阅读说明：本技术 充气轮胎 (Pneumatic tire ) 是由 末野顺也 羽山晃平 于 2019-07-16 设计创作，主要内容包括：本发明提供一种充气轮胎(2),确保刚性并实现质量及滚动阻力的降低。在该轮胎(2)中,从胎圈(10)的芯(30)与三角胶(32)的边界的轴向中心到三角胶(32)的外端的长度为10mm以上15mm以下。在组装至标准轮辋,内压调整为标准内压的状态下,位于从胎面(4)与胎侧(6)的边界部分到三角胶(32)的外端(PA)的区域的胎体帘布(34)的主体部(36)的形状由单个的圆弧表示,该圆弧的直径为胎体(14)的截面高度的75％以上90％以下。(The invention provides a pneumatic tire (2) which ensures rigidity and realizes reduction of mass and rolling resistance. In the tire (2), the length from the axial center of the boundary between the core (30) of the bead (10) and the apex (32) to the outer end of the apex (32) is 10mm to 15 mm. When assembled to a standard rim and the internal pressure is adjusted to the standard internal pressure, the shape of the main body (36) of the carcass ply (34) in the region from the boundary between the tread (4) and the sidewall (6) to the outer end (PA) of the apex (32) is represented by a single circular arc having a diameter of 75% to 90% of the cross-sectional height of the carcass (14).)

1. A pneumatic tire, comprising:

a pair of beads having a core extending in a circumferential direction and an apex radially outward of the core;

a carcass extending from one bead to the other bead inside a tread and a pair of sidewalls connected to ends of the tread;

a pair of heel rubbers located radially inside the sidewalls; and

a pair of rubber reinforcing layers located between the carcass and the heel rubber,

the carcass includes a carcass ply having: a main body part spanning the one core and the other core; and a pair of folding portions connected to the main body portion and folded back along the periphery of the core from the axially inner side to the axially outer side,

the length from the axial center of the boundary between the core and the apex to the outer end of the apex is 10mm to 15mm,

when the wheel rim is assembled and the internal pressure is adjusted to the standard internal pressure,

the shape of the main body portion located in a region from a boundary portion between the tread and the sidewall to an outer end of the apex is represented by a single circular arc having a diameter of 75% to 90% of the cross-sectional height of the carcass.

2. A pneumatic tire according to claim 1,

when the tire is mounted on a standard rim and the internal pressure is adjusted to 10% of the standard internal pressure,

the main body portion extending along the inner side surface of the apex is inclined with respect to the axial direction, and the angle formed by the main body portion with respect to the axial direction is 45 ° to 50 °.

3. A pneumatic tire according to claim 1 or 2,

the radial distance from the bead base line to the outer end of the rubber reinforcing layer is 35% to 45% of the tire sectional height.

4. A pneumatic tire according to any one of claims 1 to 3,

the maximum thickness of the rubber reinforced layer is more than 2mm and less than 4 mm.

5. A pneumatic tire according to any one of claims 1 to 4,

the apex has a composite elastic modulus (E a) of 70MPa to 130MPa, and a loss tangent (LTa) of 0.18 or less.

6. A pneumatic tire according to any one of claims 1 to 5,

the heel rubber has a composite elastic modulus E c of 7MPa to 13MPa, and a loss tangent LTc of 0.08 or less.

7. A pneumatic tire according to any one of claims 1 to 6,

the radial distance from the bead base line to the end of the turn-back portion is 20mm to 30 mm.

8. A pneumatic tire according to any one of claims 1 to 7,

the carcass cord fabric comprises a plurality of carcass cords arranged in parallel, and the fineness of each carcass cord is more than 1500dtex and less than 1700 dtex.

9. A pneumatic tire according to any one of claims 1 to 8,

the composite elastic modulus E r of the rubber reinforced layer is larger than the composite elastic modulus E c of the bead heel rubber.

10. A pneumatic tire according to any one of claims 1 to 9,

the heel rubber has a loss tangent LTc less than the loss tangent LTr of the rubber reinforcing layer.

11. A pneumatic tire according to any one of claims 1 to 10,

the composite elastic modulus E r of the rubber reinforced layer is the same as or less than the composite elastic modulus E a of the apex.

12. A pneumatic tire according to any one of claims 1 to 11,

the loss tangent LTr of the rubber reinforcing layer is the same as or less than the loss tangent LTa of the apex.

Technical Field

The present invention relates to a pneumatic tire.

