Abstract:
An improved, light weight ball member for universal connections having a hollow interior both in its ball portion and connecting portion for providing high strength and light weight and method for forming it through an improved forging process, using improved forging dies.

Description:
PRIORITY INFORMATION 
       [0001]    This is a Divisional Application of U.S. patent application Ser. No. 11/872,187, filed Oct. 15, 2007, which is based on and claims priority to Japanese Patent Application No. 2006-283509 filed Oct. 18, 2006, the entire contents of both of which is hereby expressly incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to an improved ball joint and method of forming one. 
         [0004]    2. Description of the Related Art 
         [0005]    Ball joints are used in a large number of applications for providing pivotal connections that transmit motion for one connected member to another, particularly when the relationship of the connected elements changes during the motion transmission. A typical application in which this invention may be utilized is shown in  FIG. 1 , that illustrates in perspective a steering arrangement for a wheel of a dirigible front wheel suspension for a vehicle, such as an automobile. Only the steering system of the vehicle is shown, as it is believed that those skilled in the art how the ball joint constructed and manufactured in accordance with the invention may be used in such combinations. Those skilled in the art will also understand that ball joint elements constructed and manufactured in accordance with the invention are capable of use in other combinations using joints of this general type. 
         [0006]    The vehicle steering system, indicated generally at  11 , includes a steering wheel  12  is positioned in a known manner in the driver&#39;s compartment of the vehicle. Greater detail of the vehicle is not shown as noted above to permit easier understanding of a typical application of the invention. The steering wheel  12  is connected to the upper end of a steering shaft  13  that extends at least in part outside of the driver&#39;s compartment typically into the vehicle engine compartment. 
         [0007]    There it is connected to a steering box  14  for effecting control rotation of a steering pitman arm  15 . The outer end of the pitman arm  15  carries, in a manner to be described later, to a ball joint element, indicated generally by the reference numeral  16  constructed and configured in accordance with the invention, as will be described later, by reference to the remaining figures. 
         [0008]    The ball joint  16  forms a universal pivotal connection to a linkage system including links  17 ,  18  and  19  with like ball joints  16  providing the pivotal connections between the directly connected ends of the links. The final pivotal connection is to the supporting element  21  that journals a wheel  22  for both rotation about the wheel axis and for suspension and steering movement, as is well known in the art. 
         [0009]    From the foregoing description it should be readily apparent that a ball joint must be capable of providing smooth transmission of movement between connected members with a minimum of friction. Also in many applications such as in vehicle steering linkages it should be robust and also light in weight. The latter desired condition is because it forms a portion of what is referred to as unsprung weight. Also a low cost of fabrication from a strong material is desired. 
         [0010]      FIG. 2  illustrates a prior art attempt at achieving these goals. This type of ball joint is used in a large number in the steering system of vehicles and is typified in Japanese Published Application JP-A-2005-31605. The essential part of this prior art type ball joint is comprised generally of a ball joint member  101  rotatably contained in a casing  102 . The ball joint member  101  comprised of a smooth ball portion  101   a  having a spherical sliding surface  101   b  suitably journalled in the casing  102  and a connecting shaft  101   c  extending in radial direction from part of the smooth ball portion  101   a.    
         [0011]    Recently it has been recognized that in such ball joints, there is desired a reduction in excess material to save resources and reduce weight. A typical method known for this purpose is to provide a weight reducing hole  101   d  in the smooth ball portion  101   a  of the ball joint member  101 . The hole is bored along the axis from the opposite side of the connecting shaft  101   c  by forging or machining. 
         [0012]    However, if the diameter of weight reducing hole  101   d  in the ball joint member  101  is enlarged to provide the weight reduction, the sliding surface area of the smooth ball portion decreases, resulting in restricted pivoting angle of the connecting shaft possible. Therefore, there is a restriction to the increase in the size of the weight reducing hole  101   d.  Alternatively, while it is possible to enlarge the weight reducing hole  101   d  by machining the inside surface  101   b  with a cutting tool bit inserted through the opening of the weight reducing hole  101   d,  the number of machining steps increases and the time of forming increases, which is a factor of increasing manufacturing cost. Therefore, this method is hard to practice. 
         [0013]    It is, therefore, a principal object of this invention to provide a light weight, strong ball joint having a large spherical surface and a low cost method of forming it. 
       SUMMARY OF THE INVENTION 
       [0014]    A first feature of the invention is adapted to be embodied in a ball member for a ball and joint pivotal connection being formed from a single piece comprised of a ball portion adapted to be pivotally connected within a socket formed by one of the elements to be connected and a shank portion adapted to be fixedly secured in a complimentary opening of the other element to be pivotally connected. The ball member has an inner cavity complimentary in shape to said ball and shank portions and closed at both ends. 
