pneumatic tires

Abstract

To provide a pneumatic tire which can improve rim fitting properties and also improve operation stability.SOLUTION: A pneumatic tire 1 comprises: a tread 10; a side wall 20; and a bead part 30. The bead part 30 includes: a bead base surface 34 which extends along a first linear line L1 slanted to a tire radial direction outer side toward a tire axial direction outer side at a tire radial direction inner end of the bead part 30 on the external surface when viewed in a tire meridian cross section; a bead back face 35 which extends in the tire radial direction outer side at the tire axial direction outer end of the bead part 30, and extends along a second linear line L2 in which a tire radial direction inner end is along the tire radial direction; and a bead heel surface 36 which extends along a third linear line L3 further slanted to the tire radial direction outer side toward the tire axial direction outer side than the first linear line L1 between the tire axial direction outer end of the bead base surface 34 and the tire radial direction inner end of the bead back face 35.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a pneumatic tire in which a heel cut portion is formed in the heel of the bead portion by chamfering the cross section in a linear manner, while the base surface of the bead portion is configured with a two-stage taper consisting of a heel side portion and a toe side portion that have different angles relative to the tire axial direction, and the inclination angle of the toe side portion relative to the tire axial direction is larger than the inclination angle of the heel side portion (similar to Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-209032 [Patent Document 2] International Publication No. 2014 / 126098 Summary of the Invention [Problem to be solved by the invention]

[0004] In the pneumatic tires of Patent Documents 1 and 2, the bead base surface is configured with a two-stage taper in which the inclination angle of the toe side portion is greater than that of the heel side portion, and coupled with the chamfering formed on the bead heel, which is the axially outer and inner diameter side portion of the bead portion, the bead portion tends to collapse axially outward when assembled to the rim. As a result, the fitting pressure of the bead base surface decreases while the fitting pressure of the bead back surface tends to increase, leaving room for improvement in rim fitting.

[0005] An object of the present invention is to provide a pneumatic tire that can improve rim fitting performance and handling stability. [Means for solving the problem]

[0006] The present invention provides The tire has a tread, a sidewall extending radially inward from an axial end of the tread, and a bead portion continuing to the radially inward end of the sidewall, The bead portion has an outer surface in a meridian cross section. a bead base surface extending along a first straight line inclined radially outward toward the tire axially outer side at an inner end of the bead portion in the tire radial direction; a bead back surface that extends radially outward in the tire radial direction at an axially outer end of the bead portion and has an inner end in the tire radial direction extending along a second straight line along the tire radial direction; a bead heel surface extending along a third straight line inclined further outward in the tire radial direction than the first straight line toward the tire axially outer side between an outer end of the bead base surface in the tire axial direction and an inner end of the bead back surface in the tire radial direction; With And, The third straight line is geometrically defined as a straight line connecting both end points of an imaginary arc that tangently connects the first straight line and the second straight line with a curvature radius of more than 3 mm and less than 8 mm in a meridian cross section. , provides pneumatic tires.

[0007] According to the present invention, the bead base surface is configured with a single inclined surface (sometimes referred to as a single-step taper), which prevents the bead portion from tilting axially outward when assembled to the rim, compared to when the bead base surface has an additional inclined surface whose inclination angle toward the tire radially inward increases toward the tire axially inward (sometimes referred to as a two-step taper).As a result, when assembled to the rim, the fitting pressure at the bead back surface is reduced, while the fitting pressure at the bead base surface is increased, compared to when the bead base surface is two-step tapered.

[0008] Furthermore, because the bead heel surface is configured as a chamfer that linearly connects the bead base surface and the bead back surface, interference of the bead heel surface with the rim heel of the genuine rim is suppressed when the rim is assembled. As a result, the bead portion can be fitted to the rim seat of the genuine rim at the correct axial position, which prevents the bead portion from collapsing axially outward due to insufficient fitting, and also suppresses an increase in fitting pressure at the bead back surface.

[0009] Therefore, when a load is applied, the bead base surface with increased fitting pressure makes it easier to maintain fitting with the rim seat of the regular rim, improving rim fitting, while the bead back surface with reduced fitting pressure makes it easier for the sidewall to flex and deform, improving handling stability. Furthermore, the third straight line is geometrically defined as a straight line connecting the end points of an imaginary arc that tangentially connects the first and second straight lines with each other at a radius of curvature greater than 3 mm and less than 8 mm in a meridian cross section. As a result, the bead heel surface is formed with an appropriate size, which makes it easier for the bead heel surface to abut against the rim heel of a standard rim when the pneumatic tire is mounted on a standard rim and inflated to the specified internal pressure, ensuring rim fit. If the curvature radius of the imaginary arc is 3 mm or less, the bead heel surface will interfere with the rim heel during rim mounting, making it difficult to fit the tire to the appropriate axial position. On the other hand, if the curvature radius of the imaginary arc is 8 mm or more, it will be difficult for the bead heel surface to abut against the rim heel even after inflation during rim mounting, making it easier for rim fit to deteriorate.

[0010] The inclination angle of the first straight line with respect to the tire axial direction may be equal to or greater than 5° and equal to or less than 15°.

[0011] According to this configuration, the bead base surface is moderately inclined, which increases the mating pressure at the bead base surface while suppressing an increase in the mating pressure at the bead back surface. If the inclination angle of the first straight line is less than 5°, the sidewall will deform excessively due to insufficient mating pressure at the bead back surface, which is likely to lead to a decrease in handling stability. On the other hand, if the inclination angle of the first straight line is more than 15°, the excessive mating pressure at the bead back surface will hinder the sidewall from bending, which is likely to lead to a decrease in the load support performance of the sidewall.

[0012] In the meridian section, an intersection point between the first straight line and the second straight line is defined as a first intersection point; an intersection of the first straight line and the third straight line is defined as a second intersection; When the intersection of the second line and the third line is defined as a third intersection, The bead heel surface may have a radial dimension, which is the dimension in the tire radial direction between the first intersection and the third intersection, that is equal to or greater than an axial dimension, which is the dimension in the tire axial direction between the first intersection and the second intersection, and less than twice the axial dimension.

[0013] According to this configuration, the bead heel surface is configured to be long in the tire radial direction, making it easier to secure the bead base surface and suppress the bead portion from collapsing axially outward. If the radial dimension of the bead heel surface is less than the axial dimension, it is likely to be insufficient to suppress interference of the bead heel with the rim seat of a standard rim when assembled to the rim. On the other hand, if the radial dimension of the bead heel surface is more than twice the axial dimension, the bead back surface becomes excessively small, causing the fitting pressure to be concentrated locally on the bead back surface, hindering flexural deformation of the sidewall.

[0014] A bead core is embedded in the bead portion, In the meridian cross section, the bead heel surface is located axially outward of a fourth straight line extending in the tire radial direction at a position spaced axially inward from an axially outer end of the bead core by a predetermined length, The predetermined length may be 2 mm, or may be 30% of the axial dimension of the bead core of the tire.

[0015] This configuration prevents the bead heel surface from excessively intruding axially inward in the radially inner region of the bead core, making it easier to ensure a bead base surface on the radially inner side of the bead portion, and preventing the bead portion from collapsing axially outward.

[0016] The bead portion is provided in a pair, the pair of bead portions are positioned at a distance from each other so that the width between the outer surfaces in the axial direction of the tire in an unassembled state is wider than the rim width of a corresponding regular rim, Each of the pair of bead portions has a recess formed on the back surface of the bead in an unrim-assembled state, the recess being recessed axially inward of an axially outer end of the bead heel surface, When assembled to the rim, the bead back surface may be in close contact with substantially the entire surface of a radial portion of the rim flange of the regular rim that extends parallel to the tire radial direction.

