Constant velocity universal joint

Abstract

In a constant velocity universal joint in which an internal joint member and a shaft are assembled with a twist angle provided on one of the male and female splines, the invention facilitates the intervention of a lubricant between the tooth surfaces of the male and female splines. [Solution] In constant velocity universal joints 2 and 3, in which the internal joint members 5 and 9 and the shaft 13 are assembled with a twist angle θ provided on one of the male and female splines 14 and 15, a recess 18 is formed on at least one of the tooth root surface 14ac of the female spline 14 and the tooth tip surface 15ab of the male spline 15. As a result, when torque is applied to the constant velocity universal joints 2 and 3, the recess 18, which functions as a lubricant reservoir, makes it easier for lubricant to spread between the tooth surfaces 14aa and 15aa of the male and female splines 14 and 15, and facilitates the intervention of lubricant between the tooth surfaces 14aa and 15aa.

Description

Technical Field

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

Background Art

[0002] In the power transmission system of an automobile, a drive shaft is provided to transmit power from a reduction gear (differential) to a drive wheel. As disclosed in Patent Document 1, in a drive shaft, a sliding constant velocity joint is often arranged on the reduction gear side of the shaft, and a fixed constant velocity joint is arranged on the drive wheel side.

[0003] In each of the sliding and fixed constant velocity joints, the end of the shaft is inserted into the inner circumference of an inner joint member (inner ring or trunnion) provided in the joint. At this time, male and female splines are fitted together, namely, a female spline formed on the inner circumferential surface of the inner joint member and a male spline formed on the outer circumferential surface of the shaft.

[0004] In the power transmission system of an automobile, it is required to suppress play as a countermeasure against NVH characteristics, that is, noise, vibration, and harshness. Therefore, in a constant velocity joint, as disclosed in Patent Document 2, a torsional angle may be provided on one of the male and female splines (for example, the male spline of the shaft) in order to minimize the play in the circumferential direction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, when a torsional angle is provided, the positive clearance at the mating portion of the male and female splines decreases. As a result, the lubricant (grease, etc.) sealed inside the constant velocity universal joint has difficulty intervening between the tooth surfaces of the male and female splines. Consequently, oil film breakdown between the tooth surfaces becomes more likely, leading to a problem where fretting wear is more likely to occur.

[0007] In light of the circumstances described above, the problem to be solved is to facilitate the introduction of lubricant between the tooth surfaces of the male and female splines in a constant velocity universal joint in which the internal joint member and the shaft are assembled with a twist angle provided on one of the male and female splines. [Means for solving the problem]

[0008] A first constant velocity universal joint for solving the above problems comprises an outer joint member, an inner joint member housed in the inner circumference of the outer joint member, a torque transmission member for transmitting torque between the outer joint member and the inner joint member, and a shaft inserted into the inner circumference of the inner joint member, wherein a female spline formed on the inner circumferential surface of the inner joint member and a male spline formed on the outer circumferential surface of the shaft are fitted together with a twist angle provided on one of them, and a recess is formed on at least one of the tooth root surface of the female spline and the tooth tip surface of the male spline.

[0009] In the first constant velocity universal joint, a recess formed on at least one of the tooth root surface of the female spline and the tooth tip surface of the male spline functions as a reservoir for lubricant sealed inside the universal joint. Thus, a recess is provided with a set depth so as to be able to store an amount of lubricant (grease, etc.) that can fill the tooth surface matching range of the male and female splines. Due to the presence of this recess, when torque is applied to the universal joint, the lubricant can easily spread from the recess to the space between the tooth surfaces of the male and female splines. As a result, it becomes easier for the lubricant to intervene between the tooth surfaces of the male and female splines.

[0010] In the first constant velocity universal joint, as described above, it becomes easier to introduce lubricant between the tooth surfaces, thus preventing oil film breakdown between the tooth surfaces and suppressing fretting wear. This also makes it easier to avoid a decrease in the strength of the male and female splines due to wear, and improves the strength of the male and female splines. As a secondary effect of the first constant velocity universal joint, the presence of the recess makes it easier to bleed air during the assembly of the constant velocity universal joint.

[0011] The second constant velocity universal joint is a configuration in which, in the first constant velocity universal joint described above, when the portion where the male and female splines are fitted together is defined as the spline fitting portion, recesses are formed at least at locations corresponding to both axial ends of the spline fitting portion.

