2017 Volume 52 Issue 1 Pages 101-110
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. 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 side lobe at the sliding surface is shifted from where it should be due to manufacturing errors. And then, design guidelines for four-lobe hydrodynamic journal bearings were discussed based on the results of the analysis. The results of the study show that when the position of the lobe is moved inside of the bearing from the original location due to manufacturing errors, minimum oil film thickness becomes smaller in comparison with the situation in which the lobe stays at the original location. The results also show that in this case, friction coefficient between the bearing and journal becomes slightly higher when it is compared with the situation in which the side lobe is shifted inside of the bearing from the original location with higher bearing load. If arithmetic average roughness Ra of the sliding surface of the journal and lobe is below 0.2, a shift up to 0.2 times as large as machined clearance cp in the inner or outer direction of the bearing at the sliding surface near the side and bottom lobes will be tolerable.