Background

The bead of the tire is composed of a core and a bead apex. The apex is made of hard cross-linked rubber. In order to ensure rigidity, an apex having a length of about 30mm to 40mm is generally used.

In view of the environment, the tire is required to be lightweight and to reduce rolling resistance. Therefore, the use of small apex having a length of about 5mm to 15mm has been studied.

For example, patent document 1 discloses a bead including a first apex and a second apex axially outward of the first apex. The first apex is the small apex described above. The second apex is axially outward of the first apex and is sandwiched between the carcass and the heel rubber. In patent document 1, the shape of the second apex is adjusted to improve durability and the like.

Patent document 1: japanese patent laid-open publication No. 2017-030620

Disclosure of Invention

If a small apex is used for the bead apex in order to reduce the tire mass and rolling resistance, the reduction in the rigidity of the bead portion is undeniable. As described in patent document 1, if the second bead filler is provided between the carcass and the heel rubber, an improvement in rigidity can be expected. However, in this case, since the small apex is used, the effect of reducing the mass and the rolling resistance is weakened. Therefore, it is necessary to establish a technique for ensuring rigidity and reducing mass and rolling resistance.

The present invention has been made in view of such circumstances, and an object thereof is to provide a pneumatic tire which ensures rigidity and achieves reduction in mass and rolling resistance.

The present inventors have conducted extensive studies in order to ensure rigidity and achieve reduction in mass and rolling resistance, and have found that when a main body portion of a carcass ply located in a region from a boundary portion between a tread and a sidewall to an outer end of an apex has a predetermined shape, the main body portion contributes to ensuring rigidity and reduction in mass and rolling resistance, thereby completing the present invention.

A preferred pneumatic tire of the present invention is a pneumatic tire comprising:

a pair of beads having a core extending in a circumferential direction and an apex radially outward of the core;

a carcass extending from one bead to the other bead inside a tread and a pair of sidewalls connected to ends of the tread;

a pair of heel rubbers located radially inside the sidewalls; and

a pair of rubber reinforcement layers located between the carcass and the heel rubber.

The carcass includes a carcass ply having: a main body part spanning the one core and the other core; and a pair of folding portions connected to the main body portion and folded back along the periphery of the core from the axially inner side to the axially outer side. The length from the axial center of the boundary between the core and the apex to the outer end of the apex is 10mm to 15 mm. When the wheel rim is assembled and the internal pressure is adjusted to the standard internal pressure,

the shape of the main body portion located in a region from a boundary portion between the tread and the sidewall to an outer end of the apex is represented by a single circular arc having a diameter of 75% to 90% of the cross-sectional height of the carcass.

Preferably, in the pneumatic tire, the body portion extending along the inner side surface of the bead apex is inclined with respect to the axial direction in a state where the tire is mounted on a standard rim and the internal pressure is adjusted to 10% of the standard internal pressure, and an angle of the body portion with respect to the axial direction is 45 ° to 50 °.

Preferably, in the pneumatic tire, a radial distance from the bead base line to an outer end of the rubber reinforcing layer is 35% or more and 45% or less of a tire sectional height.

Preferably, in the pneumatic tire, the maximum thickness of the rubber reinforcing layer is 2mm to 4 mm.

Preferably, in the pneumatic tire, the apex has a complex elastic modulus E a of 70MPa to 130MPa, and a loss tangent LTa of 0.18 or less.

Preferably, in the pneumatic tire, the heel rubber has a complex elastic modulus E ∈ c of 7MPa to 13MPa, and a loss tangent LTc of 0.08 or less.

Preferably, in the pneumatic tire, a radial distance from the bead base line to an end of the turn-up portion is 20mm or more and 30mm or less.

Preferably, in the pneumatic tire, the carcass cord includes a plurality of carcass cords arranged in parallel, and a fineness of each carcass cord is 1500dtex or more and 1700dtex or less.

Preferably, in the pneumatic tire, the complex elastic modulus E r of the rubber reinforcing layer is larger than the complex elastic modulus E c of the heel rubber.

Preferably, in the pneumatic tire, the heel rubber has a loss tangent LTc smaller than a loss tangent LTr of the rubber reinforcing layer.

Preferably, in the pneumatic tire, the complex elastic modulus E r of the rubber reinforcing layer is the same as or smaller than the complex elastic modulus E a of the apex.

Preferably, in the pneumatic tire, the loss tangent LTr of the rubber reinforcing layer is the same as or less than the loss tangent LTa of the apex.

