JP2001153149A - Fixed constant velocity universal joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixed constant velocity universal joint capable of easily realizing a wide angle of an operating angle without enlarging an outer diameter of an outside joint member. SOLUTION: In this fixed constant velocity universal joint provided with an outside joint member 25 for forming plural track grooves 22 toward the opening end 23 in the shaft direction at circumferential directional equal intervals on an inner spherical surface 21, an inside joint member 28 for forming plural track grooves 27 making a pair with the track grooves 22 of the outside joint member 5 in the shaft direction at circumferential directional equal intervals on an outer spherical surface 26, plural balls 29 for transmitting torque by being interposed between both track grooves 22, 27 of the outside joint member 25 and the inside joint member 28 and a cage 30 for holding the balls 29 by being interposed between the inner spherical surface 21 of the outside joint member 25 and the outer spherical surface 26 of the inside joint member 28, the opening side groove bottom of the track groove 22 of the outside joint member 25 is formed in a taper shape of linearly expanding a diameter toward the opening end 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed type constant velocity universal joint and, more particularly, to a fixed type constant velocity universal joint used in a power transmission system of an automobile or various industrial machines. The present invention relates to a fixed type constant velocity universal joint that allows only a fixed velocity universal joint.

[0002]

2. Description of the Related Art In recent years, a wheelbase is sometimes lengthened from the viewpoint of improving the collision safety of an automobile. However, in order to keep the turning radius of the vehicle from being increased accordingly, the angle of a fixed type constant velocity universal joint is increased. There is a demand for an increase in the steering angle of the front wheels. In order to meet this need for a high angle, a UF in which the track groove shape on the opening side of the outer joint member is parallel to the axial direction is used.
At present, it is supported by a (undercut free) type fixed type constant velocity universal joint.

[0003] This UF type fixed type constant velocity universal joint is
As shown in FIGS. 9 and 10, an outer joint member 5 having a mouth portion 4 in which a plurality of track grooves 2 are formed on an inner spherical surface 1 at circumferentially equal intervals along an axial direction toward an open end 3, An inner joint member 8 having a plurality of track grooves 7 formed in the spherical surface 6 and forming a pair with the track groove 2 of the outer joint member 5 at equal circumferential intervals along the axial direction; an outer joint member 5 and an inner joint member 8;
A plurality of balls 9 interposed between the two track grooves 2 and 7 for transmitting torque, and each ball 9 is interposed between the inner spherical surface 1 of the outer joint member 5 and the outer spherical surface 6 of the inner joint member 8. And a cage 10 for holding. The plurality of balls 9 are accommodated in pockets 13 formed in the cage 10 and are arranged at regular intervals in the circumferential direction.

FIG. 9 shows a state where the operating angle θ is 0 °, and FIG. 10 shows a state where the operating angle θ is the maximum angle (50 °). Although not shown, the outer joint member 5 or the inner joint member 8
Has a drive-side rotation shaft, and the other has a driven-side rotation shaft. The operating angle θ means an angle formed between the rotation axis X of the outer joint member 5 and the rotation axis Y of the inner joint member 8. Also, the rotation axis X of the outer joint member 5 and the inner joint member 8
When the rotation axis Y takes an operation angle θ other than 0 °, a plane perpendicular to the bisector of the angle θ formed by both rotation axes X and Y is referred to as a joint plane P. If all the balls 9 are on the joint plane P when the operating angle θ is taken, the distances from the ball center to both the rotation axes X and Y are equal, and therefore,
Rotational motion is transmitted at a constant speed between the two rotation axes X and Y. The intersection between the joint plane P and the rotation axes X and Y is referred to as a joint center O. In the fixed type constant velocity universal joint, the center O of the joint is fixed regardless of the operating angle θ.

In a fixed type constant velocity universal joint of the UF type, both track grooves 2, 7 of the outer joint member 5 and the inner joint member 8 are provided.
All have no undercut, and can have a large operating angle. FIG. 11 shows an enlarged cross section (hatching omitted) of FIG. 9 for explaining the shapes of the track grooves 2 and 7 of the outer joint member 5 and the inner joint member 8 and the cage offset amount.

