What If You Had to Build a Socially Responsible SUV?

At GM's Challenge X, turbodiesel electric hybrids running on biodiesel are par for the course. Even hydraulic hybrids and ultracapacitors don't raise eyebrows.

8 min read

Car fanatic or not, few 20-year-olds can knowledgeably discuss the pros and cons of hydrogen fuel cells, ultracapacitors, and batteries for automotive energy storage—perhaps even fewer in scorching desert heat.

The scene was General Motors' Mesa Proving Grounds in Arizona. It is one of GM's two main North American test facilities, with 75 miles (121 kilometers [km]) of roads and a high-speed test track over 5000 acres (20 km2). The heat—up to 120 degrees Fahrenheit (49 degrees Celsius)—makes it ideal for testing vehicles and their air-conditioning under intense conditions. Half a century ago, the area was empty and remote, visited only by a few cattle. Now, this top-secret facility is rapidly being engulfed by hundreds of beige stucco houses in walled subdivisions.

The event was the second-year finals of the three-year Challenge X competition among teams from 17 North American universities. Sponsored by the U.S. Department of Energy, GM, and several equipment manufacturers, it's the latest in a series of university auto-design contests that date back to 1987.

Talking to dozens of young engineers in the competition was both impressive and informative. All were members of university teams who designed and built passenger vehicles using advanced powertrain technology to reduce fuel usage and emissions. The project vehicles had been lovingly crafted by electrical, mechanical, and chemical engineering students and computer scientists, supplemented by the odd nuclear or industrial engineer.

The actual car? Oh, that's not till Year Two.

Photo: Brenda Priddy

Challenge X regalia was painted on the vehicles, printed on everything, even worn by the participants. No word on tattoos, though.

Challenge X follows a real-world corporate vehicle design process—in this case, GM's—over three full years. The students' first year was largely devoted to computer modeling, simulation, and design testing. Only then was each team given a 2005 Chevrolet Equinox, which in the U.S. is a ”compact” sport-utility—4.8 meters long, weighing 1724 kilograms (kg) with all-wheel-drive—fitted with a 185-horsepower (138 kilowatt [kW]), 3.4-liter V6 gasoline engine. Teams also got access to engines, battery packs, motors, electronic controllers, software, and other equipment from 28 corporate sponsors.

Year Two was all about implementation: Students had to turn their design files into a modified, running vehicle, which was trucked to the Desert Proving Grounds in May and put through an exhaustive series of tests. The driving event for invited press closed the second year of the competition, after prizes were awarded for overall scoring on a variety of factors—everything from emissions, fuel consumption, and on-road performance to technical writing, electronic control strategy, and community outreach.

During the third year, teams will refine their vehicles to provide a ”showroom” auto that meets consumer requirements—a new and challenging element in such competitions. This may include the ability to tow a trailer weighing 453 kg (1000 pounds) or more up a 5 percent grade for many miles in 110 degree F (43 degrees C) heat, or instant starting in temperatures well below 0 degree F (-18 degrees C). It means air-conditioning that works flawlessly, comfortable seats, the storage space that buyers expect in an SUV—and enough acceleration to merge comfortably into freeway traffic with a full load of people and luggage while towing that same trailer.

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 [https://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.

Lurching and stalling

Photo: Brenda Priddy

Like most, the University of Ohio had to fit new components into an existing vehicle--in this case, by taking a hacksaw to plastic trim.

For the uninitiated, driving a turbodiesel electric hybrid—especially one early in its development—can be tough. The students were surprisingly sympathetic to (theoretically) car-savvy reporters who stalled or lurched their cars on takeoff, repeatedly. As Dan Bocci, a member of the second-place ”Moovada” Wisconsin team, explained, ”Electric assist for launch while the engine powers up from stop, that's in our Year Three plan. It reduces the stalling considerably � but we didn't quite get it done yet.”

Other first-hand impressions among several vehicles included: requiring 1 to 2 second power-up routines before the ignition would engage, many clunks in the drivelines, and considerable noise from uninsulated electric motors during the charge cycle.

But this was precisely where the vehicles were supposed to be. A year prior, no team had even received its silver Equinox. Now untutored civilians were driving the vehicles into which teams had put wrinkled brows, sweat, and many, many late nights. All things considered, the students exhibited considerable grace as reporters flogged their vehicles.

That composure only faltered when GM's executive director for global integration and safety, Ken Morris, ran Ohio State's fourth-place vehicle through the slalom course. He did the entire course probably twice as fast as anyone else. Loaded with five people, the tall SUV leaned considerably as he snaked it through the pylons, tires squealing. And then he took an unscheduled detour onto the high-speed banked test track, not a part of the approved press tour.

The students were sympathetic to (theoretically) car-savvy reporters who stalled or lurched their cars on takeoff, repeatedly.

Mashing the accelerator to the floor, Morris listened intently for the rear motor to kick in with its power assist. As he drove—with both hands on the wheel, like all good test drivers—he quizzed team members in detail about their control logic. During one answer, he suddenly lifted off the accelerator entirely. The car jerked and pitched forward, the motor's whir changed to a noticeable whine as it switched to regenerative mode, and the vehicle slowed quickly until he mashed the pedal again. And so it went.

After one lap, he exited (passing a lightly camouflaged version of a future GM sport-utility to be introduced for 2008). Perhaps it was just imagination, but some of the team seemed to look slightly relieved.

Photo: Brenda Priddy

Weight: The enemy

That relief will be short-lived. Next year, the teams face their most formidable challenge: the showroom demands of the average U.S. consumer who buys an SUV. Fuel saving? That's a good thing, certainly. But towing capacity, storage space, dozens of cup holders, iPod jack, imposing attitude, blazing acceleration? As they say, that's where the pedal hits the metal. Year Three promises to be every bit as challenging as the prior two.

While it's far from laid-back, Challenge X is nowhere as flashy as the recently concluded DARPA Grand Challenge (see: /oct05/comments/1145). Its First Place prize of US $7000 seems almost insignificant next to the $2 million won by the Stanford University team that created ”Stanley” for the Grand Challenge. But Challenge X emulates the process of designing vehicles for real-world users. In the end, technologies like these are likely to be on the roads—and at your local dealer—well before cars that drive themselves autonomously.

The students take great pride in their in-process creations. They also matter-of-factly include advanced electrotechnology as an integral and necessary part of socially responsible vehicle designs. Their attitudes, and the various technologies they are working with, promise exciting automobiles in the years to come.

About the Author

John Voelcker covers auto technology for IEEE Spectrum , Popular Science, and other media. He is executive editor of ROVE , and founder of Profuse Media, a consultancy specializing in the interactive media business. (He gratefully acknowledges the assistance General Motors provided for the coverage of this assignment.)

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