Inside Line: GM Lied, Volt Uses ICE For Propulsion
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.
More by Edward Niedermeyer
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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.”
It sounds to me like GM kick started the development of the Volt by using technology from their quasi-stillborn two-mode hybrid system, basically an advanced THM with a couple of electric motors built into it that allow a large range of gear ratios and torque loads. Since those motors can operate in genset mode when recovering energy from braking, my guess is that GM decided to adapt the two-mode hybrid to use one of the motors for driving the car and the other for generating electricity.
The "GM Lied" headline piqued my interest. So I looked into this a little more. Yesterday's Motor Trend article on the Volt system is pretty good. It is at: www.motortrend.com/roadtests/alternative/1010_2011_chevrolet_volt_test/index.html Electric motors do have problems at high speeds, when torque tails off. Gearing is important, as Tesla Motors found out with its Roadster. The two-gear transmission Magna designed for them did not work, and Tesla had to get creative with their gearing to get the higher speeds it had promised its drivers. GM has, in much the same way, used creative gearing to get around the problem of high-speed torque tail-off. Did GM thereby spoil the purity of their architecture? Can they no longer claim that the Volt is a virgin electric vehicle? Or has the Volt been spoiled by a mating between the transmission and (shudder) the gasoline engine? In my opinion, the Volt is still virgin. But I can see how other people might disagree. After all, I've always thought that oral sex was still sex. But the President of the United States disagreed, quite publicly, with that. From what I heard, many teenage "virgins" also thought the same way. I still think TTAC is being puritan about something that matters little. Still, many seem to agree with you. To each his own.