Systematic Design and Optimization Method of Multimode Hybrid Electric Vehicles Based on Equivalent Tree Graph

Multimode hybrid electric vehicles (HEVs) have been widely applied due to its high efficiency and excellent overall performance. However, the introduction of multimode HEVs makes it difficult to choose reasonable design factors (architectures, component parameters, and control strategies) and determine correct mode shift rules, which undoubtedly enhances design complexity. To improve the design efficiency and reduce screen difficulty of optimal multimode configurations, a systematic design method is proposed to generate, screen, and optimize multimode HEVs with a single planetary gear. Based on equivalent tree graph method, the novel architectures are first generated. Then, considering mode shift rules and component parameters, requirements of speed and torque in corresponding main mode and minimum shift rule graph of working modes are taken as constraints to complete configuration screening. Finally, the equivalent consumption minimization strategy considering the proposed mode shift rules is put forward to evaluate and optimize energy management. The numerical results show that fuel economy of optimized configurations is improved by at least 22.1%, which proves the effectiveness of proposed systematic design method. Furthermore, it reveals that the multimode configuration can achieve better fuel economy when adopting the appropriate mode shift rule and designing the right arrangement and number of clutches and brakes.