Torque Converter: Description and Operation
1. Impeller
2. Turbine wheel
3. Reactor
4. Stator shaft
5. Front cover
6. Primary pump, input flange
7. Cover shell
8. Freewheel
9. Input shaft
Design
The principal components of a torque converter are the impeller (1), turbine wheel (2) and reactor (3).
The impeller (1), also known as the primary wheel, is bolted by the cover shell (7) to the crankshaft of the engine.
The turbine wheel (2), also known as the secondary wheel, is connected to the input shaft (9) of the transmission.
The reactor (3), also known as the stator, is connected to the transmission housing by the freewheel unit (8) and stator shaft (4).
The torque converter is a self-contained unit. The turbine wheel (2) rotates freely in the cover shell (7) which is connected to the impeller (1), the reactor (3) is mounted on a freewheel unit (8) and locks in the counter-enginewise direction of rotation.
The vanes of impeller, turbine wheel and reactor are curved and have defined inlet and outlet angles relative to each other.
The torque converter is filled with oil.
Function
When the impeller (1) rotates, the oil is flung outward into the turbine wheel (2) as a result of the centrifugal force.
The mechanical energy provided by the engine passes in the form of flow energy to the turbine wheel.
The flow energy of the oil is again converted within the turbine wheel (2) into mechanical energy (torque and rotational speed) as a result of being deflected in the curved vane passages.
The oil flowing out of the turbine wheel (2) against the direction of rotation now impinges on the reactor (3). which is held by the freewheel unit in the direction of rotation shown by the shaded arrow. The oil is again deflected by the vanes of the reactor in the direction of rotation of the impeller (1).
This deflection produces a torque in the reactor which is supported by the freewheel unit (8) and also by the stator shaft (4) at the housing and is passed by the oil to the impeller.
The total of the two torques, the input torque passed by the engine to the impeller and the torque passed by the reactor via the oil to the impeller, is equal to the torque which the turbine wheel passes to the transmission.
1. Impeller
2. Turbine wheel
3. Reactor
The ratio of output torque to input torque at the moment of starting off (starting-off torque conversion) is 1:1.8-2.0. This ratio drops steadily as turbine speed increases. The flow direction to the reactor and also the deflection in the reactor also change.
If the oil flow impinges on the rear of the reactor vanes, no further deflection takes place in the reactor. The reactor begins to rotate in the same direction as the impeller and turbine. The ratio of Output torque to input torque reaches approximately the value 1:1.
This operating point is achieved at a rotational speed ratio of impeller to reactor of 1:0.87-0.9 and is known as the lock-up point. Above the lock-up point, the torque converter operates as a hydraulic coupling and achieves a maximum efficiency of approximately 98%.
The heat produced as a result is dissipated by the oil between stator shaft and input shaft flowing to the oil cooler and between stator shaft and primary pump-input flange flowing back to the torque converter.