Explanation for Variability in Lower Frequency Structure-Borne Noise and Vibration: Roles of Rear Subframe Dynamics and Right-Left Spindle Phasing

This investigation focuses on a class of rear suspension systems that contain both direct and intersecting structural paths from the tire contact patches to the vehicle body. The structural paths intersect through a dynamically active rear subframe structure. New experiments and computational models are developed and analyzed in this article to investigate the variability of structure-borne noise and vibration due to tire/road interactions in the lower- to mid-frequency regimes. Controlled operational experiments are conducted with a mass-production minivan on a chassis dynamometer equipped with rough road shells. Unlike prior literature, the controlled experiments are analyzed for run-run variations in the structure-borne noise up to 300 Hz in a single vehicle to evaluate the nature of excitations at the spindle as the key source of variation in the absence of significant manufacturing, assembly and instrumentation errors. Further, a deterministic modal expansion approach is used to examine these variations. Accordingly, an illustrative eleven-degree-of-freedom lumped parameter half vehicle model is developed and analytically utilized to demonstrate that left-right spindle excitation phasing dictates the participation of the subsystem vibrational modes in the system forced response. The findings are confirmed through the analysis of a reduced finite element model of the vehicle system with a high-fidelity, modally dense suspension model, where the left-right rolling excitation phasing at the spindle alone is found to affect the component dynamic vibration amplitudes up to ±30 dB depending upon the component location and frequency range. These results are in qualitative agreement with the type of variations observed in the experiments.