JP2021066394A - Pneumatic tire for heavy load - Google Patents

Abstract

To provide a pneumatic tire 2 for a heavy load with excellent rib tear resistance.SOLUTION: A tire 2 comprises: a tread 4 in which a plurality of circumferential grooves is carved; a belt 14 located radially inside the tread 4; and a pair of cushion layers 16 supporting end portions of the belt 14 from radially inside. The tread 4 includes base layers 24 located radially outside the belt 14; and cap layers 26 located radially outside the base layers 24. A complex elastic modulus of the base layer 24 is 1.5 times or more and 1.9 times or less of a complex elastic modulus of the cushion layer 16. Destructive energy of the cushion layer 16 is 1.3 times or more and 1.6 times or less of destructive energy of the base layer 24.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pneumatic tire for heavy loads.

The tread of a heavy-duty pneumatic tire mounted on a vehicle such as a truck or a bus is engraved with a plurality of circumferential grooves to form a plurality of land areas. The tread has a base layer and a cap layer located radially outward of the base layer and covering the base layer.

The base layer is inferior to the cap layer in terms of reinforcing properties. Of the plurality of circumferential grooves, strain tends to be concentrated on the bottom of the circumferential groove located on the outer side in the axial direction, that is, the shoulder circumferential groove. Therefore, when a flaw that has entered the bottom of the shoulder circumferential groove reaches the base layer, there is a concern that cracks will develop in this base layer and the shoulder land portion will be partially torn off.

Such damage accompanied by tearing in the land area is also referred to as rib tear, and studies aimed at improving rib tear resistance have been conducted so that this rib tear does not occur (for example, Patent Document 1 below).

Japanese Unexamined Patent Publication No. 2017-210077

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pneumatic tire for heavy loads, which has excellent rib tear resistance.

The heavy-duty pneumatic tire according to one aspect of the present invention has a tread in which a plurality of circumferential grooves are carved, a belt located inside the tread in the radial direction, and an end portion of the belt from the inside in the radial direction. It is provided with a pair of supporting cushion layers. The tread includes a base layer located on the outside of the belt in the radial direction and a cap layer located on the outside of the base layer in the radial direction. The complex elastic modulus of the base layer is 1.5 times or more and 1.9 times or less the complex elastic modulus of the cushion layer. The breaking energy of the cushion layer is 1.3 times or more and 1.6 times or less of the breaking energy of the base layer.

Preferably, in this heavy load pneumatic tire, the cushion layer is a molded body of a rubber composition containing a base rubber and carbon black, and the carbon black is a HAF grade carbon black.

Preferably, in this heavy load pneumatic tire, the loss tangent of the base layer is equivalent to the loss tangent of the cushion layer, or the loss tangent of the base layer is smaller than the loss tangent of the cushion layer.

Preferably, in the pneumatic tire for heavy load, among the plurality of circumferential grooves, the circumferential groove located on the outer side in the axial direction is the shoulder circumferential groove, and the circumferential groove is on the radial inner side of the shoulder circumferential groove. The cushion layer is located.

According to the present invention, a heavy load pneumatic tire having excellent rib tear resistance can be obtained.

FIG. 1 is a cross-sectional view showing a part of a heavy-duty pneumatic tire according to an embodiment of the present invention. FIG. 2 is a schematic view illustrating an arrangement of belt cords included in the tire belt shown in FIG.

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

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

Regular rims are rims defined in the standards on which the tire relies. The "standard rim" in the JATTA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

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

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

FIG. 1 shows a part of a heavy-duty pneumatic tire 2 (hereinafter, may be simply referred to as “tire 2”) according to an embodiment of the present invention. The tire 2 is mounted on a vehicle such as a truck or a bus.

FIG. 1 shows a part of a cross section of the tire 2 along a plane including a rotation axis of the tire 2. In FIG. 1, the left-right 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. In FIG. 1, the alternate long and short dash line CL represents the equatorial plane of the tire 2. In FIG. 1, the tire 2 is incorporated in the rim R (regular rim).

