A torque converter is a component of an automatic transmission. The torque converter is a hydraulic coupler that connects the transmission to the engine and transfers torque from the engine to the transmission.
The torque converter is a large cylindrical housing partially filled with transmission fluid. One side of the torque converter is connected to the engine’s flywheel, and the other side is attached to the input shaft of the transmission.
When your engine is idling, the torque converter allows it to spin free of the transmission. Little or no torque is transmitted. But as engine RPMs rise, centrifugal force inside the torque converter causes fluid to move from one side of its housing to the other in order to rotate a turbine and, ultimately, the transmission input shaft. This rotation is used to turn gears to move your vehicle.