JP2008062716A - Run flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve run flat durability while suppressing deterioration of ride comfort in normal traveling. <P>SOLUTION: This run flat tire 1 includes: a carcass 6 passing from a tread portion 2 through a side wall portion 3, folded back at the bead core 5 of a bead portion 4 to be locked, and having at least one carcass ply 6A; a belt layer 7 arranged on the outer side of the carcass 6; and a side reinforcing rubber layer 9 arranged in a side wall area and formed into a substantially crescent cross section. A reinforcing cord layer 10 formed of at least one reinforcing ply having plural steel cords arranged in parallel at an angle of 0 to 45 degrees with respect to a radial direction is arranged between the side reinforcing rubber layer 9 and the carcass 6. The reinforcing cord layer 10 extends in a radial direction in a side outside area Sa sandwiched between a tire maximum width position M and the outer edge 7e of the belt layer 7 without surpassing the area Sa. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a run-flat tire capable of improving run-flat durability performance while suppressing deterioration in ride comfort during normal running.

  Conventionally, various run-flat tires have been proposed that can continue to travel safely over a certain distance at a relatively high speed even when the air from the tire is removed due to puncture or the like. In these various run-flat tires, a side reinforcing rubber layer having a substantially crescent-shaped cross section is provided in the sidewall portion, and after the air escapes, the sidewall portion including the side reinforcing rubber layer is the tire. Will support the load.

  Conventionally, a method of increasing the thickness of the side reinforcing rubber layer has been adopted in order to increase the travel distance in the puncture state (hereinafter, such travel is sometimes referred to as “run-flat travel”). Yes. However, such an improvement method has a drawback of causing a significant increase in tire mass. This leads to an increase in the so-called unsprung weight of the vehicle, which is disadvantageous for steering stability and deteriorates fuel efficiency.

  In recent years, a run flat tire in which a reinforcing cord layer is provided between a side reinforcing rubber layer and a carcass has been proposed (see, for example, Patent Document 1 below). However, since this run flat tire uses an organic fiber cord as a reinforcing cord layer, there is room for further improvement in the reinforcing effect of the sidewall portion.

JP 2005-262922 A

  The inventors have conducted various experiments, and by using a steel cord for the reinforcing cord layer and regulating the cord angle within a certain range, the reinforcing effect of the side portion during run-flat running can be maximized. On the other hand, it has been found that, when the region where the steel cord is disposed is limited to the side outer region, it is possible to suppress deterioration in riding comfort during normal driving.

  As described above, the main object of the present invention is to provide a run-flat tire capable of further improving the durability during run-flat running while suppressing deterioration in riding comfort during normal running. .

  The invention according to claim 1 of the present invention includes a carcass having at least one carcass ply that is folded and locked by a bead core of a bead portion through a sidewall portion from a tread portion, and a radially outer side of the carcass and A run-flat tire comprising: a belt layer disposed inside a tread portion; and a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass and in a sidewall region, wherein the side reinforcing rubber layer A reinforcing cord layer made of at least one reinforcing ply having steel cords arranged in parallel at an angle of 0 to 45 degrees with respect to the radial direction is disposed between the carcass and the carcass, and the reinforcing cord layer is a tire. A side outer region sandwiched between the maximum width position and the outer end of the belt layer extends in a radial direction without protruding from the region. To.

  The invention according to claim 2 is the run flat tire according to claim 1, wherein the steel cord has a wire diameter of 0.54 to 0.78 mm.

  The invention according to claim 3 is the run flat tire according to claim 1 or 2, wherein the side reinforcing rubber layer has a maximum thickness of 8 to 10 mm.

