eeee

1. AUTOMOTIVE
assembling and solving the multibody
The Aprilia Shiver model of the full powertrain. Dynamic
effects due to the crankshaft’s torsional
flexibility were taken into account when
importing the MNF into Adams. Other
slender components’ flexibility was
modeled when generating the MNFs
inside the ANSYS Workbench platform.
The whole powertrain motion was
simulated when subject to the real
pressure cycles inside the cylinders’
combustion chambers. The MBS
No Shivers While provided the time histories of the forces
and moments acting on the crankshaft
and of the crankshaft’s acceleration.
Developing the Shiver The most severe dynamic equilibrium
conditions were chosen and exported
as environments to another ANSYS
Workbench model, which was used to
Tools within the ANSYS Workbench environment evaluate the stress state inside the
have allowed engineers to get a handle on crankshaft. The Fatigue Module of
ANSYS Workbench was used to
crankshaft behavior before a motorcycle is built. evaluate the safety factor based on
By Riccardo Testi, Piaggio & C. SpA, Italy infinite life, which was compared to the
minimum allowable value according to
Motorcycle enthusiasts around the The component’s geometry initially was Aprilia standards. The relative stress
world are drawn to vehicles that deliver imported from the CAD environment gradient effect was taken into account,
high style and top performance. More into ANSYS Workbench to generate a by means of an ANSYS Workbench
often than not, they are drawn to Modal Neutral File (MNF). The MNF Command Object, used to evaluate the
Piaggio Group, one of the biggest was subsequently included in a stress gradient at the most stressed
two-wheeler manufacturers in the world, multibody system (MBS), which was point along the normal of the
with products ranging from mopeds to analyzed using Adams® motion crankshaft’s external surface. The
sport motorbikes and famous brands simulation software. The MNF contains APDL inside the Command Object
such as Vespa, Aprilia and Moto Guzzi. data that describe the dynamic singled out the most stressed point,
ANSYS products are widely used at flexibility of a component. Generation built the normal to the surface and,
Piaggio Group for the development of of the MNF was automated by means finally, evaluated the relative stress
most critical vehicle components and of an ANSYS Workbench Command gradient by means of path operations.
subsystems. One of the most recent Object, including all the ANSYS Using these methods, the manual
applications was part of the develop- Parametric Design Language (APDL) operations throughout the calculation
ment of the 750 cc twin engine for the commands needed to generate the process were drastically reduced so
new Aprilia Shiver motorcycle, which is interface elements and run the Adams that different geometric configurations
being brought to market in 2007. macro itself. could be investigated with little effort.
The ANSYS Workbench environ- Once the MNF file was generated, This allowed engineers to single out the
ment was used to assess the fatigue an Aprilia standard engine endurance best design while reducing the need for
resistance of the engine’s crankshaft. bench test was simulated by physical testing. I
www.piaggio.com
The cycle of motorcycle design
The CAD model of the full engine The ANSYS model generated by ANSYS The multibody model The stress field computed by ANSYS
Workbench to obtain the Modal Neutral File Workbench
www.ansys.com ANSYS Advantage • Volume I, Issue 1, 2007 25