Natural characteristics analysis on herringbone planetary gear trains with slide bearing support

A dynamic model of herringbone planetary gear trains is developed considering the axial vibration of two rings and asymmetry and interaction of oil film stiffness. Four stiffness coefficients are used to describe the oil film stiffness of slide bearings for planets' support. The free vibration characteristic is analyzed and the vibration modes are divided into five groups: rotational-axial vibration mode of center gears, rotational-axial vibration mode of rings, translational vibration mode of center gears, translational vibration mode of rings and planets vibration mode. For each class of mode, the reduced-order inherent characteristics formulas are derived according to the properties of each vibration mode. The distribution range of natural frequencies is smaller than those of spur and helical planetary gear trains. It reveals that although the asymmetry of oil film stiffness has little influence on the vibration modes properties, the significant changes of translational vibration mode of center gears will happen if there is asymmetry interaction of oil film stiffness: the corresponding twofold natural frequencies will turn into two different frequencies and new characteristics of vibration mode will appear.