WO1989005747A1

WO1989005747A1 - Vehicle antilock braking systems

Info

Publication number: WO1989005747A1
Application number: PCT/GB1988/001070
Authority: WO
Inventors: Alastair John Young
Original assignee: Automotive Products Plc
Priority date: 1987-12-23
Filing date: 1988-12-05
Publication date: 1989-06-29
Also published as: GB8729946D0; GB2213888A

Abstract

A vehicle antilock braking system includes a master cylinder (11) which will produce a source of fluid under pressure upon brake actuation, said master cylinder (11) is connected to a brake circuit including a brake actuator (50) associated with one of the wheels of the vehicle, the brake actuator being connected to the master cylinder (11) via a displacement valve (51) which includes a piston (52), movement of the piston (52) is controlled by means of a power fluid source (27) via an antilock control valve (66), so that during braking of the vehicle upon initiation of an antilock operation fluid in the brake actuator (50) may be displaced into the displacement valve (51) to reduce the braking effort, a change-over valve (70) is provided to apply master cylinder pressure to the piston (52) to prevent displacement of fluid from the brake actuator (50) to the displacement valve (51) should the power fluid source (27) fail.

Description

VEHICLE ANTILOCK BRAKING SYSTEMS

The present invention relates to vehicle antilock braking systems and in particular such systems in which reduction or reapplication of braking effort during an antilock cycle is effected by means of a power fluid source.

According to one aspect of the present invention a vehicle antilock braking system comprises a master cylinder which will produce a source of fluid under pressure upon brake actuation, said master cylinder being connected to a brake circuit including a brake actuator associated with one of the wheels of the vehicle, said brake actuator being connected to the master cylinder via a displacement valve, said displacement valve including a piston, movement of said piston being controlled by means of a power fluid source via an antilock control valve, so that when the brake is applied fluid in the brake actuator may be displaced into the displacement valve to reduce the braking effort should deceleration of the wheel associated with that brake actuator rise above a level at which locking of the wheel is liable to occur, characterised in that a change-over valve is provided to apply master cylinder pressure to the piston to prevent displacement of the fluid from the brake actuator to the displacement valve should the^'power fluid source fail. With the system disclosed above, when the brake is applied the brake pressure will also be applied to the displacement valve and will act on one end of the piston thereof. It is consequently necessary to apply an opposing force to the piston in order to prevent movement thereof during normal braking. This may be achieved by applying the power fluid to the piston so that it will apply a force thereto in the opposite direction to the brake pressure. Means must however be provided to prevent movement of the piston or displacement of fluid from the brake actuator to the displacement valve in case of failure of the power fluid source. This is achieved by said change-over valve, which exposes the piston of the displacement valve to brake pressure in the opposite direction.

The antilock control valve will also control movement of the displacement valve to reapply pressure to the brake actuator and thus the braking effort, when the conditions under which a wheel is liable to lock cease to prevail.

Various embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic illustration of a vehicle antilock braking system in accordance with the present invent ion ;

Figure 2 is a diagrammatic illustration of a modification to the system illustrated in figure 1; and

Figure 3 is diagrammatic illustration of a further modification to the system illustrated in figure 1.

Figure 1 illustrates a dual circuit braking system controlled by a servo assisted master cylinder 11. The master cylinder 11 is of conventional design, having a control plunger 12 which, upon movement of the brake pedal 13, v/ill cause a pair of pistons 14 and 15 to move within cylinder 16 and expel fluid under pressure from the cylinder 16 via a pair of outlets 17 and 18. Fluid is introduced into the chamber 16 from reservoir 19 via inlets cylinder 16 via a pair of outlets 17 and 18. Fluid is introduced into the chamber 16 from reservoir 19 via inlets 20 and 21.

The control plunger 12 is slidingly mounted within an axial bore of a servo piston 25 which acts against the end of piston 14. A circumferential groove 26 in the external surface 33 of piston 25 provides a chamber which is connected to a pressure fluid accumulator 27. A circumferential groove 28 is provided ϊ plunger 12 and bores 29, 30 and 31 are provided in the servo piston 25 between the internal surface 32 and external surface 33, the internal surface 32 and end face 34, and the internal surface 32 and end face 35, respectively. The end of cylinder 16 adjacent face 34 of piston 25 is closed to define a chamber 36. A further chamber 37 is defined adjacent the end 35 of piston 25 this chamber 37 surrounding the piston 14 and being connected to the reservoir 19 via an outlet 38. The groove 28 and bores 29, 30 and 31 are positioned such that when the brake is not applied, bore 29 will be closed by the plunger 12 while bores 30 and 31 will be interconnected by groove 28, so that the chamber 36 is connected via chamber 37 and outlet 38 to the reservoir 19. Upon movement of plunger 12, communication between groove 28 and bore 31 is closed and bore 29 is interconnected with bore 30 so that pressurised fluid from accumulator 27 may be introduced into the chamber 36 and will act against the end of piston 25 to reinforce the force applied to pistons 14 and 15 by the plunger 12. When the brake is again released, fluid from chamber 36 is permitted to drain back to the reservoir 19 via bore 30, groove 28, bore 31, chamber 27 and outlet 38.

