, 36, 43, 44 are not illustrated for the sake of simplicity.

The circuitry 28 can be realised in a known fashion by hard-wired circuits or by programmed electronic units, such as microcomputers or microcontrollers.

The switch-on signal for the start-up of the drive motor of the hydraulic pump 26, which only runs during a 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 thus allowing braking pressure to develop now in the pressure chambers 8, 9 and hence in the brake circuits I, II which propagates via the valves 29, 30 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 the indicated spring. However, this remains without any effect because at first 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 28, slip control will commence. The drive motor M of the pump 26 is switched on, thereby permitting an auxiliary pressure proportional to the pressure in the control chamber 22 and in the pressure (working) chamber 8, respectively, and thus to the pedal force F to develop in the auxiliary-pressure supply system and in the feed line 40.

A signal of the circuitry 28 results in change-over of the electromagnetically actuatable valves 29, 30 and thus in closure of the brake circuits I, II. 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 sufficient pressure is attained, the auxiliarypressure supply system takes over to perform the function of the braking pressure generator 1 via the feed line 40 and the non-return valves 38, 39 now opening. Pressure fluid flows dynamically into the brake circuits 1, II via the non-return valves 38, 39 and the intake valves 43, 44.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 slip-controlling braking pressure control signals via the lines A1 to A4.

Defects of various type can be detected reliably by virtue of an arrangement (not illustrated in detail) when comparing the pressure in the pressure chamber 8 of the master cylinder 2 and, respectively, that in the line 27 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 operating condition, that means is it a normal braking action or a response action of the slip control. In the case of a braking action without slip control, pressure must build up in the pressure chamber 8, but not in the auxiliarypressure supply system.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, pressure will be maintained in the pressure chamber 8 that is in excess of that in the auxiliary-pressure feed line 40 even after the commencement of slip control. Hence it follows that defects can be detected and sig nalled by logically combining these conditions and others by virtue of the circuitry 28. Depending on the type of defect, the circuitry 28 will then automatically disconnect the 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.

As can be seen from the drawing, the inlet and separating valves 29, 30, respectively, are still protected by non-return valves 41, 42 connected in parallel. In special cases, these non-return valves 41, 42 permit a termination of the braking pressure control and release of the wheel brakes, respectively, since a small quantity of pressure fluid can flow back out of the wheel brakes into the pressure chambers 8, 9, with the separating valves 29, 30 still closed.

A special advantage of the brake system illustrated resides in that the intake valves 43, 44 can be designed with a diaphragm, that means their flow cross-sections can be dimensioned such as to prevent the pressure fluid delivered by the pump 26 from entering the wheel brakes too abruptly in the case of braking pressure control. In contrast thereto, the inlet or separating valves 29, 30 are sized more generously in respect of their flow cross-sections, whereby a 'spongy' pedal feeling can be prevented.

Finally, a major advantage of the brake system described can be seen in that, in the case of braking pressure control, the noises produced by the brake system can be diminished to a minimum owing to the fact that a low pressure gradient can be maintained. If, for instance, an amount of pressure of 100 bar is attained at the outlet of the pump 26 and the intake valves 43, 44 subsequently are opened abruptly, the pressure at the pump; outlet and in the feed line, respectively, will decline comparatively slowly, since the flow cross-sections in this branch of the brake system can be dimensioned to be relatively small.

Claims (11)

1. A brake system with slip control, which brake system comprises a pedal-actuated, braking pressure generator, to which wheel brakes are connected via pressure-fluid conduits, an auxiliary-pressure hydraulic supply system with a hydraulic pump, with a pressurecompensating and pressure-fluid supply reservoir and with an auxiliary-pressure control valve, and wheel sensors and electronic circuits for determining the wheel rotational behaviour and for generating electric braking-pressure control signals serving to control electromagnetically actuatable pressure-fluid inlet valves and outlet valves inserted into the pressure-fluid conduits for the purpose of slip control, characterised by a respective separating valve (29, 30) having little throttling effect inserted into each pressure-fluid conduit (I, II) from the pressure chamber (8, 9) to the wheel brakes (31, 32, 33, 34), by there being provision of a respective supply line (45, 46) terminating into each pressure-fluid conduit from the respective separating valve (29, 30) to the respective wheel brake (31, 32, 33, 34), which supply lines each contain one intake valve (43, 44) of comparatively greater throttling effect which, in turn, is in communication via a feed line (40) with the auxiliary-pressure source (23, 26), with a return line (37) being connected to the wheel brakes (31, 32, 33, 34), into which return line a respective outlet valve (35, 36) is interposed so that, for the purpose of pressure build-up in the wheel brakes on actuation of the master cylinder (2), only the separating valve (29, 30) and in the event of control action only the intake valve (43, 44) will be penetrated by fluid.

2. A brake system as claimed in claim 1, characterised in that each non-return valve (38, 39) is interposed into the feed line (40) connecting the auxiliary-pressure supply system (23, 26) with the intake valve (43, 44), the said non-return valve precluding the return flow of pressure fluid from the wheel brake (31, 32, 33, 34) via the intake valve (43, 44) to the auxiliary-pressure supply system (23, 26).

3. A brake system as claimed in claim 1 or claim 2, characterised in that connected in parallel to each separating valve (29, 30) is a respective non-return valve (41, 42) so that, with the separating valve (29, 30) shut off, by-pass of the shut-off valve (29, 30) takes place from the wheel brake (31, 32, 33, 34) to the pressure chamber (8, 9) of the master cylinder (2), if the pressure in the wheel brake (31, 32, 33, 34) is higher than the pressure in the pressure chamber (8, 9).

4. A brake system as claimed in any one of the preceding claims, characterised in that a control input (21) of the auxiliary-pressure control valve (23) is connected to one of the two brake circuits (I, II) and, respectively, to one of the two pressure chambers (8, 9) of the tandem master cylinder (2).

5. A brake system as claimed in any one of the preceding claims, characterised in that the brake circuits (I, II), that is the pressure-fluid circuits of the braking pressure generator (1), are adapted to be shut off by change-over of the separating valves (29, 30) to their second switching position.

6. A brake system as claimed in any one of the preceding claims, characterised in that the separating valves (29, 30) are electromagnetically actuatable separating valves in the form of two-way/two-position directional control valves which are inserted into the pressurefluid conduits from the braking pressure generator (1) to the wheel brakes (31, 32, 33, 34), which valves are open in their inactive position and which close after their change-over.

7. A brake system as claimed in claim 1; characterised in that the separating valves (29, 30) are electromagnetically actuatable separating valves in the form of two-way/two-position directional control valves which are in each case structurally united with a parallel connected non-return valve (41, 42) which admits pressure reduction towards the braking pressure generator (1).

8. A brake system as claimed in any one of the preceding claims, characterised in that a pressure port and the feed line (40) of the auxiliary-pressure supply system (23, 26), respectively, is in communication with the wheel brakes (31, 32, 33, 34) via an intake valve which is designed as an electromagnetically actuatable two-way/two-position directional control valve (43, 44), which is closed in its inactive position and which can be switched to open.

9. A brake system as claimed in any one of the preceding claims, characterised in that the outlets (45, 46) of the intake valves (43, 44) are connected in parallel to the outlets (47, 48) of the separating valves (29, 30).

10. A brake system as claimed in any one of the preceding claims wherein the braking pressure generator is auxiliary4orce-assisted.

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