Fixed constant velocity universal joint

Abstract

This invention provides a fixed constant velocity universal joint that achieves both high efficiency and a wide operating angle, while also exhibiting excellent NVH characteristics. [Solution] In a track groove intersecting type fixed constant velocity universal joint 1, the track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3 have a first track groove portion 7a and 9a provided in the axial region including the joint center O, and a second track groove portion 7b and 9b for accommodating high operating angles. The ball trajectory centerlines Xa and Ya of the first track groove portions 7a and 9a form an arc shape with curvature centers Oo1 and Oi1 that are not offset axially with respect to the joint center O. The curvature centers Oo1 and Oi1 are offset by Fy in the radial direction with respect to the joint axis NN toward the ball trajectory centerlines Xa and Ya.

Description

Technical Field

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

Background Art

[0002] On the inboard side (differential gear side) of the front drive shaft of an automobile, a sliding constant velocity joint that has a relatively small maximum operating angle but can be axially displaced while taking an operating angle is usually incorporated. On the outboard side (wheel side), 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. In recent years, for the purpose of improving the environmental performance of automobiles, further higher efficiency has been demanded, and joint types such as track groove intersection types shown in Patent Document 1 and Patent Document 2 have been proposed. Conventionally, as the maximum operating angle, 47° for a ZF type constant velocity joint (BJ type) and 50° for an undercut-free type constant velocity joint (UJ type) are common. However, from the viewpoint of improving the turning performance and small turning performance of automobiles, the demand for exceeding 50° is increasing. Thus, as functions of a fixed constant velocity joint, the coexistence at a high level of high efficiency and a 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, it is necessary to provide a second track groove section that accommodates high operating angles in a track groove crossing type structure such as those described in Patent Documents 1 and 2. Various shapes have been proposed for this second track groove section so as to ensure a contact point for the ball when a 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 (Noise, Vibration, Harshness) 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, a structure with a second track groove section corresponding to a high operating angle basically changes the balance of forces acting on the retainer when a ball enters the second track groove section from the first track groove section, causing the retainer to come into contact with the outer joint member and the inner joint member. As a result, the power transmission efficiency 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 12 to 14 show a prototype of a track groove crossing type fixed constant velocity universal joint 101 with a maximum operating angle exceeding 50°. As shown in Figure 12(A), the second track grooves 107b and 109b corresponding to operating angles exceeding 50° require an arc shape opposite to that of the first track grooves 107a and 109a (convex towards the inner diameter). In this case, the ball 104 enters the range of the second track grooves 107b and 109b, and as the operating angle increases, the clamping angle acting on the ball 104 increases, so the force with which the ball 104 located in the second track grooves 107b and 109b pushes the retainer 105 increases. Furthermore, the connection between the first track grooves 107a and 109a, which are arc-shaped and convex on the outer diameter side, and the second track grooves 107b and 109b, which are arc-shaped and convex on the inner diameter side, is a significant inflection point. As a result, the clamping angle acting on the ball changes rapidly when the ball 104 moves from the first track grooves 107a and 109a to the second track grooves 107b and 109b.

[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 may be disrupted, causing the retainer 105 to deviate from the bisecting plane of the operating angle, and investigated its behavior.

[0011] (3) Examination of the degree to which the operating angle range of the ball entering the second track groove influences the behavior of the retainer. (3-1)(i) The connection between the first track grooves 107a and 109a, which are arc-shaped and convex to the outer diameter, and the second track grooves 107b and 109b, which are arc-shaped and convex to the inner diameter, is a significant inflection point, and (ii) the clamping angle acting on the ball 104 changes rapidly when the ball 104 moves from the first track grooves 107a and 109a to the second track grooves 107b and 109b. These points were analyzed and evaluated. Note that, in the track grooves 107, the connection part co between the first track groove 107a and the second track groove 107b is formed at the point where the ball 104, whose center is located at the connection part a between the ball trajectory centerline xa of the first track groove 107a and the ball trajectory centerline xb of the second track groove 107b, comes into contact. Furthermore, a connection portion ci between the first track groove 109a and the second track groove 109b is formed at the point where a ball 104, whose center is located at the connection portion b between the ball trajectory centerline ya of the first track groove portion 109a and the ball trajectory centerline yb of the second track groove portion 109b, comes into contact with the track groove 109.

