JP2000335206A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire which can be light in weight without sacrificing dynamic properties of the tire by employing flat steel cords composed of filaments with high tensile strength in belt plies. SOLUTION: In a pneumatic tire having belt plies 3 composed of steel cords 4 made by twisting a plurality of filaments at a tread part, the steel cords 4 have a flat cross section. An aspect ratio to be defined as a ratio a/b of a smaller diameter a over a larger diameter b is 0.40-0.65. The steel cords are laid so that their flat surfaces face along the surfaces of the belt plies 3. The filaments have strength of 1500α+4000 (MPa) and above, where α is a diameter of the filament in mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of reducing weight and improving high-speed durability without impairing tire dynamic characteristics (corner characteristics).

[0002]

2. Description of the Related Art Conventionally, as a belt layer reinforcing element of a pneumatic tire, a steel cord in which a plurality of filaments such as a 1 × 4 structure and a 1 × 5 structure are twisted has been used. It is desired to reduce the weight of pneumatic tires because of environmental considerations such as energy saving and resource saving.However, since pneumatic tires are pressure vessels used dynamically, steel belts must be used to reduce the weight of the belt layer. The trend is to increase the area strength of the filaments that make up the cord and reduce the amount of steel used.

[0003] However, when the amount of steel used is reduced by increasing the area strength of the filament, the breaking strength of the belt layer is maintained, but the tensile stiffness in the circumferential direction of the belt layer and the in-plane bending stiffness of the belt layer are reduced by the amount of steel used. There is a problem that the tire dynamic characteristics are deteriorated due to the large dependence.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to use a flat steel cord made of a high-strength filament for a belt layer, thereby reducing the tire dynamic characteristics (corner characteristics), reducing the weight, and achieving high-speed durability. An object of the present invention is to provide a pneumatic tire that has improved performance.

[0005]

The present invention relates to a pneumatic tire having a belt layer made of a steel cord in which a plurality of filaments are twisted in a tread portion, wherein the steel cord has a flat cord cross-sectional shape,
The flattening ratio defined by the ratio a / b of the major axis b to the minor axis a in the cord cross section is 0.40 to 0.65, and the flat surface of the cord cross section is set along the surface direction of the belt layer. And the strength of the filament is -1500d + 4000 (MPa) or more (d is the filament diameter (mm)).

[0006] By increasing the strength of the filament constituting the steel cord to -1500d + 4000 (MPa) or more, even if the amount of steel cord used in the belt layer is reduced, the breaking strength of the belt layer is equivalent. It is possible to In addition, the filament strength of the conventional belt reinforcing cord has a strand diameter of 0.25 mm and a so-called high tensile material of about 3200 to 3300 MPa is mainstream, and a very small part of a high tensile material of 3500 to 3600 MPa is called a super high tensile material. Used.

If the number of cords is reduced and the tire is reduced in weight without increasing the area strength of the filament and reducing the breaking strength of the belt layer, the centrifugal force generated in the belt layer during high-speed rotation of the tire is reduced, resulting in high-speed durability. However, the dynamic characteristics of the tire are reduced because the circumferential tensile stiffness of the belt layer and the in-plane bending stiffness (bending stiffness in the width direction of the belt layer) are reduced. Here, the flatness of the steel cord is set to 0.40 to 0.65, which is lower than that of a generally used flat cord, and the flat surface of the cord is arranged along the surface direction of the belt layer, so that the cord itself can be formed. Since the flexural rigidity in the in-plane direction of the belt is increased and the interlayer shear force between the plies works effectively, it is possible to suppress a decrease in the dynamic characteristics of the tire. Here, the cord cross section means a cross section perpendicular to the cord longitudinal direction.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pneumatic tire according to the present invention is shown in FIG.
As shown in FIG. 1, both end portions of the carcass layer 1 are mounted on a pair of left and right bead portions, and two belt layers 3 and 3 are provided on the tread portion 2 outside the carcass layer 1 in the tire circumferential direction.
It is arranged over the circumference. The two belt layers 3, 3
A plurality of steel cords 4 each having a flat cross section
Are buried in rubber so that the uneven plane is along the surface direction of the belt layer. The cross-sectional shape of the steel cord 4 is configured as shown in FIG.

