JP3495079B2 - Pneumatic radial tire for heavy loads - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire for heavy loads, and more particularly to an off-the-road radial tire having excellent durability of a belt layer.
It relates to radial tires. 2. Description of the Related Art An off-the-road radial tire whose mission is to work on a site where foreign matters such as crushed stones and large and small ores are scattered, especially a heavy load radial tire, is a steel reinforcement core.
It is known to have a reinforced structure in which a steel cord-ply ply, usually composed of four or more belt layers, is placed between the radial arcus and the thick tread. By increasing the number of belt plies or optimizing the inclination angle of the cords of the belt plies,
Measures have been taken against input to the belt layer received through the tread. [0003] The input received through the tread and its mitigation will be further described. When the tire travels on a work site or a rough road where the foreign matter is scattered, the tire steps on a relatively blunt projection. In this case, the belt layer is greatly bent,
The cord often breaks due to high tension on the radially inner ply. The breaking failure of this inner ply code is
If the number of plies of the belt layer is increased in consideration of the damage caused by the cut caused by the sharp projections, the thickness of the belt layer increases accordingly, and the tension of the inner ply at the time of bending deformation increases. And lead to increased costs. On the other hand, for the same purpose, raising the inclination angle of the belt ply code with respect to the equatorial plane is effective,
The circumferential stiffness is reduced, which leads to a diameter growth due to the internal pressure of the filling and a corresponding reduction in wear resistance. [0004] It is an object of the present invention to provide a heavy duty radial tire having a belt layer that solves the above-mentioned problems. According to the present invention, a crown portion of a carcass extending in a toroidal shape is provided with a belt layer comprising at least four layers of steel-code inclined arrangement plies, wherein the belt layer comprises Is divided into an inner layer group located on the radially inner side and an outer layer group located on the outer side in the same direction, the tire has a code in which the codes intersect in at least different directions between at least the adjacent plies of both groups. The cord of at least one belt ply in the inner layer group is 6.0 ° with respect to the axis of the cord.
A heavy-duty pneumatic radial tire having a multiple twist structure having the following strand twist angles. In a relatively small tire in which a relatively thin layer twist or a single twist cord in which a plurality of steel filaments are bundled and twisted is used, the number of plies of the belt layer is limited to some extent. Even if the number increases, there is almost no problem that the ply code of the inner layer group is cut. In the case of a heavy-duty tire such as an off-the-road tire, a multi-strand core is obtained by thickening a strand in which a large number of steel filaments are twisted according to the tire size and further twisting a plurality of strands.
Must be used, but in this case the specific problems described above arise. In the tire of the present invention, as described above, at least one reinforcing code of the inner layer group consisting of a plurality of plies of steel code is attached to the belt layer by the axial line of the code. Has a multiple twist structure having a strand twist angle of 6.0 ° or less. Thereby, even when the belt layer is bent so as to wrap around the dull protrusion at the work site or rough road running, the cord is crushed in the bending direction, and the tension of the strand outside the bending direction is reduced. The tension load on the steel filaments constituting the strand is reduced. Therefore, the code is hardly broken. FIG. 4 shows, in order to confirm this, a simulation of the relationship of the cord breaking strength of a multi-twisted steel cord when a bending element is added due to the difference in the strand twist angle.
This is the result of an experiment performed using a steel code having a 7 × (3 + 9) +1 structure. In the figure, the abscissa indicates the twist angle of the strand with respect to the axis of the cord, and the ordinate indicates the strength when bending and pulling the cord against the uniaxial tension.
The bending tensile strength is obtained by measuring the tensile strength of a cord through three rollers under an Ω shape. According to FIG. 4, the strength of the cord with the bending element changes abruptly at the twist angle α of the strand of 6.0 °.
In the range of 6.0 ° or less, it can be seen that even when a bending element is added, the reduction ratio of the bending tensile strength to the uniaxial tensile strength is extremely small. In this experiment, when the breaking condition of the cord was observed, as the twist angle α became smaller than 6.0 °, the cord was flattened while its cross section was gradually broken while maintaining the original circular shape. The entire filament as a cord constitutional unit is united to bear the strength, and is directed to the direction in which the tension becomes uniform, so that a breaking strength close to uniaxial tension can be obtained, while the twist angle α is 6 As the angle exceeded 0.0 °, the portion subjected to bending deformation could not withstand the tension from the filament of the strand located outside the bending while maintaining the circular cross section of the cord, and tended to break sequentially. As a result, it was found that the code strength was reduced. In the present invention, the multi-strand cord having a strand twist angle of 6.0 ° or less, when the tire is stepped on a protrusion when the belt layer is viewed in a circumferential section, the neutral axis is a boundary. It is preferable that the innermost layer of the inner layer group be applied mainly to the innermost ply in the radial direction and the innermost layer of the inner layer group. Further, as long as the purpose is not impaired, the above-mentioned multiply twisted cord can be applied to all plies of the belt layer including the outer layer group. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 is a partial sectional view of a tire showing the present invention, FIG. 2 is an enlarged partial sectional view of a belt layer in FIG. 1, and FIG. 3 is a perspective view showing a main part of a belt layer reinforcing code in the present invention. . In FIG. 1, a tire 1 has a carcass extending in a toroidal shape.
