Fixed constant velocity universal joint

Abstract

A fixed constant velocity universal joint 1 is of a track groove intersection type in which forces acting on a cage 5 are balanced, and the fixed constant velocity universal joint 1 has second track groove sections 7b, 9b corresponding to a high operating angle. The setting angle η2 of balls 4 positioned in the second track groove sections 7b, 9b and the setting angle η1 of balls positioned in first track groove sections 7a, 9a are set to be equal to each other in an operating angle region where a plurality of the balls 4 enter the second track groove sections 7b, 9b.

Description

Fixed constant velocity universal joint

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

[0002] For example, the front drive shaft of an automobile typically incorporates a sliding constant velocity universal joint on the inboard side (differential gear side) that has a relatively small maximum operating angle but is capable of axial displacement while taking an operating angle, while the outboard side (wheel side) incorporates a fixed constant velocity universal joint that is capable of a large operating angle but does not displace axially, as the wheels are steered.

[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 improvements in efficiency have been required, and track groove cross-type joints have been proposed, as disclosed in Patent Documents 1 and 2. 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 levels of efficiency and a high working angle is becoming an important 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 a high operating angle in a structure that balances the forces acting on the cage, as described in Patent Documents 1 and 2. Various shapes have been proposed for this second track groove portion so that the contact point of the balls can be secured at the high operating angle 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 characteristics.

[0007] The present inventors have conducted various studies and investigations to achieve the above object, and have arrived at the present invention through the following findings and inferential 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 of the balls pushing the cage is lost. In a structure in which second track groove portions are provided to accommodate a high operating angle, when the balls move from the first track groove portions to the second track groove portions, the balance basically changes and the cage comes into contact with the outer joint member and the inner joint member. As a result, the efficiency of the joint 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° Figures 9 to 11 show prototypes of track groove intersecting type fixed constant velocity universal joints with a maximum operating angle exceeding 50°. As shown in Figure 9A, the second track groove portions 107b, 109b corresponding to operating angles exceeding 50° require an arc shape with a reverse radius to the arc shape of the first track groove portions 107a, 109a. In the case of second track groove portions 107b, 109b with such an arc shape with a reverse radius, the larger the angle of entry of balls 104 into the range of second track groove portions 107b, 109b, the larger the included angle acting on balls 104, and therefore the greater the force with which balls 104 positioned in second track groove portions 107b, 109b press against cage 105. Furthermore, the connection between the arc-shaped first track groove portions 107 a, 109 a and the reverse-radius arc-shaped second track groove portions 107 b, 109 b forms a significant inflection point. When the ball 104 moves from the arc-shaped first track groove portions 107 a, 109 a into the reverse-radius arc-shaped second track groove portions 107 b, 109 b, the angle acting on the ball changes abruptly.

[0010] As described above, attention was paid to the possibility that the balance between the force of the balls 104 located in the first track groove portions 107a and 109a pressing the retainer 105 and the force of the balls 104 located in the second track groove portions 107b and 109b pressing the retainer 105 becomes unbalanced, causing the retainer 105 to deviate from the bisecting plane, and this behavior was investigated.

[0011] (3) Study on the degree of influence of the angle range of the balls entering the second track groove portions on the behavior of the cage (3-1) (i) The analysis and evaluation were conducted focusing on the fact that the junctions between the arc-shaped first track groove portions 107 a, 109 a and the reverse-radius arc-shaped second track groove portions 107 b, 109 b are significant inflection points, and (ii) the sandwiched angle acting on the ball 104 changes suddenly when the ball 104 moves from the arc-shaped first track groove portions 107 a, 109 a into the reverse-radius arc-shaped second track groove portions 107 b, 109 b. Note that the ball 104, whose center is located at the junction a between the ball track center line xa of the first track groove portion 107 a and the ball track center line xb of the second track groove portion 107 b of the outer joint member 102, comes into contact with the junction co between the first track groove portion 107 a and the second track groove portion 107 b. Furthermore, the ball 104, whose center is located at the connection portion b between the ball track center line ya of the first track groove portion 109a of the inner joint member 103 and the ball track center line yb of the second track groove portion 109b, comes into contact with the connection portion ci of the first track groove portion 109a and the second track groove portion 109b.

[0012] (3-2) As a result, the researchers arrived at the following problem in the angle range where a plurality of balls 104 enter the second track groove portions 107b, 109b (particularly, the angle range where two balls enter). As shown in Fig. 10 , at an operating angle θ where a plurality of balls 104 (two balls) 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 small. In this state, an included angle η2' opening toward the opening side is generated for the balls 104 located in the second track groove portions 107b, 109b that are closer to the opening than the joint center O, and an included angle η1' opening toward the opening side is generated for the balls 104 located in the first track groove portions 107a, 109a that are deeper than the joint center O. In the operating angle range shown in Figure 10, a difference occurs in the magnitude of these included angles η1', η2', and this difference changes rapidly, so the angle of the retainer 105 also fluctuates greatly, which may lead to a decrease in efficiency and NVH (Noise, Vibration, Harshness) performance.

[0013] (3-3) The included angle η is shown in FIG. 11 . The included angle η refers to the angle at which the ball 104 is sandwiched between the track groove 107 of the outer joint member 102 and the track groove 109 of the inner joint member 103 when the track groove 107 of the outer joint member 102 and the track groove 109 of the inner joint member 103 are cut in a longitudinal cross section including the center line. When the ball 104 and the track grooves 107, 109 are in angular contact with each other, the ball 104 and the track grooves 107, 109 contact each other in the contact angle direction (including the side surfaces). However, for the sake of evaluating the difference in the sandwiched angle between the first track groove portions 107 a, 109 a and the second track groove portions 107 b, 109 b and taking into account the reliability and simplification of the measurement procedure, it is effective to use the included angle at the track groove bottom as a substitute for the angle. This also applies to the embodiments described later. In this specification and claims, the included angle η is used in the above sense.

