JP2007232033A - Fixed type constant speed universal joint, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixed type constant speed universal joint which copes with an in-line type, and suppresses the generation of scales after the high-frequency heat treatment, and reduces its dimensional change, and further can have the rolling life equivalent to or higher than that of a carburized universal joint even when it is used in a further high-temperature atmosphere. <P>SOLUTION: The fixed type constant speed universal joint comprises: an outer member having a plurality of track grooves 22 formed on an inner spherical surface 21; an inner member having a plurality of track grooves 25 formed on an outer spherical surface 24; a plurality of balls 27 which are arranged between the track grooves 22 of the outer member and the track grooves 25 of the inner member and transmit a torque; and a cage 28 which is arranged between the inner spherical surface of the outer member and the outer spherical surface of the inner member, and holds the balls 27. A carburized hardened layer is formed on a hardened surface layer 30 at the ball contact portion which is not finished after the high-frequency heat treatment of at least either one of the inner member and the outer member by carrying out the high-frequency induction hardening in oil. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixed type constant velocity universal joint and a manufacturing method thereof.

  Constant velocity universal joints are used in power transmission systems of automobiles and various industrial machines, for example, and are fixed to a kind of constant velocity universal joints used as means for transmitting rotational force from automobile engines to wheels at constant speed. There is a constant velocity universal joint. This fixed type constant velocity universal joint has a structure in which two shafts on the driving side and the driven side are connected and the rotational torque can be transmitted at a constant speed even if the two shafts have an operating angle. In general, as the above-mentioned fixed type constant velocity universal joint, a Barfield type (BJ) and an undercut free type (UJ) are widely known.

  For example, the BJ type fixed type constant velocity universal joint has an inner ring in which a plurality of track grooves are formed on the inner spherical surface as outer members and a plurality of track grooves that are paired with the outer groove track grooves are formed on the outer spherical surface. The inner ring as a member, a plurality of balls that are interposed between the outer ring track grooves and the inner ring track grooves, and a ball that is interposed between the inner spherical surface of the outer ring and the outer spherical surface of the inner ring to hold the balls. And a cage. Further, a shaft (not shown) is fitted into the inner ring.

  By the way, constant velocity universal joints used for automobile drive shafts are required to be lightweight and compact in order to improve fuel efficiency and power performance. Downsizing (miniaturization) is effective for reducing weight and size. However, in the constant velocity universal joint as described above, a ball (steel ball) is used as the torque transmission member. For this reason, improvement in durability of the track grooves of the inner ring and the outer ring and the ball rolling surface (ball contact portion) of the cage pocket has been an issue.

  Thus, there is a conventional technique that improves the life by performing shot peening on the carburized inner ring (Patent Document 1). In addition, some mechanical parts having rolling elements such as constant velocity universal joints are carbonitrided and quenched to precipitate residual austenite to improve the life (Patent Document 2). Furthermore, in the heat treatment method of the inner joint member of the constant velocity universal joint, there is one that improves the life by optimizing the heating method of induction hardening (Patent Document 3).

Non-Patent Document 1 describes a high-speed steel having a white layer (residual austenite) generated by vacuum oil quenching. That is, it is described that retained austenite is generated on the surface layer by vacuum oil quenching to improve wear resistance. Further, Patent Document 4 describes that a steel product (ball screw shaft) is subjected to buffing for removing scales after induction hardening. Further, as scale removal, there is one that performs electrolytic polishing after induction hardening (Patent Document 5), and another that removes scale by increasing the pressure of cooling water at the time of induction hardening (Patent Document 6).
JP-A-1-182625 Japanese Patent Laid-Open No. 5-240253 JP 2000-227123 A JP 2003-119518 A JP 2003-25152 A JP 2002-129231 A Paper “Abrasion resistance of high-speed steel with white layer formed by vacuum oil quenching” Journal of the Japan Institute of Metals, Vol. 41 (1977), pages 639 to 646

  In the thing of the said patent document 1, since a carburizing process is performed for a long time at high temperature, there exists a problem which cannot be made in-line. Furthermore, there has been a problem that the processing cost increases due to the shot peening process. Further, as described in Patent Document 2, in the case of performing the carbonitriding process, the carbonitriding process is effective for improving the life in an atmosphere where wear powder is generated. There are problems that cannot be achieved.

  In the thing of the said patent document 3, since induction hardening is performed, in-line-ization is possible, but softening resistance is low compared with a carburizing process, and the heat_generation | fever by sliding of a high temperature atmosphere or a rolling element generate | occur | produces There is a problem in that the service life is reduced. Moreover, the surface hardening of induction hardening consists of the systematic hardness by the production | generation of a martensite and the hardness by a compressive residual stress. For this reason, when the induction-hardened component is used in a high temperature atmosphere, the hardness due to the compression residue is drastically reduced and the surface hardness is lowered. There is a problem that the rolling life is reduced due to the decrease in hardness.

