GB2244107A

GB2244107A - Anti-lock controlled brake system

Info

Publication number: GB2244107A
Application number: GB9104763A
Authority: GB
Inventors: Hans-Dieter Reinartz; Helmut Steffes
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1990-05-17
Filing date: 1991-03-07
Publication date: 1991-11-20
Anticipated expiration: 2011-03-07
Also published as: FR2662128B1; FR2662128A1; GB2244107B; DE4015884A1; GB9104763D0; JPH04231250A

Abstract

in an anti-lock-controlled brake system comprising a braking pressure generator (6) with a master cylinder, an auxiliary hydraulic pressure pump (2) and slip-controlled electromagnetically-operable inlet valves (7) and outlet valves (14) inserted into the pressure medium lines a hydraulically-controlled pressure limiting valve (3) is provided and acted on at its control in lets (15) both by the pressure of the pump (2) and by a pressure acting on the wheel brake (1), the pressure limiting valve (3) opening towards a pressure-less return line (13) in order to control the pump pressure in the event of the differential pressure exceeding a defined pre-pressure. The defined pressure may be set by a spring (16). <IMAGE>

Description

1 1 2:2 A- 'I X 0 17-1 ANTI-LOCK-CONTROLLED BRAKE SYSTEM, IN PARTICULAR

FOR AUTOMOTIVE VEHICLES This invention relates to an anti-lock-controlled brake system.

More specifically, the present invention relates to an anti-lock-controlled brake system for automotive vehicles, comprising a pedal-operated braking pressure generator accommodating a master cylinder to which at least one wheel brake is connected via a main pressure line, an auxiliary hydraulic pressure pump connected to an auxiliary pressure line, associated wheel sensor and electronic control means for detecting the rotational behaviour of wheels of the vehicle and for generating electric braking pressure control signals which, for the purpose of slip control, control electromagnetically operable inlet valves and outlet valves inserted into the pressure lines.

In a known slip-controlled brake system of the above type described in German Published Patent Application No. 3627000, a tandem master cylinder with a pneumatic brake booster connected upstream thereof is used as braking pressure generator. An auxiliary pressure supply system comprises two hydraulic pumps allocated, respectively, to associated brake circuits connecting wheel brakes diagonally. In the event of a slip-controlled brake operation, an auxiliary pressure, proportional to the foot pressure, is introduced by means of control valves from auxiliary pressure supply system. This dynamic auxiliary 1 2 pressure, on the one hand, is transferred to the static brake circuits connected to the master cylinder. On the other hand, the dynamic pressure acts on the wheel brakes. Inlet valves are inserted into the hydraulic circuit for the purpose of slip control. Normally, the inlet valves are open but it is possible to block pressure medium delivery to the respective wheel brakes by means of the inlet valves upon an imminent lock-up of a wheel.

Further, outlet valves are provided at the wheel brakes. If necessary, it is possible to drain pressure medium from the wheel brake to the storage reservoir via the outlet valves. Upon the onset of slip control, the auxiliary pressure pumps are activated via an electric motor and a controlled pressure is introduced into the wheel brakes via the inlet and outlet valves. For reasons of safety, moreover, the pistons within the tandem master cylinder are reset or arrested by means of the dynamic hydraulic circuit.

A disadvantage of the above-described brake system is that, in dependence on the dynamic flow conditions and on the pressure modulated by the operating frequencies of the valves, sound vibrations are transmitted to the brake system via the fluid so that parts associated with the brake system and having mass constituting an oscillatory circuit, tend to build up resonance vibrations, according to their specific natural frequency of oscillation. Apart from the mechanic strain caused by pressure pulses of varying intensity, the resultant noise level desirably needs to be reduced. The relatively high delivery pressure of the auxiliary pressure pump is a further disadvantage. This pressure does not permit adaptation to the actual needs during brake slip control and can thus, beyond the actual control characteristic, contribute to the increase in noise level.

It is thus an object of this invention to improve an anti-lock-controlled brake system of the aforesaid type so as to be able to reduce the above-described noise development, caused by pressure pulses of varying intensity, 1 3 and the sound emissions caused thereby. Further, it is an object of this invention to provide an improvement in the control characteristic beyond maintaining the high quality of control.

