Fixed-type constant-velocity universal joint

Abstract

A fixed-type constant-velocity universal joint 1 comprises: an outer joint member 2 in which a plurality of track grooves 7 extending in a substantially axial direction are formed in a spherical inner peripheral surface 6 and which has an opening side and an interior side spaced apart from each other in the axial direction; an inner joint member 3 in which a plurality of track grooves 9 extending in a substantially axial direction are formed in a spherical outer peripheral surface 8; a plurality of balls 4 that are disposed between the track grooves 7 of the outer joint member 2 and the track grooves 9 of the inner joint member 3 corresponding to the track grooves 7 and that transmit torque; and a cage 5 that has pockets 5a for storing the balls 4 and has a spherical outer peripheral surface 12 and a spherical inner peripheral surface 13 which slide along the spherical inner peripheral surface 6 of the outer joint member 2 and the spherical outer peripheral surface 8 of the inner joint member 3, respectively. A ball raceway center line Y of each of the track grooves 9 of the inner joint member 3 is formed to be mirror-image symmetrical with a ball raceway center line X of the paired track groove 7 of the outer joint member 2 with respect to a plane P including a joint center O and orthogonal to a joint axial line at an operating angle of 0°. The fixed-type constant-velocity universal joint 1 is characterized in that the track grooves 7, 9 of the outer joint member 2 and / or the inner joint member 3 is provided with a recessed portion TRo, TRi over the entire region of the track grooves 7, 9 exceeding the axial position of each of the balls 4 at a maximum operating angle θ1.

Description

Fixed type constant velocity universal joint

[0001] The present invention relates to a fixed type constant velocity universal joint, which is used in power transmission systems of automobiles and various industrial machines, and relates to a fixed type constant velocity universal joint that allows only angular displacement between a driving shaft and a driven shaft.

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

[0003] As fixed type constant velocity universal joints, Zeppa-type constant velocity universal joints (also referred to as BJ type) and undercut free-type constant velocity universal joints (also referred to as UJ type) are known. In recent years, there is an 8-ball type fixed type constant velocity universal joint that is both lightweight and compact (Patent Document 1). In recent years, further higher efficiency has been demanded for the purpose of improving the environmental performance of automobiles. In order to achieve higher performance than the aforementioned 8-ball type fixed type constant velocity universal joint, a cross groove type fixed type constant velocity universal joint aiming at reducing contact between the spherical outer peripheral surface and spherical inner peripheral surface of a cage to achieve lower heat generation has been proposed (Patent Document 2). In addition, for the purpose of improving efficiency, the cage window clearance may be set as an intermediate fit (Patent Document 3).

[0004] Japanese Patent No. 3859267, Japanese Patent No. 5138449, Japanese Patent No. 6125186

[0005] In a fixed constant velocity universal joint, when assembling the inner joint member, retainer, and ball into the outer joint member, the assembly of the inner joint member, retainer, and ball needs to be tilted at an angle greater than the maximum operating angle. Therefore, the length of the track grooves in the outer and inner joint members is set to a length greater than the length required to achieve the maximum operating angle. We focused on the fact that if the length of the track groove is shortened to the length required to achieve the maximum operating angle in order to reduce weight and cost, the ball may fall out of the track groove during ball assembly and get caught on the end of the inner or outer joint member, potentially causing assembly failure. We also focused on the problem that if there is a gap between the retainer window and the ball, the ball is not restrained by the retainer window and is therefore more likely to fall out.

[0006] In view of the above-mentioned problems, the present inventors arrived at the present invention by conceiving of providing a recess in the track groove of the outer joint member and the inner joint member in the region where the ball moves beyond the maximum operating angle. The present invention aims to provide a fixed constant velocity universal joint that prevents the ball from falling out during ball assembly, shortens the length of the track groove finishing process, reduces processing costs, and ensures productivity.

[0007] As a technical means for achieving the aforementioned objectives, the present invention provides an outer joint member having a plurality of track grooves extending substantially axially on its spherical inner surface and an opening side and a back side spaced apart in the axial direction; an inner joint member having a plurality of track grooves extending substantially axially on its spherical outer surface; a plurality of balls that transmit torque, disposed between the track grooves of the outer joint member and the corresponding track grooves of the inner joint member; and a pocket for housing these balls, wherein the spherical inner surface of the outer joint member and the spherical outer surface of the inner joint member are respectively A fixed constant velocity universal joint is provided with a retainer having a spherical outer surface and a spherical inner surface that slide against each other, wherein the ball trajectory centerline of the track groove of the inner joint member is formed in mirror image symmetry with the ball trajectory centerline of the pair of track grooves of the outer joint member, with respect to a plane P that includes the joint center O and is perpendicular to the axis of the joint when the operating angle is 0°, and the track groove of at least one of the outer joint member and the inner joint member is provided with a recessed portion over the entire area of ​​the track groove region that exceeds the axial position of the ball at the maximum operating angle θ1. With the above configuration, it is possible to realize a fixed constant velocity universal joint that prevents the ball from falling out when the ball is assembled, shortens the length of the track groove finishing process, reduces processing costs, and ensures productivity.

