在某装载机驱动桥大螺旋齿轮的开发过程中发现，齿轮在工作一段时间后出现早期断齿失效的情况。通过宏观检验、断口分析、化学成分分析、硬度以及金相检验等方法，对大螺旋齿轮断齿失效原因进行了分析。结果表明：齿根圆角曲率半径和啮合斑点尺寸过小以及轮齿心部硬度较低，导致齿轮根部应力集中作用加强是该大螺旋齿轮轮齿过早疲劳断裂失效的主要原因。最后根据断齿失效原因，对大螺旋齿轮进行了相应的改进，并取得了良好的效果。

Tooth fracture failure phenomenon occurred in the early stage after the large helical gear of a wheel loader driving axle worked for a period of time during its development process. Through macroscopic inspection, fracture analysis, chemical composition analysis, hardness test, metallographic examination and other methods, the reasons of tooth fracture failure of the large helical gear were analyzed. The results show that the small radius of curvature of the root fillet, the small meshing spot and the low hardness of the tooth center resulted in the intensifying of stress concentration at the tooth root, which was the main reason for the early fatigue fracture failure of teeth of the large helical gear. Finally, according to the failure reason of the tooth fracture, the large helical gear was improved correspondingly, and good results were achieved.