pneumatic tires

Abstract

Pneumatic tire (1) that can be mounted on a predetermined rim tapered by 15°, wherein the pneumatic tire (1) comprises the following: a pair of bead sections (20) arranged on each side of a tire equatorial plane (CL) in a tire transverse direction; a tire bead core (21) which is provided in each of the two bead sections (20); a carcass (6) which is supported by the pair of tire bead cores (21), the carcass comprising a carcass body part (61) and a carcass refold section (62) formed by the carcass (6) which refolds back on the tire bead core (21); a steel cord reinforcement layer (35) arranged on an outer surface of the carcass (6) which is folded back on the tire bead core (21); a bead rubber layer (K), wherein at least one section thereof is arranged between the carcass body part (61) and the carcass refolding section (62); and a first reinforcing rubber layer (L) arranged adjacent to an outer edge section (35E) of the steel cord reinforcing layer (35) located outwards in the tire radial direction, and an outer edge section (62E) of the carcass foldback section (62) located outwards in the tire radial direction, wherein the first reinforcing rubber layer (L) extends outwards in the tire radial direction; wherein the bead rubber layer (K) comprises a second reinforcing rubber layer (K1) arranged adjacent to the tire bead core (21) and a shock-absorbing rubber layer (K2) arranged adjacent to the second reinforcing rubber layer (K1), wherein the shock-absorbing rubber layer (K2) is located between the carcass body part (61) and the first reinforcing rubber layer (L); where, if the pneumatic tire (1) is not mounted on the specified rim, a distance from a second line segment (J) to a third line segment (F) is 4 mm to 12 mm, a complex modulus of the first reinforcing rubber layer (L) is between 6 MPa and 10 MPa, the elongation at break of the first reinforcing rubber layer (L) is 300% to 450%, a complex modulus of the second reinforcing rubber layer (K1) is 10 MPa to 15 MPa, and a complex modulus of the shock-absorbing rubber layer (K2) is 2 MPa to 6 MPa, wherein a first line segment (D) passes through an outermost projection point (E) of the tire bead core (21) in the transverse direction of the tire and is parallel to a longest side of the tire bead core (21), a side (P) of a bead base section (26) is closer to a bead heel (27), where the bead base section (26) is a section of the bead section (20) and is configured to come into contact with the specified rim, a curved line (G) of a tire outer surface (40), where the tire outer surface (40) is a section of the bead section (20), is arranged in the tire transverse direction outwards from the bead base section (26), a first intersection point (H) of the side (P) and the curved line (G) exists, the second line segment (J) passes through the first intersection point (H) and is perpendicular to the first line segment (D), and the third line segment (F) passes through the projection point (E) and is perpendicular to the first line segment (D).

Description

Technical field

[0001] The present invention relates to a pneumatic tire. State of the art

[0002] A pneumatic tire encloses a bead section with a tire bead core on each side in the tire's transverse direction. A pneumatic tire is mounted to a rim by the engagement of the bead section and the rim. JP 28 55327 B describes a technology designed to improve the durability of a bead section through a specific relationship between a tire bead core (tire bead wire) and a bead base section.

[0003] JP 2005 112 042 A discloses a steel cord reinforcement layer as a reinforcing layer, consisting of a layer formed by coating steel cord with a topping rubber. Furthermore, a first reinforcing rubber layer and a bead rubber layer are present, which in turn comprise a second reinforcing rubber layer and a shock-absorbing rubber layer. The rubbers have a complex modulus of elasticity of 8.0 to 14.0 MPa.

[0004] JP H03 204 314 A reveals a tire, and US 8 232 340 B2 reveals a rubber compound. Summary of the invention: Technical problem

[0005] In a pneumatic tire, a folded section of the carcass is arranged within a bead section. However, cracking can occur at the edge of the folded section of the carcass, and a countermeasure is needed.

