Germany: Lightweight Construction Summit 2017
"What's the Point of Lightweight Construction in an Electric Vehicle?"
BMW's CEO responsible for lightweight construction, Florian Schek, opened the Lightweight Construction Summit 2017 in Würzburg with his keynote address. His focus was on the benefits of lightweight construction for electric and hybrid vehicles.
Würzburg/Germany — The focus of his keynote speech was on the benefits of lightweight construction technology for electric and hybrid vehicles. He also took the new BMW 5 Series as an example for this field of applications. “In the past months, I have often heard statements claiming that e-mobility can go without lightweight construction — that its advantages could be balanced out by means of recuperation," said Schek, opening his presentation. "That's only partially true. However, many vehicles are heavier than two tons — the average limousines or SUVs, for instance. The joy of driving also includes lateral dynamics, and it’s not easy to achieve this goal with such a heavy vehicle," said Schek. He referred to the acceptance of electromobility and thus to the actual benefits of lightweight construction. “The world's population will increasingly converge in urban agglomerations. The cities are very active in managing traffic and it is obvious that the individual mobility of the future cannot continue to cause the same pollution problems associated with conventional combustion engines. Electromobility will be under a lot of pressure in this regard."
Customers Demand "Sustainable" Concepts
According to Schek, another topic is in culture. The premium segment, is subject to customers demanding concepts in line with environmental issues: the keyword is "footprint". In this context, we must gradually break away from the idea that the piston engine is the drive of the future," said Schek. It is obvious that electromobility will come — the question is only when and with what kind of drive: "Electrical power is not the only option, there are also good combinations — at least until we have made substantial progress in developing adequate solutions for energy storage, i.e. the energy that is available in the vehicle," explained Schek. “Electric cars and plug-in hybrids have already been on the streets for some while and we are a seeing a gradual increase in sales in this area. So far, there are around 100,000 vehicles — therefore we are expanding our fleet of plug-in vehicles and purely electric vehicles accordingly," Schek explained. We also see that buyers of conventional internal combustion engines are increasingly willing to switch to electric vehicles. 20 to 25 % of our customers consider buying a n electric car the next time they buy a vehicle. Customers who have already had experience with electrified vehicles are even more convinced: "More than 90 % would buy an electric vehicle again," Schek points out.
Schek illustrated the benefits of lightweight construction for electromobility in an example. “If I reduce the mass of the vehicle equipped with an internal combustion engine and one with an electric drive by ten percent each. What benefits do I achieve? Acceleration values give us a good idea: If the vehicles have approximately the same specific power, electric vehicles often contribute more power to acceleration because of the advantage they gain by the weight reduction. This is because nowadays most vehicles with internal combustion engines continuously provide optimum tractive power thanks to modern transmission technology. The full torque of the electric vehicle is available almost from the start, but the vehicles are usually designed for one or two gears. Therefore, the maximum tractive force is not available in every situation. Additionally, the following principle applies: The greater the ratio of kilowatt to kilogram, the lower is the impact of lightweight construction. This applies both to vehicles with internal combustion engines and electric vehicles."
Recuperation Cannot Replace Lightweight Construction
“We evaluate our vehicles on the basis of an in-house, "customer-oriented" cycle," said Schek. The energy requirement due to the weight amounts to about 40 % in a current vehicle with an internal combustion engine — this includes the resistance of the weight, i.e. the mass inertia, rolling friction and braking losses. The powertrain of an electric vehicle is much more efficient. Without recuperation, we would have a weight-induced energy requirement of around 50 %, 28 % of which would be due to brake losses — but in fact this is the amount of energy that is recuperated by the battery to a large extent." According to Schek, recuperation contributes a lot to e-mobility and diminishes the contribution of lightweight construction in an electric vehicle. However, it’s effects depend on the driving profile. In city traffic, weight has a higher share of fuel consumption than it has during a constant ride. The driving and speed profiles therefore determine whether the lightweight construction in question is reasonable or not. The benefit of lightweight construction therefore strongly depends on the individual vehicle: for usual "megacity vehicles", which are mainly used in the city and partly serve for commuting purposes, it is worthwhile to invest in lightweight construction. This is a different story in the case of long-distance vehicles — air resistance has the greatest influence on the range, which is why all OEMs are increasingly working on aerodynamics," explained Schek.
Automotive manufacturers are currently trying to integrate electromobility into their existing car design. This approach quickly exceeds the design limits of the models and has consequences on the design, the costs and the properties of the components. For this reason, it is important to develop lightweight components which for instance ensure that plug-in hybrid combining two drive trains remain below the design limits that are generally intended. However, it is of fundamental importance to take the overall vehicle concept into consideration. One such example is acoustics: "There's no point in designing a vehicle as light as possible, if this results in a higher need of insulation material, so that in the end, the vehicle is not lighter at all,” concluded Schek.
This article was first published by Automobil Industrie.
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