Fixed constant velocity universal joint

Abstract

To provide a fixed constant velocity universal joint that achieves both high efficiency and a wide operating angle, while also exhibiting good NVH characteristics. [Solution] A fixed constant velocity universal joint 1 of the track groove crossing type in which the forces acting on the retainer 5 are balanced, and a second track groove section 7b, 9b corresponding to a high operating angle is provided, and the ends A, B of the ball trajectory centerlines Xa, Ya of the first track groove section 7a, 9a The ball trajectory centerlines Xb and Yb of the second track grooves 7b and 9b are connected to the first track. Connection parts Co and Ci are formed between the track grooves 7a and 9a and the second track grooves 7b and 9b. In the operating angle region beyond the continuation sections Co and Ci, multiple balls 4 enter the second track grooves 7b and 9b. The present invention is characterized in that the clamping angle η2 of the balls 4 located in the second track grooves 7b and 9b and the clamping angle η1 of the balls located in the first track grooves 7a and 9a are set to be equal.

Description

Technical Field

[0001] The present invention relates to a fixed constant velocity joint, and more particularly to a fixed constant velocity joint applied to the power transmission system of automobiles and various industrial machines.

Background Art

[0002] For example, in the front drive shaft of an automobile, a sliding constant velocity joint that can axially displace while taking an operating angle with a relatively small maximum operating angle is usually incorporated on the inboard side (differential side), and on the outboard side (wheel side), since the wheel is steered, a fixed constant velocity joint that can take a large operating angle but does not axially displace is incorporated.

[0003] As functions required for a fixed constant velocity joint, it is important to transmit power to the wheels with as little loss as possible and to take a high operating angle in accordance with the steering of the wheels. Recently, for the purpose of improving the environmental performance of automobiles, further higher efficiency has been demanded, and joint types with track groove intersections such as those in Patent Document 1 and Patent Document 2 have been proposed. Also, as the maximum operating angle, conventionally, 47° for a ZF type constant velocity joint (BJ type) and 50° for an undercut-free type constant velocity joint (UJ type) are common, but from the viewpoint of improving the turning performance and small turning performance of automobiles, the demand for more than 50° is increasing. Thus, as functions of a fixed constant velocity joint, the compatibility at a high level of high efficiency and high operating angle has become important.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] To achieve both high efficiency and high operating angles at a high level, as described in Patent Documents 1 and 2, it is necessary to provide a second track groove that accommodates high operating angles in a structure where the forces acting on the retainer are balanced. Various shapes have been proposed for this second track groove so as to ensure that the ball contact point is secured when the joint is required at high operating angles.

[0006] In view of the above-mentioned problems, the present invention aims to provide a fixed constant velocity universal joint that achieves both high efficiency and a wide operating angle, and has good NVH characteristics. [Means for solving the problem]

[0007] The inventors of this invention conducted various studies and verifications to achieve the above objectives, and arrived at the present invention through the following findings and exploratory activities.

[0008] (1) Imbalance in the force with which the ball presses against the holder In a fixed constant velocity universal joint of the track groove crossing type where the forces acting on the retainer are balanced, in a structure that includes a second track groove section to accommodate high operating angles, when a ball enters the second track groove section from the first track groove section, the balance changes, and the retainer comes into contact with the outer joint member and the inner joint member. As a result, the efficiency of the joint decreases.

[0009] (2) Examination of the development process for a fixed constant velocity universal joint of the track groove crossing type with a maximum operating angle exceeding 50° Figures 9(A) to 11 show a prototype of a fixed constant velocity universal joint of the track groove crossing type with a maximum operating angle exceeding 50°. Figure 9(A) is a partial longitudinal section view of the prototype fixed constant velocity universal joint, and Figure 9(B) is a right side view of the fixed constant velocity universal joint in Figure 9(A). Figure 10 is a partial longitudinal section view showing the state in which the ball is in the second track groove, and Figure 11 is a partial longitudinal section view explaining the clamping angle. As shown in Figure 9(A), the second track grooves 107b and 109b that correspond to operating angles exceeding 50° require an arc shape with an inverse radius to the arc shape of the first track grooves 107a and 109a. In the case of the second track grooves 107b and 109b having an inverted arc shape, as the ball 104 enters the range of the second track grooves 107b and 109b and the angle increases, the clamping angle acting on the ball 104 increases, and the force with which the ball 104 located in the second track grooves 107b and 109b pushes the retainer 105 increases. Also, the connection point between the arc-shaped first track grooves 107a and 109a and the inverted arc-shaped second track grooves 107b and 109b becomes a significant inflection point. When the ball 104 enters the inverted arc-shaped second track grooves 107b and 109b from the arc-shaped first track grooves 107a and 109a, the clamping angle acting on the ball changes rapidly.

[0010] As described above, we focused on the possibility that the balance between the force with which the balls 104 located in the first track grooves 107a and 109a push the retainer 105 and the force with which the balls 104 located in the second track grooves 107b and 109b push the retainer 105 could become unbalanced, causing the retainer 105 to deviate from the bisecting plane, and investigated its behavior.

[0011] (3) Examination of the degree to which the angle range of the ball entering the second track groove affects the behavior of the retainer. (3-1)(i) First track grooves 107a and 109a with an arc shape and an inverted arc shape The analysis and evaluation focused on the fact that (ii) the connection point with the arc-shaped second track grooves 107b and 109b becomes a significant inflection point, and (ii) the clamping angle acting on the ball changes rapidly when the ball 104 enters the arc-shaped second track grooves 107b and 109b, which have an inverse radius. The ball trajectory centerline xb of the second track groove 107b is connected to the end a of the ball trajectory centerline xa of the first track groove 107a, forming a connection point co between the first track groove 107a and the second track groove 107b. In addition, the ball trajectory centerline yb of the second track groove 109b is connected to the end b of the ball trajectory centerline ya of the first track groove 109a, forming a connection point ci between the first track groove 109a and the second track groove 109b.

[0012] (3-2) As a result, we found that the following problem exists in the angle range where multiple balls 104 enter the second track grooves 107b and 109b beyond the connection parts co and ci (especially in the angle range where about two balls enter). As shown in Figure 10, in the operating angle θ range where multiple balls 104 (about two) are placed in the second track grooves 107b and 109b, the force with which the balls 104 push against the retainer 105 is small. As a result, the contact force between the retainer 105 and the outer joint member 102 and the inner joint member 103 is also small. In this state, a difference occurs between the clamping angle η2' of the balls 104 located in the second track grooves 107b and 109b, which are on the opening side of the joint center O, and the clamping angle η1' of the balls 104 located in the first track grooves 107a and 109a, which are on the inner side of the joint center O, and the clamping angle η1' of the balls 104 located on the opening side of the joint center O. Because the change in this difference is also rapid, the angle of the retainer 105 also fluctuates greatly, raising concerns that this may lead to a decrease in efficiency and NVH (Noise, Vibration, Harshness) performance.

