IE54433B1

IE54433B1 - A security system

Info

Publication number: IE54433B1
Application number: IE44083A
Authority: IE
Original assignee: Malcolm Macnaughton
Priority date: 1983-03-02
Filing date: 1983-03-02
Publication date: 1989-10-11
Also published as: GB8405403D0; IE830440L; GB2136620B; GB2136620A

Abstract

A security system for a vehicle comprises a crystal oscillator circuit with a crystal (10) which is located inside the vehicle and removable by the driver, a filter circuit (Fig. 2) tuned to the frequency of the oscillator circuit 1 and means such as a solenoid (Fig. 4) or relay (Fig. 8) for preventing starting of the vehicle except upon receipt of a signal from the oscillator circuit via the tuned filter circuit. The technique described may be used generally to disable apparatus against unauthorised use.

Description

This invention, relates to a security system to prevent use o£ an apparatus except by an authorised user, and has particular though not exclusive application to an electronic anti-theft system for a motor vehicle.

According to the invention there is provided a security system to prevent unauthorised use of an apparatus, the system comprising an oscillator circuit with a component which is removable for keeping by an authorised user, the said component defining the frequency of oscillation of the oscillator circuit, a filter circuit tuned to the frequency of the oscillator circuit, and means disabling the said apparatus against operation except upon receipt of a signal from the oscillator circuit via the tuned filter circuit when the said component is inserted in the oscillator circuit by the authorised user.

In a preferred form of the invention the oscillator - circuit is a crystal oscillator circuit and the removable component is a crystal which defines the frequency of oscillation of the oscillator circuit.

Where the said apparatus is a motor vehicle, the disabling means may comprise means preventing starting of the vehicle, for example by disabling the ignition circuit or by cutting off the supply of fuel to the carburretor. However, the invention can be applied far more generally, and in effect constitutes an electrically operated locking or immobilising system.

In the case of a vehicle anti-theft system, the authorised user (i.e. the keeper of the crystal) would be the owner/driver, or any other person authorised by the owner to drive the vehicle. Naturally more than one crystal could be provided if there were more than one authorised user.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which; Figures 1 and 2 illustrate an oscillator circuit and ignition coil respectively which together comprise a vehicle anti-theft system according to a first embodiment of the invention, Figures 3 and 4 illustrate a modified oscillator circuit and modified ignition coil respectively which together comprise a second embodiment of the invention, Figure 5 is a side elevation of the solenoid forming part of the ignition coil of Figure 4, Figure 6 is a plan view of the solenoid of Figure 5, Figure 7 illustrates a bonnet lock mechanism controlled by a solenoid of the type shown in Figures 5 and 6, Figure 8 is a circuit diagram of a relay which may be used in association with the oscillator circuit of Figure 1 as an alternative to the solenoid, and Figure 9 is a further relay circuit which can be used in association with the oscillator circuit of Figure 1.

Referring first to Figure 1 of the accompanying drawings, a crystal oscillator circuit is shown which is mounted inside the passenger compartment of the vehicle.

The circuit comprises resistors R1 to R5, transistors Tl and T2, and a crystal 10 connected in the arrangement shown to the vehicle battery supply (+12V, earth). The components may have the following values: R1 R2 R3 R4 R5 Tl T2 The main oscillator circuitry comprising the resistors R1 to R5 and the transistors Tl and T2 are contained in a metal housing 11; however, the crystal 10 is removably resistor 1K5 II 47K II 47K II 22K II Type 2N834 Tvne 2N834 mounted in a holder external to the housing 11 whereby the crystal 10 may be removed by the driver. The frequency of oscillation of the oscillator circuit may be selected in the range 100MHz to 10MHz depending solely on the crystal 10 which is used, all other component values and types remaining the same. The removable crystal 10 effectively constitutes an electronic key for the vehicle ignition system as will be described.

The output 12 of the oscillator circuit is fed via a coaxial cable 13 to the vehicle ignition coil 14, Figure 2, which is contained in a metal casing 15 mounted in a conventional position inside the engine compartment. The outer sheath of the cable 13 is connected both to the metal housing 11 of the oscillator circuit and to the metal casing 15 of the coil 14, thereby minimising interference by the oscillator circuit or external interference to the band pass filters.