  In addition, scale is generated by oxidation on the surface that has been induction-hardened. As a result, there is a problem that the surface roughness is lowered and the life is shortened. Further, since this scale is peeled off and the thickness is not constant, there is a problem that the dimensional accuracy is lowered and the dimensional variation is increased.

  Non-Patent Document 1 describes that although it is not a constant velocity universal joint, vacuum oil quenching is performed to improve wear resistance. In this case, a vacuum device is necessary and the device itself is required. There is a problem that it is expensive and cannot be inlined. Further, if induction hardening is performed, scale is generated on the surface layer. Therefore, it is necessary to remove the scale, and methods for removing the scale include those described in Patent Documents 4 to 6. However, as described in Patent Document 4, when a scale generated later is processed by buffing, it may not be completely removed, and there is a problem that processing time is long. In addition, as described in Patent Document 5, when the scale is removed by electropolishing, it is possible to completely remove the scale, but the processing time is greatly increased, the surface becomes rough, and the chemical reaction heat is generated. There are problems such as softening of the surface. Furthermore, as described in Patent Document 6, the cooling water pressure at the time of induction quenching cannot be removed uniformly, and a black scale remains minutely in the form of spots, requiring a separate descaling process. .

  As described above, the carburizing treatment cannot cope with in-line processing, and the induction hardening has a problem of a reduction in life in an atmosphere where scale is generated and heat is generated.

  In view of the above problems, the present invention can cope with in-line, suppresses the generation of scale after high-frequency heat treatment, has a small dimensional change, and has rolling equivalent to or better than that carburized even when used in a high-temperature atmosphere. Providing fixed-type constant velocity universal joints with long life.

  The fixed type constant velocity universal joint according to the present invention includes an outer member having a plurality of track grooves formed on an inner spherical surface, an inner member having a plurality of track grooves formed on the outer spherical surface, and a track groove of the outer member. A plurality of balls that transmit torque between the inner member and the track groove of the inner member, and a cage that holds the balls interposed between the inner spherical surface of the outer member and the outer spherical surface of the inner member. In a fixed type constant velocity universal joint provided with a carburized and hardened layer on the surface hardened layer of the ball contact portion where the finishing process is not performed after the induction heat treatment of at least one of the inner member and the outer member. is there.

  In the fixed type constant velocity universal joint of the present invention, the carburized hardened layer formed at the ball contact site by induction hardening in oil has a carbon concentration that is higher than that of the base material (portion other than the hardened layer). This is because carbon diffused (carburized) from the ambient oil to the surface of the ball contact portion. Oxidation reaction is suppressed by this carburization and generation of scale is suppressed.

  In addition, this carburization causes the hardened layer to have a higher surface hardness than usual induction hardening. This hardness is due to an increase in the carbon content, increasing the softening resistance in a high-temperature atmosphere, maintaining the initial hardness, improving the wear resistance and peeling resistance, and the life (rolling life). To increase.

  Residual austenite is generated in the surface hardened layer. Thereby, the life is further improved by the improvement of the conformability and the relaxation hardening of the surface pressure.

  The manufacturing method of the fixed type constant velocity universal joint according to the present invention includes an outer member having a plurality of track grooves formed on an inner spherical surface, an inner member having a plurality of track grooves formed on the outer spherical surface, and the outer member. A plurality of balls that transmit torque by being interposed between the track grooves of the inner member and the track grooves of the inner member, and the balls are interposed between the inner spherical surface of the outer member and the outer spherical surface of the inner member. In a method for manufacturing a fixed type constant velocity universal joint provided with a cage, at least one of an inner member and an outer member is induction-quenched in oil to form a carburized and quenched layer. .

  In the method for producing a fixed type constant velocity universal joint according to the present invention, the hardened layer formed by induction hardening in oil diffuses (carburizes) the carbon of the oil, and the carbon from the base material (part other than the hardened layer) Concentration increases. For this reason, in a hardened layer, an oxidation reaction is suppressed and generation | occurrence | production of a scale is suppressed.

  Moreover, the hardened layer becomes higher than the normal induction-hardened surface hardness due to the increase in the carbon amount due to the carburization. For this reason, the softening resistance in a high-temperature atmosphere is increased, the initial hardness is maintained even after a long period of use, the wear resistance and peel resistance are improved, and the life (rolling life) is increased.