[0013] (3-3) The clamping angle η is shown in Figure 11. The clamping angle η refers to the angle at which the ball 104 is clamped between the track groove 107 of the outer joint member 102 and the track groove 109 of the inner joint member 103 when the track groove 107 of the outer joint member 102 and the track groove 109 of the inner joint member 103 are cut in the longitudinal section direction including their centerlines. When the ball 104 and the track grooves 107 and 109 make angular contact, the ball 104 and the track grooves 107 and 109 contact in the direction of the contact angle (including the side surface). However, considering the evaluation of the difference in the clamping angle between the first track groove portions 107a and 109a and the second track groove portions 107b and 109b, and the reliability and ease of measurement, it was concluded that it is effective to use the clamping angle at the bottom of the track groove as a substitute for convenience. The same applies to the embodiments described later. The clamping angle η in this specification and the claims is used in the sense described above.

[0014] (3-4) When the operating angle θ is increased beyond the angle range in which multiple balls 104 (about two) can enter the second track grooves 107b and 109b shown in Figure 10, the clamping angles η1' and η2' of the balls 104 located in the second track grooves 107b and 109b and facing the opening side also increase. As a result, the retainer 105 is strongly pushed in the opening side, and the contact force between the retainer 105 and the outer joint member 102 and the inner joint member 103 also increases, and it was found that this works to stabilize the position of the retainer 105. In addition, it was found that the angle range in which the operating angle θ is increased further is not used very often, so it has little impact on the deterioration of NVH performance.

[0015] (4) A novel idea that achieves both high efficiency and a wide operating angle while ensuring NVH characteristics. Based on the above analysis, evaluation, and findings, we conceived a new idea that, in a fixed constant velocity universal joint 101 of the track groove crossing type where the forces acting on the retainer 105 are balanced, and which is equipped with second track grooves 107b and 109b that correspond to operating angles exceeding 50°, the key to ensuring efficiency and NVH (Noise, Vibration, Harshness) performance is to suppress fluctuations from the bisecting plane of the retainer 105 in the operating angle θ range where multiple balls 104 (approximately two) enter the second track grooves 107b and 109b that correspond to high angles. This led to the present invention.

[0016] As a technical means to achieve the aforementioned objectives, the present invention provides: an outer joint member having a plurality of track grooves extending generally in the axial direction formed on its spherical inner circumferential surface, and having an opening side and a back side spaced apart in the axial direction; an inner joint member having a plurality of track grooves extending generally in the axial direction formed on its spherical outer circumferential surface, paired with the track grooves of the outer joint member; a plurality of balls interposed between the track grooves of the outer joint member and the track grooves of the inner joint member to transmit torque; and a spherical outer circumferential surface that holds these balls in a pocket and fits between the spherical inner circumferential surface of the outer joint member and the spherical outer circumferential surface of the inner joint member. In a fixed constant velocity universal joint comprising a surface and a retainer having a spherical inner surface, the track groove of the outer joint member consists of a first track groove portion 7a located on the inner side and a second track groove portion 7b located on the opening side, the first track groove portion 7a has an arc-shaped ball trajectory centerline Xa having a center of curvature that is not offset axially with respect to the joint center O, and the plane M containing the ball trajectory centerline Xa and the joint center O is inclined with respect to the joint axis NN, and the direction of this inclination is formed in opposite directions in adjacent first track groove portions 7a in the circumferential direction. The second track groove 7b has a ball trajectory centerline Xb with a different shape from the ball trajectory centerline Xa of the first track groove 7a, the end A of the ball trajectory centerline Xa of the first track groove 7a is located on the opening side of the joint center O, and the ball trajectory centerline Xb of the second track groove 7b is connected to the end A to form a connection portion Co between the first track groove 7a and the second track groove 7b, and the ball trajectory centerline Y of the track groove of the inner joint member is in a plane P that includes the joint center O and is perpendicular to the joint axis NN when the operating angle is 0° As a reference, the ball trajectory centerline X of the pair of track grooves of the outer joint member is formed in mirror image symmetry, and the ball trajectory centerline Y of the track groove of the inner joint member is connected to the end B located on the far side of the ball trajectory centerline Ya of the first track groove 9a by the ball trajectory centerline Yb of the second track groove 9b, forming a connection part Ci between the first track groove 9a and the second track groove 9b, and in the operating angle range beyond the connection part Co, Ci, in the second track groove 7b,The characteristic feature is that the clamping angle η2 of the ball located at 9b and the clamping angle η1 of the ball located at the first track grooves 7a and 9a are set to be equal. With this configuration, it is possible to achieve both high efficiency and a wide operating angle, and to realize a fixed constant velocity universal joint with good NVH characteristics.

[0017] The process involves multiple balls entering the second track grooves 7b and 9b beyond the above-mentioned connection points Co and Ci. A key feature is that the number of balls in the dynamic angle range is two. This allows for a reliable and easy determination of the internal specifications that suppress fluctuations from the bisecting plane of the retainer.

[0018] The ball trajectory centerlines Xa and Ya of the first track grooves 7a and 9a are characterized in that they have a curvature center O1 that is located on the side of the first track grooves 7a and 9a with respect to the axis (N-N) of the joint and is radially offset. As a result, the clamping angle η1 can be easily adjusted by changing the amount of radial offset and the radius of curvature of the curvature center O1 of the ball trajectory centerlines Xa and Ya of the first track grooves 7a and 9a.

[0019] The characteristic feature is that the operating angle θ1 at which the center of the ball on the most open side is positioned at the end A of the ball trajectory centerline Xa of the first track groove 7a of the outer joint member is set to 15° or more. This suppresses the increase in the clamping angle of the second track groove, thereby suppressing spherical force and ensuring efficiency.

[0020] The ball trajectory centerline Xb of the second track groove 7b of the outer joint member is characterized by having an arc shape with a center of curvature Oo2 radially outward from the outer diameter surface of the outer joint member. This allows for an increased effective track length at the maximum operating angle θmax, ensuring contact between the ball and the track groove even at the maximum operating angle θmax exceeding 50°.

[0021] By setting the number of the balls to be eight or more, a fixed constant velocity universal joint that is lightweight, compact, achieves both high efficiency and a large operating angle, and has good NVH characteristics can be realized.