In the pneumatic tire of the present invention, a small bead apex is used as compared with the conventional tire, and a rubber reinforcing layer is provided between the carcass and the heel rubber. When the tire is mounted on a standard rim and the internal pressure is adjusted to the standard internal pressure, the shape of the body portion located in the region from the boundary portion between the tread and the sidewall to the outer end of the apex is represented by a single circular arc having a diameter of 75% to 90% of the cross-sectional height of the carcass.

In this tire, the main body portion located in a region from the boundary portion between the tread and the sidewall to the outer end of the apex contributes particularly to a reduction in the amount of the bead portion. In this tire, reduction in mass and rolling resistance is achieved despite the use of the rubber reinforcing layer. Further, since the main body portion is supported by the rubber reinforcing layer in the bead portion, a decrease in-plane twisting rigidity can be suppressed. In this tire, a required rigidity is ensured.

According to the present invention, a pneumatic tire can be obtained in which the rigidity is ensured and the reduction of the mass and the rolling resistance is achieved.

Drawings

Fig. 1 is a sectional view showing a part of a pneumatic tire of one embodiment of the present invention;

fig. 2 is a sectional view showing a portion of the tire of fig. 1.

[ notation ] to show

2 tyre

4 Tread

6 side wall

8 heel rubber

10 bead

14 tyre body

16 belted layer

18 reinforcing layer

22 rubber reinforcement layer

24 tread surface

30 core

32 triangular glue

34 carcass ply

36 main body part

38 turn-back part

40 end of the folded-back part 38

44 inner end of rubber reinforcement layer 22

46 outer end of the rubber reinforcement layer 22

48 outer end of bead heel rubber 8

50 ends of the belt 16

Inner side of 52 apex 32

54 outer side of the rubber reinforcement layer 22

Detailed Description

The present invention will be described in detail below according to preferred embodiments with reference to the accompanying drawings as appropriate.

Fig. 1 shows a part of a 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 passenger car.

Fig. 1 shows a portion of a section of a tyre 2 along a plane comprising the rotation axis of the tyre 2. In fig. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper of fig. 1 is the circumferential direction of the tire 2. In fig. 1, a chain line CL indicates an equatorial plane of the tire 2.

In fig. 1, a tire 2 is assembled into a rim R. The rim R is a standard rim. The inside of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted to a standard internal pressure. There is no load on the tire 2.

In the present invention, a state in which the tire 2 is assembled to a rim R (standard rim), the internal pressure of the tire 2 is adjusted to a standard internal pressure, and no load is applied to the tire 2 is referred to as a standard state. In the present invention, unless otherwise specified, the dimensions and angles of the tire 2 and each portion of the tire 2 are measured in a standard state.

In the present specification, the standard rim refers to a rim specified in a specification that the tire 2 conforms to. The "standard Rim" of the JATMA specification, "Design Rim" of the TRA specification, and "Measuring Rim" of the ETRTO specification are standard rims.

In the present specification, the standard internal pressure refers to an internal pressure defined in a specification that the tire 2 complies with. The "maximum air pressure" in the JATMA specification, "maximum value" described in the "tie LOAD coefficients AT varias color mixing pressure" in the TRA specification, and "mixing pressure" in the ETRTO specification are the standard internal pressures.

In the present specification, the standard load refers to a load specified in a specification that the tire 2 complies with. The "maximum LOAD CAPACITY" in the JATMA specification, "the" maximum value "described in the" tie LOAD LIMITSAT variaus COLD inertia preservation previous "in the TRA specification, and the" LOAD CAPACITY "in the ETRTO specification are standard LOADs.

In fig. 1, a solid line BBL extending in the axial direction is a bead base line. The bead base line is a line that defines a rim diameter (see JATMA and the like) of a rim R (standard rim).

The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of heel caps 8, a pair of beads 10, a pair of anti-friction layers 12, a carcass 14, a belt 16, a reinforcing layer 18, an inner liner 20, and a pair of rubber reinforcing layers 22.

The tread 4 is in contact with the road surface at its outer surface. The outer surface of the tread 4 is the tread surface 24. Grooves 26 are cut into the tread 4. In this tire 2, the tread 4 includes a base portion 4a and a cap portion 4b located radially outward of the base portion 4 a. The base portion 4a is made of a crosslinked rubber in consideration of adhesiveness. The cover 4b is made of crosslinked rubber in consideration of abrasion resistance and grip performance.

In fig. 1, the symbol PE denotes the equator of the tire 2. The equator is an intersection point of the imaginary tread surface 24 and the equator surface, which is assumed to have no groove 26. The double arrow HS is the radial distance from the bead base line to the equator PE. The radial distance HS is a sectional height of the tire 2 (see JATMA and the like).

