JP2023031213A - Heavy duty pneumatic tire - Google Patents

Abstract

To provide a heavy duty pneumatic tire 2 that can achieve suppression of mass increase and suppression of shape change due to running.SOLUTION: A tire 2 comprises a reinforcing layer 20 and a buffer layer 22. The reinforcing layer 20 comprises a belt 40 and a band 42. The belt 40 comprises a first belt ply 44A, a second belt play 44B and a third belt ply 44C. A direction in which belt cords 50 included in the first belt play 44A are tilted is opposite to a direction in which belt cords 50 included in the second first belt play 44A are tilted. The band 42 comprises a full band 46 and a pair of edge bands 48. The full band 46 is located between the first belt ply 44A and the second belt ply 44B. The buffer layer 22 is formed from crosslinked rubber.SELECTED DRAWING: Figure 1

Description

The present invention relates to heavy duty pneumatic tires.

At least three circumferential grooves are formed in the tread of a heavy-duty pneumatic tire (hereinafter referred to as "tire") from the viewpoint of drainage. Of the circumferential grooves formed on the tread, the circumferential grooves located on the outer side in the axial direction are the shoulder circumferential grooves. The rigidity of the portion with the circumferential groove is lower than the rigidity of the portion without the circumferential groove.

A belt or band is provided between the tread and the carcass. The belt is composed of a plurality of belt plies arranged in the radial direction. Each belt ply includes a number of parallel belt cords. Steel cords are usually used for belt cords. The band includes a helically wound band cord. Cords made of organic fibers such as nylon fibers or steel cords are used as band cords. By adjusting the configuration of the belt or band, the stiffness of the tread portion is controlled (see, for example, Patent Document 1 below).

Deformation and restoration are repeated in a running tire. This changes the shape of the tire. Since the contact shape changes, there is a concern that uneven wear resistance may decrease.
In the running state of the tire, the tread edge portion actively moves. Low-profile tires having an aspect ratio of 65% or less include tires having a wide tread surface. A tire with a low profile tends to undergo a greater change in shape than a tire with a high profile. In order to suppress shape change, adoption of a full band including spirally wound band cords is considered.

JP-A-9-105084

Belts for heavy-duty pneumatic tires are usually composed of four belt plies that are radially laminated. Adding a full band for deformation control increases the mass of the tire. Tire mass affects the fuel efficiency and load capacity of a vehicle. There is a need to establish a technology that can suppress shape changes due to running while considering the impact on tire mass.

The band cords included in the full band extend substantially in the circumferential direction. A force acts on the full band of the tire in a running state so as to expand radially from the inside to the outside. This force increases the tension in the band cord.

A tire flexes when it contacts the road surface. This reduces the tension in the band cords as the forces acting on the full band are reduced. When the tire recovers from the road surface, the force acting on the full band increases and the tension on the band cord increases. The band cords of a tire in running condition undergo repeated tension fluctuations. Depending on the degree of tension fluctuation, there is concern that the band cord may break. When the band cord breaks, the binding force is reduced. In this case, the full band may not be able to contribute to the suppression of shape change. Adding edge bands for full band protection further increases tire mass.

The present invention has been made in view of such circumstances. SUMMARY OF THE INVENTION An object of the present invention is to provide a heavy-duty pneumatic tire capable of suppressing an increase in mass and suppressing shape change due to running.

A heavy duty pneumatic tire according to an aspect of the present invention has a nominal aspect ratio of 65% or less. This heavy-duty pneumatic tire includes a tread with at least three circumferential grooves, a pair of sidewalls extending from the edge of the tread and positioned inside the tread in the radial direction, and the side walls in the radial direction. A pair of beads located inside the wall, a carcass located inside the tread and the pair of sidewalls and bridging between one bead and the other bead, and a carcass located inside the tread in the radial direction. A reinforcing layer and a cushioning layer radially positioned between the carcass and the reinforcing layer. Of the at least three circumferential grooves, the circumferential groove located on the outer side in the axial direction is the shoulder circumferential groove. The reinforcement layer includes a belt including a large number of belt cords arranged in parallel and a band including spirally wound band cords. The belt comprises a first belt ply, a second belt ply and a third belt ply. The first belt ply, the second belt ply and the third belt ply are arranged in this order in the radial direction. The inclination direction of the belt cords included in the first belt ply is opposite to the inclination direction of the belt cords included in the second belt ply. The band includes a full band having opposite ends across the equator and a pair of edge bands positioned radially outside the ends of the full band. The full band is located radially between the first belt ply and the second belt ply. The buffer layer is made of crosslinked rubber.

Preferably, in this heavy duty pneumatic tire, the complex elastic modulus of the buffer layer is 7.0 MPa or more and 12.0 MPa or less.

Preferably, in this heavy duty pneumatic tire, the end of the full band is positioned axially outside the shoulder circumferential groove.

Preferably, in this heavy duty pneumatic tire, the axial distance from the end of the full band to the inner end of the edge band is 10 mm or more.

Preferably, in this heavy-duty pneumatic tire, the end of the buffer layer is located inside the inner end of the edge band in the axial direction.

Preferably, in this heavy duty pneumatic tire, the ratio of the axial width of the buffer layer to the axial width of the first belt ply is 50% or more.

Preferably, the heavy-duty pneumatic tire includes a pair of cushion layers located outside the buffer layers in the axial direction. Each of the pair of cushioning layers is positioned between the reinforcing layer and the carcass at the ends of the reinforcing layer. In the axial direction, the end of the cushioning layer is located outside the inner end of the cushioning layer.

Preferably, in this heavy duty pneumatic tire, the complex elastic modulus of the buffer layer is higher than the complex elastic modulus of the cushion layer.

ADVANTAGE OF THE INVENTION According to this invention, the heavy duty pneumatic tire which can achieve suppression of a mass increase and suppression of a shape change by driving|running|working is obtained.

FIG. 1 is a cross-sectional view showing a portion of a heavy-duty pneumatic tire according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the configuration of the reinforcing layer. 3 is an enlarged cross-sectional view showing a portion of the tire of FIG. 1. FIG. 4 is a cross-sectional view along the equatorial plane of the tire of FIG. 1; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

In the present disclosure, a state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to the tire is referred to as a regular state.

In the present disclosure, the dimensions and angles of each portion of the tire are measured under normal conditions unless otherwise specified.
The dimensions and angles of each part in the meridian cross section of the tire, which cannot be measured with the tire mounted on a regular rim, are obtained by cutting the tire along a plane that includes the axis of rotation. to match the bead-to-bead distance of a tire on a regular rim.

Regular rim means a rim defined in the standard on which the tire relies. A "standard rim" in the JATMA standard, a "design rim" in the TRA standard, and a "measuring rim" in the ETRTO standard are regular rims.

The normal internal pressure means the internal pressure defined in the standard on which the tire relies. The "maximum air pressure" in JATMA standards, the "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standards, and the "INFLATION PRESSURE" in ETRTO standards are regular internal pressures.

Normal load means the load specified in the standard on which the tire relies. "Maximum load capacity" in the JATMA standard, "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "LOAD CAPACITY" in the ETRTO standard are normal loads.

In the present disclosure, the "nominal aspect ratio" is the "nominal aspect ratio" included in the "nominal aspect ratio" defined in JIS D4202 "Automobile tires - designation and specifications".

