Abstract:
A connecting rod includes an elongate rod shank with a small end at a first axial end of the rod shank and a big end at the second axial end of the rod shank. The big end includes a body part and a cap part adapted to releasably couple to the body part. When the cap part is coupled to the body part, the cap part and body part cooperate to define a crank pin receiving bore and abut at first and second spaced apart interfaces. The cap part defines an aperture proximate the first interface that is adapted to receive a threaded fastener that engages and clamps the cap part to the body part. The cap part includes a side portion that extends radially beyond a largest radius from a crank pin bore center to the first interface. The side portion is substantially radially concentrated adjacent the first interface.

Description:
TECHNICAL FIELD 
       [0001]    This description relates to internal combustion engines, and in particular connecting rods for use in connecting a piston to a crankshaft. 
       BACKGROUND 
       [0002]    Connecting rods are employed in reciprocating piston engines to connect pistons to the crankshaft. Connecting rods allow the reciprocating motion of the piston to be translated into rotational motion of the crankshaft. The connecting rod can be subjected to enormous stress from the changing forces acting on those points where the rod connects to the piston and the crankshaft. In internal combustion engines, the piston is provided within a piston cylinder, its reciprocating motion guided laterally by the cylinder wall. Portions of the connecting rod are also typically within the engine cylinder, reciprocating in conjunction with the piston within the cylinder. The forces applied to the connecting rod can potentially result in wear and damage to the connecting rod. 
       SUMMARY 
       [0003]    In one aspect, the disclosure encompasses a connecting rod that includes an elongate rod shank with a small end at a first axial end of the rod shank and a big end at the second axial end of the rod shank. The big end includes a body part and a cap part adapted to releasably couple to the body part. When the cap part is coupled to the body part, the cap part and body part cooperate to define a crank pin receiving bore and abut at first and second spaced apart interfaces. The cap part defines an aperture proximate the first interface that is adapted to receive a threaded fastener that engages and clamps the cap part to the body part. The cap part includes a side portion that extends radially beyond a largest radius from a crank pin bore center to the first interface. The side portion is substantially radially concentrated adjacent the first interface. 
         [0004]    In one aspect, the disclosure encompasses an engine with an engine block defining a piston cylinder, a crank having a crank pin and being supported to rotate in the engine block, a piston residing in the piston cylinder, and an elongate connecting rod connecting the crank to the piston. The connecting rod coupled to the crank pin at a big end of the connecting rod. The big end of the connecting rod includes a body part and a cap part releasably coupled to the body part by a plurality of threaded fasteners. The cap part abuts the body part at first and second spaced apart interfaces. The cap part, in a region adjacent the first interface, extends laterally beyond the first interface. The cap part has a lateral dimension greater than an inner diameter of the cylinder and smaller than a largest lateral dimension of the connecting rod. 
         [0005]    In one aspect, the disclosure encompasses a method of operating an engine. According to the method a piston that is reciprocating within a cylinder of the engine is connected to a crank of the engine with an elongate connecting rod. The elongate connecting rod includes a body part and a cap part releasably coupled to the body part by a plurality of threaded fasteners and abutting the body part at first and second spaced apart interfaces. Loads exerted by the crank on the connecting rod are supported with a region of the cap part adjacent the first interface that extends laterally beyond the first interface. The connecting rod in the region adjacent the first interface has a largest lateral dimension that is greater than an inner diameter of the cylinder and smaller than a largest lateral dimension of the connecting rod. 
         [0006]    The features above can include one or more or none of the following features. The cap part and the body part can include interlocking peaks and valleys at the first interface. The side portion can extend radially beyond the body part about the first interface. The side portion can extend radially beyond the first interface in an amount greater than the body part extends radially beyond the first interface. The side portion can extend radially beyond the first interface in an amount greater than the cap part extends radially beyond the second interface. A total volume of the side portion radially beyond a plane through an end of the first interface and orthogonal to the first interface has a centroid, and the centroid can reside radially within a smallest radius from the crank pin bore center to a perimeter of the cap part. The side portion can reside radially within a largest radius from the crank pin center to a perimeter of the cap part. The first and second interfaces can be non-orthogonal to the longitudinal axis of the rod shank. The first and second interfaces can be coplanar. 
