Abstract:
A constant velocity transmission joint having a male element ( 10 ) having a plurality of arms ( 14 ); a female element ( 20 ) defining a pair of facing tracks ( 22, 23 ) for each arm ( 14 ), which tracks are situated on opposite sides of the arm; and, mounted on each arm, a mechanical transmission member ( 30 ) that is movable in the longitudinal direction of the pair of tracks ( 22, 23 ), being held axially by the tracks, and establishing a connection with the arm that is swiveling and axially movable along the axis (Y—Y) of the arm. The transmission member includes a circularly symmetrical outer roller placed between the corresponding tracks to roll on one or other of them. For each arm, the outside profile in meridian half-section of the outer roller ( 32 ) comprises two arcs ( 32 A,  32 B) having curvature of the same sign and cooperating with two arcs ( 22 A,  22 B) of the substantially complementary profile of the associated tracks ( 22, 23 ) so as to form two spaced-apart contact zones ( 37 A,  3 TB). The invention is applicable to constant velocity joints for motor vehicle transmissions.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to constant velocity transmission joints having a male element having a plurality of arms, a female element defining a pair of facing tracks for each arm, the tracks being situated on opposite sides of the arm, and mounted on each arm, a mechanical transmission member. The mechanical transmission member is moveable along the longitudinal direction of the pair of tracks and establishes a connection with the arm that is swivelling and axially moveable along the axis of the arm. The mechanical transmission members each include a circularly symmetrical outer roller disposed between the corresponding tracks. 
     The invention applies in particular to constant velocity joints for motor vehicle transmissions. 
     In the text below, the terms “axial” and “radial” are used relative to the axis of the arm in question. Similarly, the terms “inner” and “outer” are used relative to the axis of revolution of the outer roller, said axis coinciding with that of the arm for a joint bent at a deflection angle of zero. 
     In the field of such joints, it is known that each arm of the male element moves relative to the corresponding pair of tracks in reciprocating translation along the axis of the arm. Those movements are inevitable because of the structural geometry of the joint. They result from the way the joint operates when there is a deflection angle between the two shafts coupled together by the joint, and they also come from the “offset” phenomenon which consists in orbital movement performed by the center of the male element at a frequency which is three times the frequency of rotation of the joint. 
     When transmitting torque, friction causes those movements to generate an axial component of the drive force which gives rise to a reciprocating tilting force to which each outer roller is subjected, with the outside surfaces of the rollers generally being toroidal. That force tends to cause the outer roller to oscillate about its point of contact with the track on which it is running. The portion of the outside surface of the roller that is diametrically opposite its portion that is applying pressure then oscillates strongly relative to the surface of the tracks against which the roller is not applying pressure, thus reducing the transmission efficiency of the joint. 
     Those oscillations also generate a high level of noise which is disagreeable for the user. They also require the surface hardness of the zones of the tracks that are subject to oscillating contact with the roller to be reinforced by appropriate surface treatments, which treatments are often complex because of the shape of the female element. Finally, those oscillations run the risk of an outer roller becoming jammed at the ends of the track. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a constant velocity transmission joint of the type mentioned in which any oscillating motion of the outer roller is prevented by means that are simple, thereby imparting remarkable stability to the roller. 
     According to the invention, this object is achieved by a constant velocity transmission joint of the type specified wherein, for each arm, the outside profile in meridian half-section of the outer roller comprises two arcs having curvature of the same sign cooperating with two substantially complementary arcs of the associated track to form two spaced-part contact zones, each contact zone defining a contact resultant that is substantially perpendicular to the axis of the outer roller. 
     In various embodiments of the invention, the arcs of the roller may be convex or circular. The outside profile of the roller may also be symmetrical about a midplane of the roller. In another aspect of the invention, the transmission member includes an inner ring disposed inside the outer roller and a coupling mechanism for coupling the inner ring and outer roller together. The inner ring allows only relative pivoting between the inner ring and the outer roller about a common axis of revolution, and the inner ring is mounted to swivel and slide relative to the arm. In one aspect, the inner ring is mounted to swivel inside the outer roller. In another aspect, the inner ring is mounted to slide on the arm along a common axis of revolution, and the inside surface of the roller and outside surface of the ring are spherical and substantially complementary. In another example, the inner ring is slidable relative to the outer roller along the axis of revolution of the roller, and the inner ring is prevented from moving axially relative to the arm. 
