Abstract:
A constant velocity joint for a drive system having a first rotating shaft and a second rotating shaft coupled with the constant velocity joint, wherein the constant velocity joint comprises: a hollow housing having an opening at one end, and a closing at its opposite end fixed to an end of the first rotating shaft, an inner face of the housing including a plurality of guide grooves extending in an axial direction of the housing and spaced equally apart in a circumferential direction of the housing, each groove having a pair of side faces opposing to each other; and a tripod disposed at an end of the second rotating shaft, having a plurality of trunnions each positioned in a corresponding one of the guide grooves and being spaced equally apart in a circumferential direction of and at an angle normal to the second rotating shaft; and, an inner roller mounted to an outer end portion of each of the trunnions, an outer roller mounted on an outer face of each inner roller with needle rollers engaged between the inner and outer rollers, and allowing the outer face of each outer roller to roll and move in the corresponding one of the guide grooves and for transmitting a load between the first and second rotating shafts to drive the driving system. Each trunnion includes an at least partially spherical surface in a circumferential area subjecting to the load, and a cylindrical protrusion disposed at the at least partially spherical surface and protruded to a distance from the at least partially spherical surface in a direction normal to the axis of the respective trunnion, the cylindrical protrusion having an at least partially spherical surface at its distal end for surface-to-surface contact with an at least partially spherical inner face of the respective inner roller while defining a gap around the cylindrical protrusion and between the at least partially spherical surface of the respective trunnion and the at least partially spherical inner face of the respective inner roller.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a constant velocity joint of tripod type, which is disposed between a drive shaft and a driven shaft coupled to each other and typically used in a drive axle of, for example, an automobile for transmitting rotational torque between the rotating shafts. 
       BACKGROUND OF THE INVENTION 
       [0002]    Tripod type constant velocity joints are well known in the automobile industry as one type of constant velocity joints used in the drive system of automobiles. For instance, one example of the tripod type constant velocity joint was illustrated in Japanese Patent Application, S62-233522 as shown in FIG.  1 and  FIG. 2 . This tripod type constant velocity joint typically includes tripod  15  fixed to an end of the second rotating shaft, which functions as a driven member, and hollow cylindrical housing  13  fixed to an end of the first rotating shaft  12  which functions as a drive member. Grooves  16  are formed at three locations on the inner face of the housing  13  at equal spacing in the circumferential direction and extend in the shaft direction of the housing  13 . 
         [0003]    The tripod  15  comprises a boss  17  connected to the second rotating shaft  14 , and trunnions  18  each having a cylindrical shape and extending radially from three locations at equal spacing around the boss  17 . Each trunnion  18  has a roller  19  fixed at a distal end of the trunnion and with needle rollers  20  engaged therein. In this arrangement, each roller  19  can freely rotate about the trunnion  18  while also be displaced in the axial direction of the trunnion  18 . The constant velocity movement between the first and second rotating shafts is ensured with the rollers  19  rotatably and displaceably engaging in the grooves  16  disposed along the inner face of the housing  13 . In order to facilitate the sliding movement, a pair of side faces  16   a  are formed in circular recesses on each side of the respective grooves  16 , and each roller  19  is supported rotatably and pivotally along the side faces  16   a  of the grooves. 
         [0004]    As the first rotating shaft  12  rotates, its rotational force is transmitted from housing  13 , through roller  19 , needle rollers  20 , trunnions  18 , and to the boss  17  of the tripod  15 . This makes the boss  17  rotate, and which also causes rotation of the second rotating shaft  14 . When the joint angle of the two rotating shafts  12  and  14  is not zero, a central axis of the first rotating shaft  12  is not aligned with that of the second rotating shaft  14 , and each of the trunnion  18  displaces relative to the side face  16   a  of the guide grooves  16  to move around the tripod  15 , as shown in  FIG. 1  and  FIG. 2 . As a result, the rollers  19  supported at the ends of the trunnions  18  move along the axial directions of the trunnions  18 , respectively, while rolling on the side faces  16   a  of the guide grooves  16 . Such movement ensures that a constant velocity between the first and second rotating shaft is achieved. 
         [0005]    When the first and second shafts rotate with a joint angle present, each roller  19  moves with complexity. For example, each roller  19  moves in the axial direction of the housing  13  along each of the side faces  16   a  of the respective guide grooves  16 , while the rollers  19  change in orientation and further displace in the axial direction of the trunnion  18 . Such movement of the rollers  19  cannot cause a relative movement between a peripheral outside face of each of the rollers  19  and each of the side faces  16   a  to be smoothly made. Thus, a relatively large friction occurs between the faces. As a result, this tripod type constant velocity joint produces three-directional axial forces as the shafts rotate. In the application of a tripod joint to the vehicles, it is known that the axial forces may cause a transverse vibration typically referred to as “shudder”, if a large torque is transmitted with a relatively large joint angle present. 
         [0006]    In order to restrain such a shudder problem from occurring, FR 275280 discloses a structure as shown in  FIG. 3 , and U.S. Pat. No. 6,533,668 B2 discloses a structure as shown in  FIG. 4 . In the structure shown in  FIG. 3(   a ), roller  19   a  is guided parallel to the housing groove and spherical trunnion  18  can swing and pivot around an inner spherical roller surface of inner roller  19   b . In this case, the contact area between the inner spherical surface of the inner roller  19   b  and the trunnion  18 , when receiving torque for a load, is of an elliptical shape as shown in  FIG. 3(   b ). It has a longer contact diameter “a” and a shorter contact diameter “b”, because a radius “r” of a longitudinal cross-sectional shape of the spherical trunnion  18  is smaller than a radius “r3” of the trunnion  18 . 
