Double offset constant-velocity universal joint

Abstract

A double offset constant-velocity universal joint 1 comprises an outer joint member 2 in which outer track grooves 7 are formed at equal intervals in the circumferential direction, an inner joint member 3 in which inner track grooves 9 are formed at equal intervals in the circumferential direction, balls 4 disposed between the outer track grooves 7 and the inner track grooves 9, a cage 5 for retaining the balls 4, a boot 21 for sealing an opening of the outer joint member 2, a shaft 22, and grease accommodated in a joint interior space 26 inside the outer joint member 2 and the boot 21. The volume of grease is set to be greater than the volume of a joint interior space 26a on the outer diameter side of a boundary 27, the boundary 27 being defined as a virtual cylindrical surface in the axial direction passing through contact points C3, C4 between the inner track grooves 9 and the balls 4 at an operating angle of 0°.

Description

Double Offset Constant Velocity Universal Joint

[0001] The present invention relates to a double offset constant velocity universal joint used in power transmission systems of automobiles and various industrial machinery, for example, drive shafts and propeller shafts of automobiles.

[0002] Constant velocity universal joints applied to automobile drive shafts are broadly classified into fixed constant velocity universal joints that allow only angular displacement between two shafts, and sliding constant velocity universal joints that allow both angular displacement and axial displacement. An automobile drive shaft generally uses a fixed constant velocity universal joint on the driving wheel side (also called the outboard side) and a sliding constant velocity universal joint on the differential side (also called the inboard side), and the drive shaft is formed by connecting these two constant velocity universal joints via an intermediate shaft. Various types of constant velocity universal joints are selected according to respective usage conditions and applications.

[0003] Typical examples of sliding constant velocity universal joints include double offset constant velocity universal joints (DOJ) and tripod constant velocity universal joints (TJ). DOJ-type sliding constant velocity universal joints are widely used due to their low manufacturing cost and small rotational play inside the joint. In addition, DOJ-type sliding constant velocity universal joints are known to have 6 or 8 balls. Patent Document 1 describes a compactly designed DOJ with 8 balls, and Patent Document 2 describes a DOJ that achieves a higher operating angle, lighter weight and more compact size, and can achieve a maximum operating angle of 30° or more.

[0004] Japanese Patent Laid-Open No. 10-73129 Japanese Patent Laid-Open No. 2007-85488

[0005] With the expansion of the market for electric vehicles (EVs) and hybrid electric vehicles (HEVs) that use motors as a power source for driving, the functions required of drive shafts have been changing in recent years to accommodate electric vehicles. For example, in electric vehicles, in order to secure space for mounting the battery, the mounting position of the drive unit 103, which consists of an e-axle 101 and a drive shaft 102, needs to be lowered overall, as shown in Figure 9 (Factor 1). Furthermore, as shown in Figure 10, the e-axle 101 requires a large space in the width direction of the vehicle, so the length of the drive shaft 102 tends to be shortened (Factor 2). Note that the e-axle 101 refers to a unit in which the motor, inverter, and reduction gear are integrated.

[0006] Based on factors 1 and 2 described above, the operating angle of the sliding constant velocity universal joint tends to be larger in drive shafts for electric vehicles compared to engine-driven vehicles. Here, the operating angle refers to the angle of operation of the sliding constant velocity universal joint when the steering wheel is in the straight-ahead position in a single-occupant vehicle traveling on a horizontal, flat road surface. The operating angle is determined according to the design conditions for each vehicle type, and in sliding constant velocity universal joints for engine-driven vehicles, the operating angle is often set within the range of 2° to 6°.

