JP2023089362A - Run-flat tire - Google Patents

Abstract

To provide a run-flat tire 2 which has necessary run-flat durability and excellent ride comfort.SOLUTION: The tire 2 comprises a pair of support layers 18 positioned inside in an axial direction of a side wall 6. A bead 8 comprises a core 32 and an apex 34. A carcass 10 comprises a carcass ply 36 which has a ply main body 36a bridging a gap between a core 32 of the first bead 8 and a core 32 of the second bead 8 and a pair of folded back parts 36b led to the ply main body 36a and each folded back around the core 32 of the bead 8. An end of the folded-back part 36b is positioned closer to inside in a radial direction than an outer end of the apex 34. The support layer 18 is positioned inside in the axial direction of the ply main body 36a. The support layer 18 has a maximum thickness TM inside in the radial direction than a cross sectional width position PW of the tire 2.SELECTED DRAWING: Figure 2

Description

The present invention relates to runflat tires. In particular, the present invention relates to a side reinforcement type runflat tire.

A run-flat tire is known as a tire that can travel a certain distance while being punctured. A support layer having a crescent-shaped cross section is provided on the side portion of the tire.
The support layer increases the rigidity of the side portions. This tire is inferior in ride comfort to a tire (normal tire) having no reinforcing layer on the side portion. With regard to this tire, improvements in performance such as durability are being studied in consideration of the impact on ride comfort (for example, Patent Document 1 below).

Japanese Unexamined Patent Application Publication No. 2017-121900

A carcass ply that constitutes a carcass of a tire includes a ply body that bridges between beads on both sides and a pair of folded portions that are folded around the beads.
In run-flat tires, running in a punctured state (hereinafter referred to as run-flat running) is generally taken into account, and the carcass is constructed so that the end of the folded portion is located between the end of the belt and the ply body.

As mentioned above, the support layer has a crescent-shaped cross-sectional shape. The support layer is thick in its central portion and tapers towards the ends. The support layer occupies most of the side portion. If the cross-sectional shape of the support layer can be controlled, it is expected that performance such as ride comfort and durability can be improved.

In tire vulcanization molding, an unvulcanized tire (hereinafter, unvulcanized tire) is pressurized and heated in a mold. An unvulcanized tire is pressed into a mold.
In the carcass having the construction described above, the ends of the cuffs are constrained. A force is exerted on the support layer within the mold to cause the support layer to flow radially outward. It is difficult to adjust the cross-sectional shape of the support layer to a desired shape. There is a need to establish a technology that can improve ride comfort while taking into consideration the impact on durability in run-flat driving (hereinafter referred to as run-flat durability).

The present invention has been made in view of such circumstances. It is an object of the present invention to provide a runflat tire with the required runflat durability and good ride comfort.

A run-flat tire according to an aspect of the present invention includes a tread that contacts a road surface, a pair of sidewalls that are connected to ends of the tread and positioned radially inward of the tread, and radially inner side walls of the sidewalls. a pair of beads, a carcass bridging between a first bead and a second bead of the pair of beads on the inner side of the tread and the pair of sidewalls, and an axial inner side of the sidewalls A tire comprising a pair of support layers located in the
In this tire, the bead has a core and an apex located radially outside the core. The carcass comprises a ply body that bridges between the first bead core and the second bead core, and a pair of folded parts that are connected to the ply body and folded around the bead cores. a carcass ply having The end of the folded portion is positioned radially inward of the outer end of the apex. The support layer is positioned axially inside the ply body. The support layer exhibits a maximum thickness on the radially inner side of the cross-sectional width position of the tire.

Preferably, in this run-flat tire, the sidewall is provided with an outwardly projecting rim guard. The outer edge of the apex is located radially inward of the top of the rim guard.

Preferably, in this run-flat tire, a normal to the ply body passing through the cross-sectional width position of the tire, a line of intersection with the support layer, a normal to the ply body passing through the crest of the rim guard, and the support Between the lines of intersection with the layers, the support layer exhibits its greatest thickness.

Preferably, in this run-flat tire, the ratio of the thickness of the support layer measured along the normal line of the ply body passing through the crest of the rim guard to the maximum thickness of the support layer is 0.7 or more. be.

