Analysis and Maintenance of Common Faults in the Transmission System of ZL500 Loader

Abstract

Loaders are important mechanical equipment in engineering construction and have a wide range of applications. The transmission system of domestic loaders often experiences various faults during operation. Based on the structural principles of the transmission system of domestic loaders, combined with the usage and maintenance conditions, several points of analysis and maintenance experience for faults in the transmission system of loaders are summarized.

Key words

Fault usage and Maintenance of Loader Transmission System

During the operation of loaders, the transmission system often experiences faults. Here, we take the ZL50D loader produced by Shandong Construction Machinery Factory as an example for fault analysis and maintenance.

In one gear, the movement is weak or not moving at all, while in the other gears, the movement is normal

Weak or no movement refers to the situation where the traveling speed in a certain gear is significantly lower than the normal traveling speed of that gear, or the bucket stops moving after slightly inserting into the material pile.

If the movement of a certain gear is weak or does not move at all, it can be ruled out that there are problems with the common oil circuit and components of each gear such as the torque converter, walking pump, and pressure reducing valve. The location where the fault occurs can only be in the oil circuit between the transmission control valve and the clutch piston of that gear. At this point, the rotation of the main drive shaft between the torque converter and the gearbox should be observed first: Shift into the corresponding gear. After the bucket is inserted into the material pile and the loader stops moving forward, if the main drive shaft continues to rotate but the output shaft of the gearbox does not, the following problems can be confirmed:

(1) The bearing cover or nylon sleeve of the corresponding gear clutch is severely worn;

(2) If the bearing cover or nylon sleeve is in good condition or slightly worn, it indicates that the inner and outer sealing rings of this clutch are not well sealed. When weak components such as bearing covers, nylon sleeves, and inner and outer sealing rings wear out, the oil supplied to the clutch leaks in large quantities from the worn parts, resulting in a decrease in control oil pressure and slippage of the clutch. Such faults are often accompanied by excessively high oil temperatures.

Troubleshooting method: Replace the corresponding damaged parts, namely the bearing cover or nylon sleeve, inner and outer sealing rings, and readjust the bearing and the bearing cover to ensure that the bearing clearance is 0.05-0.09mm. If the slippage lasts too long, it may burn out the friction plates. New parts should be replaced. If the oil is contaminated, the filter element and filter screen should be cleaned or new oil should be replaced.

The engine is normal. When in any gear, the vehicle does not move or moves weakly

If each gear does not move or moves weakly, the fault range can be limited to the common oil circuits and components of each gear such as the torque converter, walking pump, and pressure reducing valve. When this kind of malfunction occurs, it can be observed that the main drive shaft does not rotate when the entire machine is not working.

For this type of malfunction, first check if the hydraulic oil in the transmission is sufficient. The method is to keep the engine idling and observe that the oil level should be in the middle of the oil gauge on the side of the transmission. If the oil level is not visible, replenish the oil. After the oil level returns to normal, distinguish whether the fault occurs suddenly or gradually. In case of sudden failure, the pressure reducing valve should be disassembled and inspected to see if it is dirty and whether the surface of the valve core is scratched and stuck at the minimum oil supply position. This can be solved by cleaning and grinding. Then, check whether the splines of the connecting sleeve of the walking pump are damaged. If the signs of failure appear slowly, it is generally caused by the gradual wear of the components of the walking system or poor cleanliness of the oil. The following sequence can be followed for inspection:

(1) Determine whether the fault lies in the torque converter. Check the mechanical oil return filter installed on the rear frame of the vehicle. If there is a large amount of aluminum dust adhering to the filter screen, it can be determined that the bearing inside the torque converter is damaged, causing wear of the "three wheels". The torque converter should be disassembled, the damaged parts replaced and the oil circuit cleaned.

When in operation, the transmission oil in the working oil chamber of the torque converter must be kept full. Insufficient oil will lead to a decrease in output torque, causing the main drive shaft to rotate weakly or stop rotating. When conducting the inspection, disengage the low-pressure rubber hose of the return oil (torque converter overflow) from the torque converter to the transmission, and observe the overflow flow of the return oil pipe when the engine is idling. Under normal conditions, there is only a small flow rate. As the engine speed increases and the relief valve inside the torque converter pressure reducing valve suddenly opens, the flow rate will suddenly increase. If the flow rate is also large when the engine is idling, it can be determined that the sealing ring inside the torque converter is severely worn, causing internal leakage.

