JP5226268B2 - Run flat tire - Google Patents

Description

  The present invention relates to a run-flat tire that can travel a certain distance even in a punctured state.

  Tires need rigidity. For the purpose of imparting rigidity, a short fiber reinforced rubber may be used as a member constituting the tire. Japanese Patent Laid-Open No. 2001-347809 discloses a tire in which a tread includes a base layer and a cap layer, and the base layer includes a large number of short fibers. These short fibers are oriented in the radial direction.

In recent years, run flat tires having a support layer inside a sidewall have been developed and are becoming popular. For this support layer, a highly hard crosslinked rubber is used. This run flat tire is referred to as a side reinforcing type run flat tire. In the side-reinforced run-flat tire, when the internal pressure is reduced due to puncture, the load is supported by the support layer. This support layer suppresses the bending of the tire in the puncture state. Even if traveling is continued in a punctured state, the hardened crosslinked rubber suppresses heat generation in the support layer. This run-flat tire can travel a certain distance even in a punctured state. Automobiles equipped with this run-flat tire need not have spare tires. By adopting this run flat tire, tire replacement at an inconvenient place can be avoided.
JP 2001-347809 A

  In the puncture state, the side portions (sidewalls and support layers) bend. Furthermore, in the puncture state, the shoulder of the tread is strongly pressed by the support layer, and the crown is lifted from the road surface. The deflection of the side portion and the lifting of the crown hinder the durability of the tire in a punctured state.

  If a hard support layer is employed, excellent durability can be obtained. However, a tire having a hard support layer has a large longitudinal spring constant. If a thick support layer is employed, excellent durability can be obtained. However, a tire having a thick support layer has a large longitudinal spring constant. A tire having a large longitudinal spring constant is inferior in riding comfort in a normal state (a state in which a normal internal pressure is applied to the tire). In conventional tires, riding comfort in a normal state and durability in a puncture state are contradictory performances.

  An object of the present invention is to provide a side-reinforced run-flat tire excellent in durability in a puncture state.

The run flat tire according to the present invention is
(1) A tread whose surface forms a tread surface,
(2) a pair of sidewalls extending substantially inward in the radial direction from the end of the tread;
(3) A pair of beads positioned substantially inward of the sidewall in the radial direction,
(4) A carcass having a cord made of an aramid fiber, which extends along the tread and the sidewall and is bridged between both beads.
(5) a reinforcing layer located between the tread and the carcass,
(6) A support layer located on the inner side in the axial direction of the sidewall and having a substantially crescent-shaped cross section, and (7) an inner layer located on the outer side of the support layer and on the inner side of the side wall in the axial direction. Provide side walls. This tire has a tread profile including a curved surface formed of a plurality of arcs having different curvature radii. The inner sidewall includes a rubber matrix and a number of short fibers dispersed in the matrix.

  Preferably, these short fibers are oriented in the radial direction. Preferably, these short fibers have an average length L of 10 μm or more and 1000 μm or less, an average diameter D of 0.05 μm or more and 50 μm or less, and an aspect ratio (L / D) of 10 or more.

  Preferably, the inner sidewall includes 100 parts by mass of base rubber and 0.5 parts by mass or more and 50 parts by mass or less of short fibers. Preferably, the loss tangent tan δ of the inner sidewall is 0.20 or more.

Preferably, the twist coefficient T of the carcass cord is 0.5 or more and 0.7 or less. This cord has a structure in which a plurality of yarns formed by twisting aramid fibers are twisted. The twist coefficient T is calculated by the following mathematical formula (I).
T = N * ((0.125 * D / 2) / ρ) ^1/2 * 10 ⁻³ (I)
In this mathematical formula (I), N represents the number of upper twists per 10 cm of cord, D represents the total fineness (dtex), and ρ represents the specific gravity (g / cm ³ ) of the cord material.

  Preferably, the tire has a profile in which the radius of curvature gradually decreases from the center point TC of the tread surface toward the outside in the axial direction.

  In the run flat tire according to the present invention, the fiber-reinforced inner sidewall suppresses the side portion from being bent in the puncture state. The inner sidewall further suppresses the crown from rising in the puncture state. This run-flat tire is excellent in durability in a puncture state.

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

  FIG. 1 is a cross-sectional view showing a part of a run flat 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. A double arrow H in FIG. 1 indicates the height of the tire 2 from the reference line BL. The reference line BL passes through the innermost point in the radial direction of the core 38 (detailed later).

  The tire 2 includes a tread 4, a wing 8, a sidewall 10, a clinch portion 12, a bead 14, a carcass 16, a support layer 18, an inner sidewall 20, a belt 22, a band 24, an inner liner 26, and a chafer 28. Yes. The sidewall 10, the support layer 18, and the inner sidewall 20 are positioned on the side portion 30 of the tire 2. The belt 22 and the band 24 constitute a reinforcing layer. The reinforcing layer may be formed only from the belt 22. The reinforcing layer may be configured only from the band 24. The tire 2 is a tubeless type pneumatic tire.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 32 that contacts the road surface. A groove 34 is carved in the tread surface 32. The groove 34 forms a tread pattern. The tread 4 has a cap layer 5 and a base layer 6. The cap layer 5 is made of a crosslinked rubber. The base layer 6 is made of other crosslinked rubber. The cap layer 5 is located on the radially outer side of the base layer 6. The cap layer 5 is laminated on the base layer 6.

  The sidewall 10 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 10 is made of a crosslinked rubber. The sidewall 10 prevents the carcass 16 from being damaged. The sidewall 10 is provided with ribs 36. The rib 36 protrudes outward in the axial direction. When traveling in a puncture state, the rib 36 comes into contact with the rim flange. By this contact, deformation of the bead 14 can be suppressed. The tire 2 in which the deformation is suppressed is excellent in durability in a puncture state.

  The bead 14 is located on the radially inner side of the sidewall 10. The bead 14 includes a core 38 and an apex 40 that extends radially outward from the core 38. The core 38 has a ring shape and includes a plurality of non-stretchable wires (typically steel wires). The apex 40 is tapered outward in the radial direction. The apex 40 is made of a highly hard crosslinked rubber.

  In FIG. 1, what is indicated by an arrow Ha is the height of the apex 40 from the reference line BL. The ratio (Ha / H) of the height Ha of the apex 40 to the height H of the tire 2 is preferably 0.1 or more and 0.7 or less. The apex 40 having a ratio (Ha / H) of 0.1 or more can support the vehicle weight in a punctured state. The apex 40 contributes to the durability of the tire 2 in a punctured state. In this respect, the ratio (Ha / H) is more preferably equal to or greater than 0.2. The tire 2 having a ratio (Ha / H) of 0.7 or less is excellent in ride comfort. In this respect, the ratio (Ha / H) is more preferably equal to or less than 0.6.

  The carcass 16 includes a carcass ply 42. The carcass ply 42 is bridged between the beads 14 on both sides, and extends along the tread 4 and the sidewall 10. The carcass ply 42 is folded around the core 38 from the inner side to the outer side in the axial direction. By this folding, a main portion 44 and a folding portion 46 are formed in the carcass ply 42. The end 48 of the folded portion 46 reaches just below the belt 22. In other words, the folded portion 46 overlaps the belt 22. The carcass 16 has a so-called “ultra-high turn-up structure”. In the carcass 16 having the super high turn-up structure, the folded portion 46 sufficiently reinforces the sidewall 10.

  As will be described later, the carcass ply 42 includes a large number of carcass 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 45 ° to 90 °, and further 75 ° to 90 °. In other words, the carcass 16 has a radial structure.

  The support layer 18 is located inside the sidewall 10 in the axial direction. The support layer 18 is sandwiched between the carcass 16 and the inner liner 26. The support layer 18 tapers inward and outwards in the radial direction. The support layer 18 has a shape similar to that of a crescent moon. The support layer 18 is made of a highly hard crosslinked rubber. When the tire 2 is punctured, the support layer 18 supports the vehicle weight. The support layer 18 allows the tire 2 to travel a certain distance even in a puncture state. The tire 2 is a “side-reinforced run-flat tire”. The tire 2 may include a support layer having a shape different from the shape of the support layer 18 illustrated in FIG.

