AWD hybrid turbodiesel? Check. NiMH batteries? Check.

Photo: Brenda Priddy

Just a few months ago, there was a perfectly good V6 gasoline engine in there.

The six top-finishing vehicles shown to the press in Mesa weren't quite ready for the showroom. Their proud but slightly glassy-eyed creators, each team in matching polo shirts, were refreshingly candid about how much was left to do—and about the complexity of the design challenges they had faced.

If the most common solutions among the 17 teams were averaged, you would end up with an Equinox retrofitted with a 1.9-liter turbodiesel running on B20 biodiesel, driving the front wheels through a six-speed manual or automatic transmission, mated to a parallel hybrid system including a nickel-metal-hydride (NiMH) battery pack and an electric motor driving the rear wheels.

Variations within this theme showed each team's tradeoffs in design and adaptation. The University of Wisconsin at Madison team replaced the Equinox rear differential with a dual-output 45-kW integrated electric motor and transaxle with attached control electronics. This required them to re-engineer the rear floor and subframe and to fabricate new suspension components.

The Ohio State University team, on the other hand, chose a single-output 67-kW motor to drive the rear wheels through the standard differential. No rear suspension work was needed, but they had to fit the motor into an enlarged transmission tunnel—ending up with a driveshaft angled so steeply that the life of its universal joints was a concern.

While a turbodiesel parallel hybrid powertrain with battery pack was the de facto standard, some more unusual choices stood out. West Virginia University, for instance, dispensed with batteries altogether and used a 750-kilojoule ultracapacitor for energy storage. Since diesels have no throttling losses, recapturing braking energy requires high power adsorption rather than energy storage, making an ultracapacitor's high power density appealing. They also chose individual wheel motors to eliminate gearing losses. Their inability to interpret fault codes in the diesel's engine-control unit until the week of the competition, however, kept them from diagnosing signals that caused their engine to default to a self-protective low-power-output mode—giving them ninth place out of 17 overall.

Hydraulics and plug-ins and mules, oh my!

Photo: Brenda Priddy

The University of Waterloo's hydrogen tank tends to interfere with load space.

Another unique solution was the “plug-in” parallel hybrid created by the University of California at Davis team. They mated a 1.5-liter Atkinson-cycle motor from a 2004 Toyota running on E85 (85 percent ethanol, 15 percent gasoline) to a Nissan continuously variable transmission. Energy was stored both in a 350V lithium ion battery pack and a 10 kW hydrogen fuel cell. Their claimed range in all-electric mode was 50 miles at up to 60 miles per hour (97 km/h), after which the vehicle operated in conventional hybrid mode with power drawn from the engine and batteries according to need, and regeneration on braking to charge the batteries. And, of course, it could be plugged into household current at night to recharge as well.

Even more experimental was the University of Michigan's decision to use hydraulics for energy storage. Like many others, they used the 1.9-liter GM turbodiesel. Unlike any other team, they used it not to power the wheels but to drive a variable-displacement hydraulic pump, rated at up to 80 cubic centimeters per revolution (cc/rev) at 2200 revolutions per minute (rpm). The engine and pump charged a high-pressure—5000 to 18 000 pounds per square inch (psi [34 474 to 124 106 kilopascals, kPa])—accumulator coupled, in parallel to a low-pressure (300 to 800 psi [2068 to 5516 kPa]) accumulator, across two hydraulic pump/motors rated up to 55 cc/rev at 2500 rpm, one on each axle.

The University of Waterloo made the most ambitious choice of all: a series fuel-cell hybrid, with a 65-kW fuel cell and a 336 volt NiMH battery pack running two 67-kW AC induction motors. In doing so, Waterloo won the “Spirit of the Challenge” award (plus honors for community outreach and best Web site [http://www.uwaft.com]). Their vehicle was on display with the six top finishers, having been deemed not quite reliable enough to risk stranding members of the press deep in the desert.

Photo: Brenda Priddy

The University of Pennsylvania's entry has some tidying left before it's ready for the showroom ....

None of these off-the-beaten-track choices garnered overall prizes, however. Scored on points, the top second-year finishers (from first to sixth) were: Virginia Tech, the University of Wisconsin—Madison, Mississippi State University, Ohio State, Pennsylvania State University, and the University of Tennessee.

All six winners were available to be driven on a closed course marked with cones in a many-acre sea of asphalt. They'd all been washed, and most were repainted in university colors. But their status as engineering “mules” was evident.

As GM's vice president of powertrain engineering operations, Dan Hancock, explained, “We call engineering prototypes ‘mules'. It's an apt word. Sometimes they're stubborn; they have a mind of their own … and once in a while, they need a swift kick to get them to go.”

Some vehicles had interior trim removed, to keep them under the weight limit after adding heavy batteries and electric motors. Others had large red power buttons, crude digital readouts or jury-rigged shift levers. The variety of Frankenstein adaptations was impressive. But they all ran.