The present invention relates to a constant velocity universal joint boot used for a drive shaft and the like of an automobile. More particularly, the present invention relates to a constant velocity universal joint boot fitted around an outer circumference of a constant velocity universal joint having a structure such as a tripod joint provided with plural groove-shaped recesses along an axial direction on an outer circumferential surface.
Conventionally, in various fields such as automobiles, constant velocity universal joints are used that couple together two shafts—an input drive shaft and output drive shaft—such that the two shafts transmit torque by rotating at equal velocity even if there is an angular difference between the two shafts. In the case of an automobile, constant velocity universal joints are used on opposite ends of the drive shafts and grease is enclosed to lubricate the constant velocity universal joints, and “constant velocity universal joint boots” adapted to cover bends of the constant velocity universal joints are used to prevent intrusion of foreign matter such as dust and water from outside.
The constant velocity universal joint boot has a large-diameter annular portion on one end, and a small-diameter annular portion on another end. Then, the constant velocity universal joint boot is configured such that the large-diameter annular portion is fixed by being fastened by a boot band to an outer circumferential surface of an outer case (casing) of the constant velocity universal joint on a hub side while the small-diameter annular portion is fixed by being fastened by a boot band to a differential gear side. Of the constant velocity universal joints, a so-called tripod joint having plural axially slidable groove-shaped recesses on an outer circumferential surface with a roller bearing placed around a shaft portion of the drive shaft is generally used as a constant velocity joint used on the differential gear side.
If the tripod joint described above is used, when the tripod joint swings with an operating angle provided (by deforming an angle), the constant velocity universal joint boot deforms and is subjected to stresses of repeated deformation. In particular, with increases in the operating angle of the tripod joint, excessive bending stress will occur around a connection with the outer case, increasing the chances for the constant velocity universal joint boot to get damaged. Also, the tripod joint is subject not only to angular displacement, but also to axial displacement involving sliding. Thus, with the constant velocity universal joint boot fitted around the tripod joint, bending stress is applied more strongly around a connection with the outer case than a fixed constant velocity universal joint that permits only angular displacement. Therefore, the constant velocity universal joint boot fitted around the tripod joint is susceptible to cracks, wear damage, and the like when used for an extended period of time. Regarding constant velocity universal joint boots (tripod joint boots) attempting to solve this problem, there are related techniques shown below.
Patent Literature 1 discloses a tripod joint boot that downsizes the boot and provides a large swing angle to the tripod joint. For the purpose of improving durability, the tripod joint boot disclosed in Patent Literature 1 is configured such that plural thick portions provided on an inner circumference of an end portion on a large-diameter side of the boot are formed by projecting from a tapered surface extending from a small-diameter portion nearest to the end portion on the large-diameter side toward the end portion on the large-diameter side in a bellows portion.
Also, Patent Literature 2 discloses a method for producing the tripod joint boot disclosed in Patent Literature 1. The method for producing the tripod joint boot disclosed in Patent Literature 2 allows the boot to be pulled out easily from a mold in an inner circumferential portion of the end portion on the large-diameter side formed as a primary molding even if an undercut portion is provided on the tapered surface extending from the small-diameter portion nearest to the end portion on the large-diameter side of the bellows portion of a secondary molding having a thick portion toward the end portion on the large-diameter side.
[Patent Literature 1]
Japanese Unexamined Patent Application Publication No. JP2006-17277A
[Patent Literature 2]
Japanese Unexamined Patent Application Publication No. JP2005-98487A
However, there are demands that recent tripod joint boots flexibly follow widening of the operating angle of the tripod joint and achieve weight reduction. To meet these demands, it is conceivable to take measures such as “increasing the number of crests and bottoms of bellows” of the boot or “increasing the outside diameter of the bellows” while maintaining the basic configuration of the boot disclosed in Patent Literature 1 and Patent Literature 2. However, there is a problem in that these measures cannot achieve reduction of production costs, size and weight reduction of the boot, and the like that lie at the foundation of the market demands.
