JP4033312B2

JP4033312B2 - Pneumatic radial tire

Info

Publication number: JP4033312B2
Application number: JP15373498A
Authority: JP
Inventors: 和伸小山
Original assignee: Toyo Tire and Rubber Co Ltd
Current assignee: Toyo Tire Corp
Priority date: 1998-05-18
Filing date: 1998-05-18
Publication date: 2008-01-16
Anticipated expiration: 2018-05-18
Also published as: JPH11321214A

Description

【０００１】
【発明の属する技術分野】
本発明は、ミニバン、ワンボックス車等のハイルーフ車などに好適に用いることができる空気入りラジアルタイヤにおいて、特に、乗り心地を悪化させることなしにタイヤの偏摩耗を防止することができる空気入りラジアルタイヤに関する。
【０００２】
【従来の技術】
従来、トレッドのショルダー部の形状に関し種々のタイヤが提供されている。
【０００３】
例えば、タイヤトレッドのショルダー部の形状について、タイヤ装着時に車両の外側に位置するショルダー部、及び内側に位置するショルダー部とも、同一の曲率半径のラウンド形状とするタイヤである。
【０００４】
また、タイヤ装着時に車両の外側に位置するショルダー部及び内側に位置するショルダー部ともスクエア形状又はテーパカット形状とするタイヤも提供されている。
【０００５】
さらには、タイヤ装着時に車両の外側に位置するショルダー部及び内側に位置するショルダー部ともスクエア形状又はテーパカット形状とするタイヤも提供されている。
【０００６】
また、タイヤ装着時に車両の外側に位置するショルダー部の形状をラウンド形状にし、内側に位置するショルダー部の形状をスクエア形状とするタイヤも提供されている。またこれとは逆に、タイヤ装着時に車両の外側に位置するショルダー部の形状をスクエア形状にし、内側に位置するショルダー部の形状をラウンド形状としたタイヤも提供されている。
【０００７】
また、ショルダー部の形状を車両の外側及び内側ともに同一とし、そしてラウンド形状及びスクエア形状をブロックごと若しくはブロック内に交互にタイヤ周方向に配置したタイヤも提供されている。
【０００８】
【発明が解決しようとする課題】
しかし、車両の外側に位置するショルダー部及び内側に位置するショルダー部とも同一の曲率半径のラウンド形状としたタイヤの場合、そのラウンド形状の曲率半径を大きくすると乗り心地は向上するが、耐偏摩耗性は悪化する。一方、ラウンド形状の曲率半径を小さくすると耐偏摩耗性は向上するが、乗り心地は悪化する。
【０００９】
また、車両の外側に位置するショルダー部及び内側に位置するショルダー部ともスクエア形状又はテーパカット形状としたタイヤの場合、耐偏摩耗性は向上するが乗り心地は悪化する点で好ましくない。
【００１０】
この点で、車両の外側に位置するショルダー部の形状をラウンド形状にし、内側に位置するショルダー部の形状をスクエア形状とするタイヤの場合、乗り心地を損なわずに、内側のスクエア形状によりトラクションを確保できる点で好ましい。しかし、かかるタイヤの場合、コーナリング時に負荷が大きく作用する外側のショルダー部において摩耗し易く、肩落ち摩耗などの偏摩耗が発生する。一方、タイヤ装着時に車両の外側に位置するショルダー部の形状をスクエア形状にし、内側に位置するショルダー部の形状をラウンド形状としたタイヤは、耐偏摩耗性の向上には有利であるが、乗り心地は悪化する。
【００１１】
また、ショルダー部の形状を車両の外側及び内側ともに同一とし、そしてラウンド形状及びスクエア形状をブロックごと若しくはブロック内に交互にタイヤ周方向に配置したタイヤの場合も、乗り心地は向上するが、耐偏摩耗性の向上の点では必ずしも十分ではない。
【００１２】
このように、従来のタイヤは、タイヤトレッドのショルダー形状を改善して耐偏摩耗性と乗り心地を同時に向上させたタイヤであるとは必ずしもいえるものではない。特に、ミニバン、ワンボックス車等のハイルーフ車などの場合、重心が高いこともあって、タイヤ装着時に車両の外側に位置するショルダー部には偏摩耗が通常の乗用車タイヤ以上に発生し易く、その一方、この種のタイヤは通常の乗用車タイヤと同様の乗り心地が求められている。
