Abstract:
Disclosed is a caulking tool used for a ring gear press-fit in the outer periphery of a flange of a differential case constituting a differential subassembly, in order to caulk a caulking portion provided on at least either end of the flange in the axial direction, with respect to a plurality of notches formed in at least either end of the ring gear in the axial direction. The notches are formed along the inner periphery of the ring gear. Each notch has a bottom part slanted at a predetermined angle with respect to the radial direction of the ring gear, and a plurality of protrusions which correspond to the notches and are projected from the slant portion, in order to press the caulking portion in the axial direction of the ring gear.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a 371 national phase application of PCT/JP2010/061528 filed on 7 Jul. 2010, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is related to a differential sub-assembly to be mounted on a vehicle and, more particularly, to a method for caulking or fixing a ring gear to a flange, the ring gear being press-fitted to an outer periphery of a differential case constituting the differential sub-assembly, a caulking tool used for the method, and a ring gear. 
       BACKGROUND OF THE INVENTION 
       [0003]    Heretofore, as one example of techniques in this field, for example, Patent Document 1 listed below discloses a technique that a ring gear is press-fitted to a flange of a differential case, and after that, inner peripheral edges at both ends of the ring gear are fixed by caulking by caulking portions formed on both ends of the flange. Then, predetermined components as well as the ring gear are assembled to the case, and thereby a differential sub-assembly used for a power transmission mechanism of a vehicle is obtained. 
         [0004]      FIG. 29  shows a partial perspective view of a ring gear  81  in a prior art. On inner peripheral edges at both ends of the ring gear  81 , a plurality of notches  82  are formed as caulked portions to be caulked by a caulking portion of a flange. Heretofore, caulking of the ring gear  81  is performed in such a way that the caulking portion plastically flows in the notches  82 . These notches  82  are formed inside the ring gear  81 , and the ring gear  81  is caulked by press-widening the flange from inside to outside. Patent Documents 2 to 6 listed below are related to a technique of caulking metal components. 
       RELATED ART DOCUMENTS 
     Patent Documents 
       [0000]    
       
         Patent Document 1: EP0647789B1 
         Patent Document 2: JP2003-294114A 
         Patent Document 3: JP56 (1981)-102326A 
         Patent Document 4: JP02 (1990)-075424A 
         Patent Document 5: JP2001-276939A 
         Patent Document 6: JP05 (1993)-076961A 
         Patent Document 7: JP09 (1997)-239480A 
       
     
       SUMMARY OF INVENTION 
     Problems to be Solved by the Invention 
       [0012]    According to a fastening structure in Patent Document 1, a flange of a differential case needs to be strongly press-widened from inside to outside for increasing a fastening strength of the ring gear fastened to the differential case. However, when the flange is strongly press-widened as described, an excessive forming load is applied to the caulking portion, and thereby there is a possibility that a forming performance of the caulking portion is worsened. Further, in  FIG. 29 , the ring gear  81  may suffer from deformation and distortion due to the forming load acting on the ring gear  81 . In particular, when teeth  83  on an outer periphery of the ring gear  81  are distorted, a gear contact pattern of the ring gear  81  with respect to a counterpart gear is worsened, which could result in worsened noise and oscillation properties of the ring gear. 
         [0013]    The present invention has been made to solve the above problems and has a purpose to provide a method for fastening a ring gear by caulking, whereby reducing deformation and distortion of the ring gear when the ring gear is fastened to a differential case by caulking, a caulking tool used for this method, and a ring gear. 
       Means of Solving the Problems 
       [0014]    (Deleted) 
         [0015]    (Deleted) 
         [0016]    (1) One aspect of the present invention to achieve the above-mentioned purpose is to provide a caulking tool for use in caulking a caulking portion formed on at least one of both ends of a flange in an axial direction thereof to a caulked portion formed on at least one of both ends of a ring gear in an axial direction thereof, the ring gear being press-fitted on an outer periphery of the flange of a differential case constituting a differential sub-assembly, wherein the caulked portion is a plurality of notches formed along an inner peripheral edge of the ring gear, each notch including a bottom part slanted at a predetermined angle with respect to a radial direction of the ring gear, and the caulking tool includes: a slant portion slanted at a predetermined angle with respect to the radial direction of the ring gear to press the caulking portion in the axial direction of the ring gear; and a plurality of protrusions protruding from the slant portion, the protrusions being arranged corresponding to the plurality of notches, and each of the protrusions has a shape conforming to a shape of each of the notches and a size smaller than that of each notch. 
         [0017]    According to the configuration in (1), when the caulking tool presses the caulking portion and each notch is closed at a bottom dead center of the caulking portion, each of the protrusions protruding from the slant portion is in point contact with the caulking portion, thus reducing friction between the caulking portion and the protrusions, and thereby a material forming the caulking portion flows around the contact portion. The material of the caulking portion also flows in the vicinity of the bottom part of each notch. 
         [0018]    (2) A second aspect of the present invention to achieve the above-mentioned purpose is to provide a caulking tool for use in caulking a caulking portion formed on at least one of both ends of a flange in an axial direction thereof to a caulked portion formed on at least one of both ends of a ring gear in an axial direction thereof, the ring gear being press-fitted on an outer periphery of the flange of a differential case constituting a differential sub-assembly, wherein the caulked portion is a plurality of notches formed along an inner peripheral edge of the ring gear, and the caulking tool includes: a flat portion extending in a direction intersecting the axial direction of the ring gear to press the caulking portion in the axial direction of the ring gear; a slant portion slanted to a central direction of the ring gear from the flat portion to press the caulking portion; and a holding portion protruding from the flat portion toward the ring gear on an opposite side from the slant portion with respect to the flat portion for holding the caulking portion. 
         [0019]    According to the configuration in (2), the pressing force is hardly applied to the bottom part of each notch when the caulking portion is pressed by the caulking tool. 
