GB2280313A

GB2280313A - A security device

Info

Publication number: GB2280313A
Application number: GB9315408A
Authority: GB
Inventors: Stephen Day
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1993-07-24
Filing date: 1993-07-24
Publication date: 1995-01-25
Also published as: GB9315408D0

Abstract

The device has an armature 4 and a first coil 6, which is inductively coupled to a second coil 8. The armature 4 is movable to block or unblock the passage of fluid in a pipe. The second coil 8 is connected to a power supply which provides a continuously varying voltage when a key is operated so that it induces a current and magnetic field in the first coil 6. The magnetic field in the first coil 6 causes the armature 4 to move. A DC field applied to the second coil 8 does not move the armature 4. The device may be used to prevent theft of a vehicle by blocking the flow of fuel to the engine. <IMAGE>

Description

A SECURITY DEVICE The present invention relates to a security device for interrupting the flow of fluid in a pipe, for use particularly, but not exclusively, for interrupting the flow of fuel through the distributor pump in a motor vehicle powered by a diesel engine.

In many motor vehicles with conventional diesel engines the fuel supply may be interrupted by the operation of a solenoid controlled valve. Such a valve typically comprises a solenoid which partially surrounds an armature which is operatively connected to the distributor pump of the engine.

When no current flows in the solenoid the armature is at rest and blocks the supply of fuel to the pump. When current flows in the solenoid the resultant magnetic field causes the armature to move so as to open up the flow of fuel to the pump. The flow of DC current through the solenoid is typically controlled by a switch which is operated by a key.

If a car thief does not have access to the key, he may still be able to start the engine by "hot wiring". This involves by-passing the switch associated with the key, to cause a DC current to flow through the solenoid without the key being turned.

According to the present invention there is provided a security device comprising a solenoid valve, a key, and a power supply which provides a continuously varying voltage when the key is used correctly; the solenoid valve comprising a first conductive coil and a second conductive coil and an armature movable from a rest position relative to the first coil in response to a flow of current in the first coil, the armature being adapted in its rest position to block the flow of fluid in a pipe, wherein the current is made to flow in the first coil by induction caused by the application of a continuously varying voltage from the power supply to the second coil, and wherein the magnetic field generated by the second coil does not directly cause the armature to move.

In a preferred embodiment the pipe is connected to the distributor pump of a diesel engine for a motor vehicle so that in the rest position the armature prevents the passage of diesel fuel to the distributor pump, and when moved by the first coil the armature permits the passage of fuel.

When the device is used in a motor vehicle the key may conveniently be the ignition key for that vehicle.

The continuously varying voltage causes the second coil to produce an alternating flux which cuts the turns of the first coil and induces a current and a magnetic field in the first coil. The voltage may be AC or it may be pulsed DC.

Preferably the voltage is pulsed 12 volt DC.

The varying voltage may be produced by any suitable power supply. The power supply may be part of a security module which includes a lockable robust housing to make it more difficult for a thief to gain access to it. When the device is used in a diesel engine for a motor vehicle it is preferred that the varying voltage be produced by generating pulses of the 12 volt DC of a standard car battery.

The pulse generation means is preferably located within a robust housing near the key to make it difficult for a thief to tamper with it. Hot wiring of DC voltage to the second coil will induce a constant magnetic field in the second coil which is not strong enough to move the armature.

Because the magnetic field is constant it does not induce current in the first coil which therefore does not cause the armature to move.

The pulse or AC generator may be actuable only when a correct password has been entered by means of a key pad or like device. Unless the user enters the correct password the pulse or AC generator will not operate and therefore the valve will not operate. This provides an added layer of security against theft.

Preferably the first coil is electrically isolated. This makes it difficult for a thief to hot wire, because this would require access to both ends of the coil and the making of an electrical connections to each end.

The two coils and the armature may be mutually arranged in any suitable relative orientation. In a preferred embodiment the coils are wound to form hollow cylinders and the first coil is located within the second coil, the two cylinders being coaxial. The armature is elongate and located axially within or adjacent to the first coil. The armature is closer to the first coil than to the second coil so a magnetic field induced in the second coil is not sufficient to move the armature. This arrangement allows the solenoid valve of a security device according to the invention to be readily substituted for a conventional DC solenoid valve.

After operation of the valve the armature may be constrained to return to its rest position by spring means or under gravity.

The invention also extends to a solenoid valve for use in a security device, the valve comprising a first conductive coil and a second conductive coil and an armature movable from a rest position relative to the first coil in response to a flow of current in the first coil, wherein the current is made to flow in the first coil by induction caused by the application of a continuously varying voltage to the second coil, and wherein the magnetic field generated by the second coil does not directly cause the armature to move.

