Mechanism of Temperature’s Acting on Electro-Hydraulic Servo Valve

Abstract

To understand temperature's influence on the electro hydraulic servo valve, a theoretical model of describing the detailed mechanism is necessary. For a servo valve experiencing actual working conditions, the temperature variation acts on the performance of the torque motor, which results from drifts of the air gaps' thicknesses, the permanent magnets' reluctances, and the polarization magnetomotive force. And with the temperature variation, the nozzle orifice's size and its flow coefficient also change, which will act on the performance of the valve's pilot hydraulic amplifier. Furthermore, the mechanical characteristics, including the stiffness of the spring tube, the stiffness of the feedback rod and the armature's arm of force, are also related to temperature. Then, considering all these factors, a comprehensive temperature influencing model, referred to as the temperature-induced angular drift model (TAD), is constructed. With fluid, structure and electromagnetic field integrated, this theoretical model reflects complexity of the system and can be characterized by a ninth-order equation with nonlinear time-variant coefficients. On this basis, the routes by which temperature affects the servo valve's control accuracy are investigated. Calculations show that when the temperature ranges from 20°C to 270°C, the valve's control error will exceed 15% of the expected output. Among the temperature's acting routes, the flow coefficient is dominant, the nozzle orifice's diameter and the magnetomotive force are secondary, and others are insignificant. An experiment shows that the TAD model correctly predicts the tendency of the control error caused by temperature's rise, and it will aid in optimizing the servo valve's temperature performance.