Experimental Modal Test for Structure Refinement of an Automotive Chassis

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.