Modular bearing system for planetary wind turbine gearboxes

The new bearing assemblies offer standardisation of the bearings used in this application, a reduced diversity of parts and simplified logistics. The system is already in use in the 1.5, 2 and 2.5MW wind turbine gearboxes of a German gearbox manufacturer. Most wind turbines use gearboxes to transform the relatively low rotational speed of the main shaft into higher speeds required for power generation. Because the forces a modern wind turbine gearbox has to transmit are forever increasing while the gearbox itself has to remain compact, single or two tage planetary gearboxes are commonly used. According to NKE, the bearings of the planetary gears are among the highest loaded in this specific application. In modern gearboxes an integrated planetary bearing arrangement is used, in which cylindrical roller bearings without an outer ring are fitted in the planetary gears, with the bore of the gear forming the outer raceway. Each bearing set is packaged as a unit and is marked to prevent inadvertent swapping of matched components within each set. The modular concept is based on single row cylindrical roller bearings of the RN range, which do not have an outer ring. These bearings are equipped with a one piece solid brass cage, which is guided by the inner ring (MPB). This cage features inspection grooves for endoscopic inspection of the inner raceways as standard. These single row bearings can be assembled to sets of two, three or four bearings to conform with the individual load and design parameters of a specific gearbox. NKE supplies ready to install matched bearing sets. Each bearing set includes the components required to secure the bearings axially in the planetary gears – such as retaining rings and loose rib rings. If required, the overall width of each bearing set can be adapted to the operating conditions and the available space with spacer rings fitted between the individual bearings. Used consistently throughout the gearbox assembly, the modular concept allows the designs of planetary bearings to be simplified; the bearing design can be standardised for the first and second gear stage and across various gearbox sizes and the required number of bearing variants is reduced. NKE says that the modular design simplifies the adaptation of bearing set characteristics to the requirements of each gear stage, while the one piece solid brass cage provides rolling element guidance.