JP4624541B2

JP4624541B2 - Pneumatic tire

Info

Publication number: JP4624541B2
Application number: JP2000336862A
Authority: JP
Inventors: 勝信北條
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 2000-11-06
Filing date: 2000-11-06
Publication date: 2011-02-02
Anticipated expiration: 2020-11-06
Also published as: JP2002144826A

Description

【０００１】
【発明の属する技術分野】
この発明は、空気入りチューブレスタイヤ、より詳細にはトラックやバスなどの重車両の使途に供する重荷重用空気入りタイヤに関し、特に、ビード部耐久性を向上させた空気入りチューブレスタイヤに関する。
【０００２】
【従来の技術】
冒頭で述べた種類の重車両に装着する空気入りタイヤは、その荷重負荷転動下にて、接地部に対応するビード部からその近傍のサイドウォール部に至る領域がタイヤ外側に大きく倒れ込む変形を生じる。この変形に伴い、ビード部に位置するカーカスの折返し部端とその近傍に大きな圧縮ひずみが発生し、加えて、リムのフランジからの突き上げにより折返し部端とその近傍には大きな断面内せん断ひずみが発生する。これらひずみは、タイヤ走行中に多数回にわたり折返し部端に繰り返し作用する結果、タイヤの走行が進むにつれ、折返し部端に亀裂が発生し、この亀裂は折返し部のセパレーション故障にまで発展する。
【０００３】
そこで、折返し部端の亀裂発生を抑制する上で有効な、図４に左半断面図を示すタイヤ１１が提案されている。すなわち、図４において、タイヤ１１の最大の特徴は、ビードコア１５近傍位置からタイヤ１１の断面幅（最大幅）ＳＷ近傍位置にわたる間のカーカス本体部１６b のカーカスラインを、内圧がゲージ圧ゼロで略直状とし、非平衡形状に設定する点にある。なお、カーカスラインとは、カーカスプライの厚み中央を連ねる線である。
【０００４】
この非平衡形状カーカスラインにより、リムに組付けたタイヤ１１に所定内圧を充てんすると、略直状のカーカスラインはタイヤ外側に向け凸状に張出し、その分だけカーカスの張力が増加する結果、ビード部１４からサイドウォール部１３に至る部分の剛性が高まり、当該部分は、タイヤ１１の荷重負荷時の倒れ込みが減少し、折返し部のひずみが緩和される、というものである。
【０００５】
【発明が解決しようとする課題】
しかし、近年では、タイヤ１１の荷重負担増加に伴う撓み率の増加及び発熱量の増加及び一層の偏平化傾向に伴い、直状カーカスラインによるカーカス張力の向上による剛性向上には限界は生じ、さらに剛性向上のため、ワイヤーチェーファ１８s 、ナイロンチェーファ１８n などの補強コード層追加が余儀なくされている。
【０００６】
これら直状カーカスラインと補強コード層１８s 、１８n との併用は、結局、ビード部１４の著しい断面ゲージ増加と容積増加とをもたらす。これらは、タイヤ重量増加をもたらすのみに止まらず、それにも増して、より厚ゲージとなるビード部１４は、タイヤの荷重負荷転動下で、倒れ込み度合いが低減する反面、発熱量の増加により一層高温度となり、しかも、リムのフランジによる突き上げにより、補強コード層端部のセパレーション故障及び補強コード層のタイヤ半径方向に沿うセパレーション故障が発生し易くなる。加えて、肝心の折返し部端のセパレーション抑制効果も僅かなものとなり、却って、故障形態が複雑になり、ビード部耐久性向上は不十分となる。
【０００７】
従って、この発明の請求項１〜８に記載した発明は、上記の問題に鑑み、タイヤの荷重負荷転動下で、最もひずみが集中して亀裂の発生からセパレーション故障を起こす折返し部端のひずみを最小化し、併せて、補強コード層を配置せずともビード部倒れ込みに対抗する剛性を高め、もって、ビード部耐久性を高度に向上させることが可能な空気入りチューブレスタイヤを提供することを目的とする。
【０００８】
【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、トレッド部と、そ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、これら各部を各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ゴム被覆コードプライのカーカスを備え、該カーカスは、一対のビードコア内側相互間のカーカス本体部と、ビードコアの周りを内側から外側に折返す折返し部とを有し、ビードコア外周からトレッド部端に向け、カーカス本体部と折返し部とに沿い先細り状に延びるスティフナーゴムを備える空気入りチューブレスタイヤにおいて、スティフナーゴムは、２種類以上の互いに硬度が異なるゴムの合体から成り、該合体ゴムのうち最高硬度ゴムは、ビードコアからカーカス本体部に沿わせ配置し、最低硬度ゴムはビードコアから折返し部に沿わせ配置して成り、上記空気入りチューブレスタイヤをその標準リムに組付け、これにゲージ圧で５０kPa の内圧を充てんしたタイヤとリムとの組立体の断面にて、カーカス本体部は、ビードコア最外側位置を通るタイヤ軸線への垂線Ｌv1 と本体部プライの厚み中央との交点Ｐ1と、トレッド部の接地幅端からタイヤ軸線へ下ろす垂線Ｌv2 と本体部プライの厚み中心との交点Ｐ2 との間にわたるプライ部分が、タイヤ外側に向け凸の湾曲形状を有し、かつ、カーカス折返し部は、上記交点Ｐ2 を通るタイヤ軸線と平行な直線Ｌ2 から、標準リムのフランジの曲率半径中心を通るタイヤ軸線への垂線Ｌv3 と本体部プライの厚み中央との交点Ｐ3 を通るタイヤ軸線と平行な直線Ｌ3 までの間にわたる領域に折返し終端を有し、スティフナーゴムの最高硬度ゴムは、少なくとも前記垂線Ｌv1 よりタイヤ軸線方向内側位置を占めて成り、ビード部は、少なくとも折返し部からビードコアに至る間にわたって延びる補強コード層を備え、該折返し部側補強コード層のタイヤ半径方向外方端末位置を、スティフナーゴムの最高硬度ゴムの終端高さ以下とし、かつ、ビードコアの最外側位置を通るタイヤ軸線と平行な直線（Ｌ4 ）以上として成り、補強コード層は、タイヤ半径方向に対し傾斜配列のスチールコードのゴム被覆層から成り、折返し部に沿う補強コード層の端末にて、該スチールコードに直交する配列間隔のコード外径に対する比の値を１．０〜３．０の範囲内として成ることを特徴とする空気入りチューブレスタイヤである。
【０００９】
ここに、標準リムとは、JATMA YEAR BOOK (2000)、ETRTO SANDARDS MANUAL 2000、TRA(THE TIRE and RIM ASSOCIATION INC.) YEAR BOOK(2000)などの規格に記載したリムであり、JATMA 規格では、タイヤ種類毎に定める適用リムの表のうち下線を施したリムを用い、ETRTO 規格では、ＴIRE SIZE/SECTION CODE 毎に定めるMEASURING RIM WIDTH CODEに従い、TRA 規格では、DESIGN RIM WIDTHに従い、標準リムのフランジの曲率半径中心もこれら諸規格に記載した位置のうち、フランジとタイヤとの離反側の曲率半径中心を用いる。また、トレッド部の接地幅は、タイヤを上記標準リムに装着し、上記各規格が定める最高内圧（ゲージ圧）を充てんし、静止した状態で平板に対し垂直に置き、最高内圧に対応する最大負荷能力に相当する荷重(N) を加えたときの、平板との接触面におけるタイヤ軸方向最大直線距離を指し、接地幅端は、この最大直線距離を示す端を言う。
【００１０】
請求項１に記載した発明に関し、請求項２に記載した発明のように、スティフナーゴムの最低硬度ゴムは、カーカスのプライコード被覆ゴム硬度に比しより低硬度を有し、該最低硬度ゴムは、最高硬度ゴムのタイヤ半径方向終端を該方向に越えて延びる終端高さを有する。
【００１１】
請求項１、２に記載した発明に関し、請求項３に記載した発明のように、スティフナーゴムの最低硬度ゴムは、タイヤ半径方向に、カーカス折返し部の終端を越えて延びる形状を有する。
【００１２】
請求項１〜３に記載した発明に関し、請求項４に記載した発明のように、スティフナーゴムの最高硬度ゴムの終端を通るカーカス本体部の法線Ｌv₄からタイヤ半径方向内方に位置するスティフナーゴムにつき、その最高硬度ゴムが、タイヤ断面におけるスティフナーゴム面積の６０〜８０％の範囲内の面積を占める。
【００１３】
また、請求項１〜４に記載した発明に関し、請求項５に記載した発明のように、カーカス本体部は、上記交点Ｐ₁ を通るタイヤ軸線と平行な直線に対し６０°以下の傾斜角度を有する。
