WO2025204357A1 - Boot for constant velocity joint - Google Patents

Abstract

Provided is a boot 30 for a constant velocity joint in which a large diameter cylindrical part 31, a small diameter cylindrical part 32, an elastic part 33 that has one valley section 33a curved in an arc shape and that extends from the small diameter cylindrical part 32 toward the large diameter cylindrical part 31, and a connection part 34 connecting the large diameter cylindrical part 31 and the elastic part 33 are integrally molded with a flexible material, and the elastic part 33 is elastically deformed following a relative angular displacement of two joint members 21, 24, wherein the connection part 34 is formed thicker than the elastic part 33.

Description

Boots for constant velocity universal joints

The present invention relates to a boot for a constant velocity universal joint that is attached as a sealing member to a constant velocity universal joint incorporated into the power transmission mechanism of an automobile or various industrial machines.

For example, automobiles equipped with a drive source such as an engine or electric motor mounted on the chassis are equipped with a power transmission device for transmitting the output of the drive source to the drive wheels. An example of this type of power transmission device is a drive shaft equipped with a fixed constant velocity universal joint that allows only angular displacement of the two connected shafts, a sliding constant velocity universal joint that allows angular and axial displacement of the two connected shafts, and a shaft member that connects the inner joint members of the two constant velocity universal joints, which are spaced apart in the width direction of the automobile, so that torque can be transmitted. The shaft member is also called an "intermediate shaft" or "power transmission shaft."

In the above-mentioned drive shaft, a cylindrical boot (constant velocity universal joint boot) that functions as a sealing member is provided between the shaft member and the outer joint member of each constant velocity universal joint. A large-diameter cylindrical portion and a small-diameter cylindrical portion are provided at one and the other axial ends of the boot, respectively; the large-diameter cylindrical portion is attached to the outer joint member, and the small-diameter cylindrical portion is attached to the shaft member. This prevents the lubricant filled inside the joint from leaking out and foreign matter from entering the joint.

A section (elastic portion) is provided between the large-diameter cylindrical portion and the small-diameter cylindrical portion of the boot, which elastically deforms in response to the relative displacement of the outer joint member and the inner joint member (or the shaft member connected to them). This elastic portion can be bellows-shaped or non-bellows-shaped, with the latter example described in Patent Document 1 below being well-known.

The boot in Patent Document 1 is formed entirely from a flexible material (elastic material) such as resin or rubber, and the elastic portion has a generally J-shaped cross section with a single arc-shaped valley (folded portion) in a free state. This elastic portion is connected to the large-diameter cylindrical portion via a connecting portion (referred to as the "boot shoulder portion" in Patent Document 1), and the connecting portion is provided with multiple axially extending reinforcing ribs spaced circumferentially. This increases the rigidity (strength) of the connecting portion and prevents the elastic portion from expanding and deforming due to the centrifugal force generated when the constant velocity universal joint rotates, thereby stably fulfilling the sealing function required of the boot. Furthermore, the boot in Patent Document 1, which is formed entirely from a flexible material, has the advantage of being less expensive than boots in which the portions corresponding to the connecting portion and large-diameter cylindrical portion are constructed from metallic tubular (annular) members.

Japanese Unexamined Patent Publication No. 11-190358

Incidentally, constant velocity universal joints are sometimes used in high-speed rotation transmission applications where a large centrifugal force is generated that causes the elastic portion of the boot to expand and deform, and sometimes used in relatively low-speed rotation transmission applications where only a small centrifugal force is generated that does not cause the elastic portion of the boot to expand and deform. In the latter case in particular, there is thought to be little need to take the rigidity (strength) improvement measures adopted in Patent Document 1, which lead to a more complex boot shape and higher costs. However, when transporting or carrying a constant velocity universal joint (including a drive shaft) or when attaching it to an object, the weight of the shaft member (and the resulting bending moment) may cause the constant velocity universal joint to bend (the two joint members to undergo a relative angular displacement). In this case, if the boot's rigidity is insufficient, the elastic portion of the boot may become pinched (bitten) between the outer joint member and the shaft member, resulting in damage.

In light of this situation, the main object of the present invention is to provide a boot for a constant velocity universal joint that has a simple structure yet can effectively prevent bending of the constant velocity universal joint due to the weight of the shaft member connected to the inner joint member, thereby contributing to the simplification and efficiency of the transportation and handling of constant velocity universal joints and the assembly work into vehicles.

The boot for a constant velocity universal joint according to the present invention, which has been devised to achieve the above object, comprises:
a large-diameter cylindrical portion attached to an outer joint member of the constant velocity universal joint; a small-diameter cylindrical portion attached to a shaft member that rotates together with the inner joint member of the constant velocity universal joint; an elastic portion having one arc-shaped valley portion and extending from the small-diameter cylindrical portion toward the large-diameter cylindrical portion; and a connecting portion connecting the large-diameter cylindrical portion and the elastic portion, which are integrally molded from a flexible material;
The outer joint member and the shaft member undergo elastic deformation in response to the relative angular displacement between them.
The connection portion is formed to be thicker than the elastic portion.

In the above-mentioned boot for a constant velocity universal joint (hereinafter simply referred to as "boot") according to the present invention, the elastic portion is maintained in a non-contact state with the outer joint member against the moment load due to the weight of the shaft member, mainly by controlling the thickness of the connection portion, which is made thicker than the elastic portion. Therefore, while the boot according to the present invention has a simple configuration that does not take measures that would complicate the shape, it prevents the constant velocity universal joint from bending excessively due to the weight of the shaft member (excessively large relative angular displacement between the two joint members), contributing to easier and more efficient transportation and handling of constant velocity universal joints (including drive shafts, etc.) and installation on vehicle bodies.

Here, an example of a method (procedure) for determining whether "the elastic portion is maintained in a non-contact state with the outer joint member against the moment load due to the weight of the shaft member" will be shown below.
First, in a drive shaft having a fixed constant velocity universal joint and a sliding constant velocity universal joint connected to one and the other axial end of a shaft member, respectively, the sliding constant velocity universal joint is removed to expose the other axial end of the shaft member.
Next, the outer joint member of the fixed type constant velocity universal joint equipped with the boot according to the present invention is fixed in a horizontal position, and then the shaft member is released, allowing the shaft member (and the inner joint member connected to it) to tilt under its own weight.
Finally, it is confirmed whether or not the elastic portion of the boot is in contact with the outer joint member.