Preferably, in this run-flat tire, the ratio of the radial distance from the bead base line to the top of the rim guard to the cross-sectional height of the tire is 0.20 or more and 0.25 or less.

Preferably, in this run-flat tire, along a normal to said ply body passing through a position on the outer surface of said tire at a radial distance from said equator of said tire that is 0.23 times the cross-sectional height of said tire. The ratio of the thickness of the support layer as measured by the thickness of the support layer to the maximum thickness of the support layer is less than or equal to 0.7.

ADVANTAGE OF THE INVENTION According to this invention, the runflat tire which has the required runflat durability and good ride comfort is obtained.

1 is a cross-sectional view showing part of a run-flat tire according to one embodiment of the present invention; FIG. 2 is an enlarged cross-sectional view showing a portion of the run-flat tire of FIG. 1; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

In the present disclosure, a state in which the tire is mounted on a normal rim, the internal pressure of the tire is adjusted to the normal internal pressure, and no load is applied to the tire is referred to as a normal state.

In the present disclosure, the dimensions and angles of each portion of the tire are measured under normal conditions unless otherwise specified.
The dimensions and angles of each part in the meridian cross section of the tire, which cannot be measured with the tire mounted on a regular rim, are obtained by cutting the tire along a plane that includes the axis of rotation. to match the bead-to-bead distance of a tire on a regular rim.

Regular rim means a rim defined in the standard on which the tire relies. A "standard rim" in the JATMA standard, a "design rim" in the TRA standard, and a "measuring rim" in the ETRTO standard are regular rims.

The normal internal pressure means the internal pressure defined in the standard on which the tire relies. The "maximum air pressure" in JATMA standards, the "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standards, and the "INFLATION PRESSURE" in ETRTO standards are regular internal pressures.

Normal load means the load specified in the standard on which the tire relies. "Maximum load capacity" in the JATMA standard, "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "LOAD CAPACITY" in the ETRTO standard are normal loads.

In the present disclosure, the tread portion of a tire is the portion of the tire that contacts the road surface. A bead is that part of the tire that fits onto the rim. A side portion is a portion of the tire that bridges between the tread portion and the bead portion. A tire includes a tread portion, a pair of bead portions, and a pair of side portions as parts.

FIG. 1 shows a portion of a run-flat tire 2 (hereinafter referred to as tire 2) according to one embodiment of the present invention. This tire 2 is a pneumatic tire for passenger cars.
FIG. 1 shows part of a cross section of this tire 2 along a plane containing the axis of rotation of the tire 2 (hereinafter referred to as a meridional cross section). In FIG. 1 , the lateral direction is the axial direction of the tire 2 and the vertical direction is the radial direction of the tire 2 . The direction perpendicular to the paper surface of FIG. 1 is the circumferential direction of the tire 2 . A dashed-dotted line CL represents the equatorial plane of the tire 2 .

The tire 2 is assembled on the rim R. Rim R is a regular rim. The inside of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted. The tire 2 assembled on the rim R is also called a tire-rim assembly. A tire-rim assembly includes a rim R and a tire 2 mounted on the rim R.

In FIG. 1, the axially extending solid line BBL is the bead baseline. This bead baseline is a line that defines the rim diameter of the rim R (see JATMA, etc.).

This tire 2 comprises a tread 4 , a pair of sidewalls 6 , a pair of beads 8 , a carcass 10 , a belt 12 , a band 14 , an innerliner 16 and a pair of support layers 18 .

The tread 4 contacts the road surface on its outer surface. This outer surface is the tread surface 20 . Grooves 22 are cut in the tread 4 . This constitutes a tread pattern.
The tread 4 is made of crosslinked rubber. Although not shown, the tread 4 has a base portion and a cap portion. The base portion is made of cross-linked rubber with low heat build-up. The cap portion is positioned radially outward of the base portion and is made of crosslinked rubber in consideration of abrasion resistance and grip performance.