  A portion of the carcass 16 that overlaps the support layer 18 is separated from the inner liner 26. In other words, the carcass 16 is curved due to the presence of the support layer 18. In the puncture state, a compressive load is applied to the support layer 18, and a tensile load is applied to a region of the carcass 16 adjacent to the support layer 18. Since the support layer 18 is a rubber lump, it can sufficiently withstand the compressive load. The carcass cord can sufficiently withstand a tensile load. The support layer 18 and the carcass cord suppress vertical deflection of the tire 2 in a punctured state. A tire in which longitudinal deflection is suppressed is excellent in steering stability in a puncture state.

  From the viewpoint of suppressing longitudinal strain in the puncture state, the hardness of the support layer 18 is preferably 60 or more, and more preferably 65 or more. From the viewpoint of riding comfort in a normal state (a state where a normal internal pressure is applied to the tire 2), the hardness is preferably 90 or less, and more preferably 80 or less. The hardness is measured with a type A durometer in accordance with the provisions of “JIS K6253”. The durometer is pressed against the cross section shown in FIG. 1, and the hardness is measured. The measurement is made at a temperature of 23 ° C.

  The lower end 50 of the support layer 18 is located on the inner side in the radial direction than the upper end 52 of the apex 40. In other words, the support layer 18 overlaps the apex 40. In FIG. 1, what is indicated by an arrow L <b> 1 is a radial distance between the lower end 50 of the support layer 18 and the upper end 52 of the apex 40. The distance L1 is preferably 5 mm or greater and 50 mm or less. In the tire 2 in which the distance L1 is within this range, a uniform rigidity distribution is obtained. The distance L1 is more preferably 10 mm or more. The distance L1 is more preferably 40 mm or less.

  The upper end 54 of the support layer 18 is located on the inner side in the axial direction than the end 56 of the belt 22. In other words, the support layer 18 overlaps the belt 22. In FIG. 1, an arrow L <b> 2 indicates an axial distance between the upper end 54 of the support layer 18 and the end 56 of the belt 22. The distance L2 is preferably 2 mm or greater and 50 mm or less. In the tire 2 in which the distance L2 is within this range, a uniform rigidity distribution is obtained. The distance L2 is more preferably 5 mm or more. The distance L1 is more preferably 40 mm or less.

  From the viewpoint of suppressing vertical strain in the puncture state, the maximum thickness of the support layer 18 is preferably 3 mm or more, more preferably 4 mm or more, and particularly preferably 7 mm or more. From the viewpoint of light weight of the tire 2, the maximum thickness is preferably 25 mm or less, and more preferably 20 mm or less.

  The inner sidewall 20 is located outside the support layer 18 in the axial direction. The inner sidewall 20 is located outside the carcass 16 in the axial direction. The inner sidewall 20 is located on the inner side in the axial direction of the sidewall 10. The inner sidewall 20 is sandwiched between the sidewall 10 and the carcass 16.

  The belt 22 is located on the radially outer side of the carcass 16. The belt 22 is laminated with the carcass 16. The belt 22 reinforces the carcass 16. The belt 22 includes an inner layer 58 and an outer layer 60. As is clear from FIG. 1, the width of the inner layer 58 is slightly larger than the width of the outer layer 60. Although not shown, each of the inner layer 58 and the outer layer 60 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 absolute value of the tilt angle is usually 10 ° to 35 °. The inclination direction of the cord of the inner layer 58 with respect to the equator plane is opposite to the inclination direction of the cord of the outer layer 60 with respect to the equator plane. A preferred material for the cord is steel. An organic fiber may be used for the cord. The axial width of the belt 22 is preferably 0.85 to 1.0 times the maximum width W of the tire 2 (detailed later). The belt 22 may include three or more layers.

  The band 24 covers the belt 22. Although not shown, the band 24 is composed of a cord and a topping rubber. The cord extends substantially in the circumferential direction and is wound spirally. The band 24 has a so-called jointless structure. Since the belt 22 is restrained by this cord, lifting of the belt 22 is suppressed. The cord is usually made of organic fibers. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The tire 2 may include an edge band that covers only the vicinity of the end of the belt 22 instead of the band 24. The tire 2 may include an edge band together with the band 24.

