Abstract:
A connecting rod is cracked by mounting it on a fixture having a split mandrel and driving a pair of opposed wedges between the mandrel halves. The fixture is mounted on a support and is transported by a conveyor through a series of stations where the rod is split, separated into two pieces, the crack zone is cleaned, and the pieces are reunited along the crack lines. The use of two opposed wedges cancels out the horizontal forces of the wedges and results in a vertical force that cracks the rod. The fixture floats relative to the support allowing the connecting rod to be centered relative to the wedges. A break limiter limits the displacement of the first side of the rod to crack to prevent distortion of the second side before it cracks. In the event the fixture malfunctions, the entire fixture is removed from the conveyor and replaced by another fixture, thus reducing downtime.

Description:
FIELD OF THE INVENTION 
     The invention relates to an apparatus and method of cracking connecting rods used in internal combustion engines in which the rods are supported on a fixture mounted on a conveyor that transports the rods through a plurality of stations where each rod is split into a body and cap, the crack zone is cleaned, and the body and cap are reunited and bolted together before being removed from the fixture. 
     BACKGROUND OF THE INVENTION 
     The connecting rod in an internal combustion engine couples the crankshaft to a piston. The small end of the connecting rod has a small bore that is coupled to the wrist pin on a piston and big end of the connecting rod has a big bore that is coupled to the eccentric pin on a crankshaft. Because of the physical construction of the crankshaft, the big end of the connecting rod has to be separated into two pieces in order to be mounted on the pin. In the past, the normal practice was to initially mold and machine the connecting rod in two pieces that would then bolted together on the crankshaft pin. 
     As engine manufacturers required greater precision, it was found that molding and machining the connecting rod in two pieces and then assembling the pieces together would not give as perfect a fit on the crankpin as could be achieved if the rod was initially cast in one piece and then split or cracked at the centerline of the big bore. The two pieces will fit perfectly together because the irregularities of the split match up to one another when the two pieces are reassembled. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     According to the invention, the big end of a connecting rod is mounted on a split mandrel that is carried by a fixture. The fixture is transported through several operations by means of a conveyance system, and the conveyance system transports a plurality of similarly equipped fixtures. The big end of the connecting rod is split or cracked using two opposing wedges that are driven into a passageway formed between the mandrel halves. The two opposing wedges create equal and opposite horizontal forces and accumulative vertical forces. The horizontal forces cancel each other out, and the vertical forces separate the split mandrel along a line that is parallel to the plane of the connecting rod and perpendicular to the axis of the bore in the big end. A low pressure is first used to push the two wedges toward each other to take out any clearance between the components. A high pressure is then applied to the wedges to rapidly separate the connecting rod cap from the connecting rod body. Means are provided to limit the separation between the connecting rod cap and body after one side of the rod has cracked in order to limit the distortion of the uncracked side before it also cracks. Once both sides of the rod have cracked and the connecting rod cap is separated from the body, the gap between the cap and the body is increased and held open until the crack zone can be cleaned. After cleaning, the connecting rod cap and body are bolted together and are then removed from the fixture. 
     It is accordingly an object of the invention to provide a connecting rod cracking apparatus in which the connecting rod is mounted on a fixture that circulates through several operations by means of a conveyance system. 
     It is another object of the invention to provide a connecting rod cracking apparatus in which the connecting rod is cracked by a single force acting in a single direction by using two opposing wedges that are driven into a passageway formed between the halves of a split mandrel. 
     It is another object of the invention to provide a connecting rod cracking apparatus in which means are provided to limit the separation between the connecting rod cap and body after one side of the rod has cracked in order to limit bending distortion of the uncracked side. 
     It is another object of the invention to provide a connecting rod cracking apparatus in which means are provided to separate the cap from the body after the cracking has occurred so that crack debris can be removed from the crack zone before the cap and the body are reunited. 