  In the present invention, the generation of scale is suppressed, the dimensional accuracy is stabilized, and the durability life is remarkably improved by increasing the hardness. Further, since the surface of the ball contact portion is carburized, the required surface hardness can be obtained even if the material is low carbon steel. For this reason, the carbon of the material can be reduced, the deformability is improved, and cold working can be performed in the same manner as carburizing.

  An embodiment of a fixed type constant velocity universal joint according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the fixed type constant velocity universal joint includes an outer ring 23 as an outer member in which a plurality of track grooves 22 are formed in the inner spherical surface 21 along the axial direction at equal intervals in the circumferential direction, and the outer spherical surface. 24, a plurality of track grooves 25 paired with the track grooves 22 of the outer ring 23 are formed along the axial direction at equal intervals in the circumferential direction, and the track grooves 22 and the inner rings 26 of the outer ring 23 are formed as inner members. A plurality of balls 27 that transmit torque by being interposed between the track grooves 25 and a cage 28 that is interposed between the inner spherical surface 21 of the outer ring 23 and the outer spherical surface 24 of the inner ring 26 and holds the balls 27. I have.

  The track groove 22 of the outer ring 23 shifts its center of curvature O1 from the joint center O in the axial direction toward the opening side of the outer ring 23, and the track groove 25 of the inner ring 26 sets its center of curvature O2 from the joint center O to the outer ring in the axial direction. The track grooves 22 are provided on the back side opposite to the center of curvature O1 of the track grooves 22 by an equal distance f. A stem 29 is provided on the outer ring 23.

  In this constant velocity universal joint, a ball contact portion (ball contact surface) which is an inner surface of each of the track grooves 22 and 25 of the outer ring 23 and the inner ring 26 is a hardened layer 30. This hardened layer 30 is subjected to induction hardening in oil. For example, induction hardening is performed with the outer ring 23 and the inner ring 26 immersed in oil. Here, induction hardening means that an induction current is generated in the surface portion of the derivative (workpiece) by passing a high-frequency current through the quenching coil to generate heat, and this heat rapidly heats the surface of the workpiece. And quenching. In this case, the high-frequency heating temperature is preferably 900 ° C. or higher and 1350 ° C. or lower.

  The carburized and hardened layer 30 of the surface hardened layer formed at the ball contact site by induction hardening in oil has a carbon concentration higher than that of the base material (a portion other than the hardened layer). This is because carbon diffused (carburized) from the ambient oil to the surface of the ball contact portion. Oxidation reaction is suppressed by this carburization and generation of scale is suppressed.

  Further, the hardness of the hardened layer 30 is as shown in FIG. 2, and is higher than the surface hardness subjected to normal induction hardening. This is because the carburizing treatment was performed as described above, and this hardness is due to an increase in the amount of carbon as shown in FIG. For this reason, the softening resistance in a high temperature atmosphere increases, the initial hardness is maintained, the wear resistance and the peel resistance are improved, and the life (rolling life) is increased.

  Moreover, as shown in FIG. 3, residual austenite (γ) is formed on the surface portion of the hardened layer 30 (the carburized layer in FIG. 3). Here, retained austenite means that when a steel is quenched and the martensitic transformation end temperature (Mf point) of the steel is below room temperature, the austenite that has not yet undergone transformation remains as it is after quenching. This is what remains. This retained austenite improves toughness and rolling fatigue strength. For this reason, the lifetime of the hardened layer 30 is further improved by improving the conformability and relaxing hardening of the surface pressure.

  Thus, in the present invention, the generation of scale is suppressed, the dimensional accuracy is stabilized, and the durability life is remarkably improved by increasing the hardness. Further, since the surface of the ball contact portion is carburized, the required surface hardness can be obtained even if the material is low carbon steel. For this reason, the carbon of the material can be reduced, the deformability is improved, and cold working can be performed in the same manner as carburizing. In particular, by setting the temperature of the high frequency heating to 900 ° C. or more and 1350 ° C. or less, the oxidation reaction due to carburization can be stably suppressed, and the generation of scale can be reliably suppressed. In addition, when the temperature of the high frequency heating is less than 900 ° C., sufficient hardness cannot be obtained, the oxidation reaction is promoted, the generation of scale increases, the carburization amount decreases, and the temperature of the high frequency heating exceeds 1350 ° C. Although the carburized layer increases, the crystal grains become coarse and become brittle.

