GB2218764A

GB2218764A - Vehicle anti-skid hydraulic brake system

Info

Publication number: GB2218764A
Application number: GB8911614A
Authority: GB
Inventors: Alwin Stegmaier; Karl-Heinz Willmann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-05-20
Filing date: 1989-05-19
Publication date: 1989-11-22
Also published as: DE3817178A1; JPH0218148A; GB8911614D0; FR2631598A1

Description

1 2218764

- 1 DESCRIPTION VEHICLE HYDRAULIC BRAKE SYSTEM HAVING AN ANTI-SKID SYSTEM

The invention relates to a vehicle hydraulic brake system.

Vehicle brake systems are known from German Offenlegungsschrift 34 13 430 and also from German Offenlegungsschrift 34 40 972. The auxiliary chamber forming part of the respective anti-skid system can be relieved of pressure by two valves which are disposed in parallel and each of which is controllable by means of an individual solenoid. This has the advantage that, in the event of one of the valves sticking or being clogged when in its cut-off position, or even in its pressure build-up position, the respective auxiliary chamber can be relieved of pressure. However, it is a disadvantage that the sticking or clogging of one of the two valves, for example the two-port, two-position valve provided as a safety by-pass valve, is not detectable during operation and consequently the safety advantage is lost, possibly without being noticed.

In accordance with the present invention, a vehicle brake system with wheel brakes having a master brake cylinder, a brake force booster which may be supplied from an auxiliary source of pressure and which has at least one booster piston, and an anti-skid system which has at least one auxiliary cylinder which is associated with the brake force booster and an auxiliary piston for reducing the brake pressures, a valve arrangement which controls the action of a pressure medium on the auxiliary piston and which has redundancy valves for relieving the auxiliary piston of pressure, and a control unit for controlling the valve arrangement, wherein a pressure switch is associated with the valve arrangement, and that the control unit is connected to the pressure switch and is equipped to perform test programs for at least the redundancy valves in such a way that the redundancy valves are individually and successively controllable into their flow-through and cut-off positions, and thereby the redundancy valves are tested by way of the pressure switch if the change-over of the valves effects logically associated changes in pressure.

This has the-advantage that the valves may be tested successively for tightness and the ability to permit the flow-through of pressure medium. If no faults are indicated, the margin of safety provided by the valves disposed in parallel exists. There is also the advantage that troublesome leaks in the region of the auxiliary cylinder and its auxiliary piston also lead to fault indication.

1 The vehicle brake systems, wherein the valve arrangement is connected by way of a throttle to the source of auxiliary pressure and an additional valve connects the source of auxiliary pressure to the auxiliary cylinder and the valve arrangement is further connected to the working chamber of the brake force booster by way of a non-return valve, has the advantage that the valve arrangements may be tested without actuating a brake pedal.

However, when the valve arrangement is connected by a throttle to the source of auxiliary pressure and to the working chamber of the brake force booster by the non-return valve, as above, this has the further advantage that pressure medium from the working chamber of the brake force booster may be used for the anti-skid d e v i c e.

Whilst, if the vehicle brake system has the pressure switch permanently connected to the auxiliary piston, this has the advantage that the pressure switch is subjected to pressure only during test cycles and during anti-skid operation.

Additionally, if the pressure switch is connected to a line leading from the throttle and the non-return valve to the valve arrangement and that a valve, connected to the line, of the valve arrangement may be maintained in its open position for the purpose of successively testing the functional ability of two valves which are disposed in parallel and redundance and which act to reduce pressure, specify an alternative to when the first valve arrangement is connected to the source of auxiliary pressure, the pressure s.witch advantageously being usable also to monitor the source of auxiliary pressure.

Additionally, the control unit could be additionally equipped to operate the valve, additionally disposed between the source of auxiliary pressure and the auxiliary cylinder, during anti-skid operation result in greater safety when the brake is reduced. However, these features may also be used to influence the rate at which the pressure is reduced.

If the additional valve is controllable, particularly for the purpose of rapid and simultaneous reduction in pressure in a plurality of wheel brakes enable the valves to be controlled in dependence upon the number of wheels in danger of locking.

