First, an overview Electrohydraulic 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. Second, the development process The history of hydraulic control technology can be traced back to 240 BC, when an ancient Egyptian invented the history of mankind's first hydraulic servo system - the water clock. 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 electric 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. Third, the status quo at home and abroad 1, the market situation At present, the domestic manufacturers of servo valves are: Sixth OIA Aviation Industry Corporation Institute, Aviation Industry Corporation Institute of the six hundred and eighteen, Aviation Industry Corporation Qinfeng Machine Tool Plant, Beijing Machine Tool Research Institute, Eighth Institute of China Academy of Launch Vehicle Technology, Shanghai Aerospace Control Engineering Institute 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-related 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, the research status of the current Electro-hydraulic servo valve research mainly in the structure and process improvement, material replacement and test methods change. 1) In the structural improvement, the main is the use of redundant technology to 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. Fourth, the development trend At present, the development trend of new electro-hydraulic servo valve technology is mainly reflected in the new structure design, the use of new materials and electronic, digital technology and hydraulic technology combined with several other aspects. A new type of structure design In the 1990s, foreign direct-drive electro-hydraulic servo valve developed a greater achievement. A series of products are now formed Moog's D633, D634 series of direct-acting valve, Eaton Vickers LFDC5V company, Germany Bosch's NC10-type, Japan's Mitsubishi and KYB Co., Ltd. jointly developed MK-type valve and Moog company and the Russian Wo Shute factory developed by the direct-acting valve. This type of servo valve removes the pre-stage of a typical servo valve and uses a higher-power torque motor to directly pull the spool and a high-precision spool displacement sensor as feedback. The most prominent feature of this valve is that it has no pre-stage and improves the anti-pollution ability of the servo valve. At the same time as many difficult to remove the parts, reducing the processing costs, can be widely used in industrial servo control of the occasion. Some domestic units such as Beijing Machine Tool Research Institute, Zhejiang University of Technology and other units have also developed a prototype of related products. In addition, Park developed the "Voice Coil Drive" technology (VCD) and the DFplus control valve developed on the basis of this technology. The so-called voice coil drive technology, as its name implies, is similar to a speaker drive, the basic structure is set on a fixed cylindrical permanent magnet moving coil, when the signal current input coil, the role of the electromagnetic effect, The coil generates an axial force corresponding to the signal current and drives the spool connected directly to the coil, with a large driving force. The built-in displacement feedback sensor coil, therefore, the use of VCD-driven DFplus valve is essentially closed-loop control, linearity is quite good. In addition, the moving parts of the VCD drive only move the coil, the inertia is extremely small, and there is no support between the relative moving parts. The full support of the DFplus valve is the mating surface between the valve core and the valve body, greatly reducing the friction Influence of Nonlinear Factors on Control Quality. The above technical features, combined with built-in digital control module, DFplus valve control performance is good, especially in the frequency response is superior, up to 400Hz. From the development trend of view, the new direct acting electro-hydraulic servo valve in some industries to replace the traditional servo valve nozzle baffle-style servo valve, in particular the trend, but it is the biggest problem is bulky, heavy weight, only for Site requirements for lower industrial servo control applications. If it can reduce its weight and reduce its volume, it also has great potential in the military and aerospace industries such as aviation and aerospace. In addition, in recent years servo valve new type of driving method in addition to direct torque motor drive, there have been used stepper motor, servo motor, a new type of electromagnet drive structure and the light - liquid direct conversion servo valve structure. The application of these new technologies not only improves the performance of servo valve, but also opens up a new idea for the development of servo valve, which injects new vitality into the electro-hydraulic servo valve technology. 2 The use of new materials Currently in the field of electro-hydraulic servo valve research and development of new materials, mainly based on piezoelectric elements, giant magnetostrictive materials and shape memory alloy converter based on research and development. They each have their own fine qualities. 2.1 Piezoelectric elements Piezoelectric elements are characterized by "piezoelectric effect": a certain electric field will have a change in shape dimensions, within a certain range, deformation and electric field strength is proportional to. Piezoelectric elements are mainly made of piezoelectric ceramics (PZT), electrostrictive materials (PMN) and the like. The typical piezoelectric ceramic materials are Japan TOKIN company's piezoelectric stack telescopic ceramics. PZT direct acting servo valve principle is: at both ends of the spool through the ball were connected with two multi-layer piezoelectric components. Through the piezoelectric effect, the piezoelectric material to produce telescopic drive spool movement. Achieve electrical - mechanical conversion. PMN nozzle baffle servo valve is set in the nozzle at a fixed connection with the piezo stack baffle, the piezoelectric stack stretch, shrinkage to achieve the gap between the baffle and the nozzle increases and decreases, so that both ends of the spool generated Differential pressure to promote the spool movement. Currently piezoelectric piezoelectric - mechanical converter developed more mature and has been more widely used. It has the characteristics of fast frequency response, servo valve bandwidth up to even thousands of hertz, but also hysteresis large, easy to drift and other shortcomings, restricting the further application of piezoelectric components in the electro-hydraulic servo valve. 