The invention will now be further described, by way of example, with reference to the following drawings in which: Figure 1 is a section through a solenoid valve of a security device in accordance with the invention; Figure 2 is a schematic drawing of a circuit for operating the solenoid valve of Figure 1.

Figure 1 shows a solenoid valve comprising a housing 2 in which is located a first coil 6, a second coil 8, and an armature 4. The second coil 8 is connected to a source of pulsed DC electricity 10 at one end and is earthed 12 at its other end. The first coil 6, which is electrically isolated, is coaxial with the second coil 8 and located within the second coil 8. The armature 4 is located partially within the first coil 6.

When a pulsed DC voltage is applied to the second coil 8 it induces an alternating magnetic flux which cuts the turns of the first coil 6 and induces a current in the first coil 6.

The magnetic field which is generated in the first coil 6 as a result of the passage of induced current causes the armature 4 to rise further into the housing.

The armature 4 may block or unblock the passage of fluid in a pipe, for example to prevent or allow the passage of fuel into a diesel distributor pump.

If a steady DC voltage is applied across the second coil 8, for example if a thief hot wires the valve, it will produce a magnetic field. However the magnetic field is not strong enough to cause the armature 4 to move because the armature 4 is separated from the second coil 8 by too great a distance.

Figure 2 shows a circuit for use with the valve of Figure 1.

The circuit may be used in any suitable environment, but it will be here described for convenience by reference to its use in a motor vehicle.

The second coil 8 is connected to the vehicle battery 12 through a pulse generator 18 and a switch 14. The switch 14 is opened or closed by the operation of a key. The first coil 6 is electrically isolated from the circuit. When the switch 14 is closed to complete the circuit the pulse generator 18 provides a source of pulsed DC voltage across the second coil 8 via the wire 20. This induces a current in the first coil 6 as described above. If a thief hot wires the engine by making a direct connection 22 between the battery 12 and the second coil 8 this will not induce a current in the first coil 6 and will therefore not operate the valve. The pulse generator is here shown connected to a controller 16 which is used to provide an additional control over the operation of the pulse generator. When the controller 16 is in use it requires a password to be entered before it will permit the pulse generator to operate.

By indirectly linking the battery with the first coil in this way the vehicle is made more secure from theft.

For convenience the invention has been described by reference to its use in a motor vehicle, however the invention is not limited to this embodiment and may be used in any suitable device or machine which requires an electrically operated valve.

References to a key should be understood to include any key means which permit a user to operate the valve. This includes a mechanical key for a lock, an encoded magnetic strip, a bar code, password or any other like device.

Claims

1 A security device comprising a solenoid valve, a key, and a power supply which provides a continuously varying voltage when the key is used correctly; the solenoid valve comprising a first conductive coil and a second conductive coil and an armature movable from a rest position relative to the first coil in response to a flow of current in the first coil, the armature being adapted in its rest position to block the flow of fluid in a pipe, wherein the current is made to flow in the first coil by induction caused by the application of a continuously varying voltage from the power supply to the second coil, and wherein the magnetic field generated by the second coil does not directly cause the armature to move.

2 A device as claimed in Claim 1, wherein the pipe is connected to the distributor pump of a diesel engine for a motor vehicle so that in the rest position the armature prevents the passage of fuel to the pump, and when moved by the first coil the armature permits the passage of fuel.

3 A device as claimed in Claim 1 or Claim 2, wherein the voltage is pulsed DC.

4 A device as claimed in any one of the preceding claims, wherein the varying voltage is produced by generating pulses of the 12 volt DC of a standard car battery.

5 A device as claimed in Claim 3 or Claim 4, wherein the pulse generating means are located in a robust housing near the key.

6 A device as claimed in any one of claims 3-5, wherein the pulse generating means is not actuable without the input of a correct password or code.

7 A device as claimed in any one of the preceding claims wherein the first coil is electrically isolated.

8 A device as claimed in any one of the preceding claims wherein the coils are wound to form hollow cylinders and the first coil is located within the second coil, the two cylinders being coaxial, and the armature being located axially within or adjacent to the first coil.

9 A device as claimed in any one preceding claim wherein the armature is constrained by spring means to return to its rest position after operation of the valve.

10 A solenoid valve for use in a security device, the valve comprising a first conductive coil and a second conductive coil and an armature movable from a rest position relative to the first coil in response to a flow of current in the first coil, wherein the current is made to flow in the first coil by induction caused by the application of a continuously varying voltage to the second coil, and wherein the magnetic field generated by the second coil does not directly cause the armature to move.

11 A security device substantially as herein described with reference to the accompanying drawings.

12 A solenoid valve substantially as herein described with reference to the accompanying drawings.