A concept EV developed by Daimler and BASF features a variety of efficiency-enhancing innovations.
The term ’range anxiety’ is now so firmly entrenched in the motoring lexicon it’s become something of a cliché – a stick with which stubborn petrol-heads beat down the latest electric car renaissance.
Looking for an edge, it approached BASF, which has a wealth of experience in making energy-efficient materials for use in construction, machine tooling and coatings.
Indeed, the car takes some lessons from BASF’s concept house at Nottingham University, which addresses issues of temperature management.
’If you build a house, you expect that in the winter it’s warm, and your walls are properly insulated, but at the moment no-one expects that of a car, so that was one of the first questions we posed,’ said Dr Olaf Kriha, BASF project manager of thermoplastics research.
Of course, there’s more at stake in EVs, since heating and cooling systems are a major drain on the battery, constraining range. Plus, EV designers have no residual engine heat to use, as is the case with combustion models.
Furthermore, a car, especially one as small as the Smart, presents significantly greater challenges when it comes to insulation.
’Look at the door; there is no space. In my house I have 20cm of insulation; I cannot put that into a car like this,’ said Prof Volker Warzelhan, BASF senior vice-president of thermoplastics research. ’So we developed a special foam just 1cm thick, which is as efficient as any house.’
The material is a vacuum-insulated, nanostructured polyurethane foam with a claimed lambda value (λ; a measure of heat transfer) of five – compared with construction industry standards of around 30-35λ.
This means that the heating system has less work to do in winter; but the team believed it could make additional savings there as well.
Studies show that the human body only absorbs heat efficiently through certain points, for example the lower back. So rather than heating the entire seat the team focused on these points. This is achieved using a special conductive ’e-textile’ that heats up immediately upon application of a current by way of a resistive paste that incorporates graphene.
For keeping cool in the summer, meanwhile, the car uses infrared (IR) reflective paint additives and windscreen film. This is nothing new – a number of production cars have tinted windscreen compounds that are IR reflective. But being metallic they can create problems with electronic communications such as GPS. BASF’s IR-reflective solution mitigates this by using a transparent organic polymer film.
Putting cars on a crash diet is one of the most obvious ways of increasing range – with both combustion and electric drivetrains. But with the Forvision, BASF wanted to make more of statement.
Enter what the company claims is the first all-plastic, mass-producible wheel offering a 30 per cent reduction in weight. It’s made from ultramid, a polyamide reinforced with long glass fibres.
Variations of the material have been used previously for machine parts and some automotive components such as the fuel pan. But the wheels present more of a challenge: not only are they subject to the loading of the car but dynamic forces such as cornering and braking.
To come up with a sufficiently robust design, the team developed a dedicated software simulation package that could replicate these forces. This allowed them to test how different orientations of the glass fibres affected performance.
Once they came up with a promising prototype it underwent traditional mechanical testing required by the automotive industry. But even if the team can present an impressive set of testing results, it will likely face an uphill battle persuading manufacturers and more importantly consumers that they will be safe rolling on plastic rims.
’The same discussion happened 20 years ago when aluminium wheels started replacing steel ones people said: “It’s not stiff enough there are problems with fatigue. I could never imagine driving with an aluminium wheel.” But now on the street more than half of all cars have aluminium wheels,’ said Dr Heiko Heb of BASF, who heads the wheel team.
Even with these temperature-control and weight-saving measures, the battery will inevitably be called upon for non-drivetrain functions such as the multimedia system and lighting, as well as heating and cooling.
To delegate responsibility for providing this energy, the team came up with probably the most ambitious feature of the car.
In the roof is a series of transparent hexagonal panes composed of a bi-layer with organic, dye-sensitised photovoltaic (OPV) material on the outside and organic light-emitting diodes (OLEDs) on the inside.
“In my house I have 20cm of insulation. We developed a foam 1cm thick that is as efficient”
PROF VOLKERWARZELHAN, BASF
These dye-based cells have a lower overall conversion efficiency than traditional silicon solar cells, but can capture scattered light coming from different directions. This makes them more suitable for use in a car, which is constantly moving with respect to the sun, as Kriha explained.
’So nobody would think: “Well, the sun is rising so I can only drive to the east, or the sun is going down so I have to go to the west.” It makes no sense.’
So what does all this fine tuning and attention to detail with regards to energy efficiency actually achieve? Best estimates suggest somewhere in the region of a 20 per cent increase in range relative to Smart’s latest production-ready Fortwo ED.
Admittedly it doesn’t sound like much: an extra 17 miles perhaps. But it’s encouraging, and the whole project adds to the sense that manufacturers are serious about the EV renaissance. EVs are here to stay this time, and every small detail is going to count.
The Smart Forvision represents the latest stage in the EV renaissance
Range: Non-drivetrain energy-efficiency modifications achieve up to a 20 per cent increase in range relative to the production Smart Fortwo (ED) model, giving an approximate total range of 168km (104 miles).
Insulation: In the door and panels is a 1cm-thick vacuum-insulated, nanostructured polyurethane foam with a heat transfer rating of 5λ.
Temperature: Infrared reflective paint and windscreen film achieve a 20ºC decrease in car surface temperature in the summer and a corresponding 4°C decrease inside the cabin.
Wheels: Polyamide reinforced with long glass fibres achieves a 30 per cent decrease in weight relative to aluminium and 50 per cent relative to steel at an extra cost of around 10-20 per cent.
Energy harvesting: Organic-dye-sensitised solar cells generate enough electricity in diffuse light to power a multimedia system and cooling fans.