JP5519167B2 - Pneumatic tire - Google Patents

Pneumatic tire Download PDF

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JP5519167B2
JP5519167B2 JP2009064583A JP2009064583A JP5519167B2 JP 5519167 B2 JP5519167 B2 JP 5519167B2 JP 2009064583 A JP2009064583 A JP 2009064583A JP 2009064583 A JP2009064583 A JP 2009064583A JP 5519167 B2 JP5519167 B2 JP 5519167B2
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rubber layer
tire
tread
tread rubber
thickness
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JP2010215115A (en
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明愛 清水
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Bridgestone Corp
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Description

本発明は、トレッドの耐偏摩耗性能を向上した空気入りタイヤに関するものである。   The present invention relates to a pneumatic tire with improved uneven wear resistance performance of a tread.

従来、空気入りタイヤにおいては、種々の性能を同時に満足させるために、トレッドを２層のトレッドゴム層から形成する、いわゆるキャップ／ベース構造を適用することが行われている。   Conventionally, in a pneumatic tire, in order to satisfy various performances simultaneously, a so-called cap / base structure in which a tread is formed of two tread rubber layers has been applied.

例えば、タイヤ径方向外側のキャップゴム層には、路面グリップ性能に優れたゴム組成物を用い、タイヤ径方向内側のベースゴム層には、キャップゴム層より硬いゴム組成物を用いて、低発熱を実現するとともに操縦安定性能を向上させるための手法が提案されてきた。   For example, a rubber composition excellent in road surface grip performance is used for the cap rubber layer on the outer side in the tire radial direction, and a rubber composition harder than the cap rubber layer is used for the base rubber layer on the inner side in the tire radial direction to reduce heat generation. A method has been proposed for realizing the above and improving the steering stability performance.

特開２００４−１１４８７８号公報JP 2004-114878 A

しかし、上述した空気入りタイヤでは、不均一な接地圧により、トレッドに生じた偏摩耗に対して、十分な対策がなされてはいなかった。
そこで、本発明の目的は、トレッドの耐偏摩耗性能を向上した空気入りタイヤを提供することにある。 However, in the pneumatic tire described above, sufficient countermeasures have not been taken against uneven wear occurring in the tread due to uneven contact pressure.
SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire with improved uneven wear resistance performance of a tread.

本発明の要旨は、以下のとおりである。
[１]１対のビードコア間でトロイド状に延びるカーカスを骨格とし、このカーカスの径方向外側に、ベルトおよびトレッドを具えるタイヤにおいて、
前記トレッドを複数のトレッドゴム層から形成し、
タイヤ径方向最外側に位置する外側トレッドゴム層の動的弾性率が、タイヤ径方向最内側に位置する内側トレッドゴム層の動的弾性率より低く、
前記内側トレッドゴム層のタイヤ赤道面を含む領域における厚さが、前記内側トレッドゴム層のその他の位置における厚さよりも厚く、
前記トレッドに、タイヤ周方向に延びる周方向溝が設けられ、
前記内側トレッドゴム層が、前記周方向溝の溝内に露出しなく、
タイヤ赤道面における前記内側トレッドゴム層の厚さｄ１と、
トレッド半幅をＷとしたとき、タイヤ赤道面からＷ／３の位置における前記内側トレッドゴム層の厚さｄ２と、
タイヤ赤道面から２Ｗ／３の位置における前記内側トレッドゴム層の厚さｄ３と、
トレッド接地端を通る、前記カーカスの法線が前記内側トレッドゴム層を横切る線分の長さｄ４とが、下記（１）〜（４）式を満足することを特徴とする空気入りタイヤ。
記
３ｍｍ≦ｄ１≦１２ｍｍ （１）
０．５×ｄ１≦ｄ２≦１．１×ｄ１ （２）
０≦ｄ３≦０．４×ｄ１ （３）
０≦ｄ４≦０．４×ｄ１ （４） The gist of the present invention is as follows.
[1] In a tire having a carcass extending in a toroidal shape between a pair of bead cores and having a belt and a tread outside in the radial direction of the carcass,
Forming the tread from a plurality of tread rubber layers;
The dynamic elastic modulus of the outer tread rubber layer located on the outermost side in the tire radial direction is lower than the dynamic elastic modulus of the inner tread rubber layer located on the innermost side in the tire radial direction,
The thickness of the inner tread rubber layer in the region including the tire equatorial plane is thicker than the thickness at other positions of the inner tread rubber layer,
The tread is provided with a circumferential groove extending in the tire circumferential direction,
The inner tread rubber layer, rather exposed in the groove of the circumferential groove,
A thickness d1 of the inner tread rubber layer on the tire equatorial plane;
When the tread half width is W, the thickness d2 of the inner tread rubber layer at a position W / 3 from the tire equatorial plane;
A thickness d3 of the inner tread rubber layer at a position of 2W / 3 from the tire equatorial plane;
A pneumatic tire characterized in that a length d4 of a line segment passing through the tread grounding edge and traversing the carcass normal line across the inner tread rubber layer satisfies the following expressions (1) to (4) .
Record
3mm ≦ d1 ≦ 12mm (1)
0.5 × d1 ≦ d2 ≦ 1.1 × d1 (2)
0 ≦ d3 ≦ 0.4 × d1 (3)
0 ≦ d4 ≦ 0.4 × d1 (4)

