JP2001328404A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a crack by strain caused in a buttress part 9. SOLUTION: In this pneumatic tire having a carcass 10 over a tread part 2, a shoulder part 3 and a sidewall part 4 and having a belt 8 on the outer peripheral side of the carcass 10 in the tread part 2, when a radius of curvature of section of a carcass 10A in the shoulder part 3 before filling air is R1 and a radius of curvature of section of the carcass 10A after filling air is R2, the relationship between both is set to R1<=R2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire suitable for heavy loads such as trucks and buses.

[0002]

2. Description of the Related Art A pneumatic tire, particularly a pneumatic tire having a radial structure, is formed in a toroidal shape by a tread portion, a shoulder portion, a sidewall portion and a bead portion, and a radially structured carcass extends from right and left bead portions to a tread portion. The belt is arranged and buried in the tread portion on the outer peripheral side of the carcass to control the radial expansion of the carcass. FIG. 5 shows a change in cross-sectional shape of the conventional tire having such a structure before and after air filling in the shoulder portion 100.

In this case, the cross-sectional radius of curvature R1 'of the carcass 101 before air filling shown by a solid line gradually becomes smaller as shown by a two-dot chain line (R2') as the air is filled, and the carcass 101 is directed outward of the tire. The shape is changed so as to shift.

[0004]

When the carcass 101 in the shoulder portion 100 undergoes the above-mentioned shape change due to air filling, a distortion in the tensile direction occurs in the buttress portion 102. On the other hand, when the tire runs on the road surface,
The buttress portion 102 is distorted in the compression direction, and as a result, the compression / tensile strain is repeated.
2 to cause cracks and the like. The occurrence of such damage to the buttress portion increases with the passage of time even when an anti-aging agent is added. Particularly, in trucks, buses, and the like, the tire internal pressure is high, and the load due to running and the like also increases. The problem became conspicuous, and the durability was significantly impaired.

[0005] In view of the above problems, an object of the present invention is to provide a pneumatic tire that suitably prevents damage due to distortion of a buttress portion and improves durability.

[0006]

The present invention employs the following technical means to achieve the above object. That is, the present invention provides a pneumatic tire in which a carcass is disposed over a tread portion, a shoulder portion, and a sidewall portion, and a belt is provided on an outer peripheral side of the carcass in the tread portion. When the sectional radius of curvature of the carcass is R1 and the sectional radius of curvature of the carcass after air filling is R2, the relationship between the two is R
It is characterized in that 1 ≦ R2 is set.

In this case, when air is filled in the tire,
A change in the radius of curvature of the cross section of the carcass causes a compressive strain in the buttress portion. On the other hand, when a load is applied to the tire due to running or the like, a compressive strain is also generated in the buttress portion. Therefore, the difference in strain before and after the load is applied is smaller than in the conventional case, and cracks can be prevented from being generated and durability can be improved. Further, it is preferable that the buttress surface of the shoulder portion before filling with air is formed into a flat surface or a protruding surface. Thereby, it is possible to increase the rigidity of the buttress portion against the compressive strain caused by the change in the shape of the carcass as described above, or the compressive strain generated by a load due to running or the like, and it is possible to prevent cracks and the like. Become.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows a cross section of the right half of the pneumatic tire 1 according to the present invention. The pneumatic tire 1 has a tread portion 2 and shoulder portions 3 provided on both left and right sides of the tread portion 2. And a side wall portion 4 connected radially inward from the shoulder portion 3, and a bead portion 5 connected to the radial inner end of the side wall portion 4 to form a toroidal cross section. , Bead part 5
Is embedded with an annular bead core 6.

