Study and analysis of fractures in gears from automotive transmissions.

Abstract

Premature wear and fractures in automotive transmissions represent considerable negative costs for automakers, as they cause the vehicle to be disabled and its repair is usually costly and time consuming. Thus, understanding the source of these defects could permit us to more reliably propose alternatives, making this a valuable area of research. In this study, distinct defects in the helical gears of manual transmissions were selected and mechanical analysis was carried out focusing on the root cause of the failures. The study included hardness tests, liquid penetrate inspection (LPI) and visual inspection. In the Rockwell hardness test, values were obtained for the steel pieces which had been thermally treated by carbonitriding. In the liquid penetrate inspection, cracks were found present inside the teeth of the evaluated gears. The results obtained are consistent with the literature. It is noteworthy that the gears analyzed already had explicit defects, which prevented their reuse. We conclude that the failures in automotive transmission gears are related to various factors, usually related to torques above the design limit or lack of lubrication and maintenance, which implies premature failures and consequently a shorter than expected service life.