A vehicle suspension system is the main component in a ground vehicle that functions to achieve good ride comfort by isolating vibration of the road from the passenger. Active suspension system has the capability to continuously adjust itself, hence has a better design trade-offs compared to a conventional suspension system. Active disturbance rejection control (ADRC) is a relatively new control method and has not been thoroughly investigated in the area of ride comfort and advanced automotive suspension. In this thesis, ADRC with and without input decoupling transformation (IDT) is proposed to improve the ride quality performance of a vehicle with active suspension system according to several performance criteria: minimizing vehicle body accelerations, suspension working space, and road holding. Three vehicle models: quarter-car, half-car, and full-car model were used in this thesis. The models used in the analysis were limited to discrete models which break down the vehicle model into lumped systems. Through experimental simulation studies, the ability of the proposed controllers to cope with varying process is investigated. The optimized controllers are then compared to an ideal skyhook control to benchmark the performance. Results show that ADRC-IDT was able to produce comparable performance to a typical ADRC control structure, but with less number of control parameters. Both controllers were able to significantly reduce vehicle body acceleration while maintaining other responses. Furthermore, On the whole, it is shown that the performance of the optimized ADRC and ADRC-IDT is close to the performance of an ideal skyhook control especially for the sprung mass vertical acceleration which is the main indicator of vehicle ride comfort.

In designing passive suspensions, a compromise has to b~ made between ride comfort and car handling. For an off-road vehicle that requires both good ride comfort and good handling capability, a passive suspension alone is not enough. Therefore, there is a need to introduce active elements to further improve vehicle suspensions, which could offer both better ride comfort and car handling to this type of vehicle. This work deals with dynamics and control methods analysis of active suspension systems for off-road vehicles. Comprehensive comparison on three different configurations; 2- axle, 3-axle and 4-axle half-vehicle models were conducted to analyze the effect of using active control methods. The application of two control methods, namely LQR and fuzzy logic controls have been analyzed and compared with passive systems. Sprung mass vertical and pitch acceleration responses were analyzed for measurements of ride quality and road handling. Suspension deflection and tire deflection responses were observed to identify any compromise in the other aspects of vehicle dynamics. Results show that the LQR and FLC successfully controlled the active suspension, improving ride quality and handling of the vehicles without compromising the rattle-space requirement and road holding performance of the vehicles. Comparison of all models also shows that in general, improving ride quality performance will also improve vehicle handling. Moreover, it is observed that FLC control requires less amount of actuator force compared to LQR control to achieve the desired performances.