Heavy load pneumatic tire

Abstract

To provide a heavy load pneumatic tire which is excellent in fuel consumption and hardly causes PTL.SOLUTION: A tire 2 comprises: a pair of beads 38; a carcass ply 82 which includes a ply body 84 and a folding part 86; a pair of side walls 36 which are positioned at outer sides of the carcass ply 82 in an axial direction; and a buffer rubber layer 22. A recess 96 is arranged on a lateral face of the tire 2 at a zone between a maximum width position and an edge of the folding part 86. The bead 38 includes: a core 64; a first apex 70 which surrounds the core 64; and a second apex 72 which is positioned at an outer side of the first apex 70 in a radial direction. The buffer rubber layer 22 is positioned in the axial direction between the side wall 36 and the second apex 72. The edge 88 of the folding part 86 is sandwiched in the axial direction between the buffer rubber layer 22 and the second apex 72. A complex elastic modulus of the buffer rubber layer 22 at 70°C is higher than that of the second apex 72 at 70°C.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a heavy-duty pneumatic tire. [Background technology]

[0002] In order to improve the fuel efficiency of tires, it has been proposed to provide recesses in the sidewalls of the tires (for example, Patent Document 1). This technology reduces energy loss in the sidewalls, thereby improving fuel efficiency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-066242 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a heavy-duty pneumatic tire that is improved in fuel economy and durability. [Means for solving the problem]

[0005] A tire according to one aspect of the present invention includes: a pair of beads; a carcass ply having a ply body that bridges between one bead and the other bead, and a turn-up portion that is continuous with the ply body and turned up around the bead from the inside to the outside in the axial direction; A pair of sidewalls located axially outward of the carcass ply; a cushioning rubber layer; A recess is provided in a zone of the side of the tire between the maximum width position and an end of the turned-up portion, The bead has a core, a first apex surrounding the core, and a second apex located radially outward of the first apex, the cushioning rubber layer is located between the sidewall and the second apex in the axial direction, an end of the folded portion is sandwiched between the cushion rubber layer and the second apex in the axial direction, The complex modulus of elasticity of the cushioning rubber layer at 70°C is higher than the complex modulus of elasticity of the second apex at 70°C. [Effects of the Invention]

[0006] The present invention provides a heavy-duty pneumatic tire that has good fuel economy and is less susceptible to PTL (Ply Turn-up Loose). This heavy-duty pneumatic tire has improved durability while also improving fuel economy. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a heavy-duty pneumatic tire according to one embodiment. [Figure 2] FIG. 2 is a partial cross-sectional view showing a bead portion of the tire of FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the same location as FIG. [Figure 4] FIG. 4 is a partial cross-sectional view showing a bead portion of a heavy-duty pneumatic tire according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] The tire of the present invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly includes a rim and a tire mounted on the rim.

[0009] In the present invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is called the standard state.

[0010] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part of the tire's meridian cross section, which cannot be measured when the tire is mounted on a regular rim, are measured on a cut surface of the tire obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads of the tire mounted on a regular rim. Note that the tire configuration, which cannot be confirmed when the tire is mounted on a regular rim, is confirmed on the cut surface.

[0011] A genuine rim is a rim specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "design rim" in the TRA standard, and the "measuring rim" in the ETRTO standard are all genuine rims.

[0012] Normal tire pressure refers to the pressure specified in the standard on which the tire is based. The "maximum tire pressure" in the JATMA standard, the "maximum tire pressure" listed in the TRA standard's "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0013] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0014] In the present invention, the loss tangent (tan δ) and complex modulus of an element made of crosslinked rubber among elements constituting a tire are measured using a viscoelasticity spectrometer in accordance with the provisions of JIS K 6394. The measurement conditions are as follows: Initial strain = 10% Dynamic strain = ±1% Frequency = 10 Hz Mode = Decompression mode Temperature=70℃ In this measurement, a test piece (length 40 mm x width 4 mm x thickness 1 mm) is sampled from the tire. The longitudinal direction of the test piece is aligned with the circumferential direction of the tire. If it is not possible to sample a test piece from the tire, the test piece is sampled from a sheet of crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes. In the present invention, the loss tangent and complex modulus are expressed as loss tangent and complex modulus at 70°C.

[0015] In the present invention, the rubber hardness of an element made of crosslinked rubber among the elements constituting the tire is a durometer A hardness measured in an atmosphere at a temperature of 23°C using a type A durometer in accordance with the provisions of JIS K6253-3. In this measurement, a test piece of a predetermined size is sampled from the tire, and the measurement is carried out using this test piece. If it is not possible to sample test specimens from tires, test specimens are prepared from the aforementioned rubber sheets.

[0016] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions.

[0017] [Findings that form the basis of the present invention] The tire described in Patent Document 1 has a recess in the sidewall. Specifically, the recess is provided in the zone between the maximum width position of the tire and the end of the folded-up portion of the carcass ply. The recess reduces the volume of rubber in the sidewall of the tire, thereby suppressing energy loss due to heat generation and improving fuel economy. Because the sidewall of a tire is prone to movement when inflated or under load, providing a recess in this area to reduce the rubber volume is effective from the perspective of improving fuel economy. Furthermore, providing the recess reduces the tire's weight and improves fuel economy. On the other hand, if a recess is made in the tire sidewall, the distance between the end of the turned-up part of the carcass ply and the outer surface of the tire becomes shorter, which increases the risk of Ply Turn-up Loose (PTL), a damage in which the end of the turned-up part of the carcass ply peels off.

