JP2020066243A - Pneumatic tire for heavy load - Google Patents

Abstract

To provide a pneumatic tire 32 for a heavy load which achieves improvement of bead durability and reduction of rolling resistance while achieving weight reduction.SOLUTION: This tire 32 includes: a pair of beads 40; a carcass ply 82 having a ply body 84 spanned between one bead 40 and the other bead 40 and folded parts 86, each of which continues into the ply body 84 and is folded from the axial inner side to the outer side around the bead 40; and a pair of fillers 52, each of which is located at the outer side of the folded part 86 in an axial direction and includes a metal cord. The bead 40 includes: a core 64; a first apex 70 which encloses the core 64; and a second apex 72 located at the radial outer side of the first apex 70. An outer periphery of the first apex 70 has a rounded profile. A recess 96 is provided at a zone, located between a maximum width position and an end 88 of the folded part 86, of a side surface 34 of the tire 32.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a heavy duty pneumatic tire.

  FIG. 3 shows a bead 4 portion (hereinafter, also referred to as a bead portion B) of the conventional heavy duty pneumatic tire 2. The bead portion B is fitted to the rim R (regular rim).

  In this tire 2, the carcass ply 6 is folded back around the bead 4 from the inner side to the outer side in the axial direction. The carcass ply 6 includes a ply body 8 and a folded portion 10.

  In this tire 2, the bead 4 includes a core 12 and an apex 14. In the tire 2, the apex 14 includes a first apex 16 and a second apex 18 that is softer than the first apex 16. As shown in FIG. 3, the outer end 16a of the first apex 16 is located outside the end 10a of the folded portion 10 in the radial direction.

  The tire 2 is provided with a filler 20 in order to secure the rigidity of the bead portion B. Although not shown, the filler 20 is composed of a large number of steel cords and topping rubbers arranged in parallel.

  The filler 20 is located between the folded-back portion 10 and the chafer 22. As shown in FIG. 3, the inner end 20 a of the filler 20 is located inside the core 12 of the bead 4 in the radial direction. The outer end 20b of the filler 20 is located inside the end 10a of the folded portion 10. This filler 20 does not have a structure folded around the bead 4, unlike a conventional filler (hereinafter also referred to as a normal filler). This filler 20 is also called a short filler.

  The tire 2 is mounted on a vehicle such as a truck or a bus. Since a large load acts on the bead portion B of the tire 2, it is important to improve the durability of the bead portion B, that is, the bead durability. In heavy-duty pneumatic tires, improving the bead durability by adjusting the configuration of the bead portion B to control the rigidity has been studied (for example, Patent Document 1 below).

JP, 2015-157524, A

  For example, in the core 12 configured by winding the wire 24, the number of turns of the wire 24 is increased, the volume of the apex 14 located radially outside the core 12 is increased, and the rigidity of the bead portion B is increased. If it is improved, the bead durability can be improved. However, in this case, there is a concern that the mass of the tire 2 increases and the heat generated by the movement of the bead portion B, that is, the energy loss increases. An increase in energy loss increases rolling resistance. The increase in rolling resistance of the tire 2 affects the fuel consumption performance of the vehicle.

  The present invention has been made in view of such an actual situation, and it is possible to provide a heavy-duty pneumatic tire in which improvement in bead durability and reduction in rolling resistance are achieved while achieving weight reduction. To aim.

  A preferred heavy duty pneumatic tire according to the present invention is a pair of beads, a ply body bridging between one bead and the other bead, and an axially inner side to an outer side around the bead that is continuous with the ply body. A carcass ply having a folded-back portion that is folded back into a pair, and a pair of fillers located outside the folded-back portion in the axial direction and including a metal cord. The bead includes a core, a first apex surrounding the core, and a second apex located radially outside the first apex. The outer circumference of the first apex has a rounded contour. The first apex is harder than the second apex. On the side surface of the tire, a recess is provided in the zone between the maximum width position and the end of the folded portion.

  Preferably, in this heavy duty pneumatic tire, the side surface of the tire corresponds to the outer end of the contact surface with the flange of the rim to which the tire is fitted, when the position on the side surface is the flange contact end, In the radial direction, the outer end of the first apex is located inside the end of the folded portion and outside the flange contact end.

  Preferably, in this heavy duty pneumatic tire, the radial distance from the radial inner end of the core to the outer end of the first apex is 15 mm or more and 45 mm or less.

  Preferably, in this heavy duty pneumatic tire, the distance from the axially inner end of the core to the carcass ply is 1 mm or more.

  Preferably, in this heavy duty pneumatic tire, the minimum thickness from the ply body to the recess is measured along a line segment indicating the minimum thickness, and is obtained from the ply body without the recess. The ratio to the virtual thickness up to the virtual side surface is 0.3 or more and 0.7 or less.

  Preferably, in this heavy duty pneumatic tire, the radial distance from the end of the folded portion to the inner end of the recess is 10 mm or more and 20 mm or less.

  Preferably, in this heavy duty pneumatic tire, the recess includes a bottom portion and an outer boundary portion located radially outside the bottom portion. The profile of the outer boundary portion is represented by an arc that is convex outward, and the radius of the arc is 40 mm or more.

  Preferably, in this heavy-duty pneumatic tire, the recess includes a bottom portion and an inner boundary portion located radially inward of the bottom portion. The profile of the inner boundary portion is represented by an arc that is convex outward, and the radius of the arc is 40 mm or more.

  Preferably, in this heavy duty pneumatic tire, the profile of the bottom portion is represented by an inwardly convex arc, or the profile of the bottom portion is represented by a straight line.

  Preferably, in this heavy-duty pneumatic tire, in the radial direction, the first end of the filler is located inside the bead baseline, and the second end of the filler is the end of the folded portion and the bead baseline. Located between.

