JP2014008866A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire compatibly achieving improvement in durability and weight reduction.SOLUTION: A pneumatic radial tire includes a belt composed of at least two sheets of belt layers. Both of the first belt layer to be the first layer of the belt and the second belt layer to be the second layer are composed by arranging steel cords 10 composed of cores in which two core filaments 11 are arranged in parallel without being twined together and N (2≤N≤4) sheath filaments 12 twined together around the cores, in parallel in a belt width direction and burying the steel cords 10 in coating rubber. When a diameter of the core filament 11 is d1 and a diameter of the sheath filament 12 is d2, d1>d2 is satisfied, and a long diameter direction in a tire width direction cross section of at least one steel cord 10 of the steel cords 10 in the belt layers has an angle of ±45 to ±135° with respect to a tire width direction.

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 both improved durability and reduced weight.

  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.

  Therefore, an object of the present invention is to provide a pneumatic radial tire that achieves both improvement in durability and weight reduction.

  As a result of intensive studies on the structure of the belt in order to solve the above-mentioned problems, the present inventors set the diameter of the core filament and the sheath filament in the steel cord having the 2 + N structure and the arrangement position of the steel cord in the belt as predetermined. Thus, the present inventors have found that the above problems can be solved, 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 composed of N (2 ≦ N ≦ 4) sheath filaments and juxtaposed in the belt width direction are 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 major axis direction in at least one tire width direction cross section of the steel cord in the belt layer is It has an angle of ± 45 to ± 135 ° with respect to the tire width direction.

  In the present invention, the cord flatness ratio represented by the minor axis / major axis of the steel cord is preferably 0.56 to 0.95. In the present invention, it is preferable that the d1 is 0.16 to 0.32 mm, and the d2 is 0.12 to 0.29 mm.

  According to the present invention, it is possible to provide a pneumatic radial tire that achieves both improved durability and reduced weight.

It is a half sectional view of a suitable example of the pneumatic radial tire of the present invention. It is sectional drawing which shows the comparison of the short diameter of a steel cord, respectively, (a) represents the case where d1 = d2, and (b), (c) and (d) represent the case where d1> d2. It is an expanded partial sectional view of the belt of the pneumatic radial tire concerning the present invention. It is an expanded partial sectional view which shows the vicinity.

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) When a steel cord composed of two sheath filaments is juxtaposed in the tire width direction and embedded in the coating rubber, and the core filament diameter is d1 and the sheath filament diameter 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 11. Therefore, the short diameter of the steel cord can be reduced by making the diameter d2 of the sheath filament 11 smaller than d1 of the core filament diameter 12. Moreover, since the amount of steel used can be reduced, the weight of the tire can be reduced.

  In the tire according to the present invention, at least one of the steel cords constituting the first belt layer 5a and the second belt layer 5b has a major axis direction in the tire width direction cross section of ± 45 to ±± with respect to the tire width direction. It has an angle of 135 °, preferably ± 50 to ± 130 °. FIG. 3 is an enlarged partial sectional view of a belt of a pneumatic radial tire according to the present invention. In general, a steel cord having a 2 + N structure has a code flatness ratio ε (steel cord minor axis r1 / major axis r2) having a maximum value of about 1.00. However, in the tire according to the present invention, the steel cord constituting the belt layer is d1> d2, and the cord flatness ratio is smaller than 1.00. Therefore, as shown in the figure, when the major axis direction in the tire width direction cross section of the steel cord 10 constituting the belt layer has an angle θ with respect to the tire width direction, the interval w between adjacent steel cords is widened. Thereby, BES resistance improves. In order to obtain the above effect satisfactorily, at least one of the steel cords constituting one belt layer preferably has an angle θ of ± 45 to ± 135 ° with respect to the tire width direction. The cord flat ratio ε is preferably 0.56 to 0.95. The above effect cannot be obtained with a steel cord having a 2 + 6 structure or a 2 + 7 structure having a large number of sheath filaments.

  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 0.32 mm, and the diameter d2 of the sheath filament 12 is preferably 0.12 to 0.29 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.

