Thrust bearing

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A self-aligning roller thrust bearing

A thrust ball bearing

A fluid film thrust bearing

A thrust bearing is a particular type of rotary bearing. Like other rotary bearings they permit rotation between parts, but they are designed to support a high axial load while doing this.

Thrust bearings come in several varieties.

Ball thrust bearings, comprised of ball bearings supported in a ring, can be used in low thrust applications where there is little radial load.
Tapered roller bearings consist of small tapered rollers arranged so that their axes all converge at a point on the axis of the bearing. The length of the roller and the diameter of the wide and the narrow ends need to be carefully calculated to provide the correct taper so that each end of the roller rolls smoothly on the bearing face without skidding. These are the type most commonly used in automotive applications (to support the wheels of a motor car for example), where they are used in pairs to accommodate axial thrust in either direction, as well as radial loads. They can support rather larger thrust loads than the ball type due to the larger contact area, but are more expensive to manufacture.
Fluid bearings where the axial thrust is supported on a thin layer of pressurized liquid - these give incredibly low drag.

They are commonly used in automotive, marine, and aerospace applications.

Thrust bearings are used in cars because the forward gears in modern car gearboxes use helical gears which, while aiding in smoothness and noise reduction, cause axial forces that need to be dealt with. André Citroën invented a double helical gear which neutralized the thrust caused by normal helical gears.

One specific thrust bearing in an automobile is the clutch 'throw out' bearing, sometimes called the clutch release bearing.

Fluid-film thrust bearings were invented by Australian engineer George Michell (pronounced Mitchell) who patented his invention in 1905. Michell bearings contain a number of sector-shaped pads, arranged in a circle around the shaft, and which are free to pivot. These create wedge-shaped regions of oil inside the bearing between the pads and a rotating disk, which support the applied thrust and eliminate metal-on-metal contact.

The small size (one-tenth the size of old bearing designs), low friction and long life of Michell's invention made possible the development of larger propellers and engines in ships. They were used extensively in ships built during World War I, and have become the standard bearing used on turbine shafts in ships and power plants worldwide.