Combined design and robust control of a vehicle passive/active suspension

System performance can significantly benefit from optimally integrating the passive and active elements of vehicle suspension systems. The present article introduces an approach that combines passive and active elements to improve the robustness of a vehicle suspension system with respect to a worst-case scenario. This integrated passive and active suspension approach leads to a coupled optimization problem that is often difficult to solve. To reduce the computational effort, a sequential strategy that optimizes the passive elements first, and then the active elements, is used depending on the strength of the coupling. The effect of level of uncertainty, tire stiffness, and unsprung mass parameters on this coupling is then studied. Varying such parameters leads to establishing a relationship between coupling and robustness of the control system. This link between coupling and robustness can be utilized to aid the designer in assessing the parameters' influence on coupling and robustness. Results show that the coupling between design and robust control tends to increase as the level of uncertainty increases. In addition, demanding more robustness for vehicle suspensions with harsh ride characteristics increases coupling much more rapidly compared to suspensions with soft ride characteristics.