Abstract:
A constant velocity joint includes a cylindrical outer cup which has three guide grooves on an inner wall surface thereof, and an inner member which is housed inside of the aforementioned outer cup and has three trunnions. The aforementioned guide grooves are formed to have a large width and to be close to the center of the aforementioned outer cup, and the aforementioned trunnions are formed to have a large width corresponding to the aforementioned guide grooves. Further, annular rollers are mounted on the periphery of the trunnions, and the periphery surfaces of the aforementioned rollers contact rolling surfaces of the aforementioned guide grooves.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a constant velocity joint for joining one transmission shaft to another transmission shaft, and for transmitting drive power through the transmission shafts in a drive power transmitting mechanism of an automobile, for example. 
       BACKGROUND ART 
       [0002]    The present applicant has proposed a constant velocity joint in which a first shaft, which makes up one transmission shaft, and a second shaft, which makes up another transmission shaft, are joined to each other. The constant velocity joint transmits rotational power through the first and second shafts to axles in a drive power transmitting mechanism of an automobile. As disclosed in Japanese Patent No. 4068824, the constant velocity joint has a tubular outer joint member mounted on one end of the first shaft, an inner joint member fitted over the second shaft and which is housed in the outer joint member, and rotors that are mounted rotatably on respective trunnions of the inner joint member. When rotational power from the first shaft is transmitted through the outer joint member and the inner joint member to the second shaft, the first shaft and the second shaft rotate in unison with each other, and the inner joint member is displaced along an axial direction of the outer joint member. 
       SUMMARY OF INVENTION 
       [0003]    It is a general object of the present invention to provide a constant velocity joint which is reduced in size and weight. 
         [0004]    According to the present invention, there is provided a constant velocity joint comprising a tubular outer member, which has a plurality of guide grooves defined in an inner circumferential surface thereof, the guide grooves being spaced from each other and extending in an axial direction, the outer member being coupled to a first transmission shaft, and an inner member, which is inserted in the outer member and coupled to a second transmission shaft, wherein: 
         [0005]    the guide grooves of the outer member have ceilings, and rolling portions provided as flat surfaces substantially perpendicular to the ceilings, the rolling portions being held in abutment against rotors mounted on the inner member, the guide grooves being recessed radially outward with respect to the inner circumferential surface; 
         [0006]    the inner member has a plurality of trunnions inserted respectively in the guide grooves, the rotors being rotatably mounted on respective outer circumferential surfaces of the trunnions; and 
         [0007]    each of the trunnions has spherical surfaces that are arcuate in cross section, and which are fitted in a holder with one of the rotors being rotatably held thereon, and a set of flat surfaces lying perpendicular to an axial direction of a joint hole to which the second transmission shaft is coupled. 
         [0008]    According to the present invention, each of the trunnions includes the spherical surfaces that are arcuate in cross section, and which are fitted in the holder with one of the rotors being rotatably held thereon, and the set of flat surfaces lying perpendicular to the axial direction of the joint hole to which the second transmission shaft is coupled. 
         [0009]    Therefore, the inner member may be smaller in thickness than the constant velocity joint according to the background art, thereby making it possible to reduce the weight of the constant velocity joint including the inner member. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a vertical cross-sectional view of a constant velocity joint according to an embodiment of the present invention; 
           [0011]      FIG. 2  is an enlarged cross-sectional view of the constant velocity joint shown in  FIG. 1 ; 
           [0012]      FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 1 ; 
           [0013]      FIG. 4  is an enlarged cross-sectional view showing the shape of a constant velocity joint according to the background art, in comparison with the constant velocity joint shown in  FIG. 2 ; 
           [0014]      FIG. 5  is a perspective view of an inner member of the constant velocity joint shown in  FIG. 1 ; and 
           [0015]      FIG. 6  is an enlarged cross-sectional view of a constant velocity joint according to a modification. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0016]    A constant velocity joint according to a preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. 
         [0017]    In  FIG. 1 , reference numeral  10  designates a constant velocity joint according to an embodiment of the present invention. 