Effect of the Invention

[0022] According to the present invention, a fixed constant velocity universal joint that achieves both high efficiency and a large operating angle and has good NVH characteristics can be realized.

Brief Description of the Drawings

[0023] [Figure 1] (A) FIG. is a partial longitudinal sectional view of a fixed constant velocity universal joint according to an embodiment of the present invention, and (B) FIG. is a right side view of the fixed constant velocity universal joint of (A) FIG. [Figure 2] (A) FIG. is a partial longitudinal sectional view of an outer joint member of a fixed constant velocity universal joint according to the present embodiment, and (B) FIG. is a right side view of the outer joint member of (A) FIG. [Figure 3] (A) FIG. shows an inner joint member of a fixed constant velocity universal joint according to the present embodiment, (B) FIG. is a left side view of the inner joint member of (A) FIG., and (B) FIG. is a view showing the outer peripheral surface of the inner joint member of (A) FIG. [Figure 4] It is a partial longitudinal sectional view showing details of a track groove of an outer joint member in FIG. 2(A). [Figure 5] It is a longitudinal sectional view showing details of a track groove of an inner joint member in FIG. 3(B). [Figure 6] It is a schematic longitudinal sectional view showing a state in which a fixed constant velocity universal joint according to the present embodiment takes a maximum operating angle. [Figure 7] It is a partial longitudinal sectional view showing a state of a clamping angle of an operating angle range in which a plurality of balls enter a second track groove portion of a fixed constant velocity universal joint according to the present embodiment. <000​​​​ [Figure 10] Figure 9(A) is a partial longitudinal cross-sectional view showing the clamping angle in the operating angle range where multiple balls fit into the second track groove of the fixed constant velocity universal joint. [Figure 11] This is a partial longitudinal cross-sectional view illustrating the angle between the teeth. [Modes for carrying out the invention]

[0024] A fixed constant velocity universal joint 1 according to one embodiment of this invention will be described with reference to Figures 1 to 8. Figure 1(A) is a partial longitudinal cross-sectional view of a fixed constant velocity universal joint according to one embodiment of this invention, and Figure 1(B) is a right side view of the fixed constant velocity universal joint of Figure 1(A). Figure 2(A) is a partial longitudinal cross-sectional view of the outer joint member of the fixed constant velocity universal joint according to this embodiment, and Figure 2(B) is a right side view of the outer joint member of Figure 2(A). Figure 3(A) shows the inner joint member of the fixed constant velocity universal joint according to this embodiment, and Figure 3(B) is a left side view of the inner joint member, and Figure 3(B) is a diagram showing the outer circumferential surface of the inner joint member of Figure 3(A). Figure 4 is a partial longitudinal cross-sectional view showing details of the track groove of the outer joint member of Figure 2(A), and Figure 5 is a longitudinal cross-sectional view showing details of the track groove of the inner joint member of Figure 3(B). Figure 6 is a schematic longitudinal cross-sectional view showing the fixed constant velocity universal joint according to this embodiment in the state where the maximum operating angle is taken. Figure 7 is a partial longitudinal cross-sectional view showing the clamping angle state in the operating angle range in which multiple balls enter the second track groove of the fixed constant velocity universal joint according to this embodiment. Figure 8 is an exploded view of the outer joint member as seen from the inside, showing the state in the operating angle range in which multiple balls enter the second track groove of the fixed constant velocity universal joint according to this embodiment.

[0025] As shown in Figure 1(A), the fixed constant velocity universal joint 1 mainly consists of an outer joint member 2, an inner joint member 3, balls 4, and a retainer 5. A track groove 7 is formed on the spherical inner circumferential surface 6 of the outer joint member 2, generally along the axial direction. The spherical outer circumferential surface 12 of the retainer 5 is fitted and guided by the spherical inner circumferential surface 6. A track groove 9 is formed on the spherical outer circumferential surface 8 of the inner joint member 3, generally along the axial direction. The spherical inner circumferential surface 13 of the retainer 5 is fitted and guided by the spherical outer circumferential surface 8. Eight balls 4 are housed one by one in the pockets 5a of the retainer 5.

[0026] As shown in Figures 1(B), 2(A), 2(B), 3(A), and 3(B), the eight track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3, respectively, are inclined circumferentially with respect to the joint axis NN, and the direction of inclination is formed in opposite directions for adjacent track grooves 7A, 7B and 9A, 9B in the circumferential direction. Eight balls 4 are placed one at each intersection of the 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 and 9 will be described later.

[0027] Figure 1(A) shows a longitudinal section of the fixed constant velocity universal joint 1. In order to accurately describe the form and shape of the track groove, which extends roughly in the axial direction, this specification uses the term "ball trajectory centerline." Here, the ball trajectory centerline refers to the trajectory traced by the center of a ball when it moves along the track groove. Therefore, the state of the track groove, such as its arc shape, is the same as the state of the ball trajectory centerline.

[0028] As shown in Figure 1(A), the track groove 7 of the outer joint member 2 has a ball trajectory centerline X, and the track groove 7 consists of a first track groove section 7a having an arc-shaped ball trajectory centerline Xa, and a second track groove section 7b having an arc-shaped ball trajectory centerline Xb with a radius opposite to that of the arc shape of the ball trajectory centerline Xa, and the ball trajectory centerline Xb of the second track groove section 7b is smoothly connected tangently to the ball trajectory centerline Xa of the first track groove section 7a. On the other hand, the track groove 9 of the inner joint member 3 has a ball trajectory centerline Y, and the track groove 9 consists of a first track groove section 9a having an arc-shaped ball trajectory centerline Ya, and a second track groove section 9b having an arc-shaped ball trajectory centerline Yb with a radius opposite to that of the arc shape of the ball trajectory centerline Ya, and the ball trajectory centerline Yb of the second track groove section 9b is smoothly connected tangently to the ball trajectory centerline Ya of the first track groove section 9a.

[0029] The first track groove 7a of the outer joint member 2 is located on the inner side of the outer joint member 2. The ball trajectory centerline Xa of the first track groove 7a is an arc shape with O1 as the center of curvature. The center of curvature O1 has no axial offset with respect to the joint center O, and is located on the side of the first track groove 7a with respect to the joint axis N-N, and is offset radially. The second track groove 7b of the outer joint member 2 is located on the opening side of the outer joint member 2. The ball trajectory centerline Xb of the second track groove 7b is an arc shape with Oo2 as the center of curvature (see Figure 4). The center of curvature Oo2 is offset radially outward from the outer diameter surface of the outer joint member 2. Therefore, the arc shape of the ball trajectory centerline Xb of the second track groove 7b is the opposite radius to the arc shape of the ball trajectory centerline Xa of the first track groove 7a.