         [0007]    The trunnion and roller structure shown in  FIG. 4  has a structure similar to that shown in  FIG. 3 , however, with certain modifications thereof. The trunnion  18 ′ has an elliptical shape in the cross sectional view taken normal to the trunnion axis, which comprises a shorter diameter “B” in the length not receiving a load, and a longer diameter “A” in the length for receiving a load. This is to make a contact pattern between the inner spherical surface of the inner roller  19   b  and the trunnion  18 ′ closer to a circle, when receiving a torque for a load. As a result, a longer contact diameter a′ in  FIG. 4  becomes smaller than the longer contact diameter a in  FIG. 3  due to the elliptical shape of the trunnion  18 ′. However, it still has an elliptical contact pattern even though the degree of ellipse becomes less than that shown in  FIG. 3  because a curvature of a longitudinal cross-section of the trunnion  18 ′ formed by radius r 2  and R is not equal to a curvature of an axial cross-section of the trunnion  18  formed by an ellipse  18   a  defined as a longer diameter A and a shorter diameter B. 
         [0008]    Moreover, for manufacturing the constant velocity joint of  FIG. 4 , there are considerable difficulties not only to machine a complex spherical surface defined by a curvature of a longitudinal cross-section of the trunnion  18 ′ formed by radius r 2  and R and the ellipse shape  18 ′ defined as a longer diameter A and a shorter diameter B, but also to measure the trunnion  18 ′ having a complex three dimensional profile, in terms of both inspection and quality control. These difficulties cause the contact pattern mentioned above to be inconsistent in terms of quality, which leads to high costs in manufacturing perspective and also to potential quality control issues. 
         [0009]    When these conventional joints rotate with a joint angle present upon receiving loads, as shown in  FIG. 3(   b ) and  FIG. 4(   b ), a pivotal movement of counterclockwise direction of trunnion  18  and  18 ′ causes a pivotal sliding action to take place on the contact ellipse. Then the pivotal sliding action operates as a frictional spinning moment (of a direction indicated by arrows “Ts” in  FIG. 3(   b )) so as to change a rolling direction of the roller assembly  19 , which comprises the inner roller  19   b  and the outer roller  19   a  with needle bearings  20  engaged there-between. As a result, direction of the roller assembly  19  changes and it is in contact with inner or outer face of the guide groove  16 , and thus, increasing a frictional contact force there-between. Moreover, the roller assembly  19  displaces not to parallel to the guide groove  16 . Hence it is difficult for the roller assembly  19  to be smoothly rolled, and causes a significant rolling resistance. 
         [0010]    Moreover, in order to provide grease-entry space for better durability and smooth operation, space “s” is provided between the lower end at the inner face of the inner roller  19   b  and the spherical face of the trunnion  18 , as shown in  FIG. 3(   a ). Alternatively, space “s” can also be provided between the upper and lower ends at the inner face of the inner roller  19   b  and the upper and lower portions of the spherical face of the trunnion  18 , as shown in  FIG. 4(   a ). However, sufficient grease cannot permeate into the space of the upper end between the inner roller  19   b  and the trunnion  18  easily, in the structure shown in  FIG. 3  and  FIG. 4 . In the case shown in  FIG. 3 , space is not provided to the upper end of the trunnion, even in the axial direction thereof, and space in the circumferential direction is smaller than that in the axial direction, due to an ellipse contact in which a longer contact diameter “a” in the circumferential direction is bigger than a shorter diameter “b” in the axial direction, thereby blocking grease from the contact area by the difference of the longer contact diameter and the shorter diameter, especially in terms of the circumferential direction, in the structures shown both in  FIG. 3  and  FIG. 4 . As such, because the space is too narrow to accommodate sufficient grease in the circumferential and axial direction, it is difficult for the grease to be introduced into the space. This becomes more problematic when the grease is in high density condition, for example, during the initial driving stage of automobile particularly at a cold outside temperature, which causes a significant rolling resistance in the drive system. 
         [0011]    A clearance can be provided between the needle roller  20  and the outer roller  19   a  and the inner roller  19   b , all in the radial direction and in the circumferential direction to reduce the rolling resistance. However, the clearance is not sufficient to facilitate the grease to penetrate between the needle roller  20  and the outer roller  19   a  and the inner roller  19   b , because rims  19 a 1  and  19 a 2  inwardly protruded at both circumferential ends of the outer roller  19   a  block the grease from flowing between the needle roller  20 , the outer roller  19   a  and the inner roller  19   b . This inadequate greasing condition causes the needle rollers  20  not to be rolled smoothly between the inner roller  19   b  and the outer roller  19   a.    
       SUMMARY OF THE INVENTION 
       [0012]    One object of the present invention is to provide a tripod type constant velocity joint having a simple structure which is both strong and durable, which can also reduce the frictional spinning force acting on the contact ellipse made between the outer face of the trunnion and the inner face of the inner roller, due to the pivotal sliding movement of the trunnion axis known in the art. The present invention can also provide sufficient lubrication mechanism between the inner race and the trunnion, and between the outer roller, the needle rollers, and the inner roller, to minimize the rolling resistance when rotating with any joint angle present. 
         [0013]    To solve the above described problems and other problems to be recognized by following disclosure, a tripod type constant velocity joint is provided for a drive system, the drive system including first and second rotating shafts coupled with the constant velocity joint, in which the constant velocity joint comprises: a hollow housing having an opening at one end, and a closing at its opposite end fixed to an end of the first rotating shaft, an inner face of the housing including a plurality of guide grooves extending in an axial direction of the housing and spaced equally apart in a circumferential direction of the housing, each groove having a pair of side faces opposing to each other; and a tripod disposed at an end of the second rotating shaft, having a plurality of trunnions each positioned in a corresponding one of the guide grooves and being spaced equally apart in a circumferential direction of and at an angle normal to the second rotating shaft; and, an inner roller mounted to an outer end portion of each of the trunnions, an outer roller mounted on an outer face of each inner roller with needle rollers engaged between the inner and outer rollers, and allowing the outer face of each outer roller to roll and move in the corresponding one of the guide grooves and for transmitting a load between the first and second rotating shafts to drive the driving system. 
