GB2244315A

GB2244315A - A hydraulic dual-circuit braking system

Info

Publication number: GB2244315A
Application number: GB9107020A
Authority: GB
Inventors: Wolf-Dieter Jonner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-04-07
Filing date: 1991-04-04
Publication date: 1991-11-27
Also published as: GB9107020D0; KR910018251A; DE4011329A1; JPH04228348A

Abstract

A hydraulic dual-circuit braking system for motor vehicles having anti-skid (ABS) and drive slip control (ASR) has control valves (31-34), a return pump (27) with separate pump elements (28, 29) and a valve unit (30) for drive slip control. The valve unit (30) is formed of simple, inexpensive valves comprising a change-over solenoid valve (46) which isolates the pump outlet from the master-cylinder (15) during drive slip control, a solenoid connecting valve (47) which connects the pump inlet to the reservoir (18) of the master-cylinder and a pressure-controlled blocking valve (48) which is closed by master-cylinder pressure during normal braking but during drive slip control connects the pump outlet to a pressure limiting valve (51) in a return line to the reservoir (18). A pre-charging pump (52) may be provided. In the embodiment shown the two driving wheels (11, 12) are in the same circuit. Alternatively a diagonal connection may be used in which case two valves (46) and two valves (47) are required for the two driving wheels. <IMAGE>

Description

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-1DESCRIPTION

A HYDRAULIC DUAL-CIRCUIT BRAKING SYSTEM The invention relates to a hydraulic dual-circuit braking system for a motor vehicle and an anti-skid system (ABS) and drive slip control (ASR).

In a known dual-circuit braking system (DE 38 16 073 Al) having a master cylinder with two brake circuit outlets for a front/rear axle or front/rear brake circuit distribution, a valve unit has a charging valve and a change-over valve. The charging valve, which is a two-port, twoposition solenoid valve with a hydraulic control inlet, is disposed in the intake line between the inlet of a respective pump element of a return pump associated with the brake circuit of the drive wheels and a brake fluid reservoir, and is connected by its control inlet to a brake circuit outlet of the master brake cylinder. When the brake pedal is actuated, the charging valve closes the intake line. A change-over valve, which is a three-port. two-position solenoid valve with spring return, is disposed in the connecting line between the master brake cylinder and the brake circuit of the drive wheels. In its non-excited basic position, it connects the control valves of the brake circuit at the inlet side of the pump element to the master brake -2cylinder, and, in its switched-over position which is caused in the event of drive slip control, it cuts-off this connection and connects the outlet of the respective pump element to the brake fluid reservoir by way of a pressure-limiting valve. In drive slip control operation, the pump element in the brake circuit of the drive wheels sucks brake fluid out of the brake fluid reservoir by way of the charging valve and delivers it by way of the control valves into the wheel brake cylinders of the drive wheels, namely into the wheel brake cylinder of the drive wheel which is slipping. Excess brake fluid is delivered by way of the switched-over change-over valve and by way of the pressure-limiting valve back into the brake fluid reservoir. Because the pressure-limiting valve is separated by the change-over valve from the brake circuit and is not connected to the brake circuit until, in drive-slip control operation, said brake circuit is separated from the master brake cylinder, the pressure limiting threshold of the brake pressure supply in drive slip control operation can be fixed arbitrarily and independently of other influencing factors, for example brake pressure on brake pedal actuation or brake supply pressure in anti-skid operation.