[0017] According to this configuration, a recess is formed in the bead back surface, so that in the unassembled state, the inner diameter side portion of the bead back surface, located on the inner diameter side from the deepest part of the recess, is inclined radially inward and axially outward in the tire. In the rim-assembled state where the pair of bead portions are brought close to the rim width of a standard rim, the inner diameter side portion is likely to bend axially inward from the periphery of the deepest part of the recess and generally follow the tire radial direction. In other words, in the rim-assembled state, the recess is eliminated and the bead back surface is likely to come into close contact with almost the entire radial portion of the rim flange, thereby increasing the contact area.

[0018] In this way, when the tire is assembled to the rim and no load is applied, surface pressure acts over almost the entire surface of the bead back surface that is in close contact with the radial portion of the rim flange, so the load borne by the entire bead back surface is distributed more evenly than when surface pressure acts only on a portion of the bead back surface.In other words, compared to when high surface pressure acts locally on the bead back surface, there is more room for compression to allow the bead back surface to elastically deform.

[0019] Therefore, when a load or lateral force is applied, the bead back surface can be further compressed by the amount of the excess compression. In this case, the sidewall can deform in the vicinity of the bead portion due to the further compression of the bead back surface, and the sidewall can be deformed so that it bends overall from the bead portion side to the tread side. This improves the efficiency of load support at the sidewall, thereby improving handling stability.

[0020] The recess may have an axial depth of less than 1.0 mm.

[0021] According to this configuration, the inner diameter side portion is moderately inclined axially outward when the tire is not mounted to the rim, so when the tire is mounted to the rim, it is easily bent axially inward to eliminate the axially outward inclination and easily align with the radial portion of the rim flange. If the recess depth is 1.0 mm or more, the inner diameter side portion is easily inclined axially outward excessively when the tire is not mounted to the rim, so it is difficult to eliminate the axially outward inclination even when the tire is bent axially inward when mounted to the rim. In this case, the recess is difficult to eliminate when the tire is mounted to the rim, making it difficult to abut the back surface of the bead over substantially the entire radial portion of the rim flange.

[0024] At least a portion of the bead heel surface is formed by rim strip rubber, and may have vent hole traces.

[0025] According to this configuration, the rubber flow around the bead heel surface during vulcanization molding is improved, so that defects such as bare spots caused by poor rubber flow during vulcanization molding are suppressed while forming a linear bead heel surface on the outer surface of the bead portion. [Effects of the Invention]

[0026] According to the present invention, it is possible to improve rim fitting and steering stability. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a meridian cross-sectional view of a pneumatic tire according to one embodiment of the present invention. [Figure 2] A meridian cross section of the bead area of ​​a pneumatic tire before it is mounted on a rim. [Figure 3] An enlarged view of the bead heel surface area in Figure 2. [Figure 4] FIG. 4 is a front view of the bead heel surface as viewed from arrow A in FIG. 3. [Figure 5] 1 is a meridian cross-sectional view of the vicinity of a bead portion of a pneumatic tire assembled to a rim. [Figure 6] 6 is a graph showing fitting pressure on the outer surface of the bead portion during inflation. [Figure 7] 1 is a meridian cross-sectional view of the periphery of a bead portion of a pneumatic tire according to Comparative Example 1 in a rim-assembled state. [Figure 8] FIG. 10 is a meridian cross-sectional view of the periphery of a bead portion of a pneumatic tire according to Comparative Example 2 in a rim-assembled state. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following description is essentially merely exemplary and is not intended to limit the present invention, its applications, or its uses. The drawings are schematic, and the ratios of dimensions, etc., may differ from those of the actual objects.

[0029] 1 is a meridian cross-sectional view of a pneumatic tire 1 according to one embodiment of the present invention, showing only one side with respect to a tire equator line CL. The pneumatic tire 1 includes a tread 10, a pair of sidewalls 20 extending radially inward from both axial ends of the tread 10, and a pair of bead portions 30 respectively continuing to the radially inward sides of the pair of sidewalls 20.

[0030] A bead core 31 and a bead filler 32 connected to the bead core on the radially outer side of the tire are embedded in the bead portion 30. The bead core 31 is configured by covering an annular bundle formed by winding a bead wire made of steel wire multiple times with rubber. The cross-sectional shape of the bead core 31 is formed into a polygonal shape so that the bead core has a bead core radially outer end surface 31a extending in the tire axial direction at the end on the radially outer side of the tire. In this embodiment, the height Hb of the bead core radially outer end surface 31a in the tire radial direction based on the nominal rim diameter (specified in JIS 4102) NR (also called reference rim diameter) is 6.7 mm.

[0031] The bead filler 32 is made of hard rubber extending in a ring shape along the radially outer end surface 31a of the bead core, and its cross-sectional shape in the meridian direction is formed into a triangular shape that narrows in the axial direction of the tire toward the radially outer side of the tire.

[0032] A carcass ply 2 is laid across the tread 10 and sidewall 20 between a pair of bead cores 31. The carcass ply 2 is folded back from the inner surface of the tire to the outer surface of the tire around the bead cores 31. An inner liner 3 for maintaining air pressure is provided on the inner surface of the carcass ply 2.

[0033] In the tread 10, a belt layer 11 and a belt reinforcing layer 12 are laminated in this order on the tire radially outer side of the carcass ply 2. In this embodiment, the belt layer 11 is composed of two layers. A tread rubber 13 is laminated on the tire radially outer side of the belt reinforcing layer 12. The tread rubber 13 forms the outer surface of the pneumatic tire 1 in the tire radial direction.

[0034] A tire side rubber 21 is arranged axially outward of the carcass ply 2, spanning the sidewall 20 and the bead portion 30. The tire side rubber 21 has a sidewall rubber 21a extending radially inward from the axial end of the tread rubber 13, and a rim strip rubber 21b connected to the inner diameter end and extending further radially inward. The tire side rubber 21 forms the outer surface of the pneumatic tire 1 in the axial direction.

[0035] The sidewall rubber 21a constitutes the majority of the sidewall 20. The rim strip rubber 21b is provided corresponding to at least the portion of the tire side rubber 21 that abuts against the rim flange 53 when the tire is assembled to a corresponding regular rim 50 (see FIG. 2) (referred to as a rim-assembled state). A rubber with superior abrasion resistance compared to the sidewall rubber 21a is used for the rim strip rubber 21b.

[0036] A rim protector 4 that protrudes axially outward is formed on the tire side rubber 21. The rim protector 4 is located radially inward of the tire's maximum width position Z. The maximum width position Z is the position where the profile line of the outer surface of the sidewall 20 is farthest from the tire equator line CL in the tire axial direction. In other words, the tire side rubber 21 gradually increases in thickness from the maximum width position Z toward the rim protector 4, and gradually decreases in thickness from the rim protector 4 toward the tire's radially inward direction.

[0037] The rim protector 4 is bent axially inward from an end portion extending radially inward from the maximum width position Z, and has an apex 4a where it is thickest. The apex 4a is located at a height H3 radially outward from the nominal rim diameter NR. The height H3 of the apex 4a is located radially outward from the rim flange 53 of the corresponding genuine rim 50 when assembled to the rim.

[0038] In this specification, the portion located on the outer diameter side of the tip 32a of the bead filler 32 in the tire radial direction is referred to as the sidewall 20, and the portion located on the inner diameter side is referred to as the bead portion 30. The rim protector 4 is located in the bead portion 30. In this specification, the thickness of the tire side rubber 21 is defined as the direction perpendicular to the outer surface of the carcass ply 2.

