JP2815097B2 - Radial tires for heavy loads - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heavy duty radial tire capable of improving belt durability by specifying a belt cord and regulating a distance between cords.

[Conventional technology]

For example, in the case of radial tires used for heavy-duty vehicles such as trucks and buses, in order to increase tire rigidity and improve running performance, a plurality of layers of squeal cords are arranged on the outside of the carcass, usually three to four layers. Belt layer is wound.

As this type of steel cord, generally, as shown in FIGS. 7 (a) and 7 (b), a 7 × 4 type in which seven strands S in which four filaments fs are twisted are further twisted together ( (Filament diameter: 0.22 mm), an inner layer I composed of 3n inner filaments fi, and 5n outer filaments fo around a core C obtained by twisting n core filaments fc. An n + 3n + 5n + 1 type, usually a 3 + 9 + 15 + 1 type (filament diameter: 0.22 mm) layer-twisted structure, in which an outer layer O is sequentially formed and the outer side is covered with wrapping fr, is used.

[Problems to be solved by the invention]

However, in the case of the composite twisted structure, the contact pressure between the strands S is high, so that abrasion is caused between the adjacent filaments fs, and so-called fretting, in which the filaments fs are broken at an early stage, easily occurs.

Also, in the layered structure, although the fretting is reduced, the gap between the inner filaments fi and the outer filaments fo is too small, so that the prime rubber cannot sufficiently penetrate into the cord, and Poor corrosion resistance, such as formation of a cavity through which moisture and the like propagate in the cord.

On the other hand, since such cords have a relatively large diameter, in order to alleviate the shearing force acting between the cords and suppress the separation between the cords and the ply rubber, the cords in each ply are provided. It is necessary to set both the distance between cords and the distance between cords between adjacent plies to be large.

However, the increase in the distance between cords in the ply, for example, the impact force locally acting on the tread surface concentrates on a small number of belt cords, causing so-called concussions in which the cords are broken, and the cord distance between the plies increases. The increase causes the belt thickness to increase, increasing the tread heat generation and impairing high-speed durability.

Therefore, in the conventional tire using such a cord, the durability of the belt is greatly reduced due to both the durability of the cord itself and the distance between cords that increase when the cord is used, and the tire service life is reduced. There is a problem that impairs.

In addition, as shown in FIG.
A 3 + 6 type in which an outer layer O composed of six outer filaments fo having a filament diameter of 0.38 mm is formed around a core C composed of three core filaments fc having a diameter of 2 mm is also partially employed. In this case, although the diameter of the cord is small, the cord strength is weak, and similarly, concussion occurs frequently and belt damage is caused.

An object of the present invention is to provide a heavy-duty radial tire capable of effectively suppressing belt damage caused by both the belt cord itself and the cord-to-cord distance and greatly improving the service life thereof.

[Means for solving the problem]

In order to achieve the above object, the heavy load radial tire of the present invention has a structure in which steel belt cords are arranged in parallel with each other on the tire radial outside of the carcass and inside the tread portion, and the carcass is arranged from the outer surface side of the tread portion. And a belt layer including at least a first belt ply, a second belt ply, and a third belt ply, which are sequentially disposed toward the first and second belt plies, and each of the first and second belt plies has n belt cords. Cores helically twisted with each other, and 3n-
It has an inner layer in which x inner filaments are helically twisted, and an outer layer in which 5 ny outer filaments are helically twisted around the inner layer. The following integer and x is an integer of 1 or more and y or less, and the diameters of the core filament, the inner layer filament, and the outer layer filament are the same and are equal to 0.
15 to 0.40 mm, and a layer twist structure in which the number of filaments in the inner layer is larger than the number of filaments in the core and the number of filaments in the outer layer is larger than the number of filaments in the inner layer. The interval t between the belt cords in each of the first and second belt plies is set to 0.3 times or more and 0.6 times or less of the diameter D of the belt cords, and the belt cords of the first belt plies and the second belt plies are used. The interval T between the belt cord and the first belt ply in a direction perpendicular to the first belt ply is 0.5 times or more the interval t and 0.7.
It is less than double.

[Action]

The radial tire for heavy load configured as described above adopts a layer twist structure in each belt cord of the first belt ply located on the outermost side and the second belt ply on the inner side thereof, while the number of filaments is reduced to that of the conventional one. By reducing the number of x-layers in the inner layer and the number of y-layers in the outer layer, and increasing the gaps between the inner filaments and the outer filaments, the permeability of the ply rubber into the cord can be increased.
As a result, the corrosion resistance can be improved, and the durability of the cord itself can be improved while maintaining the required cord strength in combination with the suppression of fretting by adopting the layered twist structure.

