JP3647977B2

JP3647977B2 - Heavy duty pneumatic radial tire

Info

Publication number: JP3647977B2
Application number: JP17912096A
Authority: JP
Inventors: 靖彦小林
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1996-07-09
Filing date: 1996-07-09
Publication date: 2005-05-18
Anticipated expiration: 2016-07-09
Also published as: JPH1024712A

Description

【０００１】
【発明の属する技術分野】
この発明は、トラック、バス、産業車両や建設車両などの重車両の使途に供する重荷重用空気入りラジアルタイヤに関し、特にタイヤビード部の重量増加を伴うことなくビード部耐久性を向上させた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】
重車両に用いる重荷重用空気入りラジアルタイヤは負荷転動中ビード部に作用する力が大きいため、ビード部故障、主としてセパレーション故障が発生し勝ちであり、そのためこれまで耐セパレーション性を主とする各種のビード部耐久性向上手段が提案されていて、それらのうちナイロンチェーファやワイヤーチェーファなどの補強部材の追加配置によるビード部剛性の一層の向上や、カーカスラインの適正化による剛性配置の修正などが良く知られている。
【０００３】
これら改善手段は内圧充填時、荷重負荷時のサイドウォール部からビード部に至る間の部分の撓曲変形、いわゆる倒れ込み変形の抑制、タイヤ転動時のビード部における踏み込み部、蹴り出し部に発生する円周方向剪断変形の抑制に有効であり、この種の変形抑制手段はビード部耐久性向上に寄与するため広く採用されている。
【０００４】
【発明が解決しようとする課題】
しかし上記補強部材の追加配置は当然重量増加をもたらす上、材料費用及び製造工数の増加によるコストアップを招き、現状の厳しい価格競争時代にそぐわない。またカーカスラインの修正など重量増加によらない手段の適用は、確かに比較的マイルドな使用条件下で所期の効果を発揮する反面、使用条件が益々酷しくなる現状に適応することはできず、所期のビード部耐久性発揮に不十分であることが分かった。
【０００５】
重車両用タイヤのなかでも特に大型建設車両用空気入りラジアルタイヤではサイドウォール部の耐カット性向上のためカーカス折返し部の高さを他の種類のタイヤ対比大幅に高く設定し、時にタイヤ断面幅（最大幅）位置前後の高さに設定するいわゆるハイターンアップ構造を採用するのが一般であり、そのため折返し端部のセパレーション故障改善を主たる対象とする従来手段は何れも有効な改善手段とはなり難い。なぜならタイヤ転動中最も大きな歪が作用するのはリムのフランジ高さ近傍位置であり、しかも上記大型タイヤは負荷時の撓み率が他の種のタイヤ対比著しく大きいからである。
【０００６】
上記大型タイヤの場合は特に、上述したように大きな撓み率により負荷転動時にリムのフランジと接触する領域に存在する、折返し端から程遠い折返し途中部分のプライに沿いセパレーション故障（ビード部故障）が発生するのが特異な点である。よってこの大型タイヤの特異な故障に対し先に述べた従来の改善手段も含めた従来手段は何れも市場要求を満たすビード部耐久性発揮の決め手とならないのも止むを得ない。
【０００７】
従ってこの発明の目的は、タイヤ重量の増加やコスト上昇を伴うことなく、カーカスラインの適正化などでは対応できない程の過酷な使用条件の下でも十分なビード部耐久性を発揮し得る重荷重用空気入りラジアルタイヤを提供することにある。
【０００８】
【課題を解決するための手段】