The invention shall be described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 shows a first embodiment of a vehic hydraulic brake system with an anti-skid system according to the present invention; 1 e Fig. 2 shows a second embodiment of a vehicle hydraulic brake system with anti-skid system; and Fig. 3 shows a third embodiment of a vehicle hydraulic brake system with anti-skid system.

The vehicle brake system 2 of Fig. 1 has wheel brakes 3, 4, 5, 6, a master brake cylinder 7, a brake force booster 8, a source of auxiliary pressure and an anti-skid system which comprises an auxiliary cylinder 10, an auxiliary piston 11, a first valve arrangement 12, a second valve arrangement 13 and a control unit 14.

The master brake cylinder 7 is, for example constructed as a tandem master cylinder in a manner known per se and its main components are a first master brake cylinder piston 15, a second master brake cylinder piston 16, two return springs 17 and 18, two supply connections 19, 20 by means of which pressure medium is introduced into the master brake cylinder 7 from a reservoir (not illustrated), and two brake line connections 21 and 22. The master brake cylinder pistons 15 and 16 are sealed relative to a cylindrical bore 24 of the master brake cylinder 2 by means of sealing rings 23 in a manner known per se.

The brake force booster 8 has a housing 25 with a cylindrical bore 26, a booster piston 27 which is displaceable in the said bore 26, a brake valve 28 which is fitted in the booster piston 27 and which has a valve stem 29, and a pedal push rod 30. The booster piston 27 is sealed relative to the cylindrical bore 26 by means of a sealing ring 31. A further sealing ring 32, axially spaced from the sealing ring 31, is disposed on the booster piston 27. The housing 25 has a pressure supply connection 33 in a region between the two sealing rings 31 and 32.- The pressure supply connection 33 is connected to the pressure supply 9 by way of a pressure line 34. The housing 25 also has a return connection 35 which is connected to the source of the auxiliary pressure 9 by way of a return line 36. The cylindrical bore 26 and the booster piston 27 define a working chamber 37. The working chamber 27 is relieved of pressure to the return connection 35 by means of the brake valve 28 when the brake pedal (not shown) acting on the pedal push rod 30, is released. The working chamber 37 may be disconnected from the return connection 35 and connected to the pressure supply connection 33 by actuating the brake valve 28 by means of the brake pedal by way of the pedal push rod 30 and the valve stem 29. The pressure of the source 9 of auxiliary pressure can thereby be introduced partially or entirely into the working chamber 37.

The source 9 of auxiliary pressure has a reservoir 38, a pump 39, a oneway valve 40 disposed downstream of 1 z- 1 1 - the pump 39, and a pressure accumulator 41. The pump 39 can be driven, in a known manner, by an individual electric motor (not illustrated) or by a vehicle engine. The pressure accumulator 41 is, for example, a so-called gas cushion accumulator. It will be appreciated that a piston-type accumulator, known from the general prior art, could be fitted instead of a gas cushion accumulator.

The auxiliary cylinder 10 is formed on the housing 25 towards the master brake cylinder 7 and coaxially of the cylindrical bore 26, and is connected to the master brake cylinder 7 by way of an attachment extension 42. cylindrical bore 43 of the auxiliary cylinder 10 has a larger diameter than that of the cylindrical bore 26. The auxiliary piston 11 is, for example, a cup-shaped construction and is sealed relative to the cylindrical bore 43 by means of a sealing ring 44. The auxiliary piston 11 has a wall 46 which is contiguous to a front end 45 of the booster piston 27. A thrust rod 47 is located between the wall 46 and the first master brake cylinder piston 15 for the purpose of transmitting forces from the booster piston 27 to the first master brake cylinder piston 15 by way of the wall 46. The thrust rod 47 is sealed relative to the auxiliary cylinder 10 by means of a sealing ring 48 which is carried by fitting 49 disposed in the attachment A i extension 42.

