Fixed constant velocity universal joint

Abstract

To provide 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. [Solution] In a fixed constant velocity universal joint comprising an outer joint member 2, an inner joint member, a plurality of balls, and a retainer having pockets for housing the balls, the ball trajectory centerline of the track groove of the inner joint member is formed in mirror image symmetry with the pair of ball trajectory centerlines X of the outer joint member 2, with reference to a plane perpendicular to the axis that includes the joint center O when the operating angle is 0°, and the track groove 7 of the outer joint member 2 is formed in the range necessary for ball assembly from the axial position at the maximum operating angle, and a relief portion Tr is formed in the range of the track groove 7 between the radial position Sr leaving the ball contact point C and the spherical inner surface 6, and the radial dimension E is larger than the radial dimension of a chamfered portion Tc of substantially constant width provided in substantially the entire axial area between the spherical inner surface 6 and the track groove 7 of the outer joint member 2.

Description

[Technical Field]

[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. [Background technology]

[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 8 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 8-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. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 3859267 [Patent Document 2] Patent No. 5138449 [Overview of the Initiative] [Problems that the invention aims to solve]

[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. [Means for solving the problem]

[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 curvature center 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. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0019] [Figure 1] The fixed constant velocity universal joint according to the first embodiment of the present invention is shown. Figure (A) is a partial longitudinal sectional view of the fixed constant velocity universal joint, and Figure (B) is a front view of the fixed constant velocity universal joint in Figure (A) viewed from the axial direction. [Figure 2] The outer joint member of the fixed constant velocity universal joint in FIG. 1 is shown. Figure (A) is a partial longitudinal sectional view of the outer joint member, and Figure (B) is a front view of the outer joint member in Figure (A) viewed from the axial direction. [Figure 3] The inner joint member of the fixed constant velocity universal joint in FIG. 1 is shown. Figure (A) is a front view of the inner joint member viewed from one side in the axial direction, Figure (B) is a side view of the inner joint member viewed from the outer periphery, and Figure (C) is a rear view of the inner joint member viewed from the other side in the axial direction. [Figure 4] It is a partial longitudinal sectional view showing the details of the track groove of the outer joint member in FIG. 1(A). [Figure 5] It is a longitudinal sectional view showing the details of the track groove of the inner joint member in FIG. 1(A). [Figure 6] It is a schematic view showing the state where the fixed constant velocity universal joint in FIG. 1(A) takes the maximum operating angle. [Figure 7] It is a partial longitudinal sectional view showing the state of ball incorporation into the outer joint member of the fixed constant velocity universal joint in FIG. 1(A). [Figure 8] Figure (A) is a partial longitudinal sectional view of the outer joint member of the fixed constant velocity universal joint in FIG. 22 to be considered, and Figure (B) is an enlarged sectional view at line A1 - A1 of the track groove on the back side of the outer joint member in Figure (A). [Figure 9] Figure (A) is a partial longitudinal sectional view of the outer joint member of the fixed constant velocity universal joint in FIG. 23 to be considered, and Figure (B) is an enlarged sectional view at line A2 - A2 of the track groove on the back side of the outer joint member in Figure (A). [Figure 10] It is a partial longitudinal sectional view showing the processing state of the track groove of the outer joint member of the fixed constant velocity universal joint in FIG. 23 to be considered. [Figure 11]In the machining process shown in Figure 10, (A) is a partial longitudinal cross-sectional view showing the state in which the machining tool interferes with the bottom of the cup portion at the rear when in close proximity, and (B) is a partial longitudinal cross-sectional view showing the state in which the machining tool interferes with the end of the track groove at the rear when in close proximity. [Figure 12] (A) is a perspective view of the outer joint member of the fixed constant velocity universal joint shown in Figure 23, and (B) is a view of a portion of the inner circumferential surface of the outer joint member of the fixed constant velocity universal joint shown in Figure (A). [Figure 13] This is a partial longitudinal cross-sectional view showing the adjustable range of the relief portion of the track groove in the outer joint member of the fixed constant velocity universal joint shown in Figure 23, which is the subject of the study. [Figure 14] Figure 1(A) is a partial longitudinal cross-sectional view showing the track groove machined surface of the outer joint member of a fixed constant velocity universal joint of the track groove crossing type, which is the first embodiment. Figure (B) is an enlarged cross-sectional view along line XX in Figure (A). Figure (C) is a cross-sectional view of Figure (B) with the ball contact point added. Figure (D) is an enlarged cross-sectional view along line X'-X' in Figure (A). [Figure 15] Figure (A) is a perspective view of the outer joint member of a fixed constant velocity universal joint according to the first embodiment, and Figure (B) is a view showing a part of the inner circumferential surface of the outer joint member of the fixed constant velocity universal joint in Figure (A). [Figure 16] (A) 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, (B) is an enlarged cross-sectional view of (A) along the YY line, and (C) is an enlarged cross-sectional view of (A) along the Y'-Y' line. [Figure 17] This is a partial longitudinal cross-sectional view showing a track groove crossing type fixed constant velocity universal joint according to a second embodiment of the present invention. [Figure 18] This is a schematic diagram illustrating the offset angle. [Figure 19] This is a partial longitudinal cross-sectional view showing a track groove crossing type fixed constant velocity universal joint according to a third embodiment of the present invention. [Figure 20] This is a partial longitudinal cross-sectional view showing a track groove crossing type fixed constant velocity universal joint according to a fourth embodiment of the present invention. [Figure 21]This is a partial longitudinal cross-sectional view showing a cage-offset type fixed constant velocity universal joint according to a fifth embodiment of the present invention. [Figure 22] (A) is a longitudinal cross-sectional view of a conventional fixed constant velocity universal joint (track offset type), and (B) is a front view of the fixed constant velocity universal joint shown in (A) as seen from the axial direction. [Figure 23] Figure (A) is a longitudinal cross-sectional view of a conventional fixed constant velocity universal joint (track groove crossing type), and Figure (B) is a front view of the fixed constant velocity universal joint shown in Figure (A) as seen from the axial direction. [Modes for carrying out the invention]