The invention resides in a hydraulic dual-circuit braking system for a motor vehicle having an anti-skid system and drive-slip control, and having a master brake cylinder, which has two separate brake circuit outlets, for discharging brake pressure upon actuating a brake pedal, a brake fluid resevoir which is connected to the master brake cylinder, a four-passage hydraulic aggregate, which is connected to the two brake circuit outlets of the master brake cylinder and has four outlet passages divided in pairs between two brake circuits, for connection to wheel brake cylinders of the vehicle wheels, electromagnetic control valves associated with each outlet passage for discharging a wheel-slip- dependent brake pressure in the wheel brake cylinders, and a return pump having two separate pump elements, effective in each brake circuit respectively, for returning brake fluid in the event of brake pressure reduction, which pump elements are each connectible at their inlet side by the control valves to outlet passages belonging to one brake circuit and are connected at their outlet side to the brake circuit outlet, associated with the brake circuit, of the master brake cylinder, and a valve unit for providing a brake supply pressure in the event of drive slip control by connecting the or each pump element of the return pump, which is associated -4with a brake circuit containing at least one drive wheel, on the one hand by its inlet side to the brake fluid reservoir and, on the other hand by separating such pump element at its outlet side from the master brake cylinder and, with the insertion of a pressurelimiting valve, connects it to the brake fluid reservoir, wherein said valve unit comprises at least one changeover valve and at least one connecting valve which are two-port, two-position solenoid valves, and a pressure- controlled shut-off valve, which is connected by its hydraulic control inlet to a brake circuit outlet of the master brake cylinder, the or each changeover valve being disposed in the connecting line respectively between the or each pump element of the return pump associated with a brake circuit having at least one drive wheel and the master brake cylinder and, in its switched-over position which is brought about in the event of drive-slip control, closing such connecting line, the or each connecting valve being disposed in an intake line between the inlet of the or each pump element associated with a brake circuit having at least one drive wheel and the brake fluid reservoir, and only opening the intake line when in its valve position brought about in the event of drive slip control, and wherein a pressure-limiting valve is disposed in a return flow line, which connects the -5outlet of the or each pump element of the return pump associated with a brake circuit having at least one drive wheel to the brake fluid reservoir, and a shutoff valve is disposed in the line portion of the return line between such pump element or elements and the pressurelimiting valve and, in the event of control pressure at its control inlet, switches into a valve position which closes the return line.

This has the advantage that, while keeping the freely selectable pressurelimiting threshold of the brake supply pressure in drive slip control operation, the valve unit can be made with simpler and less expensive valves. With respect to a three-port, twoposition valve, the two-port, two-position valve used in accordance with the invention has a less complex hydraulic interface.

The dual-circuit braking system according to the invention is suitable both for front axle/rear axle brake circuit distribution as well as for diagonal brake circuit distribution. In the case of diagonal brake circuit distribution, the valve unit must have two changeover and connecting valves respectively; in the case of front/rear brake circuit distribution, one changeover valve and one connecting valve are sufficient.

In the case of long line portions between the brake fluid reservoir and the return pump, it is advantageous, in accordance with a further embodiment of the invention, to provide a pre-charging pump, which is connected at its inlet side to the brake fluid reservoir and at its outlet side to the inlet of each pump element of the return pump associated with a brake circuit with at least one drive wheel. A pressure- limiting valve, which is connected in parallel with the pre-charging pump, limits the precharging pressure of the pre-charging pump to, for example, 10 bar. The connection of the pre-charging pump, as well as the connection of the intake line existing between the inlet of the pump element to the brake fluid reservoir is advantageously made at the underside of the brake fluid reservoir, and the connection of the return line existing in drive slip control operation from the outlet of the pump element to the brake fluid reservoir is made at the top of the brake fluid reservoir. In this way, any air bubbles, which are formed on relief of the brake fluid at the pressure-limiting valve, are prevented from entering directly into the pre-charging circuit of the precharging pump.

The invention is further described, by way of example, with reference to the accompanying drawings, in which:

Fig.1 is a block diagram of a dual-circuit braking system, having front/rear brake circuit distribution, an anti-skid system and drive slip control, for a passenger vehicle; and Fig.2 is a block diagram of a dual-circuit braking system, having diagonal brake circuit distribution, an anti-skid system and drive slip control, for a passenger vehicle.

In the hydraulic dual-circuit braking system shown in the block diagram in Fig.1 and having front/rear or front 4xle/rear axle brake circuit distribution, also known as black/white brake circuit distribution, an anti-skid system (ABS) and drive slip the latter also being known as predrive control, for a passenger vehicle, the wheel brake cylinders 10 of the drive wheels 11,12 are disposed in one brake circuit and the wheel brake cylinders 10 of the non-driven wheels 13,14 are disposed in the other brake circuit. In general, the drive wheels 11,12 are in such case the rear wheels of the passenger vehicle. The dual-circuit braking system includes in a known manner a master brake cylinder 15, which has two separate brake circuit outlets 16, 17 connected respectively to the two brake circuits, and is connected to a brake fluid reservoir control (ASR) -818. When a brake pedal 19 is actuated, an equally high brake pressure is discharged by way of the two brake circuit outlets 16,17 into the brake circuits.