As described above, the boot according to the present invention is configured so that the connection portion is thicker than the elastic portion. However, if the connection portion is made too thick, a number of other problems can arise, such as impairing the boot's deformability and reducing the operability of the constant velocity universal joint, increasing the cost and weight of the boot (and the constant velocity universal joint inclusive), and reducing the moldability of the boot (making it more susceptible to molding defects). Therefore, after extensive research, the inventors have discovered the specific configuration described below, which makes it possible to achieve the above-mentioned objectives without causing the above-mentioned various other problems.

First, the connecting portion is composed of an annular portion having a thickness of 2 mm or more and 4 mm or less, extending radially outward from the end of the elastic portion on the large-diameter cylindrical portion side, and a tapered portion connecting the annular portion and the large-diameter cylindrical portion, the tapered portion gradually increasing in diameter from the annular portion side toward the large-diameter cylindrical portion side,
Furthermore, when the thickness x of the annular portion is set to be 2 mm or more and less than 3 mm, the ratio δ1 (= y/x) of the thickness y of the tapered portion to the thickness x of the annular portion satisfies the following relational expression (1), and when the thickness x of the annular portion is set to be 3 mm or more and 4 mm or less, the ratio δ1 satisfies the following relational expression (2).
-0.21x+1.24≦δ1≦-0.67x+3.31...(1)
-0.04x+0.71≦δ1≦-0.33x+2.33...(2)

When the thickness x of the annular portion is 2 mm or more and less than 3 mm, the ratio δ1 may satisfy the following relational expression (3), which is a partial modification of the relational expression (1), and when the thickness x of the annular portion is 3 mm or more and 4 mm or less, the ratio δ1 may satisfy the following relational expression (4), which is a partial modification of the relational expression (2).
-0.21x+1.24≦ δ1≦(-0.21x+1.24)×1.2...(3)
-0.04x+0.71≦ δ1≦(-0.04x+0.71)×1.2...(4)

Furthermore, when the thickness x of the annular portion is 2 mm or more and less than 3 mm, the ratio δ1 may satisfy the following relational expression (5), which is a partial modification of the relational expression (1), and when the thickness x of the annular portion is 3 mm or more and 4 mm or less, the ratio δ1 may satisfy the following relational expression (6), which is a partial modification of the relational expression (2).
-0.21x+1.24≦ δ1≦(-0.21x+1.24)×1.1...(5)
-0.04x+0.71≦ δ1≦(-0.04x+0.71)×1.1...(6)

As a second configuration that can achieve the above object without causing the various other problems described above, the connecting portion is configured with an annular portion having a wall thickness of 2 mm or more and 4 mm or less, extending radially outward from the end of the elastic portion on the large-diameter cylindrical portion side, and a cylindrical portion that connects the annular portion and the large-diameter cylindrical portion,
Furthermore, when the thickness x of the annular portion is set to be 2 mm or more and less than 3 mm, the ratio δ2 (=z/x) of the thickness z of the cylindrical portion to the thickness x of the annular portion satisfies the following relational expression (7), and when the thickness x of the annular portion is set to be 3 mm or more and 4 mm or less, the ratio δ2 satisfies the following relational expression (8).
0.6 ≦ δ2 ≦ -0.67x+3.31...(7)
0.6 ≦ δ2 ≦ -0.33x+2.33...(8)

As a third configuration that can achieve the above object without causing the various other problems mentioned above, the connecting portion is configured to include an annular portion having a thickness of 2 mm or more and 4 mm or less, extending radially outward from the end of the elastic portion on the large-diameter cylindrical portion side, and a cylindrical portion that connects this annular portion to the large-diameter cylindrical portion, and further, the ratio δ2 (= z/x) of the thickness z of the cylindrical portion to the thickness x of the annular portion satisfies the following relational expression (9).
0.6≦δ2≦0.6×1.2...(9)

As a fourth configuration that can achieve the above object without causing the various other problems mentioned above, the connecting portion is configured to include an annular portion having a thickness of 2 mm or more and 4 mm or less, extending radially outward from the end of the elastic portion on the large-diameter cylindrical portion side, and a cylindrical portion that connects this annular portion to the large-diameter cylindrical portion, and further, the ratio δ2 (= z/x) of the thickness z of the cylindrical portion to the thickness x of the annular portion satisfies the following relational expression (10):
0.6≦δ2≦0.6×1.1...(10)

Whether the above relationship formulas (1) to (10) are satisfied will be determined under room temperature conditions.

As described above, the present invention provides a boot for a constant velocity universal joint that has a simple structure but is capable of preventing bending of the constant velocity universal joint due to the weight of the shaft member connected to the inner joint member, and further preventing the elastic portion from becoming jammed due to this. Such a boot can contribute to simplifying and streamlining the transportation and handling of constant velocity universal joints and the assembly work into vehicles.

1 is a longitudinal sectional view of a power transmission device including, as a component, a constant velocity universal joint to which a boot for a constant velocity universal joint according to a first embodiment of the present invention is attached. 2 is a diagram showing a state in which the fixed type constant velocity universal joint shown in FIG. 1 has an operating angle. FIG. FIG. 2 is a vertical cross-sectional view of the boot shown in FIG. 1 in a free state. FIG. 10 is a scatter diagram showing the analysis results of the numerical analysis carried out in the process of completing the boot according to the first embodiment, the scatter diagram showing the analysis results for the first joint model. FIG. 10 is a scatter plot showing the analysis results for the second joint model. FIG. 10 is a scatter plot showing the analysis results for the third joint model. FIG. 10 is a scatter plot showing the analysis results for the fourth joint model. FIG. 10 is a scatter plot showing the analysis results for the fifth joint model. FIG. 9 is a scatter diagram created based on FIGS. 4 to 8 to show the relationship between the thickness of the annular portion of the boot according to the first embodiment and the ratio δ1. FIG. 10 is a diagram showing the results of an analysis that confirmed the effect of the inclination angle of the tapered portion of the boot on the elongation strain of the elastic portion of the boot. FIG. 10 is a longitudinal sectional view of a boot according to a second embodiment of the present invention in a free state. FIG. 10 is a scatter diagram showing the analysis results of the numerical analysis carried out in the process of completing the boot according to the second embodiment, and is a diagram showing the analysis results for the sixth joint model. FIG. 10 is a diagram showing an analysis result for a seventh joint model. FIG. 10 is a diagram showing an analysis result for an eighth joint model. FIG. 15 is a scatter diagram created based on FIGS. 12 to 14 to show the relationship between the thickness of the annular portion of the boot according to the second embodiment and the ratio δ2.

The following describes an embodiment of the present invention with reference to the drawings.

