Technology news: October 2010
Hollow rollers help prevent bearing slippage
Schaeffler has developed a novel rolling bearing for wind turbine gearboxes, which not only resists the effects of slippage, but prevents slippage from occurring in the first place. Instead of conventional rolling elements, the bearing incorporates three tube rollers, allowing it to rotate without slippage under all load conditions without affecting its load rating or life.
Slippage is the natural enemy of all rolling bearings. The life and performance of a rolling bearing will suffer if it is overloaded or under-loaded. This is because rolling bearings need a minimum load to function optimally. If this is not met, slippage occurs and the rolling elements not only rotate, but also slide on the bearing raceways. Eventually, this can lead to surface damage.
In wind turbines, the rolling bearings need to withstand extremely low and high loads during calm or strong wind conditions. The risk of damage to a bearing increases significantly when the rollers in a bearing with high slippage are suddenly subjected to extremely high acceleration forces.
The tube roller bearing (shown above) is a cylindrical roller bearing that incorporates three hollow cylindrical rollers with a slightly larger diameter than the others. These rollers are supported by a roller in the inner bore. They generate preload in the bearing and drive the bearing cage (and therefore the entire roller set) at low loads.
At higher loads, the rollers’ bore ensures sufficient deflection of the larger rollers to avoid overloading. This means that the load is distributed evenly across all the rolling elements, as in a conventional rolling bearing.
The support roller in the inner bore has a slight clearance to ensure that the roller is more flexible at higher loads. At the same time, this also prevents the tube roller from deflecting excessively. Together, the tube roller and support roller provide increased fatigue strength to the bearing, resulting in a rigid rolling element that withstands peak load conditions.
Initial prototypes of the novel bearing have been manufactured and tested, and pilot applications in wind turbine gearboxes are planned for the end of 2010.