[0008] The recessed portion is provided in the track groove of the outer joint member. This prevents the balls from falling out during ball assembly, shortens the length of the track groove finish on the outer joint member, and enables the realization of a fixed constant-velocity universal joint that reduces processing costs while ensuring productivity.

[0009] The aforementioned recess is provided in the track groove of the inner joint member. This prevents the ball from falling out during ball assembly, shortens the length of the track groove finish on the inner joint member, and enables the realization of a fixed constant-velocity universal joint that reduces processing costs while ensuring productivity.

[0010] The recessed portion is provided in both the track groove of the outer joint member and the track groove of the inner joint member. This prevents the balls from falling out during ball assembly, while shortening the length of the track groove finishing process for both the outer and inner joint members, thereby realizing a fixed constant-velocity universal joint that promotes reduced processing costs and improved productivity.

[0011] By making the depth of the recessed area 0.3 mm or less, the ball can smoothly return from the recessed area to the track groove when it is installed.

[0012] A key feature of this design is that the pocket gap of the retainer housing the ball is fitted in the middle. Even if the pocket gap becomes a positive gap, the recess prevents the ball from falling out, thus enabling further reduction of torque loss, heat generation, and increased efficiency of the fixed constant velocity universal joint.

[0013] The track grooves of both the outer and inner joint members described above have an arc-shaped ball trajectory centerline, and the plane containing the arc-shaped ball trajectory centerline and its center of curvature is inclined circumferentially with respect to the axis of the joint, and the direction of this inclination is formed in opposite directions in adjacent track grooves in the circumferential direction. This makes it possible to realize a fixed constant velocity universal joint of the track groove intersection type that promotes reduced processing costs and ensures productivity, and has a good balance of power transmission for rotation in both left and right directions.

[0014] The track grooves of the outer and inner joint members, which extend substantially in the axial direction, each have an arc-shaped ball trajectory centerline. This arc-shaped ball trajectory centerline is not inclined in the circumferential direction with respect to the joint axis, and the center of curvature of the arc-shaped ball trajectory centerline of the track groove of the outer joint member and the center of curvature of the arc-shaped ball trajectory centerline of the track groove of the inner joint member are offset by an equal amount on the opposite side of the axial direction with respect to the joint center O. This makes it possible to realize a Zeppa-type fixed constant-velocity universal joint that prevents balls from falling out during ball assembly, shortens the length of the track groove finishing process, reduces processing costs, and ensures productivity.

[0015] According to the present invention, it is possible to realize a fixed constant velocity universal joint that prevents balls from falling out during ball assembly, shortens the length of the track groove finishing process, reduces processing costs, and ensures productivity.

[0016] This is a partial longitudinal cross-sectional view of a fixed constant velocity universal joint according to the first embodiment of the present invention. This is a front view of the fixed constant velocity universal joint shown in Figure 1A, viewed from the axial direction. This is a partial longitudinal cross-sectional view of the outer joint member of the fixed constant velocity universal joint shown in Figures 1A and 1B. This is a front view of the outer joint member shown in Figure 2A, viewed from the axial direction. This is a front view of the inner joint member of the fixed constant velocity universal joint shown in Figures 1A and 1B, viewed from one side in the axial direction. This is a side view of the inner joint member of the fixed constant velocity universal joint shown in Figures 1A and 1B, viewed from the outer circumference. This is a rear view of the inner joint member of the fixed constant velocity universal joint shown in Figures 1A and 1B, viewed from the other side in the axial direction. This is a partial longitudinal cross-sectional view showing details of the track groove of the outer joint member shown in Figure 1A. This is a longitudinal cross-sectional view showing details of the track groove of the inner joint member shown in Figure 1A. This is a longitudinal cross-sectional view showing details of the gap between the pocket and the ball of the retainer shown in Figure 1A. This is a schematic diagram showing the fixed constant velocity universal joint shown in Figure 1A in the state where the maximum operating angle is taken. This is a partial longitudinal cross-sectional view showing the ball assembly state into the outer joint member of the fixed constant velocity universal joint shown in Figure 1A. This is a partially enlarged longitudinal cross-sectional view of the fixed constant velocity universal joint shown in Figure 1A. This is a cross-sectional view along line A1-A1 in Figure 9A. This is a cross-sectional view along line A2-A2 in Figure 9A. This is a partial longitudinal cross-sectional view of the fixed constant velocity universal joint according to the second embodiment of the present invention. This is a front view of the fixed constant velocity universal joint shown in Figure 10A, viewed from the axial direction. This is a partial longitudinal cross-sectional view of the fixed constant velocity universal joint according to the third embodiment of the present invention. This is a front view of the fixed constant velocity universal joint shown in Figure 11A, viewed from the axial direction.

[0017] Embodiments of the present invention will be described based on the drawings.

