Pneumatic tire

Abstract

To provide a pneumatic tire which can reduce maximum cornering force effectively by adjusting a contour of tread outside surface.SOLUTION: A pneumatic tire is provided with a tread 30. The tread 30 contains a tread rubber 37, a ground plane 38 on which the tread rubber 37 grounds to road surface, a pair of ground contact ends 38a which are ends of tire axial direction outside of the ground plane 38 and a plurality of major grooves 39 which are formed on the ground plane 38 and extend in a tire circumferential direction. The ground plane 38 includes ground contact half-width W1 from tire axial direction center over the ground contact ends 38a. Contour of the tread in tire axial direction cross section includes a first circular arc 71, a second circular arc 72 and a third circular arc 73 in order from the tire axial direction center in range from the tire axial direction center to at least the ground contact ends 38a. If the radius of curvature of the first circular arc 71 is R1, the radius of curvature of the second circular arc 72 is R2, and the radius of curvature of the third circular arc 73 is R3, their relation satisfies as R1>R3>R2.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, there has been known a pneumatic tire in which the contour of the outer surface of the tread in the tire axial direction cross section is formed to have a plurality of arcs to optimize various characteristics of the tire. For example, Patent Document 1 discloses a pneumatic tire provided with an asymmetric tread pattern, in which the contour of the outer surface of the tread has two arcs on each side of the tire equator, and by setting the connection points of the two arcs on each side to asymmetric positions in the left-right direction, improvements in steering stability and uneven wear resistance are achieved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, generally in a pneumatic tire, when the maximum cornering force is large, if the steering angle is large during vehicle turning, there may occur problems such as the grip force of the tire being too strong and the vehicle rolling over. Here, adjusting the shape of the tire contact surface to be overall round, that is, to have a round shape, is considered effective as a means for reducing the maximum cornering force. Since the contour of the outer surface of the tread in the tire axial direction cross section affects the contact surface shape, adjusting the contour of the outer surface of the tread is considered effective for reducing the maximum cornering force.

[0005] An object of the present invention is to provide a pneumatic tire capable of effectively reducing the maximum cornering force by adjusting the contour of the outer surface of the tread.

Means for Solving the Problem

[0006] The pneumatic tire of the present invention is a pneumatic tire provided with a tread, the tread including tread rubber, a ground contact surface where the tread rubber contacts the road surface, a pair of ground contact ends that are the outer ends of the ground contact surface in the tire axial direction, and a plurality of main grooves formed in the ground contact surface and extending in the tire circumferential direction. The ground contact surface has a ground contact half-width from the tire axial center to the ground contact end. The contour of the tread in the tire axial cross-section has, in the range from the tire axial center to at least the ground contact end, a first arc, a second arc, and a third arc in order from the tire axial center. When the radius of curvature of the first arc is R1, the radius of curvature of the second arc is R2, and the radius of curvature of the third arc is R3, R1 > R3 > R2.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a pneumatic tire capable of effectively reducing the maximum cornering force by adjusting the contour of the outer surface of the tread.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a view showing the internal structure of a pneumatic tire 1 according to an embodiment, and is a half-sectional view showing the right half. The tire 1 according to the embodiment is, for example, a pneumatic tire for a passenger car. Note that the configuration of the tire 1 according to the embodiment can be adopted for various vehicles such as light trucks, trucks, and buses in addition to passenger cars.

[0010] The cross-sectional view of FIG. 1 is a half-sectional view in the tire axial direction (tire meridian half-sectional view) of the tire 1 mounted on a regular rim (not shown) and filled with a regular internal pressure in an unloaded state. The regular rim is the rim defined for each tire in a standard system including the standard on which the tire is based. For example, it is the standard rim in JATMA, and "Measuring Rim" in TRA and ETRTO. The regular internal pressure is the air pressure defined for each tire in a standard system including the standard on which the tire is based. In the case of tires for truck buses and light trucks, in JATMA, it is the maximum air pressure; in TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; in ETRTO, it is "INFLATION PRESSURE". In the case of passenger car tires, it is usually 180 kPa, but in the case of tires marked with Extra Load or Reinforced, it is 220 kPa.