【００１４】
また、請求項１〜５に記載した発明に関し、請求項６に記載した発明のように、カーカス本体部に沿う補強コード層の端末を、折返し側の補強コード層の端末高さより高くする。
【００１５】
また、請求項１〜６に記載した発明に関し、請求項７に記載した発明のように、カーカスは、少なくとも一対のサイドウォール部相互間にわたる領域にラジアル配列コードのゴム被覆プライ部分を有し、タイヤ軸線を含む平面によるタイヤ断面にて、ビードコアの最内側と最外側とを通る、ビードベース面に垂直な２本の直線が挟む領域に存在するビードコア下カーカスプライ部分は、上記平面を斜めに横切る傾斜コード配列を有し、該傾斜コードは、前記平面に対し５〜４５°の範囲内の傾斜角度を有する。
【００１６】
ここに、請求項１〜７に記載した発明に関し、請求項８に記載した発明のように、カーカスのプライコードにスチールコードを適用した重荷重用タイヤとする。
【００１８】
【発明の実施の形態】
以下、この発明の実施の形態を図１〜図３に示す例に基づき説明する。図１は、この発明の空気入りチューブレスタイヤ(以下、空気入りタイヤと称する)とリムとに５０kPa の内圧を充てんした組立体のタイヤ軸線を含む平面による左半断面図であり、図２は、補強コード層の一部のコード透視平面図であり、図３は、図１に示す矢印Ａ方向からのカーカスプライのコードとビードコアとの透視図である。
【００１９】
図１において、空気入りタイヤ（以下タイヤという）１は、トレッド部２と、その両側に連なる一対のサイドウォール部３（片側のみ示す）及び一対のビード部４（片側のみ示す）とを有する。また、タイヤ１は、各ビード部４内に埋設したビードコア５相互間にわたり延びるカーカス６を備え、カーカス６は各部２〜４を補強し、カーカス６の外周にはベルト７を備える。また、タイヤ１は、スティフナーゴム８を備える。スティフナーゴム８は、ビードコア５からトレッド部端に向け、カーカス６本体部６b と折返し部６t とに沿い先細り状に延びる。なお、タイヤ１は、タイヤ赤道面Ｅを挟んで両側対称である。
【００２０】
カーカス６は、一対のビードコア５内側相互間にわたり延びる本体部６b と、ビードコア５の周りをタイヤ１の内側から外側に折返す折返し部６t とを有する。カーカス６は１プライ以上のゴム被覆コードプライを有し、図示例のカーカス６は１プライである。そして、カーカス６は、少なくとも一対のサイドウォール部３相互間にわたる領域にラジアル配列コードのゴム被覆プライ部分を有する。カーカス６のプライコードは、高弾性率コード、なかでもスチールコードが適合する。
【００２１】
ここに、タイヤ１を前記した標準リムＲ（前記の規格に従う）に組付け、タイヤ１にゲージ圧で５０kPa の内圧を充てんしたタイヤ１とリムＲとの組立体の断面にて、
（１）カーカス６の本体部６b は、
ビードコア５の最外側位置を通るタイヤ１軸線（図示省略）への垂線Ｌv₁と本体部６b のプライ厚み中央とが交わ点を交点Ｐ₁ とし、
トレッド部の接地幅端ＴＥ（前記の規定に従う）からタイヤ軸線へ下ろす垂線Ｌv₂と本体部６b のプライ厚み中心とが交わる点を交点Ｐ₂ とするとき、
交点Ｐ₁ と交点Ｐ₂ との間にわたるカーカス６本体部６b のプライ部分が、タイヤ１の外側に向け凸の湾曲形状を有する。
【００２２】
かつ、上記断面にて、
（２）カーカス６の折返し部６t は、
上記交点Ｐ₂ を通るタイヤ１軸線と平行な直線Ｌ₂ から、標準リムＲのフランジＲf の外輪郭円弧（半径ｒ）の曲率中心Ｃを通るタイヤ１軸線への垂線Ｌv₃と本体部６b のプライ厚み中央との交点Ｐ₃ を通るタイヤ軸線と平行な直線Ｌ₃ までの間にわたる領域に折返し部６t 終端６tEを有する。この場合、直線Ｌ₂ 上と直線Ｌ₃ 上とを含むものとする。
【００２３】
さて、タイヤ１の荷重負荷転動下にて、荷重直下のビード部４は、リムＲのフランジＲf からの突き上げにより、タイヤ１の回転軸方向外側に変形中心をもつ曲げ変形を生じる。その一方、荷重直下のサイドウォール部３は、タイヤ１の回転軸方向内側に変形中心をもつ曲げ変形を生じる。この２種の変形は曲げ方向が異なる故、カーカスラインで見て、本体部６b には第一の変曲点が存在する。
【００２４】
また、タイヤ１の荷重直下にて、トレッド部２両端と各サイドウォール部３とが連なるショルダ部領域にも、タイヤ１内側に向く曲げ変形（路面に沿う平坦化変形）を生じるとトレッド部２と、タイヤ１外側へ向う凸状張出変形を生じるサイドウォール部３との間に、カーカスラインで見て、本体部６b には第二の変曲点が存在する。
【００２５】
前述の第一の変曲点よりタイヤ半径方向（以下、半径方向という）内方及び第二の変曲点より半径方向外方向それぞれのタイヤ１外側部分には圧縮ひずみが作用し、これら両外側部分に折返し部終端を位置させれば、この終端に大きな圧縮ひずみが作用することを解明している。従来タイヤでは、第一の変曲点より半径方向内方に折返し部終端を位置させているため、この圧縮ひずみの作用に、フランジＲf からの突き上げによる断面内せん断ひずみの作用が加わるため、折返し部終端に亀裂〜セパレーション故障が生じている。
【００２６】
第一の変曲点位置及び第二の変曲点位置それぞれは、タイヤ種類、充てん内圧（ゲージ圧）及び負荷荷重などの条件により変動して一定ではない。そこで、想定し得る全ての条件にて、確実に圧縮ひずみが作用しない本体部６b の外側位置範囲、すなわち、第一の変曲点〜第二の変曲点の間に存在する本体部６b の外側位置範囲を実測し、解析した結果、いずれのタイヤ１でも、前出の直線Ｌ₂ から直線Ｌ₃ までの間にわたる領域には確実に圧縮ひずみが発生していないことを突き止めた。
【００２７】
それも、前記交点Ｐ₁ と前記交点Ｐ₂ との間にわたる本体部６b のプライ部分が、タイヤ１の外側に向け凸の湾曲形状を有するとの前提条件が必要である。この条件の下、折返し部６t 終端６tEを、直線Ｌ₂ から直線Ｌ₃ までの間にわたる領域に配置することにより、折返し部６t 終端６tEに圧縮ひずみが作用せず、かつ、リムＲのフランジＲf からの突き上げによる断面内せん断ひずみの作用も著しく低減するので、折返し部６t 終端６tEの耐亀裂性及び耐セパレーション性に係る耐久性は飛躍的に向上する。加えて、折返し部６t の半径方向長さが大幅に長くなるので、ビード部４の曲げ剛性が向上し、これが折返し部６t 終端６tEの耐久性向上に寄与する。
【００２８】
しかし、上記の曲げ剛性向上は、本体部６b と折返し部６t との間のスティフナーゴム８のひずみ負担増加をもたらし、この増加は折返し部６t に沿う広範囲なセパレーションを発生させる傾向を示し、該故障の初期発生位置がリムＲのフランジＲf 付近であることを突き止めている。よって、セパレーション故障の初期発生を防止するため、スティフナーゴム８は、２種類以上、図示例は２種類の互いに硬度が異なるゴム８-1、８-2の合体から形成し、この合体ゴムのうち最高硬度ゴム８-1はビードコア５からカーカス６本体部６b に沿わせて配置し、最低硬度ゴム８-2は、ビードコア５から折返し部６t に沿わせて配置することで応力を緩和し、最高硬度ゴム８-1は、少なくとも前記垂線Ｌv₁よりタイヤ１軸線方向内側位置の略三角形断面を占めるものとし、倒れ込み抑制のための剛性向上に寄与させる。
【００２９】
また、最高硬度ゴム８-1の半径方向高さを高くすることは、ビード部４の倒れ込みを更に一層抑制することができる反面、その抑制効果は上記の略三角形断面の最高硬度ゴム８-1ほどではなく、最高硬度ゴム８-1の半径方向外方端と本体部６b のコード被覆ゴムとの間に亀裂を生じ易くさせるため、最高硬度ゴム８-1は、直線Ｌ₃ の半径方向高さ以下の終端８-1E 高さに設定するのが望ましい。
【００３０】
これにより、最高硬度ゴム８-1が本体部６b に亀裂を発生させる不都合はなくなる。なお、ここに言う高さとは、リムＲの直径位置を通る、タイヤ１軸線と平行な直線、すなわちリム径ラインＲＬからの高さを指す。以下同じである。また、倒れ込み抑制効果を有利に実現するため、最高硬度ゴム８-1はJIS A 硬度が７５〜９５°の範囲内にするのが適合する。
【００３１】
これに対し、最低硬度ゴム８-2は、カーカス６のプライコード被覆ゴム硬度に比しより低硬度を有するゴムとし、かつ、最高硬度ゴム８-1の終端８-1E を半径方向に越えて延びる終端８-2E 高さに設定する。これにより最低硬度ゴム８-2は、直線Ｌ₃ の半径方向高さを越えても、カーカス６のプライコード被覆ゴムに対し応力緩和部材として働く。この意味で、最低硬度ゴム８-2は、その終端８-2Eが折返し部６t の終端６tEを越えて半径方向外方に延びる配置とすることで、本体部６b と折返し部６t との間の応力緩和部材として機能させ、折返し部６t 沿い全域にわたり耐セパレーション性を向上させる。
