JP4242956B2

JP4242956B2 - Heavy duty pneumatic radial tire

Info

Publication number: JP4242956B2
Application number: JP30529098A
Authority: JP
Inventors: 大祐伊丹
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1998-10-27
Filing date: 1998-10-27
Publication date: 2009-03-25
Anticipated expiration: 2018-10-27
Also published as: JP2000127718A

Description

【０００１】
【発明の属する技術分野】
この発明は、重荷重用空気入りラジアルタイヤ、より詳細には主として高内圧重荷重条件の下で使用する航空機用ラジアルプライタイヤに関し、特に、最大荷重の２倍に相当する超重荷重負荷の下で実際上必要とする距離を無故障で転動可能なビード部耐久性を備える重荷重用空気入りラジアルタイヤに関する。
【０００２】
【従来の技術】
一般に航空機用空気入りラジアルタイヤを典型例とする重荷重用タイヤは、複輪使用で対をなす一方タイヤがパンクしても、正常な他方タイヤがそれまでの負荷荷重の２倍荷重負荷の下で所定距離を故障なく、特に航空機のランディング終了までの間は少なくとも故障なく、望ましくはターミナルまで故障なく走行し得る耐久性、なかでもビード部耐久性が要求される。
【０００３】
このビード部耐久性を確保するため、例えばビードコアからタイヤ半径方向外側に向け先細り状に延びる硬質スティフナゴム高さを最適化したり、ビード部の、リムのフランジと接触するゴム部分のモジュラスを最適化することなどの改善が試みられてきた。しかし上記のような２倍荷重に達する程のオーバーロード走行条件の下では、上記のゴム部分とカーカスプライとの間にセパレーション故障が発生し、上記のような改善手段ではビード部耐久性が不足することが分かっている。
【０００４】
また一方では、ビードコアの周りをタイヤ内側から外側に向け巻上げた巻上げ部を有する、いわゆるターンアッププライのみのカーカスプライ構成を有するタイヤでは、長期間の高内圧使用による巻上げ部の引き抜き作用がセパレーションをもたらすとして、ターンアッププライをその巻上げ部も含め外包みするダウンプライをも備える、いわゆるアップ−ダウン構造のカーカスプライを採用し、ダウンプライにより巻上げ部の引き抜き作用を抑制してセパレーションを改善する手段の採用が一般化されている。
【０００５】
しかし、カーカスプライにアップ−ダウン構造を採用した上で、硬質スティフナゴムの高さを最適化し、かつリムのフランジと接触するゴム部分のモジュラスも最適化した空気入りラジアルタイヤを、室内のドラム試験機によりタイヤの最大静止荷重（後述する）に対するオーバーロードの条件、特に２倍ロード条件でビード部耐久性試験を実施してみると、ビード部の最外側プライに沿うセパレーション、ビード部のタイヤ外側ゴム部分のブローアウト及びビード部バーストなどの故障が発生することが分かった。
【０００６】
これら故障の原因を究明したところ、セパレーション故障はビード部断面の外側輪郭形状が不適切であることにより、リムのフランジに押圧されるビード部の断面内せん断ひずみが大きくなることに由来し、ビード部のブロー、バーストは上記ビード部の断面内せん断ひずみが大きくなることと共に、ビード部におけるゴムゲージ分布が不適切であることにより、ゴムの圧縮ひずみが過大となり多量の発熱がもたらされることに由来することを解明した。
【０００７】
【発明が解決しようとする課題】
従ってこの出願の請求項１〜４に記載した発明は、前記の故障原因究明結果に基づき、前記したオーバーロード条件下走行、特に２倍ロード条件下走行でのビード部耐久性を実用上十分なレベルまで向上させることができる重荷重用空気入りラジアルタイヤ、なかでも航空機用タイヤの提供を目的とする。
【０００８】
【課題を解決するための手段】
前記目的を達成するため、この出願の請求項１に記載した発明は、トレッド部と、トレッド部の両側に連なる一対のサイドウォール部及び一対のビード部とを有し、これら各部をビード部内に埋設したビードコア相互間にわたり補強する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を具え、カーカスは、ビードコア周りをタイヤ内側から外側に巻上げる１プライ以上のターンアッププライと、該ターンアッププライをその巻上げ部も含み外包みして少なくともビードコア直下に終端を有する１プライ以上のダウンプライとを有しまた、トレッド部を強化するベルトを具える重荷重用空気入りラジアルタイヤにおいて、
上記タイヤを正規のリムに組み付けたタイヤ及びリム組立体に対する０．０５〜０．１kgf/cm²の範囲内の微圧充てん下で、
上記組立体の断面におけるビード部外輪郭は、上記組立体の回転軸線と直交する直線上に存在するビードベース側直線部分と、該直線部分に、リムのフランジ高さの０．８〜１．０倍の範囲内で接する、タイヤ外側に曲率中心をもつ円弧部分とを有し、
上記円弧部分の曲率半径が、リムのフランジの曲率半径の２．０〜３．０倍の範囲内にあり、
ビードコアの断面図形の重心を通り前記回転軸線に平行な直線とビード部外輪郭との交点を点（Ａ）とし、点（Ａ）を通る、最外側カーカスプライ外側表面の法線の延長線と最外側プライコード最外側表面との交点を点（Ｂ）として、法線の延長線上で点（Ａ）と点（Ｂ）との間に存在する総ゴムゲージ（Ｇ _１）が、
カーカスの各プライのコード１本の直径を全プライで合計したコード径の総和（Ｐｇ）の１．２０〜２．５１倍の範囲内にあることを特徴とする重荷重用空気入りラジアルタイヤである。
【００１０】
