1 Introduction
 
The electro-hydraulic proportional valve is a component that generates a corresponding action according to the input voltage signal in the valve, and causes the working valve spool to be displaced, the valve port size is changed, and the pressure and flow output are proportional to the input voltage. The spool displacement can also be fed back mechanically, hydraulically or electrically. Since the electro-hydraulic proportional valve has various forms and is easy to form various electro-hydraulic systems using electrical and computer control, high control precision, flexible installation and strong anti-pollution capability, the application field is increasingly broadened. The cartridge-type proportional valve and proportional multi-way valve developed and produced in recent years fully take into account the use characteristics of construction machinery, and have the functions of pilot control, load sensing and pressure compensation. Its emergence is of great significance to the improvement of the overall technical level of mobile hydraulic machinery. Especially in the aspects of electronically controlled pilot operation, wireless remote control and wired remote control operation, it has shown its good application prospects.
 
2 Types and forms of electro-hydraulic proportional valves for construction machinery
 
The electro-hydraulic proportional valve includes a proportional flow valve, a proportional pressure valve, and a proportional reversing valve. According to the characteristics of hydraulic operation of engineering machinery, there are two main types of electro-hydraulic proportional valves divided into structural forms: one is a spiral-injection proportional valve, and the other is a spool-type proportional valve.
 
The spiral insert type proportional valve is a component for fixing the electromagnetic proportional inserting member on the oil circuit block by thread. The spiral inserting valve has the characteristics of flexible application, saving pipeline and low cost, and has been applied to engineering machinery in recent years. More and more extensive. Commonly used spiral-injection proportional valves are in the form of two-way, three-way, four-way and multi-pass. The two-way proportional valve is mainly a proportional throttle valve, which often forms a composite valve together with other components to carry out flow and pressure. Control; the three-way proportional valve is mainly a proportional pressure reducing valve, and is also a proportional valve widely used in the mobile mechanical hydraulic system. It is mainly for operating the pilot oil circuit of the hydraulic operating multi-way valve. The three-way proportional pressure reducing valve can replace the traditional manual decompression pilot valve, which has more flexibility and higher control precision than the manual pilot valve. The proportional servo control manual multi-way valve as shown in Fig. 1 can be made. According to different input signals, the pressure reducing valve makes the output piston have different pressure or flow rate to realize proportional control of the displacement of the multi-way valve spool. Four-way or multi-pass spiral-injection proportional valves provide individual control of the work unit.
 
The spool type proportional valve, also known as the distribution valve, is one of the more basic components of the mobile mechanical hydraulic system, and is a composite valve that can achieve direction and flow regulation. The electro-hydraulic spool type 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 increases the advanced control methods such as proportional servo operation and load sensing of position electric feedback. . Therefore, it is a new generation of engineering machinery distribution valves. Due to the consideration of manufacturing cost and the low requirements of engineering machinery control accuracy, the displacement proportional sensor is not arranged in the general proportional multi-way valve, and the electronic detection and error correction function is not provided. Therefore, the displacement of the spool is easily affected by the pressure fluctuation caused by the load change, and the operation is to ensure the completion of the operation by visual observation. At the time of electronic 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 people use displacement sensors such as differential transformers to construct the detection of the movement of the spool position, and realize the closed-loop control of the spool displacement. The highly integrated proportional valve consisting of an electromagnetic proportional valve, a position feedback sensor, a drive amplifier and other electronic circuits has a certain correction function, which can effectively overcome the shortcomings of the general proportional valve and greatly improve the control precision.
 
3 Load sensing and pressure compensation technology of electro-hydraulic proportional multi-way valve
 
In order to save energy, reduce oil temperature and improve control accuracy, and also make several actuators of synchronous action do not interfere with each other during motion, more advanced engineering machinery now uses load sensing and pressure compensation technology. Load sensing and pressure compensation are a very similar concept. They use the pressure changes caused by load changes to adjust the pressure and flow of the pump or valve to suit the working needs of the system. For the quantitative pumping system, load sensing is to introduce the load pressure through the load sensing oil passage to the remote pressure regulating relief valve. When the load is small, the relief valve setting pressure is also small; the load is large, setting The pressure is also large, but there is always a certain overflow loss. For the variable 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 and the system The actual demand flow is equal, no overflow loss, and energy saving is achieved. Pressure compensation is a guarantee that is taken to improve the control performance of the valve. The load pressure behind the valve port is introduced into the pressure compensating valve, and the pressure compensating valve adjusts the pressure in front of the valve port so that the pressure difference between the valve port and the front is normal, so that the flow rate through the valve port according to the flow regulating characteristic of the throttle port It 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 engineering machinery
 