         [0007]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a cross-sectional view of an engine incorporating a connecting rod constructed in accordance with the concepts described herein. 
           [0009]      FIG. 2A  is a front view of one implementation of a connecting rod depicted proportionally to scale. 
           [0010]      FIG. 2B  is a first cross-sectional view of the big end cap of  FIG. 2A  showing the location of one implementation of a sectional centroid. 
           [0011]      FIG. 2C  is a second cross-sectional view of the big end cap of  FIG. 2A  showing the location of another implementation of a sectional centroid. 
           [0012]      FIG. 3  is a cross-sectional view of the connecting rod of  FIG. 2A  superimposed on a cross-sectional view of an engine cylinder liner, both depicted proportionally to scale. 
       
    
    
       [0013]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0014]    Various implementations of a connecting rod are provided in an engine for connecting a crankshaft to a piston to translate the reciprocating motion of the piston into rotational motion at the crankshaft. One or more connecting rods may be provided within the engine, typically one per piston of the engine. The connecting rod has a small end adapted to connect to the piston, and a big end adapted to connect to the crankshaft. The big end incorporates a separable cap part adapted to allow the big end to receive a crank pin of the crankshaft. A side portion is provided on the cap part, extending radially beyond an interface between the cap part and the remainder of the big end. 
         [0015]    As shown in  FIG. 1 , in some examples, an engine  100  is provided with an engine block  102 , a piston  105  and a crankshaft  112 . A connecting rod  115  connects the piston  105  to a crankpin  110  of the crankshaft  112 . The connecting rod  115  connects to a wrist pin  107  of the piston  105  at a small end  117  of the connecting rod  115  and to the crankpin  110  at a big end  135 . The small end  117  has a bore hole  119  that closely receives the wrist pin  107  and may be sleeved or otherwise formed to define a bearing  152  (e.g., a journal type bearing or other bearing). Similarly, the big end  135  has a bore hole  145  that closely receives the crank pin  110  and may be sleeved or otherwise formed to define a bearing  150  (e.g., a journal type bearing or other bearing). The piston  105  can be provided in a cylinder  120 . A top end  125  of the cylinder  120  is typically closed off by a cylinder head  126  and the opposing end of the cylinder  120  is open. The cylinder  120  can be configured so as to constrain the lateral movement of the piston  105  as it reciprocates in the cylinder  120 . At least some portion of the connecting rod  115  is disposed within the cylinder  120 , with at least a portion disposed outside the cylinder  120 , accommodating the motion of the big end  135  of the connecting rod  115  moving in coordination with the cycling motion of the crankpin  110 . The engine  100  may have a single cylinder configuration, comprising a single cylinder  120 , piston  105 , crankpin  110 , and connecting rod  115 , or may be a multi-cylinder engine  100  comprising multiple cylinders  120 , pistons  105 , crankpins  110  and connecting rods  115 . In a multi-cylinder engine  100 , the number of pistons  105 , crankpins  110  and connecting rods  115  correspond in number with the number of cylinders  120 . Also, the engine  100  can be in different cylinder configurations, for example, a “V” configuration, straight-line configuration, or another reciprocating engine configuration. 
         [0016]    In some examples, the connecting rod  115  has a cap part  137  at the big end  135 . The cap part  137  is releasably coupled to the remainder of the connecting rod  115 , allowing for the crankpin  110  to be received into the bore  145  of the big end  135 . Once the crankpin  110  is positioned in the bore  145 , the cap part  137  can be replaced and fastened to the remainder of the connecting rod  115  so as to closely receive the crankpin  110  within the bore  145 . In some implementations, fasteners  148  received in apertures of the cap part  137  and remaining big end  135  engage the cap part  137  and remaining big end  135  and clamp the cap part  137  to the remainder of the connecting rod  115 , although other fastening mechanisms can be implemented to fasten the cap part to the connecting rod  115 . The displaceable nature of the cap part can aid, not only in connecting the connecting rod  115  to the crankpin  110 , but also in ingress of the connecting rod  115  into the cylinder  120 , positioning the bearing  150  around the crankpin  110  within the bore  145 , replacing worn bearings  150 , or providing other service. 
