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This may be obvious, but I'll ask anyway: What is the idea behind multiple clutches in a torque converter? Thanks.
The most common clutches in a torque converter would be a lockup clutch and a Sprag (or one way) clutch that has positive drive in one direction and freewheels in the opposite direction. The lockup clutch locks the Impeller and Turbine together eliminating the internal slippage inefficiency of a torque converter or fluid coupling providing a positive drive like you have with the clutch engaged in a standard transmission. The Sprag clutch goes between the torque converter Stator and the ground sleeve that it's mounted on. The purpose of the Stator is to redirect the oil flow in between the Impeller and Turbine and by so doing torque multiplication takes place. The down side is that this is most efficient and effective at converter stall which is the point where the output turbine is not turning or turning very slowly compared to the impeller. As the Turbine speed increases and the load decreases a problem develops as a stationary Stator (as it would be under stall conditions) would create a lot of resistance and drag to the internal flow of oil and at high speed with a light output load the oil flow would actually be hitting the stator blades on their back sides generating a lot of heat and a parasitic power draw. The solution is that the Sprag clutch allows the Stator to free wheel so that with the lockup clutch engaged the Impeller, Stator and Turbine all rotate in unison.
Word of warning here, the different manufacturers can't seem to agree on a standard of terms for the internals of these torque converters as some call Stators redirectors and Impellers Pumps or also call Impellers Turbines just to make it more confusing.