[0014] (3-4) When the operating angle θ is increased beyond the angle range in which a plurality of balls 104 (two balls) can fit in the second track groove portions 107b, 109b shown in Figure 10, 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 stabilizing the position of the cage 105. In addition, the large angle range described above is not used very frequently, so it has little effect on the deterioration of NVH performance.

[0015] (4) A new idea that achieves both high efficiency and a high operating angle and ensures NVH characteristics Based on the above analytical evaluations and findings, in a fixed constant velocity universal joint 101 of a track groove crossing type in which the forces acting on the cage 105 are balanced, and in a fixed constant velocity universal joint provided with second track groove portions 107b, 109b corresponding to an operating angle exceeding 50°, the key to ensuring efficiency and NVH (Noise, Vibration, Harshness) performance is to suppress fluctuations from the bisecting plane of the cage 105 in the operating angle θ range in which a plurality of balls 104 (two balls) enter the second track groove portions 107b, 109b corresponding to a high angle, which led to the present invention.

[0016] As technical means for achieving the above-mentioned object, the present invention provides 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, with one axial side as an opening side and the other axial side as a rear side; an inner joint member having a plurality of track grooves formed on its spherical outer peripheral surface, each pairing with the track grooves of the outer joint member; a plurality of balls interposed between the track grooves of the outer joint member and the track grooves of the inner joint member to transmit torque; and a cage having a spherical outer peripheral surface and a spherical inner peripheral surface, which holds the balls in pockets and fits with the spherical inner peripheral surface of the outer joint member and the spherical outer peripheral surface of the inner joint member, wherein the track grooves of the outer joint member have a first track groove portion 7a and a second track groove portion 7b located on the opening side of the first track groove (7a), and the first track groove portion 7a has an arc-shaped ball raceway center line Xa having a center of curvature that is not offset in the axial direction with respect to a joint center O, a plane M including the ball track center line Xa is inclined in the circumferential direction with respect to the joint axis N-N, and the ball track center lines Xa of the first track groove portions 7a that are adjacent in the circumferential direction are inclined in opposite circumferential directions to each other, the second track groove portion 7b has a ball track center line Xb that has a shape different from the ball track center line Xa of the first track groove portion 7a, a connection portion A between 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 is located on the opening side of the joint center O, and the ball track center line Y of the track groove of the inner joint member is formed in mirror symmetry with the ball track center line X of the mating track groove of the outer joint member, with respect to a plane P that includes the joint center O and is perpendicular to the joint axis N-N in a state where the operating angle is 0°, In the working angle range where a plurality of balls fit in the second track groove portions 7 b, 9 b, the angle η2 between the balls positioned in the second track groove portions 7 b, 9 b and the angle η1 between the balls positioned in the first track groove portions 7 a, 9 a are set to be equal. With the above configuration, it is possible to achieve a fixed type constant velocity universal joint that achieves both high efficiency and a large working angle and has good NVH characteristics.

[0017] In the above-mentioned fixed type constant velocity universal joint, it is preferable that the angle (η2) between the balls located in the second track groove portions (7b, 9b) and the angle (η1) between the balls located in the first track groove portions (7a, 9a) are set to be equal in the operating angle range where two balls fit in the second track groove portions (7b, 9b). This makes it possible to use this as an index to reliably and easily determine the internal specifications that suppress variation from the bisecting plane of the cage.

[0018] It is preferable that the ball raceway center lines Xa, Ya of the first track groove portions 7a, 9a have a center of curvature O1 that is offset toward the first track groove portions 7a, 9a in the radial direction with respect to the joint axis (N-N).Therefore, by changing the radial offset amount and the curvature radius of the center of curvature O1 of the ball raceway center lines Xa, Ya of the first track groove portions 7a, 9a, the included angle η1 can be easily adjusted.

[0019] It is preferable to set the operating angle θ1, at which the center of the ball closest to the opening is located at the connection A between the ball raceway center line Xa of the first track groove portion 7a and the ball raceway center line Xb of the second track groove portion 7b of the outer joint member, to 15° or more. This makes it possible to suppress an increase in the sandwiching angle of the second track groove portion, suppress spherical force, and ensure efficiency.

[0020] The ball raceway center line Xb of the second track groove portion 7b of the outer joint member is preferably an arc having a center of curvature Oo2 radially outward from the ball raceway center line Xb, thereby making it possible to lengthen the effective track length at the maximum operating angle θmax and ensure contact between the balls and the track grooves even at a maximum operating angle θmax exceeding 50°.

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

[0022] 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] FIG. 1B is a partial longitudinal sectional view of a fixed type constant velocity universal joint according to one embodiment of the present invention. FIG. 1C is a right side view of the fixed type constant velocity universal joint of FIG. 1A. FIG. 1D is a partial longitudinal sectional view of an outer joint member of the fixed type constant velocity universal joint according to this embodiment. FIG. 1E is a right side view of the outer joint member of FIG. 2A. FIG. 2F is a side view of the inner joint member of the fixed type constant velocity universal joint according to this embodiment. FIG. 3A is a front view of the inner joint member of FIG. 3A. FIG. 3C is a partial longitudinal sectional view showing details of track grooves of the outer joint member of FIG. 2A. FIG. 3D is a longitudinal sectional view showing details of track grooves of the inner joint member of FIG. 3B. FIG. 3E is a schematic longitudinal sectional view showing a state in which the fixed type constant velocity universal joint according to this embodiment has a maximum operating angle. FIG. 1F is a partial longitudinal sectional view showing a state in which the fixed type constant velocity universal joint according to this embodiment has a maximum operating angle. FIG. 1G is a development view seen from the inside of the outer joint member showing a state in which the operating angle range in which a plurality of balls fit into the second track groove portion of the fixed type constant velocity universal joint according to this embodiment has a maximum operating angle. 9B is a partial vertical cross-sectional view illustrating the state of the included angle in an operating angle range in which a plurality of balls fit into the second track groove portion of the fixed type constant velocity universal joint of FIG. 9A.

