Principle of Operation
Principle of Operation
In the electrical parking lock, a combination of mechanical lock engagement (as described above) and electric/hydraulic activation are used. The electrical components include magnetic solenoid valves (MV2 and MV3) mounted on the valve body. MV3 is mounted into the parking lock hydraulic cylinder.
Electrical activation of the parking lock is triggered by a push-button on the selector lever or by removing the ignition key. Activation of the solenoid valves is controlled by the Mechatronic Control Module.
When the parking lock is engaged the solenoid valve (MV3) for the parking lock cylinder is deactivated, cancelling the electro-mechanical lock and the piston released. The solenoid valve (MV2) is also deactivated and the chamber of the parking lock cylinder is vented. The piston is pulled to the parking lock position by a preloaded barrel spring behind the operating lever. The linking rod is extended to pivot the paw to engage in the parking lock disc.
When the parking lock is disengaged (below) the MV2 solenoid valve is activated and the main pressure is applied in the chamber of the parking lock cylinder. This pushes the piston, operating lever and linking rod back to release the parking lock. The parking lock pawl is lifted by a spring to disengage from the gear teeth of the parking lock disc gear wheel. The MV3 solenoid valve for the parking lock cylinder is also activated. The piston is additionally held by locking (detent) balls in position "N" when the engine is not running.
The transmission can be shifted from the park position to position "N" only with the engine running (main pressure required). If engine operation is not possible, the parking lock can be released manually by an additional bowden cable.
Examples:
- The parking lock is engaged by pressing the "P" push button on the selector lever when the speed signal is less than 2 km/h.
- The parking lock is automatically engaged when the ignition key is removed and the speed signal is 0.
- Position "N" is automatically engaged when the engine is turned off (ignition switched off) with the key remaining in the lock. The park position will be automatically engaged after approximately 30 minutes. Position "N" can remain engaged for a further 30 minutes if position N is selected again before the 30 minutes have elapsed.
- The parking lock is disengaged only by moving the selector lever in position R, D or N with the engine running and the brake pedal pressed.
Interaction Between Parking Lock and EMF: An electromechanical parking brake (EMF), is fitted in the E65/E66. Based on the operating status of the EMF, it is possible to engage the parking lock when the engine is not running in the event of a fault in the EMF.
Interaction During EMF "AUTO HOLD" Function: The parking brake and parking lock is engaged when the driver leaves the vehicle with the engine running with position D or R engaged, seat is not occupied and the door is opened.
Interaction Between EMF and EGS in the Case of Fault: If the EMF cannot switch from the "hold" to "lock" mode, the parking lock is engaged following a plausibility check in the EGS control unit The plausibility check determines whether position N is engaged, the speed is 0 km/h and the engine and ignition are off.