上記目的を達成するため、この発明による重荷重用空気入りラジアルタイヤは、一対のビード部及び一対のサイドウォール部と、トレッド部とからなり、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ラジアル配列コードのゴム被覆になるカーカスプライと、該カーカスプライの外周に配置したベルトとを備え、カーカスプライはビードコア周りを巻上げた折返し部を有する重荷重用空気入りラジアルタイヤにおいて、
上記タイヤの正規内圧を該タイヤとその適用リムとの組立体に充填して正規荷重を負荷し解放したときの組立体断面に関し、荷重負荷時におけるビード部表面のリムのフランジとの接触終端位置を通るカーカスプライからの法線と、タイヤ断面幅位置を通る直線との間に挟まれる領域内に、カーカスプライ折返し部の外側表面に沿ってカーカスプライコードの被覆ゴムより高い硬度をもつ硬質ゴム層を配置する一方、該硬質ゴム層のタイヤ半径方向内側面に接合させると共に同上折返し部の外側表面に沿わせて上記被覆ゴムより低い硬度をもつ軟質ゴム層を配置して成ることを特徴とする。
【０００９】
【発明の実施の形態】
この発明による重荷重用空気入りラジアルタイヤ（以下タイヤ又はラジアルタイヤという）を一実施例に基づき以下詳細に説明する。
図１は、この発明による一実施例タイヤ２０を適用リム１０(JATMA YEAR BOOKに記載されたタイヤサイズに対応する適用リム）に組込んだ組立体の線図的要部断面図であり、いずれのタイヤ２０も上記YEAR BOOK に記載した最高空気圧（以下正規内圧と記す）を充填したときの、タイヤ断面幅（最大幅）部分の図示を省略したビード部〜サイドウォール部内側部分の左側断面図である。
【００１０】
図１において、タイヤ２０は一対のビード部１及び一対のサイドウォール部２（いずれも片側のみ示す）とトレッド部（図示省略）からなり、ビード部１内に埋設したビードコア３相互間にわたりこれらビード部１、サイドウォール部２及びトレッド部を補強するラジアル配列コード、特にスチールコードのゴム被覆になる１プライのカーカスプライ４と、このカーカスプライ４の外周でトレッド部を強化するベルト（図示省略）とを備えるのは慣例に従う。
【００１１】
カーカスプライ４は本体としてのプライの他にビードコア３の回りをタイヤ内側から外側（以下単に内側、外側という）に向けて巻上げた折返し部４ｔを有し、図に示す例はハイターンアップである。カーカスプライ４は、２本の曲線にて簡略図解したが厚み中央にコード、望ましくはスチールコードを有し、その場合は１プライで構成するものとし、各コードの周囲は隙間なく被覆ゴムが取り囲む。
【００１２】
サイドウォール部２のゴム５は図示を省略したトレッド部側方からビード部１領域まで延び、ビード部１にてゴムチェーファ８とオーバーラップさせて連結する。そのときゴムチェーファ８の外側表面のタイヤ半径方向（以降半径方向と略す）外側端は配設目的からしてリム１０のフランジ１０ｆの外側縁を越える。
【００１３】
以上述べた各種構成部材とそれらの配置関係の下で、タイヤ２０とリム１０との組立体に正規内圧に対応する正規荷重を負荷すると、荷重直下位置のビード部１及びサイドウォール部２はタイヤ幅方向外側にそして半径方向内側に向け撓曲変形、いわゆる倒れ込み変形を生じる。この変形によりビード部１の外側表面がリム１０のフランジ１０ｆと接触する終端位置、すなわち半径方向最外側位置を図に符号Ａにて示すとき、位置Ａは図の矢印の向きに倒れ込みリム１０のフランジ１０ｆの位置Ａｆにとどまる。荷重負荷とそれからの解放で位置Ａの点は位置Ａｆと位置Ａとの間で離合を繰り返す最外側点であるから、ここでは位置Ａをタイヤ２０断面での最外側離合点と呼ぶ。
【００１４】
タイヤ２０とリム１０との内圧充填組立体断面において、最外側離合点Ａを通るカーカスプライ４の本体からの法線Ｌと、図示は省略したが図の上方のタイヤ断面幅位置を通る直線との間に挟まれる領域Ｒ内において、まずカーカスプライ４の折返し部４ｔの外側表面に沿って硬質ゴム層６（図中、特に太い斜線を施して示す）を配置するものとし、この硬質ゴム層６のゴム硬度はカーカスプライ４の被覆ゴム硬度より高いものとする。
【００１５】
