| With large power/weigh ratio, fast response, high immunity to load variations and high level of control precision, the electrohydraulic servo control system has been widely used in many industrial applications such as metallurgy, mining, marine, construction machinery and aerospace. As key components of an electrohydraulic servo control system, the electrohydraulic servo valves can transfer low-power electrical signal to large-power hydraulic output quickly and precisely, and have a direct influence on performance and characteristics of the whole servo system. Rotary direct-drive servo valve, due to its compact structure, fast response, high flow resolution, zero acceleration drift and easy maintenance, has come to be an important trend in fluid power transmission and control. Improving the working performance of the rotary servo valve, will enhance the control performance of the electrohydraulic servo system, satisfying the market requirements and pushing advancement in techniques of fluid power transmission and control.Based on theory analysis, analytical computation, numerical simulation and experimental study, the rotary direct-drive servo valve is systematically, deep analyzed and researched in the thesis. A high-pressure bi-directional rotary proportional solenoid with permanent-magnet polarizing, ring type working air-gap and moving-magnet rotor, is put forward. It works in differential mode with the polarizing and control flux interactions. With magnetic circuit analysis and finite element simulation, the action mechanism and matching relations of the solenoid structural parameters are analyzed in detail. The experimental results indicate the solenoid has positive magnetic stiffness and output torques of±0.65 Nm with the torque non-linearity and angle non-linearity less than 1% and 0.5% respectively at±5°working range. Its torque hysteresis and angle hysteresis is less than 4.5% and 4% respectively and the frequency bandwidth is 190 Hz. For improving the control precision of the rotary servo valve, a high-pressure eddy current angle sensor is also presented. An oblique ring-shaped sensing coil and a symmetric semi-cylindrical rotor are utilized, making the coil impedance and the output voltage proportional to the angular displacements. Based on theoretical analyses of the sensor temperature drift, the differential eddy current angle sensor structure and temperature compensation method employing non-inductive coil and bridge circuit are also presented, achieving better temperature stability. The measured and simulation results show that the sensor has a linear working range of 50°with inductance sensitivity 7.7×10-4 mH/degree and voltage sensitivity 9.8 mV/°. Its non-linearity is less than 0.8% at working range 40°-70°, and the temperature less than 1% over 30℃-90℃. Together with the high-pressure bi-directional rotary proportional solenoid and the high-pressure eddy current angle sensor, two types of rotary direct-drive servo valve, one with and one without angular displacement feedback, are raised. Based on simulation, the static and dynamic characteristics of the rotary valve are analyzed, and the influence of the structural parameters and angle feedback is also presented.The main content of each chapter is summarized as following:In chapter 1, the research progress of electrical-mechanical converter, angle sensor and rotary valve, which constituting the whole rotary direct-drive valve, is introduced. The design feature and development trend of the whole rotary direct-drive valve and its key components are summarized.In chapter 2, the bi-directional rotary electrical-mechanical converters are classified by different structures. Based on magnetic circuit principal, the magnetic circuit models of different kinds of torque motors are established, and the analytical functions describing the static characteristics of the solenoid are also deduced. The working characteristics of torque motors are compared and the effects of magnetization type, air-gap shape, rotor style and polar-face form are summarized. Then a novel high-pressure bi-directional proportional solenoid is presented, and its working principals are analyzed. The key technologies of the solenoid, including high-pressure structure design, permanent magnet material, soft magnet material, excitation coil and loading spring, are also discussed.In chapter 3, the magnetic circuit model of the high-pressure bi-directional proportional solenoid is established, and the influences of structural parameters are analyzed based on the deduced static and dynamic analytical functions. The finite element model of the solenoid is also established and the action mechanism of the solenoid structural parameters is analyzed in detail. Together with the magnetic circuit analysis results, the specific structural parameters are determined. Then the static and dynamic characteristics of the solenoid are measured and compared with the simulation results. Furthermore the power amplifiers for solenoids are introduced, and the working principals of the PWM double-way inverse-relief power amplify are analyzed.In chapter 4, the structural features and working characteristics of different kinds of high-pressure angle sensor are compared, and the effects of coil magnetization type, sleeve structure, air-gap type and rotor style on sensor characteristics are summarized. Then a novel high-pressure eddy current angle sensor is presented, and its operation principals and structural features are analyzed. The key technologies of the sensor, including the sleeve material and sensor driving circuit, are also discussed.In chapter 5, the equivalent circuit model and finite element model of the high-pressure eddy current angle sensor are established, and the action mechanism of the sensor structural parameters is analyzed in detail based on simulation. The specific structural parameters of the sensor are determined according to the FEM simulation results. Based on theoretical analyses of the sensor temperature drift, the differential eddy current angle sensor structure and temperature compensation method employing non-inductive coil and bridge circuit are also presented. The inductance, bridge circuit output and temperature drift characteristics of the sensor are measured with an experiment platform.In chapter 6, based on the high-pressure bi-directional proportional solenoid and the high-pressure eddy current angle sensor, two types of rotary direct-drive servo valve, one with and one without angular displacement feedback, are put forward. Its working principals and performance features are discussed, and the transfer functions are also given. The static and dynamic characteristics of the rotary valve are analyzed based on MATLAB numerical simulation model, then the effects of the structural parameters and angle feedback on valve performance features are discussed in detail.In chapter 7, all achievements of the dissertation are summarized and the further research work is put forward.
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