         [0018]    As shown in  FIGS. 1 through 3 , the constant velocity joint  10  includes a tubular outer cup (outer member)  16  integrally coupled to one end of a first shaft  12 , which makes up one transmission shaft, the outer cup  16  having an opening  14  therein, and an inner member  20  fixed to one end of a second shaft  18 , which makes up another transmission shaft, and which is housed in a hole  16   a  defined in the outer cup  16 . 
         [0019]    The outer cup  16  has three guide grooves  22   a  through  22   c  defined in an inner wall surface thereof and extending axially, the guide grooves  22   a  through  22   c  being angularly spaced from each other by roughly 120 degrees about the axis of the outer cup  16 . Each of the guide grooves  22   a  through  22   c  has a flat ceiling  24 , rolling surfaces (rolling portions)  26  defined by flat surfaces, which lie substantially perpendicular to the ceiling  24  and are held in contact with the outer circumferential surface of a roller  52 , to be descried later, and slanted surfaces  28  that join the ceiling  24  and the rolling surfaces  26  to each other. 
         [0020]    The ceiling  24  extends substantially perpendicular to a central line (axial line) L 1 , which extends from the center A of the outer cup  16  through the transverse center of each of the guide grooves  22   a  through  22   c.  The rolling surfaces  26  lie substantially parallel to the central line L 1 . The slanted surfaces  28  are slightly slanted from opposite ends of the ceiling  24  toward the center A of the outer cup  16 . The central lines L 1  of the outer cup  16  are aligned with the axial lines of trunnions  36   a  through  36   c  of the inner member  20 , which is housed in the outer cup  16 . 
         [0021]    As shown in  FIG. 4 , the guide grooves  22   a  through  22   c  have a widthwise dimension B 1  perpendicular to the central line L 1  of the outer cup  16 , which is greater than the widthwise dimension B 2  of a guide groove  22   a ′ ( 22   b ′,  22   c ′) of a constant velocity joint  10 A (indicated by the two-dot-and-dash lines shown in  FIG. 4 ) according to the background art. The slanted surfaces  28 , which are joined to the ends of the ceiling  24 , include portions that are joined to the rolling surfaces  26  at positions near the outer circumferential surface of the outer cup  16 . 
         [0022]    The guide grooves  22   a  through  22   c,  which include the respective ceilings  24 , are disposed at positions closer (radially inward) to the center A of the outer cup  16  than the guide groove  22   a ′ ( 22   b ′,  22   c ′) of the constant velocity joint  10 A according to the background art. 
         [0023]    The guide grooves  22   a  through  22   c  are thus disposed such that the rolling surfaces  26 , which are located on transverse outermost sides of two adjacent guide grooves  22   a,    22   b,  guide grooves  22   b,    22   c,  and guide grooves  22   c ,  22   a,  are closer to each other as compared with the constant velocity joint  10 A according to the background art. Further, as shown in  FIG. 1 , radially inward bulging portions are provided between two adjacent ones of the guide grooves  22   a  through  22   c  of the outer cup  16 . 
         [0024]    As shown in  FIG. 4 , the bulging portions  30  are narrower in the circumferential direction (in the direction indicated by the arrows C in  FIG. 4 ) than bulging portions  30 ′ of the constant velocity joint  10 A according to the background art. Therefore, the mass of the outer cup  16  is reduced owing to the reduction in size of the bulging portions  30 . 
         [0025]    As shown in  FIGS. 1 through 5 , the inner member  20  includes a ring-shaped spider boss  34  having a penetrating shaft hole  32  defined centrally therein, and three trunnions  36   a  through  36   c  disposed on the outer circumferential surface of the spider boss  34  and projecting radially outward toward the respective guide grooves  22   a  through  22   c.  The trunnions  36   a  through  36   c  are angularly spaced from each other by roughly 120 degrees about the axis of the inner member  20 . The trunnions  36   a  through  36   c  have respective curved portions  38 , each of the curved portions  38  having an arcuate cross section of a prescribed curvature, provided on the respective outer circumferential surfaces thereof. Spline grooves  40 , which extend axially (in the direction indicated by the arrow D in  FIG. 5 ), are defined in the inner circumferential surface of the shaft hole (joint hole)  32 . The second shaft  18  has spline keys  42  fitted respectively into the spline grooves  40 . 
