JP2009121502A - Constant velocity universal joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the fatigue strength of a male spline part by mitigating the stress concentration of both tensile stresses and shear stresses at the male spline part of a stem part of an outer joint member. <P>SOLUTION: A male spline part Sm is formed on an outer circumference of a stem part of an outer joint member. An expansion part 21b with its outside diameter dimension being gradually increased toward a counter shaft end side is provided on a part on the counter shaft end side out of a valley part 21 of the male spline part Sm. Round parts 21b1 of an arc-shaped section are formed on both sides of the circumferential direction of the expanded part 21b, and the radius of curvature of the round parts 21b1 is gradually increased toward the counter shaft end side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a constant velocity universal joint that transmits torque at a constant speed while allowing angular displacement between two axes.

  In recent years, with increasing interest in environmental issues, for example, automobiles are strongly required to tighten exhaust gas regulations and improve fuel efficiency. As part of these measures, constant velocity universal joints used for drive shafts, propeller shafts, etc. However, further weight reduction and strength improvement are strongly demanded. In this type of constant velocity universal joint, a male spline is formed on the outer periphery of the stem portion extending from the mouth portion of the outer joint member, and a female spline is formed on the inner periphery of the female member (for example, a differential gear). It is formed. By fitting the male spline portion on the outer periphery of the stem portion and the female spline portion on the inner periphery of the female side member, the constant velocity universal joint and the female side member are coupled so as to transmit torque. Such an outer joint member is formed, for example, by joining end surfaces of a mouth part and a stem part formed separately (see, for example, Patent Document 1).

  Since the strength of the stem part of the outer joint member having a male spline part is required, usually steel is used as a material, and after forming the male spline part by rolling or pressing, at least the male spline part is formed. Used after quenching and curing. As a method of quenching and hardening after molding, induction hardening is often used, but there are also cases of submerged hardening and carburizing and hardening.

  FIG. 8 shows a so-called end portion of the valley portion 100 on the opposite axis end side (left side in the drawing) connected to an outer peripheral surface (smooth portion) 101 via a diameter-expanded portion 102 whose outer diameter is gradually increased. It is a top view which shows a male spline part of a round-up type. The fatigue failure of the male spline portion of this form usually occurs near the joint between the valley portion 100 and the enlarged diameter portion 102 or at the enlarged diameter portion 102. There are two crack generation modes at that time, one is due to the tensile stress concentrated in the A portion, and the other is due to the shear stress concentrated in the B portion. In the case of steel, cracks are mainly governed by shear stress below Vickers hardness 700 as a guide, and if it is more than that, the stress is governed by tensile stress.

So far, several methods have been proposed as means for improving the fatigue strength of the male spline part. For example, Patent Document 2 discloses a technique for reducing stress concentration by blunting the boundary between the enlarged diameter portion and the tooth surface. Further, Patent Document 3 discloses a high strength technology in which two or more diameter-expanded portions are usually arranged in the axial direction.
JP 2006-64060 A JP 2005-147367 A Japanese National Patent Publication No. 11-514079

  However, although the technique described in Patent Document 2 is effective in reducing the tensile stress concentration, the effect of reducing the shear stress concentration is insufficient. Further, the technique of Patent Document 3 can reduce the concentration of shear stress, but the effect of reducing the concentration of tensile stress is insufficient. As described above, there is a technology that can relieve one of the two stresses that govern crack initiation, but there is no technology that relieves both simultaneously, and there is room for improvement in order to achieve further improvement in fatigue strength. was there.

  Therefore, an object of the present invention is to improve the fatigue strength of the male spline part by reducing the stress concentration of both the tensile stress and the shear stress in the male spline part of the stem part of the constant velocity universal joint.

  The inventors of the present invention manufactured a test piece having a notch in a parallel portion, and used it for a rotational bending fatigue test and a torsional fatigue test, respectively, to determine the relationship between the stress concentration factor and the fatigue strength.

  As a test piece, a medium carbon steel having the same chemical composition shown in FIG. 9 was used, and a test piece having the shape and dimensions (unit: mm) shown in FIGS. 10a and 11a was produced. FIG. 10 a is a test piece for a rotating bending fatigue test, and FIG. 11 a is a test piece for a torsional fatigue test. In the specimen of the rotating bending fatigue test, the radius of curvature of the notch tip is set to five levels of 0.10, 0.15, 0.25, 0.50, and 1.40, and the stress concentration coefficient α is 3.5. , 3.0, 2.5, 2.0, 1.5 (see FIG. 10c). In the torsional fatigue test specimen, the radius of curvature of the notch tip is set to four levels of 0.15, 0.25, 0.50, 1.40, and the stress concentration coefficient α is 3.0, 2.5, 2.0 and 1.5 were set (see FIG. 11c). All of these test pieces were subjected to induction quenching in parallel portions including the notches and then subjected to low temperature tempering. All the test pieces had a surface hardness of about HV650 after the heat treatment.

  First, the rotating bending fatigue test was performed with an Ono type rotating bending fatigue tester in a room temperature atmosphere at a load frequency of 50 Hz.

