JP3422694B2 - Heavy duty tire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty tire capable of improving bead durability while reducing the weight of a bead portion.

[0002]

2. Description of the Related Art For example, in a heavy-duty tire for trucks, buses, etc., in order to maintain the bead durability, conventionally, as shown in FIG. Bead apex rubber filled in b
By increasing the rubber volume and increasing the bead rigidity, the tire deformation itself due to the applied load is reduced. The thickness t of the bead apex rubber b at this time is about 9 to 20 mm at the outer end position of the winding portion a2.
Has also reached.

On the other hand, in recent years, the bead structure has been reviewed to reduce the weight of tires, and as shown in FIG.
On the contrary, the volume and height of the bead apex rubber b are greatly reduced and the winding portion a2 is raised to be close to the carcass body a1 (hereinafter referred to as a new bead structure).
Therefore, a technique for reducing the weight while maintaining the bead durability has been proposed.

[0004]

However, in the tire having such a new bead structure, since the carcass body a1 extends from the bead core c in a substantially straight line shape, the carcass is strongly pulled at the contact position cp between the carcass and the bead core c. Stress is applied to the carcass cord, and the carcass cord peculiar to this structure is easily broken.

Therefore, the present invention is based on the fact that the contact region of the bead core which comes into contact with the carcass ply is covered with a protective rubber layer containing a short fiber, and the breakage damage of the carcass cord can be suppressed to improve the bead durability. The purpose is to provide heavy duty tires.

[0006]

In order to achieve the above object, the heavy-duty tire according to claim 1 of the present invention is characterized in that the carcass ply body extending from the tread portion to the side wall portion to the bead core of the bead portion, A carcass having a carcass ply that is folded back at the bead core and extends along the bead apex rubber extending radially outward from the bead core, and a belt layer disposed inside the tread and outside the carcass. In the winding portion of the carcass, the bead core is formed in a polygonal shape while a proximity area is formed near the carcass ply body by crossing the outer end of the bead apex rubber.
And the average fiber diameter is 1 to 10 in the entire circumference including the contact area where the carcass ply contacts by folding back.
It is covered with a protective rubber layer containing short fibers in the range of 0 μm , and the protective rubber layer covers the bead core.
It has a polygonal shape that is closer to the bead core, and the bead core
A, the thickness T of the protective rubber layer at the corner is 0.5 to
The feature is that it is 2.0 mm .

[0007] Also in the heavy duty tire according to claim 2, wherein the bi
The core has a flat hexagonal cross section and
The fibers have an average fiber length of 10 to 6000 μm, and
The protective rubber layer contains 5 short fibers per 100 parts by weight of the rubber base material.
It is characterized in that it is made of short fiber compounded rubber compounded in an amount of 0 to 80 parts by weight .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a tire cross section in a 50 kpa internal pressure state in which a heavy-duty tire 1 of the present invention is assembled on a standard rim and filled with an internal pressure of 50 kpa. The standard rim means a standard rim defined by JATMA.

In the drawing, a heavy-duty tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 located at an inner end of each sidewall portion 3. And with. The heavy load tire 1 is reinforced by a toroidal carcass 6 extending between the bead portions 4 and 4, and a belt layer 7 arranged radially outside the carcass 6 and inside the tread portion 2.

The carcass 6 is, in this example, a steel carcass cord of 75 to 90 with respect to the tire equator CO.
It consists of one carcass ply 9 arranged at an angle of degrees,
The carcass ply 9 includes a carcass ply body 9A extending from the tread part 2 to the side wall part 3 to a bead core 5 of a bead part 4 on both sides of the carcass ply body. With 9B.

Between the carcass ply body 9A and the hoisting portion 9B, a bead apex rubber 10 that extends in a tapered shape from the bead core 5 toward the tire radial outside is filled.

The bead apex rubber 10 is JI
The bead baseline 1 made of a relatively hard rubber having an SA hardness of, for example, 70 to 100 degrees and having a radially outer end 13 thereof.
The height h from 6 is reduced to a range of 0.1 to 0.3 times the carcass height Hk from the bead baseline 16 on the outer surface of the carcass 6 on the tire equator CO. by this,
The rubber volume is reduced to reduce the weight.