[0011] In FIG. 1, reference numeral S1 is the tire equatorial plane. The tire equatorial plane S1 is a plane perpendicular to the tire rotation axis (tire meridian) and is located at the center in the tire axial direction. The basic internal structure of the tire 1 is bilaterally symmetric with the tire equatorial plane S1 as the plane of symmetry in the cross-section in the tire axial direction.

[0012] Here, the tire axial direction is the direction parallel to the tire rotation axis and is the left - right direction of the paper surface in the cross - sectional view of FIG. 1. In FIG. 1, it is illustrated as the tire axial direction X. And the inner side in the tire axial direction is the direction approaching the tire equatorial plane S1, which is the left side of the paper surface in FIG. 1. The outer side in the tire axial direction is the direction away from the tire equatorial plane S1, which is the right side of the paper surface in FIG. 1. Also, the tire radial direction is the direction perpendicular to the tire rotation axis and is the up - down direction of the paper surface in FIG. 1. In FIG. 1, it is illustrated as the tire radial direction Y. And the outer side in the tire radial direction is the direction away from the tire rotation axis, which is the upper side of the paper surface in FIG. 1. The inner side in the tire radial direction is the direction approaching the tire rotation axis, which is the lower side of the paper surface in FIG. 1.

[0013] The tire 1 includes a pair of beads 10 provided on both sides in the tire axial direction, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 disposed between the pair of sidewalls 20, a pair of shoulders 40 which are portions transitioning from each of the pair of sidewalls 20 to the tread 30, a belt 31 disposed within the tread 30, a carcass ply 50 spanned and disposed between the pair of beads 10, and an inner liner 60 disposed on the tire inner cavity side of the carcass ply 50.

[0014] The pair of beads 10 are disposed at both ends in the tire axial direction and on the inner side in the tire radial direction. The bead 10 has a bead core 11, a bead filler 12 extending radially outward from the bead core 11, a chafer 13, and a rim strip rubber 14.

[0015] The bead core 11 is an annular member in which a metal bead wire coated with rubber is wound a plurality of times in the tire circumferential direction. The bead core 11 is a member that serves to fix the air-filled tire 1 to the rim. The bead filler 12 has a tapered shape in which the thickness decreases as it extends from the inner side in the tire radial direction to the outer side in the tire radial direction. The bead filler 12 is provided to increase the rigidity of the peripheral portion of the bead 10 and ensure high maneuverability and stability. The bead filler 12 is composed of, for example, rubber having a higher hardness than the surrounding rubber members. The bead filler 12 is joined to the outer surface of the bead core 11 in the tire radial direction.

[0016] The chafer 13 is provided in a manner that further surrounds the outside of the carcass ply 50 surrounding the bead core 11 and the bead filler 12.

[0017] The rim strip rubber 14 is disposed on the outer side in the tire axial direction of a part of the carcass ply 50 and the chafer 13. The rim strip rubber 14 extends to near the inner end of the chafer 13 in the tire radial direction.

[0018] The sidewall 20 includes a sidewall rubber 21 disposed on the outer side in the tire axial direction of the carcass ply 50. The sidewall rubber 21 is the rubber that constitutes the outer surface of the tire 1. The outer end 21a of the sidewall rubber 21 in the tire radial direction is covered by the outer end 37a in the tire axial direction of the tread rubber 37 described later. The inner end 21b of the sidewall rubber 21 in the tire radial direction covers the outer end 14a in the tire radial direction of the rim strip rubber 14. At the tip of the inner end 21b of the sidewall rubber 21 in the tire radial direction, a rim line 21c is formed along the tire circumferential direction. The sidewall rubber 21 is the portion that bends the most when the tire 1 acts as a cushion, and usually, a flexible rubber having fatigue resistance is adopted.

