flywheel

Dictionary: fly·wheel (flī'hwēl', -wēl') pronunciation

A heavy-rimmed rotating wheel used to minimize variations in angular velocity and revolutions per minute, as in a machine subject to fluctuation in drive and load.
An analogous device, especially one used to regulate the speed of clockwork.

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Britannica Concise Encyclopedia: flywheel

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Heavy wheel attached to a rotating shaft to smooth out delivery of power from a motor to a machine. The inertia of the flywheel opposes and moderates fluctuations in the speed of the engine and stores the excess energy for intermittent use. In automobile engines, the flywheel smooths out the pulses of energy provided by the combustion in the cylinders and provides energy for the compression stroke of the pistons. In power presses the actual punching, shearing, and forming are done in only a fraction of the operating cycle. During the longer, nonactive period, the speed of the flywheel is built up slowly by a comparatively low-powered motor. When the press is operating, most of the required energy is provided by the flywheel.

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Sci-Tech Encyclopedia: Flywheel

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A rotating mass used to maintain the speed of a machine between given limits while the machine releases or receives energy at a varying rate. A flywheel is an energy storage device. It stores energy as its speed increases, and gives up energy as the speed decreases. The specifications of the machine usually determine the allowable range of speed and the required energy interchange.

The difficulty of casting stress-free spoked flywheels leads the modern designer to use solid web castings or welded structural steel assemblies. For large, slow-turning flywheels on heavyduty diesel engines or large mechanical presses, cast-spoked flywheels of two-piece design are standard (see illustration). See also Energy storage.

Typical flywheel structures.

Columbia Encyclopedia: flywheel

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flywheel, heavy metal wheel attached to a drive shaft, having most of its weight concentrated at the circumference. Such a wheel resists changes in speed and helps steady the rotation of the shaft where a power source such as a piston engine exerts an uneven torque on the shaft or where the load is intermittent, as in piston pumps or punches. By slowly increasing the speed of a flywheel a small motor can store up energy that, if released in a short time, enables the motor to perform a function for which it is ordinarily too small. The flywheel was developed by James Watt in his work on the steam engine.

Wikipedia: Flywheel

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For other uses, see Flywheel (disambiguation).

Video of a flywheel that keeps its rotation rate higher than in a rigid design, constructed based on drawings by Leonardo da Vinci

A flywheel is a mechanical device with a significant moment of inertia used as a storage device for rotational energy. Flywheels resist changes in their rotational speed, which helps steady the rotation of the shaft when a fluctuating torque is exerted on it by its power source such as a piston-based (reciprocating) engine, or when an intermittent load, such as a piston pump, is placed on it. Flywheels can be used to produce very high power pulses for experiments, where drawing the power from the public network would produce unacceptable spikes. A small motor can accelerate the flywheel between the pulses. Recently, flywheels have become the subject of extensive research as power storage devices for uses in vehicles and power plants; see flywheel energy storage.

1 Physics
2 Examples of energy stored
3 High energy materials
4 Applications
- 4.1 History
- 4.2 Flywheel in the internal combustion engine
5 See also
6 References
7 External links

Physics

Spoked flywheel

Energy is stored in the rotor as kinetic energy, or more specifically, rotational energy:

$E_k=\frac{1}{2}\cdot I\cdot \omega^2$

where

ω

is the angular velocity, and

I

is the moment of inertia of the mass about the center of rotation.

The moment of inertia for a solid-cylinder is $I_z = \frac{1}{2} mr^2$ ,
for a thin-walled cylinder is $I = m r^2 \,$ ,
and for a thick-walled cylinder is $I = \frac{1}{2} m({r_1}^2 + {r_2}^2)$ .

where m denotes mass, and r denotes a radius. More information can be found at list of moments of inertia

When calculating with SI units, the standards would be for mass, kilograms; for radius, meters; and for angular velocity, radians per second. The resulting answer would be in Joules

The amount of energy that can safely be stored in the rotor depends on the point at which the rotor will warp or shatter. The hoop stress on the rotor is a major consideration in the design of a flywheel energy storage system.

$\sigma_t = \rho r^2 \omega^2 \$

where

σ t

is the tensile stress on the rim of the cylinder

ρ

is the density of the cylinder

r

is the radius of the cylinder, and

ω

is the angular velocity of the cylinder.

