JP3771545B2 - Pneumatic tire - Google Patents

Description

【００３９】
【発明の効果】
本発明は叙上の如く構成しているため、ビード部をスリム化した場合にも、接地面形状の悪化を招くことがなく、トレッドショルダー部分での偏摩耗、及び温度上昇を抑制しながらタイヤの軽量化を達成できる。
【図面の簡単な説明】
【図１】本発明の空気入りタイヤの一実施例を示す断面図である。
【図２】そのビード部を拡大して示す断面図である。
【図３】（Ａ）、（Ｂ）は、従来のビード構造を説明するビード部の断面図である。
【符号の説明】
２ トレッド部
２Ｓ トレッド面
３ サイドウォール部
４ ビード部
５ ビードコア
５Ｃ 中心点
６Ａ カーカスプライ
６ａ プライ本体部
６ｂ プライ折返し部
ＢＬ ビードベースライン
Ｐ１ 交点
Ｐ２ カーカスプライ最大幅点
Ｘ 半径方向線[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic tire that is suitable for heavy-duty vehicles and that reduces the weight at the bead portion without deteriorating the tire ground contact surface shape.
[0002]
[Prior art]
For example, in heavy-duty tires for trucks, buses, etc., the use conditions are particularly severe, such as a high air pressure to be filled and a large load. Therefore, the bead part a is strengthened by increasing the size of the bead apex rubber b as shown in FIG. 3A, and the thickness thereof is very thick. Accordingly, the profile at the bead portion a of the carcass ply main body portion c1 is generally curved in a concave arc shape having an arc center on the outer side of the tire.
[0003]
On the other hand, in recent years, as shown in FIG. 3 (B), the volume and height of the bead apex rubber b are greatly reduced, and the bead portion a is slimmed to reduce the weight while improving the bead durability. A technique for achieving this has been proposed (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
JP-A-9-11715 [0005]
[Problems to be solved by the invention]
However, the tire slimmed down in this way has a low rigidity of the bead part a, so that the bead part a falls more outward in the tire axial direction during inflation. Therefore, the tension of the carcass ply main body portion c1 is increased on the lower side of the sidewall portion, and a force that pushes the carcass ply main body portion c1 of the tread shoulder portion radially inward acts. Particularly in a slim tire, the profile of the carcass ply main body portion c1 in the bead portion a is linear or a convex arc shape having an arc center on the tire inner side, so that the pressing force is further increased.
[0006]
As a result, the tread radius of curvature at the time of inflation is reduced, the contact surface shape is deteriorated such as shortening the contact length at the tread shoulder portion, and there is a problem that uneven wear occurs at the tread shoulder portion. Although it may be possible to increase the tread thickness at the tread shoulder to increase rigidity and make it difficult to push down, this method has the negative effect of reducing high-speed durability, such as causing a temperature rise during high-speed running due to heat storage. Occurs.
[0007]
Therefore, the present invention is based on the restriction of the radial distance from the bead core to the carcass ply main body, the radius of curvature of the tread surface, and the camber height to predetermined ranges, respectively, even when the bead is slimmed. An object of the present invention is to provide a pneumatic tire capable of achieving weight reduction of the tire while suppressing uneven wear at the tread shoulder portion and temperature rise without causing deterioration of the ground shape.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 of the present application is folded back from the inner side in the tire axial direction around the bead core to the ply body part extending from the tread part through the sidewall part to the bead core of the bead part. A pneumatic tire having a carcass ply provided with a series of ply turn-up parts,
In the meridional section of the tire in a state where the rim is assembled to the normal rim and the internal pressure of 5% of the normal internal pressure is filled,
The tread portion has a radius of curvature RT of the tread surface of 800 to 1500 mm, and a camber height h which is a distance in the tire radial direction between the radial maximum point of the tread surface and the tread edge, and is 1.0 to 10 mm. In addition, the total tread thickness t at the edge of the tread is 38 to 45 mm,
On the radial line passing through the center point of the bead core, the radial distance L1 from the center point of the bead core at the intersection point where the radial line intersects the outer surface of the ply body part on the bead part side is defined as It is characterized by being 0.15 to 0.28 times the radial distance L2 from the bead base line of the carcass ply maximum width point where the outer surface extends most outward in the tire axial direction.
[0009]
According to a second aspect of the present invention, the ply turn-up portion of the carcass ply is wound along the peripheral surface of the bead core and is sandwiched between the bead core and the bead apex rubber and is interrupted.