When the height h is less than 0.1 × Hk, it is difficult to manufacture the tire, and the bead apex rubber 10 is too small to provide the necessary bead rigidity, and the carcass 6 near the outer end 13 is not provided. Is easily bent, and defects such as air accumulation are likely to occur, and the bent portion serves as a starting point to induce breakage of the carcass cord during traveling. On the other hand, if it exceeds 0.3 × Hk, heat generation is impaired, durability is lowered and unnecessary weight increase is caused. Therefore, it is preferably 0.25 × Hk or less, more preferably 0.20.
× Hk or less. The bead baseline 16 is defined as a tire axial direction line (rim diameter reference line) that passes through the tire axially outer end of the bead bottom surface 4S1.

Further, in the carcass 6, the carcass ply body 9A is the outer end 13 of the bead apex rubber 10.
In the region Y between the position closest to the carcass ply body 9A and the position where the carcass ply body 9A starts to separate from the bead core 5 outward in the radial direction.
Is formed in a substantially linear shape in the above-mentioned 50 kpa internal pressure state.

Thus, the carcass ply body 9A is
By forming a substantially linear shape at least in the region Y, the code path of the carcass 6 is shortened, and when the standard internal pressure is filled or when a load is applied, the carcass 6
Can be suppressed from protruding outward, and the amount of deformation itself of the bead portion 4 can be reduced. Also, by forming the above-mentioned substantially straight line,
The thickness of the bead apex 10 is reduced, and the winding portion 9B
Relatively approaches the neutral line of stress, and the compressive force acting on the winding portion 9B can be greatly reduced with the effect of reducing the deformation amount itself of the bead portion 4.

On the other hand, the hoisting portion 9B of the carcass 6 has a high turn-up hoisting structure which projects radially outward from the outer end 13 of the bead apex rubber 10.
The protruding portion of the winding portion 9B is the carcass ply body 9A.
To form a proximity area 15 close to. The length L0 of the adjacent region 15 along the carcass 6 is in the range of 35 to 70 mm, and thereby the necessary bead rigidity is imparted.

In the proximity area 15, the rubber thickness between cords between the carcass cords of the adjacent carcass ply body 9A and the carcass cord of the winding portion 9B is, in this example,
The shear force acting between the carcass cords in the range of 0.5 to 4.0 mm is relaxed by the elasticity of the rubber material interposed between the cords.

Next, in this example, the bead core 5 is a so-called single-wind type in which one rubberized bead wire is spirally wound in multiple layers. In this example, the bead core 5 has a flat hexagonal cross-sectional shape, and the long major axis thereof is arranged substantially parallel to the rim sheet inclined at an angle of, for example, 15 degrees, so that the bead core 5 is lightweight and The fitting force with the rim is enhanced over a wide range.

However, since the bead core 5 has a polygonal shape, its corners come into contact with the carcass 6 and the substantially straight ply body 9A is strongly pulled when a load is applied, so that breakage damage of the carcass cord occurs at this contact point. It tends to occur.

Therefore, the contact region 17 of the bead core 5 that comes into contact with the carcass 6 is covered with the protective rubber layer 19.

The protective rubber layer 19 contains 50 to 80 parts by weight of short fibers with respect to 100 parts by weight of a rubber base material using a diene rubber such as natural rubber, isoprene rubber, styrene-butadiene rubber or butadiene rubber. It consists of short fiber compounded rubber reinforced by the above, and by smoothly covering the corners of the bead core 5 in an arc shape, the bending and contact pressure of the carcass 6 can be reduced, and direct contact between the carcass cord and the bead wire can be prevented, As a result, breakage damage of the carcass cord can be effectively suppressed.

The protective rubber layer 19 is formed in the contact area 17
It is preferable for productivity to cover substantially the entire circumference of the bead core 5 including. The thickness T of the protective rubber layer at the corners of the bead core 5 is preferably 0.5 to 2.0 mm, whereby the corners can be smoothly and surely covered and protected with a larger arc, and the cord Guarantee the effect of suppressing breakage damage. Furthermore, the protective rubber layer 19 is clearly shown in FIGS.
So that each side of the bead core 5 is covered with a substantially uniform thickness.
The outer surface of this protective rubber layer 19 is
It has a polygonal shape close to the core 5.

The short fibers are not particularly limited, but those having an average fiber diameter in the range of 1 to 100 μm and an average fiber length in the range of 10 to 6000 μm can be preferably used.
Organic fibers such as nylon, rayon, vinylon, polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, aromatic polyamide, polyethylene terephthalate, polypropylene and cellulose are preferred, but inorganic fibers such as glass and alumina can also be used. Note that low modulus organic fibers such as nylon have high elongation and excellent flexibility. Preferred for coating bead cores of relatively small diameter.

