ANALYTICAL DEVELOPMENT & MODAL ANALYSIS OF CRANKSHAFT

Abstract

Crankshaft is most complicated and highly strained internal combustion engine part, which is subjected to cyclic bending and torsional loads due to gas pressure and inertia forces. These forces induce high bending and torsional stress mainly concentrating at crankpin and journal bearing fillet. In this project, stresses and torsional frequencies are calculated analytically and verified using Finite Element Analysis. Stresses are calculated analytically using the theory of constant energy of distortion at critical location of crankshaft i.e. crankpin and journal bearing fillet and 3-D finite element analysis is carried out using commercial software for single crank throw to study the correlation between analytical and Finite Element Analysis results. Analytical calculations and Finite Element Analysis is done for Top Dead Centre position at rated power operating condition. The calculated force considering the gas and inertia forces is applied at top surface of crankpin to
find out the stresses. Torsional frequency has been calculated analytically using Holzer method for free free condition considering torsional stiffness and polar moment of inertia of crank throw. Torsional stiffness is derived analytically and is correlated with finite element results for single crank web Polar moment of inertia is calculated using CAD software. Further finite element model analysis is carried out at component level to study the torsional frequency correlation between analytical and Finite Element results. The stresses, torsional frequencies and torsional stiffness observed from FE analysis are well correlated with 
analytically calculated results.