Pneumatic tire

Abstract

To provide a pneumatic tire excellent in aerodynamic performance.SOLUTION: A pneumatic tire 1 includes a tread 10, a sidewall 2, and a shoulder 4, and has an angular ground contact end shape. Each of the shoulders 4 has a shoulder front surface 26 having substantially no corner, and the shoulder front surface 26 has a curved surface 26b having an arc shape curved so as to protrude outward in the tire axial direction. The curvature radius of the curved surface 26b is, for example, not less than 5mm and not more than 15mm.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a heavy-duty tire suitable for large vehicles such as trucks and buses. [Background technology]

[0002] Heavy-duty pneumatic tires generally have angular contact edge shapes to ensure a large contact area of ​​the tread (see, for example, Patent Documents 1 and 2). As disclosed in Patent Document 2, it is preferable that the shoulder protrudes axially outward. In this case, the contact area becomes large on muddy, sandy, snowy roads, etc. The shoulder of the tire disclosed in Patent Document 2 has a bent portion that protrudes axially outward. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-136936 [Patent Document 2] Japanese Patent Publication No. 2020-1617 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, improvements in quietness and fuel efficiency have been required even for large vehicles such as trucks and buses. However, in conventional heavy-duty tires, emphasis has been placed on traction performance, with little consideration given to aerodynamic performance. As a result, heavy-duty tires generally have high air resistance and are prone to generating wind noise. Furthermore, improving the aerodynamic performance of tires is an important issue, especially for vehicles without engines, such as electric vehicles, where tire noise is easily noticeable. [Means for solving the problem]

[0005] The pneumatic tire according to the present invention comprises a tread, a sidewall, and a shoulder located between the ground contact edge of the tread and the sidewall, wherein the ground contact edge has a corner formed thereat, and the shoulder has a shoulder surface that is substantially free of corners, and the shoulder surface has an arc shape that is curved so as to be convex outward in the axial direction of the tire. [Effects of the Invention]

[0006] The pneumatic tire according to the present invention has excellent aerodynamic performance and contributes to, for example, improving the quietness and fuel efficiency of a vehicle. The pneumatic tire according to the present invention is suitable for heavy-duty tires, and is particularly suitable for vehicles such as electric vehicles that do not have an engine. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view of a pneumatic tire as an example of an embodiment. [Figure 2] 1 is a diagram showing a preferred mounting form of a pneumatic tire, which is an example of an embodiment, on a vehicle. FIG. [Figure 3] 1 is a plan view of a pneumatic tire as an example of an embodiment. [Figure 4] FIG. 2 is a plan view of a region R1 of the tread. [Figure 5] FIG. 2 is a plan view of a region R2 of the tread. [Figure 6] 1 is a side view of a pneumatic tire as an example of an embodiment. [Figure 7] 1 is a side view of a pneumatic tire according to an embodiment, showing an enlarged view of a portion of the tire side surface. [Figure 8] FIG. [Figure 9] FIG. 4 is a cross-sectional view taken along line AA in FIG. [Figure 10] FIG. 10 is an enlarged view of the shoulder and its vicinity in FIG. 9. [Figure 11] FIG. 10 is a diagram showing a part of the outline along the tire surface and the profile surface of the sidewall in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, the present invention includes configurations obtained by selectively combining the components of the embodiment described below.

[0009] FIG. 1 is a perspective view of a pneumatic tire 1 as an example of an embodiment. As shown in FIG. 1, the pneumatic tire 1 includes a tread 10, which is the portion that comes into contact with a flat road surface, a pair of sidewalls 2, a pair of beads 3, and a pair of shoulders 4. The beads 3 are fixed to the rim of a wheel. The shoulders 4 are portions located between the sidewalls 2 and the ground-contact edges E1 and E2 of the tread 10, and are also called buttresses. The sidewalls 2, the beads 3, and the shoulders 4 extend radially inward from both left and right ends (ground-contact edges E1 and E2) of the tread 10, forming the tire side surfaces.

[0010] In this embodiment, the region from the ground contact edges E1, E2 of the tread 10 to the side rib 5 is defined as the shoulder 4. That is, the ground contact edges E1, E2 are the boundary positions between the tread 10 and the shoulder 4, and the side rib 5 is the boundary position between the sidewall 2 and the shoulder 4. The side rib 5 is a protrusion formed in an annular shape continuously in the tire circumferential direction on the left and right tire side surfaces. The side rib 5 is formed, for example, at the boundary position between the mold sector and the side plate during tire molding. For convenience of explanation, the right side of the paper in FIG. 1 is the right side of the pneumatic tire 1, and the left side of the paper in FIG. 1 is the left side of the pneumatic tire 1.

[0011] The pneumatic tire 1 has angular shaped ground contact edges E1, E2, and corners are formed at the ground contact edges E1, E2. In this specification, a corner refers to a sharp bend, and a line is formed at the ground contact edges E1, E2 along the tire circumferential direction. Note that the corner includes a slightly rounded corner, and specifically, a sharp bend with a curvature radius of less than 0.1 mm is defined as a corner. Because the pneumatic tire 1 has angular ground contact edge shapes, the ground contact surface of the tread 10 can be made large. The pneumatic tire 1 is a heavy-duty tire suitable for large vehicles such as trucks and buses.

[0012] The contact edges E1 and E2 of the tread 10 are defined as the axial ends of the area (contact patch) that comes into contact with a flat road surface when a new tire is mounted on a standard rim, inflated to a standard internal pressure, and subjected to a standard load. Note that the tire maximum width position P, which will be described later, is also defined under the same conditions as the contact edges E1 and E2.

[0013] Here, "regular rim" refers to the rim specified for each tire by the market standard for which the tire is used. For JATMA, this refers to the applicable rim. For TRA, this refers to the "Approved Rim Contours." For ETRTO, this refers to the "Approved Rim." "Regular internal pressure" refers to the air pressure specified for each tire by the market standard for which the tire is used. For JATMA, this refers to the air pressure corresponding to the maximum load capacity of the tire in question. For TRA, this refers to the air pressure corresponding to the maximum load capacity of the tire listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" table. For ETRTO, this refers to the "INFLATION PRESSURE." "Regular load" refers to the allowable load specified for each tire by the market standard for which the tire is used. For JATMA, this refers to the maximum single-wheel load capacity of the tire in question. For TRA, this refers to the maximum single-wheel load capacity of the tire listed in the table above. For ETRTO, this refers to the single-wheel "LOAD CAPACITY PER AXLE" value of the tire in question.

[0014] The pneumatic tire 1 has a tread pattern including a plurality of blocks and main grooves 11, 12, and 13, which are circumferential grooves separating the blocks. The main groove 11 is located on the tire equator CL and is formed in a continuous ring shape in the tire circumferential direction. The equator CL is an imaginary line that runs through the center of the tread 10 in the axial direction of the tire and extends along the tire circumferential direction. The main groove 12 is located between the equator CL and the ground contact edge E1, and the main groove 13 is located between the equator CL and the ground contact edge E2, and both are formed in a continuous ring shape in the tire circumferential direction.

[0015] The tread 10 has, in order from the ground contact edge E1 side, a first shoulder block 20, a first center block 30, a second center block group 40, and a second shoulder block group 50. A main groove 11 separates the first center block 30 from the second center block group 40, a main groove 12 separates the first shoulder block 20 from the first center block 30, and a main groove 13 separates the second center block group 40 from the second shoulder block group 50. The blocks of the tread 10 are convex parts that protrude radially outward in the tire direction, and are sometimes called "lands" in the tire industry.

