Research on the transmission efficiency of multi-speed transmission mechanisms

Gear shifts in a multi-speed transmission alter component interconnections and power-flow paths. Conventional methods often address a single gear train or a fixed configuration. They therefore cannot directly provide a unified efficiency calculation across gears. This study integrates the meshing power method, the transformed-mechanism method, and virtual power theory. The resulting method handles multiple gears, multiple epicyclic gear trains, and multiple power-flow paths. First, shifting logic and control-element states define the component constraints and power-flow path in each gear. The mechanism is then decomposed into fixed-axis, planetary, and differential transmission units. The equivalent mechanical efficiency of each unit is calculated separately. Finally, unit efficiencies are combined according to series, parallel, or series-parallel relationships. A seven-speed transmission with three epicyclic gear trains serves as the case study. The theoretical results are compared with steady-state bench-test measurements. For the six comparison gears, all relative errors are below 3%. This agreement supports the engineering applicability of the proposed method. The method supports efficiency analysis, concept comparison, and structural optimization of multi-speed transmission mechanisms.