WO2020195487A1

WO2020195487A1 - Tripod-type constant-velocity universal joint

Info

Publication number: WO2020195487A1
Application number: PCT/JP2020/007754
Authority: WO
Inventors: 将太河田; 弘昭牧野; 卓板垣; 石島　実
Original assignee: Ntn株式会社
Priority date: 2019-03-22
Filing date: 2020-02-26
Publication date: 2020-10-01

Abstract

A leg shaft (7) comprises: a high hardness part (A) that is formed on the surface of the leg shaft (7) such that the carbon content gradually decreases from the surface toward the core of the leg shaft (7); a medium hardness part (B) that is formed closer to the core than the high hardness part (A) and has lower hardness than the high hardness part (A); and a low hardness part (D) that is formed closer to the core than the medium hardness part (B) and has lower hardness than the medium hardness part. The hardness of the high hardness part (A) and the medium hardness part (B) is made to be at least 550 HV and the hardness of the low hardness part is made to be lower than 550 HV.

Description

Tripod type constant velocity universal joint

The present invention relates to a tripod type constant velocity universal joint used for power transmission of automobiles and various industrial machines.

In the drive shaft used in the power transmission system of automobiles, a sliding constant velocity universal joint is connected to the inboard side (center side in the vehicle width direction) of the intermediate shaft, and the outboard side (end in the vehicle width direction). In many cases, a fixed constant velocity universal joint is connected to the side). The sliding type constant velocity universal joint here allows both angular displacement and axial relative movement between the two axes, and the fixed constant velocity universal joint allows angular displacement between the two axes. However, relative movement in the axial direction between the two axes is not allowed.

A tripod type constant velocity universal joint is known as a sliding constant velocity universal joint. As this tripod type constant velocity universal joint, there are a single roller type and a double roller type. In the single roller type, a roller inserted into the track groove of the outer joint member is rotatably attached to the leg shaft of the tripod member via a plurality of needle-shaped rollers. The double roller type includes a roller inserted into the track groove of the outer joint member and an inner ring that is fitted onto the leg shaft of the tripod member to rotatably support the roller. Compared to the single roller type, the double roller type allows the roller to swing and swing with respect to the leg shaft, so compared to the single roller type, induced thrust (axial force induced by friction between parts inside the joint) and slide. It has the advantage that a reduction in resistance can be achieved. An example of a double roller type tripod type constant velocity universal joint is described in, for example, Japanese Patent No. 35999618.

Japanese Patent No. 35999618

In the double roller type tripod type constant velocity universal joint described in Patent Document 1, the outer peripheral surface of the leg shaft of the tripod member and the inner peripheral surface of the inner ring come into contact with each other in a form close to a point on the torque load side. Especially when the load torque is high, the surface pressure at the contact portion becomes high, which affects the durability of the outer peripheral surface of the leg shaft. If the durability of the leg shaft can be improved, the stable movement of the roller can be maintained, and the deterioration of the vibration characteristics with time can be prevented.

In order to improve the durability of the leg shaft, it is effective to deepen the depth of the hardened layer formed on the surface of the leg shaft. In tripod members, it is common to apply carburizing, quenching and tempering to hardened steel to form a hardened layer on the surface, so it is conceivable to increase the carburizing time as a method of deepening the depth of the hardened layer. However, since the carburizing time increases in proportion to the square of the increase in depth, an enormous amount of carburizing time is required to form a deep hardened layer, which increases the manufacturing cost.

As another measure, the tripod member may be made of a steel material with an increased carbon content, for example, carbon steel for mechanical structure such as S50C to S55C (see JIS G4051), and a hardened layer may be formed on the surface by induction hardening. Conceivable. However, in this method, since the steel material becomes hard due to the increase in carbon content, the processing load when forming the tripod member by forging increases. Therefore, the size of the forging equipment is increased and the life of the forging die is shortened.

Therefore, an object of the present invention is to improve the durability of the leg shaft of the tripod member while suppressing the soaring manufacturing cost.

