JPH06344720A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To enhance the high-speed durability of a pneumatic radial tire by providing a belt reinforcing layer comprising a spirally wound strip of rubberized thermally contracting cords, and specifying the cross section per unit width and the twist coefficient of the cords of the belt reinforcing layer. CONSTITUTION:A pneumatic radial tire having at least one peripheral main groove 5 and a plurality of flat portions 7 provided n a tread portion is provided with at least two belt layers 4 each having cords that intersect those of the other. A belt reinforcing layer 5, comprising a strip consisting of a plurality of rubberized thermally contracting cords which is spirally wound so that the thermally contracting cords are arranged substantially parallel to the circumferential direction of the tire, is provided outside the belt layer 4 along the radial direction of the layer 4 and throughout the width of the belt layer. The cross section per unit width of the cords of the belt reinforcing layer 5 is greater in the area of the main groove 6 than in the area of the flat portions 7, and the twist coefficient of the cords of the belt reinforcing layer 5 is set to the range of 0.10-0.30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire having a small flatness expressed by a tire height with respect to a maximum tire width.

[0002]

2. Description of the Related Art In recent years, high performance pneumatic radial tires with high speed durability have been required due to high performance of vehicles, maintenance of road networks, etc. A so-called flat tire having a small driving force and improved driving force is known, and a flat pneumatic radial tire of this type has a flatness ratio (H / S) is 0.45-0.6
5, especially in recent years, it has become extremely flat with 0.35 to 0.40.

Generally, on the outer side in the tire radial direction of two belt layers that cross each other at a predetermined angle with respect to the tire circumferential direction,
In order to prevent the belt layer from squeezing outwards in the radial direction of the tire due to centrifugal force when the tire rotates at high speed, a strip of rubber with a plurality of heat-shrinkable cords is applied in the tire circumferential direction. A belt reinforcing layer formed by spirally winding is arranged so as to be arranged substantially in parallel, and, if necessary, one or more layers having the same constitution as the belt reinforcing layer are provided in both side areas of the belt layer. A pneumatic radial tire in which a narrow belt reinforcing layer is arranged is known. Especially when it comes to super flat tires, it is 270 to 340 km /
Since the vehicle travels at a speed of h, it tends to increase the belt reinforcing layer as a countermeasure against centrifugal force. Further, as the material of the cord of the belt reinforcing layer, nylon 6, nylon 66 or the like is generally used in consideration of the fatigue resistance of the belt reinforcing layer, the adhesiveness, the shaping amount at the time of manufacturing, the heat shrinkage rate and the like.

[0004]

When the flatness of the pneumatic radial tire is small, the tire absorbs and relaxes the shrinkage force generated by the shrinkage of the heat-shrinkable organic fiber cords constituting the belt reinforcing layer during vulcanization. Since the side part becomes narrow, the pneumatic radial tire will be excessively tightened by the contracting force of the heat-shrinkable organic fiber cord, the tire side part will be deformed, and the bead part will rise from the rim. As a result, the uniformity of the pneumatic radial tire is deteriorated and the high-speed durability is deteriorated. In addition, flat spots are generated due to the increase in the belt reinforcing layer, and the uniformity is deteriorated.

An object of the present invention is to solve the problems of the pneumatic radial tire having a small flatness ratio as described above and to provide a pneumatic radial tire having excellent uniformity and high speed durability.

[0006]

As a result of various studies, the inventors of the present invention have realized a pneumatic radial tire having the following constitution and improved uniformity and high-speed durability.

That is, the present invention has at least one tire circumferential main groove and a plurality of land portions or blocks (hereinafter, simply referred to as "land portions") on the tread surface, and the cords intersect each other. A belt-shaped strip having at least two belt layers and a plurality of heat-shrinkable cords covered with rubber, wound in a spiral shape so that the heat-shrinkable cords are arranged substantially parallel to the tire circumferential direction, A pneumatic radial tire having a belt reinforcing layer arranged radially outward of the belt layer and substantially over the entire width of the belt layer, wherein the cross-sectional area per unit width of the cord of the belt reinforcing layer is A pneumatic radial tire in which the land area is larger than the tire circumferential main groove area and the cord twist coefficient of the belt reinforcing layer is in the range of 0.10 to 0.30. That.