The steel cord 4 is, as shown in FIG.
It has an 1 × N structure in which N filaments 10 are twisted (N = 5 in FIG. 2), and has an open structure in which a gap is formed between the filaments, and the cross-sectional shape of the cord is flat. It has a shape crushed by. N is preferably 3 to 12.

The open structure of the steel cord 4 illustrated in FIG. 2 may be an imperfect open structure in which the filaments are in contact with each other at at least one place in the cross section and all the filaments are not in contact with each other. Ideally, the filament has a completely open structure in which all filaments are separated from each other at any point in the longitudinal direction.

The major axis b in the cross section of the steel cord 4
The flattening ratio a / b defined by the ratio of the minor axis a is in the range of 0.40 to 0.65. When the aspect ratio is less than 0.40, the crack progresses rapidly when the ply separation occurs at the belt edge, resulting in poor durability. Such a flat cord is obtained by rolling a steel cord which has been subjected to a large shaping in a preforming (molding) process immediately before a stranded wire and then passed between straightening rollers.

The strength of the filament 10 is -1500d + 4000
(MPa) or more (d is the filament diameter (mm)) is important. If the strength is less than -1500d + 4000 (MPa) and the amount of steel cord used is reduced, the function of the tire as a pressure vessel is reduced. The weight fraction of carbon in the filament 10 is preferably 0.90 to 1.05 wt%. -1500d + 4000 for less than 0.90wt%
In order to achieve a strength of (MPa) or more, it is necessary to perform a high-strength wire drawing process, so that the degree of surface work of the filament becomes relatively higher than that of the inside and the toughness is inferior. If it exceeds 1.05 wt%, the carbide (cementite) fraction in the pearlite structure becomes high, so that wire drawing is difficult and the toughness is poor, which is not preferable.

[0013] The diameter of the filament 10 is 0.15-0.
It is better to set the range to 45 mm. If it is less than 0.15 mm, the filament 10 becomes too thin, the rigidity of the belt layer 3 becomes insufficient, and the abrasion resistance of the tread surface may be reduced. On the other hand, if it exceeds 0.45 mm, the out-of-plane bending stiffness of the belt layer is inferior, so that the riding comfort is inferior and the slalom durability is inferior (the belt cord is likely to break), which is not preferable.

The gauge between the belt layers at the end in the width direction of the belt layer 3 (hereinafter, referred to as a belt edge) is the gauge between the belt layers at the center in the width direction of the belt layer 3 (hereinafter, referred to as a belt center). It is good to make it 2 times or more and 5 times or less. In other words, when a flat steel cord is used for the belt layer, it is more advantageous to develop an effective interlaminar shearing force than when a steel cord having a perfect circular cross section is used. Due to the high degree of heat, the amount of heat generated due to the interlayer shear force is large as compared with the belt center, and as a result, there is a disadvantage that the load durability at the belt edge is easily reduced. Therefore,
If the gauge between the belt layers at the belt edge is made twice to five times the gauge between the belt layers at the belt center and the gauge between the belt layers at the belt edge is increased, the This is because the movement of the code can be suppressed to reduce the degree of freedom of the code. Here, the gauge between belt layers (that is, the gauge between plies) is
It means the distance between the cord of one belt layer and the cord of the other belt layer in two adjacent belt layers.

On the other hand, in order to reduce the degree of freedom of the cord at the belt edge, instead of or in addition to increasing the gauge between the belt layers at the belt edge as described above, the outside of the belt edge may be reduced. In addition, a belt cover layer made of fiber cords may be provided, wherein the cord angle with respect to the tire circumferential direction is substantially zero degrees. The fibers constituting the fiber cord may be any of inorganic fibers such as steel filament and carbon fiber, and organic fibers such as nylon fiber and polyester fiber. Arrangement of the belt cover layer is, for example, a tape-like material formed by embedding one or several fiber cords in rubber, outside the belt edge, the cord angle with respect to the tire circumferential direction is substantially zero degree, and the spiral shape is formed. It may be wound. Further, it is not necessary to dispose the belt cover layer over the entire belt width, and it is important to cover at least the width direction end. From the viewpoint of improving the durability and reducing the weight, it is preferable that the film is wound in a width of 20 to 40 mm.

