pneumatic tires

Abstract

To provide a pneumatic tire configured so that the inside of the tire can be suppressed from distorting, and yet air resistance during high-speed rotation can be reduced to easily achieve low-fuel consumption.SOLUTION: A tire 1 comprises: a pair of bead cores 26 positioned with an interval in a width direction; a carcass 18 laid over the pair of bead cores 26, and including a first fiber material part 18a and a second fiber material part 18b which is higher in strength than the first fiber material part 18a; a belt 16 arranged at an outer periphery side of the carcass 18; and an inner liner 19 arranged at an inner periphery side of the carcass 18. The second fiber material part 18b is extended along an outer peripheral surface of the inner liner 19 from an outside position closer to the outside in the width direction than a belt end 23 to an inside position closer to the inside in the width direction than the outside position.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to pneumatic tires. [Background technology]

[0002] Conventionally, there is a pneumatic tire described in Patent Document 1. This pneumatic tire includes a reinforcing material disposed between an inner liner and a carcass. The reinforcing material includes an overlapping portion that overlaps with a belt end disposed on the outer circumferential side of the carcass when viewed from the radial direction. The reinforcing material includes organic fibers. The organic fibers extend at an angle of 0° or more and 70° or less with respect to the circumferential direction of the tire. The reinforcing material is provided to suppress lift-up of the shoulders during high-speed driving. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-199758 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned pneumatic tire, a reinforcing material that is a separate component from the liner and ply is placed between them, which increases strain inside the tire and makes the tire more susceptible to deterioration. Patent Document 1 also states that if the angle of the organic fiber relative to the circumferential direction exceeds 70°, the reinforcing effect of the shoulder is insufficient and the effect of preventing the shoulder from lifting up during high-speed driving is insufficient. However, if the shoulder can be efficiently rounded (curved) radially inward during high-speed rotation of the tire, the air resistance of the tire during high-speed rotation can be efficiently reduced, which is preferable because it can achieve low fuel consumption.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a pneumatic tire that can suppress distortion inside the tire, and also reduce air resistance during high-speed rotation, thereby making it easier to achieve low fuel consumption. [Means for solving the problem]

[0006] The pneumatic tire of the present invention comprises a pair of bead cores spaced apart in the width direction, a carcass stretched across the pair of bead cores and including a first fiber material portion and a second fiber material portion having higher strength than the first fiber material portion, a belt arranged on the outer periphery of the carcass, and an inner liner arranged on the inner periphery of the carcass, wherein the second fiber material portion extends along the outer surface of the inner liner from an outer position located widthwise outside the belt end to an inner position located widthwise inside the outer position.

[0007] In this specification, when the belt has a multi-layer structure of two or more layers, the belt end is defined as the outer end in the width direction of the belt located most inward in the width direction.

[0008] According to the present invention, a high-strength second fibrous material portion, which forms part of the carcass located radially inward of the belt, extends along the inner circumferential surface of the carcass from an outer position located laterally outward of the belt end to an inner position located laterally inward of the outer position. Therefore, by arranging a high-rigidity second fibrous material portion in a location with a small radius of curvature where stress tends to concentrate, the moment (bending moment) required to bend that location can be increased, preventing the tire from expanding radially due to centrifugal force during high-speed tire rotation and causing the rounded shoulder shape to collapse. Therefore, even when centrifugal force is applied to the tire during high-speed tire rotation, the shoulder can more easily maintain its rounded shape, reducing changes in airflow and suppressing the generation of unnecessary turbulence. As a result, tire air resistance can be reduced, resulting in improved fuel economy.

