With the two initial research prototypes, the dual chassis sections were connected with four block-like mounts (rubber and metal) and this solution already showed promising results. However, the possibility of replacing the elastic mounts with adaptive hydraulic rubber mounts was also analysed. With this design, the rigidity and the damping capacity of the mounts were able to adapt to variations in G-force, therefore improving vehicle behaviour in various conditions. 

At CRF, they are currently also working in supports which continuously adjust: this solution is rendered possible by employing electromagnetic fluid, the viscosity of which can be modified in the inside of each hydraulic mount via a magnetic field. With the first two prototypes, the car bodies were made from steel, as weight reduction was not a crucial goal of their purpose. However, with the Sportiva Latina, weight reduction was to be one of the project’s main focuses: initial benchmarking went to show that the required performance in terms of acceleration and top speed would be achievable only if the weight to power ratio were lower than 3.5 kg/HP.

Reasoning on a possible power output of 400 bhp and an estimated weight of 820 kg for the engine, chassis, engine mounts, suspension and the other mechanical systems, and 200 kg for the glass sections, interior, air-conditioning system and electrics, the objective weight of the car’s total body-in-white lay at a challenging 200 kg.

As a “split-frame” concept was adopted for the above mentioned reasons, a drastic decision was taken to set the target for chassis and upper body design: the former would have to ensure the required handling performance of the car by means of an adequate torsional and flexural stiffness, as well as the withstanding of crash conditions, while the latter could be maximally lightened as minimal structural behaviour was expected (i.e. only static roof crash resistance should be taken in account for design). However, even when considering the application of Fibre Reinforced Plastic (FRP), an 80 kg mass target for the body shell without fittings seemed to be the lowest achievable figure. This implied that the actual reference target mass of the chassis lay at an exceptionally challenging figure of below 120 kg.
 

Weight reduction was therefore the first step in the Sportiva Latina’s planning, and hereby a dedicated look at the main structures of the chassis was called for. Considering that years of experience have demonstrated that a satisfying result can only be obtained using a methodological approach, topological computer software was used right from the start of the project. This type of numerical optimisation allows engineers to determine optimal material distribution within a given package space and in relation to mechanical loads.

Topological optimisation, now well implemented within a number of commercialised CAE software programmes, can reduce time-to-design and the sequence of trials needed to select the best solution. In greater detail, the concept design for the chassis was split into four steps, with each subsequent step adding information and details to the previous one, while the boundary conditions of the whole project were defined.

Starting from scratch, the first step was to identify which archetype of central floor carried the best trade off between weight and stiffness behaviour, choosing among a combination of central (tunnel) or sided (side rails) floor structures and open or closed tunnels; all these structure archetypes were subjected to torsional and bending loads. The topological optimisation software helped to create a list of solutions ordered by a weight over stiffness ratio, with a clear indication of the solution’s behaviour and way of working. The design of the open floorpan with only a closed rigid tunnel section was chosen because it offered the best performance in terms of rigidity and weight over the list of other solutions.

The second step started from where the previous information left off, adding the front and the rear structures to the design space. In terms of volumes these were left free by the engine, suspension, wheels and 4WD driveline. The structure was subjected to torsional and bending loads and front crash impact loads distributed on one front rail or on both. The results given by topological optimisation showed the load transfer from front rails to rear structure, passing through the firewall panel and the central floor structure. This result helped to design the shape and geometry of the chassis front structure, with two straight crash members at a different Z position, jointed by a vertical structure and the connection between the front rails and central floor structure. From this stage on, the front structure was designed according to crash energy absorption criteria.