JP2005153731A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire whose bead part is equipped with an enhanced durability. <P>SOLUTION: The pneumatic tire is equipped with at least one carcass ply 6A set over between a pair of bead cores 5. The carcass ply 6A has a body part 6a leading from the tread part 2 to each bead core 5 of the bead part 4 via the side wall part 3 and a folded-back part 6b continued to the body part 6a and folded back round the bead core 5 outward from the inside in the tire axial direction. The folded-back part 6b has an outer extremity 6be extending inward in the tire axial direction on the outside in the tire radial direction of the bead core 5 and terminating in front of the body part 6a. The minimum rubber thickness A between the outer extremity 6be of the folded-back part and the outer surface of the bead core 5 is made 5-15 mm, while the minimum rubber thickness B between the outer extremity of the folded-back part and the body part 6a is 1-5 mm, and a covering cord layer 12 is provided arranged in contact with the outer surface in the tire radial direction of the folded-back part 6b and covering the part 6b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire that can enhance the durability of a bead portion.

  For example, in a general heavy-duty pneumatic tire, as shown in FIG. 5, at least one carcass ply a in which a steel cord or the like is covered with a topping rubber is bridged between a pair of bead cores b and b (note that In the figure, only one bead portion is shown, but the other bead portion is also configured symmetrically.) The carcass ply a includes a toroid-shaped main body portion a1 and a turn-back portion a2 which is connected to both ends thereof and is turned around the bead core b from the inner side to the outer side in the tire axial direction. Reference symbol d denotes a cord reinforcing layer.

  However, the outer end c of the folded portion a2 is not plated and has a low adhesive force with rubber. In particular, in a heavy-duty pneumatic tire in which a heavy load is applied during load running, rubber separation occurs at the outer end c due to bending deformation of the bead portion, and the separation is caused by growth along the carcass ply c. Damage is likely to occur. Conventionally, Patent Document 1 below has been proposed to prevent such damage.

JP-A-8-40026

  In Patent Document 1, as shown in FIG. 6, the carcass ply a is folded around the bead core b from the main body a1 and both ends thereof from the inner side to the outer side in the tire axial direction, and the axis along the outer surface of the bead core b. It is composed of a folded portion a2 that extends inward and terminates in front of the main body portion a1. In addition, a ring-shaped body e arranged in contact with the outer surface of the folded portion a2 is provided.

  Such a structure of the bead portion of the pneumatic tire can effectively suppress separation damage and the like at the outer end c because the outer end c of the turned-up portion a2 is arranged in a region where distortion during load running is very small. .

  However, in the configuration of Patent Document 1, when the folded portion a2 is properly aligned with the outer surface of the bead core b during manufacture, as shown schematically in FIG. 7, the vicinity of the outer end c of the folded portion a2 having a small inner diameter is provided. In the carcass ply a, wrinkles and undulations are likely to occur, and the carcass cords vary. Further, since there is no rubber having a substantial thickness between the folded portion a2 and the bead core b, vulcanization is performed while air is contained between the bead core b although the ring-shaped body e is included. May be. Such tires are likely to vary in manufacturing, and there is a risk of structural destruction of the bead part starting from an air reservoir between the bead core b and the folded part a2.

  The present invention has been devised in view of the above problems, and is the minimum rubber thickness between the outer end of the folded portion and the outer surface of the bead core, and between the outer end of the folded portion and the main body portion. An object of the present invention is to provide a pneumatic tire capable of enhancing the durability of the bead portion, particularly a pneumatic tire suitable for heavy loads, on the basis of appropriately regulating the minimum rubber thickness.

  According to a first aspect of the present invention, there is provided a pneumatic tire including a carcass using at least one carcass ply spanned between a pair of bead cores, wherein the carcass ply has a side from a tread portion. A main body extending through the wall portion to the bead core of the bead portion; the main body portion being connected to the main body portion and folded around the bead core from the inner side in the tire axial direction to the outer side in the tire radial direction; A folded portion having an outer end that terminates in front of the portion, a minimum rubber thickness A between the outer end of the folded portion and the outer surface of the bead core is 5 to 15 mm, and the outer end of the folded portion and the main body The minimum rubber thickness B between the first and second portions is 1 to 5 mm, and a covering cord layer is provided in contact with the outer surface in the tire radial direction of the turned-up portion so as to cover the turned-up portion. To do.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the covering cord layer is formed of a wound ply formed by jointing both ends of the reinforcing ply.