The dual-circuit braking system further includes a four-passage hydraulic aggregate 20, having four outlet passages 21 to 24, which are divided in pairs between two brake circuits, and two inlet passages 25,26, which are divided between the two brake circuits. A respective wheel brake cylinder 10 of the wheels 11 to 14 is connected to each outlet passage 21 to 24. A control valve 31 to 34 is associated with each outlet passage 21 to 24. The control valves 31 to 34 are controlled by a control electronics (not shown) and build up a brake pressure in the associated wheel brake cylinders 10 which is dependent upon wheel slip. A return pump 27, which is a component of the four-passage hydraulic aggregate 20, has two pump elements 28,29 which are driven jointly by an electric motor 35. The pump elements 28,29 serve to return brake fluid in the event of pressure reduction in the brakes. A respective pump element 28 or 29 is effective in each brake circuit and is connected at its inlet side to the control valves 33,34 or 31,32 respectively which are effective in the brake circuit, and at its outlet side to an inlet passage 25 or 26 respectively of the four-passage hydraulic aggregate -920. In the connection between the pump element 29 and the associated control valves 31,32 for the wheel brake cylinders 10 of the drive wheels 11,12, there is disposed a non-return valve 45, with a flow-through direction towards the pump element 29. A pump inlet valve 36 and a pump outlet valve 37 are disposed upstream of and beyond each pump element 28, 29. Lowpressure accumulators 38,39 are connected to the pump inlet valves 36 of the two pump elements 28,29, while a damping chamber 40 is disposed in the connection between the pump outlet valves 37'and the associated inlet passage 25 or 26 respectively. The two inlet passages 25,26 of the four-passage hydraulic aggregate 20 are connected by way of a respective connecting line 41 or 42 to the associated brake circuit outlet 16 or 17 of the master brake cylinder 15. Each control valve 31 to 34 is constituted by a valve combination of an inlet valve 43 and an outlet valve 44. In their basic position, the inlet valves 43 permit unimpeded flow from the inlet passages 25,26 to the outlet passages 21 to 24 of the four-passage hydraulic aggregate 20 and hence to the wheel brake cylinders 10 of the wheels 11 to 14. In the operating position, which can be brought about by solenoid excitation, the inlet valves 43 close these off. In their operated position, which can be brought about by magnetic 1 _10excitation, the outlet valves 44 connect the outlet pasages 21 to 24, and hence the wheel brake cylinders 10, to the pump inlet valves 36 of the two pump elements 28,29 and, in their non-excited basic position, they close off this connection. The abovementioned non-return valve 45 is disposed in the connection of the outlet valves 44 of the control valves 31,33 associated with the drive wheels 11,12.

A valve unit 30 serves to provide a brake supply pressure in the event of drive slip control (ASR operation). To do this, the valve unit 30 has a changeover valve 46, a normally-closed or connecting valve 47 and a normally-open or shut-off valve 48. The changeover valve 46 and the connecting valve 47 are two-port, two-position solenoid valves with spring return, while the shut-off valve 48 is a pressurecontrolled two- port, two-position valve. The changeover valve 46 is disposed in the connecting line 42 between the brake circuit outlet 17 of the master brake cylinder 15 and the inlet passage 26 of the four-passage hydraulic aggregate 20 and blocks this connecting line 42 in its switched-over position, which is brought about in the event of drive slip control. The connecting valve 47 is disposed in an intake line 49, which connects the pump inlet valve 36 of the pump element associated with the brake circuit of the drive wheels 11,12 to the brake fluid reservoir 18. In its non-excited basic position, the connecting valve 47 closes the intake line 49 and, in its switched-over position brought about in the event of drive slip control, opens the latter. The shut-off valve 48 is disposed in a return line 50, which connects the inlet passage 26 to the brake fluid reservoir 18, while its hydraulic control inlet is connected to the brake circuit outlet 17 of the master brake cylinder 15. In the event of control pressure at the control inlet, the shut-off valve 48 switches over and closes the return line 50. In the line portion of the return line 50 between the shut-off valve 48 and the brake fluid reservoir 18 there is disposed a pressure-limiting valve 51 having a direction of opening which is towards the brake fluid reservoir 18.