The valve arrangement 12 includes an electromagnetically controllable three-port, three-position valve 50 and a electromagnetically controllable twoport, two-position valve 51-. Valve 50 has a solenoid 52 and valve 51 has a solenoid 53. The two solenoids 52 and 53 are individually connected to the control unit 14. The normal positions of the two valves 50 and 51 are flow-through positions. When in t"illese normal positions, the valves 50 and 51 connect an auxiliary piston connection 54 to the reservoir 38 in the source of auxiliary pressure 9. For this purpose, lines 55, 56, 57 and 58 are located between the auxiliary cylinder connection 54 and the two valves 50 and 51. Lines 59, 60, 61 and 62 are located between the valves 50 and 51 and the source of auxiliary pressure 9. As will be seen in Fig. 1, the valves 50 and 51 form two pressure-relief paths to the reservoir 38. A first switching position of the three-port, three-position valve 50 is a cut-off position, that is, a pressure-holding position in which the auxiliary cylinder connection 54 is isolated from the pressure accumulator 41 and from the reservoir 38 of the source 9 of auxiliary pressure. A second switching position connects the pressure accumulator 41 to the auxiliary cylinder connection 54.

1 M A pressure switch 64 is connected between the lines 55 and 56 by way of a further line 63 and is a component part of the anti-skid system.

Advantageously, the second valve arrangement 13 includes four electromagnetically controllable two-port, two-position valves 65, 66, 67 and 68. When in their normal positions, the valves 65 to 68 are open and thereby connect the brake line connections 21 and 22 to their respective, associated wheel brakes 3 to 6. Solenoids 69 to 72 are individually connected to the control unit 14 for the purpose of controlling the valves 65 to 68.

The vehicle brake system 2 operates in the following manner:

When the brake pedal (not illustrated) is actuated, the working chamber 37 is isolated from the return connection 35 by way of the push rod 30 and the valve stem 29 of the brake valve 28 and is connected to the pressure supply connection 33. Pressure medium thereby flows from the source 9 of auxiliary pressure into the working chamber 37, with the result that the booster piston 27 is acted upon in the operative direction of the push rod 30. Consequently, the end 45 of the booster piston 27 is pressed against the wall 46 and the latter is in turn urged against the thrust rod 47 which in turn displaces the first master brake cylinder piston towards the second master brake cylinder piston 16. Brake pressures are thereby produced in the master brake cylinder 7 by the master brake cylinder pistons 15 and 16 and are applied to the wheel brakes 3 to 6 by way of the brake line connections '21 and 22 and the valve arrangement 13. Partial release of the brake pedal terminates communication between the working chamber 37 and the pressure supply connection 33. Full releas-e of the brake pedal finally causes the working chamber 37 to be relieved of pressure to the return connection 35, with the result that the brake pressure and the return springs 17 and 18 displace the master brake cylinder pistons 15, 16 and also the booster piston 27 into their initial positions.

If the brake pedal is actuated so vigorously during a braking operation that there is a risk that the wheel brake 3 will lock its associated wheel as result of, for example, too high a brake pressure, the control unit 14 actuates the valves 66,- 67 and 68 of the second valve arrangement 13 and also the valve 51 of the first valve arrangement 12 into their cut-off positions. Furthermore, the control unit 14 actuates the valve 50 into its second switching position, whereby pressure medium flows from the pressure accumulator 41 and into the auxiliary cylinder 10 and subjects the auxiliary 2 - 11 piston 11 to pressure in the direction opposite to the operative direction of the booster piston 27. Since the diameter of the auxiliary piston 11 is larger than that of the booster piston 27, the booster piston is also returned towards its initial position against a force acting upon the push rod 30. Consequently, the first master cylinder piston 15 also moves towards its initial position, so that a drop in the brake pressure occurs in the master brake cylinder 7. This drop in the brake pressure is propagated to the wheel brake 3 by way of the brake line connection 21 and the valve 65 which has remained open, so that the wheel brake 3 releases its associated wheel. The said wheel is consequently accelerated, and the risk of wheel-lock is thereby eliminated. When the risk of wheel locking has passed, for example because the wheel associated with the wheel brake 3 moves onto a roadway having a better grip, the valves 50 and 51 are first actuated into their normal positions by the control unit 14. Consequently, the booster piston 27 can, under the action of the pressure acting upon it, again displace the master brake cylinder pistons 15 and 16, hence resulting again in a rise in the brake pressures in the master brake cylinder 7. The control unit 14 then allows the valves 66, 67 and 68 to return to their initial positions. From then onwards, the vehicle brake system operates normally again. If the risk of locking occurs at several wheels, the brake pressures of several wheels can, of course, be reduced simultaneously in the manner described above.