[0019] The tread 30 includes an endless belt 31, a cap ply 34, and tread rubber 37. The belt 31 is disposed on the outer side in the tire radial direction of the carcass ply 50. The cap ply 34 is disposed on the outer side in the tire radial direction of the belt 31. The tread rubber 37 is disposed on the outer side in the tire radial direction of the cap ply 34.

[0020] The belt 31 is a member that reinforces the tread 30. The belt 31 of the embodiment has a two-layer structure including an inner belt 32 disposed on the outer side in the tire radial direction of the inner liner 60 and an outer belt 33 disposed on the outer side in the tire radial direction of the inner belt 32. Both the inner belt 32 and the outer belt 33 have a structure in which a plurality of belt cords such as steel cords are covered with rubber. The inner belt 32 is wider than the outer belt 33. By providing the belt 31, the rigidity of the tire 1 is ensured and the grounding performance of the tread 30 on the road surface is improved. Note that the belt 31 is not limited to a two-layer structure and may have a single-layer or three-layer or more structure.

[0021] The cap ply 34 is a member that reinforces the tread 30 together with the belt 31. The cap ply 34 of the embodiment is wider than the belt 31 and covers the entire belt 31 from the outer surface side of the tire. The cap ply 34 has a structure in which a plurality of insulating organic fiber cords such as polyamide fibers are covered with rubber. The cap ply 34 has an overlapping portion 34b in which the outer end 34a in the tire axial direction is folded back inward in the tire axial direction and overlapped with the surface on the inner side in the tire radial direction. This overlapping portion 34b covers a part of the inner belt 32, a part of the outer belt 33, and a part of the carcass ply 50. By providing the cap ply 34, it is possible to improve the durability of the tire 1 and reduce the road noise during driving. Note that the cap ply 34 is not limited to a single-layer structure as in the embodiment and may have a two-layer or three-layer or more structure.

[0022] The tread rubber 37 includes a ground contact surface 38 that is the outer surface of the tread 30 and contacts the road surface. A plurality of main grooves 39 extending along the tire circumferential direction are formed at intervals in the tire axial direction on the ground contact surface 38. The outer end 37a of the tread rubber 37 in the tire axial direction protrudes outward in the tire axial direction from the outer end 34a of the cap ply 34 and bends inward in the tire radial direction. The outer end 37a of the tread rubber 37 in the tire axial direction covers the outer end 21a of the sidewall rubber 21 in the tire radial direction.

[0023] A tread pattern is formed on the outer surface of the tread 30 by grooves or the like engraved in the tread rubber. The tread pattern includes a plurality of main grooves 39 formed on the ground contact surface 38. The plurality of main grooves 39 include a first main groove 39A closest to the tire axial center, that is, the tire equatorial plane S1, and a second main groove 39B disposed on the outer side in the tire axial direction of the first main groove 39A, that is, on the side of the shoulder 40. These main grooves 39A and 39B are formed over the entire circumference of the ground contact surface 38 along the tire circumferential direction.

[0024] The tread 30 includes a central land 35A between the left and right first main grooves 39A sandwiching the tire equatorial plane S1, a pair of intermediate lands 35B between the first main groove 39A and the second main groove 39B, and a pair of shoulder lands 35C on the shoulder 40 side of the second main groove 39B. The ground contact surface 38 includes the outer surfaces of the central land 35A, the intermediate lands 35B, and the shoulder lands 35C.

[0025] The ground contact surface 38 is the surface that contacts the road surface under the condition that the tire 1 mounted on a regular rim and filled with a regular internal pressure contacts the road surface and a regular load is applied thereto. Both ends of the ground contact surface 38 in the tire axial direction become the ground contact ends 38a. In the tire axial cross section, the portion of the ground contact surface 38 from the equatorial plane S1 to the ground contact end 38a is the ground contact half-width W1. The ground contact half-width W1 in the embodiment is the ground contact half-width under the conditions defined by ETRTO.

[0026] The tread 30 has a more characteristic configuration in the present disclosure, and details thereof will be described later.

