JP3398065B2 - Radial tires for heavy loads - Google Patents

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 weight while maintaining 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. Particularly, a truck, a bus, etc. equipped with a diesel engine that emits harmful exhaust gas, etc. Then, the demand is increasing. Reducing the rolling resistance of a tire is effective in reducing the fuel consumption of a vehicle, and one of the reasons for this is reducing 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 cord as a carcass cord which forms the framework of the tire and is radially arranged. However, this method has a drawback that the strength of the tire, particularly the cut resistance of the tread portion, is deteriorated and the tire cannot be used practically.

As shown in Table 1, the inventors of the present invention have shown two types of carcass plies in which the size of the carcass cord and its end (the number of cords to be driven) are changed for the radial tire for heavy load of size 445 / 65R22.5. Then, tires were made as prototypes and tire weight and carcass ply strength were compared. As a result of the test shown in Table 1, the tire weight of the modified example could be reduced by 21% compared to the conventional example, but it was found that the strength of the carcass ply was decreased by 27%.

[0005]

[Table 1]

The inventors conducted various experiments to reduce the weight and maintain the tire strength. As shown in FIG. 4 (A), the conventional heavy-duty radial tire includes a carcass a and a belt layer b composed of a plurality of belt plies arranged on the outer side in the tire radial direction. Layer b was directly overlaid on carcass a. Therefore, between the carcass cord e and the belt cord f of the innermost belt ply b1 located on the innermost side in the tire radial direction, as shown in FIG. 4B in which the X portion of FIG. 4A is enlarged. The distance was about 0.6 mm or less, which was very small. However, it has been found that the tire strength increases when a rubber layer is interposed between the carcass a and the inner belt ply b1 and the distance between the cords is increased.

In FIG. 5, the vertical axis indicates the plunger performance index in which the plunger energy (breaking energy) representing the tire strength is indexed, and the horizontal axis indicates the inter-cord distance between the carcass cord and the belt cord of the above belt ply ( mm) is shown. In the figure, the white symbols are the specifications of the conventional example, the black symbols are the specifications of the modified example,
Tests were carried out on each of four sizes. Further, the plunger energy was measured according to the tire strength test of JIS D4230 with a plunger diameter of 38.0 (mm) and a plunger pressing speed of 50.0 (mm / min), and the minimum breaking energy of 1.
It is displayed as an index with 1 times 100, and it is judged that this index is 100 or more.

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

The present invention has been devised as a result of intensive studies on the physical properties of the rubber that separates the cords based on the above knowledge, and it is possible to reduce the tire weight and maintain the tire strength. It is intended to provide a heavy duty radial tire.

[0010]

The invention according to claim 1 of the present invention is a carcass having a carcass cord extending from the tread portion to the bead core of the bead portion through the sidewall portion and arranged in the radial direction, and the carcass. A radial tire for heavy load having a belt layer composed of a plurality of belt plies rubber-covered by arranging belt cords made of steel, which are arranged radially outside of the tire and inside the tread portion, between the belt ply and the carcass of which is disposed on the top inside of the tire radial direction of the layer thickness (d2) is 0.7mm or more, and a carcass cord adjacent the motor <br/> tire radial direction The distance (d1) between the cords on the tire equatorial plane with the belt cord is 1.
A reinforcing rubber layer having a thickness of 5 to 3.0 mm is arranged, and the reinforcing rubber layer has a JISA altitude of 70 to 100 ° and a complex elastic modulus (E *) of 8.0 to 43.0 (MPa) and 100. % Modulus (M100) is 4.0 to 8.0
(MPa) rubber composition.

The invention according to claim 1 is the reinforcing rubber layer.
The width (SW) in the tire axial direction of the belt ply
0.5 to 1.0 times the width (BW1) in the tire axial direction and
The center line of is arranged almost along the tire equator.

