JPH0796720A - Bead core structure in tire - Google Patents

Abstract

PURPOSE:To provide bead core structure enabling light weight in addition to satisfying strength as a tire, shape retainability and fitting force to a rim by using fiber cords with high tension such as Aramid fiber cords in combination with steel wire cords as the constituent wire material of a bead core. CONSTITUTION:An annular bead core 1 disposed at the bead part B of a tire is formed of steel wires 3a and fiber cords 3b with high tension such as Aramid fiber cords so as to have steel wires 3a in at least a first layer 1a on the core inner diameter side. The bead core 1 thereby has strength against shearing stress generated to the winding start part by compressive force caused by fitting to a rim so as to prevent the lowering of fitting force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a bead core structure which is a constituent element of a pneumatic tire such as a radial tire.

[0002]

2. Description of the Related Art A bead core (1), which has the highest rigidity among tire components, has a carcass ply (2) at a bead portion (B) of the tire, as shown in FIG. Has a role of retaining the bead portion (B) of the tire and keeping the bead portion (B) of the tire fitted on the rim (R). Usually, the bead core (1) is a piano wire or the like. The steel wire rod, a so-called bead wire (3), is a bundle.

The number and cross-sectional shape of the bead wires (3) differ depending on the tire size, tire structure, etc. For example, in the case of passenger car tires, as shown in FIG. 7, 20 (length × width = 4 × 5) ) Or 25 (length x width = 5)
A bead core (1) in which a bead wire (3) of × 5) is laminated in a rectangular shape is used. In the case of tires for buses, trucks, etc., a bead core (1) in which, for example, 51 bead wires (3) are stacked in a hexagonal shape as shown in FIG. 8 is used.

However, in general pneumatic tires, the weight of the bead core has become a problem as the demand for weight reduction of the tire has increased, and it is desired to reduce the weight of the bead core.

Therefore, in place of the steel wire, a fiber cord such as aramid fiber having a smaller specific gravity and a lighter weight and a relatively higher tension is used as a wire material constituting the bead core.

However, the cord made of aramid fiber or the like has a weaker tensile strength than a steel wire and has a drawback that it is inferior in rigidity and is easily deformed into an ellipse, and sufficient fitting force cannot be secured to the rim. There's a problem.

As a further examination of this, whether the wire core of the bead core is made of steel wire or fiber cord, in order to form these wire rods into a bundle, for example, the length × width 5 ×. In the case of stacking on No. 5, it is made by drawing five wire rods in parallel and forming a ribbon shape and winding them five times, or by winding one wire rod five times in five layers. A tire is manufactured by arranging this in the bead portion and molding and vulcanizing the tire, which is usually vulcanized and molded so that the inner diameter side surface of the bead portion is slightly smaller than the rim diameter. It

However, there is a step at the beginning of winding of the bead core due to the overlapping of wire materials such as wires, and the rubber layer attached to this portion is flushed so that it can be fitted to the rim surface. In order to mold, at the beginning of this winding, a reaction force is exerted to push out excess rubber. Also, since the inner diameter of the bead portion is slightly smaller than the outer diameter of the rim base, it is fitted to the rim, so that the rubber molding layer on the inner diameter side of the bead portion is compressed and shear stress occurs at the winding start portion. Occurs.

However, the fiber cord such as the aramid fiber cord is weaker than the steel wire against the compressive force and the shear stress, and the fiber cord is impregnated with the resin having the high hardness and the low elongation at break to be solidified and used. Is common,
The filaments that make up the cord are in a constrained state, with their movement within the cord being sealed.

Therefore, as described above, it is considered that the rupture resistance when the shear stress is applied by the fitting to the rim is small, and therefore the rupture occurs and the fitting force to the rim is reduced or insufficient.

On the other hand, the steel wire has a large elongation after reaching the yield point as compared with the aramid fiber cord, as shown in the graph showing the relationship between elongation and load in FIG.
Therefore, it does not easily break even when subjected to shear deformation as described above.

In view of the above, the present invention uses a fiber cord having a high tensile strength such as an aramid fiber cord in combination with a steel wire as a wire rod constituting a bead core, and has strength and shape retention as a tire, and It is intended to provide a bead core structure that enables weight reduction without impairing the fitting force to the rim.

