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Fuel Cells, CO2 & Composite Supercars:
The Scene in StuttgArt
German automakers probably debut more cutting
edge technology than any of their competitors and the legendary
region of Stuttgart, home to both DaimlerChrysler and Porsche, is
at the center of much of what is new.
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Porsche's new supercar the Carrera GT is a study in
lightweight material use. The chassis and engine subframe are
fashioned from carbon fiber reinforced plastic, and there is
extensive use of magnesium, ceramics, aluminum and a new
lightweight steel grade – H400.
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If you remove Detroit from the ranking, in the world of
distributed automotive centers, Stuttgart is preeminent. Home to
DaimlerChrysler, Porsche and mega-supplier Bosch, Stuttgart is a
place where many automotive suppliers, ranging from software
developers to plastic injection molders, feel they must have a
presence in order to stay on the cutting edge. And unlike many
areas where the importance of the automotive industry has been
eclipsed by other high-tech industries, the Stuttgart region has
actually seen the percentage of its total manufacturing output
represented by automotive manufacturing rise from 28.7% in 1980 to
41.1% in 2000. The majority of that growth has been in small and
medium-sized companies; to keep them flowing into the area the
Stuttgart Region Economic Development Corporation has helped create
a network of 17 “Competence Centers,” each of which focus on a
specific area of technology like telematics or fuel cells. These
centers allow smaller companies to pool resources with local
universities to carry out R&D projects that would otherwise be
out of their reach. But many of the more well-established players
have the deep pockets needed to stay at the forefront of
technological development. Here’s a look at some of the latest
developments to come from companies based in Stuttgart.
DAimlErChryslEr: Fuel cell forefront. In 1994 the company
then known as Daimler-Benz unveiled its first fuel cell vehicle. It
was a full-size van with a massive fuel cell unit that took up the
entire rear cargo area, effectively turning the van into a heavy
two-seater with no storage space. Not exactly a marketable
commodity. Since then, DaimlerChrysler’s research center at Nabern
near Stuttgart has refined its fuel cell system to the point that
it now fits into an A-Class without any intrusion into the
passenger compartment. It can be assembled into vehicles on the
same line as its internal combustion-powered counterparts. Dr.
Andreas Truckenbrodt, director, Fuel Cell and Alternative
Powertrain Vehicles, says that the tremendous advances in reducing
the size and increasing the range of fuel cell vehicles have put
commercialization within reach. He outlines DaimlerChrysler’s
four-stage fuel cell strategy:
- Market preparation. This initial research phase has greatly
matured fuel cell hardware and is nearly complete.
- “Fit for Daily Use.” This phase is kicking off now and will
encompass a program to provide 30 fuel cell buses for regular
routes in 10 European cities. In addition, by the end of 2004 the
company plans to have 100 of its A-Class-based fuel cell vehicles
(each with a range of about 150 km) in daily use.
- Ramp-up. This phase will run from 2007 through 2010 and see the
gradual increase of production.
- Commercialization. Truckenbrodt says fuel cell vehicles will be
a mass-production reality by 2010, though they will remain a small
part of the overall market for a long time.
Arriving at this strategy required abandoning some other
alternatives. For example, there’s using hydrogen as a fuel for
modified internal combustion engines (an approach often touted by
BMW). About that, Truckenbrodt says, “We have spent a lot of money
on hydrogen combustion engines and we have given up.” He explains
that the lower power density of hydrogen compared to gasoline or
diesel fuel together with the greater inefficiency of an internal
combustion engine (due to the excessive amount of energy that must
be dissipated as waste heat) essentially drives a stake in the
heart of this alternative. Truckenbrodt also reveals that
DaimlerChrysler has essentially given up on on-board fuel reformers
that crack hydrogen from fuels like methanol: “Reformation is a
non-starter from the efficiency point of view. And the reformer
itself adds too much weight and complexity. Also, you usually need
to provide a separate water supply which opens up problems with
freezing.” Though he embraces hydrogen, Truckenbrodt rejects using
it in liquid form which has to be stored hundreds of degrees below
zero, “You can’t stop it from getting warmer and it will evaporate
from the tank within two weeks,” he explains. Compressed hydrogen
is what DaimlerChrysler engineers think is the best form, and
though range is a problem, the standard for hydrogen compression in
the industry will soon double from 5,000 psi to 10,000 psi, which
Truckenbrodt says will increase range by 80%.
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WHAT A DIFFERENCE A DECADE MAKES. DaimlerChrysler’s first fuel
cell took up most of the cargo area of a full-size van. The
company’s latest fuel cell vehicle, imaginatively called
“Fuel-Cell”, fits everything neatly under the floorpan of a
diminutive A-Class.
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DaimlerChrysler’s research teams are currently focusing on ways
to improve the power density of their fuel cells by experimenting
with the use of bi-polar metallic plates that would more
efficiently lead the hydrogen over the membranes, and membrane
materials that can function at higher temperatures. With an eye
toward reducing cost and complexity the teams are also determining
if the sophisticated electronic sensors that measure the voltage in
each fuel cell are really necessary. And though every vehicle
development program targets weight reduction, it is particularly
important for the A-Class since the fuel cell version is currently
300 kg heavier than a conventional model.