In the present disclosure, the tread portion of a tire is the portion of the tire that contacts the road surface. A bead is that part of the tire that fits onto the rim. A side portion is a portion of the tire that bridges between the tread portion and the bead portion. A tire includes a tread portion, a pair of bead portions, and a pair of side portions as parts.

In the present disclosure, the number of cords contained per 5 cm width of a tire element containing parallel cords is expressed as the density of the cords contained in this element (unit: ends/5 cm). Cord densities are given in cross-sections of the element obtained by cutting in a plane perpendicular to the length of the cord, unless otherwise stated.

In the present disclosure, the crosslinked rubber is a molded article of a rubber composition obtained by pressurizing and heating the rubber composition. A rubber composition is an uncrosslinked rubber obtained by mixing a base rubber and chemicals in a kneader such as a Banbury mixer. Crosslinked rubber is also called vulcanized rubber and rubber composition is also called unvulcanized rubber.

Base rubbers include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile-butadiene rubber (NBR). and butyl rubber (IIR). Chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, anti-aging agents, processing aids, sulfur and Vulcanization accelerators are exemplified. The selection of the base rubber and chemicals, the content of the selected chemicals, and the like are appropriately determined according to the specifications of each element to which the rubber composition is applied, such as the tread and sidewalls.

In the present disclosure, among the elements constituting the tire, the complex elastic modulus of the element made of crosslinked rubber at a temperature of 70 ° C. conforms to the provisions of JIS K6394 and is measured by a viscoelastic spectrometer ("VES ”) under the following conditions.
Initial strain = 10%
Dynamic strain = 2%
Frequency = 10Hz
Deformation Mode = Tensile For this measurement, a specimen is sampled from the tire. If a test piece cannot be sampled from the tire, a sheet-like crosslinked rubber (hereinafter referred to as a rubber sheet A specimen is sampled from the

In the present disclosure, the breaking load of the steel cord is measured according to JIS G3510. The pull speed to obtain the cutting load is set at 50 mm/min.

FIG. 1 shows part of a heavy-duty pneumatic tire 2 (hereinafter also simply referred to as "tire 2") according to one embodiment of the present invention. This tire 2 is mounted on a vehicle such as a truck or a bus. The nominal aspect ratio of this tire 2 is 65% or less. In other words, this tire 2 has a nominal aspect ratio of 65% or less. This tire 2 is a low-profile tire.

FIG. 1 shows part of a cross section of this tire 2 along a plane containing the axis of rotation of the tire 2 (hereinafter referred to as a meridional cross section). In FIG. 1 , the lateral direction is the axial direction of the tire 2 and the vertical direction is the radial direction of the tire 2 . The direction perpendicular to the paper surface of FIG. 1 is the circumferential direction of the tire 2 . A dashed-dotted line CL represents the equatorial plane of the tire 2 .

The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of beads 8, a pair of chafers 10, a carcass 12, a pair of cushioning layers 14, an inner liner 16, a pair of steel fillers 18, a reinforcing layer 20, and a shock absorber. A layer 22 is provided.

The tread 4 contacts the road surface on its outer surface. This outer surface is the tread surface 24 . Reference character PC in FIG. 1 indicates an intersection point between the tread plane 24 and the equatorial plane. The point of intersection PC is also referred to as the equator of tire 2 .

In FIG. 1, the symbol PE is the edge of the tread surface 24. As shown in FIG. A double arrow WT is the width of the tread surface 24 . The tread surface 24 width WT is the axial distance from the edge PE of one tread surface 24 to the edge PE of the other tread surface 24 . If the end PE of the tread surface 24 of the tire 2 cannot be identified from the appearance, a normal load is applied to the tire 2 in a normal state, the camber angle is set to 0°, and the tire 2 is brought into contact with a flat surface. The location on the tread surface 24 corresponding to the axially outer edge of the resulting ground contact patch is defined as the edge PE of the tread surface 24 .

The tread 4 includes a base portion 26 and a cap portion 28 located radially outside the base portion 26 . The base portion 26 is made of low heat-generating crosslinked rubber. The cap portion 28 is made of crosslinked rubber in consideration of abrasion resistance and grip performance. As shown in FIG. 1, the base portion 26 covers the entire reinforcement layer 20 . The cap portion 28 covers the entire base portion 26 .

In this tire 2 , at least three circumferential grooves 30 are cut in the tread 4 . Four circumferential grooves 30 are formed in the tread 4 of the tire 2 shown in FIG. These circumferential grooves 30 are arranged in parallel in the axial direction and extend continuously in the circumferential direction.

Of the four circumferential grooves 30 formed on the tread 4, the circumferential groove 30 located on the outer side in the axial direction is the shoulder circumferential groove 30s. The middle circumferential groove 30m is the circumferential groove 30 located inside the shoulder circumferential groove 30s in the axial direction. In this tire 2, the four circumferential grooves 30 are composed of a pair of middle circumferential grooves 30m and a pair of shoulder circumferential grooves 30s.

In the tire 2, the axial width of the middle circumferential groove 30m is preferably 2% or more and 10% or less of the tread surface 24 width WT from the viewpoint of contribution to drainage performance and traction performance. The depth of the middle circumferential groove 30m is preferably 13 mm or more and 25 mm or less. The axial width of the shoulder circumferential groove 30s is preferably 1% or more and 7% or less of the tread surface 24 width TW. The depth of the shoulder circumferential groove 30s is preferably 13 mm or more and 25 mm or less.

As mentioned above, the tread 4 is cut with at least three circumferential grooves 30 . Thereby, at least four land portions 32 are formed on the tread 4 . Four circumferential grooves 30 are formed in the tread 4 of the tire 2 shown in FIG. 1 to form five land portions 32 . These land portions 32 are arranged in parallel in the axial direction and extend continuously in the circumferential direction.

Of the five land portions 32 formed on the tread 4, the land portion 32 located on the outer side in the axial direction is the shoulder land portion 32s. The shoulder land portion 32 s is positioned axially outside the shoulder circumferential groove 30 s and includes the edge PE of the tread surface 24 . The land portion 32 located inside the shoulder land portion 32s in the axial direction is the middle land portion 32m. The land portion 32 located inside the middle land portion 32m in the axial direction is the center land portion 32c. In this tire 2, the five land portions 32 are composed of a center land portion 32c, a pair of middle land portions 32m, and a pair of shoulder land portions 32s.

In this tire 2, the axial width of the center land portion 32c is 10% or more and 18% or less of the tread surface 24 width WT. The axial width of the middle land portion 32m is 10% or more and 18% or less of the tread surface 24 width WT. The axial width of the shoulder land portion 32s is 15% or more and 25% or less of the tread surface 24 width WT. The axial width of the land portion 32 is represented by the axial width of the top surface of the land portion 32 forming part of the tread surface 24 .

In this tire 2, among the land portions 32 formed in the tread 4, the land portion 32 located in the center in the axial direction, that is, the center land portion 32c is located on the equatorial plane. This tire 2 has a tread 4 configured such that land portions 32 are positioned on the equatorial plane. The tread 4 may be configured such that the circumferential grooves 30 are positioned on the equatorial plane.

Each sidewall 6 continues to the edge of the tread 4 . Sidewalls 6 extend radially inward from the ends of tread 4 . The sidewall 6 is positioned radially inside the tread 4 . The sidewall 6 is made of crosslinked rubber.

Each bead 8 is located inside the sidewall 6 in the radial direction. Bead 8 comprises core 34 and apex 36 .

