GB2121495A

GB2121495A - A method of detection and separation of wheel drag and braking forces suitable for incorporation into braking control systems

Info

Publication number: GB2121495A
Application number: GB08211755A
Authority: GB
Inventors: Derek Allcock
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-04-23
Filing date: 1982-04-23
Publication date: 1983-12-21

Abstract

This invention relates to an arrangement for monitoring selected forces acting on the members supporting the road wheel assemblies of a vehicle. The arrangements consist of strain or force transducers strategically placed to measure these forces. The output signals from the transducers could be suitably processed and used in an anti-lock braking system to; (i) ascertain when any wheel is about to lock, (ii) provide a measure of the tyre/road adhesion conditions in terms of reacted brake torque at the instant the wheel is about to lock. The output signals when suitably processed could further be used to provide a measure of the forces acting at transverse wheel positions to detect in equality in these forces due typically to tyre deflation. When used in conjunction with the output signal from a strain or force transducer on the brake pedal mechanism, the output signals from the wheel positions could be processed to provide a measure of the brake efficiency. <IMAGE>

Description

SPECIFICATION Amethodofdetection and separation of wheel drag and braking forces suitable for incorporation into braking control systems This invention relates to an arrangement for monitoring selected forces acting on the members supporting the road wheel assemblies of a vehicle. From this information action may be taken to initiate: a) the prevention of the wheels locking during braking together with a driver information signal, b) a reduction in unequal drag forces between transverse wheels caused, typically, by a rapid tyre deflation,togetherwith a driver information signal.

The arrangement will also provide a measure of the efficiency ofthe braking system of a vehicle.

In general three components are necessary: 1) A means of detecting and reporting on the changing conditions at each wheel position.

2) A means of processing the information obtained in 1) and evaluating whether remedial action is required in relation to a) and b) above.

3) A means of carrying outthe required remedial action decided upon in 2).

This invention is limited to 1).

It is envisaged that a microprocessorwill be used in 2) to decide when: i) wheels are about to lock and that a reduction in the applied brake torque is required, ii) the drag forces on transverse wheels are unequal andthatwhen braking, a reduction in the applied brake torque on one of the wheels is required until the drag forces are equal, iii) the brakes are considered inefficient.

It is further envisaged that the means of carrying out remedial action in i) and ii) above, will be a pressure adjustment valve and to carry out iii) above, a driver information signal to indicate to thedriverthatthe brake efficiency has fallen belowa prescribed value.

The use of a microprocessor, pressure adjustment valve and driver information signal are described here to illustrate howthe invention might be incorporated into a braking control system of a vehicle. It is intended that the subject of this invention should not be limited solely in its application to the brake control system outlined above.

This invention is a means of continually monitoring selected forces acting on the members supporting the wheel assemblies of a vehicletogetherwith a means of monitoring the force applied atthe brake pedal when the vehicle is braked.

It comprises an arrangementofstrain or force transducers strategically placed to measure how the forces in the members supporting the wheel assemblies of the vehicle are changing during; u) motion without braking, v) the braking ofthevehicle.

Astrain orforce transducer is also located atthe brake pedal. The actual location ofthe strain or force transducers on the wheel assemblies of the vehicle will depend on the design of these assemblies for a particularvehicle, howevertheywill be placed such that the output from them will contain: x) Cia a component ofthe reacted brake torque, y) C2, a component ofthe applied brake torque, z) C3, a component of the rolling resistance of the wheel.

The strain orforce transducers at the wheel positions will produce a continuous output in the form of an electric signal which will depend on the forces acting on the members carrying the strain or force transducers. As these forces change during motion of the vehicle, braking of the vehicle ortypically tyre deflation, their changing values will be reflected in the output signalsfrom the strain orforce transducers.

These signals will be processed and a decision on the necessity for remedial action obtained.

The point at which a wheel is about to lock due to overbraking, would be detected by comparing (C1 + C3) with (C2). The value (C1 ) atthe point where the wheel is about to lock is also a measure of the tyre/road adhesion conditions.

By a regular comparison ofthe values (Cl + C3) for the transverse wheel positions, unequal forces at these wheels can be detected when the vehicle is being braked. Unequal forces on transverse wheels can also be detected when the vehicle is in motion without braking by a regular comparison of C3 for these wheels.

A measure of the brake efficiency for each wheel can be obtained by comparing (C1 + C3) with the brake pedal effort Sp measured by the strain or force transducer located at the brake pedal. The ratio value (C1 + C3)/Sp can be compared to a reference value for that wheel, as determined by legislation for the vehicle.

