Load Distribution and Tooth Root Stress of Highly Crowned Spherical Gear Couplings Working at High Misalignment Angles

Spherical gear couplings are commonly used mechanical components to transmit power between highly misaligned rotating shafts. For that, gear couplings are manufactured with high longitudinal crowning and are usually small due to space restrictions, with the probability to contain undercutting sections. High misalignment angles cause the number of teeth in contact to decrease drastically, resulting in the failure of the component by tooth root fatigue breakage. This paper investigates the load distribution and the tooth root stress of highly crowned spherical gear couplings working at high misalignment angles using a finite element model. Moreover, a deep understanding of the bending tooth root stresses in terms of the operating conditions is presented, which is novel for such high misalignment angles (gamma >= 3 degrees). Results show that different mechanical behaviors are observed at low or high misalignment angles since teeth in the pivoting position lose contact. This results in a tooth root stress history change from a sinusoidal cycle to a pulsating cycle. Finally, this study shows evidence that current sizing methods are not suitable, and underlines the need for further research to determine the spherical gear coupling life to tooth root bending fatigue.