JP5421815B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire mounted on a passenger car or the like.

  The tire includes a tread, a sidewall, a bead, a carcass, a belt, and the like. The belt consists of an inner layer and an outer layer. Each of the inner layer and the outer layer is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The belt contributes to the rigidity of the tire.

  The tread usually has a plurality of main grooves. Each main groove extends in the circumferential direction. This main groove contributes to drainage. The surface of the tread is separated by these main grooves.

  At the bottom of the main groove, the tread is relatively thin. Due to this thinness, the strength of the tread can be reduced. In the vicinity of the main groove, cracks are likely to occur.

  Proposals have been made to increase the strength of the bottom of the main groove. Japanese Patent Application Laid-Open No. 2006-199067 discloses a tire in which the base rubber is not disposed on the radially inner side of the main groove but only the cap rubber is disposed. Japanese Patent Application Laid-Open No. 2004-314783 discloses a tire provided with a cut protective layer in which short fibers are blended, and this cut protective layer is provided at the bottom of the groove.

Japanese Patent Laid-Open No. 2006-199067 Japanese Patent Application Laid-Open No. 2004-314783

  In the tire of the above document, the boundary between different types of rubber is exposed on the inner surface of the main groove. Cracks can occur at this exposed boundary. A tire having higher durability is preferred.

  On the other hand, tires with low rolling resistance are preferable because they can contribute to low fuel consumption of the vehicle. In order to suppress rolling resistance, it is conceivable to reduce the loss tangent tan δ of the tread. However, when the loss tangent tan δ is reduced, the durability of the tread tends to decrease. A tire having low rolling resistance and excellent durability is preferable.

  An object of the present invention is to provide a pneumatic tire excellent in various performances.

The pneumatic tire according to the present invention includes a tread provided with a main groove extending in the circumferential direction, a pair of sidewalls each extending substantially inward in the radial direction from the end of the tread, and each of which is more than the sidewall. A pair of beads positioned substantially inside in the radial direction, a carcass extending between one bead and the other bead along the inside of the tread and the sidewall, and the tread and the carcass in the radial direction. And a reinforcing layer that exists locally in the axial direction and that is positioned inside the main groove in the radial direction. The tread has a cap and a base located on the radially inner side of the cap. The reinforcing layer is located on the radially inner side of the base. The loss tangent tan δ of the cap is δc, the loss tangent tan δ of the base is δb, the loss tangent tan δ of the reinforcing layer is δr, the complex elastic modulus E ^{* of the} cap is Ec, and the reinforcing layer When the complex elastic modulus E ^* is Er, the axial width of the reinforcing layer is Wr (mm), and the axial width of the main groove is Wg (mm), the tire has the following relationship: The expressions (1), (2), (3) and (4) are satisfied.
3 × δc ≦ δr (1)
δc ≧ δb (2)
Ec ≦ Er (3)
Wr ≧ (4/3) × Wg (4)

  Preferably, the minimum value of the thickness of the tread on the radially inner side of the main groove is T1 (mm), and the thickness of the reinforcing layer on the radially inner side of the position where the thickness of the tread is T1 is T2 (mm). The ratio [T2 / (T1 + T2)] is 0.3 or more and 0.7 or less.

  Preferably, the tread is formed using strip winding.

  Preferably, short fibers are blended in the reinforcing layer.

  Preferably, the belt includes a plurality of cords arranged in parallel and a topping rubber, and the material of the belt cord is steel. Preferably, the number of layers of the belt is two or more. Preferably, the carcass includes a plurality of cords arranged in parallel and a topping rubber, and the carcass cord is made of steel.

  In the pneumatic tire according to the present invention, the reinforcing layer improves the strength in the vicinity of the main groove. In this tire, even when the rolling resistance is suppressed, the strength in the vicinity of the main groove is not significantly reduced.

FIG. 1 is a conceptual diagram showing a pneumatic tire according to a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire of FIG. FIG. 3 is a cross-sectional view in which a part of FIG. 2 is further enlarged. FIG. 4 is a conceptual diagram showing a pneumatic tire according to a second embodiment of the present invention.

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

  FIG. 1 is a conceptual diagram showing a part of a heavy duty tire 2 according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire 2 of FIG. 1 and 2, the vertical direction is the radial direction, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. The tire 2 has a substantially left-right symmetric shape centered on a one-dot chain line CL in FIG. This alternate long and short dash line CL represents the equator plane of the tire 2. The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, a belt 12, a reinforcing layer 14, a bead reinforcing layer 16, an inner sidewall 18, an inner liner 20, and a chafer 22. The tire 2 is a tubeless type. The tire 2 is attached to a truck, a bus or the like. The tire of the present invention is not limited to heavy loads. However, a heavy-duty tire is preferable from the viewpoint that the effect of the reinforcing layer 14 is easily manifested.

  The tread 4 is made of a crosslinked rubber having excellent wear resistance. The tread 4 has a shape protruding outward in the radial direction.

  As shown in FIG. 2, the tread 4 includes a cap 24, a base 26, and a tread surface 28. The base 26 is located on the radially inner side of the cap 24. The base 26 is stacked on the carcass 10.

  The tread surface 28 is in contact with the road surface. The tread surface 28 is formed by the cap 24. On the tread surface 28, fine grooves (not shown) and a main groove 30 are engraved. A tread pattern is formed by these grooves.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 6 is made of a crosslinked rubber. The sidewall 6 absorbs an impact from the road surface by bending. Furthermore, the sidewall 6 prevents the carcass 10 from being damaged.

  The bead 8 includes a core 32, an apex 33 that extends radially outward from the core 32, and a packing rubber 34 that extends radially outward from the apex 33. The core 32 has a ring shape. The core 32 includes a plurality of non-stretchable wires (typically steel wires). The apex 33 is tapered outward in the radial direction. The apex 33 is made of a highly hard crosslinked rubber. The packing rubber 34 is tapered outward in the radial direction. The packing rubber 34 is soft. The packing rubber 34 relieves stress concentration at the end 35 of the carcass 10.

  The carcass 10 includes a carcass ply 36. The carcass ply 36 is bridged between the beads 8 on both sides, and extends along the inside of the tread 4 and the sidewall 6. The carcass ply 36 is folded around the core 32 from the inner side to the outer side in the axial direction.

  Although not shown, the carcass ply 36 includes a plurality of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is usually 70 ° to 90 °. In other words, the carcass 10 has a radial structure. The cord is made of steel. Cords made of organic fibers may be used.

  The belt 12 is located on the radially outer side of the carcass 10. The belt 12 is laminated with the carcass 10. The belt 12 reinforces the carcass 10. The belt 12 includes a first layer 38, a second layer 40, a third layer 42, and a fourth layer 44. Each of the first layer 38, the second layer 40, the third layer 42, and the fourth layer 44 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is made of steel. This cord is inclined with respect to the equator plane. The absolute value of the angle formed by this cord with respect to the equator plane is 15 ° to 70 °.

  The bead reinforcing layer 16 is laminated with the carcass ply 36. The bead reinforcing layer 16 is wound around the core 32. The bead reinforcing layer 16 includes a large number of cords arranged in parallel and a topping rubber. Each cord is made of steel. This bead reinforcement layer 16 is also called a steel filler. The bead reinforcing layer 16 contributes to the durability of the tire 2.

  The inner sidewall 18 is located outside the bead 8 in the axial direction. The inner sidewall 18 is partially laminated with the bead reinforcement layer 16. The composition of the inner sidewall 18 is equivalent to the composition of the packing rubber 34. The inner sidewall 18 is soft. The inner sidewall 18 is interposed between the chafer 22 and the bead reinforcement layer 16. The inner sidewall 18 relieves stress between the chafer 22 and the bead reinforcement layer 16.

  The chafer 22 is located in the vicinity of the bead 8. The chafer 22 is partially laminated with the inner sidewall 18. When the tire 2 is incorporated into the rim, the chafer 22 comes into contact with the rim. By this contact, the vicinity of the bead 8 is protected. The chafer 22 is usually made of a cloth and rubber impregnated in the cloth. A chafer made of a single rubber may be used.

  The main groove 30 extends in the circumferential direction. The main groove 30 is continuous over the entire circumferential direction (360 °). The groove | channel which continues over the whole circumferential direction is a main groove.

  The main groove 30 is formed in the tread 4. More specifically, the main groove 30 is formed in the cap 24. The inner surface (side surface and bottom surface) of the main groove 30 is formed by the tread 4. More specifically, the inner surface of the main groove 30 is formed by the cap 24.

