Effect of the preload in the general static load‐carrying capacity of four‐contact‐point slewing bearings for wind turbine generators: theoretical model and finite element calculations

Abstract

This paper presents a generalization of previous works developed by the authors in the field of the calculation and selection of slewing bearings, where a theoretical model for the estimation of the static load-carrying capacity of four-contact-point slewing bearings was obtained. Those previous works assumed that there was no preload in the balls; in the present work, the model has been improved in order to consider the effect of the preload, in such a way that it provides more realistic results because this type of bearings are preloaded in several applications to increase the stiffness and therefore the accuracy of the system. In parallel, and for comparison purposes, the finite element model built by the authors in previous works has been also adapted to include the preload in the balls. Both models, theoretical and FE, assess in complete agreement the increase of the stiffness with the preload level; the results show that the static load-carrying capacity does not vary appreciably with the usual values adopted for the preload.

An engineering approach for the estimation of slewing bearing stiffness in wind turbine generators

“…Figure compares the results for rigid and deformable rings to demonstrate the effect of the flexibility of the rings on the bearing stiffness. The results for rigid rings were obtained through the analytical model by the authors . From the figure, it is concluded that rigid ring assumption largely overestimates the stiffness of the bearing, especially for large bearings.…”

“…The aim of decoupling the problem was to consider separately the effect of the different parameters on the stiffness. By doing this, contact parameters such as ball preload or conformity ratio only affect δ contact as described in the analytical model by the authors . On the other hand, δ rings is affected by the rest of the geometrical parameters, being D w and D pw the main ones.…”

“…It is important to remark that these equations are valid and offer reliable results for any of the studied DPs, so they can be used to estimate the global stiffness of any bearing within the defined design space . Figure summarizes the results for DP7: in red dots, the total displacement values from the DOE; in blue lines, the contact deformation results from the analytical model; in green lines, ring deformation values according to the proposed equations ; finally, red lines are the summation of blue and green lines, ie, total displacement, demonstrating that the proposed formulation for ring stiffness calculation accurately fits the DOE results. For this DP, the WARE i was 0.36%, 2.29%, and 4.44% for axial, radial, and tilting cases, respectively, so it is a representative DP considering the mean values of the errors in Table .…”

“…These bearings are subjected to very specific working conditions, where small amplitude oscillatory rotations and high combined loads are involved. For these reasons, the selection criteria is complex, and many factors need to be considered, like the static load capacity, the dynamic capacity, and the fatigue behaviour or the friction torque . Other specific phenomena must be also considered, like false brinelling and fretting corrosion …”

“…For these reasons, the selection criteria is complex, and many factors need to be considered, like the static load capacity, the dynamic capacity, and the fatigue behaviour or the friction torque. [1][2][3] Other specific phenomena must be also considered, like false brinelling and fretting corrosion. 4 In this context, the global stiffness is a key parameter to account for the structural response of WTG under external static and dynamic loads.…”