Uncontrollable and highly variable wind forces adversely affect the performance and reliability of planetary gears inside wind-turbine power transmissions. A couple developments from The Timken Co., Canton, Ohio, can lower maintenance on rolling elements and carry greater load in a planetary gearset. In the first, the Integrated Flexpin Bearing (IFB) equalizes gear loads, reduces internal stresses and significantly extends wind turbine reliability. One wind turbine gearbox in Scotland’s Orkney Islands, for instance, uses IFB units and has been operating for four years. The company says it has demonstrated a more than fourfold increase in the accumulated service life compared to what previous designs could deliver. “The condition of the gears and bearings is like the day they were installed,” says Timken chief technologist Gerald Fox. The IFB can be used in open planetary gear sets and consists of a double-cantilevered pin supporting the bearing and gear. The cantilevered pin attaches to a single carrier wall, and a cantilevered sleeve mounts to the free end of the pin. Gears and bearings mount on the sleeve.
The integrated bearing and gear construction is simplified to provide more space for bearing rolling elements to maximize the power rating of the bearing system. For max durability, coatings may be applied to the rolling and sliding surfaces, making this design the most power dense in the industry, according to the company. The result: More evenly distributed torque among multiple planet gears and longer gear and bearing life. In addition, combining shafts, bearings, and gears in one unit, the design also cuts weight and lowers cost. When compared with an equivalent sized, conventional open planetary gear system, the highly engineered IFB can transfer greater power and maintain its reliability. “This solution creates new and substantial opportunities for wind-energy machine designers to either downsize systems or upgrade the rated horsepower of their existing machinery,” says Fox.
The company has developed the technology so it can also work in closed-carrier planetary drive systems. Using two opposing arrays of IFBs mounted on a double-wall planetary carrier, there is potential to increase the torque density available today in this type of drive by as much as 50%. This patented innovation, called Integrated Flex Drive, lets a closed-carrier system gear-box designer reduce the size and mass atop turbine towers, one way to create higher-capacity, lighter-weight wind turbines. “In addition to increasing torque density, these systems can reduce gear loads and reduce the need for gear profile and lead correction. These improvements can reduce the costs of generating electricity from wind,” adds Fox.