GF27.51-P-1000AHT Starting Clutch Function

GF27.51-P-1000AHT Starting Clutch Function
- TRANSMISSION 722.931 in MODEL 221.074 /174, 216.374

Function Requirements, Startup Clutch, General

^ Circuit 87 ON
^ Circuit 61 (engine running)

starting clutch, general

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

A lubricating oil volume flows through the housing of the startup clutch. In the process a lubrication oil pressure adjusts which has an opening action on the clutch piston. 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 startup clutch.

The control unit for the fully integrated transmission control (VGS) (Y3/8n4) uses the required specified clutch torque (the torque to be transferred at the startup clutch) to determine the specified valve pressure.

The pressure regulator adjusts the valve pressure, the regulator output quantity being a specified valve current. A cascade-controlled flow regulator sets the required valve flow at the startup clutch control solenoid valve (VGS).

starting 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 brake.

"Start-off", function sequence

The startup clutch makes possible a strategy-capable startup.

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 startup clutch is activated. The specified clutch torque is calculated so that a microslip is adjusted at the startup clutch. This suppresses driveline vibrations.

"Clutch change", function sequence

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

"Stopping", function sequence

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

Temperature model of startup clutch

By means of a temperature model of the startup clutch and by means of measured state variables the temperature at the steel multidisks of the startup clutch is calculated. If the calculated temperature exceeds a limit value, then depending on the driving condition protective functions are activated which cause the friction power at the startup clutch to be minimized. Substitute values are calculated in the event of mechanical and hydraulic sensor faults. If a hydraulics fault is detected, then the startup clutch control solenoid valve (VGS) is flushed out in a controlled manner.