次に硬質ゴム層６の半径方向内側で折返し部４ｔの外側表面に沿って軟質ゴム層７を配置する。この配置は硬質ゴム層６の半径方向内側端面Ｓに軟質ゴム層７の半径方向外側端面を接合させるものとし、また字句通り軟質ゴム層７のゴム硬度はカーカスプライ４の被覆ゴム硬度より低いことが必要である。
【００１６】
ここで、先に述べたサイドウォール部２からビード部１に至る間の倒れ込み変形が生じるとき、ビード部１はあたかもビードコア３を支点とする回転形態を採る。その結果、法線Ｌより半径方向内側での折返し部４ｔ、より正確には折返し部４ｔのコード、特にスチールコードより外側の領域Ｒ_Oに存在するゴムはリム１０のフランジ１０ｆとの間で著しく圧縮される。
【００１７】
この大きな圧縮による歪はフランジ１０ｆに沿って半径方向外側に向け軟質ゴム層７に大きな流動変位を生じさせるので、ゴムは大きな剪断変形を受けることになる。この剪断変形は繰り返しカーカスプライ４の折返し部４ｔの外側表面に伝達される結果、従来はタイヤ走行が進むにつれ折返し部４ｔのコード、特にスチールコードと被覆ゴムとの界面に、乃至コード近傍のゴムにセパレーションを発生させることになる。
【００１８】
これに対し前記構成になるビード部１は、領域Ｒ_Oより半径方向外側の領域Ｒにカーカスプライ４の被覆ゴム硬度より高い硬度をもつ硬質ゴム層６を折返し部４ｔに沿って配置しているので、タイヤへの荷重負荷転動に伴い発生するリム１０のフランジ１０ｆから伝達される軟質ゴム層７の流動は硬質ゴム層６があたかも堰止めるように働き、少なくとも軟質ゴム層７の流動変位量を抑制する。
【００１９】
この流動変位の抑制はカーカスプライ４の折返し部４ｔ外側表面に作用する剪断歪を大幅に低減し、これにより、元来折返し部４ｔに作用する剪断応力緩和を狙いとしてカーカスプライ４の被覆ゴムより低硬度の軟質ゴム層７を配置した効果はさらに顕著に高まり、セパレーション耐久性を改善することができる。いうならば硬質ゴム層６と軟質ゴム層７との組合せ連係プレーの下でセパレーション耐久性を向上させるのである
【００２０】
硬質ゴム層６と軟質ゴム層７との外側には、耐屈曲性や耐候性に優れたサイドウォールゴム５と、その半径方向下端でオーバーラップ接合するゴムチェーファ８を設けるのは慣例に従う。
【００２１】
また硬質ゴム層６はビード部１における半径方向内側からの軟質ゴム層７の流動変位を半径方向外側から抑制する役を有利に果たすため、硬質ゴム層６の半径方向内側端が最外側離合点Ａから大きくかけ離れて位置するのは好ましくなく、よって硬質ゴム層６の半径方向内側端は、最外側離合点Ａと、そこから測ってタイヤ断面高さの１０％に相当する高さ位置との間に存在する配置が望ましい。
【００２２】
また上記同様な流動抑制の役を果たす上で、硬質ゴム層６はある程度の厚さを有するのが望ましく、好適には最大厚さＴはこの厚さ位置の直線ｍ上で測った折返し部４ｔの外側ゴム厚さｔの４０％以上である。また上記同様に実際上硬質ゴム層６の１００％モジュラスは５０kgf/cm²以上であることが望ましい。
【００２３】
また軟質ゴム層７の１００％モジュラスが２０kgf/cm²以下であれば、硬質ゴム層６との組合せで折返し部４ｔに作用する剪断応力低減効果に十分に寄与し、さらに硬質ゴム層６と軟質ゴム層７との１００％モジュラス差が大きい程剪断応力低減効果も大きくなるが、実際上は軟質ゴム層７に対する硬質ゴム層６の１００％モジュラス比の値が３倍以上であるのが適合する。
【００２４】
なお図１に示す符号９はスティフナであり、そのうち９ａは硬スティフナ、９ｂは軟スティフナであり、符号１１はインナーライナである点は従来構造に従うが、特に硬スティフナ９ａ、軟スティフナ９ｂは硬質ゴム層６と軟質ゴム層７との関連で最適な硬度及び配列を考慮するのが良い。
【００２５】
【実施例】
建設車両用ラジアルタイヤ２０でサイズが３７．００Ｒ５７であり、カーカスプライ４は１プライでスチールコードのゴム被覆になる。ビード部１〜サイドウォール部２に至る構成について実施例１、２は図１に、実施例３は図２に、そして実施例４は図３に従う。実施例１〜４の図における主たる相違点は硬質ゴム層６の半径方向内側端位置にあり、該内側端位置の最外離合点Ａから測った高さはタイヤ断面高さの、実施例１、２は２％、実施例３は８％、実施例４は３％とした。
