JP2004182036A - Run flat radial-ply tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a run flat durability from being lowered without reducing degree of freedom in design of a tread pattern. <P>SOLUTION: There are provided a radial carcass 6 and a reinforcing rubber layer 10 arranged between the carcass 6 and an inner liner 9 at its inner circumferential side at a portion corresponding to the side wall 2. This is positioned outside a tread ground contact width under an attitude where a load of 1.1 times of a maximum load capability is applied while filling a maximum pneumatic pressure in a rim assembled tire. In turn, under an attitude in which the tire inner pressure is reduced down to an atmospheric pressure and a mass corresponding to the maximum load capability is applied, a circumferential groove 11 positioned inside the tread ground contact width and continuous circumferentially is arranged at an outer surface of the shoulder region and a depth of each of the circumferential grooves is set to be more than 1/4 of a total tire thickness before forming the circumferential groove. Further, a circumferentially extending angle of the circumferential groove 11 is set at 0 to 30° and then a fibrous reinforcing layer 12 independent from another reinforcing member is arranged in a band-like manner in an area overlapping on the circumferential groove at the inner circumferential side of the circumferential groove 11. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００４０】
表１によれば、周溝の形成によって、ランフラット時のトレッド部のバックリングが抑制されて、トラクション性能が大きく向上することが明らかであり、また、繊維補強層により、ランフラット耐久性能が大きく向上することが明らかである。そして、このランフラット耐久性能は、補強ゴム層の最大厚み部分の位置を選択することでより一層向上することになる。
この一方で、タイヤの正常時の振動乗り心地は、繊維補強層を配設してなお、周溝による、横断面内での曲げ剛性の低減によって有利に向上されることが解る。
【００４１】
【発明の効果】
かくしてこの発明によれば、通常はトレッド接地幅の外側に位置する少なくとも一対の周溝を設けることで、トレッドパターンの設計の自由度を挟めることなく、ランフラット時のトレッド部のバックリングを十分に防止することができ、同時に、周溝の形成に起因するランフラット耐久性の低下を、位置を選択して配設した繊維補強層によって十分に防止することができる。
【図面の簡単な説明】
【図１】トレッド部へのバックリングの発生態様を例示する説明図である。
【図２】バックリングの防止対策を例示する説明図である。
【図３】この発明の実施の形態をタイヤの半部について示す横断面図である。
【図４】他の実施形態を示す同様の横断面図である。
【図５】他の実施形態を示す同様の横断面図である。
【図６】他の実施形態を示す同様の横断面図である。
【図７】他の実施形態を示す同様の横断面図である。
【図８】さらに他の実施形態を示す同様の横断面図である。
【図９】従来タイヤを示す同様の図である。
【図１０】比較例タイヤ１を示す同様の図である。
【図１１】比較例タイヤ２を示す同様の図である。
【符号の説明】
１ トレッド部
２ サイドウォール部
３ ビ−ド部
４ ショルダ部
５ ビ−ドコア
６ ラジアルカーカス
７ ベルト
８ ベルト補強層
９ インナライナ
１０ 補強ゴム層
１１，１３ 周溝
１２ 繊維補強層
Ｔ タイヤ総厚み
ｒ リム[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a run-flat radial tire capable of ensuring safe running while leaking tire internal pressure, among others, a radial tire for a passenger car having an aspect ratio of 0.6 or less, which is used at a relatively high speed, In particular, it proposes a technology that not only enhances the running durability under the leak condition of the tire internal pressure, in other words, the run flat durability, and also effectively suppresses the vibration under the normal use condition of the tire. It is.
[0002]
[Prior art]
For example, in a vehicle running at high speed, generally, a high flexibility is used to prevent the kinetic stability of the vehicle from being greatly impaired due to a sudden loss of tire internal pressure or the like and the tire losing its load supporting ability. The tire's sidewall portion is thickly reinforced with rubber having a relatively large modulus so that even if the tire internal pressure drops to the atmospheric pressure, the wheel load does not extremely increase the deflection deformation of the sidewall portion. Various types of run flat tires have been proposed in the past, in which the tire can be loaded, the reduction in the rolling radius of the tire is suppressed, and the separation of the tire from the rim is prevented.
