1、 Fault characteristics of hydraulic system of construction machinery
The hydro mechanical transmission system is mainly composed of hydraulic pump, control valve, torque converter, transmission and power shift valve. Its fault usually shows weak walking or poor engagement of hydraulic clutch. The hydraulic system of the working device is mainly composed of hydraulic pump, control valve, hydraulic motor and hydraulic cylinder. Its faults are mainly manifested in the weak walking or rotation of the motor and the slow extension and retraction of the piston of the hydraulic cylinder. The common characteristics of these two system faults are: insufficient system pressure.
2、 Fault inspection method of hydraulic system of construction machinery
1. Visual inspection method for some relatively simple faults, parts can be inspected by means of eye, hand mold, ear, ear and smell.
2. The replacement diagnosis method should be used when there is a lack of diagnostic instruments at the maintenance site or the inspected components are relatively precise and should not be disassembled. First remove the suspected faulty components, replace them with new parts or components of the same model that work normally on other machines, and test them to see whether the fault can be eliminated.
3. Instrument measurement and inspection method instrument measurement and inspection method is to judge the fault point of the system by measuring the pressure, flow and oil temperature of the hydraulic oil in each part of the hydraulic system. In general field detection, the failure of hydraulic system is often manifested as insufficient pressure, which is easy to detect; The flow detection is more difficult. The size of the flow can only be judged by the speed of the action of the actuator.
4. Principle reasoning method the basic principle of the hydraulic system of construction machinery is composed of different hydraulic components and matched according to the circuit of the hydraulic system. When there is a fault, it can be analyzed and reasoned according to this, preliminarily judge the location and cause of the fault, apply the medicine to the case and eliminate it quickly. For the fault of the on-site hydraulic system, the fault cause can be analyzed by forward reasoning on the system diagram according to the working principle of the hydraulic system and the sequence of power element → control element → executive element. In the fault diagnosis of on-site hydraulic system, we should master some laws or common sense according to the working principle of the system; First, analyze whether the fault process is gradual change or sudden change. If it is gradual change, it is generally due to the change of original size and fit caused by wear and loss of original function; If it is a sudden change, it is often caused by the sudden damage of parts. If the spring is broken, the seal is damaged, the moving parts are stuck or blocked by dirt, etc. Second, it is necessary to distinguish between vulnerable parts or non vulnerable parts, or moving parts under high-frequency heavy load, or hydraulic components prone to failure. The components at low frequency, light load or basically relatively static are not prone to failure.
5. Strictly implement the shift handover system. When the shift handover driver parks the construction machinery, ensure the safety and convenience of the shift handover driver during inspection. The inspection contents include whether the hydraulic system leaks, whether the connection is loose, whether the piston rod and hydraulic hose are damaged, whether the low-pressure oil inlet pipe of the hydraulic pump is connected reliably, whether the oil level of the hydraulic oil tank is correct, etc. In addition, the vent hole of the atmospheric hydraulic oil tank should be checked and cleaned to keep it unblocked, so as to prevent the blockage of the vent hole from causing a certain vacuum degree in the hydraulic oil tank, which makes it difficult or damaged for the hydraulic oil pump to absorb oil.
6. Maintain proper hydraulic oil temperature. The working temperature of the hydraulic system is generally controlled between 30 ~ 80 ℃. Too high oil temperature of hydraulic system will lead to: the viscosity of hydraulic oil will be reduced, which is easy to cause leakage and reduce efficiency; The strength of lubricating oil film decreases and accelerates the wear of machinery; Formation of carbide and sludge; Oil oxidation accelerates and oil quality deteriorates; Premature aging of oil seal and high-pressure hose, etc. In order to avoid excessive temperature; Do not overload for a long time; Pay attention to the radiator and heat sink not to be polluted by oil, so as to affect the heat dissipation effect due to the adhesion of dust-proof soil; Keep enough oil to facilitate the circulation and heat dissipation of hydraulic oil; Don't work all day in hot summer. Avoid the high temperature time at noon. When the hydraulic oil temperature is too low, it has high viscosity, poor fluidity, high resistance and low working efficiency; When the oil temperature is lower than 20 ℃, sharp turns are easy to damage the hydraulic motor, valve, pipeline, etc. At this time, it is necessary to warm up the engine. After starting the engine, run at no-load idle speed for 3 ~ 5min, then increase the engine speed with the medium speed throttle, operate the handle to make any action of the working device (such as excavator bucket) to the limit position, and keep it for 3 ~ 5min to raise the temperature of the hydraulic oil through overflow. If the oil temperature is lower, it is necessary to appropriately increase the warm-up operation time.
