WO2020004109A1

WO2020004109A1 - Run-flat tire

Info

Publication number: WO2020004109A1
Application number: PCT/JP2019/023948
Authority: WO
Inventors: 正志山口
Original assignee: 株式会社ブリヂストン
Priority date: 2018-06-25
Filing date: 2019-06-17
Publication date: 2020-01-02
Also published as: JP7128273B2; JPWO2020004109A1

Abstract

This run-flat tire is provided with: a pair of bead cores; a carcass comprising a main body part that straddles the pair of bead cores, and a fold-back part where the bead core is folded back; a belt which is disposed outside of the carcass in the tire radial direction; side reinforcement rubber which is disposed inside of the carcass in the tire width direction; and a rim guard which is disposed on the outside surface of the tire and which limits collapse of the bead to outside of the tire in the axial direction during run-flat travel. The shape of a case line passing through the center of the carcass thickness is optimized, and the position of the apex of the rim guard is arranged in an optimal position.

Description

Run flat tire

The present disclosure relates to a run flat tire.

As a run flat tire that can travel a certain distance even when the internal pressure of the tire is reduced, there is a run-flat tire of a side reinforcement type in which a tire side portion is reinforced with side reinforcement rubber (for example, see Japanese Patent Application Laid-Open No. 2012-116212). ).

As a run flat tire, it is difficult to achieve both ride comfort during normal running and durability during run flat running, so-called run flat durability, and there is room for improvement.
For example, there is a method of lowering the longitudinal spring constant in order to improve the riding comfort during normal running. However, if the side reinforcing rubber is made thinner or softer, the run flat durability is reduced.
Further, when the side reinforcing rubber is thickened in order to ensure run-flat durability, the longitudinal spring constant increases, the riding comfort during normal running deteriorates, and the tire weight increases.

The present disclosure has been made in consideration of the above-described facts, and has as its object to provide a run-flat tire that can achieve both ride comfort during normal running and run-flat durability.

The run-flat tire according to the first aspect is provided with a carcass including a pair of bead cores, a main body that straddles the pair of bead cores, and a folded portion that folds the bead cores, and is provided outside the carcass in the tire radial direction. A belt, a side reinforcing layer provided on the inner side in the tire width direction of the carcass, and having a thickness gradually reduced toward both sides in the tire radial direction; and a bead core provided on the outer surface of the tire and in contact with a rim flange during run flat running. A rim guard that restricts the bead portion in which the buried part is embedded from falling outward in the tire axial direction, and a center line passing through the center of the thickness of the carcass is used as a case line, and the tire is mounted on a standard rim at zero internal pressure. When viewed in a cross section along the rotation axis, the tire core passes through the tire radially outer end of the bead core and is tied from a reference line parallel to the tire rotation axis. The height dimension of the case line measured in the radial direction is the side height SH, and the first dimension is parallel to the tire rotation axis along the tire rotation axis through a position 10% away from the reference line in the tire radial direction and away from the side height SH. An intersection point of the imaginary line and the case line is 0.1 SHp, and a second imaginary line that is parallel to the tire rotation axis through a position 20% of the side height SH outward in the tire radial direction from the reference line. An intersection point with the case line is 0.2SHp, a third imaginary line parallel to the tire rotation axis passing through a position 40% of the side height SH outward in the tire radial direction from the reference line and the case line. And the fourth imaginary line parallel to the tire rotation axis passing through a position 60% of the side height SH radially outward from the reference line in the tire radial direction. When the intersection with the in is 0.6SHp, the case line between the intersection 0.1SHp and the 0.2SHp when viewed in a cross section along the tire rotation axis has an average radius of curvature R1. The case line between the intersection point 0.4SHp and the 0.6SHp when viewed in a cross section along the tire rotation axis is an arc shape having a single radius of curvature R2; The position of the vertex of the rim guard is set within a range of 10 to 20% of the side height SH outward in the tire radial direction from the reference line.

