JP2017214016A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire achieving improvement in durability.SOLUTION: In a pneumatic tire 2, a bead 10 comprises: a core 36; a first apex 38 extending outward in a radial direction from the core 36; and a second apex 40 contacted with the first apex 38 and positioned between the first apex 38 and a folding part 50 of a carcass ply 46. The second apex 40 is tapered inward in a radial direction. Hardness H1 of the first apex 38 is higher than hardness H2 of the second apex 40. In the radial direction, an inner end 44 of the second apex 40 is positioned closer to outside than an outer end parallel to a cross section 54 of wire in a cross section of the core 36. A ratio (L4/WC) of a height L4 from the outer end parallel to the cross section 54 of the wire to the inner end 44 of the second apex 40 to a width WC of the core 36 is 0.4 or more and 0.9 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire. In particular, the present invention relates to heavy duty pneumatic tires for trucks, buses and the like.

  As the tire travels, the tire repeats deformation and restoration. In heavy duty pneumatic tires for trucks, buses, etc., large loads are often applied. In a heavy-duty pneumatic tire, deformation at the bead portion is particularly large. This deformation can cause damage to the bead portion when the tire is used for a long time. High durability is required for the bead portion.

  In many tires, the carcass ply is folded around the bead, whereby a main portion and a folded portion are formed in the carcass ply. When a load is applied to the tire, the bead portion is greatly distorted toward the outside. Due to this distortion, a stress is exerted on the main portion outward in the radial direction. Stress is applied to the folded portion inward in the radial direction. These stresses can cause the core to rotate. The reciprocating sliding between the core and the carcass ply is repeated at the part where the carcass ply and the core of the bead contact. This can lead to the cutting of the cord of the carcass ply (cord cutting) at this contact portion. Further, the stress acting on the folded portion may cause separation (separation) of the cord from the peripheral rubber at the end of the folded portion.

  In order to prevent separation at the end of the folded portion, a reinforcing layer may be provided outside the end of the folded portion. In addition, a bead apex is composed of two types of rubber, hard rubber and soft rubber, and soft rubber is disposed inside the end of the folded portion. As a result, the stress at the end of the folded portion is relaxed. In order to prevent the cord from being cut, the number of turns of the core wire is increased to suppress the movement of the core. Further, a rubber sheet is also interposed at a portion where the carcass ply and the core are in contact with each other. An example of a tire having these structures is disclosed in Japanese Patent Application Laid-Open Nos. 2012-106531 and 2015-157583.

JP 2012-106531 A JP2015-157583A

  In the conventional tires, the stress applied to the carcass ply is relaxed in the vicinity of the end of the folded portion and the contact portion between the carcass ply and the core. However, in these tires, strain concentration can occur in a portion of the folded portion that extends from the outer side in the axial direction of the core to the outer side in the radial direction (referred to as a core proximity portion of the folded portion in this specification). In the vicinity of the core, the cord may be peeled off from the surrounding rubber. Suppression of damage in the vicinity of the core is important for further improving the durability of the bead portion.

  An object of the present invention is to provide a pneumatic tire with improved durability.

  The pneumatic tire according to the present invention includes a pair of beads and a carcass. The carcass includes a carcass ply. The carcass ply includes a main portion that extends from one bead to the other bead, and a folded portion that extends in the radial direction outside the bead in the axial direction. Each bead includes a core, a first apex extending radially outward from the core, and a second apex in contact with the first apex and positioned between the first apex and the folded portion. And. The second apex is tapered inward in the radial direction. The hardness H1 of the first apex is higher than the hardness H2 of the second apex. The core includes a non-stretchable wire, and a plurality of cross sections of the wire are arranged in a cross section perpendicular to the circumferential direction of the core. In the radial direction, the inner end of the second apex is located on the outer side of the outer end of the cross section of the wire. The ratio (L4 / WC) of the height L4 from the outer end of the section of the wire to the inner end of the second apex with respect to the width WC of the core is 0.4 or more and 0.9 or less.

  Preferably, the outer end of the first apex is located outside the outer end of the folded portion in the radial direction. In a portion where the first apex and the second apex are in contact with each other, a boundary line between the first apex and the second apex has a concave recess on the inner side in the axial direction.

