tannhjul

Tannhjul, commonly called a gear, is a wheel with teeth around its rim that mesh with another gear to transmit torque and rotation between shafts. Gears enable changes in speed, torque, and the direction of rotation in mechanical systems.

Gear pairs achieve a ratio equal to the number of teeth on the driven gear divided by the number of teeth on the driving gear. This ratio, together with center distance and tooth size (module or pitch), governs speed and torque in the arrangement.

Common types include spur gears with straight teeth for simple, high-efficiency transmission; helical gears with angled teeth for smoother operation and greater load capacity; bevel gears for motion between intersecting shafts; and worm gears that produce large reductions in compact space. Internal gears are used in planetary trains to gain compact, efficient multi-speed arrangements.

Materials include steel, cast iron, bronze, and engineering plastics. Manufacturing methods include hobbing, shaping, broaching, and milling, often finished by grinding or lapping to achieve tight tolerances. Standards such as ISO or AGMA specify geometry, tolerances, and gear quality, as well as lubrication and reliability requirements for different applications.

Applications span automotive transmissions, industrial machinery, robotics, wind turbines, clocks, and consumer appliances. Gears are frequently combined in gear trains to achieve complex speed and torque profiles while optimizing efficiency and space.

Historically, gears have played a central role in mechanical engineering, with early uses in clocks and machinery. The Antikythera mechanism and later medieval and industrial gear systems illustrate the long development of gear technology and its impact on technology.