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Electro-hydraulic proportional valve is the proportion of the solenoid valve according to the input voltage signal corresponding action, the work valve spool displacement, valve size changes and thus complete with the input voltage proportional to the pressure and flow output components. Spool displacement can also be mechanical, hydraulic or electrical feedback form. As the electro-hydraulic proportional valve has a variety of forms, easy to use the electrical and computer control of the various electro-hydraulic system, high control accuracy, ease of installation and use of anti-pollution ability and many other advantages, so increasingly widened applications. In recent years, R & D and production of cartridge proportional valve and proportional multi-way valve fully take into account the use of construction machinery features, with pilot control, load sensing and pressure compensation functions. Its emergence is of great significance to the overall technical level of mobile hydraulic machinery. Especially in the electronic pilot operation, wireless remote control and wired remote control operation shows its good application prospects. 2 Construction Machinery Electro-hydraulic proportional valve type and form Electro-hydraulic proportional valve, including proportional flow valve, proportional pressure valve, proportional valve. According to the characteristics of hydraulic operation of construction machinery, there are mainly two types of electro-hydraulic proportional valves divided by structure: one is screwin cartridge proportional valve and the other is spool proportiona lvalve ). Screw-type proportional valve is through the solenoid to the electromagnetic ratio of the fixed components in the oil manifold manifold components, screw-in cartridge valve with flexible application, saving piping and low cost and other characteristics of the application in recent years in construction machinery More and more widely. Commonly used spiral cartridge proportional valve with two, three, four and multi-pass and other forms, two-way proportional valve is the proportion of throttle, it often constitutes a composite valve with other components, the flow, pressure Control; three-way proportional valve is mainly proportional pressure reducing valve, but also mobile mechanical and hydraulic systems more than the proportion of the valve, it is mainly for the hydraulic operation of the pilot valve multi-way valve operation. The use of three-way proportional relief valve can replace the traditional manual decompression pilot valve, which has more flexibility than the manual pilot valve and higher control accuracy. Can be made as shown in Figure 1 proportional servo control manual multi-channel valve, depending on the input signal, the pressure reducing valve so that the output piston with different pressures or flow rate and thus achieve multi-valve spool displacement proportional control. Four-way or multi-way screw-type proportional valve can work on the device to achieve a separate control. Sliding valve proportional valve, also known as distribution valve, is one of the most basic components of mobile mechanical hydraulic system, is to achieve the direction and flow control valve complex. The electro-hydraulic slide valve proportional multi-way valve is an ideal electro-hydraulic switching control element. It not only retains the basic functions of the manual multi-way valve but also adds advanced control measures such as proportional servo operation and load sensing with position feedback . So it is the construction machinery distribution valve replacement product. Due to the consideration of manufacturing cost and the low control precision of construction machinery, displacement sensors are not usually installed in multi-way proportional valves and do not have the functions of electronic detection and error correction. Therefore, the spool displacement easily affected by pressure fluctuations caused by load changes, the operation depends on visual observation to ensure the completion of the operation. In the electronic control, remote control operation should pay attention to the impact of external interference. Recently, due to the development of electronic technology, more and more people use the built-in differential transformer (LDVT) and other displacement sensors constitute the detection of valve spool position movement, valve displacement closed-loop control. The highly integrated proportional valve composed of electromagnetic proportional valve, position feedback sensor, driver amplifier and other electronic circuits has a certain correction function, which can effectively overcome the shortcomings of the general proportional valve, so that the control accuracy is greatly improved. 3 Electro-hydraulic proportional multi-way valve load sensing and pressure compensation technology In order to save energy, reduce oil temperature and improve control accuracy, but also to synchronize the action of several executive elements do not interfere with each other in motion, and now more advanced construction machinery Using load sensing and pressure compensation technology. Load sensing and pressure compensation are a very similar concept, both using pressure changes caused by load changes to regulate the pressure and flow of the pump or valve to suit the needs of the system. Load sensing on the quantitative pump system is the load pressure induced by the load sensing circuit to remote pressure relief valve, when the load is small, the relief valve setting pressure is smaller; load larger, set Pressure is also greater, but there is always a certain amount of overflow loss. For variable displacement pumping systems, the load sensing circuit is introduced into the variable mechanism of the pump to increase the output pressure of the pump as the load pressure increases (always at a small fixed differential pressure) so that the pump output flow is proportional to the system The actual needs of the same flow, no overflow loss, to achieve energy conservation. Pressure compensation is a guarantee measure to improve the control performance of the valve. The load pressure after the valve port into the pressure compensation valve, the pressure compensation valve to adjust the pressure before the valve port so that the pressure difference before and after the valve port is constant, so according to the throttling of the flow characteristics of the flow through the valve size It is only related to the opening degree of the valve port, not affected by the load pressure. 