JP2008196635A - Fixed type constant velocity universal joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve torque transmission efficiency by sufficiently interlaying a lubricant between balls and track grooves to reduce frictional force. <P>SOLUTION: This fixed type constant velocity universal joint is provided with: an outer ring 12 having a plurality of axially-extending track grooves 11 formed thereon; an inner ring 15; a plurality of balls 16 interlaid between the inner and outer rings 15 and 12 and transmitting torque; and cages 17 holding the balls 16. The centers of curvature of the track grooves 14 and 11 of the inter ring 15 and the outer ring 12 are oppositely offset in the axial direction by an equal distance with respect to the joint center; multiple minute recessed parts are formed on the surface of each ball 16 in a random manner; and a PCD gap 2×m in a ball track formed by the track grooves 14 and 11 of the inner and outer rings 15 and 12, a spherical surface gap 2×n<SB>1</SB>between the outer spherical surface 13 of the inner ring 15 and the inner spherical surface 19 of the cage 17, and a spherical surface gap 2×n<SB>2</SB>between the outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12 are set not smaller than 25 μm, not smaller than 40 μm and not smaller than 40 μm, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixed type constant velocity universal joint that is used, for example, in a power transmission system of an automobile or various industrial machines and allows only an operating angle displacement between two axes of a driving side and a driven side.

  For example, there is a fixed type constant velocity universal joint as a kind of constant velocity universal joint used as means for transmitting rotational force from an engine of an automobile to wheels at a constant speed. 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.

  15, 16, 17, and 18 illustrate two examples of, for example, a Barfield type constant velocity universal joint. These constant velocity universal joints are paired with an outer ring 112 as an outer joint member in which a plurality of track grooves 111 extending in the axial direction are formed at equal intervals in the circumferential direction of the inner spherical surface 110, and the track grooves 111 of the outer ring 112. A plurality of track grooves 114 extending in the axial direction are formed between the inner ring 115 as an inner joint member formed at equal intervals in the circumferential direction of the outer spherical surface 113, and interposed between the track grooves 111 of the outer ring 112 and the track grooves 114 of the inner ring 115. Thus, a plurality of balls 116 that transmit torque, and a cage 117 that is interposed between the inner spherical surface 110 of the outer ring 112 and the outer spherical surface 113 of the inner ring 115 and holds the balls 116 are provided.

The track grooves 111 and 114 in this constant velocity universal joint have a single circular arc surface shape in the longitudinal section in the axial direction. The center of curvature O ₁ of the track groove 111 of the outer ring 112 and the center of curvature O ₂ of the track groove 114 of the inner ring 115 are offset in the axial direction by an equal distance F and f with respect to the joint center O including the ball center O _3. (Track offset). The center of curvature of the inner spherical surface 110 of the outer ring 112 (outer spherical surface 118 of the cage 117) and the center of curvature of the outer spherical surface 113 of the inner ring 115 (inner spherical surface 119 of the cage 117) coincide with the joint center O described above. Thus, by providing the track offset, the pair of track grooves 111 and 114 form a ball track in a wedge shape in which the radial interval gradually increases from the back side of the outer ring 112 toward the opening side.

  When this type of constant velocity universal joint is used for, for example, a drive shaft of an automobile, the outer ring 112 is connected to a driven shaft, and the drive shaft extends from a sliding type constant velocity universal joint attached to the inner ring 115 on a differential on the vehicle body side. A structure in which the two are connected by spline fitting is generally used. In this constant velocity universal joint, when an operating angle is applied between the outer ring 112 and the inner ring 115, the ball 116 accommodated in the cage 117 is always within the bisector of the operating angle at any operating angle. This maintains the constant velocity of the joint.

  The plurality of balls 116 are accommodated in pockets 120 formed in the cage 117 and arranged at equal intervals in the circumferential direction. The constant velocity universal joint shown in FIGS. 15 and 16 has a structure with six balls 116, and the constant velocity universal joints shown in FIGS. 17 and 18 have a structure with eight balls 116. Eight-ball type constant velocity universal joints have higher efficiency by reducing ball diameter (d <D) and track offset (f <F) than six-ball type constant velocity universal joints. Realizes a compact constant velocity universal joint.

FIG. 19 shows a state where a six-ball type constant velocity universal joint has an operating angle (for example, 40 °). Similarly, FIG. 20 shows an eight-ball type constant velocity universal joint having an operating angle (for example, 40 °). Indicates the state of taking. As indicated by a broken line in FIG. 19, L6 _IN indicates a contact point locus between the inner ring 115 and the ball 116 due to the angular contact, and L6 _OUT indicates a contact point locus between the outer ring 112 and the ball 116 due to the angular contact. Further, as indicated by the broken line in FIG. 20, L8 _IN indicates a contact point locus between the inner ring 115 and the ball 116 due to the angular contact, and L8 _OUT indicates a contact point locus between the outer ring 112 and the ball 116 due to the angular contact.

In the eight-ball type constant velocity universal joint shown in FIG. 20, the length of the contact point locus L8 _IN between the inner ring 115 and the ball 116 and the outer ring 112 and the ball are reduced by reducing the ball diameter as shown in FIG. the length of the contact point trace L8 _OUT 116 is shorter than the constant velocity universal joint of the six ball type _{(L8 iN <L6 iN, L8} OUT <L6 OUT), in between the track grooves 111 of the outer ring 112 and the ball 116 Sliding speed is reduced and torque transmission efficiency is improved.

In the eight ball type constant velocity universal joint, the length of the contact point locus L8 _IN between the inner ring 115 and the ball 116 and the outer ring 112 are reduced by reducing the track offset (f <F) as shown in FIG. And the contact point locus L8 _OUT of the ball 116 is shorter than the six-ball type constant velocity universal joint (L8 _IN <L6 _IN , L8 _OUT <L6 _OUT ), and between the track groove 111 of the outer ring 112 and the ball 116 The slip speed at the time is reduced, and the torque transmission efficiency is improved.

  In addition, in the eight ball type constant velocity universal joint (see FIG. 17), by reducing the track offset, the sandwich angle γ8 of the ball 116 with respect to the track grooves 111 and 114 is six ball type constant velocity universal joint (see FIG. 17). 15) (γ8 <γ6), and the force M8 for pushing the ball 116 toward the outer ring opening side in the axial direction decreases (M8 <M6).