The pressure switch 64 is connected to the control unit 14 by way of a line 73. Pressure rises occurring in the auxiliary cylinder 10 are signalled to the control unit 14 by way of the line 73. The control unit 14 is also equipped to fulfil test functions. In order to perform test functions, the control unit actuates, at the commencement of operation for example, the valve 51 into its cut-off position and the valve 50 into its second control position in which the valve 50 transmits pressure medium from the source 9 of auxiliary pressure and into the auxiliary cylinder 10. As already indicated, this event is detected by the pressure switch 64 and is signalled to the control unit 14 by way of the line 73. If the event does not occur, the control unit 14 detects that either the valve 50 cannot be switched into its second control position or that the valve 51 is sticking in its open position. The vehicle brake system is out of order in both cases, and this is indicated by the control unit 14 by means known per se.

If a rise in pressure has been signalled by means of the pressure switch 64, the control unit 14 allows the control valve 50 to return to its normal position, z 0 11 - -13with the result that, provided the valve 50 is capable of functioning, the pressure switch 64 signals a drop in pressure to the control unit 14. If a signal of this kind does not occur, the control unit 14 initiates the indication of a fault. Aft-er the valve 50 has been tested, pressure is again built up in the auxiliary cylinder 10 by actuating the valve 50 into its second control position. The valve 50 is then returned to its first switching position in which it acts as a cut-off valve between the auxiliary cylinder 10 and the return line 62. If the pressure remains constant, there are no leaks. The valve 51 is then returned to its normal position, and the auxiliary cylinder 10 is thereby connected to the return line 62. If the valve 51 is operating in good order, the pressure drop occurring is again signalled by the pressure switch 64 to the control unit 14 which detects that the valve 51 is operating in good order. The control unit 14 gives a warning if the pressure does not drop. It is also pointed out that, of course, a combination of valves of simple construction, such as two-port, two-position valves, may be fitted instead of three-port, three-position valve 50. Consequently, the control unit 14 would then be further developed to control, for example, an additional valve. Furthermore, the test logic would then also be developed accordingly.

arrangement master brak the source of cylinder 10a eauivalents The second embodiment of a ve'hicle brake system 2a, shown in Fig. 2, also has wheel brakes 3, 4, 5 and 6, a master brake cylinder 7a, a brake force booster 8a, a source of auxiliary pressure 9a, an auxiliary cylinder 10a having an auxiliary piston 11a, a first valve.

12a and a second valve arrangement 13a. The cylinder 7a, the brake force booster 8a, auxiliary pressure 9a, and the auxiliary with its auxiliary piston 11a are technical of those elements which were described in connection with the embodiment of Fig. 1. By way of example, the source of auxiliary pressure 9a differs from the source of auxiliary pressure 9 only in that a piston-type accumulator already mentioned is now used instead of the gas cushion accumulator used in the embodiment of Fig. 1.

The valve arrangement 13a differs from the valve arrangement 13 inthat throttles 74 and 75 are fitted respectively between the valves 65, 67 and the wheel brakes 3, 5 are disposed downstream thereof. The throttles 74, 75 intentionally serve for slower changes in the brake pressure in the wheel brakes 3 and 5 which, in the present embodiment, are rear wheel brakes of a vehicle.