【００３２】
また、最高硬度ゴム８-1の終端８-1E を通るカーカス６本体部６b の法線Ｌv₄から半径方向内方に位置するスティフナーゴム８につき、最高硬度ゴム８-1が、タイヤ１断面におけるスティフナーゴム面積の６０〜８０％の範囲内の面積を占めるものとする。これにより、ビード部４の倒れ込み抑制と、折返し部６t の応力緩和とが適度に調和する。最高硬度ゴム８-1の面積が６０％未満ではビード部４の倒れ込み抑制が不十分であり、８０％を超えると折返し部６t の応力緩和効果が不十分であるため、いずれも耐セパレーション性を損ねるので不適合である。
【００３３】
ところで、これら最高硬度ゴム８-1と最低硬度ゴム８-2とは、硬度が著しくことなることから、両ゴム接合面に剥離が生じるうれいがある。この剥離現象は、タイヤ１への内圧充てん時にカーカス６本体部６b がタイヤ１外側に向けせり出す結果、接合面にひずみが集中するのが支配的要因である。このせり出しを成るべく抑制するには、前出の交点Ｐ₁ を通るタイヤ１軸線と平行な直線Ｌ₁ に対する本体部６b の傾斜角度θ（交点Ｐ₁ における本体部６b の接線の傾斜角度θ）を小さくするのが有効である。しかし、傾斜角度θの上限値はタイヤ種類により異なるため、各種タイヤについて、傾斜角度θと耐久性との関係を実験し解析して得た結果、全タイヤサイズにつき傾斜角度θは６０°以下とするのが適合することを解明することができた。
【００３４】
また、タイヤ１の荷重負荷転動下の踏込み部及び蹴出し部で、接地部の折返し部６t は周方向にせん断変形し、この変形は折返し部６t にセパレーション故障を発生させる一の要因となるので、この変形抑制のため、ビード部４に、少なくとも折返し部６t からビードコア５に至る間にわたって延びる補強コード層９を設ける。図１に示す補強コード層９は、ビードコア５の周りを経て本体部６b に至る。折返し部６t に沿う補強コード層９の半径方向外方端末９Eo位置を、最高硬度ゴム８-1の終端８-1E 高さ以下とし、かつ、ビードコア５の最外側位置を通るタイヤ軸線と平行な直線Ｌ₄ 以上とする。
【００３５】
端末９Eoを最高硬度ゴム８-1の終端８-1E 高さ以下とするのは、終端８-1E 高さより半径方向外方の領域を周方向にフレキシブルな領域として容易に周方向に変形させ、折返し部６t のセパレーション発生領域に周方向変形抑制を集中させて周方向に変形し難くさせるのが、セパレーション防止に一層有効であるからに他ならない。補強コード層９のコードは、半径方向に対し４５〜７５°の範囲内の傾斜配列とするのが適合する。また、最高硬度ゴム８-1の終端８-1E より高い端末９Eoは、その部分に大きな周方向ひずみが生じ、それが、補強コード層９のコードを傾斜配列とする端末９Eo部分のコードとその被覆ゴムとの間に大きな圧縮ひずみとなり、コード端の亀裂を発生させるので不適合である。
【００３６】
また、図１に示す本体部６b に沿う補強コード層９の端末９Eiを、折返し部６t 側の補強コード層９の端末９Eo高さより高くし、これによりビード部４における本体部６b 部分の周方向剛性を高め、折返し部６t に沿う側の補強コード層９の端末９Eoに作用する圧縮ひずみのうち周方向ひずみ成分を軽減し、端末９Eo部分の亀裂発生を抑制する。
【００３７】
図２において、補強コード層９は、スチールコード９scと、その被覆ゴム９cgとで構成するのが周方向剛性向上に適合する。このとき、補強コード層９の端末９Eoにて、スチールコード９scに直交する配列間隔ｄ₂ のコード外径ｄ₁ に対する比ｄ₂ ／ｄ₁ の値を１．０〜３．０の範囲内とする。これにより、補強コード層９の端末９Eoからの亀裂故障の発生防止と、折返し部６t の周方向変形抑制効果とを高いレベルで両立させることができる。比ｄ₂ ／ｄ₁ の値が１．０未満では、ゴムと未接着のスチールコード切断端のコード端末径ｄ₁ よりゴム間隔ｄ₂が小さいため、亀裂核が繋がり易く、セパレーション故障が発生し易くなり、３．０を超えると周方向剛性向上効果が不十分となるので、いずれも不適合である。
【００３８】
以上述べたタイヤ１のカーカス６は、ラジアル配列コードのゴム被覆プライから成る場合と、次に述べるプライから成る場合との双方を含む。すなわち、図１及び図３において、カーカス６は、ビードコア５の最内側と最外側とを通る、ビードベース面４Ｂに垂直な２本の直線ＶＬi 、ＶＬo が挟む領域に存在するビードコア下カーカスプライ部分６p が、タイヤ１軸線を含む平面Ｐ（図３参照）を斜めに横切る傾斜コード６pC配列を有する。
【００３９】
さて、発明者は、ビードコア５周りのうちカーカス６のビードコア５に対する拘束度合いの寄与が最も高い位置は、ビードコア５の直下であること解明している。より正確に言えば、拘束度合いの寄与が最も高い位置は、２本の直線ＶＬi、ＶＬo が挟むビードコア５の下領域である。ビードコア５の下とは、タイヤ１の半径方向で見てビードコア５の内方を指す。
【００４０】
この解明によれば、カーカス６がビードコア５の延びる周方向に対し直交してビードコア５下を横断するコード配列を有するラジアルプライは、カーカス６のビードコア５に対する拘束度合いが小さく、よって、ビード部４の倒れ込みにより、比較的容易にビードコア５からのカーカス６の引き抜き挙動が生じていることが分かる。
【００４１】
これに対し、カーカスプライ部分６p が傾斜コード６pC配列を有するタイヤ１は、傾斜コード６pCのビードコア５に対する横断長さが長く、かつ、カーカス６の引き抜き力に対する抵抗力が大きいので、カーカス６のビードコア５に対する拘束度合いが、ラジアル配列コードのゴム被覆プライから成るカーカス６を有するタイヤ１のそれに比し大幅に高まる。これにより、タイヤ１への内圧充てん時はもとより、タイヤ１の荷重負荷転動下でのビード部４の倒れ込み時においても、折返し部６t 沿い全域に作用する断面内せん断ひずみは大幅に低減し、折返し部６t 沿いの亀裂発生及び進展を抑制することができ、結局、ビード部４の耐久性向上に寄与する。
【００４２】
補強コード層９を適用するときは、ビードコア５下の２本の直線ＶＬi 、ＶＬo が挟む領域にて、平面Ｐに関し、カーカスプライ部分６p のコード６pCの傾斜方向と逆方向に傾斜するコード９scの配列とすることが好ましい。換言すれば、コード６pCとコード９scとは、平面Ｐを挟み互いに交差する配列とすることが好ましい。このコード交差構成により、カーカス６の引き抜き方向の剛性がさらに向上し、カーカス６のビードコア５における拘束度合い向上に寄与する。なお、図３では、コード９scを二点鎖線で示す。
【００４３】
また、ビードコア５下カーカスプライ部分６p のコード６pCは、平面Ｐに対し５〜４５°の範囲内の傾斜角度αとするのが適合する。なお、傾斜角度αが５°未満では効果が十分に発揮できず、傾斜角度αが４５°を超えると、平面Ｐに沿う方向の剛性が低くなり過ぎるため、ビードコア５とカーカスプライ部分６p との間のせん断ひずみ及びカーカスプライ部分６p と補強コード層９との間のせん断ひずみが共に大きくなる結果、これらの間にセパレーション故障が発生し易くなるので、いずれも不適合である。この種のセパレーション故障によりコード６pCは隣接部との間で擦れ合い切断し、結局、タイヤ１がバーストに至ることもある。補強コード層９のコード９SCの平面Ｐに対する傾斜角度βは、先に述べた４５〜７５°の範囲内とするのが望ましい。
【００４４】
以上述べたタイヤ１は、重荷重用空気入りタイヤ、なかでもトラック及びバス用タイヤに適合し、とりわけチューブレスタイヤに有効な構造である。
【００４５】
【実施例】
トラック及びバス用ラジアルプライタイヤで、サイズが２７５／７０Ｒ２２．５のチューブレスタイヤであり、実施例１〜２４の構成は図１及び図２に従い、実施例２４〜２９の構成は図１〜図３に従う。カーカス６は１プライのゴム被覆スチールコード層であり、補強コード層９は１層のゴム被覆スチールコード層である。各実施例に共通する高さ及びゴム硬度は下記の通りである。
直線Ｌ₁ のリム径ラインＲＬからの高さ＝２９ｍｍ、
直線Ｌ₂ のリム径ラインＲＬからの高さ＝１５４ｍｍ、
直線Ｌ₃ のリム径ラインＲＬからの高さ＝５４ｍｍ、
直線Ｌ₄ のリム径ラインＲＬからの高さ＝９ｍｍ、
最高硬度ゴム８-1のJIS A 硬度＝８５°、
カーカス６のコード被覆ゴムのJIS A 硬度＝７０°、
補強コード層９のスチールコード９scの直径ｄ₁ ＝１．０ｍｍ、
最高硬度ゴム終端８-1E の高さ＝４１ｍｍ。
これら以外の諸元は表１〜表３に示す。高さは全てリム径ラインＲＬからの高さであり、ゴム硬度はJIS A の値である。
【００４６】
【表１】

