GB2226858A

GB2226858A - Vehicle traction slip control system

Info

Publication number: GB2226858A
Application number: GB8900336A
Authority: GB
Inventors: Eric Charles Hales
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1989-01-07
Filing date: 1989-01-07
Publication date: 1990-07-11
Also published as: GB8900336D0

Abstract

A vehicle traction control system includes a fluid pressure operated brake (16) for a driven wheel 16 of the vehicle, sensing means (72) to detect slipping of the wheel and a servo actuator (25) associated with said brake (16), and comprising a plunger (40) slidably sealed within a cylinder (26) and resiliently biassed towards one end thereof. A valve seat member (45) is slidably sealed in the cylinder (26) and spaced axially of, but resiliently biassed towards, the plunger (40). The valve seat member (45) defines a control port (49), the cylinder (26) being connected on the side of the valve seat member (45) remote from the plunger (40) to the brake (16) and intermediate of the valve seat member (45) and plunger (40) to a brake pressure modulator (20). A servo piston (50) is provided to move the plunger (40) towards the valve seat member (45), so that the plunger (40) will close the control port (49) and will move the valve seat member (45) axially of the cylinder (26) to apply the brake (16) when slipping of the wheel rises above a predetermined value. <IMAGE>

Description

VEHICLE TRACTION CONTROL SYSTEMS The present invention relates to a vehicle traction control system.

According to one aspect of the present invention a vehicle traction control system includes a fluid pressure operated brake associated with a driven wheel of the vehicle, sensing means associated with said wheel to detect slipping of the wheel and a servo actuator associated with said brake, the servo actuator comprising a plunger slidably sealed within a cylinder and resiliently biassed towards one end thereof, a valve seat member slidingly sealed in the cylinder and spaced axially of the plunger, said valve seat member being resiliently biassed towards the plunger, the valve seat member defining a control port, the cylinder being connected on the side of the valve seat member remote from the plunger to the brake, and intermediate of the valve seat member and plunger to a fluid source, and means being provided to move the plunger towards the valve seat member, so that the plunger will close the control port and will move the valve seat member axially of the cylinder to apply the brake when slipping of the wheel rises above a predetermined value.

In a preferred embodiment the plunger and valve seat member are of equal diameter.

Brakes with associated servo control means are preferably associated with each of the driven wheels of the vehicle.

The brakes may be the service brakes of the vehicle.

The vehicle traction control system may also include an engine control modulator which will reduce the power output of the engine when one or more of the wheels of the vehicle slip.

Various embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a vehicle braking system with traction control system in accordance with the present invention; and Figure 2 illustrates a modification to the traction control system illustrated in Figure 1.

Figure 1 illustrates a two circuit, three channel antilock braking system for a rear wheel drive vehicle. One outlet 11 of a servo assisted dual master cylinder 10 of conventional design, is connected in known manner to the actuator 14 of a brake 13 associated with the offside front wheel via an anti lock modulator 15 , and to actuator 17 of brake 16 associated with the nearside rear wheel. The other outlet 11' of the master cylinder 10 is connected in similar manner to actuator 14' of brake 13' associated with the nearside front wheel via antilock modulator 15' and to actuator 17' of brake 16' associated with the offside rear wheel.The actuators 17, 17' of brakes 16, 16' associated with the rear wheels, are connected to outlets 11, 11' of the master cylinder 10 via separate chambers of a tandem antilock modulator 20 of the type disclosed in PCT Patent Application PCT/GB88/00525, and via separate chambers of a dual servo actuator 25.

