Abstract:As a key component of hydraulic control systems, hydraulic servovalves influence their performance significantly. Unpredictable self-excited noise inside hydraulic servovalves may cause instability and even failure. Being functional, with higher saturation magnetization and increased viscosity when exposed to a magnetic field, magnetic fluids (MFs) have been widely used in dampers, sealing, and biomedical treatment. In this paper, magnetic fluids are applied in the torque motor of a hydraulic servovalve to exert damping and resistance for vibration and noise suppression. Construction of the torque motor armature with magnetic fluids is introduced and the forces due to magnetic fluids on the torque motor armature are studied. Based on a bi-viscosity-constituted relationship, a mathematical model of the damping force from magnetic fluids is built when magnetic fluids are filled in the working gaps of the torque motor. Measurements of the properties of an Fe 3 O 4 composite magnetic fluid are carried out to calculate the parameters of this mathematical model and to investigate the influence of magnetic fluids on the vibration characteristics of the armature assembly. The simulated and tested harmonic responses of the armature with and without magnetic fluids show the good suppression effects of magnetic fluids on the self-excited noise inside the servovalve.

Two-stage electrohydraulic servo-valves play an important role in the most modern hydraulic servo control systems for fight wing controls, manufacturing robots, and many engineering applications. The existence of cavitation inside the pilot stage is one of the root causes of self-excited noise, cavitation erosion, system jam, and frequent failures of electrohydraulic servo-valves. Thus, experimental and numerical investigations of the flow field and cavitation phenomena inside the pilot stage of deflector jet servo-valve under different supply pressures conditions are conducted in this paper. An assembly for experimental verification of the flow visualization process that represents the deflector jet pilot stage is produced and discussed. To test and verify the numerical simulations for cavitation phenomena, the flow field characteristics in the deflector jet pilot stage are investigated by using experimental flow visualization. The cavitation inception inside the pilot stage of the deflector jet servo-valve is experimentally confirmed through flow visualization. More importantly, the attached cloud-like cavitation or bubble shedding is observed along with the jet flow and the significant locations of cavitation inception are also identified for varying supply pressures. The profile of turbulent intensity confirms to conclude that turbulent pressure fluctuations contribute to cavitation. The result also shows that the increment of supply pressure intensifies cavitation and output pressure plays a significant role in reducing the intensity of cavitation inside the pilot stage of deflector jet servo-valve. Finally, the numerical results show good agreement with experimental results. INDEX TERMS Servo-valve, deflector jet servo-valve, turbulent flow, cavitation, numerical simulations.

The resonance of the armature assembly is the main problem leading to the fatigue of the spring pipe in a torque motor of hydraulic servo valves, which can cause the failure of servo valves. To predict the vibration characteristics of the armature assembly, this paper focuses on the mathematical modeling of the vibration characteristics of armature assembly in a hydraulic servo valve and the identification of parameters in the models. To build models more accurately, the effect of the magnetic spring is taken into account. Vibration modal analysis is performed to obtain the mode shapes and natural frequencies, which are necessary to implement the identification of damping ratios in the mathematical models. Based on the mathematical models for the vibration characteristics, the harmonic responses of the armature assembly are analyzed using the finite element method and measured under electromagnetic excitations. The simulation results agree well with the experimental studies.

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