Application of Electrohydraulic Proportional Valve for Steering Improvement of an Autonomous Tractor
2022
Lee, C.J. | Jeon, C.W. | Han, X.Z. | Kim, J.H. | Kim, H.J.
PURPOSE: The most common solution to achieving automated steering in an agricultural tractor is the use of electric motors along with conventional manual steering systems called an electric power steering (EPS) system. However, EPS systems have limited use in automated tractor steering requiring fast and accurate responses. Another solution is to use the electrohydraulic proportional (EHPV) valve technology, but EHPV systems have highly nonlinear characteristics. The objective of this study is to develop an electrohydraulic (E/H) steering system that is applicable to a conventional steering circuit and to compare the performance with an EPS system. A proportional-feedforward control algorithm was implemented to effectively compensate for the nonlinear behaviors of EHPV systems. METHODS: A computer-controlled hardware-in-the-loop E/H steering simulator consisting of EPS and EHPV subsystems was designed and built to develop the steering control algorithms and to verify the feasibility of the developed steering controller. A field test was conducted using a real-time kinematic GPS-based autonomous tractor equipped with the developed E/H steering system and an EPS system as a control to compare and investigate their potentials. RESULTS: Compared with the EPS system, the use of the E/H steering system was shown to improve the tracking errors by about 29% and 50% for straight and curved paths at a speed of 2 km/h and about 85% for straight path at a speed of 5.5 km/h. CONCLUSIONS: The proportional-feedforward steering controller is the feasible solution to controlling and reducing any nonlinear characteristics and is a suitable steering system for high-speed operations.
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