JPH05294101A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic radial tire being light and capable of improving substantially durability in condition of low internal pressure. CONSTITUTION:Rubber 24 for covering a carcass ply cord 14 of a carcass ply 16 is made to have elasticity higher than that used in a conventional carcass ply (dynamic modulus of elasticity E' is around 1.3X10<8>dyn/cm<2>), and a dynamic modulus of elasticity E' after curing is made within 2.0-6.0X10<8>dyn/cm<2>. When an internal pressure of a tire is extremely lower than a specified one, deformation of a section of the carcass ply cord 14 is restricted owing to high-stiffness of the rubber 24, though a carcass is bent by a small radius of curvature. This results in reducing substantially break of a filament 13 and restricting reduction of break life of the carcass ply cord 14. And because a spiral cord is not required, reduction of a weight becomes possible together with improvement in durability against fatigue during normal traveling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire having improved durability at low internal pressure.

[0002]

2. Description of the Related Art As shown in FIG. 5, a coated cord is used for a carcass ply 16 of a pneumatic radial tire. This coated cord is obtained by coating a plurality of aligned cords 34 (only one is shown in FIG. 5) with the coating rubber 24, and the dynamic elastic modulus E ′ of the coating rubber 24 after vulcanization is Generally, it is set around 1.7 × 10 ⁸ dyn / cm ² .

As is well known, the cord of this coated cord is formed by twisting a plurality of filaments.

As for the type of cord, as shown in FIG. 5, a so-called with-spiral cord 34 having a spirally wound spiral spiral cord 32 with a plurality of filaments 13 in a layer-twisted structure is shown. As shown in FIG. 1, there is a so-called non-spiral cord 14 that does not have the spiral cord 32.

The following properties are generally known for the with-spiral cord 34 and the non-spiral cord 14.

[0006] With the spiral cord 32, the outer circumference is wound around the with spiral cord 34, so that the deformation of the cross section of the cord when bending is small, but on the other hand, with the spiral cord 32, the weight is heavy and the cost is high. Has become.

On the other hand, the non-spiral cord 14 is more excellent in fretting resistance, corrosion resistance and fatigue resistance than the with spiral cord 34, and is light because it does not have the spiral cord 32. However, the non-spiral cord 14 is the with spiral cord 34.
Compared to the above, the cord cross section is largely deformed when bent (see FIG. 2), and an abnormally large force is applied to a specific filament.
Therefore, the pneumatic radial tire in which the non-spiral cord 14 is applied to the carcass ply withstands sufficient use when traveling at a normal internal pressure, but the carcass ply normally travels when traveling at a low internal pressure such as a flat tire. When it is used in a state in which the radius of curvature is extremely reduced due to a larger bending deformation, the cord breaking life becomes extremely short.

[0008]

SUMMARY OF THE INVENTION In consideration of the above facts, it is an object of the present invention to provide a pneumatic radial tire that is lightweight and can significantly improve durability at low internal pressure.

[0009]

The invention according to claim 1 is
A pneumatic radial tire provided with at least one layer of a carcass having a toroidal shape and a cord covered with a coating rubber that extends between a pair of bead portions, and a plurality of belts arranged on the outer periphery of the carcass crown portion. In addition, the elasticity of the coating rubber is high.

The invention according to claim 2 is the pneumatic radial tire according to claim 1, characterized in that the structure of the cord is 3 + 8, 3 + 9, 1 × 12 or 1 + 6 + 12.

The invention according to claim 3 provides the pneumatic radial tire according to claim 1 or 2,
The dynamic elastic modulus E ′ of the coating rubber is 2.0 to 6.
The feature is that it is 0 × 10 ⁸ dyn / cm ² .

The invention according to claim 4 is the same as claim 1,
The pneumatic radial tire according to claim 2 or 3 is characterized in that the tensile strength of the filaments forming the cord is 270 to 500 kg / mm ² .

[0013]

According to the first aspect of the invention, since the elasticity of the coating rubber coated on the carcass cord is high, the elasticity is high even when the cord is bent and the radius of curvature is reduced. Since the outer periphery of the cord is pressed by the rubber, the cord does not have a so-called spiral cord that surrounds the periphery of the cord, and thus the cross-sectional shape of the cord is not deformed and the cord is not twisted. Therefore, even when the vehicle equipped with the pneumatic radial tire of the present invention travels in a low internal pressure state such as a flat tire and the carcass is greatly deformed, the specific filaments forming the cord are excessively large. No stress acts. Therefore, the durability of the cord at low internal pressure is improved as compared with the conventional cord that does not have the spiral cord, and since the spiral cord is not required, the weight of the tire can be reduced.

According to the second aspect of the present invention, the structure of the carcass cord is 3 + 8, 3 + 9, 1 × 12 or 1 + 6.
Since it is +12, the fretting resistance, corrosion resistance and fatigue resistance of the cord are further improved.

According to the third aspect of the invention, the dynamic elastic modulus E'of the coating rubber is 2.0 to 6.0 × 10 ⁸ dyn /
Since it is cm ² , deformation of the cord cross section when the cord is bent is suppressed, and ply separation does not occur and workability during tire assembly is not impaired.