[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 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 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 1(B)}. 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 1(A)}. 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 columnar portion 5e {see Figure 1(B)} 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 NN 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 1(A)) will be referred to as the "joint opening side," and the opposite side (left side in Figure 1(A)) 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 1(A), 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 axis direction of the joint NN). 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. In addition, to distinguish between track grooves with different inclination directions, the labels 7A and 7B are used, 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 2(A), 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 NN. The track groove 7B, which is circumferentially adjacent to the track groove 7A, 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 NN in the opposite direction to the inclination of the track groove 7A. A relief section Tr is formed at the far end of the track groove 7. Details of the relief section 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 3(B), the plane Q containing the ball trajectory centerline Y of track groove 9A (more specifically, the plane containing the ball trajectory centerline Ya and its center of curvature of the first track groove portion 9Aa of track groove 9A) is inclined by an angle γ with respect to the joint axis NN. 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 and its center of curvature of the first track groove portion 9Ba of track groove 9B) is inclined by an angle γ with respect to the joint axis NN 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 NN, 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 2(A) 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 NN 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 NN [see Figure 1(A)] as it approaches the joint opening side. This ensures the effective track length at the maximum operating angle and suppresses excessive wedge angle. Figure 1(A) shows the track grooves 7 and 9 with an inclination angle γ of 0°.

[0033] As shown in Figure 4, let L be the line connecting point A, the connection point of the ball trajectory centerlines Xa and Xb, and the joint center O. The joint axis N'-N' projected onto the plane M (see Figure 2(A)) containing the ball trajectory centerline X of the track groove 7A is inclined by γ with respect to the joint axis NN, and let β' be the angle between the perpendicular K of axis N'-N' at the joint center O and the line L. The perpendicular K mentioned above lies on the plane P that contains the joint center O when the operating angle is 0° and is perpendicular to the joint axis NN. Therefore, the angle β that the line L makes with respect to the plane P that contains the joint center O when the operating angle is 0° and is perpendicular to the joint axis NN 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 containing the ball trajectory centerline Y of the track groove 9A in Figure 3(B) mentioned above. Therefore, as with Figure 4, strictly speaking, it is not a longitudinal section in a plane containing the axis NN of the joint, but rather a cross-section 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 NN {see Figure 1(A)} as it moves towards the joint. This ensures the effective track length at the maximum operating angle and suppresses excessive wedge angle. As mentioned above, Figure 1(A) 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 3(B)) containing the ball trajectory centerline Y of the track groove 9A is inclined by γ with respect to the joint axis NN, and let β' be the angle between the perpendicular K at the joint center O of axis N'-N' and the line R. The perpendicular K mentioned above lies on the plane P that contains the joint center O when the operating angle is 0° and is perpendicular to the joint axis NN. Therefore, the angle β that the line R makes with respect to the plane P that contains the joint center O when the operating angle is 0° and is perpendicular to the joint axis NN 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 NN 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 for 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 at 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, Figure 6 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.

