Tire mold, tire manufacturing method, and tire

Abstract

To provide a mold for a tire that is able to optimize the shape of a ground contact surface and the distribution of ground contact pressure.SOLUTION: A mold comprises a tread forming surface 64 for shaping a tread surface. The tread forming surface 64 includes a projection 74 for forming a circumferential groove and a land surface forming portion 76 for forming a land surface. Among the three land surface forming portions 76 arranged sandwiching the projection 74 in an axial direction, the land surface forming portion 76 located between the two projections 74 is a curved land surface forming portion 76B. The contour of the curved land surface forming portion 76B is shown by one or more arcs. A boundary between a reference side surface 80a of the projection 74 and the curved land surface forming portion 76B is a reference boundary point BBm, and the reference boundary point BBm is located inside the reference forming surface FBL of the tread forming surface 64.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a tire mold, a tire manufacturing method, and a tire. [Background technology]

[0002] A tire is obtained by pressurizing and heating an uncrosslinked tire (hereinafter referred to as a green tire) in a mold. A plurality of circumferential grooves arranged in parallel in the axial direction are carved into the tread of the tire to form land portions. To form the circumferential grooves, ridges corresponding to the circumferential grooves are provided on the tread forming surface of the mold. The green tire is pressed against the ridges to form the circumferential grooves in the tread.

[0003] A tire has, for example, a belt including many parallel cords on the radially inner side of the tread. Various measures are taken in tire manufacturing to prevent the belt from rippling when the green tire is pressed against the ridges (for example, see Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-61602 Summary of the Invention [Problem to be solved by the invention]

[0005] When the ridges are pressed against a raw tire, part of the unvulcanized rubber composition (hereinafter referred to as unvulcanized rubber) pressed by the ridges flows into the area that will form the land portion. If the unvulcanized rubber does not flow easily at this time, the inner shape of the tread may become disordered, and there is a concern that the belt may become wavy. In particular, when the groove width is 9 mm or more and the 2When forming circumferential grooves having such large cross-sectional areas in a tread, the volume of unvulcanized rubber pressed by the convex ribs is large, and there is a concern that the unvulcanized rubber pushed aside by the convex ribs will disrupt the overall flow of unvulcanized rubber flowing into the areas where the land portions are to be formed. In this case, it is difficult to form land portions that reflect the shape of the areas where the land portions of the mold are to be formed, and there is a risk that land portions will be formed that are thin in the center and thick at the edges, in other words, land portions with land surfaces configured in an inwardly convex shape.

[0006] Figure 9 shows the contact patch shape of a conventional tire (size = 205 / 55R16) manufactured without considering the flow of unvulcanized rubber pushed aside by the ridges. Figure 9 also shows the outlines of each land portion L included in the contact patch. Figure 10 shows the contact pressure distribution of this tire. In Figure 10, the right side shows the contact pressure distribution of the shoulder land portion Ls, and the left side shows the contact pressure distribution of the middle land portion Lm.

[0007] As shown in Figure 9, the circumferential outer edge of each land portion L in the contact patch shape has an inwardly convex shape. As shown in Figure 10, it has been confirmed that the contact pressure locally increases at the edge of each land portion L. Specifically, a contact pressure difference of about 200 kPa has been confirmed in the middle land portion Lm, and a contact pressure difference of about 250 kPa has been confirmed in the shoulder land portion Ls. Furthermore, it has been confirmed that this tire has a disturbance in the inner surface shape of the tread.

[0008] The flow of unvulcanized rubber in the mold affects the tire's contact patch shape and contact pressure distribution. In other words, controlling the flow of unvulcanized rubber in the mold can ensure that the tire makes more sufficient contact with the road surface, potentially further improving handling stability. In this case, local increases in contact pressure can also be suppressed, potentially improving wear resistance.

[0009] The present invention has been made in consideration of the above-described circumstances, and aims to provide a tire mold and a tire manufacturing method that can optimize the contact patch shape and contact pressure distribution, as well as to provide a tire in which the contact patch shape and contact pressure distribution are optimized. [Means for solving the problem]

[0010] A tire mold according to one embodiment of the present invention is a mold used for manufacturing tires, the tire comprising a tread having a tread surface that comes into contact with a road surface, at least two circumferential grooves cut into the tread to form at least three land portions, and the tread surface including the at least two circumferential grooves and at least three land surfaces that are outer surfaces of the at least three land portions. The tire mold also comprises a tread forming surface that shapes the tread surface. The tread forming surface includes a convex streak that forms the circumferential grooves and a land surface forming portion that forms the land surface. The surface that has a contour represented by at least one arc and is in contact with the three land surface forming portions, arranged axially on either side of the convex streak, is a reference forming surface of the tread forming surface. Of the three land surface forming portions, the land surface forming portion located between two of the convex streaks is a curved land surface forming portion. The convex streak includes a reference side surface that is the side facing the land surface forming portion and a back side that is the side behind the reference side. The point of contact between the curved land surface forming portion and the reference forming surface is the reference tangent point. The boundary between the reference side surface and the curved land surface forming portion is the reference boundary point. The intersection of the reference forming surface with an imaginary line of the reference side surface extending from the reference boundary point toward the reference forming surface is the reference virtual intersection point. The contour of the curved land surface forming portion is represented by one or more arcs. The reference boundary point is located inside the reference forming surface. When one convex streak has a small cross-sectional area and the other convex streak has a large cross-sectional area, the distance from the reference virtual intersection point on one convex streak side to the reference boundary point is short, and the distance from the reference virtual intersection point to the reference boundary point on the other convex streak side is long.

[0011] Preferably, in this tire mold, when the distance from one of the reference virtual intersections to the reference tangent point is Xw1m, the distance from one of the reference virtual intersections to the other reference virtual intersection is Wcm, the cross-sectional area of ​​one of the convex ridges is Sam, and the cross-sectional area of ​​the other of the convex ridges is Sbm, the distance Xw1m from one of the reference virtual intersections to the reference tangent point is set so as to satisfy the following formula (1): Sam / (Sam+Sbm)×100-10≦Xw1m / Wcm×100≦Sam / (Sam+Sbm)×100+10...(1)

[0012] Preferably, in the tire mold, a ratio of the distance from the reference virtual intersection point to the reference boundary point to a cross-sectional area of ​​the ridge is equal to or greater than 0.0008 and is equal to or less than 0.0040.

[0013] Preferably, in this tire mold, the contour of the curved land surface forming portion from the reference tangent point to the reference boundary point is represented by an arc that passes through the reference boundary point and is tangent to the reference forming surface at the reference tangent point.

[0014] Preferably, in this tire mold, of the land surface forming portions included in the tread forming surface, the land surface forming portion located on the outer side in the axial direction is the shoulder land surface forming portion. Of the land surface forming portions on three surfaces, the land surface forming portion located next to the curved land surface forming portion is the shoulder land surface forming portion. Of the convex stripe located between the shoulder land surface forming portion and the curved land surface forming portion, the side facing the curved land surface forming portion is the reference side, and the side facing the shoulder-side land surface forming portion is the back side. The point of contact of the shoulder land surface forming portion with the reference forming surface is the shoulder reference tangent point. The boundary between the back side and the shoulder land surface forming portion is the shoulder reference boundary point. The intersection point of the reference forming surface with an imaginary line of the back side extending from the shoulder reference boundary point toward the reference forming surface is the shoulder reference imaginary intersection point. The distance from the shoulder reference imaginary intersection point on the back side to the shoulder reference boundary point is the same as the distance from the reference imaginary intersection point on the reference side. The distance from the shoulder reference virtual intersection to the shoulder reference junction is the same as the distance from the reference virtual intersection to the reference junction. Of the contours of the shoulder land surface forming portion, the contour from the shoulder reference junction to the shoulder reference boundary point is represented by an arc that passes through the shoulder reference boundary point and is tangent to the reference forming surface at the shoulder reference junction.

[0015] Preferably, in this tire mold, any position on the virtual line of the reference side surface between the reference boundary point and the reference virtual intersection point is a vertical point. An arc that passes through the vertical point and is tangent to the reference forming surface at the reference tangent point is a tangent point side arc. Any position on the reference forming surface between the reference tangent point and the reference virtual intersection point is a horizontal point. An intersection between the tangent point side arc and a normal to the reference forming surface that passes through the horizontal point is an intermediate boundary point. An arc that passes through the reference boundary point and is tangent to the tangent point side arc at the intermediate boundary point is a boundary side arc. Of the contours of the curved land surface forming portion, the contour from the reference tangent point to the intermediate boundary point is represented by the tangent point side arc, and the contour from the intermediate boundary point to the reference boundary point is represented by the boundary side arc.

[0016] Preferably, in the tire mold, the ratio of the distance from the reference virtual intersection point to the vertical point to the distance from the reference virtual intersection point to the reference boundary point is 0.40 or more and 0.60 or less, and the ratio of the distance from the reference virtual intersection point to the horizontal point to the distance from the reference virtual intersection point to the reference tangent point is 0.40 or more and 0.60 or less.

[0017] Preferably, in this tire mold, of the land surface forming portions included in the tread forming surface, the land surface forming portion located on the outer side in the axial direction is the shoulder land surface forming portion. Of the land surface forming portions on three surfaces, the land surface forming portion located next to the curved land surface forming portion is the shoulder land surface forming portion. Of the convex stripe located between the shoulder land surface forming portion and the curved land surface forming portion, the side facing the curved land surface forming portion is the reference side, and the side facing the shoulder-side land surface forming portion is the back side. The point of contact of the shoulder land surface forming portion with the reference forming surface is the shoulder reference tangent point. The boundary between the back side and the shoulder land surface forming portion is the shoulder reference boundary point. The intersection point of the reference forming surface with an imaginary line of the back side extending from the shoulder reference boundary point toward the reference forming surface is the shoulder reference imaginary intersection point. The distance from the shoulder reference imaginary intersection point on the back side to the shoulder reference boundary point is the same as the distance from the reference imaginary intersection point on the reference side. The distance from the shoulder reference imaginary intersection to the shoulder reference junction is the same as the distance from the reference imaginary intersection to the reference junction. Any position on the imaginary line of the rear side surface between the shoulder reference boundary point and the shoulder reference imaginary intersection is a shoulder vertical point. An arc that passes through the shoulder vertical point and is tangent to the reference forming surface at the shoulder reference junction is a shoulder contact point side arc. Any position on the reference forming surface between the shoulder reference junction and the shoulder reference imaginary intersection is a shoulder horizontal point. An intersection of a normal to the reference forming surface that passes through the shoulder horizontal point and the shoulder contact point side arc is a shoulder intermediate boundary point. An arc that passes through the shoulder reference boundary point and is tangent to the shoulder boundary side arc at the shoulder intermediate boundary point is a shoulder boundary side arc. Of the contours of the shoulder land surface forming portion, the contour from the shoulder reference junction to the shoulder intermediate boundary point is represented by the shoulder contact point side arc, and the contour from the shoulder intermediate boundary point to the shoulder reference boundary point is represented by the shoulder boundary side arc. The distance from the shoulder reference virtual intersection point to the shoulder vertical point is the same as the distance from the reference virtual intersection point to the vertical point.The distance from the shoulder reference virtual intersection point to the shoulder lateral point is the same as the distance from the reference virtual intersection point to the lateral point.

[0018] Preferably, in this tire mold, the tread has a cap portion including the tread surface, and the unvulcanized rubber for the cap portion has a Mooney viscosity of 80 or higher.

[0019] A method for manufacturing a tire according to one aspect of the present invention includes a step of pressurizing and heating a green tire using any one of the tire molds described above.

[0020] A tire according to one aspect of the present invention includes a tread having a tread surface that comes into contact with a road surface, wherein at least two circumferential grooves are cut into the tread to form at least three land portions, and the tread surface includes the at least two circumferential grooves and at least three land surfaces that are outer surfaces of the at least three land portions. In this tire, a surface that has a contour represented by at least one circular arc and is in contact with the three land surfaces, arranged on either side of the circumferential groove in the axial direction, is the reference surface of the tread surface. Of the three land surfaces, the land surface located between two of the circumferential grooves is a curved land surface. The circumferential groove includes a reference wall that is a wall on the curved land surface side and an opposing wall that is a wall opposing the reference wall. The point of contact between the curved land surface and the reference surface is a reference tangent point. The boundary between the reference wall and the curved land surface is a reference boundary point. The point of intersection between an imaginary line of the reference wall extending from the reference boundary point toward the reference surface and the reference surface is a reference imaginary intersection point. The contour of the curved land surface is represented by one or more arcs. The reference boundary point is located inside the reference plane. When one circumferential groove has a small groove cross-sectional area and the other circumferential groove has a large groove cross-sectional area, the distance from the reference virtual intersection point to the reference boundary point on one circumferential groove side is short, and the distance from the reference virtual intersection point to the reference boundary point on the other circumferential groove side is long. [Effects of the Invention]

[0021] The tire mold and tire manufacturing method of the present invention enable optimization of the tire contact patch shape and contact pressure distribution, and the tires obtained by this tire mold and tire manufacturing method have an appropriate contact patch shape and contact pressure distribution, which allows for improved handling stability and wear resistance. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a portion of the tire of FIG. [Figure 3] FIG. 3 is a cross-sectional view showing a portion of a tire mold according to one embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing a portion of the mold of FIG. [Figure 5] FIG. 5 is a schematic diagram showing an example of the shape of the contact patch of a tire manufactured using the mold having the configuration shown in FIG. [Figure 6] FIG. 6 is a graph showing an example of the contact pressure distribution of a tire manufactured using the mold having the configuration shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view showing a modification of the tread surface shown in FIG. [Figure 8] FIG. 8 is a cross-sectional view showing a modification of the tread forming surface shown in FIG. [Figure 9] FIG. 9 is a schematic diagram showing an example of the shape of the contact patch of a tire manufactured using a conventional mold. [Figure 10] FIG. 10 is a graph showing an example of the contact pressure distribution of a tire manufactured using a conventional mold. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0024] In this disclosure, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as a standard state. In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the standard state.

