Study On Strength Of Asymmetric Involute Planetary Gear Transmissions

With the rapid development of science and technology, demand for high performance planetary gear transmission is also growing. Therefore it becomes very urgent to research a kind of planetary gear transmission with higher bearing capacity and higher power density. In ordinary planetary gear transmission, the strength of the internal engagement side is usually sufficient, while that of the external engagement side is relatively insufficient, which makes the external engagement side being the weak links of the planetary gear transmission. Studies have shown that increasing the pressure angle can effectively improve the bearing capacity of the involute gear. Thus it only make the strength of internal and external engagement sides more balanced by using larger pressure angle on the external engagement side of the planetary gear transmission, which can greatly increase the strength of external engagement side,meanwhile using smaller pressure angle on the external engagement side, which can maintain or slightly increase the strength of internal engagement side, the bearing capacity of the planetary gear transmission can be improved effectively. Therefore, this dissertation studies an asymmetric involute planetary gear transmission with higher and more balanced strength.Considering the convenience of manufacturing and processing, this dissertation adopts the traditional design method of asymmetric gears, focuses on how to improve the strength of the asymmetric planetary gear transmission, carries on a systematic research. Main research work is as follows:① Tool models of single-arc cutter and double-arc cutter of asymmetric gear have been established. According to the principles of gear geometry and tool processing, the parametric equations of whole tooth profile curves of asymmetric planetary gear are deduced. The formulas of tooth shape parameters of asymmetric gear are given and the conditions that engagement transmission of asymmetric planetary gear should meet are studied. The results lay the theoretical foundation for the study of strength of the asymmetric planetary gear transmission.② Analytical method based on the plane-section method and Hertz formula, meanwhile the loaded contact finite element method of ABAQUS based on hybrid accurately modeling are used respectively to calculate bending stress and contact stress of asymmetric gear under different pressure angle combinations. The calculation results are analyzed comparatively to verify the effectiveness and accuracy of the proposed calculation method and show that the asymmetric gear can effectively reduce the tooth root bending stress and tooth surface contact stress.③ When using the traditional design method of gear, tooth root bending strength of asymmetric gear is determined by the tool. For the reason, the effect of the cutting tool type and control parameters of dedendum height on the bending stress of asymmetric gear is studied in this dissertation, the more suitable tool types and design method of control parameters of dedendum height for asymmetric gear are obtained. The conclusion provides an optimal design of commonly used tool for the strength optimization of the asymmetric planetary gear.④ A design thought that makes the strength of internal and external engagement sides of planetary gear higher and more balanced by using asymmetric gear is proposed. For the purpose, taking pressure angles on both sides of the tooth profile as design variables, the minimum variance weighted value of safety factors as objective function, the strength optimization model of the asymmetric planetary gear transmission is established. In order to improve the accuracy of the optimization results, the effect of pressure angle on the stress of planetary gear transmission is analyzed, the reasonable initial values of pressure angle for the optimal design are determined. Compared with ordinary planetary gear with pressure angles of 20o/20o and pressure angles of 25o/25o, higher strength and power density of asymmetric planetary gear transmission are verified.