Quasi-Exact-Constraint Design of Wind Turbine Gearing

In the past two decades the wind turbine industry has witnessed a considerable number of catastrophic accidents, many of which were due to gearbox failure. Ever increasing power ratings at decreased rotor speeds result in rotor torques of some million Nm. This imposes tooth loads and planet/pinion bearing loads on the order of a hundred tons within the first step-up stage. Such heavily loaded gearboxes, correctly (or rather innocently) designed according to the relevant codes, can be self-destructive. Due consideration should be given to the elastic environment in which the gears exist. Otherwise, appreciable, unsymmetrical/unequal elastic deformations in unwanted directions lead to gear tooth edge loading, in addition to overloading the bearing(s) near that edge. Designers of wind turbine gearing have in recent years identified several concepts and measures to be taken for counteracting the asymmetry of elastic deformations or mitigating their effects. In addition to giving a brief survey of such new design concepts, this paper suggests the use of selected types of curved-tooth cylindrical gears (so-called C-gears), primarily for their self-aligning capability; they allow four degrees of freedom (4-DOF), in contrast to the 3-DOF spur and helical gears and the 2-DOF double-helical gears. In addition, these gears offer a unique set of further advantages. When used in at least the most heavily loaded, first step-up stage, the design will be rendered quasi-exactly constrained; largely tolerant of misalignment due to elastic deformations, and the gearbox reliability should be improved, by design.