Abstract

Design of a vehicle suspension involves a difficult compromise among the ride, handling and directional control performance characteristics. While a soft suspension is desired to enhance ride quality, hard suspension springs are required to achieve good handling and directional control performance. Auxiliary roll stiffeners, in conjunction with soft suspension, are frequently used to attain an acceptable compromise between ride and handling performance of a vehicle. Alternatively, an improved compromise between ride and handling can be realized by interconnecting hydro-pneumatic suspension struts in the roll plane. The interconnected suspension can provide soft suspension rate for improved ride quality, and firm roll stiffness and damping for adequate handling and control performance. In this dissertation, a hydro-pneumatic suspension, interconnected in the roll plane, is analytically investigated for its ride and handling performance potentials. A highway bus equipped with the interconnected hydro-pneumatic suspension system is modeled in the roll plane as a four-degrees-of-freedom dynamical system subject to excitations arising from road irregularities and roll moment caused by directional maneuvers. The static and dynamic properties of the interconnected suspension are derived and discussed in terms of its load-carrying capacity, suspension rate, roll stiffness, and damping forces. The ride and handling performance characteristics of the interconnected suspension are deterministic excitations. A passive variable damping mechanism is proposed and investigated to achieve improved vehicle ride quality. The vibration isolation performance characteristics of the interconnected suspension employing the variable damping valves are further investigated for deterministic and random excitations. From the computer simulation results, it is concluded that the interconnected hydro-pneumatic suspension with inherent enhanced anti-roll stiffness and damping characteristics can provide an improved compromise between ride comfort and handling performance of a vehicle.