JP3971831B2

JP3971831B2 - Pneumatic tire

Info

Publication number: JP3971831B2
Application number: JP32453397A
Authority: JP
Inventors: 一臣小林; 智久西川; 健司松尾
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1997-11-26
Filing date: 1997-11-26
Publication date: 2007-09-05
Anticipated expiration: 2017-11-26
Also published as: JPH11157310A

Description

【０００１】
【発明の属する技術分野】
この発明は、空気入りタイヤ、より詳細にはパンクなどにより内圧がゼロ乃至ゼロに近い微圧状態で所定距離走行可能な、いわゆるランフラットタイプのラジアルタイヤに関し、特に良好な振動乗心地性と優れたランフラット（パンク状態での走行）耐久性とを両立させた空気入りタイヤに関する。
【０００２】
【従来の技術】
ランフラットタイプのラジアルタイヤ（以下ランフラットタイヤという）は、主としてタイヤの負荷荷重が比較的小さな乗用車などの車両の使途に供するもので、タイヤがフラット（パンク）状態となっても、それがたとえ急速に生じたとしても一般道路走行中はもとより高速道路の高速走行中であっても車両、特に乗用車の操縦安定性を損なうことなく安全な走行が可能であり、走行を継続しても使用リム（適用リム）から離脱することなく、しかもタイヤが破壊することなく、安全かつ確実にタイヤ交換が可能な場所まで所定距離、例えば８０〜１６０km走行可能であることが要求される。
【０００３】
そのため各種の構造をもつランフラットタイヤが、ときには工夫をこらした使用リムとの組合わせで提案されている。これら提案のなかでコスト−パーフォーマンスに優れ、従って最も多く市場で実用に供されているランフラットタイヤは、ビード部からサイドウォール部を経てトレッド部の端部に至る最内側カーカスプライのタイヤ内面側に、対をなす断面三日月状の厚肉補強ゴムストリップを適用する構造のタイヤである。それでもこの種のタイヤはコスト高を免れず、よってスポーツカー、スポーツタイプカー、高級乗用車などいずれも高価な車種に装着されることが多く、従いランフラットタイヤは偏平比の呼びが６０以下の偏平タイヤが主たる対象となる。
【０００４】
この種の厚肉補強ゴムストリップを有するタイヤは、フラット転動下で成るべく潰れ変形度合いを軽減するため、ラジアルカーカスはビードコアの周りをタイヤ内側から外側へ巻上げるターンアッププライと、このターンアッププライを外包みするダウンプライとの２プライ乃至２プライ以上の構成とし、かつターンアッププライとダウンプライとで包み込む、ビードコア外周面からタイヤ最大幅近くまで延びる硬質のフィラーゴムを備え、ときにビード部からサイドウォール部に至る間にケブラーコード又はスチールコードのゴム被覆層（インサートプライと呼ばれる層）を配置する。
【０００５】
【発明が解決しようとする課題】
しかし上記のようにランフラットでのタイヤ離脱防止や耐久性をあまりにも重視したタイヤは、通常の使用内圧充てん下での走行において振動乗心地性が著しく低下する。このことはタイヤ寿命を通じて殆ど生じない万が一のランフラットに対し講じた対応手段により生じる性能低下であり、通常の使用内圧での走行が殆ど全てであることを考慮すると振動乗心地性低下の度合いを可能な限り抑え込んだタイヤが望まれている。
【０００６】
従ってこの発明の請求項１に記載した発明は、使用者が満足する振動乗心地性を保持した上で、パンクなどによる急速なエアー抜けでも乗用車などの車両の安全走行を保証し、かつフラット走行でのリムからのタイヤ離脱防止性能や耐久性能をランフラットタイヤとして相応しい性能まで向上させた空気入りタイヤの提供を目的とする。
【０００７】
【課題を解決するための手段】
上記目的を達成するためこの発明の請求項１に記載した発明は、一対のビード部内に埋設したビードコア相互間にわたり一対のサイドウォール部とトレッド部とを補強する１プライ以上のラジアル配列コードのゴム被覆になるカーカスと、カーカスの外周でトレッド部を強化する２層以上のコード交差層を有するベルトとを備え、ビード部のビードコア近傍位置からサイドウォール部を経てトレッド部の端部までにわたる最内側カーカスプライ内面側に対をなす、断面三日月状の厚肉補強ゴムストリップを有する空気入りタイヤにおいて、上記タイヤを適用リムに適正に組付けたタイヤ内圧ゼロの状態にて、上記適用リム断面のフランジ外輪郭の円弧中心からタイヤ回転軸線と平行な直線に対し４５°の角度でビード部に向け延びる傾斜線と、上記円弧中心から前記直線と直交して延びるタイヤ半径線とで囲まれるフランジ外輪郭部分にほぼ沿う輪郭が形成する曲面を内周面に有する、連続又は断続環状ゴム突起部をビード部外側に備え、該環状ゴム突起部の内周面は適用リムのフランジとの間に隙間ｄを有し、かつタイヤの放射方向断面における最内側カーカスプライは、内圧ゼロのタイヤに該タイヤの最大負荷能力に対応する空気圧の０．７５〜１．００倍に相当する空気圧を充てんしたタイヤの放射方向断面における最内側のカーカスプライの自然平衡形状と対比したとき、（１）上記最内側カーカスプライの最大幅位置Ｍが上記自然平衡形状カーカスプライの最大幅位置Ｍｐよりタイヤ半径方向内方に存在し、（２）自然平衡形状カーカスプライの最大幅位置Ｍｐよりタイヤ半径方向外方領域にて、自然平衡形状カーカスプライに対しタイヤ内側に位置するカーカスプライ部分と、（３）自然平衡形状カーカスプライの最大幅位置Ｍｐよりタイヤ半径方向内方領域にて、自然平衡形状カーカスプライに対しタイヤ外側に位置するカーカスプライ部分と、を有することを特徴とする空気入りタイヤである。
【０００８】
