JP4102151B2

JP4102151B2 - Pneumatic tire

Info

Publication number: JP4102151B2
Application number: JP2002289031A
Authority: JP
Inventors: 克司谷本
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2002-10-01
Filing date: 2002-10-01
Publication date: 2008-06-18
Anticipated expiration: 2022-10-01
Also published as: JP2004122904A

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]
BACKGROUND 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, for example, in a pneumatic tire for a light truck having a flatness ratio of 70% or less, the contact surface shape a as shown in FIG. In the ground contact surface shape a, the contact length Le on the shoulder side is larger than the contact length Lc of the tire equator C. As a result of experiments by the inventors, it has been found that such a ground contact surface shape a deteriorates the wear resistance performance such that the durability of the tire is low and uneven wear tends to occur. Such a cause is often used under high load conditions. Especially in this type of tire, it is considered that the curvature deformation of the tread surface is conventionally formed with a single curvature radius. It is done.
[0003]
The inventors repeated various experiments. As shown in FIG. 6A, the ground contact surface shape b in which the ground contact length Lc of the tire equator C is larger than the ground contact length Le on the shoulder side is obtained. The present inventors have found that such a ground contact surface shape b can be obtained by appropriately changing the radius of curvature of the tread surface, which is preferable for the durability and wear resistance of the tire. .
[0004]
As described above, an object of the present invention is to provide a pneumatic tire, particularly a small truck tire, which can optimize the ground contact shape and improve durability and wear resistance.
[0005]
[Means for Solving the Problems]
According to the first aspect of the present invention, the tread surface has a central land portion extending over the tire equator, an outer land portion extending over the shoulder portion, and an intermediate land between the central land portion and the outer land portion. In the tire meridian cross-section including the tire shaft in a normal state with no load, which is divided by a longitudinal groove in the tire circumferential direction and is assembled with a normal rim and filled with a normal internal pressure, the radius of curvature of the outer surface of the central land portion R1 is larger than the curvature radius R2 of the outer surface of the intermediate land portion, and the centers of the curvature radii R1 and R2 are at the same position.
[0006]
Here, the “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based. For example, a standard rim for JATMA and a “Design Rim” for TRA. Or “Measuring Rim” for ETRTO. In addition, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. It is the maximum air pressure for JATMA and the table “TIRE LOAD LIMITS” for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, but 180 kPa for tires for passenger cars.
[0007]
The invention according to claim 2 is characterized in that the difference (R1-R2) between the curvature radius R1 of the central land portion and the curvature radius R2 of the intermediate land portion is 0.1 to 1.0 mm. 1. The pneumatic tire according to 1.
[0008]
According to the invention described in claim 3, 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. The pneumatic tire according to claim 1 or 2, wherein the centers of the curvature radii R2 and R3 are at the same position.
[0009]
According to a fourth aspect of the present invention, 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. The pneumatic tire according to any one of the above.
[0010]
In the invention according to claim 5, the contact surface obtained when a normal load is applied in the normal state and the tire is pressed against a flat surface includes a contact length Lc in the tire circumferential direction at the tire equator and a tread from the tire equator. The ratio (Lc / Ls) with the contact length Ls in the tire circumferential direction at the shoulder portion separating 40% of the contact width outward in the tire axial direction is 1.0 to 1.3. The pneumatic tire according to 1 to 4.
[0011]
Here, “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is specified for JATMA, and the table “TIRE LOAD” is set for TRA. The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” for ETRTO. Further, the “tread contact width” is the maximum distance in the tire axial direction between the tread contact ends when a normal load is applied to the normal state and contacted with a flat surface.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a contour diagram of a tire meridian cross section including a tire shaft in a normal state with no load in which a pneumatic tire for a small truck is assembled on a normal rim (not shown) and filled with a normal internal pressure as a present embodiment, FIG. 2 is an unfolded view showing the tread portion.
[0013]
In the figure, a pneumatic tire 1 has a tread surface 2 between a central land portion 3 extending over the tire equator C, an outer land portion 5 extending over a shoulder portion, and between the central land portion 3 and the outer land portion 5. The intermediate land portion 4 is divided by a longitudinal groove 6 in the tire circumferential direction. The outer land portion 5 includes a ground contact 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 composed of rib rows extending continuously in the tire circumferential direction, and the intermediate land portion 4 is a block B divided by a lateral groove 7 extending in a substantially V shape. It consists of a row of blocks arranged in the circumferential direction. In addition, although it can determine suitably whether each land part is made into a rib row | line | column or a block row | line, Preferably, like this example, the outer side where a big lateral force acts at the time of the central land part 3 where a contact pressure becomes high It is preferable to use a highly rigid rib row for the land portion 5. Note that siping, lug-like grooves, and the like can be appropriately provided in the rib row.