[0007] When the operating angle of a sliding constant velocity universal joint increases, the contact pressure between parts during torque transmission increases, leading to increased heat generation at the contact points. This increased heat generation in the joint causes deterioration of the grease sealed inside the joint, specifically a decrease in grease consistency. When the grease consistency decreases, the centrifugal force acting during high-speed rotation of the sliding constant velocity universal joint makes the grease more likely to stick to the inner surface of the outer joint member. This can lead to grease depletion on the inner diameter side of the joint's internal space inside the outer joint member and boot, potentially reducing the joint's durability or NVH (Noise, Vibration, Heat, and Harshness) characteristics. In particular, in double offset type constant velocity universal joints, the relative movement between internal parts becomes sliding, making the decrease in durability and NVH characteristics due to grease depletion especially pronounced.

[0008] Therefore, the present invention aims to provide a double-offset constant velocity universal joint that can improve durability or NVH characteristics even when the normal operating angle is increased.

[0009] To achieve the above objective, the present invention provides a double offset type constant velocity universal joint comprising: an outer joint member having linear outer track grooves extending axially at equal intervals in the circumferential direction formed on a cylindrical inner circumferential surface and an open end on one side in the axial direction; an inner joint member having linear inner track grooves extending axially at equal intervals in the circumferential direction formed on a spherical outer circumferential surface; a plurality of balls disposed between a pair of outer track grooves and inner track grooves; a cage for holding the plurality of balls; a boot for sealing the opening of the outer joint member; a shaft coupled to the inner joint member in a torque-transmitting manner; and grease contained in the joint internal space inside the outer joint member and boot, characterized in that the volume of the grease is greater than the volume of the joint internal space on the outer diameter side of a boundary with respect to a virtual cylindrical surface in the axial direction passing through the contact point between the inner track groove and the ball at an operating angle of 0°.

[0010] With this double-offset constant velocity universal joint, even in the worst lubrication conditions caused by a decrease in grease consistency, for example, when all the grease sticks to the inner circumference of the outer joint member or the inner circumference of the boot, the contact points between the outer track groove of the outer joint member and the ball, and furthermore, the contact points between the inner track groove of the inner joint member and the ball, remain immersed in grease. Therefore, oil film breakdown can be prevented at all contact points, and even when used in applications requiring a large operating angle, a double-offset constant velocity universal joint with the necessary durability and NVH performance can be provided.

[0011] Preferably, the volume of the grease is 75% or less of the volume of the internal space of the joint inside the outer joint member and boot.

[0012] The double offset constant velocity universal joint described above can be applied when the normal operating angle is greater than 6°.

[0013] It is preferable to use a urea-based thickener as the thickener for the aforementioned grease.

[0014] The outer track groove and inner track groove are preferably finished by forging.

[0015] The number of balls can be six or more and eight or less.

[0016] According to the present invention, it is possible to provide a double-offset type constant velocity universal joint that can improve durability and NVH characteristics even when the normal operating angle is increased.

[0017] This is a longitudinal cross-sectional view of a double offset type constant velocity universal joint along the line B-N-B in Figure 2. This is a transverse cross-sectional view of a double offset type constant velocity universal joint along the line A-A in Figure 1. This is a magnified transverse cross-sectional view of one track groove, ball and cage along the line B-N in Figure 2. This is a longitudinal cross-sectional view of a double offset type constant velocity universal joint with an operating angle along the line B-B' in Figure 2. This is a perspective view of the outer joint member from the opening side. This is a magnified perspective view of area A in Figure 5. This is a longitudinal cross-sectional view of a double offset type constant velocity universal joint with grease sealed in along the line B-B' in Figure 2. This is a longitudinal cross-sectional view of a double offset type constant velocity universal joint with grease sealed in along the line B-B' in Figure 2. This is a front view of an automobile. This is a front view of an automobile.

