Study on crankshaft strength of engines with multi-academic subjects

摘要

Crankshaft is one of the most important parts for engine. The reliability and life of engine are affected to a great extent by the strength of crankshaft. Therefore, the examination to crankshaft strength must be made out strictly when designing engine. There is direct interaction in work between crankshaft and bearing of engine. In present, the crankshaft fatigue strength was analyzed only in the scope of strength theory. The given film pressure distribution of bearing was generally used as load acted on journal, and the effects of crankshaft deformation and the tribological characteristics of bearing were neglected. So, there is difference between present treatment method and factual situation, which will affect directly the calculating results of crankshaft strength. In this paper, in order to study the effect of topological characteristics of bearing on the stress distribution and fatigue strength of crankshaft, the crankshaft-bearing system of a four-cylinder engine was taken as the studying object, on the basis of lubrication analyses of bearings considering and not considering crankshaft deformation under load, the stress and fatigue strength of crankshaft were calculated when gained film pressure distribution status of bearing was used as boundary condition of load. The crankshaft deformation and bearing load were calculated by whole crankshaft beam-element method. The lubrication of crankshaft bearing was analyzed by kinetics method. The crankshaft stress was calculated by finite element method. The results show that when the effect of crankshaft deformation under load is considered, the offset distribution of film pressure of bearing appears and the highest film pressure increases remarkably, which result in the stresses of local area on surface of journal fillet of crankshaft increase obviously and the safety factor of crankshaft decreases. It is obvious that, in order to make crankshaft design more reasonable and close to the factual condition, the crankshaft strength should be studied by means of taking crankshaft-bearing system as the study object and adopting the theories of multi-academic subjects of strength, stiffness and tribology.