[0016] The tread 10 has a narrow groove 14 extending in the tire circumferential direction, and the second shoulder block group 50 includes an outer shoulder block 51 and an inner shoulder block 55 separated by the narrow groove 14. The narrow groove 14 is a tire circumferential groove located between the main groove 13 and the ground contact edge E2, with a groove width smaller than that of the main groove, and is formed continuously in a ring shape in the tire circumferential direction. The narrow groove 14 improves traction performance by increasing the number of block edges while ensuring the rigidity of the second shoulder block group 50. The outer shoulder block 51 and the inner shoulder block 55 separated by the narrow groove 14 can support each other, for example, when a force is applied that causes the blocks to collapse laterally.

[0017] The tread 10 further has lateral grooves extending in the tire axial direction. The lateral grooves include lateral grooves 21, 22, 31, and 32 that terminate within the blocks and lateral grooves 42, 52, and 56 that circumferentially separate the blocks. As will be described in detail later, the first shoulder blocks 20 and the first center blocks 30 are rib-shaped blocks that are continuous in the tire circumferential direction. The second center block group 40 and the second shoulder block group 50 are composed of multiple blocks separated in the tire circumferential direction by the lateral grooves 42, 52, and 56: multiple second center blocks 41, multiple outer shoulder blocks 51, and multiple inner shoulder blocks 55. This tread pattern not only significantly contributes to achieving both traction and uneven wear resistance, but also contributes to improved aerodynamic performance through a synergistic effect with the tire sidewall shape, which will be described later.

[0018] The tread pattern is preferably formed at variable pitches (unequal intervals) that vary in the tire circumferential direction. In this case, pattern noise is reduced and quietness is improved. The tread pattern has, for example, a total pitch number of 20 to 30, and is configured using three or more patterns with different pitch lengths.

[0019] The sidewall 2 is provided with a side protector 60 that protrudes axially outward. The side protector 60 is a side block that protrudes axially outward from the profile surface α of the sidewall 2 (see FIG. 11 described later), improving side cut resistance and suppressing damage to the sidewall 2. The side protector 60 is located between the side rib 5 and the tire maximum width position P on the profile surface α, where the tire axial length is at its maximum, and is formed in a continuous ring shape around the tire. As will be described in detail later, the portion of the side protector 60 located radially outward in the tire is not angular, but is gently curved so as to protrude axially outward.

[0020] The sidewall 2 may be provided with letters, numbers, symbols, etc. called serials. The serials include information such as the size code, the time of manufacture (year and week of manufacture), and the place of manufacture (factory code). The side protector 60 also has serrations 68, which are fine uneven structures extending in the tire circumferential direction. The serrations 68 are formed on the surface of the side protector 60 and contribute to improving the aerodynamic performance of the tire. Note that the serials may be formed by a fine uneven structure extending in the tire circumferential direction, and may have the function of serrations.

[0021] The shoulder 4 is formed by the side surfaces of the first shoulder block 20 and the outer shoulder block 51, which face axially outward. That is, the first shoulder block 20 and the outer shoulder block 51 form the shoulder 4. As will be described in detail later, the surface of the shoulder 4 has a substantially corner-free arc shape that is curved so as to be convex axially outward. By giving the surface of the shoulder 4 a gently curved arc shape, air flows smoothly along the tire sidewall. As a result, the aerodynamic performance of the tire is effectively improved, air resistance is reduced, and quietness is improved. The radius of curvature of the arc shape of the shoulder 4 is, for example, 5 mm or more and 15 mm or less.

[0022] Conventionally known structures can be applied to the rubber composition and internal structure of the pneumatic tire 1. The pneumatic tire 1 includes, for example, a carcass, a belt, an inner liner, and a cap ply. The carcass is a cord layer coated with rubber and forms the skeleton of the tire that withstands load, impact, air pressure, etc. The carcass is made up of two carcass plies and has a radial structure in which carcass cords are arranged in a direction perpendicular to the circumferential direction of the tire. The inner liner is a rubber layer that maintains air pressure and is provided inside the carcass.

[0023] The pneumatic tire 1 preferably includes a plurality of belts (see FIG. 9, described later). The belts are reinforcing bands disposed between the rubber constituting the tread 10 and the carcass, and tighten the carcass to increase the rigidity of the tire. The belts are formed, for example, by covering metal cords with rubber. From the viewpoint of improving handling and aerodynamic performance, the arc shape of the shoulder 4 is preferably formed in an area located axially outward of the belt end (see FIG. 9, described later).

[0024] FIG. 2 is a diagram showing a preferred mounting form of the pneumatic tire 1 on a vehicle 100. In FIG. 2, dot hatching is applied to a region R1 of the tread 10 where the rib-shaped first shoulder blocks 20 and first center blocks 30 (collectively referred to as "first blocks") are arranged. Region R1 is the region from the equator CL to the ground contact edge E1. Note that in region R2 of the tread 10 from the equator CL to the ground contact edge E2, a row of multiple blocks (collectively referred to as "second blocks") constituting the second center block group 40 and the second shoulder block group 50 is arranged.

[0025] 2, the pneumatic tire 1 is a tire with a specified mounting direction relative to the vehicle 100, and when used as a front tire, is mounted so that region R1 of the tread 10 is located on the outer side of the vehicle. That is, when the pneumatic tire 1 is mounted on the vehicle 100 as a front tire, the tread 10 has rib-like first blocks that are continuous in the tire circumferential direction in a region located on the outer side of the vehicle from the equator CL, and has second blocks that are separated in the tire circumferential direction in a region located on the inner side of the vehicle from the equator CL. In this case, it is possible to achieve a high level of both traction and uneven wear resistance.

[0026] Traction and uneven wear resistance are generally opposing characteristics that are difficult to achieve together. However, the circumferentially continuous, ribbed first blocks provide high rigidity and improve uneven wear resistance, while the circumferentially separated second blocks have many edges, improving traction. In a front tire, by positioning the first blocks on the vehicle's outer side and the second blocks on the vehicle's inner side, excellent traction and uneven wear resistance can be achieved. Furthermore, the tread pattern on the vehicle's outer side has a significant impact on aerodynamic performance, and the ribbed first blocks also work to advantage in this regard. With the pneumatic tire 1, the improved tire sidewall shape and the first blocks on the vehicle's outer side have a synergistic effect, further improving aerodynamic performance.

[0027] In the example shown in FIG. 2, two pneumatic tires 1 are mounted on each of the left and right sides of the vehicle 100 as rear tires. This configuration is called a double tire. In the case of a double tire, the tire on the inside of the vehicle is mounted so that region R1 of the tread 10 is located on the outside of the vehicle, and the tire on the outside of the vehicle is mounted so that region R2 of the tread 10 is located on the outside of the vehicle. In other words, it is preferable that the mounting direction of the pneumatic tire 1 relative to the vehicle 100 is specified even when used as a rear tire. In this case, traction and uneven wear resistance can be more effectively achieved at the same time.

[0028] The vehicle 100 is a large vehicle such as a truck or bus, and the pneumatic tire 1 is suitable as a heavy-duty tire. The vehicle 100 may also be an electric vehicle (EV) that does not have an engine. Compared to vehicles with engines, EVs have characteristics such as lower noise while driving, a heavier vehicle weight, and superior acceleration performance. For this reason, tires for EVs are required to have particularly excellent quietness and wear resistance. As described above, the pneumatic tire 1 is suitable as an EV tire because it has excellent quietness and wear resistance. Furthermore, the pneumatic tire 1 has low air resistance, which contributes to improving the fuel efficiency (electricity cost) performance of the vehicle 100. The pneumatic tire 1 is suitable, for example, as a tire for a large EV.

[0029] Below, the configuration of the pneumatic tire 1 will be explained using an example in which the pneumatic tire 1 is applied to a front tire and is mounted on a vehicle so that region R1 of the tread 10 is located on the outside of the vehicle and region R2 of the tread 10 is located on the inside of the vehicle.

