WO2012032926A1

WO2012032926A1 - External joint member of constant velocity universal joint and friction pressure welding method therefor

Info

Publication number: WO2012032926A1
Application number: PCT/JP2011/068917
Authority: WO
Inventors: 吉田　和彦; 中川　亮; 不破　守康; 辰幸鈴木; 貴章柴田
Original assignee: Ntn株式会社
Priority date: 2010-09-08
Filing date: 2011-08-23
Publication date: 2012-03-15
Also published as: JP5718003B2; JP2012057696A

Abstract

Disclosed is an external joint member (11) for a constant velocity universal joint provided with a cup portion (12) comprising track grooves (30, 31) formed on the inner periphery of the cup portion so that torque transmission elements (19, 41) engage with the track grooves (30, 31), and a shaft (13) formed on the bottom portion of the cup portion (12), wherein the external joint member (11) is composed of two members which are a cup member (12') and a shaft member (13'), a solid short shaft (31) of the cup member (12') and the solid shaft member (13') are subjected to friction pressure welding, both the cup member (12') and the shaft member (13') are made of medium-carbon steel, at least the cup member (12') comprises the short shaft (31) subjected to a forging process to have a diameter smaller than the bottom portion of the cup portion, a recess (32) is provided on an end surface of the short shaft (31) to form an annular joint surface (34), a recess (33) is provided on one end surface of the shaft member (13') to form an annular joint surface (35), and both the annular joint surfaces (34, 35) are abutted and subjected to friction pressure welding.

Description

Outer joint member of constant velocity universal joint and friction welding method thereof

The present invention relates to an outer joint member of a constant velocity universal joint and a friction welding method thereof.

The constant velocity universal joint that constitutes the power transmission system of automobiles and various industrial machines connects the two shafts on the drive side and the driven side so that torque can be transmitted, and transmits rotational torque at a constant speed even if the two shafts have an operating angle. can do. Constant velocity universal joints are broadly classified into fixed constant velocity universal joints that allow only angular displacement and sliding constant velocity universal joints that allow both angular displacement and axial displacement. In the drive shaft that transmits power to the drive wheel, a sliding type constant velocity universal joint is used on the differential side (inboard side), and a fixed type constant velocity universal joint is used on the drive wheel side (outboard side). The

Regardless of sliding type or fixed type, the constant velocity universal joint is composed of a cup part in which a track groove that engages a torque transmitting element is formed on the inner peripheral surface, and an axial direction from the bottom part of this cup part. And an outer joint member having an extended shaft portion. In many cases, the outer joint member integrally forms the cup portion and the shaft portion by subjecting a solid bar-shaped material to cold plastic working such as forging and ironing, and machining such as cutting and grinding. .

Incidentally, as the outer joint member, a member having a long shaft portion (long stem) may be used. In order to make the lengths of the left and right drive shafts equal, the inboard side outer joint member of the drive shaft on one side is made a long stem, and this long stem is rotatably supported by a rolling bearing. The length of the long stem portion varies depending on the vehicle type, but is approximately 300 to 400 mm. In this outer joint member, since the shaft portion is long, it is difficult to integrally form the cup portion and the shaft portion with high accuracy. For this reason, a cup member that forms the cup portion and a shaft member that forms the shaft portion are constituted by two members, and both members are joined by friction welding. As a joint member joined by such friction welding, for example, a solid stem type is described in Patent Document 1, and a hollow stem part is described in Patent Document 2.

JP-A-61-132284 JP 2006-64060 A

The material described in Patent Document 1 is made of a steel based on carbon steel and having at least 0.2 to 0.8 mass% of Cr as an element for improving hardenability, as a joining shaft used for a drive shaft or the like. As described above, after the shafts are joined by friction welding, the joint is locally reheated and quenched by high frequency, and the bainite-like abnormal structure formed in the joint is extinguished by reheating and quenching. And, by hardening after quenching to the center of the joint by cooling after reheating, the strength of the joint is improved, and the strength of the joint is given as a higher strength than other parts. . Cr is added in an amount greater than that of carbon steel to further increase the depth of reheating and quenching. However, since a special material to which Cr is added is used, there are problems such as an increase in material cost, difficulty in obtaining the material, and a decrease in workability.

The outer joint member of a long stem type constant velocity universal joint described in Patent Document 2 is subjected to heat treatment after joining a member forming a cup part and a pipe-shaped part forming a shaft part. By forming splines (including serrations, the same applies hereinafter) on the outer peripheral surface at one axial end of the parts forming the shaft part, the cost is reduced by reducing the number of parts and the number of joints. Furthermore, by increasing the diameter of only the joint, the strength of the joint is increased, and the strength can be improved by applying heat treatment to almost the entire area in the axial direction of the component forming the shaft. For this reason, a shaft part can be made thin and weight reduction can be achieved. However, since the entire length of the long shaft portion is hollowed out, there are problems such as a significant increase in material cost and an increase in manufacturing cost.

The present inventors diligently studied as described later in order to investigate an important problem for industrial production of an outer joint member of a constant velocity universal joint having a solid long stem portion.

