JP2009166661A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of suppressing the growth of the diameter of a tread part and improving the durability and abrasion resistance of a belt. <P>SOLUTION: The tire has the belt composed of at least one circumferential belt layer and at least two inclined belt layers which are disposed on one after another. The at least one circumferential belt layer is composed of a number of cords coated with rubber, extending along the equatorial plane of the tire. The at least two inclined belt layers are composed of a number of cords coated with rubber, extending in the direction inclined relative to the equatorial plane of the tire. The width of the circumferential belt layer is at least 60% of the total width of the tire, and the width of the inclined belt layer is wider than the width of the circumferential belt layer. When the circumferential belt layer direction is divided into a center area in the cross direction and end areas in the cross direction located outside of the center area in the cross direction, the elastic modulus of the cords disposed in the end areas in the cross direction is lower than the elastic modulus of the cords disposed in the center area in the cross direction. The distance between the cord disposed in the outermost side in the cross direction of the circumferential belt layer and the cord disposed in the outermost side in the cross direction of the inclined belt layer is at least 5 mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire having, as a belt, a circumferential belt layer in which reinforcing elements such as cords and filaments extend along the tire equator, and particularly to a heavy-duty pneumatic tire.

In recent years, due to demands for higher speeds and lower floors of vehicles, mounted tires have become flatter, and accordingly, the amount of radial growth of the tread portion when applying standard internal pressure tends to increase further. This increase in the amount of radial growth in the tread portion amplifies stress concentration at the belt end portion and leads to a decrease in durability at that portion, and is a factor that particularly causes belt end separation early.
In other words, in a tire with a small aspect ratio, there is a problem in that the amount of diameter growth in the tread portion, particularly in the vicinity of the shoulder portion, when inner pressure is applied increases, so in the circumferential belt layer by reinforcing elements arranged in the tire circumferential direction. A technique for suppressing diameter growth is required.

  Regarding the technology for suppressing the radial growth in the circumferential belt layer, Patent Document 1 discloses that a large number of cords or filaments cross each other across the tire equator at an inclination angle of 10 to 40 ° with respect to the tire equator around the carcass. The tire equator comprises a plurality of cords or filaments of reinforcing elements having at least two layers of slanted belts, and at least one layer of corrugated or zigzag shape located under the slanted belts. A structure having a circumferential belt layer with strips oriented along the axis is disclosed.

JP-A-2-208101

  However, when the flatness ratio is further reduced, specifically, when the flatness ratio, which is the ratio of the cross-sectional height to the cross-sectional width of the tire, is 0.70 or less, the width of the circumferential belt layer is not further increased. As a result, it is difficult to suppress the intended diameter growth. However, increasing the circumferential belt layer width leads to the following new problem.

  That is, when the circumferential belt layer width is widened, a tensile input (hereinafter referred to as a result of the belt layer extending in the circumferential direction due to bending of the circumferential end of the circumferential belt layer in the contact area and bending in the circumferential direction as the tire travels) , Tensile amplitude input) repeatedly acts strongly, and as a result, the cord is likely to undergo fatigue fracture at the end in the width direction of the circumferential belt layer. When the cord of the circumferential belt layer is fractured due to fatigue, it becomes impossible to bear the circumferential tension, the tire shape cannot be maintained, and its use becomes difficult.

  When the circumferential belt layer is widened, the most serious problem is fatigue breakage of the cord at the end in the width direction of the circumferential belt layer. This is because the tensile amplitude input acts on the cord at the end of the circumferential belt layer as the tire travels, and suppressing the tensile amplitude input is indispensable for solving this problem.

  Therefore, as a result of earnest investigation of the method for suppressing the tensile amplitude input, adjusting the elastic modulus of the cord embedded in the circumferential belt layer is extremely effective in suppressing the fatigue breakage of the cord. found.

  Accordingly, an object of the present invention is to increase the durability of the belt and improve the wear performance by improving the fatigue resistance of the cord, particularly at the end of the circumferential belt layer, and in particular, a heavy load with a small aspect ratio. It is to provide a heavy duty radial tire.

