Created on:2021-06-25 09:07

Hydraulic fault diagnosis of combine

Hydraulic fault diagnosis of combine

(1) Fault phenomenon

The gear pump driven by the engine runs normally, the steering system works normally, and the multi-way directional valve fails to work. When the handle is operated, the header hydraulic cylinder, the threshing wheel hydraulic cylinder and the walking CVT Hydraulic cylinder can not work normally.

(2) Working principle of multi way directional valve

Isi-l15e-t-oaa * multi way directional valve is used in a Xinjiang-2 combine. It is composed of oil inlet valve (with overflow valve and one-way valve), three groups of manual directional valve and oil return valve. The overflow valve in the oil inlet valve is used to regulate the working pressure of the system, and the one-way valve is used to prevent the backflow of hydraulic oil. When all the manual directional valves are in the middle position, the relief valve is in the unloading state, and the hydraulic oil of the system returns to the oil tank through the main valve core of the relief valve, the oil return passage and the oil return valve of each directional valve, and the outlet through the external pipeline. When any group of directional valve changes direction, the unloading port of the relief valve is cut off, and the relief valve is in working state. The pressure oil of the system flows through the one-way valve and directional valve to the actuator hydraulic cylinder. When the working pressure of the system exceeds the working pressure of the relief valve, the relief valve lifts up and the hydraulic oil overflows back to the oil tank, so as to prevent overload. When the unloading through hole (about 5mm in diameter) on the top of the relief valve core is blocked, the relief valve is overloaded because it can not be unloaded, so the relief valve is lifted, and the hydraulic oil overflows back to the oil tank. At this time, the three directional valves lose their functions. After inspection, this case is due to the relief valve spool unloading hole blockage.

The main reason for this failure is that there are impurities in the hydraulic oil, resulting in the through hole blockage of the relief valve. After removing the foreign matters and dredging the through hole, the multi-channel directional valve was installed and restored to normal operation. But the next day the same phenomenon appeared, and after repeated attacks, repeated repair. This is not only troublesome, delayed harvesting operations, but also affects safety. Therefore, the operator had to thoroughly clean the oil tank, oil return filter and hydraulic cylinder before the operation. During the operation, the gear pump, single way stable shunt valve and multi-way directional valve were replaced successively. After that, although the fault was relieved, it was still not completely solved, so he had to go to the service station for maintenance.

(3) Diagnosis process

The fault must be at the overflow valve of the multi way valve. The oil inlet valve was disassembled. In order to avoid the blockage of the unloading hole of the new multi way valve, the top of the valve was improved and a filter screen (about 4.0 mm in diameter) was added. After dismantling, it was found that a layer of black particles accumulated on the filter screen, which sealed the filter screen, causing the relief valve to lift and return oil. Analysis confirmed that these small particles are not oil sludge, but rubber particles. So where do rubber particles come from? If the seal ring of the hydraulic cylinder is worn, it will cause the hydraulic cylinder to rise and fall slowly. Moreover, the return oil must be filtered by the return oil filter, so the impurities can not go to the multi way valve. Therefore, the fault should be from the oil tank to the multi way valve, but if the seal ring of the gear pump is damaged, the oil pressure will certainly decrease, and the steering system will not work normally. So in the tank and gear pump between the connection hose attracted people's attention.

(4) The root cause of the trouble

Between the hydraulic oil tank and the gear pump, there is a section of cloth oil delivery hose( φ 32mm × Due to the erosion of high temperature hydraulic oil, the vibration of the machine and the distortion of the oil tank, the inner wall of the pipeline is aged and cracked, and the falling rubber particles flow with the oil to the multi way valve, resulting in failure.

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