JP2007069850A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which can make durability improvement highly compatible with weight reduction in the bead part of a tire having a nipped bead structure. <P>SOLUTION: This pneumatic tire comprises a pair of bead parts 1, and a carcass ply 3 coating a ply cord 2 with rubber and extending between a pair of bead parts in a toroid-like manner. A pair of bead cores 5, 6 constituted by bundling bead wires 4, 5 extending in an approximately peripheral direction and positioned on inner and outer face sides of a radial carcass ply respectively are embedded in the bead part 1. A reinforcing layer 7 made of an organic fiber cord and rubber is located between the carcass ply 3 and at least one of the bead cores 5 and 6. The reinforcing layer 7 is preferably made by coating a plurality of cords 8 parallel arranged in a direction crossing with a tire peripheral direction C with rubber, and an angle α formed by the cords 8 and the tire peripheral direction is preferably within a range of 30°-70°. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a pair of bead portions and a ply cord covered with rubber, a carcass ply extending in a toroidal shape between the pair of bead portions, and a pair of bead cores embedded in each bead portion and sandwiching the carcass ply In particular, the improvement of the durability and weight reduction of the bead portion of such a tire is achieved at a high level.

  In general pneumatic tires, a carcass ply is formed around the bead core having sufficient circumferential rigidity in order from the inside to the outside in the tire width direction in order to prevent the carcass from being pulled out during tire rolling. The carcass ply is firmly fixed to the bead core by embedding the end portion of the carcass ply in a rubber member on the outer side of the rim line in the tire radial direction. In such a prior art, the end portion of the carcass ply is positioned on the outer side in the tire radial direction from the contact area of the bead portion with the rim, and the bead portion or the sidewall portion where the end portion is located Unlike the radially inner end portion of the bead portion that is firmly held by the rim and is strongly reinforced by the bead core, the bead filler, etc., the tire is positioned on the outer side in the tire radial direction than the rim flange surface when rolling the tire. The part falls down toward the outside in the tire width direction and repeats deformation. As a result, stress tends to concentrate particularly on the end portion of the carcass ply, and separation may occur from the stress, which may proceed along the folded portion of the carcass ply. In such a tire, since the carcass ply is disposed so as to wrap the bead core, the degree of freedom of the case shape on the inner surface side is low, and the case thickness at the bead portion has to be increased.

  In order to prevent such separation from the carcass ply end and an increase in case thickness, for example, in Patent Document 1, a bead core that is vertically divided in the tire radial direction is disposed, and the end of the carcass ply is connected to these bead cores. A pneumatic tire is described which is inserted between the two split surfaces from the outside in the tire width direction and sandwiched between the split surfaces.

  Patent Document 2 discloses a meridian profile that is composed of a non-stretchable reinforcing element that forms an angle of −2.5 ° to + 2.5 ° with the circumferential direction instead of the bead core, and is substantially parallel to the meridian profile of the carcass. Reinforcing the end of the carcass using two additional layers with a rubber decoupling layer between the outer radial end of the additional layer placed along the carcass inner surface and the carcass A pneumatic tire is described.

JP 2002-67630 A JP-T-2001-523608

  Although the tires described in Patent Documents 1 and 2 can prevent separation from the end portion of the carcass ply, the tire described in Patent Document 1 has a large rigidity step between the end portion of the bead core and the carcass ply. Therefore, stress concentrates on the end of the bead core, which may cause a failure, and the bead wire and the ply cord of the carcass are approximately orthogonal to each other. Was intriguing. In addition, the tire described in Patent Document 2 eliminates the rigidity step by disposing a rubber decoupling, but the non-stretchable reinforcing element constituting the additional layer and the carcass ply cord are also used. Since they are substantially orthogonal, the reinforcing element and the ply cord are in point contact with each other, which causes wear of the cord due to fretting. For this reason, in either of Patent Documents 1 and 2, carcass ply cords are easily damaged by fretting, and the bead durability cannot be improved as expected.

