Patent Publication Number: US-2010119300-A1

Title: Outer joint member for constant velocity universal joint

Description:
TECHNICAL FIELD 
     The present invention relates to an outer joint member for a constant velocity universal joint and a manufacturing method therefor. 
     BACKGROUND ART 
     A constant velocity universal joint (tripod type constant velocity universal joint, for example) includes, as main components, an outer joint member, a tripod member serving as an inner joint member, and a roller serving as a torque transmitting member. 
     An example of the outer joint member is one including a bottomed cylindrical cup portion and a flange portion fitted onto the cup portion so as to protrude therefrom. Track grooves extending axially are formed at trisected positions in a circumferential direction of an inner periphery of the cup portion. An inner surface of the cup portion exhibits, when viewed at a section orthogonal to the axial direction, a non-cylindrical shape in which large diameter portions and small diameter portions exist alternately. In the cup portion, the three track grooves extending axially are formed in an inner surface thereof by being provided with the large diameter portions and the small diameter portions. 
     In the case of forming the above-mentioned outer joint member, there is used, for example, a method in which the cup portion and the flange portion are integrally formed by cold forging or hot forging (Patent Document 1). Further, as illustrated in  FIG. 6 , there is also used a method in which the cup portion and the flange portion are formed as separate members (cup member  101  and flange member  102 ), and both the members are fixed by welding. Specifically, the flange member  102  is mounted to the cup member  101  by forming a protrusion  108  having a small diameter and protruding axially to a bottom portion  112  of the cup member  101 , fitting (press-fitting) the flange member  102  onto the protrusion  108 , and then welding one axial end of a fitting portion therebetween while forming a round welding track  118  as illustrated in  FIG. 7 . Patent Document 1: Patent Application Laid-open No. Hei 07-185730 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the method described in Patent Document 1, when adopting the cold forging, a degree of processing is high and hence it is difficult to mold the flange. When adopting the heat forging, it is necessary to provide a final inner dimension by performing a separate processing such as broaching after a forging step, and hence the number of manufacturing steps is increased. Further, in the case of performing a heat treatment after broaching, the broaching is conceivably performed by feed-backing the amount of deformation involved in the heat treatment. However, taking the processing mode of the broaching into consideration, it is difficult to perform feed back control. 
     Further, in the method in which the cup portion and the flange portion are fixed by welding, treatment of a bead portion  113  (welding trace formed on the welded portion) formed as a result of the welding becomes a problem. That is, the bead portion  113  is normally raised with respect to a surface of a base material, and hence, when the bead portion  113  protrudes from an end surface  111  (mounting end surface) for mounting the flange portion  102  to other member, the other member cannot be mounted with accuracy to the mounting end surface  111 . In this case, it is necessary to eliminate a raise of the bead portion  113  by post-processing such as cutting. Therefore, cutting step is required, thereby leading to a disadvantage that the number of processing steps and manufacturing cost are increased. 
     In view of the above-mentioned problems, the present invention provides an outer joint member for a constant velocity universal joint, which can be manufactured at low cost. 
     Means for Solving the Problems 
     An outer joint member for a constant velocity universal joint according to the present invention includes: 
     a cup member having a bottom portion at one axial end thereof; and 
     a flange member mounted to the cup member,
         the cup member being provided with a protrusion having a small diameter at the one axial end thereof, the flange member being fitted to an outer diameter surface of the protrusion, and the flange member having an inside surface which is bonded to the outer diameter surface of the protrusion by welding. A relief portion into which molten metal flows is formed in a fitting portion between an outer surface of the cup member and the inside surface of the flange member.       

     In the outer joint member for the constant velocity universal joint according to the present invention, at the time of welding of the cup member and the flange member, the molten metal flows into the relief portion provided in the fitting portion between the outer surface of the cup member and the inside surface of the flange member. This inflow of the molten metal occurs when, as illustrated in  FIG. 5A , the base material is melted in part of a contour of the relief portion  9  and the molten metal  19  flows into the remained relief portion  9 , or when, as illustrated in  FIG. 5B , the base material is melted in a region including the entire contour of the relief portion  9  and the molten metal flows into a region where the relief portion has once existed. In both the cases, the molten metal is received in the relief portion by the volume thereof. Therefore, the raise of the bead portion generated after the welding can be reduced or eliminated. As a result, it is possible to simplify or omit elimination process of the bead portion, and hence it is possible to make the manufacturing cost of the outer joint member low. 