Each sidewall 6 is connected to an end of the tread 4. The sidewalls 6 extend radially inward from the ends of the tread 4 along the carcass 14. The sidewalls 6 are made of crosslinked rubber. The sidewalls 6 protect the carcass 14. In this tire 2, a tread side surface 28 is disposed between the sidewall 6 and the tread 4.

Each heel rubber 8 is located radially inside the sidewall 6. As shown in fig. 1, a part of the heel rubber 8 is in contact with the flange FR of the rim R. The heel rubber 8 is made of a crosslinked rubber in consideration of abrasion resistance.

In fig. 1, the symbol PW is the axially outer end of the tire 2. The outer end PW is specified based on an imaginary side surface S which is assumed to be the outer surface of the sidewall 6 and the heel rubber 8, that is, the side surface S of the tire 2 without decoration such as patterns and characters. The axial distance from one outer end PW to the other outer end PW is the maximum width of the tire 2, i.e., the cross-sectional width (refer to JATMA and the like). The outer end PW is a position indicating the maximum width of the tire 2.

The bead 10 is located axially inward of the heel rubber 8. The bead 10 comprises a core 30 and an apex 32. The core 30 extends in the circumferential direction. As shown in fig. 1, the core 30 has a rectangular sectional shape. The core 30 comprises a wire of steel wire. Apex 32 is radially outward of core 30. In the cross section of the tire 2 shown in fig. 1, the apex 32 is tapered radially outward. In this tire 2, the apex 32 is composed of a crosslinked rubber having high rigidity.

Each anti-friction layer 12 is located radially inside the bead 10. As shown in fig. 1, at least a portion of the scuff layer 12 is in contact with the bead seat SR of the rim R. In this tire 2, the anti-friction layer 12 is composed of a cloth and rubber impregnated in the cloth.

The carcass 14 is located inside the tread 4, the pair of sidewalls 6, and the pair of heel rubbers 8. The carcass 14 extends from one bead 10 to the other bead 10. The carcass 14 includes at least one carcass ply 34. In this tire 2, the carcass 14 is constituted by one carcass ply 34.

Although not shown, the carcass ply 34 includes a plurality of carcass cords arranged in parallel. These carcass cords are covered with a rubberizing. Each carcass cord crosses the equatorial plane. In the tire 2, the angle of the carcass cord with respect to the equatorial plane is 70 ° to 90 °. The carcass 14 of the tire 2 has a radial structure. In the tire 2, a cord made of an organic fiber is used as a carcass cord. Examples of the organic fiber include nylon fiber, polyester fiber, rayon fiber, and aramid fiber.

In this tire 2, the carcass ply 34 is folded back around the respective cores 30. The carcass ply 34 has a main body portion 36 spanning the one core 30 and the other core 30, and a pair of turn-up portions 38 connected to the main body portion 36 and turned up from the axially inner side to the axially outer side along the periphery of each core 30. In this tire 2, an end portion 40 of this turn-up portion 38 is covered with the rubber reinforcing layer 22 from the outside in the axial direction.

The belt 16 is laminated with the carcass 14 radially inside the tread 4. In the tire 2, the belt 16 is constituted by 2 belt plies 42.

Although not shown, each belt ply 42 includes a plurality of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The belt cords form an angle of 10 DEG to 35 DEG with respect to the equatorial plane. In the tire 2, the belt cord is made of steel wire.

The reinforcing layer 18 is located radially between the tread 4 and the belt 16. The reinforcing layer 18 covers the entire belt 16. The reinforcing layer 18 has a jointless structure. Although not shown, the reinforcing layer 18 includes a spirally wound belt cord. Cords composed of organic fibers are used as the belt cords.

An inner liner 20 is positioned inside the carcass 14. The inner liner 20 constitutes an inner surface of the tire 2. The inner liner 20 is made of a crosslinked rubber having excellent air-shielding properties. The inner liner 20 maintains the internal pressure of the tire 2.

Each rubber reinforcing layer 22 is made of a crosslinked rubber. The rubber reinforcing layer 22 is located axially outside the apex 32. The rubber reinforcing layer 22 is located between the carcass 14 and the heel rubber 8. As shown in fig. 1, the rubber reinforcing layer 22 has the largest thickness at the portion of the outer end PA of the apex 32. The rubber reinforcing layer 22 is tapered radially inward from the portion having the maximum thickness. The inner end 44 of the rubber reinforcement layer 22 is located radially adjacent the core 30. The rubber reinforcing layer 22 is tapered radially outward from the portion having the maximum thickness. The outer end 46 of this rubber-reinforcing layer 22 is located radially between the outer end 48 of the heel rubber 8 and the position PW representing the maximum width.