In the run flat tire according to the first aspect, since the shape of the case line is optimized as described above, the vertical spring constant is reduced without thinning the side reinforcing layer, and the normal running time is reduced. Ride comfort can be improved.
In addition, since the rim guard is provided on the tire outer surface, the bead portion can be prevented from excessively falling down during run flat running, and run flat durability can be ensured.
Thereby, the run-flat tire according to the first aspect can achieve both the riding comfort performance and the run-flat durability.

According to the run flat tire of the present disclosure, it is possible to achieve both riding comfort during normal running and run flat durability.

BRIEF DESCRIPTION OF THE DRAWINGS It is a half cross-sectional view which shows one side of the cut surface which cut | disconnected the run flat tire which concerns on one Embodiment of this invention along a tire axial direction. BRIEF DESCRIPTION OF THE DRAWINGS It is a half cross-sectional view which shows one side of the cut surface which cut | disconnected the run flat tire which concerns on one Embodiment of this invention along a tire axial direction.

(Configuration of run flat tire)
Hereinafter, a run flat tire 10 according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a run flat tire 10 for a passenger car will be described.

Here, the arrow TW in the figure indicates the width direction of the run flat tire 10 (tire width direction), and the arrow TR indicates the radial direction of the run flat tire 10 (tire radial direction).

タイヤ Here, the tire width direction refers to a direction parallel to the rotation axis of the run flat tire 10, and is also referred to as a tire axial direction. The tire radial direction refers to a direction perpendicular to the rotation axis of the run flat tire 10.

{Circle around (4)} indicates the equatorial plane (tire equatorial plane) of the run flat tire 10. Further, in the present embodiment, the rotational axis side of the run flat tire 10 is “inside in the tire radial direction” along the tire radial direction, and the opposite side of the rotational axis of the run flat tire 10 along the tire radial direction is “tire”. Radially outside ".

On the other hand, the equator plane CL side of the run flat tire 10 along the tire width direction is “inside in the tire width direction”, and the side opposite to the equatorial plane CL of the run flat tire 10 along the tire width direction is “outside in the tire width direction”. It is described.

リム In the following description, the rim is a standard rim (or “Approved @ Rim” or “Recommended @ Rim”) in an application size described in the following standard. Standards are determined by industry standards that are in effect in the area where the tire is manufactured or used. For example, in the United States, "The Book of the Tire and Rim Association of Inc., Inc., Year Book", in Europe, "The European, Tire and Rim, Technical, Organization, Standards of Automotive, Japan Association of Motorcycles, Japan Motor Company, Japan Association of Motorcycles, Japan Association of Motorcycles, Japan Association of Motorcycles, Japan Association of Motorcycles, Japan. Have been.

FIGS. 1 and 2 are cross-sectional views of the run flat tire 10 in a state where the internal pressure is not filled (the same atmospheric pressure as the outside air) by being assembled to the standard rim 30.
As shown in FIG. 1, the run flat tire 10 according to the present embodiment has a pair of bead portions 12, a carcass 14, a belt 16, a belt reinforcing layer 18, a tread portion 20, and a tire side portion 22. And a side reinforcing rubber 24 as a side reinforcing layer, and an inner liner 32.

(4) A pair of left and right bead portions 12 are provided at an interval in the tire width direction (only one bead portion 12 is shown in FIG. 1). A bead core 26 is embedded in each of the pair of bead portions 12, and the carcass 14 extends between the bead cores 26.

(Carcass)
The carcass 14 of the present embodiment is constituted by one carcass ply 15, and the carcass ply 15 covers a plurality of cords (not shown; for example, an organic fiber cord or a metal cord) with a covering rubber. It is formed. The carcass 14 thus formed extends from one bead core 26 to the other bead core 26 in a toroidal shape, and forms a tire skeleton. The run flat tire 10 of the present embodiment is a tire having a radial structure, and a cord of the carcass ply 15 extends in a tire radial direction (radial direction) on a tire side portion, and a tire equatorial plane on a tire outer peripheral portion. It extends in a direction crossing CL.