Some existing anti-lock braking systems rely on rotating devices to generate signals which aresubse- quently processed in order to identifythe onset of wheel lock.

The invention as described above requires no additional moving parts as the output signals result from normal suspension forces. These output signals are suitable for incorporation into a self-adaptive braking control system.

Further advantages ofthis arrangement are the provision of a means of detection of unequal drag forces on transverse wheels along with regular monitoring of brake efficiency.

This invention is further illustrated by example 1 which displays a schematic view of a suspension system.

EXAMPLE 1.

Fig. 1 shows a wheel during normal unbraked motion,theforce FD and its reaction F'D being due to tyre drag, and varying with tyre pressure, road speed and other factors.

Fig. 2 shows the wheel during braking, where the drag force FD is still applied, but in addition the brake lining applies a force Fp and causes a reaction force F'p at the wheel bearing. The tyreforce is increased by Fs, a force which is dependent on the tyre to road conditions and the amount of slip between the tyre and the road. The reaction F's to this force is additional to F'D at the wheel bearing.

Fig. 3 shows a hypothetical wheel suspension consisting of four links A,B,C,D, pin-jointed horizontal ly at each end. E is the wheel bearing support and Fis the extension ofthis supporting the brake caliper F'p is the reaction to the braking force Fp, and F"p is the reaction to F'p.F"p is not supplied bythe links A,B,C,D, since they are free to rotate about the pin joints. The forces F1, F2, F3, and F44 are the forces applied bythe vehicle chassis to the links at the inner pin joints, as reactions to the other forces shown.

The horizontal force F"D is directly proportional to the brake reacted torque FD x R of the wheel. The force couple Fp X risthe brake applied torque ofthe wheel, and F'p X r is the reaction torque applied to the links.

Each link is subjected to bending moments in a plane passing through its pin-joint axes. The forces at each link causing bending are: a) C1, a component proportional tothe reacted brake torque FD x R, b) C2 a component proportional to the applied braketorque Fp X r, c) C3 a component proportional to the rolling resistance FD. Fig. 4 shows the directions ofthese force components on the links A and Bforthe unbraked condition, and Fig. 5 the force components forthe braked condition.

One or more strain gauges are bondedto each ofthe links A and B, situated as shown in Fig. 6 to measure the bending moment in each link in the plane through the pin axes. Let SA be in the signal from the gauge or gauges on link A, and Sus the signal from those on link B.

In the unbraked condition, SA = KC3 and Se = KC3.

where K is a constant of proportionality.

During braking, SA = K (C1 + C2 + C3) and Sa = K (C1 -C2+C3).

The signals SA and Sg are processed to provide values proportional to C2 and C1 + C3, these being in turn proportional to the brake applied torque and the brake reaction torque plus the rolling resistance respectively. Thus: SA + SB = 2KC3 hence C3 = (SA + SB)/2Kforthe unbraked condition.

Forthe braked condition: SA + SB = 2K(C1 +C3)henceC1 +C3=(SA+SB)/2K and SA - SB = 2K C2 hence C2 = (SA - SB)!2K.

The onset of the wheel lock may be detected by the conditions: a) the applied brake torque is not decreasing, and b) the reacted braketorque plus the rolling resist ance is decreasing, but not at a rate greaterthan a preset value Z.

Thus the onset of wheel lockmay be detected buy a system which processes the signals SA and SB and then processes the resulting signals C1 + C3 and C2.

Unequal drag forces between transverse wheel positionsduring unbraked motion, such as mayoccur due to a partly orfully deflated tyre, may be detected by regularly comparing the values of C3 = (SA + Se)/2K for the two wheels at an axle position, such as the wheels Q and R orthewheels Sand T shown in Fig. 7 where one ofthe pair of wheels has a sustained higher value than the other, of more than a preset proportion H, then a driver warning signal ofafaultatthewheel is initiated, and the brake slave cylinderforthatwheel is isolated from the brake master cylinder, by a brake pressure adjusting valve.

When the brakes are applied, braking pressure is not applied to the wheel with excess drag until the value of (SA + Ss)/2K at the transverse wheel exceeds that at the excess drag wheel. The system then keeps the drag atthetwo wheels virtually the same as each other byadjustingthe brake pressure in increments, and at the sametime prevents wheel lock as previously described.

The efficiency ofthe braking system at each wheel may be established relative to a preset value Es fixed with regard to the legal brake efficiency requirements.

The measured brake efficiency EM at each wheel is calculated regularly from the signals SA and Sg from thetransducersand from the signal Spfromthe brake pedal force transducer.

