JP2009023552A - Run-flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a run-flat tire capable of reducing thickness of a side reinforcing rubber layer while ensuring durability in run-flat running to improve riding comfortableness and stability in steering in usual running. <P>SOLUTION: This run-flat tire 1 provided with the side reinforcing rubber layer 11 in a side wall part 3 is constituted by using aramid fiber cord 21 having a two fiber bundle twined structure formed by intertwining two bundles 22 of preliminarily twined aramid fiber filaments mutually by final twining as a carcass cord 20, and twist coefficient T of the cord shown by the expression; T= N×√ä(0.125×D/2)/ρ}×10<SP>-3</SP>is in a scope of 0.5-0.7 (wherein, N expresses the number of final twinings (times/10 cm), D expresses total display decitex (fineness), and ρ expresses specific gravity of a cord material). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a run-flat tire capable of reducing the thickness of a side reinforcing rubber layer and improving ride comfort and steering stability (particularly steering response) in normal running while maintaining run-flat durability. .

  For example, as a run-flat tire that can travel relatively long distances even in a deflated state in which the air in the tire has escaped due to puncture or the like, a so-called side-reinforcement type in which a side reinforcing rubber layer having a crescent-shaped cross section is provided on the sidewall portion. (For example, see Patent Document 1). In this type of tire, the tire temperature during run-flat driving is significantly higher than during normal driving in an inflated state, so from the viewpoint of ensuring run-flat durability, rayon fibers with excellent heat resistance as a carcass cord Code is being used.

JP 2000-351307 A

  However, the tire having the above structure can ensure the required run-flat durability, but the side reinforcing rubber layer becomes thick, which increases the tire weight, and also makes the ride comfortable and handling stability (especially steering) in normal driving. There is a problem of impairing responsiveness. If the side reinforcing rubber layer is simply thinned, the required run-flat durability cannot be obtained.

  Therefore, the present invention is based on the use of aramid fibers, which are superior in heat resistance and high elasticity compared to rayon fibers, and are used in carcass cords by twisting them with a higher twisting coefficient than in the past. An object of the present invention is to provide a run-flat tire that can reduce the thickness of the side reinforcing rubber layer while ensuring it, and can improve riding comfort and steering stability in normal driving.

In order to achieve the above object, the invention of claim 1 of the present application includes a carcass extending from a tread portion through a sidewall portion to a bead core of the bead portion, and a tread disposed inside the tread portion and radially outside the carcass. A run-flat tire comprising a reinforcing cord layer and a side reinforcing rubber layer having a crescent-shaped cross section extending in a radial direction from the center portion disposed on the sidewall portion and having a maximum thickness,
In the tire meridional section including the tire shaft center in the normal internal pressure state that is mounted on the normal rim and filled with the normal internal pressure, the profile of the tire outer surface is formed by a curved surface composed of a plurality of arcs with different curvature radii,
Moreover, the carcass is composed of a carcass ply in which a carcass cord arranged at an angle of 45 to 90 ° with respect to the tire circumferential direction is covered with a topping rubber,
The carcass cord is composed of a two-strand aramid fiber cord in which two twisted aramid fiber filament bundles are twisted together by an upper twist, and the aramid fiber cord is a twist represented by the following formula (1): The coefficient T is in the range of 0.5 to 0.7.
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.)

  In the invention according to claim 2, the profile of the tire outer surface is a curved surface formed 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 C, toward the ground contact end side. It is characterized by being formed by.

In the invention according to claim 3, when the profile of the tire outer surface is P, a point on the tire outer surface that is separated from the tire equatorial plane C by a distance SP of 45% of the maximum tire cross-sectional width SW 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 equatorial plane C, respectively , When the radial distance from the tire equator point CP is Y60, Y75, Y90 and Y100, respectively, and the tire cross-section height is SH,
0.05 <Y60 / SH ≦ 0.1
0.1 <Y75 / SH ≦ 0.2
0.2 <Y90 / SH ≦ 0.4
0.4 <Y100 / SH ≦ 0.7
It is characterized by satisfying the relationship.

  According to a fourth aspect of the present invention, the carcass cord is characterized in that the twist coefficient T is 0.6 or more.

  In the invention of claim 5, the topping rubber of the carcass ply has a complex elastic modulus E * of 5 MPa or more.

