GB2239913A

GB2239913A - Hydraulic brake system with braking slip and/or traction slip control

Info

Publication number: GB2239913A
Application number: GB9022076A
Authority: GB
Inventors: Jochen Burgdorf
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1990-01-13
Filing date: 1990-10-11
Publication date: 1991-07-17
Anticipated expiration: 2010-10-11
Also published as: FR2657059B1; DE4000837B4; GB2239913B; DE4000837A1; FR2657059A1; GB9022076D0; JPH04212664A

Abstract

A hydraulic brake system with braking slip and/or traction slip control has a pump 4 inserted into a brake conduit 2 through which pressure fluid is displaced from the master brake cylinder 1 to the wheel brake 3 in a normal deceleration process, the pump being inserted with its intake side in communication with the master cylinder and the pressure side in communication with the wheel brake. As the master cylinder pressure prevails on the intake side of the pump when it is switched on at the beginning of the braking slip control, the pump can very quickly reach the full discharge capacity, thereby enhancing the control quality. Moreover, the risk of air being sucked into the brake system is reduced. A low pressure accumulator 10 and high pressure accumulator 16 are provided. The latter may be combined with an isolation valve 12 and actuate the latter by pressure. The accumulator 16 may also include a valve which opens when a predetermined quantity of fluid is stored and diverts the surplus to the intake of the pump. <IMAGE>

Description

1 1 1 HYDRAULIC BRAKE SYSTEM INCLUDING A DEVICE FOR THE BRAKE SLIP ANDIOR

TRACTION SLIP CONTRO The present invention relates to a hydraulic brake system including a device for brake slip and/or traction slip control and relates more specifically to such brake systems comprising a pedal-operated master cylinder associated with at least one wheel brake which is in communication with the master cylinder through a brake conduit wherein upon actuation of the pedal fluid pressure is displaced from the master brake cylinder through the brake conduit into a wheel brake cylinder, the system also comprising a hydraulic pump.

A brake system of this type has been described, for example, in published West German Patent Application No. DE OS 38 31 426.

The pump of the system has the function to deliver the pressure fluid discharged during a control from the wheel brakes back into- the brake conduit. For that purpose, an intake side of the pump is in communication with a pressure fluid collector capable of being connected to the wheel brakes, while a pressure side of the pump is in communication with the master brake cylinder. The pump, hence, is connected in shunt with the brake conduit so that no pressure fluid flows therethrough in a non-controlled declerating process.

A connection of the intake side to the master brake cylinder is established only during a traction slip control.

2 In that case, the pump will suck off pressure fluid from the reservoir associated to the master brake cylinder, delivering the same to the wheel brake. However, this will occur only in the inoperative condition of the master brake 5 cylinder, i.e. in non-pressurised condition.

A system of the above-described type suffers from two disadvantages. Firstly, in brake slip control, the pump delivers from the nonpressurised pressure fluid collector against the pressure in the master cylinder with the consequence that especially with a cold and viscous brake fluid, the full power of the pump will be reached only after an extended start-up phase which, in turn, will result in a deteriorated control quality.

Secondly, the automatic-suction pump forms vacuum if no adequate pressure fluid is available on the intake side thereof. Air is liable to f low into the said vacuum if damage is done to the corresponding sealings. It is difficult to remove such air f rom the brake system as the pump is in shunt with the brake conduit, with air voids in the brake system being likely to result in a failure of the brake system.

It is, therefore, an objective of the present invention to provide a hydraulic brake system which. irrespective of the ambient temperature, permanently ensures a high control quality and exhibits a low failure probability, thus permitting a particularly easy ventilation.

According to the present invention therefore there is provided a hydraulic brake system comprising a device f or controlling brake slip and/or traction slip, a pedalactuated master cylinder associated with at least one wheel brake which is in communication with the master brake cylinder through a brake conduit wherein, upon actuation of the pedal, pressure fluid is displaced from the master brake cylinder, through the brake conduit, into a wheel brake cylinder and a hydraulic pump, characterised in that the pump is inserted into the brake conduit so that the intake 1 i 3 side S of the pump is in communication with the master brake cylinder and the pressure side D of the pump is in communication with the wheel brake cylinder.

As the pump is provided in the brake conduit, in the start-up of the pump, there is a pressure equilibrium on the intake and pressure sides thereof, thereby ensuring, especially at low temperatures, a substantially enhanced pumping power. Unavoidable air pockets, during a deceleration process, will be removed from the pump, thereby maintaining the efficiency thereof.

