1. Fault conclusion
The main reason for the fracture failure of the rivet of the failed bearing cage is the defect of the ML15 steel wire material, and the secondary reason is the unreasonable selection of the fitting relationship between the rivet and the rivet hole. The extraction power of the AC motor on the aircraft is significantly higher than that of other platforms, and the vibration of the driving bevel gear under the oblique transmission will also increase. In this case, the carbon content of the bearing rivet material is lower than the technical standard, and the unreasonable fitting clearance between the rivet and the rivet hole will significantly increase the impact force of the steel ball on the cage, thus increasing the rivet stress accordingly. At the same time, the repeated fluctuation of the extracted power of the aircraft platform will exert alternating stress on the bearing rivets, thus accelerating the fatigue failure of the rivets.
2. Failure mechanism
The lower driving bevel gear of oblique transmission is of long shaft structure, the lower end is supported by bearings, and the upper end is supported and transmitted by splines. The gear has poor running stability compared with the lower driven bevel gear. Compared with other double-fulcrum bearings, the bearing in this position has special installation mode and support structure, and the working condition is even worse.
According to the simulation calculation, the fit size of rivet hole and rivet and the preload after rivet riveting have a great impact on the stress of the rivet, but the bearing will not have fatigue fracture if the rivet material is qualified; When the carbon content of the rivet is lower than the standard, the mechanical properties of the material will decline, and fatigue fracture will occur under the condition of large gap or large interference.
At the same time, the simulation calculation shows that if the matching gap between the cage rivet and the rivet hole is not properly selected, the stress of the rivet rod will increase during the working process, the rivet rod will be elongated during the working process, the gap between the two halves of the cage will occur, and the stability of the steel ball and cage will be reduced. After working for a period of time, the rivet rod will have fatigue fracture. The gap between the two halves of the cage at the fracture of the rivet is further increased, the running stability of the cage and the steel ball is further reduced, and the bearing is not running smoothly, which leads to the fatigue fracture of other rivets one after another, and the two halves of the cage are completely separated. The unstable operation of the bearing causes vibration, which eventually leads to wear of the lock washer.