[２]前記内側トレッドゴム層の厚さが、タイヤ赤道面からトレッド接地端に向かって漸減することを特徴とする上記[１]に記載の空気入りタイヤ。 [2] The pneumatic tire according to [1], wherein the inner tread rubber layer gradually decreases in thickness from the tire equatorial plane toward the tread ground contact edge.

[３]前記内側トレッドゴム層の動的弾性率が、前記外側トレッドゴム層の動的弾性率の１．１５倍以上２０倍以下であることを特徴とする上記[１]または[２]に記載の空気入りタイヤ。 [3] In the above [1] or [2], the dynamic elastic modulus of the inner tread rubber layer is 1.15 to 20 times the dynamic elastic modulus of the outer tread rubber layer The described pneumatic tire.

本発明によれば、トレッドの耐偏摩耗性能を向上した空気入りタイヤを提供することができる。   ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire which improved the uneven wear-proof performance of a tread can be provided.

本発明の空気入りタイヤの半部の幅方向断面図である。It is width direction sectional drawing of the half part of the pneumatic tire of this invention. 本発明の空気入りタイヤの半部の幅方向断面図である。It is width direction sectional drawing of the half part of the pneumatic tire of this invention. 従来の空気入りタイヤの半部の幅方向断面図である。It is sectional drawing of the width direction of the half part of the conventional pneumatic tire. 発明例タイヤおよび従来例タイヤの耐偏摩耗性能の測定結果を示す図である。It is a figure which shows the measurement result of the anti-wearing performance of an example tire and a conventional example tire.

以下、図面を参照しながら本発明を詳細に説明する。
図１に本発明の空気入りタイヤのトレッド半部の幅方向断面図を示す。本発明のタイヤは、１対のビードコア間でトロイド状に延びるカーカス２を骨格とし、このカーカス２の径方向外側に、図示例では３層のベルト層からなるベルト４およびトレッド６を具える。
この３層のベルト層４ａ、４ｂ、４ｃは、タイヤ径方向内側から順に配置されており、ベルト層４ａはタイヤ赤道面ＣＬに沿って延びるコードの多数本をゴムで被覆した周方向ベルト層であり、ベルト層４ｂ、４ｃは、タイヤ赤道面ＣＬに対して斜めに、かつ層間で互いに交差する向きに延びるコードの多数本をゴムで被覆した傾斜ベルト層である。なお、これらのベルト構造は一例であり、本発明はこれに限定されることはない。 Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional view in the width direction of the tread half of the pneumatic tire of the present invention. The tire according to the present invention has a carcass 2 extending in a toroidal shape between a pair of bead cores as a skeleton, and includes a belt 4 and a tread 6 each including three belt layers in the illustrated example on the outer side in the radial direction of the carcass 2.
The three belt layers 4a, 4b, and 4c are sequentially arranged from the inner side in the tire radial direction, and the belt layer 4a is a circumferential belt layer in which a large number of cords extending along the tire equatorial plane CL are covered with rubber. The belt layers 4b and 4c are inclined belt layers in which a large number of cords extending obliquely with respect to the tire equatorial plane CL and extending in directions intersecting with each other are covered with rubber. In addition, these belt structures are examples, and this invention is not limited to this.

