GB2382205A

GB2382205A - System for detecting theft of vehicle wheels

Info

Publication number: GB2382205A
Application number: GB0223177A
Authority: GB
Inventors: Christopher Richard Bottomley; Kevin Trevor Talbot; Jeremy John Greenwood
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2001-10-11
Filing date: 2002-10-07
Publication date: 2003-05-21
Also published as: GB0124386D0; GB0223177D0

Abstract

A system for detecting removal of a vehicle wheel 14 from a vehicle 10, comprising a control unit 16 and a tyre pressure sensor 24 mounted in each tyre 26, such that the control unit is in radio communication with the sensors via transmitter/receivers 28 mounted on the vehicle.. The control unit monitors changes in tyre pressure and if the pressure changes in a manner consistent with the removal of the wheel then an alarm 20 is raised. In an alternative embodiment, an alarm signal is raised when the system detects that the transponder 24 mounted on the tyre has moved out of range of the transmitter/receiver 28 on the vehicle. The system may be combined with a vehicle anti-theft system.

Description

Vehicle Wheel Theft Detection The present invention relates to vehicle security and in particular to the detection of theft of vehicle wheels.

With the increasing use of alloy wheels, incidences of theft of vehicle wheels are increasing, and it is therefore desirable to provide vehicles with some means of detection of the theft of wheels.

It is known from DE 198 53 696 A 1 to use a proximity sensor for security purposes to detect when a vehicle wheel is removed from a vehicle. However such a proximity sensor will generally need to be fitted specifically for this purpose, and therefore adds to the cost of the vehicle.

It is also known, for example from US 5541574, to provide transponders mounted in vehicle tyres which can transmit data to a receiver on the vehicle regarding the condition of the tyres, such as tyre pressure.

The present invention aims to provide a system for detecting the theft of vehicle wheels which makes use of components which are used on the vehicle for other purposes also.

Accordingly the present invention provides a detection system for detecting removal of a vehicle wheel having a tyre from a vehicle, the system comprising a control unit and wheel movement detection means, wherein the control unit is arranged to monitor signals from the wheel movement detection means to detect theft of the vehicle wheel, and wherein the wheel movement detection means comprises a tyre pressure sensor.

The tyre pressure sensor may be arranged to detect a change of tyre pressure as the weight of the vehicle is taken off the wheel and the wheel is removed. Alternatively the tyre pressure sensor may be of the type comprising a transponder mounted in the tyre, and when the wheel is removed out of range of the transmitter/receiver on the vehicle, this can also be detected.

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 wheel theft according to a first embodiment of the invention; Figure 2 shows changes of tyre pressure in the vehicle of Figure 1 under various circumstances; and Figure 3 is a diagrammatic representation of a vehicle including apparatus for detecting wheel theft according to a second embodiment of the invention.

Referring to Figure 1 a vehicle 10 has a body 12 and four wheels 14. A security system is fitted to the vehicle and includes a security control unit 16, an ultrasonic sensor 18 for sensing movement within the vehicle, and a siren 20. A hand held transmitter unit 22 is also provided for activation and de-activation of the security system.

A tyre pressure sensing system is also fitted to the vehicle and includes a transponder unit 24 mounted in each of the vehicle tyres 26 and a transmitter/receiver unit 28 mounted on the vehicle body near each of the wheels, the transmitter/receiver units 28 are connected to the control unit 16. The transponder units 24 each include a tyre pressure sensor, an accelerometer and an RF transmitter and receiver. They are arranged such that they can transmit to the transmitter/receiver units 28 a tyre pressure

signal indicating the tyre pressure at regular time intervals, and also so that they can respond at any time to a request signal from the transmitter/receiver units 28 by transmitting a tyre pressure signal.

During normal operation while the vehicle is running the security system is disarmed, the transponder units 24 detect using their accelerometers when the vehicle is moving and transmit a tyre pressure signal at regular intervals of one minute. The control unit monitors the tyre pressures and warns the driver if the pressure in one or more of the tyres drops due to a puncture, or if variations in the tyre pressure occur which are indicative of some other event, such as imminent delamination of a tyre or over-inflation of the tyres.

When the vehicle is stationary the transponder units 24 detect this using their accelerometers and transmit tyre pressure signals at much greater intervals, such as once every hour. When the driver leaves the vehicle and arms the security system using the transmitter unit 22, the control unit 16 monitors the tyre pressure signals. If movement of one of the wheels occurs this will be detected by the accelerometer and the transponder unit 24 will start to transmit a tyre pressure signal every minute. If the control unit 16 receives tyre pressure signals at this increased rate while the security system is armed then this is taken as an indication that one of the wheels may be being removed. Alternatively the rate of transmission need not be directly measured, and the control unit 16 can be arranged to detect that a tyre pressure signal has been received within a period which is less than the normal one hour period. In either case the change of timing of the tyre pressure signals can either trigger an alarm, or start a checking process described further below.