[0018] First, the basic configuration of the fixed constant velocity universal joint 1 of the track groove crossing type according to the first embodiment of the present invention will be described based on Figures 1 to 5. The fixed constant velocity universal joint 1 mainly consists of an outer joint member 2, an inner joint member 3, a ball 4, and a retainer 5.

[0019] Eight track grooves 7 are formed on the spherical inner surface of the outer joint member 2, and eight track grooves 9 are formed on the spherical outer surface of the inner joint member 3 (see Figure 1B). On the inner surface of the outer joint member 2, spherical portions 6 remain between the track grooves 7 in the circumferential direction, and on the outer surface of the inner joint member 3, spherical portions 8 remain between the track grooves 9 in the circumferential direction (see Figure 1A). The center of curvature of the spherical portions 6 on the inner surface of the outer joint member 2 and the center of curvature of the spherical portions 8 on the outer surface of the inner joint member 3 both coincide with the joint center O. Hereafter, the spherical portions 6 on the inner surface of the outer joint member 2 will also be called the spherical inner surface 6, and the spherical portions 8 on the outer surface of the inner joint member 3 will also be called the spherical outer surface 8. One ball 4 is placed between each of the radially opposing track grooves 7 and 9. The retainer 5 has a spherical outer surface 12 that fits into the spherical portion 6 on the inner surface of the outer joint member 2, a spherical inner surface 13 that fits into the spherical portion 8 on the outer surface of the inner joint member 3, and eight pockets 5a that each hold one ball 4. The retainer 5 has a pair of annular portions 5b and 5c provided on both sides of the pockets 5a in the axial direction, and a columnar portion 5e (see Figure 1B) that connects the pair of annular portions 5b and 5c in the axial direction. At the axial end of the inner surface of the retainer 5, in the illustrated example, a cylindrical surface 5d centered on the axis N-N is provided on the inner surface of one of the annular portions 5c.

[0020] In the following, the opening side (right side in Figure 1A) of the cup-shaped outer joint member 2 in the axial direction will be referred to as the "joint opening side," and the opposite side (left side in Figure 1A) will be referred to as the "joint rear side." Furthermore, in order to accurately describe the form and shape of the track grooves 7 and 9, such as their inclination and curvature, this specification will use 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 inclination of the track groove is the same as the inclination of the ball trajectory centerline, and the arc-shaped or straight shape of the track groove is the same as the arc-shaped or straight shape of the ball trajectory centerline.

[0021] As shown in Figure 1A, the track groove 7 of the outer joint member 2 has a ball trajectory centerline X. Specifically, the track groove 7 consists of a first track groove portion 7a having an arc-shaped ball trajectory centerline Xa and a second track groove portion 7b having a linear ball trajectory centerline Xb. The center of curvature of the ball trajectory centerline Xa of the first track groove portion 7a (i.e., the center of the sphere containing all the ball trajectory centerlines Xa) is not axially offset with respect to the joint center O (the intersection of the plane P containing the centers of the eight balls 4 and the axis N-N when the operating angle is 0°). In this case, the center of curvature of the ball trajectory centerline Xa of the first track groove portion 7a and the joint center O coincide. The ball trajectory centerline Xa of the first track groove portion 7a and the ball trajectory centerline Xb of the second track groove portion 7b are smoothly continuous. In other words, the ball trajectory centerline Xb of the second track groove 7b coincides with the tangent to the ball trajectory centerline Xa of the first track groove 7a at the joint opening side end.

[0022] The track groove 9 of the inner joint member 3 has a ball trajectory centerline Y. Specifically, the track groove 9 consists of a first track groove portion 9a having an arc-shaped ball trajectory centerline Ya, and a second track groove portion 9b having a linear ball trajectory centerline Yb. The center of curvature of the ball trajectory centerline Ya of the first track groove portion 9a (i.e., the center of the sphere containing all the ball trajectory centerlines Ya) is not offset axially with respect to the joint center O. Similar to the ball trajectory centerline Xa of the first track groove portion 7a of the outer joint member 2, in this case, the center of curvature of the ball trajectory centerline Ya of the first track groove portion 9a coincides with the joint center O. The ball trajectory centerline Ya of the first track groove portion 9a and the ball trajectory centerline Yb of the second track groove portion 9b are smoothly connected. In other words, the ball trajectory centerline Yb of the second track groove 9b coincides with the tangent to the ball trajectory centerline Ya of the first track groove 9a at the joint's inner end.

[0023] 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 is in contact with the side surface of the track grooves 7 and 9, slightly away from the groove bottom. Alternatively, the cross-sectional shapes of the track grooves 7 and 9 may be made into an arc shape, resulting in so-called circular contact between the track grooves 7 and 9 and the ball 4.