  Preferably, when a straight line connecting both ends of the portion where the first apex and the second apex are in contact with each other is taken as LA, the ratio of the depth DA of the depression with respect to the straight line LA to the width WC (DA / WC) is 0.2 or more and 0.5 or less.

  Preferably, a ratio (I2 / I1) of a thickness I2 of the second apex to an interval I1 between the main portion and the folded portion at an outer end of the folded portion is 0.6 or more and 0.9 or less. .

  Preferably, a ratio (I1 / WC) of the interval I1 between the main portion and the folded portion at the outer end of the folded portion to the width WC of the core is 0.6 or more and 0.9 or less.

  Preferably, the hardness of the first apex is 80 or more, and the hardness of the second apex is 45 or more and 70 or less.

  In the pneumatic tire according to the present invention, the second apex having a low hardness is located between the folded portion and the first apex. The second apex effectively absorbs distortion at the outer end of the folded portion. In this tire, the separation at the outer end of the folded portion is suppressed. In this tire, the inner end of the second apex is located outside the outer end of the core wire cross-section. Around the core, the first apex having high hardness is located. This suppresses the movement of the core when a load is applied. In this tire, cutting of the cord of the carcass ply at the portion where the carcass ply contacts the core is suppressed. Furthermore, in this tire, the ratio (L4 / WC) of the height L4 from the outer end of the section of the wire to the inner end of the second apex with respect to the width WC of the core is 0.4 or more and 0.9. It is as follows. With this structure, the concentration of distortion in the core proximity portion of the folded portion is effectively reduced while suppressing the cord cutting. In this tire, peeling of the cord from the peripheral rubber is suppressed in this portion. This bead portion is excellent in durability.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 shows a pneumatic tire 2 for heavy load. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In the figure, the alternate long and short dash line CL represents the equator plane of the tire 2. A solid line BBL represents a bead baseline. The bead base line is a line that defines the rim diameter (see JATMA) of the rim to which the tire 2 is fitted. The shape of the tire 2 is symmetrical with respect to the equator plane except for the tread pattern.

  The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of chafers 8, a pair of beads 10, a carcass 12, a belt 14, a pair of first fillers 16, a pair of second fillers 18, and a pair of third fillers. 20, a pair of intermediate layers 22, a pair of bead sheets 24, an inner liner 26, an insert 28, and a pair of cushion layers 30. The tire 2 is attached to a truck, a bus or the like.

  Although not shown, the tire 2 further includes a tube. The internal pressure of the tire 2 is adjusted by filling the tube with air. The tire 2 is a tube type.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 32 that contacts the road surface. A groove 34 is carved in the tread surface 32. The groove 34 forms a tread pattern. The tread 4 is made of a crosslinked rubber having excellent wear resistance, heat resistance, and grip properties.

  Each sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. A radially outer portion of the sidewall 6 is joined to the tread 4. The radially inner portion of the sidewall 6 is joined to the chafer 8. The sidewall 6 is located on the outer side in the axial direction than the carcass 12. The side wall 6 prevents the carcass 12 from being damaged. The sidewall 6 is made of a crosslinked rubber having excellent cut resistance and weather resistance.

  Each chafer 8 extends from the sidewall 6 substantially inward in the radial direction. The chafer 8 is located outside the beads 10 and the carcass 12 in the axial direction. The chafer 8 extends to the inside of the bead 10 in the radial direction. The chafer 8 abuts against the seat surface and the flange of the rim. The chafer 8 is made of a crosslinked rubber having excellent wear resistance.

  Each bead 10 is located radially inward of the sidewall 6. The bead 10 is positioned on the inner side in the axial direction than the chafer 8. In the tire 2, the bead 10 includes a core 36, a first apex 38, and a second apex 40.

  The core 36 has a ring shape. The core 36 includes a wound non-stretchable wire. A typical material for the wire is steel. As shown in the figure, in this embodiment, the outline of the core 36 is a hexagon. The outline of the core 36 may not be hexagonal. The outline of the core 36 may be rectangular. The outline of the core 36 may be circular.

