Abstract:
A constant velocity tripode joint is disclosed as having an outer joint part with an inner aperture and with uniformly circumferentially distributed recesses which widen the inner aperture and each of which include two opposed tracks. An inner joint part includes a center piece and three uniformly distributed tripode arms arranged radially relative to the center piece and each of which extends into one of the recesses. A roller assembly is mounted on each arm and in rolling contact with the tracks of the respective recess. Each roller assembly comprises at least two rollers that are independently rotatable relative to their respective tripode arm and that are at least indirectly supported on the tripode arm in the radial direction relative to the arm axis. A first roller rolls on the first of the two tracks and is spaced from the other track. A second roller rolls on the other one of the two tracks and is spaced from the first track.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a constant velocity tripode joint having an outer joint part with an inner aperture and three uniformly circumferentially distributed recesses which widen the inner aperture. Each recess includes two opposed tracks. The tripode joint also has an inner joint part with a center piece having three uniformly circumferentially distributed tripode arms that are arranged radially relative to the center piece and that each extend into one of the recesses. The tripode joint further includes roller assemblies each of which is rotatably supported on one of the tripode arms and that are in rolling contact with the tracks of their respective recesses. 
     Tripode joints of this type serve to transmit torque between the inner joint part and the outer joint part and are used especially in the drivelines of motor vehicles. When the joint rotates and when the longitudinal axes of the inner joint part and of the outer joint part are articulated relative to one another, the roller assemblies, in their respective recess, periodically move longitudinally to and fro. In tripode joints wherein the roller assemblies are held coaxially on the tripode arms, the roller assemblies carry out periodic angular movements that are superimposed on the longitudinal movements and their angle is twice the size of the angle of articulation between the longitudinal axes. To the extent that the roller assemblies are held angularly movably on the tripode arms, the longitudinal to- and fro- movements take place with the roller axes of the roller assembly extending parallel relative to one another. 
     During the transmission of torque, the roller assemblies each rest against one of the tracks of the recesses in a coinciding circumferential direction, whereas there necessarily exists a gap between the roller assembly and the other one of the tracks of the respective recess. There exist some restrictive effects because the edges of the second track are alternately contacted by outer annular edges of the roller assemblies. When the tripode joint rotates in a torque-free way, such as is the case when a vehicle changes from operating under load to a pushing operation or when it is operated in a substantially load-free condition, the contact of the roller assemblies changes between the two tracks of each of the recesses. The change in contact is associated with noise generating pulses and the noise adversely affects driving comfort. 
     It is therefore the object of the present invention to develop a constant velocity tripode joint of the above-mentioned type in such a way that the noise generated by the change in contact of the roller assemblies between the tracks of the recesses during torque-free operation is reduced. 
     SUMMARY OF THE INVENTION 
     The objective is achieved by designing each roller assembly to comprise at least two rollers that are independently rotatable relative to their respective tripode arm and that are at least indirectly supported on the tripode arm in the radial direction relative to the axis of the arm. A roller assembly includes a first roller that rolls on the first of the two tracks of its recess and is rotatable with a gap between it and the second track. The roller assembly further includes a second roller that rolls on the second of the two tracks of its recess and is rotatable with a gap between it and the first track. 
     As a result of the geometric arrangement, a roller assembly can be designed so that it is inserted almost without play between the track contact with the first track and the track contact with the second track, and at the same time, because of the free rotatability of the two rollers relative to one another, rolling movements take place at both tracks, should any contact occur at the same time. Because of the very small amount of designed play, any noise pulse resulting from a change in contact from one track to the other track due to a change in torque is avoided almost completely. The independent rotatability of the two rollers of each roller assembly avoids an increase in the sliding friction percentage at the respective unloaded track because, when contact occurs, the respective roller is able to roll freely in the right sense. 
     According to a preferred embodiment in each roller assembly, a first roller is supported by a first needle bearing on its respective tripode arm and a second roller is supported by a second needle bearing on the first roller. In such an embodiment, the roller assemblies are held coaxially relative to their respective tripode arm, while they are movable on the first needle bearings in the direction of the arm axis. When the rotating tripode joint is at an angular position, the axial rolling movements of the roller assemblies are superimposed by pivot movements within the recesses, and care has to be taken to ensure that the width of a longitudinal groove in the first track is great enough to accommodate a pivot movement of the second roller within the longitudinal groove without there occurring any edge contacts. 
