JP2009001051A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire having excellent durability by solving the problem of conventional separation, while satisfying a request of reinforcing for a tire crown part. <P>SOLUTION: In this pneumatic radial tire, carcasses 1 extending in the toroidal shape between bead cores are made as skeletons, and three to six layers of reinforcing belts having a plurality of cords or filaments as reinforcing elements are provided on the outer periphery. At least two layers of the reinforcing belts are peripheral direction crown reinforced layers 3a and 3b formed by strips constituted by orienting a rubber-steel cord composite body as a whole along a tire peripheral direction. Of the strips, at least one layer is constituted of a rubber-steel cord composite body reinforced by steel cords molded into wave shapes in a two-dimension. The remaining one layer or more are constituted of rubber-steel cord composite bodies reinforced by steel cords having a multi-twist-structure in which N (N=2 to 8) strands twisted with a plurality of wires are twisted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more particularly to improvement of durability in a pneumatic radial tire using a steel cord as a rubber reinforcing material.

  Tires, especially tires for large vehicles such as trucks and buses that run for a long time while supporting a high load, have high strength and rigidity to withstand long-term severe use and to provide stable performance. Dimensional stability is important. In particular, the crown portion of the tire always receives a tensile input in the circumferential direction due to internal pressure during use, and creeps and extends the circumferential length due to use, resulting in distortion and deterioration of the tire's cross-sectional shape. It may be changed to deteriorate the wear characteristics.

On the other hand, as a technique related to the reinforcement of the tire crown portion, for example, in Patent Document 1, the tread portion around the carcass includes two layers of crossing belts and at least one layer located in the lower layer, and has a waveform. Alternatively, a technology that effectively prevents separation without increasing the weight of the tire by arranging a reinforcing element of a plurality of zigzag-shaped cords (or filaments) and a crown reinforcing layer formed by a strip oriented along the equator as a whole. It is disclosed.
JP-A-2-208101 (Claims etc.)

  Due to the recent high demand for improved wear characteristics and improved steering stability, the tire crown is required to have appropriate rigidity not only in the tire circumferential direction but also in the tire width direction. However, when rigidity is imparted in the tire width direction, high shear strain is generated between the crown reinforcing layer oriented in the tire circumferential direction and separation may occur. Therefore, establishment of a technique for solving such a separation problem while satisfying various performance requirements for the tire as described above has been demanded.

  Accordingly, an object of the present invention is to provide a pneumatic radial tire excellent in durability by solving the above-mentioned problem of separation while satisfying the demand for strengthening the tire crown portion.

  As a result of intensive studies, the present inventor applied a steel cord having a predetermined structure that can alleviate shear strain generated by the cord itself being appropriately stretched to the reinforcing belt arranged for reinforcing the tire crown portion. Thus, the present inventors have found that the separation problem can be solved, and have completed the present invention.

That is, the pneumatic radial tire of the present invention has at least a pair of carcass extending in a toroid shape between at least a pair of bead cores as a skeleton, and a plurality of cords or filaments on the outer periphery of the carcass as reinforcing elements. In a pneumatic radial tire having 3 to 6 layers of reinforcing belts,
At least two of the reinforcing belts are circumferential crown reinforcing layers formed of a strip formed by orienting a rubber-steel cord composite as a whole along the tire circumferential direction, and at least one of the strips. Is composed of a rubber-steel cord composite reinforced with a steel cord that is wave-shaped in two dimensions, and the remaining one or more layers are N strands in which a plurality of strands are twisted (N = 2-8) It is characterized by comprising a rubber-steel cord composite reinforced with a steel cord having a twisted double twist structure.

