JPH0749242B2 - Pneumatic radial tires for heavy loads - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in a bead portion of a heavy-duty pneumatic radial tire, for example, a tubeless radial tire having a carcass layer of a steel cord used in a heavy-duty vehicle.

(Prior Art) As a conventional pneumatic radial tire for heavy load, there is one as shown in FIG. 7, for example. In FIG.
Reference numeral 31 is a bead portion, and the bead portion 31 is arranged in a circumferential direction in a pair of planes orthogonal to a rotation axis of the tire (not shown in the drawing) (a line parallel to the rotation axis is indicated by A '). A pair of bead cores 32, a rubber stiffener 33 disposed on the radial outer surface of the bead core 32, and a rubber coating made of at least one layer in which the circumferences of the bead core 32 and the rubber stiffener 33 are folded back in the radial direction of the rotation axis from the tire inner side to the outer side. Steel cord carcass layer 34 and carcass layer 34
3-layer textile cord 36 to further reinforce the perimeter of the
a, 36b, 36c (nylon cord 1260d / 2, cord number 4
1.4 lines / 50 mm). The code angle of the three chafer layers 36 is approximately 60 degrees with respect to the radial direction, and the adjacent chafer layers 36 are arranged so as to intersect each other.

(Problems to be Solved by the Invention) In a tubeless pneumatic radial tire having such a bead structure, the reinforcing effect of the bead portion is insufficient, and in particular, it is worn and worn when mounted on a heavy-duty vehicle. When the tread portion (not shown) is rehabilitated (replaced) several times, the durability of the bead portion 31 is insufficient, and the end portion 34a of the carcass layer 34 extends in the direction of the rubber stiffener 33 and the chafer layer 36a, There is a problem that a failure 37 occurs that disconnects 36b and 36c in the outward direction. Further, if the number of chafer layers is increased to reinforce the bead portion 31, there is a problem that the thickness of the bead portion increases, heat generation in the bead portion increases, and durability performance deteriorates.

Therefore, in the present invention, a chafer layer that reinforces the bead portion is effectively arranged in response to the deformation of the bead portion, and a necessary and sufficient reinforcement effect can be obtained without increasing the number of layers of the chafer layer. By providing so as to obtain, there is no failure from the end 34a of the carcass layer 34, it is used under a heavy load, and a tubeless having sufficient durability of the bead portion that can be used even after the tread portion is rehabilitated several times. An object is to provide a pneumatic radial tire.

(Means for Solving Problems) A heavy-duty pneumatic radial tire according to the present invention includes a pair of bead cores arranged in a circumferential direction in a pair of planes orthogonal to a rotation axis of the tire, and the rotation axis of the rotation axis. In a pneumatic radial tire having a bead portion, which is arranged in the radial direction and at least one carcass layer in which the circumference of the bead core is folded back from the tire inner side to the outer side, is arranged around the carcass layer of the bead portion. At least three first to third chafer layers for reinforcing the bead portion are provided, and adjacent chafer layers have cords intersecting each other, and the first to third chafer layers are arranged in the radial direction of the rotation axis. The cord angles θ ₁ , θ ₂ , and θ ₃ formed with respect to each other are represented by the following equations 35 degrees ≤ θ ₁ ≤ 55 degrees, 35 degrees ≤ θ ₂ ≤ 55 degrees, and 70 degrees ≤ θ ₃ <90 degrees. Third Choi Radial chafer height h _1, h _2, h ₃ is a radial carcass end from the folded distal end of the carcass layer to the heel position of the bead portions from respective radiation outermost end of Fa layer to the heel position of the bead portion For the height H, , The chafer height h ₃ is the chafer height h ₁ ,
It is characterized by higher than any of h ₂ .

(Operation) First, the process by which the inventor has led to the above means will be described with reference to the drawings.

