October 23, 2004 Italian automobile manufacturer Pininfarina has been investing in car research and development programs for over thirty years, tackling environmental issues, alternative energy sources, fuel consumption and more efficient vehicle construction. Now Pininfarina have gone back to the drawing board to rethink the car design process and revolutionise safety in small automobiles. The result has been the innovative Nido, (Italian for 'nest') which provides an ergonomic protective inner sled shell and creature comforts in a striking two seater prototype.
The Nido project was conceived through an intensive collaboration of the Pininfarina design and engineering departments, using extensive virtual product development to run computer simulations for static and dynamic analyses, structural and biomechanical crash testing and acoustic and vibration analyses. The objective was to increase the levels of safety for both the occupants and pedestrians. Current safety provisions in the event of a head-on collision focus on programmed deformation of components to absorb impact energy, leaving sufficient space for passenger mobility. But applying this principle in a compact vehicle poses more problems than in a larger car as the crumple zone is minimised. This in turn leads to problems with the design of structural components that must comply with strict legislation. The rigidity of a small chassis combined with the limited passenger space of most small cars means a significant proportion of energy is transferred to the occupants.
Pininfarina solved these safety issues through a total systems approach to automobile design. Rather than basing the safety characteristics of the car on its mass, as is done traditionally, the Nido follows a new blueprint consisting of three principal elements:
1. A chassis, accounting for approximately two thirds of the total vehicle mass, which supports all the mechanical components, such as the front and rear suspension, the engine etc. This chassis consists of a deformable front section and a rigid safety cell surrounding the occupants.
2. A shell for the occupants, accounting for approximately one third of the vehicle mass. This shell holds the driver and the passenger, together with the driving controls and instruments. This shell is actually a sled, which can run horizontally along a central runner within the rigid cell.
3. The rigid cell and the sled are connected in normal conditions by a third element, consisting of two energy dissipating absorbers with controlled rigidity achieved by the combination of three honeycomb sections of different density.
In the event of a head-on collision, the vehicle absorbs part of the energy with the deformable front section of the chassis, constructed of two metal struts with internal plastic foam absorbers. These components are shaped as truncated cones in order to dissipate the energy over the cellular sheet metal firewall, which in turn transfers the energy along the central tunnel and the side members. The remaining energy shifts the sled itself forward and compresses the two honeycomb absorbers between the rigid cell and the dashboard of the sled shell, resulting in the gradual and controlled deceleration.
The insertion of honeycomb absorber elements between the rigid cell and the sled shell means that, in a collision, the deceleration curve for the sled is lower than the curve for the rigid cell. Additional, smaller absorber elements may also be fitted between the rear of the sled and the rigid cell, to provide occupant protection in the event of a rear-on collision. This principle, applied here in a small, rear-engined two-seater city car may also be used in a mid-engined two-seater sports car. Simulations also showed that thanks to the mobile sled system, the deceleration sustained by the occupants during a collision is low enough to render the use of airbags unnecessary in certain cases, meaning that the way in which they are currently used may be reconsidered.
The concept developed by the Nido project also includes the use of suitably sized transverse structures in the sled near the dash and at the base of the seats, which transfer lateral impact energy from one side of the car to the other. As a consequence, the doors rest on these transverse structures, an arrangement which also prevents door intrusion.
The overall architecture of the car was also chosen for functionality: the single-box shape allows more room for the motion of the sled shell of structural plastic reinforced by a sub-frame in stainless steel tubing to help keep the overall weight of the system as low as possible. A new concept of chassis construction has also been developed, replacing the traditional floor tray, tunnel and firewall configurations with a structure in cellular sheet metal. This improves the energy absorption capacity in collisions and provides excellent torsional stiffness. Cellular sheet metal technology consists of a sandwich made up of four or more thin layers: flat sheets are used for outside sections, whereas for internal parts, two or more ribbed sheets were assembled together with their respective corrugations opposed.
The front moulding is completely covered with a cushion of energy absorbing material to present safer surfaces in the event of collision with a pedestrian, and thus minimise injury; it houses, among other elements, the windscreen wiper and windscreen washer fluid filler cap. To reduce head injuries in the event of a collision with a pedestrian, the windscreen pillar is also fitted with a collapsible covering consisting of an external plastic section to fit in with the rest of the bodywork and an internal energy absorbing section made of the same foam used for the cushion. The headlights are mounted high to increase the deformable area presented during collision with a pedestrian. In addition to an indicator light, the wing mirror incorporates a white reflector to ensure visibility at night when the vehicle is parked. The low waistline, wide windscreen and transparent roof ensure excellent visibility. Lastly, the use of solid coloured plastics for the external body panels means that the painting process can be eliminated completely for high environmental value.
Inside the Nido the designers have ensured a stylish and comfortable interior that also maximises safety considerations down to the smallest detail. The space normally taken up by the steering column and traditional pedal box has been freed up by the use of a 'steer and brake by wire' system, which means that these components no longer intrude into the passenger compartment and also allow the use of a spokeless steering wheel, maximising instrument visibility.
The doors are fitted with rhomboid aluminium alloy hinges and are oversized in comparison with average comparable components on other cars to facilitate the exit of occupants after an accident. The inner door panel has been designed so that there are no hazardous protuberances during a collision. Inside the passenger compartment a number of parts are also made from soft materials. The door handles, for example, also function as emergency door releases. The dash assembly serves a dual role: it houses the instruments and is an integral part of the sled shell, acting to compress the honeycomb absorber during a collision. It also performs an energy-absorbing role, as its internal components (heater, air pipes) have been designed to contribute to dissipating energy in a collision.
A veltex trim has been applied on the dash and tunnel, so that any loose object (mobile phone, MP3 player, satellite navigator etc) can be fixed by simply applying a Velcro type strip on the object itself. This contributes to cutting the basic cost of the car by balancing the expense of safety features with a simpler internal trim; it also means that the interior of the car can be personalised according to individual tastes and requirements.
With the prototype Nido now complete, Pininfarina will undertake an industrial feasibility study for hypothetical production 100-120 cars per day for a total of 20,000 units over 5 years.
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