     It is another object of the invention to provide a connecting rod cracking apparatus in which the means to crack the cap from the body travels with the fixture so that only external forces are needed at the cracking station to cause the rod to crack. 
     These and other objects of the invention will become apparent from the following detailed description in which reference numerals used throughout the description correspond to numerals found on the drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a connecting rod cracking apparatus with a conveyance mechanism according to the invention. 
     FIG. 2 is a front view of a fixture with a connecting rod mounted thereon and a break limiter in the raised position. 
     FIG. 2A is a front view of a fixture with a connecting rod mounted thereon and a break limiter in the lowered position. 
     FIG. 3 is a top view of the fixture and connecting rod of FIG.  2 . 
     FIG. 4 is a side sectional view of the fixture and connecting rod taken along line  4 — 4  of FIG.  2 . 
     FIG. 4A is a view similar to FIG. 4 but showing the upper mandrel portion and the connecting rod cap in the raised position at the Cleaning Station. 
     FIG. 5 is a detail view of the wedges that are mounted in the mandrels and are used to crack the big end of the connecting rod. 
     FIG. 6 is a side view of the Cracking Station showing the press ram apparatus used to crack the connecting rod. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a plan view of a connecting rod cracking and assembly installation  10  according to the invention. A precision link transfer conveyor  12  or other suitable means of conveyance is laid out on an elongated oval path. Eight connecting rod cracking fixtures  13  are mounted at uniform intervals along the length of the conveyor  12 . The conveyor is driven so that each of the fixtures  13  stop in turn at eight stations spaced around the elongated oval path. The use of the traveling fixture  13  through the several stations eliminates handling the connecting rod during any secondary operations that may be performed, and in the event a fixture is in need of repair, the entire fixture can be removed from the conveyor  12  and another fixture mounted on the conveyor  12  in its place, thus minimizing downtime. At the Loading Station  1 , connecting rods are placed by an operator  14  over a split mandrel carried by a fixture  13 , or alternatively, automation may be provided to load connecting rods onto the fixtures. At the Cracking Station  2 , a press ram mechanism  16  is used to separate the connecting rod cap from the connecting rod body. At the Cleaning Station  3 , the connecting rod cap is lifted 1-2 inches relative to the connecting rod body, and a compressed air and vacuum source  17  is used to clean debris caused by the cracking operation in the crack zone between the body and the cap before the body and the cap are reunited. 
     At the Assembly Station  4 , a rapping force is applied to the cap to seat the cap to the connecting rod body. At the Bolt Loading Station  5 , bolts from a bolt hopper  18  are loaded into the cap and run down to loosely secure the cap to the body. At the Bolt Tightening Station  6 , the bolts are tightened to the specified torque so that the bore can be reamed to the correct size after the connecting rod is removed from the transfer conveyor  12 . 
     At the Bushing Station  7 , wrist pin bushings from a bushing hopper  19  are oriented and pressed into the lower end of the connecting rod. At the Unload Station  8  the completed connecting rod assembly is removed from the transfer conveyor and placed into a completed assembly tray  21 . The entire connecting rod cracking and assembly apparatus  10  can be surrounded by a safety enclosure  22 . An access opening  23  is provided at the Loading Station  1  to allow the operator  14  to load uncracked connecting rods onto the fixtures  13 . Access doors  24  allow personnel to enter the enclosure  22  in order to maintain and repair the apparatus. It will be understood that the operations performed at Stations  4 - 8  are secondary operations that are not essential to the invention, but are included here in order to provide a full and complete description of the environment in which the invention may be utilized. 
     FIGS. 2-4A show detail views of the fixture  13  used to transport and crack the connecting rods. Each fixture is supported on pins  28  mounted on a base plate  26  that is mounted to the conveyor  12 . The pins  28  allow the fixture to float forward and backward relative to the base plate  26  during the cracking operation as more fully described below. The fixture comprises a support plate  27  and a slide plate  29  that is mounted to the support plate  27  by a pair of side retainers  31 . The side retainers  31  allow the slide plate  29  to slide vertically relative to the support plate  27 . 
