JP2010030477A - Run-flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a run-flat tire of a side reinforced type having excellent durability in a punctured state. <P>SOLUTION: The tire 2 includes a tread 4, sidewalls 6, a clinch part 8, beads 10, a carcass 12, a supporting layer 14, a belt 16 and a band 18 wherein cords of the carcass 12 are composed of aramid fibers, and also includes a twist coefficient T of 0.5-0.7 including limits. The tire 2 is further arranged at each shoulder 56 with a swelling part 54, and the swelling part 54 is positioned outside a grounding end Pe when viewed in the axial direction. The swelling part 54 includes a maximum thickness of 1-5 mm, and a width of 3-15 mm. The swelling part 54 does not contact with the road surface in a normal state, and in the punctured state, the swelling part 54 contacts with the road surface so as to suppress the lifting of the tread 4. The tire 2 has such a profile that its radius of curvature decreases gradually from a center point TC on the tread surface toward the outside of the axial direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  The tire profile (surface shape from the tread to the sidewall when it is assumed that there are no irregularities) affects the basic performance of the tire, such as handling stability and ride comfort. An appropriate profile needs to be determined according to the tire concept. Japanese Patent Application Laid-Open No. 8-337101 discloses a method for determining a profile using a function. In the profile determined by this method, the radius of curvature gradually decreases from the equator plane toward the outside in the axial direction. This profile is called a CTT profile. By adopting the CTT profile, various performances of the tire can be improved.

  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 called a side reinforcing type. In this type of run flat tire, when the internal pressure is reduced by 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.

  This support layer is highly rigid. A tire having this support layer has a large longitudinal spring constant in a normal state. This tire is inferior in ride comfort. The normal state means a state in which the tire is assembled on a normal rim, the tire is filled with air so as to have a normal internal pressure, and a normal load is applied to the tire.

Further improvement in durability in a punctured state (a state where air is extracted from a tire in a normal state and the internal pressure becomes atmospheric pressure) is desired. Japanese Patent Application Laid-Open No. 2007-290553 discloses a run flat tire having a bulging portion on a shoulder. This bulging portion is in contact with the road surface in the puncture state. In the tire provided with the bulging portion, lifting of the tread crown in a punctured state is suppressed. The bulging portion contributes to the durability of the tire.
JP-A-8-337101 JP 2007-290553 A

  There is still room for improvement in durability in the puncture state. If a harder 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 thicker support layer is employed, excellent durability can be obtained. However, a tire having a thick support layer has a large longitudinal spring constant. 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) tread,
(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 that runs along the tread and the sidewall and spans between both beads and has an angle with respect to the circumferential direction of 45 ° or more and 90 ° or less.
(5) A reinforcing layer positioned between the tread and the carcass and (6) a pair of supporting layers positioned on the inner side in the axial direction of the sidewall and having a substantially crescent-shaped cross section. The tire includes a pair of bulging portions that are separated from the road surface in a normal state and are in contact with the road surface in a puncture state on a shoulder of the outer surface. The outer surface has a profile including a curved surface composed of a plurality of arcs having different curvature radii. The carcass cord has a structure in which a plurality of yarns made of aramid fibers are twisted. The twist coefficient T calculated by the following mathematical formula (I) of this 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 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 bulging portion has a maximum thickness of 1 mm to 5 mm and a width of 3 mm to 15 mm. Preferably, the bulging portion is annular and extends in the circumferential direction.

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

Preferably, the profile from the center point TC of the tread surface to the point P ₉₀ where the axial distance from the center point TC is 90% of the half width of the tire is formed by three or more arcs. Each arc touches an arc adjacent thereto. The radius of curvature of each arc is smaller than the radius of curvature of the arc on the inner side in the axial direction.

