JP3949939B2

JP3949939B2 - Pneumatic tire

Info

Publication number: JP3949939B2
Application number: JP2001349192A
Authority: JP
Inventors: 忠雄松本
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2001-11-14
Filing date: 2001-11-14
Publication date: 2007-07-25
Anticipated expiration: 2021-11-14
Also published as: JP2003146018A

Description

【０００１】
【発明の属する技術分野】
本発明は、偏摩耗や乾燥路面での操縦安定性を損ねることなく耐ハイドロプレニング性能を向上しうる空気入りタイヤに関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
高速でウエット路面を走行すると、タイヤが水膜上に乗り上げ操舵不能に陥るいわゆるハイドロプレーニング現象が発生することが知られている。種々の実験の結果、このハイドロプレーニング現象の発生速度をより高速域へと移行させること、即ち耐ハイドロプレニング性能を向上するためには、トレッド面に凹設される縦溝の溝容積を増大することや、この縦溝に連通する傾斜溝などを多数配置することが効果的であることが判明している。
【０００３】
しかしながら、トレッド面に縦溝、傾斜溝を配する場合、その用い方によっては偏摩耗が発生したり、またパターン剛性が低下するため乾燥路面での操縦安定性を損ねる等の問題が生じうる。本発明は、このような実状に鑑み案出なされたもので、トレッド面の中央領域に設けた縦溝の溝壁面の形状、及び傾斜溝の傾き角度や縦溝との相対関係を規制することを基本として、耐偏摩耗性能や乾燥路面での操縦安定性を損ねることなく耐ハイドロプレニング性能を向上しうる空気入りタイヤを提供することを目的としている。
【０００４】
【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、タイヤ赤道を中心としてトレッド接地巾の４５％の領域をなすトレッド面の中央領域に、タイヤ周方向に連続してかつ溝中心がタイヤ赤道から離れてのびる少なくとも１本の縦溝を具え、前記中央領域において最もタイヤ軸方向外側の前記縦溝のタイヤ軸方向外側の溝壁面は、溝縁からタイヤ半径方向内方に小距離を隔てた高さまでの外側部分に、前記トレッド面に向かって溝巾を拡大させる向きに傾く面取り状の斜壁部を含むとともに、前記縦溝のタイヤ軸方向外側の陸部に、前記縦溝の前記溝縁からトレッド接地巾の１〜５％の小距離δをタイヤ軸方向外側に隔てる位置に内方端部を有しかつタイヤ周方向に対して５〜３０゜の角度で傾いてタイヤ軸方向外側にのびる急傾斜溝をタイヤ周方向に隔設したことを特徴としている。
【０００５】
本明細書において、「トレッド接地巾」はタイヤを正規リムにリム組しかつ正規内圧を充填するとととも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距離とする。また前記「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、前記「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。さらに「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"とするが、タイヤが乗用車用である場合には、上記荷重の０．８倍の荷重とする。なお以下、特に言及しない場合、タイヤの各部の寸法等は、タイヤを正規リムにリム組しかつ正規内圧を充填した無負荷の状態で特定されるものとする。
【０００６】
さらに請求項１に係る発明は、かつ中央領域の各外側をなすショルダー領域に、それぞれタイヤ周方向に連続してのびる外の縦溝が形成されるとともに、
前記急傾斜溝のタイヤ周方向の略中間部と前記外の縦溝との間を、前記急傾斜溝と同向きかつタイヤ周方向に対する角度が前記急傾斜溝よりも大きい緩傾斜溝により接続したことを特徴とする。
【０００７】
また請求項２記載の発明は、前記中央領域は、タイヤ赤道の両側に配された一対の縦溝を具えることにより、タイヤ赤道上に中央リブを具えることを特徴とする。
【０００８】
また請求項３記載の発明は、前記トレッド面は、その中央領域の各外側をなすショルダ領域に、それぞれタイヤ周方向に連続してのびる外の縦溝が形成されるとともに、前記急傾斜溝は、この外の縦溝に連通することなく終端する外方端部を有し、しかもタイヤ周方向に前記内方端部が隣り合う前記急傾斜溝は、各々、タイヤ周方向に延在することによりタイヤ軸方向に互いに重なる重複部を形成することを特徴とする。
【０００９】
また請求項４記載の発明は、前記斜壁部は、前記縦溝の溝縁を通るトレッド面の法線に対して５０〜８０゜の角度で傾くことを特徴とする。
【００１０】
【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は本発明の実施形態を示すトレッドパターンの展開図、図２（Ａ）はそのＡ−Ａ線断面図、図２（Ｂ）はそのＢ−Ｂ線断面図、図３は図２（Ａ）の斜視図、図４は図２（Ｂ）の斜視図をそれぞれ示す。図において、本実施形態の空気入りタイヤは、トレッド面２に、タイヤ赤道Ｃの両側に実質的に左右対称で配された一対の内の縦溝３ａ、３ａと、その外側に実質的に左右対称に配された一対の外の縦溝３ｂ、３ｂとが設けられており、例えば乗用車用ラジアルタイヤとして好適に用いられる。
