Stability boundaries and bifurcation analysis of an AWD vehicle: the influence of the drive torque distribution

Abstract

All-wheel drive electric vehicles, equipped with independent motors at the front axle and the rear axle, allow for adaptive drive torque distribution between the axles to influence handling and stability characteristics. To analyse manoeuvres at combined longitudinal and lateral accelerations, a quasi-steady-state assumption is used to apply bifurcation and continuation techniques. Different types of loss of stability are found and analysed. The Takens–Bogdanov bifurcation is studied in more detail, and it is shown that the respective branch represents the boundary between final understeer and final oversteer, and defines the stable envelope in the GG diagram. The drive torque distribution at the Takens–Bogdanov branch is therefore considered a good design criterion for a safe and performant powertrain control. Besides the Takens–Bogdanov branch, related Hopf and Fold branches are identified that define limits for practically reasonable drive torque distributions.