JP2000071716A - Heavy duty radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide heavy duty radial tire that reduces the tire weight while keeping its strength. SOLUTION: A heavy duty radial tire is provided with a carcass 6 having a carcass chord arranged in the radial direction and a belt layer 7 formed of a belt ply where a belt chord made of a steel, disposed outside of the radial direction of tire and inside of a tread portion of the carcass 6, is arranged. In this radial tire, a reinforcing rubber layer 9 is interposed between the belt ply 7A and the carcass 6 at the innermost portion in the radial direction of tire. The distance between the carcass chord and the neighboring belt chord in the radial direction of tire having the reinforcing rubber layer 9 therebetween in the radial direction of tire on the equatorial plane is set to 1.1 mm or greater. The reinforcing rubber layer 9 is formed of a rubber layer having JIS A altitude from 70 to 100 deg., complex modulus of elasticity (E*) from 8.0 to 43.0 MPa, and particularly, 100% modulus (M100) from 4.0 to 8.0 MPa. The width SW of the reinforcing rubber layer 9 is set to 0.1 to 1.0 times the width BW1 of the inner belt ply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty radial tire capable of reducing the weight while maintaining the tire strength.

[0002]

2. Description of the Related Art In recent years, it has been desired to reduce the fuel consumption of vehicles in consideration of global environmental problems. In particular, trucks, buses, etc., equipped with a diesel engine that emits harmful exhaust gas, are required. Then, the demand is increasing. Reducing the rolling resistance of the tire is effective in reducing the fuel consumption of the vehicle, and one factor for that is to reduce the weight of the tire.

As a method of reducing the weight of a heavy-duty radial tire, there is a method of reducing the weight by using a thin carcass cord that forms a tire skeleton and is radially arranged. However, this method has a disadvantage that the strength of the tire, particularly the cut resistance of the tread portion, is reduced, and the tire cannot be put to practical use.

[0004] As shown in Table 1, the inventors of the present invention have proposed two types of radial tires for heavy loads of 445 / 65R22.5 in which the size of carcass cords and the end (the number of cords to be driven) were changed. Each of the tires was prototyped, and the tire weight and the strength of the carcass ply were compared. As a result of the test shown in Table 1, the tire weight was reduced by 21% in the modified example as compared with the conventional example, but the strength of the carcass ply was reduced by 27%.

[0005]

[Table 1]

[0006] The inventors have conducted various experiments to maintain tire strength while reducing weight. As shown in FIG. 4A, a conventional heavy duty radial tire includes a carcass a and a belt layer b including a plurality of belt plies disposed radially outward of the carcass a. Layer b was overlaid directly on carcass a. For this reason, as shown in FIG. 4B in which the X portion of FIG. 4A is enlarged, the carcass cord e and the belt cord f of the belt ply b1 located on the innermost side in the tire radial direction. Was about 0.6 mm or less, which was very small. However, it has been found that a rubber layer is interposed between the carcass a and the inner belt ply b1, and the tire strength increases as the distance between the cords increases.

FIG. 5 shows a plunger performance index obtained by indexing plunger energy (breaking energy) representing tire strength on the vertical axis, and the inter-cord distance between the carcass cord and the belt cord of the above-mentioned belt ply (horizontal axis). mm). In the figure, the open symbols are the specifications of the conventional example, and the black symbols are the specifications of the modified example,
Tests were performed at four sizes each. The plunger energy is measured according to a tire strength test of JIS D4230 with a plunger diameter of 38.0 (mm) and a plunger pressing speed of 50.0 (mm / min).
It is indicated by an index where 1 is set to 100, and when this index is 100 or more, it is judged to be acceptable.

In the conventional specification in which the carcass cords are relatively thick, the distance between the cords is generally in the range of 0.2 to 0.6 mm, and in any case, the plunger performance index is 100 or more. . On the other hand, in the modified example in which the carcass cord is relatively thin, if the inter-cord distance is small, the plunger performance index falls below 100, and sufficient strength cannot be obtained. However, even in the modified example, the plunger performance index increases as the inter-code distance increases as described above, and a positive correlation (Y = 63.0 + 34.
1X).

The present invention has been made based on such findings, and has been devised as a result of intensive studies on the physical properties of rubber separating the cords, and can maintain tire strength while reducing tire weight. It is intended to provide a radial tire for heavy loads.

[0010]

According to a first aspect of the present invention, there is provided a carcass having a carcass cord arranged in a radial direction from a tread portion through a sidewall portion to a bead core of a bead portion, and a carcass having the carcass cord. A radial tire for heavy load, comprising: a belt layer comprising a plurality of belt plies rubber-coated by arranging belt cords made of steel and arranged radially outside and inward of the tread portion of the tire. A reinforcing rubber layer is disposed between the innermost belt ply and the carcass disposed in the tire radial direction of the layer, and a tire equatorial plane is disposed between the carcass cord and the belt cord adjacent in the tire radial direction. The distance between cords (d1) is 1.1 mm or more, and the reinforcing rubber layer has a JISA height of 70 to 10
0 ° and a complex elastic modulus (E *) of 8.0 to 43.0 (M
Pa) and 100% modulus (M100) is 4.0
And the tire width in the tire axial direction (SW) of the reinforcing rubber layer is 0.1 to 1.0 of the tire axial width (BW1) of the inner belt ply. It is characterized in that it is doubled and its center line is arranged almost along the tire equator.