Preferably, the 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)
In the mathematical expressions (1) to (4), H represents the height of the tire, and Y ₆₀ , Y ₇₅ , Y ₉₀ and Y ₁₀₀ are the center point TC, the point P ₆₀ , the point P ₇₅ , the point P ₉₀ and the point, respectively. It represents the radial distance between P _100. Point P ₆₀ , point P ₇₅ , point P ₉₀ and point P ₁₀₀ are points on the profile whose axial distance from the center point TC is 60%, 75%, 90% and 100% of the half width of the tire, respectively. It is.

  A carcass cord excellent in strength and fatigue resistance is used in the run flat tire according to the present invention. This carcass cord suppresses the longitudinal distortion of the tire in the puncture state. Further, in this tire, the bulging portion suppresses lifting of the crown. By suppressing the longitudinal distortion and lifting, damage to the tire is suppressed. This 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. In FIG. 1, 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. In FIG. 1, what is indicated by a double arrow H is the height of the tire 2 from the reference line BL (detailed later).

  The tire 2 includes a tread 4, a sidewall 6, a clinch portion 8, a bead 10, a carcass 12, a support layer 14, a belt 16, a band 18, an inner liner 20, and a chafer 22. The belt 16 and the band 18 constitute a reinforcing layer. The reinforcing layer may be formed only from the belt 16. A reinforcing layer may be formed only from the band 18. The tire 2 is a tubeless type pneumatic tire.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 has a tread surface 24. A groove 26 is carved in the tread surface 24. The groove 26 forms a tread pattern. The tread 4 is made of a crosslinked rubber.

  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 prevents the carcass 12 from being damaged. The sidewall 6 is provided with ribs 28. The rib 28 protrudes outward in the axial direction. When traveling in a puncture state, the rib 28 comes into contact with the flange of the rim. By this contact, deformation of the bead 10 can be suppressed. The tire 2 in which the deformation is suppressed is excellent in durability in a puncture state.

  The clinch portion 8 is located substantially inside the sidewall 6 in the radial direction. The clinch portion 8 is located outside the bead 10 and the carcass 12 in the axial direction. The clinch portion 8 abuts on the flange of the rim.

  The bead 10 is located on the radially inner side of the sidewall 6. The bead 10 includes a core 30 and an apex 32 that extends radially outward from the core 30. The core 30 is ring-shaped and includes a plurality of non-stretchable wires (typically steel wires). The apex 32 is tapered outward in the radial direction. The apex 32 is made of a highly hard crosslinked rubber.

  In FIG. 1, what is indicated by an arrow Ha is the height of the apex 32 from the reference line BL. The reference line BL passes through the innermost point of the core 30 in the radial direction. The reference line BL extends in the axial direction. The ratio (Ha / H) of the height Ha of the apex 32 to the height H of the tire 2 is preferably 0.1 or more and 0.7 or less. The apex 32 having a ratio (Ha / H) of 0.1 or more can support the vehicle weight in a punctured state. The apex 32 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 12 includes a carcass ply 34. The carcass ply 34 is bridged between the beads 10 on both sides, and extends along the tread 4 and the sidewall 6. The carcass ply 34 is folded around the core 30 from the inner side to the outer side in the axial direction. By this folding, a main portion 36 and a folding portion 38 are formed in the carcass ply 34. An end 40 of the folded portion 38 reaches just below the belt 16. In other words, the folded portion 38 overlaps the belt 16. The carcass 12 has a so-called “ultra-high turn-up structure”. The carcass 12 having an ultra high turn-up structure contributes to the strength of the side portion of the tire 2.

  As will be described later, the carcass ply 34 includes a large number 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 45 ° to 90 °, and further 75 ° to 90 °. In other words, the carcass 12 has a radial structure.

  The support layer 14 is located inside the sidewall 6 in the axial direction. The support layer 14 is sandwiched between the carcass 12 and the inner liner 20. The support layer 14 tapers inward in the radial direction and also tapers outward. The support layer 14 has a shape similar to a crescent moon. The support layer 14 is made of a highly hard crosslinked rubber. When the tire 2 is punctured, the support layer 14 supports the load. The support layer 14 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 14 illustrated in FIG.