In the carcass 14, a portion extending from one bead core 26 to the other bead core 26 is referred to as a main body portion 14A, and a portion in which the bead core 26 is folded from the inside to the outside of the tire is referred to as a folded portion 14B. In the present embodiment, the end portion 14BE of the folded portion 14B is sandwiched between the belt 16 and the main body portion 14A of the carcass 14 near the outermost end 16E in the tire width direction of the belt 16 described later.
Further, the end portion 14BE of the folded portion 14B is located outside the other end portion 24B of the side reinforcing rubber 24 described later in the tire width direction, and is located radially inside the belt end of any of the

belt plies

16A and 16B described later. Preferably, they are arranged.

において In the following description, the “case line 14CL” indicates the center line of the thickness of the carcass 14. For example, in a portion where the carcass ply 15 is a single sheet, the center line of the thickness of the carcass ply 15 is defined as a “case line 14CL”. The center line of the thickness is referred to as “case line 14CL”. Further, in a portion where the main body portion 14A and the folded portion 14B of the carcass 14 are present (a portion where a bead filler 28 described later is disposed), the center line between the main body portion 14A and the folded portion 14B (two-dot chain line in FIG. 1). Are shown as “case line 14CL”.

Further, in the present embodiment, in the run-flat tire 10 in a state in which the internal pressure is not filled by being assembled to the standard rim 30, the bead core 26 is made parallel to the tire rotation axis (not shown) through the tire radial outer end. The maximum height SH of the case line 14CL measured outward from the reference line BL in the tire radial direction is referred to as a side height (see FIG. 1).

Furthermore, in the present embodiment, a virtual line (an example of a first virtual line) FL1 which is parallel to the tire rotation axis through a position 10% of the side height SH outward in the tire radial direction from the reference line BL and is parallel to the case An imaginary line that is 0.1SHp at the intersection with the line 14CL and is parallel to the tire rotation axis through a position 20% of the side height SH outward in the tire radial direction from the reference line BL (an example of a second imaginary line) The intersection of FL2 and the case line 14CL is 0.2SHp, and is parallel to the tire rotation axis through the position 40% away from the reference line BL in the tire radial direction and the side height SH away from the reference line BL (an example of a third virtual line). ) The intersection of the imaginary line FL4 and the case line 14CL is 0.4SHp, and is parallel to the tire rotation axis through a position 60% of the side height SH outward in the tire radial direction from the reference line BL. The intersection of the imaginary line (an example of a fourth imaginary line) FL6 and the case line 14CL is referred to as 0.6SHp.

The case line 14CL of the carcass 14 of the present embodiment is such that an arc between the intersection 0.1SHp and the intersection 0.2SHp has a center of curvature inside the tire and is convex to the outside of the tire where the average radius of curvature is R1. Between the intersection 0.4SHp and the intersection 0.6SHp is a circular arc shape having a single radius of curvature having a center of curvature inside the tire and having a radius of curvature of R2 and convex to the outside of the tire. Have been. Note that the case line 14CL between the intersections 0.2SHp and 0.4SHp is the arc shape between the intersections 0.1SHp and 0.2SHp, and the arc between the intersections 0.4SHp and 0.6SHp. The arc shape is smoothly connected to the arc shape and is convex toward the outside of the tire.

In the present embodiment, the radius of curvature R1 is set to be larger than the radius of curvature R2, and the ratio R2 / R1 is set to be larger than 0.3. Further, the ratio R2 / R1 is preferably set to be larger than 0.4. Note that the ratio R2 / R1 is preferably set to be smaller than 1.3.
Further, the radius of curvature R1 is preferably set within the range of 100 to 200% of the side height SH, and the radius of curvature R2 is set within the range of 50 to 150% of the side height SH. preferable.

Here, the radius of curvature R1 is an average value, and the case line 14CL between the intersection 0.1SHp and the intersection 0.2SHp and the case line 14CL between the intersection 0.4SHp and the intersection 0.6SHp are single. May be an arc shape having a radius of curvature of, an arc shape having a plurality of radii of curvature, or a substantially arc shape in which the radius of curvature changes gradually. The radius of curvature of the case line 14CL between the intersection 0.4SHp and the intersection 0.6SHp is infinite in some cases, in other words, the case line 14CL between the intersection 0.4SHp and the intersection 0.6SHp is a straight line. It may be shaped.

