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Drive Point Mobility is commonly used in lab tests and structural analysis for the purposes of measuring and evaluating the N&V performance of a dynamic system. Unless the drive point itself is also the point of interest (for responses), the author finds that it can only provide very limited information about the whole system's dynamic / vibrational characteristics. Thus one should always try to measure, analyze, and then improve, instead of Drive Point Mobility alone, the non-drive point mobility or the generalized transmissibility as well, for their structural N&V performance. A simplified 3-DOF spring/mass/damper system is first used to illustrate the dynamic characters of the system. For more realistic structures, a FE model of the body/floor and (body side) hanger (for exhaust) is used. Then a more complete system model, consisting of a full exhaust, it's hangers/isolators, and part of the vehicle chassis/body/floor structure, is used in this paper to illustrate the above points.

Rubber isolators and bushings are very important components for vehicle performance. However, one often finds it is difficult to get the dynamic properties to be readily used in CAE analysis, either from suppliers or from OEM's own test labs. In this paper, the author provides an analytical method to obtain the dynamic stiffness of an exhaust isolator, using ABAQUS and iSight, with tested or targeted isolator static stiffness information. The analysis contains two steps. The first step is to select the (rubber/EPDM) material properties for the FE isolator model by matching the static stiffness with either the targeted spring rate (linear or nonlinear) or the (tested) load / deflection curve. The second step is to perform dynamic analysis on the statically “validated” FE isolator model to obtain its dynamic properties.

4-Post durability test simulations using a nonlinear FEA model have been executed by engineers responsible for structural durability performance and validation. An integrated Body and Chassis, full FEA model has been used. All components of the test load input were screened and only the most damaging events were incorporated in the simulation. These events included the Potholes, Belgian Block Tracks, Chatter Bump Stops, Twist Ditches, and Driveway Ramps. The CAE technology Virtual Proving Ground (eta/VPG®*) was used to model the full system and the 4-Post test fixtures. The nonlinear dynamic FE solver LS-DYNA** was used in this analysis. The fatigue damage of each selected event was calculated separately and then added together according to the test schedule. Due to the lack of stress/strain information from hardware test, only the analyzed fatigue damage results of the baseline model were scaled to correlate with physical test data.