     According to a second embodiment in each roller assembly, a first roller is pivotably held on a spherical sleeve that is supported on the tripode arm by a first needle bearing and a second roller is supported on the first roller by a second needle bearing. In this embodiment, the roller assemblies of the tripode joint rotating in an angular position are guided in a form-fitting way within the recesses, with the axes of rotation being held so as to extend parallel relative to one another. The longitudinal groove within the first track can be adapted relatively closely to the width of the second rollers without functioning being adversely affected. The width of the running faces in the recess are increased accordingly. 
     According to a third embodiment in each roller assembly, a first roller is rotatably supported by a first needle bearing on a sleeve which, in turn, is pivotably guided on a spherical tripode arm and a second roller is supported on the first roller by a second needle bearing. The functioning of such a tripode joint substantially corresponds to the latter tripode joint functioning described above. Instead of a rotatably supported spherical sleeve which is pivotable relative to the first roller, there is provided an intermediate sleeve which is pivotable relative to the tripode arm and on which the first roller is rotatable. 
     According to a further preferred embodiment, the first roller is composed of two parts that form a central annular groove for a respective second needle bearing and a second roller. This design permits the second needle bearing and the second roller to be assembled without the need for a plurality of securing elements. When using spherical sleeves to achieve pivotability of the roller assemblies on the tripode arms, the spherical sleeves can also be assembled quite easily with the first rollers. According to a further advantageous embodiment the running face of the second roller projects beyond the running face of the first roller and in the respective first tracks there is provided a longitudinal groove to allow the respective second roller contact-free engagement relative to the running face. In each position of contact of the roller assemblies on one of the two tracks of each recess one of the rollers of the roller assembly is loaded substantially symmetrically and it may be advantageous for the size conditions to be such that in a preferred direction of torque transmission the contacting rollers are subjected to a reduced specific load. 
     Preferably, the running face of the first roller and the running face of the second roller, relative to one another, form concentric spherical surfaces of different diameters. This is a preferred embodiment especially when the roller assemblies are held so as to extend coaxially relative to the axes of the tripode arms. If the roller axes are pivotable relative to the tripode arm axes, different shapes of running faces, especially entirely cylindrical shapes of the first and second rollers can be used. 
     In a further embodiment each roller assembly includes a pair of first rollers with a second roller between them, the first rollers and second roller are supported either by individual needle bearings directly on their respective tripode arms or on a sleeve which is pivotable on the tripode arm. This embodiment is particularly advantageous and easy to put into effect if the roller assemblies are provided with an intermediate sleeve which is pivotable relative to the tripode arm. 
     Below, the invention will be explained in greater detail with reference to the embodiments illustrated in the drawings wherein common elements have the same reference numbers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross-section of a tripode joint and a roller assembly having rollers that are fixed on their respective tripode arms relative to the axial direction and include a the second roller supported on a first roller; 
     FIG. 2 shows a cross-section of a tripode joint and a roller assembly having rollers that are pivotable relative to the axial direction of their respective tripode arms, with the second rollers being supported on the first rollers; 
     FIG. 3 shows a cross-section of a tripode joint and a roller assembly having rollers that are fixed on their respective tripode arms relative to the axial direction, with the first and the second rollers directly supported on the tripode arms; 
     FIG. 4 shows a cross-section of a tripode joint and a roller assembly having rollers that are pivotable relative to the axial direction of their respective tripode arms, with the first and the second rollers supported on a sleeve held on a spherical tripode arm; 
     FIG. 5 shows a cross-section of a tripode joint and a roller assembly having rollers that are fixed on their respective tripode arms relative to the axial direction, with the second rollers being supported on one piece first rollers; 
     FIG. 6 shows a cross-section of a tripode joint and roller assembly having rollers that are pivotable relative to the axial direction of their respective tripode arms with the second rollers supported on one piece first rollers held on spherical tripode arms. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The tripode joint shown generally at  10  in FIG. 1 comprises an outer joint part  11  with a longitudinal axis A 1  and having a central inner aperture  12 . Three axially extending recesses  13  widen the central inner aperture  12  and are circumferentially distributed at identical angular distances in the outer joint part  11 . Each recess  13  is provided with a first track  14  in which, in the central portion, there is provided a longitudinal groove  15  that is recessed relative to a uniform surface. Each recess  13  includes a second track  16  that is opposite to the first track  14  and which has a uniform surface. The recesses  13  extend in the direction of the longitudinal axis A 1  of the outer joint part  11 , with a constant cross-section and with the tracks  14  and  16  and the longitudinal groove  15  extending in an axis-parallel way. 