[0030] The first track groove 9a of the inner joint member 3 is located on the opening side of the outer joint member 2. The ball trajectory centerline Ya of the first track groove 9a is an arc shape with O1 as the center of curvature, similar to the ball trajectory centerline Xa of the first track groove 7a of the outer joint member 2. The second track groove 9b of the inner joint member 2 is located on the inner side of the outer joint member 2. The ball trajectory centerline Yb of the second track groove 9b is an arc shape with Oi2 as the center of curvature (see Figure 5). The center of curvature Oi2 is offset radially outward from the outer diameter surface of the outer joint member 2, similar to the center of curvature Oo2. Therefore, the arc shape of the ball trajectory centerline Yb of the second track groove 9b is the opposite radius to the arc shape of the ball trajectory centerline Ya of the first track groove 9a.

[0031] The cross-sectional shapes of the track grooves 7 and 9 are formed in an elliptical or Gothic arch shape, and the track grooves 7 and 9 and the ball 4 make contact with a contact angle (approximately 30° to 45°), resulting in so-called angular contact. Therefore, the ball 4 and the track grooves 7 and 9 make contact in the direction of the contact angle, that is, on the side of the track grooves 7 and 9, slightly away from the bottom of the groove.

[0032] Based on Figures 2(A) and 2(B), the state in which the track groove 7 of the outer joint member 2 is inclined circumferentially with respect to the joint axis NN will be described in detail. The track grooves 7 of the outer joint member 2 are denoted as track grooves 7A and 7B due to the difference in their inclination direction. As shown in Figure 2(A), the plane M containing the ball trajectory centerline X and the joint center O of track groove 7A is inclined by an angle γ with respect to the joint axis NN. The track groove 7B, which is circumferentially adjacent to track groove 7A, is not shown in the figure, but the plane M containing the ball trajectory centerline X and the joint center O of track groove 7B is inclined by an angle γ with respect to the joint axis NN in the opposite direction to the inclination direction of track groove 7A. The track grooves 7A and 7B (and 9A and 9B, which will be described later) are inclined by an angle γ, but generally extend in the axial direction. In this specification and in the claims, the concept of a track groove that generally extends in the axial direction includes those inclined by an angle γ as described above.

[0033] Here, we will provide some supplementary information regarding the designations for the track grooves. When referring to the entire track groove of the outer joint member 2, the designation 7 is used, with the first track groove portion designated as 7a and the second track groove portion as 7b. Furthermore, when distinguishing between track grooves with different inclination directions, the designations 7A and 7B are used, with the first track groove portions designated as 7Aa and 7Ba, and the second track groove portions as 7Ab and 7Bb, respectively. The track grooves of the inner joint member 3, which will be described later, are designated in a similar manner.

[0034] Next, based on Figures 3(A) and 3(B), the state in which the track groove 9 of the inner joint member 3 is inclined circumferentially with respect to the joint axis NN will be described in detail. The track grooves 9 of the inner joint member 3 are denoted as track groove 9A and 9B due to the difference in their inclination direction. As shown in Figure 3(B), the plane Q containing the ball trajectory centerline Y and the joint center O of track groove 9A is inclined by an angle γ with respect to the joint axis NN. The track groove 9B, which is circumferentially adjacent to track groove 9A, is not shown in the figure, but the plane Q containing the ball trajectory centerline Y and the joint center O of track groove 9B is inclined by an angle γ with respect to the joint axis NN in the opposite direction to the inclination direction of track groove 9A. The inclination angle γ is preferably 4° to 12°, taking into consideration the operability of the constant velocity universal joint 1 and the spherical width F on the closest side of the track groove of the inner joint member 3. The ball trajectory centerline Y of the track groove 9 of the inner joint member 3 is formed in mirror image symmetry with the ball trajectory centerline X of the corresponding track groove 7 of the outer joint member 2, with reference to a plane P that includes the joint center O and is perpendicular to the joint axis NN when the operating angle is 0°.

[0035] Based on Figure 4, the details of the track groove as seen from the longitudinal section of the outer joint member 2 will be explained. The partial longitudinal section in Figure 4 is a cross-sectional view taken in a plane M that includes the ball trajectory centerline X and the joint center O of the track groove 7A in Figure 2(A) mentioned above. Therefore, strictly speaking, it is not a longitudinal section in a plane that includes the joint axis NN, but rather a cross-section that is inclined by an angle γ. Figure 4 shows the track groove 7A of the outer joint member 2, but the track groove 7B is the same as the track groove 7A except that the inclination direction is opposite, so its explanation will be omitted.

[0036] As shown in Figure 4, the first track groove portion 7Aa of the outer joint member 2 is located on the inner side of the outer joint member 2 with respect to the axis N'-N' of the joint projected onto the plane M (see Figure 2(A)) containing the ball trajectory centerline X of the track groove 7A and the joint center O. The ball trajectory centerline Xa of the first track groove portion 7Aa is an arc shape with O1 as the center of curvature. The center of curvature O1 has no axial offset with respect to the joint center O, and is located on the side of the first track groove portion 7Aa with respect to the axis N'-N' of the joint, and is offset radially (offset amount Fy). The radius of curvature of the ball trajectory centerline Xa of the first track groove portion 7Aa is r1.

[0037] The second track groove 7Ab of the outer joint member 2 is located on the opening side of the outer joint member 2. The ball trajectory centerline Xb of the second track groove 7Ab is an arc shape with Oo2 as the center of curvature. The center of curvature Oo2 is located on a straight line L1 connecting the center of curvature O1 and the end A on the opening side of the ball trajectory centerline Xa of the first track groove 7Aa, and is offset radially outward from the outer diameter surface of the outer joint member 2. The radius of curvature of the ball trajectory centerline Xb of the second track groove 7Ab is r2. The connection part Co between the first track groove 7Aa and the second track groove 7Ab is located radially outward from end A on the straight line L1. The arc shape of the ball trajectory centerline Xb of the second track groove 7Ab is the opposite radius to the arc shape of the ball trajectory centerline Xa of the first track groove 7a. The arc shape of the ball trajectory centerline Xb of the second track groove 7Ab is one specific example of a ball trajectory centerline Xb whose shape differs from that of the ball trajectory centerline Xa of the first track groove 7Aa. In this specification and in the claims, the ball trajectory centerline Xb whose shape differs from that of the ball trajectory centerline Xa of the first track groove 7a has the meaning described above.

