The Advanced Electric Systems and Aerodynamics for Efficiency Improvements in Heavy Duty Trucks program (DE-FC26-04NT42189), commonly referred to as the AES program, focused on areas that will primarily benefit fuel economy and improve heat rejection while driving over the road. The AES program objectives were to: (1) Analyze, design, build, and test a cooling system that provided a minimum of 10 percent greater heat rejection in the same frontal area with no increase in parasitic fan load. (2) Realize fuel savings with advanced power management and acceleration assist by utilizing an integrated starter/generator (ISG) and energy storage devices. (3) Quantify the effect of aerodynamic drag due to the frontal shape mandated by the area required for the cooling system. The program effort consisted of modeling and designing components for optimum fuel efficiency, completing fabrication of necessary components, integrating these components into the chassis test bed, completing controls programming, and performance testing the system both on a chassis dynamometer and on the road. Emission control measures for heavy-duty engines have resulted in increased engine heat loads, thus introducing added parasitic engine cooling loads. Truck electrification, in the form of thermal management, offers technological solutions to mitigate or even neutralize the effects of this trend. Thermal control offers opportunities to avoid increases in cooling system frontal area and forestall reduced fuel economy brought about by additional aerodynamic vehicle drag. This project explored such thermal concepts by installing a 2007 engine that is compliant with current regulations and bears additional heat rejection associated with meeting these regulations. This newer engine replaced the 2002 engine from a previous project that generated less heat rejection. Advanced power management, utilizing a continuously optimized and controlled power flow between electric components, can offer additional fuel economy benefits to the heavy-duty trucking industry. Control software for power management brings added value to the power distribution and energy storage architecture on board a truck with electric accessories and an ISG. The research team has built upon a previous truck electrification project, formally, 'Parasitic Energy Loss Reduction and Enabling Technologies for Class 7/8 Trucks', DE-FC04-2000AL6701, where the fundamental concept of electrically-driven accessories replacing belt/gear-driven accessories was demonstrated on a Kenworth T2000 truck chassis. The electrical accessories, shown in Figure 1, were controlled to provide 'flow on demand' variable-speed operation and reduced parasitic engine loads for increased fuel economy. These accessories also provided solutions for main engine idle reduction in long haul trucks. The components and systems of the current project have been integrated into the same Kenworth T2000 truck platform. Reducing parasitic engine loading by decoupling accessory loads from the engine and driving them electrically has been a central concept of this project. Belt or gear-driven engine accessories, such as water pump, air conditioning compressor, or air compressor, are necessarily tied to the engine speed dictated by the current vehicle operating conditions. These conventional accessory pumps are sized to provide adequate flow or pressure at low idle or peak torque speeds, resulting in excess flow or pressure at cruising or rated speeds. The excess flow is diverted through a pressure-minimizing device such as a relief valve thereby expending energy to drive unnecessary and inefficient pump operation. This inefficiency causes an increased parasitic load to the engine, which leads to a loss of usable output power and decreased fuel economy. Controlling variable-speed electric motors to provide only the required flow or pressure of a particular accessory system can yield significant increases in fuel economy for a commercial vehicle. Motor loads at relatively high power levels (1-5 kW, or higher) can be efficiently provided current from high-efficiency generators or batteries with system voltages in the range of 250 to 360 volts DC (VDC). In the previous project, the electric accessories could be powered from one of three sources: an AC voltage source ('shore power'), an on-board diesel generator (auxiliary power unit), or an ISG located in the flywheel housing and driven by the main engine. The electric accessories and power sources, including the ISG, have remained in place for the current upgrade of the research platform vehicle. In this project, more emphasis has been placed on determining the best way to use the ISG to power the vehicle and accessories, thereby yielding additional value from existing hardware.