(2) If the return oil from the torque converter to the transmission is normal, the engine will run at high speed. If the return oil volume is small, it is necessary to check whether there is any dirt blockage or air leakage in the suction pipeline of the walking pump. The main inspection is to check whether the oil suction filter screen installed in the gearbox and the rubber hose of the walking pump are aged, internally detached or bent, etc.

(3) If the above is normal, it can be determined that the volumetric efficiency of the walking pump is low, and the walking pump should be replaced.

(4) The fault of weak walking power generally does not take into account the fault of the return oil heat dissipation circuit of the torque converter.

The loader can move automatically in neutral. It can also drive normally when the forward gear is engaged. However, when the reverse gear is engaged, the loader cannot move, but the working pressure in all gears is normal

The first, third, second and fourth gear control levers are engaged in any one gear. When the forward and reverse control levers are in the middle position and the loader moves forward, it indicates that the forward clutch is engaged. After shifting into reverse gear, the reverse clutch engages while the forward clutch does not disengage normally. Both clutches are engaged simultaneously, resulting in the entire machine not moving. In this regard, the forward clutch should be disassembled for inspection. Generally, it is due to the sintering and seizing of the driving and driven plates of the clutch, or the partial disengagement of the retaining ring causing the friction plates to tilt and fail to return to their original position. In addition, jamming of the forward clutch piston and blockage of the check valve at the support can also cause the clutch to disengage slowly or not at all. The jamming of the check valve is generally related to the cleanliness of the oil in the traveling system. When necessary, clean the filter element and replace the hydraulic oil.

When working, the vehicle suddenly stopped moving after shifting into second gear. It was checked that the working pressure of each gear was normal

The reason is that the clutch shaft of the transmission is broken. Replace the clutch shaft and readjust the bearing clearance.

During operation, the vehicle suddenly stopped moving. None of the gears could move forward or backward, but the working pressure was normal

The main drive shaft rotates normally, but suddenly it fails to shift gears. Generally, faults in the public oil circuits such as the clutches and torque converters inside the transmission and the walking pump can be ruled out. The main reason is that the pneumatic isolation valve stem of the variable speed distribution valve is in the off position, and the oil cannot enter each clutch. The reasons for the isolation valve stem being in the "off" position are, first, there is no supply of compressed air at the pneumatic control end of the isolation valve stem, and second, the isolation valve stem itself. In this case, the first situation should be checked first. It can basically determine the location of the fault through visual inspection without disassembly. The determination method is to start the engine, keep the air pressure above 0.5MPa, press the manual brake valve to the "driving" position, step on the brake pedal and release it to release the brake. During the lifting process, observe whether the air vent of the brake valve can be smoothly discharged. If no air is discharged, the amount of air discharged is very small or not smooth, adjust the brake valve control screw or replace the brake valve. If it is normal, observe whether there is air discharged when the pneumatic stop valve is stepped on. If not, it can be determined that the valve core of the air stop valve is stuck, and cleaning or replacement should be carried out.

If the above is normal, then check whether there are any scratches on the surface of the isolation valve stem, whether there is any dirt inside the speed change valve, and whether the reset spring is broken or its elasticity is weakened.

The engine was running normally, but the loader suddenly lost steering, failed to lift and stopped moving

The power of the engine is transmitted to the main drive shaft and the gearbox respectively through the torque converter, and then drives the working pump, the running pump and the steering pump through the drive gears inside the torque converter. If no steering, no movement (the main drive shaft does not rotate) and no action of the working device occur simultaneously, it can be determined that the engine power has not been transmitted to the torque converter. The causes of the malfunction are generally the breakage of the elastic connecting plate and the teeth of the connecting wheel.

All gears move normally, but when operating under load, there is a feeling of insufficient power

First, check whether the high and low speed control levers are in the low speed position and whether the reversing lever or gearshift lever is in place. If everything is normal, you can refer to Article 1 for handling and further check whether there is a large amount of metallurgical powder in the transmission fluid and whether the friction plates of the first and third gear clutches or the forward clutch are damaged.

