JP2010115981A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radical tire with superior durability by improving fatigue resistance of a cord to inhibit the occurrence of a fatigue fracture, when the cord profiled in the form of waves is adapted to a peripheral-direction belt layer. <P>SOLUTION: In the pneumatic radial tire, a carcass extending astride in a toroidal form between bead-cores buried respectively in a pair of right and left beads, and a belt and a tread are sequentially layered outside in a tire radial direction. The belt includes at least one peripheral-direction belt layer including a plurality of steel cords profiled in the form of waves in two dimensions and arranged in parallel along a tire circumferential direction, each steel cord is formed of 28 to 50 filaments with 0.12 to 0.18 mm wire diameters twisted together, and an extension strain of the steel cord is within a range of 0.3% to 2.0%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more specifically, as a belt for reinforcing a tire crown, a reinforcing cord is arranged in a direction substantially along the tire circumferential direction. The present invention relates to a heavy-duty pneumatic radial tire including a directional belt layer.

  Generally, a steel cord is used as a reinforcing material for a belt in a pneumatic radial tire. Conventionally, as a reinforcing cord for such a belt, a cord that has been shaped into a corrugated or zigzag shape within the belt surface has been used, and the cord structure is 3 + 9 × 0.20 mm, 3 + 9 + 15 × 0.20 mm. The thing of layer twist structure, such as, is used.

For example, Patent Document 1 discloses a pneumatic radial tire for trucks in which a cord of a 3 + 9 twist structure is shaped into a waveform and applied to a circumferential belt layer, and Patent Document 2 discloses 3 + 9 + 15 × 0. A tire in which a cord having a structure of 22 mm is molded into a corrugated shape and applied to a belt is disclosed. Each of these belt reinforcing cords is a cord composed of 27 or less filaments.
JP 2007-38906 A ([0030] etc.) JP 2006-274461 A ([0033] etc.)

  In a tire to which a circumferential belt layer made of reinforcing cords arranged in a direction substantially along the circumferential direction is applied as a belt, a large burden is placed on the circumferential belt layer due to its structure. Since the circumferential cord layer is directly subjected to circumferential strain, when the belt strength is low, there is a concern that fracture may occur if the belt is subjected to a large deformation such as stepping on a protrusion.

  Further, when the tire rolls, the reinforcing cords applied to the circumferential belt layer are subjected to repeated strain deformation. Therefore, when the tire is flattened and enlarged, these cords are fatigued and broken due to an increase in input. There is also a concern. Therefore, in order to cope with an increase in the burden due to future increase in tire size and flattening, it is desired to increase the strength and durability of the reinforcing cord applied to the circumferential belt layer.

  Therefore, the object of the present invention is to improve the fatigue resistance of such cords and prevent the occurrence of fatigue rupture, particularly when applying a cord typed into a corrugated shape to the circumferential belt layer. Another object is to provide a pneumatic radial tire.

  As a result of diligent study, the present inventor has applied a cord obtained by using filaments having a relatively small diameter compared to the conventional number as a corrugated cord used for the circumferential belt layer, thereby improving the fatigue resistance of the cord. As a result, the present invention has been completed.

That is, the pneumatic radial tire of the present invention has a carcass extending in a toroidal shape between bead cores embedded in a pair of left and right bead portions, and a belt and a tread on the outer side in the tire radial direction of the carcass. In pneumatic radial tires that are sequentially stacked,
The belt has at least one circumferential belt layer formed by aligning a plurality of steel cords shaped in a waveform in two dimensions in parallel along the tire circumferential direction, and the steel cord has a wire diameter of 0 It is formed by twisting 28 to 50 filaments of 12 to 0.18 mm, and the elongation strain amount of the steel cord is in the range of 0.3% to 2.0%. Is.

  In the present invention, the steel cord has a layer twist structure in which a sheath composed of a plurality of filaments is arranged in two or three layers around a core composed of one or a plurality of filaments. It is preferable to do. Moreover, it is preferable that the said circumferential belt layer is arrange | positioned by 1-4 layers, and the said belt has 1-3 cross belt layers which consist of the steel cord extended in the direction inclined with respect to the tire circumferential direction. It is also preferable. Furthermore, the tensile strength of the steel cord constituting the circumferential belt layer is preferably 2000 N or more.

  According to the present invention, the above-described configuration improves the fatigue resistance of the corrugated cord applied to the circumferential belt layer and prevents the occurrence of fatigue breakage. It became possible to realize radial tires.

Hereinafter, preferred embodiments of the present invention will be described in detail.
The pneumatic radial tire of the present invention has a carcass extending in a toroidal shape between bead cores embedded in a pair of left and right bead portions, and a belt and a tread are sequentially stacked on the outer side in the tire radial direction. It will be.