1 shows a longitudinal cross-sectional view of a power transmission device including a fixed constant velocity universal joint fitted with a boot for a constant velocity universal joint (hereinafter simply referred to as "boot") according to the first embodiment of the present invention, and FIG. 2 shows the fixed constant velocity universal joint shown in FIG. 1 at an operating angle. The power transmission device shown in FIG. 1 is a drive shaft (rear wheel drive shaft) 1 that is arranged on the chassis of an automobile along the vehicle width direction and transmits torque output from a drive source such as an engine or electric motor to wheels (particularly the rear wheels). This drive shaft 1 comprises a sliding constant velocity universal joint 10 arranged on the drive source side (inboard side), a fixed constant velocity universal joint 20 arranged on the wheel side (outboard side), and a shaft member 2 connected to the inner joint members of both constant velocity universal joints 10, 20 so as to be able to transmit torque (rotate integrally). The terms "axial direction," "radial direction," and "circumferential direction" used in the following description refer to the direction parallel to the axis O of the shaft member 2, and the radial direction and circumferential direction of a circle centered on the central axis O, respectively.

The sliding type constant velocity universal joint 10 shown in the figure is a so-called double offset type, and includes an outer joint member 11 having a bottomed cylindrical cup portion 12 and a plurality of linear outer track grooves 13 formed on the cylindrical inner diameter surface of the cup portion 12; an inner joint member 14 having a plurality of linear inner track grooves 15 formed on the convex spherical outer diameter surface and one end of a shaft member 2 spline-fitted into a shaft hole; a plurality of balls 16 interposed between the paired track grooves 13, 15 to transmit torque between the two joint members 11, 14; and a cage 17 that holds the balls 16 at intervals in the circumferential direction. Instead of the double offset type, other well-known types of sliding type constant velocity universal joints, such as a tripod type or cross groove type, may be used for this sliding type constant velocity universal joint 10.

A resin boot 3 is provided between the outer joint member 11 and the shaft member 2. It is molded into a cylindrical shape from a resin material whose main ingredient is a thermoplastic elastomer and functions as a sealing member. This boot 3 integrally comprises a large-diameter cylindrical portion 4 attached to the cup portion 12 of the outer joint member 11, a small-diameter cylindrical portion 5 attached to the shaft member 2, and a bellows portion 6 which is provided axially between the cylindrical portions 4, 5 and serves as an elastic portion that elastically deforms in response to relative angular and/or axial displacement between the outer joint member 11 and the inner joint member 14 (or the shaft member 2 connected thereto).

The large-diameter cylindrical portion 4 of the boot 3 is attached to the cup portion 12 of the outer joint member 11 by fastening its outer peripheral surface with a boot band 7A, and the small-diameter cylindrical portion 5 of the boot 3 is attached to the shaft member 2 by fastening its outer peripheral surface with a boot band 7B. Attaching the boot 3 to the outer joint member 11 and the shaft member 2 in the above manner minimizes leakage of the lubricant filled in the internal space of the cup portion 12 (inside the joint) and prevents foreign matter from entering the inside of the joint.

The fixed type constant velocity universal joint 20, also shown in Figure 2, is a so-called Birrfield type and includes an outer joint member 21 having a cup-shaped mouth portion 22 with a plurality of outer track grooves 23 formed on the concave spherical inner diameter surface of the mouth portion 22, an inner joint member 24 having a plurality of inner track grooves 25 formed on the convex spherical outer diameter surface and having the other end of the shaft member 2 spline-fitted into the shaft hole, a plurality of balls 26 interposed between the paired track grooves 23, 25 to transmit torque between the two joint members 21, 24, and a cage 27 that holds the plurality of balls 26 at intervals in the circumferential direction. Other types of fixed type constant velocity universal joints, such as an undercut-free type, may also be used for this fixed type constant velocity universal joint 20.

A cylindrical boot 30 is provided between the outer joint member 21 and the shaft member 2. Like the boot 3 described above, it is molded from a resin material whose main ingredient is a thermoplastic elastomer and functions as a sealing member. This boot 30 is integrally formed with a large-diameter cylindrical portion 31 attached to the mouth portion 22 of the outer joint member 21, a small-diameter cylindrical portion 32 attached to the shaft member 2, an elastic portion 33 provided between the two cylindrical portions 31, 32 and elastically deforms in response to relative angular displacement between the outer joint member 21 and the inner joint member 24 (the shaft member 2 connected thereto), and a connecting portion 34 connecting the elastic portion 33 to the large-diameter cylindrical portion 31.

The large-diameter cylindrical portion 31 of the boot 30 is attached to the outer joint member 21 (mouth portion 22) by fastening its outer peripheral surface with a boot band 8A, and the small-diameter cylindrical portion 32 of the boot 30 is attached to the shaft member 2 by fastening its outer peripheral surface with a boot band 8B. Attaching the boot 30 to the outer joint member 21 and shaft member 2 in the above manner minimizes leakage of the lubricant filled in the internal space of the mouth portion 22 (inside the joint) and prevents foreign matter from entering the inside of the joint.

Thermoplastic elastomers that can be used to mold the boots 3, 30 described above include polystyrene-based (TPS), polyvinyl chloride-based (TPVC), polyurethane-based (TPU), polyester-based (TPEE), and polyamide-based (TPA). Only one type may be selected and used, or multiple types may be mixed and used. The boots 3, 30 can also be molded using flexible materials other than the resin materials listed above, such as rubber materials. The boots 3, 30 can be molded using methods such as injection molding, blow molding, and extrusion molding. The optimal molding method is selected depending on the shape, etc., but injection molding is preferred as the molding method for the boots 30 of this embodiment.

In particular, it is desirable to use a thermoplastic elastomer with an ISO 48-4 Shore D hardness of 35 or more and 60 or less for the boot 30 attached to the fixed constant velocity universal joint 20. This is because if the Shore D hardness is 35 or less, the rigidity of the boot 30 itself is insufficient, making the elastic portion 33 more likely to come into contact with the outer joint member 21 when the fixed constant velocity universal joint 30 forms a working angle, and this contact could result in damage to the elastic portion 33. On the other hand, if the Shore D hardness is greater than 60, the fatigue strength of the boot 30 itself is insufficient, increasing the likelihood of early damage when the fixed constant velocity universal joint 30 rotates while forming a working angle.

The boot 30 of this embodiment is characterized by the elastic portion 33 and the connecting portion 34. The characteristic configuration employed in the boot 30 of this embodiment will be explained in detail below, with reference to the longitudinal cross-sectional view of the boot 30 in its free state (a state in which each part is not subjected to any stress) shown in Figure 3.

