Effect of Semi-Active Front Axle Suspension Design on Vehicle Comfort and Road Holding for a Heavy Truck

The capabilities of a semi-active front axle suspension are investigated for a commercial vehicle. A half truck model of a 4×2 tractor and semitrailer combination is developed in Matlab/Simulink for this purpose. Also, a 2 DOF roll plane model is considered to capture the roll motion of the vehicle body mass. Employing the above-mentioned models, results from on-off and continuous variable semi-active damping systems are compared to the ones from the passive suspension system according to ride comfort and handling safety characteristics. Ride comfort is evaluated using the acceleration signals in the cab by studying acceleration peak values as well as PSD plots of the iso-filtered accelerations. Cab center of gravity pitch and body roll motions are also assessed. Furthermore, handling in terms of road holding characteristics is examined by means of analyzing dynamic tire forces while monitoring rattle space (suspension deflection) simultaneously. The control strategies of the semi-active damping are based on the skyhook theory, in which the damping coefficient is either switchable or continuously controlled. Skyhook, groundhook and hybrid control laws have been implemented and evaluated in the vehicle models. The results of the comparison analysis that are presented quantitatively and qualitatively clearly show the great influence of the semi-active dampers on the vehicle dynamic properties for the conducted simulations. With continuous semi-active dampers accelerations in the cab are drastically decreased particularly up to front axle resonance frequency. Hence, unlike passive suspension that is a compromise between ride comfort and handling, semi-active suspension facilitates enhancing both target criteria