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An overview of electro-hydraulic servo valve is the key component of electro-hydraulic servo control, it is a kind of analog electrical signal, the corresponding output modulation of the flow and pressure of the hydraulic control valve. Electro-hydraulic servo valve has the advantages of fast dynamic response, high control precision and long service life. It has been widely used in electro-hydraulic servo control system in the fields of aviation, spaceflight, shipbuilding, metallurgy and chemical industry. The history of the hydraulic control technology of the second development dates back to 240 BC, when an ancient Egyptian invented the first hydraulic servo system in human history - the water bell. However, in the long historical period that followed, hydraulic control technology remained stagnant until some significant progress was made until the late 18th and early 19th century. On the eve of World War II, with the needs of industrial development, hydraulic control technology has emerged by leaps and bounds, many early control valve principles and patents are the product of this era. Such as: Askania Regulator Company and Askania-Werke invented and applied for the patent of the jet valve principle. Similarly, Foxboro invented the patent of the nozzle flapper valve principle. The German Siemens company invented a permanent magnet motor and receive mechanical and electrical signals two input dual input valve, and pioneered the use of aviation. At the end of World War II, the servo valve is a single-stage open-loop control valve that uses a solenoid to directly actuate the spool movement. However, with the maturity of control theory and the needs of military applications, the development and development of servo valves have made great achievements. In 1946 Tinsiey, UK, obtained a two-stage valve patent; Raytheon and Bell Aviation invented a two-stage valve with feedback; and MIT replaced the solenoid with a torque motor to make the motor consume less power and better linearity. In 1950, WCMoog invented the first single-nozzle two-stage servo valve. THCarson invented a mechanical feedback two-stage servo valve from 1953 to 1955; WCMoog invented a two-nozzle, two-stage servo valve; and Wolpin invented a dry-torque motor that eliminates the oil-contaminated torque motor originally immersed in the fluid Bring the reliability problem. In 1957 R. Atchley developed a two-stage jet tube servo valve using the Askania jet principle. And in 1959 developed a three-stage electric feedback servo valve. February 1959 a foreign magazine of hydraulic and pneumatic servo valve at the time made a 12-page report shows the status of the servo valve was booming. At that time there were more than 20 manufacturers of various types of servo valves. The manufacturers compete for the servo valve hegemony in the production of fierce competition. Recalling the history, we can see the final win several manufacturers, most of the production of two-stage servo valve with feedback and torque motor. We can see that the 1960 servo valve has many of the features of modern servo valves. For example, the second stage forms the closed-loop control to the first stage feedback. The dry-type torque motor is adopted. The pressure recovery of the front stage to the power stage can usually reach 50%. The first stage of mechanical symmetry reduces the temperature and pressure changes. Zero effect. At the same time, the direct-acting open-loop control valve developed from the early changes in the direct acting two-stage closed-loop control servo valve has also emerged. At that time, the servo valve was mainly used in the military field. With the advent of the space age, the servo valve was widely used in the aerospace field and developed cutting-edge products such as redundant servo valves with high reliability. At the same time, with the continuous expansion of the servo valve industrial applications, some manufacturers have developed industrial servo valves that are specifically used in industrial applications. For example, Moog introduced the first Series 73 Servovalves for industrial use in 1963. Subsequently, more and more developed for industrial use servo valve appeared. They have the following characteristics: a larger volume for the convenience of manufacturing; aluminum body (if necessary, can also be used steel); independent of the first level to facilitate the adjustment and maintenance; mainly used in low pressure situations below 14MPa; try to form Series, standardized products. However, Moog's German subsidiary focuses its servovalve applications on high-pressure applications, with typical service pressures of 21 MPa and even up to 35 MPa, which make the design of the valve more specific to the reliability of use under high pressure. With the widespread use of servo valves in industrial applications, companies have introduced their own proportional valves for industrial applications. Its characteristics are low cost, although the control accuracy servo valve, but through advanced control technology and advanced electronic devices to make up for its deficiencies, the performance and effectiveness of servo valves. In 1973, Moog converted some of the servovalves to standard valve-scale interfaces for industrial applications as needed for industrial use. Bosch developed its iconic jet tube pilot and electric feedback flat servo valve. In 1974, Moog introduced a low-cost, high-flow three-stage electrical feedback servovalve. Vickers developed a pressure compensated KG-type proportional valve. Rexroth, Bosch and others have developed proportional valves that control the spool movement in both directions, respectively, using two coils. The current situation of the three countries at home and abroad 1 Market conditions At present, the domestic manufacturers of servo valves are: Sixth OIA Institute of Aviation Industry Corporation, Aviation Industry Corporation Institute of the six hundred and eighteen, Aviation Industry Corporation Qin Feng Machine Tool Plant, Beijing Institute of Machine Tool, Eighth Institute of China Academy of Launch Vehicle Technology, Shanghai Institute of Aerospace Control Engineering and China Shipbuilding Industry Corporation Seventh O four Institute. Foreign manufacturers of servo valves are: the United States Moog, the United Kingdom Dowty, Team USA, Russia's "motherland" Design Bureau, Worth Huode plant, in addition to the United States Park, EatonVickers, Germany Bosch, Rexroth Also have their own servo valve products. Electro-hydraulic servo valve