WO2013154015A1

WO2013154015A1 - Inner member of constant velocity universal joint and method for producing same

Info

Publication number: WO2013154015A1
Application number: PCT/JP2013/060287
Authority: WO
Inventors: 吉田　和彦; 正登長久; 佳宏鶴見
Original assignee: Ntn株式会社
Priority date: 2012-04-11
Filing date: 2013-04-04
Publication date: 2013-10-17
Also published as: JP2013217478A; JP5917249B2

Abstract

This inner member (3, 33) of a constant velocity universal joint (1, 31) at the outer periphery of which a raceway surface (15, 37) is formed that supports torque transmission elements (4, 5, 22, 34) and at the inner periphery of which a spline section (13, 46) is formed is characterized by the inner member (3, 33) comprising a steel material and being subjected to carburizing, quenching, and tempering of which the carburizing is locally suppressed, the spline section (13, 46) being a slack quenched section, at least the surface of the spline major diameter having a metal structure not having a carburized abnormal layer, and a quenched section having a higher carbon concentration than the spline section being formed at the surface other than the spline section (13, 46).

Description

Inner member of constant velocity universal joint and manufacturing method thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner member of a constant velocity universal joint and a manufacturing method thereof, and more particularly to an inner member of a constant velocity universal joint used in a power transmission part of an automobile, an aircraft, a ship, various industrial machines, and the like. About.

For example, there are two types of constant velocity universal joints built into drive shafts and propeller shafts that transmit rotational force from an automobile engine to wheels at a constant speed: fixed constant velocity universal joints and sliding constant velocity universal joints. is there. These constant velocity universal joints have a structure in which two shafts on the driving side and the driven side are connected and rotation can be transmitted at a constant speed even if the two shafts have an operating angle.

The drive shaft that transmits power from the engine of the automobile to the drive wheel must cope with the angular displacement and axial displacement caused by the change in the relative positional relationship between the differential and the wheel. Side) is equipped with a sliding type constant velocity universal joint that can handle angular displacement and axial displacement, and a fixed constant velocity universal joint with a large operating angle on the drive wheel side (outboard side). It has a structure in which joints are connected by a shaft. As a connection structure between the inner member of the constant velocity universal joint and the shaft, spline coupling (including serration coupling; hereinafter the same applies in the present specification and claims) is used.

For example, one type of sliding constant velocity universal joint is a tripod type constant velocity universal joint. As shown in FIG. 14, the tripod constant velocity universal joint 61 mainly includes an outer joint member 62, a tripod member 63 as an inward member, a rolling element 65, and a spherical roller 64. Three track grooves 66 are formed in the axial direction on the inner peripheral portion of the outer joint member 62, and roller guide surfaces 67 are formed in the axial direction on both sides of each track groove 66. The tripod member 63 has three leg shafts 63b formed radially from the boss portion 63a. A spherical roller 64 is fitted to the leg shaft 63b via a large number of rolling elements 65, and

washers

69, 70 are interposed at both ends of the rolling elements, and the washer 69 is positioned by a retaining ring 68. The outer peripheral surface of the leg shaft 63 b forms the inner raceway surface of the rolling element 65, and the inner peripheral surface of the spherical roller 64 forms the outer raceway surface of the rolling element 65. With the above configuration, the row of rolling elements 65 is guided on the leg shaft 63b, and the spherical roller 64 is rotatable on the rolling element 65 and is movable in the axial direction of the leg shaft 63b. The spherical roller 64 is rotatably accommodated on the roller guide surface 67 of the outer joint member 62. With such a structure, relative axial displacement and angular displacement between the outer joint member 62 and the tripod member 63 are absorbed, and rotation is transmitted at a constant speed. A spline 73 is formed on the inner peripheral surface 72 of the boss portion 63a of the tripod member 63, and the spline 73 and the spline 74 of the shaft 71 are fitted and connected so as to transmit torque.

On the other hand, there is a Rzeppa constant velocity universal joint as a type of fixed constant velocity universal joint. As shown in FIGS. 17 and 18, the Rzeppa constant velocity universal joint 91 mainly includes an outer joint member 92, an inner joint member 93 as an inner member, a ball 94, and a cage 95. A plurality of track grooves 96 are formed in the spherical inner peripheral surface 98 of the outer joint member 92 at equal intervals in the circumferential direction and along the axial direction. On the spherical outer peripheral surface 99 of the inner joint member 93, track grooves 97 facing the track grooves 96 of the outer joint member 92 are formed at equal intervals in the circumferential direction and along the axial direction. A plurality of balls 94 for transmitting torque are interposed between the track grooves 96 of the outer joint member 92 and the track grooves 97 of the inner joint member 93. A cage 95 that holds the ball 94 is disposed between the spherical inner peripheral surface 98 of the outer joint member 92 and the spherical outer peripheral surface 99 of the inner joint member 93. The centers of curvature of the spherical inner peripheral surface 98 of the outer joint member 92 and the spherical outer peripheral surface 99 of the inner joint member 93 are both formed at the center O of the joint. Further, the centers of curvature of the spherical outer peripheral surface 100 and the spherical inner peripheral surface 101 of the cage 95 are also formed at the center O of the joint. On the other hand, the center of curvature A of the track groove 96 of the outer joint member 92 and the center of curvature B of the track groove 97 of the inner joint member 93 are offset by an equal distance in the axial direction with respect to the center O of the joint. . Thereby, when the joint takes an operating angle, rotation is transmitted at a constant speed between the two shafts of the outer joint member 92 and the inner joint member 93. A spline 106 is formed on the inner peripheral surface 105 of the inner joint member 93, and the spline 106 and the spline 107 of the shaft 102 are fitted and connected so that torque can be transmitted.

