Abstract:
The present disclosure relates to bearings, for example, an improved journal bearing. A bushing ( 44 ) for use with a journal bearing ( 40 ) includes: a cylindricarinterior defining an interior bearing surface ( 46 ); a longitudinal axis ( 45 ) and an internal diameter (ID); a groove region of the interior bearing surface ( 46 ) having a length H along the longitudinal axis; and a set of grooves ( 48 ) in the grooved region of the interior bearing surface ( 46 ), where N is the number of grooves in the set of grooves ( 48 ). Each groove is disposed at a helix angle (θ) offset from the longitudinal axis ( 45 ) of the bushing ( 44 ). The helix angle is approximately equivalent to the following equation: tangent (θ)=(π×ID)/(N×H).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/144,055 filed on Jan. 12, 2009, entitled “JOURNAL BEARING DESIGN”, which is incorporated herein in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates in general to bearings for use with rotating equipment. Additionally, the present disclosure relates to an improved design for journal bearings. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Bearings are typically used in rotating equipment to allow relative motion between two parts. For example, a ball bearing or a roller bearing may be used to allow a shaft to rotate within a fixed housing. A journal bearing is a simple bearing for use with a rotating shaft. In a journal bearing, the “journal” refers to a portion of the shaft and the “bushing” is a hollow cylinder surrounding the journal. The bushing is set into a housing or other casing which may be called the “journal box.” 
         [0004]    Typically, both the journal and the bushing are smooth polished cylinders. The gap between the journal and the bushing may be referred to as the “clearance” of the bearing. In a journal bearing, a lubricant is added within the clearance between the journal and the bushing. The lubricant is typically viscous enough to provide a cushion between the rotating journal and the stationary bushing. 
         [0005]      FIG. 1  illustrates an example of a prior art system including a rotating device  1 . Rotating device  1  may include any sort of rotating equipment (e.g., a motor, a pump, etc.). Rotating device  1  includes a stationary housing  10  with an end cap  12  and a journal box  14 . Rotating device  1  also includes a rotating shaft  20  with a rotating element  22  and a journal bearing  24 . Rotating element  22  may include any component of rotating device  1  (e.g., a rotor, an impeller, etc.). 
         [0006]      FIGS. 2A-2D  illustrate various aspects of prior art journal bearing  24 .  FIG. 2A  shows a longitudinal cross-section of a bushing  26  with a bushing interior surface  28 . Bushing  26  is a hollow cylinder configured to house a journal  27 .  FIG. 2B  shows journal  27  having a journal exterior surface  29 . As shown in  FIG. 2C , journal  27  rests inside bushing  26  to form bearing  24 . 
         [0007]      FIG. 2D  shows a cross-section of bearing  24  taken along line  2 D- 2 D shown in  FIG. 2C , with arrow  30  showing the direction of rotation of rotating shaft  20  and journal  27 . The gap between bushing  26  and journal  27  is a clearance  34 . A lubricant  32  is introduced into clearance  34 . The rotation of journal  27  within bushing  26  creates a “wedge” of lubricant  32 . Journal  27  rests on the wedge of lubricant  32  without coming in direct contact with bushing  26 . 
         [0008]    In some applications, lubricant  32  is circulated through the interior of rotating device  1  and any bearings  24  to both remove heat and provide lubrication. In normal canned motor applications, the amount of lubricant  32  adequate to cool bearing  24  is smaller than the amount of lubricant  32  needed to cool the motor and/or its components. In those applications, some portion of lubricant  32  bypasses bearing  24  avoiding the pressure drop attendant to passing through clearance  34 —there is a high resistance to flow through the clearance  34  of many journal bearings. The design of a close clearance journal bearing is significantly constrained by the balance between the pressure drop of the lubricant and the minimum allowable flow rate. In addition, as the rate of rotation of rotational device  1  increases, so does the resistance to flow through clearance  34 . Some journal bearings include one or more grooves in a bearing surface—reducing the resistance to flow through the clearance. 
       SUMMARY 
       [0009]    The present disclosure relates, according to some embodiments, to journal bearings. As an example, the teachings of the present disclosure provide a bushing for use in a journal bearing. The bushing may include a cylindrical interior defining an interior bearing surface, a longitudinal axis and an internal diameter (ID), a grooved region of the interior bearing surface having a length H along the longitudinal axis, and a set of grooves in the grooved region of the interior bearing surface, where N is the number of grooves in the set of grooves. Each groove may be disposed at a helix angle (θ) offset from the longitudinal axis of the bushing. The helix angle may be approximately equivalent to the following equation: 
         [0000]      tangent(θ)=(π×ID)/( N×H ).