Further, the steel cord 4 preferably has an elongation under a tensile load of 49 Newton of less than 0.6% before the belt layer is formed. If the elongation is 0.6% or more, the cord is roll-coated with rubber, that is, the so-called calendering step is not preferable because the dimensional change in the longitudinal direction of the cord is too large and the workability is poor.

[0017]

EXAMPLES The structure of the belt layer of the tire is shown in FIG. 1, the tire size is 195/65 R15, and the steel cords constituting the belt layer are different as shown in Tables 1 to 3. (Examples 1 to 12,
Comparative Examples 1 to 5). With respect to these tires, the belt weight (belt layer weight), hydraulic durability, cornering characteristics, high-speed durability, load durability, and load durability test fracture mode were evaluated as follows. The results are shown in Tables 1 to 3.

Belt weight : The weight of the unvulcanized belt material before tire molding is measured. It is represented by an index with Comparative Example 1 being 100. A smaller index value is lighter.

Similarly, the weight of the belt layer + belt cover layer in the unvulcanized state before the tire was formed was measured.

Water pressure durability : Each test tire assembled on a rim for a water pressure test of 15 × 6 JJ is subjected to an internal pressure of 200 kPa by water pressure.
And hold for 15 minutes. Then 150 kPa / m
in. Then, the pressure at the time when the tire was broken was determined, and the pressure was expressed as an index with Comparative Example 1 being 100. The larger the index, the better the hydraulic durability.

Cornering characteristics : A drum tester having a smooth drum surface made of steel and having a diameter of 1707 mm was used. The ambient temperature was controlled at 25 ± 3 ° C., and the test piece was assembled on a rim having a rim size of 15 × 6JJ at a test internal pressure of 200 kPa. Test tires,
Apply a load of 4000N, find the average of the absolute value of the lateral force when the running speed is 10km / hr and the slip angle is 1 ° right, and the absolute value of the lateral force when the slip angle is 1 ° left. did. The larger the value, the more excellent the cornering characteristics.

High-speed durability : A drum tester having a smooth drum surface made of steel and having a diameter of 1707 mm was used.
Test tires controlled at 38 ± 3 ° C and mounted on a rim with a rim size of 15 × 6JJ at a test internal pressure of 220kPa, running speed of 120kPa
m / hr, load JATMA (1998 version) 20% under the condition of 88% of the maximum load
Run for a minute. After completing the run, increase the speed by 10km / hr and run for 20 minutes. In this way, the test is repeated until the tire is destroyed by increasing the speed and repeating the running for 20 minutes without interruption. Compare total mileage to destruction tire
The index is expressed as an index with 1 as 100. The larger the index value, the better the high-speed durability.

Load durability and load durability test :
Using a drum testing machine with a smooth drum surface and a diameter of 1707 mm, the ambient temperature was controlled to 38 ± 3 ° C, and the test tires with a test internal pressure of 180 kPa mounted on a rim with a rim size of 15 × 6 JJ at a running speed of 80km / hr, load JATMA (19
Run for 2 hours under the condition of 88% of the maximum load. After completing the run, increase the load by 13% and run for 2 hours. In this way, the test is repeated until the tire is broken by repeating the load increase and running for 2 hours without interruption.
The total mileage to destruction was indicated as an index, with the comparative tire 1 as 100. The larger the index value, the better the load durability. Further, the broken test tire was disassembled and the form of tire breakage was investigated. It is presumed that the belt edge separation causes the movement of the bead filler (bead apex) to have a greater effect on load durability.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

In Table 1, Comparative Example 1 is a case in which a conventional steel cord having a low filament strength (3250 MPa) and a flat cross section having a cord cross section of 1 is used. Comparative Example 2 is a flat cord having an aspect ratio of 0.5, but having a low filament strength (3250MP).
a), the weight can be reduced, but the hydraulic durability is poor. Comparative Example 3
Although the filament strength is high ((3900 MPa) but the aspect ratio is too large (0.7), the weight can be reduced but the cornering characteristics are poor. Comparative Example 4 has a high filament strength ((3900 MPa) and the aspect ratio is low). Is too small (0.38), the weight can be reduced but the load durability is poor, whereas in Examples 1 to 3, the weight can be reduced and the hydraulic durability, cornering characteristics, high-speed durability, and load can be reduced. It does not impair any of the durability.