  By the way, in the said embodiment, although the ball contact site | part (ball contact surface) which is the inner surface of each track groove 22 and 25 of the outer ring | wheel 23 and the inner ring | wheel 26 was made into the hardened layer 30, either one of these may be sufficient. That is, only the inner surface of the track groove 22 of the outer ring 23 can be the hardened layer 30, or only the track groove 25 of the inner ring 26 can be the hardened layer 30. Further, the inner spherical surface 21 of the outer ring 23 may be simultaneously processed when the track groove 22 is induction-quenched in oil. The same applies to the inner ring 26.

  For the inner ring of the fixed type constant velocity universal joint having the structure shown in FIG. 1, the conventional product A which has been subjected to conventional carburizing treatment, the conventional product B which has been subjected to normal induction hardening, and the invention which has been induction-hardened in oil. A, B, and C were manufactured and their characteristics were compared. The results are shown in Table 1 below. Conventional product A used carburized steel SCM420 (chromium molybdenum steel), and conventional product B and invention products A to C used medium carbon steel. Further, the carbon content of the conventional product B was 0.53 wt%, and the carbon content of the invention products A to C was 0.46 wt%. Then, the conventional products A and B and the invention products A, B and C were subjected to cutting after cold forging and grinding of the outer diameter (track groove). As for cooling after quenching, only the conventional product B was cooled with water, and the others were cooled in oil. In addition, the induction hardening in oil in invention products A, B and C was started by quenching at the same time as turning off the overheating power after induction heating in the atmosphere of the hardening oil.

  As can be seen from Table 1, the inventive product A produced some scale, but the inventive products B and C produced almost no scale. Further, a large amount of scale was generated in the conventional product B subjected to normal induction hardening. In addition, the scale is slightly generated even in the conventional product A subjected to the carburizing treatment.

  In terms of surface hardness, the conventional products A and B and the invention products A, B, and C are almost the same at a depth of 0.1 mm, but the conventional products are at a depth of 0.05 mm. Whereas A is Hv600 and the conventional product B is Hv712, the invention product A is Hv770, the product B is Hv785, and the product C is Hv795. Thus, the surface sides of the inventive products A, B and C are hard, and in particular, the inventive products B and C are hard. Invented product B produced residual austenite in the range of 5 μm from the surface, and Invented product C produced residual austenite in the range of 10 μm from the surface, and the diffusion of carbon increased from that of invention A.

  A vibration durability test was performed at a rotational speed of 600 r / min, a surface pressure of 3 GPa, an operating angle of 0 to 45 degrees, and an operating time of 15 hours. The x in the conventional product B in Table 1 indicates the occurrence of damage that cannot be continued, the ○ in the conventional product A and the invention A indicates the occurrence of minor damage, and the ◎ in the invention products B and C indicates the occurrence of damage. It shows no.

  Thus, it can be seen that in the invention product, the generation of scale is suppressed and the durable life is increased. In addition, because the material is carburized from the surface by induction quenching in oil, the required surface hardness can be obtained even if the material is low carbon steel. Is also possible.

It is principal part sectional drawing of the fixed type constant velocity universal joint which shows embodiment of this invention. It is a graph which shows the hardness of the hardened layer of the said fixed type constant velocity universal joint. It is a simplified diagram showing the range of the carburized layer of the fixed type constant velocity universal joint. It is a graph which shows the carbon content of the hardened layer of the said fixed type constant velocity universal joint.

Explanation of symbols

21 inner spherical surface 22 track groove 23 outer ring 24 outer spherical surface 25 track groove 26 inner ring 27 ball 28 cage 29 stem 30 hardened layer

Claims (3)

An outer member having a plurality of track grooves formed on the inner spherical surface, an inner member having a plurality of track grooves formed on the outer spherical surface, and between the track grooves of the outer member and the track grooves of the inner member. In a fixed type constant velocity universal joint comprising a plurality of balls interposed to transmit torque, and a cage for holding the balls interposed between the inner spherical surface of the outer member and the outer spherical surface of the inner member,
A fixed type constant velocity universal joint, wherein a carburized and hardened layer is formed on a surface hardened layer of a ball contact portion where a finishing process after high frequency heat treatment of at least one of an inner member and an outer member is not performed.   2. The fixed constant velocity universal joint according to claim 1, wherein retained austenite is generated in the surface hardened layer. An outer member having a plurality of track grooves formed on the inner spherical surface, an inner member having a plurality of track grooves formed on the outer spherical surface, and between the track grooves of the outer member and the track grooves of the inner member. Manufacture of a fixed type constant velocity universal joint including a plurality of balls interposed to transmit torque, and a cage for holding the balls interposed between the inner spherical surface of the outer member and the outer spherical surface of the inner member In the method
A method for manufacturing a fixed type constant velocity universal joint, wherein at least one of an inner member and an outer member is subjected to induction hardening in oil to form a carburized and quenched layer.

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