GM outlines light-duty engine plans

General Motors is "exploring every technology we can to increase fuel economy," including E85, advanced fuel management systems, diesel engines and new hybrid powertrain designs, according to Dr. Terry J. Woychowski, GM's vehicle chief engineer for full-size trucks.

In the near term, the new light-duty 2007 GMC Sierra and Chevrolet Silverado will be offered with a number of E85-capable engines that can run on ethanol, gasoline or some combination of the two fuels.

"We've been making alcohol for a lot longer than we've been making gasoline, and America is basically an agrarian country," Woychowski said at the official launch of the new light-duty line. "E85 is a good solution to oil import problems."

Building E85 production capacity "is a chicken or egg situation," the GM engineer said. "We want to start creating the demand to help push production up."

With or without E85 capability, most of the 2007 pickup engine options also incorporate GM's Active Fuel Management (AFM) technology. By turning off four of the engine's eight cylinders in low-power situations, AFM is said to increase fuel economy by 7% over standard fuel systems, according to Woychowski.

Combined with close attention to aerodynamic drag, AFM is a major contributor in pushing the truck's EPA highway rating to over 20 mpg for a number of its powertrain combinations. While the 2500HD and 3500HD versions of the new truck will continue offering a Duramax diesel option, the light-duty models will not, at least for the time being.

Characterizing a light-truck diesel as "a great idea" and one that GM is "absolutely evaluating," Woychowski refused to speculate on what form or size such a diesel might take. He also pointed out that coming U.S. emissions standards for diesel, especially the 2010 standards, would increase the cost of a diesel engine option, which is already considerably more expensive than gasoline engines. "Still, there probably is a market here for many more diesels," he said.

The parallel hybrid developed two years ago for the Sierra/Silverado will not be carried forward with the new models. Instead, GM will introduce a new "two-mode hybrid" in the near future, according to Woychowski.

The new system will incorporate a transmission with two planetary gear sets, allowing it "to act like a step transmission with gears or like an infinitely variable CVT (constant velocity transmission) depending on operating conditions," he said. For example, it would act like a standard geared transmission while accelerating, then switch to the infinitely variable mode for constant speed cruising.

"That allows you to maximize fuel economy without any performance loss in truck applications," Woychowski said.

Overall, GM's goal for its pickup engines is "to provide powertrain performance and fuel economy," the chief engineer said. "The 'and' is what's important, because in the past it's been one or the other."

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