The core 34 extends circumferentially. Core 34 comprises a wound steel wire. Core 34 has a substantially hexagonal cross-sectional shape.

Apex 36 is located radially outside core 34 . The apex 36 comprises an inner apex 36u and an outer apex 36s. Inner apex 36u extends radially outward from core 34 . The outer apex 36s is located radially outside the inner apex 36u. The inner apex 36u is made of hard crosslinked rubber. The outer apex 36s is made of crosslinked rubber that is softer than the inner apex 36u.

Each chafer 10 is located outside the bead 8 in the axial direction. The chafer 10 is positioned inside the sidewall 6 in the radial direction. Chafer 10 contacts a rim (not shown). The chafer 10 is made of crosslinked rubber in consideration of abrasion resistance.

The carcass 12 is positioned inside the tread 4 , the pair of sidewalls 6 and the pair of chafers 10 . A carcass 12 spans between one bead 8 and the other bead 8 .

Carcass 12 includes at least one carcass ply 38 . The carcass 12 of this tire 2 consists of one carcass ply 38 . The carcass plies 38 are folded axially inwardly outwardly around each core 34 . The carcass ply 38 includes a ply body 38a extending from one core 34 toward the other core 34, and a pair of folded backs that are connected to the ply body 38a and folded back around each core 34 from the inner side in the axial direction to the outer side. and a portion 38b.

Although not shown, the carcass ply 38 includes a number of parallel carcass cords. These carcass cords are covered with a topping rubber. Each carcass cord intersects the equatorial plane. In this tire 2, the angle formed by the carcass cords with respect to the equatorial plane (hereinafter referred to as the crossing angle of the carcass cords) is 70° or more and 90° or less. This carcass 12 has a radial structure. The carcass cords of this tire 2 are steel cords.

Each cushion layer 14 is located outside the cushion layer 22 in the axial direction. The cushioning layer 14 is located between the reinforcing layer 20 and the carcass 12 (more specifically, the ply body 38a of the carcass ply 38) at the end 20e of the reinforcing layer 20. As shown in FIG. In the axial direction, the inner end 14ue of the cushion layer 14 is located inside the end 20e of the reinforcing layer 20. As shown in FIG. In the axial direction, the outer edge 14se of the cushioning layer 14 lies outside the edge 20e of the reinforcing layer 20. As shown in FIG. In the radial direction, the outer edge 14se of the cushion layer 14 lies inside the edge 20e of the reinforcing layer 20. As shown in FIG. The cushion layer 14 is made of soft crosslinked rubber. From the viewpoint of preventing damage to the end 20e of the reinforcing layer 20, the complex elastic modulus E*c of the cushion layer 14 is preferably 3.0 MPa or more and 6.0 MPa or less.

An inner liner 16 is positioned inside the carcass 12 . The inner liner 16 is joined to the inner surface of the carcass 12 via insulation (not shown). The inner liner 16 constitutes the inner surface of the tire 2 . The inner liner 16 is made of crosslinked rubber with excellent air shielding properties. The inner liner 16 keeps the internal pressure of the tire 2 .

Each steel filler 18 is located in the bead portion B. The steel filler 18 is folded axially from the inside to the outside around the core 34 along the carcass plies 38 . Although not shown, the steel filler 18 includes a large number of parallel filler cords. Steel cords are used as filler cords.

The reinforcing layer 20 is located inside the tread 4 in the radial direction. A reinforcing layer 20 is located between the tread 4 and the carcass 12 . The reinforcing layer 20 includes belts 40 and bands 42 .

Belt 40 includes at least three belt plies 44 . Each belt ply 44 is arranged such that both ends 44e face each other across the equatorial plane.
The belt 40 includes a first belt ply 44A, a second belt ply 44B and a third belt ply 44C. The first belt ply 44A, the second belt ply 44B and the third belt ply 44C are radially arranged in this order.
In this tire 2, of the at least three belt plies 44 that make up the belt 40, the belt ply 44 positioned radially innermost is the first belt ply 44A. A second belt ply 44B and a third belt ply 44C are arranged. The belt 40 includes a first belt ply 44A, a second belt ply 44B positioned radially outside the first belt ply 44A, and a third belt ply 44C positioned radially outside the second belt ply 44B. and In this tire 2, the belt 40 may be configured such that a first belt ply 44A, a second belt ply 44B, and a third belt ply 44C are arranged in order from the radially outer side.

In this tire 2 , the belt 40 may be composed of four or more belt plies 44 . From the viewpoint of weight reduction of the tire 2, the belt 40 is preferably composed of three belt plies 44, that is, a first belt ply 44A, a second belt ply 44B and a third belt ply 44C.

As shown in FIG. 1, the end 44Ae of the first belt ply 44A is located axially outside the shoulder circumferential groove 30s. The end 44Be of the second belt ply 44B is positioned axially outside the shoulder circumferential groove 30s. An end 44Ce of the third belt ply 44C is positioned axially outside the shoulder circumferential groove 30s. In this tire 2, the end 44Ce of the third belt ply 44C may be located inside the shoulder circumferential groove 30s in the axial direction. From the viewpoint of damage prevention, the third belt ply 44C is arranged so that the end 44Ce of the third belt ply 44C does not overlap the shoulder circumferential groove 30s in the radial direction.

In FIG. 1, the length indicated by symbol W1 is the axial width of the first belt ply 44A. The length indicated by symbol W2 is the axial width of the second belt ply 44B. The length indicated by symbol W3 is the axial width of the third belt ply 44C. The axial width of each belt ply 44 is the axial distance from one end 44e of the belt ply 44 to the other 44 end e.

In this tire 2, the first belt ply 44A has the widest axial width W1, and the third belt ply 44C has the narrowest axial width W3. The axial width W2 of the second belt ply 44B is narrower than the axial width W1 of the first belt ply 44A and wider than the axial width W3 of the third belt ply 44C.
In this tire 2, of the at least three belt plies 44 forming the belt 40, the radially innermost belt ply 44 is the first belt ply 44A having the widest axial width W1. This belt 40 effectively increases the rigidity of the tread portion T. As shown in FIG.

In this tire 2, from the viewpoint of effectively increasing the rigidity of the tread portion T, the ratio (W1/WT) of the axial width W1 of the first belt ply 44A to the width WT of the tread 4 is 0.75 or more and 0.95. The following are preferred. The ratio (W2/WT) of the axial width W2 of the second belt ply 44B to the width WT of the tread 4 is preferably 0.70 or more and 0.90 or less. The axial width W3 of the third belt ply 44C is appropriately set according to the specifications of the tire 2. As shown in FIG.

In this tire 2, the axial width of the belt 40 is represented by the axial width of the belt ply 44 having the widest axial width. As previously mentioned, the first belt ply 44A has the widest axial width W1. The axial width of the belt 40 of the tire 2 is represented by the axial width W1 of the first belt ply 44A. In this tire 2 , the end 44Ae of the first belt ply 44A is the end 40e of the belt 40 . The edge 40 e of the belt 40 is also the edge 20 e of the reinforcing layer 20 .

Band 42 includes a full band 46 and a pair of edge bands 48 . The full band 46 is arranged so that both ends 46e face each other across the equatorial plane. Axially, the end 46e of the full band 46 is located inside the end 40e of the belt 40. As shown in FIG.
A pair of edge bands 48 are axially spaced apart across the equatorial plane. In this tire 2, a third belt ply 44C forming part of the belt 40 is positioned between a pair of edge bands 48. As shown in FIG.

