JP3021451B1 - Radial tires for heavy loads - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To improve plunger strength without increasing the amount of steel as compared with a conventional belt layer, and to achieve high-speed durability and weight reduction while maintaining steering stability. The belt cord includes two belt plies, and a belt cord crosses between the plies. At least in the tread central region, the sum MB of the amount of steel per ply unit area of each belt ply is 6 to 10 of the amount of steel MC per ply unit area of the carcass ply.
Times. The rubber thickness between the carcass cord of the adjacent carcass ply and the belt cord of the belt ply in the radial direction is 0.7 to 3.0 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty radial tire suitable for heavy duty vehicles such as trucks and buses.

[0002]

2. Description of the Related Art In recent years, with the improvement of road networks, the speeding up of vehicles, and the performance of vehicles, radialization has been promoted even for heavy load tires such as trucks and buses. I have.

In this type of tire, it is necessary to sufficiently increase the rigidity and strength of the belt layer in order to support a high load. Conventionally, as shown in FIG. The cord angle of the first ply A1 on the carcass side with respect to the tire equator is relatively deep as 50 to 70 degrees, and the second to fourth ply A2
The cord angle of the second ply A2 is substantially the same as the cord angle of the second ply A2 within the range of 10 to 30 degrees.
3. Arranged in a direction crossing the A4 cord to form a strong truss structure.

However, when a tire steps on a projection such as a rock, the belt layer A tends to bend radially inward while changing its cord angle. At this time, in the belt layer A having the multi-sheet structure, the first ply A1 disposed on the innermost side causes the second and third plyes A on the outer side.
2. The movement of the chord A3 is restricted, and the chord angle is hard to change. In addition, when bending inward in the radial direction, the tensile strain increases as the inner ply increases, but the difference in tensile strain (nonuniformity) is further promoted by the multi-ply structure. As a result, there is a problem that, due to these interactions, cord breakage occurs intensively, particularly in the second ply A2, and the plunger strength is impaired.

In the belt layer A having a multi-sheet structure, the tread thickness t is increased, and the chance of peeling damage starting from the end of the ply is increased. It is with.

In the present invention, the belt layer is formed by two plies of steel cord, and the amount of steel of the belt layer in the central region of the tread, and the rubber thickness between the cords between the carcass and the belt layer are each determined. Basically, while maintaining steering stability, it can increase the plunger strength without increasing the amount of steel compared to the conventional belt layer, and can also contribute to high-speed durability and weight reduction. It aims to provide heavy duty radial tires.

[0007]

In order to achieve the above object, a radial tire for heavy load according to the present invention comprises a steel carcass cord extending from a tread portion to a sidewall portion, extending to a bead core of a bead portion, and a tire equatorial line. Consisting of a single carcass ply arranged at an angle of 70 to 90 degrees with respect to the tire, and a steel belt cord disposed inside the tread portion and outside the carcass and 0 to 45 with respect to the tire equator. A belt layer composed of two belt plies arranged at an angle of degrees, and the belt cords of the two belt plies cross each other and have a belt width WB of at least 0.25 in the tire axial direction of the belt layers. A ply unit area of each belt ply in a tread central region between circumferential lines separated from the tire equator by a double distance L on both sides. Sum MB steel of or the per ply unit area of the carcass ply steel amount MC
The thickness of the rubber between the carcass cord of the adjacent carcass ply and the belt cord of the belt ply is set to 0.7 to 3.0 mm.

It is preferable that the amount of steel in each belt ply be substantially the same from the viewpoints of steering stability, plunger strength, high-speed durability and the like.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, a heavy load radial tire 1 (hereinafter referred to as a tire 1)
A tire for a truck or a bus, the tread portion 2;
The vehicle includes a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 disposed at an inner end of each sidewall portion 3. Further, the tire 1 has a toroidal carcass 6 spanned between the bead portions 4, 4,
It is reinforced by a strong belt layer 7 disposed outside the carcass 6 and inside the tread portion 2.

The carcass 6 is composed of a single carcass ply 6A which is turned around the bead core 5 of the bead portion 4 from the tread portion 2 to the side wall portion 3;
The carcass ply 6A has a steel carcass cord (steel cord) 70 to 9 with respect to the tire equator C.
They are arranged at an angle of 0 degrees, usually 90 degrees.

