Research on the characteristics and application of

2022-07-26
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Research on the characteristics and application of electro-hydraulic proportional valve in construction machinery

1 introduction

electro-hydraulic proportional valve is an element that the proportional electromagnet in the valve generates corresponding action according to the input voltage signal, causes the displacement of the working valve spool, changes the valve port size, and completes the pressure and flow output proportional to the input voltage. Spool displacement can also be fed back mechanically, hydraulically or electrically. Because the electro-hydraulic proportional valve has many advantages, such as various forms, easy to form various electro-hydraulic systems controlled by electricity and computer, high control accuracy, flexible installation and use, and strong anti pollution ability, its application field is expanding day by day. The cartridge proportional valve and proportional multi-channel valve developed and produced in recent years fully consider the use characteristics of construction machinery, and have the functions of 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, it shows a good application prospect in electronic control pilot operation, wireless remote control and wired remote control

2 types and forms of electro-hydraulic proportional valves for construction machinery

electro-hydraulic proportional valves include proportional flow valve, proportional pressure valve and proportional directional valve. According to the characteristics of hydraulic operation of construction machinery, there are mainly two types of electro-hydraulic proportional valves in structural form: one is screw cartridge proportional valve, and the other is spool proportional valve

the screw cartridge proportional valve is a component that fixes the electromagnetic proportional cartridge on the oil circuit manifold block through the thread. The screw cartridge valve has the characteristics of flexible application, pipeline saving and low cost. In recent years, it has been more and more widely used in construction machinery. The commonly used screw cartridge proportional valve has two-way, three-way, four-way and multi-way forms. The two-way proportional valve is mainly a proportional throttle valve, which often forms a composite valve with other components to control the flow and pressure; The three-way proportional valve is mainly a proportional reducing valve, which is widely used in mobile mechanical hydraulic system. It mainly operates the pilot oil circuit of the hydraulically operated multi-channel valve. The three-way proportional reducing valve can replace the traditional manual reducing pilot valve. It has more flexibility and higher control accuracy than the manual pilot valve. It can be made into a proportional servo controlled manual multi-channel valve as shown in Figure 1. According to different input signals, the pressure reducing valve makes the output piston have different pressure or flow, so as to realize the proportional control of the displacement of the multi-channel valve spool. The four-way or multi-way screw cartridge proportional valve can control the working device independently

slide valve proportional valve, also known as distribution valve, is one of the most basic components of mobile mechanical hydraulic system. It is a composite valve that can adjust direction and flow. The electro-hydraulic slide valve proportional multi-channel valve is an ideal electro-hydraulic conversion control element. It not only retains the basic function of the manual multi-channel valve, but also adds advanced control means such as position feedback proportional servo operation and load sensing. Therefore, it is an updated product of distribution valve of construction machinery

due to the consideration of manufacturing cost and the low requirements for control accuracy of construction machinery, generally, the proportional multi-channel valve is not equipped with displacement sensor, nor has the function of electronic detection and error correction. Therefore, the displacement of the valve element 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. In electric control and remote control operation, attention should be paid to the influence of external interference. Recently, due to the development of electronic technology, more and more displacement sensors such as built-in differential transformer (LDVT) are used to detect the spool position movement and realize the closed-loop control of spool displacement. This highly integrated proportional valve, which is composed of electromagnetic proportional valve, position feedback sensor, driving amplifier and other electronic circuits, has a certain correction function, which can effectively overcome the shortcomings of general proportional valves and greatly improve the control accuracy

3 load sensing and pressure compensation of electro-hydraulic proportional multi-channel valve

technology

in order to save energy, reduce oil temperature and improve control accuracy, and at the same time, make several actuating elements of synchronous action do not interfere with each other during movement, now more advanced construction machinery adopt load sensing and pressure compensation technology. Load sensing and pressure compensation are very similar concepts. They both use the pressure change caused by load change to adjust the pressure and flow of pump or valve to meet the working requirements of the system. For the quantitative pump system, load sensing is to lead the load pressure to the relief valve for remote pressure regulation through the load sensing oil circuit. When the load is small, the set pressure of the relief valve is also small; The load is large and the set pressure is large, but there is always a certain overflow loss. For the variable displacement pump system, the load sensing oil circuit is introduced into the variable mechanism of the pump, so that the output pressure of the pump increases with the increase of the load pressure (always a small fixed differential pressure), so that the output flow of the pump is equal to the actual required flow of the system, without overflow loss, and energy saving is realized

pressure compensation is a guarantee measure taken to improve the control performance of the valve. 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 to make the pressure difference before and after the valve port constant. In this way, according to the flow regulation characteristics of the throttle port, the flow through the valve port is only related to the opening of the valve port, and is not affected by the load pressure

