Patent Description:
A carcass of a tire includes at least one carcass ply. The carcass ply includes a large number of carcass cords aligned with each other. As each carcass cord, a cord having a cord structure of <NUM> dtex/<NUM> or <NUM> dtex/<NUM> is normally used. An inner liner which forms a tire inner surface is located inward of the carcass.

In a vulcanization step for the tire, an unvulcanized tire (hereinafter, referred to as green tire) is pressed against a mold by a bladder located inside the unvulcanized tire. At this time, the inner liner may flow into the space between the carcass cords. In this case, thread-like irregularities (also called open thread) occur on the tire inner surface.

The open thread influences the appearance quality of the tire. Various studies have been conducted in order to prevent occurrence of open thread (for example, <CIT>).

In order to meet the demand for mass reduction, forming a carcass, which has been composed of two carcass plies, by a single carcass ply is considered.

If the number of carcass plies that form a carcass is reduced, the strength of the carcass decreases. In order to achieve mass reduction of a tire while suppressing a decrease in strength, the use of a cord thicker than those used so far, specifically, a large-diameter cord having a total fineness of <NUM> to <NUM> dtex, as each carcass cord is considered.

In the vulcanization step, the interval between the carcass cords tends to widen at a boundary portion (hereinafter, referred to as "buttress portion") between a tread portion and each side portion.

In a carcass composed of one carcass ply, carcass plies do not hold each other as in a carcass composed of two carcass plies. The interval between the carcass cords at the buttress portion tends to widen, so that there is a concern that open thread may occur at the buttress portion.

In order to achieve mass reduction while suppressing a decrease in the strength of a carcass, establishment of a technology capable of suppressing occurrence of open thread is required.

Document <CIT> discloses a tire according to the preamble of claim <NUM>. Documents <CIT> and <CIT> disclose further tires.

The present invention has been made in view of such circumstances. Starting from a tire as disclosed in <CIT> an object of the present invention is to provide a tire that can achieve mass reduction while suppressing a decrease in the strength of a carcass without impairing appearance quality.

A tire according to an aspect of the present invention includes: a tread configured to come into contact with a road surface; a pair of sidewalls each connected to an end of the tread and located radially inward of the tread; a pair of beads each located radially inward of the sidewall; a carcass located inward of the tread and the pair of sidewalls and extending on and between a first bead and a second bead out of the pair of beads; a belt located between the tread and the carcass in a radial direction; an inner liner located inward of the carcass; and an insulation located between the carcass and the inner liner. Each of the beads includes a core and an apex located radially outward of the core. The carcass includes one carcass ply. The carcass ply includes a ply body extending between the core of the first bead and the core of the second bead, and a pair of turned-up portions connected to the ply body and turned up at the cores. The carcass ply includes a plurality of carcass cords aligned with each other and a topping rubber covering the carcass cords. The insulation is located between the first bead and the second bead. Each of the carcass cords has a total fineness of not less than <NUM> dtex and not greater than <NUM> dtex. A ratio of a thickness of the topping rubber located between the insulation and the carcass cords to a thickness of the insulation is not less than <NUM> and not greater than <NUM>.

Preferably, in the tire, the inner liner includes an inner layer forming a tire inner surface, and an outer layer stacked outward of the inner layer. The inner layer is a crosslinked product of a rubber composition containing a butyl-based rubber. The outer layer is a crosslinked product of a rubber composition containing natural rubber. A ratio of a complex elastic modulus of the insulation to a complex elastic modulus of the outer layer is not less than <NUM> and not greater than <NUM>. The complex elastic modulus is measured using a viscoelasticity spectrometer according to the standards of JIS K6394 at an initial strain of <NUM>%, at a dynamic strain of <NUM>%, at a frequency of <NUM>, under the deformation mode tension, and at a temperature of <NUM>.

Preferably, in the tire, an end of the insulation is located radially outward of an outer end of the apex. A ratio of a distance in the radial direction from the end of the insulation to the outer end of the apex to a tire cross-sectional height is not less than <NUM> and not greater than <NUM>.

Preferably, in the tire, an end of each of the turned-up portions is located radially inward of the end of the insulation. A ratio of a distance in the radial direction from the end of the insulation to the end of the turned-up portion to the distance in the radial direction from the end of the insulation to the outer end of the apex is not less than <NUM> and not greater than <NUM>.

Preferably, in the tire, the insulation includes a pair of rubber layers arranged so as to be spaced apart from each other in an axial direction with an equator plane therebetween. An outer end of each of the rubber layers is located axially inward of an end of the belt. A distance in the axial direction from the outer end of the rubber layer to the end of the belt is not less than <NUM> and not greater than <NUM>.

Preferably, in the tire, a ratio of a distance between the carcass cords in the carcass ply to an outer diameter of the carcass cord is not less than <NUM> and not greater than <NUM>.

Preferably, in the tire, a large number of dimples are provided on a tire outer surface so as to be aligned in a circumferential direction. A shortest distance from each dimple to the end of the turned-up portion is not less than <NUM> and not greater than <NUM>.

According to the present invention, a tire that can achieve mass reduction while suppressing a decrease in the strength of a carcass without impairing appearance quality is obtained.

A tire is fitted on a rim. The interior of the tire is filled with air to adjust the internal pressure of the tire. In the present invention, the tire fitted on the rim is a tire-rim assembly. The tire-rim assembly includes the rim and the tire fitted on the rim.

In the present invention, a state where a tire is fitted on a standardized rim, the internal pressure of the tire is adjusted to a standardized internal pressure, and no load is applied to the tire is referred to as a standardized state.

In the present invention, unless otherwise specified, the dimensions and angles of each component of the tire are measured in the standardized state.

The dimensions and angles of each component in a meridian cross-section of the tire, which cannot be measured in a state where the tire is fitted on the standardized rim, are measured in a cross-section (hereinafter, referred to as reference cut plane) of the tire obtained by cutting the tire along a plane including a rotation axis. In this measurement, the distance between right and left beads is set so as to be equal to the distance between the beads in the tire that is fitted on the standardized rim.

The standardized rim means a rim specified in a standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are standardized rims.

The standardized internal pressure means an internal pressure specified in the standard on which the tire is based. The "highest air pressure" in the JATMA standard, the "maximum value" recited in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are standardized internal pressures.

The standardized load means a load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" recited in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are standardized loads.

In the present invention, a rubber composition refers to a composition that is obtained by mixing a base rubber and chemicals in a kneading machine such as a Banbury mixer and that contains the uncrosslinked base rubber. A crosslinked rubber refers to a crosslinked product, of the rubber composition, obtained by pressurizing and heating the rubber composition. The crosslinked rubber contains a crosslinked product of the base rubber. The crosslinked rubber is also referred to as vulcanized rubber, and the rubber composition is also referred to as unvulcanized rubber.

Examples of the base rubber include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and isobutylene-isoprene-rubber (IIR). Examples of the chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. Selection of a base rubber and chemicals, the amounts of the selected chemicals, etc., are determined as appropriate according to the specifications of components, such as a tread and a sidewall, for which the rubber composition is used.

In the present invention, a complex elastic modulus of a component formed from a crosslinked rubber, of the components included in the tire, is measured using a viscoelasticity spectrometer ("VES" manufactured by Iwamoto Seisakusho) under the following conditions according to the standards of JIS K6394. The complex elastic modulus in the present invention is a complex elastic modulus at <NUM>.

In this measurement, a test piece is sampled from the tire. When a test piece cannot be sampled from the tire, a test piece is sampled from a sheet-shaped crosslinked rubber (hereinafter, also referred to as rubber sheet) obtained by pressurizing and heating a rubber composition, which is used for forming the component to be measured, at a temperature of <NUM> for <NUM> minutes.

In the present invention, the configuration (cord structure) of a cord formed from an organic fiber is represented in accordance with "<NUM> Indication method of cord structure" of JIS L1017. In the case where a cord is formed, for example, by twisting two single yarns (filaments) each having a fineness of <NUM> dtex, the cord structure of the cord is represented by <NUM> dtex/<NUM>. The total fineness (dtex) of the cord is represented by the product (<NUM>×<NUM> = <NUM>) of the fineness of the single yarn (<NUM> dtex) and the number of single yarns (<NUM>).

In the present invention, a tread portion of the tire is a portion of the tire that comes into contact with a road surface. A bead portion is a portion of the tire that is fitted to a rim. A side portion is a portion of the tire that extends between the tread portion and the bead portion. The tire includes a tread portion, a pair of bead portions, and a pair of side portions as portions thereof. A boundary portion between the tread portion and each side portion is also referred to as buttress portion.

<FIG> shows a part of a tire <NUM> according to a first embodiment of the present invention. The tire <NUM> is a pneumatic tire for a passenger car.

