There are many advantages of Epicyclic gear type automobile transmissions. It is composed more densely and weights lighter. It provides higher gear ratio and can transmit power differentially. Therefore, this type of transmissions are applied to almost every automobiles in recent years. However, the design process of an Epicyclic gear type automobile transmission is more complicated than Counter shaft type one. In the world, there are just two kinds of 8-speed Epicyclic gear type automobile transmission in production. This study introduced a design methodology of Parallel epicyclic gear type automobile transmission by decomposing and recomposing of Lever diagram. First we drew the Lever diagram from given rotation speed ratios. Next we listed all 3-point lever diagrams which are decomposed from the original Lever diagram, and deleted those with unreasonable value of K. Then we listed all combinations of 3-point lever diagram which composed the original Lever diagram, and we got all feasible epicyclic gear train mechanisms. After choosing feasible epicyclic gear train mechanism, we set up necessary clutches and breakes in clutch graphs. Finally, based on the clutch graph, we draw the schematic diagram of mechanisms, and embodies out results. Methodology of this study is better than old ones because our methodology based on Lever diagram did not need to find the usable mechanisms from the catalog of epicyclic gear train mechanisms. Thus, the new methodology simplifies the process of designing a epicyclic gear type automobile transmission.

Epicyclic-type automatic transmissions are used in automobiles widely. There are many advantages of epicyclic-type automatic transmissions. It is composed more densely, smaller and provide higher gear ratio. We can get different output speed by actuating different clutches or brakes. There are a lot of patents for epicyclic-type automatic transmissions, but most of them tends to be three degrees of freedom automatic transmissions or using embedded clutches or brakes and other complex constructions. It is a better choice if we could use relatively simple manufacturing and control of two degrees of freedom and external clutches and brakes in the same multi speeds, speed ratio of the same premise. Therefore, this study aims to propose a set of design process for two degrees of freedom parallel-connected epicyclic gear automatic transmissions and computerize the process. First, we established the lever diagram for eight-speed automatic transmissions. By decomposing lever diagrams to all possible three-point lines, then composing four different lines to get all possible eight-speed automatic transmission constructions. Then, we use direct-member -number method to get member number of all constructions. Determining the possibility of configuring clutches and brakes, excluding the construction which can¡¦t configure the clutch and brake, establish the database can be configured. Finally, we determine a speed ratio for the eight-speed automatic transmissions, excluding the constructions doesn¡¦t match the appropriate gear ratios. Drawing the diagram which comply the restriction for eight-speed automatic transmissions. Keywords: automatic transmission, lever diagram, direct-member-number method, member number, configuration of clutches

¡@An automatic transmission that is a transmission device between the engine and drive wheel, offers the vehicle while increasing and decreasing the speed mainly. Its job keeps the engine within a certain working rotational speed range.¡@Although there are many epicyclic-type automatic transmissions in production, the related design methods of lever diagram is not well developed.¡@Thus, the purpose of this research is to develop a systematic design of the epicyclic gear transmissions for automobiles with lever diagrammatical methodology.¡@First, fundamentals and gear-shifting operations of the four-speed and six-speed epicyclic-type automatic transmissions are illustrated to establish the design requirements.¡@Second, based on the basic theories of lever diagram, a procedure is applied to kinematic analysis for automatic transmission existed, and set up composite lever diagrams of 13 two-DOF seven-link epicyclic gear mechanisms and 190 two-DOF nine-link epicyclic gear mechanisms.¡@Next, a general clutching-sequence synthesis of lever diagrammatical method are proposed and illustrated. According to the limit range of lever dimensions established for four and five coaxial components, the clutching-sequences and the ranges of basic gear ratio of the feasible gear trains can be derived.¡@Finally, the planar-graph representation for arranging desired clutch and the number of teeth based on lever dimensions are applied to design six-forward speeds automatic transmission. The result of this work shows that the seven-link two-DOF epicylic gear mechanisms, and the nine-link two-DOF parallel-connected epicylic gear mechanisms could reach four- and six-forward speeds at most, respectively.