This paper analyzes three kinds of fault causes and maintenance methods that may cause the excavator to walk weakly with the modern R225LC-7 excavator as an example. It has certain reference value for solving the problem of the excavator walking weak.
1. Electromagnetic proportional valve failure
According to the analysis, the possible causes are that the final drive motors control oil circuit, pilot oil circuit, pressure sensor, main relief valve, main hydraulic pump, safety valve and differential pressure sensor have failed. Through the analysis of the main hydraulic control circuit It is found that the cause of the failure may occur on the control oil circuit of the traveling motor. When the excavator is normally walking, if the other oil circuit works normally, the pilot oil circuit, the pressure sensor, the main relief valve, the main hydraulic pump, and the safety may be eliminated. If the valve fails, it is inferred that the faulty component may be a pressure compensating valve for controlling the walker, a PVC controller, a main spool valve, an electromagnetic proportional valve, a travel switch or a travel motors.
The first step is to check the travel switch to prove whether the circuit is normally turned on or off. In the second step, remove the upper cover, check the main slide valve, and use a relatively clean screwdriver to press down on the valve stem. The result is that the valve stem is flexible. After the cleaning inspection, no abnormality is found. In the third step, the pressure compensation valve is inspected. Since the pressure compensation valve is not easy to disassemble, the rotary oil circuit and the oil guiding pipe should be replaced each other during the inspection, and then the engine is started. And found that the excavator walks normally, indicating that the final drives and the pressure compensation valve are working normally. The fourth step is to check whether the PVC signal on the electromagnetic proportional valve works normally. The small bulb with a power of 1-5 watts is connected in parallel with the electromagnetic proportional valve. Connect the wiring to the two wires on the plug, then start the engine and find that the bulb is still on, indicating that the PVC has a signal. After the flameout, the electromagnetic proportional valve is removed and the resistance test of the electromagnetic proportional valve is performed. The result is 3.5Ω. If it is a normal value, it means that the coil works normally. In the fifth step, the valve core of the hydraulic part of the electromagnetic proportional valve is inspected. First, the oil pipe between the electromagnetic proportional valve and the rotary joint that controls the walking action is removed. Install the pressure gauge on the electromagnetic proportional valve and start the engine to operate it. The following phenomena occur: the pressure position is 6 MPa in the high speed gear and the pressure is 1.7 MPa in the middle and low speed gear. However, the normal value should be the high gear 5 MPa, the middle and low gear is 0.6MPa, the reason can be judged that the output oil pressure of the electromagnetic proportional valve is not normal, so it is judged that there is a problem with the valve core of the electromagnetic proportional valve. The valve core is disassembled and inspected, and it is found that it has been worn and blackened, and The gap between the valve seats is too large, and the deformation and sliding are not flexible. Under normal circumstances, the PVC signal of the valve core is generated under the action of electromagnetic force, which changes with the change of the electromagnetic force. The worn valve core is generated. The action is not flexible and cannot generate enough PVC signal, so the fault is judged to be on the spool of the electromagnetic proportional valve.
[Modern Walking Case] Reasons and Maintenance Methods for R225-7 Walking Failure
The troubleshooting method is mainly to slightly lengthen the spring on the spool to make the return force generated by the electromagnetic proportional signal larger, in order to eliminate a part of the stuck force. After the test machine, after 5 hours of normal driving, it appears again. The same fault indicates that the spring has recovered its original shape. Because of the integration of the electromagnetic proportional valve valve group, the replacement needs to be replaced as a whole, which inevitably results in a high cost. Therefore, the repair should be based on the wear of the spool. In the case of appropriate measures, the valve core can be reworked according to the accuracy and scale requirements of the valve core, and then installed. The test proves that although there are some slight changes in high-speed walking and low-speed walking, they are all within the normal range. Within it, it has normal climbing ability, thus eliminating the failure of walking.