【００１１】
前記各縦溝３（総称するとき、符号３を用いる）は、本実施形態では、いずれもタイヤ周方向に直線状でかつ連続してのびるものが示される。縦溝３は、トレッド面の排水性を向上するために、例えば図２に示す如く、トレッド面２と溝壁面６との交点である溝縁３ｅ、３ｅ間の溝巾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ＧＤについては、例えば６．５〜１０．０mm、より好ましくは７．０〜９．０mmとするのが望ましい。
【００１２】
前記内の縦溝３ａは、その溝中心がタイヤ赤道Ｃから離れて設けられるが、その配設位置（溝中心線がある位置）は、タイヤ赤道Ｃを中心としてトレッド接地巾ＴＷの４５％の領域をなすトレッド面の中央領域Ｃｒに設けられる。このような中央領域Ｃｒは、走行中の接地圧が高くしかも接地長さも大となるため、かかる領域に縦溝３ａを設けることによって、路面の水膜を効果的に除去、排出することができる。なおタイヤ赤道Ｃから離して縦溝３を設けた場合、乾燥路などでパターン剛性が不足するのを効果的に防止しうる。
【００１３】
また中央領域Ｃｒは、本例のようにタイヤ赤道Ｃの両側に一対の内の縦溝３ａ、３ａを設けてタイヤ赤道Ｃ上に中央リブＬ１を具えるのが好適である。中央リブＬ１の巾は、好適にはトレッド接地巾ＴＷの５〜１０％、より好ましくは７〜１０％である。なお中央領域Ｃｒに設ける縦溝３の本数は１本以上であれば特に限定はされないが、好ましくは本例のように複数本が望ましい。
【００１４】
前記外の縦溝３ｂは、中央領域Ｃｒの各外側の領域をなすショルダ−領域Ｓｈにその溝中心線が位置している。このため、ショルダ−領域Ｓｈにおいてもトレッド面２の水膜を除去して排水効果を高めることができる。また、本例のトレッド面２には、内の縦溝３ａと外の縦溝３ｂとの間に中の陸部Ｌ２が形成され、さらに外の縦溝３ｂと接地端ｅとの間には外の陸部Ｌ３がそれぞれ形成される。
【００１５】
前記中央領域Ｃｒにおいて、最もタイヤ軸方向外側に配される縦溝、即ち本例では各内の縦溝３ａ、３ａは、図２（Ａ）に示すように、タイヤ軸方向の外側の溝壁面６ｏが、溝縁３ｅからタイヤ半径方向内方に小距離ｈを隔てた高さまでの外側部分４に、トレッド面２に向かって溝巾を拡大させる向きに傾く面取り状の斜壁部８を含んで構成される。この外側部分４は、例えば全てが斜壁部８により構成されても良いが、本例では斜壁部８と、この斜壁部８の外側縁８ｏからタイヤ半径方向にのび溝縁３ｅに至る小高さの縦壁部１０とを含むものが例示される
。
【００１６】
前記斜壁部８は、内の縦溝３ａのトレッド面２付近の溝巾を局部的に拡大することによって、溝容積の拡大ないし路面に滞留した水を効果的に縦溝３内へ流入させることができ、排水性をより向上するのに役立つ。一方、縦壁部１０は、溝縁３ｅをより明瞭な鋭いエッジとし、このエッジを利用して路面の水膜を切断しうるため、縦溝３内への前記水の取り込みをさらに助長し斜壁部８の効果を高める。
【００１７】
外側部分の高さｈは、特に限定はされないが、例えば内の縦溝３ａの深さＧＤの１０〜６０％、より好ましくは２０〜５０％とするのが望ましい。前記高さｈが内の縦溝３ａの深さＧＤの１０％未満であると、斜壁部８による縦溝３の溝容積の拡大効果が低下する傾向があり、逆に６０％を超えると、接地面積が減少したり溝縁３ｅ付近の陸部剛性を低下させ偏摩耗などが生じやすくなるため好ましくない。
【００１８】
また斜壁部８は、その溝壁面６ｏの溝縁３ｅを通るトレッド面の法線Ｎに対する傾き角度θｏを５０〜８０゜、さらに好ましくは６０〜７５゜程度とすることが好ましい。前記角度θｏが５０゜未満であると、溝巾を拡大させる効果が小さく、逆に８０゜を超えると、十分な斜壁部８の高さを確保するのが困難となり、同様に溝容積の拡大化には寄与し得ない傾向がある。また縦壁部１０の高さＦは、好ましくは０．５〜１．５mm、さらに好ましくは０．５〜１．０mmの小高さとするのが望ましい。なお深さＨを有する溝壁面６の内側部分５は、溝底との交わり部を除き前記法線Ｎに対して５〜１５゜程度で傾く通常の主壁部７が形成される。
【００１９】
また、図３及びそのＣ−Ｃ線断面図である図５に示すように、本例では溝壁面６ｏの前記斜壁部８には、小巾かつ小深さの微細溝９…が本例ではタイヤ軸方向にほぼ平行にのびかつタイヤ周方向に隔設されているものを示す。このような微細溝９は、斜壁部８の濡れ性を高め該斜壁部８への水の付着性を向上しうることによって、内の縦溝３ａ内での排水性をより良く改善する。とりわけ新品時の溝壁面などには離型剤や油脂類が多く付着してるため水をはじきやすいが、斜壁部８に微細溝９を設けることにより、濡れ性を高めてウエット性能を向上することができる。また斜壁部８に微細溝９を設けると、斜壁部８と路面との間の水を溝内部へと効果的に押し出すことができ、その押し出された水によって図６に示すように内の縦溝３ａの内部で渦状の水流が発生する。このような流れは、溝内部を通過する流水の排水効率を高める効果を有する。
【００２０】
