Reduced Length Eight_Velocity Automatic Transmissions


Although there are many epicyclic-type automatic transmissions in production, some of the related configurations are still far from attaining maximum sequential velocity ratios. This work in part will attempt to attain the maximum possible velocity ratios for any given epicyclic gear train.A methodology for the design of two-ring Ravigneaux-type epicyclic gear transmissions for automobiles is presented. First, based on the kinematic nomographs of the corresponding basic gear ratios, clutching-sequences are enumerated. Second, a planar-graph representation is used to arrange the desired clutches for each possible clutching sequence into the epicyclic gear mechanism. Then, with the above methods, the designs of the epicylic gear mechanisms are given for demonstrating the feasibility of the proposed methodology. Next, following the general trend of increased shift stages and a wider range of velocity ratios, new six-, seven- and eight-velocity automatic transmissions are enumerated from the two-ring nine-link Ravigneaux gear mechanisms. The result of this work shows that the nine-link two-DOF Ravigneaux-type epicylic gear mechanisms could reach eight-forward speeds at most. It is a major breakthrough to design eight-speed automatic transmissions from the nine-link Ravigneaux gear mechanism since it has only nine links. This structural design has realized a reduced length automatic transmission, while having minimal number of gears.