GB2372861A

GB2372861A - Vehicle tyre damage detection

Info

Publication number: GB2372861A
Application number: GB0104913A
Authority: GB
Inventors: Kevin Trevor Talbot; Jeremy John Greenwood
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2001-02-28
Filing date: 2001-02-28
Publication date: 2002-09-04
Anticipated expiration: 2021-02-28
Also published as: GB0104913D0; GB2372861B

Abstract

Apparatus for detecting damage to a vehicle tyre comprises a tyre pressure sensor 18, mounted on the tyre 16, for measuring the pressure of the tyre 16, and for analysing variations in tyre pressure. If a regular sequence of pressure impulses is detected, a signal is sent to a receiver 20 on the vehicle body indicating the existence of the pattern and the frequency of the impulses. A processor 22, which receives wheel speed signals from e.g. a brake control system, compares the frequency of the impulses with the frequency of rotation of the wheel and, if they correspond, issues a warning to the driver of possible tyre damage.

Description

Vehicle Tyre Damage Detection

The present invention relates to the detection of damage to vehicle tyres, and in particular to the use of tyre pressure monitoring systems to detect damage to vehicle tyres.

Damage to vehicle tyres, such as delamination where a section of the tread of the tyre becomes detached, can be a cause of serious accidents. It is therefore desirable to be able to detect delamination of vehicle tyres quickly so that the driver can be warned before the tyre bursts or becomes detached from the wheel.

It is known, for example from WO 96/28311, to provide pressure sensors embedded in vehicle tyres. A pressure sensor, processor and radio frequency transmitter, and a power source, are mounted in the tyre, and a radio frequency receiver is mounted on the vehicle near the relevant wheel so that it can receive signals from the wheel-mounted transmitter. Such systems are used to monitor the pressure of vehicle tyres to provide a warning of decreasing tyre pressure.

The present invention provides apparatus for detecting damage to a vehicle tyre, the apparatus comprising a tyre pressure sensor for measuring the pressure of the tyre, and processing means arranged to receive signals from the tyre pressure sensor, to analyse the signals to detect the presence of regular variations in pressure, and in response to detection of such variations, to issue a signal indicating tyre damage.

Preferably the apparatus further comprises a wheel speed sensor for measuring the frequency of rotation of a wheel of which the tyre forms a part, and the processing means is arranged to compare the frequency of variations in the pressure of the tyre with the frequency of rotation of the wheel and, if there is a correspondence between the two frequencies, to issue the signal indicating tyre damage.

Preferably the processing means is arranged to detect impulses in the pressure of the tyre, to divide the impulses into selected groups, and to check for regularity within the groups. For example, the processing means may be arranged to divide the impulses into sets of equal numbers of subsequent impulses, and then to form each of said groups using one or more pulses from each set. This means that if there are several points in the tyre where unevenness produces a pressure impulse on contact with the ground, provided each set corresponds to one full revolution of the wheel, the group of pulses will comprise those pulses caused by only one of these points contacting the ground.

Because known tyre pressure sensor units include some level of processing which processes the raw pressure signal before transmitting an RF or other signal to the receiver on the vehicle body, the processing means can be at least partly included on the wheel-mounted unit. However, information about the vehicle, specifically vehicle speed, will generally only be available in the body-mounted processor or controller, so part of the processing means may be located there.

Preferably the number of impulses in each set is increased between checks for regularity. This enables a systematic check to made until the number of pulses in the set corresponds to the number if irregularities in the tyre.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a vehicle including apparatus for detecting tyre damage according to the invention; Figure 2 shows a transponder unit forming part of the vehicle of Figure 1; and

Figure 3 is a flow diagram showing the operation of the a processor forming part of the apparatus of Figures 1 and 2.

Referring to Figure 1 a vehicle 10 has two front wheels 12 and two rear wheels 14, each wheel including a pneumatic tyre 16. Embedded in each tyre 16 is a tyre pressure sensor unit 18, which measures and analyses the pressure of the tyre and transmits a radio frequency signal containing information about the tyre pressure. Four receivers 20, each mounted on the vehicle body close to a respective one of the wheels, are arranged to receive the signals from the sensor units 18 and transmit them electrically to an electronic control unit 22 on the vehicle.

As shown in Figure 2, each of the sensor units 18 comprises a pressure sensor 24, a processor 26 and a radio frequency transmitter 28, as well as a power source 30.

These components are mounted on a flexible substrate 32 to form the unit 18, and the whole unit is embedded in the wall of the tyre 16. The pressure sensor may, for example, take the form of a strain gauge mounted on silicon, and produces a signal, the voltage of which varies with the air pressure in the tyre. This signal is input to the processor 26 which analyses it to detect regular variations in the pressure which might indicate that, for example, the tyre is damaged. In order to do this the processor includes a 50 microsecond analogue/digital converter which samples the pressure signal 20,000 times a second. This enables it to detect variations in pressure of frequencies up to nearly 10kHz. If the processor 26 detects a variation or pulse in the tyre pressure which is of a regular frequency it sends out, via the transmitter 28 a signal indicating this, which is received by the receiver 20 and passed on to the control unit 22.

As the tyres 16 travel over a road surface, variations in pressure of differing frequencies will occur for different reasons, and the system needs to be able to distinguish those variations which indicate tyre damage. There will be random

variations with no steady frequency caused by road surface inputs, cyclical variations in pressure at between zero and about 20Hz caused by oscillatory motion of parts of the vehicle and the suspension, higher frequency variations at up to several kHz caused by road noise, and regular pulses or bursts at regular frequencies up to about 50Hz caused by tyre defects. There is therefore a problem that road surface inputs, which are random, will occasionally produce variations in tyre pressure similar to a damaged tyre. However, these variations will generally not persist at a constant frequency for a significant length of time. Similarly vibrations of the wheels at wheel hop frequencies will also occur at similar frequencies. Again, however, these vibrations will die away with time. The processor 26 therefore checks that regular variations in tyre pressure persist at a sufficiently constant magnitude and frequency, and over a sufficiently long period, for example 30 seconds, for them to be caused by tyre damage.

