IN SEARCH OF A SUITABLE CONTROL POLICY FOR INTELLIGENT VEHICLE SUSPENSIONS

ABSTRACT Many control policies, such as skyhook and groundhook control, are now being considered for intelligent vehicle suspensions. Past studies have shown the performance limitations of these policies, as well as others that have been considered for vehicle applications. The performance of three semi-active control policies were studied experimentally under steady-state and transient inputs. Experimental results were obtained using a quarter-car rig and a magneto-rheological damper. The commonly considered skyhook and groundhook control policies were employed and evaluated under a steadystate, or pure tone, input and a transient, or step input. An alternative control technique called "hybrid control," which attempts to merge the performance benefits of skyhook and groundhook control was also considered. Peak-to-peak displacement and peak-to-peak acceleration were used to evaluate performance. The results indicate that while skyhook and groundhook can offer benefits to either the sprung or unsprung masses, hybrid control can offer benefits to both masses. The compromise inherent in both skyhook and groundhook is eliminated with the use of hybrid control. Both the steady-state and transient dynamics of the sprung and unsprung masses can be reduced below those of passive using hybrid control with an α of 0.5. This corresponds to equal contributions from skyhook control and groundhook control. INTRODUCTION As technology advances, semi-active suspensions continue to gain considerable attention. Semi-active suspensions consist of a spring element and a damper which offers variable damping. Whether through mechanically changing orifices or fluid with adjustable viscosity, a semi-active damper has the ability to adjust the damping level. First introduced by Crosby and Karnopp [1,2], semi-active systems have since been considered for vehicle primary suspensions. Semi-active suspensions have been shown to offer valuable benefits for vehicle primary suspension