JP2000085320A - Tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire for heavy load excellent in durability of a bead part. SOLUTION: This tire for heavy load is provided with a carcass 6 of a steel code and mounted on a 15 degree deep bottom rim J. The carcass 6 comprises a sheet of carcass ply 6A provided integrally with a folding part 6b for folding a periphery of a bead core 5 to a main body part 6a astride bead cores 5, 5 from an inside of a tire-axial direction to its outside. The folding part 6b has a parallel part 9 extended substantially parallelly to the main part 6a neighboring to the main body part 6b. The bead core 5 has a substantially regular hexagonal cross section in a meridian cross-section including a tire axis and is provided with an inner circumferential side 5i in an inside of a tire radial direction substantially parallel to the tire-axial direction. The maximum distance (d) from the side 5i of the bead core 5 to the steel code of the carcass 6 measured perpendicularly to the side 5i is 1.0-2.5 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 type heavy duty tire is usually mounted on a 15 ° deep rim J specified by JATMA, JIS or the like. Such a 15 ° deep bottom rim moves the bead base a along the rim base b toward the larger rim diameter by filling the internal pressure after assembling the tire t (only the bead portion is shown). Can be done. For this reason, the tire t and the rim J can be firmly fitted to each other, and even in this type of tire in which a high internal pressure and a high load act, the airtightness of the internal pressure is maintained.

A bead core c that does not substantially extend is embedded in a bead portion of the heavy duty tire, and a carcass d of a steel cord forming a skeleton of the tire is folded back around the bead core c and locked. I have. The illustrated one is provided with a cord chafer e for reinforcing the bead portion. The bead core c has a hexagonal shape whose cross-sectional profile is horizontally long, and has a long side c in the tire radial direction inside.
1 is arranged substantially parallel to the surface of the rim sheet b, that is, at an angle of about 15 ° with respect to the tire axial direction line, and secures a wide range of large compression force (bead compression) between the bead core c and the rim sheet b. What you try is common. This is because if the bead compression is low, the bead portion is easily pushed to the rim flange Jf side, and ply separation is apt to occur due to a strong compressive force during this period.

Further, in the conventional heavy duty tire, the bead compression is increased, and the durability of the bead is improved by increasing the rigidity of the bead by increasing the rubber thickness of the bead.

However, in recent years, Japanese Patent Application Laid-Open No. 9-66711 has been proposed in which the profile of a carcass ply and the like are reviewed to improve the durability of a bead portion of a heavy duty tire. In this proposal, as shown in FIG.
It has a slim bead as if the inner surface of the bead was cut away from the conventional shape shown by the chain line. Also, the profile shape of the carcass is changed in accordance with this.
For example, the body portion d2 of the carcass ply extending between the bead cores c has a substantially radially 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. And a parallel portion g extending substantially parallel to the body portion d2 of the carcass ply.

In such a carcass profile, the folded portion d1, which is apt to be damaged, approaches the neutral line (neutral axis) side of the deformation, so that the compressive force on the folded portion d1 is greatly reduced, and the bead portion is reduced. Can be prevented from being concentrated at a specific position. As a result, the rubber thickness of the bead portion can be reduced (the bead portion can be made slim), and the heat generation of the bead portion can be greatly reduced, thereby improving the durability and the like.

However, in such an improved heavy load tire, particularly in the case where the folded portion d1 of the carcass ply forms the parallel portion g, it is necessary to make the profile of the carcass d function effectively. Since the bead portion needs to be firmly fixed to the rim, bead compression becomes more important than before.

[0008] The inventors of the present invention have conducted various studies on such heavy-duty tires mounted on the deep rim at a depth of 15 ° in order to increase the bead compression. The cross-sectional shape and arrangement of the bead core and the tire radius of the bead core were investigated. The inventors have found that it is effective to regulate the distance between the inner periphery on the inner side in the direction and the steel cord of the carcass ply turned up by the bead core, and have completed the present invention.

As described above, an object of the present invention is to provide a heavy-duty tire capable of improving the durability of a bead portion.

[0010]

According to the first aspect of the present invention, there is provided a 15 ° deep rim provided with a carcass having a steel cord extending from a tread portion to a sidewall portion to a bead core of a bead portion. A heavy-duty tire to be mounted, wherein the carcass is integrally formed with a folded portion that turns around the bead core from the inside in the tire axial direction to the outside from the tread portion to the bead core of the bead portion through the sidewall portion. And the folded portion has a parallel portion extending close to and substantially parallel to the main body portion, and the bead core includes a tire meridian including a tire axis. In cross-section, the cross-section has a substantially regular hexagonal shape and has an inner periphery in the tire radial direction substantially parallel to the tire axial direction, and the bead core has Maximum distance d from the near to the steel cord of the inner peripheral perpendicular to the measured carcass 1.0
２．５2.5 mm.

