Design and analysis of compound stepped planetary gear drives for better transmission performances

Due to the possibility of high speed-ratios, compound stepped planetary gear drives (CSPG) are very suitable for applications with size restrictions, e.g., gear reducers for actuators in electrical vehicles. However, the design of the numbers of teeth of CSPG is more complicated due to the compound planets. A set of equations is derived for checking the assembly of gears as well as for calculation of the tooth contact. Six design rules based on the equations are thus proposed to determine suitable numbers of teeth for correct assembly. In addition, a modified model for analysis of gear meshing and loaded tooth contact is proposed. A total of six design rule-based study cases without and with profile crowning modification were analysed using this proposed analysis model. These cases are classified into three types: full factorizing, partial factorizing and non-factorizing. The influences of these different combinations of tooth numbers on the transmission errors and load sharing were systematically explored. The results show that the transmission errors will be enlarged and the shared loads among the planets are the same, if the planets mesh with the ring and sun gear all in phase. A better design with the smallest transmission error and evener load sharing is that the planets mesh with the sun gear in phase and with the ring gear in sequential phase. The design guidelines are finally summarized.