【００１３】
本発明の目的は、乗り心地を悪化させることなしにタイヤの偏摩耗を防止することができ、ミニバン、ワンボックス車等のハイルーフ車などに好適に使用することができる空気入りラジアルタイヤを提供するところにある。
【００１４】
【課題を解決するための手段】
上記目的を達成するため鋭意検討した結果、本発明はタイヤトレッドの両ショルダー部の形状に着目し、当該両ショルダー部の形状をラウンド形状にするとともに、さらに車両の外側に位置するショルダー部の曲率半径と、内側に位置するショルダー部の曲率半径との関係を調整することにより解決できることを見出した。
【００１５】
本発明は、タイヤトレッドのクラウン部とバットレス部の間のタイヤ横断面に現れるショルダー部におけるタイヤ外周面の輪郭がラウンド形状で構成された空気入りラジアルタイヤにおいて、
上記クラウン部の表面に現れた曲率半径Ｒtの輪郭と、上記バットレス部の表面に現れた曲率半径Ｒbの輪郭とにそれぞれ内接している、上記ショルダー部の表面に現れた曲率半径Ｒso、Ｒsiの輪郭が、タイヤ赤道線に対して左右非対称であって、
上記クラウン部の表面に現れた輪郭の曲率半径Ｒ t はタイヤ赤道線に対して左右対称であり、
かつ、タイヤ装着時に車両の外側に位置する上記ショルダー部の表面に現れた輪郭の曲率半径Ｒsoを、タイヤ装着時に車両の内側に位置する上記ショルダー部の表面に現れた輪郭の曲率半径Ｒsiより小さくしたことを特徴とする空気入りラジアルタイヤである。
【００１６】
従って、本発明のタイヤは、タイヤ装着時に車両の外側に位置するショルダー部の表面に現れた輪郭の曲率半径Ｒsoが、タイヤ装着時に車両の内側に位置するショルダー部の表面に現れた輪郭の曲率半径Ｒsiより小さいため、タイヤ装着時に車両の外側に位置するショルダー部の接地幅が、車両の内側に位置するショルダー部の接地幅より大きくなる。その結果、タイヤ装着時に車両の外側に位置するタイヤトレッドのショルダー部において、タイヤの有効な接地面積が増大するため、耐偏摩耗性の向上を図ることができる。
【００１７】
また、本発明のタイヤは、タイヤ装着時に車両の内側に位置するショルダー部の表面に現れた輪郭の曲率半径Ｒsiが、タイヤ装着時に車両の外側に位置するショルダー部の表面に現れた輪郭の曲率半径Ｒsoより大きいため、乗り心地の悪化を防止することができる。
【００１８】
【発明の実施の形態】
図１は本発明の一実施形態を示す空気入りタイヤの外周断面の輪郭を示す概略図、図２は同要部右側拡大図である。
【００１９】
図１において、１はタイヤトレッド、２はタイヤトレッド１のクラウン部、３はショルダー部、４はバットレス部である。５はタイヤトレッド１の中央を走るタイヤ赤道線、６はタイヤ最大幅を示す仮想線である。
【００２０】
本実施形態のタイヤは、図１及び図２に示す様に、タイヤトレッド１のクラウン部２とバットレス部４の間のタイヤ横断面に現れたショルダー部３におけるタイヤ外周面の輪郭７１、７２はラウンド形状で構成されている。
【００２１】
このショルダー部３におけるタイヤ外周面の曲率半径Ｒso、Ｒsiの輪郭７１、７２は、図に示す通り、上記クラウン部２の表面に現れた曲率半径Ｒtの輪郭８１、８２と、上記バットレス部４の表面に現れた曲率半径Ｒbの輪郭９１、９２にそれぞれ内接している。なお、図２中、波線８１１は上記曲率半径Ｒtの輪郭８１の仮想延長線であり、波線９１１は上記曲率半径Ｒbの輪郭９１の仮想延長線である。
【００２２】
また、ショルダー部３の表面に現れた曲率半径Ｒso、Ｒsiの輪郭７１、７２は、図１に示す様に、タイヤ赤道線５に対して左右非対称である。すなわち、タイヤ装着時に車両の外側に位置する上記ショルダー部の表面に現れた輪郭７１と、同内側に位置する上記ショルダー部の表面に現れた輪郭７２が非対称の曲率半径にて構成されている。
【００２３】
更に、車両の外側に位置する上記ショルダー部の輪郭７１の曲率半径Ｒsoは、車両の内側に位置する上記ショルダー部の輪郭７２の曲率半径Ｒsiより小さく構成されている。
【００２４】
