JP4188310B2 - Constant velocity universal joint - Google Patents

Description

The present invention relates to a constant velocity universal joint provided with a hollow connecting shaft .

  Constant velocity universal joints can be broadly divided into fixed types that allow only angular displacement between two axes, and sliding types that allow angular displacement and axial displacement, depending on the use conditions and applications. Selected. The fixed type is typically a Zepper type constant velocity universal joint (ball-fixed joint), and the sliding type is typically a double offset type constant velocity universal joint.

  The constant velocity universal joint as described above is widely used for a power transmission device of an automobile, for example, for connecting a drive shaft or a propeller shaft of an automobile. Usually, a fixed type and a sliding type constant velocity universal joint are used as a pair for connecting a drive shaft and a propeller shaft of an automobile. For example, a power transmission device that transmits the power of an automobile engine to a wheel needs to cope with an angular displacement and an axial displacement caused by a change in the relative positional relationship between the engine and the wheel. One end of a drive shaft 20 interposed between the engine side and the wheel side is connected to a differential 22 via a sliding type constant velocity universal joint 21, and the other end is connected to a wheel via a fixed type constant velocity universal joint 23. 24.

  In a constant velocity universal joint, a damper is attached to a connecting shaft (drive shaft 20 in the example shown in FIG. 5) connected to the fitting portion of the inner joint member as a countermeasure against vibration of a vehicle or the like. There is a case where a large-diameter and hollow structure ensures high torsional rigidity and bending rigidity, while at the same time reducing weight. In addition, it has been found that tuning of the primary natural frequency of bending is effective for measures against beat noise, medium / high-speed booming noise, etc. ing. However, the installation of the damper leads to an increase in cost and the frequency can be tuned, but the torsional rigidity of the connecting shaft cannot be improved.

  On the other hand, as a hollow connecting shaft, currently, a pipe material welded (or friction welded) to a stub, or an integral type pipe material drawn by swaging or the like is used. However, the former has a high manufacturing cost, and it is difficult to achieve high rigidity and light weight simultaneously in terms of design. The latter is generally less expensive than the former, but uses a pipe material of a size that can secure the required shaft rigidity as a vibration countermeasure and fits it to the fitting part of the inner joint member of the constant velocity universal joint In order to squeeze to a size that can be achieved, it is necessary to increase the squeezing rate δ (%), which increases the manufacturing cost.

Aperture ratio δ (%) = {(dm−ds) / dm} × 100
dm: Outer diameter of pipe material
ds: outer diameter after drawing In general, in the case of rotary swaging or link type swaging (a processing method suitable for hollow shaft products having a large drawing ratio), drawing with a drawing ratio δ of 50% or more in one step. However, in reality, when the drawing ratio δ exceeds 60%, the material cost and the heat treatment cost (pretreatment such as annealing is required) are increased, and the workability is increased. If too much priority is given, product functions may not be satisfied. On the other hand, in order to keep the drawing ratio δ low and to secure the required shaft rigidity, the size of the constant velocity universal joint may have to be increased more than necessary, which increases the mounting space and weight, Design disadvantages come out.

An object of the present invention is to simultaneously achieve high rigidity and light weight of the hollow connecting shaft in this type of constant velocity universal joint , and to reduce the manufacturing cost.

In order to solve the above-mentioned problems, the present invention provides an outer joint member in which eight guide grooves extending in the axial direction are formed on the inner diameter surface, and eight guide grooves extending in the axial direction on the outer diameter surface. The inner joint member having a fitting portion having a tooth shape on the inner joint member, the guide groove of the outer joint member and the corresponding guide groove of the inner joint member are arranged on eight ball tracks formed in cooperation with each other. comprising the eight torque transmitting balls is, the axial end portion having a tooth die to be connected to the fitting portion of the inner joint member, and, a hollow connecting shaft having an intermediate portion which is continuous to the axial end portion, The ratio r2 (= D _OUTER / PCD _SERR ) between the outer diameter (D _OUTER ) of the outer joint member and the pitch circle diameter (PCD _SERR ) of the fitting portion of the inner joint member is 2.5 ≦ r 2 ≦ 3. 5, and the fitting portion of the outer diameter (dm) and the inner joint member of the intermediate portion of the connecting shaft Providing constant velocity universal joint, wherein the ratio of the tooth form of the pitch circle diameter _{(PCD SERR) r4 (= dm} / PCD SERR) is 1 ≦ r4 ≦ 3.5.