The present invention made based on the above findings is provided with track grooves extending in the axial direction at three locations in the circumferential direction, and each track groove has a pair of roller guide surfaces arranged so as to face each other in the circumferential direction. A joint member, a tripod member having three leg shafts protruding in the radial direction, and a roller mounted on each leg shaft are provided, and the roller is provided along the roller guide surface in the axial direction of the outer joint member. In a tripod type constant velocity universal joint in which a hardened layer is formed by heat treatment on the surface of each leg shaft of the tripod member, the leg shaft is formed on the surface of the leg shaft and is formed from the surface side. A high-hardness portion in which the amount of carbon gradually decreases toward the core portion, a medium-hardness portion formed on the core portion side of the high-hardness portion and having a lower hardness than the high-hardness portion, and a core rather than the medium-hardness portion. A low hardness portion formed on the portion side and having a lower hardness than the medium hardness portion is provided, the hardness of the high hardness portion and the medium hardness portion is 550 HV or more, and the hardness of the low hardness portion is less than 550 HV. It is characterized by.

By forming the above hardness distribution on the surface of the leg shaft, the depth of the hardened layer (high hardness part and medium hardness part) exceeding 550 HV is deepened, while the hardness of the low hardness part which is the core part is increased. Can be lowered. Therefore, the durability of the leg shaft can be ensured even when the surface of the leg shaft becomes locally high due to the load of excessive torque on the tripod type constant velocity universal joint. Further, since the core portion of the leg shaft has high toughness, it is possible to avoid a decrease in the repeated fatigue strength of the tripod member.

The tripod-type constant-velocity universal joint includes an inner ring that is fitted onto the leg shaft and rotatably supports the roller. A roller unit is formed by the roller and the inner ring, and the roller unit is the roller unit. A configuration that can swing and swing with respect to the leg axis can be adopted.

In this tripod type constant velocity universal joint, the outer peripheral surface of the leg shaft has a shape of being straight in the vertical cross section and substantially elliptical in the cross section, and the inner peripheral surface of the inner ring is formed by a convex curved surface. The outer peripheral surface of the leg shaft comes into contact with the inner peripheral surface of the inner ring in a direction orthogonal to the axis of the joint, and a gap is formed between the outer peripheral surface of the leg shaft and the inner peripheral surface of the inner ring in the axial direction of the joint.

The carbon content in the low hardness portion is preferably 0.10% or more. In addition, "%" representing a carbon content means mass% (hereinafter, the same).

According to the present invention, it is possible to improve the durability of the leg shaft of the tripod member while suppressing the increase in manufacturing cost.

It is a vertical cross-sectional view which shows the double roller type tripod type constant velocity universal joint. It is a vertical cross-sectional view taken along the line KK of FIG. It is a cross-sectional view taken along the line LL of FIG. It is a vertical cross-sectional view which shows the state which took the working angle of the tripod type constant velocity universal joint of FIG. It is a vertical sectional view which shows the hardened layer formed in the tripod member. It is a figure which shows the hardness distribution in the leg shaft of a conventional product. It is a figure which shows the hardness distribution in the leg axis of an improved product. It is a figure which shows the hardness distribution in the leg axis of an improved product. It is a figure which shows the hardness distribution with the leg axis of this embodiment. It is a cross-sectional view of a single roller type tripod type constant velocity universal joint. It is a vertical cross-sectional view of the tripod member seen by the arrow KK of FIG. It is a cross-sectional view taken along the line MM in FIG. 11A. It is a cross-sectional view taken along the line MM of FIG. 11A.

The first embodiment of the tripod type constant velocity universal joint according to the present invention will be described with reference to FIGS. 1 to 9.

The tripod type constant velocity universal joint 1 of the present embodiment shown in FIGS. 1 to 4 is a double roller type. Note that FIG. 1 is a vertical cross-sectional view showing a double roller type tripod type constant velocity universal joint, and FIG. 2 is a partial cross-sectional view taken along the line KK of FIG. FIG. 3 is a cross-sectional view taken along the line LL of FIG. 1, and FIG. 4 is a vertical cross-sectional view showing a tripod type constant velocity universal joint when an operating angle is taken.