  Here, the sandwiching angles γ6 and γ8 of the balls 116 with respect to the track grooves 111 and 114 are the contact points between the track grooves 111 of the outer ring 112 and the track grooves 114 of the inner ring 115 and the balls 116 (see the broken lines in FIGS. 15 and 17). ) Means an angle formed by two tangents in the axial direction. 15 and 17, the broken line in the ball 116 indicates the contact point locus between the ball 116 and the track grooves 111 and 114 due to the angular contact.

  The force M8 for pushing the ball 116 in the axial direction toward the outer ring opening is transmitted to the cage 117. As a result, in the eight ball type constant velocity universal joint, the outer spherical surface 118 of the cage 117, the inner spherical surface 110 of the outer ring 112, and the cage. The spherical force between the inner spherical surface 119 of 117 and the outer spherical surface 113 of the inner ring 115 is smaller than that of the six-ball type constant velocity universal joint, and friction loss (heat generation) at the spherical contact portion is reduced, and torque transmission efficiency is improved. (For example, refer to Patent Documents 1 and 2).

  Furthermore, in order to ensure the operability of this constant velocity universal joint, it is necessary to set a clearance in each part. For example, it is necessary to set a PCD (pitch circle diameter) clearance or a spherical clearance to an appropriate value (for example, And Patent Documents 3 and 4).

  Here, the PCD clearance refers to the PCD of the ball 116 (outer ring PCD) in contact with the track groove 111 of the outer ring 112 and the PCD (inner ring PCD) of ball 116 in contact with the track groove 114 of the inner ring 115. Means the difference. The spherical clearance means a clearance between the outer spherical surface 113 of the inner ring 115 and the inner spherical surface 119 of the cage 117, or a clearance between the outer spherical surface 118 of the cage 117 and the inner spherical surface 110 of the outer ring 112.

The PCD clearance may be caused by the processing accuracy, the operability, and the working torque of the track groove 111 of the inner ring 115 and the track groove 111 of the outer ring 112. It is set in consideration of heat generation due to frictional resistance and fatigue durability. Similarly, the spherical clearance is set in consideration of the processing accuracy, operability, and ease of installation of the outer spherical surface 113 of the inner ring 115 and the inner spherical surface 110 of the outer ring 112.
Japanese Patent No. 3460107 JP-A-9-317784 Japanese Patent Laid-Open No. 2002-323061 JP 2005-188620 A

  By the way, in the 8-ball type constant velocity universal joint disclosed in Patent Documents 1 to 4, the ball diameter and the track offset are reduced, or the PCD clearance and the spherical clearance are set to appropriate values. Various joint functions in constant velocity universal joints are improved.

  That is, in Patent Document 1, by defining the ratio of the pitch circle diameter to the diameter of the ball in the range of 3.3 to 5.0, the constant velocity universal joint is made compact and at the same time, the six ball type constant velocity is achieved. The strength, load capacity and durability equal to or better than those of universal joints are ensured. Further, in Patent Document 2, the ratio between the track offset amount and the length of the line segment connecting the center of the track groove of the outer ring or the center of the track groove of the inner ring and the center of the ball is in the range of 0.069 to 0.121. By stipulating, the constant velocity universal joint is made compact, and at the same time, the strength, load capacity, durability and operating angle equal to or higher than those of the six-ball type constant velocity universal joint are ensured.

  On the other hand, in Patent Document 3, by defining the PCD clearance in the ball track in the range of 5 to 50 μm, the contact ellipse between the ball and the track groove is difficult to protrude from the track groove at high load, and chipping and flaking It is easy to suppress the occurrence of this, and the durability is improved. In Patent Document 4, the ratio of the spherical clearance x1000 between the inner spherical surface of the cage and the outer spherical surface of the inner ring and the cage reference inner diameter (inner ring reference outer diameter) is specified in the range of 0.9 to 2.3. Thus, the bending direction load generated when the operating angle of the joint changes is reduced.

  However, in the 8-ball type constant velocity universal joint, as disclosed in Patent Documents 1 to 4 described above, the ball diameter and track offset are reduced, or the PCD clearance and spherical clearance are set to appropriate values. In this way, various joint functions in constant velocity universal joints have been improved. However, there is a demand for further improvement in torque transmission efficiency without changing the configuration of eight ball type constant velocity universal joints. Has been.

  In this type of constant velocity universal joint, a lubricant is generally enclosed in the outer ring in order to reduce the friction between the ball and the track groove and improve the torque transmission efficiency. However, when the joint rotates, a large pressing force acts on the contact portion between the ball and the track groove, so that it is difficult to form an oil film layer of lubricant on the contact portion, and it is difficult to sufficiently exert the friction force reducing effect. Met.

  Accordingly, an object of the present invention is to provide a fixed type constant velocity that can reduce the frictional force by sufficiently interposing a lubricant between the ball and the track groove without greatly changing the configuration, thereby further improving the torque transmission efficiency. It is to provide a joint.

  As technical means for achieving the aforementioned object, the present invention provides an outer joint member in which a plurality of axially extending track grooves are formed on an inner spherical surface and filled with a lubricant, and a track of the outer joint member. Torque is transmitted by interposing between the track groove of the outer joint member and the track groove of the inner joint member, and the inner joint member in which a plurality of track grooves extending in the axial direction in pairs with the groove are formed on the outer spherical surface A plurality of balls, and a cage for holding the balls interposed between the inner spherical surface of the outer joint member and the outer spherical surface of the inner joint member, and the center of curvature of the track groove of the outer joint member and the track groove of the inner joint member In a fixed type constant velocity universal joint whose center of curvature is offset in the axial direction by an equal distance from the joint center, a large number of minute recesses are randomly formed on the surface of the ball, and the outer joint member The PCD clearance in the ball track formed by the rack groove and the track groove of the inner joint member is 25 μm or more, the spherical clearance between the outer spherical surface of the inner joint member and the inner spherical surface of the cage is 40 μm or more, and the outer spherical surface and the outer side of the cage A spherical clearance between the joint member and the inner spherical surface is 40 μm or more. The number of balls, the number of track grooves on the outer joint member, and the number of track grooves on the inner joint member are preferably eight.

  Here, the PCD clearance means the PCD (outer joint member PCD) of the ball in contact with the track groove of the outer joint member, and the PCD (inner joint member) of the ball in contact with the track groove of the inner joint member. PCD). The spherical clearance means a clearance between the outer spherical surface of the inner joint member and the inner spherical surface of the cage, or a clearance between the outer spherical surface of the cage and the inner spherical surface of the outer joint member.

