JP6022752B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire (hereinafter also simply referred to as “tire”), and more particularly, to a pneumatic radial tire that achieves weight reduction without reducing durability.

  At present, a belt generally used as a reinforcing member for a carcass forming a skeleton of a radial tire for a passenger car, particularly a reinforcing member for a crown portion of a carcass, is mainly a steel cord (hereinafter simply referred to as “ Two or more steel belt layers made of a rubberized layer (also referred to as “cord”) are used, and the steel cords in these belt layers intersect each other.

  Conventionally, various studies have been made on improvement of the belt layer. For example, Patent Document 1 discloses a technique for improving the durability of a belt by forming a bundle of reinforcing elements within several bundles and driving the bundle with constant dispersion. Further, in Patent Document 2, by using a steel cord having a (1 × 2) structure as a belt reinforcing material, separation (BES) generated at the belt end can be suppressed, and the weight of the tire can be reduced. That is disclosed.

JP-A-5-213007 Japanese Patent Laid-Open No. 62-234922

  In recent years, with higher performance of automobiles, higher performance has been required for tires. In addition, weight reduction of tires has become an important issue in order to improve automobile fuel efficiency. Under such circumstances, the belt structures described in Patent Documents 1 and 2 are not necessarily sufficient in terms of tire durability and light weight.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire that achieves weight reduction without reducing durability.

  As a result of intensive studies on the structure of the belt in order to solve the above problems, the present inventor has found that the above problems can be solved by adopting the following configuration, and has completed the present invention.

That is, the pneumatic radial tire of the present invention is disposed on the outer side in the tire radial direction of the carcass formed of at least one carcass layer straddling a toroidal shape between a pair of left and right bead cores, and in the crown region of the carcass. In a pneumatic radial tire comprising a tread portion forming a portion, and a belt composed of at least two belt layers that are disposed between the tread portion and the crown region of the carcass to form a reinforcing portion,
When the reinforcing material constituting the belt layer is a bundle in which two steel cords are aligned without shifting the phase, and the diameter of the steel filament constituting the steel cord is a (mm), the belt The interlayer gauge of the layer is increased by more than a / 4 (mm) as an expected value from the interlayer gauge represented by using the circumscribed circle of the cord, and two steel cords in at least a part of the bundle have a circumscribed circle. By being arranged a / 4 (mm) or more closer than the width expressed, it has an interval between bundles where the distance between adjacent bundles increases by a / 4 or more,
The steel cord has a (1 × 2) structure.

In the present invention, the thickness of the belt layer is preferably greater than 0.70 mm and less than 1.20 mm, the steel filament diameter is preferably 0.24 to 0.26 mm, and the steel layer The tensile strength T (MPa) before the filament strand is expressed by the following formula:
T ≧ 4400-3460 × a
It is preferable to satisfy the relationship represented by:

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic radial tire which implement | achieved weight reduction without reducing durability can be provided.

It is a half sectional view showing a pneumatic radial tire of one suitable example of the present invention. It is sectional drawing which shows the example of a change of the cross section of a bundle at the time of making two cords of (1 * 2) structure into a bundle. It is sectional drawing which shows the example of the change of the cross section of a bundle at the time of making two cords of the (1 + 1) structure into a bundle. It is an example of the fragmentary sectional view of the belt of the pneumatic radial tire of FIG. It is explanatory drawing for calculating the expected value of the increase amount of an interlayer gauge at the time of making two cords of (1 × 2) structure into a bundle. It is explanatory drawing for calculating the expected value of the increase amount of an interlayer gauge at the time of making two cords of (1 × 2) structure into a bundle. It is a schematic sectional drawing for demonstrating the bundle width | variety at the time of making two cords of the (1x2) structure into a bundle.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 shows a pneumatic radial tire according to an embodiment of the present invention. The illustrated tire includes a tread portion 1 that is disposed in a crown region of the carcass and forms a ground contact portion, and a pair of sidewall portions 2 that extend continuously inward in the tire radial direction on both sides of the tread portion 1; A bead portion 3 is provided on the inner peripheral side of each sidewall portion 2.

  The tread portion 1, the sidewall portion 2, and the bead portion 3 are reinforced by a carcass 4 including a single carcass layer extending in a toroidal shape from one bead portion 3 to the other bead portion 3. The tread portion 1 has at least two layers disposed in the tire radial direction outside of the crown region of the carcass 4, which will be described in detail below, and in the illustrated example, two layers of the first belt layer 5a and the second belt layer 5b. It is reinforced by a belt consisting of Here, a plurality of carcass layers of the carcass 4 may be used, and an organic fiber cord extending in a direction substantially orthogonal to the tire circumferential direction, for example, an angle of 70 to 90 ° can be suitably used.

