Strength Performance Analysis Of Pitch Bearing And Bolt Combination Structure

Pitch bearing and bolts combination are important parts of the variable pitch system in the wind turbine. They are mainly loaded with axial force, radial force and tilting moment.Their whole structure is complex and has low rigidity. It is necessary to study the pitch bearings and bolt combination structure under severe environment in order to provide a theoretical basis and to support for the reliable operation of the work.Therefore, combined with the project "Liao ning province science and technology major projects (No.201303006)", this paper analyses the static and fatigue strength of pitch bearing along with the support structure and bolt uniting. Along with the results of "bolt-bearing" on testing device, bearing and hub bolt combination structure are discussed.The main research contents of this paper include:Based on Herzs contact theory, ?Wind Turbine Design Guideline DG03:Yaw and Pitch Rolling Bearing Life? and ?VDI2230—Systematic calculation of high duty bolted joints?,we study bearing performance,static and fatigue strength of the high strength bolt in theory,as well as considering the working environment and performance of pitch bearing and bolt connection structure.A testing device for analysing "bearing-bolt" model is built by myself, meanwhile a finite element model of it was established and carried out. We used nonlinear spring to match the contact between bearing-balls and bearing-raceway, and then, beam element, the bolt connection. By comparing load distribution resulted between the test model and the finite element model, it was verified that using Beam188 beam element to simulate bolt connection in the finite element model was feasible.An integral equivalent finite element model was established for the "blade-pitch bearing-hub" connection structure in which the bolts and bearing support structure stiffness were not neglect; this equivalent method for contacting between bearing balls and bearing raceway and for bolt uniting was the same as finite element model of the testing devices; this model can be used to calculate the static strength of pitch bearing considering bolts combination to form a method to estimate the fatigue strength of pitch bearing accordingly.Based on the integral equivalent “blade-pitch bearing-hub”finite element model in which bolt combination and bearing support structure stiffnessare rebuilt,the author studies the influence factors off atigue strength of the bolt uniting structure,such as bolt pre-tightening force, bolt stiffness (bolt length, bolt diameter), surface friction coefficient.Measures are put forward for enhancing bolt fatigue strength,which include suitable high pre-tightening force,reasonable lower bolt stiffness (by increasing bolt length, or reducing bolt diameter), correspondingly bigger binding surface friction coefficient.