Boot for constant velocity universal joint

A boot for a constant velocity universal joint, having an inner surface that is prevented from contacting an edge portion of an outer housing of a constant velocity universal joint regardless of the bend of the boot. The boot includes a large end portion, a small end portion, and a bellows formed between the large and small end portions. The large end portion has an annular face portion facing the end face of a tip portion of the outer housing of the constant velocity universal joint, and defining a concave face portion dented to define an annular gap with the peripheral edge portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a boot for protecting a constant velocity universal joint disposed, for example, on a driving shaft (power transmission shaft) or the like which transmits power to an axle hub from a differential gear of an automobile, particularly to prevention of damages of a boot by a sharp edge of an end face portion of an outer housing of a constant velocity universal joint.

2. Description of the Related Art

Constant velocity universal joints are used in opposite end portions, for example, in a driving shaft for an automobile. Moreover, a flexible boot is attached in such a manner as to cover a bent portion of the constant velocity universal joint in order to seal grease for lubricating the constant velocity universal joint and to prevent entrance of foreign matters such as dust and water from the outside. Large and small end portions of the boot are usually fastened and fixed to an outer peripheral surface of an outer housing of the constant velocity universal joint on a differential side or a hub side and an outer peripheral surface of a driving shaft portion by fastening means such as bands (see, e.g., page 1 andFIG. 1of Japanese Patent Application Laid-Open No. 2002-39208).

Moreover, it is known that a surface portion facing the end face of the tip portion of the outer housing of the constant velocity universal joint is formed on the large end portion of the boot on an inner peripheral side in order to prevent the large end portion of the boot for the constant velocity universal joint and the outer housing of the constant velocity universal joint from being shifted in an axial direction.

However, in the above-described boot for the constant velocity universal joint, when the boot for the constant velocity universal joint is bent accompanying a stroke of a suspension or bend of the driving shaft caused by a steering operation, the inner peripheral surface of the boot contacting the end face of the tip portion of the outer housing of the constant velocity universal joint is pressed onto the tip portion of the outer housing of the constant velocity universal joint, and a so-called “bite-in” occurs in some case. When such bite-in occurs, the boot needs to be prevented from being damaged by a sharp edge or burr of the tip portion of the outer housing of the constant velocity universal joint by machining.

SUMMARY OF THE INVENTION

The present invention has been developed in consideration of the above-described problem, and an object of the present invention is to prevent an inner surface of a boot for a constant velocity universal joint from being bitten by an edge portion of an outer housing of the constant velocity universal joint.

To solve the above-described problem, according to the present invention, there is provided a boot for a constant velocity universal joint, comprising: a large end portion into which an outer housing of the constant velocity universal joint is inserted; a small end portion into which a shaft portion connected to the constant velocity universal joint is inserted; and bellows formed between the large end portion and the small end portion, the large end portion having a face portion facing the end face of a tip portion of the outer housing of the constant velocity universal joint, a portion facing an end face inner peripheral portion of the tip portion of the outer housing being dented to form the face portion.

According to the present invention, a gap is formed between the inner surface of the boot for the constant velocity universal joint and an inner peripheral edge portion of the outer housing of the constant velocity universal joint, on which a sharp edge or burr is easily formed. Moreover, even when the boot is bent to a predetermined maximum bend angle, a shape of the face portion is appropriately set in such a manner as to prevent the gap from being 0. Accordingly, the inner surface of the boot can be prevented from being brought into contact with the sharp edge regardless of the bend of the boot, occurrence of the bite-in can be prevented, and the inner surface of the boot for the constant velocity universal joint can be prevented from being bitten by an edge portion of the outer housing of the constant velocity universal joint.

According to the present invention, the inner surface of the boot for the constant velocity universal joint can be prevented from being bitten by the edge portion of the outer housing of the constant velocity universal joint.

DESCRIPTION OF THE PREFERRED EMBODIMENT

One embodiment of a boot for a constant velocity universal joint, to which the present invention is applied, will be described hereinafter.FIG. 1is an elevation view showing an appearance of a boot for a constant velocity universal joint of the present embodiment. As shown inFIG. 1, a boot1is formed into a cylindrical shape, and has a large end portion3fixed to a constant velocity universal joint side, and a small end portion5fixed to a shaft portion side of a driving shaft connected to this constant velocity universal joint. Moreover, bellows7having flexibility and constituted to be bendable are formed between the large end portion3and the small end portion5. It is to be noted that in the present embodiment, the boot1is formed of a resin having elasticity, such as thermoplastic polyester-based elastomer.

The bellows7are constituted by repeatedly arranging convex portions7aand concave portions7bextending in a peripheral direction in a cylinder shaft direction of the boot1, that is, in a vertical direction inFIG. 1. That is, a cross section of the bellows7is convex on an outer peripheral side in the convex portion7a, and that of the bellows7is convex on an inner peripheral side in the concave portion7b. In the present embodiment, for example, five convex portions7aare disposed, and the corresponding concave portion7bis disposed on a large end portion3side of each convex portion7a. Moreover, diameters of each convex portion7aand concave portion7bare set to be large toward the large end portion3from a small end portion5side. As a result, the bellows7are entirely formed into substantially conical shape.

A face portion9formed into a substantially constant outer diameter is disposed over a shaft direction in a side-portion outer peripheral surface of the large end portion3. A band (not shown) for fastening the boot1to the outer peripheral surface portion of the outer housing of a tripod joint (not shown) which is a constant velocity universal joint is attached to the face portion9. It is to be noted that the tripod joint is one type of constant velocity universal joint, rollers arranged in a trifurcate lock are disposed around a shaft, and a groove portion in which these rollers slide is formed in a casing or outer housing on an inner peripheral side. A stepped portion11for preventing the band from being shifted in an axial direction is formed on the end of the face portion9on the small end portion5side of the boot1in a cylindrical axial direction.

