Study of Riding Assist Control Enabling Self-standing in Stationary State

In motorcycles traveling at medium to high speed, roll stability is usually maintained by restoration forces generated by a self-steering effect. However, when the vehicle is stationary or traveling in low speed, sufficient restoring force does not occur because some of the forces, such as centrifugal force, become small. In our study, we aimed at prototyping a motorcycle having roll stability when the vehicle is stationary or at low speed with a steering control for self-standing assist, while maintaining stability properties in medium to high speed. A model was built to represent dynamics of roll motion, which is composed of a fixed point mass located above the vehicle’s center of gravity and another movable point mass below that gravity center. According to the model, when steered, the roll moment direction generated by the shift of the movable point mass becomes the same as the direction generated by the ground contact point shift of the front tire. Thus, the total roll moment is enough to restore the vehicle inclination only by steering control is producible and the possibility of establishing a viable self-standing control for the stationary state was indicated. However, with negative trail length, the roll stability cannot be maintained because the self-steering effect does not work in medium to high speed. With these investigations, a prototype vehicle was produced equipped with a switching function from negative to positive trail lengths activated when traveling at above a predetermined speed. In addition, a handlebar angle compensator is equipped to prevent interferences between the steer control and rider’s maneuvers. With this control, the self-standing function in stationary state was realized and the feasibility was confirmed for a smooth transition to ordinary characteristics of a motorcycle, enabled by altering the trail length from negative to positive and by gradual decrease of intervention by the steering control.