Acoustic Characteristic Analysis And Optimization For SUV Structure

The interior noise of a vehicle has significant influence on the passenger’s comfort and body healthy. The NVH level is an important indicator of the design and manufacturing quality of a vehicle, which closely linked to the competitiveness in the market. In this paper, for the issues of vibration and noise in idle condition of a SUV in pre-production stage, the structure acoustic characteristics were analyzed and optimized.The finite element models of BIW body and frame of the SUV were established respectively. The modal frequencies and mode shapes were solved by numerical modal analysis, and verified through modal testing. On this basis, the whole car FEA model with doors and windows were established. Then a modal analysis of the whole SUV was conducted.On the basis of whole vehicle FEA model, the structure-acoustic coupled FEA model including the effect of space occupied by the seat was established. The modal of the acoustic cavity was solved with FEA. A frequency response analysis on structure-acoustic coupled model was conducted to verify the validity of the model. The body acoustic sensitivity of driver’s right ear and rear passenger seat was solved within the range of 0~200Hz。The sound pressure and suspension excitation force of the SUV was tested in idle condition. By considering the influence of structure modal, sound pressure and suspension excitation the acoustic and vibration characteristic of the SUV was analyzed. The result showed that: the low order modal frequencies and the excitation frequency were coupled, which led to bad acoustic characteristic in idle condition. And the peak of the body acoustic response in excitation frequencies exacerbated the acoustic and vibration coupled effect.Optimization of body modal frequencies was conducted. The modal sensitivity of the panels were analyzed. On this basis, made the key panels as variable, the minimum of body mass as objective and the BIW body 1st and 2nd modal frequency as constraints, conducted modal frequency optimization. After optimization, the 1st order and 2nd order modal frequency of BIW body reached to 27.94 and 30.52 Hz respectively. The 1st and 2nd modal frequency of the vehicle reached to 28.02 and 29.03 Hz respectively, which satisfied the requirements of engine vibration isolation. The bend stiffness and torsional stiffness were checked and the acoustic response was calculated after optimization.The panel acoustic contribution analysis in the peak frequency was performed to decide which panel to be optimized. The interior noise was controlled by reducing the vibration velocity on panel’s surface. In this paper, two optimizations were performed to control the interior noise, including panel optimization and adding damping materials to the panel. The former one made the minimum of weighted panel vibration velocity as objective, the modal frequencies and mass as constraints, conducted panel thickness optimization. The latter one based on modal strain energy theory to add damping material on the panel. Both modified programs were verified by simulation. Under both scenarios, the peak amplitude of the sound pressure inside the car have been effectively reduced.