Abstract:
A connecting rod ( 24 ) has a modified end adapted to ensure that a lubricant film of sufficient thickness exists in an end bearing thereof when the connecting rod is placed in both tension and compression. The connecting rod includes an elongated body portion or shaft ( 40 ), a big end ( 42 ) defining a first coupling bore ( 44 ) at a first longitudinal end of the body portion ( 40 ), and a small end ( 46 ) defining a second coupling bore ( 48 ) at a second longitudinal end of the body portion ( 40 ). The small end ( 46 ) and the big end ( 42 ) each have a proximal side ( 50,52 ) nearest the shaft ( 40 ) and a distal side ( 54,56 ) furthest from the shaft ( 40 ). An opening ( 100 ) is formed in the shaft ( 40 ) adjacent the proximal side ( 52 ) for adjusting a stiffness of the proximal side ( 52 ).

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The disclosure relates generally to the field of reciprocating drive mechanisms, and more particularly to an improved connecting rod design for use in such mechanisms. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    A conventional reciprocating drive mechanism typically includes one or more connecting rods that translate the rotary movement of a crankshaft into linear, reciprocating movement for driving respective piston rods. A typical connecting rod includes an elongated shaft that terminates at a first longitudinal end in a so-called “big end” having a relatively large, transverse bore formed therethrough for facilitating coupling to a crankshaft. The shaft terminates at a second longitudinal end in a so-called “small end” having a relatively smaller transverse bore formed therethrough for facilitating coupling to a piston or piston rod. The big end and the small end thus define respective, generally annular members at opposing longitudinal ends of the shaft of the connecting rod, each annular member having a proximal side that is connected directly to the shaft and a distal side that is spaced apart from, and not connected directly to, the shaft. 
         [0003]    An annular journal bearing is typically shrink-fit within the small end bore of a connecting rod for rotatably engaging a cylindrical crosshead pin that extends therethrough. A film of lubricant can be provided in a small annular gap between the crosshead pin and the journal bearing to ensure smooth rotation of the pieces and to minimize wear. Since the orientation of the journal bearing is fixed relative to the small end of the connecting rod, the journal bearing has a proximal side and a distal side that correspond to the proximal side and distal side of the small end, respectively. 
         [0004]    As the connecting rod reciprocates during operation, the small end of the rod and its respective journal bearing rotate about and alternatingly push and pull the crosshead pin that extends transversely therethrough. It has been observed that, during such reciprocation, the small end and the journal bearing may undergo asymmetric deformation. Particularly, when the small end and the journal bearing pull the crosshead pin (i.e., when the connecting rod is in tension), the distal sides of the small end and the journal bearing may deflect or deform away from the crosshead pin due to resistance from the crosshead pin and from the film of lubricant located between the crosshead pin and the distal side of the journal bearing. By contrast, when the small end and the journal bearing push the crosshead pin (i.e., when the connecting rod is in compression), the proximal side of the small end, which is directly connected to and supported by the rigid shaft of the connecting rod, resists deformation. The proximal side of the journal bearing, which is supported by the proximal side of the small end, therefore also resists deformation. Thus, instead of deforming or deflecting away from the crosshead pin, the proximal sides of the small end and the journal bearing overcome the resistance of the lubricant film, causing the gap between the proximal side of the journal bearing and the crosshead pin to be compressed. Some or all of the lubricant in the gap is thereby forced out and the film of lubricant in the gap is thereby thinned or entirely evacuated. Such thinning of the lubricant film can result in excessive and/or uneven wear on the journal bearing and the crosshead pin, which may have a deleterious effect on the reciprocating compressor as a whole. 
         [0005]    One attempted solution that has been implemented for mitigating the above-described lubricant thinning is the use of high viscosity lubricants that provide greater resistance against compression. However, the use of such high viscosity lubricants results in increased friction and associated losses in power. Another attempted solution has been to use a larger diameter bearing, but an efficient solution has yet to be achieved. 
       SUMMARY 
       [0006]    In view of the foregoing, it would be advantageous to provide a compressor having a connecting rod that is adapted to maintain a lubricant film of sufficient thickness in a small end journal bearing thereof when the connecting rod is placed in both tension and compression without incurring significant power losses. 
