JP2005271638A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of suppressing the occurrence of troubles in a vicinity of a return ply end and enhancing the durability of a bead part by improving a bead part structure. <P>SOLUTION: The pneumatic tire comprises a carcass 3 which is returned from the inner side to the outer side and locked around a bead core 2 embedded in a pair of bead parts 1, and at least one reinforcing layer 4 arranged on the outer side in the tire axial direction of the carcass 3, and the reinforcing layer 4 mainly consists of a cord and rubber to cover the cord. An outer end X of the tire axial direction of the reinforcing layer 4 extends to the outer side of the tire radial direction of a return end Y of the carcass, and a crack propagation speed retarding member is wound around the cord surface of a part extending to the outer side in the tire radial direction from at least the return end Y of the reinforcing layer 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire (hereinafter also simply referred to as “tire”), and more particularly to a heavy-duty pneumatic radial tire that is suitably applied to heavy-duty vehicles such as trucks and buses.

  In a pneumatic tire that rolls under a load condition, a pair of sidewall portions positioned corresponding to the ground contact surface are greatly bent, and accordingly, a bead portion positioned on the outer side in the tire radial direction from the rim flange is outside the tire. The phenomenon of falling down occurs. Due to this phenomenon, it is known that a large shear strain acts on the end portion of the folded ply.

  In addition, in the tire described above, deformation occurs in a substantially circumferential direction in the portion from the bead portion to the side portion corresponding to the stepping portion and the kicking portion with respect to the contact surface of the tread portion, and this deformation causes the folded ply end. Circumferential shear strain also acts on the part. On the other hand, for example, in Patent Document 1, a stiffener is integrally formed of two or more types of rubbers having different hardnesses, and a rubber having the highest hardness is overlapped on the ply end as a deformation input blocking rubber member. The pneumatic radial tire having the excellent bead portion durability is realized by disposing it at the position so as to prevent such distortion.

Further, in Patent Document 2 and the like, the failure end is folded back on the basis of the sag of the bead core portion by prescribing the bead core reinforcing layer and the arrangement steel cord inclination angle. A tire is described that achieves improved bead durability by moving from the end to the chafer end.
JP-A-8-225005 (Claims etc.) JP-A-11-020423 (Claims etc.)

  However, in recent years, the flattening of heavy-duty pneumatic tires has also progressed, and the number of rehabilitation (recap) operations has increased. Conventional means for improving the durability of the bead portion have become insufficient. In particular, in the bead portion structure described in Patent Document 2, a failure may still occur at the end of the folded ply, resulting in a problem that the protective action of the main failure portion by the chafer is not sufficient. In particular, in flat large tires with a flatness ratio of about 60% or less, the problem of bead failure has not only hindered the complete running of new tires, but also has had a serious impact on repeated use of recaps.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pneumatic tire that improves the bead portion durability by improving the bead portion structure to suppress the occurrence of a failure near the folded ply end portion.

As a result of intensive studies to solve the above problems, the present inventor has reached the following findings.
That is, in heavy-duty tires to which high internal pressure is applied, when the rim is assembled and the internal pressure is filled, the internal pressure reacts against the rubber in the bead portion between the folded carcass ply end and the rim flange (back portion). Compression deformation occurs due to force. However, since rubber is non-compressed, this reaction force moves by the amount of compression deformation toward the radially outer side released at the rim flange tip. On the other hand, since the ply reinforced with the steel cord is difficult to deform, shear strain is generated in the rubber on the outer side in the circumferential direction of the end portion of the folded ply. In addition, when a load is applied, the bead portion bends, and as a result, the reaction force received from the rim flange increases, so that the shear strain is promoted.

  Therefore, in order to suppress the shear strain at the end of the folded ply, it is considered effective to reduce the compression deformation of the rubber at the back surface. On the other hand, by placing a chafer as a reinforcement layer on the back surface so as to overlap the ply end, this rubber's compressive deformation is absorbed outside in the axial direction of the chafer and not transmitted to the ply end. Thus, it has been found that the strain at the ply end can be greatly reduced.

