Synthesis of a six-coaxial-link planetary gear train for seven-speed automatic transmissions

This paper presents a methodology for the kinematic synthesis of seven-speed automatic transmissions with a two-degree-of-freedom and six-coaxial-link planetary gear train. A detection proof is used to filter out unsuitable planetary gear trains for seven-speed automatic transmissions. A six-coaxial-link compact planetary gear train with three mutually meshed planet gears is selected as the design target. Based on the requirements for clutch-to-clutch shifts and decreasing speed ratios, an existing algorithm is used to generate feasible clutching sequences. An exhaustive searching method for the optimum numbers of teeth on gears is used to minimize the differences between the set of desired speed ratios and that of generated speed ratios. The ten best combinations of the numbers of teeth on gears for each clutching sequence are then found. Finally, the mechanical efficiencies of the ten sets are calculated for evaluation. Six valid configurations with only six clutches are obtained for seven-speed automatic transmissions.