Fixed constant velocity universal joint

Abstract

To prevent a ball from running on an edge part of a track groove which is caused by formation of a cage assembling chamfer, in a UJ type constant velocity universal joint with six balls.SOLUTION: A cage assembling chamfer 24 comprising a surface (such as conical surface) of which transverse plane has a curvature radius that gradually decreases as proceeding on a joint depth side is provided in a joint opening-side end of a boundary between a track groove 22 and an inner diameter spherical surface part 21 of an outside joint member 2 of a UJ type constant velocity universal joint 1.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a fixed type constant velocity universal joint. [Background technology]

[0002] As a fixed type constant velocity universal joint that can accommodate a high operating angle (for example, 50° or more), an undercut-free fixed type constant velocity universal joint (hereinafter referred to as a "UJ type constant velocity universal joint") in which the ball center locus of the track groove has an arc portion and a straight portion is known. UJ type constant velocity universal joints that have six balls are often used (for example, see Patent Document 1 below).

[0003] If the pitch diameter of the balls is reduced while maintaining strength and load capacity in order to make a six-ball UJ-type constant velocity universal joint more compact and lightweight, it may not be possible to easily incorporate the cage into the outer joint member even if the shape of each member is optimized by design.

[0004] That is, when the cage 105 is fitted to the inner periphery of the outer joint member 102, first, the cage 105 is inserted from the opening side of the outer joint member 102 in a state in which the axial center L102 of the outer joint member 102 and the axial center L105 of the cage 105 are perpendicular to each other, as shown in Figures 14 to 16. Then, after the cage 105 is pushed deep into the outer joint member 102, the cage 105 is rotated by 90° about the Y axis (an axis perpendicular to both the axial center L102 of the outer joint member 102 and the axial center L105 of the cage 105) to place it in the correct position.

[0005] However, when the cage 105 is inserted from the opening side of the outer joint member 102 as described above, as shown in an enlarged view in FIG. 17 , the vicinity of the edge portion 151 a (hatched area) provided at the axial end of the pocket 151 of the cage 105 interferes with the vicinity of the track chamfer 125 provided at the boundary between the track groove 122 and the inner diameter spherical surface portion 121 of the outer joint member 102.

[0006] Therefore, in the following Patent Document 1, as shown in FIG. 18, a cage assembling chamfer (chamfered portion) 124 having a circumferential width larger than that of a track chamfer 125 is provided at the opening side end of the boundary between the track groove 122 and the inner diameter spherical portion 121 of the outer joint member 102, thereby avoiding interference between the two when assembling the cage 105 into the outer joint member 102.

[0007] This cage-mounting chamfer 124 is formed by cold forging (ironing forging) using an ironing punch. Specifically, a pre-forged product 200 having a cup 223 and a stem portion 224 as shown by the two-dot chain line in Fig. 19 is formed by cold forging (pre-forging), and then track grooves 122 and the like are formed on the inner peripheral surface of the cup portion 223 of the pre-forged product 200 using an ironing punch 300 and dies 310, 320 as shown by the solid lines in the same figure.

[0008] 20, the outer peripheral surface of the ironing punch 300 has a track groove forming portion 301, an inner diameter surface forming portion 302, and a notch forming portion 303. The notch forming portion 303 is formed along the longitudinal direction of the track groove forming portion 301 over the entire length of the track groove forming portion 301. The cross-sectional shape of the notch forming portion 303 (a cross section perpendicular to the longitudinal direction) is uniform in the longitudinal direction, and in the illustrated example, forms a cylindrical surface that curves along the track groove forming portion 301.

[0009] 21 , the inner peripheral surface of the pre-forged product 200 (hereinafter referred to as the "ironing forged product 400") that has been subjected to the above-described ironing forging has track grooves 122, notches 140, and an inner diameter surface 160 that are transferred from the shapes of the track groove forming portion 301, inner diameter surface forming portion 302, and notch forming portion 303 of the ironing punch 300. The notches 140 are formed along the longitudinal direction of the track groove 122 over the entire length of the track groove 122, and have a cylindrical surface shape that curves along the track groove 122.