  Accordingly, an object of the present invention is to solve such problems of the prior art, and the object thereof is to improve the durability and weight reduction of a pneumatic radial tire having a sandwich bead structure. Is to achieve both at a high level.

  In order to achieve the above object, the present invention comprises a pair of bead parts and a ply cord covered with rubber, and a carcass ply extending in a toroid shape between the pair of bead parts, embedded in each bead part, In a pneumatic tire including a pair of bead cores that sandwich a carcass ply, a reinforcing layer made of an organic fiber cord and rubber is disposed between the carcass ply and at least one bead core. It is a pneumatic tire. By adopting such a configuration, the reinforcing layer can relieve the rigidity step between the carcass ply and the bead core, and can buffer the fretting between the bead core and the carcass ply cord. Moreover, there are few restrictions to a carcass line, and the case thickness of a bead part can be made thin easily.

  The reinforcing layer is preferably formed by rubber-covering a plurality of cords arranged in parallel in a direction intersecting the tire circumferential direction, and extends beyond both end portions of adjacent bead cores. Is particularly preferably in the range of 30 ° to 70 ° with respect to the tire circumferential direction.

  Further, the surfaces sandwiching the carcass ply of each bead core have at least one bent portion and are in a complementary relationship with each other, and the carcass ply extends in a toroidal shape between the two bead portions, and the tire width direction It is preferable to enter between the pair of bead cores from the outside.

  In addition, the carcass ply is preferably folded back from the inner side in the tire width direction toward the outer side along the bead core, and both end portions thereof are located between the bead base and the bead core.

  Further, the carcass ply has both end portions protruding from each pair of bead cores, and each end portion is covered with a pull-out suppression rubber that suppresses pull-out of the carcass ply from the bead core, and / or each end portion. It is preferable to have a bent part between the bead core and the bead core. Here, the “draw-out suppressing rubber” refers to a rubber that generates a resistance against the tension in cooperation with the bead core when a tension is applied to the carcass ply.

  According to the present invention, by arranging the reinforcing layer, the rigidity step of the tire having the sandwich bead structure is relaxed and the fretting is prevented, so that the bead portion durability is improved and the case thickness of the bead portion is also increased. The weight can be reduced because the thickness can be easily reduced.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a cross section in the tire width direction of a bead portion of a typical pneumatic tire (hereinafter referred to as “tire”) according to the present invention, and FIG. 2 is a cutaway perspective view of the bead portion of the tire shown in FIG. FIG. 3 is a diagram for illustrating an arrangement state of the cords constituting the ply cord, the bead wire, and the reinforcing layer of the tire illustrated in FIG. 1.

  The tire of the embodiment shown in FIGS. 1 and 2 has a pair of bead portions (only one bead portion 1 is shown in FIG. 1) and a ply cord 2 covered with rubber. A carcass ply 3 extending in a toroidal shape from the portion to the bead portion 1 through the sidewall portion. As the ply cord 2, an organic fiber cord such as nylon, rayon, polyester, and aromatic polyamide, and a metal cord such as steel can be used in the same manner as the cord constituting the conventional carcass ply. Also, in the bead portion 1, a bead wire 4 extending in a substantially circumferential direction is bundled, and an inner bead core 6 positioned on the inner surface side of the carcass ply 3 and an outer bead core 7 positioned on the outer surface side are embedded, so-called. The sandwich bead structure is configured. Here, the “substantially circumferential direction” means that a small inclination that is inevitably generated in production is included, such as when a bead core is formed by continuously winding one bead wire in a spiral shape. More specifically, it means a direction in which an angle formed with the tire circumferential direction is within a range of ± 5 °. The “inner surface” of the radial carcass ply means a surface facing the cavity in the tire, and the “outer surface” means a surface facing the outer surface of the tire.

  The main structural feature of the present invention is that a reinforcing layer 7 made of an organic fiber cord and rubber is disposed between the carcass ply 3 and at least one bead core, and the inner bead core 5 in the embodiment shown in FIGS. It is to arrange in.

