The rotor shaft bearings are of critical importance in wind turbines. The locating bearing is subject to very high axial loads. With this in mind, Schaeffler has optimised its tried and tested standard spherical roller bearings in order to meet the specific requirements of wind turbines. In addition, Schaeffler has developed an asymmetrical bearing design.
With regard to micro-geometry, developers have improved the surfaces in order to reduce friction and thus the application of energy and wear. In addition, they have adjusted osculation to transmit rolling element normal forces across a large surface, reducing contact pressure. The rolling elements have also been specially profiled.
Adjustments in macro-geometry primarily comprise two aspects. First, the engineers have reduced the internal bearing clearance, which has improved the operating clearance. This has also reduced the rolling bearing forces and the axial sliding of the drive train. Second, they have used a firm centre rib for the locating bearings of the wind turbine rotor and increased axial rigidity, which reduced the axial displacement of the drive train. In addition, the firm centre rib helps to distribute the contact pressures along the rollers.
With these two measures, it has been possible to increase the robustness of the bearings against wear, which is caused by axial displacement. As part of validation, the bearings were subjected to comprehensive testing and granted Schaeffler’s “X-life” seal of approval. The necessary validation steps have been certified by Germanischer Lloyd (certificate GL-CER-002-2015).
The asymmetrical bearing design represents yet another major step forward. This design significantly increases the axial load-carrying capacity and therefore the service life of the main bearings in wind turbines. It allows a greater contact angle on the row of rollers supporting the axial load and a flatter contact angle on the row of rollers that primarily support radial loads. This results in better load distribution, reduced contact pressures and a significant reduction of the axial sliding distance.
Go to www.schaeffler.co.uk for more information about the company’s bearings for wind turbines.