JPWO2020004111A1 - Run flat tire - Google Patents

Abstract

Run-flat tires consist of a pair of bead cores with a drop-shaped cross section, a carcass in which the main body and the folded portion are overlapped from the bead core toward the outside in the tire radial direction, and a side provided inside the carcus in the tire width direction. It is provided with a reinforcing layer and a rim guard provided on the outer surface of the tire to limit the bead portion from falling outward in the tire axial direction, and the (t / G) between the reference line and the intersection (0.07SHp) is 40. It is set within the range of ~ 80%, the (t / G) between the intersection (0.07SHp) and the intersection (0.44SHp) is set within the range of 55-95%, and the position of the apex of the rim guard is set. , It is set within the range of 10 to 20% of the side height from the reference line.

Description

The present disclosure relates to run-flat tires.

As a run-flat tire capable of traveling a certain distance even when the internal pressure of the tire is lowered, there is a side-reinforced run-flat tire in which the tire side portion is reinforced with side reinforcing rubber (see, for example, 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 vertical spring constant in order to improve the riding comfort performance during normal running, but if the side reinforcing rubber is made thinner or softer, the run-flat durability is lowered.
If the side reinforcing rubber is thickened in order to ensure the run-flat durability, the vertical spring constant becomes high, the riding comfort during normal driving deteriorates, and the tire weight increases.

Further, in a general pneumatic radial tire, a bead filler is provided on the outer side of the bead core in the tire radial direction, and the carcass is wound around the bead filler and the bead core and locked.
During run-flat running, the bending deformation of the bead portion that collapses to the outside of the tire becomes larger than that during normal running. When bending deformation occurs in the bead portion, a compressive force acts on the bead portion and the carcass on one side in the tire width direction with the bead filler sandwiched therein, and tension acts on the carcass on the other side.

A radial carcass cord for reinforcement is embedded in the carcass of the radial tire, but in the bead part, the direction of the radial carcass cord is the tire radial direction (radial direction), so that the bead part and the bead filler A compressive force acts on the radial carcass cord of the carcass on one side in the tire width direction.

Organic fibers are generally used for radial carcass cords, but organic fibers have a property of being weak in compression as compared with tension. For this reason, if a compressive force is repeatedly applied to the radial carcass cord by running on the runflat, the radial carcass cord may become tired and the runflat durability may decrease.
Therefore, it is preferable that the compressive force is not applied to the radial carcass cord of the run-flat tire as much as possible.

In consideration of the above facts, it is an object of the present disclosure to provide a run-flat tire capable of achieving both ride comfort performance during normal driving, run-flat durability, and radial carcass cord durability.

The run-flat tire according to the present disclosure has a pair of bead cores and a plurality of radial tires in which the thickness gradually decreases toward the outside in the tire radial direction and the tire radial dimension is larger than the tire axial dimension. It is configured to include a carcass cord, includes a main body portion that straddles the pair of bead cores, and a folded portion that folds the bead core. The main body portion and the folded portion cover the entire outer circumference of the bead core, and the bead core to the tire. A carcass in which the main body portion and the folded portion are overlapped toward the outer side in the radial direction, a belt provided on the outer side in the tire radial direction of the carcass, and a belt provided on the inner side in the tire width direction of the carcus, and provided in the tire radial direction. A side reinforcing layer that gradually decreases in thickness toward both sides, and a rim guard that is provided on the outer surface of the tire and contacts the rim flange during run-flat running to limit the bead portion in which the bead core is embedded from falling outward in the tire axial direction. The tire diameter of the bead core when viewed in a cross section along the tire rotation axis with zero internal pressure, with the center line passing through the center of the thickness of the carcass as the case line. The height dimension of the case line measured in the tire radial direction from the reference line parallel to the tire rotation axis through the outer end in the direction is the side height SH, and the side height SH is 7% away from the reference line in the tire radial direction. The intersection of the virtual line parallel to the tire rotation axis and the case line is 0.07 SHp, and the tire rotation axis passes through a position 44% away from the reference line in the tire radial direction and 44% away from the side height SH. The intersection of the virtual line parallel to the case line and the case line was 0.44 SHp, the total gauge from the inner surface of the tire to the outer surface of the tire excluding the rim guard was G, and the gauge from the inner surface of the tire to the case line was t. In addition, the t / G between the reference line and the intersection 0.07SHp is set within the range of 40 to 80%, and the t / G between the intersection 0.07SHp and the intersection 0.44SHp is set. It is set within the range of 55 to 95%, and the position of the apex of the rim guard is set within the range of 10 to 20% of the side height SH from the reference line to the outside in the tire radial direction.