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 belt 14, a pair of cushion layers 16, an inner liner 18, and a pair of reinforcing layers 20.

The tread 4 comes into contact with the road surface on its outer surface 22, that is, the tread surface 22. The code PC is the intersection of the tread surface 22 and the equatorial surface. The intersection PC is the equator of tire 2.

In FIG. 1, reference numeral PE is the end of the tread surface 22. When the end PE of the tread surface 22 cannot be identified from the appearance of the tire 2, a normal load is applied to the tire 2 in a normal state, the camber angle is set to 0 °, and the tread 4 is brought into contact with a flat surface. The outer end in the axial direction is defined as the end PE of the tread surface 22.

In FIG. 1, the double-headed arrow RT is the width of the tread surface 22. This width RT is represented by the axial distance from the end PE of one tread surface 22 to the end PE of the other tread surface 22.

The tread 4 includes a base layer 24 and a cap layer 26. The base layer 24 is located outside the belt 14 in the radial direction. The base layer 24 is made of crosslinked rubber in consideration of low heat generation. The cap layer 26 is located outside the base layer 24 in the radial direction. The cap layer 26 is made of crosslinked rubber in consideration of wear resistance and grip performance.

The tread 4 is carved with a plurality of circumferential grooves 28 that extend continuously in the circumferential direction. In this tire 2, at least three circumferential grooves 28 are carved in the tread 4. As a result, at least four land portions 30 are formed in the tread 4. In the tread 4 shown in FIG. 1, four circumferential grooves 28 are carved in the tread 4, and five land portions 30 are formed.

In the tire 2, the width of the circumferential groove 28 is represented by the shortest distance from one edge of the circumferential groove 28 to the other edge. The width of the land portion 30 is represented by the axial distance from one edge of the land portion 30 to the other edge.

Of the four circumferential grooves 28, the circumferential groove 28c located inside in the axial direction, that is, the circumferential groove 28c close to the equator PC is the center circumferential groove. The circumferential groove 28s located on the outer side in the axial direction, that is, the circumferential groove 28s near the end PE of the tread surface 22, is the shoulder circumferential groove. When the circumferential groove 28 carved in the tread 4 includes the circumferential groove 28 located on the equator PC, the circumferential groove 28 located on the equator PC is the center circumferential groove. When the circumferential groove 28 exists between the center circumferential groove 28c and the shoulder circumferential groove 28s, the circumferential groove 28 is the middle circumferential groove.

From the viewpoint of contributing to drainage and traction performance, the width of the center circumferential groove 28c is preferably 1 to 10% of the width RT of the tread surface 22. The depth of the center circumferential groove 28c is preferably 13 to 25 mm.

From the viewpoint of contributing to drainage and traction performance, the width of the shoulder circumferential groove 28s is preferably 1 to 10% of the width RT of the tread surface 22. The depth of the shoulder circumferential groove 28s is preferably 13 to 25 mm.

Of the five land portions 30, the land portion 30c located inside in the axial direction, that is, the land portion 30c located on the equator PC is the center land portion. The land portion 30s located on the outer side in the axial direction, that is, the land portion 30s including the end PE of the tread surface 22, is the shoulder land portion. Further, the land portion 30 m located between the center land portion 30c and the shoulder land portion 30s is the middle land portion. Of the land portions 30 configured in the tread 4, when the land portion 30 located inside in the axial direction is located near the equator PC instead of on the equator PC, it is located near the equator PC. The land portion 30, that is, the land portion 30 located on the equator PC side is the center land portion.

In this tire 2, from the viewpoint of steering stability and wet performance, the width of the middle land portion 30 m is preferably 0.9 times or more and 1.1 times or less the width of the center land portion 30c. From the same viewpoint, the width of the shoulder land portion 30s is preferably 1.1 times or more and 1.4 times or less the width of the center land portion 30c.

Each sidewall 6 runs along the edge of the tread 4. The sidewall 6 extends radially inward from the end of the tread 4. The sidewall 6 is made of crosslinked rubber.

