JP2001039110A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tire suitable for an automobile and a small-sized truck by forming a ply cord of a carcass by a specified steel cord, and separating the carcass in the cross direction of the tire, taking a crown part as a boundary to improve fatigue resistance and maneuverability of a carcass, especially operational stability. SOLUTION: This tire is formed by a carcass 2 extending like a toroid between a pair of bead cores 1, and a two-layer belt 3 and tread 4 positioned in order on the outside of the tire in the radial direction in a crown part. In this case, the carcass 2 is separated in the central area of the crown part, and divided into two parts 2a, 2b on both sides in the cross direction of the tire. A designated space D is secured between the respective dividing ends 20a, 20b of the respective carcasses 2a, 2b. The ply cord of the carcass 2 is formed by a steel cord of 1×N, 1+N or 2+N structure made by N-number (N: 2-7) of steel filaments with a diameter of 0.125 to 0.250 mm.

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 improved exercise performance and durability.

[0002]

2. Description of the Related Art Generally, in a radial tire for trucks and buses, a steel cord is used as a reinforcing material for a belt and a carcass. In a radial tire for a passenger car,
Steel belts are used for the belt, and textile cords such as polyester, nylon and rayon, which have excellent fatigue resistance, are used for the carcass.
However, using a textile code for the carcass,
Radial tires for passenger cars are liable to occur when the tire side contacts a curb, cause insufficient resistance to trauma or poor adhesion between cord and rubber, which may lead to cord breakage or separation. . In addition, textile cords generally have low bending stiffness,
It is difficult to increase the rigidity of the side portion of the tire, which is disadvantageous in that there is a limit in exercise performance.

[0003]

On the other hand, as an example of applying a steel cord to a carcass of a radial tire for a passenger car in place of a textile cord, JP-A-62-137202 discloses 1 × n (n is the number of filaments). , An integer of 1 to 5), a tire using a carcass cord layer formed by embedding a steel cord having a single twist structure in rubber, and JP-A-64-30803 discloses 1+ (1 × n) twist ( n
Is an integer of 3 to 5 in terms of the number of metal filaments, and the core is rubber or synthetic fiber). According to these proposals, exercise performance and durability are improved as compared with the case where the carcass is formed of a textile cord.

[0004] However, the steel cord used for the carcass undergoes repeated bending deformation over a long period of time as the tire rolls. Particularly, in the crown portion of the carcass, since the bending portion undergoes repeated bending and compression deformation due to the input from the road surface, the stress tends to concentrate on the crown portion, and the concentration of the compressive stress is repeated, whereby the material fatigue of the cord progresses, and the cord breaks. Occurs. Further, when the vehicle is turning, a lateral force is applied to the tire, and a compression input is generated in the carcass ply. Therefore, in order to apply the steel cord to the carcass of the radial tire for a passenger car, it is important to improve the fatigue resistance of the steel cord particularly at the crown of the carcass.

Accordingly, an object of the present invention is to provide a pneumatic radial tire suitable for passenger cars and small trucks, which has improved carcass fatigue resistance and improved kinetic performance, particularly steering stability.

[0006]

Means for Solving the Problems The inventors of the present invention have intensively studied a method of improving the fatigue resistance of a carcass, and as a result, a carcass extending continuously between both bead portions is divided by a crown portion thereof. The inventors have found that the above problems can be solved, and have completed the present invention.

The gist configuration of the present invention is as follows. (1) A pneumatic radial tire having a carcass composed of plies of a radially arranged cord extending in a toroidal shape between a pair of bead cores, wherein the ply cord of the carcass is a steel filament having a diameter of 0.125 to 0.250 mm. 1 × N, 1 + N or 2 consisting of N (N: 2 to 7)
A pneumatic radial tire, which is a steel cord having a + N structure, wherein the carcass is cut off in a tire width direction at a crown portion thereof.

(2) The pneumatic radial tire according to (1), wherein the separated ends of the separated carcass are located at positions separated from each other.

(3) The pneumatic radial tire according to (1), wherein the cut ends of the cut carcass are overlapped with each other.

(4) The pneumatic radial tire according to (1), wherein the separated ends of the separated carcass are located close to each other.

(5) The pneumatic radial tire according to any one of (1) to (4), wherein the steel cord has a 1 × N structure.

(6) The pneumatic radial tire according to any one of the above (1) to (5), wherein the steel cord has a total elongation at cut of 3.0 to 7.0%.