Each track groove 2 of the outer joint member 5 is formed at a predetermined depth from the inner spherical surface 1 of the outer joint member 5, and the depth gradually changes in the axial direction. The track groove 2 is in the back side of the mouth portion 4, and the circular arc bottom 2a having a curvature center O ₁ on the rotation axis X of the outer joint member 5, line segment track grooves extending from the center of curvature O ₁ in the radial direction It has a straight bottom 2b parallel to the rotation axis X on the opening side of the mouth part 4 with a part m intersecting with the bottom of the second part as a boundary. Each track groove 7 of the inner joint member 8 is provided with an outer spherical surface 6 of the inner joint member 8.
To a predetermined depth, but the depth is gradually changing in the axial direction. The track groove 7 has an arcuate bottom 7 a having a center of curvature O ₂ on the rotation axis Y of the inner joint member 8 on the opening side of the mouth part 4, and a line segment extending radially from the center of curvature O _2. A straight bottom 7b parallel to the rotation axis Y is provided on the back side of the mouth part 4 with a portion n intersecting the bottom of the mouse 7 as a boundary.

[0007] The center of curvature of the outer spherical surface 6 of the inner joint member 8;
The center of curvature of the inner spherical surface 1 of the outer joint member 5 coincides with the centers of curvature O ₃ ′ and O ₄ ′ of the inner and outer spherical surfaces 11 and 12 of the cage 10, respectively. The centers of curvature O ₃ ′ and O ₄ ′ of the inner and outer spherical surfaces 11 and 12 of the cage 10 are offset in the axial direction by the same distance f ′ from the joint center O in the opposite direction. Similarly, the center of curvature O ₁ of the track grooves 2 of the outer joint member 5, and the center of curvature O ₂ of the track grooves 7 of the inner joint member 8, the offset in the opposite direction only in the axial direction equidistantly f 'from joint center O are doing. Therefore, the pair of track grooves 2 and 7 form a wedge-shaped track whose interval gradually changes from one axial direction to the other axial direction. Each ball 9 is rollably incorporated between the pair of track grooves 2 and 7, and when the outer joint member 5 and the inner joint member 8 transmit torque in a state where the operating angle θ is set, a wedge-shaped track is formed. It is affected by the axial force that tries to move it to the wider one.

[0008]

In recent years, there has been a need for a further increase in the angle of rotation due to a reduction in the minimum turning radius of an automobile (particularly a mini car or a small car) and a liberalization of the geometry design of the underbody of the automobile. For fixed type constant velocity universal joints,
The operating angle θmax = 50 ° is the limit, and in order to further increase the angle, it is necessary to increase the outer diameter of the mouth portion 4 of the outer joint member 5. For this reason, the current situation is that the design must be opposed to the reduction in weight and size.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to easily realize a high working angle without increasing the outer diameter of the outer joint member. An object of the present invention is to provide a fixed type constant velocity universal joint.

[0010]

As a technical means for achieving the above object, the present invention provides a method of forming a plurality of track grooves on an inner spherical surface at equal intervals in a circumferential direction toward an open end along an axial direction. Outer joint member, an inner joint member formed with a plurality of track grooves paired with the track groove of the outer joint member on the outer spherical surface at equal circumferential intervals along the axial direction, and an outer joint member and an inner joint member. A fixed constant velocity comprising a plurality of balls interposed between both track grooves to transmit torque, and a cage interposed between the inner spherical surface of the outer joint member and the outer spherical surface of the inner joint member to hold the balls. The universal joint is characterized in that the groove bottom on the opening side of the track groove of the outer joint member has a tapered shape whose diameter is linearly increased toward the opening end. The inner bottom of the track groove of the inner joint member has a tapered shape whose diameter is linearly increased toward the inner side.

As a result, according to the present invention, the operating angle between the rotation axis of the outer joint member and the rotation axis of the inner joint member can be up to 5 degrees.
2 ° is possible.

In the fixed type constant velocity universal joint according to the present invention, the center of the outer spherical surface and the center of the inner spherical surface of the cage are offset by the same distance in the axial direction with respect to the joint center plane including the ball center. It is desirable that the cage offset amount is set large so that the protrusion of the ball from the open end of the outer joint member can be restrained by the cage pocket.

Here, by setting the cage offset amount (f) to be large, there is an advantage that the thickness at the entrance side of the cage into which the inner joint member is incorporated can be increased to improve the strength. Further, since the wall thickness on the entrance side of the cage can be increased, it is possible to restrain the ball from jumping out of the open end of the outer joint member by the cage pocket when the operating angle is set.

