| As the main power and motion transmission device, the gear system is the most widely used in industrial production. So it puts forward higher requirements for the design and manufacture of the gear transmission. The paper is based on a school-enterprise cooperation project called "The Design And Development Of A Rice Transplanter". In order to research the performance of the rear axle system transmission, the paper simulates its dynamic performance with ADAMS, and makes the finite element analysis of gear contact strength with Ansys Workbench. Then the paper studies the Box’s strength and inherent characteristics and makes the appropriate improvements.The results of the paper are as follows:1. The paper establishes the dynamics model of spur gears system based on the gear system dynamics, and accordance with the principles of the Rayleigh method derives the general expression of equivalent mass of the gear-axis. Due to the different numbers of the gears that involved in the meshing process, the meshing composite stiffness will be changed. Researchers in the past in order to simplify the research process ignored the time-varying characteristics and treated as constants, and thus failed to draw accurate dynamic meshing force variation. The paper solves the dynamic model with Simulink for getting the dynamic meshing force curve, and find that the gear’s meshing force occurs periodically impact. Contrast the meshing force in constant stiffness and variable stiffness, it can be found:when the speed gets a stable state,,the meshing force will be a certain value that considering a constant stiffness, however, it will reflect the cyclical impact in the other case. So considering variable stiffness can better reflect real characteristics.2. The paper establishes a virtual prototype model of the rear axle drive, and makes the drive system dynamics simulation to get the gears’dynamic meshing force, and verifies the theoretical model’s justifiability. The paper further reveals the gear meshing impact of reasons, and points out that the gear cyclical impact not only by its own time variable stiffness but also by other gears’meshing. These impact factors can not be ignored. According to the study, it can be found that the impact peak of meshing force at the speed of800r/min account for35%of the peak at200r/min. By finite element analysis, the paper points out that the gear’s contact stress increased for each additional200r/min gear contact stress increased by approximately9%. So when the speed reaches a certain value, the contact stress will exceed the contact fatigue strength limit. Thus the risk of pitting and other damage on gears will increase.3. Compared with the contact stress in finite element method, the results in Hertz theory is higher. The theoretical value is about1.25times of the value in the finite element. So the results of the traditional methods are safer. The raditional gear’s design methods during the gear contact fatigue strength check, taking into account the load factor K is often based on the safety point of view. Sometimes, these coefficients are so large that causing the waste of resources. The paper overcomes this drawback with the modern CAE method.4. By the finite element analysis of the stress distribution and the inherent characteristics of draw the rear axle’s box, it checks the strength and finds the unreasonableness of the design of box and the stress concentrations. According to the results, the paper makes some optimization, and the maximum equivalent stress of the improved box decreased by about23.33%. In a certain extent the stress distribution is improved. |
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