【００２６】
各実施例の効果を検証するため図４に同様断面を示す従来例のタイヤ２０Ａを準備した。従来例も含め表１に、ゴムの１００％モジュラス（kgf/cm²)につき、カーカスプライ４の被覆ゴムはカーカスゴムＭ₁₀₀（kgf/cm²)、硬質ゴム層６は硬質ゴム層Ｍ₁₀₀（kgf/cm²)、軟質ゴム層７は軟質ゴム層Ｍ₁₀₀（kgf/cm²)、そして硬質ゴム層６の厚さＴの折返し部外側ゴム厚さｔに対する比率（％）を硬質ゴム層厚さＴ比率（％）、とそれぞれ略記してそれぞれの値を示す。
【００２７】
【表１】

【００２８】
上記５種類のタイヤを供試タイヤとして、ドラムによるビード耐久性試験により比較評価した。試験方法及び試験条件は下記の通り。
（１）ベルト故障を先行させず、確実にビード部故障が発生するように、トレッド部のトレッドゴムを削り取った。
（２）正規内圧７kgf/cm²を充填し、表面速度１０km/hで回転するドラムに当初荷重は５１．５トン（約１００％ロード）を負荷し、所定時間走行後は段階的に荷重を増加させ、５種類のタイヤの何れか１種類のタイヤにビード部故障が生じたところで試験は全数打ち切りとする。
【００２９】
最初に従来例のタイヤに外観から明確に確認できるビード部故障（ビード部外側の故障）が発生したので、全タイヤの試験を打ち切り試験機から取り外してビード部故障の有無及び故障の程度を解剖により確かめた。
【００３０】
その結果、従来例は更めて解剖に付すまでもなく、著しいセパレーション故障がカーカスプライ折返し部の外側表面周りに発生していたのに対し、実施例１、３は折返し部４ｔの外側に外観からそれと認めることができない程度の微小なセパレーションが見出されたに過ぎず、実施例２、４にはセパレーションの兆候すら認めることができなかった。なお試みに新品タイヤ重量を測定しところいずれのタイヤも誤差範囲程度の微差に収まっていた。
【００３１】
【発明の効果】
この発明によれば、補強部材などの追加部材の配置を必要とせず、よってタイヤ重量増加を伴うことなく高生産性を保持した上で、ビード部耐久性を有効に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】この発明による一実施例タイヤの要部断面図である。
【図２】この発明による別の実施例タイヤの要部断面図である。
【図３】この発明による他の実施例タイヤの要部断面図である。
【図４】従来タイヤの要部断面図である。
【符号の説明】
１ビード部
２サイドウォール部
３ビードコア
４カーカスプライ
４ｔ折返し部
５サイドウォールゴム
６硬質ゴム層
７軟質ゴム層
８ゴムチェーファ
９スティフナ
９ａ硬スティフナ
９ｂ軟スティフナ
１０リム
１０ｆフランジ
２０、２０Ａ重荷重用空気入りラジアルタイヤ
Ａ荷重負荷時のビード部外側表面の半径方向最外側接触位置
Ｌ位置Ａの点を通るカーカスプライからの法線
Ｒ法線Ｌとタイヤ断面幅を通る直線との間の領域
Ｒ_O法線Ｌより半径方向内側の領域
ｍ硬質ゴム層最大厚さ位置の直線
Ｔ直線ｍ上の硬質ゴム層最大厚さ
ｔ直線ｍ上の折返し部のゴム厚さ
Ｓ硬質ゴム層の半径方向内側端縁面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heavy-duty pneumatic radial tire for use in heavy vehicles such as trucks, buses, industrial vehicles and construction vehicles, and in particular, for heavy loads with improved bead portion durability without increasing the weight of the tire bead portion. The present invention relates to a pneumatic radial tire.