  In the embodiment of FIGS. 1 and 2, the total number of main grooves 30 is two. Further, the tire 2 may be provided with more main grooves 30. For example, as a main groove, a first main groove (crown main groove) disposed at an axial center position (position of the center line CL) and a second main groove (shoulder main groove) provided on the outer side in the axial direction than the center line CL. Groove) may be provided. The number of main grooves 30 is not limited.

  The reinforcing layer 14 is located between the tread 4 and the carcass 10 in the radial direction. More specifically, the reinforcing layer 14 is located between the base 26 and the belt 12 in the radial direction. The outer surface in the radial direction of the reinforcing layer 14 is in contact with the base 26. The inner surface in the radial direction of the reinforcing layer 14 is in contact with the belt 12.

  The reinforcing layer 14 is located on the radially inner side of the main groove 30. The reinforcing layer 14 extends in the circumferential direction. The reinforcing layer 14 is continuous over the entire circumferential direction.

The reinforcing layer 14 exists locally in the axial direction. Therefore, there are the following advantages compared to the case where a layer extending from one end to the other end of the belt 12 is provided in the axial direction.
(1) The mass of the tire 2 is not significantly increased.
(2) The rolling resistance of the tire 2 is not significantly increased.
(3) The longitudinal rigidity of the tire 2 is not significantly increased.
The tire 2 contributes to low fuel consumption of the vehicle. The tire 2 is excellent in ride comfort.

  Since the reinforcing layer 14 is located below the main groove 30, the deformation in the vicinity of the main groove is sufficiently suppressed even though the reinforcing layer 14 exists locally. By suppressing the deformation, the occurrence of cracks and the like is suppressed in the vicinity of the main groove 30.

  The reinforcing layer 14 can improve the strength in the vicinity of the main groove 30. The tread under the main groove 30 can be thinned by the reinforcing layer 14. By making the bottom of the main groove 30 thinner, the rolling resistance tends to be lowered. The reinforcing layer 14 contributes to low fuel consumption of the vehicle.

  In FIG. 3, the width of the reinforcing layer 14 is indicated by the arrow Wr, and the width of the main groove 30 is indicated by the arrow Wg. The width Wr and the width Wg are measured along the axial direction.

[Main groove width Wg]
From the viewpoint of drainage, the width Wg of the main groove 30 is preferably 1 mm or more, and more preferably 4 mm or more. From the viewpoint of the strength of the tread 4, the width Wg of the main groove 30 is preferably 15 mm or less, and more preferably 14 mm or less.

[Main groove depth]
From the viewpoint of drainage, the depth of the main groove 30 is preferably 3 mm or more, and more preferably 4 mm or more. From the viewpoint of the strength of the tread 4, the depth of the main groove 30 is preferably 15 mm or less, and more preferably 14 mm or less. The depth of the main groove 30 is measured along the radial direction.

[Reinforcing layer width Wr]
From the viewpoint of durability in the vicinity of the main groove 30, the width Wr of the reinforcing layer 14 is preferably 15 mm or more, and particularly preferably 20 mm or more. In light of fuel consumption and riding comfort, the width Wr is preferably equal to or less than 60 mm, and particularly preferably equal to or less than 50 mm.

[Relationship between width Wr and width Wg]
From the viewpoint of durability near the main groove 30, the width Wr is preferably not less than (4/3) times the width Wg. That is, the tire 2 satisfying the following formula (4) is preferable.
Wr ≧ (4/3) × Wg (4)

  From the viewpoint of enhancing the effect of the reinforcing layer, the ratio (Wr / Wg) is preferably 4/3 or more, more preferably 1.5 or more, as in the above formula (4). From the viewpoint of ride comfort, this ratio (Wr / Wg) is preferably 3.0 or less, and more preferably 2.0 or less.

[Arrangement area of reinforcing layer in the axial direction]
From the viewpoint of durability in the vicinity of the main groove 30, the reinforcing layer 14 is preferably present in 80% or more of the axial range of the main groove 30, and the reinforcing layer 14 is present in 100% of the axial range of the main groove 30. More preferably.

[Number of reinforcement layers installed]
In the present invention, the reinforcing layer 14 is disposed radially inside the at least one main groove. From the viewpoint of enhancing the effect of the reinforcing layer 14, the reinforcing layer 14 is preferably disposed on the radially inner side of all the main grooves. In the tire 2 and the tire 48, the reinforcing layer 14 is disposed on the radially inner side of all the main grooves. The main groove may be a crown main groove or a shoulder main groove. In the tire 2 and the tire 48, a shoulder main groove is shown.

