The problem considered in this paper is the design and analysis of a control system for semi-active suspensions in road vehicles. Three control strategies are tested: the two-state skyhook damping, the linear skyhook damping, and a newly-proposed control strategy based on two-state switching dampers. In order to assess and to compare the closed-loop performance of these control strategies, an evaluation method based on the describing-function is proposed. This evaluation approach provides, in the frequency-domain, a clear picture of the closed-loop performance on the body acceleration (comfort objective) and on the vertical load at the road-tire contact surface (handling objective). This evaluation method inherently provides a quantitative estimate of the degree of Input/Output non-linearity of the closed-loop system.
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