Fault prevention and daily maintenance of wheel loader gearboxes

The gearbox is one of the important transmission components of a wheel loader. It is responsible for transmitting the speed and torque from the engine to the final transmission system, changing the transmission ratio between the engine and the wheels, achieving the control of the forward and reverse gears of the loader, and can also cut off the power transmitted to the traveling device when the engine is running, to meet the operation and driving needs of the loader. It is convenient for the safe start and stop of the engine.

However, during the operation of loaders, the failure rate of gearboxes caused by improper use and maintenance has remained high. Especially when maintenance and repair procedures are not strictly followed during use, and timely inspections and daily maintenance are lacking, it will accelerate the damage and formation of faults in the gearbox, and even expand the harmfulness of the fault consequences.

I. The Purpose of Preventive Maintenance

By tracking and inspecting the operation of the loader, the machine should be shut down in a planned manner, and proper maintenance and repair arrangements for the gearbox should be made.

2. To prevent major mechanical failures and damage to related components, repairs should be carried out before faults occur to save a significant amount of maintenance costs.

3. Ensure that all components of the machine have a longer service life, improve the efficiency of the equipment, and maintain good working performance.

4. Reduce the difficulty and workload of maintenance.

Ii. Common Faults and Causes of Wheel Loader Gearboxes

When shifting gears, the gear cannot be smoothly entered. The reasons are:

The pressure of the pressure valve is too low;

(2) The hydraulic pump is not working properly and the seal is not good.

(3) Blockage of hydraulic pipelines;

(4) The clutch sealing ring is damaged or leaking.

(5) The gear shift valve stem is not in place.

2. When the transmission is shifting gears, the gear cannot be disengaged. The reasons are:

(1) The piston ring swelled up.

(2) The clutch friction plates are burned out;

(3) The clutch return spring fails or is damaged;

(4) The return oil pipeline is blocked.

3. The gear has been engaged, but the loader is running weakly and even unable to move. The reasons are:

(1) The friction plates are severely worn and have excessive clearance.

(2) The automatic vent valve of the clutch is not sealed tightly, causing the pressure to drop.

(3) The pipeline of the shift control valve is blocked;

(4) The shut-off valve cannot return to its original position.

(5) The positioning spring of the variable speed valve is fatigued or broken, and the steel ball jumps.

(6) The clutch piston rings and sealing rings are severely worn, resulting in severe leakage.

4. The operating pressure is too low. The reasons are:

(1) Insufficient oil in the transmission oil pan;

(2) Oil leakage in the main oil passage;

(3) The transmission filter is clogged;

(4) The steering pump (or hydraulic pump) is damaged, causing severe internal leakage;

(5) Improper pressure adjustment of the transmission pressure regulating valve;

(6) The spring of the shift pressure valve fails or breaks.

5. The transmission automatically disengages or shifts out of gear. The reasons are:

(1) The positioning device of the shift control valve malfunctions. The main reasons for the malfunction are severe wear of the positioning steel ball or the failure of the spring.

(2) Due to long-term use, the position and length of the shift lever have changed, and the proportion of the levers is inaccurate, causing a deviation in the operating position and thus resulting in misalignment.

Iii. How to Carry out preventive maintenance of the Transmission

In accordance with JB/Z194-83 and in light of the actual maintenance and repair situation, the following regulations should be followed:

(1) Regular maintenance: Check the oil level in the oil low shell.

(2) 50 hours (or weekly) : Check whether the gearshift control handle is flexible and effective;

(3) 250 hours (only after the first 250 hours of operation) : Clean the transmission oil pan and the transmission oil filter element.

(4) 500 hours: Clean the oil pan filter and replace the transmission fluid;

(5) 2000 hours: Disassemble, inspect and repair the transmission and torque converter.

2. Hydraulic transmission oil serves as the energy carrier for the normal operation of the transmission. In the hydraulic transmission system, the pressure, temperature and flow rate of the working fluid all determine whether the transmission can operate normally. Therefore, in the daily maintenance of the transmission, special attention should be paid to the inspection and replacement of the hydraulic transmission oil.

