Abstract:
Problem to be Solved: 
     A joint whose number of parts is reduced and whose production process is simplified. 
     Means to Solve the Problems: 
     The joint has spherical bodies ( 29   a - 29   d ), a circular cylindrical inner hub ( 20 ) in which hemispherical receiving sections ( 22   a - 22   d ) for receiving the spherical bodies ( 29   a - 29   d ) are formed in curved surfaces, and an outer hub ( 10 ) that has a receiving section ( 17 ) for receiving the inner hub ( 20 ) and also has longitudinal grooves ( 12   a - 12   d ) integrally formed with the receiving section ( 17 ) and in which the spherical bodies ( 29   a - 29   d ) received in the receiving sections ( 22   a - 22   d ) are received.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a joint for use in a power transmission part for automobiles, aircrafts, marine vessels or industrial machinery or the like. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventionally, there has been disclosed “a sliding constant velocity joint comprising 
         [0003]    an outer ring member which is provided with axially extending track grooves at circumferential directional equally divided positions of an inner perimeter surface, 
         [0004]    an inner ring member which is provided with axially extending track grooves at circumferential directional equally divided positions of an outer perimeter surface, and 
         [0005]    a torque transmitting part interposed between the inner/outer ring members, 
         [0006]    wherein the torque transmitting part is constituted by a journal member provided with a gear part and a roller rotatably supported on the journal member, 
         [0007]    wherein the roller is received in the track grooves of the outer ring member, 
         [0008]    wherein a gear part is provided on a bottom face of the track grooves of the inner ring member, and 
         [0009]    wherein the gear part of the journal member is engaged with the gear part of an inner ring member, so that the journal member can incline relative to the inner ring member.” (See Japanese Patent Laid-Open No. 2000-27881). 
         [0010]    Patent Literature 1: Japanese Patent Laid-Open No. 2000-27881 
       DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0011]    The joint described in the Patent Literature 1 includes a torque transmitting part apart from the outer ring member and the inner ring member. The torque transmitting part is constituted by a journal member provided with a gear part and a roller rotatably supported on the journal member. In addition, the gear part of the journal member is engaged with the gear part of the inner ring member during the manufacturing process. 
         [0012]    Thus, the above joint has problems in that the number of parts is large, and in that a troublesome engaging process is necessary during manufacturing. 
         [0013]    Thus, the object of the present invention is to provide a joint which can solve the above problems. 
       Means for Solving the Problems 
       [0014]    To solve the above problems, the joint of the present invention comprises: 
         [0015]    a plurality of spheres (for example,  29   a - 29   d  in  FIG. 1 ); 
         [0016]    a member (for example,  20  in  FIG. 1 ) wherein hemispherical recesses for receiving the spheres (for example,  22   a - 22   d  in  FIG. 2 ) are formed on a side face of a head (for example,  21  in  FIG. 2 ) and a cylindrical body (for example,  24  in  FIG. 2 ) is located in the head via a neck (for example,  23  in  FIG. 2 ); and 
         [0017]    a hub (for example,  10  in  FIG. 1 ) having a receiving section for receiving the member (for example,  17  in  FIG. 1 ), and a plurality of longitudinal grooves (for example,  12   a - 12   d  in  FIG. 2 ) which are formed integrally with said receiving section and in which the sphere received in the each recess is received. 
         [0018]    The member may be integrally formed with another hub coupled with the hub (for example,  10   FIG. 1 ). In other words, the member may construct one part of the other hub. 
         [0019]    Or, the member may be received between two hubs (for example,  10 ,  10 ′ in  FIG. 6 ). In this case, the member may be preferably provided with recesses for receiving spheres received in each longitudinal groove of the hub and spheres received in another hub coupled with the hub. 
         [0020]    In a bottom of the longitudinal groove, the depth at an opening portion may be preferably shallower than that at a central portion (for example, a shape shown in  12   a - 12   d  in  FIG. 4 ). As a result, the sphere is stopped by said opening portion, so the member and the hub are hard to detach from each other during use. 
         [0021]    The hub and a shaft coupled to said hub may be coupled by threading (for example, a structure shown in  34  in  FIG. 9 ). This is preferably used particularly when the main body of the joint is small. 
