Influence of Tooth Deflections and Local Contact Deformations on the Tooth-Root Stress of Internal Spur Gears: Definition of a Load-Sharing Coefficient for the AGMA J-Factor

Abstract The extension of the contact interval resulting from loaded tooth deflections and local contact deformations increases the effective contact ratio, which can exceed the value of 2 if the theoretical contact ratio is close to 2, as frequently occurs in internal spur gears. In these cases, the load is shared by at least two pairs of teeth throughout the entire cycle of meshing of one pair of teeth, which results in lower values of the tooth-root stress. This reduction in the root stresses is not adequately considered by the Standard’s calculation methods. This paper presents a study on the influence of load sharing on the tooth-root stress of internal gears. Additionally, a new coefficient to modify the AGMA J-factor is proposed to consider the reduced tooth-root stress in calculations when the effective contact ratio exceeds the value of 2.