How Do Centrifugal Clutches Work?

Centrifugal clutches can be found small automated maintenance tools, usually gas-powered weed trimmers and chainsaws, although they can be found in some lawnmowers, go-karts and mopeds. These give the machines a cheap but effective way for the engine to idle and not engage the output device, usually a belt, shaft or chain. When the engine is engaged, the clutch activates the output device.

A centrifugal clutch works by having an output shaft with weighted arms inside a drum. The weighted arms are fly-weights attached to springs. As the shaft turns, the weights begin to push outward through centrifugal force. When it touches the inside of the drum, it begins rotating the drum, which moves the output device, a belt, shaft or chain. The faster the internal shaft spins, the more force is pressed against the drum by the weighted arms. When the engine idles, the internal shaft stops rotating, and the weight arms retract to their original position, removing the force against the inside of the drum. This stops the output device as well.

The components that allow a centrifugal clutch to operate are important and if any pieces are missing or damaged, it could cause a safety hazard. While the internal shaft spins, the springs push the weighted arms into the drum. If the drum were missing the weighted arms would have nothing to spin against and could fly off, possibly causing injury.

Centrifugal clutches are also not as reliable as other clutches. Because its force is from weighted arms pressing against the inside of a drum, it has a limit to its torque and power. If an outside force acts against the output device that overcomes the internal centrifugal force, the output stops even if the internal shaft is still spinning. An example would be a weed trimmer getting stuck in thick weeds. The trimming device stops even if the trigger is still held.

Centrifugal clutches are less expensive than other types of clutches. They are also automatic and require no control mechanism. People who use devices with centrifugal clutches benefit from not having to turn it on and off. Once a weed trimmer's engine is started, it stays idle. Pulling the trigger activates the weed trimming arms, and letting go of the trigger idles the engine. However, because the engine is idle, it is important to stay away from the output device. Performing maintenance like changing trimmers or removing a chain only when the engine is off reduces accidents.