GB2226434A

GB2226434A - Monitoring system for vehicle tyres

Info

Publication number: GB2226434A
Application number: GB8830153A
Authority: GB
Inventors: Manuel Alfred Xavier Cocheme
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-23
Filing date: 1988-12-23
Publication date: 1990-06-27
Also published as: GB8830153D0

Abstract

The system comprises sensor means 10 for producing an output signal representative of the rotational speed of each vehicle wheel when the vehicle is travelling, comparator means 18 for comparing at least two of the output signals (or signals derived therefrom) and producing a different signal when one sensed rotational speed differs from another, and indicator means 22 for indicating that the difference signal is being produced. The system relies on the fact that, in the case of a four wheeled vehicle for example, if all the tyres are in good condition and are correctly inflated, all four wheels should rotate at equal speeds when the vehicle is travelling in a straight path. If any tyre is not fully inflated, for instance due to a puncture or due to undue wear of the tyre tread, a difference signal is generated in the system and the fault indicated. The sensor means may be an electromagnetic or electro-optical sensor, the output pulses of which may be integrated or counted over a given period of time or a given distance of travel prior to comparison. <IMAGE>

Description

Title: Monitoring System for Vehicle Tyres Field of the Invention This invention relates generally to a monitoring system for vehicle tyres, and more especially to a monitoring system for dctccting a tyre fSul F such as partial deflation or excessive wear.

Background to the Invention Given that a vehicle has four wheels, all four wheels should rotate at exactly t same steed when the vehicle is travelling in a straight line if they are of the same diameter. The wheels on the outside will rotate at a greater speed than the wheels on the inside when the vehicle is cornering, but if the rotational speeds are not the same when the vehicle is travelling in a straight path, any difference can be assumed to arise due to a difference in the effective radii of the wheels concerned.

The Invention According to the invention, there is provided a monitoring system for vehicle wheels, comprising sensor means for producing an output signal representative of the rotational speed of each vehicle wheel when the vehicle is tEaV6illNgt comparator means for comparing at least two of said output signals (or signals derived therefrom) and producing a difference signal when one sensed rotational speed differs from another, and indicator means for indicating that said difference signal is being produced.

This invention relies on the fact that, in the case of a four wheeled vehicle for example, if all the tyres are in good condition and are correctly inflated, all four wheels should rotate at equal speeds when the vehicle is travelling in a straight path.

Thus, under these conditions, if the output signals from the four wheel sensors are compared, no difference signal should be generated.

If the vehicle is designed to operate with the reii wheel tyres in a different condition of inflation to that of the front wheel tyres, it is readily possible to introduce an offset as by a bias signal into the relevant comparator, in order to enable front/rear wheel comparison to be made.

At any given moment, the effective radius and/or rotational speed of a wheel may be affected by a temporary factor, such as a bump or uneveness in the road, sudden acceleration or sudden braking. It is therefore preferred that the output signals of the sensors to be averaged or integrated over a period of time, or over a given number of wheel revolutions, prior to comparison.

Assuming the use of a two part sensor, one part mounted on the wheel and and one part on the vehicle body, for example an electromagnetic or electro-optical sensor, then the output of such a sensor will consist of a series of pulses. The output pulses may be integrated or counted over a given period (or given distance of travel) in order to provide a recurrent signal used for comparison purposes.

The indicator may be rendered inoperative during cornering. However, it is apparent that if a comparison is made of sensor outputs averaged, integrated and counted over a substantial period or substantial distance, the effects of cornering may effectively be removed, so that the indicator will not normally operate during simple cornering.

The system may be rendered more or less sensitive according to requirements, and a sensitivity adjustment control may be incorporated possibly for use by the vehicle user. Sensitivity is controllable, for example, by means of an additional comparator or other circuit means to which a threshold signal, possibly a variable threshold signal, can be applied, the difference signal being fed through such a threshold circuit to the indicator.

In one mode, the threshold may be set, for example, so that only a relatively major tyre deflation, as might be caused by a puncture, is indicated.

Alternatively in another mode, it may be set so that any undue wear of one particular tyre tread is also indicated.

Moreover, a two stage indicator means may be employed, the second stage indicator only being activated when a second thresh for example typical of a puncture, is e ded A preferred indicator may be a panel having four indicator lights, for example arranged in a pattern corresponding to the positions of the wheels, each indicator light being activated when the output of the comparator means indicates a reduced operating radius at the corresponding wheel.If the indicator is not to light up every time the vehicle corners, it is necessary to employ, as the comparator for each pair of wheels, a comparator circuit which determines whether the steering wheel is in the straight ahead position or is turned so as to distinguish between the case where the signal from the nearside wheel is different from that from the offside wheel due to cornering, and where the reverse situation applies.

It is also envisaged that it may be possible to provide one or more reference signals to the comparator circuit to enable it to distinguish, for example, between a partially deflated wheel on one side and an over-inflated wheel on the other side, or to determine that a wheel output signal is within a predetermined range.

It may be preferred to operate the system on a sampling basis, for example so that the compared sensor outputs are sampled every ten seconds or other suitable interval, the indicator means being operated only if successive sampled outputs differ by a given amount.

Description of one example A simple practical example of monitoring system in accordance with the invention is now described with reference to the accompanying drawing, the single figure of which shows the system in block diagram form.