As shown in Figure 3, the elastic portion 33 of the boot 30 in its free state has a generally J-shaped cross section, integrally comprising a cylindrical portion extending from the small-diameter cylindrical portion 32 toward the large-diameter cylindrical portion 31 and one arc-shaped valley portion 33a. The thickness t of this elastic portion 33 is generally constant throughout the entire elastic portion 33 and can be set to a value that combines flexible deformation behavior with desired durability. Specifically, the thickness t is preferably set to 2 mm or less, and the ratio of the thickness x of the annular portion 35 and the thickness y of the tapered portion 36, both of which are described below, is preferably set to a value within the range of 0.3 to 0.7 (0.3x ≤ t ≤ 0.7x and 0.3y ≤ t ≤ 0.7y).

The connecting portion 34 of the boot 30 is composed of a flange-shaped annular portion 35 extending radially outward from the end of the elastic portion 33 on the large-diameter cylindrical portion 31 side, and a tapered portion 36 that connects this annular portion 35 (the outer diameter end) to the large-diameter cylindrical portion 31 and gradually widens in diameter from the annular portion 35 side toward the large-diameter cylindrical portion 31 side. The outer diameter surface of the tapered portion 36 is formed into a conical surface with no radial irregularities, and the inner diameter surface of the tapered portion 36 is provided with an annular protrusion 37 that can axially engage with the open end surface of the mouth portion 22 of the outer joint member 21. The provision of this annular protrusion 37 makes it possible to easily and accurately position the large-diameter cylindrical portion 31 in the axial direction relative to the mouth portion 22 of the outer joint member 21.

The inclination angle α of the tapered portion 36 relative to the axial direction (here, the angle the outer diameter surface of the tapered portion 36 makes relative to the axial direction) is set primarily taking into consideration the rate of increase in strain (elongation strain) generated in the tapered portion 36 when a bending moment acts on the boot 30 due to relative angular displacement between the two coupling parts 21, 24 and the size of the boot 30, and is preferably set to between 20° and 30° (20°≦α≦30°). The upper limit of the inclination angle α (= 30°) was set based on the results of tests (numerical analysis) that confirmed the effect that the inclination angle α of the tapered portion 36 has on the rate of increase in strain generated in the tapered portion 36 when a bending moment acts on it.

In other words, as is clear from Figure 10 showing the analysis results, the larger the inclination angle α of the tapered portion 36, the greater the rate of increase in strain in the tapered portion 36 when a bending moment acts on the boot 30 (when the constant velocity universal joint 20 forms an operating angle). The rate of increase in strain when a bending moment acts becomes particularly significant when the inclination angle α exceeds 30°. The results shown in Figure 10 are the result of a numerical analysis performed using a model of a constant velocity universal joint 20 equipped with a resin boot 30 with an outer diameter of φ87.5 mm for the mouth portion 22 of the outer joint member 21, the outer diameter of the large diameter cylindrical portion 31: φ89.5 mm, the outer diameter of the small diameter cylindrical portion 32: φ33.7 mm, the thickness x of the annular portion 35: 3 mm, the thickness y of the tapered portion 36: 2 mm, and the thickness t of the elastic portion 33: 1.2 mm.

To further explain how to interpret the table shown in Figure 10, for example, when a constant velocity universal joint 20 equipped with a boot 30 having a tapered portion 36 with an inclination angle α = 10° is subjected to a relative angular displacement between the two joint parts 21, 24 from an operating angle of 0° to an operating angle of 5°, strain increases by 9%. For these reasons, the upper limit for the inclination angle α is set to 30°. On the other hand, the smaller the inclination angle α, the greater the axial length of the tapered portion 36, and therefore the boot 30 including it. For these reasons, it is preferable to set the inclination angle α of the tapered portion 36 relative to the axial direction within the range of 20° to 30°.

The connecting portion 34 (the annular portion 35 and tapered portion 36 that constitute it) is thicker than the elastic portion 33, increasing its rigidity, so that even if a moment load (bending moment) acts on the boot 30 and elastically deforms the elastic portion 33 as a result of the shaft member 2 connected to the inner joint member 24 being angularly displaced relative to the outer joint member 21 due to its own weight or other factors, the elastic portion 33 can be maintained in a non-contact state with the mouth portion 22 of the outer joint member 21 against this moment load (to prevent the elastic portion 33 from becoming pinched between the shaft member 2 and the mouth portion 22 and being damaged). Here, the thickness x of the annular portion 35 is set to 2 mm or more.

The larger the thickness x of the annular portion 35, the better the ability to prevent the elastic portion 33 from getting caught during angular displacement of the joint. However, if the thickness x is made too large, it can cause a number of other problems, such as reduced moldability of the boot 30 (making the boot 30 more susceptible to molding defects), reduced deformability of the boot 30 and reduced operability of the constant velocity universal joint 20 (making it unable to undergo smooth angular displacement), and increased cost and weight of the boot 30 (and the constant velocity universal joint 20 inclusive). For this reason, the thickness x of the annular portion 35 is set to 4 mm or less. In other words, the thickness x of the annular portion 35 is set within the range of 2 mm to 4 mm (2 mm≦x≦4 mm).

Furthermore, if the thickness y of the tapered portion 36 is too large, problems with formability will arise, just as when the thickness x of the annular portion 35 is made too large, so the upper limit is set to 4 mm, just like the thickness x of the annular portion 35.

However, in order to prevent the elastic portion 33 from getting caught while also preventing the occurrence of the various problems mentioned above, the thickness x of the annular portion 35 and the thickness y of the tapered portion 36 are set to satisfy the relationship described below, which the inventors discovered through numerical analysis as a confirmation test. First, the analysis procedure will be explained. Note that the temperature conditions during the analysis were room temperature.

