If a valid key is inserted in the ignition lock, after successful identification of the key, the EWS signals "valid key in lock" on the K-bus. Consequently the electric steering lock (ELV) begins the unlocking procedure. During the normal procedure, the EWS is activated by the ZV unlocking and the resulting K-bus telegram and remains in this status for 60 s.
If a key is inserted in the ignition lock and turned, the key turning is detected from 10° to 20° angle of rotation by the ELV with the aid of a Hall sensor. A lock facility prevents the key being turned further to terminal R. Consequently the ELV sends the "request EWS status" telegram on the K-bus and thus wakes the EWS. The further procedure is the same as when the EWS is active.
If the K-bus is defective, the unlocking procedure is initiated solely based on detecting rotation in the ignition lock. The turn inhibit is enabled after a delay, noticeable for the driver by snagging while turning the ignition key. A defective K-bus is detected when no response is received within 700 ms to the "request EWS status/enable" request telegram.
The precondition for starting the unlocking procedure is a battery voltage >9 V.
The motor of the lock plate is activated in unlock direction. Leaving the locked position is detected by the Hall sensor "end position detection locked". The locked position must be vacated within 300 ms. If this time is exceeded this indicates that there must be a fault in the motor activation system or in the motor itself as a freewheel facility is integrated in the lock plate mechanism which allows operation up to this position even when the steering is held under tension.
The "end position detection unlocked" Hall sensor must respond within 1000 ms after activating the lock plate. If this time is exceeded the locked position is re-assumed and a new unlock attempt is started. A maximum of 3 unlock attempts are carried out. Further attempts are not started before a renewed unlock request is initiated by the driver, i.e. a corresponding change in the signal edge for the rotation detection facility or the K-bus telegram "valid key in lock".
The motor is braked on reaching the "unlocked" end position. The armature of the securing solenoid is spring-loaded and falls into a recess in the lock plate. Acting as a mechanical redundant locking facilities it holds the plate in the "unlocked" position. The arresting function of the securing solenoid is signalled by the "securing solenoid Hall sensor". After correctly unlocking and securing the lock plate the interrupt relay is activated thus interrupting the connection to the motor of the lock plate.
Once the unlocking procedure has been concluded the following actions are initiated:
The following processor-independent functions ensure that the vehicle can only be started with the ELV correctly unlocked and secured and that it cannot lock while driving.
The turn inhibit remains activated for 16 minutes after turning back the ignition key to position "0" thus making it possible to immediately start the vehicle. If the key is removed from the ignition lock the EWS signals "no valid key in lock" via the K-bus. The ELV checks whether terminal 15, terminal R and the turn detection facility are inactive and then begins the locking procedure.
The system is not locked if the K-bus is defective. This situation is indicated to the driver by the delayed activation of the turn inhibit and the key snagging as a result during the start procedure.
The precondition for starting the locking procedure is a battery voltage >10 V and the "vehicle stationary" signal. "Vehicle stationary" means: The frequency of the signal from the wheel speed sensor ((DFA_HL) is lower than 18 Hz.
Initially activation of the interrupt relay is cancelled thus making the connection to the motor of the lock plate.
In the next step, the securing solenoid that held the lock plate secure while driving, is energized. Leaving the secured position is detected by the Hall sensor of the securing solenoid.
The motor of the lock plate is then activated in "lock" direction. Leaving the unlocked position is detected by the Hall sensor "end position detection unlocked". The "unlocked" position must be vacated within 300 ms.
The "end position detection locked" Hall sensor must respond within 700 ms after activating the lock plate. The motor is braked on reaching the "locked" end position. Operation of the securing solenoid is cancelled. The spring-loaded armature now rests on the lock plate.
If a fault occurs two further lock attempts are made. No further attempts are made before a renewed starting procedure is initiated. It is assumed that the ELV is in a secured unlock status for the purpose of enabling a renewed starting procedure. In this case the turn inhibit is actuated with a 2 s delay. The fault status of the ELV is indicated to the driver by the key snagging during the start attempt.
Start is not enabled if the ELV is in an intermediate state and cannot be brought into the secured unlock status.
The basic precondition for the "turn inhibit activated" status is always that the ELV is in the secured unlock status. The turn inhibit is cancelled when there is a valid key inserted in the ignition lock. The turn inhibit is enabled when key rotation is detected even if the K-bus is defective. (Ignition key snags)
In order to reduce the current intake of the ELV, the system assumes sleep mode when certain conditions are fulfilled.
Conditions for sleep mode:
Wake-up criteria:
A repeat inhibit function is realized in order to prevent overloading of the lock plate motor and of the securing solenoid. An internal counter is incremented by one for every lock procedure and decremented by one after a defined time window.
No further lock requests are accepted if the counter exceeds a defined limit.
The ELV assumes “crash mode” if the ELV control unit receives the “airbag crash” message from the airbag control unit. Locking procedures are no longer carried out in this mode.
If the EWS transponder fails while driving, after turning the key to position 0, it is possible to start the vehicle for a period of time as coded in the EWS control unit. This function is realized by the following procedure: