JP4149057B2

JP4149057B2 - Pneumatic tire

Info

Publication number: JP4149057B2
Application number: JP35613698A
Authority: JP
Inventors: 兼一郎入宮
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1998-12-15
Filing date: 1998-12-15
Publication date: 2008-09-10
Anticipated expiration: 2018-12-15
Also published as: JP2000177323A

Description

【０００１】
【発明の属する技術分野】
この発明は、空気入りタイヤ、より詳細には、小形トラック、トラック及びバス用などのラジアルプライタイヤに関し、特に、タイヤのトレッドゴムの耐偏摩耗性の改善と耐摩耗性の向上とを両立させた空気入りタイヤに関する。
【０００２】
【従来の技術】
小形トラック、トラック、バスなどの重車両と呼ばれる比較的車両総重量が重い車両に使用するラジアルプライタイヤ（以下空気入りタイヤ又はタイヤという）は、トレッド部の踏面の周りに沿って周回し連続して延びる周方向溝をトレッド部に備えるのが一般であり、この種の周方向溝をトレッド部に備える空気入りタイヤには、周方向溝縁に沿って、リバーウエア乃至レイルウエイ摩耗と呼ばれる偏摩耗が多少にかかわらず発生し、ときにはこの種の偏摩耗が進展して互いに隣り合う周方向溝相互間にわたり、トレッドゴム陸部にリブパンチと呼ばれる偏摩耗欠損部を生じさせる。これらの偏摩耗は、トレッドゴムの摩耗寿命を大幅に短くするばかりか、車両の操縦安定性や振動乗心地性を著しく損なう。また、直状周方向溝を備えるタイヤが、偏摩耗に対し最も不利であることは周知である。
【０００３】
この種の偏摩耗を改善するため、トレッド部のトレッドゴムに、踏面周方向に連続して延びる一対の溝、一対の溝及び狭い切込み、一対の狭い切込みなどを設け、これら一対の溝又は狭い切込みにより、トレッドゴム陸部から離隔され、踏面からの段下がり表面をもつ複数本の段差陸部をトレッド部に形成したタイヤが提案され、この提案は偏摩耗改善に著しく貢献している。
【０００４】
段差陸部の機能は、荷重負荷の下で転動するタイヤのトレッド部の接地面内にて、段差陸部の表面を路面に対して滑り接触させ、これにより車両の進行方向とは逆方向の周方向せん断力、いわばブレーキングフォースを段差陸部に集中させ、段差陸部を偏摩耗犠牲部とする働きにある。これにより、段差陸部をもたない周方向溝縁に生じていたブレーキングフォースによる局所摩耗発生、すなわちリバーウエアなどの偏摩耗発生を阻止するか、又は軽微なものとすることができることになる。以上から明らかなように、段差陸部は、一対の直状の溝又は狭い切込みの間に設ける場合の効果が最も著しく、一対のジグザグ状の溝又は狭い切込みの間に設ける場合がこれに次ぐ効果を発揮する。
【０００５】
偏摩耗発生阻止のためには、段差陸部の表面に成るべく大きなブレーキングフォースを作用させればよく、ブレーキングフォースの大きさは、踏面から段差陸部表面までの段下がり代が或る値に達するまでほぼリニヤに増加するので、ブレーキングフォース増加の範囲内で、踏面から段差陸部表面までの段下がり代を成るべく大きく設定しているのが現状である。
【０００６】
【発明が解決しようとする課題】
しかし、積載／非積載の頻度及び発進加速・停止の頻度が共に低く、かつ、車両の直進走行乃至直進に近い、いわゆる定常走行の時間割合が著しく多く、非定常走行時間の割合が少ない車両に装着する空気入りタイヤとしては、上述した段差陸部は顕著に優れた耐偏摩耗性を発揮する反面、例えば、地場トラック、路線バス、荷物配送トラックなどの車両のように、上記のような定常走行時間の割合が比較的少なく、却って非定常走行時間の割合が多く、この場合は必然的に旋回走行の割合も増え、タイヤへの横方向入力頻度が多い走行を行う車両に装着するタイヤとして、上述した段差陸部を備えるタイヤでは、十分な耐摩耗性が得られないことが分かった。
【０００７】
元来、先に述べたリバーウエア偏摩耗や、この種の偏摩耗は、上記した定常走行を主とする走行において顕著に現れる症状であり、よって、これまでの段差陸部は、トレッド部の周方向偏摩耗犠牲部としての諸元が最重要視され、タイヤ回転軸方向（横方向）の諸元に対する配慮、主として横方向剛性に対する配慮が殆どなされていないため、車両旋回に伴うタイヤへの横方向入力が厳しい使用条件の下では、段差陸部の摩耗仕事量が、段差陸部周囲の陸部（リブ、ブロック、ラグなど）の摩耗仕事量に比し減少し勝ちである。ここに摩耗仕事量とは、単位面積当りの接地圧（kgf/mm²）と滑り量（mm）との積に定数を掛け合わせた値である。
【０００８】
その結果、或る程度走行が進んだタイヤの段差陸部の表面が、陸部を形成する踏面から突出する、という現象が見られる。この段差陸部の突出は、耐摩耗性の点で不利である他に、耐偏摩耗性の点でも不利益をもたらす。また、かように横方向入力が厳しいタイヤ使用条件の下では、ブレーキングフォース作用の結果として捉えられるトレッド部周方向引きずり成分による偏摩耗は発生し難いため、段差陸部本来の偏摩耗犠牲部としての役割を果たす機会が、定常走行における機会に比しより少なくなるのは止むを得ないところであり、よって、全体としてみて、段差陸部が耐摩耗性向上に貢献する度合いが大幅に減少しているのが現状である。
【０００９】
そうかといって、全ての段差陸部の表面幅を大幅に広げ、段差陸部の横方向剛性を向上させれば、横方向入力が厳しいタイヤ使用条件の下では耐摩耗性向上に有利である反面、偏摩耗犠牲部としての段差陸部のトレッドゴムに占める体積割合が大幅に増加し、耐摩耗性を支配する、段差陸部を除く実際上の陸部の体積割合が大幅に減少するので、直進走行乃至直進走行に近い走行条件の下で、要求される耐摩耗性（トレッドゴムの摩耗寿命）を確保できない不利を併せもつ。
【００１０】
従ってこの発明の請求項１〜５に記載した発明は、直進走行乃至直進走行に近い走行条件では偏摩耗の発生を抑制し、横方向入力が厳しい走行条件ではトレッドゴムの耐摩耗性を向上させることができ、二つの走行条件での使用に対し、耐偏摩耗性と耐摩耗性との双方を同時に向上させた、汎用性に富む空気入りタイヤを提供することが目的である。
【００１１】
【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、トレッド部に、踏面周方向に連続して延びる一対の、溝又は狭い切込みによりトレッドゴム陸部から離隔され、踏面からの段下がり表面をもつ複数本の段差陸部を備え、該段差陸部は、その表面がタイヤの荷重負荷転動下で路面との間で滑り接触する偏摩耗犠牲部を形成して成る空気入りタイヤにおいて、
上記段差陸部の、踏面から段下がり表面までの段下がり代及び表面幅に関し、複数本の段差陸部相互間で、一方の段差陸部の段下がり代が、他方の段差陸部の段下がり代に比しより小さく、かつ、一方の段差陸部の表面幅が、他方の段差陸部の表面幅に比しより広い関係を有することを特徴とする空気入りタイヤである。
【００１２】
請求項１に記載した発明は、実際上、請求項２に記載した発明のように、前記一方の段差陸部及び他方の段差陸部双方における段下がり代が０．１〜３．０ｍｍの範囲内にあり、前記一方の段差陸部及び他方の段差陸部双方における段下がり表面幅が５．０〜３０．０ｍｍの範囲内にあるのが適合する。
