Abstract:
Reciprocating motion can be converted to rotary motion through a crankshaft and a connecting rod. In a connecting rod that is primarily in tension, two opposing connecting rods can be coupled to a single journal. Two bearing caps are placed over the journal, the bearing caps having fingers that extend away from the bearing cap with the fingers of the two bearing caps being enmeshed. Fingers of each bearing cap are coupled to the connecting rods. The resulting joint is compact and lighter weight with a shorter journal than prior joints.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority benefit from U.S. provisional patent application 61/441,915 filed 11 Feb. 2011. 
       FIELD 
       [0002]    The present disclosure relates to a pullrod connection to a journal of a rotating member. 
     
    
     BACKGROUND 
       [0003]    In  FIG. 1 , an opposed-piston, opposed-cylinder (OPOC) engine  10  is shown isometrically. An intake piston  12  and an exhaust piston  14  reciprocate within each of first and second cylinders (cylinders not shown to facilitate viewing pistons). Exhaust pistons  14  couple with a journal (not visible) of crankshaft  20  via pushrods  16 . Intake pistons  12  couple with two journals (not visible) of crankshaft  20  via pullrods  18 , with each intake piston  12  having two pullrods  18 . The first and second cylinders in which the pistons reciprocate are parallel but offset from each other in the Y direction due to pullrods  18  associated with the cylinder shown front and leftward displaced in a negative Y direction with respect to pullrods  18  associated with the cylinder shown rear and rightward. Pushrods  16  are similarly situated with respect to each other. It is cost effective that all four pullrods  18  are identical in design and the two pushrods  16  are the same. However, a disadvantage of such an offset design is that the engine is wider than it would otherwise be if the two cylinders could be collinear. A torque is introduced due to the offset of the two cylinders. 
         [0004]    One alternative to overcome the offset cylinders is a forked rod, such as is described in U.S. Pat. No. 1,322,824, invented by F. Royce. By employing a forked rod/blade rod configuration within the engine of  FIG. 1 , the length of the journal (or crank pin) can be reduced. Also, the cylinders are collinear. The width of the engine can be reduced and the unbalanced forces are reduced. However, a disadvantage of such a configuration is that the piston in one cylinder couples with the crankshaft by a forked rod and the corresponding piston in the opposing cylinder couples with the crankshaft by a blade rod thereby increasing part count for the engine. A system for coupling the rods to the crankshaft is desired which allows common parts to be used in the two cylinder, such as is possible with the configuration shown in  FIG. 1 , while allowing collinear cylinders, such as that shown U.S. Pat. No. 1,322,824. 
       SUMMARY 
       [0005]    Disclosed herein is a connecting-rod assembly that achieves a low part count while allowing for an in-line arrangement of cylinders. Such assembly includes: a cylindrical journal, first and second bearing shell portions placed on the journal, a first bearing cap placed on the first bearing shell portion and a second bearing cap placed on the second bearing shell portion. The first bearing cap has a concave surface that forms a cylindrical portion that mates with a convex surface of the first bearing shell portion. The first bearing cap has first and second fingers extending outwardly from a first end of the cylindrical portion with a gap of a predetermined width between the first and second fingers. The first bearing cap has a third finger extending outwardly from a second end of the cylindrical portion. The second bearing cap has a concave surface that forms a portion of a cylinder that mates with a convex surface of the second bearing shell portion. The second bearing cap has first and second fingers extending outwardly from a first end of the cylindrical portion with a gap of the predetermined width between the first and second fingers. The second bearing cap has a third finger extending outwardly from a second end of the cylindrical portion. The third finger of the first bearing cap engages with the first and second fingers of the second bearing cap and the third finger of the second bearing cap engages with the first and second fingers of the first bearing cap. 
         [0006]    An orifice of a predetermined diameter is defined in each of the first, second, and third fingers of both the first and second bearing caps and the orifices are located near tips of the finger. The orifices are substantially parallel to the central axis of the journal. 
         [0007]    The assembly further includes a first connecting rod with an outside edge of the connecting rod shaped roughly as an elongated isosceles triangle. The first connecting rod includes: a first corner adapted to couple with a reciprocating element, a second corner having a single tab of the predetermined width through which an orifice of the predetermined diameter is defined, and a third corner having double tabs each defining an orifice of the predetermined diameter. The double tabs are separated by a gap of the predetermined width and the first connecting rod is placed over the second bearing shell portion with the single tab meshing with the first and second fingers of the first bearing cap and the third finger of the first bearing cap meshing with the double tabs of the first connecting rod. A first pin is inserted through the orifice in the single tab and the orifices in the first and second fingers of the first bearing cap. A second pin is inserted through the orifices in the double tabs and the orifice in the third finger of the first bearing cap. 
         [0008]    The assembly further includes a second connecting rod with an outside edge of the connecting rod shaped roughly as an elongated isosceles triangle. The second connecting rod includes: a first corner adapted to couple with a reciprocating element, a second corner having a single tab of the predetermined width through which an orifice of the predetermined diameter is defined, and a third corner having double tabs each defining an orifice of the predetermined diameter. The double tabs are separated by a gap of the predetermined width. The second connecting rod is placed over the first bearing shell portion with the single tab of the second connecting rod meshing with the first and second fingers of the second bearing cap and the third finger of the second bearing cap meshing with the double tabs of the second connecting rod. A third pin is inserted through the orifice in the single tab of the second connecting rod and the orifices in the first and second fingers of the second bearing cap. A fourth pin is inserted through the orifices in the double tabs of the second connecting rod and the orifice in the third finger of the second bearing cap. 
