Abstract:
A method for forming a coupling structure ( 40, 140 ) on an end of a drive shaft and a drive shaft ( 10 ) made by the method. The method includes the steps of providing a tubular shaft ( 22, 122 ) having an open end. Forming a driving configuration at the end. Closing the open end at a point spaced from the open end. Casting a coupling structure ( 40, 140 ) on the closed end in driving engagement with the shaft ( 22, 122 ).

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to a method for manufacturing a drive shaft with a drive coupling thereon. In particular, this invention relates to a method for forming a coupling on an end of a power transmission shaft and a power transmission shaft made by the method.  
         BACKGROUND OF INVENTION  
         [0002]    Power transmission shafts, such as drive shafts, are commonly fitted with a yoke. The yoke is part of a universal type of coupling. The yoke is manufactured separately from the power transmission shaft. The yoke will have a shaft portion that is inserted into the end of the power transmission shaft and then circumferentially welded in place. The shaft is then machined to rotationally balance the shaft. Examples of power transmission shafts having a welded yoke include U.S. Pat. Nos. 5,230,658; 5,716,276; and publication no. WO 98/48186.  
           [0003]    The prior art shafts produce suitable results. However, improvements can be had in providing the yoke assembly directly onto the end of the shaft.  
         SUMMARY OF INVENTION  
         [0004]    The disadvantages of the prior art may be overcome by providing a method for forming a yoke structure directly on an end of a power transmission shaft.  
           [0005]    It is desirable to provide a method for forming a yoke structure on the end of shaft which reduces manufacturing steps, improves a rotational balance and reduces weight of the power transmission shaft.  
           [0006]    According to one aspect of the invention, there is provided a method including the steps of a tubular shaft having an open end. Forming a driving configuration at the end. Closing the open end with a cap. Casting a coupling structure on the closed end in driving engagement with the shaft.  
           [0007]    According to another aspect of the invention, there is provided a drive shaft formed by the method of the present invention. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0008]    In drawing which illustrate embodiments of the present invention,  
         [0009]    [0009]FIG. 1 is a perspective view of a power transmission shaft having a coupling structure formed thereon according to the present invention;  
         [0010]    [0010]FIG. 2 is a perspective view of a power transmission shaft in an initial stage;  
         [0011]    [0011]FIG. 3 is a perspective view of a power transmission shaft in an intermediate stage;  
         [0012]    [0012]FIG. 4 is a perspective view of a cap according to the present invention;  
         [0013]    [0013]FIG. 5 is a side elevational view of the cap of FIG. 4; and  
         [0014]    [0014]FIG. 6 is a side sectional view of a second embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring to FIG. 1, a power transmission shaft  10  embodying the present invention is illustrated. The power transmission shaft  10  is preferably a drive shaft for a motor vehicle. The drive shaft  10  can be either a conventional one piece drive shaft that has a yoke or coupling structure on each end thereof or a conventional two piece drive shaft connect by a slip joint. The yoke or coupling structure is provided on opposite ends of the shaft components of the drive shaft.  
         [0016]    Referring to FIG. 2, a tubular shaft  20  is provided. Preferably, the shaft  20  is steel. However, it is also contemplated that aluminum tubing could be employed. The tubular shaft  20  is optionally provided with a series of circumferentially spaced longitudinally extending splines  222 . An end  24  has a yoke diameter  26 . Yoke diameter  26  is slightly less than the shaft diameter  28 . Tubular shaft  20  is manufactured in accordance with known methods.  
         [0017]    Referring to FIG. 3, end  24  undergoes a forming operation to form a driving configuration in the form of a non-circular cross-sectional configuration  25 . In the preferred embodiment, the non-circular cross-sectional configuration is octagonal and formed by a swaging operation. However, it is readily understood that other non-circular shapes, such as hexagonal, rectangular would provide suitable results. Additionally other forming operations such as stamping could also be utilized with similar results.  
         [0018]    Referring to FIGS. 3 and 4, a cap  30  of the present invention is illustrated. The cap  30  is preferably made of aluminum. The cap  30  is cup shaped having an outline complementary with the non-circular cross-sectional configuration  25  of end  24 . The cap  30  is sized to frictionally fit within driving configuration  25 . The cap  30  can be inserted from the near end wherein the lip  32  will engage the end edge of the shaft  22 . Optionally, cap  30  has a lip  32  that will fit within the shaft  22  when the cap  30  is inserted from the distal end thereof in the direction of arrow A. Cap  30  will close the open end of the shaft  22  at the near end or at a point spaced from the near end of the shaft  22 .  
         [0019]    With the end  24  closed, the end  24  of shaft  22  is placed in a casting mold. The casting mold has a cavity complementary to the shape of the coupling or yoke structure  40 . A yoke structure  40  is then cast directly onto the end  24  of the shaft  22 .  
         [0020]    Yoke structure  40  generally has two legs  42  and  44  extending from a bight portion  46 . Optionally, ribs  48  are provided to improve structural strength of the yoke structure  40 .  
         [0021]    The next step for processing the power transmission shaft  10  of the present invention is to machine or bore transversely extending apertures  50  in each of the legs  42 ,  44 .  
         [0022]    The present invention has been described in terms of casting a single yoke structure  40  on an end of a shaft  22 . However, it is readily apparent to one skilled in the art that multiple yoke structures could be cast on ends of multiple shafts by designing a multi-cavity mold. Additionally, on a single drive shaft, yoke structures on opposite ends thereof could be cast simultaneously.  
         [0023]    Referring to FIG. 6, a second embodiment of the present invention is illustrated. The second embodiment is particularly useful for single tube drive shafts. In single tube drive shafts, it not convenient to insert an end cap at both ends if the end cap is inserted from the opposite end. The end  124  of tube  122  is first formed into a driving configuration by swaging the end  124  to expand the diameter thereof and forming at least one transverse aperture  123  therein. Preferably 2 or more apertures  123  are formed in the end  124 . As is apparent to those skilled in the art, the apertures  123  can be formed by any conventional process, such as piercing, lancing, drilling, laser cutting, etc., either before or after the swaging step.  
         [0024]    A cup shaped cap  130  is inserted from the near or swaged end  124  into the tube  122 . The rim  132  of the cap  130  has an outer diameter that is less than the diameter of end  124  but greater than the original diameter  128  of tube  122 . The rim  132  will frictionally engage the inside surface of the tube  122  preferably at the transition between diameters to seal the end of the tube  122 . Once inserted, the cap  130  closes the end of the tube  122  and the yoke structure  140  can be cast thereon. The cap  130  limits the extent to which the yoke structure  140  extends into the end  124 . As is apparent, the cast material will flow between the inside and outside of the tube  122  through aperture  123 . Once solidified, the yoke structure  140  will have a dowel structure to provide a driving connection with the tube  122 .  
         [0025]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is understood that the invention is not limited to the disclosed embodiments but, on the contrary, it intended to cover various modifications in the arrangements as defined in the attached claim.