  In the heavy duty pneumatic tire of the present invention, the side surface is provided with a recess in the zone between the maximum width position and the end of the folded portion. The recess contributes to the reduction of the mass and suppresses the movement of the rubber in the portion radially outside the end of the folded portion. Since the movement of the folded-back portion is suppressed, damage such as ply turn-up loose is unlikely to occur in this tire. The suppression of this movement also suppresses heat generation due to deformation.

  Furthermore, in this tire, the periphery of the core is surrounded by the hard first apex whose outer periphery has a rounded contour. Since the collapse of the bead portion due to the action of the load is suppressed, the tire has good bead durability.

  In this tire, the radial height of the first apex is low. In this tire, a region that can contribute to bending can be sufficiently secured in the side portion, and the contour of the ply body extending along the apex can be easily set. In this tire, since the lateral protrusion of the side surface in the axial direction is suppressed, the amount of strain acting on the depression is reduced. In this tire, damage such as cracks in the depression is unlikely to occur. In this tire, the above-described effect exerted by the depression is sufficiently exerted. Moreover, since the first apex is composed of a small volume, the influence of the first apex on the rolling resistance can be effectively suppressed.

  In this tire, bead durability is improved and rolling resistance is reduced while achieving weight reduction. According to the present invention, it is possible to obtain a heavy-duty pneumatic tire in which bead durability is improved and rolling resistance is reduced while achieving weight reduction.

FIG. 1 is a sectional view showing a part of a heavy duty pneumatic tire according to an embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing a bead portion of the tire of FIG. FIG. 3 is a partial cross-sectional view showing a bead portion of a conventional heavy duty pneumatic tire.

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

  In the present invention, a state in which the tire is incorporated into a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to the tire is called a regular state. In the present invention, the dimensions and angles of each part of the tire are measured under normal conditions unless otherwise specified.

  In the present invention, the regular rim means a rim defined in the standard on which the tire depends. “Standard rim” in JATMA standard, “Design Rim” in TRA standard, and “Measuring Rim” in ETRTO standard are regular rims.

  In the present invention, the normal internal pressure means the internal pressure defined in the standard on which the tire depends. "Maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in JATMA standard, "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standard, and "INFLATION PRESSURE" in ETRTO standard are normal internal pressures.

  In the present invention, the normal load means a load defined in the standard on which the tire depends. "Maximum load capacity" in JATMA standard, "Maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standard, and "LOAD CAPACITY" in ETRTO standard are normal loads.

  FIG. 1 shows a part of a heavy duty pneumatic tire 32 (hereinafter, may be simply referred to as “tire 32”) according to an embodiment of the present invention. The tire 32 is mounted on a heavy-duty vehicle such as a truck or a bus.

  FIG. 1 shows a part of a cross section of the tire 32 along a plane including the rotation axis of the tire 32. In FIG. 1, the left-right direction is the axial direction of the tire 32, and the up-down direction is the radial direction of the tire 32. The direction perpendicular to the paper surface of FIG. 1 is the circumferential direction of the tire 32. In FIG. 1, the alternate long and short dash line CL represents the equatorial plane of the tire 32.

  In FIG. 1, a solid line BBL extending in the axial direction is a bead baseline. The bead baseline is a line that defines the rim diameter (see JATMA, etc.) of the rim (regular rim).

  In FIG. 1, reference numeral PW indicates an axial outer end of the tire 32. The outer end PW is specified based on a virtual side surface obtained by assuming that the side surface 34 of the tire 32 has no decoration such as a pattern or a character. The axial distance from one outer end PW to the other outer end PW is the maximum width of the tire 32, that is, the sectional width of the tire 32 (see JATMA, etc.). The outer end PW is a position where the tire 32 exhibits the maximum width (hereinafter, also referred to as the maximum width position of the tire 32).

  The tire 32 includes a tread 36, a pair of sidewalls 38, a pair of beads 40, a pair of chafers 42, a carcass 44, a belt 46, a pair of cushion layers 48, an inner liner 50, and a pair of fillers 52.

  The tread 36 contacts the road surface at its outer surface 54. The outer surface 54 of the tread 36 is the tread surface. The aforementioned side surface 34 is continuous with the end of the tread surface 54 and extends radially inward.

  The tread 36 includes a base portion 56 and a cap portion 58. The tire 32 is provided with a pair of base portions 56. These base portions 56 are arranged at intervals in the axial direction. Each base portion 56 covers the end portion of the belt 46. The base portion 56 is made of crosslinked rubber. The cap portion 58 is located radially outside the base portion 56. The cap portion 58 covers the pair of base portions 56 and the entire belt 46. The outer surface of the cap portion 58 forms the tread surface 54 described above. The cap portion 58 is made of crosslinked rubber.

  In this tire 32, at least three circumferential grooves 60 are engraved on the tread 36. As a result, at least four circumferential land portions 62 are formed on the tread 36.

  Each sidewall 38 is continuous with the end of the tread 36. The sidewall 38 extends inward in the radial direction from the end of the tread 36. The sidewall 38 is made of crosslinked rubber. The outer surface of the sidewall 38 constitutes the side surface 34 of the tire 32.

  Each bead 40 is located radially inward of the sidewall 38. The bead 40 includes a core 64 and an apex 66.

  The core 64 extends in the circumferential direction. The core 64 includes a wound steel wire 68. The core 64 has a substantially hexagonal sectional shape. In the tire 32, the core 64 is located outside the bead baseline in the radial direction. In the cross section of the core 64, the corner portion indicated by the symbol PA is the radial inner end of the core 64, and the corner portion indicated by the symbol PB is the axial inner end of the core 64. The corners of the core 64 are specified based on the contour of the cross-section bundle of the wires 68 included in the cross section of the core 64.