[0010] Thereafter, the inner peripheral surface of the ironed forged product 400 is subjected to a turning process to form the inner diameter spherical surface portion 121, the track chamfer 125, and the cup inlet chamfer 126, as shown in Fig. 18 (the dark colored areas in Fig. 18 are the areas that have been turned). This turning process removes the entire inner diameter surface 160 of the ironed forged product 400 and also removes a portion of the cutout portion 140, with the remaining portion of the cutout portion 140 becoming the cage assembling chamfer 124. In other words, the cage assembling chamfer 124 is a portion of the cylindrical surface formed along the longitudinal direction of the track groove 122. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 6389034 Summary of the Invention [Problem to be solved by the invention]

[0012] 22 , the center of curvature O1 of the inner-diameter spherical portion 121 of the outer joint member 102 is offset toward the rear of the joint (left side in the figure) with respect to the center of curvature O2 of the curved portion 122a of the track groove 122, and a straight portion 122b parallel to the axis is provided at the end of the track groove 122 on the joint opening side. In this case, the depth of the track groove 122 should increase toward the joint opening side, but the provision of the cage assembling chamfer 124 reduces the depth of the track groove 122 accordingly (in the illustrated example, the depth of the track groove 122 in the axial region L2 where the cage assembling chamfer 124 is provided is uniform). In the illustrated example, because the cage assembling chamfer 124 has a cylindrical surface shape that follows the track groove 122, the axial length L2 of the cage assembling chamfer 124 is long, and the axial region where the track groove 122 is shallow is large. As a result, the depth of the track groove 122 near the axial center, which is frequently used, becomes shallow, and there is a risk that the balls may ride up on the edge portion of the track groove 122.

[0013] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to prevent balls from riding up onto the edges of track grooves due to the formation of a cage-mounting chamfer in a six-ball UJ-type constant velocity universal joint. [Means for solving the problem]

[0014] In order to achieve the above object, the present invention provides an outer joint member having, on an inner peripheral surface thereof, six track grooves formed at equal intervals in the circumferential direction and inner diameter spherical portions provided between adjacent track grooves; an inner joint member having, on an outer peripheral surface thereof, six track grooves formed at equal intervals in the circumferential direction and outer diameter spherical portions provided between adjacent track grooves; six balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member; a spherical outer peripheral surface that fits with the inner diameter spherical portion of the outer joint member; a spherical inner peripheral surface that fits with the outer diameter spherical portion of the inner joint member; and a cage that holds the six balls, an undercut-free fixed type constant velocity universal joint, wherein the track grooves of the outer joint member and the track grooves of the inner joint member each have an arc portion and a straight portion provided on one axial side of the arc portion, the ratio PCD(BALL) / Db of the pitch circle diameter PCD(BALL) of the six balls to the diameter Db of each ball is set within a range of 3.30 to 3.35; The present invention provides a fixed type constant velocity universal joint, in which a cage assembly chamfer is provided at one axial end of the boundary between the track groove and the inner diameter spherical surface portion of the outer joint member, the chamfer consisting of a surface whose cross-sectional radius of curvature gradually decreases as it goes toward the other axial end.

[0015] In a six-ball UJ-type constant velocity universal joint, if the ratio PCD(BALL) / Db of the ball pitch circle diameter PCD(BALL) to the ball diameter Db is 3.30 to 3.35, interference occurs when the cage is assembled into the outer joint member, making it necessary to provide a cage assembly chamfer in the outer joint member. In this case, in the present invention, the cage assembly chamfer is formed as a surface (e.g., a conical surface) whose cross-sectional curvature radius gradually decreases toward the other axial side. The axial length L1 (see FIG. 4) of such a conical cage assembly chamfer can be made shorter than the axial length L2 (see FIG. 22) of a cylindrical cage assembly chamfer, thereby narrowing the axial region where the track groove depth is shallow due to the cage assembly chamfer. This ensures the track groove depth, especially the depth near the axial center where frequent use is required, and prevents balls from riding up onto the track groove edges.

