Test and adjustment of 4WS2EE10-45 electric hydraulic servo valve with electric displacement feedback
Test and adjustment of 4WS2EE10-45 electric hydraulic servo valve with electric displacement feedback
1. 4WS2EE10-45 electrohydraulic servo valve
4ws2eel 0-45 electro-hydraulic servo valve is a product of Rexroth company in Germany. It is an electric feedback nozzle flapper servo valve. Its structure is shown in Figure 12. Compared with the common feedback rod mechanical feedback nozzle flapper valve of the same series, the main difference is that the feedback rod between the main valve and the pilot valve is cancelled, and the differential transformer potential shift feedback device is replaced. This electro-hydraulic feedback electro-hydraulic servo valve has the advantages of high positioning accuracy, high repetition accuracy, fast response speed and convenient maintenance and replacement of pilot control level. There is no common problem that the ball of the feedback rod of the mechanical feedback servo valve is easy to wear, so its reliability and service life are greatly improved.
2. Test method of 4WS2EE10-45 electrohydraulic servo valve
The test method of 4WS2EE10-45, a new type of electric feedback servo valve, is different from that of ordinary mechanical feedback servo valve. To test the mechanical displacement feedback servo valve, as long as the electro-hydraulic servo valve static tester inputs the valve current to the servo valve coil, it can be tested according to the conventional method. The 4WS2EE10-45 servo valve has a special structure, and its valve body is only in an open-loop state. If the valve coil is directly fed with the valve current, the output of the servo valve has no feedback signal, and the main valve core is unstable, so the test cannot produce normal results. It is necessary to test the servo valve, its servo amplifier and feedback channel as a whole, that is, it must be tested with the 0 ~ 10V voltage signal input by the servo amplifier matched with 4WS2EE10-45. The static tester of electro-hydraulic servo valve in a test station can only output 0 ~ 50mA valve current. In order to match with the amplifier of the servo valve under test, a simple current voltage conversion method is adopted, and a 2W, 510 Ω resistor is connected between the output end of the static tester of the electro-hydraulic servo valve and the ground. The input signal of the amplifier of the servo valve under test is taken from the voltage drop at both ends of the resistor, and the signal interface voltage matching is completed after converting the current signal into a voltage signal. The connection diagram of the test device is shown in Figure 13. The dotted box in Figure 13 shows the integrated servo amplifier matched with 4WS2EE10-45, which mainly includes servo amplification and feedback. The integrated servo amplifier needs an external ± (2228) V DC regulated power supply to work, and a ± 15V regulator is set inside for the circuit in the amplifier to work.
The amplifier of the tested servo valve amplifies the voltage signal, and then converts the voltage and current to the coil of the tested servo valve to input the test current. At the same time, the differential transformer inside the servo valve outputs the displacement feedback electrical signal to the feedback terminal of the valve servo amplifier, and controls the movement of the main valve core together with the given signal.
The test work is carried out on the electro-hydraulic servo valve test bench of the station. The principle of the hydraulic test system is shown in Figure 14. The arrow state characteristics of 4wszee10-45 servo assembly are mainly tested, and the no-load flow characteristic curve Q-I, pressure characteristic curve P-I and static consumption flow characteristic curve q0-i are drawn.
The working pressure range of 4WS2EE10-45 electrohydraulic servo valve is 1.0 ~ 31.5Mpa. When the pressure drop of the valve is 7.0Mpa, the nominal flow is 45l/min, and the rated working current of single coil is 30mA. During the test, the small flow test system is used. As shown in Figure 14, the servo valve to be tested is installed on the base Z through a special transition block. Since the oil port of the servo valve has a pilot level control oil supply port X in addition to the four ports PP, PR, P1 and P2, when designing the special transition block, the main oil port PP is connected with port X through a small hole. According to the nominal flow of the servo valve, select small pump B1 (model 25SCY14-1B) to supply oil, use fjq-1 static test hydraulic cylinder to measure the flow of the servo valve, use current servo static tester and function recorder to test and record the static characteristic curve of the servo valve. The oil circuit conversion required for testing static characteristics is realized by the three position six way change-over valve V5. When testing the no-load flow Q-I, the electromagnet YA2 is energized, the current reversing valve V4 is in the left position, the change-over valve V5 is also in the left position, and the servo valve load windows 1 and 2 are connected through the flow hydraulic cylinder fjq-1. When testing the pressure characteristic P-I, the electromagnets ya1 and YA2 lose power, the electromagnetic directional valve is in the middle position, the change-over valve V5 is also in the middle position, the load window of the servo valve is closed, and the oil return port is connected with the oil return pipe. When testing the static consumption flow characteristic q0-i, the electromagnet ya1 is energized, the electromagnetic directional valve V4 is in the right position, the change-over valve V5 is also in the right position, the load window of the servo valve is closed, and the static consumption flow enters the flow hydraulic cylinder fjq-1. The change-over switch on the static tester of the current servo valve operates the electromagnet to make the change-over valve change the test conditions. At the same time, the function recorder draws the current, flow and pressure signals recorded by the static tester into a characteristic curve. When testing the resolution characteristics of the servo valve, put the change-over valve under the flow test condition, input a certain current signal to the servo valve with the manual current adjustment knob on the static tester, so that the static hydraulic cylinder fjq-1 stops at a certain position, and then fine tune the manual current potentiometer in the opposite direction until the recorded flow change signal is just reverse. The flow value of a small section remains unchanged during the process of flow increase to decrease, The recording pen shows that the current change in the section can reflect the resolution of the servo valve.