The gist of the present invention is as follows.
(1) At least one layer in which a carcass straddling a toroidal shape between a pair of bead portions is used as a skeleton, and a large number of cords extending along the equatorial plane of the tire are coated with rubber on the radially outer side of the crown portion of the carcass A belt formed by sequentially arranging at least two inclined belt layers in which a plurality of cords extending in a direction inclined with respect to the equator plane of the tire are covered with rubber. A tire having a tread disposed radially outward of the tire,
The width of the circumferential belt layer is 60% or more of the total width of the tire;
The width of the inclined belt layer is wider than the width of the circumferential belt layer,
When each circumferential belt layer is partitioned into a widthwise central region and a widthwise end region located outside the widthwise central region, the elastic modulus of the cord disposed in the widthwise end region is Lower than the elastic modulus of the cord disposed in the central region in the width direction,
The distance between the cord disposed on the outermost side in the width direction of the circumferential belt layer and the outermost cord in the width direction of the inclined belt layer is 5 mm or more.
A pneumatic tire characterized by that.

  The pneumatic tire according to (1), wherein the distance is 40 mm or less.

  The pneumatic tire according to (1) or (2) above, wherein the width of the inclined belt layer is 65% or more of the total width of the tire.

  (1) to (3) above, wherein the circumferential belt layer is formed by spirally winding a strip material in which one or a plurality of cords are covered with rubber around a crown portion of the carcass. The pneumatic tire according to any one of the above.

The cord disposed in the end region in the width direction is an extensible metal cord having an initial elongation,
The cord disposed in the central region in the width direction is a non-stretched metal cord that is molded in a linear shape, a wave shape, or a zigzag shape.
The pneumatic tire according to any one of (1) to (4) above, wherein

The cord disposed in the end region in the width direction is an organic fiber cord,
The cord disposed in the central region in the width direction is a metal cord,
The pneumatic tire according to any one of (1) to (5) above, wherein

  The elastic modulus at a tensile strain of 1.8% of the cord disposed in the end region in the width direction and the cord disposed in the central region in the width direction is in a range of 40 GPa to 100 GPa and 80 GPa to 210 GPa, respectively. The pneumatic tire according to any one of (1) to (6) above, wherein

According to the present invention, by expanding the circumferential belt layer width, suppressing the remarkable tread diameter growth particularly in a tire having a small aspect ratio, and adjusting the elastic modulus of the cord embedded in the circumferential belt layer, In particular, the fatigue breakage of the cord at the end of the circumferential belt layer is suppressed, the durability performance of the belt is greatly improved, and the wear performance is improved by defining the width of the inclined belt layer relative to the circumferential belt layer. A tire with a small ratio can be provided.
In addition, by regulating the distance between the width direction end of the circumferential belt layer and the width direction end of the inclined belt layer, the pneumatic tire further improves the durability of the belt and improves the uneven wear resistance. Can be provided.

Hereinafter, embodiments of the pneumatic tire of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross section in the width direction of a tire according to the present invention. On the radially outer side of the crown portion of the carcass 1 straddling a toroidal shape between a pair of bead portions (not shown), at least one layer in which a large number of cords extending along the tire equator CL are covered with rubber, illustrated example The two circumferential belt layers 2a and 2b and a plurality of cords extending in a direction inclined with respect to the tire equator CL are covered with rubber, and at least two layers are arranged in a direction in which the cords cross each other between the layers. In the illustrated example, a belt 4 in which two inclined belt layers 3 a and 3 b are sequentially laminated is provided, and a tread 5 is arranged on the outer side in the radial direction of the belt 4.

The width BW ₂ of the circumferential belt layers 2a and 2b is preferably set to 60% or more of the total width TW of the tire, and more preferably set to 70% or more. This is because the region where the radial growth is large is up to a region of 60% to 70% of the total tire width TW, and therefore it is necessary to arrange a circumferential belt layer for suppressing the radial growth in that region. . The upper limit of the width BW ₂ of the circumferential belt layer 2a and 2b, the restrictions that fit into the prescribed size of the tire shape, preferably 90%.

