Patent Description:
The present invention relates to heavy duty pneumatic tires.

<FIG> (not part of the invention) shows a bead <NUM> portion (hereinafter, also referred to as a bead portion B) of a conventional heavy duty pneumatic tire <NUM>. The bead portion B is fitted to a rim R (normal rim).

In the tire <NUM>, a carcass ply <NUM> is turned around the bead <NUM> up from the inner side toward the outer side in the axial direction. The carcass ply <NUM> includes a ply main body <NUM> and a turned-up portion <NUM>.

In the tire <NUM>, the bead <NUM> includes a core <NUM> and an apex <NUM>. In the tire <NUM>, the apex <NUM> includes a first apex <NUM> and a second apex <NUM> that is more flexible than the first apex <NUM>. As shown in <FIG> (not part of the invention), an outer end 16a of the first apex <NUM> is located outward of an end 10a of the turned-up portion <NUM> in the radial direction.

To ensure that the bead portion B has desired stiffness, the tire <NUM> includes a filler <NUM>. The filler <NUM> includes a large number of steel cords aligned with each other, and a topping rubber, which are not shown.

The filler <NUM> is located between the turned-up portion <NUM> and a chafer <NUM>. As shown in <FIG> (not part of the invention), an inner end 20a of the filler <NUM> is located inward of the core <NUM> of the bead <NUM> in the radial direction. An outer end 20b of the filler <NUM> is located inward of the end 10a of the turned-up portion <NUM>. Unlike a conventional filler (hereinafter, also referred to as a normal filler), the filler <NUM> does not have a structure in which the filler <NUM> is turned up around the bead <NUM>. The filler <NUM> is also referred to as a short filler.

The tire <NUM> is mounted to a vehicle such as a truck and a bus. A large load is applied to the bead portion B of the tire <NUM>. Thus, it is important to improve the durability of the bead portion B, that is, bead durability. For heavy duty pneumatic tires, improving the bead durability by adjusting the configuration of the bead portion B and controlling the stiffness of the bead portion B is considered (for example, <CIT>). <CIT> discloses a tire according to the preamble of claim <NUM>. Further tires are disclosed in <CIT>, <CIT>, <CIT>, and <CIT>.

In the tire <NUM> in which the above-described short filler is used as the filler <NUM>, force applied to the ply main body <NUM> that is protected in a tire in which a normal filler is used and that extends radially outward along the bead <NUM> from the position of the inner end 20a of the filler <NUM>, increases. In the tire <NUM>, the holding force for the bead <NUM> by the filler <NUM> decreases, and thus movement of the bead portion B is large. Therefore, movement of the end 10a of the turned-up portion <NUM> is also large, so that there is a concern that damage called ply turn-up loose (PTL) may occur. The movement of the bead portion B causes heat generation, that is, energy loss, and thus an increase in rolling resistance may also be caused. An increase in the rolling resistance of the tire <NUM> affects the fuel economy of a vehicle.

If the stiffness of the bead portion B is improved, for example, by increasing the number of turns of a wire <NUM> in a core <NUM> that is formed by winding the wire <NUM>, or increasing the volume of the apex <NUM> located radially outward of the core <NUM>, the bead durability can be improved. However, the weight of the tire <NUM> increases, and there is also a concern that heat generation, that is, energy loss, caused by movement of the bead portion B, may be increased.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heavy duty pneumatic tire in which improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

A heavy duty pneumatic tire according to the present invention is specified in claim <NUM>.

Preferably, in the heavy duty pneumatic tire, when a position, on each side surface of the tire, corresponding to an outer end of a contact surface between the side surface and a flange of a rim to which the tire is fitted, is defined as a flange contact end, in the radial direction, an outer end of the first apex is located inward of the end of the turned-up portion and located outward of the flange contact end.

Preferably, in the heavy duty pneumatic tire, a distance in the radial direction from a radially inner end of the core to an outer end of the first apex is not less than <NUM> and not greater than <NUM>.

Preferably, in the heavy duty pneumatic tire, a distance from an axially inner end of the core to the carcass ply is not less than <NUM>.

Preferably, in the heavy duty pneumatic tire, a recess is provided on a zone of each side surface of the tire between a maximum width position and the end of the turned-up portion.

Preferably, in the heavy duty pneumatic tire, a ratio of a minimum thickness from the ply main body to the recess relative to a virtual thickness, from the ply main body to a virtual side surface obtained on the assumption that the recess is not present, measured along a line segment indicating the minimum thickness is not less than <NUM> and not greater than <NUM>.

Preferably, in the heavy duty pneumatic tire, a distance in the radial direction from the end of the turned-up portion to an inner end of the recess is not less than <NUM> and not greater than <NUM>.

Preferably, in the heavy duty pneumatic tire, the recess includes a bottom portion, an outer boundary portion located outward of the bottom portion in the radial direction, and an inner boundary portion located inward of the bottom portion in the radial direction. A profile of the outer boundary portion is represented by a circular arc that projects outward and that has a radius not less than <NUM>. A profile of the inner boundary portion is represented by a circular arc that projects outward and that has a radius not less than <NUM>.

Preferably, in the heavy duty pneumatic tire, a profile of the bottom portion is represented by a circular arc that projects inward.

Preferably, in the heavy duty pneumatic tire, a profile of the bottom portion is represented by a straight line.

A heavy duty pneumatic tire according to another aspect of the present invention includes: a pair of beads; a carcass ply having a ply main body that extends on and between one bead and the other bead, and turned-up portions that are connected to the ply main body and turned around the beads from an inner side toward an outer side in an axial direction; and a pair of fillers that are located outward of the turned-up portions in the axial direction and that include metal cords. Each bead includes a core, a first apex that surrounds the core, and a second apex that is located outward of the first apex in a radial direction. An outer periphery of the first apex has a rounded contour, and the first apex is harder than the second apex. A recess is provided on a zone of each side surface of the tire between a maximum width position and an end of the turned-up portion.

In the heavy duty pneumatic tire of the present invention, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

In the present invention, a state where a tire is mounted on a normal rim, the internal pressure of the tire is adjusted to a normal internal pressure, and no load is applied to the tire is referred to as a normal state. In the present invention, unless otherwise specified, the dimensions and angles of each component of the tire are measured in the normal state.

The normal 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 normal rims.

The normal 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 normal internal pressures.

<FIG> shows a part of a heavy duty pneumatic tire <NUM> (hereinafter, simply referred to as "tire <NUM>") according to an embodiment of the present invention. The tire <NUM> is mounted to a heavy duty vehicle such as a truck and a bus.

<FIG> shows a part of a cross-section of the tire <NUM> 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 sheet of <FIG> is the circumferential direction of the tire <NUM>. In <FIG>, an alternate long and short dash line CL represents the equator plane 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 a rim (normal rim).

In <FIG>, reference character PW represents an axially outer end of the tire <NUM>. The outer end PW is specified on the basis of a virtual side surface obtained on the assumption that decorations such as patterns and letters are not present on a side surface <NUM> of the tire <NUM>. The distance in the axial direction from one outer end PW to the other outer end PW is the maximum width of the tire <NUM>, that is, the cross-sectional width (see JATMA or the like) of the tire <NUM>. The outer end PW is a position at which the tire <NUM> has the maximum width (hereinafter, also referred to as a maximum width position of the tire <NUM>).

