Handling benefits of steering a third axle

Abstract

This work examines the steady state handling effect of steering the rear axle of a three-axle vehicle in terms of the equivalent wheelbase and understeer. These quantities are derived from steady state conditions of a three-axle vehicle model which is analogous to the two-axle model. It is found that a very simple rear-axle steer control strategy improves both the equivalent wheelbase and the understeer. The expected improvement is larger on low-friction surfaces. The equivalent wheelbase of the rear-axle-steered vehicle calculated from the steady state condition of the dynamic equations of motion equals the intuitively expected kinematic result and was demonstrated on a test vehicle, validating the three-axle steady state handling model's ability to predict the rear-axle-steering performance.