Feature 40 years of mechanical components
A design in development M
Whilst the basic design of a needle roller bearing hasn’t changed significantly over the last 40 years, continuous developments have resulted in new cage designs. Karen Preston, marketing services manager, Schaeffler (UK), looks into the benefits
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Needle roller bearings
ost design engineers are already familiar with the tech- nical advantages provided by a needle roller bearing – the ability to handle relatively high loads in a compact design envelope. Over the last 40 years, this technical advan- tage alone has made the needle roller bearing the preferred choice in many industrial and automotive power transmission applications.
What have changed significantly over the last four decades are the demands being placed by customers on bearing manufacturers. Specific applications now require higher precision, custom engineered bearings that can handle increased dynamic loads and harsher operating environments, and which can fit into ever-decreasing design envelopes. Many applications also require lower friction bearings that increase the energy efficiency of a machine or vehicle. Bearing manufacturers now also work more closely with customers, often collabo- rating much earlier in the design process.
A needle roller bearing is a component that uses small cylindrical rollers, which are used to reduce friction between moving surfaces. Compared to ball bearings, needle roller bearings have a large surface area that is in contact with the bearing raceway journals.
A needle roller bearing uses small cylindrical rollers, which are used to reduce friction between moving surfaces
It was the tendency for the early versions of INA (‘Industrie Nadellager’ or ‘Needle Bearing Factory’) needle roller bearings to lock and for the needles to skew, that led Dr Georg Schaeffler to invent the cage guided design back in 1949.
The typical structure of a needle roller bearing comprises an inner race (or sometimes just a shaft), a needle cage which orients and contains the needle rollers, the needle rollers themselves, and an outer raceway. Many different designs of needle roller bearing exist,
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 wide variety of cage materials being available, including steel, plastic (PA66) and aluminium. Multiple row bearing designs boost load carrying capacity. Caged needle roller bearings can be assembled in many varieties for the customer, including single split designs, half shell types, and single split with diagonal spring bar connections. Typical applications include gearboxes, automotive power transmission sys- tems, two and four stroke engines, plan- etary gear sets and air compressors.
Cage construction
Cages, whether steel or plastic, can now be made in a variety of different con- structions, including solid cage, single split and split halves (two-piece). These cages can also incorporate lubrication passages and other custom designed features depending on the application. Sixty years on, it is remarkable that the caged needle roller bearing is still being used in its original design today. However, the original design has not stood still over this period, but has been improved continuously and adapted to meet increasingly diverse demands. During the early years, INA’s develop- ment was closely linked with the automotive industry. Some of the first customers of the new technology were Mercedes Benz and Adler Motorcycles. Before long though, the caged needle roller bearing had become an essential component in many automotive and industrial plant and machinery designs.
Design Solutions 1971-2011 - 40TH ANNIVERSARY SUPPLEMENT -
In the late 1980s through to the early 1990s, cage design improvements were focused on thinner designs with reduced mass. Other improvements included new design features that helped to move the lubricant more effectively around the bearing, leading to improved oil flow. Originally, cages were designed simply to guide the rolling elements. However, more recently, needle roller bearings are being provided with much- 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 ele- ments and the raceway journals, creat- ing metal-to-metal contact conditions.
Automotive requirements Over the last decade, the automotive industry has come under increasing pressure to produce more fuel-efficient
vehicles with lower CO2 emissions – and this trend looks as if it will continue for the foreseeable future. One method of achieving this is to improve the fuel consumption of the vehicle by reducing friction across the complete drive train. This means reducing the weight of the overall vehicle by reducing the weight of individual components.
The INA caged needle roller bearing has made a significant contribution to the development of smaller, more efficient and cost effective vehicles. 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.
For this particular application, the company has developed a special design of cage for the needle roller bearing which improves the lubrication flow characteristics. This results in a lower friction design of bearing, which enables the customer’s planetary gear set for the electric differentials to be reduced in size, weighing 17% less than the original system. The bearings, in combination with optimised oil flow through the carrier, enable 20% higher running speeds (up to 8000rpm). The cage was custom designed for the application. Due to a restricted design envelope, the cage needed to be smaller to accommodate the shaft, and the hous- ing bore of the gear was finished to sup- port a bearing raceway. If not, an outer or inner ring would have been required.
Schaeffler T: 0121 313 5870
www.schaeffler.co.uk S25 Enter 265
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