Such measures are particularly effective for tires having a low aspect ratio, particularly 0.6 or less.
[0003]
However, in the run-flat tire in which the sidewall portion is reinforced with the reinforcing rubber layer in this manner, it is inevitable that the vertical rigidity of the tire increases under the normal use condition of the tire before a failure or the like occurs. Since the vibration of the tire is easily transmitted to the rim and, consequently, to the sprung side, for example, by transmitting the vibration of the tire generated by the unevenness of the road surface from the suspension or the like to the body side, each component of the vibration transmission path However, there is a problem that the durability has to be reduced.
[0004]
On the other hand, when the rigidity of the sidewall portion is significantly increased as compared with that of the tread portion, the central portion in the width direction of the tread tread rises significantly from the road surface due to leakage of the tire internal pressure. As described above, so-called buckling occurs, and the tire comes into contact only in its shoulder region, so that the contact area of the tire is reduced, and the driving and braking performance, steering performance, etc. are greatly reduced. .
[0005]
That is, when such a buckling in which the widthwise central portion of the tread tread rises greatly from the road surface is examined, the deformation of the contact area between the tire and the road surface and its vicinity at the time of run flat is examined. Before the failure of the tire, as shown in the half of the cross section, the outer portion or the shoulder portion of the sidewall portion of the tire in the ground contact state as shown by the broken line in the figure may fall down and deform with respect to the road surface. It has been clarified that this occurs on the basis of the occurrence of a moment M in a direction that separates the tread central portion from the road surface.
This falling deformation causes the point P existing outside the tread contact width to be retracted inward of the tread contact width before the failure of the tire, and the tendency is that the friction force between the tire and the road surface is reduced. The smaller, the larger.
[0006]
By the way, when the above-mentioned analysis of the moment M was performed, the moment M depends on the rigidity of each of the tread portion and the sidewall portion, their rigidity ratio, and the magnitude of the load. It became clear that it was directly affected by the bending stiffness in the cross section of the shoulder part.
Therefore, one useful method for preventing buckling is to reduce the in-section bending stiffness of the shoulder portion and suppress the transmission of the moment M generated due to the deformation of the sidewall portion directly to the tread portion. Is to do. That is, the moment M normally increases in accordance with the ratio of the sidewall portion rigidity to the tread portion rigidity, but a portion that functions as a hinge is provided in the shoulder portion that comes into contact with the ground during run flat. Thus, the occurrence of buckling can be effectively suppressed by eliminating the strong correlation between the deformation of the sidewall portion and the deformation of the tread portion.
[0007]
As a specific means for achieving this, as shown in FIG. 2, it is conceivable to provide a circumferential groove G extending in the circumferential direction in the shoulder portion. By absorbing the deformation and suppressing the transmission of the deformation of the sidewall portion to the tread portion, in other words, the moment M generated based on the deformation of the sidewall portion is relieved by the circumferential groove G, and The transmitted moment can be sufficiently reduced.
[0008]
In this regard, Japanese Patent Application Publication No. 2002-518231 discloses a tread having tread ribs arranged in a lateral direction, a drive surface during run-flat operation, and a drive surface during operation at a standard inflation pressure. Between the side wall ribs arranged in the vicinity of the outermost region in the radial direction of each side wall, and between each side wall rib and the tread rib adjacent thereto, so as not to contact with A pneumatic radial plug, comprising: a first separation groove provided; and a second separation groove provided in a circumferential direction between a tread rib and a tread central region adjacent thereto. An Iran flat tire is disclosed.
[0009]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2002-518231
[Problems to be solved by the invention]
However, the present invention essentially requires the first and second separation grooves, and suppresses transmission of bending force from the sidewall portion to the tread portion during run flat under the cooperation of the two grooves. In particular, the second separation groove existing in the tread surface reduces the degree of freedom in designing the tread pattern, and the presence of the first separation groove reduces the run-flat durability of the tire. There was a problem that the decline could not be denied.
[0011]
An object of the present invention is to solve such a problem in the prior art, and the purpose of the present invention is to reduce the degree of freedom in designing the tread pattern and reduce the run-flat time. An object of the present invention is to provide a run-flat radial tire that can effectively prevent occurrence of buckling and, at the same time, sufficiently prevent a decrease in run-flat durability due to the formation of a circumferential groove.
