Patent Publication Number: US-2005121263-A1

Title: Lubricant circulation system and method

Description:
BACKGROUND  
      This invention relates to a system and method for circulating and/or cooling lubricant associated with a rotating member and a stationary member.  
      Conventional lubricating arrangements associated with rotary machines often utilize lubricant that has not been properly circulated, thus resulting in a diminished useful life of the rotary machine due to improper lubrication. It is therefore desirable to provide circulated lubricant to the rotary machine such that the lubricant provides greater protection against the general wear and tear that occurs within the rotary machine. However, due to the increased cost and space constraints associated with providing pumps to circulate lubricant in a rotary machine, it is difficult to provide circulated lubricant to the rotary machine in an economical and efficient manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a bearing assembly incorporating a lubricant circulation system according to the present invention.  
       FIG. 2  is a sectional view of the bearing assembly of  FIG. 1  taken along the line  2 - 2 .  
       FIG. 3  is a sectional view of a journal bearing and a shaft of the bearing assembly of  FIG. 1  depicting a slot and a port formed in the journal bearing.  
       FIG. 4  is a perspective view of the bearing assembly of  FIG. 1  shown positioned over a sump, which is shown schematically, with portions of the bearing assembly being removed to depict a lubricant circulation path.  
       FIG. 5  is a schematic view of a bearing assembly incorporating a lubricant circulation system according to an alternative embodiment of the invention.  
       FIG. 6  is a schematic view of a pair of bearing assemblies incorporating a lubricant circulation system according to yet another alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIGS. 1-4 , a bearing assembly incorporating a lubricant circulation system is generally referred to by the reference numeral  10 . For purposes of example, the bearing assembly  10  is used as an exhaust end bearing assembly for supporting a turbine shaft  12 .  
      The bearing assembly  10  includes a bearing case  14 , which is supported in any conventional manner by a bearing support  16 . A pair of fixed annular labyrinth seals  18 ,  20  are disposed between the bearing case  14  and the shaft  12  to prevent leakage of lubricant in both axial directions of the shaft beyond the bearing case. The labyrinth seals  18 ,  20  are affixed to the bearing case  14  in any conventional manner such as via annularly-spaced bolts (not shown). A pair of axially-spaced annular flanges  24 ,  26  of the bearing case  14  extend around a journal bearing  28  of the bearing assembly  10  to position the bearing adjacent the shaft  12 . The bearing  28  is affixed to the flanges  24 ,  26  in any conventional manner including via annularly-spaced bolts (not shown). A small annular clearance  29  is defined at the interface between the bearing  28  and the shaft  12 .  
      The bearing  28  is designed for ring-oiled and/or pressure lubrication, and as such, includes a circumferentially formed slot  30  for accommodating an oil ring  32 . The width of the slot  30  is slightly greater than the width of the oil ring  32  such that the oil ring is maintained in substantially the same axial position relative to the bearing case  14 . A radially-extending pressure lube feed port  34  is formed through the bearing  28  and is axially spaced from the slot  30 . The axially-spaced flanges  24 ,  26  of the bearing case  14  define a circumferential slot  36  ( FIG. 1 ) in the upper portion of the bearing case to permit radial displacement of the oil ring  32  in an upper direction, as viewed in the drawings. However, gravity will tend to limit any radial displacement of the oil ring  32  in an upper direction, as viewed in the drawing.  
      A portion of the oil ring  32  extends through the slot  30  in contact with the shaft  12 . The oil ring  32  has a diameter that is greater than that of the shaft and is eccentrically positioned relative to the shaft so that a portion of the ring extends into a sump  38  defined in the case  14 . The oil ring  32  is in a light frictional engagement with the shaft  12  so that rotation of the shaft  12  causes rotation of the oil ring  32  about its axis at a speed that is lower than that of the shaft. As a result, rotation of the shaft causes the oil ring  32  to rotate through, and draw lubricant from the sump  38  so that a film of oil accumulates on the oil ring. The lubricant drawn from the sump  38  by the oil ring  32  is delivered to the clearance  29  and is distributed in a manner to be described.  