[0016] By forming the cage assembling chamfer into a conical surface shape as described above, the end portion on the other axial side of the cage assembling chamfer can be disposed on one axial side of the joint center O.

[0017] When a track chamfer is provided in a region of the boundary between the track groove and the spherical portion of the outer joint member on the other axial side of the cage assembling chamfer, the track chamfer and the cage assembling chamfer can be forged surfaces.

[0018] The present invention is suitably applicable to a UJ-type constant velocity universal joint in which the dimensions of each part are optimized to achieve compactness and weight reduction, as well as strength, load capacity, durability, and low transmission torque loss equal to or greater than those of conventional products. Specifically, the present invention is suitably applicable to a fixed UJ-type constant velocity universal joint in which the center of curvature Oto of the ball center locus of the arcuate portion of the track groove of the outer joint member and the center of curvature Oti of the ball center locus of the arcuate portion of the track groove of the inner joint member are offset by an equal distance on opposite sides in the axial direction from the joint center O, and the angle η formed by the straight line connecting the center of curvature Oto of the ball center locus of the arcuate portion of the track groove of the outer joint member and the center of the ball is defined as the offset angle η, and a plane P that passes through the joint center O and is perpendicular to the axis is defined as the offset angle η.

[0019] Furthermore, the present invention can be suitably applied to a UJ-type fixed type constant velocity universal joint in which the center of curvature Oco of the spherical outer peripheral surface of the cage and the center of curvature Oci of the spherical inner peripheral surface are offset by an equal distance on opposite sides of the joint center O, the axial distance between the center of curvature Oco of the spherical outer peripheral surface of the cage and the joint center O is defined as a cage offset amount f2, and the axial distance between the center of curvature Oto of the ball center locus of the arcuate portion of the track groove of the outer joint member and the joint center O is defined as a total offset amount F, and the ratio f2 / F of the cage offset amount f2 to the total offset amount F is 0.143 to 0.145. [Effects of the Invention]

[0020] As described above, the six-ball UJ type constant velocity universal joint according to the present invention can prevent the balls from riding up onto the edges of the track grooves due to the formation of the cage assembly chamfers. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an axial cross-sectional view of a fixed type constant velocity universal joint according to one embodiment of the present invention. [Figure 2] FIG. 2 is a front view of the fixed type constant velocity universal joint as viewed from the axial direction. [Figure 3] 3 is a cross-sectional view of the fixed type constant velocity universal joint at a contact point between a ball and a track groove. FIG. [Figure 4] FIG. 3 is an axial sectional view of an outer joint member of the fixed type constant velocity universal joint. [Figure 5] 15 is an enlarged front view (enlarged view of a portion corresponding to portion P in FIG. 14) of the outer joint member of the fixed type constant velocity universal joint, showing how a cage is incorporated into the outer joint member, as viewed from the axial direction of the outer joint member. FIG. [Figure 6] FIG. 10 is a cross-sectional view showing a state in which a precursor of the outer joint member is subjected to drawing forging. [Figure 7] FIG. 7 is a perspective view of a plurality of drawing punches provided in the die of FIG. 6. [Figure 8] FIG. [Figure 9] FIG. 10 is a cross-sectional view showing a state after drawing forging is completed. [Figure 10] FIG. [Figure 11] FIG. 10 is a cross-sectional view showing the state in which the mold is opened after draw forging. [Figure 12] FIG. 10 is a cross-sectional view showing the state in which the drawn forged product is released from the die. [Figure 13] FIG. [Figure 14] FIG. 10 is a front view showing how a cage is assembled into a conventional outer joint member, as viewed from the axial direction of the outer joint member. [Figure 15] FIG. 15 is a cross-sectional view taken along line AA in FIG. [Figure 16] FIG. 15 is a cross-sectional view taken along line BB in FIG. [Figure 17] FIG. 15 is an enlarged view of a portion P in FIG. [Figure 18] FIG. 10 is a perspective view of a conventional outer joint member. [Figure 19] FIG. 10 is a cross-sectional view showing how ironing is performed on a precursor of the outer joint member. [Figure 20] FIG. 20 is a perspective view of an ironing punch of the die of FIG. 19. [Figure 21] FIG. [Figure 22] FIG. 19 is an axial sectional view of the outer joint member of FIG. 18. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] 1 and 2 show a UJ-type constant velocity universal joint 1, which is a fixed type constant velocity universal joint according to one embodiment of the present invention. The UJ-type constant velocity universal joint 1 includes an outer joint member 2, an inner joint member 3, six balls 4, and a cage 5. A shaft 10 is connected to the inner joint member 3, and the shaft 10 protrudes from the outer joint member 2 to one axial side (the right side in FIG. 1 ) from the outer joint member 2. The UJ-type constant velocity universal joint 1 is provided, for example, at the outboard end of an automobile drive shaft, and a sliding-type constant velocity universal joint is attached to the opposite end (the inboard end) of the shaft 10 (intermediate shaft). Hereinafter, in the axial direction of the UJ-type constant velocity universal joint 1 in a state where the operating angle is 0°, the side where the shaft 10 protrudes from the outer joint member 2 (the right side in FIG. 1 ) will be referred to as the "joint opening side," and the opposite side (the left side in FIG. 1 ) will be referred to as the "joint inner side."