Reference character PC in FIG. 1 indicates an intersection point between the tread plane 20 and the equatorial plane. The point of intersection PC is the equator of tire 2 . The equator PC is the radially outer end of the tire 2 .
The length indicated by symbol HS in FIG. 1 is the tire section height (see JATMA, etc.). The tire section height HS is the radial distance from the bead baseline to the equator PC.
Reference numeral PD in FIG. 1 indicates a specific position (hereinafter referred to as a matching position) on the outer surface of the tire 2 . A double arrow HD is the radial distance from the equator PC of the tire 2 to the alignment position PD. In this tire 2, the radial distance HD is set to 0.23 times the tire section height HS. The alignment position PD is a position on the outer surface where the radial distance from the equator PC of the tire 2 is 0.23 times the cross-sectional height. The matching position PD is specified for the tire 2 in the normal state.

Each sidewall 6 continues to the edge of the tread 4 . The sidewall 6 is positioned radially inward of the tread 4 . The sidewalls 6 extend radially inward along the carcass 10 from the edge of the tread 4 .
A radially inner portion of the sidewall 6 contacts the rim R. This inner portion is also referred to as chafer rubber 24 . The sidewall 6 of the tire 2 includes sidewall rubber 26 and chafer rubber 24 as constituent elements. The chafer rubber 24 is positioned radially inside the sidewall rubber 26 . The sidewall rubber 26 is made of crosslinked rubber in consideration of cut resistance. The chafer rubber 24 is made of crosslinked rubber in consideration of wear resistance.

A rim guard 28 is configured on the sidewall 6 of the tire 2 .
In FIG. 1, the two-dot chain line LV is the outer surface of the main body 30 of the sidewall 6 obtained on the assumption that there is no rim guard 28 or decoration such as patterns or letters. Although not described in detail, the outline of the outer surface (hereinafter referred to as the outline of the imaginary side surface) in the meridional cross section is formed by combining a plurality of circular arcs centered inside.
The sidewall 6 comprises a body 30 and a rim guard 28 projecting outwardly from the body 30 . The rim guard 28 is positioned radially outward of the rim R as shown in FIG. A rim guard 28 prevents the rim R from being damaged.

In FIG. 1 , the position indicated by PF is the top of the rim guard 28 . The apex PF is the position where the sidewall 6 has the maximum thickness, which is represented by the distance from the carcass 10 to the outer surface of the tire 2 . The thickness of the sidewall 6 is measured along the normal line of the outer surface of the carcass 10 (specifically, the outer surface of the ply body, which will be described later).
The length designated HF in FIG. 1 is the radial distance from the bead baseline to the top PF of the rim guard 28 . The radial distance HF is also referred to as rim guard height.
In this tire 2, from the viewpoint that the rim guard 28 can effectively prevent damage to the rim R, the ratio (HF/HS) of the rim guard height HF to the section height HS is 0.20 or more and 0.25 or less. is preferred.

The position indicated by symbol PW in FIG. 1 is the cross-sectional width position of the tire 2 . This cross-sectional width position is represented by the axial outer end of the contour of the imaginary side surface described above. The axial distance from the first axial outer end PW to the second axial outer end obtained in the normal state is the cross-sectional width of the tire 2 (see JATMA, etc.).
The length indicated by symbol HW in FIG. 1 is the radial distance from the bead baseline to the cross-sectional width position PW. In this tire 2, the ratio (HW/HS) of the radial distance HW to the section height HS is set within a range of 0.4 or more and 0.6 or less.

Each bead 8 is located radially inside the sidewall 6 . Specifically, the bead 8 is located radially inside the sidewall rubber 26 and axially inside the chafer rubber 24 .

Bead 8 has core 32 and apex 34 . Although not shown, the core 32 comprises steel wire. Apex 34 is positioned radially outward of core 32 . Apex 34 tapers outwardly. The apex 34 is made of crosslinked rubber with high rigidity.

The length indicated by symbol HA in FIG. 1 is the apex height. Apex height HA is the radial distance from the bead baseline to the outer edge of apex 34 .
In this tire 2, the ratio (HA/HS) of the apex height HA to the tire section height HS is set within the range of 0.18 or more and 0.23 or less.

A carcass 10 is positioned inside the tread 4 and the pair of sidewalls 6 . The carcass 10 bridges between the first bead 8 and the second bead 8 of the pair of beads 8 . A carcass 10 of this tire 2 has a radial structure.
The carcass 10 has one carcass ply 36 . The carcass ply 36 has a ply body 36a and a pair of folded-back portions 36b. The ply body 36 a bridges between the core 32 of the first bead 8 and the core 32 of the second bead 8 . Each folded portion 36b continues to the ply body 36a and is folded back around the core 32 of the bead 8 from the inner side to the outer side in the axial direction.

