Experimental Determination of the Effect of Cargo Variations on Steering Stability

Mission demands for U.S. military tactical trucks require them to transport a broad array of cargo types, including intermodal containers. The wide range of mass properties associated with these diverse cargo requirements has resulted in potential for steering stability issues. The potential for steering stability issues largely originates from the high mobility characteristics of single-unit military tactical trucks relative to typical commercial cargo carriers. To quantify the influence of cargo variations on stability, vehicle dynamics experiments were conducted to obtain steering stability measurements for a tactical cargo truck hauling a broad range of rigid cargo loadings. The basic relationship for the understeer gradient measure of directional response behavior and observed data trends from the physical experiments were used to evaluate the relationship between the steering stability of the truck and the mass properties of the cargo. The results of the evaluation demonstrated that the steering stability condition, quantified based on the understeer gradient, can be characterized reasonably well as a function of (1) the vehicle weight, (2) the product of the vehicle weight and longitudinal center of gravity, and (3) the vehicle vertical center of gravity. The results also indicated the need to account for the influence of cargo variations on tire cornering stiffness for high confidence predictions of understeer gradient magnitudes.