An examination of alternative schemes for active and semi-active control of vertical car-body vibration to improve ride comfort

The recent tendency to reduce the weight of car bodies is posing a new challenge to vertical ride quality, since the vibrations related to car-body vertical bending modes affect heavily passengers’ comfort and cannot be fully mitigated by conventional vehicle suspensions. In this work, four mechatronic suspensions, considering active and semi-active technologies in secondary and primary suspensions, are compared to show their relative merits. LQG and H∞ model-based control strategies are established in a consistent way for each suspension scheme to perform a comparative assessment of the four concepts on objective grounds. A two-dimensional 9-DOF vehicle model is firstly built, using a simplified representation of car-body bending modes; this model is also used to design the model-based controllers. The comparison of the four mechatronic suspension schemes based on the 9-DOF model shows that full-active secondary suspension is the most effective solution whilst semi-active primary suspension is also effective in terms of mitigating car-body bending vibration. Then, a three-dimensional flexible multibody system (FMBS) vehicle model integrated with a finite-element car-body is considered to allow a more detailed consideration of the vehicle’s vibrating behaviour. The results of the FMBS model show a good agreement to the results of the 9-DOF model and the relative merits of the four mechatronic suspension schemes as found from the previous analysis are basically confirmed, although the FMBS model is more suited for a quantitative assessment of ride quality.