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Schaeffler explains why needle roller bearings with new cage designs provide a long service life and high static load ratings.

Most design engineers will already be familiar with the technical advantages provided by a needle roller bearing – the ability to handle relatively high loads in a compact design envelope.

This technical advantage has made the needle roller bearing the preferred choice of bearing in a variety of industrial and automotive power-transmission applications over the years.

Needle roller bearings that use small cylindrical rollers are used to reduce friction of a rotating surface.

Compared to ball bearings, needle roller bearings have a large surface area that is in contact with the bearing raceway journals.

The typical structure of a needle roller bearing comprises an inner race (or sometimes just a shaft), a needle cage that orients and contains the needle rollers, the needle rollers themselves and an outer raceway.

There are many different designs of needle roller bearing, including drawn cup, precision race, caged roller and thrust roller.

The function of a caged needle roller bearing is to support radial loads and rotational speeds.

Here, a cage guides and retains the rollers.

Caged designs normally come in single- and double-row designs, with a variety of cage materials being available, including steel, plastic (PA66) and aluminium.

Multiple row bearing designs boost load-carrying capacity.

Cages, whether steel or plastic, can be made in a variety of different constructions, including solid cage, single split and split halves (two-piece).

These cages can also incorporate lubrication passages and other custom-designed features.

Typical applications for caged needle roller bearings are gearboxes, automotive power-transmission systems, two- and four-stroke engines, planetary gear sets and air compressors.

Regardless of which type of the four main types of needle roller bearing is selected for an application, engineers should consider a variety of factors before making their decision as early in the design phase as possible: the size/design envelope, type of load, load capacity, speed, temperature, misalignment, housing and shaft specifications, service life and lubrication requirements.

The caged needle roller bearing has made a significant contribution to the development of smaller, more efficient and cost effective vehicles.

Today, INA needle roller bearings are manufactured in more than 15,000 variants, with new designs customised to meet the special requirements of customer applications.

Machined INA needle roller bearings form the core of the range, particularly with the recent introduction of Schaeffler’s X-life premium quality standard.

Needle roller bearings produced to X-life quality now offer a 13 per cent increase in dynamic load rating compared to conventional bearings, which corresponds to a 50 per cent increase in service life.

For the customer, these improvements mean less lubricant stress, reduced friction and lower bearing temperatures, which in turn results in a more energy-efficient bearing.

The increase in performance capacity enables the bearing to be downsized for the application, with corresponding reductions in the weight of the bearing and its space requirements.

In the unlikely event that application requirements exceed even X-life bearings, further technical performance improvements can be gained through the use of new bearing coatings and materials.

One project currently being undertaken at Schaeffler’s Automotive Division involves the redesign of a high-speed planetary gear set for an automatic gearbox transmission on a new hybrid-electric passenger vehicle.

A special design of cage for the needle roller bearing and features that improve the bearing’s lubrication flow characteristics have resulted in a lower-friction design of bearing, which has enabled the customer’s planetary gear set for the electric differentials to be reduced in size, weighing 17 per cent less than the original system.

The bearings, in combination with optimised oil flow through the carrier, have enabled 20 per cent higher running speeds (up to 8,000rpm).

Caged needle roller bearings can be assembled in many varieties for the customer.

These include single split designs, half shell types, and single split with diagonal spring bar connections.

New needle roller bearings are being provided with improved cage designs, including, for example, special precessed cages.

Precession not only helps spread wear among all the rollers, but also distributes lubricant around the bearing.

’False brinelling’ is a typical failure mode for caged needle roller bearings, particularly in power transmission applications.

These failure modes are commonly caused by micro vibration and movements between the rolling elements and the raceway journals, creating metal-to-metal contact conditions.

The result of improvements such as those outlined has led to the latest bearing caged roller designs being able to offer up to 25 per cent higher static load capacities for a similar size bearing, which equates to more than double the dynamic load rating.

For applications with multiple small movements, bearing life typically increases from three to five times.

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