Torque converter

fluid coupling that transfers rotating power from a prime mover to a rotating driven load

A torque converter, or torque multiplier, is a device for multiplying torque. It is widely used in transmission systems for road and rail vehicles with internal combustion engines.

Diagram of a hydraulic torque converter


The diagram shows a hydraulic torque converter. It contains two turbines and a stator.

  • Green = pump turbine, turned by the engine
  • Blue = stator
  • Yellow = driven turbine, connected to the wheels of the vehicle
  • Red = direction of flow of the hydraulic fluid

The driven turbine can deliver high torque at low speed. As the vehicle accelerates, the speed goes up and the torque goes down. This happens automatically, so there is no need for the driver to change gear.