WO2020004110A1

WO2020004110A1 - Run-flat tire

Info

Publication number: WO2020004110A1
Application number: PCT/JP2019/023949
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: JP7128274B2; JPWO2020004110A1

Abstract

This run-flat tire is provided with: a pair of bead cores; a carcass; side reinforcing rubber which is provided inside of the carcass in the tire width direction; and a rim guard which is provided on the outside surface of the tire and which limits collapse of the bead part to outside in the tire axial direction. When the center line through the center of the carcass thickness is set as a case line, (t/G) between the point of intersection (0.1 Hp) and the point of intersection (0.3 Hp) is set within the range 40-80%, (t/G) between the point of intersection (0.8 Hp) and the point of intersection (0.9 Hp) is set within the range 30-60%, and the position of the apex of the rim guard is set within the range of 10-20% of the side height from the reference line outwards in the tire radial direction.

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.

A run flat tire according to the present disclosure includes 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 cores, and a belt provided outside the carcass in a tire radial direction. A side reinforcing layer provided on the inner side in the tire width direction of the carcass and gradually reduced in thickness toward both sides in the tire radial direction; and a bead core provided on the outer side of the tire and contacting a rim flange during run flat running to bury the bead core. A rim guard for limiting the fall of the bead portion to the outside in the tire axial direction, a center line passing through the center of the thickness of the carcass as a case line, mounted on a standard rim, and mounted on a standard rim at a zero inner pressure state. When viewed from a cross-section along the tire core diameter, a reference line parallel to the tire rotation axis passes through the tire radial outer end of the bead core. The height dimension of the case line measured in the direction is a side height SH, and a first imaginary parallel to the tire rotation axis passing through a position 10% away from the reference line in the tire radial direction and away from the side height SH. The intersection between the line and the case line is 0.1SHp, the second imaginary line parallel to the tire rotation axis passing through the position 30% of the side height SH outward from the reference line in the tire radial direction and the tire rotation axis. An intersection with the case line is 0.3SHp, a third imaginary line parallel to the tire rotation axis passing through a position 80% of the side height SH outward in the tire radial direction from the reference line and the case line. At the intersection of 0.8SHp, a fourth imaginary line parallel to the tire rotation axis passing through a position 90% of the side height SH outward from the reference line in the tire radial direction, and the case line. Is 0.9SHp, G is the total gauge from the inner surface of the tire to the outer surface of the tire excluding the rim guard, and t is the gauge from the inner surface of the tire to the case line. 3Hp, the t / G is set within a range of 40 to 80%, and the t / G between the intersection 0.8Hp and the intersection 0.9Hp is set within a range of 30 to 60%. 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 present disclosure, since the t / G of the gauge is optimized as described above, the vertical spring constant is reduced without thinning the side reinforcing layer, and the riding during normal running is performed. 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.
As a result, the run-flat tire according to the present disclosure can achieve both riding comfort performance and 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. It is an expanded sectional view showing a tire side part. 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 FIGS. 1 to 3. 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 to 3 are cross-sectional views of the run flat tire 10 assembled with the standard rim 30 and not filled with the internal pressure (same pressure as the outside air) along the tire rotation axis.
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, the intersection of the virtual line FL1 and the case line 14CL, which is parallel to the tire rotation axis through a position 10% of the side height SH outward from the reference line BL in the tire radial direction and is parallel to the tire rotation axis, is set to 0.1. 1SHp, the intersection of the imaginary line FL2, which 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 and the case line 14CL, is 0.2SHp, the reference line BL. At the intersection of the virtual line FL4 and the case line 14CL, which are parallel to the tire rotation axis through the position 40% away from the side height SH from the reference line BL to the tire radial outside from the reference line BL. The intersection point of the virtual line FL6, which is parallel to the tire rotation axis through the position 60% away from the side height SH, and the case line 14CL is called 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 may have an arc shape having a single radius of curvature. An arc shape may be used, 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 0.1SHp and the intersection 0.2SHp may be infinite in some cases, in other words, the case line 14CL between the intersection 0.1SHp and the intersection 0.2SHp is a straight line. It may be shaped.

As shown in FIG. 2A in which the same run-flat tire 10 as that in FIG. 1 is described, the run-flat tire 10 is parallel to the tire rotation axis along the tire rotation axis through a position 10% away from the reference line BL in the tire radial direction and away from the side height SH. The intersection of the virtual line FLa and the case line 14CL is 0.1SHp, the virtual line FLb is parallel to the tire rotation axis through the position 30% of the side height SH outward from the reference line BL in the tire radial direction, and parallel to the tire rotation axis. The intersection point with the line 14CL is 0.3SHp, and the intersection point between the virtual line FLc passing through a position 55% of the side height SH outward from the reference line BL in the tire radial direction and parallel to the tire rotation axis and the case line 14C. 0.55 SHp, and a virtual line FLd that is parallel to the tire rotation axis through a position 80% of the side height SH outward in the tire radial direction from the reference line BL. The point of intersection with the line 14CL is 0.8SHp, and the point of intersection with the virtual line FLe case line 14CL, which is parallel to the tire rotation axis through a position 90% of the side height SH outward from the reference line BL in the tire radial direction and parallel to the tire rotation axis. 0.9SHp, as shown in FIG. 2B, the total gauge from the inner surface of the tire to the outer surface of the tire excluding the rim guard 34 described later is G (measured in the direction perpendicular to the tangent to the inner surface of the tire, in other words, in the direction of the normal). Assuming that the gauge from the inner surface of the tire to the case line 14CL is t, the t / G between the intersection 0.1SHp and the intersection 0.3SHp is set within a range of 40 to 80%, and the intersection 0.8SHp And the intersection point 0.9SHp is set within the range of 30 to 60%.

