JP2004122904A

JP2004122904A - Pneumatic tire

Info

Publication number: JP2004122904A
Application number: JP2002289031A
Authority: JP
Inventors: Katsushi Tanimoto; 谷本　克司
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2002-10-01
Filing date: 2002-10-01
Publication date: 2004-04-22
Anticipated expiration: 2022-10-01
Also published as: JP4102151B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of optimizing a ground shape and improving durability and abrasion resistance, especially a tire for a small truck. <P>SOLUTION: A tread surface 2 is partitioned into a central land 3 extending on a tire equator C, an outside land 5 extending in a shoulder section, and an intermediate land 4 between the central land 3 and the outside land 5 by vertical grooves 6 in the circumferential direction of the tire. On a tire meridian section including a tire axis in a regular state of no load where a rim assembling is performed to a regular rim and regular inner pressure is filled, the curvature radius R1 of the outer surface of the central land 3 is larger than the curvature radius R2 of the outer surface of the intermediate land 4, and the center of each of the curvature radii R1 and R2 lies at the same position. Therefore, in the pneumatic tire, the ground shape is optimized and the durability and abrasion resistance are improved. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、最適な接地形状を得ることができ耐久性や耐摩耗性能を向上しうる空気入りタイヤに関する。
【０００２】
【従来の技術】
従来、例えば扁平率が７０％以下の小型トラック用などの空気入りタイヤにあっては、図６（Ｂ）に示すような接地面形状ａとなりやすい。この接地面形状ａは、タイヤ赤道Ｃの接地長さＬｃよりもショルダ部側の接地長さＬｅが大となる。発明者らの実験の結果、このような接地面形状ａでは、タイヤの耐久性が低く、また偏摩耗が生じやすいなど耐摩耗性能も悪化することが判明している。このような原因としては、高荷重の条件の下で使用されることが多く、とりわけこの種のタイヤでは、慣例的にトレッド面の曲率変形を単一の曲率半径で形成していることが考えられる。
【０００３】
発明者らは、種々の実験を繰り返したところ、図６（Ａ）に示すように、タイヤ赤道Ｃの接地長さＬｃがショルダ部側の接地長さＬｅよりも大となる接地面形状ｂが、タイヤの耐久性及び耐摩耗性能について好ましいこと、そして、トレッド面の曲率半径を適正に変化させることにより、このような接地面形状ｂを得ることができることを見出し本発明を完成させるに至った。
【０００４】
以上のように、本発明は、接地形状を最適化し耐久性能と耐摩耗性能とを向上しうる空気入りタイヤ、とりわけ小型トラック用タイヤを提供することを目的としている。
【０００５】
【課題を解決するための手段】