<FIG> shows a part of a cross-section (hereinafter, referred to as meridian cross-section) of the tire <NUM> taken along a plane including the rotation axis of the tire <NUM>. In <FIG>, the right-left direction is the axial direction of the tire <NUM>, and the up-down direction is the radial direction of the tire <NUM>. The direction perpendicular to the surface of the drawing sheet of <FIG> is the circumferential direction of the tire <NUM>. An alternate long and short dash line CL represents the equator plane of the tire <NUM>.

In <FIG>, the tire <NUM> is fitted on a rim R (standardized rim). The interior of the tire <NUM> is filled with air to adjust the internal pressure of the tire <NUM>.

In <FIG>, a solid line BBL extending in the axial direction is a bead base line. The bead base line BBL is a line that defines the rim diameter (see JATMA or the like) of the rim R.

In <FIG>, a position indicated by reference character PC is the point of intersection of the outer surface of the tire <NUM> and the equator plane CL. The point of intersection PC is the equator of the tire <NUM>. In the case where a groove is located on the equator plane CL, the equator PC is specified on the basis of a virtual outer surface obtained on the assumption that no groove is provided thereon. The equator PC is also a radially outer end of the tire <NUM>.

In <FIG>, a length indicated by reference character HS is the cross-sectional height (see JATMA or the like) of the tire <NUM>. The cross-sectional height HS (also referred to as tire cross-sectional height HS) is the distance in the radial direction from the bead base line BBL to the equator PC.

In <FIG>, a position indicated by reference character PW is an axially outer end (hereinafter, referred to as outer end PW) of the tire <NUM>. In the case where decorations such as patterns and letters are present on the outer surface of the tire <NUM>, the outer end PW is specified on the basis of a virtual outer surface obtained on the assumption that the decorations are not present thereon.

The distance in the axial direction, from a first outer end PW to a second outer end PW, obtained in the standardized state is the cross-sectional width (see JATMA or the like) of the tire <NUM>. The outer end PW is also referred to as maximum width position.

In <FIG>, a position indicated by reference character PT is a toe of the tire <NUM>. The toe PT is the boundary between the outer surface (hereinafter, referred to as tire outer surface <NUM>) and the inner surface (hereinafter, referred to as tire inner surface 2N) of the tire <NUM>.

In <FIG>, reference character PD indicates a position on the tire outer surface <NUM>. A length indicated by reference character HD is the distance in the radial direction from the equator PC to the position PD. In the tire <NUM>, the distance HD in the radial direction is <NUM> times the tire cross-sectional height HS. The position indicated by reference character PD is the position at which the distance HD in the radial direction from the equator PC is <NUM> times the tire cross-sectional height HS.

Although not described in detail, a tire is obtained by pressurizing and heating a green tire in a mold. In the case where the mold is a segmented mold, the mold includes a tread ring for shaping a tread portion, a pair of side plates each for shaping a side portion, and a pair of bead rings each for shaping a bead portion. The tread ring is composed of a plurality of segments aligned in the circumferential direction.

The above-described position PD is the position, on the tire outer surface <NUM>, corresponding to the position of the boundary between a segment and a side plate on a cavity surface of a mold (not shown) for the tire <NUM>.

In the present invention, the position PD is also referred to as buttress boundary-corresponding position.

<FIG> shows a cross-section of the tire <NUM> (specifically, side portion) taken along a line II-II in <FIG>. In the surface of the drawing sheet of <FIG>, the right side is the tire outer surface <NUM> side, and the left side is the tire inner surface 2N side.

In <FIG>, the line II-II is a normal line that passes through the buttress boundary-corresponding position PD and is normal to the tire inner surface 2N. <FIG> shows a cross-section of the side portion around the buttress boundary-corresponding position PD.

The tire <NUM> includes a tread <NUM>, a pair of sidewalls <NUM>, a pair of clinches <NUM>, a pair of beads <NUM>, a carcass <NUM>, a belt <NUM>, a band <NUM>, a pair of chafers <NUM>, an inner liner <NUM>, and an insulation <NUM>.

The tread <NUM> comes into contact with a road surface at a tread surface <NUM> thereof. The tread <NUM> has the tread surface <NUM> which comes into contact with a road surface. Grooves <NUM> are formed on the tread <NUM>.

The tread surface <NUM> is a part of the tire outer surface <NUM>. Side surfaces <NUM> are connected to the tread surface <NUM>. The tire outer surface <NUM> includes the tread surface <NUM> and a pair of the side surfaces <NUM>.

The tread <NUM> includes a tread body <NUM> and a pair of wings <NUM>.

Each wing <NUM> is located axially outward of the tread body <NUM>. The wing <NUM> joins the tread body <NUM> and the sidewall <NUM>. The wing <NUM> is formed from a crosslinked rubber for which adhesiveness is taken into consideration.

The tread body <NUM> includes a cap portion <NUM> and a base portion <NUM>. The cap portion <NUM> includes the tread surface <NUM>. The cap portion <NUM> comes into contact with a road surface. The cap portion <NUM> is formed from a crosslinked rubber for which wear resistance and grip performance are taken into consideration. The base portion <NUM> is located radially inward of the cap portion <NUM>. The entirety of the base portion <NUM> is covered with the cap portion <NUM>. The base portion <NUM> is formed from a crosslinked rubber that has low heat generation properties.

Each sidewall <NUM> is connected to an end of the tread <NUM>. The sidewall <NUM> is located radially inward of the tread <NUM>. The sidewall <NUM> is formed from a crosslinked rubber for which cut resistance is taken into consideration.

Each clinch <NUM> is located radially inward of the sidewall <NUM>. An outer end 8e of the clinch <NUM> is located radially inward of the maximum width position PW. The clinch <NUM> comes into contact with the rim R. The clinch <NUM> is formed from a crosslinked rubber for which wear resistance is taken into consideration.

In <FIG>, a position indicated by reference character PS is the position, on the tire outer surface <NUM>, corresponding to the radially outer end of a contact surface between the tire <NUM> and the rim R. The position PS is also referred to as contact surface outer end position.

Each bead <NUM> is located axially inward of the clinch <NUM>. The bead <NUM> is located radially inward of the sidewall <NUM>.

The bead <NUM> includes a core <NUM> and an apex <NUM>. The core <NUM> extends in the circumferential direction. The core <NUM> includes a steel wire which is not shown. The apex <NUM> is located radially outward of the core <NUM>. The apex <NUM> is tapered radially outward. The apex <NUM> is formed from a crosslinked rubber that has high stiffness. The length of the apex <NUM> is preferably not less than <NUM> and not greater than <NUM>. The length of the apex <NUM> is represented as the length of a line segment connecting the center in the width direction of the bottom surface and an outer end 40e of the apex <NUM>.

The outer end 40e of the apex <NUM> is located radially inward of the maximum width position PW. The outer end 40e of the apex <NUM> is an outer end 10e of the bead <NUM>. The entirety of the bead <NUM> is located radially inward of the maximum width position PW.

In <FIG>, a length indicated by reference character HA is the distance in the radial direction from the bead base line BBL to the outer end 40e of the apex <NUM>.

In the tire <NUM>, the ratio (HAIRS) of the distance HA in the radial direction to the tire cross-sectional height HS is not less than <NUM> and not greater than <NUM>.

The carcass <NUM> is located inward of the tread <NUM>, the pair of sidewalls <NUM>, and the pair of clinches <NUM>. The carcass <NUM> extends on and between a first bead <NUM> and a second bead <NUM> out of the pair of beads <NUM>.

A carcass of a tire for a passenger car is normally composed of two carcass plies. The carcass <NUM> of the tire <NUM> is composed of one carcass ply <NUM>. The carcass <NUM> contributes to mass reduction of the tire <NUM>.

The carcass ply <NUM> includes a ply body 42a and a pair of first turned-up portions 42b. The ply body 42a extends between the core <NUM> of the first bead <NUM> and the core <NUM> of the second bead <NUM>. The respective turned-up portions 42b are connected to the ply body 42a and turned up from the inner side toward the outer side in the axial direction at the respective cores <NUM>.

In <FIG>, a length indicated by reference character HF is the distance in the radial direction from the bead base line BBL to an end 42be of the turned-up portion 42b. The distance HF in the radial direction is also referred to as turned-up portion height.

In the tire <NUM>, the ratio (HF/HS) of the turned-up portion height HF to the tire cross-sectional height HS is not less than <NUM> and not greater than <NUM>.

As shown in <FIG>, the carcass ply <NUM> includes a plurality of carcass cords <NUM> aligned with each other. These carcass cords <NUM> are covered with a topping rubber <NUM>. The carcass ply <NUM> includes the plurality of carcass cords <NUM> and the topping rubber <NUM>.