[0012]
[Means for Solving the Invention]
The run flat radial tire according to the present invention includes a tread portion, a pair of sidewall portions extending inward in the radial direction continuously on both sides of the tread portion, and a bead portion continuous on the inner peripheral side of each sidewall portion. Around a pair of bead cores arranged in each bead portion, a radial carcass composed of one or more carcass plies in which respective side portions are wrapped radially outward, and at least a sidewall portion. The corresponding portion is provided with a reinforcing rubber layer disposed between the radial carcass and the inner liner on the inner peripheral side of the radial carcass. Under the posture with a 1-fold load applied, while being located outside the tread contact width, the tire internal pressure is reduced to atmospheric pressure, which corresponds to the maximum load capacity. At least one pair of circumferential grooves that are located inside the tread contact width and that are continuous in the circumferential direction are provided on the outer surface of the shoulder region under the position where the mass is loaded, and the depth of each circumferential groove is set at the location where it is formed. The circumferential groove has an extension angle of 0 to 30 ° with respect to the circumferential direction, and the circumferential groove has an inner circumferential side of the circumferential groove. In a region overlapping with a part or the entirety of the belt, in addition to the carcass ply, a belt layer used for reinforcing the tread portion, an independent fiber reinforcing layer made of a reinforcing member such as a circumferential reinforcing layer is arranged in a belt shape. .
[0013]
Here, "rim" means the rim specified by the following standard, "maximum air pressure" means the air pressure corresponding to the maximum load capacity in the following standard, and "maximum load capacity" means Refers to the maximum mass that can be applied to the tire according to the following standards.
The “depth of the circumferential groove” here is こ こ of the total thickness of the tire measured from a smooth virtual extension line of the outer contour line of the tire to the circumferential groove portion after the formation of the circumferential groove. It can be specified as above.
[0014]
The standard is an industrial standard that is effective in a region where the tire is manufactured or used. For example, in the United States, "The Tire and Rim Association Inc., Year Book" is used, and in Europe, the European Tire and Technical Technical Organization. Standards Manral ”, and in Japan it is“ JATMA Year Book ”of the Japan Automobile Tire Association.
[0015]
In the tire configured as described above, when the tire is run flat, in particular, a circumferential groove formed in the shoulder region of the tire and having the specified position, extending direction, and depth is formed in the side wall portion. In response to falling on the road surface, based on its own groove width reduction deformation, it effectively suppresses the deformation of the tread part due to the falling deformation and effectively alleviates the moment generated by the falling deformation to the tread part Therefore, as shown by the solid line in FIG. 2, the occurrence of buckling on the tread portion can be effectively prevented.
[0016]
In this case, the fiber reinforcement layer on the inner peripheral side of the circumferential groove is used to protect the circumferential groove, especially the bottom of the groove, thereby sufficiently preventing the decrease in run flat durability due to the formation of the circumferential groove. can do. Here, by arranging the fiber reinforcing layer in a band in a required area, particularly, it is possible to sufficiently suppress the excessive increase in the vertical rigidity of the tire before the occurrence of the failure and to sufficiently reduce the riding comfort to the vehicle. And an unnecessary increase in tire weight can be prevented.
[0017]
By the way, since one or more pairs of circumferential grooves are located outside the tread contact width before the failure of the tire, the presence of the circumferential grooves does not hinder the design of the tread pattern.
Such a circumferential groove is formed at a position outside the tread contact width under a load of 1.1 times the maximum load capacity by filling the tire with the maximum air pressure, so that the tire can be run flat. In this case, a particularly excellent hinge function can be exerted at the location where the peripheral groove is formed.
[0018]
In addition, the depth of the circumferential groove is set to 1/4 or more of the total thickness of the tire to reduce the bending stiffness in the transverse section of the shoulder portion including the circumferential groove, thereby reducing the width of the circumferential groove. By reducing the resistance to deformation sufficiently, the falling deformation of the side wall part is absorbed more effectively with the circumferential groove, and the rising deformation of the tread caused by the falling deformation, and eventually the occurrence of buckling are effective. Can be prevented.
