The present invention relates to keyless systems for gaining entry and starting motor vehicles.
Automobiles traditionally were vulnerable to theft by a criminal forcibly removing the ignition lock cylinder thereby being able to start the vehicle without a key. With the advent of microprocessor based engine control systems came the ability to provide more sophisticated ignition control. Today many ignition keys have different types of electronic devices embedded in them which contain a special code for the key. When the key is inserted into the ignition lock, the vehicle reads the code from the key and the on-board computer system only responds to operation of the ignition switch by a properly encoded key. Thus the motor vehicle can not be started without that key, even if the ignition switch is turned somehow.
The advent of more sophisticated electronics in motor vehicle also has enabled remote keyless vehicle entry (RKE) systems to be provided to the driver. These commonly take the form of a fob which is attached to the driver's key ring. The fob houses a radio transmitter which sends a digital numerical value via a radio frequency (RF) signal to the vehicle when the driver pressing the appropriate switch on the fob. The digital numerical value prevents spurious radio frequencies from activating the motor vehicle circuitry, as well as making it difficult for unauthorized persons to gain access to the motor vehicle. The RF signal also encodes whether the user wishes the doors to be locked, unlocked or the trunk to be unlatched. A receiver mounted in the motor vehicle detects the transmission from the fob and decodes the RF signal to determine whether it is valid for that vehicle and which of the various functions is to be performed. The receiver then activates the appropriate components within the motor vehicle to perform that function.
Although the digital numerical value make it very difficult for unauthorized persons to gain access to the motor vehicle, concern has been expressed that some one with a radio receiver and a digital signal analyzer could eavesdrop on the radio transmissions and learn the security numbers. Thus a thief could "stake out" a valuable vehicle to await the return of the driver and learn the security numbers. Those security numbers then could be utilized to steal that vehicle at a later point in time.
To improve the security of remote keyless entry systems and deter eavesdropping, a "rolling code" security number is transmitted between the fob and the motor vehicle. In this technique both the motor vehicle and the fob were encoded with the identical initial security number during manufacture. Thereafter, each time a button on the fob was pressed, the previous security number is incremented by a value which is derived using a predefined algorithm. The resultant new security number then is transmitted to the motor vehicle and stored in the fob in place of the previous security number.
Upon receipt of a security number from the fob, circuitry in the motor vehicle retrieves the previously valid security number which it had stored. The motor vehicle circuitry then employs the same algorithm to increment the retrieved security number to produce its own new security number. In theory, both the fob and the motor vehicle should be synchronized so that their respective execution of the algorithm will produce identical new security numbers. Thus, a match between the security number received from the fob and new security number derived in the motor vehicle indicates a signal has been received from an authorized fob. This rolling code technique provides a greatly enhanced level of security and operates extremely well as long the security numbers in both the fob and the motor vehicle remain synchronized.
However, if a button on the fob is accidentally pressed when the motor vehicle is beyond the fob's transmission range, the rolling security number in the fob will be incremented without a corresponding incrementation of the security number in the motor vehicle. As a consequences, matches between the two codes will no longer occur and the authorized fob will not be recognized by the motor vehicle. One solution to this non-synchronization problem is for the motor vehicle to generate multiple subsequent security numbers using the rolling code algorithm and accept a fob signal as valid if any one of those subsequent security numbers matches the one received from the fob. However, this technique greatly reduces the number of possible security numbers since during each validation test the motor vehicle will accept multiple security numbers as being valid. Furthermore, the rolling code technique precludes the use of multiple authorized fobs for the same motor vehicle.
It is desirable to provide the remote keyless entry system with the ability to start the motor vehicle by adding another button to the fob. However, this latter function requires a higher level of security than that which is presently used to guard against unauthorized opening of the doors and trunk of the vehicle. In addition, the security provided for the ignition feature must also prevent an unauthorized person with the appropriate electronic equipment from being able to eavesdrop on the radio transmissions and learn the security numbers utilized to operate the vehicle.
Thus, it is desirable to provide a key fob with more activation features and a higher level of security.