JP5937395B2 - 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 and high-speed 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 of “cord” are used, and the steel cords in these belt layers intersect each other.

  In recent years, the importance of environmental performance has increased, and there is an increasing need for weight reduction in rubber articles and tires using steel cords as reinforcing members. One technique for reducing the weight of the tire is to reduce the amount of rubber used in the belt treat and to make the belt thinner. However, if the amount of rubber used is reduced, the distance between the cords of the first belt layer and the second belt layer is shortened, so that the rubber peeling starting from the cord end at the end in the belt width direction easily propagates between the cords. In other words, so-called belt edge separation (BES) is likely to occur, and durability is reduced. As a method for improving this BES, a method of making the rubber at the end of the belt thicker than usual is known, but naturally, it increases the weight, which is contrary to the intended weight reduction of the tire. .

  As a technique for reducing the weight of the tire other than reducing the amount of rubber used in the belt treat, it is conceivable to reduce the amount of steel used, for example, to reduce the number of driven steel cords. However, if the number of steel cords to be driven is reduced, the rigidity of the belt is lowered, which is not preferable. Under such circumstances, many proposals have been made regarding weight reduction and durability improvement of tires. For example, Patent Document 1 proposes a steel cord having an N (N = 2 to 5) + M (M = 1 to 3) structure and the number of filaments N ≧ M for the purpose of reducing the weight of the tire. Patent Document 2 proposes a steel cord having a 2 + 3 structure for the purpose of improving the durability of the belt. In addition to these, Patent Documents 3 to 7 propose steel cords having a 2 + 3 structure for the purpose of improving various physical properties and workability required as tire reinforcing materials.

JP 2001-98480 A Japanese Utility Model Publication No. 3-128689 JP-A-6-306784 Japanese Patent Laid-Open No. 7-126992 JP 2001-98460 A JP 2006-328557 A JP 2007-63706 A

  However, even with the steel cord described in Patent Document 1, it is difficult to say that the demand for reducing the weight of tires required today is sufficiently satisfied, and a technique for further weight reduction is required. Moreover, although the steel cord of patent document 2 is improving durability by improving the permeability | transmittance of the rubber with respect to a steel cord, the weight reduction of a tire is not examined. Furthermore, even in the steel cords described in Patent Documents 3 to 7, the current situation is that the study on weight reduction of tires is not always satisfactory. In other words, regarding the weight reduction of the tire, as described above, it is effective to reduce the diameter of the steel cord that is the reinforcing material of the belt and to reduce the number of steel filaments. Since it falls, high-speed durability will fall. Thus, it is difficult to achieve both weight reduction and high-speed durability of the tire while maintaining the durability of the tire.

  Accordingly, an object of the present invention is to provide a pneumatic radial tire that achieves weight reduction without deteriorating durability and high-speed durability.

  As a result of intensive studies on the structure of the belt in order to solve the above-mentioned problems, the present inventors have confirmed that the diameter of the core filament and the sheath filament satisfies a predetermined relationship in the steel cord of 2 + N structure, and the steel cord is The present inventors have found that the above-mentioned problems can be solved by adopting a structure, and have 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 that forms a portion; and a belt that is disposed between the tread portion and the crown region of the carcass and forms a reinforcing portion, and a belt composed of at least two belt layers.
The first belt layer of the first layer and the second belt layer of the second layer of the belt were both twisted around the core and the core in which the two core filaments were arranged in parallel without being twisted. Steel cords consisting of three sheath filaments are juxtaposed in the belt width direction and embedded in the coating rubber,
When the diameter of the core filament is d1 and the diameter of the sheath filament is d2, d1> d2, and the long diameter of the circumscribed rectangle of the steel cord is L1, the short diameter is L2, and all the filaments constituting the steel cord When the sum of the cross-sectional areas of S is S,
η (%) = S / (L1 × L2) × 100
The steel filling rate η (%) defined by the above is always greater than 43.7 and 78.5 or less.