  The invention according to claim 3 is the pneumatic tire according to claim 1, wherein the covering cord layer is composed of a jointless ply formed by spirally winding one or a plurality of cords.

  According to a fourth aspect of the present invention, the folded portion comprises a straight portion that is substantially linear from the maximum height position in the tire radial direction of the bead core to the outer end, and the straight portion is a tire. 4. The pneumatic tire according to claim 1, wherein the pneumatic tire rises at an angle [alpha] of 30 to 65 [deg.] With respect to the axial line.

  In the present invention, the minimum rubber thickness A between the outer end of the folded portion and the outer surface of the bead core and the minimum rubber thickness B between the outer end of the folded portion and the main body portion of the carcass ply are appropriately regulated. Thus, the outer end of the folded portion can be arranged in a region where the distortion is small even during load traveling. At the same time, since the rubber having a substantial thickness is interposed between the folded portion and the bead core, air pockets between the folded portion and the bead core can be reduced during manufacturing. Therefore, the durability of the bead portion can be greatly improved. In addition, since the folded portion is provided with a covering cord layer that is in contact with the outer surface in the tire radial direction and covers the folded portion, the accuracy of the finished position of the folded portion can be increased and variation can be reduced.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a cross-sectional view of a pneumatic tire 1 in a normal state in which a normal rim J is assembled with a rim, is filled with a normal internal pressure, and is unloaded. In this example, a tubeless type heavy load used for trucks, buses, etc. Heavy radial tires are exemplified. In FIG. 2, only the bead portion is taken out and enlarged.

  In the figure, a pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 positioned at an inner end of each sidewall portion 3. . The pneumatic tire 1 is provided with a toroidal carcass 6 spanned between the bead portions 4 and 4 and a belt layer 7 located outside the carcass 6 and inside the tread portion 2. Yes.

  In the present embodiment, the carcass 6 is constituted by a single carcass ply 6A. The carcass ply 6A includes a main body portion 6a that extends from the tread portion 2 through the side wall portion 3 to the bead core 5 of the bead portion 4, and is connected to the main body portion 6a and folded around the bead core 5 from the inner side to the outer side in the tire axial direction. In addition, the bead core 5 is provided with a folded portion 6b that extends inwardly in the tire radial direction and ends in front of the main body 6a. The main body portion of the carcass ply 6a refers to a portion from the tread portion 2 to the tire axial direction line N passing through the position of the maximum height Hb in the tire radial direction of the bead core 5, and from there to the outer end 6be is a turn-up portion 6b. Determine.

  As the carcass ply 6A, a sheet-like one in which a carcass cord made of a steel cord is arranged with an angle range of, for example, 80 to 90 ° with respect to the tire equator C and covered on both sides with a topping rubber is used. The carcass cord can be changed according to the category of the tire. For example, in the case of a passenger car, an organic fiber cord such as nylon, rayon, polyester, and aromatic polyamide can be used. An inner liner rubber layer that forms a tire lumen surface and is excellent in air impermeability is attached to the inside of the carcass 6.

  In this example, the belt layer 7 is formed of four belt plies 7A to 7D. Specifically, the innermost belt ply 7A in which the belt cord is inclined with respect to the tire equator C at an angle of, for example, about 60 ± 10 °, and the belt that is inclined with respect to the tire equator C at a small angle of 30 ° or less. The plies 7B, 7C, and 7D are overlapped with each other by providing one or more locations where the belt cord intersects between the plies. Steel cords are suitable for the belt cord, but organic fiber cords such as rayon, nylon, and aromatic polyamide can also be used as necessary.