[0040] Furthermore, Figure 7 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 6) 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 cage 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 cage 5 into which the ball 4 can be inserted, and the ball 4 is assembled into the pocket 5a from 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 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 θ1 to the inner side of the joint necessary for the ball to be installed. (2) The radial dimension of the relief portion is greater than the radial dimension of the chamfered portion of substantially constant width provided over substantially the entire axial area between the spherical inner 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 are provided at regular intervals in the circumferential direction and extend generally in the axial direction. 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 on the spherical inner circumferential surface 156 on which a plurality of track grooves 157 are provided at regular intervals in the circumferential direction and extend generally in the axial direction. 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 mentioned above, when installing the ball, it is necessary to tilt the inner joint member of the internal assembly, which consists of the inner joint member, cage, and ball, to an angle greater than the maximum operating angle θ1. Therefore, the length of the track groove on the far side of the outer joint member is set to a dimension greater than the length required to achieve the maximum operating angle θ1. The state of the track groove on the far side of the outer joint member is specifically shown with reference to Figures 8 and 9. Figure 8(A) is a partial longitudinal section of the outer joint member 102 of the track offset type fixed constant velocity universal joint 101 shown in Figure 22, and Figure 8(B) is an enlarged transverse cross-section of the track groove 107 on the far side of the outer joint member 102 of Figure 8(A) along the line A1-A1. Figure 9(A) is a partial longitudinal section of the outer joint member 152 of the track groove crossing type fixed constant velocity universal joint 151 shown in Figure 23, and Figure 9(B) is an enlarged transverse cross-section of the track groove 157 on the far side of the outer joint member 152 of Figure 9(A) along the line A2-A2.

[0044] Since the axial position of balls 104 and 154 at the ball insertion angle θ2 is further inward than the axial position at the maximum operating angle θ1, as shown in Figures 8(A) and 9(A), both the track offset type outer joint member 102 and the track groove crossing type outer joint member 152 have a length required for ball insertion into the rear track grooves 107 and 157 (the length corresponding to the ball insertion angle θ2 / 2) that is larger than the length required to achieve the maximum operating angle θ1 (the length corresponding to the maximum operating angle θ1 / 2). With the operating angle at 0°, the maximum operating angle θ1 / 2 is shown as a solid line and the ball insertion angle θ2 / 2 is shown as a dashed line with respect to a plane P that includes the joint center O and is perpendicular to the joint axis. In machining (grinding, cutting hardened steel) of either the track groove 107 or 157 of the outer joint members 102 or 152, there are problems with interference with the unmachined surface, the cup bottom 102b or 152b, and with the machined surface, the track groove 107 or 157, when the machining tool T (see Figure 10) is in close proximity, requiring high-precision adjustment.

[0045] As shown in Figure 8(A), 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 8(B), 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 9(A), 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 9(B), 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 8(A) and 9(A), 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 2(A)} 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] Refer to Figures 11(A) and 11(B) for further explanation of interference issues when the machining tool is in close proximity. As shown in Figure 11(A), 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 11(B), 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 9(B)} 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 12(A) shows a perspective view of the outer joint member 152 of the track groove intersection type shown in Figure 23, which is the subject of consideration. Figure 12(B) 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. However, 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, 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, to the inner side of the joint necessary for assembling the ball. After much consideration of this track groove range 157h, we arrived at a new idea: the track groove 157 range 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, it does not require torque 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 specifically described with reference to Figures 14 and 15. Figure 14(A) is a partial longitudinal cross-sectional view showing the track groove machined surface of the outer joint member of the fixed constant velocity universal joint of Figure 1(A), which is the first embodiment; Figure 14(B) is an enlarged cross-sectional view along line XX of Figure 14(A); and Figure 14(C) is a cross-sectional view of Figure 14(B) with the ball contact point added. Figure 14(D) is an enlarged cross-sectional view along line X'-X' of Figure 14(A). Figure 15(A) is a perspective view of the outer joint member of the fixed constant velocity universal joint of the first embodiment; and Figure 15(B) is a view showing a part of the inner circumferential surface of the outer joint member of Figure 15(A).

[0054] In Figure 14(A), 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 section 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 section 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 section 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 range 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 14(C), 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 approximately 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 15(A) is a perspective view of the outer joint member 2, and Figure 15(B) shows a part of the inner circumferential surface of the outer joint member 2 in Figure 15(A). 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 16(A) 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 16(B) is an enlarged cross-sectional view along the YY line of Figure 16(A). Figure 16(C) is an enlarged cross-sectional view along the Y'-Y' line of Figure 16(A). 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 that have 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 16(A) and 16(B), the relief portion Tr of the track groove 7 of the outer joint member 2 of 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 16(B) and 16(C), 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, thus simplifying the shape of the relief portion Tr and its machining.

