Four-Wheel Drive and Independent Steering for Small Electric Vehicles: Active Stability Control during High–Speed Cornering

Since car manufacturers pursue in the development of environmental -friendly vehicle, the demand for extensive research on stability, controllability, and reliability of electric vehicles (EVs) increases. Electric powered and by-wire control technology allow manufacturers to build independent four -wheel steering of an allwheel drive in-wheel EV. In past research, we investigated the advantages of a four-wheel drive and independent steering system (4WDIS) of an in-wheel small EV in comparison with a two-wheel steering (2WS) vehicle. During low-speed cornering, a 4WDIS in-wheel small EV is capable of cornering with a short radius and has a higher response to driver’s steering with the assistance of passive-control rear-wheel steering. This paper describes an active stability control of a 4WDIS in-wheel small EV during high-speed cornering using a numerical simulation. In the simulation, a 4WDIS in-wheel small EV is designed with a nonlinear model. Therefore, a feedback control cannot be implemented directly because the yaw rotational speed couples with the velocity as expressed in the dynamic equation of motion. Hence, we propose controlling the input of a state observer with a controlled linear model enabling the output to be fed forward to the vehicle. A Linear Quadratic Regulator is used to establish an optimal control for the linear model. Based on the result, a slight deviation is observed between the output of the state observer and vehicle model when using the feed-forward control method. As a solution, these output error between both models is calculated and multiplied by a high gain, then fed back into the linear model before the control input is fed forward to the vehicle . Finally, we compare the feed-forward control system with the feedback control system of the vehicle. The results show that our vehicle’s active stability control is able to achieve a steady-state cornering at high-speed. .