         [0020]    (Deleted) 
         [0021]    (Deleted) 
         [0022]    (3) A third aspect of the present invention to achieve the above-mentioned purpose is to provide a method for caulking a ring gear press-fitted on an outer periphery of a flange of a differential case constituting a differential sub-assembly, the ring gear being fastened by use of a caulking tool to caulk a caulking portion formed on at least one of both ends of the flange in an axial direction thereof to a caulked portion formed on at least one of both ends of the ring gear in an axial direction thereof, wherein the caulked portion is a plurality of notches formed along an inner peripheral edge of the ring gear, and the caulking method includes: a pressing step of pressing the caulking portion in the axial direction of the ring gear by use of a first caulking tool so that the caulking portion is deformed toward the ring gear; and a diverting step of, after the pressing step, further pressing the caulking portion by use of a second caulking tool according to a diverting method so that a material forming the caulking portion is filled in the notches. 
         [0023]    According to the configuration in (3), when the caulking portion is pressed by the second caulking tool in the diverting step, a part of the material forming the caulking portion is diverted in flow, and thereby the pressing force is reduced. 
         [0024]    (Deleted) 
         [0025]    (Deleted) 
         [0026]    (Deleted) 
         [0027]    (Deleted) 
         [0028]    (4) A fourth aspect of the present invention to achieve the above-mentioned purpose is to provide method for caulking a ring gear press-fitted on an outer periphery of a flange of a differential case constituting a differential sub-assembly, the ring gear being fastened by use of a caulking tool to caulk a caulking portion formed on at least one of both ends of the flange in an axial direction thereof to a caulked portion formed on at least one of both ends of the ring gear in an axial direction thereof, wherein the caulked portion is a plurality of notches formed along an inner peripheral edge of the ring gear, and the caulking method includes: a first pressing step of pressing the caulking portion by use of the caulking tool so that the caulking portion is deformed toward the ring gear; and a second pressing step of, after the first pressing step, further pressing the caulking portion by use of the caulking tool in the axial direction of the ring gear so that a material forming the caulking portion is filled in the notches. 
         [0029]    According to the configuration in (4), when the caulking portion is pressed by the second caulking tool in the second pressing step, the pressing force can be hardly applied to the bottom part of each notch. 
         [0030]    (Deleted) 
         [0031]    (Deleted) 
         [0032]    (Deleted) 
         [0033]    (Deleted) 
         [0034]    (Deleted) 
         [0035]    (Deleted) 
         [0036]    (5) A fifth aspect of the present invention to achieve the above-mentioned purpose is to provide a ring gear to be press-fitted to an outer periphery of a flange of a differential case constituting a differential sub-assembly, the ring gear being formed with a caulked portion on at least one of both ends in an axial direction, the caulked portion being to be caulked by a caulking portion formed on at least one of both ends in an axial direction of the flange, wherein the caulked portion is a plurality of notches formed along an inner peripheral edge of the ring gear, each notch being of a recess-like shape extending at a uniform depth and a uniform width on an inner peripheral surface of the ring gear, and the plurality of notches are formed in parallel to each other and slanted toward a circumferential direction at a predetermined angle with respect to the axial direction on the inner peripheral surface of the ring gear. 
         [0037]    According to the configuration in (5), since a clearance surface of the notch is reduced, a load applied to the clearance surface from the differential case becomes small when the ring gear is caulked by the caulking portion. In addition to this effect, the plurality of notches are formed obliquely with respect to the axial direction at a predetermined angle, so that mechanical resistance in the axial direction by the notches are increased when the ring gear is press-fitted and caulked to the flange of the differential case. 
       Effects of the Invention 
       [0038]    According to the configurations in (1) to (5), deformation and distortion of a ring gear can be decreased when the ring gear is fastened to a differential case by caulking. Thereby, a ring gear can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a side view showing a schematic configuration of a differential sub-assembly according to a first embodiment; 
           [0040]      FIG. 2  is a sectional view showing a schematic relationship between a flange of a differential case and a ring gear according to the first embodiment; 
           [0041]      FIG. 3  is a partial sectional view of a caulking device used for caulking in the first embodiment; 
           [0042]      FIG. 4  is a schematic sectional view showing a “pressing step” of a fastening method in the first embodiment; 
           [0043]      FIG. 5  is a schematic sectional view showing the “pressing step” of the fastening method in the first embodiment; 
           [0044]      FIG. 6  is a schematic sectional view showing a “caulking step” of the fastening method in the first embodiment; 
           [0045]      FIG. 7  is a partial sectional view of the ring gear in the first embodiment; 
           [0046]      FIG. 8  is a sectional view showing a relationship among notches, a caulking portion, and a caulking tool in the “caulking step” of the first embodiment; 
           [0047]      FIG. 9  is a sectional view showing a relationship among notches of a ring gear, a caulking portion, and a caulking tool in a “caulking step” of a second embodiment; 
           [0048]      FIG. 10  is a sectional view showing a relationship among a sectional shape of the notches, the caulking portion, and the caulking tool in the “caulking step” of the second embodiment; 
           [0049]      FIG. 11  is a sectional view showing a relationship among the sectional shape of the notches, the caulking portion, and the caulking tool in the “caulking step” of the second embodiment; 
           [0050]      FIG. 12  is a sectional view showing a relationship among the sectional shape of the notches, the caulking portion, and the caulking tool in the “caulking step” of the second embodiment; 
           [0051]      FIG. 13  is a sectional view showing a relationship among a notch of a ring gear, a caulking portion, and a caulking tool in a “first pressing step” of a third embodiment; 
           [0052]      FIG. 14  is a sectional view showing a relationship among the notch of the ring gear, the caulking portion, and the caulking tool in a “second pressing step” of the third embodiment; 
           [0053]      FIG. 15  is a sectional view showing a relationship among a notch of a ring gear, a caulking portion, and a caulking tool in a “caulking step” of a fourth embodiment; 
           [0054]      FIG. 16  is a sectional view showing a relationship among a sectional shape of a notch, a caulking portion, and a caulking tool in a “caulking step” of a fifth embodiment; 
           [0055]      FIG. 17  is a sectional view of a modification showing a relationship among a sectional shape of the notches, the caulking portion, and the caulking tool in the “caulking step” of the fifth embodiment; 
           [0056]      FIG. 18  is a sectional view of a modification showing a relationship among the sectional shape of the notches, the caulking portion, and the caulking tool in the “caulking step” of the fifth embodiment; 
           [0057]      FIG. 19  is a sectional view showing a relationship among a notch of a ring gear, a caulking portion, and a caulking tool in a “caulking step” of a sixth embodiment; 
           [0058]      FIG. 20  is a conceptual diagram showing an extension of a material of the caulking portion in the sixth embodiment; 
           [0059]      FIG. 21  is a sectional view showing a relationship among a notch of a ring gear, a caulking portion, and a caulking tool in a “caulking step” of a seventh embodiment; 
           [0060]      FIG. 22  is a sectional view showing a relationship among a notch of a ring gear, a caulking portion, and a caulking tool in a “pressing step” of an eighth embodiment; 
           [0061]      FIG. 23  is a sectional view showing a relationship among the notch of the ring gear, the caulking portion, and the caulking tool in a “diverting step” of the eighth embodiment; 
           [0062]      FIG. 24  is a sectional view of a comparative example showing a relationship among a notch of a ring gear, a caulking portion, and a caulking tool in a “caulking step” of a ninth embodiment; 
           [0063]      FIG. 25  is a sectional view showing a relationship among a notch of a ring gear, a caulking portion, and a caulking tool in the “caulking step” of the ninth embodiment; 
           [0064]      FIG. 26  is a partial perspective view showing an inner peripheral surface side of a conventional ring gear in a tenth embodiment; 
           [0065]      FIG. 27  is a partial perspective view of a ring gear seen from a press-fitting surface side in the tenth embodiment; 
           [0066]      FIG. 28  is a partial front view of a ring gear seen from a press-fitting surface side in an eleventh embodiment; and 
           [0067]      FIG. 29  is a partial perspective view of a ring gear in a prior art. 
