Design On Bus Interior Noise Reduction In Low Frequency Based On Structural-acoustic Coupling

Vehicle noise is one of the important indexes to evaluate the design level of modern automobile manufacturing.Automobile noise will not only pollute the environment but also seriously affect the car ride comfort.Aiming at the booming noise at the driver’s seat of a JL3128 bus with constant speed,and the low-frequency noise reduction of the bus was studied by combining test and finite element analysis.Through the real vehicle road test,the vehicle interior noise,shaft head vibration,and powertrain vibration are tested respectively under the cement road and asphalt road.The results show that there is a serious booming noise in the bus on cement road compared with the asphalt road.The driving noise of different working conditions has an obvious peak value when the frequency near 14 Hz.Through the comparative analysis of shaft head vibration,leaf spring vibration,engine excitation spectrum and interior noise response spectrum,and suspension bias test,it shows that the peak noise in the vehicle is caused by road excitation and has no relation to engine excitation.In order to analyze the main transmission path of interior roar further,the vibration response of the panel structure(bus roof and glass)perpendicular to the longitudinal axis of the vehicle was tested.Compared with the results of interior noise analysis,it shows that the vibration of the bus roof is the main contributor of interior noise.When the frequency is about 14 Hz,the interior noise and the vibration of the top cover have obvious peaks at the same time.Furthermore,the experimental modal analysis shows that there is a breathing mode near 14 Hz,which is close to the road excitation frequency and the peak frequency of the car roar.The BIW(body in white)finite element model is established by Hyper Mesh.On this foundation,the interior body model,acoustic cavity model,and structural-acoustic coupling model are successively constructed.The accuracy of the model is verified by comparing the test and analysis results of modal and interior sound pressure level response.The results of modal analysis show that there is a breathing mode with a frequency of 14.5Hz in the bus roof,which is close to the second-order modal frequency of 14.3Hz in the acoustic cavity,so the coupling resonance causes the booming noise in the bus.Then,in order to accurately determine the problematic part of the bus which has the largest contribution to the interior noise,the Panel Participation Factor(PPF)is analyzed by using the simulation method.The results show that the front part of the bus roof contributes the most to the sound pressure value of the driver’s seat,so the corresponding structure improvement scheme is proposed.The results trun out that the breathing mode of the improved tectum is increased to 17.9 Hz.Through the real vehicle test,the noise inside the vehicle disappears after the improvement and achieves a good noise reduction effect.The interior noise source is identified by testing,and the finite element model of structuralacoustic coupling is established,and based on the contribution analysis,the design problems are found and improved.The effect is remarkable,which shows that the research methods in this paper are feasible.The research results can be extended to construction machinery,aerospace,rail transit,and other vehicles or equipment,and it can improve the comfort of drivers.