Fixed-type constant-velocity universal joint

Abstract

A fixed-type constant-velocity universal joint 1 comprises: an outer joint member 2 and an inner joint member 3 in which a plurality of track grooves 7 each having a circular arc-shaped portion extending substantially in the axial direction are formed; a plurality of balls 4 disposed between the track grooves 7, 9 of both of the joint members 2, 3; and a retainer 5 having a pocket 5a for storing the balls 4, and having a spherical outer peripheral surface 12 and a spherical inner peripheral surface 13 respectively slidably contacting a spherical inner peripheral surface 6 of the outer joint member 2 and a spherical outer peripheral surface 8 of the inner joint member 3. The fixed-type constant-velocity universal joint 1 is characterized in that: a ball raceway center line Y of the track groove 9 of the inner joint member 3 is formed in mirror-image symmetry with a ball raceway center line X of the corresponding track groove 7 of the outer joint member 2 with reference to a plane P that includes a joint center O and is perpendicular to a joint axis N-N in a state where the operating angle is 0°; and the track groove 7 of the outer joint member 2 has a relief portion Tr which is formed in a back-side area required for ball insertion and starting from an axial ball 4 position at the maximum operating angel θ1, the area of the track groove 7 being located between a radial position Sr leaving a ball 4 contact point C and the spherical inner peripheral surface 6, wherein the track groove 7 has a portion in which the radial dimension E of the relief portion Tr is larger than the radial dimension F of a chamfered portion Tc having a substantially constant width and provided in a substantially whole area in the axial direction between the spherical inner peripheral surface 6 of the outer joint member 2 and the track groove 7.

Description

Fixed constant velocity universal joint

[0001] This invention relates to a fixed constant velocity universal joint, which is used in power transmission systems of automobiles and various industrial machines, and which allows only angular displacement between the two shafts, the drive side and the driven side.

[0002] For example, the front drive shafts of automobiles typically incorporate a sliding constant velocity universal joint on the inboard side (differential side), which has a relatively small maximum operating angle but allows for axial displacement while operating. On the outboard side (wheel side), where the wheels are steered, a fixed constant velocity universal joint is incorporated, which allows for a large operating angle but does not allow for axial displacement.

[0003] As fixed constant velocity universal joints, Zeppa-type constant velocity universal joints (also called BJ type) and undercut-free type constant velocity universal joints (also called UJ type) are known. In recent years, there has been a fixed constant velocity universal joint with eight balls that is lightweight and compact (Patent Document 1). As shown in Figure 22, this fixed constant velocity universal joint 101 is a Zeppa-type constant velocity universal joint and mainly consists of an outer joint member 102, an inner joint member 103, torque-transmitting balls 104, and a cage 105 that holds the balls 104. Eight torque-transmitting balls 104 are incorporated into arc-shaped track grooves 107 and 109 that extend axially in the outer joint member 102 and the inner joint member 103, and are held by the cage 105. The centers of curvature of the arc-shaped track grooves 107 and 109 are offset axially by an equal amount f on the opposite side of the joint center O.

[0004] Recently, with the aim of improving the environmental performance of automobiles, there is a demand for even higher efficiency. To achieve even higher performance than the aforementioned eight-ball type fixed constant velocity universal joint, a track groove intersecting type fixed constant velocity universal joint, as shown in Figure 23, has been proposed (Patent Document 2), which aims to reduce heat generation by reducing contact between the spherical outer surface and spherical inner surface of the cage. This fixed constant velocity universal joint 151 mainly consists of an outer joint member 152, an inner joint member 153, torque-transmitting balls 154, and a cage 155 that holds the balls 154. Eight torque-transmitting balls 154 are incorporated into intersecting arc-shaped track grooves 157 and 159 that extend axially in the outer joint member 152 and the inner joint member 153, and are held by the cage 155. The centers of curvature of the intersecting arc-shaped track grooves 157 and 159 have no axial offset with respect to the joint center O.

[0005] Patent No. 3859267 Patent No. 5138449

[0006] The fixed constant velocity universal joint shown in Figures 22 and 23 was used as the subject of study. The outer joint member of the fixed constant velocity universal joint has multiple track grooves extending generally in the axial direction at regular intervals in the circumferential direction on its spherical inner surface. Normally, to prevent the track grooves from bulging due to edge loading under torque load, a chamfer of approximately constant width is provided between the spherical inner surface and the track grooves, extending approximately over the entire axial length of the track grooves.

[0007] First, considering the assembly issues of a fixed constant velocity universal joint, when assembling the inner joint member, cage, and ball into the outer joint member, the assembly of the inner joint member, cage, and ball needs to be tilted at an angle greater than the maximum operating angle. Therefore, the length of the track groove on the inner side of the outer joint member is set to a length greater than the length required to achieve the maximum operating angle. Consequently, when machining the track groove on the inner side of the outer joint member, there is interference with the non-machined surface (the bottom of the cup) and the machined surface (the track groove) when the machining tool is close, requiring high-precision adjustment. Further details will be described later.

[0008] Furthermore, when examining the morphological issues of the track grooves in fixed constant velocity universal joints, in track offset type outer joint members, the depth of the track groove on the inner side of the outer joint member is shallower than that on the opening side. On the other hand, in track groove crossing type outer joint members with no or very small track offset, the depth of the track groove is approximately constant from the opening side to the inner side of the outer joint member. In other words, the track groove on the inner side of the track groove crossing type outer joint member is deeper than that of the track offset type outer joint member. For this reason, we focused on the fact that in track groove crossing type outer joint members with no or very small track offset, there is a greater concern about interference with the non-machined surface (cup bottom) and the machined surface (track groove surface) when the machining tool is close to the inner track groove of the outer joint member, and that even more precise adjustment is required. Details will be described later.

[0009] Furthermore, the following problems arose regarding interference with the non-machined surface (the bottom of the cup) and the machined surface (the track groove) when the machining tool is in close proximity. Regarding interference with the non-machined surface (the bottom of the cup), one could consider shifting the position of the bottom of the cup further back to reduce the risk of interference, but this would require extending the length of the outer joint member and increasing the cup volume, leading to increased weight and material costs. Regarding the problem related to interference with the machined surface (the track groove), one could consider reducing the tool movement speed when the tool is in close proximity, but this would increase machining time and thus increase machining costs.

[0010] In view of the above-mentioned problems, the present invention aims to provide a fixed constant velocity universal joint that reduces the cost of machining the track groove of the outer joint member, improves the machining quality, and reduces weight.

