Truth About Volt’s Mechanical Linkages Starts to Emerge

By · September 27, 2010

Back in June, we published a story on HybridCars.com about how the Chevy Volt is more of a conventional hybrid than previously thought. Trusted sources had been telling us for months about how the Volt might not always act purely as an electric car, but we didn’t post the article until G.M.’s Rob Peterson confirmed that Volt engineers could use the gas engine to power the wheels—a signature of a parallel hybrid system—if it meant greater efficiency. Peterson said, “You could do it. Absolutely.”

We applauded G.M. engineers for putting efficiency first, and letting the marketing department take care of itself. At the end of the day, who cares if there are mechanical linkages between the gasoline engine and the wheels? As long as the Volt delivers on its 40-plus miles of all-electric range, and maximizes the efficiency of the gas-engine when it’s called into service.

When we published the first story, and then argued that exploiting any mechanical linkages could mean better efficiency, the most ardent Volt fans accused us of bad journalism. G.M. executives were quoted as saying that we just didn’t get it.

Mounting Evidence

Well, a G.M. patent application for the Chevy Volt’s transmission was posted today on GM-Volt.com. Lo and behold, the application describes how the Volt’s two motor-generators, clutches and a planetary gearset can indeed be coupled to mechanically drive the wheels from the gasoline engine. Volt engineers might elect not to employ this linked configuration, but the application indicates that—with a software adjustment—it can be done.

G.M. Patent Application

Title sheet of G.M. patent application.

The revelation, if it bears out when the company fully discloses its design, would blur the lines between the Chevy Volt and hybrids like the Toyota Prius that use a parallel-series approach. In other words, it could call for a more common sense approach to describing any vehicle with an electric motor, a rechargeable battery pack, and a gasoline engine simply as what it is: a hybrid.

One Big Happy Family

What does it matter that the Volt is an electric car for the first 40 miles, and then can become a plug-in parallel-series hybrid? Probably not too much, except that the various pro-electric camps should stop bickering. Fans of the Chevy Volt, Toyota Prius, the Ford Escape Plug-in Hybrid, and the Toyota Prius Plug-in Hybrid can live under one tent.

“I cannot discern much of a difference between this and Toyota’s HSD,” responded one GM-Volt.com visitor to the patent story. “As for the transmission, I’ve thought all along that in the end, the Prius, the Volt, and Ford’s plug-in systems will all be splitting hairs from each other. I guessed a while back that the Volt is using a variation of the two-mode transmission. It just makes sense technically. They are all hybrids, really, by definition anyway."

Another visitor wrote, “Ah! A Toyota-like hybrid. This is the best way to get good efficiency at highway speeds and also to be able to utilize all three motors (ICE, gen, main drive motor) for extra power. You also get the benefit of having more total horsepower.” Exactly!

All major global automakers are expanding their production of electric cars, plug-in hybrids and conventional hybrids. At the end of the day, we all want to displace use of petroleum and reduce vehicle emissions—while enjoying all the benefits and enjoyments of our mobility. Any car that starts to shift us away from the stranglehold of pure internal combustion machines is a step in the right direction.

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