     In another embodiment, the outer roller includes two juxtaposed portions each presenting in meridian half-section an outside profile which includes one of the two arcs of the outer roller. In a further embodiment, each portion of the outer roller includes an inwardly-directed end shoulder on its inside face about the axis of the roller, the two shoulders defining between them, a cavity for receiving the coupling mechanism. 
     The invention also provides a transmission member for a constant velocity transmission joint as defined above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood upon reading the following description given purely by way of example and made with reference to the drawings, in which: 
     FIG. 1 is a fragmentary cross-section view of a tripod-type constant velocity transmission joint of the invention, when in the straight position; 
     FIG. 1A shows a detail of FIG. 1; and 
     FIGS. 2 to  4  are views analogous to FIG. 1, each showing a particular embodiment of a tripod-type constant velocity transmission joint of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a fragment of a tripod-type constant velocity joint  1  in a first embodiment of the invention that essentially comprises the following parts. 
     Firstly, the joint  1  comprises a male, spider element or “tripod”  10  having three-way symmetry about a central axis X—X that is orthogonal to the plane of FIG. 1, the element comprising a hub  12  and three radial arms  14  angularly spaced apart at 120°, with only one arm being shown. The end portion of each arm  14  forms a trunnion  16  of spherical shape centered on the axis Y—Y of the arm. The tripod  10  is secured to a first shaft  18 . 
     Thereafter, the joint  1  comprises a female, race element or “tulip”  20  having three-way symmetry about a central axis X′—X′, said axis coinciding with the axis X—X when the joint shown is in its straight or aligned position. On either side of each arm  14 , the tulip presents two facing tracks  22  and  23 . The tulip is secured to a second shaft (not shown). 
     Finally, for each arm  14 , the joint  1  has a mechanical transmission member  30  held axially by the pair of tracks  22 ,  23 . The mechanical transmission member  30  comprises an outer roller  32  for rolling on one or other track  22 ,  23 , an inner ring  34  placed inside the outer roller  32 , and a coupling mechanism  36  for coupling together the inner ring  34  and the outer roller  32 . The roller  32  presents an axis of revolution Z—Z that coincides with the axis Y—Y in FIG.  1 . 
     Since the three mechanical transmission members  30  are identical, and since the tripod  10  and the tulip  20  have three-way symmetry, only the portion of the joint  1  that is shown in FIG. 1 is described in greater detail. 
     The mechanical transmission member  30  establishes a swiveling and moving connection about the axis Y—Y of the arm  14  where it maintains contact between the inside surface of the inner ring  34  and the outside surface of the trunnion  16 . The inner ring  34  thus rotates, tilts, and slides about the arm  14 . 
     The transmission member  30  can also move in the longitudinal direction of the pair of tracks  22 ,  23 , i.e. in the direction perpendicular to the plane of FIG.  1 . 
     In meridian half-section, e.g. in the left half-plane relative to the axis Z—Z in FIG. 1, the outer roller  32  presents an outside profile comprising two convex circular arcs  32 A,  32 B, while the corresponding track  22  presents an inside profile comprising two concave circular arcs  22 A,  22 B that are substantially complementary to the convex arcs  32 A,  32 B of the outside profile of the roller  32 . At these arcs, for each direction in which the joint can be driven, the roller  32  and the associated track  22  forms two contact zones  37 A,  37 B presenting respective resultants R A , R B  that are substantially perpendicular to the axis Z—Z of the roller. These contact zones  37 A,  37 B are situated at the bottoms of the two arcs  22 A and  22 B of the inside profile of the track  22 , so they are spaced apart from each other. 
     More precisely (FIG.  1 A), the arcs  32 A and  32 B are of a radius that is slightly smaller than the radius of the arcs  22 A and  22 B, and the concave arc  32  interconnecting the arcs  32 A and  32 B is of radius that is small enough to ensure that there is no contact with the convex arc  22 C interconnecting the arcs  22 A and  22 B. The differences of radius are exaggerated in FIG. 1A in order to clarify the drawing. The arcs  32 A and  32 B can have equal radii, and the arcs  22 A and  22 B can have equal radii as shown. 
