JPH05262104A - Radial tire for light motor truck - Google Patents

Abstract

PURPOSE:To reduce the weight of a tire and decrease noise during traveling. CONSTITUTION:The tire is provided with a toroidal carcass 5 and a belt layer 6 composed of steel codes arranged inside a tread part and outside in the radial direction of the carcass 5. In the carcass 5, a carcass ply is used, in which complex cords are juxtaposed, wherein a high elastic filament composed of organic fiber and having a modulus of tensile elasticity 80-280g/d and a low elastic filament composed of organic fiber and having a modulus of tensile elasticity 15-60g/d are twisted together and twist coefficient thereof is set. at 1000-3100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire for a light truck, and more particularly to a radial tire for a light truck capable of reducing the weight of a tire having 8 to 12 ply rating and reducing noise during traveling.

2. Description of the Related Art Conventionally, carcass plies are often used in tires having a bias structure because nylon cords have high toughness and good adhesion with rubber. However, the nylon cord has a relatively large elongation and is inferior in dimensional stability in the tire, so that the steering performance and uniformity of the tire are inferior, and a flat spot phenomenon is likely to occur. Therefore, almost no nylon cords are used for the carcass ply of the radial tire, and polyester cords, rayon cords and steel cords are exclusively used.

However, when a tire using a polyester cord is exposed to a high temperature during use, the strength of the cord is lowered due to thermal deterioration, and the adhesive strength with rubber is greatly lowered. Further, in the case of a tire using rayon or steel cord, the adhesion is greatly reduced due to the action of water that has penetrated into the tire, resulting in very dangerous damage from ply loose to case damage. Further, when an aromatic polyamide fiber cord having a high tensile elastic modulus is used for a carcass ply, the tire has high rigidity and a tire excellent in steering stability can be obtained, but the riding comfort and durability of the tire are poor. This is inferior in flexural fatigue resistance due to the high crystallinity of the aromatic polyamide fiber and in breaking energy represented by [strength × cutting elongation] × (1/2).

On the other hand, in order to improve the high-speed durability of the tire, the cord of the belt layer is made of steel or aramid cord to increase the rigidity of the tread portion, and the band layer is provided on the outer side in the radial direction of the belt layer. By suppressing the occurrence of a so-called lifting phenomenon in which the tread portion bulges outward in the radial direction and rises due to centrifugal force generated in the tread portion as the tire rotates, high-speed durability is improved.

On the other hand, the global environment is deteriorating such as global warming and an increase in carbon dioxide. In order to prevent such environmental deterioration, even a four-wheeled vehicle is attempted to save fuel. ..

Further, the most effective way to reduce fuel consumption in a vehicle is to reduce the vehicle weight. For example, reducing the vehicle weight by 1% has the effect of improving the fuel consumption by 1%. I was requested.

[0006]

In response to the above-mentioned demand, there is also on the market the one in which the belt cord of the belt layer is replaced with steel and aramid fiber having substantially the same strength as steel is used. Although it is possible to reduce the weight of the tire by using organic fiber, which has a smaller specific gravity than steel, the steering stability deteriorates due to insufficient rigidity and the pattern noise is high due to a decrease in uniformity as compared with steel cords. There is. Especially 10 to 1
2KH significant increase in noise in the _Z.

The inventors of the present invention reduce the weight of such a tire,
As a result of intensive studies to achieve two problems of suppressing noise, as a carcass cord, by mixing and twisting a high-elasticity filament and a low-elasticity filament, the carcass cord has a low elasticity below the inflection point. The carcass ply is made to be less ply by making it function as high elasticity above the inflection point to reduce the weight and improve the steering stability by the rigidity in the high elasticity range.
It was also found that the occurrence of pattern noise can be suppressed by using a steel cord as the belt cord.

The present invention is based on the use of a carcass ply composed of a composite cord obtained by twisting a carcass with a high-elasticity filament and a low-elasticity filament, and a belt ply consisting of a steel cord for the belt layer. It is an object of the present invention to provide a radial tire for a light truck that can reduce the weight of the tire without increasing noise, save energy, and improve durability.

