Pneumatic tire

Abstract

To reduce an air resistance of a tire.SOLUTION: In a pneumatic tire 1, a buttress 4 is formed with a straight region 70 having a flat surface, and projections 80 arranged adjacently in a tire radially inside of the straight region 70 and formed in a ring shape along a tire circumferential direction. A tire radial length (d1+d2) from a tire radially outside end of the straight region 70 to a distal end 83 of the projection 80 is longer than a tire radial length from a ground contact end of the tread 10 to the tire radially outside end of the straight region 70. A height of the projection 80 is 0.5 mm or more and 1.0 mm or less.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Conventionally, tire buttresses generally have protrusions formed due to mold seams, and side protectors are formed to provide design. In tires for light trucks and sports utility vehicles (SUVs), side protectors are formed to improve side traction performance, side cut performance, etc. Also, tires are known in which multiple protrusions are formed on the buttresses to generate turbulence on the tire side and suppress temperature rise in the tread (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-176703 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a strong demand for improved fuel efficiency for vehicles, and therefore also a demand for reduced air resistance in tires. Conventionally, emphasis has been placed on design, productivity, etc. regarding the shape of buttresses, with little consideration given to aerodynamic performance, but as a result of the inventor's investigations, it has been found that the shape of the buttresses greatly affects the aerodynamic performance of tires. An object of the present invention is to reduce the air resistance of tires by improving the shape of the buttresses. [Means for solving the problem]

[0005] The pneumatic tire according to the present invention is a pneumatic tire including a tread and a buttress, wherein the buttress is formed with a straight region having a flat surface, and a protrusion arranged adjacent to the radially inner side of the straight region and formed in a ring shape along the tire circumferential direction, the tire radial length (d1+d2) from the radially outer end of the straight region to the tip of the protrusion is longer than the tire radial length (d3) from the ground contact edge of the tread to the radially outer end of the straight region, and the height of the protrusion is 0.5 mm or more and 1.0 mm or less. Effect of the Invention

[0006] INDUSTRIAL APPLICABILITY The pneumatic tire according to the present invention can effectively reduce air resistance. The pneumatic tire according to the present invention contributes to, for example, improved fuel efficiency of a vehicle. [Brief description of the drawings]

[0007] [Figure 1] 1 is a perspective view of a pneumatic tire as an example of an embodiment. [Diagram 2] 1 is a plan view of a pneumatic tire according to an embodiment, showing an enlarged view of a portion of a tread. [Diagram 3] 1 is a side view of a pneumatic tire according to an embodiment, showing an enlarged view of a portion of a buttress. [Figure 4] 4 is a cross-sectional view taken along line AA in FIG. 3. [Diagram 5] In the cross-sectional view of FIG. 4, the protrusion and the straight region are shown in an enlarged scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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. In addition, the present invention includes embodiments obtained by selectively combining the respective 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 a portion that comes into contact with the road surface, a pair of sidewalls 2 that bulge outward in the axial direction of the tire, a pair of beads 3 which are portions that are fixed to the rim of a wheel, and a pair of buttresses 4. The buttresses 4 are portions located between the tread 10 and the sidewalls 2, and are also called shoulders. The sidewalls 2, the beads 3, and the buttresses 4 extend radially inward from both the left and right ends of the tread 10, and form the tire side surfaces.

[0010] In this specification, the region from the ground contact ends E1, E2 of the pneumatic tire 1 to the radially inner end of the protrusion 80 formed in a rib shape is defined as the buttress 4. In other words, the ground contact ends E1, E2 are the boundary positions between the tread 10 and the buttress 4, and the radially inner end of the protrusion 80 is the boundary position between the sidewall 2 and the buttress 4.

[0011] The pneumatic tire 1 is a point-symmetric tire that has no designated mounting direction on a vehicle and the tread pattern and tire side shape do not change regardless of the mounting direction on the vehicle. The tread pattern and tire side shape of the pneumatic tire 1 are rotated 180° on either side of the tire equator CL. The equator CL is an imaginary line that passes through the center of the tread 10 in the axial direction along the tire circumferential direction.