     By providing the relief portion in another axial end of the fitting portion, a welding depth becomes deeper, and hence welding strength can be increased. 
     Two modes can be exemplified as a mode of the flange member. One is a mode in which the inside portion thereof is thinned, and one axial end of the fitting portion is positioned on a side of the another axial end with respect to the mounting end surface, which is to be mounted to other member, of the flange member ( FIG. 3 ). The other is a mode in which the inside portion has a uniform thickness over the entire portion in the radial direction thereof ( FIG. 4 ). The former has an advantage that, even when the bead portion is slightly raised from a surface of the base material after welding, elimination process thereof is not required. The latter has a merit that the inside portion of the flange is not required to be processed, and a press-molded product can be used without processing, and hence the flange member can be manufactured at low cost. 
     In both the modes, by setting a protruding amount of the bead portion from the mounting end surface to be zero, it is possible to mount other member to the mounting end surface with accuracy. It suffices that the protruding amount of the bead portion with respect to the mounting end surface is zero. That is, the state in which the protruding amount is zero includes a case in which a tip end of the bead portion is on the same level with the mounting end surface, and the case in which it is positioned at the another axial end side and a side of the cup member opening with respect to the mounting end surface. 
     It is preferable that a curvature radius R of the relief portion be 0.2 mm or more to 1 mm or less, and a groove depth be 0.05 mm or more to ⅔ R or less. 
     As welding, it is possible to adopt laser welding or electron beam welding. The laser welding is a method in which a laser beam as a heat source is radiated in a condensed state on mainly metal, thereby locally fusing and solidifying the metal to perform bonding. The electron beam welding is a method in which a filament is heated in a high vacuum, and ejected electrons. are accelerated by high voltage, focused by an electromagnetic coil, and caused to collide with the portion to be welded, thereby converting kinetic energy of the electron beam to heat energy to perform welding. 
     EFFECTS OF THE INVENTION 
     According to the present invention, it is possible to suppress or prevent the bead portion from raising from the surface of the base material. Therefore, it is possible to reduce the number of steps of post-processing for eliminating the raise of the bead portion, or to omit the post-processing itself, whereby the outer joint member can be reduced in cost. 
     By setting the protruding amount of the bead portion from the mounting end surface of the flange member to be zero, a mating member can be mounted with accuracy to the mounting end surface of the flange member. 
    
    
     
         FIG. 1  is a sectional view of an outer joint member before welding, illustrating an embodiment of the present invention; 
         FIG. 2  is a rear view of the outer joint member of  FIG. 1 ; 
         FIG. 3  is a sectional view of the outer joint member, illustrating the embodiment of the present invention; 
         FIG. 4  is a sectional view of an outer joint member, illustrating a second embodiment of the present invention; 
         FIG. 5A  is an enlarged sectional view of a welded portion; 
         FIG. 5B  is a sectional view illustrating a modification example of the welded portion; 
         FIG. 6  is a sectional view of a conventional outer joint member; and 
         FIG. 7  is a rear view of the conventional outer joint member. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
         
           
               1  body portion 
               2  flange member 
               3  outer diameter surface 
               4   a  small diameter inside surface 
               4   b  large diameter inside surface 
               8  protrusion 
               9  relief portion 
               12  bottom portion 
               13  cup member 
               14  mounting end surface 
               18  bead portion 
             S space 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     With reference to  FIGS. 1 to 4 , description is made of a first embodiment of an outer joint member for a constant velocity universal joint according to the present invention. 
     A constant velocity universal joint (tripod type constant velocity universal joint, for example) includes, as main components, an outer joint member, a tripod member which is provided on an inner surface side of the outer joint member and serves as an inner joint member, and a roller serving as a torque transmitting member. The constant velocity universal joint is of a plunging type which allows a relative axial movement between the outer joint member and the inner joint member, which is used as a constant velocity universal joint arranged, for example, at an inboard side (central side of a vehicle body in a vehicle width direction) of a drive shaft of an automobile. 
