Torque Converter Lockup Clutch Control, Function - GF27.20-D-3002HAG

TRANSMISSION 722.9 in MODEL 906 

Function requirements for torque converter lockup clutch control, general 

• "Circuit 87 ON" (connected circuit 15)
• "Circuit 61 ON" (Engine running)

Control of torque converter lockup clutch, general 

The torque converter lockup is a slip-controlled system. The 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 control unit.

In addition, there are special strategies for calculation of specified slip/pressure for the following operating states:

• Filling of clutch (equivalent to OPEN-SLIP state)
• Load change phases
• Gear change

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 for torque converter lockup clutch control 

The function sequence is described in the following steps:

• Function sequence for "OPEN" 
• Function sequence for "OPEN-SLIP" 
• Function sequence for "SLIP" 
• Function sequence for "SLIP-CLOSED" (for torque converter with centrifugal pendulum) 
• Function sequence for "CLOSED-SLIP" (for torque converter with centrifugal pendulum) 
• Function sequence for "SLIP-OPEN" 

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

Function sequence for "OPEN" 

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.

Function sequence for "OPEN-SLIP" 

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.

Function sequence for "SLIP" 

The required slip (specified slip) is stored in the control unit. This calculates the required control current and actuates the torque converter lockup clutch control solenoid valve which influences the position of the torque converter lockup clutch regulating valve (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 control unit. The clutch pressure in the torque converter lockup clutch can be increased or reduced by the post-regulation.

Function sequence for "SLIP-CLOSED" (for torque converter with centrifugal pendulum) 

A rising control current is applied to the control solenoid valve of the torque converter lockup clutch until the oil pressure applied in the torque converter lockup clutch regulating valve has reached the value specified by the control unit.

The specified value corresponds to the maximum value stored in the characteristics map of the control unit.

In this control state, the maximum clutch pressure is reached and the torque converter lockup clutch is closed completely. The power flow from the crankshaft to the transmission input shaft is virtually without slip.

Function sequence for "CLOSED-SLIP" (for torque converter with centrifugal pendulum) 

If engine load or vehicle speed changes, the control current of the torque converter lockup clutch control solenoid valve is temporarily reduced and the oil pressure applied by the torque converter lockup clutch regulating valve is lowered.

Clutch pressure in the torque converter lockup clutch is reduced until a target slip value suitable for the operating state is set in the torque converter lockup clutch.

This is required to minimize any torsional vibrations which arise temporarily as a result of engine load change and changes in vehicle speed.

Function sequence for "SLIP-OPEN" 

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

For a torque converter with centrifugal pendulum the fuel consumption can be reduced to match the engine by means of regulated zero slip and the response to driver's load change requests improved.

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 control unit.

Fully integrated transmission control unit, component description	Y3/8n4	GF27.60-D-5165HAG
Torque converter lockup clutch control solenoid valve, component description	Y3/8y8	GF27.19-D-5177HAG
Torque converter lockup clutch, component description		GF27.20-D-5102HAG