[0012] The tread 10 has a plurality of main grooves extending in the tire circumferential direction and a plurality of blocks partitioned by each main groove. In this embodiment, four circumferential grooves, a first main groove 11, a second main groove 12, a third main groove 13, and a fourth main groove 14, are formed, and each main groove extends parallel to each other along the tire circumferential direction. The four main grooves may have the same width, but in this embodiment, the main grooves 11 and 12 formed on the equator CL side are formed slightly wider than the main grooves 13 and 14 formed on the ground contact edges E1 and E2 sides. In addition, the four main grooves extend straight in the tire circumferential direction with a constant width. In this case, the groove area that is continuous in the tire circumferential direction can be increased, and good drainage performance can be obtained throughout the tread 10.

[0013] The multiple blocks include a center block 20, a first shoulder block 30, and a second shoulder block 40. The multiple blocks further include a first mediate block 50 disposed between the center block 20 and the shoulder block 30, and a second mediate block 60 disposed between the center block 20 and the shoulder block 40. A block is a convex portion that protrudes toward the outside in the tire radial direction, and is sometimes called a land in the tire industry.

[0014] A plurality of lateral grooves are formed in the tread 10, extending in a direction intersecting the main grooves and connected to the main grooves. The lateral grooves may extend straight in the tire axial direction, but are preferably inclined at a predetermined angle relative to the tire axial direction. In this embodiment, the lateral grooves include a slit 21 that divides the center block 20, and slits 22 and 23 (see FIG. 2 described later) that terminate within the center block 20. In addition, thin sipes are formed in the center block 20.

[0015] In this specification, a lateral groove having a width of 1.5 mm or more is defined as a slit, and a lateral groove having a width of less than 1.5 mm is defined as a sipe. The width of a slit is preferably 2.0 mm or more and 4.0 mm or less. The width of a sipe is preferably 0.3 mm or more and 1.0 mm or less.

[0016] The tread 10 further has slits 31, 32 and sipes formed in the shoulder block 30, and slits 41, 42 and sipes formed in the shoulder block 40. The tread 10 also has a slit 51 dividing the mediate block 50, and a slit 61 dividing the mediate block 60. The mediate blocks 50, 60 have a plurality of slits and sipes that terminate within the blocks, similar to the center block 20.

[0017] The center block 20 and the mediate blocks 50, 60 are each formed as a row of blocks separated by slits 21, 51, 61, lined up in the tire circumferential direction. On the other hand, the shoulder blocks 30, 40 are formed as ribs that run continuously around the tire circumferential direction. In the tire industry, a continuous land that runs around the entire tire circumference is customarily called a rib, and the shoulder blocks 30, 40 can be considered ribs.

[0018] Although details will be described later, the buttress 4 of the pneumatic tire 1 is formed with a straight region 70 having a flat surface, and a protrusion 80 arranged adjacent to the straight region 70 on the radially inner side of the tire and formed in an annular shape along the tire circumferential direction. The tire radial length (d1+d2) from the tire radially outer end of the straight region 70 to the tip of the protrusion 80 is longer than the tire radial length from the ground contact ends E1, E2 of the tread to the tire radially outer end of the straight region 70. In addition, the height of the protrusion 80 is 1.0 mm or less. This makes it possible to effectively reduce air resistance and realize a tire that contributes to low fuel consumption of a vehicle.

[0019] In this specification, the ground contact ends E1 and E2 are defined as both axial ends of the area (ground contact surface) that comes into contact with a flat road surface when a predetermined load is applied to an unused pneumatic tire 1 mounted on a standard rim and filled with air to a standard internal pressure. In the case of passenger car tires, the predetermined load is a load equivalent to 88% of the standard load.

[0020] Here, "regular rim" refers to a rim determined by tire standards, and is "standard rim" for JATMA, and "measuring rim" for TRA and ETRTO. "Regular internal pressure" refers to "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. Regular internal pressure is usually 180 kPa for passenger tires, but 220 kPa for tires labeled "Extra Load" or "Reinforced." "Regular load" refers to "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO.