  The first apex 38 extends radially outward from the core 36. The first apex 38 is tapered outward in the radial direction. The outer end 42 of the first apex 38 is located on the axially inner surface of the bead 10. The first apex 38 is made of a crosslinked rubber.

  The second apex 40 is in contact with the first apex 38. The second apex 40 is located on the outer side in the axial direction than the first apex 38. The second apex 40 is located radially outside the first apex 38. The second apex 40 is located between the first apex 38 and the folded portion of the carcass 12 ply. The second apex 40 tapers inward in the radial direction and also tapers outward. The radially inner end 44 of the second apex 40 is located on the axially outer surface of the bead 10. The second apex 40 is made of a crosslinked rubber.

  In the tire 2, the second apex 40 is softer than the first apex 38. The hardness H2 of the second apex 40 is lower than the hardness H1 of the first apex 38.

  In the present application, the hardnesses H1 and H2 are measured by a type A durometer in accordance with the provisions of “JIS K6253”. The durometer is pressed against the cross section shown in FIG. 1, and the hardnesses H1 and H2 are measured. The measurement is made at a temperature of 23 ° C.

  The carcass 12 includes a carcass ply 46. The carcass ply 46 is bridged between the beads 10 on both sides. The carcass ply 46 is folded around the core 36. The carcass ply 46 includes a main portion 48 that extends from one bead 10 to the other bead 10, and a folded portion 50 that extends radially outside the bead 10 in the axial direction. The main portion 48 extends along the inside of the tread 4 and the sidewall 6. The folded portion 50 is located between the bead 10 and the first filler 16. The folded portion 50 extends along the outside of the bead 10.

  Although not shown, the carcass ply 46 includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 75 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord material is steel. The carcass 12 may be formed from two or more carcass plies 46.

  The belt 14 is located on the inner side in the radial direction of the tread 4. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. In the tire 2, the belt 14 includes a first layer 14a, a second layer 14b, a third layer 14c, and a fourth layer 14d. The belt 14 is composed of four layers. The belt 14 may be composed of three layers. As is apparent from the figure, in this embodiment, the second layer 14b has the largest axial width among the four layers. In this embodiment, the axial width of the second layer 14 b is the axial width of the belt 14. The axial width of the belt 14 is preferably 0.7 times or more the maximum width of the tire 2.

  Although not shown, each of the first layer 14a, the second layer 14b, the third layer 14c, and the fourth layer 14d is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is made of steel. This cord is inclined with respect to the equator plane. The inclination direction of the cord of the first layer 14a with respect to the equator plane is the same as the inclination direction of the cord of the second layer 14b with respect to the equator plane. The direction of inclination of the cord of the second layer 14b with respect to the equator plane is opposite to the direction of inclination of the cord of the third layer 14c with respect to the equator plane. The inclination direction of the cord of the third layer 14c with respect to the equator plane is the same as the inclination direction of the cord of the fourth layer 14d with respect to the equator plane. In each layer, the absolute value of the angle formed by the cord with respect to the equator plane is 15 ° to 70 °.

  Each first filler 16 is located on the outer side in the axial direction than the bead 10. The first filler 16 is located on the inner side in the axial direction than the chafer 8. The first filler 16 is covered with the chafer 8.

  In this embodiment, the first filler 16 includes an inner layer 16a and an outer layer 16b. Although not shown, each of the inner layer 16a and the outer layer 16b is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is made of an organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. Each cord is inclined with respect to the radial direction. A general absolute value of the tilt angle is not less than 40 ° and not more than 70 °. The inclination direction of the inner layer 16a with respect to the radial direction of the cord is opposite to the inclination direction of the outer layer 16b with respect to the radial direction of the cord.

  Each second filler 18 is located on the inner side in the axial direction of the bead 10. The second filler 18 is laminated on the inner side in the axial direction of the carcass 12. The radially inner portion of the second filler 18 is sandwiched between the carcass 12 and the third filler 20. Although not shown, the second filler 18 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is made of steel. Each cord is inclined with respect to the radial direction. A general absolute value of the tilt angle is not less than 40 ° and not more than 70 °.

