Abstract:
In a tripod type constant velocity joint, in order to produce a recovery couple to correct the inclination of the rolling direction of a roller and to reduce surface pressure without using angular contact provided by a Gothic arch-shaped roller guide surface, it is arranged that where r 1  and r 2  are the minimum and maximum values, respectively, of the radius of curvature of the generatrix for the outer peripheral surface of the roller within the range where solid contact is effected by elastic deformation of the contact section between the roller and the roller guide surface under a predetermined torque load with respect to the radius of curvature of the roller guide surface, the radius of curvature (r) of the generatrix be set in the range r 1 ≦r≦r 2.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a tripod type constant velocity joint, which can be utilized for power transmission in automobiles and various industrial machines. For example, it may be incorporated into the driving system of an automobile to effect transmission of a turning force at constant angular velocity between rotary shafts which are in a non-straight line. 
   2. Description of the Prior Art 
   As regards means for solving the problem of shudder in vehicles concerning rotation third-order axial force in tripod type constant velocity joints, tripod type constant velocity joints which are of the so-called double roller type in which an outer roller  4  rolls in parallel with the axis of an outer joint member  1  along a track groove  2  in the outer joint member  1  are described in, for example, Japanese Patent Publication (Kouhyou) Heisei 4-503554 and Japanese Patent Publication (Koukai) Heisei 5-215141 (see  FIG. 7 ). In these tripod type constant velocity joints, the roller guide surface  3  of the outer joint member  1  is shaped in a Gothic arch to ensure that its contact with the roller  4  is in a state of angular contact, thereby generating a recovery couple to correct the inclination (in a plane in  FIG. 3 ) of the rolling direction of the roller  4 , it being said that this has the effect of holding the roller  4  in parallel with the track groove. 
   SUMMARY OF THE INVENTION 
   In order to establish angular contact with respect to a roller having a limited width, it is necessary to reduce the pressure angle (contact angle) denoted by the reference character P in  FIG. 7 , with the result that sufficient recovery couple cannot be obtained sometimes. Further, in order to control the contact angle, it is necessary to relatively increase the difference in radius of curvature between the roller guide surface and the generatrix for the outer peripheral surface of the roller. Doing so will result in an increase in contact surface pressure, which would sometimes cause premature wear of the contact region. Either case leads to a lowering in performance, sometimes causing a shudder to occur in a vehicle having the joint mounted thereon. 
   The present invention is intended to eliminate such problems. That is, the object of the invention is to provide a tripod type constant velocity joint given a construction such that a recovery couple is produced to correct the inclination of the rolling direction of the roller while reducing the surface pressure without using angular contact provided by a Gothic arch-shaped roller guide surface and such that the NVH characteristic is maintained for a long time. 
   The invention provides a tripod type constant velocity joint comprising an outer joint member formed with track grooves at three equispaced positions on the circumference of the inner peripheral surface, an inner joint member formed with radially projecting leg shafts, or trunnions, at three equispaced positions on the circumference, rollers carried each on the respective trunnions rotatably and oscillably, with the rollers rolling in the track grooves axially of the outer joint member, the tripod type constant velocity joint being characterized in that the radius of curvature of the generatrix for the outer peripheral surface of the roller is smaller than the radius of the outer diameter surface (radius of the cross section of the roller) and in that where r 1  and r 2  are the minimum and maximum values, respectively, of the radius of curvature of the generatrix for the outer peripheral surface of the roller within the range where solid contact is effected by elastic deformation of the contact section between the roller and the roller guide surface under a predetermined torque load with respect to the radius of curvature of the roller guide surface, the radius of curvature r of the generatrix is set in the range r 1 ≦r≦r 2 . 
   This setting makes it possible to provide a contact angle over the entire width of the roller and to increase the recovery couple during torque load. Further, the solid contact occurring in the high load region greatly reduces the contact surface pressure to reduce wear of the contact section. In the above setting, the radius of curvature r of the generatrix for the outer peripheral surface of the roller has its allowable range defined to be up to a value slightly smaller than the radius of curvature R of the roller guide surface. Since the roller is of torus shape, an inclination of the roller in the rolling direction results in the same state as the setting r&gt;R, that is, the area of the roller adjacent its widthwise middle separates from the roller guide surface and instead the areas of the roller adjacent its widthwise opposite ends contact the roller guide surface. 
   To give a concrete example of predetermined torque load, it is not more than ½ of a joint break torque. By the joint break torque is meant, specifically, a torque corresponding to a static torsion breakage torque found from the minimum diameter of the shaft. 
