Aerodynamics: Good air flow characteristics: The champion in the segment

Nov 28, 2018
Stuttgart

With a cd value starting at 0.24, the new B-Class trumps its predecessor (value starting at 25.0), and is the leader in its segment. Despite bigger internal dimensions, the aerodynamic engineers were simultaneously able to reduce the size of the frontal area (A) in comparison to the previous model – from 2.42 to 2.40 m2. A considerable improvement was also achieved in the aeroacoustics, which are important for understanding and hearing one another in the interior.

Although the B-Class is conceptionally at a disadvantage as an estate car rear end, it nevertheless performs better than many saloons in the wind tunnel. This is the result of extensive and detailed work at the computer and in the wind tunnel, as well as cross-unit cooperation at an early stage of development. This means that the frontal area could be reduced in size despite larger interior measurements, because from the very beginning the aerodynamics engineers were in consultation with their dimensional design colleagues. One of the results of this was to lower the roof, for example.

The good air flow characteristics, which are a major contributory factor to the vehicle's low fuel consumption in everyday conditions, result from numerous aerodynamic optimisation measures. These include an extensive sealing concept (sealing the headlamp surroundings and the lateral joints of the tailgate, among other things), a new exterior mirror in the A-pillar triangle as well as the nearly complete panelling of the underbody, which comprises the engine bay, the main floorpan, parts of the rear axle, the diffuser and other components. At the rear the large roof spoiler and the small lateral spoilers as well as the spoiler lips in the rear lamps and on the bumper reduce resistance and lift. The front and rear wheel spoilers have been specifically optimised to achieve low airflow losses around the wheels. The wheels were also fine-tuned with regard to aerodynamics.

A two-part blind system behind the radiator grille is available on request, which minimises aerodynamic losses in the engine compartment. This AIRPANEL opens adjustable louvres depending on cooling output requirements. There is an additional louvre system in the air inlet below the registration plate, which further improves system performance.

In comparison to the previous model, the wind noise has been reduced, thanks above all else the concept work carried out at an early stage and the extensive sealing concept. This translated into further important improvements in the design of the seals in the windscreen surrounds and the sealing of trim elements and detachable parts. Where the high-frequency wind noises are concerned, particular attention was paid to the shape of the A-pillars. The modified form and improved position of the exterior mirror not only reduce wind noise but also aerodynamic drag.

The B-Class thus not only appears even more mature and of higher quality, reduced noise also has practical benefits. They prevent fatigue and contribute to driver-fitness safety. At the same time, it is easier to hold a conversation in the vehicle: Using the so-called "Articulation Index", a measure for speech intelligibility, Mercedes-Benz engineers ascertained an improvement of up to 30 percent in terms of wind noise in comparison to the previous model.

At the same time, the noise, vibration and harshness characteristics have been improved. In this area, too, diverse measures were undertaken. Two examples: Instead of foam, a new combination of material is used for the interior trim of the wheel arches: A fleece spring mat combined with a heavy-duty layer reduces noise from the tyre tread, especially the hissing noises when wet.

And just like every modern car, the B-Class also has a flap for forced ventilation for pressure compensation, for example when the doors are closed. These flaps could be problematic acoustically because they transfer the sound. The developers therefore arranged the forced ventilation in the form of a labyrinth: A total of four changes in direction mean that the sound loses its energy while making its way into the interior.

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