JP2007298058A - Constant velocity universal joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant velocity universal joint reduced in cost by eliminating grinding work for an internal oxidation layer, and also improved in strength resulting in a longer rolling life (the life of a track groove). <P>SOLUTION: The constant velocity universal joint comprises: an outside joint member having a plurality of track grooves 22 formed in an inner diameter face 21; an inside joint member having a plurality of track grooves 25 formed in an outer diameter face 24; a plurality of balls 27 laid between the track groove 22 of the outside joint member and the track groove 25 of the inside joint member for transmitting torque; and a cage 28 laid between an inner diameter face 21 of the outside joint member and an outer diameter face 24 of the inside joint member for holding the balls 27. In the groove surface of the track groove 25 of at least the inside joint member, a forging finished hardened layer 35 is provided whose internal oxidation layer is 1μm or less thick. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixed or sliding constant velocity universal joint which is used in a power transmission system of an automobile or various industrial machines, and is incorporated in, for example, a drive shaft or a propeller shaft used in a 4WD vehicle or an FR vehicle.

  For example, a fixed type constant velocity universal joint (Zeper type constant velocity universal joint: BJ) used as a coupling joint for an automobile drive shaft or the like has a plurality of track grooves 2 on an inner diameter surface 1 as shown in FIG. The outer ring 3 as an outer joint member formed along the axial direction at equal intervals in the circumferential direction, and a plurality of track grooves 5 paired with the track grooves 2 of the outer ring 3 on the outer diameter surface 4 are equally spaced in the circumferential direction. An inner ring 6 as an inner joint member formed along the axial direction, a plurality of balls 7 interposed between the track groove 2 of the outer ring 3 and the track groove 5 of the inner ring 6, and the outer ring 3 And a cage 8 for holding the ball 7 interposed between the inner diameter surface 1 of the inner ring 6 and the outer diameter surface 4 of the inner ring 6.

  Further, a spline portion 9 is provided on the inner peripheral surface of the center hole of the inner ring 6, and the spline portion 11 of the shaft 10 inserted into the center hole of the inner ring 6 is engaged. A concave circumferential groove 12 is formed at the end of the spline portion 11 of the shaft 10, and a retaining ring 13 for preventing the shaft from slipping is fitted into the concave circumferential groove 12.

  The track groove 2 of the outer ring 3 has its center of curvature O1 shifted axially from the joint center O toward the opening side of the outer ring 3, and the track groove 5 of the inner ring 6 has its center of curvature O2 axially extended from the joint center O to the outer ring. The third track groove 2 is provided on the far side opposite to the center of curvature O1 by an equal distance f.

  The inner ring 6 used for such a constant velocity universal joint has a hardened layer formed on the surface thereof. This hardened layer is generally formed by carburizing and quenching. Carburizing and quenching is a heat treatment technique suitable for a relatively complicated shape such as the inner ring 6. However, since the carburizing process requires time, productivity is poor, and in carburizing and quenching, the deeper the carburized hardened layer depth, the longer the processing time and the higher the cost. For this reason, when forming a deep carburized layer required for a large inner ring, there are significant disadvantages in terms of cycle time and cost. Here, the cycle time is the time from the start to the end of one job, and includes not only the operation time but also the waiting time. That is, if carburizing treatment is performed, it takes time for heat treatment, and it is difficult to make in-line because of batch processing of the furnace.

Further, when carburizing and quenching is performed, crystal grain boundaries are clearly formed as shown in FIG. Here, the crystal grain boundary is an interface between the crystals, and eutectics and impurities having a low melting point are likely to collect. Therefore, the grain boundaries are more easily corroded than other parts, and grain boundary oxidation occurs. That is, a gas carburizing method is known as a carburizing treatment method, but the gas used in this method contains a small amount of oxidizing components such as H ₂ O and CO ₂ . Therefore, Cr, Mn, etc., which have a stronger affinity with oxygen than Fe, are preferentially oxidized at the austenite grain boundaries during carburizing, and Cr, Mn, etc. within the grain boundaries are also diffused and oxidized at the grain boundaries. The alloying elements decrease and grain boundary oxidation occurs. When grain boundary oxidation occurs, the hardenability decreases, and a hardened layer having a required hardness cannot be obtained, and the rolling life decreases due to the notch effect of the oxide.

  For this reason, in the constant velocity universal joint, if grain boundary oxidation occurs in the hardened layer of the track groove and a grain boundary oxide layer is formed, the rolling life (track groove life) is reduced. Therefore, it was necessary to remove this grain boundary oxide layer. However, if this grain boundary oxide layer is removed by grinding or the like, the thinly formed hardened layer will be scraped off, so the carburizing time is extended so that the hardened layer becomes thicker in anticipation of processing allowance. There is a need. Moreover, the cost is increased due to the additional processing of grinding.