In addition to the coil 14 proper, the casing 15 also includes two reed switches S4 and S5 which are shown in their unenergised states in Figure 2. It will be observed that in this state the switch S5 is open and thus provides an open circuit between the +12V battery supply and the coil 14. Each reed switch S4, S5 is connected between +12V and earth by a respective transistor T3, T4 which is normally OFF (non-conducting). The base of each transistor T3 and T4 is driven by a respective tuned circuit LC1 and LC2 each tuned specifically to the frequency of oscillation of the oscillator circuit (Figure 1) as determined by the crystal . Each tuned circuit LC1 and LG2 has the oscillator input 12 as input via a coupling capacitor 16, but whereas the circuit LC2 is a series tuned circuit which will only pass the frequency to which it is tuned, the circuit LC1 is a parallel tuned circuit which will pass all frequencies except the one that it is tuned to.

The operation of the system of Figures 1 and 2 is as follows. When the driver leaves the vehicle unattended he removes the crystal 10 from its holder. The ignition system of the vehicle is thus immobilised as the reed switch S5 is - 5 open. The vehicle can only be started by inserting the correct crystal 10 in its holder. This will provide an oscillating signal on the output lead 12 which is of the correct frequency to pass the series tuned circuit LC2 and turn the transistor T4 on. This provides a path for current from +12V to earth via the reed switch S5. The latter is thus energised and its contact switches over to complete a path for the +12V supply to the coil 14. The vehicle may now be started.

It will be observed that only a crystal 10 providing the correct oscillation frequency will complete the ignition coil circuit; any other frequency will not only leave the switch S5 in the open circuit position but will also open the reed switch S4 via the parallel tuned circuit LC1 and transistor T3, thus doubly ensuring the immobilisation of the ignition coil. To increase the selectivity of the transistor T4 to the precise oscillation frequency of the crystal 10 the output of the series tuned circuit LC2 is coupled to earth via a second parallel tuned circuit LC3 also tuned to the oscillator frequency. It will thus be observed that the crystal 10 effectively constitutes an electronic key to the ignition system, in addition or as an alternative to the mechanical ignition key conventionally provided.

In the modified system of Figures 3 and 4, the oscillator circuit (Figure 3) is substantially the same as Figure 1. However, in addition an on-off toggle switch SI has been inserted in the +12V supply lead to the oscillator circuit, and a +12V output lead A has been connected as shown on the opposite side of the switch SI to the +12V supply. Furthermore, an earth lead B including a push button switch S2 has been added, connected to the oscillator earth lead. The switches SI and S2 are accessible from outside the housing 11.

The modification of the ignition coil arrangement (Figure 4) is more substantial, and includes a replacement of the reed switches S4 and S5 by a special solenoid (see also Figures 5 and 6) having two axially aligned coils LX - 6 and LY and a soft iron armature or slug 20 fixedly mounted on a nylon spindle 21. The nylon spindle 21 is capable of reciprocal axial sliding movement relative to the coils LX and LY between a first position in which the slug 20 is within the coil LY and a second position in which the slug 20 is within the coil LX. The spindle 21 is supported for such movement by a polycarbonate former 22 which also supports the coils LX and LY on a reduced diameter portion thereof.

At one end the spindle 21 carries a conductive slider 23 for cooperation with a pair of contacts S8 embedded in the former 22. When the slug 20 is within the coil LY the slider 23 does not bridge the contacts S8, whereas when the slider 23 is within the coil LX it bridges the contacts S8.

As shown in Figure 4, the contacts S8 are located in the +12V supply lead to the coil 14 and therefore the slug 20 must be within the coil LX for the vehicle ignition system to be operable.

At its other end the spindle 21 has a forked end 19 which mounts a pair of contacts 24 spring-loaded towards one another by a spring 25. when the slug 20 is within the coil LY the contacts 24 bridge a first pair of contact pins S6 and establish an electrical connection between them. The bias of the spring 25 holds the contacts 24 in this position and also maintains the slug 20 within the coil LY. However, as the slug 20 is slid from, within the coil LY to within the coil LX the contacts 24 are pushed rearwardly relative to the spindle 21 by the fixed pins S6 until at some point the spring 25 becomes overcentred. At this point the contacts 24 flip over to bridge a second pair of contact pins S7 and the bias of the spring 25 both maintains the contacts 24 in this position and assists in pushing the slug 20 fully home within the coil LX. The reverse action occurs when the slug is slid from within the coil LX to within the coil LY.

