MOTOR VEHICLE ALARM AND IMMOBILISATION SYSTEM

Abstract: A motor vehicle has an alarm system (100) operable by a remote control transmitter (110) and an immobilisation system (200) operated by an encoded passive transponder (210). Recognition of the code of the passive transponder (210) is used to disarm the alarm system (200), to allow for the possibility of breakage of the remote control transmitter (110) of the alarm system.

Description: Motor vehicle alarm and immobilisation system The present invention relates to an alarm and immobilisation sy- em for a motor vehicle. Alarms systems are known that operate by remote control . In such systems, a transmitter is used to send a coded infra-red signal to a receiver in the vehicle which then arms or disarms the alarm. Such remote control operation is desirable in that it is not easy to tamper with the alarm, there being no mechanical locks that can be forced or dismantled. It is however also necessary in such systems to allow for a defective transmitter. In particular, if the transmitter ceases to function, for example because it has been dropped or its battery has run flat, it must still be possible for the vehicle owner to enter the vehicle and disable the alarm. This requirement has in the past been met by providing an additional override switch by means of which the alarm can be disabled, but such a switch involves additional cost and detracts from the security of the system. The present invention seeks therefore to provide a means of overriding alarm that does not detract from the security of the system. According to the present invention, there is provided a motor vehicle having an alarm system operable by a remote control transmitter and having an immobilisation system operated by an encoded passive transponder, wherein recognition of the code of the passive transponder serves to disarm the alarm system. Encoded passive transponders have been proposed for the purpose of immobilisation of a vehicle. An immobilisation system is not an alarm in that it is not intended to alert the owner of a vehicle to an attempted theft. Instead, its purpose is to make it as difficult as possible for a would be thief to drive the vehicle away by interfering with the operation of essential components such as the ignition system and the fuelling system. The passive transponder is a circuit incorporated in an electronic key that may, if desired, be integrated into the vehicle ignition key. The circuit is passive in that it does not have its own internal power supply. Instead, when the electronic key is inserted in a reader, power is inductively coupled into the circuit which then transmits an encoded signal. This signal is picked and decoded by the reader, which disarms the immobilisation system of the vehicle if it receives the correct code from the transponder. The advantage of such a passive transponder is that its operation may be completely automatic and need not require any special steps to be taken by the driver. The mere insertion of the ignition key in the conventional manner into the ignition lock may suffice to switch the vehicle immobilisation system on and off. The present invention takes advantage of the presence of this highly secure identification system to enable the alarm system to be disarmed automatically by the driver of the vehicle in the event of the remote control transmitter of the alarm system failing to operate correctly. The invention will now be described further, by way of example, with reference to the accompanying drawing which is a schematic block diagram of an alarm and immobilisation system of a vehicle of the invention. T ' τ single drawing shows an alarm system 100 and an i. nobilisation system 200, both operated or armed by encoded transmissions. The alarm system 100 is armed and disarmed ' a remote control infra red transmitter 110 carried by the car driver. The encoded infra red signal from the transmitter 110 and is sensed and decoded in the block 112 which then enables and disables an alarm control circuit 11 . This circuit receives signals from various sensors 116, 118 that may for example include a trembler switch sensitive to vehicle movement, micro switches sensitive to the opening of doors, passive infra red sensors mounted i- the passenger compartment or any other form of sensor for deter ng intrusion into or unauthorised tampering with the vehi'- . Once such attempted theft has been detected, the alar; >ntrol circuit operates the vehicle direction indi- ors 120 and a siren 122 to deter the would be thief and m _ also transmit a radio signal that can be picked up by the owner or the police. Because the alarm system is ge~ - -ally conventior it is believed that its operation wi. r>e well undersc -.1 by those skilled in the art without the need for more det? 3d explanation and description. The immobilisation system 200 is also in itself jwn and i sometimes referred to as a passive anti-theft system (PATS) because it requires nc special steps to be taken by the driver. The immobilisation system is operated by a PATS key 210 which is a passive transponder, conveniently integrated into the ignition key. The transponder 210 when placed near a PATS decoder 212 receives power from the decoder through inductive coupling and transmits and encoded radio signal that it picked up and decoded by the decoder 212. If the signal received contains the correct code, the PATS decoder 212 disables an immobilisation contro] 214. The latter circuit is connected to essential systems of the vehicle, s' - as the ignition system 220 and the fuelling system 222 and prevents the engine from starting while the vehicle is immobilised. The immobilisation circuit 214 may for example short circuit the ignition coil to prevent the production of sparks at the spark plugs or may open circuit the fuel supply pump and prevent fuel from reaching the engine. If the transmitter 110 should fail to operate for any reason, the driver cannot disable the alarm. This has in the past required the provision of a key operated switch or a switch hidden in the vehicle to disarm the alarm, but such a switch is not tamper proof and can also be used by thief to prevent the operation of the alarm. To overcome this problem, the output of the PATS decoder 212 is also used in the described preferred embodiment of the invention to disable the alarm control circuit. Once the driver uses the correct key to allow the vehicle to start, it can safely be assumed that the driver is an authorised user of the vehicle and that it is safe to disarm the alarm, notwithstanding the fact that it was not possible to disarm the alarm using the remote control transmitter. The invention therefore considerably simplifies authorised use of the vehicle in the event of transmitter 110 becoming damaged and it does so without reducing the security of the alarm system.

Claims: CLAIMS 1. A motor vehicle having an alarm system operable by a remote control transmitter and having an immobilisation system operated by an encoded passive transponder, wherein recognition of the code of the passive transponder serves to disarm the alarm system. 2. A motor vehicle as claimed in claim 1, wherein the remote control transmitter is an infra red transmitter. 3. A motor vehicle as claimed in claim 1 or claim 2, wherein the encoded passive transponder forms an integral part of an ignition key of the motor vehicle. 4. A motor vehicle as claimed in claim 3, wherein the transponder receives power through an inductive coupling from a code reader in the motor vehicle and transmits an encoded radio signal to the reader.

Inventors: BIDDLECOMBE DAVID ERNEST, GREGORY GORDON, STEVENS MALCOLM, BIDDLECOMBE, DAVID, ERNEST, GREGORY, GORDON, STEVENS, MALCOLM
Applicants: BIDDLECOMBE DAVID ERNEST, FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, GREGORY GORDON, STEVENS MALCOLM, BIDDLECOMBE, DAVID, ERNEST, FORD FRANCE S.A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD WERKE A.G., GREGORY, GORDON, STEVENS, MALCOLM
Application year: 1995
Main classification: B60R25
IPC codes: B60R25