  The apex 66 is located radially outside the core 64. The apex 66 extends radially outward from the core 64. In the tire 32, the apex 66 includes a first apex 70 and a second apex 72. Each of the first apex 70 and the second apex 72 is made of crosslinked rubber. The first apex 70 is harder than the second apex 72. The apex 66 includes a hard first apex 70 and a soft second apex 72.

  In the tire 32, the hardness of the first apex 70 is set in the range of 83 or more and 98 or less. The hardness of the second apex 72 is set in the range of 45 or more and 65 or less. In the present invention, the "hardness" is measured using a type A durometer under the temperature condition of 23 ° C according to JIS K6253.

  The first apex 70 surrounds the core 64. In other words, the first apex 70 is located around the core 64. The second apex 72 is located radially outside the first apex 70. The second apex 72 extends radially outward from the first apex 70. The second apex 72 is tapered outward in the radial direction.

  As shown in FIG. 1, in the tire 32, the outer periphery of the first apex 70 has a rounded contour. The first apex 70 has a round shape. Therefore, the contact surface of the second apex 72 with the first apex 70, that is, the bottom surface 74 of the second apex 72 has a shape that is convex outward in the radial direction in the cross section shown in FIG. .

  Each chafer 42 is located axially outside the bead 40. The chafer 42 is located inside the sidewall 38 in the radial direction. The chafer 42 contacts the rim. The chafer 42 is made of crosslinked rubber. In the tire 32, the outer end 76 of the chafer 42 is located inside the outer end 78 of the second apex 72, that is, the outer end 78 of the apex 66 in the radial direction.

  In FIG. 1, reference numeral PT is the toe of the tire 32. The outer surface of the chafer 42 from the toe PT to the inner end 80 of the sidewall 38 forms a part of the side surface 34.

  The carcass 44 is located inside the tread 36, the sidewall 38, and the chafer 42. The carcass 44 includes at least one carcass ply 82. The carcass 44 of the tire 32 is composed of one carcass ply 82.

  Although not shown, the carcass ply 82 includes a large number of carcass cords arranged in parallel. These carcass cords are covered with topping rubber. Each carcass cord intersects the equatorial plane. In the tire 32, the angle formed by the carcass cord with respect to the equatorial plane is 70 ° or more and 90 ° or less. The carcass 44 of the tire 32 has a radial structure. In this tire 32, the material of the carcass cord is steel. A cord made of organic fiber may be used as the carcass cord.

  In the tire 32, the carcass ply 82 is folded back around the respective beads 40 (specifically, the core 64) from the inner side to the outer side in the axial direction. The carcass ply 82 includes a ply main body 84 bridging the one bead 40 and the other bead 40, and a pair of ply main bodies 84 connected to the ply main body 84 and folded back from the inside toward the outside in the axial direction around each bead 40. And a folded portion 86. In the tire 32, the end 88 of the folded-back portion 86 is located between the outer end 76 of the chafer 42 and the inner end 80 of the sidewall 38 in the radial direction.

  The belt 46 is located inside the tread 36 in the radial direction. The belt 46 is located radially outside the carcass 44.

  In the tire 32, the belt 46 is composed of four layers 90 laminated in the radial direction. In the tire 32, the number of layers 90 forming the belt 46 is not particularly limited. The configuration of the belt 46 is appropriately determined in consideration of the specifications of the tire 32.

  Although not shown, each layer 90 includes a number of belt cords juxtaposed. These belt cords are covered with topping rubber. In the tire 32, the material of the belt cord is steel.

  In each layer 90, the belt cord is inclined with respect to the equatorial plane. The belt cords in one layer 90 intersect with the belt cords in another layer 90 laminated on the one layer 90.

  In this tire 32, of the four layers 90, the second layer 90B located between the first layer 90A and the third layer 90C has the maximum axial width. The outermost fourth layer 90D in the radial direction has the smallest axial width.

  Each cushion layer 48 is located between the belt 46 and the carcass 44 at the end portion of the belt 46. The cushion layer 48 is made of crosslinked rubber.

  The inner liner 50 is located inside the carcass 44. The inner liner 50 constitutes the inner surface of the tire 32. The inner liner 50 is made of a crosslinked rubber having an excellent air shielding property. The inner liner 50 holds the internal pressure of the tire 32.

  Each filler 52 is located on a portion of the bead 40. The filler 52 is located outside the bead 40 in the axial direction. As shown in FIG. 1, the filler 52 is located between the folded-back portion 86 and the chafer 42.

  Although not shown, the filler 52 includes a number of metal cords arranged in parallel. In the tire 32, the material of the metal cord is steel. In the tire 32, the metal cord included in the filler 52 is a steel cord. In the filler 52, the metal cord is covered with topping rubber.

  In the tire 32, the first end 92 (also referred to as the inner end) of the filler 52 is located inside the bead baseline in the radial direction. The first end 92 of the filler 52 is located between the bead baseline and the toe PT in the radial direction. In the tire 32, the first end 92 of the filler 52 is arranged at a position equivalent to the position of the inner end PA of the core 64, that is, the corner portion PA in the axial direction. The second end 94 (also referred to as the outer end) of the filler 52 is located inside the end 88 of the folded portion 86 in the radial direction. The second end 94 of the filler 52 is located between the end 88 of the folded-back portion 86 and the bead base line in the radial direction. The filler 52 is a short filler.

  The tire 32 may be configured to have a structure in which the filler 52 is folded back around the bead 40. In this case, the first end 92 of the filler 52 is arranged radially outside the core 64 and axially outside the ply body 84. The second end 94 of the filler 52 is arranged at the same position as the second end 94 of the short filler described above. The filler 52 having such a structure is also called a normal filler. From the viewpoint of weight reduction, in the tire 32, the above-mentioned short filler is preferable as the filler 52.

