JP2018044225A - Outer side joint member of constant velocity universal joint and manufacturing method of outer side joint member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an outer side joint member of a constant velocity universal joint capable of lightening weight and compacting a stem shaft and optimal for automobile drive shaft and a manufacturing method of the outer side joint member.SOLUTION: There is provided a carbon steel having a construction material with a basic component with percentage content of alloy elements by wt.% of, C:0.45 to 0.60%, Si:0.4 to 1.5%, Mn:0.4 to 1.0%, S:0.025% or less, Al:0.01 to 0.1%, B:0.001 to 0.004%, Ti:0.02 to 0.05% and N:0.008% or less with Ti/N ratio of 3.4 or more and the balance Fe with inevitable impurities. Ferrite grain size of the carbon steel of 7 or more and the carbon steel has a thermosetting layer with hardening setting ratio of 0.3 to 0.6 at at least the weakest part of a smooth part and a spline part of the stem shaft.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an outer joint member of a constant velocity universal joint used in a power transmission device of an automobile or various industrial machines, and a method for manufacturing the outer joint member.

  The constant velocity universal joint includes a fixed type constant velocity universal joint that allows only angular displacement, and a sliding type constant velocity universal joint that allows not only angular displacement but also axial displacement (plunging). For fixed type constant velocity universal joints, the bar groove type constant velocity universal joint (BJ) in which the groove bottom of the track groove consists only of an arc portion and the undercut free type in which the groove bottom of the track groove consists of an arc portion and a straight portion There are constant velocity universal joints (UJ). The sliding type constant velocity universal joint includes a tripod type constant velocity universal joint, a double offset type constant velocity universal joint, a cross groove type constant velocity universal joint, and the like.

  By the way, a drive shaft of an automobile includes a pair of constant velocity universal joints and a shaft connecting the pair of constant velocity universal joints. In general, one constant velocity universal joint of a pair of constant velocity universal joints is a fixed constant velocity universal joint, and the other constant velocity universal joint is a sliding constant velocity universal joint (Patent Document 1). .

  In recent years, there has been an increasing demand for lighter and more compact drive shafts in order to reduce the fuel consumption of automobiles and to secure space around the vehicle's undercarriage. In a constant velocity universal joint that uses balls as torque transmission members, the number of balls is eight. As a result, it was made lighter and more compact, and the shaft material was changed to one with high hardenability. By comprising in this way, weight reduction and compactization are progressing by the improvement of hardenability and high intensity | strength.

  FIG. 10 shows a Burfield type constant velocity universal joint (BJ) in which the groove bottom of the track groove is composed only of an arc portion. This constant velocity universal joint includes an outer joint member 3 having a track groove 2 formed on the inner diameter surface 1, an inner joint member 6 having a track groove 5 formed on the outer diameter surface 4, and the track groove 2 of the outer joint member 3. And a ball 7 as a torque transmitting member interposed between the outer joint member 6 and the track groove 5 of the inner joint member 6, and a pocket 9 for accommodating the ball 7 and interposed between the outer joint member 3 and the inner joint member 6. And a cage 8 to be mounted. The outer diameter surface 8 a of the cage 8 is fitted with the inner diameter surface 1 of the outer joint member 3, and the inner diameter surface 8 b of the cage 8 is fitted with the outer diameter surface 4 of the inner joint member 6.

  The outer joint member 3 includes a cup portion 10 having a track groove 2 formed on the inner diameter surface 1 and a stem shaft 11 protruding from a bottom wall 10a of the cup portion 10. The stem shaft 11 has a spline part (male spline) 11a provided at the intermediate part and a screw part 11b provided at the tip side.

  A female spline 12 is formed in the axial hole of the inner joint member 6, and the end of the shaft 13 is fitted into the axial hole of the inner joint member 6. A male spline 14 is formed at the end of the shaft 13, and the female spline 12 and the male spline 14 are fitted when the end of the shaft 13 is fitted into the axial hole of the inner joint member 6. A circumferential groove 16 is formed at the end of the male spline 14, and a retaining ring 17 is fitted into the circumferential groove 16. Thereby, the shaft 13 is prevented from coming off.

  The opening of the outer joint member 3 is closed by the boot 20. The boot 20 includes a large diameter portion 20a that constitutes one opening, a small diameter portion 20b that constitutes the other opening, and a bellows portion 20c that connects the large diameter portion 20a and the small diameter portion 20b. And the large diameter part 20a of the boot 20 is mounted | worn in the state externally fitted by the opening part of the outer joint member 3. FIG. Further, the small diameter portion 20 b of the boot 20 is mounted in a state of being externally fitted to the boot mounting portion 13 a of the shaft 13.

  The cup portion 10 of the outer joint member 3 of the constant velocity universal joint is induction-hardened carbon steel having a C amount of 0.45% to 0.60% in order to ensure the life of the contact portion between the track groove 2 and the ball 7. Or surface hardness is increased by carburizing and quenching the case-hardened steel. The stem shaft 11 of the outer joint member 3 is often integrated with the cup portion 10 and is made of the same material and heat treatment as the cup portion 10. However, in order to increase the strength of the shaft, the C amount is 0.35 to 0.45%. It is optimal to quench the carbon steel deeply by induction hardening.

