High-accuracy Dynamics Modeling And Dynamic Behavior Mechanism Of Helicopter Main Reducer In Non-inertial System

The main reducer is one of the key core components of the helicopter,and its performance is directly related to the overall performance level of the helicopter.It is of great significance to master the development technology of high-performance helicopter main reducer with independent intellectual property rights to promote the development of China’s helicopter industry.The coupling relationship of helicopter main reducer is complex and diverse,and the structure has prominent features such as irregularity and great flexibility.It is necessary to find the appropriate modeling strategy to achieve the balance between the model accuracy and calculation efficiency.In addition,the main reducer moves with the helicopter in space.The assumption that the base is fixed to the ground is no longer consistent with the actual operating environment.The effect of additional effects derived from the base motion cannot be ignored.In this paper,a helicopter main reducer is taken as an example,and a modeling method and accuracy evaluation standard for special-shaped substructures are proposed.The coupling relationship between sub-systems under complicated space angles is deduced,and a general dynamic modeling method for the overall coupling of gear-shafting-bearing-casing under a generalized coordinate system is formed.The theoretical model is verified by various steady-state vibration tests.Then,the additional effects generated by the base motion are taken into account,and the dynamics model of the ordinary gear transmission system in non-inertial system and the dynamics model of the planetary gear transmission system in internal and external dual non-inertial systems are established respectively.The influence of base motion on the dynamic behaviors of gear system is studied.The main research work includes:(1)A dynamic modeling method based on experimental modal analysis-finite element method-substructure condensation and quantified accuracy evaluation criteria based on modal parameters are proposed for the thin-walled special-shaped structures such as casing members in the helicopter main reducer.The optimal combination of beam element stiffness and element mass matrix is determined based on regular size shafting.The applicability of beam element method and condensation method in modeling irregular shafting of helicopter main reducer is discussed.The above research provides casing substructure and shafting substructure models with both accuracy and calculation efficiency for the overall system modeling of the helicopter main reducer.(2)The casing subsystem is assembled by connecting substructures.The accuracy of the connection substructure is verified,and the range of connection stiffness is determined.The meshing relations of different subtypes such as bevel gear pairs,planetary gear systems and helical gear pairs are derived,through which the shafting substructures are assembled in order to obtain the gear-rotor subsystem model.The coupling relationship between subsystems with arbitrary spatial angle is established,and finally the overall coupled dynamic model of gear-shafting-bearing-casing in generalized coordinate system is formed.Based on the vibration test platform of a helicopter main reducer,the time-frequency response signals are obtained under multiple operating conditions,and the theoretical simulation results are compared and verified.The significant difference in vibration response with or without casing demonstrates the necessity of establishing an overall coupled model of the system.(3)A kinematics analysis model is established to derive the additional inertial forces and moments due to the base motion,and the relationship between the gravity effect and the spatial posture of the base.Each additional term is involved in the system dynamics equation in the form of generalized force vector excitation,ensuring the continuity of the modeling method in the inertial system.Finally,a dynamic modeling method for ordinary gear transmission system in non-inertial system is developed.The dynamic behaviors such as shafting deflection,bearing force,and vibration time-frequency response under different motion parameters are studied,which provides theoretical reference for dynamic load calculation,structural strength and reliability prediction of ordinary gear transmission system under maneuvering flight condition.(4)In addition to the internal non-inertial system of the planetary gear transmission,the external non-inertial system of base motion is further considered.According to the characteristics of different components and the setting of coordinate system,the absolute acceleration equations under the superposition of internal and external non-inertial systems are derived categorically.Then,the dynamics model of planetary gear transmission system considering the base motion is established.The contribution of different additional terms to the dynamic response of the gear system is compared.The influence laws of base motion parameters and installation angles on component offset,bearing force,vibration,and load-sharing performance are obtained,which provide theoretical basis for the structural optimization and high reliability design of planetary gear transmission in a maneuvering flight environment.