In the run-flat tire according to the present disclosure, since t / G is optimized as described above, the vertical spring constant is lowered without thinning the side reinforcing layer, and the riding comfort during normal driving is improved. It can be improved.

In the run-flat tire according to the present disclosure, since the rim guard is provided on the outer surface of the tire, it is possible to suppress excessive collapse of the bead portion during run-flat running, thereby suppressing distortion of the bead portion and running flat. Durability can be ensured.

Further, in the run-flat tire according to the present disclosure, the cross-sectional shape of the bead core is different from the usual circular, rectangular, polygonal, etc. The shape is large in the tire radial direction, in other words, it is formed in a drop shape. The carcass that folds the bead core includes a main body that straddles the pair of bead cores and a fold-back portion that folds the bead core. The main body and the fold-back portion cover the entire outer circumference of the bead core, and the bead core is directed outward in the tire radial direction. , The main body and the folded part are overlapped.

In this way, the main body of the carcass and the folded-back portion are overlapped on the outer side of the bead core in the radial direction of the tire. Compared with the case where the main body portion and the folded portion are separated from each other, the compressive force acting on the radial carcass cord is suppressed, and the durability of the radial carcass cord can be ensured.

As a result, in the run-flat tire according to the present disclosure, it is possible to achieve both ride comfort performance during normal driving, run-flat durability, and durability of the radial carcass cord.

According to the run-flat tire of the present disclosure, it is possible to achieve both ride comfort performance during normal driving, run-flat durability, and durability of the radial carcass cord.

It is a half cross-sectional view which shows one side of the cut surface which cut the run-flat tire which concerns on one Embodiment of this invention along the tire axial direction. It is a half cross-sectional view which shows one side of the cut surface which cut the run-flat tire which concerns on one Embodiment of this invention along the tire axial direction. It is an enlarged cross-sectional view which shows the tire side part. It is a half cross-sectional view which shows one side of the cut surface which cut the run-flat tire which concerns on one Embodiment of this invention along the tire axial direction.

(Composition of run-flat tires)
Hereinafter, the run-flat tire 10 according to the embodiment of the present invention will be described with reference to FIGS. 1 to 3. In this embodiment, the run-flat tire 10 for a passenger car will be described.

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

The tire width direction referred to here refers to a direction parallel to the rotation axis of the run-flat tire 10, and is also referred to as a tire axis direction. Further, the tire radial direction means a direction orthogonal to the rotation axis of the run-flat tire 10.

Further, the reference numeral CL indicates the equatorial plane (tire equatorial plane) of the run-flat tire 10. Further, in the present embodiment, the rotation axis side of the run-flat tire 10 is "inside in the tire radial direction" along the tire radial direction, and the side opposite to the rotation axis of the run-flat tire 10 is "tire" along the tire radial direction. It is described as "diametrically outer".

On the other hand, the equator 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 equator CL of the run-flat tire 10 along the tire width direction is "outside in the tire width direction". It is described as.

Further, in the following description, the rim is a standard rim (or "Approved Rim" or "Recommended Rim") in the applicable size described in the following standard. The standards are set by industrial standards that are valid in the area where the tire is produced or used. For example, in the United States, "The Tire and Rim Association Inc.'s Year Book", in Europe, "The European Tire and Rim Technical Organization's Standard Tire", in Japan, Japan Has been done.

1 to 3 are cross-sectional views taken along the tire rotation axis of the run-flat tire 10 in a state where the run-flat tire 10 is assembled to the standard rim 30 and is not filled with the internal pressure (the same atmospheric pressure as the outside air).
As shown in FIG. 1, the run-flat tire 10 according to the present embodiment includes 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. A side reinforcing rubber 24 as a side reinforcing layer and an inner liner 32 are provided.

