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PNEUMATIC TIRE

20210394565 · 2021-12-23

    Inventors

    Cpc classification

    International classification

    Abstract

    In a pneumatic tire, a bead filler is on an outer circumference of a bead core, a carcass turned up end is inward of an outer diameter side end of the bead filler, the carcass end is spaced from a carcass body, a steel reinforcement is in each bead, a sidewall rubber extends from the sidewall to the bead, and a support layer is between the bead filler and the sidewall rubber to cover the carcass end and an end of the steel reinforcement, the support layer extending toward an outer diameter side and contacting the carcass body on an outer diameter side of the bead filler outer diameter side end, and a 100% modulus of the support layer is at least 1.5 times that of the bead filler, and the sidewall rubber, the bead filler and the sidewall rubber being adjacent to the support layer.

    Claims

    1. A pneumatic tire, comprising: a tread portion extending in a tire circumferential direction and having an annular shape; a pair of sidewall portions respectively disposed on both sides of the tread portion; a pair of bead portions each disposed on an inner side in a tire radial direction of the sidewall portions; and a carcass layer mounted between the pair of bead portions and comprising a plurality of steel cords, the carcass layer being turned up around a bead core of each of the bead portions from a tire inner side to a tire outer side, a bead filler being disposed on an outer circumference of the bead core of each of the bead portions, a turned up end portion of the carcass layer being disposed on a radially inner side with respect to a radially outer side end portion of the bead filler, the turned up end portion of the carcass layer being spaced apart from a body portion of the carcass layer, a steel reinforced layer that comprises a plurality of steel cords being disposed in each of the bead portions in such a manner as to wrap around the carcass layer, the bead core, and the bead filler, and a sidewall rubber layer exposed on a tire outer surface being disposed from the sidewall portion to the bead portion, and a rubber reinforcing support layer being disposed between the bead filler and the sidewall rubber layer in such a manner as to cover a turned up end portion of the carcass layer and an end portion of the steel reinforced layer, the rubber reinforcing support layer at least extending from a position lateral to the bead core toward a radially outer side and contacting the body portion of the carcass layer at a position on a radially outer side with respect to a radially outer side end portion of the bead filler, and a 100% modulus K.sub.M100 of the rubber reinforcing support layer being at least 1.5 times as large as each of a 100% modulus BF.sub.M100 of the bead filler and a 100% modulus S.sub.M100 of the sidewall rubber layer, the bead filler and the sidewall rubber layer being adjacent to the rubber reinforcing layer.

    2. The pneumatic tire according to claim 1, wherein the rubber reinforcing support layer has a 100% modulus K.sub.M100 of from 4.5 MPa to 10.0 MPa.

    3. The pneumatic tire according to claim 1, wherein the rubber reinforcing support layer has a thickness TK of from 2.0 mm to 6.0 mm in a region from the turned up end portion of the carcass layer to the radially outer side end portion of the bead filler.

    4. The pneumatic tire according to claim 1, wherein the rubber reinforcing support layer comprises a crack suppression layer contacting the turned up end portion of the carcass layer and an end portion of the steel reinforced layer, and a rubber reinforcing body layer contiguous with the crack suppression layer, the crack suppression layer has an elongation at break Kc.sub.EB of 300% or more, and a 100% modulus Km.sub.M100 of the rubber reinforcing body layer is greater than a 100% modulus Kc.sub.M100 of the crack suppression layer.

    5. The pneumatic tire according to claim 4, wherein the crack suppression layer has a length Ic of 30 mm or more in a region from the turned up end portion of the carcass layer to the radially outer side end portion of the bead filler, and the crack suppression layer has a thickness Tc of 3.0 mm or more at the turned up end portion of the carcass layer.

    6. The pneumatic tire according to claim 1, wherein a distance A measured along a straight line extending through an apex of the bead core projecting farthest to the outer side in the width direction, the straight line extending parallel to a long side of the bead core and the distance A being measured from the apex to a bead heel position, is 2.5 mm or more, and a shortest distance T.sub.1 from the turned up end portion of the carcass layer to an outer surface of the bead portion is 10 mm or less.

    7. The pneumatic tire according to claim 1, wherein a shortest distance T.sub.BF from the turned up end portion of the carcass layer to the body portion of the carcass layer and the shortest distance T.sub.1 from the turned up end portion of the carcass layer to the outer surface of the bead portion satisfy a relationship 0.50≤T.sub.1/T.sub.BF≤0.65.

    8. The pneumatic tire according to claim 1, wherein a distance P.sub.h from a center of the bead core to the turned up end portion of the carcass layer ranges from 26.0 mm to 40.0 mm, the shortest distance T.sub.BF from the turned up end portion of the carcass layer to the body portion of the carcass layer is 11.0 mm or more, and the shortest distance T.sub.1 from the turned up end portion of the carcass layer to the outer surface of the bead portion is 7.0 mm or more.

    9. The pneumatic tire according to claim 1, wherein the distance P.sub.h from the center of the bead core to the turned up end portion of the carcass layer and a distance S.sub.ho from the center of the bead core to the end portion of the steel reinforced layer satisfies a relationship 5.0 mm≤P.sub.h-S.sub.ho.

    10. The pneumatic tire according to claim 1, wherein the bead filler comprises a hard filler layer located on the radially inner side and a soft filler layer located on the radially outer side, the hard filler layer has a 100% modulus B1.sub.M100 of from 6.0 MPa to 18.0 MPa, and the soft filler layer has a 100% modulus B2.sub.M100 of from 1.0 MPa to 6.0 MPa.

