The concentric face gear split-torque transmission system (CFGSTTS) is a new form of drive that is primarily used in helicopter transmission systems. Its load-sharing performance among different branches and tooth contact characteristics have a great impact on the service life of helicopter transmissions. It contains ten meshing pairs, the load distribution is complicated, and the tooth contact areas are difficult to determine. Therefore, based on the multi-point constraint method and nonconforming grid, a quasi-static analysis model of the CFGSTTS coupled with flexible supports was established and the load-sharing performance and contact characteristics were studied. The model considered the support stiffness, backlash, installation error, and web structure of the upper face gear, which could comprehensively reflect the meshing state of the system. The load-sharing coefficient curves, tooth contact area diagram, and meshing force were obtained. The results indicated that (1) a larger idler support stiffness and a smaller input gear support stiffness could achieve better load equalization performance; (2) better load equalization between idler gears could be acquired with a lower face gear support stiffness factor of approximately 0.9; (3) increasing the axial mounting error caused the contact area to shift to the top and inner end of the face gear tooth, which was detrimental to the transmission; and (4) adjusting the backlash of the idler gears, input gears, and tail gear had little influence on the load balance and contact.

The concentric face-gear split-torque transmission system (CFGSTTS) is a new type of transmission that has significant applications in helicopter main gearboxes. To study the influence of various parameters on the dynamic characteristics of the CFGSTTS, a 23-degree-of-freedom translation-torsion nonlinear dynamic model was established based on the lumped parameter theory. The model includes tooth backlash, error excitation, time-varying meshing stiffness with meshing phase difference, meshing damping, and elastic support deformation. The excitation conditions for the time-varying meshing stiffness of face-gear pairs were calculated based on the strain energy theory. The bifurcation characteristics of the system with different parameters were obtained by the nonlinear dynamics numerical analysis method. The research shows that the system exhibits rich vibration response characteristics at different rotating speeds. The amplitude of the vibration displacement in the system bifurcation diagram increases significantly with the increase of the tooth backlash and input torque, whereas the amplitude decreases constantly with the increase of the meshing damping. The critical rotational speed at which chaotic motion occurs increases significantly with increasing input torque and damping ratio but decreases with increasing tooth backlash. The bearing clearance has a weak influence on the vibration displacement amplitude of the system and the speed range of chaotic motion.