Each bead 8 is located radially inside the sidewall 6. The bead 8 includes a core 32 and an apex 34.

The core 32 extends in the circumferential direction. The core 32 includes a wound steel wire. The apex 34 is located radially outward of the core 32. The apex 34 extends radially outward from the core 32.

The apex 34 includes an inner apex 34u and an outer apex 34s. The outer apex 34s is located outside the inner apex 34u in the radial direction. The inner apex 34u and the outer apex 34s are made of crosslinked rubber. The outer apex 34s is softer than the inner apex 34u.

Each chafer 10 is located axially outward of the bead 8. The chafer 10 is located radially inside the sidewall 6. The chafer 10 comes into contact with the rim R. The chafer 10 is made of crosslinked rubber.

The carcass 12 is located inside the tread 4, sidewall 6 and chafer 10. The carcass 12 bridges one bead 8 and the other bead 8. The carcass 12 has a radial structure. The carcass 12 includes at least one carcass ply 36. The carcass 12 of the tire 2 is composed of one carcass ply 36.

Although not shown, the carcass ply 36 includes a large number of carcass cords in parallel. In this tire 2, the material of the carcass cord is steel. A cord made of organic fibers may be used as a carcass cord.

In this tire 2, the carcass ply 36 is folded back from the inside to the outside in the axial direction around the core 32 of each bead 8. The carcass ply 36 is a ply body 36a extending from one core 32 toward the other core 32, and a pair of ply bodies 36a connected to the ply body 36a and folded back from the inside to the outside in the axial direction around each core 32. It has a folded-back portion 36b.

The belt 14 is located inside the tread 4 in the radial direction. The belt 14 is located on the radial outer side of the carcass 12.

The belt 14 is composed of a plurality of layers 38 laminated in the radial direction. The belt 14 of the tire 2 is composed of four layers 38. In the tire 2, the number of layers 38 constituting the belt 14 is not particularly limited. The configuration of the belt 14 is appropriately determined in consideration of the specifications of the tire 2.

In the tire 2, of the four layers 38, the second layer 38B located between the first layer 38A and the third layer 38C has the maximum axial width. The fourth layer 38D, which is located outside the third layer 38C in the radial direction, that is, the fourth layer 38D, which is located on the outermost side in the radial direction, has the minimum axial width.

FIG. 2 shows the configuration of the belt 14 of the tire 2. In FIG. 2, the left-right direction is the axial direction of the tire 2, and the vertical direction is the circumferential direction of the tire 2.

Each layer 38 constituting the belt 14 includes a large number of belt cords 40 in parallel. The number of belt cords 40 in each layer 38 is 20 or more and 40 or less per 50 mm width of the layer 38 in the cross section of the layer 38 along the plane perpendicular to the extending direction of the belt cord 40. is there. The material of the belt cord 40 is steel. The belt cord 40 is covered with the topping rubber 42. In FIG. 2, for convenience of explanation, the belt cord 40 covered with the topping rubber 42 is represented by a solid line.

The belt cord 40 is inclined with respect to the equatorial plane. In this tire 2, each layer 38 constituting the belt 14 includes a large number of belt cords 40 inclined with respect to the equatorial plane.

As shown in FIG. 2, the direction of inclination of the belt cord 40 of the first layer 38A with respect to the circumferential direction is the same as the direction of inclination of the belt cord 40 of the second layer 38B with respect to the circumferential direction. The direction of inclination of the belt cord 40 of the second layer 38B with respect to the circumferential direction is opposite to the direction of inclination of the belt cord 40 of the third layer 38C with respect to the circumferential direction. The direction of inclination of the belt cord 40 of the third layer 38C with respect to the circumferential direction is the same as the direction of inclination of the belt cord 40 of the fourth layer 38D with respect to the circumferential direction. The direction of inclination of the belt cord 40 of the first layer 38A with respect to the circumferential direction may be opposite to the direction of inclination of the belt cord 40 of the second layer 38B with respect to the circumferential direction of the belt cord 40 of the fourth layer 38D. The direction of inclination with respect to the circumferential direction may be opposite to the direction of inclination of the belt cord 40 of the third layer 38C with respect to the circumferential direction.