       
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       [0068]    A first embodiment illustrating a method for caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0069]      FIG. 1  is a side view showing a schematic configuration of a differential sub-assembly  1 .  FIG. 2  is a schematic sectional view showing a relationship between a flange  3  of a differential case  2  and a ring gear  4 . As shown in  FIG. 1 , the differential sub-assembly  1  includes the differential case  2 , the flange  3  provided on one end (left side in the figure) of an outer periphery of the differential case  2 , and the ring gear  4  of an annular shape fastened to an outer periphery of the flange  3 . In the case  2 , a pair of side gears and a pair of pinions (both are not shown in the figure) are stored and held in a rotatable manner. 
         [0070]    In  FIGS. 1 and 2 , an arrow Th indicates an axial direction of the flange  3  and the ring gear  4 , and an arrow Ra indicates a radial direction of the flange  3  and the ring gear  4  (the arrows Th and Ra similarly indicate the axial and radial directions in the other figures). 
         [0071]    This differential sub-assembly  1  is used for a power transmission mechanism of a vehicle. For example, the differential sub-assembly  1  is provided to a transmission, a transfer, a final reduction gear, and others of a vehicle. The differential sub-assembly  1  is arranged to transmit power, which is inputted from a counterpart gear (not shown) to the ring gear  4 , to a rotation member connected to the pair of pinions as allowing the rotational difference of the pair of side gears. Herein, the rotation member may be such as a left-and-right pair of driving wheels and a front-and-rear pair of driving axles of a vehicle. 
         [0072]    As shown in  FIGS. 1 and 2 , in the present embodiment, the ring gear  4  is formed of a helical gear in which a plurality of teeth  11  are formed on an outer periphery to be oblique with respect to an axial direction of the ring gear  4 . The ring gear  4  is press-fitted on a press-fitting surface  12  as an inner circumferential (peripheral) surface to an outer circumferential (peripheral) surface  21  of the flange  3  and the ring gear  4  is caulked to the flange  3 . Specifically, a caulking portion  22  is formed on one end (left side in  FIG. 2 ) in an axial direction of the flange  3 , and a bank  23  perpendicularly extending from the press-fitting surface  21  is formed on the other end (right side in  FIG. 2 ). The ring gear  4  includes a plurality of notches  13  formed obliquely in the inner peripheral edge at one end of the ring gear  4  in an axial direction thereof. The notches  13  serve as caulked portions to be caulked or crimped by the caulking portion  22 . The configuration of these notches  13  are basically similar to those of the notches  82  of the ring gear  81  in the conventional art shown in  FIG. 29 . The notches  13  are formed along the inner peripheral edge at one end of the ring gear  4  and spaced uniformly from each other. Size of each notch is determined according to a required strength for caulking (the same is the case with the following embodiments). To the notches  13 , caulking is performed by plastically working the caulking portion  22 . The notches  13  are formed inside the ring gear  4 , and caulking is conducted such that the flange  3  is press-widened from inside to outside. 
         [0073]    Then, the notches  13  are caulked by the caulking portion  22  in a state that one end surface  14  of the ring gear  4  is in contact with the bank  23 .  FIG. 3  shows a partial sectional view of a caulking device  61  used for caulking. The caulking device  61  includes a base tool  62  of an annular shape to support the differential case  2 , an outer circumferential tool  63  of a cylindrical shape, which is arranged to surround an outer periphery of the base tool  62 , and a caulking tool  31  of an annular shape, which is formed to be reciprocally movable with respect to the base tool  62 . In the base tool  62 , the case  2  in which the ring gear  4  is press-fitted to the flange  3  is held with the flange  3 . In this holding state, the outer periphery of the ring gear  4  is held by the outer circumferential tool  63 . The caulking tool  31  is driven by an actuator (not shown). The caulking tool  31  is moved downward toward the case  2  and the caulking portion  22  is pressed by the caulking tool  31  so that the ring gear  4  is caulked to the case  2  by the caulking portion  22 . The caulking tool  31  has a lower surface whose outer peripheral portion configured to press the caulking portion  22 . In this manner, the ring gear  4  is fastened to the flange  3  of the case  2  by caulking 
         [0074]    Next, a ring gear fastening method according to the present embodiment will be described.  FIGS. 4 to 6  are schematic sectional views corresponding to  FIG. 2 , showing each step of the fastening method. 
         [0075]    First, in a “press-fitting step” as shown in  FIGS. 4 and 5 , the ring gear  4  is press-fitted on its press-fitting surface  12  to the outer circumferential surface  21  of the flange  3 . At this time, the caulking portion  22  of the flange  3  remains extending in parallel with the outer circumferential surface  21 . Further, as shown in  FIG. 5 , the ring gear  4  is pressed in the axial direction of the ring gear  4  until the one end surface  14  comes into contact with the bank  23  so as to be press-fitted. In this press-fitting state, the press-fitting surface  12  of the ring gear  4  is in close contact with the outer circumferential surface  21  of the flange  3 . 
