Anti-theft system for a motor vehicle

• US 6,100,603 A
• Filed: 11/24/1998
• Issued: 08/08/2000
• Est. Priority Date: 11/24/1997
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Gold, Peter
• Primary Examiner(s): PALADINI, ALBERT WILLIAM
• Application Number:
  US09/198,886
• Time in Patent Office: 623 Days
• Field of Search: 307/10.2, 307/91, 307/89, 180/287, 340/426, 340/573, 340/579, 340/825.69, 340/825.72, 341/176
• US Class Current: 307/10.2
• CPC Class Codes: B60R 25/04 operating on the propulsion system, e.g. engine or drive motor
• CPC Class Codes: G07C 2009/00373 whereby the wake-up circuit is situated in the lock
• CPC Class Codes: G07C 2009/0042 the transmitted data signal containing a code which is changed
• CPC Class Codes: G07C 2009/00793 by Hertzian waves
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks

Abstract

Antennas of an anti-theft system are controlled with a pulse width modulated square-wave signal by a power control unit and a phase control unit. The control is such that a change in power causes no change in phase, and vice versa. This is accomplished by varying the pulse width of the square-wave signal if a change in power occurs and at the same time shifting the pulse rise time such that the phase remains constant.

Claims

1. An anti-theft system for a motor vehicle, comprising:

a transceiver unit disposed in a motor vehicle;

at least two antennas disposed separate from one another in the motor vehicle and electrically connected to said transceiver unit, each of said antennas being adapted to transmit a transmission signal and receive a receiving signal;

a main control unit connected to said transceiver unit, said main control unit evaluating receiving signals received by said antennas; and

a power control unit and a phase control unit controlled by said main control unit for selectively and individually controlling a transmission power and a phase of each of said transmission signals to prevent undesired feedback on said phase or said transmission power of said transmission signals from occurring.

2. The anti-theft system according to claim 1, wherein said control unit forms a part of said transceiver unit.

3. The anti-theft system according to claim 1, wherein said power control unit and said phase control unit control the signals with respect to a pulse width thereof.

4. The anti-theft system according to claim 1, wherein said antennas are electrical coils forming part of an LC oscillator circuit strategically disposed in the motor vehicle.

5. The anti-theft system according to claim 4, wherein said coils are disposed in a driver'"'"'s door, in a rear door on a driver'"'"'s side, in a side wall at a back seat, in a wall at a fuel tank, and at a bumper of the motor vehicle.

6. The anti-theft system according to claim 1, wherein said phase control unit is a shift register and a demultiplexer connected to said shift register.

7. The anti-theft system according to claim 1, wherein said power control unit includes an upward counter and a comparator.