Main path identification and sensitivity analysis of encased differential gear trains with cracked sun gear

Encased differential gear trains in coaxial-rotor helicopters are prone to faults. However, multiple sources and paths complicate fault identification. This study identifies the main path by combining path power with the system dynamic model, considering cracked sun gears as vibration sources, and investigates path sensitivities. The results are experimentally verified. Findings indicate contribution ratios vary with speed and torque. For encased-stage vibration source, paths incorporating ring gears r1 or r2 prevail, sensitive to internal-mesh damp (encased stage) and internal-mesh stiffness (differential stage). For the differential-stage source, paths involving carrier c2 or the ring gear r2 dominate, sensitive to external-mesh damp (encased stage), and internal-mesh stiffness (differential stage). These findings provide guidance for sensor placement and fault diagnosis in planetary gear trains.