         [0026]    As shown in  FIGS. 3 and 5 , the inner member  20  is formed with a prescribed thickness along the axis of the shaft hole  32  (in the direction indicated by the arrow D), and has one end surface (flat surface)  20   a  and another end surface (flat surface)  20   b,  which are arranged perpendicularly to the axis L 2 . The end surface  20   a  and the end surface  20   b  are joined by gradual curved surfaces to the outer circumferential surface of the spider boss  34 . 
         [0027]    Each of the trunnions  36   a  through  36   c  has a set of flat surfaces  44   a,    44   b  extending perpendicularly to the axis of the shaft hole  32  and lying flush with the respective end surfaces  20   a,    20   b  of the spider boss  34 , together with a set of spherical surfaces  46   a,    46   b  on outer sides thereof, which lie substantially perpendicular to the flat surfaces  44   a,    44   b.  Each of the spherical surfaces  46   a,    46   b  are arcuate in cross section. As shown in  FIG. 2 , each of the spherical surfaces  46   a,    46   b  has a center RC of curvature, which is positionally offset a prescribed distance from the center TC of the trunnions  36   a  through  36   c  toward the spherical surfaces  46   a,    46   b.    
         [0028]    Ring-shaped holders  48  are fitted over the respective trunnions  36   a  through  36   c.  The ring-shaped holders  48  have respective inner circumferential surfaces, each having a flat cross section, which are held in sliding contact with the spherical surfaces  46   a,    46   b  of the trunnions  36   a  through  36   c,  and out of contact with the flat surfaces  44   a,    44   b  (see  FIG. 3 ). In other words, the trunnions  36   a  through  36   c  are slidable along the axial direction of the holders  48 , and are tiltable through a prescribed angle with respect to the holders  48 . 
         [0029]    The trunnions  36   a  through  36   c  are widely formed in directions perpendicular to the axial lines L 1  in association with the respective guide grooves  22   a  through  22   c  of the outer cup  16 , and are displaced radially inward so as to be closer to the spider boss  34  than the inner member of the constant velocity joint  10 A according to the background art (see  FIG. 4 ). 
         [0030]    More specifically, the distance by which the trunnions  36   a  through  36   c  are spaced from the spider boss  34  is smaller than in the constant velocity joint  10 A according to the background art, and the trunnions  36   a  through  36   c  are positioned closer to the spider boss  34  (radially inward) and are wider in the widthwise direction. 
         [0031]    The trunnions  36   a  through  36   c  are angularly movable through prescribed angles in directions indicated by the arrows E with respect to inner circumferential surfaces of the holders  48 . The trunnions  36   a  through  36   c  are also angularly movable in a circumferential direction (the direction indicated by the arrow F in  FIG. 2 ) about the axial directions L 1  of the trunnions  36   a  through  36   c.  The trunnions  36   a  through  36   c  are displaceable in a vertical direction (the direction indicated by the arrow G in  FIG. 2 ) with respect to inner circumferential surfaces of the holders  48 . 
         [0032]    Ring-shaped rollers (rotors)  52  are fitted over the outer circumferential surfaces of the holders  48  with needle bearings  50  interposed therebetween. The needle bearings  50  and the rollers  52  are held in position by washers  56  and circlips  54 , which are fitted in annular grooves defined in the holders  48 . Alternatively, the needle bearings  50  and the rollers  52  can be held in position on the holders  48  only by the circlips  54 , and the washers  56  may be dispensed with. 
         [0033]    The constant velocity joint  10  according to the embodiment of the present invention is basically constructed as described above. Operations and advantages of the constant velocity joint  10  will be described below. 
         [0034]    When the first shaft  12 , which functions as one transmission shaft, rotates about its axis, rotational power of the first shaft  12  is transmitted through the outer cup  16  to the inner member  20 , thereby rotating the second shaft  18  in a given direction. More specifically, rotational power of the outer cup  16  is transmitted through the rollers  52  that ride in the guide grooves  22   a  through  22   c  and the needle bearings  50 , and then the rotational power is transmitted to the trunnions  36   a  through  36   c  through the spherical surfaces  46   a,    46   b,  which are held in contact with the inner circumferential surfaces of the holders  48 . Accordingly, the second shaft  18 , which is fitted in the trunnions  36   a  through  36   c,  is rotated about its axis. 