As shown in FIG. 1, each cushion layer 16 is located between the belt 14 and the carcass 12 at the end of the belt 14. The cushion layer 16 supports the end portion of the belt 14 from the inside in the radial direction. The cushion layer 16 is made of crosslinked rubber in consideration of low heat generation.

The inner liner 18 is located inside the carcass 12. The inner liner 18 constitutes the inner surface of the tire 2. The inner liner 18 is made of crosslinked rubber having excellent air shielding properties.

Each reinforcing layer 20 is located at a portion of the bead 8. In the axial direction, the reinforcing layer 20 is located outside the bead 8. The reinforcing layer 20 is located between the carcass ply 36 and the chafer 10. The inner end of the reinforcing layer 20 is located radially inside the core 32. The outer end of the reinforcing layer 20 is located between the end of the folded-back portion 36b and the core 32 in the radial direction.

Although not shown, the reinforcing layer 20 contains a large number of parallel filler cords. The material of the filler cord is steel.

In the tire 2, the end of the belt 14 is located outside the shoulder circumferential groove 28s in the axial direction. In the radial direction, the base layer 24 is located outside the end of the belt 14, and the cushion layer 16 is located inside the end. In particular, in this tire 2, the inner end 16u of the cushion layer 16 is located inside the shoulder circumferential groove 28s in the axial direction. In other words, the cushion layer 16 is located radially inside the shoulder circumferential groove 28s. In this tire 2, the rib tear resistance is improved by controlling the dynamic viscoelasticity of the base layer 24 and the cushion layer 16 and the fracture energy.

In this tire 2, the dynamic viscoelasticity of the base layer 24 and the cushion layer 16 is expressed using a complex elastic modulus and a loss tangent (also referred to as tan δ). The complex elastic modulus E ^* and the loss tangent LT are measured under the following conditions using a viscoelastic spectrometer in accordance with JIS K6394. A test piece (40 mm × 4 mm × 2 mm) is used for the measurement. This test piece is made of crosslinked rubber and is formed according to a convention using the rubber compositions of the base layer 24 and the cushion layer 16.
Initial distortion = 10%
Amplitude = ± 1%
Frequency = 10Hz
Deformation mode = tensile measurement temperature = 70 ° C

The fracture energy DE is represented by half the product of the tensile strength TB and the elongation EB at the time of cutting. The tensile strength TB and the elongation EB at the time of cutting are measured using a tensile tester in an atmosphere adjusted to a temperature of 23 ° C. in accordance with JIS K6251. In this measurement, a sheet (thickness = 2 mm) made of crosslinked rubber is prepared according to the custom using the rubber compositions of the base layer 24 and the cushion layer 16. A dumbbell-shaped test piece is formed from this sheet.

In this tire 2, the base layer 24 and the cushion layer 16 are softer than the cap layer 26. Since the base layer 24 forms a part of the land portion 30, the base layer 24 has a rigidity higher than the rigidity of the crosslinked rubber forming the cushion layer 16 in consideration of the deformation of the land portion 30 due to the action of a load. Crosslinked rubber is used.

In this tire 2, the complex elastic modulus E ^* b of the base layer 24 is higher than the complex elastic modulus E ^{* c of the cushion layer 16.} Specifically, the complex elastic modulus E ^* b of the base layer 24 is 1.5 times or more the complex elastic modulus E ^{* c of the cushion layer 16.} Since the deformation at the root of the shoulder land portion 30s is effectively suppressed, even if a flaw is formed in the bottom of the shoulder circumferential groove 28s, the growth of cracks is suppressed. The base layer 24 contributes to the improvement of rib tear resistance. Since the deformation of the shoulder land portion 30s is suppressed as a whole, the progress of wear in the shoulder land portion 30s is also suppressed. The base layer 24 also contributes to the improvement of uneven wear resistance. From this viewpoint, the complex elastic modulus E ^* b of the base layer 24 is preferably 1.6 times or more the complex elastic modulus E ^{* c of the cushion layer 16.}