【００１３】
また、一方の段差陸部と他方の段差陸部とを分けた状態では、請求項３に記載した発明のように、前記一方の段差陸部の段下がり代が０．１〜１．５ｍｍの範囲内にあり、前記他方の段差陸部の段下がり代が０．５〜３．０ｍｍの範囲内にあり、
前記段差陸部の表面幅に関し、一方の段差陸部の表面幅が１０．０〜３０．０ｍｍの範囲内にあり、他方の段差陸部の表面幅が５．０〜１５．０ｍｍの範囲内にあるのが適合する。
【００１４】
ここで、特に、段差陸部の段下がり代及び表面幅は、１９９８ＪＡＴＭＡＹＥＡＲＢＯＯＫ（ＪＡＴＭＡ規格という）に記載された、タイヤ種類毎の適用リムにタイヤを組付け、タイヤとリムとの組立体に、ＪＡＴＭＡ規格が定める最高空気圧を充てんしたタイヤで測定するものとする。なお、適用リムは、ＪＡＴＭＡ規格に記載されているように、標準リムと許容リムとを含む。
【００１５】
一方の段差陸部と他方の段差陸部とのトレッド部への配置に関しては、タイヤの種類により二通りの場合が存在し、まず、その一は、請求項４に記載した発明のように、トレッド部中央領域に１本以上の前記一方の段差陸部を有し、トレッド部中央領域の両側領域にそれぞれ１本以上の前記他方の段差陸部を有するタイヤとする。
【００１６】
次に、その二は、請求項５に記載した発明のように、トレッド部中央領域に１本以上の前記他方の段差陸部を有し、トレッド部中央領域の両側領域にそれぞれ１本以上の前記一方の段差陸部を有するタイヤとする。
【００１７】
ここに、トレッド部中央領域とは、タイヤ赤道面を挟む両側それぞれに、踏面幅を３等分した１／３幅を等分に振り分けた領域を指し、トレッド部の両側領域とは、中央領域の両側に位置し、踏面幅の１／３幅を有する領域である。トレッド部がラウンドショルダ乃至面取り状ショルダの場合は、タイヤ断面にて、バットレスの延長線と、踏面輪郭線の延長線との交点相互間距離を踏面幅と定める。
【００１８】
【発明の実施の形態】
以下、この発明の実施の形態例を図１〜図６に基づき説明する。
図１は、この発明の空気入りタイヤの回転軸線を含む平面による断面図であり、
図２は、図１に示す空気入りタイヤの踏面展開図であり、
図３は、図２に示す踏面展開図のIII −III 線に沿う拡大断面図であり、
図４は、図２に示す踏面展開図のIV−IV線に沿う拡大断面図であり、
図５は、図２に示す踏面展開図のV −V 線に沿う拡大断面図であり、
図６は、図１に示すタイヤとは別の段差陸部を有する空気入りタイヤの図２同様に示すIV−IV線に沿う拡大断面図である。
【００１９】
図１において、空気入りタイヤは、トレッド部１と、トレッド部１の両側に連なる一対のサイドウォール部２及びビード部３とを有し、これら各部１、２、３を補強するため、各ビード部３内部に埋設したビードコア４相互間にわたり延びるカーカス５と、さらにトレッド部１を強化するベルト６とを備え、トレッド部１はベルト６の外周側にトレッドゴム７を有する。カーカス５は１プライ以上、図示例は１プライのラジアル配列スチールコードのゴム被覆プライを有し、ベルト６は２層以上、図示例は４層のスチールコード層を有する。
【００２０】
図１〜図５を合わせ参照し、トレッド部１は、踏面１ｔ周方向に連続して延びる一対の溝又は狭い切込み１０、１１と、一対の狭い切込み又は溝１２及び溝１３と、一対の狭い切込み又は溝１４及び溝１５とを有し、トレッド部１は、
一対の溝又は狭い切込み１０、１１により、トレッドゴム７の陸部７Ｌ₁、７Ｌ₂から離隔され、踏面１ｔからの段下がり表面２０ｓをもつ段差陸部２０と、
一対の狭い切込み又は溝１２及び溝１３により、トレッドゴム７の陸部７Ｌ₁、７Ｌ₃から離隔され、踏面１ｔからの段下がり表面２１ｓをもつ段差陸部２１と、そして
一対の狭い切込み又は溝１４及び溝１５により、トレッドゴム７の陸部７Ｌ₂、７Ｌ₄から離隔され、踏面１ｔからの段下がり表面２２ｓをもつ段差陸部２２との複数本（図示例は３本）の段差陸部を備える。
【００２１】
これら段差陸部２０、２１、２２の表面２０ｓ、２１ｓ、２２ｓは、タイヤの荷重負荷転動の下で路面との間で接触すると共に、路面との間で不可避的に発生する踏面１ｔ周方向のタイヤ進行方向とは逆方向のせん断力、換言すればブレーキングフォースの作用を受け、路面に対し滑り接触し、それ故に、段差陸部２０、２１、２２は、他の陸部７Ｌ₁、７Ｌ₂、７Ｌ₃、７Ｌ₄に生じる筈の偏摩耗を肩代わりする偏摩耗犠牲部の役目を果たす。
【００２２】
ここで、図３〜図５において、複数本の段差陸部２０、２１、２２の、踏面１ｔの端縁から段下がり表面２０ｓ、２１ｓ、２２ｓまでの段下がり代ｄ₂₀（ｍｍ）、ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）と、タイヤ回転軸方向の段下がり表面２０ｓ、２１ｓ、２２幅ｗ₂₀（ｍｍ）、ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）とに関し、一方の段差陸部２０と、他方の段差陸部２１、２２との二つのグループに分け、これら二つのグループ相互間で、
一方の段差陸部２０の段下がり代ｄ₂₀（ｍｍ）が、他方の段差陸部２１、２２の段下がり代ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）に比しより小さく、かつ、
一方の段差陸部２０の表面２０ｓ幅ｗ₂₀（ｍｍ）が、他方の段差陸部２１、２２の表面２１ｓ、２２幅ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）に比しより広い、
という関係を満たすものとする。
【００２３】
これらの相互関係をより一層明確にするため書換えれば、
段差陸部の段下がり代ｄについては、
ｄ₂₀（ｍｍ）＜ｄ₂₁（ｍｍ）、ｄ₂₀（ｍｍ）＜ｄ₂₂（ｍｍ）であり、
段差陸部の表面幅ｗについては、
ｗ₂₀（ｍｍ）＞ｗ₂₁（ｍｍ）、ｗ₂₀（ｍｍ）＞ｗ₂₂（ｍｍ）である、
ということである。
なお、通常は、ｄ₂₁（ｍｍ）＝ｄ₂₂（ｍｍ）又はｄ₂₁（ｍｍ）≒ｄ₂₂（ｍｍ）とし、ｗ₂₁（ｍｍ）＝ｗ₂₂（ｍｍ）又はｗ₂₁（ｍｍ）≒ｗ₂₂（ｍｍ）とし、特別なケースで、ｄ₂₁（ｍｍ）≠ｄ₂₂（ｍｍ）、ｗ₂₁（ｍｍ）≠ｗ₂₂（ｍｍ）としても良い。
【００２４】
さて、研究成果を纏めた、段差陸部の段下がり代ｄとブレーキングフォースとの関係を線図として示す図７と、段差陸部の表面幅ｗとブレーキングフォースとの関係を線図として示す図８とから、段下がり代ｄをゼロから或る値ｄmax まで増加させる間にブレーキングフォースは単純に増加し、値ｄmax を超えて段下がり代ｄを増加させると、ブレーキングフォースはその最大値ＢＦmax から急激に低下し、これに対し、段差陸部表面幅ｗをほぼゼロに近い値から増加させるとブレーキングフォースは、サチュレート傾向を示しながら増加することが分かる。これらの事実は、要するに、段差陸部に生じさせるブレーキングフォースの大きさは、値ｄmax 以下の段下がり代ｄと、段差陸部表面幅ｗとの組み合わせで容易に制御することができることを意味している。
【００２５】
この事柄を別の研究成果として、段差陸部のトレッド部１周方向摩耗仕事量をパラメータとして、段差陸部の段下がり代ｄと表面幅ｗとの相互関係を纏めたところ、図９に示す線図が得られた。図９に示す線図から、同一周方向摩耗仕事量を段差陸部に課すための段差陸部の段下がり代ｄと表面幅ｗとの組み合わせは無数に存在することが分かる。
