Patent Description:
From the viewpoint of drainage performance, at least three circumferential grooves are formed on the tread of a heavy duty pneumatic tire (hereinafter, tire). Among the circumferential grooves formed on the tread, the circumferential groove located on each outer side in the axial direction is a shoulder circumferential groove.

A belt and a band are provided between the tread and a carcass. The belt includes a plurality of belt plies aligned in the radial direction. Each belt ply includes a large number of belt cords aligned with each other. Normally, steel cords are used as the belt cords. The band includes a spirally wound band cord. A cord formed from an organic fiber such as nylon fiber, or a steel cord is used as the band cord. The stiffness of a tread portion is controlled by adjusting the configuration of the belt or the band (for example <CIT>).

<CIT> discloses a tire according to the preamble of claim <NUM>. <CIT> discloses a tire having an aspect-ratio of <NUM> %, two circumferential grooves and three land portions. The tire further has a reinforcement comprising a belt and a band, the band comprising a full band whose axial ends are located outward of a shoulder circumferential groove in the axial direction. Other tires are, for example, disclosed in <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

In a tire in a running state, deformation and restoration are repeated. Accordingly, the shape of the tire is changed. The ground-contact shape of the tire is changed, so that there is a concern about a decrease in uneven wear resistance.

In a running state of the tire, a tread end portion moves actively. The stiffness of the portion where the circumferential grooves are formed is lower than the stiffness of the portion where the circumferential grooves are not formed. Low-flatness tires having an aspect ratio of <NUM>% or less include a tire having a wide tread surface. In the tire, each shoulder circumferential groove is located more outward in the axial direction than that in a high-flatness tire. In the tire, a shape change is large around the shoulder circumferential groove.

In order to suppress a shape change, use of a full band including a spirally wound band cord is considered. In a low-flatness tire, a shape change during running tends to be increased, so that there is a possibility that such a shape change cannot be sufficiently suppressed only by the full band.

The band cord included in the full band extends substantially in the circumferential direction. A force acts on the band cord of the tire in a running state, in the direction in which the band cord is pulled.

The tire bends when coming into contact with a road surface. Accordingly, the force acting on the band cord is decreased, so that the tension of the band cord is decreased. When the tire becomes separated from the road surface to be restored, the force acting on the band cord is increased, so that the tension of the band cord is increased. In the band cord of the tire in a running state, fluctuation of the tension is repeated. There is a concern that a break may occur in the band cord depending on the degree of fluctuation of the tension. The fluctuation of the tension is large at the end of the full band. As described above, in a running state of the tire, the tread end portion moves actively. When the end of the full band is located more outward in the axial direction, a break of the band cord in the full band is more likely to occur.

When the band cord becomes broken, the holding force thereof is decreased. In this case, the ground-contact shape may be changed, so that there is a possibility that uneven wear resistance and steering stability are decreased.

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 that can suppress a shape change due to running and achieve improvement of uneven wear resistance.

A heavy duty pneumatic tire according to an aspect of the present invention has a nominal aspect ratio of <NUM>% or less. The heavy duty pneumatic tire includes a tread that comes into contact with a road surface and a reinforcing layer located inward of the tread in a radial direction. At least three circumferential grooves are formed on the tread, whereby at least four land portions aligned in an axial direction are formed in the tread. Among the at least three circumferential grooves, a circumferential groove located on each outer side in the axial direction is a shoulder circumferential groove. A land portion located outward of the shoulder circumferential groove in the axial direction is a shoulder land portion. The reinforcing layer includes a belt including a large number of belt cords aligned with each other, and a band including a spirally wound band cord. The belt includes a plurality of belt plies aligned in the radial direction. The band includes a full band having ends opposed to each other across an equator plane, and a pair of edge bands located outward of the ends of the full band in the radial direction. Each end of the full band is located outward of the shoulder circumferential groove in the axial direction. The plurality of belt plies includes two belt plies having a width larger than a width of the full band, and the full band is interposed between the two belt plies.

In the heavy duty pneumatic tire, a ratio of a distance in the axial direction from the shoulder circumferential groove to the end of the full band, to a width in the axial direction of the shoulder land portion, is not less than <NUM>% and not greater than <NUM>%.

Preferably, in the heavy duty pneumatic tire, a distance in the axial direction from the end of the full band to an inner end of the edge band is not less than <NUM>.

Preferably, in the heavy duty pneumatic tire, each end of the full band is located inward of an end of the belt in the axial direction.

Preferably, in the heavy duty pneumatic tire, at least one belt ply of the plurality of belt plies is located inward of the full band in the radial direction.

According to the present invention, a heavy duty pneumatic tire that can suppress a shape change due to running and achieve improvement of uneven wear resistance is obtained.

In the present disclosure, a state where a tire is fitted 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 components 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, referred to simply as "tire <NUM>") according to an embodiment of the present invention. The tire <NUM> is mounted to a vehicle such as a truck and a bus. The nominal aspect ratio of the tire <NUM> is not greater than <NUM>%. In other words, the tire <NUM> has a nominal aspect ratio of <NUM>% or less. The tire <NUM> is a low-flatness tire.