         [0009]    The first pin has a radial groove proximate an end of the first pin and the second pin each has a radial groove proximate an end of the second pin with a first snap ring coupled to the groove in the first pin and a second snap ring coupled to the groove in the second pin. 
         [0010]    Alternatively, a snap ring is inserted into an annular groove defined in the second finger; a snap ring is inserted into an annular groove defined in the third finger; a snap ring is inserted in an annular groove defined into a first of the double tabs; and a snap ring is inserted into an annular groove defined in a second of the double tabs. 
         [0011]    In another alternative, a counterbore of a counterbore diameter is collinear with the orifice in the second finger. A snap ring is inserted into an annular groove defined in the second finger. A counterbore of the counterbore diameter is collinear with the orifice in one of the double tabs. A snap ring is inserted into an annular groove defined in the one of the double tabs. A body of the first and second pins is of the predetermined diameter and heads of the first and second pins are of the counterbore diameter. 
         [0012]    According to some embodiments, first and second through-hole orifices are defined in the first bearing shell portion near an end of the first bearing shell portion and first and second threaded orifices are defined in the second bearing shell portion near an end of the second bearing shell portion. A first screw is inserted through the first through-hole orifice of the first bearing shell portion and threads of the first screw engaged with the first threaded orifice of the second bearing shell portion. A second screw is inserted through the second through-hole orifice of the first bearing shell portion and threads of the second screw engaged with the second threaded orifice of the second bearing shell portion. 
         [0013]    According to some embodiments, the first bearing shell portion and the second bearing shell portion have fingers extending outwardly from at least one end of each the first and second bearing shell portions. An orifice is defined in the fingers with an axis of the orifice being substantially parallel to a central axis of the journal. The fingers of the first and second bearing shell portions are enmeshed to form a box joint with a dowel pin inserted through the orifices in the enmeshed fingers. 
         [0014]    In some embodiments, the first bearing cap has a cylindrical concave surface and a pin extending radially from the cylindrical concave surface. The first bearing shell portion has a cylindrical convex surface having an aperture defined in the cylindrical convex surface and the pin engages with the aperture. The aperture is substantially evenly spaced between the ends of the first bearing shell portion and the aperture may be a groove extending less than 30 degrees of the circumference of the first bearing shell portion. The second bearing cap has a cylindrical concave surface and a pin extending radially from the cylindrical concave surface. The second bearing shell portion has a groove defined in a cylindrical convex surface associated with the second bearing shell portion. The groove associated with the second bearing shell portion extends less than the circumference of the second bearing shell portion and the pin associated with the second bearing cap engages with the groove associated with the second bearing shell portion. Relative rotational motion of the first bearing shell portion with respect to the first bearing shell cap is substantially prevented by the pin engaging with the aperture. 
         [0015]    The first bearing shell portion has first and second oil holes located roughly 60 degrees from first and second ends of the first bearing shell portion, respectively; an inner surface of the first bearing shell portion has a first annular oil groove extending from the first end of the first bearing shell portion to the first oil hole; and the inner surface of the first bearing shell portion has a second annular oil groove extending from the second end of the first bearing shell portion to the second oil hole. A third oil groove defined in an outer surface of the first bearing shell portion extends between the first and second oil holes. Alternatively, a third oil groove is defined in a portion of the concave surface of the first bearing cap and the portion extends from first oil hole to the second oil hole of the first bearing shell portion at all relative positions of the first bearing cap with respect to the first bearing shell portion. 
         [0016]    The first bearing cap has an oil hole through the cylindrical portion with the oil hole of a larger diameter at an end of the hole proximate the concave surface. The pin is hollow and the hollow pin is inserted in the oil hole. 
         [0017]    According to an alternative embodiment, a threaded hole is defined in each end of the first, second, and third fingers with the threaded holes being substantially parallel. A first connecting rod having a rod portion, a journal connection portion, and a piston connection portion is provided with the journal connection portion having two parallel flanges that are substantially perpendicular with respect to an axis of the rod portion. A first of the flanges has two through holes and a second of the flanges has a single through hole. The journal connection portion further includes a surface facing away from the rod portion that defines a portion of a concave cylinder. A first bolt is placed within one of the two through holes and coupled with threads in the threaded hole defined in the first finger of the first bearing cap. A second bolt is placed within the other of the two through holes and coupled with threads in the threaded hole defined in the second finger of the first bearing cap. A third bolt is placed within the single through hole and coupled with the threads in the threaded hole defined in the third finger of the first bearing cap. A second connecting rod is similarly fixed to the second bearing cap. 
         [0018]    The first bearing cap has two parallel bearing surfaces facing inwardly with the two parallel bearing surfaces extending away from the ends of the cylindrical portion of the first bearing cap. 
         [0019]    The first connecting rod has two parallel bearing surfaces facing outwardly with the bearing surfaces of the first bearing cap bearing against the bearing surfaces of the first connecting rod. 
         [0020]    The second bearing cap has two parallel bearing surfaces facing inwardly with the two parallel bearing surfaces extending away from the ends of the cylindrical portion of the second bearing cap; and the second connecting rod has two parallel bearing surfaces facing outwardly with the bearing surfaces of the second bearing cap bearing against the bearing surfaces of the second connecting rod. 