Since the tripod member 63 and the inner joint member 93 as the inner members of the constant velocity

universal joints

61 and 91 have a shape in which the thickness in the circumferential direction changes, a countermeasure technique for heat treatment deformation of the spline is disclosed. (Patent Document 1).

Japanese Patent Laid-Open No. 2004-232697

FIG. 15 shows an enlarged tripod member. Conventionally, as shown in FIG. 16, the tripod member 63 includes a bar material cutting step S1, a spheroidizing annealing step S2, a bondering step S3, a cold forging step S4, a turning step S5, a broaching step S6, and a heat treatment. It is manufactured through step S7 and grinding step S8. Since the tripod member 63 is required to have strength, wear resistance, and peel resistance, the heat treatment such as carburizing, quenching, and tempering is performed to increase the hardness as in the above manufacturing process. However, as shown in FIG. 15, the tripod member 63 has a shape in which the leg shaft 63b protrudes radially from the boss portion 63a, so that the change in the thickness in the circumferential direction is large.

When such a part having a large change in thickness is subjected to carburizing, quenching and tempering, the heat treatment deformation increases because the cooling rate varies depending on the part. In addition, expansion occurs due to transformation during quenching, and this expansion is proportional to the volume of the part. Therefore, the thick part expands greatly, and conversely the thin part becomes small expansion. As a result, the pitch circle P of the spline 73 of the tripod member 63 changes from a perfect circular shape before heat treatment to FIG. As shown in the figure, the diameter of the pitch circle P is large in the thick leg shaft forming portion D, and the diameter of the pitch circle P is small in the thin cylindrical portion C, which has a diameter difference of about several tens of μm. Deforms into a triangular shape. In FIG. 15, the diameter difference is exaggerated for easy understanding.

Due to the heat treatment deformation as described above, when torque is transmitted by fitting and connecting the spline 74 of the shaft 71 to the spline 73 of the tripod member 63, a large load is applied to the spline 73 of the thin cylindrical portion C. A small load is applied to the spline 73 of the leg shaft forming portion D, and the stress acting on each tooth of the spline 73 becomes non-uniform. Thereby, the fall of the fatigue strength of the tripod member 63 and the big variation in fatigue strength may be caused. In addition, due to the non-uniform spline load due to the heat treatment deformation of the tripod member 63, the strength of the shaft to be fitted may be reduced. Under such circumstances, the heat treatment deformation of the spline 73 of the tripod member 63 is often used without finishing after heat treatment because it is difficult to grind easily and economically. .

FIG. 19 shows an enlarged inner joint member of the Rzeppa constant velocity universal joint. The inner joint member 93 is also manufactured through substantially the same process as the tripod member 63 described above. The inner joint member 93 includes a track groove forming portion E and a spherical outer peripheral surface forming portion F, and the thickness changes in the circumferential direction. The amount of change in the thickness of the inner joint member 93 is not as great as that of the tripod member 63, but the pitch circle P of the spline 106 formed on the inner peripheral surface 105 of the inner joint member 93 undergoes heat treatment deformation in a polygonal shape, There is a problem similar to that of the tripod member 63 described above. In FIG. 19, the polygonal heat treatment deformation is exaggerated for easy understanding.

In order to solve the above problem, the technique described in Patent Document 1 considers the shape before serration of the inner joint member, the deformation amount due to the heat treatment in advance, and the inner diameter dimension of the thin part is changed to the inner diameter dimension of the thick part. It is something that makes it bigger. However, this technique cannot eliminate variations in heat treatment deformation that inevitably occur. Therefore, there is a limit to uniform the stress acting on each tooth of the spline. Further, it was found that since an abnormal carburization layer is formed on the surface of the spline bottom (large diameter) that becomes the starting point of the tripod member destruction, improvement in strength is also necessary.

Patent Document 1 also describes that serrations are formed after heat treatment of the inner joint member. However, in this case, finishing work such as hard broaching and wire cutting with special coating on carbide tool steel is required, which leads to significant costs due to the introduction of new equipment and long processing time. This causes problems.

In view of the problems as described above, the present invention provides an inner member of a constant velocity universal joint having high strength by making the stress acting on each tooth of the spline uniform while suppressing increase in processing time and cost. For the purpose.

As a result of various studies to achieve the above object, the present inventors have made the spline forming portion of the inner member a hardness capable of general broaching, and broaching after carburizing, quenching and tempering, A new idea of forming a spline having a high degree of removal and a carburized abnormal layer was achieved, and the present invention was achieved.

As technical means for achieving the above-mentioned object, the present invention is an inner member of a constant velocity universal joint in which a raceway surface for supporting a torque transmitting element is formed on the outer periphery and a spline portion is formed on the inner periphery. The inner member is made of steel and is subjected to carburizing, quenching and tempering that suppresses carburizing locally, the spline portion is an incompletely quenched portion, and at least the surface of the spline large diameter is a carburizing abnormal layer. A hard metal part having a higher carbon concentration than the spline part is formed on the surface excluding the spline part.

With the above configuration, the spline forming portion of the inner member of the constant velocity universal joint has a hardness capable of general broaching and broached after carburizing, quenching and tempering, so that a spline having a highly round pitch circle is obtained. Since it is formed and the carburizing abnormal layer of the tooth bottom is removed, an inner member having high strength and small variation in strength can be realized. At the same time, the strength of the shaft fitted to the inner member can be improved.

Here, a general broach is a normal high-speed tool steel (SKH55 or SKH51) or a corresponding steel material (molybdenum-based high-speed tool steel), which is quenched and tempered to HRC63 or higher and then finished. Means brooches.