     A split mandrel  32  comprises an upper portion  33  that is rigidly attached to the slide plate  29 , and a lower portion  34  that is rigidly attached to the support plate  27 . The split mandrel  32  is dimensioned to fit within the big bore  36  of a connecting rod  35 . A flat  39  is formed on the top of the upper mandrel portion  33  and a similar flat  40  is formed on the bottom of the lower mandrel portion  34 . The flats  39  and  40  insure that each mandrel portion contacts the bore of the connecting rod at two places to distribute the cracking forces applied to the bore. This distribution of force limits distortion of the big bore  36  caused by the separating force of the split mandrel  32 . 
     A pair of spring loaded ball plungers  41  mounted on blocks  42  on the support plate  27  protrude through a cutout  43  in the slide plate  29  and bias the connecting rod body  37  against the lower mandrel  34 . A spring loaded pressure cap  95  is mounted on the end of a shoulder screw  96  that is slideably received by a pressure cap mount  97 . A spring  98  biases the pressure cap  95  against the connecting rod cap  38 . At the Loading Station  1 , the shoulder screw  96  is engaged by a lifting device (not shown) that raises the shoulder screw and the pressure cap  95  to allow a connecting rod to be loaded onto the split mandrel  32 . The lifting device used at Station  1  may be similar to the lifting device  99  used at the Cleaning Station  3  to engage the shoulder screw  96  in order to raise the upper mandrel  33  and the connecting rod cap  38  as more fully described below. 
     Two lateral motion restrictors  45  are mounted on a spacer block  46  that is attached to the support plate  27 . The lateral motion restrictors  45  engage the small end  47  of the connecting rod  35  to prevent the small end from swinging. Two springs  48  are attached to tabs  49  on the lower edge of the slide plate  29  to pull the side plate down in order to bias the pressure cap  95  against the connecting rod cap  38 . 
     The upper and lower mandrel portions  33  and  34  are each formed with a generally rectangular slot that together form a passage  55  with horizontal and vertical walls generally in the shape of a square as best shown in FIG.  2 . The top wall comprises two inclined portions  56  and  57  that are at an angle of 4 to 10 degrees to the horizontal and meet at a restriction point  58  as best shown in FIG.  4 A. The restriction point  58  is positioned so that it is vertically aligned with the central plane  50  of a connecting rod  35  that is mounted on the split mandrel  32 . 
     A pair of movable wedges  59  and  60  fit into the passage  55  through the split mandrel  32  from the front and back of the fixture  13 . The bottom and sides of each wedge are straight, but the top of each wedge  59  and  60  is formed with a taper  61  and  62 , respectively. The tapers  61  and  62  on the wedges match the inclines on the top walls  56  and  57  of the passage  55 . The wedges translate a horizontal force applied by a press ram  76 , as described more fully below, into a vertical force that separates the mandrel portions  33  and  34 . 
     The angle of the taper is dependent on the forces needed to crack the rod  35 . As the taper decreases, the vertical force that the wedges apply to the split mandrel  32  in response to a horizontal force applied to the ends  63  and  64  of the front and rear wedges  59  and  60 , respectively, increases. It has been found that a wedge angle of 7 degrees creates a vertical force on the split mandrel that is 8.2 times the horizontal force that is applied to the ends  63  and  64  of the wedges, and a wedge angle of 5 degrees creates a vertical force on the split mandrel  32  that is 11.5 times the horizontal force that is applied to the ends  63  and  64  of the wedges. The shallow angles on the top surface of each wedge  59  and  60  and on the inclined portions  56  and  57  of the passage  55  are locking angles which hold the wedges in place even after the force of the ram is removed. The locking angles prevent the rod cap  38  from closing and trapping debris against the rod body after the fixture and the cracked rod leave the Cracking Station  2 . The length of the two wedges  59  and  60  can be chosen so that their ends abut one another at the end of the cracking stroke to limit the separation gap created by the wedges between the connecting rod cap  38  and the body  37 . 