Usually, inclusions and segregation exist in steel materials, and the cleanliness decreases as the inclusions and segregation become the center of the steel material. That is, inclusions increase and segregation increases as the center of the steel material increases. On the other hand, the cleanliness of the outer peripheral portion is improved. Here, the inclusions inevitably refer to substances other than iron contained in the steel, for example, sulfides, oxides, etc. during steelmaking, the cleanliness refers to the number of inclusions, and the segregation degree refers to the additive element. An index of homogeneity. The same applies hereinafter. The steel material is cut to a predetermined length to form a long shaft member that forms a solid long stem portion. In this long shaft member, inclusions increase and segregation increases as it becomes the center as described above, and on the contrary, the cleanliness of the outer peripheral portion is improved.

On the other hand, the cup member forming the cup portion is forged from a billet obtained by cutting a steel material. Inclusions at the bottom of the cup side of the forged outer joint member are reduced in diameter by forging, so the number of inclusions per area increases, and the center of segregation is further concentrated. For this reason, when joining the solid member diameter-reduced by the forge process etc., this inclusion may intervene many on a joining surface. Further, when a part with a large amount of segregation intervenes in the joint surface, a hard structure of martensite or bainite may be locally scattered in the joint after joining. Thus, when a hard structure of martensite is present in the joint, the joint may become brittle or cracked. This embrittlement or crack is unlikely to occur if the carbon content of the members to be joined is low. The cause is that when air-cooled to a room temperature from a heating state of about 900 to 1100 ° C. at the time of bonding, it is locally quenched by the influence of segregation, and martensite and bainite are generated. However, since chromium steel (SCr) and chromium-molybdenum steel (SCM), which are often used for carburizing and quenching, have a low carbon content, the hardness difference between the base metal and the martensite and bainite is low. The local internal strain is small and the adverse effect on the joint is small.On the other hand, when the carbon content increases, the hardness of martensite and bainite generated by air quenching increases, and the difference in hardness from the base metal increases. This is considered to be because local internal strain increases and adverse effects on the joints increase.

Many of the outer joint members having a long stem portion are forged on the cup side and subjected to joining through machining. In the forging process, the billet obtained by cutting the steel material is heated and then forged. Specifically, the diameter of the cup portion is increased from the billet by forging, and the bottom portion of the cup portion that becomes the joint portion is reduced in diameter to a predetermined diameter. Thereafter, the cup part is finished by cold plastic working. The steel material contains inclusions and segregation. In addition, the inclusions and segregation at the bottom of the cup are reduced in diameter by forging, so that inclusions and segregation per area increase. In addition, as described above, there are forms in which inclusions and segregation increase as they become the center, and conversely, inclusions and segregation decrease as they reach the outer periphery. As a result of intensive studies, when joining solid members that have been reduced in diameter by forging, if this inclusion or segregated concentrated part intervenes in the joint surface, the probability that joint strength will decrease or crack will increase. I found. This problem does not occur in all of the outer joint members joined with solid members that have been reduced in diameter by forging, but occurs with a certain probability when mass-produced. Conventionally, after joining, 100% non-destructive inspection And a complicated process for inspecting the soundness of the joint portion is required. However, when considering the number of automobiles produced, such a problem is not acceptable and is a very important problem in industry.

The present invention has been proposed in view of the above-mentioned problems, and the object of the present invention is to prevent brittleness and cracking of a solid member of a forged constant velocity universal joint, and to stabilize the invention. An object of the present invention is to provide an outer joint member suitable for a solid long stem type constant velocity universal joint capable of reducing cost in quality.

As a result of various studies to achieve the above object, the present inventors have focused on the inclusions and segregation in the cross section of the solid portion reduced in diameter by forging, etc., and the cleanliness has deteriorated. A new idea has been reached in which the vicinity of the center is removed in advance before the joining process, and only the outer peripheral portion having a high cleanness is limited and joined.

As a technical means for achieving the above-mentioned object, the present invention comprises a cup part formed on the inner periphery with a track groove engaged with a torque transmitting element, and a shaft part formed on the bottom part of the cup part. An outer joint member of a constant velocity universal joint, the outer joint member comprising two members, a cup member forming the cup portion and a shaft member forming the shaft portion, and a solid short axis of the cup member The cup member and the shaft member are both made of medium carbon steel, and at least the cup member is forged and reduced in diameter from the bottom of the cup portion. An annular joint surface is formed by providing a shaft portion and providing a recess on the end surface of the short shaft portion, and forming an annular joint surface by providing a recess on one end surface of the shaft member. The friction welding was done The one in which the features. Thereby, it becomes possible to prevent embrittlement and cracking of the joint. In addition, since the area of the joint surface is reduced, the heating time can be greatly shortened, and at the same time, the pressurizing force and electric power are reduced, so that processing with a small capacity facility is possible and the cost is reduced.