The device for modulating the brake pressure usually comprises inlet and outlet valves controlling the pressure fluid supply to the wheel brake. The valves are electromagnetically actuated; the control signals are made available by an electronic analyser and the signals of sensors determining the rotating pattern of the wheels are evaluated.

A separating valve between the master cylinder and the intake side of the pump causes the master cylinder, during a brake slip control, to be decoupled from the brake circuit so that pressure fluctuations in the system do not involve any repercussion on the master cylinder.

A high-pressure accumulator on the pressure side of the pump takes up the pressure fluid delivered by the pump and forms the pressure generator in lieu of the master cylinder. In order to prevent the accumulator from taking up pressure fluid already during a normal deceleration process, the spring thereof is biased such that no pressure fluid is taken up by the accumulator at a pressure not yet resulting in the locking of the wheel.

A direct conduit including a check valve between the wheel brake and the master cylinder prevents the pressure in the wheel brake from being higher than the pressure in the master brake cylinder, thereby enabling the driver of the automotive vehicle to terminate a control deceleration in that he decreases the pressure on the pedal. Also the pressure decrease during a non-controlled deceleration is 4 through the direct conduit.

In order to enable a pressure to be built up in the wheel brake even with a non-actuated pedal as is required in a traction slip control, an electromagnetically actuated valve is provided in the direct conduit which, during a traction slip control, blocks the direct conduit.

A release valve between the intake and pressure sides of the pump will prevent the pressure from excessively rising on the pressure side of the pump.

is Preferably, the separating valve in the brake conduit also may be mechanically actuated; in that case, it would be advantageous to mechanically couple separating valve and accumulator thereby causing the separating valve to be closed in a displacement of the accumulator piston.

The release valve also may be operative in the accumulator, for which purpose, the piston of the accumulator will be provided with a valve which, after a predetermined distance covered by the piston of the accumulator is pushed open against the force of the spring by means of a plunger. Pressure f luid in the chamber of the accumulator can flow off into the counter-pressure chamber which is in communication with the intake side of the pump through a connecting conduit. The energy requirements for loading the accumulator are thereby reduced. Equally, an additional amount of pressure f luid (corresponding to the volume - of the counterpres sure chamber) can be brought to high- pressure level so that also in case of a failure of the pump during a control process, operation thereof may be continued. 30 A controllable throttle in the connection to the intake side and the pressure side of the pump, equally, may have a positive influence on the efficiency of the pump. Another advantage of f ered by the system resides in that a boosting effect may be attained. For that purpose, the pump is to be controlled in proportion to the pedal force.

By way of example the present invention will now be 1 described with reference to the accompanying drawings in which:

Figure 1 shows a schematic diagram of the basic brake system according to the present invention; and, Figures 2 to 4 show different embodiments of brake systems of the invention.

The basic brake system of Figure 1 comprises a master brake cylinder 1 connected to which, through a brake conduit 2, are one or a plurality of wheel brakes 3. Pump 4 to be described in closer detail hereinafter is provided in the brake conduit, with the intake side S thereof, through a first brake conduit section 5, being in communication with the master brake cylinder 1, and with the pressure side D thereof, through a second brake conduit section 6, being in communication with the wheel brake. Provided in the second brake conduit section 6 is an inlet valve 7 which is electromagnetically actuated. In its basic position, the valve keeps open the conduit 2, blocking it in its switched position. The wheel brake 3, through a return conduit 9, is in communication with a pressure fluid collector 10, with an outlet valve 8 being provided in the return conduit 9. The outlet valve 8 is electromagnetically actuated and blocks the conduit 9 in its basic position and opens the return conduit in its switched position. The pressure fluid collector 10 is a low-pressure accumulator of a restricted receiving capacity. The collector 10 is in communication, through a check valve 11, with the first brake conduit section 5 (at discharge point E). Provided between the discharge point E and the master brake cylinder 1 is a separating valve 12 which, in the present embodiment, is electromagnetically actuated and, in the basic position thereof, as shown, keeps open the brake conduit while, in the switched position, it blocks the brake conduit.

The wheel brake 3, through a direct conduit 13, is in 35 direct communication with the master brake cylinder 1. The direct conduit 13 includes a check valve 14 opening toward the master brake cylinder. Moreover, provided in the direct 6 conduit 13 is a blocking valve 15 which, in view of the function thereof, will be referred to hereinafter as an ASRvalve.

