Constant velocity universal joint

Abstract

This method suppresses the deterioration of the quality of internal joint components caused by the temporary storage of a large number of internal joint components during the manufacturing process. [Solution] The constant velocity universal joint comprises an outer joint member 2 having multiple track grooves 2b formed on its inner circumferential surface 2a, an inner joint member 3 positioned inside the outer joint member 2 and having female splines 34 formed on its inner circumference, and a torque transmission member 4 that transmits torque between the outer joint member 2 and the inner joint member 3. Relief portions 36 and 37 are provided at both ends of the female spline 34 in the joint axial direction, with the tooth tip surfaces having a larger diameter than the other tooth tip surfaces.

Description

Technical Field

[0001] The present invention relates to a constant velocity joint.

Background Art

[0002] In a drive shaft used in an automotive power transmission system, a sliding constant velocity joint is often provided on the inboard side (the center side in the vehicle width direction), and a fixed constant velocity joint is provided on the outboard side (the outer side in the vehicle width direction). The sliding constant velocity joint herein allows both angular displacement and axial relative movement between two shafts, while the fixed constant velocity joint allows angular displacement between two shafts but does not allow axial relative movement between the two shafts.

[0003] Female splines are formed on the inner circumference of the inner joint member of the sliding constant velocity joint and the fixed constant velocity joint. By fitting this female spline with the male spline formed on the shaft, the inner joint member and the shaft are connected so as to be able to transmit torque.

[0004] Among the female splines formed on the inner joint member, a relief portion may be provided at one end in the axial direction, specifically, at the end on the entrance side when the shaft is inserted, where the diameter dimension of the tooth tip surface is made larger than the diameter dimension of the tooth tip surfaces at other locations (see FIG. 4 of Patent Document 1 and FIG. 6 of Patent Document 2).

[0005] Figure 8 is a cross-sectional view showing the spline fitting portion of the inner joint member 203 (tripod member) of a tripod-type constant velocity universal joint, which is a sliding constant velocity universal joint. The dashed line in the figure represents the male spline 281 formed on the shaft. As shown in the figure, the relief portion 236 of the female spline 234 is formed on one axial side of the inner joint member 203. The relief portion 236 comprises a parallel portion 236a in which the tooth tips of the crests are parallel to the joint axis direction, and a tapered portion 236b formed on the inner side of the parallel portion 236a, in which the inner diameter of the crests gradually decreases towards the inner side. The tooth tips of the crests of the tapered portion 236b are connected to the tooth tips of the small diameter portion of the female spline 234 via an edge-shaped corner P. The valleys of the relief portion 236 are connected to a chamfer 238 formed on the inner circumferential surface of one axial end of the tripod member 203.

[0006] The relief portion 236 is provided to improve the torsional strength between the shaft and the inner joint member 203 by setting an appropriate distance between the stress concentration portion P in the spline fitting portion and the cut-off portion 281a of the structurally weak male spline 281, and to facilitate phase alignment when fitting the splines 234 and 281 together. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6169793 [Patent Document 2] Japanese Patent Publication No. 2010-112505 [Overview of the project] [Problems that the invention aims to solve]

[0008] The inner joint member 203 of the tripod-type constant velocity universal joint shown in Figure 8 is manufactured by first forming the entire piece by cold forging, then forming female splines on the inner circumferential surface by broaching or the like, and finally forming a hardened layer on the entire surface including the female splines 234 by heat treatment such as carburizing and quenching. In the manufacturing process of this inner joint member 203, a large number of inner joint members may be temporarily stored in random positions before and after the processing and transport processes. In particular, if such storage is performed before hardening by heat treatment, collisions or interference between the inner joint members may cause damage to the female serrations 234 at the end opposite the relief portion 236 and the axial direction (part A in Figure 8), and in some cases, this end may undergo partial plastic deformation, potentially leading to a decrease in product quality.

[0009] Therefore, the present invention aims to suppress the deterioration of the quality of internal joint members caused by the temporary storage of a large number of internal joint members during the manufacturing process of internal joint members. [Means for solving the problem]

[0010] To solve the aforementioned problems, the present invention provides a constant velocity universal joint comprising an outer joint member having a plurality of track grooves formed on its inner circumferential surface, an inner joint member disposed inside the outer joint member and having female splines formed on its inner circumference, and a torque transmission member that transmits torque between the outer joint member and the inner joint member, wherein angular displacement between the two members is permitted, and the female splines are provided with relief portions at both ends in the joint axial direction, where the tooth tip surfaces are larger in diameter than the tooth tip surfaces elsewhere.