[0024] As shown in Figures 2 and 3, the track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3 are inclined circumferentially with respect to the axial direction (the direction of the joint axis N-N). Adjacent track grooves in the circumferential direction are inclined in opposite directions with respect to the axial direction. Track grooves 7 and 9 facing each other in the radial direction are inclined in opposite directions with respect to the axial direction, and one ball 4 is placed at each of their intersections. The track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3 are inclined circumferentially with respect to the axial direction (the direction of the joint axis N-N). In this specification and claims, a track groove extending substantially in the axial direction is used to include a track groove inclined circumferentially with respect to the axial direction (the direction of the joint axis N-N) as described above.

[0025] Based on Figure 2, the track grooves 7 of the outer joint member 2 will be described in detail. The track grooves 7 of the outer joint member 2 are designated as track grooves 7A and 7B based on their different inclination directions. Furthermore, the entire track groove of the outer joint member 2 is designated as 7, with the first track groove portion designated as 7a and the second track groove portion as 7b. Additionally, to distinguish between track grooves with different inclination directions, they are designated as 7A and 7B, with the first track groove portions designated as 7Aa and 7Ba, and the second track groove portions as 7Ab and 7Bb, respectively. The track grooves of the inner joint member 3, which will be described later, are designated in a similar manner.

[0026] As shown in Figure 2A, the plane M containing the ball trajectory centerline X of the track groove 7A (more specifically, the plane containing the ball trajectory centerline Xa and its center of curvature of the first track groove portion 7Aa of the track groove 7A) is inclined by an angle γ with respect to the joint axis N-N. The track groove 7B adjacent to the track groove 7A in the circumferential direction is not shown in the figure, but the plane containing the ball trajectory centerline X of the track groove 7B (more specifically, the plane containing the ball trajectory centerline Xa and its center of curvature of the first track groove portion 7Ba of the track groove 7B) is 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. A recessed portion TRo is formed at the far end of the track groove 7. Details of the recessed portion TRo will be described later.

[0027] Next, the track grooves 9 of the inner joint member 3 will be described in detail based on Figure 3. The track grooves 9 of the inner joint member 3 are labeled as track grooves 9A and 9B, respectively, due to the difference in their inclination direction. As shown in Figure 3B, the plane Q containing the ball trajectory centerline Y of track groove 9A (more specifically, the plane containing the ball trajectory centerline Ya of the first track groove portion 9Aa of track groove 9A and its center of curvature) is inclined by an angle γ with respect to the joint axis N-N. The track groove 9B, which is circumferentially adjacent to track groove 9A, is not shown in the figure, but the plane Q containing the ball trajectory centerline Y of track groove 9B (more specifically, the plane containing the ball trajectory centerline Ya of the first track groove portion 9Ba of track groove 9B and its center of curvature) is inclined by an angle γ with respect to the joint axis N-N in the opposite direction to the inclination direction of track groove 9A. The ball trajectory centerline Y of each track groove 9 of the inner joint member 3 is formed in a mirror image symmetric with the ball trajectory centerline X (see Figure 1A) of the track groove 7 of the radially opposing 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°. A recessed portion TR is formed at the far end of the track groove 9. Details of the recessed portion TR will be described later.

[0028] Based on Figure 4, the details of the track groove 7A of the outer joint member 2 will be explained. Figure 4 is a cross-sectional view of the track groove 7A of Figure 2A as seen in a plane M that includes the ball trajectory centerline X. Therefore, strictly speaking, Figure 4 is not a longitudinal section view in a plane that includes the axis N-N of the joint, but rather a section inclined by an angle γ. Figure 4 shows the track groove 7A of the outer joint member 2, but the track groove 7B is the same as the track groove 7A except that the inclination direction is opposite, so its explanation will be omitted.

[0029] The track groove 7A consists of a first track groove section 7Aa having an arc-shaped ball trajectory centerline Xa with a curvature center that is not axially offset with respect to the joint center O, and a second track groove section 7Ab having a linear ball trajectory centerline Xb. The linear ball trajectory centerline Xb of the second track groove section 7Ab smoothly connects to the joint opening side end of the ball trajectory centerline Xa of the first track groove section 7Aa. In the illustrated example, since the connection point A of the ball trajectory centerlines Xa and Xb is located on the joint opening side of the joint center O, the linear ball trajectory centerline Xb is inclined to approach the joint axis N-N (see Figure 1A) as it approaches the joint opening side. This ensures the effective track length at the maximum operating angle and suppresses the wedge angle from becoming excessive. Figure 1A shows the track grooves 7 and 9 with an inclination angle γ of 0°.

[0030] As shown in Figure 4, let L be the straight line connecting the connection point A of the ball trajectory centerlines Xa and Xb to the joint center O. The axis of the joint N'-N' projected onto the plane M (see Figure 2A) containing the ball trajectory centerline X of the track groove 7A is inclined by γ with respect to the joint axis N-N, and let β' be the angle between the perpendicular K at the joint center O of the axis N'-N' and the straight line L. The above perpendicular K lies on the plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N. Therefore, the angle β that the straight line L makes with respect to the plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N is given by sinβ = sinβ' × cosγ.

