Fixed-type constant velocity universal joint

Abstract

A track groove 7 of an outer joint member 2 has a guide surface 71 for guiding balls 4. A chamfered section 30 which has an arc-shaped cross-sectional shape in a direction perpendicular to an axial direction is formed between a spherical inner circumferential surface 6 and the guide surface 71 of the outer joint member 2. The chamfered section 30 and the guide surface 71 of the outer joint member 2 are connected to an edge-like connection point E1, and the angle ε between the tangent line of the guide surface 71 and the tangent line of the chamfered section 30 at the connection point E1 is 0º<ε ≤15º.

Description

Fixed constant velocity universal joint

[0001] The present invention relates to a fixed type constant velocity universal joint used for power transmission in automobiles and various industrial machines.

[0002] In driveshafts used in automotive power transmission systems, a sliding-type constant velocity universal joint is often connected to the inboard side (the center side in the vehicle width direction) of the intermediate shaft, and a fixed-type constant velocity universal joint is connected to the outboard side (the end side in the vehicle width direction). The sliding-type constant velocity universal joint here allows both angular displacement and relative axial movement between the two shafts, while the fixed-type constant velocity universal joint allows angular displacement between the two shafts but does not allow relative axial movement between the two shafts.

[0003] Known fixed type constant velocity universal joints include a non-intersecting track groove type constant velocity universal joint (see Patent Document 1) in which the track grooves provided on the spherical inner peripheral surface of the outer joint member and the spherical outer peripheral surface of the inner joint member are not inclined in the circumferential direction, and a plane containing the ball raceway center line of each track groove and the joint center is in the same direction as the joint axis, and a crossing track groove type constant velocity universal joint (see Patent Document 2) in which a plane containing the ball raceway center line of each track groove and the joint center is inclined in the circumferential direction with respect to the joint axis. The latter is more expensive than the former, but has the advantage that axial forces in opposite directions act from the balls on circumferentially adjacent pockets of the cage, thereby suppressing the contact force between the spherical outer peripheral surface of the cage and the spherical inner peripheral surface of the outer joint member and the contact force between the spherical inner peripheral surface of the cage and the spherical outer peripheral surface of the inner joint member 3, thereby achieving high efficiency.

[0004] In the past, fixed type constant velocity universal joints generally had a maximum operating angle of 50° or less (approximately 47° for Rzeppa type constant velocity universal joints and approximately 50° for undercut-free type constant velocity universal joints), but in recent years, there have been an increasing number of cases in which large maximum operating angles exceeding 50° are required for fixed type constant velocity universal joints for drive shafts, regardless of whether they are of the non-intersecting track groove type or the intersecting track groove type, in order to improve the turning ability and maneuverability of the vehicle.

[0005] In fixed-type constant velocity universal joints, when a large maximum working angle is used, the contact ellipse caused by contact with the ball tends to extend beyond the shoulder of the track groove, which can cause excessive edge load at the shoulder of the track groove when a high torque is applied, potentially deforming the shoulder of the track groove. Deformation of the shoulder of the track groove can cause abnormal noise and vibration. As disclosed in Patent Document 1, an effective solution to this problem is to provide an R-shaped track chamfer along the boundary between the inner diameter spherical surface of the outer ring and the track groove, and to form the track chamfer continuously so that it smoothly connects the track groove and the spherical inner peripheral surface.

[0006] JP 2010-164106 A Japanese Patent No. 5885997 A

[0007] On the other hand, when mass-producing outer joint members, it is difficult to smoothly connect the track chamfer with the track groove and the spherical inner peripheral surface of the outer joint member or the spherical outer peripheral surface of the inner joint member in terms of processing errors, etc. If one were to attempt to do so, finishing processing of the track chamfer would be necessary, which would result in a problem of rising manufacturing costs.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixed type constant velocity universal joint that can suppress deformation of the shoulder portions of the track grooves of the outer joint member when a high torque load is applied, at low cost.

[0009] The present invention, made based on the above findings, provides a constant velocity universal joint comprising: an outer joint member having a plurality of track grooves formed on its spherical inner peripheral surface, and having an open side and a rear side spaced apart in the axial direction; an inner joint member having a plurality of track grooves formed on its spherical outer peripheral surface; balls arranged between the track grooves of the outer joint member and the corresponding track grooves of the inner joint member; and a cage having pockets for accommodating the balls, the cage fitting with the spherical inner peripheral surface of the outer joint member and the spherical outer peripheral surface of the inner joint member, wherein the track grooves of the outer joint member have guide surfaces for guiding the balls, and a chamfered portion having an arc-shaped cross section in a direction perpendicular to the axial direction is formed between the spherical inner peripheral surface of the outer joint member and the guide surface, wherein the chamfered portion of the outer joint member and the guide surface are connected at an edge-shaped connection point, and the angle ε between a tangent to the guide surface at the connection point and a tangent to the chamfered portion is 0°<ε≦15°.

[0010] With such a fixed-type constant velocity universal joint, measures or processing to smoothly connect the guide surface of the track groove and the chamfered portion are not required. This reduces the manufacturing cost of the outer joint member. Furthermore, by setting the angle ε between the tangent to the guide surface and the tangent to the chamfered portion at the connection point within the range of 0° < ε ≦ 15°, excessive edge load does not occur on the shoulder of the track groove due to contact with the ball, even when transmitting high torque. This suppresses deformation, etc., of the shoulder of the track groove of the outer joint member, thereby preventing the generation of abnormal noise and vibration.