Examples of energy stored

You can use those equations to do 'back of the envelope' calculations and find the rotational energy stored in various flywheels. I = kmr², and k is from List of moments of inertia

object	k (varies with shape)	mass	diameter	angular velocity	energy stored, J	energy stored, kWh
bicycle wheel	1	1 kg	700 mm	150 rpm	15 J	4 × 10⁻⁶ kWh
bicycle wheel, double speed	1	1 kg	700 mm	300 rpm	60 J	16 × 10⁻⁶ kWh
bicycle wheel, double mass	1	2 kg	700 mm	150 rpm	30 J	8 × 10⁻⁶ kWh
Flintstones concrete car wheel	1/2	245 kg	500 mm	200 rpm	1.68 kJ	0.47 × 10⁻³ kWh
wheel on train @ 60 km/h [1]	1/2	942 kg	1 m	318 rpm	65 kJ	18 × 10⁻³ kWh
giant dump truck wheel @ 18 mph	1/2	1000 kg	2 m	79 rpm	17 kJ	4.8 × 10⁻³ kWh
small flywheel battery [2]	1/2	100 kg	600 mm	20000 rpm	9.8 MJ	2.7 kWh
regenerative braking flywheel for trains [3]	1/2	3000 kg	500 mm	8000 rpm	33 MJ	9.1 kWh
electrical power backup flywheel [4]	1/2	600 kg	500 mm	30000 rpm	92 MJ	26 kWh
the planet earth [5], Rotational energy	2/5	5.97 × 10²⁴ kg	12725 km	~1 per day	2.6 × 10²³ MJ	7.2 × 10²² kWh

See [6], [7], [8], [9], and Rotational energy

High energy materials

Flywheel from stationary engine. Note the castellated rim which was used to rotate the engine to the correct starting position by means of a lever.

For a given flywheel design, it can be derived from the above equations that the kinetic energy is proportional to the ratio of the hoop stress to the material density.

$E_k \varpropto \frac{\sigma_t}{\rho}$

This parameter could be called the specific tensile strength. The flywheel material with the highest specific tensile strength will yield the highest energy storage. This is one reason why carbon fiber is a material of interest.

Applications

A Landini tractor with massive flywheel

Further information: Flywheel energy storage

In application of flywheels in vehicles, the phenomenon of precession has to be considered. A rotating flywheel responds to any momentum that tends to change the direction of its axis of rotation by a resulting precession rotation. A vehicle with a vertical-axis flywheel would experience a lateral momentum when passing the top of a hill or the bottom of a valley (roll momentum in response to a pitch change). Two counter-rotating flywheels may be needed to eliminate this effect.

1898 illustration of a White and Middleton stationary engine; note the large twin flywheels.

In a modern application, a momentum wheel is a type of flywheel useful in satellite pointing operations, in which the flywheels are used to point the satellite's instruments in the correct directions without the use of thruster rockets.

Flywheels are used in punching machines and riveting machines, where they store energy from the motor and release it during the operation cycle (punching and riveting).

History

The principle of the flywheel is found in the Neolithic spindle and the potter's wheel.^[1]

The Andalusian agronomist Ibn Bassal (fl. 1038-1075), in his Kitab al-Filaha, describes the flywheel effect employed in a water wheel machine, the saqiya.^[2]

The flywheel as a general mechanical device for equalizing the speed of rotation is, according to the American medievalist Lynn White, recorded in the De diversibus artibus (On various arts) of the German artisan Theophilus Presbyter (ca. 1070-1125) who records applying the device in several of his machines.^[1]^[3]

In the Industrial Revolution, James Watt contributed to the development of the flywheel in the steam engine, and his contemporary James Pickard used a flywheel combined with a crank to transform reciprocating into rotary motion.

Flywheel in the internal combustion engine

For internal combustion engine applications, the flywheel is a heavy wheel mounted on the crankshaft. Its main function is to maintain a fairly constant angular velocity of the crankshaft.

References

^ ^a ^b Lynn White, Jr., “Theophilus Redivivus”, Technology and Culture, Vol. 5, No. 2. (Spring, 1964), Review, pp. 224-233 (233)
^ Ahmad Y Hassan, Flywheel Effect for a Saqiya.
^ Lynn White, Jr., “Medieval Engineering and the Sociology of Knowledge”, The Pacific Historical Review, Vol. 44, No. 1. (Feb., 1975), pp. 1-21 (6)

External links

Flywheel highlight: Hypervideo showing construction and operation of four cylinder internal combustion engine (courtesy of Ford Motor Company)
Interesting Thing of the Day article on the Flywheel: Written by Joe Kissell.

Look up flywheel in Wiktionary, the free dictionary.

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Translations: Flywheel

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Dansk (Danish)
n. - svinghjul

Nederlands (Dutch)
vliegwiel

Français (French)
n. - (Mécan) volant

Deutsch (German)
n. - Schwungrad

Ελληνική (Greek)
n. - (μηχαν.) σφόνδυλος (κν. βολάν)

Italiano (Italian)
volano

Português (Portuguese)
n. - volante (m) ou disco (m) que mantém a velocidade de uma engrenagem (Mec.)

Русский (Russian)
маховое колесо

Español (Spanish)
n. - volante

Svenska (Swedish)
n. - svänghjul (mek.)

中文（简体）(Chinese (Simplified))
调速轮

中文（繁體）(Chinese (Traditional))
n. - 調速輪

한국어 (Korean)
n. - 기계의 회전 조절 바퀴

日本語 (Japanese)
n. - はずみ車

العربيه (Arabic)
‏(الاسم) دولاب الموازنه‏

עברית (Hebrew)
n. - ‮גלגל תנופה‬

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		Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more
		Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more
		Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more
		Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more
		Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Flywheel". Read more
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