A pair of left and right bead portions 12 are provided at intervals in the tire width direction (in FIG. 1, only the bead portion 12 on one side is shown). A bead core 26 is embedded in each of the pair of bead portions 12, and a carcass 14 straddles between the bead cores 26.
The bead core 26 of the present embodiment has a shape in which the thickness gradually decreases toward the outside in the tire radial direction and the dimension in the tire radial direction is larger than the dimension in the tire axial direction, in other words, the bead core 26 is formed in a drop shape. There is.
Further, the carcass 14 that folds the bead core 26 includes a main body portion 14A that straddles the pair of bead cores 26 and a folded-back portion 14B that folds the bead core 26, and the main body portion 14A and the folded-back portion 14B cover the entire outer circumference of the bead core 26. The main body portion 14A and the folded-back portion 14B are overlapped from the bead core 26 toward the outer side in the tire radial direction.

(Carcass)
The carcass 14 of the present embodiment is composed of one carcass ply 15, and the carcass ply 15 has a plurality of radial carcass cords (not shown, for example, an organic fiber cord, a metal cord, etc.) coated with rubber. It is formed by covering it. The carcass 14 thus formed extends from one bead core 26 to the other bead core 26 in a toroid shape to form a tire skeleton. The run-flat tire 10 of the present embodiment is a tire having a radial structure, and the radial carcass cord of the carcass ply 15 extends in the tire radial direction (radial direction) on the tire side portion, and the tire is on the outer peripheral portion of the tire. It extends in the direction intersecting the equatorial plane CL.

In the carcass 14, the portion extending from one bead core 26 to the other bead core 26 is referred to as a main body portion 14A, and the portion in which the bead core 26 is folded back 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-back portion 14B is sandwiched between the belt 16 and the main body portion 14A of the carcass 14 in the vicinity of the outermost end 16E of the belt 16 in the tire width direction, which will be described later.

In the following description, the "case line 14CL" refers to the center line of the thickness of the carcass 14. For example, in the portion where the carcass ply 15 is one sheet, the center line of the thickness of the carcass ply 15 is set as "case line 14CL", and in the portion where a plurality of carcass ply 15s are overlapped, the carcass ply 15 having a plurality of overlapping sheets The center line of the thickness is "case line 14CL". Further, in the portion of the carcass 14 having the main body portion 14A and the folded-back portion 14B, the center line between the main body portion 14A and the folded-back portion 14B (shown by a two-dot chain line in FIG. 2B) is referred to as a “case line 14CL”.

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

Further, in the present embodiment, the intersection of the virtual line FL1 and the case line 14CL, which pass through a position 10% away from the side height SH from the reference line BL to the outside in the tire radial direction and are parallel to the tire rotation axis, is set to 0. 1 SHp, 0.2 SHp, reference line BL at the intersection of the virtual line FL2 and the case line 14CL, which pass through a position 20% away from the side height SH from the reference line BL to the outside in the tire radial direction and are parallel along the tire rotation axis. The intersection of the virtual line FL4 and the case line 14CL, which passes through a position 40% away from the side height SH and is parallel to the tire rotation axis, is 0.4 SHp, and is outside the tire radial direction from the reference line BL. The intersection of the virtual line FL6 and the case line 14CL, which pass through a position 60% away from the heside height SH and are parallel to the tire rotation axis, is called 0.6SHp.

The case line 14CL of the carcass 14 of the present embodiment is an arc in which the intersection point 0.1SHp and the intersection point 0.2SHp have a center of curvature inside the tire and the average radius of curvature is R1 and is convex to the outside of the tire. The shape is an arc shape with a single radius of curvature between the intersection 0.4SHp and the intersection 0.6SHp, which has a center of curvature inside the tire and is convex to the outside of the tire with a radius of curvature R2. Has been done. The case line 14CL between the intersection 0.2 SHp and the intersection 0.4 SHp has an arc shape between the intersection 0.1 SHp and the intersection 0.2 SHp, and between the intersection 0.4 SHp and the intersection 0.6 SHp. It has an arc shape that is convex to the outside of the tire, which is smoothly connected to the arc shape.