According to a fourth aspect of the present invention, in the tire meridian cross section including a tire rotation axis in a normal unloaded state in which a normal rim is assembled and a normal internal pressure is filled, the tire outer surface profile includes the tire outer surface. When the point on the outer surface of the tire separating the distance (SP) of 45% of the maximum tire width (SW) from the intersection (CP) between the tire and the tire equator (C) is (P), the point from the intersection (CP) The run-flat tire according to any one of claims 1 to 3, wherein the radius of curvature (RC) of the tire outer surface gradually decreases in a section up to (P) and satisfies the following relationship.
0.05 <Y60 / H ≦ 0.1
0.1 <Y75 / H ≦ 0.2
0.2 <Y90 / H ≦ 0.4
0.4 <Y100 / H ≦ 0.7
(Where Y60, Y75, Y90 and Y100 are the tire axial distances of 60%, 75%, 90% and 100% of the half width (SW / 2) of the maximum tire width in the tire axial direction from the intersection (CP). (The distances in the tire radial direction between the points P60, P75, P90 and P100 on the outer surface of the tire and the intersections (CP), and H is the tire cross-section height.)

  The run flat tire of the present invention comprises at least one reinforcing ply having steel cords arranged at an angle of 0 to 45 degrees with respect to the radial direction between the side reinforcing rubber layer and the carcass and in the side outer region. A reinforcing cord layer is provided. During run-flat running, the side outer region undergoes the largest bending deformation, so that the bending deformation is effectively suppressed by providing a reinforcing cord layer made of steel cord in the side outer region, and consequently the run-flat running distance is reduced. Can be increased. Further, since the reinforcing cord layer is provided without protruding from the side outer region, it is possible to minimize deterioration in riding comfort during normal traveling.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of the run-flat tire 1 of the present embodiment in a normal state, FIG. 2 is a cross-sectional view of the internal pressure being zero and a normal load is applied, and FIG. 3 is a partially enlarged view of FIG. Has been. Unless otherwise specified, the dimensions of each part of the tire are the values in the normal state.

  Here, the “normal state” uniquely defines the posture of the tire and is a no-load state in which the rim is assembled to the normal rim J and the normal internal pressure is filled. 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, and ETRTO If there is, “Measuring Rim”.

  Furthermore, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA and the table “TIRE LOAD LIMITS AT” is TRA. The maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” if it is ETRTO, but if the tire is for passenger cars, it is uniformly 180 kPa. Furthermore, “regular load” is the load that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is specified for JATMA, and the table “TIRE LOAD LIMITS” for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”. If ETRTO, “LOAD CAPACITY”.

  A run-flat tire 1 includes a carcass 6 having at least one carcass ply 6A that is folded and locked by a bead core 5 of a bead portion 4 from a tread portion 2 through a sidewall portion 3, and a tire radial direction of the carcass 6 A belt layer 7 disposed outside and inside the tread portion 2, a bead apex 8 extending outwardly from an outer surface in the tire radial direction of the bead core 5, and a sidewall region inside the carcass 6. Further, a radial tire for a passenger car including a side reinforcing rubber layer 9 having a substantially crescent-shaped cross section is exemplified. An inner liner rubber 15 made of rubber that does not easily transmit air is disposed on the inner side in the tire axial direction of the side reinforcing rubber layer 9.

  In the present embodiment, the carcass 6 is formed from one carcass ply 6A. The carcass ply 6A is formed by covering a carcass cord with a topping rubber. As the carcass cord, an organic fiber such as nylon, polyester, rayon, or aromatic polyamide is suitably used. In this embodiment, a polyester cord is employed. In the present embodiment, the carcass cord is arranged to be inclined with respect to the tire equator C at an angle of 75 to 90 degrees, more preferably 90 degrees.

  The carcass ply 6A includes a main body portion 6a straddling a pair of bead cores 5 and 5 (only one is shown in the figure), and is connected to both ends of the main body portion 6a and around the bead core 5 in the tire axial direction inner side. And a folded portion 6b that is folded outward from the bead apex 8 and extends along the outer surface in the tire axial direction of the bead apex 8. In this example, the outer end 6be of the folded portion 6b is terminated at a position beyond the outer end 7e in the tire axial direction of the belt layer 7 inward in the tire axial direction.

