Torque Converter

A torque converter is the component in a conventional (automatic) transmission that sits between the engine and the gearbox and transmits power through a hydraulic fluid rather than a mechanical clutch. An impeller driven by the engine throws a flow of oil that spins a turbine wheel, passing the motion on to the gearbox; this lets the engine keep idling while the car is stopped and makes pull-aways smooth. Because fluid transmission causes a small loss of efficiency, modern converters include a lock-up clutch that engages above a certain speed.