JP2008089019A - Constant velocity universal joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant velocity universal joint capable of lengthening the rolling fatigue service life of a tripod member, and capable of enhancing strength against surface starting-point type damage. <P>SOLUTION: This tripod type constant velocity universal joint has an outside joint member 10 forming three track grooves 12 in the axial direction in an inner peripheral part and having respectively an axial directional roller guide surface 14 on both sides of the respective track grooves 12, the tripod member 20 having three leg shafts 22 projected in the radial direction, a support ring 32 fitted around the respective leg shafts 22 of the tripod member 20, and a roller 34 rotatably supported by this support ring 32 via a plurality of needle-like rollers 36 and inserted into the track grooves 12, and can oscillate and rock a roller cassette C composed of the support ring 32, the needle-like rollers 36 and the roller 34 in response to the movement of this roller 34 in the axial direction of the outside joint member 10 along the roller guide surface 14. A surface layer formed by carbonitriding quenching-tempering and having the thickness of 0.1 mm or more, is arranged in the tripod member 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a constant velocity universal joint used for a power transmission device of an automobile or various industrial machines, and more particularly to a tripod type constant velocity universal joint.

  For example, a tripod constant velocity universal joint is used to transmit rotational power from an automobile engine to wheels at a constant speed.

  In general, a tripod type constant velocity universal joint has an outer joint member formed with three track grooves in the axial direction on the inner periphery and axial roller guide surfaces on both sides of each track groove, and protrudes in the radial direction. The tripod member has three leg shafts, and rollers are rotatably disposed on the respective leg shafts. When the leg shaft of the tripod member and the roller guide surface of the outer joint member are engaged with each other in the rotational direction via the roller, the rotational torque is transmitted from the drive side to the driven side at a constant speed. Further, each roller rolls on the roller guide surface while rotating with respect to the leg shaft, so that the relative axial displacement and angular displacement between the outer joint member and the tripod member are absorbed. Further, the axial displacement of each leg shaft with respect to the roller guide surface accompanying the change in the rotational direction phase when the outer joint member and the tripod member transmit the rotational torque while taking the operating angle is absorbed.

  As a tripod constant velocity universal joint, there is one in which the roller is mounted on a cylindrical outer peripheral surface of a leg shaft through a plurality of needle rollers. In this tripod type constant velocity universal joint, when the outer joint member and the tripod member transmit the rotational torque while taking the operating angle, each roller and the roller guide surface are in a relationship of being obliquely crossed with the inclination of the leg shaft. Become. Therefore, there is a problem that slip occurs between each roller and the roller guide surface, and the sliding resistance at that time prevents smooth rolling of each roller and increases the induced thrust. Further, there is a problem that the sliding resistance when the outer joint member and the tripod member are relatively displaced in the axial direction is increased due to the sliding resistance between each roller and the roller guide surface.

  Therefore, a tripod equipped with a mechanism (roller mechanism) that freely swings the roller with respect to the leg shaft in order to eliminate the oblique state between the roller and the roller guide surface and reduce induced thrust and slide resistance. Various types of constant velocity universal joints have been proposed and put into practical use. As this type of tripod type constant velocity universal joint, for example, those having the following configurations (I) and (II) are known.

  (I) The outer peripheral surface of the leg shaft is formed into a convex spherical shape, and the roller is assembled to the support ring via a plurality of needle rollers to form a roller mechanism. The cylindrical inner peripheral surface of the support ring is formed into the convex shape of the leg shaft. A configuration that is fitted on a spherical outer peripheral surface is known (for example, see Patent Document 1). According to this configuration, the roller mechanism including the roller can swing freely by sliding between the cylindrical inner peripheral surface of the support ring and the convex spherical outer peripheral surface of the leg shaft.

