Park Pawl, Detailed Information - GF27.10-P-1103C
Model All with transmission 724.103/114/115/120
Transmission housing with park pawl, shown on transmission 724.1
Overview
This document contains information on:
- General
- Function requirements
- Function
- Park pawl position P
- Park pawl position Not P
- Status detection of park pawl position
- Fault in park pawl lift solenoid, position P actuation
- Emergency engaging and emergency release of park pawl
- Emergency-P
General
The park pawl is used as an safety feature in addition to the parking brake and secures the vehicle to prevent it from rolling away inadvertently.
Function requirements
- Engine management ON (circuit 87M)
- Hydraulic pressure supply active
- Vehicle stationary
- Ignition ON (circuit 15)
Function
The park pawl is actuated by the fully integrated transmission control electrohydraulic controller unit.
Park pawl position P, shown on transmission 724.1
Park pawl position P
In the case of a shift to drive range P, the pressure in the Not P pressure chamber is reduced. At the same time, the control unit for the fully integrated transmission control electrohydraulic controller unit energizes the park pawl lift solenoid. This solenoid lifts the detent lever out of the Not P locking contour against the spring force of the catch spring, thereby preventing mechanical locking of the piston rod.
The spring force pushes the piston (5), which is coupled to the rod, in the direction of the parking lock gear. The parking lock cone is pushed between the pilot bushing and park detent. Due to the rising profile of the parking lock cone, the park detent is raised and pushed against the parking lock gear.
If the tooth of the park detent does not engage in a tooth space when the vehicle is stationary, but rather touches a tooth of the parking lock gear, the parking lock cone is pre-tensioned by the spring and positioned ready for operation.
If the parking lock gear continues to turn, the park detent engages in the next tooth space.
If the park pawl is at position P, the fully integrated transmission control electrohydraulic controller unit ends energization of the park pawl lift solenoid.
When deenergized, the park pawl lift solenoid (6) falls back into its initial position and no longer applies any pressure on the detent lever. The detent lever is pushed into the P locking contour by the spring force of the catch spring, thereby locking the piston rod.
Park pawl position Not P, shown on transmission 724.1
Park pawl position Not P
If the transmission is shifted from drive range P to a different drive range, the park pawl moves to the Not P shift position. This movement takes place through pressure control in the Not P pressure chamber against the spring force of the compression spring (8). The detent lever is lifted as a result of energization of the park pawl lift solenoid against the force of the catch spring, whereby the mechanical lock is opened.
The park pawl is held at position Not P by hydraulic pressure if a sufficiently high working pressure is available. There is no contact between piston (5) and detent lever in the axial direction.
The piston rod only moves against the detent when the spring force of the compression spring (8) exceeds the hydraulic pressure following a pressure drop. The Not P state is held by the mechanical lock.
In the Not P state, the parking lock cone is in front of the park detent and the parking lock gear is able to rotate freely. The park detent spring holds the park detent away from the parking lock gear.
The park pawl lift solenoid (6) is actuated in pulses by the fully integrated transmission control electrohydraulic controller unit in order to minimize the power loss. If the on-board electrical system voltage is interrupted, the park pawl lift solenoid (6) is actuated by the electronic ignition lock control unit.
The time period during which the fully integrated transmission control unit energizes the park pawl lift solenoid, is usually such that the piston rod can reach the new position before energization ends.
Status detection of park pawl position
The park pawl position sensor detects the position of the permanent magnet (7).
The fully integrated transmission control electrohydraulic controller unit determines the switching status of the park pawl using the position of the permanent magnet (7).
Fault in park pawl lift solenoid, position P actuation
If the park pawl lift solenoid cannot be actuated or is defective, the mechanical lock of the detent lever is released by means of the detent lever release pin. The detent lever release pin is actuated hydraulically by pressure being applied to the P pressure chamber.
This causes the detent lever to be lifted out of the Not P locking contour of the piston rod. The park pawl is engaged by the spring force of the compression spring (8).
Emergency engaging and emergency release of park pawl
With the engine switched off, the electric auxiliary oil pump generates oil pressure and opens the park pawl (Not P). The park pawl is engaged mechanically via the compression spring (8).
If the park pawl lift solenoid (6) is defective, the actuator is unlocked by the detent lever release pin. The emergency release takes place only from the Not P position to the P direction. The P position can no longer be exited in the Not P direction. An emergency release no longer exists.
Emergency-P
The park pawl is automatically engaged if communication faults occur with the fully integrated transmission control electrohydraulic controller unit (e.g. in the case of under voltage in the on-board electrical system or open circuit).
If a malfunction occurs, the electronic ignition lock control unit actuates the park pawl lift solenoid in the fully integrated transmission control electrohydraulic controller unit. The voltage for this is provided by the park pawl capacitor via the Emergency P path.
The electronic ignition lock control unit switches the voltage through to the fully integrated transmission control electrohydraulic controller unit.
The park pawl lift solenoid (6) lifts the detent lever of the parking lock actuator out of the P locking contour or out of the Not P locking contour. The piston rod is then no longer engaged. The transmission oil can escape from the Not P pressure chamber.
The compression spring (8) then moves the piston rod in the direction of the park detent. The compression spring (8) supports itself on the housing cover.
Due to the rising profile of the parking lock cone, the park detent is raised and pushed against the parking lock gear.
If the tooth of the park detent does not engage in a tooth space when the vehicle is stationary, but rather touches a tooth of the parking lock gear, the parking lock cone is pre-tensioned by the spring and positioned ready for operation.
If the parking lock gear continues to turn, the park detent engages in the next tooth space.
The park pawl lift solenoid (6) is actuated in pulses to minimize noise in the vehicle. With Emergency-P, actuation takes place via the electronic ignition lock control unit.
If the park pawl lift solenoid malfunctions, the detent lever release pin can be moved hydraulically. With the engine switch off, the electric auxiliary oil pump generates the required oil pressure.