[0030] The tread pattern of the pneumatic tire 1 will be described in detail below with reference to Figures 3 to 5. Figure 3 is a plan view of the pneumatic tire 1. Figure 4 is an enlarged view of a region R1 of the tread 10, and Figure 5 is an enlarged view of a region R2 of the tread 10.

[0031] As shown in Figures 3 to 5, the tread 10 has three tire circumferential grooves: three main grooves 11, 12, and 13, and one narrow groove 14 that is narrower than the main grooves. All of the tire circumferential grooves are formed in a continuous ring shape in the tire circumferential direction, but while the main grooves 11 and 12 extend straight along the tire circumferential direction, the main groove 13 and the narrow groove 14 have multiple bends and are formed in a zigzag shape. The main groove 13 and the narrow groove 14 form unevenness on the block ends facing the grooves, increasing the number of edges that catch on the road surface.

[0032] The main groove 13 includes a first portion 13a and a second portion 13b that are inclined in different directions relative to the tire circumferential direction (see FIG. 5 ), and the first portions 13a and the second portions 13b are alternately repeated and extend in the tire circumferential direction. The main groove 13 is bent significantly at the boundary between the first portion 13a and the second portion 13b. The inclination of the second portion 13b relative to the tire circumferential direction is greater than that of the first portion 13a, and the length of the second portion 13b is shorter than that of the first portion 13a. The second portion 13b has an increased edge by recessing the block end of the second center block 41 that faces the main groove 13.

[0033] The narrow groove 14 includes a first portion 14a that is convex toward the equator CL and a second portion 14b that is convex toward the tread edge E1 (see FIG. 5 ), and the first portions 14a and second portions 14b extend circumferentially in an alternating pattern. Forming the linear main grooves 11 and 12 in the outer region R1 and the zigzag main groove 13 and narrow groove 14 in the inner region R2 ensures resistance to uneven wear and more effectively improves traction. Furthermore, this configuration reduces airflow disturbance in the outer region R1, improving aerodynamic performance.

[0034] The main grooves 11, 12, and 13 may have the same width, but in this embodiment, the width of the main groove 11 located on the equator CL and the width of the main groove 13 located in the vehicle-inboard region R2 are slightly larger than the width of the main groove 12 located in the vehicle-outboard region R1. The widths of the main grooves 11 and 13 are, for example, substantially the same and are 1.03 to 1.05 times the width of the main groove 12. An example of the width of the main grooves 11 and 13 is 9 mm to 11 mm. The width of the narrow groove 14 is, for example, 1.3 mm to 3.0 mm, preferably 1.3 mm to 2.0 mm. In this specification, the groove width refers to the groove width along the contact surface of the tread 10, in other words, the groove width at the groove opening.

[0035] The depths of the main grooves 11, 12, and 13 may be different from one another, but in this embodiment, they are substantially the same. Stone ejectors 15, which are protrusions for preventing stone trapping, are provided at the bottoms of the main grooves 11, 12, and 13, but the depth of each main groove in the portion where the stone ejectors 15 are not present is constant along the tire circumferential direction. Similarly, the width of each main groove is substantially constant along the tire circumferential direction. The depth of the narrow grooves 14 is shallower than the main grooves and varies along the tire circumferential direction. For example, the depth of the narrow grooves 14 at their deepest portions is 30% to 60% of the depth of the main grooves.

[0036] As described above, the tread 10 has multiple lateral grooves. In region R1 of the tread 10, lateral grooves 21, 22, 31, and 32 are formed, terminating within the first blocks, and no lateral grooves are formed separating the first blocks. On the other hand, in region R2 of the tread 10, lateral grooves 42, 52, and 56 are formed, separating the blocks in the tire circumferential direction. The lateral groove 42 connects two main grooves 11 and 13 and separates two circumferentially adjacent second center blocks 41. The lateral groove 52 extends from the narrow groove 14 to the shoulder 4 and separates two circumferentially adjacent outer shoulder blocks 51, and the lateral groove 56 connects the main groove 13 and narrow groove 14 and separates two circumferentially adjacent inner shoulder blocks 55.

[0037] A plurality of sipes are formed in each block of the tread 10. In this specification, a sipe is defined as a narrow groove with a width of less than 1.2 mm. The maximum width of a sipe is preferably 0.1 mm or more and 1.0 mm or less, more preferably 0.2 mm or more and 0.6 mm or less. The depth of a sipe is, for example, 30% or more and 60% or less of the depth of the main groove. The sipes form edges that cut into snow and ice, and also exert a drainage effect through capillary action, improving traction particularly on snowy and icy road surfaces. In a plan view of the tread 10, each sipe extends in the tire axial direction and is formed in a wave shape with projections and depressions in the tire circumferential direction. Wave-shaped sipes can efficiently increase the number of edges.

[0038] Region R1 of the tread 10 includes first shoulder blocks 20 and first center blocks 30 located closer to the equator CL than the first shoulder blocks 20 as circumferentially continuous, rib-like first blocks. The first shoulder blocks 20 and the first center blocks 30 are separated from each other by linearly extending main grooves 12 and are formed as circumferentially continuous ribs. In region R1 on the vehicle outer side, blocks are prone to uneven wear due to the influence of lateral forces generated during cornering. However, by arranging the rib-like first blocks in region R1, uneven wear resistance is significantly improved and aerodynamic performance is also improved. The rib-like first blocks are less likely to suffer uneven wear because of their high block rigidity and the ability to distribute loads acting during cornering in the circumferential direction of the tire.

[0039] In the first shoulder block 20, multiple lateral grooves 21 extending from the main groove 12 and multiple lateral grooves 22 extending from the shoulder 4 are formed alternately in the tire circumferential direction. The lateral grooves 21, 22 are arranged in a staggered pattern, offset in the tire circumferential direction, with the lateral groove 22 located exactly midway between two lateral grooves 21 or in the vicinity thereof. Each lateral groove 21, 22 terminates within the block and is formed with a length that does not reach the center of the width direction of the contact surface of the first shoulder block 20. This configuration improves block rigidity and more significantly suppresses uneven wear. The spacing between the lateral grooves 21 is, for example, slightly smaller than the width of the first shoulder block 20 (the same applies to the lateral grooves 22).

[0040] The lateral grooves 21, 22 are preferably formed with lengths that do not overlap in the tire circumferential direction. In this case, an area where no lateral grooves exist along the tire circumferential direction is formed in the widthwise center of the first shoulder block 20. The axial length of the lateral grooves 21, 22 is, for example, 30% or more and less than 50% of the width of the first shoulder block 20. Unless otherwise specified, the width of the block of the tread 10 refers to the width of the block contact surface along the tire axial direction in the portion where no lateral grooves exist. The width of the first shoulder block 20 is substantially constant along the tire circumferential direction.

[0041] The lateral grooves 21 are inclined at an angle of, for example, 5° to 15° relative to the tire axial direction and extend substantially parallel to the lateral grooves 56 of the inner shoulder blocks 55. The depth of the lateral grooves 21 decreases from the main groove 12 toward the end within the block, but there is a region in the middle of the lateral grooves 21 where the depth is constant. The lateral grooves 22 extend substantially parallel to the tire axial direction and gradually increase in width from near the end within the block toward the ground contact edge E1. The depth of the lateral grooves 22 decreases from the ground contact edge E1 toward the end within the block, but there is a region in the middle of the lateral grooves 22 where the depth is constant.