Referring to Figure 3, the operation of the processor 26 in this embodiment will be described. When the process starts, the tyre pressure is read at step 1, and again at step 3 after a 250pus delay at step 2. At step 4 these two pressure readings are compared. If there is no difference between them, the process returns to steps 2 and 3, i. e. the pressure is read again after a further 250, us delay. This is repeated, provided no change of pressure is detected, until, at step 5, it is determined that 0.2s has passed since the start of the process, when the processor goes to sleep at step 6. The length of time for which the processor has been asleep is checked at step 7, and when a fixed sleep period of, for example, 2 seconds has expired, the process re-starts at step 1. The sleep period is not essential, but may be useful in some circumstances to reduce power consumption.

If at step 4 a pressure difference greater than a predetermined difference is detected between two subsequent readings, this indicates the occurrence of a pulse in the tyre pressure, and the processor then takes time stamped pressure readings every 250us for the next second at step 8. These readings are analysed at step 9, as will be

described in more detail below, to check whether a cyclical pattern is present which is indicative of tyre damage. If no such pattern is found, the process proceeds to step 6, and the processor goes to sleep for the fixed sleep period. If a pattern is found, the processor packages a warning telegram which is transmitted via the transmitter 18 and receiver 20 to the control unit 22. This telegram can include various information including the frequency of the detected pattern of regular pressure pulses.

When the control unit 22 receives the telegram, it checks the frequency of the detected pulses against the frequency of rotation of the wheels 12, 14. If these frequencies are the same, the control unit 22 issues a warning to the driver, for example by illuminating a light on the vehicle dashboard.

In step 9, where the check is made for a regular pattern in the pressure pulses, account has to be taken of the fact that, in the event of tyre delamination, there may well be two or more impulses caused by one defect. For example if a significant portion of tyre tread is missing, both edges of the affected portion of the tyre will produce an impulse in the tyre pressure signal. The processor 26 is therefore arranged to follow a simple algorithm which will firstly look for regularity in the timing of all impulses. If this is not found, it will look for regularity in the timing of every second impulse, and then every third impulse, up to a maximum of, say, every sixth impulse. During this process, the first occurrence of a regular pattern is noted, it being assumed that the frequency of this pattern will be equal to the frequency of rotation of the wheel, if the pulses are due to tyre damage. If no pattern is found then the impulse detection threshold is increased so that only larger impulses are detected, and the check for regularity repeated.

In the example described above, the pressure pulses are detected by the occurrence of a difference in measured pressure between two subsequent samples.

Depending on the sampling frequency and the level of sensitivity and accuracy required it may be desirable to use a more complex check for the existence of a

pressure pulse caused by delamination. For example a rise in pressure of a predetermined amount within a period less than a predetermined number of samples, for example four or five, might provide more accurate detection. Also it might be desirable to measure the subsequent decay of pressure to check that it follows the pattern that would be expected, such as an oscillating decay.

In a modification to the embodiment described above, the processor 26 and the control unit 22 can be arranged to carry out a number of checks for regular impulses in the pressure signal at times which are spaced apart by much longer time periods, for example three checks at one minute or two minute intervals. Only if the regular pattern is detected, at the wheel rotation frequency, at each of these checks would the warning signal be issued. This makes it much less likely that the warning will be triggered by transient vibrations in the vehicle induced, for example, by inputs from the surface over which the vehicle is travelling. The exact number and timing of these checks could obviously be chosen to suit a particular vehicle and the type of tyre. They could also be arranged to vary with the speed of the vehicle. The faster the vehicle is travelling, the quicker tyre damage is likely to progress to total tyre failure, and therefore the more important it is to warn the driver quickly of possible tyre damage. Since the control unit 22 has an input of wheel speed, such speed dependent variation of the checking process can easily be achieved.

Claims

CLAIMS 1. Apparatus for detecting damage to a vehicle tyre, the apparatus comprising a tyre pressure sensor for measuring the pressure of the tyre, and processing means arranged to receive signals from the tyre pressure sensor, to analyse the signals to detect the presence of regular variations in pressure, and in response to detection of such variations, to issue a signal indicating tyre damage.
2. Apparatus according to claim 1 further comprising a wheel speed sensor for measuring the frequency of rotation of a wheel of which the tyre forms a part, wherein the processing means is arranged to compare the frequency of variations in the pressure of the tyre with the frequency of rotation of the wheel and, if there is a correspondence between the two frequencies, to issue the signal indicating tyre damage.
3. Apparatus according to claim 1 or claim 2 wherein the pressure sensor is mounted on the wheel.
4. Apparatus according to claim 3 wherein the pressure sensor is mounted in the tyre.
5. Apparatus according to any foregoing claim wherein the processing means includes a processor mounted on the wheel.
6. Apparatus according to claim 5 wherein the processor is mounted in the tyre.
7. Apparatus according to any foregoing claim wherein the processing means is arranged to detect impulses in the pressure of the tyre, to divide the impulses into selected groups, and to check for regularity within the groups.
8. Apparatus according to claim 7 wherein the processing means is arranged to divide the impulses into sets of equal numbers of subsequent impulses, and then to form each of said groups using one or more pulses from each set.
9. Apparatus according to claim 8 wherein the number of impulses in each set is increased between checks for regularity.
10. Apparatus for detecting damage to a vehicle tyre substantially as hereinbefore described with reference to the accompanying drawings.