The changeover valve 46 and the connecting valve 47 are also controlled by the above-mentioned control electronics. When this control electronics 30 is informed of drive slip at at least one of the drive wheels 11,12 by wheel slip sensors (not shown), the connecting valve 47 and the changeover valve 46 are switched-over. The pump element 29 in the brake circuit of the drive wheels 11,12, then sucks brake fluid out of the brake fluid reservoir 18 by way of -12the connecting valve 47 and feeds it under pressure into the wheel brake cylidners 10 of the drive wheels 11,12. If only one drive wheel slips, for example the drive wheel 11, the inlet valve 43 of the control valve 32 associated with the non-slipping drive wheel 12 is switched over, such that the wheel brake cylinder 10 of the non-slipping drive wheel 12 is shut off from the brake supply pressure. Brake pressure is then built up by way of the inlet valve 43 of the control valve 31 in the wheel brake cylinder 10 of the slipping drive wheel 11, which pressure brakes the slipping drive wheel. The required brake pressure is adjusted by pressure modulation, which is done by switching the inlet and outlet valves 43,44. Excess brake fluid is delivered by way of the shut-off valve 48 and the pressure-limiting valve 51 back into the brake fluid reservoir 18. Towards the end of the drive slip control operation, when no further drive slip is sensed, both the inlet and the outlet valves 43, 44 of the control valve 31 are switched over. In this position of the control valve 31, brake fluid flows out of the wheel brake cylinder 10 of the drive wheel 11 by way of the non-return valve 45 into the low- pressure accumulator 39 and is delivered from here by the pump element 29 by way of the return line 50 with the shut-off valve 48 and the pressure- limiting 1 -13valve 51 back into the brake fluid reservoir 18. brake pressure is once again reduced and the lowpressure accumulator 39 emptied, such that, in the event of a subsequent anti-skid operation, the full capacity of the low-pressure accumulator 39 is available for brake pressure reduction. Subsequently, the connecting valve 47 and the changeover valve 46 are moved back into their basic positions, such that the brake fluid reservoir 18 is once again closed off from the brake circuit and the latter is connected to the master brake cylinder 15. In the event of drive slip of the two drive wheels 11,12, the inlet and outlet valves 43, 44 of the two control valves 31,32 are triggered in the above-described manner. On actuation of the brake pedal, the shut-off valve 48 is switched over, such ihat the return flow line 50 from the inlet passage 26 of the four-passage hydraulic aggregate 20 to the brake fluid reservoir 18 is closed and no brake fluid can flow out of themaster brake cylinder 15 by way of the pressure-limiting valve 51 into the brake fluid reservoir 18.

If the intake line 49 between the brake fluid reservoir 18 and the pump element 29 is long, it is advisable to provide a pre-charging pump 52, as shown by the dotted lines in Fig.l. The pre-charging pump 52 is connected at its inlet side to the brake fluid -14reservoir 18 and at its outlet side by way of a nonreturn valve 53 to the inlet valve 36 of the pump element 29. A pressure limiting valve 54, which is connected in parallel with the pre-charging pump 52 with a direction of opening towards the brake fluid reservoir 18, limits.the pre- charging pressure of the pre-charging pump 52.

In the hydraulic dual-circuit braking system shown in the block diagram in Fig.2 and having diagonal brake circuit distribution, the drive wheels 11,12 belong to two different brake circuits. Generally, the drive wheels 11,12 are the front wheels of the passenger vehicle. In so far as the dual-circuit braking system coincides with the dual-circuit braking system with front/rear brake circuit distribution described with reference to Fig.1, the same components have been given the same reference numerals. The valve unit 30 has two changeover valves 46,461 as well as two connecting valves 47,47', which are each identical to the ones described with reference to Fig.l. A respective changeover valve 46 or 46, is disposed in each of the two connecting lines 42,41 between the master brake cylinder 15 and the fourpassage hydraulic aggregate 20. Each pump element 29,28 of the return pump 27 is connected by way of respective intake line 49 or 49, to the brake fluid 41 -15reservoir 18. In each intake line 49,491 there is disposed, as described, a respective connecting valve 47 or 47'. Each inlet passage 25, 26 of the fourpassage hydraulic aggregate 20 is connected to the return line 50 to the brake fluid reservoir, wherein the return line 50 is connected to the top of the brake fluid reservoir 18 and the intake line 49,49' is connected to the bottom of the brake fluid reservoir 18. This prevents air bubbles, which are formed when the brake fluid foams as a result of relief at the pressure-limiting valve 51, entering directly into the intake lines 49,49'. In the event of a long intake line, a pre- charging pump may also be provided in this case, as in the dual-circuit braking system of Fig.l.

The method of operation of the dual-circuit braking system with diagonal brake circuit distribution in drive slip control operation is the same as described with reference to Fig. 1, with the sole difference that the inlet valves 43 of the control valves 31, 34, which are associated with the wheel brake cylinders 10 of the non-driven wheels 13, 14, are triggered during the entire drive slip control operation. and close.off the wheel brake cylinders 10 from the brake supply pressure. This switching-over from the inlet valves 43 of the control valves 31 and 34 for the non-driven wheels 13, 14 may be avoided if -16these inlet valves 43 are connected on the inlet side not to the inlet passages 25, 26 of the four-passage hydraulic aggregate 20 but directly to the brake circuit outlets 17, 16 of the master brake cylinder 15.

