Non-Linear Full-Car Modeling and Sky-Hook Control for a Direct-Drive Active Suspension System

At Eindhoven University of Technology an active suspension system has been developed [1]. This system is superior to other active suspension in terms of bandwidth and power consumption. This active suspension system was tested on a quarter car setup and showed improvements of up to 48% in comfort [2]. In order to implement this suspension in a test vehicle with the same improvements, a non-linear full-car model is developed in this paper which is used to simulate and design various controllers. The non-linear model incorporates non-linear damping, bump stops, actuator saturation and actuator friction. To model the friction in the actuator a combination of Coulomb and viscous friction is used. To model the MacPherson suspension strut, two methods are described and compared. Also the implications of using acceleration sensors which are placed in line with the MacPherson strut are discussed. It is shown that the placement of the acceleration sensors limits the control performance during vehicle acceleration and cornering. To control the suspension system, a sky-hook controller is used. The implemented sky-hook controller showed improvements in a frequency region of 0.7 to 8 Hz. When comparing the nonlinear model and linear model to the measurements conducted on a test vehicle, it is shown that the non-linear model more accurately predicts the accelerations of the sprung mass.