[0027] The shoulder 40 is a portion that transitions from the tread 30 while bending toward the sidewall 20. The shoulder 40 of the embodiment is a portion that transitions from near the grounding end 38a to the sidewall 20, and is formed by a portion including the radially outer end 37a of the tread rubber 37 in the tire axial direction and the radially outer end 21a of the sidewall rubber 21.

[0028] The carcass ply 50 is spanned between a pair of beads 10. The carcass ply 50 constitutes a ply that forms the framework of the tire 1. The carcass ply 50 is embedded in the tire 1 in a manner that passes through the inner tire cavity sides of the pair of sidewalls 20, the pair of shoulders 40, and the tread 30 between the pair of beads 10. In the tread 30, a belt 31 is disposed radially outside the carcass ply 50.

[0029] The carcass ply 50 includes a ply main body portion 50A and a pair of turned-up portions 50B. The ply main body portion 50A is a portion that extends from the tread 30 through each of the pair of shoulders 40 and the pair of sidewalls 20 to the inner side in the tire axial direction of each of the pair of beads 10. The pair of turned-up portions 50B are portions that are folded back radially outward of the tire by being wound around each of the pair of bead cores 11 from the ply main body portion 50A and extend along the sidewall 20.

[0030] The carcass ply 50 of the embodiment has a two-layer structure in which a first carcass ply 51 and a second carcass ply 52 are overlapped. In the ply main body portion 50A, the first carcass ply 51 is disposed on the inner side of the tire cavity of the second carcass ply 52.

[0031] In the hoisting portion 50B, the first carcass ply 51 is disposed on the outer side in the tire axial direction of the second carcass ply 52. The first carcass ply 51 on the hoisting portion 50B side extends from the bead core 11 to the vicinity of the inner side in the tire radial direction rather than the vicinity of the center in the tire radial direction of the sidewall 20. The second carcass ply 52 on the hoisting portion 50B side extends from the bead core 11 to the middle of the bead filler 12. The portion of the second carcass ply 52 on the hoisting portion 50B side that is outside the bead filler 12 in the tire radial direction is overlapped with the second carcass ply 52 on the ply main body portion 50A side.

[0032] The above-described belt 31 is disposed on the outer side in the tire radial direction of the ply main body portion 50A. The chafer 13 of the above-described bead 10 surrounds the inner end in the tire radial direction of the carcass ply 50 that winds around the bead core 11.

[0033] The carcass ply 50 of the embodiment has a two-layer structure, but the carcass ply 50 may be a single layer or three or more layers. When the carcass ply 50 is composed of a ply having a two-layer or more layer structure, it is preferable because local deformation of the tire 1 near the rim mounting portion is sufficiently suppressed.

[0034] The inner liner 60 forms a tire inner cavity surface by covering the inner surface of the ply main body portion 50A of the carcass ply 50 and the portion on the inner side in the tire axial direction of the chafer 13 between the pair of beads 10. The inner liner 60 of the embodiment has a two-layer structure in which the first inner liner 61 and the second inner liner 62 are overlapped. The first inner liner 61 is disposed on the tire inner cavity side of the second inner liner 62. The first inner liner 61 and the second inner liner 62 are made of air permeation resistant rubber and prevent air in the tire inner cavity from leaking to the outside.

[0035] Here, as the rubber used for the bead filler 12, rubber having a hardness higher than at least the sidewall rubber 21 and the inner liner 60 is used. The hardness of the rubber is the hardness measured by "Durometer hardness Type A of JIS K6253-3:2012".

[0036] For example, when taking the hardness of the sidewall rubber 21 as a reference, the hardness of the bead filler 12 is preferably about 1.2 times or more and 2.3 times or less the hardness of the sidewall rubber 21. By setting the hardness in this way, it is possible to secure a balance between the flexibility of the tire and the rigidity near the bead 10.

[0037] The above is the internal structure of the tire 1 according to the embodiment. Next, a characteristic configuration related to the tread 30 will be described.