(II) It has a roller guided by the roller guide surface and a support ring that is fitted on the outer peripheral surface of the leg shaft and rotatably supports the roller, and the inner peripheral surface of the support ring has an arcuate convex cross section The outer peripheral surface of the leg shaft has a straight shape in the longitudinal section, and in the transverse section, contacts the inner peripheral surface of the support ring in a direction perpendicular to the joint axis, and the inner peripheral surface of the support ring in the axial direction of the joint. A configuration is known in which a gap is formed between the two (see, for example, Patent Document 2). According to this configuration, the roller mechanism including the roller can swing freely by sliding between the inner peripheral surface of the arc-shaped convex cross section of the support ring and the straight outer peripheral surface of the leg shaft, and induced thrust and Slide resistance is more effectively reduced.
Japanese Patent Publication No.7-117108 JP 2000-320563 A

  However, when the roller mechanism swings and swings with respect to the leg shaft, the contact portion between the support ring and the leg shaft slips. For this reason, peeling or smearing occurs particularly on the surface of the leg shaft, and there is a possibility that the rolling fatigue life of the leg shaft of the tripod member is shortened and surface-origin damage such as cracking is caused.

  Accordingly, an object of the present invention is to provide a constant velocity universal joint capable of extending the rolling fatigue life of the leg shaft of the tripod member and increasing the strength against surface-origin damage.

  In order to solve the above-mentioned problem, the invention of claim 1 includes an outer joint member in which three track grooves in the axial direction are formed on the inner periphery, and each has an axial roller guide surface on each side of each track groove; A tripod member having three leg shafts protruding in the radial direction, a roller mechanism rotatably supporting the roller inserted in the track groove, and a roller mechanism mounted on each leg shaft of the tripod member, In the constant velocity universal joint in which the roller is movable in the axial direction of the outer joint member along the roller guide surface and the roller mechanism is swingably swingable with respect to the leg shaft, the tripod member Further, a surface layer portion formed by carbonitriding, quenching and tempering is provided, and the thickness of the surface layer portion immediately below the contact portion with the roller mechanism is 0.1 mm or more.

  As a result of earnest research on the mechanism that the constant velocity universal joint reaches the rolling fatigue life, the inventor of this application has found that the wear depth (including the damage depth due to peeling damage) of the tripod member surface due to contact with the roller mechanism is 0.1 mm. Found that it is less than. Based on this discovery, the present invention has been made.

  According to the present invention, a surface layer portion (carbonitriding layer) is formed on a tripod member by carbonitriding and quenching and tempering, so that retained austenite and matrix (matrix) martensite are stabilized against heat due to the penetration of nitrogen. An organization that is difficult to change. Therefore, high strength against rolling fatigue and high strength against cracking can be obtained. Further, the torsional fatigue becomes a problem because the torsional stress is concentrated at the base end portion of the leg shaft of the tripod member at the time of torque transmission and is usually left in an unground state. On the other hand, by forming the carbonitrided layer, the surface hardness of the tripod member including the leg shaft is increased, and high torsional fatigue strength is obtained.

  In addition, by setting the thickness of the surface layer portion to 0.1 mm or more, even if wear due to contact with the roller mechanism occurs, the occurrence of early peeling and smearing is prevented, and the occurrence of cracks etc. starting from these is prevented. Can be prevented. Therefore, it is possible to effectively improve the resistance to rolling fatigue of the surface layer portion and the strength against surface-origin damage. Moreover, torsional fatigue strength can be improved by ensuring a sufficient thickness of the carbonitrided layer.

  The thickness of the surface layer portion is preferably 1.5 mm or less from the viewpoint of securing the toughness of the leg shaft and the formation efficiency of the carbonitriding layer.

  The surface layer portion may be formed at least directly below the contact surface with the roller mechanism of the tripod member. The surface layer portion is formed just below the contact surface, the surface layer portion immediately below the contact surface and the surrounding surface. And a configuration in which the surface layer portion is formed immediately below the entire surface of the component.

  The swinging swing means that the roller axis is inclined with respect to the leg axis in a plane including the axis of the leg axis.

  The invention according to claim 2 is characterized in that, in the constant velocity universal joint according to claim 1, the amount of retained austenite in the surface layer portion of the tripod member is 20 vol% or more and 40 vol% or less.