         [0021]    In some embodiments, the journal is a portion of a crankshaft of an internal combustion engine with the journal predominantly rotating in one direction. In alternative embodiments, the journal oscillates back and forth without always rotating. 
         [0022]    The third finger of the bearing caps has a width as measured along an axis parallel to a central axis of the journal substantially equal to the predetermined width of the gap between the first and second fingers of the bearing cap. In some embodiments, the first, second, and third fingers are substantially parallel. 
         [0023]    Also disclosed is a journal-connecting rod assembly having a first connecting rod having a first corner adapted to couple with a reciprocating element, a second corner having a single tab of the predetermined width, and a third corner having double tabs. A first bearing cap has a concave surface that forms a cylindrical portion that mates with a convex surface of the first bearing shell portion, the first bearing cap has first and second fingers extending outwardly from a first end of the cylindrical portion, the first bearing cap has a third finger extending outwardly from a second end of the cylindrical portion, the third finger of the first bearing cap is slid between the double tabs at the third corner of the first connecting rod, and the single tab at the second corner of the first connecting rod is slid between the first and second fingers of the first bearing cap. A second connecting rod has a first corner adapted to couple with a reciprocating element, a second corner having a single tab, and a third corner having double tabs. The assembly further includes a second bearing cap having a concave surface that forms a cylindrical portion that mates with a convex surface of the first bearing shell portion. The second bearing cap has first and second fingers extending outwardly from a first end of the cylindrical portion and a third finger extending outwardly from a second end of the cylindrical portion. The third finger of the second bearing cap is slid between the double tabs at the third corner of the second connecting rod. The single tab at the second corner of the second connecting rod is slid between the first and second fingers of the second bearing cap. The assembly may further include a journal and first and second roller bearing portions each including multiple needle bearings nested within a bearing race. The first and second roller bearing portions coupled to the journal wherein an inner, concave portion of the cylindrical portion of the first and second bearing caps ride upon the needle bearings. Alternatively, the assembly includes a journal. An inner, concave portion of the cylindrical portion of the first and second bearing caps mate with an outer convex surface of the journal. 
         [0024]    Also disclosed is a method to assemble two connecting rods to a single journal including: placing first and second portions of a bearing shell onto the journal; placing a first bearing cap over one of the two bearing portions wherein the first bearing cap has first and second fingers extending away from a top of the first bearing cap and a third finger extending away from a bottom of the first bearing cap; and meshing a second bearing cap with the first bearing cap. The second bearing cap has first and second fingers extending away from the bottom of the second bearing cap and a third finger extending away from a top of the second bearing cap. The meshing entails the third finger of the first bearing cap sliding into a gap between the first and second fingers of the second bearing cap and the third finger of the first bearing cap sliding into a gap between the first and second fingers of the second bearing cap. 
         [0025]    The method may also include: placing a first connecting rod onto an outside surface of the second bearing cap, inserting a first bolt into a first through hole in the first connecting rod, engaging threads in a first bolt hole in the first finger of the first bearing cap with threads of the first bolt, inserting a second bolt into a second through hole in the first connecting rod, engaging threads in a second bolt hole in the second finger of the first bearing cap with threads of the second bolt, inserting a third bolt into a third through hole in the first connecting rod, engaging threads in a third bolt hole in the third finger of the first bearing cap with threads of the third bolt, placing a second connecting rod onto an outside surface the first bearing cap, inserting a fourth bolt into a first through hole in the second connecting rod, engaging threads in a first bolt hole in the first finger of the second bearing cap with threads of the fourth bolt, inserting a fifth bolt into a second through hole in the second connecting rod, engaging threads in a second bolt hole in the second finger of the second bearing cap with threads of the fifth bolt, inserting a sixth bolt into a third through hole in the second connecting rod, and engaging threads in a third bolt hole in the third finger of the second bearing cap with threads of the sixth bolt. In some embodiments, the first bearing cap has a pin extending outwardly and an outer surface of the first portion of the bearing shell defines an aperture. The method may include engaging the pin with the aperture to limit the movement of the first bearing cap with respect to the first portion of the bearing shell. 
         [0026]    In some alternative embodiments, the method includes placing a first connecting rod onto an outside surface of the second bearing cap. A first end of the first connecting rod is adapted to couple with a reciprocating element; a first corner on a second end of the first connecting rod has a single tab having an orifice; a second corner on a second end of the first connecting rod has two tabs each having an orifice with the single tab meshing with the second and third fingers of the second bearing cap and the first finger of the second bearing cap meshing with the two tabs. The method may further include inserting a first pin through the orifice in the single tab and the orifices in the second and third fingers of the second bearing cap, inserting a second pin through the orifices in the two tabs and the orifice in the first finger of the second bearing cap, installing a first snap ring proximate the first pin, and installing a second snap ring proximate the second pin. The second connecting rod may be similarly assembled onto the journal. 