As seen in Figure 4, one of each pair of the pins S6 and S7 is connected in common to the +12V supply lead A from the oscillator circuit (Figure 3). The other pin of the pair S6 is connected to one end of the coil LX whose other - Ί end is connected to earth via a transistor T5, while the other pin of the pair S7 is connected to one end of the coil LY whose other end is connected to earth via a transistor T6. The transistors T5 and T6 are normally OFF.

The base of the transistor T5 is driven by the series tuned circuit LC2 and the base of the transistor T6 is driven by the parallel tuned circuit LC1. For reasons of space the tuned circuits LC1 and LC2 are not shown in Figure 4 but, as in the case of Figure 2, they are connected to the oscillator output lead 12 via a coaxial cable 13 whose sheath is connected to the metal casing 15 of the ignition coil 14. The earth output lead B from the oscillator circuit of Figure 3 is connected as shown to the same end of the coil LY as the transistor T6.

The system of Figures 3 and 4 operates as follows. Initially, it is assumed that the system is in the state illustrated; i.e. switches SI and S2 open and the solenoid contacts 24 bridging the pair of contact pins S6. The contacts S8 in the +12V supply lead to the coil 14 are therefore not bridged by the slider 23 and the vehicle cannot be started. To permit the vehicle to be started the driver first closes the switch SI and inserts the correct crystal 10 into its holder. This activates the oscillator circuit whose output passes via lead 12 to the tuned circuits LC1 and LC2. The latter passes the signal to the base of the transistor T5 whereupon the latter turns ON.

This completes a connection between lead A (+12V) to earth via T5. Coil LX is thus energised, the slug 20 is drawn from coil LY into coil LX, and the contacts 24 flip over to bridge the pair of contact pins S7. This movement also brings the slider 23 into a position to bridge the contacts S8, thereby connecting the +12V supply to the coil 14 and permitting the vehicle to be started.

In this position the switch SI may now be opened and (if desired) the crystal 10 removed, since the slug 20 is maintained in coil LX by the bias of the spring 25. Thus in this modified embodiment it is not necessary to leave the oscillator circuit during driving, thereby further reducing interference.

When the driver wishes to immobilise the vehicle he simply turns on the switch SI and momentarily presses the push button switch S2. This completes a path from the +12V supply to one end of coil LY via lead A and contact pins S7 (bridged by contacts 24), and from earth to the other end of coil LY via lead B. The coil LY is thus energised and the slug 20 is withdrawn from coil LX into coil LY, thereby returning the solenoid to its original state as shown in Figure 4. The vehicle cannot now be started without the proper crystal 10, as described above.

It is to be understood that although the solenoid shown in Figures 5 and 6 is used to immobilise the vehicle by open-circuiting the ignition coil circuit, it could alternatively be used to prevent starting of the vehicle by cutting off the petrol supply to the carburettor, by shortcircuiting the points, or by otherwise immobilising a vital part of the engine function until the correct crystal is used. For example, in the case where the supply of petrol to the carburettor is controlled, the nylon spindle 21 could be coupled to a fluid valve in the fuel supply.

In addition to immobilising the vehicle, a further solenoid such as that shown in Figures 5 and 6 may be used to prevent the vehicle bonnet being opened. This would prevent a would-be thief from gaining access to the engine compartment in an attempt to by-pass the crystal or thumbwheel switch systems. An example of a suitable arrangement is shown in Figure 7.

In Figure 7 the bonnet release cable 40 carries an apertured plate 41 fixed thereto. The plate 41 slides in a slot 42 in a support member 43 secured to the inside of the engine compartment. A further solenoid 44 of the type described with reference to Figures 5 and 6 is secured on the member 43 with its spindle 21 entering the aperture in the plate 41 when the slug 20 is within the coil LY. This prevents the bonnet release cable 40 from sufficient movement to permit the bonnet to be opened by the usual handle or lever inside the vehicle. The solenoid 44 is - 9 connected to the crystal oscillator in the same way and in parallel with the first solenoid which, for example, controls the ignition coil or the petrol supply. Only when the correct crystal used is the spindle 21 withdrawn into the solenoid 44 to release the plate 41 for movement.

