Created on:2021-10-08 09:47

Fault diagnosis and maintenance of loader hydraulic_ Front frame swing fault when loader is driving

Fault diagnosis and maintenance of loader hydraulic_ Front frame swing fault when loader is driving

(1) Fault phenomenon

After a 50 model loader adopts the load sensing full hydraulic steering system, the front frame swings left and right when many machines encounter uneven road surface, especially when the bucket is fully loaded, which seriously affects the service performance of the machinery.

(2) Preliminary fault diagnosis

The fault of hydraulic system has strong concealment, so it is difficult to find it. In order to avoid blind disassembly, firstly, according to the schematic diagram of its steering hydraulic system (see Figure J), use logic analysis to gradually determine the suspected object, and then narrow the scope of suspected points and find out the fault location through necessary detection means.

The steering hydraulic system of the machine is analyzed. The possible causes of the above faults are as follows.

① The hydraulic oil level in the oil tank is too low or the suction pipe leaks, causing the steering pump to suck air into the steering hydraulic cylinder.

② The steering hydraulic cylinder leaks, causing the steering hydraulic cylinder to move.

③ When the steering overload oil makeup valve is stuck and the steering gear is in the middle position, the steering hydraulic cylinder is connected with the return oil.

④ The steering column top is dead and the steering gear cannot return to the middle position.

⑤ The pull-out pin in the steering gear is broken or deformed.

⑥ The spring plate in the steering gear is broken and the steering wheel cannot return to the center automatically.

⑦ The middle position of the steering gear cannot seal the oil.

The above doubtful points involve multiple parts, and some parts are difficult to disassemble, inspect and replace. The troubleshooting shall be carried out according to the principle of outside first and then inside, and easy first and then difficult.

① Check the oil level and oil suction pipeline of the oil tank, which meet the requirements, and eliminate the doubt ①.

② Start the vehicle and turn the steering wheel to automatically return to the center to eliminate doubts ④ and ⑥.

③ It can turn freely. During steering, touch the oil inlet pipe of the steering cylinder with your hand, and there is no pressure swing. Eliminate the doubt ⑤.

④ Turn the steering to the left limit position, remove the oil pipe without pressure chamber, continue to turn to the left, remove the oil pipe oil seal, and no oil flows out, indicating that there is no internal leakage in the steering hydraulic cylinder, and eliminate the doubt ②.

⑤ Disassemble and check the overload oil makeup valve, there is no jamming, and eliminate the suspicious point ③.

Six of the above seven doubtful points have been eliminated, so it can be concluded that the fault is caused by doubtful point ⑦. In order to make further judgment, remove all the two oil pipes connected between the steering gear and the steering hydraulic cylinder, start the machine and increase the accelerator. When the steering gear does not rotate, you can see a large amount of oil flowing out of the oil port disassembled by the steering gear, indicating that the middle position of the steering gear can not seal the oil.

(3) Fault analysis

As shown in Figure K, the load sensing full hydraulic steering gear of the machine is cycloidal rotary valve type, which is composed of valve core and valve sleeve. There are four steps and four annular grooves (I, J, K and L) on the outer surface of the valve sleeve. The four annular grooves correspond to the four oil holes a, B, O and P on the valve body respectively. The oil holes a and B are connected with the steering hydraulic cylinder, and O and P are the oil return port and oil inlet of the steering gear respectively. The holes B, C, D, e, F and G on the valve sleeve are oil distribution holes, which cooperate with the grooves I, J and K on the valve core. When the steering wheel is turned, the valve core rotates relative to the valve sleeve to control the direction of liquid flow and realize steering. When turning to the middle position, slots K and j shall not be connected with hole f or hole D, so as to ensure that the two cavities of the steering hydraulic cylinder are closed. If the design size of the hole on the valve sleeve and the groove on the valve core is too large or the processing error is too large, the sealing will be lax. At this time, ports a and B connected with the steering hydraulic cylinder will be connected with the oil return port O. the steering hydraulic cylinder cannot be closed, that is, the front frame will swing on uneven road when the vehicle is driving.


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