Abstract:
A method and system for forming a cam engaged rocker arm includes a stamping process where metal is forced into die cavities to build up material in a desired area of a blank to create an intermediate article. The blank is further formed by a shaving process where the built-up material and additional material is formed into a valve guide for the rocker arm.

Description:
[0001]     This application claims the benefit of Provisional Application 60/498,076, filed on Aug. 27, 2003, the contents of which are hereby incorporated herein in their entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to a method of forming a rocker arm including a valve guide. In particular, the invention relates to using a stamping die having a pair of cavities to form the valve guides of the rocker arm.  
       BACKGROUND OF THE INVENTION  
       [0003]     In automotive and other applications, an overhead cam engine typically utilizes a plurality of cam engaged rocker arms to open valves. These rocker arms pivot at one end, contact the valve at an opposite end, and support a roller between the two ends. The roller engages the cam and the cam rotates to move the roller, thereby causing the rocker arm to pivot at a pivot end, and push the valve.  
         [0004]     Rocker arms can be manufactured by casting metals, blanking and forming, ceramic molding, and other methods. Stamping a metal blank to form a cam-engaged rocker arm including a valve stem guide is common in the art. The valve stem guides of the rocker arms are typically formed using a punch and cavity, folding or coining process. During the coining process, an upper die and a lower die punch an area of the metal blank to plastically deform the metal blank. Generally, the area of the metal blank being coined has a thickness greater than the remaining metal blank, thereby providing additional material to use in forming the valve guides.  FIG. 1  illustrates a typical metal blank  8  used in the manufacture of a cam-engaged rocker arm. The metal blank  8  illustrated is of uniform thickness and is folded by turning up two opposing edges, and valve guides are formed by plastically deforming material to the desired locations. This plastic deformation typically moves material from nearby areas of the blank to build up a valve guide. In this forming operation, the thickness of the blank area that lost material may be below a desired minimum thickness. A desired minimum thickness for a rocker arm must be maintained for purposes of strength and durability after a surface hardening treatment even if some of the material of the blank is used to form valve guides.  
         [0005]     One drawback to this method is the extreme difficulty in providing a blank with sufficient thickness in a desired area for forming the valve guides without making a remaining portion of the rocker arm too thin in a later forming operation. In practice, it has been found to be nearly impossible to balance these competing needs.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention overcomes the deficiencies of the prior art by preparing a blank of generally uniform thickness for forming the valve guides of a rocker arm. In one embodiment, a method and system for forming a cam-engaged rocker includes a stamping process where metal is forced into die cavities to build up material in a desired area of a blank to create an intermediate article. The intermediate article is further formed by a shaving process where the built-up material and additional material is formed into a pair of valve guides for the rocker arm. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a top view of a prior art metal blank used for forming a cam-engaged rocker arm.  
         [0008]      FIG. 2  is a perspective view of a cam engaged rocker arm formed in accordance with an embodiment of the present invention.  
         [0009]      FIG. 3  is a sectional side view of the rocker arm of  FIG. 1 .  
         [0010]      FIG. 4  is a top view of a metal blank before forming a cam-engaged rocker arm according to an embodiment of the present invention.  
         [0011]      FIG. 5  is a top view of an intermediate article after undergoing a first stamping process according to an embodiment of the present invention.  
         [0012]      FIG. 6  is a perspective view of a further intermediate article according to an embodiment of the present invention, after undergoing a further stamping operation to form side walls.  
         [0013]      FIG. 7  is a front view of the further intermediate article of  FIG. 6  illustrating the die used for pinch forming valve guides according to an embodiment of the present invention.  
         [0014]      FIG. 8  is a front view similar to  FIG. 7 , but illustrating the die after pinch forming the valve guides.  
         [0015]      FIG. 9  is a top view of an alternate embodiment of the metal blank of  FIG. 4 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Referring to  FIGS. 2 and 3 , a rocker arm  10  is illustrated to include a metal body  12 , a valve end  14 , a pivot end  16 , sidewalls  18 , a central portion  20  located between the valve end  14  and the pivot end  16 , and a bridge, or cross member,  22  extending between sidewalls  18 . Metal body  12  is defined by an upper surface  24 , a lower surface  26 , and an outer peripheral surface  28 . As illustrated, central portion  20  has a central aperture  30  and roller apertures  32  formed therein. Central aperture  30  is defined by an inner surface  34 . Roller apertures  32  are defined by roller aperture surfaces  36 . Valve end  14  includes valve guides  40  extending from lower surface  26 . Each valve guide  40  is defined, at least in part, by an inboard surface  42 , an outboard surface  44 , and a distal surface  46 . A pair of shaved areas, S, are illustrated on lower surface  26 , intersecting outboard surfaces  44 . Valve guides  40  are illustrated to have a height H, measured perpendicular to lower surface  26 , between distal surface  46  and lower surface  26 . As best seen in  FIG. 3 , inboard surfaces  42  are separated by a distance D. With continued reference to  FIGS. 2 and 3 , the pivot end  16  includes a cup  50  formed therein and adapted to rotate on a pivot (not shown).  
