Preview estimation and control for ( semi - ) active suspensions

The dynamic behaviour of a vehicle (e.g. the dynamic tire forces, the suspension deflection, and the vertical acceleration of the sprung mass) can be improved significantly if the passive suspension is replaced by an active suspension with preview. Preview means that a priori information of the road surface is used in the control of the suspension. In this report, the rear wheels of the tractor of a tractor-semitrailer combination are actively suspended with preview. The active suspension is tested for realistic road surfaces, i.e. rounded pulses and stochastic road surfaces, and is compared with a representative passive suspension. Moreover, an observer is designed to reconstruct the preview information (here: the road surface) from simple measurements at the front side of the tractor. Finally, a strategy is described to test the combination of the controller and the observer. It appears that the spectacular results obtained from tests of the active suspension on a step function as the road input can not be generalized for more realistic road surfaces. However, the performance of the active suspension is still significantly better than that of the passive suspension. Compared with the minimum available preview time of 1/8 second, a preview time of 1 second improves the dynamic behaviour of the vehicle especially for low-frequent road-excitations. To reconstruct the preview information, a model of the road surface is not necessary and the measurements have not to be differentiated. The estimation error due to model errors is reduced quickly. It is yet not clear whether or not this is fast enough to guarantee a good closed loop behaviour. The observer reduces the drift in the estimated road surface. The main disadvantage of the observer is that not all the measurements are filtered. The combination of the controller and the observer has yet not been tested thoroughly.