[0011] In this way, by providing relief sections at both ends of the female spline in the joint axial direction, even when a large number of internal joint members are temporarily stored in random positions before or after the processing or transport process of the internal joint members, it is possible to avoid the occurrence of dents in the female serrations due to collisions or interference between products, as well as partial plastic deformation. Therefore, it is possible to suppress a deterioration in the product quality of the internal joint member 3.

[0012] The relief portions at both ends of the female spline in the coupling axial direction can be formed to have a line-symmetric shape on any cross-section including the coupling axis, with respect to a line passing through the coupling center and perpendicular to the coupling axial direction as the axis of symmetry.

[0013] In this case, the inner joint member can be formed to have a shape that is symmetrical with respect to a line passing through the center of the joint and perpendicular to the direction of the joint axis on any cross-section including the joint axis.

[0014] This eliminates the directional orientation of the inner joint member in the joint axis direction, allowing the shaft to be inserted from either the left or right side of the inner joint member. As a result, incorrect assembly, checking the orientation of the inner joint member, and alignment become unnecessary, improving work efficiency during assembly.

[0015] It is preferable to allow further axial relative movement between the outer joint member and the inner joint member (sliding constant velocity universal joint).

[0016] The constant velocity universal joint described above is preferably positioned on the inboard side of the drive shaft. [Effects of the Invention]

[0017] As described above, according to the present invention, it is possible to suppress the deterioration of the quality of the inner joint members caused by the temporary storage of a large number of inner joint members during the manufacturing process of the inner joint members. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional view in the axial direction of a double-roller type tripod-type constant velocity universal joint. [Figure 2] Figure 1 is a cross-sectional view along the KK line. [Figure 3] This is a cross-sectional view along the LL line in Figure 1. [Figure 4] Figure 1 is a cross-sectional view showing the tripod-type constant velocity universal joint (Figure 1) in the operating angle position. [Figure 5]It is a cross-sectional view in the joint axis direction showing the tripod member shown in FIG. 1. [Figure 6] It is a cross-sectional view in the joint axis direction showing a double offset constant velocity joint. [Figure 7] It is a cross-sectional view in the joint axis direction showing the inner joint member shown in FIG. 6. [Figure 8] It is a cross-sectional view in the joint axis direction showing a conventional spline fitting portion.

Embodiments for Carrying Out the Invention

[0019] An embodiment of a constant velocity joint according to the present invention will be described based on the drawings. In the following description of the first embodiment, as the constant velocity joint, a sliding constant velocity joint, particularly a double roller type tripod type constant velocity joint will be described as an example. Before describing the characteristic configuration of the present invention, the overall configuration of the double roller type tripod type constant velocity joint will be described.

[0020] In FIGS. 1 to 4, a double roller type tripod type constant velocity joint 1 is shown. Note that FIG. 1 is a cross-sectional view in the joint axis direction of the double roller type tripod type constant velocity joint, and FIG. 2 is a cross-sectional view taken along the K-K line in FIG. 1. FIG. 3 is a cross-sectional view taken along the L-L line in FIG. 1, and FIG. 4 is a cross-sectional view in the joint axis direction showing the tripod type constant velocity joint at the operating angle. In the following description, the "joint axis direction", "joint radial direction", and "joint circumferential direction" respectively mean the axis direction, radial direction, and circumferential direction of the constant velocity joint with the operating angle set to 0° unless otherwise specified.

[0021] As shown in FIGS. 1 and 2, this tripod type constant velocity joint 1 mainly includes an outer joint member 2, a tripod member 3 as an inner joint member disposed inside the outer joint member 2, and a roller unit 4 as a torque transmission member that transmits torque between the outer joint member 2 and the inner joint member 3.

[0022] The outer joint member 2 has a cup shape with one end open, and three linear track grooves 2b extending in the joint axis direction are formed on its inner circumferential surface 2a at equal intervals in the joint circumferential direction. Each track groove 2b has a roller guide surface 6 formed thereon, which is positioned opposite the outer joint member 2 in the joint circumferential direction and extends in the joint axis direction. The tripod member 3 and the roller unit 4 are housed inside the outer joint member 2.