     The outer joint part  11  receives an inner joint part  21  having a longitudinal axis A 2 , which coincides with longitudinal axis A 1 . The inner joint part  21  comprises an approximately annular center piece  22  suitable for receiving a shaft journal (not shown) and three tripode arms  23  each of which extends from the center piece  22  into one of the recesses  13  of the outer joint part  11  approximately in a centered direction. Each arm  23  has an axis A 3  radial to A 1  and A 2 . A roller assembly  24 , which is in rolling contact with tracks  14  and  16 , is rotatably supported on each of the tripode arms  23 . One of the roller assemblies  24  will be described below by way of example. 
     The roller assembly  24  comprises a first roller  26  composed of two substantially symmetric halves  26   a  and  26   b  which are connected. The two halves  26   a  and  26   b  can be, for example, welded together. The first roller  26  is rotatably supported by a first needle bearing  25  on the tripode arm  23 . The needle bearing  25  is secured by a securing ring  27  and the roller  26 , as is required for the articulation of the joint, is freely movable along the axis of the tripode arm  23  on the needle bearing  25 . The first roller  26  forms a substantially spherical running face,  28   a  and  28   b , which is interrupted by a central annular groove  29 . A second roller  32  is supported in the annular groove  29  by a second needle bearing  31  so as to be rotatable relative to the first roller  26  and thus relative to the tripode arm  23 , independently of the first roller  26 . The second roller  32  has a spherical running face  34  which has a greater radius of curvature than the running face,  28   a  and  28   b  , of the first roller  26 . The first roller  26  is in rolling contact with the first track  14 , whereas the second roller  32  engages the longitudinal groove  15  without contacting the base of the groove  15 . Only the second roller  32 , by means of its running face  34 , is in rolling contact with the second track  16 . The running face,  28   a  and  28   b  , of the first roller  26  does not extend as far as the running face  34  and is arranged with a gap or play relative to the second track  16 . Thus, the first roller  26  is spaced apart from the second track  16  and the second roller  32  is spaced apart from the first track  14 . 
     A second embodiment of a tripode joint is generally shown at  40  in FIG.  2  and comprises outer joint part  11  having longitudinal axis A 1  and central inner aperture  12 . Three axially extending recesses  13  widen the central inner aperture  12  and are circumferentially distributed at identical angular distances in the outer joint part  11 . Each recess  13  includes first track  14  in which, in the central portion, there is a longitudinal groove  15  recessed relative to a uniform surface. Each recess  13  furthermore includes second track  16  opposite first track  14  and having a uniform surface. The recesses  13  extend in the direction of the longitudinal axis A 1  of the outer joint part  11  with a constant cross-section and with tracks  14  and  16  and longitudinal groove  15  extending in an axis-parallel way. Outer joint part  11  receives inner joint part  21  having longitudinal axis A 2 , which coincides with longitudinal axis A 1 . Inner joint part  21  includes annular center piece  22  and three tripode arms  23 , each of which extend from the center piece  22  into one recess  13  of the outer joint part  11  approximately in a centered direction. Each arm  23  has an axis A 3 . Roller assemblies  24  are in rolling contact with tracks  14 ,  16  and are rotatably supported on the tripode arms  23 . One of the roller assemblies  24  will be described below by way of example. 
