JPH06206403A - Tire for heavy load - Google Patents

Abstract

(57) [Abstract] [Purpose] To effectively suppress uneven wear in the shoulder portion of the tire. The belt layer 7 outside the carcass 6 includes a first belt ply 11 adjacent to the carcass and a second belt ply 12 adjacent to the outside of the carcass and having a maximum ply width. The second belt ply 12 has a center on the equatorial plane of the tire and a ply central portion 12A along a circular arc M1 having a radius of curvature BR1 of 3.5 to 7.5 times the tread width TW, and a central portion of the ply. 12A and having a center on the equatorial plane of the tire and having a radius of curvature BR2 of 0.4 to 0.4 of the radius of curvature BR1.
And a ply outer end portion 12B along the arc M2 that is 0.9 times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty tire capable of effectively suppressing stepped uneven wear in the shoulder portion of the tire.

[0002]

2. Description of the Related Art In recent years, with the improvement of road networks and the improvement in performance of vehicles, heavy-duty tires used in trucks, buses, etc. have a radial structure. This product has a belt layer made of high-tensile cords such as steel cords on the outside of the carcass arranged in the radial direction, giving a large hoop effect, so the tread rigidity is high and the contact pressure distribution on the tread surface is high. It tends to be non-uniform. As a result, as shown in FIG. 6, there is a problem that uneven wear K in which only the tread shoulder portion is worn in a stepped manner is caused and the tire life is reduced.

This is because the tread surface t has a substantially arcuate shape in the meridional section including the tire axis as shown in FIG. 6, so that the circumferential length of the central portion of the tread is relative to the circumferential length of the shoulder portion. It is thought that this is caused by the fact that the shoulder portion causes dragging with the road surface. Therefore, conventionally, in order to prevent the uneven wear of the stepped shape, the radius of curvature of the tread surface has been increased to reduce the circumferential difference between the central portion of the tread and the shoulder portion.

[0004]

However, with such an increase in the radius of curvature, a sufficient effect of suppressing the uneven wear cannot be obtained, and conversely, the ground contact pressure at the shoulder portion increases, so that the belt end separation is prevented. It was found that it is easy to induce and the durability is rather lowered.

Therefore, as a result of various experiments conducted by the inventor in view of such a situation, in order to prevent the uneven wear of the stepped shape, the sectional shape of the belt layer in the meridional section of the tire, particularly the belt layer It has been found that it is necessary to control the shape of the belt ply which has the greatest maximum reinforcing effect.

That is, the present invention is based on the fact that the second belt ply having the maximum width is made into a double crown radius and the radius of curvature thereof is regulated respectively, so that uneven uneven wear is effectively prevented without impairing tire durability. It is intended to provide a heavy-duty tire that can be suppressed.

[0007]

In order to achieve the above object, the heavy-duty tire of the present invention comprises a carcass folded around a bead core of a bead portion from a tread portion to a sidewall portion, and a radius of the carcass. A belt layer disposed outside in the direction and inward of the tread portion, the belt layer being adjacent to the carcass and a second belt ply adjacent to the outside and having a maximum belt ply width. In the second belt ply, the outer surface of the second belt ply in the tire radial direction has a center on the tire equatorial plane and has a radius of curvature BR1 of 3.5 to tread width TW.
The center of the ply along a 7.5-fold arc and the outer end of the center of the ply in the axial direction of the ply are centered on the tire equatorial plane, and the radius of curvature BR2 is the radius of curvature B.
And an outer end of the ply along an arc of 0.4 to 0.9 times R1.

[0008]

In the second belt ply having the greatest reinforcing effect on the belt layer, the second belt ply has the radius of curvature BR.
The radius of curvature BR2 located at the center of the ply of No. 1 and outside thereof
Of the outer ends of the plies and the ratio BR2 / BR1 is set to 0.
Double crown radius of 4 to 0.9.

As a result of the experiment conducted by the present inventor, in the tire, in addition to the slip on the road surface due to the circumferential length of the tread surface,
As shown in the rolling state of the tire in FIG. 5, the belt a of the ground contact portion A, which has been compressed and deformed, returns to the extension direction when the ground contact is released (protrusion), and at this time, a new slip occurs.

Since the amount of deformation and the amount of return of this compression become smaller toward the belt portion closer to the tire axis C, the radius of curvature B
The amount of return at the outer end of the ply with a small R2 can be reduced compared to the outer end of the conventional belt formed of a single arc, and slippage with the road surface can be suppressed. Further, by making the radius of curvature RB2 small, the thickness of the tread gauge at the outer end of the ply can be relatively increased as compared with that at the center of the ply, and the rigidity of the tread surface at the tread shoulder can be relaxed. And the slippage with the road surface due to the circumferential length can be reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a meridional section of a tire in a normal internal pressure state in which the tire is assembled on a normal rim and filled with a normal internal pressure.