[0010]
In this specification, the “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, if it is JATMA, it is a standard rim, and if it is TRA, “Design” “Rim” or “Measuring Rim” for ETRTO. The “regular internal pressure” is the air pressure specified by the tire for each tire. The maximum air pressure in the case of JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, In the case of ETRTO, it means “INFLATION PRESSURE”, but in the case of passenger tires, it is 180 kPa.
[0011]
In the present specification, unless otherwise specified, the dimensions and the like of each part of the tire are values specified in a 5% normal internal pressure state in which an internal pressure of 5% of the normal internal pressure is filled. Note that the tire shape in the 5% normal internal pressure state generally matches the tire shape in the vulcanization mold.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a 5% normal internal pressure state when the pneumatic tire 1 of the present invention is a heavy duty tire for trucks and buses, and FIG. 2 is an enlarged cross-sectional view showing its bead portion. .
[0013]
In FIG. 1, a pneumatic tire 1 is disposed on a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, on the radially outer side of the carcass 6 and on the inner side of the tread portion 2. Belt layer 7.
[0014]
The belt layer 7 is formed of two or more belt plies (three or more in the case of heavy load tires) using a belt cord. In this example, the belt layer 7 includes a first belt ply 7A on the innermost side in the radial direction in which steel cords are arranged at an angle of 60 ± 15 ° with respect to the tire circumferential direction, and 10 to 10 with respect to the tire circumferential direction. A case of a four-sheet structure with second to fourth belt plies 7B to 7D arranged at a small angle of 35 ° is illustrated. The belt plies 7 </ b> A to 7 </ b> D are provided with one or more places where the belt cords cross each other between the plies, and are superposed to enhance belt rigidity and reinforce the tread portion 2 with a tagging effect.
[0015]
The carcass 6 is formed of one or more carcass plies 6A in this example, in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. A steel cord is suitable as the carcass cord, but an organic fiber cord such as nylon, rayon, polyester, aromatic polyamide or the like is also used if necessary. Further, the carcass ply 6A has a series of ply turn-up portions 6b that are folded and locked outward from the inner side in the tire axial direction around the bead core 5 on both sides of the ply body portion 6a straddling the bead cores 5 and 5. Have.
[0016]
As shown in FIG. 2, the bead core 5 is a ring-shaped body formed by winding, for example, steel bead wires in multiple stages and multi-rows. In this example, a flat hexagonal shape having a horizontally long cross section is exemplified. The bead core 5 has an inner side and an outer side in the radial direction of the cross section substantially parallel to the rim sheet J1 of the regular rim J, thereby increasing the fitting force with the rim over a wide range. In addition, as a cross-sectional shape of the bead core 5, a regular hexagonal shape, a rectangular shape, a circular shape, or the like can be adopted as necessary.
[0017]
In this example, the ply turn-up portion 6b of the carcass 6 is wound along the peripheral surface of the bead core 5, and its end E is sandwiched between the bead core 5 and the bead apex rubber 8 and is interrupted. The thing is illustrated. The bead apex rubber 8 is made of a hard rubber having a triangular cross section with a rubber hardness (durometer A hardness) of 60 to 99 degrees, and extends outward from the bead core 5 in the tire radial direction. Reinforce over the wall 3.
[0018]
In such a wound carcass ply 6A, since the ply turn-up portion 6b is interrupted around the bead core 5, the stress at the time of tire deformation hardly acts on the end portion E. Accordingly, the cord loose starting from the end E can be effectively suppressed, and the bead durability can be improved. Moreover, since the ply turn-up portion 6b can be formed substantially short, it can greatly contribute to weight reduction of the tire. Further, since the end portion E is sandwiched between the bead core 5 and the bead apex rubber 8 and firmly locked, the blow-through phenomenon of the carcass ply 6A can be reliably prevented.
[0019]
In the present invention, the radial distance from the bead core 5 to the outer surface of the ply main body portion 6a is restricted to a predetermined range, and the bead apex rubber 8 is kept at a low rubber volume, thereby making the bead portion 4 slim and reducing the weight of the tire. We are trying to make it.