[0039] 2 shows an enlarged view of the periphery of the bead portion 30 when not assembled to a genuine rim 50 (referred to as an unassembled state), along with the periphery of the corresponding rim flange 53 of the genuine rim 50. The genuine rim 50 has a rim seat 51 extending axially outwardly of the tire, a rim heel 52 curved in an arc from the axially outer end of this rim to the radially outer side of the tire, and a rim flange 53 extending radially outwardly from the radially outer end of this rim seat 51.

[0040] The rim seat 51 is inclined radially outward in the tire direction toward the outside in the tire axial direction, and the inclination angle with respect to a line parallel to the tire axis is A0. The rim flange 53 has a flange radial portion 53a that extends radially outward in the tire direction from the rim heel 52 parallel to the tire radial direction, and a flange curved portion 53b that is continuous with the outer end in the tire radial direction and curves in an arc outward in the tire axial direction.

[0041] The outer surface of the rim heel 52, which is located on the side where the pneumatic tire 1 is fitted, extends in an arc shape with a curvature radius of R11 centered at a curvature center O11 located closer to the pneumatic tire 1 than the outer surface. A pair of flange radial portions 53a are arranged in the tire axial direction, separated by the rim width W0. The flange radial portions 53a extend from the nominal rim diameter NR outward in the tire radial direction to a height of H11. The outer surface of the flange curved portion 53b, which is located on the side where the pneumatic tire 1 is fitted, extends in an arc shape with a curvature radius of R12 centered at a curvature center O12 located on the outer surface side of the tire.

[0042] The genuine rim 50 is a rim defined for each tire by a standard system including the standard on which the tire is based, such as a "standard rim" in the case of JATMA, or a "measuring rim" in the cases of TRA and ETRTO.

[0043] The regular rim 50 according to this embodiment conforms to the flange symbol J of a 5° deep rim specified by JATMA, with the inclination angle A0 of the rim seat 51 being 5°, the radius of curvature R11 of the rim heel 52 being 6.5 mm, the height H11 of the flange radial portion 53a being 8 mm, and the radius of curvature R12 of the flange curved portion 53b being 9.5 mm. Furthermore, the angle between the rim seat 51 and the flange radial portion 53a of the regular rim 50 according to this embodiment is 95°.

[0044] The bead portion 30 has, on its outer surface in the meridian direction, a bead base surface 34 extending in the tire axial direction at its radially inner end, a bead back surface 35 extending radially outward at its axially outer end and continuing to the rim protector 4, and a bead heel surface 36 connecting the axially outer end of the bead base surface 34 and the radially inner end of the bead back surface 35 in a chamfered manner.

[0045] In an unrim-mounted state, the bead base surface 34 extends along a first straight line L1 that is inclined radially outward toward the tire axially outward. The inclination angle of the first straight line L1 with respect to a line parallel to the tire axis is A1. That is, the bead base surface 34 is composed of a single straight line portion. Specifically, the inclination angle A1 is larger than the inclination angle A0 of the rim seat 51. Preferably, the inclination angle A1 is 5° or greater and 15° or less. More preferably, the difference between the inclination angle A1 and the inclination angle A0 is 8° or less. In this embodiment, the inclination angle A1 is 12°, which is 7° larger than the inclination angle A0.

[0046] The bead back surface 35 has at least a straight portion 61 extending along a second straight line L2 along the tire radial direction at its inner end in the tire radial direction, a first curved portion 62 (recess) extending radially outward from the straight portion 61 and constituting at least a part of a recess 70 described later, and a second curved portion 63 located radially outward in the tire and reaching the apex 4a of the rim protector 4.

[0047] The first curved portion 62 extends from a first point P1, which is the outer end point of the straight portion 61 in the tire radial direction, toward the tire radial outside in a direction inclined inward in the tire axial direction, and then curves outward in the tire axial direction to reach a second point P2. The second point P2 is located axially outward of the first point P1. The first curved portion 62 is configured as an arc-shaped portion with a curvature radius R1 centered at a curvature center O1 located closer to the tire outer surface than the outer surface of the bead portion 30.

[0048] The height H1 of the center of curvature O1 in the tire radial direction, based on the nominal rim diameter NR, is equal to or greater than the height H11 of the flange radial portion 53a of the corresponding genuine rim 50. Preferably, the height H1 of the center of curvature O1 is equal to or less than 1.5 times the height H11 of the flange radial portion 53a. In this embodiment, the height H11 of the flange radial portion 53a is 8 mm, so the height H1 of the center of curvature O1 is set to be equal to or greater than 8 mm and equal to or less than 12 mm. Preferably, the height H1 of the center of curvature O1 is equal to or greater than 0.2 and equal to or less than 0.6 times the height H3 of the apex 4a of the rim protector 4.

[0049] In addition, the center of curvature O1 is located in a radial range W between a radial position V1 that is 2 mm radially inward of the tire and a radial position V2 that is 9 mm radially outward of the tire based on the bead core radial outer end surface 31a.

[0050] Furthermore, the height H1 of the center of curvature O1 is set to be less than 0.25 times the tire cross-sectional height H0 (see FIG. 1). The tire cross-sectional height H0 is calculated by subtracting the nominal rim diameter from the outer diameter of the pneumatic tire 1 and dividing the result by 2.

[0051] The radius of curvature R1 is larger than the radius of curvature R12 of the flange curved portion 53b of the corresponding regular rim 50. Preferably, the radius of curvature R1 is 1.4 times or more the radius of curvature R12, and more preferably 1.6 to 2.4 times the radius of curvature R12. In this embodiment, since the radius of curvature R12 of the flange curved portion 53b is 9.5 mm, the radius of curvature R1 is set to 14 mm or more, and more preferably 16 mm to 22 mm.

[0052] The second curved portion 63 extends from a third point P3 located at the vertex 4a of the rim protector 4, curving radially inward toward the tire axial direction and reaching a fourth point P4. The second curved portion 63 is formed by an arc-shaped portion having a radius of curvature R2 centered at a center of curvature O2 located closer to the tire outer surface than the outer surface of the bead portion 30. The radius of curvature R2 is set to be equal to or greater than the radius of curvature R1 of the first curved portion 62. Preferably, the radius of curvature R2 is 1.2 times or greater than the radius of curvature R1.

[0053] As shown in the enlarged view of Figure 2, a virtual curve 62a extending the first curved portion 62 radially outward from the tire and a virtual curve 63a extending the second curved portion 63 axially inward from the tire intersect at a virtual intersection point P5 so as to be convex toward the inner surface of the tire.

[0054] The height H5 of the virtual intersection point P5 in the tire radial direction, based on the nominal rim diameter NR, is greater than 1.5 and less than 3.0 times the height H1 of the center of curvature O1 of the first curved portion 62. More preferably, the height H5 of the virtual intersection point P5 is greater than 2 and less than 2.5 times the height H1 of the center of curvature O1. Furthermore, the height H5 of the virtual intersection point P5 is 0.7 or more times the height H3 of the apex 4a of the rim protector 4. The height H5 of the virtual intersection point P5 is, for example, 15 mm or more and 25 mm or less, and preferably 20 mm or more and 24 mm or less.

[0055] Furthermore, the height H5 of the virtual intersection P5 is smaller than the height H9 of the tip 32a of the bead filler 32 based on the nominal rim diameter NR. Specifically, the height H9 of the tip 32a of the bead filler 32 is preferably 1.1 times or more, and more preferably 1.3 times or more, the height H5 of the virtual intersection P5.

[0056] The intersection angle A3 between the imaginary curves 62a and 63a, i.e., the angle between the tangent 62b to the first curved portion 62 (imaginary curve 62a) extending from the imaginary intersection point P5 and the tangent 63b to the second curved portion 63 (imaginary curve 63a) extending from the imaginary intersection point P5, is greater than 0° and not greater than 45°. If the intersection angle A3 exceeds 45°, strain is likely to concentrate between the first curved portion 62 and the second curved portion 63, and bead durability is likely to deteriorate. Preferably, the intersection angle A3 is not greater than 30°. The intersection angle A3 is defined as the angle between the tangent 62b and the tangent 63b extending axially outward from the imaginary intersection point P5.