Further, it is necessary to make the widths BW _3a and BW _3b of the two inclined belt layers, in the illustrated example, the inclined belt layers 3a and 3b wider than the width BW ₂ of the circumferential belt layers 2a and 2b. This is because the in-plane shear rigidity of the tread portion necessary for tire wear performance and cornering performance is ensured.
Further, in the example shown in FIG. 1, the width BW _3a of the inclined belt layer 3a is wider than the width BW _3b of the 3b, Thus, it is preferable to set different widths. This is because when the widths are the same, there is a sudden change in rigidity, and there is a concern that the separation resistance at the belt layer end may deteriorate.

In addition, the width of the inclined belt layers 3a and 3b is preferably 65% or more of the total width TW of the tire. This is because the wear performance is maintained when the cords of the inclined belt layer 3a and the cords 3b intersect within a range of 65% or more of the total tire width TW. Moreover, it is preferable that the upper limit of the width | variety of inclination belt layer 3a, 3b shall be 90% from the restriction | limiting of accommodating a tire shape in a prescribed dimension.
When the cord of the inclined belt layer is inclined at 40 ° or more, preferably 50 ° or more with respect to the tire equator CL, both wear performance and durability performance can be achieved. This is because if the inclination angle of the cord of the inclined belt layer with respect to the tire equator CL is less than 40 °, the circumferential deformation of the inclined belt becomes large in the ground contact region during tire running, and the rubber between the circumferential belt end and the inclined belt layer The shear deformation increases. This is because the rubber is destroyed and the durability of the tire may be significantly reduced.

  In the example shown in FIG. 1, the circumferential belt layers 2a and 2b have the same width, but may have different widths. In particular, when the strength of the central portion in the width direction of the circumferential belt layer is increased, only one layer may be arranged wider and the other layer may be made narrower.

  Further, if the width of the circumferential belt layer is increased, the cord is likely to be fatigued at the outer end in the width direction of the circumferential belt layer, and it is difficult to obtain a sufficiently satisfactory tire life. This is because the amplitude input in the tensile direction acts on the cord at the end of the circumferential belt layer as the tire travels, and it is indispensable to suppress this tensile amplitude input to solve this problem. . Therefore, in the present invention, the elastic modulus of the cord disposed on the outer side in the width direction is made lower than the elastic modulus of the cord disposed on the inner side in the width direction of the circumferential belt layer. The tensile amplitude input concentrated on the end of the circumferential belt layer is suppressed.

  That is, in a running tire, a tensile amplitude input acts on the end of the circumferential belt layer. This tensile amplitude input is caused by the cord being stretched in the circumferential direction on the ground contact surface on the tread end side of the tire, where the maximum tensile stress acts, and in the non-contact area of the tread end, the tensile stress at the time of filling with internal pressure acts. Because. In order to suppress the amplitude of the tensile stress, it is conceivable to reduce the burden on the tire (reduce the amount of bending of the tire), but this method cannot satisfy the riding comfort of the tire.

  Therefore, when the cord is stretched in the circumferential direction of the tire within the ground contact surface, if the elastic modulus of the cord at the end in the width direction of the circumferential belt layer corresponding to the ground contact surface is low, the tensile stress applied to the cord is low. Become. However, if the elastic modulus of all the cords in the circumferential belt layer is lowered, the amount of radial growth due to internal pressure filling becomes large, and it becomes difficult to maintain the shape of the tire. Therefore, in the width direction of the circumferential belt layer, the cord elastic modulus on the outer side in the width direction corresponding to the vicinity of the end portion is made lower than the elastic modulus of the cord on the inner side in the same width direction, so If the increase in the amount is made the same as much as possible, the stress amplitude at the end portion in the width direction of the circumferential belt layer on the ground contact surface is effectively suppressed, so that fatigue breakage of the cord can be suppressed.

  The elastic modulus of the cord arranged on the outer side in the width direction of the circumferential belt layer is 0.3 to 0.8 times the elastic modulus of the cord arranged on the inner side in the width direction of the cord. It is effective for suppressing the amplitude of the tensile stress.