[0009] Furthermore, according to the present invention, instead of disposing a high-strength reinforcing material between the inner liner and the carcass, a high-strength second fiber material portion is provided in a part of the extending direction of the carcass located on the outer peripheral side of the inner liner. Therefore, distortion does not occur inside the tire due to the formation of a high-strength portion on the radially inner side of the shoulder, and the provision of the high-strength portion does not make the tire susceptible to deterioration. [Effects of the Invention]

[0010] According to the pneumatic tire of the present invention, distortion inside the tire can be suppressed, and air resistance during high-speed rotation can also be reduced, making it easier to achieve low fuel consumption. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a half cross-sectional view taken along the width direction and the radial direction of a pneumatic tire according to one embodiment of the invention, the half cross-sectional view including the radial direction and the width direction of the pneumatic tire. [Figure 2] 2 is an enlarged cross-sectional view of the shoulder area on one side in the width direction in FIG. 1. FIG. [Figure 3] FIG. 2 is a schematic cross-sectional view for explaining the advantages that can be obtained by providing a high-strength second fiber material portion in the carcass of a pneumatic tire. [Figure 4] 3 is a cross-sectional view corresponding to FIG. 2 of a pneumatic tire of a comparative example, and is an enlarged cross-sectional view corresponding to FIG. 2 of a pneumatic tire provided with a carcass having uniform strength. FIG. [Figure 5] FIG. 1 is a cross-sectional view along the width direction and the radial direction showing the outer shape of one widthwise side portion of a pneumatic tire of a comparative example when inflated and when rotating at high speed, in which the outer shape when inflated is shown by dotted lines and the outer shape when rotating at high speed is shown by solid lines. [Figure 6] FIG. 6 is an enlarged cross-sectional view of the shoulder periphery in FIG. 5. [Figure 7]FIG. 1 is a cross-sectional view along the width direction and the radial direction showing the outer shape of the pneumatic tire of Example 2 at one width direction side portion when inflated and the outer shape of the pneumatic tire of Comparative Example at one width direction side portion when inflated, in which the outer shape of the pneumatic tire of Comparative Example is shown by dotted lines and the outer shape of the pneumatic tire of Example 2 is shown by solid lines. [Figure 8] FIG. 8 is an enlarged cross-sectional view of the shoulder periphery in FIG. 7. [Figure 9] FIG. 1 is a cross-sectional view along the width direction and the radial direction showing the outline of the shoulder of the pneumatic tire of Example 2 when rotating at high speed and the outline of the shoulder of the pneumatic tire of Comparative Example when rotating at high speed, superimposed on each other, in which the outline of the pneumatic tire of Comparative Example is shown by dotted lines and the outline of the pneumatic tire of Example 2 is shown by solid lines. DETAILED DESCRIPTION OF THE INVENTION

[0012] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It is anticipated that, when multiple embodiments and variations are included below, new embodiments can be constructed by appropriately combining their characteristic features. In the following examples, the same components are denoted by the same reference numerals in the drawings, and redundant description will be omitted. The drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component do not necessarily match between different drawings. Among the components described below, components not recited in the independent claims representing the highest concept are optional components and are not essential components. In the following description, if the belt has a multi-layer structure of two or more layers, the belt end is defined as the outer widthwise end of the belt (belt layer) located most inward in the width direction. In the following description, if the belt has a multi-layer structure of two or more layers, the belt length is defined as the length of the belt located most inward in the width direction. In the following description, the width direction is the width direction of the pneumatic tire 1, the radial direction is the radial direction of the pneumatic tire 1, and the circumferential direction is the circumferential direction of the pneumatic tire 1. The width direction, the radial direction, and the circumferential direction are perpendicular to one another.

[0013] FIG. 1 is a half cross-sectional view taken along the width direction and the radial direction of a pneumatic tire 1 according to one embodiment of the present invention, and is a half cross-sectional view taken along the radial direction and the width direction of the pneumatic tire 1. As shown in FIG. 1, the pneumatic tire (hereinafter simply referred to as the tire) 1 includes a tread 10, a pair of shoulders 11, a pair of sidewalls 12, and a pair of beads 13. The tread 10 includes a contact surface 10a that comes into contact with the road surface. The tread 10 is made of, for example, crosslinked rubber. A plurality of grooves 24 are provided on the outer peripheral surface of the tread 10. As is well known, the plurality of grooves 24 serve to drain rainwater that has entered between the road surface and the tire 1, thereby ensuring a contact area between the road surface and the tire 1.

