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 It has been superseded for automotive applications by fluid coupling and automated manual transmissions.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

As we have experienced since childhood in roundabouts on playgrounds, when a mass is rotating/spinning a force is generated that points away from the axis of rotation and is known as centrifugal force. The faster the rotation gets, the stronger that force gets and that is why it is so difficult to stay in roundabouts that are spinning quickly.

The operation of the centrifugal clutch is based precisely on the generation of this centrifugal force. In particular, the rotating shaft is connected to the crankshaft of the engine and arranged in the middle of the clutch.

The outer housing is positioned concentrically and connected to the driven shaft. As the engine speed increases, the speed of the drive shaft increases, forcing the shoes installed on the inside of the assembly to expand and reach the inside wall of the drum.

Both the inside of the drum and the outside of the shoe are made of materials with high friction so that a reliable engagement is possible, similar to braking. However, this also causes high temperatures if the engagement/disengagement action occurs more frequently than intended.

As soon as the engine speed drops again, the clutch is disengaged immediately so that the driven shaft no longer receives any rotational movement energy. This helps prevent the engine from stalling when the load is overwhelming and the engine has trouble handling it and makes overall operation safe for both the systems and the user.

Centrifugal clutches can have two, three, four, five, or even six shoes that follow a symmetrical positioning on the drive shaft. In order for them to expand in a controlled manner and in relation to engine speed, manufacturers use expansion springs to compensate for this expansion.

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Manufacturers can use different spring strengths and lengths to achieve specific engagement and disengagement points for their centrifugal clutch, whereby the engagement should generally be maintained in the optimum engine torque range.

This means that not every centrifugal clutch is ideal for every type of engine and that both must be considered and optimized together in order to achieve the best possible results.

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 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

There are several reasons to choose the centrifugal clutch over alternative types:

  • Automatic. Centrifugal clutches automatically engage and disengage. You don’t need a control mechanism. The centrifugal clutch is based on the laws of physics.
  • Lower costs. Centrifugal clutches are relatively inexpensive compared to other types of a clutch. In part, because fewer parts are involved, no battery or additional components are required.
  • Low maintenance requirements. In terms of maintenance and servicing, centrifugal clutches are more cost-effective. As long as the original design and construction are solid, there is little chance the system will break or wear out.
  • Less chance of engine stalling and damage. Heavy loads and abrupt starts can put stress on the engines. Instead, progressive intervention in the load is safer. Centrifugal clutches specialize in smooth and shock-free acceleration.
  • Greater engagement speed control. The centrifugal clutch gradually engages to increase the torque from the engine to the load. This ensures a much longer lifespan and saves more energy at startup.
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Disadvantages of Centrifugal Clutch

There are also several disadvantages of centrifugal clutch:

  • Power transmission is limited due to slippage.
  • The problem of overheating is due to friction between drum and shoes. If they go too far due to poor driving/usage habits, permanent damage can completely destroy the clutch.
  • The centrifugal clutch assembly must be oiled frequently to keep the temperature at a safe level.
  • It cannot be used to transmit high torque.
  • The power transmission depends entirely on speed control.
  • There is always a loss of performance due to friction and slippage.

Applications of Centrifugal Clutch

Centrifugal clutches that correctly transmit a movement with centrifugal force are mainly used in industrial machines such as sweepers, mowers, chain saws, generator sets, motor pumps, lawnmowers, or fans. They are also used in cooling systems and mini karts.

While friction clutches offer numerous advantages, they are not always suitable for every application. Here are some considerations to keep in mind when planning to use a centrifugal clutch:

  • Low-speed Engines can cause slippage. In the case of devices with a relatively low speed, there would be greater friction values, which would heat up the clutch drum and lead to a loss of power.
  • The maximum speed of a centrifugal clutch depends on the clutch size. The smaller the clutch, the faster the speed. This is due to the centrifugal force required to lock it into place.
  • Ideal for engines with a wide speed range. When your engine reaches a certain speed, the clutch is activated. If the load exceeds its rated capacity, the clutch will automatically “slip”, protecting the motor and driven equipment.

FAQs.

What is Centrifugal Clutch?

A centrifugal clutch is a mechanical device that is used on driven rotary equipment. Most commonly used with a combustion engine, the clutch can be used to automatically transmit the torque from the drive to the driven equipment giving a “soft start” with no load engagement.

How Does a Centrifugal Clutch Work?

A centrifugal clutch works, as the name suggests, through centrifugal force. 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.

What are the advantages of Centrifugal Clutch?

Advantage:

  • Simple and inexpensive and need little maintenance.
  • The centrifugal clutch is automatic any kind of control mechanism is not necessary.
  • They help to prevent the engine from stalling.
  • The engagement speed can be precisely controlled by selecting spring.

What is the application of Centrifugal clutch?

Centrifugal clutches, which use centrifugal force to convey a movement correctly, are primarily applied to industrial machineries such as sweepers, mowers, chainsaws, generator sets, motor pumps, lawnmowers or fans. Moreover, they are also applied to refrigeration systems and mini-karts.

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What does a centrifugal clutch do?

A centrifugal clutch is a mechanical device which is used on driven rotary equipment. Most commonly used with a combustion engine, the clutch can be used to automatically transmit the torque from the drive to the driven equipment giving a “soft start” with no load engagement.

How much HP can a centrifugal clutch handle?

NORAM centrifugal clutches are designed to fit engines ranging from fractional horsepower up to 50 HP applications.

At what RPM does a centrifugal clutch engage?

A clutch starts to engage around 2,000 rpm and will lock up around 2,600 rpm. Driving at full throttle gives the clutch a chance to cool down. Full throttle locks the shoes in the clutch against the drum.

What are the disadvantages of centrifugal clutch?

Disadvantages of Centrifugal Clutch:

In the case of an engine with a low RPM, a centrifugal clutch is not suitable for that one because of the overheating problem. More heat can be produced due to friction between shoes and clutch drum. This problem of overheating can damage the clutch due to slippage and loss of power.

How long does a centrifugal clutch last?

Improper installation of the centrifugal clutch can result in its failure as quickly as in a couple of minutes. Still though, even if installed properly, it won’t last more than five years maximum.

Do you oil a centrifugal clutch?

Why is my centrifugal clutch getting hot?

Your clutch may be overheating due to several reasons. One of the most common reasons is a lack of lubrication. If your clutch is not lubricated properly, there is no agent that helps to reduce friction and disseminate heat.

Is a torque converter better than a centrifugal clutch?

Torque converters are great for lower-end torque, as they have the ability to adjust the gear ratio depending on the engine’s RPM. This makes it ideal for heavier or off-road go-karts. On the other hand, a regular clutch maintains the same gear ratio all the time.

How can I make my centrifugal clutch engage faster?

If the clutch engages too quickly, back the adjustment screw off a half-turn. If engagement is too high or slow, tighten the adjusting screw up a bit.

Why semi a centrifugal clutch is better than a centrifugal clutch?

a semi- centrifugal clutch uses lighter pressure plate springs for a given torque carrying capacity so that the engagement of the clutch in the lower speed range becomes possible. The centrifugal force supplements the necessary extra clamping thrust at higher speeds.

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