hub

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Wheel hub unit of a motor vehicle

A hub is a machine element that is pushed onto a shaft , an axis or a journal . It usually consists of a drilled workpiece into which, depending on the application, a bearing , a driver element ( feather key , wedge , interference fit , shrink disk or clamping set ) is embedded or is permanently connected to the associated shaft or axis or the associated journal via an interference fit . The hub is often part of a shaft-hub connection .

In the case of a wheel (for example on a bicycle or motor vehicle) the wheel hub is the center of the wheel. It rotates around the axis that connects it to two bearings .

Materials, built-in functions

Historically, wheel hubs were made of wood with iron-tyred wooden spoke wheels and were held together by two iron tires, could have pressed in a plain bearing bush and were greased and placed on the slightly conical and slightly downwardly inclined axle stubs of a multi-track vehicle with which they formed a plain bearing. The wheel block and impeller - because they are single-track - have, however, a horizontal, pushed-through axle. Modern horse-drawn carriages already have roller bearings on wooden spoke wheels.

While axles, even in light vehicles, are mostly made of steel, possibly hollow bored, hubs are often made of lighter aluminum, but typically hold two steel roller bearings. Wheel hubs can accommodate drum brakes and, in the case of bicycles, manual transmissions ( hub gears ) or have band or disc brakes and several pinions attached to form a derailleur . Wheel hubs on strollers have locking slots to prevent them from rolling away, while vehicle hubs often have a step indicator disc plus a sensor attached to serve as a rotary encoder for the speedometer and anti-lock braking system . Non-shiftable planetary gears in the wheel hubs of trucks and construction machinery allow lower torques in the drive train.

The first electric four-wheel vehicles were equipped with wheel hub motors around 1890; since around 2000, these have been common in electric bicycles and widespread in electric and hybrid vehicles. Internal combustion engines in wheel hubs are just a historical curiosity from around 1920–1950 in motorcycles. Working machines with crawler tracks usually have hydraulic motors installed as drives.

Hubless wheels

With smaller, simpler, more primitive wheels, the hub can gradually disappear until only one hole remains in the roller or wheel disc.

Wheels can also be designed without a hub. As a ball, cylindrical disc without drilled holes, uniform thickness or ring. In any case, a suitable guide acting at several points from the outside, in the case of the ring, alternatively also from the inside, is necessary. With a triple inside out sufficiently large ring a can -wheel design, which takes its passengers, including seat and drive - include in the wheel center, focusing the inner part typically lower than the geometric center of the wheel should be - by muscle or motor.

There is a person in the gym wheel . Hubless rolling rings around each foot form a kind of transverse roller skates . The Ultimate Wheel is a unicycle without a bearing on its axis of rotation.

literature

  • FG Kollmann: Shaft-hub connections . Springer Verlag Berlin Heidelberg, Berlin 1984.
  • G. Niemann, H. Winter, Bernd-Robert Höhn: Machine elements . Volume 1, 3rd edition, Springer Verlag Berlin Heidelberg, Berlin 2001, ISBN 978-3-662-08521-9 .

See also