[0006] One object of the present invention is to provide an air tire that can offer suppression of cracking from an edge of a carcass refold section. Solution to the problem

[0007] A pneumatic tire according to an embodiment of the present invention is a pneumatic tire that can be mounted on a predetermined rim tapered at an angle of 15°, wherein the pneumatic tire includes the following: a pair of bead sections arranged on each side of a tire equatorial plane in a tire transverse direction; a tire bead core that is provided in each of the two bead sections; a carcass supported by the pair of tire bead cores, the carcass comprising a carcass body part and a carcass backfold section formed by the carcass which folds back on the tire bead core; a steel cord reinforcement layer arranged on an outer surface of the carcass that is folded back on the tire bead core; a bead rubber layer, with at least a section of it arranged between the carcass body part and the carcass fold-back section; and a first reinforcing rubber layer arranged adjacent to an outer edge section of the steel cord reinforcing layer located outwards in the tire radial direction, and an outer edge section of the carcass foldback section located outwards in the tire radial direction, wherein the first reinforcing rubber layer extends outwards in the tire radial direction; wherein the bead rubber layer includes a second reinforcing rubber layer adjacent to the tire bead core and a shock-absorbing rubber layer adjacent to the second reinforcing rubber layer, the shock-absorbing rubber layer being located between the carcass body part and the first reinforcing rubber layer; if the pneumatic tire is not mounted on the specified rim, wherein the distance from a second line segment to a third line segment is 4 mm to 12 mm, the complex modulus of the first reinforcing rubber layer is 6 MPa to 10 MPa, the elongation at break of the first reinforcing rubber layer is 300% to 450%, the complex modulus of the second reinforcing rubber layer is 10 MPa to 15 MPa, and the complex modulus of the shock-absorbing rubber layer is 2 MPa to 6 MPa. wherein a first line segment passes through an outermost projection point of the tire bead core in the transverse direction of the tire and is parallel to a longest side of the tire bead core, a side of a bead base section is closer to a bead heel, where the bead base section is a section of the bead section and is configured to make contact with the specified rim, a curved line of a tire outer surface, where the tire outer surface is a section of the bead section, is arranged outwards from the bead base section in the transverse direction of the tire, a first intersection point of the side and the curved line is present, the second line segment passes through the first intersection point and is perpendicular to the first line segment, and the third line segment passes through the projection point and is perpendicular to the first line segment.

[0008] In an air tire according to an embodiment of the present invention, a second intersection point of the first line segment and the fold-back section of the carcass is preferably present at the second reinforcing rubber layer. Advantageous effects of the invention

[0009] The present invention provides an air tire that can offer suppression of cracking from an edge of a carcass refold section. Brief description of the drawings Fig. Figure 1 is a meridian cross-sectional view illustrating a main section of a pneumatic tire according to a present embodiment. Fig. 2 is a detailed view of section G from Fig. 1. Fig. Figure 3 is an enlarged view of a section of Fig. 2. Fig. Figure 4 is a table showing the results of performance tests of pneumatic tires according to the present embodiments. Description of embodiments

[0010] Embodiments of the present invention are described with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, components described in the following embodiments can be combined, and one or more components can be omitted.

[0011] In this context, "tire lateral direction" refers to the direction parallel to the tire's axis of rotation. "Inward in the tire lateral direction" refers to the direction toward the tire's equatorial plane in the tire's lateral direction. "Outward in the tire lateral direction" refers to the direction away from the tire's equatorial plane in the tire's lateral direction. Additionally, "tire radial direction" refers to the direction perpendicular to the tire's axis of rotation. "Inward in the tire radial direction" refers to the direction toward the tire's axis of rotation in the tire's radial direction. "Outward in the tire radial direction" refers to the direction away from the tire's axis of rotation in the tire's radial direction. "Tire circumferential direction" refers to the direction of rotation around the tire's axis of rotation.

[0012] "Tire equatorial plane" refers to a plane perpendicular to the tire's axis of rotation, running through the center in the transverse direction of the tire. "Tire equatorial line" refers to a center line where the tire equatorial plane and the surface of a tread section of the pneumatic tire intersect.

[0013] Fig. Figure 1 is a meridian cross-sectional view illustrating a major section of a tire 1 according to the present embodiment. "Meridian cross-section" refers to a cross-section passing through the tire's axis of rotation. The tire 1 is a pneumatic and tubeless tire. The tire 1 is a heavy-duty tire suitable for mounting on a truck or bus. A tire (heavy-duty tire) for a truck or bus refers to a tire specified in Chapter C of the JATMA Year Book (Standards of the Japan Automobile Tyre Manufacturers Association, Inc.), published by the Japan Automobile Tyre Manufacturers Association, Inc. (JATMA). Note that the tire 1 may be suitable for mounting on a passenger car or a light truck.