The invention according to claim 2 is the reinforcing rubber.
On both sides in the tire axial direction of the layer, from the edge of the reinforcing rubber layer
The tire extends axially outward and the tire axial direction of the belt layer
Cushion interposed between the outer end portion of the carcass and the carcass
Rubber is arranged and this cushion rubber is JIS
A altitude is 50 to 70 °, and complex elastic modulus (E *) is 2.
0-6.0 (MPa) and 100% modulus (M1
00) is 1.5 to 3.5 (MPa).
It is characterized by

The "complex elastic modulus" was measured by cutting a strip-shaped sample having a width of 4 mm, a length of 30 mm, and a thickness of 1.5 mm, and using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd.
The value is measured under the conditions of 0 ° C., frequency 10 Hz, and dynamic strain ± 2.0%.

"100% modulus" is defined by JIS
It is measured with a No. 3 dumbbell in accordance with K6301.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the heavy duty radial tire of the present embodiment includes a carcass 6 extending from a tread portion 2 to a bead core 5 of a bead portion 4 through a sidewall portion 3 and an outer side of the carcass 6 in a tire radial direction. Further, it is provided inside the tread portion 2, and further comprises a belt layer 7 made of a plurality of belt plies rubber-covered by arranging belt cords 12 (shown in FIG. 3) made of steel.

The carcass 6 is a carcass ply 6a in which a carcass cord 11 (shown in FIG. 3) made of steel is covered with a topping rubber in this example, and both ends of the carcass 6 are tire shafts. An example is shown of being folded back from the inner side in the direction to the outer side and locked. Further, the carcass cord 11 is, for example, 75 to the tire equator C.
It is formed of a radial structure that is arranged at an angle of 90 °.

The belt layer 7 has 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 of 15 to 30 with respect to the tire equator C. An example is shown in which a laminated body of four plies in total including other belt plies 7B, 7C and 7D arranged at a small angle of 0 is arranged, but the number of plies and the like can be appropriately determined. Belt layer 7
Comprises an intersection where the belt cords intersect between at least one pair of plies.

[0018] And, the between the belt ply 7A before Symbol in said carcass 6, by arranging a reinforcing rubber layer 9 that is continuous in the tire circumferential direction, as shown partially enlarged in FIG. 3 The inter-cord distance d1 on the tire equatorial plane CP between the carcass cord 11 and the belt cord 12 that are adjacent to each other in the tire radial direction is set to 1.5 to 3.0 mm. 1.
It is 1 mm or more, preferably 1.5 mm or more . The tire equator plane CP refers to a plane passing through the tire equator C. Further, in the present embodiment, the inter-cord distance d1 is set in the range over the entire width of the inner belt ply 7A.

[0019] The thus, the inter-cord distance d1
By setting the range , the reinforcing rubber layer 9 cooperates with the carcass 6 and the belt layer 7 to synergistically improve the strength of the tire even when a thin cord is adopted as the carcass cord 11 to reduce the weight. possible, and therefore, Ru earthenware pots are maintained tire strength while reducing the weight.

Here, various tires were manufactured by changing the physical properties of the rubber composition constituting the reinforcing rubber layer 9 (size 4).
45 / 65R22.5) and the plunger performance index was examined. As shown in Table 2, rubber compositions A and C were
JISA altitude is 70-100 ° and complex elastic modulus (E
It was found that *) is preferably 8.0 to 43.0 (MPa) and 100% modulus (M100) is preferably 4.0 to 8.0 (MPa). The rubber composition D had a high plunger index, but had a problem of insufficient durability due to heat generation.

[0021]

[Table 2]

Further, considering the thickness of each topping rubber covering the carcass ply 6a and the belt ply 7A therein, the thickness d2 (shown in FIG. 3) of the reinforcing rubber layer 9 is 0.7 mm or more. And The thickness d of this reinforcing rubber layer 9
When 2 is less than 0.7 mm, the reinforcing effect tends to be relatively lowered, and it may be difficult to keep the inter-cord distance d1 within the above range .

The width SW of the reinforcing rubber layer 9 in the tire axial direction is 0.5 to 1.0 times the width BW1 of the inner belt ply 7A in the tire axial direction. The width SW of the reinforcing rubber layer 9 is equal to the width BW1 of the belt ply 7A of 0.
If it is less than 1 time, improvement in tire strength cannot be expected , and
If it is 0.5 times or more, and conversely if it exceeds 1.0 times, the effect reaches the ceiling and the tire molding becomes difficult. The width SW of the belt ply 7A in the above is as shown in FIG.
It is 0.5 to 1.0 times the tread width TW shown in
It

By arranging the width center line of the reinforcing rubber layer 9 substantially along the tire equator C, the crown region of the tread portion 2 centered on the tire equator C is substantially symmetrical. It can be reinforced in good balance.

