JP2016114082A - Fixed type constant velocity joint - Google Patents

Abstract

In an inner member 14 constituting a fixed type constant velocity joint, a portion of a portion (high surface pressure portion) to which a large stress is applied is increased in hardness and strength, and a tooth of a fitting hole into which a rotating shaft is fitted. Ensure the static fracture strength of the part. An inner side ball groove is formed on an inner member to allow a torque transmitting ball to roll. A side wall portion 28 is interposed between the inner side ball grooves 26. Each side wall portion 28 is formed with a lightening portion such as a groove 34. From the surface of the high surface pressure portion 36 where a large stress is applied from the torque transmitting ball 16 to the surface of the groove 34, the first hardened layer 38 is integrally connected. On the other hand, the second hardened layer 40 is formed in the inner member 14 from the inner peripheral wall surface of the fitting hole 30. The thickness T1 of the first cured layer 38 is set to be larger than the thickness T2 of the second cured layer 40. [Selection] Figure 4

Description

  The present invention relates to a fixed type constant velocity joint, and more particularly to a fixed type constant velocity joint including a ball for transmitting a rotational driving force from an outer member to an inner member or in the opposite direction.

  BACKGROUND ART A traveling driving force transmission mechanism of an automobile includes two constant velocity joints as joints that transmit a rotational driving force from a rotating shaft to another rotating shaft. In general, one of the two constant velocity joints is a sliding type in which the rotation axis can be displaced along the longitudinal direction of the bottomed hole formed in the outer member. The remaining one is a fixed type in which the rotation axis can be inclined in the bottomed hole. The sliding type constant velocity joint is arranged on the side close to the driving force generation source such as the internal combustion engine or the motor, and the fixed type constant velocity joint is arranged on the side close to the wheel.

  This type of fixed type constant velocity joint includes an outer member having a bottomed hole, an inner member inserted into the bottomed hole while being externally fitted to a drive shaft that is a rotating shaft, and a driving force generation source. And a torque transmission ball for transmitting the rotational driving force transmitted from the inner member to the outer member or vice versa. As shown schematically in FIG. 10, an inner side ball groove 3 is formed between the side wall portions 2 of the inner member 1a. Although not shown, an outer side ball groove is formed in the outer member, and the torque transmission ball 4 is inserted into the outer side ball groove and the inner side ball groove 3. In practice, a retainer for holding the ball by the window is interposed between the outer member and the inner member 1a.

  The torque transmitting ball 4 slides along the outer side ball groove and the inner side ball groove 3 as the hub that is the rotation shaft is inclined. The fixed type constant velocity joint rotates in the direction of arrow A following the rotation of the drive shaft. At this time, for example, as indicated by an arrow X in FIG. 10, a force is applied from the torque transmission ball 4 to the sliding surface of the inner side ball groove 3. In particular, a relatively large stress is applied to the portion indicated by hatching in FIG. Hereinafter, the hatched portion is referred to as a “high surface pressure portion”, and its reference number is 5.

  If the high surface pressure portion 5 has low strength, there is a concern that cracks or chips may be generated by the force applied from the torque transmission ball 4. In order to eliminate this concern, surface hardening treatment such as carburizing, nitriding, and carbonitriding is performed on the inner member 1a formed by forging. As a result, a hardened layer such as a carbonized layer, a nitrided layer, or a carbonitrided layer is formed on the entire surface of the inner member 1a. As a result, the high surface pressure portion 5 is increased in strength and hardness.

  By the way, the inner member 1a is formed with a fitting hole 6 for fitting the drive shaft. Tooth portions are formed on the inner peripheral wall of the fitting hole 6 and the side peripheral wall of the drive shaft, and the inner member 1a is externally fitted to the drive shaft by engaging these tooth portions.

  When the depth of the hardened layer in the tooth portion in the fitting hole 6 is excessively increased (in other words, when the tooth portion is excessively hardened), the static fracture strength of the tooth portion is decreased. That is, if the time of the surface hardening treatment is increased to increase the depth of the hardened layer in the high surface pressure portion 5, the static fracture strength of the tooth portion in the fitting hole 6 is reduced. When the time of the surface hardening treatment is shortened to avoid this, a hardened layer having a sufficient depth is formed on the high surface pressure portion 5 (the high surface pressure portion 5 is sufficiently increased in strength and hardness) ) Is not easy. As a result, it is difficult to increase the static fracture strength of the tooth portion in the fitting hole 6 while increasing the strength and hardness of the high surface pressure portion 5.

