| A new approach was developed to optimize modification parameters of a pair of involute cylindrical gears, calculate gear stress accurately and research on characteristics of load sharing by floating components in a planetary gear system. This research was supported by the National Natural Science Foundation of China and the National Key Technology R&D Program.Along with the improving quality demands for the performance of a gear box and rapidly developed technology, the high-precision hardened surface involute gear transmission has become a main trend in the gear transmission industry. The modification design for gear flanks has become one of the indispensable core technologies to improve the stress distribution on the teeth, lengthen gears service lives, and reduce the vibration and noise of a gear box. Widely used high-efficiency and high-precision Computer Number Control (CNC) gear machine tools generally have the capability of gear modification, which provide technical assurance to produce high-performance modification gears economically and reliably. There is an urgent need to research an approach to optimize the gear modification parameters. Using CNC gear machine tools to produce modified gears, not only notably improves the performance of the hardened surface gears transmission, but also does not increase additional costs, so we can make the best use of the predominant performance of the expensive gear finish machining tools. Moreover, accurate calculation of gear stress and load sharing design of a planetary transmission also become important ways to exploit gear ultimate bearing capacity and improve the performance of a gear transmission.A method was put forward to build a refined3-D Finite Element Model (FEM) for a contact problem of involute cylindrical gears. The tooth profile normal method of the plane engagement theory was used to calculate a series of coordinates of a gear profile by programming the matlab code, and then topological structure of elements and nodes of the gear was generated in AN SYS software. The topological structure and the coordinates of the nodes were parsed with regular expression and transferred into a database model of Sqlserver, and then a gear node model was built. The functions of contact lines were solved by the optimization algorithm. Based on that, a node model geometric recognition algorithm was designed and used to identify the nodes on teeth flanks, and then to plan the nodes in the contact zone. After transferring the node model into ANSYS, the FEM of gears were reconstructed, and then APDL code was used to refine the elements in contact zones by grading division method and Multi-point constraints (MPC) equations method. The nodes on teeth flanks of the refined gear was precisely reconstructed, which is the base to accurately calculate the gear stress and optimize the modification parameters for a pair of involute gears. A fast and accurate method was put forward to build an involute cylindrical gear FEM with lead modification, profile modification or comprehensive modification. Based on the refined gear meshing model, the magnitude of lead modification and profile modification at a node along the generating line of an involute was accurately calculated, and then the coordinates of the node was calculated and corrected including types of spur gears, helical gears, external gear pairs and internal gear pairs. The corrected nodes on the teeth flank were rebuilt in ANSYS software, then the gear FEM with modification was built, which dramatically improves the modeling efficiency for the contact analysis FEM of modified gears. Taking stress distribution on the teeth flanks as an evaluation index of gear modification, the gear modification parameters were corrected by modifying node coordinates on the tooth flank according to the trend of stress distribution on that. The contact problem of the modified gears was solved by iteration method until ideal stress distribution on the teeth flanks was achieved.A method that flexible multi-body motion simulation evaluating the characteristics of a planetary gear system by finite element method was put forward. A planetary spur gear system can be modeled with2-D FEM; however, there are both rotation and revolution of planet gears, so the planet carrier and revolute pair have to be built for transferring loads to each planet gear. In order to study on the behaviors of load sharing among the planets, not only the gears FEM was built accurately, but also the planet carrier and the revolute pair were approximately simulated by beam element with equivalent stiffness and MPC to achieve motion simulation of the planetary gear system.
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