[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 far side with respect to the joint center O as an example, but conversely, the outer ring track center Oo1 may be positioned on the far 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 against 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 forces are generated at these contact points, resulting in energy loss corresponding to these frictional forces. 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.

number

[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 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, 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, 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), as shown in Figure 17, and it has the following characteristic configuration, similar to the fixed constant velocity universal joint of the first embodiment described above. (1) 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 θ1 to the inner side of the joint necessary for the ball to be installed. (2) The radial dimension of the relief portion is larger than the radial dimension of the conventional chamfered portion.

[0069] A track groove crossing type fixed constant velocity universal joint 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 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 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 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.

[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 Ratio f / PCD BALLThe upper limit is set to 0.009. 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 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, 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), as shown in Figure 19, and has the following characteristic configuration, similar to the fixed constant velocity universal joint of the first embodiment described above. (1) 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 θ1 to the inner side of the joint necessary for the ball to be installed. (2) The radial dimension of the relief portion is larger than the radial dimension of the conventional chamfered portion.

[0072] A fixed constant velocity universal joint according to the 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 centers Oc1 of the spherical outer surface 12 and Oc2 of the spherical inner surface 13 of the cage 5 are offset by equal amounts in the opposite direction axially 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 axially 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 axially toward the back side. With respect to the joint center O, the center of curvature Oc2 of the spherical inner surface 13 of the cage 5 and the center of curvature Oi1 of the arc-shaped ball trajectory centerline Ya of the first track groove 9a are offset in the same direction. The center of curvature Oc1 of the spherical outer surface 12 of the cage 5 is also the center of curvature of the spherical inner surface 6 of the outer joint member 2, and the center of curvature Oc2 of the spherical inner surface 13 of the cage 5 is also the center of curvature 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 pitch circle diameter PCD are used.BALL The ratio f2 / PCD with BALL is set to 0.0045, and the track offset amount f1 and the pitch circle diameter PCD of the ball BALL The ratio f1 / PCD with BALL is set to 0.0045. In addition, in this embodiment, the curvature centers Oo1 and Oc1 are arranged on the opening side with respect to the joint center O, and the curvature centers Oi1 and Oc2 are arranged on the back side. However, conversely, the curvature centers Oo1 and Oc1 may be arranged on the back side with respect to the joint center O, and the curvature centers Oi1 and Oc2 may be arranged on the opening side. Further, the offset amount f is exemplified as being equally distributed between the track offset amount f1 and the cage offset amount f2, but 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 trajectory 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 universal 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 (the length corresponding to the ball insertion angle θ2 / 2) required for inserting the ball, as shown in FIG. 20, a relief portion Tr is formed, and it has the following characteristic configurations similar to the fixed constant velocity universal joint of the first embodiment described above. (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 inserting 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 chamfer 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 center Oo1 of the arc-shaped track groove 7 of the outer joint member 2 and the curvature center 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 center Oc1 of the spherical outer surface 12 of the cage 5 and the curvature center 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, 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), as shown in Figure 21, 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 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 θ1 to the inner side of the joint necessary for the ball to be installed. (2) The radial dimension of the relief portion 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 equivalents set forth in the claims. [Explanation of Symbols]

[0083] 1. Fixed constant velocity universal joint 2. Outer joint member 3. Inner joint member 4 balls 5 cages 6 Spherical inner surface 7 Track grooves 7a First track groove 7b Second track groove 8 Spherical outer surface 9 Track grooves 9a First track groove 9b Second track groove 12 Spherical outer surface 13 Spherical inner surface C. Ball contact point E Radial dimension F Radial dimension Plane containing the ball trajectory centerline N coupling axis O joint center Oo1 Outer wheel truck center Oi1 Inner wheel truck focus Oc1 Cage outer sphere center Oc2 Cage Spherical Center Sr radial position Tr Escape Department X Ball trajectory centerline of the track groove of the outer joint member Xa Ball trajectory centerline of the first track groove Xb Ball trajectory centerline of the second track groove Y-shaped inner joint member, ball track groove, ball trajectory centerline Ya First track groove ball trajectory centerline 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 multiple 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 multiple track grooves formed on its spherical outer surface, each having an arc-shaped portion extending generally in the axial direction; 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; 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 paired track groove of the outer joint member, with respect to a plane (P) that includes the joint center (O) and is perpendicular to the joint axis when the operating angle is 0°. 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 necessary for assembling the ball. A fixed constant velocity universal joint characterized in that the radial dimension of the relief portion is greater than the radial dimension of a chamfer 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.

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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