Here, as shown in the plan development view of the circumferential belt layer in FIGS. 1B and 1C, each circumferential belt layer is placed outside the width direction central region 2 </ b> C and the width direction central region 2 </ b> C in the width direction. When the width direction end area 2E ₁ and 2E ₂ are partitioned, the elastic modulus of the cord 6 arranged in the width direction end area 2E ₁ and 2E ₂ is equal to that of the cord 7 arranged in the width direction central area 2C. Lower than elastic modulus.

That is, the cord arrangement shown as the circumferential belt layers 2a and 2b in FIG. 1 has an elastic modulus in comparison with the cord 7 arranged in the width direction end region 2E ₁ and 2E ₂ of the circumferential belt layer in the width direction central region 2C. A plurality of low cords (hereinafter referred to as “low elastic modulus cords”) 6 are arranged, and the low elastic modulus cord 6 has an elastic modulus higher than that of the low elastic modulus cord 6 in the center region 2C in the width direction inside the belt width direction. A plurality of high cords (hereinafter referred to as “high elastic modulus cords”) 7 are arranged.
Thus, as the circumferential belt layer according to the present invention, 1 to several tens of low elastic modulus cords 6 are arranged in the width direction end regions 2E ₁ and 2E ₂ , and the high elastic modulus cord 7 is arranged in the central region 2C in the width direction. Basically it is arranged.

The width t of each widthwise end portion area _2E 1, 2E ₂ is preferably from 5% to 20% of the width BW ₂ of the circumferential belt layer. This is because if the width t is less than 5% of the total width, a cord having a high elastic modulus exists in a region where the stress amplitude to the circumferential belt layer is large, so that there is still a high possibility of breakage. This is because it is difficult to suppress an increase in diameter growth.

FIG. 2A shows a partially enlarged bottom view of the belt layer of the tire according to the present invention, and FIG.
The belt 4 includes circumferential belt layers 2a and 2b and inclined belt layers 3a and 3b arranged in this order from the inner side in the tire radial direction. Here, it is important that the distance between the cord disposed on the outermost side in the width direction of the circumferential belt layer and the outermost cord in the width direction is 5 mm or more. That is, in this example, the cord 6b disposed on the outermost side in the width direction of the wide circumferential belt layer 2b among the circumferential belt layers 2a and 2b, and the narrow inclined belt layer among the inclined belt layers 3a and 3b. It is important that the distance d from the end portion in the width direction of 3a (that is, the cord end 8E of the cord 8 disposed on the inclined belt layer 3a) is 5 mm or more.
Because, when the distance is less than 5 mm, the end of the circumferential belt layer is strongly influenced by the circumferential displacement due to the shear deformation between the inclined belt layers accompanying the tire rolling, and the widthwise end region of the circumferential belt layer This is because the cord 6 disposed in the position is stretched in the circumferential direction and the durability of the cord may be deteriorated. Moreover, if the circumferential belt layer is stretched in the circumferential direction, it may cause uneven wear on the tread.
As shown in FIG. 2B, the distance d means the distance between the centers of the cords in the horizontal plane obtained by projecting the circumferential belt layer 2b onto the inclined belt layer 3a.

  The distance d is preferably 40 mm or less. This is because when the distance d is larger than 40 mm, the circumferential deformation of the inclined belt layer accompanying the tire rolling increases, and the circumferential belt layer is stretched as in the case described above.

  In the circumferential belt layer of the present invention, a strip material in which one or a plurality of low elastic modulus cords 6 and high elastic modulus cords 7 are respectively coated with rubber is spirally wound around the crown portion of the carcass. Molding is preferable because it leads to a reduction in manufacturing time and can consequently reduce costs.