【００４７】
【表２】

【００４８】
【表３】

【００４９】
比較例１〜３のタイヤ及び従来例タイヤは、実施例と異なる諸元以外は全て実施例タイヤに合わせた。これらタイヤ全てを供試タイヤとし、これらタイヤをJATMA YEAR BOOK(2000) が定める標準リム８．２５×２２．５に組付け、これに同JATMA が定める最高空気圧９００kPa の内圧を充てんし、ドラムによるビード部耐久性テストを実施した。負荷荷重は同上JATMA が定めるDUAL装着時の最大負荷能力２９００（kg質量）の２倍に相当する荷重５６．９kNとし、速度６０km/hで回転するドラムに各供試タイヤを押し当て、ビード部乃至折返し部に故障が生じるまでに走行した距離を測定し、併せて故障形態を確認した。速度は６０km/hとした。
【００５０】
走行距離の測定結果は、従来例タイヤを１００とする指数であらわし、大なるほど良いとした。この結果を故障形態と共に表１〜表３に示す。なお、各表中で、ビード部耐久性乃至折返し部耐久性はドラム耐久性と略記し、故障形態は、折返し部終端のセパレーションをPES で、折返し部に沿うセパレーションを折返し沿いSPで、補強コード層９端末のセパレーションを層９ESP で、そして、最高硬度ゴム８-1と最低硬度ゴム８-2との間のセパレーションは硬軟ゴム間SPでそれぞれあらわした。バ−ストはビード部破壊である。
【００５１】
表１〜表３に示す結果から、各実施例タイヤは、全般にわたり、従来例タイヤ対比ビード部耐久性が大幅に向上していること、また、折返し部終端高さ又は最高硬度ゴム配置が不適合な比較例タイヤは従来例タイヤ以下のビード部耐久性を示すに止まることが分かる。
【００５２】
【発明の効果】
この発明の請求項１〜８に記載した発明によれば、折返し部終端位置を大幅に高め、なおかつ、スティフナーゴムのうち最高硬度ゴムの配置を適正化することにより、折返し部の耐久性を、換言すればビード部耐久性を顕著に向上させることができ、しかも、補強コード層を用いれば、更に一層のビード部耐久性向上が可能な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】この発明の空気入りタイヤとリムとに５０kPa の内圧を充てんした組立体のタイヤ軸線を含む平面による左半断面図である。
【図２】この発明の補強コード層の一部のコード透視平面図である。
【図３】図１に示す矢印Ａ方向からのカーカスプライのコードとビードコアとの透視図である。
【図４】従来タイヤの左半断面図である。
【符号の説明】
１空気入りタイヤ
２トレッド部
３サイドウォール部
４ビード部
４Ｂビードベース面
５ビードコア
６カーカス
６b 本体部
６t 折返し部
６p ビードコア下カーカスプライ部分
６pC カーカスプライ部分コード
７ベルト
８スティフナーゴム
８-1 最高硬度ゴム
８-2 最低硬度ゴム
９補強コード層
９sc 補強コード層コード
Ｅタイヤ赤道面[0001]
BACKGROUND OF THE INVENTION
This invention is pneumaticTubelessTires, and more specifically, heavy duty pneumatic tires for heavy vehicles such as trucks and buses, especially pneumatic with improved bead durabilityTubelessRegarding tires.
[0002]
[Prior art]
Pneumatic tires mounted on heavy vehicles of the type described at the beginning are deformed such that the area from the bead portion corresponding to the ground contact portion to the sidewall portion in the vicinity falls greatly outside the tire under the load-loaded rolling. Arise. Along with this deformation, a large compressive strain is generated at and near the end of the folded portion of the carcass located in the bead portion. appear. These strains repeatedly act on the end of the folded portion during traveling of the tire. As the tire travels, a crack occurs at the end of the folded portion, and the crack develops to a separation failure of the folded portion.
[0003]
Therefore, a tire 11 shown in the left half cross-sectional view of FIG. 4 is proposed which is effective in suppressing the occurrence of cracks at the end of the folded portion. That is, in FIG. 4, the greatest feature of the tire 11 is that the carcass line of the carcass main body portion 16b from the position near the bead core 15 to the position near the cross-sectional width (maximum width) SW of the tire 11 is substantially equal to zero gauge pressure. The point is that it is straight and set to a non-equilibrium shape. The carcass line is a line that connects the thickness centers of the carcass plies.
[0004]
When a predetermined internal pressure is applied to the tire 11 assembled to the rim by the non-equilibrium shape carcass line, the substantially straight carcass line protrudes convexly toward the outer side of the tire, and the carcass tension increases accordingly. The rigidity of the part from the part 14 to the sidewall part 13 is enhanced, and the part is reduced in the collapse of the tire 11 when a load is applied, and the distortion of the folded part is alleviated.
[0005]
[Problems to be solved by the invention]
However, in recent years, with an increase in the deflection rate and an increase in the amount of heat generated due to an increase in the load burden of the tire 11 and a further flattening tendency, there is a limit in improving the rigidity by improving the carcass tension by the straight carcass line. In order to improve the rigidity, reinforcing cord layers such as a wire chafer 18s and a nylon chafer 18n are inevitably added.
[0006]
The combined use of these straight carcass lines and the reinforcing cord layers 18s and 18n results in a significant increase in cross-sectional gauge and volume of the bead portion 14. These not only cause an increase in tire weight, but the bead portion 14 that becomes a thicker gauge further reduces the degree of collapse under rolling load of the tire, but further increases due to an increase in heat generation. Further, due to the rim flange being pushed up by the rim flange, separation failure at the end portion of the reinforcing cord layer and separation failure along the tire radial direction of the reinforcing cord layer are likely to occur. In addition, the effect of suppressing the separation at the end of the folded portion is negligible. On the contrary, the failure mode becomes complicated, and the durability of the bead portion is insufficiently improved.
[0007]
Accordingly, claims 1 to 1 of the present invention.8In view of the above problems, the invention described in (1) minimizes the strain at the end of the folded portion that causes separation failure from the occurrence of cracks under the load-load rolling of the tire, and at the same time, the reinforcing cord layer Pneumatic that can improve the rigidity of the bead part and improve the rigidity against the falling of the bead part without placingTubelessThe object is to provide a tire.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 of the present invention has a tread portion, a pair of sidewall portions and a pair of bead portions that are continuous on both sides thereof, and each of these portions is embedded in each bead portion. A rubber-coated cord ply carcass that reinforces between the bead cores, the carcass having a carcass main body portion between a pair of bead core inner sides, and a folded portion that wraps around the bead core from the inside to the outside. Pneumatic with stiffener rubber extending from the outer circumference toward the end of the tread along the carcass body and turn-up sectionTubelessIn the tire, the stiffener rubber is composed of two or more kinds of rubbers having different hardnesses, and the highest hardness rubber is arranged along the carcass body part from the bead core, and the lowest hardness rubber is the folded part from the bead core. It is arranged along theTubelessIn the cross section of the tire and rim assembly in which the tire is assembled to the standard rim and filled with an internal pressure of 50 kPa as a gauge pressure, the carcass main body is perpendicular to the tire axis passing through the outermost position of the bead core. The ply portion extending between the intersection P1 with the thickness center of the main body ply, the perpendicular Lv2 extending from the contact width end of the tread portion to the tire axis, and the intersection P2 with the thickness center of the main body ply is convex outward. The carcass turn-up portion has a curved shape and a perpendicular line Lv3 from the straight line L2 parallel to the tire axis passing through the intersection P2 to the tire axis passing through the center of the radius of curvature of the flange of the standard rim and the center of the thickness of the main body ply The stiffener rubber has the highest hardness rubber at least from the perpendicular line Lv1 in the region extending to the straight line L3 parallel to the tire axis passing through the intersection point P3. Formed accounting for the linear direction inside positionThe bead portion includes at least a reinforcing cord layer extending from the folded portion to the bead core, and the position of the outer end in the tire radial direction of the folded portion side reinforcing cord layer is equal to or lower than the end hardness height of the stiffener rubber. And a straight line parallel to the tire axis passing through the outermost position of the bead core (L4) or more, and the reinforcing cord layer is composed of a rubber coating layer of steel cords that are inclined with respect to the tire radial direction, along the folded portion. At the end of the reinforcing cord layer, the ratio of the arrangement interval perpendicular to the steel cord to the cord outer diameter is set within a range of 1.0 to 3.0.Pneumatic that is characterized byTubelessTire.
