JP2013241115A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the rotation of a bead core, and to improve separation resistance properties of a bead heal.SOLUTION: A pneumatic tire for a heavy load is characterized in that, in a bead core having a polygonal shape, a metal material in a part or the whole region of a tire width inside region in changed to a metal material having a higher elasticity coefficient than steel with a perpendicular line which passes through the center O of the bead core and reaches the bottom of the bead core arranged substantially parallel with bead base face as a reference. When an area of the region in which the metal material is changed is set as A, an area of the region in which the metal material is not changed is set as B, the elasticity coefficient of the metal material not to be changed is set as Ea, and the elasticity coefficient of the region in which the metal material is not changed is set as E, an expression of 1.3≤(A×Ea+B×E)/{(A+B)×E}≤2.0 is satisfied. The metal material is tungsten (W), molybdenum (Mo), or an alloy having a higher elasticity coefficient than steel.

Description

The present invention relates to a bead core for a heavy duty pneumatic tire used for trucks, buses, and the like, and more specifically, to provide a bead core capable of suppressing the rotation of the bead core of a heavy duty pneumatic tire having a high air pressure. .

In a pneumatic tire mounted on a vehicle such as an automobile, a bead portion is provided to hold the inner pressure with the rim and to fix the rim so that the torque does not come off the rim. . The bead portion has a bead core in which a plurality of bead wires such as steel wires are arranged substantially in parallel and wound around a rotating drum having a predetermined diameter and stacked. The bead core in the bead portion of this pneumatic tire wraps and fixes the end of the organic fiber cord or steel cord that forms the carcass ply, defines the inner circumference of the tire body, and maintains the fit with the rim. ing. Thus, since the bead core is a very important component in the pneumatic tire, it is necessary to improve the durability of the bead portion so that the bead core is not deformed or moved during traveling.

However, in buses and trucks that use heavy duty pneumatic tires, if the vehicle is driven with high air pressure, defects such as separation and laceration may occur in the bead heel portion. This is presumed that the bead core rotates around the bead heel part due to use at high air pressure, the load concentrates on the bead heel part, the distortion increases, and a defect occurs.

FIG. 1 is a diagram comparing the magnitude of rotation of a bead core due to a difference in air pressure of a tire for a large vehicle (tire size 315 / 80R22.5). The bead core 3 of this tire has a substantially hexagonal shape, and the angle between the base 7 of the hexagonal bead core 3 and the bead base line 5 (a line parallel to the bead core 5) is referred to as an inclination angle of the bead core. I found that increasing it increases it. FIG. 1 shows the tilt angle of the bead core measured by a CT scanning device. The inclination angle of the bead core 3 filled with normal pressure air pressure (900 kPa) is 2.3 degrees, but at a high air pressure (1100 kPa), the inclination angle of the bead core 3 increases to 5.8 degrees. Was confirmed to rotate around the heel portion 9.

FIG. 2 is a schematic diagram showing a rotation state of the bead core in the bead portion. In the bead portion 11, a bead core 13 is provided, and the carcass 15 is wound around the bead core 13. The shape of the bead core 13 is a substantially hexagonal shape in the meridian plane cross section. When the air pressure is low, the bottom 19 of the bead core 13 is disposed substantially parallel to the bead base surface 17. Since the bead core 13 begins to rotate gradually as the air pressure increases, the bottom side 19 of the bead core 13 also tilts from the bead base surface 17. At the corner P of the bead core 13 on the outer side in the tire width direction at the bottom 19 of the bead core 13, an angle formed by a straight line 25 parallel to the bead base surface 17 and the bottom 19 of the bead core 13 (extension line 27) is α. This α corresponds to the aforementioned bead core inclination angle.

