Abstract
The optimal active suspension for the cab in a tractor-semitrailer vehicle model is obtained using the linear stochastic optimal control theory. Two state controllers, full state and limited state feedback, are determined. The control law minimizes a performance function representing operator discomfort and cab suspension travel. The randomly profiled road is modelled as a filtered white noise excitation and time delays due to the multiaxle excitation inputs are included. The performance of the optimally active controlled system is compared with the performance of an optimal passive system.