Dynamic behavior of an electrohydraulic valve: Typology of characteristic curves

The majority of off-road vehicles employed in agriculture are equipped with a hydraulic steering. An efficient way of automating the steering mechanism of these vehicles is by controlling the electrohydraulic valve that operates the steering cylinder. Electronically-controlled hydraulic valves often behave nonlinearly and, consequently, they introduce certain complexities in the analysis of the hydraulic system. Therefore, it is necessary to understand their behavior before designing a control system that is able to auto-steer an agricultural machine safely and efficiently. The objective of this work was to characterize the performance of an electrohydraulic valve with the aid of a set of experiments conducted on a hardware-in-the-loop electrohydraulic simulator. The operation of the valve was classified in four types (I, II, III, and IV) according to the valve characteristic curves and the properties of the input signal. The phenomena of deadband, hysteresis, and saturation helped to discriminate between types. The input signal, especially its frequency, was crucial in studying the functioning of the valve. The hardware-in-the-loop simulator was fed with signals that imitated the auto-steering action. The outcomes obtained from this research provide some critically supporting information for designing high performance steering controllers for agricultural vehicles.