Electronic remote control means, especially for centrally controlled locking systems in motor vehicles

Claim 1

Electronic remote control apparatus for use in centrally controlled locking systems in motor vehicles comprising: transmitter means acting as a key for transmitting, when actuated, a transmit code word in the form of an encoded multibit sequence, said transmit code word being developed as a function of a preassigned base code and changed in accordance with a predetermined sequence each time said transmitter means is actuated, said transmitter means including means for storing said preassigned base code; means for actuating said transmitter means and means in said transmitter means responsive to each actuation of said transmitter means to change a previously transmitted code word in accordance with said predetermined sequence and transmit a next transmit code word in said predetermined sequence; receiver means acting as a lock for receiving transmit code words in the form of encoded multibit sequences, said receiver means including means for storing a preassigned base code selected for a particular transmitter means having a corresponding preassigned base code; means in said receiver means for developing a receive code word as a function of said stored preassigned base code and changing said receive code word in accordance with said predetermined sequence each time a valid transmit code word is received; means in said receiver means for storing each transmit code word received by said receiver means and comparing each stored transmit code word received with a receive code word developed by said receiver means; means in said receiver means for producing an actuation signal when said stored transmit code word corresponds to said receive code word developed by said receiver means and an out of sequence signal when no correspondence occurs; means in said receiver means responsive to said out of sequence signal for producing N changed receive code words wherein each of said N changed receive code words is incremented by one step in said predetermined sequence from a preceding one of said N changed receive code words, said means for storing and comparing additionally acting to compare each of said N changed receive code wordss with said stored transmit code word, said means for producing an actuation signal producing said actuation signal when any one of said N changed receive code words corresponds to said stored transmit code word and a high level security signal when none of said N changed receive code words corresponds to said stored transmit code word; and means in said receiver means responsive to said high level security signal for producing M changed receive code words wherein each of said M changed receive code words is incremented by one step in said predetermined sequence from a preceding one of said M changed receive code words, said means for storing and comparing further acting to compare each of said M changed receive code words with said stored transmit code word in a first comparison and comparing a next one of said M changed receive code words with a next received transmit code word in a second comparison wherever said first comparison is indicative of identity between code words compared, said means for producing an actuation signal producing said actuation signal when a high level security signal is present only when said first and second comparisons both indicate identity between code words compared.