[0014] The shoulders 11, sidewalls 12, and beads 13 form the side surfaces of the tire 1 and are provided on both sides of the tire 1 in the width direction. The shoulders 11, sidewalls 12, and beads 13 extend radially inward from both widthwise ends of the tread 10. In this embodiment, the contact edge E of the tire 1 is defined as the boundary between the tread 10 and the shoulders 11. The sidewalls 12 are rubber layers between the shoulders 11 and the beads 13 and are the most flexible part of the tire 1. The sidewalls 12 protect the carcass 18 (see FIG. 2) and prevent its elongation. The tire may have annular ribs on its lateral sides. In this case, the annular ribs may be defined as the boundaries between the shoulders and the sidewalls. The contact edge E refers to both widthwise ends of the part of the tire 1 that comes into contact with the ground when the tire 1 is mounted on a standard rim, the internal pressure is adjusted to the standard internal pressure, and a standard load is applied (regular rims, etc., are the same as those described in JP 2020-131965 A).

[0015] The shoulders 11 are shoulder portions of the tire 1, and protrude outward in the width direction from both ends of the tread 10 in the width direction and extend radially inward. Like the tread 10, the shoulders 11 are provided in an annular shape along the circumferential direction. The sidewalls 12 extend radially inward from the shoulders 11 and are also provided in an annular shape along the circumferential direction. The sidewalls 12 include the portions that protrude most outward in the width direction of the tire 1, and are gently curved so as to be convex outward.

[0016] The bead 13 extends radially inward from the sidewall 12 and is formed in a ring shape along the circumferential direction. The bead 13 is a portion that is fixed to the rim of a wheel and constitutes the inner circumferential portion of the tire 1. The bead 13 is gently curved so as to convex toward the inside, and is located more inward than the sidewall 12 in the width direction.

[0017] The tire 1 further includes a bead core 26 and a bead filler 27. The bead core 26 and the bead filler 27 are provided on both sides of the bead 13 in the width direction. The bead core 26 is a ring-shaped member made of bundled steel wires covered with rubber. The bead filler 27 is made of hard rubber and has the function of increasing the rigidity of the bead 13. The bead filler 27 is arranged radially outward of the bead core 26.

[0018] Fig. 2 is an enlarged cross-sectional view of the vicinity of the shoulder 11 on one side in the width direction in Fig. 1. As shown in Fig. 2, the tire 1 includes a belt 16, a belt reinforcing material 17, a carcass 18, and an inner liner 19. The belt 16 is disposed radially inward of the tread 10. The belt 16 is installed in the entire area where it radially overlaps the tread 10 and in a part of the shoulder 11 in the width direction.

[0019] The belt 16 is a reinforcing band stretched in the circumferential direction, and tightens the carcass 18 to increase the rigidity of the tread 10. The belt 16 has a two-layer structure, for example, made of a steel belt containing steel cords, and includes two steel belts 16a and 16b. However, the number of belts to be stacked is not limited to two, and a belt containing tire cords using aramid fibers may be used instead of the steel belts. Providing the belt 16 ensures the rigidity of the tire 1 and improves the contact state between the tread 10 and the road surface.

[0020] The belt reinforcement 17 is disposed between the belt 16 and the tread 10. The belt reinforcement 17 has, for example, a two-layer structure and includes two cap plies 17a and 17b. The cap plies 17a and 17b are formed of, for example, insulating organic fiber layers such as polyamide fiber, and are covered with a topping rubber. The belt reinforcement 17 is installed for purposes such as improving durability and reducing road noise during driving. The number of layered cap plies is not limited to two. The belt reinforcement 17 is disposed in the entire area where it radially overlaps the tread 10 and in a partial area of ​​the shoulder 11 in the width direction. An outer end 22 of the belt reinforcement 17 extends outward in the width direction beyond the belt 16.