[0023] The tripod member 3 integrally comprises a body portion 31 (trunnion body portion) having a central hole 30, three leg shafts 32 (trunnion journals) protruding in the radial direction of the joint from three equally spaced positions in the circumferential direction of the joint on the outer surface of the body portion 31, and an intermediate portion 33 connecting the outer surface of the body portion 31 and the outer surface of the leg shafts 32. The tripod member 3 is coupled to the shaft 8 in a torque-transmitting manner by fitting a male spline 81 formed on the shaft 8 into a female spline 34 formed in the central hole 30 of the trunnion body portion 31. The tripod member 3 is fixed to the shaft 8 in the axial direction of the joint by engaging one end face of the tripod member 3 on the axial direction of the joint with a shoulder portion 82 provided on the shaft 8, and engaging a retaining ring 10 attached to the tip of the shaft 8 with the other end face of the tripod member 3 on the axial direction of the joint.

[0024] The roller unit 4 mainly consists of an outer ring 11, which is an annular roller centered on the axis of the leg shaft 32; an inner ring 12, which is an annular roller positioned on the inner diameter side of the outer ring 11 and fitted onto the leg shaft 32; and a number of needle-shaped rollers 13 interposed between the outer ring 11 and the inner ring 12. The roller unit 4 is housed in the track groove 2b of the outer joint member 2. The roller unit 4, consisting of the outer ring 11, the inner ring 12, and the needle-shaped rollers 13, is structured so that it cannot be separated by washers 14 and 15.

[0025] In this embodiment, the outer circumferential surface 11a of the outer ring 11 (see Figure 2) is a convex curved surface whose generatrix is ​​a circular arc with its center of curvature on the axis of the leg shaft 32. The outer circumferential surface 11a of the outer ring 11 is in angular contact with the roller guide surface 6.

[0026] The needle rollers 13 are arranged to roll freely between the outer and inner raceway surfaces, with the cylindrical inner surface of the outer ring 11 serving as the outer raceway surface and the cylindrical outer surface of the inner ring 12 serving as the inner raceway surface. The needle rollers 13 are arranged in a full-complement configuration without a cage.

[0027] The outer circumferential surface of each leg shaft 32 of the tripod member 3 is straight in the axial direction of the leg shaft 32 in a cross section (longitudinal section) in any direction including the axis of the leg shaft 32. Also, as shown in Figure 3, the outer circumferential surface of the leg shaft 32 is substantially elliptical in a cross section (transverse section) perpendicular to the axis of the leg shaft 32. The outer circumferential surface of the leg shaft 32 is in contact with the inner circumferential surface 12a of the inner ring 12 in the direction perpendicular to the axial direction, i.e., in the direction of the major axis a. In the direction of the joint axis, i.e., in the direction of the minor axis b, a gap m is formed between the outer circumferential surface of the leg shaft 32 and the inner circumferential surface 12a of the inner ring 12.

[0028] As shown in Figures 1 and 2, the intermediate portion 33 between the body portion 31 and the leg shaft 32 of the tripod member 3 is formed to draw a concave curve, such as a circular arc, in any cross-section that includes the axis of the leg shaft 32. Both ends of the concave curve are smoothly connected to the outer surface of the body portion 31 and the outer surface of the leg shaft 32, respectively, so as to have a common tangent.

[0029] The inner circumferential surface 12a of the inner ring 12 is convex in shape in any cross-section containing the axis of the inner ring 12. Because of this, and because the cross-sectional shape of the leg shaft 32 is substantially elliptical as described above, and a predetermined gap m is provided between the leg shaft 32 and the inner ring 12, the inner ring 12 becomes pivotable relative to the leg shaft 32. As described above, since the inner ring 12 and the outer ring 11 are assembled so as to be rotatable relative to each other via the needle rollers 13, the outer ring 11 can pivot together with the inner ring 12 relative to the leg shaft 32. In other words, within a plane containing the axis of the leg shaft 32, the axes of the outer ring 11 and the inner ring 12 can be inclined with respect to the axis of the leg shaft 32 (see Figure 4).

[0030] As shown in Figure 4, when the tripod-type constant velocity universal joint 1 rotates at an operating angle, the axis of the tripod member 3 is inclined with respect to the axis of the outer joint member 2. However, because the roller unit 4 is oscillating, it is possible to avoid a state in which the outer ring 11 and the roller guide surface 6 are at an oblique angle. As a result, the outer ring 11 rolls horizontally with respect to the roller guide surface 6, which reduces induced thrust and sliding resistance compared to the single-roller type tripod-type constant velocity universal joint described later, and enables low vibration of the tripod-type constant velocity universal joint 1.

