Abstract:
In accordance with an exemplary embodiment of the invention, a shaft coupling is provided. The shaft coupling comprises a first shaft having a splined outer surface, a tubular second shaft having an end surface and a splined inner surface, the second shaft receiving the first shaft along a longitudinal axis of the second shaft, and at least one stake extending axially into the second shaft end surface. The at least one stake deforms at least a portion of the splined inner surface to facilitate an interference fit between the first and second shafts and configured to resist a predetermined axial separation load being applied to the first and second shafts.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/889,726, filed Oct. 11, 2013, the contents of which are incorporated herein by reference thereto. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The following description relates to shaft assemblies, and more particularly, to a steering column assembly with anti-pull apart features. 
         [0003]    In some known tubular shaft assemblies having two or more shafts, angled stakes are formed on the outer diameter of one tubular shaft to prevent another shaft being removed from the tubular shaft. However, with some assemblies, angled stakes may create an interference condition that causes high stroke efforts and undesired drag, thereby preventing achievement of a required minimum pull-apart load. 
         [0004]    Accordingly, it is desirable to provide a steering column assembly that both achieves the minimum pull-apart load and prevents an undesired interference between two shafts. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with an exemplary embodiment of the invention, a shaft coupling is provided. The shaft coupling comprises a first shaft having a splined outer surface, a tubular second shaft having an end surface and a splined inner surface, the second shaft receiving the first shaft along a longitudinal axis of the second shaft, and at least one stake extending axially into the second shaft end surface. The at least one stake deforms at least a portion of the splined inner surface to facilitate an interference fit between the first and second shafts and configured to resist a predetermined axial separation load being applied to the first and second shafts. 
         [0006]    In accordance with another exemplary embodiment of the invention, a steering shaft assembly is provided. The assembly includes a first shaft having a first end, a second end, and a splined outer surface. A tubular second shaft includes a first end, a second end having an end surface, and a splined inner surface. The second shaft second end receives the first shaft first end along a longitudinal axis of the second shaft. At least one stake extends axially into the second shaft end surface. The at least one stake is configured to deform at least a portion of the splined inner surface to facilitate an interference fit between the first and second shafts and configured to resist a predetermined axial separation load being applied to the first and second shafts. 
         [0007]    In accordance with yet another exemplary embodiment of the invention, a method of manufacturing a shaft coupling is provided. The method includes providing a first shaft having a splined outer surface, providing a tubular second shaft having an end surface and a splined inner surface, the second shaft receiving the first shaft along a longitudinal axis of the second shaft, and providing a die pot having at least one pin. The method further includes disposing the first and second shafts in the die pot such that the at least one pin is oriented against the second shaft end surface, and forcing the at least one pin into the second shaft end surface to form at least one stake extending axially into the second shaft end surface. The at least one stake is configured to deform at least a portion of the splined inner surface to facilitate an interference fit between the first and second shafts preventing axial removal of first shaft from second shaft until a predetermined axial load is applied to the first and second shafts. 
         [0008]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0010]      FIG. 1  is a side view of an exemplary shaft assembly; 
           [0011]      FIG. 2  is a cross-sectional view of a portion of the shaft assembly shown in  FIG. 1  taken along Section  2 ; 
           [0012]      FIG. 3  is a cross-sectional view of the shaft assembly taken along line  3 - 3  of  FIG. 1 ; 
           [0013]      FIG. 4  is a cross-sectional view of an exemplary shaft and die pot assembly; 
           [0014]      FIG. 5  is a cross-sectional view of the shaft and die pot assembly taken along line  5 - 5  of  FIG. 4 ; and 
           [0015]      FIG. 6  is a cross-sectional view of a portion of the shaft and die pot assembly shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same,  FIGS. 1-3  illustrate an exemplary shaft assembly  10 . In the exemplary embodiment, assembly  10  is a steering column shaft assembly that includes a first shaft section  12  and a second shaft section  14  sliding disposed within first shaft section  12 . However, assembly  10  may be any type of suitable shaft assembly. 
         [0017]    First shaft section  12  includes a tubular shaft body  16  having a first end  32 , a second end  34 , and a splined section  18  formed on the inner surface or diameter of tubular shaft body  16 . Splined section  18  is configured to engage second shaft section  14  and includes a plurality of teeth  20  defined by tapered surfaces  22  and involute surfaces  24  ( FIG. 3 ). Alternatively, surfaces  24  may be straight sided. Shaft first end  32  includes an end surface  26  having a plurality of stakes  28  formed therein, as is described herein in more detail. Shaft second end  34  may include an attachment member  30  (e.g., a yoke) adapted to enable other portions of a steering device to be connected with steering column assembly  10 . 
