differential gear(redirected from Differential (mechanical device))
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a device that produces a resultant motion as the sum or difference of the component motions. In a differential gear with, one degree of freedom, the component motions are connected kinematically and are produced by a single drive; the resultant is produced as the difference of these motions. Differential gears with one degree of freedom are used for producing small, precise movements or great forces (for example, in instruments and metal-cutting lathes).
In differential gears with two or more degrees of freedom, the component motions are independent and each is performed by its own component element. There are a number of different types of such differential gears, but the most widely used is the differential gear with bevel gears (usually called simply a differential), which is used in motor vehicles and other transportation machines and in mechanical drives.
The relation between the effective velocities of the component elements of the differential gear is expressed by the formula ω1 + ω2 = 2ω or n1 + n2- 2nr, where ω1, ω2, and ωr and n1, n2nr are, respectively, the rates of angular motion and the frequencies of rotation of the central wheels and the carrier. In a speed regulator of the closed type, the differential gear permits broadening of the control range and makes possible reverse rotation of the driveshaft. In metal-cutting lathes the differential gear is used for simplifying tooling and reducing the number of change gears required. Differential gears are used in computers to perform the mathematical operation of parameter addition.
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