Each carcass cord <NUM> of the tire <NUM> is a cord formed from an organic fiber (hereinafter, referred to as organic fiber cord). Although not shown, the carcass cord <NUM> is formed by twisting together a plurality of filaments formed from the organic fiber. Examples of the organic fiber include nylon fibers, rayon fibers, polyester fibers, and aramid fibers. Examples of polyester fibers include polyethylene terephthalate fibers and polyethylene naphthalate fibers. In the tire <NUM>, polyethylene terephthalate fibers are preferable as the organic fiber.

In <FIG>, a length indicated by reference character GD is the outer diameter of the carcass cord <NUM>. In the tire <NUM>, the outer diameter GD of the carcass cord <NUM> is controlled by a total fineness described later. The outer diameter GD is preferably not less than <NUM> and not greater than <NUM>. In the present invention, the outer diameter GD is represented by a "cord gauge" specified in JIS L1017.

Although not shown, the carcass cord <NUM> intersects the equator plane CL. An angle of the carcass cord <NUM> with respect to the equator plane CL, that is, an intersection angle thereof, is not less than <NUM>° and not greater than <NUM>°. The carcass <NUM> of the tire <NUM> has a radial structure. At the side portion, the carcass cord <NUM> extends substantially in the radial direction.

The carcass ply <NUM> is formed using a ply material (not shown). Although not described in detail, the ply material is obtained by covering both surfaces of a cord fabric-like fabric, which is woven with the carcass cords <NUM> as warps and wefts interlaced with the warps, with the topping rubber <NUM>. In the ply material, each carcass cord <NUM> is placed such that the center of a cross-section thereof is located at the center in the thickness direction of the ply material.

In <FIG>, a length indicated by reference character tc is the thickness of the carcass ply <NUM>. The thickness tc of the carcass ply <NUM> is set in consideration of the influence on the strength of the carcass <NUM> and mass. In the tire <NUM>, the thickness tc of the carcass ply <NUM> is preferably not less than <NUM> and not greater than <NUM>.

In the present invention, an outer portion of the carcass <NUM> means a portion from the outer surface of the carcass <NUM> to the tire outer surface <NUM>. The thickness of the outer portion of the carcass <NUM> is represented as the distance from the outer surface of the carcass <NUM> to the tire outer surface <NUM>. This distance is measured along a normal line that is normal to the outer surface of the carcass <NUM>. Specifically, in the tire <NUM>, this distance is measured along a normal line that is normal to the ply body 42a.

In <FIG>, a position indicated by reference character PF is a position, on the radially inner side with respect to the maximum width position PW, at which the outer portion of the carcass <NUM> has a maximum thickness. In the present invention, the position PF is a reference position.

In the tire <NUM>, the reference position PF is located between the maximum width position PW and the rim R in the radial direction.

The belt <NUM> is located radially inward of the tread <NUM>. The belt <NUM> is stacked on the carcass <NUM>. The belt <NUM> is located between the tread <NUM> and the carcass <NUM> in the radial direction. The above-described equator plane CL intersects the belt <NUM> at the center of the width in the axial direction of the belt <NUM>.

In the tire <NUM>, the width in the axial direction of the belt <NUM> is not less than <NUM>% and not greater than <NUM>% of the cross-sectional width of the tire <NUM>.

The belt <NUM> includes a first layer <NUM> and a second layer <NUM>. The first layer <NUM> is located radially outward of the ply body 42a and is stacked on the ply body 42a. The second layer <NUM> is located radially outward of the first layer <NUM> and is stacked on the first layer <NUM>.

As shown in <FIG>, an end of the second layer <NUM> is located axially inward of an end of the first layer <NUM>. The second layer <NUM> is narrower than the first layer <NUM>. The length from the end of the second layer <NUM> to the end of the first layer <NUM> is not less than <NUM> and not greater than <NUM>. The above-described width in the axial direction of the belt <NUM> is represented as the width in the axial direction of the wider first layer <NUM>.

Each of the first layer <NUM> and the second layer <NUM> includes a large number of belt cords aligned with each other, which are not shown. These belt cords are covered with a topping rubber. Each belt cord is tilted relative to the equator plane CL. The material of the belt cord is steel.

The band <NUM> is located between the tread <NUM> and the belt <NUM> in the radial direction. The band <NUM> is stacked on the belt <NUM>.

An end 16e of the band <NUM> is located axially outward of an end 14e of the belt <NUM>. The length from the end 14e of the belt <NUM> to the end 16e of the band <NUM> is not less than <NUM> and not greater than <NUM>.

The band <NUM> includes a helically wound band cord which is not shown. The band cord is covered with a topping rubber. The band cord extends substantially in the circumferential direction. Specifically, an angle of the band cord with respect to the circumferential direction is not greater than <NUM>°. The band <NUM> has a jointless structure.

The band cord is an organic fiber cord. Examples of the organic fiber include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

The band <NUM> includes a full band <NUM> and a pair of edge bands <NUM>.

The full band <NUM> is stacked on the belt <NUM>. The full band <NUM> covers the entirety of the belt <NUM>. Each end 52e of the full band <NUM> is located axially outward of the end 14e of the belt <NUM>.

The pair of edge bands <NUM> are arranged so as to be spaced apart from each other in the axial direction with the equator plane CL therebetween. Each edge band <NUM> is stacked on the full band <NUM>. The edge band <NUM> covers a portion at the end 52e of the full band <NUM>.

From the viewpoint of mass reduction, the band <NUM> may be composed of only the full band <NUM>. The band <NUM> may be composed of only the pair of edge bands <NUM>.

Each chafer <NUM> is located radially inward of the bead <NUM>. The chafer <NUM> comes into contact with the rim R. In the tire <NUM>, the chafer <NUM> includes a fabric and a rubber with which the fabric is impregnated.

As shown in <FIG>, an inner end 18ue of the chafer <NUM> forms a part of the tire inner surface 2N. An outer end 18se of the chafer <NUM> is located radially outward of the inner end 18ue. The outer end 18se of the chafer <NUM> is located between the bead <NUM> and the clinch <NUM>.

The inner liner <NUM> is located inward of the carcass <NUM>. The inner liner <NUM> maintains the internal pressure of the tire <NUM>.

As shown in <FIG>, the inner liner <NUM> is composed of two layers including an inner layer <NUM> and an outer layer <NUM>. Out of the two layers, the inner layer <NUM> forms the tire inner surface 2N. The outer layer <NUM> is stacked outward of the inner layer <NUM>. The outer layer <NUM> is located between the inner layer <NUM> and the carcass <NUM>.

The thickness of the inner layer <NUM> is not less than <NUM> and not greater than <NUM>. The thickness of the outer layer <NUM> is not less than <NUM> and not greater than <NUM>.

The inner layer <NUM> is a crosslinked product of a rubber composition. The rubber composition for the inner layer <NUM> (hereinafter, referred to as first rubber composition) contains a butyl-based rubber as a base rubber. The main component of the base rubber of the first rubber composition is the butyl-based rubber. The inner layer <NUM> is formed from a crosslinked rubber that has an excellent air blocking property.

Examples of the butyl-based rubber include isobutylene-isoprene-rubber and halogenated isobutylene-isoprene-rubber. Examples of halogenated isobutylene-isoprene-rubber include chloro-butyl rubber and bromo-butyl rubber.

In the present invention, the fact that the main component of the base rubber is the butyl-based rubber means that the amount of the butyl-based rubber contained in the base rubber is not less than <NUM>% by mass of the total amount of the base rubber.

From the viewpoint of forming the inner layer <NUM> having a good air blocking property, the amount of the butyl-based rubber contained in the base rubber is preferably not less than <NUM>% by mass, more preferably not less than <NUM>% by mass, and further preferably not less than <NUM>% by mass of the total amount of the base rubber. The base rubber is particularly preferably the butyl-based rubber.

In the tire <NUM>, a rubber composition that is generally used for the inner layer <NUM> of the inner liner <NUM> is used as the first rubber composition.

The outer layer <NUM> is a crosslinked product of a rubber composition. The rubber composition for the outer layer <NUM> (hereinafter, referred to as second rubber composition) contains natural rubber as a base rubber. The main component of the base rubber of the second rubber composition is the natural rubber. The second rubber composition is a rubber composition for which adhesiveness to the carcass <NUM>, the insulation <NUM>, and the inner layer <NUM> is taken into consideration. In the tire <NUM>, the inner layer <NUM> is attached to the carcass <NUM> and the insulation <NUM> via the outer layer <NUM>. The base rubber of the second rubber composition does not contain any butyl-based rubber.

In the present invention, the fact that the main component of the base rubber is the natural rubber means that the amount of the natural rubber contained in the base rubber is not less than <NUM>% by mass of the total amount of the base rubber.

