During the working process of needle roller bearing, the higher the number of cycles, the more obvious the degree of fretting wear

2.3 Number of cycles

During the working process of needle roller bearing, the higher the number of cycles, the more obvious the degree of fretting wear. The number of cycles is determined by the vehicle's mileage (3 × 105 km) and speed ratio (varies with vehicle and gear). The longer the mileage, the more cycles; If the traveling gear is the driving wheel, the mileage is fixed, the smaller the speed ratio, the less the number of cycles. These two parameters are determined by the main engine manufacturer, and the mileage represents the service life of the vehicle, which is usually unchangeable. The speed ratio is related to the power and fuel consumption of the whole vehicle. On the premise of obtaining the consent of the main engine manufacturer, sometimes minor adjustments can be made to properly reduce the risk of fretting wear.

2.4 Material surface hardness

Under the same other conditions, the higher the surface hardness of the material, the higher the ability to prevent fretting wear. The needle roller is mostly made of bearing steel, and its hardness is slightly higher than that of gear and shaft, so fretting wear usually occurs in the inner hole of gear or the outer diameter of shaft. The material hardness of gears and shafts depends on the material model (20CrMnTiH, 20CrMo, 18MnCr5, etc.) and heat treatment conditions (usually carburizing and quenching). The optional optimization scheme is to properly reduce the tempering temperature to obtain higher surface hardness (above HV700) and improve wear resistance.

2.5 Surface roughness

To improve the surface roughness level, we can reduce the friction coefficient and friction work, thus achieving the effect of restraining fretting wear. The internal and external raceway roughness of grinding can reach Ra0 four μ m. It can basically meet the use requirements. When other influencing factors are not ideal, fretting wear will sometimes occur. The optional optimization scheme is to add finishing grinding process in the process flow. Properly improve the roughness level of gear inner hole and shaft outer diameter (Ra0 two μ m) It can effectively reduce the risk of fretting wear.

2.6 Lubrication

The lubrication of needle roller bearings is usually achieved by guiding the oil in the shaft center into the raceway through the oil hole. Good lubrication can ensure the formation of oil film between the needle roller and the raceway, reduce the friction coefficient, reduce the friction work, and prevent wear. The optional optimization scheme is to guide sufficient lubricating oil to the shaft center by improving the depth and angle of the oil guide groove. Secondly, by enlarging the diameter of the oil hole on the shaft or increasing the number of oil holes, the sufficient amount of oil is guided from the shaft center to the bearing raceway. Through the adjustment of additives, the extreme pressure performance of lubricating oil is improved, and the compressive stability of oil film is improved. Based on the analysis of the occurrence, countermeasures and test results of fretting wear during product development, adequate lubrication is one of the effective ways to avoid fretting wear.