The floating ring journal bearing is a special type of bearing in which a ring is inserted and kept free to move in the lubricant between the journal and sleeve and separates the lubricant film into two parts. Owing to the presence of the two films, the floating ring journal bearing has several advantages such as less friction loss and better stability characteristics than journal bearings with one film. The ring, however, makes it difficult to supply the lubricant to the inner film. Thus the lubricant is usually fed through the oil holes in the ring from the circumferential groove on the outer surface of the ring to that on the inner surface of the ring. In the circumferentially grooved floating ring journal bearing, the inner and outer films make circumferentially grooved journal bearings, respectively and there exists such difficulty in the analysis of the pressure distribution in the inner and outer films that the cavity region must be determined taking into account the continuity of the lubricant flow in all regions, which cannot be implemented by conventional boundary conditions such as Half Sommerfeld or Reynolds conditions. In this thesis, Jakobsson-Floberg-Olsson condition which satisfies the continuity of the lubricant flow in the full film and cavity regions is adopted to analyze the performance of the circumferentially grooved floating ring journal bearing more accurately than conventional theories.
The static and dynamic performance of the circumferentially grooved floating ring journal bearing is analyzed by using Elrod algorithm implementing Jakobsson-Floberg-Olsson condition. The supply pressure drop in the inner film due to the rotation of the journal and ring is also taken into account quantitatively. It is shown that the supply pressure of the lubricant has significant influence on the performance of the bearing and the supply pressure drop also varies it, especially when the supply pressure is low and the journal speed is high.
It is important to know the stability characteristics of the rotor mounted on the floating ring journal bearings, since the floating ring journal bearing is usually used in the high speed machinery. Based on the analysis of the bearing performance, the dynamic behavior of the rigid rotor system and flexible rotor system is investigated by means of the linear stability theory and nonlinear transient analysis. The flexible shaft is analyzed by the finite element method which can deal with various configurations of the rotor. It is shown that reducing the supply pressure of the lubricant tends to improve the stability of the system. The safe operation of the floating ring journal bearing at high speed region, where the circular journal bearing with one fluid film cannot be operated safely because of the instability of the system, owes to the vibration suppressing effect of the outer film at unstable region.
The experiment on the flexible rotor system is carried out order to check the validity of the present theory. It is found that the measured ring speed agrees well with the theoretical results. The instability of the system due to not only the inner film but also the outer film of the bearing can be predicted well by the present theory.
Circular journal bearings with one fluid film cannot be used when the journal and bearing rotate in opposite direction, since the load capacity of the bearing is reduced. But it is anticipated that the floating ring journal bearing can have sufficient load capacity at this circumstances. The operating characteristics of the counterrotating floating ring journal bearing is theoretically investigated by analyzing the static performance and identifying the stability of the equilibrium state according to the operating mode. It is shown that the floating ring journal bearing can have considerable load capacity even when the journal and sleeve rotate with the same speed in opposite direction, while conventional circular journal bearings with one fluid film cannot.
