JP2004262295A

JP2004262295A - Heavy duty pneumatic tire for construction vehicle

Info

Publication number: JP2004262295A
Application number: JP2003053269A
Authority: JP
Inventors: Akira Ono; 昭小野
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 2003-02-28
Filing date: 2003-02-28
Publication date: 2004-09-24

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heavy duty pneumatic tire for a construction vehicle having an increased wear resistance while suppressing side slip property without impairing traction performance. <P>SOLUTION: In this pneumatic tire, two circumferential thin grooves 2a and 2b are disposed in a tread part 1, and the tread part 1 is divided into side land parts 4 and a center land part 5 by these circumferential thin grooves and both tread ends 3a and 3b. Crossing thin grooves 6 are disposed in the center land part 5 to form a plurality of blocks on the center land part 5, and crossing thick grooves 7 are disposed in the side land parts 4 to form a plurality of blocks on the side land parts 4. A center area width W1 comes within the range of 15 to 60% of a tread width W2 with respect to a tire equatorial plane S, and the overall thickness of the tread part 1 comes within the range of 60 to 200 mm. The circumferential thin grooves 2a and 2b are so formed that shallow parts 8 having a height of 15 to 45% of the circumferential thin groove depth and a length of 5 to 20% of the side wall length of the center land part block is disposed in groove bottoms in which the side walls of the center land part 5 and the side land parts 4 are present. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
この発明は、格段に高い負荷能力及びトラクション性が要求される建設車両用重荷重用空気入りタイヤに関し、特に従来のブロックパターンを有するタイヤに比べて、トラクション性や耐横滑り性を確保しつつ、耐摩耗性等の耐久性の向上を図る。
【０００２】
【従来の技術】
建設車両用重荷重用空気入りタイヤは、例えばトラックバス用タイヤ、又は軽トラック用タイヤのような重荷重用空気入りタイヤと比べて、格段に高い耐負荷能力及びトラクション性能が要求される。そのため、かかるタイヤのトレッドパターンとしては、従来、耐摩耗性の観点から中央域にタイヤ周方向に連続して延びるリブ状陸部を配設し、トラクション性の確保の観点から両側方域に複数本のラグ溝を配設することによって、いわゆるリブラグパターンを採用するのが一般的である。しかし、中央域に配設したリブ状陸部の幅が大きくなりすぎると、登坂時のトラクションが損なわれる上、中央域に周方向に延びる溝が存在しないことから、操舵時に横滑りを誘発しやすく、さらに中央域に横断溝も存在しないため十分なトラクション性が得られないという問題がある。そこで、最近では、登坂時のトラクションと横方向へのエッヂ効果を両立させるため、中央域に配設する陸部を区画された複数のブロックとした、いわゆるラグブロックミックスパターンが多く用いられている。
【０００３】
一方、近年の建設車両の性能の向上に伴い、建設車両用重荷重用空気入りタイヤにも更なる耐負荷能力、トラクション性及び摩耗ライフの向上が強く望まれるようになっている。これらの性能向上を図るため、タイヤは益々大型化し、これに伴ってトレッドは益々厚肉化する必要が生じ、この結果、特にトレッド部の中央域において発熱量がより一層多くなっている。このため、かかる熱を放出してトレッドゴムの耐久性を向上する観点からも、中央域に溝を多く配設して中央陸部をブロックとして形成することが望ましい。
【０００４】
しかし、中央陸部をブロックで形成すると、タイヤ負荷転動時にブロックが前後又は左右に動きやすく、上述のように車両性能の向上に伴って、ブロックが早期摩耗又は欠け等の故障を発生するようになってきた。一方、中央陸部をリブ状陸部として形成したままでは、トレッドゴムの厚肉化により、例えばトレッド踏面部にカット傷を受けると、このカット傷が伝播して、やがてはベルトにまで達し、その後大きなトラクションを受けてトレッドゴムがタイヤ周方向に大きく歪変形する度に、その大きな歪変形応力伝播方向に沿って、前記カット傷がトレッドゴムとベルトとの間の亀裂となって進展してゆき、やがてはトレッドゴムとベルトとが互いに全剥離してしまう、いわゆるカットセパレーションという重大な故障を引き起こすおそれがあった。特許文献１には、ブロックの動きを抑制して耐摩耗性を向上させるため、縦溝と横溝の交差部付近の溝底を隆起させたタイヤが記載されている。しかし、このタイヤでは、建設車両用重荷重用空気入りタイヤのように格段に高い負荷が加わるタイヤのブロックの欠けを防止することはできない。
【０００５】
【特許文献１】
特開平１１−２２７４１９号公報
【０００６】
【発明が解決しようとする課題】
したがって、この発明の目的は、トレッドパターンの最適化を図ることにより、トラクション性を損なうことなく横滑り性を抑制しつつ、耐摩耗性を向上させた建設車両用重荷重用空気入りタイヤを提供することにある。
【０００７】
【課題を解決するための手段】
上記の目的を達成するため、この発明は、トレッド部に、タイヤ周方向に沿って延びる少なくとも２本の周方向細溝を配設し、これら周方向細溝と両トレッド端とによって、トレッド部をそれぞれ１列の側方陸部からなる両側方域と、少なくとも１列の中央陸部からなる中央域に区画し、中央陸部に、これを横切って延びる複数本の横断細溝を配設して、周方向細溝及び横断細溝で中央陸部を複数のブロックで形成し、側方陸部に、これを横切って延びる複数本の横断太溝を配設して、周方向細溝、横断太溝及びトレッド端で側方陸部を複数のブロックで形成し、中央域は、タイヤ赤道面を中心としてトレッド幅の１５〜６０％の範囲であり、トレッド部の総厚さは６０〜２００ｍｍの範囲であり、周方向細溝は、その中央陸部と側方陸部の側壁が存在する溝底に、高さが周方向細溝深さの１５〜４５％、長さが中央陸部ブロックの側壁長さの５〜２０％である浅底部を配設してなることを特徴とする建設車両用重荷重用空気入りタイヤである。ここで「トレッド幅」とは、ＪＡＴＭＡ、ＴＲＡ、ＥＴＲＴＯ等の、タイヤが製造、販売、又は使用される地域において有効な工業基準、規格等に定められる標準又は設計リムにタイヤをリム組みし、当該工業基準、規格等に定められる空気圧〜負荷能力対応表に定める１００％内圧を充填し、この内圧に対応する負荷能力相当の縦荷重を作用させたときのタイヤトレッド部の接地端間のタイヤ幅方向距離のことをいう。
【０００８】
また、周方向細溝は、タイヤ周方向に沿ってジグザグ状に延びるジグザグ溝であり、このジグザグ溝の屈曲点に横断太溝と横断細溝とが交互に交わる配置になり、浅底部を、ジグザグ溝の屈曲点を挟む両側壁位置の溝底に配設することが好ましい。ここでジグザグ溝の「屈曲点」とは、タイヤ周方向に対するジグザグ溝の延在角度が大きく変わる点のことをいい、この場合の中央陸部ブロックの側壁長さとは、タイヤ周方向で隣接する２つの横断細溝とジグザグ溝とが交わる屈曲点間に存在するブロックの側壁を、ジグザグ溝に沿って測定したときの長さのことをいう。
【０００９】
さらに、周方向細溝の溝幅が、８〜２０ｍｍの範囲にあることが好ましい。
【００１０】
さらにまた、周方向細溝の溝深さが、トレッドゴム総厚さの５０〜８５％の範囲にあることが好ましい。
【００１１】
また、横断細溝の溝幅が、８〜２０ｍｍの範囲にあることが好ましい。
【００１２】
さらに、横断細溝の溝深さが、トレッドゴム総厚さの５０〜８５％の範囲にあることが好ましい。
【００１３】
さらにまた、横断細溝が、タイヤ負荷転動時の接地域内で閉塞して、実質上のリブラグパターンを形成することが好ましい。ここでいう「実質上のリブラグパターン」とは、横断細溝が閉塞して、その溝幅が実質上零になり、隣接する中央陸部ブロックが接触し、タイヤ周方向に連続した状態となることをいう。
【００１４】
加えて、周方向細溝が、タイヤ負荷転動時の接地域内で閉塞することが好ましい。
【００１５】
加えてまた、周方向細溝及び横断細溝のそれぞれが、タイヤ負荷転動時の接地域内で閉塞して、実質上のラグパターンを形成することが好ましい。ここでいう「実質上のラグパターン」とは、周方向細溝及び横断細溝のそれぞれが閉塞して、それらの溝幅が実質上零になり、隣接する中央陸部ブロックが接触し、タイヤ周方向に連続するとともに、隣接する中央陸部ブロック同士及び側方陸部ブロックが接触し、タイヤ幅方向に連続した状態となることをいう。
【００１６】
また、トレッド部のタイヤ径方向内側に、コードがタイヤ赤道面に対して３〜１２°の角度で延びる少なくとも３層のコード層を、コードがタイヤ赤道面を挟んで交差するように積層してなるベルトを配設し、かつベルトを構成する最内コード層がタイヤ赤道面を中心としてトレッド幅の２５〜５０％の幅を有することが好ましい。
【００１７】
【発明の実施の形態】
以下、図面を参照しつつ、この発明の実施の形態を説明する。図１は、この発明に従う代表的な建設車両用重荷重用空気入りタイヤ（以下、「タイヤ」という。）のトレッド部の一部の展開図であり、図２は、図１のＩＩ−ＩＩ線上の断面図である。
【００１８】
図１に示すタイヤは、トレッド部１に、タイヤ周方向に沿って延びる少なくとも２本の周方向細溝、図１では２本の周方向細溝２ａ、２ｂを配設し、これら周方向細溝と両トレッド端３ａ、３ｂとによって、トレッド部１をそれぞれ１列の側方陸部４からなる両側方域と、少なくとも１列の中央陸部、図１では１列の中央陸部５からなる中央域に区画する。そして、中央陸部５に、これを横切って延びる複数本の横断細溝６を配設して、周方向細溝２ａ、２ｂ及び横断細溝６で中央陸部５を複数のブロックで形成し、側方陸部４に、これを横切って延びる複数本の横断太溝７を配設して、周方向細溝２ａ、２ｂ、横断太溝７及びトレッド端３ａ、３ｂで側方陸部４を複数のブロックで形成する。さらに、このタイヤにおいて、中央域の幅Ｗ_１は、タイヤ赤道面Ｓを中心としてトレッド幅Ｗ_２の１５〜６０％の範囲であり、トレッド部１の総厚さは６０〜２００ｍｍの範囲であり、周方向細溝２ａ、２ｂは、その中央陸部５と側方陸部４の側壁が存在する溝底に、高さｈが周方向細溝２ａ、２ｂの深さｄの１５〜４５％、長さｌ_１が中央陸部４のブロックの側壁長さｌ_２の５〜２０％である浅底部８を配設してなる。
【００１９】
以下、この発明が上記構成を採用するに至った経緯を作用とともに説明する。上述したように、最近では、建設車両用重荷重用空気入りタイヤのトレッドパターンとして、いわゆるラグブロックミックスパターンが多く用いられている。しかし、中央陸部をブロックで形成すると、横滑りの防止、及びトラクション性と放熱性の向上を図ることはできるが、早期摩耗又はブロック欠け等の故障が生じやすく耐久性には劣る。一方、中央陸部をリブ状陸部で形成すると、耐摩耗性には優れるが、タイヤの放熱性が劣る他、トレッド踏面部にカット傷を受けると、このカット傷が伝播して、やがてはベルトにまで達し、その後大きなトラクションを受けてトレッドゴムがタイヤ周方向に大きく歪変形する度に、その大きな歪変形応力伝播方向に沿って、カット傷がトレッドゴムとベルトとの間の亀裂となって進展してゆき、やがてはトレッドゴムとベルトとが互いに全剥離してしまう、いわゆるカットセパレーションを防止することができない。発明者は、中央陸部をブロックに区画する周方向溝と横断溝を細溝とすれば、接地域内では負荷により陸部が変形してこれらの細溝が実質的に閉じる結果、中央陸部は実質側方陸部と陸続きになって、耐摩耗性が向上する一方、接地域外では、これらの細溝の溝幅が復元する結果、タイヤの放熱及びカットセパレーションの進展の防止の役目を果たすことができるとの着想を得た。
【００２０】
ところが、タイヤの使用初期においては、これらの溝は細く深いため、溝底の曲率半径を大きく設定することが困難であり、溝底クラックが生じやすく、ブロック欠け等の問題が生じていた。
【００２１】
このため、周方向細溝の溝底に、区分された陸部の双方に接するように浅底部を形成すれば、溝底クラックを効果的に防止することができると同時に、加硫後の冷却時に側方陸部と中央陸部が収縮しようとしても、浅底部がその収縮を抑制する結果、周方向細溝及び横断細溝の溝幅が広がるのを効果的に防止できるという効果もあることを見出し、この発明を完成させるに至ったのである。
【００２２】
中央域の幅Ｗ_１を、タイヤ赤道面Ｓを中心としてトレッド幅Ｗ_２の１５〜６０％の範囲とするのは、１５％未満の場合には、十分なトラクションを得られないからであり、６０％を超える場合には、操舵時に横滑りを誘発しやすいからである。
【００２３】
また、トレッド部１の総厚さは６０〜２００ｍｍの範囲とするのは、６０ｍｍ未満の場合には、耐摩耗性が不十分となるからであり、２００ｍｍを超える場合には、発熱時の耐久性が不十分となるからである。
【００２４】
さらに、浅底部８の高さｈを周方向細溝２ａ、２ｂの深さｄの１５〜４５％とするのは、１５％未満の場合には、溝底クラックを防止する効果及び陸部の収縮を抑制する効果が不十分となるからであり、４５％を超える場合には、接地域内での細溝の閉塞が達成できなくなるおそれがあるからである。
【００２５】
さらにまた、浅底部８の長さｌ_１を中央陸部４のブロックの側壁長さｌ_２の５〜２０％とするのは、５％未満の場合には、溝底クラックを防止する効果及び陸部の収縮を抑制する効果が不十分となるからであり、２０％を超える場合には、接地域内での細溝の閉塞が達成できなくなるおそれがあるからである。
【００２６】
また、図３に示すように、周方向細溝２ａ、２ｂは、タイヤ周方向に沿ってジグザグ状に延びるジグザグ溝であり、このジグザグ溝の屈曲点９ａ、９ｂに横断太溝７と横断細溝６とが交互に交わる配置になり、浅底部８を、ジグザグ溝の屈曲点９ａ、９ｂを挟む両側壁位置の溝底に配設することが好ましい。周方向細溝２ａ、２ｂをジグザグ状とすることで、タイヤ周方向とタイヤ幅方向のエッジ成分を有効に増加させることができ、耐横滑り性とトラクション性の双方が一層向上するからであり、浅底部８を、屈曲点９ａ、９ｂを挟む両側壁位置の溝底に配設することにより、ブロック欠けを防止し、かつタイヤ成形時の陸部ブロックの熱収縮を一層効果的に抑制することができるからである。
【００２７】
さらに、周方向細溝２ａ、２ｂの溝幅が、８〜２０ｍｍの範囲にあることが好ましい。溝幅が８ｍｍ未満の場合には、放熱効果が低下し発熱時の耐久性が不十分となるからであり、２０ｍｍを超える場合には、トレッド接地域内での周方向細溝が大きくなりすぎ、陸部ブロックの欠けが発生するからである。
【００２８】
加えて、周方向細溝２ａ、２ｂの溝深さが、トレッドゴム総厚さの５０〜８５％の範囲にあることが好ましい。溝深さが、トレッドゴム総厚さの５０％未満の場合には、横滑りを抑制することができないからであり、８５％を超える場合には、陸部高さが高くなりすぎ、ブロックの欠けの原因となるからである。
【００２９】
また、横断細溝６の溝幅が、８〜２０ｍｍの範囲にあることが好ましい。溝幅が８ｍｍ未満の場合には、放熱効果が低下し発熱時の耐久性が不十分となるからであり、２０ｍｍを超える場合には、トレッド接地域内での周方向細溝が大きくなりすぎ、陸部ブロックの欠けが発生するからである。
【００３０】
さらに、横断細溝の溝深さが、トレッドゴム総厚さの５０〜８５％の範囲にあることが好ましい。溝深さが、トレッドゴム総厚さの５０％未満の場合には、十分な放熱面積が得られず、発熱を低減する効果が不十分となるからであり、８５％を超える場合には、陸部高さが高くなりすぎ、ブロックの欠けの原因となるからである。
【００３１】
さらにまた、耐横滑り性が重視される場合には、横断細溝６が、タイヤ負荷転動時の接地域内で閉塞して、実質上のリブラグパターンを形成することが好ましい。
【００３２】
加えて、トラクション性が重視される場合には、周方向細溝２ａ、２ｂが、タイヤ負荷転動時の接地域内で閉塞することが好ましい。
【００３３】
加えてまた、耐摩耗性が重視される場合には、周方向細溝２ａ、２ｂ及び横断細溝６のそれぞれが、タイヤ負荷転動時の接地域内で閉塞して、実質上のラグパターンを形成することが好ましい。
【００３４】
また、図４に示すように、トレッド部１のタイヤ径方向内側に、コードがタイヤ赤道面に対して３〜１２°の角度で延びる少なくとも３層のコード層、図４では３層のコード層１０ａ、１０ｂ、１０ｃを、コードがタイヤ赤道面を挟んで交差するように積層してなるベルト１１を配設し、かつベルト１１を構成する最内コード層１０ａがタイヤ赤道面Ｓを中心としてトレッド幅Ｗ_２の２５〜５０％の幅Ｗ_３を有することが好ましい。最内コード層１０ａの幅Ｗ_３がトレッド幅Ｗ_２の２５％未満の場合には、内圧による径成長を抑制する効果が小さいからであり、５０％を超える場合には、ベルト端の歪が増加し、ベルト１１の故障が発生するおそれがあるからである。
【００３５】
なお、上述したところは、この発明の実施形態の一例を示したにすぎず、請求の範囲において種々の変更を加えることができる。
【００３６】
【実施例】
次に、この発明に従う空気入りタイヤを試作し、性能評価を行ったので、以下に説明する。
【００３７】
実施例のタイヤは、タイヤサイズが４０００Ｒ５７の建設車輌用ラジアルタイヤであり、コードがタイヤ赤道面に対して５°の角度で延びる３層のコード層を、コードがタイヤ赤道面を挟んで交差するように積層してなるベルトを配設し、かつベルトを構成するコード層のうち、タイヤ径方向内側に位置する２枚のコード層がタイヤ赤道面を中心としてトレッド幅の３０％の幅を有し、トレッドパターンが図３に示すとおりであり、表１に示す諸元を有する。
【００３８】
比較のため、タイヤサイズが実施例のタイヤと同じであり、図５（ａ）に示すトレッドパターン（比較例１）又は図５（ｂ）に示すトレッドパターン（比較例２）、及び表１に示す諸元を有するタイヤについても併せて試作した。
【００３９】
（試験方法）
前記各供試タイヤを、ＴＲＡで定める標準リム（リム径：２９インチ（７３．６６ｃｍ）、フランジ高さ：６インチ（１５．２４ｃｍ））に取り付けてタイヤ車輪とし、空気圧：６８６ｋＰａ（相対圧）、タイヤ荷重：ＴＲＡ規格の１００％荷重（５８８ｋＮ）の条件下でダンプトラックの前輪に装着し、悪路のテストコースを速度１０ｋｍ／ｈにてほぼ等速で１０００時間走行した。
【００４０】
（評価方法）
トラクション性及び耐横滑り性は、テストドライバーによるフィーリングによって評価し、従来例１の値を１００とする指数にて示した。耐摩耗性は、走行後のトレッド部をタイヤ幅方向にて８等分し、それらの各位置における溝深さを測定し、初期溝深さからの摩耗量を走行時間で除して得られる値を、従来例１を１００とする指数にて表した。これらの指数はいずれも、数値が大きいほど性能が優れている。結果を表１に示す。
【００４１】
【表１】