The belt layer 7 is formed of two inner and outer belt plies 7A and 7B. In this example, as shown in FIG. 2, the inner belt ply 7A is wider than the outer belt ply 7B, and the belt width W defined by the wider ply width WA is set to the tread contact width TW. 0.80
By setting the range of about 0.95 times, in this example, about 0.90 times, substantially the entire width of the tread portion 2 is reinforced with a tag effect. The ply width WB of the outer belt ply 7B
Is set to be smaller than the ply width WA by about 4 to 10 mm to alleviate the stress concentration at the outer end of the belt.

Each of the belt plies 7A and 7B is formed by arranging steel belt cords (steel cords) at an angle of 0 to 45 degrees, preferably 10 to 30 degrees with respect to the tire equator C. The inclining directions of the cords are different from right up / left up so that the cords intersect between the plies. By the intersecting between the belt cords and the adoption of the cord angles in the above range, the in-plane rigidity and the hoop effect required for the belt layer 7 are provided, and the steering stability is maintained.

Here, when a distance L of 0.25 times the belt width W is defined as a tread center region Y, a region between circumferential lines X and X separated on both sides from the tire equator C is defined as at least a tread center region. In a region Y, the amount of steel MB per unit area of the ply of each of the belt plies 7A and 7B.
1, the sum MB of MB2 (= MB1 + MB2) is set to 6 to 10 times the steel amount MC per unit area of the carcass ply 6A.

The "steel amount" will be described by taking the outer belt ply 7B as a representative example. As shown in FIG. 3, the belt ply 7B is divided into small blocks 10 having a reference area K of, for example, size L1 × L1. Sometimes, it means a value V / K obtained by dividing the total volume V of the steel of the belt cord 11 disposed in the block 10 by the reference area K.

In a heavy-duty radial tire, the steel amount MC of the carcass 6 is usually set at 0.09 to 0.17 mm, in this example, about 0.128 mm in order to support a high filling internal pressure. Therefore, the steel amount MB of the belt layer 7
Is a range of 0.54 to 1.7 mm as a guide, preferably a range of 0.76 to 1.27 mm, and about 1.016 mm in this example, and the amount of steel in a conventional four-layer belt layer. It is set to approximately the same level. In addition,
In order to obtain the steel amount MB in the above range, one or both of a method of increasing a belt cord and a method of increasing the number of driving cords as compared with the related art are employed.

As described above, the belt layer 7 is composed of the minimum number of plies necessary for obtaining the in-plane rigidity of the belts by crossing the cords, that is, two belt plies 7A and 7B. The sum MB of the steel amounts MB1 and MB2 of the plies 7A and 7B is regulated to 6 to 10 times the steel amount MC of the carcass ply 6A.

[0017] Thus, while maintaining the required steering stability, the halving of the number of plies can reduce the tensile strain on the innermost belt ply, which is concentrated when riding over the protrusion,
In addition, the movement of the belt cord in the crossed arrangement can be flexibly changed by following the deflection of the belt layer 7. Accordingly, it is possible to suppress the cord breakage of the belt layer 7 when the vehicle rides on the protrusion, and it is possible to increase the plunger strength comprehensively. In order to effectively exhibit the effect of suppressing the cord breakage, the steel amount MB1 of the belt ply 7A and the steel amount MB of the belt ply 7B are required.
2 is preferably substantially the same, and furthermore, it is preferable that the cord configuration, the number of cords inserted, and the cord angle of the belt plies 7A and 7B are also identical.

By reducing the number of plies by half, the tread thickness t is reduced, and the chance of occurrence of peeling damage starting from the ply end E is reduced, so that high-speed durability can be improved and weight can be reduced. Further, since the number of ply attaching steps at the time of forming a green tire is reduced, productivity can be increased and cost can be reduced.

When the steel amount MB is less than 6 × MC, the breakage of the cord cannot be suppressed, and the plunger value drops significantly. On the other hand, if it exceeds 10 × MC, the weight of the tire is unnecessarily increased, the effect of reducing the weight is lost, and the cost is increased.

In the tire 1, in order to further increase the strength of the plunger, as shown in FIG. 4, between the carcass cord 12 of the adjacent carcass ply 6A inside and outside in the radial direction and the belt cord 11 of the inner belt ply 7A. At least in the tread central region Y,
It has increased to a range of 0.7 to 3.0 mm. In FIG. 4, the arrangement directions of the carcass cords 12 and the belt cords 11 are drawn in the same manner so that the rubber thickness T can be easily understood.

