Fixed constant-velocity universal joint

Abstract

In a fixed constant-velocity universal joint 1 of the cross track groove type, track grooves 7, 9 of an outer joint member 2 and an inner joint member 3 have first track groove parts 7a, 9a provided in an axial region that includes a joint center O, and second track groove parts 7b, 9b for coping with high articulation angles. Ball raceway centerlines Xa, Ya of the first track groove parts 7a, 9a form circular arc shapes having centers of curvature Oo1, Oi1 with no axial offset relative to the joint center O. The centers of curvature Oo1, Oi1 are offset radially by Fy to the side approaching the ball raceway centerlines Xa, Ya relative to a joint axis N–N.

Description

Fixed constant velocity universal joint

[0001] This invention relates to a fixed constant velocity universal joint.

[0002] A sliding-type constant velocity universal joint, which has a relatively small maximum operating angle but is capable of axial displacement while maintaining an operating angle, is typically installed on the inboard side (differential gear side) of an automobile front drive shaft, while a fixed-type constant velocity universal joint, which has a large operating angle but does not permit axial displacement, is installed on the outboard side (wheel side).

[0003] Important functions required of fixed-type constant velocity universal joints are to transmit power to the wheels with as little loss as possible and to achieve a high working angle that matches the steering of the wheels. Recently, with the aim of improving the environmental performance of automobiles, further high efficiency has been required, and track groove cross-type joints such as those shown in Patent Documents 1 and 2 have been proposed. Furthermore, while maximum working angles have traditionally been 47° for Rzeppa-type constant velocity universal joints (BJ type) and 50° for undercut-free constant velocity universal joints (UJ type), there is an increasing demand for angles exceeding 50° in order to improve the turning and maneuverability of automobiles. Thus, achieving both high efficiency and a high level of working angle is becoming important as a function of fixed-type constant velocity universal joints.

[0004] Patent No. 5885997 Patent No. 5936855

[0005] To achieve both high efficiency and a high operating angle at a high level, it is necessary to provide a second track groove portion that is compatible with high operating angles in the crossed track groove structure described in Patent Documents 1 and 2. Various shapes have been proposed for this second track groove portion so that the ball contact points can be secured at the high operating angles required for the joint.

[0006] In view of the above problems, an object of the present invention is to provide a fixed type constant velocity universal joint that achieves both high efficiency and a large working angle and has good NVH (Noise, Vibration, Harshness) characteristics.

[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) In a fixed constant velocity universal joint of the crossed track groove type, in which the forces acting on the cage are balanced, the balance of the forces acting on the cage is disrupted. In a structure in which second track groove portions are provided to accommodate a high operating angle, when balls move from the first track groove portions to the second track groove portions, the balance of the forces acting on the cage changes, and the cage comes into contact with the outer joint member and the inner joint member. As a result, power transmission efficiency decreases.

[0009] (2) Study of the Development Process for a Track Groove Intersecting Type Fixed Constant Velocity Universal Joint with a Maximum Operating Angle Exceeding 50° A prototype of a track groove intersecting type fixed constant velocity universal joint 101 with a maximum operating angle exceeding 50° is shown in FIGS. 12 to 14 . As shown in FIG. 12A , the second track groove portions 107b, 109b corresponding to operating angles exceeding 50° require an arc shape that is opposite in shape (convex toward the inner diameter) to the arc shape of the first track groove portions 107a, 109a. In this case, the larger the operating angle becomes as the balls 104 enter the range of the second track groove portions 107b, 109b, the larger the sandwiched angle acting on the balls 104, and therefore the greater the force with which the balls 104 positioned in the second track groove portions 107b, 109b press against the cage 105. Furthermore, the connection between the first track groove portions 107a, 109a, which have a convex arc shape on the outer diameter side, and the second track groove portions 107b, 109b, which have a convex arc shape on the inner diameter side, is a significant inflection point, so the angle acting on the ball 104 changes abruptly when the ball moves from the first track groove portions 107a, 109a to the second track groove portions 107b, 109b.

[0010] As described above, the balance between the force with which the balls 104 located in the first track groove portions 107a, 109a press the retainer 105 and the force with which the balls 104 located in the second track groove portions 107b, 109b press the retainer 105 is lost, and the retainer 105 may deviate from the plane bisecting the operating angle. This behavior has been investigated.

[0011] (3) Examination of the degree of influence on the behavior of the retainer due to the operating angle range of the balls entering the second track groove portion (3-1) (i) The analysis and evaluation were conducted by focusing on the fact that the connecting portion between the first track groove portions 107a, 109a, which have a convex arc shape on the outer diameter side, and the second track groove portions 107b, 109b, which have a convex arc shape on the inner diameter side, is a significant inflection point, and (ii) when the ball 104 moves from the first track groove portions 107a, 109a to the second track groove portions 107b, 109b, the sandwiched angle acting on the ball 104 changes suddenly. A connection portion co between the first track groove portion 107a and the second track groove portion 107b is formed at a portion of the track groove 107 where the ball 104, whose center is located at a connection portion a between the ball track center line xa of the first track groove portion 107a and the ball track center line xb of the second track groove portion 107b, comes into contact. Also, a connection portion ci between the first track groove portion 109a and the second track groove portion 109b is formed at a portion of the track groove 109 where the ball 104, whose center is located at a connection portion b between the ball track center line ya of the first track groove portion 109a and the ball track center line yb of the second track groove portion 109b, comes into contact.

[0012] (3-2) As a result, the inventors have found that the following problem occurs in the operating angle range where two balls 104 enter the second track groove portions 107b, 109b beyond the connection portions co, ci. As shown in Fig. 13 , in the operating angle range where two balls 104 enter the second track groove portions 107b, 109b, the force with which the balls 104 press the cage 105 is small, and therefore the contact force between the cage 105 and the outer joint member 102 and the inner joint member 103 is also small. In this state, a difference occurs between the angle η2' formed by the ball 104 (0°) located in the second track groove portion 107b and having a phase angle of 0°, and the angle η1' formed by the ball 104 (180°) located in the first track groove portion 107a and having a phase angle of 180°. Since this difference changes abruptly, the angle of the cage 105 fluctuates significantly, which may result in a decrease in efficiency and NVH performance.