また請求項１に係る発明の発展形態として、請求項２に記載した発明は、タイヤの最大静荷重負荷時の指定内圧を充てんした前記タイヤ及びリム組立体に上記最大静荷重の２倍の荷重を負荷させたタイヤのリムのフランジからの離反点を点Ｐとし、
荷重無負荷とすると共に、前記微圧充てんに戻したタイヤ及びリム組立体の断面にて、タイヤの上記点Ｐを通る、最外側カーカスプライ外側表面の法線の延長線と最外側プライコード最外側表面との交点を点Ｑとして、法線の延長線上で点Ｐと点Ｑとの間に存在する総ゴムゲージＧ₂が、前記総ゴムゲージＧ₁の０．８〜１．０倍の範囲内にあるとするものである。
【００１１】
さらに、請求項２に係る発明の発展形態としては、請求項３に記載した発明のように、前記微圧充てんのタイヤ及びリム組立体において、
前記の点Ａと点Ｂとを結ぶ線分と、前記の点Ｐと点Ｑとを結ぶ線分とで囲まれる領域内にて、最外側カーカスプライコードの最外側表面とタイヤ外輪郭との間のゴムゲージＧ₃が、前記総ゴムゲージＧ₁の０．８〜１．０倍の範囲内とする。
【００１２】
ここに前記正規のリムとは、ＴＲＡ（1998 AIRCRAFT YEAR BOOK, THE TIRE and RIM ASSOCIATION INC.) 及びＥＴＲＴＯ（The European Tyre and Rim Technical Organisation.AIR CRAFT TYRE AND RIM DATA BOOK 1998)にサイズ毎の表に記載されているリム諸元に従う。また指定内圧及び最大静止荷重も、上記ＴＲＡ及びＥＴＲＴＯにて充てん圧力（INFLATION PRESSURES)及び静止最大荷重（TRA : maximum static load,ETRTO:Maximum Static Load)として記載され、実際上は表にサイズ毎に記載されている荷重負荷時内圧（TRA :Loaded Inf.,ETRTO:Inflation Pressure(bar),Loaded)及び最大静止荷重(TRA :MAX.LOAD,ETRTO:Max. Static Load)を用いる。
【００１３】
【発明の実施の形態】
以下、この発明の実施の形態の一例を図１及び図２に基づき説明する。
図１は、この発明による重荷重用空気入りラジアルタイヤの代表例としての航空機用ラジアルプライタイヤとその正規のリムとの組立体に０．０５〜０．１kgf/cm²の微圧を充てんしたときの組立体の左半断面図であり、
図２は、図１に示す組立体の要部拡大断面図である。
【００１４】
図１において、航空機用ラジアルプライタイヤ（以下タイヤという）１は、トレッド部２と、トレッド部２の両側に連なる一対のサイドウォール部３（タイヤ赤道面Ｅからの片側のみ示す）及び一対のビード部４（片側のみ示す）とを有し、タイヤ１を先に説明した正規のリム５に組付けてタイヤ１とリム５との組立体とする。この組立体には、タイヤ１をリム５に完全にフィットさせた状態で、０．０５〜０．１kgf/cm²の微圧を充てんするものとする。完全なフィット状態を得る方法として、例えば組立体にタイヤ１の最大静止荷重負荷時に対応する指定内圧以上の空気圧を一旦充てんしてタイヤ１をリム５に完全にフィットさせた後に、上記微圧まで減圧する。
【００１５】
タイヤ１は、ビード部４内に埋設した一対のビードコア６相互間にわたる１プライ以上、図示例は６プライのカーカス７と、カーカス７の外周でトレッド部２を強化するベルト８とを具える。図示例のように、複数プライ（６プライ）の場合のカーカス７は、１プライ以上（図示例は４プライ）のターンアッププライ７ｕと、ターンアッププライ７ｕをその巻上げ部も含めタイヤ外側から外包みする１プライ以上（図示例は２プライ）のダウンプライ７ｄとを有するアップ−ダウン構造とするのが適合する。
【００１６】
カーカス７は全プライがラジアル配列コードのゴム被覆プライからなり、カーカス７のプライコードは、複数プライの場合は６，６ナイロンコードなど耐熱性に優れる有機繊維コードが適合する。
【００１７】
ここで図２を参照し、タイヤ１とリム５との組立体において、リム５のフランジ５Ｆの直立部分と一部が接触するビード部４のタイヤ外側輪郭は、組立体の回転軸線（図示省略）と直交する直線上に存在するビードベースＢｂ側直線部分Ｌｎと、この直線部分Ｌｎに、タイヤ１の半径方向外側終端Ｓで接し、かつタイヤ１の外側に曲率中心Ｃｒをもつ円弧部分Ａｃとを有する。直線部分Ｌｎの半径方向外側終端Ｓのリム径ラインＲＬから測った高さｈは、リム５のフランジ５Ｆの高さＦｈの０．８〜１．０倍の範囲内にあるものとし、円弧部分Ａｃの曲率半径Ｒは、リム５のフランジ５Ｆの外輪郭のうち円弧部分の曲率半径Ｆｒの２．０〜３．０倍の範囲内にあるものとする。なおリム径ラインＲＬとは、リムの直径位置を通る、組立体の回転軸線と平行な直線である。
【００１８】
さて、指定内圧を充てんしたタイヤ１とリム５との組立体に、オーバーロード、それも最大静止荷重の２倍に相当するオーバーロードを負荷すると、図２に二点鎖線で示すように、タイヤ１のビード部４は、極端に撓曲し、倒れ込んでリム５のフランジ５Ｆの全円弧部分乃至その延長端部を含む全円弧部分（両者を全円弧部分と略す）に押圧される。このとき、従来タイヤのビード部外輪郭のうち、リム５のフランジ５Ｆの全円弧部分に押圧されるビード部の断面外輪郭はタイヤ外側に向け凸の形状を有するので、リム５のフランジ５Ｆの全円弧部分からビード部にもたらされる反力は大きなピークをもち、この大きなピークの反力が作用するビード部のゴム部分は局部的に著しく圧縮される。このピーク部の大きな圧縮力が作用するゴム部分は、最外側カーカスプライに沿って移動し易い方向、すなわちサイドウォール部方向へ移動する結果、カーカスプライとの間に著しく大きなせん断ひずみをもたらし、結局セパレーション故障を発生させる。
【００１９】