  Therefore, in recent years, there is one in which a hardened layer is formed by performing induction hardening (Patent Document 1). Here, induction hardening is performed by causing induction current to be generated in the surface portion of the derivative (workpiece) by flowing a high frequency to generate heat, and the surface of the work piece is rapidly heated by this heat for quenching. Is the method. The thing of the said patent document 1 is made to achieve improvement in fatigue strength using the property which can control the hardening layer depth of induction hardening comparatively freely. That is, the thickness of the cured layer is made different between the thin portion and the non-thin portion, and the cured layer on the thin portion side is made thinner than the non-thin portion side.

For this reason, in the thing of the said patent document 1, while maintaining the balance of the ratio of the hardened layer and non-hardened layer in a thin part, the toughness of this thin part is improved, and the repetition produced by rolling of a torque transmission ball | bowl An attempt is made to improve fatigue strength against tensile stress.
JP 2000-227123 A

  However, in the said patent document 1, in the formed hardened layer, there is no description about a grain boundary oxidation layer, a crystal grain boundary, etc., and the property etc. of the formed hardened layer are unknown. For this reason, finishing processing such as grinding may have to be performed after induction hardening.

  In view of the above-mentioned problems, the present invention can reduce the cost by eliminating the grinding process of the grain boundary oxide layer, and is excellent in strength and can extend the rolling life (track groove life). Provide constant velocity universal joints.

  The constant velocity universal joint of the present invention includes an outer joint member having a plurality of track grooves formed on the inner diameter surface, an inner joint member having a plurality of track grooves formed on the outer diameter surface, and a track groove of the outer joint member. A plurality of balls that are interposed between the track grooves of the inner joint member and transmit torque; and a cage that is interposed between the inner diameter surface of the outer joint member and the outer diameter surface of the inner joint member and holds the balls. The forged finish hardened layer having a grain boundary oxide layer of 1 μm or less is provided at least on the surface of the track groove of the inner joint member. Here, the forged finish hardened layer is a surface layer that leaves the forged skin as it is, and is a layer that does not undergo a finishing process such as grinding.

  In the constant velocity universal joint of the present invention, since the grain boundary oxide layer of the hardened layer is 1 μm or less, the rolling life is hardly lowered even if the grain boundary oxide layer is not removed.

  The hardened layer is an induction hardening hardened layer formed on the groove surface of the track groove and the outer diameter surface of the inner joint member between the track grooves, and the crystal grain boundary on the surface portion of the hardened layer is obscured. .

  The inner joint member is preferably made of steel containing 0.4 wt% or more of carbon.

  In the present invention, since it is not necessary to perform grinding or the like for removing the grain boundary oxide layer, productivity can be improved and cost can be reduced. In addition, since there is no grain boundary oxide layer, the rolling life is not shortened, and a constant velocity universal joint with excellent durability can be obtained, thereby extending the life.

  Since the prior austenite grain boundaries in the surface portion of the hardened layer are obscured, grain boundary oxidation and corrosion can be prevented, and the life can be further increased. Moreover, induction hardening has an advantage that cycle time can be shortened compared to carburizing and quenching.

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

  As shown in FIG. 1, this constant velocity universal joint includes an outer ring 23 as an outer joint member in which a plurality of track grooves 22 are formed on the inner diameter surface 21 along the axial direction at equal intervals in the circumferential direction, and an outer diameter 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, as an inner ring member 26, and the track grooves 22 of the outer ring 23 and the inner ring 26 A plurality of balls 27 that transmit torque between the track grooves 25 and a cage 28 that holds the balls 27 interposed between the inner diameter surface 21 of the outer ring 23 and the outer diameter surface 24 of the inner ring 26. I have. The ball 27 is held in a pocket 28 a of the cage 28.

  Further, a spline portion 29 is provided on the inner peripheral surface of the center hole 34 of the inner ring 26, and the spline portion 31 of the shaft 30 inserted into the center hole of the inner ring 26 is engaged. A concave circumferential groove 32 is formed at the end of the spline portion 31 of the shaft 30, and a retaining ring 33 for preventing the shaft from slipping is fitted into the concave circumferential groove 32.

  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.

