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Manufacturers of medium- and heavy-duty engines and transmissions continually try to improve the efficiency of their components; however, it is becoming more difficult and costly to improve those technologies, and a new approach is needed to find efficiency gains in other vehicle systems. For example, most ancillary loads on the engines in medium- and heavy-duty trucks, both at idle and under driving conditions, are generated by accessories that are designed to address worst-case scenarios or to meet the minimum requirements at one operating point. Improvements to those systems would improve overall powertrain efficiency. The objectives of this cooperative research and development agreement (CRADA) between Oak Ridge National Laboratory (ORNL) and Cummins Inc. (CRADA No. NFE-13-04402) are (1) to analytically verify novel accessory electrification /hybridization approaches for medium- and heavy-duty trucks and (2) to experimentally validate prototype hardware utilizing the ORNL Vehicle Systems Integration Laboratory and the Cummins T112 test vehicle. Hybrid powertrains can provide significant reductions in fuel consumption, criteria pollutants, and greenhouse gas emissions. They provide these benefits by meeting vehicle power requirements in more flexible and optimal ways than a conventional powertrain (e.g., capture and use of braking energy, optimization of engine and component operation). Realizing the full potential of hybridization requires management of all vehicle power demands, including accessory loads. One of the major petroleum-reduction opportunities of hybridization is to shut the engine down when …