Communications: electrical – Land vehicle alarms or indicators – Of burglary or unauthorized use
Reexamination Certificate
1999-08-16
2001-04-17
Crosland, Donnie L. (Department: 2632)
Communications: electrical
Land vehicle alarms or indicators
Of burglary or unauthorized use
C340S425500, C340S539230, C340S010100, C340S010340, C340S010400, C340S870030, C340S870030, C307S010200, C307S010500
Reexamination Certificate
active
06218932
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention belongs to the automotive field. Specifically, the invention relates to an antitheft device for a motor vehicle with which doors are locked or unlocked or an electronic immobilizer is selectively released.
A prior art antitheft device—described in German patent No. DE 43 29 697 C2—has a vehicle-mounted transceiver unit which can transmit and receive signals. If a user wishes to enter the vehicle, a challenge/response dialog is triggered by activating a trigger switch. A challenge signal (also referred to as a request signal, question signal, or interrogation signal) is thereby transmitted from the transceiver unit to a code transmitter which is carried by the user. The latter automatically transmits back an encrypted response signal if it has previously received the challenge signal. In the motor vehicle, the response signal is compared with an expected reference signal and, if the two correspond (=successful authentication), the doors are locked or unlocked. In such an antitheft device, however, the response signal may be recorded illegitimately by a third party with a recording device. If the third party then activates the trigger switch and subsequently transmits the previously recorded response signal, the doors are unlocked even though the unauthorized person is in the possession of the code transmitter. The unauthorized person can thus relatively easily enter the vehicle and also use it.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a antitheft device for a motor vehicle and a method for operating the antitheft device, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for an improved level of protection against simulated response signals.
With the foregoing and other objects in view there is provided, in accordance with the invention, 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 the transceiver unit;
an evaluation unit in the 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 the 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 the code transmitter for detecting a received power of the challenge signal and for adding a value representing the received power to the response signal.
In other words, the transceiver unit transmits a first request signal whose received power is measured in the code transmitter. The measured value is transmitted back to the transceiver unit in the response signal. Likewise, the reception power of a second request signal is measured and transmitted back to the transceiver unit in the response signal. The two reception powers are compared with one another in the transceiver unit and, in dependence on the comparison, a security device is controlled.
In accordance with an added feature of the invention, the security device includes a device for protecting against unauthorized use of the motor vehicle, such as an immobilizer. Furthermore, the security device may include a motor vehicle access control device for locking and unlocking access to the vehicle.
In accordance with an additional feature of the invention, the 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.
With the above and other objects in view there is provided, in accordance with the invention, 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.
In accordance with another feature of the invention, the first challenge signal and the second challenge signal are transmitted at mutually different power levels.
In accordance with a further feature of the invention, the first challenge signal and the second challenge signal are transmitted with the same power via different antennas which are connected to the transceiver unit.
In accordance with a concomitant feature of the invention, the first challenge signal and the second challenge signal are transmitted at mutually different phase angles.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an antitheft device for a motor vehicle and method for operating the antitheft device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
REFERENCES:
patent: 5309144 (1994-05-01), Lacombe et al.
patent: 5701121 (1997-12-01), Murdoch
patent: 5790014 (1998-08-01), Campbell et al.
patent: 5796180 (1998-08-01), Glehr
patent: 5897598 (1999-04-01), Puetz
patent: 5937065 (1999-08-01), Simon et al.
patent: 4329697C2 (1995-10-01), None
Crosland Donnie L.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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