これに対し、ビード部４のタイヤ外側輪郭を、前記高さｈを有する直線部分Ｌｎと、高さｈの半径方向終端Ｓで接してタイヤ１内側に向け凸をなす前記円弧部分Ａｃとで形成することにより、前記オーバーロード時にリム５のフランジ５Ｆの全円弧部分からビード部にもたらされる反力自体が従来に比し低下すると同時に反力分布は平均化され殆どピークをもたず、これによりフランジ５Ｆの全円弧部分に押圧されるビード部の外側ゴム部分の圧縮力は軽減されるので、カーカスプライとの間のせん断ひずみが低減し、セパレーション故障発生を抑制することができ、同時に発熱量は低減し、高熱によるビード部のタイヤ外側ゴム部分のブローアウト及びビード部バーストなどの故障発生も抑制することができる。
【００２０】
前記の故障発生抑制を有利に実現するためには、
（１）ビード部４のタイヤ外側輪郭のうちビードベースＢｂ側直線部分Ｌｎのリム径ラインＲＬから測った高さｈを、リム５のフランジ５Ｆの高さＦｈの０．８〜１．０倍の範囲内とすること、
（２）円弧部分Ａｃの曲率半径Ｒを、リム５のフランジ５Ｆの外輪郭のうち円弧部分の曲率半径Ｆｒの２．０〜３．０倍の範囲内とすることを要し、
これら高さｈ及び曲率半径Ｒを上記のような範囲に規定することにより、高さｈと曲率半径Ｒとの相乗効果の下で、タイヤ１の前記の２倍最大静止荷重負荷時に、ビード部４の倒れ込み（撓曲）度合いと、リム５のフランジ５Ｆの全円弧部分に対する押圧力の均一化・低減化との最適バランスを実現することができる。この最適バランスの下で２倍最大静止荷重負荷時におけるビード部のセパレーション故障、ブローアウト故障及びバースト故障を有効に抑制化することが可能となる。
【００２１】
高さｈが、高さＦｈの０．８倍未満では、前記の２倍最大静止荷重負荷時のビード部４の撓みが著しく、ビードコア６横近傍位置とフランジ５Ｆとの接触圧が過大になるという不具合を生じる一方、１．０倍を超えると、上記のビード部４の倒れ込み量が過大になり、大きなせん断ひずみを生じるので、いずれも不可である。また曲率半径Ｒが、曲率半径Ｆｒの２．０倍未満では、タイヤ１の前記の２倍最大静止荷重負荷時に、従来タイヤとまでは言わずとも、ビード部４のゴム部分には、リム５のフランジ５Ｆの全円弧部分から局部的に大きな圧縮力が加えられ、この大きな圧縮力はカーカスプライとの間に大きなせん断ひずみをもたらし、セパレーション故障を発生し易くする一方、曲率半径Ｆｒの３．０倍を超えるとビード部４の倒れ込み量が過大になり、大きな撓曲変形による大きなせん断ひずみがカーカスプライとそれに隣接するゴムとの間に生じ、やはりプライセパレーションの原因となるので、いずれも不可である。
【００２２】
またカーカス７が前記したアップ−ダウン構造を有することを前提として、図２を参照し、ビードコア６の断面図形の重心Ｃを通り、タイヤ１とリム５との組立体の回転軸線（図示省略）に平行な直線Ｌｃとビード部１のタイヤ外側輪郭との交点を点Ａとし、点Ａを通る、カーカス７の最外側プライ、すなわちダウンプライ７ｄのタイヤ外側プライ７ｄ−２の外側表面の法線の延長線Ｌｍ、図示例では直線Ｌｃと重なる直線Ｌｍと最外側プライ７ｄ−２のコード最外側表面との交点を点Ｂとして、法線の延長線Ｌｍ上で点Ａと点Ｂとの間に存在する総ゴムゲージＧ₁（ｍｍ）と、
タイヤ１のカーカス７を構成する各プライにおける１本のコードの直径を全プライ（図示例は６プライ）につき合計したコード径の総和Ｐｇ（ｍｍ）との間で、
１．２０×Ｐｇ≦Ｇ₁≦２．５１×Ｐｇの関係を満たすものとする。ただし巻上げ部のコード径加算は除外する。
【００２３】
上記の関係は、タイヤ１のカーカス７のプライ数が増す程、より正確に言えばカーカス７の全プライの積層方向における各プライのコード径の総和Ｐｇ（ｍｍ）が増加すればする程、タイヤ１の最大静止荷重は増加し、それ故ビードコア６の断面図形の重心Ｃを通る直線Ｌｃ上とその近傍領域で、リム５のフランジ５Ｆと最外側プライ７ｄ−２のコード最外側表面との間に挟まれるゴム部分は、２倍最大静止荷重負荷の下でフランジ５Ｆから大きな押圧力を受けることになる。従って大きな押圧力がもらす大きな圧縮ひずみを成るべく緩和する必要があるため総ゴムゲージＧ₁（ｍｍ）を、コード径の総和Ｐｇ（ｍｍ）との関連で前記のように範囲を定めるものである。
【００２４】
ここに総ゴムゲージＧ₁（ｍｍ）が、１．２０×Ｐｇ未満では押圧がもたらすゴム部分の圧縮ひずみの緩和度合いが小さく、最外側プライ７ｄ−２のコードとその周囲ゴムとの間のせん断ひずみを十分に小さくすることができず、セパレーション故障のうれいが生じる一方、２．５１×Ｐｇを超えると逆にゴム部分の最外側カーカスプライに沿う移動が生じ易く、これもまた最外側プライ７ｄ−２のコードとその周囲ゴムとの間のせん断ひずみを増すことになり、セパレーション故障が発生し易くなるので、いずれも不可である。
【００２５】
また、図２に二点鎖線で示す、指定内圧充てんの下での２倍最大静止荷重負荷時のタイヤ輪郭を参照し、二点鎖線上の点Ｐはリム５のフランジ５Ｆからの離反点であり、この離反点Ｐを前記微圧充てん及び荷重無負荷状態のタイヤ１にそのまま点Ｐとしてこれを図２に示す。点Ｐを通る、最外側カーカスプライ７ｄ−２の外側表面の法線Ｌｑの延長線と、最外側カーカスプライ７ｄ−２のコードの最外側表面との交点を点Ｑとし、法線Ｌｑの延長線上で点Ｐと点Ｑとの間に存在する総ゴムゲージＧ₂（ｍｍ）を、前記総ゴムゲージＧ₁（ｍｍ）の０．８〜１．０倍の範囲内とする。
【００２６】
また前記の点Ａと点Ｂとを結ぶ線分と、前記の点Ｐと点Ｑとを結ぶ線分とで囲まれる領域内の任意位置における、最外側カーカスプライ７ｄ−２のコードの最外側表面とタイヤ１の外輪郭との間のゴムゲージＧ₃（ｍｍ）を、前記総ゴムゲージＧ₁（ｍｍ）の０．８〜１．０倍の範囲内とする。但しゴムゲージＧ₃（ｍｍ）は、最外側カーカスプライ７ｄ−２の外側表面の法線の延長線上にて定めるものとする。
【００２７】