  Such a carcass ply 6A can effectively reinforce the sidewall portion 3 with a small number of sheets. Further, the outer end 6be of the folded portion 6b having low durability is located away from the side wall portion 3 having a large deflection during run-flat travel, and is positioned between the belt layer 7 having a small distortion and the main body portion 6a of the carcass ply. As a result, damage such as separation starting from the outer end 6be is suppressed, and run-flat durability is improved. From such a viewpoint, it is desirable that the tire axial length EW where the folded portion 6b and the belt layer 7 overlap is, for example, 5 mm or more, preferably 10 mm or more, more preferably 15 to 25 mm. Needless to say, the carcass 6 may be composed of a plurality of carcass plies 6A.

  The bead apex 8 extends in a tapered manner from the outer surface of the bead core 5 to the outer side in the tire radial direction, and is preferably formed of a hard rubber having a JISA hardness of 65 to 95 degrees, more preferably about 70 to 95 degrees. . Thereby, the bending rigidity of the bead part 4 is improved and the vertical bending of the tire 1 is suppressed. In addition, in this specification, JISA hardness means the hardness by durometer type A based on JIS-K6253.

  The height ha of the bead apex 8 from the bead base line BL is not particularly limited. However, if the bead apex 8 is too small, the durability during run-flat running tends to decrease. There is a risk of an increase or a significant deterioration in ride comfort. From such a viewpoint, the height ha of the bead apex 8 is desirably 10 to 45%, more preferably about 25 to 40% of the tire cross-section height H.

  The belt layer 7 is composed of two belt plies 7A and 7B in which a belt cord made of, for example, steel is inclined with respect to the tire equator C at, for example, about 10 to 35 °. The belt plies 7 </ b> A and 7 </ b> B are overlapped so that the belt cords cross each other, and the carcass 6 can be tightly tightened to increase the rigidity of the tread portion 2. As the belt cord, a highly elastic organic fiber material such as aramid or rayon can be used as necessary in addition to the steel material. In the present embodiment, a band layer 12 made of a band ply in which organic fiber cords are arranged along the tire circumferential direction is provided outside the belt layer 7 in the tire radial direction. Thereby, lifting of the belt layer 7 and the like are effectively suppressed.

  In the run flat tire 1 of the present embodiment, the bead portion 4 is provided with a rim protector 11 protruding so as to cover the outer side in the tire radial direction of the rim flange JF of the rim J and continuously extending in the tire circumferential direction. As shown in FIG. 2, the rim protector 11 comes into close contact with the outer peripheral surface of the rim flange JF in a wide range so as to cover it due to the deformation of the bead portion 4 during the run-flat running. Thereby, the amount of vertical deflection of a tire at the time of run flat running can be controlled effectively, and durability can be improved.

  The side reinforcing rubber layer 9 is disposed inside the carcass 6. The side reinforcing rubber layer 9 is formed in a substantially crescent shape in cross section as a whole in which the thickness is gradually reduced from the thick central portion 9a toward the inner end 9i and the outer end 9o in the tire radial direction. The inner end 9 i is preferably located on the inner side in the tire radial direction than the outer end 8 T of the bead apex 8 and on the outer side in the tire radial direction than the bead core 5. Further, the outer end 9o of the side reinforcing rubber layer 9 extends to the inner cavity side of the tread portion 2, and a preferable mode is illustrated in which it terminates at a position on the inner side in the tire axial direction from the outer end 7e of the belt layer 7. Such a side reinforcing rubber layer 9 can reinforce the rigidity of the tire in the entire region of the sidewall portion 3, and helps to suppress the amount of vertical deflection during run flat running more effectively.