上述のような作用を実現するために、図５に示すように、微細溝９の溝巾Ｗは、好ましくは０．３〜１．２mm、より好ましくは０．６〜１．０mmとするのが望ましい。また微細溝９の溝深さｄは、好ましくは０．３〜１．５mm、より好ましくは０．３〜０．６mmとするのが望ましい。さらに微細溝９のタイヤ周方向のピッチＰ（図５の如く、微細溝９の溝中心線間の距離）は、好ましくは１．４〜４．０mm、より好ましくは２．０〜３．０mmとするのが望ましい。なお微細溝９のピッチＰは、溝巾Ｗ、溝深さｄと同様に、一定でも良いが、前記範囲内で違えることもできる。
【００２１】
また微細溝９の断面形状は、特に限定はされず、図５に示したような略半円状をなすものの他、角溝、三角溝（いずれも図示省略）など種々のものが採用できる。より好ましくは、微細溝９の溝容積を効率良く確保し得るとともに毛細管現象によって水の吸い上げ効果が期待できる前記略半円状が望ましい。このような微細溝９は、縦溝３の溝縁付近の剛性を低下させることがないため、乾燥路面における操縦安定性の悪化を防止しうる。
【００２２】
なお内の縦溝３の内側の溝壁面６ｉは、特に限定されず種々の態様で実施することができる。本例では外側部分４が斜壁部８だけからなる態様を示す。また内側の溝壁面６ｉの斜壁部８の角度θｉは、外側の斜壁部８の角度θｏよりも小に設定されている。このような構成により、中央リブＬ１の剛性を確保し乾燥路面での操縦安定性を維持しつつ、内の縦溝３ａ内への水の流入量に差を設け、これによって内の縦溝３ａ内でさらに好適に前記渦の発生が期待できる。そして、さらに好ましくは角度差｜θｏ−θｉ｜を例えば１０〜３０゜、より好ましくは２０〜３０゜程度とするのが望ましい。
【００２３】
また図２（Ｂ）、図４に示すように、外の縦溝３ｂのタイヤ軸方向外側の溝壁面６ｏは斜壁部８を有しているが、タイヤ軸方向内側の溝壁面６ｉには斜壁部８を設けることなく形成している。ただし、このような態様に限定されず、外の縦溝３ｂについても内の縦溝３ａと同様の構成を採用することも勿論可能である。また縦壁部１０を形成することもできる。
【００２４】
また本発明の空気入りタイヤは、図１、図７に示す如く、トレッド面２に、前記内の縦溝３ａのタイヤ軸方向外側の陸部である中の陸部Ｌ２に急傾斜溝１１がタイヤ周方向に隔設されている。急傾斜溝１１は、内の縦溝３ａのタイヤ軸方向外側の溝縁３ｅから小距離δをタイヤ軸方向外側に隔てる位置に内方端部１１ｉを有しかつタイヤ周方向に対して５〜３０゜の角度βで傾いてタイヤ軸方向外側にのびている。なお急傾斜溝１１が滑らかに湾曲するとき、前記角度βは平均の角度を採用する。また急傾斜溝１１の内方端部１１ｉと、内の縦溝３ａのタイヤ軸方向外側の溝縁３ｅとの間の前記小距離δは、トレッド接地巾ＴＷの１〜５％とする。
【００２５】
中央領域Ｃｒの排水性を向上するためには、このような急傾斜溝１１の内方端部１１ｉを前記内の縦溝３ａに連通させることないしその近傍に位置させることが望ましいものである、しかしながら、単にこのような方法を採用した場合、中央領域Ｃｒのパターン剛性、とりわけ、急傾斜溝１１と内の縦溝３ａとの間に形成される巾の狭い陸部の剛性が低下し、操縦安定性や偏摩耗において不利となる。そこで本発明では、図７のＤ−Ｄ線拡大断面である図８に示すように、前述のように内の縦溝３ａのタイヤ軸方向外側の溝壁面６ｏに前記斜壁部８を設け、小距離δをより小さく設定しても内の縦溝３ａと急傾斜溝１１とで挟まれる陸部１５の内方部分の厚さを大きく確保できるため剛性を損ねることがない。これにより、乾燥路面での操縦安定性を損ねることなく、急傾斜溝１１の内方端部１１ｉを内の縦溝３ａにより近づけて排水性能を向上しうる。
【００２６】
このように、タイヤ周方向に対して小さな角度βで傾く急傾斜溝１１は、中の陸部Ｌ２と路面との間の水膜を切断して排水するのにより効果的なものとなる。なお前記小距離δがトレッド接地巾ＴＷの１％未満であると、斜壁部８を設けていてもこの内方端部１１ｉと外の縦溝３ｂとの間に形成される陸部の剛性が著しく小となり、この部分を起点としたゴム欠けや偏摩耗性が生じ易く、また乾燥路面での操縦安定性をも悪化させ易い。また急傾斜溝１１を内の縦溝３ａに連通させると、中央領域Ｃｒのパターン剛性が低下し易くなるため好ましくない。他方、小距離δがトレッド接地巾ＴＷの５％を超えると、この内方端部１１ｉと内の縦溝３ｂの溝縁３ｅとの間に巾が大の陸部が形成され排水性の悪い部分を形成するため好ましくない。このような観点より、前記小距離δは、より好ましくはトレッド接地巾ＴＷの１〜５％、さらに好ましくは３〜５％とするのが望ましい。
【００２７】
また急傾斜溝１１の前記角度βが５゜未満であると、この急傾斜溝１１と内の縦溝３ａとで挟まれる陸部の剛性が大幅に低下し、乾燥路面での操縦安定性を低下させる他、偏摩耗を発生させやすくなる。逆に急傾斜溝１１の前記角度βが３０゜を超えると、中の陸部Ｌ２において十分な水膜除去効果が得られず、耐ハイドロプレーニング性能を高め得ない。このような観点より、前記角度βは、より好ましくは５〜２０゜、さらに好ましくは５〜１５゜とするのが望ましい。
【００２８】
また本例の急傾斜溝１１は、外の縦溝３ｂに連通することなく終端する外方端部１１ｏを有している。このため、巾の広い外の縦溝３ｂの溝縁付近の剛性低下を防止でき、さらに乾燥路面での操縦安定性の低下を抑制しうる。しかし、急傾斜溝１１の外方端部１１ｏと前記外の縦溝３ｂのタイヤ軸方向内側の溝縁３ｅとの間のタイヤ軸方向の距離Ｋが大きすぎると、中の陸部Ｌ２における排水性能の低下が生じやすく、逆に小さすぎても外の縦溝３ｂの溝縁付近の剛性が低下し、操縦安定性の悪化を招きやすい。このような観点より、前記距離Ｋは、トレッド接地巾ＴＷの３〜８％、さらに好ましくは４〜６％とするのが望ましい。