In the present disclosure, the "nominal aspect ratio" and the "nominal cross-sectional width" are the "nominal aspect ratio" and the "nominal cross-sectional width" included in "tyre designation" specified in JIS D4202 "Automobile tyres-Designation and dimensions".

<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>. An alternate long and short dash line CL represents the equator plane 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 pair of cushion layers <NUM>, an inner liner <NUM>, a pair of steel fillers <NUM>, and a reinforcing layer <NUM>.

The tread <NUM> comes into contact with a road surface at an outer surface thereof. The outer surface is a tread surface <NUM>. In <FIG>, reference character PC represents the point of intersection of the tread surface <NUM> and the equator plane CL. The point of intersection PC corresponds to the equator of the tire <NUM>.

In <FIG>, reference character PE represents an end of the tread surface <NUM>. A double-headed arrow WT represents the width of the tread surface <NUM>. The width WT of the tread surface <NUM> is represented as the distance in the axial direction from one end PE of the tread surface <NUM> to the other end PE of the tread surface <NUM>. In the tire <NUM>, when the ends PE of the tread surface <NUM> cannot be identified from the appearance, the outer ends in the axial direction of a ground-contact surface obtained when the normal load is applied to the tire <NUM> in the normal state and the tire <NUM> is brought into contact with a flat surface at a camber angle of <NUM>° are defined as the ends PE of the tread surface <NUM>.

The tread <NUM> includes a base portion <NUM> and a cap portion <NUM> located radially outward of the base portion <NUM>. The base portion <NUM> is formed from a crosslinked rubber having low heat generation properties. The cap portion <NUM> is formed from a crosslinked rubber for which wear resistance and grip performance are taken into consideration. As shown in <FIG>, the base portion <NUM> covers the entirety of the reinforcing layer <NUM>. The cap portion <NUM> covers the entirety of the base portion <NUM>.

In the tire <NUM>, at least three circumferential grooves <NUM> are formed on the tread <NUM>. On the tread <NUM> of the tire <NUM> shown in <FIG>, four circumferential grooves <NUM> are formed. These circumferential grooves <NUM> are aligned in the axial direction and continuously extend in the circumferential direction.

Among the four circumferential grooves <NUM> formed on the tread <NUM>, the circumferential groove <NUM> located on each outer side in the axial direction is a shoulder circumferential groove <NUM>. The circumferential groove <NUM> located inward of the shoulder circumferential groove <NUM> in the axial direction is a middle circumferential groove <NUM>. In the tire <NUM>, the four circumferential grooves <NUM> include a pair of the middle circumferential grooves <NUM> and a pair of the shoulder circumferential grooves <NUM>.

In the tire <NUM>, from the viewpoint of contribution to drainage performance and traction performance, the width in the axial direction of each middle circumferential groove <NUM> is preferably about <NUM> to <NUM>% of the width WT of the tread surface <NUM>. The depth of each middle circumferential groove <NUM> is preferably <NUM> to <NUM>. The width in the axial direction of each shoulder circumferential groove <NUM> is preferably about <NUM> to <NUM>% of the width WT of the tread surface <NUM>. The depth of each shoulder circumferential groove <NUM> is preferably <NUM> to <NUM>.

As described above, at least three circumferential grooves <NUM> are formed on the tread <NUM>. Accordingly, at least four land portions <NUM> are formed in the tread <NUM>. On the tread <NUM> of the tire <NUM> shown in <FIG>, four circumferential grooves <NUM> are formed, so that five land portions <NUM> are formed in the tread <NUM>. These land portions <NUM> are aligned in the axial direction and continuously extend in the circumferential direction.

Among the five land portions <NUM> formed in the tread <NUM>, the land portion <NUM> located on each outer side in the axial direction is a shoulder land portion <NUM>. Each shoulder land portion <NUM> is located outward of the shoulder circumferential groove <NUM> in the axial direction and includes the end PE of the tread surface <NUM>. The land portions <NUM> located inward of the shoulder land portions <NUM> in the axial direction are middle land portions <NUM>. The shoulder circumferential grooves <NUM> are present between the middle land portions <NUM> and the shoulder land portions <NUM>. The land portion <NUM> located inward of the middle land portions <NUM> in the axial direction is a center land portion 30c. The middle circumferential grooves <NUM> are present between the center land portion 30c and the middle land portions <NUM>. In the tire <NUM>, the five land portions <NUM> include the center land portion 30c, a pair of the middle land portions <NUM>, and a pair of the shoulder land portions <NUM>.