[0014] The in Fig. The illustrated tire 1, viewed in a meridional cross-section, is provided with a tread section 2 in its outermost section in the tire radial direction. The surface of the tread section 2, i.e., the section that comes into contact with the road surface when a vehicle to which the tire 1 is mounted is moving, is designed as a tread surface 3. A plurality of major circumferential grooves 15, extending in the tire circumferential direction, and a plurality of lug grooves (not illustrated), intersecting the major circumferential grooves 15, are formed in the tread surface 3. A plurality of rib sections 10 are defined in the tread surface 3 by the major circumferential grooves 15 and the lug grooves.It should be noted that the number of main circumferential grooves 15, the spacing between the lug grooves in the circumferential direction of the tire, the length and angle of the lug grooves, the groove width and groove depth of each of the grooves, and the like are preferably suitably adjusted. In other words, a tread pattern formed in the tread surface 3 is preferably suitably adjusted.

[0015] Both ends of the tread section 2 in the tire's transverse direction are designed as shoulder sections 4. Sidewall sections 5 are arranged inwards from the shoulder sections 4 at predetermined positions in the tire's radial direction. In other words, the sidewall sections 5 are arranged at two positions on each side of the pneumatic tire 1 in the tire's transverse direction.

[0016] Furthermore, a bead section 20 is located inside each sidewall section 5 in the tire radial direction. The bead sections 20 are arranged at two positions on each side of an equatorial plane of the tire CL in a manner similar to the sidewall sections 5. In other words, the pair of bead sections 20 is arranged on each side of the tire equatorial plane CL in the tire transverse direction. Each pair of bead sections 20 comprises a tire bead core 21. The tire bead core 21 is formed by winding a tire bead wire, which is a steel wire, into a ring shape.

[0017] The bead section 20 is configured to be mounted on a predefined rim tapered at an angle of 15°. Herein, "predefined rim" means "applicable rim" as defined by JATMA, "design rim" as defined by the Tire and Rim Association (TRA), or "measuring rim" as defined by the European Tyre and Rim Technical Organisation (ETRTO). In other words, the tire 1 according to the present embodiment can be mounted on the predefined rim, including an engagement section for the bead section 20, which is inclined at an angle of 15° with respect to the axis of rotation.

[0018] A belt layer 7 is provided inward in the tire radial direction from the tread section 2. The belt layer 7 has, for example, a multi-layer structure, including four layered belts 71, 72, 73, 74, wherein the belts are produced by a process of coating a plurality of belt cord threads made of steel or an organic fiber material, such as polyester, rayon, and nylon, and a subsequent rolling process. Furthermore, the belts 71, 72, 73, 74 have different sets of belt cord threads, defined as the inclination angle of the fiber direction of the belt cord threads relative to the tire circumferential direction, and the belts are configured such that they are layered in such a way that the fiber directions of the belt cord threads intersect, i.e., form a cross-layer structure.

[0019] A carcass 6, including cord threads in a radial layer, is provided continuously in the tire radial direction within the belt layer 7 and along one side of the sidewall section 5 closer to the tire equatorial plane CL. The carcass 6 is supported by the pair of tire bead cores 21. The carcass 6 has a single-layer structure made from a single carcass layer or a multi-layer structure made from multiple carcass layers and extends between the tire bead cores 21 on both sides in the tire transverse direction in a ring shape, forming the tire frame. In particular, the carcass 6 is arranged from one bead section 20 to the other bead section 20, where the set of bead sections 20 is located on both sides in the tire transverse direction, and bends back outwards in the tire transverse direction along the tire bead cores 21 and bead sections 20, wrapping around the tire bead cores 21.In other words, the carcass 6 is folded back around the tire bead cores 21 at the bead areas 20, such that the carcass 6 is arranged inwards in the tire bead cores 21 in the tire transverse direction, and then outwards in the tire transverse direction. The carcass layer of the carcass 6, arranged in this way, is produced by a process of covering a plurality of carcass cord threads made of steel or an organic fiber material, such as aramid, nylon, polyester, and rayon, and a subsequent rolling process.