従って、本実施形態のタイヤは、タイヤ装着時に車両の外側に位置するショルダー部３の表面に現れた輪郭７１の曲率半径Ｒsoが、タイヤ装着時に車両の内側に位置するショルダー部３の表面に現れた輪郭７２の曲率半径Ｒsiより小さいため、タイヤ装着時に車両の外側に位置するショルダー部３の接地幅が、車両の内側に位置するショルダー部３の接地幅より大きくなる結果、タイヤ装着時に車両の外側に位置するタイヤトレッドのショルダー部３において、タイヤの有効な接地面積が増大するため、耐偏摩耗性の向上を図ることができる。また、タイヤ装着時に車両の内側に位置する曲率半径Ｒsiの輪郭７２の曲率半径Ｒsiからすれば、タイヤ装着時に車両の外側に位置するショルダー部３の輪郭７１の曲率半径Ｒsoより大きいため、乗り心地の悪化を防止することができる。
【００２５】
この車両の外側に位置するショルダー部３の曲率半径Ｒsoと車両の内側に位置する輪郭７２の曲率半径Ｒsiとの関係を、具体的にいかなる数値にすることが好ましいかについては、車両の外側に位置する輪郭７１の曲率半径Ｒsoを、車両の内側に位置する輪郭７２の曲率半径Ｒsiに対して０．３Ｒsi〜０．６Ｒsiの範囲内に設定することが望ましい。輪郭７１の曲率半径Ｒsoが０．３Ｒsi未満の場合は乗り心地の悪化する傾向が生じる。一方、車両の外側に位置する輪郭７１の曲率半径Ｒsoが、０．６Ｒsiより大きいと、耐偏摩耗性の改善が充分でない。
【００２６】
具体的には、車両の外側に位置する輪郭７１の曲率半径Ｒsoとしては、５〜３０ｍｍの範囲から選択することができる。車両の外側に位置する輪郭７１の曲率半径Ｒsoが小さすぎると乗り心地が悪化し、同輪郭７１の曲率半径Ｒsoが大きすぎると、耐偏摩耗性が低下する。
【００２７】
本発明では、クラウン部の表面に現れた円弧８１、８２の曲率半径Ｒtと、バットレス部４の表面に現れた円弧９１、９２の曲率半径Ｒbは、特に制限されない。円弧８１、８２の曲率半径Ｒtとしては、例えば、２９０ｍｍ〜∞（ストレート）ｍｍ程度の範囲から選択できる。また、円弧９１、９２の曲率半径Ｒbとしては、例えば、８０ｍｍ〜∞（ストレート）ｍｍ程度の範囲から選択できる。
【００２８】
なお、本発明のタイヤの形状は、すべて標準内圧を基準に特定される。
【００２９】
ところで、本発明では、トレッドパターンは特に制限されない。しかし、本発明のタイヤは装着方向又は回転方向が規定されているので、タイヤの赤道線に対して非対称性を有しているトレッドパターンのタイヤに対して好適に適用することができる。
すなわち、本発明は、トレッド部の溝面積比がタイヤ赤道線を挟んで、両側のトレッド部で異なる非対称性のトレッドパターンを備えている空気入りラジアルタイヤ、中でもミニバン、ワンボックス車等のハイルーフ車用空気入りラジアルタイヤに好適に用いることができる。これは、上記の非対称性のトレッドパターンを備えている空気入りラジアルタイヤであっても、ミニバン、ワンボックス車等のハイルーフ車に適用した場合は、通常の乗用車タイヤ以上に当該車両の重心が高いことから、車両の外側に位置するショルダー部に、走行中、特に旋回時に力が大きく作用し、偏摩耗が発生し易いためである。
【００３０】
従って、本発明は、トレッド部の溝面積比がタイヤ赤道線を挟んで、両側のトレッド部で異なり、そのうち、タイヤ装着時に車両の外側に位置する片側のトレッド部の溝面積が、車両の内側に位置する他の片側のトレッド部の溝面積よりも小さい非対称性のトレッドパターンを備えており、
タイヤトレッドのクラウン部とバットレス部の間のタイヤ横断面に現れるショルダー部におけるタイヤ外周面の輪郭がラウンド形状で構成され、
上記クラウン部の表面に現れた曲率半径Ｒtの輪郭と、上記バットレス部の表面に現れた曲率半径Ｒbの輪郭にそれぞれ内接している上記ショルダー部の表面に現れた曲率半径Ｒso、Ｒsiの輪郭が、タイヤ赤道線に対して左右非対称であって、
かつ、タイヤ装着時に車両の外側に位置する上記ショルダー部の表面に現れた輪郭の曲率半径Ｒsoを、タイヤ装着時に車両の内側に位置する上記ショルダー部の表面に現れた輪郭の曲率半径Ｒsiより小さくしたことを特徴とする空気入りラジアルタイヤ、特にミニバン、ワンボックス車等のハイルーフ車用空気入りラジアルタイヤは、乗り心地を悪化させずに耐偏摩耗性の向上を図ることができるため、好適に用いることができる。
【００３１】
但し、本発明のタイヤは、これらに限定されず、断面幅の呼び：１４５〜２６５（ｍｍ）、偏平率：３０〜８０（％）を満たす乗用車用タイヤに好適に用いることができる。また、本発明のタイヤは、ショルダー部の曲率半径を左右非対称とした金型等を使用して加硫成形することにより簡易に製造することができる。
