GB2225397A

GB2225397A - Electrical control of braking

Info

Publication number: GB2225397A
Application number: GB8826211A
Authority: GB
Inventors: David Parsons
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1988-11-09
Filing date: 1988-11-09
Publication date: 1990-05-30
Also published as: GB8826211D0

Abstract

A vehicle braking system includes two circuits (10, 10'), each circuit (10, 10') including a brake actuator (11, 13) and a hydraulic system (15, 15') to control the pressure of fluid applied to said brake actuator (11, 13) each hydraulic system (15, 15) including an electric motor operated valve means (21, 22) (Fig 2, not shown) by which the brake actuator (11, 13) may be selectively connected to a source of fluid under pressure or to drain, the electric motor operated valve means (21, 22) in each circuit (10, 10') being controlled by a separate control module (16, 16') in response to signals from separate transducers (17, 17') associated with a brake application means (18). <IMAGE>

Description

VEHICLE BRAKING SYSTEMS The present invention relates to vehicle braking systems.

According to one aspect of the present invention, a vehicle braking system comprises two circuits, each circuit including a brake actuator and a hydraulic system to control the pressure of fluid applied to said brake actuator, each hydraulic system including an electric motor operated valve means by which the brake actuator may be selectively connected to a source of fluid under pressure or to drain, the electric motor operated valve means in each circuit being controlled by a separate control module in response to signals from separate transducers associated with a brake application means.

Preferably each circuit of the braking system will serve a plurality of brake actuators, each associated with a different wheel of the vehicle, a separate electric motor operated valve means being provided for each brake actuator.

The control modules may also process signals, for example indicative of wheel speed, road speed, steering angle and suspension travel and control each electric motor operated valve in the associated circuit to provide anti lock operation, wheel spin operation and/or differential braking operation on cornering. Means may also be provided within each hydraulic system, for example pressure monitoring transducers, position transducers and pressure differential transducers, to provide a feedback to the control module, so that each brake actuator may be controlled appropriately.

Each control module is also preferably provided with a separate power supply.

Means is also preferably provided for applying a reaction load to the brake application means which will oppose the load applied to the application means during brake application. This may simply be spring means, but preferably a hydraulic or electrical feedback mechanism is used which will provide a reaction load which is a function of the effort applied by the brake actuators.

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 dual circuit braking system in accordance with the present invention; Figure 2 illustrates the hydraulic system of one circuit of the system illustrated in Figure 1; Figure 3 illustrates an alternative form of electric motor operated valve means that may be used in the system illustrated in Figure 1; Figure 4 illustrates in part-sectional side elevation an integrated arrangement of the system illustrated in Figures 1 and 3; and Figure 5 illustrates an. end elevation of the arrangement illustrated in Figure 4.

The brake system illustrated in Figure 1 is a dual system having one circuit 10 controlling the brake 11 associated with the offside front wheel and brake 12 associated with the nearside rear wheel and circuit 10' controlling the brake 13 associated with the nearside front wheel and brake 14 associated with the offside rear wheel.

Each circuit 10, 10' includes a hydraulic system 15, 15' for controlling the brake actuators in the circuit 10, 10'. As described in greater detail below, each hydraulic system 15, 15' includes a pair of electric motor operated valves 21, 22, separate control modules 16, 16' being provided to control the electric motors 25 associated with each hydraulic system 15, 15'. The control modules 16, 16' produce signals to actuate the electric motors 25 associated with each of the hydraulic systems 15, 15' to connect the brake actuators served thereby to a source of high pressure fluid or to drain, in response to signals from a pair of sensors 17, 17' associated with brake pedal 18. The sensors 17, 17' may be contact devices, for example in the form of potentiometers or non-contact devices, for example in the form of capacitive or inductive transducers.