In the bead portion 12, a bead filler 28 extending from the bead core 26 outward in the tire radial direction is embedded in a region sandwiched between the main body portion 14A and the folded portion 14B of the carcass 14. Further, the thickness of the bead filler 28 decreases toward the outer end 28A in the tire radial direction. Bead filler 28 is formed of a rubber harder than side rubber 23. Note that the shape and material of the bead filler 28 are not limited to those of the present embodiment.

本体 Further, it is preferable that the main body portion 14A of the carcass 14 has a curved shape (substantially arc shape) in which a portion adjacent to the bead filler 28 outside the bead core 26 in the tire radial direction is convex toward the tire inside.

When the cross-sectional area of the bead filler 28 is Abf and the cross-sectional area of the side reinforcing rubber 24 is Arr when the cross section of the run flat tire 10 is taken along the tire rotation axis, the ratio Abf / Arr is 0.04 to 0.04. It is preferably in the range of 0.17, more preferably in the range of 0.08 to 0.15, and even more preferably in the range of 0.09 to 0.13.

When the cross-sectional area of the side reinforcing rubber 24 inside the tire radial direction from the virtual line FLW is Arri, and the cross-sectional area of the side reinforcing rubber 24 outside the tire radial direction from the virtual line FLW is Aro, the ratio Ari / Aro is set to 0. It is preferably in the range of 3 to 1.5, more preferably in the range of 0.3 to 1.0, and even more preferably in the range of 0.5 to 0.6.

When the sectional area of the bead core 26 is Ac, the ratio Ac / Abf is preferably in the range of 0.7 to 1.1, and more preferably in the range of 0.8 to 1.8. , 0.90 to 0.95.

The ratio ta / G between the total gauge G and the thickness ta is preferably in the range of 0.6 to 1.0, more preferably in the range of 0.6 to 0.8, and 0.7 It is even more preferred to be within the range of -0.8.

The flatness of the run flat tire 10 is preferably 65% or less, more preferably 50% or less, and even more preferably 35% or less.

As shown in FIG. 2, the intersection point where the virtual line FLH passing through the rim end of the standard rim 30 and parallel to the tire radial direction intersects with the main body portion 14A of the carcass 14 inside the tire radial direction of the tire maximum width portion Wmax is Pa, When an angle formed by an imaginary line FLα connecting the intersection Pa with the tire width direction inner end 26P of the bead core 26 with respect to the tire width direction is α, it is preferable that 30 ° <α <70 °, and 35 ° < More preferably, α <60 °, and even more preferably, 35 ° <α <45 °.

The imaginary line FLH is Pb at the intersection of the tire maximum width portion Wmax and the body portion 14A of the carcass 14 on the outer side in the tire radial direction, and the imaginary line FLβ connecting the intersection Pb and the tire width direction inner end 26P of the bead core 26 is When the angle formed with respect to the tire width direction is β, it is preferable that 50 ° <β <80 °, more preferably 55 ° <β <70 °, and 55 ° <β <65 ° Is even more preferred.

As shown in FIG. 1, the other end 24 B side of the side reinforcing rubber 24 in the tire radial direction is disposed inside the belt end of the first belt ply 16 A and the belt end of the second belt ply 16 B in the tire width direction. It is preferred that

頂点 It is preferable that the apex 34T of the rim guard 34 be disposed outside the tire width direction outer end 14max of the main body 14A of the carcass 14 in the tire width direction.

(belt)
A belt 16 is provided outside the carcass 14 in the tire radial direction. The belt 16 of the present embodiment is constituted by one or a plurality of belt plies. As an example, the belt 16 of the present embodiment includes, as an example, a first belt ply 16A inside the tire radial direction, and a second belt that is arranged outside the first belt ply 16A in the tire radial direction and is narrower than the first belt ply 16A. And a ply 16B.