  In the side reinforcing rubber layer 9, the arrangement length L (shown in FIG. 1) between the inner end 9i and the outer end 9o in the tire radial direction is not particularly limited, but if the arrangement length L is too small, During flat running, it is difficult to obtain a smooth curved state of the sidewall portion 3 as shown in FIG. On the other hand, if the arrangement length L is too large, the riding comfort is remarkably deteriorated and the rim assembling performance tends to be deteriorated during the normal running in which the internal pressure is appropriately satisfied. From such a viewpoint, the arrangement length L of the side reinforcing rubber layer 9 is preferably 35 to 70%, more preferably about 40 to 65% of the tire cross-section height H.

  In order to suppress the longitudinal deflection of the tire during the run-flat running, the JISA hardness of the side reinforcing rubber layer 9 is preferably 65 degrees or more, more preferably 70 degrees or more, and further preferably 74 degrees or more. On the other hand, if the JISA hardness of the side reinforcing rubber layer 9 is too large, the vertical spring of the tire becomes large and the ride comfort during normal running tends to be remarkably deteriorated. Therefore, it is preferably 99 degrees or less, more preferably 90 degrees. The following is desirable.

  As the rubber polymer used for the side reinforcing rubber layer 9, for example, diene rubber, more specifically, natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, chloroprene rubber or acrylonitrile butadiene rubber is preferable. A seed or a blend of two or more may be used. Particularly preferably, a low heat-generating rubber is suitable for suppressing heat generation during run-flat running. Specifically, a rubber composition having a loss tangent tan δ of 0.03 to 0.08, more preferably 0.03 to 0.06 is suitable. The loss tangent is a value measured using a viscoelastic spectrometer at a measurement temperature of 70 ° C., a frequency of 10 Hz, an initial elongation strain of 10%, and a half amplitude of 1%.

  Further, the maximum thickness t (shown in FIG. 3) of the side reinforcing rubber layer 9 is not particularly limited, but if it is too small, the side wall portion will bend greatly during run flat running, and the run flat durability performance will be reduced. There is a fear. On the other hand, if the maximum thickness t is too large, there is a risk of increasing tire mass or deteriorating riding comfort during normal driving. From such a viewpoint, the maximum thickness t of the side reinforcing rubber layer 9 is preferably 8 to 10 mm. The maximum thickness t is the largest thickness among the thicknesses measured in the direction perpendicular to the center line V of the thickness of the side reinforcing rubber layer 9.

  A reinforcing cord layer 10 is provided between the side reinforcing rubber layer 9 and the carcass 6. FIG. 4 shows a perspective view of the reinforcing cord layer 10 as seen from the outside in the tire axial direction. The reinforcing cord layer 10 is a plurality of steels arranged in parallel at an angle θ of 0 to 45 ° with respect to the radial direction RL. The reinforcing ply 10A is composed of at least one sheet having the cord 13, in this embodiment.

  As shown in FIG. 2, the side wall portion 3 is greatly bent during run flat running. Thereby, compressive stress acts on the inner side surface 9A of the side reinforcing rubber layer 9 in the tire axial direction, and tensile stress acts on the outer side surface 9B. On the other hand, the steel cord of the reinforcing cord layer 10 attached to the outer side surface 9B of the side reinforcing rubber layer 9 has a very large tensile elastic modulus as compared with rubber and organic fiber cords. The outer surface 9B can be integrated with the outer surface 9B to effectively improve the tensile strength of the outer surface 9B or the vicinity thereof, and the elongation can be suppressed. Thereby, the compressive strain acting on the inner side surface 9A of the side reinforcing rubber layer 9 is reduced, and the run-flat performance can be improved by suppressing the vertical deflection and heat generation of the tire. Note that when the cord of the reinforcing ply 10A is an organic fiber cord, the above-described effects cannot be sufficiently expected because the tensile elastic modulus is smaller than that of the steel cord.

