GF27.51-P-1000AHI Start-Up Clutch, Function

GF27.51-P-1000AHI Start-up clutch, function
- TRANSMISSION 722.930


Function requirements, start-up clutch, general
^ Circuit 87 ON
^ Circuit 61 (engine running)

Start-up clutch, general
The pressure from the start-up clutch control solenoid valve (Y3/8y9) is amplified by the start-up clutch regulating valve. A lubricating oil volume flows through the housing of the start-up 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 start-up clutch.

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

Start-up clutch, function sequence
The function sequence is subdivided into the following steps:

^ Switch-on process
^ Crawling
^ Starting off
^ Slip control
^ Clutch change
^ Stop vehicle

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.

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

Crawling
In this condition the specified clutch torque is calculated so that the vehicle starts to roll automatically when the driver deactivates the brake.

Starting off
The start-up clutch makes possible a strategy-capable start-up. If the "Race start" is activated, the wheel slip is regulated by the start-up clutch during the start-up process.
A suitable start-up strategy is selected depending on engine load and vehicle speed or vehicle acceleration.

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

Clutch change
During a clutch change the specified clutch torque at the start-up clutch is calculated so that with upshifts no slip expansion occurs but with downshifts a slip expansion at the start-up clutch occurs.

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

Temperature model of start-up clutch
By means of a temperature model of the start-up clutch and by means of measured state variables the temperature at the steel multidisks of the start-up 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 start-up 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 start-up clutch control solenoid valve is flushed out in a controlled manner.