JP2007270902A - Tripod type constant velocity joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tripod type constant velocity joint capable of preventing damage started from a location of an outer joint member in which hardness of the location corresponding to a back side of an effective roller contact range of a track groove is increased even though service conditions become severe by a compact design and thin-walled design of the outer joint member. <P>SOLUTION: The tripod type constant velocity joint has the outer joint member 1 made of steel which has the track groove 6 with roller guide faces 7 circumferentially faced to each other. The structure of the outer joint member 1 at the location corresponding to at least the back side of the effective roller contact range of the track groove 6 is either of a fine ferrite pearlite structure, a bainite structure, and a tempered martensite structure, or is a mixed structure having at least two kinds or more of them. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a tripod type constant velocity universal joint.

  Generally, a constant velocity universal joint (tripod type constant velocity universal joint) includes an outer joint member 51, a tripod member 52 as an inner joint member, and a roller 53 as a torque transmission member, as shown in FIGS. It is a major component.

  The outer joint member 51 includes a mouth portion 54 and a stem portion 55 that are integrally formed. The mouse portion 54 has a cup shape opened at one end, and a track groove 56 extending in the axial direction is formed at a position of the inner circumference in the circumferential direction. The mouse portion 54 has a non-cylindrical shape in which a large diameter portion 54a and a small diameter portion 54b appear alternately when viewed in a cross section (see FIG. 4). That is, the mouse portion 54 is formed with the large-diameter portion 54a and the small-diameter portion 54b, so that the three track grooves 56 extending in the axial direction are formed on the inner peripheral surface thereof. Roller guide surfaces 57 are formed on the side walls of each track groove 56 facing each other in the circumferential direction.

  The tripod member 52 includes a boss 58 and a leg shaft 59. The boss 58 is formed with a spline or serration hole 61 that is coupled to the shaft 60 so as to be able to transmit torque. The leg shaft 59 protrudes in the radial direction from the circumferentially divided position of the boss 58. Each leg shaft 59 of the tripod member 52 carries a roller 53.

That is, in the tripod type constant velocity universal joint, torque is transmitted by hertz contact between the roller outer peripheral surface and the roller guide surface of the track groove of the outer joint member. For this reason, medium carbon steel is generally used for the outer joint member, and there are those in which induction hardening is performed only on the roller guide surface on which high surface pressure acts (Patent Document 1 and Patent Document 2).
Japanese Utility Model Publication No.58-111431 JP 2005-9507 A

  By the way, on the outer peripheral side of the outer joint member, the portion that contacts the back side of the track groove with which the roller contacts is subjected to bending, and a tensile stress field that increases toward the outer peripheral surface is formed. As a future technical trend, the outer joint member of the tripod type constant velocity universal joint tends to be made compact and thin in order to cope with resource saving, energy saving and compactness. Accordingly, the tensile stress increases as the load per unit area increases, and there is a concern about damage caused by the tensile stress.

  Therefore, it is proposed to increase the strength by subjecting the outer peripheral side to induction hardening. However, when the strength is increased by induction hardening, tensile residual stress is generated around the quenched portion. For this reason, when this tensile residual stress is superimposed on the tensile stress acting at the time of torque transmission, it is considered that the periphery of the hardened portion is damaged as a starting point.

  In view of the above problems, in the outer joint member according to the present invention, by increasing the hardness of the portion that hits the back side of the roller groove effective contact range of the track groove, even if the use condition becomes severe with downsizing, thinning, A tripod type constant velocity universal joint capable of preventing breakage starting from a hardened portion is provided.

  The tripod type constant velocity universal joint of the present invention is a tripod type constant velocity universal joint provided with an outer joint member made of steel in which a track groove is formed, and is located at the back side of at least the roller effective contact range of the track groove of the outer joint member Is a non-standard structure portion that is any one of a fine ferrite pearlite structure, a bainite structure, and a tempered martensite structure, or a mixed structure of at least two of them.