[0024] The outer joint member 2 integrally includes a cup portion 23 having six track grooves 22 (hereinafter referred to as "outer ring track grooves 22") formed on its inner circumferential surface, and a shaft portion (not shown) protruding from the bottom wall of the cup portion 23. On the inner circumferential surface of the outer joint member 2, inner diameter spherical portions 21 are provided between the track grooves 22 in the circumferential direction (see FIG. 2). On the outer circumferential surface of the inner joint member 3, six track grooves 32 (hereinafter referred to as "inner ring track grooves 32") that form pairs with the track grooves 22 of the outer joint member 2 are formed (see FIG. 1). On the outer circumferential surface of the inner joint member 3, outer diameter spherical portions 31 are provided between the track grooves 32 in the circumferential direction (see FIG. 2). One ball 4 is disposed between each of the outer ring track grooves 22 and the inner ring track grooves 32. The outer ring track grooves 22 and the inner ring track grooves 32 are each formed at an equal pitch (60° pitch) along the circumferential direction. For this reason, the six balls 4 serving as torque transmission members are arranged at equal pitches (60° pitches) along the circumferential direction.

[0025] The inner joint member 3 has an inner hole in which a female spline portion 33 is formed (see FIG. 1 ). The end of the shaft 10 is fitted into the inner hole of the inner joint member 3, and the male spline portion 11 formed on the end of the shaft 10 is fitted into the female spline portion 33 of the inner joint member 3, thereby connecting the two so as to be able to transmit torque. A circumferential groove 12 is formed on the end of the shaft 10, and a retaining ring 6 attached to this circumferential groove 12 prevents the shaft 10 and the inner joint member 3 from coming off in the axial direction.

[0026] The outer ring track groove 22 has an arc portion 22a provided on the rear side of the joint and a straight portion 22b provided on the joint opening side. The inner ring track groove 32 has a straight portion 32a provided on the rear side of the joint and an arc portion 32b provided on the joint opening side. The ball center locus of the arc portions 22a, 32b of each track groove 22, 32 forms an arc, while the ball center locus of the straight portions 22b, 32a of each track groove 22, 32 forms a straight line. The ball center locus is the locus followed by the center of the ball 4 when it is moved along the track groove 22, 32.