[Step 1]
A plurality of boot 30 models (boot models) were created in which the wall thickness x of the annular portion 35 was varied within the above-mentioned range of 2 to 4 mm. Here, a first boot model was created in which the wall thickness x of the annular portion 35 was 2.0 mm, a second boot model was created in which x was 2.5 mm, a third boot model was created in which x was 3.0 mm, a fourth boot model was created in which x was 3.5 mm, and a fifth boot model was created in which x was 4.0 mm. In each of the boot models, the outer diameter of the large-diameter cylindrical portion 31 was φ89.5 mm, and the outer diameter of the small-diameter cylindrical portion 32 was φ33.7 mm.
[Step 2]
When a predetermined bending moment was applied to a model (joint model) of the fixed constant velocity universal joint 20 equipped with each of the above boot models and set at a working angle of 0°, we confirmed how the relative angular displacement of the shaft member 2 with respect to the outer joint member 21 (the working angle of the constant velocity universal joint 20) changed and progressed with changes in the ratio δ1 (= y/x) of the thickness y of the tapered portion 36 to the thickness x of the annular portion 35. The bending moment applied to the joint model was 1740 Nmm. Note that the bending moment of 1740 Nmm is significantly smaller than the bending moment due to the weight of the shaft member 2, being approximately 1/4 to 1/2 of the bending moment due to the weight of the shaft member 2. This was done to confirm the behavior of the boot 30 until the elastic portion 33 of the boot 30 was engaged. For comparison, bending moments of 2000 Nmm and 3000 Nmm were also applied to the joint model, but the bending moment of 3000 Nmm was also smaller than the bending moment due to the weight of the shaft member 2 itself.
[Step 3]
For each of the above joint models, a scatter diagram was created with the ratio δ1 on the horizontal axis and the amount of angular displacement on the vertical axis. Fig. 4 shows a scatter diagram for the joint model equipped with the first boot model (first joint model), and Figs. 5 to 8 show scatter diagrams for the joint models equipped with the second to fifth boot models (second to fifth joint models), respectively. It can be seen from Figs. 4 to 8 that the greater the ratio δ1 (the greater the thickness y of the tapered portion 36), the greater the effect of suppressing angular displacement when a bending moment is applied.

Next, the angular displacement of each joint model will be considered with reference to FIGS.
In the first joint model, when the thickness y of the tapered portion 36 is changed so that the ratio δ1 is between 0.4 and 1.5, the tendency of change in the amount of angular displacement changes based on the ratio δ1:0.81, regardless of the magnitude of the bending moment applied to the model ( FIG. 4 ).
In the second joint model, when the thickness y of the tapered portion 36 is changed so that the ratio δ1 is between 0.4 and 1.2, the tendency of change in the amount of angular displacement changes based on the ratio δ1:0.73, regardless of the magnitude of the bending moment applied to the model ( FIG. 5 ).
In the third joint model, when the thickness y of the tapered portion 36 is changed so that the ratio δ1 is between 0.4 and 1.0, the tendency of change in the amount of angular displacement changes based on the ratio δ1:0.6, regardless of the magnitude of the bending moment applied to the model ( FIG. 6 ).
In the fourth joint model, when the thickness y of the tapered portion 36 is changed so that the ratio δ1 is between 0.34 and 0.86, the tendency of change in the amount of angular displacement changes based on the ratio δ1:0.56, regardless of the magnitude of the bending moment applied to the model ( FIG. 7 ).
In the fifth joint model, when the thickness y of the tapered portion 36 is changed so that the ratio δ1 is between 0.3 and 0.8, the tendency of change in the amount of angular displacement changes based on the ratio δ1:0.56, regardless of the magnitude of the bending moment applied to the model ( FIG. 8 ).

4 to 8 show that for each thickness x of the annular portion 35, a line graph with a steep gradient indicating a large change in the amount of angular displacement and a line graph with a gentle gradient indicating a small change in the amount of angular displacement can be drawn. A scatter plot was then created as shown in FIG. 9, with the thickness x of the annular portion 35 on the horizontal axis and the ratio δ1 on the vertical axis. The ratio δ1 at the point where the trend in the amount of angular displacement changed was plotted in FIG. 9 for each of the joint models fitted with the first to fifth boot models, each with an annular portion 35 thickness x that varied in 0.5 mm increments. It was found that the trend in the ratio δ1 changed with the thickness x of the annular portion 35 being 3 mm as the base, and that the relationship δ1 = -0.21x + 1.24 held when the thickness x was between 2.0 mm and 3.0 mm, and the relationship δ1 = -0.04x + 0.71 held when the thickness x was between 3.0 mm and 4.0 mm. Therefore,
- When the thickness x is 2.0 mm or more and less than 3.0 mm and satisfies the relationship δ1≧−0.21x+1.24, and - when the thickness x is 3.0 mm or more and 4.0 mm or less and satisfies the relationship δ1≧−0.04x+0.71, a boot 30 can be realized that has an improved effect of suppressing angular displacement when a bending moment acts on the constant velocity universal joint 20.

As described above, the upper limit of the thickness y of the tapered portion 36 is set to 4.0 mm (y≦4.0 mm) in consideration of formability, etc. When y=4.0,
When the thickness x of the annular portion 35 is 2.0 mm, δ1=(y/x)=2.0.
If the wall thickness x of the annular portion 35 is 2.5 mm, then δ1 = 1.6.
When the thickness x of the annular portion 35 is 3.0 mm, δ1 = 1.33,
If the thickness x of the annular portion 35 is 3.5 mm, then δ1 = 1.14.
If the thickness x of the annular portion 35 is 4.0 mm, then δ1 = 1.0.
The values of δ1 corresponding to the thickness x were plotted in Fig. 9. It was found that in this case as well, the trend in the ratio δ1 changed with the thickness x of the annular portion 35 being 3 mm as the reference, and that the relational expression δ1 = -0.67x + 3.31 was established when the thickness x was between 2.0 mm and 3.0 mm, and the relational expression δ1 = -0.33x + 2.33 was established when the thickness x was between 3.0 mm and 4.0 mm.

From the above, in the boot 30 of this embodiment, the connecting portion 34 is formed to be thicker than the elastic portion 33, and the connecting portion 34 is configured with the annular portion 35 having a thickness of 2.0 mm or more and 4.0 mm or less, and the tapered portion 36 connecting the annular portion 35 and the large-diameter cylindrical portion 31 and gradually increasing in diameter from the annular portion side toward the large-diameter cylindrical portion side,
When the thickness x of the annular portion 35 is set to 2 mm or more and less than 3 mm, a ratio δ1 (= y/x) of the thickness y of the tapered portion 36 to the thickness x of the annular portion 35 satisfies the following relational expression (1):
When the thickness x of the annular portion is set to be 3 mm or more and 4 mm or less, by setting the thickness y of the tapered portion 36 so that the ratio δ1 satisfies the following relational expression (2), it is possible to realize at low cost a boot 30 that has a simple structure, is excellent in formability and ease of deformation, and is capable of preventing pinching and damage to the elastic portion 33 caused by large bending of the constant velocity universal joint 20 (large angular displacement of the shaft member 2 with respect to the outer joint member 21).
-0.21x+1.24≦δ1≦-0.67x+3.31...(1)
-0.04x+0.71≦δ1≦-0.33x+2.33...(2)