上記適用リムとは、ＪＡＴＭＡＹＥＡＲＢＯＯＫ（１９９７年版）の「“Ｇ”章一般情報」の第５項に記載された「適用リム」の記載内容に従い、この発明の適用タイヤ種類毎、例えば乗用車用タイヤでは上記ＹＥＡＲＢＯＯＫに掲載されている「乗用車用タイヤの適用リム」の表の適用サイズ欄に記載されたリムサイズを用いる。またタイヤを適用リムに適正に組付けるとは、例えばタイヤに所定圧の空気圧を一旦充てんして適用リムに十分にフィットさせた後、充てん空気圧がゼロ（大気圧）になるまで排気し、そのときタイヤが適用リムに十分にフィットした状態にあることを意味する。
【０００９】
またタイヤの最大負荷能力に対応する空気圧とは、上記ＪＡＴＭＡＹＥＡＲＢＯＯＫにて、主として乗用車用タイヤのうち乗用車用ラジアルプライタイヤの４０シリーズ〜８０シリーズ別に、サイズ毎に掲載している空気圧−負荷能力対応表の数値のうち、太字で記載されている最大負荷能力（kg) に対応する空気圧（ｋＰａ又は kgf／cm²）をいう。
【００１０】
請求項１に記載した発明を実施する上で実際には、請求項２に記載した発明のように、上記隙間ｄが、０より大きく、１ mm 以下の範囲内の値を有すること、請求項３に記載した発明のように、上記適用リムの直径位置を通るタイヤ回転軸線と平行なリム径ラインから測った上記最内側カーカスプライの最大幅位置Ｍの高さｈが、上記リム径ラインから測った最内側カーカスプライの最大高さＳＨの０．５０〜０．３０倍の範囲内であることが好ましい。
【００１１】
【発明の実施の形態】
以下、この発明の実施の一形態例を図１〜図５に基づき説明する。
図１は、充てん内圧ゼロにおける乗用車用空気入りタイヤと適用リム外輪郭との左半断面図であり、
図２は、内圧充てん前後における図１に示すタイヤの一部及びリムの外輪郭の一部の線図的断面図であり、
図３は、内圧充てん前後の環状ゴム突起部と適用リムのフランジとの間隙の関係を示す線図であり、
図４は、内圧充てんタイヤにおける、環状ゴム突起部と適用リムのフランジとの間隙とタイヤ縦ばね定数との関係を示す線図であり、
図５は、内圧ゼロ（無圧）タイヤにおける、環状ゴム突起部と適用リムのフランジとの間隙とタイヤ縦ばね定数との関係を示す線図である。
【００１２】
図１において、乗用車用空気入りタイヤ（以下タイヤという）１は、一対のビード部２（片側のみ示す）と、一対のサイドウォール部３（片側のみ示す）と、両サイドウォール部３に連なるトレッド部４とを有し、一対のビード部２内に埋設したビードコア５相互間にわたり上記各部２、３、４を補強する１プライ以上、図示例は２プライのラジアル配列コード、望ましくはレーヨンコードのゴム被覆になるカーカス６と、カーカス６の外周でトレッド部４を強化するベルト７とを有する。
【００１３】
図示例のカーカス６は、ビードコア５をタイヤ１の内側から外側へ向け巻上げる折返し部を有する内側のターンアッププライ６−１と、ターンアッププライ６−１を外包みするダウンプライ６−２とを備える。図示例の２プライカーカス６ではターンアッププライ６−１が最内側カーカスプライを形成する。ベルト７は２層以上、図示例は２層のコード交差層、望ましくは２層のスチールコード交差層を有する他、これら交差層の外周に図１で破線で示す有機繊維コード層、例えばナイロン６６コードの螺旋巻回層を有する。
【００１４】
さらにタイヤ１は、ランフラットタイヤに固有の、対をなす断面三日月状の厚肉補強ゴムストリップ８（片側のみ示す）を、カーカス６の最内側ターンアッププライ６−１の内面側に備える。補強ゴムストリップ８は内圧ゼロでも走行中の車両総重量を安定して支持し、適用リム２０からの離脱を防止し、タイヤ１の破壊を阻止するため、さらには、例えば８０〜１６０km／ｈでの高速走行での急速なパンク時にも走行安定性を保持可能とするため、タイヤ半径方向中央領域を８〜１２mmの厚肉部とする一方、タイヤ半径方向両端部は先細り部とし、さらに補強ゴムストリップ８のゴムにはＪＩＳＡ硬度で７０〜９０°の高硬度ゴムを適用する。またビードフィラーゴム９も補強ゴムストリップ８の補強を助勢するため高硬度ゴムを適用する一方で図示のように比較的高い位置まで配置する。
【００１５】
ここにまず、タイヤ１を適用リム２０に適正に組付けたタイヤ内圧ゼロの状態にて、適用リム２０の直径Ｄ位置を通るタイヤ回転軸線（図示省略）と平行なリム径ラインＲＬから測ったカーカス６の最内側プライ（ターンアッププライ）６−１の最大幅ＣＷの位置Ｍ（実際上はダウンプライ６−２の最大幅位置に対応する位置）の高さｈは、同様にリム径ラインＲＬから測ったカーカス６の最内側カーカスプライ６−１の最大高さＳＨ、それはタイヤ赤道面Ｅ上の最内側カーカスプライ６−１の外側表面における高さＳＨの１／２未満であること、実際上は高さＳＨの０．５０〜０．３０倍の範囲内であることを要する。
【００１６】
次に、同じくタイヤ１を適用リム２０に適正に組付けたタイヤ内圧ゼロの状態にて、適用リム２０の断面におけるフランジの外輪郭２０Ｆの円弧中心Ｏから、タイヤ１の回転軸線（図示省略）と平行な直線Ｌ_Oに対し４５°の角度でビード部２に向かって延びる傾斜線ＩＬと、円弧中心Ｏから直線Ｌ_Oと直交して延びるタイヤ半径線ＶＬとで囲まれるフランジ外輪郭２０Ｆ部分にほぼ沿う輪郭が形成する曲面を内周面とする環状ゴム突起部１０をビード部２に設ける。この環状ゴム突起部１０は周上連続しているか、又は周上に１箇所以上の幅狭の切れ込みをもつ断続状態であっても良い。
【００１７】
ここに適用リム２０に適正に組付けたタイヤの内圧がゼロの状態で、環状ゴム突起部１０の内周面と適用リム２０のフランジの外輪郭２０Ｆとの間の隙間ｄはゼロより大きく１ mm 以下の範囲内に止めることが必要である。その詳細な理由は後述する。
【００１８】
ここで図２を参照して、適用リム２０に適正に組付けたタイヤ内圧ゼロの状態でのタイヤ放射方向断面におけるカーカス６の最内側プライ６−１は、適用リムに組付けたタイヤ内圧ゼロの同じタイヤに該タイヤの最大負荷能力に対応する空気圧の０．７５〜１．００倍に相当する空気圧を充てんしたタイヤの放射方向断面におけるカーカスの最内側プライ６−１ｐ（破線にて示す）の自然平衡形状と対比して以下に述べる形状を有することが必須である。
【００１９】
（１）最内側カーカスプライ６−１の最大幅ＣＷの位置Ｍは、上記内圧充てんタイヤの最内側カーカスプライ６−１ｐの最大幅位置Ｍｐよりタイヤ半径方向内方に存在すること。