 
         [0010]    As another example, the present disclosure provides a bushing for use in a journal bearing. The bushing may include a cylindrical interior defining an interior bearing surface, a longitudinal axis running through the center of the cylindrical interior, a grooved region of the interior bearing surface having a length H along the longitudinal axis, and a set of helical grooves in the grooved region of the interior bearing surface. Further, any straight line extending along the grooved region of the interior bearing surface in a direction parallel to the longitudinal axis may intersect one and only one groove of the set of helical grooves. 
         [0011]    As another example, the present disclosure provides a bearing for use with rotating equipment. The bearing may include a bushing having a cylindrical interior defining an interior bearing surface, the bushing having a longitudinal axis and an internal diameter (ID), a journal mounted on a rotating shaft and configured to rotate within the bushing, the journal having a cylindrical exterior defining an external bearing surface, a grooved region of the interior bearing surface of the bushing having a length H along the longitudinal axis of the bushing, and a set of grooves in the grooved region of the interior bearing surface of the bushing, where N is the number of grooves in the set of grooves. Each groove may be disposed at a helix angle (θ) offset from the longitudinal axis of the bushing. Further, the helix angle may be approximately equivalent to the following equation: 
         [0000]      tangent(θ)=(π×ID)/( N×H ).
 
         [0012]    As another example, the present disclosure provides a bearing for use with rotating equipment. The bearing may include a bushing having a cylindrical interior defining an interior bearing surface, the bushing having a longitudinal axis running through the center of the cylindrical interior, a journal mounted on a rotating shaft and configured to rotate within the bushing, the journal having a cylindrical exterior defining an external bearing surface, a grooved region of the interior bearing surface having a length H along the longitudinal axis, and a set of helical grooves in the grooved region of the interior bearing surface. Any straight line extending along the grooved region of the interior bearing surface in a direction parallel to the longitudinal axis may intersect one and only one groove of the set of helical grooves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
           [0014]      FIG. 1  illustrates an example of a prior art system including rotating equipment and a journal bearing; 
           [0015]      FIGS. 2A-2D  illustrate various aspects of an example prior art journal bearing; 
           [0016]      FIG. 3  illustrates an example bearing incorporating teachings of the present disclosure; 
           [0017]      FIG. 4  illustrates a cross-section of the bearing from  FIG. 3  along line  4 - 4 ; 
           [0018]      FIG. 5  illustrates a cross-section of the bearing from  FIG. 3  along line  5 - 5 ; 
           [0019]      FIG. 6  illustrates selected aspects of an example bushing incorporating teachings of the present disclosure; and 
           [0020]      FIGS. 7 and 8  illustrate selected aspects of an example bushing incorporating teachings of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Embodiments of the present disclosure and their advantages are best understood by reference to  FIGS. 3-8 , wherein like numbers are used to indicate like and corresponding parts. Although the present discussion focuses on the application of the present teachings in bushings for use in journal bearings with canned motor pumps, the teachings may have applications in other rotating equipment. For example, teachings of the present disclosure may be used to improve journals for use in journal bearings. As another example, journal bearings embodying aspects of the present disclosure may be used in vertically, horizontally, and/or otherwise aligned applications. 
         [0022]      FIG. 3  illustrates an example journal bearing  40  incorporating teachings of the present disclosure. Journal bearing  40  may include a journal  42  and a bushing  44 . The difference between the outer diameter of journal  42  and the inner diameter of bushing  44  may define a clearance  41  (shown in  FIG. 4 ). Journal  42  may be mounted on rotating shaft  50 , and/or may be integral with rotating shaft  50 . Rotating shaft  50  and journal  42  rotate as a single unit in the direction shown by arrow  52 . Bushing  44  may have a longitudinal axis  45  (shown in  FIG. 5 ) generally aligned with rotating shaft  50 . Bushing  44  may have a length, shown in  FIG. 3  as L 1 . 
         [0023]      FIG. 4  illustrates a cross-section of journal bearing  40  from  FIG. 3  along line  4 - 4 . As shown in  FIG. 4 , bushing  44  may encircle journal  42 . The space between journal  42  and bushing  44  may define clearance  41 . Journal bearing  40  may include a set of grooves  48  in one of the bearing surfaces. For example, as shown in  FIG. 4 , journal bearing  40  may include a set of grooves  48  in an interior bearing surface  46  of bushing  44 . As another example, journal bearing  40  may include a set of grooves  48  in an exterior bearing surface  43  of journal  42 . If grooves are added to one of the bearing surfaces  43 ,  46  in a journal bearing, the resistance to fluid flow through clearance  41  may be reduced. Reduced resistance to fluid flow through clearance  41  may increase the volume flow rate of fluid through clearance  41  which may, in turn, provide increased cooling and/or bearing life without a required increase in fluid pressure. 