In the present invention, in the steel cord having the double twist structure, when the diameter of the strand is d (mm), the circumscribed circle diameter of the cord is D (mm), and the twisting pitch of the cord is P (mm), formula,
ε _c = √ (−b / 2 + √ (b ² / 4−c)) − 1
(In the formula, b is −1 + π ² (−4R ² + d ² ) / P ² , c is π ² d ² k (4π ² R ² + P ² ) / P ⁴ , and R is (D−d) / 2, k. the ^{tan 2 (π / 2-π} / N) ε c defined by the represented) preferably satisfies ε _c ≧ 0.005. In the two-dimensional wavy steel cord, when the length of one wavelength is λ (mm) and the net length of one wavelength is L (mm),
ε _w = L / λ−1
(Where L is the following formula,
L = λ × (1 + 2 /8 × K 2 + 13/64 × K 4 + 90/512 × K 6 + 644/4096 × K 8 + 4708.5 / 32768 × K 10)
(Where K = (b / (1 + b)) ^0.5 , b = (2π × a / λ) ² , where a is the amplitude amount (mm) of the undulating part)) It is defined epsilon _w it is also preferable to satisfy the epsilon _w ≧ 0.005.

Further, in the present invention, the steel cord of the multi-twisted structure, the steel cord of the two-dimensional wave shape, the epsilon _c and epsilon _w the following formula,
1.15 ≧ ε _c / ε _w ≧ 0.85
Preferably, the steel cord having the double twist structure and the two-dimensional corrugated steel cord are such that ε _c and ε _w are as follows:
0.040 ≧ ε _c ≧ 0.010 and 0.040 ≧ ε _w ≧ 0.010
It is also preferable that the combination is satisfied.

  Furthermore, in the present invention, the circumferential crown reinforcing layer made of the steel cord having the double twist structure is disposed on the outer side in the tire radial direction of the circumferential crown reinforcing layer made of the two-dimensional corrugated steel cord. Preferably, at least one width direction crown reinforcing layer made of a rubber-steel cord composite having an inclination angle of 10 to 40 ° with respect to the tire circumferential direction is provided outside the circumferential crown reinforcing layer in the tire radial direction. preferable.

  According to the present invention, it is possible to realize a pneumatic radial tire excellent in durability by solving the above-mentioned problem of separation while satisfying the demand for strengthening the tire crown portion by adopting the above configuration. became.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an enlarged partial cross-sectional view in the vicinity of a tread portion of a pneumatic radial tire according to an embodiment of the present invention. As shown in the figure, a pneumatic radial tire 10 of the present invention has at least a pair of carcass 1 extending in a toroid shape across at least a pair of bead cores (not shown) as a skeleton, It has 3 to 6 layers, and in the example shown, 4 layers of reinforcing belts 2a, 2b, 3a and 3b, each of which has cords or filaments as reinforcing elements.

  In the tire 10 of the present invention, at least two of the reinforcing belts, in the illustrated example, the reinforcing belts 3a and 3b are formed of a strip formed by orienting a rubber-steel cord composite as a whole along the tire circumferential direction. A circumferential crown reinforcement layer. In the present invention, at least one layer (one layer in the illustrated example) of the strip is composed of a rubber-steel cord composite reinforced with a steel cord that is wave-shaped in two dimensions, and the remaining layers. One or more layers (one layer in the example shown in the figure) were twisted N strands (N = 2 to 8) of strands 12 in which a plurality of strands 11, preferably 5 to 49 strands 11 were twisted together. It consists of a rubber-steel cord composite reinforced with a steel cord having a double twist structure (see FIG. 2).

  That is, in the present invention, as a circumferential crown reinforcing layer 3 of at least two layers, a strip using a steel cord that is wave-shaped in two dimensions and a strip using a steel cord having a double twist structure, At least one layer each is applied, and a circumferential crown reinforcing layer is formed by a combination of strips using two different types of steel cords. Among these, in the circumferential crown reinforcement layer using a steel cord having a double twist structure, the cord itself stretches appropriately, so that the shear strain generated thereby can be alleviated, and as a result, this shear strain is caused. The effect of preventing the occurrence of separation can be obtained.