         [0027]    Also disclosed is a journal and connecting rod assembly, including a cylindrical journal, first and second bearing portions coupled onto the journal, a first bearing cap placed on the first bearing portion, the first bearing cap having a concave surface that mates with a convex surface of the first bearing portion, and a second bearing cap placed on the second bearing portion. The second bearing cap has a concave surface mating with a convex surface of the second bearing portion. The first bearing cap has first and second fingers extending outwardly from a first end of a cylindrical portion of the first bearing cap and a third finger extending outwardly from a second end of the cylindrical portion of the first bearing cap. The second bearing cap has first and second fingers extending outwardly from a first end of a cylindrical portion of the second bearing cap and a third finger extending outwardly from a second end of the cylindrical portion of the second bearing cap. The third finger of the first bearing cap engages with the first and second fingers of the second bearing cap and the third finger of the second bearing cap engages with the first and second fingers of the first bearing cap. Each of first, second, and third fingers of first and second bearing caps has an orifice defined therein. The assembly may further include a first connecting rod having three orifices adapted to align with the three holes in the first, second, and third fingers of the first bearing cap and a second connecting rod having three orifices adapted to align with the three holes in the first, second, and third fingers of the second bearing cap. Axes of the three orifices in the first and second connecting rods and axes of the holes in the first, second, and third fingers of the first and second bearing caps are substantially parallel to a central axis of the journal. The orifices are aligned with the associated holes. Pins are inserted into the aligned orifices and holes. Alternatively, axes of the three orifices in the first and second connecting rods axes of the holes in the first, second, and third fingers of the first and second bearing caps are substantially perpendicular to a central axis of the journal and roughly parallel with the first second and third fingers of the associated bearing cap. The orifices are aligned with the associated hole and the holes in the bearing cap are threaded and bolts are inserted into the orifices and engaged with the threads in the holes. 
         [0028]    The assembly may further include a longitudinal oil hole defined in the journal roughly parallel with an axis of rotation of the journal, a radial oil hole defined in the journal fluidly coupling the longitudinal oil hole and a surface of the journal, oil holes defined in the first and second bearing shell portions with the oil holes located approximately one-third of the distance between ends of the bearing shell portions, an oil groove on a concave surface of the first bearing shell portion extending circumferentially between an oil hole and a proximate end of the first bearing shell portion, an oil groove on a concave surface of the second bearing shell portion extending circumferentially between an oil hole and a proximate end of the second bearing shell portion, an oil groove on a convex surface of the first bearing shell portion between oil holes, and 
         [0029]    an oil groove on a convex surface of the second bearing shell portion between oil holes. 
         [0030]    The assembly may have a pin inserted into an orifice in the concave surface of the first bearing cap with the pin extending inwardly and an aperture defined in the first bearing portion with the pin indexed with the aperture to restrict relative movement between the first bearing portion and the first bearing cap with the pin indexed with the aperture substantially prevents relative movement and the second bearing cap is unpinned. 
         [0031]    In some embodiments, the aperture is a first groove and the assembly further has a pin inserted into an orifice in the concave surface of the second bearing cap and a second groove defined in the second bearing portion with the pin indexed with the aperture. The first and second grooves extend a predetermined length on a convex surface of the first and second bearing portions so as to restrict relative movement of the first bearing portion with respect to the first bearing cap and relative movement of the second bearing portion with respect to the second bearing cap. 
         [0032]    An advantage provided by embodiments described above, is that a single, common bearing is provided for two pullrods, i.e., to accommodate two pistons thereby allowing a more compact engine. Furthermore, the friction is reduced. The friction is the same during pulling, but for the portion of the rotation with no pulling, there is no friction, thereby reducing the overall friction of the engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  illustrates an example configuration of an opposed-piston, opposed-cylinder engine in an isometric view; 
           [0034]      FIG. 2  is an isometric view of a connecting rod to crankshaft journal connection according to an embodiment of the present disclosure; 
           [0035]      FIGS. 3 and 4  show a connecting rod and a bearing cap related to the components illustrated in  FIG. 2 ; 
           [0036]      FIG. 5  is an exploded view of a connecting rod/bearing cap system according to an embodiment of the present disclosure; 
           [0037]      FIG. 6  is an illustration of the connecting rod of  FIG. 5 ; 
           [0038]      FIG. 7  is an alternative connecting rod; 
           [0039]      FIG. 8A  illustrates the bearing shell portions of  FIG. 5 ; 
           [0040]      FIG. 8B  illustrates an alternative embodiment to secure the bearing shell portions; 
           [0041]      FIG. 9  illustrates an alternative roller bearing embodiment; 
           [0042]      FIGS. 10 and 11  illustrated various embodiments for pinning the pullrod with the bearing cap; 
           [0043]      FIGS. 12 ,  14 , and  17  illustrate the arrangement of the pistons and connecting rods in different angles of crank rotation; 
           [0044]      FIGS. 13 and 15  show a detail of the crank connection at two crank positions according to one embodiment for pinning a shell bearing portion; 
           [0045]      FIGS. 16 and 18  show a detail of the crank connection at two crank positions according to one embodiment for restricting motion of the shell bearing portions; and 
           [0046]      FIGS. 19 and 20  are flowcharts of the assembly processes for two embodiments of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0048]    In  FIG. 2  an isometric view of a journal  96  with a central axis  99  that coincides with a center  97  of journal  96  is shown. Journal  96  is coupled to two connecting rod portions  100   a  and  100   b  via respective bearing caps  102   a  and  102   b . Two bearing shell portions  98   a ,  98   b  are included between bearing caps  102   a ,  102   b  and journal  96 . Each of bearing caps  102   a  and  102   b  has a first finger  104   a  ( 104   a  not visible in  FIG. 2) and 104   b , a second finger  106   a  and  106   b , and a third finger  108   a ), and  108   b . First finger  104   a  and second finger  106   a  of bearing cap  102   a  mesh with third finger  108   b  of bearing cap  102   b . A gap between first finger  104   a  and second finger  106   a  is substantially equal to the width of third finger  108   b . Furthermore, the width of first finger  104   a  is approximately equal to the width of second finger  106   a . Connecting rod  100   a  has a first flange  110   a  and a second flange  112   a ; connecting rod  100   b  has first and second flanges  110   b ,  112   b . Through holes  116   b  and  118   b  are provided in flange  112   b ; through hole  122   b  is provided in flange  110   b . Bolts  124   b ,  126   b  are slid into through holes  116   b  and  118   b , respectively, and engaged with threaded holes  128   b ,  130   b  in fingers  104   b  and  106   b , respectively. A bolt  132   b  is slid into through hole  122   b  and engaged with a threaded hole  134   b.    
