Performances of Vehicles' Active Suspensions

Most complex industrial systems are difficult to control automatically. Such difficulties are due to the non linearity and to the variation of these systems' parameters, as well as to the quality of measurable variables. In view of the efficiency and of the performances obtained by the introduction of active suspension systems in vehicles, researchers undertook more work on this field. Until now, in the modelling used for such systems, the least possible degrees of freedom are introduced in order to mitigate the difficulties of the study. Hence, many studies on models of a quarter of vehicles, with two degrees of freedom only, are available. This article deals in the first section with the performances that are obtained oil this type of model by the method of fuzzy sliding mode which uses, in the present case, the fuzzy logic techniques to adjust the control gains that occur under the sliding mode. To put into evidence the efficiency and the performances of such a control system, we have compared the results obtained through the sliding mode technique solely, then through the combination of the fuzzy logic theory and the set up by the sliding mode, and the fuzzy sliding mode. The second section of the study aims at extending this kind of work to a half vehicle model with four degrees of freedom. The computation of the command force to apply to the system in order to control the suspension was based on the fuzzy logic theory for which three essential steps were developed: fuzzification, inferences, and defuzzification. The simulations made were validated, on the one hand, through a comparison to the same passive system and, on the other hand, to results available in literature.