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Analysis of the factors affecting the micro-wear of the needle bearings

wallpapers Tech 2021-04-14
In transmission, the role of needle roller bearings is to support the floating gears on the shaft. Fretting wear is one of the main failure modes of needle roller bearings. Generally speaking, the hardness of needle rolling is slightly higher than that of the outer ring of the matching shaft and the inner hole of the gear. The following are the influencing factors and prevention of fretting wear of needle roller bearings
1. Radial vertical load
The radial vertical load of needle roller bearing mainly comes from the radial force of gear. The greater the radial force is, the greater the pressure acting on the contact parts (less than 4000MPa), and the more likely the wear is to intensify in relative motion. The size of the radial force of the gear is determined by the transmission torque and usually cannot be changed. The pressure at the contact part can be reduced by optimizing the needle roller bearing. Optional optimization is to reduce local pressure, improve wear resistance, and prevent fretting wear by increasing needle length, the number of needles, and needle diameter.
2. Displacement of reciprocating motion
The displacement of reciprocating motion is caused by the axial clearance (0.15-0.45mm) and radial clearance (0.015-0.058mm) of the needle roller bearing. The larger the clearance, the greater the displacement of reciprocating motion, the faster the speed, the higher the friction work, and the more likely it to cause local wear. There are two optional optimization schemes: one is to reduce the axial clearance (0.1~0.35mm) by improving the axial positioning accuracy of the gear and shaft; The other is to reduce the diameter tolerance of the shaft and hole or to group match the diameter tolerance of the shaft and hole to reduce the radial clearance (0.009~.048mm). By optimizing the clearance, the displacement of reciprocating motion can be significantly reduced, the friction work can be reduced and fretting wear can be prevented.
3. Quantity cycles
In the working process of needle roller bearing, the more cycles, the more obvious fretting wear. The number of bikes is determined by the mileage of the vehicle (3×105 km) and the speed ratio (which varies with the vehicle and gears). The more miles you travel, the more bikes you ride;If the walking gear is the driving wheel, the mileage is constant, and the smaller the speed ratio, the fewer the cycles. Both of these parameters are determined by OEM. Mileage represents the life of a vehicle and is usually unchangeable. The speed ratio is related to the power and fuel consumption of the vehicle. Minor adjustments can sometimes be made with OEM approval to reduce the risk of fretting wear.

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