  Thus, in the tire of the present invention, since the carcass ply 3 terminates in the bead portion, it is possible to eliminate the influence of the falling deformation of the sidewall portion and avoid stress concentration at the end portion of the carcass ply. Further, in a tire having a normal sandwich bead structure, when this is assembled to a rim and filled with an internal pressure, a tension (drawing force) T acts on the carcass ply moored at the bead portion. At this time, the ply cord of the carcass ply and the bead wire of the bead core extend in a direction crossing each other and are in point contact with each other, and therefore, fretting wear is likely to occur. In contrast, in the tire according to the present invention, the reinforcing layer 7 is disposed between the carcass ply 3 and the bead core 5, so that the ply cord 2 and the bead wire 4 can be prevented from being in direct contact with each other. Ting wear can be effectively prevented. Thereby, durability of bead part 1 improves. Also, compared to a conventional tire with a carcass ply wrapped around the bead core, there are fewer restrictions on the carcass line and it can be brought closer to the outer contour surface of the tire, so the case thickness at the bead part is thinner Thus, the weight can be reduced by the reduction of the case thickness. The reinforcing layer 7 is made of organic fiber cords and rubber. A reinforcing layer made only of rubber is disadvantageous in terms of durability, and a reinforcing layer made of metal cords and rubber is disadvantageous in terms of mass. This is because fretting wear may occur between the metal cord and the ply cord constituting the reinforcing layer, but these problems can be solved by using the organic fiber cord.

  As shown in FIG. 3, the reinforcing layer 7 is preferably one in which a plurality of cords 8 arranged in parallel in a direction intersecting the tire circumferential direction C are covered with rubber. By arranging the cord 8 in such an arrangement, the angle between the ply cord 2 constituting the carcass ply 3 and the cord 8 constituting the reinforcing layer 7 and the angle between the bead wire 4 of the bead core 5 and the cord 8 constituting the reinforcing layer 7 are formed. Since each is relatively small, the ply cord 2 constituting the carcass ply 3 and the cord 8 constituting the reinforcing layer 7 and the bead wire 4 of the bead core 5 and the cord 8 constituting the reinforcing layer 7 are in point contact. Can be prevented. Such a cord arrangement is particularly advantageous when the carcass ply 3 is a radial carcass ply. In such a reinforcing layer 7, it is preferable that an angle α formed by the cord 8 and the tire circumferential direction C is in a range of 30 ° to 70 °. If the angle α is less than 30 °, the angle formed by the bead wire 4 and the cord 8 becomes too large, and as a result of these becoming close to point contact, fretting is likely to occur, and the angle α is less than 70 °. In the case of exceeding, the angle formed by the ply cord 2 and the cord 8 becomes too large, and as a result of being close to point contact, fretting is likely to occur. Nylon, rayon, polyester, aromatic polyamide or the like can be used as the material constituting the cord 8, but is not limited thereto.

  The reinforcing layer 7 may be disposed at least in a portion where the fretting wear of the ply cord 2 is likely to occur in consideration of the shape of the bead portion 1 and the bead cores 5 and 6, but as shown in FIG. Preferably, 7 is wider than the bead core 5 adjacent thereto and extends beyond both width ends of the bead core 5. This is because by providing the reinforcing layer 7 so as to cover the entire bead core 5 as described above, fretting can be prevented more effectively. Moreover, it is because the separation resulting from the rigidity step at both ends of the bead core 5 can be prevented. The reinforcing layer 7 preferably has an extension length from the width end of the bead core of 20 mm or less on the side wall side and 5 mm or less on the bead toe side. In the embodiment shown in FIG. 1, the reinforcing layer 7 is disposed between the carcass ply 2 and the inner bead core 5. However, the reinforcing layer 7 includes the carcass ply 2 and the outer bead core 6, as shown in FIG. May be disposed between the inner surface and the outer surface of the carcass ply 2 as shown in FIG.