  In the present invention, the reinforcing material constituting the first belt layer 5a and the second belt layer 5b is a bundle in which two cords are aligned without being twisted. By making the reinforcing material into a bundle of two cords, the spacing between the reinforcing materials in the belt layer becomes wider than when the cords are not bundled, and the rubber peeling starting from the end of the cord in the belt width direction is started. Belt edge separation that easily propagates between adjacent cords can be suppressed. Further, in the present invention, when all the steel filaments constituting the cord (hereinafter also simply referred to as “filaments”) have the same filament diameter and the diameter is a (mm), the belt interlayer gauge is The expected value is a / 4 (mm) or more, preferably 4a / 11 (mm) higher than the interlayer gauge expressed using the circumscribed circle of the cord. 2 (a) to 2 (c), when two cords of (1 × 2) structure are used as a bundle 6 as a reinforcing material for the belt layer, FIGS. 3 (a) to 3 (c) are (1 + 1) structures. It is a figure which shows the example of the change of the cross section of the cord bundle when two cords are made into the bundle 16, First, the change of a cord diameter is demonstrated using these.

  Usually, the cord diameter Dc is represented by the diameter of the circumscribed circle 8 of the filament 7 as shown in FIG. However, since the cord having the (1 × 2) structure is a cord in which two filaments 7 are twisted, the position of the filament 7 continuously changes within the cord (inside the circumscribed circle 8). For example, when the position of the filament 7 changes by 45 ° as shown in FIGS. 2B and 2C, the actual cord diameter in the horizontal direction decreases from the circumscribed circle 8. The same applies to the cord of the (1 + 1) structure, and as shown in FIGS. 3A to 3C, when the position of the filament 17 is changed by 45 ° as shown in FIGS. 3B and 3C, The actual cord diameter in the horizontal direction is smaller than the circumscribed circle 18.

4 is a partial cross-sectional view of an example of the tire belt shown in FIG. 1. In the illustrated example, the reinforcing material is a bundle of two cords having a (1 × 2) structure. Usually, the interlayer gauge H ₀ of the first belt layer 5a and the second belt layer 5b is represented by the distance of the circumscribed circle of each cord constituting the belt layer. However, as described above, the actual cord diameter changes continuously. For this reason, the distance between the cords constituting the first belt layer 5a and the cord constituting the second belt layer 5b, that is, the actual interlayer gauge H is also continuously changed. In the present invention, the interlayer gauge H is increased a / 4 (mm) or more as the expected value than that of the interlayer gauge H ₀ representing using a circumscribed circle of the code. Therefore, the rubber gauge can be made thin while maintaining the thickness of the interlayer gauge, and the weight of the tire can be reduced.

Here, a method of calculating the expected value of the increase amount of the interlayer gauge H will be described. 5 and 6 are explanatory diagrams for calculating the expected value of the increase amount of the interlayer gauge H. FIG. In the figure, 26a represents a bundle in the first belt layer, and 26b represents a bundle in the second belt layer. First, as shown in FIG. 5A, the cords in the bundle 26a in the first belt layer and the bundle 26b in the second belt layer are designated as a cord X and a cord Y, respectively. Next, in the vertical direction, a state in which the distance between the circumscribed circles of the cord X and the cord Y (interlayer gauge H ₀ ) and the interfilament distance of the cord X and the cord Y are equal is the basic state of the cord X and the cord Y ( FIG. 5A). FIGS. 5A to 5H show cross-sectional shapes when the cord X is rotated by 45 ° from the basic state when the cord X rotates 360 ° at one pitch, for example. Referring to FIG. 5B, by rotating the code X by 45 ° from the basic state, the actual interlayer gauge H of the code X and the code Y increases by xz ₂ from H ₀ . Further, when the code X is rotated by 45 ° (FIGS. 5C to 5H), the actual increase in the interlayer gauge H between the code X and the code Y changes by xz _{3 to} xz ₈ . Note that xz ₁ and xz ₅ in the basic state (FIG. 5A) and the state rotated by 180 ° from the basic state (FIG. 5E) are 0.