    11. The pneumatic tire according to claim 1, having a load index of 121 or more on a single wheel, or a ply rating of 10 PR or more.

    12. The pneumatic tire according to claim 2, wherein the rubber reinforcing support layer has a thickness T.sub.K of from 2.0 mm to 6.0 mm in a region from the turned up end portion of the carcass layer to the radially outer side end portion of the bead filler.

    13. The pneumatic tire according to claim 12, wherein the rubber reinforcing support layer comprises a crack suppression layer contacting the turned up end portion of the carcass layer and an end portion of the steel reinforced layer, and a rubber reinforcing body layer contiguous with the crack suppression layer, the crack suppression layer has an elongation at break Kc.sub.EB of 300% or more, and a 100% modulus Km.sub.M100 of the rubber reinforcing body layer is greater than a 100% modulus Kc.sub.M100 of the crack suppression layer.

    14. The pneumatic tire according to claim 13, wherein the crack suppression layer has a length Ic of 30 mm or more in a region from the turned up end portion of the carcass layer to the radially outer side end portion of the bead filler, and the crack suppression layer has a thickness Tc of 3.0 mm or more at the turned up end portion of the carcass layer.

    15. The pneumatic tire according to claim 14, wherein a distance A measured along a straight line extending through an apex of the bead core projecting farthest to the outer side in the width direction, the straight line extending parallel to a long side of the bead core and the distance A being measured from the apex to a bead heel position, is 2.5 mm or more, and a shortest distance T.sub.1 from the turned up end portion of the carcass layer to an outer surface of the bead portion is 10 mm or less.

    16. The pneumatic tire according to claim 15, wherein a shortest distance T.sub.BF from the turned up end portion of the carcass layer to the body portion of the carcass layer and the shortest distance T.sub.1 from the turned up end portion of the carcass layer to the outer surface of the bead portion satisfy a relationship 0.5 0≤T.sub.1/T.sub.BF≤0.65.

    17. The pneumatic tire according to claim 16, wherein a distance P.sub.h from a center of the bead core to the turned up end portion of the carcass layer ranges from 26.0 mm to 40.0 mm, the shortest distance T.sub.BF from the turned up end portion of the carcass layer to the body portion of the carcass layer is 11.0 mm or more, and the shortest distance T.sub.1 from the turned up end portion of the carcass layer to the outer surface of the bead portion is 7.0 mm or more.

    18. The pneumatic tire according to claim 17, wherein the distance P.sub.h from the center of the bead core to the turned up end portion of the carcass layer and a distance S.sub.ho from the center of the bead core to the end portion of the steel reinforced layer satisfies a relationship 5.0 mm≤P.sub.h-S.sub.ho.

    19. The pneumatic tire according to claim 18, wherein the bead filler comprises a hard filler layer located on the radially inner side and a soft filler layer located on the radially outer side, the hard filler layer has a 100% modulus B1.sub.M100 of from 6.0 MPa to 18.0 MPa, and the soft filler layer has a 100% modulus B2.sub.M100 of from 1.0 MPa to 6.0 MPa.

    20. The pneumatic tire according to claim 19, having a load index of 121 or more on a single wheel, or a ply rating of 10 PR or more.

    Description

    BRIEF DESCRIPTION OF DRAWINGS

    [0019] FIG. 1 is a meridian cross-sectional view illustrating a heavy duty pneumatic tire according to an embodiment of the present technology.

    [0020] FIG. 2 is a cross-sectional view of a bead portion of the pneumatic tire in FIG. 1.

    [0021] FIG. 3 is another cross-sectional view illustrating the bead portion of the pneumatic tire in FIG. 1.

    [0022] FIG. 4 is yet another cross-sectional view illustrating the bead portion of the pneumatic tire in FIG. 1. FIG. 5 is a cross-sectional view illustrating a modified example of the bead portion.

    [0023] FIG. 6 is a cross-sectional view illustrating another modified example of the bead portion.

    [0024] FIG. 7 is a cross-sectional view illustrating yet another modified example of the bead portion.

    DETAILED DESCRIPTION

    [0025] Configurations of embodiments of the present technology will be described in detail below with reference to the accompanying drawings. FIG. 1 illustrates a heavy duty pneumatic tire according to an embodiment of the present technology, and FIG. 2 to FIG. 4 illustrate a bead portion of the pneumatic tire.

    [0026] As illustrated in FIG. 1, a pneumatic tire of the present embodiment includes an annular tread portion 1 extending in the tire circumferential direction, a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3, 3 disposed on an inner side of the sidewall portions 2 in the tire radial direction.

    [0027] A carcass layer 4 is mounted between the pair of bead portions 3, 3. The carcass layer 4 includes a plurality of steel cords extending in the tire radial direction and is turned up around a bead core 5 disposed in each of the bead portions 3 from a tire inner side to a tire outer side. A bead filler 6 having a triangular cross-sectional shape and formed of a rubber composition is disposed on the outer circumference of the bead core 5.

    [0028] Four belt layers 7 are embedded on the radially outer side of the carcass layer 4 in the tread portion 1. Each of the belt layers 7 includes a plurality of belt cords (steel cords) inclined with respect to the tire circumferential direction. The belt layers 7 include two central main belt layers 72 and 73 with belt cords intersecting with each other, and auxiliary belt layers 71 and 74 disposed on the radially inner side and the radially outer side of the main belt layers 72 and 73. The inclination angle of the belt cords constituting the main belt layers 72 and 73 with respect to the tire circumferential direction is set to range from 15° to 35°, for example, and the inclination angle of the belt cords constituting the auxiliary belt layers 71 and 74 with respect to the tire circumferential direction is set to range from 15° to 75°, for example.