[0011] To achieve the above objective, the inventors, based on the aforementioned study results and findings regarding the outer joint member of a fixed constant velocity universal joint, have arrived at a novel idea: to set a range of track grooves in which the ball rolls only when the inner joint member, cage, and ball are assembled into the outer joint member, and which is not used during operation. In other words, torque load does not need to be considered, and only the contact point of the ball is secured. This led to the present invention. Details of the study results and findings in the development process leading to the present invention will be described later.

[0012] As a technical means for achieving the aforementioned objective, the present invention provides a fixed constant velocity universal joint comprising: an outer joint member having a plurality of track grooves formed on its spherical inner surface, each having an arc-shaped portion extending generally in the axial direction, and having an opening side and a back side spaced apart in the axial direction; an inner joint member having a plurality of track grooves formed on its spherical outer surface, each having an arc-shaped portion extending generally in the axial direction; a plurality of balls disposed between the track grooves of the outer joint member and the corresponding track grooves of the inner joint member for transmitting 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 inner joint member The ball trajectory centerline of the track groove is formed in mirror image symmetric with the ball trajectory centerline of the pair of track grooves of the outer joint member, with reference to a plane (P) perpendicular to the axis of the joint and including the joint center (O) when the operating angle is 0°, and the track groove of the outer joint member has a relief portion formed in the range of the track groove between the radial position where the ball contact point remains and the spherical inner surface, from the axial position of the ball at the maximum operating angle (θ) to the inner side necessary for the assembly of the ball, and the radial dimension of the relief portion is larger than the radial dimension of a chamfer of substantially constant width provided in substantially the entire axial area between the spherical inner surface of the outer joint member and the track groove.

[0013] The above configuration makes it possible to realize a fixed constant-velocity universal joint that reduces the cost of machining the track groove of the outer joint member, improves machining quality, and reduces weight.

[0014] The ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member described above has a center of curvature with no axial offset relative to the joint center (O). This makes it possible to reduce the cost of track groove machining, improve machining quality, and reduce weight even in outer joint members where the groove depth of the inner track groove is deep.

[0015] The ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member described above has a center of curvature with a small offset of 1° or less relative to the joint center (O). This makes it possible to reduce the cost of track groove machining, improve machining quality, and reduce weight even in outer joint members with deep grooves in the inner track groove, at an energy loss level that does not pose a practical problem.

[0016] The ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member described above is inclined circumferentially with respect to the axis, and the direction of this inclination is formed in opposite directions in adjacent track grooves in the circumferential direction. This makes it possible to reduce the cost of processing the track grooves, improve processing quality, and reduce the weight of the outer joint member of a track groove crossing type fixed constant velocity universal joint, which is designed for even greater efficiency.

[0017] By increasing the number of balls to eight or more, this design is suitable for realizing a fixed constant velocity universal joint that reduces the cost of machining the track groove on the outer joint member, improves machining quality, and reduces weight.

[0018] According to the present invention, a fixed constant-velocity universal joint can be realized that reduces the cost of machining the track groove of the outer joint member, improves the machining quality, and reduces weight.

[0019] Figure 1A shows a fixed constant velocity universal joint according to the first embodiment of the present invention, and is a partial longitudinal cross-sectional view of the fixed constant velocity universal joint. Figure 1A is a front view of the fixed constant velocity universal joint as seen from the axial direction. Figures 1A and 1B show the outer joint member of the fixed constant velocity universal joint, and are partial longitudinal cross-sectional views of the outer joint member. Figure 2A is a front view of the outer joint member as seen from the axial direction. Figures 1A and 1B show the inner joint member of the fixed constant velocity universal joint, and are front views of the inner joint portion as seen from one side in the axial direction. Figures 1A and 1B show the inner joint member of the fixed constant velocity universal joint, and are side views of the inner joint member as seen from the outer circumference. Figures 1A and 1B show the inner joint member of the fixed constant velocity universal joint, and are rear views of the inner joint member as seen from the other side in the axial direction. Figure 1A shows a partial longitudinal cross-sectional view showing details of the track groove of the outer joint member. Figure 1A shows a longitudinal cross-sectional view showing details of the track groove of the inner joint member. Figure 1A is a schematic diagram showing the fixed constant velocity universal joint in the state where the maximum operating angle is taken. Figure 1A is a partial longitudinal cross-sectional view showing the ball assembly state into the outer joint member of the fixed constant velocity universal joint. Figures 22A and 22B are partial longitudinal cross-sectional views of the outer joint member of the fixed constant velocity universal joint under consideration. Figure 8A is an enlarged cross-sectional view of the track groove on the far side of the outer joint member along line A1-A1. Figures 23A and 23B are partial longitudinal cross-sectional views of the outer joint member of the fixed constant velocity universal joint under consideration. Figure 9A is an enlarged cross-sectional view of the track groove on the far side of the outer joint member along line A2-A2. Figures 23A and 23B are partial longitudinal cross-sectional views showing the machining state of the track groove of the outer joint member of the fixed constant velocity universal joint under consideration. Figure 10 is a partial longitudinal cross-sectional view showing the state in which the machining tool interferes with the bottom of the cup portion on the far side when in close proximity. Figure 10 is a partial longitudinal cross-sectional view showing the state in which the machining tool interferes with the end of the track groove on the far side when in close proximity. Figures 23A and 23B are perspective views of the outer joint member of the fixed constant velocity universal joint under consideration. This figure shows a portion of the inner circumferential surface of the outer joint member of the fixed constant velocity universal joint shown in Figure 12A. This is a partial longitudinal cross-sectional view showing the settable range of the relief portion of the track groove of the outer joint member of the fixed constant velocity universal joint shown in Figures 23A and 23B, which are under consideration. This is a partial longitudinal cross-sectional view showing the track groove machined surface of the outer joint member of the track groove crossing type fixed constant velocity universal joint shown in Figure 1A, which is the first embodiment. This is an enlarged cross-sectional view taken along the line X-X in Figure 14A. This is a cross-sectional view of Figure 14B with the ball contact point added.This is an enlarged cross-sectional view along the line X'-X' in Figure 14A. This is a perspective view of the outer joint member of the fixed constant velocity universal joint of the first embodiment. This is a diagram showing a part of the inner circumferential surface of the outer joint member of the fixed constant velocity universal joint of Figure 14A. This is a partial longitudinal cross-sectional view showing a modified example of the relief portion for the track groove of the outer joint member of the fixed constant velocity universal joint of the first embodiment. This is an enlarged cross-sectional view along the line Y-Y in Figure 16A. This is an enlarged cross-sectional view along the line Y'-Y' in Figure 16A. This is a partial longitudinal cross-sectional view showing a track groove crossing type fixed constant velocity universal joint of the second embodiment of the present invention. This is a schematic diagram illustrating the offset angle. This is a partial longitudinal cross-sectional view showing a track groove crossing type fixed constant velocity universal joint of the third embodiment of the present invention. This is a partial longitudinal cross-sectional view showing a track groove crossing type fixed constant velocity universal joint of the fourth embodiment of the present invention. This is a partial longitudinal cross-sectional view showing a cage offset type fixed constant velocity universal joint of the fifth embodiment of the present invention. This is a longitudinal cross-sectional view of a conventional fixed constant velocity universal joint (track offset type). This is a front view of the fixed constant velocity universal joint of Figure 22A as seen from the axial direction. This is a longitudinal cross-sectional view of a conventional fixed constant velocity universal joint (track groove crossing type). Figure 23A is a front view of the fixed constant velocity universal joint as seen from the axial direction.

