Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruisin ...

s. It is also used in a wide variety of machines besides vehicles. Most often, the power is conveyed by a roller chain, known as the drive chain or transmission chain, passing over a sprocket gear, with the teeth of the gear meshing with the holes in the links of the chain. The gear is turned, and this pulls the chain putting mechanical force into the system. Another type of drive chain is the Morse chain, invented by the Morse Chain Company of

Ithaca, New York Ithaca is a city in the Finger Lakes region of New York (state), New York, United States. Situated on the southern shore of Cayuga Lake, Ithaca is the seat of Tompkins County, New York, Tompkins County and the largest community in the Ithaca m ...

, United States. This has inverted teeth. Sometimes the power is output by simply rotating the chain, which can be used to lift or drag objects. In other situations, a second gear is placed and the power is recovered by attaching shafts or hubs to this gear. Though drive chains are often simple oval loops, they can also go around corners by placing more than two gears along the chain; gears that do not put power into the system or transmit it out are generally known as idler-wheels. By varying the diameter of the input and output gears with respect to each other, the gear ratio can be altered. For example, when the bicycle pedals' gear rotate once, it causes the gear that drives the wheels to rotate more than one revolution. Duplex chains are another type of chain which are essentially two chains joined side by side which allow for more power and torque to be transmitted.

History

The oldest known application of a chain drive appears in the Polybolos, described by the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

engineer

Philon of Byzantium Philo of Byzantium ( el, , ''Phílōn ho Byzántios'', ca. 280 BC – ca. 220 BC), also known as Philo Mechanicus, was a Greek engineer, physicist and writer on mechanics, who lived during the latter half of the 3rd century BC. Although he was f ...

(3rd century BC). Two flat-linked chains were connected to a windlass, which by winding back and forth would automatically fire the machine's arrows until its magazine was empty.Werner Soedel, Vernard Foley: ''Ancient Catapults'', ''Scientific American'', Vol. 240, No. 3 (March 1979), p.124-125 Although the device did not transmit power continuously since the chains "did not transmit power from shaft to shaft, and hence they were not in the direct line of ancestry of the chain-drive proper", the Greek design marks the beginning of the history of the chain drive since "no earlier instance of such a cam is known, and none as complex is known until the 16th century." It is here that the flat-link chain, often attributed to

Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially re ...

, actually made its first appearance." The first continuous as well as the first endless chain drive was originally depicted in the written horological treatise of the Song Dynasty by the medieval Chinese polymath mathematician and astronomer Su Song (1020-1101 AD), who used it to operate the

armillary sphere An armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (on the celestial sphere), consisting of a spherical framework of rings, centered on Earth or the Sun, that represent lines ...

of his astronomical

clock tower Clock towers are a specific type of structure which house a turret clock and have one or more clock faces on the upper exterior walls. Many clock towers are freestanding structures but they can also adjoin or be located on top of another build ...

, which is the first astronomical clock, as well as the clock jack figurines presenting the time of day by mechanically banging gongs and drums. The chain drive itself converted rotary to reclinear motion and was given power via the hydraulic works of Su's water clock tank and waterwheel, the latter which acted as a large gear.

Alternatives

Belt drive

Most chain drive systems use

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...

to transfer motion between the chain and the rollers. This results in lower frictional losses than belt drive systems, which often rely on

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding (motion), sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative la ...

to transfer motion. Although chains can be made stronger than belts, their greater mass increases drive train

inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law o ...

. Drive chains are most often made of metal, while belts are often rubber, plastic, urethane, or other substances. If the drive chain is heavier than an equivalent drive belt, the system will have a higher