[Loss tangent tan δ]
In the present application, the loss tangent tan δ of the cap is δc, the loss tangent tan δ of the base is δb, and the loss tangent tan δ of the reinforcing layer is δr. Preferably, the tire 2 satisfies the following expressions (1) and (2).
3 × δc ≦ δr (1)
δc ≧ δb (2)

  When the above formula (1) is satisfied, the strength of the reinforcing layer can be improved while the rolling resistance is suppressed by a small δc. In this respect, the ratio (δr / δc) is preferably equal to or greater than 3.5 and more preferably equal to or greater than 3.9. If the ratio (δr / δc) is excessive, the strength of the cap may decrease excessively. In this respect, the ratio (δr / δc) is preferably equal to or less than 7.0, more preferably equal to or less than 6.0, and still more preferably equal to or less than 5.6.

  When the above formula (2) is satisfied, the rolling resistance is suppressed by a small δb, and an excessive decrease in the strength of the cap can be prevented. In this respect, the ratio (δc / δb) is preferably greater than 1, more preferably 1.1 or greater, and still more preferably 1.2 or greater. From the viewpoint of heat generation, the ratio (δc / δb) is preferably 3.0 or less, and more preferably 2.0 or less.

[Cap loss tangent δc]
From the viewpoint of durability of the tread, the loss tangent δc of the cap is preferably 0.06 or more, and more preferably 0.065 or more. From the viewpoint of rolling resistance of the tire, the loss tangent δc of the cap is preferably 0.080 or less, and more preferably 0.075 or less.

[Base loss tangent δb]
From the viewpoint of durability of the tread, the loss tangent δb of the base is preferably 0.04 or more, and more preferably 0.045 or more. In light of tire rolling resistance, the loss tangent δb of the base is preferably 0.06 or less, and more preferably 0.055 or less.

[Loss tangent δr of reinforcing layer]
From the viewpoint of durability near the main groove, the loss tangent δr of the reinforcing layer is preferably 0.20 or more, and more preferably 0.25 or more. From the viewpoint of rolling resistance of the tire, the loss tangent δr of the reinforcing layer is preferably 0.50 or less, and more preferably 0.45 or less.

[Complex elastic modulus E ^* ]
In the present application, the complex elastic modulus E ^{* of the} cap is Ec, the complex elastic modulus E ^{* of the} base is Eb, and the complex elastic modulus E ^{* of the} reinforcing layer is Er. The preferred tire 2 satisfies the following formula (3).
Ec ≦ Er (3)

  By satisfy | filling the said Formula (3), the deformation | transformation of the main groove vicinity can be suppressed effectively. In this respect, the ratio (Er / Ec) is preferably greater than 1, more preferably 1.1 or greater, more preferably 1.2 or greater, and even more preferably 1.5 or greater. From the viewpoint of protecting the belt, the ratio (Er / Ec) is preferably 3.0 or less, and more preferably 2.0 or less.

[Complex elastic modulus Ec of the cap]
From the viewpoint of wear resistance, the complex elastic modulus Ec of the cap is preferably 5.5 MPa or more, and more preferably 6.0 MPa or more. From the viewpoint of wet grip, the complex elastic modulus Ec of the cap is preferably 7.5 MPa or less, and more preferably 7.0 MPa or less.

[Base complex elastic modulus Eb]
From the viewpoint of rigidity, the complex elastic modulus Eb of the base is preferably 5.0 MPa or more, and more preferably 5.5 MPa or more. From the viewpoint of ride comfort, the base complex elastic modulus Eb is preferably 7.0 MPa or less, and more preferably 6.5 MPa or less.

[Complex elastic modulus Er of reinforcing layer]
From the viewpoint of protecting the belt, the complex elastic modulus Er of the reinforcing layer is preferably 6.0 MPa or more, and more preferably 7.0 MPa or more. From the viewpoint of strain distribution, the complex elastic modulus Er of the reinforcing layer is preferably 12.0 MPa or less, and more preferably 11.0 MPa or less.

[Measurement method of loss tangent tan δ and complex elastic modulus E ^* ]
The loss tangent tan δ and the complex elastic modulus E ^* are measured by a viscoelastic spectrometer (“VESF-3” manufactured by Iwamoto Seisakusho Co., Ltd.) under the conditions shown below in accordance with the provisions of “JIS-K 6394”. .
Initial strain: 10%
Amplitude: ± 1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

[Cap material]
The cap 24 is formed by crosslinking a rubber composition.