[0021] The pneumatic tire 1 includes, for example, a carcass, a belt, and a cap ply. The carcass is a cord layer covered with rubber, and serves as the skeleton of the tire that can withstand loads, impacts, air pressure, and the like. 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 tire circumferential direction. An inner liner, which is a rubber layer for retaining air pressure, is generally provided on the inside of the carcass. The belt is a reinforcing band that is disposed between the rubber that constitutes the tread 10 and the carcass.

[0022] Generally, letters, numbers, symbols, etc., called serial numbers, are provided on the sidewall 2. The serial numbers include information such as a size code, a manufacturing time (manufacturing year and week), and a manufacturing place (manufacturing factory code).

[0023] The tread pattern will be described in detail below with reference to Fig. 2. Fig. 2 is a plan view of the pneumatic tire 1, showing a part of the tread 10 in an enlarged manner.

[0024] As shown in Fig. 2, the tread 10 has a center block 20 disposed on the equator CL. As described above, the tread 10 further has shoulder blocks 30, 40 and mediate blocks 50, 60. A main groove 11 is formed between the center block 20 and the mediate block 50, and a main groove 12 is formed between the center block 20 and the mediate block 60, separating the center block 20 from the mediate blocks 50, 60. A main groove 13 is formed between the mediate block 50 and the shoulder block 30, separating the two blocks, and a main groove 14 is formed between the mediate block 60 and the shoulder block 40, separating the two blocks.

[0025] The main grooves may be formed to the same depth, but in this embodiment, the main grooves 11, 12 are formed slightly deeper than the main grooves 13, 14. The main grooves 11, 12 have substantially the same width and depth, and the main grooves 13, 14 have substantially the same width and depth. The depth of each main groove is substantially constant over its entire length except for the portion where the wear indicator is formed. In this specification, the width of the main groove means the groove width along the profile surface of the tread 10, in other words, the groove width at the opening of the groove, and the depth of the main groove means the length from the profile surface to the bottom of the deepest part of the groove (the same applies to the lateral grooves). The profile surface of the tread 10 is a surface along the surface of the tread 10.

[0026] The walls of the main groove are inclined so that the groove volume gradually decreases toward the bottom of the groove. The walls of the main groove form the side walls of the blocks, in other words, the side walls of the blocks are inclined so that the block width increases the further away from the ground contact surface. On the other hand, the walls of the lateral grooves are formed at an angle perpendicular or close to perpendicular to the profile surface of the tread 10. The lateral grooves are also formed to be narrower and shallower than the main grooves. The slits and sipes may have the same depth, but in this embodiment, the slits are formed deeper than the sipes.

[0027] As described above, the pneumatic tire 1 has a plurality of sipes formed in each block. The pneumatic tire 1 exhibits good grip even on snowy and icy road surfaces and is suitable, for example, as an all-season tire. The total width of the pneumatic tire 1 is not particularly limited, but an example is 205 mm or more and 275 mm or less. The aspect ratio of the pneumatic tire 1 is also not particularly limited, but when the aspect ratio is 60% or more, the effect of reducing air resistance by adopting the configuration of the buttress 4 becomes more significant. An example of a suitable range of the aspect ratio of the pneumatic tire 1 is 60% or more and 80% or less, or 65% or more and 75% or less.

[0028] The slit 21 that crosses the center block 20, the slits 51 and 61 that cross the mediate blocks 50 and 60, and the slits 31, 32, 41 and 42 in the shoulder blocks 30 and 40 are formed to be located on a single line curved in an S shape. The slits 32 and 33 that terminate in the center block 20 and the slits 52 and 62 that terminate in the mediate blocks 50 and 60, respectively, are also formed to be located on a single line curved in an S shape together with the slits in the shoulder blocks 30 and 40. A plurality of these sets of slits are arranged at a predetermined interval in the tire circumferential direction. The predetermined interval is preferably a variable pitch that changes in units of a predetermined number in the tire circumferential direction.