By setting the rubber thickness T, the flexibility of the tread portion 2 is appropriately increased, and the impact force received from the road surface when passing over the protrusion is dispersed and reduced. In addition, the restraint of the carcass cord 12 on the movement of the belt cord 11 can be suppressed. Accordingly, the plunger strength can be further increased by a synergistic effect with the two belt ply structures.

FIG. 5 shows the correlation between the rubber thickness T and the plunger strength obtained by the present inventor through a test.
The test was conducted on two belt-ply tires.
Only the rubber thickness T was changed, and the plunger strength at that time was measured. As shown, when the rubber thickness T is less than 0.7 mm, the effect of improving the plunger strength is low. 3.0m
m, no further increase in the effect is expected,
Conversely, the weight is unnecessarily increased and the cost is increased.
The rubber thickness of the conventional tire is 0.3 to 0.6 m
m.

In order to secure the rubber thickness T in the above range, the topping rubber of the carcass ply 6A and the belt ply 7A may be increased. Thickness T1 is 1.0 ±
It is preferable to separately provide a rubber layer 15 (shown in FIGS. 2 and 4) having a rubber hardness of 0.5 mm and a rubber hardness substantially equal to that of the topping rubber.

[0024]

EXAMPLE A tire having a tire size of 11R22.5 and having the structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1, and the plunger strength, high-speed durability and tire weight of each sample tire were measured. The results are shown in Table 1. Table 2 shows the configuration of the carcass and the belt layer in the conventional tire. In Examples and Comparative Examples, the carcass configuration was the same as that of the conventional tire.

Plunger strength: 7.5 for test tires
A plunger destruction test according to JISD4230 was performed under a condition where the rim was assembled to a rim of 0 × 22.5 and filled with an internal pressure of 700 kpa. The breaking energy at that time was measured and compared by an index with the conventional example being 100. The larger the index value, the better.

High-speed durability: 7.55 × 2 test tires
Assemble the rim into 2.5 rim, internal pressure 850kpa, load 4
The vehicle was run on a drum at 000 kgf and a speed of 80 km / h, and the speed was stepped up by 10 km / h every 3 hours. When the tire was visually damaged, the test was terminated. Then, the running time until the occurrence of damage was compared by an index with the conventional example being 100. The larger the index value, the better.

Tire Weight The weight of the tire was represented by an index with Conventional Example 1 being 100. The smaller the value, the lighter.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

The radial tire for heavy load of the present invention is constructed as described above, so that the steering stability is maintained while maintaining the steering stability.
Plunger strength can be improved without increasing the amount of steel as compared with a conventional belt layer, and high-speed durability can be improved and weight can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a tire according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a tread portion.

FIG. 3 is a perspective view of a ply for explaining an amount of steel.

FIG. 4 is a diagram for explaining a rubber thickness.

FIG. 5 is a diagram showing a relationship between rubber thickness and plunger strength.

FIG. 6 is a cross-sectional view illustrating a belt structure of a conventional tire.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 7 Belt layer 7A, 7B Belt ply 11 Belt cord 12 Carcass cord C Tire equator Y Tread central area T Rubber thickness

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-139403 (JP, A) JP-A-3-109104 (JP, A) JP-A 8-170282 (JP, A) JP-A-5-170 302282 (JP, A) JP-A-6-183206 (JP, A) JP-A-9-105084 (JP, A) JP-A-6-40211 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 9 / 08,9 / 18,9 / 20 D07B 1/00-9/00

Claims (2)

(57) [Claims] 1. A carcass comprising a single carcass ply extending from a tread portion to a sidewall portion to a bead core of a bead portion and having steel carcass cords arranged at an angle of 70 to 90 degrees with respect to the tire equator. A belt layer consisting of two belt plies arranged inside the tread portion and outside of the carcass and having steel belt cords arranged at an angle of 0 to 45 degrees with respect to the tire equator; The belt cords of the two belt plies cross each other, and at least the belt width WB of the belt layer in the tire axial direction.
In the central region of the tread between circumferential lines separated from the tire equator by a distance L of 0.25 times the circumferential direction, the sum MB of the amount of steel per ply unit area of each belt ply is The rubber thickness between the carcass cord of the carcass ply and the belt cord of the belt ply adjacent to each other in the radial direction is 6 to 10 times as much as the steel amount MC of the steel.
m, a radial tire for heavy loads. 2. The belt ply according to claim 1, wherein the amount of steel per unit area of the belt ply is substantially the same as the amount of steel of the other belt ply.
The radial tire for heavy load described.