In the tire <NUM>, the width in the axial direction of the center land portion 30c is not less than <NUM>% and not greater than <NUM>% of the width WT of the tread surface <NUM>. The width in the axial direction of each middle land portion <NUM> is not less than <NUM>% and not greater than <NUM>% of the width WT of the tread surface <NUM>. The width in the axial direction of each shoulder land portion <NUM> is not less than <NUM>% and not greater than <NUM>% of the width WT of the tread surface <NUM>. The width in the axial direction of each land portion <NUM> is represented as the width in the axial direction of the top surface of the land portion <NUM> which forms a part of the tread surface <NUM>.

In the tire <NUM>, the land portion <NUM> located at the center in the axial direction among the land portions <NUM> formed in the tread <NUM>, that is, the center land portion 30c, is located on the equator plane CL. The tread <NUM> may be formed such that the circumferential grooves <NUM> formed on the tread <NUM> include a circumferential groove <NUM> located at the center in the axial direction and this circumferential groove <NUM> is located on the equator plane CL.

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.

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 made of steel. The core <NUM> has a substantially hexagonal cross-sectional shape.

The apex <NUM> is located radially outward of the core <NUM>. The apex <NUM> includes an inner apex 34u and an outer apex <NUM>. The inner apex 34u extends radially outward from the core <NUM>. The outer apex <NUM> is located radially outward of the inner apex 34u. The inner apex 34u is formed from a hard crosslinked rubber. The outer apex <NUM> is formed from a crosslinked rubber that is more flexible than the inner apex 34u. The outer apex <NUM> is more flexible than the inner apex 34u.

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 (not shown). The chafer <NUM> is formed from a crosslinked rubber for which wear resistance is taken into consideration.

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> is turned up around each core <NUM> from the inner side toward the outer side in the axial direction.

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

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

The inner liner <NUM> is located inward of the carcass <NUM>. The inner liner <NUM> forms an 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 steel filler <NUM> is located at a bead <NUM> portion. The steel filler <NUM> is turned up around the core <NUM> from the inner side toward the outer side in the axial direction along the carcass ply <NUM>.

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

The reinforcing layer <NUM> is located inward of the tread <NUM> in the radial direction. The reinforcing layer <NUM> is located between the carcass <NUM> and the tread <NUM>. The reinforcing layer <NUM> includes a belt <NUM> and a band <NUM>.

<FIG> shows the configuration of the reinforcing layer <NUM>. In <FIG>, the right-left direction is the axial direction of the tire <NUM>, and the up-down direction is the circumferential direction of the tire <NUM>. The direction perpendicular to the surface of the sheet of <FIG> is the radial direction of the tire <NUM>. The front side of the sheet of <FIG> is the outer side in the radial direction, and the back side of the sheet is the inner side in the radial direction.

The belt <NUM> includes a plurality of belt plies <NUM> aligned in the radial direction. Each belt ply <NUM> is disposed such that both ends thereof are opposed to each other across the equator plane CL. The belt <NUM> of the tire <NUM> includes four belt plies <NUM>. The four belt plies <NUM> include a first belt ply 42A located on the inner side in the radial direction, a second belt ply 42B located outward of the first belt ply 42A in the radial direction, a third belt ply 42C located outward of the second belt ply 42B in the radial direction, and a fourth belt ply 42D located outward of the third belt ply 42C in the radial direction.

In the tire <NUM>, the second belt ply 42B has a largest width in the axial direction, and the fourth belt ply 42D has a smallest width in the axial direction. The first belt ply 42A and the third belt ply 42C have the same width in the axial direction, or the width in the axial direction of the first belt ply 42A is larger than the width in the axial direction of the third belt ply 42C.

An end 38e of the belt <NUM> of the tire <NUM> is represented as an end of the belt ply <NUM> having the largest width in the axial direction among the plurality of belt plies <NUM> included in the belt <NUM>. In the tire <NUM>, as described above, among the four belt plies <NUM> included in the belt <NUM>, the second belt ply 42B has the largest width in the axial direction. The end 38e of the belt <NUM> of the tire <NUM> is represented as an end 42Be of the second belt ply 42B having the largest width in the axial direction. The end 38e of the belt <NUM> is also an end 20e of the reinforcing layer <NUM>.

As shown in <FIG>, an end 42Ae of the first belt ply 42A is located outward of the shoulder circumferential groove <NUM> in the axial direction. An end 42Be of the second belt ply 42B is located outward of the shoulder circumferential groove <NUM> in the axial direction. An end 42Ce of the third belt ply 42C is located outward of the shoulder circumferential groove <NUM> in the axial direction. An end 42De of the fourth belt ply 42D is located outward of the shoulder circumferential groove <NUM> in the axial direction.

In <FIG>, a double-headed arrow W1 represents the width in the axial direction of the first belt ply 42A. A double-headed arrow W2 represents the width in the axial direction of the second belt ply 42B. A double-headed arrow W3 represents the width in the axial direction of the third belt ply 42C. A double-headed arrow W4 represents the width in the axial direction of the fourth belt ply 42D. The width in the axial direction of each belt ply <NUM> is represented as the distance in the axial direction from one end 42e of the belt ply <NUM> to the other end 42e of the belt ply <NUM>.