総ゴムゲージＧ₂（ｍｍ）及びゴムゲージＧ₃（ｍｍ）の双方を総ゴムゲージＧ₁（ｍｍ）の０．８〜１．０倍の範囲内として、２倍最大静止荷重負荷時にリム５のフランジ５Ｆに押圧されるビード部４のタイヤ外側ゴムゲージ分布を一様化することにより、カーカス７のプライ数の多寡に拘わらず、カーカス７の全プライの積層方向における各プライのコード径の総和Ｐｇ（ｍｍ）の値の大小に関わらず、２倍最大静止荷重負荷の下で、リム５のフランジ５Ｆの全円弧部分がビード部４のタイヤ外側ゴムに局部的に大きなせん断ひずみ及び圧縮ひずみをもたらすことはなく、よってビード部４におけるセパレーション故障、ブローアウト故障及びバースト故障などの発生が阻止される。
【００２８】
ここに総ゴムゲージＧ₂（ｍｍ）及びゴムゲージＧ₃（ｍｍ）の双方が、総ゴムゲージＧ₁（ｍｍ）の０．８倍未満であると、上記の局部的に大きなせん断ひずみ及び圧縮ひずみの有効な低減を達成することができない一方で、総ゴムゲージＧ₁（ｍｍ）の１．０倍を超えると逆にビード部４のタイヤ外側ゴムの移動量が増し、最外側カーカスプライ７ｄ−２のコード外側表面に大きなせん断ひずみが作用し、セパレーション故障発生要因となるので、いずれも不可である。
【００２９】
先に述べた総ゴムゲージＧ₂（ｍｍ）、Ｇ₁（ｍｍ）及びゴムゲージＧ₃（ｍｍ）を得るためサイドウォールゴム３ｇ及びゴムチェーファ１０のゲージ分布を調整しても良いが、望ましくはサイドウォールゴム３ｇと最外側プライ７ｄ−２との間及びゴムチェーファ１０と最外側プライ７ｄ−２との間に別種のインサートゴム９を配置する。なお符号１１はビードコア６からタイヤ１の半径方向外側に向け先細り状に延びる硬質のスティフナゴムであり、符号１２はインナーライナゴムである。特に航空機用タイヤはチューブレスタイヤであるからインナーライナゴム１２には空気不透過性のゴムを適用する。
【００３０】
【実施例】
航空機用ラジアルプライタイヤ１で、サイズが５０×２０．０Ｒ２２２６ＰＲであり、図１、２に従う構成を有し、カーカス７は４プライのターンアッププライ７ｕと２プライのダウンプライ７ｄとを有する。カーカスプライ７ｕ、７ｄは１４００dtex×２×２の６，６ナイロン超強力糸コードを適用し、プライ７ｕ、７ｄ内カーカスコードの直径は０．８８ｍｍである。
【００３１】
タイヤ１をその正規のリム５０×２０．０Ｒ２２に組み付け、この組立体にタイヤ１の最大静止荷重に対応する指定内圧１２．４kgf/cm²を充てんし、以下の試験方法に従いビード部４の耐久性試験を実施した。試験対象タイヤは実施例タイヤの他に、同じ金型で加硫を施した従来例タイヤ及び比較例１〜３のタイヤも準備した。従来例タイヤはビード部の外輪郭及び外側ゴムゲージを除き実施例タイヤに合わせ、比較例１〜３のタイヤは比Ｇ₁／Ｐｇ、Ｇ₂／Ｇ₁、Ｇ₃／Ｇ₁それぞれの値を除き実施例タイヤに合わせた。
【００３２】
試験方法は、直径３．０ｍの室内ドラムに、その曲率半径の平板修正を施した最大静止荷重２０５０３kgf （ＴＲＡ，４５２００pounds）の約２倍荷重４１００５kgf をタイヤ１に負荷させ、７０秒の間に速度ゼロから３７８km/h（ＴＲＡ，２３５miles per hour）までリニヤに加速し、最終速度に達した時点で供試タイヤをドラムから取り外し、ビード部の故障状態を調べた。なお７０秒の試験時間の間に故障し取り外したタイヤは未完走とした。表１に比ｈ／Ｆｈ、Ｒ／Ｆｒ、Ｇ₁／Ｐｇ、Ｇ₂／Ｇ₁、Ｇ₃／Ｇ₁それぞれの値と共に試験結果を示す。
【００３３】
【表１】

【００３４】
表１に示す結果から、従来例タイヤは辛うじて完走したものの、ビード部全周にブローアウト故障が発生したのに対し、比較例１〜３のタイヤはいずれもビード部に部分的な故障を発生しながらも完走し、この発明のビード部外輪郭の有効性が立証されている。ただし完走し、かつビード部に故障が全く発生していない実施例タイヤから明らかなように、比Ｇ₁／Ｐｇ、Ｇ₂／Ｇ₁、Ｇ₃／Ｇ₁それぞれの値をこの発明の範囲内とすれば再使用が可能となり、完全である。
【００３５】
【発明の効果】
この出願の請求項１〜３に記載した発明によれば、航空機用タイヤの場合、複輪装着タイヤの一方タイヤがパンクし、他方タイヤに最大静止荷重の２倍の荷重を負荷されても、少なくともランディグ終了まではビード部に故障が発生せず、安全を確保することができ、ターミナルまでタクシーングが可能な重荷重用空気入りラジアルタイヤを提供することができる。
【図面の簡単な説明】
【図１】この発明のタイヤとリムとの組立体の左半断面図である。
【図２】図１に示すタイヤとリムとの要部拡大図である。
【符号の説明】
１航空機用タイヤ
２トレッド部
３サイドウォール部
３ｇサイドウォールゴム
４ビード部
５リム
５Ｆリムのフランジ
６ビードコア
７カーカス
７ｕターンアッププライ
７ｄダウンプライ
８ベルト
９インサートゴム
１０ゴムチェーファ
１１スティフナゴム
１２インナーライナゴム
Ｅタイヤ赤道面
Ｃビードコア断面図形の重心
ＲＬリム径ライン
ｈビード部外輪郭直線部のリム径ラインからの高さ
Ｒビード部外輪郭円弧部の曲率半径
Ｃｒ曲率半径Ｒの中心
Ｆｒリムのフランジの円弧の曲率半径
Ｇ₁、Ｇ₂、Ｇ₃ ゴムゲージ
Ｐ２倍荷重負荷時のタイヤのフランジからの離反点[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heavy-duty pneumatic radial tire, and more particularly to an aircraft radial ply tire used mainly under a high internal pressure heavy load condition, and in particular, under a super heavy load load corresponding to twice the maximum load. The present invention relates to a heavy-duty pneumatic radial tire having a bead portion durability capable of rolling at a required distance without failure.
