JP3377453B2 - Heavy duty tire - 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 tire capable of improving the durability of a bead portion.

[0002]

2. Description of the Related Art As shown in FIG. 4, a tubeless heavy-duty tire is usually mounted on a 15 ° deep rim J defined by JATMA, JIS or the like. In such a 15 ° deep rim, after the tire t (only the bead portion is shown) is assembled into the rim, the bead base a is moved along the rim base b toward the larger rim diameter by filling the internal pressure. Can be made. Therefore, the tire t and the rim J can be firmly fitted to each other, and the airtightness of the internal pressure is maintained even in this type of tire to which a high internal pressure and a high load act.

Further, a bead core c that does not substantially extend is embedded in the bead portion of the heavy-duty tire, and a carcass d of a steel cord forming the skeleton of the tire is folded back around the bead core c and locked. There is. The one shown in the figure includes a cord chafer e for reinforcing the bead portion. The bead core c has a laterally long hexagonal cross-sectional profile and has a long side c on the inner side in the tire radial direction.
1 is arranged substantially parallel to the surface of the rim sheet b, that is, inclined at an angle of about 15 ° with respect to the tire axial direction, and secures a wide compression force (bead compression) between the bead core c and the rim sheet b. What you are trying to do is common. This is because when the bead compression is low, the bead portion is easily pushed to the rim flange Jf side, and during this time, a strong compressive force is received and ply separation is likely to occur.

In the conventional heavy-duty tire, the durability of the bead portion is improved by increasing the bead compression and simultaneously increasing the bead portion rigidity such as increasing the rubber thickness of the bead portion.

However, in recent years, Japanese Patent Laid-Open No. 9-66711 has been proposed in which the profile of the carcass ply is reviewed to improve the durability of the bead portion of a heavy duty tire. In this proposal, as shown in FIG.
It has a slim bead part that is the inner surface of the bead part cut from the conventional shape shown by the chain line. The profile shape of the carcass has also been changed accordingly.
For example, the body portion d2 of the carcass ply extending between the bead cores c and c has a substantially linear inner end side in the tire radial direction, and the folded portion d1 of the carcass ply is immediately folded around the bead core c. A parallel portion g is formed near the body portion d2 of the carcass ply and extends substantially parallel to the body portion d2.

In such a carcass profile, since the folded-back portion d1 which is apt to be damaged approaches the neutral line (neutral axis) side of the deformation, the compressive force to the folded-back portion d1 is greatly reduced, and the bead portion is greatly reduced. It is possible to prevent the strain from concentrating on a specific position of. Further, as a result, the rubber thickness of the bead portion can be reduced (the bead portion can be made slim), the heat generation property of the bead portion can be significantly reduced, and the durability and the like can be improved.

However, in such a heavy-duty tire thus improved, particularly in the case where the folded portion d1 of the carcass ply has the parallel portion g, in order to effectively function the profile of the carcass d and the like. Since the bead part needs to be firmly fixed to the rim, bead compression becomes more important than ever.

The inventors of the present invention have conducted various studies to improve the bead compression in a heavy-duty tire mounted on such a deep rim of 15 °, and found that the cross-sectional shape of the bead core and its arrangement and the tire radius of the bead core. The present invention has been completed by finding out that it is effective to regulate the distance between the inner periphery of the inner side in the direction and the steel cord of the carcass ply folded back by the bead core.

As described above, the object of the present invention is to provide a heavy-duty tire which can improve the durability of the bead portion.

[0010]

According to a first aspect of the present invention, there is provided a 15 ° deep rim having a carcass having a steel cord extending from a tread portion to a sidewall portion to a bead core of a bead portion. In the heavy-duty tire to be mounted, the carcass has a body portion that extends from the tread portion to the bead core of the bead portion through the sidewall portion, and a folding portion that folds around the bead core from the inside in the tire axial direction to the outside. In addition to the carcass ply provided in, the folded portion has a parallel portion that extends close to the main body portion and is substantially parallel to the main body portion, and the bead core includes a tire meridian including a tire shaft. In the cross-section, the cross-section has a substantially regular hexagonal shape, and has an inner periphery on the inner side in the tire radial direction substantially parallel to the tire axial direction, and Maximum distance d from the near to the steel cord of the inner peripheral perpendicular to the measured carcass 1.0
It is characterized by being ~ 2.5 mm.

