Effect of stiffness on load-sharing characteristics of twin rotors concentric face gear power-split transmission system

A twin rotors concentric face-gear power-split transmission system (TRCFGPSTS) applied to the core transmission mechanism of advanced aviation twin rotors helicopter was studied. The effects of torsional stiffness and support stiffness on the load-sharing characteristics of system were mainly studied. By comprehensively considering the factors such as manufacturing error and installation error, meshing stiffness, torsional stiffness, support stiffness and elastic deformation, and according to the power flow double closed-loop mechanical characteristics of this system, the static double closed-loop torsional angle elastic deformation coordination conditions are derived. The static load-sharing model was established by combining the moment balance equation of system. The load-sharing coefficient (LSC) and sensitivity parameters characterizing the load distribution of system were obtained. The effects of the torsional stiffness of the split-torsion shaft and the double-torsion shaft and the support stiffness of each gear on the load-sharing characteristics of the system were analyzed. The results show that the torsional stiffness of the split-torsion shaft and the double-torsion shaft has a great influence on LSC and sensitivity of the system, when its value is in the range of (1–1.6) × 10 5 N·m /rad and (2.4–4.3) ×10 5 N·m /rad, the system can meet the requirements of ± 5% of load-sharing characteristics under service conditions. Reducing the torsional stiffness of the split-torsion shaft can improve the load-sharing characteristics of the system, and the torsional stiffness of the right-branching double-shaft has little effect on the load-sharing characteristics of the left-branching of the system. The support stiffness of I-stage small cone angle face gear and Ⅲ-stage face gear is the most sensitive to LSC. With the increase of the support stiffness, the LSC first decreases and then gradually flattens, and the support stiffness of Ⅲ-stage face-gear has little effect on the I-stage LSC. The research results can provide a theoretical basis for the optimal design of load-sharing structure.