  According to the constant velocity universal joint of claim 2, since the amount of retained austenite in the surface layer portion of the tripod member is in the range of 20 vol% or more and 40 vol% or less, the crack sensitivity of the surface layer portion is improved, and surface-origin damage is caused. It becomes difficult to occur. This is due to the following reason. That is, residual austenite has a relatively low hardness, and even if an indentation due to foreign object biting is formed on the contact surface, the austenite grains dispersed in the surface layer part are easily plastically deformed at the periphery of the indentation, and the stress concentration in the surface layer part Relaxes and delays crack propagation. Residual austenite is cured by causing martensitic transformation by deformation energy applied to the surface layer portion. Therefore, by including an appropriate amount of retained austenite in the surface layer portion, the crack sensitivity of the surface layer portion can be improved, the occurrence of surface-initiated damage can be suppressed, and the rolling fatigue life can be improved. If the amount of retained austenite in the surface layer is less than 20 vol%, the crack sensitivity of the surface layer cannot be sufficiently improved. Conversely, even if the amount of retained austenite in the surface layer exceeds 40 vol%, While no further improvement can be expected, the surface hardness decreases, and on the contrary, the rolling fatigue life is reduced. Therefore, the amount of retained austenite in the surface layer portion is preferably in the range of 20 vol% or more and 40 vol% or less.

  According to a third aspect of the present invention, in the constant velocity universal joint according to the first aspect, the tripod member is formed of steel having a carbon content of 0.15 to 0.40 wt%.

  According to the constant velocity universal joint of claim 3, the surface layer portion is improved in crack sensitivity by the carbonitriding layer and becomes a structure excellent in durability against rolling fatigue, while the core portion has a structure having toughness. Become. Therefore, a tripod member having a long rolling fatigue life and a high cracking strength can be obtained.

  According to a fourth aspect of the present invention, in the constant velocity universal joint of the first aspect, the tripod member has a surface hardness of HRC58 or higher.

  According to the constant velocity universal joint of claim 4, by setting the surface hardness (Rockwell hardness C scale) of the tripod member to HRC58 or more, an appropriate fatigue strength can be obtained, so that the rolling fatigue life can be extended, The strength against torsional fatigue and the like can be increased.

  According to a fifth aspect of the present invention, in the constant velocity universal joint according to the first to fourth aspects, the roller mechanism is externally fitted to a roller guided by the roller guide surface and an outer peripheral surface of the leg shaft to rotate the roller. A support ring for freely supporting, and an inner peripheral surface of the support ring is an arcuate convex cross section in a vertical cross section, and an outer peripheral surface of the leg shaft is a straight shape in the vertical cross section and a joint in a cross section. It is characterized in that it is in contact with the inner peripheral surface of the support ring in a direction orthogonal to the axis, and a gap is formed between the inner peripheral surface of the support ring in the axial direction of the joint.

  According to the constant velocity universal joint of the fifth aspect, the roller mechanism including the roller and the support ring swings with respect to the leg shaft. As a result, the oblique state between the roller and the roller guide surface can be effectively eliminated, and induced thrust and slide resistance can be effectively reduced.

  The shape of the cross section of the leg shaft is such that it is in contact with the inner peripheral surface of the support ring in the direction perpendicular to the axis of the joint, and a gap is formed between the inner peripheral surface of the support ring in the axial direction of the joint. In other words, it means a shape in which the portions of the surfaces of the tripod member that are opposed in the axial direction are biased radially inward.

  A sixth aspect of the present invention is the constant velocity universal joint according to the fifth aspect, characterized in that the cross section of the leg shaft is substantially elliptical having a major axis perpendicular to the axis of the joint.

  According to the constant velocity universal joint of claim 6, the degree of freedom of swinging of the roller mechanism fitted on the leg shaft can be increased, and induced thrust and slide resistance can be further effectively reduced. . The “substantially elliptical shape” includes not only the literally elliptical shape but also a shape generally called an oval shape or an oval shape.

  According to the present invention, the tripod member of the constant velocity universal joint is provided with a surface layer portion formed by carbonitriding, quenching and tempering, and the thickness of the surface layer portion immediately below the contact portion with the roller mechanism is 0.1 mm or more. Therefore, the rolling fatigue life of the tripod member can be extended. As a result, it is possible to provide a constant velocity universal joint that is more durable and strong while maintaining the current size, and more durable and strong than the current product while maintaining a smaller size. A constant velocity universal joint can be provided.