1 and 2 (a) and (b) are schematic views for explaining the relationship between the deformation and stress of the heavy-duty pneumatic radial tire under load, and FIG. 1 is a partial front view thereof. Second
1A is a sectional view taken along the line II-II of FIG. 1, and FIG. 2B is an enlarged sectional view of a bead portion for explaining the constitution of the present invention. In FIGS. 1 and 2, reference numeral 1 is a tubeless pneumatic radial tire (hereinafter simply referred to as a radial tire) having a steel cord carcass layer,
The radial tire 1 is a rotating body including a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4, and a carcass layer 5 arranged between the bead portions 4. The bead portion 4 has a bead cord 6 and a rubber stiffener 7 in the center thereof, and a carcass layer 5 is folded back radially from the inside of the tire to the outside of the tire, and a chafer layer 8 reinforces the periphery thereof. . The radial tire 1 is loaded with a load W in a direction (arrow) perpendicular to the rotation axis A via a rim 9 of a tubeless tire (two-dot chain line shows the shape of the tire when no load is applied). The radial tire 1 is filled with a predetermined air pressure P, and is pressed between the rim 9 and the floor surface 10 by the load W to be deformed.

When the radial tire 1 is rotating in the direction of arrow C, there are mainly the following two types of deformations that occur in the bead portion 4.

(1) Bending deformation B (indicated by arrow B in the drawing) in which the bead portion 4a immediately below the load falls outward in the radial direction.

(2) Circumferential direction L generated between the bead portions 4b and 4c of the step-in portion 1b and the kick-in portion 1c of the radial tire 1 between the portion fixed to the rim 9 and the deformed sidewall portion 3.
Shear deformation S (indicated by arrow L in the figure) (indicated by arrow S in the figure).

The deformation of these bead portions 4 is, like a tubeless tire, the flatness of the tire, that is, the ratio of the tire section height Th to the tire width Tw, and when Th / Tw is 0.9 or less, the shear deformation S in the circumferential direction is small. The ratio will increase.

Therefore, in order to increase the reinforcing effect of the bead portion 4 and improve the durability performance, the bending deformation B and the shear deformation S are reduced, and the amount of internal strain generated by these deformations is reduced. It is desirable to arrange the cords of the chafer layer 8 in a direction most suitable for suppressing these deformations.

In the bending deformation B, the bead portion 4a immediately below the load of the radial tire 1 protrudes outward in the tire width direction, and the bead portion 4a
Are extended in the circumferential direction L. Therefore, in order to suppress the bending deformation B, it is effective to increase the circumferential rigidity of the bead portion 4. Further, in the shear deformation S, in order to suppress the shear deformation S, it is effective to maximize the shear rigidity of the bead portion 4.

Next, when the angle of the cord of the chafer layer 8 with respect to the radial direction of the rotation axis A, that is, the cord angle θ changes,
How the circumferential rigidity and the shear rigidity of the bead portion change will be described.

FIGS. 3, 4, and 5 are diagrams showing the relationship between the change in the cord angle θ of the chafer layer 8 and the change in the circumferential rigidity and the shear rigidity of the bead portion, and the maximum rigidity value is 100. It is shown by the index. FIG. 3 shows the relationship between the cord angle θ and the tire radial and circumferential directions. In FIG. 4, when the cord angle θ is 70 degrees to 90 degrees, the circumferential rigidity of the bead portion is large, and the effect of suppressing the bending deformation B is large.
Further, in FIG. 5, when the cord angle θ is 35 degrees to 55 degrees, the shear rigidity of the bead portion is large, and the effect of suppressing the shear deformation S is large. That is, if the cord angle θ is less than 35 degrees or more than 55 degrees, the shear rigidity becomes small and the shear deformation S
The effect of suppressing is small. If the cord angle θ is less than 70 degrees, the rigidity in the circumferential direction becomes small, and the effect of suppressing the bending deformation B is small. When the code angle θ is 90 degrees, it is not technically realistic.

From the above, as shown in FIG. 2 (b), the chafer (in FIG. 2 (b), the bead portion 4 of FIG. 2 (a) is enlarged and shown upside down). A layer 8 is arranged around the carcass layer 5 of the bead portion 4 and is provided with at least three layers from the tire inner side to the outer side, that is, first to third chafer layers 8a, 8b, 8c having cords intersecting each other. In this case, first, in order to increase the shear rigidity, a two-layer chafer layer 8 is used, for example, the cord angle of the first chafer layer 8a is set to θ _1, and a second chafer layer 8 having adjacent and intersecting cords is used. When the code angle of the chafer layer 8b is θ ₂ , both code angles θ ₁ and θ ₂ are
35 to 55 degrees. Further, in order to increase the circumferential rigidity, the code angle θ ₃ of the other one layer, that is, the third chafer layer 8c is set to 70 degrees to 90 degrees.