  FIG. 2 shows a part of the cross section of the tire 32 of FIG. FIG. 2 shows a bead 40 portion of the tire 32 (hereinafter, also referred to as a bead portion B). In FIG. 2, the left-right direction is the axial direction of the tire 32, and the up-down direction is the radial direction of the tire 32. The direction perpendicular to the paper surface of FIG. 2 is the circumferential direction of the tire 32.

  In the tire 32, a recess 96 is provided on the side surface 34. In the tire 32, the recess 96 is provided in the sidewall 38 forming a part of the side surface 34. As shown in FIG. 2, the recess 96 has an inwardly convex shape. The recess 96 extends in the circumferential direction without interruption.

  In FIG. 2, reference numeral PS is the outer end of the recess 96. The code PU is the inner end of the recess 96. In the tire 32, the outer end PS of the recess 96 is located inside the maximum width position PW in the radial direction. The inner end PU of the recess 96 is located outside the end 88 of the folded-back portion 86 in the radial direction. In the tire 32, the recess 96 is provided in the zone between the maximum width position PW and the end 88 of the folded portion 86 on the side surface 34.

  When a load is applied to the tire 32 mounted on the rim, in the tire 32, the rubber moves toward the vicinity where the end 88 of the folded portion 86 and the second end 94 of the filler 52 are located. In accordance with this movement, the ply body 84 moves axially outward. As described above, in the tire 32, the recess 96 is located in the zone between the maximum width position PW and the end 88 of the folded portion 86. The recess 96 suppresses the movement of the rubber near the position where the end 88 of the folded portion 86 and the second end 94 of the filler 52 are located, and also suppresses the movement of the ply body 84. The recess 96 suppresses the movement of the rubber in a portion radially outside the end 88 of the folded portion 86 when a load is applied to the tire 32.

  In the tire 32, the recess 96 provided in the zone of the side surface 34 between the maximum width position PW and the end 88 of the folded-back portion 86 contributes to reduction in mass. As described above, the recess 96 suppresses the movement of the rubber in the portion radially outside the end 88 of the folded portion 86. Since the movement of the folded-back portion 86 is suppressed, the tire 32 is less likely to suffer damage such as ply turn-up loose. The suppression of this movement also suppresses heat generation due to deformation.

  In the tire 32, the periphery of the core 64 is surrounded by the hard first apex 70 having a rounded outer periphery. Since the collapse of the bead portion B due to the action of the load is suppressed, good bead durability can be obtained in this tire.

  In the tire 32, the radial height of the first apex 70 is low. In the tire 32, a region that can contribute to bending can be sufficiently secured in the sidewall 38, that is, the side portion S, and the contour of the ply body 84 extending along the apex 66 can be easily set. In this tire 32, since the side surface 34 is prevented from protruding outward in the axial direction, the amount of strain acting on the recess 96 is reduced. In the tire 32, damage such as cracks in the recess 96 is unlikely to occur. In the tire 32, the above-described effect exerted by the recess 96 is sufficiently exerted. Moreover, since the first apex 70 is configured with a small volume, the influence of the first apex 70 on the rolling resistance can be effectively suppressed.

  In the tire 32, the bead durability is improved and the rolling resistance is reduced while reducing the weight.

  In FIG. 2, the dotted line VL is an imaginary side surface obtained when the side surface 34 does not have the recess 96. The virtual side surface VL is a part of the above-described virtual side surface used for specifying the maximum width position PW. The solid line NL is the normal to the ply body 84. The double-headed arrow TA is the thickness from the ply body 84 to the recess 96 measured along the normal line NL. In the tire 32, the thickness TA is represented by the minimum thickness from the ply body 84 to the recess 96. A double-headed arrow TB is a virtual segment from the ply body 84 to the virtual side surface VL, which is measured along a line segment indicating the minimum thickness TA, that is, the normal line NL.

  In this tire 32, the ratio of the minimum thickness TA to the virtual thickness TB is preferably 0.3 or more, and preferably 0.7 or less. By setting this ratio to 0.3 or more, an increase in strain in the vicinity of the bottom of the recess 96 is suppressed, and the minimum thickness TA has a required thickness. In the tire 32, damage such as cracks in the recess 96 can be suppressed. From this viewpoint, this ratio is more preferably 0.4 or more. By setting this ratio to 0.7 or less, the movement of the rubber rim forming the sidewall 38 toward the flange LF side when a load is applied is suppressed. In the tire 32, the recess 96 effectively suppresses the movement of the rubber in the portion radially outside the end 88 of the folded portion 86. In this tire 32, bead durability is effectively improved and rolling resistance is effectively reduced. From this viewpoint, the ratio is more preferably 0.6 or less.

  In FIG. 2, a double-headed arrow DU is a radial distance from the end 88 of the folded portion 86 to the inner end PU of the recess 96. A double-headed arrow DS is a radial distance from the maximum width position PW to the outer end PS of the recess 96.

  In the tire 32, the radial distance DU from the end 88 of the folded portion 86 to the inner end PU of the recess 96 is preferably 10 mm or more and 20 mm or less. When the distance DU is set to 10 mm or more, the recess 96 is arranged with an appropriate distance from the end 88 of the folded-back portion 86, so that the interference between the recess 96 and the folded-back portion 86 is prevented. Since the concentration of strain on the end 88 of the folded-back portion 86 is suppressed and the effect produced by the recess 96 is sufficiently exerted, in the tire 32, the bead durability is effectively improved, and the rolling resistance is effective. Is reduced. By setting this distance DU to 20 mm or less, the recess 96 having a sufficient size is secured in the zone between the maximum width position PW and the end 88 of the folded portion 86. In this case as well, the effect produced by the recess 96 is sufficiently exerted, so that in the tire 32, the bead durability is effectively improved and the rolling resistance is effectively reduced.