  Further, the steel cord 13 of the reinforcing ply 10A needs to be arranged at an angle θ of 0 to 45 ° with respect to the radial direction RL. As a result of various experiments by the inventors, when the angle θ exceeds 45 °, the steel cord 13 approaches the tire circumferential direction, so that the radial reinforcement effect is reduced. In addition, in the shaping process during molding, The formation of a green tire is difficult because the opening of the carcass cord in the wall portion is hindered. From such a viewpoint, the angle θ is preferably 0 to 30 °. The radial direction means the direction of the cut surface of the tire meridian including the tire rotation axis, and the angle θ is measured at an intermediate position of the length of the reinforcing cord layer 10 in the radial direction. To do.

  The wire diameter d of the steel cord 13 is preferably 0.54 mm or more, more preferably 0.70 mm or more, and the upper limit is preferably 1.20 mm or less, more preferably 1.10 mm or less, and still more preferably. 0.85 mm or less is desirable. When the wire diameter d of the steel cord 13 is less than 0.54 mm, the cord rigidity is lowered, and as a result, the reinforcing effect on the side reinforcing rubber layer 9 may be lowered. Conversely, when the wire diameter d of the steel cord 13 exceeds 0.78 mm, the cord rigidity increases excessively, which may deteriorate the riding comfort during normal running, and also tends to increase the tire mass.

  Further, the steel cord 13 may be a multifilament cord formed by twisting a plurality of filaments, or a monofilament cord composed of a single filament. A multifilament cord is particularly preferable, and a cord configuration of 2 + 2 × 0.25, 2 + 7 × 0.22, or 3 × 0.20 + 6 × 0.35 is particularly desirable.

  The number of steel cords 13 driven into the reinforcing ply 10A is preferably 20 or more, more preferably 30 or more per 5 cm of the ply width. If the number of driving is less than 20/5 cm, the reinforcing effect on the side reinforcing rubber layer 9 tends not to be sufficiently obtained. On the other hand, if the number of driving is too large, the tire mass may increase or the riding comfort during normal running may be deteriorated. From such a viewpoint, the number of steel cords to be driven is preferably 50 or less, more preferably 45 or less per 5 cm ply width.

  As shown in FIG. 3, the reinforcing cord layer 10 extends in the radial direction without protruding from the region Sa the side outer region Sa sandwiched between the tire maximum width position M and the outer end 7 e of the belt layer 7. It is provided as follows. That is, the inner end 10i in the tire radial direction of the reinforcing cord layer 10 is provided at the same position as the tire maximum width position M or at the radially outer side than this. Similarly, the outer end 10o of the reinforcing cord layer 10 in the tire radial direction is provided at the same position as the outer end 7e of the belt layer 7 or on the inner side in the radial direction thereof. As a preferred embodiment, in order to more effectively suppress the bending deformation of the side outer region Sa, the reinforcing cord layer 10 is disposed over 80% or more, more preferably 90% or more of the side outer region Sa. It is particularly desirable.

  Here, the tire maximum width position M is a position that protrudes most outward in the tire axial direction except for the rim protector 11, characters, and patterns provided on the outer surface of the sidewall portion 3 in a normal state. Usually, it is provided at the same height as the position m of the main body portion 6a of the carcass ply 6A that protrudes outward in the tire axial direction.

  Further, as shown in FIG. 3, the side outer region Sa includes a straight line N1 passing through the tire maximum width position M and perpendicular to the tire outer surface, and a straight line passing through the outer end 7e of the belt layer 7 and perpendicular to the tire outer surface. The region includes both ends sandwiched between N2.

  The inventors have analyzed the tire during run-flat running, and found that the largest bending moment acts on the side outer region Sa, and the bending deformation of the rubber advances from the tire lumen surface side. I found out. Therefore, in the present invention, by providing the reinforcing cord layer 10 having the steel cord 13 in the side outer region Sa, the bending deformation is efficiently suppressed without increasing the size of the side reinforcing rubber layer 9.