         [0007]    An exemplary connecting rod in accordance with the present disclosure may include an elongated shaft, a big end defining a first transverse coupling bore at a first longitudinal end of the shaft, and a small end defining a second transverse coupling bore at a second longitudinal end of the shaft. The big end may have a proximal side nearest the shaft and a distal side furthest from the shaft. The small end may also have a proximal side nearest the shaft and a distal side furthest from the shaft. An opening may be formed in the shaft adjacent one of the proximal side of the big end and the proximal side of the small end for reducing a stiffness of such proximal side. 
         [0008]    An exemplary compressor in accordance with the present disclosure may include a piston for compressing a fluid within a cylinder, and a drive shaft connected at a first longitudinal end to the piston and connected at a second longitudinal end to a crosshead assembly. The compressor may further include a connecting rod having an elongated shaft, a big end defining a first transverse coupling bore at a first longitudinal end of the shaft, the big end having a proximal side nearest the shaft and a distal side furthest from the shaft, and a small end defining a second transverse coupling bore at a second longitudinal end of the shaft, the small end having a proximal side nearest the shaft and a distal side furthest from the shaft. The big end may be coupled to a crankshaft, and the small end may be coupled to the crosshead assembly by a crosshead pin that extends through the second coupling bore and the crosshead assembly. An opening may be formed in the shaft adjacent one of the proximal side of the big end and the proximal side of the small end for reducing a stiffness of such proximal side. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a side view in section illustrating an exemplary compressor in accordance with the present disclosure. 
           [0010]      FIG. 2  is a perspective view illustrating the crosshead assembly and the small end of the connecting rod of the exemplary compressor shown in  FIG. 1 . 
           [0011]      FIG. 3  is an exploded perspective view illustrating the crosshead assembly and the small end of the connecting rod of the exemplary compressor shown in  FIG. 1 . 
           [0012]      FIGS. 4 a - d    are side views illustrating exemplary alternative embodiments of the connecting rod of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    An apparatus in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the device are shown. This apparatus, however, may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the apparatus to those skilled in the art. In the drawings, like numbers refer to like elements throughout. 
         [0014]    Referring to  FIG. 1 , an exemplary embodiment of a reciprocating compressor  10  (hereinafter “the compressor  10 ”) in accordance with the present disclosure is shown. For the sake of convenience and clarity, terms such as “top,” “bottom,” “radial,” “axial,” “upper,” “lower,” “vertical,” “horizontal,” “right,” “left,” “lateral,” and “longitudinal” will be used herein to describe the relative placement and orientation of the compressor  10  and its various components, each with respect to the geometry and orientation of the compressor  10  as it appears in  FIG. 1 . Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import. 
         [0015]    The compressor  10  may include a frame  12 , a cylinder  14 , and a guide housing  15 . The cylinder  14  may contain a piston  16  which is reciprocably movable along its longitudinal axis within the cylinder  14  as further described below. A piston rod  17  may be connected at a first end to the piston  16 , and may be connected at a second end to a crosshead assembly  18  that is movably disposed within the guide housing  15 . The crosshead assembly  18  may include crosshead shoes  20 ,  22  which conformingly and slidably engage the interior surface of the guide housing  15  for facilitating reciprocating movement of the crosshead assembly  18  along a linear path within the guide housing  15 . 
         [0016]    The crosshead assembly  18  may be reciprocatingly driven by a connecting rod  24  that may be pivotably coupled at a first end to the crosshead assembly  18  by a crosshead pin  25  (as described in greater detail below) and rotatably coupled at a second end to a rotatably driven crankshaft  27 . As will be understood, the connecting rod  24  translates the rotary movement of the crankshaft  27  into reciprocating, linear movement that is imparted to the crosshead assembly  18  and the connected piston rod  17  and piston  16 . 
