Coordinated Steering Control Combining DDAS and AFS for the Front-Wheel-Independent- Drive Electric Vehicles

The differential-drive-assisted steering (DDAS) has been proved to be a novel power steering technology, while the active front steering (AFS) system has also been widely used in recent years, but when the AFS is applied to the vehicle equipped with DDAS, the two systems will interfere with each other, which will lead to drivers’ wrong perception of vehicle state, destroy the ideal steering characteristics of vehicle, and even make the vehicle lose stability. To overcome this contradiction, the interference mechanism analysis between the DDAS and AFS is revealed and a novel coordinated steering control strategy is further proposed based on a variant linear-active-disturbance-rejection-control and sliding-mode-control. This is the main scientific and theoretic novelty of this article. Furthermore, for the instability risk, a hierarchical stability control module for the DDAS control mode switching between the steering assist mode and the direct yaw-moment control mode is proposed. Then, various relevant simulations are carried out. All the results show that the proposed control strategy can not only effectively mitigate the interference between the AFS and the DDAS but also maintain the vehicle stability when facing with intensified interference from the DDAS to the AFS especially on low-adhesion road maneuvering condition.