【００２９】
また図１に示すように、タイヤ周方向に前記内方端部１１ｉが隣り合う急傾斜溝１１、１１は、各々、タイヤ周方向に延在することによりタイヤ軸方向に互いに重なる重複部２０を形成している。これにより、中の陸部Ｌ２において、バランス良く排水性能を高め得る。この重複部２０のタイヤ周方向の長さＬは、好適にはトレッド接地巾ＴＷの５〜１５％程度とすることが望ましい。なお急傾斜溝１１の溝巾は特に限定はされないが、例えばトレッド面２で測定される溝巾ｇｗ（図７に示す）が縦溝３の溝巾ＧＷの５０〜９０％、より好ましくは６０〜８０％程度とするのが望ましい。また溝深さについては、例えば縦溝３と同程度が望ましい。
【００３０】
また本例のトレッド面２には、急傾斜溝１１のタイヤ周方向の略中間部と前記外の縦溝３ｂとの間を継ぐとともに、前記急傾斜溝１１と同向きかつタイヤ周方向に対する角度ηが前記急傾斜溝１１の前記角度βよりも大きい緩傾斜溝１３を設けたものを例示している。中の陸部Ｌ２のタイヤ軸方向の外側部分の領域（換言すれば外の縦溝３ｂのタイヤ軸方向内側の溝縁近傍）は、乾燥路面での旋回走行時に大きな横力が生じるためこの部分の剛性は操縦安定性能に大きな影響を与える。一方、耐ハイドロプレーニング性能を高めるためには、中の陸部Ｌ２と路面との間の水膜の一部を外の縦溝３ｂを使って排水させる必要がある。
【００３１】
そこで本実施形態では、傾斜がきつい急傾斜溝１１を外の縦溝３ｂに連通させることなく、傾斜が緩やかな緩傾斜溝１３を別途用いて急傾斜溝１１と外の縦溝３ｂとを連通することにより、中の陸部Ｌ２の剛性を大幅に損ねることなく排水性能を高める。緩傾斜溝１３は、急傾斜溝１１よりもタイヤ周方向に対する角度ηを大とするが、より好ましくは３０〜５０゜、さらに好ましくは３５〜４５゜とするのが望ましい。前記角度ηが３０゜未満になると、急傾斜溝１１との差が小さくなって、急傾斜溝１１との間に剛性の低い陸部が形成され、この部分を起点に偏摩耗が生じやすくなる傾向があり、逆に５０゜を超えると、急傾斜溝１１に対する相対角度が大きくなり排水抵抗が大となる傾向がある。より好適には角度差（η−β）を１０〜３０°程度とするのが望ましい。
【００３２】
また緩傾斜溝１３は、前記急傾斜溝１１のタイヤ周方向長さの略中間部に接続されることが望ましい。例えば緩傾斜溝１３を急傾斜溝１１の前記外方端部１１ｏ付近に接続することも可能ではあるが、この場合、急傾斜溝１１から流れる水流は緩傾斜溝１３との接続部で大きく流れ角度が変化するため、排水抵抗が増す傾向がある。これに対して、緩傾斜溝１３を急傾斜溝１１の前記略中間部で接続した場合には、流水の一部を取り込むため、前記排水抵抗の増大を防ぐことができる。なお急傾斜溝１１のタイヤ周方向の略中間部に緩傾斜溝１３を接続するとは、図７に示す如く、急傾斜溝１１のタイヤ周方向長さＳの中間位置を基準とし周方向前後に前記長さＳの１５％の巾を含む領域内に溝中心線の交わり部ｊを有するものとする。
【００３３】
また本実施形態では、前記外の陸部Ｌ３に、一端が外の縦溝３ｂに連通しかつ他端が接地端ｅで開口する横溝１４と、この横溝間に設けられかつ接地端ｅからタイヤ軸方向内側にのびて前記外の縦溝３ｂに連通することなく終端するラグ状溝１５とが設けられる。これにより、外の陸部Ｌ３において、接地端ｅ及び外の縦溝３ｂを利用して効果的な排水性能が得られる。
【００３４】
以上、本発明の実施形態について詳述したが、本発明は上記実施形態に限定されることなく種々の態様で実施することができる。例えば縦溝３を屈曲させる態様や、図９に示すように急傾斜溝１１、緩傾斜溝１３をタイヤ赤道Ｃを挟んでハ字状に配した方向性パターンとする態様、トレッド面２に適宜サイピングを付設する態様など種々の実施態様を含むことができる。
【００３５】
【実施例】
タイヤサイズが１９５／６５Ｒ１５の乗用車用ラジアルタイヤを図１のパターンで試作するとともに、ウエット性能、乾燥路面における操縦安定性、耐偏摩耗性能をテストし評価を行った。また比較のために、図１０に示したパターンを有する同サイズのタイヤ（比較例）についても併せて試験を行った。なおランド比をはほぼ同程度とし、内部構造も実質的に同一としている。
テストの方法は下記の要領で行った。
【００３６】
＜ウエット性能＞
半径１００ｍのアスファルト路面に、水深５mm、長さ２０ｍの水たまりを設けたコース上を、速度を段階的に増加させながら供試タイヤを装着した車両（排気量２０００cm³、リム６Ｊ、内圧１８０ｋＰａ）を進入させ、横加速度（横Ｇ）を計測し、５０〜８０km／ｈの速度における前輪の平均横Ｇを算出した（ラテラル・ハイドロプレーニングテスト）。結果は、従来例を１００とする指数で表示した。数値が大きい程良好である。
【００３７】
＜操縦安定性能＞
上記車両にてタイヤテストコースのドライアスファルト路面上をテスト走行し、ハンドル応答性、剛性感、グリップ等に関する特性をドライバーの官能評価により比較例１を１００とする指数で表示している。指数の大きい方が良好である。
【００３８】
＜耐偏摩耗性能＞
上記車両にて高速道路、市街地、山岳路を合計３０００ｋｍ走行し、トレッド面の摩耗状況を目視により観察した。
テスト結果などを表１に示す。
【００３９】
【表１】

