JP5297151B2 - Run flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a run-flat tire allowing the improvement of a bead part. <P>SOLUTION: This run-flat tire 1 includes a carcass 3, a side reinforcing rubber layer 9 and a bead apex 8. In the bead part 4, a reinforcing cord layer 12 extending between the body 6a of a carcass ply 6A and the bead apex 8 and having the inner end 12i in the tire radial direction terminating without being folded back at a bead core 5 is arranged. The reinforcing cord layer 12 comprises at least a sheet of ply 12A using a reinforcing cord made of aramid fibers. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a run flat tire that can improve durability during run flat running.

  For example, various run-flat tires have been proposed that can travel relatively long distances (hereinafter, such travel is simply referred to as “run-flat travel”) even in a state in which the air in the tire has escaped due to puncture or the like. Yes. As a typical example, a side reinforcing type in which a side reinforcing rubber layer having a substantially crescent-shaped cross section is provided on the side wall is well known (see, for example, Patent Document 1).

  In this type of run flat tire, the run flat durability can be improved by increasing the thickness of the side reinforcing rubber layer and increasing the bending rigidity of the side wall portion. In addition, a multipurpose vehicle such as SUV (Sports Utility Viechle) has a larger vehicle weight than a general passenger car. Therefore, in the case of a run flat tire for SUV, the thickness of the side reinforcing rubber layer tends to be further increased, and the bending rigidity of the sidewall portion tends to be increased.

JP 2000-351307 A

  However, when the thickness of the side reinforcing rubber layer is increased, the rigidity of the bead portion is relatively decreased. For this reason, the distortion of the bead part which arises at the time of run flat running tends to become relatively large. As a result, there is a problem that damage to the bead portion is accelerated, and as a result, durability during run flat running is lowered.

  The present invention was devised in view of the actual situation as described above, and the bead portion is basically provided with a reinforcing cord layer using a reinforcing cord made of an aramid fiber having high elasticity and excellent heat resistance. The main purpose is to provide a run-flat tire capable of improving the durability of the tire.

In the invention according to the first aspect of the present invention, the main body part extending from the tread part through the sidewall part to the bead core of the bead part is provided with a series of folded parts that are folded from the inner side to the outer side in the tire axial direction around the bead core. A carcass made of a carcass ply, a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion, and a bead apex extending in a tire radial direction outward from the outer surface of the bead core. In the run-flat tire, the carcass is composed of a carcass ply in which a carcass cord made of aramid fibers arranged at an angle of 45 to 90 ° with respect to the tire equator is covered with a topping rubber, and the carcass cord is The twist coefficient T shown by the formula (1) is 0.50 to 0.70, A reinforcing cord layer extending between the main body portion of the carcass ply and the bead apex and terminating without being folded back by the bead core in the tire radial direction is disposed, and the reinforcing cord layer is made of an aramid fiber. Ri Do at least one ply with reinforcing cords made, the height h1 of the radially outer end of the reinforcing cord layer is smaller than the height h0 of the bead apex, the tire section from the bead base line BL From buttress portion thickness W1 at tire outer surface position P1, with a height of 72% of height SH spaced outward in the tire radial direction, sidewall portion thickness W2 at tire maximum cross-section width point P2, and bead base line BL The bead thickness W3 at the tire outer surface position P3, which is 17% of the tire cross-section height SH and spaced outward in the tire radial direction, is The formulas (2) and (3) are satisfied .
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)
(However, N is the number of upper twists (times / 10 cm), D is the total display decitex (fineness), and ρ is the specific gravity of the cord material.)
0.90 ≦ W3 / W1 ≦ 1.10 (2)
0.90 ≦ W3 / W2 ≦ 1.30 (3)

  The invention according to claim 2 is the run-flat tire according to claim 1, wherein the carcass cord has a two-stranded structure in which two twisted filament bundles are twisted together by an upper twist.

  The invention according to claim 3 is the run-flat tire according to claim 1 or 2, wherein a twist coefficient T of the carcass cord is 0.60 to 0.70.

  The invention according to claim 4 is the run-flat tire according to any one of claims 1 to 3, wherein the topping rubber has a complex elastic modulus E * of 5 to 13 MPa.

  In the invention according to claim 5, the profile of the tire outer surface is a curved surface formed of a plurality of arcs whose curvature radius gradually decreases from the tire equator point CP, which is the intersection of the tire outer surface and the tire equator surface, toward the contact end side. The run-flat tire according to any one of claims 1 to 4, wherein the run-flat tire is formed by:

Further, the invention according to claim 6 is a tire meridian cross section including a tire rotation axis in a normal state in which a normal rim is assembled and a normal internal pressure is filled and no load is applied.
The profile of the tire outer surface is such that when a point on the tire outer surface separating a distance SP of 45% of the maximum tire cross-sectional width SW from the tire equator surface is P, the radius of curvature RC of the tire outer surface is the above point from the tire equator point CP. While gradually decreasing until reaching P, distances X60, X75, X90 of 60%, 75%, 90%, and 100% of the half width (SW / 2) of the maximum tire cross-sectional width SW from the tire equatorial plane. And X100 and Y100, Y75, Y90 and Y100, respectively, and the radial distance between each point on the outer surface of the tire separating X100 and Y100, respectively, and the tire cross-section height SH.
0.05 <Y60 / SH ≦ 0.10
0.10 <Y75 / SH ≦ 0.20
0.20 <Y90 / SH ≦ 0.40
0.40 <Y100 / SH ≦ 0.70
The run-flat tire according to claim 5, wherein the relationship is satisfied.