The tire <NUM> includes a tread <NUM>, a pair of sidewalls <NUM>, a pair of beads <NUM>, a pair of chafers <NUM>, a carcass <NUM>, a belt <NUM>, a pair of cushion layers <NUM>, an inner liner <NUM>, and a pair of fillers <NUM>.

An outer surface <NUM> of the tread <NUM> comes into contact with a road surface. The outer surface <NUM> of the tread <NUM> is a tread surface. The above-described side surface <NUM> is connected to an end of the tread surface <NUM> and extends radially inward.

The tread <NUM> includes a base portion <NUM> and a cap portion <NUM>. In the tire <NUM>, a pair of base portions <NUM> are provided. These base portions <NUM> are disposed at an interval in the axial direction. Each base portion <NUM> covers an end portion of the belt <NUM>. The base portion <NUM> is formed from a crosslinked rubber. The cap portion <NUM> is located radially outward of each base portion <NUM>. The cap portion <NUM> covers the pair of base portions <NUM> and the entirety of the belt <NUM>. The outer surface of the cap portion <NUM> forms the above-described tread surface <NUM>. The cap portion <NUM> is formed from a crosslinked rubber.

In the tire <NUM>, at least three circumferential grooves <NUM> are formed on the tread <NUM>. Accordingly, in the tread <NUM>, at least four circumferential land portions <NUM> are formed.

Each sidewall <NUM> is connected to an end of the tread <NUM>. The sidewall <NUM> extends radially inward from the end of the tread <NUM>. The sidewall <NUM> is formed from a crosslinked rubber. The outer surface of the sidewall <NUM> forms the side surface <NUM> of the tire <NUM>.

Each 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 wound wire <NUM> made of steel. The core <NUM> has a substantially hexagonal cross-sectional shape. In the tire <NUM>, the core <NUM> is located outward of the bead base line BBL in the radial direction. In the cross-section of the core <NUM>, a corner portion indicated by reference character PA is the radially inner end of the core <NUM>, and a corner portion indicated by reference character PB is the axially inner end of the core <NUM>. Each corner portion of the core <NUM> is specified on the basis of the contour of a cross-section bundle of the wire <NUM> included in the cross-section of the core <NUM>.

The apex <NUM> is located radially outward of the core <NUM>. The apex <NUM> extends radially outward from the core <NUM>. In the tire <NUM>, the apex <NUM> includes a first apex <NUM> and a second apex <NUM>. Each of the first apex <NUM> and the second apex <NUM> is formed from a crosslinked rubber. The first apex <NUM> is harder than the second apex <NUM>. The apex <NUM> is composed of the hard first apex <NUM> and the flexible second apex <NUM>.

In the tire <NUM>, the hardness of the first apex <NUM> is set to be not less than <NUM> and not greater than <NUM>. The hardness of the second apex <NUM> is set to be not less than <NUM> and not greater than <NUM>. In the present invention, the "hardness" is measured according to JIS K6253 under a temperature condition of <NUM> using a type A durometer.

The first apex <NUM> surrounds the core <NUM>. In other words, the first apex <NUM> is located around the core <NUM>. The second apex <NUM> is located radially outward of the first apex <NUM>. The second apex <NUM> extends radially outward from the first apex <NUM>. The second apex <NUM> is tapered outward in the radial direction.

As shown in <FIG>, in the tire <NUM>, the outer periphery of the first apex <NUM> has a rounded contour. The first apex <NUM> has a round shape. Thus, a surface of the second apex <NUM> that is in contact with the first apex <NUM>, that is, a bottom surface <NUM> of the second apex <NUM>, has a shape projecting radially outward in the cross-section shown in <FIG>.

Each chafer <NUM> is located axially outward of the bead <NUM>. The chafer <NUM> is located radially inward of the sidewall <NUM>. The chafer <NUM> comes into contact with a rim. The chafer <NUM> is formed from a crosslinked rubber. In the tire <NUM>, an outer end <NUM> of the chafer <NUM> is located inward of an outer end <NUM> of the second apex <NUM>, that is, an outer end <NUM> of the apex <NUM>, in the radial direction.

In <FIG>, reference character PT represents a toe of the tire <NUM>. The outer surface of the chafer <NUM> from the toe PT to an inner end <NUM> of the sidewall <NUM> forms a part of the side surface <NUM>.

The carcass <NUM> is located inward of the tread <NUM>, each sidewall <NUM>, and each chafer <NUM>. The carcass <NUM> includes at least one carcass ply <NUM>. The carcass <NUM> of the tire <NUM> is composed of one carcass ply <NUM>.

The carcass ply <NUM> includes a large number of carcass cords aligned with each other, which are not shown. The carcass cords are covered with a topping rubber. Each carcass cord intersects the equator plane CL. In the tire <NUM>, the angle of each carcass cord relative to the equator plane CL is not less than <NUM>° and not greater than <NUM>°. The carcass <NUM> of the tire <NUM> has a radial structure. In the tire <NUM>, the material of the carcass cords is steel. A cord formed from an organic fiber may be used as each carcass cord.

In the tire <NUM>, the carcass ply <NUM> is turned up around each bead <NUM> (specifically, each core <NUM>) from the inner side toward the outer side in the axial direction. The carcass ply <NUM> has: a ply main body <NUM> that extends on and between one bead <NUM> and the other bead <NUM>; and a pair of turned-up portions <NUM> that are connected to the ply main body <NUM> and turned up around the respective beads <NUM> from the inner side toward the outer side in the axial direction. In the tire <NUM>, an end <NUM> of each turned-up portion <NUM> is located between the outer end <NUM> of the chafer <NUM> and the inner end <NUM> of the sidewall <NUM> in the radial direction.

The belt <NUM> is located radially inward of the tread <NUM>. The belt <NUM> is located radially outward of the carcass <NUM>.

In the tire <NUM>, the belt <NUM> includes four layers <NUM> layered in the radial direction. In the tire <NUM>, the number of layers <NUM> forming the belt <NUM> is not particularly limited. The configuration of the belt <NUM> is determined as appropriate in consideration of the specifications of the tire <NUM>.

Each 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. In the tire <NUM>, the material of the belt cords is steel.

In each layer <NUM>, each belt cord is tilted relative to the equator plane CL. The belt cords in one layer <NUM> intersect the belt cords in another layer <NUM> layered on the one layer <NUM>.

In the tire <NUM>, among the four layers <NUM>, a second layer 90B located between a first layer 90A and a third layer 90C has the maximum width in the axial direction. A fourth layer 90D located at the outermost side in the radial direction has the minimum width in the axial direction.

Each cushion layer <NUM> is located between the belt <NUM> and the carcass <NUM> at an end portion of the belt <NUM>. The cushion layer <NUM> is formed from a crosslinked rubber.