【００２６】
さらに、段差陸部の段下がり代ｄを一定とし、段差陸部の表面幅ｗと段差陸部の横方向（タイヤ回転軸方向）剛性との関係を線図として示す図１０から、表面幅ｗを増加させると、ほぼリニヤに段差陸部の横方向剛性が増加することが分かっている。
【００２７】
図７〜図１０に示す線図群を合わせ考慮すると、段差陸部２０の段差陸部の表面幅ｗ₂₀（ｍｍ）を、段差陸部２１、２２の表面幅ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）より広くとり、その代わりに、段差陸部２０の段下がり代ｄ₂₀（ｍｍ）を、段差陸部２１、２２の段下がり代ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）より小さくとっても、段差陸部２０における、ブレーキングフォースの大きさと、周方向摩耗仕事量の大きさとを、段差陸部２１、２２のそれらとほぼ同じにすることが可能となり、その結果、一対の溝又は狭い切込み１０、１１における耐偏摩耗性は、一対の狭い切込み又は溝１２及び溝１３及び一対の狭い切込み又は溝１４及び溝１５の耐偏摩耗性と同等に高度に保持することができる。
【００２８】
その一方で、段差陸部２０の表面幅をｗ₂₀（ｍｍ）を、段差陸部２１、２２の表面幅ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）より広くとることにより、段差陸部２０の横方向剛性が、段差陸部２１、２２の横方向剛性より高めることができるので、車両旋回時にタイヤに発生するサイドフォースに対し、一方の段差陸部２０は十分に対抗し、逃げることが少なくなり、その結果、サイドフォースの作用下で、少なくとも段差陸部２０は、その周囲の陸部７Ｌ₁、７Ｌ₂に合わせて適度に摩耗し、従来タイヤのように、段差陸部が突出する不具合が生じることはなく、しかも適度な段下がり代を確保することができ、優れた耐偏摩耗性を保持することができる。
【００２９】
よって、一方の段差陸部２０は大きなサイドフォースの作用領域に配置し、より小さなサイドフォースの作用領域に他方の段差陸部２１、２２を配置することにより、サイドフォースの作用による段差陸部２１、２２の突出は抑制され、段差陸部２１、２２本来の偏摩耗抑制機能を十分に発揮させることができ、さらに段差陸部２０、２１、２２の合計幅（ｗ₂₀＋ｗ₂₁＋ｗ₂₂）をそれほど広くとる必要はなく、トレッドゴム７の耐摩耗性も優位に保持することができる。
【００３０】
上記したところは、一方の段差陸部２０と、他方の段差陸部２１、２２との二つのグループに分けて説明したが、三つ以上のグループに分け、例えば一方の段差陸部２０を第一の段差陸部２０、他方の段差陸部２１、２２を第二の段差陸部２１、第三の段差陸部２１のよう呼び、第一の段差陸部２０と第二の段差陸部２１との相互間、第一の段差陸部２０と第三の段差陸部２２との相互間、第二の段差陸部２１と第三の段差陸部２２との相互間で、前記の段下がり代ｄ関係、前記の幅ｗ関係を満たすようにすることを可とする。勿論、第四以上の段差陸部を設けることを可とする。
【００３１】
図１〜図５に示すタイヤは、先に詳述したような相互関係をもつ、段下がり代ｄ₂₀（ｍｍ）、ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）と、表面幅ｗ₂₀（ｍｍ）、ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）とをもつ段差陸部２０、２１、２２につき、図１に示すように、両方の踏面端ＴＥ間距離である踏面幅Ｗを３等分した幅１／３Ｗをタイヤ赤道面Ｅの両側に均等に振り分けたトレッド部１中央領域Ｒｃ（図２の展開図ではＲｃｄで示す）に一方の段差陸部２０を有し、幅１／３Ｗ宛のトレッド部１両側領域Ｒｓ（図２の展開図ではＲｓｄで示す）にそれぞれ他方の段差陸部２１、２２を有するものである。このタイヤは比較的大きなサイドフォースが比較的高頻度で発生する非定常走行を行う使用条件の使用下でトレッドゴム７の耐偏摩耗性に優れ、定常走行下での耐摩耗性に優れる特徴を有する。
【００３２】
図示は省略したが、トレッド部１の中央領域Ｒｃに段差陸部２１又は段差陸部２２を１本以上備え、両側領域Ｒｓそれぞれに段差陸部２０を備えるタイヤも可とし、このタイヤは、接地圧分布がいわゆる蝶々型分布を有し、主として定常走行を行う使用条件下で、優れた耐偏摩耗性と優れた耐摩耗性とを兼ね備えるタイヤとして適合する。なお、先に述べたタイヤは、接地圧分布が、蝶々型分布をなすタイヤと、いわゆる樽型分布をなすタイヤの両者に適合する。
【００３３】
以上は両極端な使用条件下での段差陸部配分について述べたが、段下がり代ｄ₂₀（ｍｍ）、ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）と、表面幅ｗ₂₀（ｍｍ）、ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）とを、以下に述べるように適正な値の範囲内で設定すれば、殆ど全ての使用条件の下で、耐偏摩耗性と耐摩耗性との兼ね合いを最良の状態とすることが可能なタイヤを得ることができる。
【００３４】
まず、一方の段差陸部２０及び他方の段差陸部２１、２２の両者は、段下がり代ｄ₂₀（ｍｍ）、ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）は０．１〜３．０ｍｍの範囲内であること、そして、表面幅ｗ₂₀（ｍｍ）、ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）は５．０〜３０．０ｍｍの範囲内である、ということである。
【００３５】
段下がり代ｄ₂₀（ｍｍ）、ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）は、３．０ｍｍを超えると、荷重負荷転動下のタイヤの接地面で段差陸部２０、２１、２２の表面が路面と接触しなくなるうれいが生じる。なお、下限値は、直進走行乃至直進に近い走行が進むと、段下がり代ｄ₂₀（ｍｍ）、ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）は増加する傾向を有するのでほぼゼロに近い値（０．１ｍｍ）で十分である。
【００３６】
表面幅ｗ₂₀（ｍｍ）、ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）は、５．０ｍｍ未満では、ブレーキングフォースが小さ過ぎて耐偏摩耗性が低下し、合わせて、横方向剛性が小さくなり過ぎ、コーナリングの繰り返しで踏面１ｔから突出し、３０．０ｍｍを超えると段差陸部の横方向剛性は増加するが、直進走行乃至直進に近い走行での耐摩耗性には殆ど寄与しないトレッドゴム７部分が増加し過ぎるため、トレッドゴム７の摩耗寿命が低下するので、いずれも不可である。
【００３７】
段下がり代ｄ₂₀（ｍｍ）、ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）と、表面幅ｗ₂₀（ｍｍ）、ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）とを一方の段差陸部２０と他方の段差陸部２１、２２とに分けるとき、段差陸部２０の段下がり代ｄ₂₀（ｍｍ）は、０．１〜１．５ｍｍの範囲内であり、段差陸部２１、２２の段下がり代ｄ₂₁（ｍｍ）、ｄ₂₂（ｍｍ）は０．５〜３．０ｍｍの範囲内が適合する。また、段差陸部２０の表面幅ｗ₂₀（ｍｍ）は、１０．０〜３０．０ｍｍの範囲内であり、段差陸部２１、２２の表面幅ｗ₂₁（ｍｍ）、ｗ₂₂（ｍｍ）は、５．０〜１５．０ｍｍの範囲内が適合する。
