Semi-active force generators for shock isolation

Abstract

Semi-active suspensions represent a compromise between active and passive suspensions. The isolator requires virtually no power and the forces in the damper are generated by modulating its orifices for fluid flow. The shock isolation characteristics of semi-active isolators based on two different control schemes are presented. In the first type the control depends on absolute and relative velocities of the sprung mass while in the second type it depends on relative displacement and relative velocity. Both employ continuous control of damper forces as opposed to on-off control. The semi-active isolator is incorporated in a one-degree-of-freedom quarter vehicle model. The base is subjected to rounded pulse and rounded step transient displacement inputs. The performance is evaluated in terms of the resulting acceleration of the sprung mass and the relative displacement across the isolator. The performance of the semi-active isolators is compared with that of passive and active isolators. It is seen that both the semi-active control schemes can simultaneously reduce the acceleration and the relative displacement, something passive linear isolators cannot do. They also achieve a performance close to that of a fully active isolator without requiring power, or complex and expensive instrumentation.