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. 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 point 0.1 SHp and the intersection point 0.2 SHp may be an arc shape having a single radius of curvature, and may be formed from a plurality of radius of curvature. It may be an arc shape, or it may be a substantially arc shape in which the radius of curvature gradually changes.
Further, the radius of curvature of the case line 14CL between the intersection 0.1 SHp and the intersection 0.2 SHp is infinite in some cases, in other words, the case line 14 CL between the intersection 0.1 SHp and the intersection 0.2 SHp is a straight line. It may be in shape.

As shown in FIG. 2A in which the same run-flat tire 10 as in FIG. 1 is described, a virtual tire passing through a position 7% away from the reference line BL outward in the tire radial direction and parallel along the tire rotation axis. The intersection of the line FLa and the case line 14CL is 0.07SHp, and the virtual line FLb and the case line are parallel to the tire rotation axis through a position 44% away from the side height SH from the reference line BL to the outside in the tire radial direction. The intersection with 14CL is 0.44SHp, and 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 (direction perpendicular to the tangent line of the inner surface of the tire, in other words, normal line). The gauge from the inner surface of the tire to the case line 14CL is t, and the t / G between the reference line BL and the intersection 0.07SHp (in other words, near the bead portion 12) is 40 to It is set within the range of 80%, and the t / G between the intersection 0.07SHp and the intersection 0.44SHp (in other words, near the rim guard 34 described later) is set within the range of 55 to 95%.

In the bead portion 12 of the present embodiment, the bead filler used in a general pneumatic tire is not provided, and the entire outer circumference of the bead core 26 is covered by the main body portion 14A and the folded-back portion 14B of the carcass 14. At the same time, the main body portion 14A and the folded-back portion 14B are overlapped with each other from the tire radial end portion 26A of the bead core 26 toward the tire radial outer side and are in close contact with each other.
The end portion 14BE of the folded-back portion 14B is located below the maximum tire width portion Wmax.

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 Arro, the ratio Arri / Arro is 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.

The ratio ta / G of the total gauge G to 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 preferable that the range is 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 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 maximum width portion Wmax in the tire radial direction is Pa. When the angle formed by the virtual line FLα connecting the intersection Pa and the inner end 26P of the bead core 26 in the tire width direction with respect to the tire width direction is α, it is preferable that 30 ° <α <70 °, and 35 ° < It is more preferable that α <60 °, and even more preferably 35 ° <α <45 °.

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

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

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

(belt)
A belt 16 is arranged on the outer side of the carcass 14 in the tire radial direction. The belt 16 of the present embodiment is composed of one or a plurality of belt plies. As an example, the belt 16 of the present embodiment is arranged outside the tire radial direction of the first belt ply 16A and the first belt ply 16A on the inner side in the tire radial direction, and is narrower than the first belt ply 16A. It is configured to include the ply 16B.

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

A belt reinforcing layer 18 is arranged on the outer side of the belt 16 in the tire radial direction. As an example, the belt reinforcing layer 18 is configured to include a cord extending along the tire circumferential direction, and is arranged so as to cover the entire belt 16.

The tread rubber 21 constituting the tread portion 20 is arranged on the outer side of 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 20A extending in the tire circumferential direction is formed on the surface of the tread portion 20. Further, the tread portion 20 is formed with a groove in the width direction (not shown) extending in the tire width direction. The shape and number of the circumferential groove 20A and the width direction groove are appropriately set according to the performance such as drainage property and steering stability required for the run-flat tire 10.

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 to connect the bead portion 12 and the tread portion 20. In the tire side portion 22 and the bead portion 12, the side rubber 23 is arranged on the outer side of the carcass 14 in the tire width direction.

(Side reinforcement rubber)
The tire side portion 22 is configured as described below so that the load acting on the run-flat tire 10 can be borne during the run-flat running.
The tire side portion 22 is provided with a side reinforcing rubber 24 made of a single rubber material that reinforces the tire side portion 22 inside the carcass 14 in the tire width direction. The side reinforcing rubber 24 is a reinforcing rubber for traveling a predetermined distance while supporting the weights of the vehicle and the occupant when the internal pressure of the run-flat tire 10 is reduced due to a flat tire or the like. In the present embodiment, the side reinforcing rubber 24 containing rubber as a main component is arranged as an example, but the present invention is not limited to this, and the side reinforcing rubber 24 may be formed of another material, for example. , Thermoplastic resin or the like may be the main component.