[0029] The center block 20 and the mediate blocks 50, 60 may have the same width, but in this embodiment, the width of the mediate blocks 50, 60 is larger than the width of the center block 20. The ground contact area of ​​the mediate blocks 50, 60 is larger than the ground contact area of ​​the center block 20, for example, 1.1 to 1.3 times the ground contact area of ​​the center block 20. The ground contact areas of the mediate blocks 50, 60 are substantially the same. The ground contact areas of the shoulder blocks 30, 40 are substantially the same and larger than the ground contact areas of the mediate blocks 50, 60.

[0030] The configurations of the center block 20, the shoulder blocks 30, 40, and the mediate blocks 50, 60 will be described in further detail below.

[0031] [Center block] The center blocks 20 extend from the main grooves 11 to 12 and are divided in the tire circumferential direction by slits 21 that connect the main grooves 11, 12. A plurality of center blocks 20 divided by slits 21 are arranged in a row on the equator CL of the tread 10. The interval between the slits 21 in the tire circumferential direction, the length of each center block 20 in the tire circumferential direction, and the interval between the lateral grooves formed in each block in the tire circumferential direction vary at a variable pitch.

[0032] The slit 21 is formed straight from the main groove 11 to the main groove 12, and is inclined at a predetermined angle with respect to the tire axial direction. The predetermined angle is, for example, 15° or more and 40° or less. Slits 22 and 23 that terminate within the center block 20 are formed at positions that are substantially equidistant from two slits 21 adjacent to each other in the tire circumferential direction. The slit 22 is connected to the main groove 11, and the slit 23 is connected to the main groove 12, respectively, and the slits 22 and 23 are arranged opposite each other on the same straight line with a bridge 26 in between. The slits 22 and 23 are formed substantially parallel to the slit 21. The slits 22 and 23 have substantially the same dimensions (width, length, depth), and are formed slightly narrower than the slit 21.

[0033] The center block 20 is formed by connecting two blocks arranged in the tire circumferential direction with a bridge 26, which is the portion sandwiched between the slits 22, 23. By connecting the two blocks with the bridge 26 without dividing the block, for example, it is possible to increase the rigidity of the center block 20 and improve braking characteristics while improving the edge effect, drainage performance, etc. In addition, a plurality of sipes 24, 25 that terminate within the block are formed between the slit 21 and the slits 22, 23. The edge effect of the sipes 24, 25 improves snow performance.

[0034] The sipe 24 is connected to the main groove 11, and the sipe 25 is connected to the main groove 12, and the sipes 24 and 25 are formed to be located on the same straight line without being connected to each other. The sipes 24 and 25 may be formed straight, but in this embodiment, they are formed in a zigzag shape with multiple bends. In addition, there are two sipes 24 and 25 between the slit 21 and the slits 22 and 23, and a total of eight sipes 24 and 25 are present in one center block 20. The lengths of the sipes 24 and 25 are substantially the same, and the direction in which the sipes 24 and 25 extend is substantially parallel to the direction in which the slits 21, 22, and 23 extend.

[0035] [Shoulder block] The shoulder block 30 has slits 31, 32, and 33 that terminate within the block. On the other hand, the tread 10 does not have a slit that divides the shoulder block 30. The slit 31 is formed with a length that does not reach the ground contact edge E1 from the main groove 13, and the slit 32 is formed with a length that extends from a position away from the main groove 13 to the ground contact edge E1. In other words, the slit 32 is formed across the buttress 4. The slits 31 and 32 are arranged opposite each other on the same straight line, separated by a bridge 35. The interval between the slits 31 and 32 in the circumferential direction of the tire varies at a variable pitch.

[0036] The shoulder block 30 is formed into a rib shape that continues in the tire circumferential direction by a bridge 35 that is a portion sandwiched between the slits 31, 32. By making the ground contact surface of the shoulder block 30 continuous in the tire circumferential direction, for example, it is possible to improve the edge effect, drainage performance, etc., while increasing the rigidity of the shoulder block 30 and improving the CP characteristics. In addition, a slit 33 is formed between adjacent slits 32 in the tire circumferential direction, from a little toward the main groove 13 side from the ground contact edge E1 to the buttress 4.