[0018] Therefore, we investigated ways to reduce the risk of PLT, and found that by placing a buffer layer harder than the second apex between the sidewall and the second apex, it is possible to reduce distortion that occurs near the edge of the folded portion, thereby reducing the risk of PLT, which led to the completion of the invention described below.

[0019] [Details of the embodiment of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0020] 1 shows a portion of a heavy-duty pneumatic tire 2 (hereinafter sometimes simply referred to as "tire 2") according to one embodiment of the present invention. This tire 2 is mounted on a heavy-duty vehicle such as a truck or a bus.

[0021] FIG. 1 shows a portion of a cross section of the tire 2 taken along a plane including the rotation axis of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of the paper on which FIG. 1 is drawn is the circumferential direction of the tire 2. In FIG. 1, the dashed-dotted line CL represents the equatorial plane of the tire 2.

[0022] In Figure 1, the solid line BBL extending in the axial direction is the bead base line, which is a line that defines the rim diameter (see JATMA, etc.) of the rim (regular rim).

[0023] In FIG. 1, the symbol PW indicates the axial outer end of the tire 2. This outer end PW is identified based on a virtual side surface obtained by assuming that the side surface 4 of the tire 2 has no decorations such as patterns or letters. The axial distance from one outer end PW to the other outer end PW is the maximum width of the tire 2, that is, the cross-sectional width of the tire 2 (see JATMA, etc.). This outer end PW is the position where the tire 2 exhibits the maximum width (hereinafter also referred to as the maximum width position of the tire 2).

[0024] The tire 2 includes a tread 34 , a pair of sidewalls 36 , a pair of beads 38 , a pair of shock absorbing rubber layers 22 , a pair of chafers 40 , a carcass 42 , a belt 44 , a pair of cushion layers 46 , an inner liner 48 , insulation 50 and a pair of fillers 52 .

[0025] The tread 34 comes into contact with the road surface at its outer surface 6. The outer surface 6 of the tread 34 is a tread surface 54. The side surfaces 4 mentioned above are continuous with the ends of this tread surface 54 and extend radially inward.

[0026] In this tire 2, the tread 34 has a base portion 56 and a cap portion 58. In this tire 2, a pair of base portions 56 is provided. These base portions 56 are arranged with a gap between them in the axial direction. Each base portion 56 covers an end portion of the belt 44. The base portions 56 are made of crosslinked rubber. The cap portion 58 is located radially outward of the base portions 56. This cap portion 58 covers the pair of base portions 56 and the entire belt 44. The outer surface of this cap portion 58 forms the tread surface 54 mentioned above. The cap portion 58 is made of crosslinked rubber.

[0027] In the tire 2, at least three circumferential grooves 60 are formed in the tread 34. As a result, at least four circumferential land portions 62 are formed in the tread 34.

[0028] Each sidewall 36 is continuous with an edge of the tread 34. The sidewalls 36 extend radially inward from the edge of the tread 34. The sidewalls 36 are made of crosslinked rubber. The outer surfaces of the sidewalls 36 form the side surfaces 4 of the tire 2.

[0029] Each bead 38 is located radially inward of the sidewall 36. Each bead 38 includes a core 64 and an apex 66.

[0030] The core 64 extends in the circumferential direction. The core 64 includes a wound steel wire (not shown). The core 64 has a substantially hexagonal cross-sectional shape. In the tire 2, the core 64 is located radially outward from the bead base line.

[0031] The apex 66 is located radially outward of the core 64. The apex 66 extends radially outward from the core 64. In the tire 2, the apex 66 includes a first apex 70 and a second apex 72. The first apex 70 is located radially outward of the core 64. In the tire 2, the first apex 70 tapers radially outward. The second apex 72 is located axially outward of the first apex 70. The second apex 72 has a large thickness at a portion where an outer end 74 of the first apex 70 is located. The outer portion of the second apex 72 tapers radially outward. The inner portion of the second apex 72 tapers radially inward. The first apex 70 and the second apex 72 are each made of crosslinked rubber. The first apex 70 is harder than the second apex 72.

[0032] In the tire 2, 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.

[0033] Each of the cushioning rubber layers 22 is located between the sidewall 36 and the second apex 72 in the axial direction. The cushioning rubber layer 22 will be described in detail later.

[0034] Each chafer 40 is located axially outward of the bead 38. The chafer 40 is located radially inward of the sidewall 36. Although not shown, the chafer 40 comes into contact with the rim. The chafer 40 is made of crosslinked rubber.

[0035] 1, the reference character PT denotes the toe of the tire 2. The outer surface of the chafer 40 from the toe PT to the inner end 80 of the sidewall 36 forms a part of the side surface 4.

[0036] The carcass 42 is located inside the tread 34, the sidewalls 36, and the chafers 40. The carcass 42 includes at least one carcass ply 82. The carcass 42 of the tire 2 is made up of one carcass ply 82.