         [0024]      FIG. 5  illustrates a cross-section of bushing  44  from  FIG. 3  along line  5 - 5 . As shown in  FIG. 5 , bushing  44  may include a cylindrical interior defining interior bearing surface  46 . The cylindrical interior may define longitudinal axis  45 . Interior bearing surface  46  may include a soft material lining the cylindrical interior of bushing  44 . One example material for lining the cylindrical interior of bushing  44  may be commonly known as “babbit.” Babbit may include a tin- and/or a lead-based alloy. A lining made of babbit and/or another suitable material may protect rotating shaft  50  or journal  42  from damage (e.g., marring and/or gouging) if journal  42  comes into contact with bushing  44 . In addition, a lining of babbit may allow any contaminant occurring in lubricant  53  to imbed in the lining without damaging journal  42 . 
         [0025]    Bushing  44  may include one or more grooves  48  in interior bearing surface  46 . The portion of bushing  44  including groove  48  may be described as a grooved region. In some embodiments, the grooved region is the region extending in the direction of longitudinal axis  45  to include grooves  48 . For example, in the embodiment shown in  FIG. 5 , the grooved region is the region of interior bearing surface  46  bounded by imaginary lines  49  that extend perpendicular to longitudinal axis  45 . As shown in  FIG. 5 , the grooved region may have a length L 2 . In other embodiments, the length of the grooved region (L 2 ) may be approximately equivalent to L 1 . 
         [0026]      FIGS. 4 and 5 , as an example, show a grooved region with four (4) grooves  48  in interior bearing surface  46 . The grooved region may be may be described as having a number of grooves  48 , defining N as that number. A discrete groove would include any single continuous groove  48  in the grooved region. 
         [0027]    Bushing  44  may include a single groove  48  or a set of N grooves  48  in the grooved region. As discussed in relation to  FIG. 4 , the addition of groove(s)  48  to a bearing surface  43 ,  46  of journal bearing  40  may decrease the resistance to fluid flow through clearance  41 . The addition of groove(s)  48  to a bearing surface  43 ,  46  of journal bearing  40 , however, may also reduce the load carrying capacity of journal bearing  40 . The particular design and geometry of the groove(s)  48  may affect both the resistance to fluid flow through clearance  41  and the load carrying capacity of journal bearing  40 . 
         [0028]    The load carrying capacity of a journal bearing is related to the effective hydrodynamic surface area of the bearing surfaces. Typically, a grooved surface offers less total hydrodynamic surface area than a smooth surface. One challenging aspect of designing a set of grooves  48  for a bearing surface  43 ,  46  of a journal bearing is to increase the rate of fluid flow through clearance  41  without significantly reducing the load carrying capacity of journal bearing  40 . 
         [0029]      FIG. 6  illustrates an example design for groove(s)  48  for use in a bearing surface  43 ,  46  of journal bearing  40 .  FIG. 6  shows bearing surface  43 ,  46  unrolled as if a flat surface, merely for illustrative purposes. The design for groove(s)  48  shown in  FIG. 6  may be implemented on bearing surface  46  of bushing  44  as shown in  FIG. 5  and/or on bearing surface  43  of journal  42 . As shown in  FIG. 6 , imaginary lines  49  may bound the grooved region of bearing surface  43 ,  46 . The grooved region of bearing surface  43 ,  46  may have a length, L 2 , as discussed above regarding  FIG. 5 ). 
         [0030]    The design shown in  FIG. 6  includes four grooves  48  (N=4) extending at angle θ relative to longitudinal axis  45 . Although the example shown in  FIG. 6  includes four grooves, persons having ordinary skill in the art may implement the teachings of the present disclosure with any number of grooves. θ of the groove(s) may be defined by the following equation: 
         [0000]      tangent(θ)=(π× D )/( N×H ).   (Eq. 1)
 
         [0031]    Wherein θ is the helix angle between groove  48  and longitudinal axis  45 , D is the diameter of the cylindrical bearing surface, N is the number of grooves, and H is the length of the grooved region of the bearing surface. Because (π×D) is the circumference of the cylindrical bearing surface, (π×D)/N is the circumferential length covered by each groove  48 . Persons having ordinary skill in the art may be able to vary θ around the value defined by Equation 1. For example, increasing θ may provide an overlap of grooves  48  at either end of the grooved region of the bearing surface. As another example, decreasing θ may provide a gap between the ends of the grooves  48  at either end of the grooved region of the bearing surface. As an example, the helix angle may be chosen between 0.5 times θ and 1.5 times θ. As another example, the helix angle may be chosen between 0.9 times θ and 1.1 times θ. 
