GB2192683A - Brake system for motor vehicles with braking slip and traction slip control - Google Patents

Abstract

A brake system for vehicles with front wheel or rear wheel drive comprises a power-assisted brake pressure generator (1) connected to which are, via two hydraulically isolated circuits (I, II), a front and a rear wheel, respectively. The system is equipped with an auxiliary-pressure supply system (19) which is only in operation during the control phases and/or on actuating the brakes and including a normally-open by-pass valve (22) between the outlet and inlet of a pump (20). Valve arrangements comprising multi- directional control valves (9-12, 42, 43) are provided which are switched so as to be open in the inoperative position, and through the intermediary of which the brake pressure generator (1) and/or the auxiliary-pressure supply system (19) is connected to the wheel brakes (5-8). During the traction slip control phase, the pressure fluid channels to the non-driven wheels are blocked by means of the multi- directional control valves (13, 14 and/or 40, 41). In Fig. 1 only the rear non-driven wheels have individual valves (13, 14) and in Fig. 3 the valves (10, 17) and disposed immediately downstream of the check valves (27,28) <IMAGE>

Description

SPECIFICATION Brake system for motor vehicles with braking slip and traction slip control The present invention relates to a brake system with braking slip and traction slip control, for motor vehicles having one driven and one non-driven axle, including a power-assisted brake pressure generator connected to which are, via two hydraulically isolated circuits, a wheel brake of a front wheel and a wheel brake of a rear wheel, respectively; an hydraulic auxiliary-pressure supply system; valve arrangements through the intermediary of which pressure fluid flow to the wheel brakes can be blocked and pressure fluid from the auxiliarypressure supply system can be introduced into the wheel brakes during control phases; outlet valves which, after having been switched so as to be open, connect a respective pressure fluid channel leading to the two connected wheel brakes of each circuit with a pressure compensating reservoir; multi-directional control valves in pressure fluid connecting channels to the rear wheel brakes, the valves being such as to be open in the inoperative position and being switchable into a blocking position, and the brake system further including with wheel sensors and electronic switching circuits for determrining the rotational behaviour of the wheels as well as for generating brake pressure control signals.

Such a brake system has been described in West German printed and published patent application 34 07 538. In order to keep the production costs as low as possible, the system has been equipped with only two hydraulically isolated brake circuits connected to which are one front and one rear wheel each, preferably in the form of a diagonal split. In addition to the inlet/outlet valve pair required for the braking slip and traction slip control, another multi-directional control valve, which is normally switched so as to be open, has been incorporated in the pressure fluid channel leading to the non-driven wheel, said multi-directional control valve enabling a largely independent brake pressure control at the front and at the rear wheels, in spite of the limitation to two hydraulically isolated circuits.In the case of a vehicle with front wheel drive wherein, consequently, the additional valve is situated in the rear wheel connection, a pressure of any amount is introduceable into the front wheel brake without jeopardizing the stable running of the rear wheel connected to the same brake circuit by means of said valve and/or after the fluids pressure channel to the rear wheel has been blocked. A pressure reduction at the front wheel, with the rear wheel brake pressure remaining constant, is also possible. Furthermore, said additional valve enables, in connection with the cutting in of the auxiliary-pressure source, a traction slip control since after the blocking of said additional valve, brake pressure is only transmitted into the driven wheel.In the brake system according to the West German printed and published patent application 34 07 538, the auxiliary pressure is taken from the brake pressure generator in the form of a controlled pressure during the braking slip control phase, said brake pressure generator being in the form of a master cylinder with an hydraulic brake power booster. During the traction slip control phase, a three-way/two-position valve is switched over so as to establish a direct connection to the hydraulic accumulator of the auxiliary-pressure source.

In order to reduce the production costs of a brake system controlling the braking slip and the traction slip and to ensure a high functional safety, it has also been proposed to design the brake pressure generator in the form of a master cylinder with a preceding vacuum brake power booster and to equip this apparatus with a hydraulic auxiliary-pressure supply system which is only cut in during the slip control phase (West German patent application P 35 27 190.6).

The present invention now has the object to create a slip-controlled brake system which is realisable at low expenditure, and which enables a largely independent control of the brake pressure in the front and rear wheels in all cases possibly occurring during practical operation, and which also permits a traction slip control on vehicles with front wheel or rear wheel drive at, at the most, low additional expenditure.

