GB2273124A

GB2273124A - A vehicle security system

Info

Publication number: GB2273124A
Application number: GB9225484A
Authority: GB
Inventors: Bruce Macaulay
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1992-12-05
Filing date: 1992-12-05
Publication date: 1994-06-08
Anticipated expiration: 2012-12-05
Also published as: GB9225484D0; GB2273124B

Abstract

A key 10 is provided with two tracks 21, 25 of surface depressions on opposite sides of its shank 20, 24. The door lock mechanism 30 includes a pair of micro-switches 34, 36 operated by followers 38, 40 which follow the contours of the two tracks as the key is inserted. Signals produced by the operation of the switches 34, 36 one being 8 regular clock signal and the other being a code signal, are compared and, if they correspond to a stored code, an unlock signal is produced. <IMAGE>

Description

A VEHICLE SECURITY SYSTEM The present invention relates to a key operated vehicle security system.

With the increasing need for vehicle security systems, such systems are becoming ever more complex. For example systems are produced which respond to coded electromagnetic signals or to coded numbers entered on a keypad. Such systems are expensive to produce, and can be complicated to use.

The present invention provides a vehicle security system comprising: a key having first and second tracks each comprising surface contours a reader comprising means for producing first and second signals each varying in a way determined by the respective series of contours and a control means for receiving and comparing the signals and producing an unlock signal if the signals correspond to a predetermined code.

Such a system can be made quite simply. The contoured tracks can be formed using normal key grinding technology and a lock unit including means, such as micro-switches operated by the contoured tracks, for producing signals can easily be installed in place of standard door lock units.

One of the tracks may comprise a clock track on which the contours are regular.

One of the tracks may comprise a code track on which the contours are irregular.

At least one of the tracks may be on a shank of the key, and preferably the tracks are on opposite sides of the shank.

The shank may have at least one further contoured surface for operating a mechanical lock.

The reader is preferably installed in a vehicle door lock system, or in an engine ignition system.

The contours may be formed as depressions in the surface of the key.

Preferably one of the tracks comprises depressions of differing lengths.

The reader can conveniently include a pair of switches each operated by one of the tracks as the key is moved relative to the switches.

The contoured tracks are desirably arranged such that the signals produced by the reader can be used to determine in which direction the key is moving.

Preferred embodiments of the present invention will now be desribed by way of example only with reference to the accompanying drawings in which: Figure 1 is an elevation of one side of a key forming part of an embodiment of the present invention; Figure 2 is an elevation of the other side of the key of Figure 1; Figure 3 is a sectional view of the key of Figures 1 and 2 and a reader forming part of the same embodiment; Figure 4 is a diagrammatic respresentation of the reader of Figure 3 and a control means of the same embodiment of the invention; Figure 5 shows the form of signals produced by the reader of the first embodiment of the invention; and Figure 6 shows the form of signals produced by the reader of a second embodiment of the invention.

Referring to Figures 1 and 2 a key 10 comprises a head 12 and a shank 14. The shank 14 has conventional contoured edges 16, 18 for operating a mechanical lock. Along the centre of one side 20 of the shank 14 is a first contoured track 21 formed as a first series of depressions 22 which are equally spaced along the shank and of equal length and equal width. Along the centre of the other side 24 of the shank 14 is a second contoured track 25 formed as a second series of depressions 26 which are of equal width but unequal length and irregularly spaced along the shank.

The first contoured track 21 serves a clock function and the second contoured track 25 serves a code function as will be described below.

Referring to Figure 3 a lock mechanism 30 is housed in a vehicle door 32 and is shaped to receive the key 10. The lock mechanism 30 comprises a conventional mechanical lock (not shown) and a key reader comprising a pair of micro-switches 34, 36 operated by followers 38, 40 each of which follows one of the contoured tracks 21, 25 on the key shank 14 when it is moved into or out of the lock mechanism 30.