  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, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO means "Measuring Rim". The “regular internal pressure” is the air pressure determined by the standard for each tire. The maximum air pressure for JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” for TRA, In the case of ETRTO, it means “INFLATION PRESSURE”, but in the case of passenger tires, it is 180 kPa.

  The “complex elastic modulus (E *)” is a value measured using a viscoelastic spectrometer at 70 ° C., an initial tension of 1000 g, and a dynamic strain of ± 0.03% at a frequency of 10 Hz.

  As described above, the present invention employs an aramid fiber cord particularly excellent in heat resistance as a carcass cord. At this time, since the twist coefficient of the aramid fiber cord is set to be larger than that of the conventional one, the cord due to the temperature rise during run-flat running while overcoming the disadvantage inherent in the aramid fiber cord that is inferior in fatigue resistance Damage can be suppressed. Further, since the aramid fiber cord is highly elastic and can improve the load supporting capacity, the thickness of the side reinforcing rubber layer can be reduced by the amount of the improvement. Accordingly, it is possible to reduce the tire weight while ensuring run-flat durability, and to achieve an improvement in riding comfort and steering stability during normal driving.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a tire meridian cross-sectional view in a normal internal pressure state showing a run-flat tire 1 of the present invention.

  In FIG. 1, the run-flat tire 1 of the present embodiment includes a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, an inner side of the tread portion 2, and a radial direction of the carcass 6. A tread reinforcing cord layer 7 disposed on the outer side, and a side reinforcing rubber layer 11 having a crescent-shaped cross section disposed on the sidewall portion 3 and ensuring a run-flat function.

  The carcass 6 includes one or more carcass plies in which a carcass cord 20 (shown in FIGS. 4A and 4B) arranged at an angle of 45 to 90 ° with respect to the tire circumferential direction is covered with a topping rubber 25. 6A. In this example, a case is shown in which a carcass ply 6A is formed by arranging carcass cords at an angle of 80 to 90 °. The carcass ply 6A includes a series of ply folding portions 6b that are folded around the bead core 5 from the inner side to the outer side in the tire axial direction on both sides of the ply main body portion 6a straddling the bead cores 5 and 5.

  Between the ply body 6a and the ply turn-up portion 6b, for example, a bead reinforcement made of hard rubber having a rubber hardness of 65 to 98 degrees and extending from the bead core 5 radially outwardly in a tapered manner is used. Rubber 8 is arranged. In the present specification, “rubber hardness” means the hardness by durometer type A measured at a temperature of 23 ° C. The height ha of the bead apex rubber 8 from the bead base line BL in the tire radial direction is not particularly limited, but if it is too small, the run-flat durability is insufficient, and conversely if it is too large, the tire mass is excessively increased. There is a risk of worsening ride comfort. From such a viewpoint, the height ha of the bead apex rubber 8 is desirably 10 to 60%, more preferably 20 to 50% of the tire cross-section height SH.

  In this example, the ply turn-up portion 6 b of the carcass 6 rolls up over the bead apex rubber 8 radially outward, and the outer end portion 6 be is between the ply main body portion 6 a and the tread reinforcing cord layer 7. It has a so-called ultra-high turn-up folded structure that is sandwiched between and ends. Thereby, the side wall part 3 can be effectively reinforced using the one carcass ply 6A. Further, since the outer end portion 6be of the ply turn-up portion 6b is separated from the sidewall portion 3 that is greatly bent during run-flat travel, damage starting from the outer end portion 6be can be suitably suppressed. The tire axial direction width EW of the overlapping portion between the ply folded portion 6b and the tread reinforcing cord layer 7 is preferably 5 mm or more, more preferably 10 mm or more, and the upper limit is 40 mm or less, further 30 mm or less from the viewpoint of weight reduction. preferable. In the case where the carcass 6 is formed of a plurality of carcass plies, it is preferable that at least one carcass ply has this aspect.

  Next, the tread reinforcing cord layer 7 includes a belt 9 placed on the carcass 6 and a band 10 placed on the outer side thereof, in this example. The belt 9 is formed of two or more belt plies 9A and 9B in this example, in which a belt cord arranged at an angle of, for example, 10 to 45 ° with respect to the tire circumferential direction is covered with a topping rubber. Each belt cord crosses between plies to increase belt rigidity, and substantially reinforces substantially the entire width of the tread portion 2 with a tagging effect.