[0031] Furthermore, as already mentioned, since the cross-section (transverse plane) of the leg shaft 32 is approximately elliptical and the cross-section (longitudinal plane) of the inner circumferential surface 12a of the inner ring 12 is an arc-shaped convex cross-section, the outer circumferential surface of the leg shaft 32 and the inner circumferential surface 12a of the inner ring 12 make contact at a point or over a narrow area close to point contact when torque is applied. Therefore, the force that tends to tilt the roller unit 4 is reduced, and the stability of the posture of the outer ring 11 is improved.

[0032] The tripod member 3 described above is manufactured from steel material through the following main processes: forging (cold forging) → machining (turning) → broaching of the spline 34 → heat treatment → grinding of the outer surface of the leg shaft 32. The outer surface of the leg shaft 32 can also be finished by cutting hardened steel instead of grinding. For heat treatment, carburizing, quenching, and tempering are performed. By hardening the carburized layer through quenching, a hardened layer is formed on the surface of the tripod member 3. The hardened layer is formed on the entire surface of the tripod member 3, including the outer surface of the leg shaft 32 and the surface of the female spline 34.

[0033] The configuration of the characteristic parts in this embodiment will be described below with reference to Figure 5. Figure 5 is a cross-sectional view of the tripod member 3 in the direction of the joint axis.

[0034] As shown in Figure 5, in this embodiment, relief portions 36 and 37 are provided on the inner circumferential surface of the inner joint member 3, at both ends of the female spline 34 in the joint axial direction, with the tooth tip surfaces having a larger diameter than the other tooth tip surfaces. Both relief portions 36 and 37 are formed by removing the inner diameter side region of the small diameter portion of the female spline 34, thereby reducing the tooth height of each small diameter portion. Both relief portions 36 and 37 alternately have peaks and valleys in the joint circumferential direction. The phase in the joint circumferential direction between the peaks of both relief portions 36 and 37 and the small diameter portion of the female spline 34 is equal, and the phase in the joint circumferential direction between the valleys of both relief portions 36 and 37 and the large diameter portion of the female spline 34 is also equal. The valleys of both relief portions 36 and 37 have the same radial dimension as the large diameter portion (tooth root) of the female spline 34.

[0035] The relief portions 36 and 37 can be formed, for example, by cold forging the tripod member, turning the inner circumference of both ends of the tripod member 3 in the direction of the joint axis, and then broaching the inner circumferential surface, including the turned portion, to form the female spline 34.

[0036] Both relief sections 36 and 37 have parallel sections 36a and 37a in which the tooth tips of the peaks extend parallel to the joint axis direction, and tapered sections 36b and 37b formed further inward in the joint axis direction than the parallel sections 36a and 37a, with the inner diameter of the peaks gradually decreasing towards the back. The tooth tips of the peaks of the tapered sections 36b and 37b are connected to the tooth tips of the small diameter section of the female spline 34 via edge-shaped corners P. The valleys of both relief sections 36 and 37 are connected to chamfers 38 and 39 formed on the open ends on both sides of the joint axis direction of the inner circumferential surface of the tripod member 3.

[0037] When the shaft 8 is inserted into the inner circumference of the inner joint member 3 and the female spline 34 and male spline 81 (see Figure 1) are fitted together, the parallel portion 36a of the relief portion 36, which is on the inlet side of the shaft insertion (left side in Figure 5), is a region that does not fit with the male spline 81. The tapered portion 36b of this relief portion 36 fits with the male spline 81 of the shaft 8 in a portion of the joint axial direction. The relief portion 37 located on the outlet side of the inserted shaft (right side in Figure 5) has a parallel portion 37a that fits with the male spline 81, including the tapered portion 37b. However, it is not always necessary to fit the parallel portion 37a on the outlet side with the male spline 81; similar to the relief portion 36 on the inlet side, the parallel portion 37a does not need to fit with the male spline 81.