To make all systems completely secure a fuse could be incorporated inside the ignition coil, distributor or elsewhere which would blow if the incorrect crystal or thumbwheel switch setting were used.

A further embodiment of the invention is illustrated in Figure 8, which shows a multi-pole two-way relay which may be used in association with the oscillator circuit of Figure 1 as an alternative to the solenoid of Figures 4, 5 and 6.

The relay is a 4 pole 2 way relay having four sets of contacts 50 to 53 actuated by a common relay coil 54. The relay is shown in its unenergised condition in the Figure, wherein the movable centre contact of each contact set 50 to 53 engages the fixed right hand contact in each case.

The movable centre contact of the contact set 50 and the movable centre contact of the set 53 are each connected directly to ground as shown. Furthermore, the fixed left hand contact of the set 50 and the movable centre contact of the set 51 are each connected to the +12V battery supply, in the former case via the relay coil 54 and in the latter case directly. Finally, the fixed left hand contact of the set 51 is connected to the ignition coil, the movable centre contact of the set 52 is connected to a bonnet lock solenoid, the fixed left contact of the same set 52 being connected to a bonnet lock switch (not shown) in the vehicle, and the fixed left hand contact of the set 53 is connected to the starter solenoid coil.

The emitter-collector path of a first transistor T7 is connected in parallel with the relay coil 54 between the +12V battery supply via the contact set 51 and the fixed left hand contact of the set 50, the latter also being connected to ground by the emitter-collector path of a further transistor T8. The base of transistor T7 is - 10 connected to the output of the tuned circuit LC1 and the base of transistor T8 is connected to the output of the tuned circuit LC2, these tuned circuits being similar to those shown in Figure 2.

The relay operates as follows. The use of an incorrect crystal will give an output from LC1 which switches T7 ON thereby providing an effective short circuit across the relay coil 54. When the correct crystal is used, however, T7 will turn OFF and T8 will be switched ON by an output from LC2, thereby energising the relay and changing over the contact sets 50 to 53. The contact set 50 will now hold the relay in its energised condition since it grounds the coil like T8, so that T8 can be switched OFF if desired by removing the crystal from the oscillator circuit. In the energised state of the relay, an output from LC1 or LC2 will not cause the relay coil 54 to be short circuited as the fixed right hand contact of the contact set 51 is not engaged by the movable centre contact of the contact set 51. It is to be noted that in this embodiment the leads A and B of Figure 3 are not necessary.

In the energised condition of the relay the contact set supplies +12 volts to the ignition coil, the contact set 53 provides a path to ground for the starter solenoid, and the contact set 52 allows the bonnet to be opened if the bonnet lock switch in the vehicle is closed by providing a path for current through the bonnet lock solenoid which although of conventional construction has a spindle which acts on the bonnet release cable in the same way as shown in Figure 7. Thus the car can only be started and the bonnet opened when the correct crystal is used by the driver. When the driver wishes to immobilise the vehicle once more after a journey, this is simply done by temporarily opening a normally closed push-button switch (not shown) in either the +12 volt supply lead or in the ground lead. This cuts off the current through the coil 54 whereby the contact sets 50 to 53 change over to the de-energised condition shown in the Figure, Referring now to Figure 9, the circuit includes two - 11 relays, a single pole changeover relay (RELAY 1) and a four pole changeover relay (RELAY 2). When the vehicle ignition switch is OFF and the crystal 10 is not inserted in its holder the various relay contacts assume the positions illustrated, i.e. both RELAY 1 and RELAY 2 are de-energised.

When it is desired to start the vehicle, the crystal 10 is inserted and the output signal from the oscillator circuit (Figure 1) on line 12 is fed to TI and amplified.

If it is of the correct frequency it is passed by XI, C3 and R5 (which constitute a filter circuit tuned to the frequency of the oscillator circuit of Figure 1) and is amplified by T2. The signal is then detected by DI and fed to both T3 and T4, which now both conduct. The collector voltage of T3 will drop to zero holding T5 OFF and maintaining RELAY 1 in the de-energised condition shown.