  However, when the above method is used, a new problem has arisen in that separation occurs from the chafer end, which is a reinforcing layer, and causes failure at the ply end with the core as a core. Therefore, as a result of analyzing this problem, it was found that the crack generated at the chafer end was progressing toward the ply end, and further, this crack was in the twist direction along the chafer cord. It turns out that progress has been made.

  Based on the above findings, the present inventor has found that the path of the spiral direction due to the unevenness of the cord surface and the twist greatly contributes to the progress of the crack, and the growth rate can be controlled by these controlling factors. . Therefore, when the chafer is made of a treat having a predetermined structure, it becomes possible to disperse the crack growth from the end of the chafer from the surface of the cord, and the propagation path is increased. As a result, the propagation speed in the cord direction is increased. The present invention has been completed by finding that it can be suppressed.

That is, in order to solve the above-described problem, a pneumatic tire according to the present invention includes a carcass that is folded back from the inside to the outside around a bead core embedded in a pair of bead portions, and a tire axial direction of the carcass. A pneumatic tire comprising at least one reinforcing layer disposed on the outside, wherein the reinforcing layer mainly includes a cord and rubber covering the cord.
The outer end in the tire axial direction of the reinforcing layer extends to the outer side in the tire radial direction of the folded end portion of the carcass, and at least a portion of the reinforcing layer that extends outward in the tire radial direction from the folded end portion. A crack growth rate delay member is wound around the cord surface.

  In the present invention, when a plurality of the reinforcing layers are disposed, the cracks are formed on the cord surface of the reinforcing layer, at least the outer end in the tire axial direction is located on the outermost side in the tire radial direction among the plurality of reinforcing layers. It is preferable that the progress speed delay member is wound. The crack growth rate delay member is preferably a rubber layer containing an organic fiber cord, a nonwoven fabric or particles. The tire of the present invention can be suitably used as a heavy duty pneumatic tire applied to trucks, buses and the like.

  According to the present invention, with the above-described configuration, when the crack generated at the chafer end, that is, the outer end in the tire axial direction of the reinforcing layer propagates along the cord, the crack progress wound around the cord surface. Since the propagation path can be increased by the speed delay member, after the crack occurs at the chafer end, the crack propagation speed from the chafer end to the carcass folded end can be delayed. . Therefore, it is possible to lengthen the time until failure of the bead portion, and as a result, it is possible to realize bead portion durability that is extremely superior to the conventional one.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In FIG. 1, the fragmentary sectional view of the bead part vicinity of an example of the pneumatic tire of this invention is shown. As shown in the drawing, the pneumatic tire of the present invention is disposed around a bead core 2 embedded in each of a pair of bead portions 1 and folded back from the inside to the outside, and is disposed outside the tire axial direction. And a reinforcing layer 4.

  In the present invention, the outer end X in the tire axial direction of the reinforcing layer 4 needs to be disposed so as to extend to the outer side in the tire radial direction of the folded end Y of the carcass 3. Thereby, the concentration of strain on the folded end Y of the carcass 3 can be suppressed, and the occurrence of a failure from the folded end Y can be prevented.

  The reinforcing layer 4 according to the present invention is mainly composed of a cord and a rubber covering the cord, and it is necessary that a crack growth rate delay member is wound around the cord surface. FIG. 2A shows an enlarged partial perspective view of an example of the cord portion of the reinforcing layer 4 according to the present invention. In the illustrated example, an organic fiber (textile) cord 12 as an example of a crack growth rate delay member according to the present invention is wound around the surface of the cord 11. By using the reinforcing layer 4 made of a treat having such a structure (hereinafter referred to as “textile spiral structure”), even if a crack occurs at the end X of the reinforcing layer 4, the progress of the reinforcing layer 4 from the surface of the cord 11. It is possible to increase the crack propagation path by dispersing, and as a result, it is possible to suppress the propagation speed in the direction along the cord 11.

  In such a textile spiral structure treat, a relatively high-strength cord 11 is used as a measure against bending (bending) of the cord due to compression, and as shown in the figure, the organic fiber cord 12 is spiraled around the cord, so that cracks develop. The actual path to be increased is increased to suppress the progress speed in the direction along the cord 11 (see FIG. 2B). On the other hand, since the progress of the crack in the case of only the cord 11 proceeds in the direction along the cord 11 as shown in FIG. 6, it can be seen that the propagation path becomes extremely short.

