Patent Publication Number: US-2011048367-A1

Title: Crankcase and main bearing cap construction

Description:
FIELD OF THE INVENTION 
     This invention relates to internal combustion engines, including but not limited to crankcase and main bearing cap construction for an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     A typical internal combustion engine includes a crankcase having a plurality of cylinders. The cylinders contain pistons whose reciprocating motion due to combustion events that occur in a variable volume within a plurality of cylinders in the crankcase is transferred through a crankshaft to yield a torque output of the engine. Often, engine crankcases are made of cast metal, and include passages integrally formed therein for the transfer of various fluids from one location of the engine to another. 
     An engine crankcase has to have high strength and stiffness to handle the cylinder loads and to adequately journal the crankshaft for rotation. 
     To provide this stiffness it is known to provide a separately cast and machined bedplate that is assembled to the crankcase below the main bearing caps and finish machined. 
     Alternately, a deep skirt incorporating cross bolted main bearing caps, the main bearing caps being transversely bolted to the skirt, provides crankcase rigidity. The bearing caps for a traditional deep skirt design are manufactured separately and then assembled to the crankcase and finish machined. 
     U.S. Pat. Nos. 6,145,574; 5,911,349 and 5,716,145 disclose methods of manufacturing bearing caps wherein the bearing caps are cast with the crankcase and after machining of the journal-bearing opening for the crankshaft main bearings, are cracked or separated from the crankcase. 
     The present inventors have recognized that a need exists for a rigid crankcase design that also utilizes a cast-in-place and cracked-off bearing cap design. 
     SUMMARY OF THE INVENTION 
     The exemplary method of the present invention produces cast and cracked main bearing caps in a rigid crankcase structure utilizing a deep skirt design with cross bolted main bearing caps. The method eliminates the need for separately cast caps or bedplates for a rigid crankcase design. Cast windows between a crankcase skirt and the cap and a saw-cut or drill separation break the connection between the skirt and the cap to allow the caps to be cracked off. 
     An exemplary method is provided for manufacturing an engine that includes the steps of: 
     casting a side skirt having first and second opposing sidewalls of cast material; 
     casting a transverse wall of the cast material connecting the sidewalls and having an edge; 
     predetermining a main bearing journal location in the transverse wall; 
     casting a first void and a second void into the transverse wall on opposite lateral sides of the main bearing journal location, each void adjacent to one of the sidewalls; 
     predetermining a first fracture plane from the main bearing journal location to the first void and a second fracture plane from the main bearing journal location to the second void; 
     machining a circular bore though the transverse wall at the main bearing journal location and intersecting the first and second fracture planes, the circular bore being sized to be a main bearing journal; 
     removing cast material along a first removal path from the edge of the transverse wall and ending into the first void; 
     removing cast material along a second removal path from the edge of the transverse wall and ending into the second void; and 
     exerting an opening force within the circular bore to fracture the cast material along the first and second fracture planes; and 
     separating a main bearing cap from remaining portions of the transverse wall, the main bearing cap being defined between the circular bore, the first and second fracture planes, the first and second removal paths, the edge, and the first and second voids. 
     Before fracturing the cast material along the first and second fracture planes, first and second threaded cross bolt holes can be machined into the main bearing cap for receiving a threaded fasteners from the first and second sidewalls. At least one main bearing threaded bolt hole can be machined in the transverse wall on each lateral side of the bore, each main bearing threaded bolt hole extending from one of the first and second fracture planes in a direction away from the main bearing cap. 
     The cast material along both the first and second removal paths can be removed by drilling into the transverse wall along the first and second removal paths with a drill bit having a diameter at least as wide as a wall thickness of the transverse wall along each respective first and second removal paths. The transverse wall can have a reduced thickness along the first and second removal paths. Particularly, the thickness can be reduced by opposing grooves that are on opposite faces of the transverse wall and which follow the respective removal path. 
     Alternately, the cast material along the first and second removal paths can be removed by saw cutting. 
     When the engine is assembled after the main bearing caps are separated, filler or shim pieces can be installed into the removal paths to ensure that a solid material bridge is provided between the bearing caps and the sidewalls, to prevent any distortion, over stress or deflection when the cross bolts are tightened. 
     An exemplary engine block is provided that includes: 
     a cylinder block having a plurality of cylinders; 
     a skirt having first and second opposing sidewalls cast with the cylinder block; 
     a plurality of spaced apart transverse wall portions or bulkheads, each wall portion connected to both of the first and second sidewalls; 
     each the transverse wall portion having a semi-circular upper main bearing saddle and a main bearing threaded bolt hole on each side of the upper main bearing saddle; 
     a main bearing cap being fastened beneath the transverse wall portion and having a semi-circular lower main bearing saddle arranged underlying the upper main bearing saddle the main bearing cap having a first side edge spaced from the first sidewall and a second side edge spaced from the second sidewall; 
     a first filler piece arranged tightly between the first edge and the first sidewall and a second filler piece arranged tightly between the second edge and the second sidewall; 
     a first cross bolt penetrating the first sidewall and threaded into a first threaded hole in the main bearing cap and a second cross bolt penetrating the second sidewall and threaded into a second threaded hole in the main bearing cap; and 
     a fastener arranged on each side of the lower main bearing saddle penetrating the main bearing cap and threaded into a respective main bearing threaded bolt hole. 
