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Worm-and-gear sets are a simple and compact way to achieve a high torque, low speed gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm-and-gear sets vary from 10:1 to 500:1. [45] A disadvantage is the potential for considerable sliding action, leading to low efficiency. [46]
Two meshed spur gears, with a 2:1 ratio. The simplest example of a gear train has two gears. The input gear (also known as the drive gear or driver) transmits power to the output gear (also known as the driven gear). The input gear will typically be connected to a power source, such as a motor or engine.
A crossed helical gear is a gear that operate on non-intersecting, non-parallel axes. The term crossed helical gears has superseded the term spiral gears. There is theoretically point contact between the teeth at any instant. They have teeth of the same or different helix angles, of the same or opposite hand.
Transmission internals for a 2009 Volkswagen Golf. A transmission (also called a gearbox) is a mechanical device which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication/reduction in a machine.
Some important features of gears and gear trains are: The ratio of the pitch circles of mating gears defines the speed ratio and the mechanical advantage of the gear set. A planetary gear train provides high gear reduction in a compact package. It is possible to design gear teeth for gears that are non-circular, yet still transmit torque smoothly.
For examples, see the following articles on: Bevel gears are used in differential drives, which can transmit power to two axles spinning at different speeds, such as those on a cornering automobile. Bevel gears are used as the main mechanism for a hand drill. As the handle of the drill is turned in a vertical direction, the bevel gears change ...
The most common examples are adding machines and mechanical counters, which use the turning of gears to increment output displays. More complex examples could carry out multiplication and division—Friden used a moving head which paused at each column—and even differential analysis.
A rack and pinion has roughly the same purpose as a worm gear with a rack replacing the gear, in that both convert torque to linear force. However the rack and pinion generally provides higher linear speed — since a full turn of the pinion displaces the rack by an amount equal to the pinion's pitch circle whereas a full rotation of the worm screw only displaces the rack by one tooth width.