Modeling nonlinear suspension system for improved braking distance estimation

Abstract

Braking distance of a vehicle is an important safety consideration in highway geometric design. Braking distances have been commonly estimated based on vehicle wheel loads and assumed tirepavement friction. The use of classic vehicle dynamics simulation model, which simplifies tire stiffness as linear elastic function, is a main approach to estimate tire-pavement friction and predict braking distances. The interaction of nonlinear vehicle dynamics with pavement surface roughness has not been considered in analyzing its impact on vehicle braking distance. The impact of pavement roughness induced vehicle vibration on braking distance is the topic of interest in this paper. A nonlinear vehicle dynamics simulation model is proposed where tire stiffness is considered as a nonlinear elastic function in the analysis of vehicle dynamics. The model is implemented in MATLAB 11.0. A hypothetical example is given to illustrate the possible difference between models with linear and nonlinear tire stiffness in calculating braking distance on a wet pavement. Although the model presented is rather simplified considering only nonlinear tire stiffness, and a more elaborate simulation model is required to examine in detail the actual impact of considering nonlinear vehicle dynamics, the example does show that further study is necessary to examine the need for vehicle dynamics simulation in order to reliably predict vehicle braking distances on highways, taking into account the effect of pavement roughness.