[0021] The carcass 18 is a one-piece annular member disposed radially inward of the belt 16. The carcass 18 is a cord layer coated with rubber. The carcass 18 includes carcass plies and forms a tire framework that withstands loads, impacts, air pressure, etc. The carcass 18 has a radial structure in which carcass cords are arranged extending in a direction perpendicular to the circumferential direction. The rubber layer that covers and protects the carcass 18 is generally composed of multiple rubber materials such as tread rubber and sidewall rubber.

[0022] The carcass ply constituting the carcass 18 is laid across the bead core 26 from the inner side in the width direction and folded back toward the sidewall 12 so as to wrap around the bead core 26 and the bead filler 27. In the example shown in FIG. 2 , a ply end 18E, which is the end of the carcass ply, is located on the sidewall 12. When the carcass 18 includes two carcass plies, the ply end of the other carcass ply is generally located on the bead 13.

[0023] The carcass 18 includes a first fibrous material portion 18a and a second fibrous material portion 18b having higher strength than the first fibrous material portion 18a. The carcass 18 is fabricated, for example, as follows: First, a large number of organic fibers, such as nylon fibers, rayon fibers, polyester fibers such as polyethylene terephthalate (PET) fibers and polyethylene naphthalate (PEN) fibers, and polyvinyl alcohol fibers, are arranged in a carcass mold so that, after fabrication, they will extend along the entire curved direction from one end to the other in the curved direction, extending along the outer peripheral surface of the inner liner in a cross section along the width and radial directions (a cross section including the width and radial directions). Additionally, steel fibers or aramid fibers are additionally arranged in only two predetermined locations on both sides of the curved direction, spaced apart in the width direction, so as to be approximately symmetrical with respect to the tire equatorial plane. Then, rubber raw material is poured into the carcass mold and heated to convert the rubber raw material into rubber. Examples of rubber raw materials that can be used include natural rubber, acrylonitrile-butadiene rubber (NBR), isoprene rubber (IR), isobutylene rubber (IIR), butadiene rubber (BR), styrene-butadiene rubber (SBR), and blends of these rubbers.

[0024] In this way, by integrating the rubber and all the fibers, it is possible to produce a carcass 18 including a first fiber material portion 18a and a second fiber material portion 18b that is stronger than the first fiber material portion 18a. The additional fibers added only to the second fiber material portion 18b may extend in any direction. However, if the additional fibers are arranged to extend in the above-mentioned curved direction that is included in a direction substantially perpendicular to the circumferential direction, it is possible to prevent the tire from having a tendency to deflect with respect to the circumferential direction, which is its rotational direction, so the tire is more likely to roll straight and provide a more comfortable ride.

[0025] The carcass 18 has two second fibrous material portions 18b. The two second fibrous material portions 18b are arranged on both sides of the carcass 18 in the width direction, for example, spaced apart in the width direction and arranged approximately symmetrically with respect to the tire equatorial plane. The two second fibrous material portions 18b are connected together with a portion of the first fibrous material portion 18a sandwiched between them. An inner liner 19, which is a rubber layer for maintaining air pressure, is attached to the inner peripheral surface of the carcass 18. The inner liner 19 is made of, for example, air-permeable rubber and prevents air from leaking from the tire cavity to the outside. The second fibrous material portion 18b extends along the outer peripheral surface of the inner liner 19 from an outer position located outward in the width direction from the belt end 23 to an inner position located inward in the width direction from the outer position. The belt end 23 is the outer end in the width direction of the belt 6b, which is located most inward in the width direction of the two-layer belt 16.