The invention is not restricted to the embodiments described. Thus, for example, the control valves 31 to 34 may also be formed by three-port, three-position solenoid valves, which, in their basic position, permit unimpeded flow between the inlet passages 25, 26 and the outlet passages 21 to 24, in their middle position, brought about by magnetic excitation at half maximum current, they close off the outlet passages 21 to 24, and in their end position, brought about by magnetic excitation at maximum current, they connect the outlet passages 21 to 24 to the low pressure accumulators 39, 38 or the inlet valves 36 of the pump elements 29, 29 of the return pump 27.

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Claims

-17CLAIMS

1. A hydraulic dual-circuit braking system for a motor vehicle having an anti-skid system and driveslip control, and having a master brake cylinder, which has two separate brake circuit outlets, for discharging brake pressure upon actuating a brake pedal, a brake fluid resevoir which is connected to the master brake cylinder, a four-passage hydraulic aggregate, which is connected to the two brake circuit outlets of the master brake cylinder and has four outlet passages divided in pairs between two brake circuits, for connection to wheel brake cylinders of the vehicle wheels, electromagnetic control valves associated with each outlet passage for discharging a wheel-slip-dependent brake pressure in the wheel brake cylinders, and a return pump having two separate pump elements, effective in each brake circuit respectively, for returning brake fluid in the event of brake pressure reduction, which pump elements are each connectible at their inlet side by the control valves to outlet passages belonging to one brake circuit and are connected at their outlet side to the brake circuit outlet, associated with the brake circuit, of the master brake cylinder, and a valve unit for providing a brake supply pressure in the event of drive slip control by connecting the or each _18pump element of the return pump, which is associated with a brake circuit containing at least one drive wheel, on the one hand by its inlet side to the brake fluid reservoir and, on the other hand by separating such pump element at its outlet side from the master brake cylinder and, with the insertion of a pressurelimiting valve, connects it to the brake fluid reservoir, wherein said valve unit comprises at least one changeover valve and at least one connecting valve which are two-port, two-position solenoid valves, and a pressure-controlled shut-off valve, which is connected by its hydraulic control inlet to a brake circuit outlet of the master brake cylinder, the or each changeover valve being disposed in the connecting line respectively between the or each pump element of the return pump associated with a brake circuit having at least one drive wheel and the master brake cylinder and, in its switched- over position which is brought about in the event of drive-slip control, closing such connecting line, the or each connecting valve being disposed in an intake line between the inlet of the or each pump element associated with a brake circuit having at least one drive wheel and the brake fluid reservoir, and only opening the intake line when in its valve position brought about in the event of drive slip control, and wherein a pressure-limiting valve is -19disposed in a return flow line, which connects the outlet of the or each pump element of the return pump associated with a brake circuit having at least one drive wheel to the brake fluid reservoir, and a shutoff valve is disposed in the line portion of the return line between such pump element or elements and the pressure-limiting valve and, in the event of control pressure at its control inlet, switches into a valve position which closes the return line.

2. A braking system as claimed in claim 1, in which a pre-charging pump is connected by its inlet side to the brake fluid resevoir and by its outlet side by way of a non-return valve to the inlet of the or each pump element which is associated with a brake circuit

3.

having at least one drive wheel.

A braking system as claimed in claim 2, in which a pressure-limiting valve having an opening direction towards the brake fluid reservoir is connected in parallel with the pre-charging pump.

4. A braking system as claimed in any of claims 1 to 3. in which the connection of the or each intake line is made to the bottom of the brake fluid reservoir and the connection of the return line is made to the top of the brake fluid reservoir.

5. A braking system as claimed in any of claims 1 to 4, in which the wheel brake cylinders of the 1 -20drive wheels are disposed in a common brake circuit, and in which the valve unit has one change-over valve in the connecting line from the one pump element which is associated with the brake circuit of the drive wheels and the master brake cylinder. and a connecting valve in the intake line of this pump element to the brake fluid reservoir.

6. A braking system as claimed in any of claims 1 to 4, in which the wheel brake cylinders of the drive wheels are disposed in different brake circuits, and the valve unit has two change-over valves and two connecting valves, and in which each change-over valve is disposed in a respective connecting line of the respective pump element to the master brake cylinder and each connecting valve is disposed in a respective intake line from the respective pump element to the brake fluid reservoir.

7. A vehicle braking system constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

Published 1991 at The Patent Office. Concept House. Cardiff Road, Newport. Gwent NP9 1RH. Further copies njay be obtained frorn Sales Branch. Unit 6. Nine Mile Point, Cwmfelinfach. Cross Keys, Newport. NP1 7HZ. Printed by Multiplex techniques lid, St Mary Cray, Kent.

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