         [0017]    Some implementations of the engine  100  provide for service access ports  132 , allowing access to the engine&#39;s  100  internal components, including the cylinders  120 , pistons  105 , crank  112 , and connecting rod  115 . Access ports facilitate access and thus assembly and service of internal components of the engine  100 , such as the connecting rods  115  and associated bearings and fastening mechanisms. In  FIG. 1 , the access ports are provided through one or more access panels  114  on the side of the engine  100  (e.g., through the side of the engine block  102 ). 
         [0018]    To further convenience servicing of the engine  100 , the connecting rod  115  can be provided with fasteners  148  disposed so as to be accessible through an access port (e.g., access panel  114 ). For example, as illustrated in  FIG. 1 , the cap part can attach to the remainder of the connecting rod  115  at an angle a, relative the central longitudinal axis  155  of the rod. Such an orientation, in some implementations, can serve to point the heads of the fasteners  148  toward an access port (e.g., access panel  114 ), facilitating access to allow tightening/loosening fasteners  148  to displace the cap part and the crankpin  110  and surrounding bearing  150  to be serviced. Other cap  120  designs employing other fastener types can be similarly oriented to allow convenient access through an access port of the engine  100 . 
         [0019]    Some implementations of engine  100  provide for connecting rods  115  adapted to pass through the cylinder  120 , so as to permit a connecting rod  115 , pre-connected to a piston  105 , to be positioned into the cylinder  120  from the top end  125  of the cylinder  120 . Connecting rod constructions adapted to pass through the cylinder  120  can also ease servicing of the connecting rod-piston assembly by allowing the assembly to be wholly or partially removed from the cylinder  120  through the top end  125  of the cylinder  120  (with the cylinder head removed), while the connecting rod  115  is connected to the piston  105 . In that the size of the small end is already adapted to fit and move within the cylinder  120  in coordination with the piston  105 , adapting the connecting rod  115  to pass through the cylinder  120  can result in limiting the maximum lateral dimension of the big end  135  to slightly smaller than the diameter of the cylinder  120 . 
         [0020]    In some implementations of the engine  100 , limiting the dimensions of the big end  135  can lead to constraints on the amount of material used at the big end  135  for supporting the loading encountered during rotation of crankshaft  110 . Sacrificing structure on the big end  135  to allow passage of the connecting rod  115  through the cylinder  120 , while easing construction and maintenance of the connecting rod-piston assembly, can limit the supportive capabilities of the connecting rod&#39;s  115  connection to the crankshaft  110 . In some implementations of the engine  100 , the forces exerted on the big end  135 , due to the reciprocating, driving force loads of piston  105 , can cause damage to the big end bore  145  due to inadequate supportive structure at the big end  135 . For example, over time, flexure in the big end  135  can lead to ovalization of the bore  145 , fretting, and stress fractures, which can eventually lead to failure of the connecting rod  115  and catastrophic failure of the engine  100 . Providing appropriate support to the big end  135  can, among other benefits, reduce ovalization, fretting and stress fractures and help ensure uniform distribution of lubrication at the connecting rod-crankpin connection, as well as lubrication of the big end bearing  150 . 
         [0021]    As shown in  FIG. 2A , one example of a connecting rod  200  is provided with a releasably coupled cap part  205  at the big end  210 . The cap part  205  is capable of joining to a rigidly connected body part  215  of the big end  210  to form the crank pin bore  220  of radius R B  at the big end  210 . The body part  215  is connected to a rod shank  225 . The rod shank  225  is configured to accept and translate loads acting on the connecting rod  200  through the connecting rod  200  to a wrist pin of a piston at small end  230  and a crankshaft pin of a crank at big end  210 . 
         [0022]    The cap part  205  abuts the body part  215  at two interfaces  235  and  240 . Some implementations of big end  210  may provide for interfaces  235  and  240  defining a split line axis  245 , in that the split line axis  245  coincides with the interfaces  235  and  240 . While  FIG. 2A  shows interfaces  235  and  240  oriented coplanar, the interfaces might assume a non-coplanar configuration. Additionally, some implementations of the connecting rod  200  may provide for interfaces  235 ,  240  defining a split line axis  245  angled from a longitudinal axis of the rod shank  225  of the connecting rod  200  by a non-right angle β. The angular offset β of the split line axis may be a positive or negative angle relative to the longitudinal axis. 