         [0032]    In bearing  40 , the grooved region may be in either or both bearing surfaces (e.g., interior bearing surface  46  of bushing  44  and/or exterior bearing surface  43  of journal  42 ). When determining a helix angle, θ, for grooves  48 , one may use the average diameter of the journal and the bushing (e.g., journal exterior diameter plus the bushing interior diameter, all divided by two). In many journal bearings, the clearance between the journal and the bearing may be relatively small in comparison to the diameter of the journal and/or the diameter of the bushing. In example bearings incorporating teachings of the present disclosure, the design of grooves  48  may include setting a helix angle θ using the following formula. 
         [0000]      tangent(θ)=(π×( D 1 +D 2))/(2× N×H ).   (Eq. 2)
 
         [0033]    Wherein θ is the helix angle between groove  48  and longitudinal axis  45 , D 1  is the diameter of the of the bushing interior bearing surface, D 2  is the diameter of the journal exterior bearing surface, N is the number of grooves, and H is the length of the grooved region of the bearing surface. In these embodiments, (D 1 +D 2 )/2 provides an average of the two diameters. Because (π×(D 1 +D 2 ))/2 is the circumference of the average diameters, (π×(D 1 +D 2 ))/2×N is the circumferential length covered by each groove  48 . Persons having ordinary skill in the art may be able to vary θ around the value defined by Equation 2. For example, increasing θ may provide an overlap of grooves  48  at either end of the grooved region of the bearing surface. As another example, decreasing θ may provide a gap between the ends of the grooves  48  at either end of the grooved region of the bearing surface. As an example, the helix angle may be chosen between 0.5 times θ and 1.5 times θ. As another example, the helix angle may be chosen between 0.9 times θ and 1.1 times θ. 
         [0034]    As another example, each groove  48  may be described by its turn. The turn of each groove  48  is the portion of the circumference that groove  48  covers. For example, a single groove  48  that makes one rotation around circumference of bearing surface  43 ,  46  may be described as making one turn. A set of four groove(s)  48  shown in  FIG. 6  that each covers one fourth of the circumference of bearing surface  43 ,  46  may be described as making a quarter turn or 0.25 turns. In embodiments of journal bearing  40  incorporating the teachings of the present disclosure, each groove  48  may have a turn approximately equivalent to one over the number of grooves. 
         [0000]      groove turn=1/N.   (Eq. 3)
 
         [0035]    Some benefits of a journal bearing incorporating the teachings of the present disclosure may include reduced resistance to fluid (e.g., lubricant) flow through clearance  41 . Reduced resistance may allow increased volume flow for a constant pressure. Increased volume flow through clearance  41  may improve the temperature control of journal bearing  40  and/or the useful life span of journal bearing  40 . Increased bearing life may, in turn, improve the reliability of a piece of rotating equipment incorporating journal bearing  40 . In embodiments of journal bearing  40  including a set of grooves  48 , a groove design that reduces flow path length through clearance  41  may also reduce the loss of bearing surface area. Selection of grooves with a turn approximately equal to that defined by Equation 3 may also provide increased bearing life. For example, one bearing design may include grooves with a turn between 50% and 150% of the turn defined by Equation 3. As another example, one bearing design may include grooves with a turn between 90% and 110% of the turn defined by Equation 3. 
         [0036]    The selection of the number of grooves  48 , N, in the set of grooves may depend on multiple variables and/or considerations. For example, the operation of the equipment including bearing  40  may provide a range of acceptable pressure drop across bearing  40 , an expected rotational speed of journal  42 , and/or the viscosity of fluid used in bearing  40 . In some cases, a person having ordinary skill in the art may choose N to provide a helix angle, θ, similar to a flow angle provided by the geometry and operation of the bearing. As an example, one design may include between 1 and 10 grooves. As another example, a design may include between 1 and 5 grooves. 