[0018] A double-offset constant-velocity universal joint according to the first embodiment of the present invention will be described with reference to Figures 1 to 8. Figure 1 is a longitudinal cross-sectional view of the double-offset constant-velocity universal joint of this embodiment, which is a longitudinal cross-sectional view taken along the line B-N-B in Figure 2. Figure 2 is a transverse cross-sectional view of the double-offset constant-velocity universal joint of this embodiment, which is a transverse cross-sectional view taken along the line A-A in Figure 1. Figure 3 is a transverse cross-sectional view showing an enlarged view of one track groove, ball and cage along the line B-N in Figure 2. Figure 4 is a longitudinal cross-sectional view taken along the line B-B' in Figure 2, showing a double-offset constant-velocity universal joint with an operating angle. Figure 5 is a perspective view of the outer joint member as seen from the opening side, and Figure 6 is a perspective view showing an enlarged view of area A in Figure 5.

[0019] Figures 1 and 2 show a double offset type constant velocity universal joint (sometimes called DOJ or DOJ-type sliding constant velocity universal joint), which is a type of sliding constant velocity universal joint. The double offset type constant velocity universal joint 1 mainly consists of a cup-shaped outer joint member 2 with an open end on one axial side, an inner joint member 3 positioned inside the outer joint member 2, a torque-transmitting ball 4, and a cage 5 that holds the ball 4. In the following description, the axial direction and circumferential direction refer to the axial and circumferential directions of the double offset type constant velocity universal joint when the operating angle is 0°, respectively.

[0020] As shown in Figure 5, multiple (eight in this embodiment) outer track grooves 7 are formed on the cylindrical inner surface 6 of the outer joint member 2 at equal intervals in the circumferential direction and in a straight line along the axial direction. As shown in Figure 1, the same number of inner track grooves 9 as the outer track grooves 7 of the outer joint member 2 are formed on the spherical outer surface 8 of the inner joint member 3 at equal intervals in the circumferential direction and in a straight line along the axial direction, facing the outer track grooves 7 of the outer joint member 2. One ball 4 is incorporated between each of the opposing outer track grooves 7 and inner track grooves 9. The balls 4 are housed in pockets 5a of the cage 5. The cage 5 holds multiple (eight in this embodiment) balls 4 at equal intervals in the circumferential direction.

[0021] The outer track groove 7 of the outer joint member 2 and the inner track groove 9 of the inner joint member 3 are generally finished by cold forging (no finishing processes such as grinding after the quenching process are performed). In other words, the surfaces of both the outer track groove 7 and the inner track groove 9 are surfaces finished by forging.

[0022] The cage 5 has a spherical outer surface 11 and a spherical inner surface 12. The spherical outer surface 11 fits into contact with and guides the cylindrical inner surface 6 of the outer joint member 2, and the spherical inner surface 12 fits into contact with and guides the spherical outer surface 8 of the inner joint member 3. The spherical outer surface 11 of the cage 5 is formed with a radius of curvature Rc1 with its center of curvature O1, and the spherical inner surface 12 is formed with a radius of curvature Rc2 with its center of curvature O2. The spherical outer surface 8 of the inner joint member 3 is formed with a radius of curvature Ri with its center of curvature O2. The centers of curvature O1 and O2 are located on the axis N-N and are offset by an equidistant distance F on the opposite side in the axial direction from the joint center O. As a result, as shown in Figure 4, when the joint 1 takes an operating angle θ, the ball 4 is always guided on a plane that bisects the angle between the axes of the outer joint member 2 and the inner joint member 3, and as a result, the two axes rotate at a constant speed.

[0023] As shown in Figures 1, 5, and 6, a retaining ring groove 15 is provided at the open end of the outer joint member 2, and a retaining ring 17 is fitted into this retaining ring groove 15 to prevent the inner assembly I, consisting of the inner joint member 3, ball 4, and cage 5 shown in Figure 1, from coming out of the open end of the outer joint member 2. A boot mounting groove 16 is provided on the outer circumference of the open end of the outer joint member 2. As shown in Figure 5, the outer joint member 2 is integrally formed with a bottomed cylindrical cup portion 2a having an outer track groove 7 on its inner circumference, and a stem portion (shaft portion) 2b extending axially from the opposite side of the cup portion 2a. For example, in a double offset type constant velocity universal joint 1 for electric vehicles, the stem portion 2b is connected to the e-axle.