[0019]
In such a circumferential groove effectively functioning to prevent buckling, in order to prevent the occurrence of an early failure around the circumferential groove, the circumferential groove is preferably formed at an angle of 0 to 30 ° with respect to the circumferential direction. Is preferably greater than 0 °, and it is preferable that the circumferential shear strain generated at the groove bottom of the circumferential groove is somewhat dispersed in the tread width direction. In this case, if the extension angle exceeds 30 °, the so-called hinge position deviates from the optimum position by an amount that cannot be ignored, and not only can buckling not be effectively suppressed, but also the groove bottom portion of the circumferential groove can be prevented. Failure nuclei resulting from the concentration of strain on the bottom of the groove are likely to occur.
[0020]
Preferably, in such a tire, the fiber reinforcing layer is disposed at least on the outer peripheral side of the radial carcass. According to this configuration, the function of protecting the fiber reinforcing layer against a failure such as a groove bottom crack in the circumferential groove can be more effectively exerted than when the reinforcing layer is disposed on the inner peripheral side of the carcass. it can.
[0021]
Preferably, the radial position of the maximum thickness portion of the reinforcing rubber layer is positioned between the circumferential groove and the separation point between the rim and the tire in a posture in which the internal pressure of the rim-assembled tire is reduced to the atmospheric pressure.
When the shoulder portion is provided with a circumferential groove as shown in FIG. 2, for example, the deformation of the side wall portion at the time of run flat is different from the case shown in FIG. 1 where no circumferential groove is provided. In the deformed posture, the portion of the sidewall portion having the smallest radius of curvature is located closer to the circumferential groove in the former than the latter in the radial direction of the tire, and the radius of curvature R is Since the radius of curvature is smaller than the radius of curvature R _{0 of the} latter, in the former tire in which a circumferential groove is provided in the shoulder portion, the maximum thickness portion of the reinforcing layer rubber layer is positioned in correspondence with the portion where the radius of curvature is smallest, and the radius of curvature is By suppressing an excessive decrease in the thickness, it is possible to advantageously prevent a breakdown failure of the reinforcing rubber layer itself.
Accordingly, here, as described above, the maximum thickness portion is located between the circumferential groove and the separation point between the rim and the tire, more preferably, at a position particularly close to the circumferential groove, and the reinforcing rubber layer More effectively prevent the destruction of
[0022]
Here, the fibers of the fiber reinforcing layer can be non-twisted or twisted organic or inorganic fibers, and the mode of extension of the fibers can be a blind structure, a three-dimensional braided structure, or the like. However, it is particularly effective that the fiber reinforced layer is a unidirectional fiber reinforced layer in which a cord in which rayon fibers are twisted is disposed, for example, so as to extend substantially in the radial direction.
That is, the optimal cord extending direction of the fiber reinforcement layer is to separate both the deformation of the sidewall portion and the deformation of the tread portion and to avoid the concentration of strain on the cord end of the fiber reinforcement layer. This is to be determined in consideration of this, which is preferably a radial direction or a direction making a relatively small angle to the radial direction, for example an angle in the range of 0 to 30 °.
[0023]
Although the circumferential groove is effective for suppressing buckling, it is necessary to protect the circumferential groove against concentration of strain on the circumferential groove and the like in order to improve run flat durability. By the way, the durability of the peripheral groove and the like, particularly the strain related to the groove bottom crack of the peripheral groove is mainly a circumferential shear strain, and in order to reduce this distortion, the groove is formed on the outer peripheral side of the radial carcass. It is effective to dispose the fiber reinforcing layer in a band shape in a region corresponding to the bottom.
[0024]
In this case, the fibers of the fiber reinforcing layer may be formed of any of an organic material and an inorganic material, and may or may not be twisted, as long as the fibers can exert an appropriate groove bottom protecting function. The arrangement structure of the fibers may be a blind structure, a three-dimensional braided structure, a woven structure, or the like. However, considering the thermal stability in a high-temperature use environment at the time of run flat, it is preferable to use rayon fiber, and considering the destructibility of fibrils inside the fiber, the fiber reinforcing layer is formed with a twisted cord of rayon fiber. Preferably, the cord extends in a substantially radial direction in order to more effectively protect the groove portion from circumferential shear strain in the circumferential groove.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 3 is a sectional view showing an embodiment of the present invention with respect to a half of a tire.