  The present invention has the following effects.

  (1) By making the connecting shaft hollow and increasing the diameter, it is possible to simultaneously achieve high rigidity and light weight of the connecting shaft.

  (2) Since the selection range of the frequency selection (tuning) is expanded by increasing the natural frequency of the shaft portion, it is easy to perform optimum tuning for vibration reduction.

  (3) As described above, the NVH characteristics of the vehicle can be improved.

  (4) When the connecting shaft is drawn from a pipe material, the drawing rate can be kept low, so that the manufacturing cost can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In the first embodiment shown in FIGS. 1 and 2, the present invention is applied to a connecting shaft of a Zepper type constant velocity universal joint (ball-fixed joint) as a fixed type constant velocity universal joint. The constant velocity universal joint of this embodiment includes an outer joint member 1 in which eight curved guide grooves 1b are formed in an axial direction on a spherical inner surface 1a, and eight curves on a spherical outer surface 2a. The inner joint member 2 is formed with a fitting guide 2c having a tooth shape (serration or spline) on the inner diameter surface, and the guide groove 1b of the outer joint member 1 corresponding thereto. Eight torque transmission balls 3 respectively disposed on eight ball tracks formed in cooperation with the guide groove 2b of the inner joint member 2, a cage 4 for holding the torque transmission balls 3, and an inner joint It is comprised with the hollow connection shaft 5 connected with the fitting part 2c of the member 2. FIG.

  In this embodiment, the center O1 of the guide groove 1b of the outer joint member 1 is relative to the spherical center of the inner surface 1a, and the center O2 of the guide groove 2b of the inner joint member 2 is relative to the spherical center of the outer surface 2a. Each is offset to the opposite side by an equal distance (F) in the axial direction (center O1 is the opening side of the joint and center O2 is the back side of the joint). Therefore, the ball track formed by the cooperation of the guide groove 1b and the corresponding guide groove 2b has a shape opened in a wedge shape toward the opening side of the joint.

  The spherical center of the outer diameter surface 4a of the cage 4 and the spherical center of the inner diameter surface 1a of the outer joint member 1 that serves as a guide surface for the outer diameter surface 4a of the cage 4 are both the center O3 of the torque transmitting ball 3. In the joint center plane O. Further, the spherical center of the inner diameter surface 4b of the cage 4 and the spherical center of the outer diameter surface 2a of the inner joint member 2 that serves as a guide surface for the inner diameter surface 4b of the cage 4 are both within the joint center plane O. is there. Therefore, the offset amount (F) of the outer joint member 1 is the axial distance between the center O1 of the guide groove 1b and the joint center plane O, and the offset amount (F) of the inner joint member 2 is the guide groove. The axial distance between the center O2 of 2b and the joint center plane O is the same. The center O1 of the guide groove 1b of the outer joint member 1 and the center O2 of the guide groove 2b of the inner joint member 2 are opposite to the joint center plane O by an equal distance (F) in the axial direction (the center of the guide groove 1b). O1 is in a position shifted to the opening side of the joint and the center O2 of the guide groove 2b is shifted to the back side of the joint.

  When the outer joint member 1 and the inner joint member 2 are angularly displaced by an angle θ, the torque transmitting ball 3 guided by the cage 4 always has a bisection plane (θ / 2) of the angle θ at any operating angle θ. The constant velocity of the joint is ensured.

The ratio r1 (= PCD _BALL / D _BALL ) between the pitch circle diameter (PCD _BALL ) and the diameter (D _BALL ) of the torque transmitting ball 3 can be set to a value within the range of 3.3 ≦ r1 ≦ 5.0. . Here, the pitch circle diameter (PCD _BALL ) of the torque transmitting ball is twice the size of PCR (PCD _BALL = 2 × PCR). The length of the line connecting the center O1 of the guide groove 1b of the outer joint member 1 and the center O3 of the torque transmission ball 3, and the line connecting the center O2 of the guide groove 2b of the inner joint member 2 and the center O3 of the torque transmission ball 3 The length of each is PCR, and both are equal.

