TORQUE CONVERTER
In a vehicle fitted with an automatic transmission, the torque converter (TC) performs a similar function to the clutch in a manual-transmission vehicle, without any input from the driver. The TC is a fluid coupling, adapted and refined for this application, and consists of four main parts: the housing, the impeller, the turbine and the stator. The impeller is a set of radial vanes attached to the inside of the housing, which is fixed to the engine flywheel, both rotating at engine speed. Also made up of a set of radial vanes, the turbine is positioned opposite the impeller and is attached to an output shaft connected to the transmission. Rotation of the impeller creates a flow of the fluid within the housing which, in turn, causes the turbine to rotate in the same direction, albeit with some slip. The stator – a set of radial blades attached to a one-way clutch mechanism – is positioned between the impeller and turbine. Its blades are shaped to reverse the direction of the fluid passed over the turbine blades, towards the impeller at the correct angle to assist its rotation and create a torque multiplier effect. On initial acceleration from stationary, the speed differential between impeller and turbine is at its maximum, the stator is locked to redirect the fluid flow, and the torque multiplier effect is between 2,3 and 3,0.
As the vehicle accelerates and the speed differential between the impeller and turbine reduces to less than 10 to 15%, changes to the oil flow means the reversal of the oil flow is no longer required and the stator begins to rotate as well. The blades of the impeller, turbine and stator are all shaped to minimise slip. However, this cannot be eliminated and modern ATS include a lock-up clutch, which locks the two halves of the torque converter together, eliminating any slippage.
The difference between unidirec‐ tional and standard tyres is the tread pattern. Unidirectional tread patterns are typically arrow- or V-shaped to improve dispersion of standing water and avoid aqua‐ planing. Some performance tyres utilise the arrow pattern to ensure high-speed aquaplaning resistance matches their superior response and handling character‐ istics. The obvious limitation of unidirectional tyres is that they cannot be rotated and can be moved only between front and rear on the same side to even out wear. The Jazz is not made locally, and I have to assume a common tyre was selected to cover several export markets, including some countries where wet road condi‐ tions are more common than in SA. The effect would be minimal.