【００４２】
表１に示す評価結果から、実施例のタイヤは比較例１及び２のタイヤに比べて、トラクション性及び耐横滑り性は同等以上でありながら、耐摩耗性が向上していることが分かる。
【００４３】
【発明の効果】
この発明により、トラクション性を損なうことなく横滑り性を抑制しつつ、耐摩耗性を向上させた建設車両用重荷重用空気入りタイヤを提供することが可能となった。
【図面の簡単な説明】
【図１】この発明に従う代表的な建設車両用重荷重用空気入りタイヤのトレッド部の一部の展開図である。
【図２】図１に示すタイヤのＩＩ−ＩＩ線上の断面図である。
【図３】この発明に従う他の建設車両用重荷重用空気入りタイヤのトレッド部の一部の展開図である。
【図４】図３に示すタイヤの要部のタイヤ幅方向断面図である。
【図５】（ａ）はラグパターンを有する従来例１のトレッド部の一部の展開図であり、（ｂ）はラグブロックミックスパターンを有する従来例２のトレッド部の一部の展開図である。
【符号の説明】
１トレッド部
２ａ、２ｂ周方向細溝
３ａ、３ｂトレッド端
４側方陸部
５中央陸部
６横断細溝
７横断太溝
８浅底部
９ａ、９ｂ屈曲点
１０ａ、１０ｂコード層
１１ベルト[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heavy-duty pneumatic tire for construction vehicles that requires extremely high load capacity and traction, and in particular, as compared with a conventional tire having a block pattern, while ensuring traction and skid resistance, To improve durability such as abrasion.
[0002]
[Prior art]
Heavy load pneumatic tires for construction vehicles are required to have significantly higher load carrying capacity and traction performance than heavy load pneumatic tires such as truck bus tires or light truck tires. Therefore, as a tread pattern of such a tire, conventionally, a rib-shaped land portion continuously extending in the tire circumferential direction is disposed in the central region from the viewpoint of wear resistance, and a plurality of rib-shaped land portions are provided on both side regions from the viewpoint of securing traction. By arranging the lug grooves of the book, it is common to adopt a so-called rib lug pattern. However, if the width of the rib-shaped land part arranged in the central area is too large, traction when climbing uphill is impaired, and there is no circumferential groove in the central area, so it is easy to induce skidding during steering In addition, there is a problem that sufficient traction cannot be obtained because there is no transverse groove in the central region. Therefore, recently, in order to achieve both traction when climbing a hill and an edge effect in a lateral direction, a so-called rug block mix pattern in which a plurality of blocks arranged on a land portion arranged in a central area are often used. .
[0003]
On the other hand, with the recent improvement in the performance of construction vehicles, there is a strong demand for heavy load pneumatic tires for construction vehicles to further improve load-bearing capacity, traction, and wear life. In order to improve these performances, the tires are becoming larger and larger, and accordingly the tread needs to be made thicker and thicker, and as a result, the calorific value is further increased, especially in the central region of the tread portion. Therefore, from the viewpoint of improving the durability of the tread rubber by releasing such heat, it is desirable to arrange a large number of grooves in the central region and form the central land portion as a block.
[0004]
However, if the central land portion is formed of a block, the block is likely to move back and forth or left and right when the tire load rolls, and as described above, with the improvement in vehicle performance, the block may cause a failure such as early wear or chipping. It has become. On the other hand, if the central land portion is formed as a rib-shaped land portion, if the tread rubber is thickened, for example, if a cut is received on the tread tread portion, the cut is propagated, and eventually reaches the belt, Each time the tread rubber receives large traction and undergoes large strain deformation in the tire circumferential direction, along the direction of the large strain deformation stress propagation, the cut flaws develop as cracks between the tread rubber and the belt. Eventually, the tread rubber and the belt may be completely separated from each other, which may cause a serious failure called so-called cut separation. Patent Literature 1 describes a tire in which a groove bottom near an intersection of a vertical groove and a horizontal groove is raised in order to suppress the movement of the block and improve wear resistance. However, this tire cannot prevent chipping of a block of a tire to which a remarkably high load is applied unlike a pneumatic tire for heavy loads for construction vehicles.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 11-227419
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a heavy-duty pneumatic tire for a construction vehicle that has improved abrasion resistance while suppressing side slip without impairing traction by optimizing a tread pattern. It is in.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides at least two circumferential narrow grooves extending along the tire circumferential direction on a tread portion, and the circumferential narrow groove and both tread ends form a tread portion. Is divided into a side area composed of one row of lateral land portions and a central area composed of at least one row of central land portions, and a plurality of transverse narrow grooves extending across the central land portion are disposed in the central land portion. A central land portion is formed by a plurality of blocks with a circumferential narrow groove and a transverse narrow groove, and a plurality of transverse thick grooves extending across the side land portion are disposed on the lateral land portion, and the circumferential narrow groove is formed. The lateral land portion is formed by a plurality of blocks at the wide groove and the tread edge, and the central region is 15 to 60% of the tread width around the tire equatorial plane, and the total thickness of the tread portion is 60%. ~ 200mm range, the circumferential narrow groove, the central land and side land A shallow portion having a height of 15 to 45% of the circumferential narrow groove depth and a length of 5 to 20% of the side wall length of the central land block is provided at the groove bottom where the wall exists. A pneumatic tire for heavy loads for construction vehicles characterized by the following. Here, "tread width" refers to JATMA, TRA, ETRTO, etc., the tire is manufactured, sold or used in a region effective in the area where the tire is used. A tire between the grounding end of the tire tread portion when filled with 100% internal pressure defined in the air pressure to load capability correspondence table defined in the relevant industrial standards and standards, and a vertical load equivalent to the load capability corresponding to this internal pressure is applied. It refers to the distance in the width direction.
[0008]
In addition, the circumferential narrow groove is a zigzag groove extending in a zigzag shape along the tire circumferential direction, and the crossing thick groove and the crossing narrow groove alternately intersect at the bending point of the zigzag groove, and the shallow bottom portion is formed. The zigzag grooves are preferably provided at the groove bottoms at both side wall positions sandwiching the bending point. Here, the "bending point" of the zigzag groove refers to a point at which the extending angle of the zigzag groove with respect to the tire circumferential direction changes greatly. In this case, the side wall length of the central land block is adjacent in the tire circumferential direction. It refers to the length when the side wall of the block existing between the bending points where the two transverse narrow grooves intersect with the zigzag groove is measured along the zigzag groove.
[0009]
Furthermore, it is preferable that the groove width of the circumferential narrow groove is in the range of 8 to 20 mm.
[0010]
Furthermore, it is preferable that the groove depth of the circumferential narrow groove is in the range of 50 to 85% of the total thickness of the tread rubber.
[0011]
Further, the width of the transverse narrow groove is preferably in the range of 8 to 20 mm.
[0012]
Further, it is preferable that the groove depth of the transverse narrow groove is in the range of 50 to 85% of the total thickness of the tread rubber.
[0013]
Furthermore, it is preferable that the transverse narrow groove is closed in a contact area at the time of tire load rolling to form a substantially rib lug pattern. Here, the “substantially rib lug pattern” means that the transverse narrow groove is closed, the groove width becomes substantially zero, the adjacent central land block contacts, and the tire is continuous in the tire circumferential direction. It means becoming.
[0014]
In addition, it is preferable that the circumferential narrow groove is closed in the contact area when the tire load rolls.
[0015]
In addition, it is preferable that each of the circumferential narrow groove and the transverse narrow groove is closed in a contact area at the time of tire load rolling to form a substantial lug pattern. Here, the “substantially lug pattern” means that each of the circumferential narrow groove and the transverse narrow groove is closed, their groove width becomes substantially zero, and the adjacent central land block comes into contact with the tire. It means that the center land blocks adjacent to each other and the side land blocks come into contact with each other in the circumferential direction and become continuous in the tire width direction.
[0016]
Also, at least three layers of cord layers whose cords extend at an angle of 3 to 12 ° with respect to the tire equatorial plane are laminated on the inner side in the tire radial direction of the tread portion so that the cords cross the tire equatorial plane. Preferably, the innermost cord layer constituting the belt has a width of 25 to 50% of the tread width with respect to the tire equatorial plane.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a developed view of a part of a tread portion of a typical heavy-duty pneumatic tire for construction vehicles (hereinafter, referred to as “tire”) according to the present invention, and FIG. 2 is a sectional view taken along line II-II of FIG. FIG.
[0018]
The tire shown in FIG. 1 is provided with at least two circumferential