In the tire <NUM>, from the viewpoint of ensuring the stiffness of the tread <NUM> portion, the ratio (W1/WT) of the width W1 in the axial direction of the first belt ply 42A to the width WT of the tread surface <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>. The ratio (W2/WT) of the width W2 in the axial direction of the second belt ply 42B to the width WT of the tread surface <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>. The ratio (W3/WT) of the width W3 in the axial direction of the third belt ply 42C to the width WT of the tread surface <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>. The ratio (W4/WT) of the width W4 in the axial direction of the fourth belt ply 42D to the width WT of the tread surface <NUM> is preferably not less than <NUM> and preferably not greater than <NUM>.

As shown in <FIG>, in the tire <NUM>, each belt ply <NUM> included in the belt <NUM> includes a large number of belt cords <NUM> aligned with each other. In <FIG>, for convenience of description, the belt cords <NUM> are represented by sold lines, but the belt cords <NUM> are covered with a topping rubber <NUM>. The belt cords <NUM> of the tire <NUM> are steel cords.

In the tire <NUM>, the density of the belt cords <NUM> in each belt ply <NUM> is not less than <NUM> ends/<NUM> and not greater than <NUM> ends/<NUM>. The density of the belt cords <NUM> is represented as the number of cross-sections of the belt cords <NUM> included per <NUM> width of the belt ply <NUM> in a cross-section of the belt ply <NUM> along a plane perpendicular to the direction in which the belt cords <NUM> extend.

The belt cords <NUM> in each belt ply <NUM> are tilted relative to the circumferential direction. The direction in which the belt cords <NUM> included in the first belt ply 42A are tilted relative to the circumferential direction (hereinafter, the tilt direction of the first belt ply 42A) is the same as the direction in which the belt cords <NUM> included in the second belt ply 42B are tilted relative to the circumferential direction (hereinafter, the tilt direction of the second belt ply 42B). The tilt direction of the second belt ply 42B is opposite to the direction in which the belt cords <NUM> included in the third belt ply 42C are tilted relative to the circumferential direction (hereinafter, the tilt direction of the third belt ply 42C). The tilt direction of the third belt ply 42C is the same as the direction in which the belt cords <NUM> included in the fourth belt ply 42D are tilted relative to the circumferential direction (hereinafter, the tilt direction of the fourth belt ply 42D). The tilt direction of the first belt ply 42A may be opposite to the tilt direction of the second belt ply 42B, and the tilt direction of the fourth belt ply 42D may be opposite to the tilt direction of the third belt ply 42C. From the viewpoint of ensuring a stable ground-contact shape, the tilt direction of the second belt ply 42B is preferably opposite to the tilt direction of the third belt ply 42C.

In <FIG>, an angle θ1 is a tilt angle (hereinafter, first tilt angle θ1) of the belt cords <NUM> included in the first belt ply 42A relative to the equator plane CL. An angle θ2 is a tilt angle (hereinafter, second tilt angle θ2) of the belt cords <NUM> included in the second belt ply 42B relative to the equator plane CL. An angle θ3 is a tilt angle (hereinafter, third tilt angle θ3) of the belt cords <NUM> included in the third belt ply 42C relative to the equator plane CL. An angle θ4 is a tilt angle (hereinafter, fourth tilt angle θ4) of the belt cords <NUM> included in the fourth belt ply 42D relative to the equator plane CL.

In the tire <NUM>, each of the first tilt angle θ1, the second tilt angle θ2, the third tilt angle θ3, and the fourth tilt angle θ4 is preferably not less than <NUM>° and preferably not greater than <NUM>°. From the viewpoint of effectively restraining movement of the tire <NUM> and ensuring a stable ground-contact shape, the first tilt angle θ1 is preferably not less than <NUM>° and preferably not greater than <NUM>°. The second tilt angle θ2 is preferably not less than <NUM>° and preferably not greater than <NUM>°. The third tilt angle θ3 is preferably not less than <NUM>° and preferably not greater than <NUM>°. The fourth tilt angle θ4 is preferably not less than <NUM>° and preferably not greater than <NUM>°.

The band <NUM> includes a full band <NUM> and a pair of edge bands <NUM>. As shown in <FIG>, the full band <NUM> has ends 48e opposed to each other across the equator plane CL. The pair of edge bands <NUM> are disposed so as to be spaced apart from each other in the axial direction with the equator plane CL therebetween. In the tire <NUM>, the fourth belt ply 42D, which forms a part of the belt <NUM>, is located between the pair of edge bands <NUM>.

In the tire <NUM>, each edge band <NUM> is located between the tread <NUM> and the full band <NUM>. The edge band <NUM> is located outward of the end 48e of the full band <NUM> in the radial direction. In the axial direction, an inner end 50ue of the edge band <NUM> is located inward of the end 48e of the full band <NUM>. In the axial direction, an outer end 50se of the edge band <NUM> is located outward of the end 48e of the full band <NUM>. The position of the outer end 50se of the edge band <NUM> may coincide with the position of the end 48e of the full band <NUM> in the axial direction. The edge band <NUM> overlaps the end 48e of the full band <NUM> in the radial direction. In the axial direction, the outer end 50se of the edge band <NUM> is located inward of the end 42Ce of the third belt ply 42C.