【００４０】
テストの結果、実施例のものは、ウエット性能、操縦安定性能、耐偏摩耗性能をバランス良く向上していることが確認できた。
【００４１】
【発明の効果】
以上説明したように、本発明の空気入りタイヤは、偏摩耗や乾燥路面での操縦安定性を損ねることなく耐ハイドロプレニング性能を向上しうる。
【図面の簡単な説明】
【図１】本発明の一実施形態を示すトレッド部の展開図である。
【図２】（Ａ）はそのＡ−Ａ線断面図、（Ｂ）はそのＢ−Ｂ線断面図である。
【図３】図２（Ａ）の斜視図である。
【図４】図２（Ｂ）の斜視図である。
【図５】図３のＣ−Ｃ線断面図である。
【図６】縦溝内の水の流れを説明する断面略図である。
【図７】トレッド面の一部拡大図である。
【図８】そのＤ−Ｄ線拡大断面図である。
【図９】本発明の他の実施形態を示すトレッド部の展開図である。
【図１０】比較例のトレッド部の展開図である。
【符号の説明】
２トレッド面
３縦溝
３ａ内の縦溝
３ｂ外の縦溝
４外方部分
５内方部分
６溝壁面
６ｏタイヤ軸方向外側の溝壁面
６ｉタイヤ軸方向内側の溝壁面
７主壁部
８斜壁部
９微細溝
１１急傾斜溝
１１ｉ急傾斜溝の内方端部
１１ｏ急傾斜溝の外方端部
１３緩傾斜溝[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic tire capable of improving hydroplaning performance without impairing uneven wear and steering stability on a dry road surface.
[0002]
[Prior art and problems to be solved by the invention]
It is known that when driving on a wet road surface at high speed, a so-called hydroplaning phenomenon occurs in which a tire rides on a water film and becomes unsteerable. As a result of various experiments, in order to shift the generation rate of this hydroplaning phenomenon to a higher speed range, that is, to improve the anti-hydroplaning performance, the groove volume of the vertical groove recessed in the tread surface is increased. It has been found that it is effective to arrange a large number of inclined grooves or the like communicating with the vertical grooves.
[0003]
However, when the vertical groove and the inclined groove are provided on the tread surface, uneven wear may occur depending on the usage thereof, and the pattern rigidity may be lowered, so that the steering stability on the dry road surface may be impaired. The present invention has been devised in view of such a situation, and regulates the shape of the groove wall surface of the longitudinal groove provided in the central region of the tread surface, the inclination angle of the inclined groove, and the relative relationship with the longitudinal groove. The basic object is to provide a pneumatic tire capable of improving the hydro-planing performance without impairing the uneven wear-proof performance and the handling stability on the dry road surface.
[0004]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the center region of the tread surface forming 45% of the tread contact width centering on the tire equator, the groove center is separated from the tire equator continuously in the tire circumferential direction. And at least one longitudinal groove extending, and a groove wall surface on the outer side in the tire axial direction of the longitudinal groove on the outermost side in the tire axial direction in the central region extends from the groove edge to a height separated by a small distance inward in the tire radial direction. The outer portion includes a chamfered inclined wall portion inclined in a direction to increase the groove width toward the tread surface, and the tread from the groove edge of the vertical groove to the land portion on the outer side in the tire axial direction of the vertical groove. A steep ridge extending outward in the tire axial direction with an inner end at a position separating a small distance δ of 1 to 5% of the ground contact width outward in the tire axial direction and inclined at an angle of 5 to 30 ° with respect to the tire circumferential direction. Inclined grooves spaced in the tire circumferential direction It is characterized in that was.
[0005]
In this specification, the “tread ground contact width” is the distance in the tire axial direction between the tread ground contact ends when the tire is assembled on the regular rim and filled with the regular internal pressure and the regular load is applied to the plane. To do. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or For ETRTO, use “Measuring Rim”. The “regular internal pressure” is the air pressure defined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, and the table “TIRE LOAD” is TRA. Maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, but 180 KPa for tires for passenger cars. Furthermore, “regular load” is the load that each standard defines 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 LIMITS” for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” if it is ETRTO, but if the tire is for a passenger car, the load is 0.8 times the above load. In the following description, unless otherwise specified, the dimensions and the like of each part of the tire are specified in a no-load state in which the tire is assembled on a regular rim and filled with a regular internal pressure.
[0006]
Furthermore, in the invention according to claim 1, and in the shoulder region forming each outer side of the central region, outer longitudinal grooves extending continuously in the tire circumferential direction are formed, respectively,
The substantially intermediate portion in the tire circumferential direction of the steeply inclined groove and the outer vertical groove are connected by a gently inclined groove having the same direction as the steeply inclined groove and an angle with respect to the tire circumferential direction larger than that of the steeply inclined groove. It is characterized by that .
[0007]
According to a second aspect of the present invention, the central region includes a pair of longitudinal grooves disposed on both sides of the tire equator, thereby providing a central rib on the tire equator.
[0008]
According to a third aspect of the present invention, the tread surface is formed with an outer vertical groove extending continuously in the tire circumferential direction in a shoulder region forming each outer side of the central region, and the steeply inclined groove is The steeply inclined grooves that have an outer end that terminates without communicating with the outer vertical groove and that are adjacent to the inner end in the tire circumferential direction each extend in the tire circumferential direction. Thus, overlapping portions that overlap each other in the tire axial direction are formed .
[0009]
The invention according to claim 4 is characterized in that the inclined wall portion is inclined at an angle of 50 to 80 ° with respect to a normal line of a tread surface passing through a groove edge of the vertical groove .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
1 is a developed view of a tread pattern showing an embodiment of the present invention, FIG. 2A is a sectional view taken along line AA, FIG. 2B is a sectional view taken along line BB, and FIG. FIG. 4A is a perspective view of FIG. 2B, and FIG. 4 is a perspective view of FIG. In the figure, the pneumatic tire according to the present embodiment includes a pair of