The reason for 3.3 ≦ r1 ≦ 5.0 is to ensure that the strength of the outer joint member, etc., the load capacity and durability of the joint are equal to or greater than those of the comparative product (6-ball fixed type constant velocity universal joint). It is. That is, in the constant velocity universal joint, it is difficult to significantly change the pitch circle diameter (PCD _BALL ) of the torque transmitting ball within a limited space. For this reason, the value of r1 mainly depends on the diameter (D _BALL ) of the torque transmission ball. If r1 <3.3 (mainly when the diameter D _BALL is large), the thickness of the other parts (outer joint member, inner joint member, etc.) becomes too thin, which raises concerns about strength. On the contrary, when r1> 5.0 (mainly when the diameter D _BALL is small), the load capacity becomes small, and there is a concern in terms of durability. In addition, the surface pressure of the contact portion between the torque transmission ball and the guide groove increases (because the contact ellipse of the contact portion decreases when the diameter D _BALL decreases). There is concern about becoming.

  By ensuring that 3.3 ≦ r1 ≦ 5.0, the strength of the outer joint member, etc., the load capacity and durability of the joint must be equal to or better than those of the comparative product (6-ball fixed type constant velocity universal joint). Can do. More preferably, it is set to a range of 3.5 ≦ r1 ≦ 5.0, for example, r1 = 3.83 or a value in the vicinity thereof.

The ratio r2 (= D _OUTER / PCD _SERR ) between the outer diameter (D _OUTER ) of the outer joint member 1 and the pitch circle diameter (PCD _SERR ) of the tooth shape (serration or spline) of the fitting portion 2 c of the inner joint member 2 is It is possible to set the value within the range of 2.5 ≦ r2 ≦ 3.5, preferably 2.5 ≦ r2 <3.2.

The reason why 2.5 ≦ r2 ≦ 3.5 is as follows. That is, the pitch circle diameter (PCD _SERR ) of the tooth mold of the fitting portion 2 c of the inner joint member 2 cannot be changed significantly in relation to the strength of the connecting shaft 5 and the like. For this reason, the value of r2 mainly depends on the outer diameter (D _OUTER ) of the outer joint member 1. If r2 <2.5 (mainly when the outer diameter D _OUTER is small), the thickness of each component (outer joint member 1, inner joint member 2, etc.) becomes too thin, and there is concern in terms of strength. . On the other hand, if r2> 3.5 (mainly when the outer diameter D _OUTER is large), there may be practical problems in terms of dimensions and the like, and the purpose of downsizing cannot be achieved. By satisfying 2.5 ≦ r2 ≦ 3.5, the strength of the outer joint member 1 and the like and the durability of the joint can be ensured to be equal to or greater than those of the comparative product (6-ball constant velocity universal joint), and Satisfying practical requirements.

In the constant velocity universal joint of this embodiment, the number of torque transmission balls 3 is eight, and the torque transmission ball 1 occupies the total load capacity of the joint as compared with the comparative product (fixed constant velocity universal joint with six balls). Since the load ratio per unit is small, the diameter (D _BALL ) of the torque transmission ball 3 is made smaller than that of the comparative product of the same nominal type (6-ball fixed type constant velocity universal joint). It is possible to secure the wall thickness and the wall thickness of the inner joint member 2 to the same level as the comparative product (6-ball fixed type constant velocity universal joint). In addition, the ratio r2 (= D _OUTER / PCD _SERR ) is made smaller (compared to the 6-ball fixed type constant velocity universal joint) compared to the comparative product of the same nominal type (6-ball fixed type constant velocity universal joint). The general value of r2 is r2 ≧ 3.2.) While ensuring the strength, load capacity, and durability equivalent to or better than those of the comparative products, the outer diameter (D _OUTER ) is further reduced in size. be able to. In addition, it has been confirmed as a result of experiments that the heat generation is lower than that of a comparative product (fixed constant velocity universal joint with six balls).

The hollow connecting shaft 5 includes a shaft end portion 5a having a tooth mold 5c connected to the fitting portion 2c of the inner joint member 2, and an intermediate portion 5b continuous to the shaft end portion 5a. In this embodiment, the connecting shaft 5 is formed by drawing both ends of a pipe material having an outer diameter dm, and further, a tooth mold (spline or serration) 5c is rolled around the outer periphery of the drawn shaft end 5a. Molded by manufacturing or the like. The outer diameter of the shaft end portion 5a is ds, and the outer diameter of the intermediate portion 5b is the same dm as the pipe material (ds <dm). The pitch circle diameter (PCD _SERR ) of the tooth mold 5 c of the shaft end 5 a is the same as the pitch circle diameter (PCD _SERR ) of the tooth mold of the fitting part 2 c of the inner joint member 2.