In the figure, 1 is a tread portion, 2 is a sidewall portion extending inward in a radial direction continuously to a side portion of the tread portion 1, and 3 is a bead portion continuous to an inner peripheral side of the sidewall portion 2. Numeral 4 denotes a shoulder, which is also called a buttress at the boundary between the tread portion 1 and the sidewall portion 2 and protects the carcass with a thick rubber layer, while promoting heat dissipation.
[0026]
Here, at least one carcass ply is toroidally extended between a pair of bead cores 5 arranged in the bead portion 3, and a side portion of the carcass ply is wrapped around the bead core 5 radially outward. A radial carcass 6 is formed, and a belt 7 composed of two belt layers here is arranged on the outer peripheral side of the crown portion of the radial carcass 6 in such a manner that a belt layer code intersects between the layers, and On the outer peripheral side of the belt 7, one or more belt reinforcing layers 8 extending substantially in the circumferential direction of the tread and made of, for example, an organic fiber cord and having a width slightly larger than the belt width are provided. At least a portion corresponding to the sidewall portion 2, in the figure, a region extending from the side region of the tread portion 1 to the bead portion 3, and the radial carcass 6 and the inner circumferential side thereof are formed. Between Ina 9, disposed substantially crescent-shaped reinforcing rubber layer 10 made of relatively hard rubber.
[0027]
Also, here, as shown in FIGS. 1 and 2, in a state where the tire mounted on the specified rim r is filled with the maximum air pressure, a load 1.1 times the maximum load capacity is applied, and the tread contact width is still reduced. While being located on the outside, when the tire internal pressure is reduced to atmospheric pressure and a mass corresponding to the maximum load capacity is loaded, at least one pair of left and right, in the figure, at least one circumference will be located inside the tread contact width. A groove 11 is provided on the outer peripheral surface of the shoulder region 4, and the peripheral groove 11 is formed continuously in a linear or zigzag manner at an angle of 0 to 30 ° with respect to the circumferential direction. The circumferential groove 11 shown in this figure extends linearly.
Such a depth of the circumferential groove 11 is set to be equal to or more than ４ of the total thickness T of the tire before forming the circumferential groove at a location where the circumferential groove 11 is formed, thereby sufficiently reducing the in-section bending rigidity of the shoulder region 4.
[0028]
Further, at a position on the inner peripheral side of the peripheral groove 11, a radial carcass 6, a belt 7, and a belt are provided at a region overlapping part or all of the peripheral groove 11, preferably at least a region overlapping the groove bottom. A fiber reinforcing layer 12 independent of the reinforcing layer 8 and other reinforcing members is provided in a belt shape. Preferably, the fiber reinforcing layer 12 is provided by extending a cord in which rayon fibers are twisted substantially in a radial direction. It is constituted by a unidirectional fiber reinforcement layer formed and formed.
[0029]
The fiber reinforcing layer 12 can be provided along the inner periphery of the radial carcass 6 as shown in FIG. 4 in addition to being provided on the outer periphery of the radial carcass 6 as shown.
As shown in FIG. 5, the fiber reinforcing layer 12 may be provided on the outer peripheral side of the radial carcass 6 and disposed very close to the circumferential groove 11. It can be arranged on both the inside and outside of it to further enhance the circumferential groove reinforcing function.
[0030]
FIG. 6 is a view exemplifying this case. In order to further reduce the influence of the deformation of the sidewall portion 2 on the buckling of the tread portion 1, each shoulder region 4 is provided with a circumferential groove 11. In addition, another one of the circumferential grooves 13 is provided. In this case, since the amount of distortion in the circumferential grooves 11 and 13 and the vicinity thereof increases, two layers of fiber reinforcement separated by the radial carcass 6 are provided. By arranging the layer 12, sufficient reduction of circumferential shear strain is ensured.
[0031]
FIG. 7 shows another embodiment. In this embodiment, in order to suppress the concentration of strain in the circumferential groove 11 and the vicinity thereof, the corner of the circumferential groove 11 in the cross section is curved, and at the time of run flat. In order to prevent the destruction of the reinforcing rubber layer 10 and to provide excellent run flat durability, the maximum thickness of the reinforcing rubber layer 10 is set to the radial inner end of the fiber reinforcing layer 12 while keeping the total volume of the reinforcing rubber layer 10 as it is. It is located between the rim and the point of separation from the tire during run flat.