As a result of the rotating bending fatigue test, cracks occurred along the bottom of the notch regardless of the level of the notch, leading to fracture. The crack initiation mode in this case is governed by tensile stress. The fatigue curve decreased with the decrease of the stress amplitude until the number of times of loading until the fracture exceeded 10 ^5, and a clear fatigue limit phenomenon was observed in which the fracture did not occur when the stress amplitude was below a certain value. The stress amplitude here is a nominal stress amplitude that does not depend on the level of the notch, and a smooth round bar having a notch bottom diameter (φ6.5 mm) was given a bending moment of the same size as the fatigue test. It means the maximum tensile stress amplitude that sometimes acts on the surface.

  FIG. 12 shows the relationship between the stress concentration factor ασ obtained in the rotating bending fatigue test and the fatigue limit strength. As shown in the figure, the fatigue strength improved as ασ decreased. However, as shown by the broken line in the figure, the slope of the fatigue curve was large when ασ ≦ 2.7, and the fatigue strength when ασ was decreased was large. It has been found that the improvement appears more pronounced.

  Next, the torsional fatigue test was carried out under the conditions of a load frequency of 2 Hz and a full swing (stress ratio R = -1) in a normal temperature atmosphere by torque control using an electric hydraulic servo fatigue tester.

As a result of the torsional fatigue test, cracks occurred along the bottom of the notch regardless of the level of the notch, leading to fracture. The crack initiation mode in this case is governed by shear stress. Both reversed torsional fatigue test is load count went until near 10 ⁶ times at most in the range with decreasing stress amplitude fatigue curve drops. The stress amplitude here is a nominal stress amplitude that does not depend on the level of the notch, and is applied to a smooth round bar having a notch bottom diameter (φ17 mm) when a torsion torque of the same magnitude as that in the fatigue test is applied. Means the maximum shear stress amplitude acting on

FIG. 13 shows the relationship between the stress concentration coefficient ατ obtained in the above-mentioned swing-torsion fatigue test and the fatigue strength at 10 ⁵ times. As shown in the figure, the fatigue strength improved as ατ decreased, but as shown by the broken line in the figure, the fatigue curve gradient was large when ατ ≦ 2.1, and the fatigue strength when ατ was decreased It has been found that the improvement appears more pronounced.

From the above, the fatigue strength is improved by stress concentration relaxation regardless of whether the crack initiation is governed by tensile stress or shear stress, and ασ ≦ 2.7 particularly for tensile stress, and shearing It has been found that the stress concentration relaxation effect is further enhanced when ατ ≦ 2.1 against stress. Accordingly, in the diameter-expanded portion of the male spline portion that undergoes fatigue failure in both failure modes, the maximum value σ _1max of the first principal stress concentrated there is not more than 2.7 times the reference stress τ ₀ (σ _1max ≦ 2. 7τ _o ), and it is desirable to tune the shape so that the maximum value of axial shear stress τθ _zmax is 2.1 times or less of the reference stress τ ₀ (τθ _zmax ≦ 2.1τ ₀ ). Here, the reference stress τ ₀ is the torque T, the diameter d _{o of the} bottom of the valley of the male spline shown in FIG. 6, and the inner diameter d _{i of the} male spline (when the male spline is hollow. Is given by: d _i = 0).

τ ₀ = 16 Td _o / [π (d _o ⁴ −d _i ⁴ )]

As a result of various tunings of the shape of the enlarged diameter portion by the present inventors, rounded portions are provided on both sides in the circumferential direction of the enlarged diameter portion of the male spline portion, and the curvature radius of the rounded portion is gradually increased toward the opposite shaft end side. As a result, it was found that σ _1max ≦ 2.7τ _o and τθ _zmax ≦ 2.1τ ₀ can be satisfied.

  Next, a shaft-shaped test piece having male spline portions at both shaft ends is manufactured using a material having the same component (see FIG. 9) as the notched fatigue test piece of FIGS. 10 (a) and 11 (a). (See FIG. 17a) Using this test piece, a double torsional fatigue test and a single torsional fatigue test were performed. According to the involute spline specifications shown in FIG. 17b, two types of test pieces were produced in which the shape of the enlarged diameter portion was equivalent to the product of the present invention and equivalent to the conventional product. These test pieces are subjected to induction hardening and tempering under the same conditions in the atmosphere as a whole. The double torsional fatigue test is performed with four levels of torsional torque amplitude in the range of 850 to 1300 Nm, and the single torsional fatigue test gives four levels of maximum torsional torque in the range of 1250 to 2000 Nm. FIG. 18 shows a T / N diagram obtained by the double-twist torsional fatigue test, and FIG. 19 shows a T / N diagram obtained by the one-way torsional fatigue test. As is clear from both figures, the product of the present invention can achieve a significant improvement in fatigue strength in both the torsional fatigue and the single-sided torsional fatigue compared to the conventional product.

