Patent Description:
Conventionally, pneumatic tires including, as tread reinforcement layers, a belt layer and a band layer disposed outward of the belt layer in a tire radial direction have been known (see, for example, <CIT>).

<CIT> indicates that the band layer contributes to improvement in steering stability and road noise performance while exhibiting excellent fuel efficiency.

A pneumatic tire in accordance with the preamble of claim <NUM> is known from <CIT>, <CIT>, <CIT> and <CIT>. Related tires are known from <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

However, achievement of both high-speed durability and ride comfort of a pneumatic tire has been demanded in recent years.

The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a pneumatic tire in which achievement of high-speed durability, steering stability and ride comfort can be easily realized.

The present invention is directed to a pneumatic tire including: a tread portion; a pair of sidewall portions; a pair of bead portions in each of which a bead core is embedded; a carcass layer extending between the pair of bead portions so as to straddle each bead core; a belt layer disposed outward of the carcass layer in a tire radial direction; and a band layer disposed outward of the belt layer in the tire radial direction. The band layer includes a band cord arranged in a tire circumferential direction. A <NUM>% modulus of the band cord is <NUM> to <NUM> N/mm<NUM>.

In the pneumatic tire according to the present invention, it is preferable that the <NUM>% modulus of the band cord is not less than <NUM> N/mm<NUM>.

In the pneumatic tire according to the present invention, it is preferable that each sidewall portion has a sidewall rubber disposed outward of the carcass layer in a tire axial direction, and a complex elastic modulus E*<NUM> of the sidewall rubber is <NUM> to <NUM> MPa.

In the pneumatic tire according to the present invention, it is preferable that the band cord contains aramid fiber.

In the pneumatic tire according to the present invention, the pair of bead portions have bead apex rubbers each disposed outward of the corresponding bead core in the tire radial direction, and a complex elastic modulus E*<NUM> of each bead apex rubber is <NUM> to <NUM> MPa.

In the pneumatic tire according to the present invention, it is preferable that a distance in the tire radial direction from a bead base line to an outer end in the tire radial direction of each bead apex rubber is <NUM> to <NUM>% of a tire cross-sectional height.

In the pneumatic tire of the present invention, since the band layer contains the band cord arranged in the tire circumferential direction and the <NUM>% modulus of the band cord is not less than <NUM> N/mm<NUM>, the expansion of the tread portion during high-speed running is inhibited, whereby high-speed durability is easily improved. Meanwhile, since the <NUM>% modulus of the band cord is not greater than <NUM> N/mm<NUM>, the flexibility of the tread portion is ensured, whereby ride comfort is improved. Consequently, achievement of both the high-speed durability and the ride comfort can be easily realized.

<FIG> is a meridian cross-sectional view of a pneumatic tire <NUM> according to this embodiment in a normal state, including a rotational axis (not shown) of the tire. <FIG> shows a cross section of one side, relative to a tire equator CL, of the pneumatic tire in <FIG>.

The "normal state" is a state where: the pneumatic tire <NUM> is mounted to a normal rim and inflated to a normal internal pressure; and no load is applied to the pneumatic tire <NUM>. Hereinafter, the dimensions of components of the pneumatic tire <NUM> and the like are values measured in the normal state, unless otherwise specified.

The "normal rim" is a rim that is defined, in a standard system including a standard on which the pneumatic tire <NUM> is based, by the standard for each tire, and is, for example, the "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, or "Measuring Rim" in the ETRTO standard.

The "normal internal pressure" is an air pressure that is defined, in a standard system including a standard on which the pneumatic tire <NUM> is based, by the standard for each tire, and is the "maximum air pressure" in the JATMA standard, the maximum value indicated in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "INFLATION PRESSURE" in the ETRTO standard. In the case where the pneumatic tire <NUM> is for passenger cars, the normal internal pressure may be, for example, <NUM> kPa.

In cases of tires such as racing tires to which no standards are applicable, a rim and an air pressure recommended by the manufacturer are used as the normal rim and the normal internal pressure.

The pneumatic tire <NUM> includes a tread portion <NUM>, a pair of sidewall portions <NUM>, a pair of bead portions <NUM>, a carcass layer <NUM>, a belt layer <NUM>, and a band layer <NUM>.

A bead core <NUM> is embedded in each of the pair of bead portions <NUM>. The bead core <NUM> is formed in, for example, a polygonal cross-sectional shape in which a bead wire (not shown) made of steel is wound in multiple rows and multiple stages.

The carcass layer <NUM> extends between the pair of bead portions <NUM> so as to straddle each bead core <NUM>. The carcass layer <NUM> has at least one carcass ply 6A. The carcass ply 6A is formed by, for example, coating an array of carcass cords with topping rubber. As each of the carcass cords, for example, an organic fiber such as polyester fiber, nylon fiber, rayon fiber, polyethylene naphthalate fiber, or aramid fiber, or steel, is used.

