Dynamic Analysis of Needle Roller Bearings on Torque Loss

Abstract

Automatic transmissions consist of several planetary gear sets that are utilized to change gears. Needle roller bearings are widely employed in planetary gears used under high-load and high-speed conditioins, and thus the torque loss of these bearings is an important issue in designing high-efficiency transmissions. In this paper, a dynamic analysis is conducted using a multibody dynamics model to investigate friction losses in the needle roller bearings that support pinions. This numerical model takes into consideration the detailed conditions of contact and friction between the needle rollers and other parts. A discrete sphere model is used in the contact analysis to simulate the load distribution for the needle rollers. The friction coefficient is defined as a function of sliding velocity, and is used to describe the experimentally determined relationship between the skew angle and thrust force of needle rollers. The measurements obtained for the axial force of a pinion validate the predictions of the numerical model. A numerical analysis is conducted to evaluate the radial and cage pocket clearances of needle roller bearings, and it is found that the cage pocket clearance is a dominant factor affecting the friction loss of pinion. An increase in loss is caused by the thrust force generated by the skew of the needle rollers. Consequently, the cage pocket clearance needs to be small so as to lessen the friction loss of the bearing.