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1999 Tiptronic Torque Converter Lock-up


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From the 1999 Porsche Carrera Service Information Book:

"3250· Torque Converter

Functioning of the converter

The converter comprises the impeller, turbine, stator, and the oil required for torque transmission. The impeller driven by the engine causes the oil in the converter to be pumped in a circular flow. This oil flow reaches the turbine and its flow direction is changed. The oil leaves the turbine at the hub and flows to the stator where its direction is once again changed. The oil is thus supplied to the impeller in the appropriate flow direction.

The change in direction creates a lock-up of at the stator. The reaction of the fluid increases the turbine speed. The ratio of turbine speed to impeller speed is known as the torque increase.

The greater the difference in speed between the impeller and turbine, the greater the torque increase which is at its maximum when the turbine is stationary. The torque increase drops as the turbine speed increases.

If the turbine speed reaches approx. 85% of the impeller speed, the torque increase is I, i.e. the turbine speed is equal to the impeller speed.

The stator which is supported by the overrun clutch and the stator shaft to the transmission housing now runs free parallel to the flow and the overrun clutch overruns. From this point onwards, the converter functions as a pure flow clutch.

During conversion, the stator is stationary and is supported by the overrun clutch to the housing.

Regulated converter lockup clutch

The converter lockup clutch (CLC) is a device which eliminates slippage of the converter and thus contributes to the optimization of fuel consumption and to a sporty style of driving.

In the new 911 Carrera, control of the CLC actuation has been replaced by a regulation function. Intervention and opening of the CLC is regulated. During the regulation phase, a differential speed of approx. 50 rpm between pump and turbine is set. This prevents the torsional vibrations from the engine from being transmitted to the transmission which, in turn, optimizes shifting smoothness.

Pressure regulation at the CLC pistons is determined by an electronic pressure control valve (EPCV 4). When open (conversion range), the oil pressure is adjusted after the CLC pistons as well as in the turbine range. The direction of flow is determined by the turbine shaft through the area behind the

pistons to the turbine chamber.

To close the CLC, the direction of flow is changed (reversed) by a valve in the hydraulic control unit (EPCV 4). At the same time, the space behind the CLC piston is bled. The oil pressure moves from the turbine chamber to the CLC piston and forces it against the cover (outer shell) of the converter. As a result, the turbine is locked by the lining disk between the piston and cover and allows rigid through-drive to the planetary transmission without slippage or slippage (in the case of regulated operation)."

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