JP2002205514A - Pneumatic tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for heavy load that can oppose to a force in the torsional direction occurring in a buttress part in braking, and has high crack resistance. SOLUTION: A recessed and projecting surface having alternately adjacent recessed parts 9 and projecting parts 10 are formed by one circle on the surface of the buttress part S as a transfer part from the ground end P of a tread 1 to a sidewall 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic tire in which cracks occurring in a tire circumferential direction in a buttress portion are suppressed.

[0002]

2. Description of the Related Art In general, in heavy-duty pneumatic tires, stress is concentrated on a shoulder portion due to a large load load, and this causes cracks in a buttress portion. Numerous proposals have been made in which the shapes of the-part and the buttress part are devised.

[0003] These proposals are all proposals made in response to deformation due to a load applied during running. For example, FIG.
FIG. 4A shows a buttress portion S in which a concave groove 20 is formed in the tire circumferential direction (Japanese Patent Laid-Open No. 11-151910), or a tire having a bottom portion enlarged to the buttress portion S as shown in FIG. There is one provided with a narrow groove 21 in the circumferential direction (JP-A-6-32114).

However, simply providing a groove in the tire circumferential direction in the buttress portion, particularly in heavy-duty pneumatic tires used for new city traffic or route buses, which frequently start and stop, is required to provide the buttress portion in braking or driving. It was not possible to sufficiently follow the generated force in the torsional direction, so that cracks generated in the tire circumferential direction could not be prevented.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire for heavy loads which is excellent in crack resistance by improving the surface shape of a buttress portion.

[0006]

According to the present invention, there is provided a heavy-duty pneumatic tire according to the present invention, wherein a concave portion and a convex portion are formed on a surface of a buttress portion which is a transition portion from a ground contact end of a tread to a side wall. The uneven surface adjacent to the tire 1
It is characterized by being formed over the circumference.

[0007] With this, the concave portion of the uneven surface formed in the buttress portion is absorbed by the torsion force generated in the buttress portion while deforming, so that cracks can be prevented. In addition, the convex portion promotes the deformation of the concave portion while securing the rubber thickness of the buttress portion, and protects the buttress portion from trauma caused by obstacles on the road such as curbs.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each of the drawings, the same components are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a half-sectional view in the meridian direction of a heavy-duty pneumatic tire showing an outline of an embodiment of the present invention. A side wall 2 and a bead portion 4 are formed on both sides of a tread 1. A bead core 5 is buried in the
The end of the waste layer 6 surrounds the bead filler 7 and is turned up around the bead core 5 and wound up.

Outside the carcass layer 6 of the tread 1, a belt layer 8 is arranged over the circumference of the tire in the tire circumferential direction. CL is a tire center line (tire equator line).

As shown in FIG. 2, a recess 9 is formed on the surface of the buttress portion S, which is the transition from the ground contact end P of the tread 1 to the side wall 2, over the circumference of the tire in the tire circumferential direction EE '. An uneven surface in which the convex portions 10 are alternately adjacent is formed.

The range of the buttress portion S is determined by the radial distance of the tire when the tire is mounted on a regular rim and filled with a regular internal pressure. The upper end is the grounding end P of the tread 1, and the lower end is the grounding end of the tread 1. It is assumed that a distance T between P and the tire maximum width position Q is a point R internally divided by 6: 4.
In other words, the distance from the ground contact end P of the tread 1 to the point R toward the tire maximum width position Q by 0.6T in the tire radial direction. Here, the normal rim and the normal internal pressure refer to the rim and the internal pressure defined in the 1999 edition of JATMA.

The uneven surface need not be formed on the entire surface of the buttress portion S. However, in order to prevent cracks occurring in the tire circumferential direction EE ′ of the buttress portion S, the area on the tire surface occupied by the concave portion 9 is 10% or more, preferably 10% to 30% of the area on the tire surface occupied by the buttress portion S. %
It is good to

The "area on the tire surface occupied by the recess 9" refers to the area of the recess 9 obtained by projecting the recess 9 on the surface of the buttress portion where the recess 9 is not formed. The “area on the surface” refers to the area of the surface of the buttress portion where no uneven surface is formed.

In order for the concave portion 9 to sufficiently fulfill the role of absorbing the torsional force generated in the buttress portion S, the depth from the tire surface should be at least 1 mm or more, preferably 1 mm to 3 mm. Good. Further, the concave portion 9 has a radius of 1 mm or more in the tire meridian section.
mm.

The convex portion 10 not only functions to promote the deformation of the concave portion 9 while ensuring the rubber thickness of the buttress portion S, but also has a role of protecting the buttress portion S from being damaged by an obstacle on the road such as a curb. Therefore, the height of the protrusion 10 from the tire surface is 1 mm or more, and preferably 1 mm to 3 mm. Further, the convex portion 10 is preferably a spherical shape having a radius of 1 mm or more and 5 mm or less in the tire meridian section, although the influence on the crack resistance during braking / driving is less than that of the concave portion 9.

FIG. 2 is an enlarged side view showing a part of the buttress portion S of the tire shown in FIG. 1 when viewed from the side, and has a spherical recess 9 over the entire circumference in the tire circumferential direction EE ′. Spherical projections 10 are alternately adjacent to each other to form an uneven surface, which is formed in the tire radial direction by a spherical concave portion 9 and a spherical convex portion 10.
Are consecutively arranged in a plurality of rows so as to be adjacent to each other.