[0031] Similarly, the details of the track groove 9A will be explained based on the longitudinal section of the inner joint member 3, as shown in Figure 5. The longitudinal section in Figure 5 is a cross-sectional view taken in plane Q that includes the ball trajectory center line Y of the track groove 9A in Figure 3B, as described above. Therefore, as with Figure 4, strictly speaking, it is not a longitudinal section in a plane that includes the joint axis N-N, but rather a cross-section that is inclined by an angle γ. Figure 5 shows the track groove 9A of the inner joint member 3, but the track groove 9B is the same as the track groove 9A except that the inclination direction is opposite, so its explanation will be omitted.

[0032] The track groove 9A consists of a first track groove section 9Aa having an arc-shaped ball trajectory centerline Ya with a curvature center that is not axially offset with respect to the joint center O, and a second track groove section 9Ab having a linear ball trajectory centerline Yb. The linear ball trajectory centerline Yb of the second track groove section 9Ab smoothly connects to the joint-side end of the ball trajectory centerline Ya of the first track groove section 9Aa. In the illustrated example, since the connection point B of the ball trajectory centerlines Ya and Yb is located further back in the joint than the joint center O, the linear ball trajectory centerline Yb is inclined to approach the joint axis N-N (see Figure 1A) as it moves further back in the joint. This ensures the effective track length at the maximum operating angle and prevents the wedge angle from becoming excessive. As mentioned above, Figure 1A shows the track grooves 7 and 9 with an inclination angle γ of 0°.

[0033] As shown in Figure 5, let R be the line connecting the connection point B of the ball trajectory centerlines Ya and Yb to the joint center O. The axis of the joint N'-N' projected onto the plane Q (see Figure 3B) containing the ball trajectory centerline Y of the track groove 9A is inclined by γ with respect to the joint axis N-N, and let β' be the angle between the perpendicular K at the joint center O of the axis N'-N' and the line R. The above perpendicular K lies on the plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N. Therefore, the angle β that the line R makes with respect to the plane P that includes the joint center O when the operating angle is 0° and is perpendicular to the joint axis N-N is given by sinβ = sinβ' × cosγ.

[0034] Next, we will explain the angle β that the lines L and R make 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°. When the operating angle θ is taken, the ball 4 moves by θ / 2 with respect to a plane that includes the joint center O and is perpendicular to the axis of the outer joint member 2 (or inner joint member 3). The angle β is determined from half of the frequently used operating angle, and the range of the track groove that the ball 4 contacts within the range of the frequently used operating angle is determined. Here, we define the frequently used operating angle. First, the normal operating angle of the joint is the operating angle that occurs in a fixed constant velocity universal joint of the front drive shaft when the steering is in the straight position in a car with one occupant on a horizontal, flat road surface. The normal operating angle is selected and determined according to the design conditions of each vehicle type. Furthermore, the frequently used operating angle is not the high operating angle that occurs when the vehicle makes a right or left turn at an intersection, for example, but rather the operating angle that occurs in the fixed constant velocity universal joint when continuously driving on curved roads. This is also determined according to the design conditions of each vehicle type, but it is larger than the normal operating angle. In this embodiment, the angle β is set in the range of 8° to 12°.

[0035] Due to the angle β described above, in Figure 4, the connection point A between the ball trajectory centerline Xa of the first track groove 7Aa and the ball trajectory centerline Xb of the second track groove 7Ab becomes the center position of the ball when it moves furthest towards the joint opening along the axial direction at the most frequently used operating angle. Similarly, in the inner joint member 3, in Figure 5, the connection point B between the ball trajectory centerline Ya of the first track groove 9Aa and the ball trajectory centerline Yb of the second track groove 9Ab becomes the center position of the ball when it moves furthest towards the back of the joint along the axial direction at the most frequently used operating angle. With this setting, in the range of the most frequently used operating angle, the ball 4 is located in 7Ba and 9Ba (see Figures 2 and 3), which are in the opposite direction of inclination to the first track grooves 7Aa and 9Aa of the outer joint member 2 and the inner joint member 3. The above is the basic configuration of the track groove crossing type fixed constant velocity universal joint 1 according to this embodiment.

[0036] The track groove crossing type fixed constant velocity universal joint 1 according to this embodiment has the following configuration in order to further suppress torque loss, heat generation, and improve efficiency. Figure 6 is a longitudinal cross-sectional view of the retainer showing the fit state between the ball and the retainer pocket. The retainer 5 has eight pockets 5a formed in the circumferential direction. The surfaces of the pockets 5a facing each other in the axial direction are the surfaces that hold the ball 4, and the axial dimension between these two surfaces is denoted as H. When the diameter of the ball 4, shown by the dashed line, is Db, the pocket clearance δ is expressed by the following formula: Pocket clearance δ = Axial dimension of the retainer pocket H - Ball diameter Db Therefore, if the ball diameter Db is greater than the axial dimension H of the pocket, the clearance is negative, and conversely, if the ball diameter Db is smaller than the axial dimension H of the pocket, the clearance is positive.