Although not shown, the carcass ply 36 includes a large number of parallel carcass cords. Each carcass cord intersects the equatorial plane. A carcass cord is a cord made of organic fibers. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers and aramid fibers.

The belt 12 is positioned radially inside the tread 4 . The belt 12 is laminated to the carcass 10 from the outside in the radial direction.
The belt 12 is constructed of at least two layers 38 that are radially laminated. The belt 12 of this tire 2 consists of two radially laminated layers 38 . Of the two layers 38 , the inner layer 38 is the inner layer 40 and the outer layer 38 is the outer layer 42 .

Although not shown, the inner layer 40 and outer layer 42 each include a number of belt cords in parallel. Each belt cord is inclined with respect to the equatorial plane. The belt cord material is steel.

Band 14 is located radially between tread 4 and belt 12 . A band 14 is laminated to the belt 12 inside the tread 4 . Band 14 covers belt 12 entirely.

Although not shown, band 14 includes a spirally wound band cord. The band cord extends substantially in the circumferential direction. Specifically, the angle formed by the band cord with respect to the circumferential direction is 5° or less. Band 14 has a jointless structure. In this tire 2, cords made of organic fibers are used as band cords. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers and aramid fibers.

A band 14 of this tire 2 comprises a full band 44 and a pair of edge bands 46 . Both ends of the full band 44 face each other across the equatorial plane. The full band 44 covers the entire belt 12 from the outside in the radial direction. A pair of edge bands 46 are axially spaced apart across the equatorial plane. Each edge band 46 radially covers the end of the full band 44 from the outside. The band 14 may consist of only a full band 44 or only a pair of edge bands 46 .

An inner liner 16 is positioned inside the carcass 10 . The inner liner 16 constitutes the inner surface of the tire 2 . The inner liner 16 is made of crosslinked rubber with a low gas permeability coefficient. The inner liner 16 keeps the internal pressure of the tire 2 .

Each support layer 18 is located axially inside the sidewall 6 . The support layer 18 is located axially inside the ply body 36a. In this tire 2 , the ply body 36 a is positioned between the support layer 18 and the sidewall 6 . The folded portion 36b is not located between the support layer 18 and the sidewall 6. As shown in FIG.
The outer edge of the support layer 18 is located axially inward of the edge of the belt 12 . The inner end of support layer 18 is located radially inward of the outer end of apex 34 . The support layer 18 has a cross-sectional shape resembling a crescent moon. Support layer 18 tapers toward its outer end and tapers toward its inner end.

The support layer 18 is made of crosslinked rubber in consideration of rigidity and low heat build-up. The support layer 18 contributes to supporting the load acting on the tire 2 when the tire 2 is punctured. A vehicle equipped with this tire 2 can travel a certain distance even if the tire 2 is punctured. The tire 2 is a side reinforcement type run-flat tire.

FIG. 2 shows a portion of the meridional section shown in FIG. FIG. 2 shows side portions and bead portions of the tire 2 .
In this tire 2, the thickness of the support layer 18 is measured along the normal to the outer surface of the ply body 36a in the meridian section.

In FIG. 2, the solid line LW is the normal line of the ply body 36a passing through the cross-sectional width position PW. The position indicated by symbol BW is the intersection of the normal LW and the outer surface of the support layer 18 . The intersection point BW is a position on the outer surface of the support layer 18 corresponding to the cross-sectional width position PW. A line segment indicated by a double arrow SW is a line of intersection between the normal LW and the support layer 18 . The length TW of the intersection line SW is the thickness of the support layer 18 at the position BW corresponding to the cross-sectional width position PW. A normal line LW of the tire 2 extends in the axial direction.

A solid line LF is normal to the ply body 36a passing through the crest PF of the rim guard 28. The position labeled BF is the intersection of the normal LF and the outer surface of the support layer 18 . The intersection point BF is the location on the outer surface of the support layer 18 corresponding to the top PF of the rim guard 28 . A line segment indicated by a double arrow SF is a line of intersection between the normal LF and the support layer 18 . The length TF of the line of intersection SF is the thickness of the support layer 18 at the location BF corresponding to the top PF of the rim guard 28 .