  In Patent Document 1, as shown in FIG. 12, in order to allow elastic deformation in the circumferential direction of the side wall 2 of the inner member 1b, a slit 7 extending along the thickness direction of the inner member 1b is formed. It is described. In this case, when the surface hardening process is performed on the inner member 1b, the hardened layer 8 is formed in a portion indicated by hatching in FIG. 13 which is a cross-sectional view along a direction orthogonal to the thickness direction.

  Accordingly, when the Vickers hardness is measured from the surface of the high surface pressure portion 5 of the inner side ball groove 3 toward the inside, that is, along the depth direction (arrow Y in FIG. 13), it gradually increases as shown in FIG. Reduction. And in the site | part which the hardening | curing agent has not spread | diffused, compared with the hardened layer 8, it becomes still lower hardness. In the tooth portion, the depth and the Vickers hardness are substantially the same.

  Further, in Patent Document 2, in order to reduce the weight, a hollow portion 9 having a substantially circular cross section that penetrates along the thickness direction of the inner member 1c is provided with a fitting hole 6 and a side wall portion as shown in FIG. It is proposed to form between the two. When surface hardening treatment is performed on the inner member 1c having such a shape, the hardened layer 8 is formed in a portion indicated by hatching in FIG. 16 which is a cross-sectional view along a direction orthogonal to the thickness direction.

JP 2012-149754 A JP 2007-139064 A

  As understood from FIGS. 13 and 16, the depth of the hardened layer in the high surface pressure portion is increased while merely increasing the static fracture strength of the tooth portion in the fitting hole only by forming the hollow portion or slit. It is difficult to make this sufficiently large.

  The present invention has been made to solve the above-described problems, and includes an inner member in which the high contact pressure portion is sufficiently increased in strength and hardness and the static fracture strength of the tooth portion in the fitting hole is large. An object of the present invention is to provide a fixed type constant velocity joint.

In order to achieve the above object, the present invention provides an outer member having a bottomed hole, an inner member inserted into the bottomed hole of the outer member with a rotation shaft fitted into the fitting hole, A plurality of outer side ball grooves that are interposed between the outer member and the inner member and are recessed in the inner wall of the bottomed hole, and a plurality of inner portions that are recessed in the side wall of the inner member In a fixed type constant velocity joint having a plurality of torque transmission balls inserted into each of the side ball grooves and a retainer for holding the torque transmission balls,
A side wall portion between the inner side ball grooves of the inner member is formed with a lightening portion extending from the lower end surface to the upper end surface of the side wall portion,
A first hardened layer is formed which is continuous from the surface of the inner-side ball groove to the surface of the lightening portion,
And a second hardened layer is formed on the inner peripheral wall surface of the fitting hole of the inner member,
The thickness of the first hardened layer from the surface of the inner side ball groove to the surface of the lightening portion is larger than the thickness of the second hardened layer.

  That is, in the inner member constituting the fixed type constant velocity joint according to the present invention, the first hardened layer having a sufficient thickness is formed on the side wall portion. For this reason, since the high surface pressure portion and the vicinity thereof are sufficiently increased in hardness and strength, the concern that cracks and chips are generated in the high surface pressure portion is eliminated.

  On the other hand, the thickness of the second hardened layer formed from the inner peripheral wall (tooth portion) surface of the fitting hole toward the inside of the inner member is smaller than the thickness of the first hardened layer. For this reason, the balance between hardness and toughness is achieved on the inner peripheral wall (tooth portion) of the fitting hole. Therefore, sufficient static fracture strength is ensured in the tooth portion.

  For the reasons described above, an inner member that exhibits excellent durability and has a long life can be formed.

  Generally, the high surface pressure portion is located outside a virtual circle connecting the bottom portions of the plurality of inner side ball grooves. Therefore, it is preferable to form the thinned portion outside the virtual circle. This is because the first hardened layer can be easily formed in the high surface pressure portion and the vicinity thereof.

  Moreover, it is preferable to form the thinned portion so as to extend substantially parallel to the thickness direction of the inner member. In this case, the first hardened layer is formed over the entire thickness direction of the inner member. Therefore, the load (stress) from the torque transmitting ball can be received substantially evenly by the first hardened layer. For this reason, durability of a high surface pressure part and its vicinity improves further.