  Each third filler 20 is folded around the core 36. On the inner side in the axial direction of the bead 10, the third filler 20 is laminated on the inner side in the axial direction of the second filler 18. The third filler 20 extends along the carcass ply 46 from the radially inner side of the bead 10 to the axially outer side of the bead 10. As is clear from the figure, the first end of the third filler 20 is located on the inner side in the axial direction than the second filler 18. The second end of the third filler 20 is located between the folded portion 50 and the first filler 16. Although not shown, the third filler 20 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is made of steel. Each cord is inclined with respect to the radial direction. A general absolute value of the tilt angle is not less than 40 ° and not more than 70 °.

  The tire 2 may not include the first filler 16. The tire 2 may not include the second filler 18. The tire 2 may not include the third filler 20.

  Each bead sheet 24 is folded around the core 36 inside the carcass 12. The bead sheet 24 is located between the core 36 and the carcass 12. The bead sheet 24 is made of a crosslinked rubber. The bead sheet 24 relieves the stress that the carcass 12 receives from the core 36. The bead seat 24 prevents the carcass 12 from being damaged due to the movement of the core 36. The tire 2 may not include the bead sheet 24.

  Each intermediate layer 22 is located between the bead 10 and the first filler 16 in the axial direction. As shown in the drawing, the intermediate layer 22 covers the end of the folded portion 50. The intermediate layer 22 is made of a crosslinked rubber. The intermediate layer 22 is softer than the inner sidewall 6. The soft intermediate layer 22 relieves stress applied to the outer end of the folded portion 50.

  The inner liner 26 is located inside the carcass 12. The inner liner 26 is joined to the inner surface of the insert 28. The inner liner 26 is made of a crosslinked rubber. The inner liner 26 is made of rubber having excellent air shielding properties. A typical base rubber of the inner liner 26 is butyl rubber or halogenated butyl rubber. The inner liner 26 contributes to maintaining the internal pressure of the tire 2.

  The insert 28 is located between the carcass 12 and the inner liner 26. The insert 28 is made of a crosslinked rubber having excellent adhesiveness. The insert 28 is firmly joined to the carcass 12 and is also firmly joined to the inner liner 26. The insert 28 prevents the inner liner 26 from peeling from the tire 2.

  Each cushion layer 30 is located near the end of the belt 14. The cushion layer 30 is sandwiched between the belt 14 and the carcass 12. The cushion layer 30 is made of a soft crosslinked rubber. The cushion layer 30 absorbs stress at the end of the belt 14. The cushion layer 30 suppresses lifting of the belt 14.

  FIG. 2 is an enlarged cross-sectional view showing a portion of the bead 10 of the tire 2 of FIG. In FIG. 2, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2.

  In FIG. 2, a double arrow L <b> 1 is a height from the bead 10 base line BBL to the outer end of the folded portion 50 in the radial direction. A double-headed arrow L3 is a height from the bead 10 base line BBL to the inner end 44 of the second apex 40. In the tire 2, the inner end 44 of the second apex 40 is located inside the outer end 52 of the folded portion 50. That is, the ratio (L3 / L1) of the height L3 to the height L1 is smaller than 1.

  As described above, the core 36 includes a wound non-stretchable wire. FIG. 2 shows the wire of the core 36. As shown in the drawing, a plurality of wire cross sections 54 (wire cross sections 54) are arranged in a cross section perpendicular to the circumferential direction of the core 36. In the core 36, a plurality of rows in which the wire cross sections 54 are arranged are stacked. The direction in which this row extends is referred to as the wire row direction. In the illustrated embodiment, the wire row direction is a substantially axial direction. The radially outer end of the wire cross section is referred to as the wire outer end. The wire outer end is the outer end of the wire cross section 54 located on the outermost side in the arrangement of the cross sections of these wires.

  In FIG. 2, a double-headed arrow B is the height from the base line BBL in the radial direction to the outer end of the wire. In the tire 2, the inner end 44 of the second apex 40 is positioned outside the wire outer end. That is, the height L3 is larger than the height B.

