Working principle of proportional solenoid valve
The electro-hydraulic proportional valve is the corresponding action of the input voltage signal of the proportional electromagnet in the valve to cause the displacement of the working valve spool, the size of the valve port changes, and the pressure and flow output components proportional to the input voltage are thus completed. Spool displacement can also be fed back in mechanical, hydraulic or electrical form. The electro-hydraulic proportional valve has various forms, is easy to form, uses electrical and computer control of various electro-hydraulic systems, has high control accuracy, flexible installation and use, and strong anti-pollution ability. The application fields are increasingly widening. In recent years, it has developed and produced plug-in proportional valves and proportional multi-way valves that fully take into account the characteristics of construction machinery. It has functions such as pilot control, load sensing and pressure compensation. Its appearance is of great significance to the improvement of the overall technical level of mobile hydraulic machinery. In particular, the electric control pilot operation, wireless remote control and wired remote control operation have shown their good application prospects.
2 Types and forms of electro-hydraulic proportional valves for construction machinery Electro-hydraulic proportional valves include proportional flow valves, proportional pressure valves, and proportional directional valves. There are two main types of electro-hydraulic proportional valves divided by structure in the hydraulic operation characteristics of construction machinery: one is the screw-in cartridge proportional valve (screwin cartridge propor TIonal valve), and the other is the spool propor TIonal valve.
Spiral plug-in proportional valve is a component that fixes the electromagnetic proportional plug-in part of the oil circuit block with a screw thread. The spiral plug-in valve has the characteristics of flexible application, pipeline saving and low cost. In recent years, it has been widely used on construction machinery. Commonly used spiral plug-in proportional valves have two-way, three-way, four-way and multi-way forms. The two-way proportional valve is the main proportional throttle valve. It often forms a composite valve with other components to control the flow and pressure; The general proportional pressure valve is the main proportional pressure reducing valve, which is also used in the mobile mechanical hydraulic system. It mainly operates the pilot oil circuit of the hydraulically operated multi-way valve. The three-way proportional pressure reducing valve can replace the traditional manual pressure reducing pilot valve, which has more flexibility and higher control accuracy than the manual pilot valve. Can be made as shown in Figure 1 proportional servo control manual multi-way valve, different input signals, reducing valve makes the output piston have different pressure or flow rate to achieve proportional control of the multi-way valve spool displacement. The four-way or multi-way spiral plug-in proportional valve can realize independent control of the working device.
Spool valve proportional valve, also known as distribution valve, is one of the most basic components of mobile mechanical hydraulic system. It is a compound valve that can realize direction and flow adjustment. Electro-hydraulic spool type proportional multi-way valve is an ideal electro-hydraulic conversion control element. It retains the basic functions of manual multi-way valve, and also adds advanced control methods such as position electric feedback proportional servo operation and load sensing. It is a replacement product for construction machinery distribution valves.
Due to manufacturing cost considerations and the low accuracy requirements of engineering machinery control, the general proportional multi-way valve is not equipped with a displacement sensor, with electronic detection and error correction functions. The displacement of the spool is easily affected by the pressure fluctuation caused by the load change. During the operation, visual observation is required to ensure the completion of the operation. Attention should be paid to the influence of external interference during electric control and remote control operation. Recently, with the development of electronic technology, more and more people use displacement sensors such as built-in differential transformers (LDVT) to form spool position movement detection to achieve closed-loop control of spool displacement. This type of highly integrated proportional valve is composed of an electromagnetic proportional valve, a position feedback sensor, a drive amplifier and other electronic circuits. It has a certain correction function, which can effectively overcome the shortcomings of the general proportional valve and greatly improve the control accuracy.
3 Electro-hydraulic proportional multi-way valve load sensing and pressure compensation technology save energy, reduce oil temperature and improve control accuracy, but also make several actuators move synchronously without disturbing each other. Now more advanced construction machinery uses load sensing With pressure compensation technology. Load sensing and pressure compensation are very similar concepts, both of which use the pressure changes caused by the load changes to adjust the pump or valve pressure and flow to suit the system's working requirements. For the quantitative pump system, load sensing leads the load pressure load sensing oil path to the remote pressure relief valve. When the load is small, the set pressure of the relief valve is also small; the load is large, and the set pressure is also It is large, but there is always a certain overflow loss. The variable pump system is to introduce the load sensing oil circuit to the pump variable mechanism, so that the pump output pressure increases with the load pressure (always a small fixed pressure difference), so that the pump output flow is equal to the actual flow required by the system, no Overflow loss achieves energy saving.
