The intermediate gearbox of a helicopter operates under splash lubrication.If the bearing produces metal particles due to insufficient lubrication or wear,whether it can be adsorbed by the metal particles signal at th...The intermediate gearbox of a helicopter operates under splash lubrication.If the bearing produces metal particles due to insufficient lubrication or wear,whether it can be adsorbed by the metal particles signal at the bottom of the gearbox and alarm directly affects the flight safety of the helicopter.Based on the CFD method,the factors affecting the accessibility of metal particles are analyzed by using the volume of fluid-discrete phase model(VOFDPM)coupling model,the RNG k-ɛturbulence model and the dynamic grid technology.Furthermore,the optimization research on the casing structure is conducted.Experimental results show that the accessibility of metal particles is optimal when the gear speed is 6000 rad/min or the immersion depth is 24 mm.The density of metal particles exhibits a nonlinear relationship with their accessibility,and the particle size has a relatively small impact on their accessibility without an order of magnitude change.展开更多
Nonlinear dynamic analysis was performed on a planetary gear transmission system with meshing beyond the pitch point.The parameters of the planetary gear system were optimized,and a two-dimensional nonlinear dynamic m...Nonlinear dynamic analysis was performed on a planetary gear transmission system with meshing beyond the pitch point.The parameters of the planetary gear system were optimized,and a two-dimensional nonlinear dynamic model was established using the lumped-mass method.Time-varying meshing stiffness was calculated by the energy method.The model consumes the backlash,bearing clearance,time-varying meshing stiffness,time-varying bearing stiffness,and time-varying friction coefficient.The time-varying bearing stiffness was calculated according to the Hertz contact theory.The load distribution among the gears was computed,and the time-varying friction coefficient was calculated according to elastohydrodynamic lubrication(EHL)theory.The dynamical equations were solved via numerical integration.The global bifurcation characteristics caused by the input speed,backlash,bearing clearance,and damping were analyzed.The system was in a chaotic state at natural frequencies or frequency multiplication.The system transitioned from a single-period state to a chaotic state with the increase of the backlash.The bearing clearance of the sun gear had little influence on the bifurcation characteristics.The amplitude was restrained in the chaotic state as the damping ratio increased.展开更多
基金supported by the Na‑tional Natural Science Foundation of China(No.52075241)the National Key Laboratory of Science and Technology on Helicopter Transmission(Nanjing University of Aeronau‑tics and Astronautics)(Nos.HTL-A-22K04 and HTL-O21G13).
文摘The intermediate gearbox of a helicopter operates under splash lubrication.If the bearing produces metal particles due to insufficient lubrication or wear,whether it can be adsorbed by the metal particles signal at the bottom of the gearbox and alarm directly affects the flight safety of the helicopter.Based on the CFD method,the factors affecting the accessibility of metal particles are analyzed by using the volume of fluid-discrete phase model(VOFDPM)coupling model,the RNG k-ɛturbulence model and the dynamic grid technology.Furthermore,the optimization research on the casing structure is conducted.Experimental results show that the accessibility of metal particles is optimal when the gear speed is 6000 rad/min or the immersion depth is 24 mm.The density of metal particles exhibits a nonlinear relationship with their accessibility,and the particle size has a relatively small impact on their accessibility without an order of magnitude change.
基金supported by the National Natural Science Foundation of China(No. 51975274)National Key Laboratory of Science and Technology on Helicopter Transmission(Nanjing University of Aeronautics and Astronautics)(No. HTL-A-19K03)
文摘Nonlinear dynamic analysis was performed on a planetary gear transmission system with meshing beyond the pitch point.The parameters of the planetary gear system were optimized,and a two-dimensional nonlinear dynamic model was established using the lumped-mass method.Time-varying meshing stiffness was calculated by the energy method.The model consumes the backlash,bearing clearance,time-varying meshing stiffness,time-varying bearing stiffness,and time-varying friction coefficient.The time-varying bearing stiffness was calculated according to the Hertz contact theory.The load distribution among the gears was computed,and the time-varying friction coefficient was calculated according to elastohydrodynamic lubrication(EHL)theory.The dynamical equations were solved via numerical integration.The global bifurcation characteristics caused by the input speed,backlash,bearing clearance,and damping were analyzed.The system was in a chaotic state at natural frequencies or frequency multiplication.The system transitioned from a single-period state to a chaotic state with the increase of the backlash.The bearing clearance of the sun gear had little influence on the bifurcation characteristics.The amplitude was restrained in the chaotic state as the damping ratio increased.