         [0017]    The compressor  10  may be of the double-acting type, having compression chambers  26 ,  28  located on either side of the piston  16  within the cylinder  14 . Each of the compression chambers  26 ,  28  may be provided with an inlet valve  30 ,  32  and an outlet valve  34 ,  36 , respectively. Upon movement of the piston  16  in the direction of the crank mechanism (i.e., to the left in  FIG. 1 ), a fluid (e.g., any compressible substance) at a suction pressure may be introduced by way of the inlet valve  30  into the compression chamber  26 . At the same time, the fluid present in the compression chamber  28  may be compressed and discharged at a discharge pressure by way of the outlet valve  36 . Similarly, upon movement of the piston  16  away from the crank mechanism (i.e., to the right in  FIG. 1 ), fluid at a suction pressure may be introduced by way of the inlet valve  32  into the compression chamber  28 . At the same time, the fluid present in the compression chamber  26  may be compressed and discharged at a discharge pressure by way of the outlet valve  34 . Fluid is thereby continuously moved into and out of the cylinder  14 . Although not shown, a source of fluid may be coupled to the inlet valves  30 ,  32  of the compression chambers  26 ,  28 , and the outlet valves  34 ,  36  may be coupled to appropriate discharge conduits. 
         [0018]    The connecting rod  24  of the compressor  10  may include a body portion  40  that terminates in a so-called “big end”  42 . The big end  42  may have a relatively large, transverse coupling bore  44  formed therethrough for receiving the crankshaft  27 . At its opposite end, the body portion  40  may terminate in a so-called “small end”  46 . The small end  46  may have a relatively smaller transverse coupling bore  48  formed therethrough. The smaller transverse coupling bore  48  may receive the crosshead pin  25  to couple the connecting rod  24  to the crosshead assembly  18 , as further described below. The big end  42  and the small end  46  of the connecting rod  24  thus may define respective, generally annular elements on opposing longitudinal ends of the body portion  40 . Thus, the big end  42  and small end  46  may each have a respective proximal side  50 ,  52  disposed directly adjacent to the body portion  40 , and a respective distal side  54 ,  56  that is spaced longitudinally apart from the body portion. 
         [0019]      FIGS. 2 and 3  illustrate the crosshead assembly  18  and the small end  46  of the connecting rod  24 . The body portion  40  of the connecting rod  24  is shown as having an I-profile, but this is not critical, and it will be appreciated that the body portion  40  can have any of a variety of other appropriate profiles without departing from the present disclosure. 
         [0020]    The crosshead assembly  18  may include a crosshead body  60  which is provided with two curved crosshead shoes  20 ,  22  that are arranged to slide along corresponding rectilinear guides (not shown) within the guide housing  15  (shown in  FIG. 1 ). As best shown in  FIG. 3 , the connecting rod  24  may be pivotably coupled to the crosshead body by a cylindrical crosshead pin  25  that extends through opposing eyelets  68 ,  70  provided in the sidewalls of the crosshead body  60 , and through an annular sleeve bearing  74  that may be fixed within a bore  48  of the small end  46  of the connecting rod  24 , such as by shrink fitting, mechanical fasteners, or adhesives. The sleeve bearing  74  may have a proximal side  76  and a distal side  78  that correspond to, and are located adjacent, respective proximal and distal sides  52  and  56  of the small end  46  of the connecting rod  24 . Referring again to  FIG. 1 , a film of lubricant (hereinafter referred to as “the lubricant film  73 ”) may be provided in an annular gap located radially intermediate the crosshead pin  25  and the sleeve bearing  74 . The small end  46  of the connecting rod  24  and the sleeve bearing  74  may therefore pivot freely and smoothly about the crosshead pin  25  within the crosshead body  60 . 
         [0021]    The crosshead assembly  18  may also couple to the piston rod  17  of the compressor. Thus, the piston rod  17  may extend through a mounting flange  82  of the crosshead assembly  18 , and an optional abutting spacer plate  84 , and may be held in firm engagement therewith by a threaded nut  86  that may extend into an opposing side of the mounting flange  82  and spacer plate  84  and may be fastened to a threaded end  88  of the piston rod  17 . The mounting flange  82  and spacer plate  84  may be disposed in flat abutment with the crosshead body  18  and may be connected directly to the crosshead pin  25  by threaded studs  90  that are secured at one end by nuts  91  and that extend through corresponding holes  92 ,  94 ,  96 , formed in the mounting flange  82 , the spacer plate  84 , and the crosshead body  60 , respectively, and engage threaded bores  97  that are formed in the crosshead pin  25 . The piston rod  17  may thereby be rigidly fixed to the crosshead pin  25  while simultaneously allowing the crosshead pin  25  to rotate freely about its axis relative to the sleeve bearing  74  and the small end  46  of the connecting rod  24  during operation of the compressor  10 . 
