There has been a trend in the design of wind turbine gearboxes toward using integrated planet bearings with both Cylindrical Roller Bearings (CRBs) and Tapered Roller Bearings (TRBs). The integrated bearing concept reduces the total number of components in the assembly by directly machining bearing races into the surrounding components of the gearbox.
Most commonly used is the semi-integrated design, which eliminates the separate bearing outer race by building the bearing race into the inner bore of the planet gear. This technique presents a number of advantages including:
- Greater gearbox power density stemming from increasing load capacity;
- Reduction in total gearbox mass, as well as;
- Elimination of any fretting in the integrated component and the;
- Potential of improved load sharing among the planets.
There are hurdles to adopting this technology for gear manufacturers. The gears must use bearing quality steel and involve more complex manufacturing processes. In addition, there are several commercially available gearboxes using a “fully-integrated” planet bearing design, where the outer race is integrated into the gear bore and the inner race is integrated into the planet shaft pin. These advances are driving improved gearbox reliability in the wind industry, and are being introduced as upgraded retrofits for some older gearbox models.