Abstract:
A plunging, constant-velocity, tripode universal joint comprising a first rotary member ( 30 ) having three trunnions ( 31 ), a roller ( 34 ) having a cylindrical bore mounted on a spherical surface ( 32 ) on each trunnion so that the cylindrical bore engages the spherical surface and so that each roller can rotate, tilt and slide relative to its supporting trunnion, a second rotary member ( 40 ) having three grooves parallel to its rotary axis, each roller being engaged with one of the grooves, the engagement between each roller and track surfaces in its associated groove being at three points such that the orientation of the roller with respect to the second member is determined solely by said engagement and wherein when the joint is transmitting torque each roller ( 34 ) is only in contact with the track surface(s) ( 42, 43 ) through which the torque is being transmitted.

Description:
TECHNICAL FIELD 
     This invention relates to shudderless, tripode, plunging, constant-velocity, universal joints. 
     One type of such a constant-velocity, universal joint comprises a first rotary member having a rotary axis, three trunnions extending from the first member, a roller mounted directly or indirectly on a spherical surface on each trunnion, such surface being provided by the trunnion itself or by a member rotatably mounted on the trunnion, the roller including a cylindrical bore which engages the spherical surface so that each roller can rotate, tilt and slide relative to its supporting trunnion, the centers of the spherical surfaces on all the trunnions lying in a plane perpendicular to said rotary axis, a second rotary member having a rotary axis, three grooves formed in said second rotary member so as to extend parallel to the rotary axis of the second rotary member, each roller being engaged with one of the grooves, the engagement between each roller and its associated groove being such that the orientation of the roller with respect to the second member is determined solely by said engagement. In such a joint there is relative radial movement between the spherical surface of the trunnion and the roller. 
     BACKGROUND ART 
     One known form of shudderless, plunging, tripode joint is shown in cross section in FIG.  1 . Referring to this figure there is a spider or inner member  10  of the joint which has three trunnions, one of which is shown at  11 . The trunnion has a part-spherical surface  12  which receives an inner roller  13  having a cylindrical bore  14 . The inner roller  13  can slide and tilt relative to the trunnion and moves radially relative to the center of the trunnion when the joint is articulated and rotating. An outer roller  15  is mounted on the inner roller  13  to rotate relative thereto, there being a needle roller bearing  16  between the rollers  13  and  15 . The parts of the roller assembly are kept together by two rings  17  and  18 . The outer race of the joint is indicated at  19  and has three grooves, each groove being formed by a pair of opposed tracks one of which is shown at  20 . The cross-sectional shape of each track is formed by two circular arcs which give a “Gothic arch” form and angular contacts between the track and the roller. The centers  21  of the spherical surfaces of all of the trunnions lie in a plane perpendicular to the rotary axis  21   a  of the spider. 
     When torque is to be transmitted from the outer race  19  to the spider  10  in an anticlockwise direction in FIG. 1, there is a reaction force F 0  which acts from the trunnion to the inner roller  13  and thence to the outer roller  15 . The force F 0  is generally perpendicular to the rotary axis of the roller  13 , ignoring friction. There is two-point contact between the roller  15  and the right-hand track  20  and the reaction forces are shown at F 1  and F 2 . The roller  15  is able to rotate about the intersection of these forces at  22  and without further constraint would be unstable. Because the roller  15  is free to tilt about the intersection  22 , in order for the roller to be stable it will also engage the left-hand track so that there will be one or more reaction forces such as F 3  or F 4  on the circumference of the roller and/or a force F 5  on the upper surface of the roller which limits its tilting movement. These additional forces on the left-hand side of the roller are intermittent and are due to the fact that, as the trunnion  11  moves up and down through the roller bore  14 , the position of the roller  15  relative to the outer race  19  can, in general, only be defined by two points of contact (i.e. those of the forces F 1  and F 2 ) instantaneously when the trunnion is in a certain position with respect to the roller so that other forces are generally required to determine the orientation of the roller. These intermittent other forces F 3 , F 4  and F 5  increase the resistance of the roller to rolling along the tracks and hence the plunge resistance of the joint, i.e the passive resistance. They may also cause the joint to generate a cyclic net axial force when it rotates with the rotary axes of the spider and outer race misaligned, this can give rise to shudder vibration in a vehicle in which the joint forms part of the driveline. 
