Detailed main bearing hydrodynamic characteristics for crankshaft -block dynamic interaction in internal combustion engines.

Abstract

The current research contributes to the computational study of the crankshaft-block dynamic interaction through the development of two detailed main bearing models for this system to include effects of hydrodynamic characteristics. The bearing hydrodynamic models offer high computational efficiency without sacrificing the accuracy. The differential governing equations are solved numerically using the finite element and the finite difference approaches without imposing any limitations in the number of degrees of freedom to accommodate for the structural deformation of the bearing and the journal tilting. The finite element approach and the finite difference approach are implemented as alternatives to achieve the highest efficiency through comparison. In addition a new condensation procedure for reducing the resulting cross-coupled terms in the fluid film stiffness matrix and the fluid film damping matrix is developed. Thus, savings in memory and CPU requirements are achieved without compromising the accuracy of the computations. A data mapping procedure is developed in order to allow transformation of the structural deformation and the hydrodynamic characteristics between the mesh of the structural model and the mesh of the model for the main bearings when the two models have incompatible mesh densities. The data mapping algorithm allows to perform accurate calculations of the hydrodynamic characteristics in the high-density mesh of the bearing model without imposing an increase in the required structural mesh density. The analytical and numerical validations of the new bearing models are presented. The new developments are validated by comparing results from the new algorithms to an established, sophisticated, but computationally intensive bearing solver. The computational savings achieved by the new developments are also identified. The detailed hydrodynamic bearing model developed in this work is incorporated into a system level analysis including the coupled rigid and flexible body dynamic of the crankshaft and flexible engine block. Finally, the resulting system level analysis was utilized to study dynamic behavior of a typical V6 engine for automotive applications. A side-by-side comparison of the results for bearing reaction forces was presented to demonstrate the impact of the hydrodynamic bearing model on the quality of the solution.