  In the present invention, since a large number of minute recesses are randomly formed on the surface of the ball, even when a pressing force acts between the ball and the track groove during rotation of the joint, The lubricant that has penetrated into the gap can be interposed in the contact interface between the ball and the track groove to form a good oil film layer. Thereby, friction generated between the ball and the track groove can be reduced.

  Note that the friction coefficient of the above-described lubricant is desirably 0.07 or less. As the lubricant, it is desirable to use urea grease having a consistency of 0-2. If such a lubricant is used, friction generated between the ball and the track groove can be effectively reduced.

  Further, the surface roughness of the ball having a large number of minute recesses is Ra 0.03 to 0.6 μm, preferably Ra 0.05 to 0.15 μm, and the parameter SK value of the ball surface roughness is −1.0 or less, Preferably, it is -4.9 to -1.0, and the ratio of the total area of the minute recesses to the surface area of the ball is 10 to 40%. If the value is set to such a value, the lubricant can be appropriately entered and held in the minute recesses on the surface of the ball, and an oil film layer made of the lubricant can be formed between the ball and the track groove. Thereby, the friction between the ball and the track groove can be effectively reduced.

  In the present invention, by setting the PCD clearance in the ball track to 25 μm or more, preferably 40 to 85 μm, that is, by setting the PCD clearance to be larger than that in the prior art, when the rotational torque is transmitted, the non-load side of the ball track Since the contact of the ball with the part can be reduced, the loss of the transmission torque due to the ball contact with the non-load side part of the ball track can be reduced.

  Further, the spherical clearance between the outer spherical surface of the inner joint member and the inner spherical surface of the cage and the spherical clearance between the outer spherical surface of the cage and the inner spherical surface of the outer joint member are set to 40 μm or more, preferably 50 to 120 μm. In other words, by setting the spherical clearance larger than before, spherical contact between the outer spherical surface of the inner joint member and the inner spherical surface of the cage, and spherical contact between the outer spherical surface of the cage and the inner spherical surface of the outer joint member are achieved. Since it can be reduced, frictional heat generation due to the spherical contact can be reduced, and loss of transmission torque due to the frictional heat generation can be reduced. The spherical clearance needs to be set so as to reliably reduce the spherical contact in consideration of the PCD clearance.

  Further, in the present invention, the pinching angle γ8 with respect to the track groove of the ball located between the track groove of the outer joint member and the track groove of the inner joint member is 8.5 to 12.5 °, and the contact angle of the ball with respect to the track groove It is desirable that α8 be 30 to 38 °.

Here, the sandwiching angle γ8 (see FIG. 1) with respect to the track groove of the ball is a contact point between the track groove 11 of the outer joint member 12 and the track groove 14 of the inner joint member 15 and the ball 16 (see the broken line in FIG. 1). The contact angle α8 (see FIG. 3) of the ball 16 with respect to the track grooves 11 and 14 (refer to FIG. 3) means the ball center O ₃ and each contact point (the clearance in the figure). It means the angle formed by the straight line P passing through the exaggeration), the ball center O ₃ and the straight line Q passing through the joint center O.

  As described above, when the sandwiching angle γ8 of the ball with respect to the track groove is set to 8.5 to 12.5 °, the axial pushing force acting on the ball during torque transmission can be reduced. Accordingly, the contact surface pressure between the cage and the joint members can be suppressed, friction can be reduced, and loss of rotational torque can be reduced. Further, if the contact angle α8 of the ball with respect to the track groove is 30 to 38 °, the durability of the ball riding on the edge of the track groove when high torque is input, the amount of sliding between the track groove of the outer ring and the ball, rolling The contact surface pressure that affects the fatigue life can be in a favorable range.

  The present invention also relates to a Barfield type fixed constant velocity universal joint (BJ) having an outer joint member and an inner joint member having track grooves having a single arcuate surface in the longitudinal direction in the axial direction, The present invention is applicable to both an outer joint member having a track groove having a straight bottom parallel to the direction and an undercut free type fixed constant velocity universal joint (UJ) having an inner joint member.

  According to the present invention, since a large number of minute concave portions are randomly formed on the surface of the ball, an oil film layer made of a lubricant is easily formed between the ball and the track groove. It is possible to reduce friction and improve torque transmission efficiency. Further, the rolling fatigue life of the ball and track groove can be extended.

  Also, by setting the PCD clearance in the ball track to 25 μm or more, it is possible to reduce the contact of the ball with the non-load side portion of the ball track during transmission of rotational torque. Loss of transmission torque due to contact can be reduced.

  Furthermore, the spherical clearance between the outer spherical surface of the inner joint member and the inner spherical surface of the cage, and the spherical clearance between the outer spherical surface of the cage and the inner spherical surface of the outer joint member are 40 μm or more. Since the spherical contact between the outer spherical surface and the inner spherical surface of the cage and the spherical contact between the outer spherical surface of the cage and the inner spherical surface of the outer joint member can be reduced, the frictional heat generated by the spherical contact can be reduced. The loss of the transmission torque resulting from it can be reduced.

  In this way, by forming a large number of minute recesses on the ball surface and setting the PCD clearance and spherical clearance to the appropriate value range, loss of transmission torque due to ball contact and frictional heat generation can be reduced. Without greatly changing the configuration of the constant velocity universal joint, it is possible to reduce the frictional force by sufficiently interposing a lubricant between the ball and the track groove, and to improve the torque transmission efficiency in the constant velocity universal joint.

  An embodiment of a fixed type constant velocity universal joint according to the present invention will be described in detail. The embodiment shown in FIGS. 1 and 2 is a barfield type fixed constant velocity universal joint having an outer joint member having a track groove whose longitudinal section in the axial direction has a single arcuate shape and an inner joint member ( BJ) is illustrated. In addition, as shown in FIG. 14, this invention is an undercut-free fixed type constant velocity universal joint provided with the outer joint member which has the track grooves 21 and 24 which have a straight bottom parallel to an axial direction, and the inner joint member. (UJ) is also applicable, and the same parts as those in FIG. The present invention is also applicable to other fixed type constant velocity universal joints having track groove shapes other than these bar field type and undercut free type.