  A portion of the carcass 12 that overlaps the support layer 14 is separated from the inner liner 20. In other words, the carcass 12 is curved due to the presence of the support layer 14. In the puncture state, a compressive load is applied to the support layer 14. In the punctured state, a tensile load is applied to a region of the carcass 12 that is close to the support layer 14. Since the support layer 14 is a rubber lump, it can sufficiently withstand the compressive load. The carcass cord can sufficiently withstand a tensile load. The support layer 14 and the carcass cord suppress the vertical deflection of the tire 2 in the punctured state. The tire 2 in which the vertical deflection is suppressed is excellent in handling stability in the puncture state.

  From the viewpoint of suppressing longitudinal strain in the puncture state, the hardness of the support layer 14 is preferably 60 or more, and more preferably 65 or more. From the viewpoint of riding comfort in a normal state, 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 42 of the support layer 14 is located on the inner side in the radial direction than the upper end 44 of the apex 32. In other words, the support layer 14 overlaps the apex 32. In FIG. 1, an arrow L <b> 1 indicates a radial distance between the lower end 42 of the support layer 14 and the upper end 44 of the apex 32. 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 46 of the support layer 14 is located on the inner side in the axial direction than the end 48 of the belt 16. In other words, the support layer 14 overlaps the belt 16. In FIG. 1, an arrow L <b> 2 indicates an axial distance between the upper end 46 of the support layer 14 and the end 48 of the belt 16. 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 14 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 belt 16 is located on the radially outer side of the carcass 12. The belt 16 is laminated with the carcass 12. The belt 16 reinforces the carcass 12. The belt 16 includes an inner layer 50 and an outer layer 52. As is clear from FIG. 1, the width of the inner layer 50 is slightly larger than the width of the outer layer 52. Although not shown, each of the inner layer 50 and the outer layer 52 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 50 with respect to the equator plane is opposite to the inclination direction of the cord of the outer layer 52 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 16 is preferably 0.85 to 1.0 times the maximum width W of the tire 2 (detailed later). The belt 16 may include three or more layers.

  The band 18 covers the belt 16. Although not shown, the band 18 is composed of a cord and a topping rubber. The cord is wound in a spiral. The band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the belt 16 is restrained by this cord, lifting of the belt 16 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 16 instead of the band 18. The tire 2 may include an edge band together with the band 18.

FIG. 2 is an enlarged cross-sectional view showing a part of the tire 2 of FIG. The tire 2 includes a bulging portion 54 on the outer surface thereof. As is clear from FIGS. 1 and 2, the bulging portion 54 is located on the shoulder 56. A two-dot chain line in FIG. 2 is a part of the profile of the tire 2 when it is assumed that there is no bulging portion 54. Chain line these two points is a part of a smooth curve drawn from ground terminal Pe (later described in detail) to the maximum width position P _100. The bulging portion 54 protrudes from the profile. The bulging portion 54 is annular and extends in the circumferential direction. A large number of discontinuous bulging portions in the circumferential direction may be provided.

  In FIG. 2, what is indicated by a symbol Pe is a ground terminal. The grounding end Pe is an outer end in the axial direction of the grounding surface in the normal state. The bulging portion 54 is located outside the ground contact end Pe in the axial direction.

  As is clear from FIG. 2, the contour of the cross section of the bulging portion 54 is arcuate. The bulging portion 54 is thickest at the center. The thickness of the bulging portion 54 gradually decreases from the center toward the one end 58. The thickness of the bulging portion 54 gradually decreases from the center toward the other end 60. The tire 2 may include a bulging portion having another cross-sectional shape.