If the dynamic elastic modulus E'of the coating rubber is less than 2.0 × 10 ⁸ dyn / cm ² , the effect of suppressing the deformation of the carcass ply cord cross section is lost,
If it exceeds 6.0 × 10 ⁸ dyn / cm ² , the rubber becomes brittle and ply separation easily occurs, and the adhesion between the rubbers is deteriorated to deteriorate the workability during tire assembly.

According to the invention described in claim 4, since the tensile strength of the filaments forming the cord is 270 to 500 kg / mm ² , the weight of the tire can be reduced and the degree of embrittlement does not decrease. ..

Here, the tensile strength of the filament is 270 kg.
If it is less than / mm ^2, the weight of the carcass ply cord increases to obtain the same strength, and it becomes impossible to reduce the weight of the tire and the cost increases, and if the tensile strength exceeds 500 kg / mm ² , it becomes brittle. And the filament is likely to break.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 3, the pneumatic radial tire 10 to which the present invention is applied has a normal radial structure, and the carcass 12 has a carcass ply cord 14 (not shown in FIG. 3) around the tire. Substantially 90 ° to the direction
At least one carcass ply 16 arranged at an angle of
Have layers.

Both ends of the carcass ply 16 in the tire width direction are folded back around a pair of bead cores 18 arranged in a ring shape on the inner peripheral portion in the tire radial direction (direction of arrow R in FIG. 3).

Outside the carcass 12 in the radial direction of the tire,
A belt 20 having a cord formed at a predetermined angle with respect to the tire circumferential direction is arranged.
A thick tread 22 is arranged on the outer side in the tire radial direction of 0.

The carcass ply cord 14 has a layered structure of steel wire. For the structure of the carcass ply cord 14, for example, 3 + 8, 3 + 9 (see FIG. 1), 1 × 12 or 1 + 6 + 12 can be applied. However, other structures may be used. The carcass ply cord 14 is a so-called non-spiral cord that does not have a spiral cord that surrounds the outer periphery in a spiral shape.

On the other hand, the rubber 24 (see FIG. 1) for covering the carcass ply cord 14 of the carcass ply 16 is the rubber (dynamic modulus E '=
1.7 × 10 ⁸ dyn / cm ² ), and the dynamic elastic modulus E ′ after vulcanization is 2.0 to 6.0.
It is preferably within a range of × 10 ⁸ dyn / cm ² , more preferably within a range of 2.5 to 6.0 × 10 ⁸ dyn / cm ² , and further preferably within a range of 3.0 to 6.0 × 10 ⁸ dyn / cm 2. Within the range of ² (where, the dynamic elastic modulus E ′ has a strain of 1% and a frequency of 50H).
z was measured at room temperature of 20 ° C., and the dynamic elastic modulus E ′ used a spectrometer (Rheograph Solid L-IR type) manufactured by Toyo Seiki. ).

As a method for increasing the elastic modulus of the rubber 24, a conventional method for increasing the elastic modulus is to highly fill carbon black and sulfur, which has a high reinforcing property, or a short fiber such as glass fiber in the rubber. The method of compounding can be applied.

Further, tensile strength of the filaments 13 of the carcass ply cord 14 is preferably in the range of 270~500kg / mm ^2, further preferably in the range of 400~500kg / mm ^2.

Next, the operation of this embodiment will be described. When the tire internal pressure is extremely lower than the specified internal pressure at the time of tire puncture, etc., the carcass 12 of the pneumatic radial tire 10
Is largely bent, and in particular, the carcass 12 near the bead core 18 is bent outward in the tire width direction (direction W, direction W in FIG. 3) with a small radius of curvature (see imaginary line in FIG. 3). In the pneumatic radial tire 10 to which the present invention is applied, since the rubber 24 covering the carcass ply cord 14 has high rigidity, the carcass ply cord 14 may be bent with a very small radius of curvature. However, the deformation of the cross section of the carcass ply cord 14 is suppressed by the rubber 24 having high rigidity. Therefore, the forces act on the filaments 13 of the carcass ply cord 14 substantially evenly. Thus, a specific filament 1
Since there is no excessive force on 3
The breakage of No. 3 is greatly reduced, and the decrease in the breaking life of the carcass ply cord 14 is suppressed.

In particular, since the carcass ply cord 14 to which the present invention is applied has high durability when bent with a small radius of curvature, it is filled with a normal internal pressure and at the time of 100% load,
A great effect is exhibited by applying it to a tire in which the curvature of the largest curvature of the carcass ply cord 14 between the hump portion and the rim line is 70 mm or less. The reason for this is that when a tire having a curvature of 70 mm or less in the portion with the largest curvature of the carcass ply cord 14 has an internal pressure of zero, that is, when traveling in a punctured state, the portion with the smallest radius of curvature of the case line of the tire is very small. Because it will be in a harsh state.