[0002]
[Prior art]
In general, heavy-duty tires, typically pneumatic radial tires for aircraft, are used under the condition that even if one pair of tires is punctured due to the use of multiple wheels, the normal other tire is under a load twice that of the previous load. There is a demand for durability over a predetermined distance, particularly at least until the end of the landing of the aircraft, with no failure, and preferably with a durability that can travel to the terminal without failure, in particular, bead durability.
[0003]
In order to ensure the durability of the bead part, for example, the height of the hard stiffener rubber that tapers outward from the bead core in the tire radial direction is optimized, or the modulus of the rubber part of the bead part that contacts the flange of the rim is optimized. There have been attempts to improve things. However, under the overload running condition that reaches the double load as described above, a separation failure occurs between the rubber part and the carcass ply, and the improvement means as described above has insufficient bead durability. I know you will.
[0004]
On the other hand, in a tire having a carcass ply configuration with only a so-called turn-up ply that has a winding portion wound around the bead core from the inside to the outside of the tire, the pulling-out action of the winding portion due to use of a high internal pressure for a long time separates the tire. As a result, a carcass ply having a so-called up-down structure including a down ply that encloses the turn-up ply including its winding part is adopted, and means for improving the separation by suppressing the pulling-out action of the winding part by the down ply. The adoption of is generalized.
[0005]
However, a pneumatic radial tire that uses an up-down structure for the carcass ply, optimizes the height of the hard stiffener rubber, and optimizes the modulus of the rubber part that contacts the flange of the rim. When the bead part durability test is carried out under the condition of overload against the maximum static load of the tire (described later) by the machine, especially the double load condition, the separation along the outermost ply of the bead part, the tire outer part of the bead part It was found that failures such as blowout of the rubber part and burst of the bead part occurred.
[0006]
As a result of investigation of the causes of these failures, the separation failure originates from the fact that the outer contour shape of the cross section of the bead portion is inappropriate, and the shear strain in the cross section of the bead portion pressed against the flange of the rim increases. Blowing and bursting of the part originates from the fact that the shear strain in the cross section of the bead part increases and the rubber gauge distribution in the bead part is inappropriate, resulting in excessive rubber compression strain and a large amount of heat generation. I clarified that.
[0007]
[Problems to be solved by the invention]
Therefore, the invention described in claims 1 to 4 of the present application has practically sufficient bead durability in running under the above-described overload condition, in particular, under double load condition, based on the result of investigation of the cause of failure. An object is to provide a heavy-duty pneumatic radial tire that can be improved to a level, especially an aircraft tire.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 of the present application has a tread portion, a pair of side wall portions and a pair of bead portions that are connected to both sides of the tread portion, and these portions are included in the bead portion. comprising a carcass scan comprising the rubber coating of one ply or radial sequence code to reinforce over between embedded the bead core cross, carcass 1 and the ply or more turnup ply wound outward from the tire inner side around bead cores, said turn-up and wrapped outside comprises a ply also the winding portion and a 1 ply or more down ply having end to at least the bead core just below also, in the heavy duty pneumatic radial tire obtain immediately a belt reinforcing a tread portion,
Under slight pressure filling within a range of 0.05 to 0.1 kgf / cm ² for a tire and a rim assembly in which the tire is assembled to a regular rim,
The outer contour of the bead portion in the cross section of the assembly includes a bead base side straight portion existing on a straight line orthogonal to the rotation axis of the assembly, and a rim flange height of 0.8-1. Having a circular arc part with a center of curvature on the outer side of the tire, which is in contact within the range of 0 times,
The radius of curvature of said arcuate portion, Ri range near 2.0 to 3.0 times the radius of curvature of the rim flange,
An intersection of a straight line that passes through the center of gravity of the cross-sectional figure of the bead core and is parallel to the rotational axis and the outer contour of the bead is defined as a point (A), and an extension of the normal line of the outermost carcass ply outer surface passing through the point (A) With the point of intersection with the outermost surface of the outermost ply cord as the point (B), the total rubber gauge (G ₁ ) existing between the point (A) and the point (B) on the extended line of the normal line ,
A heavy-duty pneumatic radial tire characterized by being in a range of 1.20 to 2.51 times the total cord diameter (Pg) obtained by adding the diameters of one cord of each ply of carcass for all plies. .
[0010]
Further, as a development form of the invention according to claim 1, the invention described in claim 2 is such that the tire and the rim assembly filled with the specified internal pressure at the time of the maximum static load load of the tire have a load twice the maximum static load. Point P is the point of separation from the rim flange of the tire loaded with
In the cross section of the tire and rim assembly returned to the fine pressure filling , the normal line extension of the outermost carcass ply outer surface and the outermost ply cord outermost in the cross section of the tire and the rim assembly returned to the fine pressure filling. With the point of intersection with the outer surface as a point Q, the total rubber gauge G ₂ existing between the point P and the point Q on the extended line of the normal line is within a range of 0.8 to 1.0 times the total rubber gauge G ₁ . It is supposed to be in
[0011]
Furthermore , as a development form of the invention according to claim 2 , as in the invention according to claim 3 , in the tire and rim assembly filled with the above-mentioned slight pressure,
The outermost surface of the outermost carcass ply cord and the tire outer contour are within a region surrounded by a line segment connecting the point A and the point B and a line segment connecting the point P and the point Q. rubber gauge G ₃ between the shall be the range of 0.8 to 1.0 times the total rubber gauge G _1.
