JP2008240971A - Power transmission shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance fatigue strength of a male spline part of a power transmission shaft by easing both of tensile stress and shear stress in the male spline part, and also to enhance fatigue strength in a small diameter cylinder part. <P>SOLUTION: The male spline part Sm is formed along an outer periphery of both shaft ends of the power transmission shaft. A diameter enlarged part 21b of which outside diameter dimension is gradually enlarged to an anti-shaft end side is provided on the anti-shaft end side part of a valley part 21 of the male spline part Sm. A round part 21b1 having an arc shaped cross section is provided on circumferential both sides of the diameter enlarged part 21b, and a radius of curvature of the round part 21b1 is gradually increased toward the anti-shaft end side. When a surface area of a small diameter cylinder part having the smallest outside diameter dimension in a region between the male spline parts on both shaft ends is A, and a cross sectional area is A<SB>0</SB>, 0<A/A<SB>0</SB>≤25. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power transmission shaft coupled to a female member through a spline (including serrations, the same applies hereinafter).

  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, power transmission shafts used for drive shafts, propeller shafts, etc. There is a strong demand for further weight reduction and strength improvement. In this type of power transmission shaft, a male spline is formed on the outer periphery, and a female spline is formed on the inner peripheral surface of the inner joint member of the constant velocity universal joint. By fitting the male spline portion on the outer periphery of the power transmission shaft and the female spline portion on the inner peripheral surface of the inner joint member, the power transmission shaft and the inner joint member are coupled so as to be able to transmit torque.

  Since a power transmission shaft with a male spline part requires strength, usually steel is used as the material, and after forming the male spline part by rolling or pressing, at least the male spline part is hardened and hardened. Used. 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, and if it is swung torsional fatigue, it 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 Literature 1 discloses a technique for reducing stress concentration by blunting the boundary between the enlarged diameter portion and the tooth surface. Further, Patent Document 2 discloses a high strength technology in which two or more diameter-expanded portions are usually arranged side by side in the axial direction.
JP 2005-147367 A Japanese National Patent Publication No. 11-514079

  However, in the technique described in Patent Document 1, an effect is recognized in reducing the tensile stress concentration, but the effect of reducing the shear stress concentration is insufficient. Further, in the technique of Patent Document 2, the shear stress concentration can be reduced, but the effect of reducing the tensile stress concentration 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.

Even if the fatigue strength of the male spline part is increased, if the fatigue strength of the material itself forming the power transmission shaft is low, fatigue fracture such as cracks may occur in other parts. For example, as shown in FIG. 1, when the constant velocity universal joints J ₁ and J ₂ are coupled to both ends of the power transmission shaft 2, the outer joint when the joint of the power transmission shaft 2 takes a large operating angle. Small diameter cylindrical portions 2a and 2b may be formed at portions that interfere with the open ends of the members 4 and 14 to increase the limit operating angle of the joint. At this time, fatigue breakage such as a crack may occur in the small diameter cylindrical portions 2a and 2b of the power transmission shaft 2 having relatively low strength.

  Therefore, in the present invention, the stress concentration of both the tensile stress and the shear stress in the male spline portion of the power transmission shaft is relaxed to improve the fatigue strength of the male spline portion and increase the fatigue strength of the small diameter cylindrical portion. With the goal.

  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 loadings until the break 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 conducted at four levels in the range of 850 to 1300 Nm, and the single torsional fatigue test gives a maximum torsional torque of four levels in the range of 1250 to 2000 Nm. FIG. 18 shows a T / N diagram obtained in the double swing torsional fatigue test, and FIG. 19 shows a T / N diagram obtained in the single swing 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 double torsional fatigue and the single swing torsional fatigue compared to the conventional product.

