JPH11165512A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability of a bead section by effectively restraining a layer line in the second layer from the outermost side. SOLUTION: When a tire runs, a bead core 12 is bent and twisted repeatedly, as a result, the layer lines 33 of the layers adjacent to each other pressingly contact each other. In this case, if the turning pitch of the layer line 33a of the outermost side layer is made larger than that of the layer line 33b to make a Young's modulus (spring constant) small, the tension torsion generated in the layer 33b becomes large, as a result, the total torsion of the compression torsion caused by bending is always in the tension side, restraining fatigue faulure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pneumatic tire having a bead core formed by laminating three or more layer layers around a core wire.

[0002]

2. Description of the Related Art Generally, in a pneumatic tire used under high speed and heavy load, for example, a pneumatic tire for an aircraft, a large stress acts on a bead portion during running. Bead cores must be installed.

Conventionally, as a bead core capable of withstanding such a large stress, for example, a bead core as described in Japanese Patent Application Laid-Open No. 53-51804, that is, a small-diameter layer is provided around one large-diameter core wire. There is known a bead core called so-called Cabilbead, which is formed by laminating a plurality of layer layers formed by winding a wire in a substantially spiral shape. In such a bead core, the winding direction of the layer wire of the layer layer is one layer. The direction was reversed every time. Then, when the pneumatic tire having such a bead core is mounted on the rim and the internal pressure is filled, the bead core slightly expands in diameter by mounting on the rim and filling with the internal pressure, whereby the core wires and layers constituting the bead core are formed. A predetermined tensile strain was generated inside the wire.

[0004]

However, when such a conventional pneumatic tire provided with a bead core is used for a long period of time, a fatigue failure occurs in a layer wire in a second layer layer from the outermost layer, resulting in a bead portion. There is a problem that durability is reduced. The reason is as follows. That is, when the above-described pneumatic tire runs under a heavy load, a large bending and twisting repeatedly acts on the bead core. Then, due to the former bending, a compressive strain is generated in the bead core on one side from the neutral plane, and a tensile strain is generated on the other side from the neutral plane. It becomes larger as it approaches the layer layer. Here, as described above, since the tensile strain is generated inside the bead core due to the diameter expansion, the core wire and the layer wire constituting the bead core have the tensile strain due to the diameter expansion, the compression strain due to the bending, and the tensile strain. However, in the layer line having a large value of the compressive strain due to the bending, the compressive strain due to the bending may exceed the tensile strain due to the diameter expansion. As a result, compression distortion occurs inside the layer line. On the other hand, when the twist as described above, for example, a clockwise (clockwise) twist acts on the bead core, in the layer layer in which the winding direction of the layer wire is the Z twist, the layer wire opens in the direction (radially outward). In a layer layer in which the winding direction of the layer wire is S-twist, the layer wire is deformed in the closing direction (inward in the radial direction).
The direction in which the layer wire closes in the opposite direction (radially inward) in the twisted layer layer, and the direction in which the layer line opens in the S twisted layer layer (radially outward).
Therefore, if the layer wire of a certain layer layer is Z-twisted and the layer wires of both layer layers adjacent to this Z-twisted layer layer are S-twisted, the radius becomes When the layer wire of the Z twist layer layer deforming outward in the direction and the layer wire of the outer S twist layer layer deforming inward in the radial direction press against each other, and conversely, when a counterclockwise twist is applied to the bead core Then, the layer wire of the Z twist layer layer deforming inward in the radial direction and the layer wire of the inner S twist layer layer deforming outward in the radial direction press against each other. And, since the above-mentioned deformation becomes larger in the outer layer, when the above-mentioned Z-twist layer is the second layer from the outermost layer, the outermost layer is added to the layer line of the second layer. The maximum pressing force is applied repeatedly from the layer line of the layer, and the next highest pressing force is applied from the layer line of the third layer layer from the outermost layer. Here, when compressive strain is generated in the layer line of the second layer layer as described above, when the above-described pressing force is repeatedly received from both the outermost and the layer lines of the third layer layer, The layer wire of the second layer layer buckles due to these press-contact forces and is repeatedly and locally deformed significantly in the opposite direction (bent) to cause fatigue failure. The maximum compressive strain and pressing force in the bead core are applied to the layer line of the outermost layer layer, but there is no layer line that contacts the outermost layer layer when deformed radially outward. Therefore, the fatigue fracture as described above hardly occurs.

An object of the present invention is to provide a pneumatic tire capable of improving bead portion durability by effectively suppressing fatigue destruction of a layer wire in a second layer layer from the outermost layer. .

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to form three or more layer layers formed by winding a thin layer wire in a substantially spiral shape around a single large diameter core wire. In addition, in a pneumatic tire having a bead core having a bead core in which the winding direction of the layer wire in each of these layer layers is reversed for each layer, the number of winding pitches of the layer wire in the outermost layer layer is set to the second from the outermost. This can be achieved by making the number larger than the number of winding pitches of the layer wire in the layer layer.