  The material of the connecting shaft 5 is carbon steel for mechanical structures such as STKM15A and STKM16A, alloy steel to which an alloy element is added for improving workability and hardenability based on them, or SCr, SCM Carburized steel such as SNCM can be used. When the carbon steel for mechanical structure or alloy steel is used as the material of the connecting shaft 5, induction hardening (partially carburized, carbonitrided carbon) can be mainly used as the heat treatment. Moreover, when the said carburized steel is employ | adopted as a material of the connection shaft 5, carburizing hardening can be mainly employ | adopted as heat processing.

  Moreover, as a drawing method of the connecting shaft 5, swaging, particularly rotary swaging can be employed. Rotary swaging is a pipe that is inserted by rotating a pair or dies built into the main shaft of the machine and a backer in a rotary motion and moving up and down by a fixed stroke with the outer rollers and protrusions on the backer. The material is blown and a part of the material is drawn. In this processing method, processing is relatively fast, the processing surface is smooth and beautiful, and the drawing ratio δ (%) [= {(dm−ds) / dm} × 100] is increased as compared with other processing methods. There is a feature that can be. However, since the material cost and heat treatment cost increase when the drawing ratio δ exceeds 60%, it is preferable that the drawing ratio δ does not exceed 60% in order to reduce the manufacturing cost.

As described above, the constant velocity universal joint of this embodiment has a ratio r2 while ensuring strength, load capacity and durability equal to or higher than those of a comparative product of the same nominal type (6-ball fixed type constant velocity universal joint). (= D _OUTER / PCD _SERR ) can be reduced to further reduce the outer diameter (D _OUTER ). For example, when the pitch circle diameter (PCD _SERR ) of the fitting portion 2c is made equal to that of the comparative product, the outer diameter (D _OUTER ) can be reduced by two sizes (about 8%) by the identification number. On the contrary, when the outer diameter (D _OUTER ) is made equal to that of the comparative product, the pitch circle diameter (PCD _SERR ) of the fitting portion 2c can be increased by 5 sizes or more.

Taking the # 71 size of the comparative product (6-ball fixed type constant velocity universal joint) as an example, the outer diameter (D _OUTER ) is 65.3 mm, and the pitch circle diameter (PCD _SERR ) is 19.05 mm. Here, assuming a solid shaft with a total length of 350 mm and a uniform outer diameter as the connecting shaft, the bending primary natural frequency is about 310 Hz. When the processing limit when drawing the hollow shaft from the pipe material is 60% in terms of the drawing ratio δ, the outer diameter dm of the pipe material is about 47.5 mm. Here, assuming a hollow shaft having a total length of 350 mm, an outer diameter of 47.5 mm, a thickness of 2 mm, and a uniform outer diameter as the connecting shaft, the bending primary natural frequency is about 1056 Hz.

On the other hand, in the constant velocity universal joint of this embodiment, when the outer diameter (D _OUTER ) is set to 65.3 mm, which is the same as the comparative product, the pitch circle diameter (PCD _SERR ) of the fitting portion 2c is increased to 26.3 mm. Is possible. Therefore, if the processing limit when drawing the hollow shaft from the pipe material is 60% in terms of the drawing ratio δ, the outer diameter dm of the pipe material can be about 65.7 mm. Here, assuming a hollow shaft having a total length of 350 mm, an outer diameter of 65.7 mm, a wall thickness of 2 mm, and a uniform outer diameter as the connecting shaft, the bending primary natural frequency is about 1478 Hz. Thus, when the hollow connecting shaft 5 is combined with the constant velocity universal joint of this embodiment, the bending primary natural frequency can be made higher than that of the comparative product. Therefore, the range of frequency selection (tuning) is widened, and it becomes easy to perform optimum tuning. Regarding the rigidity of the connecting shaft (torsional rigidity), when the torsional rigidity of the solid shaft with an outer diameter of 19.05 mm is 100, that of the hollow shaft with an outer diameter of 47.5 mm and a wall thickness of 2 mm is 1438, The hollow shaft having an outer diameter of 65.7 mm and a wall thickness of 2 mm is 3943. Therefore, when the hollow connecting shaft 5 is combined with the constant velocity universal joint of this embodiment, it is possible to obtain the connecting shaft 5 having higher rigidity than the comparative product.