         [0022]    In addition, it is preferable that a diameter of the each sphere is in a range of generally ¼-⅛ of the body&#39;s diameter, in consideration of durability of each sphere. Within this range, stress on each sphere in use of the joint does not become excessive so as to influence durability. 
         [0023]    In addition, a prevention part for preventing the member and the hub from detaching from each other may be provided. There are several types of prevention parts. The type to be used may be selected by the wall thickness between the bottom face of the longitudinal groove of the hub and an outer wall of the hub. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    Embodiments of the invention will be described with reference to the drawings. 
       Embodiment 1 
       [0025]      FIG. 1  is an exploded perspective view of a joint according to an embodiment 1 of the present invention. The joint shown in  FIG. 1  is roughly classified into an outer hub  10 , an inner hub  20 , spheres  29   a - 29   d,  and shafts  30 ,  40 , which will be described below. 
         [0026]    In order to couple the outer hub  10  to the inner hub  20 , a head  21  ( FIG. 2 ) of the inner hub  20  is received in a receiving section  17  formed in the outer hub  10 . 
         [0027]    As discussed below, the inner hub  20  is constituted so that hemispherical recesses for receiving the spheres  29   a - 29   d  are formed on a side face of the head  21  and a cylindrical body  24  is located in the head  21  via a neck  23 . In a bottom face of the body  24 , an opening  25  is formed so as to receive the shaft  40 . 
         [0028]    The outer hub  10  has the receiving section for receiving the inner hub  20 , and a plurality of longitudinal grooves which are formed integrally with said receiving section and in which the sphere received in said each recess is received. 
         [0029]    The spheres  29   a - 29   d  are composed of, for example, magnetic substances such as stainless, ceramic, metal or the like, and their sizes are of the order of 4φ (φ: diameter) when the size of the joint itself is that of the following examples. The number of spheres  29   a - 29   d  is not limited to 4. Generally, the number of spheres  29   a - 29   d  may be determined depending on the size of the main body of the joint and material (hardness). In addition, the diameter of spheres  29   a - 29   d  may range from generally ¼-⅛ of the diameter of the body  24  ( FIG. 2 ) of the inner hub  20 , in consideration of durability of spheres  29   a - 29   d.    
         [0030]      FIG. 2  ( a ) is a side view of the inner hub  20  in  FIG. 1  seen from a screw hole  26   b  side.  FIG. 2  ( b ) is a side view of the inner hub  20  seen from a head  21  side.  FIG. 2  ( c ) is an enlarged view near a sphere receiver  22   a  in  FIG. 2  ( b ). 
         [0031]    The inner hub  20  is made of plastic, metal or the like. The inner hub  20  includes an almost cylindrical head  21  in which hemispherical sphere receivers  22   a - 22   d  receiving a plurality of spheres  29   a - 29   d  are formed on a curved surface. In this case, a hemispherical shape also includes an almost conical shape (a shape having a V-shaped cross section shown in  FIG. 2  ( a )). Grease is applied between the spheres  29   a - 29   d  and the sphere receivers  22   a - 22   d.  The inner hub  20  includes the body  24  in which an opening  25  for receiving a shaft  40  is formed in the bottom face and screw holes  26   a,    26   b  for receiving screws  46 ,  48  to screw the shaft  40  received in the opening  25  from its side face are formed in the side face. Further, the inner hub  20  includes the neck  23  which performs functions of connecting the head  21  to the body  24  and allowing a curve between shafts  30 ,  40 . 
         [0032]    In addition, an example of sizes of the inner hub  20  is as follows. 
         [0033]    Head  21 
       a diameter at an end face: 12.4 mm   a diameter at a boundary with the neck  23 : 12.7 mm   a length: 6.7 mm   a length of the end face to the bottom of sphere receivers  29   a - 29   d:  3.7 mm   a length from a shaft center to the bottom of sphere receivers  29   a - 29   d:  4.47 mm   a depth from the diameter at the boundary with the neck  23  to the bottom of sphere receivers  29   a - 29   d:  1.88 mm   an opening diameter of sphere receivers  29   a - 29   d:  4.8-5.0 mm       
 
         [0041]    Neck  23 
       a length from the boundary with the head  21  to a head  21  side of a small-diameter section: 2.8 mm   a small-diameter section in diameter: 9.2 mm   a length from the head  21  side of the small-diameter section to the boundary with the body  24 : 4.5 mm   an angle of the portion directed from the body  24  to the small-diameter section: 67 degrees       
 
         [0046]    Body  24 
       a diameter: 20 mm   a length: 13 mm   a length from an end face to shaft centers of screw holes  26   a,    26   b:  5 mm   a diameter of the opening  25 : 5.7 mm   a depth of the opening  25 : 12 mm   a diameter of the screw holes  26   a,    26   b:  3.35 mm       
 
         [0053]    In addition, the inner hub  20  may be die casted, but for example, sphere receivers  22   a - 22   d  may be also formed such as by excavating. 