[0011] The radius of curvature R of the chamfered portion is preferably in the range of 3.0 mm≦R≦9.0 mm. If the radius of curvature R of the chamfered portion is less than 3 mm, the chamfering amount becomes small, which results in an insufficient relief effect on the edge load and a reduced effect in suppressing deformation of the shoulder portion. If the radius of curvature R exceeds 9 mm, the edge of the connection point becomes sharp, making it difficult to maintain the angle ε at 15° or less.

[0012] The track grooves of the outer joint member preferably have a portion in which the center line of the ball raceway is an arc.

[0013] The radius of curvature of the chamfered portion may be non-uniform in the axial direction.

[0014] The chamfered portion may be provided on the inner side of the center of curvature of the ball track center line.

[0015] The center of curvature of the ball track centerline and the center of curvature of the spherical inner peripheral surface may be offset in the axial direction.

[0016] The radius of curvature of the chamfered portion may be uniform in the axial direction.

[0017] The chamfered portion may be provided over the entire axial length of the track groove of the outer joint member.

[0018] The offset amount in the axial direction between the center of curvature of the ball track center line and the center of curvature of the spherical inner peripheral surface can be set to zero.

[0019] A fixed type constant velocity universal joint can be used in which a plane containing the ball raceway center lines of the track grooves of the outer joint member and the joint center is inclined with respect to the joint axis, and the inclination directions are opposite to each other in the track grooves adjacent to each other in the circumferential direction, and the ball raceway center lines of the track grooves of the inner joint member are formed in mirror symmetry with the ball raceway center lines of the mating track grooves of the outer joint member, with respect to a plane that includes the joint center and is perpendicular to the joint axis in a state where the operating angle is 0°.

[0020] According to the present invention, deformation of the shoulder portions of the track grooves of the outer joint member under high torque load can be suppressed at low cost.

[0021] 1. A longitudinal sectional view of a fixed type constant velocity universal joint according to a first embodiment of the present invention. A right side view of the fixed type constant velocity universal joint. A cross-sectional view showing an enlarged view of one ball and track grooves taken along line P-P in FIG. 1. A cross-sectional view showing an enlarged view of the spherical inner peripheral surface and track grooves of the outer joint member shown in FIG. 3. A cross-sectional view showing an enlarged view of region C in FIG. 4. A longitudinal sectional view of the outer joint member. A cross-sectional view taken along line A-A in FIG. 6. A cross-sectional view taken along line B-B in FIG. 6. A longitudinal sectional view of the fixed type constant velocity universal joint at the maximum operating angle. A partial longitudinal sectional view of the fixed type constant velocity universal joint according to the first embodiment. A right side view of the fixed type constant velocity universal joint according to the first embodiment. A partial longitudinal sectional view of the outer joint member of the fixed type constant velocity universal joint. A right side view of the outer joint member of the fixed type constant velocity universal joint. A left side view of the inner joint member of the fixed type constant velocity universal joint. A plan view showing the outer peripheral surface of the inner joint member of the fixed type constant velocity universal joint. A right side view of the inner joint member of the fixed type constant velocity universal joint. 14A and 14B are partial longitudinal sectional views showing details of track grooves of an outer joint member; FIG. 14A are longitudinal sectional views showing details of track grooves of an inner joint member; FIG. 14B are longitudinal sectional views of an outer joint member; FIG. 14C are sectional views taken along line A'-A' in FIG. 14; and FIG. 14C are sectional views taken along line B'-B' in FIG.

[0022] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 15A and 15B.

[0023] Fig. 1 is a longitudinal sectional view of a fixed type constant velocity universal joint 1 according to a first embodiment, and Fig. 2 is a right side view thereof (a boot 20 and a boot band 21 are omitted from the illustration). This constant velocity universal joint 1 is a Rzeppa type constant velocity universal joint, and its main components are an outer joint member 2, an inner joint member 3, torque transmission balls 4 (hereinafter simply referred to as balls), and a cage 5. An undercut-free type constant velocity universal joint can also be used as the fixed type constant velocity universal joint 1.

[0024] 1 and 2, the outer joint member 2 has a cup-shaped mouth portion 2a that is open at one axial end and closed at the other axial end, and a shaft portion 2b that protrudes from the other axial end of the mouth portion 2a. In the following description, the one axial end side of the mouth portion 2a will be referred to as the open side, and the other axial end side will be referred to as the rear side. The inner peripheral surface 6 of the mouth portion 2a is formed in a spherical shape. The inner joint member 3 is housed inside the mouth portion 2a of the outer joint member 2, and its outer peripheral surface 8 is spherical.

[0025] A plurality of (e.g., eight) track grooves 7 are formed on the spherical inner peripheral surface 6 of the outer joint member 2 at equal intervals in the circumferential direction and along the axial direction. A plurality of (e.g., eight) track grooves 9 facing the track grooves 7 of the outer joint member 2 are formed on the spherical outer peripheral surface 8 of the inner joint member 3 at equal intervals in the circumferential direction and along the axial direction. A plurality of (e.g., eight) balls 4 for transmitting torque are incorporated into each of the track grooves 7 of the outer joint member 2 and the track grooves 9 of the inner joint member 3. A cage 5 for holding the balls 4 is disposed between the spherical inner peripheral surface 6 of the outer joint member 2 and the spherical outer peripheral surface 8 of the inner joint member 3. The balls 4 are accommodated in pocket portions 5a of the cage 5. A spherical outer peripheral surface 12 of the cage 5 is slidably fitted on the spherical inner peripheral surface 6 of the outer joint member 2, and a spherical inner peripheral surface 13 of the cage 5 is slidably fitted on the spherical outer peripheral surface 8 of the inner joint member 3.