[0013] (3-3) The included angle η is shown in Figure 14. The included angle η with respect to the ball 104 means the angle formed by a tangent to the track groove 107 of the outer joint member 102 in the extending direction at the contact point with the ball 104 and a tangent to the track groove 109 of the inner joint member 103 in the extending direction at the contact point with the ball 104. When the ball 104 and the track grooves 107, 109 are in angular contact, the ball 104 comes into contact with the side surfaces of the track grooves 107, 109 rather than the groove bottoms. Even in this case, it is effective to use the included angle at the groove bottoms of the track grooves as a substitute for the angle η, for convenience, in order to evaluate the difference in the angles included by the first track groove portions 107a, 109a and the second track groove portions 107b, 109b and to ensure a reliable and easy measurement procedure. That is, the included angle η is the angle formed by the tangents in the extending direction of each track groove 107, 109 at the intersections J1, J2 of the groove bottoms of the track grooves 107, 109 with the planes K1, K2 that include the contact points between the track grooves 107, 109 and the ball 104 and the center of the ball 104. This also applies to the embodiments described later.

[0014] (3-4) When the operating angle θ is increased beyond the operating angle range in which two balls 104 can fit in the second track groove portions 107b, 109b shown in Figure 13, the angles η1', η2' relative to the balls 104 positioned in the second track groove portions 107b, 109b also increase. These balls 104 press the cage 105 strongly toward the opening, increasing the contact force between the cage 105 and the outer joint member 102 and the inner joint member 103, and working to stabilize the position of the cage 105. In addition, such a large operating angle range is not used very frequently, so it has little effect on deterioration of NVH performance.

[0015] (4) A novel idea that achieves both high efficiency and high operating angle and ensures NVH characteristics. Through analysis, evaluation, and insights beyond a simple idea, we came up with a novel idea that in a fixed constant velocity universal joint 101 with a track groove crossing type in which the forces acting on the retainer 105 are balanced and which is provided with second track grooves 107b and 109b that correspond to operating angles exceeding 50°, the key to ensuring efficiency and NVH performance is to suppress the fluctuation of the retainer 105 from the bisecting plane of the operating angle in the operating angle range in which two balls 104 are placed in the second track grooves 107b and 109b that correspond to high angles, and this led to the present invention.

[0016] In order to achieve the above object, the present invention provides a fixed type constant velocity universal joint including an outer joint member having a plurality of track grooves formed on its spherical inner peripheral surface, an inner joint member having a plurality of track grooves formed on its spherical outer peripheral surface, 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 plurality of pockets for holding the plurality of balls, a spherical outer peripheral surface that fits with the spherical inner peripheral surface of the outer joint member, and a cage having a spherical inner peripheral surface that fits with the spherical outer peripheral surface of the inner joint member, wherein the track grooves of the outer joint member have a first track groove portion provided in an axial region including a joint center and a second track groove portion provided on one axial side of the first track groove portion, and the track grooves of the inner joint member have a first track groove portion provided in an axial region including a joint center and a second track groove portion provided on the other axial side of the first track groove portion, the ball raceway center lines (Xa, Ya) of the first track groove portions of the track grooves of the outer joint member and the inner joint member form arc shapes having centers of curvature that are not offset in the axial direction with respect to the joint center (O); the ball raceway center lines (Xa, Ya) of the first track groove portions of the outer joint member and the inner joint member are inclined in the circumferential direction with respect to the joint axis (N-N); the ball raceway center lines (Xa, Ya) of the first track groove portions that are adjacent in the circumferential direction are inclined in opposite circumferential directions with respect to the joint axis (N-N); the ball raceway center line (Xa) of the first track groove portion of the outer joint member and the ball raceway center line (Ya) of the first track groove portion of the inner joint member that are opposed in the radial direction are inclined in opposite circumferential directions with respect to the joint axis (N-N); a ball raceway center line (Xb) of the second track groove portion of the outer joint member is arranged on the outer diameter side of an arc formed by extending the ball raceway center line (Xa) of the first track groove portion to one side in the axial direction, and a ball raceway center line (Yb) of the second track groove portion of the inner joint member is arranged on the outer diameter side of an arc formed by extending the ball raceway center line (Ya) of the first track groove portion to the other side in the axial direction,Provided is a fixed type constant velocity universal joint in which the centers of curvature of the ball raceway center lines (Xa, Ya) of the first track groove portions are offset radially relative to a joint axis (N-N) toward the ball raceway center lines (Xa, Ya).

[0017] Thus, the present invention relates to a fixed constant velocity universal joint of the track groove crossing type having a second track groove for handling high operating angles, characterized in that the curvature centers of the ball trajectory centerlines Xa and Ya of the arc-shaped first track groove are offset radially with respect to the joint axis N-N toward the side closer to the ball trajectory centerlines Xa and Ya (i.e., the side with a smaller radius of curvature). In this case, a clamping angle is generated for balls in the first track groove that are positioned axially offset from the joint center. Therefore, by adjusting the amount of offset and the radius of curvature of the curvature center of the first track groove to adjust the clamping angle with respect to the ball, in the operating angle range in which two balls are located in the second track groove, the clamping angle η2 for the ball on the far axial side (e.g., the opening side of the outer joint member) in the second track groove and the clamping angle η1 for the ball on the far axial side (e.g., the inner side of the outer joint member) in the first track groove can be made substantially equal. In other words, the shape of the first track groove is set such that there exists an operating angle in the operating angle range where two balls enter the second track groove where the clamping angle η1 and the clamping angle η2 coincide. As a result, in the operating angle range where two balls enter the second track groove, not only the ball on the opening side of the second track groove but also the ball on the innermost side of the first track groove pushes the retainer towards the opening side, thereby suppressing the fluctuation of the retainer with respect to the bisecting plane of the operating angle and improving the NVH characteristics.

