New B-Class 'shows maturity of full-grown Mercedes'

  • 20-Dec-2011 03:36 EST
Merc10-11BClass Aero 2.jpg

The new Mercedes-Benz B-Class achieves a Cd of 0.26. An even more slippery model will achieve 0.24 with further optimization.

Dr. Dieter Zetsche, Daimler’s Chairman of the Board of Management and Head of Mercedes-Benz Cars, knows the absolute significance of allying technology (particularly safety systems) and quality for his company’s products. That is why the arrival of the new Mercedes B-Class is so significant.

“We have added more new features than we’ve had in any other model change in the history of Mercedes-Benz,” he said. “And our second-generation B-Class shows the maturity of a full-grown Mercedes.” That means it has been engineered, tested, and is manufactured to the levels that Zetsche sees helping the company become number one in premium-segment sales. “But we are also shooting for more emotion; we need that too—and have it with the new B-Class.”

Zetsche singled out as the technologies the car’s dynamics, with all-new running gear including four-link rear suspension supported by an advanced ESP system; its packaging, with more rear legroom than many business sedans; its safety (Euro NCAP 5-star) with standard Collision Prevention Assist; dual-clutch transmission option; and perhaps most importantly, its overall efficiency.

A significant element of that is its ability to house multiple powertrain types. “We have revealed the Concept B-Class E-Cell Plus with range extender, the space for the battery already reserved in a dedicated intermediate floor in front of the rear axle.”

Zetsche’s Chief Engineer and Program Director, Compact Class, Prof. Dr. Hans-Georg Engel, said of the powertrain options, which also cover gasoline, diesel, hydrogen fuel cell, CNG (compressed natural gas), and LPG (liquid petroleum gas): “It is a question of what makes sense and the market response for a car with a certain type of powertrain.”

Mercedes is not going to foist technology onto the public just because it can do the design and engineering; it will ensure that it is wanted. “Customers have never been more educated than they are today,” stated Zetsche.

It was a big challenge to develop a car that meets such broad criteria for potential variants, and it is the first time Mercedes has attempted to do so from design inception. A key part of this is the modularity of a platform that can comprise a single or systems/battery housing-double floor by relatively simple adaptation and without re-engineering. Mercedes refers to the created gap between the two floors as the “energy space.”

Sandwich construction is, of course, not new to Mercedes, but an “intelligent” adaptable solution stretching from the front seat row to the rear axle is. The height of the energy space is 210 mm (8.3 in).

Increased efficiency also requires optimized aerodynamics. Zetsche is delighted with a best Cd figure of 0.26 for the new B-Class, but that is not the end of the story, he said.

Engel explained that a Cd of 0.24 would be achieved for the forthcoming ECO Package version of the car (the same as that for the E-Class Coupe) thanks to ultrafine aerodynamic “tweaking” of almost every aspect of the vehicle’s exterior. “We call it optimization of the outer bodyshell—of the skin, the surfacing, the detail—as we try to avoid unwanted vortices. We have achieved something similar before but not in the same way as we have with the B-Class—not as sophisticated.”

The 0.24 figure for a station-wagon type body is very impressive and may signal still further reductions. Zetsche and Engel are cautious about commenting on this, as any reduction below 0.25 is very hard to achieve. But while a Cd of 0.20 is not likely in the near future, trimming it to 0.23 or even 0.22 is understood to represent realistic targets, although neither executive would comment on the likelihood. “Reducing the Cd for a coupe is rather easier,” added Engel wryly.

Notable efficient aerodynamic elements on the new B-Class include managing the airflow around the wheels, an extrapolation of a technique previously developed by Mercedes. Air is guided through two vents, or slots, from the front fender and bumper, one of which guides it away from the root cause of turbulence—the wheel. “We have achieved something similar before the new model but not as effectively. It is now very sophisticated,” said Engel.

Other methods to reduce Cd include sacrificing some of the aspects that stylists might prefer, he explained. This may involve smoothing details and possibly further encapsulation of lights. Tailgate spoiler size and roof shapes are also part of this. “We may be talking about just a millimeter or so here and there; what is important is the total sum of this detail development.”

Underbody aerodynamics includes a huge diffuser and aerodynamically optimized exhaust system. “Each part of the car’s body has been optimized individually,” added Engel. The cost of developing such solutions has to be a consideration, but he explained that new tools make the design and development of ever more slippery and efficient shapes easier and quicker.

Most of the aerodynamic work is done in-house by Mercedes, although the University of Stuttgart’s wind tunnel, with its capability to simulate a street environment, is also used, particularly for work on evaluating the wheel-arch slots.

A sport version of the new car sits 20 mm (0.8 in) lower at the front and 15 mm (0.6 in) at the rear; this slight wedge profile helps the aerodynamics marginally but is more about the car’s dynamic balance—and its dynamic effects form part of Zetsche's "emotion" message.

As for weight control, fenders, hood, and some chassis components use aluminum. Magnesium is used only for the steering wheel and the structures of some components.

Zetsche regards high-strength steel as still having “significant future potential.”

Enhanced safety is a central aspect of the B-Class design. As well as the fitment as standard of a radar-based Collision Prevention Assist (CPA) system with Brake Assist to reduce the risk of rear-end collision, the B-Class has a strengthening beam above the rear axle which also adds to the car’s torsional rigidity of 25,700 N·m (19,000 lb·ft) per degree and, interestingly, added front-end crash-load-path capability.

The standard path via the main longitudinal members is complemented by others to the A-pillars and a third application that uses the whole underbody structure, so providing a triple load path solution.

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