(7) The pneumatic radial tire according to any one of (1) to (6), wherein the tensile strength of the steel filament is 2700 N / mm ² or more.

[0014]

FIG. 1 illustrates a specific example of a radial tire for a passenger car according to the present invention. The tire includes a carcass 2 extending in a toroidal shape between a pair of bead cores 1, and a belt 3 having at least one layer, two layers in the illustrated example, disposed outside a crown portion of the carcass 2 in the tire radial direction.
And a tread 4 disposed radially outward of the belt 3 in the tire radial direction.

It is important that the carcass 2 is formed by extending one of plies made of a steel cord extending in the radial direction between the bead cores 1 in a toroidal shape, and separated from the crown portion in the tire width direction. It is. That is, the carcass 2 is separated at the center of the crown portion and divided into carcass 2a and 2b on both sides in the tire width direction, so that the crown portion is provided with flexibility and the compression input to the carcass ply is separated from the carcass ply. The structure allows escape to the free end. As a result, the fatigue resistance of the carcass can be significantly improved.

Here, if the carcass 2 is cut off at any position of its crown portion, the compression input to the carcass ply concentrated below the tread can be missed. It is recommended that the faces be separated and centered. Because the equatorial plane of the tire is separated and set as the center, the stress distribution under the tread is symmetrical on both sides of the equatorial plane of the tire, and the compression input applied to the carcass can be most effectively relieved. is there.

Further, the separated carcass 2a and 2a
b, as shown in FIG. 1, separating the cut ends 20a and 20b from each other, as shown in FIG. 2, placing the cut ends 20a and 20b on top of each other, or as shown in FIG. In addition, any one of the arrangements in which the separation ends 20a and 20b are arranged close to each other may be used.

That is, in the carcass structure shown in FIG. 1, since the distance D between the carcass 2a and 2b (hereinafter, referred to as divided carcass) obtained by separating the carcass 2 is widened, the rigidity inside the tread in the radial direction is reduced. This is particularly effective in reducing the compression force applied to the carcass ply when the tire receives a lateral force. In addition,
The distance D between the divided carcass 2a and 2b is preferably 10 mm or less in order to maintain the rigidity of the tire.

Next, the carcass structure shown in FIG. 2 is obtained by superposing the separated ends 20a and 20b of the divided carcass 2a and 2b. The carcass structure shown in FIG. This is an advantageous structure in terms of properties. The overlap width t of the cut ends 20a and 20b is preferably set to 10 mm or less in order not to excessively increase the rigidity of the tire.

As described above, each of the carcass structures shown in FIGS.
Since the cut end of the divided carcass is made free, the compression input in the carcass ply can be released to the free end side of each divided carcass, so that the compression input in the carcass can be reduced.

The steel cord 5 has a diameter of 0.12.
N of steel filament of 5 to 0.250 mm (N: 2 to 2)
7) Use a 1 × N, 1 + N or 2 + N structure code composed of books. That is, when the filament diameter is less than 0.125 mm, the carcass strength is reduced, and it becomes necessary to increase the number of cords driven in the carcass, and the gap between the cord end faces exposed at the carcass ply ends is reduced,
There is a risk of causing separation at the ply end. On the other hand, when the diameter of the filament exceeds 0.250 mm, the amount of bending strain when an extreme bending input is applied to the cord increases, so that the cord is easily broken, and the cord breaking resistance is deteriorated.

Then, the code is expressed as 1 × (2-7), 1+
The (2-7) or 2+ (2-7) structure is used for the following reason. That is, in other structures, fretting wear easily occurs between filaments, and rubber infiltration between filaments is poor. In particular, in the 1 × (2 to 7) single-twisted structure, all filaments constituting the steel cord have the same spiral shape, so that when the cord is subjected to compressive deformation, all the filaments are uniformly deformed. As a result, concentration of stress can be avoided.

Further, it is advantageous to use a steel cord having a total elongation at break of 3.0 to 7.0%. That is, by setting the total elongation at the time of cutting of the steel cord to 3.0% or more, the modulus, particularly the initial modulus, becomes lower than that of the conventional steel cord, and the elongation at a low stress is secured. Thus, it becomes possible to impart appropriate flexibility to the carcass of the tire. Therefore, by applying such a steel cord to the carcass, the riding comfort when the steel cord is used for the carcass is improved.

