IEEE Spectrum December, 2008 - 32

the F700's "magic carpet" active suspension maps the road so accurately
that a driver going over a pothole at high speed barely feels a jolt

uspension was next on
Kohler's list. Naturally,
the car would have the
most advanced electronic sys-

ProActiVe susPeNsioN:
Lidar sensors in the headlights
scan the road ahead of the car.

tems for safety and comfort absorb or counter the loads on in hand, Kohler and Pfeiffer
used in Mercedes cars-trac- each wheel.
contacted the company 's
tion control that varies power
Programming the suspen- design studios in Germany,
and braking on each wheel sion's controller, fitted with Japan, and California and
and adaptive cruise control multiple processors, brought asked them for proposals.
that maintains a safe distance its own challenges. Among Above all, the design had to
behind the car ahead at any other things, the control- denote a sense of inherent fuel
road speed. But as a vision state- ler had to keep track of the efficiency and environmental
ment, the F700 needed more.
motion of the car body-where concerns-and, of course, still
Once again, Kohler turned the sensors were mounted- convey the instant emotional
to Ellenrieder, who suggested relative to that of the wheels impression of a large, prestiwhat he called the "magic car- and suspension. And because gious Mercedes-Benz.
pet." Like today's active sus- the lidar sensors mapped the
In July 2006, Mercedes's
pension systems, it would road so accurately-they could board of directors reviewed
take in data like road speed, "measure" the thickness of the s e v e r a l p r o p o s a l s a n d
acceleration rate, brake appli- painted lines on the asphalt- c h o s e a d e s i g n s u b m i tcation, and force from each the controller also had to clev- ted by the California stususpension component. But erly smooth out the input data dio, the Advanced Design
on top of that, it would moni- to make sense of different road North America division, in
tor the conditions of the road surfaces. But the result paid Irvine. Its chief designer is
just ahead of the vehicle.
off: sitting behind the wheel of Chris Rhoades, who, like
If the system worked, the the F700, a driver going over several of his colleagues, is a
F700 would whiz over the a pothole at high speed barely surfer. "Design is inspired by
asphalt almost as if floating feels a jolt.
nature," he says, "to give back
in midair, already prepared
to nature." After Rhoades
to smooth out the bumps and
inally, it was time to sketched, pondered, surfed,
irregularities it "knew" were
consider what the car and sketched some more, what
coming-something no other
would look like. Kohler emerged in his flowing shapes
vehicle could do. There were discussed his early ideas with and design elements was the
doubts inside Mercedes on Peter Pfeiffer, head of the com- image of a dolphin breaching
whether the system-aptly pany's design department, and the waves. Sleek, smart, effinamed Pre-Scan-was far they settled on rough dimen- cient, it seemed to Rhoades
enough along to be exposed sions. The length would be the perfect metaphor for the
to the global glare of public- about 5 meters, the size of the F700. The board agreed, and
ity. But Ellenrieder prevailed, current S-Class. With the small the dolphin got the nod.
after what he diplomatically engine up front, the wheelbase
The result was a f lowtermed a "push-pull process," could be a full 3.5 meters-about ing roof and gently rounded
and the system went into full- as long as that of ultraluxury shoulder lines, highest in the
on development.
vehicles like the Maybach 57 or center, and a short snout up
The key innovation was a Rolls-Royce Phantom-giv- front. A dorsal fin down the
the use of lidar, or light detec- ing interior space that would be car's roof added aerodynamic
tion and ranging technology. impossible in regular cars.
stability-and undeniable
Originally developed for miliKoh ler a ske d P fei f fer marine overtones. Over the
tary remote-sensing appli- what to do with this roomi- next five months, the design
cations, lidar is now used by ness. Pfeiffer told him that the team worked frantically to
geoscientists and construction company's advanced design build a full-size clay study,
crews to map the elevations of studio for interiors in Como, refine every detail and sura terrain. The device emits Italy, had experimented with face, and produce a f inal
pulsed beams of infrared laser repositioning seats to let pas- h a r d-fo a m mo de l . F r om
light, detects their reflections, sengers have more relaxing this model, the template for
and computes the distance to conversations or do business the actual F700 metal body
the target. The idea was to use more effectively. One idea finally emerged.
lidar sensors in the headlights that emerged: if the rear seats
But challenges still loomed.
to scan the road so that the rotated 180 degrees, passen- As it turned out, the paint job
car's suspension could firm gers would be able to talk face almost ruined the car. The
up or soften its damping and to face, limousine style.
process was multilayered,
direct the hydraulic shocks to
With those and other specs with many cycles of painting,

NA * iEEE SpEctrum * DEcEmbEr 2008

www.spectrum.ieee.org

Steffen Jahn

engine controllers keep combustion efficient and emissions low by const a nt ly
adjust i ng t he a mou nt of
fuel injected and the timing
of the ignition. They make
adjustments based on data
received from dozens of sensors measuring parameters
as varied as engine rotation,
atmospheric pressure, and
tailpipe oxygen levels.
Designing such controllers
is fiendishly complicated, even
for standard cars. Designing
the F700 controller-which
had to manage such a complex
range of combustion modes-
was "an order of magnitude"
worse, as Ellenrieder puts it.
The switching between spark
and compression-ignition
modes proved especially hard.
In the end, the engineers
realized that the controller
can figure out which mode
to use from the data coming
from the pressure transducers inside each cylinder. The
controller then automatically
adjusts the compression ratio,
the amount of fuel injected,
the valve timing, and other
parameters. It's the main
brain behind the DiesOtto.

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Table of Contents for the Digital Edition of IEEE Spectrum December, 2008