Effect of structural parameters and load states on PTRB’s load distribution

Abstract

The planetary thread roller bearing (PTRB), as a new type of ball bearing, has the advantages of high-power density, no need to be used in pairs or combinations, and the ability to carry axial-radial combined load and bidirectional axial load. Its load distribution characteristics serve as the basis for building PTRB’s performance models, such as dynamic load rating, static load rating, and friction torque. In this paper, PTRB’s structure and the transmission paths of force were briefly introduced, and the elastic deformation of the threaded roller, inner ring, and outer ring was analyzed on the basis of the Hertz theory and Hooke’s law. Next, the methods for calculating the compressive deformation of shaft when PTRB was under different load states were presented. In view of the nonlinear relation between force and elastic deformation as well as the compatibility equation, the theoretical model of PTRB’s load distribution was set up accordingly. There was a discrepancy between the variation trends and values of load distribution under four axial load states, with a larger load distribution coefficient at the contact point closer to the flange. With the increase of load from 10 to 30 kN, the increase rates of the axial and radial load distribution coefficients were ≯1.2%, so that the load distribution coefficient could be approximately deemed as an inherent characteristic of PTRB. Within the value range of each structural parameter, the variation of the pitch diameter of threaded roller had the most significant effect on axial load distribution coefficient, with a variation rate of 7%; the variation of the number of threaded rollers had a significant effect on radial load distribution coefficient, with a variation rate of 37%; the variation of the remaining structural parameters had a minimal effect on load distribution coefficient, with a variation rate of ≯3%. When a follow-up optimization design is conducted on the performance of PTRB with a fixed dimension, and the contact angle, number of thread teeth per roller, and pitch diameter of threaded roller are deemed as design variables, the load distribution coefficient can be set as a constant value, and the number of threaded rollers can be set as the maximum value to simplify the optimization design process of PTRB’s performance and improve the optimization design efficiency.