Further, a one-sided torsional fatigue test was performed using a shaft-like test piece simulating the outer joint member shown in FIG. This test piece is composed of a mouse portion equivalent portion M1 made of S53C material and a stem portion equivalent portion M2 made of S45C material. A male spline portion X conforming to the involute spline specifications shown in FIG. 31 is formed on the outer periphery of the mouse portion corresponding portion M1, and the male spline portion X has a strength margin by increasing the pitch circle diameter with respect to the stem portion. It has a certain shape. A male spline portion Y conforming to the involute spline specifications shown in FIG. 17b is formed on the outer periphery of one end of the stem portion corresponding portion M2, and the other end has a cylindrical shape with a diameter of 25 mm. Examples 1 to 4 in which the shape of the enlarged diameter portion of the male spline portion Y of the test piece was equivalent to the product of the present invention and comparative products 1 to 4 equivalent to the conventional product were prepared (see FIG. 32). Among these, the stem part of the test piece according to the implementation product 1 and the comparison product 1 has a constant central diameter of 22 mm, and the center part of the stem portion of the test piece according to the implementation product 2 to 4 and the comparison product 2 to 4 A minimum smooth part having a diameter D is provided, and the ratio D / D ₀ between the diameter D of the minimum smooth part and the pitch circle diameter D ₀ of the male spline part Y is 0.92, 0.94, and 0.96. It was. Each test piece was molded into male spline parts X and Y using a rolling rack, and the end faces of the mouse part equivalent part M1 and the stem part equivalent part M2 were joined to each other by friction welding (the joined parts are shown in FIG. In addition, induction hardening and tempering are performed. This single swing torsional fatigue test was carried out by torque control by applying four levels of maximum torsional torque in the range of 1250 to 2000 Nm. The load waveform was a sine wave, and the load frequency was in the range of 0.5 to 3.0 Hz depending on the load torque amplitude.

The T / N diagrams obtained in this test are shown in FIG. 33 and FIG. FIG. 33 is a diagram illustrating the results of the implementation product 1 and the comparison product 1 in which the minimum smooth portion is not provided at the center of the stem portion. From this figure, all the comparative products 1 were ruptured from the male spline portion Y, whereas all of the practical products 1 were ruptured from the flat portion beside the male spline portion Y, and showed higher strength than the comparative product. It was. FIG. 34 is a diagram illustrating the results of the implementation products 2 to 4 and the comparison products 2 to 4 having different diameters D of the minimum smooth portion. From this figure, all of the comparative products 2 to 4 were broken from the male spline portion Y, whereas the working products 2 and 3 were from the minimum smooth portion, and the working product 4 was the male spline portion Y as in the working product 1. Breakage occurred from the horizontal flat part. From the above, by making the enlarged diameter part of the male spline part equivalent to the product of the present invention, the breakage from the male spline part is suppressed, and the female side member (for example, a differential gear) fitted to the male spline part is damaged. The fear of giving can be avoided. If the ratio D / D ₀ between the diameter D of the minimum smooth portion provided at the center of the stem portion and the pitch circle diameter D ₀ of the male spline portion Y is 0.94 or less (Examples 2 and 3), Since the first rupture can be generated at the minimum smooth portion, the first rupture of the outer joint member can be generated at an arbitrary position by adjusting the position of the minimum smooth portion.

  As described above, the present invention is characterized by the following matters.

  (I) The end surfaces of the mouse part and the stem part are joined to each other, a male spline part is formed on the outer periphery of the stem part, and the outer diameter dimension is gradually increased on one end side in the axial direction of the valley part of the male spline part. In the constant velocity universal joint provided with the outer joint member provided with the expanded diameter portion and the inner joint member accommodated in the inner periphery of the mouth portion, on both sides in the circumferential direction of the increased diameter portion of the male spline portion. A rounded portion is provided, and the radius of curvature of the rounded portion is gradually increased toward one end in the axial direction.

(II) When the torque T is applied, the first principal stress acting on the diameter-expanded portion of the male spline portion and the maximum value of the shear stress in the axial direction are σ _1max and τθ _zmax , respectively. When the reference stress τ ₀ given by the equation (1) is set to the diameter d _{o of} the trough portion and the inner diameter d _i of the male spline portion, the following equations (2) and (3) are satisfied simultaneously.

τ ₀ = 16 Td _o / [π (d _o ⁴ −d _i ⁴ )]... 1)

σ _1max ≦ 2.7τ _o … 2)

τθ _zmax ≦ 2.1τ ₀ … 3)

  As a result of verification by the inventor, in the above configuration, the rate of increase in the radius of curvature of the rounded portion is dR / dL, and the angle of the straight line connecting the small diameter end and the large diameter end of the axial section of the enlarged diameter portion is θ. When the respective values are set in the ranges of 0.05 ≦ dR / dL ≦ 0.60 and 5 ° ≦ θ ≦ 20 °, it has been found that the above equations 2) and 3) are satisfied.

