What are the disadvantages of the centrifugal clutch

Things to know about centrifugal clutches on scooters and motorcycles

What is a centrifugal clutch?

A centrifugal clutch is a so-called self-switching shaft clutch that uses the centrifugal force to transmit power. This is why it is also known as a centrifugal clutch. This functional principle means that the clutches are independent of an external energy supply. Due to their simple construction principle, centrifugal clutches have the advantage of being compact, accident-proof and largely maintenance-free, but still working effectively. Conversely, the same construction principle can also be used as a centrifugal brake, which develops an automatic braking effect as the speed increases.

How do centrifugal clutches work?

In the case of a centrifugal clutch, the frictional connection is established by the centrifugal force of the motor rotation pushing moving parts such as flaps or slides, which are located inside the clutch housing and are provided with the clutch linings, outwards. In the idle state, the flaps or slides are pulled inwards by springs; when the engine is running, the centrifugal force pushes them outwards against the action of the spring. In this way, they make contact with the inside of the clutch housing, the clutch bell, via the clutch linings. The engine can therefore be started without load without having to disengage. Only at a certain speed, the so-called cut-in speed, does it build up the transmission torque through the centrifugal clutch, which slowly increases with increasing speed due to decreasing slip. At a certain speed, the centrifugal clutch is finally engaged and the torque is completely transferred to the chain and drive wheel. Conversely, the clutch releases itself when driving slowly and when stopping, so that there is no need to disengage and the engine cannot stall when stopping. The strong slippage of the clutch creates a smooth, flowing transition between idling and power transmission.

How is the centrifugal clutch connected to the engine and chain?

A centrifugal clutch has a drive and an output. The internal drive is connected to the motor. In the case of the external output, the clutch housing is directly connected to the chain via a toothed ring, which is usually fitted with 10 or 12 teeth.

What are the design principles of the centrifugal clutch?

Two design principles are common for centrifugal clutches: the tangential and the radial clutch.

  • The tangential centrifugal clutch works with arched flaps that are mounted on pivot points that are far out. This construction principle has the advantage of being simple and robust. The disadvantage is that only a small part of the bell's circumference is available for power transmission.
  • With a radial centrifugal clutch (usually three) radially attached slides move outwards due to the centrifugal force. This principle has the advantage that almost 100 percent of the bell's circumference can be used for power transmission. Radial centrifugal clutches are more effective, but also a little more prone to tilting and must therefore be manufactured more precisely.

What is the cut-in speed?

The centrifugal clutch engages automatically at a certain speed. This so-called cut-in speed can be precisely adjusted by means of the spring strength in the clutch.

For which shaft diameter are centrifugal clutches available?

The shaft diameter of centrifugal clutches for scooters is usually between 20 and 25 millimeters, the bore is 3/4 inch.

In which areas of application is a centrifugal clutch useful?

  • Conventional centrifugal clutches are particularly suitable for small gasoline engines with high speed and low torque. Therefore, they are primarily used in small motorcycles such as mopeds and scooters. In motor scooters, centrifugal clutches have established themselves as the standard because of their simple functional principle and the high level of driving comfort, which makes them easy to use even for beginners. Here they are mostly available in connection with a stepless automatic gearshift (variomatic), which transmits the power of the engine to the rear wheel with a V-belt instead of a chain. But they are also used in karts or quads, in karts even in racing.
  • In larger motorcycles, centrifugal clutches are mainly used in the enduro sector, but they are unusual on road machines. From the American manufacturer Rekluse there are centrifugal clutches in the motorcycle accessory trade that can be retrofitted. They should provide more driving comfort through the smoother clutch processes and also make the clutch lever superfluous. Furthermore, with a centrifugal clutch, the clutch lever no longer has to be pulled when stopping with the engine running, since the engine disengages itself with this clutch. Accordingly, the engine can no longer stall. Therefore, Rekluse clutches are considered to be "more beginner-friendly" than normal clutches such as are common in motorcycles. As of 2020, the Turismo Veloce 800 Lusso SCS from MV Agusta is the only street motorcycle to be equipped with a centrifugal clutch as standard.
  • Centrifugal clutches are also common in smaller power tools such as chainsaws because they increase operational safety.