Further electrical inputs may be applied to each of the control modules 16, 16' corresponding, for example, to wheel speed, road speed, steering angle and suspension travel, these inputs being produced in known manner. Furthermore, inputs may be applied to the control modules 16, 16' corresponding to, for example pressures and pressure differentials in each of the hydraulic systems 15, 15' respectively. The control modules 16, 16' may then control the hydraulic systems 15, 15' so that the braking effort applied to each wheel is adjusted appropriately to provide antilock braking control, wheel spin control and differential braking on cornering or any combination thereof.

In order to safeguard against power failure, each of the control modules 16, 16' is provided with an independent power source 19, 19' so that if the power supply to one of the control modules 16, 16' fails, normal braking may still be achieved in the brakes served by the circuit 10, 10' associated with the other control module 16 The brake pedal 18 is connected to a reaction element 20, which will apply a load to the pedal 18 opposing that load applied to the pedal 18 to apply the brakes, thereby providing an artifical feel.The reaction element 20 may merely be spring or spring and damper means but preferably includes hydraulic or electrical feedback means so that the reaction load applied to the pedal 18 is proportional to the braking effort applied to the wheels of the vehicle or to some other parameter or parameters, for example, vehicle speed, wheel acceleration or deceleration, steering angle etc. The reaction element 20 may also provide tactile warning, for example kickback when, for example, an antilock cycle is initiated.

The hydraulic systems 15, 15' of each circuit 10, 10' are of identical configuration and consequently only one system 15, is illustrated in Figure 2 and described in detail below.

As illustrated in Figure 2 the hydraulic system 15 comprises a pair of motorised valve units 21 and 22, one valve unit 21 selectively connecting the actuator of brake 11 to a source of pressurised fluid P1 or to drain R1 and the other valve unit 22 selectively connecting the actuator of brake 12 to a source of pressurised fluid P2 or to drain R2. The motorised valve units 21 and 22 each comprise a torque motor 25 which is connected by a crank 26 and connecting rod 27 to a valve spool 28 which is slidingly sealed within a cylinder 29. The valve spool 28 has three axially spaced enlarged diameter portions 30, 31 and 32 which sealingly engage the walls of the cylinder 29 to divide the cylinder 29 into two fluid tight chambers 33 and 34. A return spring 35 acts against the end 32 of tile valve spool 28 adjacent portion 32.

Axially spaced ports 36 and 37 are provided to the cylinder 29, port 36 opening to chamber 33 and port 37 opening to chamber 34. A third port 38 is provided intermediate of the ports 36 and 37 and positioned such that at a first position of the spool valve 28, port 38 will be closed by portion 31, at a second position ports 36 and 38 will be interconnected via chamber 33 and at a third position ports 37 and 38 will be interconnected via chamber 34. The ports 36 of the valves 21 and 22 are connected to pressure sources P1 and P2 respectively. The ports 36 may be connected directly to pump means which will provide fluid at the required pressure or to pressure fluid accumulators. A common pressure source may be connected to both valve units 21 and 22, although preferably separate sources are used so that if one source should fail, the brake served by the other pressure source may still be actuated. Ports 37 of the valve units 21 and 22 are connected to drain R1 and drain R2 respectively and via those drains to separate reservoirs. Port 38 of valve unit 21 is connected to the actuator associated with brake 11 and port 38 of valve unit 22 is connected to the actuator associated with brake 12. The ports 38 of valve units 21 and 22 are also connected to opposite sides of differential pressure transducer 40, the output from which is connected to the control module 16. The port 38 of valve unit 21 is furthermore connected tb a pressure transducer 41, the output of which is connected to a control unit 42 which controls valve unit 21.Also, the valve unit 21 is provided with a position sensor, for example displacement measuring means 43 located at the end of cylinder 29, which provides an output indicative of the position of the valve spool 28, this output being applied to the control unit 42.

Similarly, a pressure transducer 44 is connected to the port 38 of valve unit 22 and the output from this pressure transducer 44 and a position sensor 46 are fed back to control unit 45 for the valve unit 22.