[0018] In the above-mentioned fixed type constant velocity universal joint, it is preferable that the track grooves of the outer joint member include a third track groove portion having a smoothly continuous, linear ball raceway center line (Xc) on the other axial side (rear side) of the ball raceway center line (Xa) of the first track groove portion. By providing the linear third track groove portion on the rear side of the arc-shaped first track groove portion in this way, the groove depth can be made deeper than if the arc-shaped first track groove portion were extended toward the rear, thereby ensuring strength and durability at high operating angles.

[0019] In the above-mentioned fixed type constant velocity universal joint, it is preferable that the working angle (θ2) at which the center of the ball closest to the other axial side (rear side) is located at the junction between the ball raceway center line (Xa) of the first track groove portion and the ball raceway center line (Xc) of the third track groove portion of the track grooves of the outer joint member is larger than the working angle (θ1) at which the center of the ball closest to one axial side (opening side) is located at the junction between the ball raceway center line (Xa) of the first track groove portion and the ball raceway center line (Xb) of the second track groove portion of the track grooves of the outer joint member. This allows the deepest ball to be located in the first track groove portion in the working angle range in which two balls can fit in the second track groove portion, making it easier to set the angle of inclusion relative to the ball located closest to the opening side and the angle of inclusion relative to the ball located closest to the innermost side to be equivalent.

[0020] The operating angle (θ1), at which the center of the ball closest to one axial side is located at the connection between the ball raceway center line (Xa) of the first track groove portion and the ball raceway center line (Xb) of the second track groove portion of the track grooves of the outer joint member, is preferably 15° or more. By setting this operating angle (θ1) to 15° or more, an increase in the sandwich angle of the second track groove portion can be suppressed, and spherical force can be suppressed and torque transmission efficiency can be ensured.

[0021] The ball track center line (Xb, Yb) of the second track groove portion can be, for example, an arc shape that is convex toward the inner diameter side.

[0022] As described above, according to the present invention, it is possible to realize a fixed type constant velocity universal joint that achieves both high efficiency and a large operating angle and has good NVH characteristics.

[0023] This is an axial cross-sectional view of a fixed constant velocity universal joint according to one embodiment of the present invention. This is a front view of the fixed constant velocity universal joint shown in Figure 1A, viewed from one axial side (the opening side of the outer joint member). This is an axial cross-sectional view of the outer joint member of the fixed constant velocity universal joint shown in Figure 1A. This is a front view of the outer joint member shown in Figure 2A, viewed from one axial side (the opening side). This is a side view of the inner joint member of the fixed constant velocity universal joint shown in Figure 1A, viewed from a direction perpendicular to the axis. This is a front view of the inner joint member shown in Figure 3A, viewed from one axial side (the opening side of the outer joint member). This is a cross-sectional view of the outer joint member of the fixed constant velocity universal joint shown in Figure 1A in a plane including the ball trajectory centerline of the track groove. This is a cross-sectional view of the inner joint member of the fixed constant velocity universal joint shown in Figure 1A in a plane including the ball trajectory centerline of the track groove. This is a cross-sectional view of the outer joint member of the fixed constant velocity universal joint shown in Figure 1A. This is a cross-sectional view of the fixed constant velocity universal joint shown in Figure 1A, showing the state with the maximum operating angle. Figure 1A is a cross-sectional view of a fixed constant velocity universal joint, showing the state where the operating angle is set so that two balls are in the second track groove. Figure 12A shows the clamping angle η2' for the outermost ball and the clamping angle η1' for the innermost ball of a fixed constant velocity universal joint (conventional product) shown in Figure 12A. Figure 1A shows the clamping angle η2' for the outermost ball and the clamping angle η1' for the innermost ball of the fixed constant velocity universal joint (inventive product) shown in Figure 12A. Figure 13 is an exploded view of the outer joint member of the fixed constant velocity universal joint shown in Figure 1A, viewed from the axial side. Figure 12A is an axial cross-sectional view of a conventional fixed constant velocity universal joint. Figure 13 is a front view of the fixed constant velocity universal joint shown in Figure 12A, viewed from one axial side (the opening side of the outer joint member). Figure 12A is a cross-sectional view of the fixed constant velocity universal joint shown in Figure 12A with the operating angle set. Figure 13 is an enlarged view.

[0024] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0025] As shown in Figure 1, a fixed constant velocity universal joint 1 according to one embodiment of the present invention has an outer joint member 2, an inner joint member 3, a ball 4, and a retainer 5. The outer joint member 2 is cup-shaped with one side open in the axial direction and the other side closed in the axial direction. Hereinafter, the axial direction N-N of the fixed constant velocity universal joint 1 with an operating angle of 0° will be referred to as the "axial direction". Also, in the axial direction, the open side of the outer joint member 2 (right side in Figure 1A) will be referred to as the "open side", and the closed side (left side in Figure 1A) will be referred to as the "inside side".

[0026] Eight track grooves 7 are formed on the spherical inner peripheral surface 6 of the outer joint member 2. Eight track grooves 9 are formed on the spherical outer peripheral surface 8 of the inner joint member 3. The spherical inner peripheral surface 6 of the outer joint member 2 is mated with a spherical outer peripheral surface 12 of the cage 5. The spherical outer peripheral surface 8 of the inner joint member 3 is mated with a spherical inner peripheral surface 13 of the cage 5. The cage 5 is provided with eight pockets 5a, and each pocket accommodates one ball 4.