According to the present invention there is provided a brake system with braking slip and traction slip control for motor vehicles having one driven and one non-driven axle, including a power-assisted brake pressure generator connected to which are, via two hydraulically isolated circuits, a wheel brake of a front wheel and a wheel brake of a rear wheel, respectively; an hydraulic auxiliary-pressure supply system; valve arrangements through the intermediary of which pressure fluid flow to the wheel brakes can be blocked and pressure fluid from the auxiliary-pressure supply system can be introduced into the wheel brakes during control phases; outlet valves which, after having been switched so as to be open, connect a respective pressure fluid channel leading to the two connected wheel brakes of each circuit with a pressure compensating reservoir; multi-directional control valves in pressure fluid connecting channels to the rear wheel brakes, the valves being such as to be open in the inoperative position and being switchable into a blocking position, and the brake system further including wheel sensors and electronic switching circuits for determining the rotational behaviour of the wheels as well as for generating brake pressure control signals, characterised in that the auxiliary-pressure supply system comprises an hydraulic pump which can be cut in during the control action and/or on actuating the brakes, an auxiliary-pressure control valve and a multidirectional control valve which is incorporated in a pressure fluid circuit from the pressure side to the suction side of the pump, which is switched so as to be open in the inoperative position and which is switchable so as to be blocked during the traction slip control phase, and in that the valve arrangements are provided with multi-directional control valves, which are switched so as to be open in the inoperative position, which are switchable so as to be blocked, and which are incorporated in pressure fluid channels leading from the brake pressure generator and from the auxiliary-pressure supply system to the wheel brakes, and through the intermediary of which valves the auxiliary-pressure supply system is, instead of the brake pressure generator, connectible to the wheel brakes during the control phases.

In spite of the comparatively very low expenditure required at the component parts, said system comprises, so to speak, three control channels and is also suitable for the traction slip control of a vehicle with front wheel drive without necessitating any additional components-apart from an extension of the electronic control unit. As will be described in detail in the following, only two additional valves will be required for the traction slip control when used in vehicles with rear wheel drive.

According to a favourable embodiment of the present invention, the valve arrangements are, in each of the two hydraulically isolated circuits, in the pressure fluid channels leading from the brake pressure generator and from the auxiliary-pressure supply system to the wheel brakes, each provided with at least one multi-directional control valve, which is switched so as to be open in the inoperative position. By means of said valves, the brake pressure generator and the auxiliary-pressure supply system are hydraulically connectible in parallel to the wheel brakes.In another embodiment, on the other hand, the multi-directional control valves of the valve arrangements, which valves are incorporated in the pressure fluid channels between the brake pressure generator and between the auxiliarypressure supply system and the wheel brakes, and are switched so as to be open in the inoperative position, are connected in series in the pressure fluid channels leading from the brake pressure generator to the wheel brakes, the auxiliary-pressure supply system being, via non-return valves, hydraulically connected-in each case between these two multi-directional control valves -to the pressure fluid channel connecting the brake pressure generator with the wheel brakes.

In the case of a vehicle with rear wheel drive, both a braking slip control and a traction slip control are achievable with such a brake system, as has already been mentioned above, provided an additional multi-directional control valve, which is switched so as to be open in the inoperative position, is incorporated in each of the pressure fluid connecting channels to the front wheel brakes; during the traction slip control phases, the pressure fluid flow to the non-driven front wheel is then blockable by means of said additional valves.

In a dual-circuit brake system of the type according to the invention, the vehicle wheels are, expediently, connected to the two hydraulic brake circuits in a diagonal manner.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a simplified and, in part, schematic illustration of the most important components of an embodiment of brake system according to the invention for vehicles with front wheel drive; Figure 2 shows an embodiment of brake system for vehicles with rear wheel drive, illustrated as in Figure 1; Figure 3 shows a similar illustration of another embodiment, also for vehicles with rear wheel drive.

The brake system according to Figure 1 comprises a brake pressure generator 1 which, in its turn, comprises a tandem master cylinder 2 and a preceding vacuum booster 3.

The brake force is exerted onto the brake pressure generator 1 via a brake pedal 4.

The brake pressure generator is connected to two hydraulically isolated brake circuits 1, it.

The wheel brakes of a front wheel VL; VR and of a rear wheel HR; HL, respectively, are connected to the brake circuits I, ll, i.e. in the form of a diagonal brake circuit split. In the pressure fluid channels from the brake pressure generator 1 to the wheel brakes 5, 6; 7, 8, two multi-directional control valves 9, 10; 11, 12 each are incorporated, said valves being normally, i.e. in the inoperative position, switched so as to be open and being connected in series. In the pressure fluid channels to the rear wheels HR; HL, a respective additional multi-directional valve 13; 14 is incorporated which is also open in the inoperative position so that the hydraulic fluid can be transmitted through it. The driven front wheels VR, VL, on the other hand, are directly connected to the second multi-directional control valve 10; 12 situated in the pressure fluid channel leading from the brake pressure generator 1 to the wheel brakes 5; 7.