[0012]
Here, the regular rims are listed in TRA (1998 AIRCRAFT YEAR BOOK, THE TIRE and RIM ASSOCIATION INC.) And ETRTO (The European Tire and Rim Technical Organization. AIR CRAFT TYRE AND RIM DATA BOOK 1998). Follow the listed rim specifications. Also, the specified internal pressure and maximum static load are described as filling pressure (INFLATION PRESSURES) and static maximum load (TRA: maximum static load, ETRTO: Maximum Static Load) in the above TRA and ETRTO. The load internal pressure (TRA: Loaded Inf., ETRTO: Inflation Pressure (bar), Loaded) and maximum static load (TRA: MAX.LOAD, ETRTO: Max. Static Load) are used.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a case where an aircraft radial ply tire as a representative example of a heavy duty pneumatic radial tire according to the present invention and its normal rim are filled with a fine pressure of 0.05 to 0.1 kgf / cm ^2. Is a left half sectional view of the assembly of
FIG. 2 is an enlarged cross-sectional view of a main part of the assembly shown in FIG.
[0014]
In FIG. 1, an aircraft radial ply tire (hereinafter referred to as a tire) 1 includes a tread portion 2, a pair of sidewall portions 3 (shown only on one side from the tire equatorial plane E) and a pair of beads connected to both sides of the tread portion 2. The tire 1 is assembled to the regular rim 5 described above to form an assembly of the tire 1 and the rim 5. This assembly is filled with a slight pressure of 0.05 to 0.1 kgf / cm ^{2 in} a state where the tire 1 is completely fitted to the rim 5. As a method for obtaining a perfect fit state, for example, after the assembly 1 is filled with an air pressure equal to or higher than a specified internal pressure corresponding to the maximum static load of the tire 1 and the tire 1 is completely fitted to the rim 5, Reduce pressure.
[0015]
Tire 1 comprises a pair of bead cores 6 over a mutual 1 ply or more embedded in the bead portion 4, the illustrated example the carcass 7 of the 6-ply, obtain ingredients and a belt 8 to strengthen the tread portion 2 in the outer periphery of the carcass 7. As shown in the example, the carcass 7 in the case of a plurality of plies (6 plies) includes a turn-up ply 7u of 1 ply or more (4 plies in the illustrated example), and the turn-up ply 7u including the winding portion from the outside of the tire. An up-down structure having one or more plies (2 plies in the illustrated example) of the down ply 7d is suitable.
[0016]
The carcass 7 is composed of a rubber-coated ply in which all plies are radially arranged cords, and the ply cord of the carcass 7 is suitable for organic fiber cords having excellent heat resistance such as 6,6 nylon cords in the case of a plurality of plies.
[0017]
Referring now to FIG. 2, in the assembly of the tire 1 and the rim 5, the tire outer contour of the bead portion 4 where the upright portion of the flange 5F of the rim 5 comes into contact with the upright portion of the bead portion 4 is the rotational axis of the assembly (not shown). A bead base Bb-side straight line portion Ln existing on a straight line orthogonal to), and an arc portion Ac that is in contact with the straight line portion Ln at the radially outer end S of the tire 1 and has a center of curvature Cr on the outside of the tire 1; Have The height h measured from the rim diameter line RL of the radially outer end S of the straight line portion Ln is assumed to be within a range of 0.8 to 1.0 times the height Fh of the flange 5F of the rim 5, and the arc portion It is assumed that the curvature radius R of Ac is in the range of 2.0 to 3.0 times the curvature radius Fr of the arc portion of the outer contour of the flange 5F of the rim 5. The rim diameter line RL is a straight line passing through the rim diameter position and parallel to the rotational axis of the assembly.
[0018]
Now, when an overload, which is equivalent to twice the maximum static load, is applied to the assembly of the tire 1 and the rim 5 filled with the specified internal pressure, as shown by a two-dot chain line in FIG. The one bead portion 4 is extremely bent and falls down and is pressed by the entire arc portion of the flange 5F of the rim 5 or the entire arc portion including the extended end portion (both are abbreviated as the entire arc portion). At this time, among the outer contours of the bead portion of the conventional tire, the outer contour of the cross section of the bead portion pressed against the entire arc portion of the flange 5F of the rim 5 has a convex shape toward the outer side of the tire. The reaction force brought from the entire arc portion to the bead portion has a large peak, and the rubber portion of the bead portion to which the reaction force of the large peak acts is locally compressed significantly. The rubber part to which a large compressive force acts at the peak part moves in a direction that is easy to move along the outermost carcass ply, that is, in the direction of the side wall part. Causes a separation failure.
[0019]
On the other hand, the tire outer contour of the bead portion 4 is formed by the straight portion Ln having the height h and the circular arc portion Ac that is in contact with the radial end S of the height h and protrudes toward the inside of the tire 1. As a result, the reaction force itself brought from the entire arc portion of the flange 5F of the rim 5 to the bead portion at the time of overloading is lowered as compared with the conventional case, and at the same time, the reaction force distribution is averaged and has almost no peak. Since the compressive force of the outer rubber portion of the bead portion pressed against the entire arc portion of the flange 5F is reduced, the shear strain with the carcass ply can be reduced, the occurrence of a separation failure can be suppressed, and the amount of heat generated at the same time. And the occurrence of failures such as blowout of the tire outer rubber portion of the bead portion and bead portion burst due to high heat can be suppressed.
[0020]
In order to advantageously realize the above-mentioned failure occurrence suppression,
(1) The height h measured from the rim diameter line RL of the bead base Bb side straight portion Ln in the tire outer contour of the bead portion 4 is 0.8 to 1.0 times the height Fh of the flange 5F of the rim 5. Within the range of
(2) The radius of curvature R of the arc portion Ac needs to be within a range of 2.0 to 3.0 times the radius of curvature Fr of the arc portion of the outer contour of the flange 5F of the rim 5;
By defining the height h and the radius of curvature R in the above ranges, the bead portion is applied when the tire 1 is subjected to the above-mentioned double maximum static load under the synergistic effect of the height h and the radius of curvature R. 4 and the optimal balance between the degree of falling (bending) and the equalization / reduction of the pressing force on the entire arc portion of the flange 5F of the rim 5 can be realized. Under this optimal balance, it is possible to effectively suppress the separation failure, blowout failure and burst failure of the bead portion when the maximum static load is doubled.
