Motor-vehicle central lock system with transponder in key

Abstract

A lock system has a remote operator, a lock provided with a switch actuatable by a key part of the operator, a central controller in the vehicle connected to elements of the vehicle for actuating same, a receiver, and a transceiver. The operator is separate from the motor vehicle and has the key part, an energy source, a transmitter powered by the energy source and actuatable to transmit a main signal containing a current main code word, and a transponder substantially independent of the transmitter and of the energy source for receiving an interrogation signal and thereupon generating a callback signal containing a callback code word. When the receiver in the motor vehicle receives the transmitted code work it sends a release signal to the controller. Alternately the transceiver can, when the switch is actuated, generate the interrogation signal, receive the callback signal, and send a release signal to the controller when the callback signal corresponds to the predetermined callback code word. After exchange of the energy source or something else that causes a lose of synchronization the key part is inserted in the lock to actuate the switch to generate the interrogation signal and initiate a time window of a predetermined length. The transmitter then is actuated to generate a main signal including a new current code word. The new main code is received by the receiver during the time window and the stored code word in the receiver is reset to the received new main code word.