バンプフォイル軸受の理論安定限界速度とホワール比（第1報）―過大な静摩擦と組立予圧の影響―

摘要

In the authors’ previous report two models were presented to bump foil journal bearings and the assembly preload was shown to influence the maximum load capacity of the bearing. One model corresponds to the bearing with an excessive static friction between the top and bump foils and the other to the bearing without friction. This study aims at predicting the stability threshold speed and whirl frequency ratio of a horizontal rigid rotor supported in the bearings, by applying the frequency response method. The following results are obtained. Relatively small deformation of the top foil with the excessive friction contributes to little change in the stability threshold speed of the rotor-bearing system when comparing with that of the circular bearing. On the contrary the compliance of the top foil with no friction can change the speed, because it forms a relatively steep wedge in the steady-state equilibrium while it smoothens the wedge when the air film pressure is fluctuated by the small oscillation of the journal. Stability charts standardized by the mean radial clearance in the assembled bearing clearly show that the large assembly preload results in a decrease in stability threshold speed of the bearing with no friction.