[0057] The bead back surface 35 further has a third curved portion 64 that connects the second point P2 and the fourth point P4 in an arc shape.

[0058] The straight portion 61 is tangentially continuous with the first curved portion 62. In other words, the first point P1 constitutes the point of contact between the first curved portion 62 and the straight portion 61. The straight portion 61 extends parallel to a second straight line L2 that is inclined axially inward toward the tire radially outward, and has an inclination angle A2 with respect to the straight line parallel to the tire radial direction. The inclination angle A2 is set to be smaller than the inclination angle A1 of the bead base surface 34. In this embodiment, the inclination angle A2 is 10° or less. Furthermore, the inclination angle A2 is set so that the angle A4 between the straight portion 61 and the bead base surface 34 is 95° or more and 105° or less. The inclination angle A2 is set to be smaller than the value obtained by subtracting the inclination angle A0 of the rim seat 51 from the inclination angle A1 of the bead base surface 34 (A2 <A1-A0)。

[0059] The third curved portion 64 tangentially connects the first curved portion 62 and the second curved portion 63, and is formed by an arc-shaped portion having a curvature radius R3 centered at a curvature center O3 located on the tire outer surface side of the bead portion 30. In other words, the second point P2 forms the point of contact between the first curved portion 62 and the third curved portion 64, and the fourth point P4 forms the point of contact between the second curved portion 63 and the third curved portion 64.

[0060] The radius of curvature R3 of the third curved portion 64 is smaller than the radii of curvature R1 and R2 of the first curved portion 62 and the second curved portion 63.

[0061] Fig. 3 is an enlarged view of the periphery of the bead heel surface 36 in Fig. 2. As shown in Fig. 3, the bead heel surface 36 is located radially inward and axially outward with respect to the bead core 31. The bead heel surface 36 extends axially outward along a third straight line L3 that is inclined radially outward in the tire direction further than the first straight line L1, between the axially outer end of the bead base surface 34 and the radially inner end of the bead back surface 35.

[0062] Specifically, when the intersection of the first line L1 and the second line L2 is defined as the first intersection X1, the intersection of the first line L1 and the third line L3 is defined as the second intersection X2, and the intersection of the second line L2 and the third line L3 is defined as X3, the radial dimension K of the bead heel surface 36, which is the dimension in the tire radial direction between the first intersection X1 and the third intersection X3, is equal to or greater than the axial dimension G, which is the dimension in the tire axial direction between the first intersection X1 and the second intersection X2, but is less than twice the axial dimension G.

[0063] The bead heel surface 36 is located axially more inward than a fourth straight line L4 extending in the tire radial direction at a position axially inward by a predetermined length J from the bead core axially outer end surface 31b, which is the axially outer end surface of the bead core 31. In other words, the value obtained by adding the predetermined length J to the dimension Q in the tire axial direction from the third intersection X3 to the bead core axially outer end surface 31b is longer than the dimension T in the tire axial direction between the third intersection X3 and the second intersection X2. For example, the predetermined length J is 2 mm. The predetermined length J may also be 30% of the axial dimension M of the bead core 31.

[0064] The second intersection point X2 and the third intersection point X3 are geometrically set as both end points of an imaginary circular arc 38 that tangentially connects the first straight line L1 and the second straight line L2 with a radius of curvature Ra greater than 3 mm and less than 8 mm in the meridian cross section. In other words, the third straight line L3 is defined as a straight line that linearly connects the both end points X2 and X3 of the imaginary circular arc 38 that tangentially connects the first straight line L1 and the second straight line L2 with a radius of curvature Ra greater than 3 mm and less than 8 mm.

[0065] The bead heel surface 36 has a bead heel straight portion 36a that extends linearly along the third straight line L3, a bead heel first R chamfered portion 36b that tangentially connects the bead heel straight portion 36a to the bead base surface 34, and a bead heel second R chamfered portion 36c that tangentially connects the bead heel straight portion 36a to the bead back surface 35. The radii of curvature of the bead heel first R chamfered portion 36b and the bead heel second R chamfered portion 36c are 2 mm or more and equal to or less than the radius of curvature Ra of the imaginary arc 38.

[0066] At least a portion of the bead heel surface 36 is formed by the rim strip rubber 21b. Fig. 4 is a front view of the bead heel surface 36 as viewed from the arrow A in Fig. 3. As shown in Fig. 4, the bead heel surface 36 is formed by the rim strip rubber 21b, and is formed with a vent hole mark 36z, which is a trace of a gas release vent provided in a tire mold (not shown) that vulcanizes and molds the pneumatic tire 1. The vent hole mark 36z may be a vent spew formed by a vent hole, or a burr or unevenness formed by a spring vent.

[0067] Returning to Figure 2, in the non-rim-mounted state, a recess 70 is formed on the radially inner side of the bead portion 30, extending across the bead heel surface 36 and the bead back surface 35. The recess 70 refers to the portion of the bead heel surface 36 and the bead back surface 35 that is located axially inner with respect to a fifth straight line L5, which is a tangent to the bead heel second R chamfered portion 36c and extends parallel to the tire radial direction. In other words, the recess 70 is made up of the portion of the bead heel second R chamfered portion 36c that is located radially outer, the straight portion 61, and the portion of the first curved portion 62 that is located radially inner.

[0068] The recess 70 has a deepest portion 71 that is recessed most axially inward of the tire. The deepest portion 71 is located on the first curved portion 62. The deepest portion 71 is located radially outward of the straight portion 61. In other words, the straight portion 61 is located radially inward of the deepest portion 71. The depth D of the deepest portion 71 is set to less than 1.0 mm, preferably 0.8 mm or less, and more preferably 0.3 mm or more and 0.5 mm or less, based on the fifth straight line L5.

[0069] The height H10 of the deepest part 71, based on the nominal rim diameter NR, is equal to or greater than the height H11 of the flange radial portion 53a of the corresponding regular rim 50. Preferably, the height H10 of the deepest part 71 is equal to or less than 1.5 times the height H11 of the flange radial portion 53a. In this embodiment, the height H11 of the flange radial portion 53a is 8 mm, and therefore the height H11 of the deepest part 71 is set to be equal to or greater than 8 mm and equal to or less than 12 mm.

[0070] In this embodiment, the deepest part 71 is located on the sixth straight line L6 extending parallel to the tire axial direction from the center of curvature O1 of the first curved part 62 extending in an arc shape, and therefore the height H10 of the deepest part 71 is equal to the height H1 of the center of curvature O1 of the first curved part 62.

[0071] Here, in the pneumatic tire 1, when not assembled to a rim, the pair of bead portions 30 are spaced apart at a distance wider than the rim width W0. Specifically, the outer width W1 (i.e., the distance between the fifth straight lines) in the tire axial direction between the pair of bead heel surfaces 36 (specifically, the bead heel second R chamfered portions 36c) is greater than the rim width W0. For example, the difference between the outer width W1 and the rim width W0 is 1.5 inches or less, and preferably 1 inch or less.

[0072] 5 shows the periphery of the bead portion 30 before the pneumatic tire 1 is mounted on a corresponding regular rim 50 and inflated to a specified internal pressure, with the imaginary line showing the pneumatic tire 1 before mounting on the rim and the dashed line showing the pneumatic tire 1 when a load is applied after inflation. Since the pneumatic tire 1 has an outer width W1 between the pair of bead portions 30 that is wider than the rim width W0 of the corresponding regular rim 50, when mounting the pneumatic tire 1 on the rim, the pair of bead portions 30 must be brought close to each other axially inward. At this time, the pneumatic tire 1 is deformed so that it tilts axially inward toward the tire radial direction across the sidewall 20 and the bead portion 30 (arrow Y1 in the figure).

