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{{short description|Mechanical power transmission by friction between components}}
{{refimprove|date=December 2013}}
[[File:1906 Lambert 2-cylinder chassis.png|thumb|right|A [[Lambert (automobile)|Lambert automobile]] from 1906 with the friction drive revealed.]]

A '''friction drive ''' or '''friction engine''' is a type of [[Transmission (mechanics)|transmission]] that utilises two [[wheel]]s in the transmission to transfer power to the driving wheels rather than a [[chain]] and sprockets system. This kind of transmission is often used on [[scooter (motorcycle)|scooters]], mainly go-peds, in place of a chain.
The problem with this type of drive system is they are not very efficient, since the output wheel (leather covered wheel) has width, the area of contact is spread across various radii on the primary disc. Because the tangential velocity varies as radius varies, the system must overcome velocity differentials across the surface. The compromise is slippage of the leather to metal contact area which creates friction, which in turn converts much of the energy transfer of this system into heat. Heat generation also requires a cooling system to keep the transmission working effectively.

==In phonographs==
Friction drive has been most successfully used in low-power applications, such as driving [[phonograph]] turntables.

==In automobiles==
[[File:Lambert friction-gearing transmission patent 761384.png|thumb|Lambert friction drive transmission. patent 761384]]
Automobiles using this drive system included the [[Anglo-Dane]], the [[Arista (1912 automobile)|Arista]], the [[Armadale (automobile)|Armadale]], the [[Astra (1922 automobile)|Astra]], the [[Allvelo]], the [[Bukh & Gry]], the [[Cartercar]], the [[Crown (automobile)|Crown]] 12HP Model Two (1905-1906), the [[Davis Totem]], the [[Kelsey (automobile company)|Kelsey]], the [[Lambert (automobile)|Lambert]], the [[LuLu]], the [[Metz Company|Metz]], the [[Ner-a Car]], the [[Richardson (1919 cyclecar)|Richardson]] and the [[Turicum (automobile)|Turicum]]. The Turicum's friction drive consisted of a flat steel disk coupled directly to the engine. This primary disk subsequently drove a smaller [[leather]] covered wheel oriented normal to its surface. Assuming a constant rotational velocity on the primary wheel, the angular velocity on the disk's surface will increase proportionally to the distance from the center of rotation. Therefore, positioning the smaller wheel at different points along the larger wheel's surface varies the [[gear ratio]]. Furthermore, since there are no limitations beyond the minimum and maximum positions, the gear ratios are infinitely adjustable. The Lambert's friction drive (illustrated) was similar but used an aluminium-faced driving disk and a fiber-faced driven wheel.

==In railway locomotives==
[[Plymouth Locomotive Works]]'s first three models, the AL, BL and CL were equipped with a friction drive.<ref>Floyd B. Carter, Locomotive, {{US patent|1283665}}, Granted Nov. 5, 1918.</ref><ref>Chas. A. Trask, Tractor Friction Transmissions, [https://books.google.com/books?id=QWnmAAAAMAAJ&pg=PP446 Journal of the Society of Automotive Engineers], Vol. II, No. 6 (June 1918); page 440. Page 444 discusses the Plymouth locomotive, with a drawing and photograph on page 445.</ref>

Early models of the [[permanent way]] maintenance ganger's [[Wickham trolley]] used a vee-twin [[JA Prestwich Industries|JAP]] engine. This drove through a large flat flywheel and a friction drive.<ref>{{Cite web
|title=Wickham Motor Trolley
|date=April 5, 2013
|publisher=[[South Devon Railway (heritage railway)|South Devon Railway]]
|url=http://www.southdevonrailwayassociation.org/Wickham.html
}}</ref>

==Belt drives==
{{main|Belt (mechanical)}}
A belt drive is a form of friction drive but is usually categorized separately from the "disk and wheel" type of friction drive.

==See also==
* {{annotated link|Contact mechanics}}
* {{annotated link|Frictional contact mechanics}}
* {{annotated link|Adhesion railway}}
* {{annotated link|Rolling (metalworking)}}
* {{annotated link|Continuously variable transmission#Toroidal or roller-based CVT (Extroid CVT)|Toroidal or roller-based CVT (Extroid CVT)}}
* {{annotated link|Tribology}}

==References==
{{Commons category|Friction drive}}
{{Reflist}}

== External links ==
* [http://static.howstuffworks.com/gif/cvt-17.gif Animated image of a toroidal CVT on HowStuffWorks]

{{Powertrain}}

[[Category:Automotive transmission technologies]]
[[Category:Continuously variable transmissions]]

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