In other words, the portion where the radius of curvature of the sidewall portion becomes the smallest at the time of run flat of the tire in which buckling is prevented appears somewhat from the bead portion than the radially inner end of the fiber reinforcing layer 12, so that the reinforcing rubber layer 10 By adjusting the maximum thickness portion to the position, an extreme decrease in the radius of curvature can be prevented, and a decrease in the durability of the reinforcing rubber layer itself can be prevented.
[0032]
FIG. 8 shows still another embodiment, in which the cross-sectional shape of the circumferential groove 11 is curved like the one shown in FIG. 7, and the circumferential groove 11 has an angle of 30 ° or less with respect to the circumferential direction. In this case, the grooves are extended in a zigzag pattern to distribute the groove bottom strain.
[0033]
【Example】
Hereinafter, an example regarding traction performance, run flat durability performance, and vibration riding comfort of a run flat tire of size 215 / 45R17 provided for a general passenger car will be described.
This run-flat tire is normally used under an air pressure of 230 kPa and a load load of 4165 N. However, the inner side of the radial carcass is designed to withstand the use of the tire under reduced pressure to atmospheric pressure. In addition, a reinforcing rubber layer having a thick rubber thickness is provided, and as a reinforcing member, a radial carcass made of 1650D / 3 rayon fiber and a cord obtained by twisting five layers of 0.22 mm steel filaments in parallel are arranged in parallel. Two steel belt layers intersecting each other whose axis makes an angle of 15 to 30 ° with the tire equator direction, and one or more steel belt layers are arranged so as to cover the belt from the radial outer side and are substantially circumferentially wound. A belt reinforcing layer comprising a ribbon-like aromatic polyamide fiber is provided.
[0034]
In the shoulder region of the conventional tire shown in FIG. 9, a shallow decorative groove is carved. At the formation position of the decorative groove, the tire thickness before forming the groove is 13 mm, and the groove depth is 2.2 mm.
The comparative tire 1 shown in FIG. 10 has a circumferential groove having a groove depth of 4.0 mm provided at a position (tire thickness: 14 mm) closer to the tread by 8 mm from the decorative groove position. This groove can exert the function of reducing the buckling moment by separating the rigidity of the sidewall portion and the rigidity of the tread portion.
In the comparative example tire 2 shown in FIG. 11, the entire side wall portion is rolled in a circumferential direction from the outside of the radial carcass by a IDC made of rayon fiber in order to prevent an early failure occurring near the circumferential groove during the run flat durability test. It is reinforced by turning.
[0035]
In Example Tire 1 shown in FIG. 3, the width of the fiber reinforcement layer used in Comparative Example Tire 2 was reduced so that it did not overlap the folded portion of the carcass ply, and Example Tire 2 shown in FIG. Only the portion corresponding to the groove is reinforced from the inside of the radial carcass. In the example tire 3 shown in FIG. 5, the vicinity of the circumferential groove is reinforced outside the radial carcass.
[0036]
The tire 4 of the embodiment shown in FIG. 6 has two circumferential grooves in order to further reduce the influence of the sidewall portion rigidity on the tread buckling phenomenon. In this case, the strain in the vicinity of the circumferential groove increases, so that the fiber reinforcing layer at the position is made of two layers.
The example tire 5 shown in FIG. 7 is based on the example tire 1, and aims at optimizing the inner shape of the cross section of the circumferential groove to suppress the concentration of strain in the vicinity thereof. This is between the radial inner end of the fiber reinforcing layer and the separation point between the rim and the tire.
[0037]
The tire 6 of the example shown in FIG. 8 is also based on the tire 1 of the example, and the inside shape of the cross-section of the circumferential groove is optimized, and the circumferential groove is zigzag at a swing angle of 20 ° with respect to the circumferential direction. Is extended.
[0038]
For each of these tires, while reducing the tire internal pressure to atmospheric pressure, the traction performance and the drum durability performance when a load of 4165 N was applied were measured, and the tire internal pressure was 230 kPa and the load was 4165 N. The vertical riding force was measured to determine the riding comfort, and the results shown in Table 1 with the indices were obtained. The larger the index value, the better the result.
