JP2001239811A - Bead core and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bead core structure for make compatible both rim slip-off resistance and rim assembly in a safety tire aiming at safe traveling under low internal pressure. SOLUTION: A bead core as a central structure of a tire bead part is constituted of two or more kinds of wires.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having excellent rim assembling property and rim detaching resistance, and a bead core applied to the tire.

[0002]

2. Description of the Related Art A bead portion of a pneumatic tire has a bead toe and a bead base which are in close contact with a rim base to prevent air leakage in the tire and falling off of the rim from the rim. It is responsible for fixing the both side ends of the tire and maintaining the internal pressure, and is an important component of the tire for providing the tire with basic performance. In particular, the bead core is important for fixing both ends of the carcass ply, which serves as the skeleton of the tire, and for helping to lock the tire to the rim.

[0003]

When the carcass is repeatedly deformed due to an input from a road surface, a rotational torque in a twisting direction is applied to the bead core. Therefore, if the torsional rigidity of the bead core is low, there is a problem that the tire falls inside the rim during low-pressure running and the tire tends to come off from the rim, for example, during run-flat running of a safety tire. This problem can be solved by increasing the torsional rigidity of the bead core. On the other hand, if the torsional rigidity of the bead core is high, the rim assemblability is impaired. In other words, the rim resistance and the rim assemblage were in a trade-off relationship.

[0004] In particular, in a safety tire that is oriented to stable running in a low internal pressure state such as a puncture, the bead core is required to have a higher torsional rigidity than normal tires because it is necessary to enhance the resistance to rim detachment as compared with a normal tire. Naturally, the rim assemblability of the tire is extremely deteriorated, and it has been extremely difficult to achieve both the rim removal resistance and the rim assemblage in this kind of tire.

Accordingly, an object of the present invention is to propose a novel bead core structure which realizes both the rim detach resistance and the rim assembling property, particularly in a safety tire intended for stable running under low internal pressure. Another object of the present invention is to provide a tire which is excellent in rim separation resistance and rim assembly resistance.

[0006]

Means for Solving the Problems The inventor of the present invention has made intensive studies on the structure of a bead core that controls both the rim detaching resistance and the rim assembling property. Because it is made of wire, it is isotropic with respect to the rotational torque, and therefore, giving anisotropy to the rotational torque to the bead core is necessary to achieve both rim removal resistance and rim assembly. They have found that they are effective and have completed the present invention.

That is, the gist of the present invention is as follows. (1) A bead core having a central structure of a bead portion of a tire, wherein the bead core includes two or more types of wires.

(2) Two or more kinds of wires are 0 to 0.5%
The ratio E _C / of the initial compression stiffness E _C defined by the slope of the stress-strain line during compression and the initial tensile stiffness E _T defined by the slope of the stress-strain line at 0 to 0.5% elongation. The bead core according to the above (1), wherein E _T is different from each other.

(3) A pneumatic tire having a skeleton of a carcass straddling in a toroidal manner between a pair of bead cores, wherein the bead core is composed of two or more kinds of wires.

(4) In the cross section of the tire in the width direction, the bead core extends outside the center of the bead core in the radial direction of the tire and bisects the bead core. The wire mainly forming A and the wire mainly forming the bead core region B inside the tire at the same boundary line have an initial compression rigidity E _C defined by the slope of the stress-strain line at 0 to 0.5% compression. And 0
0.5% elongation at the stress - pneumatic tire according to the above (3) the ratio E _C / E _T of the initial tensile rigidity E _T defined by the slope of the strain lines are different from each other.

(5) Constituting over 80% of bead core area A
Wire ratio E_C / E_T Is less than 1.0 and
Ratio E of the wire constituting 80% or more of the core region B_C 
/ E _T Is not less than 1.0.
Or the pneumatic tire according to (4).

(6) The pneumatic tire according to (3), (4) or (5), wherein the wire is made of one or two of steel and aromatic polyamide.

(7) The tire according to the above (3) to (6), wherein a side reinforcing rubber layer is provided inside the side portion of the tire.
The pneumatic tire according to any one of the above.

[0014]

FIG. 1 shows a cross section of a pneumatic safety tire according to the present invention. In the figure, 1 is a pair of bead cores, 2 is a carcass formed by extending at least one ply in a toroidal manner between a pair of bead cores 1, 3 is a belt composed of at least two layers, 4 is a tread, and 5 is side reinforcement. It is a rubber layer. When the safety tire falls into a low internal pressure state such as a puncture, the side reinforcing rubber layer 5 having a crescent-shaped cross section in a tire width direction cross-section is used to minimize deflection and reduce the internal pressure. It made it possible to run.

