Characteristics and Application of Electro-hydraulic Proportional Valves for Construction Machinery
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The electro-hydraulic proportional valve is a proportional solenoid that generates a corresponding action based on the input voltage signal, which causes the spool of the working valve to displace, and the size of the valve port changes to complete the pressure and flow output proportional to the input voltage. Spool displacements can also be fed back mechanically, hydraulically, or electrically. Since the electro-hydraulic proportional valve has various advantages such as various types of forms, easy use of various electro-hydraulic systems controlled by electric and computer, high control precision, flexible installation, and strong anti-pollution capability, the application field is increasingly widened. In recent years, cartridge-type proportional valves and proportional multi-way valves developed and produced have fully taken into account the characteristics of the use of construction machinery, and have 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. Especially in the electronically controlled pilot operation, wireless remote control and wired remote control operations and other aspects demonstrated its good application prospects.
Type and form of electro-hydraulic proportional valve for construction machinery
Electro-hydraulic proportional valves include proportional flow valves, proportional pressure valves, and proportional directional valves. According to the characteristics of hydraulic operation of construction machinery, there are mainly two types of electro-hydraulic proportional valves divided into structural types: one is a screw-in cartridge proportional valve and the other is a spool proportional valve.
The spiral cartridge type proportional valve is a component that fixes an electromagnetic proportional insert on a manifold of a hydraulic circuit through a screw thread. The spiral cartridge valve has the advantages of flexible application, saving pipelines, and low cost, and has been applied to construction machinery in recent years. More and more extensive. Commonly used spiral cartridge type proportional valves are two-way, three-way, four-way, and multi-pass. The two-way proportional valve is mainly a proportional throttle valve. It often forms a compound valve together with other components to perform flow and pressure. Control; Tri-proportional proportional valve is mainly a proportional pressure reducing valve, which is also a proportional valve used in a mobile mechanical hydraulic system. It is mainly operated on the pilot oil circuit of a hydraulically operated multi-way valve. The use of three-way proportional pressure reducing valve can replace the traditional manual pressure reducing type pilot valve, which has more flexibility and higher control precision than the manual pilot valve. Can be made as shown in Figure 1 proportional servo control manual multi-way valve, according to different input signals, pressure reducing valve so that the output piston has different pressure or flow and thus achieve multi-way valve spool displacement control. Four-way or multi-way screw-in cartridge type proportional valves allow individual control of the working device.
Sliding valve type proportional valve, also known as distribution valve, is one of the most basic components of a mobile mechanical hydraulic system and it is a compound valve that can realize direction and flow regulation. The electro-hydraulic spool type proportional multi-way valve is an ideal electro-hydraulic conversion control element. It not only retains the basic functions of a manual multi-way valve, but also adds advanced control means such as proportional servo operation and load sensing of position electrical feedback. . So it is a replacement product of engineering machinery distribution valve.
Due to the consideration of manufacturing cost and the low requirement of control precision of the construction machinery, the proportional proportional multi-way valve is not equipped with a displacement sensing sensor, nor does it have an electronic detection and correction function. Therefore, the displacement of the spool is easily affected by the pressure fluctuation caused by the load change, and visual observation is required during the operation to ensure the completion of the operation. In the electronic control, remote control operation should pay attention to the influence of outside interference. Recently, due to the development of electronic technology, people increasingly use built-in differential transducers (LDVT) and other displacement sensors to detect the movement of the spool position to achieve closed-loop displacement control of the spool. This kind of highly integrated proportional valve 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 the general proportional valve and greatly improve the control accuracy.
Load sensing and pressure compensation technology for electro-hydraulic proportional multi-valve
In order to save energy, reduce the oil temperature and improve the control accuracy, at the same time, several actuators that operate synchronously do not interfere with each other during movement. Nowadays, more advanced construction machinery adopts load sensing and pressure compensation technologies. Load sensing and pressure compensation are very similar concepts. They use pressure changes caused by load changes to regulate the pressure and flow of the pump or valve to suit the working requirements of the system. Load sensing refers to the quantitative pump system. The load pressure is led to the remote pressure relief relief valve through the load sensing oil passage. When the load is small, the relief valve setting pressure is also smaller; the load is larger and the load is set. The pressure is also large, but there is always a certain overflow loss. Variable pump system is a variable mechanism that introduces the load sensing oil circuit into the pump, so that the pump output pressure increases with the increase of the load pressure (always a small fixed pressure difference), so that the pump output flow and system The actual needs of the flow are equal, no overflow losses, and energy savings.