  From the viewpoint of increasing the locking force of the carcass ply 3, as shown in FIG. 6, the surfaces 9a and 9b for sandwiching the carcass ply 3 of each bead core 5 and 6 are each at least one bent portion, as shown in FIG. In an embodiment, the inner bead core 5 has three bends 10a, 10b, 10c, the outer bead core 6 has three bends 10d, 10e, 10f and is complementary to each other, ie Concave bent portions 10d and 10f are disposed on the clamping surface 9b at portions facing the convex bent portions 10a and 10c of the clamping surface 9a, and the concave bent portion of the clamping surface 9b is located on the clamping surface 9b. A convex bent portion 10e is arranged at a portion facing 10b, and when the sandwiching surfaces 9a and 9b are brought into contact with each other, they are in meshing relationship, and the carcass ply 3 has both beads Part The toroidally extending, it is preferable to enter between the pair of bead cores 5,6 from the tire width direction outside. As described above, a tension T is applied to the carcass ply 3, and particularly when the tension T is large, such as a heavy load tire, in the conventional sandwich bead structure, the carcass ply is pulled out from the bead core, resulting in an early failure. There was a case. This is presumably because the extending direction of the carcass ply between the bead cores substantially coincides with the direction of action of the tension T, so that there is nothing to prevent the movement of the carcass ply and the force that resists the tension T is insufficient. Therefore, in the tire of this embodiment, at least one bent portion is provided on each of the sandwiching surfaces 9a and 9b of the bead cores 5 and 6, and the carcass ply 3 is pulled even when the tension T acts on the carcass ply 2 and the carcass ply 3 is pulled. By engaging the ply 3 and the bent portions 10a to 10f, the movement of the carcass ply 3 is prevented, the locking force is improved, and the bead portion durability is maintained at a high level.

  Furthermore, as shown in FIG. 7, the carcass ply 3 is folded back along the outer bead core 6 from the inner side to the outer side in the tire width direction, and the end portion 11 is located between the bead base 12 and the bead core 6. Is preferred. When the tire is assembled to the rim and the internal pressure is filled, the region of the bead portion 1 sandwiched between the bead core 6 and the bead base 12 is compressed and deformed. By disposing the end portion 11 of the carcass ply 3 in this region, the carcass ply 3 is more effectively prevented from being pulled out, and the durability of the bead portion 1 is further improved.

  Furthermore, as shown in FIG. 8, the end portion 11 of the carcass ply 3 protrudes from the bead cores 5 and 6, and the end portion 11 pulls out to prevent the carcass ply 2 from pulling out from the bead cores 5 and 6. It is preferably covered with the suppression rubber 13. As described above, a tension T is applied to the carcass ply 3. However, in the tire according to this embodiment, the pull-out restraining rubber 13 is firmly bonded to the ply cord 2 of the carcass ply 3. When the tension T is applied, it tries to move together with the carcass ply 3, while the bead cores 5 and 6 try to keep their positions even in such a case because of high rigidity in the circumferential direction. For this reason, as a result of the movement of the pull-out suppression rubber 13 being blocked by the bead cores 5 and 6, the bead cores 5 and 6 and the pull-out suppression rubber 13 add a resistance against the tension T to the carcass ply 3, thereby further pulling out. Effectively suppressed, the durability of the bead portion 1 is further improved.

