With the Nido project, Pininfarina has chosen to rethink the current methodology of the car design process, resulting in an innovative concept, which reexamines safety in small automobiles.
The Nido concept builds upon Pininfarina's grand tradition of continuous investment in research and development programs in each of the Company's areas - Design, Engineering and Manufacturing - to quickly and methodically tackle contemporary problems as they arise in the automotive industry. For example, during the 70's energy crisis, the industry looked towards aerodynamics and alternative energy sources to cut fuel consumption. Pininfarina responded by developing the CNR Energetica 1 prototype, an ideal aerodynamic body shape, and the electric powered Ecos. In the 80's Pininfarina's pioneering research into lightweight material application bore the Audi Quartz and Lancia Hit prototypes, which explored the use of new light metallic and composite materials.
The 90's witnessed to heightened environmental awareness, spawned research into recyclability of materials, improved ergonomics and more efficient vehicle packaging. Pininfarina offered solutions with the Ethos macro-project, a family of three cars with aluminum chassis, recyclable plastic bodywork and innovative, low emission internal combustion engines, highlighted by the 1995 Ethos 3EV zero emissions vehicle. More recently Pininfarina turned their attention to hybrid vehicle research in the Eta Beta and Metrocubo projects which, with reduced dimensions and modular cabins, also answered the problems of both urban and medium range usage.
Today the industry is concerned with a problem that Pininfarina had already anticipated with the Sigma, Alfa Romeo P33 and Sigma Grand Prix prototypes: safety.
The Nido project dives into the concept of total design: coherent integration of all aspects of the design and engineering of the car. This concept was in fact conceived through an intense collaboration between design and engineering, two poles often opposed, with the singular goal of creating an attractive, small and safe vehicle.
By focusing and redefining their respective approaches on a singular goal from day one, new innovative solutions were discovered in the overlap between the aesthetic and the technical view points.
Nido demonstrates Pininfarina's ability to combine user's desires with the technical feasibility that allows the project to be built. It marks Pininfarina not only as an innovator today, but shows how Pininfarina is providing solutions for a better tomorrow.
The principle of the Nido project
When examining the issues of safety, we can no longer simply consider the effects of a collision on a single vehicle. Problems of incompatibility between vehicles of small and large masses in collisions have taken on a fundamental importance in automotive safety engineering. This is even more significant if we consider current development trends in cars, which are getting larger and heavier, in order to comply with increasingly severe legislation and to offer more passenger space. In this context, the safety of a small light car assumes particular relevance.
For this reason, the Nido project has concentrated on the development and prototyping of new solutions involving both the structure and the design of a small two-seater car with the objective of increasing levels of safety for both the occupants and pedestrians.
The principle normally applied to protect occupants in the event of a head-on collision entails ensuring that sufficient space is maintained to accommodate the biometric parameters of the passengers, by using the programmed deformation of components to absorb impact energy. This is achieved in part through the deformation of the front of the vehicle, in part transferring the remaining loads to the rear of the vehicle (via floor panels, side members, doors and the structure as a whole) and in part with active retention systems (seatbelts and airbags).
Applying this principle in a compact vehicle poses many more difficulties than in a larger car, as there is very limited space to accommodate crumple zones. This leads to problems in the design of structural components that comply with increasingly strict legislation. While the structure will withstand a violent impact, the very rigidity of the chassis, together with the limited space available, means that a significant proportion of the energy is transferred to the occupants. As the dimensions of the front of the vehicle cannot be increased, it is necessary to find an alternative solution to reduce the forces of deceleration acting on the occupants to levels comparable with those of larger vehicles.
Rather than basing the safety characteristics of the car on its mass, as is the traditionally accepted method, Nido puts forward a new principle.
Nido consists 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, due to the mass of the dummies and the sled, 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 of the dummies.
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.
Virtual validation of the principle
During the Nido project, a strong cooperative relationship between the different company divisions involved was established, and Pininfarina's experience in virtual product development was put to full use, employing computer simulation for static and dynamic analyses, structural and biomechanical crash testing and acoustic and vibration analyses.
