Design and Optimization Strategies for Multi-Gear Power Split Hybrid Systems Based on Topological Tree Graphs

Energy-efficient configuration schemes are critical to the fuel economy and performance of hybrid vehicles. Single planetary gear (PG) configurations are highly integrated, simple and reliable, but have limited fuel saving potential. To overcome these problems, a new multi-gear power split (PS) powertrain has been proposed due to its high efficiency and excellent overall performance. Only one PG and one synchronizer are required. In order to systematically explore all possible designs of multi-gear PS hybrid designs, this paper proposes a topological tree graph method: 1) inspired by the "D" matrix automatic modeling method, a new configuration tree matrix is proposed, which is used to complete the isomorphism determination, mode feature classification, and dynamics modeling; a design synthesis method for the multi-gear PS configuration is investigated; 2) a new near-optimal energy management strategy, the Improved Rapid-DP (IR-DP), is proposed for the fast computation of the near-optimal control rules for candidate designs. The computational results of IR-DP are similar to those of Dynamic Programming (DP), but the computational time is reduced by a factor of more than 1000; 3) The newly proposed scheme is comprehensively analyzed in terms of performance and fuel consumption. The case results show that the proposed design method can effectively screen out the multi-gear configuration scheme with better performance, and under different driving cycles, the fuel economy is improved by 6.12% on average and the dynamics are improved by 50%, which verifies the effectiveness of the design method proposed in this study. At the same time, this study provides a new theoretical basis for the selection and integration of the technology paths of power split and multi-gear series-parallel HEVs.