JP2004017668A - Runflat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a runflat tire excellent in durability. <P>SOLUTION: This runflat tire 1 is furnished with a cross-section crescent reinforcing layer 10 on the inner surface side of a carcass 5. The reinforcing layer 10 is constituted of a pair of end parts 13a, 13b thickness t<SB>1</SB>of which gradually increases in accordance with an expression t<SB>1</SB>=ax<SP>n</SP>(but a>0. n>1) by specifying a distance from an end edge 11 as (x) seen from a cross-section in the tire cross direction, a pair of transfer parts having an inflection point at a boundary position of the end parts 13a, 13b and thickness of which gradually increases toward a point where thickness of the reinforcing layer becomes maximum and a central part 17 positioned between the both transfer parts 16a, 16b. <P>COPYRIGHT: (C)2004,JPO

Description

但し、−φ／２≦θ≦φ／２である。
【００２８】
上式より、最大圧縮応力σは、θ＝−φ／２またはφ／２において最小となり、θ＝０において最大となることが分かる。
【００２９】
また、サイドウォール部３の剛性を高めるため、カーカス５内面側に補強層１０を配設した場合の最大圧縮応力σ′は、補強層１０のタイヤ周方向断面積をａとすると、次式のように表される。
【００３０】
【数２】

【００３１】
したがって、任意の角度θにおける最大圧縮応力σ′を均一にするためには、上式の右辺第二項が右辺第一項に反比例して変化する必要がある。すなわち、ｃｏｓθが最小のときにＷ／（Ａ＋ａ）が最大になる、すなわちａが最小となり、ｃｏｓθが最大のときにＷ／（Ａ＋ａ）が最小になる、すなわちａが最大となる必要がある。このような断面積ａの変化を有する補強層１０のタイヤ幅方向断面形状は三日月状となる。
【００３２】
しかしながら、このような断面形状の補強層１０を用いたとしても、補強層１０がサイドウォール部３と接合する両端縁１１においては、補強層１０とこれに隣接する部材との間に剛性段差を生じやすいため、補強層１０の端縁１１近傍に応力が集中し、早期に故障が生じやすいという問題があった。
【００３３】
発明者は、この問題を解決するためには、補強層１０とこれに隣接する部材との間で剛性が連続的に変化するように端部１３ａ、１３ｂの形状を加工すればよいことを見出した。そこで、材料力学の断面二次モーメントを用いて曲げ剛性を考慮し、補強層１０とこれに隣接する部材との間で剛性が連続的に変化するには、両端部１３ａ、１３ｂにおいて断面二次モーメントの２階微分が連続であり、かつ両端縁１１ａ、１１ｂにおいて実質上零となればよいことを見出した。
【００３４】
すなわち、補強層１０の一方の端部１３ａまたは１３ｂについて考察すると、補強層１０のタイヤ径方向端縁１１から補強層の外周面１２に沿って測定した距離を変数ｘとし、補強層１０の厚さをｔ_１とするとき、０≦ｘ≦１／２の領域において、曲げ剛性として周方向単位幅あたりの断面二次モーメントＩは次のように表される。
【００３５】
【数３】

【００３６】
ここで、ｘ＜０でｔ_１＝０、Ｉ＝０の領域を含めてｘ＝０でＩおよび１階微分、２階微分が常に実質上連続となる、すなわちＩ（０）＝Ｉ^（１）（０）＝Ｉ^（２）（０）＝０となる取扱いの簡便な一般関数形としては、定数項を含まない工事関数形が考えられる。さらに、ここでは端部領域についてのみ議論しているので、この領域では変曲点を含まない漸増状態を常に満足することが好ましい。ここで高次多項式について考えると、最高次数項についてのみ取り上げると前述の条件が満足されるので、ｔ_１はｘの累乗、すなわちｔ_１＝ａｘ^ｎと表すことができる。これを上式に代入し、１階微分および２階微分を求めると次のようになる。
【００３７】
【数４】