  The band 10 is composed of one or more band plies in which a band cord wound spirally at an angle of 5 ° or less with respect to the tire circumferential direction is covered with a topping rubber, and restrains the belt 9. Improve handling stability and high-speed durability. The band ply includes a pair of left and right edge band plies that covers only the outer end portion of the belt 9 in the tire axial direction, and a full band ply that covers substantially the entire width of the belt 9, and these are used alone or in combination. The In this example, the band 10 is exemplified by one full band ply. The tread reinforcing cord layer 7 can be formed of only the belt 9 or of the band 10 alone.

  Next, the side reinforcing rubber layer 11 has a crescent-shaped cross section extending gradually from the central portion 11a having the maximum thickness toward the inner end 11i and the outer end 11o in the tire radial direction. The inner end 11 i is located on the inner side in the tire radial direction from the outer end of the bead apex rubber 8, and the outer end 11 o is located on the inner side in the tire axial direction from the outer end 7 e of the tread reinforcing cord layer 7. At this time, the overlapping width Wi in the tire radial direction between the side reinforcing rubber layer 11 and the bead apex rubber 8 is 5 to 50 mm, and the overlapping width Wo in the tire axial direction between the side reinforcing rubber layer 11 and the tread reinforcing cord layer 7 is 0. It is preferable that the thickness is set to ˜50 mm, thereby suppressing the occurrence of a rigid step at the outer end 11o and the inner end 11i.

  In the present example, the side reinforcing rubber layer 11 is disposed on the inner side (tire lumen side) of the ply main body portion 6a of the carcass 6. Therefore, when the sidewall portion 3 is bent and deformed, a compressive load is mainly applied to the side reinforcing rubber layer 11, and a tensile load is mainly applied to the carcass ply 6A having the cord material. Since rubber is strong against compressive load and cord material is strong against tensile load, the arrangement structure of the side reinforcing rubber layer 11 as described above efficiently increases the bending rigidity of the side wall portion 3, and the tire during run flat running Can be effectively reduced. The rubber hardness of the side reinforcing rubber layer 11 is preferably 60 degrees or more, and more preferably 65 degrees or more. If the rubber hardness is less than 60 degrees, the compressive strain during run flat running becomes large, and the run flat performance becomes insufficient. On the other hand, even if the rubber hardness is too high, the longitudinal spring constant of the tire is excessively increased and the ride comfort is lowered. From such a viewpoint, the upper limit of the rubber hardness of the side reinforcing rubber layer 11 is preferably 90 degrees or less, and more preferably 80 degrees or less.

  In this example, the bead portion 4 is exemplified by a case where a rim protect rib 12 is provided in a projecting manner. As shown in FIG. 2, the rim protect rib 12 is a rib body protruding from the reference contour j so as to cover the rim flange JF, and protrudes most outward in the tire axial direction beyond the tip of the rim flange JF. A projecting surface portion 12c, a radially inwardly inclined surface portion 12i that is smoothly connected to the outer surface of the bead from the projecting surface portion 12c, and a radial direction that is smoothly connected to the reference contour j at a position near the tire maximum width point M from the projecting surface portion 12c. It forms a trapezoidal cross section surrounded by the outer slope portion 12o. The inner inclined surface portion 12i is formed of a concave arc surface formed with a radius of curvature r larger than the arc portion of the rim flange JF, and protects the rim flange JF from curbs or the like during normal travel. Also, during run flat running, the inner slope 12i leans against and contacts the arc portion of the rim flange JF, so that the amount of bead deformation can be reduced, which helps to improve steering stability and run flat durability during run flat.

  In the present invention, an aramid fiber cord 21 is employed for the carcass cord 20.

  The aramid fiber has a property that the decrease in elastic modulus is small compared to other organic fiber cord materials even at a high temperature of 100 to 150 ° C. and is excellent in heat resistance. Accordingly, it is possible to prevent the carcass cord from being reduced in strength and causing damage due to a rise in tire temperature during run-flat running, or an increase in tire deformation due to a drop in elastic modulus and a further increase in tire temperature associated therewith. .