Specifically, it is preferable that the surface hardness of the large spline diameter is Hv230 or more and Hv390 or less. More preferably, it is set to Hv260 or more and Hv340 or less. When the surface hardness exceeds Hv390, the life of the broach is remarkably reduced and the strength of the trunnion is also reduced. On the other hand, if the surface hardness is less than Hv230, the spline strength is reduced, and on the carburizing work surface, it is necessary to completely prevent the carburization from spreading, which requires a large jig and tool, resulting in a decrease in productivity. This increases the cost and is not preferable. The surface hardness measurement site is 0.2 mm from the large-diameter surface of the circumferential section at the center of the spline axis direction.

It is preferable that the inner member is chrome steel. Chrome steel has a lower inner peripheral hardness than chromium molybdenum steel, so the life of the broach is improved. It was also found that low-strength chromium steel with no molybdenum added has high strength.

The above-mentioned inner member is a tripod member. Since the tripod member has a shape in which the three leg shafts protrude radially from the boss portion, the change in the thickness in the circumferential direction is large, and the heat treatment deformation is large. Therefore, it is more effective when applied to a tripod member.

Further, as a manufacturing method, there is a manufacturing method of an inner member of a constant velocity universal joint in which a raceway surface for supporting a torque transmitting element is formed on an outer periphery and a spline portion is formed on an inner periphery, the inner member being a steel material By performing carburizing quenching and tempering that locally suppresses carburizing, the portion forming the spline portion is an incompletely quenched portion, and a quenched portion is formed on the surface excluding the portion. A part that forms the spline hole is broached.

With the above configuration, the spline forming part of the inner member of the constant velocity universal joint has a hardness that allows general broaching, and broaching after carburizing, quenching and tempering can improve the life of the broach and provide new equipment. The increase in cost and the decrease in productivity due to the introduction of the material and the long processing time can be suppressed. Further, the inner member based on this manufacturing method is formed with a spline having a pitch circle with a high roundness, and the carburizing abnormal layer at the bottom of the tooth is removed, so that it has high strength and small variation in strength. An inward member can be obtained.

According to the present invention, the spline hole portion of the inner member of the constant velocity universal joint is formed in a pitch circle having a high roundness, and the carburizing abnormal layer in the tooth bottom portion is removed, thereby providing high strength and strength. It is possible to realize an inner member with a small variation. Further, according to the manufacturing method of the present invention, it is possible to improve the life of the broach, and to suppress an increase in cost and a decrease in productivity due to the introduction of new equipment and a long processing time.

It is a longitudinal cross-sectional view of the constant velocity universal joint incorporating the tripod member as an inward member of the 1st Embodiment of this invention. It is the front view which expanded and showed said tripod member. It is a figure which shows the manufacturing process of the tripod member in embodiment about the manufacturing method of this invention. It is a longitudinal cross-sectional view which shows the tripod member after a turning process. It is a general-condition figure which shows the heat processing process. It is a figure which shows the tripod member after heat processing. It is a figure which shows the metal structure of the G section of FIG. 6a. It is a longitudinal cross-sectional view which shows the tripod member of broaching. It is a partial longitudinal cross-sectional view of the tripod member of 2nd Embodiment. It is a front view of said tripod member. It is a longitudinal cross-sectional view of the constant velocity universal joint incorporating the inner side coupling member as an inward member of the 3rd Embodiment of this invention. It is a side view of said constant velocity universal joint. It is the front view which expanded and showed said inner joint member. It is a longitudinal cross-sectional view of the inner joint member of 4th Embodiment. FIG. 12b is a transverse cross-sectional view at the axially central portion of FIG. 12a. It is a longitudinal cross-sectional view which shows the drive shaft incorporating the inner member of embodiment. It is a longitudinal cross-sectional view of the constant velocity universal joint incorporating the conventional tripod member. It is the front view which expanded and showed said tripod member. It is a figure which shows the manufacturing process of said tripod member. It is a longitudinal cross-sectional view of the constant velocity universal joint incorporating the conventional inner joint member. It is a side view of said constant velocity universal joint. It is the front view which expanded said inner joint member.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 show an inner member of the constant velocity universal joint according to the first embodiment of the present invention. This constant velocity universal joint is a sliding tripod type constant velocity universal joint. The tripod type constant velocity universal joint 1 includes an outer joint member 2, a tripod member 3 as an inner member, rolling elements 5 and a spherical roller 4 as torque transmission elements. Three track grooves 6 are formed in the axial direction on the inner periphery of the outer joint member 2, and roller guide surfaces 7 are formed in the axial direction on both sides of each track groove 6. The tripod member 3 has three leg shafts 3b formed radially from its boss 3a. The spherical roller 4 is fitted to the leg shaft 3 b via a large number of rolling elements 5, and

washers

9 and 10 are interposed at both ends of the rolling elements, and the washer 9 is positioned by a retaining ring 8. The outer diameter surface of the leg shaft 3 b forms the inner raceway surface of the rolling element 5, and the inner diameter surface of the spherical roller 4 forms the outer raceway surface of the rolling element 5. The row of rolling elements 5 is guided on the leg shaft 3b, and the spherical roller 4 is rotatable on the rolling element 5 and is movable in the axial direction of the leg shaft 3b. The spherical roller 4 is rotatably accommodated on the roller guide surface 7 of the outer joint member 2. With such a structure, relative axial displacement and angular displacement between the outer joint member 2 and the tripod member 3 are absorbed, and rotation is transmitted at a constant speed.

A spline 13 is formed on the inner peripheral surface 12 of the boss 3a of the tripod member 3, and the spline 13 and the spline 14 of the shaft 11 are fitted and connected so as to transmit torque.

