A Study of the Mechanism of Lubrication in Porous Journal Bearings: Effects of Dimensionless Oil-Feed Pressure on Frictional Characteristics

The frictional characteristics of a porous bronze bearing are investigated experimentally under hydrodynamic and mixed lubrication conditions. The results show that under the same value of dimensionless oil-feed pressure pˆ_s, the relationship between the coefficient of friction μ and the Sommerfeld number S can be represented by a single friction curve extending from the hydrodynamic regime to the mixed regime. With decreasing S, μ decreases in the hydrodynamic regime and then steeply increases in the initial stage of the mixed regime. However, at lower values of S, μ becomes steady and its value remains almost the same for various pˆ_s. The value of S at the transition point from the hydrodynamic regime to the mixed regime is significantly affected by pˆ_s, becoming smaller for higher pˆ_s. To estimate μ in the mixed regime, a simple frictional model is proposed on the basis of the assumption that the load supported by the fluid film and the coefficient of fluid friction in the mixed regime are determined by the oil film extent and that they are the same as those at the transition point. The calculated values of μ based on the model are found to approximately agree with the experimental results.