In the basic position of the blocking valve, it keeps the direct conduit 13 open while in its switched position assumed by it during a traction slip control, it blocks the direct conduit. The pressure side D of the pump is connected to a high-pressure accumulator 16 which in this embodiment is a piston-type accumulator. The piston 17 of the accumulator is so loaded by a strong spring 18 that the accumulator chamber is of a minimum volume. The spring-type accumulator 18 is pre- stressed so that a minimum pressure must be available on the pressure side D of the pump to cause the accumulator to take up volume.

The pump 4, according to this embodiment, is in the form of a piston-type pump, the pump piston 19 of which is moved through a power-driven eccenter 20. The pump chamber 21 ahead of the pump piston 19,. is in communication with the intake side S and the pressure side d of the pump 4 through respective check valves 22 and 23. The check valve 22 opens toward the pump chamber while the check valve 23 blocks toward the pump chamber. A release valve 24 connects the pressure side of the pump to the intake side, preventing overload on the pressure accumulator 16 from occurring.

The operation of the brake system, as shown, is as follows:

1. Uncontrolled vehicle Deceleration:

Through actuation of the pedal (shown schematically), pressure fluid is displaced from the master brake cylinder 1 into the wheel brake 3. The pressure path leads through the open separating valve 12, the first check valve 22, the pump chamber 21, the second check valve 23 and the open inlet valve 7. A pressure is built up in the wheel brake 3 resulting in a wheel deceleration and, consequently, in a deceleration of the automotive vehicle. Once 7 the pedal is released, pressure fluid will flow f rom the wheel brake 3 via the opening check valve 14 through the direct conduit 13 and the open ASR valve 15 back into the master brake cylinder 1. It is important for the pressure built-up path to lead, during a normal deceleration, through the pump 'chamber 21.

2. Brake Slip Control The braking pattern of' the wheel to be decelerated is permanently monitored by means of sensors (not shown). Accordingly, an electronic analyser is able to detect without delay once the wheel tends to lock. Upon occurrence thereof, the analyser will initiate the following steps: First, inlet valve 7 is switched to thereby block the brake conduit 2. outlet valve 8 is opened to thereby enable pressure fluid to flow back from the wheel brake 3 into the low-pressure accumulator 10. Valve 12 is closed causing the master brake cylinder 1 to be decoupled from the brake circuit. The pump drive motor M is switched on thereby enabling the pump 4 to deliver pressure fluid from the low-pressure accumulator 10 into the high-pressure accumulator 16. Piston 17 moves against the force of the spring 18 causing a pressure on the output of the pump D to correspondto the force of the spring. Through successive switching of the inlet valve 7 and of the outlet valve 8, pressure fluid can be supplied to and discharge from the wheel brake 3. This is in accordance with a fixed algorithm thereby enabling an optimum slip value to be adjusted on the wheel. Through the direct line 13, the pressure in the wheel brake is limited to the pressure in the master brake cylinder. once the driver reduces the pedal force the 8 pressure in the wheel brake will, accordingly, decrease, thereby terminating the decelerating or control process.

3. Traction Slip Control If the vehicle wheel is a driven wheel it may happen that the torques transmitted by the engine of the automotive vehicle exceed the torques that can be transmitted between tyre and roadway, resulting in wheelspin. This can be prevented by a brake management whereby the driving torque is compensated to such an extent by a brake torque that the remaining torque is in harmony with the forces than can be transmitted between tyre and roadway. The afore-mentioned sensors are able to detect a wheel racing tendency. The electronic analyser initiates the following steps: The pump motor M is turned on causing the pump 4 to deliver pressure fluid from the reservoir associated to the master brake cylinder through the master brake cylinder 1 and the open separating valve 12 to the wheel brake 3. The ASR-valve 15 is closed so that the pressure fluid delivered to the wheel brakes is unable to flow back, through the direct conduit 13, into the master brake cylinder. As in a brake slip control, now an optimum brake pressure can be adjusted in the wheel brake through switching of the valves 7 and 8. If a brake system is to have this option, the pump 4 must be of the self-sucking type since, in the event of a traction slip control, there is no static pressure on the intake side S of the pump. The release valve 24 prevents an excessive pressure from being built up on the pressure side of the pump. - Now, the embodiment shown in Figure 2 will be described. This embodiment corresponds generally to the one 4 A 1 9 of Figure 1 but the separating valve is not actuated electromagnetically as in the Figure 1 embodiment but rather mechanically in dependence on the filling level of the highpressure accumulator 16.