  The organic fiber cord 12 in the textile spiral structure is not particularly limited, and any one can be used. For example, examples of the material include polyamide, polyester, polyvinyl alcohol, and the like. Suitable examples of the polyamide include polyhexamethylene adipamide, polycaproamide, polytetramethylene adipamide, and copolymers thereof. Examples of suitable polyesters include polyethylene terephthalate (PET), polypropylene terephthalate, polybutylene terephthalate (PBT), polyethylene-2,6-naphthoate, poly-1,4-cyclohexanedimethanol terephthalate and copolymers thereof. Etc., respectively. Polyesters that are readily available and have high tensile rigidity are preferred. Further, the organic fiber cord 12 may have either a twisted structure in which a plurality of filaments are twisted or a monofilament structure made of single fibers. For example, a filament having a fineness of about 500 to 3500 dtex can be used. . The winding pitch of the organic fiber cord 12 around the cord 11 can be, for example, about 1 to 20 mm.

  FIG. 3A shows an enlarged partial perspective view of another example of the cord portion of the reinforcing layer 4 according to the present invention. In the illustrated example, the nonwoven fabric 13 as another example of the crack growth rate delay member according to the present invention is wound around the surface of the cord 11. Also by using the reinforcing layer 4 made of a treat having such a structure (hereinafter referred to as “nonwoven fabric coating structure”), the progress of cracks generated at the end X of the reinforcing layer 4 is dispersed from the surface of the cord 11. The crack propagation path can be increased, and as a result, the propagation speed in the direction along the cord 11 can be suppressed.

  In such a non-woven fabric coating structure treat, the cord 11 having relatively high rigidity is used as a countermeasure against bending (bending) of the cord by compression, and as shown in the figure, the non-woven fabric 13 is coated around the non-woven fabric 13 so that cracks are formed. It will progress along the inner fibers. In this case, since the crack can travel through the fiber in every direction, the actual path through which the crack progresses is increased as in the case of the textile spiral structure, and the propagation speed in the direction along the cord 11 is thereby increased. Can be suppressed (see FIG. 3B).

  The nonwoven fabric 13 having the above structure is not particularly limited, and any one can be used. Nonwoven fabric production methods include a carding method, a papermaking method, an air array method, a melt blow method, and a spun bond method, and a web can be produced by these production methods. Further, as a method for bonding fibers in a web other than melt blow and spun bond, it is preferable to use heat fusion, a method using a binder, a water entanglement method in which fibers are entangled with water or a needle force, and a needle punch method. it can. In particular, non-woven fabrics obtained by a water entanglement method and a needle punch method in which fibers are entangled with a water flow or the force of a needle, and a melt blow or spun bond method are suitable.

Specifically, for example, a thickness of about 0.05 to 2.0 mm (measured under a pressure of 20 g / m ² ) and a basis weight (weight per 1 m ² ) of about 10 to 300 g can be used. If the thickness is less than 0.05 mm, it will be difficult to maintain uniformity as a nonwoven fabric, while if it is 2.0 mm or more, it will be too thick and unsuitable as a crack growth rate retarding member according to the present invention. Further, if the basis weight is less than 10 g, it is difficult to maintain the uniformity of the nonwoven fabric itself. Further, as the material of the nonwoven fabric 13, natural polymer fibers such as cotton, rayon and cellulose, synthetic polymer fibers such as aliphatic polyamide, polyester, polyvinyl alcohol, polyimide and aromatic polyamide, and carbon fibers and glass fibers. Steel wire etc. can be mentioned, and the filament fiber of the multilayer structure from which a raw material differs from an adjacent layer may be sufficient. Furthermore, a core-sheath structure in which different materials are arranged in the inner layer and the outer layer, or a composite fiber such as a rice character shape, a petal shape, or a layered shape can also be used.

