Relaxed static stability for four-wheel independently actuated ground vehicle

In order to maximize the advantage of four-wheel independently actuated (FWIA) technology, the paper proposes a new configuration and dynamics control method. It is called relaxed static stability (RSS). First, RSS allows lateral dynamics system of the vehicle to be inherently unstable to enhance overall structure design flexibility. Three FWIA electric vehicles (a racecar, a passenger car, and a military vehicle) are shown to demonstrate the benefit of RSS. By applying the RSS, the configuration flexibilities of the battery pack location of these vehicles are improved by 95.4%, 167% and 20%, respectively. Second, the closed-looped handling stability could be improved by yaw moment control through the pole assignment technique. The target pole's positions of closed-looped lateral dynamics system are selected according to various performance requirements. Four cases of target pole locations are given as examples to show the principle of selecting the target pole locations for different type vehicles. A pole assignment controller is designed with the consideration of the parametric uncertainties caused by tire nonlinear behavior. Finally, an FWIA electric vehicle, which is built by the authors, is used as testbed to show the benefit of the RSS. The experiments in step steer and sine steer conditions prove the efficiency and robustness of the controller, as well as the convenience of adjusting target pole locations according to various performance requirements.