  In the present invention, the belt has at least one circumferential belt layer formed by aligning a plurality of steel cords shaped in a waveform in two dimensions in parallel along the tire circumferential direction. As the steel cord used for the circumferential belt layer, it is important to use a steel cord formed by twisting 28 to 50 filaments having a wire diameter of 0.12 to 0.18 mm. This is due to the following reasons.

  In order to suppress cord breakage in the circumferential belt layer, it is considered that the cord itself only needs to be strong against strain input. However, in a cord that is wrinkled in a waveform, local distortion occurs in the wrinkled portion, and fatigue breakage of the cord starting from that portion occurs. In order to prevent this, it is only necessary to reduce the filament diameter to reduce the surface distortion when the waveform is bent. However, if the filament diameter is reduced, the belt strength is reduced. Therefore, in the present invention, in order to ensure the belt strength while reducing the filament diameter, the filaments are twisted together in a larger number than in the prior art.

  Although the belt strength can be ensured by increasing the number of belts, the increase in the number of belts causes the tire tread portion to become thicker and increases the heat generation at the time of tire high-speed rolling. Increase in heat generation promotes deterioration of the rubber, resulting in deterioration of belt peelability during high-speed running. Therefore, it is more desirable to increase the strength per cord without increasing the number of belts.

  If the number of filaments is 27 or less, the cord strength cannot be secured. On the other hand, if the number exceeds 50, the sheath has four layers and the cord diameter becomes too large, so that the amount of plastic deformation when processing into a corrugated shape increases and fatigue resistance deteriorates.

  Further, the filament diameter needs to be 0.18 mm or less, and if it exceeds 0.18 mm, the surface strain increases and fatigue resistance cannot be satisfied. On the other hand, if the wire diameter is less than 0.12 mm, the strength of the cord cannot be ensured.

  Moreover, in this invention, it is also necessary for the elongation distortion amount of the steel cord used for this circumferential belt layer to be in the range of 0.3% to 2.0%. If the elongation strain amount of the cord is less than 0.3%, the cord is fully stretched at the time of internal pressure and diameter growth, and the tire buckles and does not have a normal shape, which causes deterioration of uneven wear. On the other hand, if the elongation strain amount of the cord exceeds 2.0%, the diameter growth due to the internal pressure becomes too large. As a result, the tread rubber on the tire surface becomes in a tensile state, which causes a disadvantage of deterioration in wear resistance and cut resistance. Here, the amount of elongation strain of the cord is the value of strain at the intersection of the tangent at the point where the cord stiffness is maximum and the strain axis in the tensile load-strain (SS) curve of the cord (see FIG. 1).

  As a preferred cord structure of the steel cord used for the circumferential belt layer according to the present invention, a sheath made of a plurality of filaments is arranged in two or three layers around a core made of one or more filaments. And a layer twist structure. Specifically, for example, a code structure such as 3 + 9 + 15 + 21 × 0.165 can be given. Here, since the layer-twisted structure has a nearly circular cross section, for example, using a manufacturing method as disclosed in Japanese Patent Application Laid-Open No. 64-75227 has an advantage that variations in wavelength and amplitude of molding can be suppressed. Yes, it is suitable for the waveform shaping code according to the present invention.

  In the present invention, the twist pitch of the core constituting the steel cord can be 3.5 to 10 mm, and the twist pitch of the sheath can be 6.5 to 25 mm. The amplitude a of waveform shaping in the steel cord can be set to 1 to 5 mm, and the radius of curvature R can be set to 10 to 100 mm (see FIG. 2). Further, the number of corrugated steel cords driven in the circumferential belt layer can be 10/50 mm to 30/50 mm.

  In the tire of the present invention, the circumferential belt layer is preferably arranged in 1 to 4 layers, more preferably 1 layer to 2 layers. If the circumferential belt layer is 5 layers or more, the tread portion becomes too thick, resulting in deterioration of belt peelability during high-speed running.

  In the tire of the present invention, as a belt, in addition to the circumferential belt layer made of the predetermined steel cord, 1 to 3 cross belt layers made of steel cords extending in a direction inclined with respect to the tire circumferential direction are used. It is preferable to have. If the crossing belt layer is not disposed, the deformation in the tire width direction cannot be suppressed, and therefore, the partial wear property may be deteriorated. On the other hand, when four or more crossing belt layers are arranged, the tread portion becomes too thick, and the belt peelability during high speed running deteriorates. Such a crossing belt layer may be disposed on the outer side in the tire radial direction of the circumferential belt layer or on the inner side.