[0025] A genuine rim is a rim specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "design rim" in the TRA standard, and the "measuring rim" in the ETRTO standard are all genuine rims.

[0026] The normal internal pressure refers to the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal internal pressures. The normal internal pressure of a passenger car tire is, for example, 180 kPa.

[0027] The normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads. The normal load of a passenger car tire is, for example, a load equivalent to 88% of the above load.

[0028] 1 shows a portion of a pneumatic tire 2 (hereinafter, sometimes simply referred to as "tire 2") according to one embodiment of the present disclosure. This tire 2 is mounted on a passenger vehicle.

[0029] FIG. 1 shows a portion of a cross section of the tire 2 taken along a plane including the rotation axis of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of the paper in FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, the dashed-dotted line CL represents the equatorial plane of the tire 2.

[0030] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of clinches 8 , a pair of beads 10 , a carcass 12 , a cord reinforcing layer 14 , a pair of chafers 16 , an inner liner 18 and a pair of rubber reinforcing layers 20 .

[0031] The outer surface of the tread 4 is a tread surface 22. The tread 4 comes into contact with the road surface at the tread surface 22. The tread 4 has a tread surface 22 that comes into contact with the road surface. The tread 4 is located radially outward of the cord reinforcing layer 14.

[0032] The tread 4 includes a base portion 24 and a cap portion 26. The base portion 24 constitutes the radially inner portion of the tread 4. The base portion 24 is made of cross-linked rubber that takes heat generation properties into consideration. The cap portion 26 is located radially outward of the base portion 24. In this tire 2, the cap portion 26 comes into contact with the road surface. The outer surface of the cap portion 26 is the above-mentioned tread surface 22. The cap portion 26 is made of cross-linked rubber that takes wear resistance and grip performance into consideration. The tread 4 may be made of only the cap portion 26.

[0033] Each sidewall 6 extends radially inward from an end of the tread 4 along the carcass 12. The sidewall 6 is made of crosslinked rubber.

[0034] Each clinch 8 is located radially inward of the sidewall 6. Although not shown, the clinch 8 comes into contact with a rim (not shown). The clinch 8 is made of crosslinked rubber in consideration of wear resistance.

[0035] Each bead 10 is located axially inside the clinch 8. The bead 10 includes a core 28 and an apex 30. The core 28 includes a steel wire. The apex 30 is located radially outside the core 28. The apex 30 is made of cross-linked rubber with high rigidity. As shown in FIG. 1, the size of this apex 30 is smaller than that of a conventional apex.

[0036] Although not shown, the core 28 may be configured with two cores arranged side by side in the axial direction. In this case, the carcass ply, which will be described later, is not folded around the core 28, but the end of the carcass ply is sandwiched between the two cores.

[0037] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 12 spans between one bead 10 and the other bead 10. The carcass 12 has a radial structure. The carcass 12 includes at least one carcass ply 32. The carcass 12 of this tire 2 is composed of one carcass ply 32. The carcass ply 32 is folded up around the core 28 of each bead 10. Although not shown, the carcass ply 32 includes a large number of cords arranged in parallel.

[0038] The cord reinforced layer 14 includes a belt 34 and a band 36. The belt 34 forms an inner portion of the cord reinforced layer 14, and the band 36 forms an outer portion of the cord reinforced layer 14. The cord reinforced layer 14 may be composed of only the belt 34 or only the band 36.

[0039] The belt 34 is laminated with the carcass 12 radially inside the tread 4. The belt 34 is made up of at least two belt plies 38 laminated in the radial direction. The belt 34 of this tire 2 is made up of two belt plies 38. Although not shown, each of the two belt plies 38 includes a large number of cords arranged in parallel. These cords are inclined with respect to the equatorial plane. The cords are made of steel.

[0040] The band 36 is located radially inside the tread 4. The band 36 is located radially between the tread 4 and the belt 34. The band 36 of the tire 2 is composed of a full band 36f and a pair of edge bands 36e located outside the full band 36f. The band 36 may be composed of only the full band 36f, or may be composed of only the pair of edge bands 36e.

[0041] Although not shown, the band 36 includes a cord. The cord is wound spirally in the circumferential direction in each of the full band 36f and the edge band 36e. The cord of the band 36 is made of organic fiber.

[0042] Each chafer 16 is located radially inward of the bead 10. Although not shown, the chafers 16 come into contact with the rim. The chafers 16 are made of cloth and rubber impregnated into the cloth. The chafers 16 may also be made of a member made of crosslinked rubber.

[0043] The inner liner 18 is positioned inside the carcass 12. The inner liner 18 forms the inner surface of the tire 2. The inner liner 18 is made of a crosslinked rubber with low gas permeability.

[0044] Each rubber reinforcing layer 20 is located axially outside the apex 30. The rubber reinforcing layer 20 is located between the carcass 12 and the clinch 8. The rubber reinforcing layer 20 is made of cross-linked rubber. In the tire 2, the material of the rubber reinforcing layer 20 is the same as the material of the apex 30. The tire 2 may not require the rubber reinforcing layer 20. In this case, an apex of a conventional size is used.

[0045] As shown in FIG. 1, grooves 40 are cut into the tread 4 (more specifically, the cap portion 26) of the tire 2. This forms a tread pattern. The grooves 42 of the tire 2 shown in FIG. 1 are part of the grooves 40 that form the tread pattern. These grooves 42 extend in the circumferential direction. These grooves 42 are circumferential grooves. Although set appropriately depending on the specifications of the tire 2, the circumferential grooves 42 have a groove width of 9 mm or more and 20 mm or less. The circumferential grooves 42 have a groove depth of 5 mm or more and 15 mm or less. The groove width is expressed as the distance from one edge to the other edge of the groove 40. The groove depth is expressed as the distance from the edge to the bottom. If the edges are rounded, the groove width and groove depth are determined based on imaginary edges obtained by assuming that the edges are not rounded.

[0046] 1 shows an example in which a plurality of circumferential grooves 42 cut into the tread 4 are arranged symmetrically with respect to the equatorial plane. These circumferential grooves 42 may also be arranged asymmetrically with respect to the equatorial plane.

[0047] At least two circumferential grooves 42 are formed in the tread 4 of the tire 2. As a result, at least three land portions 44 are formed in the tread 4. In the tire 2, the circumferential grooves 42 are part of the tread surface 22. The tread surface 22 includes at least two circumferential grooves 42 and at least three land surfaces 46 that are outer surfaces of the at least three land portions 44. In the tread surface 22, the at least three land surfaces 46 are arranged in the axial direction with the circumferential groove 42 sandwiched therebetween.

[0048] The tread 4 shown in FIG. 1 has three circumferential grooves 42. Of the three circumferential grooves 42, the circumferential groove 42 located on the outer side in the axial direction is a shoulder circumferential groove 42s. The circumferential groove 42 located next to the shoulder circumferential groove 42s is a middle circumferential groove 42m. In this tire 2, the middle circumferential groove 42m is located on the equator. The middle circumferential groove 42m is also referred to as a crown circumferential groove.

[0049] In the tire 2, the shoulder circumferential grooves 42s have a depth approximately equal to that of the middle circumferential grooves 42m. In the tire 2, the shoulder circumferential grooves 42s may be shallower than the middle circumferential grooves 42m, and the middle circumferential grooves 42m may be shallower than the shoulder circumferential grooves 42s. When two contrasting circumferential grooves 42 have a ratio of the groove depth of one circumferential groove 42 to the groove depth of the other circumferential groove 42 that is equal to or greater than 0.9 and equal to or less than 1.1, the two circumferential grooves 42 are determined to have equivalent groove depths.

[0050] In this tire 2, three circumferential grooves 42 arranged in parallel in the axial direction are cut into the tread 4, thereby forming four land portions 44. Of these land portions 44, the land portion 44 located on the outer side in the axial direction is the shoulder land portion 44s. The land portion 44 located on the inner side of the shoulder land portion 44s in the axial direction is the middle land portion 44m. The middle land portion 44m is located in the central portion of the tread 4, so it is also referred to as a crown land portion. In this tire 2, the four land portions 44 formed in the tread 4 are formed by a pair of middle land portions 44m and a pair of shoulder land portions 44s.

[0051] Fig. 2 shows a portion of the tread 4 shown in Fig. 1. In Fig. 2, the left-right direction is the radial direction of the tire 2, and the up-down direction is the axial direction of the tire 2. The direction perpendicular to the paper surface is the circumferential direction of the tire 2. Fig. 2 schematically shows the contour of the tread surface 22.

[0052] The land portion 44 of the tire 2 includes a land portion 44 in which the land surface 46 has a rounded shape. In Fig. 2, for the sake of convenience of explanation, the rounded shape of the land surface 46 is exaggerated.

[0053] In this tire 2, the shoulder circumferential groove 42s is located between the land surface 46s of the shoulder land portion 44s (hereinafter referred to as the shoulder land surface) and the land surface 46m of the middle land portion 44m (hereinafter referred to as the middle land surface). The circumferential groove 42 between the left and right middle land surfaces 46m is the middle circumferential groove 42m. The land surface 46 located on the left side of the paper in FIG. 2 is the middle land surface 46m. The middle circumferential groove 42m is located next to this middle land surface 46m. Another middle land surface 46m is located next to the middle circumferential groove 42m. The shoulder circumferential groove 42s is located next to this middle land surface 46m. The shoulder land surface 46s is located next to this shoulder circumferential groove 42s. In other words, three land surfaces 46 are lined up in the axial direction, with the circumferential groove 42 sandwiched between them.

[0054] In FIG. 2 , of the three land surfaces 46 arranged in the axial direction with the circumferential grooves 42 interposed therebetween, the land surface 46 located between two of the circumferential grooves 42, i.e., the middle land surface 46m, has an outwardly convex shape. This middle land surface 46m is also referred to as a curved land surface 46B. The land surface 46 located adjacent to the curved land surface 46B across the middle circumferential groove 42m, i.e., the other middle land surface 46m, is also referred to as a first land surface 46f. In this case, the middle circumferential groove 42m is also referred to as a first circumferential groove 42f. The land surface 46 located adjacent to the curved land surface 46B across the shoulder circumferential groove 42s, i.e., the shoulder land surface 46s, is also referred to as a second land surface 46n. In this case, the shoulder circumferential groove 42s is also referred to as a second circumferential groove 42n.

[0055] In the tire 2, the groove cross-sectional area of ​​the first circumferential groove 42f is smaller than the groove cross-sectional area of ​​the second circumferential groove 42n. The first circumferential groove 42f has a small groove cross-sectional area, and the second circumferential groove 42n has a large groove cross-sectional area. In the tire 2, the groove cross-sectional area of ​​the first circumferential groove 42f may be larger than the groove cross-sectional area of ​​the second circumferential groove 42n, or the groove cross-sectional area of ​​the first circumferential groove 42f may be the same as the groove cross-sectional area of ​​the second circumferential groove 42n.

[0056] In the tire 2, when the ratio of the groove cross-sectional area of ​​one circumferential groove 42 to the groove cross-sectional area of ​​the other circumferential groove 42 is 0.95 or more and 1.05 or less, the two adjacent circumferential grooves 42 are determined to have equivalent groove cross-sectional areas. The method for determining the groove cross-sectional area will be described later.

[0057] In Fig. 2, the two-dot chain line TBL is the reference plane of the tread surface 22. This reference plane TBL of the tread surface 22 represents a virtual tread surface obtained assuming that the tread 4 does not have the grooves 40. In this tire 2, the reference plane TBL of the tread surface 22 is a surface that has a contour represented by at least one circular arc and is in contact with three land surfaces 46 that are arranged on either side of the circumferential groove 42 in the axial direction. In Fig. 2, the reference plane TBL of the tread surface 22 is in contact with the first land surface 46f, the curved land surface 46B, and the second land surface 46n.

[0058] Although not shown, when the contour of the reference surface TBL is represented by a plurality of arcs arranged in parallel in the axial direction, the contour of the reference surface TBL is configured so that one arc and another arc positioned adjacent to this one arc are tangent to each other at the boundary between the two arcs, and the arc positioned on the inner side in the axial direction has a larger radius than the arc positioned on the outer side. In this case, the one arc and the other arc may be connected by a straight line tangent to both arcs.

[0059] A state in which the tire 2 is mounted on a standard rim, the internal pressure of the tire 2 is adjusted to 5% of the standard internal pressure, and no load is applied to the tire 2 is referred to as a reference state. The outline of the tread surface 22 of the tire 2 is represented by the outline of the tread surface 22 in the reference state or the outline of the tread forming surface of a mold described below. Note that, if the outline configuration of the tread surface 22 is unclear, the outline of the reference surface TBL of the tread surface 22 may be identified based on the outline of the tread surface 22 obtained by analyzing, for example, cross-sectional image data of the tire 2 in the reference state photographed by X-ray computed tomography (hereinafter referred to as X-ray CT) or shape data of the tread surface 22 of the tire 2 in the reference state measured using a profile measuring device (not shown) having a laser displacement meter. In this case, the outline of the reference surface TBL of the tread surface 22 is represented by a single arc tangent to three land surfaces 46 aligned in the axial direction.

[0060] The circumferential groove 42 has a bottom 48 and a pair of walls 50. In FIG. 2, the symbol Bt denotes the boundary between the wall 50 and the land surface 46. This boundary Bt is also referred to as a boundary point. The two-dot chain line Lt is a straight line that extends from the boundary point Bt toward the reference plane TBL and is tangent to the outline of the wall 50 at this boundary point Bt. This straight line Lt is a virtual line of the wall 50. The symbol Vt denotes the intersection point between the virtual line Lt and the reference plane TBL. The intersection point Vt is also referred to as a virtual intersection point.