The dual servo actuator 25 is of symmetrical arrangement having a pair of stepped cylinders 26 arranged back to back with their larger diameter portions 27 adjacent one another and connected together by a larger diameter fluid-tight casing 28. The end 29 of the smaller diameter portion 30 of each cylinder 26 is closed and a port 31 is provided adjacent the closed end 29. A second port 32 opens into the larger diameter portion 27 of each cylinder 26. A sleeve 35 is sealed in the end of portion 27 of cylinder 26 and a plunger 40 of equal cross-sectional area to the smaller diameter portion 30 of cylinder 26 is slidingly sealed in a sleeve 35.A flange formation 43 is provided around the plunger 40 to abut the end of sleeve 30 and restrict movement of the plunger 40 away from the closed end of cylinder 26 and a reduced diameter portion 42 extends from the flanged portion of the plunger 40 towards the closed end of cylinder 26. A compression spring 41 acts upon the flange formation 43 biassing the plunger 40 away from the closed end 29 of cylinder 26 and towards the plunger 40 associated with the other cylinder 26.

A valve seat member 45 is slidingly sealed in the smaller diameter portion 30 of each cylinder 26, spring means 46 acting between the closed end 29 of cylinder 26 and the valve seat member 45 to bias the valve seat member 45 towards the associated plunger 40.

Cylindrical member 47 with radially inwardly directed flange 48 is mounted within the larger diameter portion 27 of cylinder 26 and abuts the sleeve 35. The flange 48 of member 47 is disposed adjacent the stepped portion of cylinder 26 and extends radially inwardly of the smaller diameter portion 30 to provide a stop for the valve seat member 45. An axial control port 49 is provided through the valve seat member 45. The flange 48 is positioned such that when the valve seat member 45 abuts flange 48 and the flange formation 43 on plunger 40 abuts sleeve 35, there will be a clearance between the reduced diameter portion 42 of plunger 40 and the valve seat member 45. The port 31 of each cylinder 26 is connected to one of the actuators 17, 17' of the brakes 16, 16' and the port 32 is connected to the associated chamber of the tandem antilock modulator 20.

A piston 50 is located within the casing 28 and is abutted on opposite sides by the plungers 40 associated with the cylinders 26. The piston 50 is sealed with respect to the casing 28 by means of a diaphragm 51 which is sealed at its inner periphery 52 to the piston 50 and its outer periphery 53 to the cylindrical wall of casing 28, thereby dividing the casing 28 into two fluid-tight chambers 54 and 55.

Compression springs 56 and 57 act between the opposite sides of piston 50 and adjacent end walls of casing 28 to bias the piston 50 towards the centre of casing 28.

Inlets 58 and 59 are provided to chambers 54 and 55. The inlets 58 and 59 are each connected to a solenoid valve 60, 62 by means of which they are selectively connected to atmosphere or to a common source of vacuum 61.

The solenoid valves 60 and 62 comprise a pair of coaxial valve seats 63 and 64 with a valve member 65 disposed therebetween. The valve member 65 is resiliently biassed towards valve seat 63 by means of compression spring 66 and a solenoid plunger 67 when energised acts on the valve member 65 to move it against the bias of spring 66 into engagement with seat 64. The inlets 58 and 59 of the servo actuator 25 are connected intermediate of the seats 63 and 64 of the respective solenoid valve 60, 62 and an inlet 68 disposed on the opposite side of seat 63 to the valve member 65 is open to atmosphere while an outlet 69 disposed on the opposite side of seat 64 to the valve member 65 is connected to the vacuum source 61. The solenoid valves 60 and 62 are connected to outputs of an electronic control unit 70.An output of the electronic control unit 70 is also connected to control means, for example a solenoid control valve 71, for the tandem antilock modulator 20.

Wheel speed sensors 72 and 73 of known design, for example in the form of toothed wheels with electromagnetic pickups, are provided on both of the driven rear wheels. These wheel speed sensors 72 and 73 provide a signal which alternates at a frequency proportional to the rotational speed of the wheel with which they are associated. The signals from the wheel speed sensors 72 and 73 are fed to inputs of the electronic control unit 70.

An engine control modulator 80 is located between the accelerator pedal 81 and throttle control of the engine.

