Assessing the effect of chassis torsional stiffness on the accuracy of heavy vehicle understeer and rollover modeling

Over the past 30 years, vehicle dynamics simulations have advanced from simple engineering investigative tools to complex vehicle design simulation and real-time vehicle dynamics assessment tools. As passenger and race car markets have been leading the development of simulation tools of this type, much of the research and development to improve vehicle dynamics simulation capabilities has been centered on the needs of the passenger / race car segments with the heavy vehicle market tending to adopt proven modeling methods from the passenger car domain. This policy of heavy vehicle designers adopting proven passenger car modeling techniques has generally been effective but there have been a few areas where the existing simulation tools did not completely meet the needs of heavy vehicle simulations.;One of the areas in which heavy vehicle modeling needs have differed significantly from the modeling needs of passenger cars is in the modeling of the chassis torsional deformation. As the chassis of most passenger cars is usually significantly stiffer than the suspensions, the models can often assume a rigid chassis behavior with little degradation of the resulting solutions. However, for many heavy vehicles, this assumption that the chassis is rigid is not valid as the torsional deformation of the chassis can result in significant errors in the modeling results.;While the need to account for the chassis torsional flexibility in heavy vehicle modeling has been acknowledged for many years, there has been little research into the subject to document the effects of chassis compliance on modeling results or to define the significance of the need to account for chassis flexibility. This lack of research is primarily due to two issues: The lack of vehicle characterization data to develop models from and the lack of field test data to validate the models. The material presented in this work seeks to address both of these issues by developing vehicle dynamics models which account for the torsional chassis deformation and then validating the simulation results against field test results obtained by testing the actual vehicles on a closed track.