The Influence Study of Time-Varying Stiffness on the Vibration Impact of Planetary Gear Set System

Abstract

Planetary gear sets are widely used in the transmission system. Multiple time-varying stiffness from sun-planet and planet-ring meshing areas leads to multiple meshing impacts, but researches on the relationship between the multiple stiffness and the impacts are still superficial. To have a further study, the time-varying stiffness and a 18 degree of freedom dynamic model of a planetary gear set were built respectively in this paper. First the sun-planet pair meshing stiffness was compared when different level of crack happened in a sun and planet gear respectively. The results show that meshing stiffness variation decreases more when the cracked level increases. While for a certain crack level, the decrease variation increases when cracked on sun gear while the variation decreases when cracked on planet gear with the system running. Then the connection between meshing stiffness mutation and system impacts were studied when the gears were perfect. The results show that there are 4N times of impacts in a complete meshing period for a planetary gear set with N planets, and the impact amplitude generated from planet-ring meshing pair stiffness mutation is higher than that of the sun-planet meshing pair. Then the impacts starting moment and amplitude were analyzed to study the impacts influence caused by the sun gear fault. It is found that the impact initial point appears in the first single-tooth meshing duration of the fault sun-planet gear meshing pair when a small crack happens on the sun gear, which is induced by the suddenly increased stiffness of the planet-ring meshing pair. Besides, the fault impact amplitude increases with the fault level.