[0026] At least a part of the second fiber material portion 18b is arranged in a range (hereinafter referred to as a first range) from a position where it substantially overlaps with the belt end 23 in the radial direction to a length along the outer peripheral surface of the inner liner 19 that corresponds to 15% of the belt length in a cross section along the width direction and a cross section including the width direction and the radial direction. Here, the belt length is the length of the belt 6b that is located most inward in the width direction in the two-layer belt 16. In addition, the position where it substantially overlaps with the belt end 23 in the radial direction may be defined as a position included in the range from a position that is shifted inward in the width direction along the outer peripheral surface of the inner liner 19 by 1% of the belt length from the position where it overlaps with the belt end 23 in the radial direction to a position that is shifted outward in the width direction along the outer peripheral surface of the inner liner 19 by 1% of the belt length from the position where it overlaps with the belt end 23 in the radial direction.

[0027] In the embodiment shown in Figures 1 and 2, all of the second fiber material portions 18b are located in the first range. More precisely, the second fiber material portions 18b are located in cross sections along the width and radial directions from the position where they overlap the belt end 23 in the radial direction to a position shifted laterally by a length along the outer peripheral surface of the inner liner 19 that corresponds to 15% of the belt length. If the second fiber material portions 18b extend beyond the position where they overlap the ply end 18E in the width direction, the tire rigidity may increase, which may affect the ride comfort of a vehicle equipped with the tire. Therefore, it is preferable that the second fiber material portions 18b be located in the range from the position where they approximately overlap the belt end 23 in the radial direction to the position where they overlap the ply end 18E in the width direction, in the direction along the outer peripheral surface of the inner liner 19. The Young's modulus of the second fiber material portions 18b is preferably 20 GPa or more, and more preferably 150 GPa or more.

[0028] <Advantages of providing the second fiber material portion according to the present disclosure> Fig. 3 is a schematic cross-sectional view for explaining the advantages that can be obtained by providing the second fiber material portion 18b, which has high strength, around the shoulder 11 of the carcass 18. When a bending moment M acts on the cross section shown in Fig. 3, the following formula (1) holds. 1 / ρ=M / (EI) (1) where ρ is the radius of curvature [cm] and E is the modulus of elasticity of the material [kg / cm 2 ] and I is the second moment of area [cm 4 ] and E·I is the bending stiffness [kg·cm 2 ].

[0029] In the above formula (1), the second moment of area I is a factor that is independent of the material and depends only on the shape. Therefore, by placing a material with a high Young's modulus E in a location with a small radius of curvature ρ, the bending moment M in that location can be increased. Furthermore, the shoulder 11 has fewer belts 16 than the widthwise center, resulting in lower rigidity. Therefore, by placing the second fibrous material portion 18b with high rigidity in a location with a small radius of curvature where stress tends to concentrate, the moment (bending moment) required to bend that location can be increased, preventing the tire 1 from expanding radially due to centrifugal force during high-speed tire rotation and collapsing the rounded shoulder shape. As a result, even when centrifugal force is applied to the tire 1 during high-speed tire rotation, the shoulder 11 can more easily maintain its rounded shape, reducing changes in airflow and the generation of unnecessary turbulence, thereby reducing the air resistance of the tire 1.

[0030] (Air resistance and vertical stiffness test) The inventors of the present application produced the following tires of Examples 1 to 5 and a tire of a comparative example, and calculated the air resistance and vertical rigidity of each tire through tests.

[0031] [Example 1] A tire was produced that differed only in the arrangement position of the second fibrous material portion compared to the tire described in Figures 1 and 2. Regarding the production of the carcass, acrylonitrile-butadiene rubber (NBR) was used as the base rubber, nylon fibers were used as the fibers contained in both the first fibrous material portion and the second fibrous material portion and extending from one end to the other in the curved direction, and steel fibers were used as the fibers added only to the second fibrous material portion. The carcass was then produced by integrating these materials. The tire of Example 1 was produced by arranging the second fibrous material portion in a cross section along the width direction and the radial direction (a cross section including the width direction and the radial direction) from the belt end to a position shifted laterally along the outer peripheral surface of the inner liner by a length of 10% of the belt length. The steel fibers added only to the second fibrous material portion were arranged to extend in a direction approximately perpendicular to the circumferential direction.