[0020] Below, the carcass 6, which folds back on the tire bead core 21 arranged on the bead section 20, includes a section that is suitably arranged inwards from the tire bead core 21 in the transverse direction of the tire, which is referred to as a carcass body part 61, and a section that is formed by folding back the carcass 6 on the tire bead core 21, which is suitably arranged outwards from the tire bead core 21 in the transverse direction of the tire, which is referred to as a carcass folding-back section 62.

[0021] Furthermore, an inner liner 8 is formed along the carcass 6 on the inside of the carcass 6 or on the inner side of the tire 1 of the carcass 6.

[0022] Fig. 2 is a detailed view of section G from Fig. 1. A steel cord reinforcement layer 35, consisting of steel cord threads, is arranged in a section where the carcass 6 folds back around the tire bead core 21. The steel cord reinforcement layer 35 is in contact with the outer surface of the carcass 6 that is folded back around the tire bead core 21 and reinforces the carcass 6. The steel cord reinforcement layer 35 is arranged in layers on the outside of the carcass 6 in the section where the carcass 6 is folded back and is folded back around the tire bead core 21 in a manner similar to how the carcass 6 is folded back from the inside out in the transverse direction of the tire and is arranged continuously in the circumferential direction of the tire.In other words, the steel cord reinforcement layer 35 is arranged in the section where the carcass 6 is arranged in the transverse direction inwards from the tire bead core 21, and in the section where the carcass 6 is arranged in the transverse direction outwards from the tire bead core 21, is arranged in the transverse direction outwards from the carcass 6.

[0023] Additionally, the tire bead core 21, which is formed by winding a tire bead wire into a ring-shaped form, has a shape that is essentially hexagonal when viewed in a meridional cross-section. In particular, the tire bead core 21, when viewed as a whole, has an essentially hexagonal shape and includes an inner circumferential surface 22 and an outer circumferential surface 23, which have an essentially parallel orientation and, when running from outside to inside in the tire transverse direction, are inclined inwards in the tire radial direction; a corner section 24, which projects outwards at an outer position in the tire transverse direction; and a corner section 25, which projects inwards at an inner position in the tire transverse direction.It should be noted that the inner circumferential surface 22 is a surface of the tire bead core 21 that points inwards in the tire radial direction, and the outer circumferential surface 23 is another surface of the tire bead core 21 that points outwards in the tire radial direction.

[0024] In the present embodiment, of the six sides of the hexagonal shape of the tire bead core 21, when viewed in a meridional cross-section, the side designated as the outer circumferential surface 23 is the longest. It should be noted that the side designated as the inner circumferential surface 22 may be the longest, or the side designated as the outer circumferential surface 23 and the side designated as the inner circumferential surface 22 may be of equal length.

[0025] Similarly, a bead base section 26, which is the inner circumferential surface of the bead section 20, slopes inwards in the tire radial direction, while in the tire transverse direction it slopes from outside to inside. It should be noted that the inner circumferential surface of the bead section 20 is a surface of the bead section 20 that faces inwards in the tire radial direction. In other words, on the bead base section 26, a bead heel 28, which is an inner end section of the bead base section 26 in the tire transverse direction, is more steeply inclined inwards in the tire radial direction than a bead heel 27, which is an outer end section of the bead base section 26 in the tire transverse direction. The bead base section 26 is provided as an engagement section that engages with and comes into contact with the specified rim when the tire 1 is mounted on the specified rim according to the present embodiment.

[0026] In the bead section 20, a tire outer surface 40 is formed such that it is curved and projects outwards in the transverse direction of the tire. In other words, the section of the tire outer surface 40 at the bead section 20, where the outer surface 40 is a surface on the side of the tire 1 exposed to the outside air, is curved and projects outwards in the transverse direction of the tire. The bead heel 27, i.e., an end section of the bead base section 26, is the intersection between the tire outer surface 40 and the bead base section 26.