[0012] At both axial ends of the spline fitting section, it is particularly difficult for lubricant to intervene between the tooth surfaces of the male and female splines. Therefore, as in the second constant velocity universal joint, the presence of recesses at least at the axial ends of the spline fitting section is advantageous for intervening lubricant between the tooth surfaces. [Effects of the Invention]

[0013] The constant velocity universal joint of this disclosure makes it possible to facilitate the intervention of a lubricant between the tooth surfaces of the male and female splines. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view showing a drive shaft incorporating a constant velocity universal joint. [Figure 2] This diagram conceptually shows the spline fitting section unfolded on a plane. [Figure 3] This is a cross-sectional view showing a cross-section perpendicular to the axial direction of the spline fitting portion. [Figure 4] This is a cross-sectional view showing the teeth of a male spline. [Figure 5] This is a cross-sectional view showing a method for forming recesses in the teeth of a male spline. [Figure 6]It is a cross-sectional view showing a method of forming a concave portion in the teeth of a male spline. [Figure 7] It is a cross-sectional view showing a cross-section orthogonal to the axial direction of the spline fitting portion. [Figure 8] It is a cross-sectional view showing the teeth of a female spline. [Figure 9] It is a cross-sectional view showing a method of forming a concave portion in the teeth of a female spline.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of a constant velocity universal joint will be described with reference to the accompanying drawings. In this embodiment, a fixed constant velocity universal joint and a sliding constant velocity universal joint incorporated in a drive shaft will be taken as examples. Needless to say, the constant velocity universal joint may be incorporated in a power transmission shaft (such as a propeller shaft) other than the drive shaft, for example.

[0016] Here, in the following description, the "axial direction" is the direction in which the axis of the drive shaft extends. The "circumferential direction" is the circumferential direction around the axis of the drive shaft. The "radial direction" is the radial direction from the axis of the drive shaft.

[0017] <First Embodiment> First, based on FIG. 1, an overview of the drive shaft 1 will be described.

[0018] As shown in FIG. 1, the drive shaft 1 has a structure in which a fixed constant velocity universal joint 2 is arranged on one end side of the drive shaft 1 and a sliding constant velocity universal joint 3 is arranged on the other end side. The fixed constant velocity universal joint 2 of this embodiment is a so-called Zeppa type. On the other hand, the sliding constant velocity universal joint 3 of this embodiment is a so-called tripod type.

[0019] The fixed constant velocity universal joint 2 comprises an outer joint member 4, an inner joint member 5 housed on the inner circumference of the outer joint member 4, a plurality of balls 6 as torque transmission members, and a retainer 7 that holds the plurality of balls 6 at equal intervals in the circumferential direction. The plurality of balls 6 are arranged between a plurality of track grooves 4a formed on the inner circumferential surface of the outer joint member 4 and a plurality of track grooves 5a formed on the outer circumferential surface of the inner joint member 5. The number of balls 6 is arbitrary, for example, 6 or 8.

[0020] Furthermore, other types of fixed constant velocity universal joints, such as undercut-free types, can also be used as fixed constant velocity universal joint 2.

[0021] The sliding constant velocity universal joint 3 comprises an outer joint member 8, an inner joint member 9 (trunnion) housed on the inner circumference of the outer joint member 8, and a roller 10 as a torque transmission member. Three linear track grooves 8a extending in the axial direction are formed at equal intervals in the circumferential direction on the inner circumferential surface of the cylindrical outer joint member 8. The inner joint member 9 integrally has a cylindrical boss 11 and three leg shafts 12 extending radially from the outer circumferential surface of the boss 11. The roller 10 is rotatably mounted on the outer circumferential surface of the leg shafts 12 via needle rollers.

[0022] Furthermore, other types of sliding constant velocity universal joints, such as ball-type joints, can also be used as sliding constant velocity universal joints.

[0023] In the fixed constant velocity universal joint 2 and the sliding constant velocity universal joint 3, the ends of the shaft 13 are inserted into the inner circumference of the inner joint members 5 and 9, respectively. The shaft 13 may be either a hollow shaft or a solid shaft, but the shaft 13 in this embodiment is a hollow shaft.