         [0049]    In  FIG. 4 , a single pullrod  100  is shown having a first flange  110  with a hole  122  and a second flange  112  with two orifices  116  and  118  (as the two orifices are in line, only one is shown in phantom). A concave surface  136  forms a portion of a cylinder. Pullrod  100  also has a rod portion with a small end portion  142  at one end. Pullrod  100  also has bearing surfaces  144 . Bearing surfaces  144  lie in planes parallel to each other and are located at ends of concave surface  136 . Bearing surfaces  144  face outwardly. Pullrod  100  can be described as having a piston connection portion (alternatively referred to as small end portion  142 ), journal connection portion  143 , and rod portion  145  between the two connection portions.  FIG. 4  illustrates a bearing cap  102  that can be coupled to pullrod  100 . Of first and second fingers  104  and  106 , only one is visible in this view. On the other end of bearing cap  102  is third finger  108 . Threaded hole  134  aligns with through hole  110  of pullrod  100 . Threaded holes  128  and  130  align with through holes  116  and  118  of pullrod  100 . Bearing cap  102  has a concave surface  146  that forms a portion of a cylinder. Extending from the ends of concave surface  146  are bearing surfaces  148  which are parallel and face each other. When bearing cap  102  is assembled with pullrod  100 , bearing surfaces  144  of pullrod  100  bear against bearing surfaces  148  of bearing cap  102 . Bearing surfaces  144  support bearing cap  102  from crushing as it is pulled at fingers  104 ,  106 , and  108 . If bearing cap  102  is even slightly deformed, it becomes out of round and increases friction in the journal. 
         [0050]    An alternative embodiment of a pullrod/bearing cap system  158  is shown in  FIG. 5  in an isometric, exploded view. Pullrods  160   a  and  160   b  have small ends  162   a  and  162   b  adapted to couple with reciprocating elements, such as pistons. Pullrod  160   a  has a first tab  164   a  and a second tab  166   a  separated by a gap  168   a  of a predetermined width. Pullrod  160   a  has a third tab  170   a . Each of first, second, and third tabs  164   a ,  166   a , and  170   a  has orifices:  174   a ,  176   a , and  180   a , respectively, each of a predetermined diameter. Pullrods  160   a  and  160   b  have concave surfaces  172   a  and  172   b  that form a portion of a cylinder. Pullrod  160   a  and  160   b  have bearing surfaces that are in contact with bearing surfaces of the bearing caps. Most of these bearing surfaces are not visible in  FIG. 5 , except for bearing surface  182   b  of pullrod  160   b . A corner of bearing surface  180   b  is visible on the far side of third tab  170   b ; another bearing surface (not visible) is provided between first and second tabs  164   b  and  166   b . Pullrod  160   a  has similar bearing surfaces as pullrod  160   b , but none of such bearing surfaces on pullrod  160   a  are visible in this view. These bearing surfaces are provided to prevent crushing of the bearing cap, as will be described in more detail below. 
         [0051]    Also shown in  FIG. 5  is a bearing cap  184   a  that has first and second fingers  186   a  and  188   a  separated by a gap of the predetermined width (substantially the same width as the gap between the first and second tabs, i.e., gap between  164   a  and  166   a ; and gap between  164   b  and  166   b ). Bearing cap  184   a  also has a third finger  190   a  having a width of the predetermined width. Fingers  186   a ,  188   a ,  190   a ,  186   a ,  188   a , and  190   a  each have an orifice,  192   a ,  194   a ,  196   a ,  192   a ,  194   a , and  196   a , respectively located substantially parallel to a central axis of the journal (not shown in  FIG. 5 ). First and second fingers  186   a  and  188   a  are substantially the same width; third finger  190   a  is approximately twice the width of first finger  186   a . The gap between first and second fingers  186   a  and  188   a  is substantially the same as the width of third finger  190   a . Bearing cap  184   a  has three bearing surfaces: two bearing surfaces  198   a  on first and second fingers  186   a  and  188   a  and one bearing surface (not visible) on third finger  190   a . The bearing surface on third finger  190   a  is substantially parallel with and faces toward bearing surfaces  198   a  on first and second fingers  186   a  and  188   a . Bearing cap  184   b  is identical to bearing cap  184 ; however, as oriented in  FIG. 5 , only one of three bearing surfaces  198   b  is visible, i.e., bearing surface  198   b  associated with third finger  190   b.    
