A New Variable Stiffness Suspension System

This paper chronicles the research on the design, analysis, experimentation and application of a high efficient, low-power variable stiffness suspension system. The central concept is based on a recently designed variable stiffness mechanism which consists of a horizontal control strut and a vertical strut. The horizontal strut is used to vary the load transfer ratio by controlling the location of the point of attachment of the vertical strut to the car body. This movement is controlled either passively using the horizontal strut, actively using a hydraulic actuator, or semiactively using a magneto-rheological (MR) damper. All the three cases are considered. The system i s analyzed using an L2-gain analysis based on the concept of energy dissipation. The analyses, simulation, and experimental results show that the variable stiffness suspension achieves better performance than the constant stiffness counterpart. The performance criteria used are; ride comfort, characterized by the car body acceleration, suspension deflection, and road holding, characterized by tire deflection. Moreover, the variable stiffness architecture is used in the suspension system to counteract the body roll moment, thereby enhancing the roll stability of the vehicle. To this effect, the lateral dynamics of the system is developed using a bicycle model. The accompanying roll dynamics are also developed and validated using experimental data. The positions of the left and right control masses are optimally allocated to reduce the effective body roll and roll rate. Simulation results show that the resulting variable stiffness suspension system has more than 50% improvement in roll response over the traditional constant stiffness counterparts. The simulation scenarios examined are the fishhook and the double lane change maneuvers.