トレッド６は複数のトレッドゴム層、図示例では、タイヤ径方向最外側に位置する外側トレッドゴム層であるキャップゴム層６Ｃと、タイヤ径方向最内側に位置する内側トレッドゴム層であるベースゴム層６Ｂとの２層から形成される、いわゆるキャップ／ベース構造である。
ここで、キャップゴム層６Ｃの動的弾性率が、ベースゴム層６Ｂの動的弾性率より低く、ベースゴム層６Ｂのタイヤ赤道面ＣＬを含む領域における厚さが、ベースゴム層６Ｂのその他の位置における厚さよりも厚いことが肝要である。以下にこの理由を説明する。
なお、「タイヤ赤道面ＣＬを含む領域（以下、タイヤ赤道面領域という）」とは、タイヤ赤道面ＣＬを中心として、タイヤ幅方向にＷ／３以内の領域をいい（Ｗ：タイヤ半幅）、「ベースゴム層６Ｂのタイヤ赤道面領域における厚さ」とは、ベースゴム層６Ｂの当該領域の平均厚さを意味するものとする。 The tread 6 includes a plurality of tread rubber layers, in the illustrated example, a cap rubber layer 6C that is an outer tread rubber layer positioned on the outermost side in the tire radial direction, and a base rubber layer that is an inner tread rubber layer positioned on the innermost side in the tire radial direction. This is a so-called cap / base structure formed from two layers with 6B.
Here, the dynamic elastic modulus of the cap rubber layer 6C is lower than the dynamic elastic modulus of the base rubber layer 6B, and the thickness of the base rubber layer 6B in the region including the tire equatorial plane CL is other than that of the base rubber layer 6B. It is important that it is thicker than the thickness at the location. The reason for this will be described below.
The “region including the tire equator plane CL (hereinafter referred to as the tire equator plane region)” refers to a region within W / 3 in the tire width direction centering on the tire equator plane CL (W: tire half width), “The thickness of the base rubber layer 6B in the tire equatorial plane region” means the average thickness of the region of the base rubber layer 6B.

さて、ベルト４の張力は、トレッド幅方向中央部分、すなわち、タイヤ赤道面領域が最も高く、ベルト４の端部に近付くほど低くなる。このように、ベルト４の張力分布がトレッド幅方向に不均一なため、トレッドのタイヤ赤道面領域のゴムは大きくつぶれて変形し、トレッド接地端Ｅのゴムはあまり変形しない。それゆえ、タイヤの接地圧は、接地中央部分、すなわち、タイヤ赤道面領域が最も高く、トレッド接地端Ｅに近付く程低下し、不均一な接地圧によりトレッド６に偏摩耗が生ずるという問題がある。
そこで、本発明者は、トレッド６を複数層のトレッドゴム層で構成し、タイヤ径方向最内側のベースゴム層６Ｂのタイヤ赤道面領域における厚さを、ベースゴム層６Ｂのその他の位置における厚さよりも厚くすることにより、トレッドゴムのタイヤ赤道面領域における部分の変形量と、タイヤ赤道面領域以外の領域における部分の変形量とを同様のものとすることに想到した。このように、ベースゴム層６Ｂの不均一な厚さが、ベルト４の不均一な張力分布を吸収し、結果として接地圧が均一となり、トレッドの偏摩耗を抑制することが可能となった。
さらに、タイヤ径方向最外側のキャップゴム層６Ｃの動的弾性率を、ベースゴム層６Ｂの動的弾性率より低くして、路面グリップ性能および低発熱性能を維持することとした。 Now, the tension of the belt 4 is highest in the center portion in the tread width direction, that is, the tire equatorial plane region, and becomes lower as the end of the belt 4 is approached. As described above, since the tension distribution of the belt 4 is not uniform in the tread width direction, the rubber in the tire equatorial plane region of the tread is largely crushed and deformed, and the rubber at the tread ground contact edge E is not so deformed. Therefore, the ground contact pressure of the tire is the highest in the ground contact central portion, that is, the tire equatorial plane region, and decreases as it approaches the tread ground contact end E, and there is a problem that uneven wear occurs in the tread 6 due to uneven contact pressure. .
Therefore, the present inventor configures the tread 6 with a plurality of tread rubber layers, and sets the thickness of the innermost base rubber layer 6B in the tire radial direction in the tire equatorial plane region to the thickness at other positions of the base rubber layer 6B. By making the thickness thicker than that, it was conceived that the deformation amount of the tread rubber in the tire equatorial plane region and the deformation amount of the portion in the region other than the tire equatorial plane region were made similar. Thus, the non-uniform thickness of the base rubber layer 6B absorbs the non-uniform tension distribution of the belt 4, and as a result, the ground contact pressure becomes uniform and the uneven wear of the tread can be suppressed.
Further, the dynamic elastic modulus of the cap rubber layer 6C on the outermost side in the tire radial direction is made lower than the dynamic elastic modulus of the base rubber layer 6B to maintain road surface grip performance and low heat generation performance.