Further, in the present embodiment, the edges 9e of the reinforcing rubber layer 9 are provided on both sides of the reinforcing rubber layer 9 in the tire axial direction.
9e, a cushion rubber 10 extending in the tire axial direction and disposed between the outer end portion 7E of the belt layer 7 in the tire axial direction and the carcass 6 is provided. In this example, the outer end of the cushion rubber 10 in the axial direction of the tire extends beyond the belt layer 7 in the axial direction.

The cushion rubber 10 is preferably made of a rubber composition which is softer than the reinforcing rubber layer 9, so that the strain can be favorably applied at both ends of the belt layer 7 where the strain tends to concentrate. The tire durability can be further improved by mitigating and preventing, for example, cord separation. The cushion rubber 10 may have 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 heavy duty radial tire having a tire size of 425 / 65R22.5 was experimentally manufactured (example, conventional example),
The above-mentioned plunger performance index and tire weight were compared. The example is different from the conventional example in that a carcass cord thinner than the conventional example is used and a reinforcing rubber layer is provided. The test results are shown in Table 3.

[0028]

[Table 3]

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

[0030]

As described above, the heavy duty radial tire of the present invention can reduce the tire weight while maintaining the tire strength.

[Brief description of drawings]

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

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

FIG. 3 is an enlarged view of the Y portion.

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

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

[Explanation of symbols] 2 tread section 3 Side wall part 4 bead section 5 bead core 6 carcass 6a Carcass ply 7 Belt layer Belt ply in 7A 9 Reinforced rubber layer 10 cushion rubber 11 car cascode 12 belt cord CP tire equatorial plane

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-5-294108 (JP, A) JP-A-61-57408 (JP, A) JP-A-9-323506 (JP, A) JP-A-9- 207510 (JP, A) JP 7-172106 (JP, A) JP 7-237407 (JP, A) JP 63-134309 (JP, A) JP 2000-502307 (JP, A) (JP 58) Fields investigated (Int.Cl. ⁷ , DB name) B60C 9/18-9/20

Claims (2)

(57) [Claims] 1. A carcass having a carcass cord extending from a tread portion to a bead core of a bead portion through a sidewall portion and arranged in a radial direction, and a carcass arranged radially outside of the carcass and inside the tread portion, and A radial tire for heavy load having a belt layer composed of a plurality of belt plies coated with rubber and arranging belt cords made of steel, wherein the inner belt ply arranged on the innermost side in the tire radial direction of the belt layer. Between the carcass and the carcass, the thickness (d2) is 0.7 mm or more, and the inter-cord distance (d1) on the tire equatorial plane between the carcass cord and the belt cord that are adjacent in the tire radial direction is 1.5. A reinforcing rubber layer having a thickness of up to 3.0 mm is provided, and the reinforcing rubber layer has a JISA hardness of 70 to 100 ° and a complex elastic modulus (E ) Is 8.0~43.0 (MPa) Moreover, the 100% modulus (M100) is 4.0 to 8.0
(MPa) of the rubber composition, and the width (SW) of the reinforcing rubber layer in the tire axial direction is 0.5 to 0.5 of 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 its center line substantially along the tire equator. 2. On both sides of the reinforcing rubber layer in the axial direction of the tire, between the end edge of the reinforcing rubber layer and the axially outer side of the tire, and between the outer end portion of the belt layer in the axial direction of the tire and the carcass. Cushion rubber is placed between the cushion rubber and the cushion rubber has a JIS A hardness of 50 to 70 °.
The complex elastic modulus (E *) is 2.0 to 6.0 (MPa) and the 100% modulus (M100) is 1.5 to 3.5.
The radial tire for heavy load according to claim 1, which is made of a rubber composition of (MPa).