The inner liner <NUM> is located inward of the carcass <NUM>. The inner liner <NUM> forms the inner surface of the tire <NUM>. The inner liner <NUM> is formed from a crosslinked rubber that has an excellent air blocking property. The inner liner <NUM> maintains the internal pressure of the tire <NUM>.

Each filler <NUM> is located at a bead <NUM> portion. The filler <NUM> is located outward of the bead <NUM> in the axial direction. As shown in <FIG>, the filler <NUM> is located between the turned-up portion <NUM> and the chafer <NUM>.

The filler <NUM> includes a large number of metal cords aligned with each other, which are not shown. In the tire <NUM>, the material of the metal cords is steel. In the tire <NUM>, the metal cords included in the filler <NUM> are steel cords. In the filler <NUM>, the metal cords are covered with a topping rubber.

In the tire <NUM>, in the radial direction, a first end <NUM> (also referred to as an inner end) of the filler <NUM> is located inward of the bead base line BBL. The first end <NUM> of the filler <NUM> is located between the bead base line BBL and the toe PT in the radial direction. In the tire <NUM>, in the axial direction, the first end <NUM> of the filler <NUM> is disposed at a position that coincides with the position of the inner end PA of the core <NUM>, that is, the position of the corner portion PA. A second end <NUM> (also referred to as an outer end) of the filler <NUM> is located inward of the end <NUM> of the turned-up portion <NUM> in the radial direction. The second end <NUM> of the filler <NUM> is located between the end <NUM> of the turned-up portion <NUM> and the bead base line BBL in the radial direction. The filler <NUM> is a short filler.

In the tire <NUM>, a so-called short filler is used as each filler <NUM>. The filler <NUM> contributes to weight reduction. In the tire <NUM>, the core <NUM> is surrounded by the hard first apex <NUM> the outer periphery of which has a rounded contour. In the tire <NUM>, falling of the bead <NUM> portion (hereinafter, also referred to as a bead portion B) due to application of a load is inhibited, and thus good bead durability is obtained. In addition to falling of the bead portion B being inhibited, the first apex <NUM> is formed with a small volume, and thus the rolling resistance of the tire <NUM> can be reduced. In the tire <NUM>, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

<FIG> shows a part of the cross-section of the tire <NUM> shown in <FIG>. In <FIG>, the bead portion B of the tire <NUM> is shown. 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 sheet of <FIG> is the circumferential direction of the tire <NUM>.

In the tire <NUM>, in the radial direction, an outer end <NUM> of the first apex <NUM> is located inward of the end <NUM> of the turned-up portion <NUM>. In the tire <NUM>, concentration of strain on the end <NUM> of the turned-up portion <NUM> is inhibited. In the tire <NUM>, good bead durability is obtained. Since the first apex <NUM> is formed with a small volume, the rolling resistance of the tire <NUM> can be further reduced. From this viewpoint, in the tire <NUM>, in the radial direction, the outer end <NUM> of the first apex <NUM> is preferably located inward of the end <NUM> of the turned-up portion <NUM>.

In <FIG>, reference character PF represents a position, on the side surface <NUM>, corresponding to the radially outer end of a contact surface between the tire <NUM> and a flange LF of the rim, that is, a flange contact end. In the tire <NUM>, the outer end <NUM> of the first apex <NUM> is located outward of the flange contact end PF in the radial direction. In the tire <NUM>, the stiffness of the first apex <NUM> is appropriately maintained, and protrusion of the side surface <NUM> at a portion outward of the flange contact end PF is effectively inhibited. In the tire <NUM>, good bead durability is effectively maintained. From this viewpoint, in the tire <NUM>, in the radial direction, the outer end <NUM> of the first apex <NUM> is preferably located outward of the flange contact end PF.

In <FIG>, a double-headed arrow HA represents the distance in the radial direction from the radially inner end PA of the core <NUM> to the outer end <NUM> of the first apex <NUM>. A double-headed arrow DB represents the distance from the axially inner end PB of the core <NUM> to the carcass ply <NUM>. The distance DB is represented as a shortest distance.

In the tire <NUM>, the distance HA in the radial direction from the radially inner end PA of the core <NUM> to the outer end <NUM> of the first apex <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>. When the distance HA is set to be not less than <NUM>, falling of the bead portion B due to application of a load is inhibited. Thus, in the tire <NUM>, good bead durability is obtained. From this viewpoint, the distance HA is more preferably not less than <NUM> and further preferably not less than <NUM>. When the distance HA is set to be not greater than <NUM>, concentration of strain on the end <NUM> of the turned-up portion <NUM> is inhibited in the tire <NUM>. In the tire <NUM>, good bead durability is obtained. Since the first apex <NUM> is formed with a small volume, the rolling resistance of the tire <NUM> can be further reduced. From this viewpoint, the distance HA is more preferably not greater than <NUM> and further preferably not greater than <NUM>.

In the tire <NUM>, the distance DB from the axially inner end PB of the core <NUM> to the carcass ply <NUM> is preferably not less than <NUM>. When the distance DB is set to be not less than <NUM>, rubbing between the carcass ply <NUM> and the core <NUM> in a state where a load during running is applied is prevented. In the tire <NUM>, the carcass cords near the axially inner end PB of the core <NUM> are effectively prevented from being cut. From this viewpoint, the distance DB is preferably not less than <NUM>. From the viewpoint that the first apex <NUM> is formed with an appropriate volume and influence of the first apex <NUM> on rolling resistance is inhibited, the distance DB is preferably not greater than <NUM>.

<FIG> shows a part of a heavy duty pneumatic tire <NUM> (hereinafter, simply referred to as "tire <NUM>") according to another embodiment of the present invention.

In <FIG>, a bead portion B of the tire <NUM> is shown. 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 sheet of <FIG> is the circumferential direction of the tire <NUM>.

In <FIG>, a modification of the bead portion B of the tire <NUM> shown in <FIG> is shown. The tire <NUM> has the same structure as the tire <NUM> shown in <FIG>, except that a recess is provided on the bead portion B. In <FIG>, members that are the same as the members of the tire <NUM> shown in <FIG> are designated by the same reference characters, and the description thereof is omitted.

In the tire <NUM>, a recess <NUM> is provided on the side surface <NUM>. In the tire <NUM>, the recess <NUM> is provided on the sidewall <NUM> which forms a part of the side surface <NUM>. As shown in <FIG>, the recess <NUM> has a shape that projects inward. The recess <NUM> extends in the circumferential direction without interruption.

In <FIG>, reference character PS represents an outer end of the recess <NUM>. Reference character PU represents an inner end of the recess <NUM>. In the tire <NUM>, in the radial direction, the outer end PS of the recess <NUM> is located inward of the maximum width position PW. The inner end PU of the recess <NUM> is located outward of the end <NUM> of the turned-up portion <NUM> in the radial direction. In the tire <NUM>, the recess <NUM> is provided on a zone of the side surface <NUM> between the maximum width position PW and the end <NUM> of the turned-up portion <NUM>.