[0012] (3-2) As a result, we found that the following problem exists in the operating angle range where two balls 104 enter the second track grooves 107b and 109b beyond the connection parts co and ci. As shown in Figure 13, in the operating angle range where two balls 104 enter the second track grooves 107b and 109b, the force with which the balls 104 push against the retainer 105 is small, and therefore 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' for the ball 104 (0°) with a phase angle of 0° located in the second track groove 107b and the clamping angle η1' for the ball 104 (180°) with a phase angle of 180° located in the first track groove 107a, and because the change in this difference is also rapid, the angle of the retainer 105 fluctuates greatly, which may lead to a decrease in efficiency and NVH performance.

[0013] (3-3) The clamping angle η is shown in Figure 14. The clamping angle η with respect to the ball 104 refers to the angle formed by the tangent in the extending direction of the track groove 107 of the outer joint member 102 at the point of contact with the ball 104, and the tangent in the extending direction of the track groove 109 of the inner joint member 103 at the point of contact with the ball 104. When the ball 104 and the track grooves 107 and 109 make angular contact, the ball 104 contacts the side surface of the track grooves 107 and 109, rather than the bottom surface. Even in this case, considering the evaluation of the difference in angle between the first track grooves 107a and 109a and the second track grooves 107b and 109b, and the need for reliable and easy measurement procedures, it was concluded that it is effective to use the clamping angle at the bottom surface of the track groove as a substitute for convenience. Specifically, the angle η is defined as the angle formed by the tangent lines in the extending direction of each track groove 107, 109 at the intersection points J1, J2 of the groove bottoms of the track grooves 107, 109 and planes K1, K2 which include the contact point between the track grooves 107, 109 and the ball 104 and the center of the ball 104. The same applies to the embodiments described later.

[0014] (3-4) If the operating angle θ is increased beyond the operating angle range in which two balls 104 can fit into the second track grooves 107b and 109b shown in Figure 13, the clamping angles η1' and η2' with respect to the balls 104 located in the second track grooves 107b and 109b also increase. As these balls 104 strongly push the retainer 105 toward the opening side, the contact force between the retainer 105 and the outer joint member 102 and the inner joint member 103 increases, and the position of the retainer 105 becomes more stable. In addition, such a large operating angle range is not used very often, so its impact on the deterioration of NVH performance is low.

[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 with a track groove crossing type where 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 plane that bisects the operating angle in the operating angle range where two balls 104 are placed in the second track grooves 107b and 109b that correspond to high angles. This led to the present invention.

[0016] To solve the above problems, the present invention provides a fixed constant velocity universal joint comprising: an outer joint member having a plurality of track grooves formed on its spherical inner circumferential surface; an inner joint member having a plurality of track grooves formed on its spherical outer circumferential 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; a retainer having a plurality of pockets for holding the plurality of balls, a spherical outer circumferential surface that fits with the spherical inner circumferential surface of the outer joint member, and a spherical inner circumferential surface that fits with the spherical outer circumferential surface of the inner joint member, The track groove of the outer joint member has a first track groove portion provided in the axial region including the joint center, and a second track groove portion provided on one side of the axial direction of the first track groove portion. The track groove of the inner joint member has a first track groove portion provided in the 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 trajectory centerlines (Xa, Ya) of the first track groove portion of the track grooves of the outer joint member and the inner joint member have an arc shape with a center of curvature that is not offset axially with respect to the joint center (O). The ball trajectory centerlines (Xa, Ya) of the first track grooves of the outer joint member and the inner joint member are inclined circumferentially with respect to the joint axis (NN), The ball trajectory centerlines (Xa, Ya) of the first track grooves adjacent to each other in the circumferential direction are inclined on the opposite side in the circumferential direction with respect to the joint axis (NN), The ball trajectory centerline (Xa) of the first track groove of the outer joint member and the ball trajectory centerline (Ya) of the first track groove of the inner joint member, which are radially opposed to each other, are inclined on opposite sides in the circumferential direction with respect to the joint axis (NN). The ball trajectory centerline (Xb) of the second track groove of the outer joint member is positioned on the outer diameter side of the arc obtained by extending the ball trajectory centerline (Xa) of the first track groove in one axial direction. The ball trajectory centerline (Yb) of the second track groove of the inner joint member is positioned on the outer diameter side of the arc obtained by extending the ball trajectory centerline (Ya) of the first track groove in the other axial direction. The present invention provides a fixed constant velocity universal joint in which the centers of curvature of the ball trajectory centerlines (Xa, Ya) of the first track groove are offset radially with respect to the joint axis (NN) toward the ball trajectory centerlines (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 NN 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 occurs for balls positioned in the first track groove that are 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 where two balls are 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 angles η1 and η2 coincide. As a result, in the operating angle range where two balls enter the second track groove, not only the ball on the farthest side of the second track groove but also the ball on the farthest side of the first track groove pushes the retainer toward the opening side, thereby suppressing the fluctuation of the retainer with respect to the plane that bisects the operating angle, and improving the NVH characteristics.