  The invention according to claim 7 is the run-flat tire according to any one of claims 1 to 6, wherein the reinforcing cord has a twist coefficient T expressed by the preceding formula (1) of 0.50 to 0.70. is there.

In the invention according to claim 8 , the difference (h0-h1) between the height h0 of the bead apex and the height h1 of the outer end of the reinforcing cord layer is 0.07 times or more of the tire cross-section height SH. The run flat tire according to any one of claims 1 to 7, wherein the run flat tire is 0.14 times or less.

  The invention according to claim 9 is the run flat tire according to any one of claims 1 to 8, wherein a thickness W4 of the side reinforcing rubber layer at a tire maximum cross-sectional width point P2 is 9.0 to 11.0 mm. It is.

  The regular rim is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA, “Design Rim” for TRA, Or, for ETRTO, “Measuring Rim”.

  The “regular internal pressure” is the air pressure defined by the standard for each tire. The maximum air pressure described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is the maximum air pressure for JATMA and TRA for TRA. If the value is ETRTO, “INFLATION PRESSURE” is assumed, but in the case of a passenger car tire, it is 180 kPa.

  The run flat tire of the present invention includes a carcass ply in which a carcass cord made of an aramid fiber is covered with a topping rubber. Thereby, the rigidity and load supporting ability of the tire are increased. The bead portion is provided with a reinforcing cord layer using a reinforcing cord made of an aramid fiber. Since this reinforcing cord layer can increase the bending rigidity of the bead portion, it is possible to suppress distortion and heat generation that occur in the bead portion during run-flat running, and thus to suppress early damage of the bead portion. And since a reinforcement cord consists of aramid fiber, even when the temperature of a bead part rises, there is little fall of an elasticity modulus. Therefore, since the increase in distortion of the bead portion and the accompanying temperature rise can be prevented even when the bead portion generates heat, the durability during run-flat running and the like is further improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a meridional sectional view of a tire in a normal state of a run-flat tire (hereinafter sometimes simply referred to as “tire”) 1 of the present embodiment.

  The tire 1 according to this embodiment includes a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a side reinforcement with a substantially crescent-shaped cross section disposed inside the carcass 6 of the sidewall portion 3. A rubber layer 9 and a bead apex 8 extending from the outer surface of the bead core 5 to the outside in the tire radial direction are provided. In the tire 1 of this embodiment, a belt layer 7 is provided on the outer side in the radial direction of the carcass 6, and a band layer 10 is provided on the outer side in the radial direction of the belt layer 7.

  The carcass 6 is formed of one or more carcass plies 6A in which a carcass cord 20 (shown in FIG. 4) arranged at an angle of 45 to 90 ° with respect to the tire equator is covered with a topping rubber. The carcass 6 of the present embodiment is composed of one carcass ply 6A in which the carcass cord 20 is arranged at an angle of 80 to 90 ° with respect to the tire equator C.

  The carcass ply 6A includes a toroid-shaped main body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead cores 5 and 5 of the bead portion 4, and a tire shaft connected to the main body portion 6a and around the bead core 5. A pair of folded portions 6b folded from the inner side to the outer side.

  In the present embodiment, the folded portion 6b of the carcass ply 6A winds up beyond the bead apex 8 radially outward, and the outer end portion 6be is sandwiched between the main body portion 6a and the belt layer 7 and terminates. . Thereby, the sidewall part 3 is effectively reinforced by one carcass ply 6A. Further, since the outer end portion 6be of the turned-up portion 6b moves away from the sidewall portion 3 that is greatly bent during run-flat travel, damage starting from the outer end portion 6be is suitably suppressed.

  The bead apex 8 is made of, for example, a hard rubber having a rubber hardness of 65 to 98 degrees, and increases the bending rigidity of the bead portion 4 to suppress the longitudinal deflection of the tire 1. In the present specification, “rubber hardness” means hardness according to JIS durometer type A measured at a temperature of 23 ° C. in accordance with the provisions of JIS-K6253.

  The height h0 from the bead base line BL at the outer end in the tire radial direction of the bead apex 8 is not particularly limited. However, if it is too small, the bending rigidity of the bead portion 4 may be lowered. There is a risk of excessive weight increase and significant deterioration in ride comfort. From such a viewpoint, the height h0 of the bead apex 8 is preferably 25% or more, more preferably 26% or more of the tire cross-section height SH, and 30% or less, more preferably 29% of the tire cross-section height SH. % Or less is desirable. The tire cross-section height SH is a radial height from the bead base line BL to the outermost position in the tire radial direction (point CP in FIG. 1) in a normal state.