The outer diameter dm of the pipe material (= the outer diameter dm of the intermediate portion 5b) can be selected within a range where the ratio r3 (= dm / D _OUTER ) is 0.29 ≦ r3 ≦ 1.0. When r2 (= D _OUTER / PCD _SERR ) is set within the range of 2.5 ≦ r2 ≦ 3.5, the outer diameter (dm) of the intermediate portion 5b and the shaft end portion 5a are determined from the relationship between the ratio r2 and the ratio r3. The ratio r4 (= dm / PCD _SERR ) to the pitch circle diameter (PCD _SERR ) of the tooth mold 5c is 0.725 ≦ r4 ≦ 3.5. From dm ≧ ds, 1 ≦ r4 ≦ 3.5. Further, the drawing ratio δ (%) of the pipe material can be set to 0% ≦ δ (%) ≦ 60%. Therefore, the processing cost when the shaft end portion 5b is drawn by rotary swaging or the like can be kept low. Note that δ = 0% is when the connecting shaft 5 is not drawn, that is, when the connecting shaft 5 has a uniform outer diameter (ds = dm), but when the pitch circle diameter (PCD _SERR ) is increased, the connecting shaft 5 is connected. Since the outer diameter (ds = dm) of the shaft 5 can be increased, the optimum tuning of the vibration frequency is possible, and when the required shaft rigidity is obtained, the connecting shaft 5 has a uniform outer diameter (ds = dm). ) Hollow shaft.

  In the second embodiment shown in FIGS. 3 and 4, the present invention is applied to a double offset type constant velocity universal joint as a sliding type constant velocity universal joint. The constant velocity universal joint of this embodiment includes an outer joint member 1 ′ having eight linear guide grooves 1b ′ formed in the axial direction on a cylindrical inner surface 1a ′, and a spherical outer surface 2a ′. An inner joint member 2 ′ having eight linear guide grooves 2b ′ formed in the axial direction and having a fitting portion 2c ′ having a tooth shape (serration or spline) on the inner diameter surface, and an outer joint member 1 ′. Eight torque transmission balls 3 ′ respectively disposed on eight ball tracks formed in cooperation with the guide groove 1b ′ and the corresponding guide groove 2b ′ of the inner joint member 2 ′, and torque transmission The cage 4 ′ is configured to hold the ball 3 ′ and the hollow coupling shaft 5 ′ coupled to the fitting portion 2c ′ of the inner joint member 2 ′.

  In this embodiment, the spherical center of the outer diameter surface 4b ′ and the spherical center of the inner diameter surface 4a ′ of the cage 4 ′ are opposite to each other by an equal distance in the axial direction with respect to the pocket center of the cage 4 ′. It is offset.

The ratio _{r1 (= PCD BALL / D BALL} ) of the pitch circle diameter and (PCD _BALL) to the diameter (D _BALL) of the torque transmitting balls 3 ', for the same reason as the constant velocity universal joint of the first embodiment described above It is possible to set the value within the range of 2.9 ≦ r1 ≦ 4.5, preferably within the range of 3.1 ≦ r1 ≦ 4.5. Here, the pitch circle diameter (PCD _BALL ) of the torque transmission balls is equal to the distance between the centers of the two torque transmission balls located in the ball tracks facing each other by 180 degrees at the operating angle of 0 °. The PCR in FIG. 4 has a size half the pitch circle diameter (PCD _BALL ) (PCD _BALL = 2 × PCR).

Further, the ratio r2 between the outer diameter (D _OUTER ) of the outer joint member 1 ′ and the pitch circle diameter (PCD _SERR ) of the tooth shape (serration or spline) of the fitting portion 2 c ′ of the inner joint member 2 is as described above. For the same reason as the constant velocity universal joint of the first embodiment, it is possible to set the value within the range of 2.5 ≦ r2 ≦ 3.5, preferably 2.5 ≦ r2 <3.1.

Similar to the constant velocity universal joint of the first embodiment, the constant velocity universal joint of this embodiment has eight torque transmission balls 3 'and is a comparative product (six-ball sliding type constant velocity universal). Compared with the joint), the load ratio per torque transmission ball occupying the total load capacity of the joint is small, so torque transmission is possible for the comparative product of the same nominal type (six-ball sliding type constant velocity universal joint). The diameter of the ball 3 ′ (DBALL) is reduced, and the wall thickness of the outer joint member 1 ′ and the wall thickness of the inner joint member 2 ′ are secured to the same level as the comparative product (six-ball sliding type constant velocity universal joint). Is possible. In addition, the ratio r2 (= D _OUTER / PCD _SERR ) is reduced (six-ball sliding type constant velocity universal) compared to the comparative product of the same nominal type (six-ball sliding type constant velocity universal joint). The general value of r2 in the joint is r2 ≧ 3.1.) While ensuring the strength, load capacity and durability equivalent to or better than those of the comparative products, the outer diameter (D _OUTER ) is further _downsized . Can be achieved. In addition, it has been confirmed as a result of experiments that the heat generation is lower than that of a comparative product (sliding type constant velocity universal joint with six balls).