According to the present invention there is provided an anti- lock-contro 1 led brake system for automotive vehicles comprising a pedal-operated braking pressure generator accommodating a master cylinder to which at least one wheel brake is connected via a main pressure line, an auxiliary hydraulic pressure pump connected to an auxiliary pressure line, associated wheel sensor and electronic control means for detecting the rotational behaviour of wheels of the vehicle and for generating electric braking pressure control signals which, for the purpose of slip control, control electromagnetically operable inlet valves and outlet valves inserted into the pressure lines, characterised in that a pressure limiting valve is arranged to be acted on by the pressure of the auxiliary pressure pump and by pressure acting on a wheel brake and to establish hydraulic communication towards a pressure-less return line in order to control the pump pressure in the event of a defined prepressure at the valve being exceeded.

Thus, this invention is essentially based on the fundamental idea to effect a control or rather a limitation of the pump pressure and pump volume in dependence on the wheel brake pressure in order to adapt the relatively high pump pressure individually to the real needs of brake slip control.

In order to prevent pressure medium from unintentionally returning into a master cylinder of the generator and, hence, into the pressureless storage reservoir during automatic braking pressure control an embodiment of the invention includes a locking valve inserted into the main pressure line between the generator master cylinder and the inlet valve associated with the wheel brake, the locking valve interrupting pressure medium communication between the braking pressure generator and the 4 wheel brake in dependence on the controlled pressure of the auxiliary pressure pump.

In carrying out the invention the brake system may be provided with a compression spring for generating the pre- pressure in the pressure limiting valve (e.g. 20 bar) in order to maintain the desired pressure difference at the inlet valve.

A non-return valve, opening in the direction of the generator master cylinder and arranged in parallel with the main pressure line, is expediently provided between the braking pressure generator and the hydraulically actuatable locking valve so that, for operationally relevant considerations, a rapid pressure reduction is ensured in the wheel brake, if needed.

Because of the axle load distribution typical of driving dynamics and because of the resultant braking force distribution between the front and rear axle brakes control of the auxiliary pressure pump, in dependence on the braking pressure in the front wheel brake, may be achieved by arranging that the pressure limiting valve has a hydraulic connection towards the brake of a front axle.

A construction of embodiment for realising a variable pump delivery volume or pump pressure, may provide for varying the pump stroke of the usual piston-type pumps via an eccentric or other adjusting mechanism.

A further embodiment of the invention in terms of control engineering provides for the adaptation of the pump pressure and delivery volume, respectively, to a characteristic-data-specific speed/torque variation while maintaining a constant pump performance.

By way of example the present invention will now be described with reference to the single-figure accompanying drawing which shows the basic hydraulic circuitry of an anti-lock-controlled brake system according to the present invention with diagonal brake circuit allocation. For the sake of clarity only one of the two brake circuit diagonals is shown in the drawing and described in the following II tt description.

The brake system shown in the drawing includes a braking pressure generator 6 which, via branched main pressure lines 5, establishes hydraulic communication with the wheel brakes having diagonal allocation. The braking pressure generator 6 has a tandem master cylinder 10 and a vacuum booster 11, a storage reservoir 4 being attached directly in a conventional manner to the tandem master cylinder 10. Disposed in one main pressure line 5 are a locking valve 8 associated with the braking pressure generator 6 and an inlet valve 7 appertaining to a wheel brake 1 of the front axle. The inlet valve 7 as shown in the drawing is electromagnetically actuatable, but the arrangement also permits the replacement of the electromagnetically actuatable inlet valve 7 by a hydraulically operable orifice. This, however, requires a special adaptation of the control algorithm, to the needs of automatic braking pressure control. In a branch between the locking valve 8 and the inlet valve 7 and including the main pressure line 5, associated with a second diagonal wheel brake 11 there is provided an inlet valve 7, as well as an auxiliary pressure line 12 connecting an auxiliary pressure pump 2 with main pressure lines 5. A return line 13, connecting the diagonal wheel brakes 1 and 11 with the storage reservoir 4, accommodates electromagnetically controllable outlet valves 14 at positions between the wheel brakes 1 and 11 and their appertaining inlet valves 7 and further communicates with the suction line of the auxiliary pressure pump 2 as well as with a hydraulic connection of a pressure limiting valve 3. Via control pressure lines 15, branched off from the auxiliary pressure line 12 and from the main pressure line 5, the pressure limiting valve 3 communicates with the auxiliary pressure pump 2, on the one hand, and with the wheel brake 1 of the front axle, on the other hand. Further, in an OR logic circuit, the second wheel brake 11 may be linked with the pressure limiting valve 3. Due to the provision of a compression spring 16 at 6 the pressure limiting valve 3 a pre-stressing force is effectively provided for the generation of a desired hydraulic pre-pressure. Branched off between the braking pressure generator 6 and the hydraulically controllable locking valve 8 is a non-return valve 9 connected in a pressure medium connection line 18 arranged in parallel to the main pressure line, the non-return valve 9 communicating with the respective appertaining wheel brake 11.

