In-Use and Vehicle Dynamometer Evaluation and Comparison of Class 7 Hybrid Electric and Conventional Diesel Delivery Trucks

This study compared fuel economy and emissions between heavy-duty hybrid electric vehicles (HEVs) and equivalent conventional diesel vehicles. In-use field data were collected from daily fleet operations carried out at a FedEx facility in California on six HEV and six conventional 2010 Freightliner M2-106 straight box trucks. Field data collection primarily focused on route assessment and vehicle fuel consumption over a six-month period. Chassis dynamometer testing was also carried out on one conventional vehicle and one HEV to determine differences in fuel consumption and emissions. Route data from the field study was analyzed to determine the selection of dynamometer test cycles. From this analysis, the New York Composite (NYComp), Hybrid Truck Users Forum Class 6 (HTUF 6), and California Air Resource Board (CARB) Heavy Heavy-Duty Diesel Truck (HHDDT) drive cycles were chosen. The HEV showed 31% better fuel economy on the NYComp cycle, 25% better on the HTUF 6 cycle and 4% worse on the CARB HHDDT cycle when compared to the conventional vehicle. The in-use field data indicates that the HEVs had around 16% better fuel economy than the conventional vehicles. Dynamometer testing also showed that the HEV generally emitted higher levels of nitric oxides than the conventional vehicle over the drive cycles, up to 77% higher on the NYComp cycle (though this may at least in part be attributed to the different engine certification levels in the vehicles tested). The conventional vehicle was found to accelerate up to freeway speeds over ten seconds faster than the HEV. CITATION: Burton, J., Walkowicz, K., Sindler, P., and Duran, A., "In-Use and Vehicle Dynamometer Evaluation and Comparison of Class 7 Hybrid Electric and Conventional Diesel Delivery Trucks," SAE Int. J. Commer. Veh. 6(2):2013, doi: 10.4271/2013-01-2468. then using that energy to assist the powertrain during INTRODUCTION accelerations. These systems still rely on the traditional Companies that rely on heavy-duty fleet vehicles are powertrain of the vehicle, but complement it with additional continually investigating ways to improve the performance of power through the electric motor so that the demand on the their vehicles, whether it is better fuel economy, enhanced petroleum-driven power plant is decreased. durability, or improved air quality by reducing harmful The main purpose of this study was to evaluate and vehicle emissions. Hybrid electric vehicles (HEVs) play an compare fuel economy and emissions of HEVs with their important role in the strategy to reduce fuel consumption in conventional diesel truck counterparts of the equivalent the mediumand heavy-duty trucking industry markets. capabilities. Because heavy-duty hybrid electric powertrain technology is relatively new, there is still a need for investigations into the BACKGROUND AND METHODS overall performance of these systems in vehicles. FedEx Express recently purchased and implemented Mediumand heavy-duty parallel hybrid electric several new HEV and conventional powertrain straight trucks drivetrains typically consist of electricity storage in batteries into their fleets in California. The National Renewable and use of electrical motors integrated into traditional Energy Laboratory (NREL) worked in conjunction with powertrain systems. These HEV systems offer fuel economy FedEx Express to perform an in-use field and dynamometer benefits by recapturing energy via regenerative braking and Burton et al / SAE Int. J. Commer. Veh. / Volume 6, Issue 2(October 2013) evaluation of many of the vehicles from this new fleet. The field evaluation took place in Ontario, California. In-Use Field Evaluation Setup Vehicles with 2010 emissions certification levels were evaluated in the field. These vehicles have diesel aftertreatment technology including diesel oxidation catalysts (DOCs), diesel particulate filters (DPFs), and selective catalytic reduction (SCR) systems in the exhaust. The Ontario, California, FedEx fleet included several 2010 Freightliner M2-106 Class 7 straight trucks that met these criteria. The fleet also included one HEV of the same make and model. Ontario was an ideal location for this evaluation as the fleet there operates over varying types of duty cycles, from city to highway driving. Isaac Instruments DRU900/908 data loggers were deployed on 12 of the original Ontario vehicles in the fleet, including the one HEV, for three weeks. They recorded J1939 controller area network (CAN) bus communication and global positioning system (GPS) data as the FedEx drivers worked their usual daily routes. This data was then analyzed for drive cycle analysis, as described in the DriveTM Analysis section later. After the drive cycle analysis was performed, five additional Freightliner M2-106s HEVs were transferred to Ontario from another FedEx Express location, making a total of six HEVs in the fleet. These six HEVs, in addition to six equivalent conventional diesel vehicles of the same make and model, were included in a six-month performance evaluation over routes selected for their representative kinetic intensities (KI) [1]. The drivers of these 12 vehicles were asked to complete fuel logs so that fuel economy comparisons could be made. Other maintenance records of vehicles included in the study were kept as well. Also, during the six-month study period, one conventional vehicle and one HEV recorded operational data with the Isaac loggers.