[0042] The first shoulder block 20 is formed with a plurality of sipes 23 aligned with the lateral grooves 21 in the tire circumferential direction, and a plurality of sipes 24 aligned with the lateral grooves 22 in the tire circumferential direction. The sipes 23, 24 are formed with a length that does not reach the main groove 12 or the ground contact edge E1, and both longitudinal ends are located within the block. It is also preferable that the sipes 23, 24 are formed with a length that does not overlap with each other in the tire circumferential direction. In this embodiment, a region where no lateral grooves or sipes exist is formed in the widthwise center of the first shoulder block 20 along the tire circumferential direction. This configuration improves block rigidity and more significantly suppresses uneven wear.

[0043] A plurality of sipes 23, 24 are formed between two lateral grooves. In this embodiment, five sipes 23 are formed between two lateral grooves 21 at intervals in the tire circumferential direction. Each sipe 23 extends in the same direction as the lateral groove 21 and has the same length as the other sipes. Furthermore, four sipes 24 are formed between two lateral grooves 22 and have the same length as the other sipes. The first shoulder block 20 further has a notch 25 (see FIG. 4) at the block end facing the main groove 12. In this specification, a notch means a recess recessed in the tire axial direction or a groove with a short length. The notch 25 is located exactly in the middle of or near the middle of the two lateral grooves 21.

[0044] In the first center block 30, multiple lateral grooves 31 extending from the main groove 11 and multiple lateral grooves 32 extending from the main groove 12 are alternately formed in the tire circumferential direction. The lateral grooves 31, 32 are staggered and offset in the tire circumferential direction, and the lateral groove 32 is located exactly midway between two lateral grooves 31 or nearby. The lateral grooves 31, 32 each terminate within the block and are formed to lengths that do not overlap in the tire circumferential direction. The axial length of the lateral grooves 31, 32 is, for example, 25% to 45% of the width of the first center block 30. The width of the first center block 30 is substantially constant along the tire circumferential direction. A region without lateral grooves is formed in the widthwise center of the second center block group 40 along the tire circumferential direction. This improves block rigidity and more significantly suppresses uneven wear.

[0045] The lateral grooves 31, 32 are inclined at an angle of, for example, 10° to 20° relative to the tire axial direction and extend substantially parallel to the lateral grooves 42 of the second center block group 40. The depth of the lateral grooves 31, 32 decreases from each main groove toward the end of the block, but there is a region where the depth is constant in the middle of the lateral grooves 31, 32. A notch 36 having a shorter axial length than the lateral groove 31 is formed on the extension of the lateral groove 31, and a notch 35 having a shorter axial length than the lateral groove 32 is formed on the extension of the lateral groove 32. The lateral grooves 31 and the notches 35 are alternately arranged in the tire circumferential direction on the main groove 11 side of the first center block 30, and the lateral grooves 32 and the notches 36 are alternately arranged in the tire circumferential direction on the main groove 12 side.

[0046] The first center block 30 has a shape with large constrictions at the portions between the lateral groove 31 and the notch 36, and at the portions between the lateral groove 32 and the notch 35. These constrictions are formed at predetermined intervals around the tire circumference, improving traction. The first center block 30 also has notches 37 and 38 (see FIG. 4) that are smaller than the notches 35 and 36 at the block ends facing the main grooves 11 and 12, respectively. The notch 37 is located exactly halfway between the lateral groove 31 and the notch 35 or nearby, and the notch 38 is located exactly halfway between the lateral groove 32 and the notch 36 or nearby.

[0047] In this embodiment, the spacing between the lateral grooves 32 and the notches 36, i.e., the spacing between the constricted portions, is substantially the same as the spacing between the lateral grooves 21 of the first shoulder blocks 20, and the lateral grooves 32 or the notches 36 and the notches 25 of the first shoulder blocks 20 are arranged opposite each other in the tire axial direction. Furthermore, the notches 38 and the lateral grooves 21 are arranged opposite each other in the tire axial direction. In this case, mud, sand, snow, and the like are more easily trapped in the grooves, improving traction. Meanwhile, the lateral grooves 32 or the notches 36 and the lateral grooves 21 are arranged in a staggered pattern so that they are not aligned in the tire axial direction, thereby ensuring the rigidity of the first blocks and suppressing uneven wear.

[0048] The first center block 30 is formed with sipes 33 and 34 that extend in the same direction as the lateral grooves 31 and 32. The sipes 33 are formed in the constricted portions sandwiched between the lateral groove 31 and the notch 36 and in the constricted portions sandwiched between the lateral groove 32 and the notch 35, connecting the lateral grooves and the notches. That is, the sipes 33 cross the blocks at the constricted portions, but there are no lateral grooves that divide the first center block 30. The portions of the sipes 33 on both sides of the axial direction of the tire can support each other when the sipes 33 close under load, so this configuration can improve traction while maintaining block rigidity.

[0049] The sipes 34 are formed with a length that does not reach the main grooves 11, 12, and both longitudinal ends are located within the blocks. In this embodiment, a plurality (five) of sipes 34 are formed between the two lateral grooves 31, 32 at intervals in the tire circumferential direction. The sipes 34 include two types of sipes with different lengths, and the two types are arranged alternately in the tire circumferential direction. The axial length of the longer first sipe is, for example, 50% to 80% of the block width. The length of the shorter second sipe is preferably 50% to 90% of the length of the first sipe. This configuration can improve traction while ensuring block rigidity. Furthermore, ground contact pressure can be made uniform, resulting in a more pronounced effect of suppressing uneven wear.

[0050] Region R2 of the tread 10 includes a second center block group 40 and a second shoulder block group 50 as rows of multiple second blocks separated in the tire circumferential direction. The second center block group 40 and the second shoulder block group 50 are separated from each other by the zigzag-extending main groove 13, and each block group comprises multiple second center blocks 41, outer shoulder blocks 51, and inner shoulder blocks 55, each of which is formed in the tire circumferential direction. By arranging rows of multiple blocks separated in the tire circumferential direction in region R2 on the vehicle inner side, traction is significantly improved.

[0051] The second center block group 40 is composed of a plurality of second center blocks 41 lined up in a row in the tire circumferential direction. Each second center block 41 is separated by a lateral groove 42 and is arranged alternately with the lateral grooves 42 in the tire circumferential direction. The second shoulder block group 50 is composed of two rows of blocks arranged in the tire circumferential direction. Each of the two rows of blocks constituting the second shoulder block group 50 includes a plurality of outer shoulder blocks 51 and a plurality of inner shoulder blocks 55. Each outer shoulder block 51 is separated by a lateral groove 52 and is arranged alternately with the lateral grooves 52 in the tire circumferential direction. Furthermore, each inner shoulder block 55 is separated by a lateral groove 56 and is arranged alternately with the lateral grooves 56 in the tire circumferential direction.

[0052] The second center blocks 41 are wider than the first center blocks 30. While the width of the second center blocks 41 varies slightly along the tire circumferential direction, their maximum and average widths are, for example, 1.03 to 1.10 times the width of the first center blocks 30. Because the rib-shaped first blocks are arranged in region R1 of the tread 10, the rubber volume tends to be large in region R1. However, by making the second center blocks 41 wider, the difference in rubber volume between regions R1 and R2 can be reduced. As a result, the effect of suppressing uneven wear is more pronounced. Furthermore, by making the second blocks wider in the center region of the tread 10, where ground pressure is high, traction is further improved.

[0053] The lateral grooves 42 are inclined at an angle of, for example, 10° to 20° relative to the tire axial direction, and the lateral grooves 56 are inclined at an angle smaller than that of the lateral grooves 42 relative to the tire axial direction. The lateral grooves 52 extend substantially parallel to the tire axial direction and gradually widen from the intermediate portion between the narrow groove 14 and the tread edge E2 toward the tread edge E2. The lateral grooves 42 are circumferentially offset from the lateral grooves 31 and notches 35 of the first center block 30 so as not to overlap with them in the tire axial direction. This arrangement improves traction while ensuring block rigidity in the center region of the tread 10. A notch 44 (see FIG. 5) is formed at the block end of the second center block 41 facing the main groove 11.

