Dynamic Analysis of Needle Roller Bearings on Torque Loss

Abstract

This study concentrates on torque loss of needle roller bearings used in a planetary gear set. Dynamic analysis is conducted to investigate mechanisms of friction loss by a multibody dynamicss (MBD) model, which is developed to consider dynamic effects on the planetary gear and contact conditions. Contact analysis of needle rollers with other parts utilizes the discrete ball model to obtain the distribution of contact points and to decrease computational cost. The sliding friction coefficient is defined by experimental results that evaluate the relationships between the thrust force and the skew angle of the needle rollers. The MBD analysis evaluates bearing clearances between the needle rollers and other parts in the radial and circumferential directions. It is found that the clearances between the needle rollers and the cage in the circumferential direction are a dominant factor in friction loss. Moreover, numerical results confirm that the skew angle of the needle roller with respect to its rotation axis has the most significant effect on the friction loss of the bearing. The skew of the needle roller causes thrust force that pushes the pinion gear onto the side washer that supports the axial motion of the pinion gear. Finally, this study suggests an appropriate clearance between the needle rollers and the cage to reduce the skew angle of the needle rollers and the friction loss between the pinion gear and the thrust side contact. The circumferential clearance should be desined as small as possible.