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Benz focuses on aero over weight to meet fuel tests

Aero bar: Benz engineers focused heavily on aerodynamics with the new-gen A-Class.

Changed Euro fuel testing regime forces Benz engineering rethink

8 Feb 2018


MERCEDES-BENZ A-Class program manager Oliver Zolke has revealed that an increased average speed of incoming European fuel consumption tests now places greater emphasis on improved aerodynamics over weight reduction, with vehicle development priorities now being altered to suit new regulations.

Later this year, published data on fuel consumption, and CO2 and NOX emissions will switch from being based on the 20-year-old New European Driving Cycle (NEDC) to a new Worldwide Harmonised Light Vehicle Test Procedure (WLTP).

While still laboratory assessed, it has been derived from real-world driving data and now runs for 30 minutes and 23.5 kilometres, versus 20 minutes and 11km previously. It also has increased dynamic phases, a 10km/h-higher top speed of 130km/h, and overall average speed of 46.5km/h – up from the former 34km/h.

It has been the latter changes that Mr Zolke pointed to as affecting the way Mercedes-Benz would engineer its vehicle to ensure a lower figure is achieved in the new WLTP.

“So in WLTP, the new regulations, weight is not that important anymore,” he told GoAuto at the global reveal of the new A-Class in Amsterdam this week.

“It (weight loss) is still important, but not that important anymore. The cycle is faster, the average speed is faster, and so aerodynamics is much more important and also rolling resistance is much more important than weight loss.”

Mercedes-Benz spruiked the aerodynamic performance of the fourth-generation A-Class, which claims a new drag record for compact cars with an 0.25Cd rating – down 0.03Cd on the previous model from 2012.

The car-maker further revealed that the improved Cd value alone has improved the yet-to-be-released WLTP figure by 0.15 litres per 100 kilometres or the equivalent of removing 100kg from the kerb weight of the new A-Class.

The effects become even more pronounced based on ‘interstate’ driving, where the new five-door hatchback has shown a 0.24L/100km improvement, or the claimed equivalent of removing 200kg from a vehicle’s kerb weight.

Although kerb weight figures for the A-Class have yet to be revealed, Mr Zolke said the new model has been slimmed by only between 10kg and 20kg, with aluminium used for the bonnet and guards only – but not the body structure.

When asked why more aluminium was not employed, he pointed to the WLTP as playing a part in the decision not to use the lighter material: “There are two reasons, one is money, and the other is the new regulations.

“So I think in the C-segment it will also take a lot of time to use aluminium in the structure like we do in the upper classes.”

While the higher average speed of the WLTP could be in contrast to lower urban average speeds, as congestion increasingly takes hold in many global cities, and this would be where greater weight loss would be more beneficial than enhanced aerodynamics, Mr Zolke said engineers still looked at all scenarios.

“Don’t get me wrong, we still work hard on weight reduction, but to introduce in a standard steel body aluminium parts, this for the factory is a big step and also for the purse a big step,” he said.

“So in this generation (of A-Class) we said no.”

According to a publication by the European Automobile Manufacturers’ Association (ACEA) there are several upsides to the new WLTP over the NEDC (although the old system will form the basis of emissions standards until 2021).

These include “more realistic driving behaviour a greater range of driving situations (urban, suburban, main road, motorway) longer test distances more realistic ambient temperatures, closer to the European average higher average and maximum speeds higher average and maximum drive power more dynamic and representative accelerations and decelerations shorter stops and stricter car set-up and measurement conditions.”

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