Piston engine residual imbalance caused by the connecting rod geometry

Results of numerical analysis of the multi-cylinder piston engine balance in the specialized software products environment do not always coincide with data from the analytical computation. This is most often observed in studying engines with the short connecting rods. The paper proposes a hypothesis that the reason for this discrepancy lies in introducing the two-mass static models of the crank mechanism in analytical computation. The eight-cylinder V-shaped engine was used as an example to determine unbalanced moments of the inertia forces developed by the third substituting masses of such a mechanism dynamic model with the short connecting rods, which were able to reach 10% of the moments determined in the analytical computation. Introduction of long connecting rods into the engine design could practically eliminate the difference between results of the analytical and numerical computation, even when using static models of the crank mechanism. This is also confirmed by computing the other multi-cylinder engines. It explains the reason for discrepancy between the analytical and numerical results in computing external imbalance of the multi-cylinder engines with the short connecting rods. It is shown that when analyzing balance, it is preferable to use the three-mass dynamic models of the connecting rods (especially, short and/or asymmetrical).
EDN: GVUNOA, https://elibrary/gvunoa

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