Clean slate: design and production of electric vehicles

Car manufacturers are starting to capitalise on the design freedom offered by low-carbon electric vehicles .

However, some of Nissan’s concepts on the way to the Leaf made much greater use of by-wire technology, taking advantage of the system’s ability to decouple the power system and the motors from the driver. For example, the Pivo city car concept included a cabin that rotated, so the driver didn’t have to face backwards when reversing. Another concept vehicle uses hub-mounted electric motors – an increasingly common idea for electric vehicles – in an innovative way, allowing the wheels to rotate so that the vehicle slips into parking spaces sideways and changing the car’s centre of gravity when it corners.

Nissan decided against incorporating such radical changes into its first full-EV offering, but there is a feeling among industry observers that it’s been too conservative. Paul Niewenhuis noted that other hybrid and EV manufacturers, such as Toyota and GM, had deliberately gone for a more outlandish design. ’A few years ago, Honda tried to compete with the Toyota Prius with what was essentially a conventional Civic with a hybrid-electric powertrain, and the feeling was that they missed out because it didn’t look different enough. We think that people like driving a Prius because it looks different and it lets everyone know they’re driving a hybrid.’

we’re at the beginning of a transition phase, and all the car designers and engineers in the industry have very little experience of battery electric vehicles; it’s not in their DNA

Paul Niewenhuis, Cardiff business school

Niewenhuis explained that the essential design decision for an EV is a safety-driven one: how to keep the batteries away from the most likely collision points. ’GM has put the battery of its EV, the Ampera, towards the back of the car; Toyota put the battery pack of the Prius between the back seat and the boot. The batteries tend to be heavy, so once you’ve placed it you have weight distribution issues, so you have to change chassis settings. And it also dictates materials selection: if you’re fully electric, the batteries are very heavy, so it’s tempting to go for more lightweight engineering to compensate for that; you need materials that are stronger but lighter.’

BMW is also looking at electric car development in its ’project i’, and is looking closely at the issues of battery capacity and materials choice. According to Ulrich Kranz, who is heading up project i, the company’s experience with a battery-powered Mini has shown that driver anxiety over the vehicle’s range on a single charge tends to evaporate after a couple of weeks, but have found that the space the batteries occupy is an issue – the electric Mini only has two seats.

The company is developing an electric vehicle for city use, called the Megacity car, and is therefore looking at smaller batteries with a lower capacity, to free up space, and is considering using much more carbon fibre in the car to keep the weight of the vehicle down. One advantage of carbon fibre is that production offcuts can be recycled, Kranz said; the company is working in partnership with SGL Carbon, a German carbon-fibre specialist, which is providing the fibre and is also working on methods of recycling the composite formed by the fibre and the hardened resin that binds it together.

BMW is keeping its designs for project i and the Megacity car under wraps, but Niewenhuis is adamant that the further away from a conventional design it is, the more successful it could be. ’The industry doesn’t really understand the customer’s desire for something new,’ he said. ’But if you look at the Smart Car, it was regarded as unsuccessful, but they were still selling 120,000-130,000 per year. By any standards, that’s successful for, when it was introduced, a very innovative, radical vehicle.’

Niewenhuis’s argument, which the success of the odd-looking Prius and the equally unusual-looking Mitsubishi iMiev seems to support, is that the customer wants a different vehicle to look different – and that to design something that looks so similar to an existing car might lead to problems. However, the conservatism of the automotive sector, which stems in part from the large investment needed to set up manufacturing facilities, tends to lead it away from large leaps in design. ’It would be too radical – not necessarily for the customer, but for the industry – to make that leap at the moment,’ he said.

Design leads directly into production, with the path from drawing-board to manufacturing plant now smoothed by the design-for-manufacture philosophy and by the integration of design software with production systems. ’We’ve long argued that the current car-making paradigm is dictated by the technology that underpins it, and the moment you change the technology in a fundamental way – such as the powertrain – then the way you make cars will change too,’ Niewenhuis said. ’It will take a while, but in 20-30 years, you will see that change in the industry.’

Quality control

Validating the safety features of electric vehicles is presenting the industry with a number of challenges

While electric cars will have to be designed and built according to new rules, systems used to test them will also need updating. The Fraunhofer LBF Institute for Structural Durability and System Reliability, based in Darmstadt, is looking at how the safety of the new designs, materials and architectures can be proven.

’These new designs will impose different loads on the chassis, which will spur on new methods for testing and appraisal,’ explained Prof Holger Hanselka, director of the Institute. For example, the need to incorporate a battery weighing up to 150kg means the structure of the car has a different job to do.

’Heavy batteries require a significant increase in the strength and stiffness of the vehicle’s body structure without a comparable increase in weight,’ said Erich Lücker, who is leading an EV testing project at the Institute. ’This is a big challenge.’

The Institute has built a testing rig that can apply higher forces both parallel and perpendicular to the chassis of the vehicle, while also simulating braking forces. Featuring 26 electronically controlled hydraulic cylinders to apply the forces, along with measuring wheels from specialist manufacturer Kistler, which incorporate sensors to measure acceleration and the effects of material expansion, heating and cooling.

The test rig can accommodate anything from a small city car to a six-tonne bus, according to Lücker, and can take a vehicle through a 300,000km test cycle in three weeks. The LBF is aiming to work with vehicle manufacturers as a contract laboratory to validate new EV designs, Lücker said.