Application of Electro-Hydraulic Proportional Valve for Steering Improvement of an Autonomous Tractor

Abstract

The most common solution to achieving automated steering in an agricultural tractor is the use of an electric motor in parallel with a conventional hydrostatic valve-based hydraulic steering system owing to its simplicity and low cost. However, the existing overlap, or dead band, of a hydrostatic valve has limited its potential benefit to automated tractor steering in terms of providing various agricultural operations, including planting and spraying, at higher speeds. The main objective of this study was to develop an electro hydraulic steering system applicable to an auto-guidance system, and to compare the performance of the developed system with a conventional automatic steering system. A proportional-feedforward control algorithm was implemented to effectively compensate the non-linear behaviors of the hydraulic cylinders used for changing the steered wheel angle of the tractor. A computer-controlled hardware-in-the-loop electro-hydraulic steering simulator consisting of two different types of valve sub-systems s, i.e., hydrostatic valve and EHPV sub-system, was designed and built for the development of the steering control algorithms and to 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 Real Time Kinematic GPS based autonomous tractor equipped with the developed EHPV-based steering system and an EPS-based steering system used as a control to compare and investigate their potential in enhancing the path tracking functionality of an auto-guided system. The use of the EHPV-based steering controller was shown to improve the tracking error by about 29% and 50% for straight and curved paths, respectively, as compared to the EPS-based steering system.