An Engineer’s Guide for Working of a Centrifugal Clutch

Have you ever wondered how gearless transmissions are made possible? For gearless transmission, an automatic clutch is used, which is commonly called a centrifugal clutch. Centrifugal clutch works on centrifugal force.

We all know what a centrifugal force is. Imagine that you have tied a stone to a string. When you rotate the string, a force acts on the stone that would push the stone away from the axis of rotation. This force exerted by the stone on the string is called centrifugal force. The string is replaced by springs in a centrifugal clutch, and the spider replaces the stone. Read ahead to learn the construction of centrifugal clutch, the application of centrifugal clutch and also about semi centrifugal clutch.

Construction of Centrifugal Clutch

Before learning about the construction, you must understand the different parts of centrifugal clutch. A centrifugal clutch has a spring, spider or guides, sliding shoes, friction lining and driving and driven member. The driving member is the input shaft from the engine, and the driven member is the output shaft connected to the transmission system. The driven member looks like a drum and has a friction lining on its inner surface. The driving member encloses the driven member and is attached to the spiders. The spiders have sliding shoes with friction lining on their outer end. The shoes are connected to the driving shaft by springs on their inner surface. 

Working of a Centrifugal Clutch

The centrifugal clutch mechanism is very simple to understand. When the engine starts, the driving shaft along with the spider rotates. The sliding shoes tend to move away due to the centrifugal force, but the spring holds it in its position. When the engine speed increases, the centrifugal force overcomes the spring force. Hence the shoes move away from the centre and press against the drum. This makes the driven member rotate at the speed of the driving member. Thus the clutch automatically engages at a predetermined speed. When the engine's speed is decreased, the centrifugal force also decreases. Therefore the shoes disengage the driven shaft and come back to their original position. This is how a centrifugal clutch works.

Applications of Centrifugal Clutch

• Scooters
• Lawnmowers
• Mopeds
• Go-Karts

These are some of the applications where you can find a centrifugal clutch. The centrifugal clutch is advantageous in many ways. The centrifugal clutch maintenance is simple. There is no necessity for a clutch pedal, and it is fully automatic. The construction is also simple, yet there is a drawback. It cannot be used in low-speed applications. At low speed, the spiders may not be engaged properly with the driven shaft, and there is a possibility of slipping. This may eventually lead to power loss. 

We have another type of centrifugal clutch called a semi centrifugal clutch. Let us understand 

Working of Semi Centrifugal Clutch

So far, we have seen the working of a full centrifugal clutch. There is a difference between the full centrifugal clutch mechanism and the semi centrifugal clutch mechanism. In a semi centrifugal clutch, you can find a pressure plate and a weighted lever in addition to the parts of a centrifugal clutch. At low speed, the clutch springs keep the clutch engaged, and the weighted lever has nothing to do with the pressure plate. At high speed, the weighted lever would pressurise the pressure plate, and the transmission of power takes place. A semi centrifugal clutch is not a fully automatic clutch; instead, the driver's effort is reduced during the clutch operation. Some common application of a semi centrifugal clutch is racing car engines and high powered engines. You can explore more about automotive and its subsystem through Skill-Lync’s course for mechanical engineers.