The corner portion P of the bead core 13 is located in the vicinity of the turn-up portion 23 of the carcass 15 corresponding to the bead heel portion 21. When the air pressure increases, the bead core 13 appears to rotate around the bead heel portion 21 as described above, but actually rotates around the corner portion P of the bead core 13. When the air pressure is low, α = 0. As described above, α = 2.3 degrees at the normal air pressure (900 kPa), and α = 5.8 degrees at the high air pressure (1100 kPa). According to FEM (finite element method) analysis, it was found that the distortion of the bead heel portion is increased by the rotation of the bead core. For example, when the tilt angle is 5.8 degrees, the amount of strain increases by about 15%.

JP2010-274853 Special table 2008-542099 JP2009-280119 JP2002-002237

As described above, the use of the heavy-duty pneumatic tire at high air pressure causes the bead core to rotate around the bead heel part, causing the load to concentrate on the bead heel part, resulting in increased distortion and causing defects such as separation in the bead heel part. . As means for preventing this, it is conceivable to increase the bead rigidity. For example, there is a means for increasing the total number of windings of the bead wire to achieve high bead rigidity. However, although this method of increasing the total number of turns of the bead wire can achieve improvement in rigidity, it is considered that the effect is small for the rotation of the bead core by use in a high air pressure state. Further, there are problems that the cost is increased, the weight is increased, the bead core size is increased, and the rim assembly property is deteriorated. Patent Document 1 proposes that a restraint member made of a rubber member having high hardness is provided in a part of the bead core to suppress the rotation of the bead core, but the rubber member is essentially an elastic body. Therefore, it is presumed that there is not much effect on the rotation of the bead core due to the use in the above-described high air pressure state in the heavy tires for heavy vehicles. As described above, there has been no effective solution to the defect occurrence problem of the bead heel portion based on the bead core rotation due to the use of the tire at high air pressure.

The present invention reduces rotation of the bead core due to use in a high air pressure state by changing a part of the bead core part to a material having a higher elastic modulus than steel. Specifically, it has the following characteristics.
(1) In the bead core having a polygonal shape, the present invention provides a part or all of the inner region in the tire width direction with reference to a perpendicular line passing through the center O of the bead core and being arranged substantially parallel to the bead base surface. The heavy duty pneumatic tire is characterized in that the metal material in the region is changed to a metal material having a higher elastic modulus than steel.

(2) In addition to the above, in the present invention, the area of the region in which the metal material is changed is changed to A in the tire width direction inner region from the perpendicular line that passes through the center O of the bead core and extends from the center O of the bead core to the bottom of the bead core. When the area of the area not to be changed is B, the elastic coefficient of the metal material to be changed is Ea, and the elastic coefficient of the area not to be changed is E,
1.3 ≦ (AxEa + BxE) / {(A + B) xE} ≦ 2.0
It is characterized by satisfying.

(3) According to the present invention, in addition to the above, the modified metal material is tungsten (W), molybdenum (Mo), or an alloy having a high elastic modulus. It contains at least one of (Ni), copper (Cu), or iron (Fe), and the elastic modulus of the alloy is 300 to 400 GPa.

The deformation in the region where the material of the bead core portion is changed can be reduced, and even when the air pressure is increased, the rotation of the bead core is suppressed, and the strain applied to the bead heel portion can be reduced. As a result, even when used at a high air pressure, the occurrence of defects such as separation can be prevented and the separation resistance can be improved. Further, since it is not necessary to increase the number of times the bead wire is wound, the bead core size is not increased. Furthermore, the workability is also good because the rim assembly property can be secured.

There are several prior art documents regarding changing the material of the bead core. (Patent Documents 2, 3, and 4) Patent Document 2 is an arrangement of a bead core in which strands made of metal and carbon fiber are combined. This realizes a tire excellent in bead unseatability and weight reduction. The purpose is that. In Patent Document 3, a wire core made of an organic fiber cord is wound around the innermost diameter portion, and a bead core is placed around the outermost diameter portion with a steel wire wound. This increases vibration absorption and excels in quietness. The purpose is to realize a tire. Patent document 4 arrange | positions the bead core which combined the strand which consists of a metal and an organic fiber cord, and aims at realization of the tire which can achieve weight reduction. As described above, various bead cores using a combination of materials other than steel and steel (steel) have been proposed, but no prior art has been disclosed in the past for the purpose of suppressing rotation of the bead core.