  FIG. 3 is an enlarged cross-sectional view showing a part of the inner sidewall 20 of the tire 2 of FIG. In FIG. 3, the vertical direction is the radial direction of the tire 2, and the direction indicated by the arrow A is the circumferential direction of the tire 2. The inner sidewall 20 is formed by crosslinking a rubber composition. The inner sidewall 20 includes a rubber matrix 62 and a large number of short fibers 64. These short fibers 64 are dispersed in the matrix 62. In other words, the inner sidewall 20 is made of fiber reinforced rubber. These short fibers 64 are oriented in the radial direction.

  In the punctured state, tensile stress is generated in the inner sidewall 20. The direction of this stress is the radial direction. The short fibers 64 oriented in the radial direction suppress the discarding of the inner sidewall 20 even when traveling in a punctured state is continued. The inner sidewall 20 contributes to the durability of the tire 2 in a punctured state. Further, the short fibers 64 suppress the bending of the side portion 30 of the tire 2. By suppressing the bending of the side portion 30, the floating of the crown of the tread 4 is suppressed. The tire 2 in which the bending of the side portion 30 and the lifting of the crown are suppressed is excellent in durability in a puncture state.

  In a normal state, the short fiber 64 has little influence on the longitudinal spring constant. The inner sidewall 20 does not hinder the riding comfort of the tire 2. The inner sidewall 20 provides both riding comfort in a normal state and durability in a puncture state.

  FIG. 4 is a schematic view showing the short fibers 64 of the inner sidewall 20 of FIG. In FIG. 4, the vertical direction is the radial direction of the tire 2. In FIG. 4, an angle θ indicates the angle of the short fiber 64. The angle θ is an absolute value of an angle formed by the straight line S1 and the straight line S2. The straight line S1 extends in the radial direction. The straight line S <b> 2 passes through one end 66 and the other end 68 of the short fiber 64. The angle θ is 0 ° or more and 90 ° or less.

  From the viewpoint of durability in a puncture state, the ratio of the number of short fibers 64 having an angle θ of 20 ° or less to the total number of short fibers 64 is preferably 50% or more, more preferably 70% or more, and 90% or more. Is particularly preferred. In calculating the ratio, the angle of the short fibers 64 exposed in the cross section of the inner sidewall 20 along the radial direction is measured. Angle measurement is performed on 100 randomly extracted short fibers 64.

  An organic fiber and an inorganic fiber can be used for the inner sidewall 20. Specific examples of the organic fiber include aramid fiber, nylon fiber, polyester fiber, and rayon fiber. Specific examples of the inorganic fiber include glass fiber, carbon fiber, and boron fiber. Aramid fibers are preferred. Aramid fibers are highly elastic. Due to the aramid fiber, bending of the side part 30 in the punctured state is suppressed. The inner sidewall 20 including an aramid fiber contributes to the durability of the tire 2.

  Paper fibers may be used for the inner sidewall 20. Since the paper fiber is inexpensive, the tire 2 can be obtained at low cost by this paper fiber. In the production of paper fibers, the raw paper is cut or crushed. This raw paper is further defibrated by beating to obtain paper fibers. Since it is beaten, the surface area of this paper fiber is large.

  The average length L (see FIG. 4) of the short fibers 64 is preferably 10 μm or more. The inner sidewall 20 is sufficiently reinforced by the short fibers 64 having an average length L of 10 μm or more. In this respect, the average length L is more preferably 50 μm or more, further preferably 100 μm or more, and particularly preferably 300 μm or more. In light of dispersibility in the matrix 62, the average length L is preferably 1000 μm or less, more preferably 800 μm or less, and particularly preferably 700 μm or less.

  The average diameter D of the short fibers 64 is preferably 0.05 μm or more. The inner sidewall 20 is sufficiently reinforced by the short fibers 64 having an average diameter D of 0.05 μm or more. In this respect, the average diameter D is more preferably 0.10 μm or more, further preferably 1 μm or more, and particularly preferably 5 μm or more. In light of dispersibility in the matrix 62, the average diameter D is preferably 50 μm or less, more preferably 30 μm or less, and particularly preferably 20 μm or less.

