Non-Standard spur gear tooth profiles for improved epicyclic gear system performance in low speed applications

This study aims to improve the performance of epicyclic gear sets specifically for low-speed high-torque operating conditions. The influence of geometric and functional parameters such as profile shift coefficient and working pressure angle, on load carrying capacity is systematically analysed through a parametric study [1]. Maximum fillet and contact stresses of symmetric spur gears are evaluated using the finite element method. The gear design approach followed is based on the simple assumption that tooth size is directly dependent on the load carried. Since only low speeds are considered, vibrations and the resulting noise are considered to be negligible and consequently the design process is dictated by the stress levels. Considering the relationship between gears in epicyclic systems, non-standard profiles have been generated by using multi parametric contour plots. This technique is based both on functional limitations such as contact ratio and minimum top land thickness, as well as limitations typically addessed in manufacturing processes such as the condition of undercutting. Contour plots for the two gear pairs- sun/planet and planet/ring - are generated to define the domain of existence of all possible values for the considered parameters. For two epicyclic systems with different pressure angle configurations, comparable in terms of centre distance and transmission ratio, the simultaneous influence of pressure angle and profile shift on tooth flank load capacity and bending stress is studied [2]. Based on these results, suitable suggestions are made for the design of gears working in epicyclic systems for enhanced torque carrying capacity and physical packaging volume reduction, for applications characterized by low speed and high loads conditions.