In this tire 2 each edge band 48 is located between the tread 4 and the full band 46 . Edge band 48 is located radially outside end 46 e of full band 46 . In the axial direction, the inner edge 48ue of the edge band 48 lies inside the edge 46e of the full band 46. As shown in FIG. Outer end 48se of edge band 48 is located axially outside end 46e of full band 46 . Edge band 48 radially overlaps end 46 e of full band 46 . The position of the outer end 48se of the edge band 48 may coincide with the position of the end 46e of the full band 46 in the axial direction. In this case also, the edge band 48 is located radially outside the end 46 e of the full band 46 .

FIG. 2 shows the structure of the reinforcing layer 20. As shown in FIG. In FIG. 2 , the lateral direction is the axial direction of the tire 2 and the vertical direction is the circumferential direction of the tire 2 . The direction perpendicular to the paper surface of FIG. 2 is the radial direction of the tire 2 . The front side of the paper surface is the radially outer side, and the back side is the radially inner side.

As shown in FIG. 2, each belt ply 44 forming the belt 40 includes a large number of belt cords 50 arranged in parallel. In FIG. 2, the belt cords 50 are represented by solid lines for convenience of explanation, but the belt cords 50 are covered with the topping rubber 52 .
The belt cord 50 of this tire 2 is a steel cord. The density of the belt cords 50 in each belt ply 44 is 15 ends/5 cm or more and 30 ends/5 cm or less.

The belt cords 50 in each belt ply 44 are inclined with respect to the circumferential direction.
The inclination direction of the belt cords 50 included in the first belt ply 44A (hereinafter referred to as the inclination direction of the first belt cords 50A) is the same as the inclination direction of the belt cords 50 included in the second belt ply 44B (hereinafter referred to as the second belt The direction of inclination of the cord 50B) is opposite to the direction of inclination of the cord 50B. In this tire 2, the belt 40 is configured such that the first belt cord 50A and the second belt cord 50B intersect.
The direction of inclination of the belt cords 50 included in the third belt ply 44C (hereinafter referred to as the direction of inclination of the third belt cords 50C) is the same as the direction of inclination of the second belt cords 50B. The inclination direction of the third belt cord 50C may be opposite to the inclination direction of the second belt cord 50B.

In FIG. 2, the angle θ1 is the angle formed by the belt cord 50 included in the first belt ply 44A with respect to the equator plane (hereinafter referred to as the inclination angle θ1 of the first belt cord 50A). The angle θ2 is the angle formed by the belt cord 50 included in the second belt ply 44B with respect to the equator plane (hereinafter referred to as the inclination angle θ2 of the second belt cord 50B). The angle θ3 is the angle formed by the belt cord 50 included in the third belt ply 44C with respect to the equator plane (hereinafter referred to as the inclination angle θ3 of the third belt cord 50C).

In this tire 2, the inclination angle θ1 of the first belt cord 50A, the inclination angle θ2 of the second belt cord 50B, and the inclination angle θ3 of the third belt cord 50C are preferably 10° or more and 60° or less.
From the viewpoint of effectively restraining the movement of the tread portion T and obtaining a stable ground contact surface, the inclination angle θ1 of the first belt cord 50A is more preferably 15° or more, and more preferably 30° or less. The inclination angle θ1 of the first belt cord 50A is more preferably 20° or less. The inclination angle θ2 of the second belt cord 50B is more preferably 15° or more, and more preferably 30° or less. The inclination angle θ2 of the second belt cords 50B is more preferably 20° or less. The inclination angle θ3 of the third belt cord 50C is more preferably 15° or more, and more preferably 50° or less.

As described above, the carcass ply 38 includes carcass cords, and the crossing angle of the carcass cords is 70° or more and 90° or less. In this tire 2, the belt ply 44 closest to the carcass ply 38 is the first belt ply 44A. In this tire 2, the difference between the inclination angle θ1 of the first belt cords 50A and the intersection angle of the carcass cords is large.

As shown in FIG. 2, the full band 46 and edge band 48 that make up the band 42 include helically wound band cords 54 . In FIG. 2 , the band cord 54 is represented by a solid line for convenience of explanation, but the band cord 54 is covered with a topping rubber 56 .

In this tire 2, the band cords 54 are steel cords or cords made of organic fibers (hereinafter referred to as organic fiber cords). When an organic fiber cord is used as the band cord 54, examples of the organic fiber include nylon fiber, polyester fiber, rayon fiber, and aramid fiber. In this tire 2, the same cord may be used for the band cord 54F of the full band 46 and the band cord 54E of the edge band 48, or different cords may be used. The band cords 54 used for the full band 46 and edge band 48 are determined according to the specifications of the tire 2 .

As previously mentioned, the full band 46 includes a helically wound band cord 54F. Full band 46 has a jointless structure. In the full band 46, the angle formed by the band cords 54F with respect to the circumferential direction is preferably 5° or less, more preferably 2° or less. The band cord 54F extends substantially in the circumferential direction.

The density of the band cords 54F in the full band 46 is 20 ends/5 cm or more and 35 ends/5 cm or less. The density of the band cords 54F is represented by the number of sections of the band cords 54F included per 5 cm width of the full band 46 in the section of the full band 46 included in the meridional section.

As previously mentioned, the edge band 48 includes a spirally wound band cord 54E. The edge band 48 has a jointless construction. In the edge band 48, the angle formed by the band cords 54E with respect to the circumferential direction is preferably 5° or less, more preferably 2° or less. A band cord 54E of the edge band 48 extends substantially in the circumferential direction.

The density of the band cords 54E in the edge band 48 is 20 ends/5 cm or more and 35 ends/5 cm or less. The density of the band cords 54E is the number of sections of the band cords 54E included per 5 cm width of the edge band 48 in the section of the edge band 48 along the plane perpendicular to the extending direction of the band cord 54E. is represented by

FIG. 3 shows a part of the cross-section of the tire 2 shown in FIG. This FIG. 3 shows the tread portion T of this tire 2 .

In this tire 2, the end 44Ae of the first belt ply 44A and the end 44Be of the second belt ply 44B are covered with the rubber layer 58, respectively. Between the end 44Ae of the first belt ply 44A covered with the rubber layer 58 and the end 44Be of the second belt ply 44B, a plurality of rubber layers 58 are further arranged. In this tire 2, an edge member 60 composed of a total of four rubber layers 58 is formed between the end 44Ae of the first belt ply 44A and the end 44Be of the second belt ply 44B. The edge member 60 is made of crosslinked rubber. The edge member 60 contributes to maintaining the distance between the end 44Ae of the first belt ply 44A and the end 44Be of the second belt ply 44B. In this tire 2, change in the positional relationship between the end 44Ae of the first belt ply 44A and the end 44Be of the second belt ply 44B due to running is suppressed. Edge member 60 is part of reinforcing layer 20 . The reinforcing layer 20 of this tire 2 includes a pair of edge members 60 in addition to the belt 40 and band 42 .

The cushioning layer 22 is located radially between the carcass 12 and the reinforcing layer 20 . The buffer layer 22 is arranged such that both ends 22e face each other across the equatorial plane. Axially, the edge 22e of the cushioning layer 22 lies inside the edge 46e of the full band 46. As shown in FIG.
In FIG. 1, the length indicated by symbol WB is the axial width of the buffer layer 22 . The axial width of the buffer layer 22 is the axial distance from one end 22e of the buffer layer 22 to the other end 22e.

