Steering Controller for SBW Vehicle with Trajectory Curvature as Controlled Variable

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In this research project, we have studied a front active steering using a steer-by-wire system. The discussion is based on our curvature output driver model and the concept of D^* control, where the curvature command is translated into the reference D^* value taking accounts of the vehicle speed, and is fed to the vehicle controller. In the first year (2001), we have performed simulation experiments of path following cruising using this steering control concept and the basic version of curvature output driver model. The simulations were supported by a multi-degree-of-freedom vehicle simulation software (CarSim). For example, prevention effects for unwilled steep turns at hard brakings are tested. In 2002, we extended our driver model. Its framework is very similar to the conventional first order preview model . Our model no longer cares variation of dynamical characteristics of the real vehicle but assumes that the steering controller will realize the curvature command. This simple preview model is sufficiently effective for the path following and then the fact implies that the active front steered vehicle will be easily driven even with a violent fluctuation of road surface condition. We have experimented simulations to evaluate the effect of driver response time, the vehicle delay, and the phase-leading compensation. We constructed a real-time simulator based on VR technologies to experiment with human subjects. The active front steering was also augmented by a traction / braking force distribution. The augmentation is effective under severe driving conditions and will prevent large sideslip angles.