The fluid pressure accumulator 27 is provided, with fluid under pressure by means of an electric pump 40 via non-return valve 41. The electric pump 40 is controlled by pressure switch 43, to maintain the accumulator 27 at the required pressure. A pressure release valve 42 is provided to ensure that the accumulator 27 is not over pressurised, should switch 43 fail to switch off the electric pump 40.

The outlets 17 and 18 from the master cylinder 11 are connected to separate braking circuits, each circuit being split to control two brake actuators 50 (only one shown), typically one brake actuator 50 in each circuit being associated with one of the front wheels of the vehicle and the other brake actuator 50 in each circuit being associated with the diagonally opposite rear wheel. The two circuits of the system and the two splits of each circuit are identical in arrangement and operation and only one split of one circuit is described in detail below and illustrated in the drawings.

In the system illustrated in figure 1, the outlet 17 of master cylinder 11 is connected via a displacement valve 51 to the brake actuator 50. The displacement valve 51 comprises a piston 52 with enlarged diameter central portion 53 which is slidingly sealed within a correspondingly stepped closed cylinder 54, so as to define four fluid tight chambers 55, 56, 57 and 58. Chamber 55 is connected via' an inlet 60 and ball valve 61 to outlet 17

* and via outlet 62 to brake actuator 50. A reduced diameter extension 53 of the end 54 of piston 52 extends through the inlet 60 to engage ball valve 61 and keep it open when the piston 52 is hard over to the left, as illustrated in figure 1. A compression spring 65 acts between face 68 defined by the portion 53 of piston 52 and the opposite face of the stepped portion of cylinder 54, to bias the piston 52 towards the ball valve 61.

The chamber 56 of displacement valve 51 is selectively connected to the reservoir 19 via chamber 37 and outlet 38 or to the accumulator 27 via groove 26, by means of a proportional flow solenoid control valve 66, so that pressurised fluid may be applied to the face 67 of piston 52 to exert a force on the piston 52 to the right.

Chamber 57 of displacement valve 51 is connected to the accumulator 27 via groove 26, so that pressurised fluid may be applied to the face of 69 of piston 52 to exert a force opposing movement of the piston 52 towards the right.

Chamber 58 of the displacement valve 51 is selectively connected to inlet 17 or to the reservoir 19, via chamber 37 and outlet 38, by means of a change-over valve 70.

The change-over valve 70 has a stepped piston 71 which is slidably located within a correspondingly stepped cylinder 72, the piston 71 being sealed with respect to the cylinder 72 so as to define two fluid tight end chambers 73 and 74 and fluid tight intermediate chamber 75.

Chamber 73 of change-over valve 70 is connected via inlet 76 and ball valve 77 to outlet 17 of master cylinder 11. A reduced diameter extension 79 of piston 71 extends through inlet 76 to engage and hold open the ball valve 77, when the piston 71 is hard over to the left. Chamber 73 is connected to chamber 58 of displacement valve 51 and also to the corresponding chamber 58 of the displacement valve 51 controlling the other brake actuator 50 in the brake circuit connected to outlet 17. Spring means 78 acts against the other end of piston 71 to urge the piston 71 towards the ball valve 77.

Chamber 75 of change-over valve 70 is connected to the accumulator 27 via groove 26, and chamber 74 is connected to reservoir 19 via chamber 37 and outlet 38.

The piston 71 has a longitudinal bore 80 which interconnects chambers 73 and 74. A ball valve 81 is provided in the bore 80, the ball valve 81 closing towards chamber 74.^' A plunger 82 extends from the end wall of cylinder 72 adjacent chamber 74, so that when the piston 71 moves to the right, the plunger 82 will engage and unseat ball valve 81.

Under normal operation, pressure fluid from accumulator 27 will be applied to chamber 57 of displacement valve 51 and chamber 75 of change-over valve 70. The pressure in chamber 75 will force piston 71, against the force applied by spring 78, to the right, thus closing ball valve 77 and opening ball valve 81. This connects chamber 58 to the reservoir 19, so that the chamber will be filled with non-pressurised fluid. If the brakes are now applied, the force exerted by the .brake pressure acting on end 64 of piston 52 will be opposed by the force exerted by pressure of fluid from the accumulator 27 in chamber^* 57 and the force applied by spring 65. The piston 52 is dimensioned such that there is a excess force to the left thus preventing movement thereof.