【００３８】
補強層１０とこれに隣接する部材との間で剛性が連続的に変化するためには、０≦ｘ≦１／２の領域において、少なくとも上記３つの式が連続であることが必要である。さらに、端縁１１において剛性段差を生じないためには、ｘの減少に伴ってＩも漸減して零に収束すること、すなわち２階微分が１次関数系よりも大きいこと、望ましくは２次関数以上であることが必要である。
【００３９】
したがって、Ｉ^（２）の累乗の指数部について、
３ｎ−２＞１、　∴ｎ＞１
望ましくは、
３ｎ−２≧２、　∴ｎ≧４／３
であることが必要である。
【００４０】
移行部１６ａ、１６ｂの形状は、特に限定されず、曲線状、直線状等とすることができるが、移行部１６ａ、１６ｂの厚さの変化率が、変曲点から補強層１０の厚さが最大となる点に向かって漸減する、例えば上に凸形状の曲線であると、剛性段差をより一層回避できることから、好ましい。
【００４１】
よってこの発明では、端部１３ａ、１３ｂの形状の適正化を図ることにより、補強層１０とこれに接する部材との間で生じる剛性段差を小さくすることができる。
【００４２】
また、一方の端部１３ａ、１３ｂとこれに隣接する移行部１６ａ、１６ｂとを合わせた幅が補強層１０の幅Ｗ_１の０．２倍以上であることが好ましい。剛性段差に起因する応力の集中現象を回避するには、剛性が漸増する断面形状を有することが重要であるが、一方の端部１３ａ、１３ｂとこれに隣接する移行部１６ａ、１６ｂとを合わせた幅が補強層１０の幅の０．２倍未満では、その効果は不十分であり、補強層１０全体として十分に応力の集中を抑制することができなくなるおそれがあるからである。
【００４３】
さらに、補強層１０の厚さの最大値ｔ_ｍａｘが補強層１０の幅Ｗ_１の０．１４倍以上であることが好ましい。厚さの最大値ｔ_ｍａｘが幅Ｗ_１の０．１４倍より小さいと、ランフラットタイヤに必要とされるタイヤの剛性が不足する傾向があるからである。なお、補強層１０の厚さの最大値ｔ_ｍａｘとは、図２に示すように、タイヤ貼り付け前の補強層１０の形状で測定したときの厚さの最大値ｔ_ｍａｘを意味する。
【００４４】
さらにまた、変曲点の位置は、補強層１０の厚さの最大値の７０％以下の範囲にあることが好ましい。変曲点の位置を補強層１０の厚さの最大値の７０％以下の範囲とすることで、移行部分１６ａ、１６ｂにおける補強層１０の厚さをなだらかに漸増させることが可能となり、補強層１０の厚さの変化が急激となる部分が無くなり、タイヤのランフラット性能を向上させることができるからである。
【００４５】
さらにまた、補強層１０の中央部１７においては、端部１３ａ、１３ｂに比べると曲げ剛性が十分に大きくなっており、実質上応力の集中は発生しないため、端部１３ａ、１３ｂや移行部１６ａ、１６ｂのように必ずしも曲げ剛性が上述した３つの式で連続である必要はなく、少なくとも曲げ剛性、すなわち厚さの分布が連続していればよい。したがって、中央部１７は平坦であってもよく、または角部や凹部を有していてもよいが、加工適正の観点からは図２に示すように中央部１７の厚さはほぼ一定であることが好ましく、タイヤの軽量化の観点からは図３に示すように中央部１７の中央域１９の厚さが両端域１８のそれに比べて薄いことが好ましい。
【００４６】
加えて、補強層１０は、そのタイヤ径方向外側に位置する端部１３ｂをベルト９の端部下方にオーバーラップさせて配設し、かかるオーバーラップ範囲をタイヤ幅方向に測定したときの幅Ｗ_２が、カーカス高さＨ_ｃの０．２倍以上であることが好ましい。補強層１０とベルト９とがオーバーラップしていないと、ベルト９の端部直下での剛性が相対的に低くなる結果、この領域に応力が集中して早期に故障することがあるからである。
