(Park Pawl, Detailed Information - GF27.10-P-1103A)
Model all with transmission 724.033/044/045
Sectional view of transmission housing with park pawl
Overview
This document contains information on:
- General
- Function requirements
- Function
General
The park pawl acts as a safety feature in addition to the parking brake. The park pawl secures the vehicle to prevent it from rolling away inadvertently. The park pawl is actuated by the fully integrated transmission control electrohydraulic controller unit.
Function requirements
- Engine management ON (circuit 87 M)
- Hydraulic pressure supply active
Function
Components
The fully integrated transmission control electrohydraulic controller unit contains the control elements for the following components:
- Park pawl switchover valve
- Shift valve 1/2
- Piston for mechanical locking of the end position
- Lift solenoid to release the mechanical lock
The mechanical part of the park pawl comprises the following components:
- Tapered roller spring
- Tapered roller
- Park detent
- Coil spring
- Park pawl gear
The piston is locked mechanically by the spring-loaded locking pin. The spring-loaded locking pin is integrated in the pilot bushing. When the locking pin is lifted by the park pawl lift solenoid, the piston is released and can be moved. When the park pawl lift solenoid is no longer energized, the spring-loaded locking pin holds the piston in place.
Park pawl position P
The oil pump (primary pump) or the electric auxiliary oil pump generates the hydraulic pressure supply to the pressure chamber (position P) and actuates the park pawl lift solenoid hydraulically. The hydraulic actuation of the park pawl lift solenoid unlocks the mechanical locking of the piston.
The fully integrated transmission control electrohydraulic controller unit actuates the park pawl switchover valve. The park pawl switchover valve opens the hydraulic flow via the control edge of the shift valve and the downstream position P shift valve to the pressure chamber (position P) of the park pawl.
When the park pawl lift solenoid is no longer actuated, the piston of the park pawl is moved in the direction of park pawl position P and locked in the end position.
The locking of the park pawl can be overridden in the event of a malfunction in the direction of park pawl position P. The park pawl may be overridden e.g. due to a defect in the park pawl lift solenoid. When the park pawl is in the park pawl position Not P, the locking of the park pawl cannot be overridden.
Park pawl position Not P
When the park pawl switchover valve is not energized, the pressure in the pressure chamber (position P) decreases. At the same time, pressure builds up in the pressure chamber (position Not P). By the preceding actuation of the park pawl lift solenoid, the locking of the piston is released. The change from park pawl position P to Not P occurs.
Status detection of park pawl position
The park pawl position sensor detects the position of the permanent magnet. The fully integrated transmission control electrohydraulic controller unit uses the position of the permanent magnet to determine the switching status of the park pawl.
Park pawl lock
When the piston is moved in the direction of park pawl position P, the tapered roller spring pushes the park detent upwards. The park detent is pushed against the spring force of the coil spring and onto the park pawl gear.
If the park detent fails to engage in a tooth space when the vehicle is stationary, the tapered roller is preloaded by the tapered roller spring. Due to the preload of the tapered roller, the park detent is in the ready position. When the park pawl gear turns further, the park detent engages in the next tooth gap.