JP2002316513A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the wandering performance while ensuring the high steering stability on a smooth road surface. SOLUTION: The following inequalities are satisfied, where α1C, α2C and α3C are the code angles on a belt center area Yc of first to third belt plies 11-13, and α1S, α2S and α3S are the code angles at a belt outer area Ys thereof. 40 deg.<=α1C<=70 deg., 15 deg.<=α2C<=25 deg., 15 deg.<=α3C<=25 deg., 1 deg.<=α1S-α1C<=5 deg., 1 deg.<=α2S-α2C<=5 deg., and 1 deg.<=α3S-α3C<=5 deg..

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 suitable for heavy-load vehicles and having improved wandering performance while ensuring high steering stability on a smooth road surface.

[0002]

2. Description of the Related Art In a radial tire for a heavy load vehicle, it is necessary to sufficiently increase the rigidity of a belt layer in order to support a high internal pressure and a high load. As shown in FIG. 3, at least three belted plies are used for the belt layer a, and the cord angle α1 of the first ply a1 on the carcass side with respect to the tire circumferential direction is relatively deep as 40 to 70 °. And the cord angle α of the second and third plies a2 and a3 outside thereof.
2, α3 is substantially the same in the range of 15 to 25 °, and the inclination direction of the cord of the third ply a3 is changed to the first and second ply a.
The cords are arranged in the direction opposite to the inclination direction of the cords 1 and 2 to form a strong truss structure.

In a tire reinforced with such a belt layer a, the cornering force is increased, and therefore, on a smooth road surface, excellent steering stability can be exhibited in both straight traveling and turning. However, on the other hand,
Since the rigidity of the tread shoulder portion also increases uniformly, there is a problem that when traveling on a rutted road surface or the like, a so-called wandering phenomenon in which the tire fluctuates due to an external force received from the road surface.

As described above, the steering stability on a smooth road surface and the wandering performance are in a trade-off relationship. Conventionally, the tread edge is rounded, or the tread edge is cut, or the tread edge is cut in the vicinity of the tread edge. The wandering performance has been improved by a technique such as reducing the rigidity of the tread shoulder portion by providing a narrow groove in the direction.

[0005] The present invention is based on the fact that the belt angle of the belt cord is different between the belt central region and the belt outer region in each belt ply, and the steering stability on a smooth road surface is improved without employing the above method. The aim is to provide a pneumatic radial tire that can improve wandering performance while securing it.

[0006]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present application provides a belt cord which is inclinedly arranged in the tire circumferential direction inside the tread portion and outside the carcass in the radial direction. A first belt ply, and a second belt ply that sequentially overlaps radially outward from the carcass side;
A pneumatic radial tire provided with a belt layer including at least a belt ply and a third belt ply,
The cord angle of the belt cord of the first to third belt plies with respect to the tire circumferential direction in the central portion of the belt having a width of 1/3 of the maximum width of the belt around the tire equator is α1.
c, α2c, α3c, and α1s, α2s, α3s of the belt angles of the belt cords of the first to third belt plies with respect to the tire circumferential direction in the belt outer region having a width 1/6 of the maximum belt width from the outer end of the belt. , The following relational expression is satisfied. 40 ° ≦ α1c ≦ 70 ° 15 ° ≦ α2c ≦ 25 ° 15 ° ≦ α3c ≦ 25 ° 1 ° ≦ α1s-α1c ≦ 5 ° 1 ° ≦ α2s-α2c ≦ 5 ° 1 ° ≦ α3s-α3c ≦ 5 °

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described.
This will be described together with the illustrated example. FIG. 1 is a meridional section when the pneumatic radial tire of the present invention is a heavy-duty radial tire for trucks and buses.

In FIG. 1, a pneumatic radial tire 1 is shown.
The tire 1 (hereinafter, referred to as a tire 1) is disposed on the carcass 6 extending from the tread portion 2 to the bead core 5 of the bead portion 4 through the sidewall portion 3, and inside the tread portion 2 and outside the carcass 6 in the tire radial direction. And a belt layer 7.