  In addition, when the outer joint member is formed by joining the end surfaces of the mouse part and the stem part, the joint part of the mouse part and the stem part has lower strength against torque load than other parts. By increasing the fatigue strength of the male spline portion by adopting this shape, there is a possibility that fatigue fracture such as a crack may occur in the joint portion. In view of this point, if the stem portion has the maximum diameter at the joint portion with the mouse portion, the area of the joint portion can be increased, and the strength of the joint portion can be ensured. In addition, by increasing the area of the joint and improving the strength in this way, it is possible to reduce the portion subjected to the quenching process for improving the strength, so the time required for the quenching process is shortened and the production efficiency is reduced. Improvements can be made.

Further, from the above test results, a minimum smooth portion having a minimum outer diameter is provided on one end side of the male spline portion of the stem portion, and the diameter D of the minimum smooth portion and the pitch circle diameter D ₀ of the male spline portion are provided. And satisfying D / D ₀ ≦ 0.94, the first rupture can be caused at the minimum smooth portion of the stem portion. Therefore, the position where the first fracture of the outer joint member occurs can be adjusted by changing the location where the minimum smooth portion is formed.

  Moreover, it is preferable that content of C of steel which forms the mouse | mouth part and stem part of an outer joint member is in the following ranges. That is, C is an element having the greatest influence on the hardenability, and contributes effectively to improving the strength by increasing the hardness and depth of the hardened layer after induction hardening. However, if the carbon content is less than 0.40%, the hardened layer ratio (ratio of the hardened layer depth after heat treatment to the axial radius) must be considerably increased in order to ensure the required strength. Therefore, there is a risk that defects such as the occurrence of burning cracks become prominent. On the other hand, when carbon is contained exceeding 0.55%, the grain boundary strength is lowered, and further, the machinability, the cold forgeability, and the fire cracking resistance are also lowered. From the above, it is desirable that the C content be in the range of 0.40% to 0.55%.

  Moreover, it is preferable that content of S of steel which forms the mouse | mouth part and stem part of an outer joint member is in the following ranges. That is, S is a useful element that improves the machinability by forming MnS in steel, and if the S content is less than 0.01%, the machinability is insufficient. On the other hand, if S is contained in an amount exceeding 0.035%, the bondability between the mouse part and the stem part deteriorates, such as weld cracking. From the above, the content of S is preferably in the range of 0.01 to 0.035%.

  As described above, according to the present invention, the stress concentration of both the tensile stress and the shear stress at the male spline portion of the stem portion of the outer joint member can be relaxed, and the fatigue strength of the male spline portion can be increased.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1A shows a tripod type constant velocity universal joint 1 as a constant velocity universal joint according to the present invention. The tripod type constant velocity universal joint 1 is mounted between, for example, a rear differential gear (not shown) of a vehicle and a power transmission shaft 2, and transmits torque at a constant speed while allowing these angular displacements and axial displacements. To do.

  The tripod type constant velocity universal joint 1 includes an inner joint member 3 coupled to the power transmission shaft 2, an outer joint member 4 accommodating the inner joint member 3 on the inner periphery, and the inner joint member 3 and the outer joint member 4. A roller 5 as a rolling element that transmits torque between them is a main component. Leg shafts 3 a are projected from three locations in the circumferential direction of the inner joint member 3. A track groove 4a1 extending in the axial direction is formed at a position of the inner circumference of the mouth portion 4a of the outer joint member 4 in the circumferential direction, and the roller 5 rolls along the track groove 4a1. The distal end of the stem portion 4b of the outer joint member 4 is coupled to a differential gear (not shown). In addition, when the number of rolling elements of the constant velocity universal joint 1 is made to be coprime with the number of rolling elements of the constant velocity universal joint (not shown) attached to the opposite end of the power transmission shaft 2, The NVH characteristics of the automobile can be improved.

  FIG. 1B shows the outer joint member 4 of the tripod type constant velocity universal joint 1. The outer joint member 4 is formed using steel having a C content of 0.40 to 0.55% and an S content of 0.01 to 0.035%. It has a mouse part 4a for accommodating the member 3 and a stem part 4b extending from the mouse part 4a. The outer joint member 4 is formed by joining the end surfaces of the stem portion 4b and the mouth portion 4a. Specifically, the end surface of the protruding portion 4a2 protruding from the mouth portion 4a and the end surface of the stem portion 4b are, for example, They are joined by friction welding or welding (the joint is indicated by Q in FIG. 1B). In the present embodiment, both the protruding portion 4a2 and the stem portion 4b are formed solid, and are hardened in the region indicated by cross-hatching in FIG. 1B, that is, the region including the joint portion Q between the mouse portion 4a and the stem portion 4b. Is given. In addition, in FIG.1 (b), although the hardening process is given only to the surface part of the protrusion part 4a2 and the stem part 4b, you may harden even an inside. Moreover, although illustration is abbreviate | omitted, the hardening process is performed also to the inner periphery of the mouse | mouth part 4a. A male spline portion Sm is formed at the end of the stem portion 4b, and this male spline portion Sm is coupled to a female spline portion Sf provided on the inner periphery of the differential gear De so as to transmit torque (see FIG. 3).