In this way, by separating the functions of the chafer layers 8, the circumferential rigidity and the shear rigidity of the bead portion 4 can be effectively increased at the same time.

Next, how the position of the terminal 13 of the chafer layer 8 in the bead portion 4 affects the effect of rigidity and the tire performance will be described.

In FIG. 2B, the first to third chafer layers 8
a, 8b, the outermost radiation of each of 8c, that is, the terminal 13a,
The distance in the tire radial direction R from the position of 13b, 13c and the position of the end 5a of the carcass layer 5 to the heel position 4e of the bead portion (that is, the intersection of the bead base 4d and the rim flange 9a) is determined by the chafer height of each chafer. When h ₁ , h ₂ , h ₃ and the carcass edge height H are set, the terminals 13a and 13b of the first and second chafer layers 8a and 8b having high shear rigidity are the carcass layer 5 respectively.
If the terminal 5a of the carcass layer 5 is not covered with the terminal 5a and extends in the direction of the sidewall portion 3, the occurrence of the failure of the terminal 5a of the carcass layer 5 cannot be prevented. That is, if the ratios h ₁ / H and h ₂ / H of the chafer heights h ₁ and h 2 to the carcass edge height H are less than 1, the terminal 5a of the carcass layer 5 will fail. Also, if the terminals 13a13b extend too much in the direction of the sidewall portion 3, that is, if the chafer height is too high, the flexible region of the sidewall portion 3 becomes narrow, and a failure occurs near the terminals 13a, 13b having high shear rigidity. Occur. That is, it is preferable that the ratios h ₁ / H and h ₂ / H between the chafer heights h ₁ and h ₂ and the carcass edge height H do not exceed 2.0.

The third chafer layer 8c having a large circumferential rigidity (here, the case of one layer of the third chafer layer will be described, but even when two layers of the third and fourth chafer layers 8c, 8d are provided, The same applies to the following description) If the terminal 13c is lower than the terminals 13a and 13b having high shear rigidity, a failure is likely to occur near the terminals 13a and 13b, and the terminal 13c is preferably higher than the terminals 13a and 13b. That is, the chafer height h ₃ is higher than both the chafer heights h ₁ and h ₂ . Further, if the terminal 13c is too high, the end portion 13c comes too close to the central portion 3b of the sidewall portion 3 where the tire is largely deformed, and a failure is likely to occur near the terminal 13c. That is, it is desirable that the ratio h ₃ / H between the chafer height h ₃ and the carcass edge height H does not exceed 2.5.

As described above, the terminals 13 of at least three chafer layers 8 have higher shear rigidity, and the terminals 13a and 13b of the chafer layers 8a and 8b are located at a higher position than the terminals 5a of the carcass layer 5, so that the rigidity of the circumferential direction is high. The terminal 13c of the large chafer layer 8c is preferably provided at a position higher than the terminals 13a and 13b of the chafer layers 8a and 8b.

The height of the terminals 13 of these three-layer or four-layer chafer layers 8 for reinforcing the bead portion 4 is set in order to avoid stress concentration due to overlapping of the terminals 13 of each chafer layer 8.
It is desirable that the heights of the respective terminals 13a, 13b, 13c, 13d in the radial direction R have a difference of at least 5 mm or more. Further, when the chafer layer 8 is arranged in more than four layers, the bead portion 4 becomes too thick, which causes an increase in heat generation,
On the contrary, the durability performance decreases.

The above-mentioned means is derived from the above description, and the bead portion 4 of the heavy duty pneumatic radial tire according to the present invention has the cord angle of the three chafer layers 8 and the chafer height h. The bead portions 4 are effectively arranged, so that the bending deformation and the shear deformation S of the bead portion 4 are extremely small, and the internal strain is also small. Therefore, the durability of the bead portion is greatly improved.

(Example) Hereinafter, one example of a heavy duty pneumatic radial tire according to the present invention will be described with reference to the drawings.

