JP2000158911A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent growth of a crack developed at a groove on a tread of a pneumatic tire. SOLUTION: A crack 26 developed at a bottom of a lug groove 22 grows as a tire rolls and is gradually extended toward an inside of the tire. An excellent crack growth resistant rubber layer 24 of thickness (t) which is more than or equal to 1 percent of a depth T from a tread surface to a bottom of a groove is applied on a groove wall surface of this pneumatic tire, whereby the rubber layer 24 delays growth of the crack 26. Accordingly, it is prevented that the crack 26 reaches a belt or the like inside of the tread before a wear life of the pneumatic tire, and also it can prevent a failure such as a separation of belt ply, and the like, caused by growth of the crack 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire having a tread having grooves such as lug grooves and circumferential grooves.

[0002]

2. Description of the Related Art Generally, tread rubber of a pneumatic tire has rubber characteristics that emphasize abrasion resistance and cut resistance (for a vehicle traveling on an unpaved rough road).

[0003]

However, rubbers having excellent wear resistance and cut resistance generally have poor crack growth resistance.

[0004] For example, at a site where a large traction is applied such as a construction vehicle, the tread block is greatly deformed, strain is concentrated on the groove bottom surface, and cracks are easily generated.

[0005] The generated crack grows with the rolling of the tire and gradually progresses inside.

[0006] In the case of rubber having poor crack growth resistance, the growth speed is so fast that the crack reaches the belt before the tread is completely worn (before the wear life has come), and the separation of the belt ply due to the ingress of moisture and the like. Otherwise, it may cause a failure.

An object of the present invention is to provide a pneumatic tire capable of suppressing the growth of a crack generated in a groove in consideration of the above fact.

[0008]

The invention according to claim 1 is a pneumatic tire having a groove in a tread, wherein the tread is provided at least on a groove wall surface or near the groove wall surface from the groove bottom. A pneumatic tire having a rubber layer having a thickness of at least 1% of a thickness up to a surface and having excellent crack growth resistance.

Next, the operation of the pneumatic tire according to the first aspect will be described.

[0010] In a pneumatic tire, the tread is greatly deformed by running on a rough road or the like, and strain is concentrated on the groove bottom surface, and a crack may be generated from the vicinity of the groove bottom.

The generated crack grows with the rolling of the tire and gradually progresses inside. In the pneumatic tire according to claim 1, at least the groove wall surface or the vicinity of the groove wall surface has a groove. Since a rubber layer having a thickness of 1% or more of the thickness from the bottom to the tread surface and having excellent crack growth resistance is provided, crack growth can be delayed by the rubber layer.

Thus, it is possible to prevent the crack from reaching the belt or the like inside the tread before the end of the wear life of the pneumatic tire, and the failure such as separation of the belt ply or the like due to the propagation of the crack. Can be prevented.

If the thickness of the rubber layer is less than 1% of the thickness from the groove bottom to the tread surface, the thickness of the rubber layer for delaying the growth of cracks becomes too thin, and the generated cracks Early, and the effect of delaying the growth of cracks becomes insufficient.

Since the cracks are easily generated from the groove bottom, the rubber layer may be provided at least on the groove wall surface or near the groove wall surface. However, the rubber layer is provided over the entire tread surface (or the entire surface vicinity). May be.

According to a second aspect of the present invention, in the pneumatic tire according to the first aspect, the rubber layer having excellent crack growth resistance has a 100% modulus of 15 kg / cm ² or more and 20 kg.
/ cm ² , and the crack growth rate at the number of bending 1000 times in the bending test specified in JIS K6301 is 1.0
It is characterized in that rubber having a diameter of not more than mm is used.

Next, the operation of the pneumatic tire according to the second aspect will be described.

In general, rubber is superior in crack propagation when it is softer than when it is hard. Therefore, if the rubber has a 100% modulus of less than 20 kgf / cm ² , the crack growth rate can be sufficiently reduced as compared with a general tread rubber (100% modulus has a modulus of 20 to 30 kgf / cm ² ).

In the pneumatic tire according to claim 2, 1
Since a rubber having a 00% modulus of 15 kg / cm ² or more and less than 20 kg / cm ² and a crack growth rate of 1,000 mm or less at a bending number of 1000 times in a bending test specified in JIS K6301 was used for the rubber layer. In addition, the growth of the crack generated at the groove bottom can be reliably delayed.

