1. Characteristics of hydraulic system failure of construction machinery
The hydraulic mechanical transmission system is mainly composed of a hydraulic pump, a control valve, a torque converter, a transmission, and a power shift transmission valve. Its failure usually manifests itself as weak walking or poorly engaged hydraulic clutches. The hydraulic system of the working device is mainly composed of a hydraulic pump, a control valve, a hydraulic motor and a hydraulic cylinder. Its failure is mainly manifested in the weakness of the motor walking or turning, and the delay of the extension and retraction of the hydraulic cylinder piston. The common characteristics of these two system failures are: insufficient system pressure.
2. Failure inspection method of hydraulic system of construction machinery
1. Intuitive inspection method For some simple faults, parts can be inspected by means of sight, hand model, ear hearing and smell.
2. Replacement diagnosis method This method should be used when there is a lack of diagnostic equipment at the maintenance site or if the component being checked is relatively precise and should not be disassembled. First, remove the suspected faulty component, and replace it with a new one or a component of the same model that works normally on other machines to test, and see if the fault can be eliminated to make a diagnosis.
3. Instrument measurement and inspection method Instrument measurement and inspection method is to judge the fault point of the system by means of the measurement of the pressure, flow rate and oil temperature of each part of the hydraulic system. In the general on-site inspection, the failure of the hydraulic system is often manifested as insufficient pressure, which is easy to detect; while the detection of the flow rate is more difficult, the size of the flow rate can only be wrongly judged by the speed of the actuator.
4. Principle reasoning method The basic principles of the hydraulic system of construction machinery are made by using different hydraulic components and matching according to the hydraulic system circuit combination. When a fault phenomenon occurs, it can be analyzed and reasoned according to this, and the location and cause of the fault can be preliminarily determined , Administer the right medicine and quickly rule out. For the failure of the on-site hydraulic system, according to the working principle of the hydraulic system, the reason of the failure can be analyzed by forward reasoning on the system diagram in the order of power element → control element → actuator. In the field hydraulic system fault diagnosis, according to the working principle of the system, we must master some laws or common sense; one is to analyze whether the fault process is gradual change or abrupt change. It is abrupt, often caused by sudden damage to parts, such as broken springs, damaged seals, stuck moving parts, or clogged dirt. The second is to distinguish between wearing parts and non-wearing parts, or moving parts under high-frequency heavy load, or hydraulic components that are prone to failure. Components that are at low frequencies, lightly loaded, or basically relatively stationary are less prone to failure.
5. Strictly implement the shift system. When the shift driver parks the construction machinery, he must ensure the safety and convenience of the shift driver during the inspection. Check whether the hydraulic system is leaking, whether the connection is loose, whether the piston rod and hydraulic hose are damaged, whether the connection of the low-pressure oil inlet pipe of the hydraulic pump is reliable, and the hydraulic oil tank oil level is correct. In addition, the normal-pressure hydraulic oil tank also needs to check and clean the vent hole to keep it unblocked to prevent a certain degree of vacuum from appearing in the hydraulic oil tank due to the blockage of the air hole, which makes the hydraulic oil pump difficult or damaged.
6. Maintain proper hydraulic oil temperature The operating temperature of the hydraulic system is generally controlled between 30 ~ 80 ℃. Excessive oil temperature in the hydraulic system will cause: the viscosity of the hydraulic oil is reduced, it is easy to cause leakage, and the efficiency is reduced; the strength of the lubricating oil film is reduced, which accelerates the wear of the machinery; the formation of carbides and sludge; the acceleration of the oil fluid, the deterioration of the oil quality; the oil seal , Premature aging of high-pressure hose, etc. In order to avoid excessive temperature; do not overload for a long time; pay attention to the radiator and fins are not contaminated with oil, and the dust dissipation soil will affect the heat dissipation effect; keep enough oil to facilitate the circulation of hydraulic oil; do not work all day in hot summer , Avoid high temperature at noon. When the temperature of the hydraulic oil is too low, its viscosity is large, its fluidity is poor, its resistance is high, and its working efficiency is low; when the temperature of the oil is lower than 20 ℃, sharp turns can easily damage the hydraulic motor, valves, and pipes. At this time, it is necessary to perform warm-up operation.After starting the engine, run it at idle speed for 3 to 5 minutes, and then increase the engine speed with a medium-speed throttle. 3 ~ 5min makes the hydraulic oil warm up through the overflow. If the oil temperature is lower, you need to increase the warm-up operation time.