【００４７】
また、補強層１０のタイヤ径方向内端縁１１ａとリム径ライン２０との間のタイヤ径方向距離ｄが、標準リムのフランジ高さの１．３倍以上であることが好ましい。ビード部２には、ビードワイヤ、ビードフィラー等の補強部材が埋設されている上、リムと嵌合することでビード部はリムフランジからも支持されるので、標準リムのフランジ高さの１．３倍未満の領域にまで補強層１０を配設してもタイヤ重量を増加させるばかりで、十分な剛性増大効果は得られない傾向があるからである。
【００４８】
さらに、補強層１０の材質は、ゴム、樹脂またはこれらの材料中に大量の空隙部を有するもの、例えば発泡ゴム、発泡ウレタン等を用いることが可能であるが、操縦安定性と乗心地性の双方をバランスよく確保する観点からは硬質ゴムであることが好ましい。
【００４９】
さらにまた、補強層１０の１００％モジュラスが４ＭＰａ以上であることが好ましい。１００％モジュラスが４ＭＰａ未満の場合には、ランフラット走行に必要な剛性を確保できないからである。
【００５０】
加えて、カーカスを構成する少なくとも１枚のプライが、ナイロン６、ナイロン６６、ポリエチレンテレフタレート（ＰＥＴ）、レーヨン、ポリエチレンナフタレート（ＰＥＮ）およびアラミドからなる群より選択されたコードを有することが好ましい。ランフラット走行時にはタイヤ内圧がほぼ零となり、カーカスに張力が付与されない状態で走行するため、柔軟性および耐摩耗性を具えたカーカスコードが必要となるからである。
【００５１】
なお、上述したところは、この発明の実施形態の一例を示したにすぎず、請求の範囲において種々の変更を加えることができる。
【００５２】
補強層は、図１ではカーカス５の内面側に配設した例を示したが、例えば図４に示すようにカーカス５が２枚以上のプライから構成される場合には、補強層１０ａをカーカスプライの間に挟んで配設してもよく、また、双方に配設してもよい。双方に配設する場合には、２つの補強層１０ａ、１０ｂを合わせて寸法を測定する。
【００５３】
【実施例】
次に、この発明に従うランフラットタイヤを試作し、性能評価を行ったので、以下に説明する。
【００５４】
（試験例１）
実施例１〜４のタイヤは、図１に示す幅方向断面を有し、タイヤサイズが２４５／４５Ｒ１８であるランフラットタイヤであって、補強層は、１００％モジュラスが１０．５ＭＰａである硬質ゴムで構成され、補強層の幅が８０ｍｍであり、補強層の端部と移行部とを合わせた幅は補強層の幅の０．２２倍であり、補強層の端部における厚さｔ_１は、
ｔ_１＝ａｘ^ｎ
で表され、ｎが表１に示す値をとり、ｘ＝０で実質ｔ_１＝０、ｘ＝０．２でｔ_１＝６．０ｍｍであり、補強層は、中央部の厚さが一定であって、厚さの最大値が８ｍｍであり、カーカスはレーヨンコードからなる２枚のプライで構成され、補強層とベルトとのオーバーラップ範囲をタイヤ幅方向に測定したときの幅がカーカス高さの０．２５倍であるランフラットタイヤである。
【００５５】
比較のため、図６に示す補強層を用いた従来タイヤ（従来例）と、累乗の指数ｎがこの発明の適正範囲外であるタイヤ（比較例１および２）についても併せて試作した。
【００５６】
（試験方法）
前記各供試タイヤを標準リム（８ＪＪ）に組み付けてタイヤ車輪とし、空気圧０ｋＰａ（相対圧）、試験負荷荷重５２９０Ｎ、走行速度９０ｋｍ／ｈの条件下でドラム試験機上を走行させ、タイヤが故障するまでの走行距離を測定し、この測定値によって耐久性を評価した。その評価結果を表１に示す。なお、表１中の耐久性は従来例の耐久性を１００としたときの指数比で示してあり、数値の大きいほど耐久性が優れている。
【００５７】
【表１】