[0027] To accurately describe the shape of the track grooves, the term "ball track centerline" is used in this specification. Here, the "ball track centerline" refers to the path traced by the center of a ball placed in a track groove as it moves along the track groove. Therefore, the shape of the track groove in its extension direction is the same as the shape of the ball track centerline.

[0028] As shown in Fig. 2A, the ball raceway center lines X of the track grooves 7 of the outer joint member 2 are inclined in the circumferential direction with respect to the joint axis N-N. Specifically, a plane M including the ball raceway center lines X of the track grooves 7 of the outer joint member 2 and the joint center O is inclined by an angle γ with respect to the joint axis N-N. As shown in Fig. 3A, the ball raceway center lines Y of the track grooves 9 of the inner joint member 3 are inclined in the circumferential direction with respect to the joint axis N-N. Specifically, a plane Q including the ball raceway center lines Y of the track grooves 9 of the inner joint member 3 and the joint center O is inclined by an angle γ with respect to the joint axis N-N. 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 minimum circumferential width F (see Fig. 3B) at the axial end of the spherical outer circumferential surface 8 formed between the track grooves 9 of the inner joint member 3.

[0029] The ball raceway center lines X of the track grooves 7 adjacent to each other in the circumferential direction of the outer joint member 2 are inclined in opposite circumferential directions with respect to the axis N-N (see FIG. 2). The ball raceway center lines Y of the track grooves 9 adjacent to each other in the circumferential direction of the inner joint member 3 are inclined in opposite circumferential directions with respect to the axis N-N (see FIG. 3). The ball raceway center lines X, Y of the track grooves 7 of the outer joint member 2 and the track grooves 9 of the inner joint member 3 that are opposed to each other in the radial direction are inclined in opposite circumferential directions with respect to the axis N-N, and one ball 4 is disposed at each intersection of these lines.

[0030] As shown in FIG. 4, the track grooves 7 of the outer joint member 2 have a first track groove portion 7a provided in an axial region including the joint center O, a second track groove portion 7b provided on the opening side of the first track groove portion 7a, and a third track groove portion 7c provided on the rear side of the first track groove portion 7a.

[0031] The ball track center line Xa of the first track groove portion 7a has an arc shape that is convex toward the outer diameter side with the center of curvature at Oo1 and the radius of curvature is Ro1. The center of curvature Oo1 is not offset in the axial direction from the joint center O, but is offset by Fy in the radial direction from the joint axis N-N toward the ball track center line Xa (i.e., the side where the radius of curvature becomes smaller).

[0032] The second track groove portion 7b is provided to achieve a higher operating angle than when the arc-shaped first track groove portion 7a is extended to the opening-side end of the track groove 7. Specifically, the ball track center line Xb of the second track groove portion 7b is located radially outward of an arc Xa' (see dotted line) formed by extending the ball center locus Xa of the first track groove portion 7a toward the opening side. For example, the ball track center line Xb becomes increasingly separated from the arc Xa' toward the outer diameter as it approaches the opening side. In the illustrated example, the ball track center line Xb of the second track groove portion 7b has an arc shape with a curvature radius Ro2 and a center of curvature Oo2. The center of curvature Oo2 is located radially outward of the ball track center line Xb, and in the illustrated example, it is located radially outward of the outer diameter surface of the outer joint member 2. Therefore, the ball track center line Xb of the second track groove portion 7b has an arc shape that is opposite to the arc shape of the ball track center line Xa of the first track groove portion 7a, i.e., an arc shape that is convex toward the inner diameter side. 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 smoothly continuous. In the illustrated example, the arc-shaped ball track center lines Xa and Xb have a common tangent at their connection portion A1.

[0033] The ball track center line Xc of the third track groove portion 7c is linear. The ball track center line Xa of the first track groove portion 7a and the ball track center line Xc of the third track groove portion 7c are smoothly continuous. In the illustrated example, the ball track center line Xc of the third track groove portion 7c is tangent to the ball track center line Xa of the first track groove portion 7a at the inner end A2 (the connection portion with the ball track center line Xc). The angle ε formed between the ball track center line Xc of the third track groove portion 7c and the joint axis N-N is, for example, 25° to 35°.

[0034] 2A described above. Therefore, strictly speaking, this is not a longitudinal cross-sectional view taken on a plane including the joint axis N-N, but rather a cross-section taken on a plane inclined at an angle γ with respect to the joint axis N-N. Circumferentially adjacent track grooves 7 of the outer joint member 2 are inclined in opposite circumferential directions with respect to the axis N-N, but all of the track grooves 7 have the cross-sectional shape shown in FIG. 4 on the plane M including the ball raceway center line X and the joint center O.

[0035] 5 , the track grooves 9 of the inner joint member 3 have a first track groove portion 9a provided in an axial region including the joint center O, a second track groove portion 9b provided on the back side of the first track groove portion 9a, and a third track groove portion 9c provided on the opening side of the first track groove portion 9a. The ball track center line Y of the track groove 9 of the inner joint member 3 and the ball track center line X of the track groove 7 of the outer joint member 2 have mirror-symmetric shapes with respect to a plane P that passes through the joint center O and is perpendicular to the axis N-N.

[0036] The ball track center line Ya of the first track groove portion 9a has an arc shape that is convex toward the outer diameter side with the center of curvature at Oi1 and the radius of curvature is Ri1. The center of curvature Oi1 is not offset in the axial direction from the joint center O, but is offset by Fy in the radial direction from the joint axis N-N toward the ball track center line Ya (i.e., the side where the radius of curvature becomes smaller).

