JPH0672110A - Pneumatic radial tire - Google Patents

Abstract

(57) [Summary] [Purpose] To improve durability by reducing the strain generated in the bead portion during tire running. [Structure] Regarding the clincher thickness F, which is the thickness of the clincher rubber that forms the outer wall surface 11 of the bead portion 4, and the bead portion thickness T, the middle point M of the outer wall surface that is equal to the flange height G of the rim J, and the flange height. The inner point I is 0.8 times the height G and the outer point O is 1.2 times the flange height G.

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 which can improve the durability of a bead portion.

[0002]

2. Description of the Related Art Pneumatic tires have been required to have a high degree of durability even with tires because the traveling distance of vehicles has increased with the maintenance of road networks and small delivery networks.
Especially for small trucks and commercial vehicles with 1 to 3 ton capacity, there is a strong demand for high speed running, and even tires with high performance have high durability (overloading) to cope with high speed. It was also requested.

[0003]

When a load is applied to the tire, as shown in FIG. 3, a bending action force which causes a compressive stress on the outer wall side b and a tensile stress on the inner wall side c at the bead portion a, as shown in FIG. When the tire travels, the acting force is repeatedly applied to the bead portion, so that the bead portion a is cracked and the durability of the tire is impaired. The crack of the part a occurs early.

In order to prevent the bead cracking, it is conceivable to increase the thickness of the bead portion as a whole, but by increasing the thickness of the bead portion as a whole, the weight of the bead portion increases and the cost and fuel consumption increase. In addition, there are drawbacks such as difficulty in assembling the rim.

As a result of investigating the distribution of the force acting on the bead portion in order to solve the above-mentioned problems, the inventor has found that the distribution of the rubber thickness of the clincher rubber forming the outer wall of the bead portion, and the rubber thickness and the bead portion. It was found that the strain locally generated in the bead portion can be significantly reduced and the durability can be improved by controlling the ratio with the thickness of the bead portion at a plurality of positions.

According to the present invention, the bead thickness at the bead portion is
It is an object of the present invention to provide a pneumatic radial tire in which the strain generated in the bead portion during tire running can be significantly reduced and the durability of the bead portion can be improved by controlling the thickness of each clincher rubber.

[0007]

DISCLOSURE OF THE INVENTION The present invention is directed to a carcass having a carcass cord of radial arrangement and folding back around a bead core of a bead part from a tread part to a sidewall part, and inside the tread part and outside the carcass. Of the clincher rubber that is in contact with the tire axially outer side of the folded portion of the carcass and forms the outer wall surface of the bead portion, in a state where the rim is assembled to a regular rim and a regular internal pressure is applied. The clincher thickness F, which is the axial thickness of the tire, and the bead base thickness T, which is the shortest length in the direction that extends from the outer wall surface to the inner wall surface facing the tire inner cavity and intersects the inner wall surface at a right angle, regarding the bead base. The creator at the midpoint M of the outer wall surface whose distance from the line in the radial direction of the tire is equal to the flange height G of the regular rim. Is Fm and F, the bead thickness T Tm,
The clincher thickness F at the inner point I of the outer wall surface separating 0.8 times the flange height G is Fi, the bead thickness T is Ti, and the outer wall surface separating 1.2 times the flange height G is outside. When the clincher thickness F at the point O is Fo and the bead thickness T is To, the pneumatic radial tire is characterized by satisfying the following expressions together.

| Ti-Tm | ≤1.0 mm | Tm-To | ≤1.0 mm 0.2≤Fi / Ti≤0.3 0.3≤Fm / Tm≤0.4 0.3≤Fo / To ≤0.4

The clincher rubber preferably has a JISA hardness of 60 degrees or more and 75 degrees or less.

[0010]

The clincher thickness F of the clincher rubber forming the outer wall surface of the bead portion and the bead thickness T are set to the midpoint M equal to the flange height G of the rim and the flange height G of 0.
The inner point I is 8 times and the outer point O is 1.2 times the flange height G. In this way, by controlling the bead thickness T and the clincher thickness F at three points arranged in the tire radial direction, the cross-sectional shape of the bead portion and the clincher rubber can be set to the most preferable shapes. I can.

Absolute value of dimensional difference between bead thicknesses Ti, Tm and To passing through each of the inner point I, the intermediate point M and the outer point O |
When each value of Ti-Tm | and | Tm-To | exceeds 1.0 mm, the bead thickness T changes abruptly, strain is concentrated at the inflection point, and breakage easily occurs, and durability is deteriorated.

