JP2003237324A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which can suppress any creep and improve the fracture resistant characteristic without entirely increasing the distance between a bead core and a ply cord. <P>SOLUTION: Rubber creep of a bead cover 22 while a vehicle is traveling can be suppressed, and the fracture resistant characteristic can be improved at the same time by containing short fibers in the rubber in the bead cover 22. In addition, the modulus of unvulcanized rubber is increased, reduction in thickness in the vicinity of a top part of the bead core 12 by the heat and the pressure during the vulcanization can be suppressed, and the thickness of the bead cover 22 in the vicinity of the top part after the vulcanization can be ensured. Therefore, any contact of a ply cord of a carcass 14 with the bead core 12 can be prevented for a long time, and the durability of the bead part 18 is improved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a heavy-duty vehicle in which breakage of a ply cord due to contact between a bead core and a ply cord of a carcass is prevented and durability of a bead portion is improved. A suitable pneumatic tire.

[0002]

2. Description of the Prior Art For heavy-duty vehicles such as trucks and buses,
Pneumatic tires for heavy loads are used.

[0003] In such a pneumatic tire, generally, a radial of a steel cord having a main body portion straddling in a toroidal shape between a pair of bead cores, and a folded portion where the bead core is folded back from the tire inner side to the outer side. A carcass consisting of array plies is provided.

Various structures have been applied to the bead core, which is the core of the bead portion of the tire.
Pneumatic tires for trucks / buses and construction vehicles have a strong bead core with a polygonal cross-sectional profile such as a quadrangle or a hexagon.

A bead cover made of thin rubber is provided on the outer peripheral surface of the bead core.

A ply cord having a so-called multiple twist structure, in which a plurality of slands made of a plurality of steel filaments are twisted together, is applied to a carcass in a pneumatic tire of this type, and the strength of the carcass is enhanced similarly to a bead core. Has been.

By the way, when a pneumatic tire used in a heavy vehicle is subjected to load rolling, the bead cover rubber is broken due to the strong pressure and shearing force between the bead wire and the ply cord, so that they may come into contact with each other. Therefore, various measures have been developed from the past.

As a conventional measure, for example, it has been typical to improve the physical properties and thickness of the rubber of the bead cover.

[0009]

However, when aiming to improve the fracture resistance of the bead cover by the physical properties of rubber, it is necessary to solve the trade-off between suppressing creep and improving the fracture resistance under high stress. Has been difficult.

On the other hand, although the stress can be dispersed by increasing the distance between the bead wire and the ply cord, the shear rigidity is lowered.

Therefore, there is a possibility that the pulling-out property of the ply cord may be deteriorated or that the distortion of the upper end of the ply may be increased to cause an early failure (ply end separation).

In consideration of the above facts, an object of the present invention is to provide a pneumatic tire capable of suppressing creep and improving fracture resistance without increasing the distance between the bead core and the ply cord as a whole. Is.

[0013]

According to a first aspect of the present invention, a bead core having a polygonal cross section embedded in the left and right bead portions and a plurality of ply cords are arranged in parallel with each other and covered with a ply coating rubber. At least one carcass ply having a main body portion extending from one bead core to the other bead core, and a folded-back portion in which a terminal is folded back around a pair of bead cores, and a pneumatic tire comprising: A bead cover made of rubber containing short fibers is interposed between the bead core and the ply cord.

Next, the operation of the pneumatic tire according to claim 1 will be described.

The break of the ply cord generally occurs at the apex of the polygonal bead core, particularly near the bead base on the inner side in the tire axial direction and at a position above it.

The stress generated between the bead core and the ply cord at this position is large and the bead cover is broken,
The cause is that they are in direct contact.

Generally, in the bead cover, a sheet-shaped rubber of about 0.4 to 1.0 mm is interposed between the two before the vulcanization, but the polygonal bead core is formed by heat and pressure during vulcanization. The thickness in the vicinity of the apex is drastically reduced.

Therefore, if the thickness of the sheet-shaped rubber near the apex is increased, the strain at the ply winding end increases.

Since the rubber of the bead cover contains short fibers, the creep of the rubber of the bead cover during running can be suppressed and the fracture resistance can be improved at the same time.

Furthermore, by including short fibers in the rubber of the bead cover, the modulus of the rubber when unvulcanized is increased, and the thickness near the apex of the polygonal bead core is increased by the heat and pressure during vulcanization. It is possible to suppress the decrease. Therefore, the thickness of the bead cover near the apex after vulcanization can be secured.

