JP2004017692A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the bead section of a heavy load pneumatic tire used for heavy load vehicles such as trucks and buses. <P>SOLUTION: This tire is provided with a carcass 6 wherein a folding section 6b folded outside from the inside of the axial direction of the tire around a bead core 5 in the body section extending from a tread section 2 to the bead section 4 through a side wall section 3 integrally, and a belt layer 7. The radius R1 of curvature of a carcass ply at a place of height 0.8 times the carcass height Hc separated from a bead base line 0.8 times the distance from a bead base line BL to the place at the most outside in the tire radius direction of the carcass 6 with the tire assembled temporarily to a normal rim J and charged with a pressure of 50kPa, and the radius R2 of curvature of the carcass ply at a place of a height 0.25 times the distance 0.25 times the carcass height Hc from a bead base line have their respective centers inside the tire and the ratio (R1/R2) of the radius of curvature is made to 0.75 yo 1.25. <P>COPYRIGHT: (C)2004,JPO

Description

【００３８】
テストの結果、実施例のものは、ビード部の耐久性を向上していることが確認できた。
【００３９】
【発明の効果】
以上説明したように、本発明の空気入りタイヤは、仮組み状態において、カーカス高さＨｃの０．８倍高さ位置でのカーカスプライの曲率半径Ｒ１と、カーカス高さＨｃの０．２５倍高さ位置でのカーカスプライの曲率半径Ｒ２とは、タイヤ内側にそれぞれ中心を有し、かつ前記曲率半径の比（Ｒ１／Ｒ２）を０．７５〜１．２５と実質的に同一としたことにより、正規内圧充填時においてカーカスプライの曲率変化を最小限とし、タイヤ外表面とタイヤ内部とに発生する歪を小さくする。これにより、ビード部の耐久性を向上しうる。
【図面の簡単な説明】
【図１】本発明の実施形態を示す仮組み状態のタイヤ子午線断面図である。
【図２】本発明の実施形態を示す正規内圧状態のタイヤ子午線断面図である。
【図３】図１のＡ−Ａ’断面図である。
【図４】図１のビード部を拡大して示す拡大断面図である。
【図５】本発明の他の実施形態を示す正規内圧状態のビード部の断面図である。
【図６】（Ａ）、（Ｂ）は、ビード部の部分断面図である。
【図７】比較例タイヤのビード部の拡大断面図である。
【図８】比較例タイヤのビード部の拡大断面図である。
【図９】比較例タイヤのビード部の拡大断面図である。
【符号の説明】
１　空気入りタイヤ
２　トレッド部
３　サイドウォール部
４　ビード部
５　ビードコア
６　カーカス
６Ａ　カーカスプライ
６ａ　カーカスプライの本体部
６ｂ　カーカスプライの折返し部
７　ベルト層
Ｈｃ　カーカス高さ
Ｐ１　０．８倍高さ位置
Ｐ２　０．２５倍高さ位置
Ｒ１　仮組み状態における０．８倍高さ位置でのカーカスプライの曲率半径
Ｒ２　仮組み状態における０．２５倍高さ位置でのカーカスプライの曲率半径[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pneumatic tire suitable for heavy-duty vehicles that can improve the durability of a bead portion.
[0002]
Problems to be solved by the prior art and the invention
Pneumatic tires for heavy loads used for heavy load vehicles such as trucks and buses are used under severe conditions such as high internal pressure and high load. For this reason, it is an important subject to improve the durability, particularly the durability of the bead portion where damage is likely to occur.
[0003]
For example, in Japanese Patent No. 2816143, a wedge rubber having a convex lens-shaped cross-sectional shape disposed on the inner side of the carcass is provided near a position corresponding to the height of the ply winding end measured from the rim diameter line on the carcass pass line. It has been proposed to increase the durability of the bead portion. In this proposal, by interposing the wedge rubber, an attempt is made to generate a compressive stress in the rubber near the ply winding end to reduce tensile strain at the outer end of the winding portion.
