A model free control design approach for a semi-active suspension of a passenger car

Comfort in passenger cars can be improved by including a semi-active suspension system, controlled by online varying the damping based on measurements of the car motions. The selection of an appropriate control structure is crucial, since it determines the complexity of the control design and parameter tuning process. This paper presents a flexible model-free control structure based on physical insights in the car and semi-active suspension dynamics which are used to linearize and decouple the system. A static decoupling is used to decouple the system into its modal motions heave, roll and pitch, which are then controlled by modal (diagonal) controllers, consisting of several feedback and feedforward modules, each taking care of a specific comfort or handling issue. The feedback controller is based on the Skyhook principle. Steering angle, throttle, and break pedal feedforward control roll during cornering, and pitch during acceleration and deceleration, respectively. All control parameters are physically interpretable and therefore can be easily tuned online according to guidelines given by test pilots.