Resistor coded theft deterrent system

• US 4,148,372 A
• Filed: 09/21/1977
• Issued: 04/10/1979
• Est. Priority Date: 09/21/1977
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Schroeder, Thaddeus
• Primary Examiner(s): Lazarus, Ira S.
• Application Number:
  US05/835,220
• Time in Patent Office: 566 Days
• Field of Search: 123/198 B, 123/146.5 B, 123/179 BG, 70/DIG. 46, 180/114, 307/10 AT, 340/285, 340/63, 340/64
• US Class Current: 180/287
• CPC Class Codes: B60R 25/04 operating on the propulsion system, e.g. engine or drive motor
• CPC Class Codes: B60R 25/20 Means to switch the anti-theft system on or off
• CPC Class Codes: G07C 9/00714 with passive electrical components, e.g. resistor, capacitor, inductor
• CPC Class Codes: Y10S 70/46 Conducting key

Abstract

A resistor coded anti-theft system particularly adapted for incorporation as original equipment on a motor vehicle is disclosed. The ignition system is defeated unless an ignition key having both the proper mechanical code and proper code resistor is used to start the vehicle. A selectively destructible fuse device is incorporated in the circuitry to permit determination of the value of the proper code resistor during a final stage of vehicle assembly.

Claims

1. A resistor value coded anti-theft system for a motor vehicle comprising in combination,

a key actuable ignition lock means adapted to receive a key and including contact elements effective to engage and define a circuit path including a resistance integral with said key,

means defining a circuit responsive to the value of the resistance between said contact elements and effective to enable engine start when such resistance is of a predetermined value in relation to an internal resistance of selectable value in said circuit means,

said circuit means further initially having a fusible element which enables engine start independent of the value of said resistance so as to permit engine start at will during assembly operations,

whereby at an appropriate stage of vehicle assembly said fusible element may be destroyed and thereby permit said circuit means to discriminate between different values of said resistance between said contact elements.

2. A motor vehicle theft deterrent system comprising

an ignition switch connected with a source of DC potential, ignition lock means for closing said ignition switch in response to insertion and rotation of an ignition key having the proper mechanical code, said ignition key including a key code resistor forming an integral part thereof, said ignition lock means including contact means arranged to be engaged by said key code resistor means upon insertion of said ignition key in said lock means,

decoder circuitry connected with said ignition switch and said contact means, said decoder circuitry developing a disable signal for inhibiting the operation of said motor vehicle in response to closure of said ignition switch if said key code resistor means is not within predefined limits established by said decoder circuitry, said decoder circuitry further including time delay means for maintaining said disable signal for a predetermined time interval after opening of said ignition switch, fuse means providing a destructible circuit path connected to said decoder circuitry for determining a suitable value for said key code resistor during assembly of said motor vehicle.

3. A motor vehicle theft deterrent system comprising an

ignition switch connected with a first source of DC potential, ignition lock means for closing said ignition switch in response to insertion and rotation of an ignition key having the proper mechanical code, said ignition lock means including contact means arranged to be engaged by a key code resistor forming an integral part of said ignition key upon insertion of said ignition key in said lock means, said lock means further including means providing an electrical ground path for said key code resistor means,

decoder circuitry located in a compartment of said motor vehicle other than the passenger compartment, said decoder circuitry comprising window detector means including resistor means establishing upper and lower voltage limits for said detector means, conductor means extending between said compartments and connecting said contact means with said detector means, fusible link means connected with said detector means providing an interruptable circuit path for measuring the value of said resistor means to thereby permit selection of the proper key code resistor, latch means having an enable state and a disable state first time delay means for driving said latch means to said disable state a predetermined interval after closure of said ignition switch, and for maintaining said latch means in said disable state for a predetermined interval of time after opening of said ignition switch, said latch means preventing the operation of said vehicle when in said disable state, said detector means developing a trigger signal if the resistance of a key code resistor establishes a voltage input to said detector which is within said upper and lower voltage limits, second time delay means having a time constant which is shorter than the time constant of said first time delay means responsive to said trigger pulse for driving said latch means to said enable state and inhibiting said first time delay means, said latch means permitting the operation of said motor vehicle when in said enable state.

4. A motor vehicle theft deterrent system comprising,

an ignition switch connected with a first source of DC potential, ignition lock means for closing said ignition switch in response to insertion and rotation of an ignition key having the proper mechanical code, said ignition lock means including contact means arranged to be engaged by a key code resistor forming an integral part of said ignition key upon insertion of said ignition key in said lock means, said lock means further including means providing an electrical ground path for said key code resistor means,

decoder circuitry located in a compartment of said motor vehicle other than the passenger compartment, said decoder circuitry comprising window detector means including resistor means establishing upper and lower voltage limits for said detector means, fusible link means connected with said detector means providing an interruptable circuit path for measuring the value of said resistor means to thereby permit selection of the proper key code resistor, conductor means extending between said compartments and connecting said contact means with said detector means, said conductor means including additional fusible link means, voltage breakdown means connected with said detector means and responsive to an input voltage on said conductor means above a predetermined value for causing a current to pass through said additional fusible link means sufficient to interrupt the circuit between said contact means and said detector means, latch means having an enable state and a disable state first time delay means for driving said latch means to said disable state a predetermined interval after closure of said ignition switch, and for maintaining said latch means in said disable state for a predetermined interval of time after opening of said ignition switch, said latch means preventing the operation of said vehicle when in said disable state, said detector means developing a trigger signal if the resistance of a key code resistor establishes a voltage input to said detector which is within said upper and lower voltage limits, second time delay means having a time constant which is shorter than the time constant of said first time delay means responsive to said trigger pulse for driving said latch means to said enable state and inhibiting said first time delay means, said latch means permitting the operation of said motor vehicle when in said enable state.