  The outer joint member 4 is not limited to that shown in FIG. 1B. For example, as shown in FIG. 28, the end portion of the protruding portion 4a2 of the mouse portion 4a is hollow and the stem portion 4b is hollow over the entire length. Also good. In this case, the weight can be significantly reduced, and the rigidity can be increased by increasing the outer diameter of the stem portion 4b. The hollow stem portion 4b can be formed from, for example, an electric sewing tube formed from a plate material, or a seamless tube that opens a hole in the material. If the stem portion 4b is formed from an electric sewing tube, the dimensional system is good and relatively inexpensive. However, if the stem portion 4b is formed from a seamless tube, the seam portion is not formed. It becomes difficult to make the thickness uniform.

  In addition, as shown in FIG. 29, in the stem portion 4b, when the outer diameter of the joint portion Q with the protruding portion 4a2 of the mouse portion 4a is the maximum diameter, the joint area at the joint portion Q increases, and the mouse portion The bonding strength between 4a and the stem portion 4b can be increased. Thereby, since the quenching effect process in the outer peripheral part of the joint Q can be omitted, the range for performing the quench process is reduced as compared with the cases shown in FIG. 1B and FIG. 28, and the cycle time required for the process is reduced. It can be shortened. In the above example, the stem portion 4b is integrally formed. However, for example, a portion where the male spline portion Sm is formed can be formed separately and then joined by friction welding or the like (not shown).

In the example shown in FIGS. 1B, 28, and 29, the stem portion 4b has the smallest outer diameter at the male spline portion Sm. For example, the outer diameter is at the center of the stem portion 4b. You may provide the minimum smooth part which becomes the minimum (refer FIG. 30). At this time, the ratio D / D ₀ between the diameter D of the minimum smooth portion and the pitch circle diameter D ₀ of the male spline portion Sm is set to 0.94 or less, thereby causing the first break in the minimum smooth portion. Therefore, by changing the formation position of the minimum smooth portion, the first break can be caused outside the differential case, and maintenance can be facilitated.

  As shown in FIGS. 2, 3, and 6, the male spline portion Sm formed in the stem portion 4 b of the outer joint member 4 has alternating trough portions 21 and ridge portions 22 extending in the circumferential direction in the circumferential direction. Have. The male spline portion Sm of this embodiment is a so-called up-round type formed by rolling, and each valley portion 21 is formed on the straight portion 21a having the same diameter in the axial direction and on the opposite end side. It is comprised with the enlarged diameter part 21b. Similarly, each peak portion 22 includes a straight portion 22a having the same diameter in the axial direction and a reduced diameter portion 22b formed on the opposite end side. As shown in FIG. 4, the starting ends of the enlarged diameter portion 21 b and the reduced diameter portion 22 b are at the same position in the axial direction, and the terminal ends are also at the same position in the axial direction. This male spline part Sm can also be formed by cold forging. In this case, normally, the reduced diameter part 22b of the peak part 22 is not formed, and the entire opposite end side of the peak part 22 has the same outer diameter. It becomes. The male spline part Sm after molding is subjected to heat treatment by induction hardening or the like.

  As shown in FIG. 3, the valley 31 of the female spline portion Sf has the same diameter and is formed up to the end on the opposite shaft end side. On the other hand, the peak portion 32 has a small diameter portion 32a, a large diameter portion 32b, and a rising portion 32c between the small diameter portion 32a and the large diameter portion 32b. The inner diameter dimension of the large diameter part 32b is smaller than the maximum outer diameter dimension (outer diameter dimension of the straight part 22a) of the peak part 22 of the male spline part Sm, and the stem part formed on the opposite end side of the male spline part Sm. It is larger than the outer diameter of the smooth portion 25 of 4b.

  When the male spline portion Sm and the female spline portion Sf are fitted to each other, the tooth surface 23 of the male spline portion Sm and the tooth surface (not shown) of the female spline portion Sf are in strong pressure contact. At this time, the fitting portions (represented by a dotted pattern) of both tooth surfaces extend to the outer diameter side region of the enlarged diameter portion 21b as shown in FIG.

  In addition, although FIG. 3 illustrates the case where both the axial sections of the enlarged diameter portion 21b and the reduced diameter portion 22b are formed in a linear taper shape, both axial sections are formed in a curved shape. You can also. Moreover, it can also be set as the composite shape of a linear form and a curvilinear form.

  As shown in FIG. 2, in the present invention, the enlarged diameter portion 21b of the male spline portion Sm is formed between the rounded portion 21b1 (shown by a dotted pattern) formed on both sides in the circumferential direction and the rounded portion 21b1. And a planar flat portion 21b2. The radius portion 21b1 has a circular cross section in the radial direction, and both circumferential sides thereof are smoothly connected to the tooth surface 23 and the flat portion 21b2.

