Improving the performance of a semi-active suspension at the damping-invariant point

The problem considered in this paper is the design and analysis of control strategies for semi-active suspensions in road vehicles. In particular, this paper focuses on the analysis of a suspension at the so-called "c-invariant point", namely the working point (in the frequency domain) where the filtering effect of the suspension is invariant with respect to the damping coefficient c of the shock absorber. In this paper it is shown how a fast-acting modulation of the damping coefficient can significantly improve the filtering effect of the suspension even at the c-invariant point. This is an interesting example of fast switching between two linear time-invariant dynamic systems, which results in a time-varying system having better dynamic properties.