JP3564096B2 - Radial tire for heavy loads - Google Patents

Description

【００３４】
【表２】

【００３５】
【発明の効果】
叙上の如く本発明は、多層構造のトレッドゴムにおいて、キャップゴムおよびベースゴムの夫々のゴム硬度及び硬度差を規制し、かつ前記ベースゴムを、途切れ部を隔ててタイヤ赤道両側に配される一対のベースゴム片で形成するとともに、このベースゴム片のゴム厚さをタイヤ軸方向内側から外側に向かって増加せしめ、しかもトレッド端縁近傍点Ｐにおけるベースゴムとキャップゴムとのゴム厚さの比を特定している。従って、耐摩耗性を高く維持しながら、トレッド温度、特にトレッドショルダー部での温度上昇を効果的に抑制でき、高速耐久性を向上しうる。
【図面の簡単な説明】
【図１】本発明の一実施例を示すタイヤの断面図である。
【図２】トレッド部を拡大して示す断面図である。
【符号の説明】
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
７ ベルト層
１０ 途切れ部
１１ ベースゴム片
Ｃ タイヤ赤道
Ｅ トレッド端縁
Ｇ トレッドゴム
Ｇｂ ベースゴム
Ｇｃ キャップゴム
Ｐ トレッド端縁近傍点[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a heavy duty radial tire having a multilayer structure in which a tread rubber includes a radially innermost base rubber and an outermost cap rubber, and suppresses a temperature rise of the tread without impairing abrasion resistance and durability. The present invention relates to a heavy-duty radial tire having an improved performance.
[0002]
[Prior art]
In a heavy-duty radial tire mounted on a truck, a bus, or the like, heat generated in the tire is accumulated due to a large load applied to the tire or a long continuous running time, and the tire temperature increases. At this time, in the vulcanized rubber constituting the tire, physical properties change due to the heat of the rubber occurs, such as the vulcanized sulfur being cut off once and being re-crosslinked, and particularly in the tread portion where the temperature rise is large, the tread rubber and the belt layer Induce peeling damage on the adhesive surface with
[0003]
Therefore, conventionally, in order to suppress the temperature rise and improve the durability, a tread rubber is formed by a multilayer of a cap rubber on the tread surface side having excellent abrasion resistance and a base rubber having a low heat generation disposed inside thereof. Structured tires are employed.
[0004]
[Problems to be solved by the invention]
However, in recent years, in radial tires for heavy loads, the tread width has tended to be wider in order to improve braking performance, and as a result, the rubber thickness of the tread shoulder portion has increased, and heat has accumulated more in this tread shoulder portion. The structure is easy to do. Therefore, in order to further suppress the rise in the tread temperature and improve the durability while maintaining the wear resistance, a multilayer structure corresponding to the increase in the rubber thickness of the above-described tread shoulder portion is used as the tread rubber. It is necessary to adopt
[0005]
Therefore, the present invention, in a tread rubber having a multilayer structure , regulates the rubber hardness and hardness difference of the cap rubber and the base rubber, respectively, and the base rubber, a pair of arranged at both sides of the tire equator across the break. Forming a base rubber piece, increasing the rubber thickness of the base rubber piece from the inside to the outside in the tire axial direction, and specifying the ratio of the rubber thickness of the base rubber to the cap rubber near the tread edge. On the basis of this, it is an object of the present invention to provide a heavy duty radial tire capable of further suppressing the rise in tread temperature and improving durability while maintaining high wear resistance.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 of the present application is directed to a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, and a belt layer disposed inside the tread portion and outside the carcass. A heavy load radial tire having
The ratio TB / TA of the total tread thickness TA at the tire equator of the tread portion to the total tread thickness TB at a point P near the tread edge on the tread surface separated by 10 mm inward in the tire axial direction from the tread edge is , 1.1-1.7,
The tread rubber forming the tread portion extends in the tire axial direction along the belt layer, and is arranged on both sides of the equator of the tire with a break at a distance g of 0.01 to 0.30 times the tread width TW. A radially innermost base rubber consisting of a pair of base rubber pieces, and a multilayer structure including a radially outermost cap rubber forming a tread surface,
The rubber hardness Hc of the cap rubber is 60 ° or more, the rubber hardness Hb of the base rubber is 57 ° or less, and the hardness difference Hc−Hb of the rubber hardness Hc and Hb is 5 to 15 °,
In addition, the base rubber piece has a rubber thickness Tb substantially increasing from the inner side to the outer side in the tire axial direction,
The ratio Tb / Tc of the rubber thickness Tb of the base rubber to the rubber thickness Tc of the cap rubber at the point P near the tread edge is 0.5 to 1.5.
