# Patent Analysis and Structural Synthesis of Epicyclic Gear Trains Used in Automatic Transmissions
## 3 Research of AT Patents
### Search Results  
Searching the SooPAT and the Espacenet databases results in 673 AT patents equipped with EGTs. These results are analyzed based on the search strategy. It should be indicated that 549 patents are obtained from the SooPAT database, while the other 124 patients are supplemented from the Espacenet database. Figures 4 and 5 show the annual number of patents on ATs and the share of each country distribution in patent assignees, respectively. Figure 4 indicates that the number of AT patents in every five years is increasing as time goes on, which means that more and more attention is paid to the innovation of ATs. Figure 5 indicates that about 17.8 percent of the searched patents belong to China, while most of the rest belong to developed countries, such as Germany, U.S., Japan and Korea. Figure 4: Number of annually published patents. Note: The value on the bar graph represents the number of published AT patents in the respective year intervals. Figure 3: (**a**) A double-planet EGT, (**b**) the simplified configuration, (**c**) the corresponding DBG. After patent processing, 274 DBGs and 67 basic graphs are obtained. To categorize and screen DBGs conveniently and intuitively, they are sorted into 13 groups in accordance with the mobility of the corresponding DBGs and degree of hollow vertices. Some of the patents with more than one configuration of EGTs are put into different groups. Table 1 shows the results of the conducted survey. Because of the space limitation, only part of the search results are presented here. The whole results, including DBGs and corresponding basic graphs, are presented in the Supplementary Materials. Group 1: two-DOF DBGs with hollow vertex of degree four  
For a two-DOF DBG with a hollow vertex of degree four, the corresponding EGT has one DOF and four coaxial links. There are five DBGs in the group, and they are put into two link assortments. The results are shown in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **Mobility of** \\ **DBG** \\ \end{tabular} & \begin{tabular}{c} **Degree of** \\ **Hollow Vertex** \\ \end{tabular} & \begin{tabular}{c} **Number of Link** \\ **Asortments** \\ \end{tabular} & \begin{tabular}{c} **Number of** \\ **Basic Graphs** \\ \end{tabular} & \
\begin{tabular}{c} **Number of** \\ **DBG** \\ \end{tabular} &
\begin{tabular}{c} **Number of** \\ **Patents** \\ \end{tabular} \\ \hline \multirow{4}{*}{2} & 4 & 2 & 2 & 5 & 69 \\ \cline{2-6}  & 5 & 5 & 5 & 13 & 21 \\ \cline{2-6}  & 6 & 5 & 7 & 9 & 11 \\ \cline{2-6}  & 7 & 2 & 2 & 2 & 2 \\ \cline{2-6}  & 8 & 1 & 1 & 1 & 1 \\ \hline \multirow{4}{*}{3} & 5 & 1 & 1 & 3 & 23 \\ \cline{2-6}  & 6 & 4 & 7 & 31 & 96 \\ \cline{2-6}  & 7 & 6 & 20 & 62 & 109 \\ \cline{2-6}  & 8 & 1 & 1 & 1 & 1 \\ \hline \multirow{4}{*}{4} & 7 & 2 & 2 & 10 & 89 \\ \cline{2-6}  & 8 & 4 & 13 & 105 & 258 \\ \cline{2-6}  & 9 & 3 & 3 & 9 & 5 \\ \hline
5 & 9 & 2 & 3 & 23 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Groups of the double bicolor graphs (DBGs) from the survey results. Figure 5: Comparison of some country’s share in publishing AT patent assignees. Note: the value on the bar graph represents the number of published AT patents in each country. The first and the fifth EGTs shown in Table 2 are known as the Simpson planetary mechanism and the Ravigneaux planetary mechanism, respectively. These mechanisms are widely used in the AT industry. Group 2: two-DOF DBGs with hollow vertex of degree five  
For a two-DOF DBG with a hollow vertex of degree five, the corresponding EGT has one DOF and five coaxial links. There are 13 DBGs in the group, and they are put into five link assortments. Table 3 shows some of these results.