[0013]

SUMMARY OF THE INVENTION The present invention is an annular bead core arranged in a bead portion of a tire, which comprises a aramid fiber cord or the like having a high tensile strength and a steel wire, at least the core inner diameter side. In the first layer, a wire made of steel is arranged and configured.

[0014]

According to the above bead core structure, since the constituent wire is composed of the steel wire and the fiber cord having a smaller specific gravity than that of the steel wire, the constituent wire is entirely made of steel wire as compared with the conventional bead core. The weight can be reduced.

Moreover, since at least the first layer on the inner diameter side of the bead core is provided with a steel wire that is strong against shear stress, appropriate rigidity and shape retention are maintained, especially when fitted to the rim. Even if a shearing stress is generated at the beginning of winding by the compressive force, the constituent wire will not be cut, and the tightening force for the rim can be maintained well.

Therefore, although a fiber cord such as an aramid fiber cord is used as the wire material constituting the bead core, there is no fear of deterioration in rigidity or tensile strength, and the shape retaining property is good and sufficient. The fitting force can be secured.

[0017]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a partial sectional view of a bead portion (B) on which an annular bead core (1) having a quadrangular cross section is arranged.
Carcass ply (not shown) around the bead core (1)
The end portion of is folded back and locked from the inside to the outside, for example.

The bead core (1) is composed of a steel wire (3a) and a fiber cord (3b) having a relatively high tension such as an aramid fiber cord as its constituent wire material, and is fitted particularly to the rim. At least the first layer (1a) on the inner diameter side to be attached is provided with a steel wire (3a) similar to the conventional one, and a fiber cord (3b) alone or in combination with the steel wire (3a) in the remaining layer. Are distributed.

For example, in the embodiment shown in FIG. 1, the first layer (1a) on the inner diameter side is an array of steel wires (3a), and all the other second to fourth layers are made of the fiber cord (3b). 2 shows a case of stacking in an array, and in the embodiment of FIG. 2, the steel wire (3
It shows the case where the fiber cord (3b) is arranged only in the inner part of the a). In the embodiment of FIG. 3, the first layer, the third layer, and the fifth layer are steel wires (3a) from the inner diameter side, and the second layer and the fourth layer are fiber cords (3b) and are alternately arranged. The case is shown. Besides this, as shown in FIG.
It is also possible to use all the intermediate layers as fiber cords (3b).

The bead core (1) of the above embodiment shows the case where the number of constituent wire rods is 20 × 5 × 4 or 4 × 5 in length × width. It can be carried out as appropriate depending on the tire size and tire structure.

FIGS. 5 and 6 show a bead core structure for a tire for trucks, buses, etc., in which a steel wire (3a) is arranged at least on the first layer (1a) on the inner diameter side, and a fiber cord is formed on the remaining layer. The example which arranged (3b) is shown.

In particular, FIG. 5 shows a fiber cord (3a) in the central two layers.
Fig. 6 shows the case where the steel wire (3a) is arranged.
And an example in which the fiber cord (3b) is arranged alternately.

The bead core (1) having the above structure is
Depending on the layer structure, the steel wire (3a) and the fiber cord (3b), which are the constituent wire materials, are wound one by one and laminated, and the steel wire (3a) and the fiber cord (3b) are preliminarily formed into a ribbon shape. There is a case where they are arranged in the form of, and wound and laminated, and a case where they are used together and laminated. As for the first layer (1a), it is preferable that the winding start end is a single winding having one steel wire (3a).

The steel wire (2a) and the fiber cord (3b) are coated with rubber in order to improve the adhesiveness with the rubber molded body portion of the tire. The fiber cord (3b) is used after being treated with an adhesive for the purpose of improving the adhesiveness to rubber, but a cord having a small twist with a large contribution to tensile strength is used so that the fibers are not separated. It is used after being treated with an adhesive. That is, if it is hardened by resin processing, it becomes vulnerable to shear stress, so it is advisable to lightly treat with an adhesive so that the fibers do not separate as described above.