[0007]
In the invention according to claim 2, the carcass is formed of one carcass ply using a steel carcass cord, and the belt layer is formed of three or more belt plies using a steel belt cord. It is characterized by:
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to illustrated examples. FIG. 1 is a meridional sectional view of a radial tire for heavy load according to the present invention.
In FIG. 1, a heavy-duty radial tire 1 (hereinafter referred to as a tire 1) includes a carcass 6 extending from a tread portion 2 to a bead core 5 of a bead portion 4 through a sidewall portion 3, a carcass 6 inside the tread portion 2 and the carcass 6. And a belt layer 7 disposed outside the belt.
[0009]
The carcass 6 is formed from one or more carcass plies 6A in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction, in this example, one carcass ply 6A. As the carcass cord, a steel cord is preferable, but an organic fiber cord such as nylon, rayon, polyester, or aromatic polyamide may be employed, for example, when the carcass 6 is composed of a plurality of carcass plies.
[0010]
The carcass ply 6A includes a folded portion 6b that is folded back from inside to outside around the bead core 5 and is locked on both sides of the ply body 6a straddling the bead cores 5,5. A bead apex rubber 8 extending radially outward from the bead core 5 is disposed between the ply body 6a and the folded portion 6b, and reinforced from the bead 4 to the sidewalls 3.
[0011]
In the present embodiment, the bead portion 4 is provided with a bead reinforcing layer 9 which wraps around the bead core 5 in a U-shape via a carcass 6 and reinforces the bead core 5 to increase rigidity and improve bead durability. In this example, the bead reinforcing layer 9 is made of one steel cord ply.
[0012]
Next, the belt layer 7 is formed from three or more belt plies using a steel cord as a belt cord. In the present example, the innermost first belt ply 7A in which the belt cords are arranged at an angle of, for example, 60 ± 15 ° with respect to the tire circumferential direction, and at a small angle of, for example, 10 to 35 ° with respect to the tire circumferential direction. The case of a four-sheet structure with the second to fourth belt plies 7B to 7D arranged is illustrated. In the belt layer 7, the belt cord has one or more locations where the plies intersect each other between the plies, thereby increasing the rigidity of the tread portion 2 and improving the wear resistance and the like.
[0013]
The ply width W1 of the first belt ply 7A is smaller than the ply width W2 of the second belt ply 7B, and is substantially the same as the ply width W3 of the third belt ply 7C. W2 is 0.98 to 0.85 times the tread width TW, and the ply widths W1 and W3 are about 0.8 to 0.95 of the ply width W2. Thereby, substantially the entire width of the tread portion 2 is reinforced, and the tread rigidity is increased. The ply width W4 of the fourth belt ply 7D is smaller than the ply width W3 by 10 to 45%, and protects the first to third belt plies 7A to 7C from damage.
[0014]
Further, in the tire 1 of the present embodiment, the tread portion 2 has a width in which the tread width TW is at least 0.75 times the tire cross-sectional width W0, whereby the tread shoulder portion extends from the tread edge E. The total tread thickness TB at a point P near the tread edge on the tread surface separated by 10 mm on the inner side in the tire axial direction is formed so as to be 1.1 to 1.7 times the total tread thickness TA at the tire equator C. Have been.
[0015]
In the tire 1 having such a thick tread shoulder portion, the tread forming the tread portion 2 is formed in order to effectively suppress a rise in tread temperature and improve durability while ensuring high wear resistance. The rubber G is configured as described below.
[0016]
That is, as shown in FIG. 2, the tread rubber G is formed of a multilayer structure extending in the tire axial direction along the belt layer 7, and is formed with a radially outermost cap rubber Gc forming a tread surface and a radial direction. It is formed including the innermost base rubber Gb. In this example, the case where the tread rubber G is formed of a two-layer structure of the cap rubber Gc and the base rubber Gb is illustrated.
