Rule-Based Power Management Strategy of Electric-Hydraulic Hybrid Vehicles: Case Study of a Class 8 Heavy-Duty Truck 2022-01-0736

Mobility in the automotive and transportation sectors has been experiencing a period of unprecedented evolution. A growing need for efficient, clean and safe mobility has increased momentum toward sustainable technologies in these sectors. Toward this end, battery electric vehicles have drawn keen interest and their market share is expected to grow significantly in the coming years, especially in light-duty applications such as passenger cars. Although the battery electric vehicles feature high performance and zero tailpipe emission characteristics, economic and technical issues such as battery cost, driving range, recharging time and infrastructure remain main hurdles that need to be fully addressed. In particular, the low power density of the battery limits its broad adoption in heavy-duty applications such as class 8 semi-trailer trucks due to the required size and weight of the battery and electric motor. Motivated by the high power density, low cost and potential for improving energy efficiency through regenerative braking of a hydraulic pump and accumulator, this work numerically investigates the application of an electric-hydraulic hybrid powertrain to heavy-duty class 8 semi-trailer trucks. A simulation model which includes an electric motor/generator, lithium-ion battery, hydraulic pump/motor and hydraulic accumulator is developed. Using the simulation model, a rule-based power management strategy is developed to benefit from the different characteristics of the electric and hydraulic power sources and demonstrated with the numerical simulation of different driving cycles. The simulation results reveal that hybridization with the hydraulic pump/motor and accumulator can improve overall electric energy conversion efficiency by operating the electric motor in high energy efficiency zones, storing kinetic energy during deceleration using hydraulic regenerative braking, and reusing the regenerated energy during heavy acceleration at low speed. In addition, the peak electric power and total electric energy consumption are significantly reduced. Such reduced electric stress offers significant benefits including lower vehicle cost by reducing battery capacity and longer battery service life by reducing cyclic charging and discharging of the battery.