[0027] The center of curvature Oto of the ball center locus of the arcuate portion 22a of the outer ring track groove 22 and the center of curvature Oti of the ball center locus of the arcuate portion 32b of the inner ring track groove 32 are offset in the axially opposite direction by equal distances F and F from the joint center O. In the illustrated example, the center of curvature Oto of the ball center locus of the arcuate portion 22a of the outer ring track groove 22 is offset toward the joint opening from the joint center O, and the center of curvature Oti of the ball center locus of the arcuate portion 32b of the inner ring track groove 32 is offset toward the joint rear from the joint center O. The straight portion 22b of the outer ring track groove 22 extends in the tangential direction from the end of the arcuate portion 22a on the joint opening side and is parallel to the axial direction in the illustrated example. The straight portion 32a of the inner ring track groove 32 extends in the tangential direction from the end of the arcuate portion 32b on the joint rear side and is parallel to the axial direction in the illustrated example.

[0028] The cage 5 is provided with six pockets 51, and each pocket 51 accommodates one ball 4. A spherical outer peripheral surface 52 of the cage 5 is fitted with the inner spherical portion 21 of the outer joint member 2, and a spherical inner peripheral surface 53 of the cage 5 is fitted with the outer spherical portion 31 of the inner joint member 3. The diameter of the outer peripheral surface 52 of the cage 5 is approximately equal to the diameter of the inner spherical portion 21 of the outer joint member 2, and the diameter of the inner peripheral surface 53 of the cage 5 is approximately equal to the diameter of the outer spherical portion 31 of the inner joint member 3. The center of curvature Oco of the outer peripheral surface 52 of the cage 5 (i.e., the center of curvature of the inner spherical portion 21 of the outer joint member 2) and the center of curvature Oci of the inner peripheral surface 53 of the cage 5 (i.e., the center of curvature of the outer spherical portion 31 of the inner joint member 3) are offset in the axially opposite direction by an equal distance f2 from the joint center O. In the illustrated example, the center of curvature Oco of the outer peripheral surface 52 of the cage 5 is offset toward the joint opening relative to the joint center O, and the center of curvature Oci of the inner peripheral surface 53 of the cage 5 is offset toward the rear of the joint relative to the joint center O.

[0029] Here, the track offset amount f1 is the axial distance between the center of curvature Oto of the ball center locus of the arc portion 22a of the outer ring track groove 22 and the center of curvature Oco of the outer peripheral surface 52 of the cage 5 (= the axial distance between the center of curvature Oti of the ball center locus of the arc portion 32b of the inner ring track groove 32 and the center of curvature Oci of the inner peripheral surface 53 of the cage 5). Also, the axial distance between the center of curvature Oco of the outer peripheral surface 52 of the cage 5 and the joint center O (= the axial distance between the center of curvature Oci of the inner peripheral surface 53 of the cage 5 and the joint center O). The sum of the track offset amount f1 and the cage offset amount f2, i.e., the axial distance between the center of curvature Oto of the ball center locus of the arc portion 22a of the outer ring track groove 22 and the joint center O (= the axial distance between the center of curvature Oti of the ball center locus of the arc portion 32b of the inner ring track groove 32 and the joint center O), is the total offset amount F.

[0030] 3 is a cross-sectional view of the contact point between the ball 4 and the track grooves 22, 32. The cross-sectional shapes of the outer ring track groove 22 and the inner ring track groove 32 are elliptical or Gothic arch shapes. The ball 4 is in angular contact with the outer ring track groove 22 at two points C1 and C2, and with the inner ring track groove 32 at two points C3 and C4.

[0031] The dimensions of each part of the above UJ type constant velocity universal joint 1 are optimized to achieve compactness and light weight, as well as strength, load capacity, durability, and low transmission torque loss equal to or greater than conventional products. Specifically, the dimensions of each part of the UJ type constant velocity universal joint 1 are as shown in Table 1 below.