         [0017]     Referring now to  FIG. 4 , a metal blank  110  is shown according to an embodiment of the present invention. As illustrated, metal blank  110  has a valve end  114 , a pivot end  116 , and a central portion  120  located between the valve end  114  and the pivot end  116 . The metal blank  110  has an upper surface  124 , a lower surface  126 , and an outer surface  128 . Upper surface  124  and lower surface  126 , as illustrated, are preferably identical in outline. The metal blank  110  has a substantially uniform cross-sectional thickness T as measured between the upper surface  124  and the lower surface  126 . The metal blank  110  includes an additional material volume, forming ears  140 , about the valve end  114 . The ears  140  include the volume circumscribed by a Line L, the outer surface  128 , upper surface  124 , and lower surface  126 , adjacent valve end  114 , and define an outboard portion  160  of the metal blank  110 . Metal blank  110  is segmented into zones A, B, C, D, E, F, and G, each having a thickness T, as discussed below.  
         [0018]      FIG. 5  illustrates an intermediate article  210 . As illustrated, metal intermediate article  210  has a valve end  214 , a pivot end  216 , and a central portion  220  located between the valve end  214  and the pivot end  216 . The intermediate article  210  has an upper surface  224 , a lower surface  226 , and an outer surface  228 . The intermediate article  210  has a substantially uniform cross-sectional thickness T as measured between the upper surface  224  and the lower surface  226 . Intermediate article  210  is shown to include projections  240  defined, at least in part, by an inboard surface  242 , an outboard surface  244 , and a distal surface  246 . As illustrated, inboard surfaces  242  are separated by a distance W. Intermediate article  210  is segmented into zones A, B, C, D, E, H, and I. Zones A, B, C, D, E, and H, each have a thickness T substantially equal to the thickness of metal blank  110 . Zone I differs from Zone G in that Zone I has projections  240  and Zone G has ears  140 . Peripheral surface  228 , viewed along the Z-axis, closely approximates the outline of the metal blank  110  without ears  140 , as defined by peripheral surface  128  and Lines L. Thus provided, the metal blank  110  of  FIG. 4  can be formed into the intermediate article  210  of  FIG. 5 , as described below. As illustrated, Zones A, B, C, D, and E of metal blank  110  and intermediate article  210  are substantially identical. Zone G contains ears  140  that are plastically deformed, by a Force P and resulting Force P′ ( FIG. 4 ), inward toward each other to produce a resulting Zone I. Zones F and H are preferably identical, although Zone H may be slightly distorted with respect to Zone F as a result of the forming operation described herein.  
         [0019]     With reference to  FIG. 6 , a further formed intermediate article  310  in the manufacture of rocker arm  10  is illustrated to include a valve end  314 , a pivot end  316 , and a central portion  320  located between the valve end  314  and the pivot end  316 . The further formed intermediate article  310  has an upper surface  324 , a lower surface  326 , and an outer surface  328 . The further formed intermediate article  310  has a substantially uniform cross-sectional thickness T as measured between the upper surface  324  and the lower surface  326 . Preferably, thickness T does not vary between rocker arm  10 , metal blank  110 , intermediate article  210 , and further formed intermediate article  310 . Further formed intermediate article  310  is shown to include sidewalls  318 , a cross member  322 , and projections  340  defined, at least in part, by an inboard surface  342 , an outboard surface  344 , and a distal surface  346 . As illustrated, inboard surfaces  342  are separated by a Distance X. Preferably, Distance X is substantially equal to Distance W, although a slight variation between these distances caused by the forming operations described herein may be experienced. In the embodiment illustrated, sidewalls  318  are about identical in outline to sidewalls  18 .  
         [0020]     Referring now to  FIGS. 7 and 8 , an embodiment of a stamping die  400  for forming valve guides  40  is illustrated to include a center post  402 , a pair of cams  404  having a shaving edge  410 . Center post  402  is illustrated to include a valve guide forming surface  414 . Shaving edge  410  is preferably curved to match the curve of the intersecting line between valve guide  40  and lower surface  26 , as best seen in  FIG. 3 . As illustrated in  FIG. 6 , stamping die  400  has a further formed intermediate article  310  positioned therein and prepared for a shaving operation to create valve guides  40 . As illustrated in  FIG. 8 , stamping die  400  has one rocker arm  10  positioned therein after the shaving operation has formed valve guides  40 .  
         [0021]     An embodiment of the method of forming the rocker arm  10  from metal blank  110  will now be described. The metal blank  110  undergoes a first stamping process in which a stamping die (not shown), having a pair of cavities (not shown) which are used to form the projections  240  of intermediate article  210 . The cavities of the stamping die are centrally located about the valve end  14  of the metal blank  110 . The metal blank  110  is stamped such that during the stamping process, the ears  140  from the outboard portion  160  of the metal blank  110  are forced inward toward the cavities of the stamping die, thereby displacing material adjacent lower surface  126  into the cavities to form projections  240  ( FIG. 5 ). Projections  240  are formed by drawing the ears  140  from the outboard portion  160  while minimizing any change to the cross-sectional thickness of the intermediate article  210  that does not include projections  240 . The ears  140  are driven inward, plastically deforming material of metal blank  110  into the pair of cavities of the stamping die, producing projections  240 . Preferably, each ear  140  produces a projection  240  during this forming operation. Thus formed, intermediate article  210  has an identical outline defined by outer surface  228  as outer surface  128  of metal blank  110  with the exclusion of the ears  140 . Thus, the material volume of ears  140  is about equal to the material volume of the projections  240 .  