  The eight-ball type fixed type constant velocity universal joint shown in FIGS. 1 and 2 has an outer ring 12 as an outer joint member in which a plurality of track grooves 11 extending in the axial direction are formed at equal intervals in the circumferential direction of the inner spherical surface 10. An inner ring 15 as an inner joint member in which a plurality of track grooves 14 extending in the axial direction in pairs with the track grooves 11 of the outer ring 12 are formed at equal intervals in the circumferential direction, and the track grooves of the outer ring 12 11 and the track groove 14 of the inner ring 15 are interposed between the eight balls 16 for transmitting torque, and the ball 16 is held between the inner spherical surface 10 of the outer ring 12 and the outer spherical surface 13 of the inner ring 15. And a cage 17.

The track grooves 11 and 14 in this constant velocity universal joint have a single circular arc surface shape in the longitudinal section in the axial direction. The center of curvature O ₁ of the track groove 11 of the outer ring 12 and the center of curvature O ₂ of the track groove 14 of the inner ring 15 are offset in the opposite axial direction by an equal distance f with respect to the joint center O including the ball center O _3. Yes (track offset). The center of curvature of the inner spherical surface 10 of the outer ring 12 (the outer spherical surface 18 of the cage 17) and the center of curvature of the outer spherical surface 13 of the inner ring 15 (the inner spherical surface 19 of the cage 17) coincide with the joint center O described above. Thus, by providing the track offset, the pair of track grooves 11 and 14 form a ball track in a wedge shape in which the radial interval gradually increases from the back side of the outer ring 12 toward the opening side.

  FIG. 3 shows an outer ring 12, an inner ring 15, a ball 16 disposed between the outer ring 12 track groove 11 and the track groove 14 of the inner ring 15, and an inner spherical surface 10 of the outer ring 12 and an outer spherical surface 13 of the inner ring 15. 3 is a cross-sectional view showing the cage 17. As shown in the figure, the cross-sectional shape of the track grooves 11 and 14 has a Gothic arch shape formed with a radius of curvature R larger than the radius (d / 2) of the ball 16. By making the cross-sectional shape of the track grooves 11 and 14 into a Gothic arch shape, the ball 16 is in an angular contact that contacts the track grooves 11 and 14 at two points.

  In FIG. 3, the balls 16 do not come into contact with the track grooves 11 of the outer ring 12 and the track grooves 14 of the inner ring 15 for the purpose of explaining the PCD clearance and the spherical clearance, and the outer spherical surface 18 of the cage 17 The clearances are exaggerated in a state where the inner spherical surface 10 of the outer ring 12 and the inner spherical surface 19 of the cage 17 and the outer spherical surface 13 of the inner ring 15 are not in contact with each other. 12 track grooves 11 and the track groove 14 of the inner ring 15 are in contact with each other, and the outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12 and the inner spherical surface 19 of the cage 17 and the outer spherical surface 13 of the inner ring 15 are in contact with each other. .

  In order to ensure the operability of this constant velocity universal joint, it is necessary to set a clearance in each part. For example, it is necessary to set a PCD (pitch circle diameter) clearance or a spherical clearance to an appropriate value. Further, in order to improve the movement of the ball 16 on the ball track, it is necessary to set the sandwiching angle γ8 (see FIG. 1) and the contact angle α8 (see FIG. 3) of the ball 16 with respect to the track grooves 11 and 14 to appropriate values. is there.

Here, as shown in FIG. 3, the clearance m is in contact with the outer ring PCR (1/2 of the outer ring PCD) of the ball 16 in contact with the track groove 11 of the outer ring 12 and the track groove 14 of the inner ring 15. This is a difference from the inner ring PCR (1/2 of the inner ring PCD) of the ball 16 in the state, and the PCD clearance is twice the radial clearance m. The clearance n ₁ is the difference between the radius of the outer spherical surface 13 of the inner ring 15 and the radius of the inner spherical surface 19 of the cage 17, and the clearance n ₂ is the radius of the outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12. The spherical clearance is twice the radial clearances n ₁ and n ₂ .

Further, the sandwiching angle γ8 (see FIG. 1) of the ball 16 with respect to the track grooves 11 and 14 is the contact point between the track groove 11 of the outer ring 12 and the track groove 14 of the inner ring 15 and the ball 16 (see the broken line in FIG. 1). Means an angle formed by two tangents in the axial direction. In FIG. 1, a broken line in the ball 16 indicates a contact point locus between the ball 16 and the track grooves 11 and 14 due to the angular contact. Further, the contact angle α8 (see FIG. 3) of the ball 16 with respect to the track grooves 11 and 14 is a ball contact center P (in the figure, the ball 16 and the track grooves 11 and 14 are in contact with each other with respect to the center O _{3 of the} ball 16). It means the angle formed between the ball 16 and the track grooves 11 and 14 and the groove bottom center Q of the track grooves 11 and 14.

  When these constant velocity universal joints are used for, for example, a drive shaft of an automobile, an outer ring 12 is connected to a driven shaft, and a drive shaft (shaft) extending from a sliding type constant velocity universal joint attached to a differential on the vehicle body side is provided. The inner ring 15 is connected by spline fitting. In this constant velocity universal joint, when an operating angle is provided between the outer ring 12 and the inner ring 15, the ball 16 accommodated in the cage 17 is always within the bisector of the operating angle at any operating angle. This maintains the constant velocity of the joint.

  The plurality of balls 16 are accommodated in pockets 20 formed in the cage 17 and arranged at equal intervals in the circumferential direction. Similar to the number of balls 16, the number of track grooves 11 and 14 and the number of pockets 20 of the cage 17 are also eight. In this 8-ball type constant velocity universal joint, the ball diameter is reduced (d <D) and the track offset is reduced compared to the 6-ball type constant velocity universal joint (see FIG. 15). (F <F), realizing a compact constant velocity universal joint with high torque transmission efficiency.

  As a result of investigating the effect of the internal configuration of this constant velocity universal joint on torque transmission efficiency by mechanism analysis, if the clearance of each contact portion in the internal configuration is changed, the PCD clearance will contribute to the torque transmission efficiency within a certain range. It has been found that a larger spherical clearance contributes to torque transmission efficiency (see FIG. 4). FIG. 5 shows the degree of contribution to the torque transmission efficiency with respect to changes in the PCD clearance and spherical clearance at each contact portion of the joint internal configuration when the internal friction coefficient due to the change of the lubricant enclosed in the outer ring is also considered as a variable. Shown in

In this constant velocity universal joint, the PCD (pitch circle diameter) clearance (2 × m), the spherical clearance (2 × n ₁ ), (2 × n ₂ ), the pinching angle γ8 of the ball 16 with respect to the track grooves 11, 14 and the contact From the necessity of setting the angle α8 to an appropriate value, they are defined as follows.