FIG. 1 is a diagram comparing the magnitude of rotation of a bead core due to the difference in air pressure of a tire for a large vehicle. FIG. 2 is a schematic diagram showing a rotation state of the bead core in the bead portion. FIG. 3 is a diagram showing an embodiment of the present invention. FIG. 4 is a diagram showing the degree of rotation after a test of a bead core in which the material in a partial region of the bead core is changed from a normal steel to a tungsten material.

The present inventor changed the material constituting the bead core for the rotation of the bead core portion, and if the elastic modulus (longitudinal elastic modulus, that is, Young's modulus) is made larger than that of steel that is normally used, the rotation of the bead core can be reduced. It has been found that the strain generated in the bead heel portion can be suppressed by reducing the size.

In particular, in a bead core having a polygonal shape, a metal material in a part or all of the inner region in the tire width direction with reference to a perpendicular line passing through the center O of the bead core and being arranged substantially parallel to the bead base surface By using a material having a higher elastic modulus than steel, rotation of the bead core can be reduced. The polygon referred to here is the shape seen in the meridional section of the bead core (cross-sectional view cut along the meridional plane including the rotation axis of the tire). Strictly speaking, each side is not a straight line but an uneven curve. Including some cases. In this drawing, the bead core is shown as a substantially hexagonal shape, but the bead core shape may be a triangular shape such as a triangular shape, a rectangular shape or a trapezoidal shape, a pentagonal shape or a polygonal shape such as a hexagonal shape or more. Although the term center is used here, the center of the bead core is the same as the center of gravity if the material of the bead core is the same. In the present invention, since a plurality of metals are used as the material of the bead core, the center of gravity of the bead core moves, but the center of the bead core does not move. Therefore, if the shape of the bead core is the same, the center of the bead core is always constant.

FIG. 3 is a diagram for explaining the above contents of the present invention. A metal material in a partial region 33 (region indicated by oblique lines) or a whole region (region 35 itself) of the inner region 35 in the tire width direction from a perpendicular line 31 drawn from the center O of the bead core 13 to the bottom side 19 of the bead core 13. A material with a higher elastic modulus than steel. Here, the base 19 of the bead core 13 is a side (side closest to the parallel) that is substantially parallel to the bead base surface (line) 17 among the sides constituting the polygonal bead core 13, and is a bead base surface ( Line) Say the side close to 17. The metal material in the remaining region is steel, which is a conventional material. The elastic modulus (Young's modulus) of steel is about 200 GPa. By doing in this way, the deformation | transformation in this changed area | region can be made small, even if it raises an air pressure, rotation of the bead core 13 is suppressed and the distortion concerning the bead heel part 21 can be reduced. Specific examples of the change material include tungsten (W, elastic modulus of about 400 GPa) and molybdenum (Mo, elastic modulus of about 330 GPa). Further, a tungsten alloy (an alloy containing W as a main component metal and containing at least one of nickel (Ni), copper (Cu), and iron (Fe)) or a molybdenum alloy is also effective. The elastic modulus in the case of an alloy changes with the ratio of the metal which comprises an alloy, but it is desirable that it is about 300-400 GPa.

Further, according to the present invention, the area 33 of the metal material changing region A is not changed in the inner region 35 in the tire width direction from the perpendicular 31 drawn from the center O of the bead core 13 to the bottom side 19 of the bead core 13 through the center O of the bead core 13. Assuming that the area of the region 37 is B, the elastic coefficient of the metal material to be changed is Ea, and the elastic coefficient of the region not to be changed is E (this is a steel value), it is desirable to satisfy the following equation.