【００５８】
表１に示す結果から、補強層の端部の形状がこの発明の累乗の指数ｎの適正範囲を満足する場合に耐久性が優れている。
【００５９】
（試験例２）
次に、実施例５〜９のタイヤは、タイヤサイズが２２５／５０Ｒ１６であり、補強層の幅が７５ｍｍであり、補強層の厚さの最大値が９ｍｍであり、端部および移行部の補強層幅に対する比が表２に示す値であること以外は実施例３のタイヤと同様の構造を有するランフラットタイヤである。
【００６０】
（試験方法）
前記各供試タイヤを標準リム（７ＪＪ）に組み付けてタイヤ車輪とし、空気圧０ｋＰａ（相対圧）、試験負荷荷重５２９０Ｎ、走行速度８０ｋｍ／ｈの条件下でドラム試験機上を走行させ、タイヤが故障するまでの走行距離を測定し、この測定値によって耐久性を評価した。その評価結果を表２に示す。なお、表２中の耐久性は実施例５の耐久性を１００としたときの指数比で示してあり、数値の大きいほど耐久性が優れている。
【００６１】
【表２】

【００６２】
表２に示す結果から、実施例５〜９のタイヤのうち、特に補強層の端部の幅が補強層の幅の０．２倍以上である実施例７〜９は耐久性が格段に向上している。
【００６３】
【発明の効果】
この発明によれば、耐久性に優れたランフラットタイヤを提供することが可能となった。
【図面の簡単な説明】
【図１】この発明に従う代表的なランフラットタイヤの幅方向半断面図である。
【図２】この発明に従う補強層１０のタイヤ貼付け前の幅方向断面図である。
【図３】この発明に従う他の補強層１０のタイヤ貼付け前の幅方向断面図である。
【図４】この発明に従う他のランフラットタイヤの幅方向半断面図である。
【図５】（ａ）および（ｂ）はいずれも従来のランフラットタイヤの幅方向半断面図である。
【図６】図５（ａ）に示す従来タイヤの補強層１０３のみを抜き出して示した拡大図である。
【符号の説明】
１　　タイヤ
２　　ビード部
３　　サイドウォール部
４　　トレッド部
５　　カーカス
６　　クラウン部
７　　タイヤ赤道面
８ａ、８ｂ　　コード層
９　　ベルト
１０　　補強層
１１ａ、１１ｂ　　タイヤ径方向端縁
１２　　外周面
１３ａ、１３ｂ　　端部
１４ａ、１４ｂ　　境界位置
１５　　タイヤ径方向中心位置
１６ａ、１６ｂ　　移行部
１７　　中央部
１８　　中央部両端域
１９　　中央部中央域
２０　　リム径ライン[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a run flat tire having a reinforcing layer on the inner surface side of a carcass and at least on a side wall portion, and in particular, aims to improve the durability of such a tire.
[0002]
[Prior art]
In a normal pneumatic radial tire, in order to express the rigidity required for the tire, a bead core or bead filler is embedded in the bead part to secure the fitting with the rim of the wheel and secure the rigidity, Ring rigidity is obtained by arranging the belt around the crown of the carcass. Further, by filling the inside of the tire with air, tension is applied to the belt, and the above-described ring rigidity is further increased. A similar tension is also applied to the side wall portion, which is usually formed mainly of the carcass ply, and the side wall portion has a stiffness developed by the tension, such as a spring between the belt and the bead portion. Elastically coupled to As described above, in a normal pneumatic radial tire, the ride comfort during normal running is ensured by not arranging an additional member on the sidewall portion.
[0003]
However, it may be necessary to increase the rigidity of the sidewall portion of the pneumatic radial tire for reasons such as improving the steering stability of the vehicle.
[0004]
In particular, pneumatic radial tires that can travel for a certain distance even during puncturing, so-called run-flat tires, need to suppress bending deformation when a load is applied under a low internal pressure or punctured state. It is required that the tire alone or a combination with a rim exhibit sufficient rigidity without depending on the tire.
[0005]
As a means for increasing the rigidity of the tire, for example, as shown in FIG. 5A, a crescent-shaped reinforcing layer 103 having a cross section is arranged on the side wall portion 101 on the inner surface side of the carcass 102. When the carcass 102 is composed of a plurality of plies, it is useful to interpose the reinforcing layer 103 between the plies, as shown in FIG. 5B. As the material of the reinforcing layer 103, a hard rubber material or the like is used. In general, a material having high tensile and compressive rigidity is generally used from the viewpoint of increasing the rigidity. Further, in order to reduce the rigidity step generated between the reinforcing layer 103 and a member adjacent thereto, the thickness of the reinforcing layer 103 becomes thinner toward the tire radial edges 104a, 104b as shown in FIG. Although the shape is formed as described above, the shape of the end portions 105a and 105b of the reinforcing layer 103 is not optimized, so that the rigidity step tends to be still large, and the vicinity of the end portions 105a and 105b of the reinforcing layer 103 As a result of the concentration of stress, there is a problem that a failure is likely to occur at an early stage.
[0006]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to reduce the rigidity step generated between the reinforcing layer and a member in contact with the reinforcing layer by optimizing the cross-sectional shape in the thickness direction of the reinforcing layer, particularly its end portion and the transition portion. Accordingly, it is an object of the present invention to provide a run flat tire having excellent durability.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention extends in a toroidal manner over a pair of beads, a pair of sidewalls extending radially outward from the beads and a tread portion extending between both sidewalls. A carcass comprising at least one ply is disposed, and a belt comprising at least two cord layers laminated so that cords intersect each other with a tire equatorial plane interposed between a crown portion and a tread portion of the carcass. In a run-flat tire having a crescent-shaped reinforcing layer across the inner surface side and / or ply of the carcass and at least over the area of the sidewall portion, the reinforcing layer is a tire of the reinforcing layer when viewed in a cross section in the tire width direction. The distance measured from the radial edge position along the outer peripheral surface of the reinforcing layer is defined as a variable x, and the thickness of the reinforcing layer is defined as t _1. When the thickness (t ₁ ) has a pair of ends gradually increasing so as to satisfy the following relational expression (1), there is an inflection point at a boundary position with the ends, and the reinforcing layer has A run-flat tire comprising a pair of transition portions whose thickness gradually increases toward a point where the thickness becomes maximum, and a central portion located between the transition portions.
Note that t ₁ = ax ⁿ (1)
However, a> 0 and n> 1.
[0008]
The “inflection point” here includes an intersection of a curve and a straight line, in addition to a point at which the state of unevenness of the curve changes.
[0009]
