JPH1120419A - Radial tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracking of the outer surface of a tire. SOLUTION: A radial tire for heavy load has a carcass 6 of radial structure with a folded part 6B folded at a bead core 5, integrally provided at a body part 6A, and a bead apex 8 extended in tapered shape to the radial outside from the bead core 5. The folded part 6B is provided with a parallel part G extended along the axial outer side face of the bead apex 8 and extended parallel in proximity to the body part 6A from the tire radial outer end 8t of the bead apex 8. The radial height H1 of the folded part 6B is to be 20% or more of carcass section height Hc. In case of the tire being assembled to a normal rim and changed to expand up to normal internal pressure, surface maximum main distortion ε m of an area between a tire maximum width point P1 and an inward point P2 in contact with a flange of the rim is to be 4% or less, and the difference between the maximum main distortion εm and maximum main distortion εp at the tire maximum width point P1 is to be less than 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 radial tire capable of suppressing the occurrence of cracks for a long period of time.

[0002]

2. Description of the Related Art With the recent improvement of road networks and higher performance of vehicles, high running not only for tires for passenger cars but also for tires for heavy loads used for trucks, buses and the like. Performance is required, and in recent years, a radially structured carcass and a heavy duty radial tire in which the outside of the carcass is fastened with a highly rigid belt layer have been widely used. Such a heavy-load radial tire has high tread rigidity, excellent high-speed performance, and improved wear resistance, low fuel consumption, and the like.

[0003] However, in the radial tire for heavy load, large repetitive stress generated during running acts intensively from the sidewall portion to the bead portion, and fine cracks occur in these regions due to the action of ozone in the atmosphere. (Hereinafter, simply referred to as cracks). This crack may cause separation damage in which a ply such as a carcass ply peels off at the bead portion and progresses into the tire.

[0004] Further, there is a problem that the cracked tire does not have a standard as a base tire at the time of correction, such as retreading the tire, and cannot be corrected even.

The inventors of the present invention have conducted intensive studies in view of the above problems. As a result, when the maximum principal strain on the tire surface is large when the tire is rim assembled and expanded, the cracks are formed. And the maximum principal strain εm of the surface in the area between the tire maximum width point and the contact outside point which is the radial outside point of the contact area in contact with the rim flange
And the maximum principal strain εp at the tire maximum width point P1 (ε
When m-εp) was large, it was found that cracks were concentrated and generated at relatively large strains.

In order to control the maximum principal strain, a folded portion is provided integrally on the main body of one carcass ply with a bead core to be folded from inside to outside in the tire axial direction. It has been found that it is preferable to provide a parallel portion extending parallel to the main body portion and to regulate the length and the like.

As described above, the present invention effectively prevents a crack from a sidewall portion to a bead portion for a long period of time, and further improves the durability of the bead portion to enable tire rehabilitation. It aims to provide radial tires.

[0008]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention is characterized in that the bead core is attached to a main body extending from a tread portion to a sidewall portion to a bead core. A carcass consisting of one carcass ply, which is integrally provided with a folded portion that is folded outward from the tire axial direction inside and extends radially outward, and the cords are arranged at an angle of 70 to 90 ° with respect to the tire equator, A heavy-duty radial tire having a bead apex extending in a radially outward direction from the bead core in a tire radial direction between the carcass main body portion and the folded portion, wherein the folded portion is formed on an axially outer surface of the bead apex. Along the carcass body from the tire radially outer end of the bead apex. Comprises a parallel portion, moreover radially outer end height H1 of the folded portion, the bead base line BL
Is at least 20% of the carcass cross-sectional height Hc from the carcass to the outermost end of the carcass in the tire radial direction, and the tire is rim-assembled to a regular rim and filled with an internal pressure of 0.5 kgf / cm ² from a temporarily assembled state to a normal internal pressure. When the inflation is changed to the standard state filled with the rim, the tire maximum width point P1 which is the outermost in the tire axial direction and the contact outer point P2 which is the radial outer point of the contact area in contact with the rim flange. The maximum principal strain εm of the surface in the region between the regions is 4% or less, and the maximum principal strain εm in the region is
And the maximum principal strain εp at the tire maximum width point P1 (ε
m-εp) is less than 2%.

Further, in the invention according to claim 2, the height H1 of the turn-back portion in the radial direction is equal to the carcass sectional height Hc.
2. The radial tire for heavy load according to claim 1, wherein the normal rim is a 5 ° taper rim.