     A similar arrangement is shown in FIG. 2 except that in this case the trunnion  22  is cylindrical and an inner roller  23  provides the part-spherical outer surface  24  which engages a cylindrical bore  25  of the outer roller  26 . The inner roller  23  is mounted on the trunnion by a needle roller bearing  27  and can not tilt or slide relative to the trunnion. The outer roller  26  can rotate, tilt or slide relative to the trunnion and to the part-spherical outer surface  24  which moves up and down within the bore  25 . The forces on the roller  26  are similar to those described in relation to the joint shown in FIG.  1  and are shown by the same reference characters. 
     Because in each of the above examples the rollers  15  and  26  can tilt, slide and rotate relative to the trunnions and because the rollers are “shaped” to fit the grooves, the orientation of each roller with respect to its associated groove is determined solely by the engagement of the roller with the groove. There are other configurations of tripode joints in which the orientation of each roller relative to the outer race is determined by the engagement of the roller with the groove. 
     There is described in WO 97/25545 a further type of tripode shudderless joint and reference is made particularly to FIG. 17. In this joint, the tripode trunnions are cylindrical and mounted on each trunnion by needle roller bearings is an inner roller with a part-spherical outer surface. This engages an outer roller with an inner spherical-surface. The outer roller can tilt with respect to the inner roller but any sliding radial movement takes place between the trunnion and the inner roller. The outer spherical surface does not move radially with respect to the outer roller so that, unlike the joint of the current invention as will be described below, the force between the trunnion and the roller assembly acts at a fixed position relative to the roller assembly. Therefore there may be no tendency for the roller assembly to twist about an axis parallel to the axis of the second member. 
     In the prior joint the outer roller has a trapezoidal outer surface which engages a track surface of corresponding shape. It is suggested that contact may take place between three faces of the outer roller and the track but this would seem to require a very accurate fit between roller and track. This is acknowledged by the fact that the roller and track inclined surfaces are described as facing one another with “a gapless contact or a very small gap”. In practice the two trapezoids will generally only be in contact on one or two of their sides. 
     WO 97/25545 also describes how the rollers are only in contact with the track surface through which torque is being transmitted. This may be achieved by making the driving track (i.e. the track through which torque is transmitted) narrower than the other track. This results in asymmetric grooves and a requirement for different components to be used on the left and right hand sides of a vehicle. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to reduce the resistance of the rollers to rolling along the tracks and thus to reduce the plunge resistance whilst ensuring that the rollers are stable and that there is continuous three-point contact between the roller and the track, without requiring the profiles of the roller and the track to be matched with extreme accuracy. 
     Another object of the invention is to provide a shudderless, tripode joint in which the stability of each roller is determined solely by its engagement with the driving track and there are no intermittent contacts between the roller and the other track. 
     Another object of the invention is to reduce the NVH (noise, vibration, harshness) associated with clearance in the joint by damping the backlash movement of the roller when the torque is reversed. 
     Another object of the invention is to provide a joint in which the grooves to receive the rollers have a simple form making the second rotary member or outer race easy to manufacture. 
     Another object of the invention is to provide a joint in which the grooves are symmetrical. 
     Another object of the invention is to provide a joint in which all the contacts between the roller and the track are Hertzian (as hereinafter described); 
     According to one aspect of the invention we provide a plunging, constant-velocity universal joint comprising a first rotary member having a rotary axis, three trunnions extending from the first member, a roller mounted directly or indirectly on a spherical surface on each trunnion, such surface being provided by the trunnion itself or by a member rotatably mounted on the trunnion, the roller including a cylindrical bore which engages the spherical surface so that each roller can rotate, tilt and slide relative to its supporting trunnion, the centers of the spherical surfaces on all the trunnions lying in a plane perpendicular to said rotary axis, a second rotary member having a rotary axis, three grooves formed in said second rotary member so as to extend parallel to the rotary axis of the second rotary member, each groove comprising spaced-apart track surfaces which extend parallel to the rotary axis of the second member, each roller being engaged with a track surface in one of the grooves, the engagement between each roller and its associated track surface through which torque is being transmitted being at three points which hilly determine the roller&#39;s orientation with respect to the second member and wherein, when the joint is transmitting torque, each roller is only in contact with the track surface through which the torque is being transmitted. 