  Further, as the steel cord constituting the circumferential belt layer of the present invention, it is preferable to use a steel cord having a tensile strength of 2000 N or more, particularly 2500 to 3500 N, from the viewpoint of securing a desired belt strength.

  The pneumatic radial tire of the present invention only needs to use the above-described specific steel cord for the circumferential belt layer, and other details of the tire structure and the material of each member are in accordance with ordinary methods as desired. It can be determined as appropriate and should not be particularly limited.

Hereinafter, the present invention will be described in more detail with reference to examples.
A pneumatic radial tire in which a carcass extending in a toroidal shape between bead cores embedded in a pair of right and left bead portions is used as a skeleton, and a belt and a tread are sequentially stacked on the outer side in the tire radial direction. It produced with size 495 / 45R22.5. As a belt, two circumferential belt layers formed by aligning a plurality of steel cords shaped in a waveform in two dimensions in parallel along the tire circumferential direction, and the tire radial direction outside the tire circumferential direction 2 layers of crossing belt layers made of steel cords extending in a direction that forms an angle of 40 ° with respect to each other. Of these, the steel cord conditions used for the circumferential belt layer were changed as shown in Table 1 below to provide test tires for each of the examples and comparative examples.

  In addition, the amplitude a of waveform shaping in the steel cord used for the circumferential belt layer is 1.8 mm, the radius of curvature R is 20 mm (see FIG. 2), and the number of driving of the waveform shaping steel cord in the circumferential belt layer is 22/50 mm.

<Elongation strain amount of cord>
The elongation strain amount of the cord was determined from the result of preparing an SS curve by a tensile test for the steel cord of the circumferential belt layer taken out from each test tire.

<Internal pressure growth>
The internal pressure growth was evaluated based on the rate of change of the outer circumference on the center line when each test tire was filled with an internal pressure of 900 kPa. The case where the diameter growth rate was less than 1% was evaluated as ○, and the case where the diameter growth rate was 1% or more was evaluated as ×.

<Uneven friction>
The partial friction was measured by measuring the wear amount M _{Cl at the} tire center position and the wear amount M _{sho at} a position 200 mm from the center after running 50,000 km with a load of 5.8 t applied to each test tire. It was evaluated by the ratio _M Cl _{/ M sho} of. The case where this ratio M _Cl / M _sho was less than 150% was _marked with ◯, and the case where the ratio M _Cl / M _sho was 150% or more was _marked with ×.

<Out of cord fatigue>
Cord fatigue breakage was evaluated for occurrence of cord breakage in the steel cord of the circumferential belt layer after running 50,000 km with a load of 5.8 t applied to each test tire. The case where there was no code breakage was marked as ◯, and the case where there was a cord breakage was marked as x.

<Punk resistance>
The anti-puncture property was evaluated on whether or not puncture occurred when a 8 cm high protrusion was stepped on with each test tire loaded with a load of 4 t. The case where puncture did not occur was marked with ○, and the case where puncture occurred was marked with ×.

  These results are also shown in Table 1 below.

  As shown in Table 1 above, the test tires of the examples in which the steel cords satisfying specific conditions according to the present invention were applied to the circumferential belt layer were free from fatigue fracture in the cords and strong against punctures. It was excellent in durability. Further, it was confirmed that the inner diameter growth was suppressed and the uneven wear property was excellent.

It is a tensile load-strain (SS) curve in a steel cord. It is a schematic explanatory drawing which shows a waveform shaping steel cord.

Claims (5)

In a pneumatic radial tire in which a carcass extending in a toroidal shape between bead cores embedded in a pair of right and left bead portions is used as a skeleton, and a belt and a tread are sequentially stacked on the outer side in the tire radial direction of the carcass. ,
The belt has at least one circumferential belt layer formed by aligning a plurality of steel cords shaped in a waveform in two dimensions in parallel along the tire circumferential direction, and the steel cord has a wire diameter of 0 It is formed by twisting 28 to 50 filaments of 12 to 0.18 mm, and the elongation strain amount of the steel cord is in the range of 0.3% to 2.0%. Pneumatic radial tire.   The pneumatic steel according to claim 1, wherein the steel cord has a layer twist structure in which a sheath made of a plurality of filaments is arranged in two or three layers around a core made of one or more filaments. Radial tire.   The pneumatic radial tire according to claim 1 or 2, wherein the circumferential belt layer is arranged in 1 to 4 layers.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the belt has 1 to 3 cross belt layers made of steel cords extending in a direction inclined with respect to the tire circumferential direction.   The pneumatic radial tire according to any one of claims 1 to 4, wherein a tensile strength of a steel cord constituting the circumferential belt layer is 2000 N or more.

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