[0038] Both relief sections 36 and 37 are formed to the same length in the joint axis direction. Specifically, the lengths of both parallel sections 36a and 37a in the joint axis direction are equal, and the inclination angles of the tapered sections 36b and 37b on both sides are also equal (although the inclination directions are opposite). Therefore, the shapes of both relief sections 36 and 37 are symmetrical with respect to a line R that passes through the joint center Q and is perpendicular to the joint axis direction on any cross section containing the joint axis O. The chamfers 38 and 39 also have opposite inclination directions, but their inclination angles are the same.

[0039] The contour of the tripod member 3, excluding the central hole 30, is typically formed symmetrically with respect to a line R that passes through the joint center Q and is perpendicular to the joint axis direction, on any cross-section containing the joint axis O. Therefore, by giving symmetry to the shapes of the relief portions 36 and 37 as described above, the entire tripod member 3 becomes symmetrical with respect to the symmetry axis R on any cross-section containing the joint axis O.

[0040] In this way, by providing a relief portion 37 on the exit side end of the inner circumferential surface of the inner joint member 3, in addition to the relief portion 36 on the inlet side end when the shaft is inserted, it is possible to avoid the occurrence of dents on the female serrations 34 due to collisions or interference between products and partial plastic deformation, even when a large number of inner joint members 3 are temporarily stored in random positions before or after the processing or transport process of the inner joint member 3. Therefore, a decrease in the product quality of the inner joint member 3 is suppressed, and when the shaft 8 is finally assembled to the inner joint member 3, the assembly work can be performed smoothly. This effect can be particularly noticeable when the storage process of the tripod member 3 is performed before hardening by heat treatment.

[0041] Providing relief portions 36 and 37 at both ends of the female spline 34 in the direction of the coupling axis shortens the effective length of the female spline 34 compared to the conventional case where the relief portion 36 is formed only on one side in the direction of the coupling axis, raising concerns that the torque load capacity of the spline fitting portion may be insufficient. However, in reality, conventional female splines 34 are designed with a sufficient safety factor, so even if the effective length of the female spline 34 is shortened by adding the relief portion 37 on the outlet side, as in this embodiment, a sufficient torque load capacity can be secured.

[0042] In conventional products, as shown in Figure 8, there is a relief portion 236 on only one side in the direction of the joint axis, and the tripod member 3 has a directionality in the direction of the joint axis. Therefore, if the direction of insertion of the shaft 8 into the tripod member 3 is incorrect, it will result in incorrect assembly. To prevent this, it is necessary to check the direction of the tripod member 3 and align its direction before inserting the shaft 8, which reduces the workability when assembling the shaft. In contrast, as in this embodiment, if the shape of the tripod member 3 is determined so that the whole is symmetrical with respect to the axis of symmetry R on any cross section including the joint axis O, the directionality of the tripod member 3 is eliminated, and the shaft 8 can be inserted from either the left or right side of the tripod member 3. Therefore, the above-mentioned problems can be resolved.

[0043] A second embodiment will be described below with reference to Figures 6 and 7. In the second embodiment, the present invention is applied to a double-offset type constant-velocity universal joint 1', which is a sliding type constant-velocity universal joint. The main parts of the double-offset type constant-velocity universal joint 1' consist of an outer joint member 2, an inner joint member 3 positioned inside the outer joint member 2, and a ball 41 as a torque transmission member that transmits torque between the outer joint member and the inner joint member. The overall structure of the double-offset type constant-velocity universal joint will be described below.

[0044] The inner circumferential surface 2a of the cup-shaped outer joint member 2 is formed in a cylindrical shape. Multiple track grooves 2b extending in the direction of the joint axis are formed at equal intervals in the circumferential direction of the joint on the inner circumferential surface 2a of the outer joint member 2. A female spline 34 is formed on the inner circumference of the cylindrical inner joint member 3. By fitting the female spline 34 with the male spline 81 formed on the shaft 8, the inner joint member 3 and the shaft 8 are coupled in a torque-transmitting manner. A retaining ring 10 attached to the shaft end of the shaft 8 prevents the shaft 8 from coming off the inner joint member 3. The outer circumferential surface 3a of the inner joint member 3 is spherical. Multiple track grooves 3b extending in the direction of the joint axis are formed at equal intervals in the circumferential direction of the joint on the spherical outer circumferential surface 3a of the inner joint member 3.

[0045] A ball track is formed by the track groove 2b of the outer joint member 2 and the track groove 3b of the inner joint member 3 that is opposite to it. Ball tracks are provided at multiple locations in the circumferential direction of the joint, and one ball 41 is placed on each ball track.