On the other hand, when the total elongation of the steel cord at the time of cutting exceeds 7.0%, the dimensional change in the longitudinal direction of the cord becomes large, and the curl and warpage generated in the treat material become large in the treat material serving as a carcass ply. Therefore, the workability at the time of tire production deteriorates. Therefore, by setting the total elongation at break of the steel cord to 7.0% or less, workability during tire production can be guaranteed.

Further, a filler constituting a steel cord is provided.
2700N / mm ^Two Above
But mainly in securing the strength needed for passenger car tires.
Good.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A code having the specifications shown in Table 1 was applied to a carcass 2 of a radial tire for a passenger car having the structure shown in FIGS. Further, the belt 3 is placed on the carcass 2 with respect to the equatorial plane of the tire.
The first belt is placed in a direction where a steel cord of × 3 × 0.30 (mm) structure is inclined at an angle of 68 ° left, and the steel cord is further placed on it at an angle of 68 ° right with respect to the equatorial plane of the tire. The second belt is arranged in an inclined direction. In addition,
The number of cords to be driven was 30/50 mm.

The tire thus obtained was mounted on a rim having a size of 6 J × 14, and then charged with an internal pressure of 2.0 kgf / cm ² , and the steering stability of the tire and the breakability of the cord in the carcass were examined. As a comparison, a tire of the same size in which a conventional fiber cord was applied to a continuous carcass was prototyped and similarly evaluated. The number of cords to be driven into the carcass of each prototype tire was appropriately adjusted so that the total strength of the carcass was equal to that of the comparative example regardless of the type of cord. Table 1 also shows the results of these surveys.

Here, the steering stability is determined by arranging tires on a drum having an outer diameter of 3000 mm, applying a load of 400 kg to the tires, preliminarily running at a speed of 30 km / h for 30 minutes, and then applying a load. Was removed and readjusted to the above internal pressure, and then again under the same speed and the same load conditions, a slip angle was continuously positively and negatively added up to ± 4 ° on the drum.
Next, the cornering force (CF) at each of the positive and negative angles was measured, and the following formula:

(Equation 1) The cornering power (CP) was determined at. Then, the CP of each test tire was represented by an index when the CP of the tire of Comparative Example 1 was set to 100. The larger the index, the better the steering stability.

Further, resistance to ply cord breakage resistance, the each tire was 40,000 km running in general road, then 30,000 constant Yamasaka path after reducing the internal pressure from 2.0 kgf / cm ² to 1.7 kgf / cm ² After running for km, the tires were dissected, and the presence or absence of a broken cord in the carcass ply at the carcass turn-back portion was examined.

[0030]

[Table 1]

[0031]

According to the present invention, it is possible to improve the durability of a pneumatic radial tire whose driving performance is improved by applying a steel cord to the carcass ply, and in particular, the durability of the carcass ply.

[Brief description of the drawings]

FIG. 1 is a diagram showing a tire structure of the present invention.

FIG. 2 is a diagram showing another tire structure of the present invention.

FIG. 3 is a view showing still another tire structure of the present invention.

[Explanation of symbols]

 1 bead core 2 carcass 2a split carcass 2b split carcass 3 belt 4 tread

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B60C 9/02 B60C 9/02 B

Claims (7)

[Claims] 1. A pneumatic radial tire having a carcass formed by a ply of radially arranged cords extending in a toroidal shape between a pair of bead cores, wherein the ply cord of the carcass has a steel filament having a diameter of 0.125 to 0.250 mm. 1 × N, 1 + N consisting of N (N: 2 to 7)
Alternatively, the pneumatic radial tire is a steel cord having a 2 + N structure, wherein the carcass is separated in a tire width direction at a crown portion thereof. 2. The pneumatic radial tire according to claim 1, wherein the separated ends of the separated carcass are located at positions separated from each other. 3. The pneumatic radial tire according to claim 1, wherein the separated ends of the separated carcass are overlapped with each other. 4. The pneumatic radial tire according to claim 1, wherein the separated ends of the separated carcass are located close to each other. 5. The method according to claim 1, wherein
A pneumatic radial tire, wherein the steel cord has a 1 × N structure. 6. The method according to claim 1, wherein
A pneumatic radial tire having a total elongation at break of a steel cord of 3.0 to 7.0%. 7. The method according to claim 1, wherein
A pneumatic radial tire, wherein the steel filament has a tensile strength of 2700 N / mm ² or more.