Abstract: As magnetic fluids show a higher saturation magnetization and larger viscosity when they are exposed to a magnetic field, a new method using magnetic fluids to improve the dynamic characteristics of a hydraulic servo-valve torque motor is presented. If magnetic fluid is filled into the working gaps of a torque motor, the forces owing to the magnetic fluid on the torque motor armature can increase the damping of the motor and the servo-valve. Therefore, the stability and dynamic performance of the torque motor can be improved. The self-excited oscillations and noise frequently appearing in a hydraulic servo-valve can be reduced. After the working mechanism of magnetic fluids and the magnetic circuit of the torque motor are studied, the mathematical models of the forces owing to the magnetic fluid on the torque motor armature and the dynamic mathematical model of the torque motor are given. By using MATLAB/Simulink software, the dynamic characteristics of a hydraulic servo-valve torque motor are simulated in the frequency domain when the magnetic fluid is applied or not in the motor. Experiments are carried out to test the dynamic characteristics of the torque motor with or without magnetic fluids by using a laser displacement transducer. The simulation and experimental results show that magnetic fluids can be used to increase the damping ratio of a servo-valve torque motor, so that the stability and anti-disturbing capability of a hydraulic servo-valve can be improved.

Key words: Frequency response, Magnetic fluids, Servo-valve, Torque motor, Community detection and reorganization, Co-occurrence network, Function innovation, Functional verb, International patent classification (IPC)