The core hints: the fault characteristics and diagnosis of the hydraulic system of the engineering machinery: the characteristics of the failure of the hydraulic system of the engineering machinery. The hydraulic mechanical transmission system mainly consists of the hydraulic pump, the control valve, the torque converter, the transmission and the power shift transmission valve and so on. The faults usually show the weakness of walking or the joint of the hydraulic clutch.
The hydraulic system is mainly composed of hydraulic pump, control valve, torque converter, transmission and power shift shift valve and so on. The fault usually shows the weakness of walking or hydraulic clutch. The hydraulic system of the working device is mainly composed of hydraulic pump, control valve, hydraulic motor and hydraulic cylinder. The main faults are the walking or rotary powerlessness of the motor, the protruding of the piston of the hydraulic cylinder and the retracting of the retardation. The common faults of these two systems are: insufficient system pressure.
Fault site detection and diagnosis:
(1) preliminary examination and diagnosis of the site
In order to avoid unnecessary loss, we can not ignore the reasons that appear to be very simple and can not be blindly disassembled. In the specific inspection process, the following steps should be taken.
(1) understand the situation to the driver, make a detailed understanding of the state and sound of the machine when the fault occurs, and avoid making a mountain out of a molehill. As a 966D loader, after changing the oil to the transmission, it is found that the machine is unable to walk. The temperature of the torque converter is too high. The inspection found that the transmission oil number was wrong, and after clearing up the cause of the fault, the trouble could be eliminated quickly.
Carry out the necessary concrete operation. Sometimes, the driver's statement about the cause and effect of the machine failure is unclear, which makes it difficult to diagnose.
(3) inspection of oil and oil. This content seems to be simple, but society is often ignored. For example, a 966D loader (its moving mechanism is hydraulic pressure transmission system), the driver has released the transmission oil during the vacation. When the assistant to the site was moved to drive, it was found that the machine could not walk. It thought it was a big fault, but the maintenance personnel only made the problem by listening to the sound and checking the oil scale in the scene, and avoided the accident. For example, a Hitachi EX220-2 excavator, after the repair of the hydraulic cylinder after the repair of hydraulic oil, and the on-site procurement of hydraulic oil for the regenerated oil extracted from the soil, continued to be added to the oil tank to cause oil pollution. Metamorphic bubbling causes the machine to act incapable, and the malfunction can be eliminated after the replacement of hydraulic oil. Therefore, sufficient attention should be paid to the inspection of oil quality and oil content; otherwise, the hydraulic pump will be burned and the transmission system will be damaged.
Check all kinds of filter cartridges. The oil filter is the cleaning tool of the hydraulic system. In the fault diagnosis, the inspection of the oil filter (the degree of the fouling of the filter oil and the characters of various impurities on the filter core) can provide the basis for the further analysis of the fault. If a HD820 type excavator is added, it is found that the whole machine is weak after running about 4000H. When removing the oil filter of its hydraulic system, it is found that the filter core is damaged, the oil back is blocked, and the fault can be removed after the filter core is replaced.
If the above preliminary inspection is still unable to remove the fault, then more detailed inspection should be done with the aid of the instrument.
(2) instrument diagnosis of hydraulic system
In the general field detection, because of the difficulty in detecting the flow, and the failure of the hydraulic system, it is often shown that the pressure is insufficient. Therefore, in the field detection, more is the method of measuring the pressure of the system. For example, a 966D loader, after running 6000h, found its walking weakness, testing the pressure value of the inlet and outlet of the torque converter, the result is very normal; the operation power shift shift valve, when measuring the direction of the clutch pressure, the pressure is only 0.5MPa, that is, the normal pressure can not be set up. After the full transmission is found, the oil seal in the clutch oil passage of the direction is damaged, resulting in leakage of hydraulic oil, and the fault is eliminated after replacing the oil seal. For example, a EX220-5 excavator, after running 3000h found walking deviation, detection of the pressure of the walking system, the left is 32MPa, the right only 26MPa, then adjust the right walking safety valve pressure, the fault can be excluded.
(3) computer diagnosis
With the extensive application of Mechatronics in engineering machinery, a single pressure test can not meet the needs of field testing. Now more and more imported engineering machines have to do the fault diagnosis with the help of special testing computers, and the testing of computer is rich in data, small volume and convenient to carry. Like a Hitachi EX220-2 excavator, the hydraulic system of the working device is weak. When operating the excavator handle, it will be accompanied by noise and smoke. It is found that there is no significant change in the flow rate of the hydraulic pump and the noise of the engine when the pressure rises. It is believed that the flow of the hydraulic pump is too large to adjust the flow. The servo valve of the hydraulic pump is disassembled, and the flow of the servo valve and the hydraulic pump is adjusted, and the connecting pin shaft of the swashplate is broken. After the pin is replaced, the trouble is eliminated.
(4) other diagnostic methods
In the field maintenance, the replacement diagnosis method is often used without instruments. This method is often used in the whole test of different types of machines. It can be quickly diagnosed if there is no detection instrument in the field or if the device is not unsuitable to be disassembled. If a CAT320L excavator does not work to 500h, the hydraulic system of the working device is weak. At that time, no detection instrument was used, and the main safety valve was judged according to experience. But the main safety valve on the spot found that there was no obvious wear and scar on the conical surface of the pilot needle valve, and then the other same type of 320L excavator would be in the same field. The main safety valve is exchanged with the safety valve, and the trouble is eliminated after trial. This diagnostic method is simple and accurate.