[0037] Although not shown, the carcass ply 82 includes a large number of carcass cords arranged in parallel. These carcass cords are covered with a topping rubber. Each carcass cord intersects with the equatorial plane. In this tire 2, the angle that the carcass cords make with the equatorial plane is between 70° and 90°. The carcass 42 of this tire 2 has a radial structure. In this tire 2, cords made of steel are used as the carcass cords. In the tire 2, the material of the carcass cords may be organic fiber.

[0038] In the tire 2, the carcass ply 82 is turned up from the inside to the outside in the axial direction around each of the beads 38 (more specifically, the core 64). The carcass ply 82 has a ply body 84 that spans between one bead 38 and the other bead 38, and a pair of turn-up portions 86 that are continuous with the ply body 84 and are turned up from the inside to the outside in the axial direction around each of the beads 38. In the tire 2, the end 88 of the turned-up portion 86 is located radially inward of the outer end 74 of the first apex 70. The end 88 of the turned-up portion 86 may be located radially outward of the outer end 74 of the first apex 70. The radial position of the end 88 of the turned-up portion 86 may coincide with the outer end 74 of the first apex 70.

[0039] The belt 44 is located radially inside the tread 34. The belt 44 is located radially outside the carcass 42 (carcass ply 82).

[0040] In this tire 2, the belt 44 is made up of four belt plies 90 laminated in the radial direction. In this tire 2, there is no particular limit to the number of belt plies 90 constituting the belt 44. The configuration of this belt 44 is determined as appropriate, taking into consideration the specifications of the tire 2.

[0041] Although not shown, each belt ply 90 includes a number of belt cords arranged in parallel. These belt cords are covered with a topping rubber. In this tire 2, the belt cords are made of steel.

[0042] The belt cords are inclined with respect to the equator plane in each belt ply 90. The belt cords in one belt ply 90 intersect with the belt cords in another belt ply 90 laminated on the one belt ply 90.

[0043] In the tire 2, the second belt ply 90B located between the first belt ply 90A and the third belt ply 90C has the largest axial width among the four belt plies 90. The fourth belt ply 90D located at the outermost position in the radial direction has the smallest axial width.

[0044] Each cushion layer 46 is located at an end portion of the belt 44 between the belt 44 and the carcass 42. The cushion layer 46 is made of crosslinked rubber.

[0045] The inner liner 48 is positioned inside the carcass 42. The inner liner 48 is joined to the inner surface of the carcass 42 via insulation 50 made of cross-linked rubber. The inner liner 48 forms the inner surface of the tire 2. The inner liner 48 is made of cross-linked rubber that has excellent air barrier properties. The inner liner 48 maintains the internal pressure of the tire 2.

[0046] Each filler 52 is located in the bead portion B. The fillers 52 are located between the chafer 40 and the carcass 42. The fillers 52 are also located between the chafer 40 and the cushioning rubber layer 22. The fillers 52 are folded back at the beads 38.

[0047] Although not shown, the filler 52 includes a large number of parallel metal cords. In the tire 2, the material of the metal cords is steel. In the tire 2, the metal cords included in the filler 52 are steel cords. In the filler 52, the metal cords are covered with a topping rubber.

[0048] In the tire 2, a first end 92 (also referred to as an inner end) of the filler 52 is located between the bead base line and the outer end 74 of the first apex 70 in the radial direction. In the tire 2, a second end 94 (also referred to as an outer end) of the filler 52 is located between the bead base line and the end 88 of the turned-up portion 86 in the radial direction.

[0049] FIG. 2 shows a part of the cross section of the tire 2 in FIG. 1. FIG. 2 shows a bead 38 portion of the tire 2 (hereinafter also referred to as bead portion B). In FIG. 2, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of FIG. 2 is the circumferential direction of the tire 2. FIG. 3 is a cross-sectional view showing the same location as FIG. 2. FIG. 3 is mainly referred to for explaining the dimensions of the tire 2.

[0050] In this tire 2, a recess 96 is provided in the side surface 4. In this tire 2, this recess 96 is provided in the outer surface of the sidewall 36 that forms part of the side surface 4. As shown in Fig. 2, the recess 96 has an inwardly convex shape. The recess 96 extends without interruption in the circumferential direction.

[0051] In FIG. 2 , the symbol PS indicates the outer end of the recess 96. The symbol PU indicates the inner end of the recess 96. In the tire 2, the outer end PS of the recess 96 is located radially inward of the maximum width position PW. The inner end PU of the recess 96 is located radially outward of the end 88 of the turned-up portion 86. In the tire 2, the recess 96 is provided in a zone of the side surface 4 between the maximum width position PW and the end 88 of the turned-up portion 86.

[0052] When a load acts on the tire 2 mounted on a rim, the rubber in the tire 2 moves toward the vicinity of the end 88 of the turned-up portion 86 and the second end 94 of the filler 52. As described above, in the tire 2, the recess 96 is located in the zone between the maximum width position PW and the end 88 of the turned-up portion 86. By providing this recess 96, it is possible to reduce the volume of rubber that moves when a load acts on the tire 2. This recess 96 suppresses the movement of the rubber in the portion radially outward of the end 88 of the turned-up portion 86 when a load acts on the tire 2. This suppression of movement also suppresses heat generation associated with deformation. Therefore, energy loss when a load acts on the tire 2 is suppressed, contributing to improved fuel efficiency. The recess 96 also contributes to reducing the weight of the tire 2. From this perspective, the recess 96 can also contribute to improved fuel efficiency of the tire 2.