本発明のうち請求項１記載の発明は、トレッド面を、タイヤ赤道上をのびる中央陸部と、ショルダ部をのびる外側陸部と、前記中央陸部と前記外側陸部との間の中間陸部とにタイヤ周方向の縦溝により区分し、かつ正規リムにリム組みしかつ正規内圧を充填した無負荷の正規状態におけるタイヤ軸を含むタイヤ子午線断面において、前記中央陸部の外面の曲率半径Ｒ１が、、前記中間陸部の外面の曲率半径Ｒ２よりも大であり、しかも各曲率半径Ｒ１、Ｒ２の中心が同じ位置にあることを特徴としている。
【０００６】
ここで、前記「正規リム」とは、タイヤが基づいている規格を含む規格体系において、当該規格がタイヤ毎に定めるリムであり、例えばＪＡＴＭＡであれば標準リム、ＴＲＡであれば　”Ｄｅｓｉｇｎ　Ｒｉｍ”　、或いはＥＴＲＴＯであれば　”Ｍｅａｓｕｒｉｎｇ　Ｒｉｍ”とする。また、「正規内圧」とは、タイヤが基づいている規格を含む規格体系において、各規格がタイヤ毎に定めている空気圧であり、ＪＡＴＭＡであれば最高空気圧、ＴＲＡであれば表　”ＴＩＲＥ　ＬＯＡＤ　ＬＩＭＩＴＳ　ＡＴ　ＶＡＲＩＯＵＳ　ＣＯＬＤ　ＩＮＦＬＡＴＩＯＮ　ＰＲＥＳＳＵＲＥＳ”　に記載の最大値、ＥＴＲＴＯであれば　”ＩＮＦＬＡＴＩＯＮ　ＰＲＥＳＳＵＲＥ”　とするが、タイヤが乗用車用である場合には１８０ｋＰａとする。
【０００７】
また請求項２記載の発明は、前記中央陸部の曲率半径Ｒ１と中間陸部の曲率半径Ｒ２との差（Ｒ１−Ｒ２）が０．１〜１．０ｍｍであることを特徴とする請求項１記載の空気入りタイヤである。
【０００８】
また請求項３記載の発明は、前記外側陸部の外面の曲率半径Ｒ３は、前記中間陸部の曲率半径Ｒ２と同一か又はそれよりも大かつ前記曲率半径Ｒ１よりも小であり、しかも各曲率半径Ｒ２、Ｒ３の中心が同じ位置にあることを特徴とする請求項１又は２に記載の空気入りタイヤである。
【０００９】
また請求項４記載の発明は、前記中央陸部は、そのタイヤ軸方向の外縁部に、面取り状に切り欠いた小高さの面取部を設けたことを特徴とする請求項１乃至３のいずれかに記載の空気入りタイヤである。
【００１０】
また請求項５記載の発明は、前記正規状態で正規荷重を負荷しタイヤを平面に押し付けたときに得られる接地面は、タイヤ赤道でのタイヤ周方向の接地長さＬｃと、タイヤ赤道からトレッド接地巾の４０％をタイヤ軸方向外側に隔てたショルダ部でのタイヤ周方向の接地長さＬｓとの比（Ｌｃ／Ｌｓ）が１．０〜１．３であることを特徴とする請求項１乃至４記載の空気入りタイヤである。
【００１１】
ここで「正規荷重」とは、タイヤが基づいている規格を含む規格体系において、各規格がタイヤ毎に定めている荷重であり、ＪＡＴＭＡであれば最大負荷能力、ＴＲＡであれば表　”ＴＩＲＥ　ＬＯＡＤ　ＬＩＭＩＴＳ　ＡＴ　ＶＡＲＩＯＵＳ　ＣＯＬＤ　ＩＮＦＬＡＴＩＯＮ　ＰＲＥＳＳＵＲＥＳ”　に記載の最大値、ＥＴＲＴＯであれば　”ＬＯＡＤ　ＣＡＰＡＣＩＴＹ”とする。また「トレッド接地巾」とは前記正規状態に正規荷重を付加して平面に接地させたときのトレッド接地端間のタイヤ軸方向の最大距離とする。
【００１２】
【発明の実施の形態】
以下本発明の実施の一形態を図面に基づき説明する。
図１は、本実施形態として小型トラック用の空気入りタイヤを正規リム（図示省略）にリム組みしかつ正規内圧を充填した無負荷の正規状態におけるタイヤ軸を含むタイヤ子午線断面の輪郭線図、図２はトレッド部を展開して示す展開図である。
【００１３】
図において、空気入りタイヤ１はトレッド面２を、タイヤ赤道Ｃ上をのびる中央陸部３と、ショルダ部をのびる外側陸部５と、前記中央陸部３と前記外側陸部５との間の中間陸部４とにタイヤ周方向の縦溝６により区分している。なお外側陸部５は、接地端Ｅを含み、本例ではトレッド面を５列の陸部に区分している。
【００１４】
本例では、前記中央陸部３及び外側陸部５がタイヤ周方向に連続してのびるリブ列からなり、また中間陸部４は略Ｖ字状にのびる横溝７によって区分されたブロックＢがタイヤ周方向に並ぶブロック列からなる。なお各陸部をリブ列とするか又はブロック列とするかは適宜定めうるが、好ましくは、本例のように、接地圧が高くなる中央陸部３と旋回時に大きな横力が作用する外側陸部５とに剛性の高いリブ列を用いるのが好適である。なおリブ列には、サイピング、ラグ状溝などを適宜設けることができる。
【００１５】