[0011] In the invention according to claim 2, the bead core has a core aspect ratio of 0.75 to 1.10, which is a ratio (h / w) of a width w in the tire axial direction to 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.
2. The heavy load tire according to claim 1, wherein the angle θ is ゜.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a normal state and no load in which a heavy load tire 1 (hereinafter, sometimes referred to as a tire 1) used for a truck, a bus or the like is mounted on a 15 ° deep rim J and filled with a normal internal pressure. I have. The "normal internal pressure" is the air pressure specified 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
RESSURES ", the maximum value in ETRTO," INFL
ATION PRESSURE ".

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

The carcass 6 is, in this embodiment, a tread portion 2.
A single carcass ply 6A integrally provided with a folded portion 6b that folds around the bead core 5 from the inside in the tire axial direction to the outside in the body portion 6a that extends from the inside to the bead core 5 of the bead portion 4 through the sidewall portion 3. Consists of
The carcass ply 6A has a sheet shape in which both sides of a cord array in which steel cords 6C are arranged are covered with thin topping rubber. In addition, the carcass 6 is configured such that the steel cord 6C is, for example, 75 to 90 with respect to the tire equator C.
゜, this example illustrates an arrangement in which the array is inclined at an angle of about 90 °.

The main body 6a of the carcass ply 6A
A bead apex rubber 8 made of a hard rubber tapering from the outer surface of the bead core 5 in the tire radial direction to the outer side in the tire radial direction is disposed between the bead portion 4 and the folded portion 6b to reinforce the bead portion 4. The bead apex rubber 8 has a tire radial height from the bead base line BL of 6 to 31% of the tire cross-sectional height H, for example.
More preferably 8 to 22%, more preferably 8 to 14%
Is preferably set to about 11% in this example. The "bead base line" is defined as a tire axial line passing through a rim diameter position defined by the standard on which the tire is based, and the tire section height H is defined as a value obtained from the bead base line BL in the normal state and under no load. The height up to the outermost side in the tire radial direction.

As shown in FIG. 2, in the present embodiment, the bead apex rubber 8 is formed in a substantially linear shape in which the inner side surface 8i in the tire axial direction is inclined substantially parallel to the carcass ply body 6a. The outer surface 8 in the tire axial direction
An example in which o is formed by an inwardly bulging arcuate surface recessed inward in the tire axial direction is illustrated. This bead apex rubber 8
Is preferably formed of hard rubber having a JIS (A) hardness of 60 to 99 °, more preferably 70 to 95 °.

In the present embodiment, the belt layer 7 includes a steel cord in the innermost belt ply 7A in which the steel cord is inclined at an angle of about 60 ± 10 ° with respect to the tire equator C, and a steel cord in the tire equator C. For example, there is illustrated a four-layer structure in which belt plies 7B, 7C, and 7D arranged at an angle of a small angle of 30 ° or less and at least one or more locations where the belt cords cross each other between the plies are provided. I have. For the belt layer 7, other cord materials such as rayon, nylon, aromatic polyamide, and nylon can be used as needed.

The carcass ply folded portion 6b
Has a parallel portion 9 which is folded around the bead core 5 from the inside to the outside in the tire axial direction, and which extends close to and substantially parallel to the main body 6a. In this example, the folded portion 6b extends outward in the tire radial direction while approaching the main body 6a along the arcuate surface 8o of the inward bulge of the bead apex rubber 8.
The folded portion 6b exemplifies a portion forming the parallel portion 9 continuously from the outer end 8t of the bead apex rubber 8 to the outer end 6t of the folded 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 times 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 to 4.5 times, preferably about 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 a topping rubber of the carcass ply 6A, or a cushion rubber layer or the like may be separately provided.
The rubber hardness of the cushion rubber layer can be set variously.

In the present embodiment, such a parallel portion 9 is formed in a substantially linear shape, and the inner surface of the tire is also formed in a substantially linear shape along the same. In addition, the thickness of the bead portion is reduced 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 at the time of internal pressure filling. As a result, the tire 1 of the present embodiment is excellent in the durability of the bead portion 4. The length L of the parallel portion 9 (measured as shown in FIG. 1)
Is particularly preferably, for example, 35 to 70 mm.