[0024] A fixed type constant velocity universal joint 1 according to one embodiment of the present invention will be described with reference to FIGS.

[0025] As shown in FIG. 1A , a fixed type constant velocity universal joint 1 mainly comprises an outer joint member 2, an inner joint member 3, balls 4, and a cage 5. Track grooves 7 are formed on a spherical inner peripheral surface 6 of the outer joint member 2, generally along the axial direction. A spherical outer peripheral surface 12 of the cage 5 is fitted and guided into the spherical inner peripheral surface 6. Track grooves 9 are formed on a spherical outer peripheral surface 8 of the inner joint member 3, generally along the axial direction. A spherical inner peripheral surface 13 of the cage 5 is fitted and guided into the spherical outer peripheral surface 8. Eight balls 4 are accommodated in pockets 5 a of the cage 5, one for each. Hereinafter, the direction of the axis N-N of the fixed type constant velocity universal joint 1 with an operating angle of 0° will be referred to as the "axial direction." Furthermore, in the axial direction, the open side of the outer joint member 2 (the right side in FIG. 1A ) will be referred to as the "open side," and the closed side (the left side in FIG. 1A ) will be referred to as the "rear side."

[0026] 1B , 2A , 2B , 3A and 3B , the eight track grooves 7 and 9 of each of the outer joint member 2 and the inner joint member 3 are inclined in the circumferential direction with respect to the joint axis N-N. Circumferentially adjacent track grooves 7A and 7B are inclined in opposite circumferential directions with respect to the joint axis N-N, and circumferentially adjacent track grooves 9A and 9B are inclined in opposite circumferential directions with respect to the joint axis N-N. Eight balls 4 are disposed at each intersection of the paired track grooves 7A, 9A and 7B, 9B of the outer joint member 2 and the inner joint member 3. Details of the track grooves 7 and 9 will be described later.

[0027] A longitudinal cross section of a fixed type constant velocity universal joint 1 is shown in Figure 1A. In order to accurately indicate the form and shape, such as the arc shape, of the track grooves extending generally in the axial direction, the term "ball track center line" will be used in this specification. Here, the ball track center line refers to the trajectory traced by the center of a ball placed in the track groove as it moves along the track groove. Therefore, the state of the arc shape, etc. of the track groove is the same as the state of the arc shape, etc. of the ball track center line.

[0028] As shown in FIG. 1A , the track groove 7 of the outer joint member 2 has a ball track centerline X. The track groove 7 is made up of a first track groove portion 7a having an arc-shaped ball track centerline Xa and a second track groove portion 7b having an arc-shaped ball track centerline Xb that has an inverse arc to the arc shape of the ball track centerline Xa. The ball track centerline Xa of the first track groove portion 7a and the ball track centerline Xb of the second track groove portion 7b are smoothly connected. The track groove 9 of the inner joint member 3 has a ball track centerline Y. The track groove 9 is made up of a first track groove portion 9a having an arc-shaped ball track centerline Ya and a second track groove portion 9b having an arc-shaped ball track centerline Yb that has an inverse arc to the arc shape of the ball track centerline Ya. The ball track centerline Ya of the first track groove portion 9a and the ball track centerline Yb of the second track groove portion 9b are smoothly connected.

[0029] The first track groove portion 7a of the outer joint member 2 is located on the far side. The ball track center line Xa of the first track groove portion 7a has an arc shape with a center of curvature at O1. The center of curvature O1 is not offset in the axial direction from the joint center O, but is located on the first track groove portion 7a side with respect to the joint axis N-N and is offset in the radial direction. The second track groove portion 7b of the outer joint member 2 is located on the opening side of the first track groove portion 7a. The ball track center line Xb of the second track groove portion 7b has an arc shape with a center of curvature at Oo2 (see FIG. 4). The center of curvature Oo2 of the ball track center line Xb of the second track groove portion 7b is located radially outward of the ball track center line Xb, and in the illustrated example, is located radially outward of the outer diameter surface of the outer joint member 2. Therefore, the arc shape of the ball track center line Xb of the second track groove portion 7 b is opposite to the arc shape of the ball track center line Xa of the first track groove portion 7 a. That is, the ball track center line Xa of the first track groove portion 7 a has an arc shape that is convex radially outward, while the ball track center line Xb of the second track groove portion 7 b has an arc shape that is convex radially inward.

[0030] The first track groove portion 9a of the inner joint member 3 is located on the opening side. The ball track center line Ya of the first track groove portion 9a has an arc shape having the same center of curvature O1 as the ball track center line Xa of the first track groove portion 7a of the outer joint member 2. The second track groove portion 9b of the inner joint member 2 is located on the far side of the first track groove portion 9a. The ball track center line Yb of the second track groove portion 9b has an arc shape with a center of curvature at Oi2 (see FIG. 5). The center of curvature Oi2 of the ball track center line Yb of the second track groove portion 9b is located radially outward of the ball track center line Yb, and in the illustrated example, it is located radially outward of the outer diameter surface of the outer joint member 2. Therefore, the arc shape of the ball track center line Yb of the second track groove portion 9b has an inverse curvature to the arc shape of the ball track center line Ya of the first track groove portion 9a. That is, the ball track center line Ya of the first track groove portion 9a has an arc shape that is convex radially outward, and the ball track center line Yb of the second track groove portion 9b has an arc shape that is convex radially inward.

