Experimental determination of automotive system response characteristics

Vehicle NVH performance is significantly affected by the dynamics of various primary systems. In the automotive industry, different design activities or vendors are responsible for designing various different systems simultaneously. Therefore, it is highly desirable to gain a better understanding of the individual system characteristics and the interaction between the primary systems to achieve a desirable overall NVH performance. Unfortunately, it is usually quite difficult to construct a proper fixture to accurately measure and quantify the actual uncoupled system characteristics. This paper examines an alternate approach of applying the FRF-based substructuring method to back-calculate the system response characteristics from the full vehicle system measurements. The results are then used to forward-compute the dynamic response of the vehicle, which are also validated by comparison to the direct response function measurements. In this paper, a two-system formulation is developed based on the assumption that there is very little cross-axis coupling between the different mounting points of the two distinct systems of interest. The calculated system FRFs can be analyzed to expose critical structural areas and paths that contribute significantly to the interior noise and vibration levels.