Therefore, the contact between the ply cord of the carcass and the bead core is prevented for a long time, and the durability of the bead portion is improved.

The invention according to claim 2 is the pneumatic tire according to claim 1, characterized in that the short fibers are at least one of carbon fibers and aramid fibers.

Next, the operation of the pneumatic tire of claim 2 will be described.

Since carbon fiber and aramid fiber have particularly high rigidity among the fibers, they are suitable as a reinforcing material for rubber.

Further, the carbon fiber has good adhesiveness to rubber.

The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, characterized in that the blending ratio of the short fibers is within the range of 2 to 5 by weight. I am trying.

Next, the operation of the pneumatic tire according to claim 3 will be described.

If the blending ratio of the short fibers is less than 2 parts by weight (relative to 100 parts by weight of the rubber component), the effect of incorporating the short fibers is insufficient.

Generally, the effect increases as the number of short fibers increases, but when the mixing ratio of the short fibers exceeds 5 by weight, the frequency of contact between the short fibers increases, which is the core of destruction. It will be easier.

The invention according to claim 4 is the pneumatic tire according to any one of claims 1 to 3, wherein:
The short fibers have an average diameter of 0.01 to 0.1 mm and an average length of 10 mm or less.

Next, the operation of the pneumatic tire according to claim 4 will be described.

When the average diameter of the short fibers is less than 0.01 mm, it becomes impossible to secure the dispersibility when the short fibers are dispersed in the rubber.

When the average diameter of the short fibers exceeds 0.1 mm, the effect of improving the elastic modulus becomes small.

When the average length of the short fibers exceeds 10 mm,
Workability during rubber kneading tends to decrease.

The invention according to claim 5 is the pneumatic tire according to any one of claims 1 to 4, wherein:
The rubber of the bead cover is NR type rubber.

Next, the operation of the pneumatic tire according to claim 5 will be described.

It is preferable to use NR type rubber as the rubber of the bead cover, as compared with synthetic rubber because the adhesiveness to metal is easier and the breaking strength is higher.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a pneumatic tire 10 of the present embodiment comprises a pair of bead cores 12 (only one side is shown in FIG. 1) and a carcass straddling a pair of bead cores 12 in a toroidal shape. 14 and.

The bead core 12 of this embodiment has a normal structure in which a steel wire is wound a plurality of times so that the cross-sectional shape is hexagonal. The cross-sectional shape of the bead core 12 may be another polygon.

The hexagonal bottom side of the bead core 12 (the side on the rim base side) is the bead seat portion 24A of the rim 24.
Is almost parallel to.

The carcass ply 16 has a normal structure in which a plurality of steel ply cords are arranged in parallel with each other, and the plurality of ply cords are embedded in a ply coating rubber.

The ply cord extends substantially in the radial direction.

The carcass ply 16 is folded back around the bead core 12 arranged in the bead portion 18 from the inner side to the outer side in the tire axial direction.

A stiffener 20 made of a combination of a plurality of rubbers is provided between the main body portion 16A and the folded portion 16B of the carcass ply 16 in order to secure the rigidity of the bead portion 18 and prevent separation of the ply end. It is arranged.

A sheet-shaped bead cover 22 is provided between the bead core 12 and the carcass ply 16.

The bead cover 22 of this embodiment is made of rubber containing innumerable short fibers.

The rubber of the bead cover 22 is preferably NR type rubber.

The gauge of the bead cover 22 is preferably set within the range of 0.4 to 1.0 mm in the state of tire molding.

As the short fibers, those having high rigidity such as carbon fibers and aramid fibers are preferable, but other kinds of fibers may be used as long as they have high rigidity.

The short fibers have an average diameter of 0.01 to 0.1 m.
m, and the average length is preferably 10 mm or less.

In addition, the aspect ratio of the short fibers (average length /
The average diameter) is preferably 8 or more.

The mixing ratio of the short fibers is 2 to 5 by weight.
It is preferably within the range (relative to 100 parts by weight of the rubber component).

Inside the bead portion 18, a chafer 24 for reinforcing the bead portion 18 is arranged on the opposite side of the carcass ply 14 from the bead core 12 side.

The structure of the pneumatic tire 10 of the present embodiment other than the bead portion 18 is the same as that of a normal heavy-duty pneumatic radial tire. (Operation) Next, the operation of the pneumatic tire 10 of the present embodiment will be described.