[0024] Female splines 14 are formed on the inner circumferential surfaces of the inner joint members 5 and 9. On the other hand, male splines 15 are formed on the outer circumferential surfaces at both ends of the shaft 13. The male splines 15 are press-fitted into the female splines 14. When these male and female splines 14 and 15 are fitted together, the inner joint members 5 and 9 and the shaft 13 are connected, and torque can be transmitted between the inner joint members 5 and 9 and the shaft 13. In the following description, the area where the male and female splines 14 and 15 are fitted together will be referred to as the spline fitting portion 16.

[0025] In the fixed constant velocity universal joint 2 and the sliding constant velocity universal joint 3, a lubricant such as grease is sealed in the internal space of the outer joint members 4 and 8. To prevent leakage of this lubricant and the intrusion of foreign matter from the outside into both joints 2 and 3, resin or rubber boots 17 are fitted between the openings of the outer joint members 4 and 8 and the shaft 13, respectively.

[0026] Next, the structure of the spline fitting portion 16 will be described based on Figures 2 to 4.

[0027] Figure 2 conceptually shows the spline fitting portion 16 unfolded in a plane. In this figure, the directions in which arrows R1 and R2 extend are circumferential directions, and the directions perpendicular to the directions in which arrows R1 and R2 extend are axial directions. Each of the multiple teeth 14a constitutes a female spline 14. On the other hand, each of the multiple teeth 15a constitutes a male spline 15.

[0028] In this embodiment, of the male and female splines 14 and 15, the male spline 15 (multiple teeth 15a) is provided with a helix angle θ. As a result, when no torque is acting on both couplings 2 and 3, the tooth surfaces 14aa of tooth 14a and tooth surfaces 15aa are in contact at the areas enclosed by circles A and B at both axial ends of the spline fitting portion 16. In some cases, the helix angle θ may be provided on the female spline 14 (multiple teeth 14a) instead of the male spline 15.

[0029] Here, we assume that as torque is applied to the fixed constant velocity universal joint 2, the multiple teeth 15a constituting the male spline 15 begin to rotate in the direction of arrow R1. At this time, a gap is formed between the tooth surface 14aa of tooth 14a and the tooth surface 15aa of tooth 15a at the area enclosed by circle A on one axial end of the spline fitting portion 16, allowing lubricant to intervene.

[0030] On the other hand, consider the case where a torque opposite to the above torque acts on the fixed constant velocity universal joint 2, causing the multiple teeth 15a constituting the male spline 15 to begin rotating in the direction of arrow R2. At this time, a gap is formed between the tooth surface 14aa of tooth 14a and the tooth surface 15aa of tooth 15a at the area enclosed by circle B on the other axial end of the spline fitting portion 16, allowing lubricant to intervene.

[0031] The gaps into which the above-mentioned lubricant can intervene are formed not only in the fixed constant velocity universal joint 2, but also in the sliding constant velocity universal joint 3 when torque is applied.

[0032] As shown in Figure 3, the tooth surfaces 14aa of the teeth 14a constituting the female spline 14 and the tooth surfaces 15aa of the teeth 15a constituting the male spline 15 are both formed as curved surfaces, and in this embodiment, they are formed as curved surfaces with an involute curve in cross-section. Note that the tooth surfaces 14aa and 15aa may also be formed as flat surfaces.

[0033] The tooth tip surfaces 14ab of tooth 14a and 15ab of tooth 15a are formed as partially cylindrical or flat surfaces. The tooth root surfaces 14ac of tooth 14a and 15ac of tooth 15a are also formed as partially cylindrical or flat surfaces. A recess 18 with a trapezoidal cross-section is formed on the tooth tip surface 15ab of tooth 15a. The recess 18 only needs to be formed in the portion of the tooth tip surface 15ab that extends axially (perpendicular to the plane of the paper in Figure 3) that corresponds to at least both axial ends of the spline fitting portion 16, but in this embodiment, it is formed along the entire length of the tooth tip surface 15ab.

[0034] The trapezoidal recess 18 is formed such that the opening width in the circumferential direction (left-right direction in Figure 3) gradually increases as it moves toward the tooth root surface 14ac side (radially outward) of tooth 14a. Furthermore, the recess 18 is formed approximately in the center of the width of the tooth tip surface 15ab of tooth 15a.

