Study On Diagnosis Of Cylinder Liner-piston Wear State Based On Fractal Dimension Analysis Of Internal Combustion Engine Vibration Signal

The cylinder liner-piston group is the heart of the internal combustion engine (IC Engine), which influences the main performance of the IC Engine, such as economical efficiency, power performance and working life, etc. Therefore, the prompt diagnosis of the working state of the internal combustion engine is the key problem of the effective operation. Besides, the piston slap motion, correlated with the surface wear of the cylinder liner-piston component and the vibration noise of the IC Engine, is affected by structural parameters of piston, and is the main factor affecting the quality of IC Engine. Therefore, the study on the piston slap motion is the basic to predict the wear of cylinder liner-piston components and to evaluate the vibration of IC Engine.The vibration of IC Engine that contains the information of working state is an important diagnosis instrumentality, and the piston slap motion that relates to the surface vibration of the cylinder liner is the main excitation source of the vibration of IC Engine. Therefore, it is completely feasible to diagnose the technical condition of the cylinder liner-piston on the basis of IC Engine surface vibration signal. The core of mechanical vibration diagnosis is the characteristic parameter analysis of the vibration signal. In view of the fractal characteristics of IC Engine vibration signal, the methods of the frequency domain analysis, time-frequency analysis and wavelet analysis, etc., are the normal analysis methods. However, they cannot be accurate in both of nonlinear and non-stationary. At present, the fractal theory is significant and focused in the domain of nonlinear science, and the researchers are also increasingly attracted to the application of fractal dimension in mechanical vibration signal analysis.In this paper, focus on the technology state diagnosis of the cylinder liner-piston group based on fractal dimension of the IC Engine vibration signal, the characteristic of piston slap motion was analyzed, the evaluation of cylinder liner-piston component wear was researched, from the IC Engine vibration signal the vibration signal by the piston slap was separated and the fractal characteristic of vibration signal was also researched.To begin with, the piston and piston ring dynamics simulation software AVL EXCITE Piston & Rings was used to analyze the motion characteristic of piston slap, the contact force and motion characteristics of the piston rings. The piston slap motion parameters, the force acting on all nodes of piston surface, the movement characteristics of piston ring in ring groove and the pressure of piston ring for the cylinder liner were all obtained. According to the contact forces of piston-cylinder liner surface nodes and the movement parameters of piston-piston ring as well as the respective relationship between abrasion and its affecting factors, the attrition trend of piston and cylinder liner surface was evaluated.Besides, the multi-body dynamics simulation software-AVL EXCITE Power Unit was used to simulate the impact between cylinder liner and piston, the impact forces on each node of the cylinder liner inner surface were obtained. The impact forces were thereupon inputted to the simulation of cylinder liner surface vibration, the vibration acceleration signals of each node were consequently obtained. The spectrum and power spectrum analysis of vibration signal were carried out, and the fractal dimension (i.e. correlation dimension) of vibration acceleration signal was further analyzed based on the G-P algorithm. Simultaneously, the changes of the total energy of cylinder liner surface vibration signal and the correlation dimension along with the increase of cylinder liner-piston wear gap were also analyzed. It was found that there is a good corresponding relationship between the correlation dimension of the vibration signal after the certain wear of the cylinder liner-piston and the wear state.Finally, in order to reduce the total energy of the vibration signal caused by the piston slap, the piston structure parameters optimization was carried out, the suitable design scheme of the three structure parameters with the large influence on the vibration signal total energy-were obtained.