[0038] Similarly, the details of the track groove will be explained based on the longitudinal section of the inner joint member 3, using Figure 5 as a reference. The longitudinal section in Figure 5 is a cross-sectional view taken in plane Q that includes the ball trajectory centerline Y and the joint center O of the track groove 9A in Figure 3(B) mentioned above. Therefore, as with Figure 4, strictly speaking, it is not a longitudinal section in a plane that includes the joint axis NN, but rather a cross-section that is inclined by an angle γ. Figure 5 shows the track groove 9A of the inner joint member 3, but the track groove 9B is the same as the track groove 9A except that the inclination direction is opposite, so its explanation will be omitted.

[0039] As shown in Figure 5, the first track groove portion 9Aa of the inner joint member 3 is located on the opening side of the outer joint member 2 with respect to the axis N'-N' of the joint projected onto the plane Q (see Figure 3(B)) containing the ball trajectory centerline Y of the track groove 9A and the joint center O. The ball trajectory centerline Ya of the first track groove portion 9Aa is an arc shape with O1 as the center of curvature. The center of curvature O1 has no axial offset with respect to the joint center O, and is located on the side of the first track groove portion 9Aa with respect to the axis N'-N' of the joint, and is offset radially (offset amount Fy). The radius of curvature of the ball trajectory centerline Ya of the first track groove portion 9Aa is r1.

[0040] The second track groove 9Ab of the inner joint member 3 is located on the inner side of the outer joint member 2. The ball trajectory centerline Yb of the second track groove 9Ab is an arc shape with Oi2 as the center of curvature. The center of curvature Oi2 is located on a straight line R1 connecting the center of curvature O1 and the inner end B of the ball trajectory centerline Ya of the first track groove 9Aa, and is offset radially outward from the outer diameter surface of the outer joint member 2. The radius of curvature of the ball trajectory centerline Yb of the second track groove 9Ab is r2. The connection part Ci between the first track groove 9Aa and the second track groove 9Ab is located radially inward from end B on the straight line R1. The arc shape of the ball trajectory centerline Yb of the second track groove 9Ab is the opposite radius to the arc shape of the ball trajectory centerline Ya of the first track groove 9Aa. The arc shape of the ball trajectory centerline Xb in the second track groove 7Ab is one specific example of the shape of the ball trajectory centerline Yb, which differs in shape from the ball trajectory centerline Ya in the first track groove 9Aa.

[0041] When the operating angle θ is taken, the ball 4 moves by θ / 2 relative to a plane P that includes the joint center O of the outer joint member 2 and the inner joint member 3 and is perpendicular to the joint axis NN. Based on the frequently used operating angle, the positions of the ends A and B of the ball trajectory centerlines Xa and Ya of the first track grooves 7a and 9a (boundaries with the ball trajectory centerlines Xb and Yb of the second track grooves 7b and 9b) are determined. Here, the commonly used angle of the joint and the frequently used operating angle will be explained. First, the commonly used angle of the joint refers to the operating angle that occurs in a fixed constant velocity universal joint of the front drive shaft when the steering is in the straight position in a vehicle with one occupant on a horizontal, flat road surface. The commonly used angle is usually selected and determined between 2° and 15° according to the design conditions of each vehicle type.

[0042] Furthermore, the frequently used operating angle refers not to the high operating angle that occurs when the vehicle makes a right or left turn at an intersection, but rather to the operating angle that occurs in the fixed constant velocity universal joint on curved roads during continuous driving, and this is also determined according to the design conditions for each vehicle type. The frequently used operating angle is aimed to be around 15°. The ball trajectory centerlines Xb and Yb of the second track grooves 7b and 9b, which correspond to high operating angles, are connected to the ends A and B of the first track grooves 7a and 9a. The setting of the positions of the ends A and B of the ball trajectory centerlines Xa and Ya of the first track grooves 7a and 7b was examined.

[0043] Considering the maximum operating angle of 15°, which is frequently used, the functional aspects of the joint were also examined. As a result, when the center of the ball 4 on the most open side is positioned at end A of the ball trajectory centerline Xa of the first track groove 7a of the outer joint member 2, and the center of the ball 4 on the innermost side is positioned at end B of the ball trajectory centerline Ya of the first track groove 9a of the inner joint member 3, the operating angle of the joint when this operating angle θ1 is 15° or more suppresses the increase in the clamping angle of the second track groove, thereby suppressing spherical force and ensuring efficiency. On the other hand, when the operating angle θ1 is less than 15°, the clamping angle of the second track groove increases, the spherical force becomes larger, and the efficiency deteriorates. Based on this, it was concluded that the operating angle θ1 should be 15° or more. Note that Figures 4 and 5 are cross-sectional views in planes M and Q inclined at an angle γ with respect to the axis NN (see Figures 2(A) and 3(B)). Therefore, the angle β between the perpendicular K, which is perpendicular to the axis N'-N' projected onto planes M and Q and passes through the joint center O, and the lines L2 and R2, which pass through the boundary A between the joint center O and the ball trajectory centerlines Xa and Xb, is not strictly half of the joint's operating angle θ1, but they are roughly equal (β ≈ θ1 / 2).

[0044] Due to the above operating angle θ1, in Figure 4, the end A of the ball trajectory centerline Xa of the first track groove 7Aa becomes the center position of the ball when it moves furthest towards the opening along the axial direction at the frequently used operating angle. Similarly, in the inner joint member 3, in Figure 5, the end B of the ball trajectory centerline Ya of the first track groove 9Aa becomes the center position of the ball when it moves furthest towards the inner side along the axial direction at the frequently used operating angle. With this setting, in the range of frequently used operating angles, the ball 4 is located in 7Ba and 9Ba (see Figures 2 and 3) which are in the opposite direction of inclination to the first track grooves 7Aa and 9Aa of the outer joint member 2 and the inner joint member 3. As a result, opposing forces act from the ball 4 on adjacent pocket portions 5a in the circumferential direction of the retainer 5, and the retainer 5 stabilizes at the joint center O (see Figure 1(A)). Therefore, the contact force between the spherical outer surface 12 of the retainer 5 and the spherical inner surface 6 of the outer joint member 2, and the contact force between the spherical inner surface 13 of the retainer 5 and the spherical outer surface 8 of the inner joint member 3 are suppressed, allowing the joint to operate smoothly under high load and high rotation speeds, reducing torque loss and heat generation, and improving durability.