（２）最内側カーカスプライ６−１ｐの最大幅位置Ｍｐより少なくともトレッド部の端部（ショルダ部）までのタイヤ半径方向外方領域にて、最内側カーカスプライ６−１（実線）は自然平衡形状に成る最内側カーカスプライ６−１ｐ（破線）に対しタイヤ内側に存在すること。そのとき最内側カーカスプライ６−１の厚み中央を連ねる曲線の曲率は最内側カーカスプライ６−１ｐの厚み中央を連ねる曲線の曲率より小さくなければならないのは勿論である。
（３）最内側カーカスプライ６−１ｐの最大幅位置Ｍｐから少なくとも前記の傾斜線ＩＬとプライ６−１ｐとの交点Ｑまでのタイヤ半径方向内方領域にて、最内側カーカスプライ６−１（実線）は自然平衡形状に成る最内側カーカスプライ６−１ｐ（破線）に対しタイヤ外側に存在すること。そのとき最内側カーカスプライ６−１の厚み中央を連ねる曲線の曲率は最内側カーカスプライ６−１ｐの厚み中央を連ねる曲線の曲率より大きくなければならないのは勿論である。
【００２０】
上記のような内圧充てん前後でのカーカスプライ形状の変化を実現するための手段の一つは、先に述べたようにタイヤ内圧ゼロの状態にて、最内側カーカスプライ６−１の最大幅ＣＷの位置Ｍの高さｈが、該プライ６−１の最大高さＳＨの１／２未満とすること、すなわち高さＳＨの０．５０〜１．３０倍の範囲内とすることである。
【００２１】
しかしこれだけでは不充分であるから、実際上は所定内圧を充てんしたタイヤの放射方向断面における最内側カーカスプライ６−１ｐの自然平衡形状を予め設定しておき、この設定自然平衡形状に対し内圧ゼロ状態のタイヤの放射方向断面における最内側カーカスプライ６−１を上述の（１）〜（３）項に記載したように外すのである。ここにカーカスプライの自然平衡形状とは、カーカスプライの厚み中央を連ねる曲線が自然平衡形状曲線に従うことを意味し、自然平衡形状曲線とは以下に記す曲線をいう。
【００２２】
図２を参照して、所定内圧を充てんしたタイヤ１の最内側カーカスプライ６−１ｐを例とし、このプライの厚み中央を連ねる曲線Ｎ（符号Ｎの図示省略）が、いわゆる自然平衡形状理論に則って次式、
cos φ＝（Ｒ²−Ｒ_E ²)／（Ｒ_S ²−Ｒ_E ²)、ここで、
φは、タイヤ回転軸線（図示省略）から距離Ｒを隔てる曲線Ｎ上の点における接線と、この点を通る回転軸線に平行な直線との成す角度、
Ｒ_Eは、曲線Ｎがタイヤ回転軸線方向最大距離をとる点（最大幅位置Ｍｐを通るタイヤ回転軸線に平行な直線上の点）から該回転軸線までの距離、
Ｒ_Sは、曲線Ｎ上方の延長線の接線がタイヤ回転軸線と平行になる点からタイヤ回転軸線までの距離、
であらわされる曲線を自然平衡形状曲線Ｎという。
【００２３】
以上述べたところに従い、図２を参照して、内圧ゼロ状態のタイヤ１にそのタイヤ１の最大負荷能力に対応する空気圧の０．７５〜１．００倍の空気圧を充てんすると、タイヤ１の放射方向断面における最内側カーカスプライ６−１（実線）は、
（ａ）最内側カーカスプライ６−１ｐの最大幅位置Ｍｐより少なくともトレッド部の端部（ショルダ部）までのタイヤ半径方向外方領域では矢印ａで示す向きに張り出し、
（ｂ）最内側カーカスプライ６−１ｐの最大幅位置Ｍｐから少なくとも前記の傾斜線ＩＬとプライ６−１ｐとの交点Ｑまでのタイヤ半径方向内方領域では矢印ｂの向きにずれ込み、
（ｃ）これらの張り出し変形及びずれ込み変形につれ、環状ゴム突起部１０はタイヤ半径方向外方に拡径し、その結果隙間ｄの値が著しく増加する。この増加量は最内側カーカスプライ６−１を自然平衡形状に成る最内側カーカスプライ６−１ｐからどの程度外すかで制御可能であるが、製造面で無理が生じない範囲でできるだけ外すのが良い。以下、実際の実験結果に基づき作用効果を説明する。
【００２４】
上記の無理のない範囲で最内側カーカスプライ６−１を自然平衡形状から外したタイヤ１について、通常の乗用車用タイヤの使用内圧はそのタイヤの最大負荷能力に対応する空気圧の０．７５〜１．００倍の範囲内であるから、代表値として内圧ｐ＝２．０ kgf／cm²をとり、そのときの隙間ｄ_p（mm）と内圧ｐ＝０（ゼロ）のときの隙間ｄ（mm）とは図３に示すような関係を有し、これは乗用車に供するタイヤ１全般に共通である。３点の測定値を直線で近似するとｄ_p＝１＋２ｄとなる。
【００２５】
一方、環状ゴム突起部１０を備えていないタイヤのｐ＝０のときの縦ばね定数ｋ₀＝２０ kgf／mmを１００とする指数であらわしたとき、ｐ＝０のときの隙間ｄ（mm）とタイヤ１の縦ばね定数ｋ₀（ kgf／mm）の指数との関係は図４の線図に示す通りであり、環状ゴム突起部１０を備えていないタイヤのｐ＝２．０kgf ／cm²のときの縦ばね定数ｋ_p２８ kgf／mmを１００とする指数であらわしたとき、内圧ｐ＝２．０ kgf／cm²における隙間ｄ_p（mm）とタイヤ１の縦ばね定数ｋ_p（ kgf／mm）の指数との関係は図５の線図に示す通りである。
【００２６】
内圧ゼロのランフラットにおける性能を環状ゴム突起部１０を備えていないタイヤより実際上高めるためには縦ばね定数の指数で１０５以上は必要であり、そのため図４に示す線図より隙間ｄ＝０〜１ mm （ただし、「０」を除く）の範囲内であることを要し、隙間ｄが１mmを超えれば従来の環状ゴム突起部１０を備えていないタイヤ対比、ランフラットにおける諸性能の向上が不足することが分かる。
【００２７】
図３の線図が示すところに従い、隙間ｄ＝０〜１ mm （ただし、「０」を除く）の範囲内であれば隙間ｄpは１〜３mmの範囲内の値を得ることがわかり、隙間ｄp がこの範囲内であれば、図５に示す線図より、内圧ｐ＝２．０ kgf／cm2 での縦ばね定数ｋp が従来の環状ゴム突起部１０を備えていないタイヤと同等の縦ばね定数をもつことがわかる。
【００２８】
以上述べたところを要するに、ランフラットでは、隙間ｄ＝０〜１ mm （ただし、「０」を除く）の範囲内であればゴム突起部１０がリム２０のフランジ外輪郭面に確実に乗り上げるので内圧ゼロの状態におけるタイヤの縦ばね定数の値が大幅に上昇する結果、ランフラットでのリムからのタイヤ離脱防止性能や耐久性能を著しく向上させることができる。その一方、内圧２ kgf／cm2 充てん下で負荷転動するタイヤの環状ゴム突起部１０がリム２０のフランジ外輪郭面と接触しない状態を実現することができ、その結果環状ゴム突起部１０を設けても振動乗心地性の低下が生じることはない。よってランフラットでのリムからのタイヤ離脱防止性能及び耐久性能と振動乗心地性とを同時に向上させることが可能となる。