According to a second aspect of the present invention, the bead core has a core flatness ratio of 0.75 to 1.5 which is a ratio (h / w) of a width w in the tire axial direction and a height h in the tire radial direction. 0, and the inner periphery is 0 to 2 with respect to the tire axial direction line.
The heavy duty tire according to claim 1, wherein the tire has an angle θ of °.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a normal state and no load in which a heavy-duty tire 1 (hereinafter also referred to as tire 1) used for trucks, buses, etc. is mounted on a 15 ° deep rim J and filled with a normal internal pressure. There is. "Regular internal pressure" is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. For JATMA, the "maximum air pressure" and for TRA, the table "TIRE LOAD" LIMITS AT VARIOUS COLD INFLATION P
The maximum value described in "RESSURES" or "INFL" for ETRTO
ATION PRESSURE ".

In FIG. 1, a tire 1 has a tread portion 2
A carcass 6 having a steel cord 6C (shown in FIG. 2) extending from the side wall part 3 to the bead core 5 of the bead part 4, and a belt arranged radially outside the carcass 6 and inside the tread part 2. 1 illustrates a tubeless type heavy load radial tire including a layer 7.

The carcass 6 has a tread portion 2 in this example.
A carcass ply 6A integrally provided with a folded-back portion 6b that folds around the bead core 5 from the inner side in the tire axial direction to the outer side in a main body portion 6a extending from the side wall portion 3 to the bead core 5 of the bead portion 4. Composed of.
The carcass ply 6A has a sheet shape in which both sides of a cord arrangement body in which steel cords 6C are arranged are covered with a thin topping rubber. Further, the carcass 6 has the steel cord 6C with respect to the tire equator C, for example, 75 to 90.
.Degree., In this example, an example in which the elements are arranged at an angle of about 90.degree.

The body portion 6a of the carcass ply 6A
A bead apex rubber 8 made of hard rubber is formed between the bent portion 6b and the folded-back portion 6b so as to extend radially outward from the outer surface of the bead core 5 in the tire radial direction to reinforce the bead portion 4. The bead apex rubber 8 has, for example, a tire radial direction height ha from the bead base line BL of 6 to 31% of a tire cross-sectional height H,
More preferably 8 to 22%, more preferably 8 to 14%
It is preferable to set the height to a small value, and in this example, it is set to about 11%. The "bead baseline" is defined as the tire axial direction line passing through the rim diameter position defined by the standard on which the tire is based, and the tire cross-sectional height H is the normal state and no-load bead baseline BL. Height to the outermost side in the tire radial direction.

As shown in FIG. 2, the bead apex rubber 8 is formed in a substantially straight line in which an inner side surface 8i in the tire axial direction is inclined substantially parallel to the carcass ply body 6a, as shown in FIG. Outer surface 8 in the tire axial direction
An example is shown in which o is formed by an arcuate surface having an inner bulge that is recessed inward in the tire axial direction. This bead apex rubber 8
Is preferably made of hard rubber having a JIS (A) hardness of 60 to 99 °, more preferably 70 to 95 °.

In the belt layer 7, in the present embodiment, the steel cord is tilted with respect to the tire equator C at an angle of, for example, about 60 ± 10 °, and the steel cord is applied to the tire equator C. An example is a four-layer structure in which belt plies 7B, 7C, and 7D that are inclined and arranged at a small angle of 30 ° or less are overlapped with each other by providing at least one or more places where the belt cords intersect each other between the plies. There is. For the belt layer 7, other cord materials such as rayon, nylon, aromatic polyamide, nylon can be used if necessary.