In this tire 2, the cushioning layer 22 is positioned radially between the carcass ply 38 and the first belt ply 44A. The cushioning layer 22 is positioned between the pair of cushioning layers 14 in the axial direction. The buffer layer 22 of the tire 2 is made of a crosslinked rubber different from the crosslinked rubber of the cushion layer 14 .

As described above, in this tire 2, the full band 46 is arranged so that both ends 46e face each other across the equatorial plane. The full bands 46 extend axially from the equatorial plane toward respective ends 46e. Further, in this tire 2 , the edge band 48 is positioned radially outside the end 46 e of the full band 46 .

Although this tire 2 is a low-flat tire, the full band 46 and the pair of edge bands 48 effectively suppress the deformation of the tread portion T. As shown in FIG. Since a change in the shape of the tire 2, for example, a change in the outline of the carcass 12 (hereinafter also referred to as a case line) is suppressed, a change in contact shape is suppressed.

As mentioned above, the band cords 54F included in the full band 46 extend substantially in the circumferential direction. A force acts on the full band 46 of the tire 2 in the running state so as to expand radially from the inside to the outside. This force increases the tension in the band cord 54F.

A tire flexes when it contacts the road surface. This reduces the tension in the band cords as the forces acting on the full band are reduced. When the tire recovers from the road surface, the force acting on the full band increases and the tension on the band cord increases. The band cords of a tire in running condition undergo repeated tension fluctuations. Depending on the degree of tension fluctuation, there is concern that the band cord may break. When the band cord breaks, the binding force is reduced. In this case, the full band may not be able to contribute to the suppression of shape change.

In this tire 2 , the edge band 48 restrains the end 46 e of the full band 46 . Since the tension fluctuation of the band cord 54F included in the full band 46 is suppressed, the band cord 54F is prevented from breaking due to the tension fluctuation. The full band 46 of the tire 2 can stably exhibit the function of suppressing shape change. Edge band 48 is narrower than full band 46 . Therefore, the band cords 54E of the edge band 48 are less likely to experience tension fluctuations like the full band 46 does. The band cord 54E of the edge band 48 is less likely to break.

Further, in this tire 2, a full band 46 is positioned radially between the first belt ply 44A and the second belt ply 44B.
The first belt ply 44A and the second belt ply 44B restrain forces acting on the full band 46 . In particular, since the belt cords 50 included in the first belt ply 44A and the belt cords 50 included in the second belt ply 44B intersect each other, the force acting on the full band 46 is effectively suppressed. Since the change in tension of the band cords 54 included in the full band 46 is suppressed, the occurrence of breakage of the band cords 54 due to this change in tension is suppressed. The full band 46 of the tire 2 can stably exhibit the function of suppressing shape change.

As described above, in the tire 2, of the belt plies 40 that make up the belt 40, the first belt ply 44A is closest to the ply body 38a of the carcass ply 38, and the first belt cord included in the first belt ply 44A is the first belt ply 44A. The difference between the inclination angle θ1 of 50A and the intersection angle of the carcass cords in the ply body 38a is large.

When the tire 2 is mounted on a rim (not shown) and the inside of the tire 2 is filled with air, the tire 2 is inflated. At this time, a strain is generated between the carcass ply 38 and the first belt ply 44A due to the difference between the crossing angle of the carcass cords and the inclination angle θ1 of the first belt cords 50A. Depending on the degree of strain, damage may occur between the carcass ply 38 and the first belt ply 44A, and the belt 40 may not restrain the carcass 12 sufficiently.
In the conventional tire, the inclination angle of the belt cord is set between the belt ply corresponding to the first belt ply 44A of the tire 2 (hereinafter referred to as the corresponding ply) and the carcass ply in order to reduce distortion. A belt ply (hereinafter referred to as an angled ply) is provided which is adjusted to an angle smaller than the angle and larger than the inclination angle of the belt cord of the corresponding ply. In a conventional tire, the belt is composed of at least four belt plies in order to secure the binding force and relax the strain.

In this tire 2 , a buffer layer 22 is provided between the carcass 12 and the reinforcing layer 20 . Specifically, a buffer layer 22 is provided between the carcass ply 38 and the first belt ply 44A.
The buffer layer 22 is made of crosslinked rubber. The cushioning layer 22 does not include cords like the carcass ply 38 and the first belt ply 44A. The cushioning layer 22 is softer than the carcass ply 38 and the first belt ply 44A. The cushioning layer 22 contributes to the relaxation of strain generated between the carcass ply 38 and the first belt ply 44A due to the difference between the crossing angle of the carcass cords and the inclination angle θ1 of the first belt cords 50A.
In this tire 2, since the carcass 12 and the belt 40 are kept together, the belt 40 can sufficiently restrain the carcass 12.例文帳に追加In this tire 2, the full band 46 and the pair of edge bands 48, that is, the band 42 can sufficiently exhibit the function of suppressing shape change. This buffer layer 22 contributes to suppression of shape change.
Further, since the cushioning layer 22 does not contain cords, the cushioning layer 22 is lighter than the angled plies provided for strain relief in conventional tires. Although the tire 2 is provided with the full band 46 and the pair of edge bands 48 for suppressing shape change, an increase in mass is suppressed.

In the conventional tire, the inclination angle of the belt cord included in the inclined ply is larger than the inclination angle of the belt cord included in the corresponding ply, so the contribution of the inclined ply to securing the binding force of the belt is low. Although the belt 40 of the tire 2 is composed of at least three belt plies 44, it exerts a binding force comparable to that of a conventional belt composed of at least four belt plies. In this tire 2, shape change is suppressed to the same extent as in the case where the full band 46 is combined with the conventional belt.

In this tire 2, suppression of increase in mass and suppression of change in shape due to running are achieved. This tire 2 can achieve an improvement in uneven wear resistance while suppressing an increase in rolling resistance.

FIG. 4 shows a section along the equatorial plane of the tire 2 shown in FIG. This FIG. 4 shows a cross section of the tread portion T. As shown in FIG. In FIG. 4, the length indicated by symbol TC is the distance between the carcass 12 and the reinforcing layer 20. As shown in FIG. Specifically, this distance TC is the distance between the carcass ply 38 and the first belt ply 44A.
This distance TC is represented by the distance (inter-cord distance) between the carcass cords 62 included in the carcass ply 38 and the first belt cords 48A included in the first belt ply 44A on the equator plane. This distance TC is the thickness of the rubber component located between the carcass cords 62 and the first belt cords 48A. The rubber component includes the buffer layer 22 . This distance TC is controlled mainly by adjusting the thickness of the buffer layer 22 .

In this tire 2, the distance TC between the carcass 12 and the reinforcing layer 20 is preferably 1.5 mm or more and 3.0 mm or less.
By setting the distance TC to 1.5 mm or more, the rubber component between the carcass 12 and the reinforcing layer 20 can effectively contribute to strain relaxation. The occurrence of damage caused by this rubber component is prevented. From this point of view, the distance TC is more preferably 1.8 mm or more.
By setting the distance TC to 3.0 mm or less, the rubber component between the carcass 12 and the reinforcing layer 20 can contribute to suppressing the increase in mass. From this point of view, the distance TC is more preferably 2.5 mm or less, and even more preferably 2.0 mm or less.