[0015]
The longitudinal groove 6 includes an inner longitudinal groove 6A extending between the central land portion 3 and the intermediate land portion 4, and an outer longitudinal groove 6B extending between the intermediate land portion 4 and the outer land portion 5. In the present embodiment, the tires are arranged symmetrically about the equator C. Each longitudinal groove 6 is relatively wide, continuous in the tire circumferential direction, and linearly extending, but may be appropriately bent. The groove width of the longitudinal groove 6 is not particularly limited, but the groove width GW measured on the tread surface 2 is set to about 2 to 7%, more preferably about 2 to 5% of the tread grounding width TW. desirable. The depth of the longitudinal groove 3 is, for example, 5 mm or more, more preferably 6 mm or more, and further preferably about 7 to 15 mm.
[0016]
Further, the inner longitudinal groove 6A may have a groove centerline that is separated from the tire equator C by a distance X1 of 7 to 12%, more preferably 8 to 10% of the tread ground contact width TW. When the distance X1 is less than 7% of the tread ground contact width TW, the rigidity of the central land portion 3 is insufficient, wear energy is concentrated on the central land portion 3 and uneven wear tends to occur, and conversely exceeds 12%. Then, the rigidity of the central land portion 3 becomes excessive, and the wear energy tends to concentrate on other land portions.
[0017]
The outer longitudinal groove 6B may have a groove centerline separating a distance X2 from the tire equator C of 27 to 33%, more preferably 29 to 31% of the tread ground contact width TW. When the distance X2 is less than 27% of the tread ground contact width TW, the rigidity of the intermediate land portion 4 is insufficient, and wear energy is concentrated on the intermediate land portion 4 and uneven wear tends to occur. 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 a tire is new, the curvature radius R1 of the outer surface of the central land portion 3 is larger than the curvature radius R2 of the outer surface of the intermediate land portion 4, and each curvature is One feature is that the centers O of the radii R1 and R2 are at the same position. The center O is located in the tire equator 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 protruded outward in the tire radial direction compared to the intermediate land portion 4, The contact length in the vicinity of the tire equator C on the contact surface can be increased. Then, as shown in FIG. 6A, 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 toward the outer side in the tire axial direction can be obtained. Since such a pneumatic tire 1 has a good contact pressure balance of the tread surface 2, durability and wear resistance can be improved.
[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 preferably set to 0.1 to 1.5 mm, for example. When 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 it is difficult to obtain the effect. On the other hand, 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 ground pressure of the intermediate land portion 4 becomes excessively low. Uneven wear is likely to occur due to dragging of 4. More preferably, the difference (R1-R2) is about 0.5 to 1.0 mm.
[0021]
Here, the radius of curvature R1 of the central land portion 3 is not particularly limited. For example, it is desirable that the radius of curvature R1 is 350 to 500% of the tread ground contact width TW, more preferably 420 to 480%, and still more preferably about 440 to 460%. . When the curvature radius R1 is less than 350% of the tread ground contact width TW, the central land portion 3 becomes more rounded, and uneven wear tends to occur in the central land portion 3. On the other hand, when the radius of curvature R1 exceeds 500% of the tread ground contact width TW, contrary to the above, uneven wear tends to occur at 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 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 aspect in which R3 = R2. In this aspect, the contact length of the shoulder portion is reduced particularly in a tire having a flatness ratio of 65 to 70%. This helps to improve the tire circumferential length in the ground contact shape to a preferred shape that gradually decreases from the tire equator toward the shoulder.
[0024]
FIG. 4 shows an aspect in which R3> R2. This aspect is useful for improving the ground contact shape as described above particularly in a tire having a flatness ratio of 60% or less.
[0025]
When R3> R2, the curvature radius R3 of the outer land portion 5 needs to be smaller than the curvature radius R1 of the central land portion 3, that is, R3> R1. When R3> R1, the ground contact shape tends to approach 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 between the curvature radius R3 of the outer land portion 5 and the curvature radius R2 of the intermediate land portion 4 (R3-R2) is the difference between the curvature radius R1 of the central land portion 3 and the curvature radius R2 of the intermediate land portion 4 ( It is desirable to make it smaller than R1-R2).
[0027]
Moreover, in the aspect shown in FIG. 3, the outer edge part 3e of the tire land direction of the central land part 3 has illustrated the thing provided with the chamfering part 9 of the small height notched by chamfering shape. Similarly, a chamfered portion 9 having a small height that is notched in a chamfered shape is also provided on the outer edge portion 4e outside the intermediate land portion 4 in the tire axial direction. The chamfered portion 9 of the central land portion 3 can alleviate a local height change with respect to the outer surface of the intermediate land portion 4, and can promote uniform contact pressure between the