[0004]
Japanese Patent Application Laid-Open No. 2001-80316 proposes that the folded portion of the carcass ply be further folded along the outer surface of the bead core in the tire radial direction. In this proposal, it is expected that the input of compression and tension to the end of the folded portion of the carcass ply is reduced to prevent damage at the end.
[0005]
As a result of intensive studies, the inventors have found that it is effective to reduce the strain generated on the outer surface of the tire and the inside of the tire as one means for improving the durability of the bead portion. For this purpose, it has been found that it is effective to make the radius of curvature at each position of the bead portion and the buttress portion of the carcass ply at the time of filling the internal pressure of 50 kPa substantially effective, and completed the present invention. It led to.
[0006]
As described above, an object of the present invention is to provide a pneumatic tire that can improve the durability of a bead portion.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 of the present invention is characterized in that a body portion extending from the tread portion to the bead core of the bead portion via the sidewall portion is integrally provided with a folded portion which is folded around the bead core from the inside in the tire axial direction to the outside. Pneumatic tire provided with a carcass and a belt layer disposed radially outward of the carcass in the tire radial direction and inside the tread portion, in a rim-assembled state with a regular rim and filled with 50 kPa in a temporary unloaded state. , The distance of 0.8 times the carcass height Hc from the bead base line BL to the outermost position in the tire radial direction of the carcass is set at 0.8 times the height of the carcass ply separated from the bead base line. The radius of curvature R1 and the car at a height of 0.25 times that is separated from the bead base line by a distance of 0.25 times the carcass height Hc. The radius of curvature R2 of the splice, have respective centers inside the tire, and the ratio of the radius of curvature (R1 / R2) is characterized by a 0.75 to 1.25.
[0008]
In the invention described in claim 2, the folded portion has a proximity portion where the distance between the carcass cords between the folded portion and the main body portion is minimized, in the tire radial direction inside of the outer end of the folded portion. 2. The pneumatic tire according to claim 1, wherein the distance between the carcass cords gradually increases from the proximity portion to the outer end of the folded portion. 3.
[0009]
According to a third aspect of the present invention, the bead portion is provided with a cord reinforcing layer extending along the turning portion in the tire axial direction outside of the turning portion, and an outer end of the cord reinforcing layer in the tire radial direction. 3. The pneumatic tire according to claim 1, wherein the tire is located at least 4 mm inward in the tire radial direction from an outer end of the folded portion.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIGS. 1 and 2 are cross-sectional views of a tubeless heavy duty radial tire 1 (hereinafter sometimes simply referred to as “tire 1”) used as a pneumatic tire for trucks, buses, and the like. FIG. 1 shows the tire 1 mounted on a regular rim J (15 ° taper deep bottom rim) and a non-loaded temporary assembly filled with 50 kPa. FIG. 2 shows the tire 1 mounted on the regular rim J and regular internal pressure. Respectively show the no-load normal internal pressure state filled with.
[0011]
In the present specification, the "regular rim" is a rim defined for each tire in a standard system including a standard on which a tire is based. For example, a standard rim for JATMA, and a "Design Rim" for TRA. ”Or“ Measuring Rim ”for ETRTO. The "normal internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. For JATMA, the maximum air pressure is used. For TRA, the table "TIRE LOAD LIMITS" is used. The maximum value described in AT VARIOUS COLD INFLATION PRESSURES ”is“ INFLATION PRESSURE ”for ETRTO, but is 180 kPa when the tire is for a passenger car.
[0012]
In the figure, a tire 1 is located at a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and an inner end of each sidewall portion 3, and is seated on the regular rim J. And a bead part 4. Further, the tire 1 has a body portion 6a extending from the tread portion 2 to the bead core 5 of the bead portion 4 through the side wall portion 3 and integrally provided with a folded portion 6b which is folded back from the inside in the tire axial direction to the outside by the bead core 5. The carcass 6 includes at least one carcass ply 6A.
