Study On Vibration And Noise Prediction And Structural Optimization Of Oil Pan Of A Three-cylinder Supercharged Direct Injection Engine

In this paper,the oil pan of a three-cylinder supercharged directed injection gasoline engine is taken as the research object,the vibration performance and noise of this engine are predicted and analyzed.The region with strong radiation noise when the oil pan vibrates is obtained.Based on the change of structural parameters in the region with large radiation noise,the change of structural rigidity of the oil pan is explored.The vibration and noise are studied and the conclusions are drawn as the follows:(1)Based on modal theory,the free modal analysis of oil pan is carried out by using the simulation software ansysworkbench,and then the results of the free modal tests are obtained through modal experimental analysis.The precision and accuracy of the simulation model are verified by comparing the modal vibration frequency and modal shape,so the next simulation calculation can be carried out.Based on the correct finite element model,the oil pan bolts are further restrained,and the modal results in the restrained state are calculated.(2)Considering the influence of lubricating oil on the dynamic characteristics of oil pan,the unidirectional fluid-structure coupling and bidirectional fluid-structure coupling modal analysis models are designed and built based on ansysworkbench software.Compared with the constrained modal results,the coupled modal shapes are basically the same as those without oil,but the modal frequency is slightly reduced,which indicates that the existence of oil has certain influences on the oil pan modal.(3)Based on the acoustic simulation software LMS Virtual.lab,the radiated noise of the oil pan is analyzed and the plate contribution is solved,and the radiated noise of the oil pan is predicted.The highest sound pressure level at the whole field point of the oil pan is 81.6d B when the frequency is 800 Hz.The determined area is the deep bottom of the oil pan,which contributes 56% at 300 Hz and the sound pressure level reaches 96 d B.(4)Based on modal shape,the structural parameters of the oil pan change with the vibration response and noise contribution of different plates.The structural form of the oil pan is changed by changing the arrangement of stiffeners,spacing,height,width and cross-sectional area of stiffeners.The results show that:(1)When the spacing of stiffeners is small,the modal natural frequency does not increase obviously.And the modal natural frequency increases obviously when the spacing is 25mm;(2)The modal simulation results show that the first-order natural frequency of the oil pan increases slightly with the increase of the width of the stiffener.(3)By changing the height of stiffener,it can be found that the modal natural frequency of oil pan increases with the increase of stiffener height on its bottom surface.It increases obviously when the height reaches 4mm,which shows that higher stiffener can be selected as far as possible without special restrictions on oil pan,and it suggests that increasing the height of stiffener will improve the natural frequency more than the width of stiffener.(4)Through several regular different stiffener arrangements,it is found that the orthogonal stiffener arrangement has the greatest improvement on the natural frequency compared with other arrangements in this paper,and other shapes have improved the modal natural frequency but the effect is not obvious;(5)It is found that the first-order natural frequency decreases with the decrease of the cross-sectional area of the stiffener,so the stiffener with larger cross-sectional area should be selected as far as possible.