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By
Steven Boyd, Dustin Sheffield, Irene Berry, Erin Hissong, Kurt Johnson, and Douglas J. Nelson, Virginia Tech, Department of Mechanical Engineering
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The Hybrid Electric Vehicle Team of Virginia Tech (HEVT) is participating in the 2005-2007 Challenge X advanced vehicle technology competition, sponsored by National Instruments (NI), General Motors, the U.S. Department of Energy, and Argonne National Lab. Challenge X challenges teams to take a stock Chevy Equinox crossover SUV and transform it into a more fuel efficient, lower emissions vehicle while maintaining performance and safety.
In addition to meeting the competition goals, HEVT's principal goal is to reduce overall vehicle petroleum consumption. This goal was developed with sustainable mobility in mind. Fossil fuels like petroleum are non-renewable, and they release greenhouse gasses and other harmful emissions into the atmosphere when burned. Petroleum is also an imported resource, so reducing its use has economic benefits as well.
To meet these goals, HEVT designed and built the Equinox REVLSE, which stands for Renewable Energy Vehicle, Larsen Special Edition. The REVLSE runs on E85, which is 85% ethanol and 15% gasoline. The figure below represents the split parallel hybrid (SPA) power train of the vehicle. This architecture includes a 2.0L inline turbocharged 4-cylinder engine, a small belted alternator starter (BAS) motor coupled to the engine, a large (52 kW peak) rear traction motor (RTM) powering the rear wheels, and a 336V nickel-metal- hydride (NiMH) battery pack.
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Vehicle control strategy
The overall control strategy is to select a vehicle mode and command the engine and electric motors in a way that meets both competition and HEVT defined vehicle technical specifications (VTS). The table below outlines the specifications selected during the Challenge X vehicle design process.
Satisfying the increased fuel economy goal of over 30 miles per gallon gasoline equivalent (mpgge) requires maximizing vehicle efficiency. Meeting performance specs such as initial vehicle movement to 30 miles per hour (IVM-30) or IVM-60 times requires maximum vehicle power output. The control strategy must use all vehicle components efficiently and focus on when and how to use the engine versus electric motors. In addition, the control strategy must be transparent to the driver, flexible to meet changes during the development process, and, most importantly, safe.
To maintain vehicle safety, the control system should monitor all the warnings, indications, and faults from each component and act accordingly. For example, when the battery pack is overheating, the control strategy should limit all current withdraw from the battery pack and possibly disconnect the high voltage lines. The control strategy should also limit propulsion when the engine is overheating.
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