Research On Gear Modification Of High-Power Speed Increasing Gearboxes For Wind Turbines

A new methodology for gear modification of high-power speed increasing gearboxes for wind turbine is presented. This research is supported by the National High Technology Research and Development Program of China (863 program) under Grant No. 2006AA04Z101.Firstly, the mathematics model of modified helical gear is established. The unified expression of the modification surface equation on action plane is built according to the geometric definition of modification parameters, the tangent-polar coordinate equation of gear tooth is put forward with involute generation line roll angle and cross-section twist angle as surface parameters and the meshing equation of modified tooth flank is built based on the continuous tangent contact condition. These mentioned above are the theory foundation of the following geometric model and finite element model of modificated gears.Secondly, the flexibility matrix of gearbox is generated by advantage of finite element rigid coupling method in order to calculate the deformation of gearbox housing and the deformation of rolling bearings is calculated by Hertz law. The information structure model of helical gear finite element analysis based on SQL Server data base is put forward. The parameterized modeling program for tooth contact finite element analysis is developed. The original spur gear finite element model is established by APDL, then, node and element is input in to SQL Server data base. The rotation transformation of node coordinates is made and the elements are built according to the correlation of original node and element in order to create quickly helical gear finite element model. A hierarchical subdivision algorithm is developed for mesh refinement of tooth contact zone instead of entire tooth flank. So, the number of nodes is reduced significantly. Accordingly, computation efficiency and computation precision is increased.Then, the tooth flank is discreted to a set of points which are called reference points, and the tooth contact is replaced by the contact of these point pairs on the gears. The digitized surface to surface contact analysis model is established based on the deformation compatibility condition of teeth meshing and force equilibrium relationship. The optimum design model is put forward based on the considerations in the whole deformation of gearbox. In which, the modification parameters are regarded as design variables and Avoiding dynamic impact and geometric interference at both mesh-in position and mesh-out position as well as axial uniformly distributed load is regarded as goal function. The deformation including gearbox housing, rolling bearing, shaft and gear body is maped to the contact points on tooth flanks and the normal deformation of the contact points is fited by cubic spline. The gear is modified based on the thought of reverse deformation to determine the modification parameters by analyzing the tooth contact zone and von Mises stress etc.Finally, an example of a Speed Increasing Gearboxes for Wind Turbines is presented to demonstrate the influences of the gear's modification parameters on meshing characteristics so as to determine the optimum modification parameters. Furthermore, the speed Increasing Gearbox's vibration signal under four work conditions is measured by DP1500 type vibration signal collector at a 1.5MW gear test rig. It is demonstrated that the amplitude of vibration under design work condition at gear meshing frequency is minimum. It proves that the modification parameters determined is correct and the theory and method proposed is available.