また、図１では、トレッドに設けられた周方向溝７ａから、ベースゴム層６Ｂが露出しないように、ベースゴム層６Ｂの厚さを調節していたが、図２に示すように、ベースゴム層６Ｂの厚さが、タイヤ赤道面ＣＬからトレッド接地端Ｅに向かって漸減することが好適である。   Further, in FIG. 1, the thickness of the base rubber layer 6B is adjusted so that the base rubber layer 6B is not exposed from the circumferential groove 7a provided in the tread. However, as shown in FIG. It is preferable that the thickness of the layer 6B gradually decreases from the tire equatorial plane CL toward the tread ground contact edge E.

また、ベースゴム層６Ｂの動的弾性率が、キャップゴム層６Ｃの動的弾性率の、１．１５倍以上２０倍以下であることが好適である。１．１５倍未満である、すなわち、ベースゴム層６Ｂの動的弾性率とキャップゴム層６Ｃの動的弾性率との差が小さい場合、各層の効果が十分に発揮できないおそれがあり、一方、２０倍超の場合、キャップゴム層６Ｃの動的弾性率が低すぎて、摩耗性能が悪化するおそれがあるためである。
また、具体的なトレッドゴム層の動的弾性率としては、キャップゴム層６Ｃの動的弾性率が１．０ＭＰａ〜７．０ＭＰａであり、ベースゴム層６Ｂの動的弾性率が８．０ＭＰａ〜２０ＭＰａであることが好適である。なお、動的弾性率とは、ショアＡに準ずる。 The dynamic elastic modulus of the base rubber layer 6B is preferably 1.15 times or more and 20 times or less than the dynamic elastic modulus of the cap rubber layer 6C. If the difference between the dynamic elastic modulus of the base rubber layer 6B and the dynamic elastic modulus of the cap rubber layer 6C is small, the effects of each layer may not be sufficiently exerted, This is because if it exceeds 20 times, the dynamic elastic modulus of the cap rubber layer 6C is too low, and the wear performance may be deteriorated.
Further, as specific dynamic elastic modulus of the tread rubber layer, the dynamic elastic modulus of the cap rubber layer 6C is 1.0 MPa to 7.0 MPa, and the dynamic elastic modulus of the base rubber layer 6B is 8.0 MPa to It is suitable that it is 20 MPa. The dynamic elastic modulus is based on Shore A.