From the viewpoint of forming the outer layer <NUM> having good adhesiveness, the amount of the natural rubber contained in the base rubber is preferably not less than <NUM>% by mass, more preferably not less than <NUM>% by mass, and further preferably not less than <NUM>% by mass of the total amount of the base rubber.

In the tire <NUM>, a rubber composition that is generally used for the outer layer <NUM> of the inner liner <NUM> is used as the second rubber composition.

In the tire <NUM>, a complex elastic modulus E*t of the outer layer <NUM> is not less than <NUM> MPa and not greater than <NUM> MPa.

The insulation <NUM> is located between the carcass <NUM> and the inner liner <NUM>.

An end 22e of the insulation <NUM> is located radially inward of the maximum width position PW. The position of the end 22e of the insulation <NUM> may coincide with the maximum width position PW in the radial direction. The end 22e of the insulation <NUM> may be located radially outward of the maximum width position PW.

The insulation <NUM> is located between the carcass <NUM> and the inner liner <NUM> and is located between the first bead <NUM> and the second bead <NUM>.

As described above, the carcass ply <NUM> of the tire <NUM> includes the plurality of carcass cords <NUM> aligned with each other. As shown in <FIG>, the plurality of carcass cords <NUM> are arranged so as to be spaced apart from each other.

Around the buttress boundary-corresponding position PD, the insulation <NUM> is stacked on the outer layer <NUM> of the inner liner <NUM>. The carcass ply <NUM> is stacked on the insulation <NUM>. The insulation <NUM> and the topping rubber <NUM>, which covers the carcass cords <NUM>, are located between the outer layer <NUM> and the carcass cords <NUM>.

In <FIG>, a length indicated by reference character td is the thickness of the insulation <NUM>. A length indicated by reference character ta is the thickness of the topping rubber <NUM> located between the insulation <NUM> and the carcass cords <NUM>.

The thickness td of the insulation <NUM> and the thickness ta of the topping rubber <NUM> are measured along a normal line that passes through the buttress boundary-corresponding position PD and is normal to the tire inner surface 2N.

As described above, in the tire <NUM>, from the viewpoint of mass reduction, the carcass <NUM> is composed of one carcass ply <NUM>.

In a conventional tire, a carcass is composed of two carcass plies. In the tire <NUM>, the number of carcass plies <NUM> included in the carcass <NUM> is reduced as compared to that of the conventional tire. There is a concern that the strength of the carcass <NUM> may decrease.

In the tire <NUM>, a cord that is thicker than a conventional cord is used as each carcass cord <NUM>. Specifically, a cord having a total fineness in the range of <NUM> to <NUM> dtex is used as each carcass cord <NUM>. Each carcass cord <NUM> of the tire <NUM> has a total fineness of not less than <NUM> dtex and not greater than <NUM> dtex.

Since the total fineness of each carcass cord <NUM> is not less than <NUM> dtex, even though the carcass <NUM> is composed of one carcass ply <NUM>, the carcass <NUM> has the required strength. In other words, a decrease in the strength of the carcass <NUM> is suppressed.

Since the total fineness of each carcass cord <NUM> is not greater than <NUM> dtex, the influence of the carcass cord <NUM> on the tire mass is suppressed. The carcass ply <NUM> including the carcass cords <NUM> can contribute to mass reduction of the tire <NUM>.

In the tire <NUM>, each carcass cord <NUM> is thicker than a conventional carcass cord, and the carcass <NUM> is composed of one carcass ply <NUM>.

In a vulcanization step, there is a concern that the intervals between the carcass cords <NUM> may widen at the buttress portion and the outer layer <NUM> of the inner liner <NUM> may flow into the space between the carcass cords <NUM>. In this case, open thread occurs and the appearance quality of the tire decreases.

As described above, in the tire <NUM>, the insulation <NUM> is located between the carcass <NUM> and the inner liner <NUM> and is located between the first bead <NUM> and the second bead <NUM>. In particular, in the tire <NUM>, at the buttress portion at which the intervals between the carcass cords <NUM> widen, the ratio (ta/td) of the thickness ta of the topping rubber <NUM> located between the insulation <NUM> and the carcass cords <NUM> to the thickness td of the insulation <NUM> is not less than <NUM> and not greater than <NUM>.

Since the ratio (ta/td) is not less than <NUM>, the influence of the insulation <NUM> on mass is suppressed. In the tire <NUM>, the fact that the carcass <NUM> is composed of one carcass ply <NUM> can effectively contribute to mass reduction.

Since the ratio (ta/td) is not greater than <NUM>, the insulation <NUM> suppresses the flow of the outer layer <NUM> into the space between the carcass cords <NUM>. The insulation <NUM> contributes to suppressing occurrence of open thread. The tire <NUM> has good appearance quality.

The tire <NUM> achieves mass reduction while suppressing a decrease in the strength of the carcass <NUM> without impairing appearance quality.

In a conventional tire in which no insulation <NUM> is provided, in the case of using a thick cord as each carcass cord, in order to suppress occurrence of open thread, for example, adjustment such as decreasing the holding force of wefts in a fabric including the carcass cords as warps is required.

On other hand, in the tire <NUM>, even though a thick cord is used as each carcass cord <NUM>, adjustment of the wefts, etc., is unnecessary. In other words, in the tire <NUM>, it is not necessary to provide a special step for obtaining the carcass <NUM> that can contribute to mass reduction. The carcass <NUM> is formed in the same manner as in a conventional tire for which adjustment of the wefts, etc., is unnecessary.

The tire <NUM> achieves mass reduction while suppressing a decrease in the strength of the carcass <NUM> without increasing the production cost and without impairing appearance quality.

As described above, in the tire <NUM>, the ratio (ta/td) of the thickness ta of the topping rubber <NUM> located between the insulation <NUM> and the carcass cords <NUM> to the thickness td of the insulation <NUM> is not less than <NUM> and not greater than <NUM>.

From the viewpoint of obtaining the tire <NUM> that can achieve mass reduction while suppressing a decrease in the strength of the carcass <NUM> without impairing appearance quality, the ratio (ta/td) is preferably not less than <NUM> and preferably not greater than <NUM>.

In the tire <NUM>, the ratio (E*r/E*t) of a complex elastic modulus E*r of the insulation <NUM> to the complex elastic modulus E*t of the outer layer <NUM> is preferably not less than <NUM> and not greater than <NUM>.

When the ratio (E*r/E*t) is set to be not less than <NUM>, the insulation <NUM> suppresses the flow of the outer layer <NUM> into the space between the carcass cords <NUM>. In the tire <NUM>, occurrence of open thread is effectively suppressed. From this viewpoint, the ratio (E*r/E*t) is more preferably not less than <NUM> and further preferably not less than <NUM>.

When the ratio (E*r/E*t) is set to be not greater than <NUM>, heat generation of the insulation <NUM> itself is suppressed. In the tire <NUM>, low rolling resistance is maintained. From this viewpoint, the ratio (E*r/E*t) is more preferably not greater than <NUM> and further preferably not greater than <NUM>.

In the tire <NUM>, the thickness td of the insulation <NUM> is preferably not less than <NUM> and not greater than <NUM>.

When the thickness td is set to be not less than <NUM>, the insulation <NUM> can effectively contribute to suppressing the flow of the outer layer <NUM> into the space between the carcass cords <NUM>. In the tire <NUM>, occurrence of open thread is more effectively suppressed. From this viewpoint, the thickness td is more preferably not less than <NUM> and further preferably not less than <NUM>.

When the thickness td is set to be not greater than <NUM>, the influence of the insulation <NUM> on mass is suppressed. The insulation <NUM> can contribute to mass reduction of the tire <NUM>. From this viewpoint, the thickness td is more preferably not greater than <NUM> and further preferably not greater than <NUM>.

In <FIG>, a length indicated by reference character D is the distance between the carcass cords <NUM> in the carcass ply <NUM>. As described above, in the tire <NUM>, a cord having a total fineness in the range of <NUM> to <NUM> dtex is used as each carcass cord <NUM>.

In the tire <NUM>, the ratio (D/GD) of the distance D between the carcass cords <NUM> in the carcass ply <NUM> to the outer diameter GD of the carcass cord <NUM> is preferably not less than <NUM> and not greater than <NUM>.

When the ratio (D/GD) is set to be not less than <NUM>, the carcass <NUM> can effectively contribute to mass reduction of the tire <NUM>. From this viewpoint, the ratio (D/GD) is more preferably not less than <NUM>.

When the ratio (D/GD) is set to be not greater than <NUM>, the strength of the carcass <NUM> is appropriately maintained. From this viewpoint, the ratio (D/GD) is more preferably not greater than <NUM>.

