Dynamic Characteristics Analysis Of Medium And Heavy-duty Diesel Engine And Research On Radiated Noise Of The Key Parts

Reducing engine radiated noise is an important part of reducing the whole vehicle noise.In the paper, a six-cylinder diesel engine is taken as the research object. The whole engineradiated noise has been systematically studied, as well dynamic characteristics of its importantparts. Significance conclusion, which is useful to engineering, has been gotten.Modal test analysis techniques and finite element modal analysis are used in this paper.The diesel engine’s key parts are studied about their dynamic characteristics. From the study,we get the modal parameters of these parts. Modal Assurance Criterion (MAC) is used tojudge the consistency of the mode shapes of test and the mode shapes of calculating. MACaffirms the reliability of the finite element model. On this basis, commercial finite elementsoftwares, ABAQUS, is used to study constrained mode of the assembly structure of thecylinder block, cylinder head, oil pan and flywheel shell, as well their single-model mode.The mode shapes of assemblage of the engine obtained in constraint condition show that localmodes of the oil pan occupy the larger proportion in the whole modal. Detailed optimizationanalysis about the oil pan has been done.Oil pan, as the main source of radiated noise in the diesel engine, is a thin-walledstructure. Detailed studying about the oil pan is done. First of all, the free modal test andmodal calculation about it is done to establish the reliability of the finite element model. Then,its mode in constrained condition is studied and the mode parameters in constrained conditionare acquired. Secondly, direct method is used to study its surface vibration, which is the baseon studying its radiated noise. The position of local mode shapes in constrained condition isfound by looking into the shapes obtained. The sidewall of the oil pan is the main location ofthe local vibration. What’s more, the main affecting factors on radiated noise, such asstructural stiffness, structural damping and material properties, are studied. An oil pan modelwith better structural stiffness, whose thickness is alterable, is obtained by topologyoptimization analysis. By changing structural damping of the oil pan, the radiated noise isstudied. Then, the results of the radiated noise of the oil pan of the different materials are compared with each other. The results show that the optimized oil pan has lower radiatednoise.The mode shapes of the whole engine in constrained condition are obtained. Afteranalyzing of vibration characteristics of the oil pan, the local modes of the oil pan below1000Hz are the main modes of the whole engine. From the cylinder pressure measured in thetime domain, the frequency-domain signals are obtained by the Fast Fourier Transform (FFT).The results obtained are input load of surface vibration analysis. Then, the direct method isused to analyze the overall structural response by ABAQUS software. The results of thewhole surface vibration analysis are obtained, which are the input of the whole engineradiated noise.Before and after optimizing of the oil pan, the radiated noise of the engine is studied.Results show that the oil pan optimized gets smaller low-frequency radiated noise. Thisanalysis process provides a reference method for engineers who are engaged in engine noiseanalysis. Besides, this approach has important reference value to the engineering practice.