  However, since it is difficult to increase the strength with the material of the cup portion 10 and heat treatment, it is necessary to increase the shaft diameter to ensure the strength, and it is not possible to reduce the weight and size. By the way, conventionally, C: 0.50 to 0.80%, Si: 0.15% or less, Mn: 0.60% or less, B: 0.0005 to 0.0050%, Ti: 0.05% The following high strength induction hardening steels with excellent machinability have been proposed (Patent Document 2).

JP 2000-240669 A JP-A-8-81733

  If the high-strength induction hardening steel described in Patent Document 2 is used for the outer joint member, Mn and Si can be reduced, and machinability can be ensured. Moreover, the hardenability is reduced by reducing Mn and Si, but the addition of B prevents the hardenability from being lowered. However, this is not a sufficient measure for reducing the weight and size of the stem shaft.

  Therefore, the present invention provides an outer joint member of a constant velocity universal joint and a method for manufacturing the outer joint member which are capable of reducing the weight and size of a stem shaft and are optimal for an automobile drive shaft.

  In the outer joint member of the constant velocity universal joint of the present invention, the cup portion having a track groove formed on the inner diameter surface and the stem shaft protruding from the bottom wall of the cup portion are integrally formed of the same material. An outer joint member of a constant velocity universal joint having a smooth portion and a spline portion formed on a shaft, wherein the material has an alloy element content of% by weight, C: 0.45 to 0.60%, Si : 0.4-1.5%, Mn: 0.4-1.0%, S: 0.025% or less, Al: 0.01-0.1%, B: 0.001-0.004% , Ti: 0.02 to 0.05%, N: 0.008% or less, and a Ti / N ratio of 3.4 or more as a basic component, and the balance being carbon steel made of Fe and inevitable impurities. Carbon steel ferrite grain size number is 7 or more, among the smooth portion and spline portion of the stem shaft, At the site to be even without weakest, those having thermosetting layer hardened ratio is 0.3 to 0.6.

  The quench hardening ratio is expressed by the effective hardened layer depth / shaft radius ratio. When this is less than 0.3, the quench hardening ratio is insufficient, and the strength of the stem shaft that is induction-hardened into ordinary carbon steel is not changed. Compactness cannot be achieved. On the other hand, if it exceeds 0.60%, a burning crack occurs in a notch part such as a spline part.

  If C is less than 0.45%, the surface hardness after heat treatment is too low, and sufficient durability cannot be obtained in the track of the outer ring cup portion. If it exceeds 0.60%, the surface hardness is too high. Since it is too high, the notch sensitivity of a notch part will increase and a strength fall will be caused.

  Si is added as a deoxidizer in the steelmaking stage and further for strengthening grain boundaries. If this is less than 0.40%, the effect of strengthening the grain boundary cannot be obtained, and if it exceeds 1.5%, the cold workability (forgeability, machinability) is remarkably lowered.

  Mn is necessary for improving the hardenability (improving the quench hardening ratio) and fixing / dispersing sulfur in the steel as MnS. If this is less than 0.4%, the hardenability decreases. The quenching depth cannot be obtained. If it exceeds 1.0%, the hardenability is saturated and the cold workability is lowered.

  S is combined with Mn and exists as MnS inclusions. However, since S serves as a starting point for occurrence of cracking during cold working, it is set to 0.025% or less. Further, P is 0.02% or less because it precipitates at grain boundaries in steel and remarkably impairs hot workability and remarkably reduces material strength.

  Al is a deoxidizing agent. In order to remove oxygen in the steel as oxide inclusions and adjust grain boundaries in the steelmaking stage, the content is adjusted to 0.01% or more. However, if there are too many oxide inclusions, the toughness decreases. In order to become a starting point of occurrence of cracks during cold working, the content is made 0.10% or less.

  B is added for the purpose of improving hardenability, strengthening grain boundaries, lowering susceptibility to fire cracking, and the like. If it is less than 0.001%, these effects cannot be sufficiently obtained, and if it exceeds 0.004%, BC is generated at the grain boundary, causing a decrease in strength.

  Ti is added to fix N by generation of TiN and prevent formation of TiN. If it is less than 0.02%, the formation of BN cannot be prevented, and if it exceeds 0.05%, the cleanliness is lowered and the strength is lowered. N is contained in the steel as an impurity, but if it exceeds 0.08%, BN is generated and the effect of adding B is lost.

  The Ti / N ratio is a weight ratio of Ti and N and represents how much N is fixed by Ti. The larger this is, the smaller the amount of BN produced. If the Ti / N ratio is less than 3.4, it is difficult to ensure effective B.

  If the ferrite grain size in the steel structure is too large, the susceptibility to fire cracks increases remarkably, so the ferrite crystal grain size number of the carbon steel is 7 or more.