  Hereinafter, the constant velocity universal joint of the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1A is a transverse sectional view showing a tripod type constant velocity universal joint as an embodiment of the present invention, and FIG. 1B shows a longitudinal section of the joint in a state where an operating angle θ is taken. (C) shows a cross section perpendicular to the leg axis, and FIG. 1 (D) shows a cross section of the support ring. In FIG. 1B, the symbol e represents the amount of eccentricity.

  As shown in FIGS. 1A to 1D, a roller cassette C as a roller mechanism is fitted to the leg shaft 22 of the tripod member 20 so as to swing freely. The roller cassette C includes an assembly body including a support ring 32, a roller 34, and needle rollers 36 interposed between the support ring 32 and the roller 34.

  Specifically, the outer joint member 10 has three track grooves 12 extending in the axial direction on the inner peripheral surface. Roller guide surfaces 14 are formed on the side walls of each track groove 12 facing each other in the circumferential direction. The tripod member 20 has three leg shafts 22 projecting in the radial direction, and a roller cassette C is attached to each leg shaft 22. The roller 34 of the roller cassette C is accommodated in the track groove 12 of the outer joint member 10. The outer peripheral surface of the roller 34 is a convex curved surface that matches the roller guide surface 14.

  The outer peripheral surface of the roller 34 is a convex curved surface having an arc having a center of curvature on the axis of the leg shaft 22 as a generating line, and the cross-sectional shape of the roller guide surface 14 is a Gothic arch shape. The surface 14 forms an angular contact [see the dashed line in FIG. 1A]. Even if the cross-sectional shape of the roller guide surface 14 is tapered with respect to the spherical outer peripheral surface of the roller 34, angular contact between the two is realized.

  By adopting a configuration in which the roller 34 and the roller guide surface 14 form an angular contact in this manner, the posture of the roller 34 is stabilized because the roller 34 is less likely to shake. When the angular contact is not adopted, for example, the roller guide surface 14 is constituted by a part of a cylindrical surface whose axis is parallel to the axis of the outer joint member 10, and the cross-sectional shape thereof corresponds to the generatrix of the outer peripheral surface of the roller 34. It can also be a circular arc.

  A support ring 32 is fitted on the outer peripheral surface of the leg shaft 22. The support ring 32 and the roller 34 are unitized via a plurality of needle rollers 36 to form a roller cassette C that can be rotated relative to the unit. That is, the cylindrical outer peripheral surface of the support ring 32 is the inner raceway surface, and the cylindrical inner peripheral surface of the roller 34 is the outer raceway surface, and the needle rollers 36 are interposed between these inner and outer raceway surfaces so as to roll freely.

  As shown in FIG. 1 (C), the needle rollers 36 are incorporated in a so-called full roller state in which as many rollers as possible are inserted and there is no cage. Reference numerals 33 and 35 indicate a pair of washers mounted in an annular groove formed on the inner peripheral surface of the roller 34 to prevent the needle rollers 36 from falling off. These washers 33 and 35 have a cut at one place in the circumferential direction, and are mounted in an annular groove on the inner peripheral surface of the roller 34 in a state of being elastically reduced in diameter.

  The outer peripheral surface of the leg shaft 22 has a straight shape parallel to the axis of the leg shaft 22 when viewed in a longitudinal section [FIG. 1A or FIG. 1B], and is viewed in a transverse section [FIG. 1C]. And the long axis is an elliptical shape perpendicular to the axis of the joint. The cross-sectional shape of the leg shaft 22 is substantially elliptical by reducing the wall thickness seen in the axial direction of the tripod member 20. In other words, the cross-sectional shape of the leg shaft 22 is such that the surfaces of the tripod member 20 facing each other in the axial direction are retracted in the mutual direction, that is, on the smaller diameter side than the virtual cylindrical surface.

  The inner peripheral surface of the support ring 32 has an arcuate convex cross section as shown in FIG. That is, the generatrix of the inner peripheral surface is a convex arc with a radius r. Since the cross-sectional shape of the leg shaft 22 is substantially elliptical as described above and a predetermined clearance is provided between the leg shaft 22 and the support ring 32, the support ring 32 is provided with the leg shaft 22 as described above. In addition to being able to move in the axial direction of 22, it can swing and swing with respect to the leg shaft 22.

