Effective measures to prevent the burning of the transmission clutch of a bulldozer

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After two years of use, a YT220 bulldozer found that the transmission clutch could not work properly. It was replaced with a new transmission and continued to be used, but after about 20 days, it was found that the bulldozer was weak in operation. Check that the working oil pressure of the forward I gear of the transmission is only 0.50MPa, while the normal value should be (1.25±0.10)MPa. The oil pressure of other gears is 1.50-1.80MPa. The normal value should be (2.50±0.20)MPa. So, the user sent the transmission to our factory for repair.

After disassembling the transmission clutch, it was found that the clutch friction plates of the forward gear were severely sintered and damaged. The lubricating expansion oil grooves of the driven friction plates had been ground flat, and deep annular grooves had been ground on the contact end face with the forward gear gear ring. The grooves were filled with oil sludge and dirt. The sealing rings of each gear were worn to varying degrees. There was a layer of black oxide on the surface of all parts inside the entire transmission clutch. The remaining oil is black, mixed with a large amount of grinding debris and sludge, and has an unpleasant smell, indicating that the hydraulic oil has been severely oxidized and deteriorated.

The main reasons for the burnout of the friction plates in a transmission clutch

The oil temperature is too high

Based on the oxidation degree of the surface of the transmission parts and the hydraulic oil, it is determined that the oil temperature of the hydraulic system is too high. The excessively high oil temperature is caused by the influence of components such as the hydraulic pump, oil filter, and cooler in the hydraulic system, as well as the hydraulic oil. That is, excessive impurities in the oil of the hydraulic system cause the oil filter to be blocked, the circulation of the hydraulic system to be hindered, poor cooling, and too fast circulation, which leads to an increase in the oil temperature. The increase in oil temperature causes the rubber sealing parts inside the transmission clutch to age, deform and crack, reducing their performance and lifespan. This leads to poor engagement between the driving and driven plates of the clutch, slippage between them, incomplete clutch disengagement, and increased frictional resistance, thereby accelerating the severe wear of the clutch friction plates.

(2) Improper selection of hydraulic oil

Based on the degree of oxidation and deterioration of the residual oil in the transmission, it is confirmed that the hydraulic oil was improperly selected. In the hydraulic system, hydraulic oil not only transmits power but also serves to lubricate and cool. If the hydraulic oil is not properly selected, it will directly affect the working quality of the hydraulic system. Practical experience has shown that 80% of faults in hydraulic systems are caused by the oxidation and deterioration of hydraulic oil. In hydraulic systems, components such as variable speed pumps, control valves, and slide valves all require very precise fit clearances. Some components are equipped with resistance holes, control valve holes, lubricating oil holes, and working oil pressure inlet ports, etc. Once the hydraulic oil oxidizes and deteriorates or is mixed with a large amount of impurities, This will clog these oil holes, impede the flow of hydraulic oil, and prevent these components from functioning properly.

(3) Too low pressure

If impurities in the hydraulic oil enter the transmission, it will cause blockage of the oil inlet and lubricating oil holes. If impurities in the oil enter the clutch piston and the hydraulic cylinder, it will cause the sealing ring to get stuck in the hydraulic cylinder and fail to expand outward, resulting in poor sealing between the piston sealing ring and the hydraulic cylinder body. This leads to leakage of pressure oil, a decrease in the working oil pressure of the clutch, and causes slippage and weak operation. Subsequently, it results in severe wear of the clutch friction plates and poor engagement. Moreover, the driving and driven plates of the clutch are not adequately lubricated, which aggravates the burning of the clutch friction plates.

