Patent Publication Number: US-2007107197-A1

Title: Method for rotational coupling

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates generally to methods used for joining or coupling members, and more particularly, to a method for rotationally coupling a first member and a second member adapted for receiving a portion of the first member therein.  
      Some rotational couplings are used in relatively low-torque applications. For example, a splined connection between a halfshaft axle bar and a hub of a tripot-type joint assembly transmits relatively low levels of torque. Generally, the components constituting a rotational coupling assembly are heat-treated after formation of the coupling features, to increase their strength and resilience. However, heat treatment of the components increases their cost, and the heat treatment used for hardening and strengthening components used in higher-torque applications may not be necessary for lower-torque applications. In addition, in rotational couplings utilizing axial splines, finish rolling and broaching of complementary splines on the components is relatively costly. Furthermore, in splined components produced by conventional rolling and broaching, rotational backlash between the mating splines is also a problem. Also, due to mismatches between the mating splines, a portion of the splines may carry a substantially lower proportion of the torque load than the remaining splines. This force imbalance reduces the effective strength of the components, necessitating an increase in component size.  
     SUMMARY OF THE INVENTION  
      The present invention provides a method for rotationally coupling a first member and a second member. In a first step, a first member and a second member are provided, one of the first member and the second member including a portion having cutting edge(s) extending therealong. The second member defines an orifice for receiving therein at least a portion of the first member. The orifice is configured relative to the first member such that, as the portion of the first member is inserted into in the orifice, the cutting edges on one of the first member and the second member engage a surface on the other one of the first member and the second member in a single-pass broaching operation to shave a layer of material from the surface such that the surface acquires a shape substantially conforming to a shape of the cutting edges, thereby providing tight-fitting abutting contact between the surface and the portion having the portion incorporating the cutting edges. The portion of the first member is then inserted into the orifice to generate the abutting contact between the surface and the portion incorporating the cutting edges. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the drawings illustrating embodiments of the present invention:  
       FIG. 1  is a side view of a halfshaft axle bar incorporating rotational coupling features in accordance with a first embodiment of the method of the present invention;  
       FIG. 2  is an enlarged view of a portion of the axle bar shown in  FIG. 1 ;  
       FIG. 3  is an end view of a hub of a tripot-type joint assembly incorporating rotational coupling features in accordance with the first embodiment of the method of the present invention;  
       FIG. 4  is a side cross-sectional view of a tripot-type joint assembly incorporating the axle bar of  FIG. 1  and the hub of  FIG. 3 ;  
       FIGS. 5 and 6  are side views showing the assembly of  FIG. 4  being engaged by a staking tool in accordance with the first embodiment of the method of the present invention;  
       FIG. 7  is a side view of a halfshaft axle bar incorporating rotational coupling features in accordance with a second embodiment of the method of the present invention;  
       FIG. 8  is an end view of a hub of a tripot-type joint assembly incorporating rotational coupling features in accordance with the second embodiment of the method of the present invention;  
       FIG. 9  is an enlarged view of a portion of the assembly shown in  FIG. 8 ; and  
       FIG. 10  is a cross-sectional side view of the hub shown in  FIG. 8  showing the extent of interfering splines along an interior orifice of the hub. 
    
    
     DETAILED DESCRIPTION  
       FIGS. 1-6  show rotational coupling between a first member  12  and a second member  14  in accordance with a first embodiment of the method of the present invention. In the embodiment shown in  FIGS. 1-6 , first member  12  is in the form of a halfshaft axle bar and second member  14  is a hub of a tripot-type joint assembly. U.S. Pat. Nos. 6,390,926 and 6,533,667 disclose examples of representative tripot joint assemblies including the basic components described herein, and are incorporated herein by reference.  
      Referring to  FIGS. 1 and 2 , axle bar  12  includes an insertion portion  12   a  sized for insertion into a complementary orifice  14   a  ( FIG. 3 ) formed in hub  14 . A chamfer  12   m  may be provided on an end of axle bar portion  12   a  to align the axle bar with hub orifice  14   a  and to ease initial insertion of the axle bar into the hub orifice.  
      Referring to  FIGS. 3 and 4 , hub orifice  14   a  includes a plurality of internal splines  14   b  extending along an interior of the orifice in the direction of insertion of axle bar portion  12   a  into orifice  14   a . End portions of splines  14   b  have sharp corners defining cutting edges  14   c  therealong for engaging a surface  12   b  of axle bar insertion portion  12   a  during insertion of the insertion portion into the orifice, in a manner described in greater detail below. More specifically, in the embodiment shown in  FIGS. 1-6 , axle bar insertion portion  12   a  and splines  14   b  extending along the interior of orifice  14   a  are configured relative to each other such that, as insertion portion  12   a  is inserted into in the orifice, cutting edges  14   c  on splines  14   b  engage surface  12   b  of insertion portion  12   a  in a single-pass finish broaching operation to shave a layer of material from surface  12   b  such that the surface acquires a shape substantially conforming to a shape of the cutting edges  14   c.    