Referring to Figure 4 each of the switches 34, 36 is connected between ground and a respective input 44, 46 of a control unit 42. The inputs 44, 46 are each held at a fixed voltage until the respective switch is closed which reduces the voltage at the input to zero.

The control unit 42 has a memory in which a security code is stored for comparison with that entered at the input 46.

In order to maximise security it is necessary to provide a secure way of entering the particular security code into the memory of the control unit 42. In order to do this an input 50 for a serial diagnostic link is provided whereby a code can be entered into the memory only following the application of a security procedure recognised by the control unit 42.

An alternative way of entering the code into the control unit would be to have a master key having on it a master code, which the control unit would recognise and respond to by putting the control unit into a write mode. A coded key could then be inserted and its code written onto the memory of the control unit. Either of these methods of code entry would enable the memeory to be accessed if, for example, all the keys for a unit were lost.

The operation of the security system will now be described.

In order to unlock the car door in the normal way the key 10 is inserted into the lock mechanism 30. As it is inserted the followers 38, 40 follow the contoured tracks 21, 25, opening and closing the microswitches 34, 36 and producing signals at the inputs 44, 46 of the control unit 42 which have a form as shown in Figure 5. The signal Vcl at input 44 acts as a clock signal and, if the key is inserted smoothly, is a regular pulsed signal. The pulses will however not necessarily be regular as they will depend on the rate at which key 10 is inserted.

However that does not affect the operation of the system.

The signal Vco at input 46 acts as a code signal which is compared with the clock signal Vc1 by the control unit 42. This is done by checking the code signal Vco during each pulse of the clock signal Vc1 to see whether it is high or low, and checking the result against a code stored in memory. If the code signal corresponds the code stored in memory, the control unit 42 issues an unlock signal which is used to unlock an engine immobilisation system (not shown).

As can be seen from Figure 5, in the first embodiment of the invention the code signal Vco goes from high to low at the beginning or the end of one of the pulses in the clock signal Vcl. In a second embodiment of the invention, otherwise identical to the first, the two tracks of surface contours are slightly offset along the shank of the key so that the signals produced are as shown in Figure 6. By comparing the clock signal Vc1 and the code signal Vco the control unit can detect which signal is 'ahead' of the other and therefore tell which way the key is moving. This enables the control unit to keep track of which pulse in the series is being produced, and thus to keep track of the position of the key. Thus it can check the code signal Vco corresponding to each pulse of the clock signal even if the key is partially withdrawn during its insertion into the lock mechanism.

Claims

1) A vehicle security system comprising: a key having first and second tracks each comprising surface contours a reader comprising means for producing first and second signals each varying in a way determined by the respective series of contours and a control means for receiving and comparing the signals and producing an unlock signal if the signals correspond to a predetermined code.

2) A system according to claim 1 wherein one of the tracks comprises a clock track on which the contours are regular.

3) A system according to claim 1 or claim 2 in which one of the tracks comprises a code track on which the contours are irregular.

4) A system according to any foregoing claim wherein the tracks are on a shank of the key.

5) A system according to claim 4 wherein the tracks are on opposite sides of the shank.

6) A system according to claim 4 or claim 5 wherein the shank has at least one further contoured surface for operating a mechanical lock.

7) A system according to any foregoing claim wherein the reader is installed in a vehicle door lock system.

8) A system according to any foregoing claim wherein the contours are formed as depressions in the surface of the key.

9) A system according to claim 8 wherein one of the tracks comprises depressions of differing lengths.

10) A system according to any foregoing claim wherein the reader includes a pair of switches each operated by one of the tracks as the key is moved relative to the switches.

11) A system according to any foregoing claim wherein the contoured tracks are arranged such that the signals produced by the reader can be used to determine in which direction the key is moving.

12) A system according to claim 11 wherein the contours of the code track and the clock track are formed in unit lengths which are the same length for each track, but offset along the shank.

13) A system substantially as hereinbefore described with reference to the accompanying drawings.