. Theoretically, this can lead to a greater flywheel effect, however in practice the belt or chain inertia often makes up a small proportion of the overall drivetrain inertia. One problem with roller chains is the variation in speed, or surging, caused by the acceleration and deceleration of the chain as it goes around the sprocket link by link. It starts as soon as the pitch line of the chain contacts the first tooth of the sprocket. This contact occurs at a point below the pitch circle of the sprocket. As the sprocket rotates, the chain is raised up to the pitch circle and is then dropped down again as sprocket rotation continues. Because of the fixed pitch length, the pitch line of the link cuts across the chord between two pitch points on the sprocket, remaining in this position relative to the sprocket until the link exits the sprocket. This rising and falling of the pitch line is what causes chordal effect or speed variation. In other words, conventional roller chain drives suffer the potential for vibration, as the effective radius of action in a chain and sprocket combination constantly changes during revolution ("Chordal action"). If the chain moves at constant speed, then the shafts must accelerate and decelerate constantly. If one sprocket rotates at a constant speed, then the chain (and probably all other sprockets that it drives) must accelerate and decelerate constantly. This is usually not an issue with many drive systems; however, most motorcycles are fitted with a rubber bushed rear wheel hub to virtually eliminate this vibration issue. Toothed belt drives are designed to limit this issue by operating at a constant pitch radius). Chains are often narrower than belts, and this can make it easier to shift them to larger or smaller gears in order to vary the gear ratio. Multi-speed bicycles with derailleurs make use of this. Also, the more positive meshing of a chain can make it easier to build gears that can increase or shrink in diameter, again altering the gear ratio. However, some newer synchronous belts claim to have "equivalent capacity to roller chain drives in the same width". Both can be used to move objects by attaching pockets, buckets, or frames to them; chains are often used to move things vertically by holding them in frames, as in industrial toasters, while belts are good at moving things horizontally in the form of conveyor belts. It is not unusual for the systems to be used in combination; for example the rollers that drive conveyor belts are themselves often driven by drive chains.

Drive shafts

Drive shafts are another common method used to move mechanical power around that is sometimes evaluated in comparison to chain drive; in particular belt drive vs chain drive vs shaft drive is a key design decision for most motorcycles. Drive shafts tend to be tougher and more reliable than chain drive, but the bevel gears have far more friction than a chain. For this reason virtually all high-performance motorcycles use chain drive, with shaft-driven arrangements generally used for non-sporting machines. Toothed-belt drives are used for some (non-sporting) models.

Use in vehicles

Bicycles

Chain drive was the main feature which differentiated the safety bicycle introduced in 1885, with its two equal-sized wheels, from the direct-drive penny-farthing or "high wheeler" type of bicycle. The popularity of the chain-driven safety bicycle brought about the demise of the penny-farthing, and is still a basic feature of bicycle design today.

Automobiles

Many early cars used a chain drive system, which was a popular alternative to the Système Panhard (which used a rigid

Hotchkiss drive The Hotchkiss drive is a shaft drive form of power transmission. It was the dominant means for front-engine, rear-wheel drive layout cars in the 20th century. The name comes from the French automobile manufacturer Hotchkiss, although other maker ...

system with universal joints). A common design was using a differential located near the centre of the car, which then transferred drive to the rear

axle An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, beari ...

via roller chains. This system allowed for a relatively simple design which could accommodate the vertical axle movement associated with the rear suspension system. Chain drive also resulted in less unsprung mass at the rear wheels than the Hotchkiss drive (where the differential and half of the driveshaft contributes to the unsprung mass), resulting in greater effectiveness of the rear suspension and therefore a smoother ride. Frazer Nash were strong proponents of this system using one chain per gear selected by dog clutches. The Frazer Nash chain drive system, (designed for the GN Cyclecar Company by Archibald Frazer-Nash and Henry Ronald Godfrey) was very effective, allowing extremely fast gear selections. The Frazer Nash (or GN) transmission system provided the basis for many "special" racing cars of the 1920s and 1930s. The last popular chain drive automobile was the Honda S600 of the 1960s. Many modern

piston engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common fea ...

s use a roller chain (called a "timing chain") to drive the camshaft(s), replacing the previous designs of pushrods or toothed timing belts. For this application, chains last longer, but are often harder to replace, as they must be enclosed in a space into which lubricating oil can be introduced. The transfer case in a car or light truck is another application where chain drives are used.

Motorcycles

Chain drive versus belt drive or use of a driveshaft is a fundamental design decision in motorcycle design; nearly all motorcycles use one of these three designs.

References

Bibliography

* * Needham, Joseph (1986). ''Science and Civilization in China: Volume 4, Chemistry and Chemical Technology, Part 2, Mechanical Engineering''. Taipei: Caves Books Ltd. * Sclater, Neil. (2011). "Chain and belt devices and mechanisms." ''Mechanisms and Mechanical Devices Sourcebook.'' 5th ed. New York: McGraw Hill. pp. 262–277. . Drawings and designs of various drives.

External links

The Complete Guide to Chain

{{Authority control Mechanics Automotive transmission technologies Chinese inventions Mechanical power control Mechanical power transmission