[0053] In FIG. 3 , the dotted line VL is a virtual side surface obtained if the recess 96 were not present on the side surface 4. This virtual side surface VL is a part of the aforementioned virtual side surface used to identify the maximum width position PW. The solid line NL is a normal to the ply body 84. The double-headed arrow TA indicates the thickness from the ply body 84 to the recess 96, measured along this normal line NL. In this tire 2, this thickness TA is represented by the minimum thickness from the ply body 84 to the recess 96. The double-headed arrow TB indicates the line segment indicating this minimum thickness TA, i.e., the virtual thickness from the ply body 84 to the virtual side surface VL, measured along the normal line NL.

[0054] In this tire 2, the ratio of the minimum thickness TA to the virtual thickness TB is preferably 0.3 or greater, and more preferably 0.7 or less. By setting this ratio to 0.3 or greater, an increase in strain near the bottom of this recess 96 is suppressed, and the minimum thickness TA is configured to have the necessary thickness. In this tire 2, the occurrence of damage such as cracks in this recess 96 is suppressed. From this viewpoint, this ratio is more preferably 0.4 or greater. By setting this ratio to 0.7 or less, the volume of the rubber constituting the sidewall 36 that moves toward the flange side of the rim when a load is applied can be reduced. Therefore, in this tire 2, energy loss is suppressed and fuel efficiency is improved. From this viewpoint, this ratio is more preferably 0.6 or less.

[0055] 2, the double-headed arrow DU indicates the radial distance from the end 88 of the folded portion 86 to the inner end PU of the recess 96. The double-headed arrow DS indicates the radial distance from the maximum width position PW to the outer end PS of the recess 96.

[0056] In this tire 2, the radial distance DU from the end 88 of the turned-up portion 86 to the inner end PU of the recess 96 is preferably 5 mm or more and preferably 30 mm or less. By setting this distance DU to 5 mm or more, the recess 96 is positioned with an appropriate gap between it and the end 88 of the turned-up portion 86, thereby preventing interference between the recess 96 and the turned-up portion 86. By setting this distance DU to 30 mm or less, the recess 96 is ensured to have a sufficient size in the zone between the maximum width position PW and the end 88 of the turned-up portion 86. From the same viewpoint, the radial distance DU is more preferably 10 mm or more and more preferably 20 mm or less.

[0057] In this tire 2, the radial distance DS from the maximum width position PW to the outer end PS of the recess 96 is preferably 3 mm or more and preferably 20 mm or less. By setting this distance DS to 3 mm or more, the recess 96 is disposed at an appropriate distance from the maximum width position PW. In this tire 2, the sidewall 36 has an appropriate thickness at the maximum width position PW, thereby maintaining good cut resistance. By setting this distance DS to 20 mm or less, the recess 96 is ensured to have a sufficient size in the zone between the maximum width position PW and the end 88 of the turned-up portion 86. From the same viewpoint, the radial distance DS is more preferably 5 mm or more and more preferably 10 mm or less.

[0058] In this tire 2, the radially inner portion of the side surface 4 from the maximum width position PW includes the aforementioned recess 96, an outer portion 98 extending radially outward from the outer end PS of this recess 96, and an inner portion 100 extending radially inward from the inner end PU of this recess 96.

[0059] The aforementioned imaginary side surface VL is located between the outer portion 98 and the inner portion 100. The outer end PU of the recess 96 is the boundary between the outer portion 98 and the imaginary side surface VL. The inner end PU of the recess 96 is the boundary between the inner portion 100 and the imaginary side surface VL. In the tire 2, the profile of the imaginary side surface VL and the profile of the outer portion 98 are in contact with each other at the boundary PS. The profile of the imaginary side surface VL and the profile of the inner portion 100 are in contact with each other at the boundary PU.

[0060] In this tire 2, the recess 96 has a bottom 102, an outer boundary 104, and an inner boundary 106.

[0061] The outer boundary 104 bridges the bottom portion 102 and the aforementioned outer portion 98. The profile of the outer boundary 104 meets the profile of the outer portion 98 at an outer edge PS, which is also the boundary between the outer boundary 104 and the outer portion 98.

[0062] 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 an inner end PU. This inner end PU is also the boundary between the inner boundary portion 106 and the inner portion 100.

[0063] In FIG. 3 , the symbol PSb denotes the outer end of the bottom portion 102. The symbol PUb denotes the inner end of the bottom portion 102. In this tire 2, the outer boundary portion 104 is located radially outward of 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. This outer end PSb is the boundary between the bottom portion 102 and the outer boundary portion 104. The inner boundary portion 106 is located radially inward of the bottom portion 102. The profile of the bottom portion 102 contacts the profile of the inner boundary portion 106 at the inner end PUb. This inner end PUb is the boundary between the bottom portion 102 and the inner boundary portion 106.