In this tire 2, the complex elastic modulus E*b of the buffer layer 22 is preferably 7.0 MPa or more and 12.0 MPa or less.
By setting the complex elastic modulus E*b of the buffer layer 22 to 7.0 MPa or more, the tire 2 can constitute the buffer layer 22 having an appropriate thickness. This buffer layer 22 can contribute to suppression of mass increase. From this point of view, the complex elastic modulus E*b of the buffer layer 22 is more preferably 8.0 MPa or more, more preferably 9.0 MPa or more.
By setting the complex elastic modulus E*b of the buffer layer 22 to 12.0 MPa or less, the buffer layer 22 can effectively contribute to strain relaxation. In this tire 2, the occurrence of damage caused by the buffer layer 22 is prevented. From this point of view, the complex elastic modulus E*b of the buffer layer 22 is more preferably 11.0 MPa or less, and even more preferably 10.0 MPa or less.

In FIG. 3 , the length indicated by symbol TB is the thickness of the buffer layer 22 . This thickness TB is measured along the equatorial plane.

In this tire 2, the thickness TB of the buffer layer 22 is preferably 0.5 mm or more and 2.0 mm or less.
By setting the thickness TB of the buffer layer 22 to 0.5 mm or more, the buffer layer 22 can effectively contribute to strain relaxation. In this tire 2, the occurrence of damage caused by the buffer layer 22 is prevented. From this point of view, the thickness TB of the buffer layer 22 is more preferably 0.8 mm or more.
By setting the thickness TB of the buffer layer 22 to 2.0 mm or less, the buffer layer 22 can contribute to suppression of increase in mass. From this point of view, the thickness TB of the buffer layer 22 is more preferably 1.5 mm or less, and even more preferably 1.0 mm or less.

In the running state of the tire, the tread edge portion actively moves. The rigidity of the portion with the circumferential groove is lower than the rigidity of the portion without the circumferential groove.
As described above, this tire 2 is a low-flat tire. When this tire 2 has a wide tread surface 24, the shoulder circumferential grooves 30s of this tire 2 are positioned axially outward compared to those of a highly flat tire. In this case, there is a concern that the shape change in the vicinity of the shoulder circumferential groove 30s becomes large.

In this tire 2, the end 46e of the full band 46 is located outside the shoulder circumferential groove 30s in the axial direction. The full band 46 is located radially inside the shoulder circumferential groove 30s.

Although this tire 2 is a low-flat tire, the full band 46 effectively suppresses deformation in the vicinity of the shoulder circumferential groove 30s. Since the edge band 48 is positioned outside the end 46e of the full band 46, this deformation is sufficiently suppressed. In this tire 2, shape change is effectively suppressed particularly in the vicinity of the shoulder circumferential groove 30s. From this point of view, in this tire 2, the end 46e of the full band 46 is preferably located outside the shoulder circumferential groove 30s in the axial direction.

In FIG. 3, the double arrow SF is the axial distance from the shoulder circumferential groove 30s, more specifically, the outer edge of the shoulder circumferential groove 30s to the end 46e of the full band 46. As shown in FIG. A double arrow WS indicates the axial width of the shoulder land portion 32s. The axial width WS extends from the inner end of the top surface of the shoulder land portion 32s (that is, the outer edge of the shoulder circumferential groove 30s) to the outer end of the top surface (the edge PE of the tread surface 24 in this tire 2). is represented by the axial distance of

In this tire 2, the ratio (SF/WS) of the axial distance SF from the shoulder circumferential groove 30s to the end 46e of the full band 46 to the axial width WS of the shoulder land portion 32s is preferably 50% or less. As a result, the end 46e of the full band 46 is arranged away from the end portion of the tread 4 that actively moves in the running state, so tension fluctuations in the band cord 54 are suppressed. In this tire 2, occurrence of breakage of the band cord 54 is suppressed. The full band 46 of this tire 2 contributes to suppression of shape change. From this point of view, this ratio (SF/WS) is more preferably 35% or less, and even more preferably 25% or less.

By setting the ratio (SF/WS) to 10% or more, the end 46e of the full band 46 is arranged at an appropriate distance from the shoulder circumferential groove 30s, specifically the bottom of the shoulder circumferential groove 30s. be done. In this tire 2, the occurrence of damage originating from the bottom of the shoulder circumferential groove 30s is suppressed. Since the width of the full band 46 is ensured, the full band 46 contributes to suppressing the shape change of the tire 2 . From this point of view, this ratio (SF/WS) is more preferably 15% or more.

As described above, in this tire 2, the end 46e of the full band 46 is located inside the end 40e of the belt 40 in the axial direction. Belt 40 is wider than full band 46 . This belt 40 restrains the end 46 e of the full band 46 . This belt 40 contributes to suppressing tension fluctuations of the band cords 54 included in the full band 46 . Since the occurrence of breakage of the band cord 54 due to tension fluctuation is suppressed, the full band 46 can stably exhibit the function of suppressing shape change. From this point of view, the end 46e of the full band 46 is preferably located inside the end 40e of the belt 40 in the axial direction.

In this tire 2, the first belt ply 44A is positioned inside the full band 46 in the radial direction, and the second belt ply 44B is positioned outside the full band 46. As shown in FIG. A full band 46 is sandwiched between a first belt ply 44A and a second belt ply 44B.
As shown in FIG. 3, in the axial direction, the end 46e of the full band 46 is located inside the end 44Ae of the first belt ply 44A, and the end 46e of the full band 46 is located inside the end 44Be of the second belt ply 44B. located inside. In other words, the first belt ply 44A is wider than the full band 46. The second belt ply 44B is also wider than the full band 46. In this tire 2, the full band 46 is sandwiched between a first belt ply 44A wider than the full band 46 and a second belt ply 44B. Since the tension variation of the band cords 54 included in the full band 46 is more effectively suppressed, the band cords 54 of the full band 46 are less likely to break. The full band 46 of the tire 2 can stably exhibit the function of suppressing shape change. From this point of view, in this tire 2, the full band 46 is located between the first belt ply 44A and the second belt ply 44B in the radial direction, and the end 46e of the full band 46 is located axially between the first belt ply 44A and the first belt ply 44A. The end 46e of the full band 46 is preferably positioned inside the end 44Be of the second belt ply 44B.

As described above, in this tire 2, the inner end 48ue of the edge band 48 is positioned inside the end 46e of the full band 46 in the axial direction. 3, the length We is the axial distance from the end 46e of the full band 46 to the inner end 48ue of the edge band 48. In FIG.

In this tire 2, the axial distance We from the end 46e of the full band 46 to the inner end 48ue of the edge band 48 is preferably 10 mm or more. This effectively constrains edge band 48 to end 46 e of full band 46 . Since the change in tension of the band cords 54 included in the full band 46 is suppressed, the occurrence of breakage of the band cords 54 due to this change in tension is suppressed. The full band 46 of the tire 2 can exhibit the function of suppressing shape change more stably. From this point of view, the axial distance We is preferably 20 mm or more. From the viewpoint of suppressing the influence of the edge band 48 on the mass of the tire 2, the axial distance We is preferably 50 mm or less.

In this tire 2, the setting of the position of the inner end 48ue of the edge band 48 takes into consideration the involvement in the occurrence of damage originating from the bottom of the shoulder circumferential groove 30s. From the viewpoint of effectively suppressing the occurrence of damage originating from the bottom of the shoulder circumferential groove 30s, the inner end 48ue of the edge band 48 is positioned outside the bottom of the shoulder circumferential groove 30s in the axial direction. is preferred, and it is more preferred to be positioned further outside the shoulder circumferential groove 30s. In this tire 2, the inner end 48ue of the edge band 48 may be located inside the bottom of the shoulder circumferential groove 30s in the axial direction. In this case, it is more preferable that the inner end 48ue of the edge band 48 be located further inside than the shoulder circumferential groove 30s in the axial direction.