[0026] In this specification, the term "ball track centerline" is used to describe the form and shape of the track grooves extending in the axial direction. The ball track centerline refers to the path traced by the center of the ball 4 disposed in the track groove as it moves along the track groove.

[0027] The centers of curvature of the spherical inner peripheral surface 6 of the outer joint member 2 and the spherical outer peripheral surface 8 of the inner joint member 3 are each located on the joint center O. The centers of curvature of the spherical outer peripheral surface 12 of the cage 5, which fits with the spherical inner peripheral surface 6 of the outer joint member 2, and the spherical inner peripheral surface 13 of the cage 5, which fits with the spherical outer peripheral surface 8 of the inner joint member 3, also lie on the joint center O.

[0028] The track grooves 7 of the outer joint member 2 have an arc-shaped ball raceway center line X, and the track grooves 9 of the inner joint member 3 have an arc-shaped ball raceway center line Y. A center of curvature O1 of the ball raceway center line X of the outer joint member 2 and a center of curvature O2 of the ball raceway center line Y of the track groove 9 of the inner joint member 3 are offset by an equal distance f on opposite axial sides with respect to the joint center O. As a result, when the fixed type constant velocity universal joint 1 forms an operating angle, the balls 4 are always guided on a plane that bisects the angle (operating angle) formed by the axes of the outer joint member 2 and the inner joint member 3, and rotational torque is transmitted at a uniform speed between the two shafts.

[0029] In this way, the center of curvature O1 of the track grooves 7 of the outer joint member 2 and the center of curvature O2 of the track grooves 9 of the inner joint member 3 are offset by an equal distance in the axial direction from the joint center O, so that the opposing track grooves of the outer joint member 2 and the inner joint member 3 form a wedge shape widening from the back side toward the opening side of the outer joint member 2, and each ball 4 is accommodated in the wedge-shaped track groove to transmit torque between the outer joint member 2 and the inner joint member 3. A cage 5 is incorporated to hold all the balls 4 on a plane bisecting the operating angle.

[0030] Figure 3 is an enlarged cross-sectional view of one ball and track groove taken along line P-P in Figure 1. As shown in Figure 3, the track groove 7 of the outer joint member 2 and the track groove 9 of the inner joint member 3 have guide surfaces 71 and 91, respectively, that guide the ball 4. The cross-sectional shapes of the guide surfaces 71 and 91 are elliptical or Gothic arch-shaped. The ball 4 is in angular contact with the guide surface 71 of the track groove 7 of the outer joint member 2 at two points C1 and C2, and is in angular contact with the guide surface 91 of the track groove 9 of the inner joint member 3 at two points C3 and C4. Therefore, the ball 4 is in contact with the guide surfaces 71 and 91 on the side surfaces of the track grooves 7 and 9, which are slightly separated from the groove bottoms of the track grooves 7 and 9. The angle (contact angle α) formed by the line passing through the center Ob of the ball 4 and each of the contact points C1, C2, C3, and C4 and the line passing through the center Ob of the ball 4 and the joint center O (see Figure 1) is preferably set to 30° to 45°. The cross-sectional shape of the track grooves 7 and 9 may be an arc, and the contact between the track grooves 7 and 9 and the ball 4 may be circular contact.

[0031] As shown in Figure 1, a female spline 16 (spline includes serrations; the same applies hereinafter) is formed in the bore 15 of the inner joint member 3, and a male spline 19 of a shaft 17 is fitted into this spline 16, thereby connecting the inner joint member 3 and the shaft 17 so as to be able to transmit torque. The inner joint member 3 and the shaft 17 are positioned in the axial direction by a retaining ring 18. A bellows-shaped boot 20 is attached to the outer periphery of the outer joint member 2 and the outer periphery of the shaft 17 connected to the inner joint member 3. Both ends of the boot 20 are fastened and fixed to the outer joint member 2 and the shaft 17 by boot bands 21, 22. Grease is sealed inside the joint covered with the boot 20 as a lubricant.

[0032] 4 is an enlarged cross-sectional view of the spherical inner peripheral surface 6 and the track grooves 7 of the outer joint member 2 shown in FIG. 3, and FIG. 5 is an enlarged cross-sectional view of an area C in FIG.

[0033] As shown in Fig. 4, a convex arc-shaped chamfered portion (track chamfer) 30 having a radius of curvature R is formed between the spherical inner peripheral surface 6 of the outer joint member 2 and the guide surface 71 of the track groove 7. As shown in Fig. 5, the chamfered portion 30 and the guide surface 71 of the track groove 7 are not smoothly connected, and an edge exists at a connection point E1 between them. Furthermore, an angle ε between a tangent T1 to the guide surface 71 of the track groove 7 and a tangent T2 to the chamfered portion 30 at this connection point E1 is greater than 0° and not greater than 15° (0° < ε ≦ 15°). In this embodiment, an edge E2 is also provided between the chamfered portion 30 and the spherical inner peripheral surface 6 of the outer joint member 2; however, the chamfered portion 30 and the spherical inner peripheral surface 6 may be smoothly connected so that they share a common tangent.

[0034] The outer joint member 2 is manufactured through the following main steps: cold forging of steel material → heat treatment → finishing of the spherical inner peripheral surface 6 and the track grooves 7. Each step will be briefly described below.

[0035] In cold forging, the spherical inner peripheral surface 6, the track grooves 7, and the chamfered portion 30 are each formed by a die. During this cold forging, the connection point between the chamfered portion 30 and the guide surface 71 of the track groove 7 is formed to form an edge. Therefore, even in the stage of an intermediate product before finishing after cold forging, an edge exists between the chamfered portion 30 and the guide surface 71 of the track groove 7.