Pressure compensation is a guarantee measure taken to improve the valve control performance. The load pressure after the valve port is introduced into the pressure compensation valve, and the pressure compensation valve adjusts the pressure in front of the valve port so that the pressure difference between the front and the rear of the valve port is a constant value, so that the flow rate through the valve port is adjusted according to the flow regulation characteristics of the throttle port. It is only related to the opening of the valve port, and is not affected by the pressure of the load.
Pilot Control and Remote Control of Electro-hydraulic Proportional Valves for Construction Machinery
Technical advances in electro-hydraulic proportional valves and other specialized devices have made electrical control of various systems such as gears, steering, brakes, and working devices of construction vehicles a reality. For a mechanism that generally requires a displacement output, a proportional multi-valve valve actuator similar to that of FIG. 1 can be used. The electrical operation has the advantages of fast response, flexible wiring, integrated control, and easy interface with the computer. Therefore, hydraulic valves of modern engineering machinery have increasingly used electro-hydraulic proportional valves (or electro-hydraulic on-off valves) controlled by electronically controlled pilots. Instead of manually operated or hydraulic pilot controlled multi-way valve. Another significant advantage of the use of electro-hydraulic proportional valves (or electro-hydraulic on-off valves) is that the number of operating handles can be greatly reduced in construction vehicles. This not only makes the cab layout simple, but also can effectively reduce the complexity of operations and improve the operation. Both quality and efficiency have important practical implications. FIG. 2 is a TECNORD company JMF type joystick, which can effectively control a plurality of electro-hydraulic proportional valves and on-off valves as shown in FIG. 2 using one rocker. The rocker can realize proportional control or switch control in the X-axis and Y-axis directions, and the application is very convenient.
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, and a remote control receiving device arranged on a mobile machine can convert the received radio signal into a controlled electro-hydraulic ratio. The proportional signal of the valve and the switching signal of the electrohydraulic on-off valve are controlled, and the corresponding signals of other devices are controlled, so that each element of the original manual operation can receive the command of the remote electric signal and perform the corresponding action. At this time, the construction machinery has actually Become a remote control type of construction machinery.
Wireless remote control transmission and receiving systems have been successfully applied to the remote control of a variety of engineering machinery. From a security point of view, 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 responds to transmitted signals with the same address code. Other wireless signals, even if they are at the same frequency, will not affect the receiving device. With the adoption of other safety measures, the reliability of the system has been fully guaranteed. Successful in the remote control of many kinds of mobile machinery such as loaders, rock drills, concrete pump trucks, aerial work vehicles, and bridge inspection 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. The remote control device also enables the electro-hydraulic proportional valve to play a greater role.
Application of electro-hydraulic proportional valve on construction machinery
A schematic diagram of the hydraulic system of a certain type of truck crane. Only the part related to the electrohydraulic proportional valve is shown in the figure. The machine uses three proportional TECNORDT DV-4/3LM-LS/PC type proportional valves. Three shuttle valves in the load sensing circuit select the maximum pressure among the three working loads and send them to the remote pressure relief and overflow. The remote control port of the valve adjusts the overflow pressure of the overflow valve so that the output pressure of the hydraulic pump can exactly meet the requirements of the system load, so as to achieve a certain energy saving purpose. The pressure compensation circuit allows the flow through each valve to only be related to the opening of the valve, regardless of the load it carries, and has nothing to do with the load on other valve plates, so that it can be controlled at will under any load. The purpose of the load speed.
Bulldozer Dozer Manual and Electrohydraulic Proportional Pilot Control Example. When the three-position three-way solenoid valve is not energized, the pilot pressure communicates with the manual decompression 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 The control pressure oil leads to a three-way proportional decompression type pilot valve, and the hydraulic valve is controlled by a shuttle valve.