As shown in FIGS. 1 and 2, the tripod type constant velocity universal joint 1 is mainly composed of an outer joint member 2, a tripod member 3 as an inner joint member, and a roller unit 4 as a torque transmission member. Has been done. The outer joint member 2 has a cup shape with one end open, and three linear track grooves 5 extending in the axial direction are formed on the inner peripheral surface at equal intervals in the circumferential direction. Each track groove 5 is arranged so as to face the outer joint member 2 in the circumferential direction, and a roller guide surface 6 extending in the axial direction of the outer joint member 2 is formed. A tripod member 3 and a roller unit 4 are housed inside the outer joint member 2.

The tripod member 3 integrally has a trunnion body portion 3a and three leg shafts 7 (trunnion journals) protruding in the radial direction from the circumferential trisecting position of the trunnion body portion 3a. The tripod member 3 has a torque with the shaft 9 by fitting a male spline 24 (see FIG. 1) formed on the shaft 9 as a shaft into a female spline 23 formed in the central hole 8 of the trunnion body 3a. Communicably combined. By engaging the retaining ring 10 mounted on the tip of the shaft 9 with the end surface of the tripod member 3, the tripod member 3 is fixed to the shaft 9 in the axial direction.

The roller unit 4 is located between the outer ring 11 which is a roller, the annular inner ring 12 which is arranged inside the outer ring 11 and is fitted on the leg shaft 7, and between the outer ring 11 and the inner ring 12. The main portion is composed of a large number of intervening needle-shaped rollers 13, and is housed in the track groove 5 of the outer joint member 2. The roller unit 4 including the inner ring 12, the needle roller 13, and the outer ring 11 has a structure that is not separated by the

washers

14 and 15.

In this embodiment, the outer peripheral surface of the outer ring 11 is a convex curved surface having an arc having a center of curvature on the axis of the leg axis 7 as a bus bar. The outer peripheral surface of the outer ring 11 is in angular contact with the roller guide surface 6.

The needle roller 13 has a cylindrical inner peripheral surface of the outer ring 11 as an outer raceway surface and a cylindrical outer peripheral surface of the inner ring 12 as an inner raceway surface, and can roll freely between these outer raceway surfaces and the inner raceway surface. Is placed in.

The outer peripheral surface of each leg shaft 7 of the tripod member 3 has a straight shape in a vertical cross section including the axis of the leg shaft 7. Further, as shown in FIG. 3, the outer peripheral surface of the leg shaft 7 has a substantially elliptical shape in a cross section orthogonal to the axis of the leg shaft 7. The outer peripheral surface of the leg shaft 7 comes into contact with the inner peripheral surface 12a of the inner ring 12 in the direction orthogonal to the axis of the joint, that is, in the direction of the long axis a. In the axial direction of the joint, that is, in the direction of the short axis b, a gap m is formed between the outer peripheral surface of the leg shaft 7 and the inner peripheral surface 12a of the inner ring 12.

The inner peripheral surface 12a of the inner ring 12 has a convex curved surface shape, specifically, a convex arc shape in a vertical cross section including the axis of the inner ring 12. In addition to this, the cross-sectional shape of the leg shaft 7 is substantially elliptical as described above, and a predetermined gap m is provided between the leg shaft 7 and the inner ring 12, so that the inner ring 12 has a leg shaft 7. It is possible to swing and swing. As described above, since the inner ring 12 and the outer ring 11 are assembled so as to be relatively rotatable via the needle roller 13, the outer ring 11 is integrated with the inner ring 12 and swings with respect to the leg shaft 7. It is movable. That is, the axes of the outer ring 11 and the inner ring 12 can be tilted with respect to the axis of the leg axis 7 in the plane including the axis of the leg axis 7 (see FIG. 4).

As shown in FIG. 4, when the tripod type constant velocity universal joint 1 rotates at an operating angle, the axis of the tripod member 3 tilts with respect to the axis of the outer joint member 2, but the roller unit 4 swings and swings. Since it is possible, it is possible to prevent the outer ring 11 and the roller guide surface 6 from being obliquely crossed. As a result, the outer ring 11 rolls horizontally with respect to the roller guide surface 6, so that induced thrust and slide resistance can be reduced, and low vibration of the joint can be realized.

