An Efficient Multibody Dynamics Model for Internal Combustion Engine Systems

The equations of motion for the major components in an internal combustion engine are developed herein using a recursive formulation. These components include the (rigid) engine block, pistons, connecting rods, (flexible) crankshaft, balance shafts, main bearings, and engine mounts. Relative coordinates are employed that automatically satisfy all constraints and therefore lead to the minimum set of ordinary differential equations of motion. The derivation of the equations of motion is automated through the use of computer algebra as the precursor to automatically generating the computational (C or Fortran) subroutines for numerical integration. The entire automated procedure forms the basis for an engine modeling template that may be used to support the up-front design of engines for noise and vibration targets. This procedure is demonstrated on an example engine under free (idealized) and firing conditions and the predicted engine responses are compared with results from an ADAMS model. Results obtained by using different bearing models, including linear, nonlinear, and hydrodynamic bearing models, are discussed in detail.