Failure analysis of a secondary driving helical gear in transmission of electric vehicle

Abstract The failure cause of a secondary driving helical gear in transmission system of electric vehicle(VE) was analyzed in this paper. The macroscopic fractography, microscopic metallographic observation, hardening depth and hardness and chemical composition inspection, non-metallic inclusions analysis were carried out to evaluate the gear failure mechanism. The stress distributions of the tooth flank using static and dynamic contact finite element simulation were obtained based on ANSYS Workbench software. The results showed that the fracture surfaces of the failed gear originate from the tooth root and exhibit the intergranular brittle fracture, the main reason was low Ti content of the material, hardening depth and hardness in the root region and a number of large carbides on the on the matrix of martensite due to improper heat treatment, also FE simulation results revealed that the high contact stress in the root position and high impact load at the initial stage of gears meshing during the reducer in service possibly led to the fatigue failure.