Modal Analysis Approach for Analysis and Design of Vehicle Transient Behavior

In order to solve the increasingly serious global environmental problems, the automobile industry is rapidly shifting to EVs and plug-in hybrid EVs, so vehicle weights are increasing. In addition, the use of low rolling resistance tires to improve energy efficiency is increasing. In order to ensure the maneuverability and stability of such vehicles, it is becoming increasingly necessary to design performance based on better understanding of the basic principles of vehicle dynamics. Vehicle dynamics is fundamentallilly based on planar motion, but the accompanying roll motion also affects the planar motion and also driver's subjective evaluation. Vehicle dynamics analysis considering roll has been discussed by parameter studies, by characteristic analysis using equivalent models, or by characteristic root analysis. However, with the exception of R.S Sharp's report, which mentions the three vibration modes of motorcycles, there are very few examples of vehicle dynamics analysis in terms of "vibration modes," and this perspective has long remain an unexplored area of vehicle dynamics. In this report, we propose a method to analytically extract the sprung mass vibration modes by applying a modal analysis method to the governing equations of vehicle handling stability. Specifically, the complex eigenvalues and complex eigenvectors of the system are found from the generalized eigenvalue problem of the vehicle's equations of motion, and these are then used to uncouple the equations of motion. Then solve each vibration mode, and the original vehicle behavior is reconstructed by superimposing those vibration modes. In this way, it becomes easier to understand and control each vibration mode, which is the essence of vehicle behavior, and it becomes possible to design the desired sprung mass behavior while better understanding and grasping the phenomena.