Systematic Design of Six-Speed Automatic Transmissions With an Eight-Link Two-DOF Ravigneaux Gear Mechanism

The purpose of this paper is to present an efficient methodology for the design of six-speed Ravigneaux-type automatic transmissions based on the concepts of basic gear ratios and speed ratio equations. First, the speed ratio equations of an eight-link two-degree-of-freedom Ravigneaux gear mechanism are derived, which are functions of basic gear ratios. Next, the ranges of the derived speed ratio equations are estimated and classified into three groups to synthesize all possible clutching sequences. Then, a planar-graph representation is proposed to arrange the desired clutches for each possible clutching sequence into the Ravigneaux gear mechanism. Finally, the number of teeth of all gears is synthesized from assigning three desired speed ratios by the analytic method presented by Hsu. The result of this paper shows that the eight-link two-degree-of-freedom Ravigneaux gear mechanism could reach six forward speeds at most, and only a particular set of speed ratios is practical for use.