The belt plies 16A and 16B are formed by covering a plurality of cords (steel cords in this embodiment) arranged in parallel with each other with a covering rubber. The cords constituting the belt plies 16A and 16B are arranged to be inclined with respect to the tire circumferential direction (as an example, inclined at an angle of 15 to 30 degrees with respect to the tire circumferential direction). The cord of the belt ply 16A and the cord of the belt ply 16B are inclined in directions opposite to each other with respect to the tire equatorial plane CL. That is, the belt 16 of the present embodiment is a so-called cross belt.

ベルト A belt reinforcing layer 18 is disposed outside the belt 16 in the tire radial direction. The belt reinforcing layer 18 includes, for example, a cord extending along the tire circumferential direction, and is disposed so as to cover the entire belt 16.

ト A tread rubber 21 constituting the tread portion 20 is disposed outside the belt 16 and the belt reinforcing layer 18 in the tire radial direction. The tread portion 20 is a portion that comes into contact with the road surface during traveling, and a circumferential groove 20 A extending in the tire circumferential direction is formed on the surface of the tread portion 20. The tread portion 20 has a not-shown width direction groove extending in the tire width direction. The shape and number of the circumferential grooves 20A and the width grooves are appropriately set in accordance with the required performance of the run flat tire 10, such as drainage performance and steering stability.

タイヤ A tire side portion 22 is provided between the bead portion 12 and the tread portion 20. The tire side portion 22 extends in the tire radial direction and connects the bead portion 12 and the tread portion 20. In the tire side portion 22 and the bead portion 12, a side rubber 23 is arranged outside the carcass 14 in the tire width direction.

(Side reinforcement rubber)
The tire side portion 22 is configured as described below so as to be able to bear the load acting on the run flat tire 10 during run flat running.
In the tire side portion 22, a side reinforcing rubber 24 made of a single rubber material for reinforcing the tire side portion 22 is provided inside the carcass 14 in the tire width direction. The side reinforcing rubber 24 is a reinforcing rubber for running a predetermined distance while supporting the weight of the vehicle and the occupant when the internal pressure of the run flat tire 10 decreases due to puncture or the like. In the present embodiment, the side reinforcing rubber 24 mainly composed of rubber is provided as an example. However, the present invention is not limited to this, and the side reinforcing rubber 24 may be formed of another material. , And a thermoplastic resin or the like as a main component.

In the present embodiment, the side reinforcing rubber 24 is formed of one type of rubber member, but is not limited thereto, and may be formed of, for example, a plurality of rubber members having different hardnesses. The side reinforcing rubber 24 may include a filler, a short fiber, a resin, and other materials as long as the rubber member is a main component. Further, in order to enhance the durability during run flat running, the rubber member constituting the side reinforcing rubber 24 may include a rubber member having a JIS hardness of 70 to 85 measured at 20 ° C. using a durometer hardness tester. . Further, the loss coefficient tan δ measured using a viscoelastic spectrometer (for example, a spectrometer manufactured by Toyo Seiki Seisakusho) at a frequency of 20 Hz, an initial strain of 10%, a dynamic strain of ± 2%, and a temperature of 60 ° C. is 0.10 or less. A rubber member having physical properties may be included.

The side reinforcing rubber 24 extends in the tire radial direction along the inner surface of the main body portion 14A of the carcass 14, and has a shape in which the thickness t decreases toward the bead core 26 and the tread portion 20 side, for example, a substantially crescent cross section. Have been. Here, the thickness t refers to a length of the side reinforcing rubber 24 measured perpendicularly from the tire inner surface in a state where the run flat tire 10 is mounted on the standard rim 30 and the internal pressure is set to zero.

One end 24 A side of the side reinforcing rubber 24 in the tire radial direction is overlapped with the bead filler 28 with the carcass 14 interposed therebetween. That is, the one end 24A side of the side reinforcing rubber 24 is disposed so as to overlap the bead filler 28 in the tire radial direction.
On the other hand, the other end 24 B of the side reinforcing rubber 24 on the outer side in the tire radial direction overlaps with the belt 16 with the carcass 14 interposed therebetween. That is, the other end 24B side of the side reinforcing rubber 24 is disposed so as to overlap the belt 16 in the tire width direction.