         [0014]    Each of the trunnions includes an at least partially spherical surface in a circumferential area subjecting to the load, and a cylindrical protrusion disposed at the at least partially spherical surface and protruded to a distance from the at least partially spherical surface in a direction normal to the axis of the respective trunnion, the cylindrical protrusion having an at least partially spherical surface at its distal end for surface-to-surface contact with an at least partially spherical inner face of the respective inner roller while defining a gap around the cylindrical protrusion and between the at least partially spherical surface of the respective trunnion and the at least partially spherical inner face of the respective inner roller, the gap around the cylindrical protrusion of the respective trunnion allowing a lubricant to introduce in the gap for lubrication. 
         [0015]    Each of the trunnions preferably includes a flat surface in a circumferential area not subjecting to the load and thereby providing larger space between the flat surface and the at least partially spherical inner face of the respective inner roller, the space allowing a lubricant to introduce therein for lubrication. 
         [0016]    Each of the inner rollers preferably includes a pair of grooves each formed at an area subjecting to the load and on the bottom portion of the respective inner roller facing a boss of the tripod, and further includes another pair of grooves each formed at an area not subjecting to the load and on the top portion of the respective inner roller, wherein the respective inner roller is elastically deformable about the pair of grooves formed on the top portion of the inner roller to expand the inner opening of the inner roller to install the corresponding trunnion in the inner roller. 
         [0017]    The cylindrical protrusion has a cross section of circular shape, or alternatively, of elliptical shape. Each of the trunnions may have a central portion recessed or cut out from said cylindrical protrusion for reducing a contact area between the inner rollers and trunnions. 
         [0018]    According to another aspect of the invention, a method of assembling a roller assembly of a constant velocity joint on a trunnion of the joint, comprises the steps of:
       providing a roller assembly for a constant velocity joint, the roller assembly including: an outer roller with a tapered cylindrical surface formed on the inner face of the outer roller; an inner roller with a tapered cylindrical surface formed on the outer face of the inner roller and with at least partially spherical inner face, the tapered outer cylindrical surface of the inner roller having a same taper angle with the tapered inner cylindrical surface of the outer roller, the inner roller including a pair of grooves formed on a bottom portion of the inner roller facing a boss of the trunnion and in a diametric direction, and another pair of grooves formed on a top portion of the inner roller and in a diametric direction perpendicular to the direction of the pair of grooves formed on the bottom portion; and needle rollers for receiving between the inner and outer rollers;   providing a constant velocity joint having a tripod with at least one trunnion, the trunnion including a pair of cylindrical protrusions protruded normal to the axis of the trunnion to a predetermined height from an outer surface of the trunnion, each of the cylindrical protrusions having a generally spherical end surface for contacting with the at least partially spherical inner face of the inner roller;   mounting the outer roller on a shoulder portion of the tripod disposed below the trunnion, in such a manner that the tapered inner cylindrical surface of the outer roller is converged in a radial direction facing a boss of the tripod, the outer roller having the needle rollers assembled in the tapered inner cylindrical surface of the outer roller;   placing the inner roller in an opening defined by the needle rollers assembled in the outer roller with the pair of cylindrical protrusions received in the pair of grooves on the bottom of the inner roller, in such a manner that a tapered cylindrical surface formed on the outer face of the inner roller are converged in the radial direction facing the boss and the pair of grooves on the top portion of the inner race are positioned in the direction not receiving the load; and   applying a gripping force on the upper edges of the inner roller in the direction receiving the load, and forcing the inner opening of the inner roller elastically expanded around the grooves formed on the top portion of the inner roller and in the direction receiving the load, the elastic expansion being within a radial clearance of the roller assembly provided between the tapered cylindrical outer face of the inner roller, the tapered cylindrical inner face of the outer roller, and the needle rollers, and thereby mounting the inner roller to the trunion with the generally spherical end surface of the cylindrical protrusions contacting against the at least partially spherical inner face of the inner roller.       
 
         [0024]    According to another aspect of the invention, a method of assembling a roller assembly of a constant velocity joint on a trunnion of the joint, comprises the steps of:
       providing a roller assembly for a constant velocity joint, the roller assembly including: an outer roller with a tapered cylindrical surface formed on the inner face of the outer roller; an inner roller with a tapered cylindrical surface formed on the outer face of the inner roller and with at least partially spherical inner face, the tapered outer cylindrical surface of the inner roller having a same taper angle with the tapered inner cylindrical surface of the outer roller, the inner roller including a pair of grooves formed on a bottom portion of the inner roller facing a boss of the trunnion and in a diametric direction, and another pair of grooves formed on a top portion of the inner roller and in a diametric direction parallel to the direction of the pair of grooves formed on the bottom portion; and needle rollers for receiving between the inner and outer rollers;   providing a constant velocity joint having a tripod with at least one trunnion, the trunnion including a pair of cylindrical protrusions protruded normal to the axis of the trunnion to a predetermined height from an outer surface of the trunnion, each of the cylindrical protrusions having a generally spherical end surface for contacting with the at least partially spherical inner face of the inner roller;   mounting the outer roller on a shoulder portion of the tripod disposed below the trunnion, in such a manner that the tapered inner cylindrical surface of the outer roller is converged in a radial direction facing a boss of the tripod, the outer roller having the needle rollers assembled in the tapered inner cylindrical surface of the outer roller;   placing the inner roller in an opening defined by the needle rollers assembled in the outer roller with the pair of cylindrical protrusions received in the pair of grooves on the bottom of the inner roller, in such a manner that a tapered cylindrical surface formed on the outer face of the inner roller are converged in the radial direction facing the boss and the pair of grooves on the top portion of the inner race are positioned in the direction receiving the load; and   applying a gripping force on the upper edges of the inner roller in the direction not receiving the load, and forcing the inner opening of the inner roller elastically expanded around the grooves formed on the top portion of the inner roller and in the direction not receiving the load, the elastic expansion being within a radial clearance of the roller assembly provided between the tapered cylindrical outer face of the inner roller, the tapered cylindrical inner face of the outer roller, and the needle rollers, and thereby mounting the inner roller to the trunion with the generally spherical end surface of the cylindrical protrusions contacting against the at least partially spherical inner face of the inner roller.       
