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

Transmission 725.0 (except 725.096) in model 253 

Function requirements, general 

• Terminal 15 ON
• Internal combustion engine running

Control of torque converter lockup clutch, general 

The torque converter lockup clutch solenoid (Y3/8y20) is actuated by the fully integrated transmission control unit (Y3/8n4) and influences the torque converter lockup clutch regulating valve. The housing of the torque converter is flowed through by a lubricating oil volume flow. Here, a given lubrication oil pressure is set which acts on the piston of the torque converter lockup clutch and opens the torque converter lockup clutch. The lubrication oil pressure is therefore fed back hydraulically to the torque converter lockup clutch regulating valve and is taken into account when the piston pressure is adjusted. The lubrication oil volume flow ensures optimum cooling of the torque converter.

Control of torque converter lockup clutch 

Control of the torque converter lockup clutch is described in the following points:

• Torque converter lock-up clutch open 
• Torque converter lock-up clutch OPEN SLIP 
• Torque converter lock-up clutch SLIP 
• Torque converter lock-up clutch SLIP OPEN 

The shift strategy for the condition transitions is dependent on the engine load and vehicle speed or vehicle acceleration.

Torque converter lock-up clutch open 

The torque converter lockup clutch solenoid is in the control position. The working pressure acts upon the torque converter lockup clutch regulating valve. Pressure from the compensation line for the converter internal pressure compensation is applied to the control surfaces of the torque converter lockup clutch regulating valve. This compensates the converter internal pressure that has an opening effect on the torque converter lockup clutch in the torque converter and the solenoid pressure characteristic of the torque converter lockup clutch thus becomes independent from the lubricating pressure. The solenoid is not energized, thus no power is transmitted through the torque converter lockup clutch. The torque converter alone transfers the torque.

Torque converter lock-up clutch OPEN SLIP 

The torque converter lockup clutch solenoid is in the control position. Along with the pressure from the compensation line for the converter internal pressure compensation, energization of the solenoids also induces a force to act on the torque converter lockup clutch solenoid. This increases the pressure in the torque converter lockup clutch, whereupon it is filled.

Torque converter lock-up clutch SLIP 

The required slip (specified slip) is filed in the fully integrated transmission control unit. This calculates the control current required and actuates the torque converter lockup clutch solenoid. This influences the pressure on the piston of the torque converter lockup clutch, thus controlling the torque and therefore the slip at the torque converter lockup clutch. 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 post-regulation.

Torque converter lock-up clutch SLIP OPEN 

In this control state the clutch pressure in the torque converter lockup clutch is reduced in stages until it is eliminated.

Torque converter with centrifugal pendulum 

Fuel consumption can be reduced, depending on engine version, and the response to the driver's load change requests improved by means of a regulated minimum slip with low rpm.

Emergency running 

The torque converter lockup clutch is not actuated in limp-home mode. Protection functions are used which constantly monitor the transmission oil temperature, the frictional energy and the functionality in the clutch.