[0024] As already mentioned, a linear inner track groove 9 is formed on the spherical outer surface 8 of the inner joint member 3. Therefore, as shown in Figure 1, the groove depth of the inner track groove 9 becomes shallower as you move from the axial center of the inner joint member 3 towards both ends. A spline (including serrations, the same applies hereinafter) 14 is formed in the connecting hole 13 of the inner joint member 3. As shown in Figure 4, the shaft end of the intermediate shaft 22 is spline-fitted to this spline 14. The intermediate shaft 22 is fixed axially to the inner joint member 3 by a shoulder portion 22a integrally formed on the intermediate shaft 22 and a retaining ring 23 fitted into a retaining ring groove provided at one end of the intermediate shaft 22. The other end of the intermediate shaft 22 is connected to a fixed constant velocity universal joint (not shown) to form a drive shaft.

[0025] Eight pockets 5a are provided at equal intervals in the circumferential direction at the axial center of the cage 5 shown by line A-A in Figure 1, and columnar sections 5b (see Figure 2) are located between adjacent pockets 5a. A notch 5c for incorporating the inner joint member 3 is provided on the inner circumference of the large-diameter end of the cage 5. The stopper surface 5d of the cage 5 is formed in a conical shape that connects tangentially to the spherical outer surface 11. In the sliding constant velocity universal joint 1 of this embodiment, the maximum operating angle is set to, for example, 25°. When the joint takes an operating angle, the cage 5 tilts by half the angle between the axes of the outer joint member 2 and the inner joint member 3, so the inclination angle S of the stopper surface 5d is set to 12.5°. This allows the maximum allowable angle of the sliding constant velocity universal joint 1 to be restricted.

[0026] Based on Figure 3, the contact state between the outer track groove 7 of the outer joint member 2 and the ball, and the contact state between the inner track groove 9 of the inner joint member 3 and the ball 4 will be explained. Figure 3 shows one track groove 7, 9, ball 4 and cage 5 along the line B-N in Figure 2.

[0027] As shown in Figure 3, the cross-sections of the outer track groove 7 of the outer joint member 2 and the inner track groove 9 of the inner joint member 3 are formed in a Gothic arch shape, which is a combination of two circular arcs. Therefore, the ball 4 makes angular contact with the track grooves 7 and 9 at two contact points C1, C2, C3, and C4, respectively. The cross-sectional shape of the outer track groove 7 and the inner track groove 9 is not limited to the Gothic arch shape described above, but may also be elliptical. During torque transmission, contact ellipses E1 and E2 are formed at contact points C1, C2, C3, and C4 based on Hertz's elastic contact theory. As shown in Figure 6, the contact ellipses E1 and E2 have an elliptical shape with the circumferential direction of the track grooves 7 and 9 of the outer joint member 2 and the inner joint member 3 as their major axes.

[0028] The track grooves 7 and 9 and the ball 4 are in contact with each other at a track contact angle α. The track contact angle α is the angle α between the line La and the line Lb in Figure 3. Line La is the center line of the cross-section of the track grooves 7 and 9, and corresponds to the line B-N in Figure 2. Line Lb is the line connecting the contact points C1, C2, C3, and C4 of the ball 4 on the side surface of the track grooves 7 and 9 and the center Ob of the ball 4. The radius of curvature of the cross-section of the track grooves 7 and 9 is R2, and the radius of the ball 4 is R1. The radius of curvature R2 of the track grooves 7 and 9 is greater than the radius R1 of the ball 4 (R2 > R1).