According to a third aspect of the present invention, the length L of the parallel portion is 2.0 to 8.0 times the maximum sectional width CW of the bead core. It is a radial tire for heavy load of description.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a meridional section of the right half of a no-load state in which a heavy-duty radial tire 1 (hereinafter, sometimes referred to as a tire 1) used for a truck, a bus, or the like is mounted on a regular rim J and filled with a regular internal pressure. ing.

In this specification, the “regular rim” is J
Standard rim specified by ATMA, "Desi specified by TRA"
gn Rim "or" Measuring Ri "defined by ETRTO
m ", and" regular internal pressure "is the maximum air pressure specified by JATMA, and the TRA table" TIRELOAD LIMITS AT VARIOUS C "
OLD INFLATION PRESSURES "or E
It is "INFLATION PRESSURE" specified by TRTO.

In this embodiment, the regular rim J is
Rim sheet JS is a 5 ° taper rim with an inclination of 5 ° ± 1 ° with respect to the tire axial line (R05-1 in JATMA)
Wide flat bottom rim specified by).

1 and 2, a tire 1 is located at a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and an inner end of each sidewall portion 3. A bead portion 4 seated on the regular rim J and a body portion 6A extending from the tread portion 2 to the bead core 5 of the bead portion 4 through the side wall portion 3 to the bead core 5 from the inside in the tire axial direction to the outside. The carcass 6 includes a single carcass ply 6a integrally provided with a folded portion 6B to be folded. By configuring the carcass 6 from one carcass ply in this way, it is useful to reduce the weight of the tire.

The carcass ply 6a is in the form of a sheet in which carcass cords are arranged in an angle range of 70 to 90 ° with respect to the tire equator C and both sides of which are covered with topping rubber. A steel cord is preferably used as the carcass cord, but if necessary, an organic fiber cord such as nylon, rayon, polyester, or aromatic polyamide can also be used. In the carcass 6 of the present embodiment, the steel cord is
Is formed from one carcass ply 6a inclined at an angle of about 90 ° with respect to the carcass ply 6a.

A belt layer 7 is disposed radially outside the carcass 6 and inside the tread portion 2. Belt layer 7
In this example, the steel cord is attached to the tire equator C,
For example, an innermost belt ply 7A inclined at an angle of about 60 ± 10 ° and a belt ply 7B in which a steel cord is inclined at a small angle of 30 ° or less with respect to the tire equator C,
7C and 7D are overlapped, for example, by providing one or more places where the belt cords cross each other between plies.
It has a layered structure. The belt layer 7 can be made of another cord material such as rayon, nylon, aromatic polyamide, and nylon, if necessary.

The bead portion 4 is provided between the main portion 6A of the carcass ply 6a and the folded portion 6B.
The bead apex 8 made of hard rubber is tapered and extends outward in the tire radial direction. The bead apex 8 has, for example, as shown in FIG. 1, the height H2 in the tire radial direction from the bead base line BL is 6 to 31% of the carcass sectional height Hc (shown in FIG. 1), more preferably 8 to 31%. It is preferably set to 22%, more preferably 8 to 14%. In this example, the height is set to about 11%.

The bead base line BL is defined by the JA.
Defined as a tire axial line passing through a rim diameter defined by standards such as TMA, and the “carcass sectional height” is defined as the distance from the bead base line BL to the tire radially outermost end of the carcass 6 in the unloaded state. Is defined as the tire radial distance.

As shown in FIG. 2, in this embodiment, the bead apex 8 has an inner surface 8i in the tire axial direction formed in a substantially linear shape inclined substantially parallel to the carcass main body 6A, and also has a shape in the tire axial direction. The outer side surface 8o is formed in the shape of an inwardly bulging arc depressed inward in the tire axial direction, and the volume of the bead apex 8 is reduced in combination with the height H2 in the tire radial direction. In addition, Bead Apex 8
Is preferably formed of a hard rubber having a JISA hardness of 60 to 99 °, more preferably 70 to 95 °.

In the present embodiment, the bead core 5 is formed by rubber-coating a steel wire having a substantially hexagonal cross section by spirally winding a steel wire a predetermined number of times, so that the inner piece 5i is along the tire axial line. Is configured. Further, since the tire according to the present embodiment is mounted on a 5 ° taper rim, the inner diameter φA of the bead core 5 is equal to the regular rim J.
Must be larger than the nominal diameter φB of the rim. If the inner diameter φA of the bead core 5 is smaller than the nominal rim diameter φB of the regular rim J, there arises a problem that the cord of the carcass 6 is exposed on the bead seat surface or the rim cannot be assembled. The bead core 5 may be made of an aromatic polyamide wire material or the like in addition to steel.