  FIG. 4A shows an enlarged partial perspective view of still another example of the cord portion of the reinforcing layer 4 according to the present invention. In the illustrated example, a rubber layer 14 containing particles as still another example of the crack growth rate delay member according to the present invention is wound around the surface of the cord 11. Even by using the reinforcing layer 4 made of a treat having such a structure (hereinafter referred to as “particle-containing rubber coating structure”), the progress of cracks generated at the end X of the reinforcing layer 4 is dispersed from the surface of the cord 11. As a result, it is possible to increase the crack propagation path, and as a result, it is possible to suppress the propagation speed in the direction along the cord 11.

  In such a particle-containing rubber coating structure treat, a relatively rigid cord 11 is used as a countermeasure against bending (bending) of the cord due to compression, and as shown in the figure, the particle-containing rubber 14 is coated around the crack, Advances from the particles 15 on the surface of the cord 11 to the particles 15 (see FIG. 4B). Thereby, the actual path | route which a crack progresses similarly to the case of the said structure can be increased, and the propagation speed in the direction along the code | cord | chord 11 can be suppressed.

  The particle 15 in the particle-containing rubber coating structure and the rubber containing the particle 15 are not particularly limited, but as the particle 15, for example, a plurality of polymer fibers having a particle diameter of about 100 to 1000 μm are bundled. (Rounded), particles made of polymer, carbon, glass, etc. can be used, and such particles need not necessarily have the same shape and size. Examples of the rubber include acrylonitrile-butadiene copolymer rubber (NBR), acrylonitrile-styrene-butadiene copolymer rubber (NSBR), styrene butadiene rubber (SBR), butadiene rubber (BR), and natural rubber (NR). And diene rubbers such as isoprene rubber (IR), styrene isoprene rubber (SIR) and styrene isoprene butadiene rubber (SIBR), and butyl rubbers such as butyl rubber (IIR) and halogenated butyl rubber (Hal-IIR). it can. That is, the particle-containing rubber coating structure may be formed in a state in which fine foreign substances of a material different from rubber are dispersed in the rubber.

  The crack propagation speed delay member may be wound around at least the surface of the cord 11 in the portion of the reinforcing layer 4 that extends outward in the tire radial direction from the folded end portion Y. An effect of suppressing the progress of cracks extending from the portion X to the folded end Y can be obtained.

  Further, in the present invention, at least one reinforcing layer 4 needs to be arranged. When a plurality of reinforcing layers 4 are arranged, at least the cord of the reinforcing layer 4 in which the outer end in the tire axial direction is located on the outermost side in the tire radial direction. The crack propagation speed delay member is wound around the surface. For example, in another example of the pneumatic tire of the present invention in which the partial cross-sectional view in the vicinity of the bead portion is shown in FIG. 5, the tire axial direction outer side end is the tire radial direction most among the three reinforcing layers 4A to 4C arranged. The crack growth rate delay member is applied to the reinforcing layer 4B located outside. More preferably, the crack propagation speed delay member is applied to all of the plurality of reinforcing layers 4 whose outer end X in the tire axial direction extends to the outer side in the tire radial direction of the folded end Y of the carcass 3. It is effective to do.

  As the cord 11 constituting the reinforcing layer 4, a high-rigidity cord is suitable. For example, a cord made of high-strength organic fibers such as a steel cord or Kevlar can be suitably used. The cord 11 may have either a twisted structure in which a plurality of filaments are twisted or a monofilament structure made of a single fiber, and the number of driving thereof may be, for example, about 5 to 40/5 cm.

  In the present invention, it is only important that the reinforcing layer 4 using the cord wound with the crack propagation speed delay member is disposed on the outer side in the tire axial direction of the carcass 2, and other tire structures, components, and materials About etc., it can select suitably according to a conventional method, and it does not restrict | limit in particular. For example, although not shown, a tread that is formed in an annular shape by a rubber material and contacts the road surface is disposed on the crown portion of the tire of the present invention, and a tread pattern is appropriately formed on the tread surface. A sidewall portion is disposed on the carcass 3 that connects the bead core 2 and both ends of the tread, and an inner liner is formed in the innermost layer of the tire. Further, a belt layer is disposed between the carcass 3 and the tread. Between the body portion extending between the bead cores 12 of the carcass 3 and the folded portion folded around the bead core 2, the bead core 2 is connected to the tire. A stiffener is disposed extending radially outward and extending substantially radially.