Similarly, for the code Y, when the code Y rotates 360 ° at one pitch, the cross-sectional shapes when the code Y is rotated by 45 ° are shown in FIGS. 6A to 6H, respectively. As shown in the drawing, by rotating the code Y by 45 ° from the basic state (FIG. 6A), the actual interlayer gauge H of the code X and the code Y is increased by yz ₂ from H ₀ (FIG. 6 ( b)). Further, when the angle is rotated by 45 ° (FIGS. 6C to 6H), the actual increase in the interlayer gauge H of the code X and the code Y changes by yz _{3 to} yz ₈ .

により、層間ゲージの増加量の期待値を算出する。なお、コード構造が（１×２）構造を例として説明したが、（１＋１）構造のコードについても同様の手順で層間ゲージの期待値を算出することができる。 Up to this point, the case where the code X and the code Y are rotated by 45 ° as an example has been described as a method for calculating the increase amount of the interlayer gauge, but in the present invention, the code is calculated based on the same concept. When X and code Y rotate 360 ° at one pitch, code X and code Y are rotated by 1 ° from the basic state, and xz _{1 to} xz ₃₆₀ and yz _{1 to} yz ₃₆₀ are obtained. Based on the obtained value, the following formula:

Thus, an expected value of the increase amount of the interlayer gauge is calculated. Although the code structure has been described by taking the (1 × 2) structure as an example, the expected value of the interlayer gauge can be calculated in the same procedure for the code having the (1 + 1) structure.

  Furthermore, in the tire of the present invention, the actual bundle width is obtained by arranging two cords in at least a part of the cord bundle closer to a / 4 (mm) or more than the width represented by the circumscribed circle. Decreases by that amount, and there is a space between the bundles where the distance between adjacent bundles increases by a / 4 or more. FIGS. 7A and 7B are schematic cross-sectional views for explaining the bundle width when two cords having a (1 × 2) structure are bundled. Conventionally, when a bundle 36 in which two cords are aligned without being twisted, the bundle interval has been considered to be the sum of circumscribed circles 38 of the two cords. In the case of a cord having a (1 × 2) structure, as shown in FIG. 7A, when two cords in which two filaments 37 are twisted at the same pitch are bundled so that the phases match, The width of the cord bundle is the sum of the circumscribed circles 38 of the cord.

  However, as shown in FIG. 7B, the cord having the (1 × 2) structure has large irregularities, and therefore, when the cords of the two cords are bundled with the phase shifted, the circumscribed circle 38 of one cord becomes the cord of the other cord. It is possible to bite into the circumscribed circle 38. Therefore, the bundle width of the cord bundle 36 is smaller than the sum of the circumscribed circles 38 only in the region w where the circumscribed circles 38 overlap. As a result, since the interval between adjacent bundles is increased, the bundle interval can be increased even with the same number of driving, and the durability of the belt can be improved. In order to obtain this effect satisfactorily, the distance between adjacent bundles is preferably 30% or more, preferably 50% or more, between the bundles where the distance between adjacent bundles increases by a / 4 (mm) or more. is there. The same applies to a (1 + 1) structure code.

In the present invention, in order to ensure the durability of the belt, the bundle interval is preferably 0.7 mm. Further, since the distortion increases as the width of the cord bundle increases, the BES resistance may deteriorate. Therefore, in order to ensure BES resistance, the space ratio defined by the following formula,
Space ratio (%) = (true code interval) / (true bundle width) × 100
Is preferably 80% or more.

  In the present invention, it is preferable that the number of reinforcements to be driven into the belt is 35 to 65/50 mm. If the number of implantations is less than the above range, the tensile strength may not be ensured. On the other hand, when the number of implantations is larger than the above range, the bundle interval is narrowed, BES may be generated, and durability may be lowered.

  In the present invention, the thickness of the belt layer is preferably greater than 0.70 mm and less than 1.20 mm from the viewpoint of weight reduction and durability improvement of the tire. If the thickness of the belt layer is 0.70 mm or less, sufficient durability may not be obtained. On the other hand, if the thickness of the belt layer is 1.20 mm or more, a sufficient light weight effect may not be obtained. More preferably, it is 0.80 to 1.10 mm.

  Furthermore, in the present invention, the filament diameter of the filament constituting the cord is preferably 0.24 to 0.26 mm. If the filament diameter is less than 0.24, sufficient strength may not be exhibited. On the other hand, if the filament diameter is larger than 0.26, the belt becomes thick and a sufficient light weight effect may not be obtained.

In the present invention, the tensile strength T (MPa) before twisting of the filament constituting the cord is expressed by the following formula:
T ≧ 4400-3460 × a
It is preferable to satisfy the relationship represented by: If the tensile strength T does not satisfy the above relational expression, the belt strength may not be sufficiently obtained.