With the braking system described above, when the brakes are applied by depression of the pedal 18, the sensor 17 will apply a signal to the control module 15. This signal is processed together with the signals from the other sensors measuring, for example, wheel speed, road speed, steering angle and suspension travel, to produce control signals corresponding to the optimum brake effort to be applied by the actuators of brakes 11 and 12, these control signals being applied to the control units 42 and 45 respectively.

The control units 42 and 45 each apply a signal to the motors 25 of the associated valve 21, 22 which energise the motors 25 and moves the valve spools 28 to their second position, connecting the actuators of brakes 11 and 12 to the sources P1 and P2 respectively. When the valve spools 28 are at their second position, the signals from the position sensors 43 and 4.6 switch control units 42 and 45 to de-energise the motors 25.The pressure in lines from ports 38 to the actuators associated with brakes 11 and 12 will thus increase until the pressure applied to the actuator associated with each of the brakes 11 and 12 is at its optimum, when a signal from transducer 41, 44 will switch control unit 42, 45 to re-energise the motors 25 associated with valves 21, 22 and cause the valve spools 28 thereof to return to their first positions in which the ports 38 are isolated from the pressure sources P1, P2 and the drains R1, R2 respectively.

The actuator associated with the brakes 11 and 12 will thus be held to apply optimum braking, until, upon a change in the signals applied to the control module 16, the output signals to the control units 42 and 45 will be modified, thus switching each of the control units 42 and 45 to control the motor. 25 associated with each of the valve units 21 and 22, to move the valve spool 28; to its-third position connecting the actuator of the associated brake 11 and 12 to drain R1, R2, thus permitting release of pressure from the brake actuator; or to its second position thus causing further increase in the pressure applied to the brake actuator associated with brake 11, 12.

In this manner, the pressure applied to the actuators associated with brakes 11 and 12 may be controlled independently to maintain optimum braking efficiency on each of the brakes 11 and 12.

In the modified electric motor operated valve means illustrated in Figure 3, the motor 25 acts upon the valve spool 28 by means of a ball screw mechanism 50 of known design. The motor 25 is controlled in similar manner to that described above, to provide independent control of the brake actuator associated with the valve 21.

As illustrated in Figures 4 and 5, motorised valve units 21, 22 and 21', 22' of the type illustrated in Figure 3, for both ciruits 10, 10' of the brake system may be mounted on one side of a common pate 60, the plate 60 being adapted to be mounted to the pedal box 61 of the vehicle. The brake pedal 18 is pivotally mounted on the other side of the plate 60 on lug 62. Integrated control module 63 comprising control module 16, control units 42, 45, control module 16' and control units 42', 45' is mounted on the other side of plate 60, sensors 17, 17' associated therewith being connected to the pedal 18 by a crank 68 and link 69. The control units 42, 42', 45 and 45' are connected to their respective motors 25, by hard electrical connections 64.A reaction element 20 is also mounted on the plate 60 and connected to pedal 18 by means of a suitable linkage, this reaction element 20 providing a load proportional to the pressure applied to the brake actuators, to oppose movement of the pedal 18 upon application of the brakes.

A push rod 65 is mounted coaxially of each of the motor 25/ball screw 50 assemblies of the motorised valves 21 and 21' controlling the actuators of the front brakes 11 and 13, said push rods 65 engaging the valve spools 28. These push rods 65 are connected to the pedal 18 by means of pins 66 which engage in elongated slots 67, spring means (not shown) being provided to maintain engagement between the push rods 65 and the valve spools 28.

Under normal electronic control, the brakes are fully applied before the pins 66 reach the end of elongated slots 67. However, should electronic brake control fail, there will be no load applied to the pedal 18 by reaction element 20 and consequently a load applied to the pedal 18 will move pins 66 until they engage the ends of elongated slots 67, the load then being applied directly to the valve spools 28 of valves 21 and 21', to move the valve spools 28 to their second positions in which the actuators of brakes 11 and 13 will be connected to the fluid pressure sources P1 and P1', so that brakes 11 and 13 will be applied. In this manner a mechanical override is provided for emergency operation of the front brakes 11 and 13 in the event of total failure of electronic control system.