     Cross pins  65  and  66  mounted in the lower and upper mandrel portions  34  and  33  engage slots  67  and  68 , respectively, in the front and back wedges  59  and  60  to keep the wedges from falling out of the passage  55 . A knockout pin  70  is positioned in a through hole  71  in the front wedge  59  and a separating spring  72  is mounted in a pair of opposed pockets  73  and  74  formed in the front and rear wedges  59  and  60 , respectively. 
     The shoulder screw  96  that is threaded into the pressure cap  95  can be engaged by a lifting device  99  at the Cleaning Station  3  to raise the upper mandrel  33  and the connecting rod cap  38  in order to clean the crack debris from between the connecting rod cap and body as shown in FIG.  4 A. When the lifting device separates the two mandrel portions and the connecting rod cap from the connecting rod body, the separating spring  72  mounted in the opposed pockets  73  and  74  forces the two wedges  59  and  60  apart so that the connecting rod body and cap can be reunited at the Assembly Station  4 . In the event both sides of the rod do not crack at the Cracking Station, the knockout pin  70  is used to separate the wedges  59  and  60  so that the mandrel portions  33  and  34  will come back together, allowing the connecting rod body and cap to be removed from the fixture  13 . 
     FIG. 6 is a side view taken along line  6 — 6  of FIG. 1 showing the Cracking Station  2 . The press ram mechanism includes the press ram actuator  75  and a ram  76 . When the fixture  13  is in the cracking station, the ram  76  is in alignment with the front wedge  59  and a back-up anvil  77  is in alignment with the rear wedge  60 . The back-up anvil  77  is mounted on an abutment  78  which is rigidly attached to a bridge  79 . The bridge  79  extends from the rear portion  81  of the base  82  to the front portion  83  of the base on which the ram actuator  75  is mounted. When a fixture with an uncracked connecting rod is in the Cracking Station  2 , the press ram  76  is advanced until it contacts the front wedge  59 . A clearance hole  80  in the front of the press ram  76  allows the press ram to engage the end  63  of the front wedge  59  without engaging the knockout pin  70 . Further advancement of the press ram  76  causes the wedge  59  to advance into the passageway  55 , and the support plate  27  with the split mandrel  32  and the connecting rod  35  mounted thereon to slide rearwardly on the mounting pins  28  until the rear wedge  60  contacts the back-up-anvil  77 . The upper mandrel  33  then begins to separate from the lower mandrel  34  causing the connecting rod  35  to stretch and crack. The reaction force of the back-up anvil  77  on the rear wedge  60  allows the wedges  59  and  60  to apply equal and opposite forces to the upper and lower mandrel portions  33  and  34 , with the resultant force vector being aligned with the central plane  50  of the connecting rod  35  throughout the cracking process, although only the front wedge has the force of the moving ram  76  applied to it. The press ram actuator  75  is controlled by a controller  91  and operates first at a low pressure level to push the two wedges  59  and  60  toward each other to take out any clearance between the components, and then at a high pressure to force the two wedges  59  and  60  together causing the upper and lower mandrel portions  33  and  34  to separate. 
     The separating mandrel portions will cause the connecting rod body  37  and cap  38  to crack along pre-defined lines as well known in the art. The use of the two opposing wedges limits the distortion caused by rotational deflection of the connecting rod in the region of the break since bending moments normal to the plane of the connecting rod are eliminated. As the two wedges  59  and  60  approach the restriction point  58  formed in the passage  55 , the separating force exerted on the connecting rod bore  36  by the split mandrel  32  will be centered on the vertical central plane  50  of the connecting rod  35 . 