[0027] In the bead section 20, an inner tire surface 50 is formed such that it is curved and projects inwards in the transverse direction of the tire. In other words, the section of the inner tire surface 50 on the bead section 20, where the inner surface 50 is an air-filled surface on the side of the tire 1, is curved and projects inwards in the transverse direction of the tire. The bead base 28, i.e., the other end section of the bead base section 26, is the intersection between the inner tire surface 50 and the bead base section 26.

[0028] Furthermore, the bead section 20 is provided with a bead rubber layer K. At least one section of the bead rubber layer K is arranged between the carcass body part 61 and the carcass refolding section 62. The bead rubber layer K is also known as a bead filler.

[0029] The first reinforcing rubber layer L is adjacent to an outer surface of the bead rubber layer K in the tire transverse direction, an outer edge section 62E of the carcass foldback section 62 located outwards in the tire radial direction, and an outer edge section 35E of the steel cord reinforcement layer 35 located outwards in the tire radial direction. In a meridional cross-section, the first reinforcing rubber layer L extends in the tire radial direction and comes into contact with the outer surface of the bead rubber layer K in the tire transverse direction, the outer edge section 62E of the carcass foldback section 62 located outwards in the tire radial direction, and the outer edge section 35E of the steel cord reinforcement layer 35 located outwards in the tire radial direction.The hardness of the first reinforcing rubber layer L is greater than the hardness of the bead rubber layer K (a shock-absorbing rubber layer K2 described below), but less than the hardness of the carcass 6 and the steel cord reinforcing layer 35. It should be noted that the hardness is a value measured using a Type A durometer in accordance with Japanese Industrial Standards (JIS) K 6253-3:2012.

[0030] In the present embodiment, the bead rubber layer K includes a second reinforcing rubber layer K1, which is aligned adjacent to the bead core 21 and the shock-absorbing rubber layer K2, which is adjacent to the second reinforcing rubber layer K1. The shock-absorbing rubber layer K2 is arranged between the carcass body part 61 and the first reinforcing rubber layer L. The boundary between the second reinforcing rubber layer K1 and the shock-absorbing rubber layer K2 extends in the tire radial direction. The reinforcing rubber layer L is in contact with the shock-absorbing rubber layer K2. The outer edge section 62E of the foldback section 62 of the carcass is arranged adjacent to the shock-absorbing rubber layer K2.

[0031] The outer edge section 62E of the carcass foldback section 62 is arranged outwards in the tire radial direction from the outer edge section 35E of the steel cord reinforcement layer 35. An outer edge section LE of the first reinforcing rubber layer L is arranged outwards in the tire radial direction from the outer edge section 62E of the carcass foldback section 62.

[0032] Fig. Figure 3 is an enlarged view of a section of Fig. 2. Specified values, such as the respective dimensions of the components of the bead section 20 according to the present embodiment, are below with reference to the Fig. 2 and Fig. 3 described. The specified values ​​described below are specified values ​​when the tire 1 is not mounted on the specified rim. In other words, the specified values ​​are specified values ​​of the tire 1 in a state prior to mounting on the specified rim and are specified values ​​in a meridional cross-section of the tire 1 after vulcanization molding over a casting mold. For simplicity, the specified values ​​are in a meridional cross-section of the tire 1 defined by the linear distance between imaginary intersection points H (the distance between the imaginary intersection points H of the pair of bead sections 20), as described below, when the tire is standing upright on its own.

[0033] As in Fig. As illustrated in Figure 3, in a meridional cross-section of the bead section 20, a first line segment D, passing through an outermost projection point E of the tire bead core 21 in the tire transverse direction and parallel to a longest side of the tire bead core 21, a side P of a bead base section 26 that is closer to a bead heel 27, where the bead base section 26 of the bead section 20 is configured to contact the specified rim, a curved line G of a tire outer surface 40, where the tire outer surface 40 of the bead section 20 is arranged outside the bead base section 26 in the tire transverse direction, a first intersection point H of the side P and the curved line G, a second line segment J passing through the first intersection point H and perpendicular to the first line segment D, and a third line segment F passing through the projection point E The line segment D runs and is perpendicular to the first line segment.