The medium carbon steel, which is a material for the cup member and shaft member, has a carbon content of 0.43 mass% or more and 0.66 mass% or less. If the amount of carbon is less than 0.43 mass%, the required strength and durability cannot be obtained, which is undesirable. On the other hand, if the amount of carbon exceeds 0.66 mass%, forgeability and machinability are deteriorated, and the hardness is remarkably increased by air quenching after joining. Preferably, it is 0.45 mass% or more and 0.58 mass% or less.

The medium carbon steel, which is the material of the cup member and shaft member, has its carbon content varied between the two members. Productivity can be improved by making the amount of carbon in the cup and shaft differ.

The vertical section of the recess was curved and had no step. In the heat affected zone of the joint, the thickness is the smallest and the thickness increases toward the center of the recess, and suddenly enters the inner surface of the recess of the base metal part from the boundary between the heat affected zone and the base metal part that is air-quenched. By having a smooth shape without any level difference, it becomes possible to prevent the inclusions and the segregation-enriched portion from flowing into the joint, thereby preventing the joint from becoming brittle and the joint from being cracked. Furthermore, the cycle time of the joining work can be greatly shortened, the productivity can be improved, and the quality can be stabilized and the cost can be reduced.

By forming the recess at the same time as forging of the cup member, the coaxiality with the cup part is improved, the deflection of the joint part is reduced, the bending after joining and the machining allowance can be reduced, and the cup part is cooled. By being finished by interplastic processing, the cost can be further reduced with high accuracy.

¡The tip of the burr produced by friction welding is not in contact with the inner surface of the recess. Although the burr tip is hardened, it is not in contact with the inner surface of the recess, so that wear and stress concentration due to the burr tip does not occur on the inner surface of the recess, and embrittlement can be prevented.

The diameter for removing burrs generated by friction welding on the short shaft portion of the cup member and the outer diameter surface of the shaft member was made larger than the outer diameter of the adjacent portion. Thereby, the outer diameter before joining can be made smaller, which is effective for cost reduction.

The outer peripheral surface of the joint surface is machined, and at least the inside of the cup portion and the shaft portion are locally hardened. Moreover, surface hardening is induction hardening. Thereby, it is possible to obtain higher strength.

¡By grinding the induction-quenched surface of the shaft, it is possible to impart compressive residual stress and further improve fatigue strength. The compressive residual stress is desirably −200 MPa to −400 MPa.

By applying the outer joint member of the present invention to a solid long stem type constant velocity universal joint, it becomes possible to prevent embrittlement and cracking of the joint. In addition, since the area of the joint surface is reduced, the heating time can be greatly shortened, and at the same time, the pressurizing force and electric power are reduced, so that processing with a small capacity facility is possible and the cost is reduced.

It is a figure which shows the whole structure of the drive shaft which uses the outer joint member of the constant velocity universal joint of the 1st Embodiment of this invention. It is the fragmentary longitudinal cross-sectional view which expanded the outer joint member of 1st Embodiment. It is a cross-sectional view of the cup portion of the outer joint member. It is a fragmentary longitudinal cross-section which shows the structure of the outer joint member before joining. It is a longitudinal cross-sectional view which shows the formation state of the burr | flash of a junction part. It is a longitudinal cross-sectional view which shows the heat influence state of a junction part. It is a longitudinal cross-sectional view which shows the shape of the cup member before joining. It is a longitudinal cross-sectional view which shows the measurement position of a recessed part. It is a graph which shows the measurement result of the amount of sulfur (S) in the measurement position of a crevice. It is a graph which shows the measurement result of the segregation degree of carbon (C) in the measurement position of a crevice. It is a longitudinal cross-sectional view which shows the completion state of an outer joint member. It is a longitudinal cross-sectional view which shows the modification of the recessed part of a junction part. It is a longitudinal cross-sectional view which shows the modification of the removal shape of the burr | flash part of a junction part. It is a longitudinal cross-sectional view which shows the knowledge investigated in the process leading to this invention. It is a longitudinal cross-sectional view which shows the knowledge investigated in the process leading to this invention. It is a fragmentary longitudinal cross-section which shows the 2nd Embodiment of this invention. It is the fragmentary longitudinal cross-sectional view which expanded the outer joint member of 2nd Embodiment.

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

FIG. 1 to FIG. 10 show a first embodiment of the present invention. FIG. 1 is a diagram showing an overall structure of a drive shaft 1 in which an outer joint member 11 of a constant velocity universal joint 10 of the present embodiment is used. The drive shaft 1 includes a sliding type constant velocity universal joint 10 disposed on the differential side (right side in the figure: hereinafter also referred to as inboard side) and a drive wheel side (left side in the figure: hereinafter also referred to as outboard side). The fixed type constant velocity universal joint 20 and the intermediate shaft 2 that couples the two constant velocity

universal joints

10 and 20 so as to transmit torque are the main components.