The engine control modulator comprises a rod 82 slidingly mounted through opposed end walls of the cylindrical casing 83 and sealed with respect thereto. A piston 84 is mounted on the rod 82 within the casing 83 and is sealed with respect to the casing 83 by means of diaphragm 85, to define two fluid-tight chambers 86 and 87. A compression spring 88 biasses the piston 84 towards one end of casing 83. An inlet 89 is provided to chamber 86 and is connected to the vacuum source 61 and an outlet 90 to chamber 87 is selectively connected to a vacuum source 61 or to atmosphere via a solenoid control valve 92 of identical construction to solenoid control valves 60 and 62. Solenoid valve 92 is connected to a further output of the electronic control unit 70. When the accelerator pedal is depressed it will move rod 82 and piston 84 to the left as illustrated to open the throttle control valve.If the solenoid valve 92 is actuated to connect chamber 87 to atmosphere, the pressure differential established across piston 84 will apply a load thereto moving the piston 84 back to the right closing the throttle control valve and reducing the power output of the engine.

Switches 95 and 96 associated with the brake pedal 97 and accelerator pedal 81 are connected to inputs to the electronic control unit 70.

Under normal operation, solenoid control valves 60, 62, 71 and 92 will be de-energised and the master cylinder 10 will be connected to the actuators 14, 14' of the front brakes 13, 13' via an open path through antilock modulators 15, 15', and to the actuators 17, 17' of rear brakes 16, 16' via an open path through tandem antilock modulator 20, to port 32 of the servo actuator 25, through cylinder 26, control port 49 and port 31. The brakes may consequently be actuated normally by depression of the brake pedal 97.

If during braking, either of the front wheels engage a surface of low frictional coefficient, so that the wheel is liable to lock and deceleration of the wheel rises above a predetermined value, a wheel speed sensor similar to the sensors 72 and 73, associated with that wheel and a separate electronic control unit will produce a signal to actuate the antilock control module 15, 15' associated with that wheel and reduce the braking effort applied to that wheel, in known manner.

If one of the rear wheels engages a surface of low frictional coefficient, so that the rear wheel is liable to lock and deceleration of that wheel rises above a predetermined value, the electronic processing unit 70 will process the signal from the wheel speed sensor 72, 73 associated with that wheel and produce a signal to energise solenoid valve 71. Energisation of solenoid valve 71 will actuate tandem antilock modulator 20 which will interrupt communication between the master cylinder 10 and both actuators 17 and 17' and will then reduce the fluid pressure applied to both the brake actuators 17 and 17', in known manner to reduce the braking effort of brakes 16 and 16'.

If while the brakes are not applied, the driven rear wheel associated with brake 16 spins, so that the acceleration of the wheel rises above a predetermined value, electronic control unit 70 will produce a signal to energise solenoid valve 62. Upon energisation of the solenoid valve 62, the solenoid plunger 67 will move valve member 65 to open seat 63 and close seat 64. The chamber 55 of the servo actuator 25 will thus be connected to atmosphere and a pressure differential will be established across the piston 50. This pressure differential will move piston 50 to the left as illustrated, first moving the extension 42 of plunger 40 into engagement with the valve seat member 45 to close control port 49 and then moving the valve seat member 45 axially of the cylinder 26 towards a closed end 29 thereof.

Movement of the valve seat member 45 in this manner will displace fluid from the cylinder 26 to actuator 17 and apply the brake 16. Application of the brake 16 will thus reduce the speed of the wheel associated therewith, until when the wheel acceleration has fallen sufficiently the solenoid valve 62 is de-energised, reconnecting chamber 55 to vacuum so that piston 50 and plunger 40 will move back to their initial position and the brake 16 will be released. Brake 16' may be applied in similar manner by energisation of solenoid valve 60, if the wheel associated with the brake 16' accelerates above the predetermined value.

If spinning of either wheel is particularly excessive, then the electronic control unit 70 may energise solenoid valve 92 in addition to either solenoid valve 60 or 62.

Energisation of solenoid valve 92 will connect chamber 86 of the engine control modulator 80 to atmosphere, thus establishing a pressure differential across piston 84 which will move the rod 82, which has been displaced to the left by depression of the accelerator pedal back to the right, as illustrated. Movement of the rod 82 in this way will reduce the throttle opening and power output of the engine.