In the tread portion <NUM>, the belt layer <NUM> is disposed outward of the carcass layer <NUM> in a tire radial direction. The belt layer <NUM> is made of at least one belt ply. In this embodiment, the belt layer <NUM> is made of two belt plies 7A and 7B respectively on an inner side and an outer side in the tire radial direction. The belt plies 7A and 7B are each formed by, for example, coating an array of belt cords with topping rubber. Each of the belt cords of the belt plies 7A and 7B is preferably a highly elastic cord such as a steel cord.

In the tread portion <NUM>, the band layer <NUM> is disposed outward of the belt layer <NUM> in the tire radial direction. The band layer <NUM> is made of at least one band ply 9A in which band cords are arranged at a small angle, e.g., not greater than <NUM> degrees, with respect to a tire circumferential direction. The band ply 9A may be obtained by splicing either a jointless band or ply that is formed by helically winding a band cord or a ribbon-shaped band-like ply.

Note that an inner liner layer <NUM> is formed on the inner side of the carcass layer <NUM>, i.e., a tire inner cavity surface. The inner liner layer <NUM> is made of air-impermeable rubber and maintains internal pressure.

<FIG> shows a configuration of the band ply 9A. The band ply 9A includes band cords 9C. The band cords 9C are arranged in the tire circumferential direction. The band cords 9C are coated with topping rubber 9D.

As a material for each of the band cords, for example, an organic fiber such as nylon (nylon <NUM>) fiber, polyester (polyethylene terephthalate or polyethylene naphthalate) fiber, or aramid fiber, is used.

A <NUM>% modulus of each band cord 9C of this embodiment is <NUM> to <NUM> N/mm<NUM>.

Here, the "<NUM>% modulus" means a tensile elastic modulus, at an elongation of <NUM>%, that is measured at a tensile speed of <NUM> ± <NUM>/min. , in accordance with the Tensile Strength And Elongation Tests (Section <NUM>) described in the Test Methods for Chemical Fiber Tire Cords of JIS L1017. That is, the "<NUM>% modulus" is a value obtained by dividing the slope of a stress-strain curve by the cross-sectional area of the cord.

If the <NUM>% modulus of the band cord 9C is not less than <NUM> N/mm<NUM>, the expansion of the tread portion <NUM> during high-speed running is inhibited, whereby high-speed durability is easily improved. Meanwhile, if the <NUM>% modulus of the band cord 9C is not greater than <NUM> N/mm<NUM>, the flexibility of the tread portion <NUM> is ensured and impact received from a road surface or the like is absorbed by the tread portion <NUM>, whereby ride comfort is improved. Consequently, achievement of both the high-speed durability and the ride comfort can be easily realized.

From the viewpoint of further improving the high-speed durability, the <NUM>% modulus of the band cord 9C is preferably not less than <NUM> N/mm<NUM>. Such a band cord 9C can be easily implemented by, for example, a cord that contains aramid fiber. In particular, a band cord 9C having a hybrid structure obtained by combination of aramid fiber and nylon fiber contributes to achievement of both the high-speed durability and the ride comfort.

As shown in <FIG> and <FIG>, a sidewall rubber <NUM> is disposed in the sidewall portion <NUM>. The sidewall rubber <NUM> is disposed outward of the carcass layer <NUM> in a tire axial direction.

A complex elastic modulus E*<NUM> of the sidewall rubber <NUM> is preferably <NUM> to <NUM> MPa.

The complex elastic modulus of rubber in the present application is a value measured in accordance with the standard of JIS-K6394 using, for example, a dynamic viscoelasticity measurement device (EPLEXOR series) manufactured by NETZSCH-Gerätebau GmbH, under the conditions indicated below.

If the complex elastic modulus E*<NUM> of the sidewall rubber <NUM> is not less than <NUM> MPa, the stiffness of the sidewall portion <NUM> is improved, whereby steering stability is improved. Meanwhile, if the complex elastic modulus E*<NUM> of the sidewall rubber <NUM> is not greater than <NUM> MPa, the flexibility of the sidewall portion <NUM> is ensured and impact received from the road surface or the like is absorbed by the sidewall portion <NUM>, whereby the ride comfort is improved.

The bead portions <NUM> have bead apex rubbers <NUM>. Each bead apex rubber <NUM> is disposed outward of the corresponding bead core <NUM> in the tire radial direction. The bead apex rubber <NUM> is formed in a substantially triangular cross-sectional shape that is tapered toward the outer side in the tire radial direction.

A complex elastic modulus E*<NUM> of the bead apex rubber <NUM> is <NUM> to <NUM> MPa. If the complex elastic modulus E*<NUM> of the bead apex rubber <NUM> is not less than <NUM> MPa, the stiffness of the bead portion <NUM> is improved, whereby the steering stability is improved. Meanwhile, if the complex elastic modulus E*<NUM> of the bead apex rubber <NUM> is not greater than <NUM> MPa, the flexibility of the bead portion <NUM> is ensured and impact received from the road surface or the like is absorbed by the bead portion <NUM>, whereby the ride comfort is improved.