However, if the cage offset amount (f) is too large, the circumferential movement amount of the ball in the cage pocket increases, and the circumferential dimension of the cage pocket increases to ensure proper movement of the ball. Therefore, the column portion of the cage becomes thin, and the strength surface becomes a problem. The thickness of the back side located on the side opposite to the entrance side of the cage becomes small, and the strength surface becomes a problem.

From the above, it is not preferable that the cage offset amount (f) is excessive, and the cage offset amount (f) is not preferable.
There is an optimum range in which the significance of the above can be balanced with the above problem. However, since the optimum range of the cage offset amount (f) varies depending on the size of the joint, it is necessary to determine the optimum range in relation to the basic dimensions representing the size of the joint. Therefore, the cage offset amount (f) and the length of the line segment (P) connecting the center of curvature of the track groove of the outer joint member or the center of curvature of the track groove of the inner joint member to the center of the ball
CR) (f / PCR).

Therefore, the cage offset amount in the present invention is a line segment connecting the cage offset amount (f) with the center of curvature of the track groove of the outer joint member or the center of curvature of the track groove of the inner joint member and the center of the ball. Length (PC
R) and the ratio (f / PCR) is set in the range of 0.017 to 0.133.

If the ratio (f / PCR) is larger than 0.133, the above-described problem occurs. Conversely, if the ratio (f / PCR) is smaller than 0.017, it becomes meaningless to provide the cage offset amount (f). Therefore, from the viewpoint of securing the cage strength and durability, the optimum range of the cage offset amount (f) is that the ratio (f / PCR) is in the range of 0.017 to 0.133.

According to the present invention, an opening-side groove bottom of the track groove of the outer joint member with respect to a straight line connecting the center of curvature of the track groove of the outer joint member or the center of curvature of the track groove of the inner joint member and the center of the ball. Alternatively, it is desirable that the inner joint member has a tapered shape so that a bottom groove bottom of the track groove is at a right angle.

Further, in the present invention, when the number of the balls is eight, the load applied to one ball can be reduced and the efficiency can be increased, and the strength, the load torque and the durability are excellent. This is effective in that the joint can be reduced in size and the entire joint can be reduced in size.

Further, in the present invention, it is desirable to form a pocket gap so as not to restrain the ball on the deep side of the pocket of the cage. In this way, even if the depth of the cage on the back side is reduced due to the increase in the cage offset amount, the strength of the cage can be ensured.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fixed type constant velocity universal joint according to the present invention will be described in detail below.

In the fixed type constant velocity universal joint of the embodiment shown in FIGS. 1 to 3, a plurality of track grooves 22 are formed on the inner spherical surface 21 at equal intervals in the circumferential direction toward the open end 23 along the axial direction. An outer joint member 25 having a mouth portion 24;
6, an inner joint member 28 in which a plurality of track grooves 27 forming a pair with the track groove 22 of the outer joint member 25 are formed at equal intervals in the circumferential direction along the axial direction; A plurality of balls 29 interposed between the track grooves 22 and 27 and transmitting torque, and each ball 29 is held between the inner spherical surface 21 of the outer joint member 25 and the outer spherical surface 26 of the inner joint member 28. And a cage 30. The plurality of balls 29 are accommodated in pockets 33 formed in the cage 30 and are arranged at regular intervals in the circumferential direction.

FIG. 1 shows a state where the operating angle θ is 0 °, and FIG. 3 shows a state where the operating angle θ is the maximum angle (52 °).
Although not shown, the outer joint member 25 or the inner joint member 28
Has a drive-side rotation shaft, and the other has a driven-side rotation shaft. The operating angle θ means an angle between the rotation axis X of the outer joint member 25 and the rotation axis Y of the inner joint member 28. When the rotation axis X of the outer joint member 25 and the rotation axis Y of the inner joint member 28 take an operation angle θ other than 0 °, the rotation axis X is perpendicular to the bisector of the angle θ formed by the rotation axes X and Y. Such a plane is referred to as a joint plane P. When the operating angle θ is set, if all the balls 29 are on the joint plane P, the distances from the ball center to the two rotation axes X and Y are equal, and therefore, the two rotation axes X and Y are at the same speed. The transmission of the rotational movement takes place. The intersection between the joint plane P and the rotation axes X and Y is referred to as a joint center O. In the fixed type constant velocity universal joint, the center O of the joint is fixed regardless of the operating angle θ.

