GF27.20-P-3002AHC Torque Converter Lockup Clutch Control, Function

GF27.20-P-3002AHC Torque converter lockup clutch control, function
- Transmission 722.902/904/906/908


Function requirements
^ Circuit 87 ON
^ Circuit 61 ON

General
The torque converter lockup is a slip-controlled system. The fully integrated transmission control unit (Y3/8n4) compares the actual slip with the specified slip. The actual slip is calculated from the difference between engine speed and transmission input speed. The specified slip is a function of transmission input speed and engine load. Depending on the determined specified/actual deviation as well as various influencing quantities (e.g. engine torque) a pressure or current requirement for the corresponding control solenoid valve is produced by the fully integrated transmission control unit.

In addition, there are special strategies for calculation of specified slip/pressure for the following operating conditions:
- Filling of clutch (corresponds to "OPEN-SLIP" state), load change phases, gear changes.

The clutch pressure in the torque converter lockup clutch is drawn from the working pressure by means of the torque converter lockup clutch regulating valve. The position of the regulating valve is influenced by the torque converter lockup clutch control solenoid valve (Y3/8y8). The clutch pressure in the torque converter lockup clutch depends on the regulating valve position and thus on the geometry of the torque converter lockup clutch regulating valve.

Function sequence
The function sequence is described in the following steps:
^ "OPEN" function sequence
^ "OPEN-SLIP" function sequence
^ "SLIP" function sequence
^ "SLIP-OPEN" function sequence

The shifting strategy for the status transitions is based on the engine load and vehicle speed or vehicle acceleration.

"OPEN" function sequence
The regulating valve of the torque converter lockup clutch is located in the basic position. The working pressure acts on the converter regulating valve via a connecting line between the torque converter lockup clutch regulating valve and the converter regulating valve. Lubrication pressure is applied to the converter as a result. The torque converter lockup clutch is in the unpressurized condition.

"OPEN-SLIP" function sequence
The torque converter lockup clutch regulating valve is no longer in the basic position and as a result interrupts the connection between the torque converter lockup clutch regulating valve and the converter regulating valve. The torque converter lockup clutch is filled.

"SLIP" function sequence
The required slip (specified slip) is stored in the fully integrated transmission control unit. This calculates the required control current and actuates the torque converter lockup clutch control solenoid valve which influences the torque converter lockup clutch (precontrol). The clutch pressure in the torque converter lockup clutch depends on the regulating valve position and thus on the regulating valve geometry.

The actual slip is determined by the comparison of engine speed with turbine speed. If necessary, a post-regulation is introduced by the fully integrated transmission control unit. The clutch pressure in the torque converter lockup clutch can be increased or reduced by the after control.

"SLIP-OPEN" function sequence
In this control state the clutch pressure in the torque converter lockup clutch is reduced in stages until it is eliminated.

The torque converter lockup clutch is not actuated in limp-home mode. Protection and adaptation functions are deployed to continuously monitor the transmission oil temperature and the frictional energy entering the clutch. Aging effects in the hydraulic components and mechanical components are compensated for by the fully integrated transmission control unit.