[0036] Heat treatment is performed on the spherical inner peripheral surface 6 and the surfaces (guide surfaces 71) of the track grooves 7, and this heat treatment forms a hardened layer (not shown) on the surfaces of the spherical inner peripheral surface 6 and the track grooves 7. For example, induction hardening can be used as the heat treatment. Finishing is a process for finishing the spherical inner peripheral surface 6 and the guide surfaces 71 of the track grooves 7 to within a predetermined tolerance range while leaving the hardened layer intact. This finishing process involves either cutting or grinding, or both. Because the spherical inner peripheral surface 6 and the guide surfaces 71 of the track grooves 7 are finished in this way, the spherical inner peripheral surface 6 and the guide surfaces 71 of the track grooves 7 in the final product have finished surfaces (cut surfaces or ground surfaces). Because the chamfered portion 30 is not finished, the chamfered portion 30 in the final product has a forged surface.

[0037] In this embodiment, by forming an edge portion between the track groove 7 and the inner surface of the chamfered portion 30 during cold forging, it is not necessary to smoothly connect the molded portion of the track groove 7 and the molded portion of the chamfered portion 30, which reduces the mold manufacturing cost and simplifies the cold forging process. Furthermore, this edge portion does not disappear during the finish processing of the track groove 7, and after the finish processing, an edge-like connection point E1 (ε > 0°) is formed between the guide surface 71 of the track groove 7 and the chamfered portion 30. Therefore, processing to smoothly connect the guide surface 71 of the track groove 7 and the chamfered portion 30 during the finish processing is also not required. Since measures, processing, etc. for smoothly connecting the guide surface 71 of the track groove 7 and the chamfered portion 30 are thus not required, the manufacturing cost of the outer joint member 2 can be reduced.

[0038] Furthermore, verification of the present invention has revealed that, if the angle ε between the tangent T1 of the guide surface 71 and the tangent T2 of the chamfered portion 30 at the connection point E1 (hereinafter referred to as the tangent angle) is controlled to 15 degrees or less, even when transmitting high torque, an excessive edge load will not be generated at the shoulder of the track groove 7 due to contact with the balls 4, and deformation, etc. at the shoulder of the track groove 7 of the outer joint member 2 can be suppressed. From the above findings, it is preferable to set the tangent angle ε at the connection point E1 within the range of 0°<ε≦15°.

[0039] As described in Patent Document 1, it has been technically common knowledge up until now that the guide surface 71 of the track groove 7 and the chamfered portion 30 should be formed continuously so as to be smoothly connected. In contrast to this, the present invention is characterized in that it intentionally leaves an edge-like connection point E1 between the guide surface 71 of the track groove 7 and the chamfered portion 30 to reduce costs, while finding a range of the tangent angle ε of the connection point E1 that can prevent the occurrence of excessive edge load, thereby achieving both cost and strength.

[0040] The radius of curvature R of the chamfered portion 30 is preferably 3 mm or more and 9 mm or less. If the radius of curvature R is less than 3 mm, the chamfering amount becomes small, which results in an insufficient edge load mitigation effect and a reduced effect of suppressing shoulder deformation. If the radius of curvature R exceeds 9 mm, the edge of the connection point E1 (and furthermore, the connection point E2) becomes sharp, making it difficult to maintain the tangent angle ε at 15° or less.

[0041] Fig. 6 is a vertical cross-sectional view of the outer joint member 2. Fig. 7A shows a cross-sectional view taken along line AA in Fig. 6, and Fig. 7B shows a cross-sectional view taken along line BB in Fig. 6.

[0042] As shown in FIGS. 7A and 7B , in the outer joint member 2 of the Rzeppa-type constant velocity universal joint 1, the center of curvature O1 of the ball raceway center line X (radius of curvature Ro) of the track groove 7 is offset in the axial direction from the center of curvature O of the spherical inner peripheral surface 6 (radius of curvature Ros). Therefore, the depth (Ha, Hb) of the track groove 7 becomes shallower toward the back (Ha<Hb). Accordingly, the angle δ between the spherical inner peripheral surface 6 and the guide surface 71 of the track groove 7 changes in the axial direction, and the angle δ increases toward the back. This makes it difficult to form the chamfered portion 30 with a uniform radius of curvature R. Therefore, in the Rzeppa-type constant velocity universal joint 1, it is reasonable to make the radius of curvature R of the chamfered portion 30 non-uniform in the axial direction. Specifically, the radius of curvature R of the chamfered portion 30 increases toward the back. Even when the curvature radius R of the chamfered portion 30 changes in the axial direction in this manner, it is preferable to set the inter-tangent angle ε at the connection point E1 within the range of 0°<ε≦15° over the entire axial region of the chamfered portion 30. It is also preferable to set the curvature radius R of the chamfered portion 30 to be 3 mm or more and 9 mm or less over the entire region.