A solid line LD is a normal line of the ply body 36a passing through the mating position PD. The position indicated by symbol BD is the intersection of normal LD and the outer surface of support layer 18 . The intersection point BD is a position on the outer surface of the support layer 18 corresponding to the mating position PD. A line segment indicated by a double arrow SD is a line of intersection between the normal line LD and the support layer 18 . The length TD of the intersection line SD is the thickness of the support layer 18 at the position BD corresponding to the alignment position PD.

In FIG. 2, the solid line LM is the normal line of the ply body 36a. The position indicated by symbol BM is the intersection of normal LM and the outer surface of support layer 18 . A line segment indicated by a double arrow SM is a line of intersection between the normal LM and the support layer 18 . The length TM of this intersection line SM is the thickness of the support layer 18 at the intersection point BM. In this tire 2, the support layer 18 exhibits the maximum thickness TM at the intersection point BM. The intersection point BM is the position where this support layer 18 exhibits the maximum thickness TM.

As shown in FIG. 2, the line of intersection SM is positioned radially inward of a normal line LW that includes the line of intersection SW as a whole. As described above, the normal line LW passes through the cross-sectional width position PW of this tire 2 . This support layer 18 exhibits the maximum thickness TM on the radially inner side of the cross-sectional width position PW.

In a conventional run-flat tire (hereinafter referred to as a conventional tire), the carcass is constructed such that the ends of the turn-up portions are positioned between the ends of the belt and the ply body. In vulcanization molding of conventional tires, the ends of the folded portion are constrained. A force acts on the support layer within the mold to cause it to flow radially outward. The support layer is configured to have a maximum thickness at a position corresponding to the cross-sectional width position or radially outside the position corresponding to the cross-sectional width position. In conventional tires, it is difficult to adjust the cross-sectional shape of the support layer so that the support layer has the maximum thickness radially inward of the position corresponding to the cross-sectional width position.

On the other hand, in this tire 2, the end of the folded portion 36b is not positioned between the end portion of the belt 12 and the ply body 36a. As shown in FIG. 2, the end of the folded portion 36b is located radially inward of the outer end of the apex 34. As shown in FIG.
In this tire 2, the end of the folded portion 36b is not restrained. In the vulcanization molding of the tire 2, a force tending to cause the support layer 18 in the mold to flow radially outward is less likely to occur. In this tire 2, the support layer 18 can be configured to have the maximum thickness TM on the radially inner side of the cross-sectional width position PW. The tire 2 can be configured such that the rigidity of the radially outer portion of the cross-sectional width position PW is softer than that of the conventional tire, and the rigidity of the radially inner portion of the cross-sectional width position PW is harder than that of the conventional tire.
In this tire 2, the necessary run-flat durability can be obtained in spite of the fact that the ends of the folded portions are not restrained as in conventional tires. Moreover, the carcass 10 and the support layer 18 of the tire 2 contribute to the improvement of ride comfort.
This tire 2 has the necessary run-flat durability and good ride comfort.

In this tire 2, the support layer 18 exhibits the maximum thickness TM between the intersection line SW and the intersection line SF. Thereby, the support layer 18 effectively contributes to improvement of run-flat durability. From this point of view, in this tire 2, the intersection line SW between the normal LW of the ply body 36a passing through the cross-sectional width position PW and the support layer 18, and the normal LF of the ply body 36a passing through the top PF of the rim guard 28 and the support layer Between the line of intersection SF with 18, the support layer 18 preferably exhibits its greatest thickness.

The length indicated by symbol FW in FIG. 2 is the radial distance from the position BW corresponding to the cross-sectional width position PW to the position BF corresponding to the top PF of the rim guard 28 . The length indicated by symbol MW is the radial distance from the position BW corresponding to the cross-sectional width position PW to the position BM where the support layer 18 exhibits the maximum thickness TM. This radial distance MW is a positive number when the position BM at which the support layer 18 exhibits the maximum thickness TM is located radially inside the position BW corresponding to the cross-sectional width position PW, and the support layer 18 has the maximum thickness TM. When the position BM indicating the thickness TM of is positioned radially outside the position BW corresponding to the cross-sectional width position PW, it is represented by a negative number. When the radial distance MW is 0 (zero), the position BM where the support layer 18 exhibits the maximum thickness TM coincides with the position BW corresponding to the cross-sectional width position PW in the radial direction.