[0032] [Table 1]

[0033] The definitions of each item in Table 1 above are as follows:

[0034] Offset angle η In the axial cross section shown in Figure 1, when the operating angle is 0°, the angle between a plane P that passes through the joint center O and is perpendicular to the axis and a straight line that connects the center of the ball 4 and the center of curvature Oti of the ball center locus of the arc portion 32b of the inner ring track groove 32 (= the angle between the plane P and the straight line that connects the center of the ball 4 and the center of curvature Oto of the ball center locus of the arc portion 22a of the outer ring track groove 22) is defined as the offset angle η.

[0035] ·Contact angle α In the cross section shown in Figure 3, the angle formed by the line passing through the center of the ball 4 and the contact points C1, C2, C3, and C4 between the ball 4 and the track grooves 22 and 32, and the plane Q passing through the axis and the center of the ball 4 is defined as the contact angle α.

[0036] Reference shaft diameter Ds The outer diameter of the minimum diameter portion 13 of the shaft 10 in the torque load region (the region between the male spline portions formed on both axial ends) is defined as the reference shaft diameter.

[0037] ·Ball pitch circle diameter PCD (BALL) The distance between the center of curvature Oto of the ball center locus of the arc portion 22a of the outer ring track groove 22 and the center of the ball (= the distance between the center of curvature Oti of the ball center locus of the arc portion 32b of the inner ring track groove 32 and the center of the ball) is PCR (see Figure 1), and twice the value of PCR is the pitch circle diameter PCD(BALL).

[0038] Cage wall thickness Tc When the operating angle is 0°, the radial thickness of the cage 5 on a plane P that passes through the joint center O and is perpendicular to the axis is defined as the cage thickness Tc (see FIG. 1).

[0039] When the UJ-type constant velocity universal joint 1 is made compact as described above, specifically when the ratio PCD(BALL) / Db of the pitch circle diameter PCD(BALL) of the balls 4 to the ball diameter Db is set within the range of 3.30 to 3.35, the cage 5 and the balls interfere with each other when they are assembled into the inner periphery of the outer joint member 2 in the same manner as in Figures 14 to 16. Therefore, in this embodiment, a cage assembly chamfer 24 is provided at the joint opening side end of the boundary between the track grooves 22 and the inner diameter spherical portion 21 of the outer joint member 2, and this portion is recessed toward the outer diameter side.

[0040] Specifically, as shown in Fig. 4, a cage assembly chamfer 24 is provided at the joint opening side end and a track chamfer 25 is provided adjacent to the joint inner side at the boundary between the track groove 22 and the inner diameter spherical surface portion 21 of the outer joint member 2. This makes it possible to avoid interference between the edge portion 51a provided at the axial end of the pocket 51 of the cage 5 and the outer joint member 2 when assembling the cage 5 into the outer joint member 2, as shown in Fig. 5.

[0041] The chamfer 24 for cage incorporation is a surface whose cross-sectional radius of curvature gradually decreases towards the inner side of the joint, and is a conical surface in the illustrated example. The track chamfer 25 is a cylindrical surface curved along the track groove 22 and reaches the inner-side end of the track groove 22 at the joint. A conical cup inlet chamfer 26 is provided over the entire circumference at the joint opening-side end of the inner peripheral surface of the cup portion 23.

[0042] As described above, by making the chamfer 24 for cage incorporation a conical surface, the axial length can be made shorter than that of the cylindrical chamfer 124 for cage incorporation as shown in FIG. 22 (L1 < L2). Specifically, the inner-side end of the chamfer 24 for cage incorporation at the joint is arranged on the joint opening side with respect to the joint center O (see FIG. 1), and in the illustrated example, it is arranged on the joint opening side with respect to the center of curvature of the inner diameter spherical surface portion 21 (that is, the center of curvature Oco of the outer peripheral surface 52 of the cage 5). Thus, by shortening the axial length of the chamfer 24 for cage incorporation, the axial region that becomes shallower due to the chamfer 24 for cage incorporation in the track groove 22 becomes shorter. Therefore, the depth of the track groove 22, particularly the depth in the axial region near the joint center O where the usage frequency is high, is ensured, and the ball 4 can be prevented from riding up to the edge portion of the track groove 22 in this region.