  However, aramid fibers have a drawback that they have poor fatigue resistance due to their high elastic modulus. Therefore, as the aramid fiber cord 21, as shown schematically in FIG. 4 (B), a two-stranded structure in which two strands of aramid fiber filament bundles 22 (that is, strands 22) twisted together are twisted together with an upper twist. While adopting, the twisting at this time is performed at a higher twisting coefficient T than in the prior art.

Here, as is well known, the “twisting coefficient T” is, as is well known, the number of upper twists of the cord is N (unit: times / 10 cm), the total display decitex (fineness) of one cord is D (unit: dtex), When the specific gravity is ρ, it is represented by the following formula (1).
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ −−− (1)

  And the said fatigue resistance which is the fault of the aramid fiber cord 21 can be overcome by raising this twist coefficient T to the range of 0.5-0.7. When the twist coefficient T is less than 0.5, the effect of improving fatigue resistance is insufficient, and it becomes difficult to ensure the required run-flat durability. On the other hand, when the twist coefficient T exceeds 0.7, it becomes difficult to twist the cord, which is disadvantageous for productivity. From such a point of view, the lower limit of the twist coefficient T is particularly preferably 0.6 or more, which makes it possible to sufficiently improve the fatigue resistance of the cord.

  In the carcass cord 20, a two-strand structure is employed in order to exert an excellent reinforcing effect by utilizing the high elasticity that is an important characteristic of the aramid fiber. At that time, a so-called balance twist in which the number of lower twists and the number of upper twists are equal is preferable, 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 0.8. Within the range of 5 to 1.5, the number of lower twists and the number of upper twists may be made different.

  The total display decitex D (fineness) is not particularly limited, but in the case of a run flat tire, a range of 1500 to 5000 dtex is preferable. Further, the product (n × D) of the number n of cord ends (5/5 cm) in the carcass ply 6A and the total display decitex D is preferably in the range of 70,000 to 150,000. If the strength is insufficient and, on the other hand, exceeds 150,000, the carcass rigidity becomes excessive and the riding comfort is impaired, and the mass and material cost are unnecessarily increased. From such a viewpoint, the lower limit of the product (D × n) is more preferably 100,000 or more, and the upper limit is more preferably 120,000 or less.

  Further, damage to the carcass cord 20 due to fatigue resistance is likely to occur at a portion that undergoes compressive strain when the tire is deformed, that is, at the bead side portion 6b1 of the ply folded portion 6b as shown in FIG. However, in this example, since the rim protect rib 12 is projected on the bead portion 4 as described above, the bead deformation during the run-flat running is reduced, and the compressive strain hardly acts on the carcass cord 20. As a result, the fatigue damage of the carcass cord 20 when an aramid fiber is employed can be further suppressed, and the run-flat durability can be further improved. In other words, in a tire using aramid fibers for the carcass cord 20, it is preferable to use the rim protect rib 12 from the viewpoint of suppressing fatigue damage of the cord.

  In this example, as the topping rubber of the carcass ply 6A, a rubber having a complex elastic modulus E * of 5 MPa or more and higher elasticity than the conventional carcass topping rubber is used. The complex elastic modulus E * of the conventional carcass topping rubber is about 3.8 MPa. By adopting high-elasticity rubber as the topping rubber in this way, distortion applied to the carcass cord 20 when the tire is deformed can be reduced, fatigue damage of the carcass cord 20 can be further suppressed, and run-flat durability can be further improved. Can be achieved. If the complex elastic modulus E * is less than 5 MPa, the above effect cannot be expected. Conversely, if the complex elastic modulus E * is more than 13 MPa, the rubber becomes too hard, and the ride comfort deteriorates at a stretch. From such a viewpoint, the lower limit value of the complex elastic modulus E * is preferably 5.5 MPa or more, 6 MPa or more, 7 MPa or more, more preferably 8 MPa or more, and the upper limit value is preferably 12 MPa or less.

  Furthermore, the aramid fiber is known as a highly elastic fiber, and by using it in the carcass cord 20 of the run flat tire 1, the load supporting ability of the tire can be increased. Therefore, it is possible to reduce the load of the load supporting capacity in the side reinforcing rubber layer 11 by the amount of increase in the load supporting capacity, that is, to reduce the maximum thickness t of the side reinforcing rubber layer 11 as compared with the conventional case.