Pressure compensation is a guarantee measure taken to improve valve control performance. The load pressure behind the valve port is introduced into the pressure compensation valve. The pressure compensation valve adjusts the pressure in front of the valve port so that the pressure difference between the front and back of the valve port is constant, so that the flow adjustment characteristic of the throttle port flows through the valve port. The degree of opening is related, not affected by load pressure.
4 The advancement of engineering machinery electro-hydraulic proportional valve pilot control and remote-controlled electro-hydraulic proportional valve and other special devices technology advancement has made the electrical control of various systems such as gear, steering, braking and working devices of engineering vehicles a reality. Generally, the displacement output mechanism can be completed by using the proportional servo control manual multi-way valve driver similar to Figure 1. Electrical operation has the advantages of fast response, flexible wiring, integrated control and easy interface with the computer. Modern construction machinery hydraulic valves have increasingly used electronically controlled pilot-controlled electro-hydraulic proportional valves (or electro-hydraulic on-off valves) instead of manual direct Pilot operated or hydraulically controlled multi-way valve. The use of electro-hydraulic proportional valve (or electro-hydraulic on-off valve) another significant advantage is that the number of operating handles can be greatly reduced on engineering vehicles, which makes the cab layout simple, can effectively reduce the complexity of operation, and has the advantages of improving operation quality and efficiency Important practical significance. Fig. 2 is the JMF type control rocker (joysTIck) of TECNORD Company. With one rocker, the multi-piece electro-hydraulic proportional valve and on-off valve in Fig. 2 can be effectively controlled. The X-axis and Y-axis directions of the rocker can realize proportional control or switch control, and the application is very convenient.
The rapid development of digital wireless communication technology has resulted in stable performance, reliable operation, and is suitable for wireless remote control systems of construction machinery. Deploying remote control receivers on mobile machinery can convert the received radio signals into proportional signals for controlling electro-hydraulic proportional valves and controlling electro-hydraulics. The on-off valve switching signal and the corresponding signals of other devices are controlled, so that the original manual operation of each component can receive the remote control electrical signal instructions and perform corresponding actions. At this time, the construction machinery has actually become a remote control construction machinery.
The wireless remote control transmitting and receiving system has been successfully applied to the remote control transformation of various engineering machinery. From a security point of view, each digital data command it transmits has a set of special system address codes, which are only used once by the manufacturer of such address codes. Each receiver only responds to signals transmitted with the same address code, and other wireless signals with the same frequency will affect the receiving device. Coupled with the adoption of other security measures, the system reliability is fully guaranteed. A variety of mobile mechanical remote control transformations such as loader, rock drill, concrete pump truck, aerial work truck and bridge maintenance truck have been successful. The industrial remote control device and the electro-hydraulic proportional valve complement each other. The electro-hydraulic proportional valve provides a viable interface for the remote control of construction machinery. The remote control device makes the electro-hydraulic proportional valve play a greater role.
5 Application Example of Electro-hydraulic Proportional Valve Construction Machinery A simplified diagram of the hydraulic system of a certain type of truck crane. Only the relevant parts of the electro-hydraulic proportional valve are shown in the figure. This machine adopts three TECONRD TDVï¼4 / 3 LMï¼LS / PC proportional multi-way valves. The three shuttle valves in the load sensing oil circuit select the maximum pressure among the three working loads and send it to the remote pressure regulating overflow The remote control port of the valve can adjust the overflow pressure of the overflow valve to make the output pressure of the hydraulic pump just meet the needs of the system load to achieve a certain energy saving goal. The pressure compensation oil circuit makes the flow of each piece of valve only related to the opening of the valve, and has nothing to do with the load it bears. The load that the valve piece bears has no relationship. It can control the speed of the load at any load.
An example of manual and electro-hydraulic proportional pilot control of a bulldozer blade. When the two-position three-way solenoid valve is not energized, the pilot pressure communicates with the manual decompression type pilot valve. The shuttle valve selects the pressure from the manual pilot valve to control the hydraulic directional valve; when the two-position three-way solenoid valve is energized, the pilot control The pressure oil leads to a three-way proportional pressure reducing pilot valve, and the shuttle valve controls the hydraulic directional valve.
6 Summary The above briefly introduced the working principle, structural form and working characteristics of the electro-hydraulic proportional valve, and analyzed and studied the principle of proportional valve load sensing and pressure compensation. The different applications of electro-hydraulic proportional valves, especially the pilot control and remote control of construction machinery, are discussed. Electro-hydraulic proportional valves are extremely important for simplifying construction machinery operations, improving efficiency and operating accuracy, and realizing intelligent operations. The further improvement of their performance and the increasing application scope will definitely increase the technical level of construction machinery products to a greater extent.
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