Technological advances in electro-hydraulic proportional valves and other specialized devices have made electrical control of various systems such as engineering vehicle gear shifting, steering, braking, and work devices a reality. For a mechanism that generally requires a displacement output, a proportional servo-controlled manual multi-way valve driver similar to that of Figure 2 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 switching valves) with electronically controlled pilot control. A multi-way valve that replaces manual direct operation or hydraulic pilot control. Another significant advantage of using an electro-hydraulic proportional valve (or electro-hydraulic switching valve) is that the number of operating handles can be greatly reduced on an engineering vehicle, which not only simplifies the cab layout, but also reduces operational complexity and improves operation. Both quality and efficiency have important practical implications. Figure 2 shows the effective control of multiple electro-hydraulic proportional and on-off valves with a single rocker. The rocker can realize proportional control or switch control in both the x-axis and the y-axis direction, and the application is very convenient.
 
With the rapid development of digital wireless communication technology, a wireless remote control system with stable performance and reliable operation and suitable for engineering machinery has appeared. The remote control receiving device arranged on the mobile machine can convert the received radio signal into the control electro-hydraulic ratio. The proportional signal of the valve and the switching signal of the electro-hydraulic switching valve are controlled, and the corresponding signals of other devices are controlled, so that the original components of the manual operation can receive the command of the remote electric signal and perform corresponding actions. The engineering machine at this time has actually Become a remote-controlled construction machine. The wireless remote control transmitting and receiving system has been successfully applied to remote control of various engineering machines. From a security perspective, each digital data command it transmits has a special set of system address codes that are used only once by the manufacturer. Each receiver only reacts to the transmitted signal with the same address code, and other wireless signals will not affect the receiving device even if they are the same frequency signal. Together with the adoption of other security measures, the reliability of the system is fully guaranteed. Successful in the remote control of a variety of 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 the construction machinery, and the remote control device enables the electro-hydraulic proportional valve to play a greater role.
 
5 Application examples of electro-hydraulic proportional valve in construction machinery
 
The figure below shows a schematic diagram of the hydraulic system of a certain type of truck crane. Only the parts related to the electro-hydraulic proportional valve are shown. The machine adopts three proportional multi-way valves. Three shuttle valves in the load sensing oil line select the larger pressure of the three working loads and send them to the remote control port of the remote pressure regulating relief valve to adjust the overflow. The overflow pressure of the valve makes the output pressure of the hydraulic pump exactly meet the needs of the system load, thus achieving a certain energy saving purpose. The pressure compensation oil circuit makes the flow rate through each valve only related to the opening degree of the valve, and has nothing to do with the load it bears, and has no relationship with the load on other valve plates, so that it can be controlled freely under any load. The purpose of the load speed.
 
The following figure is an example of the 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 is communicated with the manual decompression pilot valve, and the shuttle valve selects the pressure from the manual pilot valve to control the hydraulically operated reversing valve; when the two-position three-way solenoid valve is energized, the pilot The control pressure oil is led to the three-way proportional decompression pilot valve, and the hydraulic reversing valve is controlled by the shuttle valve.
 
6 Summary
 
The above briefly introduces the working principle, structure and working characteristics of the electro-hydraulic proportional valve, and analyzes the load sensing and pressure compensation principles of the proportional valve. The different applications of electro-hydraulic proportional valves, especially in the application of pilot control and remote control of construction machinery, are discussed. The electro-hydraulic proportional valve is extremely important for simplifying the operation of engineering machinery, improving efficiency and working accuracy, and realizing intelligent operation. The further improvement of its performance and the widening of the application range will definitely make the technical level of engineering machinery products larger. The degree of improvement.