Research on power flow of encased differential gear train in coaxial contra-rotating gearbox

This paper investigates an encased differential planetary gear train, comprising both fixed-axis and differential gear trains, for application in coaxial counter-rotating main gearboxes. The study analyzes the conditions required to achieve equal-speed counter-rotation between the inner and outer shafts, and examines the influence of varying loading conditions on internal power flow. A dedicated load test rig was designed and built for the main gearbox, utilizing two load motors to independently apply torque to the inner and outer output shafts. Power flow within the transmission system under differential loading conditions was indirectly determined through strain measurements. The study identifies four distinct power flow scenarios in the encased differential gear train under different load combinations applied to the inner and outer output shafts. Results indicate that when the load on the inner output shaft exceeds a critical threshold, a circulating power flow emerges within the system. The power flow behavior observed during testing shows strong agreement with theoretical predictions.