Motor-vehicle central lock system with transponder in key

A method of operating a motor-vehicle lock system having:

• a remote operator separate from the motor vehicle and having
• a key part having a predetermined bitting,
• an energy source,
• transmitter means powered by the energy source and actuatable to transmit a main signal containing a current main code word, and
• transponder means substantially independent of the transmitter means and of the energy source for receiving an interrogation signal and thereupon generating a callback signal containing a callback code word;
• a lock provided with a switch and actuatable mechanically by the key part with the predetermined bitting to operate the switch;
• a central controller in the vehicle connected to elements of the vehicle for actuating same;
• receiver means in the motor vehicle connected to the controller for
• receiving the main signal including the main code word,
• extracting the current main code word from the transmitted main signal,
• comparing the extracted current main code word with a predetermined stored main code word, and
• sending a release signal to the controller when the extracted current main code word corresponds to the predetermined stored main code word to actuate the elements;
• and
• transceiver means in the motor vehicle and connected to the controller for, when the switch is actuated,
• generating the interrogation signal,
• receiving the callback signal containing the callback code word,
• extracting the callback code word from the callback signal,
• comparing the extracted callback code word with a predetermined callback code word, and
• sending a release signal to the controller when the extracted callback code word corresponds to the predetermined callback code word to actuate the elements and setting in the transponder a new callback code word based on the main code word;
• the method comprising the steps after exchange of the energy source of:
• inserting the key part in the lock and actuating the switch to generate the interrogation signal in the transceiver;
• generating the callback signal in the operator, receiving the callback signal in the receiver means, extracting the callback code word, comparing the extracted callback code word, and, on correspondence with the extracted callback code word with the predetermined callback code word, initiating a time window of a predetermined length;
• generating with the transmitter means during the time window a main signal including a new current code word;
• and
• receiving with the receiver means during the time window the new main code word and resetting the stored code word in the receiver to the received new main code word.