[0002]
[Prior art]
Heavy load pneumatic radial tires used for heavy vehicles have a large force acting on the bead portion during rolling of the load, so it is easy for a bead portion failure, mainly a separation failure to occur. The bead part durability improvement means has been proposed, among them, the rigidity of the bead part is further improved by the additional arrangement of reinforcing members such as nylon chafer and wire chafer, and the rigidity arrangement is corrected by optimizing the carcass line Are well known.
[0003]
These improvement measures are generated at the stepping part and kicking part in the bead part during tire rolling, suppression of bending deformation of the part from the sidewall part to the bead part when loading with internal pressure, so-called collapse deformation This is effective in suppressing circumferential shear deformation, and this type of deformation suppression means has been widely adopted because it contributes to improved bead portion durability.
[0004]
[Problems to be solved by the invention]
However, the additional arrangement of the reinforcing members naturally increases the weight, and also increases the cost due to an increase in material costs and manufacturing man-hours, and is not suitable for the current severe price competition era. The application of means not based on weight increase, such as carcass line correction, can certainly achieve the desired effect under relatively mild use conditions, but cannot be applied to the current situation where use conditions become increasingly severe. As a result, it was found that the desired bead portion durability was insufficient.
[0005]
Among heavy-duty tires, especially pneumatic radial tires for large construction vehicles, the height of the carcass turn-up is set to be significantly higher than other types of tires to improve the cut resistance of the sidewalls, and sometimes the tire cross-section width (Maximum width) It is common to adopt a so-called high turn-up structure where the height is set before and after the position. Therefore, any of the conventional means mainly intended to improve separation failure at the folded end is an effective improvement means. It ’s hard to be. This is because the largest strain acts on the rim flange height during rolling of the tire, and the large tire has a significantly larger deflection rate under load than other types of tires.
[0006]
Especially in the case of the above large tires, there is a separation failure (bead portion failure) along the ply in the middle of the turnback that is far from the turnup end, which exists in the region that contacts the flange of the rim at the time of load rolling due to the large deflection rate as described above. It is a peculiar point that occurs. Therefore, it cannot be helped that any of the conventional means including the conventional improvement means described above for the specific failure of the large tire is not the decisive factor for exhibiting the durability of the bead part that satisfies the market demand.
[0007]
Accordingly, an object of the present invention is to provide heavy-duty air that can exhibit sufficient bead durability even under severe use conditions that cannot be dealt with by optimization of the carcass line, etc., without increasing tire weight and cost. The purpose is to provide a radial tire.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a heavy-duty pneumatic radial tire according to the present invention comprises a pair of bead portions, a pair of sidewall portions, and a tread portion, and these portions are reinforced across bead cores embedded in the bead portions. A heavy duty pneumatic radial tire having a carcass ply that is a rubber coating of a radial arrangement code and a belt disposed on an outer periphery of the carcass ply, and the carcass ply has a folded portion wound around a bead core.
Regarding the assembly cross section when the normal internal pressure of the tire is filled in the assembly of the tire and its applicable rim and a normal load is applied and released, the contact end position with the rim flange on the surface of the bead portion when the load is applied A hard rubber having a hardness higher than that of the covering rubber of the carcass ply cord along the outer surface of the carcass ply folded portion in the region sandwiched between the normal line from the carcass ply passing through the tire and the straight line passing through the tire cross-sectional width position. And a soft rubber layer having a hardness lower than that of the coated rubber is disposed along the outer surface of the folded portion, and the hard rubber layer is bonded to the inner surface in the tire radial direction of the hard rubber layer. To do.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A heavy-duty pneumatic radial tire according to the present invention (hereinafter referred to as a tire or a radial tire) will be described in detail below based on an embodiment.
