A Vehicle Dynamics Tire Model for Both Pavement and Off-Road Conditions

This paper describes a tire model designed for the full range of operating conditions under both on- and off-road surface conditions. The operating conditions include longitudinal and lateral slip, camber angle and normal load. The model produces tire forces throughout the adhesion range up through peak coefficient of friction, and throughout the saturation region to limit slide coefficient of friction. Beyond the peak coefficient of friction region, the off-road portion of the model simulates plowing of deformable surfaces at large side slip angles which can result in side forces significantly above the normal load (e.g., equivalent coefficients of friction greatly exceeding unity).

The model allows changing the saturation function depending the surface currently encountered by a given tire in the vehicle dynamics model. Saturation functions can vary from the sharp peak function associated with radial tires on paved surfaces, to the exponential like saturation associated with various off-road surfaces. Smooth transition functions are provided between the adhesion and saturation regions, and logic is provided to ensure that tire force always opposes slip velocity no matter what operating condition is encountered.

This paper describes the model functional characteristics and response to a range of operating conditions. Data sources for the model are discussed. Cases are run with a vehicle dynamics model to illustrate model response to changing surface conditions.