Since T4 is conducting, RELAY 2 will be energised when the ignition switch is switched ON, thus changing over the movable centre contacts. The path for energising current for RELAY 2 is through contacts B of RELAY 1 and the emitter-collector path of T4. RELAY 2 is now held in its energised condition by contacts 12 and 13, so that the crystal 10 may be removed as before. Voltage is applied to the ignition coil through contacts 15 and 16 (and removed from the horn by separation of contacts 14 and 15, the horn giving a momentary sound prior to this to indicate that the system is functioning), and the bonnet lock solenoid may be operated through contacts 9 and 10. RELAY 1 is totally disabled by the separation of contacts 11 and 12 of RELAY 2 and has no further effect on the system until RELAY 2 is deenergised.

If the input frequency on line 12 is incorrect (incorrect crystal 10 used) the signal will not pass XI. Nothing will be detected by DI and neither T3 nor T4 will conduct. When the ignition is switched ON, the voltage on the collector of T3 will be applied to T5 switching the latter ON. RELAY 1 will now be energised, the centre contact will change over, and the relay will be held in the energised condition through contacts A. The separation of - 12 contacts B of RELAY 1 provides an open circuit in series with T4, so that even if a correct crystal is subsequently used RELAY 2 cannot be energised and the ignition circuit remains disabled.

The following are component types and values which we have used in the circuit of Figure 9; R1 : 820K Cl: lOOpF R2 : 100K C2: lOOpF R3 : 1K5 C3: lOOpF R4 : 100Ω C4: lOOpF R5 : 100 S C5: lOpF R6 ; 820K R7 ; 100K R8 : 1K5 DI: 0A90 R9 : 1K5 D2: BY206 RIO: 1K5 D3: BY206 Rll: 33K R12: 100K

Claims

CLAIMS:

1. A security system to prevent unauthorised use of an apparatus, the system comprising an oscillator circuit with a component which is removable for keeping by an authorised user, the said component defining the frequency of oscillation of the oscillator circuit, a filter circuit tuned to the frequency of the oscillator circuit, and means disabling the said apparatus against operation except upon receipt of a signal from the oscillator circuit via the tuned filter circuit when the said component is inserted in the oscillator circuit by the authorised user.

2. A system according to claim 1, wherein the oscillator circuit is a crystal oscillator circuit and wherein the removable component is a crystal which defines the frequency of oscillation of the oscillator circuit.

3. A system according to claim 2, wherein the disabling means comprises a solenoid having an armature movable between a first position in which the said apparatus is disabled and a second position in which the said apparatus is enabled, and a control circuit responsive to the signal from the oscillator circuit via the tuned filter circuit to cause the armature to move from the first to the second position.

4. A system according to claim 3, wherein the control circuit includes means for automatically maintaining the armature in the said second position to permit removal of the crystal from the oscillator circuit after the apparatus has been enabled for operation.

5. A system according to claim 4, wherein the control circuit further includes means under manual control to return the armature to the said first position.

6. A system according to claim 1, wherein the disabling means comprises a multi-pole two-way relay which disables the said apparatus in its unenergised condition and enables the said apparatus in its energised condition, and a control circuit responsive to the signal from the oscillator circuit via the tuned filter circuit to energise the relay. - 14

7. A system according to claim 6, wherein the control circuit includes means for automatically maintaining the relay in its energised condition to permit removal of the crystal from the oscillator circuit after the apparatus has 5 been enabled for operation.

8. A system according to claim 7, wherein the control circuit further includes means under manual control to return the relay to its unenergised condition.

9. A system according to any preceding claim, further 10 including means responsive to insertion of an incorrect component to cause the said apparatus to remain disabled even upon subsequent insertion of a correct component.

10. A system according to any preceding claim, wherein the said apparatus is a motor vehicle, and wherein the said 15 disabling means comprises means preventing starting of the vehicle.

11. A system according to claim 10, wherein the removable component is located in the vehicle passenger compartment. 20

12. A system according to claim 10 or 11, wherein the means preventing starting of the vehicle comprises means for disabling the ignition circuit of the vehicle.

13. A system according to claim 10, 11 or 12, further including means for preventing opening of the vehicle bonnet 25 except upon receipt of a signal from the oscillator circuit via the tuned filter circuit.

14. A security system substantially as described herein with reference to the accompanying drawings.