  The bead core 5 is formed of a ring body in which, for example, steel bead wires are overlapped in the tire radial direction and the tire axial direction and wound many times, and the tightening force with the rim is strengthened. The bead core 5 has a substantially rectangular cross section, but may have a substantially circular cross section, a substantially hexagonal cross section, or the like. Further, the height H4 of the outer surface 5o in the tire radial direction of the bead core 5 is not particularly limited, but is set to 0.05 to 0.06 times the tire cross-section height SH in the present embodiment. The height H5 of the inner surface 5i in the tire radial direction of the bead core 5 is set to 0.01 to 0.02 times the tire cross-section height SH.

  In this example, the belt layer 7 includes two belt plies 7A and 7B arranged such that a belt cord made of steel is inclined at about 10 to 35 ° with respect to the tire equator C so that the belt cords cross each other. Is superimposed. As the belt cord, in addition to steel, a highly elastic organic fiber cord such as aramid or rayon can be used as required.

  The band layer 10 includes one or more band plies 11 in which a band cord wound spirally at an angle of 5 ° or less with respect to the tire equator is covered with a topping rubber. The band layer 10 of the present embodiment includes a pair of left and right edge band plies 11A covering only the outer end portion in the tire axial direction of the belt layer 7, and the belt band 10 on the outer side in the tire axial direction of the edge band ply 11A and the belt layer 7. A full band ply 11B covering substantially the entire width of the layer 7 is combined. Such a band layer 10 restrains the belt layer 7 and improves steering stability, high-speed durability, and the like. The band layer 10 may be composed of the edge band ply 11A or the full band ply 11B alone.

  The side reinforcing rubber layer 9 is formed in a substantially crescent shape with a cross section extending gradually from the central portion having the maximum thickness toward the inner end 9i and the outer end 9o in the tire radial direction. In this embodiment, the inner end 9 i of the side reinforcing rubber layer 9 is provided on the inner side in the tire radial direction from the outer end of the bead apex 8, and the outer end 9 o is in the tire axial direction from the outer end 7 e of the belt layer 7. It is provided inside.

  In the present embodiment, the side reinforcing rubber layer 9 is disposed on the inner side (the tire lumen side) of the main body portion 6a of the carcass ply 6A. During run flat running, the side reinforcing rubber layer 9 is mainly subjected to compressive stress, and the carcass ply 6A is mainly subjected to tensile stress, but the side reinforcing rubber layer 9 has excellent compression resistance and carcass cords. The excellent tensile durability by means of efficiently increasing the bending rigidity of the sidewall portion 3 and effectively reducing the longitudinal deflection of the tire during run-flat running.

  The rubber hardness of the side reinforcing rubber layer 9 is preferably 60 degrees or more, and more preferably 65 degrees or more. If the rubber hardness is less than 60 degrees, the distortion of the sidewall portion 3 during run-flat running increases, and the run-flat durability may be reduced. On the other hand, even if the rubber hardness is too high, the longitudinal spring constant of the tire is excessively increased, which may deteriorate the riding comfort during normal driving. From such a viewpoint, the rubber hardness of the side reinforcing rubber layer 9 is preferably 90 degrees or less, more preferably 80 degrees or less.

  Note that the thickness W4 of the side reinforcing rubber layer 9 at the tire maximum cross-sectional width point P2 is preferably about 9.0 to 11.0 mm, for example. This helps to prevent deterioration in ride comfort while maintaining run flat durability.

  In the present invention, an aramid fiber is used for the carcass cord 20 in order to improve the handling stability and durability during the run-flat running. Aramid fibers have high strength and high elasticity compared to other organic fiber cord materials. For this reason, by using aramid fibers in the carcass cord 20, the load supporting ability of the tire can be increased.

  Furthermore, aramid fibers are excellent in heat resistance, and for example, the decrease in elastic modulus is small even at a high temperature of 100 to 150 ° C. Therefore, even if the temperature of the tire rises during run flat running, an increase in the amount of tire deformation due to a decrease in the strength and elastic modulus of the carcass cord 20 and a tire temperature rise associated therewith can be suppressed, thereby improving the run flat durability. . In addition, the carcass cord 20 made of aramid fibers can maintain the high elastic modulus and increase the tire rigidity even when the tire temperature rises.

  In the present embodiment, as schematically shown in FIG. 4, two twisted aramid fiber filament bundles 21 (that is, strands 21) are further twisted to each other by upper twisting as shown in FIG. 4. Structure is adopted. Further, the carcass cord 20 is preferably a so-called balance twist in which the number of lower twists and the number of upper twists are equal, but the ratio of the number of twists (number of lower twists / number of upper twists) is in the range of 0.2 to 2.0. Preferably, the number of lower twists and the number of upper twists may be made different within a range of 0.5 to 1.5.