  In the tire 32, the radial distance DS from the maximum width position PW to the outer end PS of the recess 96 is preferably 10 mm or more and 20 mm or less. When the distance DS is set to 10 mm or more, the recess 96 is arranged with a proper distance from the maximum width position PW. In this tire 32, since the sidewall 38 at the maximum width position PW has an appropriate thickness, good cut resistance is maintained. By setting the distance DS to be 20 mm or less, the recess 96 having a sufficient size is secured in the zone between the maximum width position PW and the end 88 of the folded portion 86. Since the effect exerted by the recess 96 is sufficiently exerted, in the tire 32, the bead durability is effectively improved and the rolling resistance is effectively reduced.

  In the tire 32, a portion of the side surface 34 radially inward from the maximum width position PW has the above-described recess 96, an outer portion 98 extending radially outward from the outer end PS of the recess 96, and the recess 96. And an inner portion 100 that extends radially inward from the inner end PU.

  The above-mentioned virtual side surface VL is located between the outer side portion 98 and the inner side portion 100. The outer end PU of the recess 96 is a boundary between the outer portion 98 and the virtual side surface VL. The inner end PU of the recess 96 is a boundary between the inner side portion 100 and the virtual side surface VL. In the tire 32, the profile of the virtual side surface VL and the profile of the outer side portion 98 are in contact with each other at the boundary PS. The profile of the virtual side surface VL and the profile of the inner side portion 100 are in contact with each other at the boundary PU.

  In the tire 32, the recess 96 includes a bottom portion 102, an outer boundary portion 104, and an inner boundary portion 106.

  The outer boundary portion 104 bridges the bottom portion 102 and the outer portion 98 described above. The profile of the outer boundary portion 104 contacts the profile of the outer portion 98 at the outer end PS. The outer end PS is also a boundary between the outer boundary portion 104 and the outer portion 98.

  The inner boundary portion 106 bridges the bottom portion 102 and the aforementioned inner portion 100. The profile of the inner boundary portion 106 contacts the profile of the inner portion 100 at the inner end PU. The inner end PU is also a boundary between the inner boundary portion 106 and the inner portion 100.

  In FIG. 2, reference numeral PSb is the outer end of the bottom portion 102. Reference numeral PUb is the inner end of the bottom portion 102. In the tire 32, the outer boundary portion 104 is located radially outside the bottom portion 102. The profile of the bottom portion 102 contacts the profile of the outer boundary portion 104 at the outer end PSb. The outer end PSb is a boundary between the bottom portion 102 and the outer boundary portion 104. An inner boundary portion 106 is located inside the bottom portion 102 in the radial direction. The profile of the bottom portion 102 contacts the profile of the inner boundary portion 106 at the inner end PUb. The inner end PUb is a boundary between the bottom portion 102 and the inner boundary portion 106.

  In the cross section of the tire 32 shown in FIG. 2, the profile of the outer boundary portion 104 is represented by an arc that is convex outward. In FIG. 2, an arrow Rs is a radius of an arc representing the profile of the outer boundary portion 104.

  In the tire 32, the radius Rs of the arc representing the profile of the outer boundary 104 is preferably 40 mm or more. This suppresses the concentration of strain on the outer boundary portion 104. In this tire 32, since the effect produced by the recess 96 is sufficiently exerted, the bead durability is effectively improved and the rolling resistance is effectively reduced. The upper limit of the radius Rs is appropriately determined in consideration of the profile configuration of the side surface 34.

  In the cross section of the tire 32 shown in FIG. 2, the profile of the inner boundary portion 106 is represented by an arc convex outward. In FIG. 2, the arrow Ru indicates the radius of an arc representing the profile of the inner boundary portion 106.

  In the tire 32, the radius Ru of the arc representing the profile of the inner boundary portion 106 is preferably 40 mm or more. This suppresses the concentration of strain on the inner boundary portion 106. In this tire 32, since the effect produced by the recess 96 is sufficiently exerted, the bead durability is effectively improved and the rolling resistance is effectively reduced. The upper limit of the radius Ru is appropriately determined in consideration of the profile configuration of the side surface 34.

  In the tire 32, from the viewpoint that the recess 96 effectively contributes to improvement of bead durability and reduction of rolling resistance, the radius Rs of the arc representing the profile of the outer boundary portion 104 is 40 mm or more, and the inner boundary portion 106 has It is more preferable that the radius Ru of the arc representing the profile is 40 mm or more.

  In the tire 32, the profile of the bottom portion 102 is represented by an arc that is convex inward. As a result, the force acting on the bottom portion 102 is effectively dispersed throughout the bottom portion 102. In the tire 32, strain is prevented from being concentrated on a specific portion of the bottom portion 102 and causing damage such as cracks. In this tire 32, since the effect produced by the recess 96 is sufficiently exerted, the bead durability is effectively improved and the rolling resistance is effectively reduced.

  In FIG. 2, the arrow Rb is the radius of the arc that represents the profile of the bottom portion 102. In the tire 32, the radius Rb is the radial distance DU from the end 88 of the folded portion 86 to the inner end PU of the recess 96 and the radial distance DS from the maximum width position PW to the outer end PS of the recess 96. , And the radius Rs of the circular arc representing the profile of the outer boundary portion 104 and the radius Ru of the circular arc representing the profile of the inner boundary portion 106 are appropriately determined. From the viewpoint of preventing damage due to stress concentration in the bottom portion 102, the radius Rb is preferably 40 mm or more.