Here, it is important that the bead core 1 is composed of two or more types of wires. A bead core, which was conventionally made of a single wire, is made up of two or more different wires and imparts anisotropy to the torsional stiffness of the bead core. Demonstrate appropriate torsional rigidity according to

In particular, FIG. 2 shows a preferred example of a bead core according to the present invention.
A line segment extending through the center of the bead core and extending in the tire radial direction and bisecting the bead core is defined as a boundary line L,
The wire mainly forming the bead core region A outside the tire at the boundary L and the wire mainly forming the bead core region B inside the tire at the boundary L are 0 to 0.5.
% -Compression stress - and the initial compressive stiffness E _C defined by the slope of the strain lines, stress at break 0 0.5% - the ratio E _C between the initial tensile rigidity E _T defined by the slope of the strain lines / regard E _T, it is advantageous to vary. Reference numeral 6 in FIG. 2 denotes a rim flange, and the rim flange 6 side is the outer side of the tire.

Here, the initial compression rigidity E _C can be measured as follows. That is, as shown in FIG. 3A, ten wires 11 to be measured are uniformly distributed in the axial direction and along the peripheral surface on a thick cylindrical body 10 formed of a predetermined rubber. Embed. Then, FIG.
As shown in FIG. 2B, both end surfaces of the cylindrical body 10 have a thickness of 1
A compression force is applied in the axial direction of the cylindrical body 10 by using an Instron testing machine or the like through the metal plate 12, sandwiching each between the 0 mm metal plates 12. Then, the relationship between the compression force and the strain with respect to the wire and the rubber composite is drawn as shown in FIG. 3 (c), and in the compression force (stress) -strain line,
The compression rigidity of the wire and the rubber composite is calculated by obtaining the inclination in the 0 to 0.5% strain region. Next, the compression rigidity of the cylindrical body 10 made of rubber alone without embedded wires is calculated by the same procedure, and the following equation {(compression rigidity of wire and rubber composite) − (compression rigidity of cylindrical rubber)} / 10 gives the initial compression stiffness of the wire alone.

If the compression stiffness of the object to be measured is large and a strain of 0.5% cannot be given, the stress at the time of 0.5% compression is obtained by linear approximation from the gradient in the minute strain region. To calculate the compression stiffness.

On the other hand, the initial tensile stiffness E _T is JIS L
It can be calculated based on the initial tensile resistance specified in 1017 (1983).

More specifically, regarding the initial compression stiffness E _C and the initial tensile stiffness E _T , more specifically, the ratio E _C / E _T of the wire constituting 80% or more of the bead core region A is less than 1.0 and the bead core region is less than 1.0. It is preferable that the ratio E _C / E _T of the wire constituting 80% or more of B is 1.0 or more.

When the bead core 1 is configured as described above, FIG.
In the bead portion shown in (1), high rigidity is exhibited with respect to the counterclockwise rotation torque (+) applied to the bead core 1, while low rigidity is exhibited with respect to the clockwise rotation torque (-).

That is, when the tire falls into a low internal pressure state such as a puncture, the movement of the bead portion falling inside the rim can be avoided beforehand because it has high rigidity against the rotational torque (+). Therefore, early occurrence of detachment of the rim can be prevented. On the other hand, affecting the rim assembly,
Since the rigidity with respect to the rotation torque (-) is low, the rim assembly is easier than in the conventional art, and excellent rim assemblability can be obtained.

The wire constituting 80% or more of the bead core region A and the bead core region B is defined by a ratio E _C / E
_T : 1.0 is defined as the boundary. By defining as above, when the bead core 1 is given a torsional strain in the (+) direction in FIG. This is because a strain in the direction in which the circumference extends is generated, that is, tensile strain is generated, and conversely, a wire in the bead core region B is subjected to a strain in the direction in which the circumference is reduced, that is, compression strain. That is, by providing a difference in rigidity between the bead core regions A and B, the bead core has anisotropy in rigidity, which is advantageous in obtaining desired characteristics.

Further, it is preferable that the wire constituting the bead core is made of one or two of steel and aromatic polyamide. Because, under the conditions of use of the tire, a large stress is applied to the bead wire, and the bead wire needs to have a strength corresponding to this stress, but it is necessary to achieve this without increasing the weight per unit cross-sectional area. Is required because of the strength of steel and aromatic polyamide. In particular,
A wire made of an aromatic polyamide is advantageous for reducing the weight of a bead core.