[0045] Figure 6 shows the fixed constant velocity universal joint 1 in a state where it has taken a maximum operating angle exceeding 50°. As shown in Figure 4 above, the arc shapes of the ball trajectory centerlines Xb and Yb of the second track grooves 7Ab and 9Ab are inversely curved (different shapes) from the arc shapes of the ball trajectory centerlines Xa and Ya of the first track grooves 7Aa and 9Aa. Therefore, the effective track length at the maximum operating angle θmax can be increased, and contact points between the ball 4 and the track grooves 7 and 9 can be secured even at the maximum operating angle θmax exceeding 50°. Here, a supplementary explanation of the effective track length is given. When the operating angle is taken, the amount of axial movement per unit angle (for example, 1°) of the contact point between the track groove 7 and the ball 4 changes depending on the shape of the track groove 7. For example, since the arc shape of the ball trajectory centerline Xb of the second track groove 7Ab is the opposite radius (different shape) to the arc shape of the ball trajectory centerline Xa of the first track groove 7Aa, the contact point between the ball 4, whose center Ob is placed on the ball trajectory centerline Xb of the second track groove 7Ab, and the second track groove 7Ab will be located on the inner side of the outer joint member. As a result, a contact point between the ball 4 and the second track groove 7Ab can be secured. Thus, the effective track length means the length of the trajectory of the contact point of the track groove, taking into account the change in the amount of axial movement of the contact point due to the shape of the track groove.

[0046] As shown in Figure 6, the minimum shaft diameter portion 15a of the intermediate shaft 15, which is fitted and connected to the spline 14 of the inner joint member 3, has a nominal diameter dimension d. At the maximum operating angle θmax, the outer diameter surface of the minimum shaft diameter portion 15a is set to leave a small clearance between it and the entrance chamfer 20 of the outer joint member 2.

[0047] The overall configuration of the fixed constant velocity universal joint 1 is as described above. Next, the characteristic configuration of the fixed constant velocity universal joint 1 according to this embodiment will be described below.

[0048] (1) A fixed constant velocity universal joint of the track groove crossing type in which the forces acting on the retainer are balanced, and a second track groove section corresponding to a high operating angle is provided, wherein the ball trajectory centerlines Xb and Yb of the second track groove sections 7b and 9b are connected to the ends A and B of the ball trajectory centerlines Xa and Ya of the first track groove sections 7a and 9a, thereby forming connection sections Co and Ci between the first track groove sections 7a and 9a and the second track groove sections 7b and 9b.

[0049] (2) Multiple balls enter the second track grooves 7b and 9b beyond the connecting parts Co and Ci. In the dynamic angle range, the angle η2 of the balls located in the second track grooves 7b and 9b and the angle η1 of the balls located in the first track grooves 7a and 9a are set to be the same.

[0050] The combination of the above-described characteristic configurations (1) and (2) suppresses fluctuations from the bisecting plane of the retainer 5, thereby achieving both high efficiency and a wide operating angle, and realizing a fixed constant velocity universal joint with good NVH characteristics.

[0051] The distinctive configuration was derived from the findings in (3-1) and (3-2) below, as well as the novel idea in (4) below, within the "(3) Examination of the degree of influence of the angle range of the ball entering the second track groove on the behavior of the retainer" section of the fixed constant velocity universal joint prototyped and examined during the development process described above.

[0052] (3-1)(i) First track grooves 107a and 109a with an arc shape and an inverted arc shape (ii) The connection point with the arc-shaped second track grooves 107b and 109b becomes a prominent inflection point, and (ii) the ball 104 is reversed from the arc-shaped first track grooves 107a and 109a. We focused on the fact that the clamping angle acting on the ball changes rapidly when it enters the arc-shaped second track grooves 107b and 109b, and analyzed and evaluated this. The ball trajectory centerline xb of the second track groove 107b is connected to the end a of the ball trajectory centerline xa of the first track groove 107a, forming a connection part co between the first track groove 107a and the second track groove 107b. In addition, the ball trajectory centerline yb of the second track groove 109b is connected to the end b of the ball trajectory centerline ya of the first track groove 109a, forming a connection part ci between the first track groove 109a and the second track groove 109b.

[0053] (3-2) As a result, we found that the following problem exists in the angle range where multiple balls 104 enter the second track grooves 107b and 109b beyond the connection parts co and ci (especially in the angle range where about two balls enter). As shown in Figure 10, in the operating angle θ range where multiple balls 104 (about two) are placed in the second track grooves 107b and 109b, the force with which the balls 104 push against the retainer 105 is small. As a result, the contact force between the retainer 105 and the outer joint member 102 and the inner joint member 103 is also small. In this state, a difference occurs between the clamping angle η2' of the balls 104 located in the second track grooves 107b and 109b, which are on the opening side of the joint center O, and the clamping angle η1' of the balls 104 located in the first track grooves 107a and 109a, which are on the inner side of the joint center O, and the clamping angle η1' of the balls 104 located on the opening side of the joint center O. Because the change in this difference is also rapid, the angle of the retainer 105 also fluctuates greatly, raising concerns that this may lead to a decrease in efficiency and NVH (Noise, Vibration, Harshness) performance.

[0054] (4) A novel idea that achieves both high efficiency and a wide operating angle while ensuring NVH characteristics. Based on the above analysis, evaluation, and findings, we have arrived at a new idea: in a fixed constant velocity universal joint 101 of the track groove crossing type where the forces acting on the retainer 105 are balanced, and which is equipped with second track grooves 107b and 109b that can handle operating angles exceeding 50°, the key to ensuring efficiency and NVH (Noise, Vibration, Harshness) performance is to suppress fluctuations from the bisecting plane of the retainer 105 in the operating angle θ range where multiple balls 104 (about two) are placed in the second track grooves 107b and 109b that can handle high angles.

[0055] The characteristic configuration will be explained in detail with reference to Figures 7 and 8. Figures 4 and 5 mentioned above will also be referred to as appropriate. Figure 7 is a partial longitudinal cross-sectional view showing the clamping angle in the operating angle range in which multiple balls are inserted into the second track groove of the fixed constant velocity universal joint according to this embodiment. Figure 8 is an exploded view of the outer joint member as seen from the inside, showing the operating angle range in which multiple balls are inserted into the second track groove of the fixed constant velocity universal joint according to this embodiment.

