Scott Noll

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 lowerto 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.

Application of a Novel Method to Identify Multi-axis Joint Properties

This article is motivated by the widespread use of shaped elastomeric body mounts that undergo broadband, multi-axis loading; whereas often in application, the principal direction mount properties are measured separately at single frequencies. An inverse method is applied to a new experiment that is constructed with an elastic metal beam end-supported by two elastomeric mounts. Due to a judiciously selected attachment location relative to the neutral axis of the beam as well as the shape of the mount, the in-plane transverse and longitudinal beam motions are found to be coupled. This method utilizes the sensitivity of the beam modal parameters, including natural frequency, mode shapes, and damping ratio, to support properties at each end to identify the multi-axis mount properties. The dynamic stiffness and loss factors of the elastomeric mounts are directly measured in a commercial elastomer test machine and agreement is found between the inverse and direct methods at small displacements. Further, this article helps provide insight into multi-axis properties with new benchmark experiments on off-the-shelf mounts that permit comparison between inverse system and direct component identification methods of the dynamic multi-axis elastomeric mount properties.