If both the rear wheels spin, so that acceleration of both wheels is above the predetermined value, the electronic control unit 70 will energise only solenoid valve 92 to reduce the power output of the engine, until spinning of the wheels is reduced sufficiently.

The inputs from switches 96 and 97 ensure that the electronic control unit 70 will only initiate an anti lock operation if brake pedal 97 is depressed to apply the brakes and will only initiate a traction control operation when the accelerator pedal 81 is depressed and the brakes are not applied that is brake pedal 97 is not depressed.

Because of lag in engine response to the closing of the throttle, control of traction by means of the engine control modulator 80 alone is relatively slow. The engine speed could be brought down more quickly by simultaneous braking of both rear wheels. This is not however possible with the embodiment described above because of the linking of the servo actuators for the two brakes 16 and 16'. This problem may however be overcome by using independent servo actuators for brakes lt and 16' as illustrated in Figure 2.

In the independent servo actuators 100, 100' illustrated in Figure 2, the piston 50 is slidably mounted in casing 28 and is sealed with respect thereto by diaphragm 51 to define two working chambers 101 and 102. A compression spring 103 acts on the piston 50 biassing it away from the cylinder 27.

The chamber 101 which is on the side of piston 50 adjacent cylinder 27, is connected to the vacuum source 61 via port 104 and chamber 102 on the other side of piston 50 is selectively connected to vacuum source 61 or to atmosphere via solenoid valve 60, 62 which is connected to port 105.

With this modification, solenoid valve 60 will control servo actuator 100 and solenoid valve 62 will control servo actuator 101, in the manner described above.

In this modified system if both rear wheels spin, then the electronic control unit 70 will energise solenoid valves 60, 62 and 92 to brake both rear wheels and simultaneously reduce the power output of the engine, so that traction of the wheels is restored rapidly.

Various modifications may be made without departing from the invention. For example while in the above embodiments, the traction control system and service brakes of the vehicle are integrated, the traction control system may be independent of the service brakes. When integrated with the service brakes, the system may be a single or multi-circuit system, with single or multi-channel antilock operation as required, the brake associated with each driven wheel of the vehicle being controlled through an individual servo actuator of the type described above.

Actuation of the servo actuators may alternatively be achieved by fluid pressure actuators or by solenoid actuators.

Instead of using acceleration of the driven wheels as an indication of wheel slip to trigger a traction control operation, sensors may be provided to compare the velocity of the driven wheel with that of a non-driven wheel and initiate a traction control operation when the speed of the driven wheel is more than a predetermined amount in excess of that of the non-driven wheel.

Claims

1. A vehicle traction control system including a fluid pressure operated brake asociated with a driven wheel of the vehicle, sensing means associatd with said wheel to detect slipping of the wheel and a servo actuator associated with said brake, the servo actuator comprising a plunger slidably sealed within a cylinder and resiliently biassed towards one end thereof, a valve seat member slidingly sealed in the cylinder and spaced axially of the plunger, said valve seat member being resiliently biassed towards the plunger, the valve seat member defining a control port, the cylinder being connected on the side of the valve seat member remote from the plunger to the brake, and intermediate of the valve seat member and plunger to a fluid source, and means being provided to move the plunger towards the valve seat member, so that the plunger will close the control port and will move the valve seat member axially of the cylinder, to apply the brake when slipping of the wheel rises above a predetermined value.

2. A vehicle traction control system according to claim 1 in which the plunger and the valve seat member are of equal diameter.

3. A vehicle traction control system according to claim 1 or 2 in which means is provided to limit movement of the valve seat member towards the plunger so that at a first position, the plunger will be clear of the valve seat member.

4. A vehicle traction control system according to claim 3 in which means is provided to limit movement of the plunger away from the valve seat member so that in said first position the clearance between the plunger and valve seat member is limited.