[0037] The second track groove 9b is provided to achieve a higher operating angle than when the arc-shaped first track groove 9a is extended to the inner end of the track groove 9. Specifically, the ball trajectory centerline Yb of the second track groove 9b is positioned on the outer diameter side of the arc Ya' (see dotted line) which is an extension of the ball trajectory centerline Ya of the first track groove 9a toward the inner side. For example, the ball trajectory centerline Yb moves further away from the arc Ya' toward the outer diameter side as it goes toward the inner side. In the illustrated example, the ball trajectory centerline Yb of the second track groove 9b is an arc shape with a radius of curvature Ri2 with Oi2 as the center of curvature. The center of curvature Oi2 is positioned radially outward from the ball trajectory centerline Yb, and in the illustrated example, it is positioned radially outward from the outer diameter surface of the inner joint member 3. Therefore, the ball trajectory centerline Yb of the second track groove 9b has an arc shape opposite to that of the ball trajectory centerline Ya of the first track groove 9a, that is, an arc shape that is convex toward the inner diameter. The ball trajectory centerline Ya of the first track groove 9a and the ball trajectory centerline Yb of the second track groove 9b are smoothly continuous. In the illustrated example, the arc-shaped ball trajectory centerlines Ya and Yb have a common tangent at their connection point B1.

[0038] The ball trajectory centerline Yc of the third track groove 9c is straight. The ball trajectory centerline Ya of the first track groove 9a and the ball trajectory centerline Yc of the third track groove 9c are smoothly continuous. In the illustrated example, the ball trajectory centerline Yc of the third track groove 9c is tangent to the ball trajectory centerline Ya of the first track groove 9a at the opening end B2 (the connection point with the ball trajectory centerline Yc). The angle between the ball trajectory centerline Yc of the third track groove 7c and the axis N-N of the joint is equal to the angle ε (see Figure 4) between the ball trajectory centerline Xc of the third track groove 7c of the outer joint member 2 and the axis N-N of the joint.

[0039] 5 is a cross-sectional view of the track grooves 9 in the above-described FIG. 3A taken on a plane Q including the ball raceway center line Y and the joint center O. Therefore, similar to FIG. 4, strictly speaking, it is not a longitudinal cross-sectional view taken on a plane including the joint axis N-N, but rather shows a cross section inclined at an angle γ with respect to the axis N-N. Circumferentially adjacent track grooves 9 of the inner joint member 3 are inclined in opposite circumferential directions with respect to the axis N-N, but all of the track grooves 9 have the cross-sectional shape shown in FIG. 5 on the plane Q including the ball raceway center line Y and the joint center O.

[0040] The cross-sectional shape of the track grooves 7, 9 is formed into an elliptical shape or a Gothic arch shape. The track grooves 7, 9 and the ball 4 come into contact with each other at a contact angle (approximately 30° to 45°), which is known as angular contact. Therefore, the ball 4 comes into contact with the side surfaces of the track grooves 7, 9 that are provided on both circumferential sides of the groove bottom.

[0041] When the center of the ball 4 is located at the connection portion A1 of the ball track center lines Xa and Xb of the track groove 7 of the outer joint member 2, the ball 4 comes into contact with the boundary Co1 between the first track groove portion 7a and the second track groove portion 7b (see FIG. 6 ). At this time, the center of the ball 4 is located at the connection portion B1 (see FIG. 5 ) of the ball track center lines Ya and Yb of the track groove 9 of the inner joint member 3, and the ball 4 comes into contact with the boundary Ci1 between the first track groove portion 9a and the second track groove portion 9b. When the center of the ball 4 is located at the connection portion A2 of the ball track center lines Xa and Xc of the track groove 7 of the outer joint member 2, the ball 4 comes into contact with the boundary Co2 between the first track groove portion 7a and the third track groove portion 7c (see FIG. 6 ). At this time, the center of the ball 4 is arranged at the connection portion B2 (see FIG. 5) of the ball track center lines Ya, Yc of the track groove 9 of the inner joint member 3, and the ball 4 comes into contact with the boundary Ci2 between the first track groove portion 9 a and the third track groove portion 9 c.

[0042] When the fixed constant velocity universal joint 1 takes an operating angle θ, the ball 4 moves by θ / 2 with respect to planes P1 and P2 that include the joint center O and are perpendicular to the axes of each joint member 2 and 3 (see Figure 8). Here, the normal operating angle of the joint and the frequently used operating angle will be explained. First, the normal operating angle of the joint is the operating angle that occurs in the fixed constant velocity universal joint of the front drive shaft when the steering wheel is set to the straight position in a vehicle with one occupant on a horizontal, flat road surface. The normal operating angle is usually selected and determined between 2° and 15° according to the design conditions of each vehicle type. The frequently used operating angle is not the high operating angle that occurs when the above vehicle is turning right or left at an intersection, for example, but the operating angle that occurs in the fixed constant velocity universal joint on a curved road during continuous driving, and this is also determined according to the design conditions of each vehicle type. The frequently used operating angle is approximately 15°.

[0043] As shown in Figure 6, the operating angle θ1 is defined as the position of the center of the ball 4 on the most open side, i.e., the ball 4 with a phase angle of 0° (0°), at the connection point A1 between the ball trajectory centerline Xa of the first track groove 7a and the ball trajectory centerline Xb of the second track groove 7b of the outer joint member 2. At this time, the angle β1 between the plane P passing through the joint center O and perpendicular to the axis N-N, and the straight line L1 passing through the connection point A1 of the ball trajectory centerlines Xa and Xb and the joint center O, is approximately equal to half of the operating angle θ1 (θ1 / 2).

[0044] In this embodiment, the operating angle θ1 is set to be greater than the range of frequently used operating angles, specifically to 15° or more. As a result, at frequently used operating angles, all balls 4 are positioned in the first track grooves 7a and 9a. In this case, the balls 4 are located at the intersection of the first track grooves 7a and 9a of the outer joint member 2 and the inner joint member 3, which are radially opposed to each other and whose inclination directions with respect to the axes N-N are opposite in the circumferential direction. Therefore, opposing forces act from the balls 4 on adjacent pockets 5a in the circumferential direction of the retainer 5, stabilizing the position of the retainer 5. This suppresses 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. As a result, the joint operates smoothly under high load and high rotation speeds, torque loss and heat generation are suppressed, and durability is improved.