In the carcass cord 20, it is desirable to twist the filament bundle 21 with a higher twisting coefficient T than before. Here, “twist coefficient T” is the number of twists of the cord N (unit: times / 10 cm), the total display decitex (total fineness) of one cord is D (unit: dtex), and the specific gravity of the cord material is ρ. Is expressed by the following formula (1).
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)

  In general, aramid fibers tend to be inferior in fatigue resistance due to their high elastic modulus, but by increasing the twist coefficient T from 0.50 to 0.70, the fatigue resistance can be improved and run-flat durability can be achieved. Can be improved. If the twist coefficient T of the carcass cord 20 is less than 0.50, the effect of improving fatigue resistance is reduced. On the contrary, when the twist coefficient T exceeds 0.70, it becomes difficult to twist the cord, and the productivity is significantly deteriorated. In particular, the twist coefficient T is preferably 0.60 or more, whereby the fatigue resistance of the cord is further improved and the run-flat durability is improved.

  The total display decitex D (fineness) of the carcass cord 20 is not particularly limited, but is preferably in the range of 1500 to 5000 dtex for passenger cars and SUVs in order to improve run-flat durability and handling stability. Further, the product of the number of driving per 5 cm width of the ply of the carcass ply 6A (hereinafter referred to as “ends”) n (lines / 5 cm) and the total display decitex D is preferably in the range of 70,000 to 150,000, more preferably 100,000. ~ 120,000 is desirable.

  Further, in the present embodiment, rubber having a complex elastic modulus E * of 5 to 13 MPa is adopted as the topping rubber of the carcass ply 6A. As described above, when a rubber having higher elasticity than the conventional rubber is used for the topping rubber, the strain acting on the carcass cord 20 can be reduced, and the run-flat durability can be further improved.

  If the complex elastic modulus E * is less than 5 MPa, the above effect cannot be sufficiently expected. Conversely, if the complex elastic modulus E * is more than 13 MPa, the rubber becomes extremely hard, and the ride comfort deteriorates at a stretch. From such a viewpoint, the complex elastic modulus E * is preferably 5.5 MPa or more, more preferably 6 MPa or more, and preferably 11 MPa or less, more preferably 9 MPa or less.

In the present specification, the complex elastic modulus is a value measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho under the following conditions in accordance with the provisions of JIS-K6394.
Initial strain: 10%
Amplitude: ± 1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

  The bead portion 4 is provided with a chafer 14 made of, for example, canvas cloth. As shown in an enlarged view in FIG. 2, the chafer 14 includes an inner rising portion 14 a extending from the tire inner surface in the radial direction of the tire, an inner rising portion 14 a, and the bead core 5. A base portion 14b located on the inner side in the radial direction and exposed at the bottom surface of the bead; and an outer rising portion 14c connected to the base portion 14b and extending on the outer side of the tire in the radial direction of the tire, and enveloping the bead portion of the carcass The cross section is formed in a substantially U shape. Such a chafer 14 is useful for preventing rim displacement during run-flat running and damage to the bead portion 4 during rim attachment / detachment.

  The height h2 of the rising portion 14c outside the chafer 14 is not particularly limited, but is set to 0.12 to 0.13 times the tire cross-section height SH in order to obtain the above effects. . The height h3 of the rising portion 14a in the chafer 14 is set to 0.10 to 0.11 times the tire cross-section height SH.

  Further, a reinforcement cord layer 12 is disposed on the bead portion 4 in order to further improve the durability during run-flat running. As the reinforcing cord layer 12, at least one ply 12A (one in this embodiment) using a reinforcing cord made of an aramid fiber is used.

  The reinforcing cord layer 12 extends between the main body portion 6a of the carcass ply 6A and the inner surface of the bead apex 8 in the tire axial direction, and the inner end 12i in the tire radial direction is folded back by the bead core 5. It is formed with no termination.

  Like the carcass cord 20 (shown in FIG. 4), such a reinforcing cord layer 12 includes a reinforcing cord made of an aramid fiber, so that a decrease in elastic modulus and an increase in strain at the time of temperature rise can be prevented. The bending rigidity of the bead portion 4 can be increased to further improve the durability.

  Further, due to the excellent tensile durability by the reinforcing cord layer 12 and the excellent compression durability of the bead apex 8, the bending rigidity of the bead portion 4 is further effectively increased, and the run flat durability is further improved. Further, since the inner end 12i of the reinforcing cord layer 12 terminates without being folded back by the bead core 5, the bending rigidity of the bead portion 4 can be increased without excessively increasing the tire weight.

  The reinforcing cords are preferably arranged at an angle of 20 to 70 ° with respect to the tire circumferential direction. If the angle is less than 20 °, the reinforcement cord approaches parallel to the tire circumferential direction, so that the bending rigidity of the bead portion 4 may not be sufficiently improved. On the other hand, if the angle exceeds 70 °, the reinforcing cord becomes substantially parallel to the carcass cord 20 (shown in FIG. 4), and thus the rigidity of the bead portion 4 may not be sufficiently improved. From such a viewpoint, the angle of the reinforcing cord with respect to the tire circumferential direction is more preferably 40 ° or more, and further preferably 55 ° or less. Furthermore, the angle difference between the reinforcing cord and the carcass cord 20 with respect to the tire circumferential direction is preferably about 20 to 50 °.