  In this example, the bead core 5 is formed in a substantially hexagonal cross section by spirally winding a steel bead wire a predetermined number of times. Further, in the contour shape of the bead core 5, the inner side 5i which is long on the inner side in the tire radial direction and the outer side 5o which is long on the outer side (each side is assumed to be a virtual straight line in contact with the contour line formed by the cross-section circular wire). Are inclined at about 10 to 17 ° with respect to the tire axial line, and are along the inclination of the rim seat J1 of the regular rim J which is a 15 ° deep bottom rim. The bead core 5 can be made of a substantially non-extensible material such as aromatic polyamide in addition to the steel material.

  In the carcass ply 6 </ b> A of the present embodiment, the folded portions 6 b on both sides are folded back from the inner side in the tire axial direction by the bead core 5. Moreover, the folded-back portion 6b extends slightly obliquely from the outside in the tire radial direction of the bead core 5 to the inside in the tire axial direction and the outside in the tire radial direction so as to wrap the bead core 5. The outer end 6be of the folded portion 6b terminates in front of the carcass ply without contacting the main body portion 6a.

  A space having a substantially triangular cross section is formed between the outer side 5o of the bead core 5, the folded portion 6b, and the main body portion 6a, and the cushion rubber 10 is filled in this space. The hardness of the cushion rubber will be described later. A bead apex 11 that is tapered and extends outward in the tire radial direction is disposed outside the cushion rubber 10 with the folded portion 6b interposed therebetween. The bead apex 11 has a sufficiently large height in the tire radial direction as compared with the cushion rubber 10, and effectively increases the bending rigidity of the bead portion 4. For the bead apex 10, a rubber composition having a rubber hardness (JIS durometer type A) hb of 40 to 70 °, more preferably 50 to 60 °, is used. If the rubber hardness hb of the bead apex 11 is less than 40 °, the bending rigidity of the bead portion 4 cannot be effectively increased, and the durability tends to deteriorate due to heat generation caused by a large bending deformation. When the angle exceeds 70 °, the bending rigidity of the bead portion 4 is remarkably increased, and the shock absorption is lowered and the riding comfort is impaired.

  In the present invention, the position of the outer end 6be of the folded portion 6b is regulated as follows. That is, the minimum rubber thickness A between the outer end 6be and the outer surface 5o of the bead core 5 is 5 to 15 mm, and the minimum rubber thickness B between the outer end 6be of the folded portion 6b and the main body 6a is 1 to 5 mm. Respectively.

  As described above, by limiting the position of the outer end 6be of the folded portion 6b, the outer end 6be can be positioned in a region having a small distortion during load traveling, and thus the durability of the bead portion 4 is enhanced. Moreover, the generation | occurrence | production of a wrinkle and a wave near the outer end of the folding | turning part 6b can be suppressed. Moreover, since the folded portion 6b is filled with the cushion rubber 10 between the bead core 5, even if wrinkles or the like occur during molding, the cushion rubber 10 is deformed along the wrinkles of the folded portion 6b, and air is vulcanized during vulcanization. Extrusion can prevent the formation of a conventional air pocket.

  Further, as a result of experiments by the inventors, when the minimum rubber thickness A is less than 5 mm, it is not possible to secure an amount of cushion rubber sufficient to absorb wrinkles and undulations near the outer end of the folded portion 6b, and the bead core 5 is not molded. Air or the like is easily sealed on the outer surface of the. On the contrary, when the minimum rubber thickness A exceeds 15 mm, the outer end 6be of the folded portion 6b is located on the outer side in the radial direction of the bead portion 4. There is a risk. From this point of view, the minimum rubber thickness A is particularly preferably 5 to 12 mm, and more preferably 5 to 9 mm.

  If the minimum rubber thickness B is less than 1 mm, the carcass cords of the main body portion 6a and the folded portion 6b are close to each other, and rubber peeling or the like is easily caused. On the contrary, when the minimum rubber thickness B exceeds 5 mm, the adhesion length between the folded portion 6a and the rubber tends to decrease, and the folded portion 6b is pulled like a slip due to the carcass cord tension acting on the main body portion 6a. Similarly, the durability of the bead portion 4 tends to be lowered, such as being easily pulled out. From this point of view, it is particularly preferable that the minimum rubber thickness B is 1 to 4 mm, more preferably 1 to 2 mm.