In the present embodiment, the side reinforcing rubber 24 is formed of one type of rubber member, but the present invention is not limited to this, and for example, a plurality of rubber members having different hardness may be formed. Further, the side reinforcing rubber 24 may contain other materials such as fillers, short fibers, and resins as long as the rubber member is the 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) under the conditions of 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 decreases toward the bead core 26 side and the tread portion 20 side, for example, a substantially crescent shape in cross section. ing. The thickness referred to here refers to the length measured vertically from the inner surface of the tire of the side reinforcing rubber 24 in a state where the run-flat tire 10 is assembled to the standard rim 30 and the internal pressure is set to zero.

One end portion 24A side of the side reinforcing rubber 24 on the inner side in the tire radial direction is located inside the bead core 26 in the tire width direction with the carcass 14 interposed therebetween.
On the other hand, the other end 24B side of the side reinforcing rubber 24 on the outer side in the tire radial direction overlaps with the belt 16 with the carcass 14 in between. That is, the other end 24B side of the side reinforcing rubber 24 is arranged so as to overlap the belt 16 in the tire width direction.

Furthermore, the total gauge from the tire inner surface to the tire outer surface when measured on the virtual line FLW that passes through the tire maximum width portion Wmax of the run-flat tire 10 and is parallel to the tire rotation axis is G, and from the tire inner surface to the case line 14CL. The distance t between the virtual line FL1 and the virtual line FL6 is within the range of 30 to 70% of the total gauge G, where t is the distance measured in the direction perpendicular to the inner surface of the tire. It is preferable that it is set.

Further, the maximum width portion position 24P of the side reinforcing rubber in which the side reinforcing rubber 24 has the maximum width (tmax) is preferably in the range of 20 to 60% of the side height SH, and is in the 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, the inner liner 32 is arranged on the inner surface of the carcass 14 and the side reinforcing rubber 24 on the inner side of the tread portion 20 in the tire radial direction. As an example, the inner liner 32 is made of rubber containing butyl rubber as a main component. The rubber constituting the inner liner 32 is more difficult for gas to permeate and has a larger loss (loss coefficient tan δ) than other rubbers (for example, tread rubber 21, side rubber 23, etc.) constituting the run-flat tire 10. Is used.

In the inner liner 32 of the present embodiment, the tire width direction end 32E is outward in the tire width direction from the virtual line FLE in which the tire width direction end 32E passes through the outermost end (width direction end portion) 16E of the belt 16 in the tire width direction. It is arranged so that it does not exceed.

A part of the tire side portion 22 and the bead portion 12 has a separation point SP from the rim flange 30A (the bead portion 12 and the rim flange when the run-flat tire 10 is mounted on the standard rim 30 and the internal pressure is set to zero). The rim guard 34 is integrally provided on the outer surface on the outer surface in the radial direction of the tire from the point where it starts to separate from 30A).

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

The distance La in the tire radial direction between the apex 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 tire radial distance Lb between the apex 34T of the rim guard 34 and the virtual line FLa parallel to the tire rotation axis passing through the outermost end in the rim radial direction of the rim flange 30A is 3 to 10% of the side height SH. It is preferable to set it within the range.
The apex 34T of the rim guard 34 is preferably provided within a range of 10 to 20% of the side height SH from the reference line BL to the outside in the tire radial direction.
Further, the thickness ta from the apex 34T of the rim guard 34 to the case line 14CL should be set within the 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 preferable.

(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, so that the side reinforcing rubber 24 is not thinned and is vertically oriented. It is possible to reduce the spring constant and improve the riding comfort during normal driving.

Further, in the run-flat tire 10 of the present embodiment, since the rim guard 34 is provided on the outer surface of the tire, it is possible to suppress excessive collapse of the bead portion 12 during run-flat running, thereby distorting the bead portion 12. Is suppressed, and run-flat durability can be ensured.