<FIG> shows a part of the cross-section of the tire <NUM> shown in <FIG>. <FIG> shows a portion from an end portion of a tread portion to a bead portion.

The end 22e of the insulation <NUM> is located radially outward of the outer end 40e of the apex <NUM>.

At a portion on the radially inner side of the outer end 40e of the apex <NUM>, the apex <NUM> is stacked on the carcass ply <NUM>. As described above, the apex <NUM> is formed from a crosslinked rubber that has high stiffness. In the tire <NUM>, the apex <NUM> restricts the movement of the carcass cord <NUM> due to a shape change in the vulcanization step. In the tire <NUM>, open thread is less likely to occur even though the insulation <NUM> is not provided at the portion on the radially inner side of the outer end 40e of the apex <NUM>. Since the end 22e of the insulation <NUM> is located radially outward of the outer end 40e of the apex <NUM>, the influence of the insulation <NUM> on the mass of the tire <NUM> is effectively suppressed. The tire <NUM> can achieve mass reduction while maintaining good appearance quality. From this viewpoint, the end 22e of the insulation <NUM> is preferably located radially outward of the outer end 40e of the apex <NUM>.

In <FIG>, a length indicated by reference character Hc is the distance in the radial direction from the end 22e of the insulation <NUM> to the outer end 40e of the apex <NUM>. In the present invention, in the case where the end 22e of the insulation <NUM> is located radially outward of the outer end 40e of the apex <NUM>, the distance Hc in the radial direction is represented by a positive number.

In the tire <NUM>, the ratio (Hc/HS) of the distance Hc in the radial direction to the tire cross-sectional height HS is preferably not less than <NUM> and not greater than <NUM>.

When the ratio (Hc/HS) is set to be not less than <NUM>, the influence of the insulation <NUM> on mass is effectively suppressed. The insulation <NUM> can contribute to mass reduction of the tire <NUM>. From this viewpoint, the ratio (Hc/HS) is more preferably not less than <NUM>.

When the ratio (Hc/HS) is set to be not greater than <NUM>, the insulation <NUM> can effectively contribute to suppressing occurrence of open thread at the buttress portion. In the tire <NUM>, good appearance quality is maintained. From this viewpoint, the ratio (Hc/HS) is more preferably not greater than <NUM>.

In the tire <NUM>, the end 42be of the turned-up portion 42b is located radially outward of the core <NUM>. The end 42be of the turned-up portion 42b is located radially inward of the maximum width position PW. The carcass <NUM> of the tire <NUM> has a low turned-up structure. For example, as shown in <FIG>, the end 42be of the turned-up portion 42b of the tire <NUM> is located radially inward of the outer end 40e of the apex <NUM>. The carcass <NUM> having the turned-up portion 42b can contribute to mass reduction of the tire <NUM>. From this viewpoint, the end 42be of the turned-up portion 42b is preferably located radially inward of the outer end 40e of the apex <NUM>.

In <FIG>, a position indicated by reference character PR is a radially outer end of the rim R. The end 42be of the turned-up portion 42b of the tire <NUM> is located radially inward of the outer end PR of the rim R. Accordingly, concentration of strain on the end 42be of the turned-up portion 42b is suppressed. The tire <NUM> can achieve mass reduction while maintaining good durability. From this viewpoint, the end 42be of the turned-up portion 42b is more preferably located radially inward of the outer end PR of the rim R.

As shown in <FIG>, in the tire <NUM>, the outer end 40e of the apex <NUM> is located radially inward of the end 22e of the insulation <NUM>, and the end 42be of the turned-up portion 42b is located radially inward of the outer end 40e of the apex <NUM>.

In the tire <NUM>, the end 42be of the turned-up portion 42b is located radially inward of the end 22e of the insulation <NUM>.

In <FIG>, a length indicated by reference character Hf is the distance in the radial direction from the end 22e of the insulation <NUM> to the end 42be of the turned-up portion 42b.

In the tire <NUM>, the ratio (Hf/Hc) of the distance Hf in the radial direction to the distance Hc in the radial direction from the end 22e of the insulation <NUM> to the outer end 40e of the apex <NUM> is preferably not less than <NUM> and not greater than <NUM>.

When the ratio (Hf/Hc) is set to be not less than <NUM>, the insulation <NUM> can effectively contribute to suppressing occurrence of open thread at the buttress portion. In the tire <NUM>, good appearance quality is maintained. From this viewpoint, the ratio (Hf/Hc) is more preferably not less than <NUM> and further preferably not less than <NUM>.

When the ratio (Hf/Hc) is set to be not greater than <NUM>, the influence of the insulation <NUM> on mass is effectively suppressed. The insulation <NUM> can contribute to mass reduction of the tire <NUM>. From this viewpoint, the ratio (Hf/Hc) is more preferably not greater than <NUM> and further preferably not greater than <NUM>.

As shown in <FIG>, the insulation <NUM> of the tire <NUM> includes a pair of rubber layers <NUM>. The pair of rubber layers <NUM> are arranged so as to be spaced apart from each other in the axial direction with the equator plane CL therebetween.

An inner end 60ue of each rubber layer <NUM> is the end 22e of the insulation <NUM>. The inner end 60ue of the rubber layer <NUM> is located radially outward of the outer end 40e of the apex <NUM>.

On the radially inner side of the inner end 60ue of the rubber layer <NUM>, the outer layer <NUM> of the inner liner <NUM> is attached to the carcass ply <NUM>. At a portion from the inner end 60ue to an outer end 60se of the rubber layer <NUM>, the outer layer <NUM> is attached to the carcass ply <NUM> via the rubber layer <NUM>. At a portion between the outer end 60se of a first rubber layer <NUM> and the outer end 60se of a second rubber layer <NUM> (not shown), the outer layer <NUM> is attached to the carcass ply <NUM>.

The tire <NUM> does not have a third rubber layer <NUM> between the first rubber layer <NUM> and the second rubber layer <NUM>. The insulation <NUM> in which no third rubber layer <NUM> exists between the first rubber layer <NUM> and the second rubber layer <NUM> can contribute to mass reduction of the tire <NUM>. From this viewpoint, the insulation <NUM> preferably includes the pair of rubber layers <NUM> arranged so as to be spaced apart from each other in the axial direction with the equator plane CL therebetween.

In a region from the outer end 60se of the first rubber layer <NUM> to the outer end 60se of the second rubber layer <NUM>, the belt <NUM> is located radially outward of the carcass <NUM>. The belt <NUM> restricts the movement of the carcass cord <NUM> due to a shape change in the vulcanization step. In the tire <NUM>, open thread is less likely to occur even though no rubber layer <NUM> is provided between the first rubber layer <NUM> and the second rubber layer <NUM>. The tire <NUM> achieves mass reduction while maintaining good appearance quality.

In the tire <NUM>, the outer end 60se of the rubber layer <NUM> is located axially inward of the end 14e of the belt <NUM>. Accordingly, the rubber layer <NUM> effectively suppresses occurrence of open thread at the buttress portion which is formed with a small thickness in the tire <NUM>. The tire <NUM> can achieve mass reduction while maintaining good appearance quality. From this viewpoint, the outer end 60se of the rubber layer <NUM> is preferably located axially inward of the end 14e of the belt <NUM>.

In <FIG>, a length indicated by reference character Lb is the distance in the axial direction from the outer end 60se of the rubber layer <NUM> to the end 14e of the belt <NUM>. In the present invention, in the case where the outer end 60se of the rubber layer <NUM> is located axially inward of the end 14e of the belt <NUM>, the distance Lb in the axial direction is represented by a positive number.

In the tire <NUM>, the distance Lb in the axial direction is preferably not less than <NUM> and not greater than <NUM>.

When the distance Lb in the axial direction is set to be not less than <NUM>, the rubber layer <NUM> can effectively suppress occurrence of open thread at the buttress portion. Moreover, since the outer end 60se of the rubber layer <NUM> is located away from the end 14e of the belt <NUM>, concentration of strain on the end 14e of the belt <NUM> is suppressed. In the tire <NUM>, good durability is maintained. From this viewpoint, the distance Lb in the axial direction is more preferably not less than <NUM> and further preferably not less than <NUM>.

When the distance Lb in the axial direction is set to be not greater than <NUM>, the insulation <NUM> composed of the pair of rubber layers <NUM> can effectively contribute to mass reduction. From this viewpoint, the distance Lb in the axial direction is more preferably not greater than <NUM> and further preferably not greater than <NUM>.

<FIG> shows a part of the cross-section of the tire <NUM> shown in <FIG>. <FIG> shows the portion from the end portion of the tread portion to the bead portion.

In the tire <NUM>, the outer end 40e of the apex <NUM> is located radially inward of the outer end 8e of the clinch <NUM>. The outer end 18se of the chafer <NUM> is located radially inward of the outer end 40e of the apex <NUM>. The end 42be of the turned-up portion 42b is located radially inward of the outer end 18se of the chafer <NUM>.

