If the history of ‘cars of the future’ teaches us a useful lesson for today, it’s that over-estimating the pace of change is all too easy, particularly when it comes to fundamental concepts of vehicle design. Back in 1958, for example, Ford unveiled a concept car called the Nucleon, which was intended to be powered by a miniature nuclear reactor. The possibilities – if not, yet, the dangers and responsibilities – of nuclear power were at the forefront of public perception and it must have seemed reasonable to speculate about a fission-powered future for road transport. But of course the reality was very different: Nucleon faded into obscurity and the cars of today are not nuclear-powered. They are still very similar in their basic concept to the cars which would have been familiar to a driver in 1958.
We’re still riding on four pneumatic tyres, usually suspended using steel springs, inside a body welded together from pressed steel panels, and reciprocating internal combustion engines still dominate. Fundamental changes of design philosophy have been few: front-wheel drive has taken over in all but premium and sports sectors, and unitary construction is now near-universal, but in few other areas has motor vehicle engineering changed so radically. It is not that vehicle development has been slow over the last five decades, but that OEMs and their suppliers have committed their engineering resources to refining and optimizing essential systems rather than overturning the conceptual status quo. But that might be about to change.
Electrical and electronic systems are taking over more and more functions within the vehicle, a trend which looks almost certain to gather pace. Practical electric drivetrains are getting ever closer, too. While all these innovations offer a range of interesting performance and efficiency advantages they also trigger new packaging possibilities for designers which might see the whole architecture of the car change over the next couple of decades.
So far, electric vehicles (EVs) powered by storage batteries or fuel cell stacks have exploited little of the potential for innovative packaging. In some cases, like the ‘Electric Drive’ Smart, that’s because they are based on an existing production vehicle with an electric powertrain replacing the original IC engine. In other cases, designers have chosen to make EVs look and behave as much like regular vehicles as possible to enhance their credibility. But there is another reason why electric drives have yet to make a big impact on vehicle architecture: most EVs have used a single traction motor, driving the wheels through a fairly conventional final drive and driveshafts. There is little to choose, packaging-wise, between this layout and a conventional IC engine and its transmission.
From a packaging point of view, a much greater advantage is gained when the single drive motor is replaced by individual wheel motors, a concept which has been suggested often but rarely made to work in practice. Michelin’s Active Wheel, demonstrated at the Paris show in 2008, is a promising version of the wheel motor idea. Developed over the last 12 years, the Active Wheel is a relatively conventional wheel/tyre assembly into which Michelin have squeezed a 30kW electric traction motor, a brake disc and caliper, and an electrically-controlled active suspension system. The assembly is mounted on the chassis using a simple linkage, and the only connection between the driven wheels and the power source is an electric cable. Driveshafts and differentials are eliminated, reducing the overall weight of the vehicle and saving space while also giving designers more freedom to introduce lower, flatter floors into passenger and luggage compartments.
Increasing use of drive-by-wire technology might also help to free designers from the need for mechanical connections, this time between the driver and the mechanical elements of the car such as the braking and steering systems. Electronic control of engine and automatic transmission functions is already a reality, and some elements of brake and steering function are now being managed by ECUs. Extend that idea to allow fully electronic control of all driving functions, in the same way that modern commercial and military aircraft rely on computer-controlled and fully-powered control surfaces, and you remove the need for mechanical links between the driver’s controls and the operating elements of the braking or steering systems. The obvious benefit is in the potential impact on vehicle dynamics that ‘smart’ control of these systems provides, but in addition there is more flexibility in the location and orientation of the driver.
A conventional steering system has to route a steering column from the interior of the car to the steering gear, perhaps along a complex path around the engine and suspension and with the added complication that the column must be able to move or telescope in the event of a collision to avoid driver injury. A steer-by-wire installation has no such limitations, so the steering wheel could be placed optimally to enhance the driving position. Elimination of friction and play could also improve steering precision and reduce load on power-assistance systems.
Combining the potential of wheel motors and drive-by-wire control liberates extra usable space for passengers and luggage, and provides an opportunity to experiment with novel seating arrangements. Because there are no longer mechanical connections to the controls, the driver does not have to sit in a specific location within the vehicle: the steering wheel and other controls can be made easily movable. Imagine a steering wheel carrying essential controls and instruments like that of a modern Formula 1 car – which already seems to be a trend which is gathering pace in production cars anyway, not always with desirable results – which could be positioned anywhere in the cabin. Instruments could be place on the wheel, or a head-up display could project information onto the windscreen in front of the driver. The only fly in the ointment might be the problem of providing suitable pedals. Perhaps conventional moving pedals could be replaced by pressure-sensitive pads, set into the toe-board in front of the front-seat occupants. For the cost of doubling up on the pressure-sensitive pedals, the car would become identical for right- and left-hand drive applications, which should lead to greater adaptability as well as a reduction in costs.