 
         [0030]    According to a further aspect of the invention, a method of assembling a roller assembly of a constant velocity joint on a trunnion of the joint, comprises the steps of:
       providing a roller assembly for a constant velocity joint, the roller assembly including: an outer roller with a tapered cylindrical surface formed on the inner face of the outer roller; an inner roller with a tapered cylindrical surface formed on the outer face of the inner roller and with at least partially spherical inner face, the tapered outer cylindrical surface of the inner roller having a same taper angle with the tapered inner cylindrical surface of the outer roller, the inner roller including a pair of grooves formed on a bottom portion of the inner roller facing a boss of the trunnion and in a diametric direction, and two pairs of grooves formed on a top portion of the inner roller both in a diametric direction parallel to and in a diametric direction perpendicular to the direction of the pair of grooves formed on the top portion; and needle rollers for receiving between the inner and outer rollers;   providing a constant velocity joint having a tripod with at least one trunnion, the trunnion including a pair of cylindrical protrusions protruded normal to the axis of the trunnion to a predetermined height from an outer surface of the trunnion, each of the cylindrical protrusions having a generally spherical end surface for contacting with the at least partially spherical inner face of the inner roller;   mounting the outer roller on a shoulder portion of the tripod disposed below the trunnion, in such a manner that the tapered inner cylindrical surface of the outer roller is converged in a radial direction facing a boss of the tripod, the outer roller having the needle rollers assembled in the tapered inner cylindrical surface of the outer roller;   placing the inner roller in an opening defined by the needle rollers assembled in the outer roller with the pair of cylindrical protrusions received in the pair of grooves on the bottom of the inner roller, in such a manner that a tapered cylindrical surface formed on the outer face of the inner roller are converged in the radial direction facing the boss and said one pair of grooves on the top portion of the inner race are positioned in the direction not receiving the load and said the other pair of grooves on the top portion of the inner race are positioned in the direction receiving the load; and   pressing the inner roller into the trunnion by a force applied in the axial direction of the trunnion, and forcing the inner opening of the inner roller elastically expanded around said two pairs of grooves formed on the top portion of the inner roller both in the direction receiving the load and in the direction not receiving the load, the elastic expansion being within a radial clearance of the roller assembly provided between the tapered cylindrical outer face of the inner roller, the tapered cylindrical inner face of the outer roller, and the needle rollers, and thereby mounting the inner roller to the trunion with the generally spherical end surface of the cylindrical protrusions contacting against the at least partially spherical inner face of the inner roller.       
 
         [0036]    According to the invention as disclosed, the contact area for transmitting torque is between the inner spherical face of the inner roller and a spherical end surface of the cylindrical protrusions protruded along the axis normal to the axis of the trunnion, and has a circular shape. This circular contact area can significantly reduce fluctuations or shudder problems in the drive system during rotation which can be caused by the frictional spinning moment owing to the elliptical contact area in the conventional constant velocity joint known in the art. 
         [0037]    The contact made in transmitting torque between the tapered cylindrical outer face of the inner roller and needle rollers and the tapered cylindrical inner face of the outer roller forces the roller assembly to be pressed to the bottom portion of the groove guides of the housing facing a boss of the trunnion, by an axial component of a load which is acting in the direction of the axis of the trunnion and at the same time facing a boss of the trunnion. Thus it is possible to help the roller assembly to rotate smoothly and without any significant fluctuation during rotation. 
         [0038]    More space is provided between the inner face of the inner roller and the trunnion in a circumferential direction as well as in the axial direction, by adopting a cylindrical protrusion having a spherical surface at its end and is positioned to the direction of receiving a load. This configuration enables grease to flow smoothly into and out of the space provided in the circumferential and axial direction which is secured by a height of a cylindrical protrusion projected from the trunnion and by its cross-section. 
         [0039]    More clearance is provided between the needle roller and the inner face of the outer roller and the outer face of the inner roller, in the radial and the circumferential direction, by providing a tapered cylindrical face to both the inner face of the outer roller and the outer face of the inner roller, which clearance in a top portion between the needle rollers and the inner roller and the outer roller is bigger than that in a bottom portion facing a boss of the tripod, both in the radial direction and in the circumferential direction. Thus, more clearance in the top portion makes grease flow easily in the joint and facilitates an initial lubrication to the roller assembly. Accordingly, the invention can bring about advantages including a stable rolling of the roller assembly, a smaller rolling resistance, and a lower axial force of the joint. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    The above described and other objects, features and advantages of the present invention will be more apparent from the presently preferred embodiments of the invention disclosed in the following description and illustrated in the accompanying drawings, in which: 
           [0041]      FIG. 1  shows a perspective view of a conventional tripod type constant velocity joint. 
           [0042]      FIG. 2  shows a side cross-sectional view of a conventional tripod type constant velocity joint. 
           [0043]      FIG. 3(   a ) is an explanatory view showing a relationship regarding the location of a conventional axis and inner roller. 
           [0044]      FIG. 3(   b ) is an explanatory view showing a frictional spinning moment generated in a conventional tripod type constant velocity joint. 
           [0045]      FIG. 4(   a ) shows both a cross-sectional view of a trunnion and a partial longitudinal cross-sectional view of the trunnion and the inner roller, according to a conventional tripod type constant velocity joint. 
           [0046]      FIG. 4(   b ) shows an explanatory view showing a frictional spinning moment generated in a conventional tripod type constant velocity joint. 