  In FIG. 2, a double arrow WC is the width of the core 36. The width WC of the core 36 is measured in the wire row direction. When the direction toward one end in the wire row direction is the first direction and the direction toward the other end is the second direction, the first direction side of the wire cross section 54 located closest to the first direction side The distance in the wire row direction between the end and the end on the second direction side of the wire cross section 54 positioned closest to the second direction is the width WC of the core 36.

  In the drawing, a double-headed arrow L4 is a height from the outer end of the wire to the inner end 44 of the second apex 40 in the radial direction. A portion of the first apex 38 that is radially outside the core 36 and inside the inner end 44 of the second apex 40 is referred to as a base portion of the first apex 38. The height L4 is approximately the thickness of the base portion of the first apex 38. In the tire 2, the ratio (L4 / WC) of the height L4 to the width WC is 0.4 or more and 0.9 or less.

  Hereinafter, the function and effect of the present invention will be described.

  In the pneumatic tire 2 according to the present invention, the second apex 40 having a low hardness is located between the folded portion 50 and the first apex 38. The second apex 40 having low hardness effectively absorbs distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In the tire 2, the inner end 44 of the second apex 40 is located outside the wire outer end. Around the core 36, a first apex 38 having high hardness is located. This suppresses the movement of the core 36 when a load is applied. In the tire 2, cutting of the cord of the carcass ply 46 at a portion where the carcass ply 46 contacts the core 36 is suppressed.

  In the tire 2, the ratio (L4 / WC) of the height L4 from the outer end of the wire to the inner end 44 of the second apex 40 to the width WC of the core 36 is 0.4 or more and 0.9 or less. is there. By setting the ratio (L4 / WC) to 0.4 or more, the base portion of the first apex 38 has a sufficient thickness. The first apex 38 suppresses the movement of the core 36. The first apex 38 effectively relieves the concentration of distortion in the vicinity of the core 36 of the folded portion 50 due to the large movement of the core 36. Concentration of distortion is effectively suppressed in the vicinity of the core 36 of the folded portion 50. In the tire 2, the cord is prevented from being peeled off from the rubber in the vicinity of the core 36 of the folded portion 50. On the other hand, when the movement of the core 36 is too small, the force with which the carcass ply 46 tightens the core 36 increases. A large stress is applied to a portion where the carcass ply 46 and the core 36 are in contact with each other. The concentration of distortion on this part can occur. This becomes a factor of the cord cut. By setting the ratio (L4 / WC) to 0.9 or less, the core 36 can move appropriately. This moderate movement of the core 36 effectively suppresses the concentration of distortion at the portion where the carcass ply 46 contacts the core 36. In the tire 2, the cord is prevented from being cut.

  The ratio (L4 / WC) is more preferably equal to or greater than 0.5 from the viewpoint of suppressing the concentration of distortion in the vicinity of the core 36 of the folded portion 50. From the viewpoint of suppressing strain concentration at the contact portion between the carcass ply 46 and the core 36, the ratio (L4 / WC) is more preferably 0.8 or less.

  In FIG. 2, a double-headed arrow L <b> 2 is a height from the bead 10 baseline BBL to the outer end 42 of the first apex 38 in the radial direction. In the tire 2, the outer end 42 of the first apex 38 is preferably positioned outside the outer end 52 of the folded portion 50. That is, the ratio of the height L2 to the height L1 (L2 / L1) is preferably larger than 1. By making the ratio (L2 / L1) larger than 1, the hard first apex 38 exists on the inner side in the axial direction of the outer end 52 of the folded portion 50. The hard first apex 38 suppresses distortion of the bead 10 in the vicinity of the outer end 52 of the folded portion 50. This effectively alleviates the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In this respect, the ratio (L2 / L1) is more preferably equal to or greater than 1.1.

  In FIG. 2, the symbol LA represents a straight line connecting the outer end 42 of the first apex 38 and the inner end 44 of the second apex 40. The first apex 38 and the second apex 40 are in contact with each other between the outer end 42 of the first apex 38 and the inner end 44 of the second apex 40. This is a straight line connecting both ends of a portion where the first apex 38 and the second apex 40 are in contact with each other.