前記縦溝６は、中央陸部３と中間陸部４との間をのびる内の縦溝６Ａと、中間陸部４と外側陸部５との間をのびる外の縦溝６Ｂとを含み、本実施形態ではタイヤ赤道Ｃを中心として左右対称に配されている。各縦溝６は、比較的巾広でタイヤ周方向連続してかつ直線状でのびるものが示されるが、適宜屈曲させることでも良い。縦溝６の溝巾は、特に限定はされないが、トレッド面２で測定した溝巾ＧＷがトレッド接地巾ＴＷの２〜７％程度、より好適には２〜５％程度に設定されるのが望ましい。また縦溝３の溝深さについては、例えば５ｍｍ以上、より好ましくは６ｍｍ以上、さらに好ましくは７〜１５ｍｍ程度が望ましい。
【００１６】
また、前記内の縦溝６Ａは、その溝中心線が、タイヤ赤道Ｃからトレッド接地巾ＴＷの７〜１２％、より好ましくは８〜１０％の距離Ｘ１を隔てるのが良い。この距離Ｘ１が、トレッド接地巾ＴＷの７％未満になると、中央陸部３の剛性が不足し、該中央陸部３に摩耗エネルギーが集中して偏摩耗が生じやすく、逆に１２％を超えると、中央陸部３の剛性が過大となり、他の陸部に摩耗エネルギーが集中しやすくなる。
【００１７】
また外の縦溝６Ｂは、その溝中心線が、タイヤ赤道Ｃからトレッド接地巾ＴＷの２７〜３３％、より好ましくは２９〜３１％の距離Ｘ２を隔てるのが良い。この距離Ｘ２が、トレッド接地巾ＴＷの２７％未満になると、中間陸部４の剛性が不足し該中間陸部４に摩耗エネルギーが集中して偏摩耗が生じやすくなり、逆に３３％を超えると、外側陸部５の剛性が過小となり、該外側陸部５に摩耗エネルギーが集中しやすくなる。
【００１８】
本発明では、図１に示すように、タイヤ新品時の正規状態において、中央陸部３の外面の曲率半径Ｒ１が、中間陸部４の外面の曲率半径Ｒ２よりも大であり、しかも各曲率半径Ｒ１、Ｒ２の中心Ｏが同じ位置にあることを特徴事項の一つとしている。なお中心Ｏは、タイヤ赤道面内に位置する。
【００１９】
発明者らの種々の実験の結果、このようにトレッド面２の曲率半径を規制することにより、中央陸部３を中間陸部４に比してタイヤ半径方向外方に突出させることができ、接地面におけるタイヤ赤道Ｃ付近の接地長さを大にできる。そして、図６（Ａ）に示したように、接地面におけるタイヤ周方向の接地長さを、タイヤ赤道Ｃからタイヤ軸方向外側に向かって徐々に減じた接地面形状ｂをうることができる。このような空気入りタイヤ１は、トレッド面２の接地圧バランスが良いため、耐久性、耐摩耗性を向上しうる。
【００２０】
ここで、中央陸部３の曲率半径Ｒ１と中間陸部４の曲率半径Ｒ２との差（Ｒ１−Ｒ２）は、例えば０．１〜１．５ｍｍとするのが望ましい。前記差（Ｒ１−Ｒ２）が０．１ｍｍ未満では、中央陸部３と中間陸部４との差が実質的なものとならず、前記効果が得られ難い。逆に前記差（Ｒ１−Ｒ２）が１．５ｍｍを超えると、中央陸部３と中間陸部４との間の段差が大きくなりすぎ、中間陸部４の接地圧が過小となり該中間陸部４が引きずられるなどして偏摩耗が生じやすくなる。より好ましくは前記差（Ｒ１−Ｒ２）を０．５〜１．０ｍｍ程度とするのが望ましい。
【００２１】
ここで中央陸部３の曲率半径Ｒ１は、特に限定はされないが、例えばトレッド接地巾ＴＷの３５０〜５００％、より好ましくは４２０〜４８０％、さらに好ましくは４４０〜４６０％程度とするのが望ましい。この曲率半径Ｒ１がトレッド接地巾ＴＷの３５０％未満であると、中央陸部３の丸みが強くなり、該中央陸部３で偏摩耗が生じやすくなる。また曲率半径Ｒ１がトレッド接地巾ＴＷの５００％を超えると、前記とは逆に中央陸部３の側縁部で偏摩耗が生じやすくなる。
【００２２】
また好ましくは、外側陸部５の外面の曲率半径Ｒ３を、中間陸部４の曲率半径Ｒ２と同一か又はそれよりも大きく設定するのが望ましい。即ち、Ｒ３≧Ｒ２とする。なお曲率半径Ｒ３も曲率半径Ｒ２の中心Ｏと同じ位置に中心を有している。
【００２３】
図３には、Ｒ３＝Ｒ２とした態様を示す。この態様では、特に偏平率が６５〜７０％のタイヤにおいて、ショルダ部の接地長さを減じる。これは、接地形状におけるタイヤ周方向長さをタイヤ赤道からショルダ側に向かって徐々に減じる好ましい形状へと改善するのに役立つ。
【００２４】
また図４には、Ｒ３＞Ｒ２とした態様を示す。この態様では、特に偏平率が６０％以下のタイヤにおいて上述の如く接地形状を改善するのに役立つ。
【００２５】
なおＲ３＞Ｒ２とした場合、外側陸部５の曲率半径Ｒ３は、中央陸部３の曲率半径Ｒ１よりも小、即ち、Ｒ３＞Ｒ１とすることが必要である。Ｒ３＞Ｒ１になると、接地形状が図６（Ｂ）に示した形状に近づき易くなり、耐久性、耐摩耗性能の面で好ましくない。即ち、この形態では、Ｒ１＞Ｒ３＞Ｒ２としている。
【００２６】
また外側陸部５の曲率半径Ｒ３と中間陸部４の曲率半径Ｒ２との差（Ｒ３−Ｒ２）は、前記中央陸部３の曲率半径Ｒ１と中間陸部４の曲率半径Ｒ２との差（Ｒ１−Ｒ２）よりも小とするのが望ましい。
