Optimization of Gear Shifting and Torque Split for Improved Fuel Efficiency and Drivability of HEVs

Abstract

Decreasing fuel consumption and emissions in automobiles has been an active research topic in recent years. Vehicles with alternative powertrain systems, especially hybrid-electric vehicles (HEVs), have shown significant reduction in fuel consumption and emissions, and therefore have attracted many researchers to this field. The focus is usually on the development of optimal power management control methods. For parallel HEVs, the primary control variable is the torque split between the internal combustion engine and the electric motor. More advanced approaches also simultaneously search for the optimal gear number and engine on/off state, which can further reduce the fuel consumption but also complicate the problem. In the literature on HEVs, the emphasis is typically only on fuel efficiency and sometimes the emissions. The drivability of the vehicle is usually not considered during the optimization process. Furthermore, gearbox models do not usually reflect the real behavior of vehicle due to over simplification in vehicle models. This paper studies the energy management problem of parallel HEVs. Fuel consumption and drivability are optimized through an integrated optimization process by searching optimal torque split and gear number simultaneously. Intelligent filters are designed to stabilize the values of gear number to avoid frequent oscillation. The method is suitable for real-time implementation and has been tested in the simulation software Autonomie.