FIG. 6 is a view showing an embodiment of a heavy duty pneumatic radial tire according to the present invention, and is an enlarged sectional view of a bead portion thereof. Except for the chafer layer in the bead portion, the pneumatic tire is the same as a normal pneumatic radial tire, and the description thereof is omitted except for the necessity. This example is a tubeless tire having a tire size of 11 / 70R22.5 and an aspect ratio of about 0.7.

First, the configuration will be described. In FIG. 6, reference numeral 4 denotes a bead portion, and the bead portion 4 is a circumference in a pair of planes orthogonal to the rotation axis of the tire (the line parallel to the rotation axis is shown by an arrow A'in the figure). Direction of the pair of bead cores 6 (only one of the pair is shown in the figure), the rubber stiffener 7 arranged radially outside the bead core 6 and the radial direction R of the rotary shaft (in the figure, Bead core 6 and rubber stiffener 7
And at least one carcass layer 5 in which the periphery of is folded back from the inside of the tire to the outside.

Reference numeral 8 denotes a chafer layer, and the chafer layer 8 is arranged around the carcass layer 5 of the bead portion 4 from the inside of the tire to the outside of the bead portion 4 to reinforce the bead portion 4. The chafer layer 8 has a nylon cord of 1260d / 2, and the number of drives is 41.4 / 50
mm, the strength of the coated rubber is elastic modulus at 100% elongation, 56 Kg / cm ²
It consists of The chafer layer 8 is composed of three layers, first to third.
The chafer layers 8a, 8b, and 8c are formed, and adjacent chafer layers have cords intersecting with each other.

Assuming that the angles formed by the radial direction R of the rotation axis of the tire and the cords of the first to third chafer layers 8a, 8b and 8c, that is, the cord angles are θ ₁ , θ ₂ and θ ₃ , respectively, the cord angle θ
₁ , θ ₂ and θ ₃ are represented by the following equations: 35 ° ≦ θ ₁ ≦ 55 °, 35 ° ≦ θ ₂ ≦ 55 ° 70 ° ≦ θ ₃ <90 °. Here, the code angle θ ₁ is the code angle of the innermost first chafer layer 8a, that is, the first chafer layer 8a arranged so as to be adjacent to the carcass layer 5, and the code angles θ ₂ and θ ₃ are These are the code angles of the second chafer layer 8b and the third chafer layer 8c that sequentially cover the outer side of the innermost first chafer layer 8a. Cord angle in this embodiment, when viewed from the tire outer, respectively cord angle theta ₁ is R50 °, the cord angle theta ₂ is L50 degrees,
The code angle θ ₃ is R78 degrees. Here, R indicates a right-upward code, and L indicates a left-upward code.

h is the chafer height, the chafer height h ₁ ,
h ₂ and h ₃ are radiation outermost ends of the first to third chafer layers 8a, 8b and 8c, that is, radial terminals 13a, 13b and 13
It is the radial distance from c to the heel position 4e of the bead portion 4. H is the carcass edge height, and the carcass edge height H
Is a radial distance from the folded tip (end 5a) of the carcass layer 5 to the heel position 4e of the bead portion 5. The following formulas , The chafer height h ₃ is the chafer height h ₁ ,
higher than any of h ₂ . In this embodiment, H is 38 mm and h ₁ is 53
mm, h ₂ is 63 mm h ₃ is 75 mm, h ₁ /H≈1.4, h ₂ /H≈1.7,
h ₃ /H≈2.0. The position of the terminal of each chafer layer 8 has a difference of 5 mm or more.
There is no big difference in rigidity between them.

Due to the arrangement of the three chafer layers 8 described above, the bending deformation B and the shearing deformation S of the bead portion 4 are significantly reduced, and the durability performance of the bead portion 4 is significantly improved.

Next, two types of test tires, a tire of the present invention (Example) and a comparative tire (Comparative Example), were manufactured, tested, and the effect of the present invention was confirmed.

The test tire has a tire size of 11 / 70R22.5 and is a tubeless pneumatic radial tire. The tire of the present invention used the above-mentioned example (FIG. 6), and the comparative tire used the conventional tire (FIG. 7). These test tires were identical except for the chafer layer and were made similarly. The following table shows the composition of the chafer layer of the test tire. The test tire was subjected to a normal bead portion durability performance test using a normal indoor drum tester, and the running distance until crack failure occurred in the bead portion was measured. The test results are shown in the following table as an index with the performance of the conventional tire as 100. The larger the index, the better.