[0029] The overall configuration of the double offset type constant velocity universal joint 1 of this embodiment is as described above. As shown in Figure 7, the opening of this double offset type constant velocity universal joint 1 is sealed by a bellows-shaped resin or rubber boot 21. Specifically, the large-diameter end of the boot 21 is fitted to the outer circumferential surface of the outer joint member 2, and the small-diameter end of the boot 21 is fitted to the outer circumferential surface of the intermediate shaft 22. By tightening the boot band 24 fitted around the outer circumference of the large-diameter end of the boot 21, the large-diameter end of the boot 21 is fixed in close contact with the outer circumferential surface of the opening end of the outer joint member 2. Also, by tightening the boot band 25 fitted around the outer circumference of the small-diameter end of the boot 21, the small-diameter end of the boot 21 is fixed in close contact with the outer circumferential surface of the intermediate shaft 22.

[0030] In this joint 1, an internal joint space 26, sealed from the outside air, is formed by the space inside the outer joint member 2 and the space inside the boot 21. The internal joint space 26 is the space inside the outer joint member 2 and the space inside the boot 21, excluding the internal components (inner joint member 3, ball 4, retainer 5, intermediate shaft 22, retaining ring 23, etc.) that are located inside the outer joint member 2 and the boot 21. An appropriate amount of grease is supplied to the internal joint space 26.

[0031] Next, we will explain the characteristic configuration of this double offset constant velocity universal joint 1.

[0032] The double-offset constant-velocity universal joint 1 of this embodiment is characterized by having a larger amount of grease contained in the joint's internal space 26 compared to conventional double-offset constant-velocity universal joints for engine-driven vehicles. Specifically, as shown in Figure 7, the volume of grease sealed in the joint's internal space 26 is larger than the volume of the joint's internal space 26a (gray-painted portion) on the outer diameter side of the boundary 27, which is a virtual cylindrical surface in the axial direction passing through the contact points C3 and C4 between the inner track groove 9 and the ball 4 at an operating angle of 0°. In Figure 7, d represents the diameter dimension of the cylindrical surface as the boundary 27. The outer diameter side means the direction perpendicular to the axis N-N at an operating angle of 0° and away from the axis N-N.

[0033] As already mentioned, in the double offset constant velocity universal joint 1 for electric vehicles, the normal operating angle is large, and for the same vehicle model, it is often set to a larger normal operating angle (a normal operating angle exceeding 6°, for example, a normal operating angle of about 8°) than the normal operating angle in engine-driven vehicles (which is set in the range of 2° or more and 6° or less). Therefore, in the double offset constant velocity universal joint 1 for electric vehicles, the grease tends to deteriorate quickly and its consistency decreases. When the consistency of the grease decreases, it tends to stick to the inner surface of the outer joint member 2 and the inner surface of the boot 21 due to the centrifugal force when the joint rotates, so the grease at the contact point on the inner diameter side of the joint inner space 26 tends to be depleted and the lubrication decreases. The inner diameter side means the direction perpendicular to the axis N-N when the operating angle is 0° and approaching the axis N-N.

[0034] In contrast, in this embodiment, even in the worst lubrication state caused by a decrease in grease consistency, that is, when the entire amount of grease adheres to the inner circumferential surface of the outer joint member 2 and the inner circumferential surface of the boot 21, the contact points C1 and C2 between the outer track groove 7 of the outer joint member 2 and the ball 4, and furthermore, the contact points C3 and C4 between the inner track groove 9 of the inner joint member 3 and the ball 4, remain immersed in grease. Therefore, oil film breakdown can be prevented at all contact points C1 to C4, and even when used in applications requiring a large operating angle, such as a double-offset type constant velocity universal joint 1 for electric vehicles, a double-offset type constant velocity universal joint 1 with the required durability and NVH performance can be provided.

[0035] The volume of grease sealed in the joint internal space 26 is preferably 60% or more of the total volume of the joint internal space 26, and more preferably 65% ​​or more. If it is 65% or more, even in the worst lubrication condition described above (where the entire amount of grease is stuck to the outer joint member 2 and the boot 21), as shown in Figure 8, not only the contact ellipse E2 formed between the outer track groove 7 and the ball 4, but also the entire contact ellipse E1 formed between the inner track groove 9 and the ball 4 can be immersed in grease.