[0038] The contour in the tire axial direction cross-section of the grounding surface 38 of the tread 30 is composed of a discontinuous curve formed by three arcs with different radii of curvature arranged from the tire axial direction center corresponding to the tire equatorial plane S1 toward the tire axial direction outside. The contour here is a line along the outer surface of the tread 30 and is also referred to as a profile line.

[0039] That is, the three arcs are a first arc 71 arranged at the tire axial direction center and straddling the tire equatorial plane S1, a third arc 73 adjacent to the shoulder 40, and a second arc 72 between the first arc 71 and the third arc 73. The first arc 71 and the second arc 72 are connected at a first inflection point 81. The second arc 72 and the third arc 73 are connected at a second inflection point 82. The third arc 73 and the shoulder arc 40A forming the outer surface of the shoulder 40 are connected at a third inflection point 83.

[0040] Here, when the radius of curvature of the first arc 71 is R1, the radius of curvature of the second arc 72 is R2, and the radius of curvature of the third arc 73 is R3, R1 > R3 > R2. That is, the contour of the tread 30 in the tire axial direction cross-section has three arcs 71, 72, and 73, and the radii of curvature of these three arcs 71, 72, and 73 do not change in order from large to small from the center in the tire axial direction to the shoulder 40. Instead, the radius of curvature is such that the first arc 71 on the center side in the tire axial direction is the largest, the third arc 73 on the shoulder 40 side is the next largest, and the two arcs 72 between the first arc 71 and the third arc 73 are the smallest.

[0041] The radius of curvature R1 of the first arc 71 is, for example, about 700 mm or more and 1800 mm or less. The radius of curvature R2 of the second arc 72 is, for example, about 200 mm or more and 800 mm or less. The radius of curvature R3 of the third arc 73 is, for example, about 100 mm or more and 400 mm or less.

[0042] The first inflection point 81 is arranged near the center in the tire axial direction of the center land 35A. The second inflection point 82 is arranged near the center in the width direction of the second main groove 39B. The third inflection point 83 is a portion that hits the outer side in the tire axial direction of the shoulder land 35C and is arranged on the inner side in the tire axial direction from the grounding end 38a.

[0043] The arc lengths of the first arc 71, the second arc 72, and the third arc 73 are not particularly limited. However, in the tire 1 of the embodiment, in the half cross-section in one tire axial direction from the center in the tire axial direction, the third arc 73 is the longest, the first arc 71 is the next longest, and the second arc 72 is the shortest.

[0044] According to the tire 1 of the embodiment, as described above, when the radius of curvature of the first arc 71 is R1, the radius of curvature of the second arc 72 is R2, and the radius of curvature of the third arc 73 is R3, R1 > R3 > R2. In this way, among the three arcs 71, 72, and 73, by making the radius of curvature R3 of the third arc 73 between the first arc 71 and the third arc 73 the smallest and the radius of curvature R1 of the first arc 71 on the center side in the tire axial direction the largest, the grounding surface shape of the tire 1 is likely to be a round shape.

[0045] Figure 2 schematically shows the contact surface shape of the tire 1. As shown in Figure 2, the contact surface shape of the tire 1 of the embodiment is a round shape and is overall round. Note that Figure 3 shows a tire contact surface shape that is generally square as a comparison target. The comparison target tire having the square contact surface shape shown in Figure 3 has the same tread pattern as the tire 1 of the embodiment, that is, the same first main groove 39A, second main groove 39B, and the same center land 35A, intermediate land 35B, and shoulder land 35C. Further, when the contour in the tire axial direction cross-section has the same first arc, second arc, and third arc, the radii of curvature of the first arc, second arc, and third arc are different from those of the tire 1 of the embodiment, and the radii of curvature are such that the first arc > the second arc > the third arc.