         [0076]    After that, in a “caulking step” in  FIG. 6 , the caulking portion  22  of the flange  3  is pressed against the notches  13  of the ring gear  4  for caulking by use of the caulking device  61  shown in  FIG. 3 . In this caulking state, the ring gear  4  is positioned in place in the axial direction with respect to the flange  3  and fixed therein. 
         [0077]    A method for caulking the ring gear in the “caulking step” will be explained in more detail. In the caulking method of the present embodiment, the ring gear  4  press-fitted to the outer circumferential surface  21  of the flange  3  of the differential case  2  is fastened by caulking in a manner that the caulking portion  22  provided on one axial end of the flange  3  is caulked to the plurality of notches  13  formed on one axial end of the ring gear  4  by use of the caulking tool  31 . 
         [0078]      FIG. 7  is a partial sectional view of the ring gear  4 .  FIG. 8  is a sectional view showing a relationship among the notches  13 , the caulking portion  22 , and the caulking tool  31  in the “caulking step.” As shown in  FIG. 7 , the plurality of notches  13  formed in the ring gear  4  are slanted at a predetermined angle θ 1  with respect to a radial direction of the ring gear  4 . In other words, each notch  13  has a bottom part  13   a  slanted at a predetermined angle θ 1  with respect to an end surface  15  (an end face opposite to the one end surface  14 ) of the ring gear  4 . In the present embodiment, the predetermined angle θ 1  is set to be in a range of 45° to 85° or more preferably in a range of 50° to 70°. As shown in  FIG. 8 , the predetermined angle θ 1  of the bottom part  13   a  in the present embodiment is larger than a predetermined angle θ 2  (about) 45° of a bottom part of each conventional notch  82 . 
         [0079]    Further, in the “caulking step,” as shown in  FIG. 8 , the caulking portion  22  of the flange  3  is pressed in the axial direction of the ring gear  4  by the caulking tool  31  so that a material forming the caulking portion  22  is filled in the notches  13 . 
         [0080]    According to the caulking method of the present embodiment, the bottom part  13   a  of each notch  13  is slanted with respect to the radial direction of the ring gear  4  at the predetermined angle θ 1  which is larger than the angle in the conventional arts. Thereby, when the caulking portion  22  is pressed in the axial direction of the ring gear  4  by the caulking tool  31 , a component F 1  (indicated with a thick line with an arrow in the figure) of a pressing force applied to the bottom part  13   a  of each notch  13  in the radial direction of the ring gear  4  is smaller than a component F 2  (indicated with a dashed thick line with an arrow in the figure) of a force applied to the conventional notch. To be specific, when caulking, a load acting on the ring gear  4  in the radial direction thereof is extremely small compared to a load acting on the ring gear  4  in the axial direction thereof. As a result, deformation and distortion of the teeth  11  of the ring gear  4  can be decreased when the ring gear  4  is caulked to the flange  3  of the differential case  2 . Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to the counterpart gear and thus exhibit improved noise and oscillation properties. 
       Second Embodiment 
       [0081]    A second embodiment illustrating a method for caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0082]    In the following explanation, same or similar elements as the first embodiment will be given the same reference numerals and not described again, and different point will be mainly explained. 
         [0083]    The present embodiment is different from the first embodiment regarding the configuration of notches  13  formed in a ring gear  4 .  FIG. 9  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , a caulking portion  22 , and a caulking tool  32  in a “caulking step.” As shown in  FIG. 9 , each notch  13  in the present embodiment has a bottom part  13   b  extending along a direction intersecting an axial direction of the ring gear  4  (a radial direction of the ring gear  4 ), i.e., along an end surface  15  in the axial direction of the ring gear  4  and having a uniform depth D 1  from the end surface  15 . 
         [0084]    In a “caulking step,” the caulking portion  22  is pressed in the axial direction of the ring gear  4  by use of the caulking tool  32  so that a material forming the caulking portion  22  is filled in the notches  13  as shown in  FIG. 9 . 
         [0085]    Herein, as shown in  FIG. 9 , the caulking tool  32  has a pressing part  32   a  for pressing the caulking portion  22  in the axial direction of the ring gear  4  and a holding part  32   b  for holding a part of the caulking portion  22  formed opposite from a part to be engaged with the notches  13 . A part of the caulking tool  32  is shown in  FIG. 9 . 
         [0086]    According to the caulking method of the present embodiment, the bottom part  13   b  of each notch  13  of the ring gear  4  extends at a uniform depth D 1  in a direction intersecting the axial direction of the ring gear  4  (the radial direction of the ring gear  4 ). Thereby, when the caulking portion  22  is pressed in the axial direction of the ring gear  4  by the caulking tool  32 , a large part of a pressing force vertically acts on the bottom part  13   b , so that a component of the pressing force hardly acts on the ring gear  4  in the radial direction thereof unlike the component F 2  (indicated with a thick dashed line with an arrow in the figure) acting on the bottom part of the conventional notch. In other words, when caulking, the ring gear  4  is hardly subjected to a load in the radial direction thereof, and a large part of the load is applied to the ring gear  4  in the axial direction thereof. As a result, deformation and distortion of teeth  11  of the ring gear  4  can be reduced when the ring gear  4  is fastened to a flange  3  of a differential case  2  by caulking. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
         [0087]    Examples of a sectional shape of the notches  13  are now illustrated.  FIGS. 10 to 12  show a relationship among a sectional shape of the notches  13 , the caulking portion  22 , and the caulking tool  32  in the “caulking step,” respectively.  FIG. 10  shows the notches  13  each having a rectangular sectional shape,  FIG. 11  shows the notches  13  each having an almost U-shaped sectional shape, and  FIG. 12  shows the notches  13  each having a V-shaped sectional shape. As shown in  FIGS. 10 to 12  respectively, the caulking portion  22  is pressed by the caulking tool  32 , and thereby a part of the material forming the caulking portion  22  is filled in the notches  13  like a wedge in conformity with the sectional shape of each notch  13 . 