[0020] Embodiments of the present invention will be described based on the drawings.

[0021] 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 1A 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 cage 5.

[0022] 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 circumferential track grooves 7, and on the outer surface of the inner joint member 3, spherical portions 8 remain between the circumferential track grooves 9 (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 both coincide with the joint center O. Hereafter, the spherical portions 6 on the inner surface of the outer joint member will also be called the spherical inner surface 6, and the spherical portions 8 on the outer surface of the inner joint member 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 cage 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 cage 5 has a pair of annular portions 5b and 5c provided on both sides of the pockets 5a in the axial direction, and a column 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 cage 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.

[0023] In the following, the opening side of the cup-shaped outer joint member 2 (right side in Figure 1A) will be referred to as the "joint opening side" in the axial direction, 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.

[0024] 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°). 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. That is, the ball trajectory centerline Xb of the second track groove portion 7b coincides with the tangent to the ball trajectory centerline Xa of the first track groove portion 7a at the joint opening side end.

[0025] 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. 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. That is, the ball trajectory centerline Yb of the second track groove portion 9b coincides with the tangent to the ball trajectory centerline Ya of the first track groove portion 9a at the joint-side end.

[0026] 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.

[0027] 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 N-N direction of the joint axis). 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.

[0028] 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.

[0029] 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 (not shown in the figure) has a 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) that is inclined by an angle γ with respect to the joint axis N-N in the opposite direction to the inclination of the track groove 7A. A relief portion Tr is formed at the far end of the track groove 7. Details of the relief portion Tr will be described later.

[0030] 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 of the track groove 7 of the radially opposing outer joint member 2 {see Figure 1(A)}, 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°.

[0031] 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.

[0032] 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°.

[0033] 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.

[0034] 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.

[0035] 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 towards the joint-side. 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°.

[0036] 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 joint axis 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 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.

[0037] 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°.

[0038] 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.

[0039] Next, FIG. 6 shows the state in which the fixed constant velocity universal joint 1 according to the present embodiment takes the maximum operating angle. The maximum operating angle θ1 is the maximum operating angle guaranteed as a product that can be used during driving in a state where the fixed constant velocity universal joint 1 is mounted on a vehicle or the like, and is determined design-wise for each product type. Specifically, at the maximum operating angle θ1, a slight margin (for example, a gap of about 0.2 mm to 0.5 mm) that allows relative rotation is provided between the outer peripheral surface of the minimum shaft diameter d of the shaft 11 and the inlet chamfer 10 of the outer joint member 2. Further, the maximum operating angle θ1 in the present invention is, for example, the maximum operating angle that occurs in the fixed constant velocity universal joint 1 mounted on the steered 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 the claims is used in this sense.

[0040] Also, FIG. 7 shows the state at the time of incorporating the balls of the fixed constant velocity universal joint 1 of the present embodiment. As shown in the figure, at the time of incorporating the balls, the shaft 11 (see FIG. 6) is not mounted on the inner joint member 3. At the time of incorporating the balls, a ball incorporation angle θ2 larger than the maximum operating angle θ1 is required. Therefore, if the shaft 11 is mounted, the shaft 11 interferes with the opening end of the outer joint member 2. Therefore, an inner ring rocking 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 cage 5 into the spherical inner peripheral surface 6 of the outer joint member 2, the inner joint member 3 is tilted at an angle θ2 (for example, 60° or more) larger than the maximum operating angle θ1 to form a gap into which the ball 4 can be inserted between the opening end of the outer joint member 2 and the pocket 5a of the cage 5, and the ball 4 is incorporated into the pocket 5a through this gap.

[0041] 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. (1) The track groove of the outer joint member has a relief portion formed in the range from the axial position of the ball at the maximum operating angle θ1 to the inner side of the joint necessary for assembling the ball, and in the range of the track groove between the radial position where the ball contact point remains and the spherical inner circumferential surface. (2) The radial dimension of the relief portion has a portion that is larger than the radial dimension of the chamfered portion of substantially constant width provided in substantially the entire axial area between the spherical inner circumferential surface of the outer joint member and the track groove (hereinafter, the chamfered portion of substantially constant width may be abbreviated as the conventional chamfered portion).

[0042] Here, we will explain the results of the studies and findings from the development process that led to the characteristic configurations described above. The outer joint member 102 of the fixed constant velocity universal joint 101 shown in Figure 22, which was the subject of study, has a spherical inner circumferential surface 106 on which a plurality of track grooves 107 extending generally in the axial direction at regular intervals in the circumferential direction are provided. This fixed constant velocity universal joint 101 is a track offset type, and as mentioned above, the center of curvature of the track grooves 107 is offset in the axial direction by an offset amount f relative to the joint center O. The outer joint member 152 of the fixed constant velocity universal joint 151 shown in Figure 23 has a plurality of track grooves 157 extending generally in the axial direction at regular intervals in the circumferential direction on the spherical inner circumferential surface 156. This fixed constant velocity universal joint 151 is a track groove intersection type, and some track grooves 157 have no axial offset or a very small offset relative to the joint center O.

[0043] As described above, when incorporating the balls, it is necessary to tilt the inner joint member of the internal assembly consisting of the inner joint member, the cage, and the balls by an angle greater than or equal to the maximum operating angle θ1. Therefore, the length of the track groove on the inner side of the outer joint member is set to a dimension greater than the length required to achieve the maximum operating angle θ1. Figures 8 and 9 are referred to for a specific illustration of the state of the track groove on the inner side of the outer joint member. Figure 8A is a partial longitudinal cross-section of the outer joint member 102 of the track offset type fixed constant velocity joint 101 shown in Figure 22, and Figure 8B is an enlarged cross-sectional view of the track groove 107 on the inner side of the outer joint member 102 of Figure 8A at the A1 - A1 line. Figure 9A is a partial longitudinal cross-section of the outer joint member 152 of the track groove intersection type fixed constant velocity joint 151 shown in Figure 23, and Figure 9B is an enlarged cross-sectional view of the track groove 157 on the inner side of the outer joint member 152 of Figure 9A at the A2 - A2 line.

