I plant ZL04 wheel loaders, often appear when the boom is no-load large oil boom lifting, heavy load does not move the phenomenon of failure. The machine hydraulic system is a single pump series circuit, shown in Figure 1.
When we repair from the following three points to find the cause of the malfunction, and the system has been improved, are presented below.
(1) check the boom cylinder leakage situation. The easiest way is to raise the boom to see if there is a clear free fall. If the whereabouts of obvious removal of fuel tank inspection, seals have been worn should be replaced.
(2) check the control valve. First clean the safety valve, check whether the spool wear, such as wear and tear should be replaced. If there is still no change after installation of safety valve, and then check the control valve spool wear, the gap limit of use is generally 0.06mm, severe wear and tear should be replaced.
(3) measure the pressure of the hydraulic pump. If the pressure is low, then make adjustments, the pressure is still not adjustable, the serious damage to the hydraulic pump.
After checking the pressure measurement of the hydraulic pump is only 5-7MPa, significantly lower than the rated pressure of the hydraulic system. After disassembling the hydraulic pump, the bushings were found to be worn. The inner wall of the low-pressure pump casing was seriously "swept" by gears, and the side walls were also slightly worn. This shows that the main reason that the boom can not be lifted is:
a. Hydraulic pump is severely worn. The pump leaks seriously at low speed. When the pump runs at high speed, the pump pressure slightly increases, but due to the pump wear and leakage, the volumetric efficiency drops significantly and it is difficult to reach the rated pressure. Hydraulic pump work for a long time has exacerbated the wear and tear, oil temperature, resulting in wear and tear of hydraulic components and seals aging, damage, loss of sealing ability, hydraulic oil deterioration, and finally lead to failure.
b. Hydraulic components selection is not reasonable. Boom cylinder specifications for 70/40 non-standard series, the seals are also non-standard parts, high manufacturing costs and seal replacement inconvenience. Boom cylinder bore is small, the system is bound to set high pressure.
c. Hydraulic system design is not reasonable. As can be seen from Figure 1, the control valve and full hydraulic steering gear for a single pump in series, safety valve setting pressure points 16MPa, while the hydraulic pump rated working pressure is also 16MPa. Hydraulic pump often at full load or prolonged overload (high pressure) work, and the system has a hydraulic impact, long-term oil does not change, the hydraulic oil contaminated, exacerbating the hydraulic pump wear and tear, resulting in hydraulic pump shell burst (was found Such failure).
2 improvements and effects
(L) Improve hydraulic system design. After several demonstrations, the final use of advanced priority valve and load sensing hydraulic steering gear form, see Figure 2. The new system can give priority to the distribution of traffic in accordance with the steering requirements, regardless of the size of the load, the steering wheel speed can ensure adequate supply of oil, the remaining part can be fully supplied to the working device circuit, thus eliminating the power supply due to excessive steering oil supply Loss, improve the system efficiency, reducing the working pressure of the hydraulic pump.
(2) Optimize the design of boom cylinder and hydraulic pump to reduce the pressure of system work. Through the optimization calculation, the boom cylinder adopts the standard system
Column 80/4. Hydraulic pump displacement increased from 10ml / r to 14ml / r, the system set pressure of 14MPa, to meet the boom cylinder lifting force and speed requirements.
(3) Pay attention to proper use and maintenance of loaders in the process of using, regularly add or replace hydraulic oil, maintain the cleanliness of hydraulic oil, and strengthen routine inspection and maintenance.
The improved hydraulic system design, gear pump work more smoothly, no longer overload conditions. At the same time, oil circuit design is reasonable, improve system efficiency, but also give full play to the whole machine performance, improve work efficiency. Smooth and reliable steering movements, to avoid the high-speed steering "Gone with the Wind" phenomenon.
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