  The rubber composition of the cap 24 includes a base rubber. Examples of the base rubber include natural rubber, polybutadiene, styrene-butadiene copolymer, polyisoprene, ethylene-propylene-diene terpolymer, polychloroprene, acrylonitrile-butadiene copolymer, and isobutylene-isoprene copolymer. Illustrated. This base rubber may be composed of two or more kinds of rubbers. The rubber composition can contain carbon black as a filler. This rubber composition may be used in combination with other fillers other than carbon black. Examples of other fillers include silica, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, alumina, clay, talc and magnesium oxide. The rubber composition may also contain chemicals such as a softener, a tackifier, a crosslinking agent such as sulfur, a vulcanization accelerator, a crosslinking aid, and an anti-aging agent.

  The adjustment of the loss tangent δc can be achieved, for example, by changing the blending ratio of polybutadiene. The adjustment of the complex elastic modulus Ec can be achieved, for example, by changing the blending ratio of silica and carbon black.

  In the tire 2, the hardness of the cap 24 is preferably 40 or greater and 70 or less. By setting the hardness to 40 or more, the cap 24 can appropriately contribute to the rigidity of the tread 4. The tire 2 is excellent in traction performance. In this respect, the hardness is more preferably equal to or greater than 45, still more preferably equal to or greater than 47, and particularly preferably equal to or greater than 50. By setting the hardness to 70 or less, excessive rigidity of the tread 4 by the cap 24 is suppressed. Since the tread 4 has appropriate flexibility, the tread surface 28 is sufficiently grounded to the road surface. The tire 2 is excellent in grip performance. In this respect, the hardness is more preferably equal to or less than 65, still more preferably equal to or less than 63, and particularly preferably equal to or less than 60.

  In the present application, the hardness is measured by a type A durometer according to “JIS K 6253”. This hardness is measured under conditions where the temperature is 23 ° C. For this measurement, a test piece formed by crosslinking the rubber composition constituting the cap 24 is used. This test piece is obtained by holding the rubber composition in a mold having a temperature of 160 ° C. for 10 minutes.

[Base material]
The base 26 is formed by crosslinking a rubber composition. This rubber composition contains a base rubber. Examples of the base rubber include natural rubber, polybutadiene, styrene-butadiene copolymer, polyisoprene, ethylene-propylene-diene terpolymer, polychloroprene, acrylonitrile-butadiene copolymer, and isobutylene-isoprene copolymer. Illustrated. This base rubber may be composed of two or more kinds of rubbers. The rubber composition can contain carbon black as a filler. This rubber composition may be used in combination with other fillers other than carbon black. Examples of other fillers include silica, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, alumina, clay, talc and magnesium oxide. The rubber composition may also contain chemicals such as a softener, a tackifier, a crosslinking agent such as sulfur, a vulcanization accelerator, a crosslinking aid, and an anti-aging agent.

  Adjustment of the loss tangent δb can be achieved, for example, by changing the blending ratio of carbon black. Adjustment of the complex elastic modulus Eb can be achieved, for example, by changing the blending ratio of silica and carbon black.

[Material of reinforcement layer]
The reinforcing layer 14 is formed by crosslinking a rubber composition. This rubber composition contains a base rubber. Examples of the base rubber include natural rubber, polybutadiene, styrene-butadiene copolymer, polyisoprene, ethylene-propylene-diene terpolymer, polychloroprene, acrylonitrile-butadiene copolymer, and isobutylene-isoprene copolymer. Illustrated. This base rubber may be composed of two or more kinds of rubbers. The rubber composition can contain carbon black as a filler. This rubber composition may be used in combination with other fillers other than carbon black. Examples of other fillers include silica, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, alumina, clay, talc and magnesium oxide. The rubber composition may also contain chemicals such as a softener, a tackifier, a crosslinking agent such as sulfur, a vulcanization accelerator, a crosslinking aid, and an anti-aging agent.

  The loss tangent δr can be adjusted, for example, by changing the blending ratio of the filler and carbon black. Adjustment of the complex elastic modulus Er can be achieved, for example, by changing the blending ratio of the filler and carbon black. In addition, an example of a filler is the short fiber mentioned later.