In the present invention, the dimensions of each part of the tire are determined by assembling the tire with the standard rim specified by JATMA, filling the tire with the air pressure corresponding to the maximum load capacity in the applicable size and ply rating, and then fitting the tire to the rim. The measurement is performed in a state where the internal pressure is reduced to an air pressure equivalent to 10% of the air pressure.
[0010]
It is preferable that the rate of change in the thickness of the transition portion gradually decreases from the inflection point to the point where the thickness of the reinforcing layer becomes maximum. Here, the “rate of change in thickness” refers to the inclination of a tangent to the reinforcing layer in the cross section in the tire width direction, and specifically, is calculated as a differential coefficient of an equation representing the cross section in the tire width direction of the reinforcing layer. be able to.
[0011]
Further, the exponent n is preferably 4/3 or more.
[0012]
In addition, it is preferable that the combined width of one end of the reinforcing layer and the transition part adjacent thereto is 0.2 times or more the width of the reinforcing layer.
[0013]
Furthermore, it is preferable that the maximum value of the thickness of the reinforcing layer is 0.14 times or more of the width of the reinforcing layer.
[0014]
Here, the “width of the end portion” and the “width of the reinforcing layer” refer to the width when measured along the outer peripheral surface of the reinforcing layer, respectively, when viewed in a cross section in the tire width direction, and the “thickness of the reinforcing layer”. "" Means the distance between the outer peripheral surface and the inner peripheral surface of the reinforcing layer measured on the normal to the outer peripheral surface of the reinforcing layer.
[0015]
Further, the position of the inflection point is preferably in a range of 70% or less of the maximum value of the thickness of the reinforcing layer.
[0016]
Further, it is preferable that the thickness of the central portion of the reinforcing layer is substantially constant.
[0017]
In addition, when dividing the central portion of the reinforcing layer into a central region and both end regions, it is preferable that the thickness of the central region is thinner than those of the both end regions.
[0018]
Furthermore, the reinforcing layer is disposed such that the end located outside in the tire radial direction is overlapped below the end of the belt, and the width when the overlapping range is measured in the tire width direction is equal to the carcass height. It is preferably at least 0.2 times the thickness.
[0019]
In addition, in a state where the tire is mounted on the standard rim, a tire radial distance between the tire radial edge of the reinforcing layer and the rim diameter line is at least 1.3 times the flange height of the standard rim. preferable. Here, the “rim diameter line” means a position where the rim diameter is measured.
[0020]
Further, it is preferable that the reinforcing layer is a hard rubber.
[0021]
In addition, the 100% modulus of the reinforcing layer is preferably 4 MPa or more.
[0022]
Furthermore, it is preferable that at least one ply constituting the carcass has a cord selected from the group consisting of nylon 6, nylon 66, polyethylene terephthalate (PET), rayon, polyethylene naphthalate (PEN) and aramid.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a half cross section in the width direction of a typical run flat tire (hereinafter, referred to as “tire”) according to the present invention.
[0024]
The tire 1 shown in FIG. 1 has a toroidal shape over a pair of bead portions 2, a pair of sidewall portions 3 extending radially outward from the bead portion 2, and a tread portion 4 extending between the two sidewall portions 3. A carcass 5 composed of at least one ply extending, two plies in FIG. 1 is disposed, and the cords cross each other between the crown portion 6 and the tread portion 4 of the carcass 5 with the tire equatorial plane 7 interposed therebetween. 1 comprises a belt 9 consisting of at least two code layers, in FIG. 1 two code layers 8a and 8b, a reinforcing layer having a crescent cross section on the inner side of the carcass 5 and at least over the area of the side wall portion 3. 10 and has a so-called side reinforcement type run flat tire structure.
[0025]
The main feature of the configuration of the present invention is to optimize the cross-sectional shape in the thickness direction of the reinforcing layer 10, particularly the end portions 13a and 13b and the transition portions 16a and 16b. When the reinforcing layer 10 is viewed in a cross section in the tire width direction, the distance measured along the outer peripheral surface 12 of the reinforcing layer 10 from the tire radial edges 11a and 11b of the reinforcing layer 10 is defined as a variable x. when a thickness of _{t 1,} a pair of end portions 13a having a thickness _{t 1} gradually increases so as to satisfy the following formula (1) in relation, and 13b, the ends 13a, 13b and the boundary position 14a, 14b And a pair of transition portions 16a and 16b whose thickness gradually increases toward a point 12 where the thickness of the reinforcing layer 10 becomes maximum, and a central portion 17 located between the transition portions 16a and 16b. Is to have.
Note that t ₁ = ax ⁿ (1)
However, a> 0 and n> 1.
[0026]
Hereinafter, a description will be given of how the present invention adopts the above configuration together with its operation. The inventor cuts out the sidewall portion 3 in a unit length in the tire circumferential direction, models the sidewall portion 3 as an arc-shaped beam, and obtains a maximum compressive stress due to bending and axial force generated when a load W is applied to the tire. σ was analyzed. That is, in the cross section in the tire width direction, the maximum compressive stress σ at a position at an angle θ from the line L passing through the center of the arc and parallel to the tire rotation axis is the radius of curvature, the tire circumferential cross-sectional area and the cross-sectional area of the sidewall portion 3. Assuming that the coefficient and the opening angle are R, A, Z, and φ, respectively, they are represented by the following equations.
[0027]
(Equation 1)

