1st March 2012
BMW Blog has posted an excellent interview with Dr. Klaus Draeger, Board Member and Head of R&D at BMW regarding the company’s use of carbon fiber composites in automotive design. We’d encourage you to visit BMW blog to read the full interview but have picked out one (abbreviated) answer which we found particularly interesting.
BMWBLOG: What is the future of CFRP (carbon fiber) for BMW?
Dr. Klaus Draeger: The first series of carbon fiber will be used for the construction of the complete body of the BMW i3. Currently we already have some experience with carbon-fiber: we are using carbon fiber on the roof of the M3 and on other parts of the M products, like the crash beam of the bumper, but in terms of production, we will see it in BMW i3 and i8.
The second project we are running is BMW ActiveE, where we are actually testing the whole drivetrain of the BMW i. So we are using the same cells as we will use in the BMW i3, the same ECU and the same electric motor. Looking at something specific now, if you convert a conventional car into an electric car, it doesn’t work. The reason is that the engine of a conventional car, the gearbox, the cooling system, the exhaust system, etc., everything is so large and it doesn’t fit the engine compartment.
When you’re taking that stuff out, and leave just the electric motor there, you will have lots of spaces there, but you can’t fit the battery in there because it causes real problems in a crash. You try to fit the battery somewhere else, usually where the fuel tank is. The fuel tank it’s pretty small – 50-60 liters, which means also 60 kg, while the battery is – depending on the size – large and heavy.
So you have to try to rebuild the car out. The result is that ActiveE has a weight of roughly 1800 kg, and the i3, which is a purpose-built electric vehicle, will have a 1250 kg. And this was the same electric motor, with the same ECU, and almost the same battery – it’s a bit smaller, because we could reduce the weight, because actually we don’t need much battery capacity aboard.
And this shows why weight is so important, and therefore we have done two things:
- We have an architecture that is specifically designed for this vehicle: we have the battery in the floor space, the electric motor and the ECU in the rear of the car, but we can keep the electric motor pretty low on the ECU, so that there is still a luggage compartment. We have a small luggage compartment in the front and we have space for four persons.
- Using carbon fiber in that case helps further reducing the weight, and this leads to reducing the amount of battery. So the tradeoff I get from reducing the weight of the electric vehicle is much bigger than in case of the conventional car. And this was the idea then, starting to use carbon fiber in the i3, as a real product for the life cell, while the drive module is this aluminum chassis with a battery and the front and the rear axle.
Interestingly, the interview also reveals that carbon fiber materials are planned for the new BMW 7 Series as part of a weight saving exercise. Read the full interview at BMW Blog
For further background on the use of composite material on the BMW i vehicles, take a look at this video from Autoline.
Autoline speak to Ian Robertson of BMW AG about the
use of Composite Material in their ‘i’ vehicles