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A dimensionless relationship that estimates the maximum bearing load of a 4-cylinder 4-stroke in-line engine has been found. This relationship may assist the design engineer in choosing a desired counterweight mass. It has been demonstrated that: 1) the average bearing load increases with engine speed and 2) the maximum bearing load initially decreases with engine speed, reaches a minimum, then increases quickly with engine speed. This minimum refers to a transition speed at which the contribution of the inertia force overcomes the contribution of the maximum pressure force to the maximum bearing load. The transition speed increases with an increase of counterweight mass and is a function of maximum cylinder pressure and the operating parameters of the engine.

This paper presents a simplified piston ring assembly (PRA) friction model accounting for the piston ring pack and the piston skirt. The ring model considers both mixed and hydrodynamic lubrication; the skirt model considers hydrodynamic lubrication only. The Reynold's equation is used as a governing equation for the hydrodynamic regimes of both models. Simplified assumptions are used for the mixed lubrication in the ring model. The ring model generates unique Stribeck curves for a given ring's geometry; the skirt model generates generic relationships between the friction force and skirt geometry, piston speed, oil viscosity, and assumed boundary conditions. Ring starvation effects are introduced by varying the boundary conditions, as appropriate. The results of the models are compared to measurements made on a motored and fired single cylinder diesel engine; the theoretical calculations provide a reasonable estimate of the measured data.