Further, the total gauge from the tire inner surface to the tire outer surface as measured on a virtual line FLW passing through the tire maximum width portion Wmax of the run flat tire 10 and parallel to the tire rotation axis is G, from the tire inner surface to the case line 14CL. Is defined as t when the distance is measured in a direction perpendicular to the tire inner surface, the distance t is between 50% and 90% of the total gauge G between the virtual line FL1 and the virtual line FL6. Preferably, it is set.

Further, the side reinforcing rubber maximum width portion position 24P at which the side reinforcing rubber 24 has the maximum width (tmax) is preferably within a range of 20 to 60% of the side height SH, and within a range of 30 to 50% of the side height SH. More preferably, the range of 30 to 40% of the side height SH is even more preferable.

(Inner liner)
In the present embodiment, an inner liner 32 is provided on the inner surface of the carcass 14 and the side reinforcing rubber 24 inside the tread portion 20 in the tire radial direction. The inner liner 32 is made of, for example, rubber containing butyl rubber as a main component. The rubber constituting the inner liner 32 has a lower gas permeability and a greater loss (loss coefficient tan δ) than other rubbers constituting the run flat tire 10 (for example, the tread rubber 21 and the side rubber 23). Is used.

In the inner liner 32 of the present embodiment, the end 32E in the tire width direction is located outside the imaginary line FLE passing through the outermost end 16E of the belt 16 in the tire width direction (the end in the width direction of the first belt ply 16A) 16E. It is arranged so as not to exceed.

At the tire side portion 22 and a part of the bead portion 12, a separation point SP between the rim flange 30A and the bead portion 12 and the rim flange when the internal pressure is reduced to zero when the run flat tire 10 is mounted on the standard rim 30. The rim guard 34 is integrally provided on the outer surface of the tire in the tire radial direction outside the point where the rim guard 34 begins to separate from the rim guard 30A.

The rim guard 34 has a substantially triangular shape protruding outward from the tire from the virtual contour line 22FL of the tire side portion 22 when viewed in a cross section along the tire rotation axis, and has a vertex 34T (most outward from the virtual contour line 22FL toward the tire outside). The inclined surface 34A on the tire radial direction outer side from the distant point) is smoothly connected to the outer surface of the tire side portion 22, and the inclined surface 34B on the tire radial direction inner side from the vertex 34T is normally located between the rim flange 30A. To each other via a gap S.

The distance La in the tire radial direction between the vertex 34T of the rim guard 34 and a virtual line (an example of a second virtual line) FL2 is preferably set within a range of 4 to 10% of the side height SH.
The distance Lb in the tire radial direction between the vertex 34T of the rim guard 34 and an imaginary line FLa parallel to the tire rotation axis passing through the outermost end of the rim flange 30A in the rim radial direction is 3 to 10% of the side height SH. It is preferable to set within the range.
The thickness ta from the vertex 34T of the rim guard 34 to the case line 14CL is set within a range of 140 to 300% of the thickness tb of the bead portion 12 at the separation point SP (measured perpendicular to the case line 14CL). Is preferred.

(Action, effect)
Next, the operation of the run flat tire 10 of the present embodiment will be described.
In the run flat tire 10 of the present embodiment, the shape of the case line 14CL is optimized as described above, so that the vertical spring constant is reduced without thinning the side reinforcing rubber 24, and riding during normal running is performed. Comfort can be improved.
Further, since the rim guard 34 is provided, it is possible to prevent the bead portion 12 from excessively falling down during run flat running, and to ensure run flat durability.
Therefore, the run flat tire 10 of the present embodiment can achieve both ride comfort performance and run flat durability.

In the run flat tire 10 of the present embodiment, the radius of curvature R1 is set within a range of 100 to 200% of the side height SH, and the radius of curvature R2 is set within a range of 50 to 150% of the side height SH. As a result, it is possible to secure a comfortable ride during normal driving.