In the tire <NUM>, similar to the tire <NUM> shown in <FIG>, a so-called short filler is used as each filler <NUM>. The filler <NUM> contributes to weight reduction. In the tire <NUM>, the core <NUM> is surrounded by the hard first apex <NUM> the outer periphery of which has a rounded contour. Falling-down of the bead portion B due to application of a load is inhibited, and thus good bead durability is obtained in the tire <NUM>. Furthermore, since falling of the bead portion B is inhibited and the first apex <NUM> is also formed with a small volume, the rolling resistance of the tire <NUM> can be reduced. In the tire <NUM>, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

When a load is applied to the tire <NUM> that is mounted on a rim, the rubber moves toward the vicinity in which the end <NUM> of the turned-up portion <NUM> and the second end <NUM> of the filler <NUM> are located, in the tire <NUM>. In accordance with this movement, the ply main body <NUM> moves axially outward. As described above, in the tire <NUM>, the recess <NUM> is located on the zone between the maximum width position PW and the end <NUM> of the turned-up portion <NUM>. The recess <NUM> inhibits movement of the rubber in the vicinity in which the end <NUM> of the turned-up portion <NUM> and the second end <NUM> of the filler <NUM> are located, and also inhibits movement of the ply main body <NUM>. The recess <NUM> inhibits movement of the rubber at a portion radially outward of the end <NUM> of the turned-up portion <NUM> when a load is applied to the tire <NUM>.

In the tire <NUM>, the recess <NUM>, which is provided on the zone of the side surface <NUM> between the maximum width position PW and the end <NUM> of the turned-up portion <NUM>, contributes to weight reduction. As described above, the recess <NUM> inhibits movement of the rubber at the portion radially outward of the end <NUM> of the turned-up portion <NUM>. Since movement of the turned-up portion <NUM> is inhibited, damage such as ply turn-up loose is less likely to occur in the tire <NUM>. This movement inhibition also inhibits heat generation caused by deformation.

In the tire <NUM>, the height in the radial direction of the first apex <NUM> is low. In the tire <NUM>, a region that can contribute to bending can be sufficiently ensured in a sidewall <NUM> portion, that is, in a side portion S, and the contour of the ply main body <NUM> extending along the apex <NUM> is easily set. In the tire <NUM>, protrusion of the side surface <NUM> outward in the axial direction is inhibited, and thus an amount of strain applied to the recess <NUM> is reduced. In the tire <NUM>, damage such as a crack at the recess <NUM> is less likely to occur. In the tire <NUM>, the above-described effect achieved by the recess <NUM> is sufficiently exhibited. In the tire <NUM>, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

In <FIG>, a dotted line VL represents a virtual side surface obtained on the assumption that the recess <NUM> is not present on the side surface <NUM>. The virtual side surface VL is a part of the above-described virtual side surface used for specifying the maximum width position PW. A solid line NL represents a line normal to the ply main body <NUM>. A double-headed arrow TA represents a thickness, from the ply main body <NUM> to the recess <NUM>, measured along the normal line NL. In the tire <NUM>, the thickness TA is the minimum thickness from the ply main body <NUM> to the recess <NUM>. A double-headed arrow TB represents a virtual thickness, from the ply main body <NUM> to the virtual side surface VL, measured along a line segment indicating the minimum thickness TA, that is, along the normal line NL.

In the tire <NUM>, the ratio of the minimum thickness TA to the virtual thickness TB is preferably not less than <NUM> and preferably not greater than <NUM>. When this ratio is set to be not less than <NUM>, an increase in strain near the bottom of the recess <NUM> is inhibited, and the minimum thickness TA becomes a necessary thickness. In the tire <NUM>, occurrence of damage such as a crack at the recess <NUM> is inhibited. From this viewpoint, this ratio is more preferably not less than <NUM>. When this ratio is set to be not greater than <NUM>, movement of the rubber forming the sidewall <NUM> toward the rim flange LF side when a load is applied is inhibited. In the tire <NUM>, the recess <NUM> effectively inhibits movement of the rubber at the portion radially outward of the end <NUM> of the turned-up portion <NUM>. In the tire <NUM>, the bead durability is effectively improved, and the rolling resistance is effectively reduced. From this viewpoint, this ratio is more preferably not greater than <NUM>.

In <FIG>, a double-headed arrow DU represents the distance in the radial direction from the end <NUM> of the turned-up portion <NUM> to the inner end PU of the recess <NUM>. A double-headed arrow DS represents the distance in the radial direction from the maximum width position PW to the outer end PS of the recess <NUM>.

In the tire <NUM>, the distance DU in the radial direction from the end <NUM> of the turned-up portion <NUM> to the inner end PU of the recess <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>. When the distance DU is set to be not less than <NUM>, the recess <NUM> is located at an appropriate interval from the end <NUM> of the turned-up portion <NUM>, and thus interference between the recess <NUM> and the turned-up portion <NUM> is prevented. Since concentration of strain on the end <NUM> of the turned-up portion <NUM> is inhibited and the effect achieved by the recess <NUM> is sufficiently exhibited, the bead durability is effectively improved, and the rolling resistance is effectively reduced, in the tire <NUM>. When the distance DU is set to be not greater than <NUM>, the recess <NUM> having a sufficient size is ensured on the zone between the maximum width position PW and the end <NUM> of the turned-up portion <NUM>. In this case as well, the effect achieved by the recess <NUM> is sufficiently exhibited, and thus the bead durability is effectively improved, and the rolling resistance is effectively reduced, in the tire <NUM>.

In the tire <NUM>, the distance DS in the radial direction from the maximum width position PW to the outer end PS of the recess <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>. When the distance DS is set to be not less than <NUM>, the recess <NUM> is located at an appropriate interval from the maximum width position PW. In the tire <NUM>, the sidewall <NUM> at the maximum width position PW has an appropriate thickness, and thus good cut resistance is maintained. When the distance DS is set to be not greater than <NUM>, the recess <NUM> having a sufficient size is ensured on the zone between the maximum width position PW and the end <NUM> of the turned-up portion <NUM>. The effect achieved by the recess <NUM> is sufficiently exhibited, and thus the bead durability is effectively improved, and the rolling resistance is effectively reduced, in the tire <NUM>.

In the tire <NUM>, a portion, of the side surface <NUM>, radially inward of the maximum width position PW includes the above-described recess <NUM>, an outer portion <NUM> extending radially outward from the outer end PS of the recess <NUM>, and an inner portion <NUM> extending radially inward from the inner end PU of the recess <NUM>.

The above-described virtual side surface VL is located between the outer portion <NUM> and the inner portion <NUM>. The outer end PS of the recess <NUM> is the boundary between the outer portion <NUM> and the virtual side surface VL. The inner end PU of the recess <NUM> is the boundary between the inner portion <NUM> and the virtual side surface VL. In the tire <NUM>, the profile of the virtual side surface VL and the profile of the outer portion <NUM> are tangent to each other at the boundary PS. The profile of the virtual side surface VL and the profile of the inner portion <NUM> are tangent to each other at the boundary PU.

In the tire <NUM>, the recess <NUM> includes a bottom portion <NUM>, an outer boundary portion <NUM>, and an inner boundary portion <NUM>.