In addition, a pressure fluid storage or pressure compensating reservoir 15 is provided with which the two brake circuits I, II and/or the working chambers inside the tandem master cylinder 2 are communicating in the usual manner as long as the brake is not actuated.

The wheel brakes 5, 7 of the driven front wheels VR, VL each communicate, in addition, with the reservoir 15 via a respective multidirectional control valve 16; 17, which valves are closed in the inoperative position, and via a pressure fluid return line 18.

Finally, the brake system is also equipped with an auxiliary-pressure supply system 19 comprising, substantially, an electromotively driven (Motor M) hydraulic pump 20, a brake pressure control valve 21 and a lock valve, i.e. a multi-directional control valve 22, which is switched so as to be open in the inoperative position. The control valve 21 and the multi-directional control valve 22 are hydraulically connected in series in the circuit of the hydraulic pump 20, which circuit connects the pressure side of the pump via pressure fluid lines 23, 24 with the suction side of the pump. The line 24 is also connected to the compensating reservoir 15. A relief valve 25 ensures that the maximum permissible pressure is not exceeded.

The pressure control valve 21 is connected to one of the two brake circuits, in this case to the brake circuit I of the tandem master cylinder 2, via the pressure fluid line 26, illustrated as a broken line, and comprises an internal throttle point (not depicted) by means of which-in dependence upon the master cylinder pressure which is transmitted via the line 26-the auxiliary pressure is set to a value which is proportional to the pressure in the master cylinder 2 and thus to the force acting onto the brake pedal 4. After the switching over of the multi-directional control valve 22 and thus after the blocking of the circuit including the pressure fluid lines 23, 24, however, the auxiliary pressure in the supply system 19 will rise in a short time to the maximum value which is defined by the relief valve 25.

The auxiliary-pressure supply system 19 is, via two non-return valves 27, 28 which decouple the two circuits and which interrupt pressure fluid transmission to the pump 20 when the auxiliary-pressure supply system 19 is not cut in, connected to the two brake circuits I, II of the brake pressure generator 1, that is between the two valves 9, 10; 11, 12 which are connected in series, are switched so as to be open in the inoperative position, and which connect the master cylinder 2 with the wheel brakes 5, 6; 7, 8, respectively, of a diagonal.

In the inoperative position, namely, when the brake is not actuated or during normal, i.e.

uncontrolled braking operations, all multi-directional control valves assume the depicted switching positions. In this connection, all valves are in the form of electromagnetically actuatable two-way/two-position valves, Finally, a pressure differential switch 29 for monitoring the functioning of the brakes is provided, which switch compares the pressure in the two brake circuits I, II and/or in the working chambers of the tandem master cylinder 2 with each other and with the auxiliary pressure of the auxiliary-pressure supply system 19.By means of a travel-sensitive switch 30 which, in the event of an advance movement of the intermediate piston 31 of the tandem master cylinder 2, is actuatable via an inclined ramp 32 of said piston in co-operation with a tappet 33, a warning signal is obtainable in the case of an excessive advance movement of the piston, and certain switching functions, e.g. a cutting in of the hydraulic pump 20 of the auxiiiary-pressure supply system 19, are achievable.

Finally, a switch 34 is also provided which is coupled with the brake pedal 4, which may serve as a stop-light switch, and through the intermediary of which the auxiliary-pressure supply system 19 (the pump 20) can be cut in on operating the brakes, possibly in dependence upon further conditions or criteria such as, for instance, the presence of an anti-lock control signal.

The brake system according to the invention comprises, in addition, an electronic control unit 35 to the inlets E1-E4 of which signals regarding the rotational behaviour of the wheels are transmitted, said signals being picked up by means of wheel sensors, e:g.

inductive transducers. After a processing and a logical linkage of said sensors signals by means of electronic switching circuits or micro-computers inside the control unit 35, electrical brake pressure control signals are generated which are transmitted via the outlets A, An to the individual multi-directional control valves 9-14, 16, 17, and 22 via electrical lines which are not illustrated. The signals generated by means of the pressure differential switch 29, the travel-sensitive switch 30 and the pedal switch 34 can also be transmitted to the control unit 35. The electronic control unit 35 is, expediently, also equipped with control outlets for the motor M of the hydraulic pump 20, for warning lamps (not illustrated) and the like.