land portions

3 and 4. Thereby, edge wear or the like that tends to occur at each side edge of the intermediate land portion 4 and the central land portion 3 can be effectively prevented, and 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 chamfered portion 9 of the central land portion 3 has an inner edge 9i in the tire radial direction located inward in the tire radial direction from an 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, for example, preferably 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 of the chamfered portion 9 (intersection with the tread surface) and the virtual extension line Y3 of the groove wall of the longitudinal groove 6 is 1-2 mm. Is more effective.
[0029]
As shown in FIG. 4, in the aspect where R3> R2, as shown in FIG. 5 (B), the inner edge portion 5i on the inner side in the tire axial direction of the outer land portion 5 is also a chamfered surface. It is desirable to provide a catch 9. Thereby, the change of the protrusion height between the middle land part 4, the central land part 3, and the outer land part 5 can be relieved more, and edge wear etc. which are likely to occur in each side edge part can be suppressed more effectively. It is desirable that the inner edge 9i of the chamfered portion 9 is also separated from the arc edge Y2 by a distance S inward in the tire radial direction. Further, the chamfered portion 9 of this aspect is preferably set so that the length K ′ measured along the intermediate land portion 4 is 2-30 mm, more preferably 5-20 mm. This significantly reduces edge wear.
[0030]
Further, in the pneumatic tire 1 of the present embodiment, the contact surface obtained when a normal load is applied in the normal state and the tire is pressed against a flat surface is, as shown in FIG. The ratio (Lc / Ls) between the contact length Lc in the tire circumferential direction and the contact length Ls in the tire circumferential direction at a shoulder portion that divides 40% of the tread contact width TW from the tire equator C to the outer side in the tire axial direction. It can be set to 1.0 to 1.3, more preferably 1.1 to 1.2, and a particularly preferable ground contact shape can be obtained.
[0031]
【Example】
A radial tire for a light truck having a tire size of 225 / 60R17.5 was prototyped based on the specifications shown in Table 1, and tested for ground contact shape, durability, and wear resistance. Each test tire had the same internal structure.
[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 broke. Evaluation was carried out under the following conditions after evaluating with an index of Comparative Example 1 as 100.
Test load: 16.33KN
Internal pressure: 600 kPa
Travel speed: 80km / H
[0033]
In addition, the wear resistance was evaluated by visually observing uneven wear conditions by running an actual vehicle including 1000 km each of an urban area, a mountainous area, and a highway.
Table 1 shows the test results.
[0034]
[Table 1]

[0035]
【The invention's effect】
As described above, the pneumatic tire of the present invention can improve the durability and wear resistance performance by optimizing the contact shape.
[Brief description of the drawings]
FIG. 1 is a contour diagram in a normal state of a pneumatic tire showing an embodiment of the present invention.
FIG. 2 is a development view of a tread pattern of the pneumatic tire of the present embodiment.
FIG. 3 is an enlarged contour diagram of a tread portion of the pneumatic tire according to the present embodiment.
FIG. 4 is an enlarged outline diagram of a tread portion showing another embodiment of the present invention.
5A is an enlarged view of the vicinity of the inner vertical groove, and FIG. 5B is an enlarged view of the vicinity of the 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 longitudinal groove 6B inside longitudinal groove 6B outer longitudinal groove 9 slope portion R1 curvature radius R2 of outer surface of central land portion curvature radius R3 of outer surface of intermediate land portion Radius of curvature E of outer surface of outer land

Claims

The tread surface is divided into a central land portion extending over the tire equator, an outer land portion extending over 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 addition, in a tire meridian cross section including a tire shaft in a normal state in which a normal rim is assembled and filled with a normal internal pressure, a curvature radius R1 of the outer surface of the central land portion is a curvature radius R2 of the outer surface of the intermediate land portion. And a center of each of the radii of curvature R1 and R2 is in the same position.

The pneumatic tire according to claim 1, wherein a difference (R1-R2) between a curvature radius R1 of the central land portion and a curvature radius R2 of the intermediate land portion is 0.1 to 1.0 mm.

A radius of curvature R3 of the outer surface of the outer land portion is equal to or greater than a radius of curvature R2 of the intermediate land portion and smaller than the radius of curvature R1.
And the center of each curvature radius R2 and R3 exists in the same position, The pneumatic tire of Claim 1 or 2 characterized by the above-mentioned.

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 cut out in a chamfered shape at an outer edge portion in a tire axial direction.

The contact surface obtained when a normal load is applied in the normal state and the tire is pressed against a flat surface 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 in the tire axial direction. 5. The pneumatic tire according to claim 1, wherein a ratio (Lc / Ls) to a contact length Ls in a tire circumferential direction at a shoulder portion separated outward is 1.0 to 1.3.