[0032] [Example 2] 1 and 2 were produced. The tire of Example 2 was a tire that differed from Example 1 only in that the second fiber material portion was arranged from the belt end to a position shifted laterally along the outer peripheral surface of the inner liner by a length of 15% of the belt length in a cross section along the width direction and the radial direction.

[0033] [Example 3] In comparison with Example 1, the tire of Example 3 was a tire that differed only in that the second fiber material portion was positioned in a cross section along the width and radial directions from the end of the belt to a position shifted to the side along the outer peripheral surface of the inner liner for a length of 20% of the belt length.

[0034] [Example 4] In comparison with Example 1, the tire of Example 4 was a tire that differed only in that the second fiber material portion was positioned in a cross section along the width and radial directions from the end of the belt to a position 35% of the belt length along the outer peripheral surface of the inner liner.

[0035] [Example 5] In comparison with Example 1, the tire of Example 5 was a tire that differed only in that the second fiber material portion was positioned from the belt end to a position shifted to the side along the outer peripheral surface of the inner liner for a length of 45% of the belt length in the cross section along the width direction and radial direction.

[0036] [Comparative Example] In comparison with Example 1, the comparative tire was a tire that differed only in that nylon fiber was used as the fiber extending from one end to the other in the curved direction, no other fiber was added, and a carcass with approximately constant strength from one end to the other in the curved direction was used.

[0037] <Evaluation of air resistance reduction> In order to objectively determine the effect of reducing air resistance, the inventors measured the drag, i.e., the force acting on a tire placed in an air flow, in the same direction as the flow and parallel to the flow, for each tire produced, and calculated the drag coefficient Cd (drag coefficient) using the following equation (2). Cd=D / (1 / 2ρU 2 S)···(2) where D is the drag force generated, ρ is the air density, and 1.225 kg / m 3 ]. U is the representative speed, which is the relative speed between the tire and the air, and is set to 27.8 [m / s]. S is the representative area of ​​the object. The inventors calculated Cd from these values ​​and the frontal projected area. Cd is expressed as a relative index where the value of the comparative example is set to 100. The smaller the index, the smaller the air resistance.

[0038] In Examples 1-5, the carcass was fabricated using acrylonitrile-butadiene rubber (NBR) as the base rubber, nylon fibers as the fibers contained in both the first and second fibrous material sections and extending from one end to the other in the curvature direction, and steel fibers as the fibers added only to the second fibrous material section. These materials were then integrated to fabricate the carcass. However, even if a different rubber was used as the base rubber, organic fibers other than nylon fibers were used as the fibers contained in both the first and second fibrous material sections and extending from one end to the other in the curvature direction, and fibers other than steel fibers were used as the fibers added only to the second fibrous material section, the drag coefficient Cd and the longitudinal rigidity, as described below, did not differ significantly.

[0039] <Vertical stiffness evaluation> Vertical stiffness is the radial stiffness of the tire. Each tire was mounted on a 19x7.0J rim at an air pressure of 250 kPa, and the vertical stiffness was calculated by dividing the change in vertical force between vertical loads of 4.5 kN ± 490 N with a camber angle of 0° by the change in vertical deflection. Vertical stiffness is expressed as a relative index, with the value of the comparative example set to 100. A higher index indicates greater vertical stiffness. Excessive stiffness may result in a decrease in ride comfort. In this way, ride comfort can be evaluated by calculating vertical stiffness.