In <FIG>, a length indicated by reference character H2 is the distance in the radial direction from the end 42be of the turned-up portion 42b to the outer end 8e of the clinch <NUM>. A length indicated by reference character H3 is the distance in the radial direction from the end 42be of the turned-up portion 42b to the outer end 40e of the apex <NUM>. A length indicated by reference character H4 is the distance in the radial direction from the end 42be of the turned-up portion 42b to the outer end 18se of the chafer <NUM>.

In the tire <NUM>, the end 42be of the turned-up portion 42b is located radially inward of the outer end 8e of the clinch <NUM>. The end 42be of the turned-up portion 42b is located so as to be spaced apart from the outer end 8e of the clinch <NUM>. Accordingly, occurrence of damage starting from interface separation between the sidewall <NUM> and the clinch <NUM> is suppressed. In the tire <NUM>, good durability is maintained. From this viewpoint, the distance H2 in the radial direction from the end 42be of the turned-up portion 42b to the outer end 8e of the clinch <NUM> is preferably not less than <NUM> and more preferably not less than <NUM>. From the viewpoint of forming the turned-up portion 42b having a sufficient length and stably fixing the carcass ply <NUM> to the bead <NUM>, the distance H2 in the radial direction is preferably not greater than <NUM> and more preferably not greater than <NUM>.

In the tire <NUM>, the end 42be of the turned-up portion 42b is located radially inward of the outer end 40e of the apex <NUM>. The end 42be of the turned-up portion 42b is located so as to be spaced apart from the outer end 40e of the apex <NUM>. Accordingly, occurrence of damage starting from interface separation around the outer end 40e of the apex <NUM> is suppressed. In the tire <NUM>, good durability is maintained. From this viewpoint, the distance H3 in the radial direction from the end 42be of the turned-up portion 42b to the outer end 40e of the apex <NUM> is preferably not less than <NUM> and more preferably not less than <NUM>. From the viewpoint of forming the turned-up portion 42b having a sufficient length and stably fixing the carcass ply <NUM> to the bead <NUM>, the distance H3 in the radial direction is preferably not greater than <NUM> and more preferably not greater than <NUM>.

In the tire <NUM>, the end 42be of the turned-up portion 42b is located radially inward of the outer end 18se of the chafer <NUM>. The end 42be of the turned-up portion 42b is located so as to be spaced apart from the outer end 18se of the chafer <NUM>. Accordingly, occurrence of damage starting from interface separation around the outer end 18se of the chafer <NUM> is suppressed. In the tire <NUM>, good durability is maintained. From this viewpoint, the distance H4 in the radial direction from the end 42be of the turned-up portion 42b to the outer end 18se of the chafer <NUM> is preferably not less than <NUM> and more preferably not less than <NUM>. From the viewpoint of forming the turned-up portion 42b having a sufficient length and stably fixing the carcass ply <NUM> to the bead <NUM>, the distance H4 in the radial direction is preferably not greater than <NUM> and more preferably not greater than <NUM>.

<FIG> shows a modification of the tire <NUM> shown in <FIG> (hereinafter, tire 2a). <FIG> shows a part of a meridian cross-section of the tire 2a.

In the tire 2a shown in <FIG>, the end 42be of the turned-up portion 42b is located radially inward of the maximum width position PW. The carcass <NUM> of the tire 2a has a low turned-up structure.

The end 42be of the turned-up portion 42b is located radially inward of the outer end 40e of the apex <NUM>. The end 42be of the turned-up portion 42b is located radially outward of the outer end PR of the rim R.

As described above, each carcass cord <NUM> is thicker than a conventional one. There is a concern that strain may be concentrated on the end 42be of the turned-up portion 42b.

As shown in <FIG>, in the tire 2a, a dimple <NUM> is provided on the tire outer surface <NUM>. The dimple <NUM> is provided on a portion, of the tire outer surface <NUM>, between the reference position PF and the contact surface outer end position PS.

<FIG> shows a part of the tire outer surface <NUM> of the tire 2a. <FIG> is a development of the portion on which the dimple <NUM> is provided. In <FIG>, the right-left direction is the circumferential direction of the tire 2a. The up-down direction is the radial direction of the tire 2a.

As shown in <FIG>, a large number of dimples <NUM> are provided on the tire outer surface <NUM> so as to be aligned in the circumferential direction. These dimples <NUM> are arranged at equal intervals. Each dimple <NUM> has a rectangular shape. The dimple <NUM> is long in the circumferential direction and short in the radial direction.

During running of the tire 2a, each dimple <NUM> moves against the wind, which disturbs the air flow around the dimple <NUM>. Accordingly, a rise in the temperature around the dimple <NUM> is suppressed.

As shown in <FIG>, the dimple <NUM> is located near the end 42be of the turned-up portion 42b. Even if strain is concentrated on the end 42be of the turned-up portion 42b, the dimple <NUM> promotes heat dissipation, so that a rise in temperature is suppressed. In the tire 2a, good durability and low rolling resistance are maintained. From this viewpoint, in the case where the end 42be of the turned-up portion 42b is located radially outward of the outer end PR of the rim R, the dimple <NUM> is preferably provided near the end 42be of the turned-up portion 42b.

In <FIG>, a length indicated by reference character DF is the shortest distance from the dimple <NUM> to the turned-up portion 42b.

From the viewpoint of maintaining good durability and low rolling resistance, the shortest distance DF is preferably not greater than <NUM>. From the viewpoint that the dimple <NUM> can sufficiently exhibit its heat dissipation effect, the shortest distance DF is preferably not less than <NUM>.

In <FIG>, a length indicated by reference character DL is the length of the dimple <NUM>. The length DL is measured along a width center line of the dimple <NUM> in the radial direction. A length indicated by reference character DW is the width of the dimple <NUM>. The width DW is measured along a length center line of the dimple <NUM> in the circumferential direction.

From the viewpoint that the dimple <NUM> can sufficiently exhibit its heat dissipation effect, the length DL of the dimple <NUM> is preferably not less than <NUM> and more preferably not less than <NUM>. The length DL is preferably not greater than <NUM> and more preferably not greater than <NUM>.

From the same viewpoint, the width DW of the dimple <NUM> is preferably not less than <NUM> and more preferably not less than <NUM>. The width DW is preferably not greater than <NUM> and more preferably not greater than <NUM>.

<FIG> shows a cross-section of the dimple <NUM>. A line VII-VII in <FIG> includes the width center line of the dimple <NUM> in the radial direction. In <FIG>, a length indicated by reference character DD is the depth of the dimple <NUM>.

In the tire 2a, from the viewpoint that the dimple <NUM> can sufficiently exhibit its heat dissipation effect, the depth DD of the dimple <NUM> is preferably not less than <NUM> and more preferably not less than <NUM>. The depth DD is preferably not greater than <NUM> and more preferably not greater than <NUM>.

<FIG> shows a modification of the tire <NUM> shown in <FIG> (hereinafter, tire 2b). <FIG> shows a part of a meridian cross-section of the tire 2b.

In the tire 2b shown in <FIG>, the end 42be of the turned-up portion 42b is located radially outward of the maximum width position PW. The carcass <NUM> of the tire 2b has a high turned-up structure.

This carcass <NUM> particularly contributes to improvement of the stiffness of each side portion. The mass of the tire 2b is slightly increased as compared to that of the tire <NUM> shown in <FIG>, but the steering stability of the tire 2b is improved.

The carcass <NUM> is lighter than a conventional carcass that is composed of two carcass plies and has a high turned-up structure. The tire 2b also achieves mass reduction while suppressing a decrease in the strength of the carcass <NUM> without impairing appearance quality.

<FIG> shows a modification of the tire 2b shown in <FIG> (hereinafter, tire 2c). <FIG> shows a part of a meridian cross-section of the tire 2c.

As shown in <FIG>, in the tire 2c, a dimple 62a is provided near the end 42be of the turned-up portion 42b. The dimple 62a is formed with the same specifications as those of the dimple <NUM> shown in <FIG>.

In the tire 2c, the dimple 62a is located near the end 42be of the turned-up portion 42b. Even if strain is concentrated on the end 42be of the turned-up portion 42b, the dimple 62a promotes heat dissipation, so that a rise in temperature is suppressed. In the tire 2c, good durability and low rolling resistance are maintained. From this viewpoint, in the case where the carcass <NUM> has a high turned-up structure, the dimple 62a is preferably provided in a zone from the position away radially outward from the end 42be of the turned-up portion 42b by <NUM> to the position away radially inward from the end 42be of the turned-up portion 42b by <NUM>. Furthermore, in this case, the shortest distance DF from the dimple 62a to the end 42be of the turned-up portion 42b is more preferably not less than <NUM> and not greater than <NUM>.