[0061] In this tire 2, the groove cross-sectional area of ​​the circumferential groove 42 is expressed as the area of ​​the region surrounded by one wall 50, the bottom 48, the other wall 50, the imaginary line Lt of the other wall 50, the reference plane TBL, and the imaginary line Lt of the one wall 50.

[0062] As described above, the curved land surface 46B is located between two circumferential grooves 42. In the circumferential groove 42 located adjacent to this curved land surface 46B, the wall 50 located on the curved land surface 46B side is also referred to as the reference wall 50a. The wall 50 opposing this reference wall 50a is also referred to as the opposing wall 50b. The circumferential groove 42 located adjacent to the curved land surface 46B includes the reference wall 50a, which is the wall 50 on the curved land surface 46B side, and the opposing wall 50b, which is the wall 50 opposing this reference wall 50a.

[0063] In FIG. 2, the symbol BB1t denotes the boundary between the reference wall 50a of the first circumferential groove 42f (hereinafter referred to as the first reference wall) and the curved land surface 46B. The boundary BB1t is a reference boundary point (hereinafter referred to as the first reference boundary point). The two-dot chain line BL1t is a virtual line of the first reference wall 50a. The symbol BV1t is a virtual intersection represented by the intersection of the virtual line BL1t of the first reference wall 50a and the reference surface TBL. The virtual intersection BV1t is a reference virtual intersection point (hereinafter referred to as the first reference virtual intersection point). The double-headed arrow Xd1t is the distance from the first reference virtual intersection point BV1t to the first reference boundary point BB1t. This distance Xd1t is measured along the virtual line BL1t of the first reference wall 50a.

[0064] In FIG. 2, the symbol BB2t denotes the boundary between the reference wall 50a (hereinafter referred to as the second reference wall) of the second circumferential groove 42n and the curved land surface 46B. The boundary BB2t is a reference boundary point (hereinafter referred to as the second reference boundary point). The two-dot chain line BL2t is a virtual line of the second reference wall 50a. The symbol BV2t is a virtual intersection represented by the intersection of the virtual line BL2t of the second reference wall 50a and the reference surface TBL. The virtual intersection BV2t is a reference virtual intersection point (hereinafter referred to as the second reference virtual intersection point). The double-headed arrow Xd2t is the distance from the second reference virtual intersection point BV2t to the second reference boundary point BB2t. This distance Xd2t is measured along the virtual line BL2t of the second reference wall 50a.

[0065] The tire 2 described above is manufactured as follows. Although not described in detail, in the manufacture of this tire 2, an unvulcanized rubber composition (hereinafter also referred to as unvulcanized rubber) is prepared for the elements that make up the tire 2, such as the tread 4, sidewall 6, and bead 10. The unvulcanized rubber is obtained by mixing base rubber and chemicals using a kneader (not shown) such as a Banbury mixer.

[0066] Examples of base rubbers include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). Examples of chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. Although not described in detail, the selection of base rubber and chemicals, the content of the selected chemicals, etc., are determined appropriately depending on the specifications of the components to which the rubber is applied.

[0067] In manufacturing the tire 2, a preform of tire components is prepared by shaping unvulcanized rubber in a rubber molding machine (not shown) such as an extruder. In the tire molding machine (not shown), preforms such as the tread 4, sidewalls 6, and beads 10 are combined to prepare the tire 2 in an unvulcanized state (hereinafter also referred to as a green tire).

[0068] In manufacturing the tire 2, a green tire is placed in a mold of a vulcanizer (not shown). The green tire is pressurized and heated in the mold to obtain the tire 2. The tire 2 is a vulcanized product of the green tire.

[0069] The manufacturing method of this tire 2 includes a step of preparing a green tire and a step of pressurizing and heating the green tire using a mold. Although not described in detail, there are no particular limitations on the vulcanization conditions such as temperature, pressure, and time in the manufacturing of this tire 2, and general vulcanization conditions are adopted.

[0070] FIG. 3 shows a portion of a cross section of a tire mold 56 taken along a plane including the rotation axis of the tire 2. This mold 56 is used to manufacture the tire 2 shown in FIG. 1. In FIG. 3, the left-right direction is the radial direction of the tire 2, and the up-down direction is the axial direction of the tire 2. The direction perpendicular to the plane of the page is the circumferential direction of the tire 2. The dashed-dotted line CL is the equatorial plane of the tire 2. For ease of explanation, hereinafter, the dimensions of the mold 56 will be represented by the dimensions of the tire 2.

[0071] The mold 56 includes a tread ring 58, a pair of side plates 60, and a pair of bead rings 62. The mold 56 is a split mold. In Fig. 3, the mold 56 is in a state in which the tread ring 58, the pair of side plates 60, and the pair of bead rings 62 are assembled, i.e., in a closed state.

[0072] The tread ring 58 constitutes the radially outer portion of the mold 56. The tread ring 58 has a tread forming surface 64 on its inner surface. The tread forming surface 64 forms the tread surface 22 of the tire 2 on the outer surface of the green tire 2r. The tread ring 58 of the mold 56 is composed of a number of segments 66. These segments 66 are arranged in a ring shape.

[0073] Each side plate 60 is located radially inside the tread ring 58. The side plates 60 are continuous with the ends of the tread rings 58. The side plates 60 have sidewall forming surfaces 68 on their inner surfaces. The sidewall forming surfaces 68 form the side surfaces of the tire 2 on the outer surface of the green tire 2r.

[0074] Each bead ring 62 is located radially inward of the side plate 60. The bead ring 62 is continuous with the end of the side plate 60. The bead ring 62 has a bead forming surface 70 on its inner surface. The bead forming surface 70 forms the portion of the bead 10 of the tire 2, specifically the portion that fits onto the rim, on the outer surface of the green tire 2r.

[0075] In this mold 56, a number of segments 66, a pair of side plates 60, and a pair of bead rings 62 are combined to form a cavity surface 72 that shapes the outer surface of the tire 2. The cavity surface 72 is made up of a tread forming surface 64, a pair of sidewall forming surfaces 68, and a pair of bead forming surfaces 70.

[0076] Although not shown, in a pressure and heat process, the green tire 2r is pressed against the cavity surface 72 of the mold 56 by a rigid core or an expanded bladder. This shapes the outer surface of the tire 2.

[0077] Fig. 4 shows a cross section of a tread ring 58 that forms part of the mold 56 shown in Fig. 3. Fig. 4 schematically shows the outline of a tread forming surface 64 that forms the tread surface 22. In Fig. 4, the left-right direction is the radial direction of the tire 2, and the up-down direction is the axial direction of the tire 2. The direction perpendicular to the plane of the page is the circumferential direction of the tire 2.

[0078] As described above, the tread surface 22 of the tire 2 includes at least two circumferential grooves 42 and at least three land surfaces 46 that are outer surfaces of the at least three land portions 44. Therefore, in the mold 56, the tread forming surface 64 that forms the tread surface 22 includes at least two ridges 74 that form the at least two circumferential grooves 42, and at least three land surface forming portions 76 that form the at least three land surfaces 46.

[0079] In this mold 56, of the at least two ridges 74, the ridge 74 that forms the first circumferential groove 42f is a first ridge 74f, and the ridge 74 that forms the second circumferential groove 42n is a second ridge 74n.

[0080] As described above, in this mold 56, the cross-sectional area of ​​the first circumferential groove 42f is smaller than the cross-sectional area of ​​the second circumferential groove 42n. The cross-sectional area of ​​the first ridge 74f is smaller than the cross-sectional area of ​​the second ridge 74n. The first ridge 74f has a small cross-sectional area, and the second ridge 74n has a large cross-sectional area.

[0081] In this mold 56, of the at least three land surface forming portions 76, the land surface forming portion 76 that forms the curved land surface 46B is the curved land surface forming portion 76B. The land surface forming portion 76 that forms the first land surface 46f is the first land surface forming portion 76f. The land surface forming portion 76 that forms the second land surface 46n is the second land surface forming portion 76n.

[0082] In the plane of FIG. 4, the first convex rib 74f is located next to the first land surface forming portion 76f. The curved land surface forming portion 76B is located next to the first convex rib 74f. The second convex rib 74n is located next to this curved land surface forming portion 76B. The second land surface 76n is located next to this second convex rib 74n. In other words, in the axial direction, the land surface forming portions 76 on three sides are lined up with the convex rib 74 between them. Of the three land surface forming portions 76, the land surface forming portion 76 located between two of the convex ribs 74 is the curved land surface forming portion 76B. The two land surface forming portions 76 located next to the curved land surface forming portion 76B are the first land surface forming portion 76f and the second land surface forming portion 76n.

[0083] Among the land surface forming portions 76 included in the tread forming surface 64, the land surface forming portion 76 located on the outer side in the axial direction is the shoulder land surface forming portion 76s that forms the shoulder land surface 46s. In this mold 56, of the three land surface forming portions 76 arranged on either side of the convex streak 74 in the axial direction, the curved land surface forming portion 76B is the middle land surface forming portion 76m that forms one of the middle land surfaces 46m. The first land surface forming portion 76f located adjacent to this curved land surface forming portion 76B is the middle land surface forming portion 76m that forms the other middle land surface 46m. The first convex streak 74f located between the first land surface forming portion 76f and the curved land surface forming portion 76B is the middle convex streak 74m that forms the middle circumferential groove 42m. The second land surface forming portion 76n located adjacent to the curved land surface forming portion 76B is the shoulder land surface forming portion 76s. The second convex rib 74n located between the second land surface forming portion 76n and the curved land surface forming portion 76B is the shoulder convex rib 74s that forms the shoulder land surface 46s.

[0084] In Figure 4, the two-dot chain line FBL is the reference forming surface of the tread forming surface 64. This reference forming surface FBL of the tread forming surface 64 corresponds to the reference surface TBL of the tread surface 22 described above. In this mold 56, the surface that has a contour represented by at least one circular arc and is in contact with the three land surface forming portions 76 that are lined up in the axial direction on either side of the convex streak 74 is the reference forming surface FBL of the tread forming surface 64. In Figure 4, the reference forming surface FBL of the tread forming surface 64 is in contact with the first land surface forming portion 76f, the curved land surface forming portion 76B, and the second land surface forming portion 76n from the left side of the page.

[0085] Although not shown, when the contour of this reference forming surface FBL is represented by multiple arcs arranged side by side in the axial direction, the contour of this reference forming surface FBL is configured so that one arc and another arc located adjacent to it are in contact at the boundary between the two arcs, and the arc located on the inside in the axial direction has a larger radius than the radius of the arc located on the outside.

[0086] The convex rib 74 has a top surface 78 and a pair of side surfaces 80. In Figure 4, symbol Bm is the boundary between the side surface 80 and the land surface forming portion 76. This boundary Bm is also referred to as a boundary point. The two-dot chain line Lm is a straight line that extends from the boundary point Bm toward the reference forming surface FBL and is tangent to the contour line of the side surface 80 at this boundary point Bm. This straight line Lm is a virtual line of the side surface 80. Symbol Vm is the intersection point between the virtual line Lm and the reference forming surface FBL. The intersection point Vm is also referred to as a virtual intersection point.

[0087] In this mold 56, the cross-sectional area of ​​the ridge 74 is represented by the area of ​​the region surrounded by one side 80, the top surface 78, the other side 80, the imaginary line Lm of the other side 80, the reference forming surface FBL, and the imaginary line Lm of the one side 80.

[0088] As described above, the curved land surface forming portion 76B is located between two convex ridges 74. In the convex ridge 74 located next to this curved land surface forming portion 76B, the side surface 80 located on the curved land surface forming portion 76B side is also referred to as the reference side surface 80a. The side surface 80 located on the back side of this reference side surface 80a is also referred to as the back side surface 80b. The convex ridge 74 located next to the curved land surface forming portion 76B has the reference side surface 80a, which is the side surface 80 on the curved land surface forming portion 76B side, and the back side surface 80b, which is the side surface 80 located on the back side of this reference side surface 80a.

[0089] In FIG. 4, symbol BB1m is the boundary between the reference side 80a (hereinafter referred to as the first reference side) of the first convex streak 74f and the curved land surface forming portion 76B. The boundary BB1m is the reference boundary point (hereinafter referred to as the first reference boundary point). The two-dot chain line BL1m is a virtual line of the first reference side 80a. Symbol BV1m is a virtual intersection represented by the intersection of the virtual line BL1m of the first reference side 80a and the reference forming surface FBL. The virtual intersection BV1m is a reference virtual intersection point (hereinafter referred to as the first reference virtual intersection point). The double-headed arrow Xd1m is the distance from the first reference virtual intersection point BV1m to the first reference boundary point BB1m. This distance Xd1m is measured along the virtual line BL1m of the first reference side 80a.

[0090] In FIG. 4, the symbol BB2m is the boundary between the reference side 80a (hereinafter referred to as the second reference side) of the second convex streak 74n and the curved land surface forming portion 76B. The boundary BB2m is the reference boundary point (hereinafter referred to as the second reference boundary point). The two-dot chain line BL2m is a virtual line of the second reference side 80a. The symbol BV2m is a virtual intersection represented by the intersection of the virtual line BL2m of the second reference side 80a and the reference forming surface FBL. The virtual intersection BV2m is a reference virtual intersection (hereinafter referred to as the second reference virtual intersection). The double-headed arrow Xd2m is the distance from the second reference virtual intersection BV2m to the second reference boundary point BB2m. This distance Xd2m is measured along the virtual line BL2m of the second reference side 80a.

[0091] In this mold 56, the flow of unvulcanized rubber caused by pressing the ridges 74 against the raw tire 2r is controlled by the shape of the land surface forming portion 76. As described above, the circumferential grooves 42 are cut into the cap portion 26 of the tread 4. The ridges 74 of the tread forming surface 64 press against this cap portion 26. In this mold 56, the flow of unvulcanized rubber for the cap portion 26 caused by pressing the ridges 74 against the raw tire 2r is controlled by the shape of the land surface forming portion 76. The shape of this land surface forming portion 76 will be described below.