         [0035]    If the second shaft  18  is tilted by a certain angle with respect to the outer cup  16 , which includes the first shaft  12 , the trunnions  36   a  through  36   c  are slidingly displaced about centers TC thereof in the direction indicated by the arrow E, while the spherical surfaces  46   a,    46   b  of the trunnions  36   a  through  36   c  are held in contact with the inner circumferential surfaces of the holders  48 , as shown in  FIG. 2 . 
         [0036]    The trunnions  36   a  through  36   c  also are displaced along a direction substantially perpendicular to the axial lines L 1 , i.e., in a longitudinal direction (the direction indicated by the arrows H in  FIG. 3 ) while the rollers  52  slide along the guide grooves  22   a  through  22   c  (see  FIG. 3 ). Therefore, rotary motion of the first shaft  12  is smoothly transmitted to the second shaft  18  without being affected by the angle (joint angle) at which the second shaft  18  is tilted with respect to the outer cup  16 . 
         [0037]    According to the present embodiment, as described above, the trunnions  36   a  through  36   c  of the inner member  20  include the spherical surfaces  46   a,    46   b,  which are arcuate in cross section. Centers of curvature of the spherical surfaces  46   a,    46   b  are positionally offset from the centers TC of the trunnions  36   a  through  36   c,  which are positioned on central lines L 1  that pass through the center A of the outer cup  16  and the centers of the guide grooves  22   a  through  22   c,  as compared with the constant velocity joint  10 A according to the background art. Therefore, the trunnions  36   a  through  36   c  are wide in directions perpendicular to the central lines L 1 , and the guide grooves  22   a  through  22   c,  in which the trunnions  36   a  through  36   c  are inserted, also are wide. As a result, the material making up the outer cup  16  is reduced between adjacent ones of the guide grooves  22   a  through  22   c,  thereby making it possible to reduce the weight of the outer cup  16 . 
         [0038]    The bulging portions  30 , which are disposed between adjacent ones of the guide grooves  22   a  through  22   c , are reduced in size, thereby reducing the material of the outer cup  16 , and hence making it possible to reduce the weight of the outer cup  16 . 
         [0039]    Insofar as the width of the trunnions  36   a  through  36   c  is increased, the trunnions  36   a  through  36   c  can be reliably and firmly joined to the spider boss  34 . Therefore, the inner member  20 , which includes the trunnions  36   a  through  36   c,  is increased in rigidity. Furthermore, the inner member  20 , which includes the trunnions  36   a  through  36   c,  is of a flat shape having the end surfaces  20   a,    20   b , which lie perpendicular to the axis of the shaft hole  32  of the inner member  20 . Therefore, the inner member  20  is reduced in size and weight, as compared with the constant velocity joint  10 A according to the background art. The increased width of the trunnions  36   a  through  36   c,  as described above, allows the rigidity and strength of the trunnions  36   a  through  36   c  to be reliably maintained, and increases the range in which the trunnions  36   a  through  36   c  are movable. 
         [0040]    With the constant velocity joint  10  according to the present embodiment, the trunnions  36   a  through  36   c  of the inner member  20  include the spherical surfaces  46   a ,  46   b.  Further, the centers RC of curvature of the spherical surfaces  46   a,    46   b  are offset from the centers TC of the trunnions  36   a  through  36   c,  which are positioned on the central lines L 1  that pass through the center A of the outer cup  16  and the centers of the guide grooves  22   a  through  22   c.  However, the present invention is not necessarily limited to such a structure. 
         [0041]    The present invention also is applicable to a constant velocity joint  100  as shown in  FIG. 6 . The constant velocity joint  100  has an inner member  102  in which the centers RC of curvature of the spherical surfaces  46   a ,  46   b  are aligned with the centers TC of the trunnions  36   a  through  36   c,  which are positioned on central lines L 1  that pass through the center A of the outer cup  16  and centers of the guide grooves  22   a  through  22   c.    
         [0042]    The constant velocity joint according to the present invention is not limited to the above embodiment, but may adopt various alternative arrangements without departing from the scope of the invention as set forth in the appended claims.