As shown in <FIG>, the full band <NUM> and the pair of edge bands <NUM> included in the band <NUM> each include a spirally wound band cord <NUM>. In <FIG>, for the convenience of description, the band cords <NUM> are represented by solid lines, but each band cord <NUM> is covered with a topping rubber <NUM>.

In the tire <NUM>, the band cords <NUM> are steel cords or cords formed from an organic fiber (hereinafter, organic fiber cords). In the case where organic fiber cords are used as the band cords <NUM>, examples of the organic fiber include nylon fibers, polyester fibers, rayon fibers, and aramid fibers. In the tire <NUM>, as the band cord <NUM> of the full band <NUM> and the band cords <NUM> of the edge bands <NUM>, the same cord may be used, or different cords may be used. The band cords <NUM> used for the full band <NUM> and the edge bands <NUM> are determined according to the specifications of the tire <NUM>.

As described above, the full band <NUM> includes the spirally wound band cord <NUM>. The full band <NUM> has a jointless structure. In the full band <NUM>, an angle of the band cord <NUM> relative to the circumferential direction is preferably not greater than <NUM>° and more preferably not greater than <NUM>°. The band cord <NUM> of the full band <NUM> extends substantially in the circumferential direction.

The density of the band cord <NUM> in the full band <NUM> is not less than <NUM> ends/<NUM> and not greater than <NUM> ends/<NUM>. The density of the band cord <NUM> is represented as the number of cross-sections of the band cord <NUM> included per <NUM> width of the full band <NUM> in a cross-section of the full band <NUM> along a plane perpendicular to the direction in which the band cord <NUM> extends.

As described above, each edge band <NUM> includes the spirally wound band cord <NUM>. The edge band <NUM> has a jointless structure. In the edge band <NUM>, an angle of the band cord <NUM> relative to the circumferential direction is preferably not greater than <NUM>° and more preferably not greater than <NUM>°. The band cord <NUM> of the edge band <NUM> extends substantially in the circumferential direction.

The density of the band cord <NUM> in the edge band <NUM> is not less than <NUM> ends/<NUM> and not greater than <NUM> ends/<NUM>. The density of the band cord <NUM> is represented as the number of cross-sections of the band cord <NUM> included per <NUM> width of the edge band <NUM> in a cross-section of the edge band <NUM> along a plane perpendicular to the direction in which the band cord <NUM> extends.

<FIG> shows a part of the cross-section of the tire <NUM> shown in <FIG>. 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>, each of the end 42Be of the second belt ply 42B and the end 42Ce of the third belt ply 42C is covered with a rubber layer <NUM>. Two rubber layers <NUM> are further disposed between the end 42Be of the second belt ply 42B and the end 42Ce of the third belt ply 42C each of which is covered with the rubber layer <NUM>. In the tire <NUM>, an edge member <NUM> including four rubber layers <NUM> in total is formed between the end 42Be of the second belt ply 42B and the end 42Ce of the third belt ply 42C. The edge member <NUM> is formed from a crosslinked rubber. The edge member <NUM> contributes to maintaining the interval between the end 42Be of the second belt ply 42B and the end 42Ce of the third belt ply 42C. In the tire <NUM>, a change of the positional relationship between the end 42Be of the second belt ply 42B and the end 42Ce of the third belt ply 42C due to running is suppressed. The edge member <NUM> is a part of the reinforcing layer <NUM>. The reinforcing layer <NUM> of the tire <NUM> includes a pair of edge members <NUM> in addition to the belt <NUM> and the band <NUM>.

As described above, the full band <NUM> has the ends 48e opposed to each other across the equator plane CL. The full band <NUM> extends in the axial direction from the equator plane CL toward each end 48e. Each end 48e of the full band <NUM> is located outward of the shoulder circumferential groove <NUM> in the axial direction. The full band <NUM> is located inward of each shoulder circumferential groove <NUM> in the radial direction.

Although the tire <NUM> has low flatness, the full band <NUM> effectively suppresses deformation around each shoulder circumferential groove <NUM>. A change of the shape of the tire <NUM>, for example, a change of the contour (hereinafter, also referred to as case line) of the carcass <NUM>, is suppressed, so that a change of the ground-contact shape is suppressed.

In the tire <NUM>, furthermore, each edge band <NUM> is located outward of the end 48e of the full band <NUM> in the radial direction. The edge band <NUM> holds the end 48e of the full band <NUM>. Fluctuation of the tension of the band cord <NUM> included in the full band <NUM> is suppressed, so that occurrence of a break of the band cord <NUM> due to the fluctuation of the tension is suppressed. The full band <NUM> of the tire <NUM> can stably exhibit the function of suppressing a shape change. The edge band <NUM> is narrower than the full band <NUM>. Therefore, tension fluctuation as in the full band <NUM> is less likely to occur in the band cord <NUM> of the edge band <NUM>. A break is less likely to occur in the band cord <NUM> of the edge band <NUM>.