  Although not shown, in the tire 32, the profile of the bottom portion 102 of the recess 96 may be represented by a straight line instead of an arc. In this case, the profile of the bottom portion 102 does not have to be in contact with the profile of the outer boundary portion 104 at the outer end PSb. The profile of the bottom portion 102 does not have to be in contact with the profile of the inner boundary portion 106 at the inner end PUb. Even when the profile of the bottom portion 102 is represented by a straight line, the force acting on the bottom portion 102 is effectively dispersed over the entire bottom portion 102, and damage to the bottom portion 102 is prevented. In this tire 32, it is preferable that the profile of the bottom portion 102 of the recess 96 is represented by a circular arc from the viewpoint that the effect produced by the recess 96 can be more sufficiently exhibited.

  In FIG. 2, reference numeral PN is the intersection of the normal line NL and the recess 96. This intersection point PN is a position on the recess 96 where the thickness from the ply body 84 to the recess 96 shows the minimum thickness, that is, a minimum thickness position. Reference numeral PC is the center position of the recess 96. The center position PC is specified at the position where the length of the recess 96 is halved, which is measured in the cross section shown in FIG.

  In the tire 32, the minimum thickness position PN of the recess 96 is located outside the center position PC of the recess 96 in the radial direction. In this tire 32, the force acting on the recess 96 is effectively dispersed throughout the recess 96. In the tire 32, strain is prevented from being concentrated at a specific portion of the recess 96 and causing damage such as cracks. In this tire 32, since the effect produced by the recess 96 is sufficiently exerted, the bead durability is effectively improved and the rolling resistance is effectively reduced. From this point of view, it is preferable that the minimum thickness position PN of the recess 96 is located outside the center position PC of the recess 96 in the radial direction.

  In the tire 32, the center position PC of the recess 96 is located between the outer end 78 of the apex 66 and the outer end 76 of the chafer 42 in the radial direction. In the tire 32, the recess 96 effectively suppresses the movement of the rubber in the portion radially outside the end 88 of the folded portion 86. In this tire 32, bead durability is effectively improved and rolling resistance is effectively reduced. From this point of view, the center position PC of the recess 96 is preferably located between the outer end 78 of the apex 66 and the outer end 76 of the chafer 42 in the radial direction.

  In FIG. 2, a double-headed arrow HW indicates a radial distance from the bead base line to the maximum width position PW. A double-headed arrow HB is a radial distance from the inner end PU of the recess 96 to the outer end PS.

  In the tire 32, the ratio of the radial distance HB to the radial distance HW is preferably 0.45 or more, and preferably 0.65 or less. By setting this ratio to 0.45 or more, the size of the recess 96 is sufficiently secured. The recess 96 effectively suppresses the movement of the rubber in the portion radially outside the end 88 of the folded portion 86. In this tire 32, bead durability is effectively improved and rolling resistance is effectively reduced. From this viewpoint, the ratio is more preferably 0.50 or more. By setting this ratio to 0.65 or less, the size of the recess 96 is appropriately maintained. In the tire 32, the influence of the recess 96 on the rigidity is effectively suppressed. From this viewpoint, the ratio is more preferably 0.60 or less.

  In the tire 32, the outer end 108 of the first apex 70 is located inside the end 88 of the folded-back portion 86 in the radial direction. In the tire 32, the concentration of strain on the end 88 of the folded portion 86 is suppressed. In addition, the tire 32 can secure a sufficient area in the side portion S that can contribute to bending, and can easily set the contour of the ply body 84 extending along the apex 66. In the tire 32, the protrusion of the side surface 34 outward in the axial direction is effectively suppressed, so that the amount of strain acting on the recess 96 is sufficiently reduced. In the tire 32, damage such as cracks in the recess 96 is unlikely to occur, so that the above-described effect exerted by the recess 96 is sufficiently exerted. Moreover, since the side surface 34 is prevented from protruding outward in the axial direction, and the first apex 70 is configured with a small volume, the tire 32 can reduce rolling resistance. From this viewpoint, it is preferable that the outer end 108 of the first apex 70 is located inside the end 88 of the folded-back portion 86 in the radial direction.

  In FIG. 2, reference numeral PF is a position on the side surface 34 corresponding to a radially outer end of a contact surface between the tire 32 and the rim flange LF, that is, a flange contact end. In the tire 32, the outer end 108 of the first apex 70 is located outside the flange contact end PF in the radial direction. In the tire 32, the rigidity of the first apex 70 is appropriately maintained, and the protrusion of the side surface 34 at the outer side portion of the flange contact end PF is effectively suppressed. In this tire 32, good bead durability is effectively maintained. From this point of view, it is preferable that the outer end 108 of the first apex 70 is located outside the flange contact end PF in the radial direction.

  In FIG. 2, a double-headed arrow HA indicates a radial distance from the radially inner end PA of the core 64 to the outer end 108 of the first apex 70. The double-headed arrow DB is the distance from the axially inner end PB of the core 64 to the carcass ply 82. This distance DB is represented by the shortest distance.

  In the tire 32, the radial distance HA from the radial inner end PA of the core 64 to the outer end 108 of the first apex 70 is preferably 15 mm or more and 45 mm or less. By setting the distance HA to be 15 mm or more, the rigidity of the first apex 70 is appropriately maintained, and the side surface 34 at the outer side portion of the flange contact end PF is effectively suppressed. In this tire 32, good bead durability is effectively maintained. From this viewpoint, the distance HA is more preferably 20 mm or more, further preferably 25 mm or more. By setting the distance HA to be 45 mm or less, the tire 32 can sufficiently secure the region that can contribute to the bending in the side portion S, and can easily set the contour of the ply main body 84 extending along the apex 66. In this tire 32, since the side surface 34 is prevented from protruding outward in the axial direction, the amount of strain acting on the recess 96 is reduced. In the tire 32, the occurrence of damage such as cracks in the recess 96 is suppressed, so that the effect produced by the recess 96 is sufficiently exerted. From this viewpoint, the distance HA is more preferably 40 mm or less, and further preferably 35 mm or less.

