Centrifugal Clutch Or Automatic Clutch
An Automatic clutch or centrifugal clutch operates on centrifugal force to connect two shafts, in which the driving shaft mounted inside the driven shaft and they get engaged when the engine reaches to a certain RPM.
The input of the clutch is connected to the crankshaft while the output may drive a shaft, chain, or belt. As engine RPM increase, weighted arms in the clutch moving outward and force the clutch to engage. The most common types nave friction pads or shoes radially mounted that engage the inside of the rim of a housing.
On the centre shaft, there is an assorted number of extension springs, which connect to a clutch shoe. When the central shaft spins fast enough, the springs extend causing the clutch shoes to engage the friction tace. It can be compared with a drum brake in reverse. This type can be found on the 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 outward to these disks together and engage the clutch.
When the engine reaches a certain limit of speed, the clutch activates, working like a continuously variable transmission. As the load increases, the RPM drops and thus disengaging the clutch, letting the speed rise again and reengaging the clutch. It 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 heat waste, but over a wide range of speeds, it is more useful than a direct drive in many applications.
Centrifugal or Automatic clutches are often used in mopeds, underbones, lawn mowers, go-karts, chainsaws, mini bikes, and some paramotors and boats to:
- This keeps the internal combustion engine from stalling when the output shaft speed is slowed or stopped abruptly.
- Disengage loads when starting and idling.
WORKING PRINCIPLE OF CENTRIFUGAL CLUTCH
The centrifugal clutch or Automatic clutch uses centrifugal force, instead of spring force for keeping it in the engaged position. Also, it does not require a clutch pedal for operating the clutch. The clutch is shifted automatically depending upon the engine speed. The vehicle can be able to stop in gear without stalling the engine.
The vehicle can be started in any gear by just pressing the accelerator pedal.
The figure shows a centrifugal clutch. It consists of weights 1 pivoted at 2. When the engine speed increases the weights fly off due to the centrifugal force, operating the bell crank levels, which press the plate 3. The movement of the plate 3 presses the spring 5, which ultimately presses the clutch plate 4 on the flywheel against the spring 7. This makes the clutch engaged. The spring 7 keeps the clutch disengaged at lows speeds at about 500 rpm. The stop 8 limits the movement of the weights due to the centrifugal force.
You can watch the working animation of Centrifugal Clutch Or Automatic Clutch from the video below
Advantages Of Centrifugal Clutch
It is simple and requires less maintenance. It is inexpensive. Since it is automatic, so it does not need the necessary control mechanism. Its engagement speed can be controlled by selecting an appropriate spring. It helps to prevent the engine from stalling.
Disadvantages Of Centrifugal Clutch
There is a slight loss of power in it due to slipping and friction. It is not capable of transferring a high amount of power and it shoes slip in heavy load condition. It experiences overheating problem. Its engagement depends upon the RPM of the driving shaft.
- Centrifugal clutch is mainly used in lawn mowers, mopeds, go karts, mini bikes, chainsaws etc.
- It is also used in some paramotors and boats to keep the engine running during stalling and disengage loads during starting and idling.
- Also used in Honda Bike engines.