         [0022]     At the completion of this stamping step, projections  240  are positioned within the cavities due to the plastic flow of material from metal blank  110 .  FIG. 5  best illustrates the intermediate article  210  after the first stamping process has been completed.  
         [0023]     A further processing step of the method presented herein involves the forming of sidewalls  18 . In this step, the intermediate article  210  of  FIG. 5  is formed into the further formed intermediate article  310  of  FIG. 6  by a folding operation. This folding operation forms sidewalls  318  by folding the sides of further formed intermediate article  310  about 90° toward upper surface  324  along the length of further formed intermediate article  310  from valve end  314  to pivot end  316 .  
         [0024]     As illustrated in  FIG. 7 , the further formed intermediate article  310  of  FIG. 6  undergoes a shaving process to form valve guides  40 . The shaving process is performed by pinching material between upper surface  324  and lower surface  326  between the cams  404  and shaving the material toward the center post  402 . As the material is shaved, the material is plastically deformed toward projections  340 , plastically deforming the material of projections  340 , until both volumes of material are formed into each valve guide  40 . This shaving process creates a shaved area S ( FIGS. 2 and 8 ), that is defined by the material of lower surface  26  that was exposed by the shaving process. As best seen in  FIG. 7 , distance X, between projections  340  of further formed intermediate article  310  is greater than the width of center post  402  adjacent lower surface  326 . In this manner, further formed intermediate article  310  can be positioned within die  400  without having to force further formed intermediate article  310  into position. In an alternate embodiment, inboard surfaces  342  may be angled such that their orientation toward lower surface  326  is less than 90°, and the distance between distal surfaces  346  is greater than the minimum distance between projections  340 , thereby eliminating any difficulty of interfering surfaces when positioning further formed intermediate article within die  400 .  
         [0025]     The shaving process results in a minimum of approximately 65% of stock thickness being maintained across the shaved area A so as not to create a through harden heat treat condition in the shaved area. The stock thickness is the original thickness of metal blank  110  as measured from upper surface  24  to lower surface  26 . This stock thickness is preferably about 3 mm (0.12 inch) to about 3.94 mm (0.16 inch). It is desired to maintain a minimum thickness of the resulting rocker arm in the shaved area A, as measured between the shaved area A and the upper surface  24 . The minimum required thickness for rocker arm  10  adjacent shaved area A is determined by the depth of hardening experienced by rocker arm  10  in a post-forming hardening treatment and the desired soft core thickness. A rocker arm with a hardened surface and soft core is typically desired for purposes of durability and wear resistance. In the embodiment shown, the post forming hardening treatment will harden the rocker arm  10  to a maximum depth of about 0.020 inches measured from all surfaces.  
         [0026]      FIG. 9  illustrates a metal blank  510  as an alternate embodiment of the metal blank  110 . As illustrated, metal blank  510  has a valve end  514 , a pivot end  516 , and a central portion  520  located between the valve end  514  and the pivot end  516 . The metal blank  510  has an upper surface  524 , a lower surface  526 , and an outer surface  528 . Upper surface  524  and lower surface  526 , as illustrated, are preferably identical in outline. The metal blank  510  has a substantially uniform cross-sectional thickness T as measured between the upper surface  524  and the lower surface  526 . The metal blank  510  includes an additional material volume, forming ears  540 , about the valve end  514 . The ears  540  include the volume circumscribed by a Line M, the outer surface  528 , upper surface  524 , and lower surface  526 , adjacent valve end  514 , and define an outboard portion  560  of the metal blank  510 . Metal blank  510  is segmented into zones A, B, C, D, E, J, and K, each having a thickness T.  
         [0027]     Metal blank  510  is formed into intermediate article  210  by forcing ears  540  into the valve end  514  as metal plastically flows into the cavities forming projections  240 , as discussed herein. Preferably, each ear  540  produces a projection  240  on Zone K at valve end  514  during this forming operation.  
         [0028]     Cup  50  and central aperture  30  may be formed in lower surface  26  at any appropriate time when processing metal blank  110  into the rocker arm  10 . As presently preferred, central aperture  30  is formed and cup  50  is formed as the last forming step, after pinch forming of valve guides  40 . Roller apertures  32  may be formed either by machining or in-die piercing. Preferably, roller apertures  32  are formed after pinch forming valve guides  40 . Outer curved, or peripheral, surfaces  28 ,  128 ,  228 , or  528  may be completely curved, have straight portions, or include straight portions intersecting at predetermined angles.  
         [0029]     While the invention has been described with respect to specific examples including preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims. For example, while valve guides are illustrated, another form of the guides may also be useful at the pivot end.