[0035] The recess 18 functions as a reservoir for lubricant sealed inside both joints 2 and 3. This makes it easier for lubricant to spread from the recess 18 to the tooth surfaces 14aa and 15aa, including the gap (the gap in which lubricant can intervene), when torque is applied to both joints 2 and 3. As a result, it becomes easier for lubricant to intervene between the tooth surfaces 14aa and 15aa. Thus, the recess 18 is provided with a depth D1 such that it can store an amount of lubricant sufficient to satisfy the tooth surface matching range 22 of the male and female splines 14 and 15. Specifically, in order for the recess 18 to function effectively as a lubricant reservoir, it is preferable that the ratio of the depth D1 of the recess 18 to the total tooth height H1 of the teeth 15a be, for example, 10% or more and 20% or less.

[0036] Here, the shape of the tooth 15a in which the recess 18 is formed is not limited to the shape shown in Figure 3, but may also be a shape like those shown in Figures 4(a) to (c).

[0037] In the configuration shown in Figure 4(a), the shape of the cross-section of the recess 18 is trapezoidal, the same as in the configuration shown in Figure 3. However, it differs in that the connection points between the tooth tip surface 15ab and the tooth surface 15aa, and the connection points between the tooth root surface 15ac and the tooth surface 15aa, are formed by smooth curved surfaces. In the configurations shown in Figures 4(b) and (c), respectively, the shape of the cross-section of the recess 18 differs from the configuration shown in Figure 4(a), being arc-shaped and triangular, respectively. In addition, the shape of the cross-section of the recess 18 may be other shapes, such as rectangular.

[0038] Next, a method for forming the tooth 15a (male spline 15) with the recess 18 will be described based on Figures 5 and 6. Figures 5 and 6 illustrate the case of forming the tooth 15a in the form shown in Figure 4(a).

[0039] As a first forming method, it is possible to form a tooth 15a with a recess 18 formed by press working. In the first forming method, as shown in Figure 5(a), a convex portion 19a having a trapezoidal cross-section is provided in the part of the press die 19 for forming the tooth tip surface 15ab of the tooth 15a. As a result, the tooth 15a formed by the press die 19 has a recess 18 formed on its tooth tip surface 15ab with a shape corresponding to the convex portion 19a. Alternatively, as shown in Figure 5(b), the recess 18 may be formed by intentionally creating an insufficient portion in the part of the press die 19 for forming the tooth 15a. In this case, the insufficient portion can be created by intentionally making the diameter of the shaft 13 (material pipe) slightly smaller before forming the male spline 15.

[0040] As a second forming method, it is possible to form teeth 15a with recesses 18 formed by rolling. In the second forming method, as shown in Figure 6, a convex portion 20a with a trapezoidal cross-section is provided in the portion of the rolling rack 20 used for forming the tooth tip surface 15ab of the teeth 15a. As a result, the teeth 15a formed by the rolling rack 20 have recesses 18 with a shape corresponding to the convex portion 20a transferred to their tooth tip surface 15ab. Alternatively, teeth 15a with recesses 18 may be formed by using a flat die or a round die instead of the rolling rack 20.

[0041] As described above, in the two joints 2 and 3, the presence of the recess 18 makes it easier for lubricant to intervene between the tooth surfaces 14aa and 15aa of the male and female splines 14 and 15. As a result, oil film breakdown between the tooth surfaces 14aa and 15aa can be prevented, and fretting wear can be suppressed. Therefore, it is easier to avoid a decrease in the strength of the male and female splines 14 and 15 due to wear, and the strength of the male and female splines 14 and 15 can be improved. As a secondary effect, the presence of the recess 18 also makes it easier to bleed air during the assembly of the two joints 2 and 3.

[0042] Furthermore, in both joints 2 and 3, only the fact that a recess 18 is formed on the tooth tip surface 15ab of tooth 15a needs to be changed, which has the advantage that there is no need to change the spline specifications currently used as standard, such as the large diameter (diameter of tooth tip surface 15ab), small diameter (diameter of tooth root surface 15ac), PCD (pitch circle diameter), OPD (over pin diameter), pitch error, module, etc.

[0043] In addition, in both joints 2 and 3, forming the recess 18 on the tooth tip surface 15ab of the tooth 15a can be done simply by providing the press die 19 and the rolling rack 20 with protrusions 19a and 20a that correspond to the shape of the recess 18. This has the advantage of eliminating the need for new equipment investment. Furthermore, since the recess 18 is formed simultaneously with the molding of the tooth 15a, additional processing to form the recess 18 is unnecessary. As a result, it is possible to avoid a rise in the manufacturing costs of both joints 2 and 3.