1.3 ≦ K = (AxEa + BxE) / {(A + B) xE} ≦ 2.0 (1)

When the K value is less than 1.3, the effect of suppressing the rotation of the bead core 13 is small. This upper limit is limited by a perpendicular line 31 drawn from the center O of the bead core 13 to the base 19 of the bead core 13. For example, if the metal material to be changed is tungsten (W), since E is 200 GPa and Ea = 400 GPa, if the metal material is changed up to the vertical line 31, B = 0, so K = 2. The upper limit is 2. If this value is exceeded, that is, if the material is changed from the vertical line 31 drawn from the center O of the bead core 13 to the bottom side 19 of the bead core 13 to the outside in the tire width direction, the rim assemblage deteriorates. In the case of a metal material having an elastic modulus between 300 GPa and 400 GPa, the upper limit of the K value is 1.5 to 2.0. When a metal having a larger elastic coefficient than tungsten (that is, 400 GPa or more) is adopted, the region where the upper limit value is 2.0 is in the tire width direction inner region 35 from the vertical line 31.

Examples of the present invention are shown in Table 1. Four types of bead cores were used: steel (elastic coefficient 200 GPa), molybdenum (elastic coefficient 330 GPa), tungsten (elastic coefficient 400 GPa), and tungsten alloy (elastic coefficient 300 GPa, 360 GPa). The bead core used has a substantially hexagonal shape (in cross-sectional area), and the above calculation formula {(with M as the reference) passing through the center of the bead core and extending to the bottom of the bead core substantially parallel to the bead base surface {( 1)} to obtain the K value. Since the area of the bead core is almost divided by the perpendicular M, if the area (cross-sectional area) of the entire bead core is 2S, S = A + B.

In the formula (1), A ≦ S, but the case where the changed bead core material includes the outer side in the tire width direction of the perpendicular M is shown as a comparative example. It was. Therefore, when the area where the material is changed is present in the inner region in the tire width direction of the perpendicular M, C = A. Further, C / S = 100% means that the material of all the inner regions in the tire width direction of the perpendicular M is changed, and C / S <100% means one of the inner regions in the tire width direction of the perpendicular M. This means that the material of the part has been changed. When the area where the material is changed extends to the outer region in the tire width direction of the perpendicular M, C / S> 100%, and when the material of the entire bead core is changed, C / S = 200%. The elastic modulus value of the tungsten alloy is produced by changing the proportion of tungsten. In Table 1, the part which changed the material of the bead core is shown as a pattern. When the bead core material is changed to the outer side in the tire width direction of the perpendicular line M, the K value cannot be defined, so the K value is not entered.

The tire is a heavy-duty pneumatic tire (tyre size 315 / 80R22.5, rim 8.25x22.5) with an internal pressure of 1100 kPa (maximum air pressure 900 kPa) and a drum tester under the condition of 140% of the standard maximum load. After running a distance of 20000 km, the presence or absence of separation at the bead heel portion was visually confirmed at 16 locations on the tire circumference, and the separation resistance was evaluated by the separation occurrence rate. The smaller the separation occurrence rate, the better the separation resistance. In addition, the number of occurrences at three locations or less (separation occurrence rate of 19% or less) was taken as OK. Also, press input and time required for assembling the rims of each tire are measured and evaluated from the measured values. The results are classified into three stages: ○ (good), △ (normal), and × (inferior). Thus, the rim assembly property was evaluated. The evaluation results are shown in Tables 1 to 3 below.

This table shows the following. When the material of the bead core in a part or all of the region in the tire width direction inner side than the perpendicular M is changed from a normal steel material (elastic coefficient is about 200 GPa) to a material having an elastic coefficient of about 300 GPa to 400 GPa, When the separation characteristic is improved and the K value is 1.3 or more, the separation occurrence rate is lost and the separation resistance is good. On the other hand, when the material of the bead core is changed to the region outside the perpendicular line M in the tire width direction, the separation rate does not occur, but the rim assemblage deteriorates. This is presumably because the elasticity of the bead portion decreases.

