Pitting failure of helical gears induced by trochoidal interference and multidirectional, interacting wear

Abstract

Improving gear mesh efficiency contributes to reducing the environmental impact of vehicles. This study examined the effect of adjusting gear specifications on improving mesh efficiency. When the gear ratio of cylindrical gears is relatively high, it tends to increase the sliding velocity between the engaging gear teeth. Moving the contact region toward the base circle of the pinion along the line of action is considered to be one solution for reducing friction loss. However, it may cause deterioration of tooth surface strength because the radius of curvature of the tooth surface becomes smaller on account of being closer to the base circle. In order to confirm the influence of the gear meshing region on tooth surface strength, gear durability tests were carried out and tooth damage states were observed in detail under a microscope. The results revealed that pitting failure occurred near the tooth root region of the pinion. Furthermore, trochoidal interference due to the high torque condition extended over the base circle. In this case, trochoidal interference has a greater influence on pitting failure. In order to investigate the effect of reducing trochoidal interference near the base circle on pitting failure, further gear durability tests were conducted using the mating gears with large tooth tip modification. However, the effect on improving pitting durability was limited. Multidirectional, interacting wear was observed not only in the profile direction due to trochoidal interference but also in the lead direction due to edge contact. Such wear changed the location of pits. The results of these detailed investigation revealed a new viewpoint for explaining the mechanism of these phenomena in terms of conflict between pitting and multidirectional, interacting wear. Presumably, pitting failure changes if the state of progression of trochoidal interference and wear in the lead direction changes. In order to confirm the influence of such wear on pitting durability, a gear durability test was conducted using gears with tooth tip modification and endface relief. The test results confirmed that the location of pits and pitting durability changed. These results revealed that pitting durability and the state of damage were influenced sensitively and compositely by multidirectional, interacting wear, i.e., wear in the profile and lead directions.