Abstract
A significant proportion of accidents in which vehicles run off the road are due to loss of control on bends. To prevent such loss of control, a study on the suitability between vehicle dynamics and geometrical characteristics of bends is necessary. The aim of the present study is to develop a simple model of the vehicle´s dynamic and its environment based on the minimum required parameters and taking into account the vehicle´s characteristics, bend characteristics (the radius of curvature, super-elevation, slope...) and the tyre/pavement contact.
Researchers and industrialists have developed both simple and complex models of vehicle dynamics: The simple ones are based upon numerous assumptions. They are only able to model a linear behaviour under weak slips, speeds and steering angles. The complex models such a Prosper Callas simulator are more complete but have a greater number of parameters and therefore require considerable calculation time. In our case, we develop a simple model, with a few parameters but close to a real behaviour of the vehicle. It contains three important aspects: tyre/pavement contact, vehicle characteristics, and road characteristics.
Tyre/pavement contact is modelled. We studied literature on existing models. The empirical model, known as «Pacejka´s model», and the physical one, known as «Guo´s model» especially interested us. We compared the lateral and longitudinal forces and observed that when used for simple cases, they have similar behaviour but require the identification of many parameters. For this reason, we introduced a new method based on the "Coulomb friction" properties, which requires less parameter (three parameters). Coulomb method links the contact force to relative velocity of wheel, normal force and friction coefficient.
The vehicle model we use is a four wheels model; it takes account of the three translations (X, Y and Z) and the three rotations: pitch, roll and yaw. The inputs of this model are the vehicle velocity, the steering angle, driving /braking torques and the road geometry characteristics (super-elevation and road gradient).
The validation of the model is based on comparison with the industrial dynamic vehicle simulator Prosper Callas. The results obtained will be detailed and clarified in the draft paper.
Keywords:Modelling, vehicle dynamics, Tire/road contact, Road geometry characteristics.