A probabilistic approach to engine balance

The paper presents an original probabilistic model of the balance of intern al combustion engines. The model considers the manufacturing tolerances and predicts the most probable value of the first-order residual unbalance for engines that-theoretically-have the first order forces and moments balance d. It has been found that, assuming normal distributions of the geometric a nd mass parameters of the reciprocating mechanisms of a multicylinder engin e, the unbalancing forces and moments are statistically distributed accordi ng to a Rayleigh law. The mode of the Rayleigh distribution, which represen ts the most probable value of the residual unbalance, is expressed in terms of the statistical characteristics of the parameters subjected to manufact uring tolerances. In this way, the tolerances and, especially the ones admi tted for the reciprocating masses, are directly correlated to the expected value of the residual unbalance making it possible to establish reasonable limits for these tolerances. Validation of the probabilistic balance model is demonstrated by computer simulation.