【００２９】
以上は各サイズのタイヤ１について共通に適用することができ、最内側カーカスプライ６−１の形状を先の（１）〜（３）に記載したように自然平衡形状の最内側カーカスプライ６−１ｐから外す結果達成することができるのであり、仮に最内側カーカスプライ６−１の形状を自然平衡形状に合わせれば隙間ｄ＝ｄ_pとなり、せいぜい１（mm）＜ｄ＝ｄ_p＜２（mm）の範囲のみに限定され、ランフラットでのリムからのタイヤ離脱防止性能及び耐久性能の向上を得ることはできない。
【００３０】
【実施例】
空気入りラジアルプライタイヤで、サイズが２２５／６０Ｒ１６であり、構成は図１及び図２に従い、カーカス６は２プライのラジアル配列１６５０Ｄ／２のレーヨンコードのゴム被覆になり、内圧ゼロにおけるタイヤ１の環状ゴム突起部１０の内周面と適用リム２０のフランジ外輪郭面との隙間ｄ＝１mm、０．５mm、０．１mmの３種類の実施例１〜３のタイヤ１を製造した。
【００３１】
環状ゴム突起部１０を備えていない他は全て実施例に合わせた従来例タイヤと、環状ゴム突起部１０を備え最内側カーカスプライ６−１が自然平衡形状に近い形状を有する比較例１のタイヤと、同じく環状ゴム突起部１０を備え最内側カーカスプライ６−１が自然平衡形状と同じ形状を有する比較例２のタイヤとを準備した。
【００３２】
実施例１〜３のタイヤと従来例タイヤとを供試タイヤとして内圧ゼロでの縦ばね定数ｋ₀（ kgf／mm）測定も含めドラムによるランフラット耐久性テストを実施し、実施例１〜３のタイヤと従来例及び比較例１、２のタイヤとを供試タイヤとして内圧ｐ＝２．０ kgf／cm²充てん下で縦ばね定数ｋ_p（ kgf／mm）測定を含めテストコースにて実車による振動乗心地性テストを実施した。縦ばね定数ｋ₀、ｋ_p（ kgf／mm）はＪＡＴＭＡＹＥＡＲＢＯＯＫ（１９９７年版）が定めるタイヤの最大負荷能力の７０％に相当する荷重位置での傾き（勾配）から求めた。
【００３３】
ランフラット耐久性テストは、上記の最大負荷能力の７５％に相当する荷重を負荷した実車走行で、前輪右タイヤのみ内圧を０とし、直進主体で速度９０km／ｈで走行させた場合に、故障が発生して車両が振動し、走行できなくなるまでの走行距離を、従来例タイヤを１００とする指数にてあらわし、このランフラット耐久性指数と縦ばね定数ｋ₀（ kgf／mm）とで整理した。指数は大なるほど良く、整理した結果を図６に示す。図６から実施例１〜３のタイヤは従来例タイヤより２０％以上も耐久性が向上し、かつ縦ばね定数ｋ₀（ kgf／mm）が高いほど良い結果を示していることがわかる。
【００３４】
振動乗心地性テストはテストドライバによるフィーリングによる評点付けにより、従来例タイヤを５点満点とした。値は大なるほど良く、テスト結果はフィーリング評点と縦ばね定数ｋ_p（ kgf／mm）とで整理し、これを図７に示す。図７から実施例１〜３のタイヤは従来例タイヤと同じ評点で優れた振動乗心地性を示す一方、縦ばね定数ｋ_p（ kgf／mm）が１００を超える比較例１、２のタイヤはいずれも振動乗心地性が低下し、それも縦ばね定数ｋ_p（ kgf／mm）が高いほど低下の度合いが大きくなることがわかる。
【００３５】
【発明の効果】
この発明の請求項１〜３に記載した発明によれば、従来タイヤのうち使用者に許容される振動乗心地性を有するタイヤと同等な振動乗心地性を保持した上で、タイヤへの充てん空気圧が急激にゼロ乃至微圧状態となっても、従来タイヤ以上の縦ばね定数を有するので、車両の走行状態をより一層安全に保持することができ、かつ走行の続行に伴うリムからの耐タイヤ離脱性能及び耐久性能をランフラットタイヤとして従来タイヤより顕著に優れた性能を発揮し得る空気入りタイヤを提供することができる。
【図面の簡単な説明】
【図１】この発明の一実施形態例の内圧ゼロにおけるタイヤとリムとの左半断面図である。
【図２】図１に示すタイヤとリムとの内圧充てん前後における左半の線図的一部断面図である。
【図３】内圧ゼロと２．０ kgf／cm²とにおける隙間の関係を示す線図である。
【図４】内圧ゼロのときの隙間と縦ばね定数との関係を示す線図である。
【図５】内圧２．０ kgf／cm²のときの隙間と縦ばね定数との関係を示す線図である。
【図６】内圧ゼロのときの縦ばね定数とランフラット耐久性との関係を示す線図である。
【図７】内圧２．０ kgf／cm²のときの縦ばね定数と振動乗心地性との関係を示す線図である。
【符号の説明】
１空気入りタイヤ
２ビード部
３サイドウォール部
４トレッド部
５ビードコア
６カーカス
６−１、６−２カーカスプライ
７ベルト
８厚肉補強ゴムストリップ
９フィラーゴム
１０環状ゴム突起部
２０適用リム
２０Ｆフランジ外輪郭
Ｅタイヤ赤道面
Ｍ最内側カーカスプライの最大幅位置
ＣＷ最内側カーカスプライの最大幅
Ｄ適用リム径
ＲＬリム径ライン
ＳＨリム径ラインからの最内側カーカスプライ最大高さ
ｈリム径ラインからの最大幅位置高さ
ｄ環状ゴム突起部とフランジ外輪郭との隙間
Ｏフランジ外輪郭断面の円弧中心[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic tire, more specifically, a so-called run-flat type radial tire capable of traveling for a predetermined distance in a state where the internal pressure is zero or close to zero by puncture or the like, and particularly good vibration ride comfort and excellent The present invention relates to a pneumatic tire that achieves both run flat (running in a puncture state) durability.