[0021]
When the height h is less than 0.8 times the height Fh, the bead portion 4 is significantly bent when the maximum static load is applied twice, and the contact pressure between the position near the bead core 6 and the flange 5F becomes excessive. On the other hand, if it exceeds 1.0 times, the amount of fall of the bead part 4 becomes excessive, and a large shear strain is generated. Further, when the radius of curvature R is less than 2.0 times the radius of curvature Fr, the rim 5 is not attached to the rubber portion of the bead portion 4 when the tire 1 is loaded with the maximum static load twice, even though it is not a conventional tire. A large compressive force is locally applied from the entire arc portion of the flange 5F of the flange 5F, and this large compressive force causes a large shear strain between the carcass ply and facilitates a separation failure, while the curvature radius Fr of 3. If it exceeds 0 times, the bead part 4 will fall too much, and a large shear strain due to a large bending deformation will occur between the carcass ply and the rubber adjacent to it, which will also cause ply separation. It is.
[0022]
Further, on the assumption that the carcass 7 has the above-described up-down structure, referring to FIG. 2, the rotation axis of the assembly of the tire 1 and the rim 5 (not shown) passes through the center of gravity C of the cross-sectional figure of the bead core 6. The point of intersection of the straight line Lc parallel to the tire and the tire outer contour of the bead portion 1 is point A, and the outermost ply of the carcass 7 passing through the point A, that is, the normal of the outer surface of the tire outer ply 7d-2 of the down ply 7d the extension line Lm, between the intersection of the straight line Lm and the outermost ply 7d-2 code outermost surface overlapping the straight line Lc as a point B in the illustrated example, the points a and B on the normal extension line Lm The total rubber gauge G ₁ (mm) present in
Between the total diameter Pg (mm) of the cord diameter obtained by summing the diameter of one cord in each ply constituting the carcass 7 of the tire 1 for all plies (in the illustrated example, 6 plies),
The relationship of 1.20 × Pg ≦ G ₁ ≦ 2.51 × Pg is satisfied. However, cord diameter addition at the winding part is excluded.
[0023]
The above relation is that as the number of plies of the carcass 7 of the tire 1 increases, more precisely, as the total cord diameter Pg (mm) of each ply in the stacking direction of all the plies of the carcass 7 increases, the tire 1 is increased, and therefore between the flange 5F of the rim 5 and the cord outermost surface of the outermost ply 7d-2 on and near the straight line Lc passing through the center of gravity C of the cross-sectional figure of the bead core 6. The rubber part sandwiched between the two parts receives a large pressing force from the flange 5F under a double maximum static load. Accordingly, since it is necessary to reduce as much as possible the large compressive strain caused by the large pressing force, the range of the total rubber gauge G ₁ (mm) is defined as described above in relation to the total cord diameter Pg (mm).
[0024]
Here, when the total rubber gauge G ₁ (mm) is less than 1.20 × Pg, the degree of relaxation of the compressive strain of the rubber portion caused by pressing is small, and the shear strain between the cord of the outermost ply 7d-2 and the surrounding rubber is small. Cannot be made sufficiently small, and the joy of separation failure occurs. On the other hand, if it exceeds 2.51 × Pg, the rubber part tends to move along the outermost carcass ply, which also causes the outermost ply 7d. -2 will increase the shear strain between the cord and its surrounding rubber, and separation failure is likely to occur.
[0025]
In addition, referring to the tire contour when the maximum static load is doubled under the specified internal pressure filling shown by the two-dot chain line in FIG. 2, the point P on the two-dot chain line is a separation point from the flange 5F of the rim 5. This separation point P is shown as a point P in the tire 1 in a state where the fine pressure is filled and no load is applied, as shown in FIG. The intersection of the normal line Lq of the outer surface of the outermost carcass ply 7d-2 and the outermost surface of the cord of the outermost carcass ply 7d-2 passing through the point P is defined as a point Q, and the normal Lq is extended. The total rubber gauge G ₂ (mm) existing between the point P and the point Q on the line is set within a range of 0.8 to 1.0 times the total rubber gauge G ₁ (mm).
[0026]
Further, the outermost side of the cord of the outermost carcass ply 7d-2 at an arbitrary position in the area surrounded by the line segment connecting the point A and the point B and the line segment connecting the point P and the point Q. The rubber gauge G ₃ (mm) between the surface and the outer contour of the tire 1 is set within a range of 0.8 to 1.0 times the total rubber gauge G ₁ (mm). However rubber gauge G ₃ (mm) shall be determined by the extension of the normal of the outer surface of the outermost carcass ply 7d-2.
[0027]
Both the total rubber gauge G ₂ (mm) and the rubber gauge G ₃ (mm) are within the range of 0.8 to 1.0 times the total rubber gauge G ₁ (mm), and the flange 5F of the rim 5 is subjected to a maximum double static load. by uniforming the tire outer rubber gauge distribution of a bead portion 4 which is pressed into, detention the amount of the number of plies of the carcass 7 Warazu, the sum of the code size of each ply in the stacking direction of all the plies of the carcass 7 Pg ( Regardless of the value of mm), the entire arc portion of the flange 5F of the rim 5 causes a large shear strain and compressive strain locally on the tire outer rubber of the bead portion 4 under a double maximum static load. Therefore, the occurrence of separation failure, blowout failure, burst failure and the like in the bead unit 4 is prevented.
[0028]
Here, when both the total rubber gauge G ₂ (mm) and the rubber gauge G ₃ (mm) are less than 0.8 times the total rubber gauge G ₁ (mm), the above-mentioned locally large shear strain and compressive strain are effective. On the other hand, if the total rubber gauge G ₁ (mm) exceeds 1.0 times, the amount of movement of the tire outer rubber of the bead portion 4 increases, and the cord of the outermost carcass ply 7d-2 increases. Since a large shear strain acts on the outer surface and causes separation failure, neither is possible.
[0029]
The gauge distribution of the side wall rubber 3g and the rubber chafer 10 may be adjusted to obtain the total rubber gauges G ₂ (mm), G ₁ (mm) and the rubber gauge G ₃ (mm) described above. Another type of insert rubber 9 is disposed between 3 g and the outermost ply 7 d-2 and between the rubber chafer 10 and the outermost ply 7 d-2. Reference numeral 11 denotes a hard stiffener rubber extending in a tapered manner from the bead core 6 toward the outside in the radial direction of the tire 1, and reference numeral 12 denotes an inner liner rubber. In particular, since aircraft tires are tubeless tires, air-impermeable rubber is applied to the inner liner rubber 12 .