[0044] Since the balls 104, 154 are located deeper axially at the ball incorporation angle θ2 than at the axial position at the maximum operating angle θ1, as shown in Figures 8A and 9A, for both the outer joint member 102 of the track offset type and the outer joint member 152 of the track groove intersection type, the length required for ball incorporation (the length corresponding to the ball incorporation angle θ2 / 2) of the track grooves 107, 157 on the inner side is set to a dimension greater than the length required to achieve the maximum operating angle θ1 (the length corresponding to the maximum operating angle θ1 / 2). With respect to the plane P that includes the joint center O and is perpendicular to the axis of the joint in the state of the operating angle of 0°, the maximum operating angle θ1 / 2 is illustrated by a solid line, and the ball incorporation angle θ2 / 2 is illustrated by a dashed line. In the processing (grinding, hardened steel cutting) of any of the track grooves 107, 157 of the outer joint members 102, 152, there are problems of interference with the cup bottom portions 102b, 152b, which are non-processed surfaces, and interference with the surfaces of the track grooves 107, 157, which are processed surfaces, when the processing tool T (refer to Figure 10) approaches, and high-precision adjustment is required.

[0045] As shown in Figure 8A, in the track offset type outer joint member 102, the depth of the track groove 107 on the inner side of the outer joint member 102 is shallower than that on the opening side, and as shown in Figure 8B, at the axial position of the track groove 107 that exceeds the length corresponding to the maximum operating angle θ1 / 2, the track groove 107 is shallow with a depth of h1. On the other hand, as shown in Figure 9A, in the track groove crossing type outer joint member 152 with no or very small track offset, the depth of the track groove 157 is approximately constant from the opening side to the inner side of the outer joint member 152. As shown in Figure 9B, at the axial position of the track groove 157 that exceeds the length corresponding to the maximum operating angle θ1 / 2, the track groove 157 is deep with a depth of h2.

[0046] Therefore, when comparing the axial positions of the track grooves 107 and 157 that exceed the length corresponding to the maximum operating angle θ¹ / 2, the depth h2 of the track groove 157 of the track groove crossing type outer joint member 152 is deeper than the depth h1 of the track groove 107 of the track offset type outer joint member 102.

[0047] As shown in Figures 8A and 9A, both the track offset type outer joint member 102 and the track groove crossing type outer joint member 152 are provided with a chamfered portion Tc of approximately constant width between the spherical inner circumferential surfaces 106 and 156 and the track grooves 107 and 157, extending over approximately the entire axial area of ​​the track grooves 107 and 157, in order to prevent the track grooves 107 and 157 from bulging due to edge loading when torque is applied.

[0048] Next, the machining of the track groove of the outer joint member will be explained with reference to Figure 10. Figure 10 shows an example of an outer joint member 152 of the track groove crossing type, in which the depth h2 of the inner track groove 157 is deep. As an example of machining, for example, the machining tool T is rotationally driven in a fixed position. The outer joint member 152 is held in a chuck (not shown) and oscillates on a plane M (see Figure 2A) with an inclination angle γ around the joint center O. Figure 10 shows the set state of the machining tool T and the outer joint member 152. From this state, when the machining tool T is rotationally driven and the outer joint member 152 held in the chuck oscillates around the joint center O, the machining tool T approaches the outer joint member 152 in the direction of the arrow, contacts the inner end of the track groove 157 and starts machining. Due to the machining area and volume of the inner end of the track groove 157 near the point of proximity of the machining tool T, there are concerns about increased machining load and reduced tool life.

[0049] Referring to Figures 11A and 11B, a supplementary explanation will be given regarding interference issues when the machining tool is in close proximity. As shown in Figure 11A, there is concern that the machining tool T may interfere with the hatched cup bottom 152b on the far side of the joint when in close proximity. As shown in Figure 11B, there is concern that the machining tool T may interfere with the hatched track groove end 157b on the far side of the joint when in close proximity. The track groove end 157b is located slightly closer to the joint opening than the cup bottom 152b. Thus, since the track groove end 157b and the cup bottom 152b are positioned very close to the inner circumference of the cup portion of the outer joint member 152, there are problems with interference with the non-machined surface, the cup bottom 152b, and with the machined surface, the track groove end 157b, when the machining tool T is in close proximity. Furthermore, since we want to improve machining efficiency by increasing the feed rate just before machining, high-precision adjustment is required.

[0050] In particular, in the track groove crossing type outer joint member 152, where there is no track offset or only a very small track offset, the groove depth h2 {Figure 9B} of the track groove 157 is deep at the axial position of the track groove 157 that exceeds the length corresponding to the maximum operating angle θ1 / 2, which is near the point of proximity of the machining tool T. Therefore, in the track groove crossing type outer joint member 152, when machining the track groove 157 near the point of proximity of the machining tool T, there is a greater concern about interference with the cup bottom portion 152b, which is the non-machined surface, and interference with the inner end portion 157b of the track groove 157, which is the machined surface, when the machining tool T is close, and it was noted that even more precise adjustment is required.

[0051] To facilitate understanding, Figure 12A shows a perspective view of the track groove intersecting type outer joint member 152 shown in Figure 23, which is the subject of consideration. Figure 12B shows a portion of the inner circumferential surface of the outer joint member 152. Between the spherical inner circumferential surface 156 and the track groove 157, a chamfered portion Tc of approximately constant width is provided over approximately the entire axial area of ​​the track groove 157, but this does not address interference with the cup bottom 152b and the far end 157b of the track groove 157, which are non-machined surfaces near the point of proximity of the machining tool T. Therefore, as indicated by the hatching, interference occurs between the machining tool T and the cup bottom 152b and the far end 157b of the track groove 157.