[0073] Furthermore, because the inclination angle A1 of the bead base surface 34 is greater than the inclination angle A0 of the rim seat 51, when the bead base surface 34 is fitted radially into the rim seat 51, the bead base surface 34 rotates clockwise in Figure 3 (arrow Y2 in the figure) by an angle obtained by subtracting the amount by which the bead base surface 34 is compressed from the angle difference between the inclination angles A0 and A1. The bead base surface 34 rotates so that the inclination angle A1 becomes smaller, and is fitted radially into the rim seat 51.

[0074] Here, since a linear bead heel surface 36 is formed on the bead portion 30, the bead heel surface 36 does not ride up on or interfere with the rim heel 52 of the regular rim 50, and the bead heel surface 36 can be moved from the inside to the outside in the axial direction of the tire relative to the rim seat 51 and rim heel 52, and assembled to the appropriate axial position of the tire.

[0075] As a result, in the bead portion 30, the portion of the recess 70 located radially inward of the deepest portion 71 is inclined so as to rotate clockwise in FIG. 3 compared to the non-rim-mounted state, starting from the periphery of the deepest portion 71 (arrow Y3 in the figure). As the bead base surface 34 rotates, the bead back surface 35 is rotated axially inward from the periphery of the deepest portion 71 so that the inclination angle A2 becomes zero, i.e., so that the straight portion 61 extends along the tire radial direction. In this embodiment, the inclination angle A1 is 7° larger than the inclination angle A0, and therefore the portion located radially inward of the deepest portion 71 rotates by an angle of 7° or less.

[0076] As a result, when the pneumatic tire 1 is mounted on a rim, the recess 70 disappears and the portion of the bead back surface 35 located radially inward of the deepest part 71 deforms so as to extend generally along the tire radial direction. Therefore, the bead base surface 34 and the portion of the bead back surface 35 located radially inward of the deepest part 71 of the bead portion 30 are in close contact with the rim seat 51 and the radial portion 53a of the rim flange 53 over substantially their entire surfaces.

[0077] On the other hand, in the rim-mounted state, the bead heel surface 36 is spaced apart from the rim heel 52. Next, when the pneumatic tire 1 is inflated by filling it with a specified internal pressure in the rim-mounted state, the bead heel surface 36 of the bead portion 30 deforms and comes into substantial contact with the rim heel 52.

[0078] As the bead core 31 moves from the non-rim-assembled state to the inflated state, the bead core 31 rotates clockwise in Figure 5 (arrow Y2 in the figure), similar to the bead base surface 34. The rotation angle A6 of the bead core 31 is approximately equal to the inclination angle A2 with respect to a line parallel to the tire radial direction. In this embodiment, the rotation angle A6 of the bead core 31 is defined by the angle between an extension line L8 of the bead core radially outer end surface 31a in the non-rim-assembled state and an extension line L9 of the bead core radially outer end surface 31a in the inflated state.

[0079] In this rim-assembled state, the bead back surface 35 is formed to be sufficiently spaced apart in the tire radial direction from the flange curved portion 53b. Specifically, the bead back surface 35 is formed so that the distance in the tire radial direction between an apex P10 of the flange curved portion 53b located at the outermost position in the tire radial direction and an intersection P11 between the bead back surface 35 and a radial line L7 that passes through the apex P10 and extends in the tire radial direction is 4 mm or more.

[0080] 5, the bead back surface 35 is formed so as to be sufficiently spaced apart in the tire radial direction from the flange curved portion 53b even in a load input state corresponding to the load index set for the pneumatic tire 1. Specifically, the bead back surface 35 is formed so that the distance in the tire radial direction between the apex P10 and the intersection P12 between the radial straight line L7 and the bead back surface 35 in a load input state is 3 mm or more.

[0081] 6 is a graph showing the fitting pressure at the fitting portion between the bead portion 30 and the regular rim 50 when the pneumatic tire 1 is mounted on the regular rim 50 and inflated. The fitting pressure was measured using a sheet-type pressure sensor sandwiched between the bead portion 30 and the regular rim 50. In this graph, the horizontal axis represents each position along the outer surface of the bead portion 30, from the axially inner end of the bead base surface 34 to the bead back surface 35, and the vertical axis represents the fitting pressure.

[0082] Fig. 6 also shows the fitting pressure of the bead portions of pneumatic tires according to comparative examples 1 and 2. As shown in Fig. 7, pneumatic tire 100 according to comparative example 1 differs from pneumatic tire 1 in that a bead heel surface 136 is formed on an arc that substantially matches the rim heel 52 and does not have a recess. As shown in Fig. 8, pneumatic tire 200 according to comparative example 2 differs from pneumatic tire 1 in that a bead heel surface 236 is formed on an arc that substantially matches the rim heel 52, and differs from pneumatic tire 100 according to comparative example 1 in that a recess 270 is provided. In Fig. 6, the fitting pressure for pneumatic tire 1 is shown by a thick solid line, the fitting pressure for pneumatic tire 100 is shown by a dashed line, and the fitting pressure for pneumatic tire 200 is shown by a thin solid line.

[0083] 6 and 7, in the pneumatic tire according to Comparative Example 1, fitting pressure is generated locally at two points: the bead base surface 134 and a contact portion 135a located on the radially outer side of the tire on the bead back surface 135. The peak at the bead base surface 134 is roughly fitting pressure A, while the peak at the contact portion 135a is lower than fitting pressure A and slightly exceeds fitting pressure B, which is lower than fitting pressure A. In other words, no fitting pressure is generated at the non-contact portion 135b located between the bead base surface 134 and the bead back surface 135 and not in contact with the genuine rim 50.

[0084] Therefore, the pneumatic tire 100 is tightly fitted locally at two locations, the bead base surface 134 and the contact portion 135a, and the bead portion 130 is tightly compressed at these two locations.

[0085] In the pneumatic tire 200 according to Comparative Example 2, fitting pressure is generated between the regular rim 50 and the bead base surface 234, the bead heel surface 236, and the bead back surface 235. That is, unlike the pneumatic tire 100, the bead heel surface 236 and the inner diameter side portion 235b of the bead back surface 235 also abut against the regular rim 50.

[0086] Specifically, the fitting pressure of the pneumatic tire 200 is lower in portions of the pneumatic tire 100 that correspond to portions of the pneumatic tire 100 that are locally tightly fitted, compared to the pneumatic tire 100. That is, the peak at the bead base surface 234 is approximately fitting pressure B, and the peak at the bead back surface 235 is slightly lower than fitting pressure C, which is lower than fitting pressure B. On the other hand, the pneumatic tire 200 has fitting pressure in portions that correspond to unfitted portions of the pneumatic tire 100. That is, the pneumatic tire 200 has fitting pressure from the bead base surface 234 to the bead back surface 235 and is in close contact with the regular rim 50, and local compression is suppressed.

[0087] On the other hand, in the pneumatic tire 1 according to this embodiment, fitting pressure is generated between the bead base surface 34, the bead back surface 35, and the bead heel surface 36 in the areas on the bead base surface 34 side and the bead back surface 35 side and between the bead base surface 34 and the bead back surface 35 side and the regular rim 50.