   The widthwise opposite ends of the outer peripheral surface of the roller may be provided with roundings having a radius of curvature smaller than the radius of curvature of the generatrix in the direction away from the roller guide groove, thereby making it possible to avoid edge load at a widthwise end of the roller. 
   According to the invention, it is possible to generate a large recovery couple to correct the inclination of the rolling direction of the roller without using angular contact provided by a Gothic arch-shaped roller guide surface and since the contact surface pressure can be reduced, wear is reduced, so that the NVH characteristic can be maintained for a long time. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a diagram, and a contact section between a roller showing an embodiment of the invention and a roller guide surface identifying the minimum values r 1  of the radius of curvature of the generatrix of the outer peripheral surface of the roller. 
       FIG. 1B  is a diagram, and a contact section between a roller showing an embodiment of the invention and a roller guide surface identifying the maximum values r 2  of the radius of curvature of the generatrix of the outer peripheral surface of the roller. 
       FIG. 2A  is an end view, partly in section, of a tripod type constant velocity joint showing an embodiment of the invention; 
       FIG. 2B  is a sectional view of a trunnion and a roller assembly, the view being taken normal to the trunnion; 
       FIG. 3  is a longitudinal sectional view showing a state in which the tripod type constant velocity joint of  FIG. 2A  has taken an operating angle; 
       FIG. 4  is an enlarged sectional view of the ring of the tripod type constant velocity joint of  FIG. 3 ; 
       FIG. 5  is a principal sectional view of a tripod type constant velocity joint showing another embodiment of the invention; 
       FIG. 6  is a principal sectional view of a tripod type constant velocity joint showing another embodiment of the invention; and 
       FIG. 7  is a principal sectional view of a tripod type constant velocity joint showing prior art. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the invention exemplified in the drawings will now be described. First, referring to  FIGS. 2A ,  2 B and  3 , the basic construction of a tripod type constant velocity joint will be described.  FIG. 2A  is an end view of a joint shown partly in section.  FIG. 2B  is a cross sectional view of a trunnion and a roller assembly.  FIG. 3  is a longitudinal sectional view of the joint taking an operating angle θ. As shown, the constant velocity joint comprises an outer joint member  10  and a tripod member  20 , wherein one of the two shafts to be connected is connected to the outer joint member  10  and the other is connected to the tripod member  20 . The outer joint member  10  comprises a bottomed cylindrical mouth section  12  and a stem section  18 , the stem section  18  being in the form of a serrated shaft, through which the outer joint member is connected to one of the two shafts to be connected. Axially extending track grooves  14  are formed at three equispaced positions on the circumference of the inner peripheral surface of the mouth section  12 . Each track groove  14  has roller guide surfaces  16  formed in the circumferentially opposed side walls thereof. The tripod member  20  comprises a boss  22  and trunnion  26 , the boss  22  being formed with a serrated hole  24 , through which the tripod member is connected to the other of the two shafts to be connected. The trunnions  26  radially project from three equispaced positions on the circumference of the boss  22 . Each trunnion  26  carries a roller assembly ( 32 ,  34 ,  36 ). The roller assemblies are received in the track grooves  14  in the outer joint member  10 . 
   In this embodiment, the outer peripheral surface  26   a  of the trunnion  26 , when seen in a cross section ( FIG. 2B ), is of the shape of an ellipse with its longer diameter crossing the joint axis at right angles, but when seen in a longitudinal section ( FIG. 3 ), it is of straight shape parallel with the trunnion, the cross section remaining the same when taken at any axial position. The cross-sectional shape of the trunnion  26  has a shorter diameter extending axially of the tripod member  20 , and the mutually opposed surfaces are retracted in opposite directions from an imaginary cylindrical surface toward the smaller diameter side. 
   The roller assembly includes a ring  32 , a roller  34 , and rolling elements  36 . The ring  32  is fitted on the trunnion  26 , and the ring  32  and the roller  34  are unitized through a plurality of rolling elements  36  to constitute a relatively rotatably roller assembly. That is, the rolling elements  36  are rollably interposed between the cylindrical outer peripheral surface  32   b  of the ring  32  and the cylindrical inner peripheral surface of the roller  34 . In this embodiment, stop rings  33  and  35  are fitted in annular grooves formed in the inner peripheral surface of the roller  34 , thereby unitizing the ring  32  and roller  34 , preventing slip-off of the rolling elements  36 . 
