Research On Identification Technology Of Vibration And Noise Source For Small And Medium Power Diesel Engine

Small and medium power diesel engine occupying an important position in Chinese engine industry has the features of production and sales volume, and supporting a wide range, vibration and noise are one of the most important factors in affecting its application. With the lightweight design for small and medium power diesel engine, its power and speed are in continuous improvement, the problem of vibration and noise is becoming more prominent, the urgent task for the manufacturers under the new situation is to reduce diesel engine vibration and noise in order to meet customer needs. To effectively control the diesel engine vibration and noise, firstly the main source of vibration and noise sources must be identified accurately. So it is of importance theoretical significance and engineering practical value to carry out vibration and noise source identification technique research on its control of small and medium power diesel engine.By summarizing and analyzing different identification technologies, the surface radiated noise source, internal excitation noise source, abnormal vibration and noise source of power assembly and inherent characteristics of structural system were studied on identification for small and medium power diesel engine systematically in this paper. The main contents of this paper are summarized as follows:(1) The joint information method of near field sound pressure and surface velocity was proposed, identification benefits of near field scan method and surface vibration measurement method based on plate idealization were integrated, with which identification of surface radiated noise sources for the single cylinder diesel engine was studied. Firstly, main radiating components of main radiating surface were identified quickly by near field scan method under engine calibration conditions; the radiation capability of main radiating components was studied based on plate radiation model; Secondly, on the basis of considering influence factor of the sound radiation coefficient, acoustic vibration characteristics of main radiating components were analyzed, compared with the traditional method, identification accuracy was improved; the main noise source from structure noise of main radiating components was further identified with sound insulation; Lastly, recognition results got by the proposed method were verified through noise reduction test.(2) The technique of fourth-order cumulants of JWSm ICA was presented, identification benefits of single cylinder misfire method, blind source separation technique based on independent component analysis and spectral analysis technique based on continuous wavelet transform were integrated, with which identification of internal excitation noise source for the V-cylinder diesel engine was studied. Firstly, single cylinder misfire method was adopted to separate combustion noise and mechanical noise in different running speed and load, the radiation spectrum characteristics of combustion noise and mechanical noise were studied under working conditions; Secondly, on the basis of identifying major transfer path of combustion noise and mechanical noise, combustion excitation and mechanical excitation source response were separated by blind source separation method, combining single cylinder misfire with ICA identification analysis results, main mechanical excitation and combustion excitation were found; double-input and single-output model between major excitation source response and internal excitation noise source was further established, time-frequency correlation property between them was studied; Lastly, recognition results got by the proposed new technique were verified through test of controlling internal excitation noise source.(3) An improved HHT new technique was presented, EEMD method as the improved method of EMD was the core of the new technique, including parameter acquisition and secondary post-processing method, with which identification of abnormal vibration source for the SUV’s power assembly of diesel engine and front abnormal noise source for forklift’s power assembly of diesel engine were studied. Firstly, based on adaptive criterion of adding white noise and similarity coefficient of delayed correlation, EEMD method was applied to adaptively decompose abnormal vibration signals of control handle under acceleration and constant speed conditions, and abnormal noise signals of gear chamber assembly under constant speed conditions, the mode mixing effecting on decomposition was avoided, major intrinsic mode functions of abnormal signals were acquired; Secondly, the time-frequency localization features of major intrinsic mode functions were extracted by use of Hilbert spectral analysis method, time and frequency resolution were improved, abnormal vibration and noise sources were identified effectively; Lastly, the accuracy of recognition results got by the improved HHT new technique was verified through vehicle setting excitation test.(4) The method of improved pulse excitation method combined with finite element modal analysis method was given, in which the measurement precision of excitation pulse signal was improved by use of the technique of variable time base, thereby the experimental modal analysis accuracy was improved. Inherent characteristics for the power assembly of diesel engine under different conditions were identified by the given method, the design structure was improved on the basis of identification of the weak link, the abnormal vibration source was finally removed. The study of the inherent characteristics of gear chamber assembly which took vibration test and numerical calculation together was carried out, the inherent characteristics between the basic gear chamber assembly and the gear housing assembly equipped forklift were analyzed and compared, the design structure was improved on the basis of identification of the weak link, the abnormal noise source was finally removed.In summary, identification technique of vibration and noise source for small and medium power diesel engines was studied systematically in this paper, the research results are beneficial for improving identification technique of vibration and noise source for small and medium power diesel engine, guiding to improve the design of low-noise diesel engine.