A needle roller bearing is a bearing which uses small cylindrical rollers. They are used to reduce friction of a rotating surface.
Needle bearings have a large surface area that is in contact with the bearing outer surfaces compared to ball bearings. Additionally there is less added clearance so they are much more compact. The typical structure consists of an a needle cage which orients and contains the needle rollers, the needle rollers themselves, and an outer race(sometimes housing itself).
Radial needle bearings are cylindrical and use rollers parallel to the axis of the shaft. Thrust needle bearings are flat and use a radial pattern of needles.
Full compliment bearings have solid inner and outer rings and rib-guided cylindrical rollers. Since these bearings have the largest possible number of rolling elements, they have extremely high radial load carrying capacity and are suitable for particularly compact designs.
Needle bearings are heavily used in engine components such as rocker arm pivots, pumps,compressors, and transmissions. The dreive shafe of a rear-wheel drive vehicle typically has at least 8 needle bearings and often more if it is particularly long, or operates on steep slopes
Additional clarification of Needle Roller: According to "Marks' Standard Handbook for Mechanical Engineers", a Needle Bearing is a roller bearing with rollers whose length are at least four times their diameter.
Needle bearing characteristics and uses:
With thin and long needle bearing roller (roller diameter, length 3 to 10 times the diameter of generally not more than 5mm), so the radial structure is compact, its diameter size and load bearing capacity and other types of the same, minimum diameter, especially for radial bearing installation dimensions restricted results. Depending on different occasions, can be used without inner ring of the bearing or needle roller and cage assemblies, this time with the match of the journal bearing surface and shell holes as bearing directly on the surface, the outer rolling surface, in order to ensure the load capacity and operating performance and have the same ring bearing, shaft or housing bore raceway surface hardness, machining accuracy and surface quality should be similar to the roller bearing rings. Such bearings can only bear the radial load.