In the fixed type constant velocity universal joint of this embodiment,
Both of the track grooves 22, 27 of the outer joint member 25 and the inner joint member 28 have no undercut, and can have a large operating angle. FIG. 4 shows the outer joint member 2.
5 and the respective track grooves 22,
In order to explain the shape of 27 and the amount of cage offset, an enlarged cross section of FIG. 1 (hatching is omitted) is shown.

Each track groove 22 of the outer joint member 25 is
It is formed at a predetermined depth from the inner spherical surface 21 of the outer joint member 25, and the depth gradually changes in the axial direction.
The track groove 22 has an arcuate bottom 2 having a center of curvature O ₁ on the rotation axis X of the outer joint member 25 on the back side of the mouth part 24.
And 2a, the boundary portion p intersects the bottom of the line segment track grooves 22 connecting the center O ₅ of the center of curvature O ₁ and the ball 29, at the opening side of the mouth portion 24, a straight line towards its open end 23 And a tapered bottom 22b that expands in diameter. The tapered bottom 22b is formed at an angle perpendicular to a straight line connecting the center of curvature O ₁ of the track groove 22 of the outer joint member 25 and the center O _{5 of the} ball 29.

Each track groove 27 of the inner joint member 28
The inner joint member 28 is formed at a predetermined depth from the outer spherical surface 26, and the depth gradually changes in the axial direction.
The track groove 27 connects the arc bottom 27 a having the center of curvature O ₂ on the rotation axis Y of the inner joint member 28 on the opening side of the mouth portion 24, and connects the center of curvature O ₂ and the center O _{5 of the} ball 29. It has a tapered bottom 27b on the back side of the mouth part 24, which linearly expands its diameter toward the back end, at a position q where the line segment intersects the bottom of the track groove 27. This tapered bottom 2
7b is formed at an angle such that the perpendicular to the straight line connecting the center O ₅ of the curvature center O ₂ and the ball 29 of the track grooves 27 of the inner joint member 28.

As described above, the mouth portion 2 of the outer joint member 25
4 is formed as a tapered bottom 22b (for example, a diameter expansion angle φ = 20 °) that is linearly expanded toward the opening end 23 of the track groove 22 on the opening side, so that the mouth portion 24 of the outer joint member 25 is formed. Without increasing the outer diameter of the
A high angle of 52 ° (conventional operating angle θmax + 2 °) has been realized.

FIGS. 5 and 6 show a fixed type constant velocity universal joint according to another embodiment of the present invention. The same or corresponding parts as those of the above-described embodiment shown in FIGS. 1 to 3 are denoted by the same reference numerals, and redundant description will be omitted.

In this embodiment, all the axial shapes of the track grooves 22 of the outer joint member 25 are straight tapered. That is, the track groove 22 of the outer joint member 25 has the straight tapered bottom 22c whose diameter is uniformly increased from the back side of the mouth portion 24 toward the opening end 23 thereof. The track groove 27 of the inner joint member 28 has a straight tapered bottom 27c whose diameter uniformly increases from the opening side of the mouth portion 24 toward the back side thereof.

As described above, the mouth portion 2 of the outer joint member 25
Since the entire groove bottom of the track groove 22 of 4 is a straight tapered bottom 22c whose diameter increases from the back side toward the opening end 23, without increasing the outer diameter of the mouth portion 24 of the outer joint member 25, It is possible to realize a high angle of operation angle θmax = 52 ° (conventional operation angle θmax + 2 °). As a result, the outer joint member 25 can be made compact, the load capacity can be increased, and the like, as in the case of the above-described embodiment. Further, by forming the track groove 22 in a straight taper shape over the entire axial direction, workability by, for example, cold forging can be improved.

