Moreover, scholars focused on the configurations synthesis of ATs, which is normally used for hybrid electric vehicles. applied the concept of kinematic unit in the representation method of rotation and displacement graphs to synthesize EGTs with up to 7 links.
Then he reported all 1-DOF non-isomorphic EGTs with up to 6 links. Kamesh applied the vertex incidence polynomial and proposed a synthesis method. Rajasri proposed an approach in accordance with the hamming number and generated EGTs with up to 7 links. Moreover, Ngo and Yan generated 48 configurations and synthesized series–parallel hybrid transmissions for vehicles in the public transportation. Based on certain functional constraints, Castillo proposed a synthesis method and then he applied the proposed method to synthesize 1-DOF PGTs with up to 9 links. Then Hsu proposed a synthesis method for GKCs based on the new graph representation. Hsu and Lam presented a new graph representation for planetary gear trains (PGTs). Kim and Kwak employed a recursive method and synthesized EGTs with up to 7 links. proposed an isomorphism detection method by computing characteristic polynomial of EGTs, the genetic graph approach to synthesize non-isomorphic EGTs with up to 6 links and non-fractionated 2-DOF EGTs with up to 7 links, and the canonical graph representation of GKCs to solve the pseudo isomorphic problem. Ravisankar and Mruthyunjaya applied the graph theory and matrix to synthesize GKCs and obtained all 1-DOF EGTs with up to 4 fundamental loops. Moreover, Buchsbaum and Freudenstein and Freudenstein applied the graph theory into the synthesis process of geared kinematic chains (GKCs), and obtained epicyclic gear chains with up to 5 links. Then they synthesized gear mechanisms with one degree of freedom (DOF) with up to 8 links. Johnson and Towfigh utilized the synthetic approach of linkage type kinematic chains and proposed a synthesis method for EGTs. In order to obtain kinematic configurations of ATs, scholars have proposed synthesis methods for EGTs.
The hydraulic transmission part mainly includes a torque converter, while the mechanical transmission part includes an epicyclic gear train (EGT) and a set of shifting elements such as clutches and brakes. An epicyclic-type AT mechanism typically consists of the hydraulic transmission and the mechanical transmission parts. The first step in the conceptual design phase of the AT is the selection of kinematic configurations to provide desired gear ratios. Nowadays, the epicyclic-type ATs are the most widely applied ATs, which originates from its remarkable superiorities, including compact structure, large gear ratios, strong bearing capacity and long-life operation. In the past few decades, many innovations have been proposed in the area of automatic transmissions. Along with the continuous development of the automotive industry, the innovation and development of ATs is of great significance. This is especially more pronounced in United States, European countries and Japan. Since then, cars equipped with automatic transmissions have attracted the vast number of consumers, and quickly occupied the automotive market. The first cars equipped with the Hydra-Matic ATs were developed and put into market by General Motors in 1940s.
Moreover, the corresponding driving performance and ride comfort are significantly improved compared to cars with manual transmissions. In the automotive industry, vehicles equipped with automatic transmissions (ATs) have significant advantages, including simple operation, smooth gear shift and long service life. The prototype of an AT is manufactured and the speed test is conducted, which proves the accuracy of analysis and the feasibility of proposed mechanisms. The comparative analysis between the proposed and existing mechanisms is carried out where obtained results show that proposed mechanisms have reasonable performance and can be used in ATs. The power flow analysis is conducted, and then transmission efficiencies are calculated based on the torque method.
In order to evaluate the performance of proposed mechanisms, the lever analogy method is applied to conduct kinematic and mechanical analyses. Then four kinematic configurations are proposed for automatic transitions. In the present study, epicyclic gear trains (EGTs) are applied to investigate mechanisms of 9-speed ATs. However, finding new configurations of ATs is one of the main limitations of configuration innovation. Current research of automatic transmission (AT) mainly focuses on the improvement of driving performance, and configuration innovation is one of the main research directions.