Automatic transmissions certainly make things easy as far as day to day commuting in traffic is concerned. However, they’re also pretty useful bits of performance equipment for the drag strip if they’re combined with the right torque converter and that’s what we’re going to talk about here – performance torque converters – in detail.
So, what does a torque converter convert? Most people answer that it ‘converts torque into more torque’ which is pretty much correct, although it’s actually speed (of fluid) that gets turned into the extra torque. Still, torque converters certainly do act as torque multipliers. How all of this happens requires an understanding of the different components within a torque converter and how they work with each other under various conditions.
The impeller consists of a circular shell containing a large number of blades, or vanes, set in a radial arrangement. The vanes create a number of semi-circular cells that are filled with oil in normal operation. The impeller assembly is welded to the front case of the converter which is bolted to the flex-plate and therefore turns at the same speed as the engine. The rotational motion of the impeller creates inertia in the oil contained the cells and, as a result, it’s flung from the outer ends of the cells with considerable force.
In very basic terms, the construction of the turbine is the same as that of the impeller except that the cells are heavily curved. The openings of the cells in the turbine correspond with the openings of the cells in the impeller and, because both sets of blades (and cells) are so close to each other, the oil flung from the outer ends of the cells in the impeller is thrown into the outer ends of the cells of the turbine. The turbine assembly is splined to the input shaft of the transmission, so the force of the fluid entering the turbine cells is transferred directly to the input shaft.
The impeller and turbine can turn at different speeds because the only connection between them is through the transmission fluid. When a car first moves off, engine revs are increased and greater amounts of oil move through the impeller as it rotates with the crankshaft. Because the wheels and transmission have been stationary, the turbine is also stationary. But as oil from the impeller is continuously flung into the turbine it starts to turn and drive the car forward. Oil entering the outer ends of the cells in the turbine is forced radially inward and emerges from the openings closest to the center of the turbine.
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