給排気孔を有する動圧気体軸受で支持された鉛直回転体の安定性

抄録

In this study we make clear dynamic characteristics of a vertical rotor supported with cylindrical gas journal bearings which have air supply and exhaust holes on each bearing surface in its circumferential direction. Natural frequency, modal damping ratio and natural vibration mode of the rotor-bearing system are measured in impact test. Threshold rotating speed of self-excited half-frequency whirl of the rotor-bearing system is also measured in rotating test. Its natural frequency and its threshold rotating speed decrease and its modal damping ratio increases as supply pressure of air film decreases. Its threshold rotating speed in case of speeding up the rotor speed is higher than that in case of slowing down of the rotor speed in all conditions. Its lower order natural vibration mode is rotating vibration mode and its higher order natural vibration mode is translational vibration mode. The vibration mode of half-frequency whirl is only translation mode and the rotating mode doesn’t becomes unstable in all conditions. Even if the supply pressure becomes zero, threshold speed doesn’t become zero. Put another way, the vertical rotor supported with the cylindrical hydrodynamic gas journal bearing, which is fabricated several supply and exhaust holes on the bearing surface, and its eccentricity of steady state is zero, becomes stably for half-frequency whirl within a certain rotating speed. The threshold speed increases as the volume of the chamber connected to air supply and exhaust holes, but it converges almost to the threshold rotating speed with the air supply and exhaust holes opened through atmosphere.