Efficient Engine Models Using Recursive Formulation of Multibody Dynamics 2001-01-1594

Engine models with fully coupled dynamic effects of the engine components can be constructed through the use of commercial multibody dynamics codes, such as ADAMS and DADS. These commercial codes provide a modeling platform for very general mechanical systems and the time and effort required to learn how to use them may preclude their use for some engine designers. In this paper, we review an alternative and specialized modeling platform that functions as a template for engine design. Relative to commercial codes, this engine design template employs a recursive formulation of multibody dynamics, and thus it leads directly to the minimum number of equations of motion describing the dynamic response of the engine by a priori satisfaction of kinematic constraints. This is achieved by employing relative coordinates in lieu of the absolute coordinates adopted in commercial multibody dynamics codes. This engine modeling tool requires only minimal information for the input data. As a further benefit, the engine models herein are cast purely as a (minimum) set of ordinary differential equations of motion in lieu of the differential-algebraic equations that result from using commercial multibody dynamics codes. These differences lead to engine models that may also be integrated with greater efficiency.

Major components of the engine model include a rigid engine block, a flexible crankshaft, any number of cylinders with rigid pistons and connecting rods, any number of main bearings (represented by linear, nonlinear, or hydrodynamic bearing models), any number of engine mounts (represented by linear or nonlinear viscoelastic engine mount models). The objective of this paper is to review the current progress on developing an engine model template to support up-front engine design for noise, vibration, and durability.