       Third Embodiment 
       [0088]    A third embodiment illustrating a method for caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0089]    In the present embodiment, while a configuration of notches  13  formed in a ring gear  4  is similar to that of the conventional art, a caulking method using a caulking tool is different from the configurations in the above-mentioned embodiments.  FIG. 13  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , a caulking portion  22 , and a caulking tool  33  in a “first pressing step” configuring a “caulking step.”  FIG. 14  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , the caulking portion  22 , and a caulking tool  34  in a “second pressing step” configuring the “caulking step.” As shown in  FIGS. 13 and 14 , each notch  13  in the present embodiment is similar to the conventional notch and has a bottom part  13   c  slanted at a predetermined angle θ 2 . 
         [0090]    As shown in  FIG. 13 , in the “first pressing step,” the caulking portion  22  is pressed in an axial direction of the ring gear  4  by use of the first caulking tool  33  so that an end portion of the caulking portion  22  is deformed toward each notch  13  of the ring gear  4 . In this deformed state, the end portion of the caulking portion  22  is separated from each notch  13 . 
         [0091]    Herein, the first caulking tool  33  has a taper surface  33   a  to be in contact with the end portion of the caulking portion  22  as shown in  FIG. 13 . The end portion of the caulking portion  22  is pressed by this taper surface  33   a , and thereby the end portion of the caulking portion  22  is deformed toward each notch  13  of the ring gear  4 . A part of the first caulking tool  33  is shown in  FIG. 13 . 
         [0092]    After that, as shown in  FIG. 14 , in the “second pressing step,” the caulking portion  22  is further pressed in the axial direction of the ring gear  4  by the second caulking tool  34  so that a material forming the caulking portion  22  is filled in the notches  13 . 
         [0093]    As similar to the caulking tool  32  used in the second embodiment, the second caulking tool  34  has a pressing part  34   a  for pressing the caulking portion  22  in the axial direction of the ring gear  4  and a holding part  34   b  for holding a part of the caulking portion  22  formed opposite to a part to be engaged with the notches  13  as shown in  FIG. 14 . A part of the second caulking tool  34  is shown in  FIG. 14 . 
         [0094]    According to the caulking method of the present embodiment, the end portion of the caulking portion  22  is pressed by the taper surface  33   a  of the first caulking tool  33  in the “first pressing step” so that the end portion of the caulking portion  22  is temporarily deformed toward each notch  13  of the ring gear  4 . After that, in the “second pressing step,” the deformed caulking portion  22  is pressed in the axial direction of the ring gear  4  by the second caulking tool  34  so that the material of the caulking portion  22  is filled in the notches  13 . When the caulking portion  22  is pressed by the second caulking tool  34  in the “second pressing step,” the pressing force can be rarely applied to the bottom part  13   c  of each notch  13 . Thereby, when caulking, the load acting on the ring gear  4  in the radial direction thereof becomes extremely small. As a result, deformation and distortion of teeth  11  of the ring gear  4  can be reduced when the ring gear  4  is fastened to a flange  3  of a differential case  2  by caulking. Therefore, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
       Fourth Embodiment 
       [0095]    A caulking tool for use in a method of caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0096]    In the present embodiment, it is premised that a configuration of notches  13  formed in a ring gear  4  is similar to that of the conventional art.  FIG. 15  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , a caulking portion  22 , and a caulking tool  35  in a “caulking step.” The caulking tool  35  includes a flat portion  35   a  extending along a direction intersecting an axial direction of the ring gear  4  (a radial direction of the ring gear  4 ) and a slant portion  35   b  slanted (tapered) toward a central direction of the ring gear  4  from the flat portion  35   a  to press the caulking portion  22  in the axial direction of the ring gear  4 . A part of the caulking tool  35  is shown in  FIG. 15 . 
         [0097]    According to the caulking tool  35  in the present embodiment, in the “caulking step,” the caulking portion  22  is pressed in the axial direction of the ring gear  4  by the caulking tool  35  as shown in  FIG. 15  so that the caulking portion  22  is pressed by the flat portion  35   a  while a part of the caulking portion  22  flows along the slant portion  35   b  to be away from the notches  13  in an opposite direction. Thereby, a material of the caulking portion  22  is filled in each notch  13 . In other words, the caulking portion  22  is subjected to swaging by the flat portion  35   a  and filled in each notch  13 . Therefore, when the caulking portion  22  is pressed in the axial direction of the ring gear  4  by the caulking tool  35 , the pressing force is hardly applied to the bottom part  13   e  of each notch  13 . Thereby, when caulking, a load acting on the ring gear  4  in the radial direction thereof is extremely small. As a result, when the ring gear  4  is fastened to a flange  3  of a differential case  2  by caulking, deformation and distortion of teeth  11  of the ring gear  4  can be reduced. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
       Fifth Embodiment 
       [0098]    A fifth embodiment illustrating a caulking tool for use in a method of caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0099]      FIG. 16  is a sectional view corresponding to  FIG. 10 , showing a relationship among a sectional shape of notches  13 , a caulking portion  22 , and a caulking tool  35  in a “caulking step.” The present embodiment is different from the fourth embodiment regarding the configuration of the notches  13 . To be specific, each notch  13  has a bottom part  13   b  formed along a direction intersecting an axial direction of the ring gear  4  (a radial direction of the ring gear  4 ) and extending at a uniform depth D 1  and has a rectangular sectional shape as shown in  FIG. 16 . Further, the present embodiment is different from the fourth embodiment regarding the configuration of a flat portion  35   a  of the caulking tool  35 . To be specific, the flat portion  35   a  is formed with protrusions  35   c  fittable with the notches  13  as shown in  FIG. 16 . Each of the protrusions  35   c  has a rectangular sectional shape conforming to the sectional shape of each notch  13 . 
