Modal Analysis Approach for Analysis and Design of Vehicle Transient Behavior

<div class="section abstract"><div class="htmlview paragraph">In order to manage the serious global environmental problems, the automobile industry is rapidly shifting to electric vehicles (EVs) which have a heavier weight and a more rearward weight distribution. To secure the handling and stability of such vehicles, understanding of the fundamental principles of vehicle dynamics is inevitable for designing their performance.</div><div class="htmlview paragraph">Although vehicle dynamics primarily concerns planar motion, the accompanying roll motion also influences this planar motion as well as the driver's subjective evaluation.</div><div class="htmlview paragraph">This roll motion has long been discussed through various parameter studies, and so on. However, there is very few research that treats vehicle sprung mass behavior as “vibration modes”, and this perspective has long been an unexplored area of vehicle dynamics.</div><div class="htmlview paragraph">In this report, we propose a method to analytically extract the vibration modes of the sprung mass by applying modal analysis techniques to the governing equations of vehicle handling and stability. Specifically, we solve the general eigenvalue problem of the system to obtain complex eigenvalues and complex eigenvectors, use these to decouple the original equations of motion, and reconstruct the original vehicle behavior by superimposing each analytically solved vibration mode.</div><div class="htmlview paragraph">As a result, it was revealed that the sprung mass behavior of the vehicle consists of two fundamental modes: “Mode 1,2,” which are primarily roll motions excited by front lateral forces, and “Mode 3,4,” which are planar motions excited by rear lateral forces coupled with roll. Furthermore, an analysis of the causal relationship between design variables and vibration modes reveals that during the initial roll response at turn-in, Mode 1,2 promote roll, whereas Mode 3,4 suppress it, making the rise gradual, or that design modification that delays planar motion associated with Mode 3,4 results in a two-stage increase in roll response, elucidating mechanisms of phenomena that could previously be understood only through parameter studies.</div></div>