[0013]
The carcass ply 6A, as shown in FIG. 3, which is a cross section taken along the line AA 'in FIG. 2, is made of a ply in which a cord array in which carcass cords 6c are arranged is covered with a topping rubber 6g. The carcass cord 6c is arranged at an angle of, for example, 70 to 90 °, more preferably 80 to 90 ° with respect to the tire equator C. In this example, a steel cord is employed as the carcass cord 6c, but an organic fiber cord such as nylon, rayon, polyester, or aromatic polyamide can be used as necessary and according to the category of the tire. Note that the carcass 6 of the present embodiment is formed of one carcass ply 6A in which a steel cord is inclined at an angle of about 90 ° with respect to the tire equator C.
[0014]
A belt layer 7 is disposed radially outside the carcass 6 and inside the tread portion 2. In this example, the belt layer 7 includes an innermost belt ply 7A in which a steel cord is inclined at an angle of, for example, about 55 ± 10 ° with respect to the tire equator C, and a steel cord whose tire cord is 30 ° or less with respect to the tire equator C. For example, a four-layer structure in which belt plies 7B, 7C, and 7D arranged at a small angle and arranged at one or more locations where the belt cords cross each other between the plies is illustrated. The belt layer 7 can be made of another cord material such as rayon, nylon, aromatic polyamide, and nylon, if necessary.
[0015]
In the bead portion 4, a bead apex 8 is provided between the main body portion 6a and the folded portion 6b. As shown in FIG. 4 in an enlarged manner, the bead apex 8 has an inner surface 8i in the tire axial direction formed in an arc shape having a center on the inner side in the tire axial direction along the main body portion 6a in the present example. The outer surface 8o in the axial direction is formed in an arc shape having a center on the outer side in the tire axial direction, and formed in a substantially drop-shaped cross section. The bead apex 8 is desirably formed of rubber having a JISA hardness of, for example, 60 to 99 °, and more preferably 70 to 95 °, so that the bending rigidity of the bead portion 4 can be sufficiently ensured.
[0016]
In the normal internal pressure state, the height ha of the bead apex 8 from the bead base line BL is, for example, 0.07 to 0.35 times, more preferably 0.07 to 0.20 times, and more preferably the carcass height Hc. Is preferably 0.13 to 0.17 times. The carcass height Hc is a height from the bead base line BL to the outermost position of the carcass 6 in the tire radial direction. If the height ha is less than 0.07 times the carcass height Hc, the tire tends to be difficult to manufacture. Conversely, if it exceeds 0.35 times, the effect of improving the bead durability is reduced and the tire weight is reduced. Increase as needed.
[0017]
In addition, as shown in FIG. 4, the folded portion 6b of the carcass ply 6A extends beyond the outer end 8t of the bead apex 8 outward in the tire radial direction. In this example, the outer end 6t of the folded portion 6b is radially inward from the maximum width point M (shown in FIG. 1) forming the tire maximum width position, and has a height h1 with a relatively small amount of distortion under load. This is shown. The height h1 from the bead base line BL is set to about 0.25 to 0.50 times, more preferably about 0.35 to 0.45 times the carcass height Hc. If the height h1 is less than 0.25 times the carcass height Hc, the shear stress generated between the main body portion 6a and the folded portion 6b cannot be sufficiently reduced, causing a decrease in bead durability. If the ratio exceeds 0.50 times, the bending stiffness of the bead portion 4 is excessively increased, and the ride comfort is likely to be deteriorated.
[0018]
In the tentatively assembled state shown in FIG. 1, the tire 1 has a distance of 0.8 times the carcass height Hc from the bead base line BL to the outermost position of the carcass 6 in the tire radial direction. The radius of curvature R1 of the carcass ply body portion 6a at the 0.8-fold height position P1 separated from the tire radially outward from BL and the distance of 0.25 times the carcass height Hc in the tire radial direction from the bead base line BL The radius of curvature R2 of the carcass ply body portion 6a at the 0.25 times height position P2 separated from the outside has the center O1 and O2 inside the tire, respectively, and the ratio of the curvature radii (R1 / R2) is It is set to 0.75 to 1.25. The curvature radii R1 and R2 are specified by the center line of the thickness of the main body 6a of the carcass ply 6A.
