Nowadays, power-split hybrid electric vehicles (PS-HEV) are very popular mainly thanks to the success of Toyota Prius. Despite their superior performance, the design and control of PS-HEVs are non-trivial due to the large number of design candidates and the complex control problems. For instance, there exist twelve ways to connect the four components (two motor/generators, an engine, and a driving wheel) with a single planetary gear-set (PG), and the number increases to 1152 possible configurations when using two PGs. Moreover, if we consider the final drive (FD) and PG ratios as design variables, finding the best design becomes intractable. In this study, we introduce a simple yet powerful way to find the optimal designs of single PG PS-HEVs. The suggested method consists of two parts — full-load analysis and light-load analysis. The full-load analysis computes 0–100kph times to evaluate acceleration performance of all designs using instantaneous optimization approach. The light-load analysis evaluates the fuel economy of selected designs (designs with acceptable acceleration performance) using equivalent consumption minimization strategy (ECMS). Note that the sun-to-ring (SR) gear ratio and the FD ratio are considered design variables, and thus one can see how fuel economy and acceleration performance of each configuration vary with SR and FD ratios. Based on these analyses, the optimal design that balances full-load and light-load performances can be selected.

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