narrow grooves

2a and 2b extending in the tire circumferential direction on the tread portion 1, and in FIG. By the groove and both tread ends 3a, 3b, the tread portion 1 is separated from both side regions each composed of one row of side land portions 4 and at least one row of center land portions, and in FIG. Into a central area. Then, a plurality of transverse narrow grooves 6 extending across the central land portion 5 are provided, and the central land portion 5 is formed of a plurality of blocks by the circumferential

narrow grooves

2a, 2b and the transverse narrow grooves 6. The lateral land portion 4 is provided with a plurality of transverse thick grooves 7 extending across the lateral land portion 4 and the circumferential

thin grooves

2a, 2b, the transverse thick grooves 7, and the tread ends 3a, 3b form the lateral land portion 4. Is formed by a plurality of blocks. Further, in this tire, the width _{W 1} of the central region is in the range 15 to 60% of the tread width _{W 2} around the tire equatorial plane S, the total thickness of the tread portion 1 is in the range of 60~200mm The height h is 15 to 45% of the depth d of the circumferential

narrow grooves

2a, 2b at the bottom of the groove where the side walls of the central land portion 5 and the side land portion 4 exist. length l ₁ is formed by arranging the shallow bottom portion 8 is 5-20% of the sidewall length l ₂ of the blocks of the center land portion 4.
[0019]
Hereinafter, a description will be given of how the present invention adopts the above configuration together with its operation. As described above, recently, a so-called lug block mix pattern is often used as a tread pattern of a heavy-duty pneumatic tire for construction vehicles. However, when the central land portion is formed of a block, it is possible to prevent skidding and improve traction and heat dissipation, but failure such as early wear or chipping of the block is likely to occur, resulting in poor durability. On the other hand, when the central land portion is formed of a rib-shaped land portion, the wear resistance is excellent, but the heat dissipation of the tire is inferior, and when a cut scratch is received on the tread tread portion, the cut scratch propagates and eventually. Each time the tread rubber reaches the belt and receives large traction, the tread rubber undergoes large strain deformation in the tire circumferential direction, and along the direction of large strain deformation stress propagation, cut scratches become cracks between the tread rubber and the belt. The so-called cut separation, in which the tread rubber and the belt eventually peel off completely from each other, cannot be prevented. If the circumferential groove and the transverse groove dividing the central land portion into blocks are narrow grooves, the land portion is deformed by the load in the contact area and the narrow grooves are substantially closed, so that the central land portion is closed. The part is substantially continuous with the land part on the side, and the wear resistance is improved.On the other hand, outside the contact area, the width of these narrow grooves is restored, and as a result, the heat radiation of the tire and the role of preventing the cut separation from progressing. I was inspired to be able to fulfill.
[0020]
However, in the early stage of use of the tire, since these grooves are thin and deep, it is difficult to set a large radius of curvature at the bottom of the groove, which easily causes cracks at the bottom of the groove and causes problems such as chipping of blocks.
[0021]
Therefore, if a shallow bottom is formed at the bottom of the circumferential narrow groove so as to be in contact with both of the divided land portions, cracks at the bottom of the groove can be effectively prevented, and at the same time, cooling after vulcanization is performed. Even if the lateral land portion and the central land portion try to shrink sometimes, the shallow portion suppresses the shrinkage, which also has the effect of effectively preventing the width of the circumferential narrow groove and the transverse narrow groove from being widened. And completed the present invention.
[0022]
The width W ₁ of the central region, in the range 15 to 60% of the tread width W ₂ around the tire equatorial plane S is, in the case of less than 15% is because not provide sufficient traction, If it exceeds 60%, side slip is likely to be induced during steering.
[0023]
The reason why the total thickness of the tread portion 1 is in the range of 60 to 200 mm is that if the thickness is less than 60 mm, the abrasion resistance becomes insufficient. This is because the property becomes insufficient.
[0024]
Further, the height h of the shallow portion 8 is set to 15 to 45% of the depth d of the circumferential