Further, as already described, since the cross section of the leg shaft 7 is substantially elliptical and the cross section of the inner peripheral surface 12a of the inner ring 12 is an arcuate convex cross section, the leg shaft 7 on the torque load side The outer peripheral surface and the inner peripheral surface 12a of the inner ring 12 come into contact with each other in a narrow area close to point contact. Therefore, the force for tilting the roller unit 4 is reduced, and the stability of the posture of the outer ring 11 is improved.

The tripod member 3 described above is manufactured from a steel material through a main process of forging → machining (turning) → heat treatment → grinding of the outer peripheral surface of the leg shaft 7. The outer peripheral surface of the leg shaft 7 can be finished by quenching steel cutting instead of grinding.

FIG. 5 is a cross-sectional view showing a cured layer 16 formed by heat treatment of the tripod member 3. As shown in FIG. 5, the cured layer 16 is formed on the outer peripheral surface of the leg shaft 7 of the tripod member 3 and the entire surface including the female spline 23. Since the outer peripheral surface of the leg shaft 7 of the tripod member 3 as a finished product is finished by grinding (or quenching steel cutting), the depth of the hardened layer 16 on the outer peripheral surface of the leg shaft 7 is ground compared to other regions. It is shallow by the amount of the allowance due to such things. Since this allowance is usually as small as about 0.1 mm, the thickness of the cured layer 16 is drawn uniformly on the entire surface in FIG.

As described above, in the double roller type tripod type constant velocity universal joint, as shown in FIG. 3, the region where the outer peripheral surface of the leg shaft 7 and the inner peripheral surface 12a of the inner ring 12 are close to the point on the torque load side. Since the contact is made with M, there is a problem that the surface pressure of the contact portion becomes high when a high torque load is applied. If the surface pressure is excessive, the durability of the leg shaft 7 will be reduced.

In order to solve this problem, the present inventors conducted the following verification.

Generally, in the tripod member 3, a hardened layer 16 is formed on the surface of the tripod member 3 by forging a chrome molybdenum steel which is a kind of skin-baked steel as a material and then carburizing, quenching and tempering as a heat treatment. In FIG. 6, the material of the conventional tripod member 3 (for example, chrome molybdenum steel of JIS G4052, equivalent material having a carbon content of less than about 0.23%) is used, and the material is carburized, quenched and tempered (quenched temperature 860 ° C.). , The tempering temperature is 180 ° C.), and the hardness distribution from the surface of the leg shaft 7 to the core is shown. The broken line in FIG. 6 indicates an estimated value (the same applies to FIG. 7). In this case, as is clear from FIG. 6, the hardness of the surface exceeds 550 HV, but the hardness is lower than 550 HV in a region very shallow from the surface. Therefore, when an excessive torque is applied, the durability of the leg shaft 7 is affected. Therefore, in order to solve the above problems, it is necessary to form the cured layer 16 as deeply as possible.

Increasing the depth of the carburized layer is the easiest way to deepen the hardened layer 16, but as already mentioned, forming a deep carburized layer requires a huge amount of carburizing time and manufacturing cost. Invites a soaring price. It is conceivable to use a steel material having a high carbon content as a material, for example, carbon steel for mechanical structure such as S50C to S55C, and change the heat treatment method to high frequency quenching which can be hardened deeper than carburizing quenching. Since the material becomes harder as the amount of carbon increases, the processing load when forging the tripod member 3 increases, which causes a problem that the forging equipment becomes larger.

Based on the above considerations, the present inventors have verified the effectiveness of using a skin-baked steel having a higher carbon content than the conventional one, while keeping the carburizing treatment conditions and the quenching and tempering conditions as before. FIG. 7 shows the hardness distribution when carburizing, quenching and tempering are performed using a material equivalent to about 0.34% carbon content of chromium / molybdenum steel as a material. The quenching temperature is 850 ° C. and the tempering temperature is 180 ° C. The horizontal axis (depth from the surface) in FIG. 7 is shown at the same scale as in FIG. 6 (the same applies to FIGS. 8 and 9).

