Abstract: The fuel-saving cruising technique is the momentous part of economical driving, of which the key issue is how to identify the fuel-saving operating strategies. The pulse-and-glide (PnG) cruising strategy for road vehicles with discrete gear ratio transmission is presented aiming to minimize the fuel consumption in cruising scenarios. The optimization of PnG cruising strategy naturally casts into the optimal control framework. The studied vehicle is featured with strong nonlinear fuel characteristics in engine and different dynamics in the pulse and the glide modes. Those features lead to a non-smooth switching problem, for which the multi-phase knotting technique is employed to cut this problem into two smooth sub-phases, i.e., accelerating and coasting. The pseudo-spectral method is employed to convert the differential type space state equation and integral type performance index. The associated nonlinear programming is finally solved to achieve optimal engine torque, transmission gear ratio, and switching time of pulse and glide. The optimization results show that for the studied vehicle, the PnG strategy can save fuel when cruising at middle speed as compared to the constant speed (CS) operation, and the highest fuel saving rate can reach up to 25%. The mechanism of PnG is discussed, and the fuel saving performance is verified by the real-vehicle tests.

Key words: cruising strategy, fuel economy, optimal control, pseudo-spectral method