Abstract
In order to improve the stability of vehicle steering on low-adhesion road surfaces, this paper designed a hybrid robust control strategy, H2/H∞, for active front-wheel steering (AFS) based on robust control theory. Firstly, we analyzed the influence of the sidewall stiffness and road adhesion coefficient of the tires on vehicle stability, through which we can study the wheel deflection characteristics of low-adhesion roads. Secondly, the reference yaw velocity of the vehicle was calculated using the three-degrees-of-freedom model as the reference model, through which, taking the norm H∞ as the objective function and the norm H2 as the limit to control the output, the hybrid robust control strategy H2/H∞ of the AFS system on a low-adhesion road surface was developed. Finally, the simulation experiment was carried out by the Simulink/CarSim co-simulation platform and a hardware-in-the-loop (HIL) experiment. In this paper, the results show that the AFS control strategy can improve the vehicle handling stability on low-adhesion road surfaces, and the controller has good path tracking performance and robustness.
Highlights
Active front-wheel steering systems enable vehicles to achieve an ideal steering performance, stability at high speed and portability at low speed by changing the angular transmission ratio of the steering system [1,2,3]
Simulations were performed, and the results indicated that the designed H2 /H∞ mixed robust controller can achieve stability control [13]
The model of active front-wheel steering (AFS) and the H2 /H∞ hybrid robust control algorithm were built by using Simulink
Summary
Active front-wheel steering systems enable vehicles to achieve an ideal steering performance, stability at high speed and portability at low speed by changing the angular transmission ratio of the steering system [1,2,3]. For AFS systems, the control methods include the PID, model predictive, sliding mode and robust control methods [4,5,6]. H∞ control theory [7] is one of the most typical theories It can maintain (system) stability, dynamic characteristics (sensitivity) and steady-state characteristics (progressive adjustment) under uncertain conditions. Tires are an important factor affecting vehicle dynamic stability. When the lateral acceleration of the vehicle is small and the tire force is in the linear region, the linear tire model can be used to design the AFS controller. When the tire–road friction coefficient is low, the tire cornering force soon reaches saturation
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