Investigation of dynamic behavior of planet gears in planetary gear sets for three-axis driving

Planetary gear set is widely used in hybrid vehicle as a power distribution system or in electric vehicle as a high reduction system. Although it has many advantages, its noise and vibration problem has emerged. There have been many reports dealing with two-axis driving or displacement of planet gear under its condition, but we can see no report dealing with about three-axis driving. As first novel point in the present report, three-axis driving is tested on the original test stand. As second novel point in this report, characteristic of instantaneous center of the planet gear is investigated based on mechanism. Planet gear rotates and revolves at the same time during working in three-axis driving condition. Instantaneous center was defined according to velocity distribution of planet gear or superposition of velocity distribution of rotation and that of revolution with simple lumped model. Tangential speed is equal to zero at the instantaneous center, and planet gear rotates around it instantaneously. Instantaneous center moves according to the driving condition or input ratio between two inputs which input from ring gear and carrier. It is very important to consider generated inertia force due to rotation around instantaneous center, to design planetary gear set for three-axis driving. The meshing force between planet gear and ring gear and the meshing force between planet gear and sun gear have same trend and close value but they are not same value, and absolute values of ring-planet meshing force are larger than those of sun-planet meshing force. It is also confirmed that the torques around planet gear are balanced in steady condition, considering both transmission and rotation