Study On Mode Synthesis Of Diesel Engine Crank-shaft Mechanism

Monitoring and fault diagnosis system for military engines is developed by equipment dynamical engineering center of NEU, Entrusted by the Troops, Shenyang Military Command. Based on the engineering research on the crank-shaft mechanism of 6BT5.9 diesel engine, as a sub-project, the dynamic analysis is conducted systematically and intensively in the paper, and experimental verification of some key parts is also performed. Meanwhile, detailed study is made on modal synthesis method.The diesel engine is composed of a lot of the complex components and parts. If its properties are studied, it is required to research the dynamic characteristics of the assembly. Based on the modal synthesis method, the Characteristics of connecting-rod structure is analyzed, and the finite element model of the connecting-rod is constructed using the CMS (component mode synthesis) technique of Ansys, and the free modes are calculated and analyzed. Then based on the finite element boundary condition processing method and the modal synthesis method, the finite element model of the connecting-rod structure, the crankshaft-connecting rod structure are established, and the free mode are calculated and analyzed simultaneously, roughly handled the joint of the combination structure, and detailed study is made on modal synthesis method. This overcomes the difficulty in application of the finite element modeling with plate and shell, and simultaneously calculates and analyzes every free modal parameter of the models.The dynamic analysis of the structures are required to describe structural systems accurately in theory, the method is a detachable structure, continuous system has become distributed relate structure in a node Through the hypotheses of the structural material and shape, the simplification of the structural constraints and joints, the theoretical calculation models are established by finite element techniques, for accumulating bias about model structure, order and parameter, are their results reliability? This is required to be verified in experiment. Based on the modal analysis theory, modal testing system is built, and a set of modal parameter identification program is established by Matlab software. Then the modal parameter of the Diesel Engine Main parts and the Combined Structure are obtained.At last, based on modal correlation theory, the modal correlation analysis is done by the end of this paper. Modal parameters achieved by finite element method coincide with those achieved in experiment, which shows the correctness of the models and adopts the proper research methods. This work establishes a foundation on the dynamic response calculation, the dynamic characteristic analysis of the diesel engine and failure diagnosis of the Diesel Engine step by step. Simultaneity, the reasons of mode irrelevance of the composite structures are analyzed profoundly, several main factors that affect the mode correlation result are discussed in detail, and puts forward improving methods.