  In the present invention, the steel filling rate η (%) is preferably greater than 45.8 and not greater than 71.3. In the present invention, it is preferable that the d1 is 0.16 to 0.28 mm, and the d2 is 0.12 to 0.24 mm. Furthermore, in the present invention, the gauge of the rubber layer between the steel cords of the first belt layer and the second belt layer at the end of the second belt layer is preferably larger than the gauge at the tire center. Moreover, in this invention, it is preferable that the thickness of the said belt layer is 0.85-1.20 mm.

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

It is a half sectional view of a suitable example of the pneumatic radial tire of the present invention. It is a comparison figure of the short diameter of a steel cord, (a) shows the case where d1 = d2, and (b), (c), and (d) show the case of d1> d2. It is explanatory drawing for demonstrating steel filling rate (eta) (%), (a) is sectional drawing of the conventional steel cord, (b) is sectional drawing of the steel cord concerning this invention. FIG. 3 is an enlarged partial cross-sectional view showing the vicinity of an end portion of a belt layer according to a preferred embodiment of the pneumatic radial tire of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, the one-side sectional view of the suitable example of the pneumatic radial tire of this invention is shown. 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, both the first belt layer 5a and the second belt layer 5b are arranged in parallel without twisting two core filaments, and N (2 ≦ N ≦) twisted around the core. 4) A steel cord comprising three, preferably three sheath filaments, is embedded in the coating rubber in parallel in the belt width direction so that the long diameter of the steel cord is in the belt width direction, and When the diameter of the core filament is d1 and the diameter of the sheath filament is d2, d1> d2. FIGS. 2A to 2D are comparative diagrams of the short diameters of the steel cords. FIG. 2A shows a case where d1 = d2, and FIGS. 2B to 4D show cases where d1> d2. As shown in the figure, the short diameter of the steel cord 10 having the 2 + N structure is governed by the diameter of the sheath filament 12. Accordingly, by making the diameter d2 of the sheath filament 12 smaller than the diameter d1 of the core filament 11, the short diameter of the steel cord 10 can be reduced. As a result, since the distance between the steel cord of the first belt layer and the steel cord 10 of the second belt layer can be increased, the durability of the belt can be improved. Moreover, since d1> d2, the amount of steel used can be reduced, leading to weight reduction of the tire.

In the steel cord 10 according to the present invention, the steel filling rate η (%) is greater than 43.7 and equal to or less than 78.5. FIG. 3 is an explanatory view for explaining the steel filling rate η (%), (a) is a sectional view of a conventional steel cord, and (b) is a sectional view of a steel cord according to the present invention. The steel filling rate η (%) is expressed by the following formula, where the long diameter of the circumscribed square of the steel cord 10 is L1, the short diameter is L2, and the sum of the cross-sectional areas of all the filaments constituting the steel cord 10 is S.
η (%) = S / (L1 × L2) × 100
Defined by The steel cord of 2 + N structure has a higher steel filling rate η (%) than the steel cord of 1 × N structure. For this reason, the steel cord of 2 + N structure has higher rigidity per cord, and the rate of circumferential rigidity is excellent. Therefore, high-speed durability can be improved by adopting a steel cord having a 2 + N structure as a reinforcing material for the belt.

  Further, as shown in FIG. 3A, in the conventional steel cord 10 having the 2 + N structure (in the illustrated example, the 2 + 3 structure), since d1 = d2, two core filaments 11 arranged in parallel are arranged. On the other hand, when the sheath filaments 12 are arranged in parallel, regions where the steel is not filled are formed on both sides of the two core filaments 11, and the steel filling rate η (%) is lowered. However, as shown in FIG. 3 (b), the steel cord 10 according to the present invention is arranged in parallel in order to satisfy the relationship that the diameter of the core filament 11 and the diameter of the sheath filament 12 are d1> d2. Even when the sheath filament 12 is arranged in parallel to the core filament 11, the steel filling rate η (%) is not greatly reduced.