The 100% modulus of the rubber in the rubber layer is 20 kg / cm ² or more, or the crack growth rate is 1.0% or less.
If it exceeds mm, the effect of delaying crack growth will be insufficient.

If the 100% modulus of the rubber in the rubber layer is less than 15 kg / cm ² , the rubber is too soft, and the rubber layer itself is easily damaged by contact with a stone or the like on a rough road.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a pneumatic tire according to the present invention will be described with reference to FIGS.

As shown in FIG. 1, the carcass 12 of the pneumatic tire 10 of the present embodiment has a bead core (not shown).
The straddle is straddled in a toroidal shape, and both ends are folded around the bead core from the inside to the outside in the tire width direction.

A belt 14 is disposed outside the carcass 12 in the tire radial direction. The belt 14 is formed by laminating a plurality of (six in the present embodiment) belt plies 16 in which a plurality of steel cords arranged in parallel with each other are coated with rubber. The steel cord is
They cross each other at adjacent belt plies.

A tread 20 formed of a thick tread rubber 18 is disposed outside the belt 14 in the tire radial direction.

As shown in FIG. 1 and FIG.
Are formed with a plurality of lug grooves 22.

Further, the tread 20 of this embodiment is provided with a rubber layer 24 having excellent crack growth resistance on the surface of the tread 20, as shown in FIG.

As shown in FIG. 3, the thickness t of the rubber layer 24 is
Preferably, the thickness of the lug groove 22 is at least 1% of the thickness T from the groove bottom to the tread surface, particularly at the vicinity of the groove bottom where cracks tend to occur at the groove bottom.

The composition of the rubber constituting the tread rubber 18 and the rubber layer 24 for tightening the main part of the tread 20 of this embodiment is as shown in the following table.

[0029]

[Table 1]

The crack growth rate in the above Table 1 is based on JIS
No. of bending 100 in the bending test specified in K6301
Crack growth rate at 0 times.

Next, the operation of the pneumatic tire 10 of the present embodiment will be described.

The tread 20 of the pneumatic tire 10 is greatly deformed by running on a rough road or the like, and the strain is concentrated on the groove bottom surface, so that a crack 26 is generated near the groove bottom as shown in FIGS. Sometimes.

The cracks 26 grow with the rolling of the tire and gradually progress toward the inside. However, the rubber layer 24 having excellent crack growth resistance delays the growth of the cracks.

Therefore, it is possible to prevent the crack 26 from reaching the belt 14 before the wear life of the tread 20 is reached.

When a crack 26 develops in the steel cord of the belt 14, the belt ply 1
6 (separation of belt treat and rubber layer, ie, separation of ply cord and rubber layer).

Further, the grown crack 26 is formed in the tread 20.
Chipping and peeling.

When the thickness t of the rubber layer 24 near the groove bottom is less than 1% of the thickness T from the groove bottom to the tread surface, the thickness of the rubber layer 24 becomes too thin and the crack 26
May traverse the rubber layer 24 early, and the crack 26 may reach the belt 14 before the wear life of the tread 20 comes.

The tread 2 which comes into contact with the road surface during running
If the thickness t of the rubber layer 24 on the outer peripheral surface of the zero (excluding the lug groove 22) exceeds 3% of the thickness T from the groove bottom to the tread surface, the wear life of the tread 20 may be reduced. It is not preferable because there is.

Further, when the 100% modulus of the rubber of the rubber layer 24 is less than 15 kg / cm ² , the rubber is too soft and the rubber layer 24 itself is easily damaged by contact with a stone or the like on a rough road. [Second Embodiment] A second embodiment of the present invention will be described with reference to FIG. Note that the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In this embodiment, the rubber layer 24 is buried about 2 mm from the surface so as not to be exposed on the surface of the tread 20 (including the groove wall surface of the lug groove 22).

Also in the present embodiment, since the rubber layer 24 having excellent crack growth resistance is provided near the surface of the lug groove 22, even if a crack 26 is formed at the groove bottom, the rubber layer 24 prevents the crack 26 from forming. Crack growth rate can be reduced.

Although the pneumatic tire 10 of the present embodiment has a lug pattern, the present invention is not limited to this, and it is sufficient that at least a groove is formed in the tread 20. Pattern may be used.