Description of drawing Referring to the drawing, each wheel 10 of a four wheeled vehicle is equipped with a sensor 12 for sensing the speed of rotation of the wheel when the vehicle is travelling and providing an output signal representative of such rotational speed.

Each sensor 12 is an electromagnetic sensor, having a wheel mounted magnet and a fixed coil on the vehicle, so as to produce one output pulse per wheel revolution.

The output pulses from each wheel are fed to one of four pulse counters 14, the outputs of which pass to averageing circuits 16. The averaged pulse counts from the front wheels 10A, 10B are fed to a comparator 18A, whilst the averaged pulse counts for the two rear wheels lOC, lOD are fed to a comparator 18B. Thence, the outputs of the comparators 18A, 18B pass to respective sign-determining circuits 20A, 20B, which jointly provide four outputs for dashboard mounted indicator 22. The indicator 22 has four light-emitting diodes 24 arranged in a rectangular pattern corresponding to that of the vehicle wheels.

In use, if a partial deflation of a tyre occurs, for example due to a puncture, the averaged pulse count for the rotational speed of that wheel will be increased above that of the others wheels if the vehicle is travelling in a straight line, and a difference signal will be produced at the output of the corresponding comparator 18A or 18B.

he circuit 20A or 20D determines if the difference signal is positive or negative, and passes an output to the approprlate light-emitting diode 24 of the indicator 22.

The illustrated and above-described tyre monitoring circuit may be modified in various ways within the scope of the invention hereinbefore defined, and in particular may include various refinements enabling sensitivity adjustment, periodic sampling and the like, as hitherto referred to.

Claims

1. A monitoring system for vehicle wheels, comprising sensor means for producing an output signal representative of the rotational speed of each vehicle wheel when the vehicle is travelling, comparator means for comparing at least two of said output signals (or signals derived therefrom) and producing a difference signal when one sensed rotational speed differs from another, and indicator means for indicating that said difference signal is being produced.

2. A system according to Claim 1 and adapted for use on vehicles designed to operate with their rear wheel tyres in a different condition of inflation to that of their front wheel tyres, the adaptation being achieved by the introduction of an offset signal into the relevant comparator so as to compensate for the difference in conditions of inflation when front/rear wheel comparisons are made.

3. A system according to Claim 1 or Claim 2, wherein the output signals of the sensor means are averaged or integrated over a period of time, or over a given number of wheel revolutions, prior to comparison.

4. A system according to any of the preceding claims, wherein the sensor means comprises two part sensors, of each of which a first part is mounted on a vehicle wheel and a second part is mounted on the vehicle body.

5. A system according to Claim 4, wherein the sensor is an electromagnetic or electro-optical sensor.

6. A system according to Claim 4 or Claim 5, wherein output signal pulses from the sensor are integrated or counted over a given period of time, or over a given distance of travel, prior to comparison.

7. A system according to any of the preceding claims, wherein the indicator means is rendered inoperative during cornering of the vehicle.

8. A system according to any of the preceding claims, additionally comprising sensitivity adjustment control means for use by the vehicle user.

9. A system according to Claim 8, wherein the sensitivity adjustment control means comprises an additional comparator to which a threshold signal can be applied, the difference signal being fed through the additional comparator to the indicator means such that the difference signal is compared to the threshold signal and any difference between the difference and threshold signals is indicated by the indicator means.

10. A system according to Claim 9, additionally comprising means for varying the threshold signal.

11. A system according to Claim 10, wherein the threshold signal is set to a first value such that only a relatively major deflation of a vehicle tyre, such as is caused by a tyre puncture, is indicated.

12. A system according to Claim 10, wherein the threshold signal is set to a second value such that any undue wear of a vehicle tyre tread is indicated.

13. A system according to any of Claims 9 to 12, wherein the indicator means comprises a two-stage indicator means, the first stage indicator being operated to indicate undue wear of a vehicle tyre tread, and the second stage indicator being operated to indicate relatively major deflation of a vehicle tyre.

14. A system according to any of the preceding claims, wherein the indicator means comprises a panel having indicator lights arranged in a pattern corresponding to the positions of the vehicle wheels, each indicator light being operated when the output of the comparator means indicates a reduced operating radius at the corresponding wheel.

15. A system according to any of the preceding claims1 wherein the comparator means additionally comprises a comparator circuit for determining whether the steering wheel of the vehicle is in the straight ahead position or is turned, such that a difference signal is not produced by the comparator means when the output signals from two sensor means differ due only to cornering of the vehicle.

16. A system according to Claim 15, wherein one or more reference signals are provided to the comparator circuit in order that the circuit can determine whether or not the output signal for a wheel is within a predetermined range, and wherein the indicator means indicates the result of the deterninatòn.

17. A system according to any of the preceding claims, wherein one or more reference signals are provided to the comparator circuit in order that the circuit can distinguish between a partially deflated wheel tyre on the one side of the vehicle and an over-inflated wheel tyre on the other side of the vehicle.

18. A system according to any of the preceding claims, wherein the compared output signals are compared at a given sampling interval, the indicator means being operated only if a given number of successive sampled output signals differ by a given amount.

19. A system according to Claim 18, wherein the sampling interval is 10 seconds.

20. A system according to any of the preceding claims and substantially as herein described with reference to the accompanying drawing.