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Volkswagen XL1 Super Efficient Vehicle

News International-French

15 Jul 2013

The XL1 is maded of large lightweight and strong carbon fibre reinforced polymer (CFRP) parts and is a fuel-efficient car, with a fuel consumption value of 0.9 l/100 km.

The monocoque with its slightly offset seats for driver and front passenger, all exterior body parts as well as functional elements such as the anti-roll bars are all made of CFRP. The preferred process for producing CFRP components at Volkswagen is the RTM process (Resin Transfer Moulding). The density of this material or its specific gravity is only around 20 per cent that of a comparable steel exterior skin. The CFRP parts exhibit a level of stiffness and strength that is by no means inferior to that of comparable steel or aluminium parts, yet the exterior skin of the XL1 is just 1.2 mm thick.

Innovative RTM process
Compared to other methods such as manufacturing CFRP in a prepreg process, CFRP production via RTM is more economical − with lower costs at higher part volumes − because it can be automated. The RTM parts are produced in multi-shell, heated and vacuum-sealed tools. This involves injecting liquid resin at high pressure into the tool containing the semi-finished carbon material whose interior has the shape of the part to be produced. The part cures afterwards in the mould.

CFRP paves the way to the future

The Volkswagen weighs just 795 kg. Of this figure, 227 kg represents the entire drive unit including the battery, 153 kg the running gear, 80 kg the equipment and 105 kg the electrical system. That leaves 230 kg, which is precisely the weight of the body – produced largely of CFRP − including wing doors, front windscreen with thin-glass technology and the highly safe monocoque.

A total of 21.3 percent of the new XL1, or 169 kg, consists of CFRP. In addition, Volkswagen uses lightweight metals for 22.5 percent of all parts (179 kg). Only 23.2 percent (184 kg) of the new XL1 is constructed from steel and iron. The rest of its weight is distributed among various other polymers (e.g. polycarbonate side windows), metals, natural fibres, process materials and electronics.

Thanks to CFRP, the XL1 is not only light in weight, but very safe as well. This is due in part to the highstrength CFRP monocoque that is also lightweight. In a crash, it provides the necessary survival space for the driver and passenger. This is achieved by intelligent design of load paths, including the use of sandwich structures in the monocoque. In addition, the front and rear aluminium car structures absorb a large share of the crash energy. These principles were also implemented in the design of the CFRP doors, where an aluminium impact beam is used to absorb crash energy; a stiff CFRP door frame also minimises intrusions into the CFRP safety cell.
Much attention was given to the rescue of occupants as well. If the XL1 is resting upside down on its roof after a rollover accident, pyrotechnic separating screws simplify opening of the doors (swing doors).
The new car is currently one of the most fuel efficient and eco-friendly automobile.

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