[0009]
Here, standard rims are rims described in standards such as JATMA YEAR BOOK (2000), ETRTO SANDARDS MANUAL 2000, TRA (THE TIRE and RIM ASSOCIATION INC.) YEAR BOOK (2000). The underlined rims in the applicable rim table for each type are used. The ETRTO standard conforms to the MEASURING RIM WIDTH CODE defined for each TIRE SIZE / SECTION CODE, and the TRA standard conforms to the DESIGN RIM WIDTH for the standard rim flange. The center of curvature radius also uses the center of curvature radius on the separation side between the flange and the tire among the positions described in these standards. The contact width of the tread is the maximum corresponding to the maximum internal pressure when the tire is mounted on the standard rim, filled with the maximum internal pressure (gauge pressure) specified by each standard, and placed perpendicular to the flat plate in a stationary state. The maximum linear distance in the tire axial direction at the contact surface with the flat plate when a load (N) corresponding to the load capacity is applied, and the contact width end is the end indicating the maximum linear distance.
[0010]
Regarding the invention described in claim 1, as in the invention described in claim 2, the minimum hardness rubber of the stiffener rubber has a lower hardness than the hardness of the carcass ply cord-coated rubber, and the minimum hardness rubber is , Having the end height extending beyond the tire radial end of the highest hardness rubber in that direction.
[0011]
With regard to the invention described in claims 1 and 2, as in the invention described in claim 3, the minimum hardness rubber of the stiffener rubber has a shape extending beyond the terminal end of the carcass folded portion in the tire radial direction.
[0012]
Regarding the invention described in claims 1 to 3, as in the invention described in claim 4, the normal line Lv of the carcass main body portion passing through the end of the highest hardness rubber of the stiffener rubber._FourAs for the stiffener rubber located inward in the tire radial direction, the highest hardness rubber occupies an area in the range of 60 to 80% of the stiffener rubber area in the tire cross section.
[0013]
Further, regarding the inventions described in claims 1 to 4, as in the invention described in claim 5, the carcass main body portion has the intersection point P described above.₁ And an inclination angle of 60 ° or less with respect to a straight line parallel to the tire axis passing through the tire.
[0014]
Moreover, regarding the invention described in claims 1 to 5, as in the invention described in claim 6,The end of the reinforcing cord layer along the carcass main body is made higher than the end height of the folded reinforcing cord layer.
[0015]
Also,Claims 1-6As in the invention described in claim 7,The carcass has a rubber-coated ply portion of a radial arrangement code in a region extending between at least a pair of sidewall portions, and passes through the innermost side and the outermost side of the bead core in a tire cross section by a plane including the tire axis. A bead core lower carcass ply portion existing in a region sandwiched by two straight lines perpendicular to the surface has an inclined cord array that obliquely crosses the plane, and the inclined cord is within a range of 5 to 45 ° with respect to the plane. The inclination angle is as follows.
[0016]
Here, the invention according to claims 1 to 7 is a heavy duty tire in which a steel cord is applied to a ply cord of a carcass as in the invention according to claim 8.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples shown in FIGS. FIG. 1 shows the pneumatic structure of the present invention.Tubelesstire(Hereinafter referred to as pneumatic tire)FIG. 2 is a left half sectional view of a plane including a tire axis of an assembly in which an internal pressure of 50 kPa is filled in the rim and the rim, FIG. 2 is a code perspective plan view of a part of the reinforcing cord layer, and FIG. It is a perspective view of the cord of the carcass ply and the bead core from the direction of arrow A shown in FIG.
[0019]
In FIG. 1, a pneumatic tire (hereinafter referred to as a tire) 1 has a tread portion 2, a pair of sidewall portions 3 (shown only on one side) and a pair of bead portions 4 (shown only on one side). The tire 1 includes a carcass 6 extending between bead cores 5 embedded in each bead portion 4. The carcass 6 reinforces each portion 2 to 4, and a belt 7 is provided on the outer periphery of the carcass 6. The tire 1 includes a stiffener rubber 8. The stiffener rubber 8 extends in a tapered manner from the bead core 5 toward the end of the tread portion along the carcass 6 main body portion 6b and the turned-up portion 6t. The tire 1 is symmetrical on both sides with respect to the tire equatorial plane E.
[0020]
The carcass 6 has a main body portion 6 b extending between the insides of the pair of bead cores 5, and a folded portion 6 t that turns around the bead core 5 from the inside to the outside of the tire 1. The carcass 6 has one or more plies of rubber-coated cord plies, and the carcass 6 in the illustrated example has one ply. The carcass 6 has a rubber-coated ply portion of a radial arrangement code in a region extending at least between the pair of sidewall portions 3. The ply cord of the carcass 6 is compatible with a high elastic modulus cord, particularly a steel cord.
[0021]
Here, in the cross section of the assembly of the tire 1 and the rim R in which the tire 1 is assembled to the standard rim R (according to the above-mentioned standard) and the tire 1 is filled with an internal pressure of 50 kPa as a gauge pressure,
(1) The main body 6b of the carcass 6 is
A perpendicular line Lv to the tire 1 axis (not shown) passing through the outermost position of the bead core 5₁And the intersection point of the ply thickness center of the main body 6b₁ age,
A vertical line Lv extending from the contact width end TE of the tread portion (according to the above provision) to the tire axis.₂The point of intersection of the ply thickness center of the main body 6b and the intersection P₂ And when
Intersection P₁ And intersection P₂ The ply portion of the carcass 6 main body 6b extending between the two has a curved shape that is convex toward the outside of the tire 1.
[0022]
And in the above cross section,
(2) The turn-up portion 6t of the carcass 6 is
Intersection P above₂ A straight line L parallel to the tire 1 axis passing through₂ To the tire 1 axis passing through the center of curvature C of the outer contour arc (radius r) of the flange Rf of the standard rim R._ThreeAnd intersection P of the ply thickness center of the main body 6b_Three A straight line L parallel to the tire axis passing through_Three In the region extending up to, the folded portion 6t has the end 6tE. In this case, straight line L₂ Top and straight line L_Three And above.
[0023]
Now, under the load-load rolling of the tire 1, the bead portion 4 immediately below the load causes a bending deformation having a deformation center on the outer side in the rotation axis direction of the tire 1 by pushing up from the flange Rf of the rim R. On the other hand, the sidewall portion 3 directly under the load undergoes bending deformation having a deformation center on the inner side in the rotation axis direction of the tire 1. Since these two types of deformations have different bending directions, the first inflection point exists in the main body portion 6b when viewed from the carcass line.
[0024]
Further, when bending deformation (flattening deformation along the road surface) toward the inner side of the tire 1 occurs in the shoulder region where both ends of the tread portion 2 and each sidewall portion 3 are connected immediately under the load of the tire 1, the tread portion 2. When viewed from the carcass line, there is a second inflection point in the main body portion 6b between the tire portion 1 and the side wall portion 3 that causes the convex overhanging deformation toward the outside of the tire 1.