As is clear from the results of FIG. 7, it was found that the depth of the hardened layer 16 can be increased as intended by increasing the carbon content of the hardened steel. On the other hand, since the hardness of the core portion after carburizing, quenching and tempering reaches about 550 HV, the toughness of the leg shaft 7 may decrease, and the repeated fatigue strength of the tripod member 3 may decrease. Simply increasing the carbon content of the calcined steel in this way reduces the fatigue strength, which is not sufficient as a countermeasure. Using the same material, we also tried to perform sub-quenching and tempering (quenching temperature 870 ° C, tempering temperature 160 ° C) instead of carburizing and tempering, but as shown in FIG. 8, the hardness of the core was 550 HV. It became clear that the same problem would occur beyond that.

From the above verification results, it became clear that in order to solve the problem, it is not enough to change the material, and it is necessary to review the heat treatment method.

Generally, the tempering temperature at the time of tempering after quenching of steel material affects the hardness after tempering. For example, up to a tempering temperature of about 250 ° C., the hardness is maintained at the same level as when the tempering is left as it is without tempering, and the higher the tempering temperature, the lower the hardness after tempering. Therefore, it is considered that the hardness of the core portion of the leg shaft 7 can be lowered by raising the tempering temperature and performing tempering at a temperature of, for example, 350 ° C. to 450 ° C. (hereinafter referred to as “high temperature tempering”).

Based on the above considerations, a tripod member 3 made of a material equivalent to about 0.34% carbon content of chromium-molybdenum steel was tempered at a high temperature after carburizing and quenching (quenching temperature 860 ° C., tempering temperature 410 ° C.). It was found that the surface hardness was 545 HV and the core hardness was 425 HV. If nothing is done, the surface hardness is insufficient, and it is necessary to further increase the surface hardness.

Based on the above findings, the present inventor has come up with the idea of performing induction hardening after carburizing and tempering (high temperature tempering) in order to compensate for the insufficient surface hardness. That is, as the heat treatment of the tripod member 13, after carburizing and quenching, high-temperature tempering was performed, and then induction hardening and tempering were further performed. With induction hardening, the heating time is about several seconds, so the increase in cycle time can be minimized. Tempering is indispensable after induction hardening, but as described above, if tempering at 250 ° C. or lower (hereinafter referred to as "low temperature tempering"), the hardness hardly decreases. Therefore, it is possible to maintain the hardness after induction hardening regardless of the surface layer and the core portion.

FIG. 9 shows the hardness distribution of the leg shaft 7 of the tripod member 3 that has been heat-treated according to the procedure described above. The material of the tripod member 3 is the above-mentioned material equivalent to about 0.34% of carbon content. Further, the quenching temperature in carburizing quenching tempering is set to 860 ° C., the tempering temperature is set to 410 ° C., and the tempering temperature in induction hardening tempering is set to 190 ° C.

As is clear from this hardness distribution, the tripod member 3 of the present embodiment has a high hardness portion A formed on the surface of the leg shaft 7 and a medium hardness portion B formed on the core portion side of the high hardness portion A. , A boundary portion C formed on the core portion side of the medium hardness portion B, and a low hardness portion D formed on the core portion side of the boundary portion C, respectively.

The high hardness part A is a region hardened by carburizing and induction hardening, and has the highest carbon concentration among the parts A to D. Further, in the high hardness portion A, the carbon concentration gradually decreases from the surface side to the core portion side due to carburizing. Therefore, the hardness of the high hardness portion A is the highest among the respective portions A to D of the leg shaft 7, and gradually decreases from the surface side to the core portion side. The medium hardness portion B is a region hardened by induction hardening without adding carbon by carburizing, and its hardness is lower than that of the high hardness portion A and is a substantially constant value (about 600 HV). The high hardness portion A and the medium hardness portion B are martensitic hardened regions, and therefore, a hardened layer 16 having a Vickers hardness exceeding 550 HV is formed in both the high hardness portion A and the medium hardness portion B. In addition, "550HV" here corresponds to the limit depth in the effective hardening layer depth specified in JIS G0557. The Vickers hardness test force is 0.3 kg.

The low hardness portion D is a region that has not been hardened, that is, a region that has not been martensitic. The hardness of the low hardness portion D (core hardness) is lower than the hardness of the medium hardness portion B, and is a substantially constant hardness (about 300 HV) lower than 550 HV. The boundary portion C is located between the medium hardness portion B and the low hardness portion D, and forms a transition layer between the cured layer 16 and the uncured region. At the boundary portion C, the hardness gradually decreases from the surface side to the core portion side. The surface side of the boundary portion C has a hardness of more than 550 HV, and the core side has a hardness of less than 550 HV.