         [0054]      FIG. 3  ( a ) is a side view of the outer hub  10  in  FIG. 1  seen from the opening  15  side.  FIG. 3  ( b ) is a cross section of the outer hub  10 .  FIG. 3  ( c ) is a side view of the outer hub  10  seen from a receiving section  17  side. 
         [0055]    The outer hub  10  is made by plastic, metal or the like. The outer hub  10  includes a first part  11  which comprises a receiving section  17  receiving the head  21  of the inner hub  20 , and a plurality of longitudinal grooves  12   a - 12   d  which are integrally formed to the receiving section  17  at constant intervals and in which spheres  29   a - 29   d  received in each sphere receiver  22   a - 22   d  are received. The outer hub  10  includes a second part  13  in which the opening  15  for receiving the shaft  30  is formed in the bottom face, and screw holes  16   a,    16   b  receiving screws  36 ,  38  to screw the shaft  30  received in the opening  15  from its side face are formed in the side face. In addition, an example of sizes of the outer hub is as follows. 
         [0056]    A first part  11 :
       a depth of the receiving section  17  of 13 mm,   a longitudinal length of longitudinal grooves  12   a - 12   d  of 10.5 mm,   a length from the bottom of the longitudinal groove  12   a  to the bottom of the longitudinal groove  12   d  of 17 mm,       
 
         [0060]    A second part  13 :
       a diameter of 20 mm,   a length of 11 mm,   a length from the end face to the shaft center of screw holes  16   a,    16   b  of 5 mm,   a diameter of the opening  15  of 5.7 mm,   a depth of the opening  15  of 11 mm,   a diameter of screw holes  16   a,    16   b  of 3.35 mm.       
 
         [0067]    If each size of the outer hub  10  and the inner hub  20  is changed so as to be substantially similar to the illustrated size, the overall size of the joint can be changed. However, if the difference between the hardness of the outer hub  10  and the inner hub  20  and the hardness of spheres  29   a - 29   d  is large, the number of spheres  29   a - 29   d  may be changed so that ones having a lower hardness do not deform in use of the joint. Generally, if the joint is increased, the number of spheres may be increased. 
         [0068]    In addition, the outer hub  10  may be die casted, but for example, longitudinal grooves  12   a - 12   d  may be also formed such as by excavating. 
         [0069]    Shafts  30 ,  40  are composed of stainless, ceramic or the like, and their sizes are of the order of the openings  15 ,  25 , and of the order of 6φ when the size of the joint itself is that of the above examples. 
         [0070]    Thus, the joint of the present embodiment comprises three parts: an outer hub  10 , an inner hub  20 , and spheres  29   a - 29   d.  Moreover, the joint of the present embodiment does not need a complicated structure. Even in the case of such a joint, a uniform velocity between coupling objects at the time of rotation has been confirmed. 
       Embodiment 2 
       [0071]      FIG. 4  ( a ) is a cross section of the outer hub  10  according to an embodiment 2 of the present invention.  FIG. 4  ( b ) is a side view of the outer hub  10  seen from the receiving section  17  side.  FIG. 4  ( c ) is a view showing a state where the outer hub  10  is coupled with the inner hub  20 . In addition, the example where the number of spheres is 6 is shown here. 
         [0072]    As shown in  FIG. 4 , in this embodiment, a longitudinal central portion of the longitudinal grooves  12   a - 12   f  is relatively deeper than the opening portion. In such a outer hub  10 , longitudinal grooves  12   a - 12   f  are formed as in the outer hub  10  shown in  FIG. 3 , and the central portion and the open end are opened such as by excavating. 
