This must be Fiat 500 News Week. How else to explain the drumbeat of announcements, from its innovative TwinAir engine to a special U.S. model offered only to current Fiat owners?

Today's item: The company will develop a mild hybrid version of its 500 minicar, fitted to the 0.9-liter TwinAir two-cylinder engine. Its goal is to reduce the little car's carbon-dioxide (CO2) emissions to just 70 grams/kilometer, far lower than any other non-electric car.

Fiat plans to pair its 900cc twin to a sophisticated dual-clutch transmission (DCT), which will include a very small 5-kilowatt electric motor inside to turn one of the gearbox's two shafts.

The system will be a mild hybrid because it won't move solely on electric power. Instead, the electric motor--which offers maximum torque from 0 rpm--will provide power to the drive wheels as well, requiring the engine to burn less gasoline.

CO2 emissions of only 70 g/km translates to roughly 80 miles per gallon, though U.S. and European test cycles differ significantly.

Given the tiny size of the engine, Fiat may be able to mount the high-voltage battery pack under the hood, simplifying the wiring considerably. The pack may also power accessories when the engine switches off at stop lights, further saving gasoline.

2012 Fiat 500 Electric/Elettra

2012 Fiat 500 Electric/Elettra

Fiat is expected to offer the hybrid for sale in the U.S., but not immediately. It's also not clear whether the hybrid transmission would be mated to the TwinAir engine, or to the larger 1.4-liter engine fitted to the rest of the 500 line for the U.S.

The first model to market will be the standard 2011 Fiat 500 three-door hatchback at the end of this year, followed by the 500C cabriolet with a roll-back cloth roof, then the 500 Abarth performance edition.

There will also be a low-volume Fiat 500 EV electric car, developed by Fiat's U.S. partner Chrysler, and possibly a four-door 500 aimed specifically at the U.S. market as well.