  The end of the ply 12A constituting the reinforcing cord layer 12 is preferably 30 (lines / 5 cm) or more, more preferably 40 (lines / 5 cm) or more, and preferably 70 (lines / 5 cm) or less, more preferably Is preferably 60 (pieces / 5 cm) or less. If the end of the ply 12A is less than 30 (lines / 5cm), the reinforcement effect of the bead portion 4 may not be sufficiently obtained. Conversely, if the end of the ply 12A exceeds 70 (lines / 5cm), a flare between adjacent cords may occur. May occur.

  In addition, the reinforcement cord preferably has a two-strand structure like the carcass cord 20 in order to exhibit the above-described function more effectively. In particular, the reinforcing cord preferably has a twist coefficient T of 0.50 to 0.70 represented by the above formula (1). In this way, when a so-called high twist aramid fiber cord is used for the bead portion 4, it can exhibit high bending fatigue resistance against repeated strain of the bead portion during run flat running, and thus the cord for a long period of time. The bead durability can be secured by suppressing breakage of the bead.

  Further, the ratio of the number of twists of the reinforcing cord (the number of the lower twists / the number of the upper twists), the total display decitex D (fineness), the complex elastic modulus E * of the topping rubber of the reinforcing cord layer 12, and the like were also described in the carcass ply 6A. The same as the numerical range is preferable. Such a reinforcing cord is particularly suitable for use in a tire for a multi-purpose automobile such as an SUV whose vehicle weight is larger than that of a general vehicle.

Moreover, in this embodiment, it is preferable that each end part of the reinforcement cord layer 12, the bead apex 8, and the chafer 14 is provided by shifting the position in the tire radial direction. Specifically, it is desirable that the height of each end portion from the bead base line BL satisfies the following relationship.
h0>h1>h2>h3> h4
However,
h0: height of the bead apex 8 h1: height of the outer end 12o of the reinforcing cord layer 12 h2: height of the rising portion 14c outside the chafer 14 h3: height of the rising portion 14a inside the chafer 14 H4: height of the inner end 12i of the reinforcing cord layer 12

  Thus, by arranging the end portions of the reinforcing cord layer 12, the bead apex 8 and the chafer 14 in the tire radial direction, it is possible to prevent the formation of a large rigidity step in the bead portion 4 and to increase the rigidity. Uniformity can be more reliably suppressed from lowering durability due to strain concentration.

  Further, the height h1 of the outer end 12o of the reinforcing cord layer 12 is preferably 0.15 times or more, more preferably 0.17 times or more, more preferably 0.21 times or less, more preferably 0.17 times or more of the tire cross-section height SH. Preferably it is 0.20 times or less. When the height h1 is less than 0.15 times the tire cross-section height SH, the bending rigidity of the bead portion 4 cannot be sufficiently increased. On the other hand, if the height h1 exceeds 0.21 times the tire cross-section height SH, the outer end 12o of the reinforcing cord layer 12 approaches the outer end of the bead apex 8, and there is a possibility that a large rigidity step occurs in the bead portion 4. is there.

  Further, the height h4 of the inner end 12i of the reinforcing cord layer 12 is preferably 0.01 times or more, more preferably 0.02 times or more, more preferably 0.08 times or less, more preferably 0.02 times or more of the tire cross-section height SH. Preferably it is 0.07 times or less. If the height h4 is less than 0.01 times the tire cross-section height SH, it cannot be set because the bead core 5 is disposed on the inner side in the tire radial direction than the inner surface 5i in the tire radial direction and the carcass ply 6A. On the other hand, when the height h4 exceeds 0.08 times the tire cross-section height SH, the inner end 12i of the reinforcing cord layer 12 approaches the outer end of the rising portion 14a in the chafer 14, and a large rigidity step is caused. May occur.

  The inner end 12i of the reinforcing cord layer 12 of the present embodiment is terminated on the inner side in the tire radial direction from the outer surface 5o of the bead core 5 in the tire radial direction. Thereby, since the reinforcement cord layer 12 can support the bead part 4 across the bead core 5 and the bead apex 8, the bending rigidity of the bead part 4 can be further improved, and durability during normal running and run flat running can be achieved. It is preferable at the point which can improve property. Further, the bead portion 4 is preferable in that the reinforcement cord layer 12 is disposed, so that the thickness of the bead portion 4 is increased, so that rim displacement during run-flat running can be suppressed. In this case, the height h4 of the inner end 12i of the reinforcing cord layer 12 is preferably set to 0.02 to 0.04 times the tire cross-section height SH.

  Further, as shown in FIG. 3, the inner end 12 i of the reinforcing cord layer 12 can be terminated on the outer side in the tire radial direction from the outer surface 5 o in the tire radial direction of the bead core 5. This is preferable in that the tire weight can be further reduced, the longitudinal spring constant can be reduced, and the riding comfort can be further improved. In this case, the height h4 of the inner end 12i of the reinforcing cord layer 12 is preferably set to 0.07 to 0.08 times the tire cross-section height SH.