  Further, the folded portion 6b of the present embodiment is formed as a straight portion 9 in which the position from the maximum height Hb of the bead core 5 in the tire radial direction to the outer end 6be of the folded portion is substantially linear. Such a straight portion 6b is excellent in moldability at the time of manufacture because it is not necessary to bend the carcass cord of the folded portion 6b. It is desirable that the straight portion 9 rises outward in the tire radial direction toward the inner side in the tire axial direction at an angle α of, for example, about 30 to 65 °, more preferably about 30 to 40 ° with respect to the tire axial line N.

  The folded portion 6b includes a bending deformation force of the steel cord that causes the folded portion 6b to fall into the cushion rubber 10 and an axial force along the longitudinal direction of the steel cord. Can be shared. Since the former force is further borne by the cushion rubber 10, it helps to improve the compressive load resistance performance in the tire radial direction in the bead portion 4.

  For the cushion rubber 10, it is desirable to use a rubber composition having a rubber hardness ha of 50 to 90 °, more preferably 60 to 80 ° from the above viewpoint. When the rubber hardness ha of the cushion rubber 10 is less than 50 °, the load depth performance is lowered, and the amount of deformation around the bead core 5 is increased during running, and the steering stability tends to be lowered. On the contrary, if the rubber hardness ha of the cushion rubber 10 exceeds 90 °, the adhesiveness with the folded portion 6b tends to be lowered, which is not preferable. Particularly preferably, the difference (ha−hb) between the rubber hardness ha of the cushion rubber 10 and the rubber hardness hb of the bead apex 11 is 10 to 40 °, more preferably about 10 to 30 °.

  Moreover, the coating | coated cord layer 12 which covers this folding | returning part 6b is provided in the outer side of the folding | returning part 6b. The coated cord layer 12 of this example is disposed in contact with the outer surface in the tire radial direction of the folded portion 6b. The covering length is preferably almost the entire area of the straight portion 9. In the present embodiment, the cords of the covering cord layer 12 are arranged substantially parallel to the tire circumferential direction. Such a covering cord layer 12 is firmly positioned and held in the vicinity of the outer end of the folded portion 6b with the cushion rubber 10, and is useful for improving the finishing accuracy of the vulcanized tire.

  As the covering cord layer 12, for example, as shown in FIG. 3A, a winding ply 15 formed by overlapping and jointing both ends 13a, 13b of a small reinforcing ply 13 or one or a plurality of winding plies 15 A jointless ply 16 formed by spirally winding the cord 17 can be suitably used. In the case where the outer surface of the folded portion 6b having a cone shape is covered, the latter is particularly preferable because of its high productivity. The cord used for the coated cord layer 12 is not particularly limited, but an organic fiber cord such as polyester, nylon, rayon, or aramid is preferred.

  Further, in the pneumatic tire 1 of the present embodiment, the cord reinforcing layer 19 is provided on the bead portion 4. The cord reinforcing layer 19 includes a first portion 19a extending along the inner surface in the tire axial direction of the main body portion 6a of the carcass ply 6a, and a second portion extending along the folded portion 6b and continuing to the first portion 19a. And a third portion 19c connected to the second portion 19b and spaced apart from the folded portion 6b and extending outward in the tire radial direction at a small height. A steel cord is preferably used as the cord. In the present embodiment, the third portion 19c of the cord reinforcing layer 19 terminates at a height that is not equal to or lower than the maximum height Hb of the bead core 5. For this reason, during the load traveling, the outer end 19ce of the third portion 19c can be positioned in a region with a small distortion, and durability can be improved. Further, since the outer end 19ce of the third portion is separated from the folded portion 6b, it is possible to prevent the adhesive force from being lowered and further improve the effect of suppressing separation and the like.

