Fuel cells point to design flexibility

By: 
March 25, 2002

In the GM fuel-cell powered AUTOnomy concept car unveiled in January, engineers threw out preconceived notions of just dropping electric propulsion and power sources into existing automobile configurations.



With the fuel-cell power system within
the "skateboard" chassis, the AUTOnomy architecture envisions various body
styles electronically docked for by-wire steering, braking, and throttle
control. Four structural attachment points secure the body to the
chassis.

They saw no reason for fuel cells and hydrogen fuel storage to conform to a predetermined form factor, only that they have enough volume for adequate range and speed. With fuel cells providing power with twice the efficiency of internal combustion (according to GM), the best way to use that electrical power, with no conversion losses, is to direct it into electrically-driven, by-wire systems-steering, throttle, and braking-as well as accessories, including climate control.

Given an electronic driver interface, engineers came up with a modular approach-put all the power systems in the chassis, a slender "skateboard" to which various car bodies could be electrically docked, much like a laptop computer mated to a desktop station. Four structural attachment points secure the body to the chassis, which may eventually be a slim six inches thick, resulting in an extremely low center of gravity. It's not merely a design exercise-GM has filed for 24 patents based on AUTOnomy's technology.

Owners may even buy multiple chassis and bodies, depending on needs. GM VP of Design Wayne Cherry says customers might lease multiple bodies, including "a mobility body that allows a wheelchair to roll right into the driving position, or a ten-seat transit bus." The company sees the chassis having a potential lifetime of 20 years, with upgrades downloaded via software. Thus overall cost of ownership is lowered, perhaps leading to greater mobility in undeveloped areas of the world.

The electronic interface offers flexibility in location of the driver and passengers, depending on individual preference. Driving controls will likely be used through turning and twisting a set of handles. Without an engine to be accommodated, or to block the view of the road, body styles could be radically different while incorporating effective impact protection in the front and rear, along with a provision for fuel cell heat dissipation.

A working prototype will be on the road by the end of
the year,



Without an engine to be accomdated or to
block the view of the road, GM design engineers would have flexibility not
only in body styles, but also in such areas as driver and passenger
placement. This design freedom comes about because all controll will
by by wire without hard, mechanical interfaces. Heat dissipation for the
fuel cells (E) could be easily integrated into the overall shape of the
car.

according to Chris Borroni-Bird, head of Design and Technology Fusion for GM. "This 4-5 passenger vehicle will run on compressed hydrogen gas, at 5,000 psi, and have a single motor powering the front wheels," he adds. Later versions will have an integral motor on each wheel. The prototype will use the Filo steer-by-wire system developed by GM technology partner SKF (Gothenburg, Sweden) (see Global Design News 10.1.2001, p. 46).

"The concept could come to fruition in, say, 10 years," says Borroni-Bird, with vehicles on the market. A full hydrogen economy could be in place by 2020. "To realize this, a breakthrough in hydrogen storage, for range, is needed. For 300 miles range, a two to threefold improvement must occur," he notes. The range with current technology is pegged around 150 miles.

What form a hydrogen infrastructure takes is hard to predict, although some choices come to the fore. Borroni-Bird says that natural gas is the cheapest way to make hydrogen at this time. But then again, the gasoline infrastructure now in place could be adopted to reform that fuel into hydrogen. With either base fuel, there is a question of reforming at the station (or home supply for natural gas) or onboard the vehicle. Then again, electricity, if made economical enough, could be used to break down water for hydrogen.

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