Modeling Of Surface Temperature In High-speed Gears And Sensitivity Analysis

Tooth surface temperature and thermal equilibrium conditions have significant effects on gear performance and failure as well as lubrication system in high-speed gear transmissions for aerospace applications. Development of an analysis approach and modelling procedure to evaluate thermal behavior and tooth temperature under high-speed operation conditions would provide a useful tool to improve gear design and lubrication with high efficiency and low cost. Based on the theories of gear engagement, contact analysis, friction and heat transfer, a three-dimensional finite element model of gear tooth was established to investigate temperature distributions and variations along the contact path over a range of applied loads and operating speeds with consideration of lubrication conditions. Sensitivity analysis of surface temperature to gear configuration, frictional heat flux, heat transfer coefficients, and oil and ambient temperature was conducted and the major parameters influencing surface temperature were evaluated. The major work is summarized as follows:I. Applying Formulae of Hertz Contact and Finite Element Method, contact stress analysis of meshing gear teeth with involute and modified profiles was conducted and the variations of contact stress along contact path was evaluated; II. The absolute velocities of the meshing teeth on pinion and gear as well as the relative sliding velocity between the tooth flanks were calculated. The approach of estimation for frictional coefficient and frictional heat flux was developed and the distributions of frictional coefficient and heat flux on meshing tooth flank with influencing factors were investigated;III. The analytical approach and procedure to calculate the gear surface heat transfer coefficient in an air and oil mist environment and the heat transfer coefficient on the tooth flank by the intermittent fling-off cooling process under high speed condition were developed; the effects of operational conditions on distributions and variations of the heat transfer coefficients were evaluated;IV. Three-dimensional finite element models of gear tooth were established to investigate temperature distributions and variations along the contact path over a range of applied loads and operating speeds with consideration of lubrication conditions. Surface and tooth temperatures under steady state predicted by finite element analysis were compared with experimental measurements obtained by infrared camera and thermocouples using slip-ring units. The exponential relationships between the maximum surface temperature of the pinion with load and speed were established.V. Sensitivity analysis of the surface temperature to relevant variables was conducted to investigate the effects of operational conditions on gear bulk temperature. A quantitative understanding of the variations of the maximum surface bulk temperature with the changes of load, speed, tooth width and module, ambient and oil inlet temperature, frictional heat flux as well as heat transfer coefficients was derived.