  The hollow connecting shaft 5 ′ includes a shaft end portion 5a ′ having a tooth mold 5c ′ connected to the fitting portion 2c ′ of the inner joint member 2 ′, and an intermediate portion 5b ′ continuous with the shaft end portion 5a ′. It consists of. In this embodiment, the connecting shaft 5 ′ is formed by drawing both ends of a pipe material having an outer diameter dm, and further, a tooth mold (spline or serration) 5c is formed on the outer periphery of the shaft end of the drawn shaft end 5a ′. 'Is formed by rolling or the like. The outer diameter of the shaft end portion 5a 'is ds, and the outer diameter of the intermediate portion 5b' is the same dm as that of the pipe material (ds <dm).

The material of the connecting shaft 5 ′, the drawing method, and the like can be the same as in the first embodiment. Further, the outer diameter dm (the outer diameter of the pipe material) of the intermediate portion 5b ′ can be selected within a range where the ratio r3 (= dm / D _OUTER ) is 0.29 ≦ r3 ≦ 1.0, When the ratio r2 (= D _OUTER / PCD _SERR ) is set within the range of 2.5 ≦ r2 ≦ 3.5, the outer diameter (dm) of the intermediate portion 5b ′ and the shaft end are determined from the relationship between the ratio r2 and the ratio r3. The ratio r4 (= dm / PCD _SERR ) to the pitch circle diameter (PCD _SERR ) of the tooth mold 5c ′ of the portion 5a ′ is 1 ≦ r4 ≦ 3.5, and the drawing ratio δ (%) of the pipe material is 0. % ≦ δ (%) ≦ 60%. Therefore, it is possible to reduce the processing cost when the shaft end portion 5b ′ is subjected to rotary swaging processing or the like. Others are the same as those in the first embodiment, and a duplicate description is omitted.

  The configurations of the first and second embodiments described above can be applied to an automobile power transmission device as shown in FIG. 5, for example.

It is a longitudinal cross-sectional view (YY cross section in FIG. 2) which shows the 1st Embodiment of this invention. It is a longitudinal cross-sectional view (XX cross section in FIG. 1) which shows the 1st Embodiment of this invention. It is a longitudinal cross-sectional view (YY cross section in FIG. 4) which shows the 2nd Embodiment of this invention. It is a longitudinal cross-sectional view (XX cross section in FIG. 3) which shows the 2nd Embodiment of this invention. It is sectional drawing which shows the power transmission device of a motor vehicle.

Explanation of symbols

1, 1 'outer joint member 1a, 1a' inner diameter surface 1b, 1b 'guide groove 2, 2' inner joint member 2a, 2a 'outer diameter surface 2b, 2b' guide groove 3, 3 'torque transmission ball 4, 4' Cage 5, 5 'hollow connecting shaft 5a, 5a' shaft end 5b, 5b 'intermediate part

Claims (1)

An outer joint member having eight guide grooves extending in the axial direction on the inner diameter surface and eight guide grooves extending in the axial direction on the outer diameter surface are formed, and a fitting portion having a tooth shape is formed on the inner diameter surface. An inner joint member, eight torque transmission balls respectively disposed on eight ball tracks formed by cooperation of a guide groove of the outer joint member and a corresponding guide groove of the inner joint member; axial end portion having a tooth die to be connected to the fitting portion of the coupling member, and a hollow connecting shaft having an intermediate portion which is continuous to the shaft end,
The ratio r2 (= D _OUTER / PCD _SERR ) between the outer diameter (D _OUTER ) of the outer joint member and the pitch circle diameter (PCD _SERR ) of the tooth mold of the fitting portion of the inner joint member is 2.5 ≦ r 2 ≦ 3.5,
The ratio r4 (= dm / PCD _SERR ) between the outer diameter (dm) of the intermediate portion of the connecting shaft and the pitch circle diameter (PCD _SERR ) of the tooth shape of the fitting portion of the inner joint member is 1 ≦ r4 ≦ 3. 5 is a constant velocity universal joint .

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