[0092] [Outline of curved land surface forming part 76B] The outline of the curved land surface forming portion 76B located between the two convex streaks 74 will be described. As described above, the reference forming surface FBL of the tread forming surface 64 contacts the first land surface forming portion 76f, the curved land surface forming portion 76B, and the second land surface forming portion 76n included in the tread forming surface 64. In FIG. 4, the symbol T1m indicates the contact point between the curved land surface forming portion 76B and the reference forming surface FBL. In this mold 56, the contact point Tm is the reference contact point.

[0093] In this mold 56, the contour of the curved land surface forming portion 76B is represented by one or more arcs. The aforementioned first reference boundary point BB1m is also the end of the curved land surface forming portion 76B on the first convex streak 74f side. The aforementioned third reference boundary point BB2m is also the end of the curved land surface forming portion 76B on the second convex streak 74n side. As shown in FIG. 4, the end BB1m of the curved land surface forming portion 76B on the first convex streak 74f side is located radially inward from the reference forming surface FBL of the tread forming surface 64. The end BB2m of the curved land surface forming portion 76B on the second convex streak 74n side is also located radially inward from the reference forming surface FBL.

[0094] In manufacturing the tire 2, the cap portion 26 is pressed against the ridges 74, causing the unvulcanized rubber of the cap portion 26 to flow toward the portion between the two ridges 74, i.e., the curved land surface forming portion 76B. In this mold 56, the contour of the curved land surface forming portion 76B is configured so that the ends BB1m and BB2m of the curved land surface forming portion 76B are positioned inside the reference forming surface FBL. Because the volume of unvulcanized rubber flowing into the curved land surface forming portion 76B is limited, turbulence in the flow of unvulcanized rubber pressed against the ridges 74 is suppressed.

[0095] As described above, in this mold 56, the first ridge 74f has a small cross-sectional area, and the second ridge 74n has a large groove cross-sectional area. The volume of unvulcanized rubber pressed against the second ridge 74n is larger than the volume of unvulcanized rubber pressed against the first ridge 74f. There is a concern that the flow of unvulcanized rubber on the first ridge 74f side will differ from the flow of unvulcanized rubber on the second ridge 74n side.

[0096] However, in this mold 56, the distance Xd2m from the second reference imaginary intersection point BV2m to the second reference boundary point BB2m on the second ridge 74n side is longer than the distance Xd1m from the first reference imaginary intersection point BV1m to the first reference boundary point BB1m on the first ridge 74f side. In other words, the distance Xd1m from the first reference imaginary intersection point BV1m to the first reference boundary point BB1m on the first ridge 74f side is short, while the distance Xd2m from the second reference imaginary intersection point BV2m to the second reference boundary point BB2m on the second ridge 74n side is long. In this mold 56, the volume of unvulcanized rubber flowing into the curved land surface forming portion 76B on the side of the second ridge 74n, which has a large cross-sectional area, is effectively limited. The flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side are controlled in a balanced manner, making it less likely for the flow of unvulcanized rubber to become turbulent. A curved land surface 46B that reflects the shape of the curved land surface forming portion 76B is formed in this mold 56. Since the disorder of the inner surface shape of the tread 4 is also suppressed, the inner surface of the tread 4 is configured in an appropriate shape.

[0097] 5 shows an example of the contact patch shape of a tire 2 (size = 205 / 55R16) manufactured using this mold 56. In FIG. 5, the left-right direction corresponds to the axial direction of the tire 2. The up-down direction corresponds to the circumferential direction of the tire 2.

[0098] This contact patch shape is obtained by using a tire contact patch shape measuring device (not shown) to trace the contours of each land portion 44 in the contact patch obtained by applying a normal load to the tire 2 in a normal state and pressing the tire 2 against the road surface. To obtain the contact patch, the tire 2 is placed so that its axial direction is parallel to the road surface, and the above-mentioned load is applied to the tire 2 in a direction perpendicular to the road surface. In this measuring device, the road surface is a flat surface. When measuring the contact patch, the tire 2 is pressed against a flat road surface. The contact patch shape of a tire manufactured using a conventional mold, shown in Figure 9, was obtained in a similar manner.

[0099] As shown in Figure 5, in the contact patch shape of the tire 2 manufactured using this mold 56, the circumferential outer edge of the middle land portion 44m located between the shoulder circumferential groove 42s and the middle circumferential groove 42m does not have an inwardly convex shape like the circumferential outer edge of the middle land portion confirmed in the tire manufactured using the conventional mold shown in Figure 9, but rather has an outwardly bulging shape. The contact patch area is clearly increased, and the tire 2 can make more sufficient contact with the road surface than tires manufactured using the conventional mold. Using this mold 56, the handling stability of the tire 2 can be further improved.

[0100] Figure 6 shows an example of the contact pressure distribution of a tire 2 (size = 205 / 55R16) manufactured using this mold 56. The vertical axis represents the contact pressure, and the horizontal axis represents the position of the contact patch in the contact width direction. In Figure 6, the left side shows the contact pressure distribution of the middle land portion 44m, and the right side shows the contact pressure distribution of the shoulder land portion 44s.

[0101] This contact pressure distribution is obtained by applying a normal load to a tire 2 in a normal state using a tire contact pressure measuring device (not shown), and pressing the tire 2 against the road surface. To obtain this contact pressure, the tire 2 is positioned so that its axial direction is parallel to the road surface, and the above-mentioned load is applied to the tire 2 in a direction perpendicular to the road surface. In this measuring device, the road surface is a flat surface. In measuring this contact pressure distribution, the tire 2 is pressed against a flat road surface. The contact pressure distribution of a tire manufactured using a conventional mold, shown in Figure 10, was obtained in a similar manner. Note that the contact pressure distribution indicated by the dotted line in Figure 6 is the contact pressure distribution of a tire manufactured using this conventional mold.

[0102] As shown in Figure 6, in the contact pressure distribution of the tire 2 manufactured using this mold 56, the increase in contact pressure at the edge of the middle land portion 44m is suppressed compared to the increase in contact pressure at the edge of the middle land portion observed in the tire manufactured using the conventional mold shown in Figure 10. In the example shown in Figure 6, the contact pressure difference within the middle land portion 44m is suppressed to about 55 kPa. Local increases in contact pressure are clearly suppressed, and this mold 56 can further improve the wear resistance of the tire 2.

[0103] According to this mold 56 and the method for manufacturing the tire 2 using this mold 56, the contact patch shape and contact pressure distribution of the tire 2 can be optimized, and the steering stability and wear resistance of the tire 2 can be improved.

[0104] In FIG. 4, the double-headed arrow Wcm is the distance from the first reference virtual intersection point BV1m to the second reference virtual intersection point BV2m. The distance Wcm is represented by the length of the line segment connecting the first reference virtual intersection point BV1m and the second reference virtual intersection point BV2m. The double-headed arrow Xw1m is the distance from the first reference virtual intersection point BV1m to the reference junction Tm. The distance Xw1m is represented by the length of the line segment connecting the first reference virtual intersection point BV1m and the reference junction Tm. The double-headed arrow Xw2m is the distance from the second reference virtual intersection point BV2m to the reference junction Tm. The distance Xw2m is represented by the length of the line segment connecting the second reference virtual intersection point BV2m and the reference junction Tm.

[0105] In this mold 56, the position of the reference tangent point Tm, which is the tangent point between the curved land surface forming portion 76B and the reference forming plane FBL, is preferably determined based on the cross-sectional area of ​​the convex ribs 74 located on both sides of the curved land surface forming portion 76B. Specifically, when the cross-sectional area of ​​the first convex rib 74f is Sam and the cross-sectional area of ​​the second convex rib 74n is Sbm, it is preferable that the distance Xw1m is set so as to satisfy the following formula (1), which is expressed using the distance Xw1m, the distance Wcm, the cross-sectional area Sam, and the cross-sectional area Sbm. Sam / (Sam+Sbm)×100-10≦Xw1m / Wcm×100≦Sam / (Sam+Sbm)×100+10...(1)

[0106] In this mold 56, the cross-sectional area Sam of the first ridge 74f is smaller than the cross-sectional area Sbm of the second ridge 74n, so the reference junction Tm is set on the side of the first reference boundary point BB1m. In this mold 56, the flow of unvulcanized rubber is promoted toward the first ridge 74f, which has a smaller cross-sectional area. In this mold 56, if the cross-sectional area Sam of the first ridge 74f is larger than the cross-sectional area Sbm of the second ridge 74n, the reference junction Tm is set on the side of the second reference boundary point BB2m. In this case, the flow of unvulcanized rubber is promoted toward the second ridge 74n.

[0107] This mold 56 controls the flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side in a balanced manner. Because disturbances in the flow of unvulcanized rubber are unlikely to occur, a curved land surface 46B is formed that reflects the shape of the curved land surface forming portion 76B. This mold 56 and the manufacturing method for a tire 2 using this mold 56 can optimize the contact patch shape and contact pressure distribution of the tire 2, thereby achieving improved steering stability and wear resistance of the tire 2.

[0108] In this mold 56, when the cross-sectional area of ​​the convex rib 74 located next to the curved land surface forming portion 76B is Sm, the ratio (Xdm / Sm) of the distance Xdm from the reference virtual intersection point BVm to the reference boundary point BBm to the cross-sectional area Sm of the convex rib 74 is preferably 0.0008 or more and 0.0040 or less.

[0109] By setting the ratio (Xdm / Sm) to 0.0008 or more, the shape of the land surface forming portion 76B effectively contributes to restricting the flow of the unvulcanized rubber pressed by the convex ribs 74. Even if there is a difference in the cross-sectional area of ​​the convex ribs 74 located on both sides of the land surface forming portion 76B, disturbances in the flow of the unvulcanized rubber are unlikely to occur. In this mold 56, a curved land surface 46B is formed that reflects the shape of the curved land surface forming portion 76B. From this perspective, the ratio (Xdm / Sm) is more preferably 0.0014 or more, and even more preferably 0.0020 or more.

[0110] By setting the ratio (Xdm / Sm) to 0.0040 or less, the flow of the unvulcanized rubber pressed by the ridges 74 is maintained appropriately. Even in this case, even if there is a difference in the cross-sectional area of ​​the ridges 74 located on both sides of the land surface forming portion 76B, disturbances in the flow of the unvulcanized rubber are unlikely to occur. In this mold 56, a curved land surface 46B is formed that reflects the shape of the curved land surface forming portion 76B. From this perspective, the ratio (Xdm / Sm) is more preferably 0.0034 or less, and even more preferably 0.0028 or less.

[0111] As described above, in this mold 56, the cross-sectional area Sam of the first ridge 74f is smaller than the cross-sectional area Sbm of the second ridge 74n. When the cross-sectional area Sam of the first convex rib 74f is different from the cross-sectional area Sbm of the second convex rib 74n, from the viewpoint of being able to control the flow of unvulcanized rubber on the first convex rib 74f side and the flow of unvulcanized rubber on the second convex rib 74n side in a balanced manner and effectively suppressing disturbances in the flow of unvulcanized rubber, on the first convex rib 74f side, the ratio (Xd1m / Sam) of the distance Xd1m from the first reference imaginary intersection point BV1m to the first reference boundary point BB1m to the cross-sectional area Sam of the first convex rib 74f is preferably 0.0008 or more and 0.0040 or less, and on the second convex rib 74n side, the ratio (Xd2m / Sbm) of the distance Xd2m from the second reference imaginary intersection point BV2m to the second reference boundary point BB2m to the cross-sectional area Sbm of the second convex rib 74n is preferably 0.0008 or more and 0.0040 or less. In this case, the ratio (Xd1m / Sam) and the ratio (Xd2m / Sbm) are set to the same value.

[0112] As described above, the contour of the curved land surface forming portion 76B is represented by one or more arcs. The contour of the curved land surface forming portion 76B is preferably represented by an arc that passes through the reference boundary point BBm and is tangent to the reference forming surface FBL at the reference tangent point Tm. Specifically, the contour of the curved land surface forming portion 76B is preferably represented by an arc that passes through the first reference boundary point BB1m and is tangent to the reference forming surface FBL at the reference tangent point Tm, and an arc that passes through the second reference boundary point BB2m and is tangent to the reference forming surface FBL at the reference tangent point Tm. This allows for well-balanced control of the flow of unvulcanized rubber on the first convex streak 74f side and the flow of unvulcanized rubber on the second convex streak 74n side. Because disturbances in the flow of unvulcanized rubber are unlikely to occur, the mold 56 forms a curved land surface 46B that reflects the shape of the curved land surface forming portion 76B. According to the mold 56 and the manufacturing method of the tire 2 using the mold 56, the tire 2's contact patch shape and contact pressure distribution can be optimized, thereby achieving improved steering stability and wear resistance of the tire 2. When the cross-sectional area of ​​the first convex streak 74f and the cross-sectional area of ​​the second convex streak 74n are equal, the contour of the curved land surface forming portion 76B is represented by a single arc.

[0113] [When the convex strip 74 located next to the curved land surface forming portion 76B is a shoulder convex strip 74s] A case where the convex rib 74 located next to the curved land surface forming portion 76B is a shoulder convex rib 74s will be described using as an example a case where the second convex rib 74n is the convex rib 74 located outermost in the axial direction. When the second convex rib 74n is the convex rib 74 located outermost in the axial direction, the shoulder land surface 46s of the tire 2 is formed by the second land surface forming portion 76n in Figure 4. Below, the second land surface forming portion 76n that forms this shoulder land surface 46s, i.e., the contour of the shoulder land surface forming portion 76s, will be described using Figure 4.

[0114] In this mold 56, the second convex rib 74n is located between the shoulder land surface forming portion 76s and the curved land surface forming portion 76B. In this second convex rib 74n, the side surface 80 on the curved land surface forming portion 76B side is the reference side surface 80a, and the side surface 80 on the shoulder land surface forming portion 76s side is the back side surface 80b.