  FIG. 3 is a schematic cross-sectional view showing a part of the tire 2 of FIG. 1 together with the road surface 62. FIG. 3 shows the tire 2 in a normal state. As is apparent from FIG. 3, the tread surface 24 is in contact with the road surface 62 on the inner side of the ground contact end Pe. The tread surface 24 is separated from the road surface 62 outside the ground contact end Pe.

  As apparent from FIG. 3, the bulging portion 54 is separated from the road surface 62 in the normal state. Therefore, there is no mechanical relationship between the bulging portion 54 and the road surface 62. The bulging portion 54 has little influence on riding comfort and durability in a normal state.

  FIG. 4 is a schematic cross-sectional view showing a part of the tire 2 of FIG. 1 together with the road surface 62. FIG. 4 shows the tire 2 in a punctured state. In the puncture state, the support layer 14 supports the load. Since the shoulder 56 of the tread 4 is close to the support layer 14, a load is applied to the shoulder 56. Due to this load, a compressive stress is generated in the tread 4 in the axial direction. Due to this stress, the crown 64 of the tread 4 is lifted.

  As shown in FIG. 4, in the tire 2 according to the present invention, the bulging portion 54 contacts the road surface 62 in the punctured state. Therefore, compared with the case where there is no bulging part 54, the compressive stress which arises in the tread 4 is suppressed and lifting of the crown 64 is suppressed. The tire 2 generates less heat at the shoulder 56 and the support layer 14 than the conventional run flat tire. The bulging portion 54 suppresses damage to the tread 4 and the support layer 14 in a punctured state. The bulging portion 54 contributes to the durability of the tire 2. In FIG. 4, what is indicated by a two-dot chain line is a crown of the tire that does not have the bulging portion 54.

  In FIG. 2, what is indicated by the arrow Tm is the maximum thickness of the bulging portion 54. The maximum thickness Tm is preferably 1 mm or more and 5 mm or less. Due to the bulging portion 54 having the maximum thickness Tm of 1 mm or more, the lifting of the crown 64 in the punctured state can be sufficiently suppressed. In this respect, the maximum thickness Tm is more preferably 2 mm or more. The bulging portion 54 having a maximum thickness Tm of 5 mm or less is difficult to be grounded during traveling in a normal state. The bulging portion 54 does not impair riding comfort. Furthermore, uneven wear due to the bulging portion 54 is suppressed by setting the maximum thickness Tm to 5 mm or less. From these viewpoints, the maximum thickness Tm is preferably 4 mm or less. The maximum thickness Tm is measured in the normal direction of the profile assumed to have no bulge 54.

  In FIG. 2, the width of the bulging portion 54 is indicated by an arrow W. The width W is preferably 3 mm or greater and 15 mm or less. Lifting of the crown 64 in the puncture state can be suppressed by the bulging portion 54 having a width W of 3 mm or more. In this respect, the width W is more preferably 5 mm or more. By setting the width to 15 mm or less, an increase in the mass of the tire 2 due to the bulging portion 54 is suppressed. In this respect, the width W is more preferably 10 mm or less.

  In FIG. 2, what is indicated by the arrow L3 is the distance from the ground contact end Pe to the bulging portion 54. The distance L3 is preferably 4 mm or greater and 12 mm or less. In the tire 2 in which the distance L3 is 4 mm or more, the bulging portion 54 is difficult to be grounded during traveling in a normal state. In this respect, the distance L3 is more preferably 6 mm or more. In the tire 2 in which the distance L3 is 12 mm or less, the bulging portion 54 sufficiently suppresses the lifting of the crown 64 in the punctured state. In this respect, the distance L3 is more preferably 10 mm or less.

  The bulging portion 54 is formed integrally with the tread 4. Accordingly, the material of the bulging portion 54 is the same as that of the tread 4. The formation of the bulging portion 54 is easy. The tire 2 may include a bulging portion 54 having a material different from the material of the tread 4. In this case, it is preferable to use a high hardness rubber for the bulging portion 54. The high hardness bulging portion 54 is excellent in wear resistance in a puncture state. The bulging portion 54 may be reinforced with short fibers.

