Shimmy evaluation using theoretical multibody model and experimental techniques

Abstract

Shimmy is the vibration in the steering rotational direction during steady-state running and gives annoyance to passengers. Passenger's comfort is a critical characteristic in vehicle. In this study, both a theoretical linear model and a numerical model are used to predict and optimize the frequencies of shimmy related modes and the level of vibration for a vehicle. A theoretical multibody linear model of 48-DOF was used for quasi-static analysis and modal analysis. The theoretical model was verified by comparing the results of modal analysis with those of a modal experiment for front suspension system using CADA-X program. The quasi-static analysis results of the theoretical model were compared with those of an ADAMS model. A full vehicle model using ADAMS was also verified with the results of the modal experiment and chassis dynamometer experiments for shimmy reproduction. From experiments and simulations, it was found that the wheel longitudinal vibration mode was the most dominant source of shimmy vibration. In addition, 13 design parameters of the front suspension system including compliance and geometric factors for reducing shimmy level were selected based on the experimental results. By performing 27 orthogonal simulations using Taguchi methodology, an optimal combination of design parameters was constructed. Through modal analysis of the theoretical model with the optimized design parameters, it was found that the wheel longitudinal vibration mode changed into two local vibration modes. Finally, a simulation of the numerical model verified that the suggested design parameters resulted in shimmy vibration reduction.