Also, because the belt cord eliminates wrapping,
The diameter D can be reduced as compared with the conventional one, whereby the separation between the belt cords in each of the first and second belt plies, t and It is possible to reduce the interval T between the belt cords between the first and second belt plies within a predetermined range. The decrease in the interval t, that is, the increase in the number of cords, has an effect of dispersing, for example, a large impact force locally applied to the tread surface to a number of belt cords, and can suppress breakage of the cords. Further, the reduction of the gap T helps to reduce the thickness of the belt, thereby uniformly increasing the in-plane rigidity of the tread portion and improving running performance, while reducing tire heat generation and improving high-speed durability.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

In the figure, the heavy-duty radial tire 1 includes a bead portion 3 through which a bead core 2 passes, a sidewall portion 4 extending outward from the bead portion 3 in the tire radial direction, and a tread portion 5 connecting between outer ends thereof.

A toroidal carcass 6 passing from the tread portion 5 through the sidewall portion 4 is bridged between the bead portions 3, and a belt layer 7 is provided outside the carcass 6 in the tire radial direction and inside the tread portion 5. Are wound in the circumferential direction.

The carcass 6 is at least 70 ° with respect to the tire equator and
One or more carcass cords in which carcass cords are arranged at an angle of 90 °, in this example, one carcass ply are formed, and both ends thereof are turned around the bead core 2 from inside to outside. A bead apex 8 made of hard rubber extending in a radially outward direction from the bead core 2 is interposed between the body portion and the folded portion of the carcass 6, and reinforced from the bead portion 3 to the sidewall portion 4. . As the carcass cord, an organic fiber cord such as nylon, rayon, or polyester is suitable, and sometimes a steel cord can be used according to the required tire performance.

Further, the belt layer 7 is sequentially arranged toward the carcass 6 which is the outer surface of the tread portion 5. In the present example having the first, second, and third belt plies 7A, 7B, and 7C, the second belt ply 7B has a three-layer structure, and its width W7B is compared with the width W7C of the third belt ply 7C. It is large.

The first belt ply 7A is the third belt ply 7C.
Of the second belt ply 7B has the maximum width, and both ends are located below the tread end.

Also, the belts 7A, 7B, 7C are respectively positioned with respect to the tire equator.
It is a cord array body in which steel belt cords 10 arranged at an angle of 10 ° or more and 30 ° or less are covered with ply rubber, and belt plies 7A, 7B, and 7C are such that each belt cord 10 crosses each other between plies. They are distributed in the wrong direction. Therefore, the belt layer 7 forms a tough truss structure by the belt cords 10 intersecting with each other, and increases the tread rigidity and restrains the carcass 6 with a high tagging effect.

In the present invention, the first and second belt ply
The belt cords used for 7A and 7B are specified, and the distance between the cords is regulated.

That is, as shown in FIG. 2, the belt cord 10 of the first and second belt plies 7A and 7B has a core 12 in which n core filaments 12f are helically twisted with each other, and the core 1
An inner layer 13 in which 3n-x inner filaments 13f are helically twisted around 2 and an outer layer 14 in which 5n-y outer filaments 14f are further spirally twisted around the inner layer 13. N + (3n-x) + (5n-y) without wrapping
It has a type of layer twist structure. Note that n, x, and y are each a positive integer, and n is 2 or more and 4 or less.
Is set to 1 or more and y or less.

FIG. 2 shows 3 + 8 where n = 3, x = 1 and y = 2.
+13 type, ie the number of filaments is core 12, inner layer
13 and the outer layer 14 are shown in the order of increase.

In such a belt cord 10, the number of filaments is larger in the inner layer 13 than in the conventional layered structure.
Since the number of the outer and outer layers 14 is reduced by y, the gap g1 between the inner filaments 13f and the gap g2 between the outer filaments 14f can be respectively increased, and the permeability of the ply rubber into the cord is increased to increase the corrosion resistance. Can improve.

Each filament 12f, 13f, 14f is made of a steel wire, and each of the filaments 12f, 13f, 14f has a diameter d1, d.
2, d3 is not less than 0.15 mm and not more than 0.04 mm, and each diameter d1, d2, d3 has the same diameter, thereby making it easy to secure the gap g1 between the inner filaments and the gap g2 between the outer filaments, In addition to maintaining good permeability of the ply rubber between the gaps and increasing the durability of the cord itself, it is easy to optimize the tensile strength and bending rigidity of the cord 10, and furthermore, the cord can be easily manufactured.

Also, such a belt cord 10 has a filament diameter of 12
f, 13f, and 14f are preferably twisted in the same direction.In such a case, the twist pitch P2 of the inner filament 13f is preferably used.
Is set to be larger than the twist pitch P1 of the core filament 12f and smaller than the twist pitch P3 of the outer filament 14. The reason why the twist direction is the same is that the same angle can reduce the crossing angle between the filaments adjacent in the radial direction and further reduce the contact pressure between the filaments. Is further suppressed,
The durability of the cord itself as well as the corrosion resistance can be greatly improved.

FIG. 3 shows the air permeability of the belt cord 10 in comparison with the conventional cord.

Also, since the belt cord 10 eliminates wrapping, its diameter D can be reduced, and in addition to the effect of reducing the cord rigidity by reducing the number of filaments, the distance between the belt cord 10 and the ply rubber can be reduced. The distance between the cords of the belt cord 10 can be reduced to a predetermined range while suppressing the separation.

Table 1 shows the diameter D of the belt cord 10 and its cord strength in comparison with a conventional cord.