【００３２】
【実施例】
図１及び図２に示した前記実施形態に示すタイヤサイズ２１５／６５Ｒ１５の実施例タイヤ及び比較例タイヤを試作し、耐摩耗性及び乗り心地をそれぞれ評価した。その結果を表１に示す。
【００３３】
なお、各タイヤは「ショルダー部の曲率半径」を除いてすべて同一の構成からなり、「ショルダー部の曲率半径」は下記表１に示す通りである。但し、比較例２のタイヤは、ショルダー部の形状はスクエア形状である。
表１中、「外側の円弧Ｒso」とはタイヤ装着時に車両の外側に位置するショルダー部の外周の円弧Ｒsoを示し、「内側の円弧Ｒsi」とはタイヤ装着時に車両の内側に位置するショルダー部の外周の円弧Ｒsiを示している。比較例２のタイヤは、ショルダー部の形状はスクエア形状であるため、ショルダー部の曲率半径は外側及び内側ともに「０」と示している。
【００３４】
【表１】

【００３５】
（耐偏摩耗試験）
実施例及び比較例の各試作タイヤを装着した国産ミニバン（２４００ＣＣ）を当社テストコースにて１２０００ｋｍを完走させた後、当該各４本のタイヤについて車両外側に位置するショルダー部とタイヤセンター部との摩耗量の差を測定し、その測定値の逆数について比較例１のタイヤを１００として指数評価した。なお、走行条件は各実施例及び比較例ともに荷重は前輪９９４ｋｇ、後輪９５０ｋｇであり、２名乗車で、完走までタイヤのローテーションを行わずに行った。この耐偏摩耗性試験の結果を表１に示す。なお、各数値は大きいほど耐偏摩耗性が良好であることを示す。
【００３６】
（乗り心地試験）
実施例及び比較例の各試作タイヤを装着した国産ミニバン（２４００ＣＣ）を実車走行させ、３名のドライバーによるフィーリング試験により評価した。評価は、各ドライバーに試作タイヤの種類をふせて実車走行の後、５点満点により点数を付け、その平均値を比較例１のタイヤを１００とした場合の指数評価により行った。この結果を表１に示す。表中の各数値は大きいほど乗り心地が良好であることを示す。
【００３７】
表１より明らかな様に、実施例に係るタイヤは、比較例１のタイヤと比べていずれも耐偏摩耗性が改善されているとともに、乗り心地の悪化が抑制又は防止されている。従って、実施例に係るタイヤは、耐偏摩耗性及び乗り心地が高いレベルで両立している。
【００３８】
特に、外側に位置するショルダー部の輪郭の曲率半径Ｒsoが、車両の内側に位置するショルダー部の輪郭の曲率半径Ｒsiの０．３Ｒsi〜０．６Ｒsiである実施例タイヤは、かかる効果が格別顕著であり、比較例のタイヤと比べて、乗り心地の悪化を充分防止しながら耐偏摩耗性の向上が認められる。
【００３９】
これに対して、比較例２に係るタイヤは、両ショルダー部の形状がスクエア形状であるため、耐偏摩耗性は優れているが、乗り心地が悪い。
【００４０】
【発明の効果】
本発明の空気入りラジアルタイヤは、ショルダー部の形状がラウンド形状であり、かつ外側のショルダー部の曲率半径が内側のショルダー部の曲率半径より小さいため、乗り心地を悪化させることなしにタイヤの偏摩耗を防止することができる。
【００４１】
従って、通常の乗用車タイヤのほか、特に重心が高いミニバン、ワンボックス車等のハイルーフ車に適用した場合でも、耐偏摩耗性を確保することができ、しかも乗り心地が優れている。
【図面の簡単な説明】
【図１】本発明に係る空気入りタイヤの一実施形態を示す外周断面の輪郭を示す概略図である。
【図２】同要部右側拡大図である。
【符号の説明】
１タイヤトレッド
２クラウン部
３ショルダー部
４バットレス部
５タイヤ赤道線
７１曲率半径Ｒsoの輪郭
７２曲率半径Ｒsiの輪郭
８１曲率半径Ｒtの輪郭
８２曲率半径Ｒtの輪郭
９１曲率半径Ｒbの輪郭
９２曲率半径Ｒbの輪郭[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic radial tire that can be suitably used for a high roof vehicle such as a minivan or a one-box vehicle, and more particularly, a pneumatic radial tire that can prevent uneven wear of the tire without deteriorating riding comfort. Regarding tires.