4 is a plan view showing the vicinity of the enlarged diameter portion 21b in the male spline portion Sm, and FIGS. 5a to 5d are the AA, BB, CC, and DD lines in FIG. FIG. As shown in FIG. 5a, the curvature radius R _A of the rounded portion connecting the straight portion 21a of the valley portion 21 and the tooth surface 23 is constant until reaching the boundary portion with the enlarged diameter portion 21b. As shown in FIGS. 5b to 5d, in the enlarged diameter portion 21b, the radius of curvature of the rounded portion 21b1 is larger than the radius of curvature R _A of the boundary portion and gradually increases toward the opposite shaft end side (R _A <R _B <R _C <R _D ). Further, as shown in FIG. 4, the width of the round portion 21b1 in the circumferential direction is on the side opposite the axis (upward in the drawing) until the position where the boundary line of the round portion 21b1 intersects the ridge line of the mountain portion and the tooth surface 23 disappears. ) Gradually expands toward (), and beyond this, the width dimension gradually decreases. The width dimension in the circumferential direction of the flat portion 21b2 is also gradually enlarged toward the opposite axis end side.

  L in FIG. 4 indicates coordinates taken in the direction of a line passing through the center of the radius of curvature in the rounded portion 21b1 of the enlarged diameter portion 21b. The increasing rate of the radius of curvature of the rounded portion 21b1 is represented by dR / dL, and is set to dR / dL = 0.18 in this embodiment. Further, θ in FIG. 4 represents the inclination angle of a straight line connecting the small diameter end and the large diameter end of the cross section in the axial direction of the enlarged diameter portion 21b. In this embodiment, θ is set to 8.3 °.

  14 to 16, the male spline portion Sm ′ described in Patent Document 1 (Japanese Patent Laid-Open No. 2005-147367), that is, the rounded portion 21b1 ′ is formed at the boundary between the enlarged diameter portion 21b ′ and the tooth surface 23 ′. A male spline portion Sm ′ formed and having a radius of curvature of the rounded portion 21b1 ′ constant over the entire length in the axial direction is shown (in FIGS. 14 to 16, a portion corresponding to the portion shown in FIGS. 2 to 4) (The same sign with (') added to it).

FEM analysis is performed for each of the male spline part Sm (product of the present invention) shown in FIG. 2 and the male spline part Sm ′ (conventional product) shown in FIG. 14, and the maximum value σ _1max of the first principal stress and the shear stress of each are analyzed. The maximum value τθ _zmax was obtained, and a value obtained by dividing these by the reference stress τ ₀ was calculated.

  This FEM analysis is a three-dimensional linear elastic analysis, and “I-deas Ver. 10” was used as analysis software. As shown in FIG. 20, the analysis model is a linear elastic body including one valley portion 21 and 21 ′ of the male spline portions Sm and Sm ′, and the model length is 100 mm. FIG. 21 shows a mesh attached to this analysis model. Each element is a tetrahedral secondary element, the total number of elements is about 200,000, and the total number of contacts is about 300,000. The element length was set to 0.2 mm or less (the minimum element length was 0.05 mm) in the main portion P (including the male spline portions Sm and Sm ′), and 0.5 mm except for the main portion P. FIG. 22 is an enlarged view showing the mesh of the main part P. FIG. 22 (a) shows the product of the present invention corresponding to FIG. 2, and FIG. 22 (b) shows the conventional product corresponding to FIG. . As shown in FIG. 23, a Rigid element was created on the end face M on the opposite end side of the analysis model, and a torque T was loaded on the central axis O of the end face M. However, since a 1 / tooth number model is used as a model, the load torque is 1 / tooth number of actual torque. As shown in FIG. 24, the analysis model has a shape in which the radial direction axis passing through the center of the valley portion 21 is an axis of symmetry, and all the nodes on both side surfaces W in the circumferential direction are cyclically symmetric. In addition, as shown in FIG. 25, the displacement of the normal direction is restrained in the contact surface (it shows with a dotted pattern) with the other party member of an analysis model.

The analysis result of the first principal stress σ ₁ is shown in FIG. 26, and the analysis result of the axial shear stress τθ _z is shown in FIG. 26A and 27B, FIG. 26A shows the product model of the present invention, and FIG. 26B shows the conventional product model. The reference stress τ ₀ in both figures is τ ₀ = 16 Td _o / [π (d _o ⁴ − −) with respect to the torque T, the diameter d _o of the valley of the male spline part Sm, and the inner diameter d _i of the male spline part. d _i ⁴ )].

From the above analysis results, in the conventional product, σ _1max / τ ₀ = 3.03, whereas in the product of the present invention, σ _1max / τ ₀ = 2.48, which is higher than the conventional product in _terms of stress concentration against tensile stress. It has been found that the relaxation effect is enhanced. This is presumably because the radius of curvature of the rounded portion 21b1 in the vicinity of the end of the tooth surface 23 is larger than the radius of curvature at the corresponding portion of the conventional product in the product of the present invention. As described above, if the stress concentration coefficient ασ with respect to the tensile stress is 2.7 or less, the stress concentration mitigating effect becomes significant. Therefore, if the product of the present invention _satisfies σ _1max / τ ₀ ≦ 2.7, Compared to conventional products, the fatigue strength against tensile stress can be greatly increased.