Next, a shaft-shaped test piece shown in FIG. 28A was manufactured using a material having the same component (see FIG. 9) as the notched fatigue test piece shown in FIGS. 10A and 11A. At both shaft ends of the test piece, there are male spline portions according to the involute spline specifications shown in FIG. 17b. A region between each male spline portion has a small diameter cylindrical portion having a diameter D _o = 19 mm and a smooth outer peripheral surface. The male spline part of this shaft-shaped test piece was prepared in two types: one with the rounded-up portion of the enlarged diameter part defined in the present invention (B series) and one with the conventional shape (C series). In addition, four levels were prepared with different A / A ₀ values when the surface area of the small-diameter cylindrical portion of the shaft-shaped test piece was A and the cross-sectional area was A ₀ (see FIG. 28B). These test pieces were subjected to induction hardening and tempering.

A double-twist torsional fatigue test was performed using the above test piece. This double-twist torsional fatigue test was performed at four levels in the range of 850 to 1300 Nm, and the number of tests was ten. From the T / N diagram obtained in this test, the ratio of 10 ⁵ times torsional fatigue strength in each test piece and its 95% confidence width were determined, and the results are shown in FIG. The ratio of torsional fatigue strength refers to each test when the 10 ⁵ times torsional fatigue strength obtained from the regression equation obtained from the T / N diagram of test piece B-1 (A / A ₀ = 10) is 100. It is the ratio of the fatigue strength of the pieces. In FIG. 29, the ratio of torsional fatigue strength of each test piece is shown on the vertical axis, and A / A ₀ is shown on the horizontal axis. All of the test pieces C-1 to C-4 (shown by triangles in FIG. 29) having the male spline portion of the conventional shape were broken from the male spline portion. On the other hand, all of the test pieces B-1 to B-4 (shown by circles in FIG. 29) having male spline portions having a shape corresponding to the present invention were broken from the small diameter cylindrical portion. When the B series and the C series were compared, the 10 ⁵ times torsional fatigue strength showed excellent values for the B series in all the test pieces. In addition, the 95% confidence width of the 10 ⁵ times torsional fatigue strength hardly changes with respect to A / A ₀ in the C series, but increases as A / A ₀ increases in the B series. Therefore, among the specimens excellent B sequence in torsional fatigue strength, it is highly reliable value of the fatigue strength torsion as A / A ₀ is small has been found. Further, focusing on the lower limit of the 95% confidence width in the B-series test piece, there is an inflection point in the vicinity of A / A ₀ = 25, and when this inflection point is exceeded, the 95% confidence in the torsional fatigue strength is rapidly increased. You can see that the width is widening. Therefore, it can be said that by setting A / A ₀ of the B series to 25 or less, the reliability of the value of the torsional fatigue strength can be increased, so that the fatigue strength of the shaft can be stably kept high.

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

  (I) In the power transmission shaft having a male spline portion provided on the outer periphery of both shaft ends and having a diameter-expanded portion on the opposite shaft end side of the valley portion of each male spline portion, the outer diameter of which is gradually increased. Round 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 round portion is gradually increased toward the opposite shaft end side.

(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 inner diameter end and the outer diameter end of the axial section of the enlarged diameter portion is θ. It was found that it is desirable to set the respective values in the ranges of 0.05 ≦ dR / dL ≦ 0.60 and 5 ° ≦ θ ≦ 20 °.

Further, from the above test results, when the surface area in the small cylindrical portion having the smallest outer diameter in the region between the axial directions of the male spline portions formed at both shaft ends is A and the cross-sectional area is A ₀ , A / It is preferable that A ₀ ≦ 25. As long as A / A ₀ ≦ 25 is satisfied, the lower limit value of A / A ₀ is not particularly limited. However, A / A ₀ > 0 because A = 0 cannot be obtained as long as the small-diameter cylindrical portion exists. It was.

  This power transmission shaft can be formed solid or hollow. When solid, excellent rigidity is obtained, and when hollow, weight reduction is achieved.

  By subjecting this power transmission shaft to induction quenching or carburizing quenching, the strength of the surface layer of the shaft can be improved.

  As described above, according to the present invention, the stress concentration of both the tensile stress and the shear stress in the male spline portion of the power transmission shaft is relaxed to increase the fatigue strength of the male spline portion, and the fatigue strength in the small diameter cylindrical portion. Can be increased.