[0054] The lateral grooves 42, 56 are arranged in a staggered pattern, offset in the tire circumferential direction, with the lateral groove 42 located exactly in the middle of or near the center between the two lateral grooves 56. Similarly, the lateral grooves 52, 56 are arranged in a staggered pattern, offset in the tire circumferential direction, with the lateral groove 52 located exactly in the middle of or near the center between the two lateral grooves 56. In this case, traction can be improved while ensuring block rigidity. In addition, a notch 58 is formed on the block end of the inner shoulder block 55 facing the main groove 13, at a position opposite the lateral groove 42 in the tire axial direction.

[0055] The depths of the lateral grooves 42, 52, and 56 may be constant throughout the entire length or may be the same as the depth of the main grooves. In this embodiment, however, the depths are shallower than the main grooves. The lateral grooves 42 gradually become shallower from both longitudinal ends toward the center, and the depth is substantially constant over a predetermined length range including the longitudinal center. The depths of the lateral grooves 52 and 56 also become shallower toward the narrow grooves 14, but, like the lateral grooves 42, are substantially constant over a predetermined length range including the longitudinal center. The depth of the narrow grooves 14 varies circumferentially, becoming shallower at and near the intersections with the lateral grooves 52 and 56 and deeper away from the intersections. Setting the depths of the lateral grooves and narrow grooves 14 in this manner improves traction while ensuring block rigidity.

[0056] In the second center block group 40, a plurality of sipes 43 extending in the same direction as the lateral grooves 42 are formed side by side in the tire circumferential direction. The sipes 43 are formed to a length that does not reach the main grooves 11 and 13, and both longitudinal ends are located within the blocks. The sipes 43 include two types of sipes with different lengths, and the two types are arranged alternately in the tire circumferential direction. The axial length of the longer first sipe is, for example, 50% to 80% of the maximum width of the block. The length of the shorter second sipe is preferably 50% to 90% of the length of the first sipe. This configuration can improve traction while ensuring block rigidity. It also makes it possible to uniformize ground pressure, thereby more significantly suppressing uneven wear.

[0057] A plurality of sipes 53, 57 are formed in the outer shoulder block 51 and the inner shoulder block 55, respectively, spaced apart in the tire circumferential direction. Each of the sipes 53, 57 is formed long enough not to reach the block ends, with both longitudinal ends located within the block's contact patch. Each sipe 57 extends in the same direction as the lateral grooves 56 and has the same length as the others. Similarly, each of the sipes 53 has the same length as the others, but there are fewer sipes 53 than there are sipes 57. Note that in the first shoulder block 20, the number of sipes 24 between the lateral grooves 22 is also fewer than the number of sipes 23 between the lateral grooves 21. By reducing the number of sipes near the contact edges E1, E2, which are susceptible to lateral forces during cornering, block rigidity can be ensured and uneven wear can be effectively suppressed.

[0058] Hereinafter, the side shape of the pneumatic tire 1, particularly the side shape from the shoulder 4 to the tire maximum width position P of the sidewall 2, will be described in detail with reference to FIGS.

[0059] FIG. 6 is a side view of the pneumatic tire 1, and FIG. 7 is an enlarged view of a portion of the tire side surface. As shown in FIGS. 6 and 7, the sidewall 2 includes a side protector 60 formed in an annular shape in a side view. As described above, the side protector 60 is an annular convex portion that protrudes axially outward from the tire and is formed between the side rib 5 and the tire maximum width position P (see FIG. 7) to improve the side cut resistance of the sidewall 2. The side protector 60 is formed with a substantially constant width along the tire circumferential direction, centered on the rotation axis γ (see FIG. 6) of the pneumatic tire 1. The side protector 60 is also formed with a gap between it and the side rib 5, with a width that does not reach the tire maximum width position P.

[0060] The radial length of the side protector 60 is preferably 50% or more of the radial length of the tire from the side rib 5 to the tire maximum width position P, and in this embodiment, it is 60% or more and 90% or less. In this case, damage to the sidewall 2 can be more effectively suppressed. Generally, side protectors increase air resistance, but with the pneumatic tire 1, by improving the surface shape of the shoulder 4, a smooth air flow can be created along the tire side surface, including the side protector 60, thereby achieving excellent aerodynamic performance.

[0061] As will be described in more detail below, the side protector 60 includes a first end face 61 located at the radially outer end of the tire, a second end face 62 located at the radially inner end of the tire, and a main surface 63 connecting the first end face 61 and the second end face 62, and a first boundary portion between the first end face 61 and the main surface 63 is curved so as to be convex outward in the tire axial direction. On the other hand, a second boundary portion between the second end face 62 and the main surface 63 is more angular than the first boundary portion. The curved surface 64 formed at the first boundary portion between the first end face 61 and the main surface 63 has a synergistic effect with the surface shape of the shoulder 4, thereby more effectively improving the aerodynamic performance of the pneumatic tire 1.

[0062] From the viewpoint of improving design and aerodynamic performance, the side protector 60 is formed with a circumferential groove 66 extending in the tire circumferential direction and a radial groove 67 extending in the tire radial direction. The depths of the circumferential groove 66 and the radial groove 67 are preferably shallower than the height of the side protector 60, and the portions where each groove is formed also protrude from the profile surface α. The side protector 60 is divided into multiple blocks by the circumferential groove 66 and the radial groove 67. The depths of the circumferential groove 66 and the radial groove 67 are, for example, the same and are 0.3 mm or more and 0.6 mm or less. An example of the width of the circumferential groove 66 is 2 mm or more and 4 mm or less, and an example of the width of the radial groove 67 is 3 mm or more and 5 mm or less.

[0063] The circumferential groove 66 is formed in the widthwise center of the side protector 60 and divides the side protector 60 into an outer block 70 and an inner block 71. The outer block 70 is located radially outward of the circumferential groove 66, and the inner block 71 is located radially inward of the circumferential groove 66. The radial groove 67 is formed from the circumferential groove 66 to the first end face 61 and divides the outer block 70 into a plurality of blocks lined up in the tire circumferential direction. In addition, the radial groove 67 is formed from the circumferential groove 66 to the second end face 62 and divides the inner block 71 into a plurality of blocks lined up in the tire circumferential direction.

[0064] The circumferential grooves 66 and the radial grooves 67, together with the serrations 68, contribute to improving aerodynamic performance. As described above, the serrations 68 are fine uneven structures extending in the tire circumferential direction and are composed of multiple protrusions and grooves that are long in the tire circumferential direction. The multiple protrusions are formed at a height that does not protrude from the main surface 63 of the side protector 60. The serrations 68 have the function of rectifying the air that comes into contact with the side protector 60 in the direction of tire rotation. At least one serration 68 is formed in each block partitioned by the circumferential grooves 66 and the radial grooves 67. The total formation area of ​​the serrations 68 is larger in the inner block 71, which protrudes more axially outward than the outer block 70.

[0065] The side protector 60 includes a plurality of blocks 73 that divide the circumferential groove 66 and are formed from the first end face 61 to the second end face 62. The blocks 73 are arranged in a line in the tire radial direction with the rotation axis γ in between in a side view of the tire. In this embodiment, the blocks 73 are arranged at 180° central angles around the rotation axis γ, and the circumferential groove 66 is divided by two blocks 73 to form a semicircular shape. The blocks 73 include an outer region that is aligned with the outer blocks 70 in the tire circumferential direction and an inner region that is aligned with the inner blocks 71 in the tire circumferential direction, and have a curved shape such that the outer region overlaps with the inner blocks 71 in the tire radial direction, and the inner region overlaps with the outer blocks 70 in the tire radial direction.