    [0029] In the pneumatic tire described above, as illustrated in FIG. 2, a turned up end portion 4e of the carcass layer 4 is disposed on the radially inner side of a radially outer side end portion 6e of the bead filler 6, that is, the turned up end portion 4e of the carcass layer 4 terminates in a middle portion of the bead filler 6. As a result, the turned up end portion 4e of the carcass layer 4 is spaced apart from the body portion of the carcass layer 4. Here, the turned up end portion 4e of the carcass layer 4 being spaced apart from the body portion of the carcass layer 4 means that the shortest distance T.sub.BF (see FIG. 4) from the turned up end portion 4e of the carcass layer 4 to the body portion of the carcass layer 4 is 8 mm or more. A steel reinforced layer 11 including a plurality of steel cords is disposed in each of the bead portions 3 in such a way as to wrap around the carcass layer 4, the bead core 5 , and the bead filler 6. Furthermore, a sidewall rubber layer 12 exposed on the tire outer surface is disposed in a region extending from the sidewall portion 2 to the bead portion 3.

    [0030] Additionally, an edge tape 13 made of rubber covers the turned up end portion 4e of the carcass layer 4 and a tire width direction outer end portion 11e of the steel reinforced layer 11. The edge tape 13 is not necessarily required, but is effective from the perspective of separation prevention. The edge tape 13 has a thickness of from 0.5 mm to 1.8 mm and covers the metal cross section of the steel cord exposed at the turned up end portion 4e of the carcass layer 4 and the end portion 11e of the steel reinforced layer 11. The edge tape 13 preferably has an elongation at break of 300% or more and a 100% modulus of 5.0 MPa or more.

    [0031] A rubber reinforcing support layer 14 is disposed between the bead filler 6 and the sidewall rubber layer 12. The rubber reinforcing support layer 14 is disposed covering the turned up end portion 4e of the carcass layer 4 and the end portion 11e of the steel reinforced layer 11, and at least extends from a position lateral to the bead core 5 toward the radially outer side, and contacts the body portion of the carcass layer 4 at a position on the radially outer side with respect to the radially outer side end portion 6e of the bead filler 6. The rubber reinforcing support layer 14 needs to be at least present at a position lateral to the bead core 5 , but may wrap around to the radially inner side of the bead core 5 and extend to the bead toe as illustrated in FIG. 2. The 100% modulus K.sub.M100 of the rubber reinforcing support layer 14 is set at least 1.5 times and preferably at least 1.7 times as large as each of the 100% modulus BF.sub.M100 of the bead filler 6 and the 100% modulus S.sub.M100 of the sidewall rubber layer 12.

    [0032] According to the pneumatic tire described above, the rubber reinforcing support layer 14 covering the turned up end portion 4e of the carcass layer 4 and the end portion 11e of the steel reinforced layer 11 is disposed between the bead filler 6 and the sidewall rubber layer 12, the rubber reinforcing support layer 14 at least extends from the position lateral to the bead core 5 toward the radially outer side and contacts the body portion of the carcass layer 4 at the position on the radially outer side with respect to the radially outer side end portion 6e of the bead filler 6, and the 100% modulus K.sub.M100 of the rubber reinforcing support layer 14 is set at least 1.5 times as large as the 100% modulus BF.sub.M100 of bead filler 6 and 100% modulus S.sub.M100 of the sidewall rubber layer 12, the bead filler 6 and the sidewall rubber layer 12 being adjacent to the rubber reinforcing support layer. Thus, the rubber reinforcing support layer 14 effectively suppresses a flow of rubber present laterally to the bead core 5 , toward the tire outer diameter side during vulcanization. As a result, it is possible to suppress a reduction in thickness of the rubber present on the side of the bead core 5 and an increase in thickness of the rubber present on the outer side in the tire width direction of the turned up end portion 4e of the carcass layer 4 is suppressed, and the carcass line of the bead portion 3 of the pneumatic tire can be brought closer to the target balanced profile. In addition, the rubber reinforcing support layer 14 suppresses a rubber flow in the bead portion 3, and thus trapping of a release agent and the like caused by the rubber flow is prevented, allowing suppression of cracking of a bead portion surface during an initial traveling stage. By thus providing the bead portion 3 with an appropriate carcass line and suppressing cracking caused by the rubber flow, the durability of the bead portions can be improved.

    [0033] In the pneumatic tire described above, the rubber reinforcing support layer 14 may have a 100% modulus K.sub.M100 of from 4.5 MPa to 10.0 MPa. Accordingly, the rubber flow during vulcanization is effectively suppressed, allowing suppression of cracking of a bead portion surface during the initial traveling stage. When the 100% modulus K.sub.M100 of the rubber reinforcing support layer 14 is less than 4.5 MPa, the effect of reinforcing and supporting the sidewall rubber layer 12 is insufficient, preventing effective suppression of the rubber flow in the sidewall rubber layer 12 and the rubber reinforcing support layer 14. Additionally, when the 100% modulus K.sub.M100 of the rubber reinforcing support layer 14 is more than 10.0 MPa, the rubber reinforcing support layer 14 is excessively rigid. This may increase strain at the turned up end portion 4e caused by displacement of the body portion of the carcass layer 4 at the time of contact with the ground, causing separation originating from the turned up end portion 4e. In particular, the 100% modulus K.sub.M100 of the rubber reinforcing support layer 14 preferably ranges from 6.0 MPa to 9.0 MPa. Note that, in a case where the 100% modulus K.sub.M100 of the rubber reinforcing support layer 14 is increased, the Mooney viscosity in the unvulcanized state tends to increase but the Mooney viscosity in the unvulcanized state defined by JIS-K6300-1 preferably ranges from 70 to 100 (ML(1+4)100° C.).

