JP3096357B2 - Heavy duty pneumatic tires - 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 pneumatic tire capable of reducing crack damage at the bottom of a tread groove and improving the service life of the tire.

[0002]

2. Description of the Related Art In recent years, metal belt cords are arranged outside the crown of a carcass at a relatively shallow angle in the circumferential direction of a tire, and the rolling properties, abrasion resistance and puncture resistance are enhanced by the tread reinforcing effect of the belt. So-called radial tires with increased performance are frequently used.

[0003] In this type of tire, from the viewpoints of high speed, wet grip resistance and the like, generally, a rib type or rib lug type in which a main groove extending linearly or zigzag in the tire circumferential direction is provided on the tread surface. 3 and 4, the main grooves having a V-shaped or U-shaped cross section as shown in FIGS. 3 and 4 are widely used.

[0004]

However, in particular, in this kind of tire, the rigidity at the groove bottom is high due to the reinforcing effect of the belt.
When a lateral force acts on the tread surface to deform the rib, strain tends to concentrate on the groove bottom. In addition, even when the tire is inflated when the stone is bitten or when the used internal pressure is inflated, the strain tends to be similarly concentrated on the groove bottom due to the expansion of the groove width. As a result, if the tire is used for a long period of time in such a situation, even if the groove bottom surface and the groove wall surface are smoothly connected, crack damage such as cracks will occur at the groove bottom at an early stage, and the tire use Shortening the service life.

According to the present invention, the groove is basically formed in a sectional shape having a single circular groove bottom surface and a groove wall surface in contact with the groove surface and inclined in a direction to reduce the groove width toward the tread surface. It is an object of the present invention to provide a heavy duty pneumatic tire capable of reducing crack damage at the bottom.

[0006]

In order to achieve the above object, a heavy duty pneumatic tire according to the present invention comprises a rib pattern having a main groove extending in a circumferential direction of the tire on a tread surface, and a load of a rib lug pattern. In a heavy-duty pneumatic tire, the main groove has, in a cross section perpendicular to the main groove, a groove bottom having a single arc and a radially outward contact with the groove bottom and from the groove bottom toward the tread surface. The groove width of the main groove at the bottom of the groove is the maximum width WO of the tread surface on the tread surface.
The groove depth D of the main groove from the tread surface is at least 2 and at most 4 times the groove width W1 of the tread surface.

Preferably, the maximum width WO is 1.5 times or more and 2.0 times or less the tread groove width W1, and the groove depth D is twice the tread groove width W1. It is better to be at least 3 times or less.

[0008]

In the cross section of the main groove, the groove bottom surface is formed as a single circular arc, and the groove wall surface is inclined (reversely inclined) in a direction in contact with the groove bottom surface and decreasing the groove width toward the tread surface. Therefore, the main groove can have the maximum width WO of the main groove at the groove bottom, and can give the maximum radius of curvature R which is 1/2 times the maximum width WO to the groove bottom surface.

As a result, when the lateral force acts on the tread surface, the groove bottom forms a single arc, so that the strain at the groove bottom can be evenly distributed over the entire bottom surface without being locally concentrated. Moreover, the development length of the groove bottom is large, such as having the maximum possible radius of curvature R as described above,
Therefore, the dispersion ratio can be increased and the occurrence of cracks and the like can be greatly reduced.

[0010] In the main groove of the present invention, since the groove wall surface is reversely inclined, the groove width on the tread surface can be increased simultaneously with the increase of the tread width due to the progress of wear, so that the appearance of the tread pattern and the drainage property are improved. Can be maintained. Moreover, since the edge angle of the rib formed between the main grooves forms an acute angle,
The water film cutting effect on a wet road surface is large, and the wet grip performance can be greatly improved.

Also, compared to conventional U-shaped and V-shaped grooves,
In order to increase the groove volume relative to the tread surface groove width, for example, when the groove volume is set equal to the conventional type groove,
The land ratio of the tread pattern can be increased, and the high-speed running on dry roads can be greatly improved.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. In the figure, a heavy-duty pneumatic tire 1 includes a tread portion 2 having a rib-lag type tread pattern formed on a tread surface S, a sidewall portion 3 extending inward in the tire radial direction from both ends thereof, and a sidewall portion 3. And a bead part 5 located at an inner end of the bead.