[Short fiber]
The reinforcing layer 14 may include a large number of short fibers. In this case, the reinforcing layer 14 is composed of a large number of short fibers and a matrix. In other words, in this case, the reinforcing layer 14 is made of fiber reinforced rubber (FRR). These short fibers are dispersed in a matrix. The longitudinal direction of these short fibers is preferably substantially along the circumferential direction. The short fiber contributes to the improvement of the strength of the reinforcing layer 14. The reinforcing layer 14 including short fibers can improve the durability in the vicinity of the main groove 30.

  The short fibers that can be included in the reinforcing layer 14 are preferably nonmetallic from the viewpoint of excellent adhesion to the matrix (crosslinked rubber). Examples of the non-metallic short fibers include organic fibers and inorganic fibers. Examples of organic fibers include nylon fibers, polyester fibers, aramid fibers, rayon fibers, vinylon fibers, cotton fibers, and cellulose fibers. Examples of the inorganic fiber material include boron, glass fiber, and carbon fiber.

  The compounding amount of the short fibers that can be included in the reinforcing layer 14 is preferably 3 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the base rubber. By setting the blending amount to 3 parts by mass or more, the reinforcing layer 14 can effectively reinforce the vicinity of the main groove 30. In this respect, the amount is more preferably equal to or greater than 7 parts by weight, and particularly preferably equal to or greater than 10 parts by weight. From the viewpoint of suppressing the rigidity of the reinforcing layer 14 from being excessive, the amount is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and particularly preferably 15 parts by mass or less.

  The fiber length of the short fibers that can be included in the reinforcing layer 14 is preferably 0.1 mm or more and 5 mm or less. By setting the fiber length to 0.1 mm or more, the short fibers can effectively reinforce the reinforcing layer 14. In this respect, the fiber length is more preferably 2 mm or more. By setting the fiber length to 5 mm or less, the adhesiveness with the short fiber matrix is maintained. In this respect, the fiber length is more preferably 3 mm or less.

  The fiber diameter of the short fibers contained in the reinforcing layer 14 is preferably 1 μm or more and 100 μm or less. By setting the fiber length to 1 μm or more, the short fibers can effectively reinforce the reinforcing layer 14. In this respect, the fiber diameter is more preferably 10 μm or more. From the viewpoint of adhesion between the short fibers and the matrix, the fiber diameter is preferably 100 μm or less, and more preferably 70 μm or less.

[Tread minimum thickness T1 under the main groove, reinforcing layer thickness T2]
In FIG. 3, a double-headed arrow T <b> 1 indicates the minimum value of the thickness of the tread 4 in the vicinity of the main groove 30. A double-headed arrow T2 indicates the thickness of the reinforcing layer on the radially inner side at the position where the thickness of the tread 4 is minimized. The thickness T1 and the thickness T2 are measured along the radial direction rd. From the viewpoint of reinforcement in the vicinity of the main groove 30, the ratio [T2 / (T1 + T2)] is preferably 0.3 or more. From the viewpoint of the strength of the tread 4 in the vicinity of the main groove 30, the ratio [T2 / (T1 + T2)] is preferably 0.7 or less.

[Measurement conditions such as dimensions]
In the present application, the dimensions and angles of the tire 2 and each member of the tire to be described later are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. In the present application, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present application, the normal internal pressure means an internal pressure determined in a standard on which the tire 2 depends. “Maximum air pressure” in JATMA standard, “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures. In the case of the passenger car tire 2, the dimensions and angles are measured in a state where the internal pressure is 180 kPa. In the case of racing cart tires, the dimensions and angles are measured in a state where the internal pressure is not applied.

[Tire manufacturing method]
In the manufacture of the tire 2, a carcass ply is wound on a former in a preforming process. A belt sheet is wound around the carcass ply. A rubber member for a reinforcing layer is wound around the belt sheet. Further, a rubber member for tread is wound. These are assembled to obtain a raw cover. In the vulcanization process, this raw cover is put into a mold. The raw cover is pressurized and heated in the mold. The rubber composition flows by pressurization and heating. By heating, a crosslinking reaction occurs in the rubber composition. In this way, the tire 2 provided with the reinforcing layer 14 is obtained.

[Strip winding]
The tread 4 is preferably formed by strip winding from the viewpoint that it can easily cope with various groove patterns. In the case of strip winding, there is little variation in groove position and tread thickness. Therefore, the finished dimensions are likely to be stable.