A sliding type constant velocity universal joint 10 shown in FIG. 1 is a so-called tripod type constant velocity universal joint (TJ), and a long shaft portion (long stem portion) extending in the axial direction from the bottom of the cup portion 12 and the cup portion 12. ) 13, the inner joint member 16 accommodated in the inner periphery of the cup portion 12 of the outer joint member 11, and torque transmission disposed between the outer joint member 11 and the inner joint member 16. And a roller 19 as an element. The inner joint member 16 is composed of a tripod member 17 in which three leg shafts 18 on which rollers 19 are rotatably fitted are provided at equal intervals in the circumferential direction.

The inner ring of the support bearing 6 is fixed to the outer peripheral surface of the long shaft portion 13, and the outer ring of the support bearing 6 is fixed to the engine via a bracket (not shown). The outer joint member 11 is rotatably supported by the support bearing 6, and by providing such a support bearing 6, the outer joint member 11 is prevented from swinging during operation or the like as much as possible.

A fixed type constant velocity universal joint 20 shown in FIG. 1 is a so-called Rzeppa type constant velocity universal joint, and has an outer side having a bottomed cylindrical cup portion 21a and a shaft portion 21b extending in the axial direction from the bottom portion of the cup portion 21a. As a torque transmission element disposed between the joint member 21, the inner joint member 22 accommodated in the inner periphery of the cup portion 21 a of the outer joint member 21, and the cup portion 21 a and the inner joint member 22 of the outer joint member 21. And a cage 24 that is disposed between the inner peripheral surface of the cup portion 21a of the outer joint member 21 and the outer peripheral surface of the inner joint member 22 and holds the balls 23 at equal intervals in the circumferential direction. An undercut-free type constant velocity universal joint may be used as the fixed type constant velocity universal joint 20.

The intermediate shaft 2 has torque transmission splines (including serrations; the same applies hereinafter) 3 and 3 at the outer diameters at both ends. The intermediate shaft 2 and the tripod member 17 of the sliding constant velocity universal joint 10 are connected by spline fitting the spline 3 on the inboard side with the hole of the tripod member 17 of the sliding constant velocity universal joint 10. Connected to transmit torque. Further, the spline 3 on the outboard side is spline-fitted with the hole of the inner joint member 22 of the fixed type constant velocity universal joint 20, so that the intermediate shaft 2 and the inner joint member 22 of the fixed type constant velocity universal joint 20 are connected. Connected to transmit torque. As the intermediate shaft 2, a solid type is shown, but a hollow type can also be used.

In the constant velocity

universal joints

10 and 20, grease as a lubricant is sealed. In order to prevent external leakage of grease and entry of foreign matter from the outside of the joint, the outer joint member 21 between the outer joint member 11 of the sliding type constant velocity universal joint 10 and the intermediate shaft 2 and the fixed type constant velocity universal joint 20 is used. Between the intermediate shaft 2 and the intermediate boot 2,

cylindrical boots

4 and 5 are mounted, respectively.

Next, the structure of the outer joint member 11 of the sliding type constant velocity universal joint 10 having the long shaft portion 13 will be described. 2 is an enlarged view of the outer joint member 11, FIG. 2 (a) is a partial longitudinal sectional view, and FIG. 2 (b) is a transverse sectional view of the cup portion. As shown in FIG. 2, the outer joint member 11 is open at one end, and has a bottom with a track groove 30 on which the roller 19 (see FIG. 1) rolls at a circumferentially equally divided position on the inner peripheral surface. A cylindrical cup portion 12 and a length that extends in the axial direction from the bottom of the cup portion 12 and is provided with a spline Sp as a torque transmission connecting portion on the outer diameter of the end opposite to the cup portion 12 (inboard side) It consists of a dimension shaft part 13. The cup portion 12 and the long shaft portion 13 of the outer joint member 11 are joined at a position indicated by a broken line A.

FIG. 3 shows a state before the cup portion 12 and the long shaft portion 13 of the outer joint member 11 are joined, and the cup member 12 ′ that forms the cup portion 12 and the long shaft member 13 that forms the long shaft portion 13. It consists of two members. A concave portion 32 having a curved longitudinal section is provided at the joint portion of the short shaft portion 31 of the cup member 12 ′. Similarly, a concave portion 33 having a curved longitudinal section is provided at the joint portion of the long shaft member 13 '. Therefore, the joint surface 34 of the cup portion 12 ′ and the joint surface 35 of the long shaft member 13 ′ are both formed as an annular joint surface located on the outer diameter side. Details of the

joint surfaces

34 and 35 and the

recesses

32 and 33 will be described later.

3 is forged, and then the outer peripheral surface of the short shaft portion 31 and the recess 32 are machined. In the forging process, the billet obtained by cutting the steel material is heated and then forged. Specifically, the diameter of the cup portion 12 is increased from the billet by forging, and the short shaft portion 31 at the bottom of the cup portion that becomes the joint portion is reduced in diameter to a predetermined diameter. Thereafter, the cup member 12 'is finished by cold plastic working. However, the inclusions and segregation originally contained in the steel material increase as the center, and conversely, the inclusions and segregation tend to decrease as the outer periphery becomes, but in addition to this, forging as described above In the cup member 12 ′ manufactured by processing, it was found that inclusions and segregation per area increase particularly in the short shaft portion 31 reduced in diameter by forging.