However, -φ / 2 ≦ θ ≦ φ / 2.
[0028]
From the above equation, it can be seen that the maximum compressive stress σ is minimum at θ = −φ / 2 or φ / 2, and is maximum at θ = 0.
[0029]
The maximum compressive stress σ ′ when the reinforcing layer 10 is disposed on the inner surface side of the carcass 5 in order to increase the rigidity of the sidewall portion 3 is given by the following equation, where a is the cross-sectional area of the reinforcing layer 10 in the tire circumferential direction. Is represented as
[0030]
(Equation 2)

[0031]
Therefore, in order to make the maximum compressive stress σ ′ uniform at an arbitrary angle θ, the second term on the right side of the above equation needs to change in inverse proportion to the first term on the right side. That is, W / (A + a) must be maximum when cos θ is minimum, that is, a must be minimum, and W / (A + a) must be minimum when cos θ is maximum, that is, a must be maximum. The cross-sectional shape in the tire width direction of the reinforcing layer 10 having such a change in the cross-sectional area a is a crescent shape.
[0032]
However, even if the reinforcing layer 10 having such a cross-sectional shape is used, a rigid step is formed between the reinforcing layer 10 and a member adjacent to the reinforcing layer 10 at both end edges 11 where the reinforcing layer 10 is joined to the sidewall portion 3. Since this is likely to occur, stress concentrates near the edge 11 of the reinforcing layer 10, and there is a problem that a failure is likely to occur early.
[0033]
The inventor has found that in order to solve this problem, the shape of the end portions 13a and 13b may be processed so that the rigidity between the reinforcing layer 10 and the member adjacent thereto is continuously changed. Was. Therefore, considering the bending stiffness by using the second moment of area of the material mechanics, in order to continuously change the stiffness between the reinforcing layer 10 and the members adjacent thereto, the second order cross section at both ends 13a and 13b is required. It has been found that the second derivative of the moment should be continuous and substantially zero at both end edges 11a and 11b.
[0034]
That is, when considering one end 13a or 13b of the reinforcing layer 10, the distance measured from the tire radial edge 11 of the reinforcing layer 10 along the outer peripheral surface 12 of the reinforcing layer is defined as a variable x, and the thickness of the reinforcing layer 10 is determined. when to t ₁ is in the region of 0 ≦ x ≦ 1/2, moment of inertia of area I per circumferential unit width as flexural rigidity is expressed as follows.
[0035]
[Equation 3]

[0036]
Here, I and the first and second derivatives are always substantially continuous at x = 0 including the region of t ₁ = 0 and I = 0 when x <0, that is, I (0) = I ^{(1 ) (0) = I (2} ) (0) = 0 and becomes as a simple general functional form of handling, it is conceivable construction functional form without the constant term. Furthermore, since only the end region is discussed here, it is preferable that the region in this region always satisfies the gradually increasing state that does not include the inflection point. Here, considering the high-order polynomial, if only the highest-order term is taken, the above condition is satisfied, so that t ₁ can be expressed as a power of x, that is, t ₁ = ax ⁿ . By substituting this into the above equation and obtaining the first and second derivatives, the following is obtained.
[0037]
(Equation 4)