In this tire 2, the complex elastic modulus E ^* b of the base layer 24 is 1.9 times or less the complex elastic modulus E ^{* c of the cushion layer 16.} As a result, the rigidity of the land portion 30 is adjusted in a well-balanced manner, so that good uneven wear resistance is maintained. From this viewpoint, the complex elastic modulus E ^* b of the base layer 24 is preferably 1.8 times or less, more preferably 1.7 times or less of the complex elastic modulus E ^{* c of the cushion layer 16.}

When the tire 2 is in the running state, the tire 2 is repeatedly bent and released from the bending. When the tire 2 bends, the base layer 24 and the cushion layer 16 are compressed. When the tire 2 is released from bending, the base layer 24 and the cushion layer 16 are restored. At the time of this restoration, a force acts on each of the base layer 24 and the cushion layer 16 in the direction of stretching them. Since the cushion layer 16 is located radially inside the base layer 24, the force acting on the cushion layer 16 is larger than the force acting on the base layer 24. Therefore, for the cushion layer 16, a crosslinked rubber that is harder to break than the crosslinked rubber forming the base layer 24 is used.

In this tire 2, the destructive energy DEc of the cushion layer 16 is higher than the destructive energy DEb of the base layer 24. Specifically, the destructive energy DEc of the cushion layer 16 is 1.3 times or more the destructive energy DEb of the base layer 24. In the tire 2, since the cushion layer 16 is hard to break, the end portion of the belt 14 is effectively restrained by the cushion layer 16. Even if a flaw is formed in the bottom of the shoulder circumferential groove 28s, the growth of cracks is suppressed. The cushion layer 16 also contributes to the improvement of rib tear resistance, like the base layer 24 described above. From this viewpoint, the breaking energy DEc of the cushion layer 16 is preferably 1.4 times or more the breaking energy DEb of the base layer 24.

In this tire 2, the destructive energy DEc of the cushion layer 16 is 1.6 times or less the destructive energy DEb of the base layer 24. As a result, the degree of deformation in the cushion layer 16 is appropriately maintained. The cushion layer 16 effectively contributes to the suppression of heat generation due to deformation. From this viewpoint, the breaking energy DEc of the cushion layer 16 is preferably 1.5 times or less the breaking energy DEb of the base layer 24.

In this tire 2, the complex elastic modulus E ^* b of the base layer 24 is 1.5 times or more and 1.9 times or less of the complex elastic modulus E ^* c of the cushion layer 16, and the fracture energy DEc of the cushion layer 16 is the base layer. It is 1.3 times or more and 1.6 times or less of the destruction energy DEb of 24. In the tire 2 having the base layer 24 and the cushion layer 16, the rib tear resistance is improved. This tire 2 has excellent rib tear resistance. Moreover, in this tire 2, good uneven wear resistance is maintained, and heat generation due to deformation is effectively suppressed.

^{In this tire 2, the complex elastic modulus E *} b of the base layer 24 is preferably 3 MPa or more, preferably 4 MPa, from the viewpoint that the base layer 24 can effectively contribute to the improvement of rib tear resistance and the maintenance of good uneven wear resistance. The above is more preferable. The complex elastic modulus E ^* b of the base layer 24 is preferably 7 MPa or less, more preferably 6 MPa or less.

In the tire 2, the fracture energy DEc of the cushion layer 16 is preferably 8000 MPa ·% or more, preferably 8500 MPa ·%, from the viewpoint that the cushion layer 16 can effectively contribute to the improvement of rib tear resistance and the suppression of heat generation due to deformation. The above is more preferable, and 9000 MPa ·% or more is further preferable. The fracture energy DEc of the cushion layer 16 is preferably 12000 MPa ·% or less, more preferably 11500 MPa ·% or less, and even more preferably 11000 MPa ·% or less.

As described above, the base layer 24 is made of crosslinked rubber. The base layer 24 is obtained by cross-linking the uncross-linked rubber composition. The base layer 24 is a molded product of a rubber composition.

