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Thursday, January 24, 2008

Fiat Bravo: In Depth

Sophisticated technologies for record-breaking development time

'A good product is always a well designed product'. This was the guideline that convinced the Fiat Bravo team to take advantage of the best design processes to develop the new car, exploiting virtual methodologies because they could optimise both individual performances and their trade-off in real time. The development of the Bravo is an excellent example of this original approach: only 18 months separated the moment that the product specifications were frozen from the market launch. This is a record in the automotive world, and an important competitive advantage, since being able to develop a car rapidly means responding better to market demands.

But to be not only fast, but rigorous and excellent too, requires cutting-edge technology and extremely precise engineering processes. This rigour has been applied at all stages of the development and industrialisation of the Bravo, applying the most advanced, innovative reliability methodologies. It was a winning project, which had three specific objectives: outstanding safety, enjoyable driving and the best quality of life on board.

Engineering excellence that goes a long way back

To build a revolutionary engine, innovative systems and cars that are a success overall, a manufacturer must employ cutting-edge technologies and methodologies that interpret the customers wishes, to achieve a level of comfort and performance that set them apart from the competition, low consumption and emissions in all conditions, and the highest levels of safety, quality and reliability. Ambitious goals that have always placed the Fiat Group among the pioneers in the application of virtual analysis to design. Even in the 1970s, the structural components of a vehicle were verified by computerised calculation techniques, and early in the 1990s, the company acquired one of the first 'super-calculators' for commercial uses (the famous Cray supercomputer), only the third in Italy, when there were very few in Europe, generally used for scientific calculations in universities or large research centres. And the company has always kept up with the latest virtual technologies on the market, in many cases actually anticipating them thanks to the work of its own Research Centres.

The Fiat Bravo is the outcome of a winning development process

At Fiat Auto, the development process starts from stringent objectification of performance, as seen by the customer first and foremost. This allows all objectives to be measured, so that the development process can be organised in three main stages: target setting, target deployment and target achieving. It is the latter that has been revolutionised by the introduction of virtual verification cycles, which drastically cut development times and costs, increasing the team confidence in the possibility of achieving its initial goals. Research in the field of simulation has focused on the creation of mathematical models that can provide an increasingly exact estimate of the physical parameters that are most representative of a vehicle performance.

We should point out that there has not only been an evolution in physical simulation calculations. Take the huge graphic potential of the new IT tools, which make it possible to visualise physical objects with the utmost realism. From the evaluation of the styling to verification of layouts and access to components, virtualisation of the assembly line and immersive verification of physical and cognitive ergonomics: all the systems on the vehicle and the plant necessary to produce it can be 'seen' by specialists exactly as they are in reality, immediately after they have been drawn by the designer.

That is not all. The development process is backed up by powerful planning, checking, technical data filing and monitoring systems. The integration and close connection between the system that established a single BoM for engineering and manufacturing, known as CAD/CAE PDM, the archive of standards and the unified system of product objectives and the authorisations, both physical and virtual, that constitute a 'backbone' for the management of information that is practically unique in the automotive world. These systems are constantly updated in real time and available both to suppliers and, obviously, to all the Fiat Auto design centres all over the world.

But we must not forget that to achieve a quality product like the Fiat Bravo, state-of-the-art CAE methodologies must be adopted at all stages of its development. To do this, the company has relied on the collaboration of its best suppliers, and has created its own model which programmes all the stages organically: from the initial scenario, through the strategic configuration, innovation, standardisation and analysis of the initiative, right down to final technical and technological development, the integration of suppliers, final quality verification and manufacturing build-up.

From styling to 'perceived quality': how the entire process is organised

As soon as the styling starts to take on a possible configuration, the feasibility of the individual parts is verified virtually, and the aerodynamic behaviour of the shapes of the vehicle are assessed; then preliminary ergonomic checks are performed on the first styling proposals. In the meantime, the styling and the virtual checks consolidate the choice of the definitive model, triggering the real design process. The skeleton takes shape, and work can begin on the shape of the bodyshell. Today, Fiat Auto CAD designers are in a position, when necessary, to perform the first static verification on the most crucial CAD parts using calculation tools that are totally incorporated into their CAD environment, simply and rapidly. The most detailed, complex calculations are performed by specialists, but even their work has been simplified, because they have direct access to CAD mathematical calculations through the company database which includes the drawings of all our models.