FIG. 2 is an enlarged front view of the tripod member 3. In the tripod member 3, three leg shafts 3b project radially from the boss portion 3a, and the outer diameter surface 15 of the leg shaft 3b serving as the inner raceway surface of the rolling element 5 is finished by, for example, grinding. Splines 13 are formed on the inner peripheral surface 12 of the boss 3a. As shown in the figure, the spline 13 of the trunnion member 3 of the present embodiment is not deformed by heat treatment, and has a high roundness pitch over the entire circumference of the thick leg shaft forming portion D and the thin thick cylindrical portion C. It is formed by a circle P. Therefore, when the spline 14 of the shaft 11 is fitted to the spline 13 and torque is transmitted, the stress acting on the teeth of the

splines

13 and 14 becomes as uniform as possible. The trunnion member 3 is subjected to carburizing, quenching, and tempering that suppresses carburizing locally, which will be described later, and the portion 13s where the spline 13 is formed is formed as an incompletely quenched portion, and the portion where the spline 13 is formed. The surface excluding 13s is a hardened part. Hereinafter, the portion 13s where the spline 13 is formed is abbreviated as a spline forming portion 13s. The spline 13 of the trunnion member 3 of the present embodiment is not deformed by heat treatment and is formed with a pitch circle P having a high roundness because the spline forming portion 13s has a hardness that allows general broaching. This is because the complete quenching portion can be used to form the spline 13 by broaching after carburizing quenching and tempering. That is, there is no problem of heat treatment deformation of the spline as in the prior art described above.

In addition, since the carburizing abnormal layer is removed by broaching, the surface of the tooth bottom (large diameter) of the spline 13 that is the starting point of the destruction of the tripod member 3 becomes a metal structure having no carburizing abnormal layer. Therefore, the fatigue strength of the tripod member 3 is improved, and at the same time, the strength of the shaft 11 fitted to the tripod member 3 can be improved.

Next, an embodiment of the manufacturing method of the present invention for obtaining the tripod member 3 described above will be described with reference to FIGS. FIG. 3 shows an outline of the manufacturing process of the tripod member 3. The tripod member 3 includes a bar cutting process S1, a spheroidizing annealing process S2, a bonding process S3, a cold forging process S4, a turning process S5, a heat treatment process S6, a broaching process S7, and a grinding process as shown in the figure. It is manufactured through step S8. The manufacturing process of this embodiment differs from the conventional manufacturing process (see FIG. 16) in that the spline broaching process S7 is performed after the heat treatment as the content of the heat treatment process S6 and the order of the manufacturing process.

The outline of each process will be explained. Each process shows a typical example, and can be changed or added as necessary.

[Bar material cutting step S1]
A billet is manufactured by cutting at a predetermined length based on the forging weight.

[Spheroidizing annealing step S2]
It is normally performed in cold forging, and improves the material fluidity (deformability) during cold forging by applying spheroidizing annealing. In order to shorten the processing time of spheroidizing annealing, a billet may be upset and processing distortion may be applied.

[Bonde treatment process S3]
In order to improve the life of the forging die and forgeability, the billet is subjected to a bondage treatment that enhances lubricity.

[Cold forging process S4]
The billet is put into the cavity of the forging die, and the billet is filled into the die by plastic working. Thereby, the cold forging goods of the tripod member in which the boss | hub part, the boss | hub part inner peripheral surface, and the leg axis | shaft were formed are obtained.

[Turning process S5]
The outer diameter surface of the leg shaft, the retaining ring groove, the root portion, the end surface, the inner peripheral surface and the chamfered portion are machined from the cold forged product.

[Heat treatment step S5]
Since the inner member of the constant velocity universal joint is required to have strength, the hardness is increased by carburizing, quenching and tempering. In the present embodiment, by carburizing quenching and tempering that locally suppresses carburization, the spline forming portion is an incompletely quenched portion having a hardness capable of general broaching, and the surface excluding the spline forming portion is a quenched portion. To form.

[Broach processing step S7]
A spline is formed by broaching the inner peripheral surface of the heat-treated product.

[Grinding process S8]
The outer diameter surface of the leg shaft that becomes the raceway surface of the rolling element is finished by grinding.

Of the manufacturing process, the bar material cutting process S1 to the turning process S5 and the grinding process S8 are the same as the conventional ones.

In this embodiment, the turned product 3 'of the tripod member 3 before spline processing shown in FIG. 4 is put into the heat treatment step S6. Specifically, in the turning process S5, the turning completed product 3 ′ is obtained from the cold forging product (not shown) to the outer diameter surface 15, the retaining ring groove 16, the root portion 17, the end surface 18, the inner surface of the leg shaft 3b ′. The peripheral surface 12 and the chamfered portion 19 are turned.

Next, the heat treatment step S6 will be described with reference to FIGS. Carburizing is performed as a heat treatment. In order to locally reduce the hardness of the spline forming portion 13s on the inner periphery of the tripod member 3 and obtain an incompletely hardened portion having a hardness capable of general broaching, the carburization to the spline forming portion 13s is suppressed. To do. In order to suppress carburizing locally, for example, when a processed product (turned product 3 ′) is put into a carburizing furnace, a carburizing suppression rod having a diameter close to the inner diameter of the processed product is skewered, and carbon It can be obtained by suppressing intrusion.

A specific example of carburizing and quenching and tempering in which carburization is locally suppressed will be described with reference to FIG. As shown in the drawing, a large number (for example, ten or more) of the completed turning products 3 ′ of the tripod member 3 including a portion indicated by a two-dot chain line are stacked and skewed into the carburization suppression rod 20. A set of (for example, a dozen) is fixed to a flat net 21 illustrated by a two-dot chain line, and this flat net 21 is appropriately stacked in a number of stages (for example, three stages) and carburized, quenched, and tempered in that state. The carburization suppression rod 20 is preferably made of heat-resistant stainless steel, and the carburization suppression rod 20 is set to an outer diameter slightly smaller than the diameter of the inner peripheral surface in consideration of skewering workability of the turned product 3 '. In FIG. 5, the fitting clearance between the inner peripheral surface of the turning completed product 3 ′ and the outer diameter surface of the carburization suppressing rod 20 is omitted.

