Effect of Manufacturing Errors on Static Characteristics of Four-Lobe Hydrodynamic Journal Bearings - In Case of Shift in Position of Bottom Lobe Due to Manufacturing Errors

Abstract

When a manufacture error occurs, the actual size of a hydrodynamic journal bearing can differ from its basic dimension. In this case, it is considered that the characteristics of the hydrodynamic journal bearing may also be different from what has been expected, due to changes in oil film pressure distribution between the bearing and journal. The purpose of this study is to elucidate effects of manufacturing errors on the static and dynamic characteristics of multi-lobe hydrodynamic journal bearings, whose structures are relatively simple and whose oscillation stability in the rotor shaft-bearing system is relatively high. The study is also intended to come up with a proposal for guidelines about the optimized design for multi-lobe hydrodynamic journal bearings. As the first step to accomplish these purposes, this paper analyzed and examined changes in the static characteristics of a four-lobe hydrodynamic journal bearing, such as oil film pressure distribution, journal center locus, minimum oil film thickness and friction coefficient between the bearing and journal, when the position of the bottom lobe at the sliding surface is shifted from where it should be due to manufacturing errors. The results of the study show that when the position of the lobe is moved inside or outside of the bearing from the original location due to manufacturing errors, minimum oil film thickness may become smaller in comparison with the situation in which the lobe stays at the original location. The results also show that friction coefficient between the bearing and journal does not change significantly irrespective of manufacturing errors.