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 Fe3O4 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.
Highlights
Magnetic fluids show a reversible transition from liquid to solid behavior, characterized by the apparent viscosity variation with several orders of magnitude under the action of an external magnetic field
From the simulation and experimental investigation above, it can be concluded that magnetic fluids can depress the self-excited vibration of armature and high-frequency noise inside a hydraulic servovalve by exerting damping forces on the armature due to the magnetic field of the torque motor
The mathematical models of the damping force from magnetic fluids can be expressed by a linear model with parameters calculated from the experimental data
Summary
Magnetic fluids show a reversible transition from liquid to solid behavior, characterized by the apparent viscosity variation with several orders of magnitude under the action of an external magnetic field. For the application in vibration absorbers and dampers, it is essential to investigate the mechanical properties of magnetic fluids [19,20,21]. Damping properties of magnetic fluids when applied in an electrohydraulic servovalve torque motor for vibration suppression were measured by Peng et al [23]. Commercial applications of the squeeze mode are still restricted due to a lack of understanding and modeling of the material behavior, while further investigations still need to be carried out on the mathematical models of damping forces and resistance from magnetic fluids in the application of vibration absorbers and dampers. The aim of the paper is to build a mathematical model of damping force from magnetic fluids for vibration suppression in a torque motor, and to study the mechanism of operation mechanism of magnetic fluids in the squeeze mode, via simulation and experiment of the harmonic response of the armature with magnetic fluids. The vibration characteristics of the armature with magnetic fluids are simulated, and the self-excited noise of the servovalve with magnetic fluids is tested
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