  The weakest part may be a spline portion provided on the stem shaft or a smooth portion provided on the stem shaft. Moreover, it is preferable that the compressive residual stress of the surface of a thermosetting layer shall be 500 Mpa or more. The fatigue strength can be improved by increasing the compressive residual stress to 500 MPa or more.

  The outer joint member manufacturing method of the present invention is an outer joint member manufacturing method for manufacturing the outer joint member of the constant velocity universal joint, and at least the weakest portion of the smooth portion and the spline portion of the stem shaft. After induction hardening and tempering to form a quenched portion, this quenched portion is subjected to shot peening to form a thermosetting layer having a surface compressive residual stress of 1000 MPa or more.

  The outer joint member of the constant velocity universal joint of the present invention can provide a stem shaft having higher strength than the conventional product, and can increase the load capacity of the stem shaft and reduce the weight and size. A constant velocity universal joint using a joint member is a constant velocity universal joint optimum for a drive shaft. Moreover, since this outer joint member is based on carbon steel, there is an advantage that the cost is low.

It is sectional drawing of the drive shaft using the outer joint member of the constant velocity universal joint of this invention. It is sectional drawing of the fixed type constant velocity universal joint of the drive shaft shown in FIG. It is sectional drawing of the sliding-type constant velocity universal joint of the drive shaft shown in FIG. It is a cross-sectional view of the sliding type constant velocity universal joint. It is a graph which shows the relationship between quench hardening ratio and torsional strength ratio. It is sectional drawing of a fixed type constant velocity universal joint of an undercut free type. It is sectional drawing of a sliding type constant velocity universal joint of a double offset type. It is sectional drawing of a cross-groove type sliding constant velocity universal joint. FIG. 9 is a development view of a track groove (ball groove) of the cross groove type constant velocity universal joint shown in FIG. 8. It is sectional drawing of the conventional fixed type constant velocity universal joint.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. FIG. 1 shows a drive shaft, which is provided with a pair of constant velocity universal joints 31 and 32 and a shaft S connecting the pair of constant velocity universal joints 31 and 32. In this example, one constant velocity universal joint 31 is a Barfield type fixed constant velocity universal joint, and the other constant velocity universal joint 32 is a tripod type sliding constant velocity universal joint.

  As shown in FIG. 2, the fixed type constant velocity universal joint 31 includes an outer joint member 35 in which a plurality of track grooves 33 extending in the axial direction are formed on the inner diameter surface 34, and a plurality of track grooves 36 extending in the axial direction. A plurality of balls that transmit torque by being interposed between the inner joint member 38 formed on the radial surface 37 at equal intervals in the circumferential direction, the track groove 33 of the outer joint member 35, and the track groove 36 of the inner joint member 38. 39 and a cage 40 that is interposed between an inner diameter surface 34 of the outer joint member 35 and an outer diameter surface 37 of the inner joint member 38 and holds the ball 39.

  As shown in FIGS. 3 and 4, the sliding type constant velocity universal joint (tripod type constant velocity universal joint) includes an outer joint member 42, a tripod member 44 as an inner joint member, and a torque transmission member 48. . The outer joint member 42 has a cup-shaped mouth portion 75 opened at one end, and a track groove 41 extending in the axial direction is formed at a circumferentially equally divided position of the inner periphery. The mouse portion 75 has a non-cylindrical shape in which a large diameter portion 75a and a small diameter portion 75b appear alternately when viewed in cross section. That is, the mouse portion 75 is formed with the large-diameter portion 75a and the small-diameter portion 75b, whereby the three track grooves 41 extending in the axial direction are formed on the inner peripheral surface thereof.

  Roller guide surfaces (roller sliding contact surfaces) 41a and 41a are formed on the side walls of each track groove 41 facing in the circumferential direction. In addition, the inner diameter surface has a three-valve corollary shape in which small inner diameter portions 42b and large inner diameter portions 42a that appear alternately in the circumferential direction are connected by a roller guide surface 41a. That is, in the outer joint member 42, the track grooves 41 including the roller guide surfaces 41a and 41a facing each other in the circumferential direction and the large inner diameter portion 42a provided between the roller guide surfaces 41a and 41a are formed at three locations on the inner periphery. It is what is done.

  The tripod member 44 includes a boss 47 and a leg shaft 43. The boss 47 is formed with a spline hole 44a coupled to the shaft S so as to be able to transmit torque. The leg shaft 43 protrudes in the radial direction from the circumferentially divided position of the boss 47.

  Further, the torque transmission member (roller member) 48 includes a roller 46 formed of a ring-shaped body whose outer diameter surface is a convex spherical surface, and a ring 45 via a plurality of rollers 49 on the roller 46. That is, the roller 46 and the ring 45 are unitized via a plurality of rollers 49, and these constitute a roller assembly (roller member). In this case, the roller 46 can be called an outer roller and the ring 45 can be called an inner roller.

