For starters, the 2011 Chevrolet Volt will be a compact 5-door sedan with front-wheel drive, four-passenger seating, and an external footprint like that of Chevrolet's conventional Cobalt compact car. It will use GM's new "Delta 2" global small-car platform, but will have unique styling and GM's much-touted "E-Flex" powertrain architecture. E-Flex differs from existing hybrid systems that use a battery-powered electric motor as an adjunct to an internal combustion engine. Instead, the gas-fueled engine serves as a electricity generator and battery charger and is not connected to the drive wheels. Technically speaking, the Volt is thus an electric vehicle (EV) as well as a "serial hybrid." The Toyota Prius and similar vehicles are termed "parallel hybrids."
The 2011 Chevrolet Volt will be one of the first retail-market vehicles to use state-of-the-art lithium-ion (LI) batteries instead of the older and more common nickel-metal-hydride (NiMH) type. LI batteries store more energy in less space, which is why they're used in cell phones, laptop computers, and other small devices that need ample juice. They're also faster to recharge. These advantages are naturally attractive for an electric car, but LI batteries have never been used on this scale, and devising suitable cells has been the major challenge in bringing the Volt to market.
GM evaluated batteries from two joint ventures, A123 Systems/Continental AG and Compact Power/LG Chem. Chemistry is the main difference: So-called nanophosphate for the former, magnesium for the latter. Accelerated lab tests are now underway to determine which type better satisfies eight GM criteria, including energy density, extreme-temperature performance, materials, and cost. In January 2009, it was announced that LG Chem will supply the battery cells, and GM will assemble the battery pack itself.
Incidentally, these competing chemistries differ completely from that of the Sony LI batteries that made scary headlines by causing some laptop computers to overheat and even catch fire. The batteries in the 2011 Chevrolet Volt are thus expected to be quite safe, though they, too, must be kept within a specific temperature range. The Volt has a separate liquid-cooling system for that purpose.
The battery pack itself, rated at 16 kilowatts/hour, comprises more than 220 separate cells wired in series. That means the failure of any one cell disables the entire array, though some existing hybrid vehicles also have this flaw. The Volt pack is about six feet long and weighs a hefty 375 pounds. As in GM's early-1990s EV1 pure-electric vehicle, it mounts in T-formation with the "leg" running beneath the center tunnel and the top situated crosswise under the rear seats. The latter precludes a middle back-seat position, but does allow spreading the outboard seats further apart than usual. For convenience, the 2011 Chevrolet Volt will include an "intelligent" control module that allows plugging in to either 120- or 240-volt household circuits. GM estimates the Volt's battery can be charged in less than three hours via a 240-volt outlet, or in about eight hours with a 120-volt outlet.
As for the battery-charger engine, it's said to be an existing 4-cylinder GM unit of 1.4 liters displacement. Two versions may appear: One running on gasoline and tuned to PZEV (partial-zero emissions vehicle) standards, the other capable of using E85 ethanol and tuned to looser ULEV (ultra-low-emissions vehicle) levels. A small diesel engine could also be used, and was in the recent Opel Flextreme concept, but GM says it has no immediate plans to offer this.
Various reports indicate that electronic controls in the 2011 Chevrolet Volt will fire up the gas engine once the battery pack runs down to 30-percent power, then keep cycling the engine to maintain power within a specified band. GM estimates the Volt's total driving range at 640 miles, which is about double that of most conventional hybrids.
GM also claims the 2011 Chevrolet Volt can run solely on electric power for 40 miles with a full battery charge. That's in line with studies showing that most Americans drive only about 40 miles a day, so in theory at least, a Volt could go for weeks without using a drop of gas or spewing any CO2. But some analysts think the real-world electric range will be closer to 30 miles and probably less, depending on vehicle speed, ambient temperature (which affects battery performance), and whether trips include steep grades. Like conventional hybrids, however, the Volt incorporates a regenerative-braking feature that helps recharge the batteries when coasting or decelerating.