Further, as shown in FIG. 1, at a height position of 20 to 40% of the side height SH outward from the reference line BL in the tire radial direction (near a switching position between an arc having a radius of curvature R1 and an arc having a radius of curvature R2). The t / G measured through the case line 14CL is preferably set within the range of 50 to 80%, and the height position of the side height SH from 40 to 60% of the side height SH from the reference line BL (the rim guard 34). It is preferable to set the t / G measured through the case line 14CL at the position between the middle and the buttress (shoulder) within the range of 60 to 80%.

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. In addition, the thickness of the bead filler 28 decreases outward 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. 3, 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 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 whose thickness decreases toward the bead core 26 side and the tread portion 20 side, for example, has a substantially crescent cross section. ing. Here, the thickness refers to the length of the side reinforcing rubber 24 measured perpendicularly from the tire inner surface when the run flat tire 10 is assembled to 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 30% and 70% 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.

(Rim guard)
As shown in FIG. 1, 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 (virtual contour). The inclined surface 34A on the tire radial direction outside from the line 22FL farthest to the tire outside) is smoothly connected to the outer surface of the tire side portion 22, and the inclined surface 34B on the tire radial direction inside from the vertex 34T is normal. , And the rim flange 30A via a gap S.

The apex 34T of the rim guard 34 is provided within a range of 10 to 20% of the side height SH outward in the tire radial direction from the reference line BL.

The distance La in the tire radial direction between the vertex 34T of the rim guard 34 and the 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.
It is preferable that the apex 34T of the rim guard 34 be provided within a range of 10% to 20% of the side height SH outward in the tire radial direction from the reference line BL.
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 value of the ratio t / G is optimized from the bead portion 12 to the tread portion 20 as described above. The spring constant can be reduced, and the riding comfort during normal running 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, a position at a height of 20 to 40% of the side height SH outward from the reference line BL in the tire radial direction (a switching position between an arc having a radius of curvature R1 and an arc having a radius of curvature R2). By setting the t / G measured through the case line 14CL (in the vicinity) within the range of 50 to 80%, the effect of lowering the longitudinal spring constant can be enhanced.

Further, in the run flat tire 10 of the present embodiment, the case line at a height position of 40 to 60% of the side height SH (near the middle position between the rim guard 34 and the buttress (shoulder)) outward from the reference line BL in the tire radial direction. By setting t / G measured through 14CL within the range of 60 to 80%, the effect of lowering the longitudinal spring constant can be enhanced.

Further, in the run flat tire 10 of the present embodiment, the position of the apex 34T of the rim guard 34 is provided within the range of 10 to 20% of the side height SH from the reference line BL outward in the tire radial direction. Excessive fall of the bead portion 12 during running is suppressed, and run-flat tire durability 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 embodiment, the run-flat tire for a passenger car has been described, but the present invention can be applied to a run-flat tire used for a vehicle other than a passenger car.

The disclosure of Japanese Patent Application No. 2018-120304 filed on June 25, 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 parallel to the tire rotation axis passing through a position 30% of the side height SH outward in the tire radial direction from the reference line is 0.3 SHp,
The intersection of the third imaginary line passing through a position 80% of the side height SH outward from the reference line in the tire radial direction along the tire rotation axis and the case line is 0.8SHp,
An intersection point of the case line with the fourth imaginary line which is parallel to the tire rotation axis at a position 90% of the side height SH outward from the reference line in the tire radial direction is 0.9SHp,
The total gauge from the tire inner surface to the tire outer surface excluding the rim guard is G,
The gauge from the tire inner surface to the case line is t,
And then
T / G between the intersection 0.1Hp and the intersection 0.3Hp is set within a range of 40 to 80%,
T / G between the intersection 0.8Hp and the intersection 0.9Hp is set within a range of 30 to 60%,
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 t / G measured through the case line at a height position of 20 to 40% of the side height SH outward from the reference line in the tire radial direction is set within a range of 50 to 80%. 2. The run flat tire according to 1.
The t / G measured through the case line at a height position of 40 to 60% of the side height SH from the reference line to the tire radial direction outside is set in a range of 60 to 80%. The run flat tire according to claim 1 or 2.
The run flat according to any one of claims 1 to 3, wherein an apex of the rim guard is provided within a range of 10 to 20% of the side height SH outward in the tire radial direction from the reference line. tire.