     Normally, one side of the connecting rod will crack before the other side cracks. A break limiter  84  mounted on the bridge  79  is lowered by a lowering mechanism  85  until it is in close proximity to the connecting rod cap  38 . In the lowered position, the break limiter  84  limits the vertical upward movement of the first side of the rod to crack, and prevents unwanted pivoting of the cracked side of the cap around the uncracked side of the cap. The break limiter  84  may comprise two pins  86  that are lowered by the lowering mechanism  85  to pass through the clearance holes  87  in the mount  97  for the pressure cap  95  until the ends  90  of the pins are within 0.002 inches to 0.005 inches of the rod cap  38 . 
     In normal operation, the break limiter  84  will limit upward movement of the cap to less than 0.003 inches. Since the break limiter  84  is mounted on the bridge  79  at the Cracking Station  2 , the connecting rod cap  38  and the upper mandrel  33  are free to move vertically on the slide plate  29  for downstream operations once the fixture leaves the Cracking Station  2 . 
     As described above, the bridge  59  performs three functions in the operation of the cracking mechanism. The bridge ties the front  83  of the base  82  to the rear  81  of the base to increase the stiffness of the base on which the cracking apparatus is mounted. The bridge provides a rigid support for the backup anvil  77  so that the horizontal forces generated by the ram actuator  75  can be converted by the wedges  59  and  60  into vertical forces that will separate the split mandrel  32  and crack the connecting rod  35 . The bridge  59  also provides a rigid support for the break limiter  84  to control the vertical movement of the connecting rod cap  38  after it has been cracked. 
     Sequence Of Operations 
     The invention described above is used to separate or crack a connecting rod cap and body according to the following sequence of operations: 
     1. Advance empty fixture  13  to Loading Station  1 ; 
     2. Engage and raise pressure cap  95  to allow connecting rod to be loaded onto fixture; 
     3. Release pressure cap to bias pressure cap against connecting rod cap  38 ; 
     4. Advance fixture to Cracking Station  2 ; 
     5. Lower break limiter  84  to within 0.003″ of connecting rod cap; 
     6. Advance press ram  76  at low pressure against front wedge  59  to take out any clearance in the components; the fixture  13  floats on the pins  28  to bring the rear wedge  60  into contact with the backup anvil  77  and to center the cracking force of the split mandrel along the central plane  50  of the connecting rod; 
     7. Advance press ram at high pressure against the front wedge  59  to crack one side of the connecting rod; 
     8. Break limiter limits displacement of first side of rod to crack to 0.003″; 
     9. Further advancement of press ram  76  at high pressure cracks second side of connecting rod; 
     10. Front and rear wedges  59  and  60  meet in center of split mandrel to limit further displacement of split mandrel; 
     11. Retract press ram and raise break limiter from engagement with fixture; 
     12. Advance fixture and cracked rod to Cleaning Station  3 ; 
     13. Engage and raise pressure cap  95  and upper mandrel portion  33  to create 1″-2″ space between connecting rod body and cap; separating spring  72  forces wedges apart; 
     14. Blow out and vacuum away debris from cracking operation; 
     15. Lower and release pressure cap and mandrel to bring connecting rod cap into contact with connecting rod body; 
     16. Advance fixture with cracked connecting rod to Assembly Station  4 ; 
     17. Rap on cap to reunite connecting rod cap to body; 
     18. Advance fixture with reunited cap and body to Bolt Loading Station  5 ; 
     19. Load bolts into connecting rod cap and body to loosely secure cap to body; 
     20. Advance fixture and connecting rod with loaded bolts to Bolt Tightening Station  6 ; 
     21. Tighten bolts to correct torque; 
     22. Advance fixture and connecting rod with torqued bolts to Bushing Station  7 ; 
     23. Press bushing into wrist pin hole in small end of connecting rod; 
     24. Advance fixture with completed connecting rod to Unload Station  8 ; 
     25. Remove completed connecting rod from fixture; 
     Having thus described the invention, various modifications and alterations will occur to those skilled in the art, which modifications and alterations are intended to be within the scope of the invention as defined by the appended claims.