  First, the PCD clearance (2 × m) in a ball track formed by the track groove 11 of the outer ring 12 and the track groove 14 of the inner ring 15 is set to 25 μm or more, preferably 40 to 85 μm. If the PCD clearance (2 × m) is defined in this way, the contact of the ball 16 with the non-load side portion of the ball track can be reduced during transmission of the rotational torque, so that the contact with the non-load side portion of the ball track is reduced. Loss of transmission torque due to ball contact can be reduced.

  Here, if the above-mentioned PCD clearance (2 × m) is smaller than 25 μm, it becomes difficult to incorporate the ball 16, and the force that restrains the ball 16 between the track grooves 11 and 14 becomes large, and the ball 16 rolls. Therefore, slippage is likely to occur at the contact portion between the ball 16 and the track grooves 11 and 14, which contributes to an increase in temperature and a decrease in service life. As a result, it is difficult to reduce transmission torque loss. On the contrary, if the PCD clearance (2 × m) is larger than 85 μm, the ball 16 rides on the track grooves 11 and 14 at the time of hitting sound, vibration or high load, and the contact ellipse protrudes from the track grooves 11 and 14. As a result, chipping of the edge is likely to occur, and the effect of reducing the loss of transmission torque becomes a factor that causes a reduction in life.

  From the analysis result of the joint internal force performed by the present applicant, when the operating angle is 0 °, the contact portion between the track groove 14 of the inner ring 15 and the ball 16 and the contact portion between the track groove 11 of the outer ring 12 and the ball 16 are There is one location each on the load side. In this contact portion, when the operating angle exceeds 0 °, the ball 16 rolls in the track grooves 11 and 14, and thus frictional heat is generated. When the operating angle increases, the non-load side, which is the opposite side of the contact portion between the track groove 14 of the inner ring 15 and the ball 16, and the non-load side, which is the opposite side of the contact portion between the track groove 11 and the ball 16 of the outer ring 12. The track grooves 11 and 14 are also loaded by the contact. The range and absolute amount of the load on the non-load side increases as the operating angle increases. The load on the non-load side is in the direction opposite to the torque transmission direction, resulting in a torque transmission loss.

  Therefore, as described above, the load on the non-load side is reduced by setting the PCD clearance (2 × m) in the ball track to 25 μm or more, preferably 40 to 85 μm larger than the conventional constant velocity universal joint. As a result, transmission torque loss can be reduced and torque transmission efficiency can be improved (see FIGS. 4, 5, and 6 (refer to FIG. 2 for the phase angle)). FIG. 6 shows that when the PCD clearance is larger than that with a small PCD clearance, the load load on the non-load side near the phase angle of 60 ° can be reduced.

Also, a spherical clearance (2 × n ₁ ) between the outer spherical surface 13 of the inner ring 15 and the inner spherical surface 19 of the cage 17 and a spherical clearance between the outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12 (2 Xn ₂ ) is set to 40 μm or more, preferably 50 to 120 μm, so that the spherical contact between the outer spherical surface 13 of the inner ring 15 and the inner spherical surface 19 of the cage 17, and the outer spherical surface 18 of the cage 17 and the inner spherical surface of the outer ring 12. Since the spherical contact with 10 can be reduced, the frictional heat generated by the spherical contact can be reduced, and the transmission torque loss caused by the frictional heat can be reduced. It should be noted that the spherical clearances (2 × n ₁ ) and (2 × n ₂ ) need to be set so as to reliably reduce the spherical contact in consideration of the PCD clearance (2 × m).

Here, when the spherical clearances (2 × n ₁ ) and (2 × n ₂ ) are smaller than 40 μm, the operability of the joint is deteriorated. On the other hand, when the spherical clearances (2 × n ₁ ) and (2 × n ₂ ) are larger than 120 μm, hitting sound and vibration are generated. In addition, the applicant of the present invention, based on the experimental results regarding the eight-ball constant velocity universal joint, is the sum of the spherical clearances (2 × n ₁ ) and (2 × n ₂ ) (2 × n ₁ ) + (2 × n ₂ ). By confirming that no abnormal noise is generated at 240 μm, the upper limit of the sum (2 × n ₁ ) + (2 × n ₂ ) of the two spherical clearances (2 × n ₁ ) and (2 × n ₂ ) Was set to 240 μm, and the two spherical clearances (2 × n ₁ ) and (2 × n ₂ ) were equally distributed, and the upper limit value was set to 120 μm. In addition, the lower limit value of the spherical clearances (2 × n ₁ ) and (2 × n ₂ ) is set to 40 μm as a limit that can exhibit the effect of reducing the transmission torque loss in consideration of the manufacturing tolerance of the joint.

  Here, with respect to the spherical contact between the outer spherical surface 13 of the inner ring 15 and the inner spherical surface 19 of the cage 17 and the spherical contact between the outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12, the track groove of the ball 16 is caused by track offset. Since the pinching angle γ8 with respect to 11 and 14 is generated, the cage 16 moves toward the opening side of the outer ring 12 by the ball 16 pressing the pocket peripheral wall surface of the cage 17 toward the opening side of the outer ring 12. As a result, the outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12 are in contact with each other on the opening side of the outer ring 12, and the inner spherical surface 19 of the cage 17 and the outer spherical surface 13 of the inner ring 15 are in contact with each other on the inner side.

When the operating angle is 0 ° in this state, when torque is applied (refer to FIG. 2 for the torque load direction), the ball 16 further presses the pocket peripheral wall surface of the cage 17 toward the opening side of the outer ring 12. In this case, since the track groove 14 of the inner ring 15 and the track groove 11 of the outer ring 12 are positioned in parallel without intersecting, the cage 17 has no spherical clearance (2 × n ₁ ) and (2 × n ₂ ). The outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12 come into contact with each other.