FIG. 4 is a diagram showing the degree of rotation after a test of a bead core in which the material in a partial region of the bead core is changed from normal steel to tungsten material. The degree of rotation of the bead core (bead core tilt angle) was measured with a CT scanning device. FIG. 4A is a conventional example (same as FIG. 1B), FIG. 4B is a diagram in which a tungsten material is changed, and the condition is that of Example 24 (C / S = A / C = 50%, K value = 1.5). In contrast to the conventional bead core tilt angle of 5.8 degrees, the bead core tilt angle of the embodiment is 3.6 degrees, which is greatly improved. As the K value increases, the bead core inclination angle is further improved. Further, according to the strain amount analysis data in the FEM (finite element method) analysis, the strain amount of the bead heel portion is also reduced by about 11%, and a great effect is obtained.

As explained above, by changing the material of a part of the bead core to a metal material having a larger elastic coefficient than normal steel, the deformation of the bead core due to an increase in air pressure is reduced, and the bead core rotates around the bead heel. It can suppress, and the distortion of a bead heel part can be reduced significantly. As a result, the separation resistance can be greatly improved.

As described above, the production method of the present invention has been described in detail. However, regarding other parts that are described and described in a certain part of the specification and that are not described, it can be applied without contradiction. It goes without saying that the content can be applied. Furthermore, the above-described embodiment is an example, and various modifications can be made without departing from the spirit of the invention. Needless to say, the scope of rights of the present invention is not limited to the above-described embodiment.

The present invention is applicable to a wide range of pneumatic tires including not only heavy vehicle tires but also passenger vehicle tires and light vehicle tires.

1 ... Bead part,
3 ... Bead core,
5 ... Bead baseline,
7 ... Bottom of bead core,
9: Bead heel part,
11: Bead part,
13 ... Bead core,
15 ... Carcass,
17 ... Bead base surface,
19 ... the bottom of the bead core,
21 ... Bead heel, part 23 ... carcass folding part,
25 ... a straight line parallel to the bead base surface,
27: Extension of the bottom of the bead core,
31 ... A perpendicular drawn from the center O of the bead core 13 to the bottom 19 of the bead core 13,
33 ... The area changed to the high elastic modulus metal material,
35 ... inner region in the tire width direction from the vertical line 31
37: Area not to be changed,
P ... Corner of the bead core,
O ... the center of the bead core,
α ・ ・ ・ Bead core tilt angle,
M ... perpendicular,
A: Area of the area where the metal material is changed,
B: Area of the area not changed,

Claims (5)

In a bead core having a polygonal shape, the metal material in a part or all of the inner region in the tire width direction is made of steel with reference to a perpendicular line passing through the center O of the bead core and being arranged substantially parallel to the bead base surface. A heavy duty pneumatic tire characterized by a metal material having a higher elastic modulus. In the inner region in the tire width direction from the perpendicular drawn from the center O of the bead core to the bottom of the bead core through the bead core center O, the area of the area where the metal material is changed is A, and the area of the non-change area is B. Where Ea is the elastic modulus and E is the elastic modulus of the region that is not changed,
1.3 ≦ (AxEa + BxE) / {(A + B) xE} ≦ 2.0
The heavy duty pneumatic tire according to claim 1, wherein: 3. The heavy duty pneumatic tire according to claim 1, wherein the changed metal material is tungsten (W), molybdenum (Mo), or an alloy having a high elastic modulus. The heavy-duty pneumatic tire according to claim 3, wherein the alloy contains tungsten as a main component metal and contains at least one of nickel (Ni), copper (Cu), or iron (Fe). 5. The heavy duty pneumatic tire according to claim 3, wherein the elastic modulus of the alloy is 300 to 400 GPa.