[0046] The contact surface shapes shown in Figures 2 and 3 can also be said to be tire marks remaining on the contact surface in the vehicle stopped state. In Figures 2 and 3, the same reference numerals are given to the marks corresponding to the center land 35A, intermediate land 35B, shoulder land 35C, first main groove 39A, and second main groove 39B. That is, in Figures 2 and 3, for example, the reference numeral 35A is the mark of the center land 35A of the tire 1 remaining on the contact surface.

[0047] As shown in Figure 2, the fact that the contact surface shape of the tire 1 of the embodiment is a round shape means that the circumferential contact length of the tire (the vertical length in Figures 2 and 3) is shorter for the intermediate land 35B than for the center land 35A, and shorter for the shoulder land 35C than for the intermediate land 35B. Thus, as the circumferential contact lengths of the lands 35A, 35B, and 35C become shorter from the center in the tire axial direction toward the outside in the tire axial direction, the factor that the contact surface shape becomes a round shape is that the radii of curvature R1, R2, and R3 of the arcs 71, 72, and 73 satisfy R1 > R3 > R2.

[0048] By making the ground contact surface shape round in this way, the maximum cornering force (hereinafter sometimes referred to as CFmax) of the tire 1 is reduced. By reducing CFmax, even when the steering angle is large during vehicle turning, it is possible to suppress problems such as the grip force of the tire being too strong and the vehicle rolling, and as a result, the riding comfort is improved.

[0049] As described above, in the tire 1 of the embodiment where the contour of the tread 30 includes the first arc 71, the second arc 72, and the third arc 73 in the tire axial direction cross section, and the radii of curvature R1, R2, and R3 of the respective arcs 71, 72, and 73 satisfy R1 > R3 > R2, it is preferable to further have the following characteristics.

[0050] The radius of curvature R2 of the second arc 72 is preferably 50% or more of the radius of curvature R3 of the third arc 73. Thereby, it is possible to suppress a sudden change in the contour from the second arc 72 to the third arc 73. For this reason, an increase in the ground contact pressure applied to the second arc 72 and the third arc 73 is suppressed, and uneven wear of the second arc 72 and the third arc 73 is suppressed.

[0051] The reference symbol W2 in FIG. 1 indicates a range of 30% or more and 40% or less of the ground contact half-width W1 from the equatorial plane S1 at the center in the tire axial direction in the tire axial direction. Here, the first inflection point 81, which is the connection point between the first arc 71 and the second arc 72, is preferably arranged within the range W2 from the equatorial plane S1 at the center in the tire axial direction in the tire axial direction. Thereby, the first arc 71 and the second arc 72 can be arranged in a well-balanced and appropriate range in the tire axial direction, and uneven wear of the tread rubber 37 is suppressed.

[0052] Reference numeral W3 in Fig. 1 indicates a range that is 50% or more and 60% or less of the contact half-width W1 from the equatorial plane S1 at the center in the tire axial direction. Here, the second inflection point 82, which is the connection point between the second arc 72 and the third arc 73, is preferably arranged within the range W3 from the equatorial plane S1 at the center in the tire axial direction. Thereby, the second arc 72 and the third arc 73 can be arranged in a well-balanced and appropriate range in the tire axial direction, and uneven wear of the tread rubber 37 is suppressed.

[0053] The depth of the first main groove 39A is preferably 86% or more and 88% or less of the thickness of the tread rubber 37, and the depth of the second main groove 39B is preferably 82% or more and 84% or less of the thickness of the tread rubber 37. Thereby, a depth of each of the first main groove 39A and the second main groove 39B that is equal to or more than a certain level is maintained over a long period, and the life of the tire 1 itself is improved together with the tread rubber 37.

[0054] In the tire 1 of the embodiment, the contact surface shape becomes a round shape and CFmax is reduced. In this case, a reduction in wear resistance is a concern as a conflicting factor. However, by making the depths of the first main groove 39A and the second main groove 39B relatively large as described above, wear resistance is ensured.

[0055] The radius of curvature R1 of the first arc 71 is preferably 2 times or more the radius of curvature R3 of the third arc 73. Thereby, the circumferential-direction contact length of the third arc 73 can be reduced, and as a result, rounding of the contact surface shape is promoted and a reduction in CFmax is achieved.