【００３８】
図６に示す段差陸部２１は、図４に示す段差陸部２１の変形例であり、狭い切込み溝１２の幅に比しより幅が広い溝１３側に面取り部２１ｐを有する。面取り部２１ｐを備える段差陸部２１の表面幅ｗ₂₁（ｍｍ）は、図示のように、面取り部２１ｐ側の基準を面取り部２１ｐ下端とする。この種のタイヤは砂利などが点在乃至散在する路面を走行する機会があるため、特に、溝１３に小石を噛み込むことがあり、そのため小石などの異物が溝１３に噛み込み難くするための面取り部２１ｐである。この面取り部２１ｐと同様な面取り部を対向する段差陸部２２にも設ける。
【００３９】
以上述べた、一対の溝又は狭い切込み１０、１１と、一対の狭い切込み又は溝１２及び溝１３と、一対の狭い切込み又は溝１４及び溝１５とは直状であるが、振幅がちいさなジグザグ状としても良い。なお、図２に示す符号Ｓ₁は長いサイプであり、符号Ｓ₂は極く短いサイプである。陸部７Ｌ₁、７Ｌ₂は、全体としてリブであるが、サイプＳ₁によりブロック状に区画されている。
【００４０】
【実施例】
トラック及びバス用ラジアルプライタイヤで、サイズは２９５／７５Ｒ２２．５（チューブレスタイヤ）であり、構成は図１〜図３及び図５、６に示すところに従い、カーカス５は１プライのラジアル配列スチールコードのゴム被覆プライになり、ベルト６は、４層のゴム被覆チールコード層からなる。
【００４１】
トレッド部１は、中央領域Ｒｃに１本の段差陸部２０と、両側領域Ｒｓにそれぞれ１本の段差陸部２１、２２とを備え、段差陸部２０の段下がり代ｄ₂₀は０．５ｍｍ、表面幅ｗ₂₀は２０ｍｍであり、段差陸部２１、２２の段下がり代ｄ₂₁、ｄ₂₂は２．５ｍｍであり、表面幅ｗ₂₁、ｗ₂₂は面取り部下端基準で５．０ｍｍである。また、一対の溝又は狭い切込み１０、１１の深さＤ₁（図３参照）は１４．５ｍｍであり、一対の狭い切込み又は溝１２及び溝１３の深さＤ₂（図４参照）と、一対の狭い切込み又は溝１４及び溝１５の深さＤ₃（図５参照）とは共に１４．５ｍｍである。
【００４２】
実施例の比較対象として、図１１に踏面展開図を示すトレッドパターンを備える比較例タイヤを準備した。比較例タイヤのトレッド部は、中央領域Ｒｃ（展開図ではＲｃｄ領域）に２本の周方向直状溝３０、３１を備え、両側領域Ｒｓ（展開図ではＲｃｄ領域）に、一対の狭い切込み３２及び溝３３により離隔される段差陸部３４と、一対の狭い切込み３５及び溝３６により離隔される段差陸部３７とを有し、段差陸部３４及び段差陸部３７は同一諸元を有し、段下がり代ｄが２．５ｍｍ、面取り部下端基準の表面幅ｗが９．０ｍｍである。上記した以外の構成及び諸元は全て実施例に合わせた。
【００４３】
以上の実施例タイヤ及び比較例タイヤと、トレッド部が、段差陸部をもたず、比較例タイヤと同じ周方向直状溝３０、３１をそれぞれ２本宛（合計４本）備える比較例タイヤとほぼ同じトレッドパターンを有する従来例タイヤとを、以下の二種の異なる使用条件のユーザで実地試験に供した。
【００４４】
（１）偏摩耗の度合いが著しく、溝乃至狭い切込みに沿うリバーウエアが陸部に進展し、遂には陸部にリブパンチと呼ばれる最も著しい偏摩耗がしばしば発生するユーザ。
（２）或る程度の偏摩耗は発生するが、リブパンチなどの著しい偏摩耗には至らないユーザ。
【００４５】
試験結果の纏めを以下に記す。
（１）項に記載したユーザ試験結果（指数であらわす。値は大なるほど良い）；
トレッドゴム摩耗により取り外すまでに走行した距離（指数表示）；
実施例タイヤは比較例タイヤの指数１００に対し１１５であり、従来例タイヤは７５に止まる。その内容は、実施例タイヤには偏摩耗が殆ど発生せず、これに対し比較例タイヤは、トレッド部中央領域で著しいリブパンチが発生し、かつ、両側領域では早期摩耗が生じていた。
なお、偏摩耗の度合いが或る程度進むと、タイヤは棄却されるのが通例であり、この棄却限界に至るまで使用したトレッドゴム厚さ（溝などの深さ）でみると、比較例タイヤ１００に対し実施例タイヤは１１５、従来例タイヤは６０である。
【００４６】
（２）項に記載したユーザ試験結果（指数であらわす。値は大なるほど良い）；
実施例タイヤは比較例タイヤと同じく偏摩耗が殆ど発生せず、トレッドゴム１ｍｍ摩耗当りの走行距離でみる耐摩耗性の指数は両者共に１００である。従来例タイヤの耐摩耗性は８５に止まった。なお、実施例タイヤのトレッド部１中央領域Ｒｃの段差陸部２０は、段下がり代ｄ₂₀はほぼゼロとなり、偏摩耗犠牲部ではなく、一種のリブ（完全な陸部）として耐摩耗性向上に大きく寄与していることが分かった。
【００４７】
【発明の効果】
この発明の請求項１〜５に記載した発明によれば、直進走行乃至直進走行に近い定常走行を主とする使用条件では偏摩耗の発生を抑制して使用限界距離を伸ばし、横方向入力が厳しい非定常走行を主とする走行条件ではトレッドゴムの耐偏摩耗性及び耐摩耗性を向上させることができ、二種の異なる走行条件での使用に対し、耐偏摩耗性と耐摩耗性との双方を同時に向上させた、汎用性に富む長寿命の空気入りタイヤを提供することができる。
【図面の簡単な説明】
【図１】この発明の一実施形態例の空気入りタイヤの断面図である。
【図２】図１に示すタイヤの踏面展開図である。
【図３】図２に示すIII − III線に沿う断面図である。
【図４】図２に示すIV− IV 線に沿う断面図である。
【図５】図２に示すV − V線に沿う断面図である。
【図６】図４に示す段差陸部の変形例の断面図である。
【図７】段差陸部の段下がり代とブレーキングフォースとの関係を示す線図である。
【図８】段差陸部の表面幅とブレーキングフォースとの関係を示す線図である。
【図９】段差陸部の段下がり代と表面幅との関係線図である。
【図１０】段差陸部の表面幅と横方向剛性との関係を示す線図である。
【図１１】比較例タイヤの踏面展開図である。
【符号の説明】
１トレッド部
１ｔ踏面
２サイドウォール部
３ビード部
４ビードコア
５カーカス
６ベルト
７トレッドゴム
７Ｌ₁、７Ｌ₂、７Ｌ₃、７Ｌ₄ 陸部
１０、１１一対の溝
１２、１３一対の狭い切込みと溝
１４、１５一対の狭い切込みと溝
２０一方の段差陸部
２０ｓ段差陸部表面
２１、２２他方の段差陸部
２１ｓ、２２ｓ段差陸部表面
２１ｐ面取り部
Ｅタイヤ赤道面
ＴＥ踏面端
Ｒｃトレッド部中央領域
Ｒｓトレッド部両側領域
Ｒｃｄ中央領域の展開幅
Ｒｓｄ両側領域の展開幅
ｄ₂₀、ｄ₂₁、ｄ₂₂ 段差陸部の段下がり代
ｗ₂₀、ｗ₂₁、ｗ₂₂ 段差陸部の表面幅
Ｓ₁ 長いサイプ
Ｓ₂ 短いサイプ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to pneumatic tires, and more particularly to radial ply tires for small trucks, trucks, buses, and the like, and in particular, achieves both improvement in uneven wear resistance and improvement in wear resistance of tire tread rubber. Related to pneumatic tires.
