An Analysis of the Tradeoff Between Fuel Consumption and Ride Comfort for the Pulse and Glide Driving Strategy

Abstract

Pulse and glide (PnG) is a driving strategy that controls vehicles in a more fuel-efficient way than driving at a constant speed does. It can be applied by the driver or, which is more likely, by an automated system with autonomy level one or higher. During the pulse phase, the vehicle is accelerated to operate the combustion engine and transmission at higher efficiency. During the following glide phase, the vehicle decelerates and the engine is decoupled from the drive train. The optimal pulse and glide strategy – as addressed in previous studies – implies high acceleration values and abrupt transitions between pulse and glide, which both degrade the ride comfort. A driveability study on PnG conducted recently identified that the acceleration, the jerk during the transitions and the duration of the glide phase have to be limited to reach the desired level of ride comfort. Thresholds have been derived for a level-eight calibration, i.e. a PnG operation that is noticeable only to skeptical customers. We use the results of the study to also provide thresholds for a level-seven calibration, i.e. a PnG operation that is noticeable to all customers without being disturbing. Subsequently, we establish a correlation between ride comfort and fuel consumption by comparing the fuel savings of three different driveability calibrations: level eight, level seven and a calibration without driveability constraints. The simulations are performed for a D-segment vehicle and two different gasoline engines. With reference to constant speed, the fuel savings of the level-seven calibration are larger than 30% below 40 km/h, decreasing gradually with increasing speed. They are around ten percent higher than those of the level-eight calibration and only a few percent lower than those of a PnG operation without driveability constraints. Hence, the level-seven calibration can nearly exploit the maximal fuel-saving potential of PnG, and, as it is not disturbing, should be considered for practical applications of PnG. The PnG strategy can be applied to any vehicle equipped with a combustion engine that features the engine-off functionality, which is the case for mild and full hybrids and for some micro hybrids. However, considering that the benefit of PnG increases with increasing engine size, the fuel saving potential of PnG is highest for micro and mild hybrids as these vehicles are commonly equipped with larger engines than full hybrids.