Mechanical Performance Analysis And Structural Optimization Design Of Yaw And Pitch Bearing

The large-scale four-point contact ball bearing is usually used as the yaw and pitch bearing, which are mainly loaded with axial force, radial force and turnover moment, in a wind turbine. The traditional analysis method of rolling element bearing is not useful for the four-point contact ball bearing any more because the bearing is with different structure and low stiffness. So it is necessary to develop a new method for analyzing the mechanical performances of a four-point contact ball bearing. In this study, the mechanical performances analysis and structural optimization design of a yaw and pitch bearing are accomplished based on the new mathematical model developed in this paper. Then, the model and results are verified by the finite element method.First, the characteristics of yaw and pitch bearing, such as the working environment, load, structure, are analyzed. The nonlinear relationship between the Hertz contact stress and deformation of a rolling bearing is introduced. The calculation method for the contact load and contact stiffness of the yaw and pitch bearing is given. And calculation theories of the static and fatigue strengths are introduced.Second, according to the working conditions, geometry structure characteristics and deformation compatibility relation of yaw and pitch bearing, a mathematical model considering all kinds of factors, such as the actual contact angle, play and groove curvature coefficients, is developed. And the detail process to solve the mathematical model using the Newton-Raphson iterative method is given. Taking one kind of four-point contact ball bearing as an example, the load distribution and the actual contact angle are researched under the different working conditions.Then, the maximal contact forces calculated by the mathematical model are compared with those gotten by the empirical formula. The validity of the mathematical model for calculating the maximal contact force and static strength is verified. The load curve and surface are drawn exactly based on the mathematical model of four-point contact ball bearing.After that, the influence of the structure parameters (groove row distances, play, contact angle, groove curvature coefficients, diameter and number of roller, etc) on the mechanical performances (contact load, contact stress, actual contact angle, number of loaded rollers, etc) is analyzed. The optimization model of four-point contact ball bearing is established taking the minimum contact stress as an objective. The optimized values of key structural parameters are obtained by the optimization model adopting genetic algorithm.Finally, using the finite element method, load and actual contact angle distributions when the finite model is with support structure or no support structure are analyzed, respectively. The results gotten by the finite element method are compared with those calculated by the mathematical model developed in this paper. The validity of the mathematical model for analyzing the mechanical performances of a four-contact ball bearing is further verified.