The rubber composition for the base layer 24 includes a base rubber. The base rubber includes 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). ) Is illustrated. In this rubber composition, the base rubber may be composed of a single rubber component, or two or more kinds of rubber components may be used in combination.

The rubber composition for the base layer 24 contains carbon black as a reinforcing agent. Examples of this carbon black include MT grade, FT grade, SRF grade, GPF grade, FEF grade, XCF grade, HAF grade, ISAF grade and SAF grade carbon black. From the viewpoint of low heat generation and reinforcing properties, HAF grade carbon black is preferable as this carbon black. In this case, the content of the HAF grade carbon black is preferably 30 parts by mass or more and 60 parts by mass or less with respect to 100 parts by mass of the base rubber.

From the viewpoint of low heat generation, the rubber composition for the base layer 24 can contain silica as a reinforcing agent in addition to the above-mentioned carbon black. In this case, the blending amount of silica is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the base rubber.

Although not described in detail, the rubber composition of the base layer 24 contains, in addition to the above-mentioned reinforcing agent, a plasticizer such as aromatic oil, a filler such as zinc oxide, a lubricant such as stearic acid, and anti-aging. Chemicals such as agents, processing aids, sulfur, vulcanization accelerators and the like can be further included. The selection of these chemicals, the content of the selected chemicals, and the like are appropriately determined according to the specifications of the base layer 24.

As described above, the cushion layer 16 is made of crosslinked rubber. The cushion layer 16 is also obtained by cross-linking the uncross-linked rubber composition, similarly to the base layer 24 described above. The cushion layer 16 is a molded product of a rubber composition.

The rubber composition for the cushion layer 16 includes a base rubber. The base rubber includes 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). ) Is illustrated. In this rubber composition, the base rubber may be composed of a single rubber component, or two or more kinds of rubber components may be used in combination.

The rubber composition for the cushion layer 16 contains carbon black as a reinforcing agent. Examples of this carbon black include MT grade, FT grade, SRF grade, GPF grade, FEF grade, XCF grade, HAF grade, ISAF grade and SAF grade. From the viewpoint of low heat generation and reinforcing properties, HAF grade carbon black is preferable as this carbon black. In this case, the content of the HAF grade carbon black is preferably 20 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the base rubber.

From the viewpoint of low heat generation, the rubber composition for the cushion layer 16 can contain silica as a reinforcing agent in addition to the above-mentioned carbon black. In this case, the blending amount of silica is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the base rubber.

Although not described in detail, the rubber composition of the cushion layer 16 contains, in addition to the above-mentioned reinforcing agent, a plasticizer such as aromatic oil, a filler such as zinc oxide, a lubricant such as stearic acid, and anti-aging. Chemicals such as agents, processing aids, sulfur, vulcanization accelerators and the like can be further included. The selection of these chemicals, the content of the selected chemicals, and the like are appropriately determined according to the specifications of the cushion layer 16.

As described above, in the tire 2, the base layer 24 and the cushion layer 16 are each made of crosslinked rubber in consideration of low heat generation. In this tire 2, the loss tangent LTb of the base layer 24 and the loss tangent LTc of the cushion layer 16 are both less than 0.1. The base layer 24 and the cushion layer 16 contribute to suppressing heat generation due to deformation.

In this tire 2, preferably, the loss tangent LTb of the base layer 24 is equivalent to the loss tangent LTc of the cushion layer 16, or the loss tangent LTb of the base layer 24 is smaller than the loss tangent LTc of the cushion layer 16. In other words, the difference (LTc-LTb) between the loss tangent LTc of the cushion layer 16 and the loss tangent LTb of the base layer 24 is preferably 0 or more.

With this tire 2, heat generation at the root portion of the shoulder land portion 30s is effectively suppressed. Therefore, even if a flaw is formed in the bottom of the shoulder circumferential groove 28s, the growth of the crack is effectively suppressed. The base layer 24 effectively contributes to the improvement of rib tear resistance. From this viewpoint, the difference (LTc-LTb) between the loss tangent LTc of the cushion layer 16 and the loss tangent LTb of the base layer 24 is more preferably 0.01 or more.