FIG. 3A is a sectional view taken along the line AA 'of FIG. 2, and FIG. 3B is a sectional view taken along the line BB' of FIG.

As described above, in the present invention, the buttress portion S is formed with an uneven surface over the circumference of the tire so as to be less susceptible to stress concentration. A heavy-duty pneumatic tire excellent in crack resistance, which can sufficiently cope with the torsional force generated in the portion S, was successfully obtained.

[0020]

EXAMPLES The ratio of the area of the tire surface occupied by the recess to the area of the tire surface occupied by the buttress portion ("recess area%" in Table 1) is changed, and the shapes of the recess and the projection are shown in Table 1. A tire (tire size 11R22.5) was manufactured in the same manner (Examples 1 to 8).

Crack resistance of these eight types of tires and the tires of Conventional Examples 1 and 2 shown below were evaluated as follows. Table 1 shows the results.
The specifications other than those shown in Table 1 were the same for each tire.

Conventional Example 1 An annular groove extending in the circumferential direction of the tire and having a depth of 2 mm, a width and a radius of 2 mm (FIG. 4) is provided in the vicinity of the tire maximum width position of the buttress portion in accordance with the description in JP-A-11-151910.
(Corresponding to (a)) in which three pneumatic tires for heavy loads are arranged.

Conventional Example 2 According to the description in JP-A-6-32114, an annular groove extending in the tire circumferential direction and having a larger groove width inside the buttress portion than the surface portion (corresponding to FIG. 4B) A pneumatic tire for heavy load, wherein eight grooves having a surface groove width of 1 mm, a maximum groove width of 2 mm, a groove depth of 2.5 mm, and a groove bottom minimum curvature radius of 1 mm are arranged.

Crack resistance : An indoor drum running test is performed in the following manner, the number of cracks generated in the buttress portion of each tire is checked, and the result is obtained by forming only a concave portion in the buttress portion and not forming a convex portion. Conventional tire 1 is represented by an index of 100. The larger the index value, the better the crack resistance.

Indoor drum running test : tire size 11R
A 22.5 tire is mounted on a rim specified by JATMA and pressed against the drum with the air pressure and load specified by JATMA (1999 version). The acceleration at start is 0.2G, the acceleration at stop is 0.4G, and the vehicle runs at a constant speed. Time speed 4
0 km / h, and a running distance of 2 km is defined as a cycle of starting, running at a constant speed and stopping.
A zero cycle drum test was performed (G: gravitational acceleration).

[0026]

[Table 1] As is clear from Table 1, it can be seen that the tires of Examples 1 to 8 are more excellent in crack resistance than the tires of Conventional Examples 1 and 2.

[0027]

As described above, according to the present invention, the concave and convex portions are formed on the surface of the buttress portion alternately over the circumference of the tire so that the concave portion and the convex portion are adjacent to each other. It is possible to prevent the generation of cracks by absorbing the directional force while the concave portion is deformed. In addition, the convex portion promotes the deformation of the concave portion and protects the buttress portion from being damaged from the outside, so that the occurrence of cracks due to external damage can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a half section in a tire meridian direction showing an outline of an embodiment of the present invention.

FIG. 2 is an explanatory view showing a part of the buttress portion in FIG. 1 in an enlarged manner as viewed from a side.

3 shows a partial cross section of FIG. 2, wherein (a) is A
-A 'arrow sectional drawing, (b) is BB' arrow sectional drawing.

4A and 4B schematically show the surface shape of a buttress portion of a conventional tire, in which FIG. 4A is a cross-sectional explanatory view in the tire meridian direction of a buttress portion having a groove formed in the tire circumferential direction, and FIG. FIG. 5 is a cross-sectional explanatory view in the tire meridian direction of a buttress portion provided with a narrow groove in the tire circumferential direction.

[Explanation of symbols]

 Reference Signs List 1 tread 2 side wall 4 bead portion 5 bead core 6 carcass layer 7 bead filler 8 belt layer 9 concave portion 10 convex portion

Claims (6)

[Claims] 1. A heavy-duty pneumatic tire in which concave and convex portions are alternately formed on the surface of a buttress portion, which is a transition portion from a ground contact end to a side wall of a tread, in which a concave portion and a convex portion are alternately formed over one circumference of the tire. . 2. The depth of the recess from the tire surface is 1 m.
The pneumatic tire for heavy load according to claim 1, which is not less than m. 3. The heavy duty pneumatic tire according to claim 1, wherein the concave portion has a spherical shape with a radius of 1 mm or more and 5 mm or less in a cross section in the tire meridian direction. 4. The pneumatic tire for heavy load according to claim 1, wherein the area on the tire surface occupied by the concave portion is 10% or more of the area on the tire surface occupied by the buttress portion. 5. The height of the projection from the tire surface is 1 m.
The pneumatic tire for heavy load according to any one of claims 1 to 4, wherein the diameter is not less than m. 6. The heavy-duty pneumatic tire according to claim 1, wherein the convex portion has a spherical shape with a radius of 1 mm or more and 5 mm or less in a cross section in the tire meridian direction.