3. Fault analysis and treatment in 4WS2EE10-45 servo Yan test
(1) Analysis and treatment of the failure of the static hydraulic cylinder and the function of the servo valve. First, adjust the flutter adjustment knob DV on the servo amplifier (see Figure 13) to increase the amplitude of the flutter voltage of the servo valve. After repeated adjustment, the static test hydraulic cylinder still does not act, so it is judged that the servo valve itself is faulty. According to the previous analysis of the structural principle of the valve, if the servo valve cannot act, the pilot control stage should be checked. The measured resistance of the valve coil is 40 Ω, and there is no open circuit. Therefore, it is judged that there is a problem in the pilot stage oil supply circuit. It can be seen from Figure 12 that there is a small precision filter element 18 on the oil supply circuit of the pilot stage. The filter may be blocked due to dirty oil, so that both nozzles 3 cannot play the role of jet flow. The baffle plate 13 is always in the middle position, and the control valve 9 is always in the middle position. The opening between it and the control valve sleeve 11 is zero, so the servo valve has no flow output, and the hydraulic cylinder does not act. Carefully take out the filter element in the valve, put it in the clean kerosene tank of the ultrasonic cleaner, vibrate and flush for 0.5h, then reinstall it, and then test it on the test bench. The action of the hydraulic cylinder indicates that the cause of the failure is indeed the blockage of the filter element.
(2) Analysis and treatment of flow saturation phenomenon in the test. During the test, use X-Y recorder to record the no-load flow characteristic curve Q-I (front) and pressure characteristic curve P-1 (front) as shown in Figure 15 below. It can be seen from the Q-I diagram that when the valve current increases to a certain value in the positive direction, the flow will no longer increase, showing a large horizontal step and unilateral flow saturation. At first, it was suspected that the control valve core was blocked, and the flutter current signal was superimposed on the test current of the servo valve, but it was useless; The problem can't be solved by repeatedly sending current in both positive and negative directions. Finally, focus on the adjustment of the valve. Because it is not difficult to see from the curve Q-I diagram that when the positive flow saturation phenomenon occurs, the negative zero bias of the valve is large, and the negative flow is small, but there is no saturation phenomenon. It is estimated that this situation is related to the large zero bias. In order not to affect the characteristics of the servo valve itself, the zero position adjustment is carried out on the servo amplifier of the valve. Figure 16 shows the no-load flow characteristic and pressure characteristic curve of the servo valve after the zero position is adjusted to the best state. It can be seen from the no-load flow characteristic curve that after zero bias adjustment, the flow in the positive and negative directions is basically symmetrical and has good linearity, which overcomes the phenomenon of unilateral flow saturation.
The reason for the unilateral flow saturation phenomenon is that the zero bias of the electro-hydraulic servo valve with electric feedback is too large. During the movement of the control valve core in one direction, the electric displacement feedback device limits the excessive displacement of the control valve core, so that the output flow of the servo valve is limited, resulting in the saturation phenomenon, which is reflected in the flow output characteristic curve, that is, a platform appears. Therefore, it can be concluded that by adjusting the zero offset of the electro-hydraulic servo valve with electric feedback and minimizing its zero offset, the phenomenon of unilateral flow saturation can be eliminated.
4. Adjustment of 4ws2eel045 servo valve
(1) Adjustment of pressure gain. The pressure gain is adjusted on the pilot control stage of the servo valve. As can be seen from Figure 12, the position of the two nozzles 3 can be adjusted from the outside. In Figure 12, 17 is the nozzle adjusting screw. By adjusting the position of the nozzle, the throttling space between the nozzle and the baffle can be changed, so that the pressure drop between the control chambers 8 and 10 changes, and the linearity of the load differential pressure current performance curve of the servo valve changes, that is, the pressure gain characteristics of the servo valve are changed. The slope of the servo valve pressure characteristic curve (see Figure 15) obtained in this test reflects the size of the pressure gain index. The steeper the curve, the better the pressure characteristic.
Generally, when the servo valve leaves the factory, the manufacturer has adjusted the pilot control level and sealed it with lead. Do not adjust it easily without special circumstances.
(2) Adjustment of zero bias. Zero bias adjustment is to adjust the zero bias of the servo valve. The hydraulic zero position can be adjusted on the second stage of the servo valve - flow output stage, and the electrical zero position can also be adjusted on the servo amplifier.
1) Hydraulic zero deviation adjustment. As shown in Figure 12, the control valve core 9 and the control valve sleeve 11 constitute the flow output stage. In order to adjust the hydraulic zero position, the position of the console shoulder of the control valve sleeve 11 relative to the control valve core 9 can be changed by rotating the hexagonal socket screw 16 at the left end of the valve cover.
2) Electrical zero bias adjustment. The electrical zero position adjustment is carried out on the integrated servo amplifier matched with the servo valve. As shown in the dotted line in Figure 13, adjust the nd knob of the amplifier to give the servo valve a reverse electrical signal, which just offsets the zero offset of the servo knob itself and returns it to the middle position.
In order to try not to change the characteristics of the servo valve itself, the adjustment work after the test is mainly to adjust the zero bias of the servo amplifier on the test bench. The specific steps are as follows: as shown in Figure 14, put the three position six way hydraulic reversing valve of the electro-hydraulic servo valve under the pressure characteristic test condition, and observe the pressures P1 and P2 at the two working ports of the servo valve. When the pointer indicators of the two pressure gauges are consistent, that is, △ p=p1-p2=0, it means that the zero bias is adjusted to the best state. At this time, the load pressure output by the servo valve p= △ p=0. This adjustment is intuitive and convenient for observation.