         [0023]    Each interface  235 ,  240  is defined by abutting coupling surfaces  250 ,  255  of the rigid portion of the big end  215  and coupling surfaces  260 ,  265  of the cap part  205 . The coupling surfaces  250 ,  255 ,  260 ,  265  may be substantially flat or may be provided with interlocking peaks and valleys. The interlocking peaks and valleys of example surfaces  250 ,  255 ,  260 ,  265  are illustrated in  FIG. 2A  as substantially linear troughs and ridges oriented parallel to a central axis of the crank pin bore; however, other configurations can be used. One such example is cracked rod manufacturing, where the cap part  205  and the body part  225  can be manufactured by cracking the cap part  205  from a unitary big end  215  piece to form distinct body part  225  and cap part  205  elements. Cracking the cap part  205  from the body part  225  under force results in an irregular fissure between the pieces, also providing coupling surfaces  250 ,  255 ,  260 ,  265  with interlocking peaks and valleys. The interlocking peaks and valleys of surfaces  250 ,  255 ,  260 ,  265  can serve to provide additional engagement at the interfaces  235 ,  240 , and thus, rigidity to the connection of the cap part  205  with the body part  215 . Threaded fasteners  270 ,  275  can also be provided, such as screws, bolts, studs with nuts, or other fasteners, for affixing the cap part  205  to the body part  215 . The fasteners  270 ,  275  are received in apertures  271 ,  276  extending through the cap part  205  and body part  215  proximate (in or near) the interfaces  235 ,  240 . The fasteners  270 ,  275  engage the cap part  205  and body part  215  and clamp the cap part  205  to the body part  215 . As illustrated in the example of  FIG. 2A , orienting the coupling interfaces  235 ,  240  at an angle relative the central longitudinal axis, can serve to orient the position of the fasteners  270 ,  275 , for example, by tipping the fastener ends an angle y from the central longitudinal axis. The fasteners  270 ,  275  may be tipped or otherwise oriented so as to provide easier access for servicing, for example by tipping the fastener ends (e.g., ends having bolt heads or nuts) toward a service access of the engine. 
         [0024]    The cap part  205  is provided with a balancing protrusion  295 . The balancing protrusion  295  can be a mass of material disposed on the perimeter of the cap part  205  so as to balance the big end  210  of the connecting rod  200 . 
         [0025]    The cap part  205  is provided with a side protrusion  280  adjacent one of the interfaces  240 . The side protrusion  280  extends radially beyond the interface  240  to provide additional material to the big end  210 , thereby providing additional rigidity to the big end  210  (particularly the connection between the cap part  205  and the body part  215 ) and to the bore  220 . The geometry, size, and location of the side protrusion  280  may be optimized based on the size and geometry of the remaining connecting rod elements as well as the functional requirements of the connecting rod  200 . In certain instances, the geometry, size, and placement of the side protrusion  280  can be optimized so as to provide for maximum big end bore  220  strength. For example, although the geometry, size, and placement of the side protrusion  280  can take many forms, the most effective placement of additional material is concentrated radially adjacent the interface  240 , rather than far outboard of the interface  240 . Material placed radially beyond the smallest radius from the center of the bore  200  to the perimeter of the cap part  205  has reduced effectiveness. Further, some implementations of the cap strengthening side protrusion  280  may be limited in size and geometry to allow for clearance of the big end  210  during operation of the engine. For example, the interior geometry of the engine, as well as the geometry of the engine block-cylinder interface may only permit cap parts  205  of limited size. 