[0002]
[Prior art]
Radial ply tires (hereinafter referred to as pneumatic tires or tires) used for heavy vehicles such as small trucks, trucks, and buses, which are relatively heavy vehicles, circulate around the tread surface and continuously. It is common to provide a circumferential groove extending in the tread portion. In a pneumatic tire having such a circumferential groove in the tread portion, along the circumferential groove edge, uneven wear called river wear or railway wear is provided. However, sometimes this type of uneven wear develops to cause uneven wear defects called rib punches in the tread rubber land between the circumferential grooves adjacent to each other. Such uneven wear not only significantly shortens the wear life of the tread rubber, but also significantly impairs the steering stability and vibration ride comfort of the vehicle. It is well known that a tire having a straight circumferential groove is most disadvantageous against uneven wear.
[0003]
In order to improve this kind of uneven wear, the tread rubber of the tread portion is provided with a pair of grooves, a pair of grooves and a narrow cut, a pair of narrow cuts, etc. that continuously extend in the tread surface circumferential direction. A tire is proposed in which a plurality of stepped land portions separated from the tread rubber land portion and having a step-down surface from the tread are formed in the tread portion by cutting, and this proposal contributes significantly to the improvement of uneven wear.
[0004]
The function of the step land portion is to slide the surface of the step land portion against the road surface in the contact surface of the tread portion of the tire that rolls under a load. The circumferential shear force, or so-called braking force, is concentrated on the step land portion, and the step land portion serves as a partial wear sacrifice portion. As a result, it is possible to prevent the occurrence of local wear due to the braking force generated at the circumferential groove edge having no step land portion, that is, the occurrence of uneven wear such as river wear or the like. . As is clear from the above, the step land portion is most effective when provided between a pair of straight grooves or narrow cuts, followed by a case where the step land is provided between a pair of zigzag grooves or narrow cuts. Demonstrate the effect.
[0005]
In order to prevent the occurrence of uneven wear, it is only necessary to act as large a braking force as possible on the surface of the stepped land portion. The size of the braking force has a step-down margin from the tread surface to the surface of the stepped land portion. Since it increases almost linearly until it reaches the value, the step-down margin from the tread to the step land surface is set as large as possible within the range of the braking force increase.
[0006]
[Problems to be solved by the invention]
However, the frequency of loading / unloading and the frequency of starting acceleration / stopping are both low, and the vehicle has a remarkably large time ratio of so-called steady running, which is close to straight running or straight running, and a low percentage of unsteady running time. As the pneumatic tires to be mounted, the above-mentioned stepped land portion exhibits remarkable uneven wear resistance, but on the other hand, for example, a vehicle such as a local truck, a route bus, a luggage delivery truck, etc. As a tire to be mounted on a vehicle that travels with a high frequency of lateral input to the tire, the proportion of unsteady travel time is relatively high, and in this case, the rate of turning travel is inevitably increased. It has been found that sufficient abrasion resistance cannot be obtained with a tire having the above-mentioned step land portion.
[0007]
Originally, the river wear uneven wear described above and this kind of uneven wear are symptoms that are prominently observed in the above-mentioned traveling mainly in steady running. The specifications as the circumferential uneven wear sacrificial part are regarded as the most important, and consideration is not given to the specifications in the tire rotation axis direction (lateral direction), mainly to the lateral rigidity. Under severe conditions of lateral input, the wear work of the step land is likely to decrease compared to the wear work of the land (ribs, blocks, lugs, etc.) around the step land. Here, the work of wear is the contact pressure per unit area (kgf / mm ² ) And the amount of slip (mm) multiplied by a constant.
[0008]
As a result, there is a phenomenon that the surface of the stepped land portion of the tire that has traveled to some extent protrudes from the tread that forms the land portion. The protrusion of the step land portion is disadvantageous in terms of wear resistance and also in terms of uneven wear resistance. Also, under tire usage conditions where the lateral input is severe, uneven wear due to the circumferential drag component of the tread that is captured as a result of the braking force action is unlikely to occur. It is inevitable that there will be fewer opportunities to play a role as a regular driving opportunity, and as a whole, the degree to which the step land contributes to wear resistance is greatly reduced. This is the current situation.
[0009]
However, if the surface width of all the step land portions is greatly expanded and the lateral rigidity of the step land portions is improved, it is advantageous for improving the wear resistance under tire use conditions where the lateral input is severe. On the other hand, the volume ratio of the stepped land as the uneven wear sacrificial part to the tread rubber is greatly increased, and the volume ratio of the actual land part excluding the stepped land that controls the wear resistance is greatly decreased. In addition, there is a disadvantage that the required wear resistance (the wear life of the tread rubber) cannot be ensured under the straight running or the running condition close to the straight running.
[0010]
Therefore, the invention described in claims 1 to 5 of the present invention suppresses the occurrence of uneven wear under a straight running or a running condition close to the straight running, and improves the wear resistance of the tread rubber under a running condition in which the lateral input is severe. Therefore, it is an object to provide a versatile pneumatic tire in which both uneven wear resistance and wear resistance are simultaneously improved for use under two driving conditions.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 of the present invention is separated from the tread rubber land portion by a pair of grooves or narrow notches extending continuously in the tread portion in the circumferential direction of the tread portion. A plurality of stepped land portions having a stepped surface, and the stepped land portions are formed by forming an uneven wear sacrificial portion in which the surface slides into contact with the road surface under the rolling load of the tire. In the tire,
Regarding the step allowance from the tread surface to the stepped surface and the surface width of the above step land portion, the step allowance of one step land portion is the step difference of the other step land portion between the plurality of step land portions. It is a pneumatic tire characterized in that it has a smaller relationship than the surface, and the surface width of one step land portion is wider than the surface width of the other step land portion.
[0012]
The invention described in claim 1 is, as in the invention described in claim 2, practically, the step allowance in both the one step land portion and the other step land portion is in the range of 0.1 to 3.0 mm. It is suitable that the stepped surface width in both the one step land portion and the other step land portion is in the range of 5.0 to 30.0 mm.