  The aspect ratio (L / D) of the short fibers 64 is preferably 10 or more. The inner side wall 20 is sufficiently reinforced by the short fibers 64 having an aspect ratio (L / D) of 10 or more. In this respect, the aspect ratio (L / D) is more preferably 20 or more. From the viewpoint of dispersibility in the matrix 62, the aspect ratio (L / D) is preferably 300 or less, and more preferably 200 or less.

  The amount of the short fibers 64 is preferably 0.5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the base rubber. The inner sidewall 20 including 0.5 mass parts or more of short fibers 64 contributes to the durability of the tire 2. In this respect, the amount of the short fibers 64 is more preferably 3 parts by mass or more. By setting the amount of the short fibers 64 to 50 parts by mass or less, the mass of the tire 2 is suppressed. In this respect, the amount to be blended is more preferably equal to or less than 20 parts by weight.

  The loss tangent tan δ of the inner sidewall 20 is preferably 0.20 or more. The inner side wall 20 having a loss tangent tan δ of 0.20 or more does not impair riding comfort in a normal state, despite including the short fibers 64. In the normal state, the run-flat tire 2 has little side portion 30 bending. Therefore, the adverse effect of increased rolling resistance due to the inner sidewall 20 having a large loss tangent tan δ can be suppressed. From the viewpoint of ride comfort, the loss tangent tan δ is more preferably 0.25 or more, and particularly preferably 0.30 or more. From the viewpoint of rolling resistance, the loss tangent tan δ is preferably 0.40 or less, and more preferably 0.35 or less.

The loss tangent tan δ is measured by a viscoelastic spectrometer (“VA-200” manufactured by Shimadzu Corporation) under the following conditions in accordance with the provisions of “JIS K 6394”.
Initial strain: 10%
Amplitude: ± 2%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

  In FIG. 2, what is indicated by an arrow Ti is the thickness of the inner sidewall 20. From the viewpoint of durability in the puncture state, the thickness Ti is preferably 1 mm or more, and more preferably 2 mm or more. From the viewpoint of light weight of the tire 2, the thickness Ti is preferably 5 mm or less, and more preferably 4 mm or less. In the case of the inner sidewall 20 having a non-uniform thickness, the thickness Ti is measured at the thickest portion.

  In FIG. 2, what is indicated by an arrow L3 is the length of the inner sidewall 20. From the viewpoint of durability in the puncture state, the length L3 is preferably 20 mm or more, and more preferably 30 mm or more. From the viewpoint of light weight of the tire 2, the length L3 is preferably 80 mm or less, and more preferably 60 mm or less.

  The short fibers 64 may be oriented in the circumferential direction. A large torsional rigidity is obtained by the short fibers 64 oriented in the circumferential direction. The inner sidewall 20 may include short fibers 64 that are not oriented in a specific direction.

  FIG. 5 is a cross-sectional perspective view showing a part of the carcass ply 42 of the tire 2 of FIG. The carcass ply 42 includes a large number of carcass cords 70 arranged in parallel and a topping rubber 72.

  FIG. 6 is an exploded view showing a part of the carcass cord 70 of the carcass ply 42 of FIG. The carcass cord 70 has a structure in which two yarns 74 are twisted. Three or more yarns 74 may be twisted. Each yarn 74 is formed by twisting aramid fibers. The tire 2 is heated by running in the puncture state. Since the temperature dependence of the elastic modulus of the aramid fiber is small, the carcass cord 70 prevents the carcass 16 from being damaged even when traveling in a puncture state.

  The twist coefficient T of the carcass cord 70 is 0.5 or more. The carcass cord 70 has a so-called “high twist structure”. Aramid fibers are high strength. On the other hand, aramid fibers are inferior in fatigue resistance. The high twist structure increases the fatigue resistance of the carcass cord 70. In the carcass cord 70, the combination of the aramid fiber and the high twist structure achieves both strength and fatigue resistance. The carcass cord 70 suppresses the longitudinal distortion of the tire 2 in the puncture state. The carcass cord 70 contributes to the steering stability of the tire 2 in the puncture state.

  Due to the synergistic effect of the inner side wall 20 that suppresses the bending of the support layer 18 and the carcass cord 70 that is excellent in fatigue resistance, extremely excellent durability is achieved in the tire 2. The tire 2 can travel for a long time even in a punctured state.