     The roller assembly  24  comprises a first roller  26  composed of two substantially symmetric halves  26   a  and  26   b , which are connected together. The first roller  26  is pivotably arranged on a spherical sleeve  30  by means of an inner annular groove  42 . The spherical sleeve  30  is rotatably supported on the arm  23  by needle bearing  25 . Needle bearing  25  is secured by securing ring  27 . The spherical sleeve  30 , as required for the articulation of the joint, is freely movable in the axial direction of the tripode arm  23  on the needle bearing  25 . The first roller  26  forms a substantially spherical running face,  28   a  and  28   b , which is interrupted by the central annular groove  29 . A second roller  32  is supported in the annular groove  29  by a second needle bearing  31  so as to be rotatable relative to the first roller  26  and thus relative to the tripode arm  23 , independently of the first roller  26 . The second roller  32  has a spherical running face  34  which has a greater radius of curvature than the running face,  28   a  and  28   b , of the first roller  26 . The first roller  26  is in rolling contact with first track  14 , whereas the second roller  32  engages longitudinal groove  15  without contacting the base of the same. Only the second roller  32 , by means of its running face  34 , is in rolling contact with the second track  16 , whereas the running face  28  of the first roller  26 , which does not extend as far as the running face  34 , is arranged with a gap or play relative to the second track  16 . 
     A tripode joint shown at  50  in FIG. 3 includes many features described in the description of FIG.  1  and corresponding features are identified by corresponding numerals. The embodiment shown in FIG. 3 differs from FIG. 1 only in the design of the roller assembly  24 . One of the roller assemblies  24  will be described below by way of example. 
     The roller assembly  24  comprises a pair of first rollers  26   a  and  26   b  that are designed as two substantially symmetric rollers spaced from each other along axis A 3 . Roller  26   a  is rotatably supported by a first needle bearing  25   a  on the tripode arm  23 . Roller  26   b  is supported by another first needle bearing  25   b . The first rollers,  26   a  and  26   b , form a substantially spherical running face,  28   a  and  28   b , which is interrupted by a central gap. A second roller  32  is supported in the gap by a second needle bearing  31  on the tripode arm  23 , so as to be rotatable relative to the tripode arm  23 , independently of the first rollers  26   a  and  26   b . The second roller  32  has a spherical running face  34  which has a greater radius of curvature than the running faces  28   a  and  28   b  of the first rollers  26   a  and  26   b . The first rollers  26   a  and  26   b  are in rolling contact with the first track  14 , whereas the second roller  32  engages the longitudinal groove  15  without contacting the base of the same. Only the second roller  32 , by means of its running face  34 , is in rolling contact with the second track  16 . The running face  28   a  and  28   b , of the first rollers  26   a  and  26   b , which does not extend as far as the running face  34 , is arranged with a gap or play relative to the second track  16 . 
     The needle bearings  25   a  ,  31  and  25   b  are secured by securing ring  27 . Between needle bearings  25   a  and  31  there is a disc or securing ring  33   a . Between needle bearings  31  and  25   b  there is a disc or securing ring  33   b . All rollers  26   a ,  32 ,  26   b , as is required for the articulation of the joint, are freely movable in the axial direction of the tripode arm  23  on the needle bearings  25   a ,  31 ,  25   b . 
     A tripode joint shown at  52  in FIG. 4 shares many features described in FIGS. 2 and 3. Corresponding features are designated by corresponding numerals. Each tripode arm  23  comprises a spherical head  35  which pivotably supports a sleeve element  36 . The sleeve element  36  holds the roller assembly  24 . One of the roller assemblies  24  will be described below by way of example. 
     The roller assembly  24  comprises a pair of first rollers  26   a  and  26   b  that are designed as two substantially symmetric rollers spaced from each other along axis A 3 . One of the first rollers,  26   a , is rotatably supported on the sleeve element  36  by a first needle bearing  25   a . The other one of the first rollers,  26   b , is supported on sleeve element  36  by another first needle bearing  25   b . The first rollers  26   a  and  26   b  form substantially spherical running faces  28   a  and  28   b , which are interrupted by a central gap. A second roller  32  is supported in the gap by second needle bearing  31  on the sleeve element  36 , so as to be rotatable relative to the sleeve element  36  independently of the first rollers  26   a  and  26   b . The second roller  32  has a spherical running face  34  which has a greater radius of curvature than the running faces  28   a  and  28   b  of the first rollers  26   a  and  26   b . The first rollers  26   a  and  26   b  are in rolling contact with the first track  14 , whereas the second roller  32  engages the longitudinal groove  15  without contacting the base of the same. Only the second roller  32 , by means of its running face  34 , is in rolling contact with the second track  16  whereas the running face  28   a  and  28   b  of the first rollers  26   a  and  26   b , which does not extend as far as the running face  34 , is arranged with a gap or play relative to the second track  16 . 