  Specifically, in the case of the tire 1A having a tire cross-section height Ho obtained from the tire size display of less than 120 mm, the maximum thickness t of the side reinforcing rubber layer 11 can be in the range of 3 to 7 mm. This corresponds to about 37-78% of the conventional maximum thickness (8-9 mm). In the case of the tire 1B having a tire cross-section height Ho of 120 mm or more and less than 135 mm, the maximum thickness t of the side reinforcing rubber layer 11 can be set in a range of 5 to 9 mm. This corresponds to about 50-82% of the conventional maximum thickness (10-11 mm). In the case of the tire 1C having a tire cross-section height Ho of 135 mm or more, the maximum thickness t of the side reinforcing rubber layer 11 can be set in the range of 7 to 15 mm. This corresponds to about 54 to 94% of the conventional maximum thickness (13 to 16 mm). In particular, in the case of the tire 1A, the lower limit value of the maximum thickness t is 5 mm or more, more preferably 6 mm or more. In the case of the tire 1B, the lower limit value of the maximum thickness t is 7 mm or more. 8 mm or more is more preferable, and in the case of the tire 1C, the lower limit value of the maximum thickness t is more preferably 11 mm or more, and the upper limit value is more preferably 13 mm or less.

Here, the “tire sectional height obtained from the tire size display” is a product of “nominal section width” and “nominal ratio / 100” shown in the tire size display (nominal section width). ) × (nominal ratio / 100). For example, if the tire size display is “195 / 60R14”,
(Tire section height) = (Nominal section width) × (Nominal aspect ratio / 100)
= 195mm × 0.60 = 117mm
And belongs to the tire 1A.

  As described above, the maximum thickness t of the side reinforcing rubber layer 11 can be reduced as compared with the conventional one. As a result, while ensuring run-flat durability, the ride comfort and the handling stability in the normal running can be improved with the normal tire ( It becomes possible to improve to a level close to a non-run flat tire without a side reinforcing rubber layer.

  Next, in the tire meridional section in the normal internal pressure state, the profile of the tire outer surface 2A is formed by a curved surface including a plurality of arcs having different curvature radii. In particular, in the case of a run-flat tire, a curved surface composed of a plurality of arcs whose curvature radius R gradually decreases from the tire equator point CP, which is the intersection of the tire outer surface 2A and the tire equator plane C, toward the ground contact Te side. It is preferable to form a profile. As a result, the rubber volume of the side reinforcing rubber layer 11 can be further reduced to reduce the weight of the tire and improve the riding comfort. In particular, by adopting a special profile as proposed in Japanese Patent No. 2999489, the above-described effects can be further enhanced.

  More specifically, as shown in FIG. 5, 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 equatorial plane C is P, the radius of curvature RC of the tire outer surface 2A is P. Is set so as to gradually decrease from the tire equator point CP to the point P. The “tire maximum cross-sectional width SW” is the maximum width at the reference contour j of the tire outer surface 2A, and the reference contour j is locally formed on the tire outer surface 2A, for example, characters, figures, symbols, etc. Means a smooth contour line excluding local irregularities such as fine ribs and grooves for decoration, information, etc., a rim protection rib 12 for preventing rim removal, and a side protection rib for preventing cut scratches.

  Further, points on each tire outer surface 2A that separate 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 equatorial plane C, respectively. Are P60, P75, P90 and P100. The radial distances between the points P60, P75, P90 and P100 on the tire outer surface 2A and the tire equator point CP are Y60, Y75, Y90 and Y100.

When the tire cross-sectional height, which is the radial height from the bead base line BL to the tire equator point CP in the normal internal pressure state, is SH, the radial distances Y60, Y75, Y90, and Y100 are as follows: It is characterized by satisfying the relationship.
0.05 <Y60 / SH ≦ 0.1
0.1 <Y75 / SH ≦ 0.2
0.2 <Y90 / SH ≦ 0.4
0.4 <Y100 / SH ≦ 0.7
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 FIGS. 5 and 6, the profile satisfying the above relationship is such that the tread is very round, so the footprint is a vertically long ellipse with a small ground contact width and large ground contact length, and noise performance and hydroplaning performance. It is reported in the above-mentioned Japanese Patent No. 299489 that it can be improved. When 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 from 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 ground contact width becomes too small to ensure the required traveling performance in normal traveling.

