China XCMG TY160.TY220 and TY320 bulldozers all use the production technology of Komatsu D65. D85 and D15 bulldozers from Japan. The gearboxes of these three models are all planetary power shift gearboxes, which are compact and identical, so they are highly versatile and interchangeable. The common failures and causes of these three gearboxes in production and use are analyzed and discussed.

　　1: Common main faults

　　The common faults of power shift transmissions are mainly manifested in the weakness of the whole vehicle. A certain gear is frequently disengaged and has no gears. This is also the most prone to special failures of mechanical shift transmissions. The root cause of the vehicle's inability to travel, a gear out of gear and a gearless failure is the failure of the shift clutch. The causes of the failure are: insufficient pressure in the hydraulic control system of the gear shift and failure of the gear clutch components.

　　2: Analysis of the cause of failure

　　( 1) Insufficient pressure in the hydraulic control system of the gear shift

　　The above three types of gearbox hydraulic control system set pressure is 1.8 MPa-2.0MPa. When the transmission pressure gauge shows that the pressure is lower than 1.6MaP, the vehicle behaves as a weak load at full load, and the light load travels slowly; when the pressure is lower than 0.5 MPa, the vehicle does not move in any gear. When the pressure is lower than 1.6MPa, due to insufficient pressure, the shift clutch of the gearbox is in a state of semi-engagement and semi-disengagement, and the relative friction between the active plate and the friction plate generates high temperature, resulting in component burnout and the clutch quickly loses function. Seriously damaged. This phenomenon often occurs in actual use, so when the pressure is lower than 1.5MPa, it should be stopped immediately for inspection.

　　Insufficient system pressure is caused by a leak in the hydraulic system or insufficient oil supply. The main reasons are damaged hydraulic components, insufficient oil quantity or inadequate addition and insufficient oil absorption. In actual use, it is easy to check out the lack of oil and make up in time. Damage to hydraulic components includes failure of seals, malfunction of control valves and pressure regulating valves. The initial operation of the gearbox is normal and seals occur after a period of time. The damage of the hydraulic parts leads to the pressure drop. This phenomenon has little to do with the quality of the hydraulic components themselves. The main reason should be due to the pollution of the hydraulic system.

　　Facts have proved that due to the presence of hard debris in the hydraulic system, the cleanliness is poor, resulting in abnormal wear of the seals and hydraulic parts, the valve core is stuck and malfunctioning, the filter is blocked and the system is leaked, and the insufficient oil supply causes the pressure to drop. Therefore, the cleanliness of the hydraulic system is the most important factor to ensure the service life of the gear shift hydraulic control system. To maintain the cleanliness of the system, simply clean the system and change the oil as required.

　　( 2) The shift clutch element is damaged

　　Shift clutch is composed of piston, driving plate and friction plate. The movement of the piston causes the clutch to engage and disengage. Most of the damage to the shift clutch is the active plate. The friction plate is caused by the failure of high temperature ablation and annealing, and the piston is rarely damaged. When the clutch becomes effective due to damage to its components, the mechanical transmission control hydraulic system works normally, but the work is weak, and the gearbox is abnormally sound.

　　The damage of the shift clutch component is not related to the use, and is mainly closely related to the quality of the component itself and the assembly quality. The main problems are:

　　① The flatness of the active plate or the friction plate is excessively poor, ② The assembly gap is too small, ③ The cooperation precision of the friction plate and the gear ring of the phase fitting is poor, and the movement is not smooth. ④ The piston does not return well and the return spring fails. ⑤ Poor lubrication. As mentioned above, the damage to the shifting clutch element mainly occurs in the form of burning of the active plate and the friction plate.

　　When the clutch is in neutral, its friction plates and active plates should be kept in a separated state with a certain gap (the gap between each plate is 0.16mm to 0.25mm). However, due to the deformation of the components, excessive flatness, poor return and poor movement, etc.,

　　In the separated state in actual work, there is no gap between the active plate and the friction plate, and the clutch is always in a semi-engaged and semi-disengaged state. At this time, the active plate and the friction plate rub against each other at high speed to generate a great amount of heat. This causes component burnout. The initial burnout causes increased deformation. The increased deformation increases friction and causes further burnout until the component fails.

　　In order to maintain the normal operation of the clutch, the flatness tolerance of the active plate and the friction plate and the quality of the fittings of the phase parts should be strictly required in the production, maintenance and assembly, to ensure the assembly gap of the clutch, the friction plate, the active plate movement should be light and free of interference jam The phenomenon, the gearbox should pass the bench test after production and assembly. If the clutch does not work normally due to component or assembly quality problems, the no-load loss of the gearbox exceeds the specified value is very high, then the machine should be disassembled for inspection and repair. To prevent the failure from further developing and causing the clutch to fail.