Analysis of the Main Causes of Burnout of the Variable Speed Clutch Friction Plate
Publication Date:
2022-11-21
Based on the oxidation level of the transmission parts' surfaces and the hydraulic oil, it is determined that the hydraulic system's oil temperature is too high. This high oil temperature is caused by components such as the hydraulic pump, oil filter, cooler, and the hydraulic oil itself within the hydraulic system. Specifically, excessive impurities in the hydraulic oil cause the oil filter to become blocked, obstructing the hydraulic system's circulation, leading to poor cooling and overly rapid circulation, which raises the oil temperature. The increased oil temperature causes the rubber seals inside the transmission clutch to age, deform, and crack, reducing their performance and lifespan. This results in poor engagement between the clutch's primary and secondary plates, slipping between these plates, incomplete clutch separation, increased friction resistance, and consequently accelerates severe wear of the clutch friction plates.
1. Main causes of friction plate burning in the transmission clutch
(1) Excessive oil temperature
(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 transmits power and also provides lubrication and cooling. If the hydraulic oil is improperly selected, it will directly affect the quality of the hydraulic system's operation. Practice has shown that 80% of failures in hydraulic systems are caused by oxidation and deterioration of the hydraulic oil. Components such as the transmission pump, control valve, and lubrication valve require very precise clearance fits. Some components have resistance holes, control valve holes, lubrication oil holes, and working oil pressure inlets. Once the hydraulic oil oxidizes or contains a large amount of impurities, these oil holes can become blocked, hindering the flow of hydraulic oil and causing these components to malfunction.
(3) Low pressure
If impurities in the hydraulic oil enter the transmission, they can block the oil inlet and lubrication oil holes. If impurities enter the clutch piston and hydraulic cylinder, the sealing ring can get stuck inside the hydraulic cylinder and fail to expand outward, causing poor sealing between the piston sealing ring and the hydraulic cylinder body. This leads to pressure oil leakage, reducing the clutch working oil pressure and causing slipping, weak operation, severe wear of the clutch friction plate, poor engagement, and insufficient lubrication of the clutch driving and driven plates, which further aggravates the burning of the clutch friction plate.
2. Preventive measures
To extend the service life of the bulldozer transmission clutch, based on our long-term work experience, the following tasks must be done:
(1) System cleaning
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 thoroughly cleaned. It is best to use No. 8 hydraulic transmission oil of the same brand as the torque converter as the cleaning fluid. The use of kerosene or diesel for cleaning is strictly prohibited. During cleaning, the flow rate of the cleaning fluid should be maximized to flush out mechanical impurities and oil sludge from the hydraulic system pipelines. After cleaning, the cleaning fluid should be promptly drained while the machine is hot.
(2) Correct oil selection
According to the requirements of the user manual, No. 8 hydraulic transmission oil should be used for the transmission and chassis hydraulic system. The selected hydraulic oil should have good low-temperature fluidity, appropriate high-temperature viscosity, good thermal oxidation stability, anti-foaming properties, and excellent anti-wear and anti-corrosion performance. Mixing different brands of hydraulic oil is strictly prohibited. Before adding oil, the oil must be strictly filtered to prevent mechanical impurities, dust, moisture, and emulsions from entering the hydraulic system.
(3) Control system pressure
Before machine operation, the hydraulic system pressure should be strictly checked by using a pressure gauge to test the pressure entering the transmission control valve. Under the action of the pressure regulating valve, the engagement pressure standard values for the transmission II and III gear clutches should be set at (2.5MPa ± 0.2MPa), the oil pressure for the I gear lock clutch at (1.25MPa ± 0.1MPa), and the oil pressure for the lubrication valve at (0.1MPa ± 0.025MPa). If the measured clutch pressure is lower than the standard value, first inspect the transmission control valve to determine whether the clearance between the valve stem and valve body hole is too large; whether the spring force of the pressure regulating valve and relief valve is too weak; and whether the O-ring seal on the transmission control valve stem is damaged. If damaged, it should be replaced and adjusted promptly. When the pressure regulating valve's relief spring force is insufficient, an appropriately thick shim can be added inside the spring seat to adjust the working oil pressure, and the assembly should be reinstalled and tested. If the measured pressure is still below the standard, the transmission control valve assembly must be replaced.
(4) Proper adjustment of meshing clearance
The transmission output end transmits power to the central drive shaft of the rear axle housing through a pair of helical bevel gears. Therefore, the correct meshing of these gears greatly affects the machine's noise, service life, and working performance. Before installation, the old large bevel gear on the main machine should be removed, and the new matched large bevel gear should be installed on the central drive shaft and secured with bolts. The side clearance of the bevel gear pair should be adjusted to 0.25-0.33mm using adjustment shims, maintaining the meshing contact pattern. These helical bevel gears must be used as matched sets.
(5) Proper maintenance
Maintaining good maintenance and care is an important prerequisite to ensure production safety, maximize the performance of the transmission clutch, and extend its service life. Operators should perform daily maintenance carefully and strictly, promptly detect and eliminate minor faults to prevent accidents. For newly manufactured bulldozers or those that have undergone major repairs, the oil should be drained while hot after 100 hours of trial operation or work, and No. 8 hydraulic transmission oil should be refilled. Subsequently, the working oil should be replaced every 1000 hours. During daily work, attention should be paid to observing the hydraulic system's working oil pressure and oil temperature to prevent continued operation under low oil pressure or high oil temperature. Regularly check the quality of the hydraulic oil, keep the hydraulic system and oil clean, and if abnormalities are found, stop the machine promptly to identify and eliminate faults, ensuring the bulldozer's transmission clutch remains in good working condition.
Hotline
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Email:HRdjmc@hzdjfm.com
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