As GM finally begins to let journalists drive its Chevy Volt, the two-year-long trickle of bad news about the project is turning into a raging torrent. The latest bit of bashing: InsideLine claims that, in direct contradiction to GM’s hype, the Volt is in fact powered by its gasoline engine under certain circumstances.
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 no 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 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.
It doesn’t take much work to discover that GM has directly concealed this reality from the public, by stating repeatedly that the Volt is powered by electricity at all times. GM even “corrected” reports that it was “considering” allowing the Volt (or its sister car, the Opel Ampera) to drive under gas power under certain circumstances. And its most recent press release calls Voltec a “pure electric” drivetrain with a gas range extender. The last thing GM needs going into its Volt launch is a credibility gap in its explanations of the Volt’s convoluted internals.