         [0015]    Another feature of the invention is adapted to be embodied in a method of forming a ball member for a ball and joint pivotal connection formed from a single piece comprised of a ball portion adapted to be pivotally connected within a socket formed by one of the elements to be connected and an integral shank portion adapted to be fixedly secured in a complimentary opening of the other element to be pivotally connected. The method comprises the steps of forging a solid cylindrical piece of metal into the integral ball and shank portions with complimentary closed ball shaped and cylindrical shaped cavities by forging steps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]      FIG. 1  is a perspective view showing a typical embodiment in which the invention may be employed. 
           [0017]      FIG. 2  is a cross sectional view showing a prior art type of ball joint element. 
           [0018]      FIG. 3  is a perspective view of a ball joint embodying the invention looking from the shank end and made in accordance with an embodiment of the invention. 
           [0019]      FIG. 4  is a perspective view of a ball joint looking from the ball end and made in accordance with an embodiment of the invention. 
           [0020]      FIG. 5  is cross sectional views taken through a forged material before forming into the final product 
           [0021]      FIG. 6  is a cross sectional view of the final product incorporating the invention. 
           [0022]      FIG. 7  is a series of cross sectional views showing in the upper portion thereof the shape of the ball joint element during the various forging steps and in the lower portion thereof the forging dies that perform the forging steps. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Referring now in detail to the drawings and initially to  FIGS. 3 and 4 , these are perspective views of a ball joint element configured and manufactured in accordance with the invention. The novel ball joint member is indicated generally by the reference numeral  31 , made in a manner to be described shortly by reference to  FIGS. 5-7 , and is comprised of a smooth ball portion  32  having a spherical journaling surface and a connecting shaft portion  33  provided to project radially from the outer surface of the smooth ball portion  32 . The smooth ball portion  32  and the connecting shaft portion  33  are made by applying machining processes such as cutting, rolling and other plastic forming processes to a forged product in a manner that will be described later, as noted above. 
         [0024]    The connecting shaft portion  33  as shown in  FIGS. 3 and 4  has an attachment portion  33   a  receiving a dust cover (not shown), and a male thread portion  33   b  for connection to an associated link such as the links  17 ,  18 ,  19  and  21  ( FIG. 1 ). The reference numeral  33   c  denotes a flange serving as a partition between the attachment portion  33   a  and the male thread portion  33   b.  A reference numeral  33   d  denotes an Allen wrench receiving hole formed in the axial center of the shaft end. A circular flat surface  32   e  is provided on the smooth ball portion  32 , on the opposite side of the connecting shaft portion  33  for improving efficiency of plastic forming and a forming dent  32   f  for positioning the operation in the die remain. 
         [0025]      FIG. 5  is a cross sectional view of a circular blank  34  of material that will be formed, from the forging steps shown in  FIG. 7  to the finally finished ball joint  31  shown in cross section in  FIG. 6 . 
         [0026]    Referring now to  FIG. 6  in detail, the reference numeral  35  denotes generally a weight reduction space formed on the inside surface of the forged product  31 . The weight reduction space  35  is formed as a single space by interconnecting a spherical space  35   a  centered on approximately the same center as that of the external surface so as to have approximately constant wall thickness with an elongated cylindrical space  35   b  formed coaxially with the connecting shaft portion  33 . Incidentally, an annular excess material rib portion  31   b  present inside the spherical space  35   a  occurs in the manufacturing process as will be described later in detail. 
         [0027]    As described above, the weight is reduced from the ball joint member  16  in the region between the smooth ball portion  32  and the connecting shaft portion  33  approximately along the external surface shape to form the space  35 . As a result, excess weight is reduced to a practical minimum. According to this example, a conventional product without weight reduction weighing 65 grams is lightened to 45. In addition, as the weight reduction is made without causing recesses on the outer surface, the same external shape as that of the conventional product results so the function and action the conventional product provides are not impaired. 
         [0028]    The actual forming process (forging) will now be described in detail by primary reference to the several views of  FIG. 7 , that also shows the forging tools employed in each step at the lower portion of this figure and the blank formed by these tools at the upper portions of the figure. The steps are numbered in sequence, but it should be noted that those skilled in the art may employ different steps and/or sequences without departing from the invention. 
         [0029]    The forging machine mainly uses in the first steps so-called two-piece split dies disposed to be movable in a generally axial direction toward and away from each other on both sides of the pellet-shaped forging blank  34 . The final two steps employ a three-piece split die. The two-piece split die, as is well-known, has die surfaces carved in opposing faces of the split die pieces that move to and away from each other relative to the longitudinal axis of the blank  34 . The three-piece split die has a third die interposed between the two split die pieces. In this example, the third die of the three-piece split die is made up of several die pieces that may be separated in radial directions. 