[0066] The outer blocks 70 are gently curved blocks having a rectangular shape in a side view, and include a plurality of blocks that differ from one another in terms of the tire circumferential length and the shape of the tire circumferential ends. A plurality of outer blocks 70 are arranged in a line in the tire circumferential direction on the tire radially outer side of the side protector 60. The outer blocks 70 have the same block pattern in units of half a circumference separated by blocks 73. In this embodiment, eight outer blocks 70 are arranged between two blocks 73.

[0067] Like the outer blocks 70, the inner blocks 71 are gently curved blocks having a rectangular shape in a side view, and include a plurality of blocks that differ from one another in tire circumferential length and tire circumferential end shape. A plurality of inner blocks 71 are arranged in a line in the tire circumferential direction on the tire radially inner side of the side protector 60. The inner blocks 71 also have the same block pattern in half-circumference units separated by blocks 73. In this embodiment, eight inner blocks 71, the same number as the outer blocks 70, are arranged between two blocks 73.

[0068] The inner block 71 includes a plurality of inner small blocks 72 that protrude radially inward relative to the other blocks. In a side view of the tire, the inner small blocks 72 are arranged side by side in the tire radial direction, sandwiching the rotation axis γ. In this embodiment, an inner small block 72 is arranged every half circumference. Similarly, block 73 also protrudes radially inward relative to the other inner blocks 71. Therefore, the width of the side protector 60 is locally increased in the areas where the inner small blocks 72 and blocks 73 are arranged. On the other hand, such locally protruding shapes do not exist on the radially outer side of the side protector 60, and the flow of air that hits the side protector 60 is less likely to be disturbed.

[0069] 8 is a perspective view of the shoulder 4 and its vicinity. As shown in FIG. 8, the surface of the shoulder 4 on the vehicle-outer side of the ground contact edge E1 is formed by the side surface of the first shoulder block 20 facing axially outward in the tire. Furthermore, the surface of the shoulder 4 on the vehicle-inner side of the ground contact edge E2 is formed by the side surface of the outer shoulder block 51 facing axially outward in the tire. The side surface shapes of the first shoulder block 20 and the outer shoulder block 51 are similar, and therefore the surface shapes of the left and right shoulders 4 are similar. Meanwhile, the first shoulder block 20 is a rib-shaped block that is continuous in the tire circumferential direction, while the outer shoulder block 51 is divided by a lateral groove 52.

[0070] The aerodynamic performance of a front tire is easily affected by the tread pattern and tire side surface shape located on the vehicle outer side. With the pneumatic tire 1, the region R1 of the tread 10, including the first shoulder blocks 20, is located on the vehicle outer side, thereby creating a smooth airflow along the tire surface from the tread 10 to the shoulder 4 and the sidewall 2. Furthermore, the linear main grooves 12 and the rib-shaped first center blocks 30 formed in the region R1 also contribute to improving aerodynamic performance. The configuration of the shoulder 4 will be described in detail below, using the vehicle outer shoulder 4 as an example.

[0071] As described above, the shoulder 4 has an arc-shaped shoulder surface 26 with virtually no corners. As disclosed in Patent Document 2, conventional heavy-duty tires have angular contact edges to ensure a large tread contact patch, and the shoulder also has an angular shape. In the past, heavy-duty tires have barely considered aerodynamic performance. However, improving the aerodynamic performance of tires is an important issue, particularly for EVs, where tire noise is more noticeable and fuel economy is also important. The inventors conducted extensive research in light of this situation and found that the angular shape of the shoulder significantly affects the aerodynamic performance of a tire, and that the arc-shaped shoulder surface 26 significantly improves aerodynamic performance.

[0072] The shoulder surface 26 is a surface connecting the ground contact edge E1 and the side rib 5, and is curved so as to convex outward in the axial direction of the tire. The shoulder surface 26 also protrudes gradually from the ground contact edge E1 toward the radially inward direction of the tire, gradually becoming more axially outward. In this case, the contact area increases on muddy, sandy, snowy roads, etc., improving traction. The shoulder surface 26 may be entirely formed by a single arc, but from the perspective of improving traction, design, etc., it is preferable that a portion of the shoulder surface 26 be curved so as to convex outward in the axial direction of the tire.

[0073] The shoulder surface 26 preferably has an arc-shaped curved surface 26b that convexly faces axially outward at a position away from the ground contact edge E1 and the side rib 5. In this embodiment, only a portion of the shoulder surface 26 is curved so as to be convex in the tire axial direction. The region from the ground contact edge E1 to the curved surface 26b is flat, and the region from the curved surface 26b to the side rib 5 is curved so as to be convex axially inward, i.e., in the opposite direction to the curved surface 26b. The shoulder surface 26 has, in order from the ground contact edge E1 side, a flat surface 26a, a curved surface 26b, and a second curved surface 26c. This configuration effectively improves aerodynamic performance while ensuring good traction and design.

[0074] In this embodiment, a corner is formed at the boundary between the surface of the first shoulder block 20 facing radially outward in the tire and the surface of the first shoulder block 20 facing axially outward in the tire, and this corner serves as the contact edge E1. The angular contact edge E1 is detrimental to aerodynamic performance, but chamfering this corner and moving the contact edge axially inward in the tire reduces the contact patch of the tread 10, leading to reduced traction. The pneumatic tire 1 includes a shoulder surface 26 including a curved surface 26b, which reduces the effect of the angular contact edge E1 and enables smooth airflow along the tire sidewall.

[0075] A lateral groove 22 is formed in the shoulder 4 from the axially inner side of the ground contact edge E1 to the side rib 5. The lateral groove 22 forms a recessed portion that is recessed axially inward in the shoulder 4. The presence of the lateral groove 22 is somewhat detrimental to achieving a smooth air flow, but the lateral groove 22 is a short groove that terminates within the first shoulder block 20 and does not significantly affect the aerodynamic performance of the pneumatic tire 1.

[0076] The sidewall 2 is formed with an annular region 2a between the side rib 5 and the side protector 60, recessed further than the side rib 5 and the side protector 60. The surface of the region 2a may be at the same height as the profile surface α. A first end face 61 located at the radially outer end of the side protector 60 is a surface connecting the region 2a, which is a recess, and the main surface 63 of the side protector 60, which is a protrusion, and the portion close to the region 2a is gently curved so as to be convex axially inward (see FIG. 11 , described later). On the other hand, the portion close to the main surface 63 is curved so as to be convex axially outward. This configuration allows smooth airflow along the surface of the side protector 60.

[0077] A curved surface 64 that is convex outward in the tire axial direction is formed at a first boundary portion between the first end face 61 and the main surface 63. The curved surface 64 is formed along the tire circumferential direction, except for the portion where the radial groove 67 opens. A corner may be formed at the portion where the radial groove 67 opens, but the height of the side protector 60 is low at the opening of the radial groove 67 and the area where the opening is formed is also small, so the impact of the corner on aerodynamic performance is small. An arc-shaped curved surface 64 that is substantially free of corners is formed at the boundary portion between the first end face 61 and the main surface 63, except for the portion where the radial groove 67 opens.

[0078] The second end face 62, located at the radially inner end of the side protector 60, is a curved surface that convexly curves inward, similar to the portion of the first end face 61 near the region 2a, but the degree of curvature is greater than that of the first end face 61. A corner 65 is formed at a second boundary portion between the second end face 62 and the main surface 63. The corner 65 emphasizes the edge of the side protector 60 and improves its design. Because the second boundary portion has less impact on aerodynamic performance than the first boundary portion, it is preferable to form the corner 65 in consideration of design.