[0043] FIG. 8 is a longitudinal cross-sectional view showing the fixed constant velocity universal joint 1 at the maximum operating angle θmax (approximately 47°). When a high operating angle is achieved as shown in FIG. 8 , the balls 4 at the farthest end (not shown in FIG. 6 ) transmit torque in a shallow region of the track groove 7. Therefore, the contact ellipse formed by the contact with the balls 4 at the farthest end of the track groove 7 tends to extend beyond the track groove 7, resulting in the generation of an edge load problem. Therefore, it is preferable to form a chamfered portion 30 in which the inter-tangent angle ε is within the range of 0°<ε≦15° at least in a region of the track groove 7 at the farthest end of the center of curvature O1 of the ball track center line X (a region at the farthest end of a plane including the center of curvature O1 and perpendicular to the axis N-N). In this case, in the chamfered portion 30 in the region closer to the opening than the center of curvature O1 of the track groove 7, the inter-tangent angle ε is set to 0°<ε≦15°, or alternatively, ε may be set to 15° or greater. Furthermore, in the region closer to the opening side than the center of curvature O1 of the track groove 7, the chamfered portion 30 may not be provided, and the guide surface 71 of the track groove 7 and the spherical inner peripheral surface 6 may be directly connected.

[0044] 9A and 9B to 15A and 15B show a second embodiment of the present invention. The fixed type constant velocity universal joint according to the first embodiment is of a non-intersecting track groove type in which the track grooves of the outer joint member and the inner joint member are arranged such that the planes containing the ball raceway center lines X and Y of each track groove and the joint center O are oriented in the same direction as the axis of the joint, whereas the fixed type constant velocity universal joint according to the second embodiment is of an intersecting track groove type.

[0045] As shown in Figures 9A and 9B, this fixed type constant velocity universal joint 1 mainly comprises an outer joint member 2, an inner joint member 3, balls 4, and a cage 5, similar to the first embodiment. As shown in Figures 10A, 10B, 11A, 11B, and 11C, a plurality of (e.g., eight) track grooves 7, 9 formed on the spherical inner peripheral surface 6 of the outer joint member 2 and the spherical outer peripheral surface 8 of the inner joint member 3, respectively, are inclined in the circumferential direction with respect to the joint axis N-N, and the inclination directions of circumferentially adjacent track grooves 7A, 7B and 9A, 9B are opposite to each other. One ball 4 is disposed at each intersection of paired track grooves 7A, 9A and 7B, 9B of the outer joint member 2 and the inner joint member 3. Details of the track grooves 7, 9 will be described later.

[0046] 9A , the track grooves 7 of the outer joint member 2 have a ball track center line X, and are composed of a first track groove portion 7a having an arc-shaped ball track center line Xa with the joint center O as the center of curvature, and a second track groove portion 7b having a linear ball track center line Xb, and the ball track center line Xb of the second track groove portion 7b is smoothly connected as a tangent to the ball track center line Xa of the first track groove portion 7a. Note that the track grooves 7 of the outer joint member 2 may be composed only of the arc-shaped portion consisting of the ball track center line Xa with the joint center O as the center of curvature.

[0047] On the other hand, the track grooves 9 of the inner joint member 3 have a ball raceway center line Y, and are composed of a first track groove portion 9a having an arc-shaped ball raceway center line Ya with the joint center O as the center of curvature, and a second track groove portion 9b having a linear ball raceway center line Yb, and the ball raceway center line Yb of the second track groove portion 9b is smoothly connected as a tangent to the ball raceway center line Ya of the first track groove portion 9a. Note that the track grooves 9 of the inner joint member 3 may be composed only of the arc-shaped portion consisting of the ball raceway center line Ya with the joint center O as the center of curvature.

[0048] By locating the centers of curvature of the ball track centerlines Xa and Ya of the first track groove portions 7a and 9a at the joint center O on the joint axis N-N, the track groove depth can be made uniform and processing can be facilitated. The cross-sectional shape of the track grooves 7 and 9 is formed into an elliptical shape or a Gothic arch shape, and the guide surfaces 71 and 91 of the track grooves 7 and 9 and the ball 4 contact with each other at a contact angle (approximately 30° to 45°), which is known as angular contact (see FIG. 3). Therefore, the ball 4 contacts the guide surfaces 71 and 91 on the side surfaces of the track grooves 7 and 9, which are slightly separated from the groove bottoms of the track grooves 7 and 9.

[0049] 10A and 10B , a state in which the track grooves 7 of the outer joint member 2 are inclined in the circumferential direction with respect to the joint axis N-N will be described in detail. FIG. 10A shows a partial vertical cross section of the outer joint member 2, and FIG. 10B shows a right side view of the outer joint member 2. The track grooves 7 of the outer joint member 2 are designated by the symbols 7A and 7B based on the difference in their inclination direction. As shown in FIG. 10A , a plane M including the ball raceway center line X of the track groove 7A and the joint center O is inclined by an angle γ with respect to the joint axis N-N. Furthermore, although not shown, a track groove 7B that is circumferentially adjacent to the track groove 7A has a plane M including the ball raceway center line X of the track groove 7B and the joint center O inclined by an angle γ with respect to the joint axis N-N in the direction opposite to the inclination direction of the track groove 7A. In this embodiment, the entire area of ​​the ball track center line X of the track groove 7A, i.e., both the ball track center line Xa of the first track groove portion 7a and the ball track center line Xb of the second track groove portion 7b, are formed on the plane M. However, this is not limiting, and it is also possible to implement a form in which only the ball track center line Xa of the first track groove portion 7a is included in the plane M. Therefore, it is sufficient that the plane M, which includes at least the ball track center line Xa of the first track groove portion 7a and the joint center O, is inclined in the circumferential direction with respect to the joint axis N-N, and that the inclination directions are opposite to each other in the first track groove portions 7a that are adjacent to each other in the circumferential direction.