     The first and second filler or shim pieces can include first and second transverse holes and the first and second cross bolts pass through the first and second transverse holes. 
     The first edge of the main bearing cap can be spaced from the first sidewall by a first gap that is partially cylindrical and the first filler piece has a corresponding cylindrical shape. The second edge of the main bearing cap can be spaced from the second sidewall by a second gap that is partially cylindrical and the second filler piece has a corresponding cylindrical shape. 
     In addition to the rigid design of the crankcase, the stresses in the bulkhead associated with the assembly of the traditional deep skirt cross bolted designs are reduced due to the shaping of the cored window. 
     A cost effective manufacturing method is provided for a cross bolted main bearing cap design. By integrating main bearing caps with the main crankcase casting and machining them together with the rest of the crankcase, casting and machining separate parts and then bringing them together for final machining is avoided. 
     Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a diesel engine incorporating the structure of the present invention; 
         FIG. 2  is a schematical side view of a portion of the engine shown in  FIG. 1 ; 
         FIG. 3  is an enlarged, fragmentary sectional view taken generally along line  3 - 3  from  FIG. 2 ; 
         FIG. 4  is a view similar to  FIG. 3  but at an earlier stage of manufacture after casting and before machining; 
         FIG. 5  is a bottom view of the engine shown in  FIG. 3  but with some parts removed for clarity; and 
         FIG. 6  is an enlarged portion taken from  FIG. 5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
       FIG. 1  illustrates an engine  10  that incorporates an exemplary embodiment of the present invention. The engine illustrated is a V6 diesel engine, such as a MAXXFORCE 5 diesel engine available from Navistar, Inc. of Warrenville, Ill., US. Although a V6 diesel engine is illustrated herein, the present invention is also applicable to other engine configurations such as V8 and inline cylinder engines. 
     The engine includes an intake manifold  12 , valve heads  16 ,  18 , valve covers  19 ,  20 , an engine block or crankcase  21 , and an oil pan  26 . The engine block  21  includes a cylinder block  32 , and a skirt  34  having left and right side walls  34   a ,  34   b . The front of the engine  10  is indicated by “F” and is noted by the presence of a crankshaft pulley  29 . The left side of the engine is indicated by “L” and the right side by “R.” The back side of the engine is indicated by “B.” The referenced directions are meaningful only for ease of description herein and the invention encompasses any particular orientation of the engine in a vehicle. 
       FIG. 2  illustrates the cylinder block and skirt separated from the oil pan and remaining components of the engine of  FIG. 1 . The cylinder block and the skirt are shown with crankshaft, rods, heads and other engine components removed. Transverse walls  33   a ,  33   b ,  33   c ,  33   d  are cast with the sidewalls  34   a ,  34   b . As described below, the transverse walls are machined to form main bearing bulkheads  36   a ,  36   b ,  36   c ,  36   d  and main bearing caps  39   a ,  39   b ,  39   c ,  39   d . The bulkheads  36   a ,  36   b ,  36   c ,  36   d  are enclosed by the skirt  34  and the oil pan  26 . Each bulkhead includes on its lower end an upper main bearing saddle  38   a ,  38   b ,  38   c ,  38   d.    
     A main bearing cap  39   a ,  39   b ,  39   c ,  39   d  is bolted to each of the bulkheads  36   a ,  36   b ,  36   c ,  36   d , having a lower main bearing saddle  40   a ,  40   b ,  40   c ,  40   d  underlying the upper main bearing saddles  38   a ,  38   b ,  38   c ,  38   d . A circular bearing journal  35   a ,  35   b ,  35   c ,  35   d  for a crankshaft is defined between each saddle pair  40   a , 38   a ;  40   b ,  38   b ;  40   c ,  38   c ;  40   d ,  38   d.    
       FIGS. 3 and 4  illustrate one bulkhead  36   a  and one main bearing cap  39   a  with the understanding that the remaining three bulkheads  36   b ,  36   c ,  36   d  and the remaining bearing caps  39   b ,  39   c ,  39   d  are identically configured. 
     Dowels or pins  55   a ,  55   b  are fit on opposite sides of the bearing caps into gaps located between the bearing cap and the sidewalls  34   a ,  34   b.    
