Free-wheel

Function

Turning into one direction, the free-wheel interrupts the frictional engagement.

How it works

Roller free-wheels make use of rollers, which are pressed by springs in one direction into a narrowing gap between the inner-and outer ring. If the inner ring drives the outer ring in the same direction as the spring, the rollers are pinched and there is frictional engagement. If the outer ring is driven, it is interrupted.
The free-wheel is used at the stator of the torque converter and for the electrical starter motor to prevent overspeeding. The device became famous when it was used in two-stroke oldtimers, because it disabled the engine brake when the vehicle was going downhill, protection the engine which was running without lubrication.