[0002]
[Prior art]
Run-flat type radial tires (hereinafter referred to as “run-flat tires”) are mainly used for vehicles such as passenger cars, where the load on the tires is relatively small. Even if it occurs rapidly, it is possible to drive safely without impairing the handling stability of vehicles, especially passenger cars, even when driving on highways as well as on general roads, and the rim used even if driving continues It is required that the vehicle can travel a predetermined distance, for example, 80 to 160 km, to a place where the tire can be changed safely and reliably without leaving the (applied rim) and without destroying the tire.
[0003]
For this reason, run-flat tires with various structures have been proposed in combination with rims for use that have been devised. Among these proposals, run-flat tires that have excellent cost-performance and are most practically used in the market are the inner surface of the innermost carcass ply that extends from the bead portion to the end portion of the tread portion through the sidewall portion. A tire having a structure in which a pair of crescent-shaped thick reinforcing rubber strips is applied on the side. Still, this type of tire is inevitable in cost, so sports cars, sports type cars, high-end passenger cars, etc. are often mounted on expensive car models, so run-flat tires have a flat ratio of 60 or less. Tires are the main target.
[0004]
Tires with this type of thick-reinforced rubber strip have a turn-up ply that winds around the bead core from the inside of the tire to the outside in order to reduce the degree of deformation under flat rolling. A hard filler rubber that extends from the outer peripheral surface of the bead core to near the maximum width of the tire and that is wrapped with the turn-up ply and the down ply is composed of two or more plies with the down ply that encloses the ply, sometimes with a bead A rubber covering layer (a layer called an insert ply) of Kevlar cord or steel cord is disposed between the portion and the sidewall portion.
[0005]
[Problems to be solved by the invention]
However, as described above, a tire that places too much emphasis on prevention of tire detachment and durability in the run-flat state has a significant decrease in vibration ride comfort during running under normal use internal pressure. This is a decrease in performance caused by the countermeasures taken in the unlikely event of a run flat that does not occur almost throughout the life of the tire. Considering that almost all running under normal operating internal pressure is considered, the degree of decrease in vibration riding comfort is reduced. There is a need for tires that are kept as low as possible.
[0006]
Therefore, the invention according to claim 1 of the present invention ensures the safe driving of a vehicle such as a passenger car even in the case of rapid air bleed due to puncture, etc. while maintaining the vibration riding comfort that the user satisfies, and the flat driving The purpose is to provide a pneumatic tire with improved performance to prevent tire detachment from the rim and durability suitable for run-flat tires.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 of the present invention is a rubber having one or more ply radial cords for reinforcing a pair of sidewall portions and a tread portion between bead cores embedded in a pair of bead portions. A carcass to be covered, and a belt having two or more cord crossing layers that reinforce the tread portion on the outer periphery of the carcass, and the innermost side extending from the position near the bead core of the bead portion to the end portion of the tread portion through the sidewall portion In a pneumatic tire having a thick reinforcing rubber strip having a crescent-shaped cross section that forms a pair on the inner surface side of the carcass ply, the flange having the cross section of the applied rim in a state where the tire is properly assembled to the applied rim and the tire internal pressure is zero. An inclined line extending from the arc center of the outer contour toward the bead portion at an angle of 45 ° with respect to a straight line parallel to the tire rotation axis; Provided on the outside of the bead portion is a continuous or intermittent annular rubber protrusion on the inner peripheral surface having a curved surface formed by a contour substantially along the outer contour portion of the flange surrounded by a tire radius line extending perpendicularly to the straight line from the arc center. The inner peripheral surface of the annular rubber projection has a gap d between the flange of the applicable rim and the innermost carcass ply in the radial cross section of the tire has a maximum load capacity of the tire. When compared with the natural equilibrium shape of the innermost carcass ply in the radial cross section of the tire filled with air pressure corresponding to 0.75 to 1.00 times the corresponding air pressure, (1) the maximum width of the innermost carcass ply The position M exists inward of the tire radial direction from the maximum width position Mp of the natural equilibrium shape carcass ply, and (2) the tire from the maximum width position Mp of the natural equilibrium shape carcass ply. A carcass ply portion located inside the tire with respect to the natural equilibrium shape carcass ply in the radially outward region, and (3) natural equilibrium in the tire radial direction inner region from the maximum width position Mp of the natural equilibrium shape carcass ply. And a carcass ply portion positioned on the outer side of the tire with respect to the shape carcass ply.
[0008]
The above-mentioned applicable rim is defined in accordance with the description of “Applicable rim” described in the fifth section of “General Information” of “G” Chapter of JATMA YEAR BOOK (1997 edition), for example, for a passenger car. For the tire, the rim size described in the applicable size column in the table “Applied Rim for Passenger Car Tires” published in the above YEAR BOOK is used. The proper assembly of the tire to the applied rim means, for example, that after the tire is filled with a predetermined pressure of air pressure to fit the applied rim sufficiently, it is exhausted until the filling air pressure becomes zero (atmospheric pressure). Sometimes it means that the tire is in a well-fitted state to the applied rim.
[0009]
The air pressure corresponding to the maximum load capacity of the tire corresponds to the air pressure-load capacity listed for each size according to the 40 series to 80 series of radial ply tires for passenger cars among the tires for passenger cars in the above JATMA YEARBOOK. Among the numerical values in the table, it means the air pressure (kPa or kgf / cm ² ) corresponding to the maximum load capacity (kg) indicated in bold.
[0010]
In practice of the invention described in claim 1, the gap d has a value in the range of more than 0 and 1 mm or less , as in the invention described in claim 2. 3, the height h of the maximum width position M of the innermost carcass ply measured from the rim diameter line parallel to the tire rotation axis passing through the diameter position of the applicable rim is from the rim diameter line. It is preferably within a range of 0.50 to 0.30 times the maximum height SH of the measured innermost carcass ply.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a left half sectional view of a pneumatic tire for a passenger car and an outer contour of an applied rim at zero filling internal pressure,
FIG. 2 is a schematic cross-sectional view of a part of the tire shown in FIG. 1 and a part of the outer contour of the rim before and after internal pressure filling,
FIG. 3 is a diagram showing the relationship between the gap between the annular rubber protrusion before and after the internal pressure filling and the flange of the applied rim,
FIG. 4 is a diagram showing the relationship between the gap between the annular rubber protrusion and the flange of the applied rim and the tire longitudinal spring constant in the tire filled with internal pressure,
FIG. 5 is a diagram showing the relationship between the gap between the annular rubber protrusion and the flange of the applied rim and the tire longitudinal spring constant in a tire with zero internal pressure (no pressure).
