Fail safe system for a mechanical lock and key set with electrical interlock

• US 5,287,098 A
• Filed: 09/15/1992
• Issued: 02/15/1994
• Est. Priority Date: 02/11/1991
• Status: Expired due to Term

• Current Assignee: Strattec Security Corporation
• Original Assignee: Briggs & Stratton Corporation
• Inventors: Janssen, David C.
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): ZIMMERMAN, BRIAN A
• Application Number:
  US07/946,017
• Time in Patent Office: 518 Days
• Field of Search: 340/825.31, 340/825.32, 340/825.34, 307/10.3, 70/278, 70/237, 235/492, 361/56, 361/111
• US Class Current: 340/5.65
• CPC Class Codes: G07C 9/00738 sensed by Hall effect devices
• CPC Class Codes: Y10T 70/5889 For automotive vehicles

Abstract

A mechanical key and lock set with a rotating cylinder includes an electronic interlock which is responsive to the insertion of a mated key in the cylinder and proper rotation of the cylinder. A sensor is placed in communication with the cylinder and senses proper rotation of the cylinder to generate an activation signal. Systems controlled by the lock cannot be enabled without the generation of the activation signal. Fail safe blocking circuitry is placed in communication with the activation signal generator and in the event the actuation signal is attempted to be read in an unauthorized manner without properly rotating the cylinder, the blocking circuitry is functional to preclude reading.

Claims

1. A fail safe circuit adapted for preventing the deciphering of a coded electronic interlock for a mechanical lock, the lock having a rotatable cylinder and a mated key applicable in a normal mode for unlocking a system when the mated key is inserted in the cylinder and the key and cylinder are rotated from a locked position to an unlocked position, the interlock precluding enabling of the system until a preselected activation signal is generated in response to the rotation of the key and cylinder, the interlock including a sensor for determining the rotation of the cylinder and the key, and a signal generator having a preselected activation code controlled by the sensor for generating a system activation signal in response to the rotation of the cylinder and key, the fail safe circuit being in communication with said signal generator, said fail safe circuit adapted for preventing the unauthorized reading of the value of the preselected code when a mated key is not present in the cylinder of the mechanical lock, the fail safe circuit comprising:

a. a transistor switch circuit in communication with the signal generator and operable when the key is not present in the cylinder; and

b. an amplifier circuit for receiving said activation signal when said transistor switch is operable, the amplifier circuit adapted for isolating the signal generator from the circuit and providing a false signal when an attempt is made to read the coded activation signal of the generator without inserting a mated key in the cylinder and rotating the key and cylinder.

2. The fail safe circuit of claim 1, further comprising a comparator circuit in communication with said signal generator for receiving the system activation signal, said comparator circuit operable for unlocking said system when the system activation signal is within an acceptable range.

3. The fail safe circuit of claim 1, wherein said fail safe device further includes a strobe element adapted for tri-stating the reflective circuit for providing a true open circuit when not energized.

4. The fail safe circuit of claim 3, further including a multiplier feed back loop with the amplifier circuit for multiplying the level of the activation signal.

5. The fail safe circuit of claim 3, further including a multiplying pre-amplifier circuit in advance of the reflective circuit for both amplifying and isolating the activation signal generated by said generator.

6. The fail safe circuit of claim 1, wherein said sensor further includes a Hall effect element for reading the presence of a magnetic field, and wherein said cylinder includes a permanent magnet located on the outer periphery thereof which is rotated in the proximity of the Hall effect element when the cylinder is properly rotated.

7. A fail safe circuit adapted for preventing the deciphering of a coded electronic interlock for a mechanical lock, the lock having a rotatable cylinder and a mated key operable in a normal mode for unlocking a system when the mated key is inserted in the cylinder and the key and cylinder are rotated from a locked position to an unlocked position, the interlock precluding the enabling of the system until a preselected resistance element is activated for a coded signal in response to the rotation of the key and cylinder, the interlock including a sensor for determining the rotation of the cylinder and key and a signal generator for activating the preselected resistance element for generating an ignition activation signal in response to rotation of the cylinder and key, the fail safe circuit being in communication with the signal generator and operable for preventing the unauthorized reading of the value of the preselected resistance element when a mated key is not present in the cylinder of the mechanical lock and the cylinder is not properly rotated, the fail safe device comprising:

a by-pass circuit disposed in parallel with the signal generator and the preselected resistance element and dormant when the cylinder is rotated to generate the activation signal and active when an attempt is made to read the preselected resistance element without rotating the cylinder for generating a false signal.

8. The fail safe circuit of claim 7, wherein said cylinder includes a permanent magnet mounted on the periphery thereof and wherein said sensor includes a Hall effect element which generates a signal in response to the proximity of the magnet relative to the sensor.

9. The fail safe circuit of claim 7, wherein said passive bypass circuit includes a diode triggered circuit, wherein the diode disengages said circuit when the cylinder is properly rotated and engages said circuit when an attempt is made to read the coded resistance value of the signal generator without rotating the cylinder.

10. The fail safe circuit of claim 7, wherein said passive bypass circuit includes a transistor switch circuit, the circuit having an ON mode and an OFF mode, the circuit normally turned OFF when the cylinder is properly rotated and turned ON to activate the bypass circuit in response to an attempt to read the coded resistance value of the signal generator without rotating the cylinder.