An Antirollover Control Strategy Based on Time-Varying Nonlinear MPC for Three-Axle Steering/Braking-by-Wire Vehicle

Under extreme working conditions, three-axle vehicle is accompanied with a huge load transfer ratio, and there is a large risk of sideslip or rollover, where the unnecessary intervention of antirollover control may worsen vehicle's unstability. In order to improve the vehicle antirollover performance and stability, a steering/braking-by-wire-integrated antirollover control strategy is proposed. The strategy mainly consists of a mode selection layer and an integrated control layer. In the mode selection layer, a multiple coupled degrees of freedom energy method combined with a nonlinear vehicle prediction model is designed to accurately evaluate rollover risk, and determine the control mode. In the integrated control layer, a novel time-varying nonlinear model prediction control is adopted to solve the desired tire forces and front wheel steering angle to inhibit load transfer and prevent rollover. Besides, the actuator constraints changing with the tires’ vertical forces dynamically are considered. The proposed strategy is evaluated with a Trucksim-MATLAB simulation and hardware-in-the-loop experiment. The results show that the proposed strategy can accurately assess the rollover risk and improve the yaw stability and antirollover performance significantly.

I. Introduction

Multiaxle vehicle is more prone to serious rollover accidents in extreme working conditions due to its high center of gravity (CG) and heavy load, which has been widely studied in recent years [1]. Among the studies, rollover risk assessment (RRA) and antirollover control (ARC) become two mainstream directions [2], [3], [4]. Generally, RRA employs load transfer ratio (LTR), roll angle, roll rate, and other indicators to evaluate vehicle rollover risk. Once, RRA determines that the rollover risk is large enough, ARC will be triggered. ARC mainly adjusts the lateral, longitudinal, and vertical forces of tires through steering-by-wire (SbW) [2], braking-by-wire (BbW), and suspension-by-wire (SubW) [5] systems to avoid rollover accidents. However, on the one hand, too aggressive RRA always caused the vehicle to work in the strong nonlinear area or even uncontrollable area, where ARC is difficult or even impossible to design with high probability of an accident. On the other hand, if RRA is too conservative, ARC can be easily designed with a linear vehicle model, but vehicle mobility will be reduced. Hence, the designs of accurate RRA and effective ARC are significant to improving vehicle antirollover performance and stability.