(Torque Converter Lockup Clutch Control, Basic Function - GF27.20-P-1001A)

Model all with transmission 725 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 
  • Function sequence for "OPFN" 
  • Function sequence for "OPFN-fil IP" 
  • Function sequence for "fil IP" 
  • Function sequence for "fil IP-OPFN" 

General 

The torque converter lockup clutch is a multiplate clutch with automatic transmissions, which is located within the torque converter housing at the back of the turbine wheel and connects it to the impeller, if necessary. The torque converter lockup clutch ensures a rigid axle through drive if the torque converter is not required. The torque converter lockup clutch is therefore a lockup clutch that connects the transmission input shaft directly to the output shaft.

Function requirements 

• Ignition ON (circuit 15)
• Engine in operation or electric auxiliary oil pump ON

Function 

The torque converter lockup clutch solenoid is actuated by the fully integrated transmission control unit and influences the torque converter lockup clutch regulating valve. The housing of the torque converter is flowed through by a lubricating oil volume flow. At the same time, a lubrication oil pressure builds up 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 adjusting the piston pressure. The lubrication oil volume flow ensures optimum cooling of the torque converter.

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

The function sequence is described in the following chapters.

Function sequence for "OPFN" 

The WUK solenoid is located in the basic position. Working pressure is applied to the torque converter lockup clutch (WUK) regulating valve.

Pressure from the compensation line for the converter internal pressure compensation is applied to the control surfaces of the WUK regulating valve. This compensates the converter internal pressure that has an opening effect on the WUK in the torque converter and the solenoid pressure characteristic of the WUK thus becomes independent from the lubricating pressure. The solenoid is not energized which in turn means that the torque converter lockup clutch does not transfer any power. The torque converter alone transfers the torque.

Function sequence for "OPEN-fil IP" 

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

Function sequence for "SLIP" 

The required slip (specified slip) is filed in the fully integrated transmission control unit. This calculates the required control current and actuates the WUK solenoid. The pressure on the torque converter lockup clutch piston is influenced by this, whereby the torque and slip on the torque converter lockup clutch are then regulated. 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.

Function sequence for "SLIP-OPFN" 

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 time to the driver's load change requests can be improved by means of a regulated minimum slip with low rotational speeds.

The WUK 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.