<FIG> shows a part of a tire <NUM> according to a second embodiment of the present invention. The tire <NUM> is a pneumatic tire for a passenger car.

In the tire <NUM>, beads <NUM> different from the beads <NUM> of the tire <NUM> shown in <FIG> are used. Accordingly, although the configurations of the clinches <NUM>, the carcass <NUM>, and the chafers <NUM> in the tire <NUM> are slightly changed, the configuration of the tire <NUM> other than the beads <NUM> are substantially the same as that of the tire <NUM> shown in <FIG>. The components of the tire <NUM> other than the beads <NUM> are designated by the same reference characters as those for the tire <NUM> shown in <FIG>, and the detailed description thereof is omitted.

In the tire <NUM> as well, the carcass <NUM> is composed of one carcass ply <NUM>. The carcass <NUM> contributes to mass reduction of the tire <NUM>.

Since the carcass ply <NUM> includes carcass cords each having a total fineness of not less than <NUM> dtex, even though the carcass <NUM> is composed of one carcass ply <NUM>, a decrease in the strength of the carcass <NUM> is suppressed. Since the carcass ply <NUM> includes carcass cords each having a total fineness of not greater than <NUM> dtex, the carcass <NUM> can contribute to mass reduction of the tire <NUM>.

The insulation <NUM> is located between the carcass <NUM> and the inner liner <NUM> and is located between a first bead <NUM> and a second bead <NUM>. The insulation <NUM> suppresses the flow of the outer layer of the inner liner <NUM> into the space between the carcass cords. The insulation <NUM> contributes to suppressing occurrence of open thread. The tire <NUM> has good appearance quality.

The tire <NUM> also achieves mass reduction while suppressing a decrease in the strength of the carcass <NUM> without impairing appearance quality.

Similar to the beads <NUM>, each bead <NUM> of the tire <NUM> also includes a core <NUM> and an apex <NUM>. The core <NUM> has the same configuration as that of the core <NUM> of the bead <NUM>. The core <NUM> extends in the circumferential direction. The apex <NUM> is located radially outward of the core <NUM>. The apex <NUM> is tapered radially outward as a whole. An outer end 78e of the apex <NUM> is located radially inward of the maximum width position PW. The outer end 78e of the apex <NUM> is an outer end 74e of the bead <NUM>. The entirety of the bead <NUM> is located radially inward of the maximum width position PW.

In the tire <NUM>, the apex <NUM> is composed of two components. The apex <NUM> includes a first apex <NUM> and a second apex <NUM>.

The first apex <NUM> is located radially outward of the core <NUM>. The first apex <NUM> is stacked on the core <NUM>. The first apex <NUM> is tapered radially outward. The material of the first apex <NUM> is the same as that of the above-described apex <NUM>. The length of the first apex <NUM> is not less than <NUM> and not greater than <NUM>. The first apex <NUM> is shorter than the apex <NUM>.

As shown in <FIG>, the core <NUM> and the first apex <NUM> are located between the ply body 42a and the turned-up portion 42b. At a portion on the radially outer side of the first apex <NUM>, the turned-up portion 42b is directly attached to the ply body 42a. The core <NUM> and the first apex <NUM> are surrounded by the carcass ply <NUM>.

The second apex <NUM> is located radially outward of the first apex <NUM>. The second apex <NUM> is located between the carcass <NUM> and the clinch <NUM>. The end 42be of the turned-up portion 42b is interposed between the ply body 42a and the second apex <NUM>. The outer end 18se of the chafer <NUM> is located between the turned-up portion 42b and the second apex <NUM>. As shown in <FIG>, the second apex <NUM> is thick around an outer end 80e of the first apex <NUM>. The second apex <NUM> is tapered radially outward from the thick portion thereof. The second apex <NUM> is tapered radially inward from the thick portion thereof.

In the tire <NUM> shown in <FIG>, a portion, but not the entirety, of each bead <NUM>, is surrounded by the carcass ply <NUM>. In the tire <NUM>, there is a concern that, as compared to a tire in which the entirety of each bead is surrounded by a carcass ply, a cross-sectional secondary moment may be smaller, resulting in a decrease in the stiffness of the bead portion. In the case where the stiffness of the bead portion is low, the cornering force decreases. In this case, for example, if a high load is applied to a vehicle during cornering, the grip of the tire <NUM> may become insufficient, and the vehicle may fall down.

In the tire 2b shown in <FIG>, the entirety of each bead <NUM> is surrounded by the carcass ply <NUM>. However, as described above, strain is concentrated on the end 42be of the turned-up portion 42b. The concentration of strain decreases the durability of the tire <NUM>.

In the tire <NUM>, as described above, the core <NUM> and the first apex <NUM> are surrounded by the carcass ply <NUM>, and the turned-up portion 42b is directly attached to the ply body 42a at the portion on the radially outer side of the first apex <NUM>. The second apex <NUM> is disposed radially outward of the first apex <NUM> with the turned-up portion 42b therebetween.

The configuration of the bead <NUM> of the tire <NUM> increases the cross-sectional secondary moment. Since a cord thicker than a conventional one is used as each carcass cord, a larger cross-sectional secondary moment is obtained in the tire <NUM> than in the tire <NUM> shown in <FIG>. A larger cornering force is generated, so that a vehicle is less likely to fall down even when a high load is applied to the vehicle during cornering. The tire <NUM> improves falling-down resistance.

Since the end 42be of the turned-up portion 42b is surrounded by the second apex <NUM>, damage due to concentration of strain on the end 42be of the turned-up portion 42b is less likely to occur. In the tire <NUM>, a decrease in durability is suppressed.

In the tire <NUM>, the carcass <NUM> composed of one carcass ply <NUM> can sufficiently exhibit its function.

In <FIG>, a length indicated by reference character TS is the thickness of the second apex <NUM> at the reference position PF. The thickness TS is measured along a normal line that passes through the reference position PF and is normal to the outer surface of the carcass <NUM>.

In the tire <NUM>, the reference position PF is located between the maximum width position PW and the rim R in the radial direction. The reference position PF is located between the outer end 80e of the first apex <NUM> and an outer end 82se of the second apex <NUM> in the radial direction.

In the tire <NUM>, the thickness TS of the second apex <NUM> at the reference position PF is preferably not less than <NUM> and not greater than <NUM>.

When the thickness TS is set to be not less than <NUM>, the second apex <NUM> can effectively contribute to generation of a cornering force. The tire <NUM> has good falling-down resistance. From this viewpoint, the thickness TS is more preferably not less than <NUM> and further preferably not less than <NUM>.

When the thickness TS is set to be not greater than <NUM>, the influence of the second apex <NUM> on mass is suppressed. The tire <NUM> achieves mass reduction. From this viewpoint, the thickness TS is preferably not greater than <NUM>.

In the tire <NUM>, a complex elastic modulus E*<NUM> of the second apex <NUM> is preferably equal to or higher than a complex elastic modulus E* <NUM> of the first apex <NUM>. Accordingly, the cross-sectional secondary moment increases drastically. In the tire <NUM>, a large cornering force is generated, so that good falling-down resistance is achieved. From this viewpoint, the complex elastic modulus E*<NUM> of the second apex <NUM> is preferably higher than the complex elastic modulus E*<NUM> of the first apex <NUM>. Specifically, the ratio (E*<NUM>/E*<NUM>) of the complex elastic modulus E*<NUM> to the complex elastic modulus E*<NUM> is more preferably not less than <NUM>. From the viewpoint of being able to suppress occurrence of strain at the boundary between the second apex <NUM> and the first apex <NUM> and maintain good durability, the ratio (E*<NUM>/E*<NUM>) is preferably not greater than <NUM> and more preferably not greater than <NUM>.

In <FIG>, a length indicated by reference character FS is the distance in the radial direction from an inner end 82ue of the second apex <NUM> to the end 42be of the turned-up portion 42b. A length indicated by reference character BS is the distance in the radial direction from the bead base line BBL to the outer end 82se of the second apex <NUM>.

In the tire <NUM>, the distance FS in the radial direction from the inner end 82ue of the second apex <NUM> to the end 42be of the turned-up portion 42b is preferably not less than <NUM> and not greater than <NUM>.

When the distance FS in the radial direction is set to be not less than <NUM>, the end 42be of the turned-up portion 42b is located at an appropriate distance from the inner end 82ue of the second apex <NUM>. Accordingly, occurrence of damage due to concentration of strain on the end 42be of the turned-up portion 42b is suppressed. In the tire <NUM>, good durability is maintained. From this viewpoint, the distance FS in the radial direction is more preferably not less than <NUM>.