[0030]
【Example】
The aircraft radial ply tire 1 has a size of 50 × 20.0R22 26PR and has a configuration according to FIGS. 1 and 2, and the carcass 7 has a 4-ply turn-up ply 7u and a 2-ply down-ply 7d. For the carcass plies 7u and 7d, a 1400 dtex × 2 × 2 6,6 nylon super-strong yarn cord is applied, and the diameter of the carcass cords in the

plies

7u and 7d is 0.88 mm.
[0031]
The tire 1 is assembled to its regular rim 50 × 20.0R22, this assembly is filled with a designated internal pressure 12.4 kgf / cm ² corresponding to the maximum static load of the tire 1, and the durability of the bead part 4 is determined according to the following test method. A sex test was performed. In addition to the example tires, the test target tires were prepared as conventional tires and vulcanized tires of Comparative Examples 1 to 3 that were vulcanized with the same mold. The conventional tires are matched to the example tires except for the outer contour of the bead portion and the outer rubber gauge, and the tires of Comparative Examples 1 to 3 except for the values of the ratios G ₁ / Pg, G ₂ / G ₁ , G ₃ / G _1. Matched to example tires.
[0032]
The test method is to apply a load of 41005 kgf, which is about twice the maximum static load 20503 kgf (TRA, 45200 pounds) with a flat plate correction of the radius of curvature, to the tire 1 on a 3.0 m diameter drum, and speed for 70 seconds. The tire was accelerated from zero to 378 km / h (TRA, 235 miles per hour), and when the final speed was reached, the test tire was removed from the drum, and the failure state of the bead portion was examined. The tire that failed and was removed during the 70-second test period was not completed. Table 1 shows the test results together with the values of ratios h / Fh, R / Fr, G ₁ / Pg, G ₂ / G ₁ , and G ₃ / G ₁ .
[0033]
[Table 1]

[0034]
From the results shown in Table 1, although the conventional tire barely completed, blowout failure occurred around the entire bead portion, whereas all the tires of Comparative Examples 1 to 3 caused partial failure in the bead portion. However, the run was completed and the effectiveness of the outer contour of the bead portion of the present invention was proved. However, as is clear from the tires of the examples that completed the run and no failure occurred in the bead portion, the values of the ratios G ₁ / Pg, G ₂ / G ₁ , G ₃ / G ₁ are within the scope of the present invention. Then it can be reused and is complete.
[0035]
【The invention's effect】
According to the invention described in claim 1 to 3 of this application, in the case of aircraft tires, one tire is punctured the Fukuwa mounting tires, be loaded with twice the load of the maximum static load to the other tires Thus, at least until the end of the randig, there is no failure in the bead portion, safety can be ensured, and a heavy-duty pneumatic radial tire that can be taxied to the terminal can be provided.
[Brief description of the drawings]
FIG. 1 is a left half sectional view of a tire-rim assembly according to the present invention.
FIG. 2 is an enlarged view of main parts of a tire and a rim shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Aircraft tire 2 Tread part 3 Side wall part 3g Side wall rubber 4 Bead part 5 Rim 5F Rim flange 6 Bead core 7 Carcass 7u Turn-up ply 7d Down ply 8 Belt 9 Insert rubber 10 Rubber chafer 11 Stiffener rubber 12 Inner liner rubber E Tire equatorial plane C Center of gravity RL of bead core cross-sectional figure Rim diameter line h Height from rim diameter line of bead outer contour straight line R Curvature radius of bead outer contour arc part Cr Center of curvature radius R Fr Arc of rim flange Radius of curvature G ₁ , G ₂ , G ₃ Rubber gauge P Separation point from tire flange when double load is applied

Claims

A tread portion, a pair of sidewall portions and a pair of bead portions communicating with both sides of the tread portion, these portions to reinforce over between bead cores each other was embedded in the bead portions, carcass scan to be rubberized radial sequence encoding The carcass includes at least one ply turn-up ply that winds around the bead core from the inside to the outside of the tire, and at least one ply that wraps around the turn-up ply including the hoisted portion and ends at least immediately below the bead core. and a down ply, and in heavy duty pneumatic radial tire obtain immediately a belt reinforcing a tread portion,
Under slight pressure filling within a range of 0.05 to 0.1 kgf / cm ² for a tire and a rim assembly in which the tire is assembled to a regular rim,
The outer contour of the bead portion in the cross section of the assembly includes a bead base side straight portion existing on a straight line orthogonal to the rotation axis of the assembly, and a rim flange height of 0.8-1. Having a circular arc part with a center of curvature on the outer side of the tire, which is in contact within the range of 0 times,
The radius of curvature of said arcuate portion, Ri range near 2.0 to 3.0 times the radius of curvature of the rim flange,
An intersection of a straight line that passes through the center of gravity of the cross-sectional figure of the bead core and is parallel to the rotational axis and the outer contour of the bead is defined as a point (A), and an extension of the normal line of the outermost carcass ply outer surface passing through the point (A) With the point of intersection with the outermost surface of the outermost ply cord as the point (B), the total rubber gauge (G ₁ ) existing between the point (A) and the point (B) on the extended line of the normal line ,
A heavy-duty pneumatic radial tire characterized by being in a range of 1.20 to 2.51 times the total cord diameter (Pg) obtained by adding the diameters of one cord of each carcass ply for all plies .

Point (P) is the separation point from the flange of the tire rim that is loaded with twice the maximum static load on the tire and rim assembly filled with the specified internal pressure at the time of the maximum static load load of the tire,
While the load unloaded, said a tire and rim assembly of the cross-section was returned to fine圧充Ten, the point of the tire through the (P), the normal of extension and outermost plies of the outermost carcass ply outer surface The total rubber gauge (G ₂ ) existing between the point (P) and the point (Q) on the extended line of the normal line with the intersection with the outermost surface of the cord as the point (Q) is the total rubber gauge (G ₁ ) The tire according to claim 1 , which is in a range of 0.8 to 1.0 times as large as.

In the tire and rim assembly filled with slight pressure,
The outermost carcass ply cord has an outermost region in a region surrounded by a line segment connecting the point (A) and the point (B) and a line segment connecting the point (P) and the point (Q). rubber gauge between the outer surface and the tire outer contour (G ₃₎ is a tire according to claim 2 which is in the range of 0.8 to 1.0 times the total rubber gauge (G _1).