The DMU, the digital mock-up of the assembly of all vehicle components, is integrated into the database, which makes it possible to verify their layout, ease of assembly and access for service, even using totally immersive virtual reality techniques. As soon as the 'body in white' has been completed designers receive immediate feedback from the ergonomists, who verify the visibility zones and reflections by calculation, to correct the design of the space, the interior systems (seats, facia, etc.), the primary and secondary controls, the mobile parts and the communications interfaces. At the same time, the first vehicle dynamic calculations begin, as does verification of the mechanical components. Specific simulation models have been developed in the field of Handling and Ride Comfort, that include all the controlled active systems that are present today, from ABS to stability control.

The bearing structure of the early stages of technical development is based on milestones of the CAD drawings present in the database. The virtual structural verification of the safety, rigidity and fatigue resistance aspects gets underway from a very clear level of maturity. In the safety field, Fiat Auto applies the latest methodologies to simulate the effects of impact on the structure, on the human body and on pedestrians, including simulation of the activation and control of the active restraint systems. These include crash and biomechanical methodologies, to ensure that the passenger compartment cell protects occupants and that the front of the vehicle is compatible with vulnerable subjects (pedestrians, cyclists, etc.), respecting current and future legislation. This means that it is possible to verify the objectives set by the initial project much earlier using virtual methods than would be possible with real simulation, using prototypes.

All the other performance parameters are approached in a similar manner: fatigue, acoustics, climate, performance and consumption. For example, CAE methodologies have been applied throughout the development of the chassis, with particular reference to the performance targets for both fatigue resistance and NVH (Noise-Vibration-Harshness) quality. First of all, the fatigue resistance of the chassis was developed and approved by calculation, using FEM methods to virtually simulate typical missions that generate fatigue, a system already in use for bench testing. Good consistency has been achieved between the calculation and the experimentation, thanks above all to the integration of multi-body calculation methodologies (dynamic simulation of the vehicle during its mission) and FEM calculation methodologies (structural calculation of stress and fatigue damage).

Even the smallest details linked to quality are carefully analysed and calculated. Design of Experiments techniques are used to explore all the possible cases related to manufacturing variables (geometries, material characteristics, coupling, etc.) in order to ascertain that there is no anomalous behaviour (bangs, squeaks, creaks, etc). Virtual approval activities related to steering-wheel vibration (crossbeam and column), engine noise (structural measures at the anchorage points) and advancement noise (suspension blocks and bushes) are all part of this process.

The end result of the entire development process is the Fiat Bravo, a top quality car that is absolutely innovative, created in record time, and the fruit of expertise that is unique in the automotive world.

A project that refutes two myths regarding virtual verification

Until now, it was widely thought that virtual verification could not completely replace the tests on physical prototypes used to reach the final approval of a project. At most, people recognised that virtual verification eliminated a few experimental cycles on the first mock-ups, which were known to be of little significance, and that they could be useful during fine-tuning and problem solving. Which is why, even with significant disadvantages (slowness, high costs, need for test tracks and laboratories), physical prototypes continue to be used, even when they were obsolete with respect to the stage of development of the project. This was certainly the case at Fiat. Until the Bravo.

But now a new approach to design was needed, to cut time and costs, while respecting the demands of an innovative, top quality project like that of the Bravo. So, taking into consideration the increase in hardware performance which has stimulated the growth of increasingly sophisticated calculation applications, the team used the latest resources in this field, drawing on the expertise gained in this field by Fiat Auto in years of experience, also verified outside the automotive field. The Bravo was the first car to be developed adopting exclusively virtual verification systems.

Another myth was that virtual verification could at most replace the corresponding physical experiments; in actual fact there is more to it than that. Virtualisation of the vehicle creates a practically infinite number of prototypes which can be subjected to a practically unlimited number of tests. This also makes it possible to apply the most advanced statistical methodologies in the field of optimisation and 'robust design'. It means that Fiat Bravo has been subjected, virtually, to many more tests than would have been possible using traditional methods and physical prototypes; plus the fact that with these tests it is possible to measure a quantity of information that cannot normally be managed by classic experimental measurements. In practice, the construction of the mathematical models and their interactive use, allows the Fiat Auto engineers to acquire much more detailed understanding of the vehicle than in the past, and to explore its behaviour in the tiniest detail. The project is therefore 'optimised' (i.e. with greater quality, obtained with less trouble and cost) as well as 'robust' (the end product will be more insensitive to the inevitable manufacturing deviance and changes over the years of its use by the customer).

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