longitudinal grooves

3a and 3a disposed substantially symmetrically on both sides of the tire equator C on the tread surface 2, and substantially left and right outside thereof. A pair of outer

longitudinal grooves

3b and 3b arranged symmetrically is provided, and is suitably used as a radial tire for passenger cars, for example.
[0011]
In the present embodiment, each of the longitudinal grooves 3 (generally referred to as reference numeral 3) is linearly and continuously extending in the tire circumferential direction. In order to improve the drainage of the tread surface, the vertical groove 3 has a groove width GW between the

groove edges

3e and 3e, which are intersections of the tread surface 2 and the groove wall surface 6, as shown in FIG. Is preferably set to about 2 to 7%, more preferably about 2 to 5%. The groove depth GD of the longitudinal groove 3 is preferably, for example, 6.5 to 10.0 mm, more preferably 7.0 to 9.0 mm.
[0012]
The inner longitudinal groove 3a is provided with the groove center away from the tire equator C, but the disposition position (the position where the groove center line is located) is 45% of the tread ground contact width TW with the tire equator C as the center. It is provided in the central region Cr of the tread surface forming the region. Since such a center region Cr has a high contact pressure during traveling and a large contact length, the water film on the road surface can be effectively removed and discharged by providing the vertical groove 3a in the region. . When the vertical grooves 3 are provided apart from the tire equator C, it is possible to effectively prevent the pattern rigidity from being insufficient on a dry road or the like.
[0013]
The central region Cr is preferably provided with a pair of

longitudinal grooves

3a and 3a on both sides of the tire equator C and a central rib L1 on the tire equator C as in this example. The width of the central rib L1 is preferably 5 to 10%, more preferably 7 to 10% of the tread grounding width TW. The number of longitudinal grooves 3 provided in the central region Cr is not particularly limited as long as it is 1 or more, but a plurality of longitudinal grooves 3 are preferable as in this example.
[0014]
The outer vertical groove 3b has a groove center line located in a shoulder region Sh that forms an outer region of the central region Cr. For this reason, the drainage effect can be enhanced by removing the water film on the tread surface 2 even in the shoulder region Sh. Further, in the tread surface 2 of this example, an inner land portion L2 is formed between the inner vertical groove 3a and the outer vertical groove 3b, and further, between the outer vertical groove 3b and the grounding end e. An outer land portion L3 is formed.
[0015]
In the central region Cr, the longitudinal grooves arranged on the outermost side in the tire axial direction, that is, the

