Test and analysis of the characteristics of 4wre6e electro-hydraulic proportional directional valve
Test and analysis of the characteristics of 4wre6e electro-hydraulic proportional directional valve
The proportional directional valve is based on the conventional electromagnetic directional valve and modified with proportional electromagnet, which is gradually developed and improved. Compared with servo valve, it has the advantages of strong pollution resistance, reliable operation, zero drift, low price and energy saving. With the further improvement of the design principle of the proportional directional valve and the combined development of proportional amplifier and digital control technology, the static and dynamic performance of the proportional directional valve has been greatly improved by using technical means such as displacement electric feedback and electric correction. Up to now, the high-performance proportional directional valve, like the flow type electro-hydraulic servo valve, can not only control the direction of flow, but also accurately and linearly control the flow under certain pressure drop. In the closed-loop control system with proportional directional valve as the electro-hydraulic conversion and power amplification control element, the proportional directional valve is the key element in the system, and its static and dynamic characteristics have a great impact on the control performance of the system. Through the experimental research on the static and dynamic characteristics of the proportional directional valve, it is proved that the proportional directional valve, like the servo valve, can be widely used in most industrial electro-hydraulic servo closed-loop control systems.
1. Working principle
The working principle block diagram of 4wre6e four-way proportional directional valve with valve core displacement electric feedback and its matching vt5005 proportional amplifier is shown in Figure 34.
The proportional directional valve and the proportional control amplifier are combined to form a control signal voltage U. Electronic hydraulic mechanical feedback control system to control the displacement XV of the four-way valve core. After the external input signal UC passes through the ramp generator and the step jump generator that compensates part of the valve dead zone, it is converted into the input voltage UA of the valve core closed-loop system. Compared with the feedback signal voltage ut of the valve core displacement XV, it forms the electromechanical closed-loop control system of the idle displacement XV. The basic parameters of the proportional directional valve are rated flow: 10l/min (valve pressure drop is 1MPa); Input voltage: 10V.
2. Experiment
(1) Experimental oil circuit. The static and dynamic characteristic experimental test system of proportional directional valve is mainly composed of 1170 frequency response analyzer (also used as signal generator), 1180 plotter, X-Y function recorder, DC tachogenerator, metering motor and constant pressure oil source. The experimental oil circuit is shown in Figure 35.
(2) Static characteristic experiment. The static characteristics of the electro-hydraulic proportional directional valve can be evaluated by the experimental research method of the static characteristics of the flow type electro-hydraulic servo valve, that is, according to the curves of no-load flow characteristics, load flow characteristics, pressure gain characteristics and the corresponding parameters obtained. Since the proportional valve does not use the nozzle and baffle pre stage, it does not test the zero flow characteristics, but only the no-load flow characteristics that reflect its main static characteristics.
The 1170 frequency response analyzer is used to output the control voltage UC, and the low-frequency triangular wave is used for continuous and repeated scanning in the whole cycle. Under different oil supply pressures PS, the input control voltage Uc of the proportional amplifier and the output voltage U0 of the tachogenerator are continuously depicted through the XY recorder, that is, the static characteristic curve QL UC between the no-load flow QL and the control voltage UC is obtained, as shown in Figure 36.
The main static indexes of the proportional valve can be obtained from the characteristic curve: linearity ≤ 6%, hysteresis ≤ 2%, symmetry ≤ 6% (after compensation for zero bias), dead band ± 5%, zero bias 5%, zero drift =0.
1) The zero bias value of 5% can be fully adjusted to 0V by the zero bias adjustment potentiometer of the proportional amplifier.
2) The dead zone of ± 5% is inherent in the proportional directional valve to reduce the process cost and low price, but it can be basically eliminated by digital compensation in the digital control system.
3) Zero drift is one of the outstanding advantages of proportional directional valve.
4) The flow gain is low when the linearity is within -4 ~ 1V (after eliminating the dead zone), which is the characteristic that the proportional valve is not as good as the electro-hydraulic servo valve, but it has little impact on the general industrial closed-loop servo control system.
5) Due to the use of valve core displacement electric feedback closed-loop control technology, its static performance indicators of linearity, hysteresis, symmetry are relatively good.
(3) Dynamic characteristic experiment. The dynamic characteristics of the proportional directional valve can be expressed by the frequency response characteristics between the control voltage UC and the valve core displacement feedback voltage UF.
Under the condition of oil supply pressure ps=7.0mpa and no-load, the midpoint UCC of the frequency characteristic input control voltage UC is taken in the middle of the rated value, that is, the "a" winding of +5v and the "B" winding of -5v. The peak and peak ucvv of UCC is taken as 50% of the rated value, that is, ucvv=5v. The 1170 frequency response analyzer is used for sine scanning at different frequencies, and the 1180 is used to draw the Bode diagram. Figure 37 shows the amplitude frequency L and phase frequency of "B" winding Ф Characteristic experimental curve.
It can be seen from the characteristic curve that: -3db amplitude frequency is 9.7hz and -90 ° phase frequency is 21Hz. Compared with the general servo valve, it has accounted for half of the natural frequency of the servo valve, not to mention that the peak and peak values of the test account for 50% of the rated value, while the peak and peak values of the dynamic test of the servo valve generally account for only 30% of the rated current.
The second-order link with a bandwidth of nearly 20Hz is sufficient to meet the application requirements of most engineering closed-loop control systems.
3. Summary
(1) The large dead zone of proportional valve caused by process and low cost is objective, but when applied to the control system, the digital compensation method of digital control system can be used to eliminate it.
(2) The static characteristic indexes such as linearity, hysteresis, symmetry and repetition accuracy can be compared with general industrial electro-hydraulic servo valves.
(3) The natural frequency of dynamic characteristics is about 20Hz, which can at least meet the requirements of moving coil electro-hydraulic servo valve in industrial servo system, so it can meet the characteristic requirements of most industrial hosts for electro-hydraulic proportional servo system.
(4) The input power of electro-hydraulic mechanical converter is larger than that of electro-hydraulic servo valve, which is one of the technical measures to ensure its reliable operation.
(5) The electro-hydraulic proportional directional valve is based on the slide valve structure principle of the conventional electromagnetic directional valve. Therefore, the filtering accuracy of the hydraulic oil is lower than that of the electro-hydraulic servo valve.
(6) When the electro-hydraulic proportional directional valve works, the pressure drop of the single port valve is about 1MPa, which is lower than that of the electro-hydraulic servo valve of 3.5Mpa. Therefore, the energy consumption and temperature rise of the electro-hydraulic proportional directional valve system will be much lower than that of the electro-hydraulic servo valve system.