Further, the folded-back portion 6b of the carcass ply.
Has a parallel portion 9 which is folded back from the inner side in the tire axial direction around the bead core 5 and which is close to the main body portion 6a and extends substantially parallel to the main body portion 6a. In this example, the folded-back portion 6b extends outward in the tire radial direction while approaching the main body portion 6a along the arcuate surface 8o of the inner bulge of the bead apex rubber 8.
The folded-back portion 6b is an example in which the parallel portion 9 is continuously formed from the outer end 8t of the bead apex rubber 8 to the outer end 6t of the folded-back portion 6b.

In the parallel portion 9, the distance N between the steel cords of the carcass ply body portion 6a and the folded portion 6b is, for example, 1.5 of the diameter D of the steel cord 6C.
It is preferable that they are close to each other so as to be about 4.5 times, preferably 1.5 to 3.5 times, and more preferably about 1.5 to 3.0 times. In the parallel portion 9, the rubber material interposed between the steel cords of the main body portion 6a and the folded portion 6b may be the topping rubber of the carcass ply 6A, or a cushion rubber layer or the like may be interposed separately.
The rubber hardness of this cushion rubber layer can be set variously.

In the present embodiment, such a parallel portion 9 is formed in a substantially straight line shape, and the inner surface of the tire is also formed in a substantially straight line shape along the same. Therefore, compared with the conventional bead portion structure. The thickness of the bead portion is small and the weight is reduced. Further, such a shape of the bead portion 4 can disperse the internal strain of the bead portion 4 even when the internal pressure is filled. Due to these, the tire 1 of the present embodiment has excellent durability of the bead portion 4. In addition, such a length L of the parallel portion 9 (measured as shown in FIG. 1)
Is particularly preferably, for example, 35 to 70 mm.

In the present example, the bead core 5 has a substantially hexagonal cross section in the tire meridian section including the tire shaft. In this example, the bead core 5 is formed by spirally winding a steel wire 10 (monofilament) having a circular cross section a predetermined number of times as shown in FIG. Specifically, a wire row in which the plurality of steel wires 10, 10 ... Are arranged in the tire axial direction is arranged in multiple stages in the tire radial direction is illustrated. The figure shows an example of a substantially regular hexagon formed by a total of 44 of 5 × 6 × 7 × 8 × 7 × 6 × 5.

The bead core 5 having such a wire wound around it is covered with a wrapping rubber 12 and used for forming a tire. In addition to steel, a substantially non-stretchable material such as aromatic polyamide can be applied to the bead core 5. The steel wire of this example has a diameter of φ1.
I am using a 55 mm one.

Since the bead core 5 is formed by winding the steel wire 10 having a circular cross section in this example, the envelope of the cross sectional contour of the wound body substantially determines the cross sectional shape of the bead core. And since it is a “general hexagonal cross section”, it is not necessary to have a perfect regular hexagonal shape, but for example, it has six substantially straight sides and has a width w in the tire axial direction and a height h in the tire radial direction. The core flatness ratio, which is the ratio (h / w), is 0.75 to 1.15, and more preferably 0.75 to 1.
0, more preferably 0.85 to 1.0 is included.

The bead core 5 is, as shown in FIG.
In the tire meridional section in a normal state in which the tire is mounted on the deep rim J of 15 ° and filled with the normal internal pressure, and in a state of no load, the inner periphery 5i of the tire radial direction substantially parallel to the tire axial direction is provided. There is. At this time, being “substantially” parallel to the tire axial direction means that the inner periphery 5i is the tire axial direction line A.
With respect to the angle θ of 0 to 3 °, preferably 0 to 2 °.

In the present embodiment, the bead core 5 has a substantially regular hexagonal cross section, and the inner periphery 5i is arranged substantially parallel to the tire axial direction. The inner circumference 5 measured vertically
Carcass steel cord 6 folded back close to i
Maximum distance d to C (shown in FIG. 2) is 1.0 to 2.5 mm
Is limited to a small value.

As described above, by limiting the cross-sectional shape of the bead core 5 and its arrangement and the maximum distance d,
The folding of the steel cord 6C of the carcass 6 can be performed while being closer to the inner periphery 5i of the bead core. On the contrary,
In the conventional heavy-duty tire shown in FIG. 5, the steel cord of the carcass has to largely wrap around the bead core c and be folded back based on the bead core shape and its arrangement.