[0088] Specifically, the peak fitting pressure at the bead base surface 34 of the pneumatic tire 1 is higher than that of either of the pneumatic tires 100 and 200, while the peak fitting pressure at the bead back surface 35 is lower than that of either of the pneumatic tires 100 and 200. This is thought to be because, unlike the pneumatic tires 100 and 200, the bead heel surface 36 of the pneumatic tire 1 is formed with a linear chamfer, making it easier to fit the pneumatic tire 1 at the appropriate axial position without it getting in the way of the rim heel 52 when assembled to the rim.

[0089] For example, as shown by the dashed line in Figure 7, when the radius of curvature of the bead heel surface 136 in the pneumatic tire 100 is excessively smaller than the radius of curvature of the rim heel 52, and the bead heel surface 136 is fitted to the axially inner side of the tire relative to the appropriate axial position for fitting to the rim heel 52, the bead portion 130 is likely to collapse significantly more axially outward during inflation due to the gap between the bead back surface 135 and the rim flange 53, and the bead back surface 135 is likely to come into local contact with the rim flange 53.

[0090] That is, in the pneumatic tires 100, 200, the bead heel surfaces 136, 236 are not linearly chamfered, and therefore depending on the magnitude of the curvature of the bead heel surfaces 136, 236, they are more likely to bend against the rim heel 52 than the pneumatic tire 1, and the bead portions 130, 230 are more likely to collapse axially outward in the tire. As a result, in the pneumatic tires 100, 200, the mating pressure between the bead base surfaces 134, 234 and the rim seat 51 decreases, while the mating pressure between the bead back surfaces 135, 235 and the rim flange 53 increases.

[0091] The pneumatic tire 1 according to this embodiment has the following advantages.

[0092] (1) Because the bead base surface 34 is configured with a single inclined surface (single-step tapered), the bead portion 30 is prevented from tilting axially outward when assembled to the rim, compared to when the bead base surface 34 has an additional inclined surface whose inclination angle toward the tire radially inward increases toward the tire axially inward (two-step tapered). As a result, when assembled to the rim, the fitting pressure at the bead back surface 35 is reduced, while the fitting pressure at the bead base surface 34 is increased, compared to when the bead base surface 34 is two-step tapered.

[0093] Furthermore, because the bead heel surface 36 is configured as a chamfer that connects the bead base surface 34 and the bead back surface 35 in a straight line, interference between the bead heel surface 36 and the rim heel 52 of the genuine rim 50 is suppressed when the rim is assembled. As a result, the bead portion 30 can be fitted to the genuine rim 50 at the correct axial position, which prevents the bead portion 30 from collapsing axially outward due to an insufficient fitting position that is too far to the axially inner side of the tire, and also suppresses an increase in fitting pressure at the bead back surface 35.

[0094] Therefore, when a load is applied, the bead base surface 34 with increased fitting pressure makes it easier to maintain the fit with the rim seat 51 of the regular rim 50, improving rim fitting, while the bead back surface 35 with reduced fitting pressure makes it easier for the sidewall 20 to flex and deform, improving handling stability.

[0095] (2) The inclination angle A1 of the first straight line L1 with respect to the tire axial direction is 5° or more and 15° or less. That is, the bead base surface 34 is moderately inclined, so that the mating pressure at the bead base surface 34 can be increased while suppressing an increase in the mating pressure at the bead back surface 35. If the inclination angle A1 of the first straight line L1 is less than 5°, the sidewall 20 will deform excessively due to insufficient mating pressure at the bead back surface 35, which is likely to lead to a decrease in handling stability. On the other hand, if the inclination angle A1 of the first straight line L1 is more than 15°, the excessive mating pressure at the bead back surface 35 will hinder the flexural deformation of the sidewall 20, which is likely to lead to a decrease in the load support performance of the sidewall 20.

[0096] (3) The radial dimension K of the bead heel surface 36 is equal to or greater than the axial dimension G but less than twice the axial dimension G. As a result, the bead heel surface 36 is configured to be long in the tire radial direction, which makes it easier to ensure the bead base surface 34 and to prevent the bead portion 30 from tipping axially outward. If the radial dimension K of the bead heel surface 36 is less than the axial dimension G, it is likely that interference of the bead heel surface 36 with the genuine rim 50 during rim assembly will be insufficient. On the other hand, if the radial dimension K of the bead heel surface 36 is equal to or greater than twice the axial dimension G, the bead back surface 35 will be excessively small, causing fitting pressure to be locally concentrated on the bead back surface 35, hindering flexural deformation of the sidewall 20.

[0097] (4) The bead heel surface 36 is located axially outward of the fourth straight line L4. As a result, the amount of intrusion of the bead heel surface 36 into the radially inner region of the bead core 31 toward the tire axially inner side is prevented from becoming excessive, making it easier to ensure the bead base surface 34 on the radially inner side of the bead portion 30, and preventing the bead portion 30 from tipping axially outward.

[0098] (5) Because the recess 70 is formed in the bead back surface 35, in the non-rim-mounted state, the inner diameter side portion of the bead back surface 35, which is located on the inner diameter side of the deepest part 71 of the recess 70, is inclined radially inward in the tire direction and axially outward in the tire direction. In the rim-mounted state in which the pair of bead portions 30 are brought close to the rim width W0 of the regular rim 50, the inner diameter side portion is likely to bend axially inward from the periphery of the deepest part 71 of the recess 70 and generally follow the tire radial direction. In other words, in the rim-mounted state, the bead back surface 35 is likely to come into close contact with substantially the entire radial portion 53a of the rim flange 53 while eliminating the recess 70, thereby increasing the contact area.

[0099] In this way, in the rim-assembled, unloaded state, surface pressure acts over almost the entire surface of the bead back surface 35 that is in close contact with the radial portion 53a of the rim flange 53, so the load borne by the entire bead back surface 35 is distributed compared to when surface pressure acts only on a portion of the bead back surface 35. In other words, compared to when high surface pressure acts locally on the bead back surface 35, there can be more room for compression to allow the bead back surface 35 to elastically deform.

[0100] Therefore, when a load or a lateral force is input, the bead back surface 35 can be further compressed by the amount of the excess compression. In this case, the sidewall 20 can deform in the portion close to the bead portion 30 due to the further compression of the bead back surface 35, so the sidewall 20 can be deformed so as to bend overall from the bead portion 30 side to the tread 10 side. This improves the efficiency of load support in the sidewall 20, thereby improving handling stability.

[0101] (6) If the depth D of the recess 70 is less than 1.0 mm, the portion located inward of the deepest part 71 is moderately inclined axially outward in the unrim-mounted state. Therefore, when the recess 70 is bent axially inward in the rim-mounted state, the axially outward inclination is easily eliminated, and the recess 70 is likely to fit exactly along the radial part 53a of the rim flange 53. If the depth of the recess 70 is 1.0 mm or more, the portion located inward of the deepest part 71 is likely to be excessively inclined axially outward in the unrim-mounted state. Therefore, even when the portion is bent axially inward in the rim-mounted state, the axially outward inclination is difficult to eliminate. In this case, the recess 70 is unlikely to disappear in the rim-mounted state, and the bead back surface 35 is unlikely to abut almost the entire radial part 53a of the rim flange 53. Furthermore, if the depth D of the recess 70 is 0.8 mm or less, the portion located inward of the deepest part 71 is moderately inclined axially outward in the unrim-mounted state, and the recess 70 is likely to fit exactly along the radial part 53a of the rim flange 53 in the rim-mounted state. Furthermore, when the depth D of the recess 70 is 0.3 mm or more and 0.5 mm or less, the portion located radially inward of the deepest part 71 is more moderately inclined toward the axially outer side of the tire when not mounted on the rim, and is more likely to fit closely to the radial portion 53a of the rim flange 53 when mounted on the rim.

