Abstract
Squeal noise often occurs in a two-stage electrohydraulic servo-valve, which is an unfavorable issue of modern hydraulic energy systems. The root causes of such noise from the servo-valve are still unclear. The objective of this paper is to explore the noise mechanism in a servo-valve excited by the pressure pulsations from the hydraulic energy system perspective. The suppressing capability of squeal noise energy is investigated by changing the pressure pulsation frequency and natural frequency of the flapper-armature assembly. The frequencies of the pressure pulsations are adjusted by setting different speeds of the hydraulic pump varying from 10,400–14,400 rpm, and two flapper-armature assemblies with different armature lengths are used in the tested hydraulic energy system. The first eight vibration mode shapes and natural frequencies of the flapper-armature assembly are obtained by numerical modal analysis using two different armature lengths. The characteristics of pressure pulsations at the pump outlet and in the chamber of the flapper-nozzle valve, armature vibration and noise are tested and compared with the natural frequencies of the flapper-armature assembly. The results reveal that the flapper-armature assembly vibrates and makes the noise with the same frequencies as the pressure pulsations inside the hydraulic energy system. Resonance appears when the frequency of the pressure pulsations coincides with the natural frequency of the flapper-armature assembly. Therefore, it can be concluded that the pressure pulsation energy from the power supply may excite the vibration of the flapper-armature assembly, which may consequently cause the squeal noise inside the servo-valve. It is verified by the numerical simulations and experiments that setting the pressure pulsation frequencies different from the natural frequencies of the flapper-armature assembly can suppress the resonance and squeal noise.
Highlights
Hydraulic control energy systems are widely used in the mechanical industry, which can control the airplane or missile wings requiring very high power density
It is reasonable to see that the unavoidable pressure pulsations of the F1 and F2 in the flapper-nozzle valve traveling from the source could result in the instability of the flapper-armature assembly, which favors the occurrence of undesirable noise
One can observe that the primary and secondary frequencies at P1 and P2 are consistent, and these frequencies are close to each other at every motor speed. This proves that the pressure pulsations with the primary and secondary frequencies were generated by the axial piston pump and traveled through the whole hydraulic energy system
Summary
Hydraulic control energy systems are widely used in the mechanical industry, which can control the airplane or missile wings requiring very high power density. Peng et al [4,16] studied how the pressure pulsations could induce resonance excitation in the flapper-nozzle valve They indicated that self-excited oscillation of the flapper-armature generated by the fluid-structure interaction can cause the self-excited noise and squeal noise. A number of studies have shown the flow field characteristic inside the flapper-nozzle valve and reported that the pressure pulsations and noise could be generated by the cavitation phenomenon under some certain conditions [17,18,19]. To explore the mechanism of the squeal noise of the servo-valve, a hydraulic energy system to control airplane swing with the characteristic of a very high power-mass ratio is investigated in this paper, which can produce squeal noise . The pressure pulsations at the pump outlet and in the chamber of the flapper-nozzle, armature vibration and noise are all analyzed from the hydraulic system perspective in this paper
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