Equilibrium Analysis of Drifting Vehicles for Control Design

Abstract

This paper presents an analysis of the dynamics of a rear wheel drive vehicle during cornering at high sideslip angles (“drifting”) using a three-state bicycle model. This model builds upon previous work with a two-state bicycle model by incorporating longitudinal dynamics and a nonlinear tire model with simplified lateral-longitudinal force coupling. Analysis of this model reveals the existence of unstable “drift equilibria” corresponding to steady state cornering at high sideslip angles with significant longitudinal force applied at the rear tire. These equilibria are saddle points, with characteristics that exhibit low sensitivity to friction and speed variation. The analysis of the equilibria provides insight into vehicle dynamics in an operating regime responsible for major safety concerns in everyday driving. It also sheds light upon aspects of the system dynamics that account for behavior observed in autonomous drift experiments and must be considered in future controller designs.