New high-precision needle roller bearings reduce friction

The three new needle roller bearings, which were unveiled for the first time at the 2011 Hanover Fair, include:

• X-life machined needle roller bearing version D
• X-life machined needle roller bearing with TWin Cage
• Slimline drawn cup needle roller bearing with a radial section height of just 1.5mm

X-life machined needle roller bearings version D

The new X-life machined needle roller bearings version D benefit from a new profiled steel cage that is manufactured using a newly-developed, optimised forming technique. This new cage provides a significantly higher load carrying capacity and is designed so that the number of needle rollers and the length of needle rollers can be increased without altering the overall dimensions of the bearing. By using more rolling elements and by extending their load-bearing length, the new X-life needle roller bearings version D offers an increase in load ratings of up to 25 per cent.

For design engineers, this means that bearings installed in the same mounting space can be subjected to significantly higher loads without increasing the physical size of the bearings. Conversely, the new X-life needle roller bearings version D create new opportunities for designers to downsize bearings without compromising the bearing's performance.

For example, the new X-life NK20/16-D-XL needle roller bearing with a 20mm diameter bore and a 16mm width offers a higher load carrying capacity than the X-life NK26/16-XL needle roller bearing, which has a larger bore diameter of 26mm. If the new bearing is used for downsizing, the section height of the bearing can be reduced by 15 per cent, the weight by 20 per cent and friction by 30 per cent, while still providing the same load carrying capacity.

In addition to the new X-life NK20/16-D-XL needle roller bearing, Schaeffler's new range also includes the NK55/25-D-XL, as well as three additional sizes: NK14/16-D-XL, NK28/16-D-XL and NK37/20-D-XL. Together, these five bearing sizes offer numerous downsizing options for radial needle roller bearings (the enveloping circle diameter of the new bearings ranges from 14mm up to 70mm).

X-life needle roller bearing TWin Cage

The new machined needle roller bearings with TWin Cage are manufactured in plastic and provide higher efficiency as a result of lower friction. Rather than a single long length needle roller, this new bearing uses two short needle rollers that are inserted next to one another in a single cage pocket. This combination of cage and rolling elements - which is claimed to be unique - reduces friction by up to 25 per cent compared with conventional needle roller bearings.

For example, the power loss due to friction of an X-life NK45/20-TV-XL machined needle roller bearing with new TWin Cage operating at 4000rpm is 25W-30W less than a bearing with a conventional plastic cage. In addition, the new bearings operate with reduced heat generation, resulting in a longer grease operating life and, therefore, longer lubrication intervals. The accuracy of the application also improves due to reduced fluctuations in temperature.

There is also an improvement in bearing kinematics due to optimum load distribution on both rows of needle rollers. Tests at Schaeffler have shown that bearings with a TWin Cage benefit from a significantly increased operating life.

Slimline drawn cup bearings

The third innovation from Schaeffler is the slimline drawn cup needle roller bearing, which also makes a significant contribution towards lowering friction and improving energy efficiency. The radial section height of the new bearings is just 1.5mm, which is described as a radical reduction in terms of slimline drawn cup needle roller bearings. For a drawn cup needle roller bearings with diameters from 15-50mm, a section height of 1.5mm is the current limit in terms of how small the bearing and cage can be manufactured. Currently the smallest section height available from most other bearing suppliers is around 2.5mm.

By developing new manufacturing methods for the cage, Schaeffler has been able to produce bearings to extremely fine tolerances. This means the new slimline drawn cup needle roller bearings are equivalent to plain bearings in terms of their external dimensions, which makes them suitable for replacing plain bearings, particularly in automotive applications such as automatic transmission systems and gearboxes.

Other advantages of slimline drawn cup needle roller bearings are that they reduce friction by up to 60 per cent compared with conventional plain bearings. They also help to simplify any adjacent structures or components and increase the accuracy and reliability of the system.

Plain bearings in automatic transmissions must always receive a direct, adequate supply of oil from inside the transmission for the system to operate reliably. This requires significant machining time and costs, as the shaft has to be provided with horizontal and vertical holes for the oil feed. In contrast, with slimline drawn cup needle roller bearings, a fine oil mist is sufficient for reliable operation. Complex oil feed systems are no longer required, while any oil pumps within the system can be replaced with smaller units costing less.

For reliable operation, plain bearings also require a load-bearing lubricant film. The reduced frictional torque of a rolling bearing compared to a sliding lubricant film or layer results in reduced breakaway torque during start up. This means that slimline drawn cup needle roller bearings offer higher operational reliability; for example, in start-stop applications. In addition, the transmission oil will not be contaminated by fine wear debris from the sliding layer found in plain bearings. The oil therefore remains cleaner if slimline drawn cup needle roller bearings are used. At the same time, accuracy also increases because the bearing clearance on the shaft also increases due to abrasion or wear in the plain bearings. The high accuracy of a drawn cup needle roller bearing throughout its operating life contributes to reduced clearance of the gear teeth, which, in turn, increases the reliability and operating life of the transmission system.

For more information about Schaeffler's range of needle roller bearings, call the Marketing Department on +44 (0)121 313 5870 or email [email protected].