  It is possible to increase the hardness of a portion of the track groove that contacts the back side of the roller effective contact range (the portion where the roller rolls and the roller guide surface) (the outer peripheral side of the roller guide surface). In this non-standard structure portion, the main structure form is a fine ferrite pearlite structure or the like, so that it is possible to prevent the generation of tensile residual stress around the non-standard structure portion (hardened portion). In addition, it becomes a fine ferrite pearlite by carrying out forced air cooling after making this austenite. By performing austempering after austenitizing, a bainite structure is obtained. After austenitizing, it is rapidly cooled and transformed into martensite and subsequently tempered to obtain a tempered martensite structure.

  The fine ferrite pearlite structure has a ferrite grain size of 8 or more as defined in JIS G 0552 (steel ferrite crystal grain size test method), and locally at a position corresponding to the back side of the roller groove effective contact range of the track groove. A non-standard tissue part is formed, and the hardness of the non-standard tissue part is set to HV600 or less.

  The tripod type constant velocity universal joint of the present invention can increase the hardness of the portion of the outer joint member of the tripod type constant velocity universal joint that is in contact with the back side of the roller effective contact range of the track groove. It is possible to prevent the generation of tensile residual stress around the standard tissue part). Thereby, even if use conditions become severe with downsizing and thinning, damage starting from a non-standard tissue part can be prevented.

  When the fine ferrite pearlite structure has a ferrite grain size defined by JIS G 0552 (a method for testing the ferrite crystal grain size of steel) of 8 or more, it is possible to further improve the fatigue strength of the non-standard microstructure part.

  By setting the hardness of the non-standard tissue part to HV600 or less, it is possible to suppress the residual tensile stress generated around the non-standard tissue part, and to effectively prevent damage starting from the non-standard tissue part. That is, when tempering after induction hardening locally and making it high hardness, in order to exhibit the effect, it is necessary to make the residual tensile stress produced | generated in a quenching boundary small enough by tempering. For this reason, as a non-standard structure part, it is desirable to temper on the conditions that hardness becomes HV600 or less.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1, the constant velocity universal joint is a tripod type constant velocity universal joint including an outer joint member 1, a tripod member 2 as an inner joint member, and a roller 3 as a torque transmission member.

  The outer joint member 1 includes a mouth portion 4 and a stem portion (not shown) that are integrally formed. The mouse portion 4 has a cup shape opened at one end, and a track groove 6 extending in the axial direction is formed at a position of the inner circumference in three equal parts. The mouse part 4 has a non-cylindrical shape in which the large diameter part 4a and the small diameter part 4b appear alternately when viewed in cross section. That is, the mouse portion 4 is formed with the large-diameter portion 4a and the small-diameter portion 4b, whereby the three track grooves 6 extending in the axial direction are formed on the inner peripheral surface thereof. Roller guide surfaces 7 are formed on the side walls of each track groove 6 facing each other in the circumferential direction.

  The tripod member 2 includes a boss 8 and a leg shaft 9. The boss 8 is formed with a spline or serration hole 11 which is coupled to a shaft (not shown) so as to be able to transmit torque. The leg shaft 9 protrudes in the radial direction from the circumferentially divided position of the boss 8. The roller 3 is externally fitted to each leg shaft 9 of the tripod member 2 so as to be rotatable about an axis (axis) as a torque transmission member. Each roller 3 is accommodated in each track groove 6 of the outer joint member 1. The roller 3 may be a double roller type having an inner roller and an outer roller, or only one single roller type.

  In the outer joint member 1, induction hardening is applied to the track groove 6 on which high surface pressure acts when torque is transmitted, particularly to the effective contact range of the track groove 6 (the roller rolling surface, which is the roller guide surface 7). The cured portion 12 is formed. That is, the surface of the curing part 12 constitutes the roller guide surface 7. Here, induction hardening is performed by heating only the surface of the processed material utilizing skin hardening by high frequency. In addition, when forming the hardening part 12, you may carry out by metal heat processing other than induction hardening.