[0050] Here, a supplementary note will be made regarding the reference numerals of the track grooves. When referring to the entire track grooves of the outer joint member 2, reference numeral 7 is used, with reference numeral 7a being used for the first track groove portion and reference numeral 7b being used for the second track groove portion. Furthermore, when distinguishing between track grooves with different inclination directions, reference numerals 7A and 7B are used, with reference numerals 7Aa and 7Ba being used for the first track groove portions and reference numerals 7Ab and 7Bb being used for the second track groove portions, respectively. Reference numerals are used in a similar manner for the track grooves of the inner joint member 3, which will be described later.

[0051] Next, with reference to Figures 11A, 11B, and 11C, a state in which the track grooves 9 of the inner joint member 3 are inclined in the circumferential direction with respect to the joint axis N-N will be described in detail. Figure 11B shows the outer peripheral surface of the inner joint member 3, Figure 11A shows the left side surface of the inner joint member 3, and Figure 11C shows the right side surface of the inner joint member 3. The track grooves 9 of the inner joint member 3 are denoted by the symbols 9A and 9B based on the difference in their inclination directions. As shown in Figure 11B, a plane Q including the ball raceway center line Y of the track groove 9A and the joint center O is inclined by an angle γ with respect to the joint axis N-N. Furthermore, although not shown, the track groove 9B adjacent to the track groove 9A in the circumferential direction has a plane Q including the ball raceway center line Y of the track groove 9B and the joint center O inclined by an angle γ with respect to the joint axis N-N in the direction opposite to the inclination direction of the track groove 9A. The inclination angle γ is preferably set to 4° to 12°, taking into consideration the operability of the constant velocity universal joint 1 and the spherical surface width F of the track grooves on the closest side of the inner joint member 3. Furthermore, as with the outer joint member described above, in this embodiment, the entire ball track center line Y of the track groove 9A, i.e., both the ball track center line Ya of the first track groove portion 9a and the ball track center line Yb of the second track groove portion 9b, are formed on the plane Q. However, this is not limiting, and a configuration in which only the ball track center line Ya of the first track groove portion 9a is included in the plane Q can also be implemented. Therefore, it is sufficient that the plane Q, which includes at least the ball track center line Ya of the first track groove portion 9a and the joint center O, is inclined in the circumferential direction with respect to the joint axis N-N, and that the inclination directions are opposite to each other in the first track groove portions 9a that are adjacent to each other in the circumferential direction. The ball raceway center line Y of the track groove 9 of the inner joint member 3 is formed as a mirror image of the ball raceway center line X of the mating track groove 7 of the outer joint member 2, with respect to a plane P including the joint center O when the operating angle is 0°.

[0052] The track grooves as viewed from a vertical cross section of the outer joint member 2 will be described in detail with reference to Figure 12. The partial vertical cross section of Figure 12 is a cross section seen on a plane M including the ball raceway center line X of the track groove 7A in Figure 10A described above and the joint center O. Therefore, strictly speaking, it is not a vertical cross section on a plane including the joint axis N-N, but rather shows a cross section inclined by an angle γ. Figure 12 shows the track grooves 7A of the outer joint member 2, but track groove 7B has the same configuration as track groove 7A except that its inclination direction is opposite to that of track groove 7A, so its description will be omitted.

[0053] Track grooves 7A are formed in the axial direction on the spherical inner peripheral surface 6 of the outer joint member 2. The track groove 7A has a ball track center line X, and is composed of a first track groove portion 7Aa having an arc-shaped ball track center line Xa with the joint center O as the center of curvature (no axial offset), and a second track groove portion 7Ab having a linear ball track center line Xb. At an end A on the opening side of the ball track center line Xa of the first track groove portion 7Aa, the linear ball track center line Xb of the second track groove portion 7Ab is smoothly connected as a tangent. In other words, the end A is the connection point between the first track groove portion 7Aa and the second track groove 7Ab. Because end A is located closer to the opening than joint center O, the linear ball track center line Xb of second track groove 7Ab, which is connected as a tangent to ball track center line Xa of first track groove 7Aa at end A on the opening side, is formed to approach joint axis N-N (see FIG. 9A) as it moves closer to the opening side. This ensures the effective track length at the maximum operating angle and prevents the wedge angle from becoming excessively large.

[0054] As shown in Figure 12, the line connecting the end A and the joint center O is designated as L. The joint axis N'-N' projected onto a plane M [see Figure 10A] that includes the ball raceway center line X of the track groove 7A and the joint center O is inclined at an angle γ with respect to the joint axis N-N, and the angle formed by the line L and a perpendicular line K at the joint center O to the axis N'-N' and the line L is designated as β'. The perpendicular line K lies on a plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N. Therefore, the angle β that the line L forms with respect to the plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N is expressed as sin β = sin β' × cos γ.

[0055] Similarly, details of the track grooves will be described with reference to a longitudinal cross section of the inner joint member 3 with reference to Fig. 13. The longitudinal cross section of Fig. 13 is a cross section seen on a plane Q including the ball raceway center line Y of the track groove 9A in Fig. 11B described above and the joint center O. Therefore, as with Fig. 12, strictly speaking, it is not a longitudinal cross section on a plane including the joint axis N-N, but shows a cross section inclined by an angle γ. Fig. 13 shows the track grooves 9A of the inner joint member 3, but the track groove 9B has the same configuration as the track groove 9A except that its inclination direction is opposite to that of the track groove 9A, and therefore description thereof will be omitted.

