Integral Sliding-Mode Tracking Control for Heavy Vehicle Electrohydraulic Power Steering System

Since heavy vehicles need all-terrain adaptability and large load drive capability, the dual hydraulic cylinders symmetrically arranged and connected in series are widely used in their steering system, which is quite different from the traditional electrohydraulic power steering systems. Accurate steering control for this dual hydraulic system is challenged due to its complicated structure and a wide range of steering loads. To solve this issue, an improved integral sliding-mode control (ISMC) is presented in this article. Specifically, a hyperbolic tangent function is integrated into the controller to mitigate the chattering caused by the sliding mode. A stability analysis is then conducted based on the finite-time Lyapunov stability theory, revealing the proposed controller's capability of achieving the asymptotic convergence of the tracking error within a finite time. A test bench is also established to experimentally validate the controller's effectiveness through multiple test scenarios, including various tire loads, supply pressures, and command signals frequencies. The results show that the tracking error of ISMC is kept within 0.5°, which is significantly superior to PID control. In addition, the ISMC can achieve high-precision control under lower supply pressure, showing the energy-saving potential of nonlinear control for the steering system in heavy vehicles.