In FIG. 2, the angle θ1 is an inclination angle formed by the belt cord 40 included in the first layer 38A with respect to the equatorial plane. The angle θ2 is an inclination angle formed by the belt cord 40 included in the second layer 38B with respect to the equatorial plane. The angle θ3 is an inclination angle formed by the belt cord 40 included in the third layer 38C with respect to the equatorial plane. The angle θ4 is an inclination angle formed by the belt cord 40 included in the fourth layer 38D with respect to the equatorial plane.

In the tire 2, the inclination angle θ1 of the belt cord 40 in the first layer 38A is preferably 48 ° or more, and preferably 53 ° or less. As a result, the belt 14 including the first layer 38A effectively restrains the movement of the tire 2. The belt 14 contributes to the improvement of rib tear resistance.

In the tire 2, the inclination angle θ2 of the belt cord 40 in the second layer 38B is preferably 14 ° or more, and preferably 23 ° or less. As a result, the belt 14 including the second layer 38B effectively restrains the movement of the tire 2. The belt 14 contributes to the improvement of rib tear resistance.

In the tire 2, the inclination angle θ3 of the belt cord 40 in the third layer 38C is preferably 14 ° or more, and preferably 23 ° or less. As a result, the belt 14 including the third layer 38C effectively restrains the movement of the tire 2. The belt 14 contributes to the improvement of rib tear resistance.

In the tire 2, the inclination angle θ4 of the belt cord 40 in the fourth layer 38D is preferably 14 ° or more, and preferably 23 ° or less. As a result, the belt 14 including the fourth layer 38D effectively restrains the movement of the tire 2. The belt 14 contributes to the improvement of rib tear resistance.

From the viewpoint of improving rib tear resistance, in this tire 2, the inclination angle θ1 of the belt cord 40 in the first layer 38A is 48 ° or more and 53 ° or less, and the inclination angle θ2 of the belt cord 40 in the second layer 38B is 14. The inclination angle θ3 of the belt cord 40 in the third layer 38C is 14 ° or more and 23 ° or less, and the inclination angle θ4 of the belt cord 40 in the fourth layer 38D is 14 ° or more and 23 °. It is more preferable that it is as follows. It is more preferable that the inclination angle θ2, the inclination angle θ3, and the inclination angle θ4 are set to the same angle.

As is clear from the above description, according to the present invention, a heavy load pneumatic tire 2 having excellent rib tear resistance can be obtained. Moreover, in this tire 2, good uneven wear resistance is maintained, and heat generation due to deformation is effectively suppressed.

The embodiments disclosed this time are exemplary in all respects and are not restrictive. The technical scope of the present invention is not limited to the above-described embodiment, and the technical scope includes all modifications within a range equivalent to the configuration described in the claims.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited to such Examples.

[Base layer]
Three types of rubber compositions A, B and C were prepared for the base layer. Table 1 below shows the fracture energy DEb, complex elastic modulus E ^* b, and loss tangent LTb of these rubber compositions, as well as the grade of carbon black (CB) used as a reinforcing agent.

[Cushion layer]
Two types of rubber compositions D and E were prepared for the cushion layer. Table 2 below shows the fracture energy DEc, complex elastic modulus E ^* c, and loss tangent LTc of these rubber compositions, as well as the grade of carbon black (CB) used as a reinforcing agent.

[Example 1]
A heavy-duty pneumatic tire (tire size = 11R22.5) having the configuration shown in FIG. 1 and having the specifications shown in Table 3 below was obtained.

In this Example 1, the base layer was composed of the rubber composition C, and the cushion layer was composed of the rubber composition D. Regarding the inclination angle of the belt cord included in each layer constituting the belt, the inclination angle θ1 of the belt cord in the first layer is set to 50 °, and the inclination angle θ2 of the belt cord in the second layer is set to 18 °. The tilt angle θ3 of the belt cord in the third layer was set to 18 °, and the tilt angle θ4 of the belt cord in the fourth layer was set to 18 °. Except for the rubber composition of the base layer and the cushion layer, and the inclination angle of the belt cord in the belt, the specifications were the same as those of the conventional tire.

