Extended range, thanks to the wind tunnel

The new era of electric mobility is about to begin: The new EQC (combined power consumption: 22.2 kWh/100 km; combined CO₂ emissions: 0 g/km, preliminary data [1])*, the Mercedes-Benz of electric vehicles, is set to hit the streets next year. Plans call for electrification of the entire passenger car fleet by 2022. In the second part of our interview with Teddy Woll, the Head of Aerodynamics at Daimler, we ask him why aerodynamic properties are so important for electric vehicles.

Mr. Woll, with the premiere of the EQC, the first fully electric Mercedes-Benz model produced by the EQ technology brand, it’s now clear that electric mobility is no longer a fantasy. What role do aerodynamics play in electric vehicles?

It’s clear that aerodynamics play an even more important role in electric cars than they do in vehicles with combustion engines.

Why is that the case?

With an electric vehicle, you can recover most of the energy you use when you accelerate or drive up a hill. In technical jargon we call this energy recuperation.

So that’s why aerodynamic factors are more important in an electric vehicle?

That's right. The vehicle’s weight loses importance due to recuperation. By contrast, irreversible losses connected with tire rolling resistance and air displacement are all the more noticeable. This means that low rolling resistance and/or air resistance lowers energy consumption by comparison with the fuel consumption of a car with a combustion engine. This, in turn, means the electric car has a longer operating range than the car with a combustion engine.

What effect do aerodynamics have on the range of an electric vehicle?

Unlike a combustion engine, which tends to perform best at a high operating load, the efficiency of an electric motor decreases when its operating load increases. In addition, the energy stored in a battery is less than the energy stored in a fuel tank by a factor of nearly one hundred. For example, the energy content of 80 kWh in the EQC battery corresponds to only eight liters of conventional fuel. So, despite the energy recovery and much higher overall efficiency factor, travel at high speeds rapidly reduces the range of an electric vehicle.

And that’s where aerodynamics come in…

Exactly! Air resistance is proportional to velocity squared, and this means that air resistance is one of the keys to achieving a longer range. You notice every minor improvement to the Cd value immediately — and the faster you drive, the more you notice it. If you lower the Cd value by one one-hundredth, the range increases by just under one percent in the NEDC, and by 1.3 percent in the WLTP. If you drive on a highway, the increase amounts to two percent, and it can reach as much as three percent at very high speeds.

What effect does a higher vehicle weight have on the aerodynamics, and thus on energy efficiency?

If the vehicle weight is high, you need larger and wider tires. That makes a car look sportier, but unfortunately it does nothing to improve the Cd value. In addition, the use of a large battery to achieve a suitable range for normal use leads to larger front surfaces — assuming that we plan to offer our customers the same amount of space they have in a vehicle with a combustion engine. The combination of the two is certainly not optimal in terms of aerodynamics and thereby energy efficiency…

What aerodynamic features do you use to counteract this effect?

We engineers would say that the EQC is truly well designed, from the radiator shutter in the front to the trailing edges in the rear. Our solution for the problem with the wheels that I mentioned before is to use new sophisticated aerodynamic wheels with a bicolor design that also appeals to the design experts. Still, the combination of the large wheels and the battery in the underbody also makes the vehicle longer and wider. Parking spaces are limited, not only in terms of their numbers but also in terms of size, so the overhangs in the front and back need to be shorter. That’s a real challenge for our aerodynamic engineers.

How do you overcome this challenge?

Two things that are really helpful here are a round nose with optimized fog lamp recesses, which ensures the best possible airflow around the front wheel arches, and a beautifully inwards-drawn rear end. The completely smooth and sealed underbody also ensures optimal airflow. This effect is reinforced by all-new and quite large 3D wheel spoilers in the front and special wheel spoilers in the rear, as well as a perfectly shaped roof with a prominent roof spoiler and side spoilers. The Cd reduction is rounded out by special side member cladding and optional aero running boards.

EQC Front

In addition, instead of the traditional radiator grille, the EQC has a prominent black panel surface. Is there an aerodynamic reason for that?

Yes and no. It’s true that we benefit from the lower need for cooling air when the vehicle is in operation. The fact that the electric motor emits virtually no heat means that the cooling air vents can often be kept closed. For this reason, the EQC has a two-tiered air-control system without basic air ventilation but with systematically sealed cooling air paths up to the cooling module. In other words, we aerodynamic specialists didn’t stand in the way of the black panel surface, which is really a design element more than anything else.

Mr. Woll, you’re responsible for airflows but also for aeroacoustics. The EQC is particularly quiet. Why is that the case?

Electric vehicles produce virtually no motor noise. As a result, tire noises and wind noises are heard much more clearly even at low driving speeds. This means that we need to pay even more attention to the areas that affect the aeroacoustics, such as the A-pillar and the exterior mirrors. That also applies to the noise insulation. This is exactly what we did with the EQC.

Infographic comparison TSG and LSG

For example, the doors have panes made from laminated safety glass with noise-damping film. This significantly reduces high-frequency wind noise as compared to conventional tempered single-pane glass. We’ve also made noticeable improvements in terms of reducing low-frequency noise with our solid and sealed underbody, and the result is a very harmonious overall noise level. That results in a high level of comfort for drivers.

In the first part of the interview, you told us that the aeroacoustic wind tunnel and its high-tech systems are indispensable to your work on reducing wind noise in particular. How often was the EQC in the wind tunnel?

Quite often — I can tell you at least that much.

Mr. Woll, thank you for this interview.

[1] The indicated values of the fuel consumption and the CO₂ emissions are based on measurements according to the New European Driving Cycle pursuant to Section 2, Nos. 5, 6, and 6a of the valid version of the Pkw-Energieverbrauchskennzeichnungsverordnung (Pkw-EnVKV) (Regulation on Energy Consumption Labeling). This information does not refer to one individual vehicle and is not part of the offer. Instead, it is provided only for comparative purposes in order to facilitate comparisons between different vehicle types. Determined on the basis of the measured CO₂ emissions in consideration of the vehicle mass.

*The figures for power consumption CO₂ emissions are provisional and were calculated by Technical Services. The figures for the vehicle’s range are also provisional. An EU type-approval certificate and a certificate of conformity with official values are not yet available. The figures given above may deviate from the official values.

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