図１に示すように、トレッド半幅をＷとしたとき、タイヤ赤道面ＣＬにおけるベースゴム層６Ｂの厚さｄ１と、タイヤ赤道面ＣＬからＷ／３の位置におけるベースゴム層６Ｂの厚さｄ２と、タイヤ赤道面ＣＬから２Ｗ／３の位置におけるベースゴム層６Ｂの厚さｄ３と、トレッド接地端Ｅを通る、カーカス２の法線がベースゴム層６Ｂを横切る線分の長さｄ４とが、下記（１）〜（４）式を満足することが好適である。
なお、ベースゴム層６Ｂの各厚さｄ１、ｄ２、ｄ３は、タイヤ回転軸の直交方向に測定する。
記
３ｍｍ≦ｄ１≦１２ｍｍ （１）
０．５×ｄ１≦ｄ２≦１．１×ｄ１ （２）
０≦ｄ３≦０．４×ｄ１ （３）
０≦ｄ４≦０．４×ｄ１ （４）
ｄ１＜３ｍｍ、ｄ２＜０．５×ｄ１、０．４×ｄ１＜ｄ３あるいは０．４×ｄ１＜ｄ４の場合、接地圧を均一にするという本発明の目的が十分に達成されないおそれがある。
１２ｍｍ＜ｄ１あるいは１．１×ｄ１＜ｄ２の場合、キャップゴム６Ｃが薄くなりすぎて、十分なグリップ性能を発揮できないおそれがある。 As shown in FIG. 1, when the half width of the tread is W, the thickness d1 of the base rubber layer 6B at the tire equatorial plane CL and the thickness d2 of the base rubber layer 6B at the position W / 3 from the tire equatorial plane CL The thickness d3 of the base rubber layer 6B at a position 2W / 3 from the tire equatorial plane CL, and the length d4 of the line segment passing through the tread grounding edge E and the normal line of the carcass 2 crossing the base rubber layer 6B. It is preferable that the following expressions (1) to (4) are satisfied.
The thicknesses d1, d2, and d3 of the base rubber layer 6B are measured in the direction orthogonal to the tire rotation axis.
3mm ≦ d1 ≦ 12mm (1)
0.5 × d1 ≦ d2 ≦ 1.1 × d1 (2)
0 ≦ d3 ≦ 0.4 × d1 (3)
0 ≦ d4 ≦ 0.4 × d1 (4)
If d1 <3 mm, d2 <0.5 × d1, 0.4 × d1 <d3, or 0.4 × d1 <d4, the object of the present invention to make the ground pressure uniform may not be sufficiently achieved.
In the case of 12 mm <d1 or 1.1 × d1 <d2, the cap rubber 6C may become too thin to provide sufficient grip performance.

図１では、トレッド６を２層のトレッドゴム層から形成される場合を説明したが、本発明はこれに限定されることはない。例えば、トレッド６を３層以上のトレッドゴム層で形成することも可能であり、この場合、タイヤ径方向最外側の外側トレッドゴム層と、タイヤ径方向最内側の内側トレッドゴム層との動的弾性率を規定し、内側トレッドゴム層の厚さを規定するものとする。   Although the case where the tread 6 is formed of two tread rubber layers has been described with reference to FIG. 1, the present invention is not limited to this. For example, it is possible to form the tread 6 with three or more tread rubber layers. In this case, the dynamics of the outer tread rubber layer on the outermost side in the tire radial direction and the inner tread rubber layer on the innermost side in the tire radial direction. The elastic modulus is defined and the thickness of the inner tread rubber layer is defined.

本発明の空気入りタイヤおよび従来例の空気入りタイヤを、後述する仕様のもとに試作し、トレッドの耐偏摩耗性能を測定した。   The pneumatic tire of the present invention and the conventional pneumatic tire were prototyped according to the specifications described below, and the uneven wear resistance of the tread was measured.

