GB2277186A

GB2277186A - Vehicle theft alarm

Info

Publication number: GB2277186A
Application number: GB9407376A
Authority: GB
Inventors: Kenneth William Marshall
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-04-17
Filing date: 1994-04-14
Publication date: 1994-10-19
Also published as: GB9307949D0; GB9407376D0

Abstract

The alarm comprises means 5 for sensing translational motion of the vehicle due to rotation of a road wheel and means 6 controlled by the motion sensing means for triggering an alarm function. The sensing means may be coupled to the vehicle transmission and is preferably an electric alternating current pulse generator. Alternatively the sensing means is driven from the vehicle's speedometer. The alarm function comprises one or more of an alarm siren, an engine immobilization device, a pager, a door locking mechanism and a vehicle braking system. <IMAGE>

Description

TITLE: VEHICLE ALARM DESCRIPTION: The invention relates to a vehicle alarm and more particularly, but not exclusively, to an anti-theft alarm for a motor vehicle.

As a result of prevailing levels of auto-theft, many vehicles are now fitted with alarm systems to prevent or discourage vandalism and theft. In spite of such precautions, motor vehicles are often stolen. A method frequently employed by thieves is to deactivate the vehicle's parking brake, e.g. by cutting the vehicle hand brake cable, and then to push the vehicle gently, to avoid setting off any alarm, from its parked position to a remote location where it is out of sight or sound and where the alarm can be de-activated so that the vehicle's engine can be started or the vehicle can be dismantled.

It is an -object of the invention to provide alarm means to trigger the vehicle alarm when it is moved in translation by an unauthorised person.

It is, of course, known to provide vehicle motion sensors which are connected to actuate an alarm and which are activated by vehicle motion in the sense of rocking of the vehicle such as might happen when the thief gains access to the vehicle's interior.

According to the invention, a vehicle alarm comprises means for sensing translational motion of the vehicle due to rotation of its road wheels and means controlled by the motion sensing means for triggering an alarm function. The motion sensor may be connected to the vehicle transmission, e.g. the vehicle gearbox output shaft or the propeller shaft or a vehicle wheel, and may take the form of a member which is driven in rotation by translational motion of the vehicle and means for detecting the rotation. Such a motion sensor may take the form of an electric alternating current pulse generator. Preferably the motion sensor will be driven from the vehicle's speedometer, which is connected to the vehicle transmission either mechanically, e.g. through a cable or electrically. Where the vehicle's speedometer is electric or electronic, the signal thus produced can be used directly, normally after amplification, to latch-in an alarm signal without the need for a separate motion detector.

The alarm signal may be used to activate one or more of a vehicle alarm siren, an engine immobilisation device, a pager, a door locking mechanism and a vehicle braking system. Preferably the alarm means of the present invention will be additional to another vehicle alarm and the two devices will preferably be entirely independent.

An advantage of the alarm of the present invention is that the device is quick acting, i.e. it can be made to trigger within half a meter of vehicle translational movement and it is activated irrespective of how slowly the vehicle is moved. Existing devices such as fuel cut-off devices permit the vehicle to move a considerable distance before they become effective, thus increasing the risk of damage and injury.

The invention is diagrammatically illustrated, by way of example, in the accompanying drawing which is a diagrammatic representation of a vehicle alarm.

In the drawing an anti-theft alarm for a motor vehicle is fitted to the vehicle's transmission to detect rotation of the transmission due to translational movement of the vehicle. In the particular embodiment shown in the drawing the alarm comprises a trigger unit or transducer 5 in the form of an alternating current generator, which may be considered as a rotating proximity switch, driven by a speedometer drive cable one end of which in conventional fashion is connected to a speedometer gearbox (not shown) driven from the motor vehicle transmission, and the other end 2 of which is connected to the vehicle speedometer (not shown). It is preferred that the transducer 5 is mounted or hidden internally of the vehicle so that it is less vulnerable to tampering. This might be achieved by fitting the transducer part-way along the speedometer drive cable, as shown.

The alternating current output from the transducer 5 (typically oscillating between 4 and 8 milliamperes) is fed to a control unit 6 which measures the signal from the transducer and is triggered by any oscillation i.e.

increase or decrease in the signal as will occur due to translational movement of the vehicle and consequent rotation of the speedometer cable. The triggering produces an amplified output signal at output lead 8 which may be used directly to activate one or more vehicle alarm selected from the group consisting of a siren, an engine immobilisation device, a pager, a door locking device or a vehicle braking system. The connection between the transducer 5 and the control unit 6 comprises four leads which are respectively a positive lead 7, which powers the transducer, an earth lead 3, the trigger or signal output lead 4 and an anti-tamper lead 9, severing of which will cause triggering of the alarm function.

The alarm may also be used to lock the doors of the motor vehicle to provide anti-hijack protection. This may be achieved by providing the vehicle doors with solenoid locks, similar to automotive central locking, which will be held off during translational motion of the vehicle using the motion sensor with the alarm function disabled to detect the motion, and the door locks being operated only when the vehicle becomes stationary and being activated via a sensor (not shown) attached to the foot brake pedal of the motor vehicle.

The invention thus provides a simple mechanism which will detect translational motion of a motor vehicle.

Claims

1. A vehicle alarm comprising means for sensing translational motion of the vehicle due to rotation of a road wheel and means controlled by the motion sensing means for triggering an alarm function.

2. A vehicle alarm according to claim 1, comprising means connecting the motion sensor to the vehicle transmission.

3. A vehicle alarm according to claim 1 or claim 2 wherein the motion sensor comprises a member which is adapted to be driven in rotation by translational motion of the vehicle and means for detecting the rotation.

4. A vehicle alarm according to claim 3, wherein the motion sensor comprises an electric alternating current pulse generator.

5. A vehicle alarm according to any preceding claim, wherein the motion sensor is adapted to be driven from the vehicle's speedometer.

6. A vehicle alarm according to any preceding claim, wherein the alarm function comprises one or more of a vehicle alarm siren, an engine immobilisation device, a pager, a door locking mechanism and a vehicle braking system.

7. A vehicle alarm, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.