Abstract
Powertrain configurations described with elementary (physical) levers can intuitively depict the connections between planetary gear (PG) shafts and powertrain components. However, finding optimal compound-split hybrid configurations using the elementary lever is practically impossible due to the large design space. In fact, each of the existing 252 compound-split configurations has three design variables: two PG gear ratios and a final drive gear ratio. In this paper, a compound (virtual) lever-based design methodology that eliminates redundant elementary lever designs is proposed to enable a full compound-split hybrid electric vehicles design domain search. The performance metrics were assessed in the compound lever design space. Later, the designs were converted back to elementary lever configurations by applying a design space conversion map, and their performance metrics were plotted on a fuel economy versus acceleration performance plane to compare the potential of the 252 compound-split configurations. Finally, an optimal configuration that can reach 0–160 kph in 15.36 sec, which is 5.90 sec faster than that of the Prius configuration, while maintaining a competitive fuel economy, was selected. The proposed method revealed that there are still many configurations that are potentially better than the commercially available split hybrids.
Highlights
Power-split hybrids, in which the transmission is replaced by electric machines and a power split device (e.g. planetary gear set (PG)), are suitable for both hybrid electric vehicles (HEV) and plug-in HEV because they provide high traction power for the electric vehicle (EV) mode and can potentially achieve high acceleration performance as well as good fuel economy if the system is properly designed [1]
This paper proposed a compound lever-based split hybrid configuration search methodology that enables the full design domain search with dramatically reduced computational load
Both fuel economy and acceleration time are assessed in the virtual compound lever design space rather than the physical design space of the compound-split HEVs in order to avoid redundant performance assessments and to observe the performance trends in the abstracted design space
Summary
Power-split hybrids, in which the transmission is replaced by electric machines (or motor/generators) and a power split device (e.g. planetary gear set (PG)), are suitable for both hybrid electric vehicles (HEV) and plug-in HEV because they provide high traction power for the electric vehicle (EV) mode and can potentially achieve high acceleration performance as well as good fuel economy if the system is properly designed [1]. To reduce the computational load by eliminating the redundant physical designs, the fuel economy and the acceleration performance of compound-split HEVs are evaluated in the compound lever design space. Where r and K refer to the wheel radius and the final drive ratio, respectively, and f0, f1, and f2 are the coast-down coefficients Both the fuel economy and the acceleration performance of all the compound-split HEV designs are evaluated by adjusting α, β, and K in Eq (4). The number of POIs per single FDratio is 33∗33 = 1,089, and the fuel economy and the acceleration performance are assessed for the total number of 5,445 POIs (FDratio = 2.5 : 0.5 : 4.5) to find optimal compound-split configurations This is a dramatically reduced number compared to the 31,500 POIs (SRratio1/2 = 0.3 : 0.1 : 0.7, FDratio = 2.5 : 0.5 : 4.5 for each of 252 configurations) of the elementary lever design space. A multi-objective configuration selection methodology is needed to find optimal compound-split HEV designs that simultaneously maximize and balance both the FE and AP
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