Antitheft device for a motor vehicle and method for operating the antitheft device

• US 6,218,932 B1
• Filed: 08/16/1999
• Issued: 04/17/2001
• Est. Priority Date: 08/14/1998
• Status: Expired due to Term

• Current Assignee: Continental Automotive GmbH (Continental AG)
• Original Assignee: Siemens AG
• Inventors: Stippler, Michael
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US09/375,070
• Time in Patent Office: 610 Days
• Field of Search: 340/426, 340/425.5, 340/539, 340/10.1, 340/10.34, 340/10.4, 340/10.41, 340/10.42, 340/825.69, 340/825.72, 341/176, 307/10.2, 307/10.5
• US Class Current: 340/426.16
• CPC Class Codes: B60R 25/04 operating on the propulsion system, e.g. engine or drive motor
• CPC Class Codes: B60R 25/245 where the antenna reception area plays a role
• CPC Class Codes: E05B 85/01 Mechanical arrangements specially adapted for hands-free locking or unlocking handles with means for initiation of a hands-free locking or unlocking process E05B81/78
• CPC Class Codes: G06K 19/0707 the arrangement being capable of collecting energy from external energy sources, e.g. thermocouples, vibration, electromagnetic radiation G06K19/0702 takes precedence
• CPC Class Codes: G06K 19/0712 the arrangement being capable of triggering distinct operating modes or functions dependent on the strength of an energy or interrogation field in the proximity of the record carrier active means for hindering electromagnetic reading or writing G06K19/07336
• CPC Class Codes: G07C 2009/00388 code verification carried out according to the challenge/response method
• CPC Class Codes: G07C 2009/00531 immobilizer
• CPC Class Codes: G07C 2009/00547 starting ignition
• CPC Class Codes: G07C 2009/00793 by Hertzian waves
• CPC Class Codes: G07C 2209/63 Comprising locating means for detecting the position of the data carrier, i.e. within the vehicle or within a certain distance from the vehicle
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks
• CPC Class Codes: G08C 17/02 using a radio link

Abstract

A first challenge signal whose reception power is measured in a portable code transmitter is transmitted by a vehicle-mounted transmission unit. Subsequently, a second challenge signal is transmitted under changed transmission conditions, and the reception power of the second challenge signal is also measured. Doors are unlocked, or the internal combustion engine is started only if the received power levels are also different. Otherwise, one or more challenge signals are transmitted once more under changed transmission conditions.

Claims

1. A motor vehicle antitheft device, comprising:

a motor vehicle mounted transceiver unit for transmitting a challenge signal and for receiving a response signal;

a motor vehicle mounted security device connected to said transceiver unit;

an evaluation unit in said transceiver unit for evaluating the response signal and for comparing an item of code information contained in the response signal with an item of expected reference code information and for controlling said security device in dependence on a result of the comparison;

a portable code transmitter for receiving the challenge signal and for transmitting a coded response signal in response to the challenge signal; and

a measuring device in said code transmitter for detecting a received power of the challenge signal and for adding a value representing the received power to the response signal.

2. The antitheft device according to claim 1, wherein said security device includes a device for protecting against unauthorized use of the motor vehicle.

3. The antitheft device according to claim 1, wherein said security device is a motor vehicle access control device.

4. The antitheft device according to claim 1, wherein said code transmitter includes a coil forming a reception antenna, and a voltage induced in the coil when the challenge signal is received is a measure of the reception power.

5. A method of operating a motor vehicle antitheft device, which comprises:

transmitting a first challenge signal with a motor vehicle mounted transceiver unit;

receiving the first challenge signal with a portable code transmitter, measuring a reception power of the challenge signal in the code transmitter, and transmitting a response signal to the transceiver unit with a value representing the first challenge signal reception power;

transmitting a second challenge signal with the transceiver unit under changed conditions as compared to the first transmitting step;

receiving the second challenge signal with the code transmitter, measuring a reception power of the second challenge signal in the code transmitter, and transmitting a response signal to the transceiver unit with a value representing the second challenge signal reception power; and

comparing the challenge signal power level with the second challenge signal power level in the transceiver unit and controlling a vehicle mounted security device in dependence on the comparison and if an item of code information contained in the response signal corresponds to an expected item of reference code information.

6. The method according to claim 5, wherein the first challenge signal and the second challenge signal are transmitted at mutually different power levels.

7. The method according to claim 5, wherein the first challenge signal and the second challenge signal are transmitted with the same power via different antennas connected to the transceiver unit.

8. The method according to claim 5, wherein the first challenge signal and the second challenge signal are transmitted at mutually different phase angles.