For the low elastic modulus cord 6, for example, a metal elastic cord, that is, a double-twisted 4 × 0.28 mm + 6 × 0.25 mm cord, so-called high elongation cord, is suitable. Is a wavy or zigzag shaped cord (see the structure of the circumferential belt layers 2a, 2b in FIGS. 1 (b) and 1 (c)), a so-called corrugated cord, or a metal non-stretch cord, i.e. layer A cord of twist (3 + 9 + 15) × 0.23 mm is suitable. In general, the elastic modulus of a high elongation cord at a tensile strain of 1.8% is smaller than that of a cord having a wave-like or zigzag-type molding, or a non-stretch cord made of metal.
Since it is known as an actual measurement that the tensile strain in the ground plane is about 1.8%, the cord elastic modulus defines the cord elastic modulus at this tensile strain of 1.8%.
Incidentally, the elastic modulus of the cord means that a tensile test is performed on a rubber-covered cord taken out by disassembling a pneumatic tire, and a stress-strain diagram is created from the result, and the strain in the diagram is 1 It is a value obtained by calculating the tangent slope (slope) at .8% and dividing the value by the cross-sectional area of the cord.

  Further, even when an organic fiber cord is used for the low elastic modulus cord 6 and a metal cord is used for the high elastic modulus cord 7, the above elastic modulus condition can be satisfied.

The elastic modulus of the low elastic modulus cord 6 is preferably in the range of 40 GPa or more and 100 GPa or less at a tensile strain of 1.8%. When the elastic modulus is lower than 40 GPa, the diameter growth due to filling with internal pressure may not be suppressed. When the elastic modulus is higher than 100 GPa, the cord breaks due to the input (stress amplitude) applied to the cord when rolling the tire, and the tire internal pressure is maintained. Can be difficult to do.
The elastic modulus of the high elastic modulus cord 7 is preferably in the range of 80 GPa or more and 210 GPa or less at a tensile strain of 1.8%. When the elastic modulus is lower than 80 GPa, the diameter growth due to the internal pressure filling may not be suppressed. When the elastic modulus is higher than 210 GPa, the cord easily breaks due to the input (stress amplitude) applied to the cord during rolling of the tire. Can be difficult to hold.

Inventive tires, conventional tires, and comparative tires were prototyped with a size of 495 / 45R22.5 under the specifications shown in FIG. 3 and Table 1. Durability tests and wear tests were performed on each prototype tire. explain.
Inventive tires 1 to 3 and comparative tires 2 and 3 have the belt structure shown in FIG. 3A, and the inclined belt layers 3a and 3b are both wider than the circumferential belt layers 2a and 2b. The distance d between the outermost cord in the width direction of the inclined belt layer 3b having the narrower width and the outermost cord in the width direction of the circumferential belt layer is changed. Although the code is not shown in the example of FIG. 3, the distance d is the distance between the centers of the cords as in FIG. A circumferential belt layer is constituted by the width direction end regions 2E ₁ and 2E ₂ including the low elastic modulus cord and the width direction central region 2C including the high elastic modulus cord.
The conventional tire has a belt structure shown in FIG. The narrower inclined belt layer 3b is narrower than the circumferential belt layers 2a and 2b, and constitutes the circumferential belt layer only from the center region 2C in the width direction including the high elastic modulus cord.
The comparative example tire 1 has a belt structure shown in FIG. 3C, and the inclined belt layers 3a and 3b are wider than the circumferential belt layers 2a and 2b, but include a high elastic modulus cord. A circumferential belt layer is formed only from the center region 2C in the direction.

  These prototype tires were assembled in a rim of size 17.00 × 22.5, the internal pressure was adjusted to 900 kPa, and the drum traveled at a distance of 30000 km under the conditions of load: 5800 kg and drum rotation speed: 60.0 km / h. After that, the tire was dissected and the fatigue strength of the cord in the circumferential belt layer was measured (endurance test). The fatigue strength is expressed as an index with the strength of the conventional tire as 100, and the larger the value, the greater the fatigue strength, that is, the better the durability performance. At the same time, the amount of tread wear was measured (wear test). The amount of wear on the tread is represented by an index representing the amount of wear of the conventional tire as 100. The larger the value, the smaller the amount of wear, that is, the better the wear performance.

