Effect of Tooth Load Distribution on Bull Gear Vibration

Abstract

A spur pinion and bull gear set was redesigned to a helical version to reduce stress and wear on the gear teeth. The spur gears had experienced significant end loading resulting in wear on the forward side. It was proposed that the uneven load distribution could excite bull gear web modes that have pitching motion of the gear rim. Analysis was performed to determine if the helical version would excite similar modes. The effect of tooth load distribution on traveling wave vibration was quantified for both the spur and the helical versions of the bull gear. The Ohio State University load distribution program (LDP) provided loads across the tooth face at incremental roll angles through one complete tooth mesh cycle. The tooth loads were applied to three-dimensional finite element models of the spur and helical gears, and transient forced response analyses were performed. The tooth loads were moved tooth-to-tooth around the circumference of the gear to simulate the bull gear rotating through mesh. Resonance of a given mode occurred when the frequency of the tooth loading coincided with the frequency of either a backward or forward traveling wave. Uneven loading excited the web modes of the bull gear to different levels in the spur and helical designs due to the nature of the tooth loading compared to the mode shapes. The spur gear was predicted to have a significantly higher web stress than the helical gear for the same amount of misalignment.Copyright © 2005 by ASME