         [0073]    In addition, when a hub  20  of the same size is used, the opening portion of longitudinal grooves  12   a - 12   f  of the outer hub  10  according to the embodiment 2 is not deeper than the opening portion of longitudinal grooves  12   a - 12   d  of the outer hub  10  according to the embodiment 1. Then, the central portion of longitudinal grooves  12   a - 12   f  of the outer hub  10  according to the embodiment 2 is for example excavated to a depth equal to that of longitudinal grooves  12   a - 12   d  of the outer hub  10  according to the embodiment 1. 
         [0074]    Concretely, in the case of the outer hub  10  shown in  FIG. 3 , a length from the bottom of the longitudinal groove  12   a  to the bottom of the longitudinal groove  12   d  is 17 mm, whereas in the case of the outer hub  10  shown in  FIG. 4 , a length from the bottom of the opening portion of the longitudinal groove  12   a  to the bottom of the opening portion of the longitudinal groove  12   d  is 16.3 mm. 
         [0075]    When the inner hub  20  is inclined around 35 degrees with respect to such an outer hub  10 , the distance between spheres  29   a,    29   d  in top and bottom direction in  FIG. 4  ( c ) can be less than or equal to the distance between longitudinal grooves  12   a,    12   d.  Therefore, by inserting the inner hub  20  into the receiving section  17  with an inclined state, the outer hub  10  can be coupled with the inner hub  20 . 
         [0076]    If, after the coupling between the inner hub  20  and the outer hub  10 , the angle between the inner hub  20  and the outer hub  10  is lost, spheres  20   a - 29   f  are restricted by protruded portions between the central portion and the open end of the longitudinal grooves  12   a - 12   f,  thereby preventing the inner hub  20  and the outer hub  10  from detaching from each other. In addition, in use, if the angle between the inner hub  20  and the outer hub  10  is around 15 degrees, the coupling between the inner hub  20  and the outer hub  10  is secured. 
         [0077]    As discussed above, a joint using the outer hub  10  according to the present embodiment is hard for the inner hub  20  and the outer hub  10  to detach from each other in use. Concretely, when the inner hub  20  and the outer hub  10  are rotated for around  2000  hours as their shaft centers are mutually inclined, in the case of around  15  degrees, they are not detached from each other. 
       Embodiment 3 
       [0078]      FIG. 5  is a variation of  FIG. 3 . In the outer hub  10  shown in  FIG. 5 , eight longitudinal grooves  12   a - 12   h  in total are formed. This outer hub  10  is die casted. 
         [0079]    Here, longitudinal grooves  12   a - 12   d  in  FIG. 5  ( b ) which are located in the vertical or lateral positions are used without excavating the central portion as in the outer hub  10  shown in  FIG. 3 . On the other hand, longitudinal grooves  12   e - 12   h  which are located between longitudinal grooves  12   a - 12   d  in  FIG. 5  ( b ) are used after excavating the central portion as in the outer hub  10  shown in  FIG. 4 . In addition, as has been indicated, longitudinal grooves  12   a - 12   d  are formed so as to be deeper than longitudinal grooves  12   e - 12   h.    
         [0080]    Thus, in this embodiment, the outer hub  10  is die casted so as to use as either type of outer hubs  10  illustrated in the embodiments 1, 2. Therefore, the outer hub  10  shown in  FIG. 5  is mass-produced, and longitudinal grooves  12   e - 12   h  may be machined depending on the application. 
       Embodiment 4 
       [0081]      FIG. 6  is a view showing a joint of the type connecting two outer hubs  10 ,  10 ′ through one joint member  20  to which a plurality of spheres are attached. 
         [0082]      FIG. 6  ( a ) is a cross section of the outer hub  10 .  FIG. 6  ( b ) is a side view of the outer hub  10  seen from the receiving section  17 .  FIG. 6  ( c ) is a side view and a cross section of the joint member  20 .  FIG. 6  ( d ) is a plane view of the joint member  20 .  FIG. 6  ( e ) is a view showing a state where the outer hubs  10 ,  10 ′ are connected to each other through the joint member  20  and axes of the outer hubs  10 ,  10 ′ are made eccentric from each other. 
