Analysis of transient mixed elastohydrodynamic lubrication in planetary roller screw mechanism

Abstract

Abstract Previous lubrication studies for planetary roller screw (PRSM) are mainly concentrated on steady-state condition without the consideration of entrainment angle. However, PRSM always operates in transient situations with frequent startup and shutdown process. In this paper, uneven friction distribution, the influence of helix angle on lubricating properties and transient behavior in the roller-screw interface are analyzed comprehensively based on transient mixed-EHL model, which considers real three-dimensional (3D) machined roughness and arbitrary entrainment velocity. The results show that smaller helix angle is beneficial to improve the lubrication performance. Increasing the rotating speed and declining axial load can moderate the uneven friction distribution. Besides, a relatively large angular acceleration may enlarge the film thickness and reduce the friction at the shut down status. The numerical simulation model can be utilized as a design optimization tool for the PRSM.