Further, in the conventional product, τθ _zmax / τ ₀ = 2.28, whereas in the product of the present invention, τθ _zmax / τ ₀ = 1.74, which is a stress relaxation effect on the axial shear stress compared to the conventional product. It was also found to increase. As described above, if the stress concentration coefficient ατ with respect to the shear stress is 2.1 or less, the stress concentration relaxation effect becomes significant. Therefore, the product of the present invention in which τθ _zmax / τ ₀ ≦ 2.1 is compared with the conventional product. In comparison, the fatigue strength against shear stress can be greatly improved. Thus, according to the present invention, it is possible to obtain a high stress concentration relaxation effect with respect to both tensile stress and shear stress in the male spline portion Sm. Therefore, the fatigue strength of the stem portion 4b of the outer joint member 4 can be increased.

As a result of further analysis by the present inventor, the rate of increase dR / dL of the radius of curvature of the rounded portion 21b1 shown in FIG. 4 is 0.05 ≦ dR / dL ≦ 0.60, and the inclination angle θ of the enlarged diameter portion 21b is In the range of 5 ° ≦ θ ≦ 20 °, it was found that σ _1max / τ ₀ ≦ 2.7 and τθ _zmax / τ ₀ ≦ 2.1 can be satisfied.

As shown in FIG. 14, in the conventional product, the maximum shear stress τθ _zmax occurs on the center line of the starting point of the enlarged diameter portion 21b ′. Thus, when the maximum shear stress is generated on the center line, when the stem portion 4b of the outer joint member 4 transmits the torque in both the forward and reverse directions, the maximum shear stress is generated in the same part during both forward and reverse rotations. As much as that, fatigue fractures progress easily. On the other hand, in the product of the present invention, as shown in FIG. 2, the maximum shear stress τθ _zmax is generated at both rounded portions 21b1 on the side opposite to the axial end from the starting point of the enlarged diameter portion 21b. Therefore, the generation site of the maximum shear stress differs between the forward rotation and the reverse rotation, and therefore the progress rate of fatigue fracture can be suppressed. From the above, the product of the present invention is particularly suitable for an application in which the torque transmission direction is frequently switched, for example, an application in which the torque transmission direction is reversed in accordance with forward / backward movement of the vehicle.

  The enlarged diameter portion 21b having the rounded portion 21b1 described above is formed by forming a molded portion having a shape corresponding to the enlarged diameter portion 21b on a rolling rack used during rolling, thereby forming the teeth of the male spline portion Sm. It can be formed at the same time. Similarly, when the male spline part is cold forged by press working, the round part is formed simultaneously with the teeth of the male spline part Sm by previously forming a molding part corresponding to the shape of the enlarged diameter part 21b on the die for press working. 21b1 can be molded.

  FIG. 7 shows another embodiment of the present invention. This embodiment is an embodiment in which either one of the male spline part Sm or the female spline part Sf (male spline part Sm in the drawing) has a twist angle β with respect to the axial direction. This is an effective method for loosening between the spline portions Sm and Sf after the combination. When the torsion angle β is provided, the contact pressure between the tooth surfaces on the torque transmission side increases, and as a result, the tensile stress and the shear stress concentrated on the enlarged diameter portion also increase, resulting in a decrease in fatigue strength. From this point of view, the conventional product has been limited to a torsion angle β of substantially 15 °. On the other hand, in the present invention product, the fatigue strength of the power transmission spline can be greatly increased as described above, so that a twist angle β of 15 ° or more can be obtained, and a high backlash effect can be obtained. is there.

  In the above-described embodiment, as the male spline portion Sm, a so-called “saddle type” in which the circumferential width of the enlarged diameter portion 21b is gradually enlarged on the opposite shaft end side is illustrated, but not limited thereto. The present invention can also be applied to a so-called “boat type” male spline portion Sm in which the circumferential width of the enlarged diameter portion 21b is constant. Also in this case, the same effects as those of the present invention can be obtained by providing rounded portions on both sides in the circumferential direction of the enlarged diameter portion 21b and gradually increasing the radius of curvature of the rounded portion toward the opposite end side.

  In the above-described embodiment, the case where the present invention is applied to a tripod type constant velocity universal joint is shown. However, the present invention is not limited to this, and for example, a sliding type constant velocity universal joint such as a cross groove type or a double offset type is shown. The present invention can also be applied to fixed type constant velocity universal joints such as a Rzeppa type.