[0056] According to the tire 1 of the above embodiment, the following effects are obtained.

[0057] (1) The tire 1 according to the embodiment is a pneumatic tire including a tread 30. The tread 30 includes a tread rubber 37, a ground contact surface 38 where the tread rubber 37 contacts the road surface, a pair of ground contact ends 38a which are the outer ends of the ground contact surface 38 in the tire axial direction, and a plurality of main grooves 39 formed in the ground contact surface 38 and extending in the tire circumferential direction. The ground contact surface 38 has a ground contact half-width W1 from the tire axial center to the ground contact end 38a. The contour of the tread 30 in the tire axial cross-section has, in the range from the tire axial center to at least the ground contact end 38a, a first arc 71, a second arc 72, and a third arc 73 in order from the tire axial center. When the radius of curvature of the first arc 71 is R1, the radius of curvature of the second arc 72 is R2, and the radius of curvature of the third arc 73 is R3, R1 > R3 > R2.

[0058] As a result, the ground contact surface shape of the tire 1 becomes a round shape, and CFmax is reduced. By reducing CFmax, for example, when the steering angle is large during vehicle turning, problems such as the grip force of the tire being too strong and the vehicle rolling can be suppressed, and the riding comfort can be improved.

[0059] (2) In the tire 1 of the above (1) according to the embodiment, it is preferable that the radius of curvature R2 of the second arc 72 is 50% or more of the radius of curvature R3 of the third arc 73.

[0060] As a result, a sudden change in the contour from the second arc 72 to the third arc 73 can be suppressed, and an increase in ground contact pressure and uneven wear can be suppressed.

[0061] (3) In the tire 1 of the above (1) and (2) according to the embodiment, in the tire axial cross-section, the first inflection point 81 which is the connection point between the first arc 71 and the second arc 72 is preferably arranged at a position in the tire axial direction that is 30% or more and 40% or less of the ground contact half-width W1 from the tire axial center.

[0062] As a result, the second arc 72 and the third arc 73 can be arranged in a well-balanced and appropriate range in the tire axial direction, and uneven wear of the tread rubber 37 can be suppressed.

[0063] (4) In the tire 1 of the above (1) to (3) according to the embodiment, in the tire axial direction cross section, the second inflection point 82, which is the connection point of the second arc 72 and the third arc 73, is preferably arranged at a position of 50% or more and 60% or less of the ground contact half-width W1 from the center in the tire axial direction in the tire axial direction.

[0064] Thereby, the second arc 72 and the third arc 73 can be arranged in a well-balanced and appropriate range in the tire axial direction, and uneven wear of the tread rubber 37 is suppressed.

[0065] (5) In the tire 1 of the above (1) to (4) according to the embodiment, the plurality of main grooves 39 include at least a first main groove 39A that is closest to the center in the tire axial direction in the tire axial direction, and a second main groove 39B arranged outside the first main groove 39A in the tire axial direction. The depth of the first main groove 39A is preferably 86% or more and 88% or less of the thickness of the tread rubber 37, and the depth of the second main groove 39B is preferably 82% or more and 84% or less of the thickness of the tread rubber 37.

[0066] Thereby, a depth of each of the first main groove 39A and the second main groove 39B that is more than a certain value is maintained over a long period of time, and the life of the tire 1 itself is improved together with the tread rubber 37.

[0067] (6) In the tire 1 of the above (1) to (5) according to the embodiment, the radius of curvature R1 of the first arc 71 is preferably 2 times or more the radius of curvature R3 of the third arc 73.

[0068] Thereby, the ground contact length in the tire circumferential direction of the third arc 73 can be reduced. As a result, rounding of the ground contact surface shape is promoted, and reduction of CFmax is achieved.

[0069] Note that the present invention is not limited to the above embodiment, and even if deformation, improvement, etc. are performed within the range that can achieve the object of the present invention, it is included in the scope of the present invention.