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

FIG. 1 shows a drive shaft 1 of a vehicle incorporating a power transmission shaft 2 according to the present invention. The drive shaft 1 in the illustrated example includes a power transmission shaft 2 and a fixed type constant velocity universal joint J ₁ that is attached to the end of the power transmission shaft 2 on the outboard side (the outside in the vehicle width direction when mounted on the vehicle). And a sliding-type constant velocity universal joint (tripod type constant-velocity universal joint) J ₂ mounted on the end portion on the inboard side of the power transmission shaft 2.

The fixed type constant velocity universal joint J ₁ includes an inner joint member 3 coupled to the power transmission shaft 2, an outer joint member 4 disposed on the outer diameter side of the inner joint member 3, and the inner joint member 3 and the outer joint member. A ball 5 that transmits torque to and from 4 is a main component. The balls 5 are arranged on a ball track formed by the track grooves 3a formed on the outer periphery of the inner joint member 3 and the track grooves 4a formed on the inner periphery of the outer joint member 4, and are arranged at equidistant positions in the circumferential direction. The plurality of balls 5 are held by the cage 6.

The tripod type constant velocity universal joint J ₂ includes an inner joint member 13 coupled to the power transmission shaft 2, an outer joint member 14 disposed on the outer diameter side of the inner joint member 13, and the inner joint member 13 and the outer joint member. A roller 15 as a torque transmission member that transmits torque to and from 14 is a main component. Leg shafts 13 a are projected from three locations in the circumferential direction of the inner joint member 13. A track groove 14a extending in the axial direction is formed at a position of the inner periphery of the outer joint member 14 in the circumferential direction, and the roller 15 rolls along the track groove 14a.

  The power transmission shaft 2 is formed of solid carbon steel (for example, carbon steel for mechanical structure S35C defined in JIS G 4051) with a carbon content of about 0.30 to 0.60 mass%, for example, and induction hardening is performed on the surface thereof. Applied. If the C content is less than 0.30 mass%, stable high hardness cannot be obtained even by induction hardening, and if it exceeds 0.60 mass%, the material hardness increases and the workability such as rolling is significantly reduced. To do. Note that the power transmission shaft 2 may be formed hollow, and in this case, the weight can be reduced. Moreover, you may carburize and quench as a hardening hardening process of the power transmission shaft 2. As shown in FIG.

  Male spline portions Sm are formed on the outer circumferences of both shaft ends of the power transmission shaft 2. By fitting this male spline portion Sm with a female spline portion Sf formed on the inner periphery of the inner joint members 3 and 13 as shown in FIG. 3, the power transmission shaft 2 and the inner joint members 3 and 13 are connected. It is connected so that torque can be transmitted. The inner joint members 3 and 13 have the inner diameter end on the opposite shaft end side (left side in FIG. 3) abutted against the shoulder 24 on the outer periphery of the power transmission shaft 2 and the inner diameter on the shaft end side (right side in FIG. 3). For example, the end portion is locked with a retaining ring (not shown) to be positioned and fixed in the axial direction with respect to the power transmission shaft 2.

Small-diameter cylindrical portions 2a and 2b are formed in a region between the axial directions of the male spline portion Sm formed on the outer periphery of both shaft ends of the power transmission shaft 2, that is, a region between the male spline portions Sm to which a torque load is applied. (See FIG. 1). The small diameter cylindrical portions 2a and 2b are formed in a cylindrical surface shape having a smooth outer peripheral surface, and are formed to have the smallest diameter in a region between the male spline portions Sm at both shaft ends. When the surface area of the small diameter cylindrical portions 2a and 2b is A and the cross-sectional area is A ₀ , A / A ₀ is set to be larger than ₀ and 25 or less, preferably 20 or less. The small-diameter cylindrical portions 2a and 2b are provided at portions that interfere with the open end portions of the outer joint members 4 and 14 when the constant velocity universal joints J ₁ and J ₂ provided at the shaft ends are bent maximum. Thereby, interference with the power transmission shaft 2 and the outer joint members 4 and 14 can be delayed, and the operating angle of the joint can be increased.