[0019]
The pneumatic tire 1 changes to a curvature at which the main body 6a of the carcass ply 6A is most stable by filling with the normal internal pressure. Specifically, the main body 6a in the section from the 0.8-fold height position P1 to the 0.25-fold height position P2 changes to approach a substantially constant curvature due to the filling of the normal internal pressure. At this time, a surface strain is generated outside the tire, and a pulling force is generated inside the tire to pull the folded portion 6b of the carcass ply 6A toward the main body 6a, and an internal strain is generated based on this force.
[0020]
However, in the tentatively assembled state, the radii of curvature R1, R2 at the 0.8-fold height position P1 and the 0.25-fold height position P2 have centers O1, O2 inside the tire, respectively, and the ratio of the radii of curvature. By setting (R1 / R2) to 0.75 to 1.25 in advance, the behavior of the curvature change of the carcass ply 6A due to the filling of the internal pressure can be minimized. As a result, the strain on the outer surface of the tire can be reduced, and the strain inside the bead portion 4 can be reduced with the decrease in the pull-out force, so that the durability of the bead portion can be improved. Particularly preferably, the ratio of the radii of curvature (R1 / R2) is desirably 0.9 to 1.1.
[0021]
In the temporarily assembled state, it is necessary to univocally determine the tire shape without applying the tension due to the internal pressure to the carcass cord 6c as much as possible. For this purpose, an internal pressure of 50 kPa is charged. If the internal pressure is less than 50 kPa, the shape is not uniquely determined even for the same tire. Conversely, if the internal pressure exceeds 50 kPa, the tension due to the internal pressure acts on the carcass cord 6c, and the shape is easily changed.
[0022]
6A, for example, as shown in FIG. 6A, the thickness of the inner liner rubber i is increased around the 0.25 times height position. As shown in B), by adding a rubber strip f or the like different from the inner liner i, the main body portion 6a is largely curved as compared with the conventional case, and the contact position of the bladder during vulcanization molding is different from the conventional case. It can be manufactured by making
[0023]
Further, in the tire 1 of the present embodiment, in the temporarily assembled state shown in FIG. 1, the profile of the section from the outer end 7 e of the belt layer 7 to the bead core 5 in the temporary assembly state shown in FIG. Is formed by a single or a plurality of arcs having a center at the center. Such a profile does not invert the curvature of the main body 6a due to the internal pressure filling, and makes the carcass cord tension at the time of normal internal pressure filling uniform. As a result, the internal strain and the surface strain of the tire can be further reduced and made uniform over the sidewall portion 3 and the bead portion 4, which helps to further improve the durability of the bead portion.
[0024]
The folded portion 6b extends radially outward along the outer surface 8o of the bead apex 8 and near the outer end 8t of the bead apex 8 between the folded portion 6b and the carcass cord 6c of the main body 6a. It has the proximity portion 10 in which the inter-cord distance t (measured as shown in FIG. 3), which is the distance, is the minimum value tmin. That is, the folded portion 6b is positioned such that the distance t between the carcass cords to the main body 6a is the smallest (the distance t is tmin) and the proximity portion 10 is closer to the tire radial direction than the outer end 6t of the folded portion 6b. Have inside. The inter-cord distance (tmin) is, for example, preferably 0.15 to 4.5 times, more preferably 1.3 to 3.5 times the diameter D of the carcass cord 6c.
[0025]
As described above, by providing the proximity portion that minimizes the inter-cord distance t inside the outer end 6t of the folded portion 6b, the folded portion 6b approaches the neutral line of the stress at the time of tire deformation, and The shear stress between the main body 6b and the main body 6a is reduced, so that damage such as cord breakage can be effectively suppressed. If the cord-to-cord distance tmin is less than 0.15 times the diameter D of the carcass cord 6c, the effect of reducing the shear stress becomes insufficient, and sometimes the carcass cord 6C may partially contact. It may cause looseness. On the other hand, when the ratio exceeds 4.5 times, not only the folded portion 6b is liable to be broken due to compression but also undesirably from the viewpoint of heat generation such as unnecessarily increasing the thickness of the bead portion 4. Such a proximity portion 10 may be localized, for example, but the carcass cord of the main body portion 6a and the folded portion 6b is substantially formed by the inter-cord distance t being continuous while forming the minimum value tmin. It is also preferable to form a parallel region G extending in parallel.
