Estimation of geometrical parameters for MacPherson suspension with rack and pinion steering system and elastokinematic analysis

Abstract

Consulta en la Biblioteca ETSI Industriales (7712)

[EN] The aim of this project is to estimate the unknown values of geometrical parameters of the MacPherson suspension and the steering system with rack and pinion on the basis of the displacement characteristics obtained from measurements of the real mechanism. The estimation of geometrical parameters on the basis of measurement results and simulation procedure can be realized, if we can describe the kinematic model with the position and orientation coordinates of the wheel knuckle as the functions of the spring length and the rack displacement. In this study some simplifying assumptions are taken into account. The joints of the mechanism will be considered as ideal and all bars of the mechanism are considered as rigid. The elasticity of the tire will be also neglected. The only elastic elements that will be considered in this work are the spring and the lower bushing silentblock, which elasticity, in both cases, will be taken into account as linear. Elastokinematic study of the MacPherson suspension and steering system of a Fiat Cinquecento is based on the measurement results for the toe angle and the camber angle of the front right wheel obtained by using a special device, and described as the displacement functions of the wheel knuckle taking into account the position of the steering system and the length of the spring. The camber and toe angles are changed according to different load conditions of a car during braking or other maneuvers. The differences between experimental and simulation results can be minimized and used to estimate the real parameters of the considered suspension system. In order to obtain the real geometrical parameters of the suspension, a sensitivity analysis is useful. This means to analyze the influence of the changes of the initial values of the parameters. If we know how the calculation results are changed with small deviations of the parameters, we can modify them in order to fit the same curves obtained from the experimental results. We have to take into account that the kinematic model introduces some simplifications, so the final results will not be exact. Moreover we have to know that the device used in the experimental analysis is not perfe