Unstable Vibrations of an Unsymmetrical Shaft at the Secondary Critical Speed due to Ball Bearings

抄録

It is clarified theoretically and experimentally that, when an unsymmetrical shaft is supported by single-row deep groove ball bearings, an unstable vibration with frequency +2ω (ω : rotating speed of a shaft) appears at the secondary critical speed due to the coexistence of a stationary directional difference and a rotating directional difference of stiffness. The stationary directional difference is due to the directional difference of support condition by means of a single-row deep groove ball bearing which has angular clearance, and the rotating directional difference is due to the flatness of the shaft. The width of this unstable region depends on the assembly of the system. No unstable vibration appears at the secondary critical speed in the system where an unsymmetrical shaft is supported by self-aligning double-row ball bearings and in an unsymmetrical rotor system.