     The needle bearings  25   a ,  31 , and  25   b  are secured by securing rings  27   a  and  27   b  , which are inserted into the outer surface of the sleeve element  36  and which hold the first rollers  26   a  and  26   b  and the second roller  32  in between them. Between the needle bearings  25   a ,  31 , and  25   b  there are provided discs  33   a ,  33   b  or further securing rings. The sleeve element  36 , as required for the articulation of the joint, is freely movable in the axial direction of the tripode arm  23 . 
     A tripode joint shown at  54  in FIG. 5 shares many features described in the description of FIG.  3 . Corresponding features are identified by the same numerals. Differences between the joints  50  and  54  are only in the roller assemblies  24 . One of the roller assemblies  24  is described below by way of example. 
     The roller assembly  24  comprises a single, one piece first roller  26 . The first roller  26  is rotatably supported by a first needle bearing  25  on the tripode arm  23 . The needle bearing  25  is secure by securing ring  27  and the roller  26 , as required for the articulation of the joint, is freely movable in the axial direction of the tripode arm  23  on the needle bearing  25 . The first roller  26  forms a substantially spherical two-portion running face  28   a  and  28   b  that is interrupted by a central annular groove  29 . A second roller  32  is supported on the first roller  26  by means of a second needle bearing  31 , so as to be rotatable relative to the first roller  26  and thus relative to the tripode arm  23 , independently of the first roller  26 . The second needle bearing  31  is held in the annular groove  29 . The second roller  32  can be axially slid over the second needle bearing  31 . The second roller  32  has a spherical running face  34  which has a greater radius of curvature than the running face  28   a  and  28   b  of the first roller  26 . The first roller  26  is in rolling contact with the first track  14 , whereas the second roller  32  engages the longitudinal groove  15  without contacting the base of the same. Only the second roller  32 , by means of its running face  34 , is in rolling contact with the second track  16 , whereas the running face  28   a  and  28   b  of the first roller  26 , which does not extend as far as the running face  34 , is arranged with a gap or play relative to the second track  16 . 
     A tripode joint shown at  56  in FIG. 6 shares many features described in the description of FIG.  4 . Corresponding features are identified by the same numerals. The tripode arms  23  comprise spherical heads  35  that pivotably support sleeve elements  36 . The sleeve elements  36  hold the roller assemblies  24 . One of the roller assemblies  24  will be described below by way of example. 
     The roller assembly  24  comprises a single one piece first roller  26 . The first roller  26  is rotatably supported on the sleeve element  36  by a needle bearing  25 . The first roller  26  forms a substantially spherical two-portion running face  28   a  and  28   b  which is interrupted by a central gap. In the gap there is a central annular groove  29 . A second roller  32  is supported in the gap by second needle bearing  31  held in the groove  29 , so as to be rotatable relative to the first roller  26  and thus relative to the sleeve element  36  independently of the first roller  26 . The second roller  32  has a spherical running face  34  that has a greater radius of curvature than the running face  28   a  and  26   b  of the first roller  26 . The first roller  26  is in rolling contact with the first track  14 , whereas the second roller  32  engages the longitudinal groove  15  without contacting the base of the same. Only the second roller  32 , by means of it running face  34  is in rolling contact with the second track  16 , whereas the running face  28   a ,  28   b  of the first roller  26 , which does not extend as far as the running face  34 , is arranged with play relative to the second track  16 . The needle bearing  25  is secured by securing rings  27   a ,  27   b , which are inserted into the outer surface of the sleeve element  36  and hold the first roller  26  axially fixed. The sleeve element  36 , as required for the articulation of the joint, is freely movable in the axial direction of the tripode arm  23 . 
     The present invention has been described in accordance with the relevant legal standards, thus the foregoing description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of this invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.