  As shown in FIGS. 2, 3, and 6, the male spline portion Sm of the power transmission shaft 2 has trough portions 21 and crest portions 22 extending in the axial direction alternately in the circumferential direction. 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 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 power transmission 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 the shaft 2.

  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 increased toward the opposite shaft 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 inner diameter end and the outer diameter end of the axial section of the enlarged diameter portion 21b, and is set to θ = 8.3 ° in the present embodiment.

  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 0.2 mm or less at the main portion P (including the male spline portions Sm and Sm ′) (minimum element length was 0.05 mm), and 0.5 mm except at the main portion P. FIG. 22 is an enlarged view showing the mesh of the main part P. FIG. 22A shows the product of the present invention corresponding to FIG. 2, and FIG. 22B 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 power transmission shaft 2 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 round 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 ′. In this way, when the maximum shear stress is generated on the center line, when the power transmission shaft 2 transmits torque in both forward and reverse directions, the maximum shear stress is generated in the same part during both forward and reverse rotations, so that fatigue failure is caused accordingly. Easy to progress. 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. For this reason, 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.

With the above measures, the male spline portion Sm can obtain high fatigue strength against both tensile stress and shear stress, and can increase the fatigue strength of the material itself forming the power transmission shaft 2. As described above, the strength of the male spline portion Sm that has been most likely to cause fatigue rupture in the past is increased, so that the first fatigue rupture can occur at a location other than the male spline portion Sm. Further, by setting the ratio A / A ₀ between the surface area A and the cross-sectional area A _{0 of} the small-diameter cylindrical portions 2a, 2b provided on the power transmission shaft 2 as described above, the small-diameter cylindrical portions 2a, 2b The fatigue strength can be kept stable and high.

  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.

It is a partial step view of the power transmission shaft according to the present invention. It is a perspective view which shows a non-shaft end side part (FIG. 1 code | symbol X part) among the male spline parts formed in the power transmission shaft. 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 side view which shows a test piece. It is a table | surface which shows the kind of test piece. It is a graph which shows the torsional fatigue strength ratio obtained by the double torsional fatigue test.

Explanation of symbols

1 drive shaft 2 power transmission shaft 2a, 2b small-diameter cylindrical portion J _1, J ₂ constant velocity universal joint 3, 13 inner joint member 4,14 outer joint member 21 troughs 21a straight portion 21b enlarged diameter portion 21b1 rounded portion 21b2 flat portion 22 Mountain part 23 Tooth surface 24 Shoulder part 25 Smooth part Sm Male spline part Sf Female spline part

Claims (7)

In the power transmission shaft having a male spline portion on the outer periphery of both shaft ends and having a diameter-expanded portion on the opposite shaft end side of the valley portion of each male spline portion, the outer diameter of which is gradually increased.
The male spline portion is provided with rounded portions on both sides in the circumferential direction, the radius of curvature of the rounded portion is gradually increased toward the opposite shaft end, and the shaft of the male spline portion provided at both shaft ends. A power transmission shaft, wherein 0 <A / A ₀ ≦ 25, where A is a surface area of a small-diameter cylindrical portion having the smallest outer diameter in a region between directions and A ₀ is a cross-sectional area. When the torque T is applied, the first principal stress acting on the enlarged diameter 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. 2. The power transmission shaft according to claim 1, wherein when the reference stress τ ₀ given by the equation (1) is set to the diameter d _{o of} the 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) 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 inner diameter end and the outer 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 power transmission shaft according to claim 2, which is in the range of.   The power transmission shaft according to any one of claims 1 to 4, which is solid.   It is hollow, The power transmission shaft in any one of Claims 1-4.   The power transmission shaft according to any one of claims 1 to 6, wherein induction hardening is performed.   The power transmission shaft according to claim 1, which has been carburized and quenched.

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