  That is, the ring (inner roller) 45 is fitted on the outer peripheral surface of the leg shaft 43. The cylindrical outer peripheral surface of the inner roller 45 is an inner raceway surface, and the cylindrical inner peripheral surface of the outer roller 46 is an outer raceway surface, and needle rollers 49 are interposed between these inner and outer raceway surfaces so as to roll freely. The needle roller 49 is incorporated in a so-called full roller state in which as many rollers as possible are inserted and no cage is provided. In addition, washers 50 a and 50 b for preventing the needle rollers 49 from coming off are attached to the annular groove formed on the inner peripheral surface of the end portion of the outer roller 46.

  As shown in FIG. 2, a male spline 51 at one end of the shaft S is fitted into the shaft hole 38a of the inner joint member 38 of the fixed type constant velocity universal joint 31 so that torque can be transmitted. A male spline 52 is fitted to the other end of the shaft S so that torque can be transmitted to the shaft hole 44a of the tripod member 44, which is an inner joint member in the sliding type constant velocity universal joint 32. In this case, as shown in FIG. 2, a female spline 53 is provided on the inner diameter surface of the shaft hole 38a of the inner joint member 38 of the fixed type constant velocity universal joint 31, and as shown in FIG. A female spline 54 is provided on the inner diameter surface of the shaft hole 44 a of the tripod member 44 of the universal joint 32.

  For this reason, the male spline 51 of the shaft S is fitted to the female spline 53 of the inner joint member 38 by fitting the male spline 51 at one end of the shaft S into the shaft hole 38 a of the inner joint member 38. Further, the male spline 52 at the end is fitted into the shaft hole 44 a of the tripod member 44 on the other side of the shaft S, so that the male spline 52 of the shaft S is fitted to the female spline 54 of the tripod member 44. Note that both ends of the shaft S are prevented from coming off by retaining rings 55, 55 such as snap rings. That is, circumferential grooves 56 and 56 are formed at both ends of the shaft S, and retaining rings 55 and 55 are fitted into the circumferential grooves 56 and 56.

  Boots 60A and 60B are installed between the shaft S and the outer joint members 35 and 42, respectively, for preventing entry of foreign matter from the outside and leakage of grease from the inside. The boots 60A and 60B include a large diameter portion 60a, a small diameter portion 60b, and a bellows portion 60c that connects the large diameter portion 60a and the small diameter portion 60b. The large diameter portions 60a and 60a of the boots 60A and 60B are fastened and fixed by the boot bands 61A and 61B at the open ends of the outer joint members, and the small diameter portions 60b are formed by the boot bands 62A and 62B at the boot mounting portions 58 and 59 of the shaft S. Tightened and fixed.

  By the way, the outer joint member 35 of the fixed type constant velocity universal joint 31 includes a cup part 70 having a track groove 33 formed on the inner diameter surface 34 and a stem shaft 71 protruding from the bottom wall 70a of the cup part 70. . The stem shaft 71 is connected to a spline portion (male spline) 71b connected to the cup portion 70 from the bottom wall 70a of the cup portion 70 via the smooth portion 71a, and connected to the spline portion 71b via a constricted portion 71c. A threaded portion 71d and an end shaft portion 71e protruding from the end face of the threaded portion 71d.

  The material of the outer joint member 35 of the fixed type constant velocity universal joint 31 is such that the alloy element content is% by weight, C: 0.45 to 0.60%, Si: 0.4 to 1.5%, Mn : 0.4-1.0%, S: 0.025% or less, Al: 0.01-0.1%, B: 0.001-0.004%, Ti: 0.02-0.05% And N: 0.008% or less and a Ti / N ratio of 3.4 or more as a basic component, and the balance being Fe and inevitable impurities. The ferrite grain size number of the carbon steel in this case (the crystal grain size number measured by the comparison method of JISG 0552 (steel ferrite grain size test method)) is 7 or more.

  And in the smooth part 71a and the spline part 71b of the stem axis | shaft 71, it has the thermosetting layer H1, as shown by cross hatching in the weakest part at least. In this case, the weakest part of the smooth part 71a and the spline part 71b of the stem shaft 71 is the spline part 71b. For this reason, at least the thermosetting layer H1 may be provided on the spline portion 71b. In this embodiment, the thermosetting layer H1 is formed from the bottom wall 70a of the cup portion 70 to the spline portion (male spline) 71b. . And this thermosetting layer H1 becomes quenching hardening ratio 0.3-0.6. Here, the quench hardening ratio is the quench depth / axial radius. That is, as shown in FIG. 2, when the quenching depth is t1 and the shaft radius is R1, the quench hardening ratio is t1 / R1, and the shaft radius is the radius of the small diameter (diameter) of the spline portion 71b. Yes, R1 = D2 / 2. For this reason, 0.3 ≦ t1 / R1 ≦ 0.6. The compressive residual stress on the surface of the thermosetting layer H is preferably 500 MPa or more.

  By the way, the outer joint member 35 has a cup part 70 and a stem shaft 71 integrally formed. After the cup part 70 and the stem shaft 71 are integrally formed by hot forging using the carbon steel, the outer joint member 35 is cooled. By performing the forging, the dimensional accuracy of the inside of the cup part 70 and the stem shaft 71 is improved. After forging, it is formed into a predetermined shape by turning, and the stem shaft 71 is formed with a spline portion 71b for fitting with a hub wheel (not shown) by rolling or pressing. At the end, a threaded portion 71d for fastening with a hub wheel and a nut is formed by rolling. Thereafter, the stem shaft 71 is subjected to induction hardening and tempering to provide the thermosetting layer H1.