      As better shown in  FIG. 4 , a conduit  40  is connected to the pressure lube feed port  34  in any conventional manner and extends to the sump  38 . Although not shown in the drawings, it is understood that the conduit  40  extends through an opening in the case  14 . A lubricant feed slot  42  is formed in the bearing  28  and generally extends in an axial direction from the oil ring slot  30  and is angularly displaced form the pressure lube feed port  34 .  
      The above arrangement defines a closed-loop circulation path P 1  extending from the sump  38 , to the oil ring  32 , through the axial feed slot  42 , through the clearance  29 , through the radial pressure lube port  34 , through the conduit  40 , and back to the sump.  
      In operation, rotation of the shaft  12  causes rotation of the oil ring  32 , which dips into the sump  38  to draw lubricant from the sump causing a thin lubricant film to form on the inner circumferential surface of the oil ring  32 . This lubricant is delivered from the oil ring  32 , via the slot  30 , to the lubricant feed slot  42  where the lubricant collects. Continual collection of lubricant in the lubricant feed slot  42  causes lubricant to overflow the slot, and pass from the slot, through that portion of the clearance  29  extending between the slot and the port  34 , and to the port. This latter flow is promoted by the pressure generated by rotation of the shaft  12  that causes a differential in the relatively high pressure in the clearance  29  and the relatively low atmospheric pressure in the conduit  40 . The lubricant thus enters the conduit  40  and flows down the conduit to the lower portion of the sump  38 , thereby completing the circulation of this portion of the lubricant through the path P 1 .  
      It is understood that while a portion of the lubricant follows the circulation path P 1  as described above, another portion of the lubricant drawn from the sump  38  generally lubricates the interface between the bearing  28  and the shaft  12 , while yet another portion of the lubricant drawn from the sump  38  spills over the oil ring slot  30  and returns to the lubricant sump without having followed the circulation path P 1  or provided general lubricating functions.  
      Thus, by utilizing the pressure generated between the shaft  12  and the bearing  28 , the above-described system effectively circulates lubricant through the bearing assembly  10  without having to employ costly and bulky pumps. Furthermore, the lubricant in the sump  38  is mixed with lubricant that is circulated through the bearing  28 . Thus, problems such as stagnation of lubricant in lower portions of the sump  38  are effectively avoided and a majority of the lubricant in the lubricant sump is circulated rather than only a top layer of lubricant.  
      The embodiment of  FIG. 5  includes the bearing  28  surrounding the shaft  12  and defining the clearance  29 , and the oil ring  32  positioned on the shaft. The bearing case  14 , the bearing support  16 , and the annular labyrinth seals  18  and  20  have been omitted in the interest of clarity, and the sump  38  has been replaced with a sump  50  which is also formed in the case  14  and which also receives the rotating oil ring  32 .  
      In this embodiment, an external cooler  52  is provided for cooling the lubricant, and a conduit  62  is provided for circulating lubricant from the clearance  29  to the cooler  52 . In the latter context it is understood that, although not shown in  FIG. 5 , a slot and a port identical to the slot  42  and port  34 , respectively of the embodiment of  FIGS. 1-4  are provided in the bearing  28  to transfer lubricant from the clearance  29  to the conduit  62 .  
      The cooler  52  is of conventional design, and, as such, includes an outer annular chamber  64  that contains cooling water and an inner reservoir portion  66  for receiving the lubricant. A conduit  68  connects the cooler  52  to the lower portion of the sump  50 .  
      Thus, a closed-loop lubricant circulation path P 2  is defined that extends from the sump  50  to the oil ring  32 , from the oil ring through the clearance  29 , through the conduit  62 , through the cooler  52 , through the conduit  68 , and back to the sump  50 .  