The working principle behind the rigid cell/honeycomb energy absorber/sled system was validated using simplified virtual models. Úsing these models to simulate a variety of types of crash (head-on, lateral and roof crushing) made it possible to study the dynamics of the Nido principle during a collision. The initial simplicity of the model permitted a number of parameters for each of the three elements (for example, the rigidity of the absorber element) to be varied in order to discern the optimum characteristics and configuration. The optimum rate of deceleration of the car was defined by analysing the crash test results of other, similar vehicles. Each structural component has been assessed individually within simplified models, and optimised to achieve the objectives set for the project.
The simulations 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.
From the virtual model to the prototype
Translating the basic principle of the project into a fully functional car meant conferring a sufficient degree of rigidity to the lower section of the chassis, locating the engine at the rear of the vehicle and optimising the use of internal space to leave enough room to allow for the motion of the sled. To achieve maximum safety cell rigidity, innovative cellular sheet metal technology was used for the firewall, floor panels and central tunnel, which enables sufficient space to be made in front of the occupants' feet to allow the forward motion of the inner shell in the event of a head-on collision.
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 and conveys an impression of a protective 'nest' (nido in Italian) surrounding the occupants.
The sled consists of a 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.
The interior trim and fittings were not simply designed for style, but have been developed in consideration of the impact dynamics of the occupants during an accident.
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.
Staying on the topic of the inside of the passenger compartment, a number of parts are made from soft materials.
The door handles, for example, also function as emergency door releases. They are fabric straps, which can be used to open the door from whichever position the occupant is in after an accident. The stowage compartments are fabric pockets.
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. Furthermore, the dash itself also performs an energy-absorbing role, as its internal components (heater, air pipes) have been designed to contribute to dissipating energy in a collision. The underdoor side member is larger than usual as it incorporates a number of ‘crashbox' elements which absorb energy in a lateral collision. Despite its larger size, it has been designed so that it still does not impede access into the car. 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.
To maximise the effectiveness of the Nido principle, 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. This last feature optimises instrument visibility, thus further contributing to safety.
The essential body styling of the prototype echoes the technological content of the project: the shape and finishings convey the concept and highlight the project's consistency of shape and structure. The technological, structural and functional solutions adopted to maximise safety transpire through the vehicle's volumes as three principal elements: the rigid cell, the sled and the energy absorber. The colour scheme also contributes to emphasise the elements directly correlated to safety and confers a friendly and reassuring character to the car.
The surfaces appear as a skin stretched over a structure, thus emphasising the shape of the structure itself. The front of the vehicle is characterised graphically by horizontal lines echoing the motion of the sled shell, while the rear is more raked to confer a dynamic quality. Remaining with the rear of the vehicle, the hatch, which covers the triangular light clusters, is also the rear screen. The screen itself is hinged under the spoiler.
The low waistline, very wide windscreen and transparent roof ensure excellent visibility.
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.
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. On the one hand, this contributes to cutting the basic cost of the car, by balancing off the greater expense of the safety features with simpler internal trim, and on the other, it means that the interior of the car can be personalised according to individual tastes and requisites.
The full scale prototype
Starting with only the elements which are directly involved in the functioning of the Nido principle, two developmental models were built to correlate the simulated experimental results of the virtual model with a physical model. A 1:1 scale prototype was then built, incorporating both solutions developed specifically for this project and other, already known and consolidated solutions. The decision to use stainless steel for the structure was taken because of the specific characteristics of this material, which has an excellent energy-absorbing capacity in the event of a collision and which increases in mechanical strength in relation to the degree of deformation (strain hardening). As it requires no anti-corrosion surface treatment, stainless steel also makes the industrial process more flexible, and means that the cataphoresis treatment can be completely omitted.
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. The advantages of this technology lie in its improved energy absorption capacity in collisions and 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.
Lastly, the use of solid coloured plastics for the external body panels means that the painting process can be eliminated completely and gives the Nido project a high environmental value.
The last stage in the project will consist in industrial feasibility studies for a hypothetical production of 100-120 cars per day for a total of 20,000 units over 5 years.
Pininfarina has applied for patents for the innovative safety features developed as part of the Nido project.Source - Pininfarina Media