[0064] 2 and 3, the profile of the outer boundary 104 is represented by an outwardly convex arc. In this Figure, arrow Rs indicates the radius of the arc representing the profile of the outer boundary 104.

[0065] In this tire 2, the radius Rs of the arc representing the profile of the outer boundary portion 104 is preferably 40 mm or more. This suppresses the concentration of strain on the outer boundary portion 104, thereby preventing the occurrence of damage such as cracks. The upper limit of this radius Rs is determined appropriately, taking into consideration the configuration of the profile of the side surface 4.

[0066] 2 and 3, the profile of the inner boundary 106 is represented by an outwardly convex arc. In this Figure, arrow Ru indicates the radius of the arc representing the profile of the inner boundary 106.

[0067] In this tire 2, 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, thereby preventing the occurrence of damage such as cracks. The upper limit of this radius Ru is determined appropriately in consideration of the configuration of the profile of the side surface 4.

[0068] In this tire 2, it is more preferable that the radius Rs of the arc representing the profile of the outer boundary 104 is 40 mm or more, and the radius Ru of the arc representing the profile of the inner boundary 106 is 40 mm or more.

[0069] In this tire 2, the profile of the bottom portion 102 is represented by an inwardly convex arc. Therefore, the force acting on the bottom portion 102 is effectively dispersed over the entire bottom portion 102. In this tire 2, strain is prevented from concentrating at a specific point on the bottom portion 102, preventing damage such as cracks from occurring.

[0070] 3, arrow Rb indicates the radius of the arc representing the profile of the bottom portion 102. In the tire 2, this radius Rb is determined appropriately in consideration of the above-mentioned radial distance DU from the end 88 of the turned-up 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, as well as the radius Rs of the arc representing the profile of the outer boundary portion 104 and the radius Ru of the arc representing the profile of the inner boundary portion 106. From the viewpoint of preventing damage due to stress concentration in the bottom portion 102, this radius Rb is preferably 40 mm or greater.

[0071] In Figure 3, the symbol PN denotes the intersection point between the normal line NL and the recess 96. This intersection point PN is the position on the recess 96 where the thickness from the ply body 84 to the recess 96 is the minimum thickness, i.e., the minimum thickness position. The symbol PC denotes the center position of the recess 96. This center position PC is identified at the position where the length of the recess 96 is half as measured on the cross section shown in Figure 3.

[0072] In this tire 2, the minimum thickness position PN of the recess 96 is located radially outward from the center position PC of the recess 96. In this tire 2, the force acting on the recess 96 is effectively dispersed throughout the recess 96. In this tire 2, strain is prevented from concentrating at a specific location of the recess 96, preventing damage such as cracks from occurring. From this perspective, it is preferable that the minimum thickness position PN of the recess 96 be located radially outward from the center position PC of the recess 96.

[0073] The cushioning rubber layer 22 is disposed between the second apex 72 and the sidewall 36 in the axial direction. This cushioning rubber layer 22 is disposed axially outward of the second apex 72. The cushioning rubber layer 22 has a central portion having approximately the same axial dimension, an outer portion tapering radially outward (toward the outer end 24), and an inner portion tapering radially outward (toward the inner end 26).

[0074] The cushion rubber layer 22 sandwiches the end 88 of the folded portion 86 between itself and the second apex 72. In other words, the end 88 of the folded portion 86 is disposed between the second apex 72 and the cushion rubber layer 22. A tire is prone to PTL when the end of the turned-up portion collapses due to internal inflation or load application, or when a load acts on the tire and distortion occurs near the turned-up portion. In contrast, in the tire 2, the end 88 of the turned-up portion 86 is located between the second apex 72 and the buffer rubber layer 22, so the second apex 72 suppresses collapse of the end of the turned-up portion and distortion near the turned-up portion caused by force from the carcass main body. Furthermore, distortion near the turned-up portion caused by force from the sidewall or rim is reduced because a sufficient distance is maintained from the side surface of the tire 2 to the end 88 of the turned-up portion 86. In addition, the provision of the buffer rubber layer 22 also suppresses deformation of the bead portion B.

[0075] In the tire 2, the complex elastic modulus of the cushioning rubber layer 22 is higher than the complex elastic modulus of the second apex 72. By disposing the cushioning rubber layer 22 having such a configuration, it is possible to suppress deformation of the bead portion B caused by the force received from the rim when the tire is inflated with internal pressure or when a load acts on the tire 2 mounted on the rim. Therefore, it is possible to suppress distortion caused in the folded portion, and it is possible to suppress PTL. The complex elastic modulus of the buffer rubber layer 22 is, for example, 15 MPa or more and 20 MPa or less. The complex elastic modulus of the second apex 72 is, for example, 3.0 MPa or more and 6.0 MPa or less. From the viewpoint of being suitable for suppressing PTL, the complex elastic modulus of the cushion rubber layer 22 is preferably 3.0 times or more and 5.5 times or less the complex elastic modulus of the second apex 72, for example.

