could, in theory, turn the wheels directly. That makes the Chevrolet Volt a plug-in hybrid, plain and simple. The revelation comes as General Motors brings journalists from around the world to Detroit to drive the Volt and sends a convoy of Volts out on a PR tour.

In some ways this is a semantic argument about highly technical points of the Volt’s drivetrain. Frankly, most consumers won’t care. But it goes to GM’s credibility, because the company has wasted no opportunity to call the Volt an electric vehicle. That has some people accusing the company of lying. That’s a bit strong, but it threatens to overshadow the launch of what is, at the bottom line, an impressive bit of engineering and a pretty special car.

First, the background. From the moment General Motors unveiled the Chevrolet Volt concept at the Detroit auto show three years ago, it has insisted the Volt is an EV. Yes, it has an internal combustion engine, but GM always said it only drives a 53-kilowatt generator. (Contrary to some reports, the engine does not recharge the battery.) That generator keeps electricity flowing to the 111 kilowatt motor when the 16 kilowatt-hour lithium-ion battery goes dead.

GM says the car will deliver 25 to 50 miles of electric range, though it long claimed you’d see 40; Popular Mechanics averaged 33 during its recent drive. Once the engine generator kicks on, you can go as far as 310 miles if you’ve got a full tank of gas. As for the fuel economy, we always knew that 230-mpg claim GM made last year was marketing BS. Popular Mechanics got 37.5 mpg city and 38.15 highway.

General Motors calls the drivetrain “Voltec” and the car it propels an extended-range electric vehicle.

“The Chevrolet Volt is not a hybrid,” General motors says in the press release, issued Sunday, announcing the car’s launch. “It is a one-of-a-kind all-electrically driven vehicle designed and engineered to operate in all climates.”

Actually, it’s not quite all-electric. The gasoline engine assists the electric motor once the car reaches about 70 mph, regardless of whether the car is running in battery mode or charge-sustaining mode (when the engine generator is providing the juice). Frank Markus of Motor Trend breaks it down in a detailed piece that says Voltec is remarkably similar to the drivetrain you’ll find in a Toyota Prius or other hybrid. Like a hybrid, Voltec uses a single planetary gearset, an internal combustion engine and two electric motor/generators.

“But the way the Chevy connects them is entirely different and — if you ask me — superior,” Markus writes.

His explanation of how the system works is highly technical, but the bottom line is the gasoline engine/generator combo directly — i.e. mechanically — assists the traction motor at highway speeds. But he is quick to add that the engine could not, for all practical purposes, drive the wheels itself.

“In defense of Chevy’s earlier stance, the only way this gasoline engine (or the Prius’) could ever drive the wheels without lots of help from the battery is if you somehow MacGuyvered up a way to jam the sun gear [the planetary geatset's central gear] to a stop,” he writes.

That’s an important distinction, and one that many people are overlooking. The gasoline engine could directly propel the wheels, but it won’t directly propel the wheels. Doing so would require physically stopping the sun gear from turning within the planetary gearbox, Tony Posawatz, vehicle line director for the Volt, told Wired.com.

“It can never run the vehicle by itself,” he said of the internal combustion engine and generator combo. “It is only a support to the traction motor. You cannot drive that car only on gasoline power. It’s an impossibility. The traction motor always has to be on.”

The internal combustion engine is bolted directly to the 53-kilowatt generator; it drives the generator with a 1:1 gear ratio. When the electric motor approaches 70 mph, it is spinning so fast that it is at the edge of its efficiency, Posawatz said. GM’s engineers decided to use the engine-generator combination as an assist to reduce the electric motor’s speed (RPMs) and increase efficiency — and therefore range.

“We literally reduce the speed of the motor by half,” Posawatz said. “In battery electric mode that’s a 5 to 10 percent increase in efficiency. In extended range electric mode (when the generator is providing the electricity), it’s a 10 to 15 percent increase in efficiency.”

Posawatz repeatedly said the Volt will not run under gasoline power alone, and he insists that makes the Volt an electric vehicle.

“Without the traction motor running, the car will not run,” he said.

Strictly speaking, then, the Volt is a plug-in hybrid because it uses two sources of energy — electricity and gasoline — and the battery is recharged by plugging the car in. And that is a semantic point that most consumers won’t know — or care — about. But GM is taking a lot of heat for calling the Volt an electric vehicle. Inside Line flat-out says, “GM lied,” a position Jalopnik repeats and other bloggers parrot.

Posawatz said, “We stand by all of our original statements that we’ve made.” GM didn’t lie, he said, but neither did it provide extensive detail about how Voltec works because it had to protect its intellectual property. The patent wasn’t approved until Sept. 21, he said.

“We wanted to make sure our patent had cleared,” before elaborating on the drivetrain, he said.

Regardless, GM clearly overstated its case when it had no obvious need to. Doing so has created a PR headache that threatens to overshadow, at least in the short term, the fact the Volt is a significant step forward for the company. We’ve driven the Volt at various stages of its development and drove a production model at Milford Proving Ground in July. The Volt is comfortable and quick, with snappy acceleration, decent handling and a smooth drivetrain. It’s handsomely styled and nicely appointed — all in all, a very nice car, even if it does cost $41,000 before the EV tax credit. And it marks a big step toward the electrification of the automobile by a company generally blamed for killing the electric car.

So the Volt is a plug-in hybrid. Big deal. There’s no shame in that. The shame is that by overstating the case, GM has people focusing on what the Volt isn’t, not what it is.

Photo: Jim Merithew / Wired.com

Authors: Chuck Squatriglia

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