[0115] In Figure 4, the symbol Tsm is the tangent point between the shoulder land surface forming portion 76s and the reference forming surface FBL. The tangent point Tsm is the shoulder reference tangent point. When the shoulder land surface forming portion 76s and the reference forming surface FBL are tangent to each other by a line rather than a point, the shoulder reference tangent point Tsm is determined by the inner end of the tangent line between the shoulder land surface forming portion 76s and the reference forming surface FBL.

[0116] In FIG. 4, the symbol BBsm denotes the boundary between the rear surface 80b of the second protrusion 74n and the shoulder land surface forming portion 76s. The boundary BBsm is the shoulder reference boundary point. The two-dot chain line BLsm is an imaginary line on the rear surface 80b. The symbol BVsm denotes an imaginary intersection represented by the intersection of the imaginary line BLsm on the rear surface 80b and the reference forming surface FBL. The imaginary intersection BVsm is the shoulder reference imaginary intersection point. The double-headed arrow Xdsm denotes the distance from the shoulder reference imaginary intersection point BVsm to the shoulder reference boundary point BBsm. This distance Xdsm is measured along the imaginary line BLsm on the rear surface 80b. The double-headed arrow Xwsm denotes the distance from the shoulder reference imaginary intersection point BVsm to the shoulder reference tangent point Tsm. The distance Xwsm is represented by the length of the line segment connecting the shoulder reference imaginary intersection point BVsm and the shoulder reference tangent point Tsm.

[0117] In this mold 56, the contour of the shoulder land surface forming portion 76s from the shoulder reference boundary point BBsm to the shoulder reference junction Tsm is configured similarly to the contour of the curved land surface forming portion 76B from the second reference boundary point BB2m to the reference junction Tm. Specifically, the distance Xdsm from the shoulder reference imaginary intersection point BVsm to the shoulder reference boundary point BBsm is the same as the distance Xd2m from the second reference imaginary intersection point BV2m to the second reference boundary point BB2m. The distance Xwsm from the shoulder reference imaginary intersection point BVsm to the shoulder reference junction Tsm is the same as the distance Xw2m from the second reference imaginary intersection point BV2m to the reference junction Tm. The contour of the shoulder land surface forming portion 76s from the shoulder reference boundary point BBsm to the shoulder reference junction Tsm is represented by an arc that passes through the shoulder reference boundary point BBsm and is tangent to the reference forming surface FBL at the shoulder reference junction Tsm, just like the contour of the curved land surface forming portion 76B from the second reference boundary point BB2m to the reference junction Tm.

[0118] In this mold 56, the shoulder reference boundary point BBsm is also the end of the shoulder land surface forming portion 76s on the second protrusion streak 74n side. As shown in Fig. 4, the end BBsm of the shoulder land surface forming portion 76s on the second protrusion streak 74n side is located radially inward of the reference forming surface FBL of the tread forming surface 64.

[0119] During the manufacture of the tire 2, the cap portion 26 is pressed against the ridge 74, causing the unvulcanized rubber of the cap portion 26 to flow toward the axially outer portion of the second ridge 74n, i.e., toward the portion forming the shoulder land portion 44s. In this mold 56, the contour of the shoulder land surface forming portion 76s is configured so that the end BBsm of the shoulder land surface forming portion 76s is located inside the reference plane FBL of the tread forming surface 64. Because the volume of unvulcanized rubber flowing into the portion forming the shoulder land portion 44s is limited, disturbances are unlikely to occur in the flow of unvulcanized rubber pressed against the second ridge 74n. In this mold 56, the shoulder land surface 46s is formed, reflecting the shape of the shoulder land surface forming portion 76s. Disturbances in the inner surface shape of the tread 4 are also suppressed, so the inner surface of the tread 4 is configured with an appropriate shape.

[0120] As shown in Figure 5, in the contact patch shape of the tire 2 manufactured using this mold 56, the circumferential outer edge of the shoulder land portion 44s does not have an inwardly convex shape like the circumferential outer edge of the shoulder land portion confirmed in the tire manufactured using the conventional mold shown in Figure 9, but rather has an outwardly bulging shape. The contact patch area is clearly increased, and the tire 2 can make more sufficient contact with the road surface than tires manufactured using the conventional mold. Using this mold 56, the handling stability of the tire 2 can be further improved.

[0121] As shown in Figure 6, in the contact pressure distribution of the tire 2 manufactured using this mold 56, the increase in contact pressure at the edge of the shoulder land portion 44s is suppressed compared to the increase in contact pressure at the edge of the shoulder land portion observed in the tire manufactured using the conventional mold shown in Figure 10. In the example shown in Figure 6, the contact pressure difference within the shoulder land portion 44s is suppressed to about 70 kPa. Local increases in contact pressure are clearly suppressed, and this mold 56 can further improve the wear resistance of the tire 2.

[0122] 1 is manufactured using the above-described mold 56 having the tread forming surface 64. Next, the contour of the tread surface 22 shaped by this tread forming surface 64 will be described.

[0123] [Contour of curved land surface 46B] The outline of the curved land surface 46B located between the two circumferential grooves 42 will be described based on the outline of the middle land surface 46m shown in Fig. 2. As described above, the middle land surface 46m is the curved land surface 46B located between the first circumferential groove 42f serving as the middle circumferential groove 42m and the second circumferential groove 42n serving as the shoulder circumferential groove 42s.

[0124] As described above, in the tire 2, the reference plane TBL of the tread surface 22 has a contour represented by at least one arc, and is in contact with the curved land surface 46B, the first land surface 46f, and the second land surface 46n. In Fig. 2, the reference symbol T1t denotes a point of contact between the curved land surface 46B and the reference plane TBL. In the tire 2, this point of contact T1t is a first reference contact point.

[0125] In the tire 2, the contour of the curved land surface 46B is represented by one or more arcs. The first reference boundary point BB1t described above is also the end of the curved land surface 46B on the first circumferential groove 42f side. The second reference boundary point BB2t described above is also the end of the curved land surface 46B on the second circumferential groove 42n side. As shown in FIG. 2 , the end BB1t of the curved land surface 46B on the first circumferential groove 42n side is located radially inward of the reference plane TBL of the tread surface 22. The end BB2t of the curved land surface 46B on the second circumferential groove 42n side is also located radially inward of the reference plane TBL of the tread surface 22.

[0126] During the manufacture of the tire 2, the cap portion 26 is pressed against the first protrusion rib 74f and the second protrusion rib 74n, causing the unvulcanized rubber of the cap portion 26 to flow toward the portion between the first protrusion rib 74f and the second protrusion rib 74n, i.e., toward the curved land surface forming portion 76B. In this tire 2, the contour of the curved land surface 46B is configured so that the ends BB1t and BB2t of the curved land surface 46B are located inside the reference plane TBL. Because the volume of unvulcanized rubber flowing into the curved land surface forming portion 76B is limited, turbulence in the flow of unvulcanized rubber pressed against the first protrusion rib 74f and the second protrusion rib 74n is suppressed.

[0127] As described above, in the mold 56 of this tire 2, the volume of unvulcanized rubber pressed against the second ridge 74n is larger than the volume of unvulcanized rubber pressed against the first ridge 74f, which raises concerns that a difference may occur between the flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side.

[0128] However, in this tire 2, the distance Xd2t from the second reference imaginary intersection point BV2t to the second reference boundary point BB2t on the second circumferential groove 42n side is longer than the distance Xd1t from the first reference imaginary intersection point BV1t to the first reference boundary point BB1t on the first circumferential groove 42f side. In other words, the distance Xd1t from the first reference imaginary intersection point BV1t to the first reference boundary point BB1t on the first circumferential groove 42f side is short, and the distance Xd2t from the second reference imaginary intersection point BV2t to the second reference boundary point BB2t on the second circumferential groove 42n side is long. In manufacturing this tire 2, the volume of unvulcanized rubber flowing into the curved land surface forming portion 76B on the second convex rib 74n side is effectively limited. The flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side are controlled in a well-balanced manner, thereby forming a curved land surface 46B that reflects the shape of the curved land surface forming portion 76B. Disturbance of the inner surface shape of the tread 4 is also suppressed, so the inner surface of the tread 4 is configured with an appropriate shape.

[0129] As described above, in the contact patch shape of tire 2 shown in Figure 5, the circumferential outer edge of the middle land portion 44m located between the shoulder circumferential groove 42s and the middle circumferential groove 42m does not have an inward convex shape like the circumferential outer edge of the middle land portion confirmed in a tire manufactured using a conventional mold shown in Figure 9, but rather has an outward bulge shape. The contact patch area is clearly increased, and tire 2 can make more sufficient contact with the road surface than tires manufactured using a conventional mold. Tire 2 can achieve further improvement in handling stability.

[0130] As mentioned above, in the contact pressure distribution of tire 2 shown in Fig. 6, the increase in contact pressure at the edge of the middle land portion 44 m is suppressed compared to the increase in contact pressure at the edge of the middle land portion confirmed in a tire manufactured with a conventional mold shown in Fig. 10. The local increase in contact pressure is clearly suppressed, and tire 2 can achieve further improvement in wear resistance.

[0131] An appropriate contact patch shape and contact pressure distribution can be obtained in this tire 2. This tire 2 can achieve improvements in steering stability and wear resistance.

[0132] 2, the double-headed arrow Wct indicates the distance from the first reference virtual intersection point BV1t to the second reference virtual intersection point BV2t. The double-headed arrow Xw1t indicates the distance from the first reference virtual intersection point BV1t to the reference junction point Tt. The double-headed arrow Xw2t indicates the distance from the second reference virtual intersection point BV2t to the reference junction point Tt.

[0133] In the tire 2, the position of the reference tangency point Tt, which is the tangency point between the curved land surface 46B and the reference plane TBL, is preferably determined based on the cross-sectional areas of the circumferential grooves 42 located on both sides of the curved land surface 46B. Specifically, when the groove cross-sectional area of ​​the first circumferential groove 42f is Sat and the groove cross-sectional area of ​​the second circumferential groove 42n is Sbt, it is preferable to set the distance Xw1t so as to satisfy the following formula (2), which is expressed using the distance Xw1t, the distance Wct, the groove cross-sectional area Sat, and the groove cross-sectional area Sbt. Sat / (Sat+Sbt)×100-10≦Xw1t / Wct×100≦Sat / (Sat+Sbt)×100+10...(2)

[0134] In this tire mold 56, the groove cross-sectional area Sat of the first circumferential groove 42f is smaller than the groove cross-sectional area Sbt of the second circumferential groove 42n, so the reference tangency point Tt is set on the side of the first reference boundary point BB1t. In the manufacture of this tire 2, the flow of unvulcanized rubber is promoted toward the first ridge 74f, which has a smaller cross-sectional area. In this tire 2, if the groove cross-sectional area Sat of the first circumferential groove 42f is larger than the groove cross-sectional area Sbt of the second circumferential groove 42n, the reference tangency point Tm is set on the side of the second reference boundary point BB2t. In this case, the flow of unvulcanized rubber is promoted toward the second ridge 74n.

[0135] In manufacturing this tire 2, the flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side are controlled in a well-balanced manner, so that a curved land surface 46B that reflects the shape of the curved land surface forming portion 76B is formed. In this tire 2, an appropriate contact patch shape and contact pressure distribution are obtained. This tire 2 can achieve improved steering stability and wear resistance.

[0136] In the tire 2, from the viewpoint of optimizing the contact patch shape and contact pressure distribution, the ratio (Xdt / St) of the distance Xdt from the reference virtual intersection point BVt to the reference boundary point BBt to the groove cross-sectional area St of the circumferential groove 42 is preferably 0.0008 or more, more preferably 0.0014 or more, and even more preferably 0.0020 or more. The ratio (Xdt / St) is preferably 0.0040 or less, more preferably 0.0034 or less, and even more preferably 0.0028 or less.

[0137] As described above, in the tire 2, the groove cross-sectional area Sat of the first circumferential groove 42f is smaller than the groove cross-sectional area Sbt of the second circumferential groove 42n. When the groove cross-sectional area Sat of the first circumferential groove 42f and the groove cross-sectional area Sbt of the second circumferential groove 42n are different, from the viewpoint of being able to control the flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side in a balanced manner and effectively suppressing turbulence in the flow of unvulcanized rubber, on the first circumferential groove 42f side, the ratio (Xd1t / Sat) of the distance Xd1t from the first reference imaginary intersection point BV1t to the first reference boundary point BB1t to the cross-sectional area Sat of the first circumferential groove 42f is preferably 0.0008 or more and 0.0040 or less, and on the second circumferential groove 42n side, the ratio (Xd2t / Sbt) of the distance Xd2t from the second reference imaginary intersection point BV2t to the second reference boundary point BB2t to the groove cross-sectional area Sbt of the second circumferential groove 42n is preferably 0.0008 or more and 0.0040 or less. In this case, the ratio (Xd1t / Sat) and the ratio (Xd2t / Sbt) are set to the same value.

[0138] As described above, the contour of the curved land surface 46B is represented by one or more arcs. In terms of optimizing the contact patch shape and contact pressure distribution of the tire 2, it is more preferable that the contour of the curved land surface 46B be represented by an arc that passes through the first reference boundary point BB1t and is tangent to the reference plane TBL at the reference tangent point Tt, and an arc that passes through the second reference boundary point BB2t and is tangent to the reference plane TBL at the reference tangent point Tt.

[0139] [When the circumferential groove 42 located next to the curved land surface 46B is the shoulder circumferential groove 42s] When the second circumferential groove 42n is the shoulder circumferential groove 42s located outermost in the axial direction, the second land surface 46n in Fig. 2 forms the shoulder land surface 46s of the tire 2. The outline of the shoulder land surface 46s will be described below with reference to Fig. 2.