  What is necessary is just to form a lightening part as a groove | channel opened on the outer peripheral side of the side wall part, for example. In this case, it is easy to form the grooves at the same time in the molding step (for example, forging) for producing the inner member. That is, since it is not necessary to form the groove in a separate process from the inner member forming step, the inner member can be easily formed without increasing the cost.

  According to the present invention, a first hardened layer having a sufficient thickness is formed on the side wall portion of the inner member, and the first hardened layer is formed in a direction from the inner peripheral wall (tooth portion) surface of the fitting hole toward the inside of the inner member. A second hardened layer having a thickness smaller than that of the second hardened layer is formed. For this reason, the inner member has a high surface pressure portion and its vicinity sufficiently hardened and strengthened, and the inner peripheral wall (tooth portion) of the fitting hole has a balance between hardness and toughness. .

  Therefore, the concern that cracks and chips occur in the high surface pressure portion is eliminated, and sufficient static fracture strength is secured in the tooth portion. That is, with the above configuration, an inner member having excellent durability and long life can be obtained.

1 is a schematic overall front view of a fixed type constant velocity joint according to an embodiment of the present invention. It is a top view of the inner member which comprises the fixed type | mold constant velocity joint of FIG. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. It is the graph which showed the change of the Vickers hardness in the depth direction which goes to the side wall of the groove | channel which is a thinning part from the high surface pressure part which is a part of inner side ball groove. It is the graph which showed the change of the Vickers hardness of the direction which goes to the inside of an inner member from the inner peripheral wall of the fitting hole of an inner member. It is a top view of the inner member which comprises the fixed type | mold constant velocity joint which concerns on another embodiment. FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 7. FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. It is a principal enlarged view of a general fixed type constant velocity joint. It is the principal part schematic enlarged view which showed the site | part which a stress acts on by hatching. 5 is a plan view of an inner member that constitutes a fixed type constant velocity joint described in Patent Document 1. FIG. It is sectional drawing which follows the direction (width direction) orthogonal to the thickness direction of the inner member shown in FIG. It is the graph which showed the change of the Vickers hardness of the direction which goes to the inside from the surface in the side wall part of the inner member shown in FIG. 6 is a plan view of an inner member constituting a fixed type constant velocity joint described in Patent Document 2. FIG. It is sectional drawing which follows the direction (width direction) orthogonal to the thickness direction of the inner member shown in FIG.

  Preferred embodiments of the fixed type constant velocity joint according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic front view of a fixed type constant velocity joint 10 according to the present embodiment. The fixed type constant velocity joint 10 includes an outer member 12, an inner member 14, a torque transmission ball 16 interposed between the outer member 12 and the inner member 14, and a retainer 18 that holds the torque transmission ball 16. It has.

  The outer member 12 has a shaft portion (none of which is shown) to which the hub is connected, and a cup portion 22 in which a bottomed hole 20 is formed. On the curved inner wall of the bottomed hole 20, six outer side ball grooves 24 that are spaced apart from each other at equal angles are recessed and formed.

  On the other hand, the inner member 14 is formed with the same number of inner side ball grooves 26 as the outer side ball grooves 24 so as to cut out the outer peripheral surface curved so as to bulge outward in the diameter direction. Hereinafter, a space between adjacent inner side ball grooves 26 and 26 is referred to as a “side wall portion”, and a reference numeral 28 is used as the reference.

  Further, a fitting hole 30 is formed through the inner member 14 along the thickness direction thereof. The fitting hole 30 is fitted with a tip of a drive shaft 32 connected to the output side of the engine (not shown). On the inner wall of the fitting hole 30 and the tip of the drive shaft 32, tooth portions (not shown) are engraved. The inner member 14 is externally fitted to the distal end portion of the drive shaft 32 by engaging these tooth portions with each other.

  Here, a plan view of the inner member 14 is shown in FIG. As shown in FIG. 2, the side wall portion 28 of the inner member 14 is formed with a groove 34 (thickening portion) extending from the lower end surface of the side wall portion 28 to the upper end surface. That is, the groove 34 extends substantially parallel to the thickness direction of the inner member 14 and opens on the outer peripheral side of the side wall 28.