Referring now to the mode of operation of the brake system illustrated it may be mentioned that the valve conditions shown in the drawing generally apply to the brake-released position as well as to the slip-free normal operative positioning of the brake.

In the slip-free operating position of the brake, the actuation of the braking pressure generator 6 will cause a pressure proportional to the foot pressure on the brake pedal to be built up in the main pressure line 5 via the locking valve 8 which is open in the basic position and via the inlet valves 7 appertaining to the wheel brakes 1 and 11. The outlet valves 14 associated with the respective wheel brakes 1 and 11 and the non-return valve 9 remain closed in their basic positions while the pressure of the main pressure line 5 is present in the hydraulic control pressure line 15 of the pressure limiting valve 3 in a manner which balances the action of the compression spring 16. The control pressure line 15, connecting the pressure limiting valve 3 with the auxiliary pressure line 12, remains unpressurised for the time being due to non-return valve 17 being. shut off in the direction of the inactive auxiliary pressure pump 2.

As soon as brake slip signals resulting from low friction values between the vehicle wheels and the road surface are transmitted to an electronic slip control unit (not illustrated in the drawing) to indicate that a vehicle wheel is overbraked, a reduction of the braking pressure, or of the pressure fluid volume, in the threatened wheel brake 1 is produced within the scope of anti-lock control by 7 C arranging that an electric signal form the electronic control unit causes the appropriate outlet valve 14 to open and the appertaining inlet valve 7 to close. The electronic control unit also brings about starting of the auxiliary pressure pump 2 so as to provide the system with auxiliary pressure. The auxiliary pressure switches the locking valve 8 into its locking position so that the braking pressure generator 6 is separated from the pump pressure prevailing in the main pressure line 5. Due to the action of pressure limiting valve 3 preadjusted by means of the compression spring 16 as well as because of the hydraulic connection of the pressure limiting valve 3 with the wheel brake 1 at the front axle and due to the hydraulic communication towards the auxiliary pressure pump 2, the pump pressure is automatically regulated in dependence on the wheel brake pressure active on the pressure limiting valve 3 in dependence on the spring-forceadjusted hydraulic prepressure. Consequently, the pump pressure is adjusted by the pressure limiting valve 3 to the respective wheel brake pressure plus the preadjusted pre-pressure. Thus, on the one hand, if needed, the pressure build-up of the auxiliary pressure pump 2 can take place more quickly since, by means of the illustrated hydraulic brake system, the auxiliary pressure has to overcome a pressure which is relatively smaller. Moreover, the noise emission of the inlet valve 7 is markedly reduced as the pressure difference at the inlet valve 7 cannot be higher than the pre-pressure of the pressure limiting valve 3 provided by the compression spring 16.

As soon as brake slip signals from known wheel sensors cause the electronic control unit to effect braking pressure control up to high friction values following the closure of the appropriate outlet valve 14 for initiating the pressure build-up phase, the appertaining inlet valve 7 is re-opened.

