Hypoïde

Hypoïde is a term used in mechanical engineering to describe a gear arrangement in which the axes of the mating gears are offset and do not intersect. In a typical hypoïde gear pair, a spiral bevel pinion engages a spiral bevel gear, with the centers displaced along a line parallel to the gear faces. The offset allows the pinion to be located below or above the ring gear’s centerline, enabling a compact layout and better clearance in certain vehicle configurations.

Advantages of hypoïde gears include the ability to achieve larger reduction ratios within a compact envelope and smooth torque transmission due to continuous tooth contact. They are widely used in automotive differentials and in some industrial gearboxes, where high torque capacity and favorable meshing characteristics are important. The offset geometry also permits a lower driveshaft position, which can improve vehicle design and packaging.

Manufacturing and maintenance aspects: Hypoïde gears require precise manufacturing and finishing processes appropriate for non-intersecting axes and spiral tooth forms, such as specialized cutting and grinding techniques. Proper lubrication is essential to manage sliding between mating surfaces, reduce wear, and control heat generation. The geometry inherently introduces some sliding contact, so alignment and lubrication quality strongly influence noise and longevity.

Etymology and usage: The term derives from hypo- meaning under and -oid meaning resembling, reflecting the offset arrangement of the axes. In English, the term hypoid gear is commonly used; in French, it is often rendered as engrenage hypoïde.

See also: bevel gears, spiral bevel gears, hypoid gear, differential.