In addition, when the wall thickness x of the annular portion 35 is set to be 2 mm or more and less than 3 mm, the ratio δ1 satisfies the following relational expression (3), which is a partial modification of the relational expression (1):
When the thickness x of the annular portion 35 is set to be 3 mm or more and 4 mm or less, the thickness y of the tapered portion 36 may be set so that the ratio δ1 satisfies the following relational expression (4), which is a partial modification of the relational expression (2) above.
-0.21x+1.24≦ δ1≦(-0.21x+1.24)×1.2...(3)
-0.04x+0.71≦ δ1≦(-0.04x+0.71)×1.2...(4)

Satisfying the above relationship (3) and (4) means that the value of the ratio δ1 is within the lightly shaded area in Figure 9. Therefore, in this case, the upper limit of the ratio δ1 is small, in other words, the range in which the thickness y of the tapered portion 36 can be set is narrow, but this is advantageous in ensuring that the above-mentioned effects of the present invention are achieved.

Furthermore, when the wall thickness x of the annular portion 35 is set to be equal to or greater than 2 mm and less than 3 mm, the ratio δ1 satisfies the following relational expression (5), which is a partial modification of the relational expression (1):
When the thickness x of the annular portion 35 is set to be 3 mm or more and 4 mm or less, the thickness y of the tapered portion 36 may be set so that the ratio δ1 satisfies the following relational expression (6), which is a partial modification of the relational expression (2) above.
-0.21x+1.24≦ δ1≦(-0.21x+1.24)×1.1...(5)
-0.04x+0.71≦ δ1≦(-0.04x+0.71)×1.1...(6)

In this case, the upper limit of the ratio δ1 becomes smaller than the above relational expressions (3) and (4), further narrowing the range in which the thickness y of the tapered portion 36 can be set, but this is advantageous in ensuring that the above-mentioned effects of the present invention can be obtained.

The boot 40 according to the second embodiment of the present invention will now be described with reference to the longitudinal cross-sectional view in the free state shown in Figure 11, as well as Figures 12 to 15. Similar to the boot 30 described with reference to Figures 1 to 3, this boot 40 is disposed between the outer joint member 21 and shaft member 2 that constitute the fixed constant velocity universal joint 20 (drive shaft 1), and functions as a sealing member that seals the internal space of the mouth portion 22.

The boot 40 shown in Figure 11 comprises a large-diameter cylindrical portion 41 attached to the mouth portion 22 of the outer joint member 21, a small-diameter cylindrical portion 42 attached to the shaft member 2, an elastic portion 43 provided between the cylindrical portions 41, 42 and elastically deforming in response to relative angular displacement between the outer joint member 21 and the inner joint member 24 (or the shaft member 2 connected thereto), and a connecting portion 44 connecting the elastic portion 43 to the large-diameter cylindrical portion 41, all of which are molded from a resin material (or rubber material) whose main ingredient is a thermoplastic elastomer.

In its free state, the elastic portion 43 of the boot 40 has a generally J-shaped cross section, integrally comprising a cylindrical portion extending from the small-diameter cylindrical portion 42 toward the large-diameter cylindrical portion 41 and one arc-shaped valley portion 43a. The thickness t of this elastic portion 43 is generally constant throughout the entire elastic portion 43 and can be set to a value that combines flexible deformation behavior with desired durability. Specifically, the thickness t is preferably set to 2 mm or less, and the ratio of the thickness x of the annular portion 45 and the thickness z of the cylindrical portion 46, both of which are described below, is preferably within the range of 0.3 to 0.7 (0.3x≦t≦0.7x and 0.3z≦t≦0.7z).

The connecting portion 44 of the boot 40 is composed of a flange-shaped annular portion 45 that extends radially outward from the end of the elastic portion 43 on the large-diameter cylindrical portion 41 side, and a cylindrical portion 46 that connects this annular portion 45 (the outer diameter end portion) to the large-diameter cylindrical portion 41. The outer diameter surface of the cylindrical portion 46 is formed into a cylindrical surface of a constant diameter with no radial irregularities.

The connecting portion 44 (the annular portion 45 and cylindrical portion 46 that constitute it) is thicker than the elastic portion 43, increasing its rigidity, so that even if the shaft member 2 connected to the inner joint member 24 is angularly displaced relative to the outer joint member 21 due to its own weight or other factors, causing a bending moment to act on the boot 40 and elastically deforming the elastic portion 43, the elastic portion 43 can be maintained in a non-contact state with the mouth portion 22 of the outer joint member 21 against this moment load (to prevent the elastic portion 43 from becoming caught between the shaft member 2 and the mouth portion 22).

The thickness x of the annular portion 45 is set within the range of 2 mm to 4 mm for the same reasons that the thickness x of the annular portion 35 of the boot 30 according to the first embodiment is set within the range of 2 mm to 4 mm. Furthermore, the upper limit of the thickness z of the cylindrical portion 46 is set to 4 mm for the same reasons that the upper limit of the thickness y of the tapered portion 35 of the boot 40 according to the first embodiment is set to 4 mm.

However, in order to prevent the elastic portion 43 from getting caught while also preventing the occurrence of the various problems mentioned above, the thickness x of the annular portion 45 and the thickness z of the cylindrical portion 46 are set to satisfy the relationship described below, which the inventors discovered through numerical analysis as a confirmation test. The analysis procedure is explained below. The temperature conditions during the analysis were room temperature.

[Step 1]
A plurality of boot 40 models (boot models) were created in which the wall thickness x of the annular portion 45 was varied within the above-mentioned range of 2 to 4 mm. Here, a sixth boot model was created in which the wall thickness x of the annular portion 45 was 2.0 mm, a seventh boot model was created in which x was 3.0 mm, and an eighth boot model was created in which x was 4.0 mm. In each boot model, the outer diameter of the large-diameter cylindrical portion 41 was φ89.5 mm, and the outer diameter of the small-diameter cylindrical portion 42 was φ33.7 mm.
[Step 2]
When a predetermined bending moment was applied to a model (joint model) of the fixed constant velocity universal joint 20 equipped with each of the above boot models and with an operating angle of 0°, it was confirmed how the relative angular displacement of the shaft member 2 with respect to the outer joint member 21 (the operating angle of the constant velocity universal joint 20) changed and progressed with changes in the ratio δ2 (=z/x) of the thickness y of the cylindrical portion 46 to the thickness x of the annular portion 45. The bending moment applied to the joint model was 1740 Nmm.
[Step 3]
For each of the above joint models, a scatter diagram was created with the ratio δ2 on the horizontal axis and the amount of angular displacement on the vertical axis. Figures 12 to 14 show scatter diagrams for the joint models (the sixth to eighth joint models) equipped with the sixth to eighth boot models, respectively. It can be seen from Figures 12 to 14 that the greater the ratio δ2 (the greater the wall thickness z of the cylindrical portion 46), the greater the effect of suppressing angular displacement when a bending moment is applied.