  The bottom wall of the groove 34 facing the fitting hole 30 side is located on the outer peripheral side of the virtual circle C <b> 1 that connects the bottom walls of the inner side ball groove 26. In addition, as shown in FIG. 3 which is a cross-sectional view taken along the line III-III in FIG. 2, chamfering is performed between the groove 34 and the lower end surface and the upper end surface of the inner member 14.

  The groove 34 is set wider than the slit 7 (see FIGS. 12 and 13) in the prior art described in Patent Document 1. For this reason, the distance from the inner side ball groove 26 (high surface pressure portion 36) to the side wall of the groove 34, that is, the thickness T0 of the side wall portion 28 is small. Accordingly, it becomes easy for a curing agent (a carburizing agent, a nitriding agent, a carbonitriding agent, etc.) to permeate or diffuse into the side wall portion 28 during the surface hardening treatment.

  4 is a cross-sectional view taken along line IV-IV in FIG. 3, that is, a cross-sectional view in a direction (width direction) orthogonal to the thickness direction of the inner member 14. The hatched portion indicates that the first cured layer 38 and the second cured layer 40 are formed.

  When the narrow slit 7 is formed as described in Patent Document 1, the hardened layer 8 is formed only in the vicinity of the surface of the high surface pressure portion 5 and the surface of each wall in the slit 7. It is not connected in the vicinity of the part 5 and the slit 7 (see FIG. 13). On the other hand, in the inner member 14, as can be seen from FIG. 4, the first hardened layer 38 surrounds the groove 34. That is, in this case, the first hardened layer 38 is integrally connected from the surface of the high surface pressure portion 36 that is the surface of the inner side ball groove 26 to the surface of the inner wall of the groove 34.

  Thus, in the present embodiment, the first hardened layer 38 is formed deep inside the side wall portion 28 and has a sufficient thickness for this purpose. This is because the curing agent can easily penetrate or diffuse into the side wall portion 28 as described above. As a result, the high surface pressure portion 36 is sufficiently hardened, and thus the strength is increased. That is, it is difficult for cracks and chips to occur in the high surface pressure portion 36.

  FIG. 5 is a graph showing changes in Vickers hardness in the depth direction (in the direction of arrow Y in FIG. 4) from the high surface pressure portion 36 toward the side wall of the groove 34. The Vickers hardness is minimum at approximately the middle between the high surface pressure portion 36 and the side wall of the groove 34, and is maximum at the high surface pressure portion 36 and the side wall of the groove 34. That is, the hardness of the first hardened layer 38 decreases from the inner wall surface of the inner side ball groove 26 and the groove 34 toward the inside. Accordingly, the hardness curve is substantially V-shaped.

  On the other hand, the thickness T2 of the second hardened layer 40 formed on the inner peripheral wall (tooth portion) of the fitting hole 30 is smaller than the thickness T1 of the first hardened layer 38 formed on the side wall portion 28. For this reason, when the Vickers hardness is measured from the inner peripheral wall surface of the fitting hole 30 toward the inside, it gradually decreases toward the inside as shown in FIG. Therefore, the balance between hardness and toughness can be achieved. As a result, sufficient static fracture strength is secured in the tooth portion.

  In short, the thickness T1 of the first hardened layer 38 from the surface of the high surface pressure portion 36 to the surface of the inner wall of the groove 34 is sufficiently larger than the thickness T2 of the second hardened layer 40. The thicknesses T1 and T2 of the first hardened layer 38 and the second hardened layer 40 are defined as regions that exceed a predetermined Vickers hardness set in advance. In other words, the thicknesses T1 and T2 are effective hardened layer depths. In addition, the suitable range of thickness T1 is about 2-3 mm, and the suitable range of thickness T2 is about 1-2 mm.

  The retainer 18 positioned on the outer peripheral side of the inner member 14 has a substantially annular shape. The inner diameter of the retainer 18 is slightly larger than the outer diameter of the side wall 28 in the inner member 14. For this reason, the inner member 14 can be easily inserted inward of the retainer 18, and is accommodated in the bottomed hole 20 in this state (see FIG. 1).

  A plurality of windows 42 penetrating from the inner peripheral wall to the outer peripheral wall are formed in the retainer 18. The torque transmission ball 16 is accommodated in the window 42 and is inserted into the outer side ball groove 24 and the inner side ball groove 26.