  In the tire, by predetermining the tire size, the tire flatness, the maximum tire cross-sectional width, the maximum tire height, etc. can be generally determined from the tire standards such as JATMA and ETRTO. Therefore, the RY60, RY75, RY90 and RY100 Can be easily calculated. Therefore, the tire outer surface 2A is smooth from the tire equator point CP to the point P so as to satisfy the ranges of RY60, RY75, RY90 and RY100 at the respective positions and so that the radius of curvature RC gradually decreases. It can be determined appropriately by drawing a curve.

  Further, the tire has a grounding width CW that is a distance in the tire axial direction between the outermost ends in the tire axial direction where the tire outer surface 2A is grounded in a state where a load of 80% of the normal load is applied to the tire in the normal internal pressure state. The tire maximum cross-sectional width SW is preferably in the range of 50% to 65%. This is because when the ground contact width CW is less than 50% of the tire maximum cross-sectional width SW, wandering performance is likely to be wobbling easily during normal running, and uneven wear tends to occur due to uneven ground pressure. Because it becomes. When the ground contact width CW exceeds 65% of the tire maximum cross-sectional width SW, the ground contact width becomes excessive, making it difficult to achieve both the above-described passing noise and hydroplaning performance.

  Such a special profile has a feature that the region of the sidewall portion 3 is short, so that the rubber volume of the side reinforcing rubber layer 11 can be reduced by adopting it in a run-flat tire. However, the amount of deformation at the tread portion 2 where the rubber volume is large is larger than that of a tire having a normal profile. Therefore, the aramid fiber carcass cord 20 with improved heat resistance can be more advantageous for tires of this special profile.

  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.

A run-flat tire having a tire size of 245 / 40R18 having the structure shown in FIG. 1 was prototyped according to the specifications shown in Table 1, and the mass and longitudinal spring coefficient of each sample tire were measured, and the ride comfort, handling stability, run The flat durability was tested and the results are listed in Table 1. The specifications other than those listed in Table 1 are the same.
-Carcass is the number of plies (1), cord angle (90 °),
・ The belt layer consists of the number of belt plies (2), cord angle (+ 24 ° / -24 °),
・ Side reinforcement rubber layer has rubber hardness (90 degrees),
It is said.

In Table 1, the twist coefficient T is represented by the following formula (1).
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ −−− (1)
The specific gravity ρ of the rayon fiber cord is 1.51, and the specific gravity ρ of the aramid fiber cord is 1.44.

  The tread profile for each tire is in the range of RY60 = 0.05 to 0.1, RY75 = 0.1 to 0.2, RY90 = 0.2 to 0.4, RY100 = 0.4 to 0.7. The one with substantially the same profile is used.

<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>
When the tire is filled with a rim (18 x 8.5 J) and internal pressure (230 kPa) and a vertical load (5 kPa) is applied with a camber angle of 0 °, the vertical load is measured. The vertical spring constant was obtained by dividing by. A result is displayed by the index | exponent which sets a prior art example to 100, and a vertical spring constant is so small that a numerical value is small.

<Ride comfort>
Tires are mounted on all wheels of a 4300cc domestic FR vehicle under the conditions of rim (18 x 8.5J) and internal pressure (230 kPa), as well as steps on dry asphalt roads, Belgian roads (cobblestone roads) On the Bitzmann road (road surface covered with pebbles), etc., sensory evaluation was performed with respect to ruggedness, push-up and dumping, and the conventional example was displayed as an index of 100. The larger the value, the better the ride comfort.

<Steering stability>
Using the vehicle, the vehicle was run on a dry asphalt tire test course, a sensory evaluation was performed on the steering response, and the conventional example was displayed as an index of 100. The larger the value, the better the steering response and the better the steering stability.

<Run flat durability performance>
Each test tire is assembled on a rim (18 x 8.5 J) from which the valve core has been removed, and run on the drum tester under the conditions of speed (80 km / h) and longitudinal load (4.14 kN) in a deflated state. The travel distance until the tire broke was measured and evaluated by an index with the conventional example being 100. The larger the value, the better the run flat durability performance.