  In order to reliably prevent the above-described rigidity step, the difference (h0-h1) between the height h0 of the bead apex 8 and the height h1 of the outer end 12o of the reinforcing cord layer 12 is 0. 06 times or more, more preferably 0.07 times or more is desirable, and preferably 0.11 times or less, more preferably 0.09 or less.

  Further, in order to sufficiently increase the bending rigidity of the bead portion 4 described above, the difference (h1−h4) between the height h1 of the outer end 12o and the height h4 of the inner end of the reinforcing cord layer 12, that is, the reinforcing cord layer 12 The length in the tire radial direction is preferably 0.14 or more, more preferably 0.16 or more of the tire cross-section height SH, and is preferably 0.20 or less, more preferably 0.19 or less.

  The bead portion 4 including the reinforcing cord layer 12 as described above has a large thickness and a large bending rigidity. Therefore, even if the side reinforcing rubber layer 9 is enlarged, the rigidity difference from the sidewall portion 3 is reduced. Can be small. Thereby, it is possible to effectively prevent strain from concentrating on the bead portion 4. In particular, when the thickness of each part of the side wall part 3, the bead part 4 and the buttress part 13 is limited to a certain range, the strain is dispersed in the tire side region during the run-flat running, thereby further improving the durability. Can be expected.

Specifically, the buttress portion thickness W1 at the tire outer surface position P1 at a height H1 of 72% of the tire cross-section height SH from the bead base line BL is spaced outward in the tire radial direction, and the side at the tire maximum cross-section width point P2. The bead thickness W3 at the tire outer surface position P3, which is a wall portion thickness W2 and a height H3 of 17% of the tire cross-section height SH from the bead base line BL and spaced outward in the tire radial direction, is expressed by the following equation (2). and to satisfy (3).
0.90 ≦ W3 / W1 ≦ 1.10 (2)
0.90 ≦ W3 / W2 ≦ 1.30 (3)

  Here, when the ratio W3 / W1 between the bead portion thickness W3 and the buttress portion thickness W1 is smaller than 0.90, strain concentrates on the bead portion 4 having a small thickness, and damage in the bead portion 4 occurs. There is a risk of speeding up. On the other hand, if the ratio (W3 / W1) exceeds 1.10, strain tends to concentrate on the buttress portion 13 and the damage to the buttress portion 13 may be accelerated. In particular, the ratio (W3 / W1) is desirably 0.95 or more, and more desirably 1.05 or less.

  Similarly, when the ratio (W3 / W2) between the bead portion thickness W3 and the sidewall portion thickness W2 is smaller than 0.90, strain concentrates on the bead portion 4 having a small thickness, and the bead portion 4 There is a risk of premature damage. On the other hand, if the ratio (W3 / W2) exceeds 1.30, the strain concentrates on the sidewall portion 3 and there is a risk that damage to the sidewall portion 3 is accelerated. In particular, the ratio (W3 / W2) is desirably 0.95 or more, and more desirably 1.25 or less.

  Further, in the tire meridional section of the run-flat tire 1 in a normal state, the profile of the tire outer surface 2A including the tread portion 2 is preferably formed by a curved surface composed of a plurality of arcs having different curvature radii.

  As shown in FIG. 5, the profile of the present embodiment is formed by a curved surface composed of a plurality of arcs whose curvature radius RC gradually decreases from the tire equator point CP toward the ground contact end side. Since such a profile can reduce the length of the sidewall portion 3, the rubber volume of the side reinforcing rubber layer 9 can be reduced, and the weight of the tire can be reduced and the ride comfort can be improved.

  In a more preferred embodiment, when a point on the tire outer surface 2A that separates the distance SP of 45% of the maximum tire cross-sectional width SW from the tire equator plane is P, the radius of curvature RC of the tire outer surface 2A is a point from the tire equator point CP. It is desirable to set so as to gradually decrease until reaching P. “Tire maximum cross-sectional width SW” is a distance in the tire axial direction between the tire maximum cross-sectional width points P2. Further, the tire maximum cross-sectional width point P2 is determined based on the reference contour line j of the tire outer surface 2A. This reference contour line j is a fine rib or groove for decoration, information, etc., which is locally formed on the tire outer surface 2A, for example, indicating characters, figures, symbols, etc., a rim protection rib for preventing rim removal, and a cut flaw It means a smooth contour line excluding local irregularities such as side protection ribs for prevention.