[0013]
Moreover, in the state which divided | segmented one level | step difference land part and the other level | step difference land part, like the invention described in Claim 3, the step-down allowance of said one level | step difference land part is 0.1-1.5 mm. Within the range, the stepped margin of the other step land portion is in the range of 0.5 to 3.0 mm,
Regarding the surface width of the step land portion, the surface width of one step land portion is in the range of 10.0 to 30.0 mm, and the surface width of the other step land portion is in the range of 5.0 to 15.0 mm. It is suitable to be in
[0014]
Here, in particular, the step-down allowance and the surface width of the step land portion are described in 1998 JATMA YEAR BOOK (referred to as JATMA standard). In addition, it shall be measured with a tire filled with the maximum air pressure defined by the JATMA standard. The applicable rim includes a standard rim and an allowable rim as described in the JATMA standard.
[0015]
Regarding the arrangement of the one step land portion and the other step land portion in the tread portion, there are two cases depending on the type of tire. First, as one of the inventions described in claim 4, A tire having one or more one step land portions in the tread portion central region and one or more other step land portions in both side regions of the tread center region.
[0016]
Next, as for the 2nd, it has one or more said other level | step difference land parts in the tread part center area | region, and 1 or more each in the both-sides area | region of a tread part center area | region like invention of Claim 5. The tire has the one step land portion.
[0017]
Here, the central region of the tread portion refers to a region in which the tread width is divided into three equal parts and divided into three equal parts on both sides of the tire equatorial plane. Is a region having a width of 1/3 of the tread width. When the tread portion is a round shoulder or a chamfered shoulder, the distance between the intersection points of the buttress extension line and the tread outline extension line is defined as the tread width in the tire cross section.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS.
FIG. 1 is a cross-sectional view of a plane including a rotation axis of the pneumatic tire of the present invention,
FIG. 2 is a development view of the tread of the pneumatic tire shown in FIG.
3 is an enlarged cross-sectional view taken along the line III-III of the tread development shown in FIG.
4 is an enlarged cross-sectional view taken along line IV-IV of the tread development shown in FIG.
FIG. 5 is an enlarged sectional view taken along line V-V of the tread development view shown in FIG.
6 is an enlarged cross-sectional view taken along the line IV-IV shown in the same manner as FIG. 2 of the pneumatic tire having a step land portion different from the tire shown in FIG.
[0019]
In FIG. 1, the pneumatic tire has a tread portion 1 and a pair of sidewall portions 2 and bead portions 3 connected to both sides of the tread portion 1. A carcass 5 extending between the bead cores 4 embedded in the portion 3 and a belt 6 that reinforces the tread portion 1 are provided. The tread portion 1 has a tread rubber 7 on the outer peripheral side of the belt 6. The carcass 5 has at least one ply, the illustrated example has a rubber-coated ply of a one-ply radial arrangement steel cord, the belt 6 has two or more layers, and the illustrated example has four steel cord layers.
[0020]
1 to 5, the tread portion 1 includes a pair of grooves or narrow notches 10 and 11 continuously extending in the circumferential direction of the tread surface 1 t, a pair of narrow notches or grooves 12 and a groove 13, and a pair of narrow It has notches or grooves 14 and grooves 15, and the tread portion 1
A land portion 7L of the tread rubber 7 by a pair of grooves or narrow notches 10, 11 ₁ 7L ₂ A step land portion 20 having a step-down surface 20s separated from the tread 1t,
The land portion 7L of the tread rubber 7 is formed by a pair of narrow cuts or grooves 12 and 13. ₁ 7L _Three A step land portion 21 having a step-down surface 21s separated from the tread surface 1t, and
The land portion 7L of the tread rubber 7 is formed by a pair of narrow cuts or grooves 14 and 15. ₂ 7L _Four A plurality of (three in the illustrated example) step land portions with the step land portion 22 having a step-down surface 22s from the tread 1t.
[0021]
Surfaces 20s, 21s, and 22s of the step land portions 20, 21, and 22 are in contact with the road surface under the load-bearing rolling of the tire, and the tread surface 1t circumferential direction that is inevitably generated between the road surfaces. Under the action of the shearing force in the direction opposite to the tire traveling direction, in other words, the braking force is applied, and the sliding contact with the road surface is caused. Therefore, the step land portions 20, 21, and 22 are connected to the other land portions 7L. ₁ 7L ₂ 7L _Three 7L _Four It plays the role of a partial wear sacrificial part that replaces the partial wear of the wrinkles.
[0022]
Here, in FIG. 3 to FIG. 5, the step-down allowance d from the edge of the tread surface 1 t to the step-down surfaces 20 s, 21 s, 22 s of the plurality of step land portions 20, 21, 22 is shown. ₂₀ (Mm), d _{twenty one} (Mm), d _{twenty two} (Mm) and stepped surfaces 20s, 21s, 22 width w in the tire rotation axis direction ₂₀ (Mm), w _{twenty one} (Mm), w _{twenty two} (Mm), divided into two groups of one step land portion 20 and the other step land portions 21 and 22, between these two groups,
The step d of the step land 20 ₂₀ (Mm) is the step-down allowance d of the other step land portions 21 and 22 _{twenty one} (Mm), d _{twenty two} Smaller than (mm), and
Surface 20s width w of one step land 20 ₂₀ (Mm) is the surface 21s, 22 width w of the other step land portion 21, 22 _{twenty one} (Mm), w _{twenty two} Wider than (mm),
It shall satisfy the relationship.
[0023]
If you rewrite these interrelationships to make it clearer,
For the step d of the step land,
d ₂₀ (Mm) <d _{twenty one} (Mm), d ₂₀ (Mm) <d _{twenty two} (Mm)
Regarding the surface width w of the step land,
w ₂₀ (Mm)> w _{twenty one} (Mm), w ₂₀ (Mm)> w _{twenty two} (Mm)
That's what it means.
Usually, d _{twenty one} (Mm) = d _{twenty two} (Mm) or d _{twenty one} (Mm) ≒ d _{twenty two} (Mm) and w _{twenty one} (Mm) = w _{twenty two} (Mm) or w _{twenty one} (Mm) ≒ w _{twenty two} (Mm) and in special cases, d _{twenty one} (Mm) ≠ d _{twenty two} (Mm), w _{twenty one} (Mm) ≠ w _{twenty two} (Mm) may be used.
[0024]
Now, FIG. 7 shows the relationship between the step-down margin d of the step land and the braking force as a diagram, and the relationship between the surface width w of the step land and the braking force. As shown in FIG. 8, the braking force simply increases while the step-down allowance d is increased from zero to a certain value dmax, and if the step-down allowance d is increased beyond the value dmax, the braking force is It can be seen that when the step land surface width w is increased from a value close to zero, the braking force increases while showing a saturating tendency. In short, these facts mean that the magnitude of the braking force generated in the step land portion can be easily controlled by the combination of the step-down allowance d below the value dmax and the step land portion surface width w. is doing.
[0025]
FIG. 9 shows the relationship between the step-down allowance d and the surface width w of the step land, using this matter as another research result, using the wear work amount in the circumferential direction of the tread of the step land as a parameter. A diagram was obtained. From the diagram shown in FIG. 9, it can be seen that there are innumerable combinations of the step allowance d and the surface width w of the step land portion for imposing the same circumferential wear work on the step land portion.
[0026]
Furthermore, the step width d of the step land portion is made constant, and the surface width w is shown in FIG. 10 as a diagram showing the relationship between the surface width w of the step land portion and the lateral direction (tire rotation axis direction) rigidity of the step land portion. It is known that the lateral rigidity of the step land portion increases almost linearly when the is increased.