[0037] A plurality of sipes 34 connected to the main groove 13 are formed in the shoulder block 30. The direction in which the sipes 34 extend is substantially parallel to the direction in which the slits 31, 32 extend. Three sipes 34 are formed between each pair of circumferentially adjacent slits 31, 32 in a zigzag shape with a length that does not reach the ground contact edge E1. The edge effect of the sipes 34 improves snow performance.

[0038] As described above, the pneumatic tire 1 is a point-symmetric tire, and the shape of the shoulder block 40 in a plan view is the same as the shape of the shoulder block 30 in a plan view when the tread 10 is rotated 180° around the axis passing through the tire rotation axis and the equator CL. Slits 41, 42, 43 and sipes 44 are formed in the shoulder block 40 as lateral grooves. In addition, the shoulder block 40 is formed in a rib shape by a bridge 45 that is continuous in the tire circumferential direction.

[0039] [Mediate Block] The mediate blocks 50 extend from the main grooves 11 to the main grooves 13, and are divided in the tire circumferential direction by slits 51 that connect the main grooves 11, 13. In the area between the two main grooves 11, 13 of the tread 10, a plurality of mediate blocks 50 divided by the slits 51 are arranged in a line in the tire circumferential direction. The interval in the tire circumferential direction of the slits 51, the tire circumferential length of each mediate block 50, and the interval in the tire circumferential direction of the lateral grooves formed in each block are changed at a variable pitch.

[0040] The slit 51 is located on an extension line of the slit 21 of the center block 20 within a predetermined length range from the main groove 11, and is bent so that the inclination angle with respect to the tire axial direction becomes small midway and extends to the main groove 13. A slit 52 is formed at a position substantially equidistant from two adjacent slits 51 in the tire circumferential direction and terminates in the mediate block 50. The slit 52 is connected to the main groove 13 and is formed substantially parallel to the slit 51. The slit 52 has a bent portion at a position aligned with the bent portion of the slit 51 in the tire circumferential direction. The slit 52 is also connected to the main groove 11 via a sipe 56.

[0041] The mediate block 50 is formed by connecting two blocks arranged in the tire circumferential direction by a bridge 53, which is a portion sandwiched between the slit 51 and the main groove 11. By connecting the two blocks by the bridge 53 without dividing them by the slit, for example, it is possible to improve the rigidity of the mediate block 50 while improving the edge effect, drainage performance, etc. In addition, a plurality of sipes 54, 55 that terminate within the block are formed between the two slits 51, 52.

[0042] The sipe 54 is connected to the main groove 11 and formed in a zigzag shape, and the sipe 55 is connected to the main groove 13 and formed in a straight line. The direction in which the sipes 54, 55 extend is substantially parallel to the direction in which the slits 51, 52 extend. There are two sipes 54, 55 between each of the slits 51, 52, for a total of eight sipes in one mediate block 50. The sipe 54 is formed longer than the sipe 55 in a range that is not connected to the sipe 55.

[0043] Since the pneumatic tire 1 is a point-symmetric tire, the planar shape of the mediate block 60 is the same as the planar shape of the mediate block 50 when the tread 10 is rotated 180° around an axis passing through the tire rotation axis and the equator CL. The mediate block 60 is formed with slits 61 and 62 and sipes 64, 65, and 66 as lateral grooves. The mediate block 60 is formed such that two blocks arranged in the tire circumferential direction are connected by a bridge 63.

[0044] The buttress 4 will be described in detail below with reference to Fig. 3 to Fig. 5. Fig. 3 is a side view of the pneumatic tire 1, showing an enlarged portion of the buttress 4. Fig. 4 is a cross-sectional view taken along line AA in Fig. 3, and Fig. 5 shows an enlarged view of the straight region 70 and the protrusion 80 in the cross-sectional view of Fig. 4.