         [0052]    Bearing surfaces  198   a  and  198   b  of bearing caps  184   a  and  184   b  bear against bearing surfaces  182   a  and  182   b  of pullrods  160   a  and  160   b , respectively. Bearing caps  184   a  and  184   b  have concave surfaces  199   a  and  199   b  that are portions of a cylinder. Also shown in  FIG. 5  are bearing shell portions  200   a  and  200   b . Concave surfaces  172   a  and  172   b  of pullrods  160   a  and  160   b  mate with convex surfaces  197   a  ( 197   a  not visible in  FIG. 5) and 197   b  of bearing caps  184   a  and  184   b , respectively. Concave surfaces  199   a  and  199   b  of and bearing caps  184   a  and  184   b  mate upon convex surfaces  201   a  and  201   b  of bearing shell portions  200   a  and  200   b , respectively. 
         [0053]    To assemble the connecting rod assembly, bearing shell portions  200   a  and  200   b  are placed over a cylindrical journal (not shown in  FIG. 5 ). Bearing shell portions  200   a  and  200   b  are coupled via four screws  202 , shown in  FIG. 5 . Bearing caps  184   a  and  184   b  are placed over bearing shell portions  200   a  and  200   b  with fingers of the bearing caps meshing: first and second fingers of one bearing cap meshing with the third finger of the other bearing cap and vice versa. One of the pullrods is placed over one of the bearing caps such that orifices in the tips of the pullrods align with orifices in fingers of the bearing cap. A pin  204  is placed through the aligned orifices, one at the top and one at the bottom, and secured with snap rings  206 , one at each end of pins  204 , as per the embodiment in  FIG. 5 . The other pullrod is similarly secured to the other bearing cap. 
         [0054]    One advantage of embodiments of the present disclosure is that pullrod  160   a  is identical to pullrod  160   b  just as bearing cap  184   a  is identical with bearing cap  184   b . In  FIG. 5 , pullrod  160   a  is “upside down” with respect to pullrod  160   b  such that the corner of pullrod  160   b  has the corner with single tab  170   b  pointing upwardly and pullrod  160   a  has the corner with single tab  170   a  pointing downwardly in  FIG. 5 . In the embodiment in  FIG. 3 , pullrods  100   a  and  100   b  are identical; and bearing caps  102   a  and  102   b  are identical. By having identical parts, the number of unique parts to assemble an engine is reduced thereby reducing cost of the product. 
         [0055]    Another advantage of the assembly shown in  FIG. 5  is that pins  204  are in shear. These can be made rather smaller in diameter than other connection schemes. Smaller pins facilitate smaller orifices in the pullrod and the bearing cap thereby allowing smaller tabs and smaller fingers, respectively. The mass of the parts can be reduced and the assembly is more compact. Reducing mass of the rotating components present many advantages: less unbalanced force, reduced cost due to reduced material, reduced size of related parts, e.g., mounts, bearings. Yet a further advantage is reduced machining and assembly steps, thereby further reducing cost of manufacture. 
         [0056]    In  FIG. 6 , it can be seen that pullrod  160  is shaped roughly in the shape of an isosceles triangle  210  with small end portion  162  at one corner of the triangle. Other edges  212  on the long sides of the roughly triangular shape are thicker than the center portion of pullrod  160 . Pullrod  160  can be considered to include a piston connection portion (which is alternatively the small end portion  162 ), a journal connection portion  213 , and a rod portion  214  between the two connection portions. In another embodiment shown in  FIG. 7 , pullrod  220  forms a lattice in the central region. 
         [0057]    An isometric drawing of the bearing shell portions in an exploded view is shown in  FIG. 8A . Bearing shell portions  200   a  and  200   b  are fastened by screws  202  that pass into through holes  222   a  which are large enough to accommodate the head of screws  202  and into through holes  223   a  and then into threaded holes (not visible in this view) associated with bearing shell portion  200   b , similar to threaded holes  224   a . Lubrication grooves  225  are provided in the concave surfaces  211   a  and  221   b  in the bearing shell caps  200   a  and  200   b . Oil supply to lubrication grooves  225  is shown in more detail in  FIGS. 13 ,  15 ,  16 , and  18 . Oil supplied to oil grooves  225  passes through oil holes  227  to oil grooves  226  formed in the convex surfaces  201   a  and  201   b  (oil groove  226  in bearing cap  200   a  is not visible in  FIG. 8A ). 
         [0058]    In an alternative embodiment illustrated in  FIG. 8B , bearing shell portions  230  and  232  have interlocking fingers at one end with holes through the fingers so that a pin  234  may be inserted through the holes. In one embodiment, shell bearing portions  230  and  232  are installed on a journal of a crankshaft with the crankshaft having weights on either side of the journal so that pin  234  cannot fall out. In other embodiments without features holding the pin in place, the pin has a head on one end and a snap ring on the other end. Alternatively, the pin is secured by snap rings in an internal fashion. Any suitable way of securing the pin can be used. 
         [0059]    In yet another embodiment, the shell bearing portions are eliminated altogether. In some alternatives, either the journal or the bearing cap inner cylindrical surface is provided with a surface coating that is suitable to serve as a bearing material. Optionally, oil grooves are included to allow passage of the oil to bearing surfaces. 