2. Safety valve failure of the travel motor
After analysis, it is found that the work of the working device and the swing system are normal, so that it can be judged that the main pump and its control system and the main unloading valve are working normally. The first step is to measure the pressure gauge of the control valve by 6MPa. The pilot oil line is tested and found that regardless of whether the engine speed is high speed or low speed, the pressure value of the pilot oil line is always within the range of 3 - 3.2 MPa, indicating that the pilot oil line is not faulty; the second step is to disassemble the travel control valve. It is found that the valve core and the valve seat are free from wear and stagnation, indicating that the control valve is normal. The third step is to detect the traveling motor, fix the track with iron blocks, and prevent it from rotating. Then the measuring range is 60 MPa. The table detects the oil inlet pressure of the traveling motor, and the result shows 20 MPa, which is far lower than the standard 36 MPa. It can be seen that the main cause of the failure is: serious leakage of the traveling motor or safety valve imbalance of the traveling motor. Install the slewing joint with the pressure gauge on the two main roads of one of the travel motors, and pull the joystick to make the other travel motor run. The result shows that the pressure measurement value has not changed, indicating the center slewing. The head is not faulty; in the fifth step, the track is fixed with iron blocks, so that it is not allowed to rotate, and then a pressure gauge with a range of 60 MPa is installed in the oil inlet system of the traveling motor, and the working pressure is applied. After 20MPa, after the safety valve is re-adjusted, the pressure of the system rises to the standard 36MPa. It can be seen that the traveling motor works normally, and the fault is caused by the imbalance of the safety valve.
3. Other reasons
3.1 Main pump pressure is low
Under normal circumstances, the main pump output oil pressure should be ≥36MPa, but if the gap between the plunger and the cylinder of the main pump is greater than the standard 0.02mm, or because the wear between the end face of the cylinder and the distribution plate exceeds the standard 90% of the contact area will cause the pressure of the main pump output to be low, which is reflected on the R225LC-7 excavator, and there will be a phenomenon of walking weakness.
3.2 The output pressure of the pressure reducing valve is low
Under normal circumstances, the output oil pressure of the main pump of the pressure reducing valve can be lowered or the pressure value can be stably controlled at 3.3 MPa to form the control oil pressure. If the oil quality is poor and dirty, the cone valve core will not be closed tightly. Therefore, the output pressure of the pressure reducing valve is less than 3.3 MPa. Thus, regardless of the action of the operating handle, the control oil pressure is in a lower state, resulting in less movement of the spools of the various main control valves. The flow to the working device cannot meet the pressure value output by the pressure reducing valve, resulting in weak walking.
3.3 The main relief valve has a lower pressure value
The main relief valve is mainly to control the maximum pressure of the hydraulic system to 32.5MPa. When the pressure exceeds 32.5MPa, the main relief valve will automatically open for pressure relief, thus protecting the system from damage. Poor, it is easy to block the small hole in the valve plug, so that it can not be closed; if the pressure of the main relief valve is set low, the same will cause the overflow pressure to be low, and the pressure of the whole system is lower.
3.4 Main pump control output flow valve group failure
When the matching of the power main pump of the engine reaches the optimal state, the function of the engine can be fully utilized, and the output of the main pump changes with the change of the engine power. If the main pump output flow control valve that regulates fails, such as LS If the valve spool is stuck, the PLS feedback circuit is blocked, the coil inside the solenoid valve is burnt out, the main pump's cooperation plate, servo piston and other parts are stuck, the flow of the main pump may be kept constant. If the flow rate is always small, the movement of the machine will be slow when working, and there will be a phenomenon of walking weakness.
3.5 Unloading valve malfunction
The hydraulic oil output from the main pump is directly returned to the fuel tank through the unloading valve when the driver starts the engine and sets the operating lever in neutral. Under normal circumstances, the unloading pressure is usually 3 MPa. If the quality of the oil is poor, it will result in The closing is not tight. When the machine is running, the output oil of the main pump passes directly through the unloading valve to the tank, resulting in insufficient pressure of the entire system; if the O-ring on the unloading valve fails, the main pump will be caused. The hydraulic oil returns directly to the tank and forms a fault. https://www.spfinaldrives.com/