FIG. 1 is a schematic cross-sectional view of an essential part of an assembly in which a tire 20 according to an embodiment of the present invention is incorporated in an applied rim 10 (applied rim corresponding to a tire size described in JATMA YEAR BOOK). When the tire 20 is filled with the maximum air pressure (hereinafter referred to as normal internal pressure) described in the YEAR BOOK, the left cross-sectional view of the inner side portion of the bead portion to the side wall portion in which the tire cross-sectional width (maximum width) portion is not shown. It is.
[0010]
In FIG. 1, a tire 20 includes a pair of bead portions 1 and a pair of sidewall portions 2 (both are shown only on one side) and a tread portion (not shown), and these beads extend between bead cores 3 embedded in the bead portion 1. 1-ply carcass ply 4 that serves as a rubber coating of a steel cord, and a belt that reinforces the tread portion on the outer periphery of the carcass ply 4 (not shown) Is in accordance with common practice.
[0011]
The carcass ply 4 has, in addition to the ply as a main body, a turn-up portion 4t wound around the bead core 3 from the inner side of the tire to the outer side (hereinafter simply referred to as the inner side and the outer side). . The carcass ply 4 is simply illustrated with two curves, but has a cord in the center of the thickness, preferably a steel cord. In this case, the carcass ply 4 is composed of one ply. .
[0012]
The rubber 5 of the sidewall portion 2 extends from the side of the tread portion (not shown) to the bead portion 1 region, and is overlapped with and connected to the rubber chafer 8 at the bead portion 1. At that time, the outer end of the outer surface of the rubber chafer 8 in the tire radial direction (hereinafter referred to as the radial direction) exceeds the outer edge of the flange 10f of the rim 10 for the purpose of installation.
[0013]
When a normal load corresponding to a normal internal pressure is applied to the assembly of the tire 20 and the rim 10 under the various constituent members described above and their arrangement relationship, the bead portion 1 and the sidewall portion 2 immediately below the load are tires. A bending deformation, that is, a so-called collapse deformation is generated outward in the width direction and inward in the radial direction. When the end position where the outer surface of the bead portion 1 contacts the flange 10f of the rim 10 by this deformation, that is, the radially outermost position is indicated by a symbol A in the drawing, the position A falls in the direction of the arrow in the drawing and the position of the rim 10 falls. It remains at the position Af of the flange 10f. Since the point at the position A is the outermost point that repeats separation between the position Af and the position A by the load load and release from the load A, the position A is referred to as the outermost separation point on the tire 20 cross section here.
[0014]
In the cross section of the inner pressure filling assembly of the tire 20 and the rim 10, a normal line L from the main body of the carcass ply 4 passing through the outermost separation point A, and a straight line passing through the tire cross-sectional width position in the upper part of the drawing although not shown in the figure. First, a hard rubber layer 6 (shown with a particularly thick diagonal line in the figure) is disposed along the outer surface of the folded portion 4t of the carcass ply 4 in the region R sandwiched between the hard rubber layers. The rubber hardness of 6 is higher than that of the carcass ply 4.
[0015]
Next, the soft rubber layer 7 is disposed along the outer surface of the folded portion 4 t on the inner side in the radial direction of the hard rubber layer 6. In this arrangement, the radially outer end surface of the soft rubber layer 7 is joined to the radially inner end surface S of the hard rubber layer 6, and the rubber hardness of the soft rubber layer 7 is literally lower than the coated rubber hardness of the carcass ply 4. is required.
[0016]
Here, when the falling deformation occurs from the sidewall portion 2 to the bead portion 1 described above, the bead portion 1 takes a rotational form as if the bead core 3 is a fulcrum. As a result, the folded portion 4t on the inner side in the radial direction from the normal L, more precisely, the cord in the folded portion 4t, particularly the rubber present in the region R _O outside the steel cord, is significantly between the flange 10f of the rim 10. Compressed.
[0017]
The strain caused by the large compression causes a large fluid displacement in the soft rubber layer 7 toward the radially outer side along the flange 10f, so that the rubber is subjected to a large shear deformation. This shear deformation is repeatedly transmitted to the outer surface of the folded portion 4t of the carcass ply 4. As a result, conventionally, as the tire travels, the cord of the folded portion 4t, particularly at the interface between the steel cord and the covering rubber, or in the vicinity of the cord Will cause separation.