For comparison, the inventor of the present invention covers the bead core 5 with a textile cloth woven of a yarn of an organic fiber such as nylon, rayon or polyester in place of the protective rubber layer 19. Tried that. As a result, the yarn thickness is, for example, 1670 dtex / 2.
If it exceeds, the textile cloth becomes too hard to wind along the bead core, and the carcass cord may fall into the gap between the yarns that are the weave parts and come into contact with the bead wire. It is difficult to surely prevent. Therefore, in order to drop into the texture portion and to secure a necessary coating thickness,
Since it is necessary to wind the textile cloth having a relatively thin yarn more than once, it causes a decrease in working efficiency and an increase in cost.

On the other hand, the protective rubber layer 19 has the advantages that it is not difficult to wind and that the required coating thickness can be secured by only winding the rubber strip once.

The belt layer 7 is composed of at least two belt plies, in this example, first, second, third and fourth belt plies 21A to 21D which are sequentially arranged from the carcass side toward the tread surface. For example, the first belt ply 21A has the belt cords arranged at an angle of about 50 to 70 degrees with respect to the tire equator CO, and the second, third, and fourth belt plies 21B to 21D. Is 10
Belt cords are arranged at an angle of about 30 degrees. The second and third belt plies 21B, 21C differ in the inclination direction of the cord with respect to the tire equator CO, thereby forming a strong truss structure and imparting necessary belt rigidity to maintain steering stability. At the same time, the dimensional change of the tire is suppressed. As the belt cord, a highly elastic one such as steel cord is used.

[0027]

EXAMPLES A heavy-duty tire having a tire size of 11R22.5 14PR and a configuration shown in FIGS. 1 and 2 was prototyped according to the specifications shown in Table 1, and the bead durability and production cost of each trial tire were measured. I compared each one.

-Bead durability: A test tire was used with a standard rim (22.5 x 8.25), a standard internal pressure (800 kpa),
Under a condition of a load (3 times the standard load = 9000 kg), the test piece was run at a speed of 20 km / h on a rotating drum tester, and the running times until bead damage occurred were compared. 6 finishes
00 hours, and the longer the running time, the better.・

Production cost: The sum of the cost of the process time required to form a green tire and the material cost is expressed as an index with Comparative Example 1 being 100. The larger the number, the higher the production cost.

[0030]

[Table 1]

As shown in Table 1, the tires of the examples can greatly improve the bead durability while suppressing an increase in production cost.

[0032]

Since the heavy-duty tire of the present invention is constructed as described above, it is possible to reduce the weight of the bead portion and to greatly improve the bead durability while suppressing the increase in production cost. You can

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a heavy duty tire of the present invention.

FIG. 2 is an enlarged sectional view showing a bead portion thereof.

FIGS. 3A and 3B are cross-sectional views illustrating a bead portion of a tire for explaining the problems of the conventional art.

[Explanation of symbols] 2 tread section 3 Side wall section 4 bead section 5 bead core 6 carcass 7 Belt layer 9 Carcass ply 9A carcass ply body 9B winding section 10 bead apex rubber 13 Bead apex rubber outer edge 15 proximity 17 contact area 19 Protective rubber layer

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B60C 15/00-15/06

Claims (2)

(57) [Claims] 1. A carcass ply body extending from a tread portion to a side wall portion to a bead core of a bead portion, and a winding portion which is folded back at the bead core and extends along a bead apex rubber extending radially outward from the bead core. Holders of example carcass, and a belt layer disposed outward of the carcass of the tread portion having a carcass ply, winding portion of the carcass, the carcass ply main body by exceeding the outer end of the bead apex rubber And a bead core having a polygonal shape, and including the contact region where the carcass ply contacts by folding back.
Is covered with a protective rubber layer containing short fibers having an average fiber diameter in the range of 1 to 100 μm , and the protective rubber layer is formed by covering the bead core.
It has a polygonal shape close to the bead core and the corners of the bead core
The thickness T of the protective rubber layer in the section is 0.5 to 2.0 m
m is a heavy-duty tire. 2. The bead core has a flat hexagonal sectional shape.
And the short fibers have an average fiber length of 10 to 6
000 μm, and the protective rubber layer is 100 weight of rubber base material.
Short fiber distribution in which 50 to 80 parts by weight of short fibers are blended per part
The heavy-duty tire according to claim 1, which is made of synthetic rubber .