         [0100]    According to the caulking tool  35  in the present embodiment, in the “caulking step,” the caulking portion  22  is pressed in the axial direction of the ring gear  4  such that a phase of each protrusion  35   c  conforms to a phase of each notch  13 , and thereby the caulking portion  22  is partially pressed by each protrusion  35   c  as shown in  FIG. 16 . Thus, a part of a material forming the caulking portion  22  is deformed in conformity with the sectional shape of each protrusion  35   c  and filled in each notch  13  like a wedge. Particularly, in the present embodiment, since the caulking portion  22  is partially pressed by each protrusion  35   c , the pressing force to be given to the caulking tool  35  can be reduced compared to the example illustrated in  FIG. 10 . Further, when caulking, a load hardly acts on the ring gear  4  in the radial direction thereof, and a large part of the load is applied to the ring gear  4  in the axial direction thereof. As a result, when the ring gear  4  is fastened to a flange  3  of a differential case  2  by caulking, deformation and distortion of teeth  11  of the ring gear  4  can be reduced. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
         [0101]    Herein, modified examples of sectional shapes of the notches and the protrusions  35   c  are illustrated.  FIGS. 17 and 18  are sectional views corresponding to  FIG. 16 , showing a relationship among a sectional shape of the notches  13 , the caulking portion  22 , and the caulking tool  35  in the “caulking step”, respectively.  FIG. 17  shows the notches  13  each having a rectangular sectional shape and the protrusions  35   c  each having a V-shaped sectional shape.  FIG. 18  shows the notches  13  and the protrusions  35   c  each of both having the V-shaped sectional shape. As shown in  FIGS. 17 and 18 , when the caulking portion  22  is pressed by the caulking tool  35 , the phase of each protrusion  35   c  conforms to the phase of each notch  13 , and thereby the caulking portion  22  is partially pressed by each protrusion  35   c . Therefore, it is confirmed that a part of the material of the caulking portion  22  is deformed in conformity to the sectional shape of each protrusion  35   c  and filled in each notch  13  like a wedge as similar to the example shown in  FIG. 16 . 
       Sixth Embodiment 
       [0102]    A sixth embodiment illustrating a caulking tool for use in a method of caulking a ring gear is described in detail with reference to the accompanying drawings. 
         [0103]      FIG. 19  is a sectional view showing a relationship among notches  13  of a ring gear  4 , a caulking portion  22 , and a caulking tool  35  in a “caulking step” using the caulking tool  35 . The caulking tool  35  in the present embodiment is different from that of the fourth embodiment with the following points. Namely, in addition to the configuration of the caulking tool  35  in the fourth embodiment, the caulking tool  35  of the present embodiment further includes a holding part  35   d  protruding from a flat portion  35   a  toward the ring gear  4  on an opposite side from a slant portion  35   b  with respect to the flat portion  35   a  to hold the caulking portion  22 . In the present embodiment, the holding part  35   d  is tapered toward an outer periphery of the ring gear  4 . A part of the caulking tool  35  is shown in  FIG. 19 . 
         [0104]    According to the caulking tool  35  in the present embodiment, in the “caulking step,” as shown in  FIG. 19 , the caulking portion  22  is pressed in an axial direction of the ring gear  4  so that the caulking portion  22  is pressed by the flat portion  35   a  while a part of the caulking portion  22  flows along the slant portion  35   b  to be away from each notch  13  in the opposite direction, and thereby a material forming the caulking portion  22  is filled in each notch  13 . In other words, the caulking portion  22  is subjected to swaging by the flat portion  35   a  and filled in each notch  13 . Therefore, when the caulking potion  22  is pressed in the axial direction of the ring gear  4  by the caulking tool  35 , the pressing force hardly acts on a bottom part  13   c  of each notch  13 . Thereby, when caulking, a load applied to the ring gear  4  in a radial direction thereof becomes extremely small. As a result, when the ring gear  4  is fastened to a flange  3  of a differential case  2  by caulking, deformation and distortion of teeth  11  of the ring gear  4  can be reduced. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
         [0105]    Further, since the caulking tool  35  in the present embodiment includes the holding portion  35   d  formed opposite to the slant portion  35   b  with respect to the flat portion  35   a , the material forming the caulking portion  22  is prevented from escaping toward the outer periphery of the ring gear  4  by the holding portion  35   d . Therefore, an excessive extension of the material of the caulking portion  22  is prevented, and the deformed caulking portion  22  is prevented from cracking on its outer peripheral edge.  FIG. 20  is a conceptual diagram showing an extension of the material forming the caulking portion  22 . The caulking portion  22  indicated with a solid circle in  FIG. 20  is extremely extended its outer periphery to a position indicated with a chain double-dashed line in the figure by caulking with use of a conventional caulking tool. There is a possibility that cracks CR may occur on the outer peripheral edge of the caulking portion  22 . On the other hand, the extension of the caulking portion  22  can be reduced to a position indicated with a broken line in  FIG. 20  by caulking the caulking portion  22  by use of the caulking tool  35  of the present embodiment, so that a length of the outer periphery becomes relatively short. Accordingly, the cracks on the outer peripheral edge of the caulking portion  22  can be prevented. 
       Seventh Embodiment 
       [0106]    A seventh embodiment illustrating a method for caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0107]    While the configuration of notches  13  of a ring gear  4  in the present embodiment is similar to that of the first embodiment, a caulking method using a caulking tool  36  is different from the above-mentioned embodiments.  FIG. 21  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , a caulking portion  22 , and the caulking tool  36  in a “caulking step.” The caulking tool  36  includes a slant portion  36   a  slanted at a predetermined angle θ 3  with respect to a radial direction of the ring gear  4  to press the caulking portion  22  in the axial direction of the ring gear  4 . A predetermined angle θ 1  of a bottom part  13   a  of each notch  13  is determined larger than the predetermined angle θ 3  of the slant portion  36   a . Namely, a relational expression θ 1 &gt;θ 3  is satisfied. In the “caulking step,” the caulking portion  22  is pressed in the axial direction of the ring gear  4  by the slant portion  36   a  of the caulking tool  36  so that a material forming the caulking portion  22  is filled in each notch  13 . A part of the caulking tool  36  is shown in  FIG. 21 . 