FIG. 4 shows a process schematic diagram of the method for manufacturing a pneumatic tire of the present invention.
In (A), the carcass ply 6A is wound on a cylindrical drum (not shown), and a ring body in which the bead core 5 and the cushion rubber 10 are integrated in advance is fitted into the carcass ply 6A from the outside in the axial direction. Next, as shown in (B), both end portions of the carcass ply 6A are folded back along the bead core 5 and the cushion rubber 10 to form the folded portion 6b, and the coated cord layer 12 is attached to the outer surface of (C). Configure as follows. The folded portion 6b is folded and positioned with high accuracy by the cushion rubber 10 and the covering cord layer 12. In particular, the folded portion 6b does not need to be folded excessively along the outer surface of the bead core 5 as shown in FIG. 7 due to the cushion rubber 10, so that the moldability is good and the occurrence of wrinkles is suppressed. Then, a bead apex 11 and other sidewall rubber or rubber chafer (not shown) are pasted on the carcass ply 6A, and the carcass ply 6A is expanded as shown in FIG. Thereby, the pneumatic tire which has the structure of the bead part shown in FIG. 1 can be obtained.

  A heavy-duty pneumatic radial tire having the basic configuration shown in FIG. 1 and having a tire size of 11R22.5 was made on the basis of the specifications shown in Table 1 and tested for finishing accuracy of the drum durability test. Regarding the minimum rubber thicknesses A and B, in a normal state, the tire meridian cross section of the tire / rim assembly was photographed by CT scan and examined as an average value at 10 locations on the tire circumference. The test method is as follows.

<Drum durability test>
An index in which a test tire is mounted on a regular rim, an internal pressure of 800 kPa is applied, a speed of 20 km / h, a longitudinal load of 75 kPa is run on the drum, the running time until damage is measured, and the running time of the comparative example is 100 Displayed. The larger the value, the better.

<Ride comfort>
A test tire was mounted on a regular rim, and an internal pressure of 800 kPa was applied to all wheels of a 16-liter truck, and the asphalt test course was run with the maximum load. The ride comfort was evaluated by the 10-point method based on the complete payment of the driver. The larger the value, the better.

<Finish accuracy>
Ten CT scan images in the normal state were acquired in the tire circumferential direction, and the blur rate obtained by dividing the maximum variation of the minimum rubber thickness A by the rubber thickness A was determined. The smaller the numerical value, the higher the finishing accuracy and the better.
The test results are shown in Table 1.

  As a result of the test, it can be seen that the tires of the examples significantly improved the durability of the bead portion. It was also confirmed that the finishing accuracy of the outer end position of the folded portion was high.

It is sectional drawing of the normal state of the pneumatic tire of this embodiment. It is the expanded sectional view which expanded the bead part. (A), (B) is a perspective view which shows an example of a covering cord layer. (A) to (E) are process schematic diagrams for explaining a method of manufacturing a pneumatic tire. It is an expanded sectional view of the bead part of the conventional pneumatic tire. It is an expanded sectional view of the bead part of other conventional pneumatic tires. It is the schematic which shows the winding state of the carcass ply around a bead core.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 6a Main part 6b Folding part 6be Folding part outer end 9 Linear part 10 Cushion rubber 12 Covering cord layer

Claims (4)

A pneumatic tire comprising a carcass using at least one carcass ply bridged between a pair of bead cores,
The carcass ply has a main body part extending from the tread part through the sidewall part to the bead core of the bead part,
A folded portion having an outer end that extends from the inner side in the tire axial direction to the outer side and is connected to the main body portion; With
The minimum rubber thickness A between the outer end of the folded portion and the outer surface of the bead core is 5 to 15 mm, and the minimum rubber thickness B between the outer end of the folded portion and the main body portion is 1 to 5 mm.
In addition, a pneumatic tire characterized in that a coated cord layer is provided so as to be in contact with the outer surface in the tire radial direction of the folded portion and to cover the folded portion.   The pneumatic tire according to claim 1, wherein the covering cord layer is formed of a winding ply formed by jointing both ends of a reinforcing ply.   The pneumatic tire according to claim 1, wherein the covering cord layer is formed of a jointless ply formed by spirally winding one or a plurality of cords.   The folded portion is a straight portion that is substantially linear from the maximum height position of the bead core in the tire radial direction to the outer end, and the straight portion is 30 to 65 with respect to the tire axial line. 4. The pneumatic tire according to claim 1, wherein the tire rises at an angle α of °.

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