Unsprung Mass Effects on Electric Vehicle Dynamics based on Coordinated Control Scheme

In electric vehicles, the propulsion configuration with the driving motor installed inside or close to the wheel has been treated as an option. Despite the advantages of the in-wheel drive system, negative effects brought by the increased unsprung mass, e.g. wheel and body vibrations, should be examined. In this work, we investigated this problem based on a proposed coordinated vehicle dynamics control system considering the desired path following as well as the body motion. The desired vehicle motion is determined by the generalized forces/moment, generated by a high-level MIMO sliding mode controller (SMC). Based on the tire normal force allocation, the generalized lateral, longitudinal forces, and yaw moment were distributed to the slip and slip angel of each tire by a fixed-point control allocation algorithm. With respect to the uneven road, a normal force robust tracking controller was proposed as a part of the low-level control. Evaluation of the unsprung mass effect was accomplished by simulations with a full-vehicle CarSim model under a fast double lane-changing maneuver. Comparison results with different unsprung mass configurations and road conditions reveal how the increased unsprung mass affects the vehicle dynamic performance in terms of vehicle planar and spatial motion.