Electronic Design

Volt Charges Up The Crowd In Detroit

Imagine filling up your gas tank once— and then ignoring it for the next 640 miles. Or if you drive less than 40 miles a day, imagine never filling it up again. That's the promise of the Chevy Volt, GM's latest concept car, unveiled at last month's North American International Auto Show in Detroit (Fig. 1).

A 16-kW lithium-ion battery pack powers the Volt, though the system only uses 8 kWh (with a state of charge between 80% and 30%). Fully charged, the Volt gets 40 city miles of pure electric vehicle range. When the battery is depleted, the car's 1-L, three-cylinder turbo-charged engine kicks in to recharge it. Drivers who travel about 60 miles a day can get up to 150 mpg.

When they get home, drivers simply plug the car in to a typical 110-V outlet for about six and a half hours to replenish the day's energy. Drivers who forget to charge the vehicle or who are traveling great distances would get 50 mpg just by using the engine to convert gasoline into electricity, for a total range of 640 miles.

"We have an on-board charger, so all you really need is a conventional extension cord that connects to a port on the front fender," says Nick Zielinski, vehicle chief engineer. "We wanted to make it as easy as possible."

GM currently is working on a battery with JC-Saft and Cobasys/A123 for the Saturn Vue Green Line of plug-in hybrid sport utility vehicles. Researchers say the results of this work may be applicable to the Volt's battery system. They also expect the Volt's battery to have a 10-year life span or 4000 recharge cycles, with a production-ready model by 2010 to 2012.

The Volt also uses GM's E-flex technology, a family of propulsion systems that fit onto a common chassis. GM is preparing separate gasoline, ethanol, bio-diesel, and hydrogen systems that will drive the Volt and recharge the battery when it is depleted (Fig. 2).

"We can tailor the propulsion to meet the specific needs and infrastructure of a given market," says Larry Burns, GM vice president of R&D and strategic planning. "Somebody in Brazil might use 100% ethanol to power an engine generator and battery. A customer in Shanghai might get hydrogen from the sun and create electricity in a fuel cell."

Designing a chassis with this kind of flexibility was a challenge, but Zielinski and his team had the advantage of experience. "What we're doing on E-flex is expanding the work we've done on the EV1, building on what we've done for the last 10 years on the EV-1, Sequel, and Equinox fuel-cell vehicles," he says.

Again drawing on their EV-1 experience, which broke all kinds of ground in relation to safety and even inspired many federal standards, GM's team sized and set all of the electrical system's components for optimum protection. For example, placing the battery down the center of the vehicle isolates it evenly from front crashes, rear crashes, and side crashes.

GM showed two versions of the Volt during the NAIAS. The first mockup, which wasn't a running vehicle, showed off the interior and exterior styling enabled by the E-flex system. The second, a chassis display, revealed how the battery will be laid out. While GM hasn't announced any specific dates for test trials or mass production, its designers don't think the Volt is a novelty—or a toy for the wealthy.

"The Volt will have a reasonable price but still offer reliability and performance," Zielinski says. "So much depends on battery development, though we're very confident we can deliver the battery pack."

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