           [0047]      FIGS. 5(   a ) and  5 ( b ) are cross-sectional views showing the first embodiment of the present invention, in which  FIG. 5(   a ) is a longitudinal cross-sectional view and  FIG. 5(   b ) is a side cross-sectional view. 
           [0048]      FIGS. 6(   a ) and  6 ( b ) are cross-sectional views of the trunnion illustrating the second embodiment of the present invention, in which  FIG. 6(   a ) is a view of an axis of receiving a load, and  FIG. 6(   a ) is a view of an axis of non-receiving a load. 
           [0049]      FIGS. 7(   a ) and  7 ( b ) are cross-sectional views of the trunnion showing the third embodiment of the present invention, in which  FIG. 7(   a ) is a view of an axis of receiving a load, and  FIG. 7(   b ) is a view of an axis of non-receiving a load. 
           [0050]      FIGS. 8(   a ) and  8 ( b ) are cross-sectional views of the trunnion showing the fourth embodiment of the present invention, in which  FIG. 8(   a ) is a view of an axis of receiving a load, and  FIG. 8(   b ) is a view of an axis of non-receiving a load. 
           [0051]      FIGS. 9(   a )- 9 ( c ) are cross-sectional views of the inner roller showing the fifth embodiment of the present invention, in which  FIG. 9(   a ) is a top view,  FIG. 9(   b ) is a side view, and  FIG. 9(   c ) is a bottom view. 
           [0052]      FIG. 10  is a cross-sectional view of the outer roller showing the sixth embodiment of the present invention. 
           [0053]      FIG. 11  is an explanatory view showing a load force acting on the roller assembly. 
           [0054]      FIG. 12  and  FIG. 13  are cross-sectional views of the seventh embodiment of the present invention, in which  FIG. 12  shows an explanatory view showing an arrangement made between the roller assembly and the trunnion before fitting the roller assembly into the trunnion, and  FIG. 13  is an explanatory view showing how to get the roller assembly into the trunnion, based on an arrangement shown in  FIG. 12 . 
           [0055]      FIG. 14  and  FIG. 15  are cross-sectional views of the eighth embodiment of the present invention, in which  FIG. 14  shows an explanatory view showing an arrangement made between the roller assembly and the trunnion before fitting the roller assembly into the trunnion, and  FIG. 15  is an explanatory view showing how to get the roller assembly into the trunnion, based on an arrangement shown in  FIG. 14 . 
           [0056]      FIG. 16  and  FIG. 17  are cross-sectional views of the ninth embodiment of the present invention, in which  FIG. 16  shows an explanatory view showing an arrangement made between the roller assembly and the trunnion before fitting the roller assembly into the trunnion, and  FIG. 17  is an explanatory view showing how to get the roller assembly into the trunnion, based on an arrangement shown in  FIG. 16 . 
           [0057]      FIG. 18  is a cross-sectional view showing the tenth embodiment of the present invention. 
           [0058]      FIG. 19  shows the eleventh embodiment; in which  FIG. 19(   a ) is a longitudinal cross-sectional view at a joint angle and  FIG. 19(   b ) is a side cross-sectional view, and  FIG. 19(   c ) is an explanatory view showing the inner face of the outer roller and needle rollers. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0059]    The first embodiment of the present invention will be described with reference to the drawings.  FIG. 5  shows cross-sectional views of a tripod joint constant velocity joint  1  according to the first embodiment of the present invention; in which  FIG. 5(   a ) is a cross-sectional view taken vertical to the second rotating shaft, and  FIG. 5(   b ) is a side cross sectional view taken in an axial direction. 
         [0060]    A tripod joint  1  shown in  FIG. 5  comprises a hollow cylindrical housing  2  with one end defining an opening, and the other end secured to an end of a first rotating shaft  9  serving as a drive shaft or the like, and a tripod secured at one end of a second rotating shaft  8  which serves as a driven shaft or the like on the wheel side. Three grooves  10  are formed on the inner surface of the housing  2  in a configuration axially extending and equally spaced about the longitudinal axis of the housing. The grooves  10  are recessed from the inner surface outwardly in radial direction of the housing  2 . 
         [0061]    A tripod  7  is secured at one end of a second rotating shaft  8  with a ring-type boss  11  for supporting the tripod  7  at the second rotating shaft  8 . Three trunnions  6  are formed at three equally spaced locations around the boss  11  and extend outwards in a radial direction. 
         [0062]    Each of the trunnions  6  has at least one generally flat surface  6 b in a circumferential area of the trunnion not receiving a load. More preferably, each trunnion  6  has two opposing flat surfaces  6 b in the circumferential area not receiving the load, with the two flat surfaces facing in the Z-Z direction, as shown in  FIG. 5(   b ) and  FIG. 6(   b ). 
         [0063]    Each trunnion  6  has two opposing, and generally or at least partially spherical surfaces in the circumferential area receiving the load, namely, with the two spherical surfaces facing in the X-X direction, as shown in  FIG. 5(   a ) and  FIG. 6(   a ). A cylindrical protrusion  6   a  is formed on each of the generally or at least partially spherical surfaces of the trunnion, with the protrusion extending outwardly (namely, extending in a direction normal to the axis of the trunnion  6 ) to a distance from the partially spherical surface and with the protrusion having a generally spherical outer surface at its distal end. This generally spherical outer surface corresponds to and in surface-to-surface contact with the generally spherical inner surface of the inner roller  4  of the constant velocity joint of the present invention. 
         [0064]    A roller assembly  12  is mounted to each of the trunnion axes. The roller assembly  12  is a double-roller type which has an outer roller  3 , an inner roller  4 , and needle rollers  5  provided between the outer and inner rollers. The inner roller  4  has a generally spherical inner face which is in contact with the generally spherical surfaces of the cylindrical protrusion  6   a  as described above. In this manner, the two cylindrical protrusions  6   a  are projected outwardly from the trunnion  6  in the X-X direction of receiving the load. 