When the operating angle is 0 °, there is no transmission torque loss regardless of the size of the spherical clearances (2 × n ₁ ) and (2 × n ₂ ), but when the operating angle is taken, the phase angle is 0 ° and the phase angle At 180 °, the track groove 14 of the inner ring 15 and the track groove 11 of the outer ring 12 are positioned in parallel, whereas at other phase angles, the track groove 14 of the inner ring 15 and the track groove 11 of the outer ring 12 intersect each other. It becomes a state to do. As a result, since the ball 16 is sandwiched between the track groove 14 of the inner ring 15 and the track groove 11 of the outer ring 12, the amount of movement of the ball 16 against the pocket peripheral wall surface of the cage 17 (cage movement amount) is the PCD clearance (2 × m).

In this case, if the spherical clearances (2 × n ₁ ) and (2 × n ₂ ) are larger than the movable amount of the cage 17 determined by the PCD clearance (2 × m), the outer spherical surface 13 of the inner ring 15 is obtained. And the spherical contact force between the inner spherical surface 19 of the cage 17 and the spherical contact force between the outer spherical surface 18 of the cage 17 and the inner spherical surface 10 of the outer ring 12 are reduced and depend on the spherical contact force. Loss of transmission torque due to frictional heat generation is reduced (see FIGS. 4, 5 and 7 (refer to FIG. 2 for the phase angle)). FIG. 7 shows that the spherical contact force can be reduced when the spherical clearance is larger than when the spherical clearance is small.

  On the other hand, when the ball 16 positioned between the track groove 11 of the outer ring 12 and the track groove 14 of the inner ring 15 with respect to the track grooves 11, 14 (see FIG. 1) is 8.5 to 12.5 °, the ball 16 The contact angle α8 (see FIG. 3) with respect to the track grooves 11 and 14 is 30 to 38 °.

  As described above, when the sandwiching angle γ8 of the ball 16 with respect to the track grooves 11 and 14 is 8.5 to 12.5 °, the axial pushing force acting on the ball at the time of torque transmission can be reduced. Accordingly, the contact surface pressure between the cage and the inner and outer rings can be suppressed, friction can be reduced, and loss of transmission torque can be reduced. Further, if the contact angle α8 of the ball 16 with respect to the track grooves 11 and 14 is 30 to 38 °, the durability of the ball riding on the edge of the track groove at the time of high torque input, the amount of sliding of the track groove of the outer ring and the ball The contact surface pressure that affects the reduction and rolling fatigue life can be in a favorable range.

  Here, when the sandwiching angle γ8 is smaller than 8.5 °, the operability is deteriorated. Conversely, when the sandwiching angle γ8 is larger than 12.5 °, the contact surface between the cage and the inner and outer rings. The pressure increases, it is difficult to reduce friction, and it is difficult to reduce the loss of transmission torque. On the other hand, if the contact angle α8 is smaller than 30 °, the track load increases, the strength decreases, and it becomes difficult to reduce friction, and it becomes difficult to reduce the loss of transmission torque. On the other hand, when the contact angle α8 is larger than 38 °, it is easy for the ball to ride on the edge of the track groove when a high torque is input, and it becomes difficult to reduce the amount of sliding between the track groove of the outer ring and the ball.

  As a result of investigating the influence of the internal configuration of the constant velocity universal joint on the torque transmission efficiency by mechanism analysis, when the friction coefficient of each contact portion in the internal configuration changes, the contact portion between the ball 16 and the track grooves 11 and 14 is changed. It has been found that low friction contributes to improvement in torque transmission efficiency, and that the spherical surfaces of the cage 17 and outer ring 12 and the cage 17 and inner ring 15 do not contribute to improvement in torque transmission efficiency even if the friction is low. (See FIG. 8).

  Here, in order to make the contact portion between the ball 16 and the track grooves 11 and 14 low in friction, it is necessary to form a sufficient oil film layer and reduce the friction coefficient. Since a large force is applied to the portion during torque transmission, a sufficient oil film layer may not be formed due to the surface pressure.

  Therefore, surface treatment is performed so that the lubricant easily intervenes in the contact portion between the ball 16 and the track grooves 11 and 14 to form a better oil film layer, thereby generating the ball 16 and the track grooves 11 and 14. It is effective to improve the torque transmission efficiency by suppressing friction caused by slipping.

  Therefore, a large number of minute recesses 41 (see the enlarged portion in FIG. 1) are randomly formed on the surface of the ball 16, and the surface roughness (arithmetic average roughness) of the surface of the ball 16 is Ra 0.03 to 0.6 μm. Preferably, Ra is 0.05 to 0.15 μm. Further, the ratio of the total area of the minute recesses 41 to the surface area of the ball 16 is set to 10 to 40%.

  Further, the parameter SK value of the surface roughness of the ball 16 is set to -1.0 to -4.9. Here, the SK value is a value representing the degree of skewness of the surface roughness distribution curve (SKEWNESS), that is, the relativity of the amplitude distribution curve of the unevenness with respect to the average line of the surface roughness, and the SK value of the surface roughness. Is expressed by the following equation.

SK = ∫ (x−x ₀ ) ³ · P (x) dx / σ ³

Here, x is the height of roughness, x _{0 is} the average height of roughness, P (x) is the probability density function of the amplitude of roughness, and σ is the mean square roughness.

  The parameter SK value is positive when the amplitude distribution curve has many peaks, zero when the peaks and valleys are equal, and negative when there are many valleys with respect to the average surface roughness line. Accordingly, the parameter SK value of the surface roughness on the surface of the ball 16 having a large number of minute recesses is a negative value.

  The numerical values of the SK value and the surface roughness Ra on the surface of the ball 16 and the total area ratio of the minute recesses 41 are each limited to an effective range for forming the oil film layer of the lubricant on the surface of the ball 16. .

  The surface roughness Ra, the SK value, and the total area ratio of the minute recesses are measured at six locations approximately 90 ° apart on the ball surface, and the average value is evaluated and determined. The determination of the effective range is also based on this method. In order to perform quantitative measurement of the minute recess 41, measurement is performed with the apparatus configuration shown in FIG. In the capture method, a ball is placed on a positioning device, the surface of the ball is magnified with a microscope, and the image is captured by a CCD camera into an image processing device composed of an image analysis device and a personal computer. The black part is analyzed as a concave part. The black portion of the image is a recess, the size / distribution is calculated, and the surface area ratio is obtained and evaluated. The details of the surface inspection method are those disclosed in Japanese Patent Application Laid-Open No. 2001-183124.