The twist coefficient T of the carcass cord 70 is calculated by the following mathematical formula (I).
T = N * ((0.125 * D / 2) / ρ) ^1/2 * 10 ⁻³ (I)
In this mathematical formula (I), N represents the number of upper twists per 10 cm of cord, D represents the total fineness (dtex), and ρ represents the specific gravity (g / cm ³ ) of the cord material. The total fineness D is the sum of the finenesses of the respective yarns.

  In light of the strength and durability of the tire 2, the twist coefficient T is more preferably equal to or greater than 0.6. From the viewpoint of easy manufacture of the carcass cord 70, the twist coefficient T is preferably 0.7 or less.

  From the viewpoint of fatigue resistance of the carcass cord 70, the number N of upper twists is preferably 40 or more, and more preferably 50 or more. The upper twist number N is preferably 100 or less.

  From the viewpoint of fatigue resistance of the carcass cord 70, the ratio (N1 / N) of the number of lower twists N1 and the number of upper twists N1 of the carcass cord 70 is preferably 0.2 or more and 2.0 or less, and 0.5 or more. 1.5 or less is preferable. The ratio (N1 / N) is ideally 1.0.

  The total fineness D of the carcass cord 70 is preferably 1500 dtex or more and 5000 dtex or less. The fineness of each yarn 74 is preferably 700 dtex or more and 3000 dtex or less. The density De of the carcass cord 70 is preferably 30/5 cm or more and 60/5 cm or less. The product (D * De) of the total fineness D and the density De in the carcass ply 42 is preferably 70000 to 150,000, and more preferably 100000 to 120,000.

The complex elastic modulus E ^* of the topping rubber 72 is 5 MPa or more. This topping rubber 72 is highly elastic. This topping rubber 72 contributes to the steering stability and durability of the tire 2 in a puncture state. In this respect, the complex elastic modulus E ^* is more preferably 6 MPa or more. The complex elastic modulus E ^* is preferably 13 MPa or less. The complex elastic modulus E ^* is measured by a viscoelastic spectrometer (“VA-200” manufactured by Shimadzu Corporation) under the conditions shown below in accordance with the provisions of “JIS K 6394”.
Initial strain: 10%
Amplitude: ± 2%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

FIG. 7 is a cross-sectional view showing a part of the tire 2 of FIG. FIG. 7 shows the tread 4, the wing 8, the sidewall 10, and the inner sidewall 20. The shape of the surface from the tread 4 through the wing 8 to the sidewall 10 is called a profile. What is indicated by an arrow W / 2 in FIG. 7 is half of the width W of the tire 2. The width W is determined based on the point P ₁₀₀ which is the outermost side in the axial direction, excluding the rib 36 (see FIG. 1). Profile, it has led to a point _{P 100} from the center point TC. In FIG. 7, points P ₆₀ , P ₇₅ and P ₉₀ are profiles whose axial distance from the point TC is 60%, 75% and 90% of the half width (W / 2) of the tire 2, respectively. Represents the top point.

The tire 2 has a CTT profile. This CTT profile, between the center point TC of the point P _90, the curvature radius gradually decreases. The CTT profile is typically determined based on an involute curve. The CTT profile may include a portion composed of a large number of arcs approximated to an involute curve. In the tire 2 shown in FIG. 7, between the center point TC of the point P _90, the profile is constructed from a number of arcs which is approximated to an involute curve. The number of arcs is preferably 3 or more, and more preferably 5 or more. Depending on other function curves, the CTT profile may be determined.

  If the CTT profile comprises a number of arcs approximated by a function curve, each arc touches an arc adjacent to it. The radius of curvature of each arc is smaller than the radius of curvature of the arc located on the inner side in the axial direction.

In FIG. 7, Y ₆₀ represents the radial distance between the point TC and the point P ₆₀ , Y ₇₅ represents the radial distance between the point TC and the point P _75, and Y ₉₀ represents the radius between the point TC and the point P _90. Y ₁₀₀ represents the radial distance between the point TC and the point P ₁₀₀ . This CTT profile satisfies the following formulas (1) to (4).
0.05 <Y ₆₀ /H≦0.10 (1)
0.10 <Y ₇₅ /H≦0.2 (2)
0.2 <Y ₉₀ /H≦0.4 (3)
_{0.4 <Y 100 / H ≦ 0.7} (4)
This CTT profile contributes to various performances of the tire 2. In this profile, the ground contact width when 80% of the normal load is applied to the tire 2 is not less than 0.50 times and not more than 0.65 times the maximum width W of the tire 2.