     According to another aspect of the invention we provide a plunging, constant-velocity universal joint comprising a first rotary member having a rotary axis, three trunnions extending from the first member, a roller mounted directly or indirectly on a spherical surface on each trunnion, such surface being provided by the trunnion itself or by a member rotatably mounted on the trunnion, the roller including a cylindrical bore which engages the spherical surface so that each roller can rotate, tilt and slide relative to its supporting trunnion, the centers of the spherical surfaces on all the trunnions lying in a plane perpendicular to said rotary axis, a second rotary member having a rotary axis, three grooves formed in said second rotary member so as to extend parallel to the rotary axis of the second rotary member, each groove comprising spaced-apart track surfaces which extend parallel to the rotary axis of the second member, each roller being engaged with a track surface in one of the grooves, the engagement between each roller and its associated track surface through which torque is being transmitted being at three points which fully determine the roller&#39;s orientation with respect to the second member, wherein the contact vectors of the reaction forces at said three points, when projected on to a common plane perpendicular to the rotary axis of the second member, form a triangle, wherein the contact vector of the force between the roller and the spherical surface, when projected onto said common plane, intersects the two sides of the triangle formed by the projected contact vectors of the reaction forces acting at a radially innermost and radially outermost of said points, the radial positions of said points being measured with respect to the rotary axis of the second member and wherein, when the joint is transmitting torque, each roller is only in contact with the track surface through which the torque is being transmitted. 
     Preferably the track surfaces in each groove are symmetrical with respect to a plane (the plane of symmetry) containing the rotary axis of the second member. 
     Preferably two of said contact vectors of the reaction forces when projected on to said common plane intersect on the plane of symmetry, said two contact vectors being one of the reaction forces acting at the radially innermost or radially outermost of said points and the contact vector of the reaction force acting at the radially intermediate point. 
     A first track surface on which the radially innermost point or the radially outermost point and the radially intermediate point is situated may be cylindrical. Said first track surfaces on each side of the groove may be parts of the same cylinder. 
     The radially innermost or radially outermost point which is not on the first track surface may be on a second track surface which is cylindrical. The first and second track surfaces may have a common tangent where they meet. 
     When the joint is transmitting torque the rotary axis of each roller may be tilted with respect to the plane of symmetry of its associated tracks. Thus when the direction of torque transfer through the joint reverses, each roller moves into contact with a track surface through which torque is then being transferred and tilts about an axis parallel to the rotary axis of the second member until its orientation is determined by said three-point contact. The tilt movement of each roller is preferably in a sense opposite to the direction of rotation of the first member after the direction of torque transfer has been reversed. 
     Each trunnion may have a part spherical surface engaged with a cylindrical bore of an inner rotary member on which the roller, is rotatably mounted. Alternatively each trunnion may have a cylindrical surface on which is rotatably mounted an inner rotary member having a spherical outer surface engaged with a cylindrical bore of the roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail by way of example with reference to the accompanying drawings in which: 
     FIG. 1 shows a cross-section through part of a shudderless, plunging, tripode joint according to the prior art. 
     FIG. 2 shows a cross-section through part of another shudderless, plunging, tripode joint according to the prior art. 
