Created on:2021-06-29 14:52

Fault diagnosis and maintenance of combine hydraulic system

Fault diagnosis and maintenance of combine hydraulic system

The direction control of the self-propelled combine, the lifting of the header and the reel, and the adjustment of the stepless wheel all work by pressing the actuator. The hydraulic system is generally composed of oil tank, gear pump, one-way stabilizing valve, multi-way distributing valve, single and two-way hydraulic cylinder, accumulator and oil pipe. The power of the gear pump is provided by the engine.

(1) The header height is not enough

When the header is raised, the reel cannot be raised and the transmission cannot change speed. The main reason is that there is too little oil in the oil tank and the oil pressure in the oil circuit is insufficient. The oil level of oil tank should be checked in time and replenished if it is insufficient; If the oil pipe leaks oil or is blocked by dirt, the oil pipe should be replaced and dredged.

(2) Header jump up

The main reason for header jumping is that there is air in the oil circuit of hydraulic system. The method of exhausting air is as follows: loosen the oil pipe joint, screw out the outer nut of the oil pipe joint for 1.5 ~ 2 turns, drain the oil outwards until there is no bubble in the oil, and then tighten the outer nut.

(3) Header lift slow

① The oil temperature is too high, the viscosity of hydraulic oil is reduced, the oil pressure is decreased, and the header lifting is slow. Should replace the standard hydraulic oil, must not use general oil instead.

② The oil pipe of the hydraulic cylinder connected to the header was damaged and deformed, which reduced the oil flow through the oil pipe and made the header lift slowly. In this case, the oil pipe should be repaired to restore its original state or replaced with a new one.

③ The sealing of safety valve is not good. The reason is oil leakage or improper adjustment, which leads to insufficient oil pressure in high-pressure oil circuit. During the inspection, the safety valve can be disassembled, and the valve ball can be gently hit with a punch on the hammer to make the valve ball close to the valve seat and seal well. When the pressure is not enough, you can use a special wrench to loosen the lock nut, screw the adjusting nut and compress the spring to increase the pressure. Generally, it should be adjusted on the test bench.

④ The pull hole of distribution valve is not aligned. Check the axial and radial position of the distribution stem and make appropriate adjustment.

⑤ The distribution valve is worn and can not return or not return enough, resulting in the oil flow is not smooth. When this kind of fault is found, the problem can be solved by moving the handle of distribution valve to align the slot.

⑥ The internal cavity of gear pump shell is worn, the clearance is increased, or the sealing ring is damaged, resulting in serious oil leakage, resulting in insufficient oil pressure in the oil circuit. The solution is: replace the sealing ring or gear pump. Too loose drive belt of hydraulic pump will also cause insufficient pump oil, which will make the header rise slowly. At this time, the pulley tension must be increased.

(4) The header cannot be lowered or automatically lowered after it is raised

The failure that the header can't descend after being raised is mainly due to improper adjustment of the length of the control flexible shaft, so that the control lever is in the neutral position while the slide valve is in the descending position, or the header and one way nylon valve core in the seven way valve are burnt (too high oil temperature fault occurs) and stuck on the valve seat. The automatic lowering of the header after lifting may also be caused by improper adjustment of the length of the control flexible shaft, burning of the nylon valve core of the check valve (seven way valve), or loose sealing between the steel ball of the check valve (five way valve) and the valve seat, and damage of the O-ring on the one-way valve seat, which may also cause the automatic lowering of the header after lifting.

(5) Reel failure

① The reason for the unsteadiness of the speed is the air entering the CVT. Loosen the hydraulic cylinder joint, exhaust the air, the speed can be stable.

② A. the hydraulic cylinder and plunger are seriously deformed, resulting in the failure of lifting and lowering of the reel, or the failure of lifting or lowering due to the plunger rod being stuck by oil. The deformed parts should be replaced or maintained in a complete set. b. The reel bracket is stuck by the coating layer (new car), or the sliding bracket is crushed, deformed and stuck, and cannot slide. The bracket should be corrected and the joints should be lubricated.

(6) Continuously variable transmission cannot move up and down

① The operating valve is worn, the limiting element is damaged, the handle pushing amount exceeds the limit, the oil circuit is blocked or the oil flow is too small, which makes the transmission unable to move up and down.

② The handle of the distribution valve is not in the working position, which hinders the free circulation of the oil, and the hydraulic oil is forced to circulate through the safety valve. Therefore, after lifting the header and the reel, or changing the speed of the reel, pull the handle of the distribution valve back to the non working position (neutral position).

③ The solid bolt on the valve stem of the control mechanism shell of the control valve is loose, which results in the wrong position of the valve stem hole and affects the normal operation of the CVT.

④ The middle plate of CVT is stuck on the shaft sleeve, which makes the middle plate unable to move and the speed cannot be changed.

(7) All hydraulic cylinders of hydraulic system cannot work

Check whether the hydraulic oil is too little and whether the double pump belt is too loose; Secondly, check whether the length of the control flexible shaft is adjusted improperly and whether the stroke of the slide valve is correct; Check the suction pipe of the double pump again for air intake or damage. If the above inspection is normal, it means that the duplex pump may be damaged, or the inlet pipe of the duplex pump may be damaged. It can be judged by moderately loosening the pressure oil pipe joint from the double pump to the seven way valve (five way valve), starting the main engine with a small throttle, and observing whether there is pressure oil (without checking the instrument).

(8) The header or reel automatically descends from the raised position

The causes of this fault are: 1. The distributor is worn, leaking oil or the position between shafts is not right; ② The check valve is not tightly sealed.

Troubleshooting: repair or replace the distributor; ② Grind the conical surface of the check valve and replace the sealing ring.

(9) High hydraulic oil temperature

In case of this phenomenon, the oil tank cap should be opened first to check whether the hydraulic oil is too little, too dirty and whether the viscosity is too high; Secondly, check whether the control ball hinge is worn excessively and whether the length of the flexible shaft is adjusted improperly, which leads to incorrect neutral position of the slide valve or stuck slide valve; Then check whether the operating handle and steering gear stay at the limit position for a long time, and whether the steering gear core adjustment does not return to the center. If the above inspection is normal, it may be that the hydraulic oil filter element is too dirty, or the safety valve is out of order, resulting in high oil return pressure or poor oil return, resulting in high oil temperature.

(10) Steering failure

There are many reasons for steering failure. First check the pressure oil circuit from the dual pump to the steering gear; If there is no pressure oil, check whether the oil inlet pipe of the duplex pump enters the air; If there is no air in and there is no damage, it means that the duplex pump is damaged and needs to be repaired or replaced. If the pressure oil from the dual pump to the steering gear is normal, check whether there is pressure oil in the oil pipe of the steering hydraulic cylinder. If there is no pressure oil, it means that the steering gear is damaged; If there is pressure oil, it proves that the sealing ring of the steering cylinder is damaged.

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