[0140] In the tire 2, the second circumferential groove 42n is located between the shoulder land surface 46s and the curved land surface 46B. In the second circumferential groove 42n, the wall 50 on the curved land surface 46B side is the reference wall 50a, and the wall 50 on the shoulder land surface forming 46s side is the opposing wall 50b.

[0141] 2, the reference symbol Tst denotes the point of contact between the shoulder land surface 46s and the reference plane TBL. The point of contact Tst is the shoulder reference contact point.

[0142] In FIG. 2, the symbol BBst denotes the boundary between the opposing wall 50b of the second circumferential groove 42n and the shoulder land surface 46s. The boundary BBst is the shoulder reference boundary point. The two-dot chain line BLts is an imaginary line of the opposing wall 50b. The symbol BVst denotes an imaginary intersection represented by the intersection of the imaginary line BLst of the opposing wall 50b and the reference plane TBL. The imaginary intersection BVst is the shoulder reference imaginary intersection point. The double-headed arrow Xdst denotes the distance from the shoulder reference imaginary intersection point BVst to the shoulder reference boundary point BBst. This distance Xdst is measured along the imaginary line BLst of the opposing wall 50b. The double-headed arrow Xwst denotes the distance from the shoulder reference imaginary intersection point BVst to the shoulder reference tangent point Tst. The distance Xwst is represented by the length of the line segment connecting the shoulder reference imaginary intersection point BVst and the shoulder reference tangent point Tst.

[0143] In the tire 2, the contour of the shoulder land surface 46s from the shoulder reference boundary point BBst to the shoulder reference junction Tst is configured similarly to the contour of the curved land surface 46B from the second reference boundary point BB2t to the reference junction Tt. Specifically, the distance Xdst from the shoulder reference imaginary intersection BVst to the shoulder reference boundary point BBst is the same as the distance Xd2t from the second reference imaginary intersection BV2t to the second reference boundary point BB2t. The distance Xwst from the shoulder reference imaginary intersection BVst to the shoulder reference junction Tst is the same as the distance Xw2t from the second reference imaginary intersection BV2t to the reference junction Tt. The contour of the shoulder land surface 46s from the shoulder reference boundary point BBst to the shoulder reference junction Tst is expressed by an arc that passes through the shoulder reference boundary point BBst and is tangent to the reference plane TBL at the shoulder reference junction Tst, similar to the contour of the curved land surface 46B from the second reference boundary point BB2t to the reference junction Tt.

[0144] In the tire 2, the shoulder reference boundary point BBst is also the end of the shoulder land surface 46s on the second circumferential groove 42n side. As shown in Fig. 2 , the end BBst of the shoulder land surface 46s on the second circumferential groove 42n side is located radially inward of the reference plane TBL of the tread surface 22.

[0145] During the manufacture of the tire 2, the cap portion 26 is pressed against the ridge 74, causing the unvulcanized rubber of the cap portion 26 to flow toward the axially outer portion of the second ridge 74n, i.e., toward the portion forming the shoulder land portion 44s. In this tire 2, the contour of the shoulder land surface 46s is configured so that the end BBst of the shoulder land surface 46s is located inside the reference plane TBL of the tread surface 22. Because the volume of unvulcanized rubber flowing into the portion forming the shoulder land portion 44s is limited, disturbances are unlikely to occur in the flow of unvulcanized rubber pressed against the second ridge 74n. In this tire 2, the shoulder land surface 46s is formed in a shape that reflects the shape of the shoulder land surface-forming portion 76s. Disturbances in the inner surface shape of the tread 4 are also suppressed, so the inner surface of the tread 4 is configured with an appropriate shape.

[0146] As described above, in the contact patch shape of tire 2 shown in Fig. 5, the circumferential outer edge of the shoulder land portion 44s does not have an inward convex shape like the circumferential outer edge of the shoulder land portion confirmed in a tire manufactured using a conventional mold shown in Fig. 9, but has an outward bulge shape. The contact patch area is clearly increased, and tire 2 can make more sufficient contact with the road surface than tires manufactured using a conventional mold. This tire 2 can achieve further improvement in handling stability.

[0147] As mentioned above, in the contact pressure distribution of tire 2 shown in Fig. 6, the increase in contact pressure at the edge of the middle land portion 44 m is suppressed compared to the increase in contact pressure at the edge of the middle land portion confirmed in a tire manufactured with a conventional mold shown in Fig. 10. The local increase in contact pressure is clearly suppressed, and tire 2 can achieve further improvement in wear resistance.

[0148] [Second embodiment] Fig. 7 shows a cross section of a tread 94 of a tire 92 according to another embodiment of the present invention. Fig. 7 schematically shows the outline of a tread surface 96. In Fig. 7, the left-right direction is the radial direction of the tire 92, and the up-down direction is the axial direction of the tire 92. The direction perpendicular to the plane of the page is the circumferential direction of the tire 92.

[0149] The profile of the tread surface 96 shown in Fig. 7 is a modified example of the profile of the tread surface 22 shown in Fig. 2. Of the profile of the tread surface 96 shown in Fig. 7, the same parts as those of the profile of the tread surface 22 shown in Fig. 2 are denoted by the same reference numerals, and their description will be omitted.

[0150] Figure 8 shows a cross section of a tread ring 100 that forms part of the mold 98 used in manufacturing the tire 92 shown in Figure 7. Figure 8 schematically shows the outline of a tread forming surface 102 that shapes the tread surface 96. In Figure 8, the left-right direction is the radial direction of the tire 92, and the up-down direction is the axial direction of the tire 92. The direction perpendicular to the plane of the page is the circumferential direction of the tire 92.

[0151] The outline of the tread forming surface 102 shown in Fig. 8 is a modified example of the outline of the tread forming surface 64 shown in Fig. 4. Of the outline of the tread forming surface 102 shown in Fig. 8, the same parts as those of the outline of the tread forming surface 64 shown in Fig. 4 are given the same reference numerals, and their description will be omitted.

[0152] [Outline of curved land surface forming part 76B] First, the outline of the curved land surface forming portion 76B included in the tread forming surface 102 shown in Fig. 8 will be described. In this tread forming surface 102, the outline of the curved land surface forming portion 76B is also represented by one or more arcs. From the viewpoint of obtaining a more appropriate contact patch shape and contact pressure distribution, the outline of the curved land surface forming portion 76B in this tread forming surface 102 can be represented by the following four arcs.

[0153] In Figure 8, the symbol K1m denotes an arbitrary position on the imaginary line BL1m of the first reference side surface 80a of the first convex streak 74f between the first reference boundary point BB1m and the first reference imaginary intersection point BV1m. This position K1m is a vertical point (hereinafter referred to as the first vertical point). The double-headed arrow Xk1m denotes the distance from the first reference imaginary intersection point BV1m to the first vertical point K1m. This distance Xk1m is measured along the imaginary line BL1m of the first reference side surface 80a. In this tread forming surface 102, the arc that passes through the first vertical point K1m and is tangent to the reference forming surface FBL at the reference contact point Tm is the contact point side arc (hereinafter referred to as the first contact point side arc).

[0154] In FIG. 8, the symbol J1m is an arbitrary position on the reference forming surface FBL between the reference tangent point Tm and the first reference imaginary intersection point BV1m. This position J1m is a horizontal point (hereinafter referred to as the first horizontal point). The double-headed arrow Xj1m is the distance from the first reference imaginary intersection point V1m to the first horizontal point J1m. This distance Xj1m is represented by the length of the line segment connecting the first reference imaginary intersection point BV1m and the first horizontal point J1m. The symbol M1m is the intersection point between the normal to the reference forming surface FBL that passes through the first horizontal point J1m and the first tangent point side arc. This intersection point M1m is the middle boundary point (hereinafter referred to as the first middle boundary point). In this tread forming surface 102, the arc that passes through the first reference boundary point BB1m and is tangent to the first tangent point side arc at the first middle boundary point M1m is the boundary side arc (hereinafter referred to as the first boundary side arc).

[0155] In Figure 8, the symbol K2m denotes an arbitrary position on the imaginary line BL2m of the second reference side surface 80a of the second convex streak 74n between the second reference boundary point BB2m and the second reference imaginary intersection point BV2m. This position K2m is a vertical point (hereinafter referred to as the second vertical point). The double-headed arrow Xk2m denotes the distance from the second reference imaginary intersection point BV2m to the second vertical point K2m. This distance Yk2m is measured along the imaginary line BL2m of the second reference side surface 80a. In this tread forming surface 102, the arc that passes through the second vertical point K2m and is tangent to the reference forming surface FBL at the reference contact point Tm is the contact point side arc (hereinafter referred to as the second contact point side arc).

[0156] In FIG. 8, the symbol J2m denotes an arbitrary position on the reference forming surface FBL between the reference contact point Tm and the second reference imaginary intersection point BV2m. This position J2m is a horizontal extension (hereinafter referred to as the second horizontal point). The double-headed arrow Xj2m denotes the distance from the second reference imaginary intersection point V2m to the second horizontal point J2m. This distance Xj2m is expressed as the length of the line segment connecting the second reference imaginary intersection point BV2m and the second horizontal point J2m. The symbol M2m denotes the intersection point between the normal to the reference forming surface FBL passing through the second horizontal point J2m and the second contact point side arc. This intersection point M1m is the middle boundary point (hereinafter referred to as the second middle boundary point). In this tread forming surface 102, the arc that passes through the second reference boundary point BB2m and is tangent to the second contact point side arc at the second middle boundary point M2m is the boundary side arc (hereinafter referred to as the second boundary side arc).

[0157] In this mold 98, of the contours of the curved land surface forming portion 76B, the contour from the reference tangency point Tm to the first intermediate boundary point M1m is represented by a first tangency side arc. The contour from the first intermediate boundary point M1m to the first reference boundary point BB1m is represented by a first boundary side arc. The contour from the reference tangency point Tm to the second intermediate boundary point M2m is represented by a second tangency side arc. The contour from the second intermediate boundary point M2m to the second reference boundary point BB2m is represented by a second boundary side arc.

[0158] The flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side are also controlled in a well-balanced manner in this mold 98. Because disturbances in the flow of unvulcanized rubber are unlikely to occur, this mold 98 forms a curved land surface 46B that reflects the shape of the curved land surface forming portion 76B.

[0159] Although not shown, it has been confirmed that in the contact patch shape of a tire 92 manufactured using this mold 98, the circumferential outer edge of the middle land portion 44m does not have an inward convex shape but rather a shape that bulges outward, and in terms of the contact pressure distribution, it has been confirmed that the contact pressure difference within the middle land portion 44m is kept to about 45 kPa. According to this mold 98 and the manufacturing method for a tire 92 using this mold 98, the contact patch shape and contact pressure distribution of the tire 92 can be optimized, and the handling stability and wear resistance of the tire 92 can be improved.

[0160] In this mold 98, from the viewpoint of optimizing the contact patch shape and contact pressure distribution of the tire 92, the ratio (Xkm / Xdm) of the distance Xkm from the reference imaginary intersection point BVm to the vertical point Km to the distance Xdm from the reference imaginary point BVm to the reference boundary point BBm is preferably equal to or greater than 0.40, and more preferably equal to or greater than 0.45. The ratio (Xkm / Xdm) is preferably equal to or less than 0.60, and more preferably equal to or less than 0.55.

[0161] In this mold 98, from the viewpoint of optimizing the contact patch shape and contact pressure distribution of the tire 92, the ratio (Xjm / Xwm) of the distance Xjm from the reference virtual intersection BVm to the lateral point Jm to the distance Xwm from the reference virtual intersection BVm to the reference tangent point Tm is preferably equal to or greater than 0.40, and more preferably equal to or greater than 0.45. The ratio (Xjm / Xwm) is preferably equal to or less than 0.60, and more preferably equal to or less than 0.55.

[0162] In this mold 98, it is more preferable that the ratio (Xkm / Xdm) of the distance Xkm from the reference virtual intersection point BVm to the vertical point Km to the distance Xdm from the reference virtual intersection point BVm to the reference boundary point BBm is 0.40 or more and 0.60 or less, and that the ratio (Xjm / Xwm) of the distance Xjm from the reference virtual intersection point BVm to the distance Xwm from the reference virtual intersection point BVm to the reference junction point Tm is 0.40 or more and 0.60 or less.

[0163] In this mold 56, the cross-sectional area Sam of the first ridge 74f is smaller than the cross-sectional area Sbm of the second ridge 74n. When the cross-sectional area Sam of the first ridge 74f is different from the cross-sectional area Sbm of the second ridge 74n, from the viewpoint of being able to control the flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side in a balanced manner, effectively suppressing disturbances in the flow of unvulcanized rubber, and optimizing the contact patch shape and contact pressure distribution of the tire 92, it is preferable that the ratio (Xk1m / Xd1m) of the distance Xk1m from the first reference imaginary intersection point BV1m to the distance Xd1m from the first reference imaginary intersection point BV1m to the first reference boundary point BB1m be 0.40 or more and 0.60 or less, and that the ratio (Xk2m / Xd2m) of the distance Xk2m from the second reference imaginary intersection point BV2m to the distance Xd2m from the second reference imaginary intersection point BV2m to the second reference boundary point BB2m be 0.40 or more and 0.60 or less. In this case, the ratio (Xk1m / Xd1m) and the ratio (Xk2m / Xd1m) are set to the same value.

[0164] From a similar viewpoint, it is preferable that the ratio (Xj1m / Xw1m) of the distance Xj1m from the first reference virtual intersection BV1m to the distance Xw1m from the first reference virtual intersection BV1m to the reference junction Tm be 0.40 or more and 0.60 or less, and that the ratio (Xj2m / Xw2m) of the distance Xj2m from the second reference virtual intersection BV2m to the second junction J2m to the distance Xw2m from the second reference virtual intersection BV2m to the reference junction Tm be 0.40 or more and 0.60 or less. In this case, the ratio (Xj1m / Xw1m) and the ratio (Xj2m / Xw2m) are set to the same value.