      In operation, lubricant is circulated from the sump  50  to the clearance  29 , via the oil ring  32 , in the same manner as described with reference to the embodiment of  FIGS. 1-4 . The rotation of the shaft  12  generates enough pressure to drive the lubricant from the clearance  29  to the conduit  62 . The lubricant flows from the conduit  62  to the cooler  52 , where the lubricant collects and is cooled by the water in the chamber  64  prior to reentering the sump  50 . When the lubricant in the cooler  52  reaches a level that is greater than the level in the sump  50 , the lubricant in the cooler circulates to the sump via the conduit  68 , thereby completing circulation of the lubricant through the closed-loop lubricant circulation path P 2 . Thus, circulation of lubricant through the external cooler  52  is accomplished without having to employ a costly external pump. Moreover, by cooling the lubricant during circulation, the useful life of the lubricant is increased, which, in turn, adds to the useful life of the bearing assembly  10 .  
      The embodiment of  FIG. 6  includes the bearing assembly  10 , including the bearing  28  surrounding the shaft  12  and defining the clearance  29 , and the oil ring  32  positioned on the shaft. The bearing case  14 , the bearing support  16 , and the annular labyrinth seals  18  and  20  have been omitted in the interest of clarity, and the sump  38  has been replaced with a sump  80  which is also formed in the case  14  and which also receives the rotating oil ring  32 .  
      A bearing assembly  10 ′, identical to the bearing assembly  10 , is axially displaced from the bearing assembly  10 . The bearing assembly  10 ′ includes a bearing  28 ′ surrounding the shaft  12  and defining a clearance (not depicted) and an oil ring  32 ′ positioned on the shaft. The remaining portions of the bearing assembly  10 ′ have been omitted in the interest of clarity and a sump  82  is defined in the case corresponding to the bearing assembly  10 ′.  
      In this embodiment, a single reservoir  84  is provided, and a conduit  86 , depicted schematically in the interest of clarity, is provided for circulating lubricant from the clearance  29  to the sump  82 . A conduit  88 , also depicted schematically, is provided for circulating lubricant from the clearance associated with bearing assembly  10 ′ to the sump  82 . It is understood that, although not shown in  FIG. 6 , a slot and a port identical to the slot  42  and port  34 , respectively of the embodiment of  FIGS. 1-4  are provided in the bearings  28  and  28 ′ to transfer lubricant from the clearance  29  and the clearance associated with bearing assembly  10 ′ to the conduits  86  and  88 , respectively.  
      A conduit  90  connects the sump  82  and the reservoir  84 , with the end of the conduit  90  that extends into the sump  82  terminating at a sufficient height to act as a standpipe, thereby maintaining the lubricant level in the sump  82  at a greater height (represented by H1) than the lubricant levels in the reservoir  84  and the sump  80 .  
      A conduit  92  connects the sump  80  and the reservoir  84 , with the end of the conduit  92  that extends into the reservoir  84  terminating at a sufficient height to act as a standpipe so that lubricant in the reservoir rising above the end of the conduit  92  will enter the conduit and circulate to the sump  80 . The end of the conduit  92  that terminates in the sump  80  has a substantially equivalent height as the end of the same conduit that terminates in the reservoir  84 , thereby maintaining substantially equivalent lubricant levels in the reservoir and the sump  80  for reasons to be described. Thus, the above-described arrangement defines a closed-loop lubricant circulation path P 3  generally extending from the sump  80 , to the oil ring  32 , through the clearance  29 , through the conduit  86 , through the sump  82 , through the conduit  90 , through the reservoir  84 , through the conduit  92 , and back to the sump  80 .  
      In operation, lubricant is circulated from the sump  80  to the clearance  29  between the shaft  12  and the bearing  28  in the same manner as described with reference to the embodiment of  FIGS. 1-4 . The rotation of the shaft  12  generates enough pressure to drive a portion of the lubricant from the clearance  29  to the conduit  86 . The lubricant in the conduit  86  flows to the lower portion of sump  82  where the lubricant mixes with lubricant already in sump  82 .  
