Impact of road slope on most fuel-economic PnG strategies for internal-combustion-engine-driven vehicles

Abstract

The pulse and glide (PnG) strategy was proven to be a fuel-economic speed strategy in car-following and free-driving scenarios. Using this strategy the powertrain periodically switches between pulse and glide modes while the vehicle repeatedly accelerates and decelerates. The switching of the operating modes and complexities of the powertrain components lead to difficulties in system modelling and control. Furthermore, the road slope influences whether the PnG strategy is more fuel-economic than the constant speed (CS) strategy. However, the precise upper and lower limits of the road slope for PnG to be fuel-economic are yet to be studied. In this study, for widespread utilization, the problem is simplified to avoid online optimization calculation. The optimal control of a powertrain, a nonlinear hybrid system with a typical modern engine, is considered. The results demonstrated that when the road slope r ϵ (-1.8%, 4.3%), the PnG strategy is more fuel-economic than CS strategy at the same average speed. The optimal engine power, initial speed, and pulse mode duration for fuel economy are obtained for given road slopes. The results indicate that when r ≤ -1.8%, no driving power is necessary regardless of the strategy employed; when r ≥ 4.3%, the speed profiles of both strategies are similar. Therefore, the results suggest that PnG strategy is more fuel-economic than CS strategy only when the road slope is limited in a range, i.e., (-1.8%, 4.3%). Furthermore, the poor fuel-saving performance of PnG strategy in other road slopes is investigated by precise analysis of the calculation results.