    [0034] In the pneumatic tire described above, as illustrated in FIG. 3, the rubber reinforcing support layer 14 may have a thickness T.sub.K of from 2.0 mm to 6.0 mm in a region X from the turned up end portion 4e of the carcass layer 4 to the radially outer side end portion 6e of the bead filler 6. Accordingly, the rubber flow during vulcanization is effectively suppressed, allowing suppression of cracking of a bead portion surface during the initial traveling stage. Note that the thickness TK of the rubber reinforcing support layer 14 is a thickness measured in a direction orthogonal to a center line passing through a center position of the rubber reinforcing support layer 14 in the thickness direction.

    [0035] When the thickness TK of the rubber reinforcing support layer 14 is less than 2.0 mm, the effect of reinforcing and supporting the sidewall rubber layer 12 is insufficient, preventing effective suppression of the rubber flow in the sidewall rubber layer 12 and the rubber reinforcing support layer 14. Additionally, when the thickness TK of the rubber reinforcing support layer 14 is more than 6.0 mm, the rubber reinforcing support layer 14 is excessively rigid, and thus strain amplitude in the tire radial direction may increase at the turned up end portion 4e of the carcass layer 4, causing separation originating from the turned up end portion 4e. In particular, the thickness TK of the rubber reinforcing support layer 14 preferably ranges from 2.5 mm to 5.0 mm.

    [0036] In the pneumatic tire described above, as illustrated in FIG. 3, a distance A measured along a straight line D extending through an apex E of the bead core 5 projecting farthest to the outer side in the width direction, the straight line extending parallel to the long sides of the bead core 5 and the distance A being measured from the apex E to a bead heel position, may be 2.5 mm or more, and the shortest distance T.sub.1 from the turned up end portion 4e of the carcass layer 4 to an outer surface of the bead portion 3 may be 10 mm or less.

    [0037] This allows formation of a carcass line less susceptible to a profile change caused by air pressure inflation (a balanced profile), and thus the strain amplitude at the turned up end portion 4e of the carcass layer 4 is suppressed, allowing effective suppression of separation of the carcass layer 4 originating from the turned up end portion 4e.

    [0038] Note that a specific determination of the distance A is as follows. The bead core 5 has a multilayer structure in which a plurality of wires are arranged in a tire meridian cross-section. The apex E is a point where a straight line extending through the center of gravity of a wire located on the outermost side of the bead core 5 in the width direction, the straight line being parallel to the long sides of the bead core 5 , meets the contour of the wire located on the outermost side in the width direction. In a case where a straight line D, a virtual intersection point H, a straight line J, and a straight line F are determined; the straight line D extending through the apex E of the bead core 5 projecting farthest to the outer side in the width direction, the straight line D that is parallel to the long sides of the bead core 5 , the virtual intersection point H is a point where an extension line of a side P forming the profile of a bead bottom surface meets an extension line of a curve G forming the profile of a bead back surface, the straight line J extending through the virtual intersection point H and being orthogonal to the straight line D, and the straight line F extending through the apex E and being orthogonal to the straight line D, the distance A is the length of a line segment on the straight line D defined between the straight line J and the straight line F.

    [0039] When the distance A is more than 2.5 mm, the position of the bead core 5 is located on the bead heel side, and thus the carcass line from the bead core 5 to the turned up end portion 4e of the carcass layer 4 is a line standing in the tire radial direction. In other words, the carcass line exhibits a significant profile change between before and after air pressure inflation. In particular, the distance A is preferably 3.0 mm or more, and the upper limit of the distance A may be 8.0 mm. On the other hand, when the shortest distance T.sub.1 from the turned up end portion 4e of the carcass layer 4 to the outer surface of the bead portion 3 is more than 10 mm, the carcass line of the body portion of the carcass layer 4 protrudes toward the tire inner side in order to keep the shortest distance T.sub.BF from the turned up end portion 4e of the carcass layer 4 to the body portion of the carcass layer 4 comparable with the shortest distance T.sub.1. Thus, the carcass line is susceptible to a significant profile change between before and after air pressure inflation. In particular, the shortest distance T.sub.1 is preferably 9.0 mm or less.

    [0040] In the pneumatic tire described above, as illustrated in FIG. 4, the shortest distance T.sub.BF from the turned up end portion 4e of the carcass layer 4 to the body portion of the carcass layer 4 and the shortest distance T.sub.1 from the turned up end portion 4e of the carcass layer 4 to the outer surface of the bead portion 3 preferably satisfy a relationship 0.50≤T.sub.1/T.sub.BF≤0.65. This effectively suppresses separation of the carcass layer 4 originating from the turned up end portion 4e and also suppresses trapping of rubber at or near the turned up end portion 4e of the carcass layer 4, allowing suppression of cracking of the bead portion surface during the initial traveling stage.