The points on the tire outer surface 2A that separate the distances X60, X75, X90, and X100 of 60%, 75%, 90%, and 100% of the half width (SW / 2) of the tire maximum cross-sectional width SW from the tire equator plane are P60. , P75, P90 and P100. Further, the distances in the radial direction between the points P60, P75, P90 and P100 on each tire outer surface 2A and the tire equator point CP are Y60, Y75, Y90 and Y100. The radial distances Y60, Y75, Y90, and Y100 and the tire cross-section height SH satisfy the following relationships, respectively.
0.05 <Y60 / SH ≦ 0.10
0.10 <Y75 / SH ≦ 0.20
0.20 <Y90 / SH ≦ 0.40
0.40 <Y100 / SH ≦ 0.70

Here, RY60 = Y60 / SH
RY75 = Y75 / SH
RY90 = Y90 / SH
RY100 = Y100 / SH
FIG. 6 illustrates a range RYi that satisfies the above relationship. As shown in FIG. 5 and FIG. 6, the profile of the present embodiment has a tread with a very round shape. Therefore, the footprint has a vertically long elliptical shape with a small ground contact width and a large ground contact length, and noise performance. Hydroplaning performance can be improved. If the values of RY60, RY75, RY90, and RY100 are below the respective lower limit values, the tire outer surface 2A is flattened around the tread portion 2, so that the difference in profile with the conventional tire is reduced. On the contrary, if the upper limit value is exceeded, the tire outer surface 2A has a remarkably convex shape centering on the tread portion 2, so that the contact width becomes too small to maintain the required running performance in normal running.

  Further, since the profile of the present embodiment has a feature that the region of the sidewall portion is short, by adopting it in a run flat tire, the rubber volume of the side reinforcing rubber layer 9 is reduced, and the mass in the run flat tire is reduced. And improved ride comfort. However, the amount of deformation at the tread portion 2 having a large rubber volume is larger than that of a tire having a normal profile. Therefore, an aramid fiber carcass cord with improved heat resistance can be more advantageous for the tire of the profile of the present embodiment.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

Run-flat tires for SUVs of size 245 / 60R20 having the structure shown in FIG. 1 were manufactured according to the specifications shown in Table 1, and various performances and the like were evaluated. The common specifications are as follows.
Rubber hardness of side reinforcing rubber layer: 65 degrees Number of carcass plies: 1
Carcass cord angle: 90 degrees (against tire equator)
Complex elastic modulus E * of carcass ply topping rubber: 6.5 (MPa)
Complex elastic modulus E * of the topping rubber of the reinforcing cord: 6.5 (MPa)
Tire cross-section height SH: 144.25 (mm)
Bead apex height h0: 40.0 (mm)

Moreover, the following two types of reinforcement cord plies in the bead portion were adopted.
<Reinforcing ply made of polyester fiber cord>
Specific gravity of cord ρ: 1.1
Code structure: 1840 (dtex)
Number of twists of cord N: 48 (times / 10cm)
Cord twist coefficient T: 0.49
Ends: 48 (book / 5cm)
<Reinforcing ply made of aramid fiber cord>
Specific gravity of cord ρ: 1.44
Code structure: 1100/2 (dtex)
Number of twists of cord N: 68 (times / 10cm)
Cord twist coefficient T: 0.66
Ends: 53 (5 / 5cm)

The following two types of carcass cords were adopted.
<Carcass cord made of rayon fiber>
Specific gravity of cord ρ: 1.51
Code structure: 1840/2 (dtex)
Number of twists of cord N: 48 (times / 10cm)
Cord twist coefficient T: 0.59
Ends: 35 (book / 5cm)
<Carcass cord made of aramid fiber>
Specific gravity of cord ρ: 1.44
Code structure: 1100/2 (dtex)
Number of twists of cord N: 68 (times / 10cm)
Cord twist coefficient T: 0.66
Ends: 53 (5 / 5cm)

The following two types of tread profiles were used.
<F1>
RY60 = 0.09
RY75 = 0.14
RY90 = 0.37
RY100 = 0.57
<F2>
RY60 = 0.06
RY75 = 0.08
RY90 = 0.19
RY100 = 0.57
The test method is as follows.

<Runflat durability>
Each test tire was assembled on a rim of 20 × 8 J, filled with an internal pressure of 200 kPa, and allowed to stand at a temperature of 38 ° C. for 34 hours, and then the valve core of the rim was removed to allow the tire lumen and the atmosphere to freely communicate with each other. In this state, the vehicle was run on a drum tester having a drum having a radius of 1.7 m under the conditions of a speed of 80 km / h and a longitudinal load of 6.21 kN, and the running time until the tire broke was measured. The results are displayed as an index with the conventional example being 100. The larger the value, the better the durability.

<Tire mass>
The mass per tire was measured and displayed as an index with the conventional example being 100. The smaller the value, the lighter the weight.

<Vertical spring constant>
The test tire mounted on the rim was grounded on a flat surface under conditions of an internal pressure of 200 kPa and a load of 4.92 kN, and the amount of vertical deflection of the tire was measured. Then, the longitudinal spring constant was approximately obtained by dividing the load of 4.92 kN by the amount of vertical deflection. The results were expressed as an index with the conventional example being 100. The smaller the numerical value, the smaller the vertical spring, and the better the riding comfort.

<Ride comfort>
The four wheels of a four-wheel drive vehicle with a displacement of 4000 cc were mounted under the conditions of the internal pressure and the rim, and traveled on a stepped road, a Belgian road, and a Bitzmann road on the dry asphalt road surface. Then, the sensation, push-up and dumping were comprehensively evaluated based on the driver's sensation, and displayed with a score of 100 in the conventional example. The larger the value, the better.