longitudinal grooves

3a and 3a in each of the central regions Cr are, as shown in FIG. 6o includes a chamfered inclined wall portion 8 which is inclined in a direction in which the groove width is increased toward the tread surface 2 on the outer portion 4 from the groove edge 3e to a height separated by a small distance h inward in the tire radial direction. Consists of. For example, all of the outer portion 4 may be constituted by the inclined wall portion 8, but in this example, the inclined wall portion 8 extends from the outer edge 8 o of the inclined wall portion 8 to the groove edge 3 e in the tire radial direction. The thing containing the vertical wall part 10 of small height is illustrated.
[0016]
The inclined wall portion 8 locally expands the groove width in the vicinity of the tread surface 2 of the longitudinal groove 3a, thereby effectively increasing the groove volume or causing water remaining on the road surface to flow into the longitudinal groove 3. Can help to further improve drainage. On the other hand, the vertical wall portion 10 makes the groove edge 3e a clearer sharp edge, and can use this edge to cut the water film on the road surface. The effect of the wall part 8 is enhanced.
[0017]
The height h of the outer portion is not particularly limited, but is preferably 10 to 60%, more preferably 20 to 50%, of the depth GD of the inner vertical groove 3a, for example. When the height h is less than 10% of the depth GD of the inner vertical groove 3a, the effect of expanding the groove volume of the vertical groove 3 by the inclined wall portion 8 tends to decrease, and conversely, when the height h exceeds 60%. This is not preferable because the ground contact area is reduced or the rigidity of the land portion in the vicinity of the groove edge 3e is reduced and uneven wear is likely to occur.
[0018]
Further, it is preferable that the inclined wall portion 8 has an inclination angle θo with respect to the normal line N of the tread surface passing through the groove edge 3e of the groove wall surface 6o to 50 to 80 °, more preferably about 60 to 75 °. If the angle θo is less than 50 °, the effect of expanding the groove width is small. Conversely, if the angle θo exceeds 80 °, it is difficult to secure a sufficient height of the inclined wall portion 8, and the groove volume is similarly reduced. There is a tendency not to contribute to expansion. The height F of the vertical wall portion 10 is preferably 0.5 to 1.5 mm, and more preferably 0.5 to 1.0 mm. The inner portion 5 of the groove wall surface 6 having the depth H is formed with a normal main wall portion 7 that is inclined at about 5 to 15 ° with respect to the normal N except for the intersection with the groove bottom.
[0019]
Further, as shown in FIG. 3 and FIG. 5 which is a cross-sectional view taken along the line C-C, in this example, the slant wall portion 8 of the groove wall surface 6o has a small groove 9 having a small width and a small depth. Fig. 1 shows a structure extending substantially parallel to the tire axial direction and spaced apart in the tire circumferential direction. Such fine grooves 9 can improve wettability of the inclined wall portion 8 and improve adhesion of water to the inclined wall portion 8, thereby improving drainage performance in the inner vertical groove 3 a better. . In particular, a lot of release agents and oils and fats adhere to the groove wall surface when new, etc., so that it is easy to repel water. However, providing the fine groove 9 in the inclined wall portion 8 improves wettability and improves wet performance. be able to. Further, when the minute groove 9 is provided in the inclined wall portion 8, the water between the inclined wall portion 8 and the road surface can be effectively pushed out into the groove, and the inner water as shown in FIG. A spiral water flow is generated inside the vertical groove 3a. Such a flow has an effect of increasing drainage efficiency of running water passing through the inside of the groove.
[0020]
In order to realize the operation as described above, as shown in FIG. 5, the groove width W of the fine groove 9 is preferably 0.3 to 1.2 mm, more preferably 0.6 to 1.0 mm. Is desirable. The groove depth d of the fine groove 9 is preferably 0.3 to 1.5 mm, more preferably 0.3 to 0.6 mm. Further, the pitch P in the tire circumferential direction of the fine grooves 9 (the distance between the groove center lines of the fine grooves 9 as shown in FIG. 5) is preferably 1.4 to 4.0 mm, more preferably 2.0 to 3.0 mm. Is desirable. The pitch P of the fine grooves 9 may be constant as in the case of the groove width W and the groove depth d, but may be different within the above range.
[0021]
The cross-sectional shape of the fine groove 9 is not particularly limited, and various shapes such as a square groove and a triangular groove (both not shown) can be adopted in addition to a substantially semicircular shape as shown in FIG. More preferably, the substantially semicircular shape that can efficiently secure the groove volume of the fine groove 9 and can expect the effect of sucking up water by capillary action is desirable. Such a fine groove 9 does not reduce the rigidity in the vicinity of the groove edge of the vertical groove 3, and therefore can prevent deterioration in steering stability on the dry road surface.
[0022]
The groove wall surface 6i inside the inner vertical groove 3 is not particularly limited and can be implemented in various modes. In this example, an aspect in which the outer portion 4 is composed only of the inclined wall portion 8 is shown. The angle θi of the inclined wall portion 8 of the inner groove wall surface 6i is set smaller than the angle θo of the outer inclined wall portion 8. With such a configuration, while ensuring the rigidity of the central rib L1 and maintaining the steering stability on the dry road surface, a difference is provided in the amount of water flowing into the inner vertical groove 3a, thereby the inner vertical groove 3a. The generation of the vortex can be expected more suitably. The angle difference | θo−θi | is more preferably about 10 to 30 °, more preferably about 20 to 30 °.
[0023]
Further, as shown in FIGS. 2B and 4, the groove wall surface 6 o on the outer side in the tire axial direction of the outer vertical groove 3 b has the inclined wall portion 8, but the groove wall surface 6 i on the inner side in the tire axial direction has The inclined wall portion 8 is formed without being provided. However, the present invention is not limited to such a mode, and it is of course possible to adopt the same configuration as that of the inner vertical groove 3a for the outer vertical groove 3b. Moreover, the vertical wall part 10 can also be formed.
[0024]
Further, as shown in FIGS. 1 and 7, the pneumatic tire of the present invention has a steeply inclined groove 11 on the tread surface 2 and on a land portion L2 that is a land portion on the outer side in the tire axial direction of the inner longitudinal groove 3a. It is spaced apart in the tire circumferential direction. The steeply inclined groove 11 has an inner end portion 11i at a position separating a small distance δ from the groove edge 3e on the outer side in the tire axial direction of the inner vertical groove 3a to the outer side in the tire axial direction. It tilts at an angle β of 30 ° and extends outward in the tire axial direction. When the steeply inclined groove 11 is smoothly curved, the angle β is an average angle. The small distance δ between the inner end portion 11i of the steeply inclined groove 11 and the groove edge 3e on the outer side in the tire axial direction of the inner vertical groove 3a is 1 to 5% of the tread ground contact width TW.
[0025]
In order to improve the drainage of the central region Cr, it is desirable that the inward end portion 11i of the steeply inclined groove 11 is communicated with or located in the vicinity of the inner vertical groove 3a. However, when such a method is simply adopted, the pattern rigidity of the central region Cr, particularly the rigidity of the narrow land portion formed between the steeply inclined groove 11 and the inner vertical groove 3a is reduced, and the steering is reduced. This is disadvantageous in terms of stability and uneven wear. Therefore, in the present invention, as shown in FIG. 8 which is an enlarged sectional view taken along the line DD in FIG. 7, the inclined wall portion 8 is provided on the groove wall surface 6o on the outer side in the tire axial direction of the inner longitudinal groove 3a as described above. Even if the small distance δ is set to be smaller, the rigidity of the inner portion of the land portion 15 sandwiched between the inner vertical groove 3a and the steeply inclined groove 11 can be secured large, and the rigidity is not impaired. Accordingly, the drainage performance can be improved by bringing the inner end portion 11i of the steeply inclined groove 11 closer to the inner vertical groove 3a without impairing the steering stability on the dry road surface.
[0026]
Thus, the steeply inclined groove 11 inclined at a small angle β with respect to the tire circumferential direction becomes more effective by cutting and draining the water film between the land portion L2 and the road surface. If the small distance δ is less than 1% of the tread ground contact width TW, the rigidity of the land portion formed between the inner end portion 11i and the outer vertical groove 3b even if the inclined wall portion 8 is provided. Is extremely small, and rubber chipping and uneven wear are likely to occur starting from this portion, and steering stability on a dry road surface is likely to deteriorate. Further, it is not preferable that the steeply inclined groove 11 communicates with the inner vertical groove 3a because the pattern rigidity of the central region Cr is likely to be lowered. On the other hand, when the small distance δ exceeds 5% of the tread ground contact width TW, a land portion having a large width is formed between the inner end portion 11i and the groove edge 3e of the inner longitudinal groove 3b, resulting in poor drainage. Since it forms a part, it is not preferable. From such a viewpoint, the small distance δ is more preferably 1 to 5%, and further preferably 3 to 5% of the tread ground contact width TW.
[0027]
If the angle β of the steeply inclined groove 11 is less than 5 °, the rigidity of the land portion sandwiched between the steeply inclined groove 11 and the longitudinal groove 3a is greatly reduced, and the driving stability on the dry road surface is improved. In addition to lowering, it tends to cause uneven wear. On the contrary, if the angle β of the steeply inclined groove 11 exceeds 30 °, a sufficient water film removing effect cannot be obtained in the inner land portion L2, and the hydroplaning resistance cannot be improved. From this point of view, the angle β is preferably 5 to 20 °, more preferably 5 to 15 °.
[0028]
Further, the steeply inclined groove 11 of this example has an outer end portion 11o that terminates without communicating with the outer vertical groove 3b. For this reason, it is possible to prevent a decrease in rigidity in the vicinity of the groove edge of the wide outer vertical groove 3b, and it is possible to suppress a decrease in steering stability on the dry road surface. However, if the distance K in the tire axial direction between the outer end portion 11o of the steeply inclined groove 11 and the groove edge 3e on the inner side in the tire axial direction of the outer vertical groove 3b is too large, the drainage in the inner land portion L2 The performance is likely to be lowered, and conversely, if it is too small, the rigidity in the vicinity of the groove edge of the outer vertical groove 3b is lowered, and the steering stability is likely to be deteriorated. From such a viewpoint, the distance K is preferably 3 to 8%, more preferably 4 to 6% of the tread ground contact width TW.
[0029]
As shown in FIG. 1, the steeply

