Managing axle saturation for vehicle stability control with independent wheel drives

This paper proposes a new stability control method that quantifies and uses the level of lateral force saturation on each axle of a vehicle featuring an independent wheel drive system. The magnitude of the saturation, which can be interpreted as a slip-angle deficiency, is determined from estimated nonlinear axle lateral forces and comparisons with linear projections that use estimates of the cornering stiffness. Once known, the per-axle saturation levels are employed in a saturation balancing control structure that biases the drive/brake torque to either the front or rear axles with the goal of minimizing excessive under- or over-steer. The approach is then combined with a direct yaw-moment controller to obtain enhanced stability and responsiveness. The benefits of the proposed approach are demonstrated for a nominally unstable vehicle in an extreme obstacle avoidance type maneuver.