The uncertainty in stiffness and damping of an automotive vehicle’s trim-structure mounts and its effect on the variability of the vibration transfer function

Ali Abolfathi,Stephen J Walsh,Amy M Dowsett,Dan J O’Boy,Stephen A Fisher

doi:10.1177/0954406217721724

Abstract

A large number of plastic clips are used in an automotive vehicle to connect the trim to the structure. These are small clips with very small masses compared to the structural elements that they connect together; however, the uncertainty in their properties can affect the dynamic response. The uncertainty arises out of their material and manufacturing tolerances and more importantly the boundary conditions. A test rig has been developed that can model the mounting condition of the clips. This allows measurement of the range of their effective stiffness and damping. Initially, the boundary condition at the structure side is replicated. The variability is found to be 7% for stiffness and 8% for damping. In order to simulate the connection of the trim side, a mount is built using a 3D printer. The variability due to the boundary condition on both sides was as large as 40% for stiffness and 36% for damping. A Monte Carlo simulation is used in order to assess the effect of the uncertainty of the clips’ properties on the vibration transfer functions of a door assembly. A simplified connection model is used in this study where only the axial degree of freedom is considered in connecting the trim to the door structure. The uncertainty in the clip stiffness and damping results in a variability in the vibration transfer function which is frequency dependent and can be as high as 10% at the resonant peaks with higher values at some other frequencies. It is shown that the effect of the uncertainty in the clips effective damping is negligible and the variability in the dynamic response is mainly due to the uncertainty in the clip’s stiffness. Furthermore, it is shown that the variability would reduce either by increasing or decreasing the effective stiffness of the clips.

Highlights

The level of noise and vibration in automotive vehicles is a major concern where the level should be kept low to ensure the satisfaction of customers
Variability in noise and vibration is common in identical vehicles due to manufacturing tolerances, variations in material properties and operational conditions,[1,2,3,4,5,6,7] which can result in vehicles with a frequency response function (FRF) that exceeds the threshold set at the design stage
Resh[14] investigated the uncertainty in the dynamic properties of engine mounts while Donders et al.[15] used a Monte Carlo simulation to study the variation in the natural frequencies of an automotive vehicle body-in-white arising from the uncertainty in the spot welds

Summary

Introduction

The level of noise and vibration in automotive vehicles is a major concern where the level should be kept low to ensure the satisfaction of customers. The variability in the natural frequencies of a car windscreen due to temperature is studied by Scigliano et al.[16] More recently, Kwon and Lee[17] modelled the uncertainty in the elastomeric joints and used the eigenvector dimension reduction method in order to obtain the variability in the dynamic response of the vehicle. They showed that the acceleration on the seat track can vary up to 6 dB due to the uncertainty in the sub-frame elastomer mounts

Methods

Results

Conclusion