Modal analyses of herringbone planetary gear train with journal bearings

A generalized dynamic model for herringbone planetary gear train (HPGT) is developed to investigate its modal properties. The model includes the axial vibration of two helical ring gears in addition to three planar degrees of freedom for the carrier and all gears. Four stiffness coefficients are applied to describe the asymmetry and the interaction of the oil film stiffness of journal bearings for supporting the planets. Vibration modes are classified into rotational and axial mode, translational mode, planet mode, rotational and axial ring mode and translational ring mode. For each type of mode, the reduced-order eigenvalue problems are derived according to the modal properties. The formulas for calculating the modal strain and kinetic energy distributions are also given for each mode. The proposed dynamic model and analysis methods can be applied to HPGT with any number of planets. Only when the asymmetric interaction exists in journal bearings, will the dramatic change of mode shape for translational mode occur. The new relations between deflections of planets in translational mode are also derived in this research.