     FIG. 3 is a cross-section through part of a joint constituting one embodiment of the invention: 
     FIG. 4 is a diagram showing what happens when the roller skews; 
     FIGS. 5 a  and  5   b  are diagrams showing the orientations of the three rollers when torque is being transmitted from the outer member to the inner member in clockwise and anticlockwise directions respectively; 
     FIG. 6 is a cross-section similar to FIG. 3 of a second embodiment of the invention; and 
     FIG. 7 is a cross section through a complete joint embodying the invention; and 
     FIGS. 8,  9  and  10  are views similar to FIG. 3 of three further embodiments. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 3, the inner member or spider of the joint is indicated at  30  and one of the trunnions at  31 . The trunnion has a part-spherical external surface  32 , the center of which is shown at  32   a . There are three trunnions as shown in FIG.  7  and the centers of the spherical surfaces of all the trunnions lie in a plane perpendicular to the rotary axis  30   a  of the inner member. Mounted on each trunnion is an inner first roller  33  which has a cylindrical bare to engage the part-spherical surface  32 . An outer roller is indicated at  34  and is mounted on the inner roller by a needle roller bearing  35  and retained in position by rings  36 . 
     The outer race  40  of the joint has three grooves as shown in FIG. 7, each groove providing a pair of tracks, one pair of which is shown in FIG. 3, the track surfaces being indicated at  41  and  42 . These surfaces form parts of the same cylinder but may be of other shapes. The tracks  41  and  42  are symmetrically arranged with respect to a plane (the plane of symmetry) containing the rotary axis of the outer race and the line  45 . The root  43  of the track is also a cylindrical surface having its center at  43   a . The tracks in the other grooves are similarly arranged. The outer race  40  has a rotary axis  40   a.    
     As shown in FIG. 3 the outer roller  34  has an external circumferential surface  37  which engages the track  42  and a surface  39  which engages the root  43  so that there is three-point contact between the roller and the track surface  42  and the root  43 . Thus assuming that torque is being transmitted from the trunnion  31  to the outer race  41  in a clockwise sense there is a force F 0  between the spherical surface  32  and the inner roller  33  and two reaction forces F 2  and F 3  at the two points where the outer roller  34  engages the track  42 . There is also a force F 1  where the surface  39  at the top of the outer roller  34  engages part of the track root  43 . The outer roller  34  is thus determined in its orientation by this three-point contact represented by the arrows F 1 , F 2  and F 3 . The contact vectors, i.e. the lines of action, of the forces F 2  and F 3  if projected on to a common plane perpendicular to the rotary axis  30   a  (i.e., the drawing sheet plane) intersect at O, the center of curvature of the tracks  41  and  42 . In other words, F 2  and F 3  intersect on a plane of symmetry containing the rotary axis of the outer race  40  and the line  45 . In the absence of the force F 1  the roller could rotate about: the point O and would be unstable. The force F 1 , if projected on to said common plane, intersects the projected contact vectors of the forces F 2  and F 3  at E and D respectively. The points O, D and E form a triangle and the contact vector, line of action, of the Force F 0  (which acts through the center  32   a  of the spherical surface  32 ) intersects two sides of the triangle, i.e. OD and DE. This arrangement, described in more detail below ensures that the roller is stable and is maintained in position with its three point contact. It is to be noted that of the triangle sides intersected by the contact vector of the force P 0  the side OD is the contact vector of the radially innermost force F 3  and the line DE is the contact vector of the radially outermost force F 1 , where the radial positions are measured with respect to the rotary axis  30   a  of the second member. As long as the force F 0 , when projected on to said common plane, intersects side DE of the triangle ODE, contact is maintained at points associated with forces F 2  and F 3 . In addition, as long as the force F 0  also intersects side CD of the triangle ODE, the moment on the roller about point O ensures contact at the point associated with force F 1 . In other words, these conditions ensure that the values of forces F 1 , F 2  and F 3  are positive so that contact is maintained at these three points. 
     Each of the forces transmitted to the outer race  40  from a trunnion  31  and reacted by the forces F 1 , F 2  and F 3  have a tangential component acting in the positive torque-transmitting direction. The point forces are preferably Hertzian, i.e. there are at least two principal radii of curvature of the outer surface  37  and the track surface  42  which results in there being discrete elliptical contact areas. 