4 pilot control and remote control of electro-hydraulic proportional valve of construction machinery

the technical progress of electro-hydraulic proportional valve and other special devices makes the electrical control of various systems such as gear, steering, braking and working devices of construction vehicles a reality. For the mechanism that generally needs displacement output, the proportional servo control manual multi-channel valve driver similar to figure 1 can be used. Electrical operation has the advantages of fast response, flexible wiring, integrated control and easy interface with computer. Therefore, modern engineering machinery hydraulic valves have increasingly adopted electro-hydraulic proportional valves (or electro-hydraulic on-off valves) controlled by electronic control pilot instead of multi-channel valves controlled by manual direct operation or hydraulic pilot. Another significant advantage of using electro-hydraulic proportional valve (or electro-hydraulic on-off valve) is that the number of operating handles can be greatly reduced on engineering vehicles, which not only makes the cab layout simple, but also can effectively reduce the complexity of operation, and has important practical significance for improving the quality and efficiency of operation. Figure 2 shows the JMF type joystick of TECNORD company, which can effectively control the multi piece electro-hydraulic proportional valve and on-off valve as shown in Figure 2. The rocker can realize proportional control or switch control in both x-axis and Y-axis directions, which is very convenient for application

with the rapid development of digital wireless communication technology, a wireless remote control system with stable performance, reliable operation and suitable for construction machinery has emerged. The remote control receiving device arranged on the mobile machinery can convert the received radio signal C. double report: fully open user report into the proportional signal of controlling the electro-hydraulic proportional valve, the switching signal of controlling the electro-hydraulic on-off valve and the corresponding signal of controlling other devices, So that the original manually operated components can accept the command of remote control electrical signal and act accordingly. At this time, the construction machinery has actually become a remote control type of construction machinery

the wireless remote control transmitting and receiving system has been successfully applied to the remote control transformation of various construction machinery. From the security point of view, each digital data instruction it sends has a group of special system address codes, which are only used once by the manufacturer. Each receiver only reacts to the transmitted signal with the same address code, and other wireless signals, even those with the same frequency, will not affect the receiving device. With the adoption of other safety measures, the reliability of the system is fully guaranteed. It has succeeded in the remote control transformation of various mobile machinery, such as loaders, rock drills, concrete pump trucks, aerial work vehicles and bridge maintenance vehicles. The industrial remote control device and the electro-hydraulic proportional valve complement each other. The electro-hydraulic proportional valve provides a feasible interface for the remote control of construction machinery, and the remote control device makes the electro-hydraulic proportional valve play a greater role

5 application example of electro-hydraulic proportional valve in construction machinery

Figure 3 shows the hydraulic system diagram of a certain truck crane, in which only the parts related to the electro-hydraulic proportional valve are drawn. The machine adopts three TECNORD tdv-4/3 lm-ls/pc proportional multi-channel valves. The three shuttle valves in the load sensing oil circuit select the maximum pressure of the three working loads and send it to the remote control port of the remote pressure regulating overflow valve. 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, so as to achieve a certain energy-saving purpose. The pressure compensation oil circuit makes the flow through each valve only related to the opening of the valve after it is matched with the steel strand clamp, and has nothing to do with the load it bears, and has nothing to do with the load borne by other valves, so that the load speed can be controlled at will under any load

Figure 4 is an example of manual and electro-hydraulic proportional pilot control for a bulldozer bulldozer. When the solenoid valve is not energized until the two position three-way valve is normal, the pilot pressure is connected with the manual pressure reducing pilot valve, and 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 pressure oil is led to the three-way proportional reducing pilot valve, which controls the hydraulic directional valve through the shuttle valve

6 summary

the above briefly introduces the working principle, structural form and working characteristics of the electro-hydraulic proportional valve, and analyzes the load sensing and pressure compensation principles of the comparative example valve. The different applications of electro-hydraulic proportional valve, especially in the pilot control and remote control of construction machinery, are discussed. The electro-hydraulic proportional valve is of great significance to simplify the operation of construction machinery, improve efficiency and operation accuracy, and realize intelligent operation. The further improvement of its performance and the widening of its application range will greatly improve the technical level of construction machinery products

references

1 wugenmao et al. Practical electrohydraulic proportional technology. Hangzhou: Zhejiang University Press  1993

2 Ruth swan.have you checked out cartridge valves Hydraulics and pneumatics  1991  8

3 hydraulic Danfoss product sample hk.51.a3.43  1997

4 delta power hydraulic cartridge valves a pipeline is equipped with switching device nd HIC manifold delta power product sample

5 TECNORD product sample

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