[0018] In the above-described fixed constant velocity universal joint, it is preferable that the track groove of the outer joint member includes a third track groove having a straight ball trajectory centerline (Xc) that is smoothly continuous with the ball trajectory centerline (Xa) of the first track groove on the other axial side (rear side). By providing a straight third track groove on the rear side of the arc-shaped first track groove in this way, the groove depth can be made deeper than when the arc-shaped first track groove is extended to the rear, thereby ensuring strength and durability at high operating angles.

[0019] In the above-described fixed constant velocity joint, at the connection portion between the ball track center line (Xa) of the first track groove portion and the ball track center line (Xc) of the third track groove portion of the outer joint member, the operating angle (θ2) at which the center of the ball on the farthest axial other side (rear side) is arranged is preferably larger than the operating angle (θ1) at which the center of the ball on the farthest axial one side (opening side) is arranged at the connection portion between the ball track center line (Xa) of the first track groove portion and the ball track center line (Xb) of the second track groove portion of the track groove of the outer joint member. Thereby, in the operating angle range where two balls enter the second track groove portion, the ball on the farthest rear side can be arranged in the first track groove portion, so that it becomes easier to set the clamping angle for the ball provided on the most opening side and the clamping angle for the ball provided on the most rear side to be substantially equal.

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

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

Effects of the Invention

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

Brief Description of the Drawings

[0023] [Figure 1] (A) is an axial cross-sectional view of a fixed constant velocity joint according to an embodiment of the present invention, and (B) is a front view of the fixed constant velocity joint in (A) viewed from the axial one side (opening side of the outer joint member). [Figure 2](A) is an axial cross-sectional view of the outer joint member of the fixed constant velocity universal joint in Figure 1, and (B) is a front view of the outer joint member in Figure (A) as seen from one axial side (opening side). [Figure 3] (A) is a side view of the inner joint member of the fixed constant velocity universal joint in Figure 1, viewed from a direction perpendicular to the axis, and (B) is a front view of the inner joint member of Figure (A), viewed from one side in the axial direction (the opening side of the outer joint member). [Figure 4] Figure 1 is a cross-sectional view of the outer joint member of a fixed constant velocity universal joint in a plane including the ball trajectory centerline of the track groove. [Figure 5] Figure 1 is a cross-sectional view of the inner joint member of a fixed constant velocity universal joint in a plane including the ball trajectory centerline of the track groove. [Figure 6] Figure 1 is a cross-sectional view of the outer joint member of a fixed constant velocity universal joint. [Figure 7] Figure 1 is a cross-sectional view of a fixed constant velocity universal joint, showing the state with the maximum operating angle. [Figure 8] Figure 1 is a cross-sectional view of a fixed constant velocity universal joint, showing the state in which the operating angle is set so that two balls are in the second track groove. [Figure 9] Figure 12 shows the clamping angle η2' with respect to the ball at the opening end and the clamping angle η1' with respect to the ball at the innermost end of the fixed constant velocity universal joint (conventional product). [Figure 10] This figure shows the clamping angle η2' with respect to the ball on the most open side and the clamping angle η1' with respect to the ball on the innermost side of the fixed constant velocity universal joint (product of the present invention) shown in Figure 1. [Figure 11] Figure 1 is an exploded view of the outer joint member of the fixed constant velocity universal joint, as seen from the axial side. [Figure 12] (A) is an axial cross-sectional view of a conventional fixed constant velocity universal joint, and (B) is a front view of the fixed constant velocity universal joint in (A) as seen from one axial side (the opening side of the outer joint member). [Figure 13] Figure 12 is a cross-sectional view of a fixed constant velocity universal joint in the operating angle position. [Figure 14] This is an enlarged view of Figure 13. [Modes for carrying out the invention]