[0076] In the tire 2, the complex modulus of elasticity of the cushioning rubber layer 22 is preferably higher than the complex modulus of elasticity of the sidewall . In this case, distortion is less likely to occur near the end 88 of the folded portion 86, and PTL is less likely to occur, compared to when the cushioning rubber layer 22 is not provided. The complex elastic modulus of the cushioning rubber layer 22 is preferably 2.5 times or more and 8.0 times or less than the complex elastic modulus of the sidewall 36, for example. The complex elastic modulus of the sidewall 36 is, for example, not less than 2.0 MPa and not more than 6.0 MPa.

[0077] In the tire 2, the loss tangent (tan δ) of the cushioning rubber layer 22 is preferably smaller than the loss tangent of the second apex 72. In this tire 2, an end 88 of the turned-up portion 86 is disposed between the second apex 72 and the buffer rubber layer 22. Therefore, in the tire 2, the end 88 of the turned-up portion 86 is located near the center of the bead portion in the axial direction, and the buffer rubber layer 22 is disposed axially outward of the end 88 of the turned-up portion 86. In this case, the total amount of rubber disposed from the side surface 4 of the tire 2 to the turned-up portion 86 is large, and the amount of heat generated in the buffer rubber layer 22 in the tire 2 is likely to increase. Furthermore, an increase in the amount of heat generated is likely to accelerate deterioration of the rubber. In contrast, if the loss tangent of the buffer rubber layer 22 is made smaller than the loss tangent of the second apex 72, the buffer rubber layer 22 itself is less likely to generate heat, thereby suppressing deterioration of the buffer rubber layer 22.

[0078] The loss tangent of the cushioning rubber layer 22 is, for example, not less than 0.02 and not more than 0.03. The loss tangent of the second apex 72 is, for example, not less than 0.05 and not more than 0.07. The loss tangent of the cushioning rubber layer 22 is preferably 0.4 to 0.5 times the loss tangent of the second apex 72, for example.

[0079] In the tire 2, the outer end 24 of the buffer rubber layer 22 is located radially outward from the center position PC of the recess 96. In this case, the buffer rubber layer 22 has a sufficient length in the radial direction. Therefore, the provision of the recess 96 is suitable for suppressing deformation of the entire bead portion, including the portion where the thickness is reduced, and making it more difficult for PTL to occur. The radial distance between the outer end 24 of the cushioning rubber layer 22 and the center position PC of the recess 96 is, for example, not less than 5 mm and not more than 20 mm.

[0080] In the tire 2, the outer end 24 of the buffer rubber layer 22 is located radially outward of the minimum thickness portion from the ply body 84 to the recess 96. In other words, the outer end 24 of the buffer rubber layer 22 is located radially outward of the normal line NL. In this case, the buffer rubber layer 22 has a sufficient length in the radial direction. Therefore, the provision of the recess 96 is suitable for suppressing deformation of the entire bead portion, including the portion where the thickness is reduced, and making it less likely for PTL to occur. The distance between the outer end 24 of the cushioning rubber layer 22 and the minimum thickness portion from the ply body 84 to the recess 96, in other words, the distance between the outer end 24 of the cushioning rubber layer 22 and the normal line NL, is, for example, 5 mm or more and 10 mm or less.

[0081] In the tire 2, the outer end 24 of the buffer rubber layer 22 is located radially outward of the outer end 78 of the second apex 72. In this case, the buffer rubber layer 22 has a sufficient length in the radial direction. Therefore, the provision of the recess 96 is suitable for suppressing deformation of the entire bead portion, including the portion where the thickness is reduced, and making it more unlikely for PTL to occur. The radial distance between the outer end 24 of the cushioning rubber layer 22 and the outer end 78 of the second apex 72 is, for example, not less than 15 mm and not more than 35 mm.

[0082] In the tire 2, the inner end 26 of the cushioning rubber layer 22 is located more inward than the inner end 79 of the second apex 72 in the radial direction. The radial distance between the inner end 26 of the cushioning rubber layer 22 and the inner end 79 of the second apex 72 is, for example, greater than 0 mm and equal to or less than 10 mm.

[0083] In Figure 3, the double-headed arrow HC indicates the radial dimension of the cushioning rubber layer 22. This radial dimension HC of the cushioning rubber layer 22 is the radial distance between the inner end 26 of the cushioning rubber layer 22 and the outer end 24 of the cushioning rubber layer 22. The double-headed arrow HD indicates the radial dimension of the second apex 72. This radial dimension HD of the second apex 72 is the radial distance between the inner end 79 of the second apex 72 and the outer end 78 of the second apex 72.

[0084] In the tire 2, the radial dimension HC of the cushioning rubber layer 22 is longer than the radial dimension HD of the second apex 72. In this case, collapse of the ply body 84 is further suppressed, and the end 88 of the turned-up portion 86 is less likely to collapse, which is suitable for avoiding the occurrence of PTL.

[0085] In this tire 2, the center position PC of the recess 96 is located between the outer end 24 of the cushioning rubber layer 22 and the outer end 76 of the chafer 40 in the radial direction. In this tire 2, a sufficient distance is ensured between the recess 96 and the end 88 of the turned-up portion 86. Therefore, the occurrence of PLC is suppressed.

[0086] 3, the double-headed arrow HW indicates the radial distance from the bead base line to the maximum width position PW, and the double-headed arrow HB indicates the radial distance from the inner end PU to the outer end PS of the recess 96.

