In order to increase the performance of a compressor or other rotating machine, it is often desirable to increase the length of the shaft supporting the rotating elements of the machine. As the length is increased, the critical rotation frequencies at which vibrations take place are reduced. The vibrations are related to the natural sag between the ends of the shaft supported by bearings at each end. While placing additional bearings near the center of the shaft has been considered, it is a considerable drawback. Access to the bearing is very difficult, if not impossible, without disassembling the entire machine. One proposal is to use magnetic bearings near the midpoint between the ends of the shaft as explained in U.S. Pat. No. 4,141,604. It is an object of the present invention to damp the vibrations of a rotating shaft and to increase the critical frequency without requiring addition of inaccessible bearings.
Briefly, according to the present invention, there is provided a rotating machine with a journal shaft having a bearing apparatus for reducing vibrations. The bearing apparatus comprises a first bearing for supporting the shaft and a second bearing spaced outboard from the first bearing for producing a moment on the shaft and additional damping counter to the direction of vibrations. The second bearing is adjustable after the first bearing is aligned. The first and second bearings are either hydrostatic or hydrodynamic bearings.
According to one embodiment of the present invention, an outboard bearing apparatus reduces vibrations in a compressor shaft carrying a rotating compressor. The outboard bearing apparatus comprises a pair of first bearings for supporting the shaft on each end of the rotating compressor and a pair of second bearings spaced outboard from the first bearings for producing a moment on the shaft and additional damping counter to the direction of vibrations. The second bearing(s) may be utilized on both ends of the shaft or only on one end of the compressor shaft.
Further features and other objects and advantages will become clear from the following detailed description made with reference to the drawings in which:
A four-bearing system has been tested and compared to the same system with the outer bearings removed. In each case, the bearing span between the inner and outer bearings was duplicated and the shaft diameter was constant. Noncontacting probes were used to detect movement of the shaft in the vertical and horizontal directions. The probes were mounted inboard of the bearings. The distance between the inner bearings was approximately 19.5 inches. The distance between inner and outer bearings at each end was about 6 inches. The vibration versus speed data for each probe position and each condition (two bearings versus four bearings) are set forth in
The four-bearing system is an alternative damper bearing system for a long rotor shaft with improvement up to 27% in critical speed/rotor stiffness. Review of the vibration plots (
Having thus defined our invention in the detail and particularity required by the patent laws what is desired protected by Letters Patent is set forth in the following claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2005/023477 | 6/30/2005 | WO | 00 | 5/8/2007 |
Publishing Document | Publishing Date | Country | Kind |
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WO2006/007549 | 1/19/2006 | WO | A |
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Number | Date | Country | |
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20070292262 A1 | Dec 2007 | US |
Number | Date | Country | |
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60584912 | Jul 2004 | US |