  The pull-out suppression rubber 13 is preferably made of a material, size, and shape capable of generating a sufficient resistance against the tension T in cooperation with the bead cores 5 and 6. Specifically, first, the 100% modulus of the pull-out suppressing rubber 13 is preferably larger than that of the covering rubber of the carcass ply 3. That is, it is preferable that the pull-out suppression rubber 13 is a rubber having less deformation than the covering rubber of the carcass ply 3 when the same force is applied. This is because the pull-out restraining rubber 13 tries to maintain the original shape even when the tension T acts, so that the effect of locking the carcass ply 3 is enhanced. The pull-out suppression rubber 13 is preferably a rubber containing an adhesion promoter that promotes adhesion of the carcass ply 3 to the ply cord 2. Since a shearing force acts between the carcass ply 3 and the pull-out suppression rubber 13, cracks are likely to occur. However, if an adhesion promoter is included in the pull-out suppression rubber 13, the carcass formed by the pull-out suppression rubber 13 is used. This is because as a result of increasing the holding power of the ply 3, the locking effect and crack resistance of the carcass ply 3 are improved, and the durability of the bead portion 1 is further improved. The adhesion promoter can be appropriately selected according to the material of the ply cord 2, but when the ply cord 2 is a steel cord, a metal salt of an organic acid, for example, a salt of cobalt, nickel, iron or the like is used. Particularly preferred are cobalt salts of organic acids. As a compounding quantity of cobalt salt, it is preferable to set it as 0.02-0.5 mass part as a cobalt element total compounding quantity with respect to 100 mass parts of rubber components. Further, the pull-out suppression rubber 13 preferably has a thickness of 1 mm or more and less than 5 mm. By setting the size of the pull-out suppression rubber 13 in such a range, the pull-out suppression rubber 13 is provided between the inner bead core 5 and the outer bead core 6 together with the carcass ply 3 without significantly increasing the mass of the tire. This is because it can be prevented from passing and the locking effect of the carcass ply 3 can be further enhanced.

  Further, as shown in FIG. 9, the end portion 11 of the carcass ply 3 protrudes from the bead cores 5 and 6, and it is preferable to have a bent portion 14 between the end portion 11 and the bead cores 5 and 6. Even when the tension T is particularly large and it is difficult to lock the carcass ply 2 with the pull-out restraining rubber 13 alone, the bent portion 14 is caught by the bead cores 5 and 6 so that the carcass ply 3 is securely locked. Because it can. Therefore, it is preferable that the angle β formed by the front and rear portions of the carcass ply 3 sandwiching the bent portion 14 is larger, and the locking effect is particularly enhanced when the angle β is 30 ° or more. In FIG. 9, the carcass ply 3 is bent so that the end portion 11 is directed toward the outer side in the tire radial direction, but may be bent so that the end portion 11 is directed toward the inner side in the tire radial direction. Further, the number of the bent portions 14 is not limited to one, and may be two or more. However, it is advantageous to set the number to one in consideration of manufacturing efficiency.

  When the end portion 11 of the carcass ply 2 is protruded from the bead core, the length p of the protruding portion is preferably 5 mm or more. When the pull-out suppression rubber 13 is provided, if the length p is less than 5 mm, it is difficult to sufficiently hold the carcass ply 2 by the pull-out suppression rubber 13, and the locking effect may not be effectively exhibited. Because. When the bent portion 14 is provided, if the length p is less than 5 mm, it may be difficult to provide the bent portion 14 at the time of manufacture. In this case, the bent portion 14 and the inner bead core 5 and This is because the locking effect of the carcass ply 2 by the outer bead core 6 may be insufficient. Note that the “length of the protruding portion” here means the length measured along the carcass line, and therefore, when it has a bent portion, it is extended and straightened. Equal to length.

  Note that the above description shows only a part of the embodiment of the present invention, and these configurations can be combined with each other or various modifications can be made without departing from the gist of the present invention. .

  Next, a pneumatic tire according to the present invention was prototyped and performance evaluation was performed, which will be described below.

  The tire of the example is a 15 ° taper radial tire for trucks and buses having a tire size of 11R22.5, and has a bead portion structure as shown in FIG. The organic fiber cords constituting the inner and outer reinforcing layers are nylon cords, and the angle formed with the tire circumferential direction is 45 °.

  For comparison, although the tire size is the same as that of the tire of the example, a comparative example in which a carcass is wound around a hexagonal bead core and a folding end is embedded in a rubber member outside the rim line in the tire radial direction. A tire of a comparative example having the same structure as that of the tire of the example except that the tire and the reinforcing layer are not provided was also manufactured.

  The cross-sectional shape of the bead portion of each tire of the conventional example, the comparative example, and the example and the mass of the entire tire were compared. Regarding the cross-sectional shape of the bead portion, the case thickness was reduced in each tire of the comparative example and the example as compared with the tire of the conventional example. Regarding the mass of the tire, the tires of the comparative example and the example were 3% lighter than the tire of the conventional example.