As shown in the above table, the tire of the present invention has extremely improved durability of the bead portion as compared with the conventional tire.

(Effects of the Invention) As described above, according to the present invention, the shear angle is increased by increasing both the cord angle θ ₁ of the first chafer and the cord angle θ ₂ of the second chafer layer to 35 degrees to 55 degrees. In addition, since the code angle θ ₃ of the third chafer is set to 70 degrees to 90 to increase the rigidity in the circumferential direction, the function of each chafer layer is separated, so that the shear rigidity and the rigidity in the circumferential direction are increased. Can be increased at the same time, and the bead portion can be sufficiently reinforced. Further, since the heights h ₁ and h ₂ of the _first and second chafer layers are set higher than the carcass edge height H within an appropriate range, it is possible to prevent the occurrence of a failure at the end of the carcass layer. You can Further, since the height h ₃ of the third chafer layer having the largest code angle is made higher than the heights h ₁ and h _{2 of the first} and second chafer layers having high shear rigidity, the first and second chafer layers are made higher. It is possible to prevent a failure from occurring near the terminal of the fur layer, and to further enhance the reinforcement of the bead portion.

As a result, the durability of the bead part can be improved without increasing the number of chafer layers, and the bead part can be used under heavy load and used well even after rehabilitating the tread part several times. A pneumatic radial tire capable of being obtained can be obtained.

[Brief description of drawings]

FIGS. 1 and 2 (a) and (b) are schematic views for explaining the deformation and stress of the heavy radial pneumatic tire under load, and FIG. 1 is a partial front view and FIG. 1A is a sectional view taken along the line II-II of FIG. 1, and FIG. 2B is an enlarged sectional view of a bead portion for explaining the constitution of the present invention. 3, 4, and 5 are diagrams showing the relationship between the cord angle θ of the chafer layer and the circumferential rigidity and shear rigidity of the bead portion, and FIG. 3 is a diagram showing the cord angle θ. , FIG. 4 is a diagram showing a change in circumferential rigidity of the bead portion,
FIG. 5 is a diagram showing changes in the shear rigidity of the bead portion. FIG. 6 is an enlarged sectional view showing an embodiment of a bead portion of a heavy duty pneumatic radial tire according to the present invention. FIG. 7 is an enlarged sectional view of a bead portion of a conventional pneumatic radial tire. 1 ... tire, 4 ... bead part, 4e ... heel position, 5 ... carcass layer, 6 ... bead core, 8,8a, 8b, 8c ... chafer layer, θ, θ ₁ , θ ₂ , θ ₃ ... Cord angle, H ... Carcass edge height, A '... Line parallel to tire rotation axis, R ... Radial direction.

Claims (2)

[Claims] 1. A pair of bead cores arranged in a circumferential direction in a pair of planes orthogonal to the tire rotation axis, and arranged in the radial direction of the rotation axis, and the periphery of the bead core is folded back from the tire inner side to the outer side. At least one carcass layer,
In a pneumatic radial tire having a bead portion constituted by, at least three first to third chafer layers, which are arranged around the carcass layer of the bead portion and reinforce the bead portion, are provided, and adjacent chafers are provided. The fur layers have cords intersecting with each other, and the cord angles θ ₁ , θ ₂ , and θ ₃ formed by the radial direction of the rotation axis and the cords of the first to third chafer layers are as follows: 35 ° ≦ θ ₁ ≦ 55 degrees, 35 degrees ≤ θ ₂ ≤ 55 degrees, 70 degrees ≤ θ ₃ <90 degrees, and the radial direction from the outermost radial end of each of the first to third chafer layers to the heel position of the bead portion. The chafer heights h ₁ , h ₂ and h ₃ are respectively expressed by the following equations for the carcass edge height H in the radial direction from the folded tip of the carcass layer to the heel position of the bead part: , The chafer height h ₃ is the chafer height h ₁ ,
Pneumatic radial tires for heavy loads, characterized by higher than any of h ₂ . 2. The first to third chafer layers are first to third from the center of the bead portion toward the outer surface of the bead portion.
The pneumatic radial tire for heavy loads according to claim (1), wherein the chafer layers are arranged in this order.