         [0018]    Second shaft section  14  includes a solid shaft body  40  having a first end  42 , a second end  44 , and a splined section  46  formed on the outer diameter of shaft body  40 . Splined section  46  is configured to engage first shaft splined section  18  and includes a plurality of teeth  48  defined by tapered surfaces  50  and involute surfaces  52  ( FIG. 3 ). Splined section  46  may include a plastic overmolding (not shown) or may be entirely formed from a different material than shaft body  40  (e.g., plastic). Shaft second end  44  may include an attachment member  54  (e.g., a yoke) adapted to enable other portions of a steering device (not shown) to be connected with steering column assembly  10 . Moreover, first and second shaft sections  12 ,  14  may be formed from any suitable material such as, for example, aluminum or steel. 
         [0019]    In the exemplary embodiment, second shaft section  14  telescopes within first shaft section  12  along a longitudinal translation axis  56 . In a fully extended position, due to stakes  28 , at least a portion of splined section  18  interferes with splined section  46  to prevent or resist second shaft section  14  from being separated or pulled apart from first shaft section  12  until a minimum predetermined axial separation or pull-apart load is met. In one embodiment, the pull-apart load is, for example, between 300N and 350N or between approximately 300N and approximately 350N. In another embodiment, the pull-apart load is at least 250N or at least approximately 250N. However, assembly  10  may be designed with any desired pull-apart load, as described herein in more detail. 
         [0020]    In the exemplary embodiment, each stake  28  is formed in first shaft end surface  26  substantially within one tooth  20  by punching or pressing a pin  60  ( FIG. 6 ) into end surface  26 . As such, tooth  20  and/or tubular shaft body  16  are deformed and create an interference fit with splined section  46  of second shaft section  14  when steering column assembly  10  is in a fully extended position. For example, the angle of orientation (i.e., the flank angle) of tapered surfaces  22  is altered during the deformation and portions of each deformed tooth  20  extend into a hollow area of tubular shaft body  16  (e.g., between adjacent teeth  48 ) and will engage teeth  48  if first and second shaft sections  12 ,  14  are in a fully extended position. 
         [0021]    As illustrated in  FIG. 3 , assembly  10  includes splined sections  18 ,  46  each with eighteen teeth. Nine stakes  28  are formed in half of splined section  18  to form a semi-circle, which produces the desired pull-apart load. However, splined sections  18 ,  46  may alternatively be formed with any suitable number of teeth or in any pattern around the circumference of first shaft end surface  26  that enables assembly  10  to function as described herein. Similarly, splined section  18  may be formed with any number of stakes  28  that enables assembly  10  to function as described herein. 
         [0022]    As illustrated in  FIG. 2 , each stake  28  is substantially conical and includes inner walls or tapered edges  62  converging at a depth ‘d’ and at an angle ‘α’. In one exemplary embodiment, angle ‘α’ is between 50° and 70° or between approximately 50° and approximately 70°. In other embodiments, angle ‘α’ is 60° or approximately 60°. However, edges  62  may be angled at any angle that enables assembly  10  to function as described herein. Moreover, each stake  28  may be formed at any suitable depth ‘d’. Alternatively, stake  28  may have any suitable shape that enables assembly  10  to function as described herein. For example, the profile of stake  28  may include a chisel point, a diamond point, a triangular point, or the like. 
         [0023]    By adjusting depth ‘d’ and ‘α’, the amount, the shape, and/or circumferential pattern of the deformation of teeth  20  may be adjusted to tune the “pull-apart force”, which enables the pull-apart load to be adjustably controlled for a desired application. For example, a certain shipping method may require a higher pull-apart load than a typical shipping method, and depth ‘d’ and angle ‘α’ may be accordingly adjusted to assure first and second shaft sections  12 ,  14  do not pull apart during loads encountered for that certain shipping method. As such, the geometry of stakes  28  provide a positive anti-pull apart feature without impacting the slip load of first and second shaft sections  12 ,  14 . The flank angle interference between first shaft section  12  and second shaft section  14  provides a positive anti-pull apart feature at their fully extended travel positions. Accordingly, slip load performance is not degraded either at the application of stake  28  or after shaft assembly  10  has been bottomed out in the fully extended position. 
         [0024]    With reference to  FIGS. 4-6 , an exemplary method of manufacturing steering column assembly  10  includes inserting second shaft section  14  into first shaft section  12 . A die pot  64  is provided with a desired number of pins  60  ( FIG. 6 ) corresponding to a desired number of stakes  28 , and die pot  64  encapsulates shaft first end  32  in the axial position along axis  56  ( FIGS. 4 and 6 ). As shown in  FIG. 4 , a force ‘F’ is placed on die pot  64  in the axial direction, and pins  60  form stakes  28  in end surface  26 . 
         [0025]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.