A centrifugal clutch is often used on a small engine. Using springs and weights to engage, a centrifugal clutch is activated by engine speed and revolutions per minute (RPMs). By changing springs to springs of a different tension, the centrifugal clutch can be made to engage sooner or later in the RPM range. Mounted on the engine's output shaft, the centrifugal clutch has a sprocket affixed to its backside and drives a chain connected to the drive axle or wheel. This clutch system was most used on go-carts and mini-bikes in place of a torque converter and a drive belt.
The clutch assembly consists of two pieces, an inner clutch mechanism and an outer shell. The inner mechanism spins on the engine's output shaft while the outer shell and its attached sprocket remains still. As the engine's RPMs are increased, weights that are held in place by springs are thrown outward by the centrifugal force of the spinning mechanism, hence the moniker centrifugal clutch. As the weights reach their fully extended positions, they contact the outer shell and begin to drive it similar to releasing the clutch in an automobile. As the centrifugal clutch begins to spin faster, the vehicle begins to come up to speed.
The stall speed of the centrifugal clutch is easily manipulated by altering the weights and springs, which allows the engine to remain in its power band while driving the vehicle. Stronger springs and lighter weights will result in a clutch that engages at a higher speed. Conversely, installing lighter springs and heavier weights will create a clutch that is engaged at much lower RPMs. Engaging the centrifugal clutch at a higher engine RPM will result in more power being applied to the tires as the clutch engages. This is fine for a racing application, but it can make operation in a street-driven vehicle very difficult due to the quick and powerful take-offs.
Much like an electromagnetic clutch that uses electricity to engage the clutch, the centrifugal clutch uses gravity and centrifugal force to engage the mechanism. The advantage in the centrifugal unit lies in the gradual application of power as the weights are swung into position. The electronic version applies the full amount of power at the flip of a switch. This instant application of power can often cause damage as the drive line is snapped into instant motion. Routine application of light oil on the weights helps to keep the clutch in operational condition.
