From Wikipedia, the free encyclopedia

A self-aligning roller thrust bearing

A thrust ball 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, 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 pressurised liquid- these give incredibly low drag.

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

Thrust bearings are necessary 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 neutralised 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).

• Ball bearing
• Slewing bearing

In 1905 the Australian engineer George Michell (pronounced Mitchell) who had improved the theory of lubrication, patented a new thrust bearing.