[0056] Track grooves 9A are formed in the axial direction on the spherical outer peripheral surface 8 of the inner joint member 3. The track groove 9A has a ball raceway center line Y, and is composed of a first track groove portion 9Aa having an arc-shaped ball raceway center line Ya with the joint center O as the center of curvature (no axial offset), and a second track groove portion 9Ab having a linear ball raceway center line Yb. At an end B on the far side of the ball raceway center line Ya of the first track groove portion 9Aa, the ball raceway center line Yb of the second track groove portion 9A is smoothly connected as a tangent. In other words, the end B is the connection point between the first track groove portion 9Aa and the second track groove portion 9Ab. Because end B is located further back than the joint center O, the linear ball track center line Yb of the second track groove 9Ab, which is connected as a tangent at the far end B to the ball track center line Ya of the first track groove portion 9Aa, is formed to approach the joint axis N-N (see FIG. 3A) as it moves further back. This ensures the effective track length at the maximum operating angle and prevents the wedge angle from becoming excessively large.

[0057] As shown in Figure 13, the straight line connecting the end B and the joint center O is designated by J. The joint axis N'-N' projected onto a plane Q [see Figure 11B] that includes the ball raceway center line Y of the track groove 9A and the joint center O is inclined by γ with respect to the joint axis N-N, and the angle formed by the perpendicular line K at the joint center O to the axis N'-N' and the straight line J is designated by β'. The perpendicular line K lies on a plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the axis N-N. Therefore, the angle β that the straight line J forms with the plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N is expressed as sin β = sin β' × cos γ.

[0058] Next, we will explain the angle β that the lines L and J form with respect to the plane P containing the joint center O when the operating angle is 0°. When the operating angle is θ, the balls 4 move by θ / 2 with respect to the plane P containing the joint center O of the outer joint part 2 and the inner joint part 3 and perpendicular to the joint axis N-N. The angle β is determined by half the frequently used operating angle, and the range of the track grooves in which the balls 4 contact within the frequently used operating angle range is determined. Here, we will define the frequently used operating angle. First, the common operating angle of the joint refers to the operating angle generated in the fixed constant velocity universal joint of the front driveshaft when the steering is in a straight-ahead position in a vehicle with one occupant on a horizontal, flat road surface. The common operating angle is usually selected and determined between 2° and 15° according to the design conditions of each vehicle model.

[0059] The frequently used operating angle does not refer to the high operating angle that occurs when the vehicle, for example, turns right or left at an intersection, but rather to the operating angle that occurs in a fixed constant velocity universal joint when the vehicle travels on a continuously curved road, and this is also determined according to the design conditions of each vehicle model. The frequently used operating angle is targeted to be a maximum of 20°. Accordingly, the angle β that the lines L and J form with respect to a plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N is set to be between 3° and 10°. However, the angle β is not limited to 3° and 10° and can be set appropriately according to the design conditions of the vehicle model. Setting the angle β to 3° to 10° allows for versatility in a variety of vehicle models.

[0060] Due to the angle β, in Fig. 12, the end A of the ball track center line Xa of the first track groove portion 7Aa is the center position of the ball when it moves furthest toward the opening along the axial direction at a frequently used operating angle. Similarly, in Fig. 13, in the inner joint member 3, the end B of the ball track center line Ya of the first track groove portion 9Aa is the center position of the ball when it moves furthest toward the rear along the axial direction at a frequently used operating angle. With this setting, within the frequently used operating angle range, the balls 4 are positioned in the first track groove portions 7Ba and 9Ba (see Figs. 10A, 10B, 11A, 11B, and 11C) that are inclined in the opposite direction to the first track groove portions 7Aa and 9Aa of the outer joint member 2 and the inner joint member 3. Therefore, forces in opposite directions are applied from the balls 4 to pocket portions 5a that are adjacent to each other in the circumferential direction of the cage 5, and the cage 5 is stabilized at the joint center O (see Fig. 9A). This reduces the contact force between the spherical outer peripheral surface 12 of the cage 5 and the spherical inner peripheral surface 6 of the outer joint member 2, and the contact force between the spherical inner peripheral surface 13 of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3, allowing the joint to operate smoothly under high load or at high rotation speeds, suppressing torque loss and heat generation and improving durability.

[0061] Also in the fixed-side constant velocity universal joint 1 of the second embodiment described above, a chamfered portion 30 (see FIG. 4 ) having an arc-shaped cross section in a direction perpendicular to the axial direction is formed between the spherical inner peripheral surface 6 of the outer joint member 2 and the guide surface 71 of the track groove 7. The chamfered portion 30 of the outer joint member 2 and the guide surface of the track groove 7 are connected at an edge-shaped connection point E1, and the angle ε between the tangent to the guide surface 71 at the connection point and the tangent to the chamfered portion 30 is set in the range of 0°<ε≦15°. In this case, the radius of curvature R of the chamfered portion 30 is preferably 3 mm or more and 9 mm or less.

[0062] 14 is a vertical cross-sectional view of the outer joint member 2 in the fixed constant velocity universal joint 1 of the cross track groove type, FIG. 15A shows the A'-A' cross section of FIG. 14, and FIG. 15B shows the B'-B' cross section of FIG.

[0063] As shown in FIGS. 15A and 15B , in the outer joint member 2 of the cross track groove type constant velocity universal joint 1, the center of curvature of the ball raceway center line X (radius of curvature Ro) of the track groove 7 coincides with the joint center O, which is the center of curvature of the spherical inner peripheral surface 6 (radius of curvature Ros). Therefore, the depth (Ha, Hb) of the track groove 7 is uniform in the axial direction (Ha = Hb). Accordingly, the angle δ between the spherical inner peripheral surface 6 and the track groove 7 is constant in the axial direction, making it possible to form the chamfered portion 30 with a uniform radius of curvature R. Therefore, in the cross track groove type constant velocity universal joint 1 of the second embodiment, it is preferable that the radius of curvature R of the chamfered portion 30 be constant in the axial direction. In this case, it is also preferable that the radius of curvature R of the chamfered portion 30 be constant within a range of 3 mm or more and 9 mm or less.