  As shown in the figure, the boundary line between the first apex 38 and the second apex 40 at the portion where the first apex 38 and the second apex 40 are in contact with each other is a recess 56 that is recessed inward in the axial direction. It is preferable to have it. In other words, the boundary line preferably has a portion recessed toward the first apex 38 with respect to the straight line LA. By providing the depression 56 with the boundary line, when a load is applied, the first apex 38 reduces distortion of the portion of the bead 10 in the vicinity of the outer end 52 of the folded portion 50. This effectively alleviates the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed.

  In the figure, the symbol DA is the depth of the recess 56 with reference to the straight line LA. In other words, the depth DA is the maximum value of the distance between the boundary line between the first apex 38 and the second apex 40 and the straight line LA measured along the perpendicular line of the straight line LA. The ratio (DA / WC) of the depth DA to the width WC of the core 36 is preferably 0.2 or more. By setting the ratio (DA / WC) to 0.2 or more, the first apex 38 is a portion of the bead 10 in the vicinity of the outer end 52 of the folded portion 50 when a load is applied to the bead 10 portion. To effectively reduce distortion. This effectively alleviates the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In this respect, the ratio (DA / WC) is more preferably equal to or greater than 0.25. The ratio (DA / WC) is preferably 0.5 or less. By setting the ratio (DA / WC) to 0.5 or less, the first apex 38 contributes to the rigidity of the bead 10 portion. The bead 10 is prevented from falling. In this respect, the ratio (DA / WC) is more preferably equal to or less than 0.45.

  In FIG. 2, a double arrow L <b> 5 is a height from the bead 10 base line BBL to the outer end 58 of the second apex 40. In the tire 2, the outer end 58 of the second apex 40 is preferably located outside the outer end 52 of the folded portion 50. That is, the ratio of the height L5 to the height L1 (L5 / L1) is preferably greater than 1. By doing so, the outer end 52 of the folded portion 50 is located between the inner end 44 and the outer end of the second apex 40. The outer end 52 of the folded portion 50 is in contact with the second apex 40. The second apex 40 effectively reduces the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed.

  In FIG. 2, a double-headed arrow I <b> 1 is an interval between the main portion 48 and the folded portion 50 at the outer end 52 of the folded portion 50. The interval I1 is measured along the normal of this surface drawn from the outer end 52 of the folded portion 50 toward the radially outer surface of the main portion 48. The interval I1 is a distance between the radially outer side surface of the main portion 48 and the radially inner side surface of the folded portion 50, measured along this normal line. In the figure, a double-headed arrow I2 is the thickness of the second apex 40 measured along this normal line.

  The ratio (I2 / I1) of the thickness I2 to the interval I1 is preferably 0.6 or more. By setting the ratio (I2 / I1) to be 0.6 or more, the second apex 40 effectively relieves the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In this respect, the ratio (I2 / I1) is more preferably equal to or greater than 0.7. The ratio (I2 / I1) is preferably 0.9 or less. By setting the ratio (I2 / I1) to be 0.9 or less, the first apex 38 suppresses the distortion of the bead 10 portion when a load is applied. This effectively alleviates the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In this respect, the ratio (I2 / I1) is more preferably equal to or less than 0.8.

  The ratio (I1 / WC) of the interval I1 to the width WC is preferably 0.6 or more. By setting the ratio (I1 / WC) to be 0.6 or more, when the load is applied, distortion of the entire bead 10 in the vicinity of the outer end can be suppressed. This effectively alleviates the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In this respect, the ratio (I1 / WC) is more preferably equal to or greater than 0.7. The ratio (I1 / WC) is preferably 0.9 or less. By setting the ratio (I1 / WC) to 0.9 or less, excessive heat generation from the bead 10 portion when the tire 2 rolls can be suppressed. In the tire 2, a decrease in durability due to heat generation is suppressed. In this respect, the ratio (I1 / WC) is more preferably equal to or less than 0.8.