  For the measurement of the surface roughness and the SK value, measurement is performed with a measuring instrument Home Talysurf (made by Taylor Hobson). The measurement conditions were cut-off type: Gaussian, measurement length: 5λ, cut-off number: 6, cut-off wavelength: 0.25 mm, measurement magnification: 10,000 times, measurement speed: 0.30 mm / s. In addition, as a method of forming a large number of minute recesses 41 on the surface of the ball 16, for example, there is a special barrel polishing process, but other than that, surface processing may be performed by shot blasting or the like.

  Further, the lubricant preferably has a low friction coefficient. For example, it is preferable that the upper limit value of the friction coefficient is 0.07 using a Sabang type frictional wear tester. Here, as shown in FIG. 10, the Sabang-type friction and wear tester is one in which a 1/4 inch steel ball 32 is pressed against a rotating ring 31 having a diameter of 40 mm and a thickness of 4 mm. The rotating ring 31 is rotated at a peripheral speed of 108 m / min, a load of 12.7 N is applied, the lubricant is supplied from the lower end of the rotating ring 31 to the surface of the rotating ring 31 via the sponge 33, and the steel ball 32 is supported. The movement of the air slide 34 was detected by the load cell 35 and the friction coefficient was measured. Specific examples of the lubricant include urea grease. The consistency of the urea grease is 0-2. If this consistency is less than No. 0, the seal structure becomes complicated, and when used at a high speed, the lubricant tends to run out due to centrifugal force. On the other hand, if it is larger than No. 2, it becomes difficult to intervene the lubricant, and the contact resistance is large, which causes torque loss.

  Even when a pressing force is applied between the ball 16 and the track grooves 11 and 14 during the rotation of the joint, the lubricant that has entered the large number of minute recesses 41 on the surface of the ball 16 is removed from the balls 16 and the track grooves. A good oil film layer can be formed by interposing at the contact interface with 11 and 14.

  FIG. 11 shows the relationship between the friction coefficient of the lubricant used in the fixed type constant velocity universal joint and the torque loss rate at that time. Four types of lubricants with different friction coefficients are used, and for each lubricant, the torque loss rate under two conditions, when the joint input torque is small and the rotation speed is low, and when the joint input torque is large and the rotation speed is high Was measured. In the explanation of the marks plotted in the figure, the circle mark is a lubricant having a friction coefficient of about 0.1, and the other triangle marks, square marks, and rhombus marks are lubricants having a friction coefficient of 0.07 or less. is there. As shown in FIG. 11, when a lubricant having a friction coefficient of 0.07 or less is used, the torque loss rate is reduced as compared with the case of using a lubricant having a friction coefficient of about 0.1, that is, torque transmission efficiency is improved. You can see that

  FIG. 12 shows the case of a joint (ball joint of the present invention) having a ball 16 in which a large number of minute recesses 41 are formed on the surface, and a case of a joint (ball joint of a comparative example) having a ball without minute recesses. This is a comparison of torque loss rates. Also in this case, for each of the joints, the torque loss rate was measured under two conditions: when the joint input torque was small and the rotation speed was slow, and when the joint input torque was large and the rotation speed was high. Note that a lubricant having the same coefficient of friction is enclosed in both the joint of the present invention and the joint of the comparative example. The circle mark shown in the figure is the test data of the joint of the present invention, and the diamond mark is the test data of the joint of the comparative example. Moreover, what is shown with a dashed-dotted line is the average line of each data of this invention, and a dotted line is an average line of each data of a comparative example. As can be seen from the difference between these two average lines, the torque loss rate of the present invention is lower than that of the comparative example, and the torque transmission efficiency is improved.

  Further, FIG. 13 shows a joint having a ball 16 formed with a lubricant having a friction coefficient of 0.07 or less and a large number of minute recesses 41, and having the PCD clearance and the spherical clearance in the above-mentioned appropriate value range (the present invention). Joint) and a joint having a lubricant with a friction coefficient of about 0.1 and a ball without a minute recess, and the PCD clearance and the spherical clearance are not set within the above-described appropriate value range (comparative joint). It is the graph which showed each torque loss rate. Also in this case, for each of the joints, the torque loss rate was measured under two conditions: when the joint input torque was small and the rotation speed was slow, and when the joint input torque was large and the rotation speed was high. The circle mark in the figure is the data of the comparative example, and the triangle mark is the data of the present invention. From the results of FIG. 13, it can be seen that in the present invention, the torque loss rate is reduced and the torque transmission efficiency is improved as compared with the comparative example.

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the scope of the present invention. The scope of the present invention is not limited to patents. It includes the equivalent meanings recited in the claims, and the equivalent meanings recited in the claims, and all modifications within the scope.

1 is a longitudinal sectional view showing an overall configuration of a barfield type fixed constant velocity universal joint in an embodiment of the present invention. It is a cross-sectional view of FIG. FIG. 3 is an enlarged cross-sectional view of a main part showing an inner ring, an outer ring, a ball and a cage for explaining a PCD gap, a spherical gap, a contact angle of a ball, and a track shape. It is a table | surface for demonstrating the contribution to the torque transmission efficiency with respect to the change of the PCD clearance in a joint internal structure of each contact part, and a spherical clearance. It is a table | surface for demonstrating the case where an internal friction coefficient is also considered as a variable by the contribution to the torque transmission efficiency with respect to the change of the PCD clearance in a joint internal structure, and a spherical clearance. It is a characteristic view which shows the non-load side track load by the change of PCD clearance. It is a characteristic view which shows the spherical contact force by the change of a spherical clearance. It is a table | surface for demonstrating the contribution to the torque transmission efficiency with respect to the change of the friction coefficient in each contact part of a coupling internal structure. It is the schematic of the measuring apparatus which performs the quantitative measurement of many micro recessed parts formed in the ball | bowl. It is a schematic diagram of a Saban type friction and abrasion tester. It is a characteristic view which shows each torque loss rate when a lubricant with a low friction coefficient is used, and a comparative example. It is a characteristic view which shows each torque loss rate with the case where the ball | bowl which formed many micro recessed parts is used, and a comparative example. It is a characteristic view which shows each torque loss rate when using the ball | bowl which formed the lubricant with a low friction coefficient, and many micro recessed parts, and setting a PCD clearance and a spherical surface clearance to an appropriate value, and a comparative example. In other embodiment of this invention, it is a longitudinal cross-sectional view which shows the whole structure of the fixed type constant velocity universal joint of an undercut free type | mold. It is a longitudinal cross-sectional view which shows the whole structure of a six ball type in the conventional example of a fixed type constant velocity universal joint. It is a cross-sectional view of FIG. It is a longitudinal cross-sectional view which shows the whole structure of an eight ball type in the conventional example of a fixed type constant velocity universal joint. It is a cross-sectional view of FIG. It is a longitudinal cross-sectional view which shows the state which the constant velocity universal joint of FIG. 15 took the operating angle. It is a longitudinal cross-sectional view which shows the state which the constant velocity universal joint of FIG. 17 took the operating angle. It is the table | surface which compared the ball diameter, the track offset amount, and the length of a contact point locus | trajectory with an 8-ball type and a 6-ball type.

