PHOTO CAPTION: Screen capture from Chevrolet Voltec drive system animation.

Chevy Volt More Hybrid Than Originally Suspected

Chevy Volt’s gas engine does turn the wheels. Sometimes.

Published: 10-Oct-2010

“It’s not a hybrid! It’s an electric car with a range-extending, gas-powered generator onboard.” That was the party line during most of the masterfully orchestrated press rollout of what we’ve been promised will be the most thoroughly new car since, what, the Chrysler Turbine? The Lunar Rover? Well, the cat is now out of the bag, and guess what? It is a hybrid, after all. Yes, Virginia, the Chevy Volt’s gas engine does turn the wheels. Sometimes.

On paper, the Voltec drivetrain has more in common with a Prius (and other Toyota, Ford, or Nissan Altima hybrids) than anyone suspected. Each system employs a single planetary gear set, a gasoline-powered piston engine, and two electric motor/generators. But the way Chevy connects them is entirely different, and—if you ask me—superior.

A planetary (or epicyclic if you’re British) gear set consists of a solid “sun” gear, with teeth on the outside, a hollow “ring” gear with teeth on the inside, and some number of little planet gears rotating around the sun and also enmeshed with the ring gear. The planets themselves are connected by a “planet carrier.” When you turn one of these three elements and stop a second one from turning, the third element turns at a different speed. By varying which elements are turned or driven and which are held, you can get three ratios out of one planetary gear set. If instead of stopping a particular element, you turn it at a different speed, you can achieve continuously variable ratios, as the Prius does.


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