Dynamic Analysis of a Slow-active Suspension System Based on a Full Car Model

In this paper, a methodology for the design and evaluation of a slow-active vehicle suspension system is developed. The suspension consists of a limited bandwidth actuator in series with a passive spring; the combination being in parallel with a passive damper. An optimal multivariable controller is designed for a full car model. The controller takes the form of a linear quadratic regulator with supplementary states for added integral action. The car model is formulated as a linear lumped parameter model, comprised of five discrete rigid bodies. The three-dimensional vibratory motions of the vehicle are described in terms of seven degrees-of-freedom: bouncing, pitching and rolling motions of the sprung mass, and the bouncing motion of each unsprung mass. An integrated investigation of vehicle dynamics, roadway excitations and performance measures is developed in order to investigate the dynamic analysis and design of vehicle suspension systems and the consequences of vehicle ride quality. The ride isolation performance and road-holding qualities of the slow-active system are compared to those of a full bandwidth active suspension and a typical passive suspension system. The simulation results lead to the conclusion that the optimal control theory provides a useful mathematical tool for the design of active suspension systems. The optimally-controlled suspension designs prove to be effective in controlling vehicle vibrations, and achieve better performance than the conventional passive suspension. The slow-active systems offer significant improvements in controlling body resonances. In fact, the slow-active system tracks its full bandwidth active counterpart. The low power consumption capabilities of this type of system compared to full bandwidth active systems render it to be an attractive candidate for providing good ride qualities, with its real time implementation being promising.