BEhr: global cooling. Behr GmbH and Co. is the number-one
supplier of air conditioning systems for the European passenger car
market—a fact that is all the more impressive when you know that in
the last decade automotive air conditioning installation rates in
Europe have soared from about 20% to 80%. But Europeans’ new found
love for A/C has raised environmental concerns about increases in
global warming gasses. So the European Union is discussing a ban of
the refrigerant R134a that would begin phasing in in 2008. That
doesn’t give suppliers much time to come up with alternatives, but
Behr already has a working system that uses simple carbon dioxide
(CO2) as its refrigerant. The benefits of using CO2 are clear: its
global warming potential is 1,300 times less than that of R134a,
and if A/C units are charged using the CO2 that is the waste
byproduct of many industrial operations, the impact on the
environment is nil. CO2 also cools more efficiently. Behr estimates
that its CO2 system consumes 14 to 25% less fuel for the same
cooling output as current units, reducing both operating costs and
emissions. So, what’s the catch? Pressure. CO2 systems must operate
at much higher pressures (120 bar vs. 30 bar for R134a) to be
effective, which means that inexpensive rubber seals must be
replaced with costlier metal (though not necessarily stainless
steel) that can stand up to the increased pressure. Still, the
efficiency savings alone should outweigh the increased part costs
once the units are in mass production. “We think CO2 will be the
future of automotive air conditioning,” says Dr. Thomas
Heckenberger, director of Behr’s Group Technology Center.
PorschE: material benefits. The grounds of the Porsche
Development Center in Weissach are a vision of a world in which
everyone owns a Porsche but are forbidden garages. 911s, Boxsters
and Cayennes are shoehorned into every nook and cranny of asphalt
along the road, leading to a Porsche-per-square-foot ratio that
must top even Southern California. But the one Porsche product not
found in this cheek-by-jowl arrangement is the yet-to-be-released
Carrera GT supercar. Since the car will go for about $400,000 a
copy when it debuts this fall, avoiding door dings is a high
priority.
In addition to being by far the most expensive vehicle in
Porsche’s model line, the Carrera GT is by far its most technically
advanced. It is essentially a street-legal F-1 machine, so it’s no
coincidence that its development criteria would be familiar to any
F-1 designer: minimal weight, maximal stiffness, lowest center of
gravity, and a midship engine. To help meet the first two criteria
Porsche designed the most carbon fiber-intensive chassis in the
world. The passenger box portion is fashioned from carbon fiber
reinforced plastic (CFRP) and integrates the windshield frame and
roll bar for maximum rigidity. (The Carrera GT is an open top car
but it has better torsional stiffness than the closed 911.) The
CFRP is made up of an upper and lower layer of carbon fiber that
sandwiches a honeycomb layer of aluminum or a resin-impregnated
material called Nomex, which is widely used in aircraft and
spacecraft. The rear subframe which houses the engine and is bolted
onto the passenger box also uses CFRP, but it features a
heat-resistant honeycomb and a special resin in the matrix that can
withstand the heat generated by the engine without deforming. (In a
gentle jab at archrival Ferrari, Porsche engineers point out that
the subframe of their competitor’s supercar the Enzo is merely
constructed of welded aluminum.)
In all, 1,000 different pieces of CFRP are used on the chassis
and each one is arranged by hand to provide maximum strength. For
example, where bending loads are high—like in the door
sills—uni-directional weaves are used to enhance bending strength.
After the CFRP pieces are laid up, the chassis is rolled into an
autoclave where it is subjected to 180°C and 6 bar of pressure for
four hours in order to harden the structure. Each chassis takes
five days to produce, so Porsche will need to have 10 identical
sets of tooling on hand to reach the planned production of two
Carrera GTs a day. All of this handwork is not cheap, but according
to Michael Holscher, the supercar’s general project manager, “We
use the most expensive way of making carbon fiber because it is the
most efficient.”
Porsche didn’t stint on using other lightweight materials in the
Carrera GT, either. The wheels (19-in. in the front and 20-in. in
the rear) are made of forged magnesium which offers what the
company describes as “optimum durability” while being 25% lighter
than aluminum. Even interior parts like the center console panel
and the gearshift lever frame are made from magnesium. In fact,
Porsche had to use a special magnesium alloy that is heated to
400°C before stamping in order to get the garnish right.
When Porsche’s engineers were forced to use something as
quotidian as steel they managed to make that exotic, as well. The
front and rear side members, suspension push rods and rear-axle
wishbone are all made of a newly developed grade of stainless
steel, H400. H400 was chosen because it has high formability and a
lower gauge of the steel can be used to absorb more impact energy
in a crash while reducing overall weight.
Porsche also went to extraordinary lengths to ensure that the
Carrera GT would have the lowest center of gravity of any
production car in the world. The first step in doing that was to
make sure that it had the lowest crankshaft height, which is key to
determining center of gravity. The car is powered by a 68° V-10
engine instead of one of Porsche’s signature horizontally opposed
designs. The reason, as Holscher explains, is that though the
crankshaft height on a horizontally opposed engine is lower than
that of a “V,” the exhaust components hang below the bottom of the
block, inhibiting the engine from being mounted as low as possible.
On the Carrera GT’s V-10 the exhaust components sit above the
bottom of the block, allowing the crankshaft height to be lowered a
few crucial (at least to Porsche) millimeters.
An even bigger factor in achieving the lowest center of gravity
is an all-new compact, lightweight clutch that was developed
specifically for the Carrera GT. Porsche engineers needed something
small and light but knew they could not use the kind of carbon
fiber clutch common in race cars since customers would have to
replace them more often than their oil. So they developed a clutch
that uses carbon fiber reinforced ceramic discs mated with titanium
backing plates that achieves maximum power density at a low
rotational mass, while giving a service life ten times that of
racing clutches.
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