ABSTRACT Hybrid electric vehicles have demonstrated their ability to significantly reduce fuel consumption for several medium- and heavy-duty applications. In this paper we analyze the impact on fuel economy of the hybridization of a tractor- trailer. The study is done in PSAT (Powertrain System Analysis Toolkit), which is a modeling and simulation toolkit for light- and heavy-duty vehicles developed by Argonne National Laboratory. Two hybrid configurations are taken into account, each one of them associated with a level of hybridization. The mild-hybrid truck is based on a parallel configuration with the electric machine in a starter-alternator position; this allows start/stop engine operations, a mild level of torque assist, and a limited amount of regenerative braking. The full-hybrid truck is based on a series-parallel configuration with two electric machines: one in a starter- alternator position and another one between the clutch and the gearbox. The truck can run in electric propulsion mode at low speed/low power, the engine being either shut down or running in series mode. That increases the braking energy recuperation rates. We first analyze the benefits of the two hybrid configurations on standard cycles. We then compare fuel economy results from a short standard highway cycle with a longer cruising scenario to illustrate the sensitivity of the benefits to the drive cycle. Finally, using simulation involving a grade scenario of periodical hills that we designed for this project, we show hybridization can be beneficial on hilly terrain. INTRODUCTION Hybridization can lead to significant fuel consumption reduction, which has now been demonstrated in numerous applications for buses [ 1,2,3], delivery trucks, and utility trucks [ 4]. However, little work has been published on the application of that technology to class 8 line-haul trucks, even though line-haul trucks consume about 20% of the total U.S.truck fuel use [ 5]. This work attempts to quantify the impact of line-haul truck hybridization through the use of PSAT (Powertrain System Analysis Toolkit), which is a modeling and simulation toolkit for light- and heavy-duty vehicles developed by Argonne National Laboratory [ 6, 7]. This work was done to support the National Academy of Science Committee to Assess Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles [ 8,9]. Most of the energy losses occurring in a truck come from the engine. Operating the engine more efficiently can be achieved mainly in two ways: not using the engine at all during low-efficiency operation moments, or shifting the operation point to a more efficient level - for example, by increasing the engine output and storing it in an energy storage system, or by decreasing the engine speed. The losses due to the tires and aerodynamic losses cannot be displaced by hybridization, because the vehicle follows the same cycle and requires the same amount of power regardless of the source of power. The losses due to the driveline could be in part displaced if the electric power source is put closer to the wheels (e.g., series w/o transmission, post-transmission parallel, in-hub motors), but that is not a practical solution for heavy-duty applications. The accessory load can be affected by hybridization because some of the mechanical accessories (pumps, compressors, etc.) can be replaced by electric systems, which are more efficient [ 10]. Electric accessories also allow the engine not to be used when it is inefficient - at idle, for example - and can use energy recuperated from regenerative braking. Accessory electrification is a difficult exercise to replicate in simulation because it requires knowledge of the mechanical accessory load in both conventional and hybrid cases. In this study, Accessory electrification is addressed by shifting some of the load from mechanical to electrical accessories. Modeling the Hybridization of a Class 8 Line-Haul Truck2010-01-1931 Published 10/05/2010 Dominik Kar