5. A vehicle traction control system according to any one of the preceding claims in which the cylinder is stepped, the valve seat member being slidably sealed in a reduced diameter portion of the cylinder and the plunger being slidably sealed in a sleeve located in a larger diameter portion of the cylinder, said sleeve being spaced axially from the smaller diameter portion of the piston, and a flange formation being provided on the plunger to abut the sleeve and limit movement of the plunger away from the valve seat member.

6. A vehicle traction control system according to claim 5 in which a cylindrical member is located in the enlarged diameter portion of the cylinder in abutting relationship with the sleeve, a flange formation being provided at the end of the cylindrical member remote from the sleeve, the said flange formation extending radially inwardly of the smaller diameter portion of the cylinder to provide a stop for the valve seat member.

7. A vehicle traction control system according to claim 6 in which a reduced diameter portion of the plunger extends from the flanged portion towards the valve seat member.

8. A vehicle traction control system according to any one of the preceding claims in which the means for moving the plunger towards the valve seat member comprises a piston, the plunger abutting one side of the piston, chambers being provided on both sides of the piston, one of the chambers being selectively connected to a high pressure source and a low pressure source so that a pressure differential may be established across the piston to move the piston and plunger abutted thereby towards the valve seat member.

9. A vehicle traction control system according to claim 8 in which the chamber on the same side of the piston as the plunger is adapted to be selectively connected to a low pressure source and the chamber on the side of the piston remote from the plunger being adapted to be connected to a low pressure source or a high pressure source, spring means being provided to bias the piston away from the plunger.

10. A vehicle antilock control system according to claim 8 in which a pair of servo actuators, each associated with an individual brake, are provided back to back, the plungers of the servo actuators acting on opposed sides of a common piston, the chambers on each side of the piston being selectively connected to a high pressure source or to a low pressure source.

11. A vehile control system according to claim 8, 9 or 10 in which the or each chamber is selectively connected to a high pressure source or to the low pressure source via a solenoid control valve.

12. A vehicle traction control system according to any one of the preceding claims including an engine control modulator.

13. A vehicle traction control system according to claim 12 in which the engine control modulator comprises a piston defining two chambers, one chamber being adapted to be connected to a low pressure source and the other chamber being adapted to be selectively connected to a low pressure source or to a high pressure source.

14. A vehicle traction control system according to claim 13 in which the other chamber is selectively connected to the low pressure source or to the high pressure source via a solenoid valve.

15. A vehicle traction control system accordng to any one of claims 1 to 14 in which a wheel speed sensor is associated with the driven wheel, a control unit processes the signal from the wheel speed sensor and generates a signal to control the means for moving the plunger, when wheel acceleration rises above a predetermined value.

16. A vehicle traction control system according to any one of claims 1 to 14 in which wheel speed sensors are associated with the driven wheel and with a non-driven wheel of the vehicle, a control unit processes the signals from the wheel speed sensors and generates a signal to control the means for moving the plunger, when the speed of the driven wheel is in excess of that of the non-driven wheel by more than a predetermined amount.

17. A vehicle traction control system according to claim 15 or claim 16 in which the control unit generates a control signal to actuate an engine control modulator, when the signal from the wheel speed sensor indicates that spinning of the driven wheel is above a predetermined value.

18. A vehicle traction control system according to any one of claims 15 to 17 in which switches associated with the brake pedal and the accelerator pedal provide signals which are applied to the control unit so that the control unit will only trigger a traction control operation when the accelerator pedal is depressed and the brakes are not applied.

19. A vehicle traction control system according to any one of the preceding claims in which a brake and associated servo actuator is associated with each of the driven wheels of the vehicle.

20. A vehicle traction control system according to any one of the preceding claims in which the brake is a service brake of the vehicle.

21. A vehicle traction control system substantially as described herein with reference to and as shown in Figures 1 and 2 of the accompanying drawings.

22. A vehicle braking system comprising a traction control system as claimed in any one of claims 1 to 21.

23. A vehicle braking system according to claim 22 including an anti lock braking system.