Oil leakage occurs in the breather at the top of the torque converter during operation or driving

The torque converter breather is mainly used to balance the pressure inside the torque converter gear chamber. Under normal circumstances, there is only a small amount of lubricating oil in the gear chamber (the oil overflowing from the pressure reducing valve). If the amount of oil inside increases or there is air pressure, it will splash the oil onto the vent hole of the breather and overflow. This kind of malfunction usually starts by checking whether there is an increase in air pressure inside the torque converter, that is, checking whether the compressed air from the braking system has entered the running gear. Since the only communication point between the gas line and the running oil line is the variable speed distribution valve, it is necessary to check whether the "O" ring on the isolation rod of the variable speed distribution valve is damaged. The method is to start the engine, turn it off when the air pressure is between 0.8 and 1.0MPa, and listen for any leakage sound at the transmission valve. Then, you can open the fuel filler cap of the transmission to check if there is continuous gas discharge. If so, it can be determined that the "O" ring is damaged.

If the above is normal, it is usually due to an increase in oil in the gear chamber, which indicates that the return oil heat dissipation circuit of the torque converter is blocked. Focus on checking whether the return oil line of the guide wheel seat, the mechanical oil return oil filter, the mechanical oil radiator and other return oil lines are blocked.

There is an abnormal noise from the torque converter

There are generally the following reasons for abnormal noise from a torque converter:

1) The torque converter connection wheel part is toothed or the elastic rubber teeth are damaged or fall off, the elastic connection plate of the torque converter is cracked, etc.

2) For 30F and 30D type torque converters, the drive gears in the gear chamber are toothed or the bearings are damaged.

3) The main drive shaft is not installed correctly, the balance plate has fallen off, or the universal joint bearing clearance is too large

The entire machine is working normally, but the oil temperature is high, the output power is insufficient, and there is aluminum dust in the transmission oil

This is because the guide wheel, pump wheel and turbine wheel of the torque converter are severely worn. The reason is usually caused by the damage of the pump wheel support bearing. When conducting maintenance, not only should the damaged parts be replaced, but also the torque converter and its return oil circuit should be thoroughly cleaned, and the return oil filter screen should be replaced. For damaged filter screens, the radiator should also be cleaned or replaced.

11. It disengages automatically at low or high speeds

The fundamental reason for the self-disengagement of gears at low or high speeds is that the high and low speed sliders inside the transmission come out of the splines in the low-speed or high-speed gears.

(1) The gap between the high and low speed control levers and the high and low speed fork shafts is too large, or the high and low speed pull rods are not adjusted properly. The high and low speed sliding sleeves and the splines inside the gears are not fully combined, and they come out when the loader jolts.

(2) The splines in the sliding sleeve and the splines inside the high and low speed gears are severely worn, resulting in a large meshing clearance.

(3) The fork is deformed or the positioning spring of the fork shaft is broken.

The hydraulic oil in the transmission has increased, while the hydraulic oil in the hydraulic oil tank has decreased

This malfunction occurred accompanied by oil leakage from the transmission breather. The reason is that the oil seal on the inner side of the pump shaft of the working pump or the steering pump has aged and leaked oil. The two pumps are installed at one end of the torque converter gear chamber. The oil leakage from the shaft seal will directly enter the walking system. To determine whether the steering pump or the working pump is leaking oil, the following methods can be referred to:

(1) Press the engine accelerator at medium speed, place the lift and bucket control levers in the "middle position", turn the steering wheel to the right and reach a dead corner. If the transmission fluid increases after a period of time, it indicates that the steering pump is leaking.

(2) Press the engine accelerator at medium speed, place the bucket control lever in the "bucket" position, and keep the steering wheel still. If the transmission fluid level increases, it indicates that the working pump is leaking oil.

The above methods are effective for faults with large leakage. If the leakage is small and the increase in transmission fluid is not significant, it will not be obvious. It is necessary to check the oil seals on the rotating shafts of the two pumps respectively.

The hydraulic oil in the transmission has decreased, while the hydraulic oil in the working hydraulic oil tank has increased

This fault is exactly the opposite of the situation mentioned in 12 above, but the faulty part is generally also the working pump or the steering pump. Due to the fact that the drive shaft of the CB pump itself has two seals, the inner axial oil seal mainly prevents external leakage, while the outer axial oil seal mainly prevents air intake. As the pump shaft is immersed in the hydraulic oil of the torque converter gear chamber and there is a certain vacuum degree at its inlet during oil suction, and the oil passage on the inner side of the drive shaft is generally the same as the oil suction port, if the outer oil seal is damaged, the oil in the torque converter will enter the working hydraulic system through the pump shaft, thus causing this fault.

In addition, the oil suction filters and oil suction rubber hoses of the two pumps can also cause an abnormal increase in vacuum during oil suction, which may lead to this kind of malfunction.

References

Loader Fault Diagnosis, Weifang News Publishing House, 1994