         [0108]    According to the caulking method of the present embodiment, the predetermined angle θ 1  of the bottom part  13   a  of each notch  13  is larger than the predetermined angle θ 3  of the slant portion  36   a  of the caulking tool  36 . Therefore, in the “caulking step,” when the caulking portion  22  is pressed in the axial direction of the ring gear  4  by the caulking tool  36  as shown in  FIG. 21 , a component F 3  (indicated with a bold line with an arrow in the figure) of the pressing force applied to the caulking portion  22  by the slant portion  36   a  in the radial direction of the ring gear  4  becomes relatively small. This component F 3  of the pressing force is small compared to a component F 4  (indicated with a bold broken line with an arrow in the figure) in a case that the predetermined angle θ 3  of the slant portion  36   a  is determined as same as the predetermined angle θ 1  of the bottom part  13   a  as indicated with a chain double-dashed line in  FIG. 21 . Thereby, when caulking, a load applied to the ring gear  4  in the radial direction thereof becomes relatively small. Further, in the present embodiment, the bottom part  13  a of each notch  13  is slanted at the predetermined angle θ 1  which is larger than the conventional art with respect to the radial direction of the ring gear  4 . Therefore, when the caulking portion  22  is pressed by the caulking tool  36 , a component of the pressing force applied to the bottom part  13   a  of each notch  13  becomes smaller than the component applied to the conventional notch. As a result, when the ring gear  4  is fastened to a flange  3  of a differential case  2  by caulking, deformation and distortion of teeth  11  of the ring gear  4  can be reduced. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
       Eighth Embodiment 
       [0109]    An eighth embodiment illustrating a method for caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0110]    While the configuration of notches  13  of a ring gear  4  in the present embodiment is similar to that of the conventional art, a caulking method using a caulking tool in the present embodiment is different from the above-mentioned embodiments.  FIG. 22  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , a caulking portion  22 , and a caulking tool  33  in a “pressing step” configuring a “caulking step.”  FIG. 23  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , the caulking portion  22 , a caulking tool  37 , and others in a “diverting step” configuring the “caulking step.” 
         [0111]    As shown in  FIG. 22 , in the “pressing step,” the caulking portion  22  is pressed in an axial direction of the ring gear  4  by use of a first caulking tool  33  so that an end portion of the caulking portion  22  is deformed toward each notch  13  of the ring gear  4 . In this “pressing step,” the first caulking tool  33  is moved until the end of the caulking portion  22  comes close to each notch  13 . 
         [0112]    Herein, the first caulking tool  33  has a taper surface  33   a  to be in contact with the end of the caulking portion  22  as shown in  FIG. 22 . The end of the caulking portion  22  is pressed by the taper surface  33   a  so that the end portion of the caulking portion  22  is deformed toward each notch  13  of the ring gear  4 . A part of the first caulking tool  33  is shown in  FIG. 22 . 
         [0113]    After that, in a “diverting step,” the caulking portion  22  is further pressed by use of a second caulking tool  37  by a diverting method as shown in  FIG. 23 , and thereby a material forming the caulking portion  22  is filled in each notch  13 . 
         [0114]    Diverting dies  38  and  39  are placed on the ring gear  4  to cover each notch  13  and the caulking portion  22 . The diverting dies  38  and  39  create a space inside, and a part of the caulking portion  22  is accommodated in the space. The second caulking tool  37  is held between the diverting dies  38  and  39  in a movable manner for pressing the caulking portion  22  accommodated in the space.  FIG. 23  shows the second caulking tool  37  and parts of the diverting dies  38  and  39 . 
         [0115]    According to the caulking method of the present embodiment, the end portion of the caulking portion  22  is pressed by the taper surface  33   a  of the caulking tool  33  in the “pressing step,” and thereby the end portion of the caulking portion  22  is temporarily deformed toward each notch  13  of the ring gear  4 . After that, in the “diverting step,” the caulking portion  22  is pressed by the second caulking tool  37  to be diverted to the space between the diverting dies  38  and  39  so that the material forming the deformed caulking portion  22  is filled in each notch  13 . Therefore, in the “diverting step,” when the caulking portion  22  is pressed by the second caulking tool  37 , a part of the material of the caulking portion  22  is diverted in the space between the diverting dies  38  and  39  as indicated with a bold line with an arrow FL, and thereby the pressing force inside the space is reduced. Thus, when caulking, a load applied to the ring gear  4  in a radial direction thereof becomes extremely small. As a result, when the ring gear  4  is fastened to a flange  3  of a differential case  2 , deformation and distortion of teeth  11  of the ring gear  4  can be reduced. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
       Ninth Embodiment 
       [0116]    A ninth embodiment illustrating a caulking tool for use in a method for caulking a ring gear according to the present invention is described in detail with reference to the accompanying drawings. 
         [0117]    While the caulking method similar to the seventh embodiment is adopted in the present embodiment, the configuration of the present embodiment is different from that of the seventh embodiment in a manner that a caulking tool  40  is adopted as an improved version of the caulking tool  36  of the seventh embodiment. 
         [0118]      FIG. 24  is a sectional view showing a relationship among notches  13  of a ring gear  4 , a caulking portion  22 , and a caulking tool  36 , shown as a comparative example similar to the seventh embodiment. In the present case, the caulking portion  22  is pressed by the caulking tool  36 , and each notch  13  is closed at the bottom dead center of the caulking tool  36 . At this time, friction between a slant portion  36   a  of the caulking tool  36  and the caulking portion  22  becomes the largest, and thereby the pressing force applied to a bottom part  13   a  of each notch  13  sharply increases. If this pressing force can be reduced, the load applied to the ring gear  4  in a radial direction thereof can further be reduced. 
         [0119]    For the above purpose, a caulking tool  40  which is an improved version of the caulking tool  36  is adopted in the present embodiment.  FIG. 25  is a sectional view showing a relationship among the notches  13  of the ring gear  4 , the caulking portion  22 , and the caulking tool  40 . The caulking tool  40  includes a slant portion  40   a  slanted at a predetermined angle θ 3  with respect to the radial direction of the ring gear  4  and a plurality of raised portions  40   b  protruding from the slant portion  40   a  as corresponding to the plurality of notches  13  of the ring gear  4  to press the ring gear  4  in the axial direction thereof. Each raised portion  40   b  has a shape conforming to a shape of each notch  13  and a size smaller than that of each notch  13 . Specifically, each raised portion  40   b  is of a hemispherical shape and has a curved outer surface. A part of the caulking tool  40  is shown in  FIG. 25 . 