[0087] In this tire 2, the ratio of the radial distance HB to the radial distance HW is preferably 0.45 or greater and preferably 0.65 or less. By setting this ratio to 0.45 or greater, the size of the recess 96 is ensured to be sufficient. This recess 96 can reduce the volume of rubber that moves when a load is applied to the tire 2 mounted on the rim. Therefore, the movement of the rubber in the portion radially outward of the end 88 of the turned-up portion 86 is effectively suppressed. From this viewpoint, this ratio is more preferably 0.50 or greater. By setting this ratio to 0.65 or less, the size of the recess 96 is appropriately maintained. In this tire 2, the effect of the recess 96 on rigidity is effectively suppressed. From this viewpoint, this ratio is more preferably 0.60 or less.

[0088] 3, the double-headed arrow WA indicates the axial dimension of the bead portion B at the end 88 of the turned-up portion 86. The double-headed arrow WB indicates the axial distance between the end 88 of the turned-up portion 86 and the ply body 84. In the tire 2, it is preferable that a ratio (WB / WA) of the axial distance WB to the axial dimension WA is equal to or greater than 0.3 and is equal to or less than 0.5. By setting the ratio (WB / WA) to 0.3 or greater, the axial dimension of the second apex 72 at the end 88 of the turned-up portion 86 can be ensured. Therefore, when a load acts on the mounted tire 2 during internal inflation or load application, the ply body 84 can be prevented from collapsing toward the side of the tire 2, thereby preventing distortion from occurring near the end 88 of the turned-up portion 86. Furthermore, by setting the ratio to 0.5 or less, the axial distance between the turned-up portion 86 provided along the second apex 72 and the sidewall 36 can be ensured, preventing distortion from occurring near the turned-up portion 86 during internal inflation or load application.

[0089] (Other embodiments) FIG. 4 shows a portion of a heavy-duty pneumatic tire 122 (hereinafter sometimes simply referred to as "tire 122") according to another embodiment of the present invention.

[0090] 4 shows a bead portion B of the tire 122. In FIG. 4, the left-right direction is the axial direction of the tire 122, and the up-down direction is the radial direction of the tire 122. The direction perpendicular to the plane of the paper on which FIG. 4 is drawn is the circumferential direction of the tire 122.

[0091] The tire 122 shown in Fig. 4 has the same configuration as the tire 2 shown in Fig. 1, except that the configuration of the bead 138 (apex 166) is different from the configuration of the bead 38 (apex 66). In Fig. 4, the same members as those of the tire 2 shown in Fig. 1 are denoted by the same reference numerals, and their description will be omitted.

[0092] In this tire 122 , the bead 138 includes a core 64 and an apex 166 . The apex 166 includes a first apex 170 and a second apex 172. Similar to the first apex 70 and second apex 72 of the tire 2 shown in FIG. In the apex 166, the hardness of the first apex 170 and the hardness of the second apex 172 are set in the same range as the hardness of the first apex 70 and the hardness of the second apex 72 of the tire 2 shown in FIG.

[0093] The apex 166 differs from the tire 2 shown in FIG. 1 in the structures of the first apex 170 and the second apex 172 . The first apex 170 of the apex 166 surrounds the core 64. In other words, the first apex 170 is located around the core 64. The second apex 172 is located radially outward from the first apex 170. The second apex 172 extends radially outward from the first apex 170. The second apex 172 tapers radially outward.

[0094] As shown in Fig. 4, in the tire 122, the outer periphery of the first apex 170 has a rounded profile. The first apex 170 is round. Therefore, the contact surface of the second apex 172 with the first apex 170, i.e., the bottom surface 174 of the second apex 172, has a shape concave radially outward in the cross section shown in Fig. 4. A tire according to an embodiment of the present invention may include such an apex 166 .

[0095] The tire according to the embodiment of the present invention may have a configuration in which the profile of the bottom 102 of the recess 96 in the tire 2 shown in FIG. 1 is represented by a straight line. On the other hand, in the tire according to the embodiment of the present invention, from the viewpoint of more fully exerting the effect achieved by the recess 96, it is preferable that the profile of the bottom 102 of the recess 96 be represented by a circular arc.

[0096] As is clear from the above description, the present invention can provide a heavy-duty pneumatic tire that has good fuel economy and is less likely to cause PTL. This heavy-duty pneumatic tire has improved durability while also improving fuel economy.

[0097] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The technical scope of the present invention is not limited to the above-described embodiments, and includes all modifications within the scope of equivalents to the configurations described in the claims. [Industrial Applicability]

[0098] The above-described techniques for improving fuel economy and durability can be applied to various types of tires.

[0099] [Note] The present invention includes the following aspects.

[0100] [1] A pair of beads; a carcass ply having a ply body that bridges between one bead and the other bead, and a turn-up portion that is continuous with the ply body and is turned up around the bead from the inside to the outside in the axial direction; A pair of sidewalls located axially outward of the carcass ply; a cushioning rubber layer; A recess is provided in a zone of the side of the tire between the maximum width position and an end of the turned-up portion, The bead has a core, a first apex surrounding the core, and a second apex located radially outward of the first apex, the cushioning rubber layer is located between the sidewall and the second apex in the axial direction, an end of the folded portion is sandwiched between the cushioning rubber layer and the second apex in the axial direction; the complex modulus of elasticity of the cushioning rubber layer at 70°C is higher than the complex modulus of elasticity of the second apex at 70°C; Heavy-duty pneumatic tires.