[0017]
The base rubber Gb is composed of a pair of base rubber pieces 11, 11 arranged on both sides of the tire equator with a break 10 therebetween. The distance g in the tire axial direction of the break 10 is defined as the distance from the tire equator C to the tread edge. The range is 0.01 to 0.30 times the tread width TW, which is the distance to E.
[0018]
The rubber hardness Hc of the cap rubber Gc is 60 ° or more, the rubber hardness Hb of the base rubber Gb is 57 ° or less, and the difference Hc-Hb between the rubber hardnesses Hc and Hb is restricted to a range of 5 to 15 °. are doing. Note that the rubber hardnesses Hc and Hb are defined as hardness by a durometer type A based on JIS-K6253.
[0019]
Here, the rubber becomes harder as the degree of cross-linking increases and as the amount of a reinforcing agent (filler) such as carbon increases, so that the tear strength and abrasion resistance can be improved. However, on the other hand, since the connection between sulfur, which is a cross-linking agent, and rubber has a greater energy loss for movement than the connection between rubbers, the calorific value of the rubber increases as the degree of cross-linking increases. Similarly, carbon, which is a reinforcing agent, increases the tear strength by hardening the rubber, but also causes a large energy loss with respect to movement and a large calorific value of the rubber.
[0020]
Therefore, the hard rubber rubber hardness Hc is excellent in wear resistance is 60 ° or more with use as cap rubber Gc, a soft rubber rubber hardness Hb is excellent in low heat build-in below 57 ° as the base rubber Gb It is used to achieve both improvement of abrasion resistance and suppression of temperature rise of the tread rubber G.
[0021]
At this time, it is generally desirable to set the rubber hardness Hc of the cap rubber Gc higher from the viewpoint of wear resistance, and to set the rubber hardness Hb of the base rubber Gb smaller from the viewpoint of heat generation. If the hardness Hb is too small, the tread will be crushed and the wear resistance will be poor. Therefore, the hardness difference Hc-Hb is restricted to the range of 5 to 15 °. If the hardness difference Hc−Hb is less than 5 °, both improvement of wear resistance and suppression of temperature rise cannot be achieved.
[0022]
In the base rubber Gb, it is also important to suppress heat generated by the movement of the outer end of the belt layer 7 and heat generation in the thick tread shoulder portion. For this purpose, the base rubber Gb substantially increases the rubber thickness Tb from the inside to the outside in the tire axial direction, and the rubber thickness Tb of the base rubber Gb at the point P near the tread edge and the rubber thickness Tb. The ratio Tb / Tc of the rubber Gc to the rubber thickness Tc is increased in the range of 0.5 to 1.5. The reason that the ratio Tb / Tc was regulated at the point P near the tread edge is that the rubber thicknesses Tb and Tc tend to fluctuate greatly and become unstable at the tread edge E due to the rubber flow during tire molding. Because.
[0023]
The rubber thickness Tb is substantially increased at least in a region from the inner end in the tire axial direction of the base rubber piece 11 to a point P near the tread edge . Thereby, heat generation in the tread shoulder portion can be suppressed. In addition, it is also preferable to substantially increase the rubber thickness ratio Tb / Tc from the inside to the outside in the tire axial direction in order to suppress heat generation.
[0024]
Here, "substantially increases" means that a portion Y under the tread groove whose rubber thickness is greatly affected by the rubber flow during tire molding is excluded. That is, the base rubber Gb is dented concavely at the lower portion Y of the groove, and the rubber thickness Tb is allowed to locally decrease.
[0025]
If the ratio Tb / Tc is less than 0.5, heat generation in the tread shoulder cannot be sufficiently suppressed, resulting in reduced durability. Conversely, if it exceeds 1.5, wear resistance will be impaired.
[0026]
Furthermore, in the base rubber Gb, as described above, the discontinuous portion 10 is formed at the position of the tire equator where a large load is applied so as to suppress the tread from being crushed due to the load and not adversely affect the wear resistance and the running performance. Has formed. If the distance g of the break 10 exceeds 0.30 times the tread width TW, internal heat generation increases and durability decreases. In addition, since a large load is applied to the tread central portion, if it is less than 0.01 times, the tread will be crushed and uneven wear will occur.
