What Is Centrifugal Clutch?- Definition, Parts, Working

What is a Centrifugal Clutch?

A centrifugal clutch is an automatic clutch that uses centrifugal force to operate. The output shaft is disengaged at low rotational speed and engages more as speed increases.

It is often used in mopeds, under bones, lawnmowers, go-karts, chainsaws, mini bikes, and some paramotors and boats to keep the engine from stalling when the output shaft is slowed or stopped abruptly and to remove load when starting and idling.

It has been superseded for automotive applications by fluid coupling and automated manual transmissions.

As the engine speed is increased to or above the set engagement speed of the centrifugal clutch the mechanical drive will become engaged.

This enables the operator to run the engine at a designated idling speed without driving the equipment, thus allowing the engine to reach its optimal torque before experiencing load.

More Resources: What is a Clutch?

How Does A Centrifugal Clutch Work?

A centrifugal clutch works, as the name suggests, through centrifugal force. The key components of a centrifugal clutch are the hub, flyweights (clutch shoes), springs, linings and housing (shown in the diagram below).

The centrifugal force, created by the revolutions of the engine is transmitted through two or more flyweights. The clutch can be driven by a number of ways depending upon the design of the machinery.

One of the most common methods is by mounting the clutch onto the parallel or taper crank shaft of the engine. When the crank shaft rotates the shaft of the clutch rotates at the same speed as the engine.

The rotation of the hub forces the shoes or flyweights outwards until they come into contact with the clutch drum, the friction material transmits the torque from the flyweights to the drum. The drive is then connected.

The springs, flyweights and friction material are responsible for determining the speed at which the clutch engages. Depending on the design of the machine the output from the clutch can be one of a variety drives, including but not limited to shaft, pulley, sprocket or flange.

Automatic clutch engagement or disengagement occurs through the following processes:

Engagement. As the engine’s speed increases, the centrifugal force increases and exceeds the force of the springs. This forces the shoes outward toward the drum. When the designated rotational speed for engagement is reached, the clutch automatically engages by pressing the shoes against the drum’s inner surface. The friction lining then allows the torque to be transmitted from the shoes to the drum.

Disengagement. When the engine slows down, the centrifugal force decreases. This causes the springs to contract, pulling the shoes back to their initial position and disengaging the clutch.

Parts of Centrifugal Clutch

#1. Shoes.

These are sliding shoes that slide in the guideways. It consists of friction lining at the end and this friction lining contacts the drum during the engagement.

#2. Spring.

Spring is a controlling element here, it is used to release the clutch when the engine is turning more slowly.

#3. Spider or Guides.

The spiders are mounted on the drive shaft (motor shaft) or the motor shaft. The spiders are evenly distributed.

Equally spaced means, if there are four guides, each guide is 90 degrees apart. The shoes are held between these guides and each guide holds a spring.

#4. Friction Lining.

The outer surface of the sliding shoes is provided with friction lining. It helps hold the inside surface of the drum in place.

#5. Drum.

The clutch drum serves as a housing that encloses all parts of the clutch, including sliding shoes, guides, springs, etc. It is connected to the driven shaft of the transmission system or to chains or belts.

Advantages of Centrifugal Clutch

Centrifugal clutches provide several distinct advantages over alternative clutch designs, including:

• Automatic engagement/disengagement. Centrifugal clutches are designed to automatically engage or disengage according to the engine’s rotational speed. This eliminates the need for external control mechanisms.
• Low cost. With fewer components required to support their operation, centrifugal clutches are one of the most cost-effective clutch options available. The wearing parts of the clutch are also inexpensive and easy to replace.
• Low maintenance. When designed and constructed properly, centrifugal clutches have much lower maintenance and servicing requirements compared with alternative clutch types.
• Less susceptible to stalling and engine damage. By gradually engaging the load to the engine, centrifugal clutches reduce the risk of abrupt starting or overloading. Benefits of this include smooth and shock-free acceleration, less stalling, safer operation, and longer engine lifespan.
• Better speed control. With centrifugal clutches, the engaging speed can be precisely controlled through spring selection.

Disadvantages of Centrifugal Clutch

There are also several disadvantages of centrifugal clutch:

• Limited Control: Offers limited control over clutch engagement, which may not be suitable for all applications.
• Reduced Efficiency: Can lead to power loss due to partial engagement at low speeds.
• Engagement RPM: Engagement speed is fixed and may not match the engine’s optimal performance range.
• Slippage: In some cases, slippage may occur during engagement, reducing efficiency.
• Heating: Continuous engagement can generate heat energy and wear on clutch components.
• Not Suitable for Heavy Loads: Less suitable for high-torque applications and heavy loads.

Centrifugal Clutch Applications

A centrifugal clutch can be useful for a range of engine-driven equipment with a high starting inertia. They are commonly found on mobile equipment with rotating parts that are driven by small diesel or petrol engines. Some of these examples include:

• Vibratory plate compactors and rollers.
• Rammers.
• Compressor/vacuum/fan drives.
• Trowel and concrete finishers.
• Compact road/street cleaners.
• Transport refrigeration units.
• Mobile water pumps.
• Ground care equipment – rotary and flail mowers, turf cutters, and scarifiers.
• Go-karts.
• Woodchippers/stump grinders/milling cutters.

FAQs.