Further, in the run-flat tire 10 of the present embodiment, the cross-sectional shape of the bead core 26 is different from the usual circular, rectangular, polygonal, etc. On the other hand, the tire has a large radial dimension, in other words, it is formed in a drop shape. The carcass 14 that folds the bead core 26 includes a main body 14A that straddles the pair of bead cores 26 and a folded portion 14B that folds the bead core 26, and the main body 14A and the folded portion 14B cover the entire outer circumference of the bead core 26. Since the main body portion 14A and the folded portion 14B are overlapped and adhered to each other from the bead core 26 toward the outer side in the tire radial direction, when the bead portion 12 is bent and deformed so as to fall to the outer side of the tire during run-flat running. Compared to the case where the main body and the folded part are separated like a conventional tire, the compressive force acting on the radial carcass cord is suppressed, and the durability of the radial carcass cord (as an example, the compressive force is repeatedly received. Durability against fatigue due to this) can be ensured.

As a result, the run-flat tire 10 of the present embodiment can achieve both ride comfort performance during normal running, run-flat durability, and durability of the radial carcass cord.

In the run-flat tire 10 of the present embodiment, a height position of 20 to 40% of the side height SH from the reference line BL to the outside in the tire radial direction (switching position between the arc of the radius of curvature R1 and the arc of the 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 position between the rim guard 34 and the buttress (shoulder)) from the reference line BL to the outside in the tire radial direction. By setting the t / G measured through 14CL within the range of 60 to 80%, the effect of lowering the vertical 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 a range of 10 to 20% of the side height SH from the reference line BL to the outside in the tire radial direction, so that the run-flat tire 10 is run-flat. Excessive collapse of the bead portion 12 during running is suppressed, and run-flat tire durability is ensured.

[Other Embodiments]
Although one embodiment of the present invention has been described above, the present invention is not limited to the above, and it goes without saying that the present invention can be variously modified and implemented within a range not deviating from the gist thereof. Is.

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

The belt 16 of the above embodiment is a so-called interlaced belt composed of two belt plies, but it 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 also be applied to a run-flat tire used for a vehicle other than a passenger car.

The disclosure of Japanese Patent Application No. 2018-120305 filed on June 25, 2018 is by reference in its entirety.
All documents, patent applications, and technical standards described herein are to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually stated to be referenced. Referenced in the specification.

Claims (2)

A pair of bead cores in which the thickness gradually decreases toward the outside in the tire radial direction and the dimension in the tire radial direction is larger than the dimension in the tire axial direction.
It is configured to include a plurality of radial carcass cords, includes a main body portion that straddles the pair of bead cores, and a folded-back portion that folds the bead core. A carcass in which the main body portion and the folded portion are overlapped from the bead core toward the outer side in the tire radial direction.
A belt provided on the outer side of the carcass in the tire radial direction and
A side reinforcing layer provided inside the carcass in the tire width direction and gradually decreasing in thickness toward both sides in the tire radial direction.
A rim guard provided on the outer surface of the tire that comes into contact with the rim flange during run-flat running and restricts the bead portion in which the bead core is embedded from falling outward in the tire axial direction.
With
The center line passing through the center of the thickness of the carcass is used as the case line.
Measured in the tire radial direction from the reference line parallel to the tire rotation axis through the tire radial outer end of the bead core when mounted on a standard rim and viewed in cross section along the tire rotation axis with zero internal pressure. The height dimension of the case line is the side height SH,
The intersection of the virtual line and the case line, which pass through a position 7% away from the tire radial direction from the reference line and are parallel to the tire rotation axis, is 0.07 SHp.
The intersection of the virtual line and the case line, which pass through a position 44% away from the tire radial direction from the reference line and are parallel to the tire rotation axis, is 0.44 SHp.
The total gauge from the inner surface of the tire to the outer surface of the tire excluding the rim guard is G,
The gauge from the inner surface of the tire to the case line is t,
In the meantime
The t / G between the reference line and the intersection 0.07SHp is set within the range of 40 to 80%.
The t / G between the intersection 0.07SHp and the intersection 0.44SHp is set within the range of 55-95%.
The position of the apex of the rim guard is set within a range of 10 to 20% of the side height SH from the reference line to the outside in the tire radial direction.
Run-flat tires. Claim that the t / G measured through the case line at a height position of 20 to 40% of the side height SH from the reference line to the outside in the tire radial direction is set within the range of 50 to 80%. The run-flat tire according to 1.

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