The outer boundary portion <NUM> extends between the bottom portion <NUM> and the above-described outer portion <NUM>. The profile of the outer boundary portion <NUM> is tangent to the profile of the outer portion <NUM> at the outer end PS. The outer end PS is also the boundary between the outer boundary portion <NUM> and the outer portion <NUM>.

The inner boundary portion <NUM> extends between the bottom portion <NUM> and the above-described inner portion <NUM>. The profile of the inner boundary portion <NUM> is tangent to the profile of the inner portion <NUM> at the inner end PU. The inner end PU is also the boundary between the inner boundary portion <NUM> and the inner portion <NUM>.

In <FIG>, reference character PSb represents an outer end of the bottom portion <NUM>. Reference character PUb represents an inner end of the bottom portion <NUM>. In the tire <NUM>, the outer boundary portion <NUM> is located radially outward of the bottom portion <NUM>. The profile of the bottom portion <NUM> is tangent to the profile of the outer boundary portion <NUM> at the outer end PSb. The outer end PSb is the boundary between the bottom portion <NUM> and the outer boundary portion <NUM>. The inner boundary portion <NUM> is located radially inward of the bottom portion <NUM>. The profile of the bottom portion <NUM> is tangent to the profile of the inner boundary portion <NUM> at the inner end PUb. The inner end PUb is the boundary between the bottom portion <NUM> and the inner boundary portion <NUM>.

In the cross-section of the tire <NUM> shown in <FIG>, the profile of the outer boundary portion <NUM> is represented by a circular arc that projects outward. In <FIG>, an arrow Rs represents the radius of the circular arc that represents the profile of the outer boundary portion <NUM>.

In the tire <NUM>, the radius Rs of the circular arc that represents the profile of the outer boundary portion <NUM> is preferably not less than <NUM>. Accordingly, concentration of strain on the outer boundary portion <NUM> is inhibited. In the tire <NUM>, the effect achieved by the recess <NUM> is sufficiently exhibited, and thus the bead durability is effectively improved, and the rolling resistance is effectively reduced. The upper limit of the radius Rs is determined as appropriate in consideration of the configuration of the profile of the side surface <NUM>.

In the cross-section of the tire <NUM> shown in <FIG>, the profile of the inner boundary portion <NUM> is represented by a circular arc that projects outward. In <FIG>, an arrow Ru represents the radius of the circular arc that represents the profile of the inner boundary portion <NUM>.

In the tire <NUM>, the radius Ru of the circular arc that represents the profile of the inner boundary portion <NUM> is preferably not less than <NUM>. Accordingly, concentration of strain on the inner boundary portion <NUM> is inhibited. In the tire <NUM>, the effect achieved by the recess <NUM> is sufficiently exhibited, and thus the bead durability is effectively improved, and the rolling resistance is effectively reduced. The upper limit of the radius Ru is determined as appropriate in consideration of the configuration of the profile of the side surface <NUM>.

In the tire <NUM>, from the viewpoint that the recess <NUM> effectively contributes to improvement of bead durability and reduction of rolling resistance, more preferably, the radius Rs of the circular arc that represents the profile of the outer boundary portion <NUM> is not less than <NUM>, and the radius Ru of the circular arc that represents the profile of the inner boundary portion <NUM> is not less than <NUM>.

In the tire <NUM>, the profile of the bottom portion <NUM> is represented by a circular arc that projects inward. Accordingly, force applied to the bottom portion <NUM> is effectively distributed over the entirety of the bottom portion <NUM>. In the tire <NUM>, concentration of strain on a specific location of the bottom portion <NUM> to cause damage such as a crack is prevented. In the tire <NUM>, the effect achieved by the recess <NUM> is sufficiently exhibited, and thus the bead durability is effectively improved, and the rolling resistance is effectively reduced.

In <FIG>, an arrow Rb represents the radius of a circular arc that represents the profile of the bottom portion <NUM>. In the tire <NUM>, the radius Rb is determined as appropriate in consideration of the above-described distance DU in the radial direction from the end <NUM> of the turned-up portion <NUM> to the inner end PU of the recess <NUM>, the above-described distance DS in the radial direction from the maximum width position PW to the outer end PS of the recess <NUM>, the radius Rs of the circular arc that represents the profile of the outer boundary portion <NUM>, and the radius Ru of the circular arc that represents the profile of the inner boundary portion <NUM>. From the viewpoint of prevention of damage due to concentration of stress on the bottom portion <NUM>, the radius Rb is preferably not less than <NUM>.

Although not shown, in the tire <NUM>, the profile of the bottom portion <NUM> of the recess <NUM> may be represented by a straight line, not by a circular arc. In this case, the profile of the bottom portion <NUM> does not have to be tangent to the profile of the outer boundary portion <NUM> at the outer end PSb. The profile of the bottom portion <NUM> does not have to be tangent to the profile of the inner boundary portion <NUM> at the inner end PUb. Even in the case where the profile of the bottom portion <NUM> is represented by a straight line, force applied to the bottom portion <NUM> is effectively distributed over the entirety of the bottom portion <NUM>, and occurrence of damage at the bottom portion <NUM> is prevented. In the tire <NUM>, from the viewpoint that the effect achieved by the recess <NUM> is more sufficiently exhibited, the profile of the bottom portion <NUM> of the recess <NUM> is preferably represented by a circular arc.

In <FIG>, reference character PN represents the point of intersection of the normal line NL and the recess <NUM>. The point of intersection PN is a position, on the recess <NUM>, at which the thickness from the ply main body <NUM> to the recess <NUM> is the minimum thickness, that is, a minimum thickness position. Reference character PC represents the center position of the recess <NUM>. The center position PC is specified at a position at which the length of the recess <NUM> measured on the cross-section shown in <FIG> is halved.

In the tire <NUM>, the minimum thickness position PN of the recess <NUM> is located outward of the center position PC of the recess <NUM> in the radial direction. In the tire <NUM>, force applied to the recess <NUM> is effectively distributed over the entirety of the recess <NUM>. In the tire <NUM>, concentration of strain on a specific location of the recess <NUM> to cause damage such as a crack is prevented. In the tire <NUM>, the effect achieved by the recess <NUM> is sufficiently exhibited, and thus the bead durability is effectively improved, and the rolling resistance is effectively reduced. From this viewpoint, the minimum thickness position PN of the recess <NUM> is preferably located outward of the center position PC of the recess <NUM> in the radial direction.

In the tire <NUM>, the center position PC of the recess <NUM> is located between the outer end <NUM> of the apex <NUM> and the outer end <NUM> of the chafer <NUM> in the radial direction. In the tire <NUM>, the recess <NUM> effectively inhibits movement of the rubber at the portion radially outward of the end <NUM> of the turned-up portion <NUM>. In the tire <NUM>, the bead durability is effectively improved, and the rolling resistance is effectively reduced. From this viewpoint, the center position PC of the recess <NUM> is preferably located between the outer end <NUM> of the apex <NUM> and the outer end <NUM> of the chafer <NUM> in the radial direction.

In <FIG>, a double-headed arrow HW represents the distance in the radial direction from the bead base line BBL to the maximum width position PW. A double-headed arrow HB represents the distance in the radial direction from the inner end PU of the recess <NUM> to the outer end PS of the recess <NUM>.

