Driving eco-smart SUVs

  • 24-Jun-2008 07:39 EDT
X in Maryland.jpg
­Challenge X's first year had students focused on modeling, simulation, and testing. Each team received an SUV in the event's second year. Year three included time at GM's Milford Proving Ground, and the final year spotlighted vehicle reliability, dependability, and consumer appeal with a stopover outside the science center in Baltimore, MD (shown).­

Transform a Chevrolet Equinox into a pollution-weakling. That was the essence of the General Motors/U.S. Department of Energy-sponsored Challenge X competition involving 17 college teams from the U.S. and Canada.

After a four-year engineering odyssey, the final prove-out spotlighted an on-road trek from New York City to Washington D.C. in May. During a stopover in Baltimore, Maryland, the revamped 2005 Equinox SUVs were parked outside the city's science center, presenting hundreds of passersby the opportunity to learn firsthand from the undergraduate and graduate engineering students the nuances of the various energy-smart technologies used on each SUV.

The University of California-Davis team had Challenge X's lone plug-in hybrid-electric vehicle. Instead of the stock vehicle's 3.4-L V6, the engine compartment had a 100-hp electric motor, a 90-hp (67-kW) 1.5-L Atkinson cycle flex-fuel spark ignition engine, and a continuously variable transmission custom-designed by U of C-Davis student engineers.

­Stowed under the cargo area floor was a 90-hp electric motor, and a 346-V/16-kW·h lithium-ion battery pack was packaged between the frame rails.

"Passenger space and cargo space have not been encumbered. This vehicle has the same ground clearance as the stock vehicle," said Team Leader Terrence Williams, a PhD candidate studying automotive system controls via the school's mechanical and aeronautical engineering department.

Using only electric power, the vehicle was capable of going a distance of up to 45 mi (72 km). "Our simulations showed 39 mpg gas equivalent with charge sustaining, but during the on-road portion of the competition we were unable to confirm that because of a malfunction," said Williams.

The University of Michigan created the competition's only series hydraulic hybrid. That unique design used a 1.9-L General Motors direct-injected turbodiesel engine to power a bent-axis pump, which stored the resulting charge in a nitrogen bladder accumulator. A 55-cm3/rev hydraulic motor supplied power to the wheels. U of M's hybrid entry, however, was not ready for primetime because the electronic control unit was stuck in limp-home mode.

"For this car, the limp-home mode essentially means that the fuel is cut off when the engine reaches about 3500 rpm," said team member and automotive systems engineering graduate student Deepak Frank. "We were unable to implement the solution (a new ECU) because the device arrived only two days before the start of the competition."

Success did materialize on the jobs scene as "several former U of M students who were involved with the Challenge X project are now working professionally with various companies to develop hybrid hydraulic delivery trucks. So from that aspect, the competition was very valuable to the students," said Bruno Vanzieleghem, one of the team's faculty advisors.

The University of Tulsa opted for a parallel through-the-road hybrid with supplemental power provided by a removable HTUGo skid supporting a 1.2-kW Ballard Nexa fuel cell. "The hydrogen skid provides the vehicle with 120-V ac on demand. The 56 volts coming from the fuel cell goes into an inverter where it converts to 120-V ac," said Matthew Walker, the freshman team member in charge of developing the control system for the hydrogen skid.

Hydrogen was the star power source for the lone Canadian participants in the competition. "We're the only team using a fuel cell as its primary energy source," said Alex Koch, the University of Waterloo's leader for mechanical technologies.

A 65-kW Hydrogenics proton-exchange-membrane fuel cell converted the hydrogen, which was stored in a cargo bay-located tank capable of holding 4 kg (8.8 lb) at 5000 psi (34.5 MPa). The resulting energy was used to drive two 67-kW Ballard electric motors. When more power was needed, a 60-kW/288-V NiMH Cobasys battery pack handled the demand. The team earned the gold medal in the drivability event, which used AVL Drive to evaluate the vehicles' drive quality.

The next challenge for the University of Waterloo and 16 other college teams from the U.S. and Canada, including seven schools that did not compete in Challenge X, is EcoCAR. The competition, sponsored by the U.S. Department of Energy, GM, and Natural Resources Canada, starts in the fall of 2008. Teams will be challenged with re-engineering a Saturn Vue to achieve improved fuel economy and reduced greenhouse gas emissions without compromising the vehicle's performance or consumer appeal.

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