Design Of Ravigneaux-type Epicyclic Gear Mechanism For Eight-speed Automatic Transmission

Epicyclic gear Mechanisms(EGMs) are wildly applied in machine fabrication, automobile,marine, aerospace and aviation in the advance of its smaller volume and better drivingperfermance. The Ravigneaux-type EGM is the typical construction in the field of automatictransmissions (ATs). The technologies of ATs are dominated by multinational AT corporationsfor the sake of the patents. This situation restrains the development in research andmanufacture of ATs in our country. If we want to turn the tide, we must develop technologiesby ourselves. We are disadvantaged in the research of ATs and the theories in design of ATsare uncompleted, specially in the synthesis of clutching sequences and the optimal synthesisfor the number of teeth on gears. In this research, the main theory is based on the method oflever analogy and planar-graph. This theory can yield the feasible solution of theRavigneaux-type EGMs clutching sequences and reduce the quantity of inappropriatesolutions efficiently. The gear tooth number can be calculated by the exhaustive searchingmethod in the restraint conditions. By the theory and the gear tooth number, we can get thefeasible transmission ratio. The systematic design theory of Ravigneaux-type EGM for ATs isestablished.First, the research is the introduction of the principle of the Ravigneaux-type EGM andthe relative analytical theory. Second, sixteen planetary gear structures that base on the fourspeed ATs in used and previous related patents are synthesized and three feasible structures ofthem that can be developed into eight-speed ATs have been selected. Third, an analyticaltheory was developed and applied to synthesize eight-speed Ravigneaux-type ATs clutchingsequences and clutch-to-clutch shifts configurations. According to this analytical theory, eightfeasible clutching sequences are generated which are consisted of three clutch-to-clutch shiftsconfigurations. After that, the irrelevant variations are reduced and the restraint conditions aresimplified by analyzing the relationship between the teeth ratio of the EGM and the desiredspeed ratios of AT. The nine valid ATs with feasible decreasing speed ratios for each clutchingsequence are carried out by the exhaustive searching method in the restraint conditions ofEGMs. Finally, the nine valid ATs are evaluated and optimized on the basis of the basic gear ratios and transmission efficiencies. In this research nine-link2-DOF Ravigneaux-type ATsare yielded, which are composed by four under drive, a direct drive, three over drive and areverse drive.