An epicyclic-type automatic transmission is a device which is connected from the engine to the driven wheels. A Lepelletier automatic transmission consists of a two-DOF epicyclic gear mechanism and a fundamental geared entity, which can provide more speed ratios. For the development of automatic transmission with eight or more speed ratios, an efficient design methodology is urgently needed and still not available. Therefore, the purpose of this article is to develop a systematic method for the design of Lepelletier automatic transmission. First, the features and requirements of the Lepelletier automatic transmissions are investigated and the corresponding design requirements are induced. Next, the theory of the analysis of speed ratios for Lepelletier automatic transmission is derived based on the concept of lever analogy. Then, the design theory of Lepelletier automatic transmission is developed based on the analysis theory. Finally, the complete atlas of six-speed and eight-speed Lepelletier automatic transmissions can be systematically synthesized from the data of three given speed ratios. In this article, the innovative and patentable six-speed and eight-speed Lepelletier automatic transmissions with the simplest structure have been. This proposed design method can also be applied to the development and design of ten-speed Lepelletier automatic transmissions.

An epicyclic gear mechanism for automobile transmissions is a device which is connected from engine to driving wheels, and the main purpose is to maintain the revolution speed of engine to be in a desired working range while accelerating or decelerating the automobile. The epicyclic gear mechanisms for automobile transmissions in production are mostly Ravigneaux-type, Parallel-connected type and Lepelletier epicyclic mechanisms, and the Lepelletier epicyclic gear mechanisms is a device which is connected with a simple epicyclic gear mechanism besides the input end to increase the total number of speed ratios of an automatic transmission. For the incompletion in the relative design methodology, a systematic methodology of designing Lepelletier epicyclic gear mechanisms for automobile transmission is described. At first, fundamental and gear-shifting operations of the Lepelletier-type automatic transmissions is introduced, and the basic principles of lever analogy is explained, the gear ratio¡¦s analysis for Lepelletier epicyclic gear mechanisms is illustrated to establish the design requirements. Secondly, gearing-sequence is devised base on the lever analogy diagrams, and a systematical procedure to arrange desired clutches and brakes into epicyclic gear mechanisms is provided, then the number of the teeth of all gears can be calculated. At last, the six-speed and eight-speed Lepelletier automatic transmissions are designed base on the above design procedure. The results of this work obtain 19 types of automatic transmission which could reach six-speed.