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

GF27.20-P-3002AHW Torque Converter Lockup Clutch Control, Function
TRANSMISSION 722.9 (except 722.930) in MODEL 204.0 as of model year 2009 /YoM 08
TRANSMISSION 722.9 (except 722.930) in MODEL 204.2 as of model year 2009 /YoM 08
TRANSMISSION 722.9 (except 722.930) in MODEL 204.3
TRANSMISSION 722.9 in MODEL 204.9

Function requirements for torque converter lockup clutch control, general
^ Circuit 87 ON
^ Circuit 61 (engine running)

Control of torque converter lockup clutch, 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 states:

Clutch filling (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.

Implementation dates and validities for torque converter with integrated centrifugal pendulum
- Model 204.0/2 as of model year 2012 /YoM 11 model refinement package with engine 276.9, 651.9
- Model 204.025/225 as of 1.6.2011 with engine 642.8
- Model 204.3 with engine 276.9, 651.9
- Model 204.9 as of 1.6.2011 with engine 651.9
- Model 204.988 as of 1.1.2011 with engine 276.9

Function sequence for torque converter lockup clutch control
The function sequence is subdivided into the following steps:
^ OPEN
^ OPEN-SLIP
^ SLIP
^ SLIP CLOSED (for torque converter with integrated centrifugal pendulum)
^ CLOSED SLIP (for torque converter with integrated centrifugal pendulum)
^ SLIP-OPEN

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

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.

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.

SLIP
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 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 fully integrated transmission control unit. The clutch pressure in the torque converter lockup clutch can be increased or reduced by the post-regulation.

SLIP CLOSED (for torque converter with integrated 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 fully integrated transmission control unit.

The specified value corresponds to the maximum value stored in the characteristics map of the fully integrated transmission 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.

CLOSED SLIP (for torque converter with integrated 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.

The coupling pressure in the torque converter lockup clutch is therefore reduced until the torque converter lockup clutch reaches an adapted specified slip value that matches the operating condition.

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

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

For torque converters with integrated centrifugal pendulum

Depending on the motorization, a regulated zero slip can help to reduce fuel consumption, and improve the response time to changes in load requests by the driver.

Limp-home mode
The fully integrated transmission control unit, with integrated protection and adaptation functions, constantly determines the transmission oil temperature and the friction energy at the disks of the torque converter lockup clutch and switches into limp-home mode for overload or implausible signals.

The torque converter lockup clutch is not actuated in limp-home mode. Aging effects in the hydraulic components and mechanical components are compensated for by the fully integrated transmission control unit.