In the tire <NUM>, the ratio of the distance HB in the radial direction to the distance HW in the radial direction is preferably not less than <NUM> and preferably not greater than <NUM>. When this ratio is set to be not less than <NUM>, the size of the recess <NUM> is sufficiently ensured. The recess <NUM> effectively inhibits movement of the rubber at the portion radially outward of the end <NUM> of the turned-up portion <NUM>. In the tire <NUM>, the bead durability is effectively improved, and the rolling resistance is effectively reduced. From this viewpoint, this ratio is more preferably not less than <NUM>. When this ratio is set to be not greater than <NUM>, the size of the recess <NUM> is appropriately maintained. In the tire <NUM>, influence of the recess <NUM> on stiffness is effectively inhibited. From this viewpoint, this ratio is more preferably not greater than <NUM>.

Meanwhile, in the case where a nominal aspect ratio of the tire <NUM> or the tire <NUM> is not greater than <NUM>% and a nominal cross-sectional width of the tire <NUM> or the tire <NUM> is not less than <NUM>, in the tire <NUM> or the tire <NUM>, a carcass height represented as a height in the radial direction from the bead base line BBL to the point of intersection of the equator plane CL and the inner surface of the carcass <NUM> is low with respect to the width in the axial direction of the tread <NUM>, and thus a region in which application of a load can be absorbed by bending (that is, the above-described region that can contribute to bending) is narrow as compared to a normal tire. Therefore, it is difficult to ensure sufficient bead durability in the tire <NUM> or the tire <NUM>.

As described above, the height in the radial direction of the first apex <NUM> in each of the tire <NUM> and the tire <NUM> is low. In the tire <NUM>, the recess <NUM> is further provided on the zone of the side surface <NUM> between the maximum width position PW and the end <NUM> of the turned-up portion <NUM>. In the tire <NUM>, the first apex <NUM> contributes to bending, and, in the tire <NUM>, the first apex <NUM> and the recess <NUM> contribute to bending. In the tire <NUM>, the recess <NUM> inhibits movement of the rubber at the portion radially outward of the end <NUM> of the turned-up portion <NUM>, and also contributes to weight reduction. Thus, even in the case where the nominal aspect ratio of the tire <NUM> or the tire <NUM> is not greater than <NUM>% and the nominal cross-sectional width of the tire <NUM> or the tire <NUM> is not less than <NUM>, in the tire <NUM> or the tire <NUM>, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

<FIG> shows a part of a heavy duty pneumatic tire <NUM> (hereinafter, simply referred to as "tire <NUM>") according to an embodiment of the present invention based on another aspect. The tire <NUM> is mounted to a heavy duty vehicle such as a truck and a bus.

In the tire <NUM>, among the four layers <NUM>, a second layer 290B located between a first layer 290A and a third layer 290C has the maximum width in the axial direction. A fourth layer 290D located at the outermost side in the radial direction has the minimum width in the axial direction.

In the tire <NUM>, each filler <NUM> may be formed such that the filler <NUM> has a structure in which the filler <NUM> is turned up around the bead <NUM>. In this case, the first end <NUM> of the filler <NUM> is disposed axially inward of the ply main body <NUM> at the radially outer side of the core <NUM>. The second end <NUM> of the filler <NUM> is disposed at a position similar to that of the second end <NUM> of the above-described short filler. The filler <NUM> having such a structure is also referred to as a normal filler. From the viewpoint of weight reduction, in the tire <NUM>, the filler <NUM> is preferably the above-described short filler.

<FIG> shows a part of the cross-section of the tire <NUM> in <FIG>. In <FIG>, a bead <NUM> portion (hereinafter, also referred to as a bead portion B) of the tire <NUM> is shown. 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 sheet of <FIG> is the circumferential direction of the tire <NUM>.

In the tire <NUM>, the core <NUM> is surrounded by the hard first apex <NUM> the outer periphery of which has a rounded contour. Falling-down of the bead portion B due to application of a load is inhibited, and thus good bead durability is obtained in this tire.

In the tire <NUM>, the height in the radial direction of the first apex <NUM> is low. In the tire <NUM>, a region that can contribute to bending can be sufficiently ensured in a sidewall <NUM> portion, that is, in a side portion S, and the contour of the ply main body <NUM> extending along the apex <NUM> is easily set. In the tire <NUM>, protrusion of the side surface <NUM> outward in the axial direction is inhibited, and thus an amount of strain applied to the recess <NUM> is reduced. In the tire <NUM>, damage such as a crack at the recess <NUM> is less likely to occur. In the tire <NUM>, the above-described effect achieved by the recess <NUM> is sufficiently exhibited. Furthermore, the first apex <NUM> is formed with a small volume, and thus influence of the first apex <NUM> on rolling resistance is effectively inhibited.

In the tire <NUM>, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

In <FIG>, a dotted line VL represents a virtual side surface obtained on the assumption that the recess <NUM> is not present on the side surface <NUM>. The virtual side surface VL is a part of the above-described virtual side surface used for specifying the maximum width position PW. A solid line NL represents a line normal to the ply main body <NUM>. A double-headed arrow TA represents a thickness, from the ply main body <NUM> to the recess <NUM>, measured along the normal line NL. In the tire <NUM>, the thickness TA is represented as the minimum thickness from the ply main body <NUM> to the recess <NUM>. A double-headed arrow TB represents a virtual thickness, from the ply main body <NUM> to the virtual side surface VL, measured along a line segment indicating the minimum thickness TA, that is, along the normal line NL.

In the tire <NUM>, in the radial direction, an outer end <NUM> of the first apex <NUM> is located inward of the end <NUM> of the turned-up portion <NUM>. In the tire <NUM>, concentration of strain on the end <NUM> of the turned-up portion <NUM> is inhibited. In addition, in the tire <NUM>, a region that can contribute to bending can be sufficiently ensured in the side portion S, and the contour of the ply main body <NUM> extending along the apex <NUM> is easily set. In the tire <NUM>, protrusion of the side surface <NUM> outward in the axial direction is effectively inhibited, and thus an amount of strain applied to the recess <NUM> is sufficiently reduced. In the tire <NUM>, damage such as a crack at the recess <NUM> is less likely to occur, and thus the above-described effect achieved by the recess <NUM> is sufficiently exhibited. Furthermore, since protrusion of the side surface <NUM> outward in the axial direction is inhibited and the first apex <NUM> is also formed with a small volume, the rolling resistance of the tire <NUM> can be reduced. From this viewpoint, in the radial direction, the outer end <NUM> of the first apex <NUM> is preferably located inward of the end <NUM> of the turned-up portion <NUM>.

In <FIG>, reference character PF represents a position, on the side surface <NUM>, corresponding to the radially outer end of a contact surface between the tire <NUM> and a flange LF of the rim, that is, a flange contact end. In the tire <NUM>, the outer end <NUM> of the first apex <NUM> is located outward of the flange contact end PF in the radial direction. In the tire <NUM>, the stiffness of the first apex <NUM> is appropriately maintained, and protrusion of the side surface <NUM> at a portion outward of the flange contact end PF is effectively inhibited. In the tire <NUM>, good bead durability is effectively maintained. From this viewpoint, the outer end <NUM> of the first apex <NUM> is preferably located outward of the flange contact end PF in the radial direction.