[0038]
In order for the stiffness to change continuously between the reinforcing layer 10 and a member adjacent thereto, it is necessary that at least the above three equations be continuous in the region of 0 ≦ x ≦ 1/2. Further, in order to prevent a rigidity step from occurring at the edge 11, it is necessary for I to gradually decrease as x decreases and to converge to zero, that is, that the second derivative is larger than the linear function system, and desirably the second order function. It must be more than a function.
[0039]
Therefore, for the exponent part of the power of I ⁽²⁾ ,
3n-2> 1, ∴n> 1
Preferably,
3n-2 ≧ 2, Δn ≧ 4/3
It is necessary to be.
[0040]
The shape of the transition portions 16a, 16b is not particularly limited, and may be a curved shape, a linear shape, or the like. It is preferable that the curve gradually decreases toward the point where the maximum value is obtained, for example, a curve having an upward convex shape, since the rigidity step can be further avoided.
[0041]
Therefore, in the present invention, by optimizing the shapes of the end portions 13a and 13b, a rigidity step generated between the reinforcing layer 10 and a member in contact with the reinforcing layer 10 can be reduced.
[0042]
Further, one end portion 13a, 13b and transition portions 16a adjacent thereto, it is preferable that the width of the combined and 16b is not less than 0.2 times the width _{W 1} of the reinforcing layer 10. In order to avoid the concentration phenomenon of stress due to the rigidity step, it is important to have a cross-sectional shape in which the rigidity gradually increases, but one end portion 13a, 13b and the transition portion 16a, 16b adjacent thereto are combined. If the width is less than 0.2 times the width of the reinforcing layer 10, the effect is insufficient, and the concentration of stress may not be sufficiently suppressed in the entire reinforcing layer 10.
[0043]
Further, it is preferable that the maximum value t _max of the thickness of the reinforcing layer 10 is 0.14 times or more of the width W ₁ of the reinforcing layer 10. If the maximum value t _max thickness is less than 0.14 times the width W _1, because the rigidity of the tire required for the run-flat tire tends to be insufficient. In addition, the maximum value t _max of the thickness of the reinforcing layer 10 means the maximum value t _max of the thickness measured in the shape of the reinforcing layer 10 before attaching the tire, as shown in FIG.
[0044]
Furthermore, it is preferable that the position of the inflection point is in a range of 70% or less of the maximum value of the thickness of the reinforcing layer 10. By setting the position of the inflection point in a range of 70% or less of the maximum value of the thickness of the reinforcing layer 10, it is possible to gradually increase the thickness of the reinforcing layer 10 at the transition portions 16a and 16b. This is because there is no portion where the change in the thickness of the tire 10 is sharp, and the run flat performance of the tire can be improved.
[0045]
Furthermore, in the central portion 17 of the reinforcing layer 10, the bending stiffness is sufficiently large as compared with the end portions 13a and 13b, and substantially no concentration of stress occurs, so that the end portions 13a and 13b and the transition portion 16a , 16b, the bending stiffness does not necessarily have to be continuous in the above three equations, but it is sufficient if at least the bending stiffness, that is, the thickness distribution is continuous. Therefore, the central portion 17 may be flat, or may have a corner portion or a concave portion, but from the viewpoint of appropriate processing, the thickness of the central portion 17 is substantially constant as shown in FIG. Preferably, the thickness of the central region 19 of the central portion 17 is smaller than that of both end regions 18 as shown in FIG.
[0046]
In addition, the reinforcing layer 10 is disposed such that the end 13b located on the outer side in the tire radial direction is overlapped below the end of the belt 9, and the width W when the overlapping range is measured in the tire width direction. ₂ is preferably equal to or more than 0.2 times the carcass height _{H c.} If the reinforcing layer 10 and the belt 9 do not overlap with each other, the rigidity immediately below the end of the belt 9 becomes relatively low, and as a result, stress concentrates in this region and a failure may occur at an early stage. .
[0047]
Further, it is preferable that the tire radial direction distance d between the tire radial inner edge 11a of the reinforcing layer 10 and the rim diameter line 20 is at least 1.3 times the flange height of the standard rim. A reinforcing member such as a bead wire or a bead filler is buried in the bead portion 2 and the bead portion is supported by the rim flange by being fitted to the rim, so that the flange height of the standard rim is 1.3. This is because, even if the reinforcing layer 10 is disposed in a region less than twice, the tire weight only increases, and a sufficient rigidity increasing effect tends not to be obtained.
[0048]
Further, the material of the reinforcing layer 10 may be rubber, resin, or a material having a large amount of voids in these materials, for example, foamed rubber, urethane foam, or the like. From the viewpoint of ensuring both of them in a well-balanced manner, a hard rubber is preferable.
[0049]
Furthermore, it is preferable that the 100% modulus of the reinforcing layer 10 is 4 MPa or more. If the 100% modulus is less than 4 MPa, the rigidity required for run flat traveling cannot be secured.
[0050]
In addition, it is preferable that at least one ply constituting the carcass has a cord selected from the group consisting of nylon 6, nylon 66, polyethylene terephthalate (PET), rayon, polyethylene naphthalate (PEN) and aramid. This is because, during run flat traveling, the tire internal pressure becomes substantially zero and the carcass travels without tension, so that a carcass cord having flexibility and wear resistance is required.
[0051]
The above description is only an example of the embodiment of the present invention, and various changes can be made within the scope of the claims.
[0052]
FIG. 1 shows an example in which the reinforcing layer is disposed on the inner side of the carcass 5, but, for example, as shown in FIG. 4, when the carcass 5 is composed of two or more plies, the reinforcing layer 10a is It may be disposed between the plies, or may be disposed on both sides. When both are provided, the dimensions of the two reinforcing layers 10a and 10b are measured together.
[0053]
【Example】
Next, a trial manufacture of a run flat tire according to the present invention was performed, and its performance was evaluated.
[0054]
(Test Example 1)
The tires of Examples 1 to 4 are run-flat tires having the cross-section in the width direction shown in FIG. 1 and the tire size is 245 / 45R18, and the reinforcing layer is a hard rubber having a 100% modulus of 10.5 MPa. The width of the reinforcing layer is 80 mm, the total width of the end of the reinforcing layer and the transition portion is 0.22 times the width of the reinforcing layer, and the thickness t ₁ at the end of the reinforcing layer is ,
t ₁ = ax ⁿ
Where n takes the value shown in Table 1, and when x = 0, substantially t ₁ = 0, and when x = 0.2, t ₁ = 6.0 mm, and the reinforcing layer has a constant thickness at the center. Wherein the maximum thickness is 8 mm, the carcass is composed of two plies of rayon cord, and the width of the carcass height measured when the overlapping range between the reinforcing layer and the belt is measured in the tire width direction. This is a run-flat tire that is 0.25 times the height.
[0055]
For comparison, a conventional tire (conventional example) using the reinforcing layer shown in FIG. 6 and a tire (Comparative Examples 1 and 2) whose exponent n is outside the appropriate range of the present invention were also trial manufactured.
[0056]
(Test method)
Each of the test tires was mounted on a standard rim (8JJ) to form a tire wheel, and was run on a drum test machine under the conditions of air pressure 0 kPa (relative pressure), test load 5290 N, and running speed 90 km / h, and the tire failed. The running distance was measured until the endurance was reached, and the durability was evaluated based on the measured values. Table 1 shows the evaluation results. The durability in Table 1 is indicated by an index ratio when the durability of the conventional example is set to 100, and the larger the numerical value, the better the durability.
[0057]
[Table 1]