         [0065]    The inner roller  4  has a generally cylindrical outer rolling face which is in contact with needle rollers  5 . More preferably, as shown in  FIG. 5(   a ), the cylindrical outer face of the inner roller  4  is tapered in the rotational axis direction of the roller, and thereby, includes a tapered or conical outer face  4 a with taper angle θ defined by the face. 
         [0066]    The inner roller  4  preferably further includes two grooves  4   b  on the bottom portion of the inner roller facing a boss  11 , which grooves formed in the X-X direction of receiving a load as shown in  FIGS. 5(   a ),  9 ( a ) and  9 ( b ), in order to have the trunnion  6  assembled into the inner roller  4  through the grooves  4   b . The inner roller  4  preferably further includes two grooves  4   c  formed on the top portion of the inner roller facing the inner face  2   b  of the housing, which grooves formed in the Z-Z direction of not receiving a load as shown in  FIGS. 5(   b ),  9 ( a ) and  9 ( b ), in order to facilitate assembly of the trunnion  6  with the inner roller  4 . Owing to the presence of the top grooves  4   c , the inner roller  4  can elastically be bent or deformed to a degree about the two recessed grooves  4   c  either by applying a gripping pressure inwardly on the upper rim portions  4   d  (see  FIG. 9(   b )) of the inner roller or by forcibly widening the opening OH at the lower portion of the inner roller  4 , or in combination of the above. This makes the distance between the opposing bottom grooves  4   b  enlarged and thereby enables the assembly of the trunnion  6  into the inner roller  4 . 
         [0067]    The outer roller  3  has a generally spherical outer surface which is in contact with the guide grooves  2   a  of the housing  2 . The outer roller  3  preferably includes a tapered inner face  3   a  with the same taper angle θ as that formed on the outer surface  4   a  of the inner roller  4  with reference to the axis of the trunnion  6 . More space is provided between the inner face the inner roller  4  and the trunnion  6  in a circumferential direction as well as in the axial direction, by adopting a cylindrical protrusion  6   a  which is protruded along a axis normal to the axis of the trunnion  6  and is positioned to the direction of receiving a load. This configuration enables grease to flow smoothly and easily into and out of the space provided in the circumferential and axial direction and around the cylindrical protrusion  6   a  of the trunnion  6 . 
         [0068]    More clearance A (as shown in  FIG. 5(   a )) is provided between the needle rollers  5  and the inner face of the outer roller  3  and the outer face of the inner roller  4  in the radial and the circumferential direction, by providing a tapered face to both the inner face  3   a  of the outer roller and the outer face  4   a  of the inner roller. The clearance in a top portion between the needle rollers and the inner roller and the outer roller is preferably bigger than that of the bottom portion facing a boss of the tripod, both in the radial direction and in the circumferential direction, in order to make grease flow more easily in the top portion. This configuration can facilitate an effective initial lubrication to the roller assembly. 
         [0069]    The tripod  7  is housed in cylindrical hollow housing  2  through its open end. The inner face of the housing  2  is provided with three guide grooves  10  (formed at locations corresponding to the roller assemblies  12 ) which extend in the direction of the first rotational shaft  9  and are spaced apart equally in a circumferential direction of the housing  2 , thus the grooves  10  spaced apart from each other by about 120° around the housing. Three roller assemblies  12  are rotatably and movably received in their corresponding guide grooves  10  of the housing  2 . Each of the guide grooves  10  of the housing has a pair of side face  2   a  and a bottom portion  2   b  continuously connected to the side faces  2   a . The side faces  2   a  correspond to the convex arc-shaped or generally spherical outer face of the outer roller  3 , and hence are formed as a concave arc-shaped or generally spherical surface of approximately the same dimension as the outer face of the outer roller  3 . The side faces  2   a  extend in the longitudinal direction of the housing or the axial direction of the first rotating shaft  9 . Each of the bottom portions  2   b  of the guide groove is provided with tracking guides (i.e., lateral guide surfaces)  2   c  for guiding each of the outer rollers in secured rolling contact with an outer spherical end surface of the outer roller. In this way, the side faces  2   a  of the guide grooves  10  provide a tracking surface on which the outer roller can slide and roll. 
         [0070]    According to the invention as illustrated above with preferable embodiments thereof, the contact area in transmitting torque is defined primarily by the contact surface between the inner spherical face of inner roller  4  and the outer spherical surface of cylindrical protrusion  6   a , which is projected to a distance from the trunnion  6 , and has a generally circular shape. Thus, unlike the conventional constant velocity joint in which its contact area has an elliptical shape as discussed above ( FIG. 3(   b )), due to its generally circular contact area between the trunnions and inner roller the joint of the present invention can significantly reduce the conventional fluctuation or shudder problem during rotation which is caused by the pivotal spinning moment of the contact ellipse. 
         [0071]    As illustrated in  FIG. 11 , the transmitting torque is transferred through the contact made between the tapered outer face  4   a  of the inner roller  4  and needle rollers  5  and between the needle rollers  5  and the tapered inner face  3   a  of the outer roller, and it causes the roller assembly  12  to be biased toward the inner portion  2   d  (i.e., toward the boss  11  of the trunnion  6 ) of the groove guides  10  of the housing  2 , by an axial component Fv of a load which is acting in the direction of the axis of the trunnion and toward the boss of the trunnion. Thus this configuration helps the roller assembly  12  to rotate smoothly without any fluctuation during rotation caused by the frictional contact between the lateral side of the outer roller  3  and the lateral tracking guide  2   c  of the housing  2 . 
         [0072]      FIG. 6  illustrates a second embodiment of the invention in which each trunnion  6  has a pair of cylindrical protrusions  6   a  with a diameter φA. The two protrusions  6   a  are disposed in the X-X direction of receiving a load and respectively protruded along the axis normal to the axis of the trunnion  6  by a height H 1 . The two protrusions  6   a  together define a generally spherical end surface with a diameter φD. Each trunnion  6  includes a pair of flat surfaces  6   b  in the Z-Z direction of not receiving a load, respectively, in order to diminish the spin moment and make grease flow easily in axial and circumferential direction and for enhancing an initial lubrication of the joint. 