As described above, when the number of winding pitches of the layer lines in the outermost layer layer is larger than the number of winding pitches of the layer lines in the outermost second layer layer, the pitch of the layer lines in the outermost layer layer is determined. Becomes shorter and the Young's modulus (spring constant) becomes smaller, so that the layer wire of the outermost layer layer does not bear much the tensile force generated in the bead core due to the above-mentioned diameter enlargement. The burden of the tensile force by the layer wire increases. As a result, the value of the tensile strain generated inside the layer line of the second layer layer exceeds the compressive strain due to the bending, and the total strain with the compressive strain due to the bending is always on the tensile side. Therefore, even if the above-described pressing force is repeatedly received from both the outermost and the third layer layers, the layer lines of the second layer layer are repeatedly moved in the reverse direction by an amount corresponding to the pressing in a wide range. Therefore, the fatigue fracture of the layer line of the second layer layer is effectively suppressed.

According to the second and third aspects of the present invention, even in the case where a fatigue break occurs in a layer line in the third layer from the outermost layer, this can be effectively suppressed. it can.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 11 denotes a pneumatic radial tire mounted on an aircraft.
Is a pair of bead portions 13 in which bead cores 12 each having a circular cross section are embedded, a sidewall portion 14 extending substantially radially outward from each of the bead portions 13, and a radially outer end of each of the sidewall portions 14. And a continuous tread portion 15 having a substantially cylindrical shape. The tire 11 is reinforced by a carcass layer 21 having a toroidal shape extending from one bead portion 13 to the other bead portion, and the carcass layer 21 is constituted by a plurality of carcass plies 22 overlapping each other. Have been. Most of these carcass plies 22 are turn-up plies in which both ends in the width direction are turned from the inside in the axial direction toward the outside in the axial direction around the bead core 12,
Further, a part of the carcass ply 22 located on the outer layer side is a down ply extending to the bead core 12 along the outside of the folded portion. In each carcass ply 22, a cord made of a large number of textiles or the like substantially embedded (extending in the radial direction) substantially perpendicular to the tire equatorial plane E is embedded. A tread rubber 23 is disposed radially outside of the carcass layer 21, and a plurality of main grooves 24 and a plurality of not-shown lateral grooves intersecting the main grooves 24 are formed on the outer surface of the tread rubber 23. Have been. The carcass layer 21
A belt layer 25 is disposed between the belt layer 25 and the tread rubber 23, and the belt layer 25 is composed of a plurality of belt plies 26 overlapping each other. Numerous cords made of textiles or the like and inclined with respect to the tire equatorial plane E, or cords wound spirally and extending substantially parallel to the tire equatorial plane E are embedded in the belt plies 26.

Referring to FIGS. 2 and 3, each bead core 12 has a single large-diameter core wire 31 having a ring shape, and the core wire 31 is made of a bare (non-rubber-coated) steel single wire. 32
Denotes three or more layers, here four layers, laminated around the core 31. Each layer 32 has a number of layer wires 33 having a diameter smaller than the core 31 in a substantially spiral shape around the core 31. Although it is configured by being wound in a close-packed state, the layer wire 33 of these layer layers 32 is also formed of a bare steel single wire like the core wire 31. The number of winding pitches of the layer line 33a in the outermost layer layer 32a (specifically, 7) is the number of winding pitches of the layer line 33b in the second outermost layer layer 32b (specifically, 6).
It is bigger. Here, the above-mentioned winding pitch number is
The number of times the layer wire 33 is wound around the core wire 31 from a certain point on the core wire 31 before returning to the point or returning to the original point. In this embodiment, the winding pitch number P of the layer wire 33 of the layer layer 32 gradually increases from the innermost to the outermost layer layer 32, and specifically, is the fourth (the outermost) from the outermost layer. The number of winding pitches of the layer wire 33d in the inner layer layer 32d is 4, the number of winding pitches of the layer wire 33c in the third outermost layer layer 32c is 5, and the number of layer wires 33b in the second outermost layer layer 32b. Is 6 as described above, and the number of winding pitches of the layer wire 33a in the outermost layer layer 32a is 7 as described above. The layer line in the layer layer 32
The winding pitch number P of 33 is from the innermost layer to the outermost layer layer.
It may be configured to increase stepwise toward 32, that is, increase toward the outer layer layer 32 while keeping the winding pitch number P of the layer wires 33 in some adjacent layer layers 32 the same. Here, as described above, as the mode of increasing in a stepwise manner, for example, the fourth, third, and second layer layers 32
The winding pitch numbers of the layer lines 33d, 33c, 33b in the d, 32c, 32b are the same, and the outermost layer layer 32a
The winding pitch number of the layer wire 33a in the
When the number of winding pitches is larger than the number of winding pitches of d, 33c, and 33b, the number of winding pitches of the layer lines 33d and 33c in the fourth and third layer layers 32d and 32c is the same value, and The winding pitch number of the layer wire 33b is larger than the winding pitch number of the layer wires 33d and 33c, and the winding pitch number of the layer wire 33a in the outermost (first) layer layer 32a is larger than the winding pitch number of the layer wire 33b. In addition, the third and second layer 32
c, 32b, the number of winding pitches of the layer lines 33c, 33b is the same, is larger than the number of winding pitches of the layer line 33d in the fourth layer layer 32d, and is the layer line 33a in the outermost (first) layer layer 32a. Is larger than the number of winding pitches of the layer wires 33c and 33b. Further, the winding direction of the layer wire 33 constituting each of the layer layers 32 is opposite for each layer, that is, the winding direction of the layer wire 33 in the two adjacent layer layers 32 is opposite. In the embodiment, the layer line 33a of the outermost layer 32a is Z
Twist, the layer wire 33b of the second layer layer 32b is S twist, the layer wire 33c of the third layer layer 32c is Z twist,
The layer wire 33d of the fourth layer 32d is S-twisted.