         [0120]    According to the caulking tool  40  of the present embodiment, the similar effects with the caulking tool  36  in the seventh embodiment can be obtained. In addition to this, when the caulking portion  22  is pressed by the caulking tool  40  and each notch  13  is closed at the bottom dead center of the caulking tool  40 , each raised portion  40   b  of the slant portion  40   a  is in point contact with the caulking portion  22 . Thereby, the friction between the caulking portion  22  and the raised portions  40   b  becomes small, and a material forming the caulking portion  22  flows in the vicinity of the contact parts. Also in the vicinity of a bottom part  13   a  of each notch  13 , the material of the caulking portion  22  flows in. Thereby, the pressing force applied to the bottom part  13   a  is reduced. Since the pressing force is reduced as described, the load applied to the ring gear  4  in the radial direction thereof can be further reduced. As a result, when the ring gear  4  is fastened to a flange  3  of a differential case  2  by caulking, deformation and distortion of teeth  11  of the ring gear  4  can be reduced. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
       Tenth Embodiment 
       [0121]    A tenth embodiment illustrating a ring gear to be fastened by a caulking method according to the present invention is described in detail with reference to the accompanying drawings. 
         [0122]    The present embodiment is different from the above-mentioned embodiments regarding the configuration of a plurality of notches formed in a ring gear  4 . 
         [0123]      FIG. 26  is a partial perspective view showing a side of an inner peripheral surface  84  of a ring gear  81  in a conventional art. In  FIG. 26 , in between a plurality of notches  82  which are formed on an inner peripheral edge of the ring gear  81 , clearance surfaces  84   a  of almost triangular shape are formed to be on the same plane surface with the inner peripheral surface  84  of the ring gear  81 . The clearance surfaces  84   a  are the region where a load is applied in a radial direction of the ring gear  81  from a differential case when a caulking portion of the ring gear  81  is caulked. If each of the clearance surfaces  84   a  can be made small, the load applied to the ring gear  81  in the radial direction thereof can be reduced. 
         [0124]    To achieve the above purpose, a shape of each notch of the ring gear  4  is made improvements in the present embodiment.  FIG. 27  is a partial perspective view of a ring gear  4  when seen from a side of a press-fitting surface  12  in the present embodiment. As shown in  FIG. 27 , each of the plurality of notches  13  of the ring gear  4  is of a V-shaped groove-like shape in section, extending at a uniform depth along an axial direction and a uniform width on the press-fitting surface  12  of the ring gear  4 . Each of the clearance surfaces  12   a  formed in between the plurality of notches  13  have a narrow width. In this manner, each clearance surface  12   a  is made as small as possible. 
         [0125]    According to the ring gear  4  of the present embodiment, the clearance surfaces  12   a  of the notches  13  are made small, and thereby the load applied to the clearance surfaces  12   a  by the differential case is reduced when the ring gear  4  is fastened with its caulking portion by caulking. As a result, when the ring gear  4  is fastened to a flange  3  of the differential case by caulking, deformation and distortion of teeth  11  of the ring gear  4  can be reduced. Thereby, the ring gear  4  can maintain a suitable gear contact pattern with respect to a counterpart gear, and thus exhibit improved noise and oscillation properties. 
       Eleventh Embodiment 
       [0126]    An eleventh embodiment illustrating a ring gear to be fastened by a caulking method according to the present invention is described in detail with reference to the accompanying drawings. 
         [0127]    The present embodiment is different from the above tenth embodiment regarding the configuration of the plurality of notches formed in a ring gear  4 .  FIG. 28  is a partial front view of the ring gear  4  when seen from a side of a press-fitting surface  12  in the present embodiment. As shown in  FIG. 28 , in the present embodiment, a plurality of notches  13  formed in parallel to each other on the press-fitting surface  12  of the ring gear  4  are slanted at a predetermined angle θ 5  with respect to an axial direction. This is different from the configuration of the tenth embodiment in which the plurality of notches  13  is formed in parallel with the axial direction. The configuration of the present embodiment is similar to that of the tenth embodiment in a manner that each of the notches  13  is of a V-shaped groove-like shape in section, formed extending at a uniform depth and a uniform width, and each clearance surface  12   a  in between the notches  13  is formed narrow in width. 
         [0128]    According to the ring gear  4  of the present embodiment, in addition to the operational effects of the tenth embodiment, the plurality of notches  13  are slanted at the predetermined angle θ 5  with respect to the axial direction, and thereby when the ring gear  4  is press-fitted to a flange  3  of a differential case and fixed, mechanical resistance by the notches  13  in the axial direction is increased. As a result, fastening force of the ring gear  4  and the flange  3  in the axial direction can be strengthened, and the ring gear  4  and the flange  3  can be hardly separated. 
         [0129]    The present invention is not limited to the above-mentioned embodiments and can be partially modified as appropriate without departing from the essential scope of the invention. 
         [0130]    For example, in the ninth embodiment, the raised portions  40   b  formed in the slant portion  40   a  of the caulking tool  40  are of hemispherical shape. Alternatively, the raised portion may be of half prorate spheroid shape. 
       INDUSTRIAL APPLICABILITY 
       [0131]    The present invention may be applied to a differential sub-assembly used for a power transmission mechanism of a vehicle and manufacturing thereof. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  Differential sub-assembly 
               2  Differential case 
               3  Flange 
               4  Ring gear 
               11  Teeth 
               12  Press-fitting surface (Inner peripheral surface) 
               12   a  Clearance surface 
               13  Notch (Caulked portion) 
               13   a  Bottom part 
               13   b  Bottom part 
               14  One end surface 
               15  End surface 
               21  Outer peripheral surface 
               22  Caulking portion 
               23  Bank 
               31  Caulking tool 
               32  Caulking tool 
               32   a  Pressing portion 
               32   b  Holding portion 
               33  First caulking tool 
               33   a  Taper surface 
               34  Second caulking tool 
               34   a  Pressing potion 
               34   b  Holding portion 
               35  Caulking tool 
               35   a  Flat portion 
               35   b  Slant portion 
               35   c  Protrusion 
               35   d  Holding portion 
               36  Caulking tool 
               36   a  Slant portion 
               37  Second caulking tool 
               38  Diverting die 
               39  Diverting die 
               40  Caulking tool 
               40   a  Slant portion 
               40   b  Raised portion 
             θ 1  Predetermined angle 
             θ 3  Predetermined angle 
             θ 5  Predetermined angle