In this tire 2, from the viewpoint that the support layer 18 can contribute to maintaining good run-flat durability and good ride comfort, the support layer 18 has the maximum thickness TM from the position BW corresponding to the cross-sectional width position PW. The ratio (MW/FW) of the radial distance MW to the indicated position BM to the radial distance FW from the position BW corresponding to the cross-sectional width position PW to the position BF corresponding to the top PF of the rim guard 28 is 0.00. is preferably 0.80 or less. This ratio (MW/FW) is more preferably 0.40 or more, and even more preferably 0.50 or more. This ratio (MW/FW) is more preferably 0.70 or less, and even more preferably 0.60 or less.

In this tire 2, the ratio (TF/TM) of the thickness TF of the support layer 18 measured along the normal LF of the ply body 36a passing through the top PF of the rim guard 28 to the maximum thickness TM of the support layer 18 is It is preferably 0.7 or more. Thereby, the support layer 18 can effectively contribute to ensuring run-flat durability. From this point of view, the ratio (TF/TM) is more preferably 0.80 or more, more preferably 0.90 or more. From the viewpoint of maintaining good ride comfort, this ratio (TF/TM) is preferably less than 1.00, more preferably 0.95 or less.

In this tire 2, the ratio (TD/TM) of the thickness TD of the support layer 18 measured along the normal line LD of the ply body 36a passing through the mating position PD to the maximum thickness TM of the support layer 18 is 0.5. It is preferably 7 or less. As a result, ride comfort is improved. From this point of view, this ratio (TD/TM) is more preferably 0.60 or less. This ratio (TD/TM) is preferably 0.40 or more from the viewpoint that the support layer 18 can effectively contribute to ensuring run-flat durability.

In this tire 2, the ratio (TW/TM) of the thickness TW of the support layer 18 measured along the normal LW of the ply body 36a passing through the cross-sectional width position PW to the maximum thickness TM of the support layer 18 is 0. 0.90 or less is preferred. As a result, ride comfort is improved. From this point of view, this ratio (TW/TM) is more preferably 0.80 or less. This ratio (TW/TM) is preferably 0.60 or more from the viewpoint that the support layer 18 can effectively contribute to securing run-flat durability.

In FIG. 1, the length indicated by symbol HT is the height of the folded portion 36b, which is the radial distance from the bead baseline to the end of the folded portion 36b.

As described above, in this tire 2 , the end of the folded portion 36 b is positioned radially inward of the outer end of the apex 34 . This carcass 10 contributes to forming the supporting layer 18 into the desired shape. From this point of view, the ratio (HT/HA) of the height HT of the folded portion 36b to the height HA of the apex 34 is preferably 0.80 or less, more preferably 0.65 or less, and further preferably 0.60 or less. preferable. From the viewpoint of improving run-flat durability, the ratio (HT/HA) is preferably 0.30 or more, more preferably 0.40 or more.

In this tire 2 , the outer end of the apex 34 is positioned radially inward of the top PF of the rim guard 28 . As a result, the rigidity in the vicinity of the rim guard 28 is prevented from becoming too high, and good ride comfort is maintained. From this point of view, the outer end of the apex 34 is preferably positioned radially inward of the top PF of the rim guard 28 . Specifically, the ratio (HA/HF) of the height HA of the apex 34 to the rim guard height HF is preferably less than 1.00, more preferably 0.90 or less. From the viewpoint of improving run-flat durability, the ratio (HA/HF) is preferably 0.50 or more, more preferably 0.60 or more.

As described above, according to the present invention, a runflat tire having necessary runflat durability and good ride comfort can be obtained.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited only to these Examples.