1 4 The first valve arrangement 12a includes a valve 51 having a solenoid 53 and is constructed in accordance with the embodiment described above. Two two-port, twoposition valves are now fitted instead of the valve 50 described in the first embodiment. The first valve 76 is interposed between an auxiliary cylinder connection 54a of the auxiliary cylinder 10a and a line 62a leading back to the source of auxiliary pressure 9a. The normal position of the valve 76 is its open position, so that the auxiliary cylinder 10a is normally relieved of pressure. A solenoid 78 is provided to actuate the valve 76 into its closed position. Thus, corresponding to the first embodiment, two pressure-relieving connections are again provided between the auxiliary cylinder 10a and the return line 62a. The second valve 77 is normally closed and is controllable into its flowthrough position by means of a solenoid 79. Corresponding to the purpose for which the valve 50 of the first embodiment is used, the valve 77 is likewise connected to the auxiliary cylinder connection 54a. However, in contrast to the first embodiment, a pressure inlet 80 of the valve 77 is not connected directly to the source of auxiliary pressure 9a, but is connected to a pressure line 34a by way of a throttle 81 and a pressure supply connection 33a. Furthermore, the pressure inlet 80 is also connected to the working chamber 37a of the brake force booster 8a by way of a non-return valve 82. The throttle 81 is fitted in a housing 25a of the brake force booster 8a. A non-return valve 82 may also be fitted in the housing 25a. A connection line 83 leads from the housing 25a to the pressure inlet 80. The non-return valve 82 is fitted in such a way that it opens when a pressure in the working chamber 37a is higher than a pressure in the pressdre line 34a.

The second embodiment of the vehicle brake system 2a operates in the following manner:

In the manner described with reference to Fig. 1, brake pressures are controlled by means of a brake pedal 30b by way of a pedal push rod 30a during normal braking operation. If the risk of wheel-lock occurs at, for example, a wheel associated with the wheel brake 3, the valves 66, 67 and 68 are actuated into their cut-off positions. Furthermore, the valves 51 and 76 are also actuated into their cut-off positions. When these valves have assumed their cut-off positions, the valve 77 is actuated into its open position by a control unit (not illustrated). As a result of a pressure present at the pressure inlet 80, the auxiliary cylinder 10a is subjected to pressure and its auxiliary piston 11a is acted upon in the direction opposite to the operative 1 -17direction of the booster piston 27a. A pressure at the pressure inlet 80 is produced on the one hand by pressure medium flowing from the pressure line 34a into the connection line 83 by way of the throttle 81 and, on the other hand, by virtue of the fact that the working chamber 37a of the brake force booster 8a acts like a source of auxiliary pressure whose pressure is controllable by way of the pedal push rod 30a. Since the non-return valve 82 makes available a larger aperture cross section than the throttle 81 of relatively narrow construction, the auxiliary cylinder 10a is filled chiefly by means of pressure from the working chamber 37a during displacement of the auxiliary piston 11a. When the brake pressure in the wheel brake 3 has been reduced to an adequate extent by adequate displacement of the auxiliary piston 11a, that is, the risk of wheel-lock has been eliminated, the control unit returns the valve 77 to its cut-off position, and the valves 51, 76 and 66, 67, 68 are opened again, so that the same mode of operation as that in the abovedescribed vehicle brake system 2 of Fig. 1 above is obtained.

The pressure for testing the ability of the valves 51 and 76 to function is provided in a different manner in that the pressure is fed into the auxiliary cylinder 10a only through the relatively narrow cross section of the throttle 81. As in the embodiment described above, the valves 51 and 76 are tested successively for their ability to open and close. For this purpose, the valve 77 disposed downstream of the switch 64 and the throttle 81, is opened. A throttle-76a fitted in the valve 76 should have larger flow-through cross section than the cross section of the throttle 81, so that a difference in pressure required to actuate the switch 64 is produced by a pressure drop between the throttles 81 and 76a. Consequently, the flow-through cross section of the throttle 81 is preferably smaller than a preselected flow-th rough cross section of the throttle 76a. If the two valves 51 and 76 are tightly closed when the valve 77 is open, the pressure prevailing upstream of the throttle 81 is established at the pressure switch 64.

A further embodiment of the vehicle brake system 2b of Fig. 3 has the wheel brakes 3 to 6, the master brake cylinder 7a, the brake force booster 8a, the pressure source 9a, the auxiliary cylinder 10a and the auxiliary piston 11a and the valve arrangements 12a and 13a of the embodiment of Fig. 2. The valve arrangement 12a is again equipped to feed the pressure medium, pressurised in the working chamber 37a of the brake force booster 8a, to the auxiliary piston connection 54 in order to act upon the auxiliary piston 11a against the force of 21 -19the booster piston 39a in the case of anti-skid operation. It is thereby unnecessary to describe further the embodiment of Fig. 3 in the case of normal braking operation and anti-skid operation.