  As shown in FIGS. 2 and 3, a forged finish hardened layer 35 is formed on the entire outer peripheral surface of the inner ring 26. In this case, steel containing 0.4 wt% or more of carbon is used for the inner ring 26, and the track grooves 25 of the inner ring 26 are formed by forging (cold forging), and thereafter, the high frequency is applied to the entire outer periphery of the inner ring 26. Quenching will be performed. For this reason, a forged finish hardened layer 35 is formed on at least the surface of the track groove 25 of the inner ring 26. That is, the forged finish hardened layer is a surface layer that leaves the forged skin as it is, and is a layer that is not subjected to finishing such as grinding. Here, induction hardening is performed by causing induction current to be generated in the surface portion of the derivative (workpiece) by flowing a high frequency to generate heat, and the surface of the work piece is rapidly heated by this heat for quenching. Is the method. In this case, the high-frequency heating temperature is preferably 900 ° C. or higher and 1100 ° C. or lower. In addition, in FIG. 3, illustration of the spline part 29 formed in the center hole 34 of the inner ring | wheel 26 is abbreviate | omitted.

  In this case, the grain boundary oxide layer of the hardened layer 35 to be formed is 1 μm or less by this induction hardening. The grain boundary oxide layer can be 1 μm or less by setting the heating temperature as described above. The optimum thickness of the hardened layer 35 varies depending on the internal dimension values such as the ball diameter and track PCD diameter used in the constant velocity universal joint.

  Further, the surface portion of the hardened layer 35 is not clear because the prior austenite grain boundary does not appear clearly as shown in FIG. 4 by performing induction hardening as described above.

  According to the present invention, since the grain boundary oxide layer of the hardened layer is 1 μm or less, the rolling life is not reduced even in this state. For this reason, it is not necessary to perform a grinding process or the like for removing the grain boundary oxide layer, and it is possible to improve productivity and reduce costs. If the grain boundary oxide layer exceeds 1 μm, the rolling life (the groove life of the track groove) may be reduced unless the grain boundary oxide layer is removed.

  Further, since the prior austenite grain boundaries in the surface portion of the hardened layer 35 are obscured, grain boundary oxidation and corrosion can be prevented, and the life can be further increased. Moreover, the induction hardening can shorten the cycle time compared to the carburizing and quenching.

  In particular, steel containing 0.4 wt% or more of carbon is an optimal material for induction hardening that can suppress the grain boundary oxide layer to 1 μm or less, and the inner ring 26 using this material has a grain boundary oxide layer of 1 μm. The following forged finish hardened layer 35 can be reliably formed.

  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 the above-described embodiment, the groove surface of the track groove 25 of the inner ring 26 and the inner ring Although the hardened layer 35 is formed on the outer diameter surface 26 (outer diameter surface other than the track groove 25), the hardened layer 35 may be formed at least on the groove surface of the track groove 25. This is because the ball 27 rolls into the track groove 25.

  As the constant velocity universal joint, the fixed type (Zepper type) constant velocity universal joint (BJ) has been exemplified in the above embodiment, but other constant velocity universal joints, for example, the fixed type (undercut free type) constant velocity universal joint. (UJ), a sliding type (cross groove type) constant velocity universal joint (LJ), a sliding type (double offset type) constant velocity universal joint (DOJ), etc. may be sufficient.

It is principal part sectional drawing of the constant velocity universal joint which shows embodiment of this invention. It is a longitudinal cross-sectional view of the inner ring | wheel of the said constant velocity universal joint. It is a cross-sectional view of the constant velocity universal joint. It is an enlarged view of the hardened layer at the time of performing induction hardening. It is an enlarged view of the hardened layer at the time of carburizing and quenching. It is principal part sectional drawing of the conventional constant velocity universal joint.

Explanation of symbols

21 Inner surface 22, 25 Track groove 24 Outer surface 27 Ball 28 Cage 35 Hardened layer

Claims (3)

An outer joint member having a plurality of track grooves formed on the inner diameter surface, an inner joint member having a plurality of track grooves formed on the outer diameter surface, and between the track grooves of the outer joint member and the track grooves of the inner joint member. In a constant velocity universal joint comprising a plurality of balls that transmit torque by being interposed therebetween, and a cage that holds the balls interposed between an inner diameter surface of the outer joint member and an outer diameter surface of the inner joint member,
A constant velocity universal joint characterized in that a forged finish hardened layer having a grain boundary oxide layer of 1 μm or less is provided at least on the surface of the track groove of the inner joint member.   The hardened layer is an induction-hardened hardened layer formed on the groove surface of the track groove and the outer diameter surface of the inner joint member between the track grooves, and the old austenite grain boundaries on the surface portion of the hardened layer are obscured. The constant velocity universal joint according to claim 1.   The constant velocity universal joint according to claim 1 or 2, wherein the inner joint member is steel containing 0.4 wt% or more of carbon.

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