[0165] [When the convex strip 74 located next to the curved land surface forming portion 76B is a shoulder convex strip 74s] When the second ridge 74n located next to the curved land surface forming portion 76B is a shoulder ridge 74s, the second land surface forming portion 76n in Figure 8 is a shoulder land surface forming portion 76s that forms the shoulder land surface 46s of the tire 92. Of the contours of the shoulder land surface forming portion 76s on the tread forming surface 102, the contour from the shoulder reference boundary point BBsm to the shoulder reference tangent point Tsm can be represented by two arcs from the viewpoint of obtaining a more appropriate contact patch shape and contact pressure distribution. Below, the contour of the shoulder land surface forming portion 76s from the shoulder reference boundary point BBsm to the shoulder reference tangent point Tsm will be described using Figure 8.

[0166] In Figure 8, the symbol Ksm denotes an arbitrary position on the imaginary line BLsm on the back surface 80b of the second convex streak 74n between the shoulder reference boundary point BBsm and the shoulder reference imaginary intersection point BVsm. This position Ksm is the shoulder vertical point. The double-headed arrow Xdkm denotes the distance from the shoulder reference imaginary intersection point BVsm to the shoulder vertical point Ksm. This distance Xdkm is measured along the imaginary line BLsm on the back surface 80b. In this tread forming surface 102, the arc that passes through the shoulder vertical point Ksm and is tangent to the reference forming surface FBL at the shoulder reference contact point Tsm is the shoulder contact point side arc.

[0167] In FIG. 8, the symbol Jsm denotes an arbitrary position on the reference forming surface FBL between the shoulder reference contact point Tsm and the shoulder reference virtual intersection point Vsm. This position Jsm is the shoulder lateral point. The double-headed arrow Xjsm denotes the distance from the shoulder reference virtual intersection point BVsm to the shoulder lateral point Jsm. This distance Xjsm is represented by the length of the line segment connecting the shoulder reference virtual intersection point BVsm and the shoulder lateral point Jsm. The symbol Msm denotes the intersection point between the normal to the reference forming surface FBL passing through the shoulder lateral point Jsm and the shoulder contact point side arc. This intersection point Msm is the shoulder mid-boundary point. In this tread forming surface 102, the arc that passes through the shoulder reference boundary point BBsm and is tangent to the shoulder contact point side arc at the shoulder mid-boundary point Msm is the shoulder boundary side arc.

[0168] In this mold 98, of the contour of the shoulder land surface forming portion 76s, the contour from the shoulder reference tangent point Tsm to the shoulder mid-boundary point Msm is represented by a shoulder tangent point-side arc, and the contour from the shoulder mid-boundary point Msm to the shoulder reference boundary point BBsm is represented by a shoulder boundary-side arc. The distance Xdsm from the shoulder reference imaginary intersection point BVsm to the shoulder reference boundary point BBsm on the back side surface 80b of the second convex rib 74n is the same as the distance Xd2m from the second reference imaginary intersection point BV2m to the second reference boundary point BB2m on the reference side surface 80a, i.e., the second reference side surface 80a, and the distance from the shoulder reference imaginary intersection point BVsm to the shoulder reference tangent point Tsm is the same as the distance Xw2m from the second reference imaginary intersection point BV2m to the reference tangent point Tm. Furthermore, the distance Xdkm from the shoulder reference virtual intersection point BVsm to the shoulder vertical point Ksm is the same as the distance Xk2m from the second reference virtual intersection point BV2m to the second vertical point K2m, and the distance Xjsm from the shoulder reference virtual intersection point BVsm to the shoulder horizontal point Jsm is the same as the distance Xj2m from the second reference virtual intersection point BV2m to the second horizontal point J2m.

[0169] In this mold 98 as well, the flow of unvulcanized rubber pressed against the second protrusion 74n is not easily disturbed, and therefore a shoulder land surface 46s is formed that reflects the shape of the shoulder land surface forming portion 76s.

[0170] Although not shown, it has been confirmed that in the contact patch shape of a tire 92 manufactured using this mold 98, the circumferential outer edge of the shoulder land portion 44s does not have an inwardly convex shape but rather has a shape that bulges outward, and in terms of contact pressure distribution, it has been confirmed that the contact pressure difference within the shoulder land portion 44s is kept to about 60 kPa. According to this mold 98 and the manufacturing method for a tire 92 using this mold 98, it is possible to optimize the contact patch shape and contact pressure distribution of the tire 92, thereby achieving improvements in the handling stability and wear resistance of the tire 92.

[0171] 7 is manufactured using the above-described mold 98 having the tread forming surface 102. Next, the contour of the tread surface 96 shaped by this tread forming surface 102 will be described.

[0172] [Contour of curved land surface 46B] First, the outline of the curved land surface 46B included in the tread surface 96 shown in Fig. 7 will be described. The outline of the curved land surface 46B in this tread surface 96 is also expressed by a plurality of circular arcs. From the viewpoint of obtaining a more appropriate contact patch shape and contact pressure distribution, the outline of the curved land surface 46B in this tread surface 96 can be expressed by the following four circular arcs.

[0173] In Figure 7, the symbol K1t denotes an arbitrary position on the imaginary line BL1t of the first reference wall 50a of the first circumferential groove 42f between the first reference boundary point BB1t and the first reference virtual intersection point BV1t. This position K1t is a vertical point (hereinafter referred to as the first vertical point). The double-headed arrow Xk1t denotes the distance from the first reference virtual intersection point BV1t to the first vertical point K1t. This distance Xk1t is represented by the length of the line segment connecting the first reference virtual intersection point BV1t and the first vertical point K1t. On this tread surface 96, the arc that passes through the first vertical point K1t and is tangent to the reference plane TBL at the reference contact point Tt is the contact point side arc (hereinafter referred to as the first contact point side arc).

[0174] In FIG. 7, the symbol J1t denotes an arbitrary position on the reference plane TBL between the reference tangent point Tt and the first reference imaginary intersection point BV1t. This position J1t is the horizontal extension (hereinafter referred to as the first horizontal point). The double-headed arrow Xj1t denotes the distance from the first reference imaginary intersection point BV1t to the first horizontal point J1t. This distance Xj1t is represented by the length of the line segment connecting the first reference imaginary intersection point BV1t and the first horizontal point J1t. The symbol M1t denotes the intersection point between the normal to the reference plane TBL passing through the first horizontal point J1t and the first tangent point side arc. This intersection point M1t is the middle boundary point (hereinafter referred to as the first middle boundary point). In this tread surface 96, the arc that passes through the first reference boundary point BB1t and is tangent to the first tangent point side arc at the first middle boundary point M1t is the boundary side arc (hereinafter referred to as the first boundary side arc).

[0175] In Fig. 7, the symbol K2t denotes an arbitrary position on the imaginary line BL2t of the second reference wall 50a of the second circumferential groove 42n between the second reference boundary point BB2t and the second reference imaginary intersection point BV2t. This position K2t is a vertical point (hereinafter referred to as the second vertical point). The double-headed arrow Xk2t denotes the distance from the second reference imaginary intersection point BV2t to the second vertical point K2t. This distance Xk2t is represented by the length of the line segment connecting the second reference imaginary intersection point BV2t and the second vertical point K2t. On this tread surface 96, the arc that passes through the second vertical point K2t and is tangent to the reference plane TBL at the reference contact point Tt is the contact point side arc (hereinafter referred to as the second contact point side arc).

[0176] In FIG. 7, the symbol J2t denotes an arbitrary position on the reference plane TBL between the reference tangent point Tt and the second reference imaginary intersection point BV2t. This position J2t is the lateral extension (hereinafter referred to as the second lateral point). The double-headed arrow Xj2t denotes the distance from the second reference imaginary intersection point BV2t to the second lateral point J2t. This distance Xj2t is represented by the length of the line segment connecting the second reference imaginary intersection point BV2t and the second lateral point J2t. The symbol M2t denotes the intersection point between the second tangent point side arc and a normal to the reference plane TBL that passes through the second lateral point J2t. This intersection point M2t is the middle boundary point (hereinafter referred to as the second middle boundary point). In this tread surface 96, the arc that passes through the second reference boundary point BB2t and is tangent to the second tangent point side arc at the second middle boundary point M2t is the boundary side arc (hereinafter referred to as the second boundary side arc).

[0177] In this tire 92, of the contours of the curved land surface 46B, the contour from the reference tangency point Tt to the first intermediate boundary point M1m is represented by a first tangency side arc. The contour from the first intermediate boundary point M1m to the first reference boundary point BB1t is represented by a first boundary side arc. The contour from the reference tangency point Tt to the second intermediate boundary point M2t is represented by a second tangency side arc. And the contour from the second intermediate boundary point M2m to the second reference boundary point BB2t is represented by a second boundary side arc.

[0178] In manufacturing this tire 92, the flow of unvulcanized rubber on the first ridge 74f side and the flow of unvulcanized rubber on the second ridge 74n side are controlled in a well-balanced manner, thereby forming a curved land surface 46B that reflects the shape of the curved land surface forming portion 76B. In this tire 92, an appropriate contact patch shape and contact pressure distribution are obtained. This tire 92 can achieve improved handling stability and wear resistance.

[0179] In the tire 92, from the viewpoint of optimizing the contact patch shape and contact pressure distribution, the ratio (Xkt / Xdt) of the distance Xkt from the reference imaginary intersection point BVt to the vertical point Kt to the distance Xdt from the reference imaginary point BVt to the reference boundary point BBt is preferably equal to or greater than 0.40, and more preferably equal to or greater than 0.45. The ratio (Xkt / Xdt) is preferably equal to or less than 0.60, and more preferably equal to or less than 0.55.

[0180] In the tire 92, from the viewpoint of optimizing the contact patch shape and contact pressure distribution, the ratio (Xjt / Xwt) of the distance Xjt from the reference virtual intersection BVt to the horizontal point Jt to the distance Xwt from the reference virtual intersection BVt to the reference tangent point Tt is preferably equal to or greater than 0.40, and more preferably equal to or greater than 0.45. The ratio (Xjt / Xwt) is preferably equal to or less than 0.60, and more preferably equal to or less than 0.55.

[0181] In this tire 92, it is more preferable that the ratio (Xkt / Xdt) of the distance Xkt from the reference virtual intersection point BVt to the vertical point Kt to the distance Xdt from the reference virtual intersection point BVt to the reference boundary point BBt is 0.40 or more and 0.60 or less, and that the ratio (Xjt / Xwt) of the distance Xjt from the reference virtual intersection point BVt to the horizontal point Jt to the distance Xwt from the reference virtual intersection point BVt to the reference tangent point Tt is 0.40 or more and 0.60 or less.

[0182] In this tire 92, the groove cross-sectional area Sat of the first circumferential groove 42f is smaller than the groove cross-sectional area Sbt of the second circumferential groove 42n. When the groove cross-sectional area Sat of the first circumferential groove 42f and the groove cross-sectional area Sbt of the second circumferential groove 42n are different, the flow of unvulcanized rubber on the first protrusion 74f side and the flow of unvulcanized rubber on the second protrusion 74n side can be controlled in a balanced manner, the occurrence of turbulence in the flow of unvulcanized rubber can be effectively suppressed, and the ground contact patch shape and ground contact pressure distribution of the tire 92 can be optimized. It is preferable that the ratio (Xk1t / Xd1t) of the distance Xk1t from the first reference imaginary point BV1t to the distance Xd1t from the first reference boundary point BB1t is 0.40 or more and 0.60 or less, and the ratio (Xk2t / Xd2t) of the distance Xk2t from the second reference imaginary point BV2t to the distance Xd2t from the second reference boundary point BB2t is 0.40 or more and 0.60 or less. In this case, the ratio (Xk1t / Xd1t) and the ratio (Xk2t / Xd1t) are set to the same value.

[0183] From a similar viewpoint, it is preferable that the ratio (Xj1t / Xw1t) of the distance Xj1t from the first reference virtual intersection BV1t to the first horizontal point J1t to the distance Xw1t from the first reference virtual intersection BV1t to the reference junction Tt be 0.40 or more and 0.60 or less, and the ratio (Xj2t / Xw2t) of the distance Xj2t from the second reference virtual intersection BV2t to the second horizontal point J2t to the distance Xw2t from the second reference virtual intersection BV2t to the reference junction Tt be 0.40 or more and 0.60 or less. In this case, the ratio (Xj1t / Xw1t) and the ratio (Xj2t / Xw2t) are set to the same value.

[0184] [When the circumferential groove 42 located next to the curved land surface 46B is the shoulder circumferential groove 42s] When the second circumferential groove 42n is the shoulder circumferential groove 42s located outermost in the axial direction, the second land surface 46n in Fig. 7 forms the shoulder land surface 46s of the tire 2. From the viewpoint of obtaining a more appropriate contact patch shape and contact pressure distribution, the contour of the shoulder land surface 46s on the tread surface 96 from the shoulder reference boundary point BBst to the shoulder reference tangent point Tst can be represented by the following two arcs. Below, the contour of the shoulder land surface 46s from the shoulder reference boundary point BBst to the shoulder reference tangent point Tst will be described using Fig. 7.

[0185] In Figure 7, the symbol Kst denotes an arbitrary position on the imaginary line BLst of the opposing wall 50b of the second circumferential groove 42n between the shoulder reference boundary point BBst and the shoulder reference imaginary intersection point BVst. This position Kst is the shoulder vertical point. The double-headed arrow Xdkt denotes the distance from the shoulder reference imaginary intersection point BVst to the shoulder vertical point Kst. This distance Xdkt is measured along the imaginary line BLst of the opposing wall 50b. In this tread surface 96, the arc that passes through the shoulder vertical point Kst and is tangent to the reference plane TBL at the shoulder reference contact point Tst is the shoulder contact point side arc.