In Table 2, Comparative Example 5 is a case where a conventional steel cord having a low filament strength (3250 MPa) and an aspect ratio of 1 and a cord having a true circular cross section was used. The gauge is 3.6 times the gauge between plies at the belt center (gauge between plies (edge / center) = 3.6), but in any of hydraulic durability, cornering characteristics, high-speed durability and load durability. There is no better place. In Examples 4 to 6, the gauge between plies (edge / center) is 2.0 to 5.0, and the gauge between plies (edge / center) is too small (Example 1) and too large (Example 1). Compared with Example 7), it is superior in any of hydraulic durability, cornering characteristics, high-speed durability and load durability.

In Table 3, Example 1 shows the case where the belt cover layer is not provided outside the belt edge, and Example 8 shows the case where the belt cover layer is provided but the width is too narrow. (10 mm), and Example 12 is a case where the belt cover layer is provided but the width is too wide (50 mm). Examples 8 to 11 are the cases where the width of the belt cover layer is 20 to 40 mm, and are higher in water pressure durability, cornering characteristics, high-speed durability and load durability than those in Examples 1, 8 and 12. Excellent for either.

[0030]

As described above, according to the present invention, in a pneumatic tire having a belt layer made of a steel cord in which a plurality of filaments are twisted in a tread portion,
The steel cord has a flat cord cross-sectional shape, and the ratio a / b of the major axis b to the minor axis a in the cord cross section is a /
the aspect ratio defined by b is 0.40 to 0.65,
The uneven plane of the cord cross section is along the surface direction of the belt layer, and the strength of the filament is -1500d + 4000 (MPa).
Since (d is the filament diameter (mm)), the weight can be reduced and the high-speed durability can be improved without impairing the tire dynamic characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view of a principal part in a tire meridian direction showing an example of a belt structure of a pneumatic tire of the present invention.

FIG. 2 is a cross-sectional view of an example of a steel cord used for a belt layer of the pneumatic tire of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carcass layer 2 Tread part 3 Belt layer 4 Steel cord 10 Filament

Claims (6)

[Claims] 1. A pneumatic tire having a belt layer made of a steel cord in which a plurality of filaments are twisted in a tread portion, wherein the steel cord has a flat cord cross-sectional shape, and a long diameter b and a short diameter in the cord cross-section. The aspect ratio defined by the ratio a / b to the diameter a is 0.40
偏 0.65, the uneven plane of the cord cross section is aligned with the surface direction of the belt layer, and the strength of the filament is -1500d + 4000 (MPa) or more (d is the filament diameter (mm))
Is a pneumatic tire. 2. The pneumatic tire according to claim 1, wherein the weight fraction of carbon in the filament is 0.90 to 1.05% by weight. 3. The gauge between the belt layers at an end portion in the width direction of the belt layer is not less than twice and not more than 5 times the gauge between the belt layers at a central portion in the width direction of the belt layer. The pneumatic tire as described. 4. A pneumatic tire according to claim 1, wherein a belt cover layer made of a fiber cord is disposed outside the belt layer in a radial direction at a cord angle of about 0 degree with respect to a tire circumferential direction. . 5. A cord having a cord angle of approximately 0 degree with respect to the tire circumferential direction and a fiber cord width of 20 to 40 mm so as to cover the belt layer radially outward and to cover the width direction end of the belt layer. The pneumatic tire according to claim 1, 2 or 3, further comprising a belt cover layer. 6. The steel cord has an elongation of 0.4 when subjected to a tensile load of 49 Newton before forming the belt layer.
The pneumatic tire according to any one of claims 1 to 5, wherein the content is less than 6%.