In this tire 2, the ratio (WB/W1) of the axial width WB of the buffer layer 22 to the axial width W1 of the first belt ply 44 is preferably 50% or more. This cushioning layer 22 bonds well with the first belt ply 44 and the carcass ply 38 . In this tire 2, strain generated between the carcass ply 38 and the first belt ply 44A is sufficiently relaxed. From this point of view, this ratio (WB/W1) is more preferably 55% or more, and even more preferably 60% or more.

As shown in FIG. 3, the end 22e of the cushioning layer 22 is located outside the inner end 14ue of the cushioning layer 14 in the axial direction. In this tire 2, the portion of the end 22e of the buffer layer 22 and the portion of the inner end 14ue of the cushion layer 14 are overlapped and joined. No gap is formed between the buffer layer 22 and the cushion layer 14 . In this tire 2, the occurrence of damage originating from the boundary between the buffer layer 22 and the cushion layer 14 is effectively suppressed. From this point of view, the end 22e of the cushioning layer 22 is preferably located outside the inner end 14ue of the cushioning layer 14 in the axial direction. In this case, the volume of the cushion layer 14 is appropriately maintained, and the influence of the cushion layer 14 on the mass of the tire 2 is effectively suppressed. More preferably, the ratio (WB/W1) to the axial width W1 of one belt ply 44 is set to 50% or more.

In FIG. 3, the symbol LB is the length of the overlapping portion between the buffer layer 22 and the cushion layer 14 (hereinafter referred to as the overlapping length). The overlapping length LB is represented by the shortest distance from the inner end 14ue of the cushion layer 14 to the end 22e of the cushioning layer 22. As shown in FIG. When the position of the end 22e of the buffer layer 22 and the position of the inner end 14ue of the cushion layer 14 are aligned in the axial direction, the overlap length LB is 0 mm.
In the tire 2, the overlapping length LB is preferably 3 mm or more, more preferably 5 mm or more, from the viewpoint of stably maintaining the joint state between the end 22e of the buffer layer 22 and the inner end 14ue of the cushion layer 14. more preferred. The overlapping length LB is preferably 15 mm or less, more preferably 10 mm or less, from the viewpoint that the buffer layer 22 is configured with an appropriate width and the buffer layer 22 can effectively contribute to suppressing the increase in mass.

In this tire 2, the buffer layer 22 is joined to a portion of the cushion layer 14 at its end 22e. As described above, the cushion layer 14 is made of soft crosslinked rubber. If the buffer layer 22 is composed of a soft cross-linked rubber like the cushion layer 14, it is necessary to increase the thickness TB of the buffer layer 22 in order to relax the strain. A thick cushioning layer 22 increases the mass of the tire.
The buffer layer 22 is formed of a cross-linked rubber harder than the cross-linked rubber of the cushion layer 14 from the viewpoint that the buffer layer 22 having an appropriate thickness TB is formed and the buffer layer 22 can effectively contribute to suppressing the increase in mass. preferably In other words, the complex elastic modulus E*b of the buffer layer 22 is preferably higher than the complex elastic modulus E*c of the cushion layer 14 . Specifically, the ratio (E*b/E*c) of the complex elastic modulus E*b of the buffer layer 22 to the complex elastic modulus E*c of the cushion layer 14 is preferably 1.2 or more, more preferably 1.4 or more. is more preferable, and 1.6 or more is even more preferable. The ratio (E*b/E*c) is preferably 3.8 or less, more preferably 3.4 or less, and even more preferably 3.1 or less.

For example, as shown in FIG. 3, in the zone of the tire 2 from the inner end 48ue of the edge band 48 to the end 46e of the full band 46, the full band 46 and the edge band 48 radially overlap. In the band of this tire 2, the zone from the inner end 48ue of the edge band 48 to the end 46e of the full band 46 has high rigidity. Therefore, when the cushioning layer 22 made of crosslinked rubber is arranged inside this zone, the strain distribution between the carcass ply 38 and the first belt ply 44A is uneven, and the inner end 48ue of the edge band 48 is strained. There is concern that damage will occur at the corresponding locations.

In this tire 2, the end 22e of the cushioning layer 22 is positioned inside the inner end 48ue of the edge band 48 in the axial direction. Since the buffer layer 22 is not arranged inside the zone from the inner end 48ue of the edge band 48 to the end 46e of the full band 46, in this tire 2, the strain generated between the carcass ply 38 and the first belt ply 44A is reduced. The occurrence of resulting damage is effectively suppressed. From this point of view, it is preferable that the end 22e of the cushioning layer 22 is located inside the inner end 48ue of the edge band 48 in the axial direction.

In FIG. 3, the length indicated by symbol DB is the axial distance from the end 22e of the buffer layer 22 to the inner end 48ue of the edge band 48. As shown in FIG.
From the viewpoint of effectively suppressing the occurrence of damage, the axial distance DB is preferably 1 mm or more, more preferably 3 mm or more. In this tire 2, as described above, from the viewpoint of alleviating strain generated between the carcass ply 38 and the first belt ply 44A, the axial width WB of the first belt ply 44 is less than the axial width WB of the buffer layer 22. The ratio (WB/W1) to W1 is preferably set to 50% or more. Therefore, a preferable upper limit of the axial distance DB is not set.

In this tire 2, the breaking load of the first belt cord 50 is preferably 2000N or more. Although the number of belt plies 44 constituting the belt 40 of the tire 2 is smaller than that of the conventional tire belt, the belt 40 effectively contributes to maintaining the strength of the tire 2 .
Since the breaking load of the first belt cord 50 is 2000 N or more, this tire 2 can use conventional belt cords 50 having a breaking load of 1000 N or more as the second belt cord 50 and the third belt cord 50 . This belt 40 contributes to maintenance of strength and weight reduction.
This tire 2 can suppress an increase in mass while maintaining strength.

As is clear from the above description, according to the present invention, a heavy-duty pneumatic tire 2 capable of suppressing an increase in mass and suppressing shape change due to running is obtained. INDUSTRIAL APPLICABILITY The present invention exhibits a remarkable effect in a low-flat heavy-duty pneumatic tire 2 having a nominal aspect ratio of 65% or less.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited only to these Examples.

[Example 1]
A heavy-duty pneumatic tire (tire size=355/50R22.5) having the basic configuration shown in FIGS. 1-3 and the specifications shown in Table 1 below was obtained.

