Frequency domain models for active suspension controller design

In the past years a lot of different chassis control system have been developed in order to improve handling performance, ride comfort and safety of the vehicle. These chassis control systems are based mainly on the active control of the steering system, the traction/braking system and the suspensions. Depending on the riding conditions one of these systems can be more effective than the others, so it difficult to choose the best compromise for al the possible scenarios. For this reason, most of the new studies on this topic are focusing on the integration of all of the available control system to obtain and Integrated Chassis Control (ICC) system able to improve the vehicle performances in a wide range of operation conditions. In this context, being able to formulate the control law for the ICC is the key to achieve the expected results. In this thesis a model-based procedure for the design of the controllers is presented taking as an example the synthesis of an anti-roll moment distribution controller for yaw rate tracking. The model used in this case is a simple model in which only 3 degrees of freedom are taken into account, but in order to apply the model-based approach to a wide range of active systems like dynamic lift or pitch control, a more advanced vehicle model is needed. For this purpose, a full vehicle model with 6 degrees of freedom with active suspensions and which takes the suspension kinematics into account is presented. The response of the newly developed model is then compared to that of a validated vehicle model by simulating different manoeuvres. Finally, the procedure to linearise the model is presented to obtain the state space formulation which can be used, by using the model-based approach, to synthetize a variety of controllers and thus to obtain the control laws needed for the implementation of an Integrated Chassis Control.