      Referring to  FIGS. 3 and 4 , prior to the broaching operation, finished splines  14   b  and cutting edges  14   c  having the desired geometries are broached or otherwise formed along the interior of the hub orifice  14   a . Hub  14  may then be heat-treated as desired to harden the splines and the associated cutting edges. In addition, insertion portion  12   a  of axle bar  12  is formed with a diameter D 1  slightly larger than the inner diameter D 2  of the splined interior portion of the hub. The diameter D 1  of axle bar insertion portion  12   a  and/or the inner diameter D 2  of the internally splined portion of hub orifice  14   a  can be adjusted to regulate the amount of material removed from the surface of insertion portion  12   a  during broaching by controlling the dimensional interference between diameters D 1  and D 2 . As insertion portion  12   a  is to be broached by cutting edges  14   c  formed along hub splines  14   b , the insertion portion is formed from a relatively softer material than the spline cutting edges. Thus, heat treatment of axle bar  12  may be omitted, thereby reducing the component cost of the axle bar.  
      Referring to  FIGS. 1-4 , as axle bar  12  is inserted into hub orifice  14   a  in the direction indicated by arrow “A” ( FIG. 3 ), cutting edges  14   c  formed along end portions of splines  14   b  engage surface  12   b  of axle bar  12  in a single-pass broaching operation to shave a layer of material from surface such that the surface acquires a shape substantially conforming to the shapes of the cutting edges. This provides a close-fitting, substantially gap-free abutting contact between surface  12   a  and cutting edges  14   c , thereby substantially eliminating the rotational backlash found in rotational couplings which use conventionally formed interengaging splines. As shown in  FIG. 4 , splines  14   b  extend backward from cutting edges  14   c  in a direction substantially parallel with the insertion direction (indicated by arrow “A” in  FIG. 4 ). Thus, as cutting edges  14   c  cut along insertion portion surface  12   b , the surfaces of the splines engage the cut portions of insertion portion  14   a  in a tight-fitting abutting contact, thereby rotationally coupling axle bar  12  to hub  14 .  
      Referring again to  FIGS. 1 and 2 , axle bar  12  includes a chip-breaking portion  12   c  formed therealong for breaking off chips formed during broaching of the axle bar. In the embodiment shown in  FIGS. 1 and 2 , the chip-breaking portion is in the form of a groove formed in a surface of the axle bar adjacent insertion portion  12   a . However, the chip-breaking portion may have any one of numerous alternative structures or locations. In addition, a chip-breaking portion may be formed on hub  14  rather than on the axle bar. Also, the chip-breaking portion may be omitted and any chips formed during broaching removed from the assembly after coupling of the axle bar and the hub.  
      When insertion portion  12   a  is fully inserted into hub orifice  14   a  and splines  14   b  have broached the surface of the insertion portion, axle bar  12  and hub  14  may be secured to each other to prevent relative axial movement of the hub and axle bar, thereby preventing removal of the insertion portion from the hub member orifice. Any one of a variety of methods may be used to secure hub  14  and axle bar  12  together. In one method, a portion of either of axle bar  12  or hub  14  is deformed after insertion of the insertion portion to create an interference between the hub and the axle bar. Referring to  FIGS. 1, 2 ,  5  and  6 , in a particular embodiment, an end portion  12   e  of axle bar  12  is staked by application of a staking tool  16  to deform the end portion of the axle bar radially outwardly, creating a flange  12   d  that abuts and overlaps an outer rim  14   e  of hub  14 . Flange  12   d  aids in preventing withdrawal of insertion portion  12   a  from hub orifice  14   a . As seen in  FIGS. 2, 5  and  6 , end portion  12   e  of axle bar  12  is hollowed out to facilitate alignment with the staking tool. Hollowing of end portion  12   e  also reduces the amount of axle bar material in the center of bar  12  facilitating radially outward spreading of the remainder of the bar material upon application of axial pressure by the staking tool.  