[0102] (7) The third straight line L3 is geometrically defined as a straight line connecting both end points of an imaginary arc 38 that connects the first straight line L1 and the second straight line L2 tangentially and continuously with a curvature radius Ra of more than 3 mm and less than 8 mm. As a result, the bead heel surface 36 is formed with an appropriate size, and when the pneumatic tire 1 is mounted on a standard rim 50 and inflated to the specified internal pressure, the bead heel surface 36 can be easily brought into contact with the rim heel 52, ensuring rim fitting.

[0103] If the curvature radius Ra of the imaginary arc 38 is 3 mm or less, the bead heel surface 36 will interfere with the rim heel 52 when assembled to the rim, making it difficult to fit the tire to the appropriate axial position. On the other hand, if the curvature radius Ra of the imaginary arc 38 is 8 mm or more, it will be difficult to bring the bead heel surface 36 into contact with the rim heel 52 even after inflation when assembled to the rim, which can lead to poor rim fitting.

[0104] (8) At least a portion of the bead heel surface 36 is formed by the rim strip rubber 21b and has vent hole traces 36z. As a result, the flow of rubber around the bead heel surface 36 during vulcanization is improved, so that defects such as bare spots caused by poor rubber flow during vulcanization are suppressed while forming a linear bead heel surface 36 on the outer surface of the bead portion 30.

[0105] (9) Because the deepest part 71 is located at a radial position equal to or higher than the outer diameter end of the radial part 53a of the rim flange 53, when assembled to the rim, the part of the recess 70 located on the inner diameter side of the deepest part 71 can easily abut against substantially the entire surface of the radial part 53a of the rim flange 53, starting from the radially inner side. If the deepest part 71 of the recess 70 is located on the inner diameter side of the outer diameter end of the radial part 53a of the rim flange 53 of a genuine rim 50, the deepest part 71 will face the inner diameter side of the outer diameter end of the radial part 53a of the rim flange 53. As a result, the part of the recess 70 located on the outer diameter side of the deepest part 71 extends axially outward toward the tire radially outward, and is therefore likely to come into strong localized abutment against the radial part 53a of the rim flange 53.

[0106] (10) The deepest part 71 is located in the tire radial direction at a distance less than 1.5 times the height H11 to the outer diameter end of the radial portion 53a of the rim flange 53, based on the nominal rim diameter NR. This makes it easy to bend the inner diameter side portion of the recess 70 axially inward, starting from the periphery of the deepest part 71, during rim assembly. In other words, if the deepest part 71 of the recess 70 is located more outer diameter than 1.5 times the length to the outer diameter end of the radial portion 53a, based on the nominal rim diameter NR, the distance from the bead base surface 34 to the deepest part 71 of the recess 70 is likely to be excessively large, and the deformation of the bead portion 30 during rim assembly is likely to start on the inner diameter side of the deepest part 71 of the recess 70. In this case, it is difficult to bend the entire inner diameter side portion of the recess 70 from the deepest part 71, making it difficult to abut the bead back surface 35 against substantially the entire radial portion 53a of the rim flange 53.

[0107] (11) The first curved portion 62 constitutes the deepest part 71 of the recess 70, and its radius of curvature R2 is larger than the radius of curvature R12 of the opposing curved portion 53b of the rim flange 53. As a result, in the rim-assembled state, the curved portion 53b of the rim flange 53 is easily enclosed within the recess 70, and the recess 70 is less likely to be obscured by the curved portion 53b, so the portion located on the inner side of the deepest part 71 is more likely to abut against substantially the entire surface of the radial portion 53a of the rim flange 53, starting from the radially inner side. If the radius of curvature R2 of the first curved portion 62 were smaller than the radius of curvature of the curved portion of the rim flange, in the rim-assembled state, the curved portion 53b would be more likely to be obscured by the inside of the recess 70, and the portion located on the inner side of the deepest part 71 of the recess 70 is less likely to abut against substantially the entire surface of the radial portion 53a of the rim flange 53, starting from the radially inner side.

[0108] (12) In the pneumatic tire 1, the height H1 of the center of curvature O1 of the first curved portion 62 is located in the tire radial range of 8 mm or more and 12 mm or less, and the radius of curvature R1 is 12 mm or more. Therefore, the effects of the above-mentioned invention are preferably exhibited when the tire is assembled to a regular rim 50 in which the height H11 of the outer diameter side end of the radial portion 53a of the rim flange 53 is 8 mm or less and the radius of curvature R12 of the curved portion 53b of the rim flange 53 is 12 mm or less, such as a regular rim with flange symbol J for a 5° deep rim specified by JATMA.

[0109] The present invention is not limited to the configurations described in the above embodiments, and various modifications are possible.

[0110] In the above embodiment, the recess 70 is formed by a part of the bead heel second R chamfered portion 36c, the straight portion 61, and at least a part of the first curved portion 62, but this is not limited to this. The bead heel second R chamfered portion 36c and the first curved portion 62 may be directly connected without using the straight portion 61. In this case, the bead heel second R chamfered portion 36c and the first curved portion 62 may be connected in a tangent-continuous manner.

[0111] In addition, in this embodiment, the recess 70 is configured as an arc-shaped portion, but this is not limited thereto. That is, the recess 70 may be formed in a trapezoidal shape, a triangular shape, or various other configurations may be adopted. Note that, by configuring the recess 70 as a tangent-continuous arc-shaped portion as in this embodiment, it is easy to smoothly deform the bead back surface 35 so that it extends parallel to the tire radial direction when assembled to the rim, resulting in excellent rim fitting.

[0112] (Reference example) Evaluation tests were conducted on the average fitting pressure at the back surface of the bead between the pneumatic tire and a regular rim, bead durability, and steering stability for the pneumatic tires of Reference Comparative Examples 1 and 2 and Reference Examples 1 to 4. In Reference Comparative Examples 1 and 2 and Reference Examples 1 to 4, the bead heel surface is not formed as a linear chamfer, but is formed as a curved portion along the rim heel 52.

[0113] In Reference Comparative Example 1, no recesses are provided. In Reference Comparative Example 2, the depth D of the recess 70 is 2 mm, which is 1 mm or more and exceeds the upper limit of the present invention, which is less than 1.0 mm. In Reference Examples 1 to 4, the depth D of the recess 70 is within the above-mentioned numerical range. In Reference Example 3, the depth D of the recess 70 is 0.9 mm, which is near the upper limit of the above-mentioned numerical range. In Reference Example 4, the depth D of the recess 70 is 0.8 mm, which is the upper limit of the above-mentioned numerical range, which is more preferably 0.8 mm or less. In Reference Examples 1 and 2, the depth D of the recess 70 is 0.4 mm, which is the median of 0.3 mm or more and 0.5 mm or less, which is an even more preferable range of the above-mentioned numerical range. The height H10 of the deepest part 71 of the recess 70 is 10 mm in Reference Comparative Example 2 and Reference Examples 1 and 2. The radius of curvature R1 of the first curved portion 62 is 18 mm for Reference Comparative Example 1, 12 mm for Reference Comparative Example 2, 18 mm for Reference Examples 1 and 4, and 22 mm for Reference Examples 2 and 3. The regular rim used for the evaluation conforms to the flange symbol J for a 5° deep rim specified by JATMA.

[0114] The average fitting pressure at the bead back surface 35 was measured by measuring the average fitting pressure in the contact area of ​​the bead back surface 35 against the radial portion 53a of the rim flange 53 during inflation, and the average fitting pressures in Reference Comparative Example 2 and Reference Examples 1 to 4 are expressed as an index, with the value for Reference Comparative Example 1 set to 100. A larger value indicates a stronger fit over a narrower contact area, and a lower value indicates that the fitting pressure is distributed over a wider contact area.

