Mercedes’ CLS: its most tested car.

  • 25-Oct-2010 03:21 EDT
Merc10-10CLS testing 2.jpg

The new Mercedes-Benz CLS is the company's most thoroughly tested car.

Work is always testing for Joachim Lindau. As Mercedes-Benz’ Senior Manager, Overall Testing for E-Class cars, he is responsible for seeing that both total quality and the company’s signature DNA are combined in vehicles that are increasingly complex and that sell into highly discerning markets.

The new CLS is his latest program to reach production and it is, he says, the most tested Mercedes-Benz ever. “Twenty years ago we would build prototype cars and take them for testing to northern Sweden or some of the hottest places on Earth,” he says. “There we would experience problems with some components—which was the point of testing. But we lost time and decided that it was not doing things in the right order. So now, we carry out all component testing and have the results certified as having reached our required standards before they are assembled on the prototype cars.”

But Lindau and his teams also need to ensure that components (particularly electronics), which may operate flawlessly in a stand-alone bench-test, can operate efficiently and consistently within an integrated architecture. “For example, a telematics system may be influenced by the controllers for brakes or engine; we need to ensure that this can be achieved and then extrapolate that to production ensuring that a model built hundreds of time a day stays within allowed tolerances.”

This is illustrated by establishing a bell curve, or Gaussian distribution, with the aim of bringing together as closely as feasible each side of the curve to achieve minimal tolerance. “That is possible—to give no problems,” says Lindau.

While increasingly efficient and effective CAD and CAE have transformed the way vehicles have been created over the past two decades, simulating test work is limited, said Lindau. “We can computer simulate each under-hood component and the temperature in the area in which it operates and how cooling air can be introduced. For example, we can do that for the wiring harness. But all that is design; to be certain that everything works, it still has to be physically tested because in the computer you do not have a precise picture of the real world.”

That real world, he said, is actually experiencing, in built-up vehicles, the effect of driving in Italy in dusty conditions that degrade to rain and then a thunderstorm bringing flooded roads, while the car is suffering the effect of electromagnetic problems from a nearby broadcast antenna: “I believe that we will always need to do final testing physically because the customer doesn’t buy an electronic program, he buys a car!”

There is also the esoteric matter of an individual marque’s DNA. It took two years to refine the CLS’ new electrohydraulic steering system to provide the required levels of driver feel, accuracy, and effort at widely varying speeds in every conceivable weather condition.

“There was a lot to do,” explains Lindau. “You can take delivery of components from suppliers and build a car. That’s fine, but it is just a car—not a Mercedes-Benz.”

So as well as checking reliability, longevity, and quality, Mercedes’ testers need to establish the expected particular signature of each model. Mercedes has what its engineers refer to as the “White Book,” its contents going some way toward defining what is required and how it may be achieved, by recording, in principle, the company’s product DNA. “But we also need the seat-of-the-pants input, too,” states Lindau.

That is something that is not possible to enter into a computer and put into the pages of a test driver’s notes; it cannot be totally analyzed and explained, only experienced.

Says Lindau: “It is like cooking. The basic ingredients may be beef, potato, and other vegetables, but a cordon bleu chef will introduce a little more of this, a little less of that, to create precisely what is required. It is the same with a Mercedes-Benz. It is called experience, and it is the only way to achieve the ‘feel’ of a Mercedes.”

This is the biggest challenge for Mercedes testers, explained Lindau. Staff turnover in the testing department is very low. He adds: “It takes three to four years to understand just what is needed to create the product DNA and how everything fits together in that sense. We know the force required to open or close a door, operate a pedal, turn the steering wheel; we can define that force but not the feeling.”

The new CLS is based on the E-Class so although it has model-specific elements, much of it comprises components and systems that have already been proved. “They have millions of kms behind them, but we tested them again in the CLS to prove their integration,” states Lindau. “In effect, they are doubly tested, so the new CLS has indeed been tested more than any of our other cars.”

Extensive testing has also resulted in a new development for the next-generation Mercedes-Benz SLK vario-roof (folding hardtop) sportscar, which will be publicly revealed at the 2011 Geneva Motor Show. The company claims that it will be the first auto manufacturer to offer a glass sunroof (the distinctly un-Mercedes-like name of “Magic Sky Control”), which can be electronically switched from transparent to darkened mode.

It uses the physics of plate condenser technology, with an electric voltage positioning particles in the glass to allow light to penetrate it. With the voltage off, the particles reposition randomly, partially blocking the light, and the glass is darkened. The control unit and converter are positioned in the front of the roof section, and the system is driver-controlled.

UV and IR are blocked in transparent mode; insulation increases in darkened mode, which helps keep components such as armrests 10°C (50ºF) cooler than conventional green glass protection. Temperatures around the occupants’ heads were also reduced.

Testing included operation in Death Valley, CA, with ambient temperatures in excess of 50ºC (122ºF). Test engineers subjected cars to 4 h heat soak in these conditions and then switched the glass roofs to nontransparent mode.

A star pyranometer test, which measures exposure to sunlight, showed that with the roof open, load from the sun reached 1000 to 1100 W/m2. With the roof raised and in transparent mode, the figure was 200 W/m2 and darkened, 40 to 50 W/m2.

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