Created on:2021-09-13 10:42

Construction machinery_ Maintenance of excavator_ Characteristics and detection methods of proportional valve of main pump

Construction machinery_ Maintenance of excavator_ Characteristics and detection methods of proportional valve of main pump

The function of the main pump controller (commonly known as the pump control computer board) on the hydraulic excavator is to output the current signal to the, and then output the secondary oil pressure after reducing the pilot oil by the proportional valve, so as to adjust the force of the servo piston of the main pump, so as to change the flow of the main pump. It can be seen that the proportional valve of the main pump is an important component of the excavator.

The fault of proportional valve can be easily detected and diagnosed by using the three in one electronic / electrical tester.

(1) Characteristics of proportional valve

Proportional valve (see Figure f) is an electrically controlled hydraulic valve between ordinary electromagnetic on-off valve and. Its requirements for the cleanliness of hydraulic oil are not as harsh as those of electro-hydraulic servo valve, and the price is much lower; Different from the switching DC electromagnet with variable air gap, the air gap of the electromagnet in the proportional valve is constant, so the output pressure of the proportional valve can change in proportion to the input current.

F.jpg

Due to the advantages of proportional valve over servo valve in cost performance, most hydraulic excavators at home and abroad use proportional valve as the control element of main pump, such as epc-pc valve and depc-ls valve on Komatsu excavator, EPR valve of Carter machine, SD valve of Hitachi machine, eppr valve of modern machine, etc. When the input current of the proportional valve is too large or too small, or the proportional valve is worn or stuck, it may cause slow action of the excavator, engine stall or even flameout.

(2) Detection method

The proportional valve has undergone strict quality inspection before delivery, including static characteristic test (input current pressure characteristic test, internal leakage test and load characteristic test) and dynamic characteristic test (frequency response test and instantaneous response test). On site fault diagnosis is on-line detection on the machine, including the measurement of the resistance of the solenoid coil of the proportional valve, the test of the input current and the test of the output secondary oil pressure.

① Measurement of the resistance of the solenoid coil turn off the ignition switch, disconnect the plug CN between the proportional valve of the main pump and the output interface of the pump controller (see Figure g), measure the resistance between the two wires and the resistance between the ground wire and the machine body, and judge whether the solenoid coil of the proportional valve has short circuit, open circuit or grounding.

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② Measurement of input current of proportional valve disconnect a wire of proportional valve, string it into multimeter, and measure the input current according to the test conditions of different models, as shown in Figure H. It is quite easy to test with a DC Clamp Meter without unplugging the plug CN and disconnecting the conductor (see figure I). Under different power modes or different engine speeds, whether the electronic control part before the proportional valve is faulty can be judged according to the correctness of the DC current signal output from the pump controller to the proportional valve.

③ The test of the output pressure of the proportional valve is shown in Figure J. connect a pressure gauge with a measuring range of 6Mpa on the measuring point of the secondary oil pressure, and check the output pressure of the proportional valve for different models according to their respective test conditions. If the pressure is incorrect, it can be adjusted. For the non adjustable proportional valve, after confirming that the input pilot oil pressure and the current of the proportional valve are normal, the valve core shall be disassembled and inspected for cleaning or replacement.

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