Failure analysis of overdrive gear of passenger car gearbox fabricated from powder metallurgy

Abstract

In this paper, investigations into the premature failure of gearbox overdrive gears were done in three passenger car models. The premature failure occurred when a replaced gear model was used instead of the original gear. A series of experiments were carried out on gears made by two manufacturers, including failed gear after an average operation of 100,000 km and gear with partial failure but usable with an average operation of 200,000 km. Numerical and experimental results showed that sharp hardness slope (reduction of 300 HV in 0.15 mm), high porosity, and Hertz stress distribution of about 90% of the allowable contact stress σHa are the factors affecting premature failure. In addition, replacement gear samples with low density compared to original gear have low yield and ultimate strength due to high porosity and interconnected structure of pores. Pores with sharp corners act as the initiation points of the cracks, resulting in final fracture.