An object of the present invention is to provide a constant velocity universal joint boot that can follow a constant velocity universal joint even if the joint swings at a large operating angle, further reduce the size and weight, improve fatigue damage resistance, and prolong the service life.
The inventors of the present invention have conducted earnest studies and solved the above problem by adopting a constant velocity universal joint boot described below.
In a constant velocity universal joint boot according to the present invention, a large-diameter annular portion mounted on a mating member whose outer circumferential surface is formed into a non-circular shape, and at least a part of the inner circumferential surface of the large-diameter annular portion formed into a non-circular shape, and the large-diameter annular portion, a boot bellows portion, and a small-diameter annular portion attached to a shaft are integrated, and an annular recess is provided in that part of the inner circumferential surface of the large-diameter annular portion which is adjacent to the bellows.
In the constant velocity universal joint boot according to the present invention, preferably the large-diameter annular portion includes a boot band-free zone and a boot band-attaching zone in sequence starting from a bellows side, the boot band-free zone being not fastened and fixed by a boot band, the boot band-attaching zone being fastened and fixed by a boot band; and an annular thick-walled portion is provided on at least a part of the inner circumferential surface of the large-diameter annular portion corresponding to the boot band-attaching zone, and an annular recess portion is provided on the large-diameter annular portion inner circumferential surface of the boot band band-free zone.
In the constant velocity universal joint boot according to the present invention, preferably the annular thick-walled portion provided on the inner circumferential surface of the large-diameter annular portion corresponding to the boot band-attaching zone includes a primary molded member made up of the small-diameter annular portion, the bellows, and the large-diameter annular portion molded integrally, and a secondary molded member provided only on the inner circumferential surface of the large-diameter annular portion of the primary molded member.
In the constant velocity universal joint boot according to the present application, preferably a thickness (t1) of the annular thick-walled portion provided on the inner circumferential surface of the large-diameter annular portion corresponding to the boot band-free zone is larger than a thickness (t2) of that bottom of the bellows which is closest to the boot band-free zone, and is two times or less the thickness (t2) of the bottom.
In the constant velocity universal joint boot according to the present invention, preferably the annular thick-walled portion provided on the inner circumferential surface of the large-diameter annular portion corresponding to the boot band-attaching zone has a fine annular protrusion on a surface thereof.
The constant velocity universal joint boot according to the present invention is suitably applied when the constant velocity universal joint is a tripod joint.
The constant velocity universal joint boot according to the present invention is made up of the small-diameter annular portion, bellows, and large-diameter annular portion, which are integrated with each other sequentially in series, and is provided with the annular recess in that part of the inner circumferential surface of the boot band-free zone which is adjacent to the bellows. Consequently, the constant velocity universal joint boot according to the present invention is subject to lower deformation stress of the bellows changing with swinging of the constant velocity universal joint than conventional constant velocity universal joint boots and has excellent flexibility. Thus, the constant velocity universal joint boot according to the present invention can follow the constant velocity universal joint even if the constant velocity universal joint swings at a larger operating angle than ever before. Furthermore, being small and lightweight and capable of exhibiting high resistance to fatigue failure, the constant velocity universal joint boot according to the present invention can achieve longer service life.
A constant velocity universal joint boot according to the present invention will be described below by assuming that the boot is applied to a tripod joint of a four-wheeled automobile. Also, although an embodiment of the present invention will be described in detail below with reference to the drawings, the present invention is not to be interpreted as being limited thereto. Note that it is sufficient that the constant velocity universal joint to which the constant velocity universal joint boot according to the present invention is applied has plural groove-shaped recesses on an outer circumferential surface thereof, and there is no restriction on the number and shape of the groove-shaped recesses.
A. Form of the Constant Velocity Universal Joint Boot According to the Present Invention
The constant velocity universal joint boot according to the present invention is used for a constant velocity universal joint that includes an outer case and a shaft extending from the outer case. Here, the “constant velocity universal joint” includes plural recessed grooves arranged on an outer circumference of the outer case at equal intervals along an axial direction of the shaft, where a vertical section of the outer case with respect to the axial direction of the shaft assumes a non-circular shape. A typical example of the constant velocity universal joint is a so-called tripod joint.