[0058]
From the results shown in Table 1, the durability is excellent when the shape of the end portion of the reinforcing layer satisfies the proper range of the exponent n of the present invention.
[0059]
(Test Example 2)
Next, in the tires of Examples 5 to 9, the tire size is 225 / 50R16, the width of the reinforcing layer is 75 mm, the maximum value of the thickness of the reinforcing layer is 9 mm, and the reinforcement of the end portion and the transition portion is performed. A run flat tire having the same structure as the tire of Example 3 except that the ratio to the layer width is a value shown in Table 2.
[0060]
(Test method)
Each of the test tires was mounted on a standard rim (7JJ) to form a tire wheel, and was run on a drum test machine under the conditions of air pressure 0 kPa (relative pressure), test load 5290 N, and running speed 80 km / h, and the tire failed. The running distance was measured until the endurance was reached, and the durability was evaluated based on the measured values. Table 2 shows the evaluation results. The durability in Table 2 is indicated by an index ratio when the durability of Example 5 is set to 100, and the larger the value, the better the durability.
[0061]
[Table 2]

[0062]
From the results shown in Table 2, among the tires of Examples 5 to 9, the durability of Examples 7 to 9 in which the width of the end portion of the reinforcing layer is 0.2 times or more the width of the reinforcing layer is particularly improved. are doing.
[0063]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it became possible to provide the run flat tire excellent in durability.
[Brief description of the drawings]
FIG. 1 is a half sectional view in the width direction of a typical run flat tire according to the present invention.
FIG. 2 is a cross-sectional view in the width direction of the reinforcing layer 10 according to the present invention before the tire is attached.
FIG. 3 is a cross-sectional view in the width direction of another reinforcing layer 10 according to the present invention before the tire is attached.
FIG. 4 is a cross-sectional half-sectional view of another run flat tire according to the present invention.
5A and 5B are half sectional views in the width direction of a conventional run flat tire.
FIG. 6 is an enlarged view showing only the reinforcing layer 103 of the conventional tire shown in FIG. 5 (a).
[Explanation of symbols]
Reference Signs List 1 tire 2 bead portion 3 sidewall portion 4 tread portion 5 carcass 6 crown portion 7 tire equatorial plane 8a, 8b cord layer 9 belt 10 reinforcing layer 11a, 11b tire radial edge 12 outer peripheral surface 13a, 13b end 14a, 14b Boundary position 15 Tire radial center position 16a, 16b Transition portion 17 Central portion 18 Center both end regions 19 Central central region 20 Rim diameter line

Claims (13)

A carcass comprising at least one ply extending in a toroidal shape over a pair of bead portions, a pair of sidewall portions extending radially outward from the bead portion and a tread portion extending between both sidewall portions is provided. A belt comprising at least two cord layers laminated so that the cords intersect each other with the tire equatorial plane interposed between the crown portion and the tread portion of the carcass. And in a run-flat tire having a crescent-shaped reinforcing layer in cross-section over at least the side wall portion,
The reinforcing layer is seen in the cross section in the tire width direction,
The distance measured along the outer peripheral surface of the reinforcing layer from the tire radial end edge position of the reinforcing layer a variable x, when the thickness of the reinforcing layer and t _1, the thickness (t ₁₎ is the following (1) A pair of ends that gradually increase to satisfy the relational expression;
A pair of transition portions having an inflection point at a boundary position with the end portion and gradually increasing in thickness toward a point where the thickness of the reinforcing layer is maximum,
A run flat tire having a central portion located between both transition portions.
Note that t ₁ = ax ⁿ (1)
However, a> 0 and n> 1. The run-flat tire according to claim 1, wherein a rate of change in the thickness of the transition portion gradually decreases from an inflection point toward a point where the thickness of the reinforcing layer becomes maximum. The run flat tire according to claim 1 or 2, wherein the exponent n is 4/3 or more. The run-flat tire according to any one of claims 1 to 3, wherein a total width of one end of the reinforcing layer and a transition portion adjacent to the one end is at least 0.2 times the width of the reinforcing layer. The run flat tire according to any one of claims 1 to 4, wherein the maximum value of the thickness of the reinforcing layer is 0.14 times or more of the width of the reinforcing layer. The run-flat tire according to any one of claims 1 to 5, wherein the position of the inflection point is in a range of 70% or less of the maximum value of the thickness of the reinforcing layer. The run-flat tire according to any one of claims 1 to 6, wherein a thickness of a central portion of the reinforcing layer is substantially constant. The run-flat tire according to any one of claims 1 to 6, wherein when the central portion of the reinforcing layer is divided into a central region and both end regions, the thickness of the central region is smaller than those of both end regions. The reinforcing layer is disposed such that an end portion including an outer edge in the tire radial direction is overlapped below an end portion of the belt, and a width when the overlapping range is measured in the tire width direction is a carcass height. The run flat tire according to any one of claims 1 to 8, which is 0.2 times or more of the following. The tire radial direction distance between the tire radial direction inner edge of the reinforcing layer and the rim diameter line in a state where the tire is mounted on the standard rim is at least 1.3 times the standard rim flange height. Item 10. The run flat tire according to any one of items 1 to 9. The run-flat tire according to any one of claims 1 to 10, wherein the reinforcing layer is a hard rubber. The run flat tire according to any one of claims 1 to 11, wherein the reinforcing layer has a 100% modulus of 4 MPa or more. The at least one ply constituting the carcass has a cord selected from the group consisting of nylon 6, nylon 66, polyethylene terephthalate, rayon, polyethylene naphthalate and aramid. Run flat tire.

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