Optimizing Hybrid Powertrains for Light Duty Commercial Vehicles

Battery electric vehicles (BEV) are well-suited for many passenger vehicle applications, but high cost, short range, and long recharging times have limited their growth in commercial vehicle markets. These constraints can be eliminated with plug-in hybrid electric vehicles (PHEVs) which combine many benefits of BEVs with those of conventional vehicles. In this study, research was conducted to determine the optimal hybrid electric powertrain system for a Class 3, light duty commercial vehicle. The key technologies used in this hybrid powertrain include engine downsizing, P3 architecture hybridization, and active thermal management of aftertreatment. A vehicle cost of ownership analysis was conducted to determine the economic viability, a very important consideration for commercial vehicles. Several combinations of E-motor and battery pack sizes were evaluated during the cost analysis and the best possible configuration was determined. The resulting vehicle powertrain demonstrated ~60% reduction in CO2 over the World Harmonized Light Duty Transient Cycle (WLTC) and Federal Transient Procedure (FTP75) test cycles compared to the baseline internal combustion engine (ICE) vehicle. The NOX emissions were also evaluated during those test cycles, and the test results indicated that intermittent engine operation (associated with PHEV operation) can result in higher NOX emissions. Advanced aftertreatment thermal management strategies are required to reduce NOX emissions in PHEVs. Finally, an exhaust heater was used to reduce tailpipe NOX emissions, and a pathway for even lower NOX emissions is identified.