Advanced Engine Dynamics Using MBS and a Mixed Nonlinear FEM and Super Element Approach

Dynamic simulations of a twin-cylinder boxer engine are carried out with rigid and flexible multibody
models. Pistons and connecting rods are considered as rigid bodies while the crankshaft is modeled as
a flexible part and meshed with brick elements. With this model, calculation of crankshaft stresses and
displacements is possible. For constant speed studies, flexible simulations are carried out on one or two
engine cycles but simulations with a variable rotation speed has to be performed on a larger number of
engine revolutions. Due to the complex shape of the crankshaft, the simulation times become important
and it is difficult to keep on working with the complete crankshaft model. Thus several simplified models,
including super element models, are developed. In this paper, a particular method, using also the super
element technique, is proposed. A large part of the crankshaft is substructured and modeled with super
elements. While a critical area, identified by a simulation performed with a coarse crankshaft mesh, is
not modified and modeled by nonlinear finite element. Several methods of linking the super elements
and the finite element mesh are experimented. Once the best connection method determined, results and
computation time of the simulation using this model will be compared to those obtained with the complete
crankshaft model and the other simplified models.