  The hardness H1 of the first apex 38 is preferably 80 or more. By setting the hardness H1 to 80 or more, the first apex 38 effectively reduces the distortion of the bead 10 portion when a load is applied. This effectively alleviates the concentration of distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. Further, the first apex 38 effectively suppresses the movement of the core 36. The first apex 38 effectively relieves the concentration of distortion in the vicinity of the core 36 of the folded portion 50 due to the large movement of the core 36. In the tire 2, the cord is prevented from being peeled off from the rubber in the vicinity of the core 36 of the folded portion 50. In this respect, H1 is more preferably equal to or greater than 85. The hardness H1 is preferably 100 or less. By setting the hardness H1 to 100 or less, the rigidity of the bead 10 is appropriately maintained. The longitudinal spring constant of the tire 2 is kept appropriate. The tire 2 maintains a good ride comfort. In this respect, H1 is more preferably equal to or less than 95.

  The hardness H2 of the second apex 40 is preferably 70 or less. By setting the hardness H2 to 70 or less, the second apex 40 effectively absorbs distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In this respect, the hardness H2 is preferably equal to or less than 65. The hardness H2 of the second apex 40 is preferably 45 or more. The second apex 40 having a hardness H2 of 45 or more is not too soft. The second apex 40 is maintained at an appropriate hardness to absorb distortion at the outer end 52 of the folded portion 50. The second apex 40 effectively absorbs distortion at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. In this respect, the hardness H2 is preferably equal to or greater than 50.

  The difference (H1−H2) between the hardness H1 and the hardness H2 is preferably 15 or more. By setting the difference (H1−H2) to 15 or more, each of the first apex 38 and the second apex 40 effectively contributes to durability. The difference (H1-H2) is preferably 35 or less. By setting the difference (H1−H2) to be 35 or less, it is possible to suppress distortion from being concentrated on the boundary between the first apex 38 and the second apex 40.

  In FIG. 1, a double-headed arrow TH is the cross-sectional height of the tire 2. The ratio (L2 / TH) of the height L2 to the height TH is preferably 0.2 or more. By setting the ratio (L2 / TH) to 0.2 or more, the first apex 38 effectively suppresses the movement of the entire bead 10. The first apex 38 contributes to the durability of the bead 10. The ratio (L2 / TH) is preferably 0.4 or less. By setting the ratio (L2 / TH) to 0.4 or less, the rigidity of the bead 10 is appropriately maintained. The longitudinal spring constant of the tire 2 is kept appropriate. In the tire 2, a good riding comfort is maintained.

  The ratio (L5 / TH) of the height L5 to the height TH is preferably 0.3 or more. By setting the ratio (L5 / TH) to 0.3 or more, the second apex 40 effectively relaxes the stress at the outer end 52 of the folded portion 50. In the tire 2, separation at the outer end 52 of the folded portion 50 is suppressed. The ratio (L5 / TH) is preferably 0.5 or less. By setting the ratio (L5 / TH) to 0.5 or less, the rigidity of the bead 10 is appropriately maintained. The longitudinal spring constant of the tire 2 is kept appropriate. In the tire 2, a good riding comfort is maintained.

  In the present invention, the dimension and angle of each member of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and is filled with air so as to have a regular internal pressure unless otherwise specified. At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A heavy-duty pneumatic tire of Example 1 having the configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained. The tire size was 12.00R20. The cross-sectional height TH of this tire was 306 mm. In this tire, the height L2 was 90 mm and the height L5 was 120 mm. In this tire, the width WC was 18.6 mm. In this tire, the boundary line between the first apex and the second apex is provided with a concave depression on the inner side in the axial direction. This is indicated by the “dent” in the “boundary line shape” column of the table.

[Comparative Example 1-3, Example 2-3]
Tires of Comparative Example 1-3 and Example 2-3 were obtained in the same manner as Example 1 except that the height L4 was changed and the ratio (L4 / WC) was changed as shown in Table 1. The height L4 was changed by changing the height of the radially inner end of the second apex (that is, the height L3).

[Example 4]
A tire of Example 4 was obtained in the same manner as in Example 1 except that the boundary line between the first apex and the second apex was formed to be convex outward in the axial direction. “Protrusions” in the “Boundary line shape” column of the table indicate that the boundary line has a shape protruding outward in the axial direction.