In contrast to the embodiment of Fig. 2, a twoport, two-position valve 84, controllable by means of a solenoid 85, is disposed between the auxiliary cylinder 10a and the pressure source 9a instead of the permanently open throttle 81. Although the present embodiment is more expensive than the embodiment of Fig. 2, the possible closing of the throttle 81 due to its narrow cross section is eliminated. The pressure switch 64 is connected to an auxiliary piston connection 54a by way of a line 63. By further development of a control unit (not shown) which is intended for control of the valve arrangements 12a and 13a, auxiliary pressure may be introduced directly into the auxiliary cylinder 10a from the source of auxiliary pressure 9a with the use of the two-port, two- position valve 84, which is normally closed, for the purpose of reducing brake pressures in a particularly rapid manner. This direct feeding of auxiliary pressure is particularly advantageous when, for example, the control unit de tects that all the wheels of a vehicle are locking. That is, in this case, the auxiliary piston 11a should cover a relatively long path towards its initial position within a prescribed period of time in order to rapidly obtain an adequate drop in the brake pressure in all the wheel brakes. The two-port, two-positionvalve 84 additionally creates the possibility of ensuring anti-skid operation in the event of failure of the valve 80.

It follows from the description of the three embodiments of Figs. 1 to 3, that anti-skid systems may be designed to operate very reliably with the use of redundancy valves and monitoring devices for the separate testing of the ability of the redundancy valves to function.

1 4 1

Claims

1. A vehicle hydraulic brake system with wheel brakes, having a master brake cylinder, a brake force booster which may be supplied from an auxiliary source of pressure and which has at least one booster piston, and an anti-skid system which has at least one auxiliary cylinder which is associated with the brake force booster and an auxiliary piston for reducing the brake pressures, a valve arrangement which controls the action of a pressure medium on the auxiliary piston and which has redundancy valves for relieving the auxiliary piston of pressure, and a control unit for controlling the valve arrangement, wherein a pressure switch is associated with the valve arrangement, and that the control unit is connected to the pressure switch and is equipped to perform test programs for at least the redundancy valves in such a way that the redundancy valves are individually and successively controllable into their flow-through and cut-off positions, and thereby the redundancy valves are tested by way of the pressure switch if the change-over of the valves effects logically associated changes in pressure.

2. A vehicle brake system as claimed in claim 1, wherein the valve arrangement is connected to the source of auxiliary pressure.

3. A vehicle brake system as claimed in claim 2, wherein the valve arrangement is additionally connected to a working chamber of the brake force booster by way of a non-return valve and that the valve arrangement is connected to the source of.auxiliary pressure by way of a throttle.

4. A vehicle brake system as claimed in claim 1, wherein the valve arrangement is connected to a working chamber of the brake force booster.

5. A vehicle brake system as claimed in claim 1, wherein the valve arrangement is connected to a working chamber of the brake force booster, and that an additional valve is connected to the source of auxiliary pressure for the purpose of connecting the said source of auxiliary pressure to the auxiliary cylinder.

6. A vehicle brake system as claimed in any one of claims 1 to 5, wherein the pressure switch is permanently connected to the auxiliary piston.

7. A vehicle brake system as claimed in claim 3, wherein the pressure switch is connected to a line which leads from the throttle and the nonreturn valve to the valve arrangement, and in that a first of the redundancy valves of the first valve arrangement is connected to the said line and said valve may be maintained in its open position for the purpose of successively testing the functional ability of a second and third of the t redundancy valves of the first valve arrangement which are disposed in parallel and in redundance and which act to reduce pressure.

8. A vehicle brake system as claimed in claim 5, wherein the control unit is additionally equipped to open the additional valve, disposed between the source of auxiliary pressure and the auxiliary cylinder, during antiskid operation.

9. A vehicle brake system as claimed in claim 8, wherein the additional valve is controllable, particularly for the purpose of rapid and simultaneous reduction in pressure in a plurality of wheel brakes.

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

Published 1989 at The Patent Office, State H ise, 6617 L High Holborn. London WC1R 4TP Further copies maybe Obtainedlr'0311 The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR,9 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Coil. 1/87