On the Pressure Distribution at the Contact between Small End of a Conrod and Gudgeon Pin

Abstract

The contact pressure profile between the small end of a connecting rod and the gudgeon pin is investigated, having in mind the evaluation of the peak stresses in the small end. An analytical expression for the maximum bending moment in the small end is traceable in the pertinent literature, which is based upon a contact pressure profile of the form p=k*cos(θ)². A series of plane finite element (F.E.) studies have been carried out, aimed at clarifying the reliability of the analytical pressure profile. The numerical findings show a pressure distribution which appreciably differs from the analytical predictions, and which remains essentially uniform along the contact arc. Such a pressure profile produces stresses in the small end which are noticeably lower than the analytical values. As a consequence the analytical modelling, although approximate, is conservative, and therefore its practical validity remains unaltered. On the other side, high performance connecting rods require accurate calculations, which must be based upon realistic pressure profiles, an observation which motivates the current study. Preliminary three-dimensional finite element studies are also included, which essentially confirm the plane analysis.