An Optimal Gear Shifting Strategy for Minimizing Fuel Consumption Based on Engine Optimum Operation Line

The increasing numbers of vehicles with limited fossil fuel resources, on the one hand, and the growing level of stringent regulations on exhaust emissions, on the other hand, have galvanized automotive industries and researchers into developing solutions for more efficient vehicles. Notwithstanding the recent developments in powertrain technologies, driving behavior is still an important attribute in lowering fuel consumption. Gear shifting strategy is a staple aspect of driving behavior that affects fuel consumption and engine emissions to a large extent in both manual and automated transmission systems. According to the definition of Optimum Operating Line (OOL), this article intends to illustrate that the closer the engine operating points to the OOL, the more efficient the driving. An optimal gear-shifting strategy is presented to minimize fuel consumption and number of gear shifts while maximizing drivability in the new European driving cycle (NEDC). In order to limit the engine operating region close to the OOL, a multi-objective grid search method is used to design the two square-root-like curves (two shifting thresholds), on both sides of the OOL, in the engine Brake Specific Fuel Consumption (BSFC) map. The results show a 4% reduction in fuel consumption and a 6% increase in the driving performance when using the square-root-like shifting boundaries compared with using RPM-constant shifting boundaries.