[0002]
[Prior art]
Conventionally, various tires have been provided regarding the shape of the shoulder portion of the tread.
[0003]
For example, regarding the shape of the shoulder portion of the tire tread, both the shoulder portion located on the outer side of the vehicle and the shoulder portion located on the inner side when the tire is attached are round tires having the same radius of curvature.
[0004]
There are also provided tires in which a shoulder portion located on the outer side of the vehicle and a shoulder portion located on the inner side when the tire is mounted have a square shape or a taper cut shape.
[0005]
Furthermore, there are also provided tires in which a shoulder portion located on the outer side of the vehicle and a shoulder portion located on the inner side when the tire is mounted have a square shape or a taper cut shape.
[0006]
In addition, a tire is also provided in which the shape of the shoulder portion located on the outside of the vehicle when the tire is mounted is round, and the shape of the shoulder portion located on the inside is a square shape. On the other hand, a tire is also provided in which the shape of the shoulder portion located outside the vehicle when the tire is mounted is a square shape, and the shape of the shoulder portion located inside is a round shape.
[0007]
There is also provided a tire in which the shape of the shoulder portion is the same on both the outside and the inside of the vehicle, and the round shape and the square shape are alternately arranged in the tire circumferential direction for each block or in the block.
[0008]
[Problems to be solved by the invention]
However, in the case of a tire having a round shape with the same radius of curvature in both the shoulder portion located on the outside of the vehicle and the shoulder portion located on the inside, the ride comfort is improved by increasing the radius of curvature of the round shape. Sex worsens. On the other hand, if the radius of curvature of the round shape is reduced, the uneven wear resistance is improved, but the riding comfort is deteriorated.
[0009]
Further, in the case of a tire having a square shape or a taper cut shape in both the shoulder portion located outside the vehicle and the shoulder portion located inside, the uneven wear resistance is improved, but the ride comfort is deteriorated.
[0010]
In this regard, in the case of a tire in which the shape of the shoulder portion located on the outer side of the vehicle is round and the shape of the shoulder portion located on the inner side is a square shape, traction is reduced by the inner square shape without impairing the ride comfort. It is preferable in terms of securing. However, in the case of such a tire, it is easy to wear at the outer shoulder portion where the load acts greatly during cornering, and uneven wear such as shoulder fall wear occurs. On the other hand, a tire having a square shoulder shape located on the outside of the vehicle and a round shape on the inside shoulder when the tire is mounted is advantageous in improving uneven wear resistance. The comfort gets worse.
[0011]
In the case of a tire in which the shape of the shoulder portion is the same on both the outside and inside of the vehicle, and the round shape and the square shape are alternately arranged in the tire circumferential direction for each block or in the block, the riding comfort is improved, It is not always sufficient in terms of improving uneven wear.
[0012]
As described above, the conventional tire is not necessarily a tire in which the shoulder shape of the tire tread is improved to improve the uneven wear resistance and the ride comfort at the same time. In particular, in the case of high roof vehicles such as minivans and one-box vehicles, the center of gravity is high, and uneven wear is more likely to occur in the shoulder portion located outside the vehicle when wearing tires than in ordinary passenger car tires. On the other hand, this type of tire is required to have the same riding comfort as a normal passenger car tire.
[0013]
An object of the present invention is to provide a pneumatic radial tire that can prevent uneven wear of a tire without deteriorating riding comfort and can be suitably used for a high roof vehicle such as a minivan or a one-box vehicle. By the way.
[0014]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present invention pays attention to the shape of both shoulder portions of the tire tread, makes the shape of both shoulder portions round, and further, the curvature of the shoulder portion located outside the vehicle. It has been found that the problem can be solved by adjusting the relationship between the radius and the radius of curvature of the shoulder portion located inside.