In the tire <NUM>, the full band <NUM> and the edge bands <NUM> suppress a shape change of the tire <NUM> due to running. In particular, a shape change around each shoulder circumferential groove <NUM> is effectively suppressed. In the tire <NUM>, occurrence of uneven wear, which is a concern with conventional tires, is suppressed. The tire <NUM> can suppress a shape change due to running and achieve improvement of uneven wear resistance.

In <FIG>, a double-headed arrow SF represents the distance in the axial direction from the shoulder circumferential groove <NUM>, specifically, the outer edge of the shoulder circumferential groove <NUM>, to the end 48e of the full band <NUM>. A double-headed arrow WS represents the width in the axial direction of the shoulder land portion <NUM>. The width WS in the axial direction is represented as the distance in the axial direction from the inner end of the top surface of the shoulder land portion <NUM> (that is, the outer edge of the shoulder circumferential groove <NUM>) to the outer end of the top surface (in the tire <NUM>, the end PE of the tread surface <NUM>).

In the tire <NUM>, the ratio (SF/WS) of the distance SF in the axial direction from the shoulder circumferential groove <NUM> to the end 48e of the full band <NUM>, to the width WS in the axial direction of the shoulder land portion <NUM>, is not greater than <NUM>% Accordingly, the end 48e of the full band <NUM> is located away from the tread <NUM> end portion which moves actively in a running state, so that fluctuation of the tension of the band cord <NUM> is suppressed. In the tire <NUM>, occurrence of a break of the band cord <NUM> is suppressed. The full band <NUM> of the tire <NUM> contributes to suppression of a shape change. From this viewpoint, the ratio (SF/WS) is more preferably not greater than <NUM>% and further preferably not greater than <NUM>%.

The ratio (SF/WS) is set to be not less than <NUM>%, the end 48e of the full band <NUM> is located at an appropriate interval from the shoulder circumferential groove <NUM>, specifically, the bottom of the shoulder circumferential groove <NUM>. In the tire <NUM>, occurrence of damage starting from the bottom of the shoulder circumferential groove <NUM> is suppressed. Since the width of the full band <NUM> is ensured, the full band <NUM> contributes to suppression of a shape change of the tire <NUM>. From this viewpoint, the ratio (SF/WS) is more preferably not less than <NUM>%.

In <FIG>, a double-headed arrow We represents the distance in the axial direction from the end 48e of the full band <NUM> to the inner end 50ue of the edge band <NUM>.

In the tire <NUM>, the distance We in the axial direction from the end 48e of the full band <NUM> to the inner end 50ue of the edge band <NUM> is preferably not less than <NUM>. Accordingly, the edge band <NUM> effectively holds the end 48e of the full band <NUM>. Fluctuation of the tension of the band cord <NUM> included in the full band <NUM> is suppressed, so that occurrence of a break of the band cord <NUM> due to the fluctuation of the tension is suppressed. The full band <NUM> of the tire <NUM> can more stably exhibit the function of suppressing a shape change. From this viewpoint, the distance We in the axial direction is preferably not less than <NUM>.

In the tire <NUM>, the position of the inner end 50ue of the edge band <NUM> is determined as appropriate in consideration of involvement in occurrence of damage starting from the bottom of the shoulder circumferential groove <NUM>. Therefore, a preferable upper limit of the distance We in the axial direction is not set. From the viewpoint of effectively suppressing occurrence of damage starting from the bottom of the shoulder circumferential groove <NUM>, in the axial direction, the inner end 50ue of the edge band <NUM> is preferably located outward of the bottom of the shoulder circumferential groove <NUM>, and more preferably located further outward of the shoulder circumferential groove <NUM>.

In the tire <NUM>, each end 48e of the full band <NUM> is located inward of the end 38e of the belt <NUM> in the axial direction. The belt <NUM> is wider than the full band <NUM>. The belt <NUM> holds each end 48e of the full band <NUM>. The belt <NUM> contributes to suppression of fluctuation of the tension of the band cord <NUM> included in the full band <NUM>. Occurrence of a break of the band cord <NUM> due to fluctuation of the tension is suppressed, so that the full band <NUM> can stably exhibit the function of suppressing a shape change. From this viewpoint, the end 48e of the full band <NUM> is preferably located inward of the end 38e of the belt <NUM> in the axial direction.

A force acts on the full band <NUM> of the tire <NUM> so as to spread from the inner side toward the outer side in the radial direction. Due to this force, tension is generated in the band cord <NUM> of the full band <NUM>. In the tire <NUM>, the second belt ply 42B is located radially inward of the full band <NUM>.