         [0026]      FIG. 2A  shows one example of the side protrusion  280 . In the illustrated example, the interface  240  extends from radius R B  (from the crank pin bore  200  center) to a radius R 2 , with its center at radius R 1 . The inner boundary  221  of the example side protrusion  280  begins at the end of interface  240  (radius R 2 ) and extends orthogonal to the interface surface  240 . In the plane of the interface  240 , the example side protrusion  280  extends to a radius R O , beyond the edge of the body portion adjacent the interface  240 . Radius R O  is smaller than a largest radius R L  of the cap part  205 , and approximately the same as (equal to, slightly larger or slightly smaller within about 10%) the smallest radius R 3  of the cap part  205  (shown slightly larger than R 3 ). The example side portion  280  extends further beyond the interface  240  than any other portion of the connecting rod  200  (e.g., the body part  215  or another portion of the cap part  205 ) adjacent an interface  235 ,  240  extends beyond the adjacent interface  235 ,  240 . The perimeter surface of the example side protrusion  280  extends from radius R O  substantially orthogonal to the plane of the interface  240  for a portion before beginning to curve inward, but could be another shape. In the illustrated example, the entire side protrusion  280  resides within radius R L . The example side protrusion  280  is longer, measured perpendicular from the plane of the interface  240 , than it is wide. The example side protrusion  280  is substantially radially concentrated adjacent the interface  240 , and in the illustrated example, a centroid of the example side protrusion  280  is radially within the smallest radius R 3  of the cap part  205 , at radius R CENT . 
         [0027]      FIGS. 2B and 2C  show examples of the location of the centroid of the big end cap  205 .  FIGS. 2B and 2C  are cross-sectional views of the big end cap  205  corresponding respectively to call-outs  2 B and  2 C shown in  FIG. 2A . The cross-section  282  illustrated in  FIG. 2B  corresponds to a section referenced by call-out  2 B near or at the cap interface  240 . As shown, in this example, a sectional centroid  283  corresponding to  2 B is located at the centroid radius R CENT1  positioned between center interface radius R 1  and the smallest outer cap part radius R 3 . In the example of  FIG. 2C , the sectional centroid  286  is shown in a cross-section  284  of big end cap  205  corresponding to call-out reference  2 C. Cross-section  284  is oriented parallel to the cross-section  282  but displaced from cross-section  282 , and cap interface  240 , by an angle A 1 . At an angle A 1 =25 degrees, the centroid radius R CENT2  of the sectional centroid of section  284  is also located between center interface radius R 1  and the smallest outer cap part radius R 3 , as shown in  FIGS. 2A and 2C . In the example of  FIG. 2C , the centroid radius R CENT2  of the centroid  286  of cross-section  284  is shorter than the centroid radius R CENT1  of the centroid  283  of cross-section  282 . At other sections between sections  282  and  284 , the centroid is located between center interface radius R 1  and the smallest outer cap part radius R 3 , for example, a section located at an angle A 1 =12.5 degrees and parallel with the cross-sections illustrated in  FIGS. 2A and 2B  (i.e.,  282  and  284 ). 
         [0028]    Returning to  FIG. 2A , it should be noted that the side protrusion  280  can assume other geometry and need not extend from the interface  240  parallel to the split line axis  245 . For example, an edge of the side protrusion  280  can be angled, relative the split line axis  245 , toward or away from the body part  215 , or curved convexly (i.e. toward the body part  215 ) or concavely (i.e., curving away from the body part  215 ). The side protrusion  280  can immediately adjoin the outside edge of coupling surface  260 , as shown in the example of  FIG. 2A , or be positioned elsewhere on the perimeter edge of the cap part  205  spaced apart from the coupling surface  260 . 
         [0029]      FIG. 3  illustrates the connecting rod  200  of  FIG. 2A , superimposed on a cross-sectional reference diagram of a piston cylinder  305 . As shown in reference  FIG. 3 , the lateral dimensions of the small end  230 , the connecting rod shank  225 , and body part  215  (i.e., measured transverse to the longitudinal axis of the rod shank) are smaller than the inner diameter of the cylinder liner walls  310 ,  315  such that the small end  230 , rod shank  225  and body part  215  can pass through the cylinder  305 . This arrangement allows for this portion of the connecting rod assembly  200  to be installed and passed through the cylinder  305  during manufacture and maintenance of the assembly  200  or the connected piston and crankshaft. In contrast, the lateral dimension of the cap part  205  is larger than connecting rod sections  215 ,  225 ,  230 , and the inner diameter of the cylinder walls  305 . Thus, the cap part  205  cannot pass through the cylinder when the cap part  205  is attached to the body part  215 . 
         [0030]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, extra supportive material may be provided on both sides of the cap part. Accordingly, other implementations are within the scope of the following claims.