The mode of operation of the brake system according to Figure 1 is as follows: During normal, uncontrolled braking operations, all multi-directional control valves 9-14, 16, 17 and 22 remain in their inoperative positions. The pressure which is controlled by actuating the brake pedal 4 and which is power-assisted by means of the unit 3 is transmitted via the hydraulically isolated brake circuits I, II and via the multi-directional control valves 9, 10, 13; 11, 12,14 to the wheel brakes 5-7, said multi-directionai control valves being switched so as to be open.

An auxiliary pressure from the supply system 19 is not required which is why the electric motor M of the hydraulic pump 20 remains out of operation-possibly apart from special cases such as, for instance, an extremely strong pedal force or a very extended advance movement of the intermediate piston 31.

If, however, a tendency to lock occurs, which tendency is reported to the electronic control unit 35 by means of the signals of the wheel sensors 36-39, the braking slip con trol action sets in. The hydraulic pump 20 is cut in. In the auxiliary-pressure supply system 19, an auxiliary pressure which is proportional to the brake pressure of the brake circuit I is generated through the intermediary of the pressure control valve 21, and is transmitted via the non-return valves 27, 28 to the two brake circuits I, II. By means of the inlet/outlet valve pairs 10, 16; 12, 17, the brake pressure in the two diagonals can now be maintained constant, reduced and, if need be, increased again, pressure fluid then being supplied from the auxiliary-pressure supply system 19.Due to a switching over of the multi-directional control valves 9, 11 situated in the pressure fluid channel from the master cylinder 2 to the wheel brakes, a further advance movement of the working pistons inside the master cylinder 2 is prevented during each control phase. By means of the multi-directional control valves 13, -14, through the intermediary of which the rear wheels are hydraulically connected, the brake pressure in the rear wheels can be maintained constant whereas, at the same time, the brake pressure in the front wheels can be further increased or reduced.

With the brake system according to Figure 1, the traction slip can, in addition, be controlled without necessitating any additional components-apart from a corresponding extension of the electronic switching circuits in the control unit 35. Namely, as soon as the sensors 37, 39 of the driven wheels signal a traction slip, the auxiliary-pressure supply system 19 is cut in and the wheel brakes 6, 8 of the non-driven rear wheels are hydraulically separated by- switching over the twoway/two-position valves 13, 14. At the same time, a transmission of pressure fluid from the auxiliary-pressure supply system 19 via the master cylinder 2 is prevented by switching over the valves 9, 11.By means of the iniet/outlet valve pairs 10, 16; 12, 17, brake pressure can now be applied onto the driven wheels in a dosed manner so that the traction slip can be reduced to an optimal value.

For generating the auxiliary pressure in the supply system 19, the hydraulic pump 20 is cut in and the pressure fluid circuit via the lines 23, 24 is blocked by switching over the two-way/two-position valve 22.

The embodiment of the inventive brake system according to Figure 2 differs from the system described in Figure 1 only in that a multi-directional control valve 40;41 is incorprorated in each pressure fluid connection to the wheel brakes 5,7 of the- frqnt wheels, said multi-directional control valves being switched so as to be open in the inoperative position.

Due to the insertion of said additional valves 40,41, the brake system can now also be used for vehicles with rear axle drive. Namely, during the traction slip control phase, the wheel brakes 5,7 of the non-driven front wheels VL, VR can be hydraulically isolated from the two diagonal circuits I, ll by means of said valves 40,41, so that the brake pressure introduced during the traction slip control phase is exclusively applied onto the driven rear wheels HR, HL.

Although in this embodiment, the multi-directional control valves 13, 14 incorporated in the connecting lines to the rear wheels are not required for the traction slip control, they are still required for the braking slip control, thus allowing the brake pressure in the front wheel brakes to be varied irrespective of the brake pressure in the rear wheel brakes, as has already been described in connection with the embodiment according to Figure 1.

The brake system according to Figure 3 differs from the embodiments according to Figures 1 and 2 in that the multi-directional control valves, through the intermediary of which the auxiliary pressure is introduced from the supply system 19 during the braking slip and traction slip control phases, have a different arrangement. In the brake system according to Figure 3, multi-directional control valves 42, 43, which are switched so as to be open in the inoperative position, are connected in series with regard to the non-return valves 27, 28. The second valve in the pressure fluid channels from the tandem master cylinder 2 to the wheel brakes namely, the valves 10 and 12 in Figure 1 and Figure 2 are omitted in the hydraulic circuitry according to Figure 3 and replaced by the valves 42 and 43.With the valve arrangement according to Figure 3, the brake pressure generator 1 and the auxiliary-pressure supply system 19 are hydraulically connected in parallel to the wheel brakes 5-7.