[0037] In conventional fixed constant velocity universal joints, due to issues such as bending operability during assembly, the fit between the ball and the retainer pocket was set to a tight fit, meaning the pocket clearance was set to a negative clearance. However, in this embodiment, the fit between the ball 4 and the retainer pocket 5a is set to a pocket clearance δ that spans from a tight fit to a clearance fit, i.e., an intermediate fit. In this embodiment of fixed constant velocity universal joint 1 where the track grooves intersect, even if the pocket clearance δ is set to a positive clearance, the pocket load of the retainer 5 is generated alternately in the circumferential direction and balanced, so the geometric constraint of the retainer 5 on the bisecting plane is stable, and it is thought that the decrease in bending operability during joint assembly is eliminated.

[0038] Next, Figure 7 shows the fixed constant velocity universal joint 1 according to this embodiment in its maximum operating angle state. The maximum operating angle θ1 is the maximum operating angle that the fixed constant velocity universal joint 1 is guaranteed to be usable for driving when mounted on a vehicle, and is determined by design for each product type. Specifically, at the maximum operating angle θ1, a small clearance (for example, a gap of about 0.2 mm to 0.5 mm) is provided between the outer circumferential surface of the minimum shaft diameter d of the shaft 11 and the inlet chamfer 10 of the outer joint member 2, allowing for relative rotation. Furthermore, the maximum operating angle θ1 in the present invention is, for example, the maximum operating angle that occurs in a fixed constant velocity universal joint 1 mounted on the steering wheel side of a front-wheel drive vehicle, and is usually a high operating angle of 40° or more. The maximum operating angle (θ1) in this specification and claims is used in this sense.

[0039] Furthermore, Figure 8 shows the state of the fixed constant velocity universal joint 1 of this embodiment when the ball is assembled. As shown in the figure, when the ball is assembled, the shaft 11 (see Figure 7) is not attached to the inner joint member 3. When assembling the ball, a ball assembly angle θ2 greater than the maximum operating angle θ1 is required, so if the shaft 11 is attached, the shaft 11 will interfere with the open end of the outer joint member 2. For this reason, an inner ring oscillating tool (not shown) is inserted into the inner joint member 3 and tilted. Specifically, after inserting the assembly of the inner joint member 3 and the retainer 5 into the spherical inner circumferential surface 6 of the outer joint member 2, the inner joint member 3 is tilted at an angle θ2 greater than the maximum operating angle θ1 (for example, 60° or more), creating a gap between the open end of the outer joint member 2 and the pocket 5a of the retainer 5 into which the ball 4 can be inserted, and the ball 4 is assembled into the pocket 5a from this gap.

[0040] The overall configuration of the fixed constant velocity universal joint 1 according to this embodiment is as described above. Next, the characteristic configuration of the fixed constant velocity universal joint 1 according to this embodiment will be described below. <Characteristic configuration> At least one of the track grooves of the outer joint member and the inner joint member has a recessed portion in the entire area of ​​the track groove region that exceeds the axial position of the ball at the maximum operating angle θ1.

[0041] The characteristic configuration of this embodiment will be described in detail with reference to Figure 9. Figure 9A is an enlarged vertical cross-sectional view of a part of the fixed constant velocity universal joint of Figure 1A, which is the first embodiment; Figure 9B is a cross-sectional view along line A1-A1 in Figure 9A; and Figure 9C is a horizontal cross-sectional view along line A2-A2 in Figure 9A. However, although the ball 4 is not located in both the cross-sections of the track groove 7 of the outer joint member 2 and the track groove 9 of the inner joint member 3 along lines A1-A1 and A2-A2 in Figure 9A, the ball 4 is shown as a dashed line and superimposed on the cross-section to make it easier to understand the relationship between the recessed portions TRo and TRi and the ball 4.

[0042] As shown in Figure 9A, recesses TRo and TRi are formed over the entire area of ​​the track grooves 7 and 9, exceeding the axial position of the ball at the maximum operating angle θ1 (a length corresponding to the maximum operating angle θ1 / 2). Both the recess TRo in the track groove 7 of the outer joint member 2 and the recess TRi in the track groove 9 of the inner joint member 3 include the area on the inner side of the joint (a length corresponding to the ball installation angle θ2 / 2) necessary for ball installation.

[0043] In the cross-section along the line A1-A1 in Figure 9A, which represents the operating angle range, the ball 4 and the track grooves 7 and 9 are in contact, as shown in Figure 9B. In the region where the recessed portions TRo and TRi, which represent the assembly angle range, are provided, there is a gap between the ball 4 and the recessed portions TRo and TRi of the track grooves 7 and 9, as shown in Figure 9C, which represents the cross-section along the line A2-A2 in Figure 9A. The recessed portions TRo and TRi are recessed by a small amount of space from the finished surface of the track grooves 7 and 9 within the operating angle range, with a maximum depth of approximately 0.3 mm. The finished surface of the track grooves 7 and 9 and the recessed portions TRo and TRi are smoothly connected by an arc shape or tapered shape. This allows the ball 4 to smoothly return from the recessed portions TRo and TRi to the finished surface of the track grooves 7 and 9 when the ball is assembled.