4 Pilot Control and Remote Control of Electro-hydraulic Proportional Valves for Construction Machinery Technical advances in electro-hydraulic proportional valves and other specialized components have made electrical control of a wide range of systems such as gear, steering, brakes and work units for construction vehicles a reality. The general need for displacement output of the mechanism can be used similar to Figure 1 servo control manual multi-way valve actuator to complete. Electrical operation has the advantages of fast response, flexible wiring, integrated control and easy interface with a computer. Therefore, modern engineering machinery hydraulic valves have increasingly adopted electro-hydraulic proportional valves (or electro-hydraulic switch valves) Instead of manual direct operation or hydraulic pilot control of multi-way valve. Another significant advantage of using electro-hydraulic proportional valve (or electro-hydraulic switch valve) is that the number of operating handles can be greatly reduced on the construction vehicle, which not only simplifies cab arrangement but also effectively reduces the operational complexity, Both quality and efficiency have important practical significance. Figure 2 is a TECNORD company JMF type joystick (joystick), the use of a joystick can be shown in Figure 2, multiple electro-hydraulic proportional valve and the on-off valve for effective control. The joystick in the X-axis and Y-axis direction can be achieved proportional control or switch control, the application is very convenient. With the rapid development of digital wireless communication technology, there has been a steady performance, reliable operation, suitable for wireless remote control system of construction machinery. The remote control receiving device arranged on the mobile machinery can convert the received radio signal into a controllable electro-hydraulic ratio Valve proportional signal and the switch signal to control the electro-hydraulic switch valve, as well as control the corresponding signals of other devices, so that the original manual operation of the various components can accept the command of remote control signals and the corresponding action, this time the construction machinery actually Become a remote control of construction machinery. Wireless remote control transmitter and receiver system has been successfully used in a variety of construction machinery remote control transformation. From a security standpoint, each digital data command it transmits has a special set of system address codes that manufacturers use only once. Each receiver responds only to transmit signals that have the same address code and other wireless signals, even at the same frequency, do not affect the receiver. Coupled with the use of other safety measures to ensure the reliability of the system has been fully protected. Success in the remodeling of various mobile machines such as loaders, rock drills, concrete pump trucks, aerial work platforms and bridge service cars. The industrial remote control device complements the electro-hydraulic proportional valve, and the electro-hydraulic proportional valve provides a viable interface for the remote control of construction machinery. The remote control device also enables the electro-hydraulic proportional valve to play a greater role. 5 electro-hydraulic proportional valve in the construction machinery application example A type of truck crane hydraulic system diagram, the figure shows only the electro-hydraulic proportional valve related parts. The machine uses three TECNORDTDV-4 / 3LM-LS / PC ratio multi-way valve, the load sensing circuit in the three shuttle valve to the maximum load of the three workloads selected to send to the remote regulator overflow Valve remote control port, adjust the relief valve overflow pressure, the output pressure of the hydraulic pump just in line with the needs of the system load, so as to achieve a certain energy-saving purposes. Pressure compensation circuit makes the flow through each valve only with the valve opening related to the load it has nothing to do with the load on the other valve has nothing to do in order to achieve any load can be freely controlled The purpose of the load speed. A bulldozer blade and manual electro - hydraulic proportional pilot control example. When the two three-way solenoid valve is not energized, the pilot pressure and the manual decompression pilot valve connected to the shuttle valve to select the pressure from the manual pilot valve hydraulic control valve; when the two three-way solenoid valve energized, the pilot Control the pressure oil to the three-way proportional decompression pilot valve, through the shuttle valve on the hydraulic control valve. 6 Summary The above briefly introduced the working principle and structure of the electro-hydraulic proportional valve, working characteristics, the proportional valve load sensing and pressure compensation principle were analyzed. Different applications of the electro-hydraulic proportional valve, especially in the pilot control of construction machinery and remote control applications are discussed. Electro-hydraulic proportional valve to simplify the construction machinery operation, improve efficiency and precision operations and intelligent operations have a very important significance, and its performance to further enhance and expand the scope of the application is bound to make the technical level of construction machinery products are larger The degree of improvement.