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Chevy Volt Sparks a Series of Plug-in Hybrids

Expect many new plug-in cars to use the gasoline engine only as an extra battery

3 min read

Iconic U.S. car company General Motors turned a page in its history on a cold day this winter in suburban New Jersey. It sold the first production version of its Chevrolet Volt to a retail buyer—a retired pilot named Jeffrey Kaffee. With that sale comes the start of the first real test of consumer appetites for two concepts long in the making: hybrid cars whose battery you can recharge by plugging them in at home, and so-called series hybrid technology.

The Volt is the world's first production series hybrid-electric vehicle. Like a conventional hybrid, it has both an electric traction motor and a gasoline engine. Once its 16-kilowatt-hour battery pack is depleted, the 1.4-liter 4-cylinder engine switches on but does not drive the wheels mechanically. Instead, it turns a 55-kW generator that provides current to the 111-kW electric motor that powers the front wheels. It's not a new concept—minus the battery pack, that's the same way diesel locomotives work. But until now, all hybrid cars have used their gasoline engines in parallel with their electric motors, combining their torque to turn the wheels.

The Volt's series-hybrid credentials came into question briefly last fall when GM power-train engineers revealed that in one mode, its engine directly contributes torque to the final drive. In other words, a Volt is sometimes a parallel hybrid, too. Crucially, in GM's view, it does not offer direct mechanical drive to the wheels. Instead, engine torque is transmitted through the generator—locked by clutches on both ends—into a set of gears that work only if they simultaneously receive torque from the electric motor.

For North America, where daily commuting distances are higher than in Europe or Asia, GM chose a series hybrid because it felt the design offered the best combination of electric use and limitless range. As the company points out, 78 percent of U.S. vehicles travel less than 64 kilometers (about 40 miles) per day—the pure electric range that it attributes to the Volt. Beyond that, the gasoline tank and combustion engine act as a backup battery.

While the Volt may be the first series hybrid, more are coming. The next one will be the 2011 Fisker Karma, a luxury sports sedan from the venture-funded car company started by former BMW designer Henrik Fisker. The Karma uses a 2.0-L 4-cylinder engine to generate current that drives a pair of 150-kW motors to power the rear wheels. Other makers plan even more complex hybrid systems that can operate in series-hybrid mode at certain times, parallel at others. Most notable of these may be Audi's planned A1 e-Tron, a subcompact hatchback that uses a tiny Wankel engine as its range extender. Even more esoteric, Jaguar's C-X75 concept car uses a pair of microturbines as its range extender.

The fossil-fueled engines alleviate the "range anxiety" that may come with such battery-powered EVs as the 2011 Nissan Leaf, which has a stated 160-km range. (Four days after that first Volt delivery, Nissan delivered a 2011 Leaf to its first paying customer.) The phenomenon refers to a driver's fear of being stranded with a dead battery pack. As the saying goes, you can't pour a gallon of electrons into the tank.

But you can dribble electrons in. Early Leaf buyers will recharge their plug-ins largely via 240-volt home recharging stations, the installation of which their Nissan dealers must coordinate. Volt buyers, on the other hand, can recharge the smaller battery overnight using 110-V power, though Chevrolet also offers a home charging station. Toyota will launch a new Prius plug-in hybrid model during 2012, and Ford will offer an as yet unidentified model with a plug-in hybrid option. By the end of 2012, major carmakers plan to offer roughly a dozen plug-in models for sale or lease.

All three forms of plug-in vehicles—battery electrics, series hybrids, and parallel hybrids—will be offered over the next three years and marketed as meeting the varying needs of different consumers. While that happens, car dealers and electric utilities will gain more experience with the installation of home charging stations. And a network of public charging stations, many of them offered by retailers as incentives to lure customers for some shopping during a recharge, is expected to spread.

Initially, availability for the Volt will be low, so their impact on the spread of charging stations will probably be minimal. According to Volt marketing director Tony DiSalle, Chevrolet plans to build 10 000 by the end of 2011 and 45 000 the following year. But the big test for plug-ins comes in 2013, when Nissan will have the capacity to build 250 000 Leafs a year. Whether the global market is ready to buy hundreds of thousands of plug-ins remains to be seen.

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