[0043] Also, in the illustrated example, the ridge line 28 provided at the boundary between the chamfer 24 for cage incorporation and the track groove 22 is inclined so as to be displaced towards the inner diameter side towards the inner side of the joint. Thereby, the track groove 22 gradually becomes deeper from the joint opening-side end to the joint inner-side end of the chamfer 24 for cage incorporation (D1 < D2 < D3). Thereby, the depth in the vicinity of the inner-side end of the chamfer 24 for cage incorporation in the track groove 22 can be ensured, and the ball 4 can be prevented from riding up to the edge portion of the track groove 22 in this portion.

[0044] The above-described conical cage assembling chamfer 24 can be formed by drawing. Specifically, the outer joint member 2 is manufactured through a pre-forging process in which a pre-forged product 2' (see FIG. 6) having a cup portion 23' and a stem portion 27' is formed, a drawing forging process in which the pre-forged product 2' is drawn to form the track grooves 22 and the cage assembling chamfer 24, etc., and a turning process in which the inner peripheral surface of the cup portion 23' is turned. The drawing forging process will be described in detail below.

[0045] The drawing forging process is performed using a drawing forging device 70 as shown in FIG. 6. This drawing forging device 70 has a die 71 and a punch unit 72. The punch unit 72 has six drawing punches 73, each divided into a track groove portion as shown in FIG. 7. As shown in FIG. 8, each drawing punch 73 has a spherical forming portion 73a, a track groove forming portion 73b, a first chamfer forming portion 73c, a second chamfer forming portion 73d, and a third chamfer forming portion 73e. The track groove forming portion 73b, the first chamfer forming portion 73c, and the second chamfer forming portion 73d have shapes corresponding to the track grooves 22, the cage assembly chamfer 24, and the track chamfer 25 of the finished product, respectively. The spherical forming portion 73a and the third chamfer forming portion 73e have shapes that are approximately the same as, but do not completely match, the inner diameter spherical portion 21 and the cup inlet chamfer 26 of the finished product, respectively.

[0046] In the drawing forging process, as shown in FIG. 6, a die 71 is lowered with the pre-forged product 2' set in a punch unit 72, thereby drawing the outer circumferential surface of the pre-forged product 2' (see FIG. 9). As a result, the shape of the drawing punch 73 is transferred to the inner circumferential surface of the pre-forged product 2', and a drawn forged product 2" is formed, as shown in FIG. 10, with a spherical portion 21', track grooves 22, cage assembling chamfers 24, track chamfers 25, and cup inlet chamfers 26' formed on the inner circumferential surface. The track grooves 22, cage assembling chamfers 24, and track chamfers 25 of the drawn forged product 2" have the same shapes as those of the finished product, and no subsequent machining is performed. The spherical portion 21' and cup inlet chamfer 26' of the drawn forged product 2" are not completely identical to the inner diameter spherical portion 21 and cup inlet chamfer 26 of the finished product, and multiple circumferential clearance marks 29' of the drawing punch 73 are formed.

[0047] Thereafter, the drawn forged product 2" and the multiple drawing punches 73 are raised together, and as a result, the multiple drawing punches 73 move closer to each other in the circumferential direction and reduce in diameter, as shown in Figure 11. Then, when the maximum outer diameter of the drawing punch 73 becomes smaller than the inner diameter of the opening of the drawn forged product 2", the drawn forged product 2" is separated from the punch unit 72, as shown in Figure 12.