  The fixed type constant velocity joint 10 according to the present embodiment is basically configured as described above. Next, the function and effect of the fixed type constant velocity joint 10 are related to the operation of the fixed type constant velocity joint 10. explain.

  The fixed type constant velocity joint 10 configured as described above is a joint that transmits a rotational driving force from a drive shaft 32 that is a driving rotating shaft to the hub that is a driven rotating shaft in a traveling driving force transmitting mechanism of an automobile. Preferably employed.

  While the automobile is traveling, the driver may perform a snake by operating the steering wheel. At this time, when the hub is inclined with respect to the extending direction of the drive shaft 32, the outer member 12 is inclined following this. At the same time, the torque transmitting ball 16 rolls while slidingly contacting the walls of the two ball grooves 24 and 26, and the inner member 14 and the retainer 18 are inclined at a predetermined angle. Further, while the automobile is traveling, the fixed type constant velocity joint 10 rotates together with the drive shaft 32 and the hub.

  With the above operation, a force is applied from the torque transmission ball 16 to the sliding surface of the inner side ball groove 26. In particular, a relatively large stress is applied to the high surface pressure portion 36.

  However, in the inner member 14 constituting the fixed type constant velocity joint 10 according to the present embodiment, the first hardened layer that is integrally connected from the high surface pressure portion 36 located on the outer peripheral side of the virtual circle C1 to the side wall portion 28. 38 is formed. For this reason, since the high surface pressure portion 36 is sufficiently hardened and strengthened, the concern that cracks and chips occur in the high surface pressure portion 36 is eliminated.

  Moreover, although the second hardened layer 40 is formed on the inner peripheral wall of the fitting hole 30, the thickness T2 of the second hardened layer 40 is sufficiently smaller than the thickness T1 of the first hardened layer 38. Therefore, hardness and toughness are balanced in the tooth portion. Therefore, sufficient static fracture strength is ensured in the tooth portion.

  As described above, in the inner member 14, the high surface pressure portion 36 on the outer peripheral side of the virtual circle C1 is sufficiently increased in strength and hardness, and the fitting hole is on the inner peripheral side of the virtual circle C1. The tooth part in 30 shows a large static fracture strength. That is, the inner member 14 exhibits excellent durability and a long life.

  The inner member 14 can be produced by forging, for example. The groove 34 may be formed simultaneously with this forging process. Since the groove 34 can be formed in a shape in which the side wall portion 28 is depressed from the outer peripheral side to the inner peripheral side, it can be easily formed by forging.

  Thereafter, the inner member 14 is subjected to a surface hardening process. That is, for example, the inner member 14 is accommodated in the processing furnace, the temperature is raised to a predetermined temperature, and a carburizing gas (carburizing agent) or the like is introduced into the processing furnace. The carburizing gas enters the inner side ball groove 26, the fitting hole 30 and the groove 34, and further, the inner wall surface of the inner side ball groove 26, the inner peripheral wall surface of the fitting hole 30, and the inner wall surface of the groove 34. Enters the inner member 14.

  Since the wall thickness T <b> 0 of the side wall portion 28 is small, the carburizing gas that has entered the inner member 14 from the surfaces of the inner ball grooves 26 and the grooves 34 easily enters and diffuses into the side wall portion 28. Accordingly, the first hardened layer 38 having a sufficient thickness T1 is formed on the side wall portion 28. On the other hand, the wall thickness T0 from the fitting hole 30 to the inner side ball groove 26 or the side wall part 28 is large. For this reason, in the same processing time, the thickness T2 of the second cured layer 40 is smaller than the thickness T1 of the first cured layer 38.

  In this way, by forming the sufficiently wide groove 34 in the side wall portion 28, the long-life inner member 14 exhibiting excellent durability can be easily obtained.

  Note that a nitriding agent may be used instead of the carburizing agent, and nitriding may be performed as the surface hardening treatment. The nitridation may be a dry process using a nitriding gas or a wet process such as an ion nitriding process. Carbonitriding can also be performed as a surface hardening treatment.

  Further, the thinned portion may be the through hole 50 shown in FIGS. Hereinafter, the inner member 52 in which the through hole 50 is formed will be described. In addition, the same reference number is attached | subjected to the component same as the component shown in FIGS. 1-6, and the detailed description is abbreviate | omitted.