According to a second aspect of the present invention, on both sides of the reinforcing rubber layer in the tire axial direction, the outer end of the belt layer extends in the tire axial direction from the edge of the reinforcing rubber layer. And a cushion rubber interposed between the carcass and the carcass.
A altitude is 50-70 ° and complex elastic modulus (E *) is 2.
0 to 6.0 (MPa) and 100% modulus (M1
2. The heavy-duty radial tire according to claim 1, wherein (00) comprises a rubber composition of 1.5 to 3.5 (MPa).

According to a third aspect of the present invention, the reinforcing rubber layer has a thickness (d2) of 0.7 mm or more and the width (SW).
Is 0.5 to 0.
8 times and the inter-code distance (d1) is 1.
The heavy-duty radial tire according to claim 1 or 2, which has a diameter of 5 to 3.0 mm.

The “complex elastic modulus” is obtained by cutting a strip sample of 4 mm width × 30 mm length × 1.5 mm thickness and using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. at a temperature of 7 ° C.
It is a value measured under the conditions of 0 ° C., a frequency of 10 Hz, and a dynamic strain of ± 2.0%.

"100% modulus" is defined in JIS.
It is measured using a No. 3 dumbbell according to K6301.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the heavy load radial tire according to the present embodiment includes a carcass 6 extending from a tread portion 2 to a bead core 5 of a bead portion 4 via a sidewall portion 3, and a radially outer portion of the carcass 6. A belt layer 7 is provided inside the tread portion 2 and includes a plurality of belt plies rubber-coated by arranging belt cords 12 (shown in FIG. 3) made of steel.

In the present embodiment, the carcass 6 is composed of a single carcass ply 6a in which a carcass cord 11 (shown in FIG. 3) made of steel is covered with topping rubber, and both ends of the carcass ply 6a are tire shafts. FIG. 3 illustrates an example in which the member is folded back from the inside to the outside and locked. The carcass cord 11 is, for example, 75 to
It is formed of a radial structure arranged at an angle of 90 °.

The belt layer 7 includes an innermost belt ply 7A inclined at a relatively large angle of about 60 ° ± 10 ° with respect to the tire equator C, and a steel cord 15 to 30 with respect to the tire equator C. Although the belt ply 7B, 7C, and 7D are arranged at a small angle of °, the belt ply 7B, 7C, and 7D are illustrated as a laminate of a total of four plies, but the number of plies and the like can be determined as appropriate. The belt layer 7
Comprises an intersection where the belt cord intersects at least one pair of plies.

In this embodiment, a reinforcing rubber layer 9 continuous in the tire circumferential direction is arranged between the inner belt ply 7A and the carcass 6, so that the rubber layer 9 is partially enlarged in FIG. As shown, the inter-cord distance d1 at the tire equatorial plane CP between the carcass cord 11 and the belt cord 12 adjacent in the tire radial direction is 1.1 mm or more, preferably 1.5 mm or more. The tire equatorial plane CP indicates a plane passing through the tire equator C. Further, in the present embodiment, an example is shown in which the inter-cord distance d1 is ensured to be 1.1 mm or more over the entire width of the inner belt ply 7A.

As described above, by setting the inter-cord distance d1 to a predetermined value or more, even when a thin cord is adopted as the carcass cord 11, the carcass 6 and the belt layer It is possible to synergistically improve the strength of the tire in cooperation with the above, so that the tire strength can be maintained while reducing the weight. If the distance d1 between the cords is too large, the weight of the tire tends to be reduced. From such a viewpoint, the inter-cord distance d1 is 1.5 to 3.5 mm, preferably 1.5 to 3.
0 mm is desirable.

Here, a tire (size 4) was manufactured by changing the physical properties of the rubber composition constituting the reinforcing rubber layer 9 in various ways.
45 / 65R22.5) and examining the plunger figure of merit, as in rubber compositions A and C shown in Table 2,
The JISA altitude is 70-100 ° and the complex modulus (E
*) Was found to be preferably 8.0 to 43.0 (MPa) and the 100% modulus (M100) was preferably 4.0 to 8.0 (MPa). In addition, the rubber composition D has a high plunger index, but has a disadvantage of insufficient durability due to heat generation.

[0021]

[Table 2]

In consideration of the thickness of the topping rubber covering the carcass ply 6a and the belt ply 7A in the carcass ply 6a, the thickness d2 (shown in FIG. 3) of the reinforcing rubber layer 9 is 0.7 mm or more. It is desirable that If the thickness d2 of the reinforcing rubber layer 9 is less than 0.7 mm, the reinforcing effect tends to decrease relatively, and the inter-cord distance d1 is set to 1.
It may be difficult to keep 1 mm or more.