    [0041] When T.sub.1/T.sub.BF is less than 0.5, the turned up end portion 4e of the carcass layer 4 is disposed on a compression side with respect to a neutral axis of bending deformation of the bead portion 3 during vulcanization. Thus, the rubber is likely to be trapped at or near the turned up end portion 4 of the carcass layer 4, and the bead portion surface may be cracked during the initial traveling stage. In contrast, when T.sub.1/T.sub.BF is more than 0.65, the thickness of the bead filler 6 corresponding to the shortest distance T.sub.BF is reduced to increase the strain amplitude at the turned up end portion 4e of the carcass layer 4 in the tire radial direction, and separation of the carcass layer 4 may originate from the turned up end portion 4e.

    [0042] In the pneumatic tire described above, as illustrated in FIG. 4, the distance P.sub.h from the center of the bead core 5 to the turned up end portion 4e of the carcass layer 4 may range from 26.0 mm to 40.0 mm, the shortest distance T.sub.BF from the turned up end portion 4e of the carcass layer 4 to the body portion of the carcass layer 4 may be 11.0 mm or more, and the shortest distance T.sub.1 from the turned up end portion 4e of the carcass layer 4 to the outer surface of the bead portion 3 may be 7.0 mm or more. This allows effective suppression of separation of the carcass layer 4 originating from the turned up end portion 4e. Note that the center of the bead core 5 is the intersection point between diagonal lines of a virtual quadrangle formed by joining center points of the four wires of the wires constituting the bead core 5 in a case where the wires are selected to maximize the area of the virtual rectangle.

    [0043] When the distance P.sub.h from the center of the bead core 5 to the turned up end portion 4e of the carcass layer 4 is less than 26.0 mm, the carcass layer 4 may get pulled out. In contrast, when the distance P.sub.h is more than 40.0 mm, the turned up end portion 4e of the carcass layer 4 is disposed in a region of the bead portion 3 where significant deformation occurs, and thus separation of the carcass layer may originate from the 4 turned up end portion 4e. In particular, the distance P.sub.h from the center of the bead core 5 to the turned up end portion 4e of the carcass layer 4 is preferably 28.0 mm to 38.0 mm. Additionally, when the shortest distance T.sub.BF from the turned up end portion 4e of the carcass layer 4 to the body portion of the carcass layer 4 is less than 11.0 mm, or the shortest distance T.sub.1 from the turned up end portion 4e of the carcass layer 4 to the outer surface of the bead portion 3 is less than 7.0 mm, an insufficient rubber volume may increase the strain amplitude at the turned up end portion 4e of the carcass layer 4 in the tire radial direction, causing separation of the carcass layer 4 originating from the turned up end portion 4e. The upper limit value of the shortest distance T.sub.BF may be 18.0 mm.

    [0044] In the pneumatic tire described above, as illustrated in FIG. 4, the distance P.sub.h from the center of the bead core 5 to the turned up end portion 4e of the carcass layer 4 and the distance S.sub.ho from the center of the bead core 5 to the end portion 11e of the steel reinforced layer 11 may satisfy a relationship 5.0 mm≤P.sub.h-S.sub.ho. This mitigates the stress concentration at the turned up end portion 4e of the carcass layer 4 and at the end portion 11e of the steel reinforced layer 11, allowing effective suppression of separation originating from the end portions 4e and 11e. When the value of P.sub.h-S.sub.ho is less than 5 mm, the strain at the turned up end portion 4e of the carcass layer 4 increases, and separation of the carcass layer 4 may originate from the turned up end portion 4e.

    [0045] FIGS. 5 and 6 each illustrate a modified example of the bead portion. In FIGS. 5 and 6, the rubber reinforcing support layer 14 includes a crack suppression layer 14A contacting the turned up end portion 4e of the carcass layer 4 and the tire width direction outer end portion 11e of the steel reinforced layer 11, and a rubber reinforcing body layer 14B contiguous with the crack suppression layer 14A. The crack suppression layer 14A and the rubber reinforcing body layer 14B are formed from different types of rubber compositions. The crack suppression layer 14A has an elongation at break KcEB of 300% or more, and the rubber reinforcing body layer 14B has a 100% modulus Km.sub.M100 greater than the 100% modulus Kc.sub.M100 of the crack suppression layer. Note that, in a case where the rubber reinforcing support layer 14 includes the crack suppression layer 14A and the rubber reinforcing body layer 14B, the 100% modulus K.sub.M100 of the rubber reinforcing support layer 14 has a value equal to the value of the 100% modulus Km.sub.M100 of the rubber reinforcing body layer 14B.

    [0046] In a case where the rubber reinforcing support layer 14 thus includes the crack suppression layer 14A and the rubber reinforcing body layer 14B, separation can be effectively suppressed by increasing the elongation at break Kc.sub.EB of the crack suppression layer, which contacts the turned up end portion 4e of the carcass layer 4 and an end portion 11e of the steel reinforced layer 11. On the other hand, for the rubber reinforcing body layer 14, the 100% modulus Km.sub.M100 can be increased with a decrease in elongation at break allowed, thus suppressing the rubber flow during vulcanization to allow effective suppression of cracking of the bead portion surface during the initial traveling stage. When the elongation at break Kc.sub.EB of the crack suppression layer 14A is less than 300%, the effect of suppressing separation is reduced. The upper limit value of the elongation at break Kc.sub.EB of the crack suppression layer 14A may be 500%.