     As illustrated in  FIG. 3 , the outer joint member includes a cup member  13  having a tubular body portion  1  and a bottom portion  12  closing an opening on one end side in the axial direction of the body portion  1 , and a ring-shaped flange member  2  mounted to the bottom portion  12  of the cup member  13 . Three track grooves  5  extending axially are formed in an inner surface of the cup member  13 , whereby large diameter portions and small diameter portions are formed alternately at a section orthogonal to the axial direction of the inner surface of the cup member  13 . Note that, in the following description, regarding the axial direction, a side provided with the bottom portion  12  of the cup member  13  is referred to as “one axial end”, and a side provided with the opening of the cup member  13  is referred to as “the other axial end”. 
     As illustrated in  FIG. 2 , the flange member  2  is a flat ring-shaped disk, in which through-holes  11  are provided with a predetermined pitch (180°, for example) along a circumferential direction. A bolt or the like is screwed in each of the through-holes  11 , whereby the outer joint member can be fixed to other member such as a differential. An inside portion of the flange member  2  is thinner than an outside portion thereof. An inside surface of the flange member  2  includes a small diameter inside surface  4   a  and a large diameter inside surface  4   b , the large diameter inside surface  4   b  being formed on the one axial side with respect to the small diameter inside surface  4   a . A shoulder surface  4   c  between the small diameter inside surface  4   a  and the large diameter inside surface  4   b  is flush with an end surface  15  of the bottom portion  12  of the cup member  13 . For example, the flange member  2  can be manufactured by eliminating, after being press-molded, a corner portion on one axial side of the inside portion by turning or the like. 
     On the bottom portion  12  of the cup member  13 , there is formed, by turning or the like, a cylindrical protrusion  8  protruding on the one axial side and having an outer diameter dimension which is smaller than that of other portions. The axial dimension of the protrusion  8  is smaller than a minimum thickness of the bottom portion  12 . A shoulder surface  6  extending radially is formed between the outer surface of the body portion  1  of the cup member  13  and an outer diameter surface  3  of the protrusion  8 . Between the shoulder surface  6  and the outer diameter surface  3  of the protrusion  8 , a groove-shaped relief portion  9  having a partially-arc like section is formed over the entire periphery by turning or the like. 
     Next, there is described a method for bonding the cup member  1  and the flange member  2  together in the outer joint member having the above-mentioned structure. First, the cup member  13  is arranged so that the opening thereof is directed downward. Then, the flange member  2  is fitted onto the protrusion  8  of the cup member  13 , and the shoulder surface  6  of the cup member  13  and an end surface  16  on the other axial side of the flange member  2  are brought into close contact with each other. As a result, the relief portion  9  constitutes a space S divided by the small diameter inside surface  4   a  and the end surface  16  on the other axial end of the flange member  2 . Next, a welding heat source (laser, electric beam, for example) is radiated toward the one axial end between the outer diameter surface  3  of the protrusion  8  and the small diameter inside surface  4   a  of the flange member  2 , and the welding heat source is moved clockwise, for example. As a result, a bead portion  18  as a welding track exhibits a circular shape as illustrated in  FIG. 2 . By this welding, a fitted region including the small diameter inside surface  4   a  of the flange member  2  and the outer diameter surface  3  of the protrusion  8  is melted, thereby integrating the flange member  2  and the cup member  13  together. As illustrated in  FIG. 5A , during the welding, a contour of the relief portion  9  is partially melted, whereby molten metal  19  flows into the remained relief portion  9 , and hence the relief portion is filled with the molten metal  19 . Apart from this, as illustrated in  FIG. 5B , a base material may be melted in a region including the entire contour of the relief portion  9 . 