[0034] The projection point E encloses the corner section 24. The projection point E in a meridian cross-section is a point where the first line segment D, which runs through the center of the outermost bead wire in the tire transverse direction of the bead wires of the bead core 21 and is parallel to the longest side of the bead core 21, intersects the profile of the bead wires. The longest side is referred to as the outer circumferential surface 23. The first intersection point H encloses the bead heel 27.

[0035] In the present embodiment, the distance A between the second line segment J and the third line segment F is from 4 mm to 12 mm.

[0036] Furthermore, in the present embodiment, a second intersection point R of the first line segment D and the inner surface of the foldback section 62 of the carcass are specified at the second reinforcing rubber layer K1. In other words, the second intersection point R is located adjacent to the second reinforcing rubber layer K1.

[0037] In addition, in the present embodiment, the complex modulus of the first reinforcing rubber layer L is 6 MPa to 10 MPa, and the elongation at break of the first reinforcing rubber layer L is 300% to 450%. The complex modulus of the second reinforcing rubber layer K1 is between 10 MPa and 15 MPa. The complex modulus of the shock-absorbing rubber layer K2 is between 2 MPa and 6 MPa. The viscoelastic properties are values ​​measured according to JIS K 7244-4:1999 (measurement temperature: 60°C, initial strain: 10%, amplitude: ±1%, frequency: 10 Hz, deformation mode: tensile strength). Elongation at break is the elongation at break according to JIS K 6251:2010.

[0038] As described above, the distance A according to the present embodiment is 4 mm to 12 mm. This allows for an angle α (see Fig. 3), formed by the carcass body part 61 and the outer circumferential surface 23 of the tire bead core 21, is reduced. This allows the amount of positional change of the carcass 6, located near the bead area 20, to be reduced in the tire 1 before and after inflation with air. This enables the stress acting on the first reinforcing rubber layer L and the bead rubber layer K (shock-absorbing rubber layer K2), which is located adjacent to the outer edge section 62E of the refold section 62 of the carcass, to be reduced, and cracking of the outer edge section 62E of the refold section 62 of the carcass to be suppressed.

[0039] Generally, a method for reducing the distance between the two bead sections 20 is used to reduce the amount of positional changes of the carcass 6 located near the bead section 20 before and after inflation. However, this method has the disadvantage of making it more difficult to mount the bead sections 20 onto the designated rim when the tire 1 is inflated with air. According to the present embodiment, cracking can be suppressed while maintaining the mountability of the bead sections 20 on the designated rim.

[0040] If the distance A is greater than 12 mm, the volume of the bead rubber layer K increases to a level that worsens heat retention and thus reduces the service life of the bead section 20. If the distance A is less than 4 mm, the angle α cannot be made small enough. This prevents the desired effect of reducing the stress acting on the first reinforcing rubber layer L and the bead rubber layer K, which is adjacent to the outer edge section 62E of the carcass's foldback section 62. Therefore, the distance A is preferably 4 mm to 12 mm, more preferably 4 mm to 8 mm, and even more preferably 5 mm to 7 mm.

[0041] In addition, in the present embodiment, the complex modulus of the first reinforcing rubber layer L is 6 MPa to 10 MPa, and the elongation at break of the first reinforcing rubber layer L is 300% to 450%. This makes it possible to reduce the stress acting on the first reinforcing rubber layer L, which is adjacent to the outer edge section 62E of the refold section 62 of the carcass, to maintain the elongation at break at a certain level, and to suppress cracking in the first reinforcing rubber layer L and the bead rubber layer K originating from the outer edge section 62E of the refold section 62 of the carcass.

[0042] If the complex modulus is greater than 10 MPa, the elongation at break is less than 300%. This increases the probability of cracking in the first reinforcing rubber layer L and the bead rubber layer K, which originates from the outer edge section 62E. If the complex modulus is less than 6 MPa, the stress acting on the first reinforcing rubber layer L, which is adjacent to the outer edge section 62E of the carcass's backfold section 62, increases. This also increases the probability of cracking in the first reinforcing rubber layer L and the bead rubber layer K. Because the physical properties of the first reinforcing rubber layer L are within the ranges described above, cracking can be suppressed.

