In hybrid electric vehicles with power-split configurations, the engine can be decoupled\nfrom the wheel and operated with improved fuel economy, while the entire efficiency of the\npowertrain is affected by the circular electric power flow. Two planetary gear (2-PG) sets with\nadding brakes/clutches, namely a type of four shaft elelctric continuously variable transmission\n(ECVT) can provide multi-mode operation for the powertrain and extend the efficient area. First,\na conventional 2-PG AT (Automatic Transmission) architecture is investigated. By analyzing and\ncomparing the connection and operating modes based on the kinematic relationship and lever analogy,\na feasible four-shaft ECVT architecture with two brakes and two simplified versions are picked. To\nmake a trade-off between fuel economy and configuration complexity, an instantaneous optimal\ncontrol strategy based on the equivalent consumption minimization strategy (ECMS) concept is then\ndeveloped and employed as the unified optimization method in the simulations of three different\nconfigurations. Finally, the simulation results show that the simplified versions are suboptimal\nsets and the fuel economy is sacrificed by the limits of different modes. From the viewpoint\nof concept design, a multi-mode power-split configuration is more suitable for hybrid electric\nvehicles. This research applied a systematic methodology from concept design to energy management\noptimization, which can provide the guidelines for researchers to select a suitable multi-mode\npower-split hybrid powertrain.
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