Active control of vehicle suspensions has been the subject of considerable investigation since the
late 1960s; see, for example, [4–6] and the references therein. Studies concerning the limitations
and potential benefits of active suspensions [7–9] have shown that suspension controllers that
focus on a fixed performance measure offer a limited improvement in performance over
conventional passive suspensions, when the improvement is assessed over the whole range of road
conditions. During driving the character of dynamical interaction between the road and the
vehicle changes dramatically depending on road surface and vehicle velocity. These changes must
be taken into account to ensure optimal (or sub-optimal) acting of the system in every condition.
In order to realize the full potential of active suspensions, the controller should have the capability
of adapting to changing road environments [10,11].