[0018]
On the other hand, in the bead portion 1 having the above-described configuration, the hard rubber layer 6 having a hardness higher than the coating rubber hardness of the carcass ply 4 is arranged along the folded portion 4t in the region R radially outside the region R _O. Therefore, the flow of the soft rubber layer 7 transmitted from the flange 10f of the rim 10 generated in accordance with the load load rolling on the tire works as if the hard rubber layer 6 blocks the flow, and at least the flow displacement amount of the soft rubber layer 7 Suppress.
[0019]
This suppression of the flow displacement significantly reduces the shear strain acting on the outer surface of the folded portion 4t of the carcass ply 4 and thereby reduces the shear stress originally acting on the folded portion 4t than the coated rubber of the carcass ply 4 The effect of arranging the low hardness soft rubber layer 7 is further remarkably enhanced, and the separation durability can be improved. In other words, the separation durability is improved under the combined linkage play of the hard rubber layer 6 and the soft rubber layer 7. [0020]
It is customary to provide the side wall rubber 5 excellent in bending resistance and weather resistance and the rubber chafer 8 that overlaps at the lower end in the radial direction outside the hard rubber layer 6 and the soft rubber layer 7.
[0021]
Further, since the hard rubber layer 6 advantageously serves to suppress the flow displacement of the soft rubber layer 7 from the radially inner side in the bead portion 1 from the radially outer side, the radially inner end of the hard rubber layer 6 is the outermost separation point. It is not preferable to be located far away from A. Therefore, the radially inner end of the hard rubber layer 6 has an outermost separation point A and a height position corresponding to 10% of the tire cross-section height measured from there. An arrangement in between is desirable.
[0022]
Further, in order to perform the same flow suppression function as described above, it is desirable that the hard rubber layer 6 has a certain thickness, and preferably the maximum thickness T is the folded portion 4t measured on the straight line m at this thickness position. The outer rubber thickness t is 40% or more. Similarly to the above, the 100% modulus of the hard rubber layer 6 is desirably 50 kgf / cm ² or more.
[0023]
If the 100% modulus of the soft rubber layer 7 is 20 kgf / cm ² or less, the combination with the hard rubber layer 6 can sufficiently contribute to the effect of reducing the shear stress acting on the folded portion 4t. The greater the difference in 100% modulus from the rubber layer 7, the greater the shear stress reduction effect. In practice, however, the value of the 100% modulus ratio of the hard rubber layer 6 to the soft rubber layer 7 is more than 3 times. .
[0024]
Reference numeral 9 shown in FIG. 1 is a stiffener, of which 9a is a hard stiffener, 9b is a soft stiffener, and 11 is an inner liner in accordance with the conventional structure. In particular, the hard stiffener 9a and the soft stiffener 9b are hard rubber. In view of the relationship between the layer 6 and the soft rubber layer 7, the optimum hardness and arrangement should be considered.
[0025]
【Example】
The construction vehicle radial tire 20 has a size of 37.00R57, and the carcass ply 4 is covered with a steel cord rubber by one ply. In the configuration extending from the bead portion 1 to the sidewall portion 2, the first and second embodiments follow FIG. 1, the third embodiment follows FIG. 2, and the fourth embodiment follows FIG. The main difference in the drawings of Examples 1 to 4 is at the radially inner end position of the hard rubber layer 6, and the height measured from the outermost separation point A of the inner end position is the tire cross-section height. 2 was 2%, Example 3 was 8%, and Example 4 was 3%.
[0026]
In order to verify the effect of each example, a conventional tire 20A having the same cross section as shown in FIG. 4 was prepared. In Table 1, including the conventional example, for 100% modulus (kgf / cm ² ) of rubber, the covered rubber of the carcass ply 4 is carcass rubber M ₁₀₀ (kgf / cm ² ), and the hard rubber layer 6 is hard rubber layer M ₁₀₀ (kgf / cm ² ), the soft rubber layer 7 is the soft rubber layer M ₁₀₀ (kgf / cm ² ), and the ratio (%) of the thickness T of the hard rubber layer 6 to the outer rubber thickness t of the folded portion is the hard rubber layer thickness. T ratio (%) is abbreviated to indicate each value.
