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

• US 20030098615A1
• Filed: 11/07/2002
• Published: 05/29/2003
• Est. Priority Date: 11/09/2001
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Fischer, Robert, Peter, Claus
• Granted Patent: US 7,053,499 B2
• Time in Patent Office: Days
• US Class Current: 307/10.5
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: G08C 19/28 using pulse code

Abstract

An antitheft device for a motor vehicle has a first receiver (2) in the motor vehicle, which is designed to receive signals in narrowband. The signals received by means of this receiver are evaluated in accordance with the code information contained in them. Furthermore, the antitheft device has a second broadband receiver (7) which receives signals outside the useful frequency band (3). If signals are received whose signal strength is above a threshold value (S), whose signal duration is shorter than a predefined time period (t₂-t₁) or whose code information corresponds largely to anticipated code information, the access to the motor vehicle, and its use, are not enabled.

Claims

1. An antitheft device for a motor vehicle comprising:

a first receiver which is arranged at the vehicle end and which is designed to receive in narrowband and to demodulate signals which are emitted by a remotely arranged transmitter, the signals of the transmitter containing code information which is modulated with a predefined carrier frequency, the carrier frequency lying within a predefined useful frequency band,

an evaluation unit to which the signals which are received and demodulated by the first receiver are passed on and which extracts the code information from the demodulated signals, compares it with setpoint code information and generates an enable signal when the two signals at least largely correspond, wherein the antitheft device has a second receiver which is designed to receive signals in broadband, the carrier frequencies of which signals lie outside the useful frequency band.

2. The antitheft device as claimed in claim 1, wherein the second receiver is arranged at the vehicle end and/or at the code generator end.

3. The antitheft device as claimed in claim 1, wherein a discriminator is connected upstream or downstream of the second receiver and permits evaluation only if those signals which are received by the second receiver and whose signal reception strength exceeds a threshold value or which have changed significantly in terms of their amplitude in comparison with previously measured reception levels, the evaluation unit not generating or suppressing the enable signal if a signal is received at a signal reception level or with a change amplitude greater than a threshold value and/or if the code information contained in the signal at least largely corresponds to setpoint code information.

4. The antitheft device as claimed in claim 1, wherein a time window decision element is arranged at the vehicle end, said time window decision element preventing the generation of the enable signal or suppressing it if the received signal is received with its signal level starting from a predefined time at which the reception of a signal is anticipated, and the signal level is above a predefined threshold value for at maximum a predefined time period (t₂-t₁).

5. The antitheft device as claimed in claim 1, wherein a triggering transmitter (11) is arranged at the vehicle end and when triggering occurs it emits a request signal by means of which a portable code generator (12) is requested to transmit back a signal after reception of the request signal.

6. The antitheft device as claimed in claim 1, wherein the request signal emits in the frequency band around 125 kHz in the case of a low-frequency carrier frequency, and the signal is transmitted back in a narrowband useful frequency band at approximately 315 MHz, or approximately 433 MHz or approximately 868 MHz, in the case of a high-frequency carrier frequency.

7. The device as claimed in one of the preceding claims, characterized in that the second receiver has a bandstop filter by means of which at least the previously defined, narrowband useful frequency band is masked out when signals are received.

8. A method for operating an antitheft device for a motor vehicle, wherein

a first receiver arranged at the vehicle end is used to receive and demodulate signals within a useful frequency band and evaluate the code information contained in them,

a second receiver can be used to receive signals outside the useful frequency band, and

an enable signal is suppressed or not generated if the second receiver is used to receive a signal which contains code information which corresponds to setpoint code information or whose signal level is above a predefined threshold value only within a predefined time period.

9. The method as claimed in claim 8, wherein the reception levels of the signals are detected and only signals whose reception levels exceed a threshold value defined as a function of the respective frequency band or differ significantly from previously measured reception levels are evaluated.

10. A method for operating an antitheft device for a motor vehicle comprising the steps of:

receiving a transmitted signal by a narrowband receiver and a wideband receiver which excludes the narrowband;

generating an enable signal if the narrowband receiver receives a valid code and the wideband receiver does not receive a signal having predefined characteristics.

11. Method as in claim 10, wherein the predefined characteristics are determined by a time discriminator.

12. Method as in claim 10, wherein the predefined characteristics are determined by a threshold value discriminator.

13. Method as in claim 10, wherein the predefined characteristics are determined by a level change discriminator.

14. Method as in claim 10, wherein the transmitted signal is triggered by sending a request signal.

15. Method as in claim 10, wherein a coded information is extracted from the received signals and compared with stored setpoint information.

16. Method as in claim 10, wherein the signal received by the wideband receiver is demodulated and compared with stored setpoint information.

17. Method as in claim 10, wherein the time period of the received signals is compared to determine whether the signal has been manipulated.

18. Method as in claim 17, wherein in addition the signal received by the wideband receiver is demodulated and compared with the information demodulated from the narrowband signal to determine whether the signal has been manipulated.

19. Method as in claim 10, wherein if no enable signal is generated a manipulation detection signal is signalized.

20. Method as in claim 19, wherein the manipulation signal is a signal from the group consisting of visible, audible, or tactile signals.