The bead core 5 has a substantially regular hexagonal cross section in the tire meridian cross section including the tire axis in this embodiment. In this example, as shown in FIG. 3, the bead core 5 is formed by spirally winding a steel wire 10 (monofilament) having a circular cross section a predetermined number of times by a so-called single winding method. Specifically, the wire row in which the plurality of steel wires 10, 10,... Are arranged in the tire axial direction is illustrated in multiple stages in the tire radial direction. The figure shows an example of a substantially regular hexagon formed by a total of 44 lines of 5 × 6 × 7 × 8 × 7 × 6 × 5 lines.

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

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

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

In the present embodiment, it is assumed that the cross-sectional shape of the bead core 5 is substantially regular hexagon and the inner periphery 5i is arranged substantially parallel to the tire axial direction. The inner periphery 5 measured vertically
Carcass steel cord 6 folded near i
The maximum distance d to C (shown in FIG. 2) is 1.0 to 2.5 mm
It is limited to a small value.

As described above, by limiting the cross-sectional shape or the arrangement of the bead core 5 and the maximum distance d,
The turning of the steel cord 6C of the carcass 6 can be performed 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 is forced to turn around the bead core c so as to be folded over based on the shape or arrangement of the bead core.

If the inner periphery 5i of the bead core is not substantially parallel to the tire axial direction, it becomes difficult to turn the carcass ply 6A around the bead core 5 while reducing the maximum distance d, and the rim assembling property is poor. There are disadvantages, such as difficulty and rim detachment.

As a result of the experiments by the inventors, the inner periphery 5i of the bead core 5 and the carcass cord 6C turned around therearound
It has been found that when the thickness of the rubber interposed between them increases, the bead compression decreases. 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 the bead core 5 can be reduced, the bead compression can be increased as compared with the conventional structure. As a result, the durability of the bead portion 4 is maintained at a higher level such that the structure of the carcass can be made effective. Incidentally, in the conventional heavy duty tire shown in FIG. 5, the 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 bend when it is folded back, and the cord is liable to break due to stress concentration or the like. Conversely, if it exceeds 2.5 mm, the bead compression is reduced, and the effect of improving the durability of the bead portion is reduced.

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

[0031]

EXAMPLES A radial tire for heavy loads having a basic structure of FIGS. 1 and 2 and a tire size of 11R22.5 14PR was prototyped based on the specifications of Table 1 (Examples 1, 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 manufactured. Then, these test tires were changed to 8.25 ×
Attached to the regular rim of 22.5, internal pressure 1000 (kPa)
And running on a drum at a load of 9000 kgf and a speed of 20 km / h. When the damage which can be visually confirmed was generated, the running was terminated and the running time until the damage was generated was measured. According to the standard, 350 hours or more pass. Table 1 shows the test results.

[0032]

[Table 1]

As a result of the test, it can be confirmed that the tires of the examples have superior bead portion durability compared to the conventional example and the comparative example.

[0034]

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

[Brief description of the drawings]

FIG. 1 is a sectional view of a tire according to an embodiment of the present invention,
The tire is mounted on the rim and is in a state of normal internal pressure and no load.

FIG. 2 is an enlarged sectional view showing the bead portion.

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 3 Sidewall 4 Bead 5 Bead core 6 Carcass 6A Carcass ply 6a Carcass ply body 6b Carcass ply turnback 6c Carcass steel cord

Claims (2)

[Claims] 1. A heavy-duty tire mounted on a deep rim having a carcass having a steel cord extending from a tread portion to a bead core of a bead portion through a sidewall portion, wherein the carcass has a tread portion. A carcass ply integrally provided with a folded portion that turns around the bead core from the inside in the tire axial direction to the outside in the tire axial direction from the body portion extending from the side wall portion to the bead core of the bead portion, and the folded portion is Having a parallel portion proximate to the main body portion and extending substantially parallel to the main body portion, wherein the bead core has a substantially regular hexagonal cross section in a tire meridian cross section including the tire axis and is substantially parallel to the tire axial direction. Of the carcass measured from the inner periphery of the bead core and perpendicular to the inner periphery. A heavy duty tire characterized in that the maximum distance d to the teal cord is 1.0 to 2.5 mm. 2. The bead core has a core aspect ratio (h / w) of a width w in the tire axial direction and a height h in the tire radial direction of 0.75 to 1.0. 2. The heavy load tire according to claim 1, wherein the periphery forms an angle [theta] of 0 to 2 [deg.] With respect to the tire axial direction line.