         [0060]      FIGS. 8A and 8B  illustrate bearing shell portions that are fixed together. This ensures that the lubrication passes through the lubrication grooves, as described below. If the pullrod is always under tension, then there is no need to secure the bearing shell portions to each other as the forces in the system cause the bearing shell portions to remain pressed against the journal. Thus, in one embodiment, there are no screws or pins holding the two together. In assembly, the bearing shell portions can be held onto the journal by a thicker oil or grease until secured in place when the bearing caps and connecting rods are installed. Even in a system with momentary instances of a loss of the pressure, it may be possible to withstand such short durations with a momentary loss of oil flow thereby also allowing the bearing shell portions to be installed without screws or pins. 
         [0061]    In an alternative embodiment roller bearing portions  280  are used instead of bearing shell portions. Roller bearing portions  280  include a cage  284  into which needle bearings  282  are retained. 
         [0062]    In  FIG. 10 , a cross section of one of the pinned joints between connecting rod  160   a  and bearing cap  184   a  is shown. Pin  204  is inserted through aligned orifices in finger  196   a , and tabs  164   a  and  166   a . One of snap rings  206  can be installed before or after insertion of pin  204 . At least one of snap rings  206  is installed in one of the annular grooves formed the orifices in one of tabs  164   a  and  166   a . A similar configuration may be used to couple the connecting rod  160   a  and bearing cap  184   a  involving fingers  186   a  and  188   a  with tab  180   a.    
         [0063]      FIG. 11  illustrates a couple of alternative embodiments. At the bottom of the joint as shown in  FIG. 11 , a pin  238  sits proud of the aligned orifices in bearing cap  184   a  and connecting rod  244 . A snap ring  237  engages with a groove on pin  238 . In configurations with sufficient space, such a configuration may be desirable to avoid providing a groove within the orifice through which the pin sits, such as is shown in  FIG. 10  to accommodate the snap rings within the orifice. In  FIG. 11 , a counter bore  242  and a groove  240  are shown, but not needed for the pin  238  to snap ring  237  connection as shown. Such counter bore  242  and groove  240  are shown to illustrate the modifications to the orifice that accommodate the upper connection scheme. In the upper example, pin  238  has a head  239  with a larger diameter than the pin body and sits on the shoulder formed by the counter bore  242 . A snap ring  245  is inserted proximate head  239  of pin  238  into the groove (not seen individually in  FIG. 11 , but is the same as groove  240  shown in the bottom joint.) The upper joint is sufficient to secure pin  238  as head  239  prevents the pin from moving downward and snap ring  245  prevents the pin from moving upward. The lower joint is shown simply for illustration convenience, i.e., to allow discussion of two embodiments relative to one figure. 
         [0064]    A number of pin embodiments are contemplated with a number of tradeoffs. It is desirable have an orifice as small as possible so that the size of the fingers of bearing cap  184   a  and the tabs on connecting rod  244  can be smaller. The pin connection at the bottom of  FIG. 11  allows this, but at a cost of additional length with the pin extending outwardly from the joint. Another desirable feature is for the parts to be symmetrical with the same machining operation on both ends to avoid potential assembly issues due to orientation. 
         [0065]    A portion of the engine is shown in  FIG. 12  at a condition where pistons  12  and  14  in the left hand cylinder (cylinder not shown) are at their position of closest approach and pistons  12  and  14  in the right hand cylinder (cylinder not shown) are their farthest position. A detail of this position is shown in  FIG. 13 . At the center is a cross section of a journal  250  that is part of a crankshaft is shown. Oil is provided along the crankshaft through a channel  252 , which is shown in cross section. An oil passage  254  fluidly couples channel  252  through the crankshaft with an outer surface of journal  250  with an opening  255 . As journal  250  rotates, opening  255  provides oil to the inside surfaces of shell bearing portions  200   a  and  200   b . Oil passes out through oil holes  227  along grooves  226  through oil holes  260  in bearing caps  184   a  and  184   b  to provide lubricating between bearing cap  184   a  and pullrod  160   b  and between bearing cap  184   b  and pullrod  160   a  which rotate relative to each other a modest amount during the revolution of the crankshaft. It is desirable to maintain oil holes  227  about 30 degrees displaced (one 30 degrees upward and one 30 degrees downward) from a point of maximum force on the bearing cap. To facilitate that and to maintain the oil passages in desirable locations, it is desirable to restrict the motion of the shell bearing portions  200   a  and  200   b  with their respective bearing caps  184   a  and  184   b . In the embodiment shown in  FIG. 13 , a pilot hole  256  is provided in the back of shell bearing portions  200   a  and  200   b . A hollow pin  258  is inserted through oil passage  260  to index with pilot hole  256 . Pilot hole  256  in bearing cap  184   b  is not used. However, for the purpose of keeping bearing shells  200   a  and  200   b  identical to reduce the number of unique parts in the engine, both bearing shells are provided with pilot holes  256 . Pin  258  is hollow to allow oil to be conducted through pin  258  and passage  260  to the interface between bearing cap  184   a  and pullrod  160   b.    
         [0066]    In  FIG. 14 , the engine is shown at a different point in the rotation with pistons  12  and  14  of the left hand cylinder at a position of about 60 degrees before top dead center (TDC) and pistons  12  and  14  of the right hand cylinder at a position of about 120 degrees after TDC. As journal  250  is at, or near, its most upward position (upward as shown in  FIG. 14 ), pushrod  264  that couples crankshaft  20  to piston  14  of the left cylinder is visible. 