     The coupling mechanism  36  between the inner ring  34  and the outer roller  32  comprises a circular set of needles  38  disposed between the outside cylindrical surface of the inner ring  34  and the inside cylindrical surface of the outer roller  32 , together with two flat bearing washers  39  and  40  placed on either side of the ring  34  and of the set of needles  38 . The periphery of each bearing washer  39 ,  40  is received in an annular groove formed in the inside surface of the outer roller. 
     Ignoring operating clearances, this coupling mechanism  36  thus allow solely for relative rotation between the outer roller  32  and the inner ring  34  about the axis Z—Z. 
     The joint  1  operates as follows. 
     Under the effect of drive torque applied to the shaft  18  and assumed to be in a counterclockwise direction in FIG. 1, the arm  14  applies a transmission force T to the mechanical transmission member  30 . The point of application of this force is the contact point between the trunnion  16  of the arm  14  and the inner ring  34  of the member  30 . This force comprises a radial component T R  that results directly from applying the drive torque as applied to the shaft  18 , plus an axial component T A  along the axis Z—Z that results from friction between the outside surface of the trunnion  16  and the inside surface of the inner ring  34 . This friction is generated by the relative sliding motion between the trunnion  16  and the ring  34  whenever the joint is operating at a non-zero deflection angle, and to the “offset” orbital motion of the axis X—X of the male member  10 , as mentioned above. 
     The radial component T R  of the force is transmitted to the female element  20  via the contact zones  37 A and  37 B maintained between the outer roller  32  subjected to the radial component T R  and the associated track  22  of the female element  20 . 
     The axial component T A  of the transmission force, whose nominal value is conventionally about one-tenth that of the radial component T R , generates a force that tends to tilt the transmission member  30 . However, this force is taken up in full by the track  22  of the female element via the contact zones  37 A and  37 B maintained between the roller  32  and the track  22 . 
     The resultants R A  and R B  in each contact zone remain perpendicular to the axis Z—Z of the roller, and the distance d of each contact zone from the midplane P of the tracks  22  and  23  is selected to be sufficient to ensure that the point of application of the force T R  remains permanently in the volume which is defined between the two parallel plans planes P A  and P B  that are both perpendicular to the axis Z—Z and that contain the respective centers of the contact zones  37 A and  3 B. 
     Thus, under the effect of driving torque, the mechanical transmission member  30  has the ability, in terms of freedom of movement, only to roll along said tracks and to slide along the longitudinal axis of said pair of tracks. 
     The invention thus makes it possible to ensure that the transmission member  30  is stable, preventing it from performing, relative to the corresponding pair of tracks, any movement in translation along the axis Z—Z of the outer roller  32 , any movement in rotation about the longitudinal axis of said pair of tracks, and any movement in rotation about an axis perpendicular to the axis Z—Z. 
     Since the stability of the outer roller  22  is improved, vibration level and transmission efficiency of the joint are improved. Similarly, the surface treatments that are essential in prior art joints for reinforcing the surface hardness of certain zones of the female element are no longer necessary. 
     A variant (not shown) of this first embodiment consists in placing an outer roller whose outside profile has two concave arcs so as to engage a track whose inside profile presents two convex arcs that are substantially complementary thereto. 
     Another embodiment of a joint  1  of the invention is shown in FIG.  2 . 
     The joint  102  has the same elements as in the first embodiment, except for the following differences. 
     Firstly, on the tripod element  110 , the trunnion  116  of the arm  114  is substantially cylindrical about the axis of revolution Y—Y. 
     Secondly, the mechanical transmission member  130  comprises a coupling mechanism between the inner ring  134  and the arm  114 . This coupling mechanism includes a circular set of needles  38  that are held radially by two shoulders  50  and  51  on either side of the trunnion  116 . The coupling mechanism thus allows relative pivoting along the axis Y—Y and movement in translation along said axis between the inner ring  134  and the arm  114 . 