The center of curvature of the outer spherical surface 26 of the inner joint member 28 and the center of curvature of the inner spherical surface 21 of the outer joint member 25 are respectively the centers of curvature O ₃ and O ₄ of the inner and outer spherical surfaces 31 and 32 of the cage 30.
Matches. The centers of curvature O ₃ and O ₄ of the inner and outer spheres 31 and 32 of the cage 30 are offset in the axial direction by the same distance f from the center O of the joint. Similarly, the center of curvature O ₁ of the track groove 22 of the outer joint member 25 and the center of curvature O ₂ of the track groove 27 of the inner joint member 28 are offset in the opposite direction in the axial direction by the same distance f from the joint center O. ing. Therefore, the pair of track grooves 22 and 27 forms a wedge-shaped track whose interval gradually changes from one axial direction to the other. Each ball 29 is rollably incorporated between the pair of track grooves 22 and 27, and the outer joint member 25 and the inner joint member 28 have an operating angle θ.
When the torque is transmitted in a state in which wedge-shaped tracks are taken, an axial force is applied to move the wedge-shaped tracks toward a wider space.

In this embodiment, the operating angle θmax = 52 °
In order to prevent the ball 29 from jumping out of the open end 23 of the mouth portion 24 of the outer joint member 25 when
The cage offset amount f is set to be larger than the conventional one so that it can be restrained by the pocket 33 of the cage 30. That is, the cage offset amount is f, the center locus radius value of the ball 29, that is, the track groove 22 of the outer joint member 25 is set.
Center of curvature O ₁ or track groove 27 of inner joint member 28
Center of curvature O ₂ in the case where the length of a line connecting the center O ₅ of the ball 29 and the PCR of, f / PCR = 0.017~0.
133.

For example, since the cage offset amount f 'of the conventional product (see FIG. 11) is 0.42 mm and the center locus radius value PCR' of the ball 9 is 25 mm, the cage offset amount f 'and the center of the ball 9 are determined. The ratio (f ′ / PCR ′) to the locus radius value PCR ′ was 0.017. On the other hand, when the maximum value of the cage offset amount f in the embodiment of the present invention (see FIG. 4) is 3.2 mm and the center locus radius value PCR of the ball 29 is 24 mm, the cage offset amount f and the center of the ball 29 are determined. Ratio to the track radius value PCR (f
/ PCR) is 0.133.

Conventionally, increasing the cage offset amount f is caused by the concern that the ball 29 jumps out of the pocket 33 of the cage 30 on the back side of the cage 30 and the wall thickness on the back side of the cage 30 becomes thin. Have been avoided. FIG.
Indicates the joint strength (torsional strength) at the maximum operating angle with respect to the joint strength at the operating angle of 0 °. Like the conventional product, even the product of the present invention has reached the target level. There is no problem in strength. Further, as shown in FIG. 3, in the phase where the ball 29 is about to pop out (phase angle 0 °), the force acting on the cage pocket of the conventional product [FIG. 8A, it is clear that the product of the present invention (FIG. 8A) hardly occurs and the load on the cage 30 is reduced. Further, when the cage offset amount f is increased, It was confirmed that this load applied to the cage 30 became smaller.

In the fixed type constant velocity universal joint according to this embodiment, it is preferable that the number of the balls 29 held in the cage 30 is eight as shown in FIG. This eight-ball constant velocity universal joint can reduce the load applied to one ball and increase efficiency, is excellent in strength, load torque, durability, and can reduce the ball diameter. This is effective in reducing the size of the entire joint.

Further, as shown in FIG. 3, it is desirable to form a pocket gap t so as not to restrain the ball 29 on the back side of the pocket 33 of the cage 30. By doing so, even if the thickness of the cage 30 at the back side is reduced due to the increase in the cage offset amount f, the cage 30 contacts the back side of the pocket 33 of the cage 30 to be positioned at the back side of the cage 30. Damage can be reduced, and the strength of the cage 30 can be ensured.

[0037]

According to the present invention, an outer joint member in which a plurality of track grooves are formed on an inner spherical surface at equal circumferential intervals toward an open end along an axial direction, and a track of the outer joint member is formed on an outer spherical surface. A plurality of track grooves forming a pair with the grooves are formed along the axial direction at equal intervals in the circumferential direction along the inner joint member, and a plurality of torque transmissions interposed between the track grooves of the outer joint member and the inner joint member are provided. In a fixed type constant velocity universal joint comprising a ball and a cage interposed between an inner spherical surface of an outer joint member and an outer spherical surface of an inner joint member, an open end side groove of a track groove of the outer joint member By making the bottom a tapered shape that is linearly enlarged toward the opening end thereof, it is possible to easily realize a high working angle without increasing the outer diameter of the outer joint member. Reduce the size of components and increase load capacity. Etc. Hakare is, correspondence performed quickly to needs for functionality and workability of up.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a state in which an operation angle is 0 ° in an embodiment of a fixed type constant velocity universal joint according to the present invention.

