Driving in anual pro gram 3 250 T o rq ue co nverter · If the gear selector lever is mo

911 Transmission 3 Driving in anual pro gram 3 250 T o rq ue co nverter If the gear selector lever is moved from "D" and to the left, the currently selected gear Functional description of torque converter remains en-gaged. By pressing the switches on the steering wheel, it is now possible to The torque converter consists of the impeller, quickly execute upshifts and downshifts. turbine, stator and the oil required for torque Manually actuated upshifts and downshifts transmission. are monitored by the Tiptronic control unit The impeller driven by the engine causes the and are not permitted above or below defined oil in the torque converter to be pumped in a limit speeds. circular flow. This oil flow reaches the turbine The transmission shifts automatically up or and its flow direction is changed. down at certain limit speeds. The oil leaves the turbine at the hub and "M" as well as the actual gear are displayed in flows to the stator where its direction is once the instrument cluster. again changed. The oil is thus supplied to the impeller in the appropriate flow direction. The change in direction creates a moment at the stator. The reaction moment of this mo- ment increases the turbine moment. The ratio of turbine moment to pump mo- ment is known as the moment increase. The greater the difference in speed between the pump and turbine is, the greater the moment increase (which is at its maximum when the turbine is stationary) will be. The moment increase drops as the turbine speed increases. If the turbine speed reaches approx. 85% of the pump speed, the moment increase is 1, i.e. the turbine moment is equal to the pump moment. The stator which is held off the transmission case by the overrunning clutch and the stator shaft now runs freely parallel to the flow and the overrunning clutch overruns. From this point onwards, the torque converter functions C11_061 purely as a hydraulic clutch. During conver- sion, the stator is stationary and is held off the case by the overrunning clutch. 2002 Service Information 3 -9