[0045] 3 to 5, the buttress 4 is formed with a straight region 70 having a flat surface, and a protrusion 80 that is disposed adjacent to the straight region 70 on the radially inner side of the tire and formed in an annular shape along the tire circumferential direction. As described above, the buttress 4 is a region from the ground contact ends E1, E2 to the radially inner end of the protrusion 80. In the range from the ground contact ends E1, E2 to the straight region 70, the surface of the buttress 4 is curved so as to convexly form toward the outside of the tire. The radius of curvature of the curved surface between the ground contact ends E1, E2 and the straight region 70 is, for example, 20 mm or more and 30 mm or less.

[0046] 3 to 5 show the tire side surface on the ground contact end E1 side, but the same is true for the ground contact end E2 side. The tire radial direction lengths from the tire rotation axis to the ground contact ends E1, E2, the straight region 70, and the protrusions 80 are the same on the left and right sides of the pneumatic tire 1.

[0047] The buttress 4 can be said to be a side portion of the shoulder block 30, and a plurality of slits 32, 33 are formed in the buttress 4. The positions of the radially inner ends of the slits 32, 33 in the tire radial direction are aligned and lined up in the tire circumferential direction. In this embodiment, the positions of the radially inner ends of the slits 32, 33 in the tire radial direction correspond to the radially outer ends of the straight region 70 in the tire radial direction. The surface of the region located between the slits 32, 33 is formed flat from the ground contact edge E1 side relative to the radially inner ends of the slits 32, 33 in the tire radial direction.

[0048] Buttresses generally have protrusions formed in areas that correspond to the mold seams, and side protectors formed to add design appeal, but as a result of research by the present inventors, it has been found that the shape of the buttress has a significant effect on the air resistance of a tire. In the buttress 4, by forming a straight region 70 with a flat surface without irregularities of at least a predetermined length, and by keeping the height of the protrusions 80 low, it is possible to suppress convection and vortexes that occur on the tire sidewalls and create an air flow that follows the tire sidewalls, thereby effectively suppressing the air resistance of the tire. Preferred configurations of the straight region 70 and protrusions 80 are described in detail below.

[0049] The buttress 4 has a tire radial length (d1+d2) from the tire radial outer end of the straight region 70 to the tip 83 of the protrusion 80 that is longer than the tire radial length (d3) from the ground contact end E1 of the tread 10 to the tire radial outer end of the straight region 70 (d1+d2>d3). Note that d1+d2>d3 is satisfied when the pneumatic tire 1 is mounted on a regular rim and a load defined as the ground contact ends E1 and E2 is applied to the tire. Furthermore, the height (h) of the protrusion 80 is 0.5 mm or more and 1.0 mm or less. When these conditions are satisfied, the air resistance of the tire is specifically suppressed.

[0050] The straight region 70 and the protrusion 80 are formed in an annular shape with a constant width in the tire circumferential direction. The straight region 70 and the protrusion 80 are formed continuously in the tire radial direction, and the tire radial length (d1+d2) means the total width of the straight region 70 and a first region 81 of the protrusion 80 described below. The tire radial length (d1+d2) is preferably 103% or more and 130% or less of the tire radial length (d3), and more preferably 105% or more and 120% or less. In this case, the effect of reducing air resistance becomes more noticeable.

[0051] The surface of the straight region 70 is, for example, flat over the entire length and does not have a curved surface. However, the straight region 70 may have minute irregularities due to designs, marks, etc., within a range that does not impair the object of the present invention, for example, within a range of less than 5% of the total area of ​​the straight region 70. The inclination angle (θ2) of the straight region 70 with respect to the tire radial direction is preferably 10° or more and 30° or less, and more preferably 15° or more and 25° or less. The inclination angle (θ2) means the angle on the inner side in the tire radial direction between a virtual line α along the tire radial direction and the surface of the straight region 70 in the radial cross section of the tire. If the inclination angle (θ2) is within the above range, the effect of reducing air resistance is more significant.