[0027]
The rubber compounding of the cap rubber Gc and the base rubber Gb is not particularly limited, but as the rubber base material, one of diene rubbers such as natural rubber, butadiene rubber, isoprene rubber, styrene butadiene rubber, or a mixture thereof. Can be used, and the content of the natural rubber is preferably 80% by weight or more. As the reinforcing agent (filler), carbon is preferable in terms of abrasion resistance, but silica or the like may be used. Sulfur is used as a cross-linking agent, and thiazole, guanidine, sulfenamide, and thiuram-based vulcanization accelerators can be used.
[0028]
As described above, particularly preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to the illustrated embodiments, and can be implemented in various forms.
[0029]
【Example】
A heavy-duty radial tire having a tire size of 11R22.5 was prototyped based on the specifications in Table 1, and the heat resistance and wear resistance of each test tire were tested. The results are shown in Table 1. Except for the tread rubber, it has substantially the same configuration as shown in Table 2.
[0030]
(1) Heat generation durability;
The test tire was run at an initial speed of 80 km / h under the conditions of a rim (7.50 × 22.5), an internal pressure (800 kPa), and a load (58.52 N) using a heat generation / durability drum tester. The speed was stepped up by 10 km / h, and the running time until peeling damage occurred between the tread rubber and the belt layer was measured and compared. The higher the value, the better.
[0031]
Also, at a running distance of 200 km, the internal temperature of the tread shoulder portion was determined, and the evaluation was made using an index with Comparative Example 1 being 100. The lower the value, the lower the temperature and the better.
[0032]
(2) Wear resistance:
The test tires were mounted on all wheels of a 2 / 2-D vehicle (loading 10 tons) under the conditions of a rim (7.50 × 22.5) and an internal pressure (800 kPa), and the dry paved road was 100,000 km. After running, the amount of wear was measured and evaluated by an index with Comparative Example 1 being 100. The larger the value, the less the abrasion and the better the abrasion resistance.
Excellent at low temperatures.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
【The invention's effect】
As described above, the present invention regulates the rubber hardness and the hardness difference between the cap rubber and the base rubber in the tread rubber having a multilayer structure, and disposes the base rubber on both sides of the tire equator with a break portion. The base rubber piece is formed from a pair of base rubber pieces, and the rubber thickness of the base rubber piece is increased from the inside to the outside in the tire axial direction. The ratio is specified. Therefore, it is possible to effectively suppress a rise in the tread temperature, particularly the temperature in the tread shoulder portion, while maintaining high wear resistance, and improve high-speed durability.
[Brief description of the drawings]
FIG. 1 is a sectional view of a tire showing one embodiment of the present invention.
FIG. 2 is an enlarged sectional view showing a tread portion.
[Explanation of symbols]
2 Tread section 3 Side wall section 4 Bead section 5 Bead core 6 Carcass 7 Belt layer 10 Break section 11 Base rubber piece C Tire equator E Tread edge G Tread rubber Gb Base rubber Gc Cap rubber P Point near tread edge

Claims (2)

A heavy-duty radial tire having a carcass that extends from a tread portion to a sidewall portion to a bead core of a bead portion, and a belt layer disposed inside the tread portion and outside the carcass,
The ratio TB / TA of the total tread thickness TA at the tire equator of the tread portion and the total tread thickness TB at a point P near the tread edge on the tread surface 10 mm inward in the tire axial direction from the tread edge is: 1.1 to 1.7,
The tread rubber forming the tread portion extends in the tire axial direction along the belt layer, and is arranged on both sides of the equator of the tire with a break at a distance g of 0.01 to 0.30 times the tread width TW. A radially innermost base rubber consisting of a pair of base rubber pieces, and a multilayer structure including a radially outermost cap rubber forming a tread surface,
The rubber hardness Hc of the cap rubber is 60 ° or more, the rubber hardness Hb of the base rubber is 57 ° or less, and the hardness difference Hc−Hb of the rubber hardness Hc and Hb is 5 to 15 °,
In addition, the base rubber piece has a rubber thickness Tb substantially increasing from the inner side to the outer side in the tire axial direction,
The ratio Tb / Tc of the rubber thickness Tb of the base rubber to the rubber thickness Tc of the cap rubber at the point P near the tread edge is 0.5 to 1.5, wherein the radial tire for heavy load is used. . The carcass is formed of one carcass ply using a steel carcass cord, and the belt layer is formed of three or more belt plies using a steel belt cord. The radial tire for heavy load described.

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