  Each of the test tires is mounted on a rim having a size of 8.25 × 22.5 to form a tire wheel. An air pressure of 700 kPa (relative pressure) is applied to the tire wheel, a running speed of 60 km / h, a tire load load. After running on a drum tester for 100,000 km under the condition of 29.4 kN, each tire was disassembled and the presence or absence of carcass pull-out and carcass ply damage was visually confirmed. As a result, pull-out and separation were not observed at all in the tires of the conventional example and the example, but in the tire of the comparative example, damage caused by fretting wear occurred in the portion of the carcass ply sandwiched between the bead cores. Was.

  As described above, the tire of the example achieved a weight reduction while maintaining the durability of the bead portion at the same level as the tire of the conventional example, and the mass at the same level as the tire of the comparative example. It can be seen that the durability of the bead portion is improved while keeping it, and the tire has excellent overall performance.

  As is apparent from the above description, the present invention makes it possible to achieve both improvement in durability and weight reduction of the tire bead portion having a sandwich bead structure at a high level.

1 is a tire width direction cross-sectional view of a bead portion of a typical pneumatic radial tire according to the present invention. FIG. 2 is a cutaway perspective view of a bead portion of the tire shown in FIG. 1. It is a figure for showing the arrangement | positioning state of the cord which comprises the ply cord of the tire shown in FIG. 1, a bead wire, and a reinforcement layer. It is tire width direction sectional drawing of the bead part of the other pneumatic tire according to this invention. It is tire width direction sectional drawing of the bead part of the other pneumatic tire according to this invention. It is tire width direction sectional drawing of the bead part of the other pneumatic tire according to this invention. It is tire width direction sectional drawing of the bead part of the other pneumatic tire according to this invention. It is tire width direction sectional drawing of the bead part of the other pneumatic tire according to this invention. It is tire width direction sectional drawing of the bead part of the other pneumatic tire according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Carcass ply 3 Ply cord 4 Bead wire 5 Inner bead core 6 Outer bead core 7 Reinforcement layer 8 Organic fiber cord which comprises a reinforcement layer 9a, 9b Carcass ply clamping surface of bead core 10a, 10b, 10c, 10d, 10e, 10f Bead core 12 bent portion of carcass ply 12 bead base 13 pull-out restraining rubber 14 bent portion of carcass ply

Claims (8)

A pair of bead portions, a ply cord covered with rubber, and a carcass ply extending in a toroid shape between the pair of bead portions, and a pair of bead cores embedded in each bead portion and sandwiching the carcass ply are provided. In pneumatic tires,
A pneumatic tire comprising a reinforcing layer made of an organic fiber cord and rubber disposed between the carcass ply and at least one bead core.   2. The pneumatic tire according to claim 1, wherein the reinforcing layer is formed by rubber coating a plurality of cords arranged in parallel in a direction intersecting the tire circumferential direction.   The pneumatic radial tire according to claim 1 or 2, wherein the cord constituting the reinforcing layer has an angle formed by a tire circumferential direction within a range of 30 ° to 70 °.   The pneumatic tire according to claim 1, wherein the reinforcing layer extends beyond both end portions of adjacent bead cores.   The surfaces of each bead core that sandwich the carcass ply have at least one bent portion and are in a complementary relationship with each other, and the carcass ply extends in a toroid shape between both bead portions, and is outside in the tire width direction. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire enters between the pair of bead cores.   The pneumatic according to any one of claims 1 to 5, wherein the carcass ply is folded back along the bead core from the inner side to the outer side in the tire width direction, and both ends are located between the bead base and the bead core. tire.   Both ends of the carcass ply protrude from each pair of bead cores, and each end is covered with a pull-out restraining rubber that suppresses pull-out of the carcass ply from the bead core. The pneumatic tire according to one item. The pneumatic tire according to any one of claims 1 to 7, wherein both ends of the carcass ply protrude from each pair of bead cores, and a bent portion is provided between each end and the bead core.

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