The cross-sectional area per unit width of the cord of the belt-reinforcing layer is preferably 2.0 to 3.0 times larger in the land area than in the tire circumferential main groove area. The area of the tire circumferential main groove has a small tread rubber volume and the centrifugal force at high speed is smaller than that of the land area.Therefore, per unit width of the cord of the belt reinforcement layer in the area of the tire circumferential main groove May have a small cross-sectional area. By reducing the cross-sectional area per unit width of the cord of the belt reinforcing layer in the area of the main groove in the tire circumferential direction, the heat shrinkage rate of the cord of the belt reinforcing layer after vulcanization can be reduced, and the tire side portion It is possible to prevent deformation and the like and reduce flat spots.

Further, the twist coefficient Nt of the heat-shrinkable cord constituting the belt reinforcing layer, which is defined below, is set in the range of 0.10≤Nt≤0.30 which is smaller than the conventional twist coefficient Nt. It is possible to prevent deformation of the tire side portion and the like due to thermal contraction of the cord of the belt reinforcing layer. Twisting coefficient Nt = T × (0.139 × D / 2 × 1 / ρ)
^1/2 × 10 ^{−3 In the} above formula, T is the twist number (turns / 10 cm), D is the total denier number, and ρ is the specific gravity (g / cm ³ ). If the twist coefficient Nt of the cord is less than 0.10, the stretchability of the heat-shrinkable cord that constitutes the belt reinforcing layer is lost and the tire fatigue is deteriorated. Also, the tension is too large during the sheeping during vulcanization, and the uniformity It will cause deterioration.
If the cord twist coefficient Nt exceeds 0.30, the shrinkage rate of the heat-shrinkable cord becomes excessively large, which causes problems such as deformation of the tire side portion, and also has a hoop effect against centrifugal force. It is also not preferable, and the high speed durability is reduced. The range of the twist coefficient Nt is 0.15 ≦ Nt ≦
It is more preferably 0.28.

[0010]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples without departing from the gist of the present invention. FIG. 1 is a schematic sectional view of a pneumatic radial tire. In FIG. 1, 1 is a rayon cord 1.
A carcass in which 650 d (denier) / 2 is arranged, which may be a single layer or a plurality of layers, 2 is a filler, and a relatively hard Shore A hardness of 80 ° (preferably 70 to 95 °) is used. . Reference numeral 3 is a bead, and by constructing the bead 3 in a structure having a great flexibility as described below, it is possible to relieve excessive shrinkage of the heat-shrinkable cord constituting the belt reinforcing layer. That is, since the bead has a mono-wire structure (one wire with rubber is wound and laminated), the wire can be freely changed, so that excessive shrinkage of the heat-shrinkable cord constituting the belt reinforcing layer can be prevented. It is absorbed by the variation of the wire, and the phenomenon such as the deformation of the tire side portion or the lifting of the bead portion from the rim is prevented. In addition, the bead has a cable bead structure (a single wire strand is wound around a core that is a core) to allow excessive shrinkage of the heat-shrinkable cord that forms the belt reinforcing layer. Is absorbed by the fluctuation of the wire wire wound around the core, and the phenomenon such as the deformation of the tire side portion or the lifting of the bead portion from the rim is prevented.

The belt layer 4 is composed of two belt layers in which steel cords are arranged at 25 ° with respect to the tire circumferential direction so that the steel cords cross each other.
Instead of the steel cord, a high modulus organic fiber cord such as aramid cord, polyparaphenylene benzbisoxazole (PBO) cord, polyvinyl alcohol (PVA) cord can be used. In particular,
It is also possible to use a cord having a 100% modulus of 2000 kg / mm ² or more. The cord angle of the belt layer 4 with respect to the tire circumferential direction is generally 22 to 3
A range of 2 °, particularly a range of 26 to 30 ° is preferable from the viewpoint of various performances.

A belt reinforcing layer 5 is arranged on the outer side in the radial direction of the belt layer 4 and between the tread rubber T. In the area of the tire circumferential main groove 6, the belt reinforcing layer 5 has a single-layer structure.
In addition, the area of the land portion 7 has a two-layer structure as a whole, and the cord cross-sectional area per unit width of the area of the land portion 7 is twice the unit width of the area of the tire circumferential main groove 6. Is configured. In this embodiment, a strip having a width of 5 mm in which four cords are embedded is used as the above-mentioned strip-shaped strip, and the cord of the belt reinforcing layer 5 is made of nylon cord 1260d (denier) / 2 and has a twist coefficient Nt of 0. 0.25.

2/3 at the land 7 in the end area of the belt layer 4
It is also possible to form a three-layer structure as a whole by winding in a spiral shape while overlapping. Further, in the area of the tire circumferential main groove 6, the strip-shaped strips are put together and wound in a spiral shape.
It has a layered structure. Furthermore, in the land area 7 in the central area, 1 /
2 was wound in a spiral shape while overlapping to form a two-layer structure as a whole.

