Wet clutch, function - GF27.51-P-1002AHX

TRANSMISSION 722.930 up to 31.5.11, 722.931 as of 1.6.11 in MODEL 212.0/2 

Function requirements for wet clutch, general 

• Status "Circuit 87 ON"
• Circuit 61 ON

Wet clutch, general 

The pressure from the wet clutch control solenoid valve (Y3/8y9) is boosted by the wet clutch regulating valve.

A lubricating oil volume flows through the housing of the wet clutch. At the same time, a lubrication oil pressure builds up which acts on the clutch piston and opens the clutch. The lubrication oil pressure is fed back hydraulically to the regulating valve and is taken into account when adjusting the piston pressure. The lubrication oil volume flow and a special geometry of the clutch linings ensure optimum cooling of the wet clutch.

A specified valve pressure is calculated from the specified clutch torque by means of an inverted distance model of the wet clutch. The pressure regulator adjusts the valve pressure, the regulator output quantity being a specified valve current. A low-mounted flow regulator sets the required valve flow at the wet clutch control solenoid valve.

Wet clutch function sequence 

The function sequence is subdivided into the following steps:

• "Engagement process", function sequence 
• "Creeping", function sequence 
• "Start-off", function sequence 
• "Slip control", function sequence 
• "Clutch change", function sequence 
• "Stopping", function sequence 

The shift strategy of condition transitions depends on engine load and vehicle speed or vehicle acceleration. The transitions between the individual conditions is controlled by a function coordinator.

"Engagement process", function sequence 

The engagement process controls the filling of the clutch piston and the application of the clutch.

"Creeping", function sequence 

In this condition, the specified clutch torque is calculated such that the vehicle starts to roll automatically when the driver releases the service brake.

"Start-off", function sequence 

The wet clutch enables a strategy-capable startup to be executed. If the "Race start" is activated, the wheel slip is regulated by the wet clutch during the startup process.

A suitable startup strategy is selected depending on engine load and vehicle speed or vehicle acceleration.

"Slip control", function sequence 

If the startup process is complete, then slip control of the wet clutch is activated. The specified clutch torque is calculated so that a microslip is adjusted at the wet clutch. This suppresses driveline vibrations.

"Clutch change", function sequence 

During a clutch change the specified clutch torque at the wet clutch is calculated so that with downshifts a slip expansion occurs, but with upshifts no slip expansion occurs at the wet clutch.

"Stopping", function sequence 

The specified clutch torque is calculated depending on the type of deceleration.

A temperature model of the wet clutch and the measured state variables are used to calculate the temperature on the wet clutch's steel lamellas. If the calculated temperature exceeds a limit value, then protective functions are activated to match the driving condition that then minimize the friction power on the wet clutch. Substitute values are calculated in the event of mechanical and hydraulic sensor faults. If a hydraulics fault is detected, then the wet clutch control solenoid valve is flushed out in a controlled manner.