  In the steel cord 10 according to the present invention, the steel filling rate η (%) is always greater than 43.7 and equal to or less than 78.5. In the steel cord 10 according to the present invention, two core filaments 11 are arranged in parallel without being twisted, and N (2 ≦ N ≦ 4) sheath filaments 12 are twisted around this. The steel filling rate η is different for each cross section of the steel cord 10. In the steel cord according to the present invention, the steel filling rate η (%) always satisfies the above range. Thereby, the outstanding code | symbol rigidity can be exhibited. When the steel filling rate η (%) is 43.7 or less, sufficient cord rigidity cannot be obtained. The upper limit of the steel filling rate η (%) is set to 78.5 because it is the theoretical maximum value in the steel cord of the 2 + N structure (2 ≦ N ≦ 4). Preferably it is greater than 45.8 and less than 71.3.

  In the present invention, it is preferable that the cords constituting the first belt layer and the second belt layer are cross belts laminated so as to intersect each other with the equator plane interposed therebetween. Further, a belt layer may be provided on the outer side in the tire radial direction of the first belt layer and the second belt layer, and a circumferential belt comprising a rubberized layer of cords arranged substantially parallel to the tire circumferential direction. A layer may be provided. As such a cord, a cord made of organic fiber can be suitably used. For example, a cord made of polyester fiber, nylon fiber, aramid fiber, or polyketone fiber can be suitably used.

  In the present invention, the diameter d1 of the core filament 11 is preferably 0.16 to 0.28 mm, and the diameter d2 of the sheath filament 12 is preferably 0.12 to 0.24 mm. If the filament diameter exceeds the above range, a sufficient light weight effect may not be obtained. On the other hand, if the filament diameter is less than the above range, the belt strength may be insufficient.

FIG. 4 is an enlarged partial cross-sectional view showing the vicinity of an end portion of a belt layer according to a preferred embodiment of the pneumatic radial tire of the present invention. As illustrated, in the present invention, the gauge H _E of the rubber layer between the steel cord 6 between the first belt layer 5a and the second belt layer 5b in the second belt layer 5b ends, the gauge in the tire center portion H It is preferable that it is larger than _C. Preferably 1.3 to 3.0 times _{H E} is the _{H C} is preferably 1.8 to 2.6 times. By disposing the thick gauge inter-belt rubber 7 at the belt end, the belt durability can be further improved. If this value is less than 1.3 times, such an effect cannot be sufficiently obtained. On the other hand, if it exceeds 3.0 times, the weight of the tire may not be sufficiently reduced.

  Furthermore, in the present invention, from the viewpoint of weight reduction and durability improvement of the tire, the belt layer thicknesses t1 and t2 are preferably 0.85 to 1.20 mm, more preferably 0.95 to 1.2. 10 mm. If the thickness of the belt layer is less than 0.85 mm, 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 cannot be obtained.

  Furthermore, in the present invention, the number of steel cords driven into the belt is preferably 28-57 / 50 mm. When the number of driving is less than the above range, there is a concern of insufficient tensile strength or a decrease in belt rigidity. On the other hand, when the number of driving is larger than the above range, it is difficult to secure the cord interval, it becomes difficult to effectively suppress the BES, and there is a concern that the belt durability is lowered.

In the present invention, it is preferable to use a steel filament having a tensile strength of 2700 N / mm ² or more in order to ensure belt strength. As the steel filament 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 present invention, the conditions such as the twist direction and twist pitch of the sheath filament are not particularly limited, and can be appropriately configured according to a conventional method.

  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. Further, the pneumatic radial tire of the present invention can be suitably used for a passenger car tire. In addition, as gas with which a tire is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Examples 1-2, Comparative Examples 1-7, and Reference Examples 1-3>
Tires having a tire size of 195 / 65R15 were manufactured using steel cords having structures shown in Tables 1 to 3 as belt reinforcements. The belt was composed of three belt layers, and steel cords shown in Tables 1 to 3 below were applied to the first belt layer and the second belt layer. The steel cord driving angle was ± 26 ° with respect to the tire circumferential direction. Further, as the outermost layer belt layer, a circumferential belt composed of a rubberized layer of organic fiber cords arranged substantially parallel to the tire circumferential direction was disposed. About each obtained tire, according to the following procedure, high-speed durability, durability (cord fatigue), and tire weight were evaluated.

