Development of experimental techniques and control strategies for two novel road vehicle mechatronic suspensions

Abstract

Two novel active mechatronic suspensions for road vehicles are studied in this thesis, including the Series Active Variable Geometry Suspension (SAVGS) and the Parallel Active Link Suspension (PALS). Compared to existing active suspension solutions, both the SAVGS and the PALS are capable of low-frequency chassis attitude control and high-frequency ride comfort and road holding enhancement, with the main features of 1) negligible unsprung mass increment, 2) small sprung mass increment, 3) mature technology employment of rotary-electromechanical-actuation, and 4) inherent fail-safe characteristics. On the other hand, the SAVGS and the PALS complement each other in the application range of vehicle categories (from light high performance vehicles to heavy SUV vehicles), depending on the sprung mass and the passive suspension stiffness. In order to evaluate the practical feasibility of these two novel active suspensions, a quarter car test rig is developed for experimental study, with the SAVGS and PALS mechanisms integrated separately. Multi-body nonlinear models of the SAVGS/PALS-retrofitted test rig are built to explore the novel suspensions’ potential in performance improvement and power demand. Practical features existing in the rig (e.g. the backlash in actuation transmission) are further taken into account to compensate simulation and testing behaviours. Linear equivalent models of the SAVGS/PALS-retrofitted quarter car are derived, with geometry nonlinearity compensated. Robust control schemes with an outer-loop H-infinity control and an inner-loop actuator reference signal tracking control are then synthesized to enhance the quarter car suspension performance, in terms of the ride comfort and the road holding. A set of road cases, including a sinusoidal road, a speed bump and hole, and a frequency swept road profile are tested respectively to validate the accuracy of the model assumptions, the robustness of the synthesized controllers and the feasibility of the overall physical implementation. Moreover, this thesis also investigates the PALS application to a SUV full car. A multi-objective PID control is utilized for the chassis levelling in low-frequency driving manoeuvres, while an H-infinity control mainly takes effect in high-frequency road cases to improve the vehicle ride comfort and road holding. Nonlinear simulations with a set of ISO driving situations are performed to evaluate the PALS potential for the full car performance enhancement.