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Hydrogen fuel cell powers latest GM E-Flex.

Although the General Motors E-Flex propulsion concept unveiled at the 2007 North American International Auto Show used an internal combustion engine (ICE) to charge the battery system, GM promised it would use the architecture to support a number of electric-driven powertrain systems besides the internal combustion-electric drive configuration that powered the Chevrolet Volt ( True to its word, GM unveils the latest E-Flex system combining fuel cell propulsion technology with a lithium-ion battery, producing up to a 300 mile range. Notably, this is the debut of GM's 5th-generation fuel cell stack, which is half the size of its predecessor--fitting into the same footprint as a 4-cylinder engine with an automatic transmission--yet produces 80 kW (94 hp) peak power. "We continue to have industry-leading power density," claims Larry Burns, GM vice president of research and development and strategic planning, of the stack that's rated at3 kW/L and 3 kW/kg. Burns credits engineers at GM's Global Alternative Propulsion Center in Honoeye Falls, NY, for improving the efficiency of the membrane along with the control of the gases and water flows, both of which were keys to reducing the footprint of the stack. "If you are not using the whole surface of the membranes that create current, then you're not getting as much power out of it as is essential," says Burns. He also notes that the use of precious metals, particularly platinum, has been minimized. "You want to have that spread out as uniformly and thinly as you possibly can, which really gets down into the nano scale of what we're working with." Membrane life-expectancy is also increased by the use of electric power--a 50 kW lithium-ion battery, to be precise--to support the vehicle during extreme driving scenarios. "If you could flatten those [power] peaks just a little by having some energy stored in a battery that you can introduce into the driving cycle, it's going to help you with durability and it's going to help you with the range and overall efficiency of the vehicle," Burns adds. The E-Flex fuel cell concept also utilizes GM's third-generation wheel hub motors, which are packaged inside the rear wheels, providing 25 kW of additional power output each, along with 500 Nm of torque. Burns is confident the 5th generation technology keeps the automaker firmly on track to meet its $50/kW, 150,000-mi., 300-mi. range operating targets by 2009. "We're pretty sure that at the end of 2009 we're going to be looking at a technology that truly can go head-to-head with conventional automobiles in terms of its performance, durability and cost," he says, noting that GM is not making a public commitment to build mass volumes of vehicles using fuel cell technology by that time, rather it is constructing a business model that could make it possible if the proper infrastructure is in place. "If you think this is a science fair project, we've spent over a billion dollars on it and that's a pretty expensive science fair project," Burns says.--KMK
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Title Annotation:NOTABLE
Author:Kelly, Kevin M.
Publication:Automotive Design & Production
Date:Jul 1, 2007
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Next Article:The lithium-ion challenge.

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