  In addition, when all the circumferential direction crown reinforcement layers are made of steel cords having a double twist structure, the unit price in production increases, which is not preferable in terms of cost. Therefore, in the present invention, productivity and durability are achieved by using a steel cord (steel filament), which is two-dimensionally wavyly shaped to ensure sufficient strength and rigidity with a small amount of steel cord, together with the steel cord having the above-mentioned double twist structure. It is compatible with sex.

  In addition, in the two-dimensional corrugated steel cord, the steel cord is corrugated by secondary processing, so that there is a problem that the wire is deformed and is easily broken by repeated input. However, the steel cord layer has a problem that the fracture durability is not sufficient. On the other hand, since the latter steel cord is formed only by twisting, it is strong against repeated input, and the former steel cord has a fracture durability. Is excellent. Therefore, in the present invention, by combining the circumferential crown reinforcing layers using these two types of steel cords, it is possible to obtain the effect of synergistically improving each performance while covering the respective difficulties.

As for the steel cord having the above-mentioned double twist structure, as shown in FIG. 2, the diameter of the strand 12 is d (mm), the circumscribed circle diameter of the cord is D (mm), and the twisting pitch of the cord is P (mm). When the following formula,
ε _c = √ (−b / 2 + √ (b ² / 4−c)) − 1
(In the formula, b is −1 + π ² (−4R ² + d ² ) / P ² , c is π ² d ² k (4π ² R ² + P ² ) / P ⁴ , R is (D−d) / 2, k Ε _c defined by tan ² (π / 2−π / N) preferably satisfies ε _c ≧ 0.005, particularly ε _c ≧ 0.010.

  As a result, as shown in the drawing, at least one gap is formed between the N strands 12 in the steel cord, and in the illustrated example, all the strands 12 are formed with a certain gap or more in a matrix such as rubber. Since there is a gap between the strands 12 even when buried in the strand (so-called open structure), the stiffness of the cord is low when the matrix is in a soft state, and up to a certain degree of strain against the tensile strain on the cord Can be easily stretched. Therefore, it becomes easy to mold the product, and the grace period at the time of vulcanization expansion at the time of manufacturing the tire becomes large, so that there is an advantage that the manufacturing is easy.

  On the other hand, if the fluidity of the matrix is reduced like rubber after vulcanization, even if there is a gap between the strands 12 as described above, the steel cord cannot be deformed like a coil spring to reduce this gap, The rigidity of steel will be demonstrated as if there is no gap. For this reason, the tensile rigidity of the steel cord of the present invention when it becomes a product is hardly affected by the magnitude of strain applied to the steel cord in the processing step, and always has high rigidity. Further, in the product, a state where a gap remains between the strands is preferable in terms of fatigue, but as described above, in the cord of the present invention, the strands 12 are in close contact with each other even in such a state. Compared to the above, the tensile rigidity is not greatly reduced.

  In the two-dimensional corrugated steel cord, the elongation at the time of expansion is secured by corrugation. In the present invention, the two-dimensional corrugated steel cord is arranged at the same time as the initial elongation of the steel cord having the double twist structure. This makes it possible to inherit the conventional ease of manufacturing as it is.

Further, in the present invention, when the length of one wavelength in the two-dimensional wave-shaped steel cord is λ (mm) and the net cord length for one wavelength is L (mm), the following formula:
ε _w = L / λ−1
(Where L is the following formula,
L = λ × (1 + 2 /8 × K 2 + 13/64 × K 4 + 90/512 × K 6 + 644/4096 × K 8 + 4708.5 / 32768 × K 10)
(Where K = (b / (1 + b)) ^0.5 , b = (2π × a / λ) ² , where a is the amplitude amount (mm) of the wave-shaped imprinting portion)) being defined epsilon _w may satisfy the epsilon _w ≧ 0.005. Thereby, the effect at the time of absorbing the expansion at the time of tire vulcanization and making it easy to manufacture is obtained.