[0043] Furthermore, in the present embodiment, the complex modulus of the second reinforcing rubber layer K1 is between 10 MPa and 15 MPa. If the complex modulus of the second reinforcing rubber layer K1 is less than 10 MPa, the fastening force on the rim wheel in the folded-back section 62 of the carcass is low, and the bead section 20 can burst due to being pulled out of the carcass 6. If the complex modulus of the second reinforcing rubber layer K1 is greater than 15 MPa, a decrease in the elongation at break of the second reinforcing rubber layer K1 causes an increase in the possibility of cracking in the second reinforcing rubber layer K1 itself, leading to bursting of the bead section 20. Accordingly, the complex modulus of the second reinforcing rubber layer K1 is preferably between 10 MPa and 15 MPa.

[0044] Furthermore, in the present embodiment, the complex modulus of the shock-absorbing rubber layer K2 is between 2 MPa and 6 MPa. If the complex modulus of the shock-absorbing rubber layer K2 is greater than 6 MPa, the function of minimizing deformation due to collapse of the carcass body part 61 is reduced, the load acting on the shock-absorbing rubber layer K2 adjacent to the outer edge section 62E of the refold section 62 of the carcass is increased, and the possibility of cracking in the first reinforcing rubber layer L and the shock-absorbing rubber layer K2 adjacent to the outer edge section 62E of the refold section 62 of the carcass increases. If the complex modulus of the shock-absorbing rubber layer K2 is less than 2 MPa, the deformation due to collapse of the carcass body part 61 itself increases.As a result, the load acting on the shock-absorbing rubber layer K2, which is located adjacent to the outer edge section 62E of the refold section 62 of the carcass, increases, and the possibility of cracking in the first reinforcing rubber layer L and the shock-absorbing rubber layer K2 increases. The complex modulus of the shock-absorbing rubber layer K2 is preferably between 2 MPa and 6 MPa.

[0045] Furthermore, in the present embodiment, the second intersection point R of the first line segment D and the inner surface of the foldback section 62 of the carcass borders the second reinforcing rubber layer K1, which has a greater hardness than the shock-absorbing rubber layer K2. If the second intersection point R borders the shock-absorbing rubber layer K2, the holding force of the foldback section 62 of the carcass is low, and the bead section 20 can burst by being pulled out of the carcass 6. If the rubber adjacent to the second intersection point R is the second reinforcing rubber layer K2, which has a relatively greater hardness than the shock-absorbing rubber layer K2, then the load generated between the rim and the tire bead core 21 is reduced, and the heat build-up of the bead section 20 is not reduced. Examples

[0046] Fig. Figure 4 is a table showing the results of performance tests of the tires 1. With regard to the tires 1 described above, performance evaluation tests are described below that were carried out on the tires 1 of the prior art examples and the comparative examples, and on the tires 1 according to embodiments of the present invention. The performance evaluation tests were carried out for the separation resistance performance with the carcass folded up, which indicates the resistance to cracking in the bead section 20 originating from the refolding section 62 of the carcass, and for the probability of the bead bursting, which indicates the probability that the bead section 20 will burst.

[0047] In the performance evaluation tests, tires 1, size 275 / 70R22.5, were mounted on the rim of a specified rim, tapered at an angle of 15°, as defined by JATMA. They were inflated to a pressure of 75% of a specified pressure, as defined by JATMA, and loaded with 1.4 times a specified load, as defined by JATMA. The tires were then run on an internal drum test machine at a speed of 49 km / h until failure. The distance traveled until failure was evaluated.

[0048] As in Fig. As listed in Figure 4, the evaluation test was carried out on the tires 1 of the prior art examples 1 and 2, the tires 1 of the comparative examples 1 to 4, and the tires 1 of examples 1 to 3, which are embodiments of the present invention. These tires 1 each have a different configuration for the bead sections 20. As described in Figure 4, the tire 1 is a representative example of the prior art examples 1 and 2. Fig. As listed in example 4, in tire 1 of prior art example 1, the distance A is outside the scope of the present invention, and in tire 1 of prior art example 2, all components are outside the scope of the present invention. The tires 1 of comparative examples 1 to 4 each have a component outside the scope of the present invention.

[0049] When evaluating the separation resistance performance for a raised carcass, the results of the evaluation are expressed as index values, with prior art example 1 assigned as the reference (100). In this evaluation, higher values ​​represented better separation resistance performance for a raised carcass.

