Technical analysis and fuel consumption evaluation of 48-V mild hybrid powertrain systems in passenger vehicle

Abstract

This thesis examines the architecture, operation, and fuel-saving potential of 48-V mild hybrid technology in passenger vehicles. The objective of the study is to analyse how low-voltage electrification enhances the efficiency of internal combustion engine powertrains and to quantify the resulting reduction in fuel consumption compared with conventional internal combustion engine vehicles and plug-in hybrid electric vehicles. The work combines a theoretical review of hybrid vehicle architectures with analytical modelling of vehicle tractive-force requirement, energy consumption, and powertrain efficiency. The dual-voltage 48-V system, including the electric machine, inverter, lithium-ion battery, and bidirectional DC–DC converter, is analysed from a system perspective. The main operating modes—regenerative braking, torque assist, start–stop operation, load point shifting, and engine-off coasting—are examined in terms of energy flow and efficiency improvement. A simplified fuel-consumption model is developed to compare three vehicle configurations under representative driving assumptions. The results indicate that 48-V mild hybrid systems can reduce fuel consumption by approximately 5–15% compared with conventional internal combustion engine vehicles, primarily due to regenerative energy recovery and improved engine load management during transient operation. Plug-in hybrid systems achieve larger reductions when operating in electric mode, but require higher system complexity and battery capacity. The findings demonstrate that 48-V mild hybrid technology provides a technically effective and economically balanced solution for improving vehicle efficiency while remaining within low-voltage safety limits. The technology, therefore, represents a practical transitional step toward higher levels of vehicle electrification.