In the present invention, the conditions such as the twisting direction and twisting pitch of each filament are not particularly limited, and can be appropriately configured according to a conventional method depending on the application. Moreover, there is no restriction | limiting in particular about the material of a filament, However, A steel filament is suitable. As the steel filament, a tensile strength of 2700 N / mm ² or more can be suitably used. As the monofilament cord having a high tensile strength, one containing at least 0.72% by mass, particularly at least 0.82% by mass of carbon can be suitably used.

  In the pneumatic radial tire of the present invention, the specific tire structure other than that is not particularly limited as long as the belt structure satisfies the above requirements. Moreover, as gas with which this tire is filled, inert gas, such as nitrogen, argon, helium other than normal or the air which adjusted oxygen partial pressure, can be used.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Examples 1 to 12, Comparative Examples 1 to 8 and Conventional Examples>
A cord having the structure shown in Tables 1 to 4 below was used as a belt reinforcing material, and a tire of the type shown in FIG. 1 was manufactured with a tire size of 225 / 45R17 using the obtained belt reinforcing material. The driving angle of the belt reinforcing material was ± 26 ° with respect to the tire circumferential direction. About each obtained tire, riding comfort, durability, and tire weight were evaluated according to the following procedure.

<Belt weight>
The weight of the belt was obtained from the gauge of the belt layer and the number of driven steel cords. Observe the cross-section cord of the surface perpendicular to the tire circumferential direction, and calculate the distance between the center of the first layer cord and the center of the second layer cord as the belt layer thickness, and calculate from the number of cords driven and the gauge of the belt layer The volume of each was obtained by further multiplying the specific gravity of each. About the obtained numerical value, index evaluation was carried out by setting the tire of the conventional example to 100. A case where this value was 86 or less was marked as ◯. The results are also shown in Tables 1-4.

<Durability>
Each test tire was mounted on a standard rim defined in the JATMA standard, filled with an internal pressure corresponding to the maximum load capacity in JATMA YEAR BOOK, and mounted on a passenger car. After running on the paved road for 40000 km, the tire was dissected and the separation length of the belt end portion was investigated, and the index was evaluated with an index of 100 as a conventional example. The smaller this value, the better the durability. In addition, a case equivalent to the tire of the conventional example (index: 100 or more and 120 or less) is indicated by ◯, an excellent case (index is less than 100) is indicated by ◎, and a case where it is inferior (index is greater than 120) is indicated by ×. The results are also shown in Tables 1-4.

<Belt strength>
The belt strength is obtained by multiplying the number of cords driven into the belt by the strength of the cord. The conventional example was evaluated as 100. The case where this value was 90 or more was rated as “◯”, 85 or more and less than 90 as Δ, and less than 85 as “x”. If the index is 85 or more, there is no practical problem.

  From Tables 1 to 4, it was confirmed that the tires of the present invention can achieve light weight without reducing durability.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass 5a 1st belt layer 5b 2nd belt layer 6, 16, 26, 36 Bundle 7, 17, 37 Filament 8, 18, 38 circumscribed circle

Claims (4)

A carcass composed of at least one carcass layer straddling a pair of left and right bead cores in a toroidal shape, a tread portion disposed on the outer side in the tire radial direction of the crown region of the carcass, and a tread portion; In a pneumatic radial tire including a belt composed of at least two belt layers, which is disposed between the crown region of the carcass and forms a reinforcing portion,
When the reinforcing material constituting the belt layer is a bundle in which two steel cords are aligned without shifting the phase, and the diameter of the steel filament constituting the steel cord is a (mm), the belt The interlayer gauge of the layer is increased by more than a / 4 (mm) as an expected value from the interlayer gauge represented by using the circumscribed circle of the cord, and two steel cords in at least a part of the bundle have a circumscribed circle. By being arranged a / 4 (mm) or more closer than the width expressed, it has an interval between bundles where the distance between adjacent bundles increases by a / 4 or more,
A pneumatic radial tire characterized in that the steel cord has a (1 × 2) structure. The pneumatic radial tire according to claim 1, wherein the thickness of the belt layer is less than greater than 0.70 mm 1.20 mm. The pneumatic radial tire according to claim 1 or 2 , wherein the steel filament diameter is 0.24 to 0.26 mm. The tensile strength T (MPa) before the stranded wire of the steel filament is expressed by the following formula:
T ≧ 4400-3460 × a
The pneumatic radial tire according to any one of claims 1 to 3 , satisfying a relationship represented by:

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