Semi-Active Suspensions

The optimum level of passive damping for minimising the RMS dynamic tyre force and RMS body acceleration of a heavy vehicle is determined by testing a damper in a ‘hardware-in-the-loop’ (HiL) test rig. Two different control strategies, (‘modified skyhook damping’ (MSD), and linear optimal control with full state feedback (FSF)), are investigated theoretically using linear models, and suspension force control laws are derived. These control laws, along with simple ‘on-off control, are then tested experimentally using a prototype semi-active damper which is controlled so as to follow the demanded force, except when power input is required. The achievable performance improvements are compared, and differences between the linear theory, computer simulations and experimental performance are discussed. It is found that using FSF control, RMS body acceleration and RMS tyre force can be reduced simultaneously by 28% and 21% of their values for optimal passive damping.