For that purpose, accumulator 16 and valve 12 are located in a common housing. The piston 17,, on its end facing the accumulator chamber, includes an extension 30 being of a smaller diameter than the accumulator piston 17. The extension 30 is sealingly guided within a bore and, on the end thereof remote from the accumulator piston 17f includes a plunger 31 which extends through a bore 32. The bore connects an inlet chamber 36 to an outlet chamber 37, with the inlet chamber 36 being in communication with the master brake cylinder 1 and the outlet chamber 37 being in communication with the pressure side of the pump 4. The outlet chamber 37 is confined by the front side of the extension 30. The separating valve comprises a valve ball 34 in the inlet chamber 36 co-operating with a valve seat 33 at the periphery of bore 32. A valve spring 35 forces the valve ball toward the valve seat 33. Once the valve piston 17 is in its basic position, i. e. in a position in which the accumulator chamber exhibits its minimum volume, plunger 31 which extends through the bore 32, maintains the valve ball 34 in spaced relationship from the valve seat 33.

There is a free pressure fluid passage from the master brake. cylinder 1 to the pump 4. During a brake slip or traction slip control, the accumulator is filled - as was explained earlier - causing the accumulator piston according to the illustration in the drawing, to move to the right as soon as there is adequate pressure on the pressure side of the pump. The plunger 31 is moved accordingly through the bore 32 causing the valve ball 36 to be seated on the valve seat 33. The brake conduit is accordingly blocked. The rest of the operation of the brake system corresponds to that of the brake system according to Figure 1.

Figure 3 shows another embodiment of the brake system generally according to Figure 1 but it being essential that the release valve is now included within the accumulator. For that purpose, the accumulator piston 17 contains a valve 43. The accumulator piston separates the chamber 40 from a counter-pressure chamber 41. The valve 43 comprises a connecting bore provided in the piston 17 between the two chambers 40 and 41. A valve body is located within the accumulator chamber 40 and is mounted on the connecting bore. Once the accumulator piston is displaced to the right, as viewed in the drawing, a plunger 44 moves into the bore, lifting a valve ball of the valve 43 off the bore so that a pressure fluid communication is established between the storage chamber 40 and the counter-pressure chamber 41. The counter-pressure chamber 41, through a connecting conduit 42, is in communication with the intake side of the pump. Once a predetermined filling level of the accumulator and, hence, a predetermined pressure within the storage chamber corresponding to the compression of the spring 18 has been attained, the valve 43 opens so that pressure fluid additionally admitted to the storage chamber, through the counterpressure chamber 41, flows back to the intake side of the pump. The remainder of design and function of the brake system corresponds to the brake system of Figure 1.

Figure 4 shows a complete brake system for a four25 wheel automotive vehicle having wheels 64,65,66,67 with the HR, HL, VL and VR codings having the following meaning:

HR = rear side to the right HL = rear side to the left VL = front side to the left VR = front side to the right.

The master cylinder 1 comprises two chambers 60,61 each of them forming one brake circuit. Connected to the chamber 60, through brake conduits 21, are the wheel brakes of the wheels HR and HL. The brake pressure in the two 35 wheel brakes is commonly controlled by a control system of the type as shown in Figure 2. The brakes of the wheels VL and VR are in communication with the chamber 61 of the c A f 11 master brake cylinder through respective branch conduits 62,63 of the brake conduit 211. Each of the branch conduits 62,63 includes a control system of the type as shown in Figure 2.

The brake system, hence, includes three control circuits each of them having a pump 41, 411, 4111. It should be noted in this connection that the control system also can orient itself by Figures 1 and 3, respectively.

Special emphasis is given to the fact that the pumps 41, 4111 4111 are actuated by a common drive electromotor EM.

Another special feature resides in that the respective inlet and outlet valves are in the form of a 3 -way/2 -position valve 68,69,70. This results in a simplified system but involves the disadvantage that no pressure maintaining phase in which both the brake conduit and the return conduit are blocked, can be realised.

Each of the control systems operates on the previously described principle, it being, of course, possible for the pressure in the wheel brakes of each control circuit to be independently adjusted.