Fi / Ti, which is the ratio of the clincher thicknesses Fi, Fm, Fo to the bead thicknesses Ti, Tm, To at the inner point I, the intermediate point M, and the outer point O, is 0.2.
When the ratio is less than Fm / Tm or Fo / To is less than 0.3, the strain between the clincher rubber of the bead portion and the folded portion of the carcass becomes large, and damage is likely to occur. On the other hand, Fi / Ti is 0.
When Fm / Tm or Fo / To exceeds 0.4 and exceeds 0.4, the movement of the bead portion becomes large during traveling, and damage occurs near the bottom surface of the bead, resulting in poor durability.

As described above, according to the present invention, as described above, the bead thickness T and the clincher thickness F are mutually and respectively at the inner point I, the intermediate point M and the outer point O of the bead portion. By relating and regulating,
It is possible to prevent damage to the bead portion and improve durability without significantly changing the volume and cross-sectional shape of the bead portion and without significantly increasing the tire weight.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2, a pneumatic radial tire 1 includes a tread portion 2, a sidewall portion 3 extending from both ends thereof inward in a tire radial direction, and the sidewall portion 3
And a bead portion 4 connected to the inner end in the tire radial direction. Further, the pneumatic radial tire 1 is folded back from the tread portion 2 to the main body portion 6a extending from the sidewall portion 3 to the bead portion 4 around the bead core 5 of the bead portion 4 from the inner side to the outer side in the tire axial direction. The carcass 6 provided with the portion 6b and the inside of the tread portion 2 and the carcass 6
A bead apex 8 in the shape of an elongated triangle extending outwardly in the tire radial direction of the bead core 5 and between the main body portion 6a of the carcass 6 and the winding portion 6b. Start up.

Further, on the outside of the folded-back portion 6b of the carcass 6, the outer wall surface 1 of the bead portion 4 is adjacent to the folded-back portion and is adjacent to the folded-back portion.
Clincher rubber 9 forming 1 is arranged.

The carcass 6 is 60 with respect to the tire equator C.
One or more, two in this example, comprising carcass cords of radial or semi-radial arrangement tilted at an angle of ~ 90 °.
It is composed of a single carcass ply, and is formed by a first carcass ply 6A that folds the bead core 5 inside and a second carcass ply 6B that folds outside the first carcass ply. In this embodiment, the upper end of the folded portion of the first carcass ply 6A is located at the intermediate height of the outward surface 8a of the bead apex 8, while the upper end of the folded portion of the second carcass ply 6B is the upper portion of the bead apex. It extends beyond the outer edge of S8. As the carcass cord, cords of organic fibers such as nylon, rayon, polyester and aromatic polyamide fibers are used.

The belt layer 7 is composed of a plurality of belt plies 7A and 7B, in this embodiment, two belt plies 7A and 7B.
Similar to the carcass ply, A and 7B are belt cords formed of organic fibers such as nylon, rayon, polyester, aromatic polyamide fibers, and inorganic fibers such as steel cords at 10 to 70 ° with respect to the tire equator C. Belt cords that are angled and adjacent to each other are arranged so as to intersect with each other. The width BW of the belt layer 7 in the tire axial direction is preferably set within the range of 0.65 to 0.75 times the maximum tire width TW.

Further, in this embodiment, a band layer 15 for covering the belt layer 7 is provided on the outer side in the radial direction of the belt layer 7. The band layer 15 is formed by spirally winding a long band-shaped band ply in which a band cord made of an organic fiber is covered with a rubber, and the band layer 15 prevents lifting of the belt layer 7 and a tread. The durability of part 2 is improved.

The bead apex 8 is made of a hard rubber having a JISA hardness of 65 to 85 degrees, and the clincher rubber 9 has a rubber hardness lower than that of the bead apex 8 and a JISA hardness of 60 degrees or more. And the range is set to 75 degrees or less.

Further, in this embodiment, the hoisting portion 6 of the carcass 6 is
A chafer 16 extending from the outward surface of b and extending along the bead bottom surface 4a is provided.

In the bead portion 4, the clincher rubber 9 has a clincher thickness F which is the axial thickness of the clincher rubber 9 and an inner wall surface 13 extending from the outer wall surface 11 toward the tire inner cavity 12 and intersects the inner wall surface 13 at a right angle. The bead portion 4 of the tire 1 with respect to the bead portion thickness T which is the shortest length in the direction
Is assembled to the regular rim J into which the tire 1 is fitted and the regular internal pressure is applied to the inner cavity 12, the outer wall surface 1
The outer wall surface 1 is located at three points that are aligned inward and outward in the radial direction of 1.
It is regulated at three points that are lined up inside and outside in the radial direction of 1.