Furthermore, in the present invention, the steel cord having the double twist structure and the steel cord having a two-dimensional wave shape are represented by the following equations: ε _c and ε _w
1.15 ≧ ε _c / ε _w ≧ 0.85
It is preferable to make the combination satisfying the above, and by this, the elongation at the time of expansion of the steel cord having the double twist structure and the steel cord having a two-dimensional wave shape becomes equivalent.

Furthermore, the steel cord having the above-mentioned double twist structure and the two-dimensional corrugated steel cord are represented by the following equations: ε _c and ε _w
0.040 ≧ ε _c ≧ 0.010 and 0.040 ≧ ε _w ≧ 0.010
It is also preferable to make the combination satisfying the above, thereby obtaining the effect of achieving both tire durability and ease of manufacture.

  In the present invention, the circumferential crown reinforcing layer 3 has two or more layers, and a strip using a two-dimensional corrugated steel cord and a strip using a steel cord having a double twist structure are applied at least one layer each. Any circumferential crown reinforcing layer made of a steel cord having a double twist structure is preferably arranged on the outer side in the tire radial direction of the circumferential crown reinforcing layer made of a two-dimensional corrugated steel cord. By disposing a circumferential crown reinforcing layer made of a steel cord having a double twist structure on the outer side in the tire radial direction, an effect of improving durability against repeated input can be obtained.

  In the present invention, the circumferential crown reinforcing layer 3 provided in at least two layers among the reinforcing belts only needs to satisfy the above-mentioned conditions, and thereby the desired effect can be obtained. As described above, at least one layer composed of a rubber-steel cord composite having an inclination angle of 20 to 50 ° with respect to the tire circumferential direction on the outer side in the tire radial direction of the circumferential crown reinforcing layer 3, in the illustrated example, two layers The width direction crown reinforcing layer 2 is disposed. The combination of the width direction crown reinforcing layer 2 and the circumferential direction crown reinforcing layer 3 can increase both the width direction and the circumferential direction rigidity of the crown portion.

  In particular, the present invention is useful when applied to a truck / bus (TBR) tire that is used at a high internal pressure and has a high circumferential tension at the crown.

  In the pneumatic radial tire of the present invention, only the combination of the steel cords with the specific structure is applied as the circumferential crown reinforcing layer, and the specific cord diameter, twist pitch, and cord in each reinforcing belt are important. In addition to the number of shots, the specific tire structure, material, and the like can be set as appropriate according to conventional methods, and are not particularly limited.

Hereinafter, the present invention will be described in more detail with reference to examples.
As shown in FIG. 1, truck radial tires having four layers of reinforcing belts 2a, 2b, 3a, 3b on the outer periphery of the carcass 1 were produced according to the conditions shown in Table 1 below. The tire size was 495 / 45R225. For the reinforcing belts 2a and 2b, two width direction crown reinforcing layers made of a rubber-steel cord composite having an inclination angle of ± 45 ° with respect to the tire circumferential direction were arranged.

  Each test tire obtained was subjected to 70,000 km at a speed of 60 km / h under a load condition of 120% of normal internal pressure and normal load, and after performing a drum durability test, the presence or absence of separation was checked by holography inspection. Observed. The results are also shown in Table 1 below.

＊１）図４に示すコード構造（波長：λ、振幅：ａ）。
＊２）図２に示すコード構造。
＊３）図３に示すコード構造。
＊４）ストランド間に、少なくとも一箇所ゴムが侵入可能な隙間が存在するよう撚り合わされた構造。

* 1) Cord structure shown in FIG. 4 (wavelength: λ, amplitude: a).
* 2) The code structure shown in FIG.
* 3) The code structure shown in FIG.
* 4) A structure in which strands are twisted together so that there is a gap where the rubber can enter at least one place.

  As shown in Table 1 above, in the tire of the example in which a circumferential crown reinforcing layer to which a specific two-dimensional corrugated steel cord and a double-strand structure steel cord are applied is arranged in the tire crown portion, generation of separation occurs. Has been confirmed to be well prevented.