[0045] Figure 7 shows the fixed constant velocity universal joint 1 at its maximum operating angle θmax. In this embodiment, the maximum operating angle θmax is greater than 50°. As shown in Figures 4 and 5 above, the ball trajectory centerlines Xb and Yb of the second track grooves 7b and 9b are arc-shaped in the opposite direction (convex towards the inner diameter) to the ball trajectory centerlines Xa and Ya of the first track grooves 7a and 9a, so the effective track length at the maximum operating angle θmax can be increased. Therefore, even at a maximum operating angle θmax exceeding 50°, the contact points between the ball 4 and the track grooves 7 and 9 can be secured.

[0046] Here, a supplementary explanation of the effective track length will be provided. When the operating angle is increased, the amount of axial movement of the contact point between the track groove 7 and the ball 4 per unit angle (e.g., 1°) varies depending on the shape of the track groove 7. In this embodiment, the ball track center line Xb of the second track groove portion 7b has an arc shape that is opposite to the ball track center line Xa of the first track groove portion 7a (convex toward the inner diameter). Therefore, near the maximum operating angle θmax, that is, when the ball 4 is positioned near the opening end of the track groove 7, the contact point between the ball 4 and the second track groove portion 7b is located further back than the ball center Ob. As a result, the contact point between the ball 4 and the second track groove portion 7b can be ensured. In this way, the effective track length means the length of the locus 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.

[0047] As shown in Fig. 7 , the intermediate shaft 15 is spline-engaged with the inner periphery of the inner joint member 3. At the maximum operating angle θmax, a small gap is formed between the outer circumferential surface of the minimum diameter portion 15a of the intermediate shaft 15 and the inlet chamfer 20 of the outer joint member 2. Note that Fig. 7 shows the intermediate shaft 15 in a simplified form.

[0048] The above is the overall configuration of the fixed type constant velocity universal joint 1. Next, a detailed description will be given of the change in the angle of inclusion with respect to the ball 4 when the operating angle of the fixed type constant velocity universal joint 1 is changed.

[0049] First, a problem that occurs in the fixed type constant velocity universal joint 101 shown in Figures 12 to 14 will be described with reference to Figure 9. Figure 9 is a graph showing the change in the included angle η2' with respect to the ball 104 on the most open side (phase angle 0°) and the included angle η1' with respect to the ball 104 on the most rear side (phase angle 180°) when the operating angle θ of the fixed type constant velocity universal joint 101 is changed.

[0050] In the smallest operating angle range S0, which includes 0°, all of the balls 4 are disposed in the first track groove portions 107a, 109a. That is, in this operating angle range S0, the number of balls 4 that enter the second track groove portions 107b, 109a is zero. Because the first track groove portions 107a, 109a are both arc-shaped with the joint center O as the center, the included angle for all of the balls 4 is zero in the operating angle range S0. Therefore, in this operating angle range S0, no force is generated that causes the balls 104 to press the cage 105 in the axial direction due to the included angle.

[0051] As the working angle θ increases, the centers of the balls 4 closest to the opening pass points a and b (see FIG. 12A ) and are positioned in the second track groove portions 107b and 109b. At this time, the working angle range in which one ball 104 can fit in the second track groove portions 107b and 109b is designated S1, the working angle range in which two balls 104 can fit in the second track groove portions 107b and 109b is designated S2, and the working angle range in which three or more balls 104 can fit in the second track groove portions is designated S3. Note that when the joint rotates while maintaining a predetermined working angle, the number of balls that fit in the second track groove portions can vary depending on the rotation angle. Therefore, "an working angle at which n balls can fit in the second track groove portions" means an working angle at which n balls can fit in the second track groove portions when the joint is rotated while maintaining that working angle, but not (n+1) balls can fit in the second track groove portions.

[0052] In these operating angle ranges S1 to S3, an angle η2' is formed toward the opening with respect to the balls 104 disposed in the second track groove portions 107b, 109b, particularly the ball 104 closest to the opening (0°) (see FIG. 13). This creates a difference with the angle η1' (=0) with respect to the other balls 104 disposed in the first track groove portions 107a, 109a, generating a force that causes the balls 104 to press the cage 105 toward the opening.

[0053] At this time, in the operating angle range S1 in which the balls 4 begin to enter the second track grooves 107b and 109b, the clamping angle η2' with respect to the ball 104 on the most open side is small (see Figure 9), so the force with which this ball 104 pushes against the retainer 105 is small and hardly affects the behavior of the joint.

[0054] On the other hand, when the operating angle range S2 is reached in which two balls 104 are positioned in the second track grooves 107b and 109b, the difference between the clamping angle η2' with respect to the balls 104 located in the second track grooves 107b and 109b and the clamping angle η1' (=0) with respect to the balls 104 located in the first track grooves 107a and 109a, which are located further back than the joint center O, becomes large. As a result, the balance of the force with which the balls 104 push the retainer 105 in the axial direction is disrupted, which may lead to a decrease in torque transmission efficiency and NVH performance.

[0055] When the operating angle is further increased to an operating angle range S3 in which three balls 104 are always positioned in the second track grooves 107b and 109b, the clamping angle η2' with respect to the balls 104 located in the second track grooves 107b and 109b becomes even larger. As a result, the retainer 105 is strongly pushed toward the opening by the balls 104, the contact force between the retainer 105 and the outer joint member 102 and the inner joint member 103 also increases, and the position of the retainer 105 becomes stable. Furthermore, since such a large operating angle range is not used very often, its impact on the deterioration of NVH performance is small.

