ABSTRACT
ABSTRACT: This paper describes an integrated control for limit handling by integrating fourwheel-drive (4WD), which decides front/rear traction, and electronic stability control (ESC), which serves differential braking of each tire. The main concept of the proposed integrated control algorithm (ICA) is optimally utilizing the friction circle with tire slip information and pre-defined sub-optimal solution to increase overall vehicle speed in cornering. The proposed algorithm consists of the following three parts: 1) a supervisor computes the desired dynamics from vehicle states and driver command; 2) an upper level controller determines the desired force and moment to track the desired state based on the sliding mode controller; and 3) a lower level controller optimally allocates virtual control inputs (desired force and moment of whole vehicle) to actuator control inputs to minimize a performance index. The performance index consists of an allocation guideline, which guides actuator control inputs near a predefined optimal solution, and a tire saturation penalty, which penalizes distributing longitudinal forces by monitoring combined slips of each tire. An interaction between the allocation guideline and the tire saturation penalty term can allow for limit handling of the vehicle. In order to validate the performance of the proposed algorithm, computer simulations are conducted. Compared to the base and ESC-equipped vehicle, the proposed algorithm shows good performance at the limits. Moreover, it has been shown that both the allocation guideline and tire saturation penalty are effective in keeping stability and maneuverability of the vehicle at the limits.