[0025]
Compressive strain acts on the outer portions of the tire 1 in the tire radial direction (hereinafter referred to as the radial direction) from the first inflection point and in the radial outer direction from the second inflection point. It has been clarified that if the end of the folded portion is positioned in the part, a large compressive strain acts on this end. In the conventional tire, since the end of the folded portion is positioned radially inward from the first inflection point, the effect of the shear strain in the cross section due to the thrust from the flange Rf is added to the effect of this compressive strain. Crack-separation failure has occurred at the end of the part.
[0026]
Each of the first inflection point position and the second inflection point position varies depending on conditions such as tire type, filling internal pressure (gauge pressure), and load load, and is not constant. Therefore, under all conditions that can be assumed, the outer position range of the main body 6b where the compressive strain does not act reliably, that is, the main body 6b existing between the first inflection point and the second inflection point. As a result of actually measuring and analyzing the outer position range, the straight line L described above is obtained for any tire 1.₂ To straight line L_Three It was ascertained that no compressive strain was generated in the region extending up to this point.
[0027]
That is also the intersection point P₁ And the intersection P₂ It is necessary that the ply portion of the main body portion 6b extending between the two has a curved shape that is convex toward the outside of the tire 1. Under this condition, the folded portion 6t and the end 6tE₂ To straight line L_Three By disposing in the region extending up to, no compression strain acts on the end portion 6tE of the folded portion 6t, and the effect of shear strain in the cross section due to the rim R being pushed up from the flange Rf is remarkably reduced. The durability related to crack resistance and separation resistance of the terminal 6tE is dramatically improved. In addition, since the radial direction length of the folded portion 6t is significantly increased, the bending rigidity of the bead portion 4 is improved, which contributes to the improvement of the durability of the folded portion 6t end 6tE.
[0028]
However, the above-described improvement in bending rigidity leads to an increase in strain on the stiffener rubber 8 between the main body portion 6b and the folded portion 6t, and this increase tends to generate a wide range of separation along the folded portion 6t. The initial occurrence position of the rim R is determined to be near the flange Rf of the rim R. Therefore, in order to prevent an initial occurrence of a separation failure, the stiffener rubber 8 is formed by combining two or more kinds of rubbers 8-1, 8-2 having different hardnesses in the illustrated example. The highest hardness rubber 8-1 is placed along the carcass 6 main body 6b from the bead core 5 and the lowest hardness rubber 8-2 is placed along the bead core 5 along the turned-up portion 6t to relieve stress. The hardness rubber 8-1 is at least the normal line Lv₁Further, it occupies a substantially triangular cross-section at the position on the inner side in the axial direction of the tire, and contributes to the improvement of rigidity for suppressing the collapse.
[0029]
Further, increasing the height in the radial direction of the highest hardness rubber 8-1 can further suppress the falling of the bead portion 4, but the suppression effect is the highest hardness rubber 8-1 having the substantially triangular cross section. Rather, in order to easily cause cracks between the radially outer end of the highest hardness rubber 8-1 and the cord covering rubber of the main body 6b, the highest hardness rubber 8-1 is a straight line L._Three It is desirable to set the end 8-1E height below the height in the radial direction.
[0030]
This eliminates the inconvenience that the highest hardness rubber 8-1 cracks the main body 6b. In addition, the height said here refers to the height from the rim diameter line RL, ie, a straight line passing through the diameter position of the rim R and parallel to the tire 1 axis. The same applies hereinafter. Further, in order to advantageously realize the fall-in suppressing effect, it is suitable that the highest hardness rubber 8-1 has a JIS A hardness within a range of 75 to 95 °.
[0031]
On the other hand, the minimum hardness rubber 8-2 is a rubber having a lower hardness than the ply cord coated rubber hardness of the carcass 6, and extends beyond the end 8-1E of the maximum hardness rubber 8-1 in the radial direction. Set to extended end 8-2E height. As a result, the minimum hardness rubber 8-2 becomes a straight line L_Three Even if the height in the radial direction is exceeded, it acts as a stress relaxation member for the ply cord covering rubber of the carcass 6. In this sense, the minimum hardness rubber 8-2 is arranged such that the end 8-2E extends radially outward beyond the end 6tE of the folded portion 6t, so that the gap between the main body portion 6b and the folded portion 6t is reached. It functions as a stress relieving member and improves separation resistance over the entire area along the folded portion 6t.
[0032]
Further, the normal Lv of the carcass 6 main body portion 6b passing through the end 8-1E of the highest hardness rubber 8-1._FourAs for the stiffener rubber 8 located radially inward from the tire, the highest hardness rubber 8-1 occupies an area within the range of 60 to 80% of the stiffener rubber area in the tire 1 cross section. Thereby, the fall suppression of the bead part 4 and the stress relaxation of the folding | returning part 6t are harmonized moderately. If the area of the highest hardness rubber 8-1 is less than 60%, the fall of the bead part 4 is not sufficiently suppressed, and if it exceeds 80%, the stress relaxation effect of the folded part 6t is insufficient. It is incompatible because it damages.
[0033]
By the way, since these highest hardness rubber 8-1 and lowest hardness rubber 8-2 have remarkably different hardness, there is a possibility that peeling occurs on both rubber joint surfaces. This peeling phenomenon is mainly caused by the fact that the carcass 6 main body portion 6b protrudes toward the outer side of the tire 1 when the tire 1 is filled with internal pressure, and as a result, strain is concentrated on the joint surface. In order to suppress this protrusion as much as possible, the above intersection P₁ A straight line L parallel to the tire 1 axis passing through₁ The inclination angle θ of the main body 6b with respect to (intersection P₁ It is effective to reduce the inclination angle θ) of the tangent to the main body 6b. However, since the upper limit value of the inclination angle θ differs depending on the tire type, as a result of experimentally analyzing the relationship between the inclination angle θ and durability for various tires, the inclination angle θ is 60 ° or less for all tire sizes. I was able to figure out that it was suitable to do.
[0034]
Further, the folded portion 6t of the ground contact portion undergoes shear deformation in the circumferential direction at the stepping portion and the kicking portion of the tire 1 under rolling load, and this deformation is a factor that causes a separation failure in the folded portion 6t. Therefore, in order to suppress this deformation, the bead portion 4 is provided with the reinforcing cord layer 9 extending at least from the folded portion 6t to the bead core 5. The reinforcing cord layer 9 shown in FIG. 1 reaches the main body portion 6 b through the bead core 5. The position of the outer end 9Eo in the radial direction of the reinforcing cord layer 9 along the turned-up portion 6t is not more than the height of the end 8-1E of the hardest rubber 8-1 and parallel to the tire axis passing through the outermost position of the bead core 5. Straight line L_Four That's it.
