A friction drive or friction engine is a type of

transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission ** ...

that utilises two

wheel A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be ...

s in the transmission to transfer power from the engine to the driving wheels. The system is naturally a

continuously variable transmission 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. ...

; by moving the two disks' positions, the output ratio changes continually. Although once used in early

automobiles A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded ...

, today the system is most commonly used on

scooters Scooter may refer to: Vehicles Ground Human or gravity powered * Eccentric-hub scooter, propelled by a standing rider making a bouncing motion * Kick scooter, propelled by a standing rider pushing off the ground * Knee scooter, a mobility dev ...

, mainly go-peds, in place of a chain and gear system. It is mechanically identical to a ball-and-disk integrator, but intended to handle higher

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

levels. The system consists of two disks, normally metal, set at right angles to each other. One disk is connected to the engine, the other to the load. The load disk is positioned so that its outer rim is pressed against the driven disk, and normally has some sort of high-friction surface applied to the outer rim to improve torque transfer. In early systems, paper and leather was often used for this surface. One of the disks, normally the load side, is mounted on a shaft that allows it to be moved in relation to the driven disk, allowing it to move from a position at the center of the driven disk to its outer radius. Moving the load disk along this shaft changes the ratio of input to output speed; when the load disk is at the center the output is zero, when it is at the outer rim, it is the ratio of the radius of the two disks. While mechanically simple and providing a variable transmission that requires no clutch, there are a number of problems with the design that limit its use. The first is that the amount of torque that can be transferred is a function of the

contact patch Contact patch is the portion of a vehicle's tire that is in actual contact with the road surface. It is commonly used in the discussion of pneumatic (i.e. pressurized) tires, where the term is used strictly to describe the portion of the tire’s ...

between the two disks, and thus a function of the width of the load disk. Increasing this width improves torque handling, but then runs into a second problem. As the "gear ratio" is a function of the distance from the center of the driven disk, any finite thickness on the driven disk means the inner and outer edges are being driven at different speeds. This causes considerable friction on the bearing surface, wearing it out and giving off significant amounts of heat. This results in a sweet spot that limits it to certain low-torque roles.

In phonographs

Friction drive has been most successfully used in low-power applications, such as driving

phonograph A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogu ...

turntables.

In automobiles

Lambert friction-gearing transmission patent 761384

Automobiles using this drive system included the Anglo-Dane, the Arista, the Armadale, the Astra, the Allvelo, the

Bukh & Gry The Bukh & Gry was a Danish automobile manufactured in 1904. Its creators, Jens Bukh and John Gry, had both worked in the American automotive industry; together they built only one car, manufactured at Horve and shown at the Tivoli Gardens in C ...

, the Cartercar, the Crown 12HP Model Two (1905-1906), the

Davis Totem The Davis Totem was an American automobile manufactured from 1921 until 1922. As many as ten were built; they boasted friction drive similar to that found in their contemporaries, the Kelsey and the Metz. The cars used four-cylinder Herschell-S ...

, the Kelsey, the Lambert, the LuLu, the

Metz Metz ( , , lat, Divodurum Mediomatricorum, then ) is a city in northeast France located at the confluence of the Moselle and the Seille rivers. Metz is the prefecture of the Moselle department and the seat of the parliament of the Grand ...

, the Ner-a Car, the

Richardson Richardson may refer to: People * Richardson (surname), an English and Scottish surname * Richardson Gang, a London crime gang in the 1960s * Richardson Dilworth, Mayor of Philadelphia (1956-1962) Places Australia * Richardson, Australian Capi ...

and the 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 Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hog ...

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 Plymouth Locomotive Works was a US builder of small railroad locomotives. All Plymouth locomotives were built in a plant in Plymouth, Ohio until 1997 when the company was purchased by Ohio Locomotive Crane and production moved to Bucyrus, Ohio ...

's first three models, the AL, BL and CL were equipped with a friction drive. Early models of the

permanent way A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleeper ...

maintenance ganger's

Wickham trolley The Wickham trolley was a railroad speeder, railway engineering personnel carrier built by D. Wickham & Co of Ware, Hertfordshire. This long established firm introduced their rail trolley in 1922 as a lightweight track inspection and maintenance ...

used a vee-twin

JAP ''Jap'' is an English abbreviation of the word "Japanese". Today, it is generally regarded as an ethnic slur. In the United States, some Japanese Americans have come to find the term very offensive, even when used as an abbreviation. Prior to t ...

engine. This drove through a large flat flywheel and a friction drive.

Belt drives

A belt drive is a form of friction drive but is usually categorized separately from the "disk and wheel" type of friction drive.

References

External links