[0015]
The present invention is a pneumatic radial tire in which a contour of a tire outer peripheral surface in a shoulder portion appearing in a tire cross section between a crown portion and a buttress portion of a tire tread is configured in a round shape,
The contour of a curvature radius Rt that appear on the surface of the crown portion, inscribed respectively to the contour of the curvature radius Rb which appear on the surface of the buttress portion, the shoulder portion radius of curvature Rso appearing on the surface of, the Rsi The contour is asymmetrical with respect to the tire equator line,
The radius of curvature R t of the contour that appears on the surface of the crown part is symmetrical with respect to the tire equator line,
The radius of curvature Rso of the contour that appears on the surface of the shoulder portion located outside the vehicle when the tire is mounted is smaller than the radius of curvature Rsi of the contour that appears on the surface of the shoulder portion located inside the vehicle when the tire is mounted. This is a pneumatic radial tire.
[0016]
Therefore, in the tire of the present invention, the curvature radius Rso of the contour that appears on the surface of the shoulder portion located outside the vehicle when the tire is mounted is the curvature of the contour that appears on the surface of the shoulder portion located inside the vehicle when the tire is worn. Since it is smaller than the radius Rsi, the ground contact width of the shoulder portion located outside the vehicle when the tire is mounted is larger than the ground contact width of the shoulder portion located inside the vehicle. As a result, the effective ground contact area of the tire is increased in the shoulder portion of the tire tread located outside the vehicle when the tire is mounted, so that uneven wear resistance can be improved.
[0017]
Further, in the tire of the present invention, the curvature radius Rsi of the contour that appears on the surface of the shoulder portion located on the inner side of the vehicle when the tire is worn is the curvature of the contour that appears on the surface of the shoulder portion located on the outer side of the vehicle when the tire is worn. Since it is larger than the radius Rso, it is possible to prevent the ride comfort from deteriorating.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view showing the outline of an outer peripheral cross section of a pneumatic tire showing an embodiment of the present invention, and FIG.
[0019]
In FIG. 1, 1 is a tire tread, 2 is a crown portion of the

tire tread

1, 3 is a shoulder portion, and 4 is a buttress portion. 5 is a tire equator line running in the center of the tire tread 1, and 6 is a virtual line indicating the tire maximum width.
[0020]
As shown in FIGS. 1 and 2, the tire according to the present embodiment has contours 71 and 72 of the tire outer peripheral surface in the shoulder portion 3 appearing in the tire cross section between the crown portion 2 and the buttress portion 4 of the tire tread 1. It consists of a round shape.
[0021]
The contours 71 and 72 of the radius of curvature Rso and Rsi of the tire outer peripheral surface in the shoulder portion 3 are contours 81 and 82 of the radius of curvature Rt appearing on the surface of the crown portion 2 and the buttress portion 4 as shown in the figure. Inscribed on the contours 91 and 92 of the radius of curvature Rb appearing on the surface, respectively. In FIG. 2, a wavy line 811 is a virtual extension line of the contour 81 having the curvature radius Rt, and a wavy line 911 is a virtual extension line of the contour 91 having the curvature radius Rb.
[0022]
Further, the contours 71 and 72 of the curvature radii Rso and Rsi appearing on the surface of the shoulder portion 3 are asymmetrical with respect to the tire equator 5 as shown in FIG. That is, the contour 71 appearing on the surface of the shoulder portion located on the outer side of the vehicle when the tire is mounted and the contour 72 appearing on the surface of the shoulder portion located on the inner side are configured with an asymmetric radius of curvature.
[0023]
Further, the curvature radius Rso of the contour 71 of the shoulder portion located outside the vehicle is configured to be smaller than the curvature radius Rsi of the contour 72 of the shoulder portion located inside the vehicle.
[0024]
Therefore, in the tire according to the present embodiment, the curvature radius Rso of the contour 71 that appears on the surface of the shoulder portion 3 positioned outside the vehicle when the tire is mounted appears on the surface of the shoulder portion 3 positioned inside the vehicle when the tire is mounted. Since the radius of curvature Rsi of the contour 72 is smaller than the ground contact width of the shoulder portion 3 positioned outside the vehicle when the tire is mounted, the contact width of the shoulder portion 3 positioned inside the vehicle becomes larger. In the shoulder portion 3 of the tire tread located on the outer side, the effective ground contact area of the tire is increased, so that it is possible to improve uneven wear resistance. Further, the radius of curvature Rsi of the contour 72 of the radius of curvature Rsi positioned inside the vehicle when the tire is mounted is larger than the radius of curvature Rso of the contour 71 of the shoulder portion 3 positioned outside the vehicle when the tire is mounted. Can be prevented.