[0052] The tire radial length (d2) of the straight region 70 is preferably 5% or more and 15% or less of the tire cross-sectional height, and more preferably 7% or more and 10% or less. The tire radial length of the buttress 4 is, for example, 15% or more and 25% or less of the tire cross-sectional height. The tire cross-sectional height is, for example, 160 mm or more and 180 mm or less. The tire radial length (d2) of the straight region 70 is preferably 30% or more of the tire radial length of the buttress 4. When the tire radial length (d2) satisfies these conditions, the effect of reducing air resistance becomes more significant.

[0053] The protrusion 80 is a convex portion that protrudes axially outward from the profile surface β (see FIG. 5) of the buttress 4. The protrusion 80 is formed, for example, due to a joint of a mold, and its height (h) can be controlled by the shape of the mold. The profile surface β means a surface along the surface of the straight region 70 and the sidewall 2. The height (h) of the protrusion 80 means the length along the normal direction of the profile surface β from the profile surface β to the tip 83, which is the highest part of the protrusion 80. The height (h) is 1.0 mm or less, and preferably 0.9 mm or less, but if it is less than 0.5 mm, air resistance may increase.

[0054] The protrusions 80 are preferably formed on the same circumference along the tire circumferential direction. In addition, the protrusions 80 preferably have substantially the same height over their entire length. In this case, the protrusions 80 have a perfect circular shape in a side view of the tire, and a stable air resistance reduction effect is obtained. The width (tire radial length) of the protrusions 80 is shorter than the tire radial length (d2) of the straight region 70, and is, for example, 3% to 8% of the tire cross-sectional height. The tip 83 of the protrusion 80 may be sharp as shown in FIG. 5, or may be slightly curved so that the corners are chamfered.

[0055] The protrusion 80 preferably includes a first region 81 formed flat from the radially inner end of the straight region 70 toward a tip 83. The surface of the first region 81 is flat over the entire length, for example, and does not have a curved surface. The protrusion 80 also includes a second region 82 located radially inward of the tip 83 and curved to be convex toward the inner side of the tire. The radius of curvature (R) of the second region 82 is 5 mm or more and 15 mm or less. When the first region 81 is flat and the second region 82 has such a curved surface, the effect of reducing air resistance becomes more significant.

[0056] The buttress 4 has a bent portion at the boundary between the straight region 70 and the first region 81 where the angle of inclination with respect to the tire radial direction changes, but its surface is formed flat in the range from the inner ends of the slits 32, 33 in the tire radial direction to the tip 83 of the protrusion 80. In this case, it becomes easy to create a smooth air flow along the tire side surface, and the air resistance of the tire can be effectively suppressed. The angle of inclination of the first region 81 with respect to the tire radial direction (imaginary line α) is slightly larger than the angle of inclination (θ2) of the straight region 70, and is preferably 15° or more and 35° or less.

[0057] The tire radial length (d1) of the first region 81 is preferably 2% to 5% of the tire cross-sectional height, and is preferably 10% or more of the tire radial length of the buttress 4. In this case, the effect of reducing air resistance becomes more significant. Furthermore, the inclination angle (θ1) of the first region 81 with respect to the profile surface β of the buttress 4 is preferably 5° to 10°, and more preferably 6° to 8°.

[0058] When the total width of the pneumatic tire 1 is 205 mm to 275 mm and the tire aspect ratio is 60% to 80%, an example of a suitable range for the tire radial length (d1) is 3.0 mm to 8.0 mm, and an example of a suitable range for the tire radial length (d2) is 10 mm to 20 mm.

[0059] [Air resistance evaluation] For a pneumatic tire 1 (size: 245 / 70R17), an evaluation of air resistance was performed by a simulation that analyzed the air flow around a rotating tire.

[0060] For the test tire, the drag (the force acting on the tire placed in the air flow, parallel to the flow and in the same direction) was measured, and the drag coefficient Cd (drag coefficient) was calculated using the following formula. Drag was calculated from the pressure difference in front of and behind the tire through simulation. The smaller the Cd value, the smaller the air resistance. Cd=D / (1 / 2ρU2S) In the formula, D is the drag force generated. ρ is the air density, 1.18415 [kg / m 3 ]. U is the representative speed, which is the relative speed between the tire and the air, and is set to 36.1 [m / s]. S is the representative area (frontal projected area) of the tire.