     In this manner, in the outer joint member for the constant velocity universal joint according to the present invention, the molten metal flows into the relief portion  9  provided to the fitting portion between the cup member  13  and the flange member  2 . Therefore, it is possible to suppress a raise of the bead  18  by the capacity of the relief portion  9   a . In addition, the inside portion of the flange member  2  is formed so as to be thinner in the axial direction, and the axial one end of the fitting portion between the small diameter inside surface  4   a  and the outer diameter surface  3  of the protrusion  3  is provided on the other axial end with respect to a mounting end surface  14  of the flange member  2 . With this structure, it is possible to prevent the bead portion  18  from protruding from the mounting end surface  14  of the flange member  2 , thereby enabling a mating member to be mounted with accuracy to the mounting end surface  19  of the flange member  2 . In this case, it is possible to simplify or omit a turning step of the bead portion  18 , and hence the manufacturing cost of the product (outer joint member) can be reduced. 
     It is preferable to set a curvature radius of the relief portion  9  to be 0.2 mm or more to 1 mm or less, and to set a depth t to be 0.05 or more to ⅔R or less. When R is less than 0.2 and a groove depth t is less than 0.05 mm, the molten metal does not flow into the space S, and hence the bead portion  18  is raised on the surface of the welded portion. When R exceeds 1 mm and the groove depth t exceeds ⅔R, the amount of molten metal flowing into the relief portion is too large to ensure a welding area (volume) necessary for providing the strength of the welded portion. 
     Next, a second embodiment of the present invention is illustrated in  FIG. 4 . In the first embodiment illustrated in  FIGS. 1 to 3 , the thickness of the inside portion of the flange member  2  is smaller than that of the outside portion. However, in the second embodiment, the thickness of the flange member  2  is uniform over the entire portion thereof. The mounting end surface  14  of the flange member  2  and the end surface  15  of the bottom portion  12  of the cup member  13  are provided so as to be flush with each other. The mounting of the flange member  2  according to the second embodiment can be performed in the same manner as in the mounting of the flange member  2  according to the first embodiment. Even when the bead portion  18  after welding is raised, the raised portion is eliminated by post-processing such as cutting, whereby the surface of the bead portion  18  can be set on the same level with the mounting end surface  14  of the flange member  2 . As a result, it is possible to ensure mounting accuracy with respect to the mating member. In this case, by the amount of the molten metal received in the relief portion  9 , the raised amount becomes smaller in comparison with the conventional structure illustrated in  FIG. 6 , and hence cost of post-processing can be reduced. Needless to say, if the bead portion  18  is not raised with respect to the mounting end surface  14  after welding, this kind of post-processing is unnecessary. 
     In the structure according to the second embodiment, the flange member  2  has a simple shape of flat plate, which can be simplified in comparison with that according to the first embodiment. Therefore, the flange member  2  can be manufactured not by cutting or the like but by a low-cost processing such as pressing. Further, welding strength comparable as that in the first embodiment can be ensured even when the axial thickness of the entire flange member  2  is reduced, whereby the flange member  2  can be reduced in weight and material cost. Note that, in the outer joint member for the constant velocity universal joint illustrated in  FIG. 4 , the same components as those of the outer joint member for the constant velocity universal joint illustrated in  FIGS. 1 to 3  are denoted by the same reference numerals as those in  FIGS. 1 to 3 , and description thereof is omitted. 
     The embodiments of the present invention are described above. However, the present invention is not limited to the above-mentioned embodiments, and can be modified variously. For example, the relief portion  9  is not limited to be formed continuously over the entire periphery of the fitting portion, and may be formed intermittently in the circumferential direction. Further, the shape thereof is not limited to the groove-shape. The sectional shape of the relief portion  9  is also arbitrary, and it is also possible to form the relief portion  9  having other sectional shape other than the partially-arc shape. Further, the relief portion  9  may be provided not only on the cup member  13  side but also on the flange member  2  side (for example, a chamfer is provided to a corner portion on the one axial side of the inside surface of the flange member  2 , and the chamfer constitutes the relief portion). Further, welding may be performed not only by moving a welding heat source side (welding rod side), but also by rotating the outer joint member side while radiating the welding heat source on a fixed point. 
     INDUSTRIAL APPLICABILITY 
     The constant velocity universal joint is not limited to the tripod type constant velocity universal joint. The present invention is also applicable to other joint system, such as other plunging type constant velocity universal joint including a double offset type one, and even a constant velocity universal joint including a birfield type one as long as it includes a flange portion on an outer joint member.