A Simple Method for Gear Ratio and Torque Analysis of Planetary Train Systems

Planetary gear train systems are widely used in automotive transmissions due to their compactness, large reduction ratios and degrees of freedom available for the selection of gear ratios. The analysis of gear ratios and torque relations among the elements of a planetary train system is often difficult due to the complexity of the planetary train structure. This is especially the case for automotive transmissions using planetary train system where the members for input and output and the members that are fixed or interconnected must be changed in the clutch engagement schedule to obtain multiple transmission speeds. This paper proposes a systematic approach that simplifies the gear ratio and torque analysis based on the basic planetary train characteristics. The approach can be effectively used for the analysis of gear ratio and static torques for power transmissions consisting of parallel planetary trains. A case study of multi-speed automotive transmission based on the approach is included in the paper.