Various modifications may be made without departing from the invention. For example, while in the above embodiments movement of the valve spools 28 is controlled in both directions by the motors 25, in an alternative embodiment the valve spools 28 may be pressure balanced. This may be achieved by applying pressure from port 38 to the end of the valve spool 28 engaged by spring 35 so that when port 38 is at the required pressure the pressure on the end of the valve spool 28 will balance the force applied by the motor 25 and will move the valve spool 28 back to isolate port 38 from the fluid pressure source. With this embodiment there is no need for the pressure transducers 41 and 44 nor the differential transducer 40.

Claims

1. A vehicle braking system comprising two circuits, each circuit including a brake actuator and a hydraulic system to control the pressure of fluid applied to said brake actuator, each hydraulic system including an electric motor operated valve means by which the brake actuator may be selectively connected to a source of fluid under pressure or to drain, the electric motor operated valve means in each circuit being controlled by a separate control module in response to signals from separate transducers associated with a brake application means.

2. A vehicle braking system according to Claim 1 in which each circuit includes a plurality of brake actuators, each brake actuator associated with a different wheel of the vehicle, separate electric motor operated valve means being provided for each brake actuator.

3. A vehicle braking system according to Claim 1 or 2 in which the control modules process signals indicative of wheel speed, road speed, steering angle, suspension travel or any combination thereof.

4. A vehicle braking system according to any one of Claims 1 to 3 in which pressure monitoring transducers, position transducers, pressure differential transducers or any combination thereof are provided in the hydraulic systems to provide a feedback to the control modules.

5. A vehicle braking system according to any one of the preceding claims in which means is provided for applying a reaction load to the brake application means.

6. A vehicle braking system according to Claim 5 in which said means includes a hydraulic or electrical feedback mechanism, so that the reaction load applied to the brake application means is a function of the effort applied by the brake actuator.

7. A vehicle braking system according to any one of Claims 1 to 6 in which the electric motor operated valve means comprises a valve spool slidably sealed within a cylinder, the cylinder being connected by axially spaced ports to a source of fluid under pressure, a brake actuator and a drain, the valve spool being adapted to be moved by the electric motor to connect the brake actuator to the source of fluid under pressure or to the drain.

8. A vehicle braking system according to Claim 7 in which the valve spool has three axially spaced enlarged diameter portions which sealingly engage the wall of the cylinder to define two fluid tight chambers, three axially spaced ports being provided to the cylinder and the valve spool being adapted to be moved by the electric motor between a first position in which the central port is isolated from the outer ports, a second position in which the central port is connected to one of the outer ports via one of the fluid tight chambers, and a third position in which the central port is connected to the other outer port by the other fluid tight chamber.

9. A vehicle braking system according to any one of Claims 1 to 8 in which the valve spool is connected to the electric motor via a crank and link.

10. A vehicle braking system according to any one of Claims 1 to 8 in which the valve spool is connected to the electric motor by a ball screw mechanism.

11. A vehicle braking system according to Claim 10 in which the electric motor operated valve means associated with both circuits of the braking system are mounted on one side of a common plate, the brake application means, control modules and brake sensors being mounted on the other side of the plate, mechanical override means being provided for operation of at least one of said valve means, upon failure of the electronic control means.

12. A vehicle braking system according to Claim 11 in which a push rod extends coaxially of the electric motor and ball screw mechanism to engage the valve spool, said push rod being connected to the brake application means in a manner which will permit relative movement therebetween over the maximum travel of the brake application means normally required to fully apply the brakes under electronic control, the load applied to the brake application means being transmitted by the push rod to the valve spool when said maximum travel is exceeded, so that the spool is moved to connect the brake actuator to the source of fluid under pressure.

13. A vehicle braking system substantially as described herein with reference to, and as shown in, Figures 1 and 2, Figure 3 or Figures 4 and 5 of the accompanying drawings.