[0064] In the second embodiment, the chamfered portion 30 is formed over the entire axial length of the track groove 7. On the other hand, as in the first embodiment, the chamfered portion 30 may be formed with an inter-tangent angle ε in the range of 0°<ε≦15° only on the deep side (deeper than the center of curvature O1) of the track groove 7 of the outer joint member 2 where a high load is generated on the ball 4 at a high operating angle.

[0065] In the above embodiment, the fixed type constant velocity universal joint has been described as having eight balls 4, but the number of balls is not limited to eight. Six to ten balls or more may also be used as appropriate.

[0066] In addition, in the fixed-type constant velocity universal joint of the second embodiment, the ball raceway center line Xb of the second track groove portion is linear, but this is not limited to this. In short, any suitable shape can be used as long as it is different from the ball raceway center line Xa of the first track groove portion and increases the effective track length to achieve a high operating angle, such as an ellipse or a linear shape. Furthermore, the first track groove portion and the second track groove portion are not limited to a single arc, but may be formed of multiple arcs taking into account factors such as the track groove depth. Furthermore, while the track grooves are shown as being arranged at equal pitches in the circumferential direction, they may also be arranged at unequal pitches. Furthermore, while the inclination angle γ of the first track grooves with respect to the joint axis N-N is shown as being equal for all track grooves, this is not limited to this. The inclination angle γ may be unequal between a paired first track groove of the outer joint member and a paired first track groove of the inner joint member and another paired first track groove. In short, it is sufficient that the inclination angles are set so that the axial force of the ball acting on all pockets in the circumferential direction of the cage is balanced overall. In addition, although an embodiment of angular contact in which the track grooves and balls come into contact with each other at a contact angle has been shown, this is not limiting, and circular contact in which the cross section of the track grooves is formed into a circular shape may also be used.

[0067] The present invention is not limited to the above-described embodiments, and can of course be embodied in various other forms without departing from the spirit of the present invention. The scope of the present invention is indicated by the claims, and further includes the equivalent meanings set forth in the claims, and all modifications within the scope of the claims.

[0068] REFERENCE SIGNS LIST 1 Fixed type constant velocity universal joint 2 Outer joint member 3 Inner joint member 4 Ball 5 Cage 5a Pocket 6 Spherical inner peripheral surface 7 Track groove 8 Spherical outer peripheral surface 9 Track groove 30 Chamfered portion 71 Guide surface 91 Guide surface E1 Connection point O Joint center O1 Center of curvature O2 Center of curvature R Radius of curvature of chamfered portion

Claims

1. A fixed type constant velocity universal joint comprising: an outer joint member having a plurality of track grooves formed on its spherical inner peripheral surface and having an open side and a rear side spaced apart in the axial direction; an inner joint member having a plurality of track grooves formed on its spherical outer peripheral surface; balls arranged between the track grooves of the outer joint member and the corresponding track grooves of the inner joint member; and a cage having pockets for accommodating the balls and fitting with the spherical inner peripheral surface of the outer joint member and the spherical outer peripheral surface of the inner joint member, wherein the track grooves of the outer joint member have guide surfaces for guiding the balls, and a chamfered portion having an arc-shaped cross section in a direction perpendicular to the axial direction is formed between the spherical inner peripheral surface of the outer joint member and the guide surface, wherein the chamfered portion of the outer joint member and the guide surface are connected at an edge-shaped connection point, and the angle ε between the tangent to the guide surface at the connection point and the tangent to the chamfered portion is 0°<ε≦15°.

2. A fixed type constant velocity universal joint according to claim 1, wherein the radius of curvature R of said chamfered portion is 3.0 mm≦R≦9.0 mm.

3. A fixed type constant velocity universal joint according to claim 1, wherein the track grooves of the outer joint member have a portion where the center line of the ball raceway is an arc.

4. A fixed type constant velocity universal joint according to claim 3, wherein the radius of curvature of said chamfered portion is non-uniform in the axial direction.

5. A fixed type constant velocity universal joint according to claim 3, wherein said chamfered portion is provided on the inner side of the center of curvature of said ball raceway center line.

6. A fixed type constant velocity universal joint according to any one of claims 3 to 5, wherein the center of curvature of the ball raceway center line and the center of curvature of the spherical inner peripheral surface are offset in the axial direction.

7. A fixed type constant velocity universal joint according to claim 3, wherein the radius of curvature of said chamfered portion is uniform in the axial direction.

8. A fixed type constant velocity universal joint according to claim 3, wherein said chamfered portion is provided over the entire axial length of the track groove of said outer joint member.

9. A fixed type constant velocity universal joint according to claim 3, 7 or 8, wherein the axial offset between the center of curvature of the ball raceway center line and the center of curvature of the spherical inner peripheral surface is set to zero.

10. A fixed type constant velocity universal joint according to claim 9, wherein a plane containing the ball raceway center lines of the track grooves of said outer joint member and the joint center is inclined with respect to the axis of the joint, and the inclination directions are opposite to each other in said track grooves adjacent in the circumferential direction, and the ball raceway center lines of the track grooves of said inner joint member are formed in mirror symmetry with the ball raceway center lines of the mating track grooves of said outer joint member, with respect to a plane which contains the joint center and is perpendicular to the axis of the joint when the operating angle is 0°.

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