The surface roughness of the

recesses

32 and 33 is related to productivity and torsional fatigue strength. The surface roughness of the

recesses

32 and 33 is preferably Ra5 or more and Ra25 or less. When it becomes Ra5 or less, productivity decreases, and when it becomes Ra25 or more, the torsional fatigue strength of the joint portion decreases. Preferably, Ra12 to Ra20 are set from the relationship between processing time and strength.

The recess 32 can be formed by forging simultaneously with the cup member 12 '. As a result, the coaxiality with the cup portion is improved, vibration during joining is reduced, bending after joining and machining allowance can be reduced, and cost can be further reduced.

As the friction welding method, the joining surface 34 of the cup member 12 'and the joining surface 35 of the long shaft member 13' shown in FIG. The joining end portion of the long shaft member 13 'is softened and at the same time a pressure is applied in the axial direction. As a result, as shown in FIG. 4, the burr | flash part 36 discharged | emitted by the plastic flow from the joining surface A in order to take out a new surface is formed in an outer peripheral side and an inner peripheral side.

Fig. 5 shows the heat-affected state of the joint. This figure shows the short shaft part 31 side of the cup member 12 ′ from the joint surface A. The joining portion includes a joining surface A, a heat-affected portion B around the joining surface A, a base material C adjacent to the joining surface A, and a burr portion 36 discharged by plastic flow from the joining surface A to obtain a new surface. The tip of the burr 36 is acute and hardened because the cooling rate after joining is fast. The longitudinal section of the inner surface of the recess 32 has a curved shape so that the thickness of the short shaft portion 31 is minimum in the heat-affected zone B of the joint and increases toward the center of the recess 32. The heat-affected zone B of the joint is air quenched.

FIG. 6 shows the short shaft portion 31 of the cup member 12 ′ before joining. A concave portion 32 is provided on the end surface 34 of the short shaft portion 31. A surrogate portion G is formed in a cylindrical shape on the end face 34 side of the recess 32. The surrogate portion G is a portion that plastically flows to produce a new surface in friction welding. The concave portion 32 is formed in a curved shape whose longitudinal section is smoothly connected to the cylindrical surrogate portion G. The recess 32 is provided in order to remove the vicinity of the center where the cleanliness has deteriorated in advance before the joining process, and has a shape that improves the cleanliness as the cleanliness of the inner surface of the recess 32 approaches the joint from the center. This makes it possible to prevent the inclusions and segregation-enriched parts from flowing into the joints, prevent brittleness of the joints and cracking of the joints, and greatly reduce the cycle time of the joining work. Productivity can be improved, and quality stability and cost reduction can be achieved.

The factor that determines the shape of the concave portion 32 is that when torsional stress mainly acts, it is desirable to increase the inner diameter from the viewpoint of improving the cleanliness of the steel material and improving the productivity of the joining process. From the viewpoint of improving the productivity of machining, it is desirable to reduce the inner diameter. The torsion of the hollow cylindrical cross section increases in the material dynamics toward the outer diameter with no stress at the center, and the maximum torsional stress acts on the outer diameter. This maximum torsional stress (τmax) is obtained by τmax = 16TD / π (D ⁴ -d ⁴ ). Here, T is the torque, D is the outer diameter, and d is the inner diameter. For example, when the shape of the hollow cylinder is an inner diameter that is ½ of the outer diameter, the maximum torsional stress of the cross section of the hollow cylinder is only increased by 6.7% of the maximum solid torsional stress having the same outer diameter. Thus, when torsion acts, the strength reduction due to hollowing out the solid is extremely small.

Furthermore, the thermal history and material characteristics of the joint were investigated, and a shape that did not decrease in strength even when the inner diameter was increased was found. Torsional strength increases with increasing hardness. Since the heat-affected zone B is hollow, the cooling rate at the time of joining is increased and the hardness is increased relatively uniformly in the cross-section compared to the solid state. Therefore, the torsional strength of the heat-affected zone B is Compared with high allowable shear stress. Further, the base material portion has a lower hardness than the heat affected zone B, and therefore the torsional strength is lower than that of the heat affected zone B. In order to make use of this material characteristic, it has been found that the thickness of the base material portion is thick and the thickness of the heat-affected zone B is reduced. Therefore, the outer joint member 11 of the present embodiment also has sufficient torsional strength from the viewpoint of acting stress.

FIG. 10 shows a longitudinal section of the outer joint member 11 in a completed state. After joining the cup member 12 ′ and the long shaft member 13 ′ (see FIG. 3), the outer peripheral surfaces of the cup portion 12, the short shaft portion 31, and the long shaft portion 13 of the outer joint member 11 are turned. Thereafter, the spline SP at the end of the long shaft portion 31 is rolled. Thereafter, the inside of the cup portion 12 and the outer peripheral surface of the long shaft portion 31 are locally hardened by induction hardening. The surface-hardened part is shown by cross-hatching. After induction hardening, the joint portion (short shaft portion 31 and the end portion of the long shaft portion joined thereto) is ground to impart compressive residual stress, and the fatigue strength is further improved. The compressive residual stress generated by surface quenching decreases as the hardening ratio (quenched depth / thickness) increases. Therefore, compressive residual stress can be imparted by grinding to improve torsional fatigue strength. This compressive residual stress is about -200 MPa to -400 MPa. In FIG. 10, the entire length of the outer peripheral surface of the long shaft portion 31 in the axial direction is shown by induction hardening, but there is also a portion in which the long shaft portion 31 is partially induction hardened in the axial direction.