     Each main bearing cap  39   a ,  39   b ,  39   c ,  39   d  is bolted to the left and right sidewalls  34   a ,  34   b  of the skirt  34  by a pair of cross bolts  56   a ,  56   b  to rigidify the engine block  21 . The cross bolts  56   a ,  56   b  are inserted though sidewall plain holes  57   a ,  57   b  in the sidewalls  34   a ,  34   b , pass though dowel plain holes  58   a ,  58   b  in the dowels  55   a ,  55   b  and are threaded into cap threaded holes  61   a ,  61   b  in the main bearing caps  39   a ,  39   b ,  39   c ,  39   d.    
     The main bearing caps  39   a ,  39   b ,  39   c ,  39   d  are bolted to the bulkheads  36   a ,  36   b ,  36   c ,  36   d  using four main bearing bolts  41   a ,  41   b ,  41   c ,  41   d  inserted though plain holes  42   a ,  42   b ,  42   c ,  42   d  and threaded into main bearing threaded holes  43   a ,  43   b ,  43   c ,  43   d  machined into the bulkheads  36   a ,  36   b ,  36   c ,  36   d.    
     During manufacture, the main bearing caps  39   a ,  39   b ,  39   c ,  39   d  are cast together in unitary fashion with the bulkheads  36   a ,  36   b ,  36   c ,  36   d  including the main bearing saddles  38   a ,  38   b ,  38   c ,  38   d , the skirt  34  and remaining portions of the engine block  21 . After the bearing journals  35   a ,  35   b ,  35   c ,  35   d , the main bearing bolt holes  42   a ,  42   b ,  42   c ,  42   d ,  43   a ,  43   b ,  43   c ,  43   d , the plain holes  57   a ,  57   b  in the sidewalls  34   a ,  34   b , and the threaded holes  61   a ,  61   b  in the main bearing caps  39   a ,  39   b ,  39   c ,  39   d  are machined, steps are taken to crack the main bearing caps from the saddles along one or more fracture split planes  72   a ,  72   b . Although the planes  72   a ,  72   b  illustrated are coplanar, the invention also encompasses planes  72   a ,  72   b  that are at an angle. 
     To accomplish the separation along the fracture split planes  72   a ,  72   b , the casting includes left and right cored windows or voids  74   a ,  74   b  that intersect the respective fracture split plane and extend through each transverse wall in a longitudinal direction (front to back). The bearing caps  39   a ,  39   b ,  39   c ,  39   d  are cast with the adjacent side skirt sidewalls  34   a ,  34   b  via respective left and right bridge pieces  76   a ,  76   b  that can be separated from the adjacent skirt sidewall  34   a ,  34   b  by being saw cut, or can have opposing vertical slots or grooves  78   a ,  78   b  partially penetrating the bridge piece  76   a ,  76   b , along a cast material removal path ( FIGS. 4 and 6 ) that extends from an edge  33   e  of the transverse wall vertically to the respective void  74   a ,  74   b . A remaining web  80  of cast material between the grooves  78   a ,  78   b  can be removed by a drilling process. A drill bit having diameter “D” that is at least as as wide as the web  80  creates a drill bore  84  (shown hatched in  FIG. 6 ) and removes the web  80  in a vertical direction from a bottom of the web to the voids  74   a ,  74   b , the bore being open into the voids  74   a ,  74   b.    
     Once this web is removed, the bearing caps can be cracked and separated from the bulkheads, with each bearing cap necessarily re-matched to its respective bulkhead for re-assembly. Detailed descriptions of methods of cracking bearing caps from bearing saddles along a fracture split plane is described for example in U.S. Pat. Nos. 6,145,574; 5,911,349 and 5,716,145, herein incorporated by reference. 
     For reassembly, bearing shells are installed within the saddles of the bearing caps and the bulkheads, the crankshaft is installed within the journals  35   a ,  35   b ,  35   c ,  35   d  and the bearing caps are bolted to the correct bulkheads using the bolts  41   a ,  41   b ,  41   c ,  41   d . The dowels  55   a ,  55   b  are tightly fit into the bores  84  on each side of each bearing cap  39   a ,  39   b ,  39   c ,  39   d  and the cross bolts are inserted through the plain holes  57   a ,  57   b  in the sidewalls  34   a ,  34   b , through the holes  58   a ,  58   b  in the dowels and threaded tightly into the threaded holes  61   a ,  61   b  in the bearing caps. The dowels  55   a ,  55   b  act as filler or spacer or shim pieces that refill the gap left by the removed cast material removed along the removal paths and provide a solid material bridge between the bearing cap and the sidewalls  34   a ,  34   b , such that tightening the bolts  56   a ,  56   b  does not introduce a lateral distortion or excessive stress on the sidewall-to-bearing cap connection. Furthermore, the shaping and presence of the voids  74   a ,  74   b  reduces stress on the sidewalls and bulkheads during cross bolting. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.