The dynamic pressure generated by the auxiliary pressure pump 2 and metered in via the pressure limiting valve 3 can adapt itself relatively fast to the required pressure level.

8 By analogy with braking pressure control down to low friction values, in the brake-slip-controlled operation up to high friction values, the pressure difference at the inlet valve 7 is kept constant at, for instance, 20 bar by the adjusted pre-pressure at the pressure limiting valve 3 under all operating conditions so that a considerable noise reduction will become evident at the inlet valve 7.

Controlling the pump pressure in dependence on the respective braking pressures prevailing in the wheel brakes, especially in the front axle brake, ensures individual adaptation of the auxiliary hydraulic energy to the varying friction values between road surface and vehicle wheel in conformity with actual needs. This means that the auxiliary pressure pump 2 meters in a lower auxiliary pressure in case of low friction values and that it increases the pressure correspondingly in case of high friction values so that, at least during slip control down to low friction values, it is possible to achieve a considerable improvement in the quality of control.

-1 9

Claims

CLAIMS:

1. An anti- lock- controlled brake system for automotive vehicles comprising a pedal-operated braking pressure generator accommodating a master cylinder to which at least one wheel brake is connected via a main pressure line, an auxiliary hydraulic pressure pump connected to an auxiliary pressure line, associated wheel sensor and electronic control means for detecting the rotational behaviour of wheels of the vehicle and for generating electric braking pressure control signals which, for the purpose of slip control, control electromagnetically operable inlet valves and outlet valves inserted into the pressure lines, characterised in that a pressure limiting valve (3) is arranged to be acted on by the pressure of the auxiliary pressure pump (2) and by pressure acting on a wheel brake (1) and to establish hydraulic communication towards a pressure-less return line (13) in order to control the pump pressure in the event of a defined pre-pressure at the valve (3) being exceeded.

2. An-anti-lock-controlled brake system as claimed in claim 1, characterised in that a locking valve (8) is arranged in the main pressure line (5) between the braking pressure generator (6) and the inlet valve (7) appertaining to a wheel brake (1), the locking valve being capable of blocking pressure medium communication between the braking pressure generator (6) and the wheel brake (1) in dependence on the controlled pressure of the auxiliary pressure pump (2).

3. An anti-lock-controlled brake system as claimed in claim 1 or claim 2, characterised in that a compression spring (16) is provided for generating the pre-pressure in the pressure limiting valve (3).

4. An anti-lock-controlled brake system as claimed in any of claims 1 to 3, characterised in that the pre-pressure is adjustable to 20 bar.

5. An anti-lock-controlled brake system as claimed in claim 2 or claim 3 or 4 dependent on claim 2, characterised in that at least one pressure medium connection line (18) is connected between the braking pressure generator (6) and the locking valve (8), and accommodates a non-return valve (9) blocking in the direction of the wheel brake (1) and 5 arranged in parallel with the main pressure line (5).

6. An anti-lock-controlled brake system as claimed in any preceding claim, characterised in that the pressure limiting valve (3) has a hydraulic connection towards the wheel brake (1) of a f ront axle in order to control the delivery pressure and the delivery volume of the auxiliary pressure pump (2).

7. An anti-lock-controlled brake system as claimed in any of the preceding claims, characterised in that an adjusting mechanism, such as an eccentric adjusting mechanism, is provided for varying the effective delivery volume of the auxiliary pressure pump (2),, the adjusting mechanism preferably being able to vary the piston stroke.

8. An anti-lock-controlled brake system as claimed in any of the preceding claims, characterised in that the auxiliary pressure pump (2) is provided with a control device adjusting respectively the pump pressure and the delivery volume in accordance with a brake-slip-adaptive speed/ torquecharacteristic-data field subject to constant pump performance.

9. An anti-lock-controlled brake system as claimed in any of the preceding claims, characterised in that the braking pressure generator is auxiliary force assisted by means of a vacuum booster.

10. An anti- lock-contro 1 led brake system substantially as hereinbefore described with reference to the accompanying drawing.

Published 1991 at The Patent Office. Concept House, Cardiff Road, NewporL Gwent NP9 IRH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Kzys. NewporL NP1 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.