This type of switching is advantageous for the functional safety of the brake system in that, during uncontrolled braking operations, there is only one instead of two (and/or two instead of three) multi-directional control valves in the pressure fluid channels from the master cylinder 2 to the wheel brakes 5-8.

The brake system according to Figure 3 is also provided for rear axle drive which is why, as in the example according to Figure 2, one additional valve 40; 41, required for the traction slip control, is incorporated in the hydraulic connecting channel to the non-driven wheels VL, VR.

As for the rest, the mode of operation of the brake systems according to Figures 2 and 3 is identical to that according to Figure 1. To simplify matters, the sensors and the electronic control unit have not been illustrated in Figures 2 and 3.

Claims (8)

1. A brake system with braking slip and traction slip control for motor vehicles having one driven and one non-driven axle, including a power-assisted brake pressure generator connected to which are, via two hydraulically isolated circuits, a wheel brake of a front wheel and a wheel brake of a rear wheel, respectively; an hydraulic auxiliary-pressure supply system; valve arrangements through the intermediary of which pressure fluid flow to the wheel brakes can be blocked and pressure fluid from the auxiliary-pressure supply system can be introduced into the wheel brakes during control phases; outlet valves which, after having been switched so as to be open, connect a respective pressure fluid channel leading to the two connected wheel brakes of each circuit with a pressure compensating reservoir; multi-directional control valves in pressure fluid connecting channels to the rear wheel brakes, the valves being such as to be open in the inoperative position and being switchable into a blocking position, and the brake system further including wheel sensors and electronic switching circuits for determining the rotational behaviour of the wheels as well as for generating brake pressure control signals, characterised in that the auxiliary-pressure supply system (19) comprises an hydraulic pump (20) which can be cut in during the control action and/or on actuating the brakes, an auxiliary-pressure control valve (21) and a multi-directional control valve (22) which is incorporated in a pressure fluid circuit from the pressure side to the suction side of the pump, which is switched so as to be open in the inoperative position and which is switchable so as to be blocked during the traction slip control phase, and in that the valve~arrangements are provided with multi-directional control valves (9 12; 42, 43), which are switched so as to be open in the inoperative position, which are switchable so as to be blocked, and which are incorporated in pressure fluid channels leading from the brake pressure generator (1) and from the auxiliary-pressure supply system (19) to the wheel brakes (5-8), and through the intermediary of which valves the auxiliary-pressure supply system (19) is, instead of the brake pressure generator (1), connectible to the wheel brakes during the control phases.

2. A brake system according to claim 1, characterised in that the valve arrangements are, in each of the two hydraulically isolated circuits (I, Ill), in the pressure fluid channels leading from the brake pressure generator (1) to the wheel brakes (5 - 8) and from the auxiliary-pressure supply system (19) to the wheel brakes (5-8), each provided with at least one multi-directional control valve (9-12); 42, 43), which is switched so as to be open in the inoperative position.

3. A brake system according to claim 2, characterised in that, through the intermediary of the multi-directional control valves (9, 11; 42, 43) of the valve arrangements, which valves are switched so as to be open in the inoperative position, the brake pressure generator (1) and the auxiliary-pressure supply system (19) are hydraulically connectible in paralllel to the wheel brakes (5-8).

4. A brake system according to claim 2, characterised in that the multi-directional control valves (9-12) of the valve arrangements, which valves are incorporated in the pressure fluid channels between the brake pressure generator (1) and between the auxiliary-pressure supply system (19) and the wheel brakes (5-8), and are switched so as to be open in the inoperative position, are connected in series in the pressure fluid channels leading from the brake pressure generator (1) to the wheel brakes (5-8).

5. A brake system according to any one of claims 1 to 4 for vehicles with rear wheel drive, characterised in that additional multi-directional control valves (40, 41), which are switched so as to be open in the inoperative position, are incorporated in pressure fluid connecting channels to the front wheel brakes (5, 7), through the intermediary of which valves the pressure fluid flow to the front wheel brakes (5, 7) is blockable during the traction slip phase.

6. A brake system according to any one of claims 1 to 5, characterised in that the vehicle wheels (VL, HR; VR, HL) are connected to the two hydraulic circuits (I, II) in the form of a diagonal split.

7. A brake system according to any one of claims 1-6, characterised in that the auxiliary pressure supply system (19) can be cut in on actuating the brakes and generates an auxiliary pressure which is proportional to the pedal force during the braking slip control phase.

8. A brake system with braking slip and traction slip control substantially as herein described with reference to and as illustrated in Figure 1, Figure 2 or Figure 3 of the accompanying drawings.