In fig. 1, the symbol PM is the axial center of the boundary between the core 30 and the apex 32. The symbol PA is the outer end of the apex 32. The double arrow LA is the length from the axial center PM of the boundary to the outer end PA of the apex 32. The length LA is the length of the apex 32.

In the tire 2, the length LA of the apex 32 is 10mm to 15 mm. In the conventional tire, the length of the apex is usually set within the range of 30 to 40 mm. The apex 32 of the tire 2 is small. The apex 32 contributes to weight reduction. Apex 32 helps to reduce rolling resistance.

In fig. 1, a point indicated by a symbol CV, a point indicated by a symbol CW, and a point indicated by a symbol CA indicate designated positions on the inner surface of the main body portion 36 forming a part of the carcass ply 34. The point CV is an intersection point of a reference line (not shown) extending in the radial direction and the inner surface through the end 50 of the belt 16. This point CV corresponds to the end 50 of the belt 16. The point CW is an intersection point of a reference line (not shown) extending in the axial direction and the inner surface, passing through the maximum width position PW. This spot CW corresponds to the maximum width position PW. The point CA is an intersection point of a reference line (not shown) extending in the radial direction and the inner surface through the outer end PA of the apex 32. This location CA corresponds to the outer end PA of apex 32.

In this tire 2, the shape of the main body portion 36 at the boundary portion between the tread 4 and the sidewall 6, i.e., in the region from the sidewall B to the outer end PA of the apex 32, is specified based on the inner surface of the main body portion 36. In the tire 2, the shape of the body portion 36 is represented by a single circular arc passing through the point CV, the point CW, and the point CA. In the present invention, when the distance from the arc to the inner surface, measured along the arc normal passing through the point CV, the point CW, and the point CA, is within 3% of the arc length, it is determined that the shape of the main body portion 36 is represented by a single arc passing through the point CV, the point CW, and the point CA.

In fig. 1, an arrow R indicates a diameter of an arc indicating the shape of the body portion 36. The symbol PC is the intersection of the inner surface of the carcass 14 and the equatorial plane. The intersection point PC is the radially outer end of the inner surface. The double arrow HC is the radial distance from the bead base line to the radially outer end PC. In the present invention, the distance HC is the cross-sectional height of the carcass 14.

In this tire 2, a small bead apex 32 is used as compared with the conventional tire, and a rubber reinforcing layer 22 is provided between the carcass 14 and the heel rubber 8. In a state where the tire 2 is assembled to a standard rim and the internal pressure is adjusted to the standard internal pressure, the shape of the body portion 36 located in a region from the sidewall B to the outer end PA of the apex 32 is represented by a single circular arc having a diameter R of 75% to 90% of the cross-sectional height HC of the carcass 14.

In the tire 2, the body portion 36 located in the region from the sidewall B to the outer end PA of the apex 32 contributes particularly to the reduction in the amount of the bead 10 portion. In the tire 2, the rubber reinforcing layer 22 is used, but the reduction of the mass and the rolling resistance is also achieved. Further, since the main body portion 36 is supported by the rubber reinforcing layer 22 in a portion of the bead 10, a decrease in-plane twisting rigidity can be suppressed. In this tire 2, necessary rigidity is ensured. In this tire 2, good steering stability is maintained. The tire 2 can ensure rigidity and achieve reduction in mass and rolling resistance.

As described above, in this tire 2, the shape of the main body portion 36 located in the region from the sidewall B to the outer end PA of the apex 32 is represented by a single circular arc. Therefore, the portion of the sidewall 6 to the heel rubber 8, i.e., the side portion, is entirely flexed. Since local distortion can be suppressed from concentrating on the side portion, the durability of the tire 2 can be improved.

Fig. 2 shows a part of a cross section of the tire 2 shown in fig. 1. Fig. 2 shows a portion of a bead 10 of the tire 2. In fig. 2, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper of fig. 2 is the circumferential direction of the tire 2.

In fig. 2, reference symbol PB denotes a position on the inner surface 52 of the apex 32 corresponding to a position half the height in the radial direction of the apex 32. The solid line BA is a straight line passing through this position PB and the outer end PA of apex 32. The solid line BA is inclined with respect to the axial direction.