The bead thickness T and the clincher thickness F
The three points serving as the measurement base points of the rim flange 21 of the rim flange 21 of the rim J have a distance in the tire radial direction from the bead base line L formed by the tire axial direction line passing through the intersection of the bead bottom surface 4a and the outer wall surface 11. Midpoint M equal to height G,
It is formed by an inner point I that separates 0.8 times the fringing height G and an outer point O that separates 1.2 times the flange height G.

Here, the clincher thickness F at the inner point I is Fi and the bead thickness T is Ti, the clincher thickness F at the middle point M is Fm, the bead thickness T is Tm, and the clincher thickness at the outer point O. When F is Fo and bead thickness T is To, the clincher thickness F and the bead thickness T at each of the points I, M, and O are dimensioned so as to satisfy the following expressions.

| Ti-Tm | ≤1.0 mm | Tm-To | ≤1.0 mm 0.2≤Fi / Ti≤0.3 0.3≤Fm / Tm≤0.4 0.3≤Fo / To ≤0.4

By satisfying the above equation, the cross-sectional shape of the clincher rubber 9 and the cross-sectional shape of the bead portion 4 are naturally regulated, strain can be prevented from occurring during tire running, cracking of the bead portion can be suppressed, and tire durability can be improved. It can improve the sex.

[0026]

SPECIFIC EXAMPLE A tire having a tire size of 235 / 85R16 and having the structure shown in FIG. 1 was prototyped according to the specifications shown in Table 1 and its performance was tested. In addition, the tires according to the conventional configuration (Comparative Example 1) and the tires other than the configuration of the present application (Comparative Examples 2 to 7) were also tested to compare their performances.

The bead durability was measured as follows. 1.6
Using a m-diameter indoor drum tester, a nominal maximum internal pressure and a nominal maximum load of 250% were applied to each of the sample tires at room temperature of 3
While traveling at a speed of 25 km / H under 5 ° C ± 5 ° C, the traveling distance until damage to the bead portion of each tire was measured, and displayed as an index with Comparative Example 1 being 100.
The larger the value, the longer the running distance until the bead portion is damaged, and the better, and 140 or more is the acceptable value. The test results are shown in Table 1-a and Table 1-b.

[0028]

[Table 1-a]

[0029]

[Table 1-b]

As a result of the test, it was confirmed that the bead durability of the example was significantly improved as compared with the comparative example.

[0031]

As described above, in the pneumatic radial tire of the present invention, the bead thickness and the clincher thickness are regulated at three points on the outer wall surface of the bead portion, so that the volume and cross-sectional shape of the bead portion are significantly changed. Without this, the strain generated in the bead portion during tire running can be significantly reduced, and the durability of the bead portion can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

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

FIG. 3 is a sectional view schematically showing the operation.

[Explanation of symbols]

 2 tread part 3 sidewall part 4 bead part 5 bead core 6 carcass 6b folded part 7 belt layer 9 clincher rubber 11 outer wall surface 12 tire inner cavity 13 inner wall surface F clincher thickness G flange height I inner point J regular rim L bead Baseline M Middle point O Outer point T Bead thickness

Claims (2)

[Claims] 1. A carcass having a carcass cord of radial arrangement and folding back around a bead core of a bead part from a tread part to a sidewall part, and a belt layer arranged inside the tread part and outside the carcass. A clincher that is the axial thickness of the clincher rubber that is in contact with the tire axially outer side of the folded portion of the carcass and that forms the outer wall surface of the bead portion in a state in which the rim is assembled to a regular rim and a regular internal pressure is applied. With respect to the thickness F and the bead portion thickness T that is the shortest length in the direction from the outer wall surface to the inner wall surface facing the tire inner cavity and intersects the inner wall surface at a right angle, the distance in the tire radial direction from the bead base line Is equal to the flange height G of the regular rim, and the creator thickness F at the midpoint M of the outer wall is F
m, the bead thickness T is Tm, and the flange height G is 0.8.
The clincher thickness F at the inner point I of the outer wall surface that divides the double is Fi, the bead thickness T is Ti, and the clincher thickness F at the outer point O of the outer wall that separates 1.2 times the flange height G is A pneumatic radial tire characterized by satisfying the following expressions together, where Fo and the bead thickness T are To. | Ti-Tm | ≦ 1.0 mm | Tm-To | ≦ 1.0 mm 0.2 ≦ Fi / Ti ≦ 0.3 0.3 ≦ Fm / Tm ≦ 0.4 0.3 ≦ Fo / To ≦ 0. Four 2. The clincher rubber has a rubber hardness of JI.
The pneumatic radial tire according to claim 1, wherein the SA hardness is 60 degrees or more and 75 degrees or less.