Each action of the working device, rotary mechanism and walking mechanism of a excavator is slow and powerless, and hydraulic oil is emitted from the filling port of the transmission gear box.
In view of the fact that all the above mechanisms are driven by hydraulic system, it is obvious that there is a fault in the hydraulic system.
The principle of fault analysis hydraulic system is divided into two parts: getting on and getting off.
The boarding hydraulic system is located above the rotating platform, with seven hydraulic cylinders, hydraulic pumps, rotary motors, control valves and other components; the boarding hydraulic system is located on the caterpillar chassis, with four walking hydraulic motors. The boarding hydraulic oil enters the boarding hydraulic system through the central rotary joint, and drives the walking hydraulic motor to rotate to make the whole machine run. Hydraulic pumps A and B are two-way swashplate axial plunger type. The displacement of the pump is 2 x 1.04 x 10-5m3/r, and the rated working pressure is 32 MPa.
The hydraulic system consists of two independent loops. The hydraulic oil output from pump A is an independent series circuit driven by multi-way valve block I, which drives rotary motor, right-walking motor, bucket cylinder and auxiliary arm cylinder.
When the executing elements of the group are not working, the confluence valve 5 (left position) makes the oil supply of pump A enter the oil supply circuit of pump B, and the two pumps flow together to the hydraulic cylinder of the moving arm and the hydraulic cylinder of the bucket rod, thus speeding up the working speed of the moving arm or the bucket rod. The hydraulic oil output from pump B is driven by multi-way valve block II to drive the boom cylinder, bucket rod cylinder, left-walking motor and bulldozer cylinder, which is another independent series circuit.
The working pressure of the secondary circuit is controlled by two relief valves respectively. Walking hydraulic motor and rotary hydraulic motor are both low-speed and high-torque motors with internal curve and multi-action. Each track of excavator is driven by a corresponding double-row hydraulic motor. The two transmission valves 14 are respectively placed in the oil distribution shaft of the hydraulic motor, and their control forms are electromagnetic.
In order to prevent over-speed sliding, a speed-limiting valve 11 is installed in the circuit, and the control oil pressure of the speed-limiting valve is introduced through shuttle valve 6. If both tracks exceed the speed limit, the speed limit valve will work. The temperature of the hydraulic oil entering the inner part of the hydraulic motor (plunger chamber, oil distribution shaft chamber) and the inner part of the motor shell (leakage low pressure chamber) is different, which makes the parts of the motor expand unequally and causes the sealing sliding surface to jam. For this reason, two oil outlets are drawn out in the motor shell (leakage chamber). One oil outlet is connected with the back pressure oil passage through the throttle valve, and the other oil outlet is straight. Connect with the tank (no back pressure).
In this way, the low-pressure oil (about 0.8-1.2 MPa) in the back pressure oil circuit is supplied to the motor housing through throttle valve decompression, so that the circulation oil can be maintained in the motor housing, so that the temperature inside and outside parts of the motor and the temperature of hydraulic oil can be kept consistent. The circulating flow of oil in the shell can also wash away the wear in the shell. A forced air-cooled cooler is installed in the hydraulic system circuit of the machine to keep the oil temperature of the system in the range of 50 70 under continuous working conditions, up to 80 C.
According to the principle of hydraulic system, the above-mentioned faults will occur only when the common components are out of order.
According to the fault, it can be preliminarily determined:
(1) Only when the axial oil seal of the two-way hydraulic pump (main pump A and B) leaks can the hydraulic oil come out from the filling port of the transmission gear box;
(2) Two-way hydraulic pumps A and B leak at the same time or hydraulic oil is too thin, too little, too dirty, oil suction port blockage, return oil circuit blockage, two main relief valve discharge at the same time, in order to make all their movements slow and powerless.
Determination of fault
Check the suction nozzle tubing and filter, oil return filter, there is no blockage. Clearly the hydraulic oil is clean.
Back pressure valve, relief valve, to be checked. Before failure is confirmed, pressure valves are best not to misadjust pressure.
Remove the pipes around the hydraulic pump, remove the hydraulic pumps A and B, and replace them with the normal two-way hydraulic pump of the same type. Every action of the three major parts is normal.
There is no oil coming out at the filling port of the transfer gear box. It is proved that the two hydraulic pumps A and B are out of order.
Trouble shooting
1. Remove the two hydraulic pumps A and B, and find that the oil seal of the pump shaft skeleton is worn out, which leads to the leakage of hydraulic oil to the transmission gear box and emerges from the filling port of the gear box. Change this skeleton oil seal.
2. Dismantle the hydraulic pump A and B to clean the parts one by one. Inspection found that the spline of the pump shaft has steps and the wear gap is too large. 3. There are pits, pits and pits on the contact surfaces between the two groups of distributors and the cylinder block, which lead to internal leakage. Grinding the contact surface between the valve plate and the cylinder block separately, removing the pitting points, can be retained.
4. Measuring each group of plungers with micrometer separately, its diameter is far out of tolerance, the clearance between cylinder and cylinder hole is too large, suction and pressure is weak, resulting in the system working pressure can not reach the rated value, resulting in the excavator each action is slow and powerless. Replace each group of plungers separately.
5. After cleaning all parts carefully, the hydraulic pumps A and B are assembled separately. At the same time, the pump body is filled with hydraulic oil, and then installed into the hydraulic system for re-commissioning. Failure phenomenon disappears and every action is normal.
Based on the above reasons and troubleshooting process, we can get the following experience: first of all, we should comprehensively, systematically, scientifically and carefully study and analyze the causes of the faults, read and analyze the schematic diagram of the hydraulic system, and work out the train of thought; when checking, we should first check and remove the relevant components nearest to the fault point, narrow the scope and gradually lock them. Fixed fault point; find out the fault components by using experience method, sequence elimination method, replacement method and instrument measurement method.
It can be seen from this that failure can not be blindly disassembled, it must be patiently confirmed, and then accurately disassembled, which will often achieve twice the result with half the effort.