Edmunds.com

(October 12, 2010) GM has insisted from the start that it is proper to call the Chevrolet Volt an E-REV, or extended-range electric vehicle. We've always maintained that it is more accurately an extended-range plug-in hybrid.

Looks like we were right.

Volt's small gas engine does drive those wheels at times.

After denying it for months, GM finally has come clean with the admission that the Volt's  gasoline engine is, indeed, used for more than just generating electricity.

The engine is connected to the driveline and helps turn the wheels at speeds of above 70 miles an hour, it seems.

Edmunds Inside Line has confirmed the news, which gives lie to GM 's claims that the Volt is an electric car with a range-extender. An engine-assisted electric-drive car, yes; an all-electric car, as has been maintained, no.

It's a small matter in the overall scheme of things, and likely won't hurt the Volt's marketability — its not like it suddenly will change from a zero emissions car (it never was one) to a smog-spewer.

But it does irk that GM wasn't upfront about things a long time ago.

Here's how Inside Line describes the Volt's workings:

    At the heart of the Volt is the "Voltec" propulsion system and the heart of Voltec is the "4ET50" electric drive unit that contains a pair of electric motors and a "multi-mode transaxle with continuously variable capacity." This is how GM describes it:

        "Unlike a conventional powertrain,there are no step gears within the unit, and do direct mechanical linkage from the engine, through the drive unit to the wheels."

    The 4ET50 is, however, in fact directly bolted to the 1.4-liter, four-cylinder Ecotec internal combustion engine. When the Volt's lithium-ion battery pack runs down, clutches in the 4ET50 engage and the Ecotec engine is lashed to the generator to produce the electric power necessary to drive the car. However under certain circumstances - speeds near or above 70 mph - in fact the engine will directly drive the front wheels in conjunction with the electric motors.

    As in the Prius, the Volt's drivetrain includes a planetary gear set that acts as a transmission. The intricacies of planetary gears are many, but in rough terms each element (electric engines and internal combustion engine) of the Prius or Volt drivetrains are hooked up to different elements of the gear set. In the Volt, its Ecotec engine is clutched to the outer ring gear and as the car's speed reaches the edge of efficiency for the electric motor, that ring is set [free] from its normally rigid mounting in the 4ET50's case and allowed to spin. That has the Ecotec driving the front wheels.

    The Volt's Vehicle Line Engineer Doug Park confirmed that there is, on occasion, a direct mechanical connection between the internal combustion engine and drive wheels in an interview with Norman Mayersohn of The New York Times. This isn't idle speculation or educated inference, it's an admitted fact.

    What's vexing here is that GM hasn't been forthright in explaining this. It's not like this sort of operation isn't an integral part of the Volt's drivetrain - the engineering team has to have known this is how the car would work for a while now. But even today, GM's press releases and consumer information insist that the Volt is always and solely electrically driven. That's simply not the case.

Uphill battle

In another piece of, well, shall we say interesting technical news, it turns out that the Volt requires the driver to activate a special "mountain mode" when facing a drive up any long, steep incline.

If the button isn't pushed 10-15 minutes in advance of entering the mountains, ordering the car's powertrain control module to kick on the gas engine-generator to start pumping extra power into the battery pack, then as the hill climb progresses the electronic brain may decide there isn't enough battery power to do the job and automatically limit power to a top speed of 40 mph.

That, we imagine, is not something all those folks climbing the hill behind you are going to appreciate.

As more Volts get to more drivers, we expect there will be more of these fun little technical adjustments to bring you, so stay tuned.

— John O'Dell, Edmunds.com