Optimal path recovery from terminal understeer

Paper in proceeding, 2011

This paper presents methods to control vehicle path in the case of limit understeer. Longitudinal forces are applied to overcome inherent vehicle understeer, and reduce speed to overcome friction limits. Desired path curvature is derived from the driver’s steering input. Optimization is applied separately to three types of model: (a) particle model with isotropic friction limits; (b) two-track model with idealized tire force constraints (c) another two-track model using more realistic tire force limits. Optimal path tracking for the particle model has a rigorous solution, in the form of a parabolic trajectory – the vehicle decelerates to a point of maximum path curvature. The parabolic reference depend on vehicle speed, mean surface friction and desired curvature inferred from the driver steering input. Overall the optimization results are found to be consistent between the three approaches.