  It is preferable that the surface of the bulging portion 54 is roughened. The friction coefficient of the bulged portion 54 that has been roughened is large. A large frictional force acts between the bulging portion 54 and the road surface 62 in the puncture state. The bulging portion 54 is difficult to move inward in the axial direction in the punctured state. The bulging portion 54 can suppress lifting of the crown 64. Roughening can be achieved by performing shot blasting, shot peening, or the like on a portion corresponding to the bulging portion 54 in the cavity surface of the molding. Many minute streaks may be formed on the surface of the bulging portion 54.

  FIG. 5 is a cross-sectional perspective view showing a part of the carcass ply 34 of the tire 2 of FIG. The carcass ply 34 includes a large number of carcass cords 66 arranged in parallel and a topping rubber 68.

  FIG. 6 is an exploded view showing a part of the carcass cord 66 of the carcass ply 34 of FIG. The carcass cord 66 has a structure in which two yarns 70 are twisted. Three or more yarns 70 may be twisted. Each yarn 70 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 66 prevents the carcass 12 from being damaged even when traveling in a puncture state.

  The twist coefficient T of the carcass cord 66 is 0.5 or more. The carcass cord 66 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 66. In the carcass cord 66, the combination of the aramid fiber and the high twist structure achieves both strength and fatigue resistance. The carcass cord 66 suppresses the longitudinal distortion of the tire 2 in the puncture state. The carcass cord 66 contributes to the steering stability of the tire 2 in the puncture state.

  Due to the synergistic effect of the bulging portion 54 that suppresses lifting of the crown 64 and the carcass cord 66 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 66 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 70.

  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 66, the twist coefficient T is preferably 0.7 or less.

  From the viewpoint of fatigue resistance of the carcass cord 66, 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 the fatigue resistance of the carcass cord 66, the ratio (N1 / N) between the number of lower twists N1 and the number of upper twists N of the carcass cord 66 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 66 is preferably 1500 dtex or more and 6000 dtex or less. The fineness of each yarn 70 is preferably 700 dtex or more and 3000 dtex or less. The density De of the carcass cord 66 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 34 is preferably 70000 to 150,000, and more preferably 100000 to 120,000.

The complex elastic modulus E ^* of the topping rubber 68 (see FIG. 5) is 5 MPa or more. This topping rubber 68 is highly elastic. The topping rubber 68 contributes to the steering stability and durability of the tire 2 in the 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: ± 1%
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 and the sidewall 6. The shape of the surface from the tread 4 to the sidewall 6 when it is assumed that there is no groove 26 and the bulging portion 54 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 a point P ₁₀₀ that is the outermost side in the axial direction except for the rib 28 (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 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 despite the presence of the support layer 14. 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. The measurement of the profile is performed by filling the tire 2 with air so that the tire 2 is assembled on a normal rim and has a normal internal pressure. At the time of measurement, no load is applied to the tire 2.

  In the tire 2 having the CTT profile, the profile of the shoulder 56 is greatly separated from the road surface 62 in the normal state. Therefore, even if a large bulge 54 is formed on the shoulder 56, the bulge 54 is unlikely to contact the road surface. By combining the CTT profile and the bulging portion 54, excellent durability in a punctured state can be achieved.

  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 the passenger car tire 2, for the sake of convenience, 180 kPa is the normal internal pressure.

  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 0.50. This tire has a pair of bulging portions. Each bulge has a maximum thickness T of 5 mm and a width W of 10 mm. The surface of the bulging portion is roughened. 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 / 40ZR18”.

[Comparative Example 1 and Example 2]
Tires of Comparative Example 1 and Example 2 were obtained in the same manner as Example 1 except that a carcass cord having a twist coefficient T shown in Table 1 below was used.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1 except that a carcass cord made of rayon was used.