But while it is easy to envisage a vehicle concept using wheel motors and drive-by-wire controls to liberate interior space and improve design flexibility, there are still limitations imposed by the locations of other essential components, such as the electricity generation and storage packs. Current designs house fuel cell stacks and storage cells low down in the centre of the car. The Chevy Volt, for instance, has a T-shaped battery pack which runs along the centre of the car and behind the rear seats. Honda’s FCX Clarity houses its fuel cell stack between the front seats, with a lithium ion battery under the rear seats and the hydrogen tank between the cabin and the luggage compartment. Future concepts should be able to take advantage of emerging technologies which will give designers more options.
Nanotechnology may provide a solution for the packaging of lithium ion cells. In 2007, researchers at MIT formed lithium ion cells using cellulose sheets impregnated with carbon nanotubes, which acted as the cell anodes. In the future it might be possible to line body or trim panels with such a material, or even form the material itself into structural panels, freeing up space which would otherwise have to be reserved for a separate battery pack. Fuel cell stacks might also benefit from nanotechnology, which could improve energy density, but they will still need supplies of hydrogen and cooling water. Hydrogen storage, in particular, is a major issue. Storing hydrogen under pressure or at low temperatures is possible, but cooling or compressing the hydrogen uses up energy which reduces the overall efficiency of the system. Research is now being focused on other storage options, such as the use of metal hydrides. These can store large amounts of hydrogen in usefully smaller volumes, but with the significant drawback of high weight, which would require compensatory weight savings to be made elsewhere in the vehicle.
Innovative seating using different materials might provide a weight and cost saving which would also provide more opportunities for improved packaging. Car seats are still heavy, bulky affairs and their construction still has much in common with a 17th century sofa. In motorsport, the state of the art is a lightweight, high-strength seat constructed from carbon-fibre or glass-fibre reinforced polymer. The design of these specialized racing seats would make them unacceptable for most consumers, as they have pronounced side bolsters to locate the driver under high lateral acceleration, and many now incorporate head-level ‘wings’ to protect the driver against injury in a side impact, both of which make them difficult to get into and out of. They are also non-adjustable, except occasionally in their longitudinal location in the vehicle. But similar materials and manufacturing techniques could be used to produce a more conventionally-shaped seat which would meet customers’ comfort, access and appearance requirements, at the same time being considerably lighter than a conventional seat and taking up less space in the cabin. The whole car could be smaller, reducing overall cost and environmental impact, without compromising the interior space which is an important factor in vehicle choice for many consumers.
To speculate a little further, powered adjustment of the seats could be improved using new materials which are now in development. EAD’s April 2007 issue reported on GM’s development of ‘smart’ or ‘active’ materials, polymers and alloys which change shape, strength or stiffness when heat, stress, a magnetic field or an electrical voltage are applied. Early applications are likely to include sensors and actuators of all sorts, and similar materials could be used for self-adjusting air inlets or active aerodynamic surfaces. In many applications, these materials will be able to reduce component size, mass and complexity, and improve design flexibility. Smart materials such as these could be used to build seats which would be multi-adjustable, moulding themselves to the occupants and offering infinitely variable adjustment without the use of heavy electric motors and gearsets by altering shape or stiffness in a predetermined way under electric control.
What is not likely to change much is the number, location and orientation of the seats within the cabin. Most passenger cars still have space for four people and seats arranged in two rows, facing forwards, and it doesn’t seem likely that consumers’ preference for this layout will change any time soon. But in a vehicle with an electric powertrain, wheel motors, and drive-by-wire controls, with no engine to accommodate, the occupants could be pushed forwards and the front end of the car optimized for crash performance. For optimum visibility a curved windscreen with rearward A-pillars might help. To assist manufacture and reduce weight this could be made from an adaptable glazing material like Bayer’s Makrolon, with a scratch-resistant coating.
How much of this is speculation, and how much grounded in reality? As far as fuel cells go, we are nearly there already. Honda and Mercedes-Benz are already involved in large-scale trials of fuel cells vehicles in Germany, the USA and elsewhere, and true production versions are promised within five years. Michelin’s Active Wheel system is due to appear in the WILL, a joint venture between Michelin, Heuliez and Orange, which is now entering development testing and is expected to appear in production form in 2010. GM has already explored some of the packaging ideas with its ‘skateboard’ chassis layout. That’s the good news.
But although some drive-by-wire systems are well advanced, it will probably be some years before the industry and its customers feel comfortable enough with electronic controls to allow all the mechanical back-up systems to be removed and the full potential to be realized. Smart materials and nano-technology lithium ion cells are another area where it will be some time before the technology is mature enough to use in a practical application: certainly we cannot expect to be using them in vehicles any time soon, however exciting the possibilities might seem to be. Over-estimating the pace of change would be all too easy.