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

[0025] As shown in Figures 1(A) and 1(B), 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, in the axial direction NN of the fixed constant velocity universal joint 1 with an operating angle of 0°, the open side of the outer joint member 2 {right side in Figure 1(A)} will be referred to as the "open side", and the closed side {left side in Figure 1(A)} will be referred to as the "inside side".

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

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

[0028] As shown in Figure 2(A), the ball trajectory centerline X of the track groove 7 of the outer joint member 2 is inclined circumferentially with respect to the joint axis NN. Specifically, the plane M containing the ball trajectory centerline X of the track groove 7 of the outer joint member 2 and the joint center O is inclined by an angle γ with respect to the joint axis NN. As shown in Figure 3(A), the ball trajectory centerline Y of the track groove 9 of the inner joint member 3 is inclined circumferentially with respect to the joint axis NN. Specifically, the plane Q containing the ball trajectory centerline Y of the track groove 9 of the inner joint member 3 and the joint center O is inclined by an angle γ with respect to the joint axis NN. 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 Figure 3(B)} at the axial end of the spherical outer surface 8 formed between the track grooves 9 of the inner joint member 3.

[0029] The ball trajectory centerlines X of adjacent track grooves 7 in the outer joint member 2 are inclined circumferentially to the opposite side of the axis NN (see Figure 2). The ball trajectory centerlines Y of adjacent track grooves 9 in the inner joint member 3 are inclined circumferentially to the opposite side of the axis NN (see Figure 3). The ball trajectory centerlines X and Y of the radially opposing track grooves 7 of the outer joint member 2 and track grooves 9 of the inner joint member 3 are inclined circumferentially to the opposite side of the axis NN, and one ball 4 is placed at each of their intersections.

[0030] As shown in Figure 4, the track groove 7 of the outer joint member 2 has a first track groove portion 7a provided in the 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 inner side of the first track groove portion 7a.

[0031] The ball trajectory centerline Xa of the first track groove 7a is a circular arc shape that is convex towards the outer diameter with Oo1 as the center of curvature, and its radius of curvature is Ro1. The center of curvature Oo1 has no axial offset with respect to the joint center O, and is offset by Fy in the radial direction with respect to the joint axis NN toward the ball trajectory centerline Xa (i.e., toward the side where the radius of curvature becomes smaller).

[0032] The second track groove 7b is provided to achieve a higher operating angle than when the arc-shaped first track groove 7a is extended to the opening end of the track groove 7. Specifically, the ball trajectory centerline Xb of the second track groove 7b is positioned on the outer diameter side of the arc Xa' (see dotted line) which is an extension of the ball center trajectory Xa of the first track groove 7a toward the opening side. For example, the ball trajectory centerline Xb moves further away from the arc Xa' toward the outer diameter side as it approaches the opening side. In the illustrated example, the ball trajectory centerline Xb of the second track groove 7b is an arc shape with a radius of curvature Ro2 with Oo2 as the center of curvature. The center of curvature Oo2 is positioned radially outward from the ball trajectory centerline Xb, and in the illustrated example, it is positioned radially outward from the outer diameter surface of the outer joint member 2. Therefore, the ball trajectory centerline Xb of the second track groove 7b has an arc shape opposite to that of the ball trajectory centerline Xa of the first track groove 7a, that is, an arc shape that is convex toward the inner diameter. The ball trajectory centerline Xa of the first track groove 7a and the ball trajectory centerline Xb of the second track groove 7b are smoothly continuous. In the illustrated example, the arc-shaped ball trajectory centerlines Xa and Xb have a common tangent at their connection point A1.