The folded portion 6B of the carcass extends radially outward beyond the outer end 8t of the bead apex 8 and radially inward from the tire maximum width point P1, that is, a relatively small amount of strain when a load is applied. By terminating at the position of H1, the concentration of strain on the outer end of the folded portion 6B can be reduced. The height H1 is equal to the bead baseline BL.
From 20% to 100%, more preferably 30 to 60%, even more preferably 40 to 60% of the carcass section height Hc.
It is desirable to set it as 41% in this example.

Radial outer end height H1 of the folded portion 6B
Is less than 30% of the carcass section height Hc,
Distortion tends to concentrate on the outer end of the turned-up portion 6B and separation tends to occur. Conversely, the radially outer end height H1 of the turned-up portion 6B is 60% of the carcass sectional height Hc.
%, It is not preferable because the improvement in durability performance reaches a plateau and rather causes an increase in tire weight.

In the present embodiment, the carcass folded portion 6B is formed so as to extend inward and extend radially outward along the outer surface 8o of the bead apex 8 and to extend substantially outwardly of the outer end 8t of the bead apex 8. From the position, a parallel portion G extending substantially parallel to and close to the body portion 6A of the carcass is formed and terminated. By forming such parallel portions G, the tire 1 was rim-assembled to the regular rim J and the inflation was changed from a temporary assembled state filled with an internal pressure of 0.5 kgf / cm ² to a standard state filled with the normal internal pressure. In this case, the tire maximum width point P1 which is the outermost in the tire axial direction
And the maximum principal strain εm of the surface of the region Y between the contact outer point P2 which is the radially outward point of the contact region in contact with the flange Jf of the rim J, and at the same time, the maximum principal strain of the region Y The difference (εm−εp) between εm and the maximum principal strain εp at the tire maximum width point P1 can be restricted to a certain range.

The length L of the parallel portion G is, for example, the maximum sectional width CW of the bead core 5 in the no-load state.
2.0 to 8.0 (measured for the wire portion)
In this embodiment, the parallel portion G is preferably about 5.5 times the maximum cross-sectional width CW of the bead core, and more preferably 3.5 to 6.5 times, and even more preferably 4.0 to 6.0 times.
It is set to 0 times.

If the length L of the parallel portion G is less than 2.0 times the maximum sectional width CW of the bead core, the region Y
, A peak of the maximum principal strain εm appears, and cracks tend to occur relatively quickly and concentrated at the peak position of the maximum principal strain εm. Conversely, if the peak exceeds 8.0 times, the improvement in durability reaches a plateau, Rather, it is not preferable because it causes an increase in tire weight.

As shown in FIG. 3, which is a cross section taken along line AA of FIG. 2, as an example of the carcass main body 6A and the folded back portion 6B approaching each other at the parallel portion G, the carcass main body 6A
And the distance N between the carcass cords of the folded portion 6B is maintained at, for example, 1.0 to 4.5 times, preferably 1.5 to 3.5 times the diameter D of the carcass cord 11, and the carcass main body 6A It is desirable that the shearing force acting between the carcass cords of the folded portion 6B be reduced by the elasticity of the rubber material interposed between the carcass cords.

When the inter-cord distance N is less than 1.0 times the diameter D of the carcass cord, the carcass cord 11
They tend to come close to each other, and the effect of reducing the shearing force by the rubber between the cords becomes insufficient, and the carcass cords 11 may partially come into contact with each other, which may cause cord looseness. Further, when the inter-cord distance N exceeds 4.5 times the diameter D of the carcass cord, the effect of reducing the maximum strain ε on the outer surface of the region Y can be reduced even when the main body 6A and the folded portion 6B extend in parallel. Tends to decrease,
In addition, the thickness of the bead portion 4 is unnecessarily increased.

The rubber material interposed between the carcass cords 11 of the carcass body 6A and the folded portion 6B may use the topping rubber of the carcass ply 6a. The figure shows a cushion rubber layer 12 interposed separately between 6A and the folded portion 6B. And the cushion rubber layer 12
May be made of a cushion rubber layer 12 having a hardness substantially equal to that of the topping rubber, a hard rubber of the same material as the bead apex 8 or the like for reinforcing the bead portion 4.

In the radial tire for heavy loads according to the present embodiment, as shown in FIG. 2, the bead portion 4 is provided with a clinch rubber on a part of the bead seat surface which comes into contact with the rim J and a part of the bead portion outer surface. Are illustrated. By using a hard rubber having a JISA hardness of 60 to 90 °, more preferably 65 to 85 °, the clinch rubber can prevent rim displacement, abrasion due to contact with the rim, and the like.