    [0047] The embodiments in FIGS. 5 and 6 differ from each other in the distribution of the rubber volume between the crack suppression layer 14A and the rubber reinforcing body layer 14B. However, the distribution of the rubber volume can be selected in a discretionary manner as long as the crack suppression layer 14A contacts the turned up end portion 4e of the carcass layer 4 and the tire width direction outer end portion 11e of the steel reinforced layer 11. Additionally, in the embodiments in FIGS. 5 and 6, a tire width direction inner end portion 11e of the steel reinforced layer 11 is also covered with the edge tape 13. The edge tape 13 as described above can be added in a discretionary manner.

    [0048] In the pneumatic tire described above, the crack suppression layer 14A may have a length Ic of 30 mm or more in a region from the turned up end portion 4e of the carcass layer 4 to the radially outer side end portion 6e of the bead filler 6, and the crack suppression layer 14A may have a thickness Tc of 3.0 mm or more at the turned up end portion 4e of the carcass layer 4. This allows effective suppression of separation of the carcass layer 4 originating from the turned up end portion 4e and separation of the steel reinforced layer 11 originating from the end portion 11e. Note that the length Ic and the thickness Tc of the crack suppression layer 14A correspond to thicknesses including the thickness of the edge tape 13.

    [0049] When the length Ic of the crack suppression layer 14A is less than 30 mm, the effect of suppressing separation is reduced. Additionally, when the thickness Tc of the crack suppression layer 14A at the turned up end portion 4e of the carcass layer 4 is less than 3.0 mm, the effect of suppressing separation is reduced.

    [0050] FIG. 7 illustrates another modified example of the bead portion. In FIG. 7, the bead filler 6 includes a hard filler layer 61 located on the radially inner side and a soft filler layer 62 located on the radially outer side, and the hard filler layer 61 has a 100% modulus B1.sub.M100 set within a range from 6.0 MPa to 18.0 MPa, and the soft filler layer 62 has a 100% modulus B2.sub.M100 set within a range from 1.0 MPa to 6.0 MPa. More specifically, the turned up end portion 4e of the carcass layer 4 terminates at a position adjacent to the soft filler layer 62.

    [0051] This allows effective suppression of separation of the carcass layer 4 originating from the turned up end portion 4e. Note that, in a case where the bead filler 6 includes the hard filler layer 61 and the soft filler layer 62, the 100% modulus BF.sub.M100 of the bead filler 6 has a value equal to the value of the 100% B2.sub.M100 of the soft filler layer 62.

    [0052] When the 100% modulus B1.sub.M100 of the hard filler layer 61 is less than 6.0 MPa, the bead portion 3 is excessively flexed when a load is applied, and thus separation of the carcass layer 4 may originate from the turned up end portion 4e. Additionally, when the 100% modulus B1.sub.M100 of the hard filler layer 61 is more than 18.0 MPa, separation may occur between the body portion of the carcass layer 4 and the hard filler layer 61. In particular, the 100% modulus B1.sub.M100 of the hard filler layer 61 preferably ranges from 8.0 MPa to 16.0 MPa.

    [0053] On the other hand, when the 100% modulus B2.sub.M100 of the soft filler layer 62 is less than 1.0 MPa, the bead portion 3 is excessively flexed when a load is applied, and thus separation of the carcass layer 4 may originate from the turned up end portion 4e. Additionally, when the 100% modulus B2.sub.M100 of the soft filler layer 62 is more than 6.0 MPa, the strain at the turned up end portion 4e of the carcass layer 4 increases, and thus separation of the carcass layer 4 may originate from the turned up end portion 4e. In particular, the 100% modulus B2.sub.M100 of the soft filler layer 62 preferably ranges from 2.0 MPa to 5.0 MPa.

    [0054] The pneumatic tire according to the embodiment described above may have a load index of 121 or more on a single wheel or a ply rating of 10 PR or more. In pneumatic tires having such a load index or ply rating, improving the durability of the bead portions is extremely meaningful.

    EXAMPLES

    [0055] Pneumatic tires according to Conventional Example, Comparative Examples 1 and 2, and Examples 1 to 18 were manufactured. The tires had a tire size of 275/70R22.5, included a tread portion, a pair of sidewall portions, and a pair of bead portions, and included a carcass layer mounted between the pair of bead portions and including a plurality of steel cords, the carcass layer being turned up around a bead core of each of the bead portions from a tire inner side to a tire outer side, the tires differing from one another only in the structure of the bead portions.

    [0056] In the tires according to Conventional Example, Comparative Examples 1 and 2, and Examples 1 to 18, the following were set as indicated in Tables 1 and 2: presence of contact of the rubber reinforcing support layer with the carcass layer body portion, the ratio K.sub.M100/BF.sub.M100 of the 100% modulus K.sub.M100 of the rubber reinforcing support layer to the 100% modulus BF.sub.M100 of the bead filler, the ratio K.sub.M100/S.sub.M100 of the 100% modulus K.sub.M100 of the rubber reinforcing support layer to the 100% modulus S.sub.M100 of the sidewall rubber layer, the 100% modulus K.sub.M100 of the rubber reinforcing support layer, the thickness T.sub.K of the rubber reinforcing support layer, the elongation at break Kc.sub.EB of the crack suppression layer, the 100% modulus Km.sub.M100 of the rubber reinforcing body layer, the 100% modulus Kc.sub.M100 of the crack suppression layer, the length Ic of the crack suppression layer, the thickness Tc of the crack suppression layer, the distance A of the bead core, the shortest distance T.sub.1 from the turned up end portion of the carcass layer to the outer surface of the bead portion, T.sub.1/T.sub.BF, the distance P.sub.h from the center of the bead core to the turned up end portion of the carcass layer, the shortest distance T.sub.BF from the turned up end portion of the carcass layer to the body portion of the carcass layer, the distance S.sub.ho from the center of the bead core to the end portion of the steel reinforced layer, the P.sub.h-S.sub.ho, the 100% modulus B1.sub.M100 of the hard filler layer, and 100% modulus B2.sub.M100 of the soft filler layer.

