Selection and Design of Planetary Gear Trains Based on Power Flow Maps

It is shown that for any planetary gear train (PGT) it is possible to find the relationship existing between the transmission ratio of the train and the power transmitted through each gear pair (gearing power). Specifically, for trains of five and six members, this functional dependence generates a family of curves parameterized by the transmission ratio. A plot of this family of curves is called a power flow map. It allows one to identify those trains that have a potentially high efficiency. In particular, it identifies the transmissions which present power recirculation, a condition that is generally undesirable. Also, an analysis of the power flow maps for the six-member trains leads to the conclusion that, for most of these trains, there is a single expression for the efficiency. The interest of the proposed method is that it is only necessary to know the expression for the PGT’s transmission ratio in order to obtain its power flow map. Also, the map is independent of the constructional solution that is adopted for the train. Finally, the power maps that are obtained are used to find alternatives to the designs of a train consisting of several stages of a basic four-member PGT.