In the tire <NUM>, the distance HA in the radial direction from the radially inner end PA of the core <NUM> to the outer end <NUM> of the first apex <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>. When the distance HA is set to be not less than <NUM>, the stiffness of the first apex <NUM> is appropriately maintained, and protrusion of the side surface <NUM> at the portion radially outward of the flange contact end PF is effectively inhibited. In the tire <NUM>, good bead durability is effectively maintained. From this viewpoint, the distance HA is more preferably not less than <NUM> and further preferably not less than <NUM>. When the distance HA is set to be not greater than <NUM>, a region that can contribute to bending can be sufficiently ensured in the side portion S, and the contour of the ply main body <NUM> extending along the apex <NUM> is easily set, in the tire <NUM>. In the tire <NUM>, protrusion of the side surface <NUM> outward in the axial direction is inhibited, and thus an amount of strain applied to the recess <NUM> is reduced. In the tire <NUM>, occurrence of damage such as a crack at the recess <NUM> is inhibited, and thus the effect achieved by the recess <NUM> is sufficiently exhibited. From this viewpoint, the distance HA is more preferably not greater than <NUM> and further preferably not greater than <NUM>.

Meanwhile, in the case where a nominal aspect ratio of the tire <NUM> is not greater than <NUM>% and a nominal cross-sectional width of the tire <NUM> is not less than <NUM>, in the tire <NUM>, a carcass height represented as a height in the radial direction from the bead base line BBL to the point of intersection of the equator plane CL and the inner surface of the carcass <NUM> is low with respect to the width in the axial direction of the tread <NUM>. In the tire <NUM>, a region in which application of a load can be absorbed by bending (that is, the above-described region that can contribute to bending) is narrow as compared to a normal tire. Therefore, it is difficult to ensure sufficient bead durability in the tire <NUM>.

As described above, the height in the radial direction of the first apex <NUM> in the tire <NUM> is low, and the recess <NUM> is further provided on the zone of the side surface <NUM> between the maximum width position PW and the end <NUM> of the turned-up portion <NUM>. The first apex <NUM> and the recess <NUM> contribute to bending of the tire <NUM>. In addition, the recess <NUM> inhibits movement of the rubber at the portion radially outward of the end <NUM> of the turned-up portion <NUM>, and also contributes to weight reduction. Thus, even in the case where the nominal aspect ratio of the tire <NUM> is not greater than <NUM>% and the nominal cross-sectional width of the tire <NUM> is not less than <NUM>, in the tire <NUM>, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved.

As is obvious from the above description, according to the present invention, a heavy duty pneumatic tire, in which improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved, is obtained.

The embodiments disclosed above are merely illustrative in all aspects and are not restrictive. The technical scope of the present invention is not limited to the above-described embodiments, and all changes which come within the scope of the configurations recited in the claims are therefore intended to be included therein.

The following will describe the present invention in further detail by means of examples, etc., but the present invention is not limited to these examples.

A heavy duty pneumatic tire (tire size = 11R22. <NUM>) having the basic structure shown in <FIG> and <FIG> and having the specifications shown in Table <NUM> below was obtained.

In Example 1a, the outer end of the first apex was disposed between the end of the turned-up portion and the flange contact end PF in the radial direction. In Table <NUM>, the outer end of the first apex being located inward of the end of the turned-up portion is represented as "in", and the outer end of the first apex being located outward of the flange contact end is represented as "out".

In Example 1a, the distance HA in the radial direction from the radially inner end PA of the core to the outer end of the first apex was set to <NUM>. The distance DB from the axially inner end PB of the core to the carcass ply was set to <NUM>.

A tire of Comparative Example 1a is the conventional tire (tire size = 11R22. <NUM>) shown in <FIG> (not part of the invention). In Comparative Example 1a, the structure is the same as in Example 1a except for the apex.

A tire of Example 2a was obtained in the same manner as Example 1a, except that the outer end of the first apex was disposed radially outward of the end of the turned-up portion. In Table <NUM>, the outer end of the first apex being located outward of the end of the turned-up portion is represented as "out".

A tire of Example 3a was obtained in the same manner as Example 1a, except that the outer end of the first apex was disposed radially inward of the flange contact end. In Table <NUM>, the outer end of the first apex being located inward of the flange contact end is represented as "in".

A heavy duty pneumatic tire (tire size = 11R22. <NUM>) having the basic structure shown in <FIG> and having the specifications shown in Table <NUM> below was obtained. The heavy duty pneumatic tire has the same structure as in Example 1a, except that a recess was provided on the side surface.

In Example 4a, the ratio (TA/TB) of the minimum thickness TA from the ply main body to the recess relative to the virtual thickness TB, from the ply main body to the virtual side surface VL obtained on the assumption that the recess is not present, measured along a line segment (that is, the normal line NL) indicating the minimum thickness TA was set to <NUM>.

Tires of Examples 5a and 6a were obtained in the same manner as Example 1a, except that the distance DB was set as shown in Table <NUM> below.

Tires of Examples 7a to 10a were obtained in the same manner as Example 1a, except that the distance HA was set as shown in Table <NUM> below.

Ply turn-up loose (PTL) resistance was evaluated as bead durability. In this evaluation, each tire was fitted onto a rim (size = <NUM>×<NUM>) and filled with air. The internal pressure of the tire was adjusted to <NUM> kPa. The tire was mounted to a bench tester having a drive drum. A vertical load of <NUM> kN was applied to the tire, running with the tire was performed at <NUM>/h, and the running time until damage to the bead occurred and the occurrence state of PTL were confirmed. The results are shown in Tables <NUM> and <NUM> below as indexes with the value of the tire of Example 1a being defined as <NUM>. A higher value represents that PTL is less likely to occur and the bead durability is better.

Each tire was fitted onto a rim (size = <NUM>×<NUM>) and filled with air. The internal pressure of the tire was adjusted to <NUM> kPa. The tire was mounted to a rolling resistance tester. A vertical load of <NUM> kN was applied to the tire, running with the tire was performed at <NUM>/h, and the rolling resistance was measured. The results are shown in Tables <NUM> and <NUM> below as indexes with the value of Example 1a being defined as <NUM>. A higher value represents that the rolling resistance is lower, which is preferable.

Casing break-up (CBU) resistance was evaluated as bead durability. In this evaluation, each tire was fitted onto a rim (size = <NUM>×<NUM>), <NUM> cc of water was put in the tire, and the tire was filled with air. The internal pressure of the tire was adjusted to <NUM> kPa. The tire was allowed to stand for <NUM> weeks in an atmosphere adjusted to <NUM>. After this pretreatment, <NUM> cc of water was put in the tire, the tire was filled with air, and the internal pressure of the tire was adjusted to <NUM> kPa. The tire was mounted to a bench tester having a drive drum. A vertical load of <NUM> kN was applied to the tire, running with the tire was performed at <NUM>/h, and the running time until damage to the bead occurred and the occurrence state of CBU were confirmed. The results are shown in Tables <NUM> and <NUM> below as indexes with the value of the tire of Example 1a being defined as <NUM>. A higher value represents that CBU is less likely to occur and the bead durability is better.