   As shown enlarged in  FIG. 4 , the inner peripheral surface  32   a  of the ring  32  is arcuately convex in section. That is, the inner peripheral surface  32   a  has a generatrix in the form of a convex arc. Whereas the inner peripheral surface  32   a  of the ring  32  may be in the form of a convex arc over substantially the entire length thereof (see  FIG. 2A ), in this case, the generatrix for the inner peripheral surface  32   a  of the ring  32  is a combination of a central arcuate section m and relief sections n on both sides thereof. The relief sections n are portions adapted to avoid interfering with the trunnion  26  when the joint takes a working angle θ as shown in  FIG. 3 , and are defined by a straight line or curve which is gradually diametrically expanded from the end of the arc m toward the end of the ring  32 . In this case, the relief section n is exemplified as part of a conical surface with a conical angle α=50°. 
   As described above, since the generatrix for the inner peripheral surface  32   a  of the ring  32  is a convex arc with a radius r 5  ( FIG. 4 ) and since the cross-sectional shape of the trunnion  26  is substantially elliptic, with a predetermined clearance defined between the trunnion  26  and the ring  32 , the ring  32  is not only movable axially of the trunnion  26  but also oscillable with respect to the trunnion  26 . Further, since the ring  32  and roller  34  are relatively rotatably unitized through the rolling element  36 , as described above, the ring  32  and roller  34  are in oscillable relation to the trunnion  26  as a unit. Oscillation in this case means that the axis of the ring  32  and roller  34  is tilted with respect to the axis of the trunnion  26  in a plane containing the axis of the trunnion  26  (see  FIG. 3 ) Thus, as a result of the roller  34  being oscillable with respect to the trunnion  26 , the roller  34  will roll on the roller guide surfaces  16  while maintaining its posture which is parallel with the axis of the outer joint member even when torque is transmitted with the joint taking an operating angle. 
   The roller guide surfaces  16  of the outer joint member  10  contacting the outer peripheral surface  34   b  of the roller  34  each have an arcuate sectional shape with a radius of curvature R. The generatrix for the outer peripheral surface  34   b  of the roller  34  is an arc whose center of curvature is located at a point radially spaced from the axis of the roller  34 . The radius of curvature r of the generatrix for the outer peripheral surface  34   b  of the roller  34  is smaller than the radius of the outer diameter surface of the roller  34 . Specifically, the radius of curvature r of the generatrix for the outer peripheral surface  34   b  of the roller  34  is such that where r 1  and r 2  are the minimum and maximum values, respectively, of the radius of curvature of the generatrix for the outer peripheral surface  34   b  of the roller within the range where solid contact is effected by elastic deformation of the contact section between the roller  34  and the roller guide surface  16  under the condition that the torque load correspond to not more than a half of the breakage torque for the constant velocity joint with respect to the radius of curvature R of the roller guide surface  16 , it is preferably set in the range r 1 ≦r≦r 2 . See  FIGS. 1A and 1B . 
   In the above setting, the radius of curvature r of the generatrix for the outer peripheral surface of the roller has its allowable range defined to be up to a value slightly smaller than the radius of curvature R of the roller guide surface  16 . Since the roller  34  is of torus shape, an inclination of the roller  34  in the rolling direction results in the same state as the setting r&gt;R, that is, the area of the roller  34  adjacent its widthwise middle separates from the roller guide surface  16  and instead the areas of the roller adjacent its widthwise opposite ends contact the roller guide surface. This setting makes it possible to provide a contact angle over the entire width of the roller  34  and to increase the recovery couple during torque load. Further, the solid contact occurring in the high load region greatly reduces the contact surface pressure, thereby reducing wear of the contact section. 
   In the illustrated embodiment, the widthwise opposite ends of the roller  34  are formed with roundings having radii of curvature r 3  and r 4  smaller than the radius of curvature r of the generatrix so as to be relieved from the roller guide surfaces. This makes it possible to avoid edge load in the widthwise ends of the roller  34 . 
     FIGS. 5 and 6  show other embodiments. In each case, the roller is rotatable and oscillable with respect to the trunnion, the relation between the radius of curvature of the roller guide surface and the radius of curvature of the generatrix for the outer peripheral surface of the roller is almost the same as in the preceding embodiment, the difference being as follows. In the constant velocity joint of  FIG. 5 , the roller assembly  130  is composed of a ring  132  and a roller  134  which are relatively rotatable through rolling elements  136 , with the cylindrical inner peripheral surface of the ring  132  being fitted on the spherical outer peripheral surface of the trunnion  126 . In the constant velocity joint of  FIG. 6 , the roller assembly  230  is composed of a ring  232  and a roller  234  which are relatively rotatable through rolling elements  236 , with the concavely spherical inner peripheral surface of the ring  232  being fitted on the spherical outer peripheral surface of the trunnion  226 .