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Mercedes A-Class Sedan (2018) wins the cW world record

A-class sedan takes the cW world record
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Working with 3D glasses -' Computer Aided Engineering 'is the name of the computer-aided work with the simulations.

The A-Class sedan will be at dealerships by the end of this year. 'From the front to the B-pillar, nothing changes compared to the hatchback model,' summarizes type supervisor Norbert Fecker. At the rear, of course, a different picture emerges, namely an aerodynamic onecheaper. A gentle spoiler lip ensures a higher pressure level of the air flow on the trunk lid.

The detailed work is done in the wind tunnel with a smoke lance to check the flow behavior of individual vehicle parts.

“We have to prevent the flow from separating from the body. Because this creates turbulence and costs energy. Energy that is paid for with increased fuel consumption, ”says Höfer. The team around Patrick Höfer was apparently not willing to pay this price. And so the A-Class sedan was meticulously optimized for its streamlined design, even if not everything could be implemented. “We have two small eddies on the taillights because the vehicle shape is rounded there and no tear-off edge has been inserted. However, it would have looked so terrible that even we aerodynamicists couldn't endorse it, ”jokes Norbert Fecker. The detailed work is done in the wind tunnel with a smoke lance to check the flow behavior of individual vehicle parts. The team works its way through the prototypes from front to back, gives the car the aerodynamic fine-tuning and then starts all over again. After all, even the smallest modifications have an effect on the overall structure.

While development work on the A-Class sedan was in progress in Sindelfingen, production of the compact sedan is ongoing in Rastatt and Aguascalientes, Mexico. In terms of engines and equipment, the same scope is available for this body variant as for the hatchback version.

Patrick Lang
No sci-fi film set, but the system used to measure wind noise at Mercedes.

'This enables us to measure precisely which wind noise occurs at which point on the body,' says Dr. Teddy Woll, head of the aerodynamics department, sheds light on the seemingly extraterrestrial darkness. The system, peppered with microphones and probes, covers a measuring area of ​​19 x 14 x 5 meters using three parallel displacement axes and four rotation axes. It is thanks to this device that the new Mercedes A-Class is around 30 percent quieter than its predecessor generation in the medium-frequency range with six to eight decibels. “The way we work with the designers across departments is team play at its best,” says Woll happily. For example, the exterior mirrors moved to the beltline and were made smaller. This is not just a question of design, it also means that the negative pressure area created by the mirror in the airstream no longer hits a joint, but rather the smooth surface of the side window. Together with the new, firmer window seals, this means that much less noise penetrates the interior. It is the sum of many small things that are brought together here to increase comfort.

Patrick Lang
For optimal aerodynamics, the underbody has to be as smooth as possible.

The overriding goal A successful aerodynamics is to bring the air currents at the rear together as quickly as possible in a closed ring vortex. For this it is important that the outflow velocity on all four sides of the vehicle is as equal as possible. To ensure this, cars have roof and side spoilers, rear diffusers and spoiler lip. It is also important that the majority of the underbody is smooth, because the car basically cuts through the air that is howeven the road, itself not moving. If you look under the new A-Class, you mainly see baffles and panels. Small openings are only allowed where air is needed for cooling, for example.

In order to simulate a realistic driving situation in the wind tunnel of the development center in Sindelfingen, the system has a five-band system which can be adjusted synchronously with the wind blower. A small treadmill runs under each wheel and a nine-meter-long central treadmill runs between the wheels - all on a turntable with a 12-meter diameter, so that the tested vehicles can also be approached from other angles. At the same time, the disk also functions as an aerodynamic balance and is used, for example, to determine pitch, roll and yaw moments. But above all, such a wind tunnel is called a wind tunnel because the wind runs through a channel. But where does it come from?

Patrick Lang
This huge heat exchanger cools the airflow down to a constant 23 to 24 degrees.

The wind comes from a blower with a diameter of nine meters and 18 carbon fiber blades that are so light that you can turn them by hand. The maximum torque of the drive motor of 202,150 Newton meters seems slightly exaggerated. Because the engine in question naturally generates a lot of heat, the airflow hits what Teddy Woll calls 'the world's largest grille' before it reaches the car. A huge heat exchanger that ensures that the air temperature is constantly between 23 and 24 degrees. The power consumption at a wind speed of 250 km /h is five megawatts, and the blower rotates 238 per minute. A maximum of wind power can be generated at a speed of 265 km /h. With such hurricane gusts, one wonders why there are extra warning lights that indicate that the system is running. Well, thanks to the sound insulation mentioned at the beginning, you hardly hear the system even during operation. And when you step into the air flow, it is already too late and you take off.

The wind tunnel in Sindelfingen was built according to the so-called 'Göttingen design'erected, that is, it is an annular system. At the end of its path, the accelerated air hits the blower again from behind and is accelerated again. That saves a lot of energy. Before the generated wind hits the vehicle, it is freed from eddies and turbulence by sieves and rectifiers in order to enable an accurate measurement result. The flow is made visible on the car itself through oil lances. These evaporate an oily mixture and thus create the characteristic streaks that surround the vehicle in the wind tunnel.

Cars should not have wheels

Now we have already learned that the designers have long since stopped are the greatest enemies of the aerodynamicist, but rather work together for the optimal compromise. But if they were allowed to eliminate part of the automobile, what would it be? We ask Woll and Schwolow. “I think cars shouldn't have wheels anymore. Then we would be in no time at a drag coefficient of 0.15 ', Schwolow realizes at lightning speed. “Yes, wheels are the aerodynamic horror,” agrees team boss Woll. However, this desire is likely to exceed the willingness of the designers to cooperate. It is already an advantage that Mercedes now has aero rims in all dimensions, says Roger Schwolow. These wheels only let in as little air as is necessary to cool the brakes. Because, especially in cars with short overhangs, an enormous amount of air flows into the front wheel arch, which is tremendously swirled around and 'transformed into loss'.

Patrick Lang
Dr. Teddy Woll (left) and Roger Schwolow explain the wind tunnel in the Mercedes development center to us.

The question remains whether there will ever be a real production car will bring a drag coefficient of less than 0.2. A question that aerodynamicists all over the world are asking. 'That is feasible,' says Teddy Woll, 'we have already made study vehicles that got it below 0.19.' However, the hunt for the one behind the decimal point depends on the customers' willingness to compromise. You would have to say goodbye to beefy shoulders, the strong “stance”, and the back tracksignificantly reduce. A teardrop shape is generally the most aerodynamically favorable body layout. However, you can forget to load a suitcase across the back, says Woll. At the moment, drivers are not only enthusiastic about the attractive wide track of the rear axle for reasons of driving dynamics. With a suppository on wheels, which at best can be described as asphalt cutting discs, nobody wants to drive around today. “But you still have to have goals in life,” Woll smiles mischievously. Let's see what else the wind tunnel will blow into our salesrooms in the future.

If you have to take a closer look at the technological marvel, then you can take a virtual walk through the system in our picture gallery. Otherwise the aeroacoustic wind tunnel is not accessible to visitors.


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