In the run flat tire 10 of the present embodiment, the distance La in the tire radial direction between the vertex 34T of the rim guard 34 and the second imaginary line FL2 is set within a range of 4 to 10% of the side height SH. Since the distance Lb in the tire radial direction between the apex 34T of the 34 and the virtual line FLa is set within the range of 3 to 10% of the side height SH, it is possible to reliably suppress the bead portion 12 from falling down during run flat running. Can be done.

In the run flat tire 10 of the present embodiment, the thickness ta from the vertex 34T of the rim guard 34 to the case line 14CL is set within a range of 140 to 300% of the thickness tb of the bead portion 12 at the separation point SP. Therefore, the thickness (rubber volume) of the rim guard 34 that abuts on the rim flange 30A during run flat traveling is ensured.

[Other embodiments]
As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above, and it goes without saying that various modifications can be made without departing from the gist of the present invention. It is.

Although the carcass 14 of the above embodiment is configured by one carcass ply 15, the present invention is not limited to this, and the carcass 14 may be configured by a plurality of carcass plies 15.

The belt 16 in the above embodiment is a so-called intersecting belt composed of two belt plies, but may be a spiral belt. Further, the belt 16 may have a structure in which a cord is embedded in a resin layer.

In the above embodiments, the run-flat tires for passenger cars have been described, but the present invention can be applied to run-flat tires used for vehicles other than passenger cars.

The disclosure of Japanese Patent Application No. 2018-120302 filed on May 30, 2018 is referred to in its entirety.
All publications, patent applications, and technical standards referred to in this specification are to the same extent as if each individual publication, patent application, or technical standard was specifically and individually stated to be referenced. Referenced in the specification.

Claims

A pair of bead cores,
A carcass including a main body portion that straddles the pair of bead cores and a folded portion that folds the bead core;
A belt provided on the tire radial outside of the carcass,
A side reinforcing layer provided on the inner side in the tire width direction of the carcass, and having a thickness gradually reduced toward both sides in the tire radial direction,
A rim guard that is provided on the tire outer surface and that restricts the bead portion in which the bead core is buried by contacting the rim flange during run flat running to prevent the bead portion from falling down in the tire axial direction,
With
A center line passing through the center of the thickness of the carcass is a case line,
Measured in the tire radial direction from a reference line parallel to the tire rotational axis through the tire radial outer end of the bead core when viewed on a cross section along the tire rotational axis at zero internal pressure when mounted on a standard rim Side height SH,
An intersection point of the first virtual line and the case line, which is parallel to the tire rotation axis through a position 10% of the side height SH outward in the tire radial direction from the reference line, is 0.1 SHp,
The intersection of the case line with the second imaginary line passing through a position 20% of the side height SH outward from the reference line in the tire radial direction and parallel to the tire rotation axis is 0.2SHp,
An intersection point of the case line with the third virtual line, which is parallel to the tire rotation axis through a position 40% of the side height SH outward in the tire radial direction from the reference line, is 0.4SHp,
When the intersection of the fourth imaginary line passing through a position 60% of the side height SH outward from the reference line in the tire radial direction and parallel to the tire rotation axis and the case line is 0.6SHp. ,
The case line between the intersection 0.1SHp and the 0.2SHp when viewed in a cross section along the tire rotation axis is formed in an arc shape having an average radius of curvature R1,
The case line between the intersection 0.4SHp and the 0.6SHp when viewed in a cross section along the tire rotation axis has an arc shape having a single radius of curvature R2,
The position of the apex of the rim guard is set within a range of 10 to 20% of the side height SH outward in the tire radial direction from the reference line.
Run flat tire.
The run-flat tire according to claim 1, wherein a distance between a vertex of the rim guard and the second virtual line in a tire radial direction is set within a range of 4 to 10% of the side height SH.
3. The method according to claim 1, wherein a thickness from a vertex of the rim guard to the case line is set within a range of 140 to 300% of a thickness of the bead portion at a point of separation of the bead portion from a rim. The run flat tire as described.
The average radius of curvature R1 is set within a range of 100 to 200% of the side height SH,
The curvature radius R2 is set within a range of 50% to 150% of the side height SH.
The run flat tire according to claim 1 or 2.