[0115] To evaluate bead durability, a drum durability test was conducted to induce bead failure, and the running distance until failure was measured. The running distance for Reference Comparative Example 1 was set at 100, and the running distances for Reference Comparative Example 2 and Reference Examples 1 to 4 were expressed as an index. A larger value indicates better bead durability.

[0116] The handling stability was evaluated by a sensory relative evaluation by the driver when the tires were fitted to an actual vehicle and driven on the road. The maximum score was 10 points, with 6.0 being the median value, and the higher the score, the better the handling stability.

[0117] [Table 1]

[0118] As is clear from Table 1, the pneumatic tires according to Reference Examples 1 to 4, in which the depth D of the deepest part 71 of the recess 70 is less than 1.0 mm, have a lower average fitting pressure at the bead back surface 35 and the fitting pressure is dispersed over a wider contact area than those of Reference Comparative Examples 1 and 2. This is thought to be because in Reference Examples 1 to 4, the depth D of the deepest part 71 of the recess 70 is appropriate, so that the recess 70 disappears when assembled to the rim and the bead back surface 35 easily conforms to the radial portion 53b of the rim flange 53.

[0119] In Reference Comparative Example 2, the depth D of the deepest part 71 of the recess 70 is 1.0 mm or more, so even when the tire is assembled to the rim and inflated, the recess 70 does not disappear and the bead back surface 35 comes into local contact, so the contact area is localized and it is thought that the average fitting pressure is higher than in Reference Examples 1 and 2. In addition, in Reference Comparative Example 2, the depth D of the deepest part 71 is too large at 2.0 mm, so the adhesion to the rim over the entire area is poor and sufficient effects cannot be obtained, and the bead durability and handling stability were similar to those of Reference Comparative Example 1.

[0120] Among Reference Examples 1 to 4, the average mating pressure at the bead back surface 35 decreases in the order of Reference Example 3, which is near the upper limit of the above-mentioned numerical range (less than 1.0 mm), Reference Example 4, which is at the upper limit of a more preferable range (0.8 mm or less), and Reference Examples 1 and 2, which are at the median of an even more preferable range (0.3 mm or more and 0.5 mm or less), and bead durability and handling stability improve in this order. Specifically, in Reference Example 1, the depth D of the deepest part of the recess 70 is an appropriate 0.4 mm. Therefore, when assembled to a rim and inflated, the recess 70 disappears, and the bead portion 30, from the bead base surface 34 to the bead back surface 35, abuts almost the entire radial portion 53a of the rim flange 53. As a result, the average mating pressure at the bead back surface 35 is lower than in Reference Comparative Example 1, and as a result, the bead durability and handling stability are superior to those of Reference Comparative Example 1.

[0121] As in Reference Example 1, Reference Example 2 also has a moderate depth D of 0.4 mm at the deepest point of the recess 70. Therefore, when the tire is assembled to the rim and inflated, the recess 70 disappears, and the bead portion 30 is in almost complete contact with the radial portion 53a of the rim flange 53 from the bead base surface 34 to the bead back surface 35. Reference Example 2 exhibits smaller improvements in both bead durability and handling stability than Reference Example 1. This is presumably because Reference Example 2 has a larger curvature radius R1 of the first curved portion 62 than Reference Example 1, which tends to position the virtual intersection point P5 axially inward. This results in a larger intersection angle A3 at the virtual intersection point P5, which increases strain concentration near the virtual intersection point P5. Reference Examples 3 and 4 have a higher average fitting pressure at the bead back surface 35 than Reference Examples 1 and 2, resulting in inferior bead durability and handling stability compared to Reference Examples 1 and 2. In Reference Example 4, the depth D of the recess 70 is in a more preferable range than in Reference Example 3, so the average mating pressure at the back surface 35 of the bead is reduced compared to Reference Example 3, resulting in improved bead durability and handling stability. [Explanation of symbols]

[0122] 1 pneumatic tire 4 Rim Protectors 10 Tread 20 Sidewall 30 Bead section 31 Bead core 31a Bead core radial outer end face 31b Axial outer end face of bead core 32 Bead filler 32a bead filler tip 34 Bead base surface 35 Bead back 36 Bead heel surface 36a Bead heel straight section 36b Bead heel 1st R chamfer 36c Bead heel 2nd R chamfer 36z Vent hole marks 38 Virtual Arc 50 genuine rim 51 Rim seat 52 Rim Heel 53 Rim flange 53a Radial section 53b Curved part 61 Straight section 62 First curved section 63 Second curved section 64 Third curve 70 dent 71 Deepest Depths L1 1st straight line L2 2nd straight line L3 3rd straight line L4 4th straight line L5 5th straight line X1 1st intersection X2 2nd intersection X3 3rd intersection K Radial dimension of rim heel surface G Axial dimension of rim heel surface J specified length M Axial dimension of bead core

Claims

1. The tire has a tread, a sidewall extending radially inward from an axial end of the tread, and a bead portion continuing to the radially inward end of the sidewall, The bead portion has an outer surface in a meridian cross section. a bead base surface extending along a first straight line inclined radially outward in the tire axial direction at an inner end of the bead portion in the tire radial direction; a bead back surface extending radially outward from an axially outer end of the bead portion and having an inner end in the tire radial direction extending along a second straight line along the tire radial direction; a bead heel surface extending along a third straight line inclined further outward in the tire radial direction than the first straight line toward the tire axially outer side between an outer end of the bead base surface in the tire axial direction and an inner end of the bead back surface in the tire radial direction; It has the third straight line is geometrically defined as a straight line connecting both end points of an imaginary arc that tangently connects the first straight line and the second straight line to each other with a curvature radius of more than 3 mm and less than 8 mm in a meridian cross section.

2. an inclination angle of the first straight line with respect to the tire axial direction is equal to or greater than 5° and equal to or less than 15°; The pneumatic tire according to claim 1 .

3. In the meridian section, an intersection point between the first straight line and the second straight line is defined as a first intersection point; an intersection of the first straight line and the third straight line is a second intersection; When the intersection of the second line and the third line is defined as a third intersection, a radial dimension of the bead heel surface, which is a dimension in the tire radial direction between the first intersection point and the third intersection point, that is equal to or greater than an axial dimension, which is a dimension in the tire axial direction between the first intersection point and the second intersection point, and that is less than twice the axial dimension; The pneumatic tire according to claim 1 or 2.

4. A bead core is embedded in the bead portion, In the meridian cross section, the bead heel surface is located axially outward of a fourth straight line extending in the tire radial direction at a position axially inwardly spaced a predetermined length from an axially outer end of the bead core, The predetermined length is 2 mm. The pneumatic tire according to any one of claims 1 to 3.

5. A bead core is embedded in the bead portion, In the meridian cross section, the bead heel surface is located axially outward of a fourth straight line extending in the tire radial direction at a position axially inwardly spaced a predetermined length from an axially outer end of the bead core, The predetermined length is 30% of the axial dimension of the bead core. The pneumatic tire according to any one of claims 1 to 3.

6. The bead portion is provided in a pair, the pair of bead portions are positioned at a distance from each other so that the width between the outer surfaces in the axial direction of the tire in an unassembled state is wider than the rim width of a corresponding regular rim, Each of the pair of bead portions has a recess formed on the back surface of the bead in an unrim-assembled state, the recess being recessed axially inward of an axially outer end of the bead heel surface, When assembled to a rim, the back surface of the bead is in close contact with substantially the entire surface of a radial portion of the rim flange of the regular rim that extends parallel to the tire radial direction. The pneumatic tire according to any one of claims 1 to 5.

7. The recess has a depth of less than 1.0 mm in the tire axial direction. The pneumatic tire according to claim 6.

8. At least a portion of the bead heel surface is formed by rim strip rubber and has vent hole traces. The pneumatic tire according to any one of claims 1 to 7.

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