[0035]
To make the terminal 9Eo below the end 8-1E height of the hardest rubber 8-1, the region radially outward from the end 8-1E height can be easily deformed in the circumferential direction as a flexible region in the circumferential direction, Concentrating the circumferential deformation suppression in the separation generation region of the folded portion 6t to make it difficult to deform in the circumferential direction is more effective for preventing separation. It is suitable that the cords of the reinforcing cord layer 9 have an inclined arrangement within a range of 45 to 75 ° with respect to the radial direction. Further, the end 9Eo higher than the end 8-1E of the highest hardness rubber 8-1 has a large circumferential strain in the portion, which is the cord of the end 9Eo portion in which the cord of the reinforcing cord layer 9 is inclined and the cord. It is incompatible because it causes a large compressive strain between the coated rubber and cracks at the end of the cord.
[0036]
Further, the end 9Ei of the reinforcing cord layer 9 along the main body portion 6b shown in FIG. 1 is made higher than the height of the end 9Eo of the reinforcing cord layer 9 on the folded portion 6t side, and thereby the circumferential direction of the main body portion 6b portion in the bead portion 4 The rigidity is increased, the circumferential strain component of the compressive strain acting on the terminal 9Eo of the reinforcing cord layer 9 on the side along the folded portion 6t is reduced, and the crack generation at the terminal 9Eo portion is suppressed.
[0037]
In FIG. 2, the reinforcement cord layer 9 composed of a steel cord 9sc and its covering rubber 9cg is suitable for improving circumferential rigidity. At this time, the arrangement interval d orthogonal to the steel cord 9sc at the end 9Eo of the reinforcing cord layer 9₂ Cord outer diameter d₁ Ratio to d₂ / D₁ Is set within a range of 1.0 to 3.0. Thereby, the occurrence of crack failure from the terminal 9Eo of the reinforcing cord layer 9 and the effect of suppressing the circumferential deformation of the folded portion 6t can be achieved at a high level. Ratio d₂ / D₁ If the value is less than 1.0, the cord terminal diameter d of the cut end of the steel cord not bonded to rubber₁ More rubber spacing d₂Therefore, crack nuclei are likely to be connected, separation failure is likely to occur, and if it exceeds 3.0, the effect of improving the rigidity in the circumferential direction becomes insufficient.
[0038]
The carcass 6 of the tire 1 described above includes both a case of a rubber-coated ply of a radial arrangement code and a case of a ply described below. That is, in FIGS. 1 and 3, the carcass 6 is a bead core lower carcass ply portion that exists in a region between two straight lines VLi and VLo that pass through the innermost side and the outermost side of the bead core 5 and are perpendicular to the bead base surface 4B. 6p has an inclined cord 6pC array that obliquely crosses a plane P (see FIG. 3) including the tire 1 axis.
[0039]
Now, the inventor has clarified that the position where the contribution of the restraint degree of the carcass 6 to the bead core 5 in the periphery of the bead core 5 is the highest is directly under the bead core 5. More precisely, the position where the contribution of the restraint degree is the highest is the lower region of the bead core 5 sandwiched between the two straight lines VLi and VLo. Under the bead core 5 refers to the inside of the bead core 5 when viewed in the radial direction of the tire 1.
[0040]
According to this clarification, the radial ply having the cord arrangement in which the carcass 6 is orthogonal to the circumferential direction in which the bead core 5 extends and crosses under the bead core 5 is less constrained to the bead core 5 of the carcass 6. It can be seen that the carcass 6 is pulled out of the bead core 5 relatively easily due to the falling of the.
[0041]
On the other hand, the tire 1 in which the carcass ply portion 6p has the inclined cord 6pC arrangement has a long transverse length with respect to the bead core 5 of the inclined cord 6pC and has a large resistance to the pulling force of the carcass 6, so The degree of restraint with respect to 5 is significantly higher than that of the tire 1 having the carcass 6 made of the rubber-coated ply of the radial arrangement cord. As a result, not only when the tire 1 is filled with internal pressure, but also when the bead portion 4 falls down under the rolling load of the tire 1, the shear strain in the cross section that acts on the entire area along the folded portion 6 t is greatly reduced. It is possible to suppress the occurrence and development of cracks along the turned-up portion 6t, which ultimately contributes to improving the durability of the bead portion 4.
[0042]
When the reinforcing cord layer 9 is applied, the cord 9sc inclined in the direction opposite to the inclination direction of the cord 6pC of the carcass ply portion 6p with respect to the plane P in the region between the two straight lines VLi and VLo below the bead core 5 is applied. An arrangement is preferred. In other words, the code 6pC and the code 9sc are preferably arranged so as to cross each other across the plane P. With this cord crossing configuration, the rigidity of the carcass 6 in the drawing direction is further improved, which contributes to an improvement in the degree of restraint of the carcass 6 on the bead core 5. In FIG. 3, the code 9sc is indicated by a two-dot chain line.
[0043]
The cord 6pC of the carcass ply portion 6p below the bead core 5 is suitable to have an inclination angle α in the range of 5 to 45 ° with respect to the plane P. If the inclination angle α is less than 5 °, the effect cannot be sufficiently exerted. If the inclination angle α exceeds 45 °, the rigidity in the direction along the plane P becomes too low, so that the bead core 5 and the carcass ply portion 6p Since both the shear strain between them and the shear strain between the carcass ply portion 6p and the reinforcing cord layer 9 become large, a separation failure is likely to occur between them. Due to this type of separation failure, the cord 6pC rubs and cuts between adjacent parts, and eventually the tire 1 may reach a burst. It is desirable that the inclination angle β of the reinforcing cord layer 9 with respect to the plane P of the cord 9SC is in the range of 45 to 75 ° described above.
[0044]
The tire 1 described above is suitable for heavy duty pneumatic tires, especially truck and bus tires, and is particularly effective for tubeless tires.
[0045]
【Example】
It is a radial ply tire for trucks and buses, and is a tubeless tire having a size of 275 / 70R22.5. The configurations of Examples 1 to 24 are in accordance with FIGS. 1 and 2, and the configurations of Examples 24 to 29 are FIGS. Follow. The carcass 6 is a one-ply rubber-coated steel cord layer, and the reinforcing cord layer 9 is a single rubber-coated steel cord layer. The height and rubber hardness common to each example are as follows.
Straight line L₁ Height from the rim diameter line RL = 29 mm,
Straight line L₂ Height from the rim diameter line RL = 154 mm,
Straight line L_Three Height from the rim diameter line RL = 54 mm,
Straight line L_Four Height from the rim diameter line RL = 9 mm,
JIS A hardness of the highest hardness rubber 8-1 = 85 °,
Carcass 6 cord coated rubber JIS A hardness = 70 °,
Diameter d of steel cord 9sc of reinforcing cord layer 9₁ = 1.0 mm,
Maximum hardness rubber end 8-1E height = 41mm.
Specifications other than these are shown in Tables 1 to 3. All the heights are the heights from the rim diameter line RL, and the rubber hardness is a value of JIS A.
[0046]
[Table 1]