[0031] The cross-sectional shape of the track grooves 7, 9 is formed into an ellipse or a Gothic arch shape, and 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 what is called angular contact. Therefore, the ball 4 comes into contact with the track grooves 7, 9 in the direction of the contact angle, that is, on the side surfaces of the track grooves 7, 9 slightly away from the groove bottoms.

[0032] 2A and 2B , a state in which the track grooves 7 of the outer joint member 2 are inclined in the circumferential direction with respect to the joint axis N-N will be described in detail. The track grooves 7 of the outer joint member 2 are designated by the symbols 7A and 7B based on the difference in their inclination direction. As shown in FIG. 2A , a plane M including the ball raceway center line X of the track groove 7A and the joint center O is inclined by an angle γ with respect to the joint axis N-N. Furthermore, although not shown, a track groove 7B circumferentially adjacent to the track groove 7A has a plane M including the ball raceway center line X of the track groove 7B and the joint center O inclined by an angle γ with respect to the joint axis N-N in the opposite direction to the inclination direction of the track groove 7A. Although the track grooves 7A and 7B (and 9A and 9B described later) are inclined by the angle γ, they extend generally in the axial direction. In this specification, the term "track grooves extending generally in the axial direction" is intended to include those inclined by the angle γ as described above.

[0033] Here, a supplementary note will be made regarding the reference numerals of the track grooves. When referring to the entire track grooves of the outer joint member 2, reference numeral 7 is used, with reference numeral 7a being used for the first track groove portion and reference numeral 7b being used for the second track groove portion. Furthermore, when distinguishing between track grooves with different inclination directions, reference numerals 7A and 7B are used, with reference numerals 7Aa and 7Ba being used for the first track groove portions and reference numerals 7Ab and 7Bb being used for the second track groove portions, respectively. Reference numerals are used in a similar manner for the track grooves of the inner joint member 3, which will be described later.

[0034] Next, with reference to FIGS. 3A and 3B , a state in which the track grooves 9 of the inner joint member 3 are inclined in the circumferential direction with respect to the joint axis N-N will be described in detail. The track grooves 9 of the inner joint member 3 are designated by the symbols 9A and 9B based on the difference in their inclination direction. As shown in FIG. 3B , a plane Q including the ball raceway center line Y of the track groove 9A and the joint center O is inclined by an angle γ with respect to the joint axis N-N. Furthermore, although not shown, the track groove 9B adjacent to the track groove 9A in the circumferential direction has a plane Q including the ball raceway center line Y of the track groove 9B and the joint center O inclined by an angle γ with respect to the joint axis N-N in the opposite direction to the inclination direction of the track groove 9A. The inclination angle γ is preferably set to 4° to 12°, taking into consideration the operability of the constant velocity universal joint 1 and the spherical surface width F of the track grooves of the inner joint member 3 on the closest side. The ball raceway center line Y of the track groove 9 of the inner joint member 3 is formed in mirror symmetry with the ball raceway center line X of the mating track groove 7 of the outer joint member 2, with respect to a plane P that includes the joint center O and is perpendicular to the joint axis N-N when the operating angle is 0°.

[0035] The track grooves as viewed from a vertical cross section of the outer joint member 2 will be described in detail with reference to Fig. 4. The partial vertical cross section of Fig. 4 is a cross section viewed on a plane M including the ball raceway center line X of the track groove 7A in Fig. 2A described above and the joint center O. Therefore, strictly speaking, it is not a vertical cross section on a plane including the joint axis N-N, but rather shows a cross section inclined by an angle γ. Fig. 4 shows the track grooves 7A of the outer joint member 2, but track groove 7B is inclined in the circumferentially opposite direction to track groove 7A, and other configurations are the same as those of track groove 7A, so a description thereof will be omitted.

[0036] FIG. 4 is a cross-sectional view of the outer joint member 2 taken along a plane M (see FIG. 2A) including the ball raceway center line X of the track groove 7A and the joint center O. The axis N'-N' in the figure is the joint axis N-N projected onto the plane M. The first track groove portion 7Aa of the outer joint member 2 is located on the far side. The ball raceway center line Xa of the first track groove portion 7Aa has an arc shape with O1 as the center of curvature. The center of curvature O1 is not offset in the axial direction from the joint center O, but is located on the first track groove portion 7Aa side with respect to the joint axis N'-N' and is offset in the radial direction (offset amount Fy). The radius of curvature of the ball raceway center line Xa of the first track groove portion 7Aa is r1.

[0037] The second track groove portion 7Ab of the outer joint member 2 is located on the opening side. The ball track center line Xb of the second track groove portion 7Ab has an arc shape with Oo2 as the center of curvature. The center of curvature Oo2 is located on a straight line L1 connecting the center of curvature O1 and a connection portion A between the ball track center line Xa of the first track groove portion 7Aa and the ball track center line Xb of the second track groove portion 7Ab. The center of curvature Oo2 is located radially outward from the ball track center line Xb, and in the illustrated example, is located radially outward from the outer diameter surface of the outer joint member 2. The radius of curvature of the ball track center line Xb of the second track groove portion 7Ab is r2. The connection portion Co between the first track groove portion 7Aa and the second track groove portion 7Ab is located on the straight line L1. The arc shape of the ball track center line Xb of the second track groove portion 7Ab is reversed in radius to the arc shape of the ball track center line Xa of the first track groove portion 7a.

[0038] Similarly, details of the track grooves will be described with reference to a longitudinal cross section of the inner joint member 3 with reference to Fig. 5. The longitudinal cross section of Fig. 5 is a cross section seen on a plane Q including the ball raceway center line Y of the track groove 9A in Fig. 3B described above and the joint center O. Therefore, as with Fig. 4, strictly speaking, it is not a longitudinal cross section on a plane including the joint axis N-N, but shows a cross section inclined by an angle γ. Fig. 5 shows the track grooves 9A of the inner joint member 3, but the track groove 9B has the same configuration as the track groove 9A except that its inclination direction is opposite to that of the track groove 9A, and therefore description thereof will be omitted.