It is an expanded partial sectional view showing the tread part neighborhood of the pneumatic radial tire of one suitable example of the present invention. It is sectional drawing which shows one structural example of the steel cord of the double twist structure which concerns on this invention. It is sectional drawing which shows the other structural example of the steel cord of the double twist structure which concerns on this invention. It is sectional drawing which shows one structural example of the two-dimensional corrugated steel cord based on this invention.

Explanation of symbols

1 Carcass 2 (2a, 2b) Width direction crown reinforcing layer
3 (3a, 3b) Width direction crown reinforcement layer
10 Pneumatic radial tire 11 Strand 12 Strand

Claims (7)

Pneumatic having at least a pair of carcass extending in a toroid shape across at least a pair of bead cores and having 3 to 6 layers of reinforcing belts having a plurality of cords or filaments as reinforcing elements on the outer periphery of the carcass In radial tires,
At least two of the reinforcing belts are circumferential crown reinforcing layers formed of a strip formed by orienting a rubber-steel cord composite as a whole along the tire circumferential direction, and at least one of the strips. Is composed of a rubber-steel cord composite reinforced with a steel cord that is wave-shaped in two dimensions, and the remaining one or more layers are N strands in which a plurality of strands are twisted (N = 2-8) A pneumatic radial tire comprising a rubber-steel cord composite reinforced with a steel cord having a twisted double twist structure. In the steel cord having the double twist structure, when the diameter of the strand is d (mm), the circumscribed circle diameter of the cord is D (mm), and the twisting pitch of the cord is P (mm),
ε _c = √ (−b / 2 + √ (b ² / 4−c)) − 1
(Wherein, b is ^{-1 + π 2 (-4R 2 +} d 2) / P 2, c is ^{π 2 d 2 k (4π 2} R 2 + P 2) / P 4, R is (D-d) / 2, k a pneumatic radial tire according to claim 1, wherein epsilon _c is defined, that satisfy the epsilon _c ≧ 0.005 by represents ^{tan 2 (π / 2-π} / N)). In the two-dimensional corrugated steel cord, when the length of one wavelength is λ (mm), and the net cord length for one wavelength is L (mm), the following formula:
ε _w = L / λ−1
(Where L is the following formula,
L = λ × (1 + 2 /8 × K 2 + 13/64 × K 4 + 90/512 × K 6 + 644/4096 × K 8 + 4708.5 / 32768 × K 10)
(Where K = (b / (1 + b)) ^0.5 , b = (2π × a / λ) ² , where a is the amplitude amount (mm) of the wave-shaped imprinting portion)) a pneumatic radial tire according to claim 1 or 2, wherein defined as epsilon _w is, satisfies epsilon _w ≧ 0.005. The steel cord of the double twist structure and the steel cord of the two-dimensional wave shape, the ε _c and ε _w are the following formulas:
1.15 ≧ ε _c / ε _w ≧ 0.85
The pneumatic radial tire according to claim 3, comprising a combination satisfying The steel cord having the double twist structure and the two-dimensional corrugated steel cord are represented by the following equations: ε _c and ε _w
0.040 ≧ ε _c ≧ 0.010 and 0.040 ≧ ε _w ≧ 0.010
The pneumatic radial tire according to claim 3 or 4, comprising a combination satisfying   The circumferential direction crown reinforcement layer which consists of the steel cord of the double twist structure is arrange | positioned in the tire radial direction outer side of the circumferential direction crown reinforcement layer which consists of the said two-dimensional corrugated steel cord. The pneumatic radial tire according to item.   The at least 1 width direction crown reinforcement layer which consists of a rubber-steel cord composite which makes the inclination angle of 10-40 degrees with respect to a tire peripheral direction is provided in the tire radial direction outside of the peripheral direction crown reinforcement layer. The pneumatic radial tire according to any one of 6.

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