  In the tire 2 having the CTT profile, an appropriate shape of the contact surface can be obtained. This ground contact surface provides excellent ride comfort. Since the short fibers 64 are oriented in the radial direction, the inner sidewall 20 does not hinder this riding comfort. The CTT profile can adversely affect durability. In the tire 2, durability is supplemented by the inner sidewall 20. The combination of the CTT profile and the inner sidewall 20 achieves both durability and ride comfort.

  Unless otherwise specified, the size and angle of each part of the tire 2 are measured in a state where the tire 2 is incorporated in a normal rim and the tire 2 is filled with air so as to have a normal internal pressure. At the time of measurement, no load is applied to the tire 2. In the present specification, 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 specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “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. However, in the case of passenger car tires, the dimensions and angles are measured with the internal pressure being 180 kPa.

  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 run flat tire having the structure shown in FIG. 1 was obtained. This tire includes a support layer having a maximum thickness of 9 mm and a hardness of 78. The tire carcass cord is made of aramid fibers. The twist coefficient T of this carcass cord is 0.43. This tire has an inner sidewall. The thickness Ti of this inner sidewall is 2 mm. The loss tangent tan δ of this inner sidewall is 0.15. The inner sidewall includes 13 parts by mass of short fibers with respect to 100 parts by mass of the base rubber. The material of this short fiber is aramid. The short fibers are oriented in the radial direction. The short fibers have an average length L of 500 μm and an average diameter D of 10 μm. This tire has a CTT profile. This profile consists of a number of arcs approximated to an involute curve. The number of arcs between the center point TC and the point P ₉₀ is five. In this profile, (Y ₆₀ / H) is 0.09, (Y ₇₅ / H) is 0.14, (Y ₉₀ / H) is 0.37, and (Y ₁₀₀ / H) is 0.57. The size of this tire is “245 / 40R18”.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the inner sidewall was not provided.

[Examples 2 to 5]
Tires of Examples 2 to 5 were obtained in the same manner as Example 1 except that an inner sidewall having a loss tangent tan δ shown in Table 1 below was provided.

[Example 6]
A tire of Example 6 was obtained in the same manner as Example 1 except that a normal profile other than the CTT profile was formed. In this tire, (Y ₆₀ / H) is 0.06, (Y ₇₅ / H) is 0.08, (Y ₉₀ / H) is 0.19, and (Y ₁₀₀ / H) is 0.57

[Examples 7 to 10]
Tires of Examples 7 to 10 were obtained in the same manner as Example 1 except that an inner sidewall having a thickness Ti shown in Table 2 below was provided.
.

[Example 11]
A tire of Example 11 was obtained in the same manner as in Example 1 except that a carcass cord having a twist coefficient T of 0.50 was used. This carcass cord has a high twist structure.

[Example 12 and Comparative Example 2]
A tire of Example 12 was obtained in the same manner as Example 1 except that a carcass cord having a twist coefficient T of 0.66 was used. A tire of Comparative Example 2 was obtained in the same manner as Example 12 except that the inner sidewall was not provided. The tires of Example 12 and Comparative Example 2 have a carcass cord having a high twist structure.

[Comparative Examples 3 and 4]
A tire of Comparative Example 3 was obtained in the same manner as in Example 1 except that a carcass cord having a rayon material and a twist coefficient T of 0.59 was used. The fineness of this carcass cord is 1840 dtex / 2. A tire of Comparative Example 4 was obtained in the same manner as Comparative Example 3 except that the inner sidewall was not provided.

[Ride comfort]
A tire was incorporated into a regular rim, and the tire was filled with air to adjust the internal pressure to 230 kPa. This tire was a front engine rear wheel drive type and was mounted on a passenger car having a displacement of 4300 cc. The passenger car was run on asphalt-paved and stepped roads, Belgian roads and Bitzmann roads, and the driver was evaluated for ride comfort. The results are shown in Tables 1 and 2 below as indices based on Comparative Example 1. Larger numbers are preferable.