[0039] FIG. 5 is a cross-sectional view of the inner joint member 3 taken along a plane Q (see FIG. 3B ) including the ball raceway center line Y of the track groove 9A and the joint center O. The axis N'-N' in the drawing is the joint axis N-N projected onto the plane Q. The first track groove portion 9Aa of the inner joint member 3 is located on the opening side. The ball raceway center line Ya of the first track groove portion 9Aa has an arc shape with O1 as the center of curvature. The center of curvature O1 is not offset in the axial direction from the joint center O, but is located on the first track groove portion 9Aa side with respect to the joint axis N'-N' and is offset in the radial direction (offset amount Fy). The radius of curvature of the ball raceway center line Ya of the first track groove portion 9Aa is r1.

[0040] The second track groove portion 9Ab of the inner joint member 3 is located on the far side. The ball track center line Yb of the second track groove portion 9Ab has an arc shape with Oi2 as the center of curvature. The center of curvature Oi2 is located on a straight line R1 connecting the center of curvature O1 and a connection portion B between the ball track center line Ya of the first track groove portion 9Aa and the ball track center line Yb of the second track groove portion 9Ab. The center of curvature Oi2 is located radially outward of the ball track center line Yb, and in the illustrated example, is located radially outward of the outer diameter surface of the outer joint member 2. The radius of curvature of the ball track center line Yb of the second track groove portion 9Ab is r2. The connection portion Ci between the first track groove portion 9Aa and the second track groove portion 9Ab is located on the straight line R1. The arc shape of the ball track center line Yb of the second track groove portion 9Ab is reversed in radius to the arc shape of the ball track center line Ya of the first track groove portion 9Aa.

[0041] When an operating angle θ is set, the balls 4 move by θ / 2 relative to a plane P that includes the joint center O of the outer joint member 2 and the inner joint member 3 and is perpendicular to the joint axis N-N. The positions of the connection points A and B between the ball track center lines Xa and Ya of the first track groove portions 7a and 9a and the ball track center lines Xb and Yb of the second track groove portions 7b and 9b are determined based on the operating angle that is frequently used. Here, the common operating angle of the joint and the frequently used operating angle will be explained. First, the common operating angle of the joint refers to the operating angle generated in the fixed constant velocity universal joint of the front drive shaft when the steering is in a straight-ahead position in a vehicle with one occupant on a horizontal, flat road surface. The common operating angle is usually selected and determined between 2° and 15° according to the design conditions of each vehicle model.

[0042] The frequently used operating angle does not refer to the high operating angle that occurs when the vehicle, for example, turns right or left at an intersection, but rather to the operating angle that occurs in a fixed constant velocity universal joint when the vehicle travels on a continuously curved road, and this is also determined according to the design conditions of each vehicle model. The frequently used operating angle is approximately 15°. The ball track center lines Xb and Yb of the second track groove portions 7b and 9b, which correspond to the high operating angle, connect to the ball track center lines Xa and Ya of the first track groove portions 7a and 9a. The setting of the positions A and B of the connection lines A and Ya of the first track groove portions 7a and 7b and the ball track center lines Xb and Yb of the second track groove portions 7b and 9b was investigated.

[0043] Considering the frequently used maximum operating angle of 15°, a study was conducted, including the functional aspects of the joint. The operating angle of the joint is defined as θ1 when the center of the ball 4 closest to the opening is located at the connection A between the ball track center line Xa of the first track groove portion 7a of the outer joint member 2 and the ball track center line Xb of the second track groove portion 7b, and the center of the ball 4 closest to the opening is located at the connection B between the ball track center line Ya of the first track groove portion 9a of the inner joint member 3 and the ball track center line Yb of the second track groove portion 9b. When this operating angle θ1 is 15° or more, an increase in the sandwich angle of the second track groove portion can be suppressed, spherical force can be suppressed, and efficiency can be ensured. On the other hand, when the operating angle θ1 is less than 15°, the sandwich angle of the second track groove portion increases, the spherical force increases, and efficiency deteriorates. From the above, it was concluded that the operating angle θ1 should be 15° or more. 4 and 5 are cross-sectional views taken along planes M and Q (see FIGS. 2A and 3B) inclined at an angle γ with respect to the axis N-N. Therefore, the angle β between a perpendicular line K that is perpendicular to the axis N'-N' projected onto the planes M and Q and passes through the joint center O, and a straight line L2, R2 that passes through the joint center O and the connection A of the ball track center lines Xa and Xb, is not strictly 1 / 2 of the operating angle θ1 of the joint, but they generally coincide (β ≈ θ1 / 2).

[0044] With the above-described operating angle θ1, in Fig. 4, a connection point A between the ball track center line Xa of the first track groove portion 7Aa and the ball track center line Xb of the second track groove portion 7b is the center position of the ball when it moves most toward the opening along the axial direction at an operating angle that is frequently used. Similarly, in the inner joint member 3, in Fig. 5, a connection point B between the ball track center line Ya of the first track groove portion 9Aa and the second track groove portion 9Ab is the center position of the ball when it moves most toward the inner side along the axial direction at an operating angle that is frequently used. Forces act in opposite axial directions on the balls 4 disposed at the intersections between the first track groove portions 7Aa of the outer joint member 2 and the first track groove portions 9Aa of the inner joint member 3 and the balls 4 disposed at the intersections between the first track groove portions 7Ba of the outer joint member 2 and the first track groove portions 9Ba of the inner joint member, and the cage 5 is stabilized at the position of the joint center O (see Fig. 1A ). As a result, the contact force between the spherical outer peripheral surface 12 of the cage 5 and the spherical inner peripheral surface 6 of the outer joint member 2, and the contact force between the spherical inner peripheral surface 13 of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3 are reduced, allowing the joint to operate smoothly under high load or at high rotation speeds, suppressing torque loss and heat generation and improving durability.