A flexible side rubber 14 is arranged on the outside of the clinch rubber 13 in the radial direction. further,
The radial tire for heavy load 1 of the present example exemplifies a tire in which a bead portion 4 is not provided with a cord reinforcing layer made of a cord ply in which an organic fiber cord or a steel cord is arranged separately from the carcass ply 6a. This helps to reduce tire weight.

FIG. 4 shows a typical bead structure of a conventional heavy load radial tire. In this tire, the folded portion b is provided integrally with the body portion a of the carcass, but there is no parallel portion as in the present invention, and the bead apex c forms 40 to 42% of the carcass sectional height Hc. Further, cord reinforcing layers d and e in which cords are arranged, clinch rubber f made of hard rubber, and the like are arranged.

Such a conventional tire has a peak Z at which the maximum principal strain εm is about 6.7% in the region Y when the internal pressure is filled from the tentatively assembled state to the standard state, as shown in FIG. . The maximum principal strain ε at the tire outermost point P1
p is as small as about 2%. For this reason,
The relative strain represented by (εm−εp) is also as large as 5.5%.

On the other hand, in the present invention, since the maximum principal strain εm of the region Y is 1.6% and εp is 1.1%, the maximum principal strain εm of the region Y and the tire maximum width point P1 are obtained. Is controlled so that the difference (εm−εp) from the maximum principal strain εp is as small as 0.5%. As a result, there is substantially no peak of the maximum principal strain εm. Distortion can also be reduced.

Thus, in the radial tire for heavy load according to the present invention, the maximum principal strain and relative strain on the tire surface can be extremely reduced in the region Y from the side wall portion 3 to the bead portion 4, so that repeated deformation and atmospheric Cracks caused by the influence of ozone in the inside can be effectively suppressed over a long period of time, and the durability of the bead portion 4 can be improved.

If the maximum principal strain εm exceeds 4%, the rubber deteriorates due to repeated deformation of the side wall portion due to running, and furthermore, due to the influence of ozone and the like in the atmosphere,
It is not preferable because cracks are generated at an early stage after being concentrated on a portion having high distortion. Also, the maximum principal strain ε of the region Y
If there is a portion where the difference (εm−εp) between m and the maximum principal strain εp at the tire maximum width point P1 exceeds 2%, the relative strain increases in the region Y, and cracks concentrate at such a position. Easier to do.

The measurement of the maximum principal strains εm and εp is as follows.
As shown in FIGS. 6 and 7, the operation is performed as follows. Buffing the surfaces of the sidewall portion 3 and the bead portion 4 of the sample tire and wiping it off with naphtha, applying an adhesive to the polished surface, and drawing a measurement reference line RL extending in the tire radial direction, using a printing screen Then, using white ink (titanium oxide + DOP + castor oil), copy the markings M in which a plurality of circles are arranged as shown in FIG. 6 onto a vinyl tape 15.
^2. Affix and transfer along the measurement reference line RL to the polished surface of the test tire filled with the internal pressure of ^2. Further, after filling the air pressure to the normal internal pressure, the marking M on the sidewall portion 3 of the tire is Copy it to a new tape, and obtain the marking M (0.5
The reference condition at the time of filling the internal pressure of kgf / cm ² and the comparison condition at the time of filling the normal internal pressure) are enlarged, and the principal points shown in FIG.

[0037]

(Equation 1)

[0038]

(Equation 2)

[0039]

(Equation 3)

[0040]

(Equation 4)

[0041]

(Equation 5)

[0042]

(Equation 6)

[0043]

(Equation 7)

[0044]

(Equation 8)

[0045]

(Equation 9)

[0046]

(Equation 10)

[0047]

[Equation 11]

[0048]

EXAMPLE A radial tire for heavy load having a tire size of 10.00R20 was prototyped based on the specifications shown in Table 1 (Examples 1 to 6, conventional example), a maximum principal strain measurement test of a side wall portion, A crack measurement test, a bead durability test, and the like were performed. The common specifications of the tires are as follows. <Carcass>-Number of plies: 1-Cord configuration Steel cord (3 x 0.20 + 7 x
0.23) ・ Cord angle 90 degrees to the tire equator ・ Cord density 38 / 5cm <Belt layer> ・ Number of plies 4 ・ Cord configuration Steel cord (3 × 0.20 + 6 ×
0.35) ・ Cord angle + from inner ply to tire equator
67 / + 18 / −18 / −18 degrees Cord density 26 lines / 5 cm The contents of the test are as follows.