      Generally, the hardness of the particular member (either the hub or the axle bar) incorporating the cutting edges will be greater than the hardness of the member being broached in order to ensure formation of a cut surface which conforms to the shapes of the cutting edges without generation of excessive cutting forces and premature dulling of the cutting edges. Desired levels of bulk or surface hardness of axle bar insertion portion  12   a  and hub interior splines  12   c  may be achieved in a known manner using appropriate heat-treatment cycles after formation of the cutting edges. To reduce the total cost of an assembly to be used in a low-torque application, the portion of the assembly incorporating the cutting edges may be heat-treated, while the portion that is to be broached is not heat-treated. Alternatively, if there is a sufficient disparity between the hardness of the material forming the cutting edge and the material to be broached, heat treatment may not be necessary for either component. Generally, the member or component incorporating the cutting edges is formed from a metal or metal alloy, while the member or component to be broached may be formed from a metal, metal alloy, or a polymer material.  
      Although the method of the present invention is described as applied to a tripot joint assembly hub and a halfshaft axle bar, the method described herein is also suitable for rotationally coupling a wide variety of other components or assemblies.  
       FIGS. 7-10  show rotational coupling between a first member  112  and a second member  114  in accordance with a second embodiment of the method of the present invention. Features in  FIGS. 7-10  similar to those shown in  FIGS. 1-6  have element numbers similar to those shown in  FIGS. 1-6 . Referring to  FIGS. 7-10 , a plurality of external splines  112   s  is formed along an exterior of insertion portion  112   a  of an axle bar  112 . Splines  112   s  extend along insertion portion  112   a  in the direction of insertion of portion  112   a  into a hub orifice  114   a . Sharp corners defining cutting edges  112   t  are formed along end portions of splines  112   s  for engaging interior surfaces of the orifice  114   a  ( FIG. 8 ) in a single-pass broaching operation during insertion of axle bar insertion portion  112   a  into the orifice. Once formed, external splines  112   s  are then heat-treated in the conventional manner to provide sufficient surface hardness for the broaching operation.  
      In addition, a plurality of complementary internal splines  114   c  is formed extending along an interior of the orifice for engagement with external splines formed along insertion portion  112   a . As seen from  FIGS. 8-10 , hub internal splines  114   c  have portions configured to provide interferences  114   g  with cutting edges  112   t  formed along the end portions of first member external splines  112   s  when insertion portion  112   a  is aligned with orifice  114   a  just prior to insertion into the orifice. Interferences  114   g  prevent external splines  112   s  of insertion portion  112   a  from being inserted into orifice  114   a  without deformation of internal splines  114   c.    
      Internal interfering splines  114   c  in along hub orifice  114   a  may be formed in any one of several ways. For example, in a first step, a plurality of internal splines that are complementary to axle bar external splines is formed along the interior of orifice  114   a , thereby providing cavities suitable for receiving corresponding ones of the external splines therein. Portions of the internal splines are then deformed such that the deformed portions of the internal splines interfere with the cutting edges on the axle bar during insertion of the axle bar into the orifice. Alternatively, the internal wall defining the hub orifice may be broached to provide internal splines having the desired profile in a single step. Once formed, internal splines may be subjected to a limited heat-treating operation, if desired.  
      Referring to  FIGS. 9 and 10 , interference portions  114   g  extend a predetermined distance D 3  along internal splines  114   c . This distance may be varied according to design requirements. External splines  112   s  along axle bar  112  will engage interference portions  114   g  along length D 3  during insertion of the axle bar into hub orifice  114   a.    
      The method of rotationally coupling axle bar  112  and hub  114  is substantially the same as described for the embodiment shown in  FIGS. 1-6 . As insertion portion  112   a  is inserted into hub orifice  114   a , cutting edges  112   t  contact the interfering end portions  114   g  of hub splines  114   c  and engage the interfering portions in a single-pass broaching operation that shaves a thin layer of material from the hub splines during insertion. This provides a close-fitting, substantially gap-free abutting contact between internal splines  114   c  and cutting edges  112   t  and splines  112   s , thereby substantially eliminating the rotational backlash found in rotational couplings which use conventionally formed interengaging splines. Engagement between internal splines  114   c  and insertion portion  112   a  incorporating the external splines provides rotational coupling of axle bar  112  to hub  114 .  
      The method for providing rotational coupling described herein provides several important advantages over conventional methods. The requirement for component heat-treatment is obviated or reduced, thereby reducing component fabrication costs. The need for a conventional external spline rolling operation is also obviated, further reducing costs. In addition, the method described herein for rotationally coupling the components provides an extremely tight fit between the components, thereby substantially eliminating rotational backlash between the coupling features of the components. Furthermore, as all of the mating splines are in intimate contact with each other, all of the splines act to transmit the applied torque and the forces on the splines are more evenly distributed, resulting in more efficient use of the component.  
      The foregoing description of several expressions of embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.