narrow grooves

2a and 2b. This is because the effect of suppressing shrinkage becomes insufficient, and if it exceeds 45%, it may not be possible to achieve closure of the narrow groove in the contact area.
[0025]
Furthermore, when the length l ₁ of the shallow portion 8 is set to 5 to 20% of the side wall length l ₂ of the block of the central land portion 4, if it is less than 5%, the effect of preventing groove bottom cracks and This is because the effect of suppressing the shrinkage of the land portion becomes insufficient, and if it exceeds 20%, the narrow groove may not be closed in the contact area.
[0026]
Further, as shown in FIG. 3, the circumferential

narrow grooves

2a and 2b are zigzag grooves extending in a zigzag manner along the tire circumferential direction, and the bending points 9a and 9b of the zigzag grooves have the transverse thick groove 7 and the transverse narrow groove. It is preferable that the grooves 6 alternately intersect with each other, and the shallow portions 8 be disposed at the groove bottoms at both side wall positions sandwiching the bending points 9a and 9b of the zigzag grooves. By forming the circumferential

narrow grooves

2a and 2b in a zigzag shape, the edge components in the tire circumferential direction and the tire width direction can be effectively increased, and both sideslip resistance and traction are further improved. By arranging the shallow portion 8 at the groove bottom at both side walls sandwiching the bending points 9a and 9b, it is possible to prevent the chipping of the block and to more effectively suppress the heat shrinkage of the land portion block during tire molding. Because it can be.
[0027]
Furthermore, it is preferable that the groove width of the circumferential

narrow grooves

2a, 2b is in the range of 8 to 20 mm. When the groove width is less than 8 mm, the heat radiation effect is reduced and the durability at the time of heat generation becomes insufficient. When the groove width is more than 20 mm, the circumferential narrow groove in the tread contact area becomes too large. This is because chipping of land blocks occurs.
[0028]
In addition, it is preferable that the groove depths of the circumferential

narrow grooves

2a and 2b be in the range of 50 to 85% of the total thickness of the tread rubber. If the groove depth is less than 50% of the total thickness of the tread rubber, side slip cannot be suppressed. If the groove depth exceeds 85%, the land height becomes too high and the block is chipped. It is because it causes.
[0029]
The width of the transverse narrow groove 6 is preferably in the range of 8 to 20 mm. When the groove width is less than 8 mm, the heat radiation effect is reduced and the durability at the time of heat generation becomes insufficient. When the groove width is more than 20 mm, the circumferential narrow groove in the tread contact area becomes too large. This is because chipping of land blocks occurs.
[0030]
Further, it is preferable that the groove depth of the transverse narrow groove is in the range of 50 to 85% of the total thickness of the tread rubber. If the groove depth is less than 50% of the total thickness of the tread rubber, a sufficient heat radiation area cannot be obtained, and the effect of reducing heat generation becomes insufficient. If the groove depth exceeds 85%, This is because the height of the land part becomes too high, which causes chipping of the block.
[0031]
Further, when importance is attached to the side slip resistance, it is preferable that the transverse narrow groove 6 be closed in the contact area at the time of tire load rolling to form a substantial rib lug pattern.
[0032]
In addition, when traction is emphasized, the circumferential

narrow grooves

2a and 2b are preferably closed in the contact area when the tire load rolls.
[0033]
In addition, when abrasion resistance is important, each of the circumferential

narrow grooves

2a and 2b and the transverse narrow grooves 6 is closed in the contact area when the tire load rolls, and a substantial lug pattern is formed. Is preferably formed.
[0034]
As shown in FIG. 4, at least three cord layers whose cords extend at an angle of 3 to 12 ° with respect to the tire equatorial plane inside the tread portion 1 in the tire radial direction, and three cord layers in FIG. 4. A belt 11 is formed by

