Finite Element Analysis And Experiment Research On Denamic Charicater Of Gear System

The general mechanical structure always consists of lots of components through the combining of the different joints. The theoretical analysis and dynamic experiment shows that the status of the combining between the joints can affect the theoretical computing precision of the structure characters well as the result of finite element analysis(FEA) for the dynamic character of the structure. In order to build the accurate FEA model and to do the dynamic analysis and dynamic design, the character of joints should be studied well and truly. But the research on the dynamic character of the joints is one of the difficult points in the dynamic research field. Although the researchers domestic and abroad have done a lot and given some identifying and analysis methods on the dynamic parameters of the joints, nowadays no mature theory or method is presented. Gear system consists of gearbox, shafts, gear pairs and some bearings. Gear transmission system is one of the most important power/motion transmission forms for machinery and mechanical equipment. In this system, some joints exist between shafts, bearings. The joints between the gear pairs, especially the stiffness of the bearing will greatly affect the dynamic character of the axis system and the whole of the gearbox. In this paper a theoretical model is built for a real gearbox, and the equivalent parameters of the joints are identified with the dynamic experiment. The parameters is referenced in the FEA, and the FEA model, which accords with the reality, is gotten. Based on theories of vibration, the modal and dynamical response finite element method combined with dynamic test technology, a series of methods, which have theoretical and practical values, are presented to solve the problems to forecast vibration of gear system. And the finer finite element analysis on the inherent character and dynamic response of the gearbox is fulfilled. The dissertation consists of the following contents and result: 1. The gear system is divided into two substructures, transmission substructure (gear and shaft) and structure substructure (box). For gear transmission substructure, mass centralized model is built up, which could simulate vibration with bend-torsion-axes-swing degree of freedom; 2. The modal parameters of the joints are identified by test modal analysis, and the corresponding physical parameters are gotten with coordinate conversion method; 3. The 3-D dynamic finite element model of gear transmission system and structural system is established with the physical parameters identified by test modal analysis. A theoretical modal analysis of the whole gear system is obtained; 4. Combined multi-vibration model of gear transmission system with finite element model of gearbox, the dynamic response of gear-shaft-bearing-gearbox system is calculated and the vibration displacement-time histories of gearbox are presented; 5. Test modal analysis for the whole gearbox was fulfilled. The result coincides with the finite element analysis solution; and the error analysis is done; The research result shows that the theoretical and experimental methods presented in this dissertation have fine simulation precision, which can meet the need of dynamic characteristics analysis of gear system, and this method could be applied to analyze engineering problems. Some creative and innovation ideas are stated in this dissertation: 1. The test and theoretical analysis were combined to get the dynamic parameters. During the research on the identification of the joints parameters, the system is tested under the real installing situation, such as the bearings pre-force and the fabrication of the joints are all almost as the same as the reality, so the data from the test are more credible; 2. In the dynamic character research of the gear system, the gearbox is included. Not only the dynamic character of the gear, the shaft and the bear themselves were considered, but also the effects of the box'dynamic character to the system are considered either, so it is more practical to meet the need of the engineering. 3. When MSC/Nastran FEA software is used to analysis the dynamic character of the gear system, the spring element is used to simulate the scroll balls of the bearings. Every scroll ball is simulated with three spring elements , which provide the stiffness and damp in three directions. This is coincident with the real situation, and the stiffness and damp of the bearings is gotten from the test, so the result is quite correct. 4. When analyzing the dynamic response of the gear system, to get the response time history in every degree, the program to solve the dynamic equation is developed. Combining with the dynamic equation of the transmission, the dynamic forces in the three directions are gotten. This load is imposed on the bearing hole of gearbox and the analysis on dynamic response of the system is done. This method could eliminate the errors which are brought by only considering the torsion vibrating direction and neglecting the effect of the other vibrating direction. Only putting the torsion time history onto the axis directly can bring quite big error.