Example

[0070] The following describes the examples. Simulation models of the tires of Examples 1 to 3 shown in Table 1 were prepared. Examples 1 to 3 have the same configuration as the above-described embodiment, and the radii of curvature of the first arc 71, the second arc 72, and the third arc 73 were changed as shown in Table 1. On the other hand, a simulation model of a tire of a comparative example having the same configuration as Examples 1 to 3 was prepared except that the radii of curvature of the first arc 71, the second arc 72, and the third arc 73 were changed.

[0071] For the tires of Examples 1 to 3 and the comparative example described above, the ratio “intermediate land / central land” of the tire circumferential contact length of the intermediate land to the tire circumferential contact length of the central land in the contact surface shape and CFmax were obtained by simulation. The results are also shown in Table 1. Note that CFmax takes the measured value of Comparative Example 1 as the index 100, and the others are index evaluations compared with Comparative Example 1.

[0072]

Table 1

[0073] According to Table 1, in Examples 1 to 3 where the radius of curvature is R1 > R3 > R2, the contact surface shape is a round shape because the tire circumferential contact length of the intermediate land is shorter than that of the central land, and it can be seen that CFmax is reduced thereby. On the other hand, in the comparative example where R1 > R2 > R3, the contact surface shape is a square shape because the tire circumferential contact lengths of the central land and the intermediate land are substantially the same, and in this case, CFmax is larger than that of the examples. Therefore, in the examples where R1 > R3 > R2, the contact surface shape becomes a round shape and CFmax is reduced.

Explanation of Signs

[0074] 1 Tire (pneumatic tire) 30 Tread 37 Tread rubber 38 Contact surface 38a Contact end 39 Main groove 39A First Main Groove 39B Second Main Groove 71 First Arc 72 Second Arc 73 Third Arc 81 First Inflection Point 82 Second Inflection Point 83 Third Inflection Point R1 Curvature Radius of the First Arc R2 Curvature Radius of the Second Arc R3 Curvature Radius of the Third Arc W1 Ground Half-Width

Claims

1. A pneumatic tire having a tread, wherein the tread includes tread rubber, a ground contact surface where the tread rubber contacts the road surface, a pair of ground contact ends that are the outer ends of the ground contact surface in the tire axial direction, and a plurality of main grooves formed in the ground contact surface and extending in the tire circumferential direction; the ground contact surface has a ground contact half-width extending from the center in the tire axial direction to the ground contact ends; the contour of the tread in the tire axial cross-section has a first arc, a second arc, and a third arc in order from the center in the tire axial direction at least in the range from the center in the tire axial direction to at least the ground contact ends; a pneumatic tire, where when the radius of curvature of the first arc is R1, the radius of curvature of the second arc is R2, and the radius of curvature of the third arc is R3, R1 > R3 > R2.

2. The pneumatic tire according to claim 1, wherein the radius of curvature R2 of the second arc is 50% or more of the radius of curvature R3 of the third arc.

3. The pneumatic tire according to claim 1 or 2, wherein a first inflection point, which is a connection point between the first arc and the second arc, is arranged at a position in the tire axial direction that is 30% or more and 40% or less of the ground contact half-width from the center in the tire axial direction.

4. The pneumatic tire according to claim 1 or 2, wherein a second inflection point, which is a connection point between the second arc and the third arc, is arranged at a position in the tire axial direction that is 50% or more and 60% or less of the ground contact half-width from the center in the tire axial direction.

5. The plurality of main grooves include at least a first main groove that is closest to the center in the tire axial direction in the tire axial direction and a second main groove arranged outside the first main groove in the tire axial direction; the depth of the first main groove is 86% or more and 88% or less of the thickness of the tread rubber; the depth of the second main groove is 82% or more and 84% or less of the thickness of the tread rubber. The pneumatic tire according to claim 1 or 2.

6. The pneumatic tire according to claim 1 or 2, wherein the radius of curvature R1 of the first arc is 2 times or more of the radius of curvature R3 of the third arc.

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