Next, the knowledge investigated in the process leading to the present invention will be described based on FIG. 13 and FIG. FIG. 13 shows that the tip of the burr 36 is in contact with the inner surface of the recess 32 after joining. The tip of the burr 36 is acute and has a fast cooling rate and is easy to harden when bonded. Therefore, it has been found that when a load is applied in a state where the tip of the burr 36 is in contact with the inner surface of the recess 32, the inner surface of the recess 32 is abraded, causing stress concentration in the portion, which may reduce the strength. .

The knowledge of the shape surface of the recess 32 is shown in FIG. In FIG. 14, steps 37 and 38 are formed on the inner surfaces of the

recesses

32 and 33. It has been found that if there are

abrupt steps

37 and 38 on the inner surface near the boundary C between the heat-affected zone B and the base metal, which are quenched by air, the sites cause stress concentration and the strength decreases. In order to prevent this, in the present embodiment, the inner surfaces of the

recesses

32 and 33 are formed in a smooth curved shape whose vertical cross section has no step.

FIG. 11 shows a modification of the concave portion of the joint portion of the present embodiment. In order to prevent the tip of the burr 36 from coming into contact with the inner surfaces of the recesses 32 and 33 (33 is not shown), the

recesses

32 and 33 are formed in a pan shape, and the tip of the burr 36 is curled. It is what I did. In this modification, the tip of the burr 36 is curled, so that the tip of the burr 36 does not contact the inner surfaces of the

recesses

32 and 33. Therefore, the cause of stress concentration due to wear on the inner surfaces of the

recesses

32 and 33 is avoided, and the strength does not decrease.

Next, a modified example of the burr removal shape on the outer peripheral surface of the joint according to this embodiment will be described. When the outer burr 36 is removed after the joining, the diameter φF for removing the burr 36 is locally increased by the radial difference δ from the outer diameter φD of the adjacent portion (the axial portion generated by the burr 36). ing. Thereby, the outer diameter of the short shaft portion 31 of the cup member 12 ′ before joining and the outer diameter of the long shaft member 13 ′ (see FIG. 3) can be further reduced, which is effective in reducing the cost.

A second embodiment of the present invention will be described with reference to FIGS. This embodiment is applied to the outer joint member of a double offset type constant velocity universal joint (DOJ), and shows only the constant velocity universal joint on the inboard side of FIG. In the present embodiment, with respect to the outer joint member, portions having the same functions as those of the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

The sliding type constant velocity universal joint 10 includes an outer joint member 11 having a cup portion 12 and a long shaft portion 13 extending in the axial direction from the bottom portion of the cup portion 12, and an inner periphery of the cup portion 12 of the outer joint member 11. The inner joint member 16 accommodated in the inner joint member 16, the ball 41 as a torque transmitting element disposed between the outer joint member 11 and the

track grooves

30, 40 of the inner joint member 16, and the cylindrical inner periphery of the outer joint member 11. The surface 42 and the spherical outer peripheral surface 43 of the inner joint member 16 are each provided with a spherical outer peripheral surface 45 and a spherical inner peripheral surface 46 that fit together, and a cage 44 that holds the ball 41. The center of curvature O ₁ of the spherical outer peripheral surface 45 of the cage 44 and the center of curvature O ₂ of the spherical inner peripheral surface 46 are offset to the opposite side in the axial direction with respect to the joint center O.

As in the first embodiment, the inner ring of the support bearing 6 is fixed to the outer peripheral surface of the long shaft portion 13, and the outer ring of the support bearing 6 is fixed to the engine via a bracket (not shown). The outer joint member 11 is rotatably supported by the support bearing 6, and the outer joint member 11 is prevented from swinging as much as possible during operation.

FIG. 16 shows an enlarged partial longitudinal section of the outer joint member 11. As shown in the figure, the outer joint member 11 has a bottomed cylindrical shape in which one end is open and six or eight track grooves 30 in which balls 41 (see FIG. 15) are arranged on the inner peripheral surface 42 are formed. Cup portion 12 and a long shaft extending in the axial direction from the bottom of the cup portion 12 and provided with a spline Sp as a torque transmission connecting portion on the outer diameter of the end opposite to the cup portion 12 (inboard side) Part 13. Similarly to the first embodiment, the cup portion 12 and the long shaft portion 13 of the outer joint member 11 are joined at the position of the broken line A.

Since the contents described above based on FIGS. 3 to 14 in the first embodiment are the same in the present embodiment, duplicate description is omitted.