  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 1-5 and Comparative Examples 1-7>
Tires having a tire size of 195 / 65R15 were manufactured using steel cords having structures shown in Tables 1 to 4 as belt reinforcing materials. The belt was composed of three belt layers, and steel cords shown in Tables 1 to 4 below were applied to the first belt layer and the second belt layer. In this case, the steel cord was arranged so that the major axis direction in the cross section in the width direction had an angle within the range of the cord rotation maximum angle in the table. 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. Each tire obtained was evaluated for cord fatigue, BES resistance and tire weight according to the following procedure.

<Cord fatigue>
After mounting each test tire on a standard rim as defined by JATMA standard, the vehicle is equipped with an autopilot system that can be filled with 100 kPa of internal pressure under a load condition of 1.05 times the normal load and can be turned 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. Example 1 to 3 and Comparative Examples 2 to 3 are Comparative Example 1, Example 4 and Comparative Example 5 are Comparative Example 4, Example 5 and Comparative Example 7 are Comparative Example 6 Was indexed, and the case of less than 100 was evaluated as ◎ (good), the case of 100 or more and less than 110 was evaluated as ◯ (equivalent), and the value of 110 or more was evaluated as x (bad). The results are also shown in Tables 1-4. The smaller this value, the better the cord fatigue.

<BES resistance>
Each test tire was mounted on a standard rim defined in the JATMA standard, then filled with 210 kPa internal pressure and mounted on a passenger car. A load twice the normal load was applied, and the pavement was run for 40000 km. Thereafter, the tires were dissected and the separation lengths at the belt ends were compared. Examples 1 to 3 and Comparative Examples 2 to 3 are indexed based on Comparative Example 1, Example 4 and Comparative Example 5 are based on Comparative Example 4, Example 5 and Comparative Example 7 are indexed based on Comparative Example 6, and BES resistance is indexed. Is less than 90 compared to the reference tire, the evaluation is ◎ (good), the case of 90 or more and 100 or less is evaluated as ○ (equivalent), and the case of exceeding 100 is evaluated as × (bad). The results are also shown in Tables 1-4. In addition, this index | exponent is excellent in durability, so that a value is small.

<Tire weight>
The weight per tire was measured. Examples 1 to 3 and Comparative Examples 2 to 3 are based on Comparative Example 1, Example 4 and Comparative Example 5 are based on Comparative Example 4, Example 5 and Comparative Example 7 are based on Comparative Example 6, and the tire weight is 100 g or more. The case where it decreased was evaluated as ◎, the case where it was decreased from 50 g to less than 100 g was evaluated as ◯, and the case where it was less than 50 g was evaluated as ×. The results are also shown in Tables 1-4.

<Comprehensive evaluation>
In the evaluation of durability, tire weight reduction, cord fatigue, and adhesion durability, ◎ is the case of ◎, ◎ is two and ○ is one, ○, ◎ is one and two is △, × is Some were marked with x. The results are also shown in Tables 1-4.

※タイヤ幅方向断面におけるスチールコードの長径方向とタイヤ幅方向とがなす角度

* An angle between the major axis direction of the steel cord and the tire width direction in the cross section of the tire width direction

※タイヤ幅方向断面におけるスチールコードの長径方向とタイヤ幅方向とがなす角度

* An angle between the major axis direction of the steel cord and the tire width direction in the tire width direction cross section

※タイヤ幅方向断面におけるスチールコードの長径方向とタイヤ幅方向とがなす角度

* An angle between the major axis direction of the steel cord and the tire width direction in the cross section of the tire width direction

※タイヤ幅方向断面におけるスチールコードの長径方向とタイヤ幅方向とがなす角度

* An angle between the major axis direction of the steel cord and the tire width direction in the tire width direction cross section

  From Tables 1 to 4, it was confirmed that the pneumatic radial tire of the present invention can reduce the weight of the tire while improving either or both of cord fatigue resistance and BES resistance.

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 10 Steel cord 11 Sheath filament 12 Core filament

Claims (3)

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 composed of N (2 ≦ N ≦ 4) sheath filaments and juxtaposed in the belt width direction are 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 major axis direction in at least one tire width direction cross section of the steel cord in the belt layer is A pneumatic radial tire having an angle of ± 45 ° to ± 135 ° with respect to the tire width direction.   2. The pneumatic radial tire according to claim 1, wherein a cord flat ratio expressed by a minor axis / major axis of the steel cord is 0.56 to 0.95.   The pneumatic radial tire according to claim 1 or 2, wherein the d1 is 0.16 to 0.32 mm, and the d2 is 0.12 to 0.29 mm.

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