[0056] As shown in Figure 4, in the fixed constant velocity universal joint 1 according to this embodiment, the end A of the ball trajectory center line Xa of the first track groove 7Aa of the outer joint member 2 is the second track groove 7Ab The ball trajectory centerline Xb is connected to the first track groove 7Aa and the second track groove 7A A connection portion Co is formed at b. As shown in Figure 5, the ball trajectory centerline Yb of the second track groove 9Ab is connected to the end B of the ball trajectory centerline Ya of the first track groove 9Aa of the inner joint member 2, forming a connection portion Ci between the first track groove 9Aa and the second track groove 9Ab. The first track grooves 7Ba and 9Ba have an inclination direction that is the first track The grooves 7Aa and 9Aa are in the opposite direction, but the other configurations are the same as the first track grooves 7Aa and 9Aa, so the illustration is omitted. Also, the first track grooves 7Aa, 9Aa, 7Ba, and 9Ba are sometimes collectively referred to as the first track grooves 7a and 9a, as shown below. Similarly, the second track grooves 7Ab, 9Ab, 7Bb, and 9Bb are sometimes collectively referred to as the first track grooves 7b and 9b.

[0057] As shown in Figure 7, multiple balls 4 (approximately 2) are placed in the second track grooves 7b and 9b beyond the connection points Co and Ci between the first track grooves 7a and 9a and the second track grooves 7b and 9b. In the operating angle θ range in which the balls 4 enter (in degrees), the clamping angle η2 of the balls 4 located in the second track grooves 7b and 9b and the clamping angle η1 of the balls located in the first track grooves 7a and 9a are set to be the same. In the operating angle θ range in which two balls 4 enter the second track grooves 7b and 9b beyond the connection parts Co and Ci, it is desirable that the clamping angles η1 and η2 of the balls 4 be set to be the same, that is, that there exists an operating angle in the operating angle θ range in which two balls 4 enter the second track grooves 7b and 9b where the clamping angles η1 and η2 coincide. In the fixed constant velocity universal joint 1 of this embodiment, the clamping angles η1 and η2 are set in the operating angle θ range in which two balls 4 enter the second track grooves 7b and 9b.

[0058] This section explains how to adjust and set the gripping angle η. For example, we will explain how to adjust the gripping angle η1 of the first track grooves 7a and 9a. As shown in Figures 4 and 5, the gripping angle η1 can be easily adjusted by changing the radial offset amount Fy and the radius of curvature r1 of the curvature center O1 of the ball trajectory centerlines Xa and Ya of the first track grooves 7a and 9a. Specifically, the gripping angle η1 can be increased by increasing the radial offset amount Fy and decreasing the radius of curvature r1. Conversely, the gripping angle η1 can be decreased by decreasing the radial offset amount Fy and increasing the radius of curvature r1. This adjustment is also performed for the ball trajectory centerlines Xb and Yb of the second track grooves 7b and 9b. Then, the gripping angles η1 and η2 are set to be equivalent in the operating angle θ range where multiple balls 4 (about 2) can enter the second track grooves 7b and 9b.

[0059] It is preferable that the radial offset amount Fy and radius of curvature r1 of the center of curvature O1 of the ball trajectory centerlines Xa and Ya of the first track grooves 7a and 9a satisfy Fy / r'≧0.25 when r'=r1+Fy. If Fy / r' is less than 0.25, the offset amount Fy becomes small, which reduces the gripping angle η1 of the balls located in the first track grooves 7a and 9a, and may not resolve the imbalance with the gripping angle η2 of the balls located in the second track grooves 7b and 9b. On the other hand, if Fy / r' exceeds 0.3, the groove depth near the far end of the first track groove 7a of the outer joint member 2 becomes shallow. Therefore, it is preferable that Fy / r'≦0.3 is satisfied. Alternatively, the region including the far end of the first track groove 7a of the outer joint member 2 may be replaced with a third track groove with a deeper groove depth than that region. In this case, a third track groove is formed in the region including the opening end of the first track groove 9a of the inner joint member 3, having a shape corresponding to the third track groove of the outer joint member 2.

[0060] The state of the operating angle range in which multiple balls (approximately two) are positioned in the second track groove will be explained based on Figure 8, an exploded view of the outer joint member as seen from the inside. In Figure 8, balls 4 are shown with dashed lines, and the inner joint member is omitted from the illustration. The phase angle is shown to the left of the outer joint member 2. The phase angle is shown with the phase angle of ball 4 at the vertex of the right side of the fixed constant velocity universal joint 1 shown in Figure 1(B) as 0°, and phase angles from 45° to 315° are shown in the counterclockwise direction. The ball with a phase angle of 0° is designated as 4(0°), and the balls are sequentially labeled 4(45°), 4(90°), 4(135°), 4(180°), 4(225°), 4(270°), and 4(315°). The center of each ball 4 is Ob, and the connection between the first track groove 7a and the second track groove 7b is Co. The arrow pointing towards the opening side of the outer joint member 2 indicates the magnitude of the clamping angle η.

[0061] As shown in Figure 8, of the eight balls 4, three balls 4(0°), 4(45°), and 4(315°) extend beyond the connection point Co between the first track groove 7a and the second track groove 7b and enter the second track groove 7b. Three balls 4(0°), 4(45°), and 4(315°) extend beyond the connection point Ci between the first track groove 9a and the second track groove 9b of the inner joint member 3 (not shown) and enter the second track groove 7b. As indicated by the arrows, the three balls 4(0°), 4(45°), and 4(315°) have a clamping angle η2 that widens toward the opening side of the outer joint member 2, with the clamping angle η2(0°) of ball 4(0°) being large, and the clamping angles η2(45°) and η2(315°) of balls 4(45°) and 4(315°) being small.

[0062] The three balls 4(135°), 4(180°), and 4(225°) located in the first track groove 7a(7Aa, 7Ba) have a gripping angle η1 that opens toward the opening side of the outer joint member 2, as indicated by the arrows. The gripping angle η1(180°) of ball 4(180°) is large, while the gripping angles η1(135°) and η1(225°) of balls 4(135°) and 4(225°) are small. As mentioned above, the curvature centers O1 of the ball trajectory centerlines Xa and Ya in the first track grooves 7a and 9a have no axial offset with respect to the joint center O, but have a radial offset amount Fy and a small radius of curvature r1. Therefore, a gripping angle η1 is generated as the balls shift axially from the plane P passing through the joint center O due to the operating angle. Since balls 4 (90°) and 4 (270°) shown in Figure 8 are located on a plane P passing through the joint center O, no clamping angle η1 that opens toward the opening side of the outer joint member 2 occurs.