[Durability in puncture]
A tire was incorporated into a regular rim, and the tire was filled with air to adjust the internal pressure to 230 kPa. This tire was held at a temperature of 38 ° C. ± 3 ° C. for 34 hours. The valve core of the rim was pulled out and the inside of the tire communicated with the atmosphere. This tire was mounted on a drum-type running test machine, and a vertical load of 4.14 kN was applied to the tire. This tire was run on a drum having a radius of 1.7 m at a speed of 80 km / h. The distance traveled until the tire broke was measured. The results are shown in Tables 1 and 2 below as indices based on Comparative Example 1. A larger numerical value is preferable.

[Rolling resistance]
A tire was incorporated into a regular rim, and the tire was filled with air so that the internal pressure was 200 kPa. This tire was mounted on a rolling resistance tester, and a load of 4.6 kN (80% of the normal load) was applied to the tire. This tire was run at a speed of 80 km / h, and rolling resistance was measured. The results are shown in Tables 1 and 2 below as indices based on Comparative Example 1. A smaller numerical value is preferable.

  As shown in Tables 1 and 2, the tire of each example is excellent in various performances. From this evaluation result, the superiority of the present invention is clear.

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

FIG. 1 is a cross-sectional view showing a part of a run flat tire 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. FIG. 3 is an enlarged cross-sectional view showing a part of the inner sidewall of the tire of FIG. FIG. 4 is a schematic view showing the short fibers of the inner sidewall of FIG. FIG. 5 is a cross-sectional perspective view showing a part of the carcass ply of the tire of FIG. 1. FIG. 6 is an exploded view showing a part of the carcass cord of the carcass ply of FIG. FIG. 7 is a cross-sectional view showing a part of the tire of FIG.

Explanation of symbols

2 ... run flat tire 4 ... tread 10 ... sidewall 14 ... bead 16 ... carcass 18 ... support layer 20 ... inner sidewall 22 ... belt 24 ... Band 30 ... Side part 36 ... Rib 40 ... Apex 42 ... Carcass ply 62 ... Matrix 64 ... Short fiber 70 ... Carcass cord 72 ... Topping rubber 74 ...・ Yarn

Claims (7)

A tread whose surface forms a tread surface,
A pair of sidewalls extending substantially inward in the radial direction from the ends of the tread,
A pair of beads positioned substantially radially inward of the sidewalls;
A carcass having a cord made of an aramid fiber, which extends along the tread and the sidewall and is bridged between both beads.
A reinforcing layer located between the tread and the carcass,
A support layer that is located on the inner side in the axial direction of the side wall and has a substantially crescent-shaped cross section; and an inner side wall that is located outside the support layer and the carcass and inside the side wall in the axial direction. And
It has a tread profile including a curved surface composed of a plurality of arcs having different curvature radii from each other,
A run flat tire in which the inner sidewall includes a rubber matrix and a number of short fibers dispersed in the matrix.   The tire according to claim 1, wherein the short fibers are oriented in a radial direction.   The average length L of the short fibers is 10 µm or more and 1000 µm or less, the average diameter D thereof is 0.05 µm or more and 50 µm or less, and the aspect ratio (L / D) thereof is 10 or more. Tires.   The tire according to any one of claims 1 to 3, wherein the inner sidewall includes 100 parts by mass of a base rubber and 0.5 to 50 parts by mass of short fibers.   The tire according to any one of claims 1 to 4, wherein a loss tangent tan δ of the inner sidewall is 0.20 or more. The carcass cord has a structure in which a plurality of yarns in which aramid fibers are twisted are twisted,
The tire according to any one of claims 1 to 5, wherein a twist coefficient T calculated by the following mathematical formula (I) of the cord is 0.5 or more and 0.7 or less.
T = N * ((0.125 * D / 2) / ρ) ^1/2 * 10 ⁻³ (I)
(In this formula (I), N represents the number of upper twists per 10 cm of cord, D represents the total fineness (dtex), and ρ represents the specific gravity (g / cm ³ ) of the cord material.)   The tire according to any one of claims 1 to 6, wherein the tire has a profile in which the radius of curvature gradually decreases from the center point TC of the tread surface toward the outside in the axial direction.

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