JP7218492B2 - pneumatic tire - Google Patents

Description

The present invention relates to pneumatic tires.

For the purpose of improving tire durability, it has been studied to increase the cord strength per unit width of one belt ply constituting the belt layer. However, when using conventional steel cords to increase the cord strength per unit width of one belt ply, it is necessary to use steel cords with a large cord diameter, which leads to poor riding comfort and an increase in tire weight. There was a problem.

JP 2013-244782 A JP 2012-66816 A

SUMMARY OF THE INVENTION In view of the above points, an object of the present invention is to provide a pneumatic tire that can improve durability and ride comfort while reducing tire weight.

Patent Document 1 describes a pneumatic radial tire using steel cords with high cord strength in the belt layer. There is no description of cord bending hardness.

Further, Patent Document 2 describes that the filament diameter of the steel cord used for the belt layer is set within a predetermined range. There is no description of cord bending hardness.

A pneumatic tire according to the present invention is a pneumatic tire having a carcass, a belt layer arranged on the outer circumference of a crown portion of the carcass, and a belt reinforcing layer arranged on the outer circumference of the belt layer, wherein the belt layer consists of a belt ply in which steel cords are arranged at an angle to the tire circumferential direction, the cord diameter of the steel cord is 0.90 mm or less, and the bending hardness of each steel cord is 800 cN. The cord strength per steel cord is 3300 N/mm ² or more, and the cord strength per unit width of one belt ply is 16 kN/25.4 mm or more.

The structure of the steel cord is an m/n structure in which a bundle consisting of a core with m filaments and a sheath with n filaments arranged around it is twisted at the same pitch. can be done.

The pneumatic tire may be for light trucks.

According to the pneumatic tire of the present invention, it is possible to obtain excellent durability and riding comfort while reducing tire weight.

1 is a half-sectional view of a pneumatic tire according to one embodiment of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows the structure of the steel cord which concerns on one Embodiment of this invention. Drawing explaining the measuring method of cord bending hardness of a steel cord. Schematic cross-sectional view showing the shape of a test track used for evaluation of ride comfort.

Matters related to the implementation of the present invention will be described in detail below.

The pneumatic tire of the embodiment shown in FIG. 1 is a radial tire for light trucks, and includes a pair of left and right bead portions 1 and sidewall portions 2, and radially outer ends of the left and right sidewall portions 2. A tread portion 3 is provided between both sidewall portions so as to connect the two, and a carcass 4 extending across a pair of bead portions is provided. Here, a "light truck" is a small truck with a gross vehicle weight of less than 8 tons and a load capacity of 1 to 3.5 tons.

The carcass 4 is composed of at least one carcass ply extending from the tread portion 3 through the sidewall portion 2 and having both ends anchored by annular bead cores 5 embedded in the bead portion 1 . The carcass ply is formed by arranging carcass cords made of organic fiber cords substantially perpendicular to the tire circumferential direction and coating them with coating rubber.

A belt layer 6 is arranged between the carcass 4 and the tread rubber portion 7 on the outer peripheral side of the carcass 4 in the tread portion 3 (that is, the outer side in the tire radial direction). The belt layer 6 is superimposed on the outer circumference of the crown portion of the carcass 4, and can be composed of one or more belt plies, usually at least two belt plies. It is composed of two belt plies, a first belt ply 6A on the side and a second belt ply 6B on the tread rubber portion side. The belt plies 6A and 6B are formed by slanting the steel cords 20 at a predetermined angle (for example, 15 to 35 degrees) with respect to the tire circumferential direction and arranging them at predetermined intervals in the tire width direction. Each belt ply has steel cords 20 coated with coating rubber. The steel cords 20 are arranged so as to cross each other between the two belt plies 6A and 6B.

A belt reinforcing layer 8 is provided between the belt layer 6 and the tread rubber portion 7 on the outer peripheral side of the belt layer 6 (that is, on the outer side in the tire radial direction). The belt reinforcing layer 8 is a cap ply covering the entire width of the belt layer 6 with the belt reinforcing ply. The belt reinforcing ply is formed by coating organic fiber cords arranged substantially parallel to the tire circumferential direction with a coating rubber. That is, the belt reinforcing layer 8 is formed by arranging organic fiber cords along the tire circumferential direction, and a ribbon-like rubber (also referred to as a rubber strip) having organic fiber cords is formed so as to cover the entire width direction of the belt layer 6 . , by spirally winding at an angle of 0 to 5 degrees with respect to the tire circumferential direction.

The structure of each steel cord 20 for the belt layer 6 of the pneumatic tire according to this embodiment is not particularly limited, but as shown in FIG. It is more preferable to have an m/n structure (m = 2 to 4, n = 5 to 7) in which a bundle consisting of a sheath 12 around which n filaments 14 of the same diameter are arranged is twisted at the same pitch. .

The cord diameter of the steel cord 20 is not particularly limited as long as it is 0.90 mm or less, but is preferably 0.7 to 0.9 mm.

Although the filament diameter of the core 11 is not particularly limited, it is preferably 0.1 to 0.15 mm.