A distance D in the tire radial direction from a bead base line BL to an outer end 8E in tire radial direction of the bead apex rubber <NUM> is preferably <NUM> to <NUM>% of a tire cross-sectional height H. If the distance D is not less than <NUM>% of the tire cross-sectional height H, the stiffness of the bead portion <NUM> is improved, whereby the steering stability is improved. Meanwhile, if the distance D is not greater than <NUM>% of the tire cross-sectional height H, the flexibility of the bead portion <NUM> is ensured, whereby the ride comfort is improved.

Although the pneumatic tire <NUM> of the present invention has been described above in detail, the present invention is not limited to the above specific embodiment but only by the appended claims.

Pneumatic tires with a size of <NUM>/65R15 having the basic structure in <FIG> were produced as test tires according to the specifications described in Table <NUM> and evaluated for the high-speed durability and the ride comfort. The <NUM>% modulus of the band cord was adjusted by changing the fineness (dtex) and number of twists of each of cord materials (nylon <NUM>, polyethylene terephthalate, and aramid). Note that the number of cords per <NUM> in each type of cord was <NUM>. Out of specifications of the test tires, specifications that are not indicated in Table <NUM> are common. The test method is as follows.

Each test tire was mounted on a rim (<NUM> × <NUM> J) and was run using a drum test machine under the conditions of an internal pressure of <NUM> kPa, a load of <NUM> kN, and a speed of <NUM>/h. The run time taken until damage occurred was measured. The results are indicated by indexes, with the run time of Comparative Example <NUM> being regarded as <NUM>. A greater value indicates better high-speed durability.

The test tires mounted on the above rims were attached to all the wheels of a vehicle having an engine displacement of <NUM> cc, under the condition of an internal pressure of <NUM> kPa. Then, a test driver drove the vehicle on a test course having a dry asphalt road surface. At that time, sensory evaluation was made by the test driver in terms of ride comfort. The results are indicated by indexes, with the score of Comparative Example <NUM> being regarded as <NUM>. A greater value indicates better ride comfort.

The test results are indicated in Table <NUM>. Note that, for example, the values indicative of the performances are summed for each example, whereby the overall performance of the example can be determined (the same applies to Table <NUM> and the following tables).

As is obvious from Table <NUM>, it has been confirmed that in the pneumatic tires of the examples, achievement of both the high-speed durability and the ride comfort is made in a well-balanced manner as compared to the comparative examples.

Pneumatic tires with a size of <NUM>/65R15 having the basic structure in <FIG> were produced as test tires according to the specifications in Table <NUM> and evaluated for the high-speed durability, the ride comfort, and the steering stability. Out of the specifications of the test tires, specifications that are not indicated in Table <NUM> are common. The test method is as follows.

The run time of each test tire was measured in the same manner as that described above. The results are indicated by indexes, with the run time of Example <NUM> being regarded as <NUM>. A greater value indicates better high-speed durability.

A test driver drove the above vehicle on the test course having the dry asphalt road surface. At that time, sensory evaluation was made by the test driver in terms of ride comfort. The results are indicated by scores, with the score of Example <NUM> being regarded as <NUM>. A greater value indicates better ride comfort.

A test driver drove the above vehicle on the test course having the dry asphalt road surface. At that time, sensory evaluation was made by the test driver in terms of steering stability. The results are indicated by scores, with the score of Example <NUM> being regarded as <NUM>. A greater value indicates better steering stability.

The test results are indicated in Table <NUM>.

Note that the formulas (PHR) and the complex elastic moduli E* of sidewall rubbers used in the test are as indicated in Table <NUM>.

The details of each formula are as follows.

A test driver drove the vehicle on the test course having the dry asphalt road surface. At that time, sensory evaluation was made by the test driver in terms of steering stability. The results are indicated by scores, with the score of Example <NUM> being regarded as <NUM>. A greater value indicates better steering stability.

Claim 1:
A pneumatic tire (<NUM>) comprising:
a tread portion (<NUM>);
a pair of sidewall portions (<NUM>);
a pair of bead portions (<NUM>) in each of which a bead core (<NUM>) is embedded;
a carcass layer (<NUM>) extending between the pair of bead portions (<NUM>) so as to straddle each bead core (<NUM>);
a belt layer (<NUM>) disposed outward of the carcass layer (<NUM>) in a tire radial direction; and
a band layer (<NUM>) disposed outward of the belt layer (<NUM>) in the tire radial direction, wherein
the pair of bead portions (<NUM>) have bead apex rubbers (<NUM>) each disposed outward of the corresponding bead core (<NUM>) in the tire radial direction
the band layer (<NUM>) includes a band cord (9C) arranged in a tire circumferential direction, and
a <NUM>% modulus of the band cord (9C) is <NUM> to <NUM> N/mm<NUM>, wherein the <NUM>% modulus is a tensile elastic modulus, at an elongation of <NUM>%, that is measured at a tensile speed of <NUM> ± <NUM>/min,
characterized in that
a complex elastic modulus (E*<NUM>) of each bead apex rubber (<NUM>) is <NUM> to <NUM> MPa, wherein the complex elastic modulus is measured in accordance with the standard of JIS-K6394 under the conditions of initial strain being <NUM>%, amplitude being ±<NUM>%, frequency being <NUM>, deformation mode being tension and measurement temperature being <NUM>.