2 and a non-extensible belt layer 4 overlying the crown 3 of the carcass. The end of the carcass 2 is wound up around the bead ring 5 to a substantially central position of the side wall 6 by a conventional method to form a winding end 2 ^' . In FIG. 1 (similarly in FIG. 2), the equatorial plane O
Although the right half is omitted, the tire 1 is symmetric with respect to the equatorial plane O. The belt layer 4 extends in a cylindrical shape with a width equal to or slightly smaller than that of the tread 7 that is located radially outward and engages with the road surface. As shown in FIG. 2, the belt layer in the present invention
4 is at least four steel cord plies (4 ₁₁ to
4 consists _22), all of this such configuration the inner layer group 4 ₁ located radially inward in response to flexural deformation, the outer layer group 4 ₂ corresponds to the cut resistance located in the same direction outward I do. The plurality of at least one inclined arrangement co of plies contained in the inner layer group 4 ₁ - per de 8, co 3 -
The twisting angle α of the strand 9 (hereinafter simply referred to as the twisting angle) with respect to the axis J of the rod is 6.0 ° or less. The reference line K representing the twist angle is the axis of the strand. In the embodiment shown in FIG.
The inner layer group 4 ₁ as twist angle α is 6.0 ° co - using two plies 4 ₁₁ and 4 ₁₂ having an array of de 8 was set to twist angle 12.6 ° to the outer layer group 4 _2-ply 4 _21, the structure of 4 _22. In FIG. 2, a layer denoted by a reference numeral S superimposed on the outer side in the radial direction of the belt layer 4 is a special layer for protecting the outer layer groups 4 ₁ and 4 ₂ of the belt layers from invasion of water or the like through an injury of the tread 7. -Two plies S ₁ in which the records are similarly tilted
A protective layer made of S _2. In the present invention, the inclination angle of the cord of the belt layer 4 with respect to the equatorial plane O is 10 to 30 °.
By weight, the case of the embodiment shown in FIG. 2, of the protective layer including S belt layer, all of the outer layer group 4 _1, 4 ₂ and 21 °, and ply 4 ₁₁ to 4 _22, S _1, Koh between each mutually S ₂ -
It has a structure in which the nodes cross in different directions. Depending on the application, the code may cross in different directions only between specific plies, such as between adjacent plies in the inner layer group and the outer layer group, and the code may be arranged in the same direction in the same layer group. You can also. [0014] inner group 4 ₁ of the belt layer, as well as the number of plies of the outer layer group 4 in ₂ respectively 3 by the tire size, use and the like
Depending on the number of plies included in the tension side when subjected to bending deformation, depending on the total thickness of the protective layer S and the belt layer 4 depending on the total thickness of the protective layer S and the belt layer 4, for example, three for the inner layer group and two for the outer layer group 5. Twist angle α is applied to at least one of the plies constituting the inner layer group.
A multi-strand code of 0 ° or less can be applied. The multi-twisted co - use of soil, or used only in the innermost ply 4 ₁₁ receiving the most vigorous bending deformation Among inner group, also or used for the second ply, the inner layer group 4 ₁ ply all of course, it is also possible to use across all of each ply 4 _21, 4 ₂₂ of the outer layer group. In order to confirm the effects of the tire according to the present invention, five different tires (Examples 1 to 5) were used by using an off-the-road tire 37.00R57 size and changing the belt structure variously within the scope of the present invention. A field test was conducted in an open pit mine with a comparative tire, and after the end of the wear life, the cord breakage of the belt layer was evaluated. 7 × carcass for tire prototype
(3 + 9 + 15) × 0.175 + 1 steel code radial ply 1
The structure shown in FIG. 2 was commonly applied to the number of sheets, the number of plies of the belt layer, and their lamination relationship. Tables 1 and 2 show the details of the codes used for the inner layer group and the outer layer group of the belt layer and the relationship of use in the inner and outer layer groups, respectively. In addition, the protective layer
For S ₁ and S ₂ , a 3 × 7 × 0.23 steel code is commonly used for all tires, and the inclination angle of the code with respect to the equatorial plane is as follows:
The structure including the protective layer at a total angle of 21 ° and intersecting in different directions between the plies was similarly applied in common. [Table 1] [Table 2] As shown in Table 2, the twist angle α is 12.6.
The de, of the belt layer, compared tires used for all plies of the outer layer group, mainly ply 4 ₁₁ co - - ° multi-twisted U-de breakage occurred frequently. In contrast, plies 4 ₁₁ and 4 _{12 of the} inner group
In the case of using a cord having a twist angle of α6.0 ° or less for both, no cord breakage is observed regardless of the angle, and the twist angle is set to one of the plies of the inner layer group. For tires using low codes, slight code breaks were observed. By using a multi-twisted cord having a twist angle of 6.0 ° or less for the inner layer group of the belt layer, it is possible to advantageously reduce breakage of the cord due to bending deformation of the belt layer. is there.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of a tire showing the present invention. FIG. 2 is an enlarged partial sectional view of a belt layer in FIG. FIG. 3 is a perspective view of a belt layer reinforcing code according to the present invention. FIG. 4 is a graph showing the relationship between the twisting angle and the tensile strength of a multi-strand cord. [Description of Signs] 1 Tire 2 Carcass 3 Crown section 4 Belt layer 4 ₁ Inner layer group 4 ₂ Outer layer group 8 Code 9 Strand J Code axis

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Claims (1)

(1) A crown portion of a carcass extending in a toroidal shape is provided with a belt layer composed of at least four layers of steel code inclined arrangement plies, and the belt layer has a diameter of at least four. When the tire is divided into two parts, an inner layer group located on the inner side in the direction and an outer layer group located on the outer side in the same direction. 3. The pneumatic radial tire for heavy loads according to claim 1, wherein the cord of at least one belt ply has a multiple twist structure having a strand twist angle of 6.0 ° or less with respect to the axis of the cord.