         [0073]    With reference to  FIG. 7 , the third embodiment is described herein. This embodiment is similar to the first and second embodiments described above. The difference of this embodiment shown in  FIG. 7  from the above embodiments is that the central portion (φA 1 ) of the spherical surface of the cylindrical protrusion  6   a  protruded from the trunnion  6  in the X-X direction of receiving a load is recessed from the surface or otherwise cut out from the trunnion, in order to reduce the contact area formed between the inner roller and the trunnion and make grease flow easily in axial and circumferential direction and also for enhancing an initial lubrication, thereby diminishing the spin moment in the joint. 
         [0074]    With reference to  FIG. 8 , the fourth embodiment is described herein. This embodiment is also very similar to the above described embodiment as shown in  FIG. 6 . The difference of this embodiment from that shown in  FIG. 6  is that the trunnion  6  has a cylindrical protrusion  6   a  in the X-X direction of receiving the load, however, the protrusion  6   a  having an elliptical shape which defines a longer diameter B 2  and shorter diameter A 2 . 
         [0075]    With reference to  FIG. 9 , the fifth embodiment is described herein.  FIG. 9  shows that the inner roller  4  has a generally spherical inner face and has a tapered outer cylindrical face with a taper angle  0 , and has two grooves  4   b  formed on the bottom portion and disposed in the X-X direction of receiving the load, in which the width “B” of each groove at the opening  4   e   1  is smaller than the width “A” at the bottom  4   e   2  of the groove. Moreover, the inner roller  4  has two recessed grooves  4   c  on the top portion and in the Z-Z direction of not receiving the load, in order to allow the distance OH between the grooves  4   b  to expand elastically by making the inner roller bent around the two recessed grooves  4   c  either by a force applied to the rims  4   d  of the inner roller on the top portion or by forcing to open the inner opening OH of the inner roller  4 . This facilitates assembly of the trunnion into the inner roller as described above. 
         [0076]    With reference to  FIGS. 10 and 11 , the sixth embodiment is described herein.  FIGS. 10 and 11  illustrate that the outer roller has a generally spherical outer face and has a tapered inner cylindrical face having the same taper angle θ as that formed on the outer surface of the inner roller shown in  FIGS. 5 and 9 , in order to force the roller assembly  12  to press toward the bottom portion  2   d  of the groove guides of the housing which faces a boss  11  of the trunnion. As illustrated in  FIG. 11 , an axial component Fv of a load F is applying in the direction of the axis of the trunnion and toward boss  11  (shown in  FIG. 5 ) of the trunnion, under a torque T acting on the joint  1 , where F is T/(3*PCR), and PCR stands for pitch circle radius of the joint, Fv is an axial component of F, and F′ is a resultant force of F and Fv. Thus, it is possible to help the roller assembly  12 , which is composed of the outer roller  3 , the inner roller  4  and the needle rollers  5 , to rotate smoothly without any fluctuation during rotation. 
         [0077]    Further embodiments and methods of assembly of the joint of the invention are described herein with reference to  FIGS. 12-19 . 
         [0078]    With reference to  FIGS. 12 and 13 , the seventh embodiment is described herein.  FIG. 12  is an explanatory view showing an arrangement made between the roller assembly  12  and the trunnion  6  before fitting the roller assembly  12  into the trunnion  6 . The outer roller  3  is mounted on the shoulder  11   a  of a boss  11  of the tripod, in such a manner that a tapered cylindrical surface  3   a  on the inner face of the outer roller  3  is converged in the radial direction toward boss  11  of the tripod, with the needle rollers  5  assembled into the tapered cylindrical surface  3   a  of the inner face of the outer roller  3 . The inner roller  4  is placed to the joint in a manner that cylindrical protrusions  6   a  (which are disposed in the X-X direction of receiving the load and protruded along the axis normal to the axis of the trunnion  6 ) are fitted in the two opposing grooves  4   b  on the bottom portion of the inner roller  4  in the X-X direction of receiving the load, as shown in  FIG. 12 , and that a tapered cylindrical surface  4   a  formed on the outer face of the inner roller  4  are converged in the radial direction toward the boss  11 , in order to secure some radial clearance (Δ) between the tapered outer cylindrical face  4   a  of the inner roller  4  and the tapered inner cylindrical face  3   a  of the outer roller  3  and the needle rollers  5 . This configuration facilitates the assembly of the roller assembly  12  with the trunnion  6 . The diameter φA ( FIG. 12(   b )) of a cylindrical protrusion  6   a  with a spherical surface at its end is smaller than the width B of the grooves formed in the X-X direction of receiving the load, and the diameter φd of the protruded spherical surfaces of the cylindrical protrusion  6   a  disposed in the X-X direction of the trunnion is larger than the diameter φD of the inner roller, in order to not only have the trunnion  6  assembled into the inner roller  4  through the grooves  4   b , but also to prevent the trunnion  6  from pulling itself out from the inner roller  4  once they all are assembled, by a difference in dimensions between the diameter φd of the protruded spherical surfaces of the cylindrical protrusion and the diameter φD of the inner roller. Two grooves  4   c  are recessed on its top portion of the inner face  4 , and formed in the Z-Z direction of not receiving the load. 
         [0079]      FIG. 13  illustrates a method of assembling the roller assembly  12  with the trunnion  6 , to be performed after the previous steps discussed above in connection with  FIG. 12 . If a force is applied at the opposing upper edges  4   d  of the inner roller  4  in the X-X direction of receiving the load, two edges  4   d  get bent around the center N of the grooves  4   c  formed on the top end and the trunnion  6  gets fitted into the roller assembly  12  by making two bottom edges  4   f  of the inner roller expanded in the X-X direction until φD becomes equal to φd, within the radial clearance (Δ) provided among the tapered cylindrical outer face  4   a  of the inner roller  4  and the tapered cylindrical inner face  3   a  of the outer roller  3  and the needle rollers  5 , as secured by the arrangement shown in  FIG. 12 . 