[0186] In FIG. 7, the symbol Jst denotes an arbitrary position on the reference plane TBL between the shoulder reference tangent point Tst and the shoulder reference imaginary intersection point Vst. This position Jst is the shoulder lateral point. The double-headed arrow Xjst denotes the distance from the shoulder reference imaginary intersection point BVst to the shoulder lateral point Jst. This distance Xjst is represented by the length of the line connecting the shoulder reference imaginary intersection point BVst and the shoulder lateral point Jst. The symbol Mst denotes the intersection point between the normal to the reference plane TBL passing through the shoulder lateral point Jst and the shoulder tangent point side arc. This intersection point Mst is the shoulder mid-boundary point. In this tread surface 96, the arc that passes through the shoulder reference boundary point BBst and is tangent to the shoulder tangent point side arc at the shoulder mid-boundary point Mst is the shoulder boundary side arc.

[0187] In the tire 92, the contour of the shoulder land surface 46s from the shoulder reference tangent point Tst to the shoulder mid-boundary point Mst is represented by a shoulder tangent point-side arc, and the contour from the shoulder mid-boundary point Mst to the shoulder reference tangent point BBst is represented by a shoulder boundary-side arc. The distance Xdst from the shoulder reference imaginary intersection point BVst to the shoulder reference tangent point BBst on the opposing wall 50b of the second circumferential groove 42n is the same as the distance Xd2t from the second reference imaginary intersection point BV2t to the second reference tangent point BB2t on the reference wall 50a, i.e., the second reference wall 50a, and the distance from the shoulder reference imaginary intersection point BVst to the shoulder reference tangent point Tst is the same as the distance Xw2t from the second reference imaginary intersection point BV2t to the reference tangent point Tt. Furthermore, the distance Xdkt from the shoulder reference imaginary intersection point BVst to the shoulder vertical point Kst is the same as the distance Xk2t from the second reference imaginary intersection point BV2t to the second vertical point K2t, and the distance Xjst from the shoulder reference imaginary intersection point BVst to the shoulder horizontal point Jst is the same as the distance Xj2t from the second reference imaginary intersection point BV2t to the second horizontal point J2t.

[0188] In manufacturing this tire 92, the flow of unvulcanized rubber pressed against the second ridge 74n is not easily disturbed, so the shoulder land surface 46s is formed to reflect the shape of the shoulder land surface forming portion 76s. In this tire 92, an appropriate contact patch shape and contact pressure distribution are obtained. This tire 92 can achieve improved handling stability and wear resistance.

[0189] As explained above, the tire mold and tire manufacturing method of the present invention can optimize the tire contact patch shape and contact pressure distribution. Furthermore, the tire obtained by this tire mold and tire manufacturing method can obtain an appropriate contact patch shape and contact pressure distribution, thereby improving steering stability and wear resistance. The present invention is directed to a tire having a groove width of 9 mm or more and a groove width of 45 mm or more. 2 When circumferential grooves having the above-mentioned large cross-sectional areas are cut into the tread, excellent effects are achieved.

[0190] As mentioned above, the convex ridges on the tread forming surface press the cap portion. 2 A significant effect is achieved when a circumferential groove having a large cross-sectional area as described above is cut into the cap portion and the Mooney viscosity of the unvulcanized rubber for the cap portion is 80 or more. The Mooney viscosity is expressed as Mooney viscosity ML 1+4 (100°C) and is measured in accordance with JIS K6300-1. [Industrial Applicability]

[0191] The above-described techniques for optimizing the tire contact patch shape and contact pressure distribution can be applied to various types of tires. [Explanation of symbols]

[0192] 2, 92... Tires 2r raw tires 4, 94... tread 14. Cord reinforcement layer 22 Tread surface 24, 96... Base 26 Cap part 34 Belt 36...Band 40...Groove 42, 42s, 42m, 42D, 42T...Circumferential groove 44, 44s, 44m...Land 46, 46s, 46m, 46B, 46f, 46n...land surface 48 Bottom of large circumferential groove 42D 50, 50a, 50b...wall of large circumferential groove 42D 52 Bottom of small circumferential groove 42T 54, 54a, 54b...wall of small circumferential groove 42T 56, 98... Mold 58, 100... Tread ring 64, 102... Tread forming surface 72 Cavity surface 74, 74D, 74T...Convex strip 76, 76B, 76f, 76n... land surface forming part 78. Top surface of large convex strip 74D 80, 80a, 80b... Side of large convex rib 74D 82 ···Top surface of small convex strip 74T 84, 84a, 84b...Side of small convex strip 74T

Claims

1. A mold for use in manufacturing a tire, comprising a tread having a tread surface that comes into contact with a road surface, at least three land portions being formed in the tread by cutting at least two circumferential grooves into the tread, and the tread surface including at least three land surfaces that are outer surfaces of the at least three land portions, A tread forming surface is provided to define the tread surface; The tread forming surface includes a convex stripe that forms the circumferential groove and a land surface forming portion that forms the land surface, a surface having a contour represented by at least one circular arc, the surface being in contact with three of the land surface forming portions arranged on either side of the protrusion in the axial direction, the surface being a reference forming surface of the tread forming surface; Among the three land surface forming portions, a land surface forming portion located between two of the convex stripes is a curved land surface forming portion, The convex strip has a reference side surface which is a side surface on the land surface forming portion side, and a back side surface which is a side surface located on the back side of the reference side surface, A tangent point between the curved land surface forming portion and the reference forming surface is a reference tangent point, A boundary between the reference side surface and the curved land surface forming portion is a reference boundary point, an intersection point between a virtual line of the reference side surface extending from the reference boundary point toward the reference forming surface and the reference forming surface is a reference virtual intersection point; The contour of the curved land surface forming portion is represented by one or more circular arcs, The reference boundary point is located inside the reference forming surface, When one ridge has a small cross-sectional area and the other ridge has a large cross-sectional area, a distance from the reference virtual intersection point to the reference boundary point on one convex stripe side is short, and a distance from the reference virtual intersection point to the reference boundary point on the other convex stripe side is long; When a distance from one of the reference virtual intersections to the reference junction is Xw1m, a distance from one of the reference virtual intersections to the other of the reference virtual intersections is Wcm, a cross-sectional area of ​​one of the convex ridges is Sam, and a cross-sectional area of ​​the other of the convex ridges is Sbm, the distance Xw1m from one of the reference virtual intersections to the reference junction is set so as to satisfy the following formula (1): Tire mould. Sam / (Sam+Sbm)×100-10≦Xw1m / Wcm×100≦Sam / (Sam+Sbm)×100+10...(1)

2. a ratio of a distance from the reference virtual intersection point to the reference boundary point to a cross-sectional area of ​​the convex strip is 0.0008 or more and 0.0040 or less; 2. The tire mold of claim 1.

3. Among the contours of the curved land surface forming portion, a contour from the reference junction to the reference boundary point is represented by an arc that passes through the reference boundary point and is tangent to the reference forming surface at the reference junction. A tire mold according to claim 1 or 2.

4. Among the land surface forming portions included in the tread forming surface, a land surface forming portion located on an outer side in the axial direction is a shoulder land surface forming portion, Among the three land surface forming portions, a land surface forming portion located next to the curved land surface forming portion is the shoulder land surface forming portion, of the convex strip located between the shoulder land surface forming portion and the curved land surface forming portion, a side surface on the curved land surface forming portion side is the reference side surface, and a side surface on the shoulder land surface forming portion side is the back side surface, a contact point between the shoulder land surface forming portion and the reference forming surface is a shoulder reference contact point; A boundary between the back side surface and the shoulder land surface forming portion is a shoulder reference boundary point, an intersection point between a virtual line of the back side surface extending from the shoulder reference boundary point toward the reference forming surface and the reference forming surface is a shoulder reference virtual intersection point; a distance from the shoulder reference virtual intersection point to the shoulder reference boundary point on the back side surface is the same as a distance from the reference virtual intersection point to the reference boundary point on the reference side surface; a distance from the shoulder reference virtual intersection to the shoulder reference junction is the same as a distance from the reference virtual intersection to the reference junction; Among the contours of the shoulder land surface forming portion, a contour from the shoulder reference junction to the shoulder reference boundary point is represented by an arc that passes through the shoulder reference boundary point and is tangent to the reference forming surface at the shoulder reference junction. The tire mold of claim 3.

5. An arbitrary position on the virtual line of the reference side surface between the reference boundary point and the reference virtual intersection point is a vertical point; a circular arc that passes through the vertical point and is tangent to the reference forming surface at the reference tangent point is a tangent point side circular arc; Any position on the reference forming surface between the reference tangent point and the reference virtual intersection point is a horizontal point; an intersection point between a normal line to the reference forming surface passing through the horizontal point and the contact point side arc is an intermediate boundary point; a boundary-side arc is a circular arc that passes through the reference boundary point and is tangent to the tangent point-side arc at the intermediate boundary point; Among the contours of the curved land surface forming portion, a contour from the reference tangency point to the intermediate boundary point is represented by the tangency side arc, and a contour from the intermediate boundary point to the reference boundary point is represented by the boundary side arc. A tire mold according to claim 1 or 2.

6. a ratio of a distance from the reference virtual intersection point to the vertical point to a distance from the reference virtual intersection point to the reference boundary point is 0.40 or more and 0.60 or less; a ratio of a distance from the reference virtual intersection to the horizontal point to a distance from the reference virtual intersection to the reference tangent point is 0.40 or more and 0.60 or less; The tire mold of claim 5.

7. Among the land surface forming portions included in the tread forming surface, a land surface forming portion located on an outer side in the axial direction is a shoulder land surface forming portion, Among the three land surface forming portions, a land surface forming portion located next to the curved land surface forming portion is the shoulder land surface forming portion, of the convex strip located between the shoulder land surface forming portion and the curved land surface forming portion, a side surface on the curved land surface forming portion side is the reference side surface, and a side surface on the shoulder land surface forming portion side is the back side surface, a contact point between the shoulder land surface forming portion and the reference forming surface is a shoulder reference contact point; A boundary between the back side surface and the shoulder land surface forming portion is a shoulder reference boundary point, an intersection point between a virtual line of the back side surface extending from the shoulder reference boundary point toward the reference forming surface and the reference forming surface is a shoulder reference virtual intersection point; a distance from the shoulder reference virtual intersection point to the shoulder reference boundary point on the back side surface is the same as a distance from the reference virtual intersection point to the reference boundary point on the reference side surface; a distance from the shoulder reference virtual intersection to the shoulder reference junction is the same as a distance from the reference virtual intersection to the reference junction; an arbitrary position on the imaginary line of the back surface between the shoulder reference boundary point and the shoulder reference imaginary intersection point is a shoulder vertical point; a circular arc that passes through the shoulder vertical point and is tangent to the reference forming surface at the shoulder reference contact point is a shoulder contact point side circular arc, an arbitrary position on the reference forming surface between the shoulder reference contact point and the shoulder reference virtual intersection point is a shoulder lateral point; an intersection point between a normal line to the reference forming surface passing through the shoulder horizontal point and the shoulder contact point side circular arc is a shoulder intermediate boundary point; a shoulder boundary side arc is a circular arc that passes through the shoulder reference boundary point and is tangent to the shoulder contact point side circular arc at the shoulder intermediate boundary point; Among the contours of the shoulder land surface forming portion, a contour from the shoulder reference junction to the shoulder mid-boundary point is represented by the shoulder junction side arc, and a contour from the shoulder mid-boundary point to the shoulder reference boundary point is represented by the shoulder boundary side arc, A distance from the shoulder reference virtual intersection point to the shoulder vertical point is the same as a distance from the reference virtual intersection point to the vertical point, The distance from the shoulder reference virtual intersection to the shoulder lateral point is the same as the distance from the reference virtual intersection to the lateral point. A tire mold according to claim 5 or 6.

8. The tread has a cap portion including the tread surface, The unvulcanized rubber for the cap portion has a Mooney viscosity of 80 or more. A tire mold according to any one of claims 1 to 7.

9. 9. A method for manufacturing a tire mold comprising the steps of: pressurizing and heating a green tire using the tire mold according to claim 1 ; A method for manufacturing tires.

10. A tire comprising a tread having a tread surface that comes into contact with a road surface, at least three land portions being formed in the tread by cutting at least two circumferential grooves in the tread, and the tread surface including at least two circumferential grooves and at least three land surfaces that are outer surfaces of the at least three land portions, Three surfaces that have a contour represented by at least one circular arc and are in contact with the land surface and are arranged on either side of the circumferential groove in the axial direction are reference surfaces of the tread surface, Among the three land surfaces, a land surface located between two of the circumferential grooves is a curved land surface, The circumferential groove includes a reference wall that is a wall on the curved land surface side and an opposing wall that is a wall opposing the reference wall, A tangent point between the curved land surface and the reference surface is a reference tangent point, The boundary between the reference wall and the curved land surface is a reference boundary point, an intersection point between a virtual line of the reference wall extending from the reference boundary point toward the reference surface and the reference surface is a reference virtual intersection point; The contour of the curved land surface is represented by one or more circular arcs; The reference boundary point is located inside the reference plane, When one circumferential groove has a small groove cross-sectional area and the other circumferential groove has a large groove cross-sectional area, A distance from the reference virtual intersection point to the reference boundary point on one circumferential groove side is short, and a distance from the reference virtual intersection point to the reference boundary point on the other circumferential groove side is long, When a distance from one of the reference virtual intersections to the reference junction is Xw1t, a distance from one of the reference virtual intersections to the other of the reference virtual intersections is Wct, a groove cross-sectional area of ​​one of the circumferential grooves is Sat, and a groove cross-sectional area of ​​the other of the circumferential grooves is Sbt, the distance Xw1t from one of the reference virtual intersections to the reference junction is set so as to satisfy the following formula (2): tire. Sat / (Sat+Sbt)×100-10≦Xw1t / Wct×100≦Sat / (Sat+Sbt)×100+10...(2)

Images