Development of a control strategy for a suspension system with an active variable kinematics

Active and semi-active suspension systems are widely diffused into the automotive industry. Most of the proposed devices try to achieve a better compromise between handling and comfort requirements by replacing traditional springs, shock absorbers and antiroll bars with active or semi-active actuators allowing to change suspension stiffness and damping according to a suitable control strategy. An alternative way for controlling passenger car suspensions is proposed in this paper. Traditional passive springs and dampers are maintained, while the geometry of the suspension and thus its kinematics is actively varied. By changing the suspension geometry, spring and damper rates are in fact varied, this modifying the vertical load on the tire and/or the vehicle height from the ground. Among the advantages concerned with this device, the most significant ones are that antiroll bars can be avoided (thus increasing the vehicle interior spaciousness), vehicle aerodynamics can be improved by regulating the vehicle height and vertical loads distribution can be modified during turns. The layout of a double wishbone suspension has thus been adapted and optimized in order to host an active hydraulic actuator connecting the coil spring to the rocker. Then a control strategy has been designed aimed at improving the vehicle handling performances during turns negotiation. The effectiveness of the proposed active suspension system has been assessed by means of numerical simulation carried out with a Multy-Body (MB) vehicle model.