[0009]

SUMMARY OF THE INVENTION The present invention comprises a tread portion, side wall portions extending inward from both ends thereof in a radial direction, and bead portions located at both radial end portions of the side wall portion. And a toroidal carcass in which both ends of a cord that extends substantially parallel to the tire radial direction through the tread portion and the sidewall portion are folded back around the bead core in the bead portion, and the inside of the tread portion and the radial direction of the carcass. A radial tire for a light truck having a belt layer made of a steel cord arranged on the outer side, wherein the carcass is made of organic fiber and has a high elastic modulus of 80 to 280 g / d in tensile modulus, and a tensile strength is made of organic fiber. 10 with a composite cord in which a low elastic filament having an elastic modulus of 15 to 60 g / d is twisted together.
The twist coefficient WT, which is the product N√D of the number N of twists per cm length and the square root of the total number of denier D of the cord, is 100.
A radial tire for a light truck, characterized in that a carcass ply formed by rubberizing a cord-woven cloth of 0 to 3100 is used.

[0010]

The carcass ply has a carcass cord composed of a composite cord in which a high elastic filament and a low elastic filament are twisted together, so that the composite cord has a low elastic region below the inflection point and a high elastic region above. Have both.

Therefore, the elasticity corresponding to the elongation (about 3%) of the carcass cord during the tire vulcanizing step is in the low elastic region, and therefore, when the tire is vulcanized by the vulcanizing die, the internal pressure inside the raw tire is The outer peripheral surface of the tire can be pressed against the inner surface of the vulcanization mold along with the elongation of the composite cord, and the vulcanization molding of the tire is facilitated while using the highly elastic filament, and the tire accuracy is also improved. Therefore, by improving the finish accuracy of the tire, uniformity can be improved and noise can be reduced.

Further, at the time of high speed rotation of the tire with high deformation,
Since the composite cord of the carcass ply exhibits high elasticity and the hoop effect of the belt layer made of steel cord is improved, so-called lifting of the belt layer is prevented,
By suppressing the occurrence of standing waves, the high speed durability of the tire is improved and vibration is suppressed.

Further, since a high-strength composite cord is used as the carcass cord, the number of carcass plies can be reduced as compared with the case where a conventional polyester or nylon cord is used. That is, the weight can be reduced by making the resply, and the fuel efficiency is improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a radial tire T for a light truck
Has a sidewall portion 3 extending inward in the radial direction from both ends of the tread portion 2, and a bead portion 4 located at an inner end in the radial direction of the sidewall portion 3, and further in a radial direction of the tire. A toroidal carcass 5 having cords extending substantially parallel to each other and having both ends folded back around the bead core 4A, and a belt layer 6 located inside the tread portion 2 and radially outside the carcass 5. ing. In this example, the band layer 7 is arranged on the outer side in the radial direction of the belt layer 6 over the entire width of the belt layer 6.

Here, the fact that the carcass 5 extends substantially parallel to the radial direction means that the carcass 5 is inclined at an angle within 30 ° with respect to the tire axis, and includes radial tires and semi-radial tires.

The belt layer 6 is composed of upper and lower two layers of belt plies 6B and 6A. The lower belt ply 6A is wider than the upper belt ply 6B, and the belt plies 6A and 6B are used in this embodiment. In the example, it has a cut end structure in which the side end is cut.

The belt plies 6A and 6B of the belt layer 6 may have the same width or different widths, or the upper belt ply 6B may have a wide width.

As shown in FIG. 2A, the ply of the carcass 5 uses a composite cord 12 in which high elastic filaments 10 ... And low elastic filaments 11 ... Are twisted together.

The inclination angle of the carcass cord is 70 ° to 90 ° with respect to the tire circumferential direction, and when a plurality of plies are used, the cords of adjacent plies are inclined opposite to each other.