Hereinafter, the present invention will be described specifically by way of examples.
Two types of heavy-duty radial tires having tire sizes 11 / 70R22.5 and 285 / 60R22.5 were produced. The structure of the reinforcing layer 4 is as shown in Tables 1 and 2 below, respectively, a steel cord having a wire diameter of 0.86 mm was used as the cord 11, and the number of driving was 25/5 cm. The dimensions and the cord weights of the reinforcing layers having different cord structures were the same.

In the table, as the organic fiber cord 12 in the textile spiral structure, a PET cord having a fineness of 2415 dtex was wound at a pitch of 5 mm. Moreover, as the nonwoven fabric 13 in a nonwoven fabric coating structure, the thickness which consists of PET 1.5 mm (measured under the pressure of 20 g / m < ² >) and the basis weight of 150 g was used. Further, glass particles having a particle diameter of 500 μm were used as the particles 15 in the particle-containing rubber coating structure, and the rubber was made a natural rubber base from the viewpoint of suppressing crack growth at the time of input.
Table 1 below also shows the results of a bead durability test performed on the test tires of the comparative examples and examples obtained.

Bead endurance test The bead endurance test was conducted at a maximum air pressure of 900 kPa, applicable rims of 8.25 × 22.5, 9.00 × 22.5, a load 1.5 times the maximum load capacity of 3150 kg, and a radius of 1. This was performed by rolling the tire with a 7 m drum tester at a speed of 60 km / h until the bead portion was broken. The test results are shown as an index when the life of Comparative Example 2 is set to 100 as the drum life. The larger the life index, the higher the bead portion durability and the better.

  As shown in Tables 1 and 2 above, in the tire of the example in which the reinforcing layer in which the crack propagation speed delay member is wound on the cord surface is applied, both are compared with the comparative example using the conventional reinforcing layer. It was confirmed that the bead durability was improved.

It is a fragmentary sectional view near the bead part of an example of the pneumatic tire of the present invention. (A) is an expanded partial perspective view of an example of the code | cord | chord part of the reinforcement layer which concerns on this invention, (b) is an image figure of the crack progress in a textile spiral structure. (A) is an expanded partial perspective view of the other example of the code | cord | chord part of the reinforcement layer based on this invention, (b) is an image figure of the crack progress in a nonwoven fabric coating structure. (A) is an expansion partial perspective view of the further another example of the code | cord | chord part of the reinforcement layer based on this invention, (b) is an image figure of the crack progress in a particle | grain containing rubber coating structure. It is a fragmentary sectional view near the bead part of other examples of the pneumatic tire of the present invention. It is an image figure of the crack growth to the direction along a code | cord | chord.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Bead core 3 Carcass 4, 4A-4C Reinforcing layer 11 Cord 12 Organic fiber cord 13 Non-woven fabric 14 Rubber layer 15 containing particles 15 Particles

Claims (6)

A carcass that is folded back from the inside to the outside around a bead core embedded in each of the pair of bead portions, and at least one reinforcing layer disposed on the outer side in the tire axial direction of the carcass. In a pneumatic tire in which a layer is mainly composed of a cord and rubber covering the cord,
The outer end in the tire axial direction of the reinforcing layer extends to the outer side in the tire radial direction of the folded end portion of the carcass, and at least a portion of the reinforcing layer that extends outward in the tire radial direction from the folded end portion. A pneumatic tire, wherein a crack propagation speed delay member is wound around a cord surface.   A plurality of the reinforcing layers are arranged, and the crack propagation speed delay member is wound around the cord surface of the reinforcing layer, at least the outer end in the tire axial direction is positioned at the outermost side in the tire radial direction among the plurality of reinforcing layers. The pneumatic tire according to claim 1.   The pneumatic tire according to claim 1 or 2, wherein the crack growth rate delay member is an organic fiber cord.   The pneumatic tire according to claim 1, wherein the crack growth rate delay member is a nonwoven fabric.   The pneumatic tire according to claim 1, wherein the crack growth rate delay member is a rubber layer containing particles.   It is a heavy-duty pneumatic tire, The pneumatic tire as described in any one of Claims 1-5.

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