Parking Lock Control, Function - GF27.10-P-5000RFH
Transmission 724.2 in model 205, 253
Function requirements, general
- Terminal 15 ON
- Combustion engine running or electric auxiliary oil pump (M42) ON (with engine OFF)
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).
Park pawl control, general
The park pawl is used in addition to the parking brake for preventing the vehicle from unintentionally rolling away. The park pawl essentially consists of the parking lock mechanism and the electrohydraulic components located on the fully integrated transmission control controller unit (Y3/8). There is no mechanical connection between the assembly parts of the park pawl and the DIRECT SELECT lever (S16/13) (Park-by-Wire). The park pawl is engaged and disengaged electro-hydraulically, either by operating the DIRECT SELECT lever or depending on various factors such as, e.g, opening the driver door while the drivetrain is operational.
The function sequence is described in the following sections:
- Shift position "Emergency P" locked
- Shift position "Emergency P" unlocked
- Shift position "P" locked
Park pawl actuation for shift position "Emergency P" locked
Shift position "Emergency P" locked
In the "Not P" shift position, the piston rod (10) is locked by the catch detent (9) against the spring force of the compression spring (6). The park pawl lift solenoid is de-energized and the catch detent (9) is held by the catch spring (8) in the "Not P" locking contour (2) of the piston rod (10). In this shift position, the park pawl cone (12) is in front of the park detent (14) and the park pawl gear can turn freely.
Park pawl actuation for shift position "P" unlocked
Shift position "Emergency P" unlocked
The fully integrated transmission control unit actuates the park pawl lift solenoid directly. This lifts the catch detent (9) against the spring force of the catch spring (8) from the "Not P" (2) locking contour and releases the lock of the piston rod (10). The park pawl switchover valve (Y3/8y11) is de-energized. Therefore, the transmission fluid escapes from the pressure chamber ("Not P"). The compression spring (6) now shifts the piston rod (10) in the direction of the park detent (14). The compression spring (6) supports itself on the piston housing here. The increasing profile of the park pawl cone (12) raises the park detent (14) and presses it against the park pawl gear. If the tooth of the park detent (14) on a stationary vehicle is not in a tooth space, but is on a tooth of the park pawl gear, then the park pawl cone (12) is pre-compressed by the spring of the rod (7) and is in the standby position. If the parking lock gear continues to turn, the park detent (14) engages in the next tooth space.
The park pawl lift solenoid is actuated in pulses to minimize noise in the vehicle. Actuation is carried out by the fully integrated transmission control unit or, with Emergency-P, the electronic ignition lock control unit.
Shift position "P" locked
The piston rod (10) is in the "P" shift position. The park detent (14) blocks the park pawl gear. The lift park pawl solenoid is no longer actuated. The catch spring (8) presses the catch detent (9) into locking contour "P" (1) and therefore locks the piston rod (10).
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