[0061] The tire of the example is a tire having the configuration of the above embodiment, and has a straight region and a buttress with protrusions formed thereon that satisfy the following conditions. As a result of evaluation using the above method, the Cd value was 0.512. d1: 5.6mm d2: 15.4mm h:0.8mm R: 9mm θ1:7° θ2:22° Tire section height: 171.5mm Radius of curvature of curved surface between ground end and straight area: 25mm

[0062] As a comparative example, a tire was also evaluated in which a block having a height of 2 mm was added at a position corresponding to the straight region of the tire of the embodiment, and the height of the protrusion was changed to 3.3 mm. As a result of evaluation using the above method, the Cd value of the comparative tire was 0.536.

[0063] As described above, the pneumatic tire 1 having the above configuration can effectively reduce air resistance. By forming the flat-surfaced straight region 70 and the long first region 81 of the protrusion 80 in the buttress 4, it is possible to create an air flow that follows the tire side surface, which is thought to result in a significant reduction in air resistance. In particular, when the aspect ratio of the pneumatic tire 1 is 60% or more, the effect of reducing air resistance is remarkable.

[0064] The above embodiment can be modified as appropriate without impairing the object of the present invention. For example, the pneumatic tire according to the present invention can be configured by combining the structure of the buttress 4 with a tread pattern other than that of the above embodiment. However, the pneumatic tire 1 configured by combining the tread 10 and the buttress 4 is one of the preferred forms for improving aerodynamic performance. [Explanation of symbols]

[0065] 1 pneumatic tire, 2 sidewall, 3 bead, 4 buttress, 10 tread, 11 first main groove, 12 second main groove, 13 third main groove, 14 fourth main groove, 20 center block, 21, 22, 23 slit, 24, 25 sipe, 26 bridge, 30 first shoulder block, 31, 32, 33 slit, 34 sipe, 35 bridge, 40 second shoulder block, 41, 42, 43 slit, 44 sipe, 45 bridge, 50 first mediate block, 51, 52 slit, 53 bridge, 54, 55, 56 sipe, 60 second mediate block, 61, 62 slit, 63 bridge, 64, 65, 66 sipe, 70 straight area, 80 protrusion, 81 first area, 82 second area, 83 Tip, CL equator, E1,E2 grounding end

Claims

1. A pneumatic tire having a tread and a buttress, The buttress includes: A straight area with a flat surface; a protrusion disposed adjacent to the straight region on the radially inner side of the tire and formed in an annular shape along the tire circumferential direction; is formed, a tire radial direction length (d1+d2) from a radially outer end of the straight region to a tip of the protrusion is longer than a tire radial direction length (d3) from a ground contact edge of the tread to a radially outer end of the straight region, The height of the protrusion is equal to or greater than 0.5 mm and equal to or less than 1.0 mm.

2. The pneumatic tire according to claim 1 , wherein a radial length (d2) of the straight region is equal to or greater than 5% and equal to or less than 15% of a tire cross-sectional height.

3. the projection includes a first region formed flat from an inner end in the tire radial direction of the straight region toward the tip, The pneumatic tire according to claim 1 , wherein a length (d1) in a radial direction of the tire of the first region is equal to or greater than 2% and equal to or less than 5% of a tire cross-sectional height.

4. The pneumatic tire according to claim 3 , wherein an inclination angle (θ1) of the first region of the projection with respect to a profile surface of the buttress is equal to or greater than 5° and equal to or less than 10°.

5. The protrusion is curved such that a second region located radially inward of the tip of the protrusion is convex toward the inner side of the tire, The pneumatic tire according to claim 3 , wherein a radius of curvature (R) of the second region is equal to or greater than 5 mm and equal to or less than 15 mm.

6. The pneumatic tire according to claim 1 , wherein an inclination angle (θ2) of the straight region with respect to a tire radial direction is equal to or greater than 10° and equal to or less than 30°.

7. The pneumatic tire according to any one of claims 1 to 5, wherein the tire aspect ratio is 60% or more.

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