Mercedes Benz- Virtual Prototyping article from Autoweek

This is a very interesting article... click on links for the photos or just link straight to the Autoweek article.

Brad
_____________________________________________

A digital prototype of a C-Class is projected onto a wall in 3-D for aerodynamic analysis.
http://cwimg.sv.publicus.com/apps/pbcsi.dll/bilde?Site=CW&Date=20070223&Category=FREE&ArtNo=70216009&Ref=AR&Profile=1528&MaxW=800

Virtual C Voyage
Mercedes-Benz ups the ante in digital prototyping


By KEVIN A. WILSON

AutoWeek | Updated: 02/16/07, 2:03 pm et
Automotive engineers and designers have been using computers to develop new cars for more than 20 years now, but Mercedes-Benz has taken the game to a whole new level with the 2008 C-Class, building a complete digital prototype in what it claims is an industry first. No other automaker has contested the claim—in fact, quite a few have scheduled visits to Sindelfingen to see how it works.

Just how “complete” is the digital prototype? Complete enough that, with the assistance of a pair of simulators, engineers were able to evaluate ride and handling months before the construction of real cars.

By these means, said Luger Dragon, senior manager for vehicle dynamics in the passenger-car development department, the company was able to ensure that its first prototypes of the car were already far advanced before the on-road evaluation and development process began. Dragon emphasized, however, that the digital model does not replace real-world testing. In fact, the new C-Class has undergone an unprecedented 15 million miles of on-road evaluation and development, and yet it arrives on the market only seven years after the previous all-new C-Class. It thereby marks a return, ironically enough, to an emphasis on real-world development testing, which was central to the company’s reputation for quality in the pre-digital era.

In 1989, when Mercedes-Benz did its first significant computer simulations of a car to evaluate crash safety, performance and fuel economy, a digital model of the W124 E-Class (originally designed without computer modeling) contained 25,000 elements; its successor, the W210, had three times that many elements in 1994. At the time, Mercedes-Benz emphasized how digital modeling was allowing it to speed up its product cycle to better address market demands. Previously, Mercedes could deliver an all-new model only every 12 years or so on average. The W124 had a 10-year run, and the W201, the original 190 “baby Benz,” ran from 1982 to 1993.

To tune the car's handling, engineers created a digital road model by laser-scanning a real road.
The digital prototype used for the C-Class W204, the production car that makes its public debut at next month’s Geneva auto show, is orders of magnitude beyond those early efforts. It contains 1.9 million elements, just in the structural model—like that for the 1994 E-Class—used for crash evaluation. The entire digital prototype incorporates many more aspects of the vehicle than were even dreamed of in 1994. It holds more than 2130 gigabytes of data, incorporating everything from shock-absorber characteristics to engine internal components, from driveline cooling and cabin climate-control systems to an aerodynamic model that maps 30 million points on the car’s exterior.

To facilitate cooperation among designers, engineers and outside suppliers, the prototype can be viewed in 3-D form in specially equipped “PowerWall” rooms at the Mercedes-Benz engineering center in Sindelfingen. Wearing special glasses to view the 3-D model projected on the wall, workers can rotate and zoom the image to examine specific details. Although the entire digital prototype is never really loaded into computers at one time (that would take supercomputers, while the system used is a network of desktop workstations), the elements are interactive. So it is possible to model, say, the aerodynamic effects at high speed while evaluating the handling or the engine cooling system. The prototype is broken down into 10 major segments: ride and handling; noise, vibration and harshness; body durability; crash; suspension dynamics and durability; thermal verification for the entire vehicle, including engine and brake cooling; energy management; climate control; engine processes and powertrain, and airflow aerodynamics.

One example shown to journalists was a model of the climate-control system and its air ducts, complete with the airflow pattern inside the cabin and the temperature and air velocity at each point, adjusted for distance traveled from the duct and absorption by the interior components, including four human occupants. This model was used to tune differing characteristics for different markets. The car can be set up to operate in modes that suit the European preference for a uniform cabin temperature or, as more commonly desired by American customers, to direct a warmer airflow into the footwell in winter or a cold stream from the dashboard vents in summer.

The exterior aerodynamic model includes the underbody and even rotating wheels, making it the virtual equivalent of a rolling-road wind tunnel. Engineers credit the digital prototyping process for helping them achieve a 0.27 Cd, in part by shaping small extensions for the frame to prevent airflow from traveling up into the wheel wells at both the front and the rear. More impressively, the aero model also was used to fine-tune the airflow so that the rear window, exterior mirrors and taillight lenses are self-cleaning. Rather than depositing dirt on these vital areas, as many cars do, the airflow around these components actually works to clean them.


To evaluate ride and handling characteristics, real humans go for a virtual "comfort test drive."
To begin development of the ride and handling characteristics, engineers used a digital road-surface model. The example demonstrated was devised by driving a truck equipped with exacting 3-D laser measuring equipment over a challenging two-lane road through the Black Forest, a stretch commonly used for decades now by Mercedes-Benz development engineers when evaluating vehicles. Then the digital prototype was “driven” over this road using a ride simulator that induces motion with fast-reacting electric motors. Digital models of the predecessor C-Class and key competitors, using data acquired by driving on the road in those cars, also were loaded into this simulator for comparison purposes.

While we won’t drive the real car until after the Geneva show, we have “ridden” in the new model on the simulator. The value of real-world testing was demonstrated by back-to-back “trips” over the same stretch of digital road using both the original digital proto-type and data captured during a drive of the same road with a real car. The improvement was evident, and the ride quality was superior to that of two competitors (not identified but thought to be the Audi A4 and the BMW 3 Series). The original digital model that preceded the construction of the prototypes rode somewhat like a mid-market sedan—say, a Hyundai Sonata or a Ford Fusion—while the final version had the smoother, more controlled ride motions of the near-luxury class in which the C competes.

Handling and braking, including the interaction among electronic assistance devices, were similarly tested—long before a real-world prototype was built—in an advanced driving simulator capable of giving the test drivers full simulations of the g-forces. We didn’t get to test that system—instead, we’ll drive the production models next month.