In this way, the hardness distribution shown in FIG. 9 can be obtained by performing high temperature tempering after carburizing and quenching, and then induction tempering (low temperature tempering). In this hardness distribution, the depth of the hardened layer 16 exceeding 550 HV reaches a depth of about 4 to 5 times that of the conventional product (see FIG. 6), while the depth of the low hardness portion D lower than 550 HV. The hardness is about the same as the conventional product or lower than the conventional product. Therefore, the durability of the leg shaft 7 can be ensured even when the contact region M (see FIG. 3) becomes a high surface pressure due to the load of excessive torque on the tripod type constant velocity universal joint. Further, since the core portion of the leg shaft 7 has high toughness, it is possible to avoid a decrease in the repeated fatigue strength of the tripod member 3.

In the above description, the case where a material equivalent to about 0.34% of carbon content is used as the material of the tripod member 3 is illustrated, but the types of materials that can be used are not limited. For example, in the case of chromium / molybdenum steel, SCM440 or the like can be used in addition to SCM435. Further, so-called H steel (for example, SCM435H, SCM440H, etc .: specified in JIS G4052) whose hardenability is guaranteed can also be used. As long as it is a skin-baked steel, other types of steel materials can be used, and for example, chrome steel (for example, SCr435, SCr440, etc.) specified in JIS G4053 can be used as a material. As for the chrome steel, for example, H steel such as SCr435H and SCr440H can be used. Not limited to hardened steel such as chrome molybdenum steel and chrome steel, carbon steel for machine structure (specified in JIS G4051) such as S10C to S35C can also be used as a material.

Considering the formability during cold forging, it is preferable to use a steel material having a carbon content of 0.44% or less, but when the formability during forging does not matter, for example, in the case of hot forging. , Steel materials containing more carbon can also be used. If the surface-baked steel has a carbon content of 1% or less, no particular problem occurs even during hot forging.

It is preferable to use a steel material containing 0.1% or more carbon as the lower limit of the carbon content, but from the viewpoint of increasing the hardness of the high hardness portion A and the medium hardness portion B as much as possible, the carbon content is 0.24% or more. More preferably, 0.32% or more of a steel material is used as the material of the tripod member 3. Normally, the carbon content of the low hardness portion D coincides with the carbon content contained in the material.

Next, a second embodiment of the present invention will be described.
As already described, when carburizing and quenching tempering (high temperature tempering) is performed using a material equivalent to about 0.34% of carbon content, when induction hardening tempering is omitted, the surface hardness of the leg shaft 7 is 545 HV. The core hardness is about 425 HV. From the comparison between this result and the hardness distribution of FIG. 9, it can be understood that the hardness of the core of the leg shaft 7 is lower in the case with induction hardening than in the case without induction hardening. This is because the core of the leg 7 is heated to about 400 ° C by heating during induction hardening and then air-cooled (slowly cooled) during subsequent tempering, thereby reducing the hardness (annealing) similar to that of high-temperature tempering. It is presumed that this was due to the fact that (ri) was obtained.

Focusing on this point, high-temperature tempering after carburizing and quenching is not always essential and can be omitted. For example, it is possible to obtain a hardness distribution similar to the hardness distribution shown in FIG. 9 by performing induction hardening without tempering after carburizing and quenching, and then performing low temperature tempering. Therefore, the durability of the leg shaft 7 against high surface pressure and the toughness of the leg shaft 7 can be compatible with each other. Except for the matters described above, the configuration and function of each part of the tripod type universal joint are common to those of the first embodiment.

Next, a third embodiment of the present invention will be described.
In the first embodiment and the second embodiment described above, induction hardening is performed after carburizing and quenching, but only carbon infiltration by carburizing is performed (quenching immediately after carburizing is omitted), and then induction hardening is performed. This also makes it possible to form the hardened layer 16. Specifically, carbon is impregnated into the surface of the tripod member 3 by a carburizing step, and then induction hardening and tempering (low temperature tempering) are performed after cooling such as air cooling. As a result, it is possible to obtain a hardness distribution similar to the hardness distribution shown in FIG. 9, and it is possible to achieve both the durability of the leg shaft 7 against high surface pressure and the toughness of the leg shaft 7. In this case, quenching and tempering immediately after carburizing are omitted, so that cost reduction can be achieved.