[Example 1]
A run-flat tire (tire size=205/55R16) having the basic configuration shown in FIG. 1 and the specifications shown in Table 1 below was obtained.
In Example 1, the ratio (HT/HA) of the height HT of the folded portion to the height HA of the apex was 0.65. The ratio of apex height HA to rim guard height HF (HA/HF) was 0.89.
The radial distance MW from the position BW corresponding to the cross-sectional width position PW to the position BM where the support layer exhibits the maximum thickness TM, from the position BW corresponding to the cross-sectional width position PW to the position corresponding to the top PF of the rim guard The ratio (MW/FW) to the radial distance FW to BF was 0.60.
The ratio of the support layer thickness TF measured along the ply body normal LF through the rim guard crest PF to the support layer maximum thickness TM (TF/TM) was 0.90.
The ratio of the support layer thickness TD measured along the ply body normal LD passing through the mating position PD to the support layer maximum thickness TM (TD/TM) was 0.60.

[Comparative Example 1]
Comparative Example 1 is a conventional run-flat tire. The ratio (HT/HA), ratio (HA/HF), ratio (MW/FW), ratio (TF/TM) and ratio (TD/TM) of Comparative Example 1 are as shown in Table 1 below. rice field.
In Comparative Example 1, the end of the folded portion was positioned between the end portion of the belt and the ply body, and the support layer exhibited the maximum thickness at position BW corresponding to cross-sectional width position PW.

[Ride comfort]
A prototype tire was mounted on a regular rim and air was filled to adjust the internal pressure of the tire to 230 kPa. The tire was mounted on a test vehicle (domestic passenger car (displacement = 1500 cc). The test vehicle was run on a dry asphalt road test course, and a sensory evaluation of ride comfort was performed. The results are shown in Table 1 below. column, indexed with Comparative Example 1 as 100. The larger the value, the better.

[Run flat durability]
A prototype tire was mounted on a regular rim, the valve core was removed, the internal pressure was set to 0 kPa, and the tire was run on a drum tester at a speed of 80 km/h, and the distance traveled until the tire was destroyed was measured. The results are shown in the column of durability in Table 1 below as an index with Comparative Example 1 set to 100. The larger the numerical value, the better.

As shown in Table 1, it has been confirmed that the Example has run-flat durability comparable to that of Comparative Example 1 as a conventional tire, and can achieve an improvement in ride comfort. From this evaluation result, the superiority of the present invention is clear.

The above-described technique capable of improving ride comfort while obtaining the required runflat durability can also be applied to various runflat tires.

2...Tire 4...Tread 6...Sidewall 8...Bead 10...Carcass 18...Support layer 28...Rim guard 32...Core 34...Apex 36. Carcass ply 36a Ply main body 36b Folded portion

Claims (6)

A tread that contacts the road surface,
a pair of sidewalls connected to the edge of the tread and positioned radially inward of the tread;
a pair of beads positioned radially inward of the sidewall;
a carcass bridging between a first bead and a second bead of the pair of beads inside the tread and the pair of sidewalls;
A tire comprising a pair of support layers positioned axially inside the sidewall,
the bead comprises a core and an apex located radially outward of the core;
The carcass comprises a ply body that bridges between the first bead core and the second bead core, and a pair of folded-back portions connected to the ply body and folded back around the bead core. a carcass ply having
The end of the folded portion is positioned radially inward from the outer end of the apex,
The support layer is positioned axially inside the ply body,
The support layer exhibits a maximum thickness radially inward of the cross-sectional width position of the tire,
run-flat tires. a rim guard from which the sidewall protrudes outward;
an outer end of the apex is located radially inward of the top of the rim guard;
The runflat tire according to claim 1. between the normal to the ply body passing through the cross-sectional width position of the tire and the line of intersection with the support layer, and the line of intersection between the normal to the ply body passing through the crest of the rim guard and the support layer , the support layer exhibits a maximum thickness,
The run-flat tire according to claim 2. a ratio of the thickness of the support layer measured along the normal of the ply body through the crest of the rim guard to the maximum thickness of the support layer is greater than or equal to 0.7;
The run-flat tire according to claim 2 or 3. The ratio of the radial distance from the bead baseline to the top of the rim guard to the cross-sectional height of the tire is 0.20 or more and 0.25 or less.
A run-flat tire according to any one of claims 2 to 4. The thickness of the support layer measured along the outer surface of the tire along the normal to the ply body passing through a location where the radial distance from the tire's equator represents 0.23 times the tire's section height. The ratio of the thickness to the maximum thickness of the support layer is 0.7 or less.
A runflat tire according to any one of claims 1 to 5.

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