Further, the crack 2
The occurrence site of No. 6 is constant. Therefore, the rubber layer 24 may be disposed only at the crack occurrence portion in order not to shorten the entire wear life.

For example, in the case of a lug pattern, a crack 26 is likely to be formed in the vicinity of the shoulder, so that the rubber layer 24 may be provided only in the vicinity of the shoulder as shown in FIG.

In the above embodiment, the rubber layer 24 is provided on the entire surface of the tread 20 or in the vicinity of the surface. However, in the present embodiment, the crack 2 generated from the bottom of the lug groove 22 is formed.
Since the purpose is to slow the growth of 6, the rubber layer 24 may be provided only near the groove bottom where cracks 26 are likely to occur, as shown in FIGS.

Further, from the viewpoint of the wear life of the pneumatic tire 10, as shown in FIGS. 5, 6, and 7, the rubber layer 24 should be provided only in the vicinity of the crack occurrence portion, and not in the portion in contact with the road surface. Is more preferred.

In the above embodiment, the rubber layer 24 has
Rubber having a 100% modulus of 18 kgf / cm ² and a crack growth rate of 0.5 mm was used, but the rubber used for the rubber layer 24 is not limited to this, and a 100% modulus of 15 kg / cm ² or more 2
It suffices if it is less than 0 kg / cm ² and the crack growth rate is 1.0 mm or less. (Test Example) In order to confirm the effect of the present invention, one kind of a conventional tire and two kinds of tires (each having a tire size of 188R33) of an example to which the present invention was applied were prepared and subjected to a real vehicle running test.

In an actual vehicle running test, two tires were mounted on a 35 ton payload dump truck, and the vehicle traveled 20,000 km.
The length of the crack generated in the groove was compared. The measurement was performed at three places on the circumference of each tire. In addition, the tread wear amount was measured for each tire.

Example 1 Tire: A pneumatic tire having the structure shown in the first embodiment.

Example 2 tire: A pneumatic tire having the structure shown in the second embodiment.

Conventional tire: A pneumatic tire without a rubber layer having excellent crack growth resistance.

The test results are as shown in Table 2 below.

The abrasion resistance is represented by an index with the conventional tire set as 100. The larger the numerical value, the smaller the abrasion and the better the abrasion resistance.

In each tire, the thickness from the groove bottom to the belt in the vicinity of the shoulder portion where cracks easily occur is 20 mm.

[0055]

[Table 2]

As a result of the test, Example 1 to which the present invention was applied was used.
In addition, it was proved that the tire of Example 2 had a lower crack growth rate of the crack generated at the groove bottom than the conventional tire.

Further, the tires of Example 1 and Example 2
Although the abrasion resistance was slightly inferior to that of the conventional tire, a rubber layer having inferior abrasion resistance to the tread rubber was provided on the outer peripheral surface of the tread when it was new (or near the outer peripheral surface of the tread). However, there is almost no problem in practical use.

[0058]

As described above, the pneumatic tire of the present invention has the above-mentioned structure, and therefore has an excellent effect that cracks generated in the grooves can be suppressed from growing.
This makes it possible to prevent separation of a belt or the like.

[Brief description of the drawings]

FIG. 1 is a sectional view (a sectional view taken along line 1-1 in FIG. 2) of a pneumatic tire according to a first embodiment of the present invention.

FIG. 2 is a plan view of a tread of the pneumatic tire shown in FIG.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view of a lug groove of a pneumatic tire according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a pneumatic tire according to another embodiment of the present invention.

FIG. 6 is a sectional view of a lug groove of a pneumatic tire according to still another embodiment of the present invention.

FIG. 7 is a sectional view of a lug groove of a pneumatic tire according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Pneumatic tire 20 Tread 22 Lug groove 24 Rubber layer

Claims (2)

[Claims] 1. A pneumatic tire having a groove in a tread, wherein the tread has a thickness of 1% or more of a thickness from a groove bottom to a tread surface at least at or near a groove wall surface of the groove. A pneumatic tire having a rubber layer having excellent crack growth resistance. 2. The rubber layer has a 100% modulus of 1
5 kg / cm ² or more and less than 20 kg / cm ² , K630 of JIS
2. The pneumatic tire according to claim 1, wherein a rubber having a crack growth rate of 1.0 mm or less at a bending number of 1000 times in the bending test specified in 1 is used.