Although the filament diameter of the sheath 12 is not particularly limited, it is preferably 0.2 to 0.3 mm.

Although the twist pitch is not particularly limited, it is preferably 11 to 15 mm.

The cord bending hardness per steel cord is not particularly limited as long as it is 800 cN or less, but is preferably 100 to 800 cN, more preferably 100 to 500 cN. Here, the "cord bending hardness" in this specification is a value defined by the maximum load when one steel cord is bent at its central portion with a distance between fulcrums of 25.4 mm. Specifically, it can be measured as follows using a tensile tester. Specifically, at room temperature, as shown in FIG. 3, steel cords 20 having a length of 50 to 80 mm were suspended at positions of 25.4 mm in the center with both ends free. , and the midpoint 20M is brought into contact with the linear upper side 21A of the inverted U-shaped fixed jig 21 from below so as to intersect at right angles. Here, the upper side portion 21A has a bar shape with a circular cross section (diameter=3.0 mm). From this state, the support 22 is pulled upward at a tensile speed of 500 mm/min, and the load applied to the support 22 is measured while bending the steel cord 20 with the jig 21 . The bending hardness of the cord is defined as the average value of the maximum load (cN) at n=5.

The cord strength per steel cord is not particularly limited as long as it is at least 3300 N/mm ² , preferably 3300 to 3800 N/mm ² and more preferably 3300 to 3700 N/mm ² . As used herein, the term "cord strength" refers to a value obtained by dividing the tensile strength per steel cord measured using a tensile tester in accordance with JIS G3510 by the cross-sectional area of the steel cord 20. be.

Although the cord strength per unit width of one belt ply is not particularly limited as long as it is 16 kN/25.4 mm or more, it is preferably 18 to 23 kN/25.4 mm. Here, in this specification, "cord strength per unit width" refers to the tensile strength per steel cord measured using a tensile tester in accordance with JIS G3510, and the number of driven cords (cord/25.4 mm ).

In the pneumatic tire of the present embodiment, the steel cord occupancy (“cord occupancy”) in the width dimension of the belt layer is not particularly limited, but is preferably 75% or less, more preferably 40 to 75%. is. When the cord occupancy is 75% or less, the belt layer 6 does not become too rigid, and excellent riding comfort is likely to be obtained. Further, when the cord occupancy is 75% or less, the distance between the steel cords 20 does not become too small, and the stress between the steel cords 20 can be sufficiently absorbed by the rubber layer. Separation between layers and peeling are less likely to occur. When such cord separation occurs, tire durability is reduced. Here, the "cord occupancy rate (%)" is a value calculated by the following formula for a so-called topping fabric in which cords are aligned at a predetermined density and covered with rubber.
<Formula 1>
Cord occupancy rate (%) = Length of cord (mm) x Number of cords driven (number/25.4mm) x 100/1 (25.4mm)
The type of the pneumatic tire according to the present embodiment is not particularly limited, and includes various tires such as tires for passenger cars, tires for heavy loads used for trucks and buses, etc., and can be suitably used as tires for light trucks. can be done.

In the above embodiment, the belt reinforcing layer 8 is a cap ply that covers the entire width of the belt layer 6. However, it is not limited to this, and the outer edge of the belt layer 6 in the tire width direction and its periphery It may be an edge ply that covers the cap ply, and the edge ply may be formed by folding back both ends of the cap ply in the tire width direction.

In the above embodiment, as a pneumatic tire for light trucks, the belt layer 6 is composed of two belt plies and the belt reinforcing layer 8 is composed of one belt reinforcing ply. It may consist of a ply, or may not have the belt reinforcing layer 8 .

Examples of the present invention are shown below, but the present invention is not limited to these examples.

A steel cord having the structure shown in Table 1 below was produced. Also, the twist pitch was 13.5 mm. In addition, 0.15 of "2 x 0.15/5 x 0.28" in Table 1 is a core filament diameter of 0.15 mm, the number is two, and 0.28 is a sheath filament diameter is 0.28 mm, indicating that the number is five.

The measuring method for steel cords is as follows.

· Filament diameter (mm), cord diameter (mm), cross-sectional area (mm ² ): The diameters of the cord and filament were measured with a prescribed thickness meter in accordance with JIS G3510. The cross-sectional area of the steel cord was obtained from the diameter of the filament and the cord structure.

- Cord bending hardness (cN/cord): For each cord, the cord bending hardness of the cord was measured by the method described above with reference to FIG. That is, at room temperature, steel cords 20 having a length of 80 mm are supported by supports 22 in a state in which both ends are free and the central portions are suspended at positions spaced by 25.4 mm as shown in FIG. Then, the midpoint 20M is applied to the linear upper side 21A of the jig 21 fixed in the inverted U shape so as to cross at right angles from below, and from this state, the tensile tester (( Autograph manufactured by Shimadzu Corporation was used to lift the support 22 upward at a tensile speed of 500 mm/min, and the load applied to the support 22 was measured while bending the steel cord 20 with the jig 21 . The bending hardness of the cord was defined as the average value of n=5 of the maximum load (cN) at that time.