  In the manufacturing process of the tire 2 in which the strip winding is adopted, a first strip made of uncrosslinked rubber and a second strip made of uncrosslinked rubber are prepared. The first strip becomes the base 26 by thermoforming. The second strip becomes a cap 24 by thermoforming. In this manufacturing method, after the rubber member for the reinforcing layer is wound, the first strip made of uncrosslinked rubber is wound spirally. The first strip extends substantially in the circumferential direction. This first strip is sequentially laminated. When the first strip is finished, the second strip is spirally wound on the first strip. The second strip extends substantially in the circumferential direction. This second strip is laminated sequentially. A green tire is thus obtained. This green tire is put into a mold, and pressurized and heated. A cross-linking reaction occurs in the rubber by heating, and the tire 2 is obtained.

[Second Embodiment]
FIG. 4 is a conceptual diagram showing a part of the pneumatic tire 48 according to the second embodiment of the present invention. In FIG. 4, the tire 48 has a radial direction in the vertical direction, an axial direction in the horizontal direction, and a circumferential direction perpendicular to the paper surface. The tire 48 has a substantially left-right symmetric shape centered on the one-dot chain line CL in FIG. This alternate long and short dash line CL represents the equator plane of the tire 48. The tire 48 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, a belt 12, a reinforcing layer 14 (14a and 14b), a bead reinforcing layer 16, an inner sidewall 18, an inner liner 20, and a chafer 22. Yes. The tire 48 is a tubeless type. The tire 48 is attached to a truck, a bus or the like.

  The tread 4 is provided with an inner main groove 50 and an outer main groove 52. A reinforcing layer 14 a is provided on the inner side in the radial direction of the inner main groove 50. A reinforcing layer 14 b is provided on the radially inner side of the outer main groove 52. The tire 48 has four main grooves. In the tire 48, the reinforcing layers 14 are arranged at four locations. The tire 48 is the same as the tire 2 except that the main groove is changed from two to four and the reinforcing layer is changed from two to four. In the present invention, a configuration like the tire 48 is also possible.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A heavy duty tire having the same structure as the tire 48 shown in FIG. 4 was produced. The tread was molded using strip winding. The size of this tire is “11R22.5”. The basic specifications of this tire are as follows.
Tread Number of main grooves: 4 Main groove width Wg: 12 mm
Main groove depth: 13 mm
Tread width: 210mm
Carcass cord material: Steel Belt cord material: Steel Cord composition: 2 + 2

  Short fibers were blended in the reinforcing layer. The type of short fiber was nylon. The fiber length of the short fibers was in the range of 1 mm to 1.5 mm. The blend amount of the short fibers was 30 parts by mass with respect to 100 parts by mass of the base rubber. The fiber diameter of the short fibers was in the range of 1 μm to 100 μm.

  The loss tangent δc, the loss tangent δb, and the loss tangent δr are as shown in Table 1 below. The complex elastic modulus Ec, the complex elastic modulus Eb, and the complex elastic modulus Er were as shown in Table 1 below. These loss tangent and complex elastic modulus were obtained by adjusting the compounding ratio between polybutadiene rubber and natural rubber and the compounding ratio between carbon black and silica. The specifications and evaluation results of Example 1 are shown in Table 1 below.

[Example 2-11]
Tires of Examples 2 to 11 were obtained in the same manner as Example 1 except for the specifications shown in Table 1 below. The specifications and evaluation results of Examples 2 to 11 are shown in Table 1 below.

[Examples 12 and 13]
Tires of Examples 12 and 13 were obtained in the same manner as Example 1 except for the specifications shown in Table 2 below. These specifications and evaluation results are shown in Table 2 below.

[Comparative Examples 1 and 2]
Tires of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1 except for the specifications shown in Table 2 below. In Comparative Examples 1 and 2, no reinforcing layer was provided. The specifications and evaluation results of Comparative Examples 1 and 2 are shown in Table 2 below.

[Comparative Example 3-6]
Tires of Comparative Examples 3 to 6 were obtained in the same manner as in Example 1 except for the specifications shown in Table 2 below. The specifications and evaluation results of Comparative Examples 3 to 6 are shown in Table 2 below.

In the above examples and comparative examples, loss tangent tan δ and complex elastic modulus E ^* were adjusted by changing the blending ratio of carbon black.