It is a fragmentary sectional view of the constant velocity universal joint concerning this invention. It is a fragmentary sectional view of an outside joint member. It is a perspective view which shows a counter-shaft end side part (FIG. 1 code | symbol X part) among the male spline parts formed in the outer joint member. It is sectional drawing which expands and shows the code | symbol X part of FIG. (A) A figure is a top view which shows the opposite-axis end side part of a male spline part, (b) A figure is the YY sectional view taken on the line in (a) figure. 4A is a cross-sectional view taken along line AA in FIG. 4A, FIG. 4B is a cross-sectional view taken along line BB, FIG. 4C is a cross-sectional view taken along line CC, and FIG. Is a sectional view taken along the line DD. It is a circumferential direction sectional view of a male spline part. It is a top view which shows schematic structure of the male spline part which has a twist angle. It is a top view of a male spline part. It is a table | surface which shows the chemical composition of the test piece used by a fatigue test. It is a side view which shows the test piece of a rotation bending fatigue test. It is the side view to which the notch part A of the said test piece was expanded. It is a table | surface which shows the relationship between the dimension of a notch part, and a stress concentration factor. It is a side view which shows the test piece of a torsional fatigue test. It is the side view to which the notch part A of the said test piece was expanded. It is a table | surface which shows the relationship between the dimension of a notch part, and a stress concentration factor. It is a figure which shows the measurement result of the fatigue limit strength calculated | required by the rotation bending fatigue test. It is a figure which shows the measurement result of the torsional fatigue strength in 10 < ⁵ > time calculated | required by the torsional fatigue test. It is a perspective view which shows the anti-shaft end side part of the conventional male spline part. It is sectional drawing which shows the anti-shaft end side part of the conventional male spline part. It is a top view which shows the non-axis end side part of the conventional male spline part. It is a side view which shows a test piece. It is a table | surface which shows the involute spline specification of a test piece. It is a T / N diagram obtained by the double torsional fatigue test. FIG. 3 is a T / N diagram obtained in a single swing torsional fatigue test. It is a perspective view which shows a FEM analysis model. It is a perspective view which shows the analysis model which attached | subjected the mesh. (A) The figure is a perspective view of the principal part P of this invention goods which attached | subjected the mesh, The figure (b) is a perspective view of the principal part P of a conventional product similarly. It is a perspective view of the edge part by the side of the non-axis end of an analysis model. It is a front view of the analysis model seen from the arrow direction of FIG. It is a perspective view of an analysis model. It is a figure which shows the analysis result of a 1st principal stress. It is a figure which shows the analysis result of an axial direction shear stress. It is a fragmentary sectional view showing other examples of an outside joint member. It is a fragmentary sectional view showing other examples of an outside joint member. It is a side view which shows a test piece. It is a table | surface which shows the involute spline specification of a test piece. It is a table | surface which shows the shape of a test piece. FIG. 3 is a T / N diagram obtained in a single swing torsional fatigue test. FIG. 3 is a T / N diagram obtained in a single swing torsional fatigue test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tripod type constant velocity universal joint 2 Power transmission shaft 3 Inner joint member 4 Outer joint member 4a Mouse | mouth part 4a1 Track groove 4a2 Projection part 4b Stem part 5 Roller 21 Valley part 21a Straight part 21b Expanded part 21b1 Earl part 21b2 Flat part 22 Mountain portion 22a Straight portion 22b Reduced diameter portion 23 Tooth surface 25 Smooth portion De Differential gear Q Joint portion M1 Mouse portion equivalent portion M2 Stem portion equivalent portion Sf Female spline portion Sm Male spline portion

Claims (7)

The end surfaces of the mouse part and the stem part are joined to each other, a male spline part is formed on the outer periphery of the stem part, and the outer diameter dimension is gradually increased on one end side in the axial direction of the valley part of the male spline part. In a constant velocity universal joint comprising an outer joint member provided with a diameter part and an inner joint member housed in the inner periphery of the mouse part,
A constant velocity universal joint characterized in that rounded portions are provided on both sides in the circumferential direction of the enlarged diameter portion of the male spline portion, and the radius of curvature of the rounded portion is gradually increased toward one end in the axial direction. When the torque T is applied, the first principal stress acting on the diameter-expanded portion of the male spline portion and the maximum value of the shear stress in the axial direction are σ _1max and τθ _zmax , respectively. The constant velocity universal joint according to claim 1, wherein the following 2) and 3) are satisfied simultaneously when the reference stress τ ₀ given by the equation (1) is satisfied with respect to the diameter d _{o of} the portion and the inner diameter d _i of the male spline portion: .
τ ₀ = 16 Td _o / [π (d _o ⁴ −d _i ⁴ )]... 1)
σ _1max ≦ 2.7τ _o … 2)
τθ _zmax ≦ 2.1τ ₀ … 3) When the rate of increase in the radius of curvature of the radius portion is dR / dL, and the angle of the straight line connecting the small diameter end and the large diameter end of the axial section of the enlarged diameter portion is θ, each value is 0.05 ≦ dR / dL ≦ 0.60,
5 ° ≦ θ ≦ 20 °
The constant velocity universal joint according to claim 2, which is in the range of.   The constant velocity universal joint according to claim 1, wherein the stem portion has a maximum diameter at a joint portion with the mouse portion. Among the stem portions, a minimum smooth portion having a minimum outer diameter is provided on one end side of the male spline portion, and the diameter D of the minimum smooth portion and the pitch circle diameter D ₀ of the male spline portion are D / D ₀ ≦ 0. The constant velocity universal joint according to claim 1 satisfying .94.   The constant velocity universal joint according to claim 1, wherein the C content of steel forming the mouse part and the stem part is within a range of 0.40 to 0.45%.   The constant velocity universal joint according to claim 1, wherein the S content of the steel forming the mouse part and the stem part is in the range of 0.01 to 0.035%.