In the bead 10 portion, the main portion 36 of the carcass ply 34 extends from the core 30 to the outer end PA of the apex 32 along the inner side 52 of the apex 32. As shown in fig. 2, in the tire 2, the main body portion 36 is inclined with respect to the axial direction. In the present invention, the inclination direction of the body portion 36 extending along the inner surface 52 of the apex 32 is specified by the inclination direction of the solid line BA described above.

In fig. 2, a solid line AL is a straight line extending in the axial direction through the axial center PM of the boundary between the core 30 and the apex 32. The angle represented by the symbol θ is an angle formed by the solid line BA with respect to the solid line AL. In the present invention, in the bead 10, the angle formed by the main body portion 36 extending along the inner side surface 52 of the apex 32 with respect to the axial direction is represented by the angle θ.

In the present invention, the above-mentioned angle θ is measured in a state where the tire 2 is assembled to a rim R (standard rim), the internal pressure of the tire 2 is adjusted to 10% of the standard internal pressure, and no load is applied to the tire 2. Although not shown, in the manufacture of the tire 2, the tire 2 is formed by pressing a green tire (the tire 2 in an uncrosslinked state) against a cavity surface of a mold. The outer surface of the tire 2 in the above state corresponds to the outer surface of the tire 2 indicated by the cavity surface of the mold.

As described above, in the tire 2, the body portion 36 extending along the inner surface 52 of the apex 32 is inclined with respect to the axial direction. In particular, in the tire 2, the angle θ of the main body portion 36 with respect to the axial direction in the bead 10 portion is preferably 45 ° or more, and preferably 50 ° or less. By setting the angle θ to 45 ° or more, the main body portion 36 contributes to suppressing a decrease in-plane torsional rigidity. In this tire 2, a required rigidity is ensured. By setting the angle θ to 50 ° or less, the main body portion 36 contributes to reducing the amount of the portion of the bead 10. In this tire 2, the mass and the rolling resistance are reduced.

Further, in the tire 2, the angle θ of the body portion 36 with respect to the axial direction is set in the range of 45 ° to 50 °, and in the tire 2 in the standard state, it is helpful to configure the body portion 36 located in the region from the sidewall B to the outer end PA of the apex 32 in a form in which the shape thereof draws a circular arc. In this region, the body portion 36, the shape of which is represented by a circular arc, contributes to a reduction in the amount of the portion of the bead 10 and suppression of a reduction in-plane distortion rigidity, as described above. In the tire 2, it is possible to secure rigidity and achieve reduction in mass and rolling resistance.

As described above, in this tire 2, the apex 32 is composed of a crosslinked rubber having high rigidity. In the tire 2, the complex elastic modulus E a of the apex 32 is preferably 70MPa or more, and preferably 130MPa or less, from the viewpoint of ensuring rigidity. From the viewpoint of suppressing heat generation, the loss tangent LTa of the apex 32 is preferably 0.18 or less.

In the present invention, the composite elastic modulus and the loss tangent (also referred to as tan δ) of the structural member of the tire 2 such as the apex 32 are measured under the following conditions using a viscoelasticity spectrometer in accordance with the regulations of JIS K6394.

Initial strain is 10%

The amplitude is plus or minus 1 percent

Frequency 10Hz

Deformation mode-stretching

The measurement temperature is 70 DEG C

In this tire 2, the heel rubber 8 is made of soft cross-linked rubber. From the viewpoint of ensuring rigidity, the complex elastic modulus E × c of the heel rubber 8 is preferably 7MPa or more. From the viewpoint of ensuring flexibility and maintaining good durability, the complex elastic modulus E × c of the heel rubber 8 is preferably 13MPa or less. From the viewpoint of suppressing heat generation, the loss tangent LTc of the heel rubber 8 is preferably 0.08 or less.

In this tire 2, the rubber reinforcement layer 22 contributes to the rigidity of the portion of the bead 10 together with the small apex 32. From this viewpoint, the complex elastic modulus E r of the rubber reinforcing layer 22 is preferably 60MPa or more. From the viewpoint of ensuring flexibility and maintaining good durability, the complex elastic modulus E × r of the rubber reinforcing layer 22 is preferably 100MPa or less. From the viewpoint of suppressing heat generation, the loss tangent LTr of the rubber-reinforced layer 22 is preferably 0.16 or less.