[0079] FIG. 9 is a diagram showing a portion of the cross section taken along line AA in FIG. 3, and FIG. 10 is an enlarged view of the shoulder 4 and its vicinity on the tread edge E1 side in FIG. 9. As shown in FIGS. 9 and 10, the pneumatic tire 1 has three belts 6, 7, and 8. The number of belts can be one or two, or four or more, but three is preferred. The belts 6, 7, and 8 are stacked in this order from the outer side in the tire radial direction to increase the rigidity of the tread 10 and suppress uneven wear of the blocks. In this embodiment, the belts 6 and 8 have the same width. The belt 7 sandwiched between the belts 6 and 8 is formed wider than the belts 6 and 8 and extends axially on both sides of the tire axial ends of the belts 6 and 8 (hereinafter simply referred to as "belt ends").

[0080] The pneumatic tire 1 has a first region Z1 where multiple belts 6, 7, and 8 overlap in the tire radial direction, a second region Z2 located axially outboard of the first region Z1 and where one belt 7 is arranged, and a third region Z3 located axially outboard of the second region Z2 and where no belt is present. Fig. 9 shows an imaginary line β1 extending along the tire radial direction and passing through the belt ends of the belts 6 and 8, and an imaginary line β2 extending along the tire radial direction and passing through the belt end of the belt 7. The region located axially inward of the imaginary line β1 is the first region Z1, the region located between the imaginary lines β1 and β2 is the second region Z2, and the region located axially outboard of the imaginary line β2 is the third region Z3.

[0081] The first region Z1 increases the rigidity of the tread 10 from the center to the shoulder, reducing uneven wear of the blocks. The third region Z3, which has lower rigidity than the first and second regions Z1 and Z2, is located slightly axially inward of the tire's contact edges E1 and E2. If the shoulder 4, which is susceptible to lateral forces, has high rigidity, rebound occurs when the shoulder 4 comes into contact with a rut or the like, resulting in poor handling. This rebound also causes airflow turbulence. In this embodiment, by making the entire shoulder 4 the third region Z3, the shoulder 4 is able to more easily absorb lateral forces when they are applied, improving handling and aerodynamic performance.

[0082] The arc shape formed on the surface of the shoulder 4 and convex outward in the axial direction of the tire is formed in the third region Z3. The following description will be given using the shoulder 4 on the tread edge E1 side shown in FIG. 10 as an example. As described above, the shoulder surface 26 has a curved surface 26b that convex outward in the axial direction of the tire. In this embodiment, the entire shoulder surface 26 is the third region Z3, so the curved surface 26b is formed in the third region Z3. The shoulder surface 26 has the curved surface 26b and is corner-free, allowing lateral forces to be dispersed along the curved surface 26b. As a result, uneven wear of the blocks is suppressed and airflow turbulence is also reduced. The curved surface 26b formed in the third region Z3 functions to disperse and absorb lateral forces.

[0083] On the other hand, if the shoulder surface has an angular shape, forces are concentrated at the corners, which makes it easier for uneven wear to occur on the blocks, and the rebounding of the blocks makes it easier for airflow to become turbulent.Furthermore, it is not possible to achieve a smooth airflow along the tire sidewall, which increases air resistance and makes it easier for wind noise to occur.

[0084] The curved surface 26b of the shoulder surface 26 is further formed on an extension of the bottom surface of the lateral groove 21. As described above, the lateral groove 22 extends from the axially inner side of the tire contact edge E1 to the shoulder 4, and the depth is substantially constant in the middle of the lateral groove 22. In this embodiment, the curved surface 26b is formed on an extension of the groove bottom of the region where the depth of the lateral groove 22 is constant. This configuration makes it easier to disperse and absorb lateral forces, resulting in more significant improvements in handling and aerodynamic performance.

[0085] Fig. 11 is a diagram showing a portion of the outline of the tire along the tire surface on the side of the contact edge E1 in the cross section of Fig. 9. In Fig. 11, the profile surface α of the sidewall 2 is indicated by a two-dot chain line. The profile surface α is a surface represented by a single curve that smoothly connects, in the tire axial cross section, a first curve that runs along the surface of the sidewall 2 radially inward of the protector 60 and a second curve that runs along the surface of the sidewall 2 radially outward of the side protector 60.

[0086] As shown in FIG. 11, the shoulder surface 26 has a radius of curvature R 26b The curved surface 26b has a radius of curvature R of 0.1 mm or less, and does not have a corner like the ground contact end E1, in other words, a bent portion with a radius of curvature R of 0.1 mm or less. 26b is set to, for example, 5 mm or more, preferably 5 mm or more and 15 mm or less, more preferably 7 mm or more and 13 mm or less, and particularly preferably 8 mm or more and 12 mm or less. 26b If is within this range, it becomes easier to achieve a smooth air flow along the tire side surface, and the effect of improving aerodynamic performance becomes more significant.

[0087] As described above, the shoulder surface 26 has a flat surface 26a formed between the ground contact edge E1 and the curved surface 26b, and a second curved surface 26c formed between the curved surface 26b and the side rib 5. There are no corners at the boundaries between the flat surface 26a, the curved surface 26b, and the second curved surface 26c, and each surface is smoothly connected. While the entire shoulder surface 26 can be made into a curved surface with a curvature radius of 5 mm or more, providing the above three surfaces effectively improves aerodynamic performance while ensuring good traction and design. The curvature radius of the second curved surface 26c is smaller than that of the curved surface 26b, for example, between 100 mm and 150 mm.

[0088] The tire radial direction length of the curved surface 26b is, for example, 20% to 60% of the tire radial direction length of the shoulder 4, and preferably 30% to 50%. The tire radial direction length of the flat surface 26a is preferably shorter than that of the curved surface 26b, and is, for example, 15% to 25% of the tire radial direction length of the shoulder 4. The tire radial direction length of the second curved surface 26c may be substantially the same as the tire radial direction length of the curved surface 26b, and is, for example, 20% to 60% of the tire radial direction length of the shoulder 4. If the tire radial direction lengths of the flat surface 26a, the curved surface 26b, and the second curved surface 26c are within these ranges, the above-mentioned effect obtained by providing three surfaces becomes more pronounced.

[0089] The flat surface 26a is preferably inclined at an angle of 30° to 50° with respect to an imaginary line β3 that passes through the contact edge E1 and extends in the tire radial direction. In this case, good traction is obtained without impairing aerodynamic performance. Note that the flat surface 26a may be changed to a curved surface with a larger radius of curvature than the curved surface 26b, as long as traction and design are not impaired. Furthermore, the second curved surface 26c is a curved surface that is convex toward the axially inward direction of the tire, but it can also be a flat surface.

[0090] As described above, the side protector 60 is a protrusion that protrudes from the profile surface α toward the outside in the tire axial direction. 60The height H is, for example, 1.0 mm or more and 3.5 mm or less at the highest part, and preferably 1.0 mm or more and 2.0 mm or less. 60 means the length from the profile surface α to the side protector 60 along a direction perpendicular to the profile surface α. The main surface 63 of the side protector 60 has a height H 60 is constant and is formed parallel to the profile plane α.

[0091] The first end face 61 and the second end face 62 of the side protector 60 are faces that connect the profile face α and the main face 63, and their heights gradually increase toward the main face 63. In this embodiment, the height of the region 2a located between the side rib 5 and the side protector 60 is the same as the profile face α. The height of the side rib 5 is lower than that of the side protector 60, for example, 1.0 mm or less. The tire radial length of the first end face 61 and the second end face 62 is the height H of the side protector 60. 60 It is preferable that the value is 2 to 5 times the maximum value of the above.