[0026]
When the adjacent portion X forms the continuous parallel region G as described above, heat generated based on the shearing force acting on this portion can be effectively dispersed, and an effect of suppressing separation and the like generated near the outer end 8t of the bead apex 8 can be effectively prevented. Is further improved, so that the durability of the bead portion can be further improved.
[0027]
Further, in the present embodiment, as shown in an enlarged manner in FIG. 4, the carcass ply main body portion 6a and the folded portion 6b are provided outside the proximity portion 10 in the tire radial direction (in this example, following the parallel region G). The inter-cord distance t gradually increases to the outer end 6t of the folded portion 6b. Such a gradual increase area Y increases the thickness t of the rubber between plies between the folded part 6b and the main body part 6a at the position of the outer end 6t relative to the proximity part 10 (to the maximum value tmax in this example). Increase), and the separation at the outer end 6t of the folded portion 6b can be suppressed for a long time. On the other hand, the thickness of the rubber between the plies between the main body portion 6a and the folded portion 6b gradually decreases in the opposite direction toward the outer end of the bead apex 8, so that the thickness near the outer end 8t of the bead apex 8 is reduced. The rubber thickness between the plies can be made relatively small, and the occurrence of the separation starting point can be prevented also in this portion.
[0028]
FIG. 5 shows another embodiment of the present invention.
In the present embodiment, one in which one layer of cord reinforcing layer 13 is arranged outside the carcass ply 6A of the bead portion 4 is shown. The cord reinforcing layer 13 includes an outer portion 14 that extends radially outward along the tire axial direction of the folded portion 6b, a radially inner end of the outer portion 14 and the tire of the bead core 5. A winding portion 15 extending radially inward.
[0029]
The cord reinforcing layer 13 is preferably a steel cord in the case of the heavy duty tire of this example, for example, but it is also possible to appropriately employ an organic fiber cord such as an aromatic polyamide or an aliphatic polyamide. In the cord reinforcing layer 13, it is preferable to arrange the cords at an angle of, for example, 30 to 90 degrees with respect to the tire circumferential direction, because the reinforcing effect is high. In the present embodiment, the outer end 14t of the outer portion 14 of the cord reinforcing layer 13 in the tire radial direction is separated from the outer end of the folded portion 6b by a distance T of 4 mm or more, more preferably 6 to 14 mm. The one located radially inside is shown. Accordingly, it is possible to prevent the outer end 6t of the folded portion 6b from approaching the outer end 14t of the cord reinforcing layer 13 so as to prevent separation or the like from occurring at each end.
[0030]
On the other hand, the end 15t of the winding portion 15 of the cord reinforcing layer 13 may be terminated at the inside of the bead core 5 as in this example, or as shown by an imaginary line in FIG. The portion 15t may extend outward in the tire radial direction along the tire axial direction inside of the main body portion 6a of the carcass ply 6A.
[0031]
As described above in detail, in the present invention, the category of the tire is not limited to the above-described example, and may be applied to various categories of tires such as those for passenger cars, light trucks, and motorcycles.
[0032]
【Example】
A heavy load radial tire having a tire size of 11R22.5 (14PR) was prototyped and tested for durability. The test contents are as follows.
[0033]
(1) Bead durability A test tire was assembled on a rim having a rim size of 8.25 × 22.5, filled with an internal pressure of 1000 kPa, and allowed to run on a drum tester under the conditions of a speed of 20 km / H and a load of 88.3 kN. The distance traveled until the tire was damaged was measured. The results were indicated by an index with Comparative Example 1 being 100. The higher the value, the better.
[0034]
(2) The road test tire was mounted on the front wheel of a truck for normal running, and the running distance when ozone cracks occurred on the outer surface of the bead portion was measured. The results were indicated by an index with Comparative Example 1 being 100. The higher the value, the better.
[0035]
The common specifications of the tires are as follows.