[0050] As in Fig.As listed in section 4, the tires 1 of examples 1 to 3 exhibit excellent separation resistance performance in the case of a folded carcass and a low probability of bead bursting, compared to the tires 1 of the prior art examples and the comparative examples. In other words, the tires 1 of examples 1 to 3 can provide effective suppression of cracking from the edge of the refold section 62 of the carcass. List of reference symbols 1 tire (pneumatic tire) 2. Tread section 3. Tread surface 4 Shoulder section 5 Side wall section 6 Carcass 7th belt layer 8 Inner Soul 10 Bridge section 15 Main circumferential groove 20 bead section 21 tire bead core 22 Inner circumference area 23 External perimeter area 24 Corner section 25 Corner section 26 Bead base section 27. Heel bulge 28 bulging heaves 35 steel cord reinforcement layer 35E Outer edge section 40 Tire outer surface 50 Tire inner surface 61 Carcass body part 62 Carcass foldback section 62E Outer edge section 71, 72, 73, 74 Belts A distance CL tire equatorial plane D First line segment E advantage point F Third line segment G Curved line H First intersection J Second line segment K bead rubber layer L First reinforcing rubber layer P page R Second Intersection Point

Claims

[1] Pneumatic tire (1) that can be mounted on a predetermined rim tapered by 15°, wherein the pneumatic tire (1) comprises the following: a pair of bead sections (20) arranged on each side of a tire equatorial plane (CL) in a tire transverse direction; a tire bead core (21) which is provided in each of the two bead sections (20); a carcass (6) which is supported by the pair of tire bead cores (21), the carcass comprising a carcass body part (61) and a carcass refold section (62) formed by the carcass (6) which refolds back on the tire bead core (21); a steel cord reinforcement layer (35) arranged on an outer surface of the carcass (6) which is folded back on the tire bead core (21); a bead rubber layer (K), wherein at least one section thereof is arranged between the carcass body part (61) and the carcass refolding section (62); and a first reinforcing rubber layer (L) arranged adjacent to an outer edge section (35E) of the steel cord reinforcing layer (35) located outwards in the tire radial direction, and an outer edge section (62E) of the carcass foldback section (62) located outwards in the tire radial direction, wherein the first reinforcing rubber layer (L) extends outwards in the tire radial direction; wherein the bead rubber layer (K) comprises a second reinforcing rubber layer (K1) arranged adjacent to the tire bead core (21) and a shock-absorbing rubber layer (K2) arranged adjacent to the second reinforcing rubber layer (K1), wherein the shock-absorbing rubber layer (K2) is located between the carcass body part (61) and the first reinforcing rubber layer (L); where, if the pneumatic tire (1) is not mounted on the specified rim, a distance from a second line segment (J) to a third line segment (F) is 4 mm to 12 mm, a complex modulus of the first reinforcing rubber layer (L) is between 6 MPa and 10 MPa, the elongation at break of the first reinforcing rubber layer (L) is 300% to 450%, a complex modulus of the second reinforcing rubber layer (K1) is 10 MPa to 15 MPa, and a complex modulus of the shock-absorbing rubber layer (K2) is 2 MPa to 6 MPa, wherein a first line segment (D) passes through an outermost projection point (E) of the tire bead core (21) in the transverse direction of the tire and is parallel to a longest side of the tire bead core (21), a side (P) of a bead base section (26) is closer to a bead heel (27), where the bead base section (26) is a section of the bead section (20) and is configured to come into contact with the specified rim, a curved line (G) of a tire outer surface (40), where the tire outer surface (40) is a section of the bead section (20), is arranged in the tire transverse direction outwards from the bead base section (26), a first intersection point (H) of the side (P) and the curved line (G) exists, the second line segment (J) passes through the first intersection point (H) and is perpendicular to the first line segment (D), and the third line segment (F) passes through the projection point (E) and is perpendicular to the first line segment (D). [2] Pneumatic tire (1) according to claim 1, wherein a second intersection point (R) of the first line segment (D) and the fold-back section (62) of the carcass (6) is present at the second reinforcing rubber layer (K1).

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