Comprehensive Design Methodology of Input- and Output-Split Hybrid Electric Vehicles: In Search of Optimal Configuration

Despite high potentials of power-split hybrid electric vehicles (PS-HEV), their design and control problems are nontrivial. For instance, there exist 24 ways of connecting four components (two electric machines, an engine, and a vehicle wheel) with a planetary gear (PG), and more than thousand ways with two PGs. Furthermore, when PG and final drive ratios are considered design variables, finding an optimal design that fulfills both high fuel economy and short acceleration time is a challenge. In this paper, a systematic configuration searching methodology is proposed to find an optimal single PG PS-HEV configuration for both performance metrics. First, by identifying all the possible single PG configurations and reorganizing them into a compound lever design space, the performance metrics are explored in the continuous design space. Then, the designs are mapped onto the “fuel economy - acceleration performance” plane to solve the multiobjective configuration selection problem. Thus, a highly promising configuration (“o6”), which outperforms Prius design in the acceleration performance, is selected among Pareto Frontier. A case study has been conducted on a sport utility vehicle specification. The study illustrates that the performance metrics of candidate configurations change significantly, and thus, selecting a proper configuration is crucial to evoke full potential of the given powertrain components.