At present, the development trend of new electro-hydraulic servo valve technology is mainly reflected in the design of new structure, the adoption of new materials and the combination of electronic technology, digital technology and hydraulic technology. A new type of structure design In the 20th century, 90's, foreign developed direct acting electro-hydraulic servo valve achieved greater success. 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 China Institute of Launch Vehicle Eighteenth Institute, Beijing Machine Tool Research Institute, Zhejiang University of Technology and other units have also developed a prototype of the relevant products. In particular, Beijing University of Aeronautics developed a rotary valve electro-hydraulic servo valve. The servo valve through the common servo valve slide sliding structure into a slide valve rotation, and in the valve core and the valve sleeve corresponding to open a few inclined with a certain axial chute. When the valve core sleeve rotates with each other, the chutes are opened or closed to each other to control the output pressure or flow rate. Since the spool valve sleeve rotates with each other during operation, the frictional resistance of the valve during operation is reduced, meanwhile, the pollutants are not easily accumulated in the rotating slide valve, thereby improving the anti-pollution performance. 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, with built-in digital control module, so that the control performance of DFplus valve is good, especially in terms of frequency response is superior, up to 400Hz. From the development trend, the new direct-acting electro-hydraulic servo valve in a Some industries have the tendency to replace the traditional servo valve, especially the nozzle baffle servo valve. However, the biggest problem is that it is bulky and heavy. It is only suitable for industrial servo control applications that require less space. 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 the "piezoelectric effect": under the action of a certain electric field, there will be a change in the overall dimensions. Within a certain range, the deformation is proportional to the electric field strength. 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. At present, electronic, digital technology in the electro-hydraulic servo valve technology, there are two main 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. Zhejiang University of Technology adopted a continuous tracking 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.