The constant velocity universal joint boot according to the present invention is formed by integrating a large-diameter annular portion attached to the outer case of the constant velocity universal joint, bellows, and a small-diameter annular portion attached to the shaft and is provided with an annular recess in that part of the inner circumferential surface of the large-diameter annular portion which is adjacent to the bellows. Here,
As shown in
As shown in
(1) Large-Diameter Annular Portion
The large-diameter annular portion 6 of the constant velocity universal joint boot 1 according to the present invention includes “the boot band-free zone not fastened and fixed by a boot band (see reference sign 6C shown in
The boot band-attaching zone 6D will be described using
Preferably the annular thick-walled portion 6B provided on the inner circumferential surface of the boot band-attaching zone 6D has a fine annular protrusion (not shown) on surfaces thereof. A reason for this is that a boot band, when attached to the boot band-attaching zone 6D, increases sealing between the large-diameter annular portion 6 and outer case. Therefore, preferably plural fine annular protrusions are provided. Also, preferably height of the fine annular protrusion in a cross section in the axial direction (direction P shown in
Next, the boot band-free zone 6C will be described using
In this way, with the annular recess 6A being provided on the large-diameter annular portion 6, the constant velocity universal joint boot 1 according to the present invention allows the bellows 5 to display a bellows function sufficiently up to near a boundary with the large-diameter annular portion 6 without increasing the numbers of crests and bottoms of the bellows 5. Generally, a coupling such as a tripod joint is placed in an outer case adapted to fix the large-diameter annular portion 6 by fitting around it. Therefore, in the case of a conventional tripod joint boot 11, when the tripod joint swings, a critical point is located in that part of bellows 15 which is slightly closer to a large-diameter annular portion 16 as shown in
In contrast, as shown in
Furthermore, as shown in
(2) Small-Diameter Annular Portion
All the technical concepts applied to the small-diameter annular portion of the conventional tripod joint boot are applicable to the small-diameter annular portion 2 of the constant velocity universal joint boot 1 according to the present invention. Generally, the small-diameter annular portion 2 has an annular shape in order to be fixed by being fitted around a shaft portion (output drive shaft 20) of the tripod joint boot. Then, to ensure sealing between the output drive shaft 20 and small-diameter annular portion 2, the boot band-attaching zone (not shown) fastened and fixed by the boot band (not shown) is provided on outer circumferential part of the small-diameter annular portion 2. This is intended to prevent grease enclosed in the tripod joint from leaking out between the small-diameter annular portion 2 and output drive shaft 20.
(3) Bellows
All the technical concepts applied to the bellows of the conventional constant velocity universal joint boot are applicable to the bellows 5 of the constant velocity universal joint boot 1 according to the present invention, and there is no particular restriction. Generally, the bellows 5 are provided with crests (outwardly-projecting portions of the boot 1) 3A to 3F and bottoms (inwardly-depressed portions of the boot 1) 4A to 4F, which alternate successively, and is connected between the small-diameter annular portion 2 and large-diameter annular portion 6. The bellows 5, which display pliability and have buffering effects, do not hinder swinging of the tripod joint and play the role of protecting a coupling (not shown) of constant velocity universal joint from flying objects such as flying stones.
Note that as shown in
B. Manufacturing Form of the Constant Velocity Universal Joint Boot According to the Present Invention
(1) Basic Configuration of the Constant Velocity Universal Joint Boot According to the Present Invention
In the constant velocity universal joint boot 1 according to the present invention, the large-diameter annular portion 6 (excluding the annular thick-walled portion 6B), small-diameter annular portion 2, and bellows 5 described above are molded integrally. If the small-diameter annular portion 2, bellows 5, and large-diameter annular portion 6 (excluding the annular thick-walled portion 6B) are formed separately and joined together subsequently, when stresses concentrate on the junction, the junction is prone to cracking, separation, and the like. This makes it impossible to increase the service life of the boot 1, causes the grease enclosed in the constant velocity universal joint to leak out of the boot 1, and so on, and thus is undesirable.