The carburizing conditions were carburizing / diffusion at 950 ° C for 180-200 minutes, and after carburizing / diffusion, heating and holding at 840 ° C for 20-30 minutes, then quenching in oil at 100-120 ° C and tempering. Is preferably 150 to 180 ° C. for 120 minutes. Of course, if the size of the processed product is different, the processing conditions are appropriately changed.

When carburizing, quenching and tempering in the above-described state, the carburization suppressing rod 20 having an outer diameter close to the diameter of the inner peripheral surface 12 of the turning-finished product 3 ′ is fitted, so that carbon intrusion can be suppressed. . However, since both ends 18 of the boss 3a 'of the turning completed product 3' are more likely to intrude carbon than the axially central spline of the inner peripheral surface 12, the hardness increases.

FIG. 6 shows the state of the tripod member 3 'after carburizing, quenching and tempering. FIG. 6 a shows a partial longitudinal section of the tripod member 3 ′, and FIG. 6 b shows the metal structure of part G of FIG. 6 a. As shown in FIG. 6a, a hardened portion H having a carbon concentration higher than that of the spline portion is formed on the surface excluding the spline forming portion 13s on the inner periphery of the heat treated product 3 ′ of the tripod member 3, that is, the surface subjected to cross hatching. Has been. The hardened portion H is formed on the outer diameter surface 15 of the leg shaft 3b ′, the retaining ring groove 16, the root portion 17, the outer surface of the boss portion 3a ′ and the end surface 18, and the hardened portion H stays in front of the chamfered portion 19. Yes. Since the carburization is a diffusion phenomenon, the carbon concentration changes continuously (not abruptly) at the boundary between the quenching portion H and the chamfered portion 19. The surface hardness of the quenched portion H is about Hv 660 to 750. The measurement site of the surface hardness is 0.2 mm from the surface at the center in the axial direction for the boss, and 0.2 mm from the surface of the raceway for the leg shaft. On the other hand, in the spline forming portion 13 s on the inner periphery of the heat treated product 3 ′ of the tripod member 3, the intrusion of carbon is suppressed and the cooling rate is also slowed, so that an incompletely quenched portion J is formed. The incompletely hardened portion J is formed beyond the large diameter of the spline (see FIG. 7) in the radial direction from the inner peripheral surface 12 of the spline forming portion 13s.

FIG. 6b shows the metal structure of the inner spline forming portion 13s. A portion of thickness I from the inner peripheral surface 12 is a carburizing abnormal layer. The thickness I of the abnormal carburizing layer increases as the carburizing time becomes longer, but is about 10 to 25 μm in the tripod member of the present embodiment. When carburizing steel such as SCM420 material or SCr420 material is carburized, quenched, and tempered, a soft structure called a carburized abnormal layer is formed in the surface layer portion. The carburized abnormal layer is a grain boundary oxide in which alloy elements such as silicon (Si), manganese (Mn), and chromium (Cr), which are more easily oxidized than iron in steel, are preferentially oxidized at the austenite grain boundary during carburizing, This grain boundary oxide formation causes a solid solution alloy element to decrease and an incompletely hardened layer generated during quenching, which is referred to as an abnormal carburizing layer in the present specification and claims.

FIG. 7 shows the tripod member 3 that has undergone the broaching step S7. The inner peripheral spline forming portion 13s has an incompletely hardened portion J, and has a hardness applicable to general broaching. Specifically, the surface hardness of the large diameter of the spline 13 is preferably Hv 230 or more and Hv 390 or less. More preferably, it is set to Hv260 or more and Hv340 or less. When the surface hardness of the large diameter of the spline 13 exceeds Hv390, the life of the broach is remarkably reduced and the strength of the broach is also reduced. On the other hand, when the surface hardness is less than Hv230, the strength of the spline 13 is reduced, and on the carburizing work surface, it is necessary to completely prevent the diffusion of carburizing. Decreasing and increasing costs. The surface hardness measurement site is 0.2 mm from the large-diameter surface of the circumferential section at the center of the spline axis direction. Splines having pitch circles P (see FIG. 2) with high roundness can be formed by setting the spline forming portion 13s to a hardness capable of broaching and performing broaching after carburizing. As a result, when the torque is transmitted by being engaged with the spline 14 (see FIG. 1) of the shaft 11, the stress of each tooth of the

spline

13, 14 becomes uniform, and as a result, the acting stress on the

spline

13, 14 is reduced. Can be made.

Further, as described above, since the thickness I of the carburizing abnormal layer is about 10 to 25 μm, the surface of the tooth bottom (large diameter) of the spline 13 that becomes the starting point of the breakage of the tripod member 3 by broaching the spline 13. The carburized abnormal layer is removed, and at least the surface of the large spline diameter has a metal structure having no carburized abnormal layer. Therefore, the tripod member 3 having high strength and small strength variation can be realized. At the same time, the strength of the shaft 11 fitted to the tripod member 3 can be improved. In addition, since the inner peripheral surface 12 of the tripod member 3 is not cut during broaching, a carburizing abnormal layer remains on the inner peripheral surface 12, but it is not a starting point of breakage at the time of torque load. Does not occur.