【００２７】
また図３に示した態様では、中央陸部３のタイヤ軸方向の外縁部３ｅには、面取り状に切り欠いた小高さの面取部９を設けたものを例示している。また同様に、中間陸部４のタイヤ軸方向の外側の外縁部４ｅにも、面取り状に切り欠いた小高さの面取部９を設けている。中央陸部３の面取部９は、中間陸部４の外面との局部的な高さの変化を緩和し、各陸部３、４間での接地圧の均一化を促進しうる。これにより、中間陸部４、中央陸部３の各側縁部に生じがちなエッジ摩耗等を効果的に防止でき、長期に亘って摩耗性能が向上しうる。
【００２８】
図５（Ａ）には、内の縦溝６Ｂの付近の拡大図を示す。
中央陸部３の面取部９は、そのタイヤ半径方向の内縁９ｉが中間陸部４の外面を仮想延長した円弧線Ｙ２よりもタイヤ半径方向の内方に位置している。これにより、中央陸部３と中間陸部４との接地圧の分布がより均一化する。とりわけ面取部９の内縁９ｉと円弧線Ｙ２との間のタイヤ半径方向の距離Ｓは、例えば０．２〜０．８ｍｍ、より好ましくは０．３〜０．５ｍｍとするのが望ましい。また面取部９の外縁９ｏ（トレッド面との交わり部）と縦溝６の溝壁の仮想延長線Ｙ３との間の中央陸部３の外面に沿った距離Ｋは１〜２ｍｍとするのがより効果的である。
【００２９】
また図４に示したように、Ｒ３＞Ｒ２とした態様では、図５（Ｂ）に示すように、外側陸部５のタイヤ軸方向内側の内縁部５ｉにも、面取り状に切り欠いた面取部９を設けることが望ましい。これにより、中間陸部４、中央陸部３及び外側陸部５間での突出高さの変化をより緩和でき、各側縁部に生じがちなエッジ摩耗等をさらに効果的に抑制しうる。なおこの面取部９の内縁９ｉも、前記円弧縁Ｙ２よりもタイヤ半径方向内方に距離Ｓを隔てるのが望ましい。またこの態様の面取部９は、中間陸部４に沿って測った長さＫ′が２〜３０ｍｍ、より好ましくは５〜２０ｍｍと大きく設定するのが良い。これによって、エッジ摩耗が顕著に緩和される。
【００３０】
また、本実施形態の空気入りタイヤ１は、前記正規状態で正規荷重を負荷しタイヤを平面に押し付けたときに得られる接地面は、図６（Ａ）に示したように、タイヤ赤道でのタイヤ周方向の接地長さＬｃと、タイヤ赤道Ｃからトレッド接地巾ＴＷの４０％をタイヤ軸方向外側に隔てたショルダ部でのタイヤ周方向の接地長さＬｓとの比（Ｌｃ／Ｌｓ）が１．０〜１．３、より好ましくは１．１〜１．２とすることができ、特に好ましい接地形状を得ることができる。
【００３１】
【実施例】
タイヤサイズが２２５／６０Ｒ１７．５の小型トラック用のラジアルタイヤを表１の仕様に基づき試作するとともに、接地形状、耐久性及び耐摩耗性をテストした。なお各供試タイヤとも内部構造は同一とした。
【００３２】
耐久性は、各供試タイヤをリム（６．７５×１７．５）にリム組みし、ドラム試験器を用い、タイヤが破壊するまでの走行距離を求めた。評価は、比較例１を１００とする指数で評価したて下記の条件で行った。
テスト荷重：　１６．３３ＫＮ
内圧　　　：　６００ｋＰａ
走行速度　：　８０ｋｍ／Ｈ
【００３３】
また耐摩耗性は、市街地、山岳地、高速道路をそれぞれ１０００ｋｍずつ含む実車走行を行い、偏摩耗状況を目視により観察した。
テストの結果などを表１に示す。
【００３４】
【表１】

【００３５】
【発明の効果】
上述したように、本発明の空気入りタイヤは、接地形状を最適化して耐久性、耐摩耗性能を向上しうる。
【図面の簡単な説明】
【図１】本発明の実施形態を示す空気入りタイヤの正規状態における輪郭線図である。
【図２】本実施形態の空気入りタイヤのトレッドパターンの展開図である。
【図３】本実施形態の空気入りタイヤのトレッド部の拡大輪郭線図である。
【図４】本発明の他の実施形態を示すトレッド部の拡大輪郭線図である。
【図５】（Ａ）は内の縦溝付近の拡大図、（Ｂ）は外の縦溝付近の拡大図である。
【図６】（Ａ）は本実施形態の接地形状図、（Ｂ）は従来例の接地形状図である。
【符号の説明】
２　トレッド面
３　中央陸部
４　中間陸部
５　外側陸部
６　縦溝
６Ａ　内の縦溝
６Ｂ　外の縦溝
９　斜面部
Ｒ１　中央陸部の外面の曲率半径
Ｒ２　中間陸部の外面の曲率半径
Ｒ３　外側陸部の外面の曲率半径
Ｅ　接地端[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pneumatic tire that can obtain an optimal ground contact shape and can improve durability and wear resistance.