When the tire 11 having such a bead core 12 in the bead portion 13 is run at a high speed under heavy load, large bends and twists of left and right rotations repeatedly occur in the bead core 12. When the number of winding pitches of the layer line 33a in the outermost layer layer 32a is larger than the number of winding pitches of the layer line 33b of the second layer layer 32b, the pitch of the layer line 33a in the outermost layer layer 32a becomes shorter. As a result, the Young's modulus (spring constant) becomes smaller, so that the layer line 33a of the outermost layer layer 32a is formed.
Does not bear much the tensile force generated in the bead core 12 by the above-described diameter expansion, and as a result of this, the burden of the tensile force by the layer wire 33b of the second layer layer 32b increases. As a result, the value of the tensile strain generated inside the layer wire 33b of the second layer layer 32b exceeds the compressive strain caused by the bending, and in the layer wire 33b, the tensile strain caused by the diameter expansion and the compressive strain caused by the bending are reduced. Is always on the tensile side. For this reason, even if the above-described pressure contact force is repeatedly received from both the outermost and third layer layers 32a and 32c, the layer lines 33b of the second layer layer 32b are kept in a wide range. , The deformation in the opposite direction is repeated only by an amount corresponding to the above, and thereby the fatigue fracture of the layer line 33b of the second layer layer 32b is effectively suppressed. Also, as described above, if the number of winding pitches of the layer wire 33 is gradually increased or increased stepwise from the innermost to the outermost layer 32, the layer wire 33c in the third layer 32c may cause fatigue failure. In such a case, this can be effectively suppressed.

In the above embodiment, the present invention is applied to the bead core 12 having four layer layers 32. However, the present invention may be applied to a bead core having three layer layers.

[0013]

Next, test examples will be described. In this test, the number of winding pitches of the layer wires in the outermost 4, 3, 2, and 1st layer layers was 6, 6, respectively.
A test having a conventional tire having a bead core of 5, 5, and a bead core of 4, 5, 6, and 7, respectively, having the above-described 4, 5, 6, and 7 winding pitches of layer wires in the outermost 4, 3, 2, and 1st layer layers. Prepared with tires. Here, the size of each of these tires is APR46 × 17R20 / 30P
R. Next, each of these tires was filled with an internal pressure of 17.1 kgf / cm ² and mounted on the rim (45 × 16-20) of a drum tester. Then, a load of 16700 kgf was applied at a speed of 64 km / h for 10 minutes per hour. I ran only 800 times. Next, about 30 cm of the layer wire in the second layer layer was taken out from such a tested tire and a new tire and set on a tensile tester, and the breaking strength of each of these layer wires was determined. As a result, assuming that the breaking strength of a new tire is an index of 100, it was 97.5 in the conventional tire, but was 99.5 in the test tire, and the residual strength was improved.

[0014]

As described above, according to the present invention, the durability of the bead portion can be improved by effectively suppressing the fatigue fracture of the layer line in the second layer from the outermost layer.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a bead core.

FIG. 3 is an explanatory diagram for explaining a winding state of a layer line of each layer layer.

[Explanation of symbols]

 11 ... pneumatic tire 12 ... bead core 13 ... bead part 31 ... core wire 32 ... layer layer 33 ... layer wire

Claims (3)

[Claims] 1. A layer layer formed by winding a small-diameter layer wire in a substantially spiral shape around one large-diameter core wire.
In a pneumatic tire having a bead core with bead portions formed by laminating more than one layer and having a winding direction of a layer wire in each of these layer layers reversed in every layer,
A pneumatic tire, wherein the number of winding pitches of the layer wires in the outermost layer layer is larger than the number of winding pitches of the layer wires in the second outermost layer layer. 2. The pneumatic tire according to claim 1, wherein the number of winding pitches of the layer wire is gradually increased from an innermost layer to an outermost layer layer. 3. The pneumatic tire according to claim 1, wherein the number of winding pitches of the layer wire is increased stepwise from the innermost layer to the outermost layer layer.