[0044] <Second Embodiment> The second embodiment will be described below. Only the differences between the second embodiment and the first embodiment will be described. The difference between the second embodiment and the first embodiment is that, as shown in Figure 7, the recess 18 is formed not on the tooth tip surface 15ab of the tooth 15a constituting the male spline 15, but on the tooth root surface 14ac of the tooth 14a constituting the female spline 14.

[0045] The recess 18 has a trapezoidal cross-sectional shape. The recess 18 only needs to be formed in the portion of the tooth root surface 14ac that extends in the axial direction (perpendicular to the plane of the paper in Figure 7) that corresponds to at least both axial ends of the spline fitting portion 16, but in this embodiment, it is formed along the entire length of the tooth root surface 14ac.

[0046] The trapezoidal recess 18 is formed such that the opening width in the circumferential direction (left-right direction in Figure 7) gradually increases as it moves toward the tooth tip surface 15ab side (radially inward) of the tooth 15a. The recess 18 is also formed approximately in the center of the width of the tooth root surface 14ac of the tooth 14a.

[0047] The recess 18 functions as a reservoir for lubricant sealed inside both joints 2 and 3. Thus, the recess 18 is provided with a depth D2 such that it can hold an amount of lubricant sufficient to satisfy the tooth surface matching range 22 of the male and female splines 14 and 15. Specifically, in order for the recess 18 to function effectively as a lubricant reservoir, it is preferable that the ratio of the depth D2 of the recess 18 to the total tooth height H2 of the teeth 14a be, for example, 10% or more and 20% or less.

[0048] Here, the shape of the tooth 14a in which the recess 18 is formed is not limited to the shape shown in Figure 7, but may also be a shape such as those shown in Figures 8(a) and 8(b).

[0049] In the configuration shown in Figure 8(a), unlike the configuration shown in Figure 7, the cross-sectional shape of the recess 18 is arc-shaped. Also, in the configuration shown in Figure 8(b), the cross-sectional shape of the recess 18 is triangular. In addition, the cross-sectional shape of the recess 18 may be other shapes, such as rectangular.

[0050] Next, a method for forming the tooth 14a (female spline 14) with the recess 18 will be described based on Figure 9.

[0051] The tooth 14a with the recess 18 can be formed by broaching. In this forming method, a convex portion 21a with a trapezoidal cross-section is provided in the portion of the broach mold 21 used for forming the tooth root surface 14ac of the tooth 14a. As a result, the tooth 14a formed by the broach mold 21 has a recess 18 formed on its tooth root surface 14ac with a shape corresponding to the convex portion 21a.

[0052] The same functions and effects as in the first embodiment can be obtained with both joints 2 and 3 of the second embodiment described above.

[0053] In the above embodiment, the recess 18 is formed on the tooth tip surface 15ab of the tooth 15a constituting the male spline 15, or on the tooth root surface 14ac of the tooth 14a constituting the female spline 14. However, this is not limited to this, and the recess 18 may be formed on both the tooth tip surface 15ab and the tooth root surface 14ac. [Explanation of Symbols]

[0054] 2. Fixed constant velocity universal joint 3. Sliding constant velocity universal joint 4. Outer joint member 5. Inner joint member 6. Ball (torque transmission member) 8. Outer joint member 9. Inner joint member 10. Rollers (torque transmission members) 13 shafts 14 Female splines 14ac pedicle 15 Male splines 15ab Tooth tip surface 16 Spline mating section 18 recesses 22 Tooth surface alignment range θ Torsion angle

Claims

1. The device comprises an outer joint member, an inner joint member housed within the inner circumference of the outer joint member, a torque transmission member for transmitting torque between the outer joint member and the inner joint member, and a shaft inserted within the inner circumference of the inner joint member. A constant velocity universal joint in which a female spline formed on the inner circumferential surface of the inner joint member and a male spline formed on the outer circumferential surface of the shaft are fitted together, with a twist angle provided on one of the male splines, A constant velocity universal joint characterized in that a recess is formed on at least one of the tooth root surface of the female spline and the tooth tip surface of the male spline.

2. When the portion where the male and female splines are fitted together is referred to as the spline fitting portion, The constant velocity universal joint according to claim 1, characterized in that the recesses are formed at least at locations corresponding to both axial ends of the spline fitting portion.

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