Next, the tripod member of the tripod type constant velocity universal joint according to the second embodiment will be described with reference to FIG. FIG. 8a is a partial longitudinal sectional view of the tripod member, and FIG. 8b is a front view of the tripod member. The tripod member 3 is incorporated into a double roller type tripod type constant velocity universal joint. Parts having the same functions as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

A double roller type roller cassette 22 is mounted on the tripod member 3 of the present embodiment as shown by a two-dot chain line in FIG. The roller cassette 22 as a torque transmission element is composed of an outer roller 4, an inner ring 23 and a rolling element 5, and a washer 24 is attached to the outer roller 4 to form an integrated unit. The cross section of the leg shaft 3b of the tripod member 3 is formed in a substantially elliptical shape, and the inner ring 23 of the roller cassette 22 is swingably mounted on the leg shaft 3b. In the present embodiment, the outer diameter surface 15 of the leg shaft 3b is fitted to the inner diameter surface of the inner ring 23 as a torque transmission element and includes a rolling motion. In the description and claims, it is called the raceway surface. The outer roller 4 is rotatably accommodated on a roller guide surface (not shown) of the outer joint member. In the double roller type tripod type constant velocity universal joint, since the outer roller 4 is guided in parallel with the roller guide surface of the outer joint member, axial induced thrust and slide resistance are reduced, and low vibration is realized.

Also in the tripod member 3 of the present embodiment, the spline forming portion 13s is formed by the incompletely quenched portion J, and at least the surface of the large diameter of the spline 13 has a metal structure having no carburizing abnormal layer. The removed surface is a hardened portion (not shown) having a higher carbon concentration than the spline portion. Then, by broaching after carburizing, quenching and tempering, the spline 13 of the trunnion member 3 is formed with a pitch circle having a high roundness without deformation by heat treatment, and the spline 14 of the shaft 11 is fitted to the spline 13 (see FIG. (See 1) When transmitting torque, the stress of each spline becomes as uniform as possible. Moreover, since the carburizing abnormal layer is removed by broaching, the fatigue strength of the tripod member 3 can be improved, and at the same time, the strength of the shaft fitted to the tripod member 3 can be improved. In addition, the details of the manufacturing process and the metal structure, dimensional accuracy, strength characteristics, and the like of the spline 13 and spline forming portion 13s formed on the inner peripheral surface 12 are the same as those in the first embodiment described above, so Description is omitted.

The inner member of the constant velocity universal joint according to the third embodiment of the present invention will be described with reference to FIGS. The constant velocity universal joint shown in FIGS. 9 and 10 is a Rzeppa type constant velocity universal joint which is a kind of fixed type constant velocity universal joint. The constant velocity universal joint 31 mainly includes an outer joint member 32, an inner joint member 33 as an inward member, a ball 34 and a cage 35 as torque transmitting elements. Six track grooves 36 are formed on the spherical inner peripheral surface 38 of the outer joint member 32 at equal intervals in the circumferential direction and along the axial direction. On the spherical outer peripheral surface 39 of the inner joint member 33, track grooves 37 facing the track grooves 36 of the outer joint member 32 are formed at equal intervals in the circumferential direction and along the axial direction. Six balls 34 for transmitting torque are interposed between the track grooves 36 of the outer joint member 32 and the track grooves 37 of the inner joint member 33. The

track grooves

36 and 37 form the track surface of the ball 34. A cage 35 for holding the ball 34 is disposed between the spherical inner peripheral surface 38 of the outer joint member 32 and the spherical outer peripheral surface 39 of the inner joint member 33. A spline 46 is formed on the inner peripheral surface 45 of the inner joint member 33, and a spline 47 of the shaft 42 is fitted into the spline 46 and is fixed in the axial direction by a retaining ring 44. The outer periphery of the outer joint member 32 and the outer periphery of the shaft 42 splined to the inner joint member 33 are covered with a boot 43, and grease is enclosed as a lubricant inside the joint.

As shown in FIG. 9, the centers of curvature of the spherical inner peripheral surface 38 of the outer joint member 32 and the spherical outer peripheral surface 39 of the inner joint member 33 are both formed at the center O of the joint. Further, the centers of curvature of the spherical outer peripheral surface 40 and the spherical inner peripheral surface 41 of the cage 35 are also formed at the center O of the joint. On the other hand, the center of curvature A of the track groove 36 of the outer joint member 32 and the center of curvature B of the track groove 37 of the inner joint member 33 are offset by an equal distance in the axial direction with respect to the center O of the joint. . As a result, when the joint takes an operating angle, the ball 34 is always guided on a plane that bisects the angle formed by the two axes of the outer joint member 32 and the inner joint member 33, and rotates at a constant speed between the two axes. Will be transmitted.

FIG. 11 shows an enlarged front view of the inner joint member 33. The inner joint member 33 is also manufactured through substantially the same process as the tripod member of the first embodiment described above. The inner joint member 33 includes a track groove forming portion E and a spherical outer peripheral surface forming portion F, and the thickness changes in the circumferential direction. Also in this inner joint member 33, the spline forming portion 46s is formed by an incompletely hardened portion, and at least the large diameter surface of the spline 46 has a metal structure without a carburizing abnormal layer, and the surface excluding the spline forming portion 46s. Is a hardened part with a higher carbon concentration than the spline part.

The spline 46 of the inner joint member 33 is not deformed by heat treatment, and is formed by a pitch circle P having a high roundness over the entire circumference of the thick spherical outer peripheral surface forming portion F and the thin track groove forming portion E. When the spline 47 of the shaft 42 is fitted to the spline 46 and torque is transmitted, the stress of each

spline

46, 47 becomes as uniform as possible. Further, since the carburizing abnormal layer is removed by broaching, the fatigue strength of the inner joint member 33 is improved, and at the same time, the strength of the shaft 42 fitted to the inner joint member 33 can be improved. In addition, the details of the manufacturing process and the metal structure, dimensional accuracy, strength characteristics, and the like of the spline 46 and the spline forming portion 46s formed on the inner peripheral surface 45 are the same as those in the first embodiment described above, and thus overlap. Description is omitted.