  In the first embodiment shown in FIG. 1, the non-standard tissue portion 13 is locally formed at a portion where a large tensile stress hits the back side of the track groove 6. These non-standard texture parts 13 are formed by heat treatment (for example, high-frequency local heating) before the hardened part 12 of the track groove 6 is formed, and the hardness can be increased. Thus, if the hardness of the part which contacts the back side of the track groove 6 is increased, the fatigue strength can be improved.

  As the non-standard structure portion 13, any one of a fine ferrite pearlite structure, a bainite structure, and a tempered martensite structure can be formed in a main structure form, and among these, at least two or more of them can be formed. The mixed tissue can be configured in the main tissue form. In the case of two or more kinds of mixed tissues, the mixing ratio of these tissues is arbitrary.

  In order to form fine ferrite pearlite, forced air cooling may be performed after austenitization. In order to form a bainite structure, austempering may be performed after austenite formation. In order to construct a tempered martensite structure, it is only necessary to rapidly cool and martensite after austenitization, followed by tempering. In the case of fine ferrite pearlite, it is preferable that the ferrite grain size defined by JIS G 0552 (method for testing the ferrite grain size of steel) is No. 8 or more.

  As described above, the portion on which the large tensile stress acting on the back side of the track groove 6 acts forms the non-standard tissue portion 13, whereby the hardness of this portion can be increased and the fatigue strength can be improved. . However, when tempering after induction hardening locally to increase the hardness, it is necessary to sufficiently reduce the residual tensile stress generated at the quenching boundary in order to exert the effect. For this reason, it is desirable that the non-standard texture portion 13 is tempered under conditions such that the hardness is HV600 or less.

  According to this constant velocity universal joint, it is possible to increase the hardness of the outer joint member 1 at the location corresponding to the back side of the roller effective contact range of the track groove 6 (the outer peripheral side corresponding to the roller guide surface 7), It is possible to prevent generation of tensile residual stress around the hardened portion (non-standard tissue portion 13). Thereby, even if use conditions become severe with downsizing and thinning, damage starting from this hardened portion can be prevented.

  When the fine ferrite pearlite structure is the main structure, the ferrite grain size defined by JIS G 0552 (steel ferrite grain size test method) is 8 or more, so that Further improvements can be achieved. If the ferrite grain size is less than 8, the improvement of the fatigue strength of the non-standard texture 13 cannot be expected so much.

  By setting the hardness of the non-standard tissue part 13 to HV600 or less, the tensile residual stress generated around the non-standard tissue part 13 can be suppressed to a small extent, and the damage starting from the non-standard tissue part 13 can be effectively prevented. Can do. If the hardness of the non-standard tissue portion 13 is less than HV600, it is difficult to suppress the residual tensile stress generated around the non-standard tissue portion 13 and cannot effectively prevent damage starting from the non-standard tissue portion 13.

  Next, FIG. 2 is a sectional view of an essential part of the second embodiment. In this case, the portion other than the hardened portion 12 is set as the nonstandard tissue portion 13. Such a non-standard structure | tissue part 13 can be comprised by heating by whole furnace heating (method to heat the whole outer joint member 1).

  As shown in FIG. 2, even if the non-standard tissue portion 13 other than the hardened portion 12 is used, the portion where a large tensile stress hits the back side of the track groove 6 acts as the non-standard tissue portion, as in the outer joint member 1 shown in FIG. By forming 13, the hardness of this portion can be increased and the fatigue strength can be improved.

  As described above, the embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in FIG. There is no standard tissue part (base material part) interposed therebetween, but when the non-standard tissue part 13 is provided on the entire circumference of the mouse part 4, the standard tissue part is provided between the non-standard tissue part 13 and the hardened part 12. May be interposed. Here, the standard tissue part is a part not subjected to heat treatment, and is a tissue part that is neither the hardened part 12 nor the non-standard tissue part 13.