<High speed durability>
Each test tire was mounted on a standard rim defined by the JATMA standard, and then the step speed method was performed in accordance with the test method of the JATMA standard to measure the speed at which the tire failure occurred. Examples 1 and 2 and Comparative Examples 2 and 3 compare Comparative Example 1, Example 3 and Comparative Example 5 compare Comparative Example 4, Examples 4, 5 and Comparative Example 7 compare Comparative Example 6, and at the same speed. The case where the failure occurred was evaluated as ◯, and the case where the failure occurred at a lower speed than the tire of Comparative Example 1 was evaluated as ×. The obtained results are also shown in Tables 1-3.

<Cord fatigue>
After mounting each test tire on the standard rim specified in JATMA standard, load a load 1.05 times the normal load, fill the internal pressure of 100 kPa, and provide a vehicle equipped with an autopilot system capable of turning in figure 8 Then, after running 300 laps in a figure 8 turning test course at a turning acceleration of 0.7 G and a speed of 25 km / h, the tires were dissected and the belt foldability was compared. Examples 1 and 2 and Comparative Examples 2 and 3 compare Comparative Example 1, Example 3 and Comparative Example 5 compare Comparative Example 4, Examples 4, 5 and Comparative Example 7 compare Comparative Example 6, When indexed with the occurrence rate of fracture as 100, less than 100 was evaluated as ◯ (good), 100 or more and less than 110 as Δ (equivalent), and 110 or more as x (bad). The results are shown in Tables 1-3. The smaller this value, the better the cord fatigue.

<Tire weight>
The weight per tire was measured. On the basis of the tire of Comparative Example 1, the case where it was reduced by 100 g or more was evaluated as ○, and the case where it was less than 100 g was evaluated as ×. The results are shown in Tables 1-3.

<Comprehensive evaluation>
In the evaluation of high-speed durability, durability, and tire weight reduction, the case where there was no x was evaluated as ◯, the case where only ○ and △ were included, the case where there was only a triangle, △, and the case where there was an x.

  From Tables 1 to 3, it was confirmed that the pneumatic radial tire of the present invention can reduce the weight of the tire without reducing durability and high-speed 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 Steel cord 7 Rubber between belts 10 Steel cord 11 Core filament 12 Sheath filament

Claims (5)

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; A pneumatic radial tire comprising a belt composed of at least two belt layers, which is disposed between the crown region of the carcass and forms a reinforcing portion.
The first belt layer of the first layer and the second belt layer of the second layer of the belt were both twisted around the core and the core in which the two core filaments were arranged in parallel without being twisted. Steel cords consisting of three sheath filaments are juxtaposed in the belt width direction and embedded in the coating rubber,
When the diameter of the core filament is d1 and the diameter of the sheath filament is d2, d1> d2, and the long diameter of the circumscribed rectangle of the steel cord is L1, the short diameter is L2, and all the filaments constituting the steel cord When the sum of the cross-sectional areas of S is S,
η (%) = S / (L1 × L2) × 100
A pneumatic radial tire characterized in that a steel filling rate η (%) defined by the formula (1) is always greater than 43.7 and equal to or less than 78.5.   The pneumatic radial tire according to claim 1, wherein the steel filling rate η (%) is greater than 45.8 and equal to or less than 71.3.   The pneumatic radial tire according to claim 1 or 2, wherein the d1 is 0.16 to 0.28 mm and the d2 is 0.12 to 0.24 mm. The pneumatic according to any one of claims 1 to 3 , wherein a gauge of a rubber layer between steel cords of the first belt layer and the second belt layer at an end portion of the second belt layer is larger than a gauge at a tire central portion. Radial tire. The pneumatic radial tire according to any one of claims 1 to 4 , wherein the belt layer has a thickness of 0.85 to 1.20 mm.

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