Stator, Alternator

The purpose of the stator is to redirect the flow of fluid returning from the turbine to assist the engine in turning the converter pump. This redirection increases the force of the fluid driving the turbine and, as a result, multiplies torque from the engine.
At low vehicle speeds, when greater torque is required, fluid from the turbine hits the front side of the stator blades (converter multiplying torque). Because the roller clutch holds the stator from moving in that direction, fluid is redirected to assist the engine in turning the converter pump. Fluid from the converter pump then has more force to turn the turbine assembly and multiply engine torque.
As vehicle speed increases, centrifugal force changes the direction of fluid from the turbine. The direction of this fluid is such that it hits the back side of the stator blades (converter at coupling speed). This causes the roller clutch to overrun and allow the stator to rotate freely, Fluid is no longer redirected and engine torque is not being multiplied.