  In the induction hardening and tempering, when a portion necessary for quenching is placed in a coil through which a high frequency current flows, an induced electromotive force is generated by electromagnetic induction. This is a quenching method applying the principle of overheating a conductive object by utilizing the generation of Joule heat by this electromagnetic induction action. For this reason, induction hardening can selectively provide a hardened layer only at a necessary portion, and is optimal for forming a hardened layer of the stem shaft of the outer joint member.

  The outer joint member 42 of the sliding type constant velocity universal joint 32 protrudes from a cup portion 75 having three track grooves 41 extending in the axial direction on the inner periphery and a bottom wall 75 c of the cup portion 75. It consists of a stem shaft 76. The stem shaft 76 includes a large-diameter boss portion 76a continuously provided on the bottom wall 75c, an intermediate shaft portion (smooth portion) 76b having a smaller diameter than the large-diameter boss portion 76a, and a spline continuously provided on the smooth portion 76b. Part (male spline) 76c.

  Similarly to the outer joint member 35 of the fixed type constant velocity universal joint 31, the material of the outer joint member 42 has an alloy element content of% by weight, C: 0.45 to 0.60%, Si: 0.4 -1.5%, Mn: 0.4-1.0%, S: 0.025% or less, Al: 0.01-0.1%, B: 0.001-0.004%, Ti: 0 Carbon steel having 0.02 to 0.05% and N: 0.008% or less and a Ti / N ratio of 3.4 or more as a basic component, the balance being Fe and inevitable impurities. The ferrite grain size number of the carbon steel in this case is 7 or more.

  A thermosetting layer H2 is formed on the stem shaft 76 of the outer joint member 42 from the large-diameter boss 76a to the spline portion 76c as shown by cross hatching. Also in this thermosetting layer H2, the quench hardening ratio is 0.3 to 0.6. When the quenching depth is t2 and the shaft radius is R2, the quench hardening ratio is t2 / R2, and the shaft radius is the radius of the small diameter (diameter) of the spline portion 76c, and R2 = D4 / 2. . For this reason, 0.3 ≦ t2 / R2 ≦ 0.6. The compressive residual stress on the surface of the thermosetting layer H is preferably 500 MPa or more.

  Also in this case, in the outer joint member 42, the cup portion 75 and the stem shaft 76 are integrally formed, and after the cup portion 75 and the stem shaft 76 are integrally formed by hot forging using the carbon steel. The dimensional accuracy of the cup portion 75 and the stem shaft 76 is improved by performing cold forging. After forging, it is formed into a predetermined shape by turning, and the stem shaft 76 is formed with a spline portion 76c by rolling or pressing, and then the stem shaft 76 is subjected to induction hardening and tempering, and the thermosetting layer H2 is provided.

  In addition, it is preferable to perform heat treatment of induction hardening and tempering in the cup portions 70 and 75 of the outer joint members 35 and 42 to provide a thermosetting layer having a predetermined hardness and a quenching depth. However, in the cup portions 70 and 75, when the outer surface is burned out, the strength is reduced. For this reason, the high hardening hardening ratio like the stem shafts 71 and 76 is unnecessary.

  When the thermosetting layers H1 and H2 are formed on the stem axis, shot peening is performed after induction hardening and tempering, and the compressive residual stress on the surfaces of the thermosetting layers H1 and H2 can be 1000 MPa or more.

  In the drive shaft shown in FIG. 1, the thermosetting layer H3 is also formed on the shaft (intermediate shaft) S as shown by cross hatching. As the shaft S, the same carbon steel as that of the outer joint members 35 and 42 may be used, or carbon steel generally used for a shaft of a conventional drive shaft may be used.

  Moreover, the thermosetting layer H3 can be formed by performing heat treatment of induction hardening and tempering. In this case, as shown in the figure, the thermosetting layer H3 is formed over almost the entire length. Also in this case, the quench hardening ratio represented by the quench depth / axial radius can be set to 0.3 to 0.6, but is not limited thereto.

  For this reason, the outer joint member of the constant velocity universal joint of the present invention can provide a stem shaft having higher strength than the conventional product, and can increase the load capacity of the stem shaft and reduce the weight and size. A constant velocity universal joint using such an outer joint member is an optimum constant velocity universal joint for a drive shaft. Moreover, since this outer joint member is based on carbon steel, there is an advantage that the cost is low.

  That is, the quench hardening ratio is expressed by the effective hardened layer depth / shaft radius ratio, and if this is less than 0.3, the quench hardening ratio is insufficient, and the strength of the stem shaft induction-hardened in ordinary carbon steel is not changed, Light weight and compactness cannot be achieved. On the other hand, if it exceeds 0.60%, a burning crack occurs in a notch part such as a spline part.