[0020]
Specifically, the radial line X passing through the center point 5C of the bead core 5 is defined as P1 at the intersection point where the outer surface of the ply main body portion 6a intersects the bead portion 4 side, and the outer surface of the ply main body portion 6a is outside the tire axial direction. The carcass ply maximum width point that protrudes most in the direction is P2 (shown in FIG. 2). At this time, the radial distance L1 from the center point 5C of the bead core 5 at the intersection P1 on the radial line X is set to 0 of the radial distance L2 from the bead base line BL at the carcass ply maximum width point P2. Restricted to the range of 15 to 0.28.
[0021]
Here, the center point 5C means the center of gravity in the cross section of the bead core 5, that is, the centroid, and the bead base line BL means a tire axial line passing through a rim diameter position determined by a standard on which the tire is based. To do.
[0022]
Thus, by setting the distance L1 to 0.28 times or less of the distance L2, the ply main body portion 6a between the intersection point P1 and the carcass ply maximum width point P2 is formed into a concave arc-shaped portion (on the tire outer side). It is possible to form a non-concave profile that does not include an arcuate portion having a center. Therefore, the rubber volume of the bead apex rubber 8 can be kept low, and weight reduction of the tire can be achieved. In particular, it is preferable that the profile is formed only by a convex arc-shaped portion (arc-shaped portion having a center inside the tire) as in this example, but a linear portion is formed at a part thereof, for example, at a position connected to the intersection P1. It can also be included. Note that the tire lumen surface needs to be substantially parallel to the outer surface of the ply body 6a.
[0023]
However, when the distance L1 is reduced to be less than 0.15 times the distance L2, the bead rigidity becomes excessively small, and the bead portion 4 is greatly collapsed during inflation. Therefore, also in the present invention, the contact surface shape is deteriorated and uneven wear in the tread shoulder portion Ys (shown in FIG. 1) cannot be suppressed. From such a viewpoint, the ratio L1 / L2 of the distances L1 and L2 is more preferably in the range of 0.20 to 0.26.
[0024]
The bead apex rubber 8 preferably has a height H0 from the bead base line BL in a range of 30 to 60% of the distance L2 from the viewpoint of weight reduction and bead rigidity. Further, the bead portion 4 is provided with a clinching rubber 9 for preventing rim misalignment that forms a bead skin. The rubber hardness (durometer A hardness) of the clinch rubber 9 is 70 to 85 ° and the bead apex rubber 8 has a rubber hardness. In this example, the lower end portion of the side wall rubber 3G that is softer than the clinch rubber 9 is interposed between the clinch rubber 9 and the bead apex rubber 8 in the shape of a sword. To reduce the delamination of the three parties.
[0025]
Next, in the tire in which the bead portion 4 is slimmed, as described above, as the bead portion 4 is greatly collapsed during inflation, the force that pushes the tread shoulder portion Ys radially inward acts strongly, and the contact surface shape is reduced. Getting worse.
[0026]
Therefore, in the present invention, in the 5% normal internal pressure state, the tread portion 2 is formed by an arc-shaped convex curve having a radius of curvature RT of the tread surface 2S of 800 to 1500 mm, and the radial maximum point of the tread surface 2S. The camber height h, which is the distance in the tire radial direction between Tc and the tread edge Te, is reduced to a range of 1.0 to 10 mm.
[0027]
The radius of curvature RT means the radius when the tread surface 2S is a single arc. However, for example, in the case of a non-single arc including a plurality of arc portions or straight portions, it means a radius of a three-point arc passing through the radial maximum point Tc and the tread edge Te, Te.
[0028]
As described above, the tire 1 regulates the curvature radius RT and the camber height h to the above ranges, and the tread surface 2S is formed flatter than the conventional tire. The radius can be optimized. Therefore, the deterioration of the contact surface shape can be suppressed, and the uneven wear at this portion Ys can be suppressed, for example, the contact length at the tread shoulder portion Ys can be sufficiently secured.
[0029]
When the radius of curvature RT is smaller than 800 mm and the camber height h is larger than 10 mm, the contact length at the tread shoulder portion Ys becomes insufficient, causing uneven wear at the portion Ys. On the other hand, when the curvature radius RT is larger than 1500 mm and the camber height h is smaller than 1.0 mm, uneven wear occurs in the tread crown portion Yc. Therefore, the radius of curvature RT is preferably in the range of 850 to 1100 mm, and the camber height h is preferably in the range of 2.0 to 7 mm.
