Abstract: Operating point drift over large temperature spans can significantly degrade the performance of servo valves. The direction and magnitude of the deviation of the operating point are uncertain. To analyze and evaluate the mechanism of this complex system with a multi-level structure and multi-variables, it is necessary to construct a theoretical model with a clear physical concept to describe it. However, since the physical processes contain complex variations of structural parameters and flow properties, there is a problem of simplifying approximations in deriving analytical mathematical relations. The advantages of multi-physics field numerical analysis can compensate for this shortcoming of analytical formulations. Based on this, we constructed a whole-valve transfer function model to realize the mechanism analysis and evaluate the operating point drift when a thermal effect acts on a servo valve. The results show that the asymmetric fit relationship between the armature-nozzle assemblies is an important reason for the drift of the operating point caused by the thermal effect. Differences in structural parameters and fluid medium characteristics at different temperatures lead to nonlinear changes in the operating point. When the deviation angle reaches ±1°, an increase in temperature will cause the absolute value of the tangent slope of the displacement deviation of the spool to decrease from 1.44×10^-5 m/°C to 1.25×10^-6 m/°C. The influence of the deviation angle is reflected in the change in the absolute value of the tangent slope of the pressure deviation from 1.14×10³ Pa/°C to 110 Pa/°C.

Key words: Servo valve; Operating point drift; Mathematical model; Numerical analysis; Thermal effect

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