  On the other hand, since the reinforcing cord layer 10 is provided without protruding from the side outer region Sa, it is possible to suppress an increase in tire mass and deterioration in riding comfort during normal running. In particular, since the steel cord 13 of the reinforcing cord layer 10 is not disposed in the side inner region Sb on the inner side in the tire radial direction from the tire maximum width position M, vibration during traveling can be effectively absorbed in the region. , Can prevent deterioration of ride comfort. Similarly, by stopping the outer end 10o of the reinforcing cord layer to the outer end of the belt layer 7, an increase in tire mass and a deterioration in riding comfort can be suppressed.

The run-flat tire 1 of the present embodiment has a tire outer surface profile (contour line) TL as shown in FIG. 6 (normal state). The profile TL is specified on the assumption that there is no groove in the tread portion 2. In the normal no-load state, the profile TL is determined from the intersection point CP, where P is a point on the tire outer surface that is separated by a distance SP of 45% of the maximum tire width SW from the intersection point CP between the tire outer surface and the tire equator C. In the section up to the point P, the radius of curvature RC of the tire outer surface gradually decreases toward the outer side in the tire axial direction, and the following relationship is satisfied.
0.05 <Y60 / H ≦ 0.1
0.1 <Y75 / H ≦ 0.2
0.2 <Y90 / H ≦ 0.4
0.4 <Y100 / H ≦ 0.7
Here, Y60, Y75, Y90, and Y100 separate the tire axial distances of 60%, 75%, 90%, and 100% of the half width (SW / 2) of the maximum tire width in the tire axial direction from the tire equator C, respectively. The distances in the tire radial direction between the points P60, P75, P90 and P100 on the tire outer surface and the intersection point CP. The “H” is a tire cross-sectional height.

RY60 = Y60 / H
RY75 = Y75 / H
RY90 = Y90 / H
RY100 = Y100 / H
Then, the range satisfying the above relationship is shown as a graph in FIG. As is clear from these, the profile TL of the tire outer surface that satisfies the above relationship becomes very round. For this reason, the ground contact shape of the tire having this profile TL has a small ground contact width and a large ground contact length. This helps to reduce tire noise while driving and improve hydroplaning performance.

  Further, the profile TL increases the area where the tread portion 2 is easily bent, but shortens the area of the sidewall portion 3. For this reason, the run flat tire 1 having the profile can significantly reduce the weight of the tire. Therefore, a substantial increase in tire mass is suppressed as compared with a run flat tire having a conventional tread profile. The radius of curvature RC is preferably continuously reduced as in the present embodiment, but may be reduced step by step. Furthermore, since the profile TL reduces the vertical spring of the tire, the riding comfort during normal driving is excellent.

  As described above, the run-flat tire 1 of the present embodiment is provided with the reinforcing cord layer 10 made of steel cord between the side reinforcing rubber layer 9 and the carcass 6 and in the side outer region Sa, so that it can be used during normal driving. The run-flat running performance can be improved without deteriorating the ride comfort. In addition, the side reinforcing rubber layer 9 can be made thinner and can contribute to a reduction in tire mass. In the above embodiment, a passenger car tire has been described as an example, but the present invention is not limited to such an embodiment, and it goes without saying that the present invention can also be applied to tires of other categories. Needless to say, the reinforcing cord layer 10 can be formed of a plurality of steel cord plies as needed.

  In order to confirm the effect of the present invention, a plurality of types of run-flat tires of size 245 / 40R18 were prototyped based on the specifications in Table 1, and run-flat durability performance, riding comfort, general durability, and tire mass were evaluated. The parameters other than those shown in Table 1 are the same.

Moreover, two types of tire outer surface profiles A and B having the following specifications were adopted for the tires of the examples.
Profile A:
RY60 = 0.06
RY75 = 0.08
RY90 = 0.19
RY100 = 0.57
Profile B:
RY60 = 0.09
RY75 = 0.14
RY90 = 0.37
RY100 = 0.57
The test method is as follows.