  As described above, since the support ring 32 and the roller 34 are unitized so as to be relatively rotatable via the needle rollers 36, the support ring 32 and the roller 34 swing as a unit with respect to the leg shaft 22. There is a possible relationship. Here, swinging means that the axes of the support ring 32 and the roller 34 are inclined with respect to the axis of the leg shaft 22 in a plane including the axis of the leg shaft 22 (see FIG. 1B).

  In this double roller type tripod type constant velocity universal joint, the roller cassette C is swingable and swingable (the roller cassette C is tiltable and axially displaceable with respect to the leg shaft 22). When the rotational force is transmitted with the tripod member 20 at the operating angle, the roller 34 and the roller guide surface 14 can be prevented from being obliquely crossed, and the roller 34 is the axis of the outer joint member 10. Is guided by the roller guide surface 14 of the outer joint member 10 so as to maintain a parallel posture, and rolls correctly on the roller guide surface 14 in the same posture. Therefore, the slip resistance during the operating angle operation is reduced, and the occurrence of slide resistance and induced thrust is suppressed.

  Further, the cross-sectional shape of the leg shaft 22 is in contact with the inner peripheral surface of the support ring 32 in a direction perpendicular to the axis of the joint, and a gap is formed between the inner peripheral surface of the support ring 32 in the axial direction of the joint. Therefore, the leg shaft 22 can be inclined with respect to the outer joint member 10 without changing the posture of the roller cassette C when the joint takes an operating angle. In addition, since the contact ellipse between the outer peripheral surface of the leg shaft 22 and the support ring 32 approaches the point from the horizontally long, the frictional moment to tilt the roller cassette C is reduced. Accordingly, the posture of the roller cassette C is always stable, and the roller 34 is held in parallel with the roller guide surface 14, so that it can roll smoothly.

  The difference between the tripod type constant velocity universal joint of this embodiment and the conventional one is that the leg shaft 22 of the tripod member 20 is provided with a surface layer portion formed by carbonitriding, quenching and tempering. The surface layer portion is not limited to the leg shaft 22 and may be provided in another portion of the tripod member 20.

  The tripod member 20 is manufactured from a steel material having a carbon content of 0.15 to 0.40 wt% through the main processes of forging, machining, carbonitriding, quenching, tempering, and grinding. In the surface layer portion formed on the leg shaft 22 of the tripod member 20, the amount of retained austenite is regulated within the range of 20 vol% or more and 40 vol% or less. The surface layer portion is formed with a thickness of 0.1 mm to 1.5 mm. Further, the surface hardness of the surface layer portion is formed to be HRC58 or higher.

  Thereby, since the surface layer part of the structure | tissue which cannot change a heat | fever easily by the penetration | invasion of nitrogen is obtained in the leg axis | shaft 22 of the tripod member 20, the tolerance with respect to rolling fatigue and the intensity | strength with respect to a surface origin type | mold damage can be improved. Further, since the surface hardness of the leg shaft 22 is increased by the surface layer portion formed of the carbonitriding layer, the torsional fatigue strength necessary for torque transmission can be increased. Furthermore, by setting the thickness of the surface layer portion to 0.1 mm or more, even if wear due to contact with the support ring 32 occurs, the occurrence of early peeling and smearing is prevented, and cracks and the like starting from these are generated. Can be prevented. Therefore, the resistance against rolling fatigue and the strength against surface-origin damage can be sufficiently increased with respect to the leg shaft 22 of the tripod member 20. Moreover, by ensuring the thickness of the carbonitrided layer, the surface hardness of the leg shaft 22 can be effectively increased, and sufficient torsional fatigue strength can be obtained.