The high elastic filament 10 is an aromatic polyamide fiber, wholly aromatic polyester fiber, carbon fiber or the like, and has a tensile elastic modulus (EH) in the range of 80 to 280 g / d. The thickness is 1000-3
A relatively thin diameter of about 000 denier is used.

Further, as the low elastic filament 11,
Nylon fibers, polyester fibers or vinylon fibers having a tensile elastic modulus (EL) in the range of 15 to 60 g / d are used.

One or a plurality of such high-elasticity filaments 10 are simultaneously ply-twisted, and one or a plurality of low-elasticity filaments 1 ply-twisted in the same direction.
The composite cord 12 is formed by twisting 1 and 1 in opposite directions. Moreover, the composite code 12 is 1
The twisting coefficient WT represented by the product N√D of the twisting number N per 0 cm length and the square root of the total denier number D of the carcass cord is in the range of 1000 to 3100.

Conventionally, some combination cords of aromatic polyamide and other fibers are known. For example, Japanese Patent Publication Sho 56
Although a composite cord of aromatic polyamide and rayon is disclosed in Japanese Patent Laid-Open No. 107038/1998, in this case, sufficient flex fatigue resistance and breaking strength are not obtained.
If it is attempted to cover this with the number of twists, the strength will be reduced and eventually the tire durability will be as high as that of the carcass material of rayon alone or the cord, and the merit of the composite cord will be lost.

Japanese Unexamined Patent Publication (Kokai) No. 54-45007 discloses a composite cord of aromatic polyamide and nylon or polyester, which shows sufficient cord properties in bending fatigue resistance and breaking strength as a carcass ply cord. It has not been.

When a plurality of high-elasticity filaments 10 and a plurality of low-elasticity filaments 11 are used, each of the filaments may be pretwisted, or the plurality of filaments may be combined and pretwisted. As shown in FIG. 2 (A), the composite cord 12 may be formed by twisting each one of the high-elasticity filament 10 and the low-elasticity filament 11, or one of them may be one and the other may be plural. Alternatively, the composite cord 12 can also be formed by twisting together a plurality of strands.

When a tensile force is applied to the composite cord 12 as described above, as shown in FIG. Further, the elongation increases the initial twist pitch P1 of the composite cord 12 to the pitch P2 due to the elongation. This extension is shown in FIG.
As schematically shown in (B), the high-elasticity filament 10A, which has a coil shape in the initial state, becomes a straight filament 10B by a predetermined elongation. Therefore, from such a state, the original high elastic modulus of the high elastic filament 10 is exhibited. As described above, by winding the high-elasticity filament 10 in a spiral shape in advance, the elongation is relatively large from the spiral state of FIG. 3A to the straight state of FIG. 3B. It is obvious that a low elastic region and a high elastic region in which elongation is small by further applying a load from the state of FIG. 3 (B) can be provided, and FIG.
The straightened state shown in (B) forms an inflection point of the elongation-stress curve.

In the composite cord 12, the inflection point V is thus set so as to be located within the range of 4 to 6% of the elongation. The composite cord 12 is a twisted body of the high-elasticity filament 10 and the low-elasticity filament 11. Therefore, as shown in FIG. 2B, the high-elasticity filament 10 and the low-elasticity filament 11 are twisted even when a load is applied. , And therefore its inflection point V is shown in FIG.
It is not remarkable as compared with the schematic case of (B). The stress-elongation curve of the composite cord 12 is illustrated in FIG.
In the figure, the curve a is 1680 d / nylon 66.
No. 1 low elastic filament 11 and curve b is 2000d
Highly elastic filament 1 made of 1/1 aromatic polyamide
An elongation curve of 0 is shown. A curve c shows the case of a composite cord 12 in which one of these high-elasticity filaments 10 and one of the low-elasticity filaments 11 are twisted together.
It can be seen that the curve c is located between the curve a and the curve b, and the inflection point V is in the range of elongation 4 to 6%. In the composite cord 12, the inflection point V is an intersection point of a vertical line passing through an intersection point X where the tangent line S1 tangent to the curve in the state of zero elongation and the tangent line S2 drawn to the curve c at the break point intersect. It is defined.