         [0083]    The joint of each previously mentioned embodiment cannot structurally make the axes of shafts  30 ,  40  eccentric. On the other hand, the joint of the present embodiment can structurally make the axes of shafts  30 ,  40  eccentric, thereby making the axes of shafts  30 ,  40  eccentric. 
       Embodiment 5 
       [0084]      FIG. 7  is an explanatory diagram of a processing step of the outer hub  10  of type shown in  FIG. 3 . In this embodiment, in order to secure the coupling between the outer hub  10  and the inner hub  20  in use, after the outer hub  10  and the inner hub  20  are coupled, bottoms near the open ends of longitudinal grooves  12   a - 12   d  are crushed by means of jigs  51 - 54  such as punch. 
         [0085]    Concretely, as shown in  FIG. 7  ( a ), outer peripheral portions corresponding to longitudinal grooves  12   a - 12   d  of the outer hub  10  are touched toward the shaft center of the outer hub  10  by jigs  51 - 54  having a sharp tip. Here, as shown in  FIG. 7  ( b ), peripheral edges of the outer hub  10  are provided with a step, this step is touched by the tip of the jigs  51 - 54  at a given angle. 
         [0086]    And, in this state, an external force is added to the jigs  51 - 54  toward the shaft center of the outer hub  10 . As a result, in the outer hub  10 , as shown in  FIG. 7  ( c ) and  FIG. 7  ( d ), the outer peripheral portions corresponding to longitudinal grooves  12   a - 12   d  are crushed. The spheres in longitudinal grooves  12   a - 12   d  can arrive at the crushed part, but are restricted by said part. Therefore, the outer hub  10  and the inner hub  20  are not detached from each other. 
         [0087]    Here, the technique shown in  FIG. 7  is devised so that the outer hub  10  and inner hub  20  do not detach from each other. However, when the size of joint increases, the wall thickness from the bottom of longitudinal grooves  12   a - 12   d  to the outer perimeter surface of the outer hub  10  increases, the technique shown in  FIG. 7  may not form an enough crushed part to such an extent that the outer hub  10  and the inner hub  20  do not detach from each other. 
         [0088]    In this case, rather than preventing the outer hub  10  and the inner hub  20  from detaching from each other, as shown in  FIG. 8 , spheres needs not to be detached from sphere receivers even if the outer hub  10  is detached from the inner hub  20 . 
         [0089]      FIG. 8  is a top view and a side view of a cover  60  for preventing spheres from detaching from sphere receivers. Here, the cover  60  with six sphere receivers is shown. 
         [0090]    As shown in  FIG. 8 , the cover  60  comprises a cover body in which an opening  61  is centrally formed, and six piece parts in total including piece parts  60   a,    60   b  rising from the edge of the cover body at a right angle to the cover body. The distance of piece parts  60   a,    60   b  is made smaller than the diameter of the sphere  29   a  or the like. 
         [0091]    The cover  60  is attached in such a manner that the head  21  of the inner hub  20  is covered by the cover  60  after the spheres are received in the sphere receivers. In addition, if the center of the end face of the head  21  in the inner hub  20  (a position corresponding to an opening  61 ) is provided with a screw hole, the cover  60  can be adhered to the inner hub  20  by means of machine screws. Of course, the inner hub  20  and the cover  60  may be adhered to each other with an adhesive. 
         [0092]    If the cover  60  is attached to the inner hub  20  as discussed above, the sphere  29   a  stays at an interval between the piece parts  60   a,    60   b,  as illustrated, and thus is prevented from dropping. 
       Embodiment 6 
       [0093]      FIG. 9  is a view showing an attaching state of shafts  30 ,  40  with respect to joints of various sizes.  FIG. 9  ( a ) is a view showing an example where the diameters of shafts  30 ,  40  are less than or equal to those of the openings  15 ,  25 . In this case, as shown in  FIG. 9  ( a ), first, the tips  34 ,  43  of the shafts  30 ,  40  are screw-cut such that screw holes are formed in the opening  15 ,  25 . Then, the tips  34 ,  43  are coupled with the joint by screwing with nuts  32 ,  42 . In this case, in the outer hub  10 , the receiving sections  17  and the opening  15  are integrally formed, so in order to position the shaft  30  to the outer hub  10 , it is required to use a nut  32 . On the other hand, in the inner hub  20 , since the opening  25  has the bottom, it is not required to use a nut  42 , but the nut  42  may be used for the purpose of the robust coupling between the inner hub  20  and the shaft  40 . 