[0025] Incidentally, the ratio E _C / E _T is less than 1.0 wire, such as an organic fiber cord as typified by steel cords and aromatic polyamide to be applied to the belt or the carcass are suitable, whereas the ratio E _C An ordinary bead wire is suitable for a wire having a value of / E _T of 1.0 or more.

Also, in the example shown in FIGS. 1 and 2, a bead core 1 having a circular cross section is applied. However, the shape of the bead core does not need to be particularly limited, as shown in FIGS. 4 and 5. , A rectangle or a hexagon.

The structure of the bead core other than those described above may be in accordance with various types of bead cores, and the present invention is applicable regardless of the type of the bead core. For example, for a bead core such as a hexagonal bead core, which is formed by laminating and winding wires to form a predetermined cross-sectional shape, bead cores A and B may be separately formed, and then the two may be combined to form a bead core.

The structure of the tire is not limited to the example shown in FIG. 1, and the bead core of the present invention can be applied to an ordinary pneumatic tire having no side reinforcing rubber layer 5.

[0029]

EXAMPLE Various bead cores prepared under the specifications shown in Tables 1 and 2 were applied to a bead core 1 of a pneumatic safety tire having the structure shown in FIG.
Prototype tires. The carcass 2 and the belt 3
Followed the general specifications of the tire.

After the tire thus obtained is mounted on a standard rim and adjusted to the atmospheric pressure, the total weight of the vehicle is 2 tons.
When mounted on a wheel and running at a speed of 50 km / h, the distance until the tire broke down was measured to evaluate run-flat durability (resistance to rim detachment). Then, it was indicated by an index when the traveling distance in Comparative Example 1-1 or Comparative Example 2-1 was set to 100. The larger the index, the better the run flat durability. In addition, the workability when incorporating the tire into the rim was also evaluated. These evaluation results are also shown in Tables 1 and 2.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

According to the present invention, it is possible to achieve both the rim detach resistance and the rim assembling property, especially in a safety tire intended for stable running under a low internal pressure. Further, according to the bead core of the present invention, it is possible to increase the torsional stiffness in the tire inner region, so that an effect of improving the steering stability during normal running can be expected.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in the width direction of a tire according to the present invention.

FIG. 2 is a schematic diagram showing a bead core structure according to the present invention.

FIG. 3 is a diagram illustrating a method for measuring an initial compression stiffness.

FIG. 4 is a schematic view showing another bead core structure of the present invention.

FIG. 5 is a schematic view showing another bead core structure of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bead core 2 Carcass 3 Belt 4 Tread 5 Side reinforcing rubber layer 6 Rim flange

Claims (7)

[Claims] 1. A bead core having a central structure of a bead portion of a tire, the bead core comprising two or more types of wires. 2. The two or more wires have an initial compression stiffness E defined by the slope of the stress-strain line at 0 to 0.5% compression.
And _C, and the stress of elongation from 0 0.5% - the ratio E _C / E _T of the initial tensile rigidity E _T defined by the slope of the strain lines, according to claim 1, wherein different from each other Bead core. 3. A pneumatic tire having a skeleton of a carcass straddling in a toroidal manner between a pair of bead cores, wherein the bead core is composed of two or more kinds of wires. 4. A bead core in a cross section of a tire in a width direction.
Through the center of the tire in the radial direction of the tire.
This core line is divided into two parts.
Of the bead core region A outside the tire
Ear and bead core area B inside the tire at the same boundary.
The wire that is configured as
Initial compression stiffness E defined by the slope of the force-strain line_C And 0
Defined by the slope of the stress-strain line at 0.5% elongation from
Initial tensile rigidity E_T Ratio E with_C / E _T Are different
The pneumatic tire according to claim 3, wherein 5. The ratio E _C / E _{T of} the wire constituting 80% or more of the bead core region A is less than 1.0, and the ratio E _C / E of the wire constituting 80% or more of the bead core region B.
The pneumatic tire according to claim 3 or 4, wherein E _T is 1.0 or more. 6. The pneumatic tire according to claim 3, wherein the wire is made of one or two of steel and aromatic polyamide. 7. The pneumatic tire according to claim 3, further comprising a side reinforcing rubber layer inside the side portion of the tire.