Design methodology of input- and output-split hybrid electric vehicles with a speed reduction gear for selecting an optimal configuration

Abstract

Recently produced power-split hybrid electric vehicles (PS-HEV), such as Toyota Prius 3rd/4th generation and the GM Volt 2nd generation, employ a speed reduction gear (SRG) to enhance their acceleration performance (AP). The impact and full potentials of this additional gear on AP and FE, however, have not yet been demonstrated due to a vast design space. The design space of the PS-HEV is vast when planetary gear configurations and the design parameters, such as a planetary gear ratio, an SRG ratio, and a final drive ratio, are considered. In this paper, a systematic design methodology of input- and output-split HEVs with an SRG is proposed for selecting an optimal configuration. First, a simplified-lever is used to eliminate the redundancy completely in a physical design space and solve the existing the design space problem. Fuel economy (FE) and AP for the entire design space of input- and output-split HEVs with an SRG are evaluated using the simplified-lever. The simplified-lever, however, cannot be directly implemented, and thus, a model inversion from simplified-lever to physical design space is also proposed to realize the optimal configurations found from the simplified-lever design space. The simulation result shows that adding an SRG for the input- and output-split HEVs can improve FE and AP. An additional SRG for the EM of ‘i1 (Prius 2nd generation configuration)’ enhances the potential FE and AP. Toyota has already been using an SRG in front of the EM. Among all the input and output-split HEVs, ‘o6 (split hybrid mode of the Volt 1st generation configuration with switched two electric machines) + SRG’ shows the best FE and AP. Furthermore, the model inversion is applied to realize the optimal configuration of ‘o6 + SRG’ as an example.