    [0057] For these test tires, the durability of the bead portions was evaluated using a test method described below, and the results are indicated in Tables 1 and 2.

    [0058] Durability of Bead Portions:

    [0059] Each of the test tires was mounted on a rim specified by JATMA (The Japan Automobile Tyre Manufacturers Association, Inc.), inflated to 75% of the air pressure specified by JATMA, and subjected to a load 1.4 times as heavy as the load specified by JATMA, and running tests were performed on a drum testing machine at a running speed of 49 km/h. After 40,000 km of running, the circumferential lengths of cracks formed on the surfaces of both bead portions were measured. In addition, each test tire was cut at eight locations at equal intervals in the tire circumferential direction along the tire meridian, and the cross-sectional direction lengths of cracks originating from the turned up end portion of the carcass layer were measured in cut surfaces at the eight locations of both bead portions (a total of 16 locations). Furthermore, the sum of the circumferential length of the cracks in the bead portion surface and the cross-sectional direction lengths of the cracks in the bead portion cross section was determined. The evaluation results were expressed, using the reciprocal of the measurement values, as index values with the value of the Conventional Example being defined as 100. Larger index values indicate superior durability of the bead portion.

    TABLE-US-00001 TABLE 1 Conventional Example Comparative Example 1 Example 1 Contact of rubber reinforcing support layer No Yes No with carcass layer body portion K.sub.M100/BF.sub.M100 — 2.9 2.9 K.sub.M100/S.sub.M100 — 3.8 3.8 Modulus K.sub.M100 (MPa) of rubber reinforcing — 8.0 8.0 support layer Thickness T.sub.K (mm) of rubber reinforcing — 3.5 3.5 support layer Elongation at break Kc.sub.EB (%) of crack — 370 370 suppression layer Modulus Km.sub.M100 (MPa) of rubber — 8.0 8.0 reinforcing body layer Modulus Kc.sub.M100 (MPa) of crack suppression — 5.5 5.5 layer Length Ic (mm) of crack suppression layer — 50 50 Thickness Tc (mm) of crack suppression — 3.5 3.5 layer Distance A (mm) of bead core 0.0 3.6 2.0 Shortest distance T.sub.1 (mm) 7.6 8.5 8.5 T.sub.1/T.sub.BF 0.54 0.61 0.61 Distance P.sub.h (mm) 33.0 33.0 33.0 Shortest distance T.sub.BF (mm) 14.0 14.0 14.0 Distance S.sub.ho (mm) 23.0 23.0 23.0 P.sub.h − S.sub.ho 10.0 10.0 10.0 Modulus B1.sub.M100 (MPa) of hard filler layer 12.6 12.6 12.6 Modulus B2.sub.M100 (MPa) of soft filler layer 2.8 2.8 2.8 Durability (index) of bead portions 100 180 120 Comparative Example Example Example Example 2 2 3 4 Contact of rubber reinforcing support Yes Yes Yes Yes layer with carcass layer body portion K.sub.M100/BF.sub.M100 1.0 1.5 4.3 2.9 K.sub.M100/S.sub.M100 1.3 2.0 5.7 3.8 Modulus K.sub.M100 (MPa) of rubber 2.8 4.2 12.0 8.0 reinforcing support layer Thickness T.sub.K (mm) of rubber 3.5 3.5 3.5 1.5 reinforcing support layer Elongation at break Kc.sub.EB (%) of crack 450 370 370 370 suppression layer Modulus Km.sub.M100 (MPa) of rubber 2.8 4.2 12.0 8.0 reinforcing body layer Modulus Kc.sub.M100 (MPa) of crack 2.8 5.5 5.5 5.5 suppression layer Length Ic (mm) of crack suppression 50 50 50 50 layer Thickness Tc (mm) of crack 3.5 3.5 3.5 3.5 suppression layer Distance A (mm) of bead core 0.5 3.6 3.6 3.6 Shortest distance T.sub.1 (mm) 12.0 8.5 8.5 8.5 T.sub.1/T.sub.BF 0.86 0.61 0.61 0.61 Distance P.sub.h (mm) 33.0 33.0 33.0 33.0 Shortest distance T.sub.BF (mm) 14.0 14.0 14.0 14.0 Distance S.sub.ho (mm) 23.0 23.0 23.0 23.0 P.sub.h − S.sub.ho 10.0 10.0 10.0 10.0 Modulus B1.sub.M100 (MPa) of hard filler 12.6 12.6 12.6 12.6 layer Modulus B2.sub.M100 (MPa) of soft filler 2.8 2.8 2.8 2.8 layer Durability (index) of bead portions 100 135 175 140 Example Example Example Example 5 6 7 8 Contact of rubber reinforcing support layer Yes Yes Yes Yes with carcass layer body portion K.sub.M100/BF.sub.M100 2.9 2.9 2.9 2.9 K.sub.M100/S.sub.M100 3.8 3.8 3.8 3.8 Modulus K.sub.M100 (MPa) of rubber reinforcing 8.0 8.0 8.0 8.0 support layer Thickness T.sub.K (mm) of rubber reinforcing 7.0 3.5 3.5 3.5 support layer Elongation at break Kc.sub.EB (%) of crack 370 200 370 — suppression layer Modulus Km.sub.M100 (MPa) of rubber 8.0 8.0 8.0 8.0 reinforcing body layer Modulus Kc.sub.M100 (MPa) of crack 5.5 10.0 5.5 — suppression layer Length Ic (mm) of crack suppression layer 50 50 10 — Thickness Tc (mm) of crack suppression 3.5 3.5 1.0 — layer Distance A (mm) of bead core 3.6 3.6 3.6 3.6 Shortest distance T.sub.1 (mm) 8.5 8.5 8.5 8.5 T.sub.1/T.sub.BF 0.61 0.61 0.61 0.61 Distance P.sub.h (mm) 33.0 33.0 33.0 33.0 Shortest distance T.sub.BF (mm) 14.0 14.0 14.0 14.0 Distance S.sub.ho (mm) 23.0 23.0 23.0 23.0 P.sub.h − S.sub.ho 10.0 10.0 10.0 10.0 Modulus B1.sub.M100 (MPa) of hard filler layer 12.6 12.6 12.6 12.6 Modulus B2.sub.M100 (MPa) of soft filler layer 2.8 2.8 2.8 2.8 Durability (index) of bead portions 140 148 153 150