[0092] A curved surface 64 that is convex outward in the tire axial direction is formed at a first boundary portion between the first end surface 61 and the main surface 63 of the side protector 60. The curvature radius R 64 is the radius of curvature R of the curved surface 26b of the shoulder surface 26 26b Although the aerodynamic performance is improved by forming the curved surface 64 at the first boundary portion, the radius of curvature R 64 If the radius of curvature R becomes too large, the edge of the side protector 60 becomes difficult to see, which is undesirable from the design point of view. Since the first boundary portion has a smaller effect on the aerodynamic performance than the shoulder surface 26, the radius of curvature R 64 <Radius of curvature R 26b It is preferable to set the following.

[0093] Radius of curvature R of curved surface 64 64The radius of curvature R is preferably 1 mm or more and 10 mm or less, and more preferably 3 mm or more and 7 mm or less. 64 If is within this range, smooth airflow along the tire side surface can be achieved without compromising the design of the sidewall 2. On the other hand, the second boundary portion between the first end face 61 and the main surface 63 of the side protector 60 is more angular than the first boundary portion, and has a corner 65. Because the second boundary portion has less of an effect on aerodynamic performance than the first boundary portion, it is preferable to use the corner 65 to emphasize the edge of the side protector 60 and improve the design.

[0094] As described above, the pneumatic tire 1 having the above configuration has excellent aerodynamic performance and contributes to improving, for example, the quietness and fuel economy of a vehicle. The pneumatic tire 1 is suitable for heavy-duty tires, and is particularly suitable for EV tires (tires for large EVs) that require high quietness and fuel economy (electricity cost) performance. The improved tire side surface shape of the pneumatic tire 1 makes it possible to create a smooth air flow along the tire side surface, including the side protector 60. As a result, air resistance is reduced and quietness is improved.

[0095] Furthermore, in the pneumatic tire 1, the linear main grooves 12 and the rib-shaped first blocks in the region R1 located on the vehicle outer side of the front tire also contribute greatly to improving the aerodynamic performance. Below, the evaluation results of the air resistance of the pneumatic tire 1 are shown.

[0096] [Air resistance evaluation] For the pneumatic tire 1 having the above configuration (hereinafter referred to as "test tire S1"), air resistance was evaluated at a vehicle speed of 40 km / h through a simulation that analyzed the air flow around the rotating tire. For comparison, test tire B1 was evaluated, in which corners were formed at corresponding positions instead of the curved surface 26b of the shoulder surface 26 and the curved surface 64 of the first boundary portion of the side protector 60. Air resistance was measured using the drag coefficient (Cd value). The evaluation results for test tires B1 and S1 are shown in Table 1.

[0097] The main specifications of the test tire S1 related to the evaluation of air resistance are as follows: Curvature radius R of curved surface 26b 26b :10mm Radius of curvature R of curved surface 64 64 :5mm Side protector 60 height H 60 :1.2mm Axial length of the first end face 61 of the side protector 60: 2.0 mm

[0098] The Cd value was calculated using the following formula, which was derived from the pressure difference between the front and rear of the tire in a simulation to determine drag (the force acting on a tire placed in an air flow, parallel to the flow and in the same direction). Cd=D / (1 / 2ρU2S) In the formula, D is the generated drag force, ρ is the air density, 1.18415 [kg / m 3 ]. U is the representative velocity, which is the relative velocity between the tire and the air, and is set to 36.1 [m / s]. S is the representative area of ​​the tire (frontal projected area).

[0099] [Table 1]

[0100] As shown in Table 1, test tire S1 has a lower Cd value and is superior in aerodynamic performance compared to test tire B1. Test tire S1 can reduce the Cd value by approximately 4.3% compared to test tire B1.

[0101] The above-described embodiment can be appropriately modified without impairing the object of the present invention. For example, the above-described embodiment illustrates a tire suitable for a winter tire with many sipes, but the configuration of the present invention can also be applied to a summer tire or all-season tire with fewer sipes. The same tire side surface shape as the pneumatic tire 1 described above and a tread pattern including circumferentially continuous rib-shaped blocks and rows of multiple blocks separated in the circumferential direction can also be applied to a summer tire or all-season tire. [Explanation of symbols]

[0102] 1 pneumatic tire, 2 sidewall, 2a region, 3 bead, 4 shoulder, 5 side rib, 6, 7, 8 belt, 10 tread, 11, 12, 13 main groove, 13a, 14a first portion, 13b, 14b second portion, 14 narrow groove, 15 stone ejector, 20 first shoulder block, 21, 22 lateral groove, 23, 24 sipe, 25 notch, 26 shoulder surface, 26a flat surface, 26b curved surface, 26c second curved surface, 30 first center block, 31, 32 lateral groove, 33, 34 sipe, 35, 36, 37, 38 notch, 40 second center block group, 41 second center block, 42 ​​lateral groove, 43 sipe, 44 notch, 50 second shoulder block group, 51 Outer shoulder block, 52 lateral groove, 53 sipe, 55 inner shoulder block, 56 lateral groove, 57 sipe, 58 notch, 60 side protector, 61 first end face, 62 second end face, 63 main surface, 64 curved surface, 65 corner, 66 circumferential groove, 67 radial groove, 68 serration, 70 outer block, 71 inner block, 72 inner small block, 73 block, 100 vehicle, CL equator, E1, E2 ground contact edge, P maximum tire width position, R1, R2 area, Z1 first area, Z2 second area, Z3 third area, α profile surface, β1, β2, β3 virtual line, γ rotation axis

Claims

1. A pneumatic tire comprising a tread, a sidewall, and a shoulder located between a ground contact edge of the tread and the sidewall, wherein a corner is formed at the ground contact edge, the shoulder has a shoulder surface that is substantially corner-free; The shoulder surface has an arcuate shape that is curved so as to be convex outward in the axial direction of the tire.

2. The pneumatic tire according to claim 1 , wherein a radius of curvature of the arc shape of the shoulder surface is equal to or greater than 5 mm and equal to or less than 15 mm.

3. The sidewall includes a side protector, the side protector includes a first end surface located at an outer end in the tire radial direction, a second end surface located at an inner end in the tire radial direction, and a main surface connecting the first end surface and the second end surface, 2. The pneumatic tire according to claim 1, wherein a first boundary portion between the first end surface and the main surface is curved so as to be convex outward in the tire axial direction, and a second boundary portion between the second end surface and the main surface is more angular than the first boundary portion.

4. The pneumatic tire according to claim 3 , wherein a radius of curvature of the first boundary portion of the side protector is smaller than a radius of curvature of the arc shape of the shoulder surface.

5. The pneumatic tire includes a first region having a plurality of belts overlapping each other in a tire radial direction, a second region located axially outward of the first region and having one belt disposed therein, and a third region located axially outward of the second region and having no belt, The pneumatic tire according to claim 1 , wherein the arc shape of the shoulder surface is formed in the third region.

6. The tread has a lateral groove extending from an axially inner side of the ground contact edge to the shoulder, The pneumatic tire according to claim 1 , wherein the arc shape of the shoulder surface is formed on an extension of a bottom surface of the lateral groove.

7. The pneumatic tire is a tire whose mounting direction on a vehicle is specified, 7. The pneumatic tire according to claim 1, wherein, when the pneumatic tire is mounted on the vehicle as a front tire, the tread has rib-shaped first blocks that are continuous in the tire circumferential direction in an area that is on the outer side of the tire equator of the vehicle, and has a row of multiple second blocks that are separated in the tire circumferential direction in an area that is on the inner side of the tire equator of the vehicle.

8. The pneumatic tire according to claim 7 , wherein the first blocks include shoulder blocks that form the shoulders, and center blocks that are disposed closer to the tire equator than the shoulder blocks.

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