[0027]
[Table 1]

[0028]
The above five types of tires were used as test tires and subjected to comparative evaluation by a bead durability test using a drum. Test methods and test conditions are as follows.
(1) The tread rubber in the tread portion was scraped off so that the bead portion failure occurred surely without causing belt failure first.
(2) An initial load of 51.5 tons (about 100% load) is applied to a drum that is filled with a normal internal pressure of 7 kgf / cm ² and rotates at a surface speed of 10 km / h. When the bead failure occurs in any one of the five types of tires, the test is terminated.
[0029]
First, the conventional tire had a bead failure (failure outside the bead) that could be clearly confirmed from the appearance. Therefore, the test of all tires was discontinued and the presence or absence of the bead failure was analyzed. Confirmed.
[0030]
As a result, the conventional example did not need to be further dissected, and a significant separation failure occurred around the outer surface of the carcass ply folded portion, whereas Examples 1 and 3 had an appearance on the outer side of the folded portion 4t. Thus, only a minute separation that could not be recognized as such was found, and even in Examples 2 and 4, no signs of separation could be recognized. In addition, when the weight of a new tire was measured in an attempt, all the tires were within a slight difference within an error range.
[0031]
【The invention's effect】
According to the present invention, it is not necessary to arrange an additional member such as a reinforcing member, and thus it is possible to effectively improve the bead portion durability while maintaining high productivity without increasing the tire weight. A pneumatic radial tire can be provided.
[Brief description of the drawings]
FIG. 1 is a sectional view of an essential part of a tire according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of an essential part of another embodiment tire according to the present invention.
FIG. 3 is a sectional view of an essential part of another embodiment tire according to the present invention.
FIG. 4 is a cross-sectional view of a main part of a conventional tire.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Bead core 4 Carcass ply 4t Turn-up part 5 Side wall rubber 6 Hard rubber layer 7 Soft rubber layer 8 Rubber chafer 9 Stiffener 9a Hard stiffener 9b Soft stiffener 10 Rim 10f Flange 20, 20A Pneumatic tire for heavy load region R _O normal L between the straight line passing through the normal R normal L and the tire section width from the carcass ply through the points of the radially outermost contact position L position a of the bead portion outer surface at a load application Radial inner area m Straight line T of hard rubber layer maximum thickness position Hard rubber layer maximum thickness t on straight line m Rubber thickness S of folded part on straight line m Radial inner edge surface of hard rubber layer

Claims

A carcass ply comprising a pair of bead portions and a pair of sidewall portions, and a tread portion, and a rubber covering of a radial arrangement cord that reinforces each portion between bead cores embedded in the bead portion, and an outer periphery of the carcass ply A heavy duty pneumatic radial tire having a folded portion wound up around the bead core.
Regarding the assembly cross-section when the normal internal pressure of the tire is filled in the assembly of the tire and its applicable rim and a normal load is applied and released, the contact end position with the rim flange on the surface of the bead portion when the load is applied A hard rubber having a hardness higher than that of the covered rubber of the carcass ply cord along the outer surface of the carcass ply folded portion in a region sandwiched between a normal line from the carcass ply passing through the tire and a straight line passing through the tire cross-sectional width position. And a soft rubber layer having a hardness lower than that of the covering rubber is disposed along the outer surface of the folded portion and the hard rubber layer is bonded to the inner surface in the tire radial direction of the hard rubber layer. Pneumatic radial tire for heavy loads.

The inner end in the tire radial direction of the hard rubber layer exists between the surface position of the bead portion of the normal line and a height position corresponding to 10% of the tire cross-section height measured from the position, and the hard rubber layer Has a maximum thickness portion on the inner side in the radial direction, and this maximum thickness is 40% or more of the rubber thickness from the folded portion measured in the thickness direction to the tire surface, and 100% modulus of the hard rubber layer. The tire according to claim 1, wherein is 50 kgf / cm ² or more.

The tire according to claim 1, wherein the soft rubber layer has a 100% modulus of 20 kgf / cm ² or less.

The tire according to claim 2 or 3, wherein a value of a 100% modulus ratio of the hard rubber layer to the soft rubber layer is three times or more.