         [0022]    As best shown in  FIG. 2 , an opening  100  may be formed in the body portion  40  of the connecting rod  24  at a position immediately adjacent the proximal side  52  of the small end  46  and vertically intermediate a pair of legs  102 ,  104  that connect the body portion  40  to the proximal side  52 . In the illustrated embodiment the opening  100  is a substantially kidney-shaped aperture that is partially defined by a sidewall  106  of the proximal side  52  which extends between the connecting legs  102 ,  104 . The sidewall  106  may have a curvature that is substantially similar to the curvature of the bore  48  in the small end  46 , and may have a radial thickness that is substantially equal to the radial thickness of the distal side  56  of the small end  46 , but this is not critical. It is contemplated that the opening  100  may have any of a variety of other shapes and configurations, as will be described in greater detail below. Additionally, while the opening  100  is shown as extending entirely through the body portion  40 , it is contemplated that the opening can alternatively extend only partially through the body portion. 
         [0023]    As will be appreciated, the opening  100  may reduce the rigidity of the connecting rod  24  at the juncture of the shaft  40  and the proximal side  52  of the small end  46 , thereby providing the proximal side  52  with greater flexibility (i.e. lower stiffness) than would be provided in the absence of the opening  100  (i.e., if the connecting rod were entirely solid at the juncture of the shaft  40  and the proximal side  52  as in conventional connecting rods). For example, the proximal side  52  of the small end  46  may have a stiffness that is substantially similar to the stiffness of the distal side  56  of the small end  46 . While the opening  100  is located adjacent the small end  46 , it is contemplated that the connecting rod  24  may additionally or alternatively be provided with a similar opening located adjacent the big end  42  for modifying the rigidity thereof in a substantially similar manner to that described above. 
         [0024]    During operation of the compressor  10 , the crankshaft  27  rotates and recriprocatingly drives the connecting rod  24 , which in-turn reciprocatingly drives the crosshead assembly  18 , the piston rod  17 , and the piston  16  as described above. As the connecting rod  24  reciprocates longitudinally, the small end  46  of the connecting rod  24  and the sleeve bearing  74  pivot about and alternatingly push and pull the crosshead pin  25  that extends transversely therethrough. When the connecting rod  24  is placed in compression (i.e. when the connecting rod  24  moves to the right in  FIG. 1 ), the proximal side  76  of the sleeve bearing  74 , which supported by the proximal side  52  of the small end  46 , forces the crosshead pin  25  to the right. Conversely, when the connecting rod  24  is placed in tension (i.e. when the connecting rod  24  moves to the left in  FIG. 1 ), the distal side  78  of the sleeve bearing  74 , which is supported by the distal side  56  of the small end  46 , forces the crosshead pin  25  to the left. 
         [0025]    As the crosshead pin  25  is alternatingly pushed and pulled by the connecting rod  24  in the manner described above, the lubricant film  73  may be compressed between the crosshead pin  25  and the sleeve bearing  74 . Particularly, when the connecting rod  24  is placed in tension, the lubricant film  73  may be compressed between the connecting rod  24  and the proximal side  76  of the sleeve bearing  74 , and when the connecting rod  24  is placed in compression, the lubricant film  73  may be compressed between the connecting rod  24  and the distal side  78  of the sleeve bearing  74 . The proximal sides  52 ,  78  and the distal sides  56 ,  76  of the sleeve bearing  74  and the small end  46  are therefore alternatingly subjected to resistance from the lubricating film  73  and the underlying crosshead pin  25 . 
         [0026]    In some embodiments the opening  100  formed in the body portion  40  of the connecting rod  24  adjacent the proximal side  52  of the small end  46  may result in a stiffness of the proximal side  52  being substantially the same as the stiffness of the distal side  56  of the small end. Thus, when the connecting rod  24  is in compression, the lubricating film  73  may be compressed and the proximal sides  52 ,  76  of the sleeve bearing  74  and the small end  46  may be forcibly deformed away from the crosshead pin  25  by substantially the same amount that the lubricating film  73  may be compressed and the distal sides  56 ,  78  of the sleeve bearing  74  and the small end  46  may be forcibly deformed away from the crosshead pin  25  when the connecting rod  24  is in compression. The thickness of the lubricating film  73  between the crosshead pin  25  and the proximal side  76  of the sleeve bearing  74  when the connecting rod is in compression may therefore be substantially equal to the thickness of the lubricating film  73  between the crosshead pin  25  and the distal side  78  of the sleeve bearing  74  when the connecting rod  24  is in tension. 
