Comparison of multi-mode hybrid powertrains with multiple planetary gears

Most hybrid electric vehicles (HEVs) currently sold are power-split HEVs that use single, double or occasionally even multiple planetary gear (PG) sets to connect their powertrain elements. Adding PG sets can provide more design flexibility; however, it also increases system complexity and cost. This paper presents a comparative study of hybrid powertrains with different numbers of PG sets, which we term configurations. The analysis of different configuration types is investigated both qualitatively and quantitatively. In the qualitative analysis, the performances of operating modes for different configurations are compared, in terms of mode number, normalized efficiency, and maximum output torque. The quantitative approach compares the designs of different configurations; the fuel economy and acceleration performance of all superior designs are evaluated to make the comparison iconic. The results show that triple-PG hybrids do not have significant fuel economy improvement compared with double-PG hybrids, but they achieve a dramatic improvement in acceleration performance; this can be beneficial for sport utility vehicles (SUVs), light trucks, and buses. For cost consideration, it is suggested that passenger cars adopt double-PG hybrid powertrains.