If an antilock cycle is now commenced, the solenoid valve 66 is controlled in known manner to permit pressurised fluid to enter chamber 56 and cause piston 52 to move to the right. This movement will first close ball valve 61, isolating the brake actuator 50 from the master cylinder 11 and then as the volume of chamber 55 increases fluid wrJri flow into the chamber 55 from the brake actuator 50, thus reducing the 'braking effort. The rate at which the piston 52 moves and braking effort is thereby reduced is controlled by the rate at which fluid is allowed to flow into chamber 56 by solenoid valve 66. Reapplication of braking effort is achieved by connecting chamber 56 to reservoir 19 via solenoid valve 66, so that fluid under pressure may flow out of chamber 56 and the piston 51 will be moved back to the left by the pressure of fluid in chamber 57 and the spring 65.

If the pressure of fluid from the accumulator 27 fails, the absence of pressure in chamber 57 will permit piston 52 to move to the right under the influence of the brake pressure applied to end 64 thereof. This movement would close ball valve 61 so that the brake actuator 50 would be isolated from the master cylinder 11 and full braking could not be applied.

However, upon failure of pressure in the accumulator 27, spring 78 will force piston 71 of the change-over valve 70 to the left, thus opening ball valve 77 and closing ball valve 81. This connects chamber 58 of the displacement valve 51 to brake pressure. Again, the piston 52 is dimensioned so that the force exerted by the brake pressure in chamber 58 and by spring 65, will be in excess of the force exerted by the brake pressure acting on end 64 of piston 52. The piston 52 will consequently be held over to the left so permitting normal braking operation. Without pressurised fluid from the accumulator 27 antilock operation cannot of course function.

In the system illustrated in Figure 1, each brake actuator 50 will have an independent displacement valve 51 and antilock control valve 66 to give independent antilock control on all four wheels. Only two change-over valves 70 are however required, one for each circuit of the system. Alternatively, the displacement valve 51 may be inserted in the brake circuit before the split so that one displacement valve 51 and antilock control valve 66 may control antilock operation of both brake actuators in each circuit.

In the modification illustrated in Figure 2, change-over valve 70 is replaced by a solenoid valve 70' which may be arranged to switch connection of chamber 58 of displacement valve 51 from the reservoir 19 to outlet 17 of master cylinder 11, when pressure in the accumulator 27 has failed. The solenoid valve 70' is controlled by pressure sensing means (not shown) associated with the accumulator 27.

The system illustrated in Figure 1 has the disadvantage that under normal operation, when pressure fluid is available .from accumulator 27 and ball valve 77 is closed while ball valve 81 is open, any malfunction of ball valve 81 will go undetected. Consequently, if upon failure of pressure in the accumulator 27, the ball valve 81 fails to close properly, leakage of brake pressure past the ball valve 81 will result in loss of half the braking system, as well as the servo effect on the master cylinder 11. This problem may be avoided by the incorporation of a main power valve 90 as illustrated in Figure 3.

The solenoid controlled main power valve 90 selectively connects chambers 75 of each of the change-over valve 70, to the reservoir 19 via chamber 37 and outlet 38 or to the accumulator 27 via groove 26. Under normal brake operation, the main power valve 90 will connect chamber 75 to reservoir 19, so that the piston 71 will be held over to the left by spring 78 and ball valve 77 will be open while ball valve 81 is closed. Brake pressure will consequently be applied to chamber 58 whenever the brakes are applied, thus holding the piston 52 of displacement valve 51 to the left whether pressure is available from accumulator 27 or not. Consequently, any leakage past ball valve 81 will be detected under normal braking. Only upon antilock operation will the main power valve 90 be switched to connect the chamber 75 of the change-over valve 70 to the accumulator 27. This will cause piston 71 to .move to the right, closing ball valve 77 and opening ball valve 81 to connect chamber 58 of displacement valve 51 to the reservoir, so that upon application of fluid under pressure to chamber 56 via solenoid valve 66 piston 52 will move to the right to reduce braking effort.

Various modifications may be made without departing from the invention. For example, while in the above embodiments, the accumulator 27 serves both the servo mechanism of the master cylinder and the antilock braking control valves, separate power sources may be used. Alternatively, a master cylinder without servo assistance or with a vacuum servo assistance may be used.

Claims

1. A vehicle antilock braking system comprising a master cylinder (11) which will produce a source of fluid under pressure upon brake actuation, said master cylinder (11) being connected to a brake circuit including a brake actuator (50) associated with one of the wheels of the vehicle, said brake actuator (50) being connected to the master cylinder (11) via a displacement valve (51), said displacement valve (51) including a piston (52), movement of said piston (52) being controlled by means of a power fluid source (27) via an antilock control valve (66), so that when the brake is applied fluid in the brake actuator (50) may be displaced into the displacement valve (51) to reduce the braking effort should deceleration of the wheel associated with that brake actuator (50) rise above a level at which locking of the wheel is liable to occur, characterised in that a change-over valve (70;70-) is provided to apply master cylinder pressure to the piston (52) to prevent displacement of the fluid from the brake actuator (50) to the displacement valve (51) should the power fluid source (27) fail.

