Identification And Reduction Of Abnormal Vibration And Noise Of Gasoline Engine

The structure of internal combustion engine is complex.Its operating state and working condition are changeable,so that the vibration and noise signals produced in the working process are complex and changeable,and have non-stationary and time-varying characteristics.With the increasing demands of life and working environment,people pay more and more attention to the pollution of vibration and noise.As one of the most widely used power sources,the vibration and noise control of internal combustion engines has become a hot spot of research.It is an important prerequisite to study the vibration and noise characteristics of the internal combustion engine,to identify the source of the vibration and noise and to the vibration and noise source of the engine.Traditional signal processing methods can not fully analyze the time-frequency information of signals,especially the processing of non-stationary signals.In this paper,on the basis of independent component analysis and wavelet transform,the research object of mower and single cylinder gasoline engine is studied on the basis of independent component analysis and wavelet transform,and the wavelet transform and independent component analysis are used to identify the vibration and noise sources of the internal combustion engine.Finally,the piston rattling excitation is confirmed as the cause of the abnormal vibration and noise of the engine and mower,and by optimizing the piston,the vibration of the mower is eliminated and the noise is obviously reduced,and the effect is very good.The main research contents are as follows:(1)Through the description of the various hazards of the vibration and noise pollution,the harm of the vibration and noise pollution of the internal combustion engine and the significance of the vibration and noise control are emphasized.The feasibility of these methods in the signal analysis of the vibration and noise of the internal combustion engine is analyzed by the introduction of the independent component analysis and the introduction of the wavelet transform and the practical application.(2)The principles and algorithms of empirical mode decomposition,independent component analysis(ICA)and wavelet transform are introduced in detail,and their advantages and shortcomings are described,which are the basis of signal analysis and processing.(3)Through the vibration contrast test analysis of the mower carrying two different engines,the vibration abnormal frequency section of the mower loading RVC190 is found.Through continuous wavelet transform and the ignition signal of the engine,the time frequency analysis of the abnormal frequency section is carried out,and the vibration of the engine is combined with the working principle and process of the engine.The frequency section of the dynamic anomaly is preliminarily judged.(4)Based on the in-depth analysis and research of the basic principles and algorithms of independent component analysis(ICA),a single channel independent component analysis based on EMD-ICA model is established,considering the limitation of the multi channel input in the actual application.According to the EMD-ICA algorithm process,each independent component is decomposed.The obtained independent component is analyzed by spectral analysis and continuous wavelet transform,and combined with the understanding of the working process and principle of the internal combustion engine,the vibration and noise sources corresponding to each independent component are identified effectively.(5)Using the advantages of wavelet packet decomposition and independent component analysis,the blind source separation analysis results of the vibration signal of the engine block are analyzed by independent component analysis.The two main excitation is decomposed into different subbands,and the combustion excitation and piston flapping excitation are combined with the working process and the original principle of the gasoline engine.Effective separation was carried out.Using the characteristics of the wavelet packet coefficient,the contribution degree of each subband of the vibration signal of the body surface is calculated by the wavelet packet decomposition.The contribution degree and the change law of the vibration of different excitation sources on the body surface vibration under different loads are obtained.The results show that the main excitation that causes the abnormal vibration of the engine is the piston rattling excitation,which plays an important guiding role in the vibration and noise control of the engine and its loader.The piston is optimized and the vibration contrast test is carried out before and after optimization,which validates the correctness of the recognition of piston flap excitation.