- Published in Features.
Fischer says that, compared to aluminium, BASF’s wheels are “competitive” but could yield further savings because they're modular.
Each comprises two pieces. The structural part is loaded with fibres so you don’t get such a nice surface, but the cover isn’t load bearing so you can use fewer fibres and get a better finish. “We can combine the structural part with different cover designs, whereas with an aluminium wheel you have to change the tooling,” Fischer says.
Testing is on-going but Fischer is confident that, for electric city cars in particular, the need to offset the weight of the batteries and therefore maintain an acceptable range will make composite wheels increasingly attractive to OEMs.
A megacity vehicle would be a good place to start. Production volumes would be low, to start with, and the relatively low speeds would limit dynamic loads. The experience gained from such a programme could be fed back into other, more demanding applications. “We won’t start with the Mercedes S-Class,” Fischer says. “We’ll start with the Smart car and do it step by step. The B-Class might be the next one, and then we’ll see.”
Glass fibre could also help to make the seats lighter. The Smart car concept used to demonstrate the composite wheels has seats made from a similar material, only these use short fibres to reinforce the injection-moulded polyamide structure.
Long fibres are used to make the reinforcement pieces that strengthen the seatback, to improve crashworthiness. The latter is one of the reasons why slim plastic seats – often a feature in concept cars – have yet to appear in series production. Cost is another.
“You have to show to the OEM that your seat passes all of the tests, but you can’t make this seat with only short fibres because then you won’t pass crash,” says Fischer. “You have to reinforce special areas with sheets or with so-called uni-directional tape, where you have endless fibres which are oriented along the mechanical load path.
“You place these in the mould and then you overmould them with the short-fibre-reinforced polyamide. This is the technology that works because it’s low cost. A fully endless or carbon-fibre seat would be too expensive.”
The weight savings from the seats are similar to those from the wheels – 3-4kg each – and, despite the thin sections, it's possible to package the custom heating and cooling systems that BASF has developed for them too.
The firm is also developing rapid-curing epoxies for carbon composites – heat triggers the latent catalyst in the epoxy, reducing cycle times from 30 minutes to just three. Used on the Smart car concept in place of the steel body structure, this saves up to 80kg, Fischer says.
OEMs won't compromise on safety for any weight saving, so the testing will be exhaustive. But, if successful, then perhaps in a few years the idea of rolling on composite rims will seem no more unusual than driving an electric vehicle does today.