(1) Fix the oil change interval

Changing the oil at the correct time intervals is the key to ensuring that the components inside the transmission have the longest working life. Only by ensuring a reasonable oil change interval can the lubricating and protective properties of the lubricating oil be brought into full play. Under normal circumstances, the maintenance cycle recommended by the whole machine manufacturer should be taken as the basis, but this can only be relative. It must be combined with the results of oil sample extraction and analysis to know the actual working situation. For instance, the maintenance manual stipulates that the oil change interval for the transmission is 500 hours. Based on the operation of the loader, we conduct a sampling analysis of the oil samples every 250 hours or 100 hours to determine when to change the oil. However, the lubricating oil should be replaced immediately after 1000 hours of use.

In addition to regularly replacing new oil, during routine inspections, if the oil is found to be deteriorated or mixed with impurities, it should also be cleaned and inspected, and new oil should be replaced.

(2) Adopt the correct methods for oil drainage and changing

When draining oil, the oil temperature should reach 40 to 50 degrees Celsius, and the oil flow should be discharged under stirring conditions. It is necessary to drain the dirty oil as thoroughly as possible. When refueling, a fuel dispenser equipped with a filtering device should be used to add fuel.

(3) Use the correct transmission system oil. The lubricating oil used in the gearbox must comply with the specifications. It should be noted that diesel engine oil must not be added to the transmission. This is because diesel engine oil can reduce the friction between moving parts such as pistons, while the oil used in the transmission system should ensure that there is a certain frictional force when the friction plates are combined. This frictional force is crucial for the normal operation of the transmission system. Only by using lubricating oil correctly can the working life of the clutch friction plates be effectively prolonged. At the same time, using oil correctly can significantly improve the anti-wear performance of gears, eliminate clutch slippage, control the trembling and abnormal noise during braking, increase braking force, and provide greater traction. At present, the most commonly used hydraulic transmission oils for gearboxes are 6 # and 8 # hydraulic transmission oils.

(4) Refer to the filter replacement cycle provided in the maintenance manual, replace the filter in a timely manner, and at the same time clean the filter screen, the screw plug of the oil drain magnet, and the air vent plug. Add lubricating oil in the standard amount. If the viscosity of the transmission fluid is too high, it will cause low transmission efficiency of the transmission, poor fluidity, which is not conducive to heat dissipation. Moreover, local dry friction may occur between the high-speed relatively moving parts, which is not conducive to lubrication. If the viscosity of the transmission fluid is too low, it can increase the leakage, causing the control oil pressure of the transmission to be too low and resulting in a malfunction. The oil film strength between the transmission components under heavy load is insufficient, leading to premature wear of the transmission components and thus being unfavorable for lubrication.

Meanwhile, during normal operation of the transmission, a small amount of bubbles will be produced due to the stirring of the gears in the oil. To prevent the bubbles from accumulating more and more, causing cavitation and reducing the thickness of the oil film, which would affect the operation of the clutch and control valves inside the transmission, the transmission fluid must have anti-foaming properties.

Therefore, using the appropriate transmission oil can not only protect the transmission, extend its service life, and reduce its failure rate, but also lower the direct cost of transmission oil change and maintenance, as well as reduce the labor required for transmission maintenance and the downtime for maintenance.

(5) All kinds of lubricating oils must be pure and have undergone a period of sedimentation to meet the specified quality requirements.

The refueling tools, containers and all refueling ports should be wiped clean to prevent moisture and dirt from entering the oil.

When checking the fuel level, the vehicle must be kept level both longitudinally and laterally.

After refueling or changing the oil, be sure to check for any oil leakage.

Therefore, it is very necessary to strengthen the prevention of faults and regular maintenance of the transmission during daily use. This can not only reduce the low work efficiency and delayed working hours caused by shutdown for maintenance, but also prevent and avoid more serious subsequent faults, lower maintenance costs, and enhance the safety guarantee of the machine.