[0025]
A specific value for the relationship between the curvature radius Rso of the shoulder portion 3 located outside the vehicle and the curvature radius Rsi of the contour 72 located inside the vehicle will be described below. It is desirable to set the curvature radius Rso of the contour 71 located within a range of 0.3 Rsi to 0.6 Rsi with respect to the curvature radius Rsi of the contour 72 located inside the vehicle. When the curvature radius Rso of the contour 71 is less than 0.3 Rsi, the riding comfort tends to deteriorate. On the other hand, if the curvature radius Rso of the contour 71 located outside the vehicle is larger than 0.6Rsi, the uneven wear resistance is not sufficiently improved.
[0026]
Specifically, the curvature radius Rso of the contour 71 located outside the vehicle can be selected from a range of 5 to 30 mm. If the radius of curvature Rso of the contour 71 located outside the vehicle is too small, the riding comfort is deteriorated, and if the radius of curvature Rso of the contour 71 is too large, the uneven wear resistance decreases.
[0027]
In the present invention, the radius of curvature Rt of the arcs 81 and 82 appearing on the surface of the crown portion and the radius of curvature Rb of the arcs 91 and 92 appearing on the surface of the buttress portion 4 are not particularly limited. The curvature radius Rt of the arcs 81 and 82 can be selected from a range of about 290 mm to ∞ (straight) mm, for example. The curvature radius Rb of the arcs 91 and 92 can be selected from a range of about 80 mm to ∞ (straight) mm, for example.
[0028]
Note that the tire shape of the present invention is all specified based on the standard internal pressure.
[0029]
By the way, in the present invention, the tread pattern is not particularly limited. However, since the mounting direction or the rotation direction of the tire of the present invention is specified, the tire can be suitably applied to a tread pattern tire having asymmetry with respect to the tire equator line.
That is, the present invention relates to a pneumatic radial tire having a tread pattern with different asymmetrical tread patterns on both sides of the tread portion, with the groove area ratio of the tread portion sandwiching the tire equator line, particularly high roof vehicles such as minivans and one-box vehicles. It can be used suitably for a pneumatic radial tire. This is a pneumatic radial tire having the above-mentioned asymmetric tread pattern, but when applied to a high roof vehicle such as a minivan or a one-box vehicle, the center of gravity of the vehicle is higher than that of a normal passenger car tire. This is because a large force acts on the shoulder portion located outside the vehicle during traveling, particularly during turning, and uneven wear is likely to occur.
[0030]
Therefore, according to the present invention, the groove area ratio of the tread portion is different between the tread portions on both sides across the tire equator line, and the groove area of the tread portion on one side located outside the vehicle when the tire is mounted is the inner side of the vehicle. It has an asymmetric tread pattern smaller than the groove area of the tread portion on the other side located at
The contour of the tire outer peripheral surface in the shoulder portion that appears in the tire cross section between the crown portion and the buttress portion of the tire tread is configured in a round shape,
The contour of the radius of curvature Rt that appears on the surface of the crown portion and the contour of the radius of curvature Rso and Rsi that appear on the surface of the shoulder portion inscribed in the contour of the radius of curvature Rb that appears on the surface of the buttress portion, respectively. The tire is symmetric with respect to the equator line,
The radius of curvature Rso of the contour that appears on the surface of the shoulder portion located outside the vehicle when the tire is mounted is smaller than the radius of curvature Rsi of the contour that appears on the surface of the shoulder portion located inside the vehicle when the tire is mounted. Pneumatic radial tires, especially pneumatic radial tires for high-roof vehicles such as minivans and one-box vehicles, can improve uneven wear resistance without deteriorating riding comfort. Can be used.
[0031]
However, the tire of this invention is not limited to these, It can use suitably for the tire for passenger cars which satisfy | fills the nominal of a cross-sectional width: 145-265 (mm) and flatness: 30-80 (%). In addition, the tire of the present invention can be easily manufactured by vulcanization molding using a mold or the like in which the curvature radius of the shoulder portion is asymmetric.
[0032]
【Example】
Example tires and comparative tires of the tire size 215 / 65R15 shown in the embodiment shown in FIGS. 1 and 2 were made as prototypes, and the wear resistance and riding comfort were evaluated, respectively. The results are shown in Table 1.
[0033]
Each tire has the same configuration except for “the radius of curvature of the shoulder portion”, and “the radius of curvature of the shoulder portion” is as shown in Table 1 below. However, in the tire of Comparative Example 2, the shape of the shoulder portion is a square shape.
In Table 1, “outer arc Rso” indicates the outer arc Rso of the shoulder portion located on the outer side of the vehicle when the tire is mounted, and “inner arc Rsi” indicates the shoulder portion positioned on the inner side of the vehicle when the tire is mounted. A circular arc Rsi on the outer periphery of is shown. In the tire of Comparative Example 2, since the shoulder portion has a square shape, the curvature radius of the shoulder portion is indicated as “0” for both the outer side and the inner side.