generally by torque motor type is divided into two kinds of moving coil and permanent magnet. Most of the traditional servo valve permanent magnet torque motor, such servo valve can be divided into nozzle baffle and jet two categories. At present, most domestic manufacturers of servo valves nozzle baffle-based. The production of jet-type servo valve to form the scale and series of only China Shipbuilding Industry Corporation seventh O 4 Institute. Foreign situation is similar to the original manufacturer of jet-tube servo valve manufacturer Abex US company has also been annexed by Park. However, due to jet pipe servo valve with anti-pollution performance, high reliability, high resolution and so on. Some manufacturers are also developing or have launched their own jet tube products, such as the Aviation Industry Corporation No. 609 Research Institute, China Institute of Launch Vehicle Eighteenth Institute, the United States Moog and Russia, and other manufacturers. The United States Moog company also held a product promotion in July 2006, introduced the jet tube D660 series of products, and that the product represents the future development trend of servo valve. At present, although the domestic research, production and use of servo valve formed a certain scale. However, the products are mainly used in military, aerospace, shipbuilding and other military fields, share in the civilian market is not large. At the same time, the production units are fighting each other, lack of cooperation, the power is dispersed, it is not conducive to the further development of the servo valve, can not form a strong competitive edge with foreign products to compete. Now the largest share of foreign products in the domestic market for the Moog company, its products occupy the vast majority of civilian products market. 2 Research Status Current electro-hydraulic servo valve research mainly in the structure and processing technology improvements, material replacement and test methods change. 1) In the structural improvement, the main is the use of redundant technology on the structure of the servo valve to transform. Because servo valve is the core component of servo system, the performance of servo valve directly represents the level of servo system. In addition, from the reliability point of view, the reliability of servo valve servo system is the most important part. Servo valve due to contamination is the main reason leading to failure of the servo valve. In this regard, many foreign manufacturers made improvements to the servo valve structure, has developed a better anti-pollution jet tube, partial-jet jet-type servo valve. In addition, Russia has also designed a double redundant position sensor at both ends of its jet tube-type servo valve spool to detect spool position. Once the fault signal can be immediately switched standby servo valve, greatly improving the reliability of the system, this two redundant technology has been widely used in the aviation industry. Moreover, the United States Moog and Russia's Worth Huode plant have developed four redundant servo for the aerospace industry. China's space system related agencies as early as the 90's have been more than three degrees and other redundant servo research, the servo valve torque motor, feedback components, made more sets of vice, the failure can be switched at any time to ensure that the system The normal work. In addition, multi-coil structure, or in the structure with zero protection devices, external filters and other types of servo valve has also been metallurgical, electric power, plastics and other industries have been widely used. 2) In the improvement of processing technology, the use of new processing equipment and processes to improve the servo valve machining accuracy and ability. As in the valve sleeve with grinding method, Shanghai Jiaotong University, Harbin Institute of Technology have developed a smart, fully automatic with the grinding system. In particular, Harbin Institute of Technology grinding system with a change of the traditional pneumatic match grinding mode, the use of hydraulic oil as the measuring medium, a more direct response to the measured slide valve deputy actual situation, improve the accuracy and accuracy of measurement results. In the torque motor welding, China Shipbuilding Heavy Industries Institute 704 and Germany well-known manufacturers, the use of the world's most advanced welding technology has achieved good results. In addition, Harbin Institute of Technology has also developed intelligent servo valve torque motor elastic components measuring device. It solves the problems of low accuracy, complicated operation and low efficiency existing in the original manual measurement method. The elastic element can efficiently measure the stiffness and get a complete measurement curve, and the non-repeatability measurement error is not more than 1%. 3) In terms of material replacement. In addition to the use of some parts of the strength, elasticity, hardness and other mechanical properties superior material. Special purpose servo valve also uses a special material. For example, the German company made the nozzle baffle with ruby ​​material to prevent the baffle and nozzle from being damaged due to gas feed, thus reducing the static and dynamic performance and shortening the working life. The ball at the head of the mechanical feedback bar is also made of ruby ​​to prevent wear between the ball and the spool slot, causing the valve to run out of control and creating a scream. Aviation six O nine, China Shipbuilding Heavy Industry Seventh O four Research Institute and other units have developed a new material to aviation kerosene, diesel-based corrosion-resistant servo valve. In addition to the sealing ring material has also been replaced, so that servo valve high pressure, corrosion resistance performance is improved. 4) In the improvement of test methods, with the rapid development of computer technology, the production units all use computer technology to test and calculate the static and dynamic performance of the servo valve. Some units also made in-depth studies on how to improve the measurement accuracy, reduce the influence of the measurement instrument's own vibration, thermal noise and external high frequency interference on the measurement results. For example, the test equipment and method of servo valve were researched and improved by using the new technologies such as frequency measurement / measuring method, signal searching method, wavelet denoising method, sinusoidal input method and digital filtering.