[0056] Based on the above, in a fixed constant velocity universal joint 101 of the track groove crossing type having second track grooves 107b and 109b that correspond to operating angles exceeding 50°, in the operating angle range S2 in which two balls 104 are placed in the second track grooves 107b and 109b, the retainer 105 is prone to deviating from the plane that bisectes the operating angle, and torque transmission efficiency and NVH performance tend to deteriorate.

[0057] Therefore, in the fixed constant velocity universal joint 1 of this embodiment, the curvature centers Oo1 and Oi1 of the ball center trajectories Xa and Ya of the first track grooves 7a and 9a are offset with respect to the axis N-N towards the side closer to the ball center trajectories Xa and Ya (see Figures 4 and 5). The changes in the clamping angle η2 with respect to the outermost ball 4 (0°) and the clamping angle η1 with respect to the innermost ball 4 (180°) when the operating angle θ of this fixed constant velocity universal joint 1 is changed will be explained using Figure 10.

[0058] In the smallest operating angle range S0, which includes 0°, all of the balls 4 are disposed in the first track groove portions 7a, 9a. In this embodiment, as described above, the centers of curvature Oo1, Oi1 of the ball center loci Xa, Ya of the first track groove portions 7a, 9a are offset in the radial direction with respect to the axis N-N. Therefore, a negative included angle η2 that is slightly open toward the rear is generated for the balls 4 (0°) on the opening side of the joint center O, and a positive included angle η1 that is slightly open toward the opening side is generated for the balls 4 (180°) on the rear side of the joint center O. Because the magnitudes (absolute values) of these included angles η1, η2 are equal, the forces with which the balls 4 press the cage 5 in the axial direction are balanced by the included angles η1, η2.

[0059] As the operating angle θ increases, the number of balls 4 disposed in the second track groove portions 7b, 9b increases to one (operating angle region S1), two (operating angle region S2), and three (operating angle region S3). In the operating angle region S0, the ball 4 (0°) closest to the opening is disposed in the first track groove portions 7a, 9a, so the angle η2 relative to this ball 4 (0°) is a negative value (open toward the back). On the other hand, when a ball 4 enters the second track groove portions 7b, 9b, the angle η2 increases as the operating angle θ increases, becoming a positive value (open toward the opening). As the operating angle θ increases further, the angle η2 relative to the ball 4 (0°) closest to the opening becomes larger than the angle η1 relative to the ball 4 (180°) closest to the opening.

[0060] In this embodiment, the shapes of the track grooves 7, 9 are set so that point G where the included angle η2 overtakes the included angle η1, that is, point G where the included angles η1 and η2 are equal, is located in the operating angle range S2 where two balls 4 fit into the second track groove portions 7b, 9b. As a result, in the operating angle range S2 where the position of the cage 5 is likely to become unstable, a force that presses the cage 5 in the axial direction toward the opening is generated on both the ball 4 (0°) closest to the opening and the ball 4 (180°) closest to the opening, thereby stabilizing the position of the cage 5 within the plane bisecting the operating angle and improving torque transmission efficiency and NVH performance.

[0061] The state of the operating angle range S2 in which two balls 4 fit into the second track groove portions 7b, 9b will be described in detail with reference to FIG. 11 . FIG. 11 is a development view of the outer joint member 2 as seen from the axial center side. The balls 4 are indicated by dashed lines and are numbered (1) to (8). The phase angle of the joint is indicated on the left side of the outer joint member 2. When the fixed type constant velocity universal joint 1 is at an operating angle, the circumferential position (phase angle) at which the inner joint member 3 projects furthest from the outer joint member 2 toward the opening side is defined as 0°, and the circumferential position (phase angle) at which the inner joint member 3 fits furthest into the outer joint member 2 is defined as 180° (see FIG. 8 ). In FIG. 11 , the arrow pointing toward the opening side of the outer joint member 2 (right side in the drawing) indicates the magnitude of the included angle η.

[0062] FIG. 11 shows a state in which the fixed type constant velocity universal joint 1 has a predetermined operating angle and a rotation angle in which the ball 4(1) is disposed at a phase angle of 0°. In this state, of the eight balls 4, only the ball 4(1) disposed at a phase angle of 0° is disposed in the second track groove portion 7b. If the fixed type constant velocity universal joint 1 is rotated slightly (for example, by about 20°) while maintaining this operating angle, the ball 4(1) moves slightly toward the back but remains disposed in the second track groove portion 7b, while the ball 4(8) moves slightly toward the opening and enters the second track groove portion 7b. As a result, two balls 4(1) and 4(8) are disposed in the second track groove portion 7b. Therefore, at this operating angle, as the fixed type constant velocity universal joint 1 rotates, a state in which only one ball 4 is disposed in the second track groove portion 7b and a state in which two balls 4 are disposed in the second track groove portion 7b alternate as shown in FIG. 11 .

[0063] 11, the angle η1 for the ball 4 (0°) located closest to the opening and the angle η2 for the ball 4 (180°) located closest to the opening are both open toward the opening and have the same value (see FIG. 8). As a result, in the operating angle range where two balls 4 fit into the second track groove portions 7b, 9b corresponding to high operating angles, it is possible to suppress variation of the cage 5 from the plane bisecting the operating angle, achieving both high efficiency and a high operating angle, and a fixed type constant velocity universal joint with good NVH characteristics.

[0064] 4, in this embodiment, the center of curvature Oo1 of the ball center locus Xa of the first track groove portion 7a is offset toward the ball center locus Xa, thereby reducing the radius of curvature Ro1 of the ball center locus Xa. Therefore, if the arc-shaped first track groove portion 7a is extended toward the back (see dotted line), the groove depth in this portion becomes shallower.