         [0027]    This is to be contrasted with a conventional connecting rod  24  that does not include an opening such as opening  100 , such that the proximal side of the small end of the conventional connecting rod has a substantially higher stiffness than the stiffness of the distal side. Such conventional configurations are therefore susceptible to asymmetric deformation, in which the lubricant film between the crosshead pin and the sleeve bearing is significantly thinned or completely evacuated during the compression stroke relative to the tension stroke, which results in excessive and/or uneven wear on the crosshead pin and the sleeve bearing. The configuration of the connecting rod  24  of the present disclosure, and particularly the provision of the opening  100 , prevent, or at least mitigate, such asymmetric deformation and excessive and/or uneven wear associated therewith. 
         [0028]      FIGS. 4 a -4 b    illustrate several embodiments of connecting rods in accordance with the present disclosure. It should be understood that these embodiments are presented by way of example only, and that many variations of such embodiments are contemplated and may be implemented with similar features for reducing the stiffness of the proximal side of a small end of a connecting rod without departing from the present disclosure. 
         [0029]    Referring to  FIG. 4 a   , the connecting rod  200  may be substantially similar to the connecting rod  24  described above, including an I-profile body portion  202  with a kidney-shaped opening  204  positioned adjacent the proximal side  206  of the small end  208  and laterally intermediate a pair of connecting legs  210 ,  212 . In the illustrated embodiment, the connecting rod  200  is also be provided with a pair of relief dimples  214 ,  216  (e.g. partial bores) formed in the connecting legs  210 ,  212 , respectively. A pair of substantially identical relief dimples (not within view) may also be formed in the opposite side the connecting legs  210 ,  212 . The relief dimples  214 ,  216  may be provided to further adjust the stiffness of the proximal side  206  of the small end  208  (i.e., in addition to the relief bore  204 ) in a desired manner. 
         [0030]    Referring to  FIG. 4 b   , the connecting rod  300  may be substantially similar to the connecting rod  24  described above, with an I-profile body portion  302  having an opening  304  formed therethrough adjacent the proximal side  306  of the small end  308  and laterally intermediate a pair of connecting legs  310 ,  312 . The opening  304  of this embodiment is shown to be deeper than the relief bore  100  described above, thereby providing the proximal side  306  of the small end  308  with a different stiffness profile than that of the proximal side  52  of the small end  46  of the connecting rod  24 . 
         [0031]    Referring to  FIG. 4 c   , the illustrated connecting rod  400  may be provided with a body portion  402  that is substantially rod-shaped, as well as a small, circular opening  404  formed therethrough adjacent a proximal side  406  of a small end  408 . The connecting rod  400  of this embodiment may also include a plurality of radially and circumferentially spaced smaller openings  410  formed in the proximal side  406  of the small end  408 . In the illustrated embodiment the smaller openings  410  include a plurality of different sizes, with larger openings positioned adjacent the body portion  402 , and smaller openings positioned adjacent the proximal side  406  of the small end  408 . The combination of the circular opening  404  and the plurality of radially and circumferentially spaced smaller openings  410  may be employed to provide the proximal side  406  with a desired stiffness profile. 
         [0032]      FIG. 4 d    shows a further embodiment of the disclosed connecting rod  500  that includes a rod-shaped body portion  502  and a substantially triangular opening  504  formed adjacent the proximal side  506  of the small end  508 . As with the prior embodiments, the disclosed opening  504  may provide the proximal side  506  with a desired stiffness profile. 
         [0033]    It will be apparent from foregoing disclosure that one or more relief bores and/or other relief features (e.g. dimples), such as may have a variety of different sizes, shapes, and configurations, can be formed in a connecting rod to tune the stiffness of the small end of the connecting rod in a desired manner. The disclosed arrangement can be used as a recriprocating drive mechanism in any of a variety of types of compressors known in the art. 
         [0034]    As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
         [0035]    While certain embodiments of the disclosure have been described herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.