Designing Multi-Mode Power Split Hybrid Electric Vehicles Using the Hierarchical Topological Graph Theory

Power split hybrid electric vehicles (PS-HEVs) dominate the US and Japanese HEV market because of their superior fuel economy and drivability. In recent years, multi-mode PS-HEVs are offered by Toyota and GM. With multiple modes, it is possible for PS-HEVs to have both good launching/towing performance and fuel economy. Multiple modes are achieved by adding clutches or brakes. However, the corresponding design space can be quite large. To expedite the design process, a hierarchical topological graph theory approach is developed to systematically design a multi-mode PS-HEV with two planetary gear sets (PGSs). The process consists of three steps: 1) model the hybrid powertrain, 2) generate the multi-mode designs with specific modes, and 3) evaluate the performance of design candidates. In the performance screening process, designs are examined using the dynamic programming (DP) algorithm to evaluate their acceleration performance (0-100 km/h); and then a rapid dynamic programming (Rapid-DP) approach is used to compute their fuel economy under a specific driving cycle. Designs that pass the screening will then be retained as final vehicle designs. This design process ensures that the best designs are found and used.