The composite cord 12 has a high elasticity region from the inflection point V to the breaking point, and an inflection point V from the origin where the elongation is zero.
3. The elastic modulus EH in the high elastic region and the elastic modulus EL in the low elastic region EH / EL are equal to 4.
The range is 5 to 5.5. Such a composite code 1
2, the thickness, number and elastic modulus of the high elastic filaments, the thickness, number and elastic modulus of the low elastic filaments are appropriately selected, and by adjusting the twisting conditions such as the filament angle, as shown in FIG. The composite cord 12 that can fill the range can be formed. It can also be adjusted by selecting the stretching process applied to the composite cord 12, the high elastic filament 10 and the low elastic filament 11.

Since the inflection point V exists in the range of 4 to 6% in elongation, when a raw tire is mounted on a vulcanization mold and an internal pressure is filled in the raw tire during tire production, Due to the internal pressure, the belt layer 7 becomes the composite cord 12
By swelling due to the expansion of and the outer peripheral surface is pressed against the inner surface of the mold, the groove shape formed in the mold can be engraved on the tread portion 2. The swelling of the green tire due to the filling with the internal pressure is performed by the expansion of the composite cord 12 in the low elasticity region. Therefore, the inflection point V is set within the range of 4 to 6% elongation. The required elongation of the composite cord 12 in the mold due to internal pressure filling is preferably located near the inflection point V. As a result, the inflation of the molded tire and the expansion of the tire due to the centrifugal force acting at the time of high-speed rotation can be suppressed by the high elasticity region as shown in FIG. Therefore, the ratio EH / EL of the elastic modulus EH in the high elastic region and the elastic modulus EL in the low elastic region is set to 4.5 to 5.5. When it is less than 4.5, the above-mentioned suppressing effect is poor, and when it exceeds 5.5, it is unnecessary from the viewpoint of tire balance.

The band layer 7 is composed of one or more band plies 7A and 7A. The band ply 7A is formed by winding a long and narrow band ply 20 around the belt layer 6. ..

As shown in FIG. 5, the band-shaped ply 20 comprises one band cord 21 or two band cords 21 arranged in parallel, and in the present embodiment, two band cords 21 are embedded in a coating rubber 22. Organic fiber cords such as nylon, Teflon, and aromatic polyaramid polyester are used. Nylon fibers have a greater elastic elongation than other organic fibers, and by winding a belt-shaped ply of the nylon fibers around the outside of the belt layer 6, the belt layer 6 is pressed inward in the radial direction of the tire to move the belt layer 6. Can be efficiently blocked.

The band ply 7A is formed by spirally winding from one end line of the band layer 7 over the tire equator CL toward the other broken line and substantially parallel to the tire equator CL. It In this embodiment, when the strip-shaped ply 20 is wound, as shown in FIG. 6, the side edges 20a, 20a of the strip-shaped ply 20 facing each other are wrapped and wound. Therefore, the looseness of the strip ply 20 is prevented.

Since the belt-shaped ply 20 is spirally wound in the tire circumferential direction, a seam in a direction intersecting with the tire circumferential direction does not occur, so that running stability and riding comfort during running can be further enhanced and noise can be further reduced. It can be lowered.

The band layer 7 may be formed of a monoply band ply, while the belt layer 6 may be formed of a belt ply 6A formed by spirally winding the band-shaped ply of the above construction.

[0035]

[Specific example] Tire size is 700R16 12PR1
4 or 650R16 10PR and the tire having the configuration shown in FIG. 1 was prototyped according to the specifications shown in Table 1 (Example 1
4) and the tire weight, running noise, high speed durability, and riding comfort of the tire having the conventional configuration (Comparative Examples 1 and 4) and the tire having a configuration other than the present application (Comparative Examples 2 and 3) were compared. ..