Examples of the present invention will be described below. In the outer joint member 11 of the constant velocity universal joint 10 of the present invention, the cup member 12 'includes the recess 32 after forging and is subjected to joining after machining. In this example, the billet obtained by cutting the steel material of S53C was heated to 780 ° C. and forged. The chemical components of S53C used were C: 0.52 mass%, Si: 0.25 mass%, Mn: 0.88 mass%, P: 0.008 mass%, S: 0.035 mass%, Cu: 0.01 mass%, Ni: 0.02 mass%, Cr: 0.17 mass%, and the diameter of the steel material was φ75.

The diameter of the short shaft portion 31 (see FIG. 3) at the bottom of the cup member 12 ′ was reduced to φ44 by forging. After forging, the recess 32 was machined to a diameter of φ26 along with finishing the joint surface. FIG. 8 and FIG. 9 show the measurement results of the sulfur (S) amount of the recess 32 and the segregation degree of carbon (C) (C / C ₀ C ₀ : carbon amount of the surface layer portion, C: carbon amount at an arbitrary site). . 8 and 9, the horizontal axis represents the inner surface of the recess 32 with a line X from the end surface 34 side, as shown in FIG. The amount of sulfur (S) and the segregation degree (C / C ₀ ) of carbon (C) are both low in the cylindrical portion H, and then increase and reach the center through the flat portion I and reach the maximum value. Yes. The cup member 12 ′ may be forged after machining the raw material as it is rolled and removing the decarburized layer or scratches. Alternatively, the surface may be cut at the material stage.

The material of the shaft member 13 ′ has a diameter φ44 of the surface texture as it is rolled, and the chemical components of S45C used are C: 0.44 mass%, Si: 0.23 mass%, Mn: 0.85 mass%, P: 0.010 mass%, S: 0.035 mass%, Cu: 0.01 mass%, Ni: 0.02 mass%, Cr: 0.15 mass%, and using this, the same as the cup part 32 ′ after cutting Machining was performed.

Thereafter, friction welding is performed. This friction welding method will be described next. The cup member 12 ′ and the long shaft member 13 ′ were joined by a friction welding apparatus. The pressure welding process includes a bonded portion cleaning process, which is a preliminary process of the pressure welding process, a new surface generation step of the bonded portion by a friction welding apparatus, a new surface bonding step, an outer peripheral burr removal step, and a bonding surface cooling step. Here, in the new surface generation step, the long shaft member 13 ′ is fixed, and the cup surface 12 ′ is rotated and pressed against the long shaft member 13 ′ (friction pressure) while being rubbed against each other. Are heated (softened at the same time), the pressing load is gradually increased, and oxides and dirt on the joint surface are removed as burrs from the joint surface (generation of a new surface). After the joining surface reaches about 1200 ° C., the pressing load (pressure contact pressure) is further increased to stop the rotation rapidly, and the relative position between the cup member 12 ′ and the long shaft member 13 ′ is brought closer (shift margin). The new surface formed by the intermolecular attractive force acting on the bonding surface is bonded. Note that the height of the burr increases with the increase in the margin. Note that removal of burrs may be performed in a separate process. The dimensions of this example product are an outer diameter of φ44 and an inner diameter of φ26, and the joining conditions conform to Japanese Industrial Standard JIS Z 3607 (carbon steel friction welding work standard), friction pressure 3 kg / cm ² , pressure welding pressure 8 kg / cm ^2. All of the margins of 10 mm were joined at a rotational speed of 1600 rpm.

Comparing the working time between the friction welding of a solid product with the same outer diameter and the friction welding of this example product, this example product can reduce time by 50% compared to the solid product. .

After friction welding, the joint was divided vertically in the axial section, and as a result of investigating the hardness at a depth of 1 mm from the surface of the recess cross section, the hardness of the base metal part on the cup part 12 side was 198 to 205 Hv, and the heat effect The part was measured on a line extending in the axial direction of the cylindrical part of the concave part 32 and had a hardness of 400 to 500 Hv. Precipitation of martensite and bainite was observed although it was very small locally, mainly the structure of ferrite and pearlite. On the other hand, the long shaft portion 13 side of S45C had a reduced hardness of 50 to 70 Hv compared to the cup portion 12 side. The texture was mainly ferrite and pearlite.

As shown in FIG. 10, after finishing the intermediate product of the outer joint member integrated after joining by machining, the inner periphery of the cup portion 12 and the outer periphery of the long shaft portion 13 were induction-hardened. Although the quenching depth differs depending on the part, the solid portion is 3 to 5 mm in effective curing depth. Further, the hardening ratio (effective hardening depth / wall thickness) was set to 0.35 at the thinnest part of the joint. The surface hardness was 705 Hv on the cup part 12 side of S53C and 660 Hv on the long shaft part 13 side of S45C. Since dissimilar materials are joined, the hardenability is different on the left and right with the joining surface as a boundary, so the hardening depth may be discontinuous at the joining surface. On the long shaft portion 13 side of S45C, since the hardenability is lower than that of S53C, the quenching depth may be shallower than the cup portion 12 side of S53C.