The dynamic elastic modulus E'of the rubber 24 is 2.0
The range of up to 6.0 × 10 ⁸ dyn / cm ² is to suppress the deformation of the cross section of the carcass ply cord 14 when the dynamic elastic modulus E ′ is less than 2.0 × 10 ⁸ dyn / cm ^2. When the amount exceeds 6.0 × 10 ⁸ dyn / cm ² , the rubber becomes brittle and ply separation easily occurs.
Further, this is because workability during tire assembly is deteriorated.

The tensile strength of the filament of the carcass ply cord 14 is set to 270 to 500 kg / mm ² .
When the tensile strength is less than 270 kg / mm ² , the weight of the carcass ply cord 14 increases to obtain the same strength, the weight of the tire cannot be reduced, and the cost increases. Therefore, the tensile strength is 500 kg / mm ² This is because when the value exceeds the above range, the degree of embrittlement increases and the filament 13 easily breaks.

[Test Example] For a test tire, 9 types of pneumatic radial tires 10 to which the present invention was applied, 3 types of pneumatic radial tires of Comparative Examples and 2 types of conventional pneumatic radial tires 10 were prepared. The breaking rate of the filament and the fretting amount of the filament of the carcass ply cord of the test tire after the test running were measured. The test results are shown in Tables 1 and 2.

The thickness t of the rubber 24 of the carcass ply cord 14 used for the test tire is 2.2 mm and the number of driving is n.
Is 26/50 mm when the cord structure is 1 × 12, 28/50 mm when the cord structure is 3 + 9, and the cord structure is 1
In the case of + 6 + 12, it is 27.4 lines / 50 mm.

All test tire sizes are 11/70 R
It was set to 22.5, and the test was conducted using an actual vehicle. In the test,
A test tire filled with the normal internal pressure was mounted on an actual vehicle and
After running 100,000 km at a% load, the inner pressure of the tire inside the compound wheels was set to 0, and a further 10,000 km was run. The tire after the test was disassembled, carcass ply cords in the range of about 10 cm to about 20 cm outside the tire width direction were sampled from the tread center, and the breaking rate and fretting amount of the filament were measured.

In the measurement of the breakage rate, the number of samplings was 10 on each side of the tire, 20 in total, and the breakage rate Y was calculated by the following equation. Breakage rate Y (%) = Number of broken filaments / Total number of filaments × 100 (Here, the total number of filaments is (3 + 9 × 0.20 when the structure of the carcass ply cord is 3 + 9 × 0.20, for example.
9) × 20 = 240. ) On the other hand, the measuring point of the fretting amount is the fretting amount between the outermost sheath and the spiral cord for the with spiral cord, and the fretting amount for the core or the first sheath for the non-spiral cord. Targeted. The fretting amount is observed by an optical microscope with both ends of the sampled carcass ply cord fixed, and the focal length D (see FIG. 4) between the deepest point of the fretting and the non-abraded portion beside the fretting is measured, 10 on each side of the tire
A total of 20 samples were sampled one by one and the average thereof was calculated.

[0035]

[Table 1]

[0036]

[Table 2] From the test results of the tests in Tables 1 and 2, it is clear that the pneumatic radial tire according to the present example has a low filament breakage rate and fretting amount even if the carcass cord has a non-spiral structure. Became.

Although the carcass ply cord 14 having the layer-twisted structure has been described in this embodiment, the present invention is not limited to this, and the carcass ply cord 14 may have a single-twisted structure. Even in this case, since the rubber 24 that coats the carcass ply cord 14 has a high elastic modulus, even if the carcass ply cord 14 is bent and has a small radius of curvature, the cord cross-section is less deformed and has good durability.

[0038]

Since the pneumatic radial tire of the present invention has the above-mentioned structure, it has an excellent effect that it is lightweight and can significantly improve the durability at low internal pressure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a carcass ply having a non-spiral cord.

FIG. 2 is a cross-sectional view of a carcass ply showing a non-spiral cord in a state where the non-spiral cord is bent and the cross-sectional shape is deformed.

FIG. 3 is a sectional view taken along the axis of a pneumatic radial tire according to an embodiment of the present invention.

FIG. 4 is a side view of a filament with fretting according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a carcass ply having a with spiral cord.

[Explanation of symbols]

 10 Pneumatic radial tire 12 Carcass 13 Filament 14 Carcass ply cord 18 Bead core 20 Belt 24 Rubber (coating rubber)

Claims (4)

[Claims] 1. A carcass of at least one layer, which has a toroidal shape and covers a cord with a coating rubber, and which extends between a pair of bead portions, and a plurality of belts arranged on the outer periphery of the carcass crown portion. A pneumatic radial tire characterized in that the elasticity of the coating rubber is made highly elastic. 2. The structure of the code is 3 + 8, 3 + 9, 1
The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is x12 or 1 + 6 + 12. 3. A dynamic elastic modulus E ′ of the coating rubber.
Was 2.0 to 6.0 × 10 ⁸ dyn / cm ^2, and the pneumatic radial tire according to claim 1 or 2, wherein 4. The pneumatic radial tire according to claim 1, wherein the tensile strength of the filament forming the cord is 270 to 500 kg / mm ² .