The inner member of the constant velocity universal joint according to the fourth embodiment of the present invention will be described with reference to FIG. 12a is a longitudinal sectional view of the inner joint member as the inner member, and FIG. 12b is a transverse sectional view at the axially central portion of FIG. 12a. The inner joint member 33 is an inner joint member of a double offset type constant velocity universal joint which is a kind of sliding type constant velocity universal joint. Linear track grooves 37 are formed on the spherical outer peripheral surface 39 of the inner joint member 33 at equal intervals in the circumferential direction and along the axial direction. The track groove 37 forms the raceway surface of the ball. The inner joint member 33 is also manufactured through substantially the same process as the tripod member of the first embodiment described above. The inner joint member 33 includes a track groove forming portion E and a spherical outer peripheral surface forming portion F, and the thickness changes in the circumferential direction.

Also in this inner joint member 33, the spline forming portion 46s is formed by the incompletely quenched portion J, and at least the large-diameter surface of the spline 46 has a metal structure having no carburizing abnormal layer, and the spline forming portion 46s is excluded. The surface is a hardened portion (not shown) having a higher carbon concentration than the spline portion. Then, by broaching after carburizing, quenching and tempering, the spline 46 of the inner joint member 33 is not deformed by heat treatment and is formed in a highly circular pitch circle, and the shaft spline is fitted to the spline 46 to transmit torque. When doing so, the stress of each spline becomes as uniform as possible. Further, since the carburizing abnormal layer is removed by broaching, the fatigue strength of the inner joint member 33 is improved, and at the same time, the strength of the shaft fitted to the inner joint member 33 can be improved. In addition, the details of the manufacturing process and the metal structure, dimensional accuracy, strength characteristics, and the like of the spline 46 and the spline forming portion 46s formed on the inner peripheral surface 45 are the same as those in the first embodiment described above, and thus overlap. Description is omitted.

FIG. 13 shows a sliding type tripod type constant velocity universal joint 1 incorporating the fixed type Zepper type constant velocity universal joint 31 incorporating the inner joint member of the third embodiment and the tripod member of the first embodiment. The front drive shaft 50 of the motor vehicle to which is applied is shown. The inner joint member 33 of the Rzeppa constant velocity universal joint 31 is splined to one end of the hollow shaft 51, and the tripod member 3 of the tripod type constant velocity universal joint 1 is splined to the other end. Bellows-shaped

boots

43, 52 between the outer peripheral surface of the Rzeppa constant velocity universal joint 31 and the outer peripheral surface of the hollow shaft 51 and between the outer peripheral surface of the tripod type constant velocity universal joint 1 and the outer peripheral surface of the shaft 51, respectively. Is fastened and fixed by

boot bands

53a, 53b, 53c, 53d. Grease as a lubricant is sealed inside the joint.

Since the splines of the inner joint member 33 and the tripod member 3 are not deformed by heat treatment and are formed by pitch circles having a high roundness, the stress between the splines of the hollow shafts to be fitted is as much as possible. It becomes uniform. Further, since the carburizing abnormal layer is removed by broaching, the fatigue strength of the inner joint member 33 is improved, and at the same time, the strength of the hollow shaft 51 fitted to the inner joint member 33 can be improved. Thereby, the high-strength automobile drive shaft 50 can be realized.

Furthermore, as a modification of the embodiment of the manufacturing method described above, as a result of various investigations of processing steps that further improve the life of the broach, the bar material of chrome steel (SCr415) is cut, spheroidized, annealed, It was found that the processes were cold forging, rough turning, heat treatment, inner peripheral finishing turning, broaching, and leg shaft grinding.

The inner peripheral finish turning after the heat treatment is performed at both ends of the boss, that is, both end faces in the axial direction of the spline and inner peripheral finish turning. This is because both end surfaces of the boss portion are more likely to intrude carbon than the axially central portion of the inner peripheral portion, and cope with the increase in surface hardness. Further, the roundness of the inner peripheral portion deteriorates after carburizing, quenching and tempering. If broaching is performed with this deformation left, the life of the broach teeth will be reduced. Therefore, it was found that the life of the broach is further improved by removing the hardened portion and improving the roundness of the inner peripheral portion by finishing turning. The embodiment of the manufacturing method of the present invention naturally includes a case where an inner peripheral surface finishing turning process as described above is added between the heat treatment step S6 and the broaching step S7 shown in FIG.

According to the embodiment of the manufacturing method of the present invention, broaching is performed by heat-treating ordinary high-speed tool steel (SKH55 or SKH51) or a corresponding steel material (molybdenum-based high-speed tool steel) to HRC63 or higher. After quenching and tempering, it can be processed with a finished general broach.

Examples and comparative examples of the present invention will be described below. Example 1 of the tripod member 3 of the first embodiment is a bar material of chrome molybdenum steel (SCM420), cutting, spheroidizing annealing, bonding process, cold forging, turning, which are the manufacturing steps of the embodiment, It was manufactured by carburizing, quenching and tempering, broaching, and grinding the leg shaft. The spline is a flat bottom spline of JIS B 1603. The main specifications are: Diametral pitch: 32/64, pressure angle: 37.5 °, number of teeth: 30, large diameter: 25.03 mm, small diameter: 23.19 mm, pitch Circular diameter (PCD): 23.813 mm. As heat treatment conditions, the finished product of tripod member is stacked on carburization suppression rods and skewered, carburized and diffused at 950 ° C for 200 minutes, held at 840 ° C for 23 minutes, and then quenched into oil at 110 ° C. It was. Thereafter, tempering was performed at 160 ° C. for 120 minutes.

Example 2 was manufactured in the same manufacturing process as Example 1 using a bar material of chromium steel (SCr420). The specifications of the flat bottom spline and the heat treatment conditions are the same as in Example 1.

Example 3 differs only in that the flat bottom spline of JIS B 1603 of Example 2 is changed to a round bottom spline.