In Example 1, the belt was composed of three belt plies, consisting of a first belt ply, a second belt ply and a third belt ply. The belt cords of each belt ply were steel cords.
The inclination angle θ1 of the first belt cord, the inclination angle θ2 of the second belt cord, and the inclination angle θ3 of the third belt cord were all set to 15° (degrees).
The inclination direction of the first belt cord was opposite to the inclination direction of the second belt cord, and the inclination direction of the second belt cord was the same as the inclination direction of the third belt cord.
The band consisted of a full band and a pair of edge bands. That the band includes the full band is indicated by a "Y" in the FB column of Table 1, and that this band includes the edge band is indicated by a "Y" in the EB column of this Table. The full band and edge band band cords were steel cords.
A full band was provided between the first belt ply and the second belt ply, and an edge band was positioned radially outward of the end of the full band.
The axial distance We from the edge of the full band to the inner edge of the edge band was 15 mm.
A cushioning layer was provided between the first belt ply and the carcass ply. This is indicated by a "Y" in the buffer layer column of Table 1. The complex elastic modulus E*b of the buffer layer was 10.0 MPa. The distance TC between the carcass and the reinforcing layer was 2.0 mm.
The axial distance DB from the edge of the buffer layer to the inner edge of the edgeband was 10 mm.
The ratio (WB/W1) of the axial width WB of the buffer layer to the axial width W1 of the first belt ply was 60%.
The overlapping length LB between the buffer layer and the cushion layer was 7 mm.
The complex elastic modulus E*c of the cushion layer was 3.4 MPa.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the cushioning layer was replaced with an inclined ply. Comparative Example 1 is a conventional tire.
The belt of Comparative Example 1 was composed of four belt plies. In Comparative Example 1, the inclination angle θt of the belt cord of the inclined ply was set to 50°. The inclination direction of the belt cords of the inclined ply was the same as the inclination direction of the first belt cords. The belt cords of the inclined plies were steel cords. The belt was constructed so that the angled ply had an axial width comparable to the axial width of the second belt ply.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1, except that no edge band was provided.

[Example 2]
A tire of Example 2 was obtained in the same manner as in Example 1, except that the distance TC was set as shown in Table 1 below.

[Example 3]
A tire of Example 3 was obtained in the same manner as in Example 1, except that the complex elastic modulus E*b of the buffer layer was set as shown in Table 2 below.

[Example 4-5]
Tires of Examples 4 and 5 were obtained in the same manner as in Example 1 except that the inner end position of the edge band was changed to set the axial distance We and the axial distance DB as shown in Table 2 below.

[Example 6]
A tire of Example 6 was obtained in the same manner as in Example 1, except that the inner end position of the cushion layer was adjusted to set the overlapping length LB to 0 mm.

[Profile change]
The prototype tire was mounted on a rim (11.75×22.5), filled with air, and the internal pressure of the tire was adjusted to the normal internal pressure. This tire was run on a drum tester for 1000 km at a speed of 80 km/h to obtain the profile of the case line inside the shoulder circumferential groove. This case line profile was compared with the case line profile before running to confirm the change in the profile before and after running. The results are shown in Tables 1 and 2 below as indexes according to the following ratings. A larger value indicates that the change in profile is suppressed. In this running test, a normal load was applied to the tire. This evaluation requires a score of 95 or higher.
Amount of change Index 0.0mm to 0.5mm 100
0.6mm to 1.0mm 95
1.1 mm to 1.5 mm 90
1.6mm to 2.0mm 85
2.1 mm to 2.5 mm 80

[JLB fracture resistance]
A prototype tire was mounted on a rim (11.75×22.5), air was filled, and the internal pressure of the tire was adjusted to the normal internal pressure. This tire was mounted on the drive shaft of a test vehicle (tractor head). A trailer loaded with cargo was towed by this test vehicle, and this test vehicle was run on a test course composed of an asphalt road surface until the wear rate of the tires reached 30% in terms of mass. After running, the tire was inspected by shearography or X-ray to confirm the presence or absence of internal damage. When internal damage was confirmed, the tire was dismantled and it was confirmed whether the internal damage was a broken band cord of the full band. The results are presented in Tables 1 and 2 below according to the ratings below. It is required not to correspond to the rating D.
If there is no break in the band cord ・・・・・・・・A
If there is one break in the band cord・・・・・・B
If there are two breakage points in the band cord: C
If there are 3 or more breaks in the band cord...D

[Tire mass]
The mass of the trial tire was measured. The results are shown in the following Tables 1 and 2 as indices with Example 1 being 100. The smaller the number, the lighter the tire. If the index indicating the result is 110 or less, it is accepted that the increase in mass is suppressed.

[Tire strength]
Conical weight from above the tread (plunger diameter 50 mm, height 100 mm, weight 5 kg) in accordance with JIS D4230 Section 5.1 “Tire strength (breaking energy) test” using a plunger test machine was dropped, and the height of the drop when the tire broke was converted into energy. The results are shown in the following Tables 1 and 2 as indices with Example 1 being 100. The higher the value, the better the tire strength. An index indicating the result is required to be 95 or higher.

As shown in Tables 1 and 2, in the example, suppression of mass increase and suppression of shape change due to running are achieved. From this evaluation result, the superiority of the present invention is clear.

The technique for achieving suppression of mass increase and suppression of shape change due to running described above can be applied to various tires.

2 Tire 4 Tread 6 Sidewall 12 Carcass 14 Cushion layer 20 Reinforcement layer 22 Buffer layer 30, 30s, 30m Circumferential groove 32, 32s, 32m, 32c Land portion 38 Carcass ply 40 Belt 42 Band 44, 44A, 44B, 44C Belt ply 46 Full band 48 Edge band 50, 50A, 50B, 50C... Belt cord 50
54: band code

Claims (8)

having a nominal aspect ratio of 65% or less,
A tread in which at least three circumferential grooves are formed, a pair of sidewalls connected to the ends of the tread and positioned inside the tread in the radial direction, and a pair of sidewalls positioned inside the sidewalls in the radial direction. a bead, a carcass located inside the tread and the pair of sidewalls and bridging between one bead and the other bead, a reinforcing layer located radially inside the tread, and a cushioning layer positioned between the carcass and the reinforcing layer;
Out of the at least three circumferential grooves, the circumferential groove located on the outer side in the axial direction is the shoulder circumferential groove,
The reinforcing layer comprises a belt containing a large number of parallel belt cords and a band containing a spirally wound band cord,
the belt comprises a first belt ply, a second belt ply and a third belt ply;
The first belt ply, the second belt ply and the third belt ply are arranged in this order in the radial direction,
the direction of inclination of the belt cords included in the first belt ply is opposite to the direction of inclination of the belt cords included in the second belt ply;
The band comprises a full band arranged so that both ends face each other across the equatorial plane, and a pair of edge bands located outside the ends of the full band in the radial direction,
the full band is positioned radially between the first belt ply and the second belt ply;
The buffer layer is made of crosslinked rubber,
Pneumatic tires for heavy loads. The buffer layer has a complex elastic modulus of 7.0 MPa or more and 12.0 MPa or less.
The heavy duty pneumatic tire according to claim 1. an end of the full band is located axially outside the shoulder circumferential groove;
The heavy duty pneumatic tire according to claim 1 or 2. the axial distance from the end of the full band to the inner end of the edge band is 10 mm or more;
The heavy duty pneumatic tire according to any one of claims 1 to 3. an end of the cushioning layer axially located inside an inner end of the edge band;
The heavy duty pneumatic tire according to any one of claims 1 to 4. A ratio of the axial width of the buffer layer to the axial width of the first belt ply is 50% or more,
The heavy duty pneumatic tire according to any one of claims 1 to 5. A pair of cushion layers positioned outside the cushion layer in the axial direction,
each of the pair of cushion layers is located between the reinforcing layer and the carcass at the end of the reinforcing layer;
an end of the cushioning layer is located outside an inner end of the cushioning layer in the axial direction;
The heavy duty pneumatic tire according to any one of claims 1 to 6. The complex elastic modulus of the buffer layer is higher than the complex elastic modulus of the cushion layer,
The heavy duty pneumatic tire according to claim 7.

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