[0045] Figure 6 shows the fixed type constant velocity universal joint 1 at a maximum operating angle exceeding 50°. As shown in Figure 4, the arc shapes of the ball raceway center lines Xb, Yb of the second track groove portions 7Ab, 9Ab are reverse-radiused to the arc shapes of the ball raceway center lines Xa, Ya of the first track groove portions 7Aa, 9Aa. This makes it possible to increase the effective track length at the maximum operating angle θmax, and ensure contact points between the balls 4 and the track grooves 7, 9 even at maximum operating angles θmax exceeding 50°. Here, a supplementary explanation of the effective track length is provided. As the operating angle increases, the amount of axial movement of the contact points between the track groove 7 and the balls 4 per unit angle (for example, 1°) varies depending on the shape of the track groove 7. In this embodiment, the arc shape of the ball track center line Xb of the second track groove portion 7Ab is reverse-radius (different in shape) from the arc shape of the ball track center line Xa of the first track groove portion 7Aa, so the contact point between the ball 4, whose ball center Ob is located on the ball track center line Xb of the second track groove portion 7Ab, and the second track groove portion 7Ab is located at the back side of the outer joint member. As a result, the contact point between the ball 4 and the second track groove portion 7Ab can be secured. 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 axial movement of the contact point due to the shape of the track groove.

[0046] 6 , the minimum shaft diameter portion 15 a of the intermediate shaft 15 that is fitted and connected to the spline 14 of the inner joint member 3 has a nominal diameter dimension d. The outer diameter surface of the minimum shaft diameter portion 15 a is set so that a slight clearance is left between the minimum shaft diameter portion 15 a and the inlet chamfer 20 of the outer joint member 2 at the maximum operating angle θmax.

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

[0048] (1) In a fixed constant velocity universal joint of the crossed track groove type in which forces acting on a cage are balanced and which is provided with a second track groove portion that is compliant with a high operating angle, the balls 4 whose centers are located at connection portions A and B between the ball track center lines Xa and Ya of the first track groove portions 7 a and 9 a and the ball track center lines Xb and Yb of the second track groove portions 7 b and 9 b come into contact with the connection portions Co and Ci between the first track groove portions 7 a and 9 a and the second track groove portions 7 b and 9 b.

[0049] (2) In the operating angle range where a plurality of balls enter the second track groove portions 7b and 9b beyond the connecting portions Co and Ci, the angle η2 between the balls positioned in the second track groove portions 7b and 9b and the angle η1 between the balls positioned in the first track groove portions 7a and 9a are set to be equal.

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

[0051] The characteristic configuration was derived from the findings, particularly (3-1) and (3-2), and the novel idea (4) in "(3) Study on the degree of influence on the behavior of the cage depending on the angular range of the balls entering the second track groove portion" in the fixed constant velocity universal joint prototyped and examined during the development process described above.

[0052] The characteristic configuration will be specifically described with reference to Figures 7 and 8. Figures 4 and 5 mentioned above will also be referred to as appropriate.

[0053] As shown in Fig. 4, in the fixed type constant velocity universal joint 1 according to the present embodiment, when a ball 4 is arranged so that its center is located at a connection portion A between the ball track center line Xa of the first track groove portion 7Aa of the outer joint member 2 and the second track groove portion 7Ab, a connection portion Co between the first track groove portion 7Aa and the second track groove portion 7Ab is formed at the contact portion between this ball 4 and the track groove 7. As shown in Fig. 5, when a ball 4 is arranged so that its center is located at a connection portion B between the ball track center line Ya of the first track groove portion 9Aa of the inner joint member 2 and the ball track center line Yb of the second track groove portion 9Ab, a connection portion Ci between the first track groove portion 9Aa and the second track groove portion 9Ab is formed at the contact portion between this ball 4 and the track groove 9. The first track groove portions 7Ba, 9Ba are inclined in the circumferentially opposite direction to the first track groove portions 7Aa, 9Aa, and other configurations are the same as those of the first track groove portions 7Aa, 9Aa, so they are not shown in the figures. Furthermore, as described below, the first track groove portions 7Aa, 9Aa, 7Ba, and 9Ba may be collectively referred to as the first track groove portions 7a and 9a. Similarly, the second track groove portions 7Ab, 9Ab, 7Bb, and 9Bb may be collectively referred to as the first track groove portions 7b and 9b.

[0054] 7, at an operating angle θ where a plurality of balls 4 fit into the second track groove portions 7b, 9b beyond the junction portions Co, Ci between the first track groove portions 7a, 9a and the second track groove portions 7b, 9b, the angle η2 between the balls 4 located in the second track groove portions 7b, 9b and the angle η1 between the balls located in the first track groove portions 7a, 9a are set to be equal. In particular, it is desirable to set the angles η1 and η2 between the balls 4 to be equal at an operating angle θ where two balls 4 fit into the second track groove portions 7b, 9b, i.e., it is desirable that there exists an operating angle where the angles η1 and η2 match within the operating angle range where two balls 4 fit into the second track groove portions 7b, 9b.

[0055] The adjustment and setting of the included angle η will be described below. For example, a method for adjusting the included angle η1 of the first track groove portions 7a and 9a will be described. As shown in FIGS. 4 and 5 , the included angle η1 can be easily adjusted by changing the radial offset Fy and the curvature radius r1 of the center of curvature O1 of the ball track center lines Xa and Ya of the first track groove portions 7a and 9a. Specifically, the included angle η1 can be increased by increasing the radial offset Fy and decreasing the curvature radius r1. Conversely, the included angle η1 can be decreased by decreasing the radial offset Fy and increasing the curvature radius r1. This adjustment is also performed for the ball track center lines Xb and Yb of the second track groove portions 7b and 9b. The included angles η1 and η2 are set to be equal in the operating angle θ range where multiple (two) balls 4 fit in the second track groove portions 7b and 9b.