An aramid fiber cord is particularly preferably used as the cord having high tension, but other organic fiber cords having high tension can also be used. Although a monofilament cord can be used for these, a multifilament cord is preferable in terms of strength against bending and shear stress.

In the tire provided with the bead core (1) having the above-mentioned structure, a fiber cord having a high tension such as an arami fiber cord having a small specific gravity and a light weight is used as a constituent wire of the bead core (1). Since 3b) is used, the weight of the bead core can be significantly reduced as compared with the conventional bead core made of steel wire. Moreover, since at least the first layer (1a) on the inner diameter side is provided with a steel wire (3a) that is strong against shear stress, it has a reasonably sufficient rigidity and shape retention, Even if the compressive force due to the fitting is applied to the beginning of the winding, no breakage occurs, sufficient tightening force and fitting force are maintained on the rim, and the tensile strength is not inferior to the conventional product.

Table 1 below shows that the bead core (1) has the structure shown in FIG. 1 (Example 1), the structure shown in FIG. 2 (Example 2), and the structure shown in FIG. 3 (Example 3). ) And a bead core (1) having the same five-layer structure as in FIG. 1 and all made of metal wire (conventional example) and all made of aramid fiber cord (comparative example). It is a comparison of the results of strength and water pressure tests.

The tire size of each of the examples, the conventional example, and the comparative example was 11R22.5 14PR, the fiber cord (3b) used was an aramid fiber cord having a fineness of 12000 denier, and the steel wire (3a) was a wire diameter. 0.9
It was constructed as a 6 mm wire.

The weight ratio in Table 1 is the weight ratio of the bead core itself, and is shown as an index with the conventional example being 100.
The tensile strength is the tensile strength of the bead core, which is 10
It was displayed as an index of 0.

In the water pressure test, a test tire is assembled on a rim,
Water was injected into the tube to pressurize it, and it was judged whether or not breakage occurred at a pressure value set based on the safety standard.

[0032]

[Table 1]

As is clear from the above results, in the case of the example of the present invention, the tensile strength of the bead core is slightly lower than that of the conventional example. The overall strength) was almost comparable, and it was possible to reduce the weight as compared with a bead core tire having only steel wires without deteriorating the performance as a tire.

On the other hand, in the case of the bead core containing only the aramid fiber cord (comparative example), although the weight was significantly reduced, the tensile strength and the fitting force to the rim (according to the result of the hydraulic pressure test) were also greatly reduced.

[0035]

As described above, according to the present invention, it is possible to significantly reduce the weight of a tire without reducing the strength and shape retention of the bead portion and the fitting force to the rim.
Moreover, by arranging the steel wire on at least the first layer on the inner diameter side, it is possible to secure a reasonably good shape retainability and rigidity, and the shearing stress is applied to the rim at the beginning of the winding due to the compression force. Even if it acts, there is no fear of breaking the constituent wire rods or reducing the fitting force, and it has sufficient durability.

[0036]

[Brief description of drawings]

[0037]

FIG. 1 is a cross-sectional view showing an example of a bead core of a passenger car tire.

[0038]

FIG. 2 is a sectional view showing another embodiment of the bead core.

[0039]

FIG. 3 is a sectional view showing still another embodiment of the bead core.

[0040]

FIG. 4 is a cross-sectional view showing still another embodiment of the bead core.

[0041]

FIG. 5 is an enlarged cross-sectional view showing an example of a bead core for a large tire.

[0042]

FIG. 6 is an enlarged sectional view showing another embodiment of the above bead core.

[0043]

FIG. 7 is a cross-sectional view of a conventional bead core structure.

[0044]

FIG. 8 is a cross-sectional view of another conventional bead core structure.

[0045]

FIG. 9 is a graph showing the relationship between elongation and load of a steel wire and an aramid fiber cord.

[0046]

[Explanation of symbols]

 (B) Bead portion (1) Bead core (1a) First layer on inner diameter side (3a) Steel wire (3b) Fiber cord

Claims (1)

[Claims] 1. A ring-shaped bead core arranged in a bead portion of a tire, wherein a fiber cord having a high tensile strength such as an aramid fiber cord and a steel wire make at least the first layer on the inner diameter side of the core made of steel. A bead core structure in a tire, which is configured by arranging wires.