When the pneumatic tire 10 is filled with air and runs with a load applied, the bead portion 18 is repeatedly deformed, and strong pressure and shearing force act between the bead core 12 and the ply cord. In the pneumatic tire 10 of the present embodiment, the bead cover 22 made of rubber reinforced with short fibers is provided between the bead core 12 and the ply cord.
By disposing, the creep of the rubber of the bead cover 22 during traveling can be suppressed and the fracture resistance can be improved at the same time.

In addition, by including short fibers in the rubber of the bead cover 22, the modulus of the rubber when not vulcanized is increased, and the thickness and the thickness of the polygonal bead core near the apex portion are increased by heat and pressure during vulcanization. Can be suppressed. Therefore, the thickness of the bead cover 22 near the apex after vulcanization can be secured.

Therefore, the ply cord and the bead core 12
The contact with the bead portion 18 is prevented for a long time, and the durability of the bead portion 18 is greatly improved.

Here, the reason why short fibers are preferable for reinforcing the rubber of the bead cover 22 is that the longer the fibers are, the more frequently the fibers come into contact with each other, which is likely to become a nucleus of fracture.

Since carbon fiber and aramid fiber have particularly high strength among the fibers, they are suitable as a reinforcing material for rubber.

Carbon fibers are preferable in terms of adhesion to rubber.

Here, the mixing ratio of the short fibers is 2 by weight.
If it is less than the above range, the effect of incorporating short fibers is insufficient.

On the other hand, when the mixing ratio of the short fibers exceeds 5 by weight, the frequency of contact between the short fibers increases, and conversely, this tends to become a nucleus of destruction.

If the average diameter of the short fibers is less than 0.01 mm, it becomes impossible to secure the dispersibility when the short fibers are dispersed in the rubber.

When the average diameter of the short fibers exceeds 0.1 mm, the effect of improving the elastic modulus becomes small.

When the average length of the short fibers exceeds 10 mm,
Workability during rubber kneading tends to decrease.

Further, since the rubber of the bead cover 22 is made of NR type rubber, it is preferable because it has better adhesiveness to metal and higher breaking strength than synthetic rubber. (Test Example) Next, in order to confirm the effect of the present invention, a tire of a conventional example and a tire of an example to which the present invention was applied were prepared and an actual vehicle running test was conducted.

In the test, the test tire was mounted on a drum tester, and the bead portion was disassembled after running for a certain distance, and the breakage rate of the bead cover was examined.・ Test conditions: mileage 10,000 km, speed 60 km /
h, internal pressure 800 kPa, load 5000 kg.

A plurality of ply cords of the carcass ply were checked one by one, and the rate at which the bead cover was broken was taken as the breaking rate of the bead cover (the number of broken pieces / the number of checked pieces (%)). Conventional tire: A tire using a bead cover made of only rubber. -Tire of the example: carbon fiber to rubber (average diameter 50μ
m, average diameter of 1000 μm) A tire using a bead cover.

The size of each tire is 11R2.
It is 2.5.

[0070]

[Table 1] From the test results, it is understood that the tires of the examples to which the present invention is applied have the bead cover fracture rate greatly reduced and the bead portion has excellent durability.

[0071]

As described above, since the pneumatic tire of the present invention has the above-mentioned structure, the ply cord is prevented from being broken due to the contact between the bead core and the ply cord of the carcass, and the durability of the bead portion is improved. It has an excellent effect that it can be made.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a bead portion of a pneumatic tire according to an embodiment of the present invention taken along a tire rotation axis.

[Explanation of symbols]

10 pneumatic tires 12 bead core 14 carcass 16 carcass ply 16A main body 16B folding section 22 bead cover

Claims (5)

[Claims] 1. A bead core having a polygonal cross section embedded in left and right bead portions, and a plurality of ply cords arranged in parallel with each other and covered with ply coating rubber, and extending from one bead core to the other bead core. Body part,
A pneumatic tire comprising: at least one carcass ply having a folded-back portion obtained by folding a terminal around a pair of bead cores, wherein a rubber containing short fibers is provided at least between the bead core and the ply cord. A pneumatic tire characterized in that a bead cover made of is interposed. 2. The pneumatic tire according to claim 1, wherein the short fiber is at least one of carbon fiber and aramid fiber. 3. The mixing ratio of the short fibers is 2 by weight.
It is in the range of -5, The pneumatic tire of Claim 1 or Claim 2 characterized by the above-mentioned. 4. The short fibers have an average diameter of 0.01 to.
The pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire has a length of 0.1 mm and an average length of 10 mm or less. 5. The pneumatic tire according to claim 1, wherein the rubber of the bead cover is NR rubber.