Energy optimization for the mild hybrid electric vehicle with CVT under driving conditions

Abstract

For a hybrid electric vehicle (HEV) equipped with CVT (Continuously variable transmission), it's an important question in developing vehicle energy management that how to make engine, motor and CVT coordinate well to maximize the overall efficiency of the hybrid system. According to this problem, an energy optimization strategy for a CVT mild HEV is proposed which takes the maximum system efficiency as optimization objective and vehicle speed, accelerator pedal degree and battery SOC as state variables while the motor torque and CVT ratio as control variables. Based on a comprehensive consideration of the driver's actual operation, driving demand and efficiencies of key components, the strategy proposed in this paper realizes the overall efficiency's maximization and gets the optimal output torque of motor and the CVT target ratio under different driving conditions. The energy management strategy based on this optimization is tested by a self-established forward simulation model, showing that compared with the proto vehicle the equivalent 100 km fuel consumption is reduced by 26.4 % under NEDC driving cycle. © 2013 Springer-Verlag.