Dynamic characteristics of ring-form structures with emphasis on automotive transmission ring gear vibrations.

摘要

Precision planetary gears are highly suited for power transmission applications in modern propulsion/drive systems due to their ultra-compact, lightweight, high-powered density design. However, these gear trains are plagued by undesirable durability and tonal noise generation problems due to the enormous dynamic load they carry. To date, most of the planetary gear dynamic models assume rigid ring gear bodies instead of flexible structures. Therefore, the elastic deformation of the overall structure is not taken into account, which renders the model incapable of describing the force transmission behavior accurately. In this research work, finite element models are developed to predict the natural modes and force response of a typical ring gear structure. Various geometrical parameters considered include thickness to radius ratio, thickness to width ratio, helix angle, number of teeth, number of splines, spline thickness, and spline width. Effects of these geometrical parameters on free and force vibrations are studied. The dynamic response of a ring gear subjected to various boundary conditions including free, simply-supports, discrete springs at various locations on the circumference, and distributed springs over certain segments and entire length of the circumference is obtained. Each one of these conditions is an attempt to represent real-life automatic transmission applications under various loading conditions to describe the vibratory motion of a ring gear due to a set of planet dynamic forces. A comprehensive free vibration and force response analysis using numerous finite element models subjected to various parametric sets is performed to study the vibratory motion of a ring gear structure. Comparisons of natural frequency values and mode shapes from free vibration analysis and the average acceleration/force response from force vibration analysis are performed. Various criteria for reducing vibration transmissibility to the transmission housing are developed, and specific conditions for minimizing vibration transmissibility are determined.