[Example 3]
A tire of Example 3 was obtained in the same manner as Example 1 except that the roughened surface was not roughened.

[Examples 4 to 7]
Tires of Examples 4 to 7 were obtained in the same manner as Example 1 except that the width W of the bulging portion was as shown in Table 1 below.

[Examples 8 to 10]
Tires of Examples 8 to 10 were obtained in the same manner as Example 1 except that the maximum thickness Tm of the bulging portion was as shown in Table 2 below.

[Comparative Example 3]
A tire of Comparative Example 3 was obtained in the same manner as in Example 1 except that the bulging portion was not formed.

[Comparative Example 4]
A tire of Comparative Example 4 was obtained in the same manner as in Example 1 except that the bulging portion was not formed and a carcass cord made of rayon was used.

[Example 11]
A tire of Example 11 was obtained in the same manner as Example 1 except that a normal profile that was not a 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.

[Comparative Example 4]
A tire of Comparative Example 4 was obtained in the same manner as in Example 1 except that the bulging portion was not formed and 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.

[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 the tire of Comparative Example 4. A larger numerical value is preferable.

[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 the tire of Comparative Example 4. Larger numbers are 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 of FIG. FIG. 3 is a schematic cross-sectional view showing a part of the tire of FIG. 1 together with the road surface. FIG. 4 is a schematic cross-sectional view showing a part of the tire of FIG. 1 together with the road surface. 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 6 ... Side wall 8 ... Clinch part 10 ... Bead 12 ... Carcass 14 ... Support layer 16 ... Belt 18 ... Band 28 ... rib 34 ... carcass ply 54 ... bulge 56 ... shoulder 64 ... crown 66 ... carcass cord 68 ... topping rubber 70 ... yarn

Claims (6)

tread,
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 that runs along the tread and the sidewall and is bridged between both beads and has an angle of 45 ° to 90 ° with respect to the circumferential direction;
A reinforcing layer positioned between the tread and the carcass, and a pair of supporting layers that are positioned on the inner side in the axial direction of the sidewall and having a substantially crescent-shaped cross section;
The shoulder of the outer surface is provided with a pair of bulging portions that are separated from the road surface in a normal state and in contact with the road surface in a puncture state,
The outer surface has a profile including a curved surface formed of a plurality of arcs having different curvature radii from each other,
The carcass cord has a structure in which a plurality of yarns made of aramid fibers are twisted,
A run-flat tire having a twist coefficient T calculated by the following mathematical formula (I) of the cord of 0.5 to 0.7.
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 claim 1, wherein the bulging portion has a maximum thickness of 1 mm to 5 mm and a width of 3 mm to 15 mm.   The tire according to claim 1, wherein the bulging portion is annular and extends in the circumferential direction.   The tire according to any one of claims 1 to 3, wherein the tire has a profile in which the radius of curvature gradually decreases from the center point TC of the surface of the tread toward the outside in the axial direction. A profile from the center point TC of the tread surface to a point P ₉₀ where the axial distance from the center point TC is 90% of the half width of the tire is formed by three or more arcs;
Each arc touches the adjacent arc,
The tire according to any one of claims 1 to 4, wherein the radius of curvature of each arc is smaller than the radius of curvature of the arc on the inner side in the axial direction. The tire according to claim 5, wherein the profile satisfies the following mathematical 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)
(In the equations (1) to (4), H represents the tire height, and Y ₆₀ , Y ₇₅ , Y ₉₀ and Y ₁₀₀ are the center point TC, the point P ₆₀ , the point P ₇₅ , the point P ₉₀ and This represents the radial distance from the point P _{100. The} point P ₆₀ , the point P ₇₅ , the point P ₉₀ and the point P ₁₀₀ have an axial distance from the center point TC of 60% and 75% of the half width of the tire, respectively. (The points on the profile are 90% and 100%.)

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