FIG. 2 is a cross-sectional view of FIG.
Sectional view along line A

FIG. 3 is a cross-sectional view illustrating a state in which an operating angle is a maximum angle of 52 ° in the embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a track groove shape and a cage offset amount of an outer joint member according to the present invention.

FIG. 5 is a cross-sectional view illustrating a state in which an operation angle is 0 ° in another embodiment of the present invention.

FIG. 6 shows a working angle of 52 ° in another embodiment of the present invention.
Sectional view showing the state of

FIG. 7 is a graph showing joint strength at a maximum operating angle with respect to joint strength at an operating angle of 0 °.

8A and 8B show a relationship between a phase angle of a ball and a force acting on a cage pocket, wherein FIG. 8A is a characteristic diagram showing a case of a product of the present invention, and FIG. 8B is a characteristic diagram showing a case of a conventional product.

FIG. 9 is a cross-sectional view showing a state in which an operating angle is 0 ° in a conventional fixed type constant velocity universal joint.

FIG. 10 is a sectional view showing a state in which an operating angle of a conventional fixed type constant velocity universal joint is a maximum angle of 50 °.

FIG. 11 is a cross-sectional view for explaining a track groove shape and a cage offset amount of an outer joint member in the related art.

[Description of Signs] 21 Inner spherical surface of outer joint member 22 Track groove 22b Taper bottom 23 Open end 25 Outer joint member 26 Outer spherical surface of inner joint member 27 Track groove 28 Inner joint member 29 Ball 30 Cage 31 Cage inner spherical surface 32 Cage 33 Pocket f f Cage offset O ₁ Center of curvature of track groove of outer joint member O ₂ Center of curvature of track groove of inner joint member O ₃ Center of inner spherical surface of cage O ₄ Center of outer spherical surface of cage t Pocket gap X Outside Rotation axis of joint member Y Rotation axis of inner joint member

Claims (7)

[Claims] 1. An outer joint member having a plurality of track grooves formed on an inner spherical surface at equal intervals in a circumferential direction toward an open end along an axial direction, and a pair of track grooves of the outer joint member formed on an outer spherical surface. An inner joint member having a plurality of track grooves formed along the axial direction at equal intervals in the circumferential direction; a plurality of balls interposed between the track grooves of the outer joint member and the inner joint member to transmit torque; A cage interposed between the inner spherical surface of the joint member and the outer spherical surface of the inner joint member for holding a ball, wherein an opening-side groove bottom of the track groove of the outer joint member faces the open end. A fixed type constant velocity universal joint characterized by a tapered shape having a linearly enlarged diameter. 2. The center of the outer spherical surface and the center of the inner spherical surface of the cage are offset axially opposite from each other by an equal distance with respect to the joint center plane including the ball center. 2. The fixed type constant velocity universal joint according to claim 1, wherein the fixed constant velocity universal joint is set so as to be large so that the protrusion of the ball from the open end can be restrained by the pocket of the cage. 3. The amount (f) of the cage offset and the length (PCR) of a line connecting the center of curvature of the track groove of the outer joint member or the center of curvature of the track groove of the inner joint member to the center of the ball. The ratio (f / PCR) is 0.017 to 0.1
The fixed type constant velocity universal joint according to claim 2, wherein the fixed constant velocity universal joint is within a range of 33. 4. The outer joint member is tapered so that an opening-side groove bottom of the track groove of the outer joint member is perpendicular to a straight line connecting the center of curvature of the track groove and the center of the ball. Item 4. The fixed type constant velocity universal joint according to any one of Items 1 to 3. 5. The fixed type constant velocity universal joint according to claim 1, wherein the number of the balls is eight. 6. The fixed type constant velocity universal joint according to claim 1, wherein a pocket gap is formed so as not to restrain the ball on the inner side of the pocket of the cage. 7. The fixed constant velocity universal freewheel according to claim 1, wherein an operating angle between a rotation axis of the outer joint member and a rotation axis of the inner joint member has a maximum of 52 °. Fittings.