In FIG. 1, a heavy load tire 1 includes a tread portion 2, sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and an annular bead core 4 located at the inner end of each sidewall portion 3. And a bead portion 5 reinforced by. A carcass 6 folded around the bead core 4 from the tread portion 2 to the sidewall portion 3 is bridged between the bead portions 5 and 5, and a belt is provided on the outer side in the radial direction and on the inner side of the tread portion 2. Layer 7 is arranged.

The tread surface TS, which is the outer surface of the tread portion 2, has a radius of curvature T centered on the tire equatorial plane.
The tread surface TS is composed of a convex arc of R1, and the tread surface TS intersects with a concave arc-shaped buttress surface BS continuous from the sidewall portion 3 or is connected via a small arc or the like. The radius of curvature TR is 2.0 to 3.5 times the tread width TW. Further, the tread surface TS has a rib type, rib lug type or block type tread pattern that divides the tread surface TS into a plurality of ribs or block rows by at least two longitudinal grooves extending in the tire circumferential direction. In the example, vertical grooves G1 and G1 on both sides of the tire equator
And the outer vertical grooves G2, G2 on the outside thereof are provided, so that the rib R1, the vertical grooves G1, G2 inside the vertical grooves G1, G1 are provided.
A rib pattern is formed of the rib R2 in the space and the rib R3 in the space between the vertical groove G2 and the tread edge Te.

In this example, the carcass 6 is composed of, for example, one ply having a radial structure in which steel carcass cords are arranged at an angle of 90 degrees with respect to the tire equator CO. A carcass cord of 60 to 90 is used as the carcass 6.
It can be formed with multiple plies of radial and semi-radial structure arranged at a time, and as a carcass cord, steel cord, nylon, polyester, rayon,
Organic fiber cords such as aromatic polyamide may be used.

Further, in the present embodiment, the belt layer 7 is composed of a first belt ply 11 and a second belt ply 12, which are arranged in order from the carcass side toward the tread surface TS.
It has a four-layer structure composed of the third belt ply 13 and the fourth belt ply 14, and the ply width W2 of the second belt ply 12 is the maximum ply width, and the ply widths of the first and second belt plies are the same. Are approximately equal to each other and smaller than the ply width W2 by about 20 mm. The ply width W2 has a value of 0.8 to 0.95 times the tread width TW, whereby the tread portion 2 is reinforced over almost the entire width with a hoop effect.

Each of the plies 11 to 14 is a steel ply in which steel belt cords are arranged in parallel to each other at an angle of 10 to 70 degrees with respect to the tire equator CO. The cords are arranged in the same direction, and the cords of the third and fourth belt plies are arranged in the same direction and in a direction intersecting with the cords of the first and second belt plies. In this example, the cord angles of the second to fourth belt plies 12, 13, and 14 with respect to the tire equator are 15 to 25 degrees, for example, 19 degrees, and the first belt ply 11 is
The cord angle of 60 is the middle of the cord angle of carcass 6
The degree is set to 70 degrees, for example, 67 degrees, whereby a strong truss structure is formed together with the carcass cord, and the rigidity step between the carcass ply and the first belt ply is mitigated.

The second belt ply 12 has a double-crown radius profile and, as shown in FIG. 2, has a first radius of curvature BR1 whose outer surface in the tire radial direction is centered on the tire equatorial plane. The ply center portion 12A on the tire equator CO side along the arc M1 is continuous with the inflection point P at the tire axial outer end and has a center on the tire equator plane, and the radius of curvature BR2 is the radius of curvature BR1. 0.4
~ 0.9 times the second ply outer end 1 along the second arc M2
2B and. The inflection point P is located below the inner rib R2, that is, between the outer longitudinal groove G2 which is the outermost side in the tire axial direction and the inner longitudinal groove G1 inside thereof.
More preferably, the distance L of 0.2 to 0.4 times the tread width TW is separated from the tire equator CO. As described above, the ply outer end portion 12B has a curvature radius BR2 equal to the curvature radius BR2.
Since it is smaller than 1, it inclines inward in the tire radial direction while being separated from the first circular arc M1. That is, since the distance from the tire axis of the ply outer end portion 12B is reduced, the amount of compressive deformation of the ply outer end portion 12B at the time of grounding,
That is, the amount of recovery in the extension direction when the ground is released can be reduced, and slippage with the road surface can be suppressed. Moreover, the separation from the first circular arc M1 can reduce the tread surface rigidity at this portion by increasing the thickness of the tread rubber gauge at the ply outer end portion 12B, and the shoulder portion caused by the circumferential length of the tread surface TS. You can also reduce the slip on the road surface.