[0002]
[Prior art]
Conventionally, in a pneumatic tire for a small truck having an oblateness of 70% or less, for example, the contact surface shape a as shown in FIG. In the contact surface shape a, the contact length Le on the shoulder portion side is larger than the contact length Lc of the tire equator C. As a result of the experiments by the inventors, it has been found that with such a contact surface shape a, the durability of the tire is low, and the wear resistance is deteriorated such that uneven wear easily occurs. Such a cause is often used under a condition of high load, and in particular, in this type of tire, it is considered that the curvature deformation of the tread surface is conventionally formed with a single radius of curvature. Can be
[0003]
When the inventors repeated various experiments, as shown in FIG. 6A, the contact surface shape b where the contact length Lc of the tire equator C was larger than the contact length Le on the shoulder portion side was determined. It was found that the durability and wear resistance of the tire were favorable, and that by properly changing the radius of curvature of the tread surface, it was possible to obtain such a ground contact surface shape b, and completed the present invention. .
[0004]
As described above, an object of the present invention is to provide a pneumatic tire, particularly a light truck tire, which can improve the durability performance and the wear resistance performance by optimizing the ground contact shape.
[0005]
[Means for Solving the Problems]
In the invention according to claim 1 of the present invention, the tread surface includes a central land portion extending on the tire equator, an outer land portion extending on the shoulder portion, and an intermediate land between the central land portion and the outer land portion. The radius of curvature of the outer surface of the central land portion in a tire meridian section including a tire shaft in a normal state of no load, which is divided into a normal rim and a rim assembled into a normal rim and filled with a normal internal pressure. R1 is larger than the radius of curvature R2 of the outer surface of the intermediate land portion, and the centers of the radii of curvature R1 and R2 are located at the same position.
[0006]
Here, the “regular rim” is a rim defined for each tire in a standard system including a standard on which the tire is based. For example, a standard rim for JATMA, and “Design Rim” for TRA. Or, in the case of ETRTO, "Measuring Rim" is set. The "normal internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. For JATMA, the maximum air pressure is used. For TRA, the table "TIRE LOAD LIMITS" is used. The maximum value described in AT VARIOUS COLD INFLATION PRESSURES ”is set to“ INFLASION PRESSURE ”for ETRTO, but is set to 180 kPa when the tire is for a passenger car.
[0007]
The invention according to claim 2 is characterized in that a difference (R1-R2) between the radius of curvature R1 of the central land portion and the radius of curvature R2 of the intermediate land portion is 0.1 to 1.0 mm. 1. The pneumatic tire according to 1.
[0008]
In the invention according to claim 3, the curvature radius R3 of the outer surface of the outer land portion is equal to or larger than the curvature radius R2 of the intermediate land portion and smaller than the curvature radius R1. 3. The pneumatic tire according to claim 1, wherein the centers of the radii of curvature R2 and R3 are located at the same position.
[0009]
The invention according to claim 4 is characterized in that the central land portion is provided with a chamfered portion having a small height cut out in a chamfered shape at an outer edge portion in the tire axial direction. A pneumatic tire according to any one of the above.
[0010]
Further, according to the invention as set forth in claim 5, the ground contact surface obtained when the tire is pressed against a flat surface by applying a normal load in the normal state is a contact length Lc in the tire circumferential direction at the tire equator and a tread from the tire equator. The ratio (Lc / Ls) to the contact length Ls in the tire circumferential direction at the shoulder portion that separates 40% of the contact width outward in the tire axial direction is 1.0 to 1.3. 5. The pneumatic tire according to any one of 1 to 4.
[0011]
Here, the “regular load” is a load defined for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is JATMA, and the table “TIRE LOAD” is TRA. The maximum value described in "LIMITS AT VARIOUS COLD INFLASION PRESSURESRES" is set to "LOAD CAPACITY" for ETRTO. The "tread contact width" is the maximum distance in the tire axial direction between the tread contact ends when a regular load is applied to the regular state and the tire is grounded on a plane.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a profile diagram of a tire meridian cross-section including a tire shaft in a normal state under no load in which a pneumatic tire for a light truck is assembled to a normal rim (not shown) and filled with a normal internal pressure according to the embodiment; FIG. 2 is a developed view showing the tread part in an expanded manner.
[0013]
In the figure, a pneumatic tire 1 has a tread surface 2, a central land portion 3 extending on a tire equator C, an outer land portion 5 extending over a shoulder portion, and a space between the central land portion 3 and the outer land portion 5. It is divided into an intermediate land portion 4 by a longitudinal groove 6 in the tire circumferential direction. The outer land portion 5 includes a ground end E, and in this example, the tread surface is divided into five rows of land portions.