12

Claims

CLAIMS:

1. A hydraulic brake system comprising a device for controlling brake slip and/or traction slip, a pedalactuated master cylinder (1) associated with at least one wheel brake (3) which is in communication with the master brake cylinder (1) through a brake conduit (2) wherein, upon actuation of the pedal, pressure fluid is displaced from the master brake cylinder, through the brake conduit, into a wheel brake cylinder and a hydraulic pump(4), characterised in that the pump (4) is inserted into the brake conduit (2) so that the intake side S of the pump (4) is in communication with the master brake cylinder (1) and the pressure side D of the pump (4) is in communication with the wheel brake cylinder.

2. A brake system according to claim 1, characterised in that an inlet valve (7) is provided in a brake conduit section (6) between the pump (4) and the wheel brake cylinder (3), which valve is open in the basic position thereof and is closed in the switched position thereof to block the brake conduit, and in that the wheel brake (3), is in communication with a pressure fluid collector (10) through a return conduit (9), an outlet valve (8) being inserted into the return conduit (9) in order to block the return conduit in the basic condition of the valve (8) and to open the conduit in the switched condition of the outlet valve (8).

3. A brake system according to claim 2, characterised in that the pressure fluid collector (10) is in communication with a brake conduit section (5) at point E between the pump (4) and the master brake cylinder (1) through a check valve (11), and in that a separating valve (12) which is inserted between the master brake cylinder and the point E is open in the basic position thereof and is closed in the switched position thereof to block the brake conduit.

4. A brake system according to claim 1 or claim 2, characterised in that a high-pressure accumulator (16) is z 13 connected to the pressure side D of the pump (4).

5. A brake system according to claim 4,-characterised in that the accumulator (16) is charged only at a minimum pressure on the pressure side of the pump D.

6. A brake system according to any preceding claim, characterised in that the wheel brake (3) is in direct communication with the master brake cylinder (1) through a direct conduit (13), with a check valve (14) being inserted into the direct conduit (13) and opening toward the master brake cylinder (1).

7. A brake system according to claim 6, characterised in that a blocking valve (ASR valve 15) is inserted into the direct conduit (13) to keep the conduit open in the basic position of the valve (15) and to block the conduit in the switched condition of the valve (15).

8. A brake system according to any preceding claim, characterised in that the pump (4) is of the reciprocating piston type with a pump chamber (21) thereof in communication with the respective intake side S and the pressure side D of the pump through check valves (22,23).

9. A brake system according to any preceding claim, characterised in that an intake side S of the pump and a pressure side D of the pump (4) are in communication with one another through a release valve (24).

10. A brake system according to claims 3 and 4, characterised in that the separating valve (12) is mechanically actuated by the piston (17) of the highpressure accumulator (16).

11. A brake system according to claim 10, characterised in that the separating valve (12) comprises a seated valve the valve body (34) of which is arranged to be actuated by a plunger (31) provided on the piston (17) so that the valve (12) closes during charging of the accumulator (16).

12. A brake system according to claim 5f characterised in that the separating piston (17) of the high-pressure accumulator (16) separates and accumulator chamber (40) from 14 a counter-pressure chamber (41), a valve (43) being located in the separating piston (17) and arranged to be actuated by means of a plunger in a manner that. at a predetermined charge level in the accumulator chamber (40).. a 5 communication is established between the accumulator chamber (40) and the counter-pressure chamber (41).

13. A brake system according to claim 12, characterised in that the counter-pressure chamber (41) is in communication with the intake side S of the pump (4) through a connecting conduit (42).

14. A brake system according to any of claims 1 to 8, characterised in that connected between an intake side S and a pressure side D of the pump (4) is a controllable throttle the cross-section of which is determined by the pressure difference between the intake side S and the pressure side D of the pump.

15. A brake system according to any one of the preceding claims, characterised in that a triple-circuit system is provided for a fourwheel automotive vehicle. with the wheel brakes of the rear axles and the wheel brakes of respectively one front axle respectively forming one control circuit, and with the pump (41, 411, 4111) provided for each control circuit exhibiting a common drive.

16. A brake system according to claim 2 or any claim dependent on claim 2, characterised in that the inlet valve (7) and the outlet valve (8) are in the form of a 3-way/2position valve.

17. A brake system substantially as hereinbefore described with reference to Pigure 1, Figure 2, Figure 3 or Figure 4 of the accompanying drawings.

Published 1991 at7be Patent Office. State House. 66/71 High Holborn, LondonWClR47P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.

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