The tire weight is shown as an index with the net weight not including the tube and the rim being measured and Comparative Example 1 being 100. The smaller the number, the lighter it is. The noise level was shown as an index with 100 as Comparative Example 1 by mounting the test tire on the vehicle and measuring the overall noise level at a position 1 m away from the tire. The smaller the number, the smaller the noise.

For high-speed durability, an inner drum tester having a diameter of 1700 mm was used to apply an internal pressure of 6 kgf / cm ^{2 and} a load 1.5 times the maximum load specified by JIS to the test tire to obtain a peripheral speed of 1.
The vehicle was run at 00 km / H, and the total running distance until cracks were generated on the tire surface was measured and indicated as an index with Comparative Example 1 being 100. The higher the value, the better the high-speed durability. The riding comfort was judged based on the driver's feeling when traveling on general roads, and Comparative Example 1 was set to 1
It is displayed with an index of 00.

[0038]

[Table 1]

It can be confirmed that the example can reduce the weight without significantly increasing the noise as compared with the comparative example 1, and can reduce the noise as compared with the comparative example 3. It was

[0040]

As described above, the radial tire for a light truck of the present invention comprises a composite cord in which a carcass is twisted with a high elastic filament made of an organic fiber and a low elastic filament made of an organic fiber. It can be suitably used as a commercial tire because it can reduce the fuel consumption and noise without reducing the tire performances, uniformizing the uniformity, and reducing the weight of the tire.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2A is a front view illustrating a composite cord.
(B) is a front view showing the extended state.

3 (A) and 3 (B) are front views schematically showing an initial state and a stretched state of a high-elasticity filament.

FIG. 4 is a diagram showing an example of an elongation curve of a cord.

FIG. 5 is a perspective view showing an example of a narrow ply forming a belt ply.

FIG. 6 is a cross-sectional view showing winding of a strip ply.

[Explanation of symbols]

 2 tread part 3 sidewall part 4 bead part 4A bead core 5 carcass 6 belt layer 6A, 6B belt ply 10 high elastic filament 11 low elastic filament

Claims (5)

[Claims] 1. A tread portion, a side wall portion, a side wall portion extending radially inward from both ends of the tread portion, and a bead portion located at both radial end portions of the side wall portion. A toroidal carcass formed by folding back both ends of a cord that extends substantially parallel to the radial direction of the tire around the bead core in the bead portion, and a steel cord arranged inside the tread portion and radially outside the carcass. A radial tire for a light truck having a belt layer, wherein the carcass is made of organic fibers and has a tensile elastic modulus of 80 to 280 g /
A square cord of the number of twists N per 10 cm length and the total number of denier D of the cord in a composite cord in which a high elastic filament of d and a low elastic filament made of organic fiber and having a tensile elastic modulus of 15 to 60 g / d are twisted together. A radial tire for a light truck characterized by using a carcass ply formed by rubberizing a cord-woven cloth having a twist coefficient WT of 1000 to 3100, which is a product N√D of 2. The radial tire for a light truck according to claim 1, wherein the high-elasticity filament is an organic fiber made of aromatic polyamide fiber or wholly aromatic polyester fiber. 3. The radial tire for a light truck according to claim 1, wherein the low-elasticity filament is a nylon fiber, a polyester fiber or a vinylon fiber. 4. The composite cord is formed by twisting one or more high-elasticity filaments twisted in the lower direction and one or more low-elasticity filaments twisted in the same direction in the opposite direction. The radial tire for a light truck according to claim 1, wherein 5. The composite cord has a low elastic region whose stress-elongation curve extends from the origin to an inflection point, and a high elastic region exceeding the inflection point, and the inflection point has an elongation of 4 to 6. % Elastic modulus EH in the high elastic range and elastic modulus EL in the low elastic range
The radial tire for a light truck according to claim 1, wherein the ratio EH / EL is 4.5 to 5.5.