Modeling and Analysis of a Dual-mode Electric Power Steering for Manual and Autonomous Driving

There have been several publications on the modeling and control of electric power steering (EPS). However, publications that address a dual-mode EPS for manual and autonomous driving are still limited. Moreover, most existing articles do not include the steering tire's moment of inertia in their models. This paper presents modeling and dynamic analysis of a dual-mode EPS in manual and autonomous driving for small vehicles. We incorporated the steering tire's moment of inertia into the model and provided a detailed analysis of dynamical characteristics. After deriving several motion equations, we present two transfer functions, i.e., from the road torque to the steering torque and from the motor current to the steering angle. The first transfer function determines the steering performance regarding driver feel during manual operation. The second one is vital for designing the EPS controller for autonomous driving. We plotted the Bode diagrams of those transfer functions. The results indicate that the first transfer function demonstrates a resonant frequency of around 12 Hz and that the magnitude of the second transfer function decreases drastically, almost to zero, at around 9.8 Hz. These results provide significant knowledge for designing an EPS controller for dual-mode operation.