  If C is less than 0.45%, the surface hardness after heat treatment is too low, and sufficient durability cannot be obtained in the track of the outer ring cup portion. If it exceeds 0.60%, the surface hardness is too high. Since it is too high, the notch sensitivity of a notch part will increase and a strength fall will be caused.

  Si is added as a deoxidizer in the steelmaking stage and further for strengthening grain boundaries. If this is less than 0.40%, the effect of strengthening the grain boundary cannot be obtained, and if it exceeds 1.5%, the cold workability (forgeability, machinability) is remarkably lowered.

  Mn is necessary for improving the hardenability (improving the quench hardening ratio) and fixing / dispersing sulfur in the steel as MnS. If this is less than 0.4%, the hardenability decreases. The quenching depth cannot be obtained. If it exceeds 1.0%, the hardenability is saturated and the cold workability is lowered.

  S is combined with Mn and exists as MnS inclusions. However, since S serves as a starting point for occurrence of cracking during cold working, it is set to 0.025% or less. Further, P is 0.02% or less because it precipitates at grain boundaries in steel and remarkably impairs hot workability and remarkably reduces material strength.

  Al is a deoxidizing agent. In order to remove oxygen in the steel as oxide inclusions and adjust grain boundaries in the steelmaking stage, the content is adjusted to 0.01% or more. However, if there are too many oxide inclusions, the toughness decreases. In order to become a starting point of occurrence of cracks during cold working, the content is made 0.10% or less.

B is added for the purpose of improving hardenability, strengthening grain boundaries, lowering susceptibility to fire cracking, and the like. If it is less than 0.001%, these effects cannot be sufficiently obtained, and if it exceeds 0.004%, BC is generated at the grain boundary, causing a decrease in strength.

  Ti is added to fix N by generation of TiN and prevent formation of TiN. If it is less than 0.02%, the formation of BN cannot be prevented, and if it exceeds 0.05%, the cleanliness is lowered and the strength is lowered. N is contained in the steel as an impurity, but if it exceeds 0.08%, BN is generated and the effect of adding B is lost.

  The Ti / N ratio is a weight ratio of Ti and N and represents how much N is fixed by Ti. The larger this is, the smaller the amount of BN produced. If the Ti / N ratio is less than 3.4, it is difficult to ensure effective B.

  If the ferrite grain size in the steel structure is too large, the susceptibility to fire cracks increases remarkably, so the ferrite crystal grain size number of the carbon steel is 7 or more.

  By the way, the carbon steel used for the outer joint member of the conventional fixed type constant velocity universal joint and the sliding type constant velocity universal joint usually has an alloy element content of% by weight, and C: 0.45 to 0.60%. , Si: 0.15 to 0.35%, Mn: 0.6 to 0.9%, S: 0.035% or less as basic components, with the balance being Fe and inevitable impurities.

  When such carbon steel is used, since B is not added, the quench hardening ratio varies in the range of 0.2 to 0.4. Therefore, when examining the torsional strength, 0.2, which has a small quench hardening ratio, is adopted. As shown in FIG. 5, when the torsional strength when the quench hardening ratio is 0.2 is 1.0, in the case of the carbon steel as in the present invention, the hardenability is improved, so that the quench hardening ratio is within the entire curing range. Therefore, the torsional strength ratio is improved to 1.25 to 1.65.

  FIG. 6 shows an undercut-free type fixed-type constant velocity universal joint, an outer joint member 83 having a plurality of track grooves 82 formed on the inner diameter surface 81, and a track of the outer joint member 83 on the outer diameter surface 84. A plurality of inner joint members 86 formed with a plurality of track grooves 85 paired with the grooves 82, and a plurality of torque transmissions interposed between the track grooves 82 of the outer joint members 83 and the track grooves 85 of the inner joint members 86. And a cage 88 that is interposed between the inner diameter surface 81 of the outer joint member 83 and the outer diameter surface 84 of the inner joint member 86 and holds the ball 87. The cage 88 is provided with a plurality of windows 88a for accommodating the balls 87 along the circumferential direction.

  In this fixed type constant velocity universal joint, the groove bottom of the track groove 82 of the outer joint member 83 has an opening-side straight portion 82a (a straight portion parallel to the axial direction of the outer joint member 83) and a back-side arc portion 82b. It consists of. The groove bottom of the track groove 85 of the inner joint member 86 includes an arc portion 85a on the opening side and a straight portion 85b on the back side (a straight portion parallel to the axial direction of the inner joint member 86). In this case, the center O1 of the track groove 82 of the outer joint member 83 and the center O2 of the track groove 85 of the inner joint member 86 are offset from the joint center O in the axial direction by the equal distances f and f, respectively. Yes. A female spline 86 a into which the male spline 51 (see FIG. 2) at the end of the shaft S is fitted is formed in the shaft hole of the inner joint member 86.

  The outer joint member 83 in this case is also made of the same carbon steel as the outer joint member 35 shown in FIG. 2 and the like, and includes a cup part 89 and a stem shaft 90 protruding from the bottom wall 89a of the cup part 89. These are integrally molded. The stem shaft 90 is formed with a spline portion (male spline) 90a and a screw portion 90b.