<Run flat durability performance>
Each test tire is assembled on a regular rim (18 x 8 JJ) from which the valve core has been removed, and is run on a drum tester at a speed of 90 km / h and a longitudinal load of 5.74 kN with zero internal pressure until the tire breaks. Time was measured. The results are indicated by an index with Comparative Example 1 as 100. The larger the value, the better.

<Ride comfort>
Each test tire is mounted on a rim of 18 x 8 JJ and is mounted on four wheels of a domestic FR vehicle with an internal pressure of 230 kPa and a displacement of 3000 cm ³ , and a stepped road on a dry asphalt road surface, a Belgian road (cobblestone) No. road), Bitzmann road (road surface covered with pebbles), etc., sensory evaluation is performed with respect to ruggedness, push-up, and damping, and is displayed as an index with Comparative Example 1 being 100. The higher the numerical value, the better.

<General durability>
Each test tire was assembled on the above-mentioned regular rim, traveled on a test drum at an internal pressure of 200 kPa, a longitudinal load of 6.8 KN, and a speed of 60 km / H, and the travel time until the tire broke was examined. The results are indicated by an index with Comparative Example 1 as 100. The larger the value, the better.

<Tire mass>
The mass per tire was measured and displayed as an index with Comparative Example 1 taken as 100. It shows that it is lightweight, so that a numerical value is large. Table 1 shows the test results.

  As a result of the test, it was confirmed that the tire of the example improved the run-flat durability performance without significantly impairing the riding comfort during the normal running as compared with the comparative example.

It is sectional drawing of the run flat tire which shows embodiment of this invention. It is sectional drawing of the run flat state. It is a fragmentary sectional view which expands and shows the bead part of FIG. It is the perspective view of the reinforcement cord layer seen from the side. It is BB sectional drawing of FIG. 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 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 7e Outer end 9 of belt layer Side reinforcement rubber layer 10 Reinforcement cord layer 10A Reinforcement ply 13 Steel cord Sa Side outer side area

Claims (4)

A carcass having at least one carcass ply which is folded and locked by a bead core of a bead part from a tread part through a sidewall part;
A belt layer disposed radially outside the carcass and inside the tread;
A run-flat tire comprising a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed on the inside and side wall region of the carcass,
A reinforcement cord layer comprising at least one reinforcement ply having steel cords arranged in parallel at an angle of 0 to 45 degrees with respect to the radial direction is disposed between the side reinforcement rubber layer and the carcass, and the reinforcement The run-flat tire is characterized in that the cord layer extends in a radial direction without protruding from a side outer region sandwiched between the tire maximum width position and the outer end of the belt layer.   The run-flat tire according to claim 1, wherein the steel cord has a wire diameter of 0.54 to 0.78 mm.   The run flat tire according to claim 1 or 2, wherein the side reinforcing rubber layer has a maximum thickness of 8 to 10 mm. In the tire meridian cross section including the tire rotation shaft in the normal unloaded state in which the rim is assembled to the regular rim and filled with the regular internal pressure,
The profile of the tire outer surface is defined as a point on the tire outer surface (P) that is separated from the intersection (CP) of the tire outer surface and the tire equator (C) by a distance (SP) of 45% of the maximum tire width (SW). In the section from the intersection (CP) to the point (P), the radius of curvature (RC) of the tire outer surface gradually decreases,
The run flat tire according to any one of claims 1 to 3, which satisfies the following relationship.
0.05 <Y60 / H ≦ 0.1
0.1 <Y75 / H ≦ 0.2
0.2 <Y90 / H ≦ 0.4
0.4 <Y100 / H ≦ 0.7
(Where Y60, Y75, Y90 and Y100 are the tire axial distances of 60%, 75%, 90% and 100% of the half width (SW / 2) of the maximum tire width in the tire axial direction from the intersection (CP). (The distances in the tire radial direction between the points P60, P75, P90 and P100 on the outer surface of the tire and the intersections (CP), and H is the tire cross-section height.)

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