AGMA 11FTM28 PDF

Introduction

Military vehicle transmissions have a very high power to ratio and carry more loads within the given volume and space than the transmission used for commercial applications. The gears used have increased load carrying capacity, less noise and vibrations. The gears used are generally profilemodified to suit the high load carrying requirement of the vehicle. One such gear pair used for increasing the load carrying capacity of the gear is the high contact ratio (HCR) gear pair. The HCR gears having a contact ratio greater than 2.0 have load sharing between two or three teeth during engagement and lowermagnitude loads per tooth [1] as compared to normal contact ratio (NCR) gear. The HCR gears guarantees that a minimum of two teeth always share the load [2,3,4]. The wearmechanisms between gears are often described as eithermild wear, surface fatigue or scuffing and are related according to Figure 1.

Wear can alter not only stress and load distributions but also the noise and vibration levels of a gear set thus justifying in--depth studies in both static and dynamic conditions. The load sharing during path of contact for gears could be estimated using the FiniteElementMethod (FEM). The wear rate comparison of the HCRgear and NCR gear having identical module and fixed center distance could be extrapolated based on the above. However, there is no reference or publication on this topic as on today. This paper predicts the wear rate for the HCR gear and NCR gear for identical load conditions by taking in to consideration the load sharing ratio and the contact pressures estimated using the finite element method (FEM) and using the Archard wear equation [5].