         [0094]    The coupling technique as shown in  FIG. 9  ( a ) is effective if the joint and the diameters of the shafts  30 ,  40  are small. If diameters of the joint or the like are small, an interval between the side face of the inner hub  20  or the like and the opening  25  is thin and thus forming the screw hole  26   a  or the like shown in  FIG. 1  in the inner hub  20  or the like becomes impossible. As a result, the coupling between the joint and the shafts  30 ,  40  without using the screw  36  is required. Concretely, if the diameter of the inner hub  20  or the like becomes less than or equal to 4φ, it will become difficult to form the screw hole  26   a  or the like. 
         [0095]      FIG. 9  ( b ) is a view showing an example where the diameters of shafts  30 ,  40  are larger than the diameters of the openings  15 ,  25 . In this case, as shown in  FIG. 9  ( b ), first, the tips  34 ,  43  of the shafts  30 ,  40  are screw-cut such that screw holes are formed in the opening  15 ,  25 . Then, the tips  34 ,  43  are coupled with the joint by screwing with the openings  15 ,  25 . In this case, a nut is unnecessary. On the bottom face of tips  34 ,  43 , the shaft  30  can be positioned to the outer hub  10 . Of course, a nut may be used as an aid for the purpose of the robust coupling between the inner hub  20  and the shaft  40  and the robust coupling between the inner hub  10  and the shaft  30 . 
         [0096]      FIG. 9(   c ) is a variation of  FIG. 9(   b ). Compared with the case shown in  FIG. 1 , there is shown an example of the coupling between the shaft  40  and the inner hub  20  where the diameter of the body  24  of the inner hub  20  was relatively made smaller. As shown, the edge of the inner hub  20  is made as a male screw and the edge of the shaft  40  is made as a female screw. Here, a nut  42  is used as an aid. 
       Embodiment 7 
       [0097]      FIG. 10  is a view showing a variation of  FIG. 1 . In  FIG. 10 , a generally C-shaped ring member  100  made of stainless or the like is shown, in addition to those shown in  FIG. 1 . The ring member  100  is of generally C-shaped, and thus has a notch  100   a.  In addition,  FIG. 10  shows a receiver part  110  which is formed in a direction crossing a shorter direction of the longitudinal grooves  12   a - 12   d  and receives the ring member  100 . 
         [0098]    The diameter of the ring member  100  and the diameter of the receiver part  110  are made generally equal. Thus, after the ring member  100  is embedded in the receiver part  110 , the ring member is not detached unless the ring member  100  is intentionally detached from the receiver part  110 . 
         [0099]    The ring member  100  and the receiver part  110 , after having coupled the inner hub  20  with the outer hub  10  once, maintain the coupling. That is, the ring member  100  and the receiver part  110  are used as alternatives to the structures illustrated in  FIG. 4  and  FIG. 7 . 
         [0100]      FIG. 11  is an explanatory diagram of the assembling principle of each member shown in  FIG. 10 .  FIG. 11  ( a )- FIG. 11  ( c ) show side views of the outer hub  10  seen from the receiving section  17  side.  FIG. 11  ( d ) shows one part of the cross section of the outer hub  10 . 
         [0101]    As shown in  FIG. 11  ( a ), the longitudinal grooves  12   a - 12   d,  as described above, are formed in the receiving section  17 . In addition, the receiver part  110  is formed in the longitudinal grooves  12   a - 12   d  or the like by die casting. In fact, if the outer hub  10  is not formed by die casting, the longitudinal grooves  12   a - 12   d  or the like may be provided with the receiver part  110  by means of cutting. 
         [0102]    As shown in  FIG. 11  ( b ), spheres  29   a - 29   d  are received in the longitudinal grooves  12   a - 12   d.  In addition, for illustrative purposes, the inner hub  20  is not illustrated. In fact, spheres  29   a - 29   d  are received in the longitudinal grooves  12   a - 12   d  in a state received in the inner hub  20 . 