発明例タイヤおよび従来例タイヤは、ともに、キャップゴム層６Ｃとベースゴム層６Ｂとを有するが、発明例タイヤでは、図１に示すように、ベースゴム層６Ｂの厚さをタイヤ赤道面領域で厚く、トレッド接地端側で薄くするとともに、ベースゴム層６Ｂの動的弾性率をキャップゴム層６Ｃの動的弾性率より高くしているのに対し、従来例タイヤでは、図３に示すように、均一厚のベースゴム層６Ｂを設けるとともに、ベースゴム層６Ｂの動的弾性率をキャップゴム層６Ｃの動的弾性率より低くしている。表１、２に各供試タイヤのベースゴム層６Ｂの厚さと、各ゴム層の動的弾性率を示す。   The inventive tire and the conventional tire both have a cap rubber layer 6C and a base rubber layer 6B. In the inventive tire, as shown in FIG. 1, the thickness of the base rubber layer 6B is set in the tire equatorial plane region. As shown in FIG. 3, in the conventional tire, the thicker and thinner at the tread ground end side, the dynamic elastic modulus of the base rubber layer 6B is higher than the dynamic elastic modulus of the cap rubber layer 6C. The base rubber layer 6B having a uniform thickness is provided, and the dynamic elastic modulus of the base rubber layer 6B is made lower than the dynamic elastic modulus of the cap rubber layer 6C. Tables 1 and 2 show the thickness of the base rubber layer 6B of each test tire and the dynamic elastic modulus of each rubber layer.

各供試タイヤ（タイヤサイズ：３１５／８０ Ｒ２２．５）をリム（リムサイズ：９．００インチ）に組み付けてタイヤ車輪とし、内圧８．４０ｋｇｆ／ｃｍ２および荷重３７５０ｋｇｆを与えて、ドラム試験機に装着し（ステア軸装着）、試験速度を７０ｋｍ／ｈとして連続走行をさせ、周方向溝７ｂより幅方向外側に位置する陸部のタイヤ赤道面ＣＬ側の端部とトレッド接地端Ｅとの摩耗量差を測定した。
従来例タイヤおよび発明例タイヤ１の摩耗量差の測定結果を図４に示す。
また、発明例タイヤ２〜４、６、１０、１２、参考例タイヤ５、７〜９、１１、１３に関して、走行距離４万ｋｍ時の摩耗量差の測定結果を表２に示す。 Each test tire (tire size: 315/80 R22.5) is assembled to a rim (rim size: 9.00 inch) to form a tire wheel, and an internal pressure of 8.40 kgf / cm 2 and a load of 3750 kgf are applied to the drum testing machine. Wearing (steer shaft mounting), running continuously at a test speed of 70 km / h, wear on the tire equatorial plane CL end of the land located on the outer side in the width direction from the circumferential groove 7b and the tread ground contact E The amount difference was measured.
The measurement results of the wear amount difference between the conventional tire and the inventive tire 1 are shown in FIG.
Table 2 shows the measurement results of the difference in wear when the running distance is 40,000 km with respect to the inventive tires 2 to 4, 6, 10, 12 and the reference tires 5, 7 to 9, 11, and 13.

Figure 0005519167
Figure 0005519167

Figure 0005519167
Figure 0005519167

図４より、従来例タイヤでは、走行距離が４．３万ｋｍのとき、摩耗量差が３．０ｍｍとなり、計測を終了した。また、発明例タイヤ１では、走行距離が６．０万ｋｍのとき、摩耗量差が０．７ｍｍ以下であった。
また、表２より、発明例タイヤ２〜４、６、１０、１２、参考例タイヤ５、７〜９、１１、１３は従来例タイヤに比較して摩耗量差が大きく減少している。
このように、発明例タイヤ、および参考例タイヤでは、耐偏摩耗性能が大きく改善されていることが分かった。 From FIG. 4, in the conventional tire, when the travel distance was 43,000 km, the wear amount difference was 3.0 mm, and the measurement was completed. In the tire 1 of the invention, the wear amount difference was 0.7 mm or less when the travel distance was 60,000 km.
Further, from Table 2, the difference in the amount of wear is greatly reduced in Invention Example Tires 2 to 4, 6, 10, 12, and Reference Example Tires 5, 7 to 9, 11, and 13 as compared to the conventional tires.
Thus, it was found that the uneven wear resistance performance was greatly improved in the inventive example tire and the reference example tire .

本発明では、トレッドを複数層のトレッドゴム層から構成し、トレッドの耐偏摩耗性能を向上させた空気入りタイヤを提供することが可能となった。   According to the present invention, it is possible to provide a pneumatic tire in which the tread is composed of a plurality of tread rubber layers and the uneven wear resistance of the tread is improved.