  Also in this case, the outer joint member 83 has the thermosetting layer H1 formed from the bottom wall 89a of the cup part 89 to the spline part (male spline) 90a. The thermosetting layer H1 has a quench hardening ratio of 0.3 to 0.6. When the quenching depth is t1 and the shaft radius is R1, the quench hardening ratio is t1 / R1, and the shaft radius is the radius of the small diameter (diameter) of the spline portion 90a, and R1 = D2 / 2. . For this reason, 0.3 ≦ t1 / R1 ≦ 0.6. The compressive residual stress on the surface of the thermosetting layer H is preferably 500 MPa or more.

  FIG. 7 shows a double offset type sliding constant velocity universal joint. The sliding constant velocity universal joint includes an outer joint member 93 having a track groove 92 formed on the inner diameter surface 91 and a track on the outer diameter surface 94. An inner joint member 96 in which a groove 95 is formed; a ball 97 as a torque transmission member that is interposed between the track groove 92 of the outer joint member 93 and the track groove 95 of the inner joint member 96; It has a pocket 99 for accommodating a ball 97 and a cage 98 interposed between the outer joint member 93 and the inner joint member 96. The center of curvature of the outer peripheral surface 98a of the cage 98 and the center of curvature of the inner peripheral surface 98b are offset in the axial direction opposite to the angular center of the joint.

  A female spline 96 a is formed in the axial hole of the inner joint member 96, and the end of the shaft S is fitted into the axial hole of the inner joint member 96. When the end of the shaft S is fitted into the axial hole of the inner joint member 96, the female spline 96a and the male spline 52 are fitted. A circumferential groove 56 is formed at the end of the male spline 52, and a retaining ring 55 is fitted in the circumferential groove. Thereby, the shaft S is prevented from coming off.

  The opening of the outer joint member 93 is closed by the boot 100. For this reason, the boot 100 includes a large-diameter portion 100a that constitutes one opening, a small-diameter portion 100b that constitutes the other opening, and a bellows portion 100c that connects the large-diameter portion 100a and the small-diameter portion 100b. . And the large diameter part 100a of the boot 100 is mounted | worn in the state externally fitted by the opening part of the outer joint member 93. FIG. Further, the small diameter portion 100b of the boot 100 is mounted in a state of being externally fitted to the boot mounting portion 59 of the shaft S. That is, the large-diameter portion 100a of the boot 100 is fastened and fixed by the boot band 101 at the open end of the outer joint member, and the small-diameter portion 100b is fastened and fixed by the boot band 102 at the boot mounting portion 59 of the shaft S.

  The outer joint member 93 is also made of carbon steel similar to the outer joint member shown in FIG. 4 and the like, and is composed of a cup portion 103 and a stem shaft 104 protruding from the bottom wall 103a of the cup portion 103, which are integrally formed. Has been. The stem shaft 104 includes a boss part 104a provided continuously with the bottom wall 103a of the cup part 103, a smooth part 104b provided continuously with the boss part 104a, and a spline part (male male) provided with the smooth part 104b. Spline) 104c.

  Also in this case, the thermosetting layer H2 is formed on the stem shaft 104 from the smooth portion 104b to the spline portion (male spline) 104c. The thermosetting layer H2 has a quench hardening ratio of 0.3 to 0.6. When the quenching depth is t2 and the shaft radius is R2, the quench hardening ratio is t2 / R2, and the shaft radius is the radius of the small diameter (diameter) of the spline portion 104c, and R2 = D4 / 2. . For this reason, 0.3 ≦ t2 / R2 ≦ 0.6. The compressive residual stress on the surface of the thermosetting layer H2 is preferably 500 MPa or more.

  FIG. 8 shows a cup-type cross groove type sliding constant velocity universal joint. The sliding type constant velocity universal joint has a ball groove 106 (106a, 106a, 106b) Inner joint members 107 (see FIG. 9) alternately formed in the circumferential direction and ball grooves 109 (109a, 109b) twisted in the opposite directions with respect to the axis on the inner circumferential surface 108 in the circumferential direction. A plurality of torque transmission balls incorporated at the intersections of the alternately formed outer joint members 110 and the ball grooves 106 of the inner joint members 107 and the ball grooves 109 of the outer joint members 110 twisted in opposite directions with respect to the axis. 111, a window portion 1 that is interposed between the outer peripheral surface 105 of the inner joint member 107 and the inner peripheral surface 108 of the outer joint member 110 and holds the torque transmission balls 111 at a predetermined interval in the circumferential direction. And a cage 112 having a 2a.

  In FIG. 9, β indicates the crossing angle of each ball groove 106a, 106b, 109a, 109b with respect to the axis. The torque transmission ball 111 is incorporated at the intersection of each ball groove 106a, 106b, 109a, 109b.