[0012]
In FIG. 1, a passenger car pneumatic tire (hereinafter referred to as a tire) 1 includes a pair of bead portions 2 (only one side is shown), a pair of sidewall portions 3 (only one side is shown), and a tread continuous to both sidewall portions 3. 1 ply or more which reinforces each of the above-mentioned parts 2, 3 and 4 between the bead cores 5 embedded in the pair of bead parts 2, and the illustrated example is a two-ply radial arrangement code, preferably a rayon cord. It has a carcass 6 to be covered with rubber and a belt 7 that reinforces the tread portion 4 on the outer periphery of the carcass 6.
[0013]
The illustrated carcass 6 includes an inner turn-up ply 6-1 having a turn-up portion that winds up the bead core 5 from the inner side to the outer side of the tire 1, and a down ply 6-2 that encloses the turn-up ply 6-1. Is provided. In the illustrated two-ply carcass 6, the turn-up ply 6-1 forms the innermost carcass ply. The belt 7 has two or more layers, the illustrated example has two cord cross layers, preferably two steel cord cross layers, and an organic fiber cord layer shown by a broken line in FIG. It has a spiral wound layer of cord.
[0014]
Further, the tire 1 includes a pair of crescent-shaped thick reinforcing rubber strips 8 (only one side is shown) inherent to the run-flat tire on the inner surface side of the innermost turn-up ply 6-1 of the carcass 6. The reinforced rubber strip 8 stably supports the total weight of the running vehicle even when the internal pressure is zero, prevents separation from the applied rim 20, and prevents the tire 1 from being destroyed. Further, for example, at 80 to 160 km / h. In order to maintain running stability even during rapid punctures at high speeds, the tire radial center region is 8 to 12 mm thick, while the tire radial ends are tapered, and reinforced rubber. As the rubber of the strip 8, a high hardness rubber having a JIS A hardness of 70 to 90 ° is applied. Also, the bead filler rubber 9 is applied to a relatively high position as shown in the figure while applying a hard rubber to assist the reinforcement of the reinforcing rubber strip 8.
[0015]
First, the tire 1 was measured from a rim diameter line RL parallel to a tire rotation axis (not shown) passing through the position of the diameter D of the applied rim 20 in a state where the tire 1 was properly assembled to the applied rim 20 and the tire inner pressure was zero. Similarly, the height h of the position M of the maximum width CW of the innermost ply (turn-up ply) 6-1 of the carcass 6 (actually the position corresponding to the maximum width position of the down ply 6-2) is the rim diameter line. The maximum height SH of the innermost carcass ply 6-1 of the carcass 6 measured from RL, which is less than ½ of the height SH on the outer surface of the innermost carcass ply 6-1 on the tire equatorial plane E; Actually, it needs to be in the range of 0.50 to 0.30 times the height SH.
[0016]
Next, the rotation axis of the tire 1 (not shown) from the arc center O of the outer contour 20F of the flange in the cross section of the application rim 20 in a state where the tire 1 is properly assembled to the application rim 20 and the tire inner pressure is zero. flange outer edge 20F portion surrounded by and the inclined line IL extending toward the bead portion 2 at an angle of 45 ° to a line parallel L _O, the tire radial line VL extending perpendicular to the straight line L _O from the arc center O The bead portion 2 is provided with an annular rubber protrusion 10 whose inner peripheral surface is a curved surface formed by a contour that substantially conforms to FIG. The annular rubber protrusion 10 may be continuous on the circumference, or may be in an intermittent state having one or more narrow cuts on the circumference.
[0017]
Here, in a state where the internal pressure of the tire properly assembled to the application rim 20 is zero, the gap d between the inner peripheral surface of the annular rubber protrusion 10 and the outer contour 20F of the flange of the application rim 20 is larger than zero and is 1 It is necessary to stop within the range of mm or less . The detailed reason will be described later.
[0018]
Here, referring to FIG. 2, the innermost ply 6-1 of the carcass 6 in the tire radial cross section in a state where the tire inner pressure is properly assembled to the application rim 20 is the tire inner pressure zero assembled to the application rim. The innermost ply 6-1p of the carcass in the radial cross section of a tire in which the same tire is filled with an air pressure corresponding to 0.75 to 1.00 times the air pressure corresponding to the maximum load capacity of the tire (indicated by a broken line) In contrast to the natural equilibrium shape, it is essential to have the shape described below.
[0019]
(1) The position M of the maximum width CW of the innermost carcass ply 6-1 should be present inward in the tire radial direction from the maximum width position Mp of the innermost carcass ply 6-1p of the inner pressure filled tire.
(2) The innermost carcass ply 6-1 (solid line) is naturally balanced in the outer region in the tire radial direction from the maximum width position Mp of the innermost carcass ply 6-1p to at least the end portion (shoulder portion) of the tread portion. Present inside the tire with respect to the innermost carcass ply 6-1p (broken line). Of course, the curvature of the curve connecting the center of thickness of the innermost carcass ply 6-1 must be smaller than the curvature of the curve connecting the center of thickness of the innermost carcass ply 6-1p.
(3) The innermost carcass ply 6-1 (in the inner region in the tire radial direction from the maximum width position Mp of the innermost carcass ply 6-1p to the intersection Q between the inclined line IL and the ply 6-1p. The solid line) should be on the outer side of the tire with respect to the innermost carcass ply 6-1p (broken line) having a natural equilibrium shape. Of course, the curvature of the curve connecting the center of thickness of the innermost carcass ply 6-1 must be larger than the curvature of the curve connecting the center of thickness of the innermost carcass ply 6-1p.
[0020]
One of the means for realizing the change in the carcass ply shape before and after the internal pressure filling as described above is the maximum width CW of the innermost carcass ply 6-1 in the state where the tire internal pressure is zero as described above. The height h of the position M is set to be less than ½ of the maximum height SH of the ply 6-1, that is, within a range of 0.50 to 1.30 times the height SH.
[0021]
However, since this is not sufficient, in practice, the natural equilibrium shape of the innermost carcass ply 6-1p in the radial cross section of the tire filled with a predetermined internal pressure is set in advance, and the internal pressure is zero with respect to this set natural equilibrium shape. The innermost carcass ply 6-1 in the radial cross section of the tire in the state is removed as described in the above items (1) to (3). Here, the natural equilibrium shape of the carcass ply means that a curve connecting the thickness centers of the carcass plies follows the natural equilibrium shape curve, and the natural equilibrium shape curve is a curve described below.