  As shown in FIG. 8, the through hole 50 opens at the lower end surface and the upper end surface of the inner member 52. In other words, the through hole 50 extends from the lower end surface of the inner member 52 to the upper end surface. Further, in the vicinity of the opening of the through hole 50, a large chamfer is formed on the side facing the side wall portion 28 and a small side on the side facing the fitting hole 30.

  Also in this case, the position of the through hole 50 is preferably formed on the outer peripheral side of the virtual circle C1 that connects the bottoms of the inner side ball grooves 26 to each other. This is because the portion (high surface pressure portion 36) to be increased in hardness and strength is located on the outer peripheral side of the virtual circle C1.

  Also in the inner member 52, since the through hole 50 is formed, the thickness T0 'of the side wall portion 28 is small. For this reason, during the surface hardening treatment, carburizing agent, nitriding agent, carbonitriding agent and the like easily enter and diffuse from the surface of each wall of the inner side ball groove 26 and the through hole 50 into the side wall portion 28.

  For this reason, as shown in FIG. 9 which is a cross-sectional view in the direction orthogonal to the thickness direction of the inner member 52 (a cross-sectional view taken along line IX-IX in FIG. 8), the through hole 50 is surrounded in the side wall portion 28. Thus, the first hardened layer 54 is formed. Eventually, the first hardened layer 54 is integrally connected from the surface of the high surface pressure portion 36 to the surface of the inner wall of the through hole 50. That is, even in this case, the first hardened layer 54 is formed deep inside the side wall 28 and has a sufficient thickness.

  On the other hand, similarly to the above, the thickness T1 ′ of the first hardened layer 54 from the surface of the high surface pressure portion 36 to the surface of the inner wall of the through hole 50 is equal to the thickness T2 ′ of the second hardened layer 56. Larger than that. For the above reasons, the inner member 52 also has a sufficiently high hardness and high strength in the high surface pressure portion 36, so that it is difficult for the high surface pressure portion 36 to be cracked or chipped. Moreover, the tooth | gear part in the fitting hole 30 shows big static fracture strength. Eventually, the inner member 52 having excellent durability and long life is formed.

  The present invention is not particularly limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1a-1c, 14, 52 ... Inner member 2, 28 ... Side wall part 3, 26 ... Inner side ball groove 4, 16 ... Torque transmission ball | bowl 5, 36 ... High surface pressure part 6, 30 ... Fitting hole 7 ... Slit 8 ... Hardened layer 9 ... Thinned portion 10 ... Fixed type constant velocity joint 12 ... Outer member 18 ... Retainer 20 ... Bottomed hole 24 ... Outer side ball groove 32 ... Drive shaft 34 ... Groove 38, 54 ... First hardened layer 40, 56 ... 2nd hardened layer 50 ... Through-hole C1 ... Virtual circle

Claims (4)

An outer member having a bottomed hole, an inner member having a rotation shaft fitted in the fitting hole and inserted into the bottomed hole of the outer member, and an intermediate member between the outer member and the inner member And a plurality of outer side ball grooves recessed in the inner wall of the bottomed hole and a plurality of torques inserted in each of the plurality of inner side ball grooves recessed in the side wall of the inner member. In a fixed type constant velocity joint having a transmission ball and a retainer for holding the torque transmission ball,
A side wall portion between the inner side ball grooves of the inner member is formed with a lightening portion extending from the lower end surface to the upper end surface of the side wall portion,
A first hardened layer is formed which is continuous from the surface of the inner-side ball groove to the surface of the lightening portion,
And a second hardened layer is formed on the inner peripheral wall surface of the fitting hole of the inner member,
The fixed type constant velocity joint, wherein the thickness of the first hardened layer from the surface of the inner side ball groove to the surface of the cutout portion is larger than the thickness of the second hardened layer. .   2. The fixed type constant velocity joint according to claim 1, wherein the lightening portion is located outside a virtual circle connecting the bottoms of the inner side ball grooves. 3.   3. The fixed type constant velocity joint according to claim 1, wherein the lightening portion extends substantially parallel to a thickness direction of the inner member.   The fixed type constant velocity joint according to any one of claims 1 to 3, wherein the lightening portion is a groove opened on an outer peripheral side of the side wall portion.

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