Electro-Hydraulic Steering Control System for Automated Steering of an Agricultural Tractor

Abstract. The most common solution to automated steering of agricultural tractors is the use of a combination of an electric motor in parallel to a conventional hydrostatic valve-based hydraulic steering system due to its simplicity and low cost. However, existing overlap, or dead band, of the hydrostatic valve has limited their use in maximizing the potential benefit from automated steering of tractors providing various agricultural operations including planting and spraying at higher speeds. This paper describes the development of an electro-hydraulic steering control system that uses an electro-hydraulic proportional valve (EHPV) and an electronic control unit (ECU). A proportional-feedforward control algorithm was implemented to effectively characterize the non-linear behaviors of the hydraulic cylinders used for changing the target angle of the tractor. A computer-controlled hardware-in-the-loop (HIL) E/H steering simulator consisting of two different types of valve sub-systems s, i.e., hydrostatic valve and EHPV sub-systems, was designed and built to develop steering control algorithms and verify the feasibility of the developed steering controller for accurate steering of the system with acceptable response times. A field test was conducted using a RTK-GPS based autonomous tractor equipped with the developed EHPV-based and EPS-based steering system to compare and investigate the potential in enhancing the functionality of the auto-guided system in terms of path tracking. Use of the steering controller improved tracking error about 29% and 50% of straight and turning paths respectively than EPS-based steering system.