This paper makes an objective analysis of the performance obtained when using a hydraulic actuator as a variable force element in the active suspension system of an automobile. A nonlinear control method is attempt to provide classical "sky-hook" damping. Experimental and simulation results obtained with the use of a standard hydraulic actuator am pre- sented. The use of the actuator results in significant overall improvement in ride quality with an acceleration reduction of as much as 50 % compared to an ordinary passive shock absorber at the sprung mass natural sent the entire car. frequency. The suspension deflection performance is also improved but the tire deflection performance is somewhat worse than the passive at frequencies close to the unsprung mass natural frequency. This is because the active controller fails to track the "sky- hook" damping force accurately at high frequencies. The cause of this failure is investigated. A theoretical analysis of the actuator dynamics are made and changes in actuator parameters for this specific application are suggested.
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