In the tire 2, the complex elastic modulus E r of the rubber reinforcing layer 22 is preferably the same as the complex elastic modulus E a of the apex 32 or smaller than the complex elastic modulus E a of the apex 32. In this tire 2, the rubber reinforcement layer 22 improves the in-plane twisting rigidity, and the apex 32 contributes to the rigidity of the bead 10 portion. Since the tire 2 has sufficient rigidity, excellent steering stability can be obtained. From this viewpoint, the complex elastic modulus E r of the rubber reinforcing layer 22 is preferably smaller than the complex elastic modulus E a of the apex 32. Specifically, the difference (E a-E r) between the complex elastic modulus E a of the apex 32 and the complex elastic modulus E r of the rubber reinforcing layer 22 is preferably 0MPa or more, and more preferably 10MPa or more. From the viewpoint of suppressing the deviation between the rigidity of the rubber reinforcing layer 22 and the rigidity of the apex 32 and maintaining good durability, the difference (ea-ar) is preferably 50MPa or less.

In this tire 2, it is preferable that the loss tangent LTr of the rubber reinforcing layer 22 is the same as the loss tangent LTa of the apex 32 or smaller than the loss tangent LTa of the apex 32. By using this rubber reinforcing layer 22, heat generation accompanying deformation in the portion of the bead 10 is suppressed. In this tire 2, the rubber reinforcing layer 22 contributes to reduction of rolling resistance. From this viewpoint, the loss tangent LTr of the rubber-reinforced layer 22 is preferably smaller than the loss tangent LTa of the apex 32. Specifically, the difference (LTa-LTr) between the loss tangent LTa of the apex 32 and the loss tangent LTr of the rubber reinforcing layer 22 is preferably 0.00 or more, and more preferably 0.05 or more. Since the smaller the loss tangent LTr of the rubber-reinforced layer 22 is, the better, the larger the difference (LTa-LTr) is, the better from the viewpoint of reduction of rolling resistance.

In this tire 2, from the viewpoint of ensuring rigidity and achieving reduction in rolling resistance, it is more preferable that the loss tangent LTr of the rubber-reinforced layer 22 is the same as the loss tangent LTa of the apex 32 or smaller than the loss tangent LTa of the apex 32, and the complex elastic modulus E r of the rubber-reinforced layer 22 is the same as the complex elastic modulus E a of the apex 32 or smaller than the complex elastic modulus E a of the apex 32. In the tire 2, it is more preferable that the loss tangent LTr of the rubber reinforcing layer 22 is smaller than the loss tangent LTa of the apex 32, and further, the complex elastic modulus E × r of the rubber reinforcing layer 22 is smaller than the complex elastic modulus E × a of the apex 32.

In this tire 2, the complex elastic modulus E r of the rubber reinforcing layer 22 is larger than the complex elastic modulus E c of the heel rubber 8. The rubber reinforcing layer 22 is harder than the heel rubber 8. This rubber reinforcement layer 22 contributes to the rigidity of the portion of the bead 10. As shown in fig. 2, between the core 30 and the maximum width position PW, the rubber reinforcing layer 22 supports the main body portion 36 from the radially inner side. In this tire 2, the rubber reinforcing layer 22 helps ensure in-plane distortion rigidity. From this viewpoint, in the tire 2, the difference (E × r-E × c) between the complex elastic modulus E × r of the rubber reinforcing layer 22 and the complex elastic modulus E × c of the heel rubber 8 is preferably 50MPa or more. From the viewpoint of suppressing the deviation of the rigidity of the rubber reinforcing layer 22 and the rigidity of the heel rubber 8 and maintaining good durability, the difference (E r-E c) is preferably 90MPa or less.

In this tire 2, the heel rubber 8 is located axially outward of the rubber reinforcing layer 22. The heel rubber 8 is located at a portion that is deformed to a greater extent than the rubber reinforcing layer 22. In this tire 2, the loss tangent LTc of the heel rubber 8 is preferably smaller than the loss tangent LTr of the rubber reinforcing layer 22. This effectively suppresses heat generation. In this tire 2, the heel rubber 8 contributes to reduction of rolling resistance. From this viewpoint, the difference (LTr-LTc) between the loss tangent LTr of the rubber-reinforced layer 22 and the loss tangent LTc of the heel rubber 8 is preferably 0, 01 or more, and more preferably 0.03 or more. The smaller the loss tangent LTc of the heel rubber 8, the better, and therefore the larger the difference (LTr-LTc) from the viewpoint of the reduction in rolling resistance, the better.