[0022]
Referring to FIG. 2, the innermost carcass ply 6-1p of the tire 1 filled with a predetermined internal pressure is taken as an example, and a curve N (not shown in the symbol N) connecting the thickness centers of the plies is a so-called natural equilibrium shape theory. As a rule,
cos φ = (R ² −R _E ² ) / (R _S ² −R _E ² ), where
φ is an angle formed by a tangent at a point on the curve N separating the distance R from the tire rotation axis (not shown) and a straight line parallel to the rotation axis passing through this point,
R _E is the distance from the point at which the curve N takes the maximum distance in the tire rotation axis direction (the point on the straight line parallel to the tire rotation axis passing through the maximum width position Mp) to the rotation axis,
R _S is the distance from the point where the tangent of the extension above the curve N is parallel to the tire rotation axis to the tire rotation axis,
The curve represented by is called a natural equilibrium shape curve N.
[0023]
In accordance with what has been described above, referring to FIG. 2, when the tire 1 in the zero internal pressure state is filled with an air pressure of 0.75 to 1.00 times the air pressure corresponding to the maximum load capacity of the tire 1, the radiation of the tire 1 is emitted. The innermost carcass ply 6-1 (solid line) in the direction cross section is
(A) In the tire radial direction outer region from the maximum width position Mp of the innermost carcass ply 6-1p to at least the end portion (shoulder portion) of the tread portion, it projects in the direction indicated by the arrow a,
(B) In the inner region in the tire radial direction from the maximum width position Mp of the innermost carcass ply 6-1p to at least the intersection Q between the inclined line IL and the ply 6-1p, the inner carcass ply 6-1p is displaced in the direction of the arrow b.
(C) As these overhanging deformation and displacement deformation occur, the annular rubber protrusion 10 expands outward in the tire radial direction, and as a result, the value of the gap d increases significantly. This increase amount can be controlled by how much the innermost carcass ply 6-1 is removed from the innermost carcass ply 6-1p having a natural equilibrium shape, but it should be removed as far as possible without causing any unreasonable manufacturing problems. . Hereinafter, the function and effect will be described based on actual experimental results.
[0024]
With respect to the tire 1 in which the innermost carcass ply 6-1 is removed from the natural equilibrium shape within the above-described range, the normal use pressure of a normal passenger car tire is 0.75 to 1 of the air pressure corresponding to the maximum load capacity of the tire. Since it is within the range of 0.000, the internal pressure p = 2.0 kgf / cm ² is taken as a representative value, and the clearance d _p (mm) at that time and the clearance d (mm) when the internal pressure p = 0 (zero) ) And the relationship shown in FIG. 3, which is common to all tires 1 used for passenger cars. When the measured values at the three points are approximated by a straight line, d _p = 1 + 2d is obtained.
[0025]
On the other hand, when the tire is not provided with the annular rubber protrusion 10, the longitudinal spring constant k ₀ = 20 kgf / mm when p = 0 is expressed as an index where 100 is 100, and the gap d (mm) when p = 0. And the index of the longitudinal spring constant k ₀ (kgf / mm) of the tire 1 is as shown in the diagram of FIG. 4, and p = 2.0 kgf / cm ^{2 of a} tire not provided with the annular rubber protrusion 10. When the vertical spring constant k _{p of} 28 kgf / mm is expressed as an index of 100, the gap d _p (mm) at the internal pressure p = 2.0 kgf / cm ² and the vertical spring constant k _{p of the} tire 1 (kgf / Mm) and the index are as shown in the diagram of FIG.
[0026]
In order to actually improve the performance in a run flat with no internal pressure from a tire not provided with the annular rubber protrusion 10, an index of a longitudinal spring constant of 105 or more is necessary, and therefore, the gap d = 0 from the diagram shown in FIG. It is necessary to be within the range of ˜1 mm (excluding “0”) , and if the clearance d exceeds 1 mm, the tires having no conventional annular rubber protrusion 10 are improved and various performances in the run flat are improved. It turns out that there is a shortage.
[0027]
As shown in the diagram of FIG. 3, it can be seen that if the gap d = 0 to 1 mm (excluding “0”) , the gap dp has a value in the range of 1 to 3 mm. If dp is within this range, the longitudinal spring constant kp at the internal pressure p = 2.0 kgf / cm @ 2 is equivalent to that of the conventional tire not provided with the annular rubber projection 10 from the diagram shown in FIG. It can be seen that it has a constant.
[0028]
In short, in the run flat, if the gap d is within a range of 0 to 1 mm (excluding “0”) , the rubber protrusion 10 can surely ride on the outer contour surface of the flange of the rim 20. As a result of a significant increase in the value of the longitudinal spring constant of the tire in a state where the internal pressure is zero, it is possible to remarkably improve the performance of preventing the tire from being detached from the rim in the run flat and the durability performance. On the other hand, it is possible to realize a state in which the annular rubber protrusion 10 of the tire rolling under load with an internal pressure of 2 kgf / cm 2 is not in contact with the outer contour surface of the flange of the rim 20. As a result, the annular rubber protrusion 10 is provided. However, the vibration riding comfort does not deteriorate. Therefore, it is possible to simultaneously improve the tire detachment preventing performance and durability performance from the rim in the run flat and the vibration riding comfort.
[0029]
The above can be applied in common to the tires 1 of each size, and the shape of the innermost carcass ply 6-1 is the innermost carcass ply 6 having a natural equilibrium shape as described in (1) to (3) above. As a result, the gap d = d _p can be obtained if the shape of the innermost carcass ply 6-1 is matched with the natural equilibrium shape, and at most 1 (mm) <d = d _p <2 (mm ) Is limited only to the range, and it is not possible to obtain an improvement in the performance of preventing the tire from being removed from the rim and the durability in the run-flat.
[0030]
【Example】
This is a pneumatic radial ply tire having a size of 225 / 60R16, the configuration is shown in FIGS. 1 and 2, and the carcass 6 is a rubber coating of a rayon cord with a 2-ply radial arrangement 1650D / 2. Three types of tires 1 to 3 of Examples 1 to 3 in which the gap d between the inner peripheral surface of the annular rubber projection 10 and the outer contour surface of the flange of the applied rim 20 was 1 mm, 0.5 mm, and 0.1 mm were manufactured.