[0033] The ball trajectory centerline Xc of the third track groove 7c is straight. The ball trajectory centerline Xa of the first track groove 7a and the ball trajectory centerline Xc of the third track groove 7c are smoothly continuous. In the illustrated example, the ball trajectory centerline Xc of the third track groove 7c is tangent to the ball trajectory centerline Xa of the first track groove 7a at its far end A2 (the connection point with the ball trajectory centerline Xc). The angle ε between the ball trajectory centerline Xc of the third track groove 7c and the axis NN of the joint is, for example, 25° to 35°.

[0034] Figure 4 is a cross-sectional view of the track groove 7 in Figure 2(A) in a plane M that includes the ball trajectory centerline X and the joint center O. Therefore, strictly speaking, it is not a longitudinal section in a plane that includes the joint axis NN, but rather a cross-section in a plane that is inclined at an angle γ with respect to the axis NN. The circumferentially adjacent track grooves 7 of the outer joint member 2 are inclined on opposite sides of the circumferential direction with respect to the axis NN, but all track grooves 7 have the cross-sectional shape shown in Figure 4 in a plane M that includes the ball trajectory centerline X and the joint center O.

[0035] As shown in Figure 5, the track groove 9 of the inner joint member 3 has a first track groove portion 9a provided in the axial region including the joint center O, a second track groove portion 9b provided on the inner 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 trajectory centerline Y of the track groove 9 of the inner joint member 3 and the ball trajectory centerline X of the track groove 7 of the outer joint member 2 have a shape that is mirror-symmetric with respect to a plane P that passes through the joint center O and is perpendicular to the axis NN.

[0036] The ball trajectory centerline Ya of the first track groove 9a is a circular arc shape that is convex towards the outer diameter with Oi1 as the center of curvature, and its radius of curvature is Ri1. The center of curvature Oi1 has no axial offset with respect to the joint center O, and is offset by Fy in the radial direction with respect to the joint axis NN toward the ball trajectory centerline Ya (i.e., toward 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 NN 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 NN of the joint.

[0039] Figure 5 is a cross-sectional view in plane Q containing the ball trajectory centerline Y and joint center O of the track groove 9 in Figure 3(A) mentioned above. Therefore, similar to Figure 4, strictly speaking, it is not a longitudinal section view in a plane containing the joint axis NN, but rather a cross-section inclined at an angle γ with respect to the axis NN. The circumferentially adjacent track grooves 9 of the inner joint member 3 are inclined on opposite sides in the circumferential direction with respect to the axis NN, but all track grooves 9 have the cross-sectional shape shown in Figure 5 in plane Q containing the ball trajectory centerline Y and joint center O.

[0040] The cross-sectional shapes of the track grooves 7 and 9 are formed in an elliptical or Gothic arch shape. 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 contacts the side surfaces of the track grooves 7 and 9 that are provided on both sides in the circumferential direction of the groove bottom.

[0041] Furthermore, when the center of ball 4 is positioned at the connection point A1 of the ball trajectory centerlines Xa and Xb of the track groove 7 of the outer joint member 2, ball 4 contacts the boundary Co1 between the first track groove 7a and the second track groove 7b (see Figure 6). At this time, the center of ball 4 is positioned at the connection point B1 of the ball trajectory centerlines Ya and Yb of the track groove 9 of the inner joint member 3 (see Figure 5), and ball 4 contacts the boundary Ci1 between the first track groove 9a and the second track groove 9b. Also, when the center of ball 4 is positioned at the connection point A2 of the ball trajectory centerlines Xa and Xc of the track groove 7 of the outer joint member 2, ball 4 contacts the boundary Co2 between the first track groove 7a and the third track groove 7c (see Figure 6). At this time, the center of the ball 4 is positioned at the connection point B2 (see Figure 5) of the ball trajectory centerlines Ya and Yc of the track groove 9 of the inner joint member 3, and the ball 4 is in contact with the boundary Ci2 between the first track groove portion 9a and the third track groove portion 9c.

[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 in 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 model. 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 model. 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 (0°) with a phase angle of 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 NN, 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 and whose inclination directions with respect to the axis NN 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. This allows the joint to operate smoothly under high load and high rotation speeds, reducing torque loss and heat generation, and improving durability.

