Parking Lock Control, Function - GF27.10-P-5000ANG
Transmission 725.0 (except 725.017) in model 205
Phantom view of automatic transmission seen from left rear (shown on vehicles with rear wheel drive and "P" gear range engaged)
Sectional view of electrohydraulic park pawl actuation
Function requirements, general
- Terminal 15 ON
- Engine running or electric auxiliary oil pump (M42) ON (only 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 automatically depending on various factors (e.g. opening of driver door with operational drivetrain).
The parking lock control is described in the following conditions:
- Actuate, hold and lock shift position "Not P"
- Actuate and lock shift position "P"
- Actuate shift position "P" in case of park pawl lift solenoid malfunction
Electrohydraulic park pawl actuation, shown with shift position "Emergency P" locked
Actuate, hold and lock shift position "Not P"
When shifting from drive range "P" to "R", "N" or "D1", the park pawl is pushed by pressure being applied in the pressure chamber "Emergency P" (11p), against the spring force of the compression spring (11l) towards the "Emergency P" shift position. This takes place after the notch lever (11d) has been raised against the force of the catch spring (11a) and the mechanical lock has been opened as a result of energization of the park pawl lift solenoid. If a sufficiently high working pressure is present, the park pawl is solely maintained in the position "Not P" by the hydraulic pressure. There is no contact between the piston rod (11f) and notch lever (11d) in an axial direction. The piston rod (11f) only moves against the detent through the force of the compression spring (11l) if the pressure is reduced (spring force of compression spring (11l) > hydraulic pressure) or there is a complete drop in pressure. The "Emergency P" state is then held by the "mechanical lock". In shift position "Not P", the park pawl cone (11j) is in front of the park detent (9a) and the park pawl gear (9) can turn freely. The park detent spring (9d) holds the park detent (9a) away from the park pawl gear (9).
Park pawl lift solenoid (Y3/8l1)
The park pawl lift solenoid (Y3/8l1) is actuated in a pulsed manner by the fully integrated transmission control unit (Y3/8n4) in order to minimize the power loss. Where the on-board electrical system voltage is interrupted, the park pawl lift solenoid (Y3/8l1) is actuated by the electronic ignition lock control unit (N73). The time period in which the fully integrated transmission control unit (Y3/8n4) energizes the park pawl lift solenoid (Y3/8l1) is usually calculated so that the piston rod (11f) reaches the new position before the energization is canceled.
Electrohydraulic park pawl actuation, shown with shift position "P" locked
Actuate and lock shift position "P"
In the case of a shift to "P" drive range, the pressure in the pressure chamber "Not P" (11p) is reduced. At the same time, the fully integrated transmission control unit (Y3/8n4) energizes the park pawl lift solenoid (Y3/8l1). The solenoid lifts the notch lever (11d) against the spring force of the catch spring (11a) out of the locking contour "Not P" (11e) and thus prevents "mechanical locking" of the piston rod (11f). The spring force of the compression spring (11l) pushes the piston rod (11f), that is coupled to the bar (11k), towards the parking lock gear (9). The park pawl cone (11j) is shifted between the pilot bushing (9b) and the park detent (9a). The increasing profile of the park pawl cone (11j) raises the park detent (9a) and presses it against the park pawl gear (9). If - for a stationary vehicle - the tooth of the park detent (9a) does not reach a tooth space, rather is on a tooth of the parking lock gear (9), the park pawl cone (11j) is preloaded by the spring of the rod (11k) and is in the ready-to-engage position. If the parking lock gear (9) continues to turn, the park detent (9a) engages in the next tooth space. If the park pawl is in the position "P", the fully integrated transmission control unit (Y3/8n4) increases the energization of the park pawl lift solenoid (Y3/8l1). In the de-energized status, the park pawl lift solenoid (Y3/8l1) returns to its initial position and no longer applies any pressure to the detent lever (11d). The lever is pushed by the spring force of the catch spring (11a) into the locking contour "P" (11c) and thus locks the piston rod (11f).
Actuate shift position "P" in case of park pawl lift solenoid malfunction
In the case of a non-actuatable or defective park pawl lift solenoid (Y3/8l1), the mechanical lock of the detent lever (11d) is released by the detent lever release pin (11g). The notch lever release pin (11g) is actuated hydraulically by pressure being applied to pressure chamber "P" (11h). This causes the notch lever (11d) to be lifted out of the locking contour "Not P" (11e) of the piston rod (11f) and the park pawl is engaged by the spring force of the compression spring (11l).
Emergency engaging and emergency release of park pawl: When the engine is switched off, the oil pressure generated by the electric auxiliary oil pump opens the "Emergency P" park pawl. The park pawl is engaged mechanically through the compression spring (11l).
If the park pawl lift solenoid (Y3/8l1) is defective, the actuator is unlocked by the detent lever release pin (11g). However, only from the "Emergency P" position towards "P". The position "P" can no longer be exited in the direction "Not P". An emergency release no longer exists.
| Overview of system components for automatic transmission (AT) | GF27.10-P-9992ANG |