The carcass 6 has at least one ply folded portion 6b provided at both ends of a ply body portion 6a extending between the bead cores 5 and 5 from the inside in the tire axial direction to the outside around the bead core 5 in the tire axial direction. In the example, a case where the carcass ply 6A is formed is shown. In the carcass ply 6A, the carcass cords are arranged at an angle of 80 to 90 degrees with respect to the tire circumferential direction, and in this example, a steel cord is used as the carcass cord.

The carcass 6 may be composed of one or more plies using an organic fiber cord such as aromatic polyamide, nylon, rayon, or polyester, in addition to the steel cord. The ply turn-up portion 6b is interrupted above the bead core 5 and below the maximum width position of the tire. Between the ply turn-up portion 6b and the ply body portion 6a, bead apex rubber 8 is filled, and the bead portion 4 is Reinforced and increased tire lateral rigidity.

Next, the belt layer 7 is covered with the carcass 6.
And at least a first belt ply 11, a second belt ply 12, and a third belt ply 13 that sequentially overlap radially outward from the side, and in the present example, the fourth belt ply is further narrowed outwardly. A four-layer structure having a belt ply 14 is illustrated. The fourth belt ply 14 can be omitted.

The first to fourth belt plies 11 to 14
The ply width W of the second belt ply 12
B and the first and third belt plies 1
1, 13 are formed with a ply width of 85 to 95% of the ply width WB. At this time, it is preferable that the maximum ply width WB is 0.7 times or more the tire width WT in order to suppress the outer diameter growth of the tread shoulder portion during running and the deterioration of rubber due to the heat generated thereby. The narrowest fourth belt ply 14 mainly functions as a breaker for protecting the inner first to third belt plies 11 to 13, increases cut-through resistance from the tread surface, and reduces puncture and the like. To prevent.

Here, in this specification, the maximum ply width WB is defined as "belt maximum width WB".

Each of the belt plies 11 to 14 is formed by arranging belt cords, which are steel cords, inclined with respect to the tire circumferential direction. In this embodiment, as shown in FIG. Each of the belt cords 11 and 12 is inclined in the same direction (for example, a right-upward direction) with respect to the tire equator C, and the third and fourth belt plies 13 and 14 are provided.
Of the first and second belt plies 1
It inclines in the opposite direction (for example, the direction to the upper left) from 1 and 12.

In the belt layer 7 of this embodiment, the cord angles of the belt cords of the first to third belt plies 11 to 13 with respect to the tire circumferential direction in the belt center region Yc are α1c, α2c, α3c, Area Y
s, the cord angle of the belt cords of the first to third belt plies 11 to 13 with respect to the tire circumferential direction is α1
When s, α2s, and α3s, the following relational expression is satisfied. 40 ° ≦ α1c ≦ 70 ° (1) 15 ° ≦ α2c ≦ 25 ° (2) 15 ° ≦ α3c ≦ 25 ° (3) 1 ° ≦ α1s−α1c ≦ 5 ° (4) 1 ° ≦ α2s−α2c ≦ 5 ° (5) 1 ° ≦ α3s−α3c ≦ 5 ° (6) In the following, code angles α1c to α3c are collectively referred to as code angles αc and α1s to α3s. It may be referred to as a code angle αs.

The "belt center region Yc" is defined as 1/3 of the maximum belt width WB around the tire equator C.
Is the region having the greatest influence on the steering stability on a smooth road surface. On the other hand, the "belt outer region Ys" is a region having a width Ws that is 1/6 of the maximum belt width WB from the belt outer end 7E and has a large influence on the wandering performance.

Here, in the belt central area Yc,
As shown in equations (1) to (3), each belt ply 11 to
Thirteen cord angles αc are controlled within a conventional range to form a strong truss structure. Thus, the belt rigidity can be sufficiently increased, and the steering stability on a smooth road surface can be exhibited at a high level.

On the other hand, in the belt outside area Ys, as shown in the equations (4) to (6), the cord angle αs of each belt ply 11 to 13 is changed to the belt central area Ys.
The code angle αc is increased in the range of 1 ° to 5 °, respectively. At this time, each belt cord is continuous in each of the belt plies 11 to 13.

Thus, in each of the belt plies 11 to 13, the inter-cord distance in the belt outer region Ys is smaller than the inter-cord distance in the belt center region Yc by sin αs /
It increases with the ratio of sinαc. That is, the amount of steel per unit area decreases, and the rigidity in the belt outer region Ys becomes smaller than the rigidity in the belt central region Yc.