[0056] When r' = r1 + Fy, the radial offset Fy of the center of curvature O1 of the ball track center lines Xa and Ya of the first track groove portions 7a and 9a and the radius of curvature r1 preferably satisfy Fy / r' ≧ 0.25. If Fy / r' is less than 0.25, the offset Fy becomes small, thereby reducing the angle η1 between the balls positioned in the first track groove portions 7a and 9a and making it difficult to eliminate the imbalance with the angle η2 between the balls positioned in the second track groove portions 7b and 9b. On the other hand, if Fy / r' exceeds 0.3, the groove depth near the innermost end of the first track groove portion 7a of the outer joint member 2 becomes shallow. Therefore, it is preferable to satisfy Fy / r' ≦ 0.3. Alternatively, the region including the innermost end of the first track groove portion 7a of the outer joint member 2 may be replaced with a third track groove portion having a deeper groove depth than the first track groove portion 7a. In this case, a third track groove portion having a shape corresponding to the third track groove portion of the outer joint member 2 is formed in a region including the opening side end of the first track groove portion 9 a of the inner joint member 3.

[0057] The state of the operating angle range in which multiple balls (two balls) fit into the second track groove portion will be described with reference to FIG. 8 , which is a development view seen from the inside of the outer joint member. In FIG. 8 , the balls 4 are indicated by dashed lines, and the inner joint member is not shown. The phase angle is indicated on the left side of the outer joint member 2. The phase angle of the ball 4 at the vertex of the right side surface of the fixed type constant velocity universal joint 1 shown in FIG. 1B is set to 0°, and phase angles of 45° to 315° are shown in the counterclockwise direction. The ball with a phase angle of 0° is designated as 4 (0°), and the balls are sequentially designated as 4 (45°), 4 (90°), 4 (135°), 4 (180°), 4 (225°), 4 (270°), and 4 (315°). The center of each ball 4 is Ob, and the connection portion between the first track groove portion 7a and the second track groove portion 7b is Co. The arrow pointing toward the opening side of the outer joint member 2 indicates the magnitude of the included angle η.

[0058] As shown in Fig. 8, only one ball 4 (0°) passes over the connection portion Co between the first track groove portion 7a and the second track groove portion 7b and enters the second track groove portion 7b. This ball 4 (0°) passes over the connection portion Ci between the first track groove portion 9a and the second track groove portion 9b of the inner joint member 3 (not shown) and enters the second track groove portion 7b. As shown by the arrow, this ball 4 (0°) has an included angle η2 (0°) expanding toward the opening side of the outer joint member 2. The included angle η2 (0°) of the ball 4 (0°) located in the second track groove portion 7b is large, and the included angles η2 (45°) and η2 (315°) of the balls 4 (45°) and 4 (315°) located at the connection portion Co of the track groove portions 7a and 7b are smaller than η2 (0°).

[0059] When the fixed type constant velocity universal joint 1 rotates slightly while maintaining this operating angle, the ball 4 (0°) in FIG. 8 moves slightly toward the back (left side in the figure), and at the same time, the ball 4 (315°) moves slightly toward the opening (right side in the figure) and enters the second track groove portion 7b. As a result, two balls 4 are placed in the second track groove portion 7b. After that, when the fixed type constant velocity universal joint 1 rotates further, only one ball 4 (0°) is placed in the second track groove portion 7b, as shown in FIG. 8. As described above, at this operating angle, as the fixed type constant velocity universal joint 1 rotates, a state in which only one ball 4 is placed in the second track groove portion 7b (see FIG. 8) and a state in which two balls are placed therein alternately appear. This operating angle is called an "operating angle at which two balls are placed in the second track groove portion." Therefore, "an operating angle at which n balls can fit in the second track groove portion" means an operating angle at which, when the joint is rotated while maintaining that operating angle, n balls can fit in the second track groove portion, but (n+1) balls cannot fit in.

[0060] Of the balls 4 located in the first track groove portions 7a (7Aa, 7Ba), three balls 4 (135°), 4 (180°), and 4 (225°) located on the back side of the plane P including the joint center O have an included angle η1 that opens toward the opening side of the outer joint member 2, as shown by the arrows. The included angle η1 (180°) of the ball 4 (180°) is large, while the included angles η1 (135°) and η1 (225°) of the balls 4 (135°) and 4 (225°) are smaller than η1 (180°). As described above, the curvature centers O1 of the ball track center lines Xa and Ya of the first track groove portions 7a and 9a are not offset in the axial direction from the joint center O, but have a radial offset amount Fy and a small curvature radius r1. Therefore, the included angle η1 occurs in response to axial deviation from the plane P passing through the joint center O due to the operating angle. The ball 4 (90°) and the ball 4 (270°) shown in FIG. 8 are located on a plane P passing through the joint center O, so no included angle occurs.

[0061] In the state shown in Fig. 8, the included angle η2 (0°) with respect to the ball 4 (0°) closest to the opening is equal to the included angle η1 (180°) with respect to the ball 4 (180°) closest to the rear. In the present embodiment, in the state shown in Fig. 8, the included angle η2 (0°) is equal to the included angle η1 (180°), and the included angles η2 (45°) and η2 (315°) are equal to the included angles η1 (135°) and η1 (225°). In this way, in the fixed type constant velocity universal joint 1 according to the present embodiment, in the operating angle θ range in which two balls 4 fit in the second track portions 7b and 9b, the included angle η2 of the balls 4 located in the second track groove portions 7b and 9b is set equal to the included angle η1 of the balls located in the first track groove portions 7a and 9a. Specifically, the shapes of the track grooves 7, 9 (particularly the radial offset Fy of the center of curvature O1 of the ball track center lines Xa, Ya of the first track groove portions 7a, 9a and the radius of curvature r1) are set so that, at an operating angle θ where the number of balls 4 arranged in the second track groove portions 7b, 9b is two, the included angle η2 (0°) with respect to the ball 4 at a phase angle of 0° is equal to the included angle η1 (180°) with respect to the ball 4 at a phase angle of 180°. This makes it possible to suppress deviation from the bisecting plane of the cage 5 in the operating angle θ range where a plurality of balls 4 (approximately two) fit in the second track groove portions 7b, 9b corresponding to a high operating angle, thereby achieving a fixed type constant velocity universal joint that achieves both high efficiency and a large operating angle and has good NVH characteristics.