[0045] Figure 7 shows the fixed constant velocity universal joint 1 in the state where it has reached 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, we will provide a supplementary explanation regarding the effective track length. When the operating angle is increased, the amount of axial movement per unit angle (e.g., 1°) of the contact point between the track groove 7 and the ball 4 changes depending on the shape of the track groove 7. In this embodiment, the ball trajectory centerline Xb of the second track groove 7b is an arc shape that is in the opposite direction (convex towards the inner diameter) to the ball trajectory centerline Xa of the first track groove 7a. 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 7b is located behind the ball center Ob. As a result, the contact point between the ball 4 and the second track groove 7b 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.

[0047] As shown in Figure 7, the intermediate shaft 15 is spline-fitted to the inner circumference of the inner joint member 3. At the maximum operating angle θmax, a small gap is formed between the outer surface of the smallest diameter portion 15a of the intermediate shaft 15 and the inlet chamfer 20 of the outer joint member 2. Note that the intermediate shaft 15 is shown in a simplified form in Figure 7.

[0048] The overall configuration of the fixed constant velocity universal joint 1 is as described above. Next, we will explain in detail how the clamping angle with respect to the ball 4 changes when the operating angle of the fixed constant velocity universal joint 1 is changed.

[0049] First, we will explain the problems that occur in the fixed constant velocity universal joint 101 shown in Figures 12 to 14 using Figure 9. Figure 9 is a graph showing the changes in the clamping angle η2' with respect to the ball 104 at the most open side (phase angle 0°) and the clamping angle η1' with respect to the ball 104 at the most inward side (phase angle 180°) when the operating angle θ of the fixed constant velocity universal joint 101 is changed.

[0050] In the smallest operating angle range S0, which includes 0°, all the balls 4 are positioned in the first track grooves 107a and 109a. That is, in this operating angle range S0, the number of balls 4 that enter the second track grooves 107b and 109a is 0. Since both the first track grooves 107a and 109a are arc-shaped with respect to the joint center O, the clamping angle for all the balls 4 is 0 in the operating angle range S0. Therefore, in this operating angle range S0, no force is generated that causes the balls 104 to push the retainer 105 in the axial direction due to the clamping angle.

[0051] As the operating angle θ increases, the center of the ball 4 on the most open side extends beyond points a and b (see Figure 12(A)) and is positioned in the second track grooves 107b and 109b. At this time, the operating angle range in which one ball 104 enters the second track grooves 107b and 109b is defined as S1, the operating angle range in which two balls 104 enter is defined as S2, and the operating angle range in which three or more balls 104 enter is defined as S3. Note that when the joint rotates while maintaining a predetermined operating angle, the number of balls that enter the second track grooves may vary depending on the rotation angle. Therefore, "an operating angle in which n balls enter the second track grooves" means an operating angle in which, when the joint is rotated while maintaining that operating angle, n balls may enter the second track grooves, but (n+1) balls will not enter.

[0052] In these operating angle ranges S1 to S3, a clamping angle η2' is generated that opens towards the opening side with respect to the balls 104 positioned in the second track grooves 107b and 109b, particularly the ball 104 on the most open side (0°) (see Figure 13). As a result, a difference is created between this angle and the clamping angle η1' (=0) with respect to the other balls 104 positioned in the first track grooves 107a and 109a, generating a force that pushes the retainer 105 towards the opening side.

[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' for the balls 104 located in the second track grooves 107b and 109b and the clamping angle η1' (=0) for 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, increasing the contact force between the retainer 105 and the outer joint member 102 and the inner joint member 103, and stabilizing the position of the retainer 105. 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 can accommodate 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 NN toward 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 balls 4 are positioned in the first track grooves 7a and 9a. In this embodiment, as described above, the curvature centers Oo1 and Oi1 of the ball center trajectories Xa and Ya in the first track grooves 7a and 9a are radially offset with respect to the axis NN. Therefore, a negative clamping angle η2 that opens slightly inward occurs for balls 4 (0°) on the opening side of the joint center O, and a positive clamping angle η1 that opens slightly inward occurs for balls 4 (180°) on the inner side of the joint center O. Since the magnitudes (absolute values) of these clamping angles η1 and η2 are equal, the force with which the balls 4 push the retainer 5 in the axial direction is balanced by the clamping angles η1 and η2.