  As the product of the present invention (Example), four outer joint members (samples) A1, A2, A3, and A4 are manufactured, and two outer joint members (samples) B1 and B2 are manufactured as comparative examples. Then, a swing-twist test was performed on each specimen. In this case, S53C was used as the material of each specimen, and the processing history up to the heat treatment was also the same. The non-standard structure part 13 of the specimens A1 and A2 was formed as shown in FIG. 2 by heating the whole furnace. The non-standard tissue portions A3, A4, and B2 were formed as shown in FIG. 1 by high-frequency local heating. Table 1 shows the heat treatment history, main structure transformation, and hardness for forming a non-standard structure portion in each specimen.

  In the heat treatment history column of Table 1, Example A1 indicates that the entire furnace is heated and then forced air cooling is performed. Example A2 indicates that the austempering is performed at 400 ° C. after the entire furnace is heated. Example A3 shows that after high-frequency local heating, water cooling and tempering at 350 ° C. were performed, and Example A4 was high-frequency local heating, water cooling and tempering at 250 ° C. It shows that. Comparative Example B1 indicates that no non-standard structure is formed, and Comparative Example B2 indicates that high-frequency local heating was performed, followed by water cooling and tempering at 150 ° C.

  For this reason, Example A1 has a main structure with a fine ferrite pearlite structure, Example A2 has a main structure with a bainite structure, and Example A3 has a main structure with a tempered martensite structure. Example A4 , The tempered martensite structure was the main structural form, Comparative Example B1 was the main structural form of the ferrite pearlite structure, and Comparative Example B2 was the main structural form of the tempered martensite structure. In addition, the fine ferrite pearlite structure of Example A1 has a ferrite grain size defined by JIS G 0552 as No. 8.2, and the ferrite pearlite structure of Comparative Example B1 has a ferrite grain size defined by JIS G 0552. 7.3.

The number of loads until a crack occurred at a position where the tensile stress on the outer peripheral side of the outer joint member 1 was maximized was determined. Table shows the 2 largest outer peripheral side to the tensile stress and the fatigue strength at 10 ⁵ times that obtained from the relationship between the crack life (maximum tensile stress value). In Examples A1 to A4, the fatigue strength was improved as compared with Comparative Example B1, which is a conventional product. On the other hand, B2 having high hardness of the non-standard tissue part was equivalent to Comparative Example B1 (conventional product). As a result of examining the fracture starting point of B2, it was found near the boundary between the non-standard tissue part and the base material part. This is presumably because the tensile residual stress generated around the quenched portion is superimposed on the tensile stress acting on the outer periphery in the fatigue test.

  From the above, it can be said that the fatigue strength can be improved by increasing the hardness of the portion corresponding to the back side of the track groove 6 on which a large tensile stress acts.

It is a cross-sectional view of the constant velocity universal joint which shows 1st Embodiment of this invention. It is principal part sectional drawing of the outer joint member of the constant velocity universal joint which shows 2nd Embodiment of this invention. It is a longitudinal cross-sectional view of the conventional constant velocity universal joint. It is a cross-sectional view of a conventional constant velocity universal joint.

Explanation of symbols

1 Outer joint member 6 Track groove 7 Roller guide surface 13 Non-standard tissue part

Claims (3)

  In a tripod type constant velocity universal joint having an outer joint member made of steel in which track grooves are formed, the structure of the portion of the track groove of the outer joint member corresponding to at least the back side of the roller effective contact range is a fine ferrite pearlite structure, a bainite structure A tripod type constant velocity universal joint characterized in that any one of tempered martensite structures, or at least a mixed structure of two or more of them is a non-standard structure part.   The tripod type constant velocity universal joint according to claim 1, wherein the fine ferrite pearlite structure has a ferrite grain size defined by JIS G 0552 of 8 or more.   The tripod type according to claim 1 or 2, wherein a non-standard tissue part is locally formed at a position corresponding to the back side of the roller effective contact range of the track groove, and the hardness of the part is set to HV600 or less. Constant velocity universal joint.

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