    TABLE-US-00002 TABLE 2 Example Example Example Example Example 9 10 11 12 13 Contact of rubber reinforcing Yes Yes Yes Yes Yes support layer with carcass layer body portion K.sub.M100/BF.sub.M100 2.9 2.9 2.9 2.9 2.9 K.sub.M100/S.sub.M100 3.8 3.8 3.8 3.8 3.8 Modulus K.sub.M100 (MPa) of rubber 8 8 8 8 8 reinforcing support layer Thickness T.sub.K (mm) of rubber 3.5 3.5 3.5 3.5 3.5 reinforcing support layer Elongation at break Kc.sub.EB (%) of 370 370 370 370 370 crack suppression layer Modulus Km.sub.M100 (MPa) of rubber 8 8 8 8 8 reinforcing body layer Modulus Kc.sub.M100 (MPa) of crack 5.5 5.5 5.5 5.5 5.5 suppression layer Length Ic (mm) of crack 50 50 50 50 50 suppression layer Thickness Tc (mm) of crack 3.5 3.5 3.5 3.5 3.5 suppression layer Distance A (mm) of bead core 1 3.6 3.6 3.6 3.6 Shortest distance T.sub.1 (mm) 8.5 11.5 8.5 8.5 5 T.sub.1/T.sub.BF 0.61 0.82 0.5 0.85 0.36 Distance P.sub.h (mm) 33 33 23 42 33 Shortest distance T.sub.BF (mm) 14 14 17 10 14 Distance S.sub.ho (mm) 23 23 23 23 23 P.sub.h − S.sub.ho 10 10 0 19 10 Modulus B1.sub.M100 (MPa) of hard 12.6 12.6 12.6 12.6 12.6 filler layer Modulus B2.sub.M100 (MPa) of soft 2.8 2.8 2.8 2.8 2.8 filler layer Durability (index) of bead portions 158 167 170 169 171 Example Example Example Example Example 14 15 16 17 18 Contact of rubber reinforcing Yes Yes Yes Yes Yes support layer with carcass layer body portion K.sub.M100/BF.sub.M100 2.9 2.9 2.9 10 1 K.sub.M100/S.sub.M100 3.8 3.8 3.8 3.8 3.8 Modulus K.sub.M100 (MPa) of rubber 8 8 8 8 8 reinforcing support layer Thickness T.sub.K (mm) of rubber 3.5 3.5 3.5 3.5 3.5 reinforcing support layer Elongation at break Kc.sub.EB (%) of 370 370 370 370 370 crack suppression layer Modulus Km.sub.M100 (MPa) of rubber 8 8 8 8 8 reinforcing body layer Modulus Kc.sub.M100 (MPa) of crack 5.5 5.5 5.5 5.5 5.5 suppression layer Length Ic (mm) of crack 50 50 50 50 50 suppression layer Thickness Tc (mm) of crack 3.5 3.5 3.5 3.5 3.5 suppression layer Distance A (mm) of bead core 3.6 3.6 3.6 3.6 3.6 Shortest distance T.sub.1 (mm) 8.5 8.5 8.5 8.5 8.5 T.sub.1/T.sub.BF 0.61 0.61 0.61 0.61 0.61 Distance P.sub.h (mm) 33 33 33 33 33 Shortest distance T.sub.BF (mm) 14 14 14 14 14 Distance S.sub.ho (mm) 30 23 23 23 23 P.sub.h − S.sub.ho 3 10 10 10 10 Modulus B1.sub.M100 (MPa) of hard 12.6 4 20 12.6 12.6 filler layer Modulus B2.sub.M100 (MPa) of soft 2.8 2.8 2.8 0.8 8 filler layer Durability (index) of bead portions 175 176 176 178 178

    [0060] As can be seen from Tables 1 and 2, the tires of Examples 1 to 18 have improved the durability of the bead portions compared to that of Conventional Example. On the other hand, the tires of Comparative Examples 1 and 2 are not sufficiently effective for improving the durability of the bead portions.