As a result, when traveling on the rut, the external force acting on the tread shoulder portion from the road surface can be absorbed and reduced, and the wandering performance can be improved while maintaining the steering stability. Here, if the angle difference αs−αc is less than 1 °, the function and effect of the present application are not exhibited. Conversely, if the angle difference αs−αc exceeds 5 °, it tends to be difficult to ensure steering stability.

The area Ym between the belt center area Yc and the belt outer area Ys is defined by a belt cord having a cord angle α.
This is a transition region in which the code angle changes from c to the code angle αs, and this change may be smooth or may be bent like in this example.

The belt layer 7 may have different belt cord thicknesses, cord driving densities, and the like for each belt ply. It can be configured as a category tire. Further, other techniques for improving the wandering performance as described above, that is, rounding the tread end, cutting in a tapered shape, or providing a circumferential narrow groove near the tread end to form a tread shoulder portion It can also be implemented in combination with a technique such as relaxing the rigidity.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment, but may be implemented in various forms.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A tire having the structure shown in FIG.
A 2.5-inch heavy duty radial tire was prototyped based on the specifications in Table 1, and the steering stability and wandering performance of each test tire on a smooth road surface were tested. The results are shown in Table 1. Other specifications are as follows and are common. Carcass Plies: 1 Carcass cord (steel); 3 × 0.2 + 7 × 0.2
3 Cord angle: 90 ° Number of cords: 23 cords / 5 cm Belt layer Number of plies: 4 Belt cords (steel); 1 × 5 / 0.38 Cord angle: Table 1 Number of cords: 19; 27; 27; 27 (1st; 2nd; 3rd; 4th) book / 5cm (belt center area)

(1) Steering stability and wandering performance: The test tires were mounted on a vehicle (2-D / 4 vehicles, vehicle weight 20 tons) under a rim (7.5 × 22.5) and an internal pressure (700 kPa). ) On all wheels, and at a load capacity (constant load) on a rutted road test course and a highway
I ran at m / h. The characteristics at that time were evaluated by a 10-point method in which Comparative Example 1 was evaluated as 6 points by sensory evaluation of the driver. The larger the index, the better.

[0026]

[Table 1]

As a result of the test, it was confirmed that the tire of the example can improve the wandering performance while ensuring high steering stability on a smooth road surface.

[0028]

Since the present invention is configured as described above,
Wandering performance can be improved while ensuring high steering stability on a smooth road surface.

[Brief description of the drawings]

FIG. 1 is a sectional view of a tire according to an embodiment of the present invention.

FIG. 2 is a development view illustrating a code arrangement of a belt layer.

FIG. 3 is a development view illustrating a cord arrangement of a belt layer of a conventional tire.

[Explanation of symbols]

 2 Tread 6 Carcass 7 Belt layer 7E Belt outer end 11-13 First to third belt plies C Tire equator Yc Belt central area Ys Belt outer area

Claims (1)

[Claims] 1. A first belt ply having a belt cord inwardly of a tread portion and a radially outer side of a carcass, the belt cord being arranged obliquely to a tire circumferential direction, and sequentially overlapping radially outward from the carcass side. A pneumatic radial tire provided with a belt layer including at least a second belt ply and a third belt ply, wherein the first and second belt plies in a belt central region having a width of 1/3 of a maximum belt width around a tire equator. The cord angle of the belt cords of the first to third belt plies with respect to the tire circumferential direction is α1
c, α2c, α3c, and α1s, α2s, α3s of the belt cords of the first to third belt plies with respect to the tire circumferential direction in the belt outer region having a width 1/6 of the maximum belt width from the outer end of the belt. A pneumatic radial tire characterized by satisfying the following relational expression. 40 ° ≦ α1c ≦ 70 ° 15 ° ≦ α2c ≦ 25 ° 15 ° ≦ α3c ≦ 25 ° 1 ° ≦ α1s-α1c ≦ 5 ° 1 ° ≦ α2s-α2c ≦ 5 ° 1 ° ≦ α3s-α3c ≦ 5 °