Next, the angular displacement of each joint model will be considered with reference to FIGS.
In the sixth joint model, when the thickness z of the cylindrical portion 46 is changed so that the ratio δ2 is between 0.4 and 1.0, the tendency of change in the amount of angular displacement changes with the ratio δ2:0.6 as the reference (FIG. 12).
In the seventh joint model, when the thickness z of the cylindrical portion 46 is changed so that the ratio δ2 is between 0.4 and 1.0, the tendency of change in the amount of angular displacement changes with the ratio δ2:0.6 as the reference (FIG. 13).
In the eighth joint model, when the thickness z of the cylindrical portion 46 is changed so that the ratio δ2 is between 0.4 and 1.0, the tendency of change in the amount of angular displacement changes with the ratio δ2:0.6 as the reference (FIG. 14).

From Figures 12 to 14, it can be seen that for each thickness x of the annular portion 45, a line graph with a steep slope indicating a large change in the amount of angular displacement and a line graph with a gentle slope indicating a small change in the amount of angular displacement can be drawn. A scatter plot was then created in Figure 15, with the thickness x of the annular portion 45 on the horizontal axis and the ratio δ2 on the vertical axis. The ratio δ2 at the point where the trend in the amount of angular displacement changed was plotted in Figure 15 for each of the joint models fitted with boot models 6 to 8, which had annular portion 45 thicknesses x that varied in 1.0 mm increments. When the thickness x of the annular portion 45 was between 2.0 mm and 4.0 mm, δ2 was constant at 0.6. Therefore, if the thickness x of the annular portion 45 is between 2.0 mm and 4.0 mm, and the relationship δ2≧0.6 is satisfied (the thickness z of the cylindrical portion 46 is set so that this is the case), a boot 40 can be realized that is more effective at suppressing angular displacement when a bending moment acts on the constant velocity universal joint 20.

As described above, the upper limit of the wall thickness z of the cylindrical portion 46 is set to 4.0 mm (z≦4.0 mm) in consideration of formability, etc., and when z=4.0,
When the thickness x of the annular portion 45 is 2.0 mm, δ2=(z/x)=2.0.
If the thickness x of the annular portion 45 is 2.5 mm, then δ2 = 1.6.
When the wall thickness x of the annular portion 45 is 3.0 mm, δ2=1.33,
If the wall thickness x of the annular portion 45 is 3.5 mm, δ2 = 1.14,
If the thickness x of the annular portion 45 is 4.0 mm, then δ2 = 1.0.
The values of δ2 corresponding to the thickness x were plotted in Fig. 15. It was found that the tendency of change in the ratio δ2 changed when the thickness x of the annular portion 45 was 3 mm, and that the relational expression δ2 = -0.67x + 3.31 was established when the thickness x was between 2.0 mm and 3.0 mm, and the relational expression δ2 = -0.33x + 2.33 was established when the thickness x was between 3.0 mm and 4.0 mm.

From the above, in the boot 40 of this embodiment, the connecting portion 44 is formed to be thicker than the elastic portion 43, and the connecting portion 44 is configured with the annular portion 45 having a thickness of 2.0 mm or more and 4.0 mm or less, and the cylindrical portion 46 having a constant diameter that connects the annular portion 45 and the large-diameter cylindrical portion 31,
When the wall thickness x of the annular portion 45 is set to be 2 mm or more and less than 3 mm, the ratio δ2 (=z/x) of the wall thickness z of the cylindrical portion 36 to the wall thickness x of the annular portion 45 satisfies the following relational expression (7):
When the wall thickness x of the annular portion 45 is set to 3 mm or more and 4 mm or less, if the wall thickness z of the cylindrical portion 46 is set so that the ratio δ2 satisfies the following relational expression (8),
A boot 40 can be realized at low cost that has a simple structure, is excellent in formability and deformability, and is capable of preventing the elastic portion 43 from becoming caught due to large bending of the constant velocity universal joint 20 (large angular displacement of the shaft member 2 relative to the outer joint member 21).
0.6 ≦ δ2 ≦ -0.67x+3.31...(7)
0.6 ≦ δ2 ≦ -0.33x+2.33...(8)

The thickness z of the cylindrical portion 46 may be set so that the ratio δ2 satisfies the following relational expression (9).
0.6≦δ2≦0.6×1.2...(9)
The case where the relational expression (9) is satisfied means that the ratio δ2 is within the range of the lightly shaded region in Fig. 15. Therefore, in this case, the upper limit of the ratio δ2 is small, in other words, the settable range of the wall thickness z of the cylindrical portion 46 is narrowed, but this is advantageous in ensuring the above-described operational effects of the present invention.

Furthermore, the thickness z of the cylindrical portion 46 may be set so that the ratio δ2 satisfies the following relational expression (10).
0.6≦δ2≦0.6×1.1...(10)
In this case, the upper limit of the ratio δ2 becomes smaller than when the above-mentioned relational expression (9) is applied, and the settable range of the wall thickness z of the cylindrical portion 46 becomes narrower accordingly, but this is advantageous in more reliably enjoying the above-mentioned effects of the present invention.

The above describes the boots 30, 40 according to an embodiment of the present invention, but appropriate modifications can be made to the boots 30, 40 without departing from the spirit and scope of the present invention.

The power transmission device including the boot 30 according to an embodiment of the present invention shown in Figure 1 is a rear wheel drive shaft, but the boots 30, 40 according to embodiments of the present invention can also be used as boots for constant velocity universal joints (fixed constant velocity universal joints) that make up front wheel drive shafts or propeller shafts.