Since the support bearing 6 may be press-fitted into the joint, it is ground as a finishing process after induction hardening. By using a grinding oil at the time of grinding and suppressing processing heat generation on the grinding surface, compressive residual stress after grinding can be applied. The lower the flash temperature of the surface due to heat generated by processing, the better. However, when the temperature becomes about 700 ° C. or higher, the surface is quenched and a white layer which is an undesirable structure is generated.

As the shape of the recess 32, the shapes of FIGS. As a result of comparing the torsional fatigue strength of the prototype shown in FIG. 14 and the prototype of FIG. 14 having a step, the fatigue strength of the prototype having a step decreased by about 10% after 5 × 10 ⁵ times.

Although the case where the present invention is applied to the tripod type constant velocity universal joint and the double offset type constant velocity universal joint as the sliding type constant velocity universal joint 10 has been described above, the present invention is a cross groove type constant velocity universal joint. The present invention can also be applied to the outer joint member of other sliding type constant velocity universal joints and the outer joint member 21 of the fixed type constant velocity universal joint 20. Further, in the above, the present invention is applied to the outer joint member of the constant velocity universal joint constituting the drive shaft 1, but the present invention is also applied to the outer joint member of the constant velocity universal joint constituting the propeller shaft. be able to.

DESCRIPTION OF SYMBOLS 1 Drive shaft 2 Intermediate shaft 3 Spline 4 Boot 5 Boot 6 Support bearing 10 Sliding type constant velocity universal joint 11 Outer joint member 12 Cup part 12 'Cup member 13 Long shaft part 13' Long shaft member 16 Inner joint member 17 Tripod member 19 Torque transmission element (roller)
20 fixed type constant velocity universal joint 21 outer joint member 22 inner joint member 23 torque transmission element (ball)
24 Cage 30 Track groove 31 Short shaft portion 32 Recess 33 Recess 34 Annular joint surface 35 Annular joint surface 36 Burr part 40 Track groove 41 Torque transmission element (ball)
A Joint surface B Heat-affected zone C Near the boundary of the base metal part D Outer diameter F Removal diameter of burr G Substitute part H Tubular part O Joint center O ₁ Center of curvature O ₂ Center of curvature

Claims

An outer joint member of a constant velocity universal joint comprising a cup portion formed on the inner periphery with a track groove engaged with a torque transmitting element, and a shaft portion formed at the bottom of the cup portion, the outer joint member Is composed of two members, a cup member that forms the cup portion and a shaft member that forms the shaft portion, and the frictional pressure welding of the solid short shaft portion and the solid shaft member of the cup member,
Both the cup member and the shaft member are made of medium carbon steel, and at least the cup member has a short shaft portion that has been forged and reduced in diameter from the bottom of the cup portion, and a recess is provided on the end surface of the short shaft portion. An annular joint surface is formed by forming a concave portion on one end surface of the shaft member, the annular joint surface is formed, and the two annular joint surfaces are abutted against each other and friction welded. Outer joint member.
2. The outer side of the constant velocity universal joint according to claim 1, wherein the medium carbon steel, which is a material of the cup member and the shaft member, has a carbon amount of 0.43 mass% or more and 0.66 mass% or less. Joint member.
The outer joint member of a constant velocity universal joint according to claim 1 or 2, wherein the carbon content of the medium carbon steel which is a material of the cup member and the shaft member is different between the two members.
The outer joint member of a constant velocity universal joint according to any one of claims 1 to 3, wherein the shaft member is a long shaft member.
The outer joint member of a constant velocity universal joint according to any one of claims 1 to 4, wherein a longitudinal section of the concave portion is curved.
The outer joint member of a constant velocity universal joint according to any one of claims 1 to 5, characterized in that the longitudinal section of the concave portion has a shape without a step.
The outer joint member for a constant velocity universal joint according to any one of claims 1 to 6, wherein the recess is formed simultaneously with the forging process of the cup member.
The outer joint member of a constant velocity universal joint according to any one of claims 1 to 7, wherein the cup portion of the cup member is formed by cold plastic working.
The outer joint member of the constant velocity universal joint according to any one of claims 1 to 8, wherein a tip of a burr generated by the friction welding is not in contact with the inner surface of the recess.
10. The diameter of the burrs generated by friction welding on the short axis of the cup member and the outer diameter surface of the shaft member is made larger than the outer diameter of the adjacent portion. The outer joint member of the described constant velocity universal joint.
The constant velocity universal joint according to any one of claims 1 to 10, wherein the outer peripheral surface of the joint surface is machined, and at least the inside of the cup portion and the shaft portion are locally hardened. Outer joint member.
The outer joint member of a constant velocity universal joint according to any one of claims 1 to 11, wherein the surface quenching is induction quenching.
The outer joint member of a constant velocity universal joint according to claim 12, wherein the induction hardening surface of the shaft portion is ground.
The friction welding method for an outer joint member of a constant velocity universal joint according to any one of claims 1 to 9.