The ambient temperature when carburizing (carbon infiltration) is 500 ° C or higher. After carburizing, both the surface and core structures become ferrite + pearlite. After that, by induction hardening and tempering, martensite is formed on the surface, martensite is not formed on the core portion, and the ferrite + pearlite structure is maintained.

In this third embodiment, it is sufficient that the hardened layer 16 formed by induction hardening is formed at least on the outer peripheral surface of the leg shaft 7 and at the base of the leg shaft 7, as shown in FIG. 11A. Since the base of the leg shaft 7 is a region where tensile stress is concentrated when torque is transmitted to the tripod type constant velocity universal joint, the torsional strength of the tripod member 3 is increased by providing the hardened layer 17 at the base of the leg shaft 7. Can be secured.

The hardened layer 16 on the outer peripheral surface of the leg shaft 7 is provided to improve its durability. The hardened layer 16 on the outer peripheral surface of the leg shaft 7 is formed over the entire circumference as shown in FIG. 11B, and is limited to the contact portion with the inner peripheral surface 12a of the inner ring 12 as shown in FIG. May be formed.

Further, since the inner peripheral surface of the tripod member 3 is generally a region where the shaft 9 (see FIG. 1) and the spline or the like (including serrations) are fitted, as shown in FIG. 11A, the inner peripheral surface of the tripod member 3 (see FIG. 1). It is preferable to form a hardened layer 16 by quenching on the tooth surface of a spline or the like. The distribution of the cured layer 16 shown in FIGS. 11A, 11B, and 12 can also be adopted in the first embodiment and the second embodiment already described.

To give an example of the manufacturing process of the tripod member 3 of the third embodiment, a) bar material cutting process → b) spheroidizing blunting process → c) bonding process → d) cold forging process → e) turning process. Step → f) Brooch processing step → g) Carbon infiltration process → h) High frequency heat treatment (hardening, tempering) step → i) Grinding process. The steps a) to f) can also be applied to the first embodiment and the second embodiment. If there is no problem in forging property during cold forging due to circumstances such as using a material having a low carbon content, the spheroidizing annealing step can be omitted. Further, when a material having a low carbon content is used, the tempering sensitivity becomes low, so that the tempering process after induction hardening may be abolished.

Each embodiment of the present invention described above can also be applied to a double roller type tripod type constant velocity universal joint having another configuration.

For example, the outer peripheral surface of the leg shaft 7 can be formed into a convex curved surface (for example, a convex arc in cross section), and the inner peripheral surface 12a of the inner ring 12 can be formed into a cylindrical surface. Further, the outer peripheral surface of the leg shaft 7 can be formed into a convex curved surface (for example, a convex arc shape in cross section), and the inner peripheral surface 12a of the inner ring 12 can be formed into a concave spherical surface that fits with the outer peripheral surface of the leg shaft. At this time, the

washers

14 and 15 can be eliminated by providing brims at both ends of the inner diameter of the outer ring.

In the above description of the embodiment, the double roller type tripod type constant velocity universal joint is illustrated, but the hardness distribution shown in FIG. 9 can be similarly applied to the single roller type tripod type constant velocity universal joint. ..

FIG. 10 is a cross-sectional view of a single roller type tripod type constant velocity universal joint 100.
As shown in FIG. 10, the tripod type constant velocity universal joint 100 mainly includes an outer joint member 102, a tripod member 103 as an inner joint member, a roller 111 as a torque transmission member, and a needle roller 113 as a rolling element. The configuration is as follows. The outer joint member 102 has a hollow cup shape having three track grooves 105 extending in the axial direction at trisecting positions in the circumferential direction on the inner circumference thereof. A roller guide surface 106 is formed on the side walls of the track grooves 105 facing each other in the circumferential direction. The roller guide surface 106 is formed by a part of the cylindrical surface, that is, a partial cylindrical surface.