[0036] On the other hand, if there is too much grease, the effects of increased weight, higher costs, and reduced ease of assembly become significant, and the centrifugal force applied to the boot 21 during rotation becomes large, causing excessive expansion of the boot 21. Therefore, the volume of grease should be 75% or less, preferably 70% or less, of the volume of the internal space 26 of the joint. Figure 8 shows the internal space 26b on the outer diameter side of the joint, which is 70% of the volume of the internal space 26 of the joint, in gray. The volume of grease should be less than or equal to the volume of this internal space 26b on the outer diameter side. In Figure 8, d' represents the diameter dimension of the virtual cylindrical surface as the boundary 27 in this case (d' < d).

[0037] To suppress the decrease in consistency due to thermal effects and grease degradation, it is preferable to use urea-based thickeners as the thickeners contained in the grease. Urea-based thickeners, which mainly consist of urea compounds, have superior heat resistance and shear stability compared to metal soap-based thickeners, and are characterized by strong adhesion to metal surfaces. Therefore, by using urea-based thickeners, it is possible to reduce metal contact and improve wear resistance.

[0038] In the above description, a double offset constant velocity universal joint 1 with eight balls was used as an example, but the present invention can also be similarly applied to a double offset constant velocity universal joint with seven or fewer balls (for example, six).

[0039] Furthermore, while the above explanation uses a double-offset constant-velocity universal joint for electric vehicles as an example, it can also be used as a double-offset constant-velocity universal joint for engine-driven vehicles, such as SUVs with high ground clearance, where the normal operating angle is large. In addition, it can be used not only for automobiles but also as a double-offset constant-velocity universal joint for general industrial machinery.

[0040] The present invention is not limited in any way to the embodiments described above, and can be implemented in various other forms without departing from the spirit of the invention. The scope of the present invention is indicated by the claims, and includes all modifications within the meaning and scope of the equivalents set forth in the claims.

[0041] 1. Double offset type constant velocity universal joint 2. Outer joint member 3. Inner joint member 4. Ball 5. Cage 6. Cylindrical inner surface 7. Outer track groove 8. Spherical outer surface 9. Inner track groove 11. Spherical outer surface 12. Spherical inner surface C1-C4 Contact points E1, E2 Contact ellipse O Joint center O1 Curvature center O2 Curvature center

Claims

1. A double offset type constant velocity universal joint comprising: an outer joint member having linear outer track grooves extending axially at equal intervals in the circumferential direction formed on its cylindrical inner surface and an open end on one side in the axial direction; an inner joint member having linear inner track grooves extending axially at equal intervals in the circumferential direction formed on its spherical outer surface; a plurality of balls disposed between a pair of outer track grooves and inner track grooves; a cage for holding the plurality of balls; a boot for sealing the opening of the outer joint member; a shaft coupled to the inner joint member in a torque-transmitting manner; and grease contained in the joint internal space inside the outer joint member and boot, wherein the volume of the grease is greater than the volume of the joint internal space on the outer diameter side of a boundary with respect to a virtual cylindrical surface in the axial direction passing through the contact point between the inner track groove and the ball at an operating angle of 0°.

2. The double offset type constant velocity universal joint according to claim 1, wherein the volume of the grease is 75% or less of the volume of the internal space of the joint inside the outer joint member and boot.

3. The double offset type constant velocity universal joint according to claim 1, wherein the normal operating angle is greater than 6°.

4. The double offset type constant velocity universal joint according to claim 1, wherein the grease contains a urea-based thickener.

5. The double offset constant velocity universal joint according to claim 1, wherein the outer track groove and the inner track groove are finished by forging.

6. The double offset type constant velocity universal joint according to claim 1, wherein the number of balls is 6 or more and 8 or less.

Images