[0047]
[Table 2]

[0048]
[Table 3]

[0049]
The tires of Comparative Examples 1 to 3 and the conventional tires were all matched to the tires of the examples except for the specifications different from the examples. All these tires are used as test tires. These tires are assembled into a standard rim of 8.25 x 22.5 as defined by JATMA YEAR BOOK (2000). A bead durability test was performed. The load is 56.9 kN, which is equivalent to twice the maximum load capacity of 2900 (kg mass) when DUAL is set by JATMA, and each test tire is pressed against a drum that rotates at a speed of 60 km / h. The distance traveled until the failure occurred in the folded part was also measured, and the failure mode was also confirmed. The speed was 60 km / h.
[0050]
The measurement result of the travel distance is represented by an index with the conventional tire as 100, and the larger the result, the better. The results are shown in Tables 1 to 3 together with the failure modes. In each table, the durability of the bead part or the durability of the folded part is abbreviated as drum durability, and the failure mode is PES for the separation at the end of the folded part, SP for the separation along the folded part, and the reinforcement cord. The separation of the end of layer 9 is represented by layer 9 ESP, and the separation between the highest hardness rubber 8-1 and the lowest hardness rubber 8-2 is represented by SP between the hard and soft rubbers. Burst is bead destruction.
[0051]
From the results shown in Tables 1 to 3, the tires of each example are significantly improved in the durability of the bead part compared to the conventional tires over the whole, and the folded part terminal height or the highest hardness rubber arrangement is incompatible. It can be seen that the comparative example tire shows only the bead portion durability lower than that of the conventional example tire.
[0052]
【The invention's effect】
Claims 1 to 1 of the present invention8According to the invention described in the above, the end position of the folded portion is significantly increased, and the durability of the folded portion is improved by optimizing the arrangement of the highest hardness rubber among the stiffener rubbers. A pneumatic tire that can be remarkably improved and that can further improve the durability of the bead portion can be provided by using a reinforcing cord layer.
[Brief description of the drawings]
FIG. 1 is a left half sectional view of a plane including a tire axis line of an assembly in which a pneumatic tire and a rim of the present invention are filled with an internal pressure of 50 kPa.
FIG. 2 is a code perspective plan view of a part of a reinforcing cord layer of the present invention.
FIG. 3 is a perspective view of a carcass ply cord and a bead core from the direction of arrow A shown in FIG. 1;
FIG. 4 is a left half sectional view of a conventional tire.
[Explanation of symbols]
1 Pneumatic tire
2 Tread
3 Side wall
4 Bead section
4B bead base surface
5 Bead core
6 Carcass
6b Body
6t turning part
6p Carcass ply part under bead core
6pC carcass ply partial code
7 Belt
8 Stiffener rubber
8-1 Highest hardness rubber
8-2 Minimum hardness rubber
9 Reinforcement cord layer
9sc reinforcement cord layer cord
E tire equator

Claims

The carcass has a tread portion, a pair of sidewall portions and a pair of bead portions that are connected to both sides thereof, and a rubber-coated cord ply carcass that reinforces each portion between bead cores embedded in each bead portion. A carcass body between the inside of a pair of bead cores, and a turn-up portion that turns the periphery of the bead core from the inside to the outside, and tapers along the carcass body and the turn-up portion from the bead core periphery toward the tread end. In a pneumatic tubeless tire having a stiffener rubber extending in the direction, the stiffener rubber is composed of two or more kinds of rubbers having different hardnesses, and the highest hardness rubber is arranged along the carcass main body from the bead core. The minimum hardness rubber is arranged along the folded part from the bead core,
In the cross section of the tire and rim assembly in which the pneumatic tubeless tire is assembled to its standard rim and filled with an internal pressure of 50 kPa as a gauge pressure,
The carcass body has an intersection (P1) between the perpendicular (Lv1) to the tire axis passing through the outermost position of the bead core and the center of the thickness of the body ply, and a perpendicular (Lv2) extending from the contact width end of the tread to the tire axis. The ply portion extending between the intersection with the center of thickness of the main body ply (P2) has a convex curved shape toward the outer side of the tire, and
The carcass folding portion is formed by a perpendicular (Lv3) from the straight line (L2) parallel to the tire axis passing through the intersection (P2) to the tire axis passing through the center of the radius of curvature of the flange of the standard rim and the thickness center of the main body ply. It has a turn-up end in a region extending up to a straight line (L3) parallel to the tire axis passing through the intersection (P3),
Hardest rubber stiffener rubber is Ri formed occupies at least the perpendicular line (Lv1) tire axial inward position than,
The bead portion includes a reinforcing cord layer extending at least from the folded portion to the bead core, and the outer radial position of the folded portion side reinforcing cord layer is set to be equal to or lower than the terminal height of the highest hardness rubber of the stiffener rubber, And a straight line (L4) parallel to the tire axis passing through the outermost position of the bead core,
The reinforcing cord layer is composed of a rubber coating layer of steel cords arranged in an inclination with respect to the tire radial direction, and a value of a ratio of an arrangement interval perpendicular to the steel cord to a cord outer diameter at the end of the reinforcing cord layer along the folded portion. In a range of 1.0 to 3.0, a pneumatic tubeless tire.

The lowest hardness rubber of the stiffener rubber has a lower hardness than that of the carcass ply cord-coated rubber, and the lowest hardness rubber has an end height extending beyond the tire radial end of the highest hardness rubber in the direction. The pneumatic tubeless tire according to claim 1.

The pneumatic tubeless tire according to claim 1 or 2, wherein the minimum hardness rubber of the stiffener rubber has a shape extending beyond the end of the carcass folded portion in the tire radial direction.

The stiffener rubber is 60% to 80% of the stiffener rubber area in the tire cross section of the stiffener rubber located inward in the tire radial direction from the normal line (Lv4) of the carcass main body portion passing through the end of the highest hardness rubber of the stiffener rubber. The pneumatic tubeless tire according to any one of claims 1 to 3, which occupies an area within the range.

The tire according to any one of claims 1 to 4, wherein the carcass main body portion has an inclination angle of 60 ° or less with respect to a straight line parallel to the tire axis passing through the intersection (P1).

The pneumatic tubeless tire according to any one of claims 1 to 5, wherein the end of the reinforcing cord layer along the carcass main body is higher than the end height of the folded reinforcing cord layer.

The carcass has a rubber-coated ply portion of a radial arrangement code in a region extending between at least a pair of sidewall portions, and passes through the innermost side and the outermost side of the bead core in a tire cross section by a plane including the tire axis. A bead core lower carcass ply portion existing in a region sandwiched by two straight lines perpendicular to the surface has an inclined cord array that obliquely crosses the plane, and the inclined cord is within a range of 5 to 45 ° with respect to the plane. The pneumatic tubeless tire according to any one of claims 1 to 6, having an inclination angle of.

The pneumatic tubeless tire according to any one of claims 1 to 7, which is a heavy duty tire in which a steel cord is applied to a carcass ply cord.