2.2 Giant magnetostrictive materials Giant magnetostrictive materials (GMM) compared with the traditional magnetostrictive material, the magnetic field can produce a much larger length or volume change. The use of GMM converter developed direct acting servo valve GMM converter is connected with the spool, by controlling the current drive coil, drive GMM telescopic, driven spool displacement to control the servo valve output flow. Compared with the traditional servo valve, the valve not only has the characteristics of high frequency response, but also has the advantages of high precision and compact structure. At present, in the development and application of GMM, the United States, Sweden and Japan and other countries are at the leading level. Domestic Zhejiang University using GMM technology on the pneumatic nozzle flapper valve and the internal combustion engine fuel injection system of high-speed powerful solenoid valve, the structural design and characteristics of the study. From the current situation GMM materials and piezoelectric materials and traditional magnetostrictive material compared with a large strain, high energy density, fast response, the output power and so on. All countries in the world attach great importance to the GMM electro-mechanical converter and related technology research. The GMM technology has been developed rapidly and has gradually entered the market development stage from the laboratory development phase. In the future, the problems of thermal deformation, magnetocrystalline anisotropy, material corrosivity, manufacturing process and parameter matching of GMM need to be solved in order to be widely used in high-tech fields. 2.3 Shape Memory Alloy Shape memory alloy (SMA) is characterized by a shape memory effect. After setting it at a high temperature, it is cooled to a low temperature and an external force is applied thereto. Metal generally undergoes permanent deformation beyond its elastic deformation, and the SMA recovers its original high temperature shape after it has been heated to a certain temperature. The servo valve developed by its characteristics is to add a set of SMA actuators wound by shape memory alloy at both ends of the valve core to drive the SMA actuator by heating and cooling to elongate the shape memory alloy at both ends of the valve core or Shrinkage, drive spool movement, while adding position feedback to improve the servo valve control performance. From the situation of the valve, although SMA large deformation, but its response is slow, and the deformation is not continuous, but also limits its scope of application. Compared with the traditional servo valve, the servo valve developed by the new material electro-mechanical converter generally has the advantages of high frequency response, high precision and compact structure. Although each of them is still in need of solving some key technologies, the application and development of new functional materials provide a new way for the development of electro-hydraulic servo valve technology. 3 The use of electronic, digital technology At present, electronic, digital technology in the electro-hydraulic servo valve technology is mainly used in two ways: First, in the electro-hydraulic servo valve analog control components by adding D / A converter to achieve Its digital control. With the development of microelectronic technology, the control components can be installed inside the valve body, through the computer program to control valve performance, digital compensation and other functions. However, there is analog circuit prone to zero drift, temperature drift, the need to add D / A conversion interface and other issues. Second, the direct acting digital control valve. By using a stepper motor drive spool, the input signal into a stepper motor signal to control the servo valve flow output. The valve has the advantages of compact structure, controllable speed and position open loop and direct digital control, which are widely used. However, in real-time control of the higher requirements of the occasion, such as conventional step-by-step method, can not take into account the accuracy and speed of response requirements. Using a continuous control approach, eliminating the conflict between the two, access to a good dynamic characteristics. In addition there are through the direct torque motor to directly drive the valve to achieve digital control and other control methods or servo valve structure change methods to form a large number of digital servo valve products. With the development of various technologies, a new type of intelligent servo valve integrating mechanical, electronic, sensor and computer self-management (fault diagnosis and troubleshooting) has been developed by adopting new sensors and computer technology. This type of servo valve can be based on the needs of the system to determine the control objectives: speed, position, acceleration, force or pressure. The same servo valve can be set according to the control requirements of the flow control servo valve, pressure control servo valve or flow / pressure composite control servo valve. And servo valve control parameters, such as flow gain, flow gain characteristics, zero, etc. can be set according to the principle of optimal control performance. Servo valve's own diagnostic information, the key control parameters (including the working environment parameters and servo valve internal parameters) can be promptly fed back to the main controller; can be long-distance servo valve monitoring, diagnosis and remote control. During host debugging, the servo valve can be downloaded through the bus port or directly set by the host computer servo valve control parameters, the servo valve and control system to achieve the best match to optimize control performance. The servo valve control parameters to download and update, even when the host can run. In the servo valve and control system to match the development of technology applications, the embedded technology for the servo valve has become a reality. According to the embedded system should be defined as: "embedded into the target system of dedicated computer system." "Embeddedness," "Specificity," and "Computer Systems" are three basic elements of an embedded system. It is embedded in the traditional servo valve dedicated microprocessor chip and the corresponding control system for customer specific application requirements and build the servo valve with the optimal control parameters and the valve control system to complete the corresponding control tasks Such as the control axis synchronous control), then embedded in the entire large control system to go. From the current technical development and control system requirements of the servo valve, servo valve self-diagnosis and self-test function should have greater development. 4 Conclusion The current hydraulic servo control technology has been able to automatic control technology, hydraulic technology and microelectronics combine to form a new generation of servo valve products. With the development and progress of electronic equipment, control strategies, software and materials, electro-hydraulic control technology and servo valve products will make great strides in the integration of machine, electricity and liquid.
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