As shown in Tables <NUM> and <NUM>, in the Examples, it is confirmed that, by using a short filler as the filler and using a round-shaped apex as the first apex, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved. The Examples are highly rated, as compared to the Comparative Example. From the evaluation results, advantages of the present invention are clear.

In Example 1b, the outer end of the first apex was disposed between the end of the turned-up portion and the flange contact end PF in the radial direction. In Table <NUM>, the outer end of the first apex being located inward of the end of the turned-up portion is represented as "in", and the outer end of the first apex being located outward of the flange contact end is represented as "out".

In Example 1b, the distance HA in the radial direction from the radially inner end PA of the core to the outer end of the first apex was set to <NUM>. The distance DB from the axially inner end PB of the core to the carcass ply was set to <NUM>.

In Example 1b, the ratio (TA/TB) of the minimum thickness TA from the ply main body to the recess relative to the virtual thickness TB, from the ply main body to the virtual side surface VL obtained on the assumption that the recess is not present, measured along a line segment (that is, the normal line NL) indicating the minimum thickness TA was set to <NUM>.

A tire of Comparative Example 1b is the conventional tire (tire size = 11R22. <NUM>) shown in <FIG> (not part of the invention). In Comparative Example 1b, the apex was formed as a conventional apex. No recess is provided on the side surface.

A tire of Reference Example 2b was obtained in the same manner as Example 1b, except that no recess was provided on the side surface.

A tire of Example 2b was obtained in the same manner as Example 1b, except that the outer end of the first apex was disposed radially outward of the end of the turned-up portion. In Table <NUM>, the outer end of the first apex being located outward of the end of the turned-up portion is represented as "out".

A tire of Example 3b was obtained in the same manner as Example 1b, except that the outer end of the first apex was disposed radially inward of the flange contact end. In Table <NUM>, the outer end of the first apex being located inward of the flange contact end is represented as "in".

Tires of Examples 4b and 5b were obtained in the same manner as Example 1b, except that the distance DB was set as shown in Table <NUM> below.

Tires of Examples 6b to 9b were obtained in the same manner as Example 1b, except that the distance HA was set as shown in Table <NUM> below.

Ply turn-up loose (PTL) resistance was evaluated as bead durability. In this evaluation, each tire was fitted onto a rim (size = <NUM>×<NUM>) and filled with air. The internal pressure of the tire was adjusted to <NUM> kPa. The tire was mounted to a bench tester having a drive drum. A vertical load of <NUM> kN was applied to the tire, running with the tire was performed at <NUM>/h, and the running time until damage to the bead occurred and the occurrence state of PTL were confirmed. The results are shown in Tables <NUM> and <NUM> below as indexes with the value of the tire of Example 1b being defined as <NUM>. A higher value represents that PTL is less likely to occur and the bead durability is better.

Each tire was fitted onto a rim (size = <NUM>×<NUM>) and filled with air. The internal pressure of the tire was adjusted to <NUM> kPa. The tire was mounted to a rolling resistance tester. A vertical load of <NUM> kN was applied to the tire, running with the tire was performed at <NUM>/h, and the rolling resistance was measured. The results are shown in Tables <NUM> and <NUM> below as indexes with the value of Example 1b being defined as <NUM>. A higher value represents that the rolling resistance is lower, which is preferable.

Casing break-up (CBU) resistance was evaluated as bead durability. In this evaluation, each tire was fitted onto a rim (size = <NUM>×<NUM>), <NUM> cc of water was put in the tire, and the tire was filled with air. The internal pressure of the tire was adjusted to <NUM> kPa. The tire was allowed to stand for <NUM> weeks in an atmosphere adjusted to <NUM>. After this pretreatment, <NUM> cc of water was put in the tire, the tire was filled with air, and the internal pressure of the tire was adjusted to <NUM> kPa. The tire was mounted to a bench tester having a drive drum. A vertical load of <NUM> kN was applied to the tire, running with the tire was performed at <NUM>/h, and the running time until damage to the bead occurred and the occurrence state of CBU were confirmed. The results are shown in Tables <NUM> and <NUM> below as indexes with the value of the tire of Example 1b being defined as <NUM>. A higher value represents that CBU is less likely to occur and the bead durability is better.

Each tire was allowed to stand for <NUM> weeks in an atmosphere adjusted to <NUM>. After this pretreatment, the tire was fitted onto a rim (size = <NUM>×<NUM>) and filled with air. The internal pressure of the tire was adjusted to <NUM> kPa. The tire was mounted to a bench tester having a drive drum. A vertical load of <NUM> kN was applied to the tire, running with the tire was performed at <NUM>/h in an atmosphere having an ozone concentration adjusted to <NUM> pphm, and the occurrence state of ozone cracks was confirmed. The results are shown in Tables <NUM> and <NUM> below as indexes with the value of the tire of Example 1b being defined as <NUM>. A higher value represents that an ozone crack is less likely to occur.

As shown in Tables <NUM> and <NUM>, in the Examples, it is confirmed that, by using a round-shaped apex as the first apex and providing a recess on the side surface, improvement of bead durability and reduction of rolling resistance are achieved while weight reduction is achieved. The Examples are highly rated, as compared to the Comparative Example. From the evaluation results, advantages of the present invention are clear.

Claim 1:
A heavy duty pneumatic tire (<NUM>, <NUM>, <NUM>) comprising:
a pair of beads (<NUM>, <NUM>);
a carcass ply (<NUM>, <NUM>) having a ply main body (<NUM>, <NUM>) that extends on and between one bead (<NUM>, <NUM>) and the other bead (<NUM>, <NUM>), and turned-up portions (<NUM>, <NUM>) that are connected to the ply main body (<NUM>, <NUM>) and turned around the beads (<NUM>, <NUM>) from an inner side toward an outer side in an axial direction; and
a pair of fillers (<NUM>, <NUM>) that are located outward of the turned-up portions (<NUM>, <NUM>) in the axial direction and that include metal cords, wherein
each bead (<NUM>, <NUM>) includes a core (<NUM>, <NUM>), a first apex (<NUM>, <NUM>) that surrounds the core (<NUM>, <NUM>), and a second apex (<NUM>, <NUM>) that is located outward of the first apex (<NUM>, <NUM>) in the radial direction,
an outer periphery of the first apex (<NUM>, <NUM>) has a rounded contour, and
the first apex (<NUM>, <NUM>) has a higher durometer type A hardness than the second apex (<NUM>, <NUM>),
the first apex (<NUM>, <NUM>) has a round shape;
characterized in that in a radial direction, a first end (<NUM>, <NUM>) of each filler (<NUM>, <NUM>) is located inward of a bead base line (BBL), and a second end (<NUM>, <NUM>) of each filler (<NUM>, <NUM>) is located between an end of the turned-up portion (<NUM>, <NUM>) and the bead base line (BBL).