[0034]
[Table 1]

[0035]
(Uneven wear resistance test)
After the Japanese minivan (2400CC) equipped with the prototype tires of the examples and comparative examples completed 12000 km on our test course, the shoulder portion and the tire center portion located on the vehicle outer side for each of the four tires. The difference in the amount of wear was measured, and the reciprocal of the measured value was indexed with the tire of Comparative Example 1 as 100. In each example and comparative example, the driving conditions were 994 kg for the front wheels and 950 kg for the rear wheels, and two passengers were used without rotating the tires until completion. The results of this uneven wear resistance test are shown in Table 1. In addition, it shows that uneven wear resistance is so favorable that each numerical value is large.
[0036]
(Ride comfort test)
A domestic minivan (2400CC) equipped with the prototype tires of Examples and Comparative Examples was run on a real vehicle and evaluated by a feeling test with three drivers. The evaluation was performed by index evaluation in which each driver was given the type of the prototype tire and scored with a maximum of 5 points after running the vehicle, and the average value was set to 100 for the tire of Comparative Example 1. The results are shown in Table 1. Each numerical value in the table indicates that the ride comfort is better as the value is larger.
[0037]
As is clear from Table 1, the tires according to the examples have improved uneven wear resistance as compared with the tire of Comparative Example 1, and the deterioration of ride comfort is suppressed or prevented. Therefore, the tire according to the example is compatible with both high levels of uneven wear resistance and ride comfort.
[0038]
In particular, the tire of the embodiment in which the curvature radius Rso of the contour of the shoulder portion located on the outer side is 0.3 Rsi to 0.6 Rsi of the curvature radius Rsi of the contour of the shoulder portion located on the inner side of the vehicle has such a remarkable effect. As compared with the tire of the comparative example, improvement in uneven wear resistance is recognized while sufficiently preventing the deterioration of riding comfort.
[0039]
In contrast, the tire according to Comparative Example 2 has a square shape in both shoulder portions, and thus has excellent uneven wear resistance but poor ride comfort.
[0040]
【The invention's effect】
In the pneumatic radial tire of the present invention, the shoulder portion has a round shape, and the radius of curvature of the outer shoulder portion is smaller than the radius of curvature of the inner shoulder portion. Wear can be prevented.
[0041]
Therefore, in addition to ordinary passenger car tires, particularly when applied to high roof vehicles such as minivans and one-box vehicles having a high center of gravity, it is possible to ensure uneven wear resistance and excellent ride comfort.
[Brief description of the drawings]
FIG. 1 is a schematic view showing the outline of an outer peripheral cross section showing an embodiment of a pneumatic tire according to the present invention.
FIG. 2 is an enlarged view of the main part on the right side.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tire tread 2 Crown part 3 Shoulder part 4 Buttress part 5 Tire equatorial line 71 Contour 72 of radius of curvature Rso Outline 81 of radius of curvature Rsi 81 Contour of radius of curvature Rt 82 Contour of radius of curvature Rt 91 Contour of radius of curvature Rb 92 Radius of curvature Rb Contour

Claims

In the pneumatic radial tire in which the contour of the tire outer peripheral surface in the shoulder portion that appears in the tire cross section between the crown portion and the buttress portion of the tire tread is configured in a round shape,
The contour of a curvature radius Rt that appear on the surface of the crown portion, inscribed respectively to the contour of the curvature radius Rb which appear on the surface of the buttress portion, the shoulder portion radius of curvature Rso appearing on the surface of, the Rsi The contour is asymmetrical with respect to the tire equator line,
The radius of curvature R t of the contour that appears on the surface of the crown part is symmetrical with respect to the tire equator line,
The radius of curvature Rso of the contour that appears on the surface of the shoulder portion located outside the vehicle when the tire is mounted is smaller than the radius of curvature Rsi of the contour that appears on the surface of the shoulder portion located inside the vehicle when the tire is mounted. Pneumatic radial tire characterized by that.

The curvature radius Rso of the contour that appears on the surface of the shoulder portion located outside the vehicle when the tire is mounted is 0.3 Rsi of the curvature radius Rsi of the contour that appears on the surface of the shoulder portion located inside the vehicle when the tire is worn. The pneumatic radial tire according to claim 1, which is -0.6Rsi.

The pneumatic radial tire according to claim 1 or 2, wherein a curvature radius Rso of a contour appearing on a surface of the shoulder portion located outside the vehicle when the tire is mounted is 5 to 30 mm.