Green Car Advisor

GM engineers work on Volt's center-mounted, "T"- shaped lithium ion battery pack. Notch in middle is to accomodate a structural crossmember.

By Bill Visnic, Senior Editor, AutoObserver

Sparks flew in Detroit last week as General Motors Corp. engineers teased us with a few more details about the development progress of the high-profile Chevrolet Volt “extended-range” electric vehicle.

The major hurdle, of course, is the task of advancing the prototype lithium ion batteries to a state of production readiness that will allow the 4-seat Volt to travel up to 40 miles solely on electric power.

GM now is confident enough of its battery progress – spearheaded by competing cell suppliers A123 Systems Inc. and LG Chemical – to say that 40 miles of all-electric range is doable.

“We have left the research stage, said Frank Weber, global vehicle chief engineer, Chevrolet Volt and E-Flex systems. “We have generated the data that said, ‘Yes, this can be done.’”

The Volt’s E-Flex system combines the power of batteries and a small engine working as a generator to allow full-time battery operation. The engine kicks in for recharging duty on drives that are longer than the battery capacity can handle.

Engineers also revealed some details of the battery pack itself: the T-shaped module (a configuration inspired by GM’s mid-‘90s EV1 electric vehicle) weighs about 375 pounds and is nearly six feet long. For comparison, the EV1’s lead-acid battery pack, offering the same 16 kW-h of energy density as the Volt’s lithium-ion module, weighed 1,200 pounds.

GM also said new computer-modeling abilities let it squeeze ten years worth of battery aging into just two years on the test stand. This is done by strategically exhausting and recharging the batteries according to the 40-mile range cycle. Only half of the batteries’ total of 16 kW-h capacity is ever used, in order to maintain consistent, reliable performance and assure 10-year-plus durability.

Engineers also announced that starting later this month, the first battery packs will be placed into a small fleet of “mules” for on-road testing.

The mules will be Chevy Malibus -- GM isn't ready yet to let anyone outsiode the company see the look it has developed for the production Volt, although we're told bodywork essentially is locked in.

Don’t expect the long hood and Coke-bottle hips of the Volt concept car, however.

Bob Boniface, E-Flex design director and chief architect of the concept car’s sinuous sheetmetal, said vital aerodynamic considerations led to certain, ah, smoothing of the concept Volt’s radical but aerodynamically blunt styling.

“I think everyone thought they were going to get an electric Camaro,” Boniface said. Instead, he said necessary wind-tunnel work has generated styling for the Volt that is “handsome and athletic.”

Because the battery runs down the center of the car, the passenger cabin offers four bucket seats, and GM says that while not a large car, the Volt will comfortably seat a 6-feet-2 male in either front or rear seats. (Men typically are bulkier than women of the same height, so it should easly fit a female of the same height). 

Why fiddle with the concept car’s popular “ponycar” styling? It was fun, but a brick in the wind tunnel.

Boniface showed figures that demonstrate a minor reduction of ten “counts” of aerodynamic drag – from 0.26 to 0.25 for example – is good for as much as an extra half-mile of driving range. Counter to conventional thinking, GM said, its research shows aerodynamic improvements essentially yield more range than a proportional amount of weight reduction.

One closely guarded secret remains the production Volt’s final aerodynamic drag figure. Boniface only will say it’s very good.

Other bits of Voltage from GM are that the car incorporates no less than five distinct heat exchangers, cooling the electronics, the drive motor and, if necessary, the combustion engine, and that designers trashed the notion of any offbeat control interfaces.

They’re deliberately avoiding basic controls that exude too much of a Starship Enterprise feel.

One example: the chunky gearshift lever is just that – a modern but traditional-acting and -feeling lever. Park, Reverse and Drive will not be selected by an electric swizzle stick such as  the Prius employs.

But one tradition that may be trashed: a fuel gauge. Designers said a more useful readout would be driving range. After all, if all goes according to plan, many Volt customers may not ever need the engine to engage, using no fuel whatsoever. 

To that end, GM said it is likely to use a pressureized fuel tank to accomodate longterm "storage" of the gasoline the Volt does carry.