Abstract:
The present invention provides a PM main bearing cap, and its precursor compact, with an undercut breathing window that is formed during a compaction process. By fabricating the undercut during the compaction process, the invention eliminates the need for a secondary machining operation to form the undercut feature in the bearing caps.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application represents the national stage application of International Application PCT/US2008/057798 filed 21 Mar. 2008, which claims the benefit of U.S. provisional application Ser. No. 60/896,551, filed on Mar. 23, 2007, which are herein incorporated by reference in their entirety for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE INVENTION 
     This invention relates to producing powder metal (PM) bearing caps with “breathing windows”, and in particular to producing breathing windows in powder metal main bearing caps for internal combustion engines. 
     BACKGROUND OF THE INVENTION 
     Crankshaft main bearing caps used in internal combustion engines can create a blockage between engine bays that results in a reduction in oil movement through the crankcase and increased localized crankcase pressures. The reduced oil movement between bays can cause excess pressure buildup below the pistons and rob the engine of horsepower. 
     A current solution is to machine an undercut breathing window in the main bearing cap blanks, whether made of powder metal or cast iron. The undercut feature or window aids in the breathing or movement of oil from one bay in the engine to the other, thereby reducing internal engine pressures and increasing horsepower. Machining in this feature however is time consuming and costly. 
     SUMMARY OF THE INVENTION 
     The present invention is to produce a PM main bearing cap, and its precursor compact, with an undercut breathing window that is formed during a compaction process. By fabricating the undercut during the compaction process, the invention eliminates the need for a secondary machining operation to form the undercut feature in the bearing caps. 
     The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a PM main bearing cap of the invention formed with breathing windows; 
         FIG. 2  is a front plan view of the bearing cap of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a die set compressing powder metal to make a compact of the bearing cap of  FIGS. 1 and 2 ; and 
         FIG. 4  is a view like  FIG. 3  with the upper punch withdrawn and the outer punch extended, with the compact ready to be slid out from between the legs of the outer punch. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a main bearing cap  10  having a top surface  11 , a bottom surface  13 , side surfaces  15 , and end surfaces  17 . The bottom surface  13  has a half cylindrical surface  12  that defines half of the bearing hole for an engine crankshaft journal. The bearing cap  10  has a bridge  14  over the surface  12  and legs  16  and  18  on opposite sides of the surface  12  and the bridge  14 . Inner bolt holes  20  and outer bolt holes  22  extend through the legs  16  and  18 , through which bolts may extend to secure the cap  10  to the engine block. A pair of side bolt holes  24  may also be provided in the end surfaces  17  of the cap  10 . The end surfaces  17  of the cap  10  also each have a groove or undercut  26 , which provides a breathing window as described above. 
     The U-shaped undercut  26  has a side surface  30  that is depressed, indented, or inwardly offset from end-facing surfaces  32  and  34  of the ends of the cap  10 . Upper inward-facing surface  36  and lower inward-facing surface  38  connect the respective side surfaces  30  with the end-facing surfaces  32  and  34 . 
     The main bearing cap  10  can be produced using, for example, CNC controlled compaction presses with at least four platens for each level of tool member including the core rods. The method of production is to use punches to produce the cap  10  shown in  FIGS. 1 and 2 . Referring to  FIGS. 3 and 4 , PM powder or compact  10 ′, corresponding in shape to cap  10  and which after compaction and sintering becomes cap  10 , is compressed between upper punch  40  and lower punches  42  and  44 , with core rods  46 ,  48 ,  50 , and  52  forming the holes  20  and  22 . 
     The undercut  26  is not possible with solid die construction as this feature would not be able to eject from the die. Therefore, an outer punch  58  is used to form the undercuts  26 . All of the punches and core rods move within a die cavity, which may be rectangular, in die  60 . 
     To produce the compact, the punches  40 ,  42  and  44  act as the “die” for the formation of the snap width with undercuts. Upon compaction, the motions are such that simultaneous compaction takes place from the lower punches  42  and  44  and upper punch  40 . This ensures even density around the outer punch  58  which is forming the undercut. Without the simultaneous compaction from the top and bottom, there is a good possibility that the punches will break. When compaction is completed, the compact  10 ′ is ejected from the die. 
     In the ejection step, the outer punch  58  forming the undercut  26  is ejected with the compact  10 ′. It is ejected so the compact  10 ′ clears the upper surface of die  60  such that the compact  10 ′ can be slid sideways or laterally out from between the two legs of the outer punch  58 , in the direction parallel to the thickness of the compact  10 ′ (i.e., in the direction either into or out of the paper in  FIGS. 3 and 4 ). This is different than conventional compaction processes where the punches remain in the die. The reason the outer punch  58  is ejected is so the compact  10 ′ can be removed from the tooling. Removal is done by either pushing the compact laterally from between the legs of the outer punch  58  with the feeder box, or using automation such as robots. After removal, the outer punch  58  moves back into the compaction position shown in  FIG. 3  for the next filling and compaction cycle and the next compact  10 ′ is made. 
     After compaction, the compact  10 ′ may be sintered to form the cap  10 . Because the compact  10 ′ had the undercut feature formed in it during the compaction step, it is unnecessary to machine the undercut feature into the cap  10  after sintering. This reduces the cost and time required to fabricate the cap  10 . 
     A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiment described.