  The outer joint member 110 is also made of carbon steel similar to the outer joint member shown in FIG. 4 and the like, and includes a cup portion 115 and a stem shaft 116 protruding from the bottom wall 115a of the cup portion 115, which are integrally formed. Has been. The stem shaft 116 includes a smoothing portion 116a provided continuously with the bottom wall 115a of the cup portion 115, and a spline portion (male spline) 116b provided continuously with the smoothing portion 116a. A female spline 107 a into which the male spline 52 (see FIG. 3) of the shaft S is fitted is formed in the shaft hole of the inner joint member 107.

  Also in this case, the thermosetting layer H2 is formed on the stem shaft 116 from the smooth portion 116a to the spline portion 116b. The thermosetting layer H2 has a quench hardening ratio of 0.3 to 0.6 at least in the smooth part 116a which is the weakest part (the quench hardening ratio of the spline part 116b may be 0.3 or less). When the quenching depth is t2 ′ and the shaft radius is R2 ′, the quench hardening ratio is t2 ′ / R2 ′, and the shaft radius is the radius of the small diameter (diameter) of the smooth portion 116a, and R2 ′ = D4 ′ / 2. For this reason, 0.3 ≦ t2 ′ / R2 ′ ≦ 0.6. The compressive residual stress on the surface of the thermosetting layer H2 is preferably 500 MPa or more.

  As described above, the outer joint member of the constant velocity universal joint shown in FIGS. 6 to 9 is also made of the same carbon steel as the outer joint member shown in FIGS. 2 and 4 and the quench hardening ratio of the thermosetting layer H. Is 0.3 to 0.6. For this reason, there exists an effect similar to the outer joint member shown in FIG.2 and FIG.4 etc. FIG.

  As described above, the embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various modifications are possible, and a ball is used as a torque transmission member (a fixed constant velocity universal joint). Or even a sliding constant velocity universal joint), the number of balls may be 6 or 8, and the increase or decrease is arbitrary. As a cross-glove type constant velocity universal joint, even if it is a float type (the maximum outer diameter of the inner joint member is set larger than the minimum inner diameter of the cage and the axial displacement is regulated by interference between the inner joint member and the cage) The non-float type may be used (the maximum outer diameter of the inner joint member is set smaller than the minimum inner diameter of the cage and the axial displacement is regulated by the interference between the ball and the cage).

  Further, in the constant velocity universal joint provided with the outer joint member according to the present invention, it is preferably used for a fixed constant velocity universal joint of a drive shaft or a sliding constant velocity universal joint, but a propeller shaft other than the drive shaft, Furthermore, it can be used for power transmission devices of various industrial machines other than those for vehicles.

  In the outer joint members 35 and 83 shown in FIGS. 2 and 6, the thermosetting layer H1 is formed from the bottom walls 70a and 89a of the cup portions 70 and 89 to the spline portions (male splines) 71b and 90a. Only the portions 71b and 90a may be provided. Further, in the outer joint members 42 and 93 shown in FIGS. 4 and 7, the thermosetting layer H2 is provided in a range extending from the smooth portions 76b and 104b to almost the entire length of the spline portions 76c and 104c, but the spline portion 76c. 104c only.

33 Track groove 34 Inner diameter surface 35 Outer joint member 41 Track groove 42 Outer joint member 70, 75 Cup portion 71, 76 Stem shaft 71a Smooth portion 71b Spline portion 76b Smooth portion 76c Spline portion

Claims (5)

A cup portion having a track groove formed on the inner diameter surface and a stem shaft protruding from the bottom wall of the cup portion are integrally formed of the same material, and a smooth portion and a spline portion are formed on the stem shaft. An outer joint member of a universal joint,
The material has an alloy element content of% by weight, C: 0.45-0.60%, Si: 0.4-1.5%, Mn: 0.4-1.0%, S: 0 0.025% or less, Al: 0.01 to 0.1%, B: 0.001 to 0.004%, Ti: 0.02 to 0.05%, and N: 0.008% or less, and Ti / Carbon steel having N ratio of 3.4 or more as a basic component, the balance being Fe and inevitable impurities, the ferrite crystal grain size number of this carbon steel being 7 or more, among the smooth part and spline part of the stem shaft, An outer joint member of a constant velocity universal joint having a thermosetting layer having a quench hardening ratio of 0.3 to 0.6 at least at the weakest part.   The outer joint member of the constant velocity universal joint according to claim 1, wherein the weakest part is a spline portion provided on the stem shaft.   The outer joint member of the constant velocity universal joint according to claim 1, wherein the weakest portion is a smooth portion provided on the stem shaft.   The outer joint member of the constant velocity universal joint according to any one of claims 1 to 3, wherein the compressive residual stress on the surface of the thermosetting layer is 500 MPa or more. An outer joint member manufacturing method for manufacturing an outer joint member of a constant velocity universal joint according to any one of claims 1 to 4,
After forming the quenching part by induction hardening and tempering at least the weakest part of the smooth part and the spline part of the stem shaft, this quenching part is subjected to shot peening, and the surface compressive residual stress is 1000 MPa or more. The outer joint member manufacturing method characterized by forming the thermosetting layer used as this.

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