[0030]
At this time, it is important that the total tread thickness t at the tread edge Te is 38 to 45 mm. If the total thickness t of the tread exceeds 45 mm, the tread shoulder portion Ys becomes too thick, and the weight reduction is hindered, and the high temperature durability is deteriorated by causing a temperature increase during high speed running due to the heat storage action. On the other hand, if it is less than 38 mm, the shoulder ground contact length on the ground contact surface is shortened, causing uneven wear.
[0031]
In this example, the case where the tread portion 2 includes a tread pattern of a rib type, a rib block type, or a block type having 3 to 4 longitudinal main grooves 20 extending in the tire circumferential direction is illustrated. The tread crown portion Yc defined between the outermost vertical main grooves 20a and 20a in the tire axial direction is formed by a single arc curve S1, and the tread defined outside the outermost vertical main groove 20a. The shoulder portion Ys is formed by an arc or straight line having a larger radius of curvature than the curve S1.
[0032]
The particularly preferred embodiment of the present invention has been described in detail above. However, the present invention is not limited to the illustrated embodiment. For example, the ply turn-up portion 6b of the carcass 6 is connected to the outer surface in the tire axial direction of the bead apex rubber 8. It is good also as a structure wound up along. The invention can be implemented in various forms, such as being applicable to tires of other categories other than heavy duty tires.
[0033]
【Example】
A heavy-duty radial tire having the structure of FIG. 1 having a tire size of 11R22.5 was prototyped based on the specifications in Table 1, and the partial wear performance and the tire weight of each sample tire were measured and compared with each other. Specifications other than those in Table 1 are the same.
[0034]
Each tire has a tread pattern of five rib types including four longitudinal main grooves having a groove depth of 14 mm, a tread width of 202 mm, and a total tread thickness t at the tread edge of 40 mm.
[0035]
(1) Contact length ratio;
The contact length Ls of the tread edge and the contact length Lc on the tire equator in the contact surface shape obtained under the conditions of the rim (7.50 × 22.5), the internal pressure (700 kPa), and the load (26.7 kN). It means the ratio Ls / Lc.
[0036]
(2) Uneven wear performance;
Tires are attached to all wheels of a 2 / 2-D vehicle (loading capacity of 10 tons) with a rim (7.50 × 22.5) and internal pressure (700 kPa), and the asphalt road is 100,000 km in the fixed volume state. Ran. After running, the remaining groove amount δc in the innermost vertical main groove in the tire axial direction and the remaining groove amount δs in the outermost vertical main groove in the tire axial direction were measured.
[0037]
(3) Tire weight;
The weight per tire was measured.
[0038]
[Table 1]

[0039]
【The invention's effect】
Since the present invention is configured as described above, even when the bead portion is slimmed, the tire does not deteriorate in the shape of the ground contact surface and suppresses uneven wear at the tread shoulder portion and temperature rise while suppressing the tire. Can be reduced in weight.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a pneumatic tire according to the present invention.
FIG. 2 is an enlarged cross-sectional view of the bead portion.
3A and 3B are cross-sectional views of a bead portion for explaining a conventional bead structure. FIG.
[Explanation of symbols]
2 tread portion 2S tread surface 3 side wall portion 4 bead portion 5 bead core 5C center point 6A carcass ply 6a ply body portion 6b ply folded portion BL bead base line P1 intersection point P2 carcass ply maximum width point X radial direction line

Claims (2)

A pneumatic tire having a carcass ply provided with a series of ply folded portions that are folded from the inner side to the outer side in the tire axial direction around the bead core on the ply body portion that extends from the tread portion to the bead core through the sidewall portion. There,
In the meridional section of the tire in a state where the rim is assembled to the normal rim and the internal pressure of 5% of the normal internal pressure is filled,
The tread portion has a radius of curvature RT of the tread surface of 800 to 1500 mm, and a camber height h which is a distance in the tire radial direction between the radial maximum point of the tread surface and the tread edge, and is 1.0 to 10 mm. In addition, the total tread thickness t at the edge of the tread is 38 to 45 mm,
On the radial line passing through the center point of the bead core, the radial distance L1 from the center point of the bead core at the intersection point where the radial line intersects the outer surface of the ply body part on the bead part side is defined as A pneumatic tire characterized by being 0.15 to 0.28 times the radial distance L2 from the bead base line of the carcass ply maximum width point at which the outer surface extends most outward in the tire axial direction. 2. The pneumatic tire according to claim 1, wherein the ply turn-up portion of the carcass ply is wound along a peripheral surface of the bead core and is nipped between the bead core and the bead apex rubber and interrupted.

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