Test of electrohydraulic pressure servo valve

Test of electrohydraulic pressure servo valve

The electro-hydraulic servo mechanism has complex structure, high accuracy of output parameters, accurate control and adjustment, and is sensitive to environmental conditions (such as medium temperature and cleanliness). In the maintenance, it is very difficult to monitor the system and detect the off-line performance of a single component, which poses a severe challenge to the detection and maintenance guarantee of the hydraulic system. The computer-aided testing system of electro-hydraulic pressure servo valve is a special testing system with digital computer as the core and integrating electro-hydraulic control and data processing. It has the characteristics of high intelligence, high testing accuracy and simple operation.

1. Structural characteristics of electrohydraulic pressure servo valve

The electro-hydraulic pressure servo valve is a pressure servo valve with internal pressure feedback, dual chamber input, single chamber output and bidirectional fixed negative gain, as shown in Figure 17. It can be used in anti-skid braking system of aircraft, train and automobile. It is composed of an polarized permanent magnetic torque motor, a nozzle baffle, a power slide valve and a pressure feedback piston. When the torque motor does not feel the speed signal of the wheel, the baffle is in the neutral position, and the high-pressure oil enters the servo valve through the control oil inlet connector "1" and leads to the left and right ends of the slide valve. Because the pressure at the left and right ends of the slide valve is equal, the slide valve is in the right limit position under the action of the spring, and at this time, the brake oil inlet connector "4" is connected with the brake connector "3" (output). When the torque motor feels the speed signal of the wheel, the torque motor gets a positive control current and drives the baffle to rotate counterclockwise. At this time, the resistance of the right nozzle increases and the resistance of the left nozzle decreases, so the hydraulic pressure at the right end of the valve core is greater than that at the left end. The slide valve moves to the left against the spring force, the brake oil inlet circuit is gradually closed, the output end is gradually connected with the oil return, and the output pressure is gradually reduced, Until the feedback force acting on both ends of the feedback piston stops the valve core. The larger the input current is, the smaller the output pressure is.

2. Composition of test system

The particularity of the structure and function of the electro-hydraulic pressure servo valve determines the uniqueness and specificity of its test system. At present, the servo valve test system developed by many universities and scientific research institutions is based on the flow servo valve, which cannot test and analyze the performance of the electro-hydraulic pressure servo valve.

The computer aided test system of electro-hydraulic servo valve takes the electro-hydraulic servo valve as the object, and uses the computer to manage the operation of the whole test system, control and adjust the input and output parameters, so as to establish the optimal test condition for the tested components; On the other hand, through data collection, processing and analysis, the test results are output in the form of charts, curves or parameters; At the same time, qualitative or quantitative analysis of the test results and errors is carried out to provide users with the mechanism of fault generation and the possible distribution location of fault parts. The system is mainly composed of hydraulic pipeline subsystem, computer hardware system and corresponding software (see Figure 18).

The function of hydraulic pipeline subsystem is to provide hydraulic energy for the dynamic and static performance test of electrohydraulic pressure servo valve and establish corresponding test conditions, mainly including hydraulic pump station, hydraulic pipeline, pressure, flow, temperature regulating elements and necessary analog quantity display instruments. Its principle is shown in Figure 19.

The system hardware includes industrial control computer, sensor and display unit, data acquisition and processing unit, measurement result output unit, etc. (see Figure 20). Its function is to complete the measurement, control, adjustment of various parameters of the system and the output of tested parameters through data acquisition, conversion and processing. The automatic completion of the test process is realized through the organic combination of hardware facilities such as sensors, a/d conversion boards and pipeline subsystems.

The detection of electrohydraulic servo valve needs to manage a large amount of interface text information, which needs to be displayed synchronously with the test process, and the result report file needs to be comprehensively displayed or printed in a standardized and neat format after the test. These contents are various and their meanings are also very different. The detection program should be able to manage all kinds of information in an orderly manner, analyze, calculate and process in real time. According to the characteristics of the test system, a special measurement and control software is compiled by using visual c++ under Windows environment. The flow of the main control program is shown in Figure 21.

3. Working principle

In the detection process, under the prompt of the main menu of the computer, click the test item command with the mouse, and with the support of the measurement and control software, the system controls the relay to put various directional control valves in the specified state according to the requirements of the specific test item; At the same time, the corresponding control command signal is sent to each electro-hydraulic proportional control element. The signal is amplified by the amplifier and directly drives the electro-hydraulic proportional element to work. The state parameters of the system such as oil inlet pressure PJ, brake oil inlet pressure psi, oil return pressure pH, brake (load) pressure PS and the corresponding voltage (or current) are automatically adjusted, so as to realize the automatic establishment of the test condition.

测试工况建立后，系统通过各种传感器采集被测试对象的输出参数，经处理后存入结果报表。

4．总结

电液伺服阀计算机辅助测试系统，能按航空大型修理厂技术条件和试验大纲完成电液伺服阀电气性能，动静态性能的总体测试。解决了目前空军航空修理厂缺乏电液伺服控制元件测试检验设备的问题。系统在工厂应用，电液伺服控制元件的地面修理变为现实，为修理厂节约了大量的财力。