[Evaluation]
A prototype tire was mounted on the rim of a drum durability tester. The drum was provided with a cylindrical protrusion having a height of 20 mm and a diameter of 50 mm. The internal pressure of the prototype tire was set to a pressure corresponding to the maximum air pressure specified in JATMA standards. A load corresponding to 200% of the maximum load load specified in JATMA standards was applied to the contact surface between the prototype tire and the drum, and the drum was rotated at a speed of 20 km / h. During rotation, the position of the convex portion was adjusted such that the convex portion hits the main groove. When the travel distance reached 5000 km, the prototype tire was removed from the testing machine, and the following “cracks at the groove bottom” and “adhesion between belts” were evaluated. The following “crack at the groove bottom” was evaluated for the main groove against which the convex portion hits. In the following evaluation of “adhesion between belt layers”, the belt positioned under the main groove against which the convex portion hits was targeted.

[Crack at groove bottom]
The occurrence of cracks at the groove bottom was visually confirmed, and the degree of occurrence of cracks was indexed. Indexing was performed with Comparative Example 1 as 100. In determining this index, the number of cracks and the length of the cracks were considered. This index is shown in Tables 1 and 2 below. The smaller the value, the better.

[Adhesion between belt layers]
A belt (4 layers) was cut out to a predetermined size to obtain a measurement sample. This measurement sample was attached to a jig. The first jig was attached to the innermost layer, and the second jig was attached to the outermost layer. After fixing the first jig, a force in the direction of separating both jigs was applied to the second jig. The force at the time when delamination occurred at any point was measured. This force was indexed with Comparative Example 1 as 100. This index is shown in Tables 1 and 2 below. Larger values are preferred.

  As shown in Tables 1 and 2, the tires of the examples are excellent in various performances. From this evaluation result, the superiority of the present invention is clear.

  The tire according to the present invention can be mounted on various vehicles.

2, 48 ... pneumatic tire 4 ... tread 6 ... sidewall 8 ... bead 10 ... carcass 12 ... belt 14 ... reinforcing layer 14a ... inner reinforcing layer 14b .... Outer reinforcement layer 16 ... Bead reinforcement layer 20 ... Inner liner 22 ... Chafer 24 ... Cap 26 ... Base 28 ... Tread surface 30 ... Main groove 50 ... Main groove (inner main groove)
52 ... Main groove (outer main groove)
CL ... Center line (tire equator)

Claims (5)

A tread provided with a main groove extending in the circumferential direction, a pair of sidewalls each extending substantially inward in the radial direction from the end of the tread, and a pair of each positioned substantially radially inward of the sidewalls A bead, a carcass spanned between one bead and the other bead along the inside of the tread and the sidewall, a belt positioned between the tread and the carcass in the radial direction, and a shaft A reinforcing layer that is locally present in the direction and located inside the main groove in the radial direction,
The tread has a cap and a base located radially inward of the cap;
The reinforcing layer is located radially inward of the base;
The loss tangent tan δ of the cap is δc, the loss tangent tan δ of the base is δb, the loss tangent tan δ of the reinforcing layer is δr, the complex elastic modulus E ^{* of the} cap is Ec, and the reinforcing layer When the complex elastic modulus E ^* is Er, the axial width of the reinforcing layer is Wr (mm), and the axial width of the main groove is Wg (mm), the following relational expression (1) , (2), (3) and a pneumatic tire satisfying (4).
3 × δc ≦ δr (1)
δc ≧ δb (2)
Ec ≦ Er (3)
Wr ≧ (4/3) × Wg (4)   When the minimum value of the thickness of the tread on the radially inner side of the main groove is T1 (mm), and the thickness of the reinforcing layer on the radially inner side of the position where the thickness of the tread is T1 is T2 (mm) The tire according to claim 1, wherein the ratio [T2 / (T1 + T2)] is 0.3 or more and 0.7 or less.   The tire according to claim 1 or 2, wherein the tread is formed using strip winding.   The tire according to any one of claims 1 to 3, wherein short fibers are blended in the reinforcing layer. The belt includes a large number of cords arranged in parallel and a topping rubber, and the material of the cord for the belt is steel,
The number of layers of the belt is 2 or more,
The tire according to any one of claims 1 to 4, wherein the carcass includes a plurality of cords arranged in parallel and a topping rubber, and the material of the cord for carcass is steel.

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