     In addition, the inside surface of the outer roller  132  is substantially spherical and co-operates with the spherical surface of the inner ring  134  which is of complementary spherical profile, thus allowing swiveling movement only between the outer roller  132  and the inner  134 . 
     This second embodiment operates in a manner analogous to that described above. 
     The force T to be transmitted from the arm  114  is applied along a line of contact between the outside surface of the trunnion  116  and the inside surface of the set of needles  38 . The inner ring  134  is then subjected to this force, and because of its substantially spherical outside profile, it takes up a position in the bottom of the curvature of the complementary inside surface of the roller  132 , thus bringing the zone of application of the force to be transmitted towards the outside of the joint at the contact zone it maintains with the outer roller  132 , i.e. a zone that amounts to a small spot. 
     The force then transmitted to the outer roller  132  by this pressure thus presents a radial component T R  as described above and an axial component T A  that is fully taken up by the two contact zones  137 A,  137 B maintained between the roller  132  and the corresponding track  22 . The point of application of the force T R  is contained in the volume lying between the two above-defined planes P A  and P B . 
     FIG. 3 shows a third embodiment of a joint  103  of the invention, which differs from that shown in FIG. 2 by the following elements only. 
     Firstly, the mechanical transmission member  230  comprises not only the above-described coupling mechanism for coupling the ring  134  to the arm  114 , but also a split bearing washer  52  partially received in an annular groove adjacent to the end of the trunnion  116  situated on the outside of the joint. The trunnion  116  also has a shoulder  53  adjacent its end situated on the inside of the joint. This shoulder  53  and the washer  52  are located at opposite ends of the circular set of needles  38  and of the ring  134 . 
     Thus, ignoring operating clearances, only relative rotation about the axis Y—Y is possible between the arm  114  and the ring  134 . 
     Furthermore, the inside surface of the outer roller  232  is cylindrical about the axis Z—Z, thus allowing the inner ring  134  to perform, via its spherical outside surface, both sliding and swiveling motion about the axis Z—Z relative to the roller  232 . 
     This embodiment operates analogously to that described above. The force T to be transmitted from the arm  114  is applied to the outer roller  232  via the zone of contact that the inner ring  134  maintains with the roller  232 . 
     Then, as in the preceding embodiment, the point of application of the radial component T R  of the force transmitted to the outer roller  232  remains permanently between the planes P A  and P B , with the axial component T A  being taken up by the two contact zones  237 A and  237 B. 
     FIG. 4 shows a fourth embodiment of a constant velocity joint  104  of the invention which differs from the first embodiment shown in FIG. 1, as follows. 
     The outer roller  232  is constituted by two juxtaposed halves  33 A and  33 B that are symmetrical about the plane P. 
     Advantageously, and as shown in FIG. 4, the inside surface of each half  33 A,  33 B presents a respective inwardly-projecting shoulder  54 A,  54 B. When the two halves  33 A and  33 B are juxtaposed to form a complete outer roller, the two shoulders  54 A,  54 B define a cavity for receiving the coupling mechanism  36 , in this case constituted by a circular set of needles  38 . 
     The inner ring  334  is held axially relative to the axis Z—Z by the set of needles  38  being received in the outside surface of the ring  334  which outside surface presents a cavity  55  that is complementary in shape to the inside surface of the set of needles  38 , having two radially outwardly directed end shoulders  56 A and  56 B. 
     This structure provides the same degrees of freedom and limitations on movement between the transmission member  330  and the arm  14  as in the first embodiment, and the joint  104  operates identically. 
     The joint  104  in this fourth embodiment presents an additional advantage since its coupling mechanism  36  does not require any washers, the inner ring  334  being held axially relative to the axis Z—Z directly by the set of needles  38  being received in the cavity  55 , said set of needles itself being held axially by the juxtaposed assembly of the two halves  33 A and  338  forming the outer roller. 
     Finally, it should be observed that the outside profile of the outer roller  32 ,  132 ,  232 ,  332  appears in all of the figures as being symmetrical about the midplane P of the roller, however that is not a requirement. It is also possible to envisage a roller that is asymmetrical.