| As an important approach to automatic control, electrohydraulic servo control system has been widely used in many sections of national economy and social surroundings due to its advantages such as high level of control precision, quick response speed and high immunity to load variations. Electrohydraulic servo valves, the key part of an EHC servo system, with its function of transferring low-power electrical signal to large-power hydraulic output quickly and precisely, play an essential role in deciding the whole performance of the system. Direct-drive servo valve has come to be an important trend in fluid power transmission and control, in that it has advantages like compact structure, quick response, strong immunity to pollution, strong reliability, no leakage in pilot stage and no influence of supply pressure to performance. Therefore, improving its performance, can be beneficial to enhancing the control performance of the EHC servo system, better satisfying the market requirements and pushing forward the fluid power technology.The thesis deep analyzed and researched the direct-drive servo valve, utilizing theory analysis, computer simulation, finite element numerical computation and experimental study. A permanent-magnet polarized, differential controlled, moving-iron type, high pressure, bi-directional electrical-mechanical converter is put forward, the matching relation between its structure parameters is determined by simulation, and the experimental results indicate that the converter has a linear working range of ± 1mm, hysteresis lower than 2%, and frequency response 160Hz. A high-pressure eddy current displacement sensor is presented, and a temperature-drift compensation method employing non-inductive coil is also brought forward through theoretical analysis on the causes of temperature drift, both the simulated and experimental results show that the sensor has an effective range of 8mm, precision of 0.5%, frequency response of 500Hz. Finally, two types of direct-drive servo valve, one with and one without displacement feedback, are raised, then the matching relation between the structure parameters and the performance are discussed, and experiments are carried out, both the simulated and experimental results prove that the valves have achieved excellent characteristics, with nominal pressure 21MPa, nominal flow 40L/min, nominal electrical current 2A, hysteresis lower than 7% (without position feedback) and 3% (with position feedback), frequency response 120Hz.In chapter 1, based on the research information abroad and overseas, the history of the servo valve is introduced, and the present technical status, especially the structure and performance of every kind, is described in the term of new structure and new material, the related technologies including cooling technology, position feedback technology and flow force compensation are both reported, finally, some trends on the development of the servo valve are summarized.In chapter 2, the traditional and new-type electrical-mechanical converters are compared on their function, classification and working principle; the performance and working mechanism of the proportional solenoid are illustrated, and furthermore, the relation between its parameters and its characteristics are discussed; then a novel permanent-magnet polarized bi-directional linear actuator is presented, and its key technology including permanent magnet material, soft magnet material, armature and excitation coil are analyzed.In chapter 3, based on finite element analysis, considering the magnetic leakage and non-linear magnet characteristics, the static mathematical model is established, and the influence of the parameters on the performance are given, then the model is confirmed by experiments. The electrical-magnetic-mechanical coupling of the actuator's dynamic procedure is analyzed, and the transient performance of the actuator is calculated employing direct coupling method, the influence of the electrical and mechanical parameters on...
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