2. Preventive measures

To extend the service life of the bulldozer's variable speed clutch, based on our long-term working experience, the following work must be done well:

(1) Clean the system

When installing a new transmission, the hydraulic pump, oil filter, torque converter, cooler, control valve and other components of the main machine's hydraulic system should be strictly cleaned. The cleaning fluid is best to use No. 8 hydraulic transmission oil of the same grade as the torque converter. It is strictly prohibited to use kerosene or diesel for cleaning. During cleaning, the flow rate of the cleaning fluid should be increased as much as possible So as to flush out mechanical impurities and oil stains in the hydraulic system pipelines. After the cleaning is completed, the cleaning solution should be promptly drained while the machine is still hot.

(2) Select the correct type of oil

According to the requirements specified in the user manual, No. 8 hydraulic transmission oil is selected for the transmission and chassis hydraulic systems. The selected hydraulic oil should have good low-temperature fluidity, appropriate high-temperature viscosity, excellent thermal oxidation stability and anti-bubble property, as well as good anti-friction and anti-corrosion performance. It is strictly prohibited to mix hydraulic oils of different grades. Before refueling, the oil must be strictly filtered to prevent mechanical impurities, dust, moisture, emulsions, etc. from entering the hydraulic system.

(3) Control system pressure

Before the machine starts to operate, the pressure of the hydraulic system should be strictly inspected. That is, use a pressure gauge to test the pressure entering the transmission control valve. Under the action of the pressure regulating valve, set the standard value of the engagement pressure of the clutch in the second and third gears of the transmission (2.5MPa±0.2MPa). The oil pressure of the I-position locking clutch (1.25MPa±0.1MPa) and the oil pressure of the slide valve (0.1MPa±0.025MPa). If the clutch pressure is measured to be lower than the standard value, first inspect the variable speed control valve to determine whether the fit clearance between the valve stem and the valve body hole of the variable speed control valve is too large. Is the spring force of the pressure regulating valve and the pressure reducing valve too weak? Check whether the O-ring on the stem of the variable speed control valve is damaged. If it is damaged, it should be replaced and adjusted in time. When the force of the pressure-reducing spring of the pressure regulating valve is insufficient, a washer of appropriate thickness can be added in the spring seat ring to adjust the working oil pressure, and the machine should be reinstalled for testing. If the measured pressure is still lower than the standard value, the variable speed control valve assembly must be replaced.

(4) Adjust the meshing clearance reasonably

A pair of helical bevel gears are connected at the output end of the transmission to transfer power to the central drive shaft of the rear axle box. Therefore, the correct degree of their meshing has a significant impact on the noise, service life and working performance of the entire machine. Before installation, the large bevel gears on the old main machine should be removed, and the newly paired large bevel gears should be installed on the central drive shaft and fastened with bolts. Adjust the tooth side clearance of the bevel gear pair by 0.25-0.33mm through the speed-regulating gasket and maintain the meshing mark. This helical bevel gear must be used in a complete set.

(5) Ensure proper maintenance and upkeep

Maintaining good maintenance and upkeep is an important prerequisite for ensuring production safety, giving full play to the performance of the transmission clutch and extending its service life. Drivers should carry out daily maintenance and upkeep carefully and strictly, and promptly detect and eliminate minor faults to prevent accidents. For newly manufactured bulldozers or those that have just undergone major overhauls, the oil should be drained while still hot after trial operation or 100 hours of operation, and then No. 8 hydraulic transmission oil should be refilled. After that, the working oil should be replaced every 1,000 hours of operation. In daily work, it is necessary to pay attention to observing the working oil pressure and oil temperature of the hydraulic system to prevent continuous operation when the oil pressure is too low or the oil temperature is too high. Regularly check the quality of the hydraulic oil, keep the hydraulic system and hydraulic oil clean. If any abnormal situation is found, stop the machine in time to identify the cause and eliminate the fault, so as to keep the transmission clutch of the bulldozer in good working condition.

Practical experience has shown that after maintenance and upkeep in accordance with the above-mentioned methods, the problem of burning out the transmission clutch has been effectively solved. The repaired bulldozer has been in use for several months, and there have been no quality issues with its transmission clutch again.