Bending rigidity (N/25.4 mm): A value obtained by multiplying the bending hardness of the cord by the number of cords driven.

- Tensile strength (N) per steel cord: In accordance with JIS G3510, the strength and elongation properties of the steel cord and filament were measured using a tensile tester (manufactured by Shimadzu Corporation, Autograph).

· Cord strength per steel cord (N/mm ² ): A value obtained by dividing the tensile strength per steel cord by the cross-sectional area of the steel cord.

Cord strength per unit width of one belt ply (kN/25.4 mm): A value obtained by multiplying the tensile strength by the number of cords driven.

Using the obtained cord as a belt layer cord, a light truck tire having a tire size of LT265/75R16 was vulcanized and molded in accordance with a conventional method. Each tire has a common configuration except for the belt layer. For the carcass, 2 plies of carcass plies were used, using organic fiber cords made of polyethylene terephthalate (PET) of 1670 dtex/2, and the number of carcass plies was 22/25 mm.

The angles of the steel cords in the belt plies (6A)/(6B) were +23°/−23° with respect to the tire circumferential direction.

The belt ply was prepared by arranging the steel cords with the number of strands shown in Table 1 so that the longitudinal direction of the cords was parallel to the belt surface, and then using a calendering device to form a topping ply.

For the belt reinforcing layer, 2 plies of belt reinforcing plies were used, using organic fiber cords made of nylon 66 of 1400 dtex/2, and the number of belt reinforcing plies was set to 28 cords/25 mm.

Belt ply weight, tire weight, riding comfort and durability were evaluated for each pneumatic tire obtained. The evaluation method for each evaluation item is shown below.

- Belt ply weight: The weight per unit area of the belt ply. The smaller the index, the lighter.

- Tire weight: The total weight of one tire, expressed as an index with the total weight of the tire of Comparative Example 1 being 100. The smaller the index, the lighter the tire, and 98 or less was evaluated as having the effect of reducing the tire weight.

・ Ride comfort: A test tire assembled on a standard rim with an internal pressure of 200 kPa was mounted on the front wheel of the test vehicle, and the test road 40 with the cross-sectional shape shown in FIG. ), sensory evaluation of tire rideability was performed. "○" indicates that the rut can be smoothly overcome, "△" indicates that the vibration is somewhat unpleasant, and "x" indicates that the vibration is large.

・Durability: Using a drum tester with a steel rotating drum with a smooth surface and a diameter of 1700 mm, the ambient temperature is 38 ± 3 ° C, the tire internal pressure is 600 kPa, and the speed is 64 km / h using a standard rim specified by JIS. , 7 hours at 70% of the maximum load specified by JATMA, then 16 hours at 88% of the maximum load, and 24 hours at 106% of the maximum load. After running at 115% for 24 hours, the tire is further run at 130% of the maximum load for 24 hours if there is no abnormality in the tire appearance and inner surface. At this time, if there were no abnormalities in the tire appearance and inner surface, the tire was further run at 160% of the maximum load until failure occurred. Table 1 shows the mileage until the occurrence of failure as an index with the conventional example being 100. The higher the index, the better the durability.

The results are as shown in Table 1. Compared with Comparative Example 1, Examples 1 to 3 had a reduced tire weight, and excellent ride comfort and durability were obtained.

Comparative Example 2 is an example in which the cord strength is less than the lower limit, and the tire weight reduction effect is not sufficient.

Comparative Example 3 is an example in which the cord strength per unit width of one belt ply was less than the lower limit, and compared with Comparative Example 1, the durability was inferior.

Comparative Example 4 is an example in which the cord diameter and cord bending hardness exceed the upper limits, and the effect of reducing the tire weight and the effect of improving ride comfort are not sufficient.

The pneumatic tire of the present invention can be used for various vehicles such as passenger cars, light trucks and buses.

Reference Signs List 1 Bead portion 2 Sidewall portion 3 Tread portion 4 Carcass 5 Bead core 6 Belt layer 6A First belt ply 6B Second belt ply 7 Tread rubber portion 8 Belt reinforcing layer 11 Core 12 Sheath 13 Core filament 14 Sheath filament 20 Steel cord 20M Middle point 21 Jig 21A Upper side 22 Supporting tool

Claims (3)

A pneumatic tire having a carcass, a belt layer arranged on the outer circumference of the crown portion of the carcass, and a belt reinforcing layer arranged on the outer circumference of the belt layer,
The belt layer is made of a belt ply in which steel cords are arranged at an angle with respect to the tire circumferential direction,
The cord diameter of the steel cord is 0.90 mm or less,
The bending hardness of each steel cord is 800 cN or less,
The cord strength per steel cord is 3300 N/mm ² or more,
A pneumatic tire, wherein the cord strength per unit width of one belt ply is 16 kN/25.4 mm or more. The structure of the steel cord is an m/n structure in which bundles of a core having m filaments and a sheath having n filaments arranged around the core are twisted at the same pitch. The pneumatic tire according to claim 1, wherein The pneumatic tire according to claim 1 or 2 , characterized in that it is for light trucks.

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