Torque Converter General

Torque Converter:

The torque converter acts as a fluid coupling which transmits the drive from the engine to the gearbox, providing smooth transmission of power to the driving wheels and adding to the torque delivered by the planetary gearbox.

Torque Converter Assembly:

Torque Converter Operation:

The torque converter consists of a pump, stator and turbine.
Rotating at engine speed, the pump (1) delivers hydraulic fluid to the turbine (2) through the stator vanes (3). After driving the turbine, the fluid is returned to the pump.

The pump, stator and turbine vanes are designed so that the angle of fluid discharge from the turbine is altered by the stator vanes when a difference exists between the pump and turbine (i.e. engine and gearbox) speeds. Under these conditions, the fluid helps to drive the pump and the stator is locked in position by the freewheel (or one-way clutch), producing a torque multiplication varying from approx. 2:1 to 1:1.

The 2:1 ratio is obtained when the turbine (i.e. the car) is at rest. The ratio is 1:1 when the turbine speed reaches 90% of the pump speed.

Under the latter conditions, the angle of fluid discharge from the turbine is such that the stator is driven in the same direction as the turbine and pump, and is no longer locked by the freewheel. The torque converter then functions as a fluid coupling with no torque multiplication.

However, some slip (or loss) inevitably occurs between the pump and turbine. Slip may be eliminated by introducing a "lock-up" function.

The AW72L transmission, as well as certain AW70 and AW71 units, is equipped with a mechanical lock-up clutch which eliminates slip by locking the pump and turbine together when the car is driven in 4th gear above a certain speed. (AW70 and AW71 units with this feature are designated AW70L and AW71L respectively.)