In this tire 2, from the viewpoint of ensuring rigidity and achieving reduction in rolling resistance, it is preferable that the complex elastic modulus E r of the rubber reinforcing layer 22 is larger than the complex elastic modulus E c of the heel rubber 8, and the loss tangent LTc of the heel rubber 8 is smaller than the loss tangent LTr of the rubber reinforcing layer 22.

In this tire 2, the complex elastic modulus E c of the heel rubber 8 is smaller than the complex elastic modulus E a of the apex 32. The heel rubber 8 is softer than the apex 32. In the tire 2 in the normal state, the heel rubber 8 contributes to a configuration in which the body portion 36 located in the region from the sidewall B to the outer end PA of the apex 32 is shaped so as to draw a circular arc. In the tire 2, the mass and the rolling resistance can be reduced while securing the rigidity. From this viewpoint, the difference (ea-ec) between the complex elastic modulus ea of the bead apex 32 and the complex elastic modulus ec of the heel rubber 8 is preferably 60MPa or more. From the viewpoint of suppressing the deviation of the rigidity of the apex 32 and the rigidity of the heel rubber 8 and maintaining good durability, the difference (E a-E c) is preferably 100MPa or less.

In this tire 2, the loss tangent LTc of the heel rubber 8 is smaller than the loss tangent LTa of the apex 32. In the heel rubber 8, heat generation accompanying deformation is suppressed as compared with the bead apex 32. The heel rubber 8 contributes to reduction of rolling resistance. From this viewpoint, the difference (LTa-LTc) between the loss tangent LTa of the apex 32 and the loss tangent LTc of the heel rubber 8 is preferably 0.05 or more. Since the smaller the loss tangent LTc of the heel rubber 8, the better, the larger the difference (LTa-LTc), the better from the viewpoint of reduction in rolling resistance.

In fig. 2, the double arrow HR is the radial distance from the bead base line to the outer end 46 of the rubber reinforcing layer 22. The double arrow HF is the radial distance from the bead base line to the end 40 of the turn-back 38.

In this tire 2, the radial distance HR from the bead base line to the outer end 46 of the rubber reinforcing layer 22 is preferably 35% or more, and preferably 45% or less of the cross-sectional height HS of the tire 2. The ratio of the radial distance HR to the sectional height HS is set to 35% or more, whereby the rubber reinforcing layer 22 contributes to effectively securing rigidity. This ratio is set at 45% or less, whereby the amount of the rubber-reinforced layer 22 is appropriately maintained. The rubber reinforcement layer 22 contributes to the reduction of mass and rolling resistance.

In this tire 2, the radial distance HF from the bead base line to the end 40 of the turn-up portion 38 is preferably 20mm or more, and preferably 30mm or less. By setting the radial distance HF to 20mm or more, the folded portion 38 contributes to effectively securing rigidity. By setting the radial distance HF to 30mm or less, the influence on the quality by the folded portion 38 is suppressed. Further, damage starting from the end 40 of the folded portion 38 is prevented, and therefore, good durability is maintained.

As described above, in this tire 2, the rubber reinforcing layer 22 has the largest thickness at the portion of the outer end PA of the apex 32. In fig. 2, the double arrow t is the maximum thickness of the rubber reinforcing layer 22. This maximum thickness is represented by the maximum value of the thickness measured along the normal to the outer side surface 54 of the rubber-reinforced layer 22.

In this tire 2, the maximum thickness t of the rubber reinforcing layer 22 is preferably 2mm or more, and preferably 4mm or less. By setting the maximum thickness t to 2mm or more, the rubber reinforcing layer 22 contributes to effectively securing rigidity. By setting the maximum thickness t to 4mm or less, the amount of the rubber reinforcing layer 22 is appropriately maintained. The rubber reinforcement layer 22 contributes to the reduction of mass and rolling resistance.

As described above, in the tire 2, the carcass ply 34 includes a plurality of carcass cords arranged in parallel. In the tire 2, the fineness of each carcass cord is preferably 1500dtex or more and 1700dtex or less. By setting the fineness of the carcass cord to 1500dtex or more, the carcass cord 34 contributes to effective securing of rigidity. By setting the fineness to 1700dtex or less, the influence of the carcass ply 34 on the quality and rolling resistance can be suppressed.

As is apparent from the above description, according to the present invention, a pneumatic tire 2 ensuring rigidity and achieving reduction in mass and rolling resistance can be obtained.

The embodiments disclosed herein are illustrative and not restrictive in all respects. The technical scope of the present invention is not limited to the above-described embodiments, and includes all modifications within a range equivalent to the structure described in the claims.