Curvic coupling fatigue life enhancement through unique compound root fillet design

This invention relates generally to coupling mechanisms for engines and, more particularly, to fixed curvic couplings used in the assembly of components that comprise rotating elements, such as impellers, turbine wheels and couplings for gas turbine engines and other types of engines having highly stressed components. A lower stress and higher service life curvic coupling design is disclosed for use on coupling mechanisms for assembly of components that comprise rotating elements, such as impellers, turbine wheels and couplings for gas turbine engines and other types of engines having highly stressed components. The curvic coupling design includes a compound fillet radius, comprised of a large and a small radius, located between the root and the pressure surface of all splined teeth on the torque transmitting coupling halves. The larger radius, with its lower stress concentration, is positioned in the root area where the background hoop stresses act, thereby resulting in a lower fillet peak stress value. The smaller radius smoothly connects the larger radius with the pressure surface, minimizing the penetration of the fillet surface towards the mating tooth, thereby allowing proper clearances to be maintained. The smaller radius is in a region where the background stresses are low, and therefore its higher stress concentration is not detrimental to the overall design. The inventive curvic coupling design ultimately resulted in a three-fold increase in service life.