Research Of Dynamic Characteristic Analysis Method Of Integrated Coach Body

At present, although the design of some buses meets requirements of static strength, there still have some problems in practical. The main reason is that the bus body sustains more complicated random excitation loads in practical working conditions. Dynamic stress has proved to be a main reason of the bus frame break by the exercises. The more accurate dynamic stress course could be attained with the road test or experiment, but the precondition is that sample cars have been manufactured .If in the early stage of design making use of FEM to build up model cars of body framework; it will get dynamic stress courses of body structure under all different kinds of road conditions. Reliability and service life of body framework can be accurately predicted and by re-optimizing the structure, the quality of the whole car will be decreased. Therefore, the study of dynamic stress response of body structure under the road random excitation has a very important practical significance.According to the theory, this paper researched the dynamic characteristic analysis method of integrated coach body combined with new high-grade bus development project of a passenger bus company; preliminary explored modal synthesis method, and applied to the analysis and calculation of the actual vehicle.This paper carries out the following work:(1)The paper explain the significance of the dynamic response analysis of the bus body structure design , analyze the main strengths and weaknesses of dynamic response of the current methods used , present the main theory of the dynamics simulation analysis.(2) In order to solve the problem of the vehicle's nonlinear behavior ,vertical dynamic displacement at the mounting points of the coach body frame were used to be the dynamic loading input for the transient analysis. Then the nonlinear suspension and tire-road system were not needed to consider any more,and the integrated coach body structure model was simplified to be a single liner elastic model.By this way ,the procedure to verify analysis model would be simplified and the solving difficulty would be reduce,while the efficiency of simulation will be improved and design cycle be shorten.(3) The paper expatiate the advantage and disadvantage of the direct transient response analysis and modal transient response analysis, refer to the structure of the integrated coach body , preliminary bring forward the methods and processes of bus body structure analysis.(4) In order to verify the reformed dynamic characteristic analysis procedure in this paper,a small partial model of the back-end bus body was set up,and a dynamic experiment were performed on it.According to the data measured in the experiment and the computer simulation result of three FEM model, the results improve the procedure of dynamic simulation analysis, then the method has been applied to dynamic response of the whole body. By the way, experiment verified the advantage and disadvantage of the direct transient response analysis and modal transient response analysis.(5) Refer to modal sensitivity theory, combined the practical project situation, the paper calculated the mode amending sensitivity of bar part in auto body, according to the special characteristic of auto body frame and the technological conditions, preliminary explored modal synthesis method by super-element, and applied it to the analysis of the whole bus body, to identify relations of the modal frequency of between the assembly and the whole body. This paper mainly focuses on finite element analysis. In the phase of the bus design, through the dynamic characteristics method research of the bus body; understand the dynamic characteristics of the bus body; provide the foundation work for guiding the bus design work, optimization work of bus structure and other follow-up fatigue analysis and test research.