[0046] The cage 9 has pockets 9a formed at predetermined intervals in the circumferential direction of the joint. One ball 41 is housed in each pocket 9a. The cage 9 holds all the balls 41 on the same plane.

[0047] The cage 9 is positioned between the outer joint member 2 and the inner joint member 3. Of the outer surface of the cage 9, the spherical portion 9b with an arc-shaped cross-section is in contact with the inner surface 2a of the outer joint member 2, and of the inner surface of the cage 9, the spherical portion 9c with an arc-shaped cross-section is in contact with the spherical outer surface 3a of the inner joint member 3. The center O1 of the spherical portion 9b on the outer surface of the cage 9 and the center O2 of the spherical portion 9c on the inner surface are offset by an equal distance from the angular center Q (joint center) of the joint to the opposite side (double offset).

[0048] Figure 7 shows a cross-sectional view in the joint axis direction of the inner joint member 3 that constitutes the double offset type constant velocity universal joint 1'. Similar to the first embodiment, in the second embodiment as well, relief portions 36 and 37 are provided on the inner circumference of the inner joint member 3 at both ends of the female spline 34 in the joint axis direction. Each of the relief portions 36 and 37 has parallel portions 36a and 37a and tapered portions 36b and 37b, respectively. The relief portions 36 and 37 are formed in a shape that is symmetrical with respect to a line R that passes through the joint center Q and is perpendicular to the joint axis direction on any cross-section including the joint axis O.

[0049] The inner joint member 3 of the double offset type constant velocity universal joint 1' is typically formed symmetrically with respect to a line R that passes through the joint center Q and is perpendicular to the joint axis direction, on any cross-section including the joint axis O, excluding the inner circumferential surface. Therefore, by giving symmetry to the shapes of the relief portions 36 and 37 as described above, the entire inner joint member 3 becomes symmetrical with respect to the symmetry axis R on any cross-section including the joint axis O. As a result, the second embodiment can enjoy the same effects as the first embodiment.

[0050] Figures 1 to 5 show a double-roller type tripod constant velocity universal joint in which two rollers (outer roller 11 and inner ring 12) are concentrically mounted on the leg shaft 32. However, the present invention can also be applied to a single-roller type tripod constant velocity universal joint in which one roller is mounted on the leg shaft 32. In this case, the tripod member supporting one roller on the leg shaft is formed in the same shape as the tripod member shown in Figure 5.

[0051] Furthermore, although the above embodiments have described sliding constant velocity universal joints, the present invention can also be similarly applied to the inner joint members of fixed constant velocity universal joints such as Zepper type, undercut-free type, and cross-groove type.

[0052] The constant velocity universal joint described above is not limited to automobile drive shafts, but can be widely used in power transmission paths for automobiles, industrial equipment, and other applications. [Explanation of Symbols]

[0053] 1. Tripod type constant velocity universal joint 1' Double offset type constant velocity universal joint 2. Outer joint member 2a Inner surface 2b Track groove 3. Tripod members (internal joint members) 4. Roller unit (torque transmission member) 8 shafts 9 cages 31 Torso 32 Leg axis 34 Female splines 36 Escape Club 37 Escape Club 41 Ball (torque transmission member)

Claims

1. A constant velocity universal joint comprising an outer joint member having multiple track grooves formed on its inner circumferential surface, an inner joint member positioned inside the outer joint member and having female splines formed on its inner circumference, and a torque transmission member that transmits torque between the outer joint member and the inner joint member, wherein angular displacement between the outer joint member and the inner joint member is permitted, A constant velocity universal joint characterized in that relief portions are provided at both ends of the female spline in the coupling axial direction, with the tooth tip surface having a larger diameter than the tooth tip surface elsewhere.

2. The constant velocity universal joint according to claim 1, wherein the relief portions at both ends of the female spline in the joint axial direction have a symmetrical shape with respect to a line passing through the center of the joint and perpendicular to the joint axial direction on any cross section including the joint axis.

3. The constant velocity universal joint according to claim 2, wherein the inner joint member has a shape that is symmetrical with respect to a line passing through the center of the joint and perpendicular to the direction of the joint axis on any cross-section including the joint axis.

4. The constant velocity universal joint according to claim 1, wherein further axial relative movement is permitted between the outer joint member and the inner joint member.

5. A constant velocity universal joint according to claim 4, which is positioned on the inboard side of the drive shaft.

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