<Carcass>
・ Number of plies: 1
・ Cord: Steel (3 / 0.20mm + 7 / 0.23mm)
・ Cord angle: 90 ° (equator to tire)
<Belt layer>
・ Number of plies: 4
・ Cord: Steel (1 × 5 × 0.38mm)
・ Number of cords: 26 / 5cm
・ Cord angle: + 50 °, + 18 °, -18 °, -18 ° (with respect to the tire equator)
[0036]
The following plies were used for those having a bead reinforcing layer.
<Bead reinforcement layer>
・ Number of plies: 1
・ Cord: Steel (3 / 0.20mm + 7 / 0.23mm)
・ Cord angle: 25 ° (with respect to the tire equator)
Table 1 shows the test results and the like.
[0037]
[Table 1]

[0038]
As a result of the test, it was confirmed that the example had improved durability of the bead portion.
[0039]
【The invention's effect】
As described above, in the temporarily assembled state, the pneumatic tire of the present invention has a radius of curvature R1 of the carcass ply at a height of 0.8 times the carcass height Hc and a radius of 0.25 times the carcass height Hc. The radius of curvature R2 of the carcass ply at the height position has a center inside the tire, and the ratio of the radius of curvature (R1 / R2) is substantially equal to 0.75 to 1.25. This minimizes the change in the curvature of the carcass ply during normal internal pressure filling, and reduces distortion generated on the tire outer surface and the tire inside. Thereby, the durability of the bead portion can be improved.
[Brief description of the drawings]
FIG. 1 is a sectional view of a tire meridian in a temporarily assembled state according to an embodiment of the present invention.
FIG. 2 is a sectional view of a tire meridian in a normal internal pressure state according to the embodiment of the present invention.
FIG. 3 is a sectional view taken along line AA ′ of FIG. 1;
FIG. 4 is an enlarged sectional view showing a bead portion of FIG. 1 in an enlarged manner.
FIG. 5 is a sectional view of a bead portion in a normal internal pressure state according to another embodiment of the present invention.
FIGS. 6A and 6B are partial cross-sectional views of a bead portion.
FIG. 7 is an enlarged sectional view of a bead portion of a comparative example tire.
FIG. 8 is an enlarged sectional view of a bead portion of a comparative example tire.
FIG. 9 is an enlarged sectional view of a bead portion of a comparative example tire.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 6a Carcass ply main body part 6b Carcass ply turnback part 7 Belt layer Hc Carcass height P1 0.8 times height position P2 0 .25 times height position R1 Curvature radius R2 of carcass ply at 0.8 times height position in tentatively assembled state Curvature radius of carcass ply at 0.25 times height position in tentatively assembled state

Claims (3)

A carcass integrally provided with a folded portion that is folded from the inside in the tire axial direction to the outside in the tire axial direction around the bead core in a main body portion extending from the tread portion through the sidewall portion to the bead core of the bead portion,
A pneumatic tire comprising a belt layer disposed radially outward of the carcass in the tire radial direction and inside the tread portion,
In a no-load temporary assembly state in which the rim is assembled to a regular rim and 50 kPa is filled, the distance between the bead base line BL and the outermost position of the carcass in the tire radial direction is 0.8 times the carcass height Hc. A radius of curvature R1 of the main body of the carcass ply at a 0.8-fold height position away from the baseline,
The radius of curvature R2 of the main body of the carcass ply at a position 0.25 times higher than the bead baseline by a distance of 0.25 times the carcass height Hc has a center inside the tire, and A pneumatic tire, wherein the ratio of the radii of curvature (R1 / R2) is 0.75 to 1.25. The folded portion has a proximity portion where the distance between the carcass cords between the folded portion and the main body portion is the smallest, radially inward of the outer end of the folded portion in the tire radial direction. The pneumatic tire according to claim 1, wherein the distance between the carcass cords gradually increases to an outer end of the pneumatic tire. The bead portion is provided with a cord reinforcing layer extending in the tire axial direction of the folded portion along the folded portion,
The pneumatic tire according to claim 1, wherein an outer end of the cord reinforcing layer in the tire radial direction is located at least 4 mm inside the outer end of the folded portion in the tire radial direction.

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