Abstract
In the nozzle flapper servo valve, the transient flow force on the flapper is the fundamental reason that affects the pressure stability. The pressure pulsation in the pilot stage causes forced vibration of the flapper, and its deviation will directly influence the control pressure difference, which will make the pressure appear unstable. In order to grasp the principle and characteristics of transient flow force and its influence on pressure stability, a mathematical model of flapper displacement and control pressure is derived. For collecting the dynamic changes of the transient flow force and recording the motion behavior of the flapper, a three-dimensional model of the pilot-stage is established. Numerical simulations of turbulence phenomenon analysis are conducted with a variation of flapper displacement ranging from 5 μm to 20 μm. It can be concluded that the change trend of the flapper displacement is similar to the steady-state flow force and the transient flow force pulsation amplitude. Under the same structural parameters, the pulsating frequency of the flow force remains basically constant. The fluctuation of the flow force of the pilot stage will cause the pressure of the servo valve control cavity to vibrate to a certain extent, which is a factor that cannot be ignored that affects the output stability of the servo valve.
Highlights
As a control element in the electro-hydraulic servo system, the servo valve converts the input low-power electric signal into high-power hydraulic energy output, which plays an important role in many fields such as aerospace
The pressure characteristics of the control chamber of the nozzle flapper servo valve calculated by the combination of theoretical formula and numerical simulation are verified by the experiment
When the flapper moves to a certain position, the main flow force on the flapper becomes relatively stable
Summary
As a control element in the electro-hydraulic servo system, the servo valve converts the input low-power electric signal into high-power hydraulic energy output, which plays an important role in many fields such as aerospace. Nozzle flapper servo valves are widely used in hydraulic servo systems due to their advantages of fast dynamic response, high control accuracy, and compact structure. Merritt [1] proposed a third-order mathematical model of the servo valve which caused high accuracy and was widely used. Some nonlinear effects are considered, and the performance of the servo valve is described more accurately through high-order mathematical models. Kim [2] believes that spool resonance and pressure feedback on the spool are more important, and, based on this, a five-order system model of the servo valve is established. Based on the theory of differential geometry, Mu [3]
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