         [0103]    As shown in  FIG. 11  ( c ), the ring member  100  is embedded in the receiver part  110 . In this case, the ring member  100  is of generally C-shaped, and thus the diameter can be narrowed by applying a force in an inner diameter direction. The ring member  100  having the narrowed diameter is embedded from the receiving section  17  into the receiver part  110 . Actually, when the ring member  100  arrives at the receiver part  110 , the narrowed diameter expands such that the ring member  100  is fit into to the receiver part  110 . 
         [0104]    To make the ring member  110  received in the receiver part  110  by the above technique, note the following. The notch  100   a  needs to be formed with such a width that the diameter of the ring member  100  is smaller than that of the receiving section  17  if a force is applied to the ring member  100  in an inner diameter direction. In addition, the ring member  100  requires such hardness that the ring member  100  returns to the original shape if a force applied in an inner diameter direction is released. SUS304 can be used as an example. 
         [0105]    As shown in  FIG. 11  ( d ), since the ring member  100  embedded in the receiver part  110  acts as a stopper, the sphere  20   a  received in the outer hub  10  is not detached from the outer hub  10 . In fact, the sphere  20   a  does not fall from the sphere receiver  22   a  in a state received in the outer hub  10 . Therefore, the coupling between the outer hub  10  and the inner hub  20  will be maintained by the sphere  20   a,  the receiver part  110  and the ring member  100 . 
       Embodiment 8 
       [0106]      FIG. 12  is a view showing a variation of  FIG. 2 .  FIG. 12  shows a cross section of the inner hub  20  corresponding to  FIG. 2(   b ). This inner hub  20  without such a stopper as shown in  FIG. 11  is suitable for coupling with the outer hub  10 . 
         [0107]      FIG. 12  shows grooves  28   a,    28   c  formed in the bottoms of the sphere receivers  29   a,    29   c,  and magnets  27   a,    27   c  received in the grooves  28   a,    28   c,  in addition to those shown in  FIG. 2 . 
         [0108]    Now, if the outer hub  10  does not have a stopper, when the outer hub  10  and the inner hub  20  are coupled with each other and used, the outer hub  10  and the inner hub  20  may be mutually detached. In this case, to prevent the sphere  29   a  or the like fall from the sphere receiver  22   a  or the like, the sphere  29   a  or the like is a magnetic substance and the magnet  27   a  or the like is provided in a magnet receiver  22   a  or the like in this embodiment. 
         [0109]    As a result, even if the outer hub  10  and the inner hub  20  are mutually detached, the sphere  29   a  or the like is adsorbed by the magnet  27   a  or the like, and not fallen from the sphere receiver  22   a.    
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0110]      FIG. 1  is an exploded perspective view of a joint according to an embodiment 1 of the present invention; 
           [0111]      FIG. 2  is side views of the inner hub  20  in  FIG. 1  and an enlarged view near a sphere receiver  22   a.    
           [0112]      FIG. 3  is a side view and a cross section of the outer hub  10  in  FIG. 1 . 
           [0113]      FIG. 4  is a cross section, a side view of the outer hub  10  according to an embodiment 2 of the present invention, and a view showing a state where the outer hub  10  is coupled with the inner hub  20 . 
           [0114]      FIG. 5  is a variation of  FIG. 3 . 
           [0115]      FIG. 6  is a view showing a joint of the type connecting two outer hubs  10 ,  10 ′ through one joint member  20  to which a plurality of spheres are attached. 
           [0116]      FIG. 7  is an explanatory diagram of a processing step of the outer hub  10  of type shown in  FIG. 3 . 
           [0117]      FIG. 8  is a top view and a side view of a cover  60  for preventing spheres from detaching from sphere receivers. 
           [0118]      FIG. 9  is a view showing an attaching state of shafts  30 ,  40  with respect to joints of various sizes. 
           [0119]      FIG. 10  is a view showing a variation of  FIG. 1 . 
           [0120]      FIG. 11  is an explanatory diagram of the assembling principle of each member shown in  FIG. 10 . 
           [0121]      FIG. 12  is a view showing a variation of  FIG. 2 . 
       
    
    
     EXPLANATION OF SIGNS 
       [0000]    
       
           10 ,  10 ′: outer hub 
           20 : inner hub 
           29 : sphere 
           30 ,  40 : shaft