In the tire <NUM>, the second belt ply 42B reduces the force acting on the full band <NUM>, so that the tension of the band cord <NUM> included in the full band <NUM> is appropriately maintained. The second belt ply 42B contributes to suppression of fluctuation of the tension of the band cord <NUM>. Since the second belt ply 42B is wider than the full band <NUM>, fluctuation of the tension of the band cord <NUM> is effectively suppressed. In the tire <NUM>, a break is less likely to occur in the band cord <NUM> of the full band <NUM>. The full band <NUM> can stably exhibit the function of suppressing a shape change. From this viewpoint, at least one belt ply <NUM> of the plurality of belt plies <NUM> included in the belt <NUM> is preferably located inward of the full band <NUM> in the radial direction. The at least one belt ply <NUM> located inward of the full band <NUM> more preferably has a width larger than the width of the full band <NUM>.

In the tire <NUM>, the first belt ply 42A and the second belt ply 42B are located inward of the full band <NUM> in the radial direction. The first belt ply 42A and the second belt ply 42B contribute to suppression of fluctuation of the tension of the band cord <NUM>. Since the first belt ply 42A and the second belt ply 42B are wider than the full band <NUM>, fluctuation of the tension of the band cord <NUM> is more effectively suppressed. In the tire <NUM>, a break is less likely to occur in the band cord <NUM> of the full band <NUM>. The full band <NUM> can stably exhibit the function of suppressing a shape change. From this viewpoint, at least two belt plies <NUM> of the plurality of belt plies <NUM> included in the belt <NUM> are more preferably located inward of the full band <NUM> in the radial direction. The at least two belt plies <NUM> located inward of the full band <NUM> further preferably have a width larger than the width of the full band <NUM>.

In the tire <NUM>, in the radial direction, the second belt ply 42B is located inward of the full band <NUM>, and the third belt ply 42C is located outward of the full band <NUM>. In the tire <NUM>, the full band <NUM> is interposed between the second belt ply 42B and the third belt ply 42C. As described above, the second belt ply 42B is wider than the full band <NUM>. The third belt ply 42C is also wider than the full band <NUM>. The plurality of belt plies <NUM> included in the belt <NUM> of the tire <NUM> include two belt plies <NUM> having a width larger than the width of the full band <NUM>, and the full band <NUM> is interposed between the two belt plies <NUM> having a large width. In the tire <NUM>, fluctuation of the tension of the band cord <NUM> included in the full band <NUM> is more effectively suppressed, so that a break is less likely to occur in the band cord <NUM> of the full band <NUM>. The full band <NUM> of the tire <NUM> can stably exhibit the function of suppressing a shape change. From this viewpoint, in the tire <NUM>, the plurality of belt plies <NUM> included in the belt <NUM> include two belt plies <NUM> having a width larger than the width of the full band <NUM>, and the full band <NUM> is interposed between the two belt plies <NUM> having a large width.

In the tire <NUM>, the first belt ply 42A, the second belt ply 42B, and the third belt ply 42C have a width larger than the width of the full band <NUM>. In the radial direction, the first belt ply 42A and the second belt ply 42B are located inward of the full band <NUM>, and the third belt ply 42C is located outward of the full band <NUM>. The pair of edge bands <NUM> are located outward of the third belt ply 42C in the radial direction. As described above, each edge band <NUM> is located outward of the end 48e of the full band <NUM> in the radial direction. The edge band <NUM> overlaps the end 48e of the full band <NUM> via the third belt ply 42C in the radial direction.

In the tire <NUM>, the full band <NUM> can stably exhibit the function of suppressing a shape change, and improvement of uneven wear resistance is achieved. From this viewpoint, preferably, in the tire <NUM>, the plurality of belt plies <NUM> included in the belt <NUM> include the first belt ply 42A located radially inward, the second belt ply 42B located outward of the first belt ply 42A in the radial direction, and the third belt ply 42C located outward of the second belt ply 42B in the radial direction, the first belt ply 42A, the second belt ply 42B, and the third belt ply 42C have a width larger than the width of the full band <NUM>, the first belt ply 42A and the second belt ply 42B are located inward of the full band <NUM> in the radial direction, the third belt ply 42C is located outward of the full band <NUM> in the radial direction, and each edge band <NUM> located outward of the full band <NUM> radially overlaps the end 48e of the full band <NUM> with the third belt ply 42C provided between each edge band <NUM> and the end 48e of the full band <NUM>.

As is obvious from the above description, according to the present invention, the heavy duty pneumatic tire <NUM> that can suppress a shape change due to running and achieve improvement of uneven wear resistance is obtained. The present invention exhibits a remarkable effect in the low-flatness heavy duty pneumatic tire <NUM> having a nominal aspect ratio of <NUM>% or less.

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

A heavy duty pneumatic tire (tire size = <NUM>/50R22. <NUM>) having the basic structure shown in <FIG> and having specifications shown in Table <NUM> below was obtained.