[0039]
[Table 1]

[0040]
According to Table 1, it is clear that the formation of the circumferential groove suppresses the buckling of the tread portion at the time of run flat and greatly improves the traction performance, and the fiber reinforcement layer improves the run flat durability performance. It is clear that the improvement is significant. The run flat durability performance is further improved by selecting the position of the maximum thickness portion of the reinforcing rubber layer.
On the other hand, it can be seen that the normal riding comfort of the tire is advantageously improved by the provision of the fiber reinforcing layer and the reduction of the bending stiffness in the cross section due to the circumferential groove.
[0041]
【The invention's effect】
Thus, according to the present invention, by providing at least a pair of circumferential grooves which are usually located outside the tread contact width, the buckling of the tread portion at the time of run flat can be sufficiently performed without restricting the degree of freedom in designing the tread pattern. At the same time, a decrease in run flat durability due to the formation of the circumferential groove can be sufficiently prevented by the fiber reinforcing layer disposed at a selected position.
[Brief description of the drawings]
FIG. 1 is an explanatory view illustrating a mode of occurrence of buckling to a tread portion.
FIG. 2 is an explanatory view illustrating a buckling prevention measure;
FIG. 3 is a cross-sectional view showing an embodiment of the present invention for a half of a tire.
FIG. 4 is a similar cross-sectional view showing another embodiment.
FIG. 5 is a similar cross-sectional view showing another embodiment.
FIG. 6 is a similar cross-sectional view showing another embodiment.
FIG. 7 is a similar cross-sectional view showing another embodiment.
FIG. 8 is a similar cross-sectional view showing still another embodiment.
FIG. 9 is a similar view showing a conventional tire.
FIG. 10 is a similar view showing a comparative example tire 1.
FIG. 11 is a similar view showing a comparative example tire 2.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Shoulder part 5 Bead core 6 Radial carcass 7 Belt 8 Belt reinforcement layer 9 Inner liner 10 Reinforcement rubber layers 11, 13 Peripheral groove 12 Fiber reinforcement layer T Total tire thickness r rim

Claims (5)

A tread portion, a pair of sidewall portions extending radially inward from both side portions of the tread portion, and a pair of bead cores provided on each bead portion, the bead portions being continuous on the inner peripheral side of each sidewall portion. A radial carcass consisting of one or more carcass plies with each side part wound back outward in the radial direction around the radial carcass, and at least a part corresponding to the sidewall part, and an inner liner on the inner peripheral side thereof A run-flat radial tire comprising a reinforcing rubber layer disposed between
In a position where the rim-assembled tire is filled with the maximum air pressure and a load of 1.1 times the maximum load capacity is applied, the tire is positioned outside the tread contact width while the tire internal pressure is reduced to atmospheric pressure to achieve the maximum load capacity Under a position loaded with a mass equivalent to the tread, at least a pair of circumferential grooves that are located inside the tread contact width and that are continuous in the circumferential direction are provided on the outer surface of the shoulder area, and the depth of each circumferential groove is set at the location where it is formed. , And at least 1/4 of the total thickness of the tire before the formation of the circumferential groove, the extending angle of the circumferential groove with respect to the circumferential direction is in the range of 0 to 30 °, and the inner circumferential side of the circumferential groove, A run-flat radial tire in which a fiber reinforcing layer independent of other reinforcing members is disposed in a band shape in a region overlapping part or all of the circumferential groove. The run-flat radial tire according to claim 1, wherein the fiber reinforcing layer is disposed at least on an outer peripheral side of the radial carcass. The radial position of the maximum thickness portion of the reinforcing rubber layer is positioned between the circumferential groove and a separation point between the rim and the tire in a posture in which the internal pressure of the rim-assembled tire is reduced to the atmospheric pressure. Or the run flat radial tire according to 2. The run-flat radial tire according to any one of claims 1 to 3, wherein the fiber of the fiber reinforcing layer is an organic or inorganic fiber with or without a twist. 5. The fiber reinforcing layer according to claim 1, wherein a cord obtained by twisting rayon fibers is provided, and the angle of the cord with respect to the radial direction of the tire ranges from 0 to 30 °. The run-flat radial tire according to 1.

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