[0052] Therefore, as shown in Figure 13, we focused on the range 157h of the track groove 157, which is hatched between the radial position where the ball contact point remains and the spherical inner surface, in the range on the inner side of the joint necessary for assembling the ball, from the axial position of the ball at the maximum operating angle θ1, which is near the point of proximity to the machining tool T. After much consideration of this range 157h of the track groove, we arrived at a new idea: the range of the track groove 157 is such that the ball 154 rolls only when assembling the inner joint member 153, cage 155, and ball 154 into the outer joint member 152, and is not used during travel. In other words, torque does not need to be applied, and only the contact point of the ball 154 is secured. Based on this, we conceived of the characteristic configuration (1) described above, in which the track groove of the outer joint member has a relief portion formed in the range of the track groove between the radial position where the ball contact point remains and the spherical inner circumferential surface, from the axial position of the ball at the maximum operating angle θ1 to the inner side of the joint necessary for the ball to be assembled, and in which the radial dimension of the relief portion is larger than the radial dimension of the conventional chamfer portion. The above are the results of considerations and findings in the development process that led to the characteristic configuration.

[0053] Next, the characteristic configurations (1) and (2) of this embodiment will be described in detail with reference to Figures 14 and 15. Figure 14A is a partial vertical cross-sectional view showing the track groove machined surface of the outer joint member of the fixed constant velocity universal joint of Figure 1A, which is the first embodiment; Figure 14B is an enlarged cross-sectional view taken along the line X-X of Figure 14A; and Figure 14C is a cross-sectional view of Figure 14B with the ball contact point added. Figure 14D is an enlarged cross-sectional view taken along the line X'-X' of Figure 14A. Figure 15A is a perspective view of the outer joint member of the fixed constant velocity universal joint of the first embodiment; and Figure 15B is a view showing a part of the inner circumferential surface of the outer joint member of Figure 15A.

[0054] In Figure 14A, the dashed line radially away from the bottom of the track groove 7 shows the trajectory of the ball's contact point C. As shown in the figure, a relief portion Tr is formed in the range from the axial position of the ball at the maximum operating angle θ1 (length corresponding to the maximum operating angle θ1 / 2) to the inner side of the joint required for ball installation (length corresponding to the ball installation angle θ2 / 2). The hatched portion of the track groove 7 is the machined surface Mt of the track groove. Although a relief portion Tr is formed in the range from the axial position of the ball at the maximum operating angle θ1 (length corresponding to the maximum operating angle θ1 / 2) to the inner side of the joint required for ball installation (length corresponding to the ball installation angle θ2 / 2), the contact point C of the ball 4 remains in the track groove 7 of the outer joint member 2 even in the axial region where the relief portion Tr is formed. Thus, the radially outer end of the relief portion Tr is formed at a radial position Sr that leaves the contact point C of the ball 4, and the radially inner end of the relief portion Tr extends to the spherical inner circumferential surface 6.

[0055] Since the radially outer end of the relief portion Tr is at a radial position Sr that leaves the contact point C of the ball 4, the axial region in which the relief portion Tr is formed is the area of ​​the track groove 7 that the ball 4 rolls only when the inner joint member 3, cage 5, and ball 4 are assembled into the outer joint member 2, as shown in Figure 14C, and is not used during running. In other words, it does not require torque to be applied and only the contact point of the ball 4 is secured, which is a characteristic configuration (1) of this embodiment.

[0056] Furthermore, the radial dimension E of the relief portion Tr is larger than the radial dimension F of the conventional chamfered portion Tc. Therefore, the radial dimension of the relief portion is larger than the radial dimension of the chamfered portion (conventional chamfered portion) of substantially constant width provided over substantially the entire axial area between the spherical inner circumferential surface of the outer joint member and the track groove, which is a characteristic configuration (2) of this embodiment. Thus, the relief portion Tr has a different configuration from the conventional chamfered portion Tc.

[0057] To facilitate understanding, Figure 15 shows the outer joint member 2 of the fixed constant velocity universal joint of this embodiment. Figure 15A is a perspective view of the outer joint member 2, and Figure 15B shows a part of the inner circumferential surface of the outer joint member 2 in Figure 15A. It can be easily seen that the relief portion Tr of the track groove 7 of the outer joint member 2 has a different configuration from the conventional chamfered portion Tc.

[0058] The track groove intersecting type fixed constant velocity universal joint 1 according to the first embodiment described above is an example in which the track groove 7 of the outer joint member 2 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 straight ball trajectory centerline Xb, and the center of curvature of the arc-shaped ball trajectory centerline Xa is not offset in the axial direction with respect to the joint center O. However, it is not limited to this and can also be applied to the outer joint member shown in Figure 23, which was the subject of study, in which the track groove consists only of an arc-shaped ball trajectory centerline.

[0059] Next, a modified example of the relief portion of the track groove of the outer joint member will be described with reference to Figure 16. Figure 16A is a partial longitudinal cross-sectional view showing a modified example of the relief portion of the track groove of the outer joint member of the fixed constant velocity universal joint of the first embodiment, and Figure 16B is an enlarged cross-sectional view along the Y-Y line in Figure 16A. Figure 16C is an enlarged cross-sectional view along the Y'-Y' line in Figure 16A. The shape of the relief portion of the track groove of the outer joint member in this modified example differs from that of the fixed constant velocity universal joint according to the first embodiment described above. The overall configuration shown in Figures 1 to 7 of the first embodiment described above, its effects and operations, and the results of the studies and findings in the development process shown in Figures 8 to 13 are also the same for the fixed constant velocity universal joint of this modified example, so they will be applied mutatis mutandis. Parts having the same function as the fixed constant velocity joint according to the first embodiment are denoted by the same reference numerals, and only the essential points will be described.

[0060] As shown in Figures 16A and 16B, the relief portion Tr of the track groove 7 of the outer joint member 2 in this modified example is formed by gradually increasing the chamfer Tc from the axial position of the ball 4 at the maximum operating angle θ1 toward the inner end of the track groove 7. The radially outer end of the relief portion Tr is formed at a radial position Sr that leaves the contact point C of the ball 4, and the radially inner end of the relief portion Tr reaches the spherical inner circumferential surface 6. Since the radially outer end of the relief portion Tr is at a radial position Sr that leaves the contact point C of the ball 4, the axial region in which the relief portion Tr is formed is, as shown in Figure 16(B), the range of the track groove 7 in which the ball 4 rolls only when the inner joint member 3, cage 5, and ball 4 are assembled into the outer joint member 2, and is not used during running. In other words, it has a characteristic configuration (1) that does not require torque to be applied and only the contact point of the ball 4 is secured.

[0061] Furthermore, as shown in Figures 16B and 16C, the radial dimension E of the relief portion Tr is larger than the radial dimension F of the conventional chamfered portion Tc. The radial dimension of the relief portion has a characteristic configuration (2) in which a portion is larger than the radial dimension of the conventional chamfered portion. In this modified example, the relief portion Tr is formed by gradually expanding the chamfered portion Tc from the axial position of the ball 4 at the maximum operating angle θ1 toward the end of the track groove 7 on the inner side, so the shape of the relief portion Tr and its processing can be simplified.

