Fuel Economy Analysis of Periodic Cruise Control Strategies for Power-Split HEVs at Medium and Low Speed

Hybridization of vehicles is considered as the most promising technology for automakers and researchers, facing the challenge of optimizing both the fuel economy and emission of the road transport. Extensive studies have been performed on power-split hybrid electric vehicles (PS-HEVs). Despite of the fact that their excellent fuel economy performance in city driving conditions has been witnessed, a bottle neck for further improving the fuel economy of PS-HEVs has been encountered due to the inherent engine-generator-motor power circulation of the power-split system under medium-low speed cruising scenarios. Due to the special mechanical constraints of the power-split device (PSD), the conventional periodic cruising strategy like Pulse and Glide cannot be applied to PS-HEVs directly. To further realize the fuel economy potential of PS-HEVs, in this paper, two different periodic cruising strategies are presented, namely three-phase strategy and two-phase strategy, and their optimized output power in each phase are identified by solving an optimization problem. By comparing with a constant speed cruising strategy, a significant improvement can be observed and the effectiveness of the proposed cruising strategies is validated. Finally, the underlying fuel-saving mechanism of the periodic strategies is discussed.