         [0030]    Referring now in detail to the steps shown in  FIG. 7 , a forging blank  34  is formed in the first step shown in FIG.  7 ( 1 ) by a pair of dies, a pressing die  41  and a receiving die  42 , movable to and away from each other, into a first partially processed piece  43  of a roughly bullet shape as a whole with its one end having a convex portion  43   a  of a semispherical outer shape. The other end is formed with a shallow circular recess portion  43   b.  This initial shaping is done to smoothen material flow within the dies  41  and  42  to reduce stresses and facilitate the forming in the next step. 
         [0031]    In the following second step, the partially processed work  43  is worked by a forming die  44  and a receiving die  45 . The partially formed piece  43  is inverted as shown in FIG.  7 ( 2 ) and is supported in the receiving die  45  that has a semispherical inside bottom. Then, the recess  46   b  and surrounding wall  46   a  of the work piece is extended by pressing by the punch-shaped pushing die  44 . This produces a second partially processed work  46  of an elongated cylindrical container-like shape having a cylindrical wall portion  46   a  around an axial hole  46   b  with its upper end open and an approximately semispherical bottom portion  46   c  continuous with the cylindrical wall portion  46   a.  As a practical matter, this step of forming the container-like member is not greatly different from that in conventional forming method. 
         [0032]    The third step, shown in FIG.  7 ( 3 ) constitutes one of the features of the invention. As shown in this figure, a pressing die  47  and receiving die  48  are employed. The bottom portion  46   c  of the second partially processed work  46  is supported in the receiving die  48  having a die surface of semispherical shape slightly greater in diameter than the bottom portion  46   c.  The punch-shaped pressing die  47  is slightly greater in diameter than the axial hole  46   b  and is pressed to draw the inside round surface of the cylindrical wall portion  46   a  to form a cylindrical wall portion  49   a  of a further reduced wall thickness, while increasing the inside diameter  49   b.    
         [0033]    In the process of the pressing die  47  being pressed into the previously formed work piece  46 , it is pressed hard against the die surface of the receiving die  48 , the bottom portion  49   b  bulges outward. At the same time, part of the material of the cylindrical wall portion  46   a  flows into the bulged portion and expands into the die  48 , so that an approximately spherical bottom portion  49   b  is formed. 
         [0034]    Also in the process of the pressing by the pressing die  47 , excess material is forced out the inside surface of the cylindrical wall portion  46   a  with the fore-end face of the drawing die  47  is left behind when the pressing die  47  is retracted to form the above-mentioned annular excess material portion  49   c  rising inward from the vicinity of the bottom portion  44   b.  In this way, the third step half-processed work  49  is formed with the approximately spherical bottom portion  49   b  continuous to one end of the thin cylindrical wall portion  49   a.    
         [0035]    Next, in the fourth step shown in FIG.  7 ( 4 ), the partially processed work piece  49  resulting from the third step is processed with a receiving die  51  having a semispherical receiving surface, as will be described in more detail shortly, and with a pressing die  52  moving toward and away from the receiving die  51 . 
         [0036]    The die surface of the pressing die  52 , as shown in the lower half of the drawing, has three step portions  52   a,    52   b,    52   c  of increasing inside diameters, and a ceiling portion  52   d.  The ceiling portion  52   d  carries an axially extending projecting member  52   e  formed with a round or hexagonal rod shape, which is decided, as will be described later. 
         [0037]    The semispherical receiving surface, previously mentioned, of the bottom central portion of the receiving die  51  includes a generally flat portion  51   a  of a small diameter with a small semispherical projection  51   b  rising in the center of the flat portion  51   a.  Further, a space remains between the inside surface of the die and the surface of the half-processed work and to receive the material escaping during the tight-closed forging step. This material receiving area is indicated by the reference numeral  51   c.    
         [0038]    Thus, as the pressing die  52  moves toward the receiving die  51 , the outer surface of a thin cylindrical wall portion  49   a  is drawn upwardly to form a portion of a further smaller diameter  54 . At the same time, the upper end portion of the cylindrical wall portion  31  is depressed by the semispherical ceiling portion  52   d  of the pressing die  52 , and flows along the wall surface while curving radially inward. Thus the wall thickness increases greatly while the outside diameter shrinks. Part of the material flowing at this time goes under the projecting member  52   e  and its fore-end portions meet together around the center of the shaft to almost close the opening. Thus a preliminary hole  54   a  for later machining of the engagement hole  19   d  is formed. 