The tripod member 103 has three leg shafts 107 protruding radially from the trunnion body at three equal positions in the circumferential direction. The tripod member 103 is spline-fitted to the shaft so that torque can be transmitted. A roller 111 is rotatably mounted around the cylindrical outer peripheral surface of the leg shaft 107 via a plurality of needle-shaped rollers 113. The outer peripheral surface of the leg shaft 7 forms the inner raceway surface of the needle-shaped roller 113. The inner diameter surface of the roller 111 is cylindrical and forms the outer raceway surface of the needle roller 113.

A retaining ring 112 is mounted near the shaft end of the trunnion journal 9 via an outer washer 113. The needle-shaped roller 113 is restricted from moving in the axial direction of the leg shaft 107 by the inner washer 114 and the outer washer 113.

The roller 111 rotatably mounted on the leg shaft 7 of the tripod member 103 is rotatably guided to the roller guide surface 106 of the track groove 105 of the outer joint member 102. With such a structure, the relative axial displacement and angular displacement between the outer joint member 102 and the tripod member 103 are absorbed, and the rotation is transmitted at a constant velocity.

Even in the single roller type tripod type constant velocity universal joint 100 described above, since the outer peripheral surfaces of the needle roller 113 and the leg shaft 107 are in line contact, the contact portion between the two becomes high surface pressure when an excessive torque load is applied. It may cause the same problems as the double roller type. Therefore, also in this case, as already described, the high hardness portion A provided on the surface of the leg shaft 107 and the carbon content gradually decreases from the surface side to the core portion side, and the high hardness portion A. A low hardness portion B formed closer to the core portion and having a lower hardness than the high hardness portion A, and a low hardness portion D formed closer to the core portion than the medium hardness portion B and having a lower hardness than the medium hardness portion B. The same effect can be obtained by setting the hardness of the high hardness portion A and the medium hardness portion B to 550 HV or more and the hardness of the low hardness portion D to less than 550 HV.

The tripod type constant velocity

universal joints

1, 100 described above are not applied only to the drive shaft of an automobile, and can be widely used in a power transmission path of an automobile, an industrial device, or the like.

1,100 Tripod type constant velocity universal joint 2,102 Outer joint member 3,103 Tripod member 4 Roller unit 5,105 Track groove 6,106 Roller guide surface 7,107 Leg shaft 9 axes (shaft)
11 Roller (outer ring)
12 Inner ring 13,113 Needle roller 16 Hardened layer 111 Roller A High hardness part B Medium hardness part C Boundary part D Low hardness part

Claims

An outer joint member having three axially extending track grooves in the circumferential direction and each track groove having a pair of roller guide surfaces arranged so as to face each other in the circumferential direction, and three legs protruding in the radial direction. A tripod type having a tripod member provided with a shaft and a roller mounted on each leg shaft, and the roller is configured to be movable in the axial direction of the outer joint member along the roller guide surface. In fittings
The leg shaft has a high hardness portion formed on the surface of the leg shaft and the amount of carbon gradually decreases from the surface side to the core portion side, and a high hardness portion formed on the core portion side of the high hardness portion. A medium-hardness portion having a lower hardness than the medium-hardness portion and a low-hardness portion formed on the core portion side of the medium-hardness portion and having a lower hardness than the medium-hardness portion are provided.
A tripod type constant velocity universal joint characterized in that the hardness of the high hardness portion and the medium hardness portion is 550 HV or more, and the hardness of the low hardness portion is less than 550 HV.
An inner ring that is externally fitted to the leg shaft and rotatably supports the roller is provided, a roller unit is formed by the roller and the inner ring, and the roller unit can swing and swing with respect to the leg shaft. The tripod type constant velocity universal joint according to claim 1.
The outer peripheral surface of the leg shaft is straight in the vertical cross section and substantially elliptical in the cross section, the inner peripheral surface of the inner ring is formed by a convex curved surface, and the outer peripheral surface of the leg shaft is a joint. The tripod type constant velocity universal joint according to claim 2, which is in contact with the inner peripheral surface of the inner ring in a direction orthogonal to the axis and forms a gap with the inner peripheral surface of the inner ring in the axial direction of the joint. ..
The tripod type constant velocity universal joint according to any one of claims 1 to 3, wherein the carbon content in the low hardness portion is 0.1% or more.