  In the tire 32, the distance DB from the axially inner end PB of the core 64 to the carcass ply 82 is preferably 1 mm or more. By setting the distance DB to 1 mm or more, rubbing between the carcass ply 82 and the core 64 under a load applied during traveling is prevented. In the tire 32, cutting of the carcass cord near the axially inner end PB of the core 64 is effectively prevented. From this viewpoint, the distance DB is preferably 1.5 mm or more. The distance DB is preferably 5 mm or less from the viewpoint that the first apex 70 is configured with an appropriate volume and the influence of the first apex 70 on the rolling resistance is suppressed.

  By the way, when the flatness of the tire 32 is 65% or less and the cross-sectional width is 385 or more, the tire 32 has an axial width of the tread 36 from the bead base line to the carcass and the carcass. The carcass height, which is represented by the radial height up to the intersection with the inner surface of 44, is low. In this tire 32, the region where the effect of the load can be absorbed by bending (that is, the region which can contribute to the above-mentioned bending) is narrower than that of a normal tire. Therefore, it is difficult for the tire 32 to secure sufficient bead durability.

  As described above, the radial height of the first apex 70 of the tire 32 is low, and the recess 96 is provided in the zone of the side surface 34 between the maximum width position PW and the end 88 of the folded portion 86. . The first apex 70 and the recess 96 contribute to the bending of the tire 32. The recess 96 suppresses the movement of the rubber in the portion radially outside the end 88 of the folded portion 86, and also contributes to the reduction of the mass. Therefore, even if the flatness of the tire 32 is 65% or less and the cross-sectional width is 385 or more, the tire 32 is lightweight and has improved bead durability. , And reduction of rolling resistance is achieved.

  As is clear from the above description, according to the present invention, it is possible to obtain a heavy-duty pneumatic tire that achieves improved bead durability and reduced rolling resistance while achieving weight reduction.

  The embodiments disclosed this time are illustrative in all points and not restrictive. The technical scope of the present invention is not limited to the above-described embodiment, and the technical scope includes all modifications within the scope equivalent to the configurations described in the claims.

  Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited to such Examples.

[Example 1]
A heavy duty pneumatic tire (tire size = 11R22.5) having the basic configuration shown in FIGS. 1 and 2 and having the specifications shown in Table 1 below was obtained.

  In the first embodiment, the outer end of the first apex is arranged between the end of the folded portion and the flange contact end PF in the radial direction. In Table 1, it is "in" that the outer end of the first apex is located inside the end of the folded portion, and the outer end of the first apex is located outside the flange contact end. It is represented by "out".

  In Example 1, the radial distance HA from the radial inner end PA of the core to the outer end of the first apex was set to 30 mm. The distance DB from the axially inner end PB of the core to the carcass ply was set to 1.5 mm.

  In the first embodiment, the minimum thickness TA from the ply body to the recess is measured along a line segment indicating the minimum thickness TA (that is, the normal line NL), and it is obtained as if there is no recess from the ply body. The ratio (TA / TB) to the virtual thickness TB up to the virtual side surface VL was set to 0.5.

[Comparative Example 1]
Comparative Example 1 is the conventional tire (tire size = 11R22.5) shown in FIG. In Comparative Example 1, the apex was composed of a conventional apex. No depression is provided on the side surface.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1 except that no recess was formed on the side surface.

[Example 2]
A tire of Example 2 was obtained in the same manner as in Example 1 except that the outer end of the first apex was arranged radially outside the end of the folded portion. In Table 1, “out” indicates that the outer end of the first apex is located outside the end of the folded portion.

[Example 3]
A tire of Example 3 was obtained in the same manner as in Example 1 except that the outer end of the first apex was arranged radially inward of the flange contact end. In Table 1, it is indicated by "in" that the outer end of the first apex is located inside the flange contact end.

[Example 4-5]
Tires of Examples 4-5 were obtained in the same manner as in Example 1 except that the distance DB was changed as shown in Table 2 below.

[Example 6-9]
Tires of Examples 4-5 were obtained in the same manner as in Example 1 except that the distance HA was changed as shown in Table 2 below.

[PTL resistance performance]
As the bead durability, PTL (ply turn-up loose) performance was evaluated. In this evaluation, the tire was mounted on a rim (size = 22.5 × 8.75) and the inside of the tire was filled with air. The internal pressure of the tire was adjusted to 1000 kPa. The tire was mounted on a bench tester with a drive drum. A longitudinal load of 76.53 kN was applied to the tire, the tire was run at 20 km / h, and the running time until damage to the bead and the PTL occurrence state were confirmed. The results are shown in Tables 1 and 2 below, using the tire of Example 1 as an index. The larger the value is, the less PTL is generated and the better the bead durability.

[Rolling resistance coefficient (RRC)]
The tire was mounted on a rim (size = 22.5 × 8.75) and the inside of the tire was filled with air. The internal pressure of the tire was adjusted to 800 kPa. This tire was mounted on a rolling resistance tester. A longitudinal load of 26.72 kN was applied to the tire, the tire was run at 80 km / h, and the rolling resistance was measured. The results are shown in Tables 1 and 2 below, using Example 1 as an index of 100. The larger the value, the smaller the rolling resistance, which is preferable.