When the distance FS in the radial direction is set to be not greater than <NUM>, the length of the turned-up portion 42b is appropriately maintained. In the tire <NUM>, the influence of the turned-up portion 42b on mass is suppressed. The tire <NUM> achieves mass reduction. From this viewpoint, the distance FS in the radial direction is more preferably not greater than <NUM>.

In the tire <NUM>, the distance BS in the radial direction from the bead base line BBL to the outer end 82se of the second apex <NUM> is preferably not less than <NUM> and not greater than <NUM>.

When the distance BS in the radial direction is set to be not greater than <NUM>, the second apex <NUM> can contribute to an increase in the cross-sectional secondary moment. In the tire <NUM>, good falling-down resistance is maintained. From this viewpoint, the distance BS in the radial direction is more preferably not less than <NUM>.

When the distance BS in the radial direction is set to be not greater than <NUM>, the volume of the second apex <NUM> is appropriately maintained. In the tire <NUM>, heat generation in the second apex <NUM> is suppressed, so that low rolling resistance is maintained. From this viewpoint, the distance BS in the radial direction is more preferably not greater than <NUM>.

As described above, according to the present invention, a tire that can achieve mass reduction while suppressing a decrease in the strength of a carcass without impairing appearance quality is obtained.

Hereinafter, the present invention will be described in further detail by means of examples, etc., but the present invention is not limited to these examples.

A pneumatic tire for a passenger car (tire designation = <NUM>/50R18) having the basic structure shown in <FIG> and having specifications shown in Table <NUM> below was obtained.

In Example <NUM>, a cord formed from a polyethylene terephthalate fiber was used as each carcass cord. The cord structure of the carcass cord was <NUM> dtex/<NUM> (total fineness = <NUM> dtex). The fact that the total fineness is not less than <NUM> dtex is indicated as "Y" in the cell for thick cord. The number of carcass cords included per <NUM> width of the carcass ply was <NUM>.

The carcass was composed of one carcass ply.

An insulation including a pair of rubber layers was provided between the carcass and the inner liner.

The ratio (ta/td) of the thickness ta of the topping rubber located between the insulation and the carcass cords to the thickness td of the insulation was <NUM>.

The distance Lb in the axial direction from the outer end of the rubber layer to the end of the belt was <NUM>.

The ratio (Hc/HS) of the distance Hc in the radial direction form the end of the insulation (inner end of the rubber layer) to the outer end of the apex to the tire cross-sectional height HS was <NUM>.

The ratio (E*r/E*t) of the complex elastic modulus E*r of the insulation to the complex elastic modulus E*t of the outer layer was <NUM>.

A tire of Comparative Example <NUM> is a conventional tire. The carcass was composed of two carcass plies. Each carcass cord was a cord formed from a polyethylene terephthalate fiber (cord structure = <NUM> dtex/<NUM>). The fact that the total fineness is less than <NUM> dtex is indicated as "N" in the cell for thick cord. The number of carcass cords included per <NUM> width of the carcass ply was <NUM>.

In Comparative Example <NUM>, an insulation is not used.

A tire of Comparative Example <NUM> was obtained in the same manner as Comparative Example <NUM>, except that the same cord as in Example <NUM> was used as each carcass cord. In Comparative Example <NUM>, the number of carcass cords included per <NUM> width of the carcass ply was <NUM>.

A tire of Comparative Example <NUM> was obtained in the same manner as Comparative Example <NUM>, except that the carcass was composed of one carcass ply. The position of the end of the turned-up portion was set so as to be the same as in Example <NUM>.

Tires of Examples <NUM> and <NUM> and Comparative Examples <NUM> and <NUM> were obtained in the same manner as Example <NUM>, except that the ratio (ta/td) was set as shown in Tables <NUM> and <NUM> below.

A tire of Example <NUM> was obtained in the same manner as Example <NUM>, except that the distance Lb in the axial direction was set as shown in Table <NUM> below.

A tire of Example <NUM> was obtained in the same manner as Example <NUM>, except that the ratio (Hc/HS) was set as shown in Table <NUM> below.

A tire of Example <NUM> was obtained in the same manner as Example <NUM>, except that the ratio (E*r/E*t) was set as shown in Table <NUM> below.

The mass of each tire was measured. The results are shown as indexes in the cells for "Mass" in Tables <NUM> and <NUM> below with the result of Comparative Example <NUM> being regarded as <NUM>. The higher the value is, the lighter the tire is.

The surface condition of each tire inner surface was visually observed. <NUM> tires were produced, and the number of tires in which open thread occurred was checked to obtain the rate of occurrence of open thread. The results are shown as indexes in the cells for "Appearance quality" in Tables <NUM> and <NUM> below with the result of Comparative Example <NUM> being regarded as <NUM>. The higher the value is, the lower the rate of occurrence is.

A breaking energy of each test tire supported horizontally under conditions of a rim (<NUM>. 5J) and an internal pressure (<NUM> kPa) was measured at a carcass maximum width position, using a plunger testing machine, in accordance with Section <NUM> "Tire strength (breaking energy) test" in JIS D4230. The results are shown as indexes in the cells for "Pinch cut resistance" in Tables <NUM> and <NUM> below with the result of Comparative Example <NUM> being regarded as <NUM>. The higher the value is, the better the pinch cut resistance is.

Each test tire was fitted onto a rim (size = <NUM>. 5J) and inflated with air to adjust the internal pressure thereof to <NUM> kPa. The tire was mounted to a drum type tire testing machine. A vertical load of <NUM> kN was applied to the tire, and the tire was caused to run on a drum (radius = <NUM>) at a speed of <NUM>/h. The running distance was measured until damage to the tire was observed. The results are shown as indexes in the cells for "Durability" in Tables <NUM> and <NUM> below with the result of Comparative Example <NUM> being regarded as <NUM>. The higher the value is, the better the durability is.

Using a rolling resistance testing machine, a rolling resistance coefficient (RRC) was measured when each test tire ran on a drum at a speed of <NUM>/h under the following conditions. The results are shown as indexes in the cells for "RRC" in Tables <NUM> and <NUM> below with the result of Comparative Example <NUM> being regarded as <NUM>. The higher the value is, the lower the rolling resistance of the tire is.

The sum of the indexes obtained in the respective evaluations was calculated. The results are shown in the cells for "Combined" in Tables <NUM> and <NUM> below. The higher the value is, the better the performance is.

As shown in Tables <NUM> and <NUM>, it is confirmed that, in each Example, mass reduction is achieved while suppressing a decrease in the strength of the carcass without impairing appearance quality. From the evaluation results, advantages of the present invention are clear.

Claim 1:
A tire (<NUM>, 2a, 2b, 2c, <NUM>) comprising:
a tread (<NUM>) configured to come into contact with a road surface;
a pair of sidewalls (<NUM>) each connected to an end of the tread (<NUM>) and located radially inward of the tread (<NUM>);
a pair of beads (<NUM>, <NUM>) each located radially inward of the sidewall (<NUM>);
a carcass (<NUM>) located inward of the tread (<NUM>) and the pair of sidewalls (<NUM>) and extending on and between a first bead (<NUM>, <NUM>) and a second bead (<NUM>, <NUM>) out of the pair of beads (<NUM>, <NUM>);
a belt (<NUM>) located between the tread (<NUM>) and the carcass (<NUM>) in a radial direction;
an inner liner (<NUM>) located inward of the carcass (<NUM>); and
an insulation (<NUM>) located between the carcass (<NUM>) and the inner liner (<NUM>),
wherein
each of the beads (<NUM>, <NUM>) includes a core (<NUM>, <NUM>) and an apex (<NUM>, <NUM>) located radially outward of the core (<NUM>, <NUM>),
the carcass (<NUM>) includes one carcass ply (<NUM>),
the carcass ply (<NUM>) includes a ply body (42a) extending between the core (<NUM>, <NUM>) of the first bead (<NUM>, <NUM>) and the core (<NUM>, <NUM>) of the second bead (<NUM>, <NUM>), and a pair of turned-up portions (42b) connected to the ply body (42a) and turned up at the cores (<NUM>, <NUM>),
the carcass ply (<NUM>) includes a plurality of carcass cords (<NUM>) aligned with each other and a topping rubber (<NUM>) covering the carcass cords (<NUM>), and
the insulation (<NUM>) is located between the first bead (<NUM>, <NUM>) and the second bead (<NUM>, <NUM>), characterized in that
each of the carcass cords (<NUM>) has a total fineness of not less than <NUM> dtex and not greater than <NUM> dtex, and
a ratio (ta/td) of a thickness (ta) of the topping rubber (<NUM>) located between the insulation (<NUM>) and the carcass cords (<NUM>) to a thickness (td) of the insulation (<NUM>) is not less than <NUM> and not greater than <NUM>.