Research On Load-sharing Characteristics Of Twin Rotors Concentric Face Gear Power-split Transmission System

The conventional coaxial transmission system has the common problems of large weight and volume and difficult tooth matching,which restricted the helicopter’s high mobility performance improvement.The main reducer of the helicopter with a face gear power-split transmission configuration had the advantages of increased efficiency,lightweight and high reliability.Load-sharing technology was the core technology of the twin rotors concentric face gear power-split transmission system.The system’s technical characteristics were adopted by the load-sharing technology of the power diversion idea.The existing load-sharing theory and method of gear power-split transmission system were not suitable very well,especially in the static and dynamic models were established and simulation analysis,resulting in the transmission system load-sharing principle of application and reliability improvement being restricted.Therefore,this paper takes the development trend of high-speed,great bearing capacity and high-efficiency helicopters as the goal and puts forward the twin rotors concentric face gear power-split transmission system combined with many advantages of face gear.The mathematical model establishment of statics and dynamics and load-sharing characteristics of this transmission system is studied.In order to study the static load-sharing characteristics of the twin rotors concentric face gear power-split transmission by comprehensively considering the factors such as manufacturing error and installation error.The torsional stiffness of the flexible split-torsion shaft and the double-torsion shaft,flexible support of floating gear 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 is established by combining the moment balance equation of the system.The least-square method is used for the solution.The load-sharing coefficient characterizing the load distribution of the system is obtained.Then,the variation law of static load-sharing characteristics of the system under the single and combined action of manufacturing and installation errors,torsional stiffness,flexible support of floating gear,and other factors is analyzed.The research found that the error of stage-Ⅲ gear is the main factor leading to the uneven load of the system,and reducing torsional stiffness of the split-torsion shaft and the double-torsion shaft can compensate for the load-sharing characteristics of the system to a certain extent.The flexible support of the floating gear can greatly improve the load-sharing characteristics of the system.Considering the cost-performance ratio and the common flexible support of the grade II floating gear,the system can meet the requirements of± 5% of load-sharing characteristics under service conditions.In order to study the dynamic load-sharing characteristics of the twin rotors concentric face gear power-split transmission,firstly,the stiffness is expanded to time-varying meshing stiffness through the Fourier series.Then based on the lumped parameter method,the bending-torsion coupling dynamic load-sharing model of the system is established by comprehensively considering the factors such as manufacturing error and installation error,time-varying meshing stiffness,torsional stiffness,supporting stiffness,and elastic deformation.The motion differential equation of the system is deduced,and dimensionless treatment is carried out.The variable step Runge-Kutta is used to solve the equation.The influence of manufacturing and installation errors and torsional stiffness on the dynamic load-sharing characteristics are revealed.The research found that the error of stage-Ⅲ gear affects the load-sharing performance of the system to the maximum extent;with the increase of the torsional stiffness,the load-sharing coefficient first decreases and then increases.Controlling the torsional stiffness of the split-torsion shaft and the double-torsion shaft in a certain range is beneficial to the load-sharing characteristics of the system.The research results in this paper can provide a theoretical basis for the reliable,optimal design of the load-sharing structure of the system.