Anti-theft vehicle security system having an engine control device and an anti-theft security device which confirm successful communication

An antitheft device for a vehicle comprising:

• anti-theft means for determining allowance to start an engine based on an external signal, and for transmitting and receiving test data for establishing a data circuit;
• engine control means for transmitting and receiving test data for establishing a data circuit, performing control to allow or prohibit start of said engine based on the determination result by said antitheft means, and controlling the engine by calculating a degree of control based on various operating conditions if the engine can be started;
• transmission data detection means for detecting whether transmission data is properly transmitted before determination of allowance to start the engine;
• data return means for returning data which causes one of said engine control means and antitheft means to recognize that data is received by another of said antitheft means and engine control means as the result of data transmission;
• data circuit establishment detection means for detecting whether or not the returned data is correct and for determining establishment of a data circuit between said engine control means and antitheft means if said returned data is correct;
• data transmission repeat means for repeating data transmission which requests again the returned data if said returned data is not correct;
• and
• normal data communication means for starting communication of engine start allowance and inhibit data between said engine control means and antitheft means when said data circuit is detected to be established by said data circuit establishment detection means.

An anti-theft vehicle security system comprising:

• a first control means for determining whether starting of an engine should be allowed based on an external signal and for providing a determination result;
• a second control means for performing start permission/start prohibition control of said engine based on the determination result of the first control means;
• and
• communication means for managing exchange of control data between the first and second control means and for setting a protocol where, when one of said first and second control means is a data transmitting side and the other is a data receiving side which is receiving data, said data receiving side sends a result indicating recognition of the data transmitted from said data transmitting side back to said data transmitting side as reply data
• wherein the communication means comprises communication conflict detection means for defining a protocol where the data transmitting side halts transmitting data and performs data receiving when the data transmitting side recognizes transmitted data from another end of the communication line.