| Air pollution, water pollution and noise are the three primary sources of pollution in the world today. And these have been a worldwide problem. In modern city environment noise resources, the noise which generated by automobile has the largest proportion and engine noise is the greatest part of the automobile noise. In recent years, as all automobile makers are facing keen competitive for sales, low noise has become a part of riding comfort and an important parameter in evaluating vehicle quality with power performance, fuel economic and emission. Therefore under this environment, it is very important to research the engine noise principle and reduction technology.In this paper, the research object is1.4TSI EA111turbocharging gasoline direct injection that made by Shanghai Volkswagen Automobile Company. First of all, the present development in this field of engine radiated noise has been detailed on the basis of a great deal of literature in home and abroad which is related to this study. Then engine noise principle, spreading ways, acoustic sources identification and isolation techniques, key technology and developing trends of structural acoustic radiation prediction have been analyzed. At last, a series research work has been elaborated by the author. Such as engine structural acoustic radiation noise prediction, computation methods and optimization, general idea and analysis process of the engine structural acoustic radiation prediction. The followings are the main research work of this thesis.(1) The engine3D model has been built by Pro/E software through parametric modeling technology. The finite element model of engine block, head, head cover, timing cover, gearbox and oil pan were created in the Hypermesh software. Furthermore, the finite element modal analysis of primary parts and whole engine were carried out. We mastered the dynamic characteristics of whole engine and related primary parts. Through the comparisons of modal shape and frequency of engine by finite element modal analysis and experiment modal analysis, the validity and rationality of finite element model are confirmed.(2) The degrees of freedom of engine primary parts finite element models are reduced by ABAQUS software. Based on AVL Excite Power Unit software platform, engine multi-body dynamic computing model has been built. We computed and analyzed engine vibration characteristics under full load operating condition. And these computation results have been compared with those of engine vibration experiments, and a good identity of results has been reached. Then we obtained engine surface vibration velocity through acoustic recover method. These surface vibration velocity will provide boundary conditions for engine radiated noise computing and analysis.(3) Combined with the engine finite element model which built in Hypermesh software, engine whole surface boundary element mesh model can be obtained in the structure module of LMS Virtual Lab software. We used the engine surface vibration velocity which obtained from the previous research to predict engine radiated noise in LMS Virtual Lab Acoustic module with indirect boundary element method. Through the computation of engine full load radiation noise, engine radiation sound power, radiated sound field and sound pressure of field point have been analyzed and researched. Then sound pressure level of field points have been validated through the experiment. The results showed that the overall trends of calculation value and experimental value of filed points sound pressure level are consistent.(4) Engine noise sources identification, intake noise, combustion noise, gearbox noise, cold start noise and shut-down process noise have been investigated through experimental method. The characteristic of main radiation sound sources, intake noise, combustion noise, gearbox noise, cold start noise and shut-down process noise have been obtained.(5) The merits and demerits of acoustic finite element method (FEM), boundary element method (BEM) and fast multipole boundary element method (FMBEM) have been detailed and analyzed. Efficient and accurate engine radiated sound power software has been developed by Matlab program based on surface vibration velocity method. The radiated sound power of simple plate, engine head cover and powertrain has been calculated and analyzed by BEM, FMBEM and Matlab program software. Comparison of results showed that there are discrepancies in radiated sound power calculated by Matlab software at low frequencies. But the difference is gradually reduced and correlated well at high frequencies. Overall, the sound power calculated by Matlab program is the highest, BEM is in the middle and the FMBEM is the lowest. The Matlab program gets the radiated sound power accurately at the peak frequency locations. Through the comparison and analysis of sound power calculation efficiency of simple plate, engine head cover and powertrain, it can be seen from the comparison that the simplified method is always more efficient than both BEM and FMBEM methods in radiated sound power calculations. FMBEM takes the longest computing time and Matlab program takes the shortest when the DOF of model is small. That is because FMBEM method is less efficient for small DOF problem. With the increasing of DOF, the computation time increases, and BEM computing time increases the fastest. When the number of nodes increases to a certain case, BEM takes the longest computing time, and FMBEM becomes more efficient. However, the computing time of Matlab program is much less than that of BEM and FMBEM.(6) At the end of this paper, Engine radiated sound optimization procedure has been put forward. After that, combine with the developed Matlab program software, we use Minitab software to analyse the main influence factors of engine block radiated sound by design of experiment (DOE) method as an example. There are seven different impact factors which influence the radiation sound power have been analyzed by the DOE methods in Minitab software. The seven factors are block side wall thickness, skirt thickness, block bottom thickness, bulkhead thickness above front end main bearing cover, side wall stiffeners thickness, skirt stiffeners thickness and rear-end sfiffeners thickness. Throguh the analysis, the influence of each factor to block radiation sound power and mass have been obtained. Then optimizations of each factor have been conducted with the goal of low radiation sound power and mass of block. The optimized block radiation power has decreased1.52dB(A) and block mass just increased0.4kg. These basically meet the requirements of the target. |
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