[0062] A track groove crossing type fixed constant velocity universal joint according to a second embodiment of the present invention will be described with reference to Figure 17. Figure 17 is a partial longitudinal cross-sectional view of the fixed constant velocity universal joint of this embodiment. The track groove crossing type fixed constant velocity universal joint according to this embodiment differs from the fixed constant velocity universal joint according to the first embodiment described above in that the center of curvature of the first track groove portion 7a, which has an arc-shaped ball trajectory centerline Xa, has a very small axial offset with respect to the joint center O. The overall configuration shown in Figures 1 to 7 of the first embodiment, its effects and advantages, the results and findings of the development process shown in Figures 8 to 13, and the characteristic configuration shown in Figures 14 to 16 are the same for the fixed constant velocity universal joint of this embodiment and will be applied mutatis mutandis. Parts having the same function as the fixed constant velocity joint according to the first embodiment are denoted by the same reference numerals, and only the essential points will be described.

[0063] As shown in Figure 17, in this embodiment, the curvature center of the ball trajectory centerline Xa of the first track groove portion 7a provided in the track groove 7 of the outer joint member 2 (hereinafter referred to as "outer ring track center Oo1") and the curvature center of the ball trajectory centerline Ya of the first track groove portion 9a provided in the track groove 9 of the inner joint member 3 (hereinafter referred to as "inner ring track center Oi1") are offset in the opposite direction axially with respect to the joint center O (this axial offset amount is referred to as "offset amount f"). In this embodiment, the outer ring track center Oo1 is positioned on the opening side and the inner ring track center Oi1 is positioned on the back side with respect to the joint center O as an example, but conversely, the outer ring track center Oo1 may be positioned on the back side and the inner ring track center Oi1 may be positioned on the opening side with respect to the joint center O. Figure 17 is shown with the inclination angle γ of the track grooves 7 and 9 set to 0°.

[0064] When the outer wheel track center Oo1 and inner wheel track center Oi1 are offset as described above, a force is generated in which the ball 4 pushes the cage 5 during torque transmission. In this case, contact occurs between the spherical inner surface 6 (spherical portion 6) of the outer joint member 2 and the spherical outer surface 12 of the cage 5, and between the spherical outer surface 8 (spherical portion 8) of the inner joint member 3 and the spherical inner surface 13 of the cage 5. Frictional force is generated at these contact points, resulting in energy loss corresponding to this frictional force. However, if the outer wheel track center Oo1 and inner wheel track center Oi1 are not intentionally offset relative to the joint center O, the direction of the offset of the outer wheel track center Oo1 and inner wheel track center Oi1 relative to the joint center O becomes random, potentially leading to variations in function. Therefore, it is desirable to offset the outer wheel track center Oo1 and inner wheel track center Oi1 axially opposite to the joint center O at a level of energy loss that does not pose a practical problem.

[0065] Here, we will explain the offset angle with reference to Figure 18. The offset angle α is calculated by the following equation, where α is the offset angle and f is the offset amount.

[0066] Therefore, we focused on small offset amounts of 1° or less, and the offset amount f and the ball's pitch circle diameter PCD BALL The ratio f / PCD BALL The upper limit is set to 0.009. On the other hand, focusing on the offset angle of 0.02° at which the offset becomes significant, the ratio f / PCD is used. BALL The lower limit of this value shall be 0.0002. In this specification and the claims, "the ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member has a curvature center with an offset angle of 1° or less relative to the joint center (O)" shall have the meaning described above.

[0067] In Figure 17, the center of curvature of the spherical portion 6 on the inner circumferential surface of the outer joint member 2, i.e., the center of curvature of the spherical outer circumferential surface 12 of the cage 5 (hereinafter referred to as "cage outer spherical center Oc1"), and the center of curvature of the spherical portion 8 on the outer circumferential surface of the inner joint member 3, i.e., the center of curvature of the spherical inner circumferential surface 13 of the cage 5 (hereinafter referred to as "cage inner spherical center Oc2"), both coincide with the joint center O. That is, the axial offset amount of the cage outer spherical center Oc1 and the cage inner spherical center Oc2 with respect to the joint center O (hereinafter referred to as "cage offset amount f2") is 0. In this case, the above offset amount f is equal to the axial offset amount of the outer wheel track center Oo1 and the inner wheel track center Oi1 with respect to the cage outer spherical center Oc1 and the cage inner spherical center Oc2 (hereinafter referred to as "track offset amount f1"). In this way, by setting the cage offset amount f2 to 0, the radial thickness of the cage 5, more specifically, the radial distance between the spherical outer surface 12 and the spherical inner surface 13, becomes uniform, and the strength of the cage can be ensured.

[0068] In the fixed constant velocity universal joint 1 according to the second embodiment, as shown in Figure 17, a relief portion Tr is formed in the range from the axial position of the ball at the maximum operating angle θ1 (length corresponding to the maximum operating angle θ1 / 2) to the inner side of the joint required for ball installation (length corresponding to the ball installation angle θ2 / 2), and similar to the fixed constant velocity universal joint of the first embodiment described above, it has the following characteristic configuration: (1) The track groove of the outer joint member has a relief portion formed in the range from the axial position of the ball at the maximum operating angle θ1 to the inner side of the joint required for ball installation, and in the range of the track groove between the radial position where the ball contact point remains and the spherical inner circumferential surface. (2) The radial dimension of the relief portion has a portion that is larger than the radial dimension of the conventional chamfered portion.

[0069] A fixed constant velocity universal joint of the track groove crossing type according to a third embodiment of the present invention will be described with reference to Figure 19. Figure 19 is a partial longitudinal cross-sectional view of the fixed constant velocity universal joint of this embodiment. The fixed constant velocity universal joint of the track groove crossing type according to this embodiment differs from the fixed constant velocity universal joint of the first embodiment described above in that the track offset amount f1 is set to 0 and a cage offset amount f2 is provided. The overall configuration shown in Figures 1 to 7 of the first embodiment, its operation and effect, the results of the study and findings in the development process shown in Figures 8 to 13, and the characteristic configuration shown in Figures 14 to 16 are the same for the fixed constant velocity universal joint of this embodiment and will be applied mutatis mutandis. Parts having the same function as the fixed constant velocity joint of the first embodiment are denoted by the same reference numerals, and only the essential points will be described.