That is, by using the belt cord 10, as shown in FIG.
The distance t between the belt cords 10 in A and 7B is within a range of 0.3 times or more and 0.6 times or less the diameter D of the belt cords 10, the belt cord 10 of the first belt ply 7A and the second belt ply 7B. A gap T between the belt cord 10 and the first belt ply 7A in a direction perpendicular to the first belt ply 7A can be set in a range of 0.5 times or more and 0.7 times or less of the distance t.

These ranges are derived from various experimental results attempted by the present invention, and examples thereof are shown in FIGS.

FIG. 5 shows the relationship between the ratio t / D between the diameter D and the interval t and the incidence of tread concussion.
That is, when the gap t is reduced and the ratio t / D is 0.6 or less, in other words, when the number of cords is large, a large impact force locally received on the tread surface can be dispersed to many belt cords, It is possible to reduce stress concentrated per cord and suppress occurrence of concussion. Note that the ratio t /
When D exceeds 0.6, the dispersion effect is inferior and the occurrence of concussion is increased.

Conversely, if t / D is less than 0.3, the shear force acting between the cords cannot be reduced by the ply rubber, resulting in separation of the belt cord 10.

FIG. 6 shows the relationship between the ratio T / t between the gap T and the gap t and the rate of occurrence of ply separation at the belt end.

This is because the belt cords of the belt layers 7 intersect each other between the plies as described above, so that the elongation directions of the respective belt plies 7A, 7B, 7C at the time of tire deformation are different. As a result, a shear stress acts between the plies, and the separation between the plies tends to proceed in order from the ply end of the belt ply 7A located on the outermost side.
Therefore, when the ratio T / t is 0.5 or more, the shear stress can be reduced by the ply rubber interposed between the cords, and the separation between the plies can be effectively suppressed.

When the ratio T / t exceeds 0.7, the thickness of the belt layer excessively increases, and the weight of the tire increases. In addition, the internal temperature of the tread is increased and the high-speed durability is impaired, while the rigidity of the tread is reduced and the running performance is reduced.

The specification of the belt cord 10 and the regulation of the inter-cord distance are performed by the outermost first belt ply 7A and the second belt ply 7B inside the outermost first belt ply 7A where the cord is most likely to be damaged and the ply is likely to be separated. To the third belt ply 7C located inside
It is preferable to similarly restrict the belt ply, and a belt ply having the same configuration may be further provided inside the third belt ply 7C.

〔The invention's effect〕

As described above, the heavy duty radial tire of the present invention has a belt cord having an n + (3n−x) + (5n−y) type layered structure, so that the durability of the cord itself is maintained while maintaining the necessary cord strength. Can be improved.

Moreover, by using this belt cord, the inter-cord distance can be reduced to a predetermined range, thereby suppressing the occurrence of concussion while suppressing the separation between plies, and increasing the belt durability. In addition, the belt thickness can be reduced, thereby suppressing tire heat generation, improving high-speed durability, and uniformly increasing rigidity in the tread surface to improve running performance. Further, by setting the diameters of the core filament, the inner filament, and the outer filament to be the same, it is easy to set the gap between the filaments, and it is possible to maintain good ply rubber permeability and further enhance the durability of the cord.

[Brief description of the drawings]

1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing an example of a belt cord, FIG. 3 is a graph showing its air permeability, and FIG. 4 is a cross-sectional view showing a belt layer. , FIG. 5 is a graph showing the relationship between the ratio t / D and the occurrence rate of tread concussion, FIG. 6 is a graph showing the relationship between the ratio T / t and the separation between plies, and FIGS. (c) is a sectional view showing a conventional technique. 5 tread portion, 6 carcass, 7 belt layer, 10 belt cord, 12 core, 13 inner layer, 14 outer layer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D02G 3/48 B60C 9/20 B60C 9/00

Claims (2)

(57) [Claims] 1. A first belt in which steel belt cords are arranged parallel to each other outside the carcass in the tire radial direction and inside the tread portion, and are sequentially arranged from the outer surface side of the tread portion toward the carcass. A belt layer including at least a ply, a second belt ply, and a third belt ply is provided, and each of the belt cords in the first and second belt plies has n core filaments helically twisted with each other. A core, an inner layer in which 3n-x inner filaments are spirally twisted around the core, and 5n around the inner layer.
An outer layer in which y outer filaments are helically twisted, wherein n is an integer of 2 or more and 4 or less, x is an integer of 1 or more and y or less, The diameter of each of the filaments of the layer and the outer layer is the same and 0.15 to 0.40 mm, and the number of filaments of the inner layer is larger than the number of filaments of the core, and the number of filaments of the outer layer is the filament of the inner layer. While the interval t between the belt cords in each of the first and second belt plies is at least 0.3 times the diameter D of the belt cords, and
0.6 or less, and a gap T between the belt cord of the first belt ply and the belt cord of the second belt ply in a direction perpendicular to the first belt ply is 0.5 or more times the interval t and Radial tire for heavy load with 0.7 times or less. 2. The heavy-duty radial tire according to claim 1, wherein x is 1 and y is 2.