From the bead portion 5 to the sidewall portion 4,
A carcass 10 is disposed inside the shoulder portion 3 and the tread portion 2 so as to cover the carcass 10.
The left and right end portions are connected to each other by rewinding the left and right bead cores 6. Carcass 1
0, an inner liner 7 is provided, and a belt 8 is provided inside the tread portion 2 on the outer peripheral side of the carcass 10. The carcass 10 includes one or two or more carcass plies formed of cords of nylon, polyester, steel, or the like forming a radial array, and the belt 8 tilts a belt cord of steel or the like with respect to the tire equator. It is composed of two or more belt plies arranged side by side.

In FIG. 1, a carcass 10A in the shoulder portion 3 (particularly, a portion outside the belt 8 in the width direction).
Before filling with air, becomes R1 as shown by a solid line, and after filling with air at a normal internal pressure, becomes R2 as shown by a two-dot chain line, and the relationship between the two is R1.
The carcass shape is set so that ≦ R2. That is, the radius of curvature R1 of the carcass 10A before air filling.
However, it is set to be smaller than the conventional tire, and the portion 10A is formed so as to bulge outside the tire as compared with the conventional tire.

The carcass 1 in the shoulder 3
OA changes its shape so as to shift to the inside of the tire relative to the carcass 10 in the tread portion 2 and the sidewall portion 4 by filling with air. Due to such a shape change, a compressive strain occurs in the buttress portion 9 of the shoulder portion 3 after air filling. FIG. 2 shows a change in distortion in the buttress portion 9. Here, the graph shown by the dashed line is the conventional example of FIG. 5, and in this conventional example, if the strain before air filling is set to 0,
The filling of the air causes tensile strain in the buttress portion 102, and further, when a load is applied by running or the like, a large compressive strain is generated in the buttress portion 102.

That is, in the conventional example, tension and compression strains are repeatedly generated in the buttress portion 102 within the range indicated by A. On the other hand, in the present invention, when the strain before air filling is set to 0, compressive strain is generated in the buttress portion 9 by filling with air, and further, when a load is applied due to running or the like, a larger compressive strain than before the load is applied. Occurs. Therefore, the buttress portion 9 is repeatedly subjected to compressive strain in a range B smaller than the range A in the conventional example, so that fatigue in the buttress portion 9 can be reduced, damage such as cracks can be prevented, and durability can be improved.

FIG. 3 shows a cross section of the vulcanizing mold 20 in the shoulder portion 3. As is apparent from the figure, the mold surface 21 corresponding to the buttress portion 9 of the tire 1 is
The outer surface of the buttress portion 9 before filling with air is formed into a straight line or an outwardly curved convex shape as shown in FIG. Is done. That is, the rigidity of the buttress portion 9 is increased against the compressive strain caused by filling the air and the compressive strain caused by the load due to running or the like, thereby also preventing the occurrence of cracks and the like.

The present invention is not limited to the above-described embodiment, and can be appropriately designed and modified. For example, although a tubeless type pneumatic tire has been described above, a tube tire may be used. In addition, the present invention is not limited to heavy-duty tires such as buses and trucks, and can also be used for passenger tires.

[0015]

As described above, according to the present invention, damage such as cracks in the buttress portion can be prevented, and the durability can be improved.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a change in distortion of a buttress portion.

FIG. 3 is a cross-sectional view showing a mold shape in a shoulder portion.

FIG. 4 is a sectional view showing a right half of the pneumatic tire.

FIG. 5 is a sectional view showing a shoulder portion of a pneumatic tire according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Shoulder part 4 Side wall part 5 Bead part 8 Belt 10 Carcass

Claims (2)

[Claims] 1. A pneumatic tire in which a carcass is disposed over a tread portion, a shoulder portion, and a sidewall portion and a belt is provided on an outer peripheral side of the carcass in the tread portion, wherein the carcass in the shoulder portion before air filling is provided. The relationship between the two is set as R1 ≦ R2, where R1 is the sectional curvature radius of the carcass and R2 is the sectional curvature radius of the carcass after air filling. 2. The pneumatic tire according to claim 1, wherein a buttress surface of the shoulder portion is formed into a flat surface or a protruding surface before air filling.