<Bead Durability> A test tire was used at 7.50 ×
20 is mounted on a regular rim, filled with an internal pressure of 1000 kPa, run on the drum at a load of 9000 kgf, and at a speed of 20 km / h. When the damage that can be visually confirmed is generated, the running is completed, and the damage generation distance L1 And the running distance L0 (1
0000 km) was evaluated by an index with the conventional example being 100. The higher the value, the better.

<Maximum principal strain in sidewall portion> As described above, the presence or absence of a peak and the maximum principal strains εm and εp were evaluated (normal rim: 7.50 × 20, internal pressure: 800 kP).
a).

<Crack Measurement Test> A test tire mounted on a regular rim of 7.50 × 20 and filled with an internal pressure of 800 kPa is placed in an ozone chamber having an ozone concentration of 40 pphm and a room temperature of 40 ° C., and cracks occur in the region Y. The time until the evaluation was evaluated using an index with the conventional example taken as 100.
The larger the value, the better the crack resistance. Table 1 shows the test results.

[0052]

[Table 1]

As a result of the test, the tire according to the embodiment showed that the area Y
, The maximum principal strain εm has no peak point and is 4.0
% Was confirmed. Also, (εm−εp)
Was less than 2%, and it was confirmed that the relative strain in the region Y was also small. It can be seen that the tires of the examples have excellent crack resistance performance in correlation with the results. Note that substantially the same measurement results are obtained for other tire sizes.

[0054]

According to the present invention, the folded portion of the carcass forms a parallel portion of a specific length extending in parallel with the body portion of the carcass, and the tire is rim-assembled to the regular rim and the weight is 0.5 kgf / When the inflation is changed from the temporary assembled state filled with the internal pressure of cm ² to the standard state filled with the normal internal pressure, the tire maximum width point P1 which is the outermost in the tire axial direction.
And the maximum principal strain εm of the surface in the region between the inner point P2 which is the radially outer point of the contact area in contact with the rim flange is 4
% Or less, and the difference (εm−εp) between the maximum principal strain εm in the region and the maximum principal strain εp at the tire maximum width point P1 is 2
%, The strain in the region can be reduced, so that cracks can be effectively suppressed over a long period of time, and the durability of the bead portion can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view (right half) of a tire according to an embodiment of the present invention.
It is.

FIG. 2 is an enlarged sectional view of a bead portion.

FIG. 3 is a sectional view taken along the line AA of FIG. 2;

FIG. 4 is a diagram showing a structure of a bead portion of a conventional tire.

FIG. 5 is a graph showing a measurement result of a maximum principal strain.

FIG. 6 is a diagram illustrating a method of measuring a maximum principal strain.

FIGS. 7A and 7B are diagrams for explaining the reference point positions of markings.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6a Carcass ply 6A Carcass ply main body 6B Carcass ply turnback part 8 Bead apex J Regular rim Jf Rim flange P1 Tire maximum width point P2 Inner point

Claims (3)

[Claims] The present invention is further characterized in that a main body portion extending from a tread portion to a side wall portion to a bead core of a bead portion is provided integrally with a folded portion which is folded back from the inside in the tire axial direction to the outside by the bead core and extends outward in the radial direction. A carcass composed of a single carcass ply arranged at an angle of 70 to 90 degrees with respect to the tire equator; A heavy duty radial tire having an apex, wherein the folded portion extends radially outward along an axially outer surface of the bead apex and is close to the carcass main body portion from a tire radially outer end of the bead apex. And a parallel portion extending in parallel with the base portion, and a height H1 of a radially outer end of the folded portion is set to a bead base line. Not less than 20% of the carcass sectional height Hc from the tire BL to the outermost end of the carcass in the tire radial direction, and the tire is assembled to a regular rim and weighed 0.5 kgf / cm ²
When the inflation is changed from the tentatively assembled state filled with the internal pressure to the standard state filled with the normal internal pressure, the tire maximum width point P1, which is the outermost in the tire axial direction, and the radial outside of the contact area in contact with the flange of the rim. The maximum principal strain εm of the surface in the region between the contact point P2 and the contact outside point P2 is 4%
The difference (εm−εp) between the maximum principal strain εm in the region and the maximum principal strain εp at the tire maximum width point P1 is 2% or less.
Radial tire for heavy load, characterized by being less than. 2. A height H1 of a radially outer end of the folded portion,
The heavy load radial tire according to claim 1, wherein the normal rim is 30 to 60% of the carcass sectional height Hc, and the regular rim is a 5 ° taper rim. 3. The radial tire for heavy loads according to claim 1, wherein the length L of the parallel portion is 2.0 to 8.0 times the maximum sectional width CW of the bead core.