Centrifugal clutch

A chainsaw clutch. The chain wraps around a sprocket behind the clutch that turns with the outer drum.

A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the driving shaft nested inside the driven shaft.

The input of the clutch is connected to the engine crankshaft while the output may drive a shaft, chain, or belt. As engine revolutions per minute increase, weighted arms in the clutch swing outward and force the clutch to engage. The most common types have friction pads or shoes radially mounted that engage the inside of the rim of a housing. On the center shaft there are an assorted number of extension springs, which connect to a clutch shoe. When the center shaft spins fast enough, the springs extend causing the clutch shoes to engage the friction face. It can be compared to a drum brake in reverse. This type can be found on most home built karts, lawn and garden equipment, fuel-powered model cars and low power chainsaws. Another type used in racing karts has friction and clutch disks stacked together like a motorcycle clutch. The weighted arms force these disks together and engage the clutch.

When the engine reaches a certain speed, the clutch activates, working somewhat like a continuously variable transmission. As the load increases, the speed drops, disengaging the clutch, letting the speed rise again and reengaging the clutch. If tuned properly, the clutch will tend to keep the speed at or near the torque peak of the engine. This results in a fair bit of waste heat, but over a broad range of speeds it is much more useful than a direct drive in many applications.

Centrifugal clutches are often used in mopeds, underbones, lawnmowers, go-karts, chainsaws, and mini bikes to

• keep the internal combustion engine from stalling when the output shaft is slowed or stopped abruptly
• disengage loads when starting and idling.

Thomas Fogarty, who is also credited with inventing the balloon catheter, is credited with inventing a centrifugal clutch in the 1940s although automobiles were already being manufactured with centrifugal clutches as early as 1936.^[1]

Advantages

• No kind of control mechanism is necessary
• It is cheaper than other clutches.
• Prevents the internal combustion engine from stalling when the output shaft is slowed or stopped abruptly therefore decreases the engine braking force.

Disadvantages

• Since it involves friction and slipping between driver and driven parts there is loss of power.
• As it involves slipping, therefore it is not desirable in cases where there is heavy load or in high torque requirements.

Dry fluid centrifugal clutch

See http://contentdm.lib.byu.edu/ETD/image/etd223.pdf for a basic description of Dry Fluid Centrifugal Clutch design and operating principle. A device such as this was reportedly used in the Taylor Aerocar roadable airplane of the late 1940s and early 1950s.

See also

• Saxomat

References

1. ^ siddeley.com

^[1]

1. ^ http://bikeadvice.in/