No shivers while developing the Shiver

Per lo sviluppo della sua nuova 750 cc, Aprilia Shiver, il Gruppo Piaggio ha ampliamente utilizzato i prodotti ANSYS nell’analisi di componenti critici e di ANSYS WORKBENCH in particolare per stimare la resistenza a fatica dell’albero motore. La geometria del componente, importata da un ambiente CAD, inserita ed analizzata in un sistema multi-body, ha permesso di condurre la simulazione di un test di resistenza del motore, prendendo in considerazione sia la flessibilità alla torsione dell’albero che la pressione reale all’interno delle camere di combustione dei cilindri. La mappa delle forze che agiscono sul componente preso in esame e la sua accelerazione sono state confrontare con i severi standard Aprilia, senza trascurare l’affetto del gradiente di stress relativo nei punti maggiormente interessati. Grazie a questo elaborato processo di calcolo, le operazioni manuali sono state notevolmente ridotte, fornendo al tempo stesso la configurazione migliore e riducendo la necessità di test fisici in fase di sviluppo.

Piaggio Group (www.piaggio.com) is one of the biggest 2-wheeler manufacturers worldwide, with products ranging from mopeds to sport motorbikes and famous brands such as Vespa, Aprilia and Moto Guzzi. ANSYS products are widely used at Piaggio Group for the development of most critical vehicle components and subsystems. One of the most recent applications has been during the development of the new 750 cc twin engine for the new Aprilia Shiver motorbike, which is being brought to the market during 2007.
The WORKBENCH environment has been used to assess the fatigue resistance of the engine’s crankshaft. The component’s geometry has been initially imported from the CAD environment into WB to generate a Modal Neutral File (MNF) to be subsequently included into a multibody system (MBS), which has been analysed by ADAMS. The MNF contains data which describe the dynamic flexibility of a component. The MNF generation has been automated by means of a WB Command Object, including all the APDL commands needed to generate the interface elements and to run the ADAMS macro itself.

Once the MNF file had been generated, Aprilia standard engine endurance bench test has been simulated by assembling and solving the multibody model of the full powertrain. Dynamic effects due to the crankshaft’s torsional flexibility have been taken into account importing the MNF into ADAMS. Other slender components’ flexibility has been modelled generating MNFs inside WB. The whole powertrain motion has been simulated when subject to the real pressure cycles inside the cylinders’ combustion chambers. The MBS has provided the time-histories of the forces and moments acting on the crankshaft, and of its acceleration. The most severe dynamic equilibrium conditions have been chosen and exported as Environments to another WB model, used to evaluate the stress state inside the crankshaft.

The Fatigue Module of WB has been used to evaluate the safety factor based on infinite life, which has been compared with the minimum allowable value according to Aprilia standards. The relative stress gradient effect has been taken into account, by means of a WB Command Object, used to evaluate the stress gradient at the most stressed point, along the normal of the crankshaft’s external surface. The APDL inside the Command object has singled out the most stressed point, built the normal to the surface and finally evaluated the relative stress gradient by means of path operations. That way, the manual operations throughout the calculation process have been drastically reduced and different geometrical configurations have been investigated with little effort, thus singling out the best one while reducing the need for physical testing.

Ing. Riccardo Testi
Piaggio & C. Spa