         [0067]    In the detail of the crank connection shown in  FIG. 15 , oil passage  254  is displaced and opening  255  is providing oil to a different location on shell bearing portion  200   a  than that shown in  FIG. 13 . In  FIG. 14 , shell bearing portion  200   a  is displaced counterclockwise, slightly, compared to the position shown in  FIG. 13 . As explained above, shell bearing portion  200   a  is pinned to bearing cap  184   a . The slight counterclockwise rotation of bearing cap  184   a  and shell bearing portion  200   a  is due to pullrod  160   a  being cocked upward at the end associated with journal  250  due to journal  250  being at its most upward position, as can be seen in  FIG. 14 . As shell bearing portion  200   a  is pinned to bearing cap  184   a  via pin  258 , they rotate together. Shell bearing portion  200   b , on the other hand, is free floating as can be seen with oil passage  260  rotated clockwise with respect to pilot hole  256  in shell bearing portion  200   b . The range of motion of shell bearing portion  200   b  is limited, however, by shell bearing portion  200   a . In fact, shell bearing portion  200   a  moves shell bearing portion  200   b.    
         [0068]    An alternative arrangement to restrict the movement of the shell bearing portions is illustrated in  FIGS. 16-18 . In  FIG. 16 , a detail of the crank connection is shown. The position of the pistons that relates to the position shown in  FIG. 16  is identical to that shown in  FIG. 12 , i.e., pistons in the left cylinder are at, or near, TDC; and pistons in the right cylinder are at, or near, BDC. Shell bearing portions  200   a  and  200   b  each have a slot  270  defined in the outside convex surface. Hollow pins  258  are inserted in oil passages  260  and extend inwardly toward shell bearing portions  200   a  and  200   b  so that they engage with slots  270 . The angle of the circumference of shell bearing portions  200   a  and  200   b  over which slots  270  extend is related to the relative movement of pullrods  160   a  and  160   b  as they rotate. (Axes of pullrods  160   a  and  160   b  are roughly collinear in  FIG. 12 ; the axes of pullrods  160   a  and  160   b  have a relative angle of about 170 degrees in  FIG. 14 .) In  FIG. 16 , shell bearing portions  200   a  and  200   b  are displaced counterclockwise compared to their position as shown in  FIG. 13 . Their position, in  FIG. 16 , is displaced toward one end of travel with respect to slots  270 . The pulling force acting through one of the pullrods  160   a  or  160   b  is greater than the force on the other pullrod thereby clamping the associated bearing cap against the associated shell bearing portion. The other shell bearing portion without so much clamping force rotates. Of course, movement of the clamped shell bearing portion is restricted by slot  270 . Nevertheless, it is the uneven forces on the shell bearing portions that causes them to end up in a displaced position as in  FIG. 15  rather than a neutral position with the interfaces between the shell bearing portions being vertical as shown in  FIG. 13 . 
         [0069]    In  FIG. 17 , the engine is shown at a position in which the pistons in the left cylinder are at 90 degrees after TDC and the pistons in the right cylinder are at 90 degrees before TDC. A small portion of each of the pushrods  264  is visible in this position. 
         [0070]    In  FIG. 18 , a detail of the crank connection related to  FIG. 17  is shown. Pin  258  that engages with shell bearing portion  200   a  is at one end of slot  270 . However, pin  258  that engages with shell bearing portion  200   b  is at an intermediate position between the ends of slot  270 . Shell bearing portions  200   a  and  200   b  shuttle back and forth, although rotating in concert, depending on the positions of pullrods  160   a  and  160   b  and the forces acting between shell bearing portions and their associated bearing cap. 
         [0071]    A flowchart indicating a method to assemble the configuration of  FIG. 2  is shown in  FIG. 19 . In block  400 , bearing shell portions are placed over the crankshaft journal and fastened together. In other embodiments not requiring it, the bearing shell portions are not fastened together, i.e., simply placed over the journal. In block  402 , the bearing shell portions are placed over the bearing caps with the fingers of the bearing caps meshing. In block  404 , flanges of one of the pullrods are aligned with one of the bearing caps with the through holes aligning with the bolt holes. In block  406 , three bolts are inserted through the three through holes and then engaged with the three threaded holes. In block  408 , the other pullrod is aligned with the other bearing cap. In block  410 , the pullrod is bolted to the bearing cap with bolts inserted through the through holes and engaged with the threads in the threaded holes. 
         [0072]    A flowchart indicating a method to assemble the configuration of  FIG. 5  is shown in  FIG. 20 . In block  420 , bearing shell portions are placed over the crankshaft journal and fastened together. In block  422 , bearing caps are placed over the bearing shell portions with the fingers of the bearing caps meshing. The pin, or pins, of the bearing caps are engaged with the pilot hole or grooves in the bearing shell portions, as appropriate. The orifices of one of the pullrods are aligned with the orifices of one of the bearing caps in block  424 . In block  426 , pins are installed through the aligned orifices. The pins are secured in the aligned orifices. In block  428 , the orifices of the other pullrods are aligned with the orifices of the other bearing caps. In block  430 , pins are installed through the aligned orifices and secured. 
         [0073]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.