Structure dynamics of the chassis determines basic NVH (Noise, Vibration and Harshness) performances and service life of any automobile. Therefore, modal test and response analysis should be carefully conducted in its structure design or refinement. This study identifies eleven modes of the Land-wind X6 chassis below the frequency of 200Hz, and analyzed the frequency response at several key points. The first-order modal frequency of 26Hz demonstrates that the chassis is readily excited by normal operations, and the entire torsional stiffness is insufficient. Vibrations at the torsion bar mounting points and the first cross member are remarkable, and there exist three obvious resonant peaks within the normal 23-26Hz range. Thus, local stiffness of the first cross member and two end mounting points should be improved. Additionally, because low frequency response at the front suspension upper arm mounting points is notable, and the stiffness is very insufficient, it is better to add a cross member between the upper arm mounting points, not only to improve structure stiffness, but also to relax dynamic tress and avoid fracture at the welded plates.

Structure dynamics of the car body-in-white fundamentally determines the interior noise level. Thus, modal analysis and response analysis should be carefully conducted in the noise and vibration reduction. In this study, eleven modes of a car body-in-white below the frequency of 200Hz are tested and identified, and the frequency responses at several key points are analyzed. The first-order modal frequency of 34Hz demonstrates that the NVH design of the car body-in-white is basically content. However, the regions around the engine mounting points and the trunk deck have a 15.5Hz local torsional mode; Frequency response function at the engine mounting point 22 has a 23.5Hz resonant frequency; Additionally, because there exist two resonant frequencies at 18Hz and 24Hz, respectively, within the normal excitation frequency range, remarkable vibration might be readily transmitted from the steering fixing point to the driver and induce noise. Therefore, to reduce the interior noise effectively, local stiffness around the engine mounting point 22, the trunk deck and the steering shaft fixing point 33 should be improved, and pertinent structure should be carefully refined.