[0014]
In this example, the central land portion 3 and the outer land portion 5 are formed of a row of ribs extending continuously in the tire circumferential direction, and the middle land portion 4 is formed of a block B divided by a substantially V-shaped lateral groove 7. It consists of a row of blocks arranged in the circumferential direction. It should be noted that it is possible to appropriately determine whether each land portion is to be a rib row or a block row, but preferably, as in this example, the central land portion 3 where the contact pressure is high and the outside where a large lateral force acts upon turning. It is preferable to use a rib row having high rigidity for the land portion 5. Note that sipes, lug-shaped grooves, and the like can be appropriately provided in the rib row.
[0015]
The vertical groove 6 includes an inner vertical groove 6A extending between the central land portion 3 and the intermediate land portion 4, and an outer vertical groove 6B extending between the intermediate land portion 4 and the outer land portion 5, In the present embodiment, they are arranged symmetrically with respect to the tire equator C. Each vertical groove 6 is shown to be relatively wide, continuous in the tire circumferential direction and extending linearly, but may be bent as appropriate. The groove width of the vertical groove 6 is not particularly limited, but the groove width GW measured on the tread surface 2 is set to about 2 to 7% of the tread contact width TW, more preferably about 2 to 5%. desirable. The depth of the vertical groove 3 is, for example, preferably 5 mm or more, more preferably 6 mm or more, and still more preferably about 7 to 15 mm.
[0016]
Also, the vertical groove 6A is preferably such that its groove center line is separated from the tire equator C by a distance X1 of 7 to 12%, more preferably 8 to 10% of the tread contact width TW. When the distance X1 is less than 7% of the tread contact width TW, the rigidity of the central land portion 3 is insufficient, and wear energy is concentrated on the central land portion 3 to cause uneven wear, and conversely, exceeds 12%. In this case, the rigidity of the central land portion 3 becomes excessive, and the wear energy tends to concentrate on other land portions.
[0017]
The outer vertical groove 6B may have a groove centerline spaced from the tire equator C by a distance X2 of 27 to 33%, more preferably 29 to 31% of the tread contact width TW. When the distance X2 is less than 27% of the tread contact width TW, the rigidity of the intermediate land portion 4 is insufficient, and the wear energy is concentrated on the intermediate land portion 4 to easily cause uneven wear, and conversely, exceeds 33%. Then, the rigidity of the outer land portion 5 becomes too small, and the wear energy tends to concentrate on the outer land portion 5.
[0018]
In the present invention, as shown in FIG. 1, in a normal state when the tire is new, the radius of curvature R1 of the outer surface of the central land portion 3 is larger than the radius of curvature R2 of the outer surface of the intermediate land portion 4. One of the features is that the centers O of the radii R1 and R2 are located at the same position. Note that the center O is located in the tire equatorial plane.
[0019]
As a result of various experiments by the inventors, by regulating the radius of curvature of the tread surface 2 in this manner, the central land portion 3 can be made to protrude outward in the tire radial direction as compared with the intermediate land portion 4, The contact length near the tire equator C on the contact surface can be increased. Then, as shown in FIG. 6A, it is possible to obtain a contact surface shape b in which the contact length in the tire circumferential direction on the contact surface is gradually reduced from the tire equator C outward in the tire axial direction. Such a pneumatic tire 1 can improve durability and abrasion resistance because the tread surface 2 has a good contact pressure balance.
[0020]
Here, the difference (R1-R2) between the radius of curvature R1 of the central land portion 3 and the radius of curvature R2 of the intermediate land portion 4 is desirably, for example, 0.1 to 1.5 mm. If the difference (R1−R2) is less than 0.1 mm, the difference between the central land portion 3 and the intermediate land portion 4 does not become substantial, and the above-described effect is hardly obtained. Conversely, if the difference (R1-R2) exceeds 1.5 mm, the step between the central land portion 3 and the intermediate land portion 4 becomes too large, and the contact pressure of the intermediate land portion 4 becomes too small, so that the intermediate land portion becomes Uneven wear is liable to occur due to drag of 4 or the like. More preferably, the difference (R1−R2) is desirably about 0.5 to 1.0 mm.
[0021]
Here, the radius of curvature R1 of the central land portion 3 is not particularly limited, but is, for example, preferably 350 to 500%, more preferably 420 to 480%, and still more preferably about 440 to 460% of the tread contact width TW. . If the radius of curvature R1 is less than 350% of the tread contact width TW, the central land portion 3 becomes more rounded, and uneven wear tends to occur in the central land portion 3. If the radius of curvature R1 exceeds 500% of the tread contact width TW, on the contrary, uneven wear tends to occur on the side edge of the central land portion 3.
[0022]
Preferably, the radius of curvature R3 of the outer surface of the outer land portion 5 is set to be equal to or larger than the radius of curvature R2 of the intermediate land portion 4. That is, R3 ≧ R2. The radius of curvature R3 also has a center at the same position as the center O of the radius of curvature R2.