2. A vehicle antilock braking system according to claim 1 characterised in that the change-over valve (70) comprises a piston (71) slidably sealed within a cylinder (72), said piston (71) dividing the cylinder (72) into three chambers (73, 74, 75), a first chamber (73) connecting the master cylinder (11) to a chamber (58) defined by a face (69) of piston (52) of displacement valve (51) via first valve means (77), the second chamber (75) being connected to the power fluid source (27) so that pressurised fluid therefrom will move the piston (71) away from the first chamber (73), spring means (78) acting upon the piston (71) to oppose movement thereof away from the first chamber (73), said first chamber (73) being connected to a third chamber (74) connected to drain (37), second valve means (81) being interposed between the first and third chambers (73, 74), the first and second valve means (77, 81) being controlled by movement of the piston (71) of said change-over valve (70).

3. A vehicle antilock braking system according to claim 2 characterised in that the second chamber (75) of said change-over valve (70) is selectively connected to the power fluid source (27) or to drain (37) by a main power valve (90).

4. A vehicle antilock braking system according to claim 3 characterised in that said main power valve (90) is controlled to connect the second chamber (75) of the change-over valve (70) to the power fluid source (27) only when an antilock operation is initiated.

5. A vehicle antilock braking system according to claim 2 or 3 characterised in that the main power valve (90) is a solenoid control valve.

6. A vehicle antilock braking system according to any one of claims 2 to 5 characterised in that the fourth chamber (58) of the displacement valve (51) is connected to the first chamber (73) of the change-over valve (70) and the third chamber (74) of the change-over valve (70) is connected to .drain (37).

7. A vehicle antilock braking system according to claim 1 characterised in that a chamber (58) defined by one face (69) of piston (52) of the displacement valve (51) is selectively connected to the master cylinder (11) or to drain (37) by means of a solenoid change-over valve (70*), said solenoid change-over valve (70') being controlled by means responsive to pressure from the power fluid source (27).

8. A vehicle antilock braking system according to any one of claims 1 to 7 characterised in that, said brake actuator (50) is connected to the master cylinder (11) via a first chamber (55) defined at one face (64) of the piston (52) of the displacement valve (51), valve means (61) being provided between the master cylinder (11) and said first chamber (55), said valve means (61) being controlled by movement of the piston (52) of the displacement valve (51).

9. A vehicle antilock braking system according to claim 8 characterised in that second and third chambers (56, 57) are defined at further faces (67, 68) of the piston (52), said second chamber (56) being selectively connected to the power fluid source (27) or to drain (37) via the antilock control valve (66), so that pressure may be increased in said second chamber (56) to move the piston (52) away from the first chamber (55), and said third chamber (57) being connected to the power fluid source (27) to exert a force on the piston (52) to prevent movement of the piston (52) away from said first chamber (55) in response to pressure of fluid in said first chamber (55).

10. A vehicle antilock braking system according to claim 9 characterised in that spring means (65) acts upon the piston (52) to provide a force opposing movement of the piston (52) away from the first chamber (55).

11. A vehicle antilock braking system according to any one- of- claims 8 to 10 characterised in m that a fourth chamber (58) is defined at another face (69) of the piston (52) such that fluid pressure within said fourth chamber (58) will exert a force on the piston (52) which will prevent movement of the piston (52) in response to a force exerted by fluid pressure in the first chamber (55), said fourth chamber (58) being selectively connected to the master cylinder (11) or to drain (37) by said change-over valve (70;70'), the change-over valve (70;70*) being controlled by pressure of fluid from the power fluid source (27), so that upon failure of the power fluid source (27), the fourth chamber (58) will be connected to the master cylinder (11).

12. A vehidle antilock braking system according to claim 11 in which the change-over valve (70;70') will connect the fourth chamber (58) to drain (37) when an antilock operation is initiated and pressurised fluid is available from the power fluid source (27).

13. A vehicle antilock braking system according to any one of the preceding claims characterised in that the system includes a plurality of brake actuators (50), each brake actuator (50) having an independent displacement valve (51) and antilock control valve (66).

14. A vehicle antilock braking system according to claim 13 characterised in that one or more change-over valves (70) are provided, each change-over valve (70) serving a plurality of brake actuators (50).

15. A vehicle antilock braking system according to claim 13 when taken with any one of claims 8 to 10 characterised in that a single main power valve (90) is associated with all the brake actuators (50).