Friction Gears

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Library > Science > Science and Technology Dictionary friction gear (′frik·shən ′gir) (mechanical engineering) Gearing in which motion is transmitted through friction between two surfaces in rolling contact.

The term "friction gears" is an oxymoron. Toothed gears are used to provide a continuous positive transfer of motion from one shaft to another with a minimum of frictional losses.

So called "friction gears" are used to transmit motion from one shaft to another by the use of rubber rimmed wheels rolling against a flat steel wheel for a variable speed drive or the rim of a steel wheel for a constant speed drive.

There are or have been variable speed transmission using tapered steel cones rolling inside steel rings conveying motion to a third steel roller. Speed range was limited, and the drive was oil filled to prevent galling of the steel components rolling under pressure to transmit motion from input to output.

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I made years ago such a speed variator in a planetary design. It worked fine but the request was as well a good choice of the oil as a very precise machining of the rolling/sliding surfaces. The principle was based on a multi-discs combination with a spring preload. The risk was an over load with sliding which could totally destroy the contact surfaces.