<Steering stability>
Using the vehicle, the vehicle was run on a dry asphalt tire test course, and sensory evaluation was performed on the steering response, grip feeling, limit speed at the time of turning, etc., and the conventional example was displayed with a score of 100. The larger the value, the better.
Table 1 shows the test results.

  As a result of the test, it was confirmed that the tire of the example was excellent in run flat durability. In addition, as is clear from the comparison between the comparative example and the example 2, the tire of the present invention maintains the run-flat durability while maintaining the ride comfort even when the thickness W4 of the side reinforcing rubber layer is reduced. It was confirmed that it could be improved.

It is sectional drawing which shows one form of a run flat tire. It is an enlarged view of the bead part and side wall part of FIG. It is an enlarged view of the bead part of FIG. It is a top view explaining a carcass cord. It is a diagram which shows the profile of a tire outer surface. It is a diagram which shows the range of RYi in each position of a tire outer surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Run flat tire 3 Carcass 4 Bead part 5 Bead core 6 Carcass 8 Bead apex 9 Side reinforcement rubber layer 12 Reinforcement cord layer 12A Ply of reinforcement cord layer

Claims (9)

A carcass made of a carcass ply provided with a series of folded portions that are folded from the inner side to the outer side in the tire axial direction around the bead core on the main body portion extending from the tread portion to the bead core through the sidewall portion;
A side-reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion;
A run-flat tire comprising a bead apex that extends in a tapered shape from the outer surface of the bead core to the outside in the tire radial direction,
The carcass is composed of a carcass ply in which a carcass cord made of aramid fibers arranged at an angle of 45 to 90 ° with respect to the tire equator is covered with a topping rubber, and the carcass cord is represented by the following formula (1). The twist coefficient T is 0.50 to 0.70,
The bead portion is provided with a reinforcing cord layer extending between the main body portion of the carcass ply and the bead apex and terminating in an inner end in the tire radial direction without being folded back by the bead core,
The reinforcing cord layer is Ri Do at least one ply with reinforcing cords made of aramid fiber,
The height h1 of the outer end of the reinforcing cord layer in the tire radial direction is smaller than the height h0 of the bead apex,
Buttress thickness W1 at the tire outer surface position P1 that is 72% of the tire cross-section height SH from the bead base line BL and spaced outward in the tire radial direction, and sidewall thickness W2 at the tire maximum cross-section width point P2. And bead part thickness W3 in tire outer surface position P3 which separated 17% of tire cross-section height SH from bead base line BL to the tire radial direction outer side satisfy | fills following formula (2) and (3). A run-flat tire characterized by that.
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)
(However, N is the number of upper twists (times / 10 cm), D is the total display decitex (fineness), and ρ is the specific gravity of the cord material.)
0.90 ≦ W3 / W1 ≦ 1.10 (2)
0.90 ≦ W3 / W2 ≦ 1.30 (3)
  2. The run-flat tire according to claim 1, wherein the carcass cord has a two-stranded structure in which two filament bundles that have been twisted are twisted together by an upper twist.   The run-flat tire according to claim 1 or 2, wherein a twist coefficient T of the carcass cord is 0.60 to 0.70.   The run-flat tire according to any one of claims 1 to 3, wherein a complex elastic modulus E * of the topping rubber is 5 to 13 MPa.   The profile of the tire outer surface is formed by a curved surface composed of a plurality of arcs whose radius of curvature gradually decreases from the tire equator point CP, which is the intersection of the tire outer surface and the tire equator surface, toward the ground contact end side. The run flat tire according to any one of the above. In the tire meridian cross section including the tire rotation axis in the normal state in which the rim is assembled to the normal rim and the normal internal pressure is filled and no load is applied,
When the point on the tire outer surface that separates the distance SP of 45% of the tire maximum cross-sectional width SW from the tire equatorial plane is P, the profile of the tire outer surface is
The radius of curvature RC of the outer surface of the tire gradually decreases from the tire equator point CP to the point P, and
Points on the outer surface of the tire separating distances X60, X75, X90 and X100 of 60%, 75%, 90% and 100% of the half width (SW / 2) of the tire maximum cross-sectional width SW from the tire equator plane, When the respective radial distances from the tire equator point CP are Y60, Y75, Y90 and Y100, respectively, and the tire cross-section height is SH,
0.05 <Y60 / SH ≦ 0.10
0.10 <Y75 / SH ≦ 0.20
0.20 <Y90 / SH ≦ 0.40
0.40 <Y100 / SH ≦ 0.70
The run flat tire according to claim 5, satisfying the relationship:   The run-flat tire according to any one of claims 1 to 6, wherein the reinforcing cord has a twisting coefficient T expressed by the previous formula (1) of 0.50 to 0.70. The difference (h0-h1) between the height h0 of the bead apex and the height h1 of the outer end of the reinforcing cord layer is 0.07 to 0.14 times the tire cross-section height SH. The run flat tire according to any one of 1 to 7.
  The run flat tire according to any one of claims 1 to 8, wherein a thickness W4 of the side reinforcing rubber layer at a tire maximum cross-sectional width point P2 is 9.0 to 11.0 mm.

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