２ カーカス
４ ベルト
４ａ 周方向ベルト層
４ｂ、４ｃ 傾斜ベルト層
６ トレッド
６Ｃ キャップゴム層
６Ｂ ベースゴム層
７ａ、７ｂ 周方向溝 2 Carcass 4 Belt 4a Circumferential belt layer 4b, 4c Inclined belt layer 6 Tread 6C Cap rubber layer 6B Base rubber layer 7a, 7b Circumferential groove

Claims (3)

１対のビードコア間でトロイド状に延びるカーカスを骨格とし、このカーカスの径方向外側に、ベルトおよびトレッドを具えるタイヤにおいて、
前記トレッドを複数のトレッドゴム層から形成し、
タイヤ径方向最外側に位置する外側トレッドゴム層の動的弾性率が、タイヤ径方向最内側に位置する内側トレッドゴム層の動的弾性率より低く、
前記内側トレッドゴム層のタイヤ赤道面を含む領域における厚さが、前記内側トレッドゴム層のその他の位置における厚さよりも厚く、
前記トレッドに、タイヤ周方向に延びる周方向溝が設けられ、
前記内側トレッドゴム層が、前記周方向溝の溝内に露出しなく、
タイヤ赤道面における前記内側トレッドゴム層の厚さｄ１と、
トレッド半幅をＷとしたとき、タイヤ赤道面からＷ／３の位置における前記内側トレッドゴム層の厚さｄ２と、
タイヤ赤道面から２Ｗ／３の位置における前記内側トレッドゴム層の厚さｄ３と、
トレッド接地端を通る、前記カーカスの法線が前記内側トレッドゴム層を横切る線分の長さｄ４とが、下記（１）〜（４）式を満足することを特徴とする空気入りタイヤ。
記
３ｍｍ≦ｄ１≦１２ｍｍ （１）
０．５×ｄ１≦ｄ２≦１．１×ｄ１ （２）
０≦ｄ３≦０．４×ｄ１ （３）
０≦ｄ４≦０．４×ｄ１ （４） In a tire having a carcass extending in a toroidal shape between a pair of bead cores and having a belt and a tread outside in the radial direction of the carcass,
Forming the tread from a plurality of tread rubber layers;
The dynamic elastic modulus of the outer tread rubber layer located on the outermost side in the tire radial direction is lower than the dynamic elastic modulus of the inner tread rubber layer located on the innermost side in the tire radial direction,
The thickness of the inner tread rubber layer in the region including the tire equatorial plane is thicker than the thickness at other positions of the inner tread rubber layer,
The tread is provided with a circumferential groove extending in the tire circumferential direction,
The inner tread rubber layer, rather exposed in the groove of the circumferential groove,
A thickness d1 of the inner tread rubber layer on the tire equatorial plane;
When the tread half width is W, the thickness d2 of the inner tread rubber layer at a position W / 3 from the tire equatorial plane;
A thickness d3 of the inner tread rubber layer at a position of 2W / 3 from the tire equatorial plane;
A pneumatic tire characterized in that a length d4 of a line segment passing through the tread grounding edge and traversing the carcass normal line across the inner tread rubber layer satisfies the following expressions (1) to (4) .
Record
3mm ≦ d1 ≦ 12mm (1)
0.5 × d1 ≦ d2 ≦ 1.1 × d1 (2)
0 ≦ d3 ≦ 0.4 × d1 (3)
0 ≦ d4 ≦ 0.4 × d1 (4) 前記内側トレッドゴム層の厚さが、タイヤ赤道面からトレッド接地端に向かって漸減することを特徴とする請求項１に記載の空気入りタイヤ。   The pneumatic tire according to claim 1, wherein the thickness of the inner tread rubber layer gradually decreases from the tire equatorial plane toward the tread ground contact end. 前記内側トレッドゴム層の動的弾性率が、前記外側トレッドゴム層の動的弾性率の１．１５倍以上２０倍以下であることを特徴とする請求項１または２に記載の空気入りタイヤ。   3. The pneumatic tire according to claim 1, wherein a dynamic elastic modulus of the inner tread rubber layer is 1.15 to 20 times a dynamic elastic modulus of the outer tread rubber layer.
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