In Comparative Example 1, a chromium-molybdenum steel (SCM420) bar material was cut, spheroidized, bonded, cold forged, turned, broached, carburized, quenched, and tempered, which are conventional manufacturing processes. Made by grinding. The heat treatment conditions were normal carburizing quenching and tempering, and the same temperature conditions and time conditions as in Example 1. The shape and specifications of the spline teeth are the same as those in the first and second embodiments.

Table 1 shows the characteristics and fatigue test results of the examples and comparative examples. However, the fatigue test is the name of the constant velocity joint in Table 3 on page 3 of the automotive standard (JASO C 304-89: constant velocity joint for automobile drive shafts, published on March 31, 1989). The test was carried out by applying a load of 1504 Nm to the 22.2 joint with an operating angle of 0 °. The surface hardness measurement sites in Table 1 are 0.2 mm from the surface at the central portion in the axial direction for the tooth surface portion, and 0.2 mm from the surface of the raceway surface for the leg shaft portion.

From the fatigue test results, the fatigue life of Examples 1 to 3 is greatly improved based on the number of breaks L ₅₀ (50% fracture life expectancy) of Comparative Example 1. It was also found that Example 2 using low-cost chromium steel (SCr420) to which no molybdenum (Mo) was added had high strength. Moreover, it turned out that the life of a broach is improved in Example 2 using chromium steel (SCr420) because the hardness of the tooth surface portion is lower than that in Example 1 using chromium molybdenum steel (SCM420).

From the fatigue test results of Example 3, it is considered that the round bottom spline is slightly more advantageous in terms of fatigue strength than the flat bottom spline as an effect of changing the shape of the spline teeth.

Next, a fatigue test was carried out in order to evaluate the fatigue strength in the assembled state in which Example 1 and Comparative Example 1 were spline fitted to the hollow shaft. The hollow shaft was manufactured by performing plastic working and machining using a steel pipe made of SAE15B35, and hardening it by induction hardening to produce a hollow shaft. The main specifications of the hollow shaft spline are: Diametral pitch: 32/64, Pressure angle: 37.5 °, Number of teeth: 30, Large diameter: 24.613 mm, Small diameter: 22.535 mm, Pitch circle diameter (PCD) : 23.813 mm. The inner diameter of the hollow shaft in the spline forming portion was 10.8 mm.

Table 2 shows the fatigue test results of the hollow shaft assemblies A and B in which the tripod member of Example 1 and the tripod member of Comparative Example 1 are spline-fitted to the hollow shaft. The load in the fatigue test was the same as in Table 1, but a double-twisted torsional fatigue test was performed.

Results of the fatigue test, based on the rupture times L ₅₀ of the hollow shaft assembly body B with assembled tripod member of Comparative Example 1, the fatigue strength of the hollow shaft assembly body A is assembled the tripod member of Example 1 It turns out that it improves significantly. Moreover, all the fracture | rupture parts were the spline parts of the hollow shaft.

In each of the above embodiments, the inner member of the Rzeppa type constant velocity universal joint as the fixed type constant velocity universal joint and the double offset type constant velocity universal joint and the tripod type constant velocity universal joint as the sliding type constant velocity universal joint are shown. However, the present invention is not limited to this. In addition to the above, as a fixed type constant velocity universal joint, an undercut-free type constant velocity universal joint, a counter track type constant velocity universal joint, and as a sliding type constant velocity universal joint, a cross groove type constant velocity universal joint, holding The inner member of a delta type constant velocity universal joint without a vessel can be appropriately implemented. In addition, although the number of balls is six, the present invention is not limited to this, and the number of balls can be 3 to 5, 8 or 10 or more.

The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the spirit of the present invention. All equivalents and equivalents of the claims, and all modifications within the scope of the claims are embraced by the claims.

DESCRIPTION OF SYMBOLS 1 Tripod type constant velocity universal joint 2 Outer joint member 3 Tripod member 4 Spherical roller (torque transmission element)
5 Rolling elements (torque transmission elements)
6 Track groove 7 Roller guide surface 11 Shaft 12 Inner peripheral surface 13 Spline 13s Spline forming portion 15 Outer diameter surface (track surface)
31 Rzeppa constant velocity universal joint 32 Outer joint member 33 Inner joint member 34 Ball (torque transmission element)
35 Cage 36 Track groove (track surface)
37 Track groove (track surface)
42 Shaft A Center of curvature B Center of curvature C Cylindrical part D Leg shaft forming part E Track groove forming part H Hardened part J Incompletely hardened part O Joint center

Claims

An inner member of a constant velocity universal joint having a raceway surface for supporting a torque transmission element on the outer periphery and a spline portion formed on the inner periphery, and the inner member is made of steel and locally suppresses carburization. Carburizing, quenching, and tempering are performed, the spline portion is an incompletely hardened portion, and at least the surface of the spline having a large diameter has a metal structure having no carburizing abnormal layer, and the spline portion is removed from the surface excluding the spline portion. An inner member of a constant velocity universal joint, wherein a hardened portion having a higher carbon concentration is formed.
The inner member of the constant velocity universal joint according to claim 1, wherein the surface hardness of the large spline diameter is Hv230 or more and Hv390 or less.
The inner member of the constant velocity universal joint according to claim 1 or 2, wherein the inner member is made of chromium steel.
The inner member of the constant velocity universal joint according to any one of claims 1 to 3, wherein the inner member is a tripod member.
A method of manufacturing an inner member of a constant velocity universal joint in which a raceway surface for supporting a torque transmitting element is formed on an outer periphery and a spline portion is formed on an inner periphery, wherein the inner member is a steel material and is locally carburized. By suppressing carburizing and quenching and tempering, the spline part is formed as an incompletely hardened part, and a hardened part having a higher carbon concentration than the spline part is formed on the surface excluding the part, and the spline hole is formed after this heat treatment. A method for manufacturing an inner member of a constant velocity universal joint, wherein a portion forming the portion is broached.