[0059] As the operating angle θ increases, the number of balls 4 placed in the second track grooves 7b and 9b increases from 1 (operating angle range S1), to 2 (operating angle range S2), and to 3 (operating angle range S3). In the operating angle range S0, the ball 4 on the most open side (0°) is placed in the first track grooves 7a and 9a, so the clamping angle η2 with respect to this ball 4 (0°) is a negative value (open towards the back). On the other hand, when balls 4 enter the second track grooves 7b and 9b, the clamping angle η2 increases as the operating angle θ increases, becoming a positive value (open towards the open side). Further increasing the operating angle θ, the clamping angle η2 with respect to the ball 4 on the most open side (0°) becomes larger than the clamping angle η1 with respect to the ball 4 on the farthest side (180°).

[0060] In this embodiment, the shape of the track grooves 7 and 9 is set such that the point G where the clamping angle η2 overtakes the clamping angle η1, that is, the point G where the clamping angles η1 and η2 coincide, is located in the operating angle region S2 in which the two balls 4 are placed in the second track grooves 7b and 9b. As a result, in the operating angle region S2 in which the position of the retainer 5 tends to become unstable, a force is generated that pushes the retainer 5 axially toward the opening side for both the ball 4 on the opening side (0°) and the ball 4 on the innermost side (180°). This stabilizes the position of the retainer 5 within the plane that bisects the operating angle, thereby improving torque transmission efficiency and NVH performance.

[0061] The state of the operating angle range S2 in which the two balls 4 are positioned in the second track grooves 7b and 9b will be explained in detail using Figure 11. Figure 11 is an unfolded view of the outer joint member 2 as seen from the axial side. The balls 4 are shown by dashed lines, and each ball 4 is numbered (1) to (8). The left side of the outer joint member 2 shows the phase angle of the joint. With the fixed constant velocity universal joint 1 in the operating angle position, the circumferential position (phase angle) where the inner joint member 3 protrudes furthest from the outer joint member 2 towards the opening is 0°, and the circumferential position (phase angle) where the inner joint member 3 is positioned furthest into the outer joint member 2 is 180° (see Figure 8). In Figure 11, the arrow pointing towards the opening side (right side in the figure) of the outer joint member 2 indicates the magnitude of the clamping angle η.

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

[0063] In the state shown in Figure 11, the clamping angle η1 for the ball 4 (0°) positioned furthest to the opening and the clamping angle η2 for the ball 4 (180°) positioned furthest to the back are both open towards the opening and have the same value (see Figure 8). As a result, in the operating angle range where the two balls 4 are positioned in the second track grooves 7b and 9b corresponding to high operating angles, fluctuations of the retainer 5 from the plane that bisects the operating angle can be suppressed, enabling a fixed constant velocity universal joint that achieves both high efficiency and a high operating angle, and has good NVH characteristics.

[0064] By the way, in this embodiment, as shown in Figure 4, the center of curvature Oo1 of the ball center trajectory Xa in the first track groove 7a is offset towards the side closer to the ball center trajectory Xa, so the radius of curvature Ro1 of the ball center trajectory Xa is reduced. Therefore, if the arc-shaped first track groove 7a is extended inward (see dotted line), the groove depth in this part becomes shallower.

[0065] Therefore, in this embodiment, a third track groove 7c having a straight ball trajectory centerline Xc is provided on the inner side of the arc-shaped first track groove 7a of the outer joint member 2. Correspondingly, a third track groove 9c having a straight ball trajectory centerline Yc is provided on the opening side of the arc-shaped first track groove 9a of the inner joint member 3. As a result, compared to the case where the arc-shaped first track groove 7a is extended to the inner end (see dotted line), for example, the groove depth at the inner end of the track groove 7 can be increased, thereby ensuring the strength and durability of the outer joint member 2 and the inner joint member 3 at high operating angles.