In Example <NUM>, each end of the full band was located outward of the shoulder circumferential groove in the axial direction. This is represented as "Y" in the cell for "full band end" in Table <NUM>. The distance We in the axial direction from the end of the full band to the inner end of the edge band was <NUM>. The ratio (SF/WS) of the distance SF in the axial direction from the shoulder circumferential groove to the end of the full band, to the width WS in the axial direction of the shoulder land portion, was <NUM>%. Two belt plies were provided radially inward of the full band. This is represented as "<NUM>" in the cell for "number of belt plies" in Table <NUM>.

A tire of Comparative Example <NUM> was obtained in the same manner as Example <NUM>, except that each end of the full band was located inward of the shoulder circumferential groove in the axial direction and no edge band was provided. The fact that each end of the full band was located inward of the shoulder circumferential groove in the axial direction is represented as "N" in the cell for "full band end" in Table <NUM>.

Tires of Examples <NUM> to <NUM> were obtained in the same manner as Example <NUM>, except that the distance We and the ratio (SF/WS) were as shown in Table <NUM> below.

Tires of Examples <NUM> to <NUM> were obtained in the same manner as Example <NUM>, except that the number of belt plies located radially inward of the full band, the distance We, and the ratio (SF/WS) were as shown in Table <NUM> below.

A test tire was fitted onto a rim (<NUM>×<NUM>) and inflated with air to adjust the internal pressure of the tire to a normal internal pressure. The tire was caused to run on a drum tester at a speed of <NUM>/h for <NUM>, and a profile of the case line on the inner side of the shoulder circumferential groove was obtained. The profile of the case line was compared with the profile of the case line before running to confirm a change in profile before and after running. The results are represented as indexes according to the following ratings in Table <NUM> and Table <NUM> below. A higher value represents that a change in profile is reduced. In the running test, a normal load was applied to the tire.

A test tire was fitted onto a rim (<NUM>×<NUM>) and inflated with air to adjust the internal pressure of the tire to a normal internal pressure. The tire was mounted to a drive shaft of a test vehicle (tractor head). A trailer loaded with luggage was towed by the test vehicle, and the test vehicle was caused to run on a general road. When the wear rate of the tire reached <NUM>% in terms of mass, the difference between the wear amount of the shoulder land portion and the wear amount of the middle land portion of the test tire was calculated. The results are represented as indexes with the value of Comparative Example <NUM> being regarded as <NUM>, in Table <NUM> and Table <NUM> below. A higher value represents that the difference in wear amount is smaller and the uneven wear resistance is better.

Each tire for which the above-described evaluation had been made for uneven wear resistance was inspected by sialography or X-ray to confirm the presence/absence of internal damage. When internal damage was confirmed, the tire was disassembled and it was confirmed whether this internal damage was a break of the band cord of the full band. The results are represented in Table <NUM> and Table <NUM> below according to the following ratings.

As shown in Table <NUM> and Table <NUM>, in the Examples, occurrence of a break of the band cord is suppressed, a shape change due to running is suppressed, and improvement of uneven wear resistance is achieved. From the evaluation results, advantages of the present invention are clear.

Claim 1:
A heavy duty pneumatic tire (<NUM>) having a nominal aspect ratio of <NUM> % or less and comprising a tread (<NUM>) that comes into contact with a road surface and a reinforcing layer (<NUM>) located inward of the tread (<NUM>) in a radial direction, wherein
at least three circumferential grooves (<NUM>) are formed on the tread (<NUM>), whereby at least four land portions (<NUM>) aligned in an axial direction are formed in the tread (<NUM>),
among the at least three circumferential grooves (<NUM>), a circumferential groove (<NUM>) located on each outer side in the axial direction is a shoulder circumferential groove (<NUM>),
a land portion (<NUM>) located outward of the shoulder circumferential groove (<NUM>) in the axial direction is a shoulder land portion (<NUM>),
the reinforcing layer (<NUM>) includes a belt (<NUM>) including a large number of belt cords (<NUM>) aligned with each other, and a band (<NUM>) including a spirally wound band cord (<NUM>),
the belt (<NUM>) includes a plurality of belt plies (<NUM>) aligned in the radial direction,
the band (<NUM>) includes a full band (<NUM>) having ends (48e) opposed to each other across an equator plane (CL), and a pair of edge bands (<NUM>) located outward of the ends (48e) of the full band (<NUM>) in the radial direction, and
each end (48e) of the full band (<NUM>) is located outward of the shoulder circumferential groove (<NUM>) in the axial direction,
characterized in that a ratio of a distance (SF) in the axial direction from the shoulder circumferential groove (<NUM>) to the end (48e) of the full band (<NUM>) to a width (WS) in the axial direction of the shoulder land portion (<NUM>) is not less than <NUM> % and not greater than <NUM> %, and in that the plurality of belt plies (<NUM>) includes two belt plies (<NUM>) having a width larger than a width of the full band (<NUM>), and the full band (<NUM>) is interposed between the two belt plies (<NUM>).