Common troubleshooting of hydraulic solenoid proportional valve
The hydraulic solenoid proportional valve section is divided into a pressure proportional regulating valve and a flow proportional section valve (the control principles are basically the same), which are commonly used in hydraulic systems with high control accuracy. After the proportional control valve has been used normally for 8,000 to 12,000 hours, it enters an unstable period of operation. Unstable oil pressure, insufficient movement, and failure of adjustment functions often occur, which seriously affects the operation of the equipment. The following describes common troubleshooting methods.
1. Common fault principles
① After the equipment replaced the proportional regulating valve body, the operation was out of control and the relationship was disordered. After the shot blasting machine replaced the valve body and started, the turntable (driven by a hydraulic motor) lost control and the interlocking logic relationship was disordered. Initially, it was thought that the control board was faulty or the replaced valve body was defective. When it was replaced again, the fault remained the same. The measurement control output voltage is U2C-32c or U2a-32a. When loaded (connected to the solenoid valve coil), the voltage is DC21.5V, AC2.2V; when no load, it is DC24V, AC2.4V. For the control power supply reset (power-off and power-on operation), the control turns off the output electric calendar week zero. Only after the input signal is activated again, the output end has power and remains unchanged (normally, the input and output are powered on or off at the same time). After analyzing the proportional throttle valve control principle, especially the working process of the displacement sensor, it is believed that the regulating valve control system is actually working in a closed-loop positive and negative state at this time. After checking the feedback circuit, we found that the displacement sensor signal lines 8c and 10c were connected incorrectly, resulting in the wrong polarity of the secondary coil output signal. After signal conversion, the polarity was reversed, that is, the polarity in 17 became negative, and after negative feedback synthesis, The system works in a closed-loop positive feedback state. Under the influence of the input multiplier, the control system quickly enters a self-excited deep saturation state, saturating the output of the control board (DC24V). Correct incorrect wiring and troubleshoot.
② When the hydraulic system is working, the running speed of the equipment is uncertain. The operating speed of the molding machine in the first phase was suddenly high and low. It was initially thought that the pressure regulating valve body was damaged or the control board output was unstable, causing the hydraulic drive motor to work abnormally. The valve body was replaced and the fault disappeared. However, after about 3 days of use, the same fault reappeared. Occasionally occurs, the control board is replaced, but the fault remains the same. It was suspected that the hydraulic oil was dirty, so all the hydraulic oil of the molding machine was filtered, the oil tank was cleaned, and the filter screen was replaced. After the equipment was put into operation, the fault disappeared.
When the equipment is used for a long time, due to poor working environment and maintenance operations, the hydraulic oil will be mixed with impurities and become dirty, causing the movement of the hydraulic regulating valve core to be blocked or gasping, causing the hydraulic drive mechanism to work unstable.
③ When operating the equipment, after the control button is activated, the hydraulic drive mechanism responds slowly. After assembling shot blasting and replacing the proportional throttle control board, the hydraulic drive turntable rotates from high to low. After disconnecting the control button, the turntable rotates in place and continues to move. It stops after about 0.8~1.2m (normally it stops immediately after the platform is in place).
By comparing the control data before and after the equipment failure, it was confirmed that the cause of the failure was improper PID processing parameters of the control board signal, and the control board slope control resistor, d3, and d4 diagram values were adjusted too small, causing the control board to control t4. (The output voltage DC0 rises to 24V. The time required) and t (the time required for the output voltage to drop from DC24V to 0) are set too long, causing the proportional valve core to lag behind in returning to zero, and the hydraulic oil cannot be shut off in time.
In the equipment controlled by the hydraulic proportional regulating valve, there are many reasons for the equipment actuator to work abnormally (not in place, offside or malfunctioning, etc.), such as excessive wear of the regulating valve core, improper adjustment of the high and low speed drive areas, and serious internal unloading of the hydraulic system. and inappropriate control parameter settings, etc.
④ There is a large difference in moving speed and time when the hydraulic cylinder moves forward and backward. The ejection action time of the main cylinder of the offline assembly phosphorus iron ring press is too long, 235, with a deviation of about 16 seconds. Initially, it was thought that the oil circuit of the equipment control solenoid valve body was blocked. We disassembled, cleaned the valve body, and filtered the hydraulic oil. However, the fault was not clearly improved. Considering that the internal leakage of the main cylinder flush valve was serious, this phenomenon would also occur, so the flush leaf valve was completely replaced, but the fault remained the same. It is understood that before the equipment failure, the equipment's hydraulic oil, clamps, and main cylinder hydraulic control flow proportional control valve control board had been replaced and other maintenance operations were carried out. Although the relevant numbers of the control board were debugged and adjusted after the replacement of the control board, the equipment was not loaded ( Adjustment without guide rod pressure). It is judged that the zero point adjustment of the flow proportional control valve is inaccurate, resulting in a smaller oil supply flow in the hydraulic cylinder ejection oil circuit, causing the cylinder ejection action time to be too long. Reset the control board parameters and correct the zero point of the hydraulic flow control valve. When working under load, the master cylinder ejection action time is significantly reduced, about 8S.
Although the model of the replaced control valve is the same, there are differences in the parameters of the electronic components of the new and old boards, and the control board's ability to process signals has undergone slight changes (this is also the reason why the electrical control device needs to be debugged after replacement or repair). The zero point of the new board feedback signal conversion stage is offset, that is, when the valve core is at zero, the output of the matching amplifier on the control board is not zero, resulting in a deviation between the displacement feedback number and the actual displacement of the valve core, and the synthesized control signal value is Change, the hydraulic cylinder ejection drive end output signal voltage is lower. The electromagnetic torque acting on the proportional center decreases, the valve core displacement is smaller during the ejection action of the pilot cylinder, and the oil supply decreases, resulting in the slow ejection action of the master cylinder, especially when the load is measured, the action becomes even more sluggish.