REFERENCE SIGNS LIST 1 Drive shaft 2 Shaft member 20 Fixed constant velocity universal joint 21 Outer joint member 22 Mouth portion 30 Boot (constant velocity universal joint boot)
31 Large diameter cylindrical portion 32 Small diameter cylindrical portion 33 Elastic portion 34 Connection portion 35 Annular portion 36 Tapered portion 40 Boot (boot for constant velocity universal joint)
41 Large diameter cylindrical portion 42 Small diameter cylindrical portion 43 Elastic portion 44 Connecting portion 45 Annular portion 46 Cylindrical portion t Wall thickness of elastic portion x Wall thickness of annular portion y Wall thickness of tapered portion z Wall thickness of cylindrical portion δ1, δ2 ratio

Claims (7)

a large diameter cylindrical portion attached to an outer joint member of a constant velocity universal joint; a small diameter cylindrical portion attached to a shaft member connected to an inner joint member of the constant velocity universal joint; an elastic portion having one arc-shaped valley portion and extending from the small diameter cylindrical portion toward the large diameter cylindrical portion; and a connecting portion connecting the large diameter cylindrical portion and the elastic portion, all of which are integrally molded from a flexible material;
the elastic portion elastically deforms in response to a relative angular displacement between the outer joint member and the shaft member,
The connection portion is formed to be thicker than the elastic portion,
the connecting portion has a wall thickness of 2 mm or more and 4 mm or less, and includes an annular portion extending radially outward from an end of the elastic portion on the large-diameter cylindrical portion side, and a tapered portion connecting the annular portion and the large-diameter cylindrical portion, the tapered portion gradually increasing in diameter from the annular portion side toward the large-diameter cylindrical portion side,
When the thickness x of the annular portion is 2 mm or more and less than 3 mm, a ratio δ1 (= y/x) of the thickness y of the tapered portion to the thickness x of the annular portion satisfies the following relational expression (1),
A boot for a constant velocity universal joint, characterized in that when the thickness x of the annular portion is 3 mm or more and 4 mm or less, the ratio δ1 satisfies the following relational expression (2):
-0.21x+1.24≦δ1≦-0.67x+3.31...(1)
-0.04x+0.71≦δ1≦-0.33x+2.33...(2) 2. A boot for a constant velocity universal joint according to claim 1, wherein, when the thickness x of the annular portion is 2 mm or more and less than 3 mm, the ratio δ1 satisfies the following relational expression (3), which is a partial modification of the relational expression (1), and when the thickness x of the annular portion is 3 mm or more and 4 mm or less, the ratio δ1 satisfies the following relational expression (4), which is a partial modification of the relational expression (2).
-0.21x+1.24≦δ1≦(-0.21x+1.24)×1.2...(3)
-0.04x+0.71≦δ1≦(-0.04x+0.71)×1.2...(4) 2. A boot for a constant velocity universal joint according to claim 1, wherein, when the thickness x of the annular portion is 2 mm or more and less than 3 mm, the ratio δ1 satisfies the following relational expression (5), which is a partial modification of the relational expression (1), and when the thickness x of the annular portion is 3 mm or more and 4 mm or less, the ratio δ1 satisfies the following relational expression (6), which is a partial modification of the relational expression (2).
-0.21x+1.24≦ δ1≦(-0.21x+1.24)×1.1...(5)
-0.04x+0.71≦ δ1≦(-0.04x+0.71)×1.1...(6) A boot for a constant velocity universal joint according to any one of claims 1 to 3, wherein the angle formed by the tapered portion with respect to the axial direction is between 20° and 30°. a large diameter cylindrical portion attached to an outer joint member of a constant velocity universal joint; a small diameter cylindrical portion attached to a shaft member connected to an inner joint member of the constant velocity universal joint; an elastic portion having one arc-shaped valley portion and extending from the small diameter cylindrical portion toward the large diameter cylindrical portion; and a connecting portion connecting the large diameter cylindrical portion and the elastic portion, all of which are integrally molded from a flexible material;
the elastic portion elastically deforms in response to a relative angular displacement between the outer joint member and the shaft member,
The connection portion is formed to be thicker than the elastic portion,
the connecting portion has a wall thickness of 2 mm or more and 4 mm or less, and includes an annular portion extending radially outward from an end of the elastic portion on the large-diameter cylindrical portion side, and a cylindrical portion connecting the annular portion and the large-diameter cylindrical portion,
When the wall thickness x of the annular portion is 2 mm or more and less than 3 mm, the ratio δ2 (= z/x) of the wall thickness z of the cylindrical portion to the wall thickness x of the annular portion satisfies the following relational expression (7),
A boot for a constant velocity universal joint, characterized in that when the wall thickness x of the annular portion is 3 mm or more and 4 mm or less, the ratio δ2 satisfies the following relational expression (8):
0.6 ≦ δ2 ≦ -0.67x+3.31...(7)
0.6 ≦ δ2 ≦ -0.33x+2.33...(8) a large diameter cylindrical portion attached to an outer joint member of a constant velocity universal joint; a small diameter cylindrical portion attached to a shaft member connected to an inner joint member of the constant velocity universal joint; an elastic portion having one arc-shaped valley portion and extending from the small diameter cylindrical portion toward the large diameter cylindrical portion; and a connecting portion connecting the large diameter cylindrical portion and the elastic portion, all of which are integrally molded from a flexible material;
the elastic portion elastically deforms in response to a relative angular displacement between the outer joint member and the shaft member,
The connection portion is formed to be thicker than the elastic portion,
the connecting portion has a wall thickness of 2 mm or more and 4 mm or less, and includes an annular portion extending radially outward from an end of the elastic portion on the large-diameter cylindrical portion side, and a cylindrical portion connecting the annular portion and the large-diameter cylindrical portion,
A boot for a constant velocity universal joint, characterized in that a ratio δ2 (=z/x) of a wall thickness z of the cylindrical portion to a wall thickness x of the annular portion satisfies the following relational expression (9).
0.6≦δ2≦0.6×1.2...(9) a large diameter cylindrical portion attached to an outer joint member of a constant velocity universal joint; a small diameter cylindrical portion attached to a shaft member connected to an inner joint member of the constant velocity universal joint; an elastic portion having one arc-shaped valley portion and extending from the small diameter cylindrical portion toward the large diameter cylindrical portion; and a connecting portion connecting the large diameter cylindrical portion and the elastic portion, all of which are integrally molded from a flexible material;
the elastic portion elastically deforms in response to a relative angular displacement between the outer joint member and the shaft member,
The connection portion is formed to be thicker than the elastic portion,
the connecting portion has a wall thickness of 2 mm or more and 4 mm or less, and includes an annular portion extending radially outward from an end of the elastic portion on the large-diameter cylindrical portion side, and a cylindrical portion connecting the annular portion and the large-diameter cylindrical portion,
A boot for a constant velocity universal joint, characterized in that a ratio δ2 (=z/x) of a wall thickness z of the cylindrical portion to a wall thickness x of the annular portion satisfies the following relational expression (10):
0.6≦δ2≦0.6×1.1 (10)