[0044] In the track grooves 7 of the outer joint member 2 and the track grooves 9 of the inner joint member 3, recesses TRo and TRi are provided in the entire region where the balls 4 move beyond the maximum operating angle θ1. Since the recesses TRo and TRi are provided before finishing the track grooves 7 and 9, the finishing length of the track grooves 7 and 9 can be shortened, and cost reduction can be achieved. In addition, since the recesses TRo and TRi are provided in the entire region where the balls 4 move beyond the maximum operating angle θ1, falling-off of the balls during ball assembling can be prevented, and productivity can be ensured.

[0045] A fixed constant velocity universal joint according to a second embodiment of the present invention will be described with reference to FIG. 10. FIG. 10A is a partial longitudinal sectional view of the fixed constant velocity universal joint of the present embodiment, and FIG. 10B is a front view of the fixed constant velocity universal joint of FIG. 10A viewed from the axial direction. This fixed constant velocity universal joint is also of a track groove crossing type. In the fixed constant velocity universal joint of the present embodiment, the track grooves of the outer joint member and the inner joint member consist only of arcuate ball track centerlines. The overall structure and effects shown in FIGS. 1 to 9 of the first embodiment described above are the same for the fixed constant velocity universal joint of the present embodiment, and therefore apply mutatis mutandis. Parts having the same functions as those of the fixed constant velocity universal joint according to the first embodiment are denoted by the same reference numerals, and only the main points will be described.

[0046] As shown in FIGS. 10A and 10B, the fixed constant velocity universal joint 1 of the present embodiment mainly includes an outer joint member 2, an inner joint member 3, balls 4 for transmitting torque, and a cage 5 for holding the balls 4. The track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3 consist only of arcuate ball track centerlines X and Y. In the track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3, recesses TRo and TRi are provided in the entire region of the track grooves 7 and 9 beyond the axial position of the balls 4 at the maximum operating angle θ1. Similarly to the fixed constant velocity universal joint of the first embodiment described above, it has the following characteristic configuration. <Characteristic Configuration> At least one of the track grooves of the outer joint member and the inner joint member is provided with a recess in the entire region of the track groove beyond the axial position of the ball at the maximum operating angle θ1.

[0047] In the fixed type constant velocity universal joint 1 of the track groove intersection type according to the first embodiment and the second embodiment, an example is illustrated in which the centers of curvature of the arcuate ball track center lines Xa, Ya, X, Y are not offset with respect to the joint center O. However, the present invention is not limited thereto, and can also be applied to a structure in which the centers of curvature of the arcuate ball track center lines Xa, Ya, X, Y have a small offset amount with respect to the joint center O.

[0048] A fixed type constant velocity universal joint according to a third embodiment of the present invention will be described with reference to FIG. 11. FIG. 11A is a partial longitudinal sectional view of the fixed type constant velocity universal joint of the present embodiment, and FIG. 11B is a front view of the fixed type constant velocity universal joint of FIG. 11A as viewed from the axial direction. This fixed type constant velocity universal joint 1 is a Rzeppa-type constant velocity universal joint, and mainly includes an outer joint member 2, an inner joint member 3, balls 4 that transmit torque, and a cage 5 that retains the balls 4. With respect to the description of the state of the pocket clearance (FIG. 6), the state of the maximum operating angle (FIG. 7), the ball assembled state (FIG. 8), the formation state of the recessed portion (FIG. 9) and their functions and effects in the fixed type constant velocity universal joint according to the first embodiment described above, the same applies to the fixed type constant velocity universal joint of the present embodiment, so the corresponding description is applied mutatis mutandis. Portions having the same functions as those of the fixed type constant velocity universal joint according to the first embodiment are denoted by the same reference numerals, and only the main points will be described. The fixed type constant velocity universal joint 1 of the present embodiment is a Rzeppa-type constant velocity universal joint. In this fixed type constant velocity universal joint 1, the arcuate ball track center lines X, Y of the track grooves 7, 9 of the outer joint member 2 and the inner joint member 3 are not inclined in the circumferential direction with respect to the axis of the joint. The term "track groove extending substantially in the axial direction" used in the present specification and claims is meant to include track grooves that are not inclined in the circumferential direction with respect to the axis of the joint described above.

[0049] As shown in FIGS. 11A and 11B, in the fixed type constant velocity universal joint 1 of the present embodiment, the balls 4 that transmit torque are incorporated into the track grooves 7, 9 having arcuate ball track center lines X, Y extending in the axial direction of the outer joint member 2 and the inner joint member 3, and are retained by the cage 5. The centers of curvature of the arcuate ball track center lines X, Y of the track grooves 7, 9 are axially offset by an equal amount f to the opposite side with respect to the joint center O.

