Centrifugal clutch

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Talbot car's 'traffic clutch' of the 1930s Talbot 'Traffic Clutch' automatic centrifugal clutch (Autocar Handbook, 13th ed, 1935).jpg
Talbot car's 'traffic clutch' of the 1930s

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, underbones, lawn mowers, 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 It has been superseded for automobile applications by the fluid coupling and automated manual transmissions.

Contents

Operation

A chainsaw's clutch. The chain wraps around a sprocket behind the clutch that turns with the outer drum. CentrifugalClutch.jpg
A chainsaw's clutch. The chain wraps around a sprocket behind the clutch that turns with the outer drum.

The input of the clutch is connected to the engine crankshaft while the output may drive a shaft, chain, or belt. As engine revolutions per minute increase, weighted arms in the clutch swing outward and force the clutch to engage. The most common types have friction pads or shoes radially mounted that engage the inside of the rim of a housing. On the center 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 face. It can be compared to a drum brake in reverse. This type can be found on 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 these disks together and engage the clutch. When the engine reaches a certain speed, the clutch activates, working somewhat like a continuously variable transmission. As the load increases, the speed drops, disengaging the clutch, letting the speed rise again, and reengaging the clutch. If 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 waste heat, but over a broad range of speeds, it is much more useful than a direct drive in many applications.

History

A centrifugal clutch shown in a patent application, 1898 US Patent 598314 detail centrifugal clutch.png
A centrifugal clutch shown in a patent application, 1898

Centrifugal clutches were used in railway locomotives before 1858, [1] and referred to (in relation to electric motors) in a patent of 1899. [2]

A patent was issued in the United States for an automotive centrifugal clutch (on an electric vehicle) in 1898. [3]

There is a design for a toy 'automatic clutch' in Meccano Magazine of June 1934. [4]

Armstrong Siddeley cars featured automatic (centrifugal) clutches beginning in 1936. [5]

Thomas Fogarty, who is also credited with inventing the balloon catheter, is credited with inventing a centrifugal clutch for small motor applications in the 1940s. [6]

Principle

This works on the principle of centrifugal force, which means when engine speed reaches a specific rpm (Revolutions per minute) it generates enough centrifugal force inside the clutch which results in clutch engagement and it transmits the engine power. At lower speeds, it disconnects itself to stop power transmission.

See also

Related Research Articles

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A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts. In these devices, one shaft is typically attached to an engine and other to power unit, while the other shaft provides output power for work. Typically the motions involved are rotary, but linear clutches also exist.

Automatic transmission Type of motor vehicle transmission that automatically changes gear ratio as the vehicle moves

An automatic transmission is a multi-speed transmission used in internal combustion engine-based motor vehicles that does not require any driver input to change forward gears under normal driving conditions. It typically includes a transmission, axle, and differential in one integrated assembly, thus technically becoming a transaxle.

Propulsion transmission Drivetrain transmitting propulsion power

Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term transmission properly refers to the whole drivetrain, including clutch, gearbox, prop shaft, differential, and final drive shafts. In the United States the term is sometimes used in casual speech to refer more specifically to the gearbox alone, and detailed usage differs. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and where different rotational speeds and torques are adapted.

Continuously variable transmission Automotive transmission technology

A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while the vehicle moves at varying speeds.

Manual transmission Motor vehicle manual gearbox; stick shift

A manual transmission (MT), also known as manual gearbox, standard transmission, or stick shift, is a multi-speed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch.

Limited-slip differential Type of differential

A limited-slip differential (LSD) is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. Limited-slip differentials are often known by the generic trademark Positraction, a brand name owned by General Motors.

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Sprag clutch One-way mechanical transmission device

A sprag clutch is a one-way freewheel clutch. It resembles a roller bearing but, instead of cylindrical rollers, non-revolving asymmetric figure-eight shaped sprags, or other elements allowing single direction rotation, are used. When the unit rotates in one direction the rollers slip or free-wheel, but when a torque is applied in the opposite direction, the sprags tilt slightly, producing a wedging action and binding because of friction.

Preselector gearbox Type of manual transmission

A preselector gearbox is a type of manual transmission mostly used on passenger cars and racing cars in the 1930s, in buses from 1940-1960 and in armoured vehicles from the 1930s to the 1970s. The defining characteristic of a preselector gearbox is that the gear shift lever allowed the driver to "pre-select" the next gear, usually with the transmission remaining in the current gear until the driver pressed the "gear change pedal" at the desired time.

Fluid coupling

A fluid coupling or hydraulic coupling is a hydrodynamic or 'hydrokinetic' device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives, where variable speed operation and controlled start-up without shock loading of the power transmission system is essential.

A slipper clutch(also known as a back-torque limiter) is a specialized clutch with an integrated freewheel mechanism, developed for performance-oriented motorcycles to mitigate the effects of engine braking when riders decelerate.

Electromagnetic clutch

Electromagnetic clutches operate electrically but transmit torque mechanically. This is why they used to be referred to as electro-mechanical clutches. Over the years, EM became known as electromagnetic versus electro-mechanical, referring more about their actuation method versus physical operation. Since the clutches started becoming popular over 60 years ago, the variety of applications and clutch designs has increased dramatically, but the basic operation remains the same today.

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Ravigneaux planetary gearset

The Ravigneaux gearset is a double planetary gear set, invented by Pol Ravigneaux, who filed a patent application on July 28, 1949, in Neuilly-sur-Seine France. This planetary gear set, commonly used in automatic transmissions, is constructed from two gear pairs, ring–planet and planet–planet.

Jackshaft

A jackshaft, also called a countershaft, is a common mechanical design component used to transfer or synchronize rotational force in a machine. A jackshaft is often just a short stub with supporting bearings on the ends and two pulleys, gears, or cranks attached to it. In general, a jackshaft is any shaft that is used as an intermediary transmitting power from a driving shaft to a driven shaft.

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Dual-clutch transmission Type of automatic transmission

A dual-clutch transmission (DCT) is a type of multi-speed vehicle transmission system, that uses two separate clutches for odd and even gear sets. The design is often similar to two separate manual transmissions with their respective clutches contained within one housing, and working as one unit. In car and truck applications, the DCT functions as an automatic transmission, requiring no driver input to change gears.

Motorcycle transmission Transmission for motorcycle applications

A motorcycle transmission is a transmission created specifically for motorcycle applications. They may also be found in use on other light vehicles such as motor tricycles and quadbikes, go-karts, offroad buggies, auto rickshaws, mowers, and other utility vehicles, microcars, and even some superlight racing cars.

References

  1. Minutes of Proceedings of the Institution of Civil Engineers, Volume 17 (1858)
  2. Patents for Inventions (Patent Office, 1899)
  3. USpatent US598314,W A Crowdus,"AUTOMOBILE VEHICLE",issued 1898-02-01
  4. "Automatic Clutch". nzmeccano.com. Meccano Ltd. June 1934. Retrieved September 8, 2019.
  5. "Armstrong Siddeley 17 HP". siddeley.com. Archived from the original on 2013-06-19.
  6. "Thomas Fogarty Lemelson-MIT Program". lemelson.mit.edu. Retrieved 2019-01-30.