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Designing AUTOnomy

One of the designers of a radical new fuel-cell-car concept explains what was done



GENERAL MOTORS
It had to have four wheels, but pretty much everything else was open for consideration. When General Motors decided to develop an all-new fuel-cell vehicle with electronic (rather than mechanical), drive-by-wire controls, our team started with a clean sheet.

Because we did not seek to shoehorn these new technologies into existing vehicle architectures, we avoided design trade-offs that had to be made in the past. We also opened up new opportunities to improve ride and handling, interior spaciousness and flexibility and exterior styling. The early result was our first concept vehicle, AUTOnomy. The working demonstration model, named Hy-wire, is being introduced officially to the world on September 26, 2002, during the Paris Auto Show.

Fuel cells cleave hydrogen atoms into protons and electrons that drive electric motors. Instead of polluting hydrocarbon emissions, fuel cell vehicles emit only water vapor from the tailpipe. Their widespread adoption could make personal transportation--a freedom already cherished by many cultures and sought with growing frequency by emerging markets--environmentally sustainable for the foreseeable future. (For more about the potential of fuel cells in automobiles, see "Vehicle of Change," by Lawrence D. Burns, J. Byron McCormick and Christopher Borroni-Bird; Scientific American, October 2002.)

Chock-full Chassis

Starting from the ground up, we placed all the "running gear"--the fuel-cell stack, drive-by-wire electronics controls and electric motors--inside the chassis. It is nicknamed for what it resembles: a skateboard. This design lowers the center of gravity compared with a conventional internal-combustion-engine-driven vehicle of similar proportions, which improves ride, handling and stability. Future advances in communication among the various by-wire systems (more on those momentarily) could supplement these advantages further, providing superior chassis performance than is possible today.

Hy-wire is a front-wheel-drive vehicle. But the AUTOnomy program goal is to place an electric motor at each of the four wheels, to improve acceleration and maneuverability. The wheel motors might allow a vehicle to almost literally turn on a dime, making parking much easier. Since wheel motors make each wheel independently variable, vehicle stability also could be improved beyond what is possible today.

The combination of wheel motors and drive-by-wire might enable the vehicle's corners to become interchangeable electronic modules, with packaging and software-tuning flexibility adaptable to multiple vehicle types. In addition, by-wire technology may make it feasible to provide remote-control operation, which could facilitate parallel parking or even let an owner back the car out of the garage in the morning when getting ready to leave for work.

Sleek, Switchable Exteriors

Beyond the functionality advances, the coupling of fuel cells with by-wire technology provides new design flexibility. There is no need to work around the awkward center cabin hump from the internal-combustion engine's driveshaft, or its conventional steering column. Planar fuel cells provide a flat foundation that offers more of a clean sheet for exterior styling--a wider variety of shapes above the plane of the skateboard chassis is possible. Moreover, eliminating the engine compartment lifts architectural constraints, enabling designers to create new vehicle profiles to tempt customers.

On the manufacturing side, by-wire technology allows automakers to reinvent the standard business model, to one centering around the use of interchangeable bodies on top of a common chassis. A limited version of this idea exists today, in the form of a type of vehicle architecture called body-on-frame, which is typically found in pickup trucks and sport-utility vehicles (SUVs). Body-on-frame design makes it easier and less costly to create new body styles (such as crossover vehicles and extended pickup trucks) than is possible with the unibody construction commonly used for passenger cars. AUTOnomy¿s skateboard-like chassis takes the idea a step further, by enabling greater front-end design variation, more freedom with interior arrangements and more flexible chassis tuning.

A manufacturing advantage is that large plants could eventually mass-produce a small number of skateboard types--for example, compact, mid-size and large--saving costs. Local suppliers could then sell "snap on" bodies designed to appeal to regional tastes. The bodies could even be replaced over time, and the by-wire controls could be upgraded with software.

Inner Beauty

The flexibility of a drive-by-wire-enabled interior matches that of the fuel-cell-enabled exterior. With all but the absolutely essential hardware moved into the chassis, the design liberates space inside the vehicle.

Consider, for example, that all of today¿s passenger vehicles have the same human-vehicle interface: a steering wheel and foot pedals. Drive-by-wire systems provide much greater opportunity for blending this interface with the vehicle. A sports-car driver might want a different way to steer, brake and accelerate the vehicle than the conventional approach preferred by the owner of a conservative luxury vehicle.

By eliminating mechanical connections between driver and vehicle, drive-by-wire systems also let the driver relocate within the cabin. For example, while commuting to work alone, a driver might prefer to sit more toward the center front-seat position. On weekends, he or she might move back to the conventional position to accommodate family members or friends. In Europe, traveling between the Continent and the United Kingdom would become easier, since the driver could control the vehicle from either the right or left seats. This flexibility is also of value to automakers in saved manufacturing costs.

All of this newly created open space gives the interior a much more living-room-like atmosphere. Thus, the occupant compartment could be reconfigured for office work, socializing or to accommodate special needs. As just one example, a battery-powered wheelchair could be docked into the floor and recharged from the fuel-cell chassis. The human-vehicle interface (steering and braking controls) might remain with the wheelchair at all times, or even be located outside the vehicle. This could give a disabled driver continuous access to driving controls and other useful features, such as a navigation system or Internet display. The vehicle¿s flat floor also facilitates sleeping--ideal for a camper-body option.

The driver isn't the only one who benefits: rear passengers get to stretch their legs, too. Even in today¿s luxury vehicles, rear-seat passengers have modest amounts of legroom. But elimination of the engine compartment increases the usable length of the interior, stretching the distance between front and rear seats.

Finally, the unique AUTOnomy concept not only is an exciting new vehicle design with great functionality: it also offers the chance to decouple body and chassis development, which can have advantages for design, engineering, manufacturing and marketing. These benefits could lead to more affordable vehicles and greater penetration of fuel cell technology, with subsequent benefits for energy security, global warming and air quality.


Christopher Borroni-Bird joined General Motors in June 2000 as director of design and technology fusion, a group that applies emerging technology to improve vehicle design. He is also director of the AUTOnomy program, which includes the Hy-wire prototype vehicle. Previously, Borroni-Bird managed Chrysler's Jeep Commander fuel-cell-vehicle program.


"Vehicle of Change," by Lawrence D. Burns, J. Byron McCormick and Christopher Borroni-Bird (Scientific American, October 2002), is available for purchase at the Scientific American Archive. "The Electrochemical Engine for Vehicles," by A. John Appleby (Scientific American, July 1999), is available for purchase at the Scientific American Archive.
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