(2) Available Constituent Materials
It is sufficient if a constituent material used in forming a primary molded member 10 of the constant velocity universal joint boot 1 according to the present invention is a thermoplastic resin, and there is no other particular restriction. As the thermoplastic resin, preferably, for example, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyurethane, polytetrafluoroethylene, ABS resin, acrylic resin. or the like is adopted. A reason for this is that these materials excel in terms of cost and ease of handling during manufacturing as well as in terms of flexibility after cure and promise a longer service life of the boot 1.
On the other hand, regarding the constituent material used in forming a secondary molding 6B, the same constituent material as the primary molded member 10 is preferably adopted. A reason for this is that this enables easy compatibilization in an interface between the primary molded member 10 once cured and the secondary molding 6B, making it easy to integrate the two. However, it is not always necessary to use the same material for the primary molded member 10 and secondary molding 6B, and different materials may be used according to required quality as long as excellent compatibility may be adopted as described above.
(3) Concrete Manufacturing Method
In forming the primary molded member 10 and secondary molding 6B described above, publicly known molding methods such as press blow molding, extrusion blow molding, injection blow molding, and injection molding are available for use. Consequently, almost all manufacturing methods disclosed in Patent Literature 2 described above can be adopted (Note that a patent application for the invention disclosed in Patent Literature 2 was filed by the applicants of the present invention in the past). Thus, because fundamental concepts of the manufacturing method for the constant velocity universal joint boot 1 according to the present invention has already been widely known among those skilled in the art from Patent Literature 2, only one example will be shown below and detailed description thereof will be omitted. For example, the constant velocity universal joint boot 1 according to the present embodiment can be formed using the following procedures.
Forming the primary molded member: Using a publicly known press blow molding method also disclosed in Patent Literature 2 described above, a melted material (e.g., thermoplastic resin such as a polyethylene-based resin) is extruded into a mold. Subsequently, the extruded resin material is sandwiched in the mold, and then air is blown in, bringing the resin material into close contact with the mold, to obtain the primary molded member 10 (see
Forming the secondary molding: The primary molded member 10 thus obtained is placed in a stationary mold 31 as shown in the sectional view of
Using enlarged schematic diagrams (see
Whereas a method for integrating the secondary molding 6B and the primary molded member 10 in a mold has been described above in the manufacturing method for the boot, the manufacturing method for the constant velocity universal joint boot 1 according to the present invention is not limited to the manufacturing method described above. For example, the effects of the present invention can also be obtained by manufacturing the secondary molding 6B separately from the primary molded member 10 and joining the secondary molding 6B to the primary molded member 10, thereby forming the annular recess 6A.
Description will be given below using an example of the present invention and a comparative example. Note that the present invention is not to be interpreted as being limited by these examples.
The constant velocity universal joint boot 1 according to the present example (hereinafter referred to as the “example boot”) is the tripod joint boot shown in
Total length: 107 mm
Total length (excluding boot band-attaching zone): 94 mm
Boot wall thickness of boot band-free zone: 1.3 mm Outside diameter of small-diameter annular portion: 29.7 mm
Outside diameter of large-diameter annular portion: 79.4 mm
Numbers of crests and bottoms in bellows: 6 each
Average wall thickness: 1.05 mm
The constant velocity universal joint boot produced in the comparative example is the tripod joint boot 11 (see
The comparative boot was produced by the method disclosed in Patent Literature 2. Specifically, in producing the comparative boot, a secondary molding (annular thick-walled portion 16B) was molded integrally with an inner circumferential surface of the large-diameter annular portion 16 by placing a stationary mold 41 and movable mold 42 as shown in
Furthermore, as shown in
By being equipped with the annular recess in that part of the inner circumferential surface of the large-diameter annular portion which is adjacent to the bellows, the constant velocity universal joint boot according to the present invention is less prone to deformation stress of the bellows regardless of behavior (swinging, sliding) of the constant velocity universal joint and is provided with excellent flexibility, and thus has extremely high industrial utility value.
Number | Date | Country | Kind |
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2018-047129 | Mar 2018 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2019/005549 | 2/15/2019 | WO | 00 |