Emergency-P Function - GF27.10-P-3029ANG

Transmission 725.0 (except 725.017) in model 205 

Sectional view of electrohydraulic park pawl actuation 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Vehicle stationary
• Terminal 15 ON

The electronic ignition lock control unit (N73) transmits the status of circuit 15 via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the fully integrated transmission control unit (Y3/8n4).

Emergency-P 

In the event of any communication faults with the fully integrated transmission control unit (Y3/8n4) (e.g. undervoltage in the on-board electrical system or open circuit), the park pawl is automatically engaged.

If a fault occurs, the electronic ignition lock control unit (N73) actuates the park pawl lift solenoid (Y3/8l1) in the fully integrated transmission control controller unit (Y3/8). The voltage for this is provided by the park pawl capacitor (C8) via the Emergency-P path. The electronic ignition lock control unit (N73) connects the voltage through to the fully integrated transmission control unit (Y3/8n4). The park pawl lift solenoid (Y3/8l1) lifts the notch lever (11d) of the parking lock actuator out of the "P" locking contour (11c) or out of the "Not P" locking contour (11e). The piston rod (11f) is then no longer engaged. The transmission oil can leak out of the pressure chamber ("Not P"). If necessary, the lubrication pressure solenoid (Y3/8y12) is energized through the park pawl lift solenoids (Y3/8l1) for this purpose. The compression spring (11l) then moves the piston rod (11f) in the direction of the park detent. When doing so, the compression spring (11l) supports itself on the piston housing (11). As a result of the increasing profile of the park pawl cone (11j), the park detent is raised and pressed against the park pawl gear. If the tooth of the park detent does not end up in a tooth space when the vehicle is stationary, but on a tooth of the park pawl gear, the park pawl cone (11j) is pre-compressed by the spring of the rod (11k) and is in the ready position. If the parking lock gear continues to turn, the park detent engages in the next tooth space.

The park pawl lift solenoid (Y3/8l1) is actuated in a pulsed manner to minimize noise in the vehicle. With Emergency-P, actuation takes place via the electronic ignition lock control unit (N73).

If the park pawl lift solenoid (Y3/8l1) malfunctions, the detent lever release pin (11g) can be moved hydraulically. When the engine is switched off, the electric auxiliary oil pump (M42) generates the required oil pressure.