[0063] The clamping angle η2(0°) and the clamping angle η1(180°) are equivalent, and the clamping angles η2(45°), η2(315°), η1(135°), and η1(225°) are equivalent. Thus, in the fixed constant velocity universal joint 1 according to this embodiment, in the operating angle θ range in which multiple balls 4 enter the second track section 7b, 9b beyond the connection parts Co, Ci between the first track grooves 7a, 9a and the second track grooves 7b, 9b, the clamping angle η2 of the balls 4 located in the second track grooves 7b, 9b and the clamping angle η1 of the balls located in the first track grooves 7a, 9a are set to be equivalent. Specifically, at an operating angle θ in which the number of balls 4 placed in the second track grooves 7b and 9b during one rotation of the fixed constant velocity universal joint 1 may be two, the shape of the track grooves 7 and 9 (in particular, the radial offset amount Fy of the curvature center O1 of the ball trajectory centerlines Xa and Ya of the first track grooves 7a and 9a) is set such that the gripping angle η2 (0°) for a ball 4 with a phase angle of 0° and the gripping angle η1 (180°) for a ball 4 with a phase angle of 180° are equal. This suppresses fluctuations from the bisecting plane of the retainer 5 in the operating angle θ range in which multiple balls 4 (about two) are placed in the second track grooves 7b and 9b corresponding to high operating angles, enabling a fixed constant velocity universal joint that achieves both high efficiency and a high operating angle, and has good NVH characteristics.

[0064] In Figure 8, the outer joint member is located beyond the connection points Co and Ci, in the second track groove 7b. Although the diagram shows two or more balls 4 with a clamping angle η2 that opens toward the opening side of 2, such as 4(0°), 4(45°), and 4(315°), as the rotation angle of the joint changes, the number of balls 4 located in the second track groove 7b and having a clamping angle η2 that opens toward the opening side of the outer joint member 2 decreases to two. Therefore, in the operating angle θ range where multiple balls 4 enter the second track grooves 7b and 9b beyond the connection parts Co and Ci, setting the number of balls in the operating angle range where multiple balls enter to two can be used as an indicator to reliably and easily determine the internal specifications that suppress fluctuations from the bisecting plane of the retainer.

[0065] In the embodiments described above, an example was shown in which the fixed constant velocity universal joint has 8 balls. However, the number of balls can be 8 or more, for example, 10 or more, as appropriate.

[0066] The present invention is not limited in any way to the embodiments described above, and can be implemented in various other forms without departing from the spirit of the invention. The scope of the present invention is indicated by the claims, and includes all modifications within the meaning and scope of equivalents set forth in the claims. [Explanation of symbols]

[0067] 1. Fixed constant velocity universal joint 2. Outer joint member 3. Inner joint member 4 balls 5 Cage 6 Spherical inner surface 7 Track grooves 7a First track groove 7b Second track groove 8 Spherical outer surface 9 Track grooves 9a First track groove 9b Second track groove 12 Spherical outer surface 13 Spherical inner surface L straight line Plane containing the ball trajectory centerline N coupling axis A end B end Co connection Ci connection O joint center O1 center of curvature Oi2 Center of curvature Oo2 Center of curvature X Ball trajectory centerline Xa Ball trajectory centerline Xb Ball trajectory centerline Y Ball trajectory centerline Ya Ball Trajectory Centerline Yb Ball trajectory centerline r1 radius of curvature r2 radius of curvature γ Tilt angle η1 angle η² angle

Claims

1. A fixed constant velocity universal joint comprising: an outer joint member having multiple track grooves extending generally in the axial direction formed on its spherical inner surface and having an opening side and a back side spaced apart in the axial direction; an inner joint member having multiple track grooves extending generally in the axial direction formed on its spherical outer surface that are paired with the track grooves of the outer joint member; multiple balls interposed between the track grooves of the outer joint member and the track grooves of the inner joint member to transmit torque; and a retainer having a spherical outer surface and a spherical inner surface that holds these balls in a pocket and fits onto the spherical inner surface of the outer joint member and the spherical outer surface of the inner joint member, The track groove of the outer joint member consists of a first track groove portion (7a) located on the inner side and a second track groove portion (7b) located on the opening side. The first track groove (7a) has an arc-shaped ball trajectory centerline (Xa) with a center of curvature that is not offset axially with respect to the joint center (O), The plane (M) containing the ball trajectory centerline (Xa) and the joint center (O) is inclined with respect to the joint axis (N-N), and the direction of this inclination is formed in opposite directions in the first track groove (7a) adjacent to each other in the circumferential direction. The second track groove (7b) has a ball trajectory centerline (Xb) that has a different shape from the ball trajectory centerline (Xa) of the first track groove (7a), The end (A) of the ball trajectory centerline (Xa) of the first track groove (7a) is located on the opening side from the joint center (O), The ball trajectory centerline (Xb) of the second track groove (7b) is connected to the end portion (A), forming a connection portion (Co) between the first track groove (7a) and the second track groove (7b). The ball trajectory centerline (Y) of the track groove of the inner joint member is formed in mirror symmetry with the ball trajectory centerline (X) of the paired track groove of the outer joint member, with reference to a plane (P) that includes the joint center (O) and is perpendicular to the joint axis (N-N) when the operating angle is 0°. The ball trajectory centerline (Y) of the track groove of the inner joint member is connected to the end (B) located on the far side of the ball trajectory centerline (Ya) of the first track groove (9a) by the ball trajectory centerline (Yb) of the second track groove (9b), thereby forming a connection portion (Ci) between the first track groove (9a) and the second track groove (9b). Beyond the aforementioned connection portion (Co, Ci), the second track groove portion (7b, 9b) contains the bo A fixed constant velocity universal joint characterized in that, in the operating angle range in which multiple balls are present, the clamping angle (η2) of the ball located in the second track groove (7b, 9b) and the clamping angle (η1) of the ball located in the first track groove (7a, 9a) are set to be equal.

2. Beyond the aforementioned connection portion (Co, Ci), the second track groove portion (7b, 9b) contains the bo The fixed constant velocity universal joint according to claim 1, characterized in that the number of balls in the operating angle range in which multiple balls are present is two.

3. The fixed constant velocity universal joint according to claim 1, characterized in that the ball trajectory centerlines (Xa, Ya) of the first track grooves (7a, 9a) have a center of curvature (O1) that is located on the side of the first track grooves (7a, 9a) with respect to the axis (N-N) of the joint and is radially offset.

4. The fixed constant velocity universal joint according to claim 1, characterized in that the operating angle (θ1) at which the center of the ball on the most open side is positioned at the end (A) of the ball trajectory center line (Xa) of the first track groove portion (7a) of the outer joint member is set to 15° or more.

5. The fixed constant velocity universal joint according to claim 1, characterized in that the ball trajectory centerline (Xb) of the second track groove portion (7b) of the outer joint member has an arc shape with a center of curvature (Oo2) radially outward from the outer diameter surface of the outer joint member.

6. A fixed constant velocity universal joint according to any one of claims 1 to 5, characterized in that the number of torque transmission balls is eight or more.

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