[0062] In the embodiment described above, a fixed constant velocity universal joint having eight balls has been exemplified, but the number of balls may be more than eight, for example, ten or more, as appropriate.

[0063] The present invention is not limited to the above-described embodiments, and can of course be embodied in various other forms without departing from the spirit of the present invention. The scope of the present invention is indicated by the claims, and further includes the equivalent meanings set forth in the claims, and all modifications within the scope of the claims.

[0064] DESCRIPTION OF SYMBOLS 1 Fixed type constant velocity universal joint 2 Outer joint member 3 Inner joint member 4 Ball 5 Cage 6 Spherical inner peripheral surface 7 Track groove 7a First track groove portion 7b Second track groove portion 8 Spherical outer peripheral surface 9 Track groove 9a First track groove portion 9b Second track groove portion 12 Spherical outer peripheral surface 13 Spherical inner peripheral surface M Plane including ball raceway center line N Joint axis A Connection portion between the ball raceway center line of the first track groove portion and the ball raceway center line of the second track groove portion of the outer joint member B Connection portion between the ball raceway center line of the first track groove portion and the ball raceway center line of the second track groove portion of the inner joint member Co Connection portion between the first track groove portion and the second track groove portion of the outer joint member Ci Connection portion between the first track groove portion and the second track groove portion of the inner joint member O Joint center O1 Oi2: Center of curvature of the ball track center line of the first track groove portion Oo2: Center of curvature of the ball track center line of the second track groove portion of the outer joint member X: Ball track center line of the track groove of the outer joint member Xa: Ball track center line of the first track groove portion Xb: Ball track center line of the second track groove portion Y: Ball track center line of the track groove of the inner joint member Ya: Ball track center line of the first track groove portion Yb: Ball track center line of the second track groove portion r1: Radius of curvature of the first track groove portion r2: Radius of curvature of the second track groove portion η1: Including angle η2: Including 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, with one axial side being the opening side and the other axial side being the rear side; an inner joint member having a plurality of track grooves formed on its spherical outer peripheral surface, each paired with the track grooves of the outer joint member; a plurality of balls that transmit torque by being interposed between the track grooves of the outer joint member and the track grooves of the inner joint member; and a cage that holds the balls in pockets and has a spherical outer peripheral surface and a spherical inner peripheral surface that fits with the spherical inner peripheral surface of the outer joint member and the spherical outer peripheral surface of the inner joint member, wherein the track grooves of the outer joint member have a first track groove portion (7a) and a second track groove portion (7b) located on the opening side of the first track groove (7a), and the first track groove portion (7a) has an arc-shaped ball raceway center line (Xa) with a center of curvature that is not offset in the axial direction from the joint center (O), a plane (M) including the ball raceway center line (Xa) is inclined in the circumferential direction with respect to a joint axis (N-N), and the ball raceway center lines (Xa) of the first track groove portions (7a) adjacent in the circumferential direction are inclined in opposite circumferential directions to each other, the second track groove portion (7b) has a ball raceway center line (Xb) having a shape different from that of the ball raceway center line (Xa) of the first track groove portion (7a), and a connection portion (A) between the ball raceway center line (Xa) of the first track groove portion (7a) and the ball raceway center line (Xb) of the second track groove portion (7b) is located on the opening side of the joint center (O), a ball raceway center line (Y) of the track groove of the inner joint member is formed in mirror symmetry with a ball raceway center line (X) of the mating track groove of the outer joint member, with respect to a plane (P) that includes the joint center (O) and is perpendicular to the joint axis (N-N) when the operating angle is 0°; and an angle (η2) between the balls located in the second track groove portions (7b, 9b) and an angle (η1) between the balls located in the first track groove portions (7a, 9a) are set to be equal in an operating angle range where a plurality of the balls fit in the second track groove portions (7b, 9b).

2. A fixed type constant velocity universal joint as described in claim 1, wherein the angle (η2) between the balls located in the second track groove portion (7b, 9b) and the angle (η1) between the balls located in the first track groove portion (7a, 9a) are set to be equal in the operating angle range in which two balls fit in the second track groove portion (7b, 9b).

3. A fixed constant velocity universal joint as described in claim 1, wherein the ball raceway center line (Xa, Ya) of the first track groove portion (7a, 9a) has a center of curvature (O1) that is offset radially toward the first track groove portion (7a, 9a) relative to the joint axis (N-N).

4. A fixed type constant velocity universal joint as set forth in claim 1, wherein the operating angle (θ1) at which the center of the ball closest to the opening is located at the connection portion (A) between the ball raceway center line (Xa) of the first track groove portion (7a) of the outer joint member and the ball raceway center line (Xb) of the second track groove portion (7b) is set to 15° or more.

5. A fixed type constant velocity universal joint as described in claim 1, wherein the ball raceway center line (Xb) of the second track groove portion (7b) of the outer joint member is an arc shape having a center of curvature (Oo2) radially outward from the ball raceway center line (Xb).

6. A fixed type constant velocity universal joint according to any one of claims 1 to 5, wherein the number of balls is eight or more.

Images