As a matter of course, the belt reinforcing layer 5 may have a wide width, and a narrow strip may be additionally arranged in each area. However, forming the belt reinforcing layer 5 by spirally winding a narrow strip strip enhances the hoop effect in a pneumatic radial tire of this type, and also reduces the tire circumferential end of the narrow strip strip. It is particularly preferable from the viewpoint of elimination uniformity and high-speed durability. When the strip strip is spirally wound to form the belt reinforcing layer 5, how many belt strips are overlapped and wound to determine how many belt reinforcing layers 5 are formed as a whole depends on the tire size, It can be appropriately set in consideration of the physical properties of the cord embedded in the strip strip, and the strip strips are wound together with the tabs of the strips in the area of the tire circumferential main groove 6 or adjacent to each other. It is also possible to properly set whether to wind the strip strips with a predetermined gap between them.

The size of the pneumatic radial tire used in the examples is 255 / 40ZR17. Table 1
The comparative example shown in FIG. 3 differs from the example of the present invention in that the structure of the bead of the comparative example is a conventional strand bead core, and the twist coefficient Nt of the cord of the belt reinforcing layer is 0.48. Also, the belt reinforcing layer has a two-layer structure in which the wide layer is wound in the tire circumferential direction without spirally winding so as to cover the belt layer, and one narrow width is added to both side areas of the belt layer. The point is the structure. Other than that, it is the same as the embodiment of the present invention.

The uniformity shown in Table 1 was obtained under the measurement conditions in accordance with the German standard (WDK) and was indexed with a comparative example being 100. The larger the index, the better. In addition, the high-speed durability was measured by installing a pneumatic radial tire with a constant internal pressure on the drum, applying a constant load, and then increasing the tire speed to 1
The speed up to a failure is measured by increasing the speed at every 0 km / h, and is indexed with a comparative example being 100. In addition, in the flat spot, the tires are run in an actual vehicle to generate heat and then parked, left for one day and night, and then run, and it is determined whether vibration due to deformation of the tire occurs.
The higher the number, the better.

[0017]

[Table 1]

As shown in Table 1, the pneumatic radial tire of the present invention has no deformation of the tire side portion, and the high-speed durability and uniformity are greatly improved as compared with those of the comparative example. There is. When the side deformation is very large as in the comparative example, the uniformity measurement may not be possible in some cases.

[0019]

Since the present invention is constructed as described above, it has the following effects.

It is possible to prevent deformation of the tire side portion due to shrinkage of the heat-shrinkable cord of the belt reinforcing layer after vulcanization, and it is possible to reduce external input to the shoulder portion at the middle stage of wear or at the end stage of wear. The high-speed durability of the pneumatic radial tire can be improved and the occurrence of flat spots can be reduced. Therefore, a pneumatic radial tire having excellent uniformity and high-speed durability can be realized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a pneumatic radial tire.

[Explanation of symbols]

 1 ・ ・ ・ ・ ・ ・ Carcass 2 ・ ・ ・ ・ ・ ・ Filler 3 ・ ・ ・ ・ ・ ・ Bead 4 ・ ・ ・ ・ ・ ・ Belt layer 5 ・ ・ ・ ・ ・ ・Belt reinforcement layer 6 ... Tire circumferential main groove 7 ... Land

Claims (4)

[Claims] 1. A tread tread having at least one main groove in the tire circumferential direction and a plurality of land portions, at least two belt layers having cords intersecting each other, and a plurality of heat-shrinkable cords covered with rubber. Formed by spirally winding the strip-shaped strips so that the heat-shrinkable cords are arranged substantially parallel to the tire circumferential direction, in the radial direction outward of the belt layer and substantially the entire width of the belt layer. A pneumatic radial tire having a belt reinforcing layer arranged over, wherein the cross-sectional area per unit width of the cord of the belt reinforcing layer is larger in the land area than in the tire circumferential main groove area,
In addition, the cord twist coefficient of the belt reinforcing layer is 0.10 to
A pneumatic radial tire characterized by being in the range of 0.30. 2. A flatness ratio (H / S) represented by a tire height (H) with respect to a maximum tire width (S) is 0.20 to 0.5.
The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is in a range of 0. 3. The belt reinforcing layer disposed on the land portion is formed by spirally winding the strip strips overlapping each other in the width direction. Pneumatic radial tire. 4. The belt reinforcing layer arranged in the main groove in the tire circumferential direction is formed such that the strips are in contact with each other in the width direction or separated from each other in the width direction. Pneumatic radial tire as described in.