         [0080]    With reference to  FIG. 14  and  FIG. 15 , the eighth embodiment is described, in which  FIG. 14  shows an explanatory view showing an arrangement made between the roller assembly  12  and the trunnion  6  before fitting the roller assembly  12  into the trunnion  6 .  FIG. 15  shows an explanatory view showing how to get the roller assembly  12  into the trunnion  6 , based on an arrangement shown in  FIG. 14 . This embodiment is similar to the seventh embodiment shown in  FIG. 12  and  FIG. 13 . The difference of this embodiment from those shown in  FIG. 14  and  FIG. 15  is that the diameter φA of the cylindrical protrusion  6 a positioned in the X-X direction receiving the load, is larger than the width B at the opening of the grooves and the diameter φd of the protruded spherical surfaces of the cylindrical protrusion  6   a  positioned in the X-X direction is the same as the diameter φD of the inner roller  4 , in order to not only have the trunnion  6  assembled into the inner roller  4  through the grooves  4   b , but also to prevent the trunnion  6  from pulling itself out from the inner roller  4  once they all are assembled by a difference in dimensions between the diameter φA of the cylindrical protrusion  6   a  and the width B at the opening of the grooves. Two grooves  4   c   1  formed in the X-X direction are recessed on its top end of the inner face  4 . If a force is applied at the opposing upper edges  4   d   1  of the inner roller in the Z-Z direction, two edges  4   d    1  get bent around the center N 1  of the grooves  4   c   1  formed on the top end and the trunnion  6  fits into the roller assembly  12  by making two edges  4   f  of the bottom side of the inner roller extended in the X-X direction of receiving the load, until B becomes equal to or larger than φA, within the radial clearance (Δ) provided between the tapered cylindrical outer face  4   a  of the inner roller  4  and the tapered cylindrical inner face  3   a  of the outer roller  3  and the needle rollers  5 , as secured by the arrangement shown in  FIG. 14 . 
         [0081]    With reference to  FIG. 16  and  FIG. 17 , the ninth embodiment is described, in which  FIG. 16  shows an explanatory view showing an arrangement made between the roller assembly  12  and the trunnion  6  before fitting the roller assembly  12  into the trunnion  6 , and  FIG. 17  shows an explanatory view showing how to get the roller assembly  12  into the trunnion  6 , based on an arrangement shown in  FIG. 16 . This embodiment is a mixture of the seventh embodiment and the eighth embodiment. The difference of the present embodiment from those shown in  FIG. 16  and  FIG. 17  is that the roller assembly  12  is assembled from the top into the trunnion  6  by a force applied in the axial direction of the trunnion  6 . If a force is applied on the top end of the inner roller in the direction stated above, both edges  4   d   1  and edges  4   d  get bent both around the center N 1  of the grooves  4   c   1  and around the center N of the grooves  4   c  formed on the top end of the inner roller, respectively, and then the trunnion  6  gets fitted into the roller assembly  12  by making two bottom edges  4 f of the inner roller  4  to be expanded in the X-X direction of receiving a load, until B becomes equal to or larger than φA, and at the same time until φD becomes equal to φd, within the radial clearance Δ provided between the tapered cylindrical outer face  4   a  of the inner roller  4  and the tapered cylindrical inner face  3   a  of the outer roller  3  and the needle rollers  5 , as secured by the arrangement shown in  FIG. 16 . 
         [0082]    With reference to  FIG. 18 , the tenth embodiment is described herein. This embodiment is also similar to the first embodiment shown in  FIG. 1 . The difference of the present embodiment from that shown in  FIG. 1  is that a convex spherical surface is formed on the outer face of the outer roller  3 , having the center line X 1 -X 1  normal to the same angle θ provided to both the tapered inner cylindrical surface  3   a  of the outer roller and the tapered outer cylindrical surface  4   a  of the inner roller. 
         [0083]    With reference to  FIG. 19 , the eleventh embodiment is described, in which  FIG. 19(   a ) is a longitudinal cross-sectional view at a joint angle,  FIG. 19(   b ) is a side cross-sectional view, and  FIG. 19(   c ) is an explanatory view showing the inner face of the outer roller and needle rollers. Greater spaces or gaps S 1  and S 2  are provided between the inner face of the inner roller  4  and the trunnion in a circumferential direction as well as in the axial direction, by adopting a cylindrical protrusion  6   a  positioned in the direction of receiving a load, having a spherical end surface and protruded along an axis normal to the axis of the trunnion. Thus, this enables grease to flow smoothly into and out of the space provided in the circumferential and axial direction which is secured by a height of a cylindrical protrusion projected from the trunnion and by its shape as described above. More clearance S 11  and Δ are provided in between the needle roller  5  and the inner face  3   a  of the outer roller  3  and the outer face  4   a  of the inner roller  4 , in the radial and the circumferential direction, by providing a tapered cylindrical face θ to both the inner face of the outer roller and the outer face of the inner roller, which clearance S 11  in a top portion between the needle rollers and the inner roller and the outer roller is bigger than that S 12  in a bottom portion facing a boss of the tripod, both in the radial direction and in the circumferential direction. Thus more clearance in the top portion makes grease more easily flow in and help provide more initial lubrication to the roller assembly. 
         [0084]    According to the present invention as described above, the tripod type constant velocity joint can maintain a low frictional spinning moment, and enables the roller assembly to rotate smoothly without fluctuations, thus reducing the problematic shudders in the vehicle. 
         [0085]    The above disclosed embodiments are representatives of a presently preferred form of the invention, but are intended to be illustrative rather than definitive thereof. Accordingly, those skilled in the art will appreciate or recognize that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.