Dynamic road damage caused by heavy vehicle rolling motion when including Road Crossfall

Abstract

The rolling motion of heavy vehicles is ignored in almost all road damage studies and is simply assumed to be symmetrical. This dissertation shows that the addition of rolling motion when incorporating road crossfall is essential to accurately capture the true dynamic road damage caused by heavy vehicles. Dual track road profiles were created with road roughness values ranging from 0.5 m/km to 10 m/km. Road crossfall values from 0% to 5% were simulated and corresponded to typical values found in South Africa and across the world. A 9 degree of freedom (DoF) model was developed and implemented in Simulink® that incorporates pitching and rolling motion of a heavy vehicle. Linear suspension was used for this investigation in order to simplify the analysis and generalize the results obtained. The model was validated using a commercially available multibody dynamics software package (TruckSim2019.1®). The road damage criteria studied include the average vertical tyre forces, the dynamic load coefficient, the first power aggregate forces and the fourth power aggregate forces. The most important road damage criterion is the 95th percentile fourth power aggregate force. The patterns produced by the fourth power aggregate forces are similar for the average, 95th percentile and 99th percentile fourth power aggregate forces. The fourth power aggregate forces increase linearly on the left side with an increase in the road crossfall value. Using a typical highway speed and roughness value of 80km/h and 2 m/km respectively, the percentage difference in the 95th percentile fourth power aggregate forces between the left and right profiles is 43.7% using a crossfall of 2%. It was noted that in the case of a crossfall value of 5% the percentage difference is in excess of 106%. Even with a crossfall of only 1% the percentage difference in the 95thpercentilefourth power aggregate forces are 21.9%. The effect of several heavy vehicle parameters on the 95th percentile fourth power aggregate force were studied. In general, it was found that any parameter that improves the roll stability of the heavy vehicle, will decrease the percentage difference in the left and right side 95thpercentile fourth power aggregate forces. Most of these vehicle parameters that decreases the percentage difference in the left and right road damage also decreased the overall road damage produced. The exception to this rule is the suspension stiffness and tyre stiffness. An increase in the suspension and tyre stiffness will decrease the percentage difference in the road damage but will increase the overall damage produced. Air suspensions are therefore still more road friendly even if there is a larger percentage difference in the left and right road damage. The damping value was found to have no effect on the percentage difference, but it does decrease the overall road damage produced by the heavy vehicle. It was noted that many of the heavy vehicle parameters had a larger relative influence than the dampers or suspension on the overall vehicle damage as well as the percentage difference in the left and right road damage when crossfall is included. Heavy vehicle rolling motion can therefore not be ignored when road crossfall is present