Clean slate: design and production of electric vehicles
Car manufacturers are starting to capitalise on the design freedom offered by low-carbon electric vehicles .
The way cars are designed and produced is dictated by mechanics. Start with the positioning of the wheels on the chassis, decide where to put the engine, and everything else follows on: how to transfer the rotational energy of the engine to the wheels; how to control the output of the engine; how to change the direction of travel; how to slow the wheels down. All of these depend on the mechanical linkages between the components of the vehicle’s powertrain - engine, clutch, gearbox, transmission, driveshaft - and other systems, as well as the devices that provide the driver’s interface with those systems.
Once those are in place, the rest of the car follows on. The shape of the vehicle, the electrical systems, the interior layout are all dependent on the mechanism and the internal combustion engine at its heart - whether that heart is at the front of the vehicle, in the middle, or at the back.
Moreover, since the days of Henry Ford, those mechanical systems and linkages have dictated how the car is built. The production line, which is still the basis for car production, is designed to build and place those components in the correct order and join them together in sequence.
It’s an insult to the technology to pretend that we’re still dealing with internal combustion engine vehicles and designing them accordingly
So what happens when those components change? When there’s no longer a fuel tank, or a single device generating power, or a gearbox to transmit that power to the wheels? What do manufacturers do when there’s no need for a mechanical linkage between driver and engine? With fully electric cars giving the automotive sector the opportunity to wipe the slate clean, some are responding by throwing out the design and manufacture rule book - while others are trying to reconcile their past with their future. ’In a sense, it’s an insult to the technology to pretend that we’re still dealing with internal combustion engine vehicles and designing them accordingly,’ said Paul Niewenhuis, who specialises in automotive design and manufacture at Cardiff University’s School of Business.
Nissan is currently leading the field in electric car production, with its Leaf model being the first fully electric car to go into mass production. Going on sale next year, the Leaf will be built in three plants: Oppama in Japan, the first on stream, which will produce 50,000 units per year for initial demand; the second plant will open in Smyrna, Tennessee, in 2012, with a full capacity of 150,000 units; and the third will be at Nissan’s production facility in Sunderland, north-east England, opening early in 2013 and initially producing 50,000 units per year.
Each plant will be accompanied by a facility to make the car’s crucial component, its advanced lithium-ion batteries; the Sunderland plant, which will start up in 2012, will have a production capacity of 60,000 units per year and will also serve Nissan’s electric car partner, Renault. The French company is unveiling all-electric concept vehicles at the Paris Motor Show next month, including a hair-raisingly styled sports coupe called the DeZir.
Nissan’s design for the Leaf, however, is more conservative. Faced with a contradictory design brief for the initial concept, product chief designer Masato Inoue had to find a compromise between a ’real-world car that can be appreciated by conventional car users comfortably’ and an ’iconic design that can be identified as an electric vehicle instantly’.
- Length: 4,445mm
- Width: 1,770mm
- Height: 1,550mm
- Wheelbase: 2,700mm
- AC Motor, front-mounted
- Power: 8kW
- Torque: 280Nm
- Maximum speed: 140kmh (90mph)
- Batteries: 48 laminated lithium-ion units
- Charging time: 8hrs using 240V AC; 80 per cent charge in 30min using 5kW DC quick-charger
- Range on full charge: 160km (100 miles)
Meeting this brief, Inoue’s team came up with something that looks much like a conventional five-seater family car on the outside, but uses the freedom imparted by the new powertrain in a subtle way that’s near-invisible to the outside observer. The bonnet of the car is low, for example, because there’s no engine underneath it. There is also no exhaust pipe, silencer or drive shaft, which means that the bottom of the car is flat; the lack of exhaust components also meant that the team could incorporate a rear diffuser to improve the car’s aerodynamics without having to fit it in around other hardware.
The interior of the car is also a compromise. ’When we made a proposal using a close-to-final interior mock-up, Nissan chairman and chief executive Carlos Ghosn asked us “why am I not sitting in the centre? Why do we have all these dials on the dashboard?” He felt that the interior needed to match the same level of innovation in its design as the EV [electric vehicle] technology underneath,’ said Inoue. The final design does look different from a standard car - notably, the driving mode selector (where the gear lever would be in a conventional manual car) looks like a computer mouse and operates using a by-wire system.
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.’
Moreover, deliberately designing an electric car so that it looks different from a conventional internal combustion engine vehicle may have a practical purpose: it helps to manage the owner’s expectations. Somebody driving a vehicle that looks and feels conventional is likely to expect it to do what a conventional vehicle does, leading to range anxiety (what happens if you want to drive more than 100 miles and don’t want to stop for eight hours to recharge?). ’If you’re driving something that obviously isn’t a conventional car, you won’t have those expectations and will take it on its own merits,’ Niewenhuis explained.
His feeling is that the industry is embracing the possibilities of electric and that Nissan’s more conservative approach may be the odd one out. ’I think that if you just do something such as sticking a fuel cell in a Ford Mondeo, for example, it’s misleading, because it gives the impression that it’s the same sort of vehicle as a conventional internal combustion engine car.’ Companies such as GM are looking at a very different approach, such as the ’skateboard’ concept’, designed by British engineer Chris Borroni-Bird, which protects fuel cells, batteries and motors within a flat chassis and operates all the car’s systems by wire; this underpins the company’s Chevrolet Volt EV. ’GM has that line of thinking within the organisation, and companies such as Michelin are developing hub motors, so the suppliers are beginning to move in that direction as well,’ Niewenhuis said. ’But 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.’
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.’
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.