[0027]
The surface width w of the step land portion of the step land portion 20 is considered in combination with the diagram groups shown in FIGS. ₂₀ (Mm) is the surface width w of the step land portions 21 and 22 _{twenty one} (Mm), w _{twenty two} Instead of (mm), instead of the step land d of the step land 20 ₂₀ (Mm) is the step allowance d of the step land portions 21 and 22 _{twenty one} (Mm), d _{twenty two} Even if it is smaller than (mm), it is possible to make the magnitude of the braking force and the amount of circumferential wear work in the step land portion 20 substantially the same as those in the step land portions 21 and 22, and as a result. The uneven wear resistance of the pair of grooves or narrow notches 10 and 11 is maintained at a high level equivalent to the uneven wear resistance of the pair of narrow notches or grooves 12 and 13 and the pair of narrow notches or grooves 14 and 15. be able to.
[0028]
On the other hand, the surface width of the step land portion 20 is set to w. ₂₀ (Mm) is the surface width w of the step land portions 21 and 22 _{twenty one} (Mm), w _{twenty two} Since the lateral rigidity of the step land portion 20 can be increased more than the lateral rigidity of the step land portions 21 and 22 by taking a larger width (mm), one of the side forces generated in the tire when turning the vehicle is The step land portion 20 sufficiently opposes and is less likely to escape. As a result, at least the step land portion 20 has a land portion 7L around it under the action of side force. ₁ 7L ₂ It can be worn moderately according to the tire, and there is no problem that the stepped land part protrudes like conventional tires, and it can secure an appropriate step-down allowance and maintain excellent uneven wear resistance Can do.
[0029]
Accordingly, one step land portion 20 is disposed in the region where the large side force is applied, and the other step land portions 21 and 22 are disposed in the region where the smaller side force is acting, thereby the step land portion 21 due to the side force operation. , 22 can be suppressed, the uneven wear suppression function inherent in the step land portions 21, 22 can be sufficiently exerted, and the total width (w of the step land portions 20, 21, 22) ₂₀ + W _{twenty one} + W _{twenty two} ) Is not required to be so wide, and the wear resistance of the tread rubber 7 can be maintained preferentially.
[0030]
The above description is divided into two groups of one step land portion 20 and the other step land portions 21, 22. However, the step land portion 20 is divided into three or more groups. The first step land portion 20 and the other step land portions 21 and 22 are called the second step land portion 21 and the third step land portion 21, and the first step land portion 20 and the second step land portion 21. Between the first step land portion 20 and the third step land portion 22 and between the second step land portion 21 and the third step land portion 22. It is possible to satisfy the relationship of the cost d and the width w. Of course, it is possible to provide a fourth or more step land portion.
[0031]
The tire shown in FIGS. 1 to 5 has a step-down allowance d having a mutual relationship as described in detail above. ₂₀ (Mm), d _{twenty one} (Mm), d _{twenty two} (Mm) and surface width w ₂₀ (Mm), w _{twenty one} (Mm), w _{twenty two} As shown in FIG. 1, for the step land portions 20, 21, and 22 having (mm), the width 1 / 3W obtained by dividing the tread width W, which is the distance between both tread ends TE, into three equal parts is defined on the tire equatorial plane E. The tread portion 1 central region Rc (indicated by Rcd in the developed view of FIG. 2) equally distributed on both sides has one step land portion 20 and the tread portion 1 both side regions Rs (width of FIG. In the developed view, it is indicated by Rsd) and has the other step land portions 21 and 22 respectively. This tire has excellent uneven wear resistance of the tread rubber 7 under use conditions in which unsteady running in which relatively large side forces are generated at a relatively high frequency, and excellent wear resistance under steady running. Have.
[0032]
Although not shown, a tire including one or more step land portions 21 or step land portions 22 in the central region Rc of the tread portion 1 and step land portions 20 in both side regions Rs is also acceptable. The pressure distribution has a so-called butterfly-type distribution, and is suitable as a tire that has both excellent wear resistance and excellent wear resistance mainly under conditions of steady running. In the tire described above, the contact pressure distribution is suitable for both a tire having a butterfly type distribution and a tire having a so-called barrel type distribution.
[0033]
The above describes the distribution of the step land under extreme extreme conditions. ₂₀ (Mm), d _{twenty one} (Mm), d _{twenty two} (Mm) and surface width w ₂₀ (Mm), w _{twenty one} (Mm), w _{twenty two} If (mm) is set within a range of appropriate values as described below, the balance between uneven wear resistance and wear resistance can be set to the best state under almost all use conditions. Possible tires can be obtained.
[0034]
First, both the step land portion 20 and the other step land portions 21 and 22 have a step-down allowance d. ₂₀ (Mm), d _{twenty one} (Mm), d _{twenty two} (Mm) is within the range of 0.1 to 3.0 mm, and the surface width w ₂₀ (Mm), w _{twenty one} (Mm), w _{twenty two} (Mm) is in the range of 5.0 to 30.0 mm.
[0035]
Step allowance d ₂₀ (Mm), d _{twenty one} (Mm), d _{twenty two} When (mm) exceeds 3.0 mm, there is a joy that the surfaces of the step land portions 20, 21, and 22 do not come into contact with the road surface at the contact surface of the tire under load rolling. It should be noted that the lower limit value is the step-down allowance d when the vehicle travels straight ahead or travels close to straight. ₂₀ (Mm), d _{twenty one} (Mm), d _{twenty two} Since (mm) has a tendency to increase, a value close to zero (0.1 mm) is sufficient.
[0036]
Surface width w ₂₀ (Mm), w _{twenty one} (Mm), w _{twenty two} If (mm) is less than 5.0 mm, the braking force is too small and the uneven wear resistance is lowered. In addition, the lateral rigidity is too small, and the cornering is repeated to protrude from the tread 1t. If exceeded, the lateral rigidity of the stepped land portion increases, but since the portion of the tread rubber 7 that hardly contributes to the wear resistance in straight running or near-straight running increases excessively, the wear life of the tread rubber 7 is reduced. So neither is possible.
[0037]
Step allowance d ₂₀ (Mm), d _{twenty one} (Mm), d _{twenty two} (Mm) and surface width w ₂₀ (Mm), w _{twenty one} (Mm), w _{twenty two} (Mm) is divided into one step land portion 20 and the other step land portions 21, 22. ₂₀ (Mm) is within a range of 0.1 to 1.5 mm, and the step-down margin d of the step land portions 21 and 22 _{twenty one} (Mm), d _{twenty two} (Mm) fits within the range of 0.5 to 3.0 mm. Moreover, the surface width w of the step land portion 20 ₂₀ (Mm) is in the range of 10.0 to 30.0 mm and the surface width w of the step land portions 21 and 22 _{twenty one} (Mm), w _{twenty two} (Mm) fits within the range of 5.0-15.0 mm.
[0038]
A step land portion 21 shown in FIG. 6 is a modification of the step land portion 21 shown in FIG. 4, and has a chamfered portion 21 p on the side of the groove 13 wider than the narrow cut groove 12. Surface width w of step land portion 21 with chamfered portion 21p _{twenty one} As for (mm), the reference | standard by the side of the chamfering part 21p is made into the lower end of the chamfering part 21p like illustration. This type of tire has an opportunity to travel on a road surface in which gravel or the like is scattered or scattered, and in particular, pebbles may be bitten into the grooves 13, so that foreign matters such as pebbles are difficult to bite into the grooves 13. A chamfer 21p. A chamfered portion similar to the chamfered portion 21p is also provided on the stepped land portion 22 facing the chamfered portion 21p.