[CBU resistance]
As the bead durability, the CBU (casing break up) performance was evaluated. In this evaluation, the tire was mounted on a rim (size = 22.5 × 8.75), 300 cc of water was poured into the tire, and air was filled therein. The internal pressure of the tire was adjusted to 800 kPa. It was allowed to stand for 2 weeks in an atmosphere adjusted to 80 ° C. After this pretreatment, 300 cc of water was added to the inside of the tire and air was filled, and the internal pressure was adjusted to 1000 kPa. The tire was mounted on a bench tester with a drive drum. A longitudinal load of 76.53 kN was applied to the tire, the tire was run at 20 km / h, and the running time until damage to the bead and the occurrence status of CBU were confirmed. The results are shown in Tables 1 and 2 below, using the tire of Example 1 as an index. The larger the value, the less likely that CBU is generated and the better the bead durability.

[Ozone crack resistance]
The tire was allowed to stand for 2 weeks in an atmosphere adjusted to 80 ° C. After this pretreatment, the tire was mounted on a rim (size = 22.5 × 8.75) and the inside of the tire was filled with air. The internal pressure of the tire was adjusted to 800 kPa. The tire was mounted on a bench tester with a drive drum. A longitudinal load of 26.72 kN was applied to the tire, and the tire was run at 40 km / h in an atmosphere in which the ozone concentration was adjusted to 50 pphm to confirm the occurrence of ozone cracks. The results are shown in Tables 1 and 2 below, using the tire of Example 1 as an index. The larger the value, the less likely ozone cracks occur.

  As shown in Tables 1 and 2, in the examples, a round apex is used as the first apex, and a recess is provided on the side surface to reduce the weight while improving bead durability and rolling resistance. It is confirmed that the reduction of The example has a higher evaluation than the comparative example. From this evaluation result, the superiority of the present invention is clear.

  The technique for achieving bead durability improvement and rolling resistance reduction while achieving weight reduction described above can be applied to various tires.

2, 32 ... Tires 4, 40 ... Beads 6, 82 ... Carcass ply 8, 84 ... Ply body 10, 86 ... Folding portion 10a ... Ends of folding portion 10 12, 64 ... Core 14, 66 ... Apex 16 ... First apex 16a ... Outer end of the first apex 18 ... Second apex 20, 52 ... Filler 20a ... -Inner end 20b of filler 20 ... Outer end of filler 20 22, 42 ... Chafer 24, 68 ... Wire 34 ... Side surface 36 ... Tread 38 ... Sidewall 44 ... Carcass 54 ... Outer surface of tread 36 (tread surface)
70 ... First apex 72 ... Second apex 74 ... Bottom surface of second apex 72 76 ... Outer end of chafer 42 78 ... Outer end of second apex 72 ( (Outer edge of Apex 66)
80 ... Inner end of sidewall 38 88 ... End of folded portion 86 92 ... First end of filler 52 94 ... Second end of filler 52 96 ... Recess 98 ... Outer part 100 ... Inner part 102 ... Bottom part 104 ... Outer boundary part 106 ... Inner boundary part 108 ... Outer end of the first apex 70

Claims (11)

A pair of beads,
A carcass ply having a ply body bridging between one bead and the other bead, and a folded portion that is continuous with the ply body and is folded back from the inner side in the axial direction around the bead,
Located outside the folded-back portion in the axial direction, including a metal cord, and a pair of fillers,
The bead includes a core, a first apex that surrounds the core, and a second apex that is located radially outside the first apex,
The outer periphery of the first apex has a rounded contour,
The first apex is harder than the second apex,
A heavy-duty pneumatic tire in which a recess is provided in a zone between a maximum width position and an end of the folded portion on a side surface of the tire. When the side surface of the tire corresponds to the outer end of the contact surface with the flange of the rim to which the tire is fitted, and the position on the side surface is the flange contact end,
The heavy duty pneumatic tire according to claim 1, wherein an outer end of the first apex is located inside an end of the folded-back portion and outside an end of the flange contact end in the radial direction.   The pneumatic tire for heavy loads according to claim 1 or 2, wherein a radial distance from a radial inner end of the core to an outer end of the first apex is 15 mm or more and 45 mm or less.   The heavy duty pneumatic tire according to any one of claims 1 to 3, wherein a distance from an inner end of the core in the axial direction to the carcass ply is 1 mm or more.   The ratio of the minimum thickness from the ply body to the recess, which is measured along a line segment indicating the minimum thickness, to the virtual thickness from the ply body to the virtual side surface obtained without the recess, The heavy duty pneumatic tire according to any one of claims 1 to 4, which is 0.3 or more and 0.7 or less.   The heavy duty pneumatic tire according to claim 1, wherein a radial distance from an end of the folded-back portion to an inner end of the recess is 10 mm or more and 20 mm or less. The recess includes a bottom portion and an outer boundary portion located radially outside the bottom portion,
The heavy-duty pneumatic tire according to any one of claims 1 to 6, wherein the profile of the outer boundary portion is represented by an arc that is convex outward, and the radius of the arc is 40 mm or more. The recess includes a bottom portion and an inner boundary portion located radially inward of the bottom portion,
The heavy-duty pneumatic tire according to any one of claims 1 to 7, wherein the profile of the inner boundary portion is represented by an arc that is convex outward, and the radius of the arc is 40 mm or more.   The heavy-duty pneumatic tire according to claim 7 or 8, wherein the profile of the bottom portion is represented by an inwardly convex arc.   The heavy duty pneumatic tire according to claim 7 or 8, wherein the profile of the bottom portion is represented by a straight line.   The first end of the filler is located inside the bead baseline in the radial direction, and the second end of the filler is located between the end of the folded portion and the bead baseline. The pneumatic tire for heavy loads according to any one of 1.