[0023]
FIG. 3 shows an embodiment in which R3 = R2. In this embodiment, the contact length of the shoulder portion is reduced particularly in a tire having an aspect ratio of 65 to 70%. This helps to improve the tire circumferential length in the ground contact shape to a preferable shape that gradually decreases from the tire equator toward the shoulder side.
[0024]
FIG. 4 shows an embodiment in which R3> R2. This aspect is particularly useful for a tire having an aspect ratio of 60% or less, as described above, to improve the ground contact shape.
[0025]
When R3> R2, the radius of curvature R3 of the outer land portion 5 needs to be smaller than the radius of curvature R1 of the central land portion 3, that is, R3> R1. When R3> R1, the grounding shape easily approaches the shape shown in FIG. 6B, which is not preferable in terms of durability and wear resistance. That is, in this embodiment, R1>R3> R2.
[0026]
The difference (R3-R2) between the radius of curvature R3 of the outer land portion 5 and the radius of curvature R2 of the intermediate land portion 4 is the difference between the radius of curvature R1 of the central land portion 3 and the radius of curvature R2 of the intermediate land portion 4 ( It is desirable to make it smaller than R1-R2).
[0027]
Further, in the embodiment shown in FIG. 3, an example in which a chamfered portion 9 having a small height which is notched like a chamfer is provided at an outer edge 3 e of the central land portion 3 in the tire axial direction. Similarly, a chamfered portion 9 having a small height, which is notched like a chamfer, is also provided on an outer edge 4e of the intermediate land portion 4 on the outer side in the tire axial direction. The chamfered portion 9 of the central land portion 3 can mitigate a local change in height with respect to the outer surface of the intermediate land portion 4, and can promote uniformization of the contact pressure between the

land portions

3 and 4. As a result, edge wear and the like, which tend to occur on the side edges of the intermediate land portion 4 and the central land portion 3, can be effectively prevented, and the wear performance can be improved over a long period of time.
[0028]
FIG. 5A shows an enlarged view of the vicinity of the inner vertical groove 6B.
The inner edge 9i in the tire radial direction of the chamfered portion 9 of the central land portion 3 is located further inward in the tire radial direction than the arc line Y2 virtually extending the outer surface of the intermediate land portion 4. Thereby, the distribution of the contact pressure between the central land portion 3 and the intermediate land portion 4 becomes more uniform. In particular, the distance S in the tire radial direction between the inner edge 9i of the chamfered portion 9 and the arc line Y2 is preferably, for example, 0.2 to 0.8 mm, more preferably 0.3 to 0.5 mm. The distance K along the outer surface of the central land portion 3 between the outer edge 9o (intersection with the tread surface) of the chamfered portion 9 and the virtual extension line Y3 of the groove wall of the vertical groove 6 is 1-2 mm. Is more effective.
[0029]
In addition, as shown in FIG. 4, in the aspect where R3> R2, as shown in FIG. 5B, the inner edge portion 5i of the outer land portion 5 on the inner side in the tire axial direction is also notched in a chamfered shape. It is desirable to provide the taking part 9. As a result, the change in the protrusion height between the intermediate land portion 4, the central land portion 3, and the outer land portion 5 can be further reduced, and edge wear or the like that tends to occur on each side edge portion can be further effectively suppressed. It is desirable that the inner edge 9i of the chamfer 9 is also separated by a distance S inward in the tire radial direction from the arc edge Y2. In addition, the chamfered portion 9 in this embodiment may have a length K ′ measured along the intermediate land portion 4 of 2 to 30 mm, more preferably 5 to 20 mm. This significantly reduces edge wear.
[0030]
Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 6 (A), the contact surface obtained when the tire is pressed against a flat surface by applying a normal load in the normal state, as shown in FIG. The ratio (Lc / Ls) of the contact length Lc in the tire circumferential direction to the contact length Ls in the tire circumferential direction at a shoulder portion that is separated from the tire equator C by 40% of the tread contact width TW outward in the tire axial direction is (Lc / Ls). 1.0 to 1.3, more preferably 1.1 to 1.2, and a particularly preferable grounding shape can be obtained.
[0031]
【Example】
A radial tire for a small truck having a tire size of 225 / 60R17.5 was prototyped based on the specifications shown in Table 1, and the contact shape, durability and wear resistance were tested. The internal structure of each test tire was the same.
[0032]
The durability was determined by assembling each test tire on a rim (6.75 × 17.5) and using a drum tester to determine the running distance until the tire was broken. The evaluation was carried out under the following conditions, using an index with Comparative Example 1 being 100.
Test load: 16.33KN
Internal pressure: 600 kPa
Running speed: 80km / H
[0033]
In addition, the wear resistance was evaluated by running the vehicle in a city area, a mountainous area, and a highway, each including 1000 km, and visually observing the uneven wear state.