     It will be seen that there is a clearance  44  (much exaggerated in the drawing) between the left-hand track  41  and the surface  37  of the outer roller  34 . The outer roller  34  is therefore only in contact with the track through which torque is being transferred, i.e. in the drawing, the track which is to the right of the plane of symmetry of the tracks  41 ,  42 . The whole of the circumference of the roller  34  therefore to the left of such plane is out of contact with the track  41  and there will be no intermittent contacts therewith as in FIGS. 1 and 2. The rotary axis of the outer roller  34  is not parallel to the line  45  which passes through the point  43   a , the center of the root cylindrical surface  43 , and the spherical center O. During operation of the joint the point of contact between the spherical surface  32  of the trunnion and the cylindrical bore of the roller  33  will move radially. 
     If the direction of torque transfer now reverses, the surface  37  of the roller  34  will come into engagement with the left-hand track  41  and the outer roller  34  will then tilt so that the left-hand portion of the surface  39  comes into contact with the root  43  of the track. The outer roller  34  will move out of contact with the track  42 . This tilting of the outer roller  34  is in a direction opposite to the direction of rotation of the inner member  30  of the joint once the reversal of torque transmission has taken place. It is thought that this motion and the sliding of the outer roller  34  across the track  41 , following the initial impact, will tend to absorb the energy of the impact and hence reduce the effects of backlash which can give rise to noise and vibration problems when the joint is installed in a vehicle. 
     If the outer roller  34  skews, i.e. rotates about an axis perpendicular to the roller axis and to the rotary axis of the outer member then, as shown in FIG. 4, the contact point between the surface  39  on the end of the outer roller  34  and the track root  43  is free to move from the position  46  to the position  47  or the position  48  or somewhere between these two positions. Movement of this contact point will limit the skew motion of the outer roller  34 . 
     FIG. 5 a  shows the three rollers in their tilted orientations as torque is being transmitted from the outer member of the joint to the inner member in a clockwise sense and FIG. 5 b  shows the outer roller  34  orientations when torque is being transmitted in an anticlockwise sense. When the torque is reversed the rollers tilt in the direction opposite to the direction of rotation of the inner member  30  once reversal of torque has taken place and engage the tracks on the other sides of the grooves so that there is a clearance between those faces of the roller which are not transmitting torque and the tracks. 
     FIG. 6 shows a joint similar to FIG. 2 but which embodies the invention. Thus referring to FIG. 6 the inner member of the joint is indicated at  50  and a trunnion at  51 . The trunnion is cylindrical and carries a needle roller bearing  52  which in turn carries an inner roller  53  having an external spherical surface  54 . An outer roller  55  has a cylindrical bore  56  which engages the spherical surface  54 . 
     The outer roller  55  is of the same shape as that described in relation to FIG. 3 as is the track  57  in the outer member  55  of the joint. Again there is three-point Hertzian contact indicated by the arrows F 1 , F 2  and F 3  and the operation of this joint is as described in relation to the joint of FIG.  3 . 
     As in FIG. 3 the contact vectors of the forces F 2  and F 3 , when projected on to a common plane perpendicular to the rotary axis of the second member intersect at O (i.e., the drawing plane), the center of curvature of the tracks  57 . The contact vector of the force F 1  when projected on to said common plane intersects the force vectors of the forces F 2  and F 3  at E and D and the points O, E and D are apices of a triangle. As shown the contact vector of the force F 0  intersects the triangle sides OD and DE so that the roller  55  is in stable equilibrium under the influence of the forces F 1 , F 2  and F 3 . As described in relation to FIG. 3 the sides OD and DE which are intersected by the contact vector of the force F 0  (which acts through the center S of the spherical surface  54 ) are the contact vectors of the radially innermost force, F 3 , and the radially outermost force, F 1 . As in FIG. 3 also the roller is out of contact with the left-hand track  57 . 
     Referring now to FIG. 8, this shows a joint similar to that shown in FIG. 3 except that in this case the roller is not twisted. Thus the inner member of the joint is indicated at  60  and a trunnion at  61 . There are three such trunnions equi-angularly spaced around the rotary axis  62  of the inner member. The trunnion has an outer spherical surface  63  which engages the cylindrical bore  64  of an inner roller  65 . The inner roller  65  is surrounded by a ring of needle rollers  66  on which runs the outer roller  67 , the whole being held together by circlips  68  as described in relation to FIG.  3 . 