In an alternative embodiment the actual value of the measured tyre pressure is used to detect movement of one of the wheels. If the pressure of one of the tyres drops by more than a predetermined amount between two consecutive measurements, this

indicates that one of the wheels may have been removed. For this to work the interval between measurements would need to be significantly less than one hour, so it would be best suited to a system in which the transponder is polled by the transmitter/receiver unit 28. If the change in tyre pressure indicates that a wheel may be being removed, then, as in the previous embodiment, this can either trigger an alarm, or, more preferably, trigger a further checking process which will now be described.

Firstly, if either one of the transponder units'transmission of tyre pressure signals, or a rapid drop of pressure in one of the other tyres, indicates within a predetermined time period of, for example, 10 minutes, that a second one of the wheels is being removed, then this is taken as an indication that somebody is systematically removing the vehicle wheels and the alarm is activated.

Secondly if the pressure sensor for the tyre which initiated the checking process ceases to respond to polling, which may be arranged to be carried out at a significantly increased rate during the checking process, then this is taken as an indication that that wheel has been removed, and the alarm is activated.

Finally the pressure of the tyre which initiated the checking process, and each of the other tyres also, is monitored over time to check whether changes in the tyre pressure are consistent with removal of one of the wheels, as will now be described with reference to Figure 2.

Referring to Figure 2, which shows the change of tyre pressure P as a function of time t, the pressure in a vehicle tyre, particularly when the vehicle is stationary, will normally remain substantially constant over time. If the tyre has a slow puncture or is leaking for some other reason, then the pressure will fall gradually at a rate which is either constant or which varies in a continuous manner, as shown by lines a and b.

However, of the wheel is removed from the vehicle, firstly the weight of the vehicle

must be lifted off the wheel. The effect of this on the tyre pressure is shown by line c. Firstly between times t1 and t2 the pressure will drop at a relatively rapid rate as the weight of the vehicle is lifted off the tyre. Then when the weight of the vehicle is removed from the tyre, the pressure will remain substantially constant at the unladen pressure, which will obviously be substantially higher than the pressure at which a punctured tyre will level off at, which would be close to atmospheric pressure. The time period between t1 and t2 which is the time taken to jack up the vehicle can obviously vary depending on the method of jacking used. For most methods it is likely to be between 1 second and 1 minute although in some cases it could obviously be outside this range.

The control unit 16 therefore monitors changes of tyre pressure over time and if it detects a drop in pressure of at least a predetermined magnitude within a fixed time, followed by a levelling off of pressure at a level consistent with the wheel being removed from the vehicle, then it takes this as an indication that one of the wheels has been removed and activates the alarm.

Referring to Figure 3, in a further embodiment of the invention the security system is substantially the same as described above, but the mechanism for detecting wheel movement comprises four accelerometers 32 each mounted on the a part 33 of the vehicle suspension close to the hub of one of the wheels of the vehicle. During normal operation of the vehicle the accelerometers 32 are used to monitor movement of the wheels, and their signals are analysed to determine the condition and state of inflation of the vehicle tyres. However, the accelerometers are also connected to the security controller 34 which, when it is armed, is arranged to be alerted by a signal from any of the accelerometers 32. When it has been alerted the controller then monitors the signals from the other accelerometers and, if another one produces, within a predetermined time, a signal indicating movement of the wheel it is associated with, then the security controller issues an alarm signal.

This embodiment can be enhanced by including some form of analysis of the signals from the accelerometers. The wheels and the suspension will have various characteristic resonant frequencies of vibration which will vary depending on whether the wheel is carrying the weight of the vehicle or not. Therefore the controller 34 can be arranged to analyse the frequencies of movement detected by the accelerometer and to use only signals indicative of movements at certain frequencies or ranges of frequencies as indications that the vehicle body is being raised and the wheels removed.

Claims

1. A detection system for detecting removal of a vehicle wheel having a tyre from a vehicle, the system comprising a control unit and wheel movement detection means, wherein the control unit is arranged to monitor signals from the wheel movement detection means to detect theft of the vehicle wheel, and wherein the wheel movement detection means comprises a tyre pressure sensor.

2. A system according to claim 1 wherein the tyre pressure sensor comprises a transponder mounted in the tyre and a transmitter/receiver on the vehicle, and the system is arranged to detect movement of the wheel by detecting when the transponder is moved out of range of the transmitter/receiver on the vehicle.

3. A detection system for according to claim 1 wherein the control unit is arranged to monitor changes in the pressure of the tyre over time and if the pressure changes in a manner consistent with removal of the wheel, produces a signal indicative of removal of the wheel.

4. A system according to claim 3 wherein said manner comprises a relatively rapid reduction in pressure indicating that the weight of the vehicle is being lifted off the tyre, followed by a period of relatively constant pressure.

5. A system according to claim 3 or claim 4 wherein said period of relatively constant pressure is at a pressure significantly above atmospheric pressure.

6. A vehicle security system including a system according to any one of claims 3 to 5 and alarm means arranged to be activated on detection of removal of the wheel.

7. Apparatus for detecting theft of a vehicle wheel substantially as hereinbefore described with reference to the accompanying drawings.