  As compared with the conventional example and Comparative Examples 1 and 2, simply changing from a rayon fiber cord to an aramid fiber cord as a carcass cord, the aramid fiber cord has a defect that it is inferior in fatigue resistance. It can be confirmed that damage tends to occur and run flat durability decreases. However, as compared with Comparative Examples 1 and 2 and Example 2, by increasing the twist coefficient T of the aramid fiber cord to 0.5 or more (0.6645 in the example), the fatigue resistance defect is reduced. It can be confirmed that the improved heat resistance and load bearing ability, which are the advantages of the aramid fiber cord, are effectively exhibited and the run-flat durability can be greatly improved.

  Further, as compared between Example 1 and Example 2, it can be confirmed that the run-flat durability can be further improved by increasing the complex elastic modulus of the carcass topping rubber. Therefore, as shown in Examples 1, 3, and 4, the thickness of the side reinforcing rubber layer can be reduced by the amount of the increase in the run flat durability, and the ride comfort is ensured while ensuring the required run flat durability. Performance and steering stability can be improved. In Examples 5 and 6, since the thickness of the side reinforcing rubber layer was reduced too much, the run-flat durability is lower than the conventional example. For example, the total display decitex D (fineness) of the carcass cord, the number of cord ends By changing the setting of the complex elastic modulus E * of the topping rubber, the lower limit value of the thickness of the side reinforcing rubber layer that can ensure the required run-flat durability can be adjusted.

  Further, as shown in Comparative Examples 3 and 4, using the carcass ply of the conventional example and the carcass ply of Comparative Example 1, in order to obtain the high level of run flat durability in Examples 1 and 2, the side reinforcing rubber layer It can be confirmed that the thickness needs to be increased to, for example, 13 mm and 16 mm, and as a result, ride comfort and steering stability are significantly reduced.

It is a meridional section showing an example of a run flat tire of the present invention. It is sectional drawing which expands and shows the tread part. It is sectional drawing which expands and shows a bead part. (A) is sectional drawing which shows a carcass ply, (B) is a perspective view which shows 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

2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 6A Carcass ply 7 Tread reinforcing cord layer 11 Side reinforcing rubber layer 20 Carcass cord 21 Aramid fiber cord 22 Aramid fiber filament bundle

Claims (5)

A carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, a tread reinforcing cord layer disposed inside the tread portion and radially outside the carcass, and disposed on the sidewall portion and having a maximum thickness A run-flat tire comprising a crescent-shaped side reinforcing rubber layer extending in a radial direction from the central portion having a crescent-shaped side reinforcing rubber layer,
In the tire meridional section including the tire shaft center in the normal internal pressure state that is mounted on the normal rim and filled with the normal internal pressure, the profile of the tire outer surface is formed by a curved surface composed of a plurality of arcs with different curvature radii,
Moreover, the carcass is composed of a carcass ply in which a carcass cord arranged at an angle of 45 to 90 ° with respect to the tire circumferential direction is covered with a topping rubber,
The carcass cord is composed of a two-strand aramid fiber cord in which two twisted aramid fiber filament bundles are twisted together by an upper twist, and the aramid fiber cord is a twist represented by the following formula (1): A run-flat tire having a coefficient T in a range of 0.5 to 0.7.
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.)   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 equatorial plane C, toward the contact end side. The run flat tire according to claim 1. When the tire outer surface profile is P, a point on the tire outer surface separating a distance SP of 45% of the tire maximum cross-sectional width SW from the tire equatorial plane C 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 equatorial plane C, respectively , When the radial distance from the tire equator point CP is Y60, Y75, Y90 and Y100, respectively, and the tire cross-section height is SH,
0.05 <Y60 / SH ≦ 0.1
0.1 <Y75 / SH ≦ 0.2
0.2 <Y90 / SH ≦ 0.4
0.4 <Y100 / SH ≦ 0.7
The run flat tire according to claim 2, wherein the relationship is satisfied.   The run-flat tire according to any one of claims 1 to 3, wherein the carcass cord has the twist coefficient T of 0.6 or more.   The run-flat tire according to any one of claims 1 to 4, wherein the topping rubber of the carcass ply has a complex elastic modulus E * of 5 MPa or more.

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