A carcass 6 whose both ends are folded around the bead core 4 of the bead portion 5 from the tread portion 2 to the side wall portion 3 is bridged between the bead portions 5, 5. A belt layer 7 is disposed radially outward of the tire and inside the tread portion 2.

The carcass 6 comprises one or more carcass plies in which carcass cords are arranged at an angle of 75 to 90 degrees with respect to the tire equatorial plane C.

The belt layer 7 is composed of one or more belt plies in which belt cords are arranged at an angle of 30 degrees or less with respect to the tire equator C. As the belt cord, a metal fiber cord such as steel is preferably used. used. As the carcass cord, in addition to the metal fiber cord similar to the belt cord, for example, an organic fiber cord such as nylon, rayon, or polyester is selected according to the required tire performance.

The tread pattern includes three main grooves G extending linearly or zigzag in the circumferential direction of the tire, and in this example, extending in a zigzag manner. Are open at the tread edge and extend in a direction intersecting with the main groove G, and are spaced in the circumferential direction.

In the present invention, the cross-sectional shape of the main groove G is specified. That is, in a cross section perpendicular to the main groove G, the main groove G has a groove bottom 9 forming a single arc and a tread contacting the groove bottom 9 and extending from the groove bottom 9 as shown in an enlarged view in FIG. And a groove wall surface 10 that extends in a direction radially outward in the tire radial direction to reduce the groove width toward the surface S. That is, the main groove G has a maximum width WO of the main groove G at the groove bottom surface 9 and is 0.5
The maximum radius of curvature R that is doubled is given to the groove bottom surface 9.

The maximum width WO of the main groove G is tread surface S
The groove width of the main groove G above, that is, the tread surface groove width W1
More than 1.0 times and not more than 2.0 times, more preferably,
It is 1.5 times or more and 2.0 times or less.

A groove depth D from the tread surface S of the main groove G
Is 2 times or more and 4 times or less of the tread surface groove width W1,
More preferably, it is 3 times or more and 4 times or less.

Here, when the maximum width WO is greater than 2.0 times the groove width W1 of the tread surface, when the tire after vulcanization molding is pulled out of the mold, excessive stress acts on the groove wall surface 10 and the rib edge Damage such as chipping. When the tread groove width W1 is 1.0 times or less, the groove wall surface 10 is not formed with the reverse inclination. When the groove depth D is smaller than twice the groove width W1 of the tread surface, the groove depth D becomes too small, which significantly impairs the balance between dry road surface running performance and drainage performance. The rib edge is easily chipped. Conversely, if the groove depth D exceeds four times the tread surface groove width W1, the groove depth D becomes excessive, and the pattern rigidity is impaired.
Deterioration of both dry and wet running performance.

The main groove G whose cross-sectional shape is specified as described above
Because the groove bottom is formed by a single arc,
At the time of inflation, when a lateral force acts on the tread surface, or the like, the strain at the groove bottom can be uniformly dispersed over the entire bottom surface. Moreover, since the radius of curvature R of this single circular arc is set to 1/2 (constant) of the maximum width WO, the development length of the groove bottom becomes large, the dispersion ratio of the strain is increased, and the occurrence of cracks and the like becomes large. Can be reduced.

When the groove bottom surface 9 is formed in a curved shape other than a single circular arc, for example, a double circle, the radius of curvature of the curved line changes at each portion, so that the strain cannot be distributed uniformly. Cracks and the like are likely to occur in portions where the rate of change of the radius of curvature is high.

In this embodiment, in order to further suppress the occurrence of cracks and the like, the tire surface is coated with the protective rubber layer 11.
It is formed by.

The protective rubber layer 11 has at least a main groove G
The outer surface of the tire including the groove bottom surface 9 and the groove bottom surface 10, in this embodiment, the outer surface from the tread portion 2 to the sidewall portion 3 has a substantially uniform thickness of 0.1 to 2.0 mm along the contour thereof. It is formed with a thickness. The protective rubber layer 11 is made of EPT
And a highly weatherable rubber containing one or both of butyl halide and butyl halide.