laminating cords

10a, 10b, and 10c so that the cords intersect with the tire equatorial plane interposed therebetween, and the innermost cord layer 10a constituting the belt 11 has a tread centered on the tire equatorial plane S. preferably it has a width _{W 3} of 25-50% of the width _{W 2.} If the width W ₃ of the innermost cord layer 10a is less than 25% of the tread width W ₂ is because the effect of suppressing the size growth due to internal pressure is small, when it exceeds 50%, distortion of the belt ends This is because there is a possibility that the number of the belts 11 increases and a failure of the belt 11 occurs.
[0035]
The above description is only an example of the embodiment of the present invention, and various changes can be made within the scope of the claims.
[0036]
【Example】
Next, a pneumatic tire according to the present invention was prototyped and its performance was evaluated, and will be described below.
[0037]
The tire of Example is a radial tire for construction vehicles having a tire size of 4000R57. The cord crosses three cord layers extending at an angle of 5 ° with respect to the tire equatorial plane, and the cord intersects the tire equatorial plane. Of the cord layers constituting the belt, two of the cord layers located radially inward of the tire have a width of 30% of the tread width with respect to the tire equatorial plane. The tread pattern is as shown in FIG. 3 and has the specifications shown in Table 1.
[0038]
For comparison, the tire size is the same as the tire of the example, and the tread pattern (Comparative Example 1) shown in FIG. 5A or the tread pattern (Comparative Example 2) shown in FIG. Tires having the specifications shown were also prototyped.
[0039]
(Test method)
Each of the test tires is mounted on a standard rim (rim diameter: 29 inches (73.66 cm), flange height: 6 inches (15.24 cm)) determined by TRA to form a tire wheel, and air pressure: 686 kPa (relative pressure). The tire was mounted on the front wheel of a dump truck under the conditions of a TRA standard 100% load (588 kN) and traveled on a rough road test course at a speed of 10 km / h at a substantially constant speed for 1000 hours.
[0040]
(Evaluation method)
The traction property and the skid resistance were evaluated by feeling with a test driver, and indicated by an index with the value of Conventional Example 1 being 100. The wear resistance is obtained by dividing the tread portion after running into eight equal parts in the tire width direction, measuring the groove depth at each of those positions, and dividing the amount of wear from the initial groove depth by the running time. The value was represented by an index with Conventional Example 1 being 100. In any of these indices, the larger the value, the better the performance. Table 1 shows the results.
[0041]
[Table 1]

[0042]
From the evaluation results shown in Table 1, it can be seen that the tires of the examples are improved in abrasion resistance as compared with the tires of the comparative examples 1 and 2, while the traction properties and the sideslip resistance are equal or higher.
[0043]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it became possible to provide the heavy duty pneumatic tire for construction vehicles which improved the abrasion resistance while suppressing the sideslip property without impairing the traction.
[Brief description of the drawings]
FIG. 1 is a developed view of a part of a tread portion of a typical heavy duty pneumatic tire for construction vehicles according to the present invention.
FIG. 2 is a cross-sectional view of the tire shown in FIG. 1 taken along the line II-II.
FIG. 3 is a developed view of a part of a tread portion of another heavy-duty pneumatic tire for construction vehicles according to the present invention.
FIG. 4 is a sectional view in a tire width direction of a main part of the tire shown in FIG. 3;
5A is a developed view of a part of a tread portion of Conventional Example 1 having a lug pattern, and FIG. 5B is a developed view of a part of a tread portion of Conventional Example 2 having a lug block mix pattern. is there.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1

Tread part

2a, 2b Circumferential

narrow groove

3a, 3b Tread end 4 Side land part 5 Central land part 6 Crossing narrow groove 7 Crossing large groove 8 Shallow

bottom part

9a,

9b Bending point

10a, 10b Cord layer 11 Belt

Claims

The tread portion is provided with at least two circumferential narrow grooves extending along the tire circumferential direction, and the tread portion is formed by a row of lateral land portions on both sides by the circumferential narrow grooves and both tread ends. And a central area consisting of at least one row of central land portions, and a plurality of transverse narrow grooves extending across the central land portion are disposed on the central land portion, and are provided with circumferential narrow grooves and transverse narrow grooves. The central land portion is formed by a plurality of blocks, and a plurality of transverse thick grooves extending across the lateral land portion are disposed, and the circumferential narrow grooves, the transverse thick grooves and the lateral land portions are formed by tread ends. Is formed in a plurality of blocks, the central region is in the range of 15 to 60% of the tread width around the tire equatorial plane, the total thickness of the tread portion is in the range of 60 to 200 mm, and the circumferential narrow groove is At the bottom of the groove where the side walls of the central land and side land exist It is 15% to 45%, construction heavy duty pneumatic tire for a vehicle, wherein a length formed by disposing a shallow bottom from 5 to 20% of the sidewall length of the central land portion blocks.

The circumferential narrow groove is a zigzag groove extending in a zigzag shape along the tire circumferential direction, the transverse thick groove and the transverse narrow groove alternately intersect at a bending point of the zigzag groove, the shallow bottom portion, 2. The pneumatic tire according to claim 1, wherein the pneumatic tire is disposed at a groove bottom at both side wall positions sandwiching a bending point of the zigzag groove.

The pneumatic tire according to claim 1, wherein a groove width of the circumferential narrow groove is in a range of 8 to 20 mm.

The pneumatic tire according to any one of claims 1 to 3, wherein a groove depth of the circumferential narrow groove is in a range of 50 to 85% of a total thickness of the tread rubber.

The pneumatic tire according to any one of claims 1 to 4, wherein a width of the transverse narrow groove is in a range of 8 to 20 mm.

The pneumatic tire according to any one of claims 1 to 5, wherein a groove depth of the transverse narrow groove is in a range of 50 to 85% of a total thickness of the tread rubber.

The pneumatic tire according to any one of claims 1 to 6, wherein the transverse narrow groove is closed in a contact area at the time of rolling the tire.

The pneumatic tire according to any one of claims 1 to 7, wherein the circumferential narrow groove is closed in a contact area at the time of tire load rolling.

The pneumatic tire according to any one of claims 1 to 8, wherein each of the circumferential narrow groove and the transverse narrow groove closes in a contact area at the time of tire load rolling.

A belt in which at least three cord layers whose cords extend at an angle of 3 to 12 ° with respect to the tire equatorial plane are laminated inside the tread portion in the tire radial direction so that the cords intersect the tire equatorial plane. The pneumatic tire according to any one of claims 1 to 9, wherein the innermost cord layer constituting the belt has a width of 25 to 50% of a tread width around the equatorial plane of the tire.