[0101] [2] The heavy-duty pneumatic tire according to the above-mentioned [1], wherein the outer end of the cushioning rubber layer is located radially outward from the center position of the recess.

[0102] [3] The heavy-duty pneumatic tire described in [1] above, wherein, in the radial direction, the outer end of the cushioning rubber layer is located outside the minimum thickness portion from the ply body to the recess.

[0103] [4] The heavy-duty pneumatic tire according to the above-mentioned [1], wherein the outer end of the cushioning rubber layer is located radially outward of the outer end of the second apex.

[0104] [5] A heavy-duty pneumatic tire according to any one of the above [1] to [4], wherein the ratio of the minimum thickness from the ply body to the recess to the virtual thickness from the ply body to a virtual side surface obtained if the recess does not exist, measured along the line segment indicating the minimum thickness, is 0.3 or more and 0.7 or less.

[0105] [6] The heavy-duty pneumatic tire according to any one of the above [1] to [5], wherein the loss tangent of the cushioning rubber layer at 70°C is smaller than the loss tangent of the second apex at 70°C.

[0106] [7] A heavy-duty pneumatic tire according to any one of the above [1] to [6], wherein the ratio of the axial distance between the end of the turned-up portion and the ply body to the axial dimension at the end of the turned-up portion is 0.3 or more and 0.5 or less.

[0107] [8] The heavy-duty pneumatic tire according to any one of the above [1] to [7], wherein the complex modulus of elasticity of the cushioning rubber layer at 70°C is 3.0 to 5.5 times the complex modulus of elasticity of the second apex at 70°C. [Explanation of symbols]

[0108] 2, 122... Tires 4. Side 6...External surface 22. Cushioning rubber layer 24: Outer end of the cushioning rubber layer 22 26: Inner end of the cushioning rubber layer 22 34 tread 36···Sidewall 38, 138... Bead 40 Chafer 42...Carcass 44 Belt 46. ​​Cushion layer 48···Inner liner 50···Insulation 52 Filler 54 Outer surface (tread surface) 56···Base 58 Cap part 60...Circumferential groove 62... Circumferential land area 64 cores 66, 166···Apex 70, 170... First apex 72, 172... Second Apex 74 Outer end of first apex 70 76 Outer end of chafer 40 78 Outer end of second apex 72 79 Inner end of second apex 72 80...Inner edge of sidewall 36 82···Carcass ply 84···Ply body 86... Folded part 88: End of folded portion 86 90 belt plies 92: First end of filler 52 94... Second end of filler 52 96...dent 98...outer part 100...Inner part 102...Bottom 104...outer boundary 106...Inner boundary

Claims

1. a pair of beads; a carcass ply having a ply body that bridges between one bead and the other bead, and a turn-up portion that is continuous with the ply body and is turned up around the bead from the inside to the outside in the axial direction; A pair of sidewalls located axially outward of the carcass ply; a cushioning rubber layer; A recess is provided in a zone of the side of the tire between the maximum width position and an end of the turned-up portion, The bead has a core, a first apex surrounding the core, and a second apex located radially outward of the first apex, the cushioning rubber layer is located between the sidewall and the second apex in the axial direction, an end of the folded portion is sandwiched between the cushion rubber layer and the second apex in the axial direction, a complex elastic modulus at 70°C of the cushioning rubber layer is higher than a complex elastic modulus at 70°C of the second apex; Heavy-duty pneumatic tires.

2. The heavy-duty pneumatic tire according to claim 1 , wherein an outer end of the cushioning rubber layer is located radially outward from a center position of the recess.

3. The heavy-duty pneumatic tire according to claim 1 , wherein an outer end of the cushioning rubber layer is located radially outward of a minimum thickness portion from the ply body to the recess.

4. The heavy-duty pneumatic tire according to claim 1 , wherein an outer end of the cushioning rubber layer is located radially outward of an outer end of the second apex.

5. 5. The heavy-duty pneumatic tire according to claim 1, wherein a ratio of a minimum thickness from the ply body to the depression to a virtual thickness from the ply body to a virtual side surface obtained assuming that the depression does not exist, measured along a line segment indicating the minimum thickness, is 0.3 or more and 0.7 or less.

6. The heavy-duty pneumatic tire according to any one of claims 1 to 4, wherein a loss tangent at 70°C of the cushion rubber layer is smaller than a loss tangent at 70°C of the second apex.

7. 5. The heavy-duty pneumatic tire according to claim 1, wherein a ratio of an axial distance between the end of the turned-up portion and the ply body to an axial dimension at the end of the turned-up portion is 0.3 or more and 0.5 or less.

8. The heavy-duty pneumatic tire according to any one of claims 1 to 4, wherein the complex modulus of the cushioning rubber layer at 70 ° C. is 3.0 to 5.5 times the complex modulus of the second apex at 70 ° C.

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