The width SW of the reinforcing rubber layer 9 in the tire axial direction is 0.1 to 1.0 times, preferably 0.5 to 0.8 times the width BW1 of the inner belt ply 7A in the tire axial direction.
It is desirable to make it twice. The width SW of the reinforcing rubber layer 9 is
If the width is less than 0.1 times the width BW1 of the belt ply 7A, improvement in tire strength cannot be expected. I do. The width SW of the belt ply 7A in the above is
According to a custom, for example, the tread width TW shown in FIG.
It is preferably about 1.0 times.

By arranging such a reinforcing rubber layer 9 such that the width center line thereof is substantially along the tire equator C, the crown region of the tread portion 2 about the tire equator C is substantially symmetrical. It can reinforce with good balance.

In the present embodiment, on both sides of the reinforcing rubber layer 9 in the tire axial direction, edges 9e of the reinforcing rubber layer 9 are provided.
9e, a cushion rubber 10 having a substantially triangular cross-section and being disposed between the carcass 6 and the outer end 7E of the belt layer 7 in the tire axial direction and extending in the tire axial direction is illustrated. In this example, the outer end of the cushion rubber 10 in the tire axial direction extends beyond the belt layer 7 outward in the axial direction.

The cushion rubber 10 is desirably formed from a rubber composition that is more flexible than the reinforcing rubber layer 9, so that distortion can be suitably reduced at both ends of the belt layer 7 where distortion tends to concentrate. It can relax and prevent, for example, code separation, and can further improve the durability of the tire. For example, the cushion rubber 10 has a JISA altitude of 50 to 70 °, preferably 50 ° or more and less than 70 °,
Complex elastic modulus (E *) is 2.0 to 6.0 (MPa) and 100% modulus (M100) is 1.5 to 3.5 (M
A rubber composition having the physical properties of Pa) is preferable.

[0027]

EXAMPLE A radial tire for heavy load having a tire size of 425 / 65R22.5 was prototyped (example, conventional example).
The aforementioned plunger performance index and tire weight were compared. The embodiment differs from the conventional example in that a carcass cord thinner than the conventional example is used and a reinforcing rubber layer is provided. Table 3 shows the test results.

[0028]

[Table 3]

As a result of the test, it was confirmed that the tire of the example maintained the tire strength while reducing the weight.

[0030]

As described above, the radial tire for heavy load according to the present invention can reduce the weight of the tire while maintaining the tire strength.

[Brief description of the drawings]

FIG. 1 is a right half sectional view of a tire showing one embodiment of the present invention.

FIG. 2 is a partially enlarged view of a tread portion.

FIG. 3 is an enlarged view of a Y part thereof.

FIG. 4A is a cross-sectional view of a tread portion of a conventional heavy load radial tire, and FIG. 4B is an enlarged view of an X portion thereof.

FIG. 5 is a graph showing a relationship between tire strength and a distance between a carcass cord and a belt cord.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6a Carcass ply 7 Belt ply in belt layer 7A 9 Reinforcement rubber layer 10 Cushion rubber 11 Carcass cord 12 Belt cord CP Tire equatorial plane

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B60C 11/00 B60C 11/00 D

Claims (3)

[Claims] 1. A carcass having a carcass cord extending from a tread portion to a bead core of a bead portion via a sidewall portion and arranged in a radial direction; A heavy duty radial tire having a belt layer composed of a plurality of belt plies rubber-coated by arranging belt cords made of steel, wherein the innermost belt ply disposed on the innermost side in the tire radial direction of the belt layer A reinforcing rubber layer is arranged between the carcass cord and the carcass, and a cord-to-cord distance (d1) on the tire equatorial plane between the carcass cord and the belt cord adjacent in the tire radial direction is set to 1.1 mm or more; The reinforced rubber layer has a JISA height of 70 to 100 ° and a complex elastic modulus (E *) of 8.0 to 43.0 (MPa) and 1 0% modulus (M100) is 4.0 to 8.0
(MPa), and the width (SW) of the reinforcing rubber layer in the tire axial direction is 0.1 to less than the width (BW1) of the inner belt ply in the tire axial direction.
A heavy duty radial tire characterized by being arranged 1.0 times and with its center line substantially aligned with the tire equator. 2. On both sides of the reinforcing rubber layer in the tire axial direction, extending from the edge of the reinforcing rubber layer outward in the tire axial direction and between the outer end of the belt layer in the tire axial direction and the carcass. The cushion rubber that intervenes is arranged, and the cushion rubber has a JIS altitude of 50 to 70 mm,
And a complex elastic modulus (E *) of 2.0 to 6.0 (MPa) and a 100% modulus (M100) of 1.5 to 3.5.
The heavy duty radial tire according to claim 1, comprising a rubber composition of (MPa). 3. The reinforcing rubber layer has a thickness (d2) of 0.7.
mm or more and the width (SW) is 0.5 to 0.8 times the width (BW1) of the inner belt ply, and the inter-cord distance (d1) is 1.5 to 3.0 mm. Item 1
Or the radial tire for heavy load according to 2.