[0031]
A tire according to the conventional example, which does not include the annular rubber protrusion 10, and a tire according to Comparative Example 1 which includes the annular rubber protrusion 10 and the innermost carcass ply 6-1 has a shape close to a natural equilibrium shape. And the tire of the comparative example 2 which similarly provided the cyclic | annular rubber | gum protrusion part 10, and the innermost carcass ply 6-1 has the same shape as a natural equilibrium shape was prepared.
[0032]
Using the tires of Examples 1 to 3 and the conventional tire as test tires, a run-flat durability test was performed with a drum including measurement of the longitudinal spring constant k ₀ (kgf / mm) at zero internal pressure. The actual tire on the test course including the measurement of the longitudinal spring constant k _p (kgf / mm) with the internal pressure p = 2.0 kgf / cm ² and the tires of the previous example and the tires of the conventional example and comparative examples 1 and 2 as test tires A vibration ride comfort test was conducted. The longitudinal spring constants k ₀ and k _p (kgf / mm) were obtained from the slope (gradient) at the load position corresponding to 70% of the maximum load capacity of the tire defined by JATMA YEAR BOOK (1997 edition).
[0033]
The run-flat durability test is an actual vehicle running with a load equivalent to 75% of the maximum load capacity described above. When the front wheel right tire has zero internal pressure and runs straight at a speed of 90 km / h, it breaks down. The distance traveled until the vehicle vibrates and can no longer travel is expressed as an index with the conventional tire as 100, and this run-flat durability index and longitudinal spring constant k ₀ (kgf / mm) are organized. did. The larger the index, the better, and the organized result is shown in FIG. It can be seen from FIG. 6 that the tires of Examples 1 to 3 have better durability than the conventional tire by 20% or more, and that the higher the longitudinal spring constant k ₀ (kgf / mm), the better.
[0034]
In the vibration riding comfort test, the conventional tires were scored out of a maximum of 5 points based on the feelings given by the test driver. The larger the value, the better. The test results are organized by feeling score and longitudinal spring constant k _p (kgf / mm), which is shown in FIG. While the tires of Examples 1 to 3 in FIG. 7 show excellent vibration riding comfort with the same scores as the conventional tires, the tires of Comparative Examples 1 and 2 having a longitudinal spring constant k _p (kgf / mm) exceeding 100 are shown in FIG. In both cases, the vibration riding comfort is lowered, and it can be seen that the higher the longitudinal spring constant k _p (kgf / mm), the greater the degree of reduction.
[0035]
【The invention's effect】
According to the invention described in claims 1 to 3 of the present invention, while maintaining the vibration riding comfort equivalent to the tire having the vibration riding comfort allowed by the user among the conventional tires, the filling to the tire is performed. Even if the air pressure suddenly becomes zero to slight pressure, it has a vertical spring constant higher than that of conventional tires, so that the running state of the vehicle can be maintained more safely, and the rim can withstand It is possible to provide a pneumatic tire capable of exhibiting performance significantly superior to conventional tires as a run-flat tire in terms of tire separation performance and durability performance.
[Brief description of the drawings]
FIG. 1 is a left half sectional view of a tire and a rim at zero internal pressure according to an embodiment of the present invention.
2 is a diagrammatic partial cross-sectional view of the left half before and after internal pressure filling between a tire and a rim shown in FIG. 1. FIG.
FIG. 3 is a diagram showing the relationship between gaps at zero internal pressure and 2.0 kgf / cm ² .
FIG. 4 is a diagram showing the relationship between the clearance and the longitudinal spring constant when the internal pressure is zero.
FIG. 5 is a diagram showing the relationship between the clearance and the longitudinal spring constant when the internal pressure is 2.0 kgf / cm ² .
FIG. 6 is a diagram showing the relationship between the longitudinal spring constant and run-flat durability when the internal pressure is zero.
FIG. 7 is a diagram showing the relationship between the longitudinal spring constant and the vibration riding comfort when the internal pressure is 2.0 kgf / cm ² .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Bead part 3 Side wall part 4 Tread part 5 Bead core 6 Carcass 6-1, 6-2 Carcass ply 7 Belt 8 Thick reinforcement rubber strip 9 Filler rubber 10 Annular rubber protrusion 20 Applicable rim 20F Flange outer contour E Tire equatorial plane M Maximum width position of innermost carcass ply CW Maximum width of innermost carcass ply D Applicable rim diameter RL Rim diameter line SH Maximum innermost carcass ply height from rim diameter line Maximum width from rim diameter line Position height d Clearance between annular rubber protrusion and flange outer contour O Arc center of flange outer contour cross section

Claims

A carcass that is rubber-coated with a radial arrangement cord of one or more plies that reinforces the pair of sidewalls and the tread between the bead cores embedded in the pair of beads, and two or more layers that reinforce the tread on the outer periphery of the carcass A thick reinforced rubber strip having a crescent cross-sectional shape that forms a pair on the inner side of the innermost carcass ply extending from the position near the bead core of the bead portion to the end portion of the tread portion. When the tire is properly assembled to the application rim and the tire has no internal pressure, the pneumatic tire has a 45 ° angle with respect to a straight line parallel to the tire rotation axis from the arc center of the flange outer contour of the application rim cross section. An inclined line extending toward the bead part at an angle, and a tire radius line extending perpendicularly to the straight line from the arc center. A continuous or intermittent annular rubber protrusion is provided on the outer side of the bead, and the inner peripheral surface of the annular rubber protrusion is connected to the flange of the applicable rim. And the innermost carcass ply in the radial cross section of the tire corresponds to 0.75 to 1.00 times the air pressure corresponding to the maximum load capacity of the tire. (1) The maximum width position (M) of the innermost carcass ply is the maximum width of the natural equilibrium shape carcass ply when compared with the natural equilibrium shape of the innermost carcass ply in the radial cross section of the tire filled with air pressure Exists in the tire radial direction from the position (Mp), and (2) the natural equilibrium shape carcass in the tire radial direction outer region from the maximum width position (Mp) of the natural equilibrium shape carcass ply. A carcass ply portion located inside the tire with respect to the ply, and (3) located outside the tire with respect to the natural equilibrium shape carcass ply in an inner region in the tire radial direction from the maximum width position (Mp) of the natural equilibrium shape carcass ply. And a carcass ply portion.

The pneumatic tire according to claim 1, wherein the gap (d) has a value in a range of greater than 0 and 1 mm or less .

The height (h) of the maximum width position (M) of the innermost carcass ply measured from the rim diameter line parallel to the tire rotation axis passing through the diameter position of the applicable rim is the innermost carcass measured from the rim diameter line. The pneumatic tire according to claim 1 or 2, wherein the pneumatic tire is in a range of 0.50 to 0.30 times the maximum height (SH) of the ply.