If the inner periphery 5i of the bead core is not substantially parallel to the tire axial direction, it becomes difficult to fold back the carcass ply 6A around the bead core 5 while reducing the maximum distance d, and the rim assembly property is also improved. There is a problem that it becomes difficult and the rim comes off easily.

As a result of the experiments by the inventors, a carcass cord 6C folded around the inner periphery 5i of the bead core 5 and its periphery.
It was found that the bead compression was reduced when the thickness of the rubber interposed between the and was increased. Therefore, in the configuration of the present embodiment in which the thickness of the rubber interposed between the inner periphery 5i of the bead core 5 and the carcass cord 6C folded around it can be reduced, the bead compression can be increased as compared with the conventional structure. Therefore, the durability of the bead portion 4 can be maintained higher because the structure of the carcass can be made effective. Incidentally, in the conventional heavy duty tire shown in FIG. 5, this d value is generally about 3.0 to 4.0 mm.

However, if the maximum distance d is less than 1.0 mm, the steel cord 6C of the carcass 6 is likely to be bent excessively, and the cord is likely to break due to stress concentration. On the other hand, when it exceeds 2.5 mm, the bead compression is lowered and the effect of improving the durability of the bead portion is lowered.

Although one embodiment of the present invention has been described in detail above, these are merely examples of the present invention, and various configurations can be adopted unless otherwise specified.

[0031]

EXAMPLE A heavy-load radial tire having a basic configuration shown in FIGS. 1 and 2 and a tire size of 11R22.5 14PR was prototyped according to the specifications shown in Table 1 (Examples 1 and 2 and Comparative Examples 1 and 2). . For comparison, a radial tire for heavy load (conventional example) having the same size as the basic structure shown in FIG. 4 was also prototyped. And these test tires are 8.25 ×
Installed on a regular rim of 22.5, the internal pressure is 1000 (kPa)
Was charged, and the drum was run at a load of 9000 kgf and a speed of 20 km / h. When the damage visually recognizable visually occurred, the running was terminated, and the running time until the damage occurred was measured. According to the standard, 350 hours or more are acceptable. The test results are shown in Table 1.

[0032]

[Table 1]

As a result of the test, it can be confirmed that the tires of the examples are superior in durability of the bead portion as compared with the conventional examples and the comparative examples.

[0034]

As described above, according to the present invention, it is possible to provide a heavy load tire capable of further improving the durability of the bead portion by increasing the bead compression.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a tire according to an embodiment of the present invention,
The tires are assembled on the rim and the tires are in normal pressure and no load.

FIG. 2 is an enlarged sectional view showing a bead portion thereof.

FIG. 3 is an enlarged sectional view of a bead core.

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

FIG. 5 is a diagram showing a structure of a bead portion of a conventional tire.

[Explanation of symbols]

2 tread section 3 Side wall part 4 bead section 5 bead core 6 carcass 6A carcass ply 6a Carcass ply body 6b Carcass ply turns 6c Carcass steel cord

Claims (2)

(57) [Claims] 1. A heavy duty tire mounted on a 15 ° deep rim, comprising a carcass having a steel cord extending from a tread portion to a sidewall portion to a bead core of the bead portion, wherein the carcass is a tread portion. From the sidewall part to the bead core of the bead part, the carcass ply is integrally provided with a folding part that folds around the bead core from the inner side in the tire axial direction to the outer side, and the folding part is A bead core having a parallel hexagonal cross section in a tire meridian section including a tire shaft and being substantially parallel to the tire axial direction. The inner circumference of the carcass is measured from the inner circumference of the bead core perpendicular to the inner circumference. A heavy-duty tire characterized in that the maximum distance d to the cheer cord is 1.0 to 2.5 mm. 2. The bead core has a core flatness ratio of 0.75 to 1.0, which is a ratio (h / w) of a width w in the tire axial direction and a height h in the tire radial direction, and The heavy duty tire according to claim 1, wherein the periphery forms an angle θ of 0 to 2 ° with respect to the tire axial direction line.