How a Torque Converter Works
As the name suggests, it converts the torque of the engine and transmits it to the transmission system.
As soon as the flywheel of engine starts rotating, the torque converter housing as well as the pump also starts rotating in same speed and direction. Because of the profile of the pump blades, the fluids inside the torque converter are pushed out centrifugally. Because of the pressure developed by the pump, the fluids are forced into the blades of the turbine and make it rotate in the same direction as the pump. The fluids enter to the outer periphery of the turbine and leave from the inner periphery and reaches to the stator blades there. The function of the stator is to guide the incoming fluid from the turbine to reach at a specific angle to the pump.
If the turbine is rotating at a speed lower than that of the pump (i.e., when the vehicle is accelerating) then the fluids from the turbine hits the front sides of the stator blades and the one way clutch prevents it from rotating. In this condition the fluids leave from the stator hits the pump at a “helping" angle to increase the torque (or multiply the torque) and thus increase the speed of the turbine.
When the vehicle achieves its constant speed, then the angle at which the fluids leaving from the stator change and no more torque multiplications happens.
While retarding, the speed of the turbine increases than that of the pump and the fluid from the turbine hits the back sides of the stator blades and make the stator rotate at the same direction as the pump and turbine and the fluid from the stator hits the pump in such angles that the torque reduces.