FIG. 2is an enlarged sectional view showing that an outer cylinder13of the constant velocity universal joint is inserted in the large end portion3of the constant velocity universal joint boot1of the present embodiment. A tip portion15of the outer housing13of the constant velocity universal joint on an insertion side into the large end portion3is formed into a cylindrical shape, and concave portions which are characteristics of the tripod joint are formed in three portions on a circumference. Moreover, an inner peripheral surface17of the tip portion15is formed into a constant inner diameter over a cylindrical shaft direction excluding the above-described inner surface of the concave portion. On the other hand, the tip portion15has an annular end face19directed on the side of the small end portion5of the boot1in the cylindrical axial direction. Moreover, a portion21tapered toward its point is formed from the outer peripheral edge portion of the end face19to the side surface of the tip portion15. A boundary portion between the end face19and the tapered portion21is subjected to R-chamfering. Further behind the tapered portion21, that is, on the left side ofFIG. 2as faced, a parallel portion23having a constant outer diameter, a tapered portion25whose outer diameter is gradually reduced toward a rear side, and a parallel portion27whose outer diameter is set to be substantially equal to that of a rear end portion of the tapered portion25are formed in order from a tip side.

On the other hand, as shown inFIG. 2, face portions having shapes adapted to those of the above-described end face19, tapered portion21, parallel portion23, tapered portion25, and parallel portion27are also formed on the inner surface of the large end portion3of the boot1. A diameter of an inner peripheral edge portion of an annular face portion31of the boot1facing the end face19of the outer housing13of the constant velocity universal joint, a diameter of an inner peripheral edge portion, or a diameter of a smallest diameter portion33is formed to be larger than a minimum diameter of the end face19of the outer housing13. Moreover, an annular concave face portion34formed in such a manner as to be dented on the small end portion5side from the annular face portion31in the cylindrical axial direction of the boot1is formed in a region of the inner surface of the boot1on the inner peripheral side from the annular face portion31. As shown inFIG. 2, the concave face portion34is formed into a concave shape having a circular sectional shape. A boundary portion of the concave face portion34contacting the annular face portion31is formed into an edge portion having an angle. For example, in the boundary portion between the annular face portion31and the concave face portion34, opposite faces have an angle, for example, of about 45 degrees. On the other hand, an innermost peripheral portion of the concave face portion34is formed into a tapered shape having a slight tilt with respect to a face crossing a cylindrical axis of the boot1at right angles. Since the concave face portion34is formed, a release portion35which is an annular gap is formed between the end face19of the outer housing13of the constant velocity universal joint and the concave face portion34.

As shown inFIG. 2, a region of the inner surface of the boot1on the inner peripheral side from the inner peripheral edge of the concave face portion34is formed into a convex surface having a circular sectional shape, and contacts the inner peripheral surface of the bellows7via a stepped portion39formed by increasing the diameter of the convex surface portion in a stepwise manner from an inner peripheral edge portion37.

FIG. 3is a sectional view showing that the bellows7are bent in a state in which the outer housing13of the constant velocity universal joint is inserted into the large end portion3of the boot1for the constant velocity universal joint according to the present embodiment. It is to be noted that this view shows a state in which the axial direction of the large end portion3is fixed, and the axial direction of the small end portion5is shifted clockwise as facingFIG. 3. Moreover, an angle formed by the axial directions of the small end portion5and the large end portion3is a maximum bend angle of the constant velocity universal joint, for example, to which the constant velocity universal joint boot of the present embodiment is attached.FIG. 4is an enlarged sectional view of part IV ofFIG. 3. It is to be noted that inFIG. 4, a contour line of the boot1before bent is shown by a broken line for reference. As shown inFIG. 4, also in this state, an interval between the concave face portion34which is the inner surface of the large end portion3of the boot1, and the end face19of the outer housing13of the constant velocity universal joint is smaller than that in a state shown inFIG. 2, but the concave face portion faces the end face at the interval without contacting the end face. It is to be noted that, as shown inFIG. 4, a diameter r1of a maximum diameter portion of the concave face portion34is set to be larger than an inner diameter r2of the end face19.

As described above, according to the present embodiment, the release portion35which is a space portion is formed between the inner surface of the constant velocity universal joint boot1, and an inner peripheral edge portion36of the end face19of the outer housing13of the constant velocity universal joint on which the sharp edge or burr is easily formed. Moreover, the concave face portion34is formed in such a manner as to prevent the interval of the release portion35from being 0 even when the boot1is bent at a predetermined maximum bend angle. Therefore, the inner surface34or the like of the boot1can be prevented from being brought into contact with the inner peripheral edge portion36of the end face19regardless of the bend of the boot1, and the inner surface of the constant velocity universal joint boot1can be prevented from being bitten by the edge portion of the outer housing13of the constant velocity universal joint.

It is to be noted that the present invention is not limited to the above-described embodiment, and can be appropriately modified in the scope of the present invention. For example, the shape of the outer housing of the constant velocity universal joint, or the shape of the large end portion may be modified. The shapes of the bellows and the small end portion may be appropriately modified. Furthermore, in the present embodiment, the boot is formed of a resin. For example, a grommet portion of the large end portion on the inner peripheral side may be separately formed of a resin or rubber having a hardness lower than that of a resin of the boot main body. The whole boot may be integrally formed only of the resin or rubber having low hardness.