Here, EPT is a terpolymer obtained by polymerizing ethylene and propylene using a Ziegler catalyst and adding a diene component, and butyl halide contains chlorine, bromine and the like in butyl rubber. It is obtained by introducing a halogen atom, and both are excellent in weather resistance such as ozone resistance and chemical resistance.

In this embodiment, the rubber is used in combination with other rubber materials such as NR, SBR and BR.
The range is from 5 to 70 phr, particularly preferably from 30 to 40 phr, based on parts by weight. By mixing in such a range, excellent weather resistance can be exhibited while maintaining necessary rubber properties such as strength, elasticity, wear resistance, and workability, and a synergistic effect with the groove shape of the main groove G. Thus, higher crack resistance can be exhibited.

In the main groove G of the present invention, since the groove wall surface is inclined in reverse, the groove width on the tread surface can be increased with the increase of the tread width due to abrasion. And can be maintained until the end of wear.

Further, since the edge angle α of the rib edge is an acute angle, the effect of cutting the water film is high, and the wet grip property can be improved. Also, since the groove volume with respect to the tread surface groove width is higher than the conventional U-shaped and V-shaped grooves, for example, when the groove volume is set equal to that of the conventional type groove, the land ratio of the tread pattern can be increased, High-speed running performance on dry road surface can be greatly improved.

(Specific Example) A tire having the tire structure shown in FIG. 1 and having a tire size of 10.00R2014PR was prototyped based on the use of Table 1, and a groove bottom crack test, a wet braking test, and a stone bite test of each tire were performed. Was compared with a conventional product and a comparative example product. Table 2 shows the rubber components of the protective rubber layer in Table 1.

[0030]

[Table 1]

[0031]

[Table 2]

In the test, a tire having a rim assembled with a standard rim of 2.0 × 7.00T at an internal pressure of 8.0 KSC was subjected to 2-D
4 trucks and 100,000 ordinary asphalt roads
The test was performed when the vehicle ran km, and a load of 2700 kgf was applied to each test tire.

[0033]

As described above, in the pneumatic tire for heavy load of the present invention, the main groove is formed by inclining the main groove with a groove bottom formed of a single arc and in a direction in which the groove width decreases toward the tread surface. Since it has a groove wall surface that extends, crack damage, particularly at the groove bottom, can be reduced, and tire life can be improved.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view showing a cross-sectional shape of a main groove.

FIG. 3 is a sectional view of a main groove showing a conventional technique.

FIG. 4 is a sectional view of a main groove showing a conventional technique.

FIG. 5 is a cross-sectional view of a main groove of a comparative example product.

[Explanation of symbols]

 9 Groove bottom 10 Groove wall G Main groove S Tread surface

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B60C 11/04 B60C 11/00 B60C 11/13

Claims (3)

(57) [Claims] 1. A heavy duty pneumatic tire having a rib pattern in which a main groove extending in a tire circumferential direction is formed on a tread surface, wherein the main groove has a cross section perpendicular to the main groove. While having a groove bottom of a single circular arc, and a groove wall surface that is in contact with the groove bottom surface and that extends from the groove bottom surface in a direction radially outward toward the tread surface so as to reduce the groove width, the groove surface extends. The maximum width WO at the groove bottom is greater than 1.0 times the groove width W1 of the tread surface on the tread surface and 2.0.
A heavy-duty pneumatic tire wherein the groove depth D from the tread surface of the main groove is not less than twice and not more than 4 times the groove width W1 of the tread surface. 2. The maximum width WO is equal to the tread surface groove width W.
2. The heavy duty pneumatic tire according to claim 1, wherein the pneumatic tire is 1.5 times or more and 2.0 times or less of 1. 3. The groove depth D is 2 times the groove width W1 of the tread surface.
The pneumatic tire for heavy loads according to claim 1, wherein the pneumatic tire is at least twice and at most three times.