The elastic modulus of the cord is the elastic modulus of the cord at a tensile strain of 1.8% when the cord is subjected to a tensile test using an Instron type tensile tester.
For the inclined belt layer, (1 + 6) × 0.32 mm layer-twisted cord was applied at a number of driven 24.5 pieces / 50 mm.
4 × (1 × 0.28 mm + 6 × 0.25 mm) highly extensible cords are applied to the circumferential belt layer width direction end areas 2E ₁ and 2E ₂ at a driving number of 20/50 mm, and the width direction central area For 2C, a wavy non-extended cord of (3 + 9 + 15) × 0.23 mm was applied at a driving number of 22.5 / 50 mm.

From the results of Table 1, the inventive tires 1 to 3 change the elastic modulus of the cord in the width direction end region and the width direction central region, and the cord disposed on the outermost side in the width direction of the circumferential belt layer, and the inclined belt layer It can be seen that the durability performance was improved by setting the distance to the outermost cord in the width direction to 5 mm or more.
It can also be seen that the tires other than the conventional tires showed good wear performance by making the two inclined belt layers wider than the circumferential belt layer.

  As described above, the elastic modulus of the cord embedded in the circumferential belt layer is adjusted to significantly improve the durability of the belt, the width of the inclined belt layer with respect to the circumferential belt layer is specified, and the wear performance is improved. By regulating the distance between the cord arranged on the outermost side in the width direction of the circumferential belt layer and the outermost cord in the width direction of the inclined belt layer, the durability performance of the belt was further improved, and the uneven wear resistance performance was improved. A pneumatic tire can be provided.

(A) is sectional drawing of the width direction of the tire according to this invention, (b), (c) is a development view of a belt. (A) is the partial expanded bottom view of the belt layer of the tire according to this invention, (b) is the width direction sectional drawing. (A)-(c) is width direction sectional drawing of the belt according to an invention example tire, a conventional example tire, and a comparative example tire.

Explanation of symbols

1 carcass 2a, 2b circumferential belt layer 2C widthwise central region 2E _1, 2E ₂ widthwise end regions 3a, 3b slant belt layer 4 belt 5 a tread 6,7,8 code CL tire equator

Claims (7)

At least one circumferential direction in which a carcass straddling a toroidal shape between a pair of bead portions is used as a skeleton, and a large number of cords extending along the equatorial plane of the tire are covered with rubber on the radially outer side of the crown portion of the carcass A belt comprising a belt layer and at least two inclined belt layers in which a plurality of cords extending in a direction inclined with respect to the equatorial plane of the tire are covered with rubber, and are arranged in the radial direction of the belt A tire with a tread on the outside,
The width of the circumferential belt layer is 60% or more of the total width of the tire;
The width of the inclined belt layer is wider than the width of the circumferential belt layer,
When each circumferential belt layer is partitioned into a widthwise central region and a widthwise end region located outside the widthwise central region, the elastic modulus of the cord disposed in the widthwise end region is Lower than the elastic modulus of the cord disposed in the central region in the width direction,
The distance between the cord disposed on the outermost side in the width direction of the circumferential belt layer and the outermost cord in the width direction of the inclined belt layer is 5 mm or more.
A pneumatic tire characterized by that.   The pneumatic tire according to claim 1, wherein the distance is 40 mm or less.   The pneumatic tire according to claim 1 or 2, wherein a width of the inclined belt layer is 65% or more of a total width of the tire.   4. The circumferential belt layer is formed by spirally winding a strip material in which one or a plurality of cords are covered with rubber around a crown portion of the carcass. The described pneumatic tire. The cord disposed in the end region in the width direction is an extensible metal cord having an initial elongation,
The cord disposed in the central region in the width direction is a non-stretched metal cord that is molded in a linear shape, a wave shape, or a zigzag shape.
The pneumatic tire according to any one of claims 1 to 4, wherein: The cord disposed in the end region in the width direction is an organic fiber cord,
The cord disposed in the central region in the width direction is a metal cord,
The pneumatic tire according to any one of claims 1 to 5, wherein:   The elastic modulus at a tensile strain of 1.8% of the cord disposed in the end region in the width direction and the cord disposed in the central region in the width direction is in a range of 40 GPa to 100 GPa and 80 GPa to 210 GPa, respectively. The pneumatic tire according to any one of claims 1 to 6.

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