[0065] Therefore, in this embodiment, a third track groove portion 7c having a linear ball raceway center line Xc is provided on the deep side of the arc-shaped first track groove portion 7a of the outer joint member 2. Correspondingly, a third track groove portion 9c having a linear ball raceway center line Yc is provided on the opening side of the arc-shaped first track groove portion 9a of the inner joint member 3. This allows the groove depth of the track groove 7 at the deep end to be greater than in the case where, for example, the arc-shaped first track groove portion 7a is extended to the deep end (see dotted line), and therefore the strength and durability of the outer joint member 2 and the inner joint member 3 at a high operating angle can be ensured.

[0066] 6 , in this embodiment, the positions of the connecting portions A1, A2 are set so that the operating angle θ2 at which the center of the innermost ball 4 (180°) is located at the connecting portion A2 of the ball track center lines Xa, Xc of the track groove 7 of the outer joint member 2 is larger than the operating angle θ1 at which the center of the outermost ball 4 (0°) is located at the connecting portion A1 of the ball track center lines Xa, Xb of the track groove 7 of the outer joint member 2. This allows the innermost ball 4 (180°) to be located in the first track groove portions 7a, 9a in the operating angle range in which two balls 4 fit in the second track groove portions 7b, 9b, and therefore makes it easier to set the angle η1 relative to this ball 4 (180°) to be equal to the angle η2 relative to the outermost ball 4 (0°).

[0067] In the embodiments described above, an example was shown in which the fixed constant velocity universal joint has eight balls. However, the number of balls can be eight or more, for example, ten or more, as appropriate.

[0068] The present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be embodied in various other forms without departing from the spirit of the present invention.

[0069] DESCRIPTION OF SYMBOLS 1 Fixed type constant velocity universal joint 2 Outer joint member 3 Inner joint member 4 Ball 5 Cage 7, 9 Track groove 7a, 9a First track groove portion 7b, 9b Second track groove portion 7c, 9c Third track groove portion O Joint center Oi1, Oo1 Center of curvature of first track groove portion Oi2, Oo2 Center of curvature of second track groove portion S0 Working angle range where the maximum number of balls that can enter the second track groove portion is 0 S1 Working angle range where the maximum number of balls that can enter the second track groove portion is 1 S2 Working angle range where the maximum number of balls that can enter the second track groove portion is 2 S3 Working angle range where the maximum number of balls that can enter the second track groove portion is 3 X, Y Ball raceway center line of track groove Xa, Ya Ball raceway center line of first track groove portion Xb, Yb Ball raceway center line of second track groove portion Xc, Yc Third track groove ball trajectory centerlines η, η1, η2 Angle θ, θ1, θ2 Operating angle θmax Maximum operating angle

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; an inner joint member having a plurality of track grooves formed on its spherical outer peripheral surface; 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 cage having a plurality of pockets for holding the balls, a spherical outer peripheral surface that fits with the spherical inner peripheral surface of the outer joint member, and a spherical inner peripheral surface that fits with the spherical outer peripheral surface of the inner joint member, wherein the track grooves of the outer joint member have a first track groove portion provided in an axial region including the joint center and a second track groove portion provided on one axial side of the first track groove portion; and the track grooves of the inner joint member have a first track groove portion provided in an axial region including the joint center and a second track groove portion provided on the other axial side of the first track groove portion, the ball raceway center lines (Xa, Ya) of the first track groove portions of the track grooves of the outer joint member and the inner joint member form arc shapes having centers of curvature that are not offset in the axial direction with respect to the joint center (O); the ball raceway center lines (Xa, Ya) of the first track groove portions of the outer joint member and the inner joint member are inclined in the circumferential direction with respect to the joint axis (N-N); the ball raceway center lines (Xa, Ya) of the first track groove portions that are adjacent in the circumferential direction are inclined in opposite circumferential directions with respect to the joint axis (N-N); the ball raceway center line (Xa) of the first track groove portion of the outer joint member and the ball raceway center line (Ya) of the first track groove portion of the inner joint member that are opposed in the radial direction are inclined in opposite circumferential directions with respect to the joint axis (N-N); a ball raceway center line (Xb) of the second track groove portion of the outer joint member is arranged on the outer diameter side of a circular arc formed by extending the ball raceway center line (Xa) of the first track groove portion to one side in the axial direction, a ball raceway center line (Yb) of the second track groove portion of the inner joint member is arranged on the outer diameter side of a circular arc formed by extending the ball raceway center line (Ya) of the first track groove portion to the other side in the axial direction, and centers of curvature of the ball raceway center lines (Xa, Ya) of the first track groove portions are offset in the radial direction relative to a joint axis (N-N) to sides approaching the ball raceway center lines (Xa, Ya).

2. A fixed type constant velocity universal joint as set forth in claim 1, wherein within the operating angle range in which two balls fit into said second track groove portion, there exists an operating angle in which the angle (η1) between the ball located in said second track groove portion closest to one side in the axial direction and the angle (η2) between the ball located in said first track groove portion closest to the other side in the axial direction coincides.

3. A fixed type constant velocity universal joint as set forth in claim 1, wherein the track grooves of the outer joint member are provided with a third track groove portion having a ball raceway center line (Xc) that is smoothly continuous and linear on the other axial side of the ball raceway center line (Xa) of the first track groove portion.

4. A fixed type constant velocity universal joint according to claim 1, wherein an operating angle (θ2) at which the center of the ball closest to the other axial direction is located at a junction between the ball raceway center line (Xa) of the first track groove portion and the ball raceway center line (Xc) of the third track groove portion of the track groove of the outer joint member is larger than an operating angle (θ1) at which the center of the ball closest to one axial direction is located at a junction between the ball raceway center line (Xa) of the first track groove portion and the ball raceway center line (Xb) of the second track groove portion of the track groove of the outer joint member.

5. A fixed type constant velocity universal joint according to claim 4, wherein the operating angle (θ1) is 15° or more.

6. A fixed type constant velocity universal joint according to claim 1, wherein the ball raceway center line (Xb, Yb) of said second track groove portion is an arcuate shape that is convex toward the inner diameter side.

Images