Investigation Into the Fuel Economy of Plug-In Hybrid Electric Vehicles With Optimized Gear-Shifting Strategies at Different Altitudes

To investigate the fuel economy of plug-in hybrid electric vehicles (PHEVs) across varying altitudes, a forward model integrating internal combustion engine (ICE) performance characteristics at different altitudes is developed. This model served as the basis for optimizing gear-shifting velocity thresholds using a genetic algorithm, tailored to altitude-specific conditions. Moreover, dynamic programming (DP) is leveraged to refine the energy management strategy (EMS) across altitudes spanning 0 to 4000 meters, evaluating its fuel-saving potential. Results demonstrate that increasing altitude adversely impacts fuel consumption for both ICE vehicles (ICEVs) and PHEVs. At 4000 meters, ICEVs exhibit a 6.30% increase in fuel consumption, while PHEVs optimized via DP show a 4.67% increase. The study highlights that altitude-dependent adjustments to gear-shifting thresholds are critical, particularly for upshifting velocity, which increases by 30.23% at 4000 meters. These optimized thresholds evolve at varying rates proportional to altitude. PHEVs consistently outperform ICEVs in fuel efficiency across all tested altitudes, achieving a maximum fuel-saving rate exceeding 26%. This superiority stems from the PHEV’s ability to harness the power of electric propulsion and optimize energy distribution to counteract the ICE’s performance degradation experienced in low-efficiency zones at elevated altitudes. The research concludes that PHEVs, particularly when equipped with an altitude-aware gear-shifting strategy, represent a robust solution for reducing fuel consumption in plateau regions.