[0050] In the fixed constant velocity universal joint 1 of this embodiment, the track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3 are provided with recessed portions TRo and TRi throughout the entire area of ​​the track grooves 7 and 9 that exceeds the axial position of the ball 4 at the maximum operating angle θ1, and have the following characteristic configuration, similar to the fixed constant velocity universal joint of the first embodiment described above. <Characteristic configuration> At least one of the track grooves of the outer joint member and the inner joint member is provided with a recessed portion throughout the entire area of ​​the track groove that exceeds the axial position of the ball at the maximum operating angle θ1.

[0051] In the embodiments described above, eight balls were used as an example for the fixed constant velocity universal joint, but the number of balls is not limited to this, and six or more balls can be used as appropriate.

[0052] In the third embodiment described above, a Zeppa-type constant velocity universal joint was given as an example of a fixed constant velocity universal joint in which the arc-shaped ball trajectory centerline of the track groove is not inclined in the circumferential direction with respect to the axis of the joint. However, the embodiment is not limited to this and can be appropriately implemented in an undercut-free type fixed constant velocity universal joint as well.

[0053] The present invention is not limited in any way to the embodiments described above, and can be implemented in various other forms without departing from the spirit of the invention. The scope of the present invention is indicated by the claims, and includes all modifications within the meaning and scope of the equivalents set forth in the claims.

[0054] 1 Fixed constant velocity universal joint 2 Outer joint member 3 Inner joint member 4 Ball 5 Retainer 6 Spherical inner surface 7 Track groove 7a First track groove section 7b Second track groove section 8 Spherical outer surface 9 Track groove 9a First track groove section 9b Second track groove section 12 Spherical outer surface 13 Spherical inner surface M Plane containing the ball trajectory centerline N Axis of the joint O Center of the joint P Plane TRo Recessed section TRi Recessed section X Ball trajectory centerline of the track groove of the outer joint member Xa Ball trajectory centerline of the first track groove section Xb Ball trajectory centerline of the second track groove section Y Ball trajectory centerline of the track groove of the inner joint member Ya Ball trajectory centerline of the first track groove section Yb Ball trajectory centerline of the second track groove section f Offset amount θ1 Maximum operating angle θ² Ball insertion angle

Claims

1. A fixed constant velocity universal joint comprising: an outer joint member having multiple track grooves extending substantially axially formed on its spherical inner surface and an opening side and a back side spaced apart in the axial direction; an inner joint member having multiple track grooves extending substantially axially formed on its spherical outer surface; a plurality of balls positioned between the track grooves of the outer joint member and the corresponding track grooves of the inner joint member to transmit torque; and a retainer having a pocket for housing these balls, and having a spherical outer surface and a spherical inner surface that slide in contact with the spherical inner surface of the outer joint member and the spherical outer surface of the inner joint member, respectively, wherein the ball trajectory centerline of the track groove of the inner joint member is formed in mirror image symmetry with the ball trajectory centerline of the pair of track grooves of the outer joint member, with respect to a plane (P) that includes the joint center (O) and is perpendicular to the axis of the joint when the operating angle is 0°, A fixed constant velocity universal joint characterized in that at least one of the track grooves of the outer joint member and the inner joint member has a recessed portion that extends over the entire area of ​​the track groove region beyond the axial position of the ball at the maximum operating angle (θ1).

2. The fixed constant velocity universal joint according to claim 1, characterized in that the recessed portion is provided in the track groove of the outer joint member.

3. The fixed constant velocity universal joint according to claim 1, characterized in that the recessed portion is provided in the track groove of the inner joint member.

4. The fixed constant velocity universal joint according to claim 1, characterized in that the recessed portion is provided in both the track groove of the outer joint member and the track groove of the inner joint member.

5. The fixed constant velocity universal joint according to claim 1, characterized in that the depth of the recessed portion is 0.3 mm or less.

6. The fixed constant velocity universal joint according to claim 1, characterized in that the pocket gap of the retainer that houses the ball is fitted in the middle.

7. The fixed constant velocity universal joint according to any one of claims 1 to 6, characterized in that the track grooves extending substantially in the axial direction of the outer joint member and the inner joint member each have an arc-shaped ball trajectory centerline, and the plane containing the arc-shaped ball trajectory centerline and its center of curvature is inclined circumferentially with respect to the axis of the joint, and the direction of inclination is formed in opposite directions for adjacent track grooves in the circumferential direction.

8. The fixed constant velocity universal joint according to any one of claims 1 to 6, characterized in that the track grooves of the outer joint member and the inner joint member, which extend substantially in the axial direction, each have an arc-shaped ball track centerline, the arc-shaped ball track centerline is not inclined in the circumferential direction with respect to the axis of the joint, and the center of curvature of the arc-shaped ball track centerline of the track groove of the outer joint member and the center of curvature of the arc-shaped ball track centerline of the track groove of the inner joint member are offset by an equal amount on the opposite side in the axial direction with respect to the joint center (O).

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