  For the tripod type constant velocity universal joint shown in FIG. 1, tripod members A and B (comparative example) in which the surface layer portion is formed by carburizing and quenching and tempering, and the tripod member in which the surface layer portion is formed to be 0.05 mm by carbonitriding and quenching and tempering A life test conducted on C (comparative example) and tripod members D and E (examples) in which the surface layer portion is formed to be 0.1 mm or more by carbonitriding quenching and tempering will be described (see Table 1). The tripod member A of the comparative example has a surface layer portion thickness of 0.05 mm, and the tripod member B of the comparative example has a surface layer portion thickness of 0.1 mm. Moreover, the tripod member D of the example provided a surface layer portion having a thickness of 0.1 mm only on the surface of the leg shaft 22, and the tripod member E of the example provided a surface layer portion having a thickness of 0.1 mm on the entire surface. The tripod members A to E were prepared to have the same dimensions by using the same materials except for the heat treatment and thickness of the surface layer portion described above.

  In the life test, the operation is performed with the same rotational torque, operating angle, and rotation speed, and the operation time in which damage (peeling, wear, etc.) of the outer peripheral surface of the leg shaft 22 exceeds a predetermined ratio is defined as the life. In the rolling fatigue life column of Table 1, “◎” is given when the target operation time is sufficiently satisfied, “◯” is given when the target operation time is satisfied, and “△” is shown when the target operation time is not satisfied.

  From Table 1, at least the leg shaft 22 of the tripod member 20 is provided with a surface layer portion formed by carbonitriding, quenching and tempering, and by making the thickness of the surface layer portion 0.1 mm or more, the rolling fatigue life is sufficiently increased. It can be said that it can be extended. Therefore, a tripod type constant velocity universal joint having higher durability and strength can be obtained while maintaining the conventional size. In addition, a smaller tripod type constant velocity universal joint can be obtained while ensuring durability and strength equal to or higher than those of conventional ones.

  In the above-described embodiment, the leg shaft of the tripod member has an outer peripheral surface with a straight vertical section and an elliptical cross section, but may have other shapes, for example, a spherical outer peripheral surface. Good.

It is a figure which shows the constant velocity universal joint of embodiment of this invention, (A) is a cross-sectional view of a joint, (B) is a longitudinal cross-sectional view of the state which took the operating angle of the joint of (A), (C) Is a cross-sectional view perpendicular to the leg axis of the roller cassette, and (D) is a cross-sectional view of the support ring.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Outer joint member 12 Track groove 14 Roller guide surface 20 Tripod member 22 Leg shaft 32 Support ring 34 Roller 36 Needle roller C Roller cassette

Claims (6)

Tripod member having three axial track grooves formed on the inner periphery, outer joint members having axial roller guide surfaces on both sides of each track groove, and three leg shafts projecting in the radial direction And a roller mechanism that rotatably supports the roller inserted in the track groove and is mounted on each leg shaft of the tripod member, and the roller extends along the roller guide surface in the axial direction of the outer joint member. And a constant velocity universal joint formed such that the roller mechanism is swingable with respect to the leg shaft.
The tripod member is provided with a surface layer portion formed by carbonitriding, quenching and tempering, and the thickness of the surface layer portion immediately below the contact portion with the roller mechanism is 0.1 mm or more. Fittings.   The constant velocity universal joint according to claim 1, wherein the amount of retained austenite in the surface layer portion of the tripod member is 20 vol% or more and 40 vol% or less.   The constant velocity universal joint according to claim 1, wherein the tripod member is made of steel having a carbon content of 0.15 to 0.40 wt%.   The constant velocity universal joint according to claim 1, wherein the tripod member has a surface hardness of HRC58 or more.   The roller mechanism includes a roller guided by the roller guide surface, and a support ring that is externally fitted to the outer peripheral surface of the leg shaft and rotatably supports the roller, and the inner peripheral surface of the support ring is In the vertical cross section is an arc-shaped convex cross section, the outer peripheral surface of the leg shaft is a straight shape in the vertical cross section, in the horizontal cross section is in contact with the inner peripheral surface of the support ring in a direction perpendicular to the axis of the joint, and The constant velocity universal joint according to any one of claims 1 to 4, wherein a gap is formed between the inner peripheral surface of the support ring in the axial direction of the joint.   6. The constant velocity universal joint according to claim 5, wherein a cross section of the leg shaft is substantially elliptical having a long axis perpendicular to the axis of the joint.

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