Table 1 shows the test results and the like.
[0034]
[Table 1]

[0035]
【The invention's effect】
As described above, the pneumatic tire of the present invention can improve durability and abrasion resistance by optimizing a ground contact shape.
[Brief description of the drawings]
FIG. 1 is a contour diagram of a pneumatic tire according to an embodiment of the present invention in a normal state.
FIG. 2 is a development view of a tread pattern of the pneumatic tire according to the embodiment.
FIG. 3 is an enlarged contour diagram of a tread portion of the pneumatic tire according to the embodiment.
FIG. 4 is an enlarged contour diagram of a tread portion showing another embodiment of the present invention.
FIG. 5A is an enlarged view around an inner vertical groove, and FIG. 5B is an enlarged view around an outer vertical groove.
6A is a grounding shape diagram of the present embodiment, and FIG. 6B is a grounding shape diagram of a conventional example.
[Explanation of symbols]
2 Tread surface 3 Central land portion 4 Intermediate land portion 5 Outer land portion 6 Vertical groove 6A Inside vertical groove 6B Outside vertical groove 9 Slope portion R1 Radius of curvature of outer surface of central land portion R2 Radius of curvature of outer surface of intermediate land portion R3 Radius of curvature E of outer surface of outer land part

Claims

トレッド面を、タイヤ赤道上をのびる中央陸部と、ショルダ部をのびる外側陸部と、前記中央陸部と前記外側陸部との間の中間陸部とにタイヤ周方向の縦溝により区分し、
かつ正規リムにリム組みしかつ正規内圧を充填した無負荷の正規状態におけるタイヤ軸を含むタイヤ子午線断面において、前記中央陸部の外面の曲率半径Ｒ１が、前記中間陸部の外面の曲率半径Ｒ２よりも大であり、しかも各曲率半径Ｒ１、Ｒ２の中心が同じ位置にあることを特徴とする空気入りタイヤ。The tread surface is divided into a central land portion extending on the tire equator, an outer land portion extending on the shoulder portion, and an intermediate land portion between the central land portion and the outer land portion by vertical grooves in the tire circumferential direction. ,
In a tire meridian section including a tire shaft in a normal state with no load loaded to a regular rim and filled with a regular internal pressure, a radius of curvature R1 of the outer surface of the central land portion is equal to a radius of curvature R2 of the outer surface of the intermediate land portion. A pneumatic tire, wherein the center of each of the radii of curvature R1 and R2 is at the same position.

前記中央陸部の曲率半径Ｒ１と中間陸部の曲率半径Ｒ２との差（Ｒ１−Ｒ２）が０．１〜１．０ｍｍであることを特徴とする請求項１記載の空気入りタイヤ。The pneumatic tire according to claim 1, wherein a difference (R1-R2) between the radius of curvature R1 of the central land portion and the radius of curvature R2 of the intermediate land portion is 0.1 to 1.0 mm.

前記外側陸部の外面の曲率半径Ｒ３は、前記中間陸部の曲率半径Ｒ２と同一か又はそれよりも大かつ前記曲率半径Ｒ１よりも小であり、
しかも各曲率半径Ｒ２、Ｒ３の中心が同じ位置にあることを特徴とする請求項１又は２に記載の空気入りタイヤ。The radius of curvature R3 of the outer surface of the outer land portion is equal to or larger than the radius of curvature R2 of the intermediate land portion and smaller than the radius of curvature R1;
3. The pneumatic tire according to claim 1, wherein the centers of the radii of curvature R2 and R3 are located at the same position.

前記中央陸部は、そのタイヤ軸方向の外縁部に、面取り状に切り欠いた小高さの面取部を設けたことを特徴とする請求項１乃至３のいずれかに記載の空気入りタイヤ。The pneumatic tire according to any one of claims 1 to 3, wherein the central land portion is provided with a chamfered portion having a small height, which is cut out in a chamfered shape, at an outer edge portion in the tire axial direction.

前記正規状態で正規荷重を負荷しタイヤを平面に押し付けたときに得られる接地面は、タイヤ赤道でのタイヤ周方向の接地長さＬｃと、タイヤ赤道からトレッド接地巾の４０％をタイヤ軸方向外側に隔てたショルダ部でのタイヤ周方向の接地長さＬｓとの比（Ｌｃ／Ｌｓ）が１．０〜１．３であることを特徴とする請求項１乃至４記載の空気入りタイヤ。The contact surface obtained when a normal load is applied and the tire is pressed against a flat surface in the normal state is the contact length Lc in the tire circumferential direction at the tire equator and 40% of the tread contact width from the tire equator to the tire axial direction. The pneumatic tire according to any one of claims 1 to 4, wherein a ratio (Lc / Ls) to a ground contact length Ls in a tire circumferential direction at a shoulder portion separated outside is 1.0 to 1.3.