[Example 5-6]
A tire of Example 5-6 was obtained in the same manner as in Example 1 except that the depth DA was changed and the ratio (DA / WC) was changed as shown in Table 2.

[Example 7-8]
Tires of Examples 7-8 were obtained in the same manner as Example 1 except that the hardnesses H1 and H2 were as shown in Table 2.

[Example 9]
A tire of Example 9 was obtained in the same manner as in Example 1 except that the height L2 was changed to 70 mm and the ratio (L2 / L1) was changed as shown in Table 2 by changing the height L1. . Since the position of the outer end of the first apex and the position of the outer end of the folded portion are changed, the values of the ratio (I2 / I1) and the ratio (I1 / WC) are also changed.

[durability]
The tire was assembled in a regular rim (20 × 8.5V), and the tire was filled with air to set the internal pressure to the normal internal pressure. This tire was mounted on a drum-type running test machine, and a longitudinal load of 73.46 kN was applied to the tire. This tire was run on a drum having a radius of 1.7 m at a speed of 20 km / h. The time until damage to the bead portion occurred was measured. The results are shown in Tables 1 and 2 below, with the index of Comparative Example 1 being 100. A larger numerical value is preferable.

  As shown in Table 1-2, the tire of the example has a higher evaluation than the tire of the comparative example. From this evaluation result, the superiority of the present invention is clear.

  The tire described above can be applied to various heavy-duty vehicles.

2 ... tyre 4 ... tread 6 ... side wall 10 ... bead 12 ... carcass 14 ... band 16 ... first filler 18 ... second filler 20 ... first Three fillers 22: intermediate layer 24 ... bead sheet 26 ... inner liner 28 ... insert 30 ... cushion layer 32 ... tread surface 34 ... groove 36 ... core 38 ... First apex 40 ... second apex 42 ... outer end of first apex 44 ... inner end of second apex 46 ... carcass ply 48 ... main part 50 ... -Folded part 52 ... Outer end of folded part 54 ... Wire cross section 56 ... Depression 58 ... Outer end of second apex

Claims (6)

It has a pair of beads and carcass,
The carcass includes a carcass ply, and the carcass ply includes a main portion extending from one bead to the other bead, and a folded portion extending in a radial direction outside the bead in the axial direction.
Each bead has a core, a first apex extending radially outward from the core, and a second apex in contact with the first apex and located between the first apex and the folded portion And
The second apex is tapered radially inward;
The hardness H1 of the first apex is higher than the hardness H2 of the second apex,
The core includes a non-stretchable wire, and a plurality of cross sections of the wire are arranged in a cross section perpendicular to the circumferential direction of the core,
In the radial direction, the inner end of the second apex is located outside the outer end of the wire cross section,
Air in which the ratio (L4 / WC) of the height L4 from the outer end of the cross section of the wire to the inner end of the second apex with respect to the width WC of the core is 0.4 or more and 0.9 or less Enter tire.   In the radial direction, the outer end of the first apex is located outside the outer end of the folded portion, and the first apex and the second apex are in contact with each other. The pneumatic tire according to claim 1, wherein a boundary line with the second apex has a recess recessed inward in the axial direction.   When a straight line connecting both ends of the portion where the first apex and the second apex are in contact is taken as LA, the ratio of the depth DA of the depression with respect to the straight line LA to the width WC (DA / The pneumatic tire according to claim 2, wherein WC) is 0.2 or more and 0.5 or less.   The ratio (I2 / I1) of the thickness I2 of the second apex to the interval I1 between the main portion and the folded portion at the outer end of the folded portion is 0.6 or more and 0.9 or less. To 4. The pneumatic tire according to any one of 3 to 4.   The ratio (I1 / WC) of the interval I1 between the main portion and the folded portion at the outer end of the folded portion to the width WC of the core is 0.6 or more and 0.9 or less. The pneumatic tire according to any one of the above.   The pneumatic tire according to any one of claims 1 to 5, wherein the hardness of the first apex is 80 or more, and the hardness of the second apex is 45 or more and 70 or less.

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