[0039]
As described above, the pair of grooves or narrow cuts 10 and 11, the pair of narrow cuts or grooves 12 and 13 and the pair of narrow cuts or grooves 14 and 15 are straight, but have a zigzag shape with a small amplitude. It is also good. Note that reference numeral S shown in FIG. ₁ Is a long sipe with the code S ₂ Is a very short sipe. Land part 7L ₁ 7L ₂ Is a rib as a whole, but Sipe S ₁ Are divided into blocks.
[0040]
【Example】
It is a radial ply tire for trucks and buses, the size is 295 / 75R22.5 (tubeless tire), the configuration is as shown in FIGS. 1 to 3, and FIGS. 5 and 6, and the carcass 5 is a single ply radial arrangement steel cord. The belt 6 is composed of four rubber-coated teal cord layers.
[0041]
The tread portion 1 includes one step land portion 20 in the central region Rc and one step land portions 21 and 22 in both side regions Rs. ₂₀ 0.5mm, surface width w ₂₀ Is 20 mm, and the step-down margin d of the step land portions 21 and 22 is _{twenty one} , D _{twenty two} Is 2.5 mm and the surface width w _{twenty one} , W _{twenty two} Is 5.0 mm based on the lower end of the chamfered portion. Also, the depth D of the pair of grooves or narrow cuts 10, 11 ₁ (See FIG. 3) is 14.5 mm and a pair of narrow cuts or depths D of grooves 12 and 13 ₂ (See FIG. 4) and a pair of narrow cuts or depths D of grooves 14 and 15 _Three Both (see FIG. 5) are 14.5 mm.
[0042]
As a comparison object of the example, a comparative example tire having a tread pattern whose tread pattern is shown in FIG. 11 was prepared. The tread portion of the comparative example tire includes two circumferential straight grooves 30 and 31 in the central region Rc (Rcd region in the developed view), and a pair of narrow cuts 32 in both side regions Rs (Rcd region in the developed view). And a step land portion 34 separated by a groove 33 and a pair of narrow cuts 35 and a step land portion 37 separated by a groove 36. The step land portion 34 and the step land portion 37 have the same specifications. The step-down allowance d is 2.5 mm, and the chamfered lower end reference surface width w is 9.0 mm. All configurations and specifications other than those described above were adapted to the examples.
[0043]
Example tires and comparative example tires as described above, and comparative example tires in which the tread portion does not have a stepped land portion and each has two circumferential straight grooves 30, 31 that are the same as the comparative example tire (four in total). A conventional tire having a tread pattern almost identical to the above was subjected to a field test by users under the following two different usage conditions.
[0044]
(1) A user who has a remarkable degree of uneven wear, and the river wear along the groove or narrow cut advances to the land, and finally the most significant uneven wear called a rib punch often occurs on the land.
(2) A user who generates a certain amount of uneven wear but does not lead to significant uneven wear such as a rib punch.
[0045]
A summary of the test results is given below.
User test results described in (1) (expressed as an index. The higher the value, the better);
Distance traveled before removal due to tread rubber wear (index indication);
The example tire is 115 with respect to the index 100 of the comparative example tire, and the conventional tire remains at 75. As for the content, uneven wear hardly occurred in the example tire, whereas in the comparative example tire, significant rib punch occurred in the central region of the tread portion, and early wear occurred in the both side regions.
When the degree of uneven wear progresses to a certain extent, the tire is usually rejected, and in terms of the thickness of the tread rubber (depth of grooves, etc.) used until reaching the rejection limit, the comparative example tire In comparison with 100, the example tire is 115 and the conventional tire is 60.
[0046]
User test results described in (2) (expressed as an index. The higher the value, the better);
The tires of the examples show almost no uneven wear as in the comparative tires, and both have an index of wear resistance of 100 in terms of travel distance per 1 mm of tread rubber wear. The wear resistance of the conventional tire was only 85. The step land portion 20 in the center region Rc of the tread portion 1 of the embodiment tire has a step-down allowance d. ₂₀ Was almost zero, and it was found that it contributed greatly to the improvement of wear resistance as a kind of rib (complete land portion) rather than a partial wear sacrifice portion.
[0047]
【The invention's effect】
According to the first to fifth aspects of the present invention, in use conditions mainly in straight running or steady running close to straight running, the occurrence of uneven wear is suppressed and the use limit distance is extended, and the lateral input is reduced. It can improve the uneven wear resistance and wear resistance of the tread rubber under the driving conditions mainly of severe unsteady driving, and it can be used for two different driving conditions. Thus, it is possible to provide a long-life pneumatic tire having improved versatility and rich in versatility.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a pneumatic tire according to an embodiment of the present invention.
FIG. 2 is a development view of a tread surface of the tire shown in FIG.
FIG. 3 is a cross-sectional view taken along line III-III shown in FIG.
4 is a cross-sectional view taken along line IV-IV shown in FIG.
5 is a cross-sectional view taken along line V-V shown in FIG.
6 is a cross-sectional view of a modified example of the step land portion shown in FIG. 4;
FIG. 7 is a diagram showing a relationship between a step-down margin of a step land portion and a braking force.
FIG. 8 is a diagram showing a relationship between a surface width of a step land portion and a braking force.
FIG. 9 is a relationship diagram between a step-down margin of a step land portion and a surface width.
FIG. 10 is a diagram showing the relationship between the surface width of a step land portion and lateral rigidity.
FIG. 11 is a development view of a tread surface of a comparative example tire.
[Explanation of symbols]
1 Tread
1t tread
2 Side wall
3 Bead section
4 Bead core
5 Carcass
6 Belt
7 Tread rubber
7L ₁ 7L ₂ 7L _Three 7L _Four Land
10, 11 A pair of grooves
12, 13 A pair of narrow cuts and grooves
14, 15 A pair of narrow cuts and grooves
20 One step land
20s Step land surface
21, 22 The other step land
21s, 22s Step land surface
21p chamfer
E tire equator
TE tread edge
Rc tread central area
Rs tread area on both sides
Rcd Center width
Rsd Expand width of both sides
d ₂₀ , D _{twenty one} , D _{twenty two} Stepping cost of stepped land
w ₂₀ , W _{twenty one} , W _{twenty two} Surface width of step land
S ₁ Long sipe
S ₂ Short sipe

Claims

The tread portion is provided with a plurality of step land portions separated from the tread rubber land portion by a pair of grooves or narrow notches extending continuously in the tread surface circumferential direction and having a stepped surface from the tread surface. In the pneumatic tire in which the surface forms a partial wear sacrificial portion that makes sliding contact with the road surface under rolling load of the tire,
Regarding the step allowance from the tread surface to the stepped surface and the surface width of the above step land portion, the step allowance of one step land portion is the step difference of the other step land portion between the plurality of step land portions. A pneumatic tire characterized in that it is smaller than a tire and the surface width of one step land portion is wider than the surface width of the other step land portion.

A step allowance in both the one step land portion and the other step land portion is in a range of 0.1 to 3.0 mm, and a step surface width in both the one step land portion and the other step land portion is The tire according to claim 1, which is in a range of 5.0 to 30.0 mm.

The step allowance of the one step land portion is in the range of 0.1 to 1.5 mm, and the step allowance of the other step land portion is in the range of 0.5 to 3.0 mm.
Regarding the surface width of the step land portion, the surface width of one step land portion is in the range of 10.0 to 30.0 mm, and the surface width of the other step land portion is in the range of 5.0 to 15.0 mm. The tire according to claim 1 or 2.

The tread portion central region has one or more one step land portions, and the tread portion central region has one or more other step land portions on each side region. The tire described in 2.

The tread portion central region has one or more other step land portions, and the tread portion central region has one or more one step land portions on both side regions thereof. The tire described in 2.