     The outer member is indicated at  69  and has three grooves as before one of which is shown at  70 . Each groove has two tracks  71  and  72  which are formed of cylindrical surfaces and form part of the same cylinder the center of which is at O. There is a second cylindrical track surface on each side of the groove shown at  74  and  75  respectively. The surfaces  71  and  74  are co-tangential as are the surfaces  72  and  75 . 
     As in FIG. 3, the outer roller  67  is in contact with the track surfaces  71  and  74  but is out of contact with the track surfaces  72  and  75 . This assumes that torque is being transferred in an anticlockwise direction from the outer member  69  to the inner member  60 . 
     The contact vector of the trunnion to roller force is shown at F 0 . There are three reaction forces FA, FB and FC which act at three points A, B and C respectively Point A is on the cylindrical surface  74  and points B and C are on the cylindrical surface  71 . 
     The contact vectors of the forces FB and FC intersect at O, i.e. the axis of the cylindrical surfaces  71  and  72 . If these force vectors are projected onto a common plane (the drawing plane) and the force vector of the force FA which acts at a point A on the cylindrical surface  74  is also projected onto the same common plane, one gets a triangle whose apices are O, E and D. It will be seen that the contact vector of the force F 0  (which acts through the center S of the spherical surface  63 ) intersects the lines OD and DE. This is a necessary condition for the roller  67  to remain in three-point contact with the surfaces  71  and  74  at the points A, B and C. It will be noted as described above that the sides which are intersected by the contact vector of the force F 0  are the sides formed by the contact vector of the radially innermost force, FC and of the radially outermost force, FA. The contact vector of the force P 0  does not intersect the contact vector of the intermediate force FB. 
     If the direction of torque transfer through the joint reverses then the roller  67  will come into contact with the surfaces  72  and  75  and out of contact with the surfaces  71  and  74 . It is to be noted that, ignoring friction, the contact vector force P 0  acts through the center of the spherical surface  63 . 
     Like parts in FIGS. 8 and 9 are shown by the same reference numbers. FIG. 9 shows a similar arrangement to FIG. 8 except that in this case the intersection point O of the contact vectors of the forces FB and FC does not lie on the plane of symmetry of the tracks. As before, the contact vector of the force P 0  intersects the sides OD and DE which are the sides of the triangle formed by the contact vectors of the radially innermost and outermost forces, i.e. FC and FA respectively, when the forces are projected on to a common plane perpendicular to the rotary axis of the outer member which is shown by the point  62  which is the same as the rotary axis of the inner member. It will be seen that in each of FIGS. 8 and 9 the intersection O of the forces FE and FC is at a point radially outwardly of the center of the spherical surface of the trunnion. 
     FIG. 10 shows a further arrangement in which the intersection O of the forces FC and FB is at a position which is radially inwardly of the center of the trunnion. In this embodiment, the point A, where the force FA acts, the force FA being that with the greatest roller-axial component, is located radially inwardly of the points B and C where the forces FB and FA act. In FIG. 10 like parts are indicated by the same reference numerals as in FIG.  8 . In FIG. 10, ignoring friction, the contact vector of the force F 0  acts through the centers of the spherical surface  63 . 
     The contact vectors of the forces FB and FC act through the points B and C respectively and when projected on to a common plane perpendicular to the rotary axis of the outer member intersect at the point O which his radially inward from the centers of the trunnion sphere. In this case the contact vector of the force F 0  intersects the sides OE and ED of the triangle. These sides are those provided by the radially outermost force FC and the radially innermost force FA. As before the contact force vector of the force F 0  does not intersect the contact vector of the force FB. 
     Preferably at all the contact points A, B and C the contacts are Hertzian since the contact surfaces have at least two identifiable radii of curvature. In fact the contact at the points A, B and C have three radii of curvature, two associated with the roller  67  and one associated with the tracks  71 ,  74  and  72 ,  75 . Such contacts should promote the ingress of lubricant into the contact zones and the resulting formation of a lubricant film should reduce the rolling resistance of the roller. 
     The invention thus provides a joint which fulfills the above-mentioned objects, has a low plunge resistance and low NVH.