[0040] [Table 1]

[0041] Table 1 shows the calculated Cd value and vertical rigidity for each tire. As shown in Table 1, air resistance gradually decreased as the length of the second fiber material portion from the belt end was increased, and air resistance plateaued and stopped decreasing when the length of the second fiber material portion was 35% of the belt length. This is presumably because when the second fiber material portion extends beyond the point on the sidewall 12 that bulges outward in the width direction, it approaches the wheel, which has high rigidity, and the extended second fiber material portion no longer contributes to tire deformation. Therefore, by setting the length of the second fiber material portion to a length that is longer than 0% and less than 35% of the belt length, air resistance can be reduced and the cost of additional fibers can be reduced.

[0042] Furthermore, from the viewpoint of vertical rigidity, up to Example 2, in which the length of the second fibrous material portion is 15% of the belt length, the increase in vertical rigidity compared to the comparative example can be suppressed to within 3%, and the vertical rigidity does not increase significantly, whereas in Example 3, in which the length of the second fibrous material portion is 20% of the belt length, the vertical rigidity increases by 6%, which may affect the ride comfort. Therefore, from the viewpoint of ride comfort, Examples 1 and 2 are preferable.

[0043] The inventors of the present invention identified the shapes of the tire of Example 2 and the tire of Comparative Example during high-speed rotation through computer simulation and investigated the degree of rounding (curvature) of the shoulders. Specifically, the inventors investigated the degree of rounding of the shoulders when the tires were rotated at 100 km / h in each computer simulation.

[0044] FIG. 4 is a cross-sectional view corresponding to FIG. 2 of a tire 101 of a comparative example. In FIG. 4, reference numeral 108 indicates a carcass that does not have a second fiber material portion. FIG. 5 is a cross-sectional view along the width direction and the radial direction showing the change in the outer shape of one side portion of the tire 101 when inflated and when rotating at high speed (when centrifugal force is applied), in which the outer shape when inflated is shown by a dotted line and the outer shape when rotating at high speed is shown by a solid line. FIG. 6 is an enlarged cross-sectional view of a shoulder 111 in FIG. 5. When inflated, the tire 101 is inflated to a predetermined air pressure and is stationary, and when rotating at high speed, the inflated tire 101 is rotating at high speed.

[0045] As shown in Fig. 5, when the tire 101 rotates at high speed, centrifugal force acts on the tire 101, making it easier for the tread to deform radially outward. Also, as shown in Fig. 6, in the tire 101 having a carcass with approximately uniform strength in the curvature direction, the outer shape of the shoulder 111 also expands significantly radially outward when rotating at high speed compared to when inflated, making it difficult for the shoulder 111 to maintain its rounded shape.

[0046] Next, the difference in shape between the tire of Example 2 and the tire of the Comparative Example when inflated will be described. Fig. 7 is a cross-sectional view along the width direction and the radial direction showing the outer shape of one widthwise side portion of tire 1 of Example 2 when inflated and the outer shape of one widthwise side portion of the tire of the Comparative Example when inflated, where the outer shape of the tire of the Comparative Example is shown by dotted lines and the outer shape of the tire of Example 2 by solid lines. Fig. 8 is an enlarged view of the shoulder area in Fig. 7. As shown in Figs. 7 and 8, when inflated, the outer shape of the tire of Example 2 is substantially the same as the outer shape of the tire of the Comparative Example, and there is no difference in the outer shapes of the two tires.

[0047] Next, the difference in the shape of the shoulder between the tire of Example 2 and the tire of the Comparative Example during high-speed rotation will be described. Fig. 9 is a cross-sectional view taken along the width direction and the radial direction, showing the outline of the shoulder of the tire of Example 2 during high-speed rotation and the outline of the shoulder of the tire of the Comparative Example during high-speed rotation superimposed on each other, in which the outline of the tire of the Comparative Example is shown by a dotted line and the outline of the tire of Example 2 by a solid line.