[0070] As shown in Figure 19, in this embodiment of the fixed constant velocity universal joint 1, the curvature center Oc1 of the spherical outer surface 12 and the curvature center Oc2 of the spherical inner surface 13 of the cage 5 are offset by an equal amount on opposite sides in the axial direction with respect to the joint center O. In this case, the curvature center Oo1 of the ball trajectory centerline Xa of the first track groove 7a of the outer joint member 2 coincides with the curvature center Oc1 of the spherical outer surface 12 of the cage 5, and the curvature center Oi1 of the ball trajectory centerline Ya of the first track groove 9a of the inner joint member 3 coincides with the curvature center Oc2 of the spherical inner surface 13 of the cage 5. That is, the track offset amount f1 is 0, and the offset amount f and the cage offset amount f2 are equal. As described above, the offset amount f and the ball pitch circle diameter PCD BALL The ratio f / PCD BALLThe upper limit is set to 0.009. In this specification and claims, "the ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member has a curvature center with a small offset amount of offset angle of 1° or less relative to the joint center (O)" includes the meaning described above. In this way, by setting the track offset amount f1 to 0, the depth of the first track grooves 7a and 9a can be made uniform, thereby preventing a decrease in durability caused by the ball 4 riding up onto the first track grooves 7a and 9a. In this embodiment, the curvature center Oc1 is positioned on the opening side and the curvature center Oc2 is positioned on the back side relative to the joint center O as an example, but conversely, the curvature center Oc1 may be positioned on the back side and the curvature center Oc2 may be positioned on the opening side relative to the joint center O. Figure 19 shows the track grooves 7 and 9 with an inclination angle γ of 0°.

[0071] In the fixed constant velocity universal joint 1 according to the third embodiment, as shown in Figure 19, a relief portion Tr is formed in the range from the axial position of the ball at the maximum operating angle θ1 (length corresponding to the maximum operating angle θ1 / 2) to the inner side of the joint required for ball assembly (length corresponding to the ball assembly angle θ2 / 2), and similar to the fixed constant velocity universal joint of the first embodiment described above, it has the following characteristic configuration: (1) The track groove of the outer joint member has a relief portion formed in the range from the axial position of the ball at the maximum operating angle θ1 to the inner side of the joint required for ball assembly, and in the range of the track groove between the radial position where the ball contact point remains and the spherical inner circumferential surface. (2) The radial dimension of the relief portion has a portion that is larger than the radial dimension of the conventional chamfered portion.

[0072] A fixed constant velocity universal joint according to a fourth embodiment of the present invention will be described with reference to Figure 20. Figure 20 is a partial longitudinal cross-sectional view of the fixed constant velocity universal joint of this embodiment. The track groove crossing type fixed constant velocity universal joint according to this embodiment differs from the fixed constant velocity universal joint according to the first embodiment described above in that it is provided with both a track offset amount f1 and a cage offset amount f2. The overall configuration shown in Figures 1 to 7 of the first embodiment, its effects and advantages, the results and findings of the development process shown in Figures 8 to 13, and the characteristic configuration shown in Figures 14 to 16 are the same for the fixed constant velocity universal joint of this embodiment and will be applied mutatis mutandis. Parts having the same function as the fixed constant velocity joint according to the first embodiment are denoted by the same reference numerals, and only the essential points will be described.

[0073] As shown in Figure 20, in this embodiment of the fixed constant velocity universal joint 1, the curvature center Oc1 of the spherical outer surface 12 of the cage 5 and the curvature center Oc2 of the spherical inner surface 13 are offset by the same amount in the opposite direction in the axial direction with respect to the joint center O. With respect to the curvature center Oc1 of the spherical outer surface 12 of the cage 5, the curvature center Oo1 of the ball trajectory centerline Xa of the first track groove 7a of the outer joint member 2 is offset in the axial direction toward the opening side. With respect to the joint center O, the offset of the curvature center Oc1 of the spherical outer surface 12 of the cage 5 and the curvature center Oo1 of the arc-shaped ball trajectory centerline Xa of the first track groove 7a are applied in the same direction. With respect to the curvature center Oc2 of the spherical inner surface 13 of the cage 5, the curvature center Oi1 of the ball trajectory centerline Ya of the first track groove 9a of the inner joint member 3 is offset in the axial direction toward the back side. With respect to the joint center O, the curvature center Oc2 of the spherical inner surface 13 of the cage 5 and the curvature center Oi1 of the arc-shaped ball trajectory center line Ya of the first track groove 9a are offset in the same direction. The curvature center Oc1 of the spherical outer surface 12 of the cage 5 is also the curvature center of the spherical inner surface 6 of the outer joint member 2, and the curvature center Oc2 of the spherical inner surface 13 of the cage 5 is also the curvature center of the spherical outer surface 8 of the inner joint member 3. Figure 20 shows the track grooves 7 and 9 with an inclination angle γ of 0°.

[0074] In this embodiment, the cage offset amount f2 and the ball's pitch circle diameter PCD are used. BALL The ratio f² / PCDBALL is set to 0.0045, and the ratio f1 / PCD of the track offset amount f1 to the pitch circle diameter PCD of the ball BALL is set to 0.0045. In addition, in this embodiment, with respect to the joint center O, the curvature centers Oo1 and Oc1 are arranged on the opening side, and the curvature centers Oi1 and Oc2 are arranged on the back side. However, conversely, with respect to the joint center O, the curvature centers Oo1 and Oc1 may be arranged on the back side, and the curvature centers Oi1 and Oc2 may be arranged on the opening side. Also, although the offset amount f is exemplified as being equally distributed between the track offset amount f1 and the cage offset amount f2, the offset amount f may be distributed in different amounts between the track offset amount f1 and the cage offset amount f2. In this specification and the claims, "the ball track center line of the arc-shaped portion of the track groove of the outer joint member has a curvature center with a small offset amount of 1° or less of the offset angle with respect to the joint center (O)" shall include the above meaning.

[0075] In the fixed constant velocity joint 1 according to the fourth embodiment as well, in the range from the axial position of the ball at the maximum operating angle θ1 (the length corresponding to the maximum operating angle θ1 / 2) to the back side of the joint required for incorporating the ball (the length corresponding to the ball incorporation angle θ2 / 2), as shown in FIG. 20, a relief portion Tr is formed, and similar to the fixed constant velocity joint of the first embodiment described above, it has the following characteristic configurations. (1) The track groove of the outer joint member has a relief portion formed in the range from the axial position of the ball at the maximum operating angle θ1 to the back side of the joint required for incorporating the ball, which is the range of the track groove between the radial position leaving the contact point of the ball and the spherical inner peripheral surface. (2) The radial dimension of the relief portion has a portion larger than the radial dimension of the conventional chamfered portion.

