A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the driving shaft nested inside the driven shaft.
It works on the principle of centrifugal force exerted on a revolving mass which acts as an engaging force.
For those who don’t know, centrifugal force is the apparent force that is felt by an object moving in a curved path that acts outwardly away from the center of rotation
Centrifugal clutch is used in an automatic transmission system. This clutch is placed between the engine shaft and the transmission shaft.
One side of the clutch is connected to the engine crankshaft and another side is connected to gearbox shaft, chain or belt.
Each centrifugal clutch is configured to optimised with an individual engine.
Centrifugal clutch is most commonly used in scooters, mopeds, lawnmowers, chainsaws and some paramotors and boats to keep the engine safe from stalling when the output shaft is slowed or stopped abruptly.
Now, the centrifugal clutch is superseded by the fluid coupling.
Parts of Centrifugal Clutch:
Shoes are the major part of the centrifugal clutch. These shoes slides in the guideways.
This shoes can move radially outwards are held in position initially by means of spring.
These shoes act as an engaging part between the guide and drum in the running condition.
2 Spider or Guide
Spider or guide is mounted on the driving shaft or motor shaft. It works as one of the pressure plate of the engine. The spiders in the centrifugal clutch are equally spaced.
It is named guide as it holds the shoes and connects them and guide their movement.
The initial position of the shoe in the guide is controlled by the springs.
Springs are used to engage the shoe with the drum when the centrifugal force on it is high and disengage it with the drum when the centrifugal force is low.
The shoes are connected with a guide through these springs. It holds shoes at its initial position until the engine shaft archive the required rpm at which the centrifugal force experienced by the shoe overcome the spring force.
4 Friction Lining
The outer surface of the driving shoe has friction lining. This friction lining is in a curved shape. The shoe connects with the inner part of the drum through this friction lining.
It helps in making a grip with the inner surface of the drum.
It avoids direct contact of shoes with the drum which reduces wear and tear of the shoe.
The drum is connected to the driven member of the centrifugal clutch. The torque from the shoes of the centrifugal clutch to the driven shaft is transmitted through this Drum. This drum is connected to the transmission system.
This drum also act as housing which encloses all parts of the clutch which includes sliding shoes, guides or spiders, springs, etc.
Working of Centrifugal Clutch:
- When the driving shaft or input shaft revolves, it exerts a radially outward centrifugal force on the shoe, magnitude of which depends upon the speed of the shaft.
- Here when the input shaft is rotated the power is transmitted from the input shaft. As the speed of the shaft increases, the centrifugal force experienced by the shoes of the centrifugal clutch increases.
- When the speed of the input shaft reaches a particular speed then the centrifugal force exerted on the shoe exceeds the binding force of spring and the shoes start moving in radially outward direction.
- When the shoes reach the drum, the friction lining gets pressurized on the inner surface of the drum. The inner surface of the drum also has some sort of friction lining.
- As soon as the inner surface of the drum gets in contact with the friction lining of the shoe, the drum also starts rotating and the torque is transmitted.
Advantages of centrifugal clutch:
1 It is easier for the driver since the operation becomes simpler.
2) It is low in price.
3) It requires very little maintenance.
4) It is safer for both the user and the system since huge loads won’t stall the engine and letting the throttle free disengages the driving shaft almost immediately.
5) The engaging speed can be preciously controlled by selecting springs.
6) If optimized in conjunction with a particular engine, the overall operation can become extremely efficient and effective.
Disadvantages of Centrifugal clutch:
1 Power transmission is limited due to slippage.
2) Overheating problem due to friction between the drum and shoes. If taken too far due to bad driving/usage habits, permanent damage may completely destroy the clutch.
3) There is a need for frequent oiling of centrifugal clutch arrangement so as to keep the temperature at a safe level.
4) It can not be used to transmit a high amount of torque.
5) The power transmission is totally dependent on controlling speed.
6) There will be always a power loss due to friction and slipping.
Applications of Centrifugal Clutch:
1) It is used in scooters, mopeds, and go-karts.
2) It is used in chain saw, lawn movers.
3) It is used in textile industries.
4) It is also used in boats and paramotors to keep the engine running during stalling (stop running) and disengage loads during starting and idling.