inclined grooves

11, 11 adjacent to the inner end portion 11 i in the tire circumferential direction have overlapping portions 20 that overlap each other in the tire axial direction by extending in the tire circumferential direction. Forming. Thereby, in middle land part L2, drainage performance can be improved with sufficient balance. The length L in the tire circumferential direction of the overlapping portion 20 is preferably about 5 to 15% of the tread ground contact width TW. Although the groove width of the steeply inclined groove 11 is not particularly limited, for example, the groove width gw (shown in FIG. 7) measured on the tread surface 2 is 50 to 90% of the groove width GW of the vertical groove 3, more preferably 60. It is desirable to be about 80%. The groove depth is preferably about the same as that of the longitudinal groove 3, for example.
[0030]
In addition, the tread surface 2 of the present example connects between the substantially intermediate portion of the steeply inclined groove 11 in the tire circumferential direction and the outer vertical groove 3b, and has the same direction as the steeply inclined groove 11 and an angle with respect to the tire circumferential direction. An example is shown in which a gently inclined groove 13 having a larger η than the angle β of the steeply inclined groove 11 is provided. The region of the outer portion of the inner land portion L2 in the tire axial direction (in other words, the vicinity of the inner groove edge of the outer longitudinal groove 3b in the tire axial direction) generates a large lateral force when turning on a dry road surface. The rigidity of the vehicle has a great influence on the handling stability. On the other hand, in order to improve the hydroplaning resistance, it is necessary to drain a part of the water film between the inner land portion L2 and the road surface using the outer vertical groove 3b.
[0031]
Therefore, in the present embodiment, the steeply inclined groove 11 and the outer vertical groove 3b are communicated separately by using a gently inclined groove 13 having a gentle inclination without connecting the steeply inclined steep groove 11 to the outer vertical groove 3b. By doing so, drainage performance is enhanced without significantly impairing the rigidity of the land portion L2. The gently inclined groove 13 has a larger angle η with respect to the tire circumferential direction than the steeply inclined groove 11, more preferably 30 to 50 °, and further preferably 35 to 45 °. When the angle η is less than 30 °, the difference from the steeply inclined groove 11 is reduced, and a land portion with low rigidity is formed between the steeply inclined groove 11 and uneven wear tends to occur from this point. Conversely, if it exceeds 50 °, the relative angle with respect to the steeply inclined groove 11 tends to increase and the drainage resistance tends to increase. More preferably, the angle difference (η−β) is preferably about 10 to 30 °.
[0032]
Further, it is desirable that the gently inclined groove 13 is connected to a substantially middle portion of the length of the steeply inclined groove 11 in the tire circumferential direction. For example, it is possible to connect the gently inclined groove 13 in the vicinity of the outer end portion 11o of the steeply inclined groove 11, but in this case, the water flow flowing from the steeply inclined groove 11 flows largely at the connecting portion with the gently inclined groove 13. Since the angle changes, drainage resistance tends to increase. On the other hand, when the gently inclined groove 13 is connected at the substantially intermediate portion of the steeply inclined groove 11, a part of running water is taken in, so that an increase in the drainage resistance can be prevented. Note that the gently inclined groove 13 is connected to a substantially middle portion of the steeply inclined groove 11 in the tire circumferential direction, as shown in FIG. It is assumed that the intersecting portion j of the groove center line is provided in a region including a width of 15% of the length S.
[0033]
Further, in the present embodiment, the outer land portion L3 is connected to the outer vertical groove 3b at one end and the lateral groove 14 having the other end opened at the grounding end e, and provided between the horizontal grooves and from the grounding end e to the tire. A lug-shaped groove 15 extending inward in the axial direction and terminating without communicating with the outer vertical groove 3b is provided. Thereby, in the outer land part L3, effective drainage performance is obtained using the ground contact end e and the outer vertical groove 3b.
[0034]
As mentioned above, although embodiment of this invention was explained in full detail, this invention can be implemented in a various aspect, without being limited to the said embodiment. For example, an aspect in which the longitudinal groove 3 is bent, an aspect in which the steeply inclined groove 11 and the gently inclined groove 13 are directional patterns arranged in a letter C shape with the tire equator C interposed therebetween, as shown in FIG. Various embodiments such as an aspect of attaching siping can be included.
[0035]
【Example】
A radial tire for a passenger car having a tire size of 195 / 65R15 was prototyped with the pattern shown in FIG. 1, and wet performance, steering stability on a dry road surface, and uneven wear resistance were tested and evaluated. For comparison, the same size tire (comparative example) having the pattern shown in FIG. 10 was also tested. The land ratio is approximately the same, and the internal structure is substantially the same.
The test method was as follows.
[0036]
<Wet performance>
A vehicle equipped with test tires (displacement 2000cm ³ , rim 6J, internal pressure 180kPa) on a course with a water depth of 5mm and a length of 20m on an asphalt road surface with a radius of 100m and gradually increasing the speed. The vehicle was allowed to enter and the lateral acceleration (lateral G) was measured, and the average lateral G of the front wheels at a speed of 50 to 80 km / h was calculated (lateral hydroplaning test). The results were expressed as an index with the conventional example being 100. The larger the value, the better.
[0037]
<Steering stability>
A test run is performed on the dry asphalt road surface of the tire test course with the above vehicle, and characteristics relating to steering wheel response, rigidity, grip, and the like are displayed as an index with Comparative Example 1 being 100 by sensory evaluation of the driver. A larger index is better.
[0038]
<Uneven wear resistance>
The vehicle traveled on a highway, urban area, and mountain road for a total of 3000 km, and the tread surface was visually observed for wear.
Table 1 shows the test results.
[0039]
[Table 1]

[0040]
As a result of the test, it was confirmed that the examples had improved wet performance, steering stability performance, and uneven wear resistance performance in a well-balanced manner.
[0041]
【The invention's effect】
As described above, the pneumatic tire of the present invention can improve the hydroplaning performance without impairing uneven wear and steering stability on a dry road surface.
[Brief description of the drawings]
FIG. 1 is a development view of a tread portion showing an embodiment of the present invention.
FIG. 2A is a cross-sectional view taken along the line AA, and FIG. 2B is a cross-sectional view taken along the line BB.
FIG. 3 is a perspective view of FIG.
FIG. 4 is a perspective view of FIG.
5 is a cross-sectional view taken along the line CC of FIG. 3;
FIG. 6 is a schematic cross-sectional view illustrating the flow of water in the longitudinal groove.
FIG. 7 is a partially enlarged view of a tread surface.
FIG. 8 is an enlarged sectional view taken along the line DD.
FIG. 9 is a development view of a tread portion showing another embodiment of the present invention.
FIG. 10 is a development view of a tread portion of a comparative example.
[Explanation of symbols]
2 tread surface 3 longitudinal groove 3b in longitudinal groove 3a outer longitudinal groove 4 outer portion 5 inner portion 6 groove wall surface 6o groove wall surface 6i outside tire axial direction groove wall surface 7 inside tire axial direction main wall portion 8 slant wall Part 9 Fine groove 11 Steeply inclined groove 11i Inward end 11o of steeply inclined groove Outer end 13 of steeply inclined groove Slowly inclined groove

Claims

Comprising at least one longitudinal groove in the central region of the tread surface that forms 45% of the tread contact width centered on the tire equator and extending in the circumferential direction of the tire and the groove center extending away from the tire equator;
In the central region, the groove wall surface on the outer side in the tire axial direction of the longitudinal groove on the outermost side in the tire axial direction is an outer portion from the groove edge to a height that is a small distance inward in the tire radial direction, toward the tread surface. Including a chamfered slanted wall that tilts in the direction of expanding the groove width,
The land portion on the outer side in the tire axial direction of the longitudinal groove has an inner end portion at a position separating a small distance δ of 1 to 5% of the tread contact width from the groove edge of the longitudinal groove to the outer side in the tire axial direction. Steeply inclined grooves that are inclined at an angle of 5 to 30 ° with respect to the tire circumferential direction and extend outward in the tire axial direction are spaced apart in the tire circumferential direction,
And in the shoulder region forming each outside of the central region, outer longitudinal grooves extending continuously in the tire circumferential direction are formed, respectively,
The substantially intermediate portion in the tire circumferential direction of the steeply inclined groove and the outer vertical groove are connected by a gently inclined groove having the same direction as the steeply inclined groove and an angle with respect to the tire circumferential direction larger than that of the steeply inclined groove. A pneumatic tire characterized by that .

The pneumatic tire according to claim 1, wherein the central region includes a pair of longitudinal grooves disposed on both sides of the tire equator, thereby providing a central rib on the tire equator.

The steeply inclined groove has an outer end that terminates without communicating with the outer vertical groove, and each of the steeply inclined grooves adjacent to the inner end in the tire circumferential direction is a tire circumferential direction. The pneumatic tire according to claim 1, wherein overlapping portions are formed so as to overlap each other in the tire axial direction.

The pneumatic tire according to any one of claims 1 to 3 , wherein the inclined wall portion is inclined at an angle of 50 to 80 degrees with respect to a normal line of a tread surface passing through a groove edge of the vertical groove.