Analysis of Causes for Burning of Friction Plate of Variable-speed Clutch

The main reason for the burning of the friction plate of the variable speed clutch

(1) The oil temperature is too high

According to 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, and the high oil temperature is caused by the hydraulic pump, oil filter, cooler and other components of the hydraulic system and the hydraulic oil. Excessive impurities in the oil in the hydraulic system cause the oil filter to be blocked, the circulation of the hydraulic system is blocked, the cooling is poor and the circulation is too fast, which causes the oil temperature to rise; the increase in oil temperature causes the rubber seal in the transmission clutch to age and cause deformation and cracking , Which reduces the performance and life of the clutch, causing poor engagement of the clutch’s main and moving-slave plates, slippage between the main and moving-slave plates, incomplete clutch separation, and increased frictional resistance, thereby accelerating the serious wear of the clutch friction plates.

(2) Improper selection of hydraulic oil

According to the degree of oxidative deterioration of the residual oil in the transmission, it is confirmed that the hydraulic oil is improperly selected. In the hydraulic system, the hydraulic oil plays the role of transmitting power, and at the same time plays the role of lubrication and cooling; if the hydraulic oil is selected improperly, it will directly affect the working quality of the hydraulic system. . Practice has proved that 80% of the failures in the hydraulic system are caused by the oxidation and deterioration of the hydraulic oil. The valve components of the variable speed pump, control valve, lubrication valve and other components in the hydraulic system require a very precise fit clearance. The components are equipped with resistance holes, control valve holes, lubricating oil holes, and working oil pressure inlets. Once the hydraulic oil is oxidized and deteriorated or mixed with a large amount of impurities, these oil holes will be blocked and the flow of hydraulic oil will be blocked, making these parts impossible. normal work.

(3) The pressure is too low

If the impurities in the hydraulic oil enter the transmission, it will cause the oil inlet and lubricating hole to be blocked; if the impurities in the oil enter the clutch piston and the hydraulic cylinder, it will cause the seal ring to be stuck in the hydraulic cylinder and unable to expand. As a result, the seal of the piston seal ring and the hydraulic cylinder is not tightly sealed, resulting in the leakage of pressure oil, which reduces the working oil pressure of the clutch, and causes slippage and weak operation, which in turn leads to severe wear of the clutch friction plate and poor engagement, and the main clutch , The driven plate is not sufficiently lubricated, which intensifies the burning of the clutch friction plate.

2. Preventive measures

In order to prolong the service life of the variable speed clutch of the bulldozer, according to our long-term work experience, we must do the following:

(1) Cleaning system

When installing a new transmission, the hydraulic pump, oil filter, torque converter, cooler, control valve and other components of the main hydraulic system should be strictly cleaned. The cleaning fluid should be the same brand as the torque converter. No. 8 hydraulic transmission oil is strictly prohibited to use kerosene or diesel for cleaning. When cleaning, increase the flow of cleaning fluid as much as possible to flush out the mechanical impurities and oil stains in the hydraulic system pipeline. After cleaning, the cleaning fluid should be drained out in time when the engine is hot.

(2) Correct selection of oil

According to the requirements of the instruction manual, the transmission and chassis hydraulic system select No. 8 hydraulic transmission oil. The hydraulic oil selected should have good low-temperature fluidity, appropriate high-temperature viscosity, good thermal oxidation stability and anti-air bubbles, as well as good anti-friction and anti-corrosion properties. It is strictly forbidden to mix hydraulic oils of different brands. The oil must be strictly filtered before refueling to prevent mechanical impurities, dust, moisture, emulsion, etc. from intruding into the hydraulic system.

(3) Control system pressure

Before the machine is running, the pressure of the hydraulic system should be strictly checked, 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 transmission II and III clutches (2.5MPa) ±0.2MPa), the oil pressure of the I-speed lock-up clutch (1.25MPa±0.1MPa) and the oil pressure of the lubrication valve (0.1MPa±0.025MPa). If the measured clutch pressure is lower than the standard value, first check the speed control valve to determine whether the clearance between the valve stem of the speed control valve and the valve body hole is too large; whether the spring force of the pressure regulating valve and the pressure reducing valve is too weak ; Whether the O-ring seal on the variable speed control valve stem is damaged, if it is damaged, it should be replaced and adjusted in time. When the pressure reducing spring force of the pressure regulating valve is insufficient, a gasket of appropriate thickness can be added to the spring seat ring to adjust the working oil pressure. And reinstall the machine for testing. If the measured pressure is still lower than the standard value, the variable speed control valve assembly must be replaced.

(4) Reasonably adjust the meshing gap

The output end of the transmission guards a pair of helical bevel gears to transmit power to the central drive shaft of the rear axle box. Therefore, the correct degree of its meshing has a great influence on the noise, service life and performance of the whole machine. It should be removed before installation. For the big bevel gear on the old main machine, install the new paired big bevel gear on the central drive shaft and fasten it with bolts; adjust the side clearance of the bevel gear pair by 0.25-0.33mm through the speed adjustment washer, and keep the meshing marks; This helical bevel gear must be used in complete sets.

(5) Do good maintenance

Maintaining good maintenance is an important prerequisite for ensuring production safety, exerting the performance of the variable speed clutch and extending its service life. The driver should carry out daily maintenance carefully and strictly, and discover and eliminate minor faults in time to avoid accidents. For new bulldozers or bulldozers that have just been overhauled, drain the oil while it is hot after 100 hours of trial operation or operation, and re-add No. 8 hydraulic transmission oil. After that, replace the working oil every 1000 hours of work. In daily work, pay attention to observe the working oil pressure and oil temperature of the hydraulic system to prevent the oil pressure from being too low and the oil temperature from being too high to continue working. 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 find out the cause and troubleshoot, so that the gear shift clutch of the bulldozer can maintain good working condition.

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