[0048] As shown in Figure 9, during high-speed rotation, the inner circumferential surface 90b of the shoulder of the tire of Example 2 curves radially inward more than the inner circumferential surface 190b of the shoulder of the tire of the comparative example, thereby achieving a rounded inner circumferential surface 90b of the shoulder of the tire of Example 2 toward the radially inward direction. As a result, during high-speed rotation, the outer circumferential surface 90a of the shoulder of the tire of Example 2 is also less likely to deform radially outward, and curves radially inward more than the outer circumferential surface 190a of the shoulder of the tire of the comparative example, thereby achieving a significant rounding of the outer circumferential surface 90a of the shoulder of the tire of Example 2 toward the radially inward direction. Therefore, by arranging the second fibrous material portion in the location described in detail up to this point, it is possible to achieve a rounded outer circumferential surface 90a of the shoulder during high-speed rotation, thereby reducing air resistance during high-speed rotation and, as a result, improving fuel efficiency.

[0049] The present disclosure is not limited to the above-described embodiment and its modified examples, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents. For example, in the above-described embodiment, the second fiber material portion 18b extends laterally along the outer peripheral surface of the inner liner 9 from a position that substantially overlaps the belt end 23 in the radial direction in a cross section taken along the width and radial directions. However, the second fiber material portion may extend laterally along the outer peripheral surface of the inner liner from a position that is located more inward in the width direction than the position that substantially overlaps the belt end in the radial direction in a cross section taken along the width and radial directions. [Explanation of symbols]

[0050] 1 tire, 10 tread, 11 shoulder, 12 sidewall, 13 bead, 16 belt, 16a, 16b steel belt ply, 17 belt reinforcement, 17a, 17b cap ply, 18 carcass, 18a first fibrous material portion, 18b second fibrous material portion, 18E ply end, 19 inner liner, 22 widthwise outer end of belt reinforcement, 23 belt end, 24 groove, 26 bead core, 27 bead filler.

Claims

1. a pair of bead cores spaced apart in the width direction; a carcass that is stretched across the pair of bead cores and includes a first fiber material portion and a second fiber material portion that is stronger than the first fiber material portion; a belt disposed on an outer peripheral side of the carcass; an inner liner disposed on the inner circumferential side of the carcass, the second fiber material portion extends along an outer peripheral surface of the inner liner from an outer position located outward of the belt end in the width direction to an inner position located inward of the outer position in the width direction, At least a part of the second fiber material portion is disposed in a cross section along the width direction and the radial direction from a position where the second fiber material portion substantially overlaps with the belt end in the radial direction, over a length range corresponding to 15% of the belt length along an outer peripheral surface of the inner liner, a pneumatic tire, wherein all of the second fiber material portions are arranged in the cross section within a range of a length along the outer peripheral surface of the inner liner from a position where the second fiber material portions substantially overlap with the belt ends in the radial direction, the length corresponding to 35% of the belt length.

2. a pair of bead cores spaced apart in the width direction; a carcass that is stretched across the pair of bead cores and includes a first fiber material portion and a second fiber material portion that is stronger than the first fiber material portion; a belt disposed on an outer peripheral side of the carcass; an inner liner disposed on the inner circumferential side of the carcass, the second fiber material portion extends along an outer peripheral surface of the inner liner from an outer position located outward of the belt end in the width direction to an inner position located inward of the outer position in the width direction, At least a part of the second fiber material portion is disposed in a cross section along the width direction and the radial direction from a position where the second fiber material portion substantially overlaps with the belt end in the radial direction, over a length range corresponding to 15% of the belt length along an outer peripheral surface of the inner liner, A pneumatic tire, wherein all of the second fabric material portions are arranged in the range.

3. The pneumatic tire according to claim 1 or 2, wherein the fibers of the carcass extend in a direction substantially perpendicular to the circumferential direction.

4. The pneumatic tire according to claim 1 , wherein the second fiber material portion has a Young's modulus of 20 GPa or more.

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