[0048] Thereafter, on the inner peripheral surface of the drawn forged product 2", the spherical portion 21' and the cup inlet chamfer 26' are turned to form the inner diameter spherical portion 21 and the cup inlet chamfer 26, thereby completing the outer joint member 2 shown in FIG. 13. The dark colored areas in FIG. 13 indicate areas that have been turned. On the inner peripheral surface of the outer joint member 2 manufactured by the above procedure, the track grooves 22, the cage assembling chamfer 24, and the track chamfer 25 are forged surfaces, and the inner diameter spherical portion 21 and the cup inlet chamfer 26 are turned surfaces. [Explanation of symbols]

[0049] 1 Fixed constant velocity universal joint (UJ type constant velocity universal joint) 2 Outer joint member 2' Precursor (pre-forged product) 2" drawn forged product 3 Inner joint member 4 balls 5 cages 21 Inner spherical part 22 Track groove (outer ring track groove) 22a Arc section 22b Straight section 23 Cup section 24 Cage mounting chamfer 25 Truck Chamfer 26 Cup entrance chamfer 31 Outer diameter spherical part 32 Track groove (inner ring track groove) 32a Straight section 32b Arc section 51 pockets 70 Forging equipment 71 Dice 72 Punch unit 73 Squeezing Punch O Joint center Oti Center of curvature of the ball center locus of the arc part of the inner ring track groove Oto: Center of curvature of the ball center locus in the arc part of the outer ring track groove Oci Cage inner surface curvature center Oco Cage outer surface curvature center

Claims

1. an outer joint member having, on its inner peripheral surface, six track grooves formed at equal intervals in the circumferential direction and inner diameter spherical portions provided between adjacent track grooves; an inner joint member having, on its outer peripheral surface, six track grooves formed at equal intervals in the circumferential direction and outer diameter spherical portions provided between adjacent track grooves; six balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member; a spherical outer peripheral surface that fits with the inner diameter spherical portion of the outer joint member; a spherical inner peripheral surface that fits with the outer diameter spherical portion of the inner joint member; and a cage that holds the six balls, an undercut-free fixed type constant velocity universal joint, wherein the track grooves of the outer joint member and the track grooves of the inner joint member each have an arc portion and a straight portion provided on one axial side of the arc portion, a ratio PCD(BALL) / Db of a pitch circle diameter PCD(BALL) of each of the six balls to a diameter Db of each of the six balls is set within a range of 3.30 to 3.35; a cage assembly chamfer, the chamfer consisting of a surface whose radius of curvature of a cross section gradually decreases toward the other axial side, is provided at one axial end of the boundary between the track groove and the inner diameter spherical surface portion of the outer joint member.

2. 2. A fixed type constant velocity universal joint according to claim 1, wherein said cage assembly chamfer comprises a conical surface.

3. 2. A fixed type constant velocity universal joint according to claim 1, wherein the other axial end of said cage assembly chamfer is disposed on one axial side of a joint center O.

4. a track chamfer is provided in a region of a boundary between the track groove and the inner diameter spherical surface portion of the outer joint member, the region being on the other axial side of the cage assembling chamfer, 2. A fixed type constant velocity universal joint according to claim 1, wherein said track chamfer and said cage assembly chamfer are forged surfaces.

5. a center of curvature Oto of a ball center locus of the arcuate portion of the track groove of the outer joint member and a center of curvature Oti of a ball center locus of the arcuate portion of the track groove of the inner joint member are offset by an equal distance on opposite sides in the axial direction with respect to a joint center O, 2. The fixed type constant velocity universal joint according to claim 1, wherein an offset angle η is an angle formed by a straight line connecting the center of curvature Oto of the ball center locus of the arc portion of the track groove of the outer joint member and the center of the ball, and a plane P that passes through a joint center O and is perpendicular to an axis, and the offset angle η is 7° to 7.1°.

6. a center of curvature Oco of the spherical outer peripheral surface of the cage and a center of curvature Oci of the spherical inner peripheral surface are offset by an equal distance on opposite sides of a joint center O; 2. The fixed type constant velocity universal joint according to claim 1, wherein a cage offset amount f2 is a cage offset amount f2 that is a distance in the axial direction between the joint center O and the center of curvature Oco of the spherical outer peripheral surface of the cage, and a total offset amount F is a distance in the axial direction between the joint center O and the center of curvature Oto of the ball center locus of the arc portion of the track groove of the outer joint member.

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