[Example 2-4 and Comparative Example 1]
Tires of Examples 2-4 and Comparative Example 1 were obtained in the same manner as in Example 1 except that the rubber compositions of the base layer and the cushion layer were as shown in Table 3 below.

[Ribtea resistance]
The prototype tire was incorporated into a regular rim and filled with air to adjust the internal pressure of the tire to 850 kPa. This tire was mounted on the front shaft of a test vehicle (10-ton truck). The vehicle was driven on a general road with 50% of the standard load capacity loaded in front of the loading platform. The appearance of the tire was observed after traveling 10000 km. If a flaw was found at the bottom of the shoulder circumferential groove, the length and depth of the flaw were measured. The reciprocal of the product of the length and depth of the flaw was calculated and used as an index of rib tear resistance. This result is shown in Table 3 below as an index with Comparative Example 1 as 100. The larger the value, the less likely it is that rib tears will occur, and the better the rib tear resistance.

[Fever]
Using a rolling resistance tester, the rolling resistance coefficient (RRC) when each prototype tire traveled on the drum at a speed of 80 km / h was measured under the following conditions. This rolling resistance coefficient was used as an index of heat generation. This result is shown in Table 3 below as an index with Comparative Example 1 as 100. The larger the value, the smaller the rolling resistance, that is, the heat generated by the deformation is suppressed.
Rim: Regular rim Internal pressure: 900kPa
Vertical load: 33.35kN

[Uneven wear resistance]
The prototype tire was incorporated into a regular rim and filled with air to adjust the internal pressure of the tire to 850 kPa. This tire was mounted on the front shaft of a test vehicle (10-ton truck). The mileage at which uneven wear occurs was measured by traveling on a general road with a load of 50% of the standard load capacity loaded in front of the loading platform. The results are shown in Table 3 below as an index. The larger the value, the less uneven wear is likely to occur and the better the uneven wear resistance.

As shown in Table 3, in the examples, the improvement of rib tear resistance is confirmed. From this evaluation result, the superiority of the present invention is clear.

The technique for improving rib tear resistance described above can be applied to various tires.

2 ... Tire 4 ... Tread 6 ... Sidewall 12 ... Carcass 14 ... Belt 16 ... Cushion layer 22 ... Tread surface 24 ... Base layer 26 ... Cap layer 28, 28c, 28s ... Circumferential groove 30, 30c, 30m, 30s ... Land 38, 38A, 38B, 38C, 38D ... Layer 40 Belt cord

Claims (4)

A tread with multiple circumferential grooves and
A belt located inside the tread in the radial direction,
A pair of cushion layers that support the end of the belt from the inside in the radial direction are provided.
The tread comprises a base layer located on the outside of the belt in the radial direction and a cap layer located on the outside of the base layer in the radial direction.
The complex elastic modulus of the base layer is 1.5 times or more and 1.9 times or less of the complex elastic modulus of the cushion layer.
A pneumatic tire for heavy loads in which the breaking energy of the cushion layer is 1.3 times or more and 1.6 times or less of the breaking energy of the base layer. The cushion layer is a molded product of a rubber composition containing a base rubber and carbon black.
The pneumatic tire for heavy loads according to claim 1, wherein the carbon black is HAF grade carbon black. The pneumatic tire for heavy load according to claim 1 or 2, wherein the loss tangent of the base layer is equivalent to the loss tangent of the cushion layer, or the loss tangent of the base layer is smaller than the loss tangent of the cushion layer. .. Of the plurality of circumferential grooves, the circumferential groove located on the outer side in the axial direction is the shoulder circumferential groove.
The pneumatic tire for heavy load according to any one of claims 1 to 3, wherein the cushion layer is located inside the shoulder circumferential groove in the radial direction.

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