      Lubricant circulates from the sump  82  to the clearance associated with bearing assembly  10 ′, via the oil ring  32 ′, in the same manner as described with reference to  FIGS. 1-4 . The rotation of the shaft  12  generates enough pressure to drive a portion of the lubricant from the clearance to the conduit  88  so that the lubricant flows through the conduit  88  to the sump  82 . Thus, the sump  82  collects lubricant from both bearing assemblies  10  and  10 ′, which causes the lubricant level of sump  82  to rise.  
      When the lubricant level in the sump  82  rises above the end of the conduit  90  that terminates in the sump  82 , lubricant enters the conduit  90  and circulates to the reservoir  84 , causing the lubricant level of the reservoir  84  to rise. When the lubricant level in the reservoir  84  rises above the end of the conduit  92  that terminates in the reservoir, the lubricant enters the conduit  92  and circulates to the sump  80  of the bearing assembly  10 . As the ends of the conduit  92  terminate at substantially the same height, gravity causes the lubricant levels in the reservoir  84  and the sump  80  to seek the same level. Thus, the lubricant circulates from the reservoir  84  to the sump  80 , thereby completing circulation of the lubricant through the closed-loop lubricant circulation path P 3 .  
      By utilizing the single external reservoir  84  to accommodate a lubricant circulation system between the two bearing assemblies  10 ,  10 ′, the cost and size restraints normally associated with using one reservoir per bearing assembly are effectively eliminated. Furthermore, the extent of the circulation of the lubricant through the above-described arrangement ensures proper circulation of the lubricant without the use of a pump, thereby increasing the useful life of the lubricant, which in turn, reduces the wear and tear on the bearing assemblies  10 ,  10 ′.  
      It is understood that several variations may be made in the foregoing without departing from the scope of the invention. For example, although described with reference to a turbine shaft, the lubricant circulation system according to the present invention may be applied to any arrangement involving a rotating member and a stationary member. Moreover, the cooler  52  of the embodiment of  FIG. 5  may alternatively be a reservoir and thus devoid of any cooling elements, and in a similar manner, the reservoir  84  ( FIG. 6 ) may alternatively include cooling elements to provide for cooling of the lubricant being circulated therethrough. Still further, the cooler  52  and the reservoir  84  may include filters for cleaning the lubricant passing therethrough.  
      Moreover, while it has been described that pressurization of the lubricant promotes flow of the lubricant in the above-described circulation systems, it will be understood that gravity may also assist in the flow of lubricant depending on the physical location of the various components defining the flow paths.  
      Furthermore, references to specific structure of various elements of the bearing assemblies and the external cooler and reservoir are meant for example purposes only. For example, various types of seals may be substituted for the labyrinth seals  18 ,  20  and the cooler  52  may alternatively employ cooling coils for cooling the lubricant passing therethrough. Still further, the bearing assemblies  10 ,  10 ′ may be any type of ring-oiled bearing assemblies.  
      Moreover, the conduits in the above-described lubricant circulation systems are not limited to a specific arrangement, and they may be attached to the various bearing assemblies in any conventional manner. Furthermore, in some embodiments, the conduits may be removed. Still further, the lubricant feed slot  42  may lead directly to the pressure lube feed port  34  ( FIG. 4 ), and thus the port would not be radially displaced from the lubricant feed slot. If opposite rotation of the shaft  12  is desired, the lubricant feed slot  42  may be formed in an opposite portion of the bearing to collect lubricant drawn from the lubricant sump  38 . Also, in some embodiments, the lubricant feed slot  42  may be omitted. Still further, the above spatial references, such as “radial,” “axial,” “upper,” and “lower” are for the purpose of illustration only and do not limit the specific orientation or location of the structure described above.  
      Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.