Explanation of symbols

10 inner spherical surface of outer joint member (outer ring) 11 track groove of outer joint member (outer ring) 12 outer joint member (outer ring)
13 Outer spherical surface of inner joint member (inner ring) 14 Track groove of inner joint member (inner ring) 15 Inner joint member (inner ring)
16 ball 17 cage 18 cage outer sphere 19 cage inner sphere 41 minute recess O joint center O ₁ center of curvature of track groove of outer joint member (outer ring) O ₂ center of curvature of track groove of inner joint member (inner ring) 2 × m PCD clearance 2 × n ₁ , 2 × n ₂ spherical clearance γ8 Nipping angle α8 Contact angle

Claims (12)

A plurality of track grooves extending in the axial direction are formed on the inner spherical surface, and an outer joint member filled with a lubricant therein and a plurality of track grooves extending in the axial direction are paired with the track grooves of the outer joint member. An inner joint member formed on a spherical surface, a plurality of balls interposed between a track groove of the outer joint member and a track groove of the inner joint member, and an inner spherical surface and an inner joint of the outer joint member A cage for holding the ball interposed between the outer spherical surfaces of the members, and the center of curvature of the track groove of the outer joint member and the center of curvature of the track groove of the inner joint member are equidistant from the joint center. In the fixed constant velocity universal joint that is offset in the opposite direction,
A large number of minute recesses are randomly formed on the surface of the ball, and a PCD clearance in a ball track formed by the track groove of the outer joint member and the track groove of the inner joint member is 25 μm or more. Fixed constant velocity universal joint. A plurality of track grooves extending in the axial direction are formed on the inner spherical surface, and an outer joint member filled with a lubricant therein and a plurality of track grooves extending in the axial direction are paired with the track grooves of the outer joint member. An inner joint member formed on a spherical surface, a plurality of balls interposed between a track groove of the outer joint member and a track groove of the inner joint member, and an inner spherical surface and an inner joint of the outer joint member A cage for holding the ball interposed between the outer spherical surfaces of the members, and the center of curvature of the track groove of the outer joint member and the center of curvature of the track groove of the inner joint member are equidistant from the joint center. In the fixed constant velocity universal joint that is offset in the opposite direction,
A large number of minute recesses are randomly formed on the surface of the ball, and the spherical clearance between the outer spherical surface of the inner joint member and the inner spherical surface of the cage is 40 μm or more, and the outer spherical surface of the cage and the inner spherical surface of the outer joint member A fixed type constant velocity universal joint characterized in that the clearance between the spherical surfaces is 40 μm or more. A plurality of track grooves extending in the axial direction are formed on the inner spherical surface, and an outer joint member filled with a lubricant therein and a plurality of track grooves extending in the axial direction are paired with the track grooves of the outer joint member. An inner joint member formed on a spherical surface, a plurality of balls interposed between a track groove of the outer joint member and a track groove of the inner joint member, and an inner spherical surface and an inner joint of the outer joint member A cage for holding the ball interposed between the outer spherical surfaces of the members, and the center of curvature of the track groove of the outer joint member and the center of curvature of the track groove of the inner joint member are equidistant from the joint center. In the fixed constant velocity universal joint that is offset in the opposite direction,
A large number of minute recesses are randomly formed on the surface of the ball, and a PCD clearance in a ball track formed by the track groove of the outer joint member and the track groove of the inner joint member is 25 μm or more, and the inner joint member A fixed constant velocity characterized in that the spherical clearance between the outer spherical surface of the cage and the inner spherical surface of the cage is 40 μm or more, and the spherical clearance between the outer spherical surface of the cage and the inner spherical surface of the outer joint member is 40 μm or more. Universal joint.   The fixed constant velocity universal joint according to claim 1 or 3, wherein the PCD clearance is 40 to 85 µm.   The spherical clearance between the outer spherical surface of the inner joint member and the inner spherical surface of the cage is 50 to 120 μm, and the spherical clearance between the outer spherical surface of the cage and the inner spherical surface of the outer joint member is 50 to 120 μm. Or the fixed type constant velocity universal joint of 3.   The PCD clearance is 40 to 85 μm, the spherical clearance between the outer spherical surface of the inner joint member and the inner spherical surface of the cage is 50 to 120 μm, and the spherical surface between the outer spherical surface of the cage and the inner spherical surface of the outer joint member The fixed type constant velocity universal joint according to claim 3, wherein the clearance is 50 to 120 μm.   The fixed type constant velocity universal joint according to any one of claims 1 to 6, wherein a friction coefficient of the lubricant is 0.07 or less.   The fixed constant velocity universal joint according to claim 7, wherein the lubricant is urea grease, and the consistency of the urea grease is 0-2.   The surface roughness of the ball formed with the minute recesses is Ra 0.03 to 0.6 μm, the parameter SK value of the surface roughness of the ball is −1.0 or less, and the number of the minute recesses with respect to the surface area of the ball The fixed type constant velocity universal joint according to any one of claims 1 to 8, wherein a ratio of a total area is 10 to 40%.   10. The fixed type constant velocity universal joint according to claim 9, wherein the surface roughness of the ball is Ra 0.05 to 0.15 [mu] m, and the parameter SK value of the surface roughness of the ball is -4.9 to -1.0. .   The fixed type constant velocity universal joint according to any one of claims 1 to 10, wherein the number of the balls is eight.   The sandwich angle between the track groove of the ball located between the track groove of the outer joint member and the track groove of the inner joint member is 8.5 to 12.5 °, and the contact angle of the ball with respect to the track groove is 30 to 38 °. The fixed type constant velocity universal joint according to claim 11.

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