As shown in FIG. 3, which shows the relationship between the radius of curvature ratio BR2 / BR1 and the stepped uneven wear, which the present inventor has confirmed by experiments, the stepped step is performed in the range of BR2 / BR1 of 0.4 to 0.9. Wear can be suppressed. However, the ratio BR2 /
When BR1 is greater than 0.9, the effect of reducing the amount of return and the effect of relaxing the rigidity of the tread surface become insufficient, and step wear cannot be suppressed. Further, when the ratio BR2 / BR1 is less than 0.4, the difference in the amount of compressive deformation between the ply central portion 12A and the ply outer end portion 12B becomes excessively large.
A large shear strain is generated between B and B, and this shear strain, in combination with external factors such as the tire posture angle and the inclination angle with the road surface, similarly worsens the step wear.

The step wear suppressing effect by setting the ratio BR2 / BR1 is as shown in FIG. 4, as shown in FIG.
The radius of curvature BR1 of A is 3.5 to 7.5 of the tread width TW.
Demonstrated when doubled. That is, the radius of curvature BR1 is 7.5T
When it is larger than W, the separation of the ply outer end portion 12B from the first arc M1 becomes insufficient, and the radius of curvature BR1 is 3.5T.
When it is smaller than W, the shear strain between the central portion 12A of the ply and the outer end portion 12B is increased to induce slippage with the road surface.

In this example, the second belt ply 12 is also used.
The first belt ply 11 that is adjacent to the inner side of the first belt ply 11 has a double crown radius profile shape that extends along the second belt ply 12 over the entire width thereof. On the other hand, the second belt ply 12 and the third belt ply 13 that is adjacent to the second belt ply 12 on the outer side of the second belt ply 12 have the lower surface over the entire width of the first arc M1.
It has a single-radius contour shape that extends along.
Therefore, the third belt ply 13 is gradually separated from the outer end portion 12B of the second belt ply at the outer end portion 13B thereof. As a result, the shearing stress acting between the second and third belt plies 12 and 13 due to the different inclination directions of the belt cords, the large ply width, and the fact that they are located on the tread surface side is eliminated. The rubber between the end portions 12B and 13B is dispersed and relaxed, and peeling of the ply ends starting from the outer end portion 13B can be prevented.

The fourth belt ply 14 is the same as the first belt ply.
-Mainly has a role of protecting the third belt plies 11 to 13 from external damage, and in this example, the third belt plies 11 to 13 are stacked along the belt ply 13 with a ply width smaller than the inflection points P and P.

[0022]

As described above, since the heavy-duty tire of the present invention is constructed, it is possible to suppress stepped uneven wear in the tread shoulder portion without impairing tire durability.

[Brief description of drawings]

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

FIG. 2 is an enlarged diagram showing a second belt ply.

FIG. 3 is a diagram showing a relationship between a curvature radius ratio BR2 / BR1 and stepped uneven wear.

FIG. 4 is a diagram showing a relationship between a ratio of a radius of curvature BR1 and a tread width TW and stepped uneven wear.

FIG. 5 is a diagram illustrating the operation of the invention.

FIG. 6 is a diagram illustrating stepped uneven wear.

[Explanation of symbols]

 2 tread part 3 sidewall part 4 bead core 5 bead part 6 carcass 7 belt layer 11 first belt ply 12 second belt ply 12A ply central part 12B ply outer end part M1, M1 arc

Claims (1)

[Claims] 1. A carcass which is folded back from a tread portion to a sidewall portion around a bead core of a bead portion, and a belt layer which is arranged radially outside the carcass and inside the tread portion, and further, the belt. The layer includes a first belt ply adjacent to the carcass and a second belt ply adjacent to the outer side thereof and having a maximum belt ply width, and the second belt ply has an outer surface in the tire radial direction. A center of the ply along a circular arc having a center on the equatorial plane of the tire and having a radius of curvature BR1 of 3.5 to 7.5 times the tread width TW, and connecting to the outer end in the tire axial direction of the center of the ply. It has a center on the equatorial plane of the tire and has a radius of curvature BR2 of 0.4 to 0.
A heavy-duty tire characterized by comprising a ply outer end portion along a 9-fold arc.