To study the effect of cavitation on the stability of the spool of a two-degree-of-freedom (2D) pressure servo valve, the simulation models of the components of the 2D pressure servo valve are established by using the basic library and HCD Library of AMESim. The theoretical analysis shows that the cavitation phenomenon will reduce the effective bulk modulus of the gas-containing oil in the valve body, and the condition for the stability of the spool considering the influence of cavitation is obtained. The simulation results show that the cavitation phenomenon will lead to oscillation when the main spool reaches the stable position, which will affect the main spool's crossing frequency from 21 Hz to 6 Hz, limiting the width of the main spool. The proper increase of the damping ratio of the main spool can improve the working stability of the main spool. To solve this problem, a damping piston structure is proposed. The model analysis shows that by improving the damping ratio of the main spool, it can improve the stability of the spool without affecting the frequency response, displacement, and anti-pollution ability of the servo valve. The experimental results show that the the damping piston can reduce the output pressure fluctuation of the 2D pressure servo valve from 9% to 2%, improving the working stability of brake valve during aircraft braking.
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