Torque converter

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