Sp = GF,where Fistheforceapplied bythedriverto the brake pedal, and G isaconstantofproportionality.

Thus: EM = (C1 + C3)/SP = (SA + SB)/2KSp.

When EM is equal to or less than Es,then a driver warning signai of brake inefficiencyforthatwheel is initiated.

Claims

1. An arrangementfor continually monitoring the braking forces on a wheeled vehicle and so provide electrical output signals which, when suitably processed could be used to; (i) detectwhen a wheel is on the point of locking due to overbraking, (ii) provide a measure of thetyre/road adhesion condition in terms of reacted brake torque at the instantthewheel is aboutto lock, (iii) detect unequal drag forces between transversewheel positions, (iv) provide a measure of brake efficiency.

The arrangement comprises; (a) a number of strain orforce transducers, the outputs from which provide a measure ofthe braking forces atthewheel positions, (b) a strain orforce transducerto provide a measure of the brake pedal effort.

2. An arrangement substantially as in claim 1 to provide electrical output signals which when suitably processed, cou Id be used to detect when a wheel is on the point of locking duetooverbraking.

The arrangement comprises a number of strain or force transducers, the outputs from which provide a measure ofthe braking forces at the wheel positions.

3. A system as in claim 2 where the output signals are provided by strain orforce transducers attached to the chassis and/or suspension members supporting each wheel.

4. Asystem as in claim 3 where the number and location of the transducers at each wheel position is determined by the design ofthe suspension system at that position.

5. A system as in claim 2where the output signals from the transducers at each wheel position contain a measure of the reacted brake torque (C1 ) when the vehicle is braked.

6. A system as in claim 2 where the output signals from the transducers at each wheel position contain a measure of the applied brake torque (C2) when the vehicle is braked.

7. Asystem as in claim 2where the output signals from thetransducers at each wheel position contain a measure of the rolling resistance ofthewheel (C3).

8. Asystem as in claims 5,6 and 7 where the point at which a wheel is about to lock due to overbraking could be detected by the regular comparison of (C1 + C3) with C2forthatwheel.

9 Asystem as in claims5and 8wherea measure ofthetyre/road adhesion condition in terms of reacted brake torque is given by the value of C1 when the wheel is about to lock.

10. An arrangement substantially as in claim 1 to provide electrical output signals which when suitably processed could be used to detect unequal drag forces between transverse wheel positions.

The arrangement comprises a number of strain or force transducers, the output from which contain a measure of the rolling resistance of each wheel.

11. A system as in claim 10 where the output signals are provided by strain orforcetransducers attached to the chassis and/or suspension members supporting each wheel.

12. Asystem as in claim 1 Owhere the number and location ofthe transducers at each wheel position it determined by the design of the suspension system at that position.

13. Asystem as in claim 10wherethe output signals from the transducers at each wheel position contain a measure of the rolling resistance ofthe wheel (C3).

14. A system as in claim 10 where the output signals from the transducers at each wheel position contain a measureofthe reacted brake torque (C1) when the vehicle is braked and claim 13, where unequal drag forces could be detected by regular comparison of (C1 + C3)forawheel position with (C1 + C3) for the transverse wheel position when the vehicle is braked and by the regular comparison of C3 for a wheel with C3 for the transverse wheel position when the vehicle is not braked.

15. An arrangement substantially as in claim 1 to provide electrical output signals which when suitably processed could provide a measure of brake efficiency.

The arrangement comprises; (a) a number of strain orforce transducers, the electrical outputs from which contain a measure ofthe braking forces at the wheel positions, (b) astrain orforcetransducerto provide a measure of the brake pedal effort.

16. A system as in claim 15 where the output signals are provided by strain orforcetransducers attached to the chassis and/or suspension members supporting each wheel.

17. Asystemasinclaim 15wherethenumberand location ofthetransducers at each wheel position is determined by the design of the suspension system at that position.

18. A system as in claim 15 where the output signals from the transducers at each wheel position contain a measure of the reacted brake torque (C1) when the vehicle is braked.

19. A system as in claim 1 5where the output signals from the transducers at each wheel position contain a measure of the rolling resistance of the wheel (C3).

20. A systemas in claim 15 whern strain or force transducer is located on the brake pedal mechanism, the electrical output from the transducer being a measure of the brake pedal effort (Sp).

21. Asystem as in claims 18,19 and 20wherea measure ofthe brake efficiency would be obtained by comparing a ratiovalueof(C1 +C3)/Spwithasuitable reference value forthe vehicle.