         [0037]    Along with varying N, the number of grooves  48  in the set of grooves, a person having ordinary skill in the art may choose to vary the turn or the helix angle of the one or more grooves  48 . One design that may reduce flow path length includes axial grooves parallel to longitudinal axis  45  (i.e., θ=0). Axial grooves provide increased flow through journal bearing  40  in comparison to a smooth journal bearing surfaces but suffer a relatively large reduction in bearing surface area and, therefore, load bearing capacity. In addition, axial grooves are not radially symmetric, so the load bearing capacity of a journal bearing including axial grooves is highly dependent on the orientation of the grooved surface. 
         [0038]    In contrast, a set of grooves  48  with a helix angle approximately equal to θ according to equation 1 may reduce resistance to fluid flow through clearance  41  without significantly reducing the load bearing capacity of journal bearing  40 . A set of grooves  48  in accordance with the teachings of this disclosure (e.g., according to  FIG. 6 ,  FIG. 7 , or  FIG. 8 ) may provide a radially symmetric bearing—any radial line parallel to longitudinal axis  45  crosses exactly one groove  48 . 
         [0039]    Modeling an example journal bearing  40   a  similar to that shown in  FIG. 6  using Computational Fluid Dynamics (CFD) demonstrates a surprising and unexpected amount of reduction in resistance to fluid flow through clearance  41  when compared to other journal bearing designs. Example journal bearing  40   a  included four grooves  48   a  in bearing surface  46   a  of bushing  44   a.  Grooves  48   a  included four semicircular grooves with a 3 mm radius. Grooves  48   a  each had a helix angle θ of approximately 52.6°. The interior diameter of bushing  44   a  was 80.188 mm. The length, L 2 , of the grooved area was 82.5 mm. Example journal bearing  40   a  included 0.1525 mm clearance  41   a.  Example journal bearing  44   a  was compared to similar journal bearings without grooves  48 . 
         [0040]    Four designs for a journal bearing were modeled with equivalent situations (e.g., the same length, journal diameter, bushing diameter, clearance, pressure drop across the bearing, journal rotation speed, fluid properties, etc.). A smooth journal bearing with no grooves (Bearing A) allowed 338 pounds/hour of fluid to pass through the bearing. A journal bearing with two spiral grooves having a helix angle of approximately nine degrees (9°) (Bearing B) allowed 1554 pounds/hour of fluid to pass through the bearing. A journal bearing with three equally spaced axial grooves (Bearing C) allowed 1647 pounds/hour of fluid to pass through the bearing. Journal bearing  40   a  (e.g., four grooves with a helix angle θ determined according to equation 1) allowed 2869 pounds/hour of fluid to pass through the bearing—significantly improved over all of the other tested designs. 
         [0041]    Using CFD to model the load carrying capacity of the same four designs demonstrates an increased load carrying capacity for example journal bearing  40   a  when compared to the other grooved designs. When compared to Bearing A (smooth bearing surfaces), Bearing B had a load carrying capacity reduced by 34% and Bearing C had a load carrying capacity reduced by between 40% and 51% depending on the orientation of the radial load. Journal bearing  40   a  (e.g., four grooves with a helix angle θ determined according to equation 1) showed a load carrying capacity reduced by 29.8% when compared to Bearing A. 
         [0042]    Journal bearing  40   a  (e.g., four grooves with a helix angle θ determined according to equation 1) demonstrated the most reduced resistance to fluid flow through its clearance and the least reduced load carrying capacity. This improved performance may be affected by the design of the set of grooves  48 . Journal bearing  40  incorporating teachings of the present disclosure may provide radial symmetry with only a single interruption of the of the bearing hydrodynamic film or wedge along the axial length of the bearing surface. 
         [0043]      FIGS. 7 and 8  illustrate example arrangements of grooves  48  on a bearing surface of journal bearing  40  in accordance with teachings of the present disclosure. Each groove  48  may be located so that an imaginary line  54  extending parallel to longitudinal axis  45  intersects one and only one groove  48 . As shown in  FIGS. 7 and 8 , imaginary lines  54   a - 54   h  each intersect one and only one groove  48 . The number and length of each groove  48  may vary while maintaining a helix angle approximately equal to θ according to equation 1. 
         [0044]    Although the figures and embodiments disclosed herein have been described with respect to journal bearings, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the disclosure as illustrated by the following claims. For example, one having ordinary skill in the art may choose to vary the helix angle, θ, of the grooves around the value defined by Equation 1. As another example, one having ordinary skill in the art may choose to vary the turn of one or more grooves around the value defined by Equation 2.