[0066] Furthermore, in this embodiment, as shown in Figure 6, the positions of connection parts A1 and A2 are set such that the operating angle θ2 at which the center of the innermost ball 4 (180°) is positioned at the connection part A2 of the ball trajectory centerlines Xa and Xc of the track groove 7 of the outer joint member 2 is greater than the operating angle θ1 at which the center of the outermost ball 4 (0°) is positioned at the connection part A1 of the ball trajectory centerlines Xa and Xb of the track groove 7 of the outer joint member 2. As a result, as shown in Figure 8, in the operating angle range where two balls 4 are placed in the second track groove parts 7b and 9b, the innermost ball 4 (180°) can be positioned in the first track groove parts 7a and 9a, making it easier to set the clamping angle η1 for this ball 4 (180°) to be the same as the clamping angle η2 for the outermost ball 4 (0°).

[0067] 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.

[0068] The present invention is not limited in any way to the embodiments described above, and it goes without saying that it can be implemented in various other forms without departing from the spirit of the invention. [Explanation of Symbols]

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

Claims

1. A fixed constant velocity universal joint comprising: an outer joint member having a plurality of track grooves formed on its spherical inner surface; an inner joint member having a plurality of track grooves formed on its spherical outer 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; a retainer having a plurality of pockets for holding the plurality of balls, a spherical outer surface that fits with the spherical inner surface of the outer joint member, and a spherical inner surface that fits with the spherical outer surface of the inner joint member; The track groove of the outer joint member has a first track groove portion provided in the axial region including the joint center, and a second track groove portion provided on one side of the axial direction of the first track groove portion. The track groove of the inner joint member has a first track groove portion provided in the 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 trajectory centerlines (Xa, Ya) of the first track groove portion of the track groove of the outer joint member and the inner joint member have an arc shape with a center of curvature that is not offset in the axial direction with respect to the joint center (O). The ball trajectory centerlines (Xa, Ya) of the first track grooves 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 trajectory centerlines (Xa, Ya) of the first track grooves adjacent to each other in the circumferential direction are inclined on opposite sides in the circumferential direction with respect to the joint axis (N-N), The ball trajectory centerline (Xa) of the first track groove of the outer joint member and the ball trajectory centerline (Ya) of the first track groove of the inner joint member, which are radially opposed to each other, are inclined on opposite sides in the circumferential direction with respect to the joint axis (N-N). The ball trajectory centerline (Xb) of the second track groove of the outer joint member is positioned on the outer diameter side of the arc obtained by extending the ball trajectory centerline (Xa) of the first track groove in one axial direction. The ball trajectory centerline (Yb) of the second track groove of the inner joint member is positioned on the outer diameter side of the arc obtained by extending the ball trajectory centerline (Ya) of the first track groove in the other axial direction. A fixed constant velocity universal joint in which the centers of curvature of the ball trajectory centerlines (Xa, Ya) of the first track groove are offset radially with respect to the joint axis (N-N) toward the ball trajectory centerlines (Xa, Ya).

2. The fixed constant velocity universal joint according to claim 1, wherein in the operating angle range in which two balls are placed in the second track groove, there exists an operating angle in which the clamping angle (η1) with respect to the ball on the axial side of the second track groove coincides with the clamping angle (η2) with respect to the ball on the axial side of the first track groove.

3. The fixed constant velocity universal joint according to claim 1, wherein the track groove of the outer joint member is provided with a third track groove having a straight ball trajectory center line (Xc) that is smoothly continuous on the other axial side of the ball trajectory center line (Xa) of the first track groove.

4. A fixed constant velocity universal joint according to claim 1, wherein the operating angle (θ2) at which the center of the ball on the far other axial side is positioned at the connection point between the ball trajectory centerline (Xa) of the first track groove portion and the ball trajectory centerline (Xc) of the third track groove portion of the track groove of the outer joint member is greater than the operating angle (θ1) at which the center of the ball on the far one axial side is positioned at the connection point between the ball trajectory centerline (Xa) of the first track groove portion and the ball trajectory centerline (Xb) of the second track groove portion of the track groove of the outer joint member.

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

6. The fixed constant velocity universal joint according to claim 1, wherein the ball trajectory centerlines (Xb, Yb) of the second track groove have a circular arc shape that is convex toward the inner diameter.

Images