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 (http://www.autofieldguide.com/articles/wip/0207wip01.html). 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