[0076] ​​A fixed constant velocity universal joint according to a fifth embodiment of the present invention will be described with reference to Figure 21. Figure 21 is a partial longitudinal cross-sectional view of the fixed constant velocity universal joint of this embodiment. The fixed constant velocity universal joint according to this embodiment is a cage offset type fixed constant velocity universal joint in which the track groove is not inclined in the circumferential direction, and differs from the track groove crossing type fixed constant velocity universal joint according to the first embodiment described above. However, the results of studies and findings in the development process shown in Figures 8 to 13 of the first embodiment, as well as the characteristic configurations shown in Figures 14 to 16, are the same for the fixed constant velocity universal joint of this embodiment and will be applied mutatis mutandis. Parts having the same function as the fixed constant velocity joint according to the first embodiment are denoted by the same reference numerals, and only the essential points will be described.

[0077] As shown in Figure 21, the fixed constant velocity universal joint 1 of this embodiment mainly consists of an outer joint member 2, an inner joint member 3, balls 4, and a cage 5. Multiple arc-shaped track grooves 7 extending in the axial direction are formed on the spherical inner circumferential surface 6 of the outer joint member 2, and the outer joint member 2 has an opening side and an inner side that are spaced apart in the axial direction. Multiple arc-shaped track grooves 9 extending in the axial direction are formed on the spherical outer circumferential surface 8 of the inner joint member 3, facing the track grooves 7 of the outer joint member 2. Multiple balls 4 that transmit torque are arranged between the track grooves 7 of the outer joint member 2 and the corresponding track grooves 9 of the inner joint member 3. The cage 5 houses the balls 4 in pockets 5a, and the spherical outer circumferential surface 12 and spherical inner circumferential surface 13 of the cage 5 slide in contact with the spherical inner circumferential surface 6 of the outer joint member 2 and the spherical outer circumferential surface 8 of the inner joint member 3, respectively.

[0078] This is a so-called double-offset type fixed constant-velocity universal joint, in which the curvature centers of the spherical outer surface and the spherical inner surface of the cage are offset axially with respect to the joint center O. The curvature centers Oo1 of the arc-shaped track groove 7 of the outer joint member 2 and Oi1 of the arc-shaped track groove 9 of the inner joint member 3 are offset by the same amount axially on opposite sides with respect to the joint center O, and the curvature centers Oo1 and Oi1 coincide with the curvature centers Oc1 of the spherical outer surface 12 of the cage 5 and Oc2 of the spherical inner surface 13 of the cage 5, respectively. Therefore, the groove depth of the track groove 7 of the outer joint member 2 is constant from the opening side to the back side. The ball trajectory centerline Y of the track groove 9 of the inner joint member 3 is formed in mirror image symmetry with the ball trajectory centerline X of the corresponding track groove 7 of the outer joint member 2, with respect to a plane P that includes the joint center O and is perpendicular to the joint axis when the operating angle is 0°.

[0079] In the fixed constant velocity universal joint 1 according to the fifth embodiment, as shown in Figure 21, a relief portion Tr is formed in the range from the axial position of the ball at the maximum operating angle θ1 (length corresponding to the maximum operating angle θ1 / 2) to the inner side of the joint required for ball assembly (length corresponding to the ball assembly angle θ2 / 2), and similar to the fixed constant velocity universal joint of the first embodiment described above, it has the following characteristic configuration: (1) The track groove of the outer joint member has a relief portion formed in the range from the axial position of the ball at the maximum operating angle θ1 to the inner side of the joint required for ball assembly, and in the range of the track groove between the radial position where the ball contact point remains and the spherical inner circumferential surface. (2) The radial dimension of the relief portion has a portion that is larger than the radial dimension of the conventional chamfered portion.

[0080] The fixed constant velocity universal joint 1 according to the fifth embodiment described above is a so-called double-offset type fixed constant velocity universal joint in which the center of curvature of the spherical outer surface of the cage and the center of curvature of the spherical inner surface are offset. However, it is not limited to this, and can also be applied to the track groove of the outer joint member of the track offset type fixed constant velocity universal joint shown in Figure 22, which was the subject of study.

[0081] In the embodiments described above, examples were given of fixed constant velocity universal joints with 8 and 6 balls, but the invention is not limited to these, and more than 8 balls can be used as appropriate.

[0082] 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.

[0083] 1 Fixed constant velocity universal joint 2 Outer joint member 3 Inner joint member 4 Ball 5 Cage 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 C Ball contact point E Radial dimension F Radial dimension M Plane containing the ball trajectory centerline N Axis of the joint O Joint center Oo1 Outer ring track center Oi1 Inner ring track center Oc1 Cage outer spherical center Oc2 Cage inner spherical center Sr Radial position Tr Relief 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 Yb: Ball trajectory centerline of the second track groove f: Offset amount f1: Track offset amount f2: Cage offset amount θ1: Maximum operating angle θ2: Ball mounting angle

Claims

1. A fixed constant velocity universal joint comprising: an outer joint member having an opening side and a back side spaced apart in the axial direction, with a plurality of track grooves having arc-shaped portions extending generally in the axial direction formed on its spherical inner surface; an inner joint member having a plurality of track grooves having arc-shaped portions extending generally in the axial direction 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 centerlines of the track grooves of the inner joint member are formed in mirror symmetry with the ball trajectory centerlines 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 the track groove of the outer joint member has a relief portion formed in the range of the track groove between the radial position where the contact point of the ball remains and the spherical inner surface, from the axial position of the ball at the maximum operating angle (θ1) to the inner side necessary for assembling the ball, and the radial dimension of the relief portion is larger than the radial dimension of a chamfer of substantially constant width provided in substantially the entire axial area between the spherical inner surface of the outer joint member and the track groove.

2. The fixed constant velocity universal joint according to claim 1, characterized in that the ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member has a center of curvature that is not offset in the axial direction with respect to the joint center (O).

3. The fixed constant velocity universal joint according to claim 1, characterized in that the ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member has a curvature center with an offset angle of 1° or less with respect to the joint center (O).

4. The fixed constant velocity universal joint according to claim 1, characterized in that the ball trajectory centerline of the arc-shaped portion of the track groove of the outer joint member is inclined in the circumferential direction with respect to the axis, and the direction of inclination is formed in opposite directions for adjacent track grooves in the circumferential direction.

5. A fixed constant velocity universal joint according to any one of claims 1 to 4, characterized in that the number of balls is eight or more.

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