         [0039]    Further, the pressing force applied with the pressing die  52  during the drawing step forms a step portion  54   b  between the thin cylindrical wall portion  49   a  and the shaft-shaped small diameter portion  54 . Part of the small diameter portion  49   a  located below the step portion  54   b  is pushed out to the bottom portion  49   b  expanded in the previous step, so that its outside round portion expands further to form an enlarged bottom portion  53   b.    
         [0040]    At this time, a small projection  51   b  provided on a flat bottom  51   a  of the receiving die  51  pierces into and axially supports the fourth step half-processed work  53 . These produce at the base of the lower portion a dent  53   c  remaining in the center of a flat surface  53   d  after the forming step. Further, the reference numeral  51   c  denotes a space remaining between the inside surface of the die and the surface of the half-processed work for receiving the material escaping during tight-closed forging step. 
         [0041]    In this way, on condition that the semispherical die surface of the receiving die  51  is made with some margin in diameter relative to the planned size of the bottom portion  37 , the fourth half-processed work  53  having a further expanded spherical portion  53   a  is formed simply by using dies that restrict the outer shape while vertically compressing the third step half-processed work  49  supported at the upper and lower axial portions. 
         [0042]    Next, in the fifth step shown in FIG.  7 ( 5 ), the fourth half-processed work  53  obtained in the previous step is further compressed in the axial direction so that axial length is shortened while the outside diameter of the spherical portion  53   a  expands further to approximate the shape of the final forged product  31 . 
         [0043]    Here are used, like the dies used in the fourth step [ FIG. 7  ( 4 )], a receiving die  61  having a semispherical bottom portion for supporting the spherical portion  53   a  of the fourth half-processed work  53  and a pressing die  62  for correcting the shape of the upper portion. 
         [0044]    The pressing die  62 , like the pressing die  52 , is provided with step portions  62   a,    62   b,    62   c,  and a rod-like projection  63  for forming the engagement hole  19   d . The receiving die  61  is provided with a small diameter flat surface portion  61   a  and a semispherical small projection  61   b  on the bottom portion of the die surface. 
         [0045]    Therefore, as the receiving die  61  and the pressing die  62  approach each other, the rod-like projection  63  engages with the preliminary hole  54   a  of the fourth half-processed work  53  to form the new fifth processed part  55 , and the semispherical small projection  61   b  engages with the forming dent  51   b  and they are supported respectively. 
         [0046]    The die surfaces formed on the inside surface of the pressing die  62  and the projection  63  are configured to form the final shape of the end  33   b  and the tool receiving hole  33   d.  Thus when the pressing step of FIG.  7 ( 5 ) is completed the upper portion of the spherical portion  55   a,  part of the material around the rod-like projection  63  and the step portion  55   b  is depressed hard and the material around the tool receiving hole  33   d  is finished into required shape. At the same time, some of the thin cylindrical wall portion  55   c  is forced into the upper part of the spherical portion  55   a.    
         [0047]    At this time, the underside part thicker than the excess material part  55   c  formed inside the spherical portion  53   a  expands in diameter and works to pull in the thin cylindrical wall portion  55   a  that comes flowing to the excess material part  55   c.  In this way, the fifth half-processed work  55  having the spherical portion  53   a  of a further increased diameter is obtained. 
         [0048]    FIG.  7 ( 6 ) shows the final, sixth step. This step employs two dies each of which is split along the axial direction (a receiving die  71 , and a pressing die  72 ). Interposed between these two dies ( 71  and  72 ) is a third, a split die  73  interposed between the two. The split die  73  is made up of three pieces split in the circumferential direction and movable in radial directions relative to the axis of the work piece  55  to form the finally shaped piece  33 . The reference numeral  74  identifies a rod like projection similar to the rod-like projection  63  used in the previous step. This projection  74  is secured to the pressing die  72 . 
         [0049]    Initially, the forming dent  51   b  of the fifth half-processed work piece  55  is engaged with the small projection  71   b  of the receiving die  71 . Then the dies  71 ,  72 , and  73  are advanced relative to each other. 
         [0050]    This includes engaging the small diameter portion  54  of the workpiece  55  with the step portion of the pressing die  72 . Then the pressing die  72  is advanced toward the die  73  while